JP2022090535A - Image forming apparatus - Google Patents

Abstract

To solve the problem in which: the difference between a predicted amount of light emission according to the voltage of a driving signal and an actual amount of light emitted from a light emitting element according to the voltage of the driving signal may lead to a reduction in the accuracy of a detection result.SOLUTION: An image forming apparatus has: a rotating body that carries a toner image or a recording material; image forming means that forms, on the rotating body, a detection pattern being a toner image used for detection of a color shift amount or a density deviation amount; pattern detection means having light emitting means that irradiates the rotating body or the detection pattern with light, and light receiving means that receives light reflected from the rotating body or the detection pattern; and current detection means that detects a current flowing in the light emitting means according to a drive voltage input to the light emitting means. The image forming apparatus has control means that controls the drive voltage according to a result of detection performed by the current detection means.SELECTED DRAWING: Figure 8

Description

The present invention relates to an image forming apparatus such as a copier, a printer, and a facsimile machine using an electrophotographic method or an electrostatic recording method.

Conventionally, as an image forming apparatus using an electrophotographic method, a configuration using an intermediate transfer belt is known. Such an image forming apparatus has a means for correcting the color shift so that the image color shift of each color does not occur, and a means for correcting the density in order to keep the image density of each color optimal (hereinafter, calibration). Called an image).

As one of the calibration means, for example, in Patent Document 1, a toner patch is formed on an image carrier, and the formed toner patch is irradiated with light. A method of correcting color shift and density shift by detecting reflected light from a toner patch on an image carrier using an optical sensor is disclosed. In this method, the amount of light received by the optical sensor and the sensor output voltage obtained by photoelectrically converting the received light vary due to various factors, which may affect the correction of color shift and density shift during calibration. be. Therefore, in Patent Document 2, in order to suppress such variation, the toner patch formed on the image carrier is detected by the optical sensor, and the drive signal of the light emitting element of the optical sensor is adjusted according to the obtained detection result. A method of adjusting the amount of light emitted from the light emitting element by adjusting the drive signal of the light emitting element (hereinafter referred to as “light amount adjustment”) has been proposed. As a method for adjusting the amount of light, a light emitting element is desired by using data such as, for example, a proportional relationship showing the relationship between the drive signal of the light emitting element and the amount of light emitted by the light emitting element (hereinafter, also referred to as LED characteristics of the light emitting element). A method of calculating a drive signal required for emitting light by the amount of light emitted is disclosed.

Japanese Patent Application Laid-Open No. 05-2497787 Japanese Unexamined Patent Publication No. 2016-004068

However, there are individual differences in the LED characteristics of the light emitting element, and light is emitted from the light emitting element according to the predicted light emission amount according to the voltage of the drive signal calculated using the data and the voltage of the drive signal calculated using the data. The actual amount of light emitted may differ. The difference between the predicted amount of light emitted according to the voltage of the drive signal calculated using the data and the actual amount of light emitted from the light emitting element according to the voltage of the drive signal calculated using the data is the detection result. There was a risk that the accuracy would decrease. Therefore, a drive signal control method for suppressing a decrease in detection accuracy is desired.

In order to solve the above problems, the image forming apparatus of the present invention is used.
A rotating body that supports a toner image or recording material,
An image forming means for forming a detection pattern, which is a toner image used for detecting a color shift amount or a density shift amount, on the rotating body, and an image forming means.
A pattern detecting means having a light emitting means for irradiating the rotating body or the detection pattern with light, and a light receiving means for receiving the light reflected from the rotating body or the detection pattern.
A current detecting means for detecting a current flowing through the light emitting means according to a drive voltage input to the light emitting means is provided.
It is characterized by having a control means for controlling a drive voltage according to a detection result by the current detection means.

According to the present invention, it is possible to provide a drive signal control method for suppressing a decrease in detection accuracy.

Schematic block diagram of the image forming apparatus 10 according to the first embodiment Functional block diagram of the image forming apparatus 10 according to the first embodiment Drive circuit of sensor 230 according to the first embodiment The output voltage by the light receiving element 232 affected by the LED current characteristic of the light emitting element 231 with respect to the duty ratio of the drive signal input to the light emitting element 231 according to the first embodiment, and the light receiving light after being adjusted by using the conventional variable resistor. The figure which shows the output voltage by the element 232 A flowchart showing a process executed by the CPU 211 in the light intensity adjustment according to the first embodiment. (A) A diagram showing a state in which a color shift correction pattern is detected by an optical sensor (b) A diagram showing a timing for adjusting the amount of light. A flowchart showing a process executed by the CPU 211 in the color shift correction calibration according to the second embodiment. The figure which shows the method of correcting the duty ratio obtained by the light amount adjustment which concerns on Example 2 (the figure explaining the method of calculating Drev using one actually measured value and Dtgt calculated by proportional calculation). A diagram showing a straight line used for correction from the relationship between the drive signal of the light emitting element and the detection current. FIG. 6 is a diagram showing a straight line used for correction from the relationship between the drive signal of the light emitting element and the detection voltage according to the third embodiment. (A) A diagram showing a state in which a light amount adjustment correction pattern according to Example 3 is detected by an optical sensor (b) A diagram showing a timing for performing light amount adjustment and light amount adjustment correction according to Example 3. A flowchart showing a process executed by the CPU 211 in the color shift correction calibration according to the third embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following embodiments do not limit the invention within the scope of the claims, and not all combinations of features described in the embodiments are essential for the means for solving the present invention.

[Image forming device]
FIG. 1A is a schematic configuration diagram of the image forming apparatus 10. The image forming apparatus 10 is an electrophotographic full-color printer that employs an intermediate transfer method. The image forming apparatus 10 includes four image forming stations for forming images of each color of yellow, magenta, cyan, and black. These four image forming stations are arranged in a row at regular intervals. In the following description, the English letters Y, M, C, and K at the end of the reference code are toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. It shows that it is a member related to formation. When it is not necessary to distinguish the colors in the following description, the reference code excluding the last alphabetic letters a, b, c and d is used.

The main body cassette 11 is loaded with, for example, a recording material 12 which is paper. The recording material 12 loaded on the main body cassette 11 is fed by the pickup roller 13. The recording material 12 fed by the pickup roller 13 is conveyed by the transfer roller pairs 14 and 15. A resist sensor 111 for detecting the presence / absence of the recording material 12 is arranged in the vicinity of the transport roller pairs 14 and 15.

The photosensitive drum 22 has a photosensitive layer on a drum-shaped substrate, and is rotationally driven at a predetermined process speed by a driving device (not shown). The process speed referred to here corresponds to the peripheral speed (surface moving speed) of the photosensitive drum 22. The charging roller 23 uniformly charges the photosensitive drum 22 to a predetermined potential. The scanner unit 20 includes a reflection mirror and a laser diode (light emitting element), and irradiates the laser beam 21 corresponding to the image information to expose the surface of the photosensitive drum 22. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 22.

The developer 25 develops the electrostatic latent image as an image by adhering the toner contained in the developer 25 to the electrostatic latent image formed on the photosensitive drum 22 by using the developing sleeve 24. The primary transfer roller 26 primary transfers the image formed on the photosensitive drum 22 to the intermediate transfer belt 30 (endless belt). The intermediate transfer belt 30 is also referred to as a rotating body. The intermediate transfer belt 30 is driven by the drive roller 33 and the driven rollers 31 and 32. The drive roller in this embodiment may be any of rollers 31, 32, and 33. The toner remaining on the photosensitive drum 22 after the primary transfer is removed from the photosensitive drum 22 by the photosensitive drum cleaning device 26 and recovered. The photosensitive drum cleaning device 26 from the photosensitive drum 22 relating to the formation of the toner image on the intermediate transfer belt 30 described above is also referred to as an image forming means. The image forming means forms a detection pattern, which is a toner image used for detecting the amount of color shift or the amount of density shift, on the intermediate transfer belt 30.

The secondary transfer roller 27 secondary-transfers the image primary-transferred on the intermediate transfer belt 30 to the recording material 12 by applying a voltage by the high-voltage power supply device 50. The toner remaining on the intermediate transfer belt 30 after the secondary transfer is removed from the intermediate transfer belt 30 by the belt cleaning device 80 and recovered. The fuser 16 fixes the secondary transferred image to the recording material 12 by heating and pressurizing. When the tip of the recording material 12 is detected by the resist sensor 111 installed on the transport path during the secondary transfer, the tip of the recording material 12 and the tip of the transferred toner image coincide with each other at the merge point 60. In addition, the transport speed of the recording material 12 is changed. Before the transferred recording material 12 reaches the merge point 60, the transfer speed is returned to the speed before the change, and the transferred recording material 12 is transferred to the secondary transfer unit.

