JP7547154B2 - Image forming device - Google Patents

Description

The present invention relates to image forming devices such as copiers and printers that use electrophotographic or electrostatic recording methods.

In image forming devices such as copiers and laser printers, a toner image formed on a photoreceptor is transferred to a recording material, and then the transferred toner image is heated and pressed under predetermined fixing conditions in an image heating device to fix the toner image to the recording material. The predetermined fixing conditions are the conveying speed and heating temperature of the recording material in the image heating device. In the image forming device, the quality of the image formed on the recording material is maintained by changing the fixing conditions in the image heating device according to the characteristics of the recording material (e.g., material, basis weight, thickness, surface condition, etc.). In conventional image forming devices, the user sets the type of recording material (e.g., thin paper, plain paper, thick paper, rough paper, glossy paper, etc.) via an operation panel provided in the image forming device or an external device such as a computer equipped with a printer driver. The image forming device then controls the fixing conditions of the image heating device based on the recording material characteristics corresponding to the set type of recording material.

To reduce the burden on the user in setting the type of recording material, for example, Patent Document 1 proposes an image forming apparatus in which a sensor for detecting the characteristics of the recording material (hereinafter referred to as a media sensor) is installed on the recording material transport path. In an image forming apparatus equipped with a media sensor, the media sensor detects the characteristics of the recording material being transported, and the fixing conditions of the recording material in the image heating device are automatically controlled according to the detected characteristics of the recording material.

Patent No. 5627363

In the above-mentioned Patent Document 1, the image forming apparatus calculates a moving average value of the detection results of multiple sheets of recording material fed continuously from a paper feed port where the recording materials are stacked, and judges the characteristics of the recording material based on the calculation result. However, in cases where the recording materials fed include recording materials with significantly different characteristics, a statistical processing method such as the moving average may not be suitable for judging the recording material characteristics.

For example, there are cases where recording materials with significantly different characteristics are fed from the same paper feed inlet where recording materials with similar characteristics are normally fed. Examples of this include when a user intentionally alternates between recording materials with different characteristics, or when recording materials with different characteristics are mixed in a single packed stack of recording materials. An example of the former can occur when a user feeds multiple sheets of recording material as one set in an image forming device with only one paper feed inlet. For example, a document may be printed using cardboard for the cover and thin paper for the rest of the document, and multiple sets may be printed. In this case, one sheet of cardboard and multiple sheets of thin paper are fed periodically.

The latter example also arises due to the method of producing stacks of recording materials. That is, stacks of recording materials are often produced by stacking recording materials cut from multiple rolls, and when the characteristics of the recording materials differ from roll to roll, the resulting stack of recording materials may be one in which recording materials with different characteristics are periodically inserted. When such a stack of recording materials is loaded into the paper feed inlet, recording materials with different characteristics are periodically fed from a single paper feed inlet.

When recording materials with significantly different characteristics as described above are fed periodically, if moving average processing is performed on the detection results of the characteristics of multiple sheets of recording material detected by the media sensor, the detection results will appear as noise. As a result, the image forming device may control the image heating device under fixing conditions that are different from the fixing conditions that should be used, which may result in a decrease in image quality.

The present invention was made under these circumstances, and aims to improve the accuracy of detecting the characteristics of recording materials and improve the quality of images formed on the recording materials.

In order to solve the above problems, the present invention has the following configuration.

(1) An image forming apparatus comprising: a loading section on which recording materials are loaded; an image forming means for forming an image on the recording materials fed from the loading section; a detection means for detecting characteristics of the recording materials fed from the loading section; and a control means for determining image forming conditions of the image forming means from the characteristics of at least one sheet of recording material detected by the detection means, and for controlling the image forming means to form an image on a recording material newly fed from the loading section under the image forming conditions . The detection means includes a transmission section for transmitting ultrasonic waves, which are disposed on either side of a transport path along which the recording materials are transported, a reception section for receiving ultrasonic waves transmitted by the transmission section, and a calculation section for calculating a transmission coefficient of the recording material based on a result of reception of the ultrasonic waves by the reception section through the recording material. and a calculation unit, wherein the characteristic of the recording material is basis weight, the control unit determines the basis weight of the recording material based on a transmission coefficient calculated by the calculation unit, and determines whether or not the characteristic of the recording material fed from the stacking unit is periodic based on a detection result of the characteristics of multiple sheets of recording material by the detection unit, and if it is determined that the characteristic of the recording material is periodic, changes the image formation conditions in accordance with the periodicity , and does not determine whether or not the characteristic of the recording material is periodic until a predetermined number of sheets or more of recording material have been fed from the stacking unit after the image forming apparatus is turned on, and determines whether or not the characteristic of the recording material is periodic when the predetermined number of sheets or more of recording material have been fed from the stacking unit after the image forming apparatus is turned on.

The present invention improves the accuracy of detecting the characteristics of recording materials, thereby improving the quality of images formed on the recording materials.

FIG. 1 is a cross-sectional view showing a configuration of an image forming apparatus according to first and second embodiments. FIG. 1 is a cross-sectional view showing a configuration of an image heating apparatus according to first and second embodiments. FIG. 1 is a control block diagram for explaining control of the media sensor in the first and second embodiments. FIG. 1 is a diagram for explaining detection of periodicity of characteristics of a recording material according to the first embodiment; FIG. 1 is a diagram for explaining detection of periodicity of characteristics of a recording material according to a first embodiment; A flowchart showing a control sequence for controlling image forming conditions in the first embodiment. Graph comparing the statistical processing methods of Example 1 A flowchart showing a control sequence for controlling image forming conditions in the second embodiment. Graph comparing statistical processing methods in Example 2

Below, an embodiment of the present invention will be described in detail with reference to the drawings.

[Image forming apparatus]
First, the configuration of the image forming apparatus will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing the configuration of the image forming apparatus of the first embodiment. The image forming apparatus shown in FIG. 1 is a laser printer 1 (hereinafter referred to as printer 1) that forms an image on a recording material P by using an electrophotographic method. The printer 1 is provided with a process cartridge 10 having a photosensitive drum 19 as an image carrier, a charging roller 16 as a charging means, a developing roller 17 as a developing means, and a cleaning blade 18 as a cleaning means. In this embodiment, the process cartridge 10 is composed of a developing unit including the photosensitive drum 19, the charging roller 16, and the developing roller 17, and a cleaning unit including the cleaning blade 18, and is configured to be detachable from the main body of the printer 1. In addition to the process cartridge 10, the printer 1 is provided with a paper feed tray 21, a feed roller 22, a pair of transport rollers 23, a top sensor 24, a media sensor 30, a transfer roller 12 as a transfer member, an image heating device 13, and a pair of discharge rollers 26. Furthermore, the printer 1 is provided with a motor 20 and an image formation control unit 40.

The motor 20 is a driving means for driving the transport members that transport the photosensitive drum 19 and the recording material P. In this embodiment, the motor 20 drives multiple transport members such as the feed roller 22, the transport roller pair 23, the photosensitive drum 19, the image heating device 13, and the discharge roller pair 26.

The photosensitive drum 19 is rotated by the motor 20 at a predetermined peripheral speed (process speed) in the direction of the arrow in the figure (counterclockwise direction). The charging roller 16 uniformly charges the surface of the photosensitive drum 19 with a predetermined polarity and potential. The photosensitive drum 19, whose surface is charged with a uniform potential, is irradiated with laser light emitted from the laser scanner 11 and exposed. The laser scanner 11, which is an exposure means, emits laser light that is on/off modulated in response to a digital signal that converts image information input from an external device such as an image scanner (not shown) or a computer. The laser light emitted from the laser scanner 11 removes the charge on the surface of the photosensitive drum 19, and an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 19. The developing roller 17 develops the electrostatic latent image into a toner image by attaching toner (developer) to the electrostatic latent image formed on the surface of the photosensitive drum 19. Laser printers generally use a reversal development method in which toner is applied to the exposed light areas of an electrostatic latent image to develop it.

The recording material P is loaded and stored in the paper feed tray 21, which is a paper feed port (also called a stacking portion), and can be freely attached and detached to the printer 1. The recording material P stored in the paper feed tray 21 is separated and fed one by one from the paper feed tray 21 by the feed roller 22 being driven in response to a paper feed start signal from the image formation control unit 40, and is conveyed to the conveying roller pair 23. In addition to the paper feed tray 21, the printer 1 is equipped with another paper feed port, the manual feed tray 27, as a paper feed port for feeding the recording material P. The recording material P placed on the manual feed tray 27 is separated and fed one by one by the feed roller 28 under the control of the image formation control unit 40, and is conveyed to the conveying roller pair 23 using the conveying roller pair 29, etc. The recording material P conveyed to the conveying roller pair 23 is conveyed by the conveying roller pair 23 to the transfer nip portion T formed by the contact between the photosensitive drum 19 and the transfer roller 12.

The top sensor 24 is installed on the transport path between the transport roller pair 23 and the transfer nip portion T, and detects the timing when the leading edge of the recording material P transported from the transport roller pair 23 reaches the top sensor 24. The image formation control unit 40 adjusts the write timing for irradiating the photosensitive drum 19 with laser light from the laser scanner 11 and forming an electrostatic latent image on the photosensitive drum 19 based on the leading edge arrival timing of the recording material P detected by the top sensor 24. In other words, the image formation control unit 40 controls the timing for starting formation of the electrostatic latent image on the photosensitive drum 19 so that the leading edge of the toner image on the photosensitive drum 19 just reaches the transfer nip portion T at the timing when the leading edge of the recording material P reaches the transfer nip portion T.

