JP6879008B2 - Image forming device - Google Patents

Description

This disclosure relates to an image forming apparatus, and more specifically, to a technique for detecting a transport speed of a recording medium in the image forming apparatus.

Conventionally, devices that measure the velocity of a moving object in a non-contact manner have been used in various products. For example, some image forming devices such as MFPs (Multi-Functional Peripheral) include an image pickup element that images a recording medium being conveyed, and specify the transfer speed of the recording medium from the image captured by the image pickup element. is there. For example, Japanese Patent Application Laid-Open No. 2017-001768 (Patent Document 1) discloses a printing apparatus in which the imaging interval by the imaging unit is lengthened when the transport speed of the medium is low as compared with the case where the transport speed is high. There is.

Further, Japanese Patent Application Laid-Open No. 2010-055064 (Patent Document 2) discloses a speed detection device that realizes miniaturization of the device by projecting light reflected by a moving member onto an area sensor via a reduction optical system. ing.

Japanese Unexamined Patent Publication No. 2017-0017168 Japanese Unexamined Patent Publication No. 2010-055064

Some image forming apparatus selects one transport speed from a plurality of transport speeds according to the type of recording medium and the like. Further, as in Patent Document 2, the image forming apparatus may have a lens for forming an image of the light reflected by the recording medium on the image pickup device. In the image forming apparatus having these configurations, due to the distortion of the lens, the larger the set transport speed, the larger the error in the transport speed of the recording medium calculated based on the image.

The present disclosure has been made to solve the above-mentioned problems, and an object in a certain aspect is to provide an image forming apparatus capable of suppressing an error variation in a calculated transport speed of a recording medium. is there. An object of another aspect of the present disclosure is to provide an image forming apparatus capable of increasing the accuracy of calculating the transport speed of a recording medium as compared with the conventional case.

An image forming apparatus according to an embodiment includes a transport mechanism configured to be capable of transporting a recording medium at a plurality of reference speeds and a light source, and irradiates light from the light source to photograph the transporting recording medium at predetermined time intervals. Then, a photographing device for generating at least two images including the first image and the second image, and a moving amount calculating device for calculating the moving amount of the recording medium in the photographing time interval of the first and second images. And. The photographing apparatus includes a lens for forming an image of the light reflected by the recording medium on the image pickup device, and a plurality of image pickup devices in the transport direction of the recording medium . The photographing apparatus is configured to set a predetermined time interval so that the amount of movement for each of the plurality of reference speeds is substantially equal. Preferably, the movement amount calculation device is configured to set a value obtained by dividing a reference distance by a reference speed as a predetermined time interval. More preferably, the reference distance is set to the distance obtained by multiplying the fastest reference speed among the plurality of reference speeds by the shortest shooting time interval that can be set in the photographing device.

Preferably, as imaging devices, the amount of movement of the recording medium which is assumed on the basis of the criteria speed and a predetermined time interval corresponds to an integer multiple of the interval, each of the plurality of image pickup elements are arranged, a predetermined Set the time interval for.

An image forming apparatus according to an embodiment can suppress an error variation in the calculated transport speed of the recording medium. An image forming apparatus according to an embodiment can increase the accuracy of calculating the transport speed of the recording medium more than before.

The above and other objectives, features, aspects and advantages of the disclosed technical features will become apparent from the following detailed description of the invention, which is understood in connection with the accompanying drawings.

It is a figure for demonstrating the process for calculating the transfer speed of a sheet by the image forming apparatus which follows the related art. It is a figure for demonstrating the process for calculating the transfer speed of a sheet by the image forming apparatus according to a certain embodiment. It is a figure explaining the configuration example of the image forming apparatus according to Embodiment 1. It is a figure explaining the configuration example of a sensor unit. It is a figure which shows the example of the data structure of a setting table. Represents two images taken at different timings. It is a figure explaining the calculation method of the movement amount. It is a flowchart which shows the calculation process of the movement amount of a sheet S. It is a flowchart which shows the process of step S820 of FIG. It is a figure for demonstrating the setting process of a shooting interval according to Embodiment 2. It is a figure for demonstrating the process which the image forming apparatus according to Embodiment 3 calculates the movement amount of a sheet S.

Hereinafter, embodiments of this technical idea will be described in detail with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of them will not be repeated. In addition, each embodiment described below may be selectively combined as appropriate.

[Related technology]
FIG. 1 is a diagram for explaining a process for calculating the transport speed of the sheet S1 by the image forming apparatus 100 according to the related technique. The image forming apparatus 100 includes a transport roller pair 110, a control device 120, a photographing device 130, and a movement amount calculation device 180.

The transport roller pair 110 and the control device 120 function as a transport mechanism for transporting the sheet S1 as a recording medium. The control device 120 controls the drive of a motor (not shown) connected to the transport roller pair. This transport mechanism is configured to be capable of transporting the sheet S1 at a plurality of reference speeds (hereinafter, also referred to as "system speed").

