JP2018120104A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a printing speed while suppressing a reduction in accuracy in detecting optical characteristics of a test toner image.SOLUTION: A printer comprises: a secondary transfer power supply 45 that outputs a superimposed voltage obtained by superimposition of a DC and AC voltages for secondarily transferring toner images to a recording sheet P sandwiched at a secondary transfer nip formed through contact of an intermediate transfer belt 31 that carries the toner images with a secondary transfer belt 41; and an optical sensor unit 40 that detects optical characteristics of a test toner image secondarily transferred to the secondary transfer belt 41. The printer uses, as the intermediate transfer belt 41, one including a substrate and an elastic layer laminated thereon formed of a material having an elasticity superior to that of the substrate, and is provided with a power supply control part that, in a test transfer mode of secondarily transferring the test toner image to the secondary transfer belt 41, executes processing of causing the secondary transfer power supply 45 to output, of the DC voltage and AC voltage, only the DC voltage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  Conventionally, an image forming apparatus having the following configuration is known. That is, a power source that outputs a superimposed voltage for transferring a toner image to a recording sheet sandwiched in a transfer nip by contact between an image carrier that carries a toner image and the contact body, and a test that is transferred to the contact body And an optical characteristic detection unit that detects an optical characteristic of the toner image.

  For example, the image forming apparatus described in Patent Document 1 includes a recording that is sandwiched in a secondary transfer nip by contact between an endless intermediate transfer belt that is an image carrier and an endless secondary transfer belt 41 that is a contact body. The toner image on the intermediate transfer belt is secondarily transferred to the sheet. For this secondary transfer, a secondary transfer bias composed of a DC and AC superimposed voltage output from the secondary transfer power source is output, and the intermediate transfer belt is directed toward the secondary transfer belt inside the loop of the intermediate transfer belt. It is applied to the pressing secondary transfer bias roller. The test toner image formed on the intermediate transfer belt is secondarily transferred to the secondary transfer belt instead of the recording sheet, and then the image density is detected by a toner adhesion amount sensor which is an optical characteristic detection unit. It is said that an image can be formed with a stable image density over a long period of time by adjusting the image forming conditions based on the detection result.

  However, in this image forming apparatus, when an attempt is made to increase the printing speed, an uneven sheet such as Japanese paper may cause significant image density unevenness. Furthermore, if an attempt is made to suppress uneven image density on the uneven sheet while realizing a higher printing speed, a smooth sheet such as surface-coated paper may cause transfer failure, or transfer dust may reduce the optical properties of the test toner image. There was a risk of reducing the detection accuracy.

  In order to solve the above-described problems, the present invention is directed to superimposing direct current and alternating current for transferring a toner image onto a recording sheet sandwiched between transfer nips by contact between an image carrier that carries a toner image and the contact body. In an image forming apparatus comprising a power source that outputs a superimposed voltage according to the above and an optical property detection unit that detects an optical property of a test toner image transferred to the contact member, the image carrier is used as a base material. In the test transfer mode in which an elastic layer made of a material having excellent elasticity is used and the test toner image is transferred to the contact body, only the DC voltage among the DC voltage and the AC voltage is used. Control means for executing processing to be output from the power supply is provided.

  According to the present invention, there is an excellent effect that a printing speed can be increased while suppressing a decrease in detection accuracy of optical characteristics of a test toner image.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating an enlarged electrophotographic unit for K in the printer. FIG. 3 is a block diagram showing a main part of an electric circuit of a secondary transfer power source in the printer, together with a secondary transfer back roller and a secondary transfer nip backing roller. FIG. 2 is a block diagram showing a main part of an electric circuit of the printer. The flowchart which shows the processing flow in process control. FIG. 3 is a schematic diagram illustrating a patch pattern image on a secondary transfer belt of the printer. FIG. 6 is a characteristic diagram illustrating a relationship between a development potential and a toner adhesion amount. FIG. 3 is an enlarged cross-sectional view partially showing a cross section of an intermediate transfer belt of the printer. FIG. 3 is an enlarged plan view showing the intermediate transfer belt partially enlarged. The graph which shows the 1st example of the waveform (duty = 50%) of the secondary transfer bias which consists of a superimposition voltage. The graph which shows the 2nd example of the waveform (duty = 50%) of the secondary transfer bias which consists of a superimposition voltage. 11 is a graph for explaining the duty in the secondary transfer bias shown in FIG. 10. The graph for demonstrating the duty in the secondary transfer bias shown by FIG. The graph which shows an example of the waveform of the secondary transfer bias which made the duty 35%. FIG. 3 is an enlarged configuration diagram showing a secondary transfer nip and its periphery in a configuration using a single-layer structure as an intermediate transfer belt, unlike the printer. FIG. 3 is an enlarged cross-sectional view showing a secondary transfer nip and its peripheral configuration in a configuration using an elastic belt having a multilayer structure as in the same printer as the intermediate transfer belt. The graph which shows an example of the waveform in the secondary transfer bias of high duty whose polarity reverses within one period and whose duty is 80 [%]. FIG. 3 is a block diagram illustrating an electric circuit of an operation display unit of the printer according to the embodiment. 6 is a graph showing a relationship among a secondary transfer rate of a toner image onto a secondary transfer belt, a secondary transfer current, and a secondary transfer bias characteristic in a printer tester having a basic configuration. The schematic diagram which shows the pattern for position shift detection with a belt. 1 is a configuration diagram illustrating a paper feed path of a printer according to a first embodiment. FIG. FIG. 5 is a schematic diagram for explaining switching of a secondary transfer bias when the type of recording sheet is changed from a concavo-convex sheet to a smooth sheet during a continuous print job. 6 is a flowchart illustrating a processing flow during a continuous print job performed by the power control unit 200 of the printer according to the first embodiment. The block diagram which shows the electric circuit of the operation display part of the printer which concerns on a 2nd Example.

  Hereinafter, an embodiment of an electrophotographic color printer (hereinafter simply referred to as a printer) will be described as an image forming apparatus to which the present invention is applied. The application field of the present invention is not limited to a printer, and the present invention can also be applied to a copying machine, a facsimile, a multifunction machine having a copying function and a FAX function.

  First, a basic configuration of the printer according to the embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to an embodiment. In the figure, the printer according to the embodiment includes an electrophotographic unit 1Y constituting a part of image forming means for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. , 1M, 1C, 1K. Also provided are a transfer unit 30, an optical writing unit 80, a fixing device 90, a feeding cassette 100, a registration roller pair 101, and the like.

  The electrophotographic units 1Y, 1M, 1C, and 1K for Y, M, C, and K use Y, M, C, and K toners of different colors, but the other configurations are the same, and the lifetime is reached. Sometimes exchanged. Taking an electrophotographic unit 1K for forming a K toner image as an example, as shown in FIG. 2, this includes a drum-shaped photosensitive member 2K as a latent image carrier, a drum cleaning device 3K, a charging device 6K, and a developing device. The apparatus 8K and the like are included. It also has a static eliminator. These devices can be exchanged at the same time by being integrally attached to and detached from the printer body while being held by a common holding body.

  The photoreceptor 2K has an organic photosensitive layer formed on the surface of a drum base, and is driven to rotate clockwise in the figure by a driving means. The charging device 6K generates a discharge between the charging roller 7K and the photosensitive member 2K while bringing the charging roller 7K to which a charging bias is applied into contact with or in proximity to the photosensitive member 2K, thereby making the surface of the photosensitive member 2K uniform. Charge like this.

  In this printer, the surface of the photoreceptor 2K is uniformly charged to the same negative polarity as the normal charging polarity of the toner. As the charging bias, one in which an AC voltage is superimposed on a DC voltage is employed. The charging roller 7K is formed by coating a metal cored bar with a conductive elastic layer made of a conductive elastic material. Instead of a method in which a charging member such as a charging roller is brought into contact with or close to the photoreceptor 2K, a method using a charging charger may be adopted.

  The uniformly charged surface of the photosensitive member 2K is optically scanned by a laser beam emitted from an optical writing unit 80 described later and carries a K electrostatic latent image. The electrostatic latent image for K is developed by the developing device 8K using K toner to become a K toner image. Then, primary transfer is performed on an intermediate transfer belt 31 described later.

  The drum cleaning device 3K removes the transfer residual toner adhering to the surface of the photoreceptor 2K after the primary transfer process (primary transfer nip described later). It includes a cleaning brush roller 4K that is driven to rotate, a cleaning blade 5K that abuts the free end of the cleaning brush roller 4K in a cantilevered state, and the like. The transfer residual toner is scraped off from the surface of the photoreceptor 2K by the rotating cleaning brush roller 4K, and the transfer residual toner is scraped off from the surface of the photoreceptor 2K by the cleaning blade.

  The static eliminator neutralizes the residual charge on the photoreceptor 2K after being cleaned by the drum cleaning device 3K. By this charge removal, the surface of the photoreceptor 2K is initialized and prepared for the next image formation.

  The developing device 8K includes a developing unit 12K that stores a developing roll 9K that is a developer carrying member, and a developer transport unit 13K that stirs and transports the K developer. The developer transport unit 13K includes a first transport chamber that houses the first screw member 10K and a second transport chamber that houses the second screw member 11K. Each of the screw members includes a rotating shaft member whose both ends in the axial direction are rotatably supported by bearings, and a spiral blade projecting spirally on the peripheral surface thereof.

  The first transfer chamber containing the first screw member 10K and the second transfer chamber containing the second screw member 11K are partitioned by a partition wall, but both ends of the partition wall in the screw axial direction. Each part is formed with a communication port for communicating both the transfer chambers. The first screw member 10K conveys the K developer held in the spiral blade from the back side to the front side in the direction orthogonal to the paper surface in the drawing while stirring in the rotation direction with the rotational drive. To do. Since the first screw member 10K and a later-described developing roll 9K are arranged in parallel so as to face each other, the conveying direction of the K developer at this time is also a direction along the rotation axis direction of the developing roll 9K. . Then, the first screw member 10K supplies K developer along the axial direction to the surface of the developing roll 9K.

  After the K developer transported to the vicinity of the front end of the first screw member 10K in the drawing passes through the communication opening provided in the vicinity of the front end of the partition wall in the drawing and enters the second transport chamber. The second screw member 11K is held in the spiral blade. And with the rotational drive of the 2nd screw member 11K, it is conveyed toward the back | inner side from the near side in a figure, stirring in a rotation direction.

  In the second transfer chamber, a toner concentration sensor is provided on the lower wall of the casing, and detects the K toner concentration of the K developer in the second transfer chamber. As the K toner density sensor, a sensor comprising a magnetic permeability sensor is used. Since the magnetic permeability of the K developer containing K toner and magnetic carrier has a correlation with the K toner concentration, the magnetic permeability sensor detects the K toner concentration.

  This printer includes Y, M, C, and K toner replenishing means for individually replenishing Y, M, C, and K toners in the second storage chamber of the developing device for Y, M, C, and K, respectively. Yes. The control unit of the printer stores Vtref for Y, M, C, and K, which are target values of output voltage values from the Y, M, C, and K toner density detection sensors, in the RAM. When the difference between the output voltage value from the Y, M, C, K toner density detection sensor and the Vtref for Y, M, C, K exceeds a predetermined value, the Y, M, C, K toner is detected for the time corresponding to the difference. M, C, K toner supply means is driven. As a result, Y, M, C, and K toners are replenished in the second transport chamber of the developing device for Y, M, C, and K, and the K toner concentration of the K developer is maintained within a predetermined range.

  The developing roll 9K accommodated in the developing unit 12K faces the first screw member 10K and also faces the photoreceptor 2K through an opening provided in the casing. The developing roll 9K includes a cylindrical developing sleeve made of a nonmagnetic pipe that is rotationally driven, and a magnet roller that is fixed inside the developing roll 9K so as not to rotate with the sleeve. Then, the K developer supplied from the first screw member 10K is carried on the sleeve surface by the magnetic force generated by the magnet roller, and is conveyed to the developing region facing the photoreceptor 2K as the sleeve rotates.

  A developing bias having the same polarity as the toner and having an absolute value larger than the potential of the electrostatic latent image on the photosensitive member 2K and smaller than the uniform charging potential of the photosensitive member 2K is applied to the developing sleeve. ing. As a result, a developing potential for electrostatically moving the K toner on the developing sleeve toward the electrostatic latent image acts between the developing sleeve and the electrostatic latent image on the photoreceptor 2K. Further, a ground potential that moves the K toner on the developing sleeve toward the sleeve surface acts between the developing sleeve and the background portion of the photoreceptor 2K. Due to the effects of the development potential and the background potential, the K toner on the development sleeve is selectively transferred to the electrostatic latent image on the photoreceptor 2K, and the electrostatic latent image is developed into a toner image.

  1, Y, M, and C electrophotographic units 1Y, 1M, and 1C also have Y, M, and C toner images on the photoreceptors 2Y, 2M, and 2C in the same manner as the K electrophotographic unit 1K. Is formed. Above the electrophotographic units 1Y, 1M, 1C, and 1K, an optical writing unit 80 serving as a latent image writing unit is disposed. The optical writing unit 80 which constitutes a part of the image forming means is a photoconductor 2Y, 2M, 2C, 2K by laser light emitted from a laser diode based on image information sent from an external device such as a personal computer. Is optically scanned. By this optical scanning, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 2Y, 2M, 2C, and 2K.

  The optical writing unit 80 irradiates the photosensitive member through a plurality of optical lenses and mirrors while polarizing the laser light L emitted from the light source in the main scanning direction by a polygon mirror rotated by a polygon motor. It is. You may employ | adopt what performs optical writing by the LED light emitted from several LED of the LED array.

  Below the electrophotographic units 1Y, 1M, 1C, and 1K, there is disposed a transfer unit 30 that moves the endless intermediate transfer belt 31 endlessly in the counterclockwise direction in the drawing. In addition to the intermediate transfer belt 31 as an image carrier, the transfer unit 30 includes a driving roller 32, a secondary transfer back roller 33, a cleaning backup roller 34, primary transfer rollers 35Y, 35M, and 35C for Y, M, C, and K. , 35K, etc. Further, it also has a belt cleaning device 37, a secondary transfer power source 45, a nip forming unit 38, and the like.

  The intermediate transfer belt 31 is stretched by a driving roller 32, a secondary transfer back roller 33, a cleaning backup roller 34, and four primary transfer rollers 35Y, 35M, 35C, and 35K disposed inside the loop. Then, it is moved endlessly in the same direction by the rotational force of the driving roller 32 that is driven to rotate counterclockwise in the figure by the driving means.

