JP2016004117A - Image forming apparatus, control method thereof, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce density unevenness of an image even if SD gap is changed with time.SOLUTION: A CPU 208 generates a correction table for correcting a developing DC voltage, on the basis of a displacement average value of an AC current detection signal output by an A/D conversion circuit, develops a patch image with a predetermined density, on a photoreceptor drum 1, by use of the developing DC voltage corrected by superimposing a gain value on the correction table, and changes the gain value to a value one step larger (step S204) when toner concentration of the developed patch image is out of a predetermined range (NO in step S203).

Description

  The present invention relates to an image forming apparatus, a control method therefor, and a program, and more particularly, to an electrophotographic image forming apparatus, a control method therefor, and a program.

  As a development technique of an electrophotographic image forming apparatus, a sine wave, a rectangular wave, or an image carrier on which an electrostatic latent image is formed and a developer carrier provided with a predetermined gap (SD gap) There is a technique in which a developing bias voltage in which an AC voltage such as a triangular wave is superimposed on a predetermined DC voltage is applied, and the density of a developed image is adjusted by a potential difference between the DC voltage and a charging potential and an exposure potential in the image carrier.

  In the developing technique, for example, the SD gap fluctuates periodically due to the eccentricity of the image carrier and the eccentricity of the developer carrier. As a result, the electric field strength between the image carrier and the developer carrier periodically changes to fluctuate the potential difference, resulting in density unevenness in the developed image.

  In order to reduce the density unevenness of the developed image, for example, in Patent Document 1, a current component corresponding to the AC voltage component of the development bias voltage is detected, and the DC voltage component is controlled based on the detected current component. The In Patent Document 2, the value of the current flowing by applying the developing bias voltage is subjected to an FFT analysis, and the SD generated by the eccentricity of the image carrier or the developer carrier from the FFT-analyzed current value. A frequency component representing the variation of the gap is extracted. Furthermore, in Patent Document 2, a signal having a phase opposite to that of the extracted frequency component is generated, and the developing bias voltage is corrected by superimposing the generated negative phase signal on the developing bias voltage, so that the SD gap varies. This reduces density unevenness in the developed image.

JP-A-9-54487 JP 2008-287075 A

  However, in the conventional image forming apparatus, for example, after the development bias voltage is corrected, the temperature in the image forming apparatus rises in the printing process of the image forming apparatus, whereby the configuration of the image carrier is configured. The members and the constituent members of the developer carrier are thermally expanded. As a result, the SD gap may change with time after the development bias voltage is corrected, and the SD gap with time may cause density unevenness of the developed image.

  An object of the present invention is to provide an image forming apparatus, a control method therefor, and a program that can reduce density unevenness of an image even when an SD gap changes with time.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image carrier that carries an electrostatic latent image, a predetermined gap between the image carrier and a development bias voltage applied to the image carrier. An image forming apparatus having a developer carrying member for developing a developer for developing the electrostatic latent image, the density detecting unit detecting the density of the developer in the developed electrostatic latent image; Current value detecting means for detecting a current value flowing from the developer carrying member to the image carrier when a developing bias voltage is applied, and for correcting the developing bias voltage based on the detected current value Using correction table generation means for generating a correction table, storage means for storing the generated correction table and a gain value having a predetermined control range, the stored correction table and the stored gain value A first correcting means for correcting the developing bias voltage; a density setting means for setting the density of the developer; and a developing bias corrected by the first correcting means corresponding to the set density of the developer. A developing unit for developing the electrostatic latent image by applying a voltage to the developer carrying member, and a second unit for correcting the developing bias voltage again by changing the gain value used by the first correcting unit. A correction unit; and a determination unit that determines whether or not the concentration of the developer of the electrostatic latent image developed by the development unit is within a predetermined region, and the second correction unit includes the development unit. When the density of the developer in the electrostatic latent image is out of a predetermined area, the gain value used by the first correction unit is changed to correct the development bias voltage again. To do.