The recording material P transported to the transfer nip area T is sandwiched and transported between the photosensitive drum 19 and the transfer roller 12 at the transfer nip area T, during which a predetermined high transfer voltage is applied to the transfer roller 12 from a power source (not shown) that generates the transfer voltage. A transfer voltage of the opposite polarity to the toner is applied to the transfer roller 12, so that the toner image formed on the surface of the photosensitive drum 19 is transferred to the surface of the recording material P. The recording material P with the transferred toner image is then transported from the transfer nip area T to the image heating device 13.

The image heating device 13 (also called the fixing device) includes a fixing member 14 and a pressure member 15. The recording material P conveyed to the image heating device 13 is nipped and conveyed through the fixing nip F formed by the fixing member 14 and the pressure member 15. During this time, the toner image on the recording material P is heated by the fixing member 14, which is controlled to a predetermined temperature (fixing temperature) according to the characteristics of the recording material P, and is pressed by the pressure member 15 to be fixed to the recording material P. The recording material P on which the toner image is fixed by the image heating device 13 passes through a pair of discharge rollers 26 that discharge the recording material P and is discharged to the discharge tray of the printer 1, completing image formation. After the toner image is transferred to the recording material P, the cleaning blade 18 removes toner, paper powder, etc. that remain on the surface of the photosensitive drum 19 without being transferred to the recording material P.

In the printer 1, the image forming operation described above is repeated to form images on the recording material P one after another. The printer 1 of this embodiment is capable of transporting A4 size (210 mm x 297 mm) plain paper at a transport speed of 230 mm/sec, and printing approximately 43 monochrome images per minute. The image forming control unit 40, which controls the image formation of the printer 1, has a CPU 41, a ROM 41a, and a RAM 41b. The CPU 41 executes various programs stored in the ROM 41a, and controls various operations related to image formation while using the RAM 41b as a working area.

[Image heating device]
Next, the configuration of the image heating device 13 will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view showing the configuration of the image heating device 13 provided in the printer 1 of this embodiment, and is an enlarged view of the image heating device 13 shown in FIG. 1. The image heating device 13 has a fixing member 14, a pressure member 15, and a heater 60 which is a heating body for heating the fixing member 14. The heater 60 is held by a heater holding member 61, and the heater holding member 61 is held by a metal stay member 63. A pressure mechanism (not shown) applies pressure between the metal stay member 63 and the pressure member 15, and the pressure member 15 is pressed toward the heater 60 via the fixing member 14 to form a fixing nip portion F. The recording material P is introduced into the fixing nip portion F from the recording material conveying direction shown in the figure, and is nipped and conveyed through the fixing nip portion F formed by the pressure member 15 rotating in the R1 direction in the figure and the fixing member 14 rotating in the R2 direction in the figure. The unfixed toner image is then heated by the fixing member 14 and pressed against the recording material P by the pressure member 15, whereby the unfixed toner image on the recording material P is fixed to the recording material P.

Thermistor 62, which is a temperature detection element, contacts heater 60 and detects the temperature of heater 60. Based on the result of temperature detection of heater 60 by thermistor 62, image formation control unit 40 controls the power supply to heater 60 so that the temperature of heater 60 becomes a target temperature according to the characteristics of recording material P.

[Media sensor]
Next, a description will be given of the media sensor 30 which is a detection means for detecting the characteristics of the recording material P in this embodiment. The media sensor 30 is a sensor for detecting basis weight as a characteristic of the recording material P. As shown in Fig. 1, the media sensor 30 is disposed on the conveying path of the recording material P between the pair of conveying rollers 23 and the transfer nip T. The media sensor 30 has a transmitting unit 31 which transmits ultrasonic waves and a receiving unit 32 which receives ultrasonic waves transmitted from the transmitting unit 31, and the transmitting unit 31 and the receiving unit 32 are disposed on either side of the conveying path along which the recording material P is conveyed.

The transmitting unit 31 and the receiving unit 32 of the media sensor 30 have the same configuration, and each is composed of a piezoelectric element (also called a piezo element), which is a conversion element that converts mechanical displacement and electrical signals into each other, and an electrode terminal. In the transmitting unit 31, when a pulse voltage of a predetermined frequency is applied to the electrode terminal, the piezoelectric element oscillates to generate ultrasonic waves, and the generated ultrasonic waves propagate through the air. When the ultrasonic waves from the transmitting unit 31 reach the recording material P being transported along the transport path between the transmitting unit 31 and the receiving unit 32, the recording material P vibrates due to the ultrasonic waves. The vibration of the recording material P propagates as ultrasonic waves through the air and reaches the receiving unit 32. In this way, the ultrasonic waves generated by the transmitting unit 31 propagate to the receiving unit 32 through the recording material P. The piezoelectric element of the receiving unit 32 outputs a voltage according to the amplitude of the received ultrasonic waves from the electrode terminal. In this embodiment, ultrasonic waves having a frequency characteristic of 32 kHz are output from the transmitting unit 31, and the receiving unit 32 receives the ultrasonic waves output from the transmitting unit 31 through the recording material P. The frequency of the ultrasonic waves is preset, and an appropriate range of frequency can be selected depending on the configuration of the transmitter 31 and receiver 32, the detection accuracy, etc.

Next, a method for controlling the media sensor 30 will be described. FIG. 3 is a block diagram for explaining a control unit that controls the media sensor 30. In FIG. 3, the media sensor 30 is controlled by the image formation control unit 40. The image formation control unit 40 has a basis weight detection control unit 42 that controls the transmission and reception of ultrasonic waves from the media sensor 30 and performs a media discrimination operation to determine the basis weight of the recording material P based on the detection result of the media sensor 30. The image formation control unit 40 controls the image formation conditions in image formation based on the detection result of the recording material P output from the basis weight detection control unit 42. Note that the "image formation conditions" refer to various conditions when forming an image, such as the transfer voltage applied to the transfer roller 12, the fixing temperature of the image heating device 13, and the conveying speed of the recording material P.

3, when detecting the basis weight of the recording material P, the CPU 41 of the image formation control unit 40 outputs a signal to the drive signal control unit 441 of the basis weight detection control unit 42 to instruct the start of measurement of the basis weight of the recording material P. When the drive signal control unit 441 receives a signal from the CPU 41 to instruct the start of measurement of the basis weight of the recording material P, it instructs the drive signal generation unit 431 to generate an ultrasonic transmission signal to generate ultrasonic waves of a predetermined frequency. In order to reduce the influence of disturbances such as reflected waves from the recording material P and members around the conveying path, the drive signal generation unit 431 outputs a pulse wave called a burst wave of a certain period so that the receiving unit 32 can receive only the direct wave irradiated by the transmitting unit 31 of the media sensor 30. In this embodiment, the drive signal generation unit 431 outputs five pulses of a pulse wave with a frequency of 32 kHz in succession in one measurement. In this way, the drive signal generation unit 431 generates a pulse signal of a preset frequency and outputs it to the amplifier 432. The amplifier 432 amplifies the level (voltage value) of the pulse signal of a predetermined frequency input from the drive signal generation unit 431 and outputs it to the transmission unit 31 of the media sensor 30. In the transmission unit 31, the piezoelectric element oscillates in response to the signal input from the amplifier 432 to generate ultrasonic waves.

On the other hand, the receiving section 32 of the media sensor 30 receives ultrasonic waves transmitted from the transmitting section 31 that have not passed through the recording material P, or ultrasonic waves that have passed through the recording material P, and outputs the ultrasonic waves to the detection circuit 442 of the basis weight detection control section 42. The detection circuit 442 has an amplification function and a rectification function for the signal (voltage signal) input from the receiving section 32, and changes the amplification factor of the input signal depending on whether the recording material P is not present between the transmitting section 31 and the receiving section 32 or not. The detection circuit 442 amplifies and rectifies the input signal, and outputs it to the A-D conversion section 443. The A-D conversion section 443 converts the signal input from the detection circuit 442 from an analog signal to a digital signal, and outputs it to the peak extraction section 444. The peak extraction section 444 extracts the peak value (maximum value) of the digital signal input from the A-D conversion section 443, and stores the extracted peak value in the memory section 446. These operations are called "peak detection operations".

The peak detection operation is performed a predetermined number of times at a predetermined interval for each of the states where the recording material P is not present between the transmitting unit 31 and the receiving unit 32 (the recording material P does not pass the media sensor 30) and where the recording material P is present (the recording material P passes the media sensor 30). The calculation unit 447, which is a calculation means, calculates the transmission coefficient of the ultrasonic wave for the recording material P from the ratio of the average value of the peak value when the recording material P is not present to the average value of the peak value when the recording material P is present, based on the peak value of the digital signal stored in the memory unit 446. The calculation unit 447 outputs the calculated transmission coefficient to the CPU 41. The transmission coefficient calculated by the calculation unit 447 is a value that has a negative correlation with the basis weight of the recording material P, and the CPU 41 calculates the basis weight of the recording material P based on the transmission coefficient calculated by the calculation unit 447, and stores the calculated basis weight in the RAM 41b.

[Recording Material Basis Weight and Image Forming Conditions]
The CPU 41 of the image formation control section 40 determines image formation conditions such as the transfer voltage applied to the transfer roller 12, the fixing temperature of the image heating device 13, and the conveying speed of the recording material P, based on the characteristic value information (basis weight in this embodiment) of the recording material P stored in the above-mentioned RAM 41b. For example, when the CPU 41 determines that the recording material P has a large basis weight, it sets the target temperature of the fixing temperature high. This is because the recording material P with a large basis weight requires a larger amount of heat in the image heating device 13 to fix the toner image.