The photographing apparatus 130 includes a light source 140, a lens 150, and a two-dimensional sensor 160. The light source 140 irradiates the sheet S1 being conveyed with light. The lens 150 forms an image of the light reflected by the sheet S1 on the two-dimensional sensor 160. The two-dimensional sensor 160 is composed of a plurality of image pickup elements arranged on a plane. The image pickup device can be realized by, for example, CMOS (Complementary Metal Oxide Semiconductor) or CCD (Charged-Coupled Devices). The photographing device 130 outputs the first image and the second image generated at different timings by the two-dimensional sensor 160 to the movement amount calculation device 180. The movement amount calculation device 180 calculates the movement amount of the sheet S1 at the shooting interval of these images based on the first image and the second image.

The photographing apparatus 130 according to the related technique generates the first image and the second image according to a predetermined time interval. The first image is an image corresponding to the sheet S1 before movement. If the system speed is slow, the seat S1 travels a distance ΔL1 during a predetermined time. On the other hand, when the system speed is high, the seat S1 moves a distance ΔL2 longer than the distance ΔL1 during a predetermined time. In FIG. 1, the thickness of the sheet S1 is changed before and after the movement of the sheet S1, but this is for easy viewing, and the thickness of the sheet S1 is not actually changed.

By the way, a lens generally has a characteristic called distortion. This is a characteristic that aberration occurs in proportion to the cube of the angle of view. Therefore, the farther away from the center of the two-dimensional sensor 160 (the position through which the optical axis AX penetrates), the larger the difference from the imaging magnification at the center.

As shown in FIG. 1, the larger the distance (movement amount) that the sheet S1 has moved in a predetermined time, that is, the faster the system speed, the farther away from the center (optical axis AX) of the two-dimensional sensor 160. It is also imaged at the position. Therefore, the error in the transport speed of the sheet S1 calculated by the movement amount calculation device 180 according to the related technology increases as the system speed increases.

In a certain aspect, the image forming apparatus 100 according to the related technique controls the timing of image forming based on the transport speed calculated by the moving amount calculating apparatus 180. In this case, in the image forming apparatus 100 according to the related technique, the faster the system speed, the larger the error of the actual printing position with respect to the ideal position may be. Further, when color printing is performed using an image forming apparatus 100 according to a related technique, the higher the system speed, the greater the degree of color shift (pixel position shift between each color). As described above, when the same image is printed at different system speeds using the image forming apparatus 100 according to the related technique, different images are obtained. Therefore, the user of the image forming apparatus 100 may feel a sense of discomfort with respect to these images. Therefore, an image forming apparatus 200 according to a certain embodiment, which can obtain the same image even when the system speeds are different, will be described.

[Technical Thought]
FIG. 2 is a diagram for explaining a process for calculating the transport speed of the sheet S1 by the image forming apparatus 200 according to a certain embodiment. Since the basic configuration of the image forming apparatus 200 is substantially the same as the basic configuration of the image forming apparatus 100, only the differences will be described.

The imaging device 130 of the image forming apparatus 200 acquires the system speed from the control device 120. The photographing device 130 sets the photographing interval so as to move by a predetermined movement amount ΔL based on the acquired system speed. According to this configuration, the image forming apparatus 200 can keep the amount of movement of the sheet S1 constant with respect to a plurality of system speeds. As a result, the error in the transport speed of the sheet S1 calculated by the movement amount calculation device 180 according to a certain embodiment can be kept constant regardless of the system speed. As a result, when the same image is printed at different system speeds using the image forming apparatus 200 according to a certain embodiment, the same image is obtained. Therefore, the user of the image forming apparatus 200 does not feel uncomfortable with these images. Hereinafter, the configuration and control for realizing such an image forming apparatus will be described.

[Embodiment 1]
(Configuration of image forming apparatus)
FIG. 3 is a diagram illustrating a configuration example of the image forming apparatus 300 according to the first embodiment. FIG. 3 shows an image forming apparatus 300 as a color printer. Hereinafter, the image forming apparatus 300 as a color printer will be described, but the image forming apparatus 300 is not limited to the color printer. For example, the image forming apparatus 300 may be a monochrome printer, or may be a monochrome printer, a color printer, and a multi-function peripheral (MFP).

As shown in FIG. 3, the image forming apparatus 300 includes an image forming unit 1, an intermediate transfer unit 2, a sheet supply unit 3, a fixing device 4, a sheet winding unit 5, a control device 6, and the like. .. The image forming apparatus 300 is connected to a network (for example, LAN: Local Area Network), and when it receives an instruction to execute a print job from an external terminal apparatus (not shown), it is yellow (Y) based on the instruction. , Magenta (M), cyan (C) and black (K) to perform color image formation.