The optical sensor unit 70 acquires information on the toner pattern transferred onto the intermediate transfer belt 30 and the surface of the intermediate transfer belt 30. The acquired information is used to correct the amount of color shift or the amount of density shift. Hereinafter, the process of detecting and correcting the amount of color shift or the amount of density shift is referred to as calibration. Details will be described later.

[Image forming device block diagram]
FIG. 2 is a functional block diagram relating to the image forming apparatus 10.

The controller 201 communicates with the host computer 200 and the engine control unit 202. When the print data is input from the host computer 200, the controller 201 expands the print data and converts it into image data for forming an image. The controller 201 generates video signals for four colors for exposing the surfaces of the photosensitive drums 22a to 22d based on the image data. When the generation of the video signal is completed, the controller 201 outputs the image formation start signal by the command to the video interface unit 210 of the engine control unit 202. After that, when the CPU 211 receives the image formation start signal from the video interface unit 210, it activates various actuators (not shown) and the high voltage power supply device 50, and starts preparing for image formation on the recording material 12. When the preparation for forming the image on the recording material 12 is completed, the CPU 211 outputs the TOP signal, which is the reference timing for outputting the video signal, to the controller 201 via the video interface unit 210, and outputs the image to the recording material 12. Perform the formation. Specifically, when the CPU 211 outputs a / TOP signal to the controller 201 via the video interface unit 210 of the engine control unit 202, the controller 201 generates and outputs a video signal. When the controller 201 outputs a video signal, the engine control unit 202 executes image formation according to the video signal.

As shown in FIG. 4, the optical sensor unit 70 is provided with the sensor 220 and the sensor 230 at the same distance on the left and right with respect to the center position in the main scanning direction, which is a direction orthogonal to the transport direction of the intermediate transfer belt 30. Has been done. By arranging the sensors on the left and right at the same interval from the center position in the main scanning direction in this way, when correcting the amount of color shift, the magnification in the main scanning direction and the amount of tilt in the sub-scanning direction are detected. Is possible.

The sensor 220 has a light emitting element 221 as a light emitting means. This is an infrared light emitting element, and is composed of, for example, an LED. The light emitting element 221 irradiates the intermediate transfer belt 30 or the detection pattern with light. Further, as a light receiving means, a mirror reflected light receiving element 222 for receiving the mirror reflected light reflected from the intermediate transfer belt 30, and a diffused reflected light for receiving the diffused reflected light reflected from the detection pattern on the intermediate transfer belt 30. It has a light receiving element 223. These light receiving means are composed of, for example, a phototransistor or the like. In addition, these light receiving means are also referred to as a light receiving element. Similar to the sensor 220, the sensor 230 has a light emitting element 231 as a light emitting means and a diffusely reflected light receiving element 232 as a light receiving means. An optical sensor having a light emitting element and a light receiving element, such as a sensor 220 and a sensor 230, is also referred to as a pattern detecting means.

Subsequently, the optical sensor unit 70 will be described with reference to FIG. By outputting a drive signal to the light emitting elements 221 and 231 from the PWM output port, the CPU 211 changes the duty ratio of the drive voltage input to the light emitting element, and changes the amount of light emitted from the light emitting elements 221, 231. Further, the specular reflected light receiving element 222 and the diffuse reflected light receiving element 223 and 232 input the voltage value corresponding to the detected reflected light amount to the A / D conversion port of the CPU 211. The specular reflected light receiving element 222, the diffusely reflected light receiving element 223, 232, and the CPU 211, which are the output voltage output by the light receiving element and detect the voltage indicating the amount of light received by the light receiving element, are also referred to as voltage detecting means. ..

Next, the light amount calculating means 212 receives the mirror-reflected light received by the mirror-reflected light receiving element 222 and the diffuse-reflected light received by the diffuse-reflected light-receiving elements 223 and 232, and inputs the voltage value to the CPU 211. Based on this, the following calculation is performed. The next calculation is the duty ratio of the drive voltage input to the light emitting element 221 when the specular reflected light is received, and the duty ratio of the drive voltage input to the light emitting elements 221 and 231 when the diffuse reflected light is received. It is a calculation to calculate.

Further, the sensor 220 and the sensor 230 in this embodiment have a light emitting element voltage detection unit 224 to detect the voltage input to the light emitting elements 221 and 231 according to the drive signal input to the light emitting elements 221 and 231 by the CPU 211. It has -1, 233-1. When the light emitting element voltage detection units 224-1 and 233-1 detect the voltage values input to the light emitting elements 221, 231, the detected voltage values are input to the CPU 211 via the A / D conversion port. The light emitting element current detection unit 224-2, 233-2 in the CPU 211 can detect the current value flowing through the light emitting elements 221 and 231 based on a look-up table in which the voltage value and the current value are associated in advance. At this time, the light emitting element voltage detecting units 224-1 and 233-1 and the light emitting element current detecting units 224-2 and 233-2 in the CPU 211 are also referred to as current detecting means. As described above, in the present embodiment, the current detecting means is the current flowing through the light emitting elements 221 and 231 according to the drive voltage input to the light emitting elements 221 and 231, and indicates the amount of light emitted by the light emitting elements 221, 231. Detects current. Subsequently, the light amount correction means 213 corrects the duty ratio calculated by the light amount calculation means 212 by using the current value flowing through the light emitting elements 221 and 231. The correction of the duty ratio at this time will be described later.

As described above, in this embodiment, by providing the current detecting means, the light amount correction means 213 corrects the duty ratio of the drive voltage input to the light emitting elements 221 and 231 according to the current value flowing through the light emitting elements 221 and 231. can do.

The storage unit 214 is a non-volatile memory, and can store information even when the power of the image forming apparatus 10 is turned off.

The CPU 211 is also referred to as a control means, and controls the correction of the color shift amount or the density shift amount according to the detection result by the pattern detecting means and the detection result by the current detecting means.

[Explanation of optical sensor unit circuit diagram]
FIG. 3A is a drive circuit of the sensors 220 and 230 in the optical sensor unit 70 of this embodiment. Hereinafter, the configuration of the circuit diagram will be described using the sensor 230 as an example.

First, the drive signal Vledon is output from the PWM port of the CPU 211 to the light emitting element 231 of the sensor 230. The drive signal Vledon is a rectangular wave signal and is a signal whose duty ratio can be changed. The voltage Vin is a voltage obtained by smoothing the rectangular wave voltage of the drive signal Vledon by the resistor R300 and the capacitor C310, and is a voltage applied to the base terminal of the transistor T330. When the duty ratio of the drive signal Vledon is changed by the CPU 211, the voltage Vin changes. When the voltage Vin changes, the voltage value applied to the resistor R303 connected to the emitter terminal of the transistor T330 changes, and the current Iled flowing through the light emitting element 231 can be variably controlled. The cathode side of the light emitting element 231 is connected to the collector terminal of the transistor T330. When infrared light is emitted from the intermediate transfer belt 30 by the light emitting element 231, it is reflected by the intermediate transfer belt 30 and the color shift correction pattern 400 formed on the intermediate transfer belt 30 described later. Then, the diffuse reflected light is detected by the light receiving element 232, and a current corresponding to the detected reflected light amount is input to the resistor R304 to perform photoelectric conversion and detect it as an analog output voltage Vaout.

Next, the voltage Vaout is input to the positive input terminal of the comparator IC340, and the threshold voltage Vth whose power supply voltage Vcc is divided by the voltage dividing resistors R305 and R306 is input to the negative input terminal. The threshold value Vth is the threshold voltage of the comparator IC340. By connecting to the comparator IC 340 in this way, when reflected light stronger than a predetermined amount of light is received by the light receiving element 232, a voltage Vaout larger than the threshold value Vth is input to the positive input terminal of the comparator IC 340. When a voltage Vaout larger than the threshold value Vth is input to the positive input terminal of the comparator IC340, the digital output voltage Vdout becomes a high level. Further, when the reflected light weaker than the predetermined amount of light is received by the light receiving element 232, the voltage vaout larger than the threshold value Vth is not input to the positive input terminal of the comparator IC340. When a voltage Vaout larger than the threshold value Vth is not input to the positive input terminal of the comparator IC340, the threshold value Vth is input to the negative input terminal of the comparator IC340. Therefore, the digital output voltage Vdout becomes a low level. In this way, the comparator IC 340 converts whether or not the analog output voltage Vaout is input to the comparator IC 340 into high-level and low-level digital output voltage Vdout, and outputs the digital output voltage Vdout to the CPU 211. Further, the CPU 211 detects the timing at which the digital output voltage Vdout changes from a high level to a low level and from a low level to a high level by an internal timer function.