The printer 1 of this embodiment has an operation mode in which the recording material P is transported at a transport speed of 230 mm/sec, which is optimal for image formation on recording material P having a basis weight of 60 g/ ^m2 to 120 ^g /m2. Also, the optimal target fixing temperature in the image heating device 13 is set according to the basis weight. Table 1 shown below is a table showing the correspondence between the basis weight (unit: g/ ^m2 ) of the recording material P and the target fixing temperature (unit: °C).

In Table 1, when the basis weight is 60, 75, 90, 105, and 120 g/ ^m2 , the target fixing temperature of image heating device 13 is 175, 185, 195, 205, and 215° C., respectively. It can be seen from Table 1 that the target fixing temperature increases by 10° C. for every 15 g/ ^m2 increase in basis weight.

Table 2 shown below indicates the degree of influence on the fixing performance of fixing a toner image onto a recording material P when the fixing temperature in image heating device 13 is set to a temperature lower than the target temperature. In Table 2, the "Temperature Difference" in the upper row indicates the temperature difference between the set fixing temperature and the target temperature, and in Table 2, the temperature difference is shown from ±0°C to -12°C. Meanwhile, the "Fixing Performance" in the lower row indicates the degree of influence on the fixing performance with "○", "○△", or "△". "○" indicates that there is no problem with the fixing performance, "○△" indicates that the fixing performance is poor but within a range where no problems occur, and "△" indicates that problems occur with the fixing performance.

From Table 2, if the fixing temperature is in the range from the target temperature to (target temperature -3°C), the target fixing performance can be met. Also, if the fixing temperature is in the range from (target temperature -4°C) to (target temperature -10°C), the fixing performance is "good" or "good", which means that the fixing performance is slightly lower than the target, but is within the range where there is no problem. On the other hand, if the fixing temperature is (target temperature -11°C or lower), there is a risk of the fixing performance being impaired. Table 2 shows the fixing performance when the fixing temperature of the image heating device 13 is equal to or lower than the target temperature. On the other hand, if the fixing temperature of the image heating device 13 is equal to or higher than the target temperature, the target fixing performance can be met, but the higher the fixing temperature is than the target temperature, the greater the power consumption of the printer 1. Therefore, it is desirable for the fixing temperature of the image heating device 13 to be as close to the target temperature as possible.

[Detection of Periodicity of Recording Material Characteristics]
Next, a method for detecting whether or not the recording material characteristics of the recording material P loaded on the paper feed tray 21 are periodic will be described based on the detection result of the media sensor 30. In this embodiment, when the recording material characteristics of the recording material P fed from the paper feed tray 21 are detected using the media sensor 30, the CPU 41 sequentially stores the detected characteristic value information of the recording material P in the RAM 41b. At this time, if the basis weight, which is a characteristic of the recording material P fed, differs in a cycle of, for example, one sheet per five sheets, the recording material characteristics of the recording material P detected by the media sensor 30 will differ from other recording materials P in a ratio of one sheet per five sheets. If the detection result of the recording material P fed by the media sensor 30 continues in this state for a while, it is predicted that the recording material having characteristics different from other recording materials will be fed while maintaining the periodicity of one sheet per five sheets, and the recording material characteristics will continue to change in a cycle of five sheets thereafter. In this embodiment, such a state will be called a "periodic" state.

In this embodiment, in order to detect the periodicity of the recording material characteristics of the recording material P being fed, a method is used in which the detection results of the recording material P being fed by the media sensor 30 are divided into groups with different periods, and the detection results of the groups with different periods are compared. Fig. 4 is a graph showing the relationship between the number (number of sheets) of recording material P and the basis weight when 40 sheets of recording material P are fed from the paper feed tray 21, with the first to ^fourth sheets being recording material P with a basis weight of ⁹⁰ g/m2 and the fifth sheet being recording material P with a basis weight of 60 g/m2. In Fig. 4, the vertical axis shows the basis weight (unit: g/ ^m2 ) of the recording material, and the horizontal axis shows the number (number of sheets) of the recording material P, which is the order of the recording material P being fed. Also, the plot of black circles shows the basis weight of the recording material P being fed.

As shown in FIG. 4, the average basis weight of the group of recording materials P that are (multiples of 5+1), such as the 1st, 6th, 11th, and 16th sheets, is 90 g/ ^m2 . The average basis weight of the group of recording materials P that are (multiples of 5+2), (multiples of 5+3), and (multiples of 5+4), is also 90 g/ ^m2 . On the other hand, the average basis weight of the group of recording materials P that are (multiples of 5), such as the 5th, 10th, 15th, and 20th sheets, is 60 g/ ^m2 . In this way, when the number of recording materials P shown in FIG. 4 is a multiple of 5, a recording material P having recording material characteristics different from the other recording materials P is fed from the paper feed tray 21. From this, it can be said that the example of recording material P shown in FIG. 4 has a "periodicity of 5 sheets".

In this way, in the cycle in which the recording material P is fed, the characteristic values of groups that are fed in different orders are compared, and if there is a group whose characteristic value differs greatly from that of other groups, there is a possibility that periodicity in the recording material characteristics exists. Therefore, in this embodiment, if there is a difference of a threshold or more in the detection results of the recording material characteristic values of each group that is fed in different orders, it is determined that there is "periodicity". The method of determining periodicity will be described in detail later.

Next, a method for determining the threshold value for judging whether the recording material has periodicity and the number of sheets of recording material P constituting the periodicity will be described. First, the threshold value for judging whether the recording material P has periodicity will be described. The threshold value for judging whether the recording material P has periodicity should be determined taking into consideration both the basis weight difference of the recording materials to be distinguished and the detection error of the media sensor 30. For example, when the threshold value for judging whether the recording material P has periodicity is large, it is less likely that the recording material P has periodicity even though the fixing control of the image heating device 13 should be changed upon detecting the periodicity. On the other hand, when the threshold value for judging whether the recording material P has periodicity is set small, there is a risk that the recording material P may be erroneously judged to have periodicity if an incorrect characteristic value of the recording material P is detected due to a detection error of the media sensor 30. Therefore, the image heating device 13 of this embodiment is configured so that the toner image is fixed to the recording material P without any problems even if the fixing temperature changes by 3° C. for recording materials of the same basis weight. Therefore, when the fixing temperature of the recording material P changes by 4° C. or more, that is, when the difference in basis weight of the recording material is 6 g/ ^m2 or more, it is determined that the type of recording material P is different, and it is determined that there is "periodicity." Note that in Table 1, the basis weight and the target fixing temperature have a relationship in which the target fixing temperature changes by 10° C. when the basis weight changes by 15 g/ ^m2 . As a result, when linear interpolation is performed based on the relationship shown in Table 1, when the fixing temperature changes by 4° C. or more, the basis weight of the recording material changes by 6 g/ ^m2 or more.

Next, the number of sheets of recording material P to be detected for detecting periodicity will be described. The more sheets to be detected, the more sheets of recording material P that need to be detected before it is determined that periodicity exists. For this reason, it is desirable to keep the number of sheets of recording material P to be detected as small as possible. In this embodiment, the periodicity of recording material P is investigated for cycles of 4 sheets to 7 sheets.

Here, we will explain the case where the detected periodicity of the recording material P is reset. First, we will explain the case where the number of sheets per period itself changes for recording material fed from the paper feed tray 21. An example of this case is when the paper feed tray 21 is pulled out of the printer 1 and a stack of recording materials with different periodicities is loaded onto the paper feed tray 21. Therefore, when the paper feed tray 21 is inserted and attached to the printer 1, it is necessary to reset the detected period of the recording material P and detect the periodicity of the recording material P fed from the paper feed tray 21 again.

The detected cycle of the recording material P is also reset when the number of sheets per cycle does not change, but the order of the recording material P in the cycle changes. An example of this case is when one bundle of paper is divided into multiple bundles and stacked in the paper feed tray 21 in an order different from the original order. In this case, even if the paper feed tray 21 has not been opened or closed (attached or detached), a deviation occurs between the basis weight of the recording material P fed from the paper feed tray 21 and the basis weight calculated for each group having the same feeding order. In such a case, it is necessary to determine that the periodicity of the recording material P has changed, reset the detected cycle of the recording material P, and detect the periodicity of the recording material P fed from the paper feed tray 21 again. In this embodiment, if there is a difference of 6 g/m ² or more between the basis weight of the recording material P fed this time and the basis weight of the recording material P in the cycle group having the same feeding order, the detected cycle of the recording material P is reset.

(Example of periodicity detection)
Next, a specific method for detecting periodicity based on the basis weight data of 40 sheets of recording material P shown in FIG. 4 will be described in detail. It is assumed that there is no variation in basis weight of the recording material P shown in FIG. 4, and there is no detection error of the recording material characteristic value by the media sensor 30. FIG. 5 is a graph showing the average basis weight of the recording material P in the order of feeding in each period group, which is divided into period groups of 4 sheets to 7 sheets, with respect to the basis weight detected by the media sensor 30 for 40 sheets of recording material with the basis weight shown in FIG. 4. In FIG. 5, (a) is a graph showing the average basis weight of the recording material P in the period of 4 sheets, (b) is a graph showing the average basis weight of the recording material P in the period of 5 sheets, (c) is a graph showing the average basis weight of the recording material P in the period of 6 sheets, and (d) is a graph showing the average basis weight of the recording material P in the period of 7 sheets, from the top. The vertical axis of (a) to (d) in FIG. 5 indicates the basis weight (g/m ² ) of the recording material P, and the horizontal axis indicates the order of feeding of the recording material P in each period.