The image forming unit 1 includes image forming units 10Y to 10K corresponding to each of the Y to K colors. The image forming unit 10Y charges the surface of the photoconductor drum 11Y rotating at a constant speed, and when an electrostatic latent image is formed on the charged photoconductor drum 11Y by exposure scanning of an exposed portion, the electrostatic latent image is formed. The latent image is developed with Y-color toner, and the developed Y-color toner image is electrostatically first-transferred to the intermediate transfer belt 21.

The other image forming units 10M, 10C, and 10K also perform the same charging, exposure, development, and primary transfer steps as the image forming unit 10Y, and perform the M color toner image on the photoconductor drum 11M and the photoconductor drum 11C. The C-color toner image and the K-color toner image on the photoconductor drum 11K are primarily transferred to the intermediate transfer belt 21. In FIG. 3, the formation timing of the Y to K color toner images is predetermined so that the Y to K color toner images representing the original image on one page are multiple-transferred on the intermediate transfer belt 21. When there are a plurality of pages of a manuscript, toner images corresponding to one page of the manuscript image are sequentially formed on the intermediate transfer belt 21 at regular intervals in the belt circumferential direction for each page of the manuscript.

The intermediate transfer unit 2 includes an intermediate transfer belt 21, a drive roller 22 for tensioning the intermediate transfer belt 21, driven rollers 23, 24, 25, a secondary transfer roller 26, and the like.

The drive roller 22 is rotated by the rotational driving force of the belt motor 71 to orbit the intermediate transfer belt 21 in the direction indicated by the arrow in the figure. The belt motor 71 includes, for example, a DC (Direct Current) brushless motor. The driven rollers 23, 24, and 25 rotate driven as the intermediate transfer belt 21 orbits.

During the orbiting of the intermediate transfer belt 21, the Y to K color toner images by the image forming units 10Y to 10K are multiple-transferred to the peripheral surface of the intermediate transfer belt 21.

The Y to K color toner images multiple-transferred on the intermediate transfer belt 21 are directed to the secondary transfer roller 26 which is arranged to face the drive roller 22 with the intermediate transfer belt 21 sandwiched by the orbital running of the intermediate transfer belt 21. Will be transported.

The secondary transfer roller 26 is in contact with the peripheral surface of the intermediate transfer belt 21 at the secondary transfer position 261 of the intermediate transfer belt 21, and is driven to rotate as the intermediate transfer belt 21 orbits.

The sheet supply unit 3 sends a long sheet S from the roll paper 33 wound around the rotating shaft 31 to the paper feed adjusting unit 34 via the supply roller 32. The paper feed adjusting unit 34 conveys the sheet S from the supply roller 32 toward the transfer roller 35 of the main body 9 of the image forming apparatus 300, and the transfer speed of the sheet S sent out from the roll paper 33 in the sheet supply unit 3 In order to absorb the speed difference from the conveying speed of the sheet S in the main body 9, the long sheet S is loosened and held, and the feeding of the sheet S to the main body 9 is adjusted. As the sheet S, not only plain paper but also label paper or the like may be used.

The sheet S supplied to the transfer roller 35 is wound by the take-up roller 51 via the secondary transfer position 261, the fixing device 4, the discharge roller 46, the paper discharge adjustment unit 53 of the sheet take-up unit 5, and the transfer roller 52. Be done. In order to absorb the speed difference between the transfer speed of the sheet S in the main body 9 and the transfer speed of the sheet S by the take-up roller 51 of the sheet take-up unit 5, the paper discharge adjusting unit 53 uses a long sheet S. Loosen and hold, and adjust the output of the sheet S from the main body 9.

During the winding of the sheet S, the Y to K colors that are multiple-transferred on the intermediate transfer belt 21 on the front side (that is, the side in contact with the intermediate transfer belt 21) of the sheet S that passes through the secondary transfer position 261. The toner image is electrostatically collectively secondarily transferred by the secondary transfer roller 26. When a plurality of pages of toner images are formed on the intermediate transfer belt 21 at regular intervals in the belt circumferential direction, the toner images of each page are formed while the elongated sheet S passes through the secondary transfer position 261. Are secondarily transferred onto the sheet S one by one. The toner image of each page secondarily transferred onto the sheet S is conveyed to the fixing device 4 together with the sheet S to be wound.

The fixing device 4 is pressed against the fixing roller 41 at a predetermined pressure at the nip portion 45 of the tubular heating roller 40 in which the heater 43 is inserted, the tubular fixing roller 41, and the fixing roller 41. A pressure roller 42 is provided. The fixing device 4 heats the heating roller 40 by heating the heater 43 to a predetermined temperature. By rotating the heating roller 40, heat is transferred to the nip portion 45 between the fixing roller 41 and the pressure roller 42. The fixing device 4 maintains the temperature of the nip portion 45 at a temperature required for fixing the toner (for example, 150 ° C.).