The voltage voltage is input to the A / D conversion port of the CPU 211 by the light emitting element voltage detection unit 233-1, and the voltage Vaout is input to the A / D conversion port of the CPU 211 by the light receiving element 232. In this way, the optical sensor unit 70 can acquire the digital output voltage value by the CPU 211 by outputting the analog voltage value obtained by detecting the toner patch or the like to the CPU 211 via the A / D conversion port. can. The CPU 211 has a look-up table in which the voltage Vled and the current Iled are associated with each other in advance, and is configured to be able to acquire the current Iled flowing through the light emitting element 231. Hereinafter, the current Iled flowing through the light emitting element 231 is also referred to as a light quantity.

In the following description, a case where diffuse reflected light is used will be described. At this time, since the processing of the sensor 220 and the sensor 230 is the same, the present embodiment will be described using the sensor 230 as an example.

[LED current characteristics with respect to duty ratio]
Subsequently, the output characteristics (also referred to as ideal LED current characteristics) of the current LED flowing through the light emitting element 231 with respect to the duty ratio of the drive signal Vledon will be described with reference to FIG. FIG. 4 shows the output voltage of the light receiving element 232 affected by the LED current characteristic of the light emitting element 231 with respect to the duty ratio of the drive signal input to the light emitting element 231 and the light receiving element 232 conventionally adjusted by using a variable resistor. It is a figure explaining the output voltage by. The horizontal axis is the duty ratio [%] of the rectangular wave of the drive signal Vledon. The vertical axis is the voltage Vaout [V] output from the light receiving element 232. Further, the intercept Lth is a value at which a current starts to flow in the light emitting element 231 in the drive circuit of the optical sensor unit 70. Further, the dark voltage Vdark is a voltage generated by the dark current of the light receiving element 232 flowing through the resistor R304 when the power supply voltage Vcc is applied in the drive circuit, and the light receiving element 232 receives light in a state where it does not receive light. This is the voltage output by the element 232. When the light emitting element 231 is driven by the CPU 211, the voltage Vin is increased by increasing the duty ratio of the drive signal Vledon. At this time, when the duty ratio becomes the intercept Lth or more, the transistor T330 of the drive circuit is turned on, and a current starts to flow in the light emitting element 231. When the duty ratio is increased, the voltage vaout output by the light receiving element 232 also increases proportionally. In FIG. 4, the duty ratio Dtgt is a duty ratio for obtaining a voltage vaout value (Vtgt) required for calibration.

Conventionally, when the output voltage output by the light receiving element 232 is the broken line 702, a variable resistor is used at the time of shipment from the factory to adjust the voltage to be as shown by the broken line 700. However, due to the LED characteristics of the light emitting element 231, the amount of light emitted may not be proportional to each other as the duty ratio is increased. Due to this LED characteristic, as shown by the solid line 701 in FIG. 4, the voltage value output by the light receiving element 232 may not be proportional as the duty ratio is increased. For example, when the light emitting element is driven by a duty ratio equal to or higher than a predetermined drive voltage (indicated by Dn in FIG. 4), the obtained light emission amount is not proportional and the output voltage by the light receiving element 232 is also as shown by the broken line 700. It will not be proportional. As a result, even if the duty ratio Dtgt for obtaining the voltage Vaout value (Vtgt) required for calibration is input to the light emitting element 231, the voltage output by the light receiving element 232 is less than Vtgt.

As described above, the conventional method of adjusting the LED characteristics using a variable resistor has room for further correction to improve the accuracy. In this embodiment, the desired output voltage is also referred to as Vtgt and also referred to as a target voltage. Further, as described above, the main factor that the output voltage by the light receiving element 232 does not have a proportional relationship as shown by the broken line 700 is due to the LED characteristics of the light emitting element 231.

Therefore, in this embodiment, the duty ratio Dtgt for obtaining the voltage vaout value (Vtgt) required for calibration as shown in FIG. 4 is set in advance in consideration of the state of the intermediate transfer belt 30 and the influence of the toner patch. Correct it. The correction of the duty ratio Dtgt will be described in the second embodiment. When the duty ratio Dtgt thus obtained is input to the light emitting element 231 and the light emitting element 231 emits light with an ideal light emitting amount, the current value flowing through the light emitting element 231 is defined as Itgt. However, even if the duty ratio Dtgt corrected in advance is input to the light emitting element 231, the current value actually flowing through the light emitting element 231 may be less than Itgt due to the above-mentioned LED characteristics. Therefore, by making it possible to actually detect the current value flowing through the light emitting element 231, the duty ratio Dtgt can be corrected in consideration of the LED characteristics of the light emitting element 231.

[Light intensity adjustment according to this embodiment]
In this embodiment, the current Iled [mA] flowing through the light emitting element 231 can be detected by using the current detecting means. Hereinafter, the process executed by the CPU 211 in the light amount adjustment in this embodiment will be described with reference to FIG.

In S501, the CPU 211 causes the light emitting element 231 to emit light with a predetermined duty ratio Dtgt. The predetermined duty ratio Dtgt here is a target drive voltage which is a drive voltage when the light emitting means can emit a light emission amount required for calibration. That is, it is the target drive voltage calculated in consideration of the state of the intermediate transfer belt 30 and the influence of the toner patch at the time of the previous calibration execution, and is the light amount adjustment result stored in the storage unit 214.

In S502, the CPU 211 detects the current value Index when the duty ratio Dtgt is input to the light emitting element 231 and causes light to be emitted by the light emitting element current detecting unit 233-2. When the CPU 211 detects the current value Index, the process proceeds to S503.

In S503, when the Index detected by the light emitting element current detection unit 233-2 is smaller than Itgt, the CPU 211 advances the process to S504. If the Index is not smaller than Itgt, the process proceeds to S506.

In S504, the CPU 211 increases the duty ratio Dtgt input to the light emitting element by, for example, 10%. At this time, the value added to the duty ratio Dtgt is also referred to as ΔD. In this embodiment, ΔD is set to 10%, but when the process of S504 is repeated, the CPU 211 gradually reduces the value of ΔD each time the Drev is corrected. The value for gradually reducing the value of ΔD can be appropriately set depending on the accuracy of the desired duty ratio Dtgt, the calculation load, the calculation time, and the like. For example, when the value to be reduced is 1% or 0.1%, the accuracy of the duty ratio Dtgt is improved by setting it to 0.1%, but the calculation load and the calculation time increase. When the value of Drev is corrected in S504, the CPU 211 advances the process to S505. In S505, the CPU 211 causes the light emitting element 231 to emit light by Drev, and returns the processing to S502.

In S506, when the Index detected by the light emitting element current detection unit 233-2 is larger than Itgt, the CPU 211 advances the process to S507. If the Index is not greater than Itgt, the process proceeds to S508. Here, as an example, it has been described that the correction of Dtgt is completed when Extract = Itgt by S503 and S506, but the present invention is not limited to this. For example, if it is determined that the difference between Extract and Itgt is within a predetermined range, the correction of Dtgt may be completed. The difference within a predetermined range can be appropriately set depending on the accuracy of the obtained Index, the calculation load, the calculation time, and the like.

In S507, the CPU 211 reduces the duty ratio Dtgt input to the light emitting element by, for example, 10%. At this time, the value subtracted from the duty ratio Dtgt is also referred to as ΔD. In this embodiment, ΔD is set to 10%, but when the process of S507 is repeated, the CPU 211 gradually reduces the value of ΔD each time the Drev is corrected. The value for gradually reducing the value of ΔD can be appropriately set depending on the accuracy of the desired duty ratio Dtgt, the calculation load, the calculation time, and the like. For example, when the value to be reduced is 1% or 0.1%, the accuracy of the duty ratio Dtgt is improved by setting it to 0.1%, but the calculation load and the calculation time increase. When the value of Drev is corrected in S507, the CPU 211 advances the process to S508. In S508, when the light emitting element 231 is made to emit light by Drev, the CPU 211 returns the process to S502.

In S509, the CPU 211 waits for 3 seconds until the amount of light of the light emitting element 231 to which the drive voltage is input stabilizes. The 3 seconds at this time is an example of the time during which the amount of light of the light emitting element 231 to which the drive voltage is input stabilizes. After 3 seconds have elapsed, the CPU 211 advances the process to S510.