  According to the present invention, the developing bias voltage corrected using the correction table and the gain value corresponding to the set developer density is applied to the developer carrying member to develop and develop the electrostatic latent image. When the developer density of the electrostatic latent image deviates from a predetermined area, the gain value is changed and the developing bias voltage is corrected again. Therefore, even if the SD gap changes with time due to a predetermined number of printing processes or the like. Density unevenness of the developed image can be reduced. Further, the developer density of the developed electrostatic latent image can be returned to a predetermined area by changing only the gain value and correcting the development bias voltage again without regenerating the correction table. The density unevenness of the developed image can be easily reduced.

1 is a diagram schematically showing an internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view schematically showing a configuration of an image forming unit in FIG. 1. FIG. 2 is a block diagram schematically illustrating a configuration of a developing bias control unit of the image forming unit in FIG. 1. It is a figure used in order to explain the development bias voltage generated by the development high voltage part in FIG. It is a figure used in order to explain the cause of density unevenness of a developed image. FIG. 4 is a diagram used for explaining a current value detected by an AC current detection circuit in FIG. 3, where (a) represents a drive signal output by a CPU, and (b) is detected by an AC current detection circuit. (C) represents the output signal output by the ripple component amplifier circuit. It is a flowchart which shows the procedure of the development DC voltage correction process performed by CPU in FIG. It is a figure used in order to demonstrate the average value for every block of the AC electric current detection signal output by the A / D conversion circuit in FIG. FIG. 8 is a diagram used for explaining the moving average value of the AC current detection signal output by the A / D conversion circuit in FIG. 3, wherein (a) represents the data of the average value of the AC current detection signal in FIG. (B) represents data obtained by moving and averaging the AC current detection signals. FIG. 8A is a diagram used for explaining the development DC voltage corrected using the correction table generated in step S104 of FIG. 7, and (a) is applied by the development bias voltage and output by the A / D conversion circuit. (B) represents the development DC voltage before correction, and (c) represents the development DC voltage after correction. It is a flowchart which shows the procedure of the correction effect confirmation process in the development DC voltage correction process of FIG. It is a flowchart which shows the procedure of the correction effect confirmation process in the development DC voltage correction process of FIG. It is a figure used in order to demonstrate the gain value in the correction effect confirmation process of FIG. FIG. 12 is a diagram used for explaining density characteristics for each toner density of a patch image in the correction effect confirmation processing of FIG. 11. FIG. 12 is a diagram used for explaining a patch image in the correction effect confirmation processing of FIG. 11, (a) showing a photosensitive drum and a patch density sensor, (b) showing a patch image developed on the photosensitive drum, (C) represents the HP detection signal, and (d) represents the output voltage of the patch density sensor for each block of the patch image. It is a figure used in order to explain the modification of the patch image in the correction effect confirmation processing of FIG. FIGS. 8A and 8B are diagrams used for explaining density unevenness of a developed image corrected by the development DC voltage correction processing of FIG. 7, where FIG. 8A shows the density of the developed image before correction, and FIG. Represents the density of the image.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically showing an internal configuration of an image forming apparatus 1000 according to an embodiment of the present invention.

  The image forming apparatus 1000 of FIG. 1 includes an image forming unit 300, a sheet feeding unit 301, an operation unit 302, a reader scanner unit 303, and a paper discharge processing unit 304. The image forming apparatus 1000 forms an image by the image forming unit 300 based on the sheet processing setting information set by the user through the operation unit 302 and the image information transmitted from the reader scanner unit 303, and the paper discharge processing unit. A printed matter is output by 304.

  The image forming unit 300 includes a laser scanner unit 7 and an image forming unit 307. The image forming unit 307 includes the photosensitive drum 1 (image carrier), the developing unit 3, the intermediate transfer belt 8, and the fixing unit 13. The sheet feeding unit 301 includes sheet feeding units 311 and 312 having a storage 11 and 372, respectively, and a conveyance sensor 350.

  The sheet feeding unit 301 feeds the sheets stored in the respective storages 11 and 372 based on a sheet request notification from the image forming unit 300. Upon receiving the sheet request notification, the sheet feeding unit 301 conveys the sheet to the conveyance sensor 350 and notifies the image forming unit 300 that preparation for sheet delivery has been completed. In response to this notification, the image forming unit 300 issues a sheet delivery request notification to the sheet feeding unit 301. Each time the sheet feeding unit 301 receives a sheet delivery request notification, the sheet feeding unit 301 conveys the sheet to the image forming unit 300 one by one.