With reference to FIG. 5(a), we will explain how to read the figure and the average basis weights displayed. In FIG. 5(a), (4n+0th sheet) indicates the average basis weight of the 10 sheets of recording material P fed as the 4th, 8th, 12th, ..., and 40th sheets of the 40 sheets of recording material P. Similarly, (4n+1)th sheet indicates the average basis weight of the 10 sheets of recording material P fed as the 1st, 5th, 9th, ..., and 37th sheets, and (4n+2)th sheet indicates the average basis weight of the 10 sheets of recording material P fed as the 2nd, 6th, 10th, ..., and 38th sheets. Also, (4n+3)th sheet indicates the average basis weight of the 10 sheets of recording material P fed as the 3rd, 7th, 11th, ..., and 39th sheets. Although the number of sheets of recording material P per cycle differs in Figures 5(b), (c), and (d), the diagrams can be viewed in the same way.

In the (4n+0th) group of 10 recording materials P, the 20th and 40th sheets include a recording material P with a basis weight of 60 g/ ^m2 , and the other 8 sheets of recording material P also have a basis weight of 60 g/ ^m2 . Therefore, the average basis weight of the group of recording materials P included in (4n+0th) is 84 g/ ^m2 (=(60 g/ ^m2 x 2 + 90 g/ ^m2 x 8)/10). In the (4n+1th) group of 10 recording materials P, the 5th and 25th sheets include a recording material P with a basis weight of 60 g/ ^m2 , and the other 8 sheets of recording material P also have a basis weight of 60 g/ ^m2 . Therefore, the average basis weight is 84 g/ ^m2 (=(60 g/ ^m2 x 2 + 90 g/ ^m2 x 8)/10). In the group of 10 recording materials P (4n+2th sheet), the 10th and 30th sheets include a recording material P with a basis weight of 60 g/ ^m2 , and the other 8 sheets of recording material P also have a basis weight of 60 g/ ^m2 . Therefore, the average basis weight is 84 g/ ^m2 (=(60 g/ ^m2 x 2 + 90 g/ ^m2 x 8)/10). In the group of 10 recording materials P (4n+3rd sheet), the 15th and 35th sheets include a recording material P with a basis weight of 60 g/ ^m2 , and the other 8 sheets of recording material P also have a basis weight of 60 g/ ^m2 . Therefore, the average basis weight is 84 g/ ^m2 (=(60 g/ ^m2 x 2 + 90 g/ ^m2 x 8)/10).

5B, the average basis weight of the (5n+0)th sheet of recording material P is 60 g/ ^m2 , and the average basis weights of the other (5n+1)th to (5n+4)th sheets of recording material P are 90 g/ ^m2 . There is a large basis weight difference of 30 g/ ^m2 (=90 g/ ^m2 - 60 g/ ^m2 ) between the average basis weight of the (5n+0)th sheet of recording material P and the average basis weights of the other recording materials P, showing a clear periodicity.

In Fig. 5C, the number of target recording materials P varies depending on the group to which the recording materials P to be fed belong. The number of target recording materials P is six for the (6n+0)th and (6n+5)th sheets, and seven for the (6n+1)th to (6n+4)th sheets. The average basis weights for each group of the (6n+0)th to (6n+5)th sheets are 85 g/ ^m2 , approximately 86 (85.7) g/ ^m2 , approximately 86 (85.7) g/ ^m2 , approximately 86 (85.7) g/ ^m2 , approximately 81 (81.4) g/ ^m2 , and 80 g/ ^m2 , respectively. The values in parentheses are the average basis weights calculated to one decimal place.

5(d), like FIG. 5(c), the number of target recording materials P differs depending on the group to which the feeding order of the recording materials P belongs. The number of target recording materials P is five for the (7n+0)th and (7n+6)th sheets, and six for the (7n+1)th to (7n+5)th sheets. The average basis weights for each group of the (7n+0)th to (7n+6)th sheets are 84 g/ ^m2 , 85 g/m2, 85 g/ ^m2 , 85 g/ ^m2 , ⁸⁵ g/ ^m2 , 80 g/ ^m2 , and 84 g/ ^m2 , respectively.

Table 3 shows the maximum basis weight (unit: g/m2), minimum basis weight (unit: g/ ^m2 ), and basis weight difference (unit: g/ ^m2 ) between the maximum basis weight and the minimum basis weight for each group of recording material P at each cycle and number of sheets, based on the basis weight data for each cycle and number of sheets shown in Figure ⁵ .

As shown in Table 3, when the number of sheets in the cycle is 4 sheets (4-sheet cycle), the maximum basis weight in the group with different feeding orders is 84 g/m ² , the minimum basis weight is also 84 g/m ² , and the basis weight difference is 0 g/m ² . When the number of sheets in the cycle is 5 sheets (5-sheet cycle), the maximum basis weight in the group with different feeding orders is 90 g/m ² , the minimum basis weight is 60 g/m ² , and the basis weight difference is 30 g/m ² . When the number of sheets in the cycle is 6 sheets (6-sheet cycle), the maximum basis weight in the group with different feeding orders is 85.7 g/m ² , the minimum basis weight is 80 g/m ² , and the basis weight difference is 5.7 g/m ² . When the number of sheets in the cycle is 7 sheets (7-sheet cycle), the maximum basis weight in the group with different feeding orders is 85 g/m ² , the minimum basis weight is 80 g/m ² , and the basis weight difference is 5 g/m ² . When comparing based on the number of sheets of recording material P per cycle, the basis weight difference is greatest when the cycle is five sheets. Furthermore, since the basis weight difference at this time is greater than the threshold value of 6 g/ ^m2 , the 40 sheets of recording material P shown in FIG. 4 are detected as having a periodicity of five sheets. Furthermore, the minimum number of sheets of recording material P fed before starting to detect the periodicity of the recording material P may be small if the detection accuracy of the media sensor 30 is high, but a larger number is required if the detection accuracy is low. In this embodiment, it is assumed that the periodicity can be detected if 40 sheets of recording material P are fed.

[Image Forming Condition Setting Control]
Next, a control operation for setting image forming conditions by the image forming control section 40 of this embodiment will be described. Fig. 6 is a flow chart showing a control sequence for controlling image forming conditions according to the basis weight of the recording material P fed from the paper feed tray 21. The process shown in Fig. 6(A) is started when the power supply of the printer 1 is turned on, and is executed by the CPU 41 of the image forming control section 40. The process shown in Fig. 6(B) is started from the process in Fig. 6(A) and is executed by the CPU 41 of the image forming control section 40. Note that in the process shown in Fig. 6(B), the statistical process for the basis weight of the recording material P to be executed uses a moving average of basis weights detected for successive recording materials P.

First, the process shown in FIG. 6A will be described. In step (hereinafter, S) 300, the CPU 41 sets the number of detected recording materials, which indicates the number of recording materials P whose characteristics (grammage here) are detected by the media sensor 30, provided in the RAM 41b, to 0. In S301, the CPU 41 determines whether the paper feed tray 21 has been opened or closed. If the CPU 41 determines that the paper feed tray 21 has been opened or closed, the process proceeds to S302, and if the CPU 41 determines that the paper feed tray 21 has not been opened or closed, the process proceeds to S303. In S302, the CPU 41 sets the number of detected recording materials provided in the RAM 41b to 0. If the paper feed tray 21 has been opened or closed, it is possible that a stack of recording materials having different periodicities is loaded on the paper feed tray 21. Therefore, in this embodiment, the period of the detected recording materials P is reset, and periodicity detection of the recording materials P fed from the paper feed tray 21 is performed again.

In S303, the CPU 41 determines whether there is a print job in response to a print request from an external device such as an image scanner or a host computer, and if there is a print job, the process proceeds to S304. If there is no print job, the process returns to S301. In S304, the CPU 41 executes a preparatory operation for executing a print job in response to a print request from an external device such as an image scanner or a host computer (starts image formation preparation). In detail, the CPU 41 drives the motor 20 to drive various rollers inside the printer 1, and also supplies power to the heater 60 of the image heating device 13, and performs temperature control so that the target temperature is reached, which allows optimal fixing control according to the characteristics of the recording material. In S305, the CPU 41 obtains the temperature of the heater 60 detected by the thermistor 62, and determines whether it has reached a predetermined temperature at which image formation is possible. If the CPU 41 determines that the temperature of the heater 60 has reached the predetermined temperature, the process proceeds to S306, and if it determines that the temperature of the heater 60 has not reached the predetermined temperature, the process returns to S305. In S306, the CPU 41 reads from the RAM 41b the number of detected sheets of recording material, which indicates the number of sheets of recording material P whose basis weight has been detected by the media sensor 30.

In S307, the CPU 41 outputs a paper feed start signal to drive the feed roller 22, feed one sheet of recording material P from the paper feed tray 21, and transport it to the transport roller pair 23. In S308, the CPU 41 acquires the detection result of the top sensor 24 and determines whether the top sensor 24 has detected the recording material P. If the CPU 41 determines that the top sensor 24 has detected the recording material P, it proceeds to S309, and if the CPU 41 determines that the top sensor 24 has not detected the recording material P, it returns to S308.

