JP7172702B2 - Image forming apparatus and its control method - Google Patents

Description

The present disclosure relates to image forming apparatuses, and more particularly to image density adjustment.

A high-load light-emitting element is sometimes used in an exposure unit of an image forming apparatus. When a high-load light-emitting element emits light by constant-current ON/OFF control, the light-emission waveform does not become an ideal rectangle, and a so-called "light-emission waveform irregularity" that emits light slowly occurs. In an image forming apparatus driven at a high speed, "abnormal light emission waveform" causes deterioration of image quality. Therefore, there is a need for a technology that suppresses the emission waveform distortion or drives the light emitting element at high speed.

Regarding the suppression of emission waveform dullness, for example, Japanese Patent Application Laid-Open No. 2011-216843 (Patent Document 1) discloses that "By correcting the drive signal according to the light emission state of the light source, pulse thinning and waveform blunting are improved, and the light source A high-speed, high-precision semiconductor laser drive device that reduces variations in the amount of light between lasers and has excellent gradation reproducibility, especially at low densities (see [Abstract]).

Further, Japanese Patent Application Laid-Open No. 2012-231097 (Patent Document 2) describes "a first current supply circuit that starts supplying a drive signal to a light emitting element in response to a drive signal, and a circuit for supplying a light emitting element in response to the drive signal. and a second current supply circuit for starting supply of the auxiliary current, wherein the second current supply circuit detects that the voltage applied to the light emitting element has reached the threshold voltage and stops the supply of the auxiliary current. 'discloses a driver circuit (see [Abstract]).

JP 2011-216843 A JP 2012-231097 A

According to the techniques disclosed in Patent Literatures 1 and 2, it is not possible to shape the light emission waveform with high accuracy when using light emitting elements with a high load. Therefore, there is a need for a technique for shaping an emission waveform with high accuracy even when using a light-emitting element with a high load.

The present disclosure has been made in view of the above background, and an object in one aspect is to provide a technique for shaping an emission waveform with high accuracy even when using a light emitting element with a high load. .

An image forming apparatus according to an embodiment includes an image station that forms a toner image on a photoreceptor, an exposure section that exposes the surface of the photoreceptor, a density detection section that detects the toner density of the toner image, and a supply to the exposure section. a waveform shaping section that shapes the current flowing through the waveform; and a control section that controls the waveform shaping section. The control unit shapes the current supplied to the exposure unit according to the shaping signal output by the waveform shaping unit, causes the exposure unit to emit light at the first frequency and the first light emission duty ratio, and causes the photoreceptor to emit the first light. A toner image is generated, the exposure section is caused to emit light at a second frequency different from the first frequency, and a first light emission duty ratio to generate a second toner image on the photoreceptor, and the density detection section detects the second toner image. The density of each of the first toner image and the second toner image is obtained, and the shaping signal is adjusted based on the density difference between the first toner image and the second toner image.

In one aspect, the controller sets the shaping signal such that the density difference between the first toner image and the second toner image is within a predetermined range.

In one aspect, shaping the current includes shaping the current multiple times while changing the setting of the shaping signal. The controller generates a first toner image and a second toner image on the photosensitive member for each setting of the shaping signal by the exposure unit, and generates the first toner image by the density detection unit for each setting of the shaping signal. and the density of each of the second toner image, obtain the density difference between the first toner image and the second toner image for each setting of the shaping signal, and set the density difference to be within a predetermined range. Set the shaping signal to .

In one aspect, the first frequency is higher in frequency than the second frequency. Based on the fact that the density of the first toner image is lower than that of the second toner image and the difference in density is below a predetermined range, the controller increases the density of the toner image on the photosensitive member. By changing the setting of the shaping signal, the density of the toner image on the photoreceptor is reduced based on the fact that the first toner image has a higher density than the second toner image and the density difference exceeds a predetermined range. Change the shaping signal settings so that

In one aspect, changing the setting of the shaping signal to increase the density of the toner image on the photoreceptor includes increasing the voltage of the rising edge of the current supplied to the exposure station.

In one aspect, changing the setting of the shaping signal so that the toner image on the photoreceptor is less dense includes decreasing the rising edge voltage of the current supplied to the exposure station.

In one aspect, the control unit sets the second frequency to 1/integer of the first frequency by the frequency divider of the control unit.

In one aspect, the light emission duty ratio of the current supplied to the exposure section is between 20% and 80%.

In one aspect, the image forming apparatus further includes a waveform shaper that transforms the shaping signal with a delay circuit. The control unit controls the waveform of the shaping signal by switching between the waveform shaper and the line of the shaping signal.

In one aspect, the image forming apparatus further comprises a bias voltage source for applying a bias voltage to the shaping signal.

In one aspect, the controller selects a constant voltage source or a constant current source to generate the shaping signal.

In one aspect, the controller adjusts the width of the shaped signal by switching a constant voltage source or a constant current source.

