JP4378065B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used in electrophotographic copying machines and printers. Image forming apparatus It is about.
[0002]
[Prior art]
As the computerization progresses, the need to output documents and images in color has expanded, and various types of printers have been produced. As a color image forming method, a sublimation type, a thermal transfer type, an ink jet method, or the like is used, and an electrophotographic method is said to be most excellent for forming an image at high speed.
[0003]
In the electrophotographic image forming apparatus, there is a problem that the image density greatly fluctuates depending on the temperature and humidity used, variations in characteristics of the photosensitive member and the developer, and durability of the developing device. In particular, the color image forming apparatus has a problem that the color changes.
[0004]
In view of these problems, various methods have been proposed for measuring the density of an image formed on a transfer material and correcting the image density based on the measurement result to obtain an image with excellent gradation reproducibility. For example, in Japanese Patent Laid-Open No. 7-182480, a control toner image is formed on a transfer material by a method similar to a normal image forming method, and the transfer material is conveyed along a predetermined conveyance path. There has been disclosed an image forming apparatus that detects density with an optical density detection sensor halfway and corrects the gradation of an image based on the detection result.
[0005]
[Problems to be solved by the invention]
However, the image forming apparatus that performs the above density control has the following problems.
[0006]
Since the density detection accuracy greatly depends on the distance fluctuation between the density detection sensor and the measurement object, that is, the transfer material, in order to improve the density detection accuracy, the distance between the transfer material and the density detection sensor is always constant. It is necessary to.
[0007]
However, since the density detection of the control toner image is performed while the transfer material is being conveyed, the distance between the transfer material and the density detection sensor is not always constant, and varies during the conveyance. In particular, when the conveyance speed is high, the behavior in which the transfer material is conveyed becomes unstable, and the density detection accuracy tends to deteriorate.
[0008]
Furthermore, if the conveyance speed is high, the time for the control toner image to pass through the sensor portion is shortened, so that the density detection accuracy is lowered. For this purpose, it is conceivable to increase the detection accuracy by enlarging the control toner image, thereby extending the time for passing through the sensor unit. However, if the size of the control toner image is increased due to restrictions on the size of the transfer material, the number of control toner images that can be formed decreases. For this reason, there is a problem that the accuracy of gradation reproducibility is lowered.
[0009]
Thus, the present invention can improve density detection accuracy and improve tone reproducibility. Image forming apparatus The purpose is to provide.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention is an image forming apparatus that discharges a transfer material on which a toner image is fixed by a fixing unit at a predetermined speed, on an image carrier. Toner image forming means for forming a plurality of control toner images each having a different gradation; transfer means for transferring the plurality of control toner images formed by the toner image forming means to a transfer material; The rear end of the transfer material is located at a position away from the fixing unit along the conveyance path along which the transfer material is conveyed, and the length of the transfer material carrying the control toner image in the conveyance direction. It is placed at a position separated by the sum of the margin distance after passing through A density detecting unit configured to detect the density of the plurality of control toner images after fixing while the transfer material on which the plurality of control toner images transferred by the transfer unit are fixed is conveyed; And The transfer material moves the margin distance after the trailing edge of the transfer material passes through the fixing unit, When the density detection means detects the density of the plurality of control toner images, the transfer material conveyance speed is changed to a speed slower than the predetermined speed, and is fixed to the transfer material. The length of the toner image is based on the speed after the change.
An image forming apparatus that discharges a transfer material, on which a toner image is fixed by a fixing unit, at a predetermined speed, and forms a plurality of control toner images each having a different gradation on an image carrier. A transfer unit that transfers the plurality of control toner images formed by the toner image forming unit to a transfer material; The rear end of the transfer material is located at a position away from the fixing unit along the conveyance path along which the transfer material is conveyed, and the length of the transfer material carrying the control toner image in the conveyance direction. It is placed at a position separated by the sum of the margin distance after passing through Chromaticity detection means for detecting the chromaticity of the plurality of control toner images after fixing, while the transfer material on which the plurality of control toner images transferred by the transfer means are fixed is conveyed. Have The transfer material moves the margin distance after the trailing edge of the transfer material passes through the fixing unit, When the chromaticity detection unit detects chromaticity of the plurality of control toner images, the transfer material conveyance speed is changed to a speed slower than the predetermined speed, and the one fixed to the transfer material The length of the control toner image is based on the speed after the change.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment] Image forming apparatus according to the present invention And control toner image detection method The first embodiment will be described with reference to the drawings. 1 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment, FIG. 2 is a diagram illustrating a configuration of a density detection unit, FIG. 3 is a diagram illustrating a configuration of the density detection unit, FIG. 4 is a timing chart of sensor control, FIG. 5 is a schematic diagram of the control toner image, and FIG. 6 is a sensing layout diagram of the control toner image and the density detection sensor.