The fixing roller 41 is driven in the direction of the arrow in FIG. 3 by a fixing motor 72 composed of a DC brushless motor, and rotates about a rotation shaft 47. The heating roller 40 may be rotationally driven instead of the fixing roller 41. The pressure roller 42 is driven to rotate by the fixing roller 41. The fixing roller 41 and the pressure roller 42 heat and pressurize the toner image after the secondary transfer onto the sheet S when the toner image passes through the nip portion 45 while sandwiching and transporting the sheet S. Heat-fixed on the front side of the sheet S.

The transport speed of the sheet S is detected by the sensor unit 44. The sensor unit 44 is located upstream of the nip portion 45 in the sheet transport direction and below the position PX of the seat S in the transport path R1 and is located near the nip portion 45. The sensor unit 44 measures the transport speed of the surface on the back side (that is, the side on which the toner image is not transferred) of the sheet S that is sandwiched and transported by the fixing roller 41 and the pressure roller 42. The sensor unit 44 measures the transport speed of the sheet surface, and sends the measurement result to the control device 6.

(Sensor unit configuration)
FIG. 4 is a diagram illustrating a configuration example of the sensor unit 44. In the example shown in FIG. 4, the sheet S is conveyed to the fixing device 4.

The sensor unit 44 includes a photographing device 70, an ADC (Analog-to-Digital Converter) 85, an FPGA 86, and a ROM 92. The sensor unit 44 functions as a movement amount detection device for calculating the movement amount of the sheet S at the shooting interval of the shooting device 70 by utilizing the speckle pattern formed on the two-dimensional sensor 84 by the reflected light from the sheet S. To do. In other words, the sensor unit 44 is a non-contact type sensor that measures the transport speed of the sheet S.

The photographing device 70 includes a light source 81 including a laser device, a lens 82 which is a collimator lens, a lens 83, and a two-dimensional sensor 84. The two-dimensional sensor 84 has a plurality of image pickup elements arranged in the horizontal direction and the vertical direction.

At the manufacturing stage of the image forming apparatus 300, the light source 81 is set to emit laser light toward a predetermined irradiation position Sp on the transport path R1. The laser beam emitted from the light source 81 passes through the lens 82 and irradiates the surface Sa of the sheet S being conveyed.

The angle θ2 formed by the laser beam incident on the surface Sa of the sheet S and the surface Sa of the sheet S is 45 ° in FIG. The angle θ2 is not limited to 45 °, and may be any angle in the range of, for example, 20 ° to 45 °.

The surface Sa of the sheet S can be said to be a rough surface having minute irregularities when viewed microscopically, and when the rough surface is irradiated with laser light (coherent light), a granular pattern called speckle is generated. The speckle is generated because the light having different phases overlaps due to the superposition of the scattered light due to the diffused reflection of the laser light from each place on the rough surface.

Of the laser light generated by the speckle, the reflected light reflected at an angle θ1 (for example, 90 °) with respect to the surface Sa of the sheet S is received through the lens 83 provided directly below the irradiation position Sp. The light is focused on the detection surface of the two-dimensional sensor 84 as a unit. As a result, on the detection surface of the two-dimensional sensor 84, it is possible to detect the speckle pattern generated on the surface Sa of the sheet S located directly above the detection surface.

The speckle does not change unless the seat S moves, but changes when the seat S moves. This is because the uneven portion of the rough surface passing through the laser beam irradiation position Sp changes at each time point due to the transfer of the sheet S, and the superposition state of the diffusely reflected light of the laser also changes at each time point.

The rate of change of the speckle depends on the transport speed of the sheet S, and the amount of laser light received on the detection surface of the two-dimensional sensor 84 also changes due to the change of the speckle. Therefore, the moving speed of the surface of the sheet S can be measured by detecting the time change of the amount of received laser light on the detection surface of the two-dimensional sensor 84. Therefore, it can be said that the irradiation position Sp of the laser beam on the sheet S is the measurement position of the moving speed of the sheet surface.

The two-dimensional sensor 84 outputs an analog voltage signal according to the amount of received laser light focused on the detection surface to an ADC (Analog to Digital Converter) for each shooting interval input from the shooting interval determination unit 88, which will be described later. Output to 85. Each time the ADC 85 receives an analog voltage signal from the two-dimensional sensor 84, it converts it into a digital signal and outputs the converted digital signal to the FPGA 86.

The FPGA 86 includes a shooting interval determination unit 88 and a movement amount calculation unit 90. In another aspect, the FPGA 86 may include a smoothing filter, a median filter, for reducing high-sensitivity noise.