According to another embodiment, a method is provided for adjusting the density of a toner image. This method includes the steps of: shaping current supplied to an exposure unit for exposing the surface of a photoreceptor by a shaping signal; generating a first toner image; and generating a second toner image on the photoreceptor by causing the exposure unit to emit light at a second frequency different from the first frequency and at the first emission duty ratio. , obtaining respective densities of the first toner image and the second toner image, and adjusting the shaping signal based on the density difference between the first toner image and the second toner image.

In one aspect, the method further includes setting the shaping signal such that the density difference between the first toner image and the second toner image is within a predetermined range.

In one aspect, shaping the current includes shaping the current multiple times while changing the setting of the shaping signal. The method comprises the steps of generating a first toner image and a second toner image on the photoreceptor for each setting of the shaping signal; obtaining the density difference between the first toner image and the second toner image for each setting of the shaping signal; and applying the shaping signal so that the density difference is within a predetermined range. and setting.

In one aspect, the first frequency is higher in frequency than the second frequency. The method reshapes the photoreceptor to increase the density of the toner image based on the first toner image being less dense than the second toner image and the density difference being below a predetermined range. The density of the toner image on the photoreceptor is reduced based on the step of changing the signal settings and the first toner image being denser than the second toner image and the density difference being greater than a predetermined range. changing the setting of the shaping signal so that it is lower.

In one aspect, changing the setting of the shaping signal to increase the density of the toner image on the photoreceptor includes increasing the voltage of the rising edge of the current supplied to the exposure station.

In one aspect, changing the setting of the shaping signal so that the toner image on the photoreceptor is less dense includes decreasing the rising edge voltage of the current supplied to the exposure station.

In some aspects, further comprising setting the second frequency to an integer fraction of the first frequency.

In one aspect, the light emission duty ratio of the current supplied to the exposure section is between 20% and 80%.

In one aspect, the method further includes controlling the waveform of the shaping signal by switching the waveform shape portion and the line of the shaping signal.

In one aspect, the method further includes applying a bias voltage to the shaped signal.

According to the present technology, it is possible to shape an emission waveform at low cost and with high precision.
The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings.

1 is a diagram showing a configuration example of an image forming apparatus 100 according to an embodiment; FIG. 2 is a diagram showing an example of a circuit 200 from a control section 50 to an exposure section 3; FIG. FIG. 3 is a diagram showing an example of a rough emission waveform 301; 3 is a diagram showing an example of the configuration of an optical waveform shaping section 203; FIG. 4 is a diagram showing an example of a procedure for generating a drive signal 210; FIG. FIG. 10 is a diagram showing an example of a method for evaluating settings of the optical waveform shaping unit 203. FIG. FIG. 3 is a diagram showing an example of an internal configuration of a control section 50 for generating drive signals 210 having the same light emission duty ratio and different frequencies. 4 is a diagram showing an example of the relationship between the light emission duty ratio of the light emission waveform 301 and the image density; FIG. 4 is a flowchart showing an example of processing for obtaining settings of the optical waveform shaping unit 203. FIG. FIG. 10 is a diagram showing an example of simultaneous evaluation of multiple settings of the optical waveform shaping unit 203; 7 is a flow chart showing an example of simultaneous evaluation processing of a plurality of settings of the optical waveform shaping unit 203. FIG.

Hereinafter, embodiments of the technical concept according to the present disclosure will be described with reference to the drawings. In the following description, the same parts are given the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[First embodiment]
<A. Device configuration>
First, the configuration of image forming apparatus 100 according to the present embodiment will be described. In the following, as a typical example, an image forming apparatus 100 implemented as a multi-functional peripheral (MFP) will be described. The image forming apparatus 100 is, for example, a color image forming apparatus, but the application target of the technical idea according to the present embodiment is not limited to the color image forming apparatus. is also applicable.

FIG. 1 is a diagram showing a configuration example of an image forming apparatus 100 according to this embodiment. Referring to FIG. 1 , image forming apparatus 100 includes image station 10 , document reading section 120 , and discharge tray 130 .

The image station 10 includes image stations 10C, 10M, 10Y, and 10K (hereinafter referred to as image stations 10) that generate respective toner images of cyan (C), magenta (M), yellow (Y), and key plate (K). ”), intermediate transfer belt 12, intermediate transfer member driving rollers 14 and 16, belt cleaning section 18, transfer rollers 20 and 21, fixing section 22, paper feeding section 30, It includes a delivery roller 32 , transport rollers 34 and 36 , a control section 50 and a storage section 51 . The image station 10 includes a photosensitive member 1, a charging unit 2, an exposure unit 3, and a developing unit 4 (4C, 4M, 4Y, and 4K corresponding to the colors of the toner images generated by the corresponding image stations 10). ), a cleaning station 5 and an intermediate transfer member contact roller 6 . Document reading unit 120 includes an image scanner 122 , a document feed table 124 , an automatic document feeder 126 , and a document discharge table 128 .