[0012]
As shown in FIG. 1, the image forming apparatus includes a rotating drum type photosensitive drum 1 as an image carrier. Around the photosensitive drum, a charging roller 2, a developing device 4 that is a developing unit, an intermediate transfer drum 6 that is an intermediate transfer member, and a photosensitive drum cleaning device 7 are disposed, and between the charging roller 2 and the developing device 4. An exposure device 3 is disposed above.
[0013]
The intermediate transfer drum 6 is in contact with the surface of the photosensitive drum 1 at the primary transfer nip portion, and is further in contact with the surface of the secondary transfer belt 8 serving as transfer means at the secondary transfer nip portion. An intermediate transfer drum cleaning roller 10 is disposed on the outer periphery of the intermediate transfer drum 6. A fixing device 9 as a fixing unit is disposed on the downstream side in the transport direction of the secondary transfer belt 8. A density detection sensor 11 serving as a density detection means for halftone control is disposed on the downstream side in the conveyance direction of the fixing device 9 so as to face the surface of the transfer material P.
[0014]
In the present embodiment, the photosensitive drum 1 is an OPC photosensitive drum having a diameter of 62 mm, and is provided with an undercoat layer, a charge injection preventing layer, a charge generation layer, and a charge transport layer on an aluminum drum. It is rotationally driven in the direction of arrow a at a high speed (100 mm / sec) and is uniformly charged by negative charging by the charging roller 2 that contacts in the rotation process. A charging roller 2 as a charging means is in contact with the surface of the photosensitive drum 1 so as to be rotatable, and charges the photosensitive drum 1 to a predetermined polarity and potential by a charging bias applied from a charging bias power source 14.
[0015]
The exposure apparatus 3 includes a laser driver (not shown), a laser diode, a polygon mirror, and the like, and a laser beam modulated in response to a time-series electric digital image signal of image information input to the laser driver is a laser diode. The laser beam is scanned with a polygon mirror that is rotated at a high speed, and the surface of the photosensitive drum 1 is subjected to image exposure L via a reflection mirror (not shown), thereby forming an electrostatic latent image corresponding to the image information. .
[0016]
The developing device 4 includes a yellow (Y) developing device 4a, a magenta (M) developing device 4b, a cyan (C) developing device 4c, and a black (Bk) developing device 4d as non-magnetic one-component developing devices mounted on a rotating body 5. The yellow (Y) developing unit 4a, the magenta (M) developing unit 4b, the cyan (C) developing unit 4c, and the black (Bk) developing unit 4d are rotated by the rotation of the rotating body 5 by a rotation driving device (not shown). Is disposed at a position facing the photosensitive drum 1 during the development process. The toner is attached to the electrostatic latent image formed on the photosensitive drum 1 by these developing devices 4a, 4b, 4c, and 4d, and developed as a toner image.
[0017]
Each color toner used in the yellow (Y) developing unit 4a, the magenta (M) developing unit 4b, and the cyan (C) developing unit 4c is a capsule-type spherical non-mag toner manufactured by a polymerization method and encapsulating wax. The black toner used in the black (Bk) developing device 4d is obtained by subjecting a pulverized toner having a particle size of 6 μm to a spheroidizing treatment, and adding 100 parts of magnetite to the polyester binder, in addition to a charge control agent, a lubricant, and the like. Internally added.
[0018]
In the present embodiment, a bias in which a rectangular wave having a frequency of 2000 Hz and a peak-to-peak voltage of 2000 Vpp is applied to each of the developing devices 4a, 4b, 4c, and 4d on a direct current of -350V, thereby exposing the exposed portion of the surface of the photosensitive drum 1. Is developed with a negatively chargeable negative toner to reveal an electrostatic latent image.
[0019]
The cleaning device 7 removes and collects the primary transfer residual toner remaining on the photosensitive drum 1 without being primarily transferred to the intermediate transfer drum 6.