  The primary transfer rollers 35Y, 35M, 35C, and 35K for Y, M, C, and K sandwich the intermediate transfer belt 31 that is moved endlessly between the photoreceptors 2Y, 2M, 2C, and 2K. As a result, a primary transfer nip for Y, M, C, and K where the front surface of the intermediate transfer belt 31 and the Y, M, C, and K photoconductors 2Y, 2M, 2C, and 2K abut is formed. Has been. A primary transfer bias output individually from a primary transfer power supply is applied to the primary transfer rollers 35Y, 35M, 35C, and 35K. As a result, a primary transfer electric field is formed between the Y, M, C, and K toner images on the photoreceptors 2Y, 2M, 2C, and 2K and the primary transfer rollers 35Y, 35M, 35C, and 35K. The Y toner formed on the surface of the Y photoconductor 2Y enters the Y primary transfer nip as the photoconductor 2Y rotates. Then, the image is primarily transferred from the photoreceptor 2Y to the intermediate transfer belt 31 by the action of the primary transfer electric field and the nip pressure. The intermediate transfer belt 31 on which the Y toner image has been primarily transferred in this way then passes sequentially through the primary transfer nips for M, C, and K. Then, the M, C, and K toner images on the photoreceptors 2M, 2C, and 2K are sequentially superimposed on the Y toner image and primarily transferred. A four-color superimposed toner image is formed on the intermediate transfer belt 31 by this superimposing primary transfer. In place of the primary transfer rollers 35Y, 35M, 35C, and 35K, a transfer charger, a transfer brush, or the like may be employed.

  In the transfer unit 30, a nip forming unit is disposed below the intermediate transfer belt 31. The nip forming unit 38 includes a secondary transfer nip lining roller 36, a separation roller 44, a tension roller 43, a cleaning backup roller 39, a secondary transfer belt 41 as a nip forming body, a belt cleaner 42, an optical sensor unit 40, and the like. ing.

  The endless secondary transfer belt 41 is tensioned by a secondary transfer nip backing roller 36, a separation roller 44, a tension roller 43, and a cleaning backup roller 39 disposed inside the loop. Endlessly moves clockwise. A secondary transfer nip is formed in contact with a portion of the intermediate transfer belt 31 that is wound around the secondary transfer back roller 33 in the entire circumferential direction on the front surface (loop outer peripheral surface).

  While the secondary transfer nip backing roller 36 disposed in the loop of the secondary transfer belt 41 is grounded, the secondary transfer back roller 33 disposed in the loop of the intermediate transfer belt 31 includes: A secondary transfer bias output from the secondary transfer power supply 45 is applied. As a result, the negative polarity toner is electrostatically moved between the secondary transfer back roller 33 and the secondary transfer nip backing roller 36 from the secondary transfer back roller 33 side to the secondary transfer nip backing roller 36 side. A secondary transfer electric field is formed.

  Below the transfer unit 30, a feeding cassette 100 that stores a plurality of recording sheets P in a bundle of sheets is disposed. In the feeding cassette 100, a sheet feeding roller 100a is brought into contact with the uppermost recording sheet P of the sheet bundle, and the recording sheet P is fed to the feeding path by being driven to rotate at a predetermined timing. Send it out.

  A registration roller pair 101 is disposed near the end of the feeding path. The leading edge of the recording sheet P conveyed on the feeding path is detected by a registration sensor (507, which will be described later) disposed slightly upstream from the registration nip due to the contact of the two rollers in the registration roller pair 101. The The conveyance of the recording sheet P is temporarily stopped after a predetermined time has elapsed from the detection timing. As a result, the recording sheet P is slightly bent in a state where the leading end of the recording sheet P abuts against the registration nip, thereby correcting the skew. Thereafter, the registration roller pair 101 is rotationally driven at a timing at which the recording sheet P can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 31 in the secondary transfer nip, and the recording sheet P is directed to the secondary transfer nip. And send it out.

  The four-color superimposed toner image on the intermediate transfer belt 31 brought into close contact with the recording sheet P at the secondary transfer nip is secondarily transferred onto the recording sheet P by the action of a secondary transfer electric field or nip pressure, and is full color toner. Become a statue. The recording sheet P having a full-color toner image formed on the surface in this way is separated from the intermediate transfer belt 31 by curvature when passing through the secondary transfer nip. Further, the curvature is separated from the secondary transfer belt 41 by the curvature of the separation roller 44 around which the secondary transfer belt 41 is wound.

  Untransferred toner that has not been transferred to the recording sheet P adheres to the intermediate transfer belt 31 after passing through the secondary transfer nip. This is cleaned from the belt surface by a belt cleaning device 37 in contact with the front surface of the intermediate transfer belt 31. A cleaning backup roller 34 disposed inside the loop of the intermediate transfer belt 31 backs up the cleaning of the belt by the belt cleaning device 37 from the inside of the loop.

  A fixing device 90 is disposed downstream of the secondary transfer nip in the sheet conveyance direction. The fixing device 90 forms a fixing nip with a fixing roller 91 containing a heat source such as a halogen lamp and a pressure roller 92 that rotates while contacting with the fixing roller 91 with a predetermined pressure. The recording sheet P that has passed through the secondary transfer nip and fed into the fixing device 90 is sandwiched between the fixing nips in such a posture that the unfixed toner image carrying surface is in close contact with the fixing roller 91. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed. The recording sheet P discharged from the fixing device 90 passes through a post-fixing conveyance path and is then discharged outside the apparatus.

  In this printer, when a monochrome image is formed, the posture of the support plate that supports the primary transfer rollers 35 (Y, M, C) for Y, M, C in the transfer unit 30 is changed by driving a solenoid or the like. Let As a result, the primary transfer rollers 35 (Y, M, C) for Y, M, C are moved away from the photoreceptor 2 (Y, M, C), and the front surface of the intermediate transfer belt 31 is moved to the photoreceptor 2. Separate from (Y, M, C). In this way, among the Y, M, C, and K electrophotographic units 1 (Y, M, C, and K) with the intermediate transfer belt 31 in contact with only the black photosensitive member 2K, Only the black electrophotographic unit 1K is driven to form a K toner image on the black photoreceptor 2K.

  FIG. 3 is a block diagram showing the main parts of the electric circuit of the secondary transfer power supply 45 and the power supply control unit 200 together with the secondary transfer back roller 33, the secondary transfer nip backing roller 36, and the like. The secondary transfer power supply 45 includes a DC power supply 110, an AC power supply 140 configured to be detachable, and the like.

  The DC power supply 110 is a power supply for outputting a DC voltage for applying an electrostatic force from the belt side to the recording sheet side in the secondary transfer nip to the toner on the surface of the intermediate transfer belt 31. A DC output control unit 111, a DC drive unit 112, a DC voltage transformer 113, a DC output detection unit 114, an output abnormality detection unit 115, an electrical connection unit 221 and the like are provided.

  The AC power source 140 is a power source that outputs an AC voltage for forming an alternating electric field in the secondary transfer nip. An AC output control unit 141, an AC drive unit 142, an AC voltage transformer 143, an AC output detection unit 144, a removal unit 145, an output abnormality detection unit 146, an electrical connection unit 242 and an electrical connection unit 243 are provided. Yes.

  The power supply control unit 200 as control means controls the output from the secondary transfer power supply, and from a control device having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. Become. The DC output control unit 111 receives a DC_PWM signal for controlling the output level of the DC voltage from the power supply control unit 200. Further, the output value of the DC voltage transformer 113 detected by the DC output detector 114 is also input. The DC output control unit 111 performs the following control based on the duty ratio of the input DC_PWM signal and the output value of the DC voltage transformer 113. That is, the driving of the DC voltage transformer 113 is controlled via the DC drive unit 112 so that the output value of the DC voltage transformer 113 is set to the output value indicated by the DC_PWM signal.

  The DC drive unit 112 drives the DC voltage transformer 113 according to the control from the DC output control unit 111. The DC voltage transformer 113 is driven by the DC drive unit 112 and outputs a negative DC high voltage. When the AC power supply 140 is not connected, the electrical connection portion 221 and the secondary transfer back roller 33 are electrically connected by the harness 301, and the DC voltage transformer 113 is connected via the harness 301. A DC voltage is output (applied) to the secondary transfer back roller 33. On the other hand, when the AC power supply 140 is connected, since the electrical connection portion 221 and the electrical connection portion 242 are electrically connected by the harness 302, the DC voltage transformer 113 is connected to the AC power supply 140 via the harness 302. Output DC voltage.

  The DC output detection unit 114 detects the output value of the DC high voltage from the DC voltage transformer 113 and outputs it to the DC output control unit 111. Further, the DC output detection unit 114 outputs the detected output value to the power supply control unit 200 as an FB_DC signal (feedback signal). This is because the power supply control unit 200 controls the duty of the DC_PWM signal so that the transferability does not deteriorate due to the environment or load. In this printer, since the AC power supply 140 can be attached to and detached from the main body of the secondary transfer power supply 45, the impedance of the output path of the high voltage output when the AC power supply 140 is connected or not connected. Changes. For this reason, when the DC power supply 110 performs constant voltage control and outputs a DC voltage, the voltage dividing ratio changes due to the impedance in the output path changing according to the presence or absence of the AC power supply 140. Furthermore, since the high voltage applied to the secondary transfer back surface roller 33 changes, the transferability changes depending on whether or not the AC power supply 140 is present.

  Therefore, in this printer, the DC power supply 110 performs constant current control to output a DC voltage, and the output voltage is changed according to the presence or absence of the AC power supply 140. As a result, even if the impedance in the output path changes, the high voltage applied to the secondary transfer back roller 33 can be kept constant, and the transferability can be kept constant regardless of the presence or absence of the AC power supply 140. it can. Furthermore, the AC power supply 140 can be attached and detached without changing the value of the DC_PWM signal. As described above, in this printer, the DC power supply 110 is controlled at a constant current, but the following configuration may be adopted. That is, if the high voltage applied to the secondary transfer back roller 33 can be kept constant by changing the value of the DC_PWM signal when the AC power supply 140 is attached or detached, a configuration in which the DC power supply 110 is controlled at a constant voltage is adopted. May be.

  The output abnormality detection unit 115 is disposed on the output line of the DC power supply 110, and outputs a signal indicating output abnormality such as leakage to the power supply control unit 200 when an output abnormality occurs due to a ground fault or the like of the electric wire. To do. As a result, it is possible to perform control for stopping the high voltage output from the DC power supply 110 by the power supply control unit 200.

  The AC output control unit 141 receives an AC_PWM signal for controlling the output level of the AC voltage and the output value of the AC voltage transformer 143 detected by the AC output detection unit 144 from the power supply control unit 200. Then, the AC output control unit 141 performs the following control based on the duty ratio of the input AC_PWM signal and the output value of the AC voltage transformer 143. That is, the driving of the AC voltage transformer 143 is controlled via the AC driver 142 so that the output value of the AC voltage transformer 143 becomes the output value indicated by the AC_PWM signal.

  An AC_CLK signal that controls the output frequency of the AC voltage is input to the AC drive unit 142. The AC driving unit 142 drives the AC voltage transformer 143 based on the control from the AC output control unit 141 and the AC_CLK signal. The AC driver 142 drives the AC voltage transformer 143 based on the AC_CLK signal, so that the output waveform generated by the AC voltage transformer 143 can be controlled to an arbitrary frequency indicated by the AC_CLK signal. .

  The AC voltage transformer 143 is driven by the AC drive unit 142 to generate an AC voltage, and generates a superimposed voltage by superimposing the generated AC voltage and a DC high voltage output from the DC voltage transformer 113. When the AC power supply 140 is connected, that is, when the electrical connecting portion 243 and the secondary transfer back roller 33 are electrically connected by the harness 301, the AC voltage transformer 143 generates the superimposed voltage generated by Applied to the secondary transfer back roller 33 via the harness 301. The AC voltage transformer 143 outputs (applies) the DC high voltage output from the DC voltage transformer 113 to the secondary transfer back roller 33 via the harness 301 when no AC voltage is generated. . The voltage (superimposed voltage or DC voltage) output to the secondary transfer back roller 33 is then fed back into the DC power source 110 via the secondary transfer nip backing roller 36.

  The AC output detection unit 144 detects the output value of the AC voltage of the AC voltage transformer 143 and outputs it to the AC output control unit 141. Further, the detected output value is output to the power supply control unit 200 as an FB_AC signal (feedback signal). This is because the power supply control unit 200 controls the duty of the AC_PWM signal so that the transferability does not deteriorate due to the environment or load. The AC power supply 140 performs constant voltage control, but may perform constant current control. Further, the waveform of the AC voltage generated by the AC voltage transformer 143 (AC power supply 140) may be either a sine wave or a rectangular wave, but this printer employs a short pulse rectangular wave. . This is because it is possible to further improve the image quality by making the waveform of the alternating voltage a short-pulse rectangular wave.

  The secondary transfer power supply 45 outputs a DC voltage by a constant current control method that adjusts the output voltage value so that the output current value matches a predetermined target current value. In addition, an AC voltage is output by a constant voltage control method in which the amplitude is adjusted so that the peak-to-peak value Vpp matches a predetermined target value.

  As described in Patent Document 1, if an alternating electric field is formed in the secondary transfer nip using a superimposed transfer voltage as the secondary transfer bias, the toner can be satisfactorily applied to the concave portions on the surface of the recording sheet rich in surface irregularities. It is already known that secondary transfer is possible. It is also known that the principle is as follows. In other words, when a secondary transfer bias consisting of only a DC voltage is used, only a very small number of toner particles constituting the toner image on the intermediate transfer belt in the secondary transfer nip are transferred from the belt surface to the sheet surface. It cannot be transferred into the recess. Even when the secondary transfer bias composed of the superimposed voltage is used, the same applies until the beginning of the AC component of the secondary transfer bias after the toner image enters the secondary transfer nip. Only a very small amount of toner particles can be transferred into the recesses on the sheet surface. However, when the next one cycle elapses, the amount of toner particles transferred from the belt surface into the sheet surface recesses slightly increases. Specifically, first, in the first half of the next one cycle, when the toner particles in the concave portion on the sheet surface return to the belt surface, the toner particles hit the toner particles that have remained on the belt surface until then. Weakens the adhesion between the toner and other toner particles and the belt surface. In the latter half, the toner particles having weakened adhesion as described above are transferred from the belt surface into the sheet surface recess together with the toner particles returning to the belt surface. Further, in the next one cycle, the number of toner particles transferred into the concave portion of the sheet surface is further increased by the same phenomenon. In the secondary transfer nip, as the toner particles reciprocate between the belt surface and the sheet surface recess many times, the number of toner particles transferred into the sheet surface recess gradually increases. When the toner image finally passes through the secondary transfer nip, a sufficient amount of toner particles are transferred into the recesses on the sheet surface.

  In FIG. 1, the optical sensor unit 40 of the nip forming unit 38 includes four reflective optical sensors, and these reflective optical sensors are disposed through a predetermined gap with respect to the front surface of the secondary transfer belt 41. The sensors are facing each other. These reflective optical sensors detect the optical characteristics of the secondary transfer belt 41 and the test toner image secondarily transferred from the intermediate transfer belt 31 to the secondary transfer belt 41 at the secondary transfer nip. Thereby, the position of the test toner image secondarily transferred onto the secondary transfer belt 41 is detected, or the image density (toner adhesion amount per unit area) of the test toner image is detected.