The shooting interval determination unit 88 acquires the system speed from the control device 6 and determines the time interval (shooting interval) at which the two-dimensional sensor 84 outputs an analog signal to the ADC 85 based on the system speed. The shooting interval determination unit 88 outputs the determined shooting interval to the two-dimensional sensor 84. Further, the shooting interval determination unit 88 stores the determined shooting interval in the setting table 94 stored in the ROM 92.

The movement amount calculation unit 90 calculates the movement amount of the sheet S at the shooting interval of the two images based on the two images taken at different timings. The movement amount calculation unit 90 outputs to the control device 6 the transport speed of the sheet S obtained by multiplying the calculated movement amount and the shooting interval. The control device 6 may be configured by, for example, a CPU (Central Processing Unit).

The control device 6 acquires the transport speed of the sheet S being transported from the sensor unit 44. The control device 6 controls the rotation speed of the secondary transfer motor 73 that drives the drive roller 22 based on the acquired transfer speed of the sheet S, and sets the transfer speed of the sheet S to the system speed. The control device 6 may further control the rotation speed of the fixing motor 72 that drives the fixing roller 41 based on the conveying speed of the sheet S acquired from the sensor unit 44.

(Setting table)
FIG. 5 shows an example of the data structure of the setting table. FIG. 5A represents a setting table 94. FIG. 5B represents a setting table 94A according to another aspect.

The setting table 94 holds the system speed and the time interval (shooting interval) at which the two-dimensional sensor 84 outputs an analog signal to the ADC 85. When the shooting interval determination unit 88 determines the shooting interval based on the system speed, the shooting interval determination unit 88 updates the setting table 94 using the system speed and the shooting interval. More specifically, the shooting interval determination unit 88 determines the shooting interval so that the multiplication value of the system speed acquired from the control device 6 and the shooting interval, that is, the movement amount becomes a predetermined movement amount ΔL. .. The predetermined movement amount ΔL may be held in the ROM 92 or may be input from the control device 6.

The setting table 94A holds the shooting interval in association with each of the plurality of system speeds that can be set by the control device 6. The shooting interval determination unit 88 determines the shooting interval corresponding to the system speed from the shooting device based on the setting table 94A. According to this configuration, the image forming apparatus 300 can reduce the process of calculating the shooting interval in the shooting interval determining unit 88.

(Movement of seat S)
FIG. 6 shows two images taken at different timings. The image shown in FIG. 6 represents an image obtained by cutting out an analysis range from a captured image of a speckle pattern of laser light focused on the detection surface of the two-dimensional sensor 84.

The image 610 represents the first image (first image), and the image 620 represents the image (second image) taken after the image 610. The sheet S when the image 620 is photographed is moved in the transport direction by the action of the fixing motor 72 or the like as compared with the sheet S when the image 610 is photographed. In the example shown in FIG. 6, the sheet S when the image 620 is photographed is moved in the transport direction from the sheet S position when the image 610 is photographed by the movement amount ΔL.

(Calculation of movement amount according to related technology)
FIG. 7 is a diagram illustrating a method of calculating the movement amount. The movement amount calculation unit 90 includes a discrete Fourier transform unit 710, a normalization processing unit 720, a synthesis unit 730, and an inverse discrete Fourier transform unit 740.

Data indicating the first image and the second image, which are two images taken at different timings, are input to the discrete Fourier transform unit 710. The discrete Fourier transform unit 710 decomposes the data into wave number components by executing the discrete Fourier transform process on the first image and the second image. The discrete Fourier transform unit 710 outputs the data decomposed for each wave number component to the normalization processing unit 720.

The normalization processing unit 720 multiplies the amplitude corresponding to the first analysis image and the amplitude corresponding to the second analysis image for each wave number component. As a result, the standardization processing unit 720 standardizes the magnitude of the amplitude for each wave number and extracts the phase information for each wave number. The standardization processing unit 720 outputs the extracted phase information to the synthesis unit 730.

The synthesis unit 730 synthesizes the phase information extracted for each wave number. The synthesis unit 730 derives the phase difference between the first analysis image and the second analysis image by calculating the peak shift amount based on the synthesized phase information. The synthesis unit 730 outputs the derived phase difference to the inverse discrete Fourier transform unit 740.

The reciprocal discrete Fourier transform unit 740 performs an inverse discrete Fourier transform process on the phase difference in the derived wave number space, so that this phase difference is the distance in the real space, that is, two images, the first image and the second image. It is converted into the movement amount of the sheet S in the shooting interval of the image of. The movement amount calculation unit 90 calculates the transport speed of the sheet S by dividing the calculated movement amount of the sheet S by the shooting interval. The movement amount calculation unit 90 outputs the calculated transfer speed to the control device 6.

(Control structure)
FIG. 8 is a flowchart showing the calculation process of the movement amount of the sheet S. The process shown in FIG. 8 can be realized by the FPGA 86. In other aspects, part or all of the processing may be implemented by the control device 6 (CPU) or by other hardware.