[0020]
In this embodiment, the intermediate transfer drum 6 has a circumference that can write an image corresponding to paper (A3 size in this embodiment) as a transfer material having a diameter of 186 mm and a maximum sheet passing size. , Rotate in the direction of arrow b. A primary transfer bias power source (not shown) is connected to the intermediate transfer drum 6, and a predetermined primary transfer bias (this embodiment) is applied from the primary transfer bias power source to a core metal (not shown) of the intermediate transfer drum 6. In this form, +200 V) is applied, and the toner image on the photosensitive drum 1 is thereby transferred onto the intermediate transfer drum 6 by the potential difference between the photosensitive drum 1 and the intermediate transfer drum 6 at the primary transfer nip N. Is done.
[0021]
In the present embodiment, the intermediate transfer drum 6 is formed with an elastic resistance layer made of a medium resistance rubber material having a thickness of 5 mm on the outer peripheral surface of the aluminum drum, and further on the surface of the intermediate transfer drum 6 in order to ensure releasability. System resin is coated. The rubber material is made of NBR and ethylene oxide, and the resistance is reduced to 1E7 Ωcm by ethylene oxide. The fluorine-based resin coated on the surface has a volume resistance value of 1E14 Ωcm. The volume resistance value of the intermediate transfer drum 6 is obtained by converting from a current measured by contacting a metal drum having a diameter of 62 mm with a nip width of 7 mm on the entire longitudinal surface of the intermediate transfer drum 6 and applying a voltage of 1000 V therebetween. It was.
[0022]
The secondary transfer belt 8 is stretched and suspended by the transfer roller 12 and the drive roller 13, and the upper surface of the belt rotates in the direction of arrow c by the rotation of the drive roller 13. The secondary transfer belt 8 is disposed so as to be in contact with and away from the intermediate transfer drum 6. Secondary transfer onto the transfer material P and then the secondary transfer belt 8 contacts the intermediate transfer drum 6.
[0023]
In order to attract the transfer material P, the secondary transfer belt 8 is coated with 30 μm PVDF on a conductive urethane belt to increase the electrostatic capacity. ² The resistance value measured by applying a voltage of 1000 V between this region and the belt substrate was 1E10Ω. The secondary transfer roller 12 and the drive roller 13 are low resistance rubber rollers, and the impedance of the secondary transfer belt 8 substantially depends only on the resistance of the surface layer of the secondary transfer belt 8. Further, a secondary transfer bias power source is connected to the secondary transfer roller 12, and a toner image is transferred onto the transfer material by supplying a + 20uA transfer current from the secondary transfer bias power source to the secondary transfer belt 8.
[0024]
A bias power supply (not shown) is connected to the intermediate transfer drum cleaning roller 10 to remove secondary transfer residual toner remaining on the surface of the intermediate transfer drum 6 without being transferred to the transfer material P. The intermediate transfer drum cleaning roller 10 charges the secondary transfer residual toner on the intermediate transfer drum 6 with a reverse polarity. The secondary transfer residual toner charged with the reverse polarity is charged on the photosensitive drum 1. Simultaneously with the primary transfer of the toner image onto the intermediate transfer drum 6, the toner image is transferred from the intermediate transfer drum 6 to the photosensitive drum 1 and removed and collected by the cleaning device 7.
[0025]
The fixing device 9 includes a fixing roller 9a and a pressure roller 9b, and nipping and conveying a transfer material P on which an unfixed toner image is transferred to a fixing nip portion between the fixing roller 9a and the pressure roller 9b. Then, the transfer material P is heated and pressurized to fix the toner image.
[0026]
The density detection sensor 11 is disposed on the downstream side of the fixing device 9 and detects the density of the patch formed on the transfer material during halftone control. The configuration of the density detection sensor 11 and halftone control will be described in detail later.
[0027]
Next, an image forming operation of the above-described image forming apparatus will be described.
[0028]
Image exposure with a laser beam is given to the charged photosensitive drum 1 by the exposure device 3, and an electrostatic latent image corresponding to a first color component image (for example, a yellow component image) of a target color image is formed. . At this time, the electrostatic latent image formed on the photosensitive drum 1 in the image-exposed portion is developed with yellow toner as the first color by the yellow (Y) developing device 4a.
[0029]
The yellow toner image of the first color formed and supported on the photosensitive drum 1 passes through the primary transfer nip portion N between the photosensitive drum 1 and the intermediate drum 6 and is primary on the outer peripheral surface of the intermediate transfer drum 6. It will be transcribed.