  For reasons that will be described later, in this printer, the intermediate transfer belt 31 is formed of a dark-tone elastic belt, so that the optical characteristics of the toner image on the intermediate transfer belt 31 can be detected well. Can not. Therefore, the test toner image is secondarily transferred from the dark tone intermediate transfer belt 31 to the light tone secondary transfer belt 41, and the optical characteristics of the test toner image on the secondary transfer belt 41 are detected by the optical sensor unit 40. It has become.

  FIG. 4 is a block diagram showing the main part of the electric circuit of this printer. In the figure, a main control unit 300 including a CPU 300a, a RAM 300b, a ROM 300c, a flash memory 300d, and the like controls the driving of each device in the printer based on a program stored in the ROM 300c, and performs various arithmetic processes. Or do. The main control unit 300 includes a registration sensor 506, a registration motor 507, electrophotographic units 1Y, 1M, 1C, and 1K for Y, M, C, and K, a transfer unit 30, a writing control unit 505, and a power supply control unit 200. Etc. are connected. Further, the optical writing unit 80 is connected via the writing control unit 505. Further, an environmental sensor 50, an operation display unit 501, a charging power supply unit 508, a development power supply unit 503, a primary transfer power supply unit 504, and a secondary transfer power supply 45 are connected via the power supply control unit 200.

  The registration motor 507 is a motor that is a driving source of the registration roller pair 101. Further, the writing control unit 505 controls driving of the optical writing unit 80 or sends image data to the main control unit 300 based on image data sent from an external personal computer or scanner.

  The environmental sensor 50 detects the temperature and humidity in the machine and sends the detection result to the power supply control unit 200. The power supply control unit 200 calculates the absolute humidity based on the temperature detection result and the humidity detection result sent from the environment sensor 50.

  The operation display unit 501 includes a touch panel and a plurality of operation keys. The operation display unit 501 receives a touch operation on the touch panel by the user, receives a key operation on the operation key, and displays an image on the touch panel.

  The charging power supply unit 508 individually outputs the charging bias applied to the charging roller of the Y, M, C, K charging device for each color. The output values of these charging biases are individually controlled by the power supply control unit 200.

  The developing power supply unit 503 outputs the developing bias applied to the developing sleeve of the developing device for Y, M, C, and K individually for each color. The output values of these developing biases are individually controlled by the power supply control unit 200.

  The primary transfer power supply unit 504 controls the primary transfer bias applied to the primary transfer rollers 35Y, 35M, 35C, and 35K for Y, M, C, and K individually for each color. The output values of these primary transfer biases are individually controlled by the power supply control unit 200.

  The main control unit 300 performs process control processing at a predetermined timing such as when the main power is turned on, when waiting after a predetermined time has elapsed, or when waiting after outputting a predetermined number of prints or more. FIG. 5 is a flowchart showing a processing flow in process control.

  When the predetermined timing comes, the main control unit 300 first acquires environmental information such as the number of sheets to be passed, the printing rate, the temperature, and the humidity (step 1: hereinafter, “step” is described as “S”). Next, the development characteristics of the electrophotographic units 1Y, 1M, 1C, and 1K are grasped. Specifically, development gamma γ and development start voltage are calculated for each color (S2).

  The calculation process is as follows. That is, first, the photosensitive members 2Y, 2M, 2C, and 2K are uniformly charged while rotating. Regarding this charging, the absolute value of the charging bias Vc is gradually increased, unlike a uniform value (for example, −700 V) during normal printing. Electrostatic latent images for patch-like Y test toner images, M test toner images, C test toner images, and K test toner images are formed on the photoreceptors 2Y, 2M, 2C, and 2K by scanning the laser beam with the optical writing unit 80. Form. By developing them with a developing device for Y, M, C, and K, the Y patch pattern image YPP, the M patch pattern image MPP, the C patch pattern image CPP, and the K patch pattern are applied to the photoreceptors 2Y, 2M, 2C, and 2K. An image KPP is formed. During development, the main control unit 300 gradually increases the absolute value of the developing bias Vb applied to the developing sleeves for Y, M, C, and K. The development bias Vb and the charging bias Vc are both composed of a negative DC voltage.

  The Y, M, C, and K patch pattern images (YPP, MPP, CPP, and KPP) are secondarily transferred from the photoreceptors 2Y, 2M, 2C, and 2K to the secondary transfer belt 41 via the intermediate transfer belt 31. The As shown in FIG. 6, the secondary transfer is performed so as to be aligned in the belt width direction without overlapping each other. Specifically, the Y patch pattern image YPP is transferred to one end in the width direction of the secondary transfer belt 41. Further, the M patch pattern image MPP is transferred to a position slightly shifted to the center side from the Y patch pattern image YPP in the belt width direction. The K patch pattern image KPP is secondarily transferred to the other end portion in the width direction of the secondary transfer belt 41. The C patch pattern image CPP is secondarily transferred to a position slightly shifted to the center side of the K patch pattern image KPP in the belt width direction.

  The optical sensor unit 40 includes a Y reflection type optical sensor 40Y, an M reflection type optical sensor 40M, a C reflection type optical sensor 40C, and a K reflection type optical sensor 40K that detect light reflection characteristics of the belt at different positions in the belt width direction. Have. Of these four reflective optical sensors, the K reflective optical sensor 40K employs a sensor that detects only specularly reflected light so as to detect a change in the light reflection characteristics of the belt surface due to adhesion of black toner. ing. On the other hand, other reflective optical sensors detect both regular reflection light and diffuse reflection light so as to detect a change in light reflection characteristics of the belt surface due to adhesion of Y, M, or C toner. Of the type.

  The Y reflection type optical sensor 40Y detects the toner adhesion amount in a plurality of Y test toner images of the Y patch pattern image YPP formed at one end in the width direction of the secondary transfer belt 41. Further, the M reflection type optical sensor 40M detects the toner adhesion amount in a plurality of M test toner images of the M patch pattern image MPP formed adjacent to the Y patch pattern image YPP on the secondary transfer belt 41. The K reflection type optical sensor 40K detects the toner adhesion amount in a plurality of K test toner images of the K patch pattern image KPP formed on the other end portion in the width direction of the secondary transfer belt 41. Further, the C reflection type optical sensor 40 </ b> C detects the toner adhesion amount in the plurality of K test toner images of the K patch pattern image KPP formed adjacent to the K patch pattern image KPP on the secondary transfer belt 41.

  The main control unit 300 calculates the light reflectance of the test toner image of each color based on the output signals sequentially sent from the four reflective optical sensors of the optical sensor unit 40, and the toner adhesion amount based on the calculation result. Is stored in the RAM 300b. Note that the test toner image of each color that has passed through the position facing the optical sensor unit 40 as the secondary transfer belt 41 travels is removed from the secondary transfer belt 41 by the belt cleaner 42.

  Next, the main control unit 300 uses the linear approximation equation (shown in FIG. 7) from the image density data (toner adhesion amount) stored in the RAM 300b and the exposure unit potential (latent image potential) data stored separately in the RAM 300b. Y = a × Vb + b) is calculated. In the two-dimensional coordinates in the figure, the x-axis indicates the value obtained by subtracting the developing bias Vb applied at that time from the exposure portion potential Vl, that is, the developing potential (Vl−Vb). The Y axis indicates the toner adhesion amount (y) per unit area. In the figure, data is plotted on the XY plane by the number corresponding to the number of test toner images. Based on the plurality of plotted data, a section on the XY plane to be subjected to linear approximation is determined. Thereafter, a linear approximation formula (y = a × Vb + b) is obtained by the method of least squares within the section. At this time, the development gamma γ and the development start voltage Vk are calculated based on the linear approximation formula. The development gamma γ is calculated as the slope of the linear approximation formula (γ = a), and the development start voltage Vk is calculated as the intersection of the linear approximation formula and the X axis (Vk = −b / a). Thus, the development characteristics of the Y, M, C, and K electrophotographic units 1Y, 1C, 1M, and 1K are calculated (S2).

  Next, based on the obtained development characteristics, the target value (target charge potential) of the charging potential (background portion potential) Vd, the target value (target exposure portion potential) of the exposure portion potential Vl, and the development bias Vb are determined. It is calculated (S3). Specifically, the target charging potential and the target exposure portion potential are obtained based on a data table in which the relationship between the development gamma γ and the charging potential Vd and the exposure portion potential Vl is determined in advance. Thereby, it is possible to select a target charging potential and a target exposure portion potential suitable for the development gamma γ. Further, the developing bias Vb is obtained as follows. That is, the development potential for obtaining the maximum toner adhesion amount is obtained by the combination of the development gamma γ and the development start voltage Vk, and the development bias Vb capable of obtaining the development potential is obtained. Then, based on the developing bias Vb and the background potential, a target charging potential is obtained. Since the surface of the developing sleeve of the developing roller has substantially the same value as the developing bias Vb, if the surface of the photosensitive member is charged to the target charging potential and appropriately exposed, the target developing potential and background potential are obtained. be able to.

  Next, the main control unit 300 determines the charging bias Vc. Specifically, the charging bias Vc at which the target charging potential is obtained varies depending on the wear amount of the surface layer of the photoreceptor, the electrical resistance of the charging roller that is influenced by the environment, and the like. Therefore, the main control unit 300 stores an algorithm for obtaining the charging bias Vc that can obtain the target charging potential from the combination of the absolute humidity and the photosensitive body travel distance. This algorithm is constructed based on previous experiments. Then, a charging bias Vc capable of obtaining a target charging potential is obtained by using an algorithm based on a combination of the temperature / humidity detection result by the environmental sensor 50 and the photosensitive body travel distance stored in the RAM.

  By periodically executing such process control processing, it is possible to form an image with a stable image density over a long period of time regardless of environmental changes.

  In a continuous print job in which images are continuously formed on a plurality of recording sheets P, the toner charge amount (Q / M) in the developer of the developing device is an average output image in the continuous print job over a long period of time. It changes according to the area ratio. Specifically, when the average output image area ratio is relatively high, the amount of toner replenishment per unit time is relatively large, and the average residence time of toner from the replenishment to the development in the developing device is relatively Shorter. As a result, the toner charge amount (Q / M) becomes relatively low and the adhesive force of the toner to the magnetic carrier becomes relatively weak, so that the developing ability of the developing device becomes relatively high and the image density is increased.

  On the other hand, when the average output image area ratio is relatively low, the toner replenishment amount per unit time is relatively small, and the average residence time of toner from the replenishment to the development in the developing device is relatively long. Then, the toner charge amount (Q / M) becomes relatively high and the adhesion force of the toner to the magnetic carrier becomes relatively strong. Therefore, the developing ability of the developing device becomes relatively low and the image density is lowered.

  In order to suppress such a change in image density due to the difference in the average output image area ratio, the main control unit 300 performs Vtref (developer target for each color of Y, M, C, and K during a continuous print job. Vtref adjustment processing for adjusting toner density is performed. In this Vtref adjustment process, every time a predetermined number of prints are made, a Y test toner image, an M test toner image, a C test toner image, and a K test toner image are formed one by one. Specifically, it is an area between the area in contact with the preceding recording sheet P and the area in contact with the succeeding recording sheet P in the secondary transfer nip among the entire area of the secondary transfer belt 41 in the circumferential direction. Those test toner images are formed in the inter-sheet corresponding area. Then, for each of Y, M, C, and K, Vtref is corrected so that a predetermined image density is obtained based on the result of detecting the toner adhesion amount of the test toner image by the optical sensor unit 40.

Next, a characteristic configuration of the printer according to the embodiment will be described.
In the old days, it has been common to use a belt composed of a hard belt substrate such as a polyimide belt as an intermediate transfer belt. However, this configuration has been found to cause the following problems. That is, for example, a toner image is formed on a concavo-convex sheet such as a surface concavo-convex sheet (trade name: Rezac 66) manufactured by Tokai Paper Co., Ltd. while the intermediate transfer belt is moved endlessly at an extremely high linear speed of about 630 [mm / s]. Assume that secondary transfer has been performed. As a result, despite the use of the superimposed transfer voltage as the secondary transfer bias, the toner cannot be satisfactorily secondary-transferred to the recesses on the surface of the concavo-convex sheet, resulting in uneven image density unevenness. It will cause. In other words, with an intermediate transfer belt consisting only of a hard belt substrate, if the printing speed is increased to an ultra-high speed for business users, even if an alternating electric field is formed in the secondary transfer nip due to the secondary transfer bias consisting of superimposed voltage, unevenness is generated. Inferior toner transfer is caused by the concave portion of the surface of the sheet.

  On the other hand, the present inventors prepared a printer tester equipped with an elastic belt as an intermediate transfer belt, and produced an uneven sheet (Rezac) at an ultra-high speed (process line speed = 630 mm / s) for business users. 66) An experiment for secondary transfer was conducted. Then, the toner was satisfactorily transferred to the concave portion on the surface of the concavo-convex sheet, and it was possible to effectively suppress the occurrence of uneven image density following the concavo-convex surface of the sheet. This is probably because the distance between the surface of the intermediate transfer belt and the concave portion of the concavo-convex sheet was reduced by flexibly changing the elastic layer of the intermediate transfer belt made of an elastic belt in the secondary transfer nip. In view of this experimental result, in the printer according to the embodiment, the intermediate transfer belt 31 is made of an elastic belt.

  FIG. 8 is an enlarged sectional view partially showing a transverse section of the intermediate transfer belt 31 formed of an elastic belt mounted on the printer according to the embodiment. The intermediate transfer belt 31 has an endless belt-like base layer (a hard belt base) 31a made of a material having a certain degree of flexibility and high rigidity, and has excellent flexibility laminated on the front surface thereof. And an elastic layer 31b made of an elastic material. Particles 31c are dispersed in the elastic layer 31b, and these particles 31c are densely packed in the belt surface direction as shown in FIG. 9 with a part of the particles 31c protruding from the surface of the elastic layer 31b. Are lined up. A plurality of protrusions are formed on the belt surface by the plurality of particles 31c.

  Examples of the material of the base layer 31a include a resin in which an electrical resistance adjusting material made of a filler or an additive for adjusting the electrical resistance is dispersed. From the viewpoint of flame retardancy, the resin is preferably a fluorine-based resin such as PVDF (polyvinylidene fluoride) or ETFE (ethylene / tetrafluoroethylene copolymer), a polyimide resin, or a polyamide-imide resin. . Further, from the viewpoint of mechanical strength (high elasticity) and heat resistance, a polyimide resin or a polyamideimide resin is particularly preferable.