In S510, the CPU 211 overwrites the value of the duty ratio Dtgt stored in the storage unit 214 with the value of the duty ratio Drive so that the duty ratio Drev can be used in the next calibration. When the CPU 211 overwrites the value of the duty ratio Dtgt stored in the storage unit 214 with the value of the duty ratio Drev, the CPU 211 advances the process to S511. In this embodiment, even if the storage unit 214 stores the duty ratio value and the Iled value each time the light emitting amount Iled value when the light emitting element 231 is made to emit light at a predetermined duty ratio is detected. good.

In S511, the CPU 211 stops the light emission by the light emitting element 231 and ends the light amount adjustment.

As described above, in this embodiment, the LED characteristic adjustment can be performed by a method different from the LED characteristic adjustment using the variable resistor. That is, a duty ratio for obtaining a desired amount of light emission can be obtained by using an actually measured value obtained by detecting the current flowing through the light emitting element 231 by the current detecting means. Therefore, it is possible to suppress the influence of the difference between the desired light emission amount and the actual light emission amount on the accuracy of the light amount adjustment. Further, by using the measured value of the current flowing through the light emitting element 231 by the current detecting means, the LED characteristics of the light emitting element 231 are considered regardless of the state of the patch formed on the intermediate transfer belt 30 or the state of the intermediate transfer belt 30. The duty ratio can be obtained. Further, since the Drev can be obtained only by causing the light emitting element 231 to emit light, the light amount adjustment can be performed without the downtime for forming the patch on the intermediate transfer belt 30 and the downtime for cleaning the patch formed on the intermediate transfer belt 30. Can be done.

In Example 1, a case where a Drev is obtained using only measured values has been described. However, in the first embodiment, it is necessary to repeatedly execute the process of correcting the Drev until the CPU 211 obtains a desired amount of light emitted. In this embodiment, the Drev for obtaining a desired light emission amount is calculated by using the measured value of the current detected by the current detecting means and the proportional calculation. As a result, in the first embodiment, the process of correcting the Drev is repeated until the CPU 211 obtains a desired amount of light emission, which may impose a calculation load on the CPU 211 or cause downtime due to the calculation time. In this case, by using the method of this embodiment, the Drev can be calculated while suppressing the calculation load and suppressing the occurrence of downtime.

[Calibration for color shift and density shift correction according to this embodiment]
In this embodiment, the duty ratio Dtgt obtained by the same proportional calculation as in the conventional case in the light amount adjustment performed at the time of performing the calibration for correcting the color shift amount or the density shift amount is the current detected by the current detecting means. Correct using the measured value. Then, in consideration of the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30, the difference between the desired light emission amount and the actual light emission amount is the accuracy of the light amount adjustment. Suppress the impact.

First, when a predetermined condition is satisfied, the CPU 211 outputs a request to the controller 201 to perform calibration for correcting the color shift amount or the density shift amount. The predetermined condition at this time is, for example, a condition such as a change in the environment around the image forming apparatus or an image forming operation on a predetermined number of recording materials 12. Hereinafter, the correction of the color shift amount will be described as an example of the calibration for correcting the color shift amount or the density shift amount.

FIG. 6A is a diagram showing how the optical sensor unit 70 detects the color shift correction pattern 400 transferred onto the intermediate transfer belt 30 in the calibration for correcting the color shift amount. FIG. 6B is a diagram showing the timing of performing light amount adjustment (calculation of Dtgt) and correction of light amount adjustment (calculation of Drev) when performing calibration for correcting the amount of color shift. FIG. 7 is a flowchart showing a process executed by the CPU 211 in the calibration for correcting the amount of color shift in this embodiment. The calibration for correcting the amount of color shift is performed in the order of calibration preparation operation, color shift correction executed by detecting the color shift correction pattern 400, light amount adjustment, light amount adjustment correction, and post-processing. .. Hereinafter, each of calibration preparation operation, color shift amount correction, light amount adjustment, light amount correction correction, and post-processing will be described with reference to FIGS. 6 and 7.

<Calibration preparation operation>
First, at the timing T8001 of FIG. 6B, the calibration for correcting the color shift amount is started, and the CPU 211 starts the processing of the flowchart of FIG. 7.

In S700, the CPU 211 detects the dark voltage Vdark as a preparatory operation for calibration. The dark voltage Vdark is a voltage generated by the dark current of the light receiving element 232 flowing through the resistor R304 when the power supply voltage Vcc is applied in the drive circuit, and the light receiving element 232 does not receive light. This is the voltage output by 232. Since it is necessary to make adjustments based on the dark voltage Vdark in the light amount adjustment described later, the dark voltage Vdark is detected in the calibration preparation operation. When the CPU 211 acquires the dark voltage Vdark, the CPU 211 advances the process to S701.

In S701, the CPU 211 causes the light emitting element 231 to emit light with a predetermined duty ratio Dnow. The predetermined duty ratio Dnow here is the light amount adjustment result stored in the storage unit 214 at the time of the previous calibration execution. Details will be described later. When the calibration is performed for the first time after the image forming apparatus 10 is manufactured, the light is emitted using a predetermined default duty ratio.

In S702, the CPU 211 waits for 10 seconds. The 10 seconds at this time is an example of the time until the amount of light of the light emitting element 231 input with the duty ratio Dnow stabilizes. The CPU 211 advances the process to S703 after 10 seconds have elapsed. At this time, the CPU 211 forms an image of the color shift correction pattern 400 on the intermediate transfer belt 30 from the timing calculated back so that the process of detecting the color shift correction pattern 400 by the optical sensor unit 70 can be started from S703. To start.

As shown in FIG. 6A, the color shift correction pattern 400 is formed as a pattern having an inclination with respect to the transport direction of the intermediate transfer belt 30. The color shift correction pattern 400 is formed in the order of yellow (Y), black (K), yellow (Y), magenta (M), and cyan (C) from the downstream side in the transport direction. The black (K) toner patch is formed so as to be superimposed on the yellow (Y) toner patch in order to distinguish it from the diffuse reflected light reflected on the surface of the intermediate transfer belt 30. Further, the toner patches are formed at predetermined intervals so that the toner patches of each color can be independently detected even when the color shift occurs.

<Color shift correction>
In S703, the CPU 211 detects the color shift correction pattern 400 formed on the intermediate transfer belt 30 by the optical sensor unit 70. At this time, the CPU 211 receives the diffuse reflected light generated by irradiating the color shift correction pattern 400 formed on the intermediate transfer belt 30 with infrared light by the light emitting element 231 by the diffuse reflected light receiving element 232. At this time, the edge portion of the toner patch of each color is detected at the timing when the digital output voltage Vdout output by the comparator IC340 of the drive circuit described above changes from high level to low level and from low level to high level. Then, the timing at which the digital output voltage Vdout changes from high level to low level and from low level to high level is sequentially stored in the RAM of the CPU 211.

The CPU 211 calculates the amount of color shift from the detection timing of the edge portion of the toner patch of each color stored in the RAM, and notifies the controller 201 via the video interface portion 210. The controller 201 corrects the color shift by finely adjusting the generation timing of the video signal from the notified color shift amount.

The CPU 211 sequentially stores the A / D conversion value of the voltage vaout detected by the diffusely reflected light receiving element 232 in the RAM (not shown) of the CPU 211 in parallel with the detection of the edge portion of each color toner patch. When the color shift correction pattern 400 finishes passing through the optical sensor unit 70, the CPU 211 advances the process to S704. The timing T8002 in FIG. 6B is the timing at which the color shift correction pattern 400 finishes passing through the optical sensor unit 70.

<Light intensity adjustment method>
In S704, the CPU 211 executes the light amount adjustment and calculates the duty ratio Dtgt for obtaining the value (Vtgt) of the voltage Vaout required for calibration. Hereinafter, using FIG. 8A, the duty ratio Dtgt for obtaining the voltage Vtgt required for calibration is calculated based on the duty ratio Dnow for obtaining the value of the voltage Vaout stored in the RAM (not shown). The method of adjusting the amount of light to be performed will be described.