[0030]
The primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer of the yellow toner image is removed by the photosensitive drum cleaning device 7 and used for forming the next yellow toner image.
[0031]
Similarly, the magenta (M) developing device 4b, the cyan (C) developing device 4c, and the black (Bk) developing device 4d are respectively formed and supported on the photosensitive drum 1 by the second color magenta toner image and the third color. The cyan toner image and the fourth color black toner image are successively superimposed on the intermediate transfer drum 6 to form a composite color toner image corresponding to the target color image.
[0032]
The secondary transfer belt 8 and the intermediate transfer drum cleaning roller 10 are separated from the intermediate transfer drum 6 in the sequential superimposing transfer process of the first to fourth color toner images from the photosensitive drum 1 to the intermediate transfer drum 6. .
Then, a transfer material P such as paper is conveyed at a predetermined timing in accordance with the leading end of the composite color toner image on the intermediate transfer drum 6.
[0033]
Then, at the timing when the transfer material P passes through the feeding path leading to the secondary transfer nip portion, the secondary transfer belt 8 swings so that the intermediate transfer belt 8 contacts the intermediate transfer drum 6, and the secondary transfer bias. A predetermined secondary transfer bias is applied to the transfer roller 12 by a power source (not shown), and the composite color image is collectively transferred onto the transfer material P in a batch.
[0034]
The transfer material P onto which the composite color toner image has been transferred is subjected to curvature separation on the downstream side in the conveyance direction of the secondary transfer belt 8, and is nipped and conveyed between the fixing roller 9a and the pressure roller 9b in the fixing device 9 to be heated. The composite color toner image is heat-fixed on the surface and output.
[0035]
Further, the secondary transfer residual toner remaining on the intermediate transfer drum 6 without being secondary transferred is converted to a reverse polarity by the intermediate transfer cleaning roller 10 to which a bias is applied and is electrostatically applied to the photosensitive drum 1. The intermediate transfer drum 6 is cleaned. The secondary transfer residual toner adsorbed on the photosensitive drum 1 is then collected by the photosensitive drum cleaning device 7.
[0036]
Next, the density detection sensor 11 will be described with reference to FIGS. FIG. 2 is a schematic diagram of density detecting means, which includes a light emitting unit 20 and a light receiving unit 21, and detects density with respect to a halftone control patch 22 that is a control toner image formed on the surface of the transfer material P. Spot light is emitted from the light emitting part 20 of the sensor, the reflected light is received by the light receiving part 21, and the density is detected by the received light quantity. In this embodiment, a storage type line sensor is used for the light receiving unit 21.
[0037]
FIG. 3 is a block diagram showing a pixel configuration of the accumulation type line sensor. Reference numeral 204 denotes a sensor array, 205 denotes a readout circuit, and 206 denotes a reset circuit. Reference numerals 207 to 209 and 220 denote pixels whose surfaces are shielded from light. Reference numerals 210 to 219 are pixels that react to light. Reference numerals 207 and 220 also serve as dummy pixels that absorb variations in sensor characteristics due to being located at the end.
[0038]
In the present embodiment, the number of pixels that react to light is 10. However, the number of effective pixels may be changed as necessary. Further, although the dark pixel is 3 bits in the first half and 1 bit in the second half, the number of bits may be increased or decreased depending on the degree of light leakage between the pixels or the requirements of the system to be used.
[0039]
FIG. 4 shows a control sequence of the accumulation type line sensor. After the sensor is reset by the reset pulse 221, the reset is released and accumulation is started. During accumulation, a storage capacitor (not shown) of the sensor is charged with a photocurrent corresponding to the amount of incident light. However, the storage capacity of the light-shielded bit is charged by the dark current generated by the sensor. After accumulation for a predetermined time ta, the output of the sensor is collectively transferred to the readout circuit by the transfer pulse 222, and serially output as an output signal 224 for each pixel based on the shift pulse 223 by the shift register in the readout circuit. At this time, an output corresponding to the dark pixel 208 is used as a representative dark output, and a signal in which an error due to the dark current of the sensor is corrected is obtained by subtracting the output from the subsequent effective pixel.
[0040]
Next, halftone control in the present embodiment will be described.
[0041]
The halftone control of this embodiment is started by the CPU 17 at an appropriate timing such as when the main body is turned on, when a predetermined time has elapsed since the power was turned on, or when the number of printed sheets reaches a predetermined number.