  Examples of the electrical resistance adjusting material dispersed in the resin include metal oxides, carbon black, ionic conductive agents, and conductive polymer materials. Examples of the metal oxide include zinc oxide, tin oxide, titanium oxide, zirconium oxide, aluminum oxide, and silicon oxide. In order to improve the dispersibility, the metal oxide previously subjected to surface treatment may be used.

For the coating liquid that is the precursor of the base layer 31a (in which the electrical resistance adjusting material is dispersed in the liquid resin before curing), a dispersion aid, a reinforcing material, a lubricant, and a heat conducting material are used as necessary. An antioxidant or the like may be added. The addition amount of the electrical resistance adjusting material contained in the base layer 31a of the seamless belt suitably equipped as the intermediate transfer belt 31 is preferably 1 × 10 ⁸ to 1 × 10 ¹³ [Ω / □] in terms of surface resistance, volume resistance 1 × 10 ⁶ to 1 × 10 ¹² [Ω · cm].

  The thickness of the base layer 31a is not particularly limited and may be appropriately selected depending on the situation, but is preferably 30 μm to 150 μm, more preferably 40 μm to 120 μm, and particularly preferably 50 μm to 80 μm. If the thickness of the base layer 31a is less than 30 μm, the belt is likely to tear due to cracks, and if it exceeds 150 μm, the belt may be broken by bending. On the other hand, when the thickness of the base layer 31a is within the particularly preferable range described above, it is advantageous in terms of durability.

  In order to improve the belt running stability, it is preferable to reduce the layer thickness unevenness of the base layer 31a as much as possible. The method for adjusting the thickness of the base layer 31a is not particularly limited, and can be appropriately selected depending on the situation. For example, measurement with a contact type or eddy current type film thickness meter or a method of measuring a cross section of the film with a scanning electron microscope (SEM) can be mentioned.

  As described above, the elastic layer 31b of the intermediate transfer belt 31 has a plurality of convex shapes formed by a plurality of dispersed particles 31c on the surface.

  Among the elastic materials constituting the elastic layer 31b, acrylic rubber is most preferable from the viewpoints of ozone resistance, flexibility, adhesion to particles, imparting flame retardancy, environmental stability, and the like.

  The proper range of the amount of the crosslinking agent is preferably 0.05 to 20 parts by weight, and more preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the acrylic rubber. When the blending amount of the crosslinking agent is too small, crosslinking is not sufficiently performed, so that it is difficult to maintain the shape of the crosslinked product. On the other hand, when there is too much content, a crosslinked material will become hard too much and the elasticity etc. as crosslinked rubber will be impaired.

  The acrylic rubber used for the elastic layer 31b may be blended with a crosslinking accelerator for the purpose of promoting the crosslinking reaction of the crosslinking agent described above.

Regarding the addition amount of the electrical resistance adjusting material, the resistance value of the elastic layer 31b is 1 × 10 ⁸ to 1 × 10 ¹³ [Ω / □] in terms of surface resistance and 1 × 10 ⁶ to 1 × 10 ¹² [Ω in terms of volume resistance. -It is preferable to adjust so that it may be in the range of cm].

  The layer thickness of the elastic layer 31b is preferably 200 μm to 2 mm, and more preferably 400 μm to 1000 μm. When the layer thickness is smaller than 200 μm, the followability to the surface irregularities of the recording sheet and the effect of reducing the transfer pressure are lowered, which is not preferable. On the other hand, if the layer thickness is larger than 2 mm, the elastic layer 31b is easily bent by its own weight, and the running performance becomes unstable, or the belt is easily cracked by being wound around a roller that stretches the belt. This is not preferable. In addition, as a measuring method of layer thickness, the method of measuring by observing a cross section with a scanning microscope (SEM) can be illustrated.

  The particles 31c dispersed in the elastic material of the elastic layer 31b have an average particle diameter of 100 μm or less, have a true spherical shape, are insoluble in organic solvents, and have a 3% thermal decomposition temperature of 200 ° C. or higher. Some resin particles are used. Although there is no restriction | limiting in particular in the resin material of particle | grains 31c, An acrylic resin, a melamine resin, a polyamide resin, a polyester resin, a silicone resin, a fluororesin, rubber | gum etc. can be illustrated. The base surface of the particles made of these resin materials may be surface treated with a different material. A hard resin may be coated on the surface of spherical base particles made of rubber. Moreover, as a base particle, you may use a hollow thing and a porous thing.

  Among the resin materials exemplified so far, silicone resin particles are most preferable from the viewpoint of excellent lubricity, releasability with respect to toner, abrasion resistance, and the like. Particles obtained by finishing a resin material into a spherical shape by a polymerization method or the like are preferable, and particles closer to a true sphere are more preferable. In addition, as the particles 31c, it is desirable to use particles having a volume average particle diameter of 1.0 μm to 5.0 μm and monodispersed particles. The monodisperse particles are not particles having a single particle size but particles having a very sharp particle size distribution. Specifically, it is a particle having a distribution width of ± (average particle size × 0.5 μm) or less. When the particle size of the particles 31c is less than 1.0 μm, the effect of promoting the transfer performance by the particles 31c cannot be sufficiently obtained. On the other hand, if the particle size is larger than 5.0 μm, the gap between the particles becomes large and the surface roughness of the belt increases, so that the toner cannot be transferred satisfactorily or the intermediate transfer belt 31 is cleaned. It becomes easy to generate a defect. Furthermore, since the particles 31c made of a resin material are generally highly insulating, if the particle size is too large, the charges of the particles 31c tend to cause image disturbance due to the accumulation of charges during continuous printing.

  As the particles 31c, specially synthesized particles or commercially available products may be used. By applying the particles 31c directly to the elastic layer 31b and leveling, the particles can be easily and uniformly aligned. By doing in this way, the overlap of the particles 31c in the belt thickness direction can be almost eliminated. The cross-sectional diameter of the plurality of particles 31c in the surface direction of the elastic layer 31b is desirably as uniform as possible, and specifically, a distribution width of ± (average particle diameter × 0.5 μm) or less is preferable. For this reason, it is preferable to use a powder having a small particle size distribution as the powder of the particles 31c. However, if a method that realizes selectively applying only the particles 31c having a specific particle size to the surface of the elastic layer 31b is employed. It is also possible to use a powder having a relatively large particle size distribution. The timing at which the particles 31c are applied to the surface of the elastic layer 31b is not particularly limited, and may be any before or after crosslinking of the elastic material of the elastic layer 31b.

  In the surface direction of the elastic layer 31b in which the particles 31c are dispersed, the projected area ratio between the portion where the particles 31c are present and the portion where the surface of the elastic layer 31b is exposed is that the particles 31c exist. It is desirable that the projected area ratio of the existing portion be 60% or more. If it is less than 60%, the chance of direct contact between the toner and the solid surface of the elastic layer 31b is increased, resulting in failure to obtain good toner transfer performance, or reduction in toner cleaning performance from the belt surface. The film surface resistance of the belt surface is reduced. It is also possible to use an intermediate transfer belt 31 in which the particles 31c are not dispersed in the elastic layer 31b.

  As shown in FIG. 9, on the surface of the intermediate transfer belt 31, the overlapping of the particles 31 c is hardly observed. The diameter of the cross section of the particle 31c on the surface of the elastic layer 31b is preferably as uniform as possible. Specifically, the distribution width is preferably ± (average particle diameter × 0.5) μm or less. In order to realize such a distribution width, it is preferable to use particle powder having a narrow particle size distribution. However, the elastic layer 31b may be formed by selectively localizing particles 31c having a specific particle size on the surface. If it is formed, a particle powder having a wide particle size distribution may be used.

  In order to satisfactorily secondary transfer the toner to the plurality of concave portions on the surface of the concavo-convex sheet as the recording sheet P and to suppress the occurrence of image density unevenness caused by the concavo-convex surface, the elastic layer 31b has a certain degree of flexibility ( It is necessary to adopt a material excellent in elasticity. And when such an elastic layer 31b is employ | adopted, since it will extend immediately if it stretches only with the elastic layer 31b alone, it cannot endure actual use. For this reason, it is an essential condition to provide a base layer 31a that is stiffer than the elastic layer 31b, and to suppress the elongation of the entire belt over a long period of time due to the rigidity of the base layer 31a.

  As described above, in the printer according to the embodiment, the intermediate transfer belt 31 including the elastic belt in which the elastic layer 31b is stacked on the base layer 31a is used. As a result, even when an image is formed at an ultra-high speed for business users with a belt linear velocity (process linear velocity) = 630 [mm / s], a sufficient amount of toner is transferred into the concave portion on the surface of the concave-convex sheet. It was possible to suppress the occurrence of image density unevenness following the surface unevenness of the sheet.

  Since the intermediate transfer belt 31 having the elastic layer 31b as described above has a low light reflectance on the surface and a dark tone, detecting the optical characteristics of the test toner image on the surface results in poor detection accuracy, or Optical characteristics cannot be detected. On the other hand, the secondary transfer belt 41 is a single layer belt made of a polyimide resin, and its surface has a high light reflectance and a bright color tone, so that the optical characteristics of the test toner image on the surface can be detected well. it can.

  Therefore, in the test transfer mode, the test toner image is secondarily transferred from the dark tone intermediate transfer belt 31 to the light tone secondary transfer belt 41, and the optical characteristics of the test toner image on the secondary transfer belt 41 are measured by an optical sensor. Detected by unit 40. Thereby, the optical characteristics of the test toner image can be detected satisfactorily. The secondary transfer belt 41 may be made of a fluorine resin such as PVDF (polyvinylidene fluoride) or ETFE (ethylene / tetrafluoroethylene copolymer), or a polyamideimide resin.

  FIG. 10 is a graph showing a first example of the waveform of the secondary transfer bias composed of the superimposed voltage output from the secondary transfer power supply 45. The waveform of the secondary transfer bias shown in the figure is a sine wave. The offset voltage Voff is the value of the DC component (DC voltage) of the secondary transfer bias composed of the superimposed voltage. The polarity of the offset voltage Voff in the figure is negative. When the waveform of the secondary transfer bias is a sine wave as illustrated, the offset voltage Voff and the average potential Vave per cycle (T) of the secondary transfer bias have the same value. Therefore, in the same figure, the average potential Vave has a negative polarity.

  In the configuration in which the secondary transfer bias is applied to the core of the secondary transfer back roller (33 in FIG. 1) as in the printer of the embodiment, the polarity of the secondary transfer bias is the same as the normal charging polarity of the toner. Sometimes, the toner in the secondary transfer nip electrostatically moves in the transfer direction. The transfer direction is a direction from the surface side of the intermediate transfer belt 31 toward the surface side of the secondary transfer belt 41 in the secondary transfer nip. On the other hand, when the polarity of the secondary transfer bias is opposite to the normal charging polarity of the toner, the toner in the secondary transfer nip is electrostatically moved in the direction opposite to the transfer direction. As shown in the figure, by making the average potential Vave a negative polarity that is the same polarity as the normal charging polarity of the toner, while reciprocating the toner between the belt surface side and the sheet surface side in the secondary transfer nip, Relatively, the belt is moved from the belt surface side toward the sheet surface side. As a result, the toner image on the surface of the intermediate transfer belt 31 can be secondarily transferred onto the surface of the recording sheet P.

  In the figure, a transfer peak value Vt is a peak value for electrostatically moving toner with the strongest electrostatic force in the secondary transfer nip in the secondary transfer nip within one cycle (cycle T) of the secondary transfer bias. . The reverse peak value Vr is a peak value that is not the transfer peak value Vt. In the secondary transfer bias shown in the figure, the reverse peak value Vr has a reverse polarity (plus polarity) to the transfer peak value Vt.

  The waveform of the secondary transfer bias is not limited to a sine wave as shown in FIG. A secondary transfer bias of a triangular wave or a rectangular wave may be employed. FIG. 11 is a graph showing a second example of the waveform of the secondary transfer bias composed of the superimposed voltage. The waveform of the secondary transfer bias shown in the figure is a rectangular wave. The sine wave of the secondary transfer bias shown in FIG. 10 and the rectangular wave of the secondary transfer bias shown in FIG. 11 have a duty of 50 [%], which will be described later. In any secondary transfer bias having a waveform having such characteristics, the average potential Vave per cycle (cycle T) has the same value as the offset voltage Voff. That is, the value of the DC component is the same as the average potential Vave.

  FIG. 12 is a graph for explaining the duty in the secondary transfer bias shown in FIG. In the figure, the center potential VC is the center potential at the peak-to-peak value Vpp of the AC component (AC voltage) of the secondary transfer bias. The reverse peak side time tr is the reverse peak value Vr from the moment when the secondary transfer bias value starts to rise from the central potential VC toward the reverse peak value Vr within one cycle (cycle T) of the AC component. It is the time until it returns to the center potential VC. The transfer peak side time tf is the transfer peak value Vt from the moment when the value of the secondary transfer bias starts to rise from the center potential VC toward the transfer peak value Vt within one cycle (cycle T) of the AC component. It is the time until it returns to the center potential VC. Further, the duty is a ratio of the reverse peak side time tr in the period T, and is 50 [%] in the case of the illustrated waveform. That is, the duty in the illustrated waveform is 50 [%].

  FIG. 13 is a graph for explaining the duty in the secondary transfer bias shown in FIG. Also in the illustrated rectangular wave, the duty as the ratio of the reverse peak side time tr in the period T is 50 [%]. Hereinafter, the characteristic that the duty is less than 50% is referred to as low duty. On the other hand, the characteristic that the duty exceeds 50% is called high duty.

  In order to electrostatically move the toner in the transfer direction in the secondary transfer nip using the secondary transfer bias of duty = 50 [%], the absolute value of the transfer peak value Vt is changed to the absolute value of the reverse peak value Vr. Need to be bigger than. If the absolute value of the transfer peak value Vt becomes too large, a discharge is generated between the surface of the intermediate transfer belt 31 and the concavo-convex sheet in the secondary transfer nip. This discharge reversely charges the toner particles and remarkably inhibits secondary transfer of the toner particles, thereby generating a lot of white spots in the image and significantly degrading the image quality. Therefore, it is necessary to keep the absolute value of the transfer peak value Vt to a certain value.

  On the other hand, if the absolute value of the reverse peak value Vr is too small, a sufficient amount of toner cannot be transferred to the surface recesses of the uneven sheet. Specifically, if the absolute value of the reverse peak value Vr is too small, the toner particles once transferred from the belt surface into the concave portion of the concave-convex sheet in the secondary transfer nip cannot be returned to the belt surface. . As a result, the toner particles returned from the inside of the surface recesses are hit against other toner particles on the belt surface or toner particles adhering to the belt surface, and the adhesion force cannot be weakened. By simply vibrating the toner particles, the number of toner particles transferred into the surface recesses of the concavo-convex sheet cannot be increased due to the vibrations, so that the amount of toner transferred into the surface recesses is insufficient. It is.