In S309, the CPU 41 detects the characteristics of the fed recording material P. In detail, the CPU 41 calculates the basis weight of the recording material P based on the transmission coefficient calculated by the calculation unit 447 of the basis weight detection control unit 42 from the characteristic data of the recording material P detected by the media sensor 30, and stores it in the RAM 41b. In S310, the CPU 41 adds 1 to the number of recording materials detected. In S311, the CPU 41 determines the characteristics of the recording material P fed this time. In detail, the CPU 41 performs statistical processing to obtain a moving average of the basis weight of the recording material P based on the basis weight of the recording material P calculated in S309, and calculates the basis weight of the recording material P fed this time. In S312, the CPU 41 determines image formation conditions such as the transfer voltage applied to the transfer roller 12, the fixing temperature of the image heating device 13, and the conveying speed of the recording material P based on the basis weight of the recording material P fed this time calculated in S309. Then, based on the determined image forming conditions, the CPU 41 performs a series of image forming operations, including electrostatic latent image formation, development processing, transfer processing, and fixing processing, to form an image on the recording material P. In S313, the CPU 41 determines whether the print job is completed, and if the print job is not completed, returns control to S307, and if the print job is completed, proceeds to S314. In S314, the CPU 41 stores the detected number of recording materials in the RAM 41b, and ends the process.

Next, the recording material characteristic discrimination process shown in FIG. 6B, which is started from the process of S311 in FIG. 6A, will be described. In the recording material discrimination process shown in FIG. 6B, the periodicity detection process for detecting the periodicity of the recording material P described above at 4-sheet, 5-sheet, 6-sheet, and 7-sheet intervals will not be performed until the number of detected recording materials reaches a predetermined number of 40 sheets or more. In addition, when the periodicity of the recording material P fed is detected by the periodicity detection process, a statistical process is performed to calculate a moving average value for the number of sheets according to the detected periodicity. On the other hand, until the periodicity is detected, a statistical process is performed to calculate a moving average value for the five recording materials P, including the recording material P fed this time and the four recording materials fed immediately before.

In S320, the CPU 41 determines whether or not the minimum number of recording materials (40 in this case) required for statistical processing has been fed from the paper feed tray 21 based on the value of the number of detected recording materials. If the CPU 41 determines that the currently fed recording material P is the 40th or greater recording material, it advances the process to S321, and if the CPU 41 determines that the currently fed recording material P is less than the 40th recording material, it advances the process to S327.

In S321, the CPU 41 obtains the basis weights of the last 40 sheets of recording material P, including the recording material P fed this time, from the RAM 41b, and executes the above-mentioned periodicity detection process for a cycle of 4 sheets of recording material P to obtain the maximum and minimum basis weights in the cycle of 4 sheets. In S322, the CPU 41 obtains the basis weights of the last 40 sheets of recording material P, including the recording material P fed this time, from the RAM 41b, and executes the above-mentioned periodicity detection process for a cycle of 5 sheets of recording material P to obtain the maximum and minimum basis weights in the cycle of 5 sheets. In S323, the CPU 41 obtains the basis weights of the last 40 sheets of recording material P, including the recording material P fed this time, from the RAM 41b, and executes the above-mentioned periodicity detection process for a cycle of 6 sheets of recording material P to obtain the maximum and minimum basis weights in the cycle of 6 sheets. In S324, the CPU 41 obtains the basis weights of the last 40 sheets of recording material P, including the recording material P that was currently fed, from the RAM 41b, and executes the above-described process of detecting periodicity of the recording material P in a cycle of seven sheets to obtain the maximum and minimum basis weights in the cycle of seven sheets.

In S325, the CPU 41 determines whether the basis weight difference between the maximum and minimum basis weight values in each sheet cycle calculated in S321 to S324 is equal to or greater than a predetermined value (here, 6 g/ ^m2 or more). If there is a sheet cycle in which the basis weight difference is equal to or greater than the predetermined value, the CPU 41 determines that the recording material P has periodicity and proceeds to S326, and if there is no sheet cycle in which the basis weight difference is equal to or greater than the predetermined value, it determines that the recording material P does not have periodicity and proceeds to S327.

In S326, the CPU 41 sets the periodic sheet count determined to be periodic in the process of S325 as the moving average sheet count of the recording material that is the subject of the moving average value calculated in S328, and proceeds to S328. In S327, the CPU 41 sets the number of recording materials that is the subject of the moving average value calculated in S328 to a predetermined number of 5 sheets, and sets it as the moving average sheet count. In S328, the CPU 41 obtains from RAM 41b the basis weight of the most recent number of recording materials P set as the moving average sheet count, including the recording material P fed this time, calculates the moving average value as the basis weight of the recording material P fed this time, and ends the process.

[Change Periodicity]
Next, a change in the number of recording materials P that are the subject of the moving average in the statistical processing of this embodiment, that is, a change in the periodicity of the recording materials P, will be described. Fig. 7 is a graph showing the transition of the detected basis weight of the recording materials P and the results of statistical processing when one out of six recording materials P with a basis weight of 60 g/ ^m2 is fed from the paper feed tray 21, and the remaining five sheets of recording paper P with a basis weight of 90 g/ ^m2 are continuously fed from the paper feed tray 21. In Fig. 7, the vertical axis shows the basis weight (unit: g/ ^m2 ) of the recording materials P, and the horizontal axis shows the number of recording materials P fed from the paper feed tray 21 (the number of sheets). The black circles in the graph of Fig. 7 are plots of the basis weights of the fed recording materials P. Also, in Figure 7, the graph shown by the solid line ("Comparative Example") is a graph connecting the moving average values of five consecutive sheets of recording material P, and the graph shown by the dashed line ("Example 1") is a graph connecting the moving average values of six consecutive sheets of recording material P.

Table 4 summarizes whether or not the basis weight of the recording material P is periodically detected in the "Comparative Example" and "Example 1" shown in Figure 7, and whether or not the number of sheets of recording material P that are the subject of the moving average is changed.

As shown in Table 4, in the case of the "Comparative Example", the periodicity of the recording material is not detected (no periodicity detection) and the number of sheets is not changed (no change in number of sheets). Therefore, in FIG. 7, the graph of the moving average value of the comparative example shown by the solid line indicates the moving average value of the basis weight of the five sheets of recording material P fed consecutively, that is, the recording material P (also called the paper) fed this time and the four sheets of recording material P fed immediately before. In FIG. 7, the first to fifth sheets of recording material P are fed with the same recording material P having a basis weight of 90 g/m ² , so the moving average value remains at 90 g/m ^2. However, the sixth sheet of recording material P is fed with a basis weight of 60 g/m ² , so the moving average value of the sixth sheet falls to 84 g/m ^2. Next, for the seventh to tenth sheets, the sixth sheet of recording material P having a basis weight of 60 g/m ² is included in the moving average value, so the same moving average value as the sixth sheet is calculated. The moving average value of the 11th recording material P rises to 90 g/m2 because the 7th to 11th recording materials P do not include any recording material P with a basis weight of 60 g/ ^m2 . The phenomenon in which the moving average value changes from 84 g/ ^m2 to 90 g ^{/ m2} also occurs in the cases of the 17th and 23rd recording materials P. As a result, the basis weights of the 17th and 23rd recording materials P and the four recording materials P fed immediately before them are erroneously determined to be different, even though there is no change in basis weight between them.

On the other hand, in the case of "Example 1", as shown in Table 4, the processes of S321 to S324 in FIG. 6B are executed to detect the periodicity of the recording material (period detection is performed), and the number of sheets is changed according to the detected periodicity of the recording material P (number of sheets is changed). Here, it is assumed that in Example 1, it is known in advance that recording materials P with different basis weights are fed from the paper feed tray 21 in a cycle of six sheets. In FIG. 7, the graph of the moving average value of Example 1 shown by the dashed line indicates the moving average value of the basis weights of the recording material P fed this time and the five sheets of recording material P fed immediately before after the number of sheets of recording paper P to be moved is changed from five sheets to six sheets. The moving average value including the sixth sheet of recording material P with a different basis weight decreases from 90 g/m ² to 85 g/m ² , as in the above-mentioned "Comparative Example". Then, the moving average value for the seventh sheet and thereafter always includes one sheet of recording material P with a basis weight of 60 g/ ^m2 , so the moving average value does not change and the recording materials P are determined to have the same basis weight.

Table 5 summarizes the basis weight and optimal fixing temperature of the fed recording material P shown in Figure 7, as well as the basis weight of the recording material P calculated using the moving average value of the basis weight of the recording material P in the "Comparative Example" and "Example 1", the fixing temperature of the image heating device 13 corresponding to the basis weight, and the fixing performance.

In Table 5, "Fed recording material" shows the "basis weight (unit: g/ ^m2 )" corresponding to the 1st to 5th and 6th to 14th recording materials P, and the "optimum fixing temperature (unit: °C)" of the image heating device 13 corresponding to the basis weight. Also, "basis weight (unit: g/ ^m2 )" of "Comparative example" shows the moving average value of the basis weight of the currently fed recording material P and the four immediately preceding recording materials. Furthermore, "fixing temperature (unit: °C)" of "Comparative example" shows the fixing temperature of the image heating device 13 corresponding to the "basis weight" of "Comparative example", and "fixing performance" shows a fixing performance evaluation comparing the "fixing temperature" of "Comparative example" with the "optimum fixing temperature" of the "fed recording material". Similarly, "basis weight (unit: g/ ^m2 )" of "Example 1" shows the moving average value of the basis weight of the currently fed recording material P and the five immediately preceding recording materials. Furthermore, the "Fixing temperature (unit: °C)" of "Example 1" shows the fixing temperature of the image heating device 13 corresponding to the "basis weight" of "Example 1", and the "Fixing performance" shows a fixing performance evaluation comparing the "Fixing temperature" of "Example 1" with the "optimum fixing temperature" of the "fed recording material".