  The image forming unit 300 forms an image on the sheet conveyed from the sheet feeding unit 301. Specifically, the image forming unit 300 emits laser light to an image forming unit 307 (to be described later) by the laser scanner unit 7 based on the image data read by the reader scanner unit 303, and electrostatic latent images are formed on the photosensitive drum 1. Form an image. The electrostatic latent image on the photosensitive drum 1 is developed by the developing unit 3 to form a toner image, and the toner image is transferred to the sheet. The transferred sheet is conveyed to a fixing unit 13, and the fixing unit 13 melts toner (developer) by heat and pressure to fix the toner image on the sheet.

  The paper discharge processing unit 304 includes a paper discharge tray 360 and is provided on the downstream side of the image forming apparatus 1000 where the sheet is conveyed. The paper discharge processing unit 304 performs processing set by the user using the operation unit 302 on the sheet on which the toner image is fixed by the image forming unit 300, for example, “folding”, “stapling”, and “hole punching”. The output sheet is output to the paper discharge tray 360.

  FIG. 2 is an enlarged view schematically showing the configuration of the image forming unit 307 in FIG.

  In addition to the photosensitive drum 1, the developing unit 3, the intermediate transfer belt 8, and the fixing unit 13, the image forming unit 307 in FIG. 2 includes a primary charger 2, a developing sleeve 3 a (developer carrying member), a primary transfer roller 4, A laser scanner unit 7, a secondary transfer unit 9, and a drum home position sensor 10 are included. The photosensitive drum 1 and the developing sleeve 3a are arranged with a predetermined gap (SD gap) therebetween.

  The photosensitive drum 1 is driven to rotate about the rotation axis of the photosensitive drum 1. The primary charger 2 charges the surface of the photosensitive drum 1. The drum home position sensor 10 detects the rotational phase of the photosensitive drum 1 and generates an HP detection signal every time the photosensitive drum 1 rotates once.

  The image forming unit 307 forms an electrostatic latent image on the photosensitive drum 1 by the laser light emitted from the laser scanner unit 7. The developing unit 3 develops the electrostatic latent image into a toner image on the photosensitive drum 1 when a developing bias voltage generated by a developing bias control unit 220 described later is applied to the rotationally driven developing sleeve 3a. . The developed toner image is primarily transferred as a toner image T onto the intermediate transfer belt 8 by the primary transfer roller 4 and conveyed to the secondary transfer unit 9. The secondary transfer unit 9 secondarily transfers the toner image T onto the sheet S conveyed from the sheet feeding unit 301. The photosensitive drum 1 and the drum home position sensor 10 constitute a development bias controller 220 described later.

  FIG. 3 is a block diagram schematically showing the configuration of the developing bias controller 220 of the image forming unit 300 in FIG.

  The developing bias control unit 220 in FIG. 3 includes a developing high voltage unit 200, a control unit 205, and a patch density sensor 210 in addition to the photosensitive drum 1 and the drum home position sensor 10.

  The development high voltage unit 200 includes an AC high voltage drive circuit 201, an AC transformer 202, a DC high voltage circuit 203, an AC current detection circuit 204 (current value detection means), a ripple component amplification circuit 209, a capacitor C1, and an output resistance R. The control unit 205 includes an A / D conversion circuit 206, D / A conversion circuits 207 and 211, a CPU 208 having a memory, and a superimposing circuit 212.

  The drum home position sensor 10 and the patch density sensor 210 are connected to the CPU 208, respectively. The CPU 208 is connected to the A / D conversion circuit 206 and the D / A conversion circuits 207 and 211, respectively. The D / A conversion circuits 207 and 211 are connected to the superimposing circuit 212, respectively. A CPU 208 is connected to the AC high voltage drive circuit 201 of the developing high voltage unit 200, a superimposing circuit 212 is connected to the DC high voltage circuit 203, and an A / D conversion circuit 206 is connected to the ripple component amplifier circuit. The AC high voltage drive circuit 201 is connected to the output resistor R through the AC transformer 202 and is connected to the AC current detection circuit 204 through the DC high voltage circuit 203 and the capacitor C1. The AC current detection circuit 204 is connected to the ripple component amplification circuit 209. The output resistor R is connected to the developing sleeve 3a.