[0042]
In order to form a patch on the transfer material P and detect the density, the above-described image forming operation is started. However, in the image formation at the time of density detection, the transfer material P, which is a feature of the present embodiment, has a conveyance speed slower than that in normal image formation. Specifically, the transfer material conveyance speed is 50 mm / sec. Accordingly, the drum peripheral speed is 50 mm / sec.
[0043]
FIG. 5 is a schematic view of a control toner image formed on the transfer material P. As shown in FIG. 5, patches of black K, cyan C, magenta M, and yellow Y are formed on the transfer material P. For example, in yellow patches Y1 to Y8, Y1 has the lowest density, and the density gradually increases to Y8. Of course, the same applies to other color component patches.
[0044]
For the pattern, image data Y1 to Y8 corresponding to Y component patches Y1 to Y8 stored in advance in a ROM (not shown) are read, and the data is sent to a laser driver (not shown) in the exposure apparatus 3, The density values of the Y patches Y1 to Y8 formed on the transfer material P are measured at appropriate timing by the density detection sensor 11, and the sensor output is stored in a RAM (not shown). Then, based on the obtained patch density, a look-up table (hereinafter referred to as “LUT”) for tone correction in the Y component is created.
[0045]
The Y component LUT is created as described above, and the same processing is performed on the other M, C, and Bk components, so that an appropriate LUT is created for each color component, and tone correction of the toner image is performed. Note that the order of the color components for generating the LUT may be arbitrary.
[0046]
FIG. 6A is a diagram showing a sensing layout of patches and density detection sensors in the present embodiment. As shown in FIG. 6A, the size of the patch includes a margin for absorbing a sensor mounting position error, a spot diameter of the density detection sensor, and a predetermined time (accumulation time ta) for detecting the patch. It is determined by the distance between which the transfer material is conveyed, that is, the distance required for measurement.
[0047]
In the present embodiment, the margin is 2 mm, the spot diameter is 3 mm, the distance required for measurement = 0.1 sec (ta) × 50 mm / sec = 5 mm, and thus the size of the patch is 12 mm. Further, since the size of the patch is 12 mm, 33 patches can be formed on the transfer material within a size of 397 mm in the conveyance direction of the transfer material. In this embodiment, 8 patches for each color, 32 patches in total were formed.
[0048]
Here, as a comparative example, a case will be described in which the conveyance speed at the time of density detection is 100 mm / sec, which is the same as in normal image formation. As shown in FIG. 6B, in the comparative example, the distance required for measurement = 0.1 sec (ta) × 100 mm / sec = 10 mm, so the patch size is 17 mm. For this reason, only 23 patches can be formed within a size of 397 mm in the transfer material conveyance direction. Therefore, if an attempt is made to form the same number of patches for each color, only 5 patches can be formed for each color, and the gradation reproducibility accuracy deteriorates.
[0049]
Furthermore, in the comparative example, since the transfer material transport speed is high, the behavior when the transfer material is transported becomes unstable, and the distance between the transfer material surface and the density detection sensor is not constant and varies. Therefore, the density detection accuracy is deteriorated.
[0050]
On the other hand, since the transfer material conveyance speed is slow in this embodiment, the behavior when the transfer material is conveyed is more stable than the comparative example, and as a result, the density detection accuracy can be improved as compared with the comparative example.
[0051]
As described above, according to the present embodiment, the density of the patch formed on the transfer material can be detected with high accuracy by making the transfer material conveyance speed at the time of density detection slower than that at the time of normal image formation. Therefore, it is possible to increase the number of patches to be formed, and to improve the gradation reproducibility accuracy.
[0052]
In this embodiment, the image forming apparatus using the density detection sensor has been described. However, instead of the density detection sensor, a chromaticity detection sensor that is a chromaticity detection unit that measures the chromaticity of the control toner image is used. However, the same effect can be obtained.
[0053]
[Second Embodiment]
Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 7 is a timing chart for conveying speed switching according to the present embodiment, and FIG. 8 is a schematic configuration diagram illustrating the image forming apparatus. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.
[0054]
The present embodiment is characterized in that the transfer material conveyance speed is reduced only at the time of patch detection, thereby improving the patch detection accuracy and shortening the time from the patch formation to the completion of calculation of the patch density.