In step S810, the control device 6 outputs a print start instruction to the FPGA 86 in response to the input of the print job.

In step S820, the FPGA 86 sets the shooting interval of the shooting device 70 according to the system speed. This process will be described later with reference to FIG.

In step S830, the FPGA 86 receives the input of the Nth image in which the sheet S being conveyed by the photographing device 70 is photographed.

In step S840, the FPGA 86 accepts the input of the N + 1th image captured by the imaging device 70 according to the set imaging interval.

In step S850, the FPGA 86 calculates the movement amount of the sheet S at the shooting interval based on the Nth image and the N + 1th image as the movement amount calculation unit 90.

In step S860, the FPGA 86 determines whether or not the print job has been completed. For example, when the print job is completed, the control device 6 notifies the FPGA 86 to that effect. Thereby, the FPGA 86 can make this judgment.

When the FPGA 86 determines that the print job has been completed (YES in step S860), the FPGA 86 terminates a series of processes after initializing the variable N in step S870. On the other hand, when the FPGA 86 determines that the print job has not been completed (NO in step S860), the FPGA 86 proceeds to the process in step S880.

In step S880, the FPGA 86 increments the variable N and then returns the process to step S820. As a result, even when the control device 6 changes the system speed during the print job, the FPGA 86 can set the shooting interval so that the movement amount of the sheet S is always constant. If the system speed is not changed during the print job, the FPGA 86 may be configured to return the process to step S830 after the process in step S880.

FIG. 9 is a flowchart showing the process of step S820 of FIG. With reference to FIG. 9, in step S910, the FPGA 86 acquires the system speed set by the print job from the control device 6.

In step S920, the FPGA 86 refers to the setting table 94 stored in the ROM 92 and determines whether or not the acquired system speed is the same as the previously acquired system speed. When the acquired system speed and the system speed stored in the setting table 94 are the same (YES in step S920), the FPGA 86 maintains the previous shooting interval (step S930). On the other hand, when the acquired system speed and the system speed stored in the setting table 94 are different from each other (NO in step S920), the FPGA 86 proceeds to the process in step S940.

In step S940, the FPGA 86 sets a reference distance for the seat S. The reference distance is the amount of movement of the sheet S assumed at the shooting interval. This reference distance can be stored in the ROM 92 in advance.

In step S950, the FPGA 86 calculates the shooting interval by dividing the reference distance by the system speed. The FPGA 86 further updates the setting table 94 with the system speed and the calculated imaging interval.

The process of setting the shooting interval will be described with reference to a specific example. In a certain aspect, the control device 6 is configured to be able to switch the system speed in three stages of 334 mm / sec (low speed), 500 mm / sec (medium speed), and 650 mm / sec (high speed). The two-dimensional sensor 84 has 256 image pickup elements arranged in the transport direction and 64 image sensors arranged in the direction orthogonal to the transport direction (16384 pixels). The image sensor is 6.45 μm square. The maximum frame rate of the photographing device 70 is 2000 fps (Flame Per Sec).

The reference distance is set to a distance obtained by multiplying the fastest system speed among a plurality of system speeds (reference speeds) by the shortest shooting time interval (maximum frame rate) that can be set in the photographing device 70 in a certain aspect. .. Under the above conditions, the reference distance is set to 325.00 μm (0.5 ms × 650 mm / sec). In this case, the shooting interval determination unit 88 sets the shooting interval to 0.97 msec when the system speed is low, 0.65 msec when the system speed is medium, and when the system speed is high. Set to 0.50 msec respectively.

When set as described above, the shooting interval of the shooting device 70 is set to be the shortest. By the way, the movement amount calculation unit 90 is configured to calculate the movement amount based on the common portion between the Nth image and the N + 1th image. Therefore, by shortening the shooting interval, the Nth image and the N + 1th image can be obtained even when only the image sensor near the optical axis AX is used among the plurality of image sensors constituting the two-dimensional sensor 84. There is a common part. The image forming apparatus 300 can calculate the moving amount of the sheet S more accurately by using only the image pickup element near the optical axis AX. The reason will be described later with reference to FIG.

The reference distance may be set to 1/3 of the length of the 2D sensor 84 in the transport direction in other aspects. Under the above conditions, the reference distance is set to 548.25 μm. In this case, the shooting interval determination unit 88 sets the shooting interval to 1.64 msec when the system speed is low, 1.10 msec when the system speed is medium, and when the system speed is high. Is set to 0.84 msec respectively.