  The CPU 208 generates a correction table for correcting a later-described developing DC voltage based on an AC current detection signal described later, and stores the correction table in a memory (not shown) in the CPU 208. The CPU 208 outputs a signal corresponding to the stored correction table and a gain value stored in advance in the memory of the CPU 208 to the superimposing circuit 212 and outputs a drive signal for generating a development AC voltage to the development high-voltage unit 200. The superimposing circuit 212 outputs an output setting signal, which is a signal obtained by superimposing the gain value output from the CPU 208 to the signal corresponding to the correction table for correcting the development DC voltage output from the CPU 208, to the DC high voltage circuit 203.

  The AC high voltage drive circuit 201 generates a development AC voltage based on the drive signal output by the CPU 208. The DC high voltage circuit 203 generates a development DC voltage based on the output setting signal output by the superimposing circuit 212. The development high voltage unit 200 generates a development bias voltage by superimposing the development DC voltage on the development AC voltage. The generated developing bias voltage is applied to the developing sleeve 3a. As shown in FIG. 4, the development bias voltage in the present embodiment is a voltage obtained by superimposing a development DC voltage of 300 V on a development AC voltage that is a rectangular wave having a frequency of 2.7 kHz and an amplitude of 1500 V, for example.

In this embodiment, the density of the dark portion of the developed image is controlled by the potential difference V _cont (FIG. 5) between the charging potential V _d and the developing DC voltage V _dc in the photosensitive drum 1, and the developing DC voltage V _dc and the photosensitive drum 1 The density of the bright part of the developed image is controlled by the potential difference V _back (FIG. 5) with the exposure potential V ₁ .

By the way, in the photosensitive drum 1, density unevenness occurs in the developed image due to variations in the potential difference V _cont and the potential difference V _back . Correspondingly, in the present embodiment, for example, when the SD gap widens and the potential difference V _cont becomes small, the potential difference V _cont is increased by correcting the development DC voltage V _dc to decrease, and the SD gap Is narrowed and the potential difference V _cont becomes large, the potential difference V _cont is reduced by correcting the development DC voltage V _dc to be increased. As described above, in this embodiment, by correcting the development DC voltage V _dc , fluctuations in the potential difference V _cont and the potential difference V _back are suppressed, and density unevenness in the developed image is reduced.

  Returning to FIG. 3, the AC current detection circuit 204 detects the value of the current flowing through the circuit 213 of the electrostatic capacitance CL via the AC transformer 202 and the output resistor R. A circuit 213 is an electrical equivalent circuit of the SD gap between the developing sleeve 3 a and the photosensitive drum 1. That is, the AC current detection circuit 204 detects a current value flowing between the developing sleeve 3 a and the photosensitive drum 1. In the present embodiment, the change in the SD gap between the developing sleeve 3a and the photosensitive drum 1 can be detected by an AC current detection signal (to be described later) obtained by A / D converting the current value.

  When the developing bias voltage is applied to the developing sleeve 3a and the driving signal having the waveform shown in FIG. 6A is output by the CPU 208, the AC current detecting circuit 204 is connected to a point A of the AC current detecting circuit 204. In FIG. 6, a current value like the waveform shown in FIG. 6B is detected. The detected current value is output to the A / D conversion circuit 206 as an output signal in which only the ripple component is amplified by the ripple component amplifier circuit 209 as shown in the waveform of FIG. The A / D conversion circuit 206 converts the output signal output from the ripple component amplification circuit 209 from an analog signal to a digital signal, and outputs the converted signal to the CPU 208 as an AC current detection signal.

  The patch density sensor 210 includes a light emitting unit such as an LED and a light receiving unit. The light emitting unit applies light to a patch image (described later) on the photosensitive drum 1, and the light receiving unit receives reflected light from the patch image. When the toner density of the patch image is high, a part of the reflected light is absorbed by the toner, so that the amount of reflected light detected by the light receiving unit is reduced. On the other hand, when the toner density of the patch image is low, the amount of reflected light detected by the light receiving unit increases. The patch density sensor 210 outputs an output signal of a voltage corresponding to the amount of reflected light received by the light receiving unit to the CPU 208.