The image station 110 performs print processing on the medium 40 in the paper feed section 30 . The medium 40 is transported from the paper feeding section 30 by the delivery rollers 32 . Furthermore, the medium 40 is transported to the transfer rollers 20 and 21 by transport rollers 34 and 36 . After the toner image is transferred to the medium 40 by the transfer rollers 20 and 21 , the medium 40 is subjected to fixing processing by the fixing section 22 and discharged to the discharge tray 130 .

Each imaging station 10 and intermediate transfer belt 12 produces a toner image for transfer to media 40 . The charging unit 2 uniformly charges the surface of the photoreceptor 1 . The exposure unit 3 forms an electrostatic latent image on the surface of the photoreceptor 1 by exposing the surface of the photoreceptor 1 according to a designated image pattern by laser writing or the like. The developing unit 4 develops an electrostatic latent image formed on the photoreceptor 1, which is an image carrier, into a toner image.

The toner image formed on the surface of photoreceptor 1 is transferred to intermediate transfer belt 12 by intermediate transfer member contact roller 6 . The toner images are sequentially transferred onto the intermediate transfer belt 12 from the respective photoreceptors 1, and the toner images of four colors are superimposed. The superimposed toner images are transferred from intermediate transfer belt 12 to medium 40 by transfer rollers 20 and 21 .

Document reading unit 120 reads a document and outputs the reading result as an input image to image station 110 . The image scanner 122 scans an original placed on the platen glass. The automatic document feeder 126 continuously scans the documents placed on the document feeding table 124 . Documents placed on the document feeding table 124 are sent one by one by a sending roller (not shown) and sequentially scanned by an image scanner 122 or an image sensor arranged in an automatic document feeder 126 . The document after scanning is discharged to the document discharge table 128 .

The control unit 50 controls the entire image forming apparatus 100 . The storage unit 51 stores firmware and various settings of the image forming apparatus 100 . The control unit 50 refers to necessary data and programs from the storage unit 51 .

FIG. 2 is a diagram showing an example of a circuit 200 from the control section 50 to the exposure section 3. As shown in FIG. The circuit 200 includes a control section 50 , a switching section 201 , a light source 202 , an optical waveform shaping section 203 and an image density detection section 204 .

The control unit 50 switches (opens and closes) the switching unit 201 according to the video signal 206 and generates a switching signal 207 from the current of the current source 205 . The control unit 50 also outputs the video signal 206 and the shaping control signal 208 to the optical waveform shaping unit 203 .

Optical waveform shaping section 203 generates shaping signal 209 based on video signal 206 and shaping control signal 208 . The light source 202 is an optical element used in the exposure unit 3, and emits light by a drive signal 210 obtained by superimposing a shaping signal 209 and a switching signal 207, and exposes the surface of the photoreceptor 1 in the image station 10. .

The image density detection unit 204 detects the density of the toner image formed on the surface of the photoreceptor 1 and outputs a density signal 211 including density information of the detected toner image to the control unit 50 . The controller 50 adjusts the shaping control signal 208 based on the density signal 211 input from the image density detector 204 .

In one aspect, when detecting the density of the toner image, the image density detection unit 204 may detect the density of the toner image on the surface of the intermediate transfer belt 12 or the medium 40 as well as the surface of the photoreceptor 1 . Note that the circuit 200 shown in FIG. 2 is mainly an example of peripheral circuits from the control unit 50 to the light source 202 of the exposure unit 3, and may include configurations not illustrated in FIG.

FIG. 3 is a diagram showing an example of a rough emission waveform 301. As shown in FIG. When the drive signal 210 is supplied to the light source 202 in FIG. 2 and the light source 202 is a laser diode or LED (Light Emitting Diode) with high output and high load, the emission waveform 301 of the light source 202 is as shown in FIG. As shown in 3, the waveform does not form an ideal rectangle but rises gently. Such symptoms are called namari. The "abnormality" of the light emission waveform 301 causes unevenness in the exposure of the surface of the photoreceptor 1, resulting in deterioration of the printed image. Therefore, it is necessary to effectively suppress the "straightening" of the light emission waveform 301 .

FIG. 4 is a diagram showing an example of the configuration of the optical waveform shaping section 203. As shown in FIG. The optical waveform shaping section 203 includes a bias voltage source 401 , a constant voltage source 402 , a constant current source 403 and a waveform shaping section 404 . The shaping control signal 208 input from the control section 50 to the optical waveform shaping section 203 includes a bias voltage control signal 405, a shaping width signal 406, a selection signal 407, a constant voltage control signal 408, and a constant current control signal 409. , and waveform shape control signals 410 .

Constant voltage source 402 is a power source for generating shaping signal 209 . The control unit 50 controls the constant voltage source 402 with the constant voltage control signal 408 when the shaping signal 209 is generated by constant voltage control.