FIG. 8A is a graph showing the relationship of the voltage vaout detected by the light receiving element 232 with respect to the duty ratio of the drive signal Vledon of the light emitting element 231. The horizontal axis is the duty ratio [%] of the rectangular wave of the drive signal Vledon. The vertical axis is the voltage vaout [V] detected by the light receiving element 232. The dark voltage Vdark is the dark voltage Vdark described in the above-mentioned <calibration preparation operation>, and the intercept Lth is the value described in the above-mentioned [LED current characteristic with respect to the duty ratio]. Further, the duty ratio Dnow is a duty ratio used at the time of calibration, and is a duty ratio as a result of adjusting the amount of light stored in the storage unit 214 at the time of the previous calibration execution. Further, Vnow is set to the maximum value of the voltage vaout obtained by detecting the color shift correction pattern 400 by the light receiving element 232 when the light emitting element 231 is made to emit light at the duty ratio Dnow. Vtgt is a target value (target voltage) of the voltage output by the light receiving element 232 in the color shift correction calibration. The purpose of the light amount adjustment is to obtain the duty ratio Dtgt input to the light emitting element 231 so that the voltage when the color shift correction pattern 400 is detected by the light receiving element 232 is Vtgt.

Here, the reason for causing the light emitting element 231 to emit light at the duty ratio Dnow, detecting the voltage Vnow, and calculating the duty ratio Dtgt for obtaining the voltage Vtgt will be described. The voltage when the color shift correction pattern 400 is detected by the light receiving element 232 is affected by the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30. Therefore, when the light emitting element 231 is made to emit light at the duty ratio Dnow, the value of the voltage Vnow obtained by detecting the color shift correction pattern 400 by the light receiving element 232 is the color shift correction formed on the intermediate transfer belt 30. It depends on the state of the pattern 400 and the state of the surface of the intermediate transfer belt 30. Since the value of the voltage Vnow is variable in this way, the value of the duty ratio Dtgt calculated by using the values of the duty ratios Dnow and Vnow and the dark voltage Vdark and the intercept Lth is also variable.

For example, when the light emitting element 231 is made to emit light at the duty ratio Dnow, the calculated value of the duty ratio Dtgt becomes large when the value of the detected voltage Vnow becomes small. That is, when the value of the voltage Vnow becomes small, the amount of light of the light emitting element 231 is small. Therefore, in order to obtain the voltage Vtgt, it is necessary to increase the amount of light of the light emitting element 231, and the duty ratio Dtgt for driving the light emitting element 231 is set. It needs to be large. In this way, the LED characteristics of the light emitting element 231 are adjusted using the duty ratio Dtgt calculated according to the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30. ..

After that, the duty ratio Dtgt is calculated. Duty ratio Dtgt calculated using the following [Equation 1] from the graph (broken line 1500) obtained by using the values of the duty ratio Dnow and the voltage Vnow and the values of the dark voltage Vdark and the intercept Lth, using the similarity relationship. Ask for. The proportional relationship shown by [Equation 1] is also referred to as a first proportional relationship.
Dtgt = (Dnow-Lth) × (Vtgt-Vdark) / (Vnow-Vdark) + Lth ... [Number 1]
When the duty ratio Dtgt is obtained from the above, the CPU 211 advances the process to S705. The timing T8002 in FIG. 6B is the timing at which the CPU 211 calculates the duty ratio Dtgt.

In S705, the CPU 211 inputs the duty ratio Dtgt calculated in S704 to the light emitting element 231 and causes the light emitting element 231 to emit light. When the CPU 211 causes the light emitting element 231 to emit light, the process proceeds to S706. The CPU 211 may wait for processing for, for example, 3 seconds as a time during which the light amount of the light emitting element 231 to which the duty ratio Dtgt is input stabilizes after the light emitting element 231 is made to emit light.

<Correction of light intensity correction>
In S706, the CPU 211 detects the current value Index detected by the current detecting means when the duty ratio Dtgt is input to the light emitting element 231 and the light is emitted. When the CPU 211 detects the current value Index, the process proceeds to S707. The timing T8003 in FIG. 6B is the timing at which the CPU 211 detects the current value Index.

In S707, the CPU 211 corrects the light amount adjustment and calculates the duty ratio Drev from the duty ratio Dtgt.

Hereinafter, a method for obtaining the duty ratio Drev will be described with reference to FIG. 8 (b). The horizontal axis is the duty ratio [%] of the rectangular wave of the drive signal Vledon input to the light emitting element 231. The vertical axis is the current Iled [mA] flowing through the light emitting element 231. The solid line 700 is a graph showing the ideal LED current characteristics, and the solid line 701 is a graph showing the actual LED current characteristics. Further, when the light emitting element 231 is made to emit light by using the duty ratio Dnow, the detected current value is defined as Inow. Further, when the light emitting element 231 is made to emit light using the duty ratio Dtgt, the detected current value is defined as Extract. The current value Index is an actually measured value of the current value detected when the duty ratio Dtgt is input to the light emitting element 231. Further, the current value Itgt is a target value (target current) of the current value required by the light emitting element 231 in the color shift and density shift correction calibration, that is, the light emitting amount of the light emitting element 231 required in the color shift and density shift correction calibration. ).

In this embodiment, the broken line 702, which is a line connecting the points 710 and 711 on the graph, is calculated. By calculating the broken line 702, when a duty ratio larger than the duty ratio Dnow is input to the light emitting element 231, the following effects are obtained. A value closer to the graph showing the actual LED current characteristics (solid line 701) than the graph showing the ideal LED current characteristics (solid line 700) can be obtained. That is, by calculating the broken line 702, the following effects are obtained. It is possible to calculate the duty ratio Drev capable of inputting a current value closer to the target current value Itgt to the light emitting element 231 than the current value Index actually detected when the duty ratio Dtgt is input to the light emitting element 231.

In this embodiment, the duty ratio Dnow is also referred to as a first drive voltage, Vnow is also referred to as a first output voltage, and the current value Inow is also referred to as a first current value. The duty ratio of the intercept Lth is also referred to as a second drive voltage, and the dark voltage Vdark is also referred to as a second output voltage. The duty ratio Dtgt is also referred to as a third drive voltage, the target voltage Vtgt is also referred to as a third output voltage, and the current value Itgt is also referred to as a third current value. The duty ratio Drev is also referred to as a fourth drive voltage, and the current value Index is also referred to as a fourth current value.

First, using a graph showing the ideal LED current characteristics of the light emitting element 231 shown by the solid line 700, the light emitting amount of the light emitting element 231 required for the color shift and density shift correction calibration, that is, the current required by the light emitting element 231. Calculate the target value Itgt of the value. That is, when the Dtgt calculated by using the above [Equation 1] is input to the light emitting element 231, the current value Itgt flowing through the light emitting element 231 is obtained by using the following [Equation 2]. It is a graph showing the ideal LED current characteristics of the light emitting element 231 shown by the solid line 700, and the proportional relationship shown by [Equation 2] is also referred to as a second proportional relationship.
Itgt = Inow × (Dtgt-Lth) / (Dnow-Lth) ... [Number 2]

Next, as shown in [Equation 3] below, by substituting the current value Itgt calculated in [Equation 2] into the mathematical formula showing the broken line 702, which is a line connecting the points 710 and 711 on the graph. , The corrected duty ratio Drev is obtained. The proportional relationship shown by the broken line 702 and [Equation 3] is also referred to as a third proportional relationship.
Drev = (Dtgt-Dnow) × (Itgt-Inow) / (Ext-Inow) + Dnow ... [Equation 3]

In this embodiment, the intercept Lth is used when calculating the target current value Itgt, but any duty ratio Dx between the intercept Lth and the duty ratio Dnow and the current value Ix corresponding to the duty ratio Dx are used. And, the current value Itgt may be calculated using. The formula [Equation 2'] used at this time is described below. At this time, the duty ratio Dx may be referred to as a second drive voltage, and the current value Ix may be referred to as a second current value.
Itgt = (Inow-Ix) x (Dtgt-Dx) / (Dnow-Dx) ... [Number 2']

By the method described above, the duty ratio Drev corrected for Dtgt, which is the result of the light intensity adjustment, can be obtained. That is, first, the duty ratio Dtgt is calculated in consideration of the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30. Then, the duty ratio Drev is calculated according to the measured value of the current flowing through the light emitting element 231 in consideration of the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30. .. Thereby, when calculating the duty ratio Drev from the duty ratio Dtgt, it is possible to execute the LED characteristic adjustment in consideration of only the LED characteristic of the light emitting element 231. When the CPU 211 calculates the duty ratio Drev, the process proceeds to S708. The timing T8003 in FIG. 8 is the timing at which the duty ratio Drev is calculated by the CPU 211.

In S708, the CPU 211 overwrites the value of the duty ratio Dnow stored in the storage unit 214 with the value of the duty ratio Drive so that the duty ratio Drev can be used in the next calibration. When the CPU 211 overwrites the value of the duty ratio Dnow stored in the storage unit 214 with the value of the duty ratio Drev, the CPU 211 advances the process to S709.