[0055]
In FIG. 7, High indicates that the transfer material conveyance speed is 100 mm / sec, and Low indicates that the transfer material conveyance speed is 50 mm / sec. As shown in FIG. 7, in this embodiment, the transfer material is transported at a transfer speed of 100 mm / sec from the patch image formation until the transfer material passes through the fixing device and the transfer material tip passes through the darkness sensor unit. The transfer speed of the transfer material is switched to 50 mm / sec after the leading end of the material has passed through the dark detection sensor.
[0056]
FIG. 8 is a schematic diagram of the image forming apparatus in the present embodiment. As a feature of the present embodiment, the conveyance distance l from which the transfer material P moves from the fixing device 9 to the density detection sensor 11 is 410 mm, which is longer than the size 397 mm in the conveyance direction of the transfer material forming the patch. Therefore, the conveyance speed of the transfer material is 100 mm / sec, which is the same as the normal image formation, until the trailing edge of the transfer material passes through the fixing device 9, and the timing at which the leading edge of the transfer material passes the density detection sensor 11, that is, the transfer material The transfer speed of the transfer material is switched to 50 mm / sec at a timing 13 mm away from the trailing edge and the transfer distance of the fixing device 9.
[0057]
In order to confirm the effect of the present embodiment, as a comparative example, the patch density is detected from the patch image formation, and the transfer conveyance speed is 50 mm / sec until the transfer material is discharged. The time required for operation was compared.
[0058]
In the present embodiment, the time required from the start of image formation until the transfer material P passes through the density detection sensor unit is 32.2 seconds, and the transfer material is discharged after the transfer material passes through the density detection sensor unit. The time to complete the operation was 8.4 sec, for a total of 40.6 sec.
[0059]
On the other hand, in the comparative example, the peripheral speeds of the rotary drum type photosensitive drum 1 and the intermediate transfer drum 6 at the time of patch formation were 50 mm / sec, and the time required for completing a series of operations was 72.8 sec.
[0060]
As described above, the series of operation time from the patch image formation until the transfer material is discharged is 72.8 sec in the comparative example, but can be significantly shortened to 40.6 sec in the present embodiment. I was able to improve.
[0061]
Further, in this embodiment, since the transfer speed is the same as the normal image operation from the patch image formation to the fixing, the process conditions at the time of patch image formation such as development, transfer, and fixing are the same as those in the normal image operation. Since halftone control is performed based on the patch density, it is preferable that the patch image forming conditions are the same as those for normal image formation. Therefore, in this embodiment, the halftone control accuracy can be improved.
[0062]
As described above, according to this embodiment, it is possible to improve the patch detection accuracy by reducing the transfer material conveyance speed only at the time of patch detection, and to shorten the time from the patch formation to the completion of calculation of the patch density. , Usability was improved. Furthermore, the halftone control accuracy can be improved.
[0063]
[Third embodiment]
Next, a third embodiment of the image forming apparatus according to the present invention will be described. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.
[0064]
In this embodiment, the sequence related to image formation at the time of patch detection is performed at a sequence other than the fastest conveyance speed among a plurality of sequences related to normal image formation, thereby improving the patch detection accuracy and newly An object is to contribute to cost reduction because it is not necessary to provide a sequence for patch detection.
[0065]
The low speed mode in this embodiment will be described below.
[0066]
In the low-speed mode, an object is to increase the amount of heat applied per unit time in the fixing unit and to secure the fixing property by reducing the transfer speed of the transfer material when thick paper is selected as the transfer material.
[0067]
The image forming operation in the low speed mode will be described below.
[0068]
Until the color image is formed on the intermediate transfer drum 6, it is not different from the normal image formation. After all the black images of the final color are transferred onto the intermediate transfer drum 6, the peripheral speed of the intermediate transfer drum is changed from 100 mm / sec to 50 mm / sec.
[0069]
Then, a transfer material P such as paper is conveyed at a predetermined timing in accordance with the leading end of the composite color toner image on the intermediate transfer drum 6. Then, at the timing when the transfer material P passes through the feeding path leading to the secondary transfer nip portion, the secondary transfer belt 8 swings so that the intermediate transfer belt 8 contacts the intermediate transfer drum 6, and the secondary transfer bias. A predetermined secondary transfer bias is applied to the transfer roller 12 by a power source (not shown), and the composite color image is collectively transferred onto the transfer material P in a batch.