As shown in Table 5, in the "Comparative Example", each time it is determined that the basis weight changes from 90 g/m ² to 84 g/m ² and from 84 g/m ² to 90 g/m ² , the fixing temperature of the image heating device 13 is switched from 195° C. to 191° C. and from 191° C. to 195° C. Note that the fixing temperature when the basis weight is 90 g/m ² is 195° C. according to Table 1. The fixing temperature of 191° C. when the basis weight is 84 g/m ² is calculated by linearly interpolating 185° C. and 195° C., which are the fixing temperatures when the basis weight is 75 g/m ² and 90 g/m ² in Table 1. When the fixing temperature of the image heating device 13 is set to 191° C. (for example, in the case of the sixth to tenth sheets of recording material P), the fixing temperature is 4° C. away from the optimal fixing temperature of 195° C. for the seventh to tenth sheets of recording material P, and therefore the fixing performance is "good". As a result, there are cases where the fixing performance is "good" (the first to sixth, eleventh, and twelfth sheets of recording material P) and cases where it is "good or bad" (the seventh to tenth, thirteenth, and fourteenth sheets of recording material P), resulting in unevenness in the fixing quality of the recording material P.

On the other hand, in "Example 1", the basis weight of the first to fifth sheets of recording material P is 90 g/ ^m2 , but the basis weight of the sixth and subsequent sheets of recording material P is constant at 85 g/ ^m2 . As a result, the fixing temperature of the image heating device 13 for the sixth and subsequent sheets of recording material P is uniformly set to 192°C. Therefore, until the print job is completed, the fixing performance is always "good", and the fixing quality of the recording material P is stable. Note that the fixing temperature of 192°C when the basis weight is 85 g/ ^m2 is calculated by linearly interpolating 185°C and 195°C, which are the fixing temperatures when the basis weights are 75 g/ ^m2 and 90 g/ ^m2 in Table 1. As described above, by changing the number of sheets of recording material P to be statistically processed according to the number of sheets of recording material P in the cycle, it is possible to achieve stable fixing performance.

As described above, this embodiment improves the accuracy of detecting the characteristics of the recording material, thereby improving the quality of the image formed on the recording material.

In the first embodiment, the number of sheets of recording material to be subjected to statistical processing to calculate the basis weight by moving average is changed according to the periodicity of the characteristic values of the recording material fed from the paper feed tray, and fixing control of the image heating device is performed based on the basis weight of the recording material calculated by the statistical processing. In the second embodiment, when the periodicity of the characteristic values of the recording material fed from the paper feed tray is detected, the degree to which the detection result of the basis weight of the recording material fed this time is reflected is increased according to the number of times the periodicity is detected, thereby improving the accuracy of the fixing temperature of the image heating device. Note that the configuration of the image forming device in this embodiment is the same as in the first embodiment, and the same devices and members are designated by the same reference numerals, and the description here is omitted.

[Image Forming Condition Setting Control]
A control operation for setting image forming conditions by the image forming control unit 40 of this embodiment will be described. FIG. 8 is a flowchart showing a control sequence for controlling image forming conditions according to the basis weight of the recording material P fed from the paper feed tray 21. The process shown in FIG. 8A is started when the power supply of the printer 1 is turned on, and is executed by the CPU 41 of the image forming control unit 40. The process shown in FIG. 8B is started from the process in FIG. 8A, and is executed by the CPU 41 of the image forming control unit 40. Note that, in FIG. 6B of the first embodiment, a moving average is used for the statistical processing of the basis weight of the recording material P, but in FIG. 8B, a weighted average is used for the statistical processing of the basis weight of the recording material P.

First, the process shown in FIG. 8A will be described. In S400, the CPU 41 sets the number of detected recording materials, which indicates the number of sheets of recording material P whose characteristics (grammage here) are detected by the media sensor 30, and the number of periodic detections, which indicates the number of periodic detections in the process of FIG. 8B described later, to 0, both of which are provided in the RAM 41b. In S301, the CPU 41 determines whether the paper feed tray 21 has been opened or closed. If the CPU 41 determines that the paper feed tray 21 has been opened or closed, the process proceeds to S401, and if the CPU 41 determines that the paper feed tray 21 has not been opened or closed, the process proceeds to S303. In S401, the CPU 41 sets the number of detected recording materials and the number of periodic detections, which are provided in the RAM 41b, to 0. If the paper feed tray 21 has been opened or closed, it is possible that a stack of recording materials having different periodicities is loaded on the paper feed tray 21. Therefore, in this embodiment, the detected period of the recording material P is reset, and the periodicity of the recording material P fed from the paper feed tray 21 is detected again.

In FIG. 8A, steps S303 to S305 are the same as steps S303 to S305 in FIG. 6A of the first embodiment, and their explanations are omitted here. In S402, the CPU 41 reads the number of detected sheets of recording material and the number of periodic detections from the RAM 41b. The processes of S307 to S312 are the same as steps S307 to S312 in FIG. 6A of the first embodiment, and their explanations are omitted here. In S313, the CPU 41 determines whether the print job has ended, and if the print job has not ended, returns control to S307, and if the print job has ended, proceeds to S403. In S403, the CPU 41 stores the number of detected sheets of recording material and the number of periodic detections in the RAM 41b, and ends the process.

Next, the recording material characteristic discrimination process shown in FIG. 8B, which is started from the process of S311 in FIG. 8A, will be described. In the recording material discrimination process shown in FIG. 8B, the periodicity detection process for detecting the periodicity of the recording material P described above is not performed until the number of detected recording materials reaches a predetermined number of 40 or more sheets. In addition, until the periodicity of the recording material P fed by the periodicity detection process is detected, a statistical process is performed to calculate a weighted average value using the same weighted average coefficient for the recording material P fed this time and the five recording materials P including the four recording materials fed immediately before. On the other hand, when the periodicity of the recording material P fed by the periodicity detection process is detected, the following process is performed. That is, a statistical process is performed to calculate a weighted average value by changing the weighted average coefficient for each recording material for the recording material P fed this time and the five recording materials P including the four recording materials fed immediately before, depending on the number of times of the periodicity of the detected recording material P. In detail, statistical processing is performed to calculate a weighted average value by increasing the weighted average coefficient of the recording material P currently fed and decreasing the weighted average coefficient of the recording material P fed immediately before, depending on the number of times the periodicity of the recording material P is detected.

In S320, the CPU 41 determines whether or not at least the minimum number of recording materials required for statistical processing (here, at least 40 sheets) have been fed from the paper feed tray 21 based on the value of the number of detected recording materials. If the CPU 41 determines that the currently fed recording material P is the 40th sheet or more of recording material, it proceeds to S321, and if it determines that the currently fed recording material P is less than the 40th sheet of recording material, it proceeds to S410. The processes of S321 to S324 are similar to those of S321 to S324 in FIG. 6B of the first embodiment, and will not be described here.

In S405, the CPU 41 changes the weighted average coefficient of the five sheets of recording material P when calculating the weighted average value according to the number of times the periodicity is detected in the processes of S321 to S324. In this case, the CPU 41 increases the weighted average coefficient reflecting the basis weight of the currently fed recording material P when calculating the weighted average value of the basis weight as the number of times the periodicity is detected increases, and decreases the weighted average coefficient reflecting the basis weight of the four sheets of recording material P fed immediately before. Specific examples of the weighted average coefficient will be described later.

In S406, the CPU 41 determines whether the basis weight difference between the maximum and minimum basis weight values in each sheet number cycle calculated in S321 to S324 is equal to or greater than a predetermined value (here, 6 g/ ^m2 or greater). If there is a sheet number cycle in which the basis weight difference is equal to or greater than the predetermined value, the CPU 41 determines that the recording material P is periodic and proceeds to S407, and if there is no sheet number cycle in which the basis weight difference is equal to or greater than the predetermined value, it determines that the recording material P is not periodic and proceeds to S408. In S407, the CPU 41 updates the number of cycle detections by adding 1, and proceeds to S411.

In S408, the CPU 41 determines whether the number of periodic detections is 0, i.e., whether the periodicity of the basis weight of the recording material P has never been detected in the processes of S321 to S324. If the number of periodic detections is 0, the CPU 41 advances the process to S411, and if the number of periodic detections is not 0, the CPU 41 advances the process to S409. In S409, the CPU 41 determines that a deviation has occurred between the basis weight of the recording material P fed from the paper feed tray 21 and the basis weight that had been calculated for each group that had the same feeding order, and that the periodicity of the recording material P has changed. The CPU 41 then resets the detected period of the recording material P and determines that it is necessary to detect the periodicity of the recording material P fed from the paper feed tray 21 again. Therefore, the CPU 41 sets the number of cycle detections to 0, sets the weighted average coefficient reflecting the basis weight of the recording material P fed this time to the same value as the weighted average coefficient reflecting the basis weights of the four sheets of recording material P fed immediately before, and proceeds to step S411.