Constant current source 403 is a power source for generating shaping signal 209 . The control unit 50 controls the constant current source 403 with the constant current control signal 409 when the shaping signal 209 is generated by constant current control.

The control unit 50 switches the switching circuit for switching between the constant voltage source 402 and the constant current source 403 according to the selection signal 407 . Further, the control unit 50 controls ON/OFF of the switch circuit on the path of the shaping signal 209 by the shaping width signal 406, and adjusts the pulse width of the shaping signal 209 generated by the constant voltage source 402 or the constant current source 403. do.

A bias voltage source 401 is a circuit that applies a bias voltage to the shaping signal 209 . The control section 50 controls the bias voltage source 401 with a bias voltage control signal 405 . The video signal 206 also controls ON/OFF of a switch circuit on the output side of the bias voltage source 401 .

The corrugated portion 404 has therein a plurality of circuits of resistors and capacitors connected to the ground (GND). Each circuit changes the shape of the shaping signal 209 by being connected to the path of the shaping signal 209 . The control section 50 controls the switching circuit on the output path of the waveform shaping section 404 according to the waveform shape control signal 410 to change the waveform of the shaping signal 209 .

Next, details of the light emission waveform 301 generated using the circuit 200 and how the image density changes by shaping the light emission waveform 301 will be described with reference to FIGS. 5 and 6. FIG.

<B. Emission Waveform 301 and Image Density>
FIG. 5 is a diagram showing an example of the procedure for generating the drive signal 210. As shown in FIG. Control unit 50 generates rectangular video signal 206 . While the video signal 206 is HIGH, the switching section 201 is ON. Therefore, ideally, switching signal 207 is generated.

Also, the control unit 50 generates a shaping width signal 406 . While the shaping width signal 406 is HIGH, the switch circuit on the path of the shaping signal 209 is turned ON to generate a rectangular shaping signal 504B.

Further, the control unit 50 connects the circuit inside the waveform shaper 404 to the path of the shaping signal 209 by the waveform shape control signal 410, thereby deforming the shaping signal 504B and generating the shaping signal 504C. The circuit inside the waveform shape portion 404 is a delay circuit made up of resistors and capacitors. By connecting the delay circuit to the path of the shaping signal 209 , the control unit 50 delays the shaping signal 209 and mainly changes the edge shape of the shaping signal 209 .

Furthermore, the control section 50 controls the bias voltage source 401 by the bias voltage control signal 405 to superimpose the bias voltage 504A on the shaping signal 504C. A shaped signal 209 is obtained by superimposing the bias voltage 504A and the shaped signal 504C. The shape of the shaped signal 504C changes depending on the internal circuit of the waveform shaping section 404 connected to the path of the shaped signal 209. FIG.

Driving signal 210 is generated by superimposing shaping signal 209 and switching signal 207 . A light emission waveform 301 shows how the light source 202 emits light when the drive signal 210 is supplied to the light source 202 . Starting edge 506A of emission waveform 301 is modified by bias voltage 504A and shaping signal 504C. Also, the end edge 506B of the emission waveform 301 is deformed by the bias voltage 504A. As shown in FIG. 5, the starting edge 506A of the emission waveform 301 may start at a position higher than the rectangle, and this phenomenon is called "overshoot."

As shown in FIG. 5, the control unit 50 can adjust the bluntness of the light emission waveform 301 and bring it closer to a rectangle by mainly adjusting the bias voltage 504A and the shaping signal 504C.

FIG. 6 is a diagram showing an example of a method for evaluating the settings of the optical waveform shaping section 203. As shown in FIG. The control unit 50 generates halftone images on the photoreceptor 1 using light emission waveforms 301 of different frequencies, and compares the densities of the generated halftone images, thereby appropriately setting the optical waveform shaping unit 203. can be detected. A halftone image is an image in which two colors are repeated at regular intervals. Here, a black-and-white halftone image will be described as an example.

First, the control unit 50 generates a light emission waveform 301 with a period 604 and a light emission duty ratio of 50% using the light source 202 to form a halftone image 605 on the photoreceptor 1 . A light emission waveform 301 is generated by a driving signal 210 in which a switching signal 207 and a shaping signal 209 are superimposed. The emission waveform 301 can be either a near-square waveform 601 , a smooth waveform 602 and an overshoot waveform 603 .

When the light emission waveform 301 is a waveform 602 with a smoothness, the area of the HIGH region of the signal waveform becomes small due to the influence of the smoothness, so the halftone image 605 becomes a light image 607 . On the other hand, if the emission waveform 301 is an overshoot waveform 603 , the area of the HIGH region of the signal waveform becomes large due to the influence of the overshoot, so the halftone image 605 becomes a dark image 608 . When the emission waveform 301 is a waveform 601 that is nearly rectangular, the halftone image 605 becomes an image 606 with appropriate density.