  One method for increasing the reverse peak value Vr is to increase the peak-to-peak value Vpp of the AC component. However, if the peak-to-peak value Vpp is increased in order to eliminate the shortage of the reverse peak value Vr, the transfer peak value Vt is increased at the same time, so that it becomes easy to cause white spots due to discharge.

  Another method for increasing the reverse peak value Vr is to decrease the offset voltage Voff. However, if the offset voltage Voff is reduced, the average potential Vave is also reduced accordingly, so that the toner cannot be electrostatically moved favorably from the belt surface side to the sheet surface side in the secondary transfer nip. There is a risk of causing secondary transfer failure.

  Therefore, in order to transfer a sufficient amount of toner to the concave portion of the surface of the concavo-convex sheet, it is desirable to set the duty to 50 [%] or less. More desirably, the low duty is less than 50%. This is because, when the duty is set to a high duty greater than 50 [%], white spots due to discharge and secondary transfer defects are likely to occur. Specifically, when the duty is set to a high duty, the average potential Vave is shifted to the reverse peak side by that amount and the absolute value thereof is reduced, so that secondary transfer failure is likely to occur. Then, in order to avoid the occurrence of the secondary transfer failure, if the peak-to-peak value Vpp is increased to increase the average potential Vave, the transfer peak value Vt is increased accordingly. White spots are easily generated. Therefore, it is desirable to set the duty to a low duty less than 50%.

  That is, when an uneven sheet having a low surface smoothness is used as the recording sheet, it is desirable to employ a secondary transfer bias having a low duty superimposed voltage. In other words, the low duty is a characteristic corresponding to low smoothness. In the present specification, low smoothness means that the surface smoothness of plain paper is inferior to that of Japanese paper. Hereinafter, the surface smoothness of the surface-coated paper, which is superior to the surface smoothness of the plain paper, is referred to as high smoothness. Moreover, the thing equivalent to the surface smoothness of plain paper is called medium smoothness.

  FIG. 14 is a graph showing an example of a waveform of the secondary transfer bias in which the duty is set to 35 [%] smaller than 50 [%]. The reverse transfer bias reverse peak value Vr shown in the figure is the same as the reverse transfer bias Vr of the secondary transfer bias shown in FIG. Further, the transfer peak value Vt of the secondary transfer bias shown in FIG. 14 is the same as the transfer peak value Vt of the secondary transfer bias shown in FIG. The difference between the secondary transfer bias shown in FIG. 14 and the secondary transfer bias shown in FIG. 11 is only the reverse peak side time tr and the transfer peak side time tf. In the secondary transfer bias shown in FIG. 11, the reverse peak side time tr and the transfer peak side time tf are the same, whereas in the secondary transfer bias shown in FIG. 14, the reverse peak side time tr is the transfer peak. It is shorter than the side time tf. More specifically, the reverse peak side time tr of the secondary transfer bias shown in FIG. 11 is 50 [%] of the period T, whereas the reverse peak side time of the secondary transfer bias shown in FIG. tr is 35% of the period T. That is, the duty of the secondary transfer bias shown in FIG. 14 is 35 [%].

  In the secondary transfer bias of duty = 50 [%] shown in FIG. 11, as described above, the offset voltage Voff and the average potential Vave have the same value. On the other hand, in the secondary transfer bias of duty = 35 [%] shown in FIG. 14, the average potential Vave is larger than the offset voltage Voff. The peak-to-peak value Vpp is the same for the secondary transfer bias shown in FIG. 7 and the secondary transfer bias shown in FIG. That is, by making the duty less than 50 [%], the average potential Vave is not changed without changing the peak-to-peak value Vpp, the transfer peak value Vt, and the reverse peak value Vr, compared to the case of 50 [%]. Can be increased. Therefore, compared with the case where the duty is set to 50 [%] or more, it is possible to suppress the occurrence of secondary transfer failure and white spots.

  Therefore, when the toner image is secondarily transferred to the concavo-convex sheet, the power supply control unit 200 reverses the polarity within one cycle as a secondary transfer bias and starts from a low duty superimposed voltage of less than 50%. Are output from the secondary transfer power supply 45. In such a configuration, compared to a configuration using a secondary transfer bias having a high duty superimposed voltage of 50 [%] or more, it is possible to suppress the occurrence of secondary transfer failure and white spots due to discharge.

  By the way, the present inventors secondarily transfer a halftone image to a smooth sheet (surface smoothness is high smoothness) made of surface-coated paper excellent in surface smoothness under the condition of using a low-duty secondary transfer bias. An experiment was conducted. Then, a remarkably insufficient image density due to the secondary transfer failure was caused in the halftone image.

  As a result of earnest research on the cause of such secondary transfer failure, the following was found. That is, in the halftone image, the entire image portion is not covered with toner, and a toner adhering portion constituting a relatively small number of dot groups and a blank portion where no toner is adhering are mixed in the image portion. doing. When the intermediate transfer belt 31 provided with the elastic layer 31b is used and a smooth sheet having excellent surface smoothness is used as the recording sheet P, the elastic layer 31b forms a small number of dots in the halftone image in the secondary transfer nip. It is deformed flexibly according to the shape of the small number of toner dots. Due to this deformation, not only the surface of the minority dot toner lump in the halftone image but also the side surface of the minority dot toner lump is wrapped with the elastic layer 31b. Then, a charge having a polarity opposite to the normal charge polarity is injected from the elastic layer 31b to each toner particle of the small-number-dot toner mass, thereby reducing the charge amount (Q / M) of the toner or reversely charging the toner. . As a result, it was found that the secondary transfer failure of the toner image was caused. In the case where an uneven sheet is used as the recording sheet P, the elastic layer 31b is deformed into an irregular shape according to the unevenness of the sheet surface. Almost nothing. For this reason, secondary transfer failure is not caused even on the surface convex portion of the concavo-convex sheet.

  FIG. 15 is an enlarged configuration diagram showing the secondary transfer nip and its periphery in a configuration in which the intermediate transfer belt 31 is different from that of the printer according to the embodiment and has a single layer structure. When the intermediate transfer belt 31 having a single layer structure as illustrated is used, the secondary transfer current flows between the secondary transfer back roller 33 and the secondary transfer nip backing roller 36 as follows. In other words, as indicated by the arrows in the figure, the secondary transfer current flows in a straight line concentrating at the nip center position (center position in the belt movement direction). Does not flow so much. Since the secondary transfer current flows in this manner, the time during which the secondary transfer current is applied to the toner in the secondary transfer nip becomes relatively short. For this reason, the secondary transfer current hardly injects an electric charge having a polarity opposite to the normal polarity to the toner.

  FIG. 16 is an enlarged cross-sectional view showing the secondary transfer nip and its peripheral configuration in a configuration using an intermediate transfer belt 31 made of an elastic belt having a multilayer structure as in the printer according to the embodiment. In the configuration using the intermediate transfer belt 31 formed of an elastic belt having a multilayer structure, the secondary transfer current flows between the secondary transfer back roller 33 and the secondary transfer nip backing roller 36 as follows. That is, the secondary transfer current flows in the belt thickness direction while spreading in the belt circumferential direction at the interface between the layers. As a result, the secondary transfer current goes not only to the center position of the nip but also to the vicinity of the nip inlet and the nip outlet, so that the time for applying the secondary transfer current to the toner in the secondary transfer nip is relatively long. It will be a long time. Then, it becomes easy to inject excessive charge having a polarity opposite to the normal polarity to the toner due to the secondary transfer current. This also greatly reduces the charge amount of the normal polarity of the toner or reversely charges the toner, thereby inhibiting the secondary transferability. When such a hindrance and the soft intermediate transfer belt 31 flexibly deform and wrap the convex shape of the toner image on the surface thereof, it becomes easy to cause a secondary transfer failure of a halftone image. Conceivable.

  Next, the present inventors use a low-duty bias or a high-duty (duty = 80%) shown in FIG. 17 instead of a low-duty or a DC voltage. An experiment was performed in which the image was secondarily transferred to a smooth sheet. As the smooth sheet, an OK top coat (128 gsm) manufactured by Oji Paper Co., Ltd. was used (so-called coated paper). When the black halftone image (2by2) was secondarily transferred onto a smooth sheet under the condition of process linear velocity = 630 [mm / s] in an environment of 27 ° C./80%, smooth transfer without causing secondary transfer failure. The black halftone image was successfully secondary transferred onto the sheet.

  The reason why the secondary transfer property of the halftone image on the smooth sheet can be improved by using the high duty secondary transfer bias is considered to be as follows. That is, when the endlessly moving intermediate transfer belt 31 enters the secondary transfer nip, charging of the belt portion that has entered the secondary transfer nip is started by the secondary transfer bias. Then, when the amount of charge exceeds a certain threshold value, the injection of reverse charge into the minority dot toner mass in the halftone image starts. Charging of the belt portion that has entered the secondary transfer nip mainly occurs within the transfer peak side time tf. Therefore, as the transfer peak side time tf becomes longer, the amount of reverse charge injected into the minority dot toner mass increases. The high-duty secondary transfer bias has a shorter transfer peak side time tf than the low-duty secondary transfer bias. It is considered possible to suppress the occurrence.

  From this experimental result, it was found that the high duty is a characteristic according to the high smoothness of the surface smoothness of the recording sheet. Therefore, when the toner image is secondarily transferred to the smooth sheet, the power supply control unit 200 outputs a secondary transfer bias with a high duty from the secondary transfer power supply 45.

  In addition, the following thing became clear by another experiment conducted by the present inventors. That is, as shown in FIG. 17, the use of a high duty secondary transfer bias that does not reverse the polarity is more effective than the high duty secondary transfer bias that reverses the polarity within one cycle. Can be improved.

  In the secondary transfer bias shown in FIG. 17, the polarity of the voltage is changed so that the direction of the electric field is reversed in the direction of returning the toner from the sheet surface side to the belt surface side within the reverse peak side time tr. The polarity is opposite to the polarity at tf. Such secondary transfer bias and secondary transfer bias that does not reverse the polarity have the same duty, and the same secondary transfer electric field intensity integrated value (Vave) within the same cycle. Try to get transferability. Then, it is necessary to make the transfer peak value Vt in the secondary transfer bias in FIG. 17 larger than the transfer peak value Vt in the secondary transfer bias that does not reverse the polarity. As a result, the secondary transfer bias in FIG. 17 has a reverse charge to the small number of dot toner clusters of the halftone image in comparison with the secondary transfer bias that does not reverse the polarity, even though the duty and the average potential Vave are the same. Increase injection volume. In other words, since the secondary transfer bias that does not reverse the polarity can reduce the transfer peak value Vt and reduce the injection amount of the reverse charge to the minority dot toner mass as compared with the secondary transfer bias of FIG. Secondary transferability can be further improved.

  FIG. 18 is a block diagram illustrating an electric circuit of the operation display unit 501 of the printer according to the embodiment. As shown in the figure, the operation display unit 501 has a smooth paper button 501a, an uneven paper button 501b, and a plain paper button 501h. In this printer, an instruction for allowing the user to perform the following operation is described in the instruction manual. That is, when a smooth sheet excellent in surface smoothness is set as the recording sheet P in the feeding cassette (100 in FIG. 1), the smooth paper button 501a is pressed. On the other hand, when an uneven sheet such as Japanese paper is set as the recording sheet P in the feeding cassette, the uneven sheet button 501b is pressed. When plain paper is set as the recording sheet P in the feeding cassette, the plain paper button 501h is pressed. That is, the operation display unit 501 functions as an information acquisition unit that can acquire the following information. In other words, the recording sheet P that is the target for secondary transfer of the toner image is at least ascertained whether it is a smooth sheet having excellent surface smoothness, or an uneven sheet having surface smoothness inferior to that of a smooth sheet or plain paper. It is information that can be done.

  Based on the result of acquiring the information by the operation display unit 501, the power control unit 200 switches the transfer mode when the toner image is secondarily transferred to the recording sheet between the uneven mode, the smooth mode, and the normal mode. Specifically, when the concavo-convex paper button 501b is pressed, a concavo-convex mode using a secondary transfer bias composed of a low-duty superimposed voltage is implemented as a sheet transfer mode for transferring a toner image to the recording sheet P. When the smooth paper button 501a is pressed, a smooth mode using a secondary transfer bias having a high duty superimposed voltage is performed as the sheet transfer mode. When the plain paper button 501h is pressed, the normal mode is executed as the sheet transfer mode. In this normal mode, the secondary transfer bias is switched between a DC voltage only and the same as the smoothing mode depending on the environment.

  In such a configuration, it is possible to suppress the occurrence of transfer failure of a halftone image due to the injection of a charge having a polarity opposite to the normal charge polarity into the toner in the secondary transfer nip.

In the smooth mode in which the toner image is transferred to the smooth sheet, there is no need to reciprocate the toner between the surface of the intermediate transfer belt 31 and the surface of the sheet in the secondary transfer nip. Therefore, it is desirable to adopt one of the following values for the reverse peak value Vr of the secondary transfer bias composed of the superimposed voltage.
(A) The reverse peak value Vr which is opposite to the normal charging polarity of the toner and whose absolute value is small enough to prevent the toner from returning from the sheet surface side to the belt surface side.
(B) Reverse peak value Vr having the same polarity as the normal charging polarity of the toner.
Whichever reverse peak value Vr is used, the toner does not reciprocate between the sheet surface and the surface of the intermediate transfer belt 31 in the secondary transfer nip.

  As already described, in the smooth mode, it is possible to suppress the secondary transfer failure of the halftone image better by using the one that does not reverse the polarity than the one that reverses the polarity in one cycle of the AC voltage. . Therefore, in this printer, in the smooth mode, the superimposed voltage of the reverse peak value Vr of (b) is output from the secondary transfer power supply 45. The same applies to the case where the secondary transfer bias having a high duty superimposed voltage is used in the normal mode.

For reference, examples of various numerical values of the secondary transfer bias used in the uneven mode are shown in Table 1 below.

Table 2 below shows examples of various numerical values of the secondary transfer bias used in the smooth mode.

  In this printer, as a combination of the secondary transfer bias in the concavo-convex mode and the secondary transfer bias in the smooth mode, a combination in which the latter peak-to-peak value Vpp is made smaller is adopted. This is for the reason explained below. That is, in the smooth mode, there is no need to reciprocate the toner in the secondary transfer nip, so that no electrostatic force in the opposite direction to the transfer direction is generated (the polarity is not reversed) or with a very weak force. Even if it exists, secondary transfer failure will not be caused. The reason why the AC voltage is used is that the voltage of the polarity (minus in this example) that generates an electrostatic force in the transfer direction is temporarily greatly reduced to suppress the injection of reverse charges into the toner. The peak-to-peak value Vpp of the AC voltage used for this reason (which agrees with the superimposed voltage Vpp) is sufficient to make the electrostatic force in the transfer direction a value necessary for transfer, and the uneven mode There is no need to make it larger. Nevertheless, if the peak-to-peak value Vpp is as large as the concave-convex mode, unnecessary alternating electric shock is applied to the intermediate transfer belt 31 and the secondary transfer belt 41 to accelerate their deterioration. In other words, the deterioration due to the alternating electric shock can be suppressed by setting the peak-to-peak value Vpp in the smooth mode to a lower value.