In S410, if the number of recording materials detected in the processing of S311 is less than 40, the CPU 41 sets the weighted average coefficient reflecting the basis weight of the recording material P currently fed and the weighted average coefficient reflecting the basis weight of the four sheets of recording material P fed immediately before to the same value. In S411, the CPU 41 obtains the basis weights of the recording material P currently fed and the four sheets of recording material P fed immediately before from RAM 41b based on the set weighted average coefficient, calculates the weighted average value as the basis weight of the recording material P currently fed, and ends the processing.

[Example of weighted average coefficient]
When the periodicity of the characteristic value (grammage in this case) of the recording material P fed from the paper feed tray 21 is detected, the characteristic value of the recording material P to be fed is known to some extent in advance. Therefore, in the past, statistical processing such as moving average values was performed taking into account detection errors, but as in this embodiment, it is possible to increase the proportion of the characteristic value of the paper, which is the recording material P fed this time, reflected in the statistical processing. Furthermore, the more times the period of the characteristic value of the recording material P is detected in the same print job, the higher the probability that the recording material P having the predicted characteristic value will be fed, so it is possible to further increase the proportion of the characteristic value of the recording material P fed this time reflected.

Table 6 shows an example of weighted average coefficients for the recording material P fed this time (shown as "corresponding paper" in Table 6) and the immediately previous recording material P, which is the recording material P fed immediately before, set in the process of FIG. 8B described above. In "period detection", "none" indicates that the process of detecting the periodicity of the recording material, that is, the process of S321 to S324 in FIG. 8B, is not executed, and "yes" indicates that the process of S321 to S324 in FIG. 8B is executed. Furthermore, "period detection count" indicates the number of times that the periodicity of the recording material is detected in the process of S321 to S324 in FIG. 8B. Furthermore, "corresponding paper", "one sheet before", "two sheets before", "three sheets before", and "four sheets before" respectively indicate the recording material P fed this time, the recording material P fed one sheet before, the recording material P fed two sheets before, the recording material P fed three sheets before, and the recording material P fed four sheets before. The numbers (unit: %) shown in each column of “Related Paper,” “1 Sheet Ago,” “2 Sheets Ago,” “3 Sheets Ago,” and “4 Sheets Ago” are weighted average coefficients for each recording material P used when calculating the weighted average value in S411 of Figure 8 (B).

As shown in Table 6, when the process of detecting the periodicity of the characteristic values of the recording material P is not performed (when "periodicity detection" is "not present"), the weighted average coefficients of "the paper in question" to "the four previous sheets" of the recording material P are each 20%. Therefore, the characteristic values (grammage) of each recording material P are uniformly reflected in the weighted average value. On the other hand, when the process of detecting the periodicity of the characteristic values of the recording material P is performed, the weighted average coefficient, which is the proportion to which the characteristic values of the target recording material P are reflected, is changed depending on how many times the periodicity of the recording material P is detected in the same print job. For example, when the processes of S321 to S324 in FIG. 8B are performed but the periodicity of the recording material is not detected, "periodicity detection" is "present" and "number of times periodicity detection" is "0 times", the weighted average coefficient of "the paper in question" is 60%, and the weighted average coefficients of the four previous sheets of recording material P are each 10%. Then, when the periodicity of the characteristic values of the recording material P is detected once, i.e., "periodicity detection" is "yes" and "number of periodicity detections" is "one time", the weighted average coefficient of "the relevant paper" is 80%, the weighted average coefficients of the two most recent sheets are 10%, and the weighted average coefficients of the other recording materials P are 0%. Furthermore, when the periodicity of the characteristic values of the recording material P is detected two or more times, i.e., "periodicity detection" is "yes" and "number of periodicity detections" is "two or more times", the weighted average coefficient of "the relevant paper" is 100%, and the weighted average coefficients of the four most recent sheets are 0%. Thus, in this embodiment, as the number of detections of the periodicity of the characteristic values of the recording material P increases from 0 times, 1 time, to 2 times, the weighted average coefficient of "the relevant paper", which is the recording material P fed this time, is increased to 60%, 80%, and 100%. As a result, as the number of times the periodicity of the recording material P is detected increases, fixing control of the image heating device 13 becomes possible according to the characteristics (here, the basis weight) of the recording material P currently fed.

[Change in weighted average coefficient]
Next, a description will be given of a change in the weighted average coefficient of the recording material P that is the subject of the weighted average in the statistical processing of this embodiment. FIG. 9 is a graph showing the transition of the detected basis weight of the recording material P and the statistical processing result when one out of six recording materials P with a basis weight of 60 ^g / ^m2 are fed from the paper feed tray 21, and the remaining five sheets of recording paper P with a basis weight of 90 g/m2 are fed continuously from the paper feed tray 21. In FIG. 9, the vertical axis shows the basis weight (unit: g/ ^m2 ) of the recording material P, and the horizontal axis shows the number of sheets of recording material P fed from the paper feed tray 21 (the number of sheets). The black circles in the graph of FIG. 9 are plots showing the basis weight of the fed recording material P. In addition, in FIG. 9, the graph shown by the solid line ("Example 1") is a graph that connects the moving average values of six consecutive sheets of recording material P, and the graph shown by the broken line ("Example 2") is a graph that connects the weighted average values of six consecutive sheets of recording material P.

Table 7 summarizes whether or not the basis weight of the recording material P is detected periodically in "Example 1" and "Example 2" shown in Figure 9, and whether or not the weighted average coefficient is changed due to the periodic detection of the basis weight of the recording material P (indicated as coefficient change in the table).

In both "Example 1" and "Example 2" shown in FIG. 9, the feeding of the recording material P from the paper feed tray 21 is started in a state where periodicity detection is performed, that is, in a state where the processes of S321 to S324 are performed in FIG. 8B. As shown in Table 7, in the case of Example 1, the periodicity of the recording material P is detected ("periodicity detection" is "yes"), but since the statistical processing calculates a moving average value, the weighted average coefficient is not changed when the periodicity is detected ("coefficient change" is "no"). In FIG. 9, the graph of "Example 1" shown by the solid line shows the moving average value of the basis weight of the recording material P fed this time and the five sheets of recording material P fed immediately before. When the sixth sheet of recording material P is fed, the moving average value including the sixth sheet of recording material P with a different basis weight decreases from 90 g/m ² to 85 g/m ² . When the seventh or subsequent sheets of recording material P are fed, one sheet of 60 g/m ² recording material P is always included, so the moving average value does not change and the recording materials P are determined to have the same basis weight.

On the other hand, in the case of "Example 2", the weighted average coefficient for each recording material P in the statistical processing is changed according to the number of times the periodicity of the recording material P is detected, and the reflection ratio of the characteristic value (here, basis weight) of the paper which is the currently fed recording material P is increased. For example, even if the processing for detecting the periodicity of the recording material P in S321 to S324 in FIG. 8B is executed, the periodicity is not detected from the first sheet to the sixth sheet of recording material P. Therefore, the weighted average coefficient for this period is the weighted average coefficient for the case where "periodicity detection" in Table 6 is "yes" and "number of times periodicity detection" is "0 times". Therefore, the basis weight of the sixth sheet of recording material P is 72 g/ ^m2 (=60 g/ ^m2 x 0.6 + 90 g/ ^m2 x 0.1 x 4).

Then, when the seventh sheet of recording material P is fed, in the process of detecting the periodicity of the recording material P in S321 to S324 in Fig. 8B, it is detected that the period is six sheets, and the weighted average coefficient when "periodic detection" in Table 6 is "yes" and "number of times of periodic detection" is "1 time" is applied. As a result, the basis weight of the seventh and eighth sheets of recording material P is 87 g/ ^m2 (= 90 g/ ^m2 x 0.8 + 60 g/ ^m2 x 0.1 + 90 g/ ^m2 x 0.1). Similarly, the basis weight of the ninth to eleventh sheets of recording material P is 90 g/ ^m2 (= 90 g/ ^m2 x 0.8 + 90 g/ ^m2 x 0.1 + 90 g/ ^m2 x 0.1). Further, the basis weight of the twelfth sheet of recording material P is 66 g/m ² (=60 g/m ² ×0.8+90 g/m ² ×0.1+90 g/m ² ×0.1).

Next, when the 13th sheet of recording material P is fed, the second 6-sheet cycle is detected in the process of detecting the periodicity of the recording material P in S321 to S324 in FIG. 8B, and the weighted average coefficient in the case where "cycle detection" in Table 6 is "Yes" and "cycle detection count" is "2 times" is applied. As a result, the basis weight of the recording material P from the 13th sheet onwards is the basis weight of the recording material P fed as is, which is the detected basis weight. In this way, in the second embodiment, the reflection ratio of the basis weight of the recording material P fed this time increases according to the number of times the cycle is detected, so that the basis weight calculated as a result of the statistical processing for the 6th sheet, the 12th sheet, and so on approaches 60 g/m ^2. Then, for the 13th sheet and onwards of recording material P, for which the cycle detection is performed for the second time, only the detection result of the recording material P fed this time, which is the relevant paper, is reflected, and the basis weight is determined by the basis weight of the recording material P fed this time.

Table 8 summarizes the basis weight and optimal fixing temperature of the fed recording material P shown in Figure 9, the basis weight of the recording material P calculated by the moving average in "Example 1" and the weighted average in "Example 2", the fixing temperature, fixing performance, and excess temperature of the image heating device 13 corresponding to the basis weight.