Therefore, the control unit 50 should adjust the setting of the optical waveform shaping unit 203 while detecting the density of the halftone image 605 formed on the photosensitive member 1 by the image density detection unit 204 . However, in reality, there is no absolute standard for image density, and the control unit 50 cannot appropriately adjust the settings of the optical waveform shaping unit 203 only by detecting the density of the halftone image 605 .

Therefore, the control unit 50 generates a light emission waveform 301 with a period 614 different from the period 604 and a light emission duty ratio of 50% as a comparison target, and forms a halftone image 615 on the photoreceptor 1 . In the example shown in FIG. 6, the period 614 is three times the period 604, but the period of the emission waveform is not limited to this. Further, although the emission duty ratio of each emission waveform 301 is 50% as an example, the emission duty ratio that can be set is not limited to this. It is sufficient that the light emission waveforms to be compared have the same light emission duty ratio.

The image density is generally proportional to the emission duty ratio of the emission waveform. For example, a halftone image generated by a light emission waveform with a light emission duty ratio of 40% and a halftone image generated by a light emission waveform with a light emission duty ratio of 80% have a double density difference.

On the other hand, when the light emission duty ratio is constant, the difference in the frequency of the light emission waveform does not affect the halftone image density unless normality and overshoot occur. This is because even if the frequency of the light emission waveform is different, the light emission duty ratio in one cycle of the light emission waveform does not change, and a halftone image with the same density is generated as a whole. However, when blurring and overshooting occur, the difference in frequency may cause density differences in the generated halftone image. Hereinafter, each light emission waveform 301 with period 604 and period 614 will be described as an example.

It can be seen that the light emission waveform 301 with the period 614 has 1/3 the number of rising edges of the signal within the same time period as compared with the light emission waveform 301 with the period 604 . Six rising edges of the light emission waveform 301 of the period 604 occur while two rising edges of the light emission waveform 301 of the period 614 occur. In addition, since sag and overshoot of the signal occur at the rising edge of the signal, the light emission waveform 301 of the low frequency period 614 is more affected by the sag and overshoot than the light emission waveform 301 of the high frequency period 604. I know it's hard.

When the emission waveform 301 is a waveform 612 with a smoothness, the area of the HIGH region of the signal waveform becomes smaller due to the influence of the smoothness, so the halftone image 615 becomes a slightly lighter image 617 . On the other hand, if the emission waveform 301 is an overshoot waveform 613 , the area of the HIGH region of the signal waveform becomes large due to the influence of the overshoot, so the halftone image 615 becomes a slightly darker image 618 . If the emission waveform 301 is a nearly rectangular waveform 611, the halftone image 615 becomes an image 616 with appropriate density.

Next, the control unit 50 compares the image density of the halftone image 605 formed by the light emission waveform 301 with the period 604 and the image density of the halftone image 615 formed by the light emission waveform 301 with the period 614 .

When the light emission waveform 301 is blurred (in the case of the waveforms 602 and 612), the halftone image 605 is affected more by the number of rising edges of the signal within the same time than the halftone image 615. The larger it is, the lighter the color. On the other hand, when an overshoot occurs in the emission waveform 301 (waveforms 603 and 613), the halftone image 605 has more rising edges than the halftone image 615 in the same time period. The color becomes darker because the effect of overshoot is large. When the emission waveform 301 is nearly rectangular (in the case of waveforms 601 and 611), halftone images 605 and 615 have similar densities because they are almost unaffected by normalization and overshoot. Therefore, the control unit 50 should detect the setting of the optical waveform shaping unit 203 that makes the colors of the halftone images generated by the light emission waveforms 301 having the same light emission duty ratio and different frequencies closer to each other.

In the description of FIG. 6, the image density detection unit 204 detects the density of the surface of the photoreceptor 1 , but the location where the image density is detected is not limited to the surface of the photoreceptor 1 . In one aspect, the image density detection unit 204 may detect the image density on the surface of the intermediate transfer belt 12 or the image density on the surface of the medium 40 .

As described above with reference to FIG. 6, the control unit 50 forms halftone images using the same setting of the shaping signal 209 and the emission waveforms 301 having the same emission duty ratio and different frequencies. do. Then, the control unit 50 compares the image densities of the halftone images and selects the shaping signal 209 that makes the image densities of the halftone images closest to each other. By doing so, the control unit 50 can appropriately remove the influences of nulls and overshoots from the light emission waveform 301 .

FIG. 7 is a diagram showing an example of the internal configuration of the control section 50 for generating light emission waveforms 301 having the same light emission duty ratio and different frequencies. The control unit 50 includes an image memory 705 and a division counter 701 . A frequency division counter 701 divides the frequency of the main clock 702 of the control unit 50 by 1/N based on the frequency division setting 703 to generate a frequency division clock 704 . The control unit 50 generates the video signal 206 based on the frequency-divided clock 704 . Note that the configuration of the control unit 50 shown in FIG. 7 is an example, and the configuration of the control unit 50 is not limited to this.