[0070]
The subsequent image forming operation is the same except that the transfer speed of the transfer material is 50 mm / sec.
[0071]
The image forming operation at the time of patch detection in this embodiment may be the same as that in the half-speed mode, and the conveyance speed is slow at the time of patch detection, so that the patch detection accuracy is improved and a new one for patch detection is used. There is no need to provide a sequence, which can contribute to cost reduction.
[0072]
【The invention's effect】
As described above, the present invention According to the control toner image density and chromaticity Transfer material transfer speed at detection To slow down Allows the transfer material to be transported stably when detecting the control toner image. Density and chromaticity Detection accuracy is improved. Further, the size of the control toner image can be reduced.
[0073]
In addition, when detecting the control toner image, the transfer speed of the transfer material is high except when detecting the control toner image by slowing the transport speed. Therefore, from the control toner image formation to the density detection. Can be shortened and usability can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of density detection means.
FIG. 3 is a diagram showing a configuration of density detection means.
FIG. 4 is a timing chart of sensor control.
FIG. 5 is a schematic diagram of a control toner image.
FIG. 6 is a sensing layout diagram of a control toner image and a density detection sensor.
FIG. 7 is a timing chart of conveyance speed switching according to the second embodiment.
FIG. 8 is a schematic configuration diagram illustrating an image forming apparatus.
[Explanation of symbols]
l ... Transport distance
L ... Image exposure
P: Transfer material
K1-Y8 ... patch
l ... Transport distance
1 ... Rotating drum type photosensitive drum
2 ... Charging roller
3 ... Exposure device
4 ... Developing device
4a to 4d ... developer
5 ... Rotating body
6 ... Intermediate transfer drum
7 ... Photosensitive drum cleaning device
8 ... Secondary transfer belt
9: Fixing device
10… Intermediate transfer drum cleaning roller
11… Concentration detection sensor
12 ... Secondary transfer roller
13… Drive roller
17 ... CPU
20… light emitting part
21… Light receiver
22 ... patch for halftone control
204… Sensor array
205… Reading circuit
206 ... Reset circuit
207-220 ... pixel
221… Reset pulse
222… Transmission pulse
223… Shift pulse
224… Output signal

Claims (4)

An image forming apparatus for discharging a transfer material on which a toner image is fixed by a fixing unit at a predetermined speed,
Toner image forming means for forming a plurality of control toner images each having a different gradation on the image carrier;
Transfer means for transferring the plurality of control toner images formed by the toner image forming means to a transfer material;
The rear end of the transfer material is located at a position away from the fixing unit along the conveyance path along which the transfer material is conveyed, and the length of the transfer material carrying the control toner image in the conveyance direction. In the middle of the transfer of the transfer material on which the plurality of control toner images transferred by the transfer unit are fixed, the distance after adding the margin distance after passing through is fixed. Density detecting means for detecting the density of the plurality of control toner images;
When the transfer material moves the margin distance after the rear end of the transfer material passes through the fixing unit, and the density detection unit detects the density of the plurality of control toner images, the transfer material And the length of one control toner image fixed on the transfer material is based on the speed after the change. An image forming apparatus for discharging a transfer material on which a toner image is fixed by a fixing unit at a predetermined speed,
Toner image forming means for forming a plurality of control toner images each having a different gradation on the image carrier;
Transfer means for transferring the plurality of control toner images formed by the toner image forming means to a transfer material;
The rear end of the transfer material is located at a position away from the fixing unit along the conveyance path along which the transfer material is conveyed, and the length of the transfer material carrying the control toner image in the conveyance direction. In the middle of the transfer of the transfer material on which the plurality of control toner images transferred by the transfer unit are fixed, the distance after adding the margin distance after passing through is fixed. Chromaticity detection means for detecting chromaticity of the plurality of control toner images,
When the transfer material moves the margin distance after the trailing edge of the transfer material passes through the fixing unit, and the chromaticity detection unit performs chromaticity detection of the plurality of control toner images, The transfer material transport speed is changed to a speed slower than the predetermined speed, and the length of one control toner image fixed on the transfer material is based on the changed speed. .   The image forming apparatus according to claim 1, wherein the image forming apparatus has a plurality of transfer material conveyance speeds and uses a conveyance speed other than the fastest conveyance speed when detecting a control toner image.   The image forming apparatus according to claim 1, wherein the sensor of the density detection unit is a storage type sensor.

Images