As described above, the image forming apparatus 300 according to the first embodiment determines the shooting interval according to the system speed. Specifically, the image forming apparatus 300 shortens the shooting interval as the system speed increases. More specifically, the image forming apparatus 300 sets the shooting interval so that the assumed movement amount is equal for each of the plurality of system speeds. According to this configuration, the image forming apparatus 300 can keep the amount of movement of the sheet S with respect to a plurality of system speeds substantially constant. As a result, the error in the transport speed of the sheet S calculated by the movement amount calculation unit 90 can be kept substantially constant regardless of the system speed. As a result, when the same image is printed at different system speeds using the image forming apparatus 300, the same image is obtained. Therefore, the user of the image forming apparatus 300 does not feel uncomfortable with these images.

Further, the image forming apparatus 300 can realize the above-mentioned operation even when a finite focus lens having no telecentric property is used as the lens 83. In general, a finite focus lens is smaller and cheaper than an infinite focus lens having telecentricity. Therefore, the image forming apparatus 300 can realize low cost and miniaturization.

In the above example, the image forming apparatus 300 sets the shooting interval so that the assumed movement amount of the sheet S (= system speed × shooting interval) is equal to each of the plurality of system speeds. However, the expected movement amount does not necessarily have to be the same. When the same image is printed at different system speeds using the image forming apparatus 300, it is assumed for each of a plurality of system speeds within the range in which the user determines (with the naked eye) that these images are the same image. The shooting interval may be set so that the amount of movement of the sheet S to be moved varies.

[Embodiment 2]
The image forming apparatus 300 according to the first embodiment performs a process of suppressing an error variation in the calculated transport speed of the recording medium, and does not suppress the error itself. Therefore, in the second and third embodiments, a process for improving the calculation accuracy of the transport speed of the recording medium will be described.

FIG. 10 is a diagram for explaining a shooting interval setting process according to the second embodiment. The state (A) represents the state of the sheet S and the two-dimensional sensor 84 corresponding to the first image. The two-dimensional sensor 84 has a plurality of image pickup devices C in the transport direction of the sheet S. These are arranged at predetermined intervals P (eg, 6.45 μm). In the state (A), each of the plurality of image pickup devices C receives the irradiation of light corresponding to the surface state of the sheet S. As a specific example, the image pickup device C1 receives the reflected light corresponding to the surface state of the portion P1 of the sheet S.

The state (B) represents a state in which the sheet S has moved from the state (A) by a distance ΔL3. It is assumed that the magnification of the image formed on the two-dimensional sensor 84 by the action of the lens 83 (including the optical system) is M times. The multiplication value of the distance ΔL3 and the magnification M does not correspond to an integral multiple of the predetermined interval P in which the image sensor C is arranged (the distance ΔL3 does not correspond to an integral multiple of the predetermined interval P in which the image sensor C is arranged. ). Therefore, the image sensor C2 in the state (B) receives the reflected light of a portion different from the portion P1 of the sheet S observed by the image sensor C1 in the state (A).

The movement amount calculation unit 90 is configured to calculate the movement amount of the shading pattern (that is, the surface state of the sheet S) in the two images. Therefore, the movement amount calculation unit 90 takes the sheet S based on the first image obtained by photographing the sheet S in the state (A) and the second image obtained by photographing the sheet S in the state (B). When the movement amount is calculated, the movement amount of the sheet S cannot be calculated accurately.

The state (C) represents a state in which the sheet S has moved from the state (A) by a distance ΔL4. The multiplication value of the distance ΔL4 and the magnification M is an integral multiple of the predetermined interval P in which the image sensor C is arranged (the distance ΔL4 corresponds to an integral multiple of the predetermined interval P in which the image sensor C is arranged). .. Therefore, the image sensor C2 in the state (C) receives the reflected light of the portion P1 of the sheet S observed by the image sensor C1 in the state (A). Under the conditions, the movement amount calculation unit 90 accurately determines the movement amount of the sheet S based on the first image corresponding to the sheet S in the state (A) and the second image corresponding to the sheet S in the state (C). Can be calculated.

Therefore, in the image forming apparatus 300 according to the second embodiment, the multiplication value of the reference distance (the amount of movement of the sheet S assumed in the shooting interval) and the magnification M is set to be an integral multiple of the arrangement interval P of the image sensor C. , Set the reference distance. That is, in the shooting interval determining unit 88 according to the second embodiment, the movement amount of the sheet S assumed based on the system speed and the shooting interval corresponds to an integral multiple of the interval P in which each of the plurality of image pickup elements C is arranged. Set the shooting interval so that As a result, the image forming apparatus 300 according to the second embodiment can improve the calculation accuracy of the moving amount of the sheet S in the moving amount calculating unit 90 as compared with the image forming apparatus 300 according to the first embodiment.