<Post-processing>
In S709, the CPU 211 stops the light emission by the light emitting element 231 and conveys the color shift correction pattern 400 transferred onto the intermediate transfer belt 30 to the belt cleaning device 80 to execute the cleaning process of the intermediate transfer belt 30. do. After that, the CPU 211 stops various actuators and ends the color shift correction calibration.

As described above, in the present embodiment, first, the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the surface of the intermediate transfer belt 30 are used in the same proportional calculation as in the conventional calibration. The duty ratio Dtgt in consideration of the state is calculated. Then, the duty ratio Drev is calculated using the calculated Dtgt value and the measured value of the light emission amount detected by the current detecting means. As a result, the desired amount of light emitted from the light emitting element 231 according to the calculated drive signal voltage is taken into consideration in consideration of the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30. It is possible to prevent the difference between the actual amount of light emission and the actual amount of light emission from becoming larger than before. Further, since it is not necessary to newly form a toner patch on the intermediate transfer belt 30 when calculating the duty ratio Drev from the duty ratio Dtgt, it is possible to suppress an increase in downtime for forming the toner patch and the consumption of toner. Can be done. Further, in the case of calculating the Drev in order to obtain the desired light emission amount using both the proportional calculation and the actually measured value, the process executed by the CPU 211 to correct the Drev is better than in the case of using only the measured value. It is possible to suppress repetition and suppress the calculation load on the CPU 211 and the downtime due to the calculation time.

In this embodiment, the duty ratio Drev was calculated by approximating the LED characteristics to the data showing the proportional relationship. However, the present invention is not limited to this, and the duty ratio Drev may be calculated by using the function fitting using the curve of the polynomial.

[Modification 1 of Example 2]
As a modification 1 of the second embodiment, another method for using the measured value of the current detected by the current detecting means and the proportional calculation will be described. That is, a method of calculating Drev by performing proportional calculation using at least two or more actually measured values of the current value detected by the current detecting means will be described.

In the second embodiment, the measured values Inow and Extract are obtained using the Dnow which is the light amount adjustment result stored in the storage unit 214 at the time of the previous calibration execution and the Dtgt value calculated by detecting the color shift correction pattern 400. I got each. However, when the light emitting element 231 is made to emit light by using the values of two arbitrary duty ratios and the values of two arbitrary duty ratios, Drev is calculated by proportional calculation using the two current values detected by the current detecting means. May be calculated. In addition, also in the modification 1 of this embodiment, the duty ratio Drev may be calculated by using the function fitting using the curve of the polynomial.

As described above, in the first modification of the second embodiment, the light emitting element uses the values of two arbitrary duty ratios without using the current which is the light amount adjustment result stored in the storage unit 214 at the time of the previous calibration execution. When the 231 is made to emit light, it is detected by the current detecting means. Then, the Drev is calculated by the proportional calculation. As a result, when calculating the duty ratio for obtaining a desired amount of light emission in consideration of only the LED characteristics of the light emitting element, Drev can be obtained only by causing the light emitting element to emit light. Therefore, the duty ratio for obtaining a desired light emission amount can be calculated without forming a toner patch on the intermediate transfer belt 30 or cleaning the intermediate transfer belt 30 on which the toner patch is formed. Further, in the case of calculating the Drev in order to obtain the desired light emission amount using both the proportional calculation and the measured value, the process executed by the CPU 211 to correct the Drev is more than in the case of using only the measured value. It is possible to suppress repetition and suppress the load applied to the CPU 211.

[Modification 2 of Example 2]
As a modification 2 of the second embodiment, another method for using the measured value of the current detected by the current detecting means and the proportional calculation will be described. That is, the measured values of at least two or more LED characteristics of the current values detected by the current detecting means at the time of manufacturing the image forming apparatus 10 are stored. Then, after the image forming apparatus 10 is shipped, the CPU 211 calculates the Drev by executing the proportional calculation using at least two or more actually measured values stored in the storage unit 214. Therefore, in the present embodiment, the duty ratio for obtaining a desired light emission amount without having the light emitting element voltage detection units 224-1 and 233-1 and the light emitting element current detection units 224-2 and 233-2. Drev can be calculated.

In FIG. 9, similarly to FIG. 8, the horizontal axis is the duty ratio [%] of the rectangular wave of the drive signal Vledon. The vertical axis is the current Iled [mA] flowing through the light emitting element 231. The point 1210 is a point on the line (solid line 700) showing the ideal LED current characteristic, and is a point where the duty ratio input to the light emitting element and the LED current characteristic are not in a proportional relationship. The duty ratio at this time is Dchg, and the current is Ichg. Further, the point 1211 is a point on the line (solid line 701) showing the actual LED current characteristics, and the duty ratio Dmem is set to a value larger than Dchg and 100% or less, which is the maximum value that can be taken as the duty ratio. The current value flowing through the light emitting element when the light emitting element is made to emit light at the duty ratio Dmem is defined as Imem.

In the second modification of the second embodiment, the above Dchg, Dmem, Ichg, and Imem are stored in the storage unit 214 at the time of manufacturing the image forming apparatus 10.

When the color shift correction calibration is executed in the modification 2 of the second embodiment, the light emitting element voltage detection units 224-1 and 233-1 and the light emitting element current detection units 224-2 and 2332 are not provided. First, the current value Inow is calculated using [Equation 4].
Inow = Ichg × (Dnow-Lth) / (Dchg-Lth) ... [Number 4]

Next, from the current value Inow calculated using [Equation 4], the current value Itgt is calculated using the above-mentioned [Equation 1] and [Equation 2]. The Dtgt is calculated using [Equation 1] because of the duty ratio in consideration of the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30 in the subsequent processing. This is to obtain the duty ratio Drev according to Dtgt. When the current value Itgt is obtained, as shown in [Equation 5] below, the current value Itgt calculated in [Equation 2] is added to the mathematical formula showing the broken line 1201 which is a line connecting the points 1210 and 1211 on the graph. By substituting, the corrected duty ratio Drev is obtained.
Drev = (Dmem-Dchg) × (Itgt-Ichg) / (Imem-Ichg) + Dchg ... [Number 5]

In the case of Itgt ≦ Ichg, since the duty ratio and the LED current characteristic are in a proportional relationship, it is not necessary to correct the light amount adjustment. Therefore, the duty ratio Dtgt may be used in the next calibration.

As described above, in the second modification of the second embodiment, the light emitting element voltage detection units 224-1 and 233-1 for detecting the current flowing through the light emitting element, and the light emitting element current detection units 224-2, 233- The duty ratio Drev can be calculated without providing 2. As a result, the desired amount of light emitted from the light emitting element 231 was calculated while reducing the cost of providing the light emitting element voltage detection units 224-1 and 233-1 and the light emitting element current detection units 224-2 and 233-2. It is possible to prevent the difference from the actual amount of light emitted according to the drive signal from becoming larger than before. Further, since it is not necessary to newly form a toner patch on the intermediate transfer belt 30 when calculating the duty ratio Drev from the duty ratio Dtgt, it is possible to suppress an increase in downtime for forming the toner patch and the consumption of toner. Can be done. Further, in the case of calculating the Drev in order to obtain the desired light emission amount by using both the proportional calculation and the measured value, the process executed by the CPU 211 to correct the Drev is better than in the case of using only the measured value. It is possible to suppress repetition and suppress the load applied to the CPU 211.

The LED characteristics of the light emitting element 231 described with reference to FIG. 4 also affect the value of the voltage vaout detected by the light receiving element 232, as shown by the solid line 1502 in FIG. That is, as the duty ratio is increased, the voltage vaout detected by the light receiving element 232 does not have a proportional relationship. Therefore, similarly to the contents described in the above-described embodiment, there is a difference between the voltage Vtgt required for calibration and the measured value of the voltage Vaout according to the Dtgt calculated by using the proportional calculation. Therefore, as described in the first embodiment, in order to obtain the duty ratio vaout using the measured value of the voltage vaout corresponding to the duty ratio Dtgt, the process of correcting the vaout is performed until the CPU 211 obtains the desired voltage vaout. Must be repeated. Further, it is necessary to continue forming the toner patch on the intermediate transfer belt 30 while the CPU 211 repeatedly executes the process of correcting the Drev, and there is a possibility that the consumption of the toner patch will increase. Further, it is necessary that the state of the intermediate transfer belt 30 is stable while the CPU 211 repeatedly executes the process of correcting the Drev. Therefore, in the second embodiment, after calculating the duty ratio Dtgt in consideration of the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30, the current value by the current detecting means is calculated. The method of calculating Drev according to the measured value is described. In this embodiment, after calculating the duty ratio Dtgt in consideration of the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30, the measured value on the light receiving side is used. Perform the same proportional calculation as in Example 2. That is, in order to detect a voltage corresponding to the amount of diffuse reflected light reflected by the color shift correction pattern 400 formed on the intermediate transfer belt 30, and to obtain a desired amount of light emission according to the obtained measured value. The duty ratio Drev is calculated.