  FIG. 7 is a flowchart showing the procedure of the development DC voltage correction process executed by the CPU 208 in FIG.

  The processing in FIG. 7 is executed by the CPU 208 at the start of printing. The processing of FIG. 7 detects a change in the SD gap from the AC current detection signal output by the A / D conversion circuit 206, and generates a correction table for correcting the development DC voltage based on the output AC current detection signal. Further, the development DC voltage is corrected by superimposing a gain value described later on the generated correction table.

  In FIG. 7, first, a developing bias voltage is applied to the developing sleeve 3a (step S101). Next, the AC current detection signal output by the A / D conversion circuit 206 is read in synchronization with the HP detection signal from the drum home position sensor 10 (step S102). The AC current detection signal is an A / D converted signal obtained by amplifying only the ripple component of the current value detected by the AC current detection circuit 204 by the ripple component amplification circuit 209 (see FIG. 6C).

  Next, the moving average value of the AC current detection signal described later is calculated by moving average of the AC current detection signal read in step S102 (step S103).

In step S103, the AC current detection signal is divided into equal blocks a0 to a19 for each rotation of the photosensitive drum 1, based on the HP detection signal from the drum home position sensor 10, as shown in FIG. The average value is calculated for each of the divided blocks a0 to a19. Further, the calculated average value of each block a0 to a19 is moved by the following equation (1) using the average value data (FIG. 9 (a)) of the blocks a0 to a19 for 20 revolutions of the photosensitive drum 1. An average value IsnsMA (n) is calculated. The data of the calculated moving average value IsnsMA (n) is represented in FIG. Isns (n) _m represents an average value in the block an of the m-th cycle, and the an represents the 20 divided block names a0 to a19.

IsnsMA (n) = (Isns (n) _m + Isns (n) _{m + 1} +... + Isns (n) _{m + 19} ) / 20 (1)
Returning to FIG. 7, based on the moving average value calculated in step S103, a correction table for correcting the development DC voltage is generated in synchronization with the HP detection signal from the drum home position sensor 10 (step S104) ( Correction table generation means). The correction table is generated for each block a0 to a19.

  The development DC voltage is represented in FIG. 10C by the correction table, for example, from the waveform represented in FIG. 10B corresponding to the AC current detection signal represented in FIG. It is corrected like a waveform.

  Returning to FIG. 7, the generated correction table is stored in the memory in the CPU 208 (step S105) (storage means), and the developing bias voltage is turned off (step S106). Next, the correction effect confirmation process of FIG. 11 described later is executed, and the toner density of the patch image developed using the developed DC voltage corrected by superimposing a gain value described later on the correction table stored in step S105. The effect of the above correction is detected (step S107), and a developing bias voltage based on the developing DC voltage for which the effect of the correction is confirmed in step S107 is applied to the developing sleeve 3a (step S108). After performing (step S109), this process is complete | finished.

  11A and 11B are flowcharts showing the procedure of the correction effect confirmation process in the development DC voltage correction process of FIG.

  The processing in FIGS. 11A and 11B is executed by the CPU 208.

  After the correction table is stored in step S105, the photosensitive drum 1 and the developing sleeve 3a are thermally expanded due to a rise in temperature in the image forming apparatus 1000, for example, in a printing process of the image forming apparatus 1000, and as a result. The SD gap changes with time, resulting in uneven density of the developed image.

  Correspondingly, in the processing of FIGS. 11A and 11B, development is performed using the development DC voltage corrected by superimposing the gain value stored in advance in the memory of the CPU 208 on the correction table stored in step S105. When the toner density of the patch image is out of the predetermined range, the gain value is changed to correct the development DC voltage.

  11A and 11B, first, the gain value stored in advance in the memory in the CPU 208 is set to an initial value to set the density of the patch image to a predetermined density (step S200) (density setting means). The patch image set to the predetermined density is developed on the photosensitive drum 1 using the corrected development DC voltage by superimposing the gain value on the correction table stored in step S105 (first correction means). (Step S201) (developing means). In the present embodiment, in step 200, the gain value is set to an initial value “1.0”, for example. As shown in FIG. 12, the gain value has a control range of “0.5” to “1.5”, for example.