  Further, in this printer, a combination in which the latter frequency is higher than that of the former is employed as a combination of the secondary transfer bias in the uneven mode and the secondary transfer bias in the smooth mode. This is for the reason explained below. That is, in the concavo-convex mode in which the toner image is secondarily transferred to the concavo-convex sheet, the time during which the electric field in the direction opposite to the transfer direction is formed is shortened as the frequency is increased. If it is too high, the time cannot be secured long enough, and the toner cannot be returned from the concave portion of the sheet surface to the surface of the intermediate transfer belt 31, so that the low transfer secondary transfer can be performed. Even if a bias is used, a transfer failure to a concave portion is caused. On the other hand, in the smooth mode in which the toner image is secondarily transferred to the smooth sheet, the lower the frequency, the longer the time during which a relatively high voltage is continuously applied on the transfer peak value Vt side. The reverse charge injection is likely to occur. By making the frequency of the high duty secondary transfer bias higher than the low duty, the following becomes possible. That is, secondary transfer of a halftone image resulting from injection of reverse charge into toner due to excessively low frequency in the smooth mode while suppressing poor transfer to the concave portion of the sheet surface due to excessively high frequency in the uneven mode The occurrence of defects can be suppressed.

  In the concavo-convex mode in which the toner image is transferred to the concavo-convex sheet, the toner is reciprocated between the sheet surface and the intermediate transfer belt 31 a plurality of times in the secondary transfer nip. It is easy to generate transfer dust that scatters particles. However, in order to preferentially suppress the latter deterioration in image quality, the deterioration in image quality due to poor transfer to the concave portion of the sheet surface caused by not moving the toner back and forth is more conspicuous than the deterioration in image quality due to transfer dust. A secondary transfer bias having a characteristic of reciprocally moving is adopted.

  In the above-described process control process and Vtref adjustment process in a continuous print job, a test transfer mode in which a test toner image is secondarily transferred from the intermediate transfer belt 31 to the secondary transfer belt 41 is executed. Since the surface of the secondary transfer belt 41 has almost no unevenness, a secondary transfer bias having a reverse duty value Vr with a low duty and a relatively high value is used as in the case of secondary transfer of a toner image onto an uneven sheet. There is no need. Nevertheless, for example, assume that the following processing is performed during a continuous print job. That is, immediately after the toner image is secondarily transferred to the concavo-convex sheet using a low-duty secondary transfer bias in the concavo-convex mode, a test toner image for Vtref adjustment processing is provided in the inter-sheet corresponding region of the secondary transfer belt 41. Assume that secondary transfer is performed with the same low duty secondary transfer bias. Then, image quality deterioration due to transfer dust occurs in the test toner image, and the detection accuracy of the toner adhesion amount (image density) is lowered.

Therefore, in the test transfer mode in which the test toner image is transferred to the secondary transfer belt 41, the power supply control unit 200 is listed next regardless of the information on the surface smoothness of the recording sheet acquired by the operation display unit 501. The secondary transfer bias is output from the secondary transfer power supply 45.
(Α) Secondary transfer bias consisting only of DC voltage.
(Β) The same secondary transfer bias as in the smooth mode.
(Γ) Unlike the secondary transfer bias in the smooth mode, the reverse peak value Vr has a value that makes the electrostatic force in the direction opposite to the transfer direction weaker than the reverse peak value Vr of the secondary transfer bias in the uneven mode. Secondary transfer bias consisting of high-duty superimposed voltage.

  Any of the secondary transfer biases (α) to (γ) is less than the case where the same secondary transfer bias as that in the concavo-convex mode is used. Occurrence can be suppressed.

FIG. 19 is a graph showing the relationship between the secondary transfer rate of the test toner image with respect to the secondary transfer belt 41, the secondary transfer current, and the characteristics of the secondary transfer bias in the printer testing machine having the basic configuration described above. It is. This graph is created based on the results of experiments conducted in a laboratory set in an environment of 27 [° C.] 80 [%] (absolute humidity 20.6 [g / m ³ ]), which is weak and humid. It is a thing. The secondary transfer rate indicates the ratio of the toner secondarily transferred onto the secondary transfer belt 41 among the toners of the test toner image composed of the solid image primarily transferred onto the intermediate transfer belt 31. In the figure, “(DC)” indicates that a secondary transfer bias composed only of a DC voltage is used. “(DC + High DutyAC)” indicates that a high duty superimposed voltage is used as the secondary transfer bias.

  In a light and high humidity environment, the toner charge amount (Q / M) is relatively small. Therefore, when a secondary transfer bias consisting only of a DC voltage is used, a relatively large amount of secondary transfer current is generated. When it is flowed, secondary transfer defects are likely to occur. In particular, in the case of K toner having a lower charge amount than Y toner, M toner, and C toner (hereinafter, these toners are collectively referred to as color toner), such secondary transfer defects tend to occur remarkably. It can be seen that the drop in the graph on the high current side is steeper for the K toner than for the color toner. As described above, even in the case of a solid image instead of a halftone image, a decrease in image density due to a secondary transfer failure occurs depending on the environment and the charge amount of toner. For this reason, when the test toner image is secondarily transferred to the secondary transfer belt 41 using the secondary transfer bias composed of only a DC voltage, the transfer failure of the test toner image is likely to occur.

  On the other hand, when a high-duty superimposed voltage is used as the secondary transfer bias, overcharging of the toner in the secondary transfer nip is suppressed, so even K toner (solid image) with a small charge amount can be obtained. A sufficient secondary transfer rate is obtained.

  For this reason, in the test transfer mode, the secondary transfer bias consisting only of the DC voltage is not adopted as in (α) above, but the superimposed voltage of high duty as in (β) and (γ) above is adopted. It tends to seem as if it is advantageous to employ a secondary transfer bias. However, the test toner image is not an image that is provided to a customer for viewing, but an image for examining how much toner is deposited on the toner image. Even if a transfer failure occurs, if the secondary transfer rate reflecting the transfer failure is obtained in advance by experiments, it is possible to accurately obtain the toner adhesion amount of the test toner image before the secondary transfer.

  When the test transfer mode is executed immediately after the toner image is secondarily transferred to the smooth sheet in the smooth mode, the power supply control unit 200 performs the following control in the test transfer mode. That is, the same secondary transfer bias as that in the smooth mode is output from the secondary transfer power supply 45. The test toner image secondarily transferred to the highly smooth secondary transfer belt 41 under these conditions hardly causes transfer failure due to the injection of reverse charge into the toner. It is not always necessary to determine the toner adhesion amount in consideration of the transfer rate. Further, generation of transfer dust can be suppressed as compared with the case where a secondary transfer bias having a low duty superimposed voltage is used. Since the same secondary transfer bias as that in the immediately preceding sheet transfer mode is used, it is possible to avoid complication of control due to unnecessary switching of the characteristics of the output voltage from the secondary transfer power supply 45.

Table 3 below shows the relationship among the transfer mode, the type of the recording sheet P, and the characteristics of the secondary transfer bias employed in this printer. In Table 3, the values of duty [%], peak-to-peak value Vpp [kV] and frequency [Hz] are 23 [° C.], 50 [%] = absolute humidity 10.3 [g / m ³ ]. This is an example in a medium-humidity environment, and the numerical value may be different if the medium-humidity environment is not used. The relationship between the environment and those values will be described later.

As shown in Table 3, in the normal mode in which the toner image is secondarily transferred to plain paper, the secondary transfer bias is composed of only a DC voltage and the high-duty superimposed voltage depending on the environment. Switch with. Hereinafter, an environment having an absolute humidity of 15.5 [g / m ³ ] or less is referred to as an environment having a medium humidity or less. An environment where the absolute humidity is more than 15.5 [g / m ³ ] to 23.8 [g / m ³ ] is referred to as a weak and humid environment. An environment where the absolute humidity exceeds 23.8 [g / m ³ ] is referred to as a strong and humid environment.

  When the normal mode is executed in an environment of medium or lower humidity, even if a secondary transfer bias consisting only of a DC voltage is employed, transfer defects due to the injection of reverse charges into the toner hardly occur. Therefore, the power supply control unit 200 causes the secondary transfer power supply 45 to output a secondary transfer bias consisting only of a DC voltage when the normal mode is executed in an environment of medium or lower humidity. Thereby, it is possible to reduce an electrical load on the secondary transfer belt 41 and the intermediate transfer belt 31 by using a secondary transfer bias including an AC component. Therefore, it is possible to suppress the deterioration of the belt due to the electrical load.

  On the other hand, in a low and high humidity environment or a high and high humidity environment, the charge amount (Q / M) of the toner is relatively low, so even if it is plain paper, it is charged by injecting reverse charge into the toner. Insufficient quantity is likely to occur. For this reason, in the normal mode, if a secondary transfer bias consisting of only a DC voltage is used, a transfer failure due to reverse charge injection is likely to occur. Therefore, the power supply control unit 200 causes the secondary transfer power supply 45 to output the same as the smoothing mode as the secondary transfer bias when the normal mode is executed in the low and high humidity environment or the high and high humidity environment. .

  As described above, this printer uses a secondary transfer bias having a low duty superimposed voltage in the concave / convex mode in which the toner image is secondarily transferred to the concave / convex sheet. In the smooth mode in which the toner image is secondarily transferred to the smooth sheet, a secondary transfer bias having a high duty superimposed voltage is used.

  In the test transfer mode executed immediately after the sheet transfer mode (normal mode) for transferring the toner image onto plain paper, the power supply control unit 200 outputs the same secondary transfer bias as that of the immediately preceding normal mode from the secondary transfer power supply 45. . At this time, depending on the environment, a secondary transfer bias consisting of only a DC voltage is output, and injection of reverse charges into the toner may cause a transfer failure of the test toner image to the secondary transfer belt 41. However, for the reason described below, the main control unit 300 can accurately obtain the toner adhesion amount of the test toner image. That is, the main control unit 300 preliminarily determines a secondary transfer rate (a value investigated by a previous experiment) when the test toner image is secondarily transferred to the secondary transfer belt 41 with a secondary transfer bias including only a DC voltage. I remember it. When the test transfer mode is executed with a secondary transfer bias consisting of only a DC voltage, the test is performed based on the secondary transfer rate and the detection result of the optical characteristics of the test toner image by the optical sensor unit 40. The toner adhesion amount of the toner image is obtained.

  Since the test transfer mode is executed using the same secondary transfer bias as that of the immediately preceding normal mode, it is possible to suppress complication of control contents due to switching of the characteristics of the secondary transfer bias according to the mode switching. Furthermore, it is possible to suppress a decrease in detection accuracy of the toner adhesion amount due to transfer dust compared to the case where a secondary transfer bias having a low duty superimposed voltage is used.

  In the test transfer mode executed immediately after the sheet transfer mode (smooth mode) for transferring the toner image to the smooth sheet, the power supply control unit 200 applies the same secondary transfer bias as that in the immediately preceding smooth mode from the secondary transfer power supply 45. Output. Since the secondary transfer bias is the same as that in the smooth mode, even if the test toner image is transferred to the highly smooth secondary transfer belt 41, the transfer failure of the test toner due to the reverse charge injection into the toner does not occur. Since the test transfer mode is executed using the same secondary transfer bias as that of the immediately preceding smooth mode, it is possible to suppress complication of control contents due to switching of the characteristics of the secondary transfer bias in accordance with the mode switching. Furthermore, it is possible to suppress a decrease in detection accuracy of the toner adhesion amount due to transfer dust compared to the case where a secondary transfer bias having a low duty superimposed voltage is used.

  In the test transfer mode executed immediately after the sheet transfer mode (concave / convex mode) for transferring the toner image to the concave / convex sheet, the power supply control unit 200 applies the same secondary transfer bias as the smooth mode to the secondary transfer bias, unlike the previous concave / convex mode. Output from the transfer power supply 45. Although the characteristics of the secondary transfer bias change when the mode is switched, the detection accuracy of the toner adhesion amount due to transfer dust is reduced compared to the case where the secondary transfer bias having the same low duty superimposed voltage as in the smooth mode is used. Can be suppressed.

  In the test transfer mode, the secondary transfer bias (γ) may be output instead of outputting the secondary transfer bias (the above (β)) having the same superimposed voltage as that in the smooth mode.

  When a secondary transfer bias composed of a high-duty superimposed bias is used in the smooth mode or test transfer mode, the secondary transfer rate varies depending on the environment. Specifically, the higher the humidity, the less the toner charge amount [Q / M] and the more likely to cause a secondary transfer failure.

Table 4 shown below was created based on the results of experiments conducted by the present inventors. The K-color secondary transfer rate represents the secondary transfer rate of a K test toner image (solid image) secondarily transferred onto the secondary transfer belt 41 in the experiment.

  In Table 4, focusing on Experiment No. 2 and Experiment No. 3, the only difference between the two is the environment, and the absolute humidity is higher by the higher temperature than in Experiment No. 3. When paying attention to the K-color secondary transfer rate of both, the experiment number 3 is about 10% lower. This is because in Experiment No. 3, the humidity was higher and the charge amount of the K toner was lower, so that the decrease in the secondary transfer rate due to the injection of the reverse charge appeared more remarkably.

  Focusing on experiment number 3 and experiment number 4, the only difference between them is the duty, and experiment number 4 has a higher duty by 5%. Paying attention to the K-color secondary transfer rate of both, Experiment No. 4 is higher by about 7 [%].

  From these facts, it can be seen that the higher the duty, the lower the secondary transfer rate due to the reverse charge injection can be further suppressed. However, under the same absolute humidity condition, the higher the duty is, the weaker the electrostatic force in the transfer direction in the secondary transfer nip is, so that a secondary transfer failure due to insufficient electrostatic force is likely to occur. In order to suppress the occurrence of such secondary transfer failure, it is necessary to prevent the weakening of electrostatic force by increasing the peak-to-peak value Vpp as much as the duty is increased. However, under the same absolute humidity conditions, the larger the peak-to-peak value Vpp, the easier it is to generate a discharge in the secondary transfer nip, and the white spot (small white spots in the image) caused by the discharge is reduced. It becomes easy to generate.

  As described above, in order to improve the secondary transfer rate of the test toner image as much as possible, there is an optimum combination of duty and peak-to-peak value Vpp according to absolute humidity. The higher the absolute humidity is, the more difficult it is to generate discharge in the secondary transfer nip. Therefore, even if the peak-to-peak value Vpp is increased, the white spot does not deteriorate. Therefore, by increasing the peak-to-peak value Vpp and increasing the duty, it becomes possible to suppress the secondary transfer failure of the test toner image due to the injection of the reverse charge into the toner.