[Embodiment 3]
FIG. 11 is a diagram for explaining a process of calculating the movement amount of the sheet S by the image forming apparatus 300 according to the third embodiment. As described above, the lens 83 has distortion. The laser beam 1110 incident on the lens 83 at an angle θ irradiates the two-dimensional sensor 84 with the locus 1110B instead of the ideal locus 1110A. In the case of the locus 1110A, the distance from the position irradiated to the two-dimensional sensor 84 to the center (optical axis AX) is defined as R1A. The distance between the position where the two-dimensional sensor 84 is irradiated in the case of the locus 1110A and the position where the two-dimensional sensor 84 is irradiated in the case of the locus 1110B is defined as R1D. At this time, the distortion D of the lens 83 related to the laser beam 1110 is (R1D / R1A) × 100 (%).

The distortion D of the lens 83 increases as the angle of view increases. Therefore, among the plurality of image pickup devices constituting the two-dimensional sensor 84, the distortion D of the lens 83 increases as the distance from the center (optical axis AX) increases. Therefore, the image forming apparatus 300 according to the third embodiment uses only the image pickup element whose distance from the optical axis AX is within a predetermined distance among the plurality of image pickup elements constituting the two-dimensional sensor 84 to obtain the image of the sheet S. Generate. The predetermined distance can be set, for example, to a distance at which the angle of view becomes a predetermined angle. In another station, the predetermined distance can be set to a distance at which the distortion D of the lens 83 becomes a predetermined value P_TH. In the example shown in FIG. 11, the hatched image sensor indicates that the distortion D is equal to or less than a predetermined value P_TH.

In still another aspect, the two-dimensional sensor 84 may be configured to have the image sensor only in a region where the distance from the optical axis AX is within a predetermined distance.

According to the above, the image forming apparatus 300 according to the third embodiment can calculate the movement amount of the sheet S (recording medium) based on the image in which the influence of the distortion D of the lens 83 is reduced. Therefore, the image forming apparatus 300 can accurately calculate the movement amount of the sheet S as compared with the image forming apparatus 300 according to the first embodiment.

The various processes described above include at least one processor-like semiconductor integrated circuit, at least one application specific integrated circuit (ASIC), at least one DSP (Digital Signal Processor), and / or other arithmetic functions. Can be performed by a circuit with.

These circuits can perform the various processes described above by reading one or more instructions from at least one tangible readable medium.

Such media may take the form of magnetic media (eg, hard disks), optical media (eg, compact discs (CDs), DVDs), volatile memories, memories of any type of non-volatile memory, and the like. It is not limited to the form.

Volatile memory may include DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory). The non-volatile memory may include ROM, NVRAM. A semiconductor memory can be a part of a semiconductor circuit along with at least one processor.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 image forming part, 2 intermediate transfer part, 3 sheet supply part, 4 fixing device, 5 sheet take-up part, 6,120 control device, 21 intermediate transfer belt, 22 drive roller, 23 driven roller, 32 supply roller, 33 roll Paper, 34 Feed adjustment unit, 35, 52 Conveyor roller, 40 Heating roller, 41 Fixing roller, 42 Pressurizing roller, 43 Heater, 44 Sensor unit, 45 Nip part, 46 Discharge roller, 51 Take-up roller, 53 Discharge Adjustment unit, 70,130 imaging device, 71 belt motor, 72 fixing motor, 81,140 light source, 82,83,150 lens, 84,160 two-dimensional sensor, 88 imaging interval determination unit, 90 movement amount calculation unit, 92 ROM , 94, 94A setting table, 100, 200, 300 image forming device, 110 transfer roller pair, 180 moving amount calculation device, 261 secondary transfer position, 610, 620 image, 710 discrete Fourier transform unit, 720 standardization processing unit, 730 synthesis unit, 740 inverse discrete Fourier transform unit, 1110 laser light, 1110A, 1110B trajectory, AX optical axis, C, C1, C2 imaging elements, D distortion, R1 transport path.

Claims (3)

A transport mechanism configured to transport recording media at multiple reference speeds,
An imaging device that includes a light source, irradiates light from the light source, photographs the recording medium being conveyed at predetermined time intervals, and generates at least two images including a first image and a second image.
It is provided with a movement amount calculation device for calculating the movement amount of the recording medium in the shooting time interval of the first and second images.
The photographing apparatus includes a lens for forming an image of light reflected by the recording medium on the image pickup device and a plurality of image pickup elements in the transport direction of the recording medium .
The photographing device is configured to set the predetermined time interval so that the movement amount with respect to each of the plurality of reference speeds is substantially equal .
The movement amount calculation device is configured to set a value obtained by dividing a reference distance by the reference speed as the predetermined time interval.
The reference distance is a distance obtained by multiplying the fastest reference speed among the plurality of reference speeds by the shortest shooting time interval that can be set in the shooting device. The photographing device is
The predetermined time interval so that the amount of movement of the recording medium assumed based on the reference speed and the predetermined time interval corresponds to an integral multiple of the interval in which each of the plurality of image pickup elements is arranged. The image forming apparatus according to claim 1. The image forming apparatus according to any one of claims 1 or 2, wherein the lens is a finite focus lens.

Images