FIG. 8 is a diagram showing an example of the relationship between the light emission duty ratio of the light emission waveform 301 and the image density. The light emission duty ratio of the light emission waveform 301 is the rate at which the output of the light emission waveform 301 becomes HIGH in one cycle of the light emission waveform 301 .

The image becomes darker as the light emission duty ratio increases, and conversely, the image becomes lighter as the light emission duty ratio decreases. When outputting the halftone image shown in FIG. 6, the emission duty ratio is preferably between 20 and 80%.

<C. Processing Flow of Signal Shaping>
FIG. 9 is a flow chart showing an example of processing for obtaining settings for the optical waveform shaping unit 203 . The control unit 50 may read a program for performing the processing of FIG. 9 from the storage unit 51 and execute it.

In step S910, the control unit 50 sets the shaping control signal 208 to be output to the optical waveform shaping unit 203 to a predetermined value. More specifically, various signals included in the shaping control signal 208 shown in FIG. 4 are set to predetermined values. The predetermined value may be, for example, an intermediate value that the shaping control signal 208 can take, but the setting of the shaping control signal 208 is not limited to this.

In step S920, the control unit 50 generates halftone images D1 and D2 on the surface of the photoreceptor 1 with the drive signals 210 having the same light emission duty ratio and different frequencies. The image D2 is an image generated with the drive signal 210 having a frequency lower than that of the image D1. Further, the control unit 50 detects the densities of the image D1 and the image D2 using the image density detection unit 204 . Note that the image density detection unit 204 may detect the density of the image formed on the surface of the intermediate transfer belt 12 or the medium 40 as well as the photoreceptor 1 .

In step S930, the control unit 50 compares the density of the image D1 detected in step S920 with the density of the image D2 to obtain a density difference. Note that when the density of the image D1 exceeds the density of the image D2, the density difference is a positive value such as "1, 2, 3...". Conversely, when the density of the image D1 is lower than the density of the image D2, the density difference becomes a negative value such as "-1, -2, -3...". It should be noted that these density differences are examples, and do not necessarily need to be represented by integers.

If the control unit 50 determines that the density of the image D1 is lighter than the density of the image D2 and that the density difference is below the predetermined density difference lower limit Dmin ("Density difference < Dmin ”), and control is transferred to step S940.

If the control unit 50 determines that the density difference between the image D1 and the image D2 is within the predetermined range (determines "Dmin<density difference<Dmax" in step S930), the control proceeds to step S950.

If the control unit 50 determines that the density of the image D1 is darker than the density of the image D2 and that the density difference exceeds the predetermined density difference upper limit Dmax ("Density difference>Dmax ”), and the control is transferred to step S960.

In step S940, the control unit 50 changes the setting of the optical waveform shaping unit 203 to the overshoot side (the side where the image density increases), and shifts the control to step S920.

In step S950, the control unit 50 saves the current settings of the optical waveform shaping unit 203 in the storage unit 51, and uses the saved settings for subsequent printing processes.

In step S960, the control unit 50 changes the setting of the optical waveform shaping unit 203 to the normal side (the side where the image density becomes lighter), and shifts the control to step S920.

As described above with reference to FIG. 9, the control unit 50 compares the densities of halftone images generated by the light emission waveforms 301 having the same light emission duty ratio and different frequencies, and determines the density difference in advance. The setting of the optical waveform shaping unit 203 is adjusted so that it falls within the range. By doing so, the control unit 50 can suppress the occurrence of blurring and overshooting of the light emission waveform 301, and can suppress deterioration of image quality.

[Second embodiment]
<D. Simultaneous Evaluation of Settings of Plurality of Optical Waveform Shaping Units 203>
Next, a second embodiment will be described. In the second embodiment, the control unit 50 compares multiple settings of the optical waveform shaping unit 203 at the same time, thereby shortening the time required to adjust the settings of the optical waveform shaping unit 203 .

FIG. 10 is a diagram showing an example of simultaneous evaluation of multiple settings of the optical waveform shaping section 203. In FIG. The control unit 50 does not change the light emission duty ratio for each of the multiple settings of the optical waveform shaping unit 203, and generates halftone images using the light emission waveforms 301 having different frequencies. In the example of FIG. 10, the control unit 50 uses each of the settings “1 to 5” of the optical waveform shaping unit 203 to generate a high frequency image and a low frequency image.

Next, for each setting of the optical waveform shaping unit 203, the control unit 50 compares the high frequency image and the low frequency image with the same light emission duty ratio generated using the same setting, and calculates the density difference. Finally, the control unit 50 selects the setting of the optical waveform shaping unit 203 that makes the density difference within a predetermined range. In the example shown in FIG. 10, the setting of the optical waveform shaping section 203 is explained in five stages, but this is an example, and the setting of the optical waveform shaping section 203 is not limited to this.