In this embodiment, in order to calculate the Drev, downtime for forming a new patch on the intermediate transfer belt 30 is required. However, there is an advantage that the duty ratio Drev can be calculated in consideration of not only the LED characteristics of the light emitting element 231 but also the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30. There is.

In the following description, the same configuration as that of the first or second embodiment will be assigned the same number and the description thereof will be omitted.

In this embodiment, after the cleaning process of the intermediate transfer belt 30 in the <post-processing> of the color shift correction calibration is completed, the light amount adjustment correction is performed again on the intermediate transfer belt 30 in order to correct the light amount adjustment. For pattern 1400 is formed. FIG. 11 is a diagram showing a state in which an optical sensor detects a light amount adjustment correction pattern 1400 formed by using cyan-colored toner. In this embodiment, cyan color toner is used as an example of the light amount adjustment correction pattern 1400, but toner of a different color may be used. Further, Vnext may be obtained by forming a plurality of patches using toners of different colors and taking the average value of the detected voltages.

FIG. 10 is a diagram showing a straight line used for correction from the relationship between the drive signal of the light emitting element and the detection voltage. Similar to FIG. 8B, the horizontal axis is the duty ratio [%] of the rectangular wave of the drive signal Vledon, and the vertical axis is the graph showing the relationship of the voltage vaout detected by the light receiving element 232. The voltage value Vtgt is the amount of light received by the light receiving element 232 required for the color shift and density shift correction calibration, that is, the target value (target voltage) of the voltage value received by the light receiving element 232 in the color shift and density shift correction calibration. Is.

In this embodiment, the broken line 1501 which is a line connecting the points 1510 and the points 1511 on the graph is calculated. The dotted line 1500 is a graph showing the voltage value input to the light receiving element 232 when the light emitting element 231 has the ideal LED current characteristic. The solid line 1502 is a graph showing a voltage value input to the light receiving element 232 when the light emitting element 231 has an actual LED current characteristic. When a duty ratio larger than the duty ratio Dnow is input to the light emitting element 231 by calculating the broken line 1501, the following effects are obtained. It is possible to obtain a value closer to the graph (solid line 1502) showing the voltage value affected by the actual LED current characteristic than the graph showing the voltage value affected by the ideal LED current characteristic (dotted line 1500). .. That is, it is possible to calculate the duty ratio Drev obtained by the light receiving element 232 with a voltage value closer to the target voltage Vtgt than the voltage value Vnext actually detected when the duty ratio Dtgt is input to the light emitting element 231.

In this embodiment, the duty ratio Dnow is also referred to as a first drive voltage, and Vnow is also referred to as a first output voltage. The duty ratio of the intercept Lth is also referred to as a second drive voltage, and the dark voltage Vdark is also referred to as a second output voltage. The duty ratio Dtgt is also referred to as a third drive voltage, and the target voltage Vtgt is also referred to as a third output voltage. The duty ratio Drev is also referred to as a fourth drive voltage, and Vnext is also referred to as a fourth output voltage.

First, the light receiving element 232 receives light in the color shift and density shift correction calibration using a graph showing the voltage value input to the light receiving element 232 when the light emitting element 231 shown by the dotted line 1500 has ideal LED current characteristics. The target voltage Vtgt to be calculated is calculated. That is, the voltage value Vtgt obtained by the light receiving element 232 when the duty ratio Dtgt calculated using the above [Equation 1] is input to the light emitting element 231 is obtained by using the following [Equation 6]. It is a graph showing the voltage value input to the light receiving element 232 when the light emitting element 231 shown by the dotted line 1500 has the ideal LED current characteristic, and the proportional relationship shown by [Equation 6] is also referred to as the fourth proportional relationship. Refer to.
Vtgt = Vnow × (Dtgt-Lth) / (Dnow-Lth) ... [Equation 6]

Next, as shown in [Equation 7] below, by substituting the target voltage Vtgt calculated in [Equation 6] into the mathematical formula showing the broken line 1501 which is a line connecting the points 1510 and 1511 on the graph. , The corrected duty ratio Drev is obtained. The proportional relationship shown by the broken line 1501 and [Equation 7] is also referred to as a fifth proportional relationship.
Drev = (Dtgt-Dnow) × (Vtgt-Vnow) / (Vnext-Vnow) + Dnow ... [Number 7]

In this embodiment, the intercept Lth and the dark voltage Vdark are used when calculating the target voltage Vtgt, but any duty ratio Dx between the intercept Lth and the duty ratio Dx and the voltage Vx corresponding to the duty ratio Dx are used. And may be used to calculate the target voltage Vtgt. The formula [Equation 6'] used at this time is described below. At this time, the duty ratio Dx may be referred to as a second drive voltage, and the voltage Vx may be referred to as a second output voltage.
Vtgt = (Vnow-Vx) × (Dtgt-Dx) / (Dnow-Dx) ... [Number 6']

By the method described above, the duty ratio Drev corrected for Dtgt obtained as a result of the light amount adjustment can be obtained.

Subsequently, the color shift correction calibration performed in this embodiment will be described with reference to FIGS. 11B and 12. FIG. 11B is a diagram showing the timing of performing the light amount adjustment and the correction of the light amount adjustment when the color shift correction calibration is executed. FIG. 11B is different from the conventional color shift correction calibration diagram shown in FIG. 6B in that the light intensity adjustment is corrected in T1603. Further, the difference is that the light emitting element 231 is made to emit light by using the duty ratio Dtgt, and the light amount adjustment correction pattern 1400 formed on the intermediate transfer belt 30 is detected. Further, FIG. 12 is a flowchart showing a process executed by the CPU 211 in the color shift correction calibration in this embodiment. Of FIG. 12, the same configuration as that of FIG. 7 is given the same number and a part of the description is omitted.

First, at the timing T1601 of FIG. 11B, the process is started from S700 of FIG. S700 to S704 are the same as in Example 2. The timing T1602 in FIG. 11B is the timing at which the CPU 211 calculates the duty ratio Dtgt in S704.

In S1200, the CPU 211 cleans the color shift correction pattern 400 formed on the intermediate transfer belt 30. When the CPU 211 completes the post-processing such as cleaning described in the above-mentioned <post-processing>, the CPU 211 advances the processing to S1701.

In S1201, the CPU 211 inputs the duty ratio Dtgt to the light emitting element 231 and starts light emission. When the light emitting element 231 is made to emit light, the CPU 211 advances the process to S1202. The CPU 211 may wait for processing for, for example, 3 seconds as a time during which the light amount of the light emitting element 231 to which the duty ratio Dtgt is input stabilizes after the light emitting element 231 is made to emit light. At this time, the CPU 211 previously forms the light amount adjustment correction pattern 1400 on the intermediate transfer belt 30 by the image forming unit so that the pattern detection can be started from S1202.

In S1202, the CPU 211 detects the light amount adjustment correction pattern 1400 formed on the intermediate transfer belt 30 by the optical sensor unit 70. At this time, the duty ratio Dtgt is input to the light emitting element 231 to emit light, and the voltage value Vnext when the light amount adjustment correction pattern 1400 is detected by the light receiving element 232 is detected by the voltage detecting means. When the CPU 211 detects that the light amount adjustment correction pattern 1400 has passed through the optical sensor unit 70, the process proceeds to S1203.

In S1203, the CPU 211 corrects the light amount adjustment using [Equation 6] and [Equation 7] to calculate Drev. When the CPU 211 calculates the Drev, the process proceeds to S708. Since S708 and S709 are the same as those in the second embodiment, the description thereof will be omitted.

As described above, in the present embodiment, not only the individual difference of the light emitting element and the LED characteristics, but also the influence of the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30. In consideration of the above, the light amount adjustment can be corrected. As a result, the duty ratio Drev can be calculated in consideration of not only the LED characteristics of the light emitting element 231 but also the state of the color shift correction pattern 400 formed on the intermediate transfer belt 30 and the state of the surface of the intermediate transfer belt 30. Further, while reducing the cost by providing the light emitting element voltage detection unit 224-1 and 233-1 and the light emitting element current detection unit 224-2, 233-2, the drive calculated with the desired light emission amount of the light emitting element 231. It is possible to prevent the difference from the actual amount of light emitted according to the signal from becoming larger than before. Further, as in the second embodiment, the CPU 211 executes to correct the Drev by calculating the Drev in order to obtain a desired light emission amount by using not only the measured value but also the proportional calculation and the measured value. It is possible to suppress the repetition of processing and suppress the load applied to the CPU 211.