Therefore, the power supply control unit 200 is based on the absolute humidity calculated based on the detection result of the temperature and humidity sent from the environment sensor 50. It is determined which is applicable. The environment of medium humidity or lower is an environment of medium humidity or lower humidity based on 23 [° C.] 50 [%] (absolute humidity 10.3 [g / m ³ ]). Is an environment having an absolute humidity of 15.5 [g / m ³ ] or less. The environment of weak and high humidity is an environment based on 27 [° C.] 80 [%] (absolute humidity 20.6 [g / m ³ ]). Specifically, the absolute humidity is 15.5 [ g / m ³ ] to 23.8 [g / m ³ ] or less. The high and high humidity environment is an environment based on 32 [° C.] 80 [%] (absolute humidity 27.0 [g / m ³ ]). Specifically, the absolute humidity is 23.8 [g. / M ³ ].

  The power supply control unit 200 that has determined the environment changes the characteristics of the superimposed voltage as follows when a secondary transfer bias including a high-duty superimposed voltage is used in the smooth mode or the test transfer mode. That is, in an environment of moderate humidity or lower, a secondary transfer bias having a superimposed voltage having the same characteristics as the experiment number 1 in Table 4 is output from the secondary transfer power supply 45. Further, in a low and high humidity environment, a secondary transfer bias having a superimposed voltage having the same characteristics as the experiment number 2 in Table 4 is output from the secondary transfer power supply 45. In a strong and humid environment, a secondary transfer bias having a superimposed voltage having the same characteristic as that of Experiment No. 4 in Table 4 is output from the secondary transfer power supply 45. That is, the higher the absolute humidity, the higher the duty and the peak-to-peak value Vpp.

  In such a configuration, the toner image can be secondarily transferred to the smooth sheet or the test toner image can be secondarily transferred to the secondary transfer belt 41 at a good secondary transfer rate regardless of the humidity change.

  As processing for forming a test toner image, misregistration correction processing is known in addition to the above-described process control processing and Vtref adjustment processing in a continuous print job. The misregistration correction process is a process for correcting the relative misregistration of Y, M, C, and K toner images. In the misregistration correction process, misregistration detection patterns shown in FIG. 20 are formed at one end, the center, and the other end in the width direction of the belt (secondary transfer belt 41 in the embodiment). Each misalignment detection pattern includes a plurality of chevron patch patterns (three in the figure) arranged in the belt moving direction. One chevron patch pattern includes four orthogonal patches (K orthogonal patch SPk, M orthogonal patch SPm, C orthogonal batch SPc, and Y orthogonal patch SPy) extending in the belt width direction. Further, four inclined patches (K inclined patch TPk, M inclined patch TPm, C inclined patch TPc, and Y inclined patch TPy) extending in a posture inclined by 45 [°] from the belt width direction are also provided.

  Each patch, which is a test toner image of a positional deviation detection pattern, is detected by an optical sensor (optical sensor unit 40 in the embodiment). If the formation timing of each patch is appropriate, the detection time intervals of the patches arranged in the belt moving direction are equal. If inappropriate, the detection time intervals are non-uniform. If there is no skew in the optical system for optical writing, patches of the same color are detected at the same timing between the three misregistration detection patterns. Come different. The control unit (for example, the main control unit 300) measures the detection time interval and detection timing deviation of each patch in the main scanning direction (same as the belt width direction) and the sub-scanning direction (same as the belt movement direction). Then, based on the measurement result, the inclination of the optical mirror as the image forming condition is adjusted, or the optical writing timing as the image forming condition is corrected. Such misregistration reduction processing can suppress misalignment of each color and image skew.

  When such misregistration correction processing is periodically performed, the secondary transfer bias in the test transfer mode (the mode in which each patch is transferred to the secondary transfer belt 41) is performed in the same manner as in the process control processing and Vtref adjustment processing. It is desirable to control. In this case, the detection error of the position of each patch due to the transfer dust generated in each patch can be suppressed. Therefore, it is possible to suppress the occurrence of the residual position shift (residual color shift) due to the detection error.

Next, the printer according to each example in which a more characteristic configuration is added to the printer according to the embodiment will be described. Note that the configuration of the printer according to each example is the same as that of the embodiment unless otherwise specified.
[First embodiment]
The printer according to the first modification has no smooth paper button, uneven paper button, or plain paper button in the operation display unit 501. For this reason, it is not a specification in which information on the surface smoothness of the recording sheet P is input by the user. Instead, a smoothness detection sensor for detecting the surface smoothness of the recording sheet is provided.

  FIG. 21 is a configuration diagram illustrating a paper feed path of the printer according to the first embodiment. The paper feed path guides the recording sheet P sandwiched between the first guide plate 509 and the second guide plate 510 to the registration nip of the registration roller pair 101. The first guide plate 509 is provided with a through hole, and a smoothness detection sensor 502 is fitted into the through hole. The smoothness detection sensor 502 including a reflective optical sensor irradiates light emitted from the light emitting element toward the recording sheet P in the paper feed path, and the specularly reflected light that is regularly reflected on the surface of the recording sheet P is received by the light receiving element. Receive light. The amount of specular reflection obtained on the surface of a smooth sheet such as coated paper is greater than the amount of specular reflection obtained on the surface of an uneven sheet such as Japanese paper.

  The smoothness detection sensor 502 is electrically connected to the power supply control unit 200. The power controller 200 calibrates the smoothness detection sensor 502 when the apparatus is started immediately after the main power of the printer is turned on. Specifically, in a state where the light emitting element is turned on and light from the light emitting element is reflected by the surface of the white second guide plate 510, the light emission amount (supply voltage) of the light emitting element is obtained so as to obtain a predetermined regular reflection light amount. ). The supply voltage value at this time is stored in the storage circuit, and when the amount of regular reflection on the surface of the recording sheet P is detected by the smoothness detection sensor 502, the same value as the supply voltage value stored in the storage circuit is used. Is supplied to the light emitting element.

  When the print job is started, the recording sheet P sent out from the feeding cassette 100 at a predetermined timing is abutted against the registration nip of the non-driven registration roller pair 101 for skew correction, and is temporarily conveyed. Stopped. At this time, it faces the smoothness detection sensor 502 in the paper feed path. In this state, the power supply control unit 200 detects the amount of regular reflection light obtained on the sheet surface by the smoothness detection sensor 502. Then, based on the detection result, it is determined whether the recording sheet P is a concavo-convex sheet, plain paper, or a smooth sheet.

  In such a configuration, it is possible to automatically determine whether the recording sheet P is a concavo-convex sheet, plain paper, or a smooth sheet without depending on the user's operation, thereby improving the operability for the user. Further, even when the user sets different types of recording sheets on the feeding cassette 100, it is possible to automatically determine the difference in type and execute the sheet transfer mode according to the determination result.

  FIG. 22 is a schematic diagram for explaining the switching of the secondary transfer bias when the type of the recording sheet P is changed from the uneven sheet to the smooth sheet during the continuous print job. In the drawing, a rectangular frame indicated by a dotted line indicates a sheet corresponding region that contacts the recording sheet P at the secondary transfer nip in the entire area of the secondary transfer belt 41. When the uneven sheet is used, the uneven mode is executed at the timing when the uneven sheet enters the secondary transfer nip. Further, at the timing when the inter-sheet corresponding area of the secondary transfer belt 41 enters the secondary transfer nip, the secondary transfer bias output from the secondary transfer power supply 45 differs depending on the state of the inter-sheet corresponding area. Specifically, when the inter-sheet corresponding region where the test toner images (YT, MT, CT, and KT) for each color for Vtref adjustment control enter the secondary transfer nip, the same two-protrusion mode as that in the immediately preceding uneven mode is used. The next transfer voltage is output. On the other hand, when the inter-sheet corresponding area on which the test toner images of the respective colors are formed enters the secondary transfer nip, the same secondary transfer bias as that in the smooth mode is output (examples with low and high humidity) ).

  When the type of the recording sheet P is changed from the uneven sheet to the smooth sheet, the toner image is secondarily transferred to the smooth sheet in the smooth mode corresponding to the smooth sheet. After the type of the sheet is changed, before the secondary transfer for the changed recording sheet P (smooth sheet in the illustrated example) is completed, the next recording sheet P is abutted against the registration nip to determine the type. The At this time, if the type is the same as the type of the previous recording sheet P, the image formation is temporarily interrupted, and the process control process is performed as shown in the figure, so that the patch pattern image ( YPP, MPP, CPP, KPP) are formed.

  As described above, in the printer according to the first embodiment, when the secondary transfer of the toner image to the same type of recording sheet P continues twice after the type of the recording sheet P changes, the second secondary is performed. Prior to the transfer, a process control process is performed. The reason why the process control process is not performed prior to the first time is that the toner image corresponding to the first secondary transfer has already been formed when the type change is detected, so the image formation cannot be interrupted. Because.

  The process control process is performed under conditions for outputting a secondary transfer bias corresponding to the changed sheet type. In the illustrated example, since the sheet type after the change is a smooth sheet, it is performed under the condition of outputting the same secondary transfer bias as the smooth mode corresponding to the smooth sheet.

  When the process control process ends, image formation is resumed. Then, at the timing when the smooth sheet next enters the secondary transfer nip, the smooth mode is performed. That is, the same secondary transfer bias as that in the previous process control process is continuously output. Thereafter, at the timing when the inter-sheet corresponding area of the secondary transfer belt 41 enters the secondary transfer nip, the same secondary transfer bias as that in the smooth mode is continuously output regardless of whether or not each color test toner image is formed. Is done.

  FIG. 23 is a flowchart illustrating a processing flow during a continuous print job executed by the power control unit 200 of the printer according to the first embodiment. In this processing flow, the power supply control unit 200 first waits until the feeding of the recording sheet P to the registration nip is completed (N in Step 1; hereinafter, Step is referred to as S). When the feeding is finished (Y in S1), after determining the type of the recording sheet P based on the detection result by the smoothness detection sensor 502 (S2), the secondary transfer bias corresponding to the type and environment is applied. Output from the secondary transfer power supply 45 (S3).

  After that, it waits until the timing between sheets arrives (N in S4). The sheet-to-sheet timing is a sheet between a region that is in close contact with the preceding recording sheet P and a region that is in close contact with the subsequent recording sheet P in the secondary transfer nip in the entire area in the circumferential direction of the secondary transfer belt 41. This is the timing when the inter-corresponding region enters the secondary transfer nip. When the inter-sheet timing arrives (Y in S4), it is determined whether secondary transfer of the test toner image within the inter-sheet timing is necessary (S5). In other words, it is determined whether or not a test toner image is formed in the aforementioned inter-sheet correspondence area.

  If the secondary transfer of the test toner image is not required (N in S5), the secondary transfer bias output having the same characteristics as in the sheet transfer mode is continued to determine the presence or absence of the next print (S10). If there is a next print (Y in S10), the process flow is looped to S1. If there is no next print (N in S10), the output of the secondary transfer bias is stopped (S11), and the series of processing flow is ended.

  On the other hand, if secondary transfer of the test toner image is necessary in S5 (Y in S5), it is determined whether or not the previous sheet transfer mode is a concavo-convex mode using a low-duty secondary transfer bias. (S6). In the case of the concave / convex mode (Y in S6), since the transfer dust is deteriorated by the secondary transfer bias as it is, the output of the secondary transfer bias is switched to the same high duty as in the smooth mode ( S7). On the other hand, when the concave / convex mode is not set (N in S6), even if the secondary transfer bias is maintained as it is, the transfer dust is not deteriorated, and the secondary transfer bias is maintained as it is (S8).

  When the secondary transfer of the test toner image to the secondary transfer belt 41 is completed after the steps S7 and S8 (Y in S9), the process flow proceeds to S10 described above.

[Second Example]
FIG. 24 is a block diagram illustrating an electric circuit of the operation display unit 501 of the printer according to the second embodiment. Unlike the embodiment, the operation display unit 501 does not have a smooth paper button, an uneven paper button, and a plain paper button. Instead, it has a menu key 501c, an up key 501d, a down key 501e, an enter key 501f, a display 501g, and the like.

  When the menu key 501c is pressed by the user, the main control unit 300 displays a menu screen on the display 501g. The user operates the up key 501d or the down key 501e to select the menu by pressing the enter key 501f with the cursor positioned on the desired menu among a plurality of menus displayed on the menu screen. be able to. When the “sheet type input” menu is selected by a user key operation, the main control unit 300 displays a list of sheet brands on the display 501g. The user can select the same brand as the recording sheet set in the feeding cassette 100 among a plurality of brands displayed in the brand list by operating the up key 501d and the down key 501e. Since the brand and the surface smoothness in the recording sheet of the brand have a one-to-one relationship, the brand can function as information indicating the surface smoothness.

  The power supply control unit 200 stores a data table in which the brand is associated with the type of recording sheet P (three types of smooth sheet, uneven sheet, and plain paper) in the data storage circuit. From this data table, the type corresponding to the brand inputted by the user is specified, and the specified result is grasped as the type of the recording sheet P.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
[Aspect A]
Aspect A is a recording sheet sandwiched in a transfer nip (for example, a secondary transfer nip) by contact between an image carrier (for example, an intermediate transfer belt 31) that carries a toner image and a contact body (for example, a secondary transfer belt 41). A power source (for example, a secondary transfer power source 45) that outputs a superimposed voltage by superimposing a direct current and an alternating current for transferring a toner image to a toner image (for example, a recording sheet P), and an optical characteristic of a test toner image transferred to the contact body In an image forming apparatus (for example, a printer) provided with an optical property detecting means (for example, an optical sensor unit 40) for detecting the above, an elastic layer made of a material having higher elasticity than that of the substrate is laminated as the image carrier. And in the test transfer mode in which the test toner image is transferred to the contact body, only the DC voltage out of the DC voltage and the AC voltage is supplied from the power source. In which it characterized in that a control means for performing processing to output (e.g., power control unit 200).

  In the aspect A, the image carrier is provided with an elastic layer that can be elastically deformed, so that the recording sheet can be conveyed at a higher speed than the case where an elastic layer is not provided. Thus, it is possible to transfer the toner image onto the uneven sheet. Thereby, it is possible to increase the printing speed. In addition, by using a voltage consisting only of a DC voltage as a voltage for transferring the test toner image to the contact body in the test transfer mode, toner is transferred between the image carrier surface and the contact body surface in the transfer nip. Avoid reciprocal movement. Accordingly, it is possible to prevent a decrease in detection accuracy of the optical characteristics of the test toner image by avoiding the generation of transfer dust caused by the reciprocating movement of the toner.