  The patch image has a plurality of densities (gradations). In the present embodiment, the density A, B, and C shown in FIG. 13 are provided, and in step 200, the density C is set. The patch image is uniformly developed at a position readable by the patch density sensor 210 and at a predetermined position of the photosensitive drum 1, and is represented by the photosensitive drum 1 shown in FIG. As shown, the image corresponds to one rotation of the photosensitive drum 1 having a predetermined width in the main scanning direction (rotational axis direction of the photosensitive drum 1). The width of the patch image is defined by the mounting position of the patch density sensor 210 and the detection accuracy of the patch density sensor 210.

  Returning to FIG. 11, the toner density of the patch image developed on the photosensitive drum 1 is detected by the patch density sensor 210 (step S202) (density detection means), and the toner density of the detected patch image is within a predetermined range. (Step S203) (discriminating means).

  In the present embodiment, a correction table is generated for each of the blocks a0 to a19 divided at equal intervals based on the HP detection signal represented in FIG. The toner density of the patch image is detected at a point indicated by a black circle in (b). The output voltage of the patch density sensor 210 for each of the blocks a0 to a19 is shown in FIG.

  In the present embodiment, the patch density sensor 210 outputs an output signal having a voltage corresponding to the amount of reflected light received by the light receiving unit. In step S203, the CPU 208 determines whether the voltage of the output signal of the patch density sensor 210 at the toner density of the patch image detected in step S202 is a predetermined density (for example, density C represented in FIG. 13). It is determined whether or not the output signal voltage (for example, 2.5 V) is within a range of ± 0.1 V (for example, 2.4 V to 2.6 V).

  Returning to FIG. 11, when the toner density of the detected patch image is out of the predetermined range as a result of the determination in step S203, the gain value is changed to a value larger by one step than the gain value (step S204). . In step S204, the gain value may be changed to a value smaller by one step than the gain value.

  The AC current detection signal representing the SD gap fluctuation tends to fluctuate uniformly (fluctuates by substantially the same amount) in the blocks a0 to a19 when the SD gap changes with time. For this reason, in this embodiment, only the gain value is changed without regenerating the correction table in the correction of the development DC voltage due to the time-dependent change of the SD gap.

  Next, the gain value changed in step S204 is superimposed on the correction table used in step S201 (second correction unit) and used on the photosensitive drum 1 in step S201 using the corrected development DC voltage. The density patch image is developed (step S205) (developing unit), and the toner density of the patch image developed on the photosensitive drum 1 is detected by the patch density sensor 210 (step S206) (density detection unit). It is determined whether the toner density of the patch image is within a predetermined range (step S207) (determination means).

  If the toner density of the detected patch image is out of the predetermined range as a result of the determination in step S207, the difference between the toner density of the patch image detected in step S206 and the toner density used in step S201 is determined. Then, it is determined whether or not the difference between the toner density of the patch image detected in step S202 and the toner density used in step S201 is smaller (step S208).

  As a result of the determination in step S208, the difference between the toner density of the patch image detected in step S206 and the toner density used in step S201 is used in step S201 and the toner density of the patch image detected in step S202. When the difference from the toner density is smaller, the correction effect can be obtained by setting the gain value one step larger than the gain value. Therefore, the process returns to step S204, and the gain value is further increased by one step from the gain value. Change to a larger value.

  As a result of the determination in step S208, the difference between the toner density of the patch image detected in step S206 and the toner density used in step S201 is used in step S201 and the toner density of the patch image detected in step S202. If the difference from the toner density is larger than the gain value, a correction effect cannot be obtained even if the gain value is increased. Therefore, the gain value is changed from the initial value to a value one step smaller (step S209).

  In step S209, when the gain value is changed to a value smaller by one step than the gain value in step S204, the gain value may be changed from the initial value to a value larger by one step.

  Next, the gain value changed in step S209 is superimposed on the correction table used in step S201 (second correction unit) and used on the photosensitive drum 1 in step S201 using the corrected development DC voltage. The density patch image is developed (step S210) (developing unit), and the toner density of the patch image developed on the photosensitive drum 1 by the patch density sensor 210 is detected (step S211) (density detection unit). It is determined whether the toner density of the patch image is within a predetermined range (step S212) (determination means).