[Modification of Example 3]
In Example 1 or 2, a duty ratio Drev for obtaining a desired light emission amount was obtained by using a current detecting means. In Example 3, a voltage corresponding to the amount of diffuse reflected light reflected by the color shift correction pattern 400 formed on the intermediate transfer belt 30 is detected, and a desired amount of light is emitted according to the obtained measured value. The duty ratio Drev for obtaining the above was calculated. In the modification of the third embodiment, the toner patch is not used to calculate the duty ratio Dtgt, and the specular reflected light receiving element 222 for receiving the specular reflected light reflected from the intermediate transfer belt 30 is used as the light receiving means. Is also good. In this case, the amount of light is adjusted according to the actually measured value obtained by using the specularly reflected light receiving element 222, and the duty for obtaining a desired voltage value required for calibration is calculated. In the modified example of the third embodiment, the state of the intermediate transfer belt 30 needs to be stable while the light receiving element 222 receives the specularly reflected light. Therefore, for example, if there is dust between the intermediate transfer belt 30 and the drive roller, or a belt made of a material that is not easily affected by disturbance is used. By using this method, it is possible to calculate the duty ratio Drev in consideration of not only the LED characteristics of the light emitting element 231 but also the state of the surface of the intermediate transfer belt 30.

Claims (12)

A rotating body that supports a toner image or recording material,
An image forming means for forming a detection pattern, which is a toner image used for detecting a color shift amount or a density shift amount, on the rotating body, and an image forming means.
A pattern detecting means having a light emitting means for irradiating the rotating body or the detection pattern with light, and a light receiving means for receiving the light reflected from the rotating body or the detection pattern.
A current detecting means for detecting a current flowing through the light emitting means according to a drive voltage input to the light emitting means is provided.
An image forming apparatus comprising a control means for controlling a drive voltage according to a detection result by the current detecting means. When the current value detected by the current detecting means is smaller than the target current, which is the current value flowing through the light emitting means when the light emitting amount is required when detecting the color shift amount or the density shift amount. The image forming apparatus according to claim 1, wherein the control means increases a drive voltage input to the light emitting means. When the current value detected by the current detecting means is larger than the target current, which is the current value flowing through the light emitting means when the light emitting amount is required when detecting the color shift amount or the density shift amount. The image forming apparatus according to claim 1 or 2, wherein the control means reduces the drive voltage input to the light emitting means. The current detecting means detects a first current value flowing through the light emitting means when the controlling means inputs a first driving voltage to the light emitting means, and the controlling means second drives the light emitting means. When a voltage is input, the second current value flowing through the light emitting means is detected, and the voltage is detected.
The control means has the color shift amount according to the information regarding the proportional relationship calculated by using the first current value, the first drive voltage, the second current value, and the second drive voltage. The image forming apparatus according to any one of claims 1 to 3, further comprising calculating a target drive voltage when the amount of light emitted is required when detecting a density shift amount. Have a memory,
When the control means overwrites the value of the drive voltage stored in the storage means with the value of the target drive voltage and stores the value, and then detects the amount of color shift or the amount of density shift, the storage means. The image forming apparatus according to any one of claims 1 to 3, wherein the target drive voltage stored in the light emitting means is input to the light emitting means. Have a memory,
Each time the control means detects a current value flowing through the light emitting means according to an arbitrary driving voltage by the current detecting means, the control means flows through the light emitting means according to the arbitrary driving voltage and the arbitrary driving voltage. The image forming apparatus according to any one of claims 1 to 3, wherein the current value is stored in the storage means. A rotating body that supports a toner image or recording material,
An image forming means for forming a detection pattern, which is a toner image used for detecting a color shift amount or a density shift amount, on the rotating body, and an image forming means.
A pattern detecting means having a light emitting means for irradiating the rotating body or the detection pattern with light, and a light receiving means for receiving the light reflected from the rotating body or the detection pattern.
A current detecting means for detecting a current flowing through the light emitting means according to a drive voltage input to the light emitting means, and a current detecting means.
A voltage detecting means for detecting an output voltage output by the light receiving means, and a voltage detecting means.
The pattern detecting means includes a control means for controlling a drive voltage input to the light emitting means when the pattern detecting means detects the amount of color shift.
The voltage detecting means detects the first output voltage output by the light receiving means when the first driving voltage is input to the light emitting means.
The current detecting means detects a first current value flowing through the light emitting means when a first driving voltage is input to the light emitting means.
When the relationship between the drive voltage input to the light emitting means and the output voltage output by the light receiving means is proportional, the control means has the first drive voltage, the first output voltage, and the like. The amount of color shift or the amount of color shift is based on the information on the first proportional relationship calculated by using the second drive voltage smaller than the first drive voltage and the second output voltage corresponding to the second drive voltage. A third drive voltage is calculated so that the output voltage output by the light receiving means becomes the third output voltage when the concentration deviation amount is detected.
When the relationship between the drive voltage input to the light emitting means and the current flowing through the light emitting means is proportional, the control means has the first drive voltage, the first current value, and the second. When the detection of the color shift amount or the density shift amount is executed based on the information regarding the second proportional relationship calculated by using the drive voltage of the above and the second current value corresponding to the second drive voltage. When the third drive voltage is input to the light emitting means, the third current value that is expected to flow to the light emitting means is calculated.
The current detecting means detects a fourth current value flowing through the light emitting means when the third driving voltage is input to the light emitting means.
The control means has the color shift based on the information regarding the third proportional relationship calculated by using the first drive voltage, the third drive voltage, the first current value, and the fourth current value. An image forming apparatus, characterized in that a fourth drive voltage is calculated in which a current flowing through the light emitting means becomes the third current value when detecting an amount or a concentration deviation amount. When the drive voltage input to the light emitting means is smaller than a predetermined drive voltage, the relationship between the drive voltage input to the light emitting means and the current flowing through the light emitting means becomes a proportional relationship and is input to the light emitting means. The image forming apparatus according to claim 7, wherein when the drive voltage is larger than a predetermined drive voltage, the relationship between the drive voltage input to the light emitting means and the current flowing through the light emitting means is not proportional. .. The image forming apparatus according to claim 8, wherein the control means calculates the fourth drive voltage when the drive voltage input to the light emitting means is larger than the predetermined drive voltage. Have a memory,
When the control means overwrites the drive voltage stored in the storage means with the fourth drive voltage and stores the drive voltage, and then detects the color shift amount or the density shift amount, the storage means stores the drive voltage. The image forming apparatus according to any one of claims 7 to 9, wherein a stored fourth drive voltage is input to the light emitting means. Have a memory,
Any of claims 7 to 9, wherein the control means stores the third current value in the storage means each time the third current value is calculated by the third drive voltage. The image forming apparatus according to one item. A rotating body that supports a toner image or recording material,
An image forming means for forming a detection pattern, which is a toner image used for detecting a color shift amount or a density shift amount, on the rotating body, and an image forming means.
A pattern detecting means having a light emitting means for irradiating the rotating body or the detection pattern with light, and a light receiving means for receiving the light reflected from the rotating body or the detection pattern.
A voltage detecting means for detecting an output voltage output by the light receiving means, and a voltage detecting means.
The pattern detecting means includes a control means for controlling a drive voltage input to the light emitting means when the pattern detecting means detects the color shift amount or the density shift amount.
The voltage detecting means detects a first output voltage output by the light receiving means when a first driving voltage is input to the light emitting means.
When the relationship between the drive voltage input to the light emitting means and the output voltage output by the light receiving means is proportional, the control means has the first drive voltage, the first output voltage, and the like. The amount of color shift or the amount of color shift is based on the information on the first proportional relationship calculated by using the second drive voltage smaller than the first drive voltage and the second output voltage corresponding to the second drive voltage. A third drive voltage is calculated so that the output voltage output by the light receiving means becomes the third output voltage when the concentration deviation amount is detected.
The voltage detecting means detects a fourth output voltage output by the light receiving means when the third driving voltage is input to the light emitting means.
The control means has the color shift based on information on a fourth proportional relationship calculated using the first drive voltage, the third drive voltage, the first output voltage, and the fourth output voltage. An image forming apparatus, characterized in that a fourth drive voltage is calculated in which a voltage output by the light receiving means becomes the third output voltage when detecting an amount or a concentration deviation amount.

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