[Aspect B]
Aspect B is a power source that outputs a superimposed voltage by superimposing direct current and alternating current for transferring a toner image to a recording sheet sandwiched in a transfer nip by contact between an image carrier that carries a toner image and the contact body; In an image forming apparatus comprising an optical property detection means for detecting an optical property of a test toner image transferred to the contact body, the image carrier is made of an elastic material made of a material superior in elasticity to the substrate. In a test transfer mode in which a stack of layers is used and the test toner image is transferred to the contact body, the toner in the transfer nip is applied from the image carrier side within one cycle of the superimposed voltage. A transfer peak value (for example, transfer peak value Vt) that exerts the strongest electrostatic force in the transfer direction toward the contact side, and a reverse peak value (for example, reverse peak value Vr) that is a peak value on the opposite side. Of these, the reverse peak value is a superimposed voltage whose value is a value that weakens the electrostatic force in the direction opposite to the transfer direction as compared to the superimposed voltage in the sheet transfer mode in which the toner image on the image carrier is transferred to a recording sheet. Is provided with a control means for executing a process of outputting the power from the power source.

  In Aspect B, the condition that the recording sheet conveyance speed is made higher by using an image bearing member provided with an elastically deformable elastic layer as compared with the case where an elastic layer is not provided is used. Thus, it is possible to transfer the toner image onto the uneven sheet. Thereby, it is possible to increase the printing speed. In addition, as a voltage for transferring the test toner image to the contact body in the test transfer mode, the superposition of the reverse peak value that makes the electrostatic force in the reverse direction weaker than the reverse peak value of the superposition voltage in the sheet transfer mode. Use voltage. When such a superimposed voltage is used, the momentum of the reciprocating movement of the toner is reduced or the reciprocating movement of the toner is almost eliminated as compared with the sheet transfer mode. Unlike the concavo-convex sheet, the contact body does not have a surface concave portion, and therefore it is not necessary to reciprocate the toner in order to suppress transfer failure of toner to the surface concave portion. For this reason, there is no problem even if the reciprocating momentum is reduced or the reciprocating movement is almost eliminated. Rather, it has the merit of suppressing transfer dust generated by reciprocating the toner. By suppressing the transfer dust, it is possible to suppress a decrease in detection accuracy of the optical characteristics of the test toner image.

[Aspect C]
Aspect C is the toner in the transfer nip within one cycle of the superimposed voltage in a sheet transfer mode in which the toner image on the image carrier is transferred to a recording sheet in aspect A, compared to a predetermined reference value. Among the transfer peak values that exert the strongest electrostatic force in the transfer direction from the image carrier side to the contact body side, and the reverse peak value that is the opposite peak value, The control means performs a process of switching between a mode in which the duty, which is a ratio within a period of the value, is higher than 50 [%] and a mode in which the duty is lower than 50 [%]. It is characterized by comprising. In such a configuration, when a toner image is transferred to the uneven sheet, a low duty superimposed voltage is output from the power source, thereby suppressing toner transfer failure to the recesses on the sheet surface. In addition, when a toner image is transferred to a smooth sheet, a high-duty superimposed voltage is output from the power source, so that transfer failure of a halftone image caused by injecting a reverse charge into the toner in the transfer nip can be suppressed. .

[Aspect D]
In the aspect D, in the test transfer mode that is performed immediately after the sheet transfer mode in which the duty is lower than 50% in the aspect C, only the DC voltage is output from the power source, while the duty is set to 50. In the test transfer mode that is performed immediately after the sheet transfer mode that is higher than [%], the control unit is configured to perform a process of outputting the same superimposed voltage from the power source as in the immediately preceding sheet transfer mode. It is characterized by comprising. In such a configuration, in the test transfer mode immediately after the sheet transfer mode in which the duty is higher than 50 [%], it is possible to avoid complication of control due to unnecessary switching of the output voltage from the power source.

[Aspect E]
In aspect E, in aspect B, the duty, which is a ratio within one cycle of the time of the reverse peak value compared to the predetermined reference value in the sheet transfer mode, is 50 [%]. The control means is configured to perform a process of switching between a mode higher than 50% and a mode lower than 50 [%]. In such a configuration, when a toner image is transferred to the uneven sheet, a low duty superimposed voltage is output from the power source, thereby suppressing toner transfer failure to the recesses on the sheet surface. In addition, when a toner image is transferred to a smooth sheet, a high-duty superimposed voltage is output from the power source, so that transfer failure of a halftone image caused by injecting a reverse charge into the toner in the transfer nip can be suppressed. .

[Aspect F]
In aspect F, in aspect E, in the test transfer mode that is performed immediately after the sheet transfer mode in which the duty is lower than 50%, the reverse peak value is higher than the superimposed voltage in the sheet transfer mode. In the test transfer mode, which is performed immediately after the sheet transfer mode in which the superimposed voltage, which is a value that weakens the electrostatic force in the reverse direction, is output from the power supply while the duty is set higher than 50%, The control unit is configured to perform a process of outputting the same superimposed voltage from the power source as in the immediately preceding sheet transfer mode. With such a configuration, it is possible to avoid complication of control due to unnecessary switching of the output voltage from the power source in the test transfer mode in which a high duty superimposed voltage is output from the power source.

[Aspect G]
For aspect G, in any one of aspects C to F, environment detection means (for example, environment sensor 50) for detecting the environment is provided, and the superimposed voltage in the sheet transfer mode in which the duty is higher than 50 [%] The control unit is configured to perform a process of changing at least one of the duty and a peak-to-peak value according to a detection result by the environment detection unit. is there. In such a configuration, by transferring at least one of the duty and the peak-to-peak value according to the environment, it is possible to effectively suppress the transfer failure of the halftone image even in a high humidity environment. In addition, when the environment is not a high humidity environment, the toner image can be satisfactorily transferred using a voltage suitable for the environment where there is no restriction on the duty or peak-to-peak value.

[Aspect H]
Aspect H provides environment detection means for detecting the environment in aspect D or F, and for the superimposed voltage in the test transfer mode, at least one of the duty and the peak-to-peak value is set as the environment. The control unit is configured to perform a process of changing according to a detection result by the detection unit. Even in such a configuration, by changing at least one of the duty and the peak-to-peak value according to the environment, it is possible to effectively suppress the transfer failure of the test toner image even in a high humidity environment. Further, when the environment is not a high humidity environment, the test toner image can be satisfactorily transferred using a voltage under conditions suitable for an environment where there are no restrictions on duty and peak-to-peak values.

[Aspect I]
In the aspect I, in any of the aspects C to H, the peak-to-peak value of the superimposed voltage in the sheet transfer mode in which the duty is higher than 50 [%] is set lower than 50 [%]. The control means is configured to perform a process of making the superposed voltage smaller than a peak-to-peak value in the sheet transfer mode. In such a configuration, when a concavo-convex sheet is used as the recording sheet, the surface of the image carrier is elastically deformed in accordance with the surface shape of the concavo-convex sheet at the transfer nip, so that the surface concave portion of the concavo-convex sheet and the image carrier are adhered. Increase sex. Thereby, it is possible to suppress the transfer failure of the toner to the surface recess. As described above, even with a high-speed machine for business use, the toner can be satisfactorily transferred to the recesses on the surface of the uneven sheet.

[Aspect J]
Aspect J is the sheet transfer according to any one of aspects C to I, wherein the frequency of the superimposed voltage in the sheet transfer mode in which the duty is higher than 50 [%] is set to be lower than 50 [%]. The control means is configured to perform processing for making the frequency higher than the frequency of the superimposed voltage in the mode. In such a configuration, by setting the peak-to-peak value in the high duty mode to a lower value, it is possible to suppress the deterioration of the image carrier and the contact body due to the alternating electric shock in the high duty mode. Further, in the low duty mode, it is also possible to suppress a transfer failure to the surface recess of the uneven sheet due to the reverse peak value being too small.

[Aspect K]
Aspect K includes information acquisition means (for example, operation display unit 501 and smoothness detection sensor 502) that acquires information on the surface smoothness of the recording sheet used in any one of aspects C to J, and the information is compared. In the case where the surface smoothness is low, the sheet transfer mode in which the duty is lower than 50% is executed, while the information is higher than the relatively low surface smoothness. In the case where smoothness is exhibited, the control means is configured to perform a process of executing the sheet transfer mode in which the duty is set higher than 50 [%]. is there. In such a configuration, the type of the recording sheet can be grasped based on the information acquired by the information acquisition unit.

[Aspect L]
Aspect L is characterized in that, in aspect K, the information acquisition means is configured to acquire information on the brand of the recording sheet as the surface smoothness information. In such a configuration, the type of the recording sheet can be grasped only by inputting the information of the brand without having the user determine the type of the recording sheet.

[Aspect M]
Aspect M is characterized in that, in aspect K, smoothness detection means for detecting the surface smoothness of the recording sheet used is used as the information acquisition means. In such a configuration, the type information can be acquired while saving the user's trouble of inputting the type information of the recording sheet.

31: Intermediate transfer belt (image carrier)
40: Optical sensor unit (optical characteristic detection means)
41: Secondary transfer belt (contact body)
45: Secondary transfer power supply (power supply)
50: Environmental sensor (environment detection means)
200: Power supply control unit (control means)
501: Operation display unit (information acquisition means)
502: Smoothness detection sensor (information acquisition means, type detection means)
Vt: transfer peak value Vr: reverse peak value YT, MT, CT, KT: test toner image YPP, MPP, CPP, KPP: patch pattern having a test toner image

JP 2006-156927 A

Claims (13)

A power source for outputting a superimposed voltage by superimposing direct current and alternating current for transferring a toner image to a recording sheet sandwiched between transfer nips by contact between an image carrier and a contact body that carries a toner image; and the contact body In an image forming apparatus comprising: an optical characteristic detection unit that detects an optical characteristic of a test toner image transferred to
As the image carrier, a substrate is used in which an elastic layer made of a material superior in elasticity is laminated,
In the test transfer mode in which the test toner image is transferred to the contact body, control means is provided for performing processing for outputting only the DC voltage from the power source among the DC voltage and the AC voltage. Image forming apparatus. A power source for outputting a superimposed voltage by superimposing direct current and alternating current for transferring a toner image to a recording sheet sandwiched between transfer nips by contact between an image carrier and a contact body that carries a toner image; and the contact body In an image forming apparatus comprising: an optical characteristic detection unit that detects an optical characteristic of a test toner image transferred to
As the image carrier, a substrate is used in which an elastic layer made of a material superior in elasticity is laminated,
Further, in the test transfer mode in which the test toner image is transferred to the contact body, static electricity in the transfer direction from the image carrier side to the contact body side with respect to the toner in the transfer nip within one cycle of the superimposed voltage. Among the transfer peak value that exerts the strongest force and the reverse peak value that is the opposite peak value, the reverse peak value is a sheet transfer mode in which the toner image on the image carrier is transferred to the recording sheet. An image forming apparatus comprising: a control unit that performs a process of outputting a superimposed voltage from the power source, which is a value that weakens an electrostatic force in a direction opposite to the transfer direction compared to the superimposed voltage of The image forming apparatus according to claim 1.
In the sheet transfer mode in which the toner image on the image carrier is transferred to a recording sheet, the toner in the transfer nip is applied from the image carrier side within one cycle of the superimposed voltage compared to a predetermined reference value. Among the transfer peak value that exerts the strongest electrostatic force in the transfer direction toward the contact side, and the reverse peak value that is the peak value on the opposite side, the time that is the value on the reverse peak value side Image formation characterized in that the control means is configured to perform a process of switching between a mode in which the duty, which is a ratio in a cycle, is higher than 50 [%] and a duty lower than 50 [%]. apparatus. The image forming apparatus according to claim 3.
In the test transfer mode that is performed immediately after the sheet transfer mode in which the duty is lower than 50 [%], only the DC voltage is output from the power source, while the duty is higher than 50 [%]. In the test transfer mode performed immediately after the sheet transfer mode, the control unit is configured to perform processing for outputting the same superimposed voltage from the power source as in the immediately preceding sheet transfer mode. Forming equipment. The image forming apparatus according to claim 2.
A mode in which, in the sheet transfer mode, a duty that is a ratio within one cycle of a time that is a value closer to the reverse peak value than a predetermined reference value is higher than 50 [%]; An image forming apparatus, wherein the control unit is configured to perform a process of switching between a mode lower than [%]. The image forming apparatus according to claim 5.
In the test transfer mode performed immediately after the sheet transfer mode in which the duty is set lower than 50%, the reverse peak value makes the electrostatic force in the reverse direction weaker than the superimposed voltage in the sheet transfer mode. In the test transfer mode that is performed immediately after the sheet transfer mode in which the superimposed voltage that is a value to be output is output from the power supply while the duty is higher than 50%, the same as the immediately preceding sheet transfer mode. An image forming apparatus, wherein the control unit is configured to perform a process of outputting the superimposed voltage from the power source. The image forming apparatus according to any one of claims 3 to 6,
An environment detection means is provided to detect the environment.
For the superimposed voltage in the sheet transfer mode in which the duty is higher than 50%, at least one of the duty and a peak-to-peak value is changed according to a detection result by the environment detection unit. An image forming apparatus characterized in that the control means is configured to perform the processing. The image forming apparatus according to claim 4 or 6,
An environment detection means is provided to detect the environment.
The control unit is configured to perform a process of changing at least one of the duty and a peak-to-peak value according to a detection result by the environment detection unit with respect to the superimposed voltage in the test transfer mode. An image forming apparatus comprising: The image forming apparatus according to any one of claims 3 to 8,
The peak-to-peak value of the superimposed voltage in the sheet transfer mode in which the duty is higher than 50 [%], and the peak-to-peak value of the superimposed voltage in the sheet transfer mode in which the duty is lower than 50 [%]. An image forming apparatus characterized in that the control means is configured to carry out a process of making the size smaller than that. The image forming apparatus according to any one of claims 3 to 9,
A process of setting the frequency of the superimposed voltage in the sheet transfer mode to make the duty higher than 50 [%] higher than the frequency of the superimposed voltage in the sheet transfer mode to make the duty lower than 50 [%]. An image forming apparatus characterized in that the control means is configured to be implemented. The image forming apparatus according to any one of claims 3 to 10,
Providing information acquisition means for acquiring surface smoothness information of the recording sheet used,
If the information indicates a relatively low surface smoothness, the sheet transfer mode is executed to make the duty lower than 50%, while the information is the relatively low surface smoothness. When the surface smoothness is higher than the above, the control means is configured to execute a process of executing the sheet transfer mode in which the duty is set higher than 50 [%]. An image forming apparatus. The image forming apparatus according to claim 11.
An image forming apparatus comprising the information acquisition unit configured to acquire information on brands of a recording sheet as information on the surface smoothness. The image forming apparatus according to claim 11.
An image forming apparatus comprising a smoothness detecting means for detecting the surface smoothness of a recording sheet used as the information acquiring means.

Images