FIG. 11 is a flowchart showing an example of simultaneous evaluation processing for multiple settings of the optical waveform shaping unit 203 . The control unit 50 may read a program for performing the processing of FIG. 11 from the storage unit 51 and execute it. In the following description, it is assumed that the optical waveform shaping section 203 has settings "1 to 5" as in FIG. The setting "1" is the setting in which the light emission waveform 301 is most uniform (the image density is the lightest). Setting "5" is the setting that causes the most overshoot in the emission waveform 301 (the highest image density). These settings are examples, and the settings of the optical waveform shaping section 203 are not limited to these.

In step S<b>1110 , the control unit 50 sets the optical waveform shaping unit 203 to the setting “1” that causes the light emission waveform 301 to be most uneven. In step S1120, the control unit 50 generates halftone images on the surface of the photoreceptor 1 by using the light emission waveforms 301 of different frequencies without changing the light emission duty ratio.

In step S1130, the control unit 50 determines whether the current setting of the optical waveform shaping unit 203 is the maximum value "5". If control unit 50 determines that the current setting of optical waveform shaping unit 203 is the maximum value “5” (YES in step S1130), control proceeds to step S1150. Otherwise (NO in step S1130), control unit 50 moves the control to step S1140.

In step S1140, the control unit 50 raises the current setting of the optical waveform shaping unit 203 by one step toward the overshoot side (for example, setting "1" to setting "2", setting "2" to "3", etc.). Regarding the processing of FIG. 11, control unit 50 may start the processing from the setting “5” and lower the setting step by step in step S1140.

In step S<b>1150 , the control unit 50 detects the density of the halftone image generated in step S<b>1120 for each setting of the optical waveform shaping unit 203 using the image density detection unit 204 , and stores the density in the storage unit 51 . Note that the image density detection unit 204 may detect the density of the image formed on the surface of the intermediate transfer belt 12 or the medium 40 as well as the photoreceptor 1 .

In step S1160, the control unit 50 refers to the density of the image stored in the storage unit 51, and for each setting of the optical waveform shaping unit 203, the halftone generated by the light emission waveform 301 having the same light emission duty ratio and different frequencies. A density difference between images is obtained. Then, the control unit 50 searches for the setting of the optical waveform shaping unit 203 in which the density difference is within a predetermined range (Dmin<density difference<Dmax).

In step S1170, the control unit 50 saves the setting of the optical waveform shaping unit 203 obtained in step S1160 in the storage unit 51, and uses it for subsequent printing.

As described above with reference to FIGS. 10 and 11, the control unit 50 controls the halftone waveforms 301 with the same emission duty ratio and different frequencies for each of the plurality of settings of the optical waveform shaping unit 203. An image is generated, and density comparison between the generated halftone images is performed. By doing so, the control unit 50 can shorten the time required to obtain the settings of the optical waveform shaping unit 203 .

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

1 photoreceptor 2 charging unit 3 exposure unit 4 developing unit 5 cleaning unit 6 intermediate transfer member contact roller 10, 10C, 10K, 10M, 10Y image station 12 intermediate transfer belt 14, 16 intermediate transfer member Drive Roller 18 Belt Cleaning Unit 20, 21 Transfer Roller 22 Fixing Unit 30 Paper Feed Unit 32 Sending Roller 34, 36 Conveying Roller 40 Medium 50 Control Unit 51 Storage Unit 100 Image Forming Apparatus 120 Document reading unit 122 Image scanner 124 Document feed table 126 Automatic document feeder 128 Document discharge table 130 Discharge tray 200 Circuit 201 Switching unit 202 Light source 203 Optical waveform shaping unit 204 Image density detection Part 205 Current source 206 Video signal 207 Switching signal 208 Shaping control signal 209, 504B, 504C Shaping signal 210 Drive signal 211 Density signal 301 Emission waveform 401 Bias voltage source 402 Constant voltage source 403 constant current source, 404 waveform shape portion, 405 bias voltage control signal, 406 shaping width signal, 407 selection signal, 408 constant voltage control signal, 409 constant current control signal, 410 waveform shape control signal, 504A bias voltage, 506A starting edge, 506B end edge, 601, 602, 603, 611, 612, 613 waveform, 604, 614 period, 605, 615 halftone image, 606, 607, 608, 616, 617, 618 image, 701 division counter, 702 main clock , 703 frequency division setting, 704 frequency division clock, 705 image memory.