  If the toner density of the detected patch image is out of the predetermined range as a result of the determination in step S212, the difference between the toner density of the patch image detected in step S211 and the toner density used in step S201 is determined. Then, it is determined whether or not the difference between the toner density of the patch image detected in step S202 and the toner density used in step S201 is smaller (step S213).

  As a result of the determination in step S213, the difference between the toner density of the patch image detected in step S211 and the toner density used in step S201 is used in step S201 and the toner density of the patch image detected in step S202. When the difference is smaller than the toner density, a correction effect can be obtained by setting the gain value one step smaller than the gain value. Therefore, the process returns to step S209, and the gain value is further increased by one step from the gain value. Change to a smaller value.

  As a result of the determination in step S213, the difference between the toner density of the patch image detected in step S211 and the toner density used in step S201 is used in step S201 and the toner density of the patch image detected in step S202. If the difference from the toner density is larger, the correction effect cannot be obtained even if the gain value is set to a small value. Therefore, the gain value is set to the initial value (step S214), and the toner density of the patch image is set in step S200. A toner density different from the set toner density is set (step S215) (density setting means), and the process returns to step S201.

  As a result of the determination in step S203, S207, or S212, when the toner density of the detected patch image is within a predetermined range, this process is terminated.

  7, 11A, and 11B, the gain value is superimposed on the correction table stored in step S105 (first correction means) and set to a predetermined density using the corrected development DC voltage. When the developed patch image is developed on the photosensitive drum 1 and the toner density of the developed patch image deviates from a predetermined area (NO in step S203), the gain value is changed and the development DC voltage is corrected again. Therefore, even if the SD gap changes with time due to a predetermined number of printing processes or the like, the density unevenness of the developed image is reduced from the waveform shown in FIG. 16A to the waveform shown in FIG. Can do. Further, the toner density of the developed patch image can be returned to a predetermined area by changing only the gain value and correcting the development DC voltage again without regenerating the correction table, so that the developed image can be easily obtained. Density unevenness can be reduced.

According to the process of FIG. 7 and FIGS. 11A and 11B, so to correct the development DC voltage of the development bias voltage, to adjust the toner concentration, the development DC voltage V _dc of the charge potential V _d and the developing bias voltage of the photosensitive drum 1 it is possible to control the potential difference _{V cont} (FIG. 5) and the potential difference _{V back} the development DC voltage _{V dc} of the developing bias voltage and the exposure potential _{V l} the photosensitive drum 1 (Figure 5) between. Thereby, the density unevenness of the developed image can be surely reduced.

  7, 11A, and 11B, the patch image is uniformly developed at a position readable by the patch density sensor 210 and at a predetermined position on the photosensitive drum 1, and is represented in FIG. In the photosensitive drum 1, as shown in FIG. 14B, the image corresponds to one rotation of the photosensitive drum 1 having a predetermined width in the main scanning direction (rotational axis direction of the photosensitive drum 1). The toner density of the patch image can be detected reliably. As a result, the correction effect can be confirmed with the toner necessary only for forming the patch image in the minimum necessary range, that is, with a small amount of toner.

  According to the processing of FIG. 7, FIG. 11A, and FIG. 11B, since the patch image has a plurality of densities (gradations), the correction effect is confirmed with the toner density of the patch image in which the correction effect is prominent among the plurality of densities. can do. Thereby, the correction effect can be confirmed efficiently.

  11A and 11B, the toner density of the patch image is changed in step S215 when density unevenness is not reduced even if the gain value is changed. However, as shown in FIG. A patch image having a different toner density may be developed for each rotation of the drum 1, and the toner density of each developed patch image may be detected, and the detected toner density of each patch image is within a predetermined range. The gain value is changed when the toner density of the predetermined patch image or the toner density of all the detected patch images out of the predetermined range is out of the predetermined range. Good. Thus, for example, at toner density C, the value representing the difference between the toner density of the patch image detected at step S206 and the toner density used at step S201 in step S208 is the patch image detected at step S202. Even if the correction effect cannot be confirmed because the value is almost the same as the value representing the difference between the toner density of the toner and the toner density used in step S201, the toner density A has two values representing the difference. Thus, a difference is generated and the correction effect can be confirmed. Thereby, the correction effect can be confirmed with certainty.