In Table 8, "Fed recording material" shows the "basis weight (unit: g/ ^m2 )" corresponding to the 1st to 23rd recording material P, and the "optimum fixing temperature (unit: °C)" of the image heating device 13 corresponding to the basis weight. Furthermore, "basis weight (unit: g/ ^m2 )" of "Example 1" shows the moving average value of the basis weight of the currently fed recording material P and the immediately preceding 5 recording materials. Furthermore, "fixing temperature (unit: °C)" of "Example 1" shows the fixing temperature of the image heating device 13 corresponding to the "basis weight" of "Example 1", and "fixing performance" shows a fixing performance evaluation comparing the "fixing temperature" of "Example 1" with the "optimum fixing temperature" of the "fed recording material". Furthermore, "excess temperature (unit: °C)" of "Example 1" shows the temperature difference between the "fixing temperature" and the "optimum fixing temperature" of the 6th, 12th, and 18th recording materials P with a basis weight of 60 g/ ^m2 .

Similarly, the "basis weight (unit: g/ ^m2 )" of "Example 2" indicates the weighted average value of the basis weights of the currently fed recording material P and the immediately preceding recording material. Furthermore, the "fixing temperature (unit: °C)" of "Example 2" indicates the fixing temperature of the image heating device 13 corresponding to the "basis weight" of "Example 2", and the "fixing performance" indicates a fixing performance evaluation comparing the "fixing temperature" of "Example 2" with the "optimum fixing temperature" of the "fed recording material". And the "excess temperature (unit: °C)" of "Example 2" indicates the temperature difference between the "fixing temperature" and the "optimum fixing temperature" of the 6th, 12th, and 18th sheets of recording material P with a basis weight of 60 g/ ^m2 .

In "Example 1", the first to fifth sheets of recording material P have a basis weight of 90 g/ ^m2 , but the basis weight of the sixth sheet and subsequent sheets of recording material P is constant at 85 g/ ^m2 . As a result, the fixing temperature of the image heating device 13 for the sixth sheet and subsequent sheets of recording material P is set uniformly to 192°C. Therefore, until the print job is completed, the fixing performance is always "good", but for the sixth, twelfth, and eighteenth sheets of recording material P, which have a basis weight of 60 g/ ^m2 , the fixing temperature is 17°C higher than 175°C, which is the optimum temperature for the basis weight, and power consumption is high.

On the other hand, in "Example 2", the weighted average coefficient is changed so as to increase the reflection ratio of the basis weight of the "relevant paper" by detecting the periodicity of the basis weight of the recording material P, so that the fixing temperature gradually approaches the optimum fixing temperature for the basis weight of the recording material P actually fed. As shown in Table 8, the basis weight of the recording material P having a basis weight of 60 g/m ² fed every sixth sheet is 72 g/m ² for the sixth sheet, but becomes 66 g/m ² for the twelfth sheet, and becomes 60 g/m ² for the eighteenth sheet. As a result, the fixing performance is always "good" until the print job is completed. Furthermore, for the sixth, twelfth, and eighteenth sheets of recording material P having a basis weight of 60 g/m ² , the excess temperature from 175° C., which is the optimum temperature for the basis weight, is +8° C., +4° C., and 0° C., respectively, and the power consumption is optimized compared to Example 1.

The optimization of fixing control using periodicity detection is described using an example in which the basis weight difference of the recording materials P is intentionally increased. In fact, the basis weight difference of the recording materials P in a single packed paper bundle is about 5 to 10 g/ ^m2 at most, but it has been confirmed that the same effect as in the above-mentioned embodiment is achieved.

As described above, when the periodicity of the recording material is detected, it becomes possible to estimate the type of recording material P that will be fed next, and it becomes possible to determine that the detection result by the media sensor 30 is most likely due to the characteristics of the recording material rather than a detection error. As a result, it becomes possible to make larger changes to the fixing operation of the image heating device 13 based on the detection result of the media sensor 30 than in the past, enabling fixing operation that is more suited to the characteristics of the recording material.

In this embodiment, in consideration of the effect of detection error of the media sensor 30, the weighted average coefficient of the paper in question is set to 60% at the beginning of the print job, and the weighted average coefficient of the other recording materials P is set to 40%. If the periodicity of the recording material P is subsequently detected within the same print job, the weighted average coefficient of the paper in question is further increased. Note that if the detection error of the media sensor 30 is small and the periodicity of the recording material P has already been detected, the weighted average coefficient of the paper in question may be set to 100% from the beginning of the print job.

In addition, in this embodiment, as the number of times the periodicity of the recording material P is detected increases, the weighted average coefficient of the characteristic values (basis weight) of the paper and the multiple sheets of recording material P fed immediately before is changed. However, when the periodicity of the recording material P is detected, the changed weighted average coefficient may also be reflected in the characteristic value information of the recording material P one cycle ago or two cycles ago.

In the above embodiment, the media sensor 30 is used as a means for detecting the characteristics (basis weight) of the recording material P, but the present invention is not limited to the media sensor 30. For example, instead of the media sensor 30, a sensor that detects the surface properties (surface roughness) or glossiness may be used, or a sensor that detects multiple characteristics of these recording material characteristics may be used. The CPU 41 may then determine whether such characteristics other than basis weight are periodic, and if it determines that there is periodicity, control may be performed to change the image formation conditions.

As described above, this embodiment improves the accuracy of detecting the characteristics of the recording material, thereby improving the quality of the image formed on the recording material.

10 process cartridge 13 image heating device 21 paper feed tray 30 media sensor 41 CPU

Claims (12)

a loading section on which recording materials are loaded;
an image forming unit for forming an image on the recording material fed from the stacking unit;
a detection means for detecting a characteristic of the recording material fed from the stacking section;
a control means for determining image forming conditions of the image forming means from the characteristics of at least one sheet of recording material detected by the detection means, and for controlling the image forming means so as to form an image on a recording material newly fed from the stacking section under the image forming conditions;
An image forming apparatus comprising:
the detection means includes a transmitting section that transmits ultrasonic waves, a receiving section that receives the ultrasonic waves transmitted by the transmitting section, and a calculating section that calculates a transmission coefficient of the recording material based on a result of receiving the ultrasonic waves through the recording material by the receiving section, the detecting section being disposed across a conveying path along which the recording material is conveyed;
The characteristic of the recording material is basis weight,
The control means
determining a basis weight of the recording material based on the transmission coefficient calculated by the calculation unit;
determining whether or not the characteristics of the recording material fed from the stacking section are periodic based on the detection results of the characteristics of the multiple sheets of recording material by the detection means, and when it is determined that the characteristics of the recording material are periodic, changing the image forming conditions in accordance with the periodicity;
An image forming apparatus characterized in that after the power of the image forming apparatus is turned on, it does not determine whether or not the characteristics of the recording material are periodic until a predetermined number of sheets or more of recording material have been fed from the stacking section, and when the power of the image forming apparatus is turned on and a predetermined number of sheets or more of recording material have been fed from the stacking section, it determines whether or not the characteristics of the recording material are periodic . The image forming apparatus according to claim 1, characterized in that the control means divides the predetermined number of recording materials fed from the stacking section into a plurality of groups corresponding to the cycle number of sheets of recording material in the order of feeding of the cycle number, and if there is a difference of more than a threshold value in the average value of the basis weight of the recording materials belonging to each divided feeding order, it determines that the basis weight of the recording materials has a periodicity corresponding to the cycle number of sheets. the loading section is detachably attached to the image forming apparatus,
The image forming apparatus according to claim 2, characterized in that, when the control means detects the attachment or detachment of the stacking unit from the image forming apparatus, it resets the number of sheets of recording material fed from the stacking unit , resets the detected periodicity, and again determines whether or not there is periodicity in the basis weight of the recording material fed from the stacking unit. The image forming apparatus according to claim 3, characterized in that, when the difference between the basis weight of the recording material detected by the detection means and the average basis weight of recording materials belonging to the same feeding sequence of the same cycle number as the recording material is equal to or greater than the threshold value, the control means resets the detected periodicity and again determines whether or not there is periodicity in the basis weight of the recording material fed from the stacking section . 5. The image forming apparatus according to claim 4, wherein the control means calculates the basis weight of the currently fed recording material based on a moving average of the basis weights of the most recently fed recording materials, including the currently fed recording material, detected by the detection means. 6. The image forming apparatus according to claim 5 , wherein, when the control unit determines that the periodicity exists, the number of recording materials to be subjected to the moving average is a periodic number corresponding to the periodicity. 7. The image forming apparatus according to claim 6 , wherein when said control means determines that there is no periodicity, the number of recording materials to be the object of said moving average is a predetermined number. 5. The image forming apparatus according to claim 4, wherein the control means calculates the basis weight of the currently fed recording material based on a weighted average of the basis weights of the most recently fed recording materials, including the currently fed recording material, detected by the detection means. 9. The image forming apparatus according to claim 8 , wherein the control means changes a weighted average coefficient of the recording material used for the weighted average when it is determined that the periodicity exists. 10. The image forming apparatus according to claim 9, wherein the control means increases the weighted average coefficient of the recording material fed this time and decreases the weighted average coefficient of other immediately preceding recording materials depending on the number of times the periodicity is detected. 11. The image forming apparatus according to claim 10 , wherein, when said control means determines that there is no periodicity, the weighted average coefficients of the recording materials that are the targets of said weighted average are the same. The image forming means includes:
an image carrier on which a toner image is formed;
a transfer means for transferring the toner image formed on the image carrier onto a recording material;
a fixing unit for fixing the toner image transferred by the transfer unit;
Equipped with
12. The image forming apparatus according to claim 1, wherein the image forming conditions determined by the control means include a voltage applied to the transfer means when a toner image is transferred to a recording material , and a temperature of the fixing means when a toner image is fixed.