Claims (22)

an image station for producing a toner image on the photoreceptor;
an exposure unit that exposes the surface of the photoreceptor;
a density detection unit that detects the toner density of the toner image;
a waveform shaping section that shapes the current supplied to the exposure section;
A control unit that controls the waveform shaping unit,
The control unit
shaping the current supplied to the exposure unit by a shaping signal output by the waveform shaping unit;
causing the exposure unit to emit light at a first frequency and a first emission duty ratio to generate a first toner image on the photoreceptor;
causing the exposure unit to emit light at a second frequency different from the first frequency and at the first emission duty ratio to generate a second toner image on the photoreceptor;
acquiring the respective densities of the first toner image and the second toner image by the density detection unit;
An image forming apparatus that adjusts the shaping signal based on a density difference between the first toner image and the second toner image. 2. The image forming apparatus according to claim 1, wherein said control section sets said shaping signal such that a density difference between said first toner image and said second toner image is within a predetermined range. shaping the current includes shaping the current multiple times while setting the shaping signal;
The control unit
The exposure unit generates the first toner image and the second toner image on the photoreceptor each time the shaping signal is set,
acquiring the respective densities of the first toner image and the second toner image by the density detection unit for each setting of the shaping signal;
obtaining a density difference between the first toner image and the second toner image for each setting of the shaping signal;
3. The image forming apparatus according to claim 1, wherein said shaping signal is set such that said density difference is within said predetermined range. the first frequency is higher than the second frequency;
The control unit
The first toner image has a lower density than the second toner image, and based on the density difference falling below the predetermined range, the density of the toner image on the photoreceptor is increased. , changing the setting of said shaping signal,
The density of the first toner image is higher than that of the second toner image, and the density of the toner image on the photoreceptor is reduced based on the density difference exceeding the predetermined range. 4. The image forming apparatus according to claim 1, wherein the setting of said shaping signal is changed. 5. The method according to claim 4, wherein changing the setting of the shaping signal so as to increase the density of the toner image on the photoreceptor includes increasing the rising edge voltage of the current supplied to the exposure unit. Image forming device. 5. The method according to claim 4, wherein changing the setting of the shaping signal so as to reduce the density of the toner image on the photoreceptor includes decreasing the rising edge voltage of the current supplied to the exposure section. Image forming device. 7. The image forming apparatus according to claim 1, wherein the control section sets the second frequency to an integer fraction of the first frequency by a frequency divider of the control section. . 8. The image forming apparatus according to claim 1, wherein the light emission duty ratio of the current supplied to said exposure section is between 20% and 80%. further comprising a waveform shaper that deforms the shaped signal by a delay circuit;
The image forming apparatus according to any one of claims 1 to 8, wherein the control section controls the waveform of the shaping signal by switching the waveform shaping section and the line of the shaping signal. The image forming apparatus according to any one of claims 1 to 9, further comprising a bias voltage source for applying a bias voltage to said shaping signal. 11. The image forming apparatus according to claim 1, wherein said control section selects a constant voltage source or a constant current source to generate said shaping signal. 12. The image forming apparatus according to claim 11, wherein the controller adjusts the width of the shaping signal by switching the constant voltage source or the constant current source. A control method for adjusting the density of a toner image, comprising:
shaping a current supplied to an exposure unit that exposes the surface of the photoreceptor, according to the shaping signal;
causing the exposure unit to emit light at a first frequency and a first emission duty ratio to generate a first toner image on the photoreceptor;
generating a second toner image on the photoreceptor by causing the exposure unit to emit light at a second frequency different from the first frequency and at the first emission duty ratio;
obtaining respective densities of the first toner image and the second toner image;
and adjusting the shaping signal based on a density difference between the first toner image and the second toner image. 14. The control method according to claim 13, further comprising the step of setting the shaping signal so that the density difference between the first toner image and the second toner image is within a predetermined range. shaping the current includes shaping the current multiple times while setting the shaping signal;
generating the first toner image and the second toner image on the photoreceptor for each setting of the shaping signal;
acquiring the density of each of the first toner image and the second toner image for each setting of the shaping signal;
obtaining a density difference between the first toner image and the second toner image for each setting of the shaping signal;
15. The control method according to claim 13, further comprising the step of setting said shaping signal such that said density difference is within said predetermined range. the first frequency is higher than the second frequency;
The first toner image has a lower density than the second toner image, and based on the density difference falling below the predetermined range, the density of the toner image on the photoreceptor is increased. , changing the setting of the shaped signal;
The density of the first toner image is higher than that of the second toner image, and the density of the toner image on the photoreceptor is reduced based on the density difference exceeding the predetermined range. , changing the setting of the shaping signal. 17. The method according to claim 16, wherein changing the setting of the shaping signal so as to increase the density of the toner image on the photoreceptor includes increasing the rising edge voltage of the current supplied to the exposure unit. control method. 17. The method according to claim 16, wherein changing the setting of the shaping signal so as to reduce the density of the toner image on the photoreceptor includes decreasing the rising edge voltage of the current supplied to the exposure unit. control method. The control method according to any one of claims 13 to 18, further comprising the step of setting said second frequency to an integer fraction of said first frequency. The control method according to any one of claims 13 to 19, wherein the light emission duty ratio of the current supplied to said exposure section is between 20% and 80%. The control method according to any one of claims 13 to 20, further comprising controlling the waveform of said shaping signal by switching a waveform shaper and a line of said shaping signal. A control method according to any one of claims 13 to 21, further comprising applying a bias voltage to said shaping signal.

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