  11A and 11B, the toner density of the patch image primarily transferred to the intermediate transfer belt 8 may be detected by a patch density sensor that detects the toner density on the intermediate transfer belt 8. Accordingly, it is possible to detect uneven toner density in the patch image immediately before being transferred to the sheet S. Thus, after the patch image is developed by correcting the development DC voltage, the patch image is transferred to the intermediate transfer belt. Thus, the correction can be performed in consideration of density unevenness that occurs before the image is transferred to the image data 8.

  Further, in the processes of FIGS. 11A and 11B, the above-described processes are executed at the start of printing. However, when the image forming apparatus 1000 is turned on, the print job is executed after the door of the image forming apparatus 1000 is opened and closed. It may be executed before and after, during execution of a print job, or after a predetermined number of sheets have been printed. That is, the correction effect may be confirmed at a desired timing, thereby improving user convenience.

  In the present embodiment described above, the correction table for the development DC voltage is stored in the memory in the CPU 208, but the correction table may be stored in a RAM, which is a CPU peripheral circuit, or a register in the ASIC or FPGA.

  In the present invention, software (program) for realizing the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and the computer (or CPU, MPU, etc.) of the system or apparatus. It may be realized by executing a process of reading and executing a program, or may be realized by executing software (program) acquired via a network or various storage media on a personal computer (CPU, processor). Good.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3a Developing sleeve 10 Drum home position sensor 200 Developing high voltage part 201 AC high voltage drive circuit 202 AC transformer 203 DC high voltage circuit 204 AC current detection circuit 205 Control part 206 A / D conversion circuit 207, 211 D / A conversion circuit 208 CPU
209 Ripple component amplification circuit 210 Patch density sensor 212 Superimposition circuit

Claims (9)

An image carrier that carries an electrostatic latent image, and a developer carrier that is disposed with a predetermined gap between the image carrier and a developer that applies a developing bias voltage to develop the electrostatic latent image. An image forming apparatus having a body,
Density detecting means for detecting the density of the developer of the developed electrostatic latent image;
Current value detection means for detecting a current value flowing from the developer carrier to the image carrier when the development bias voltage is applied;
Correction table generating means for generating a correction table for correcting the development bias voltage based on the detected current value;
Storage means for storing the generated correction table and a gain value having a predetermined control range;
First correction means for correcting a developing bias voltage using the stored correction table and the stored gain value;
A density setting means for setting the density of the developer;
Developing means for developing the electrostatic latent image by applying a developing bias voltage corrected by the first correcting means corresponding to the set developer density to the developer carrying member;
Second correction means for correcting the developing bias voltage again by changing the gain value used by the first correction means;
Determining means for determining whether or not the concentration of the developer of the electrostatic latent image developed by the developing means is within a predetermined region;
The second correcting means changes the gain value used by the first correcting means when the developer density of the developed electrostatic latent image deviates from a predetermined region. An image forming apparatus which corrects a bias voltage again.   The image forming apparatus according to claim 1, wherein the first correction unit and the second correction unit correct a DC voltage of the development bias voltage. The image carrier is driven to rotate about a rotation axis;
The electrostatic latent image developed by the developing means is developed at a position that can be detected by the density detecting means, and has a predetermined width in the rotation axis direction of the image carrier and one round of the image carrier. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a strip-shaped electrostatic latent image having a length.   The image forming apparatus according to claim 1, wherein the electrostatic latent image developed by the developing unit has a plurality of gradations.   The image forming apparatus according to claim 4, wherein the developing unit develops the electrostatic latent image having a different density each time the image carrier rotates. An intermediate transfer member for transferring an electrostatic latent image carried on the image carrier;
The image forming apparatus according to claim 1, wherein the density detecting unit detects the density of the developer in the electrostatic latent image transferred to the intermediate transfer member.   The discriminating unit is configured to perform the development when the image forming apparatus is turned on, before or after execution of a print job, during execution of a print job, after opening or closing an opening / closing door of the image forming apparatus, or after a predetermined number of images have been printed. 7. The image forming apparatus according to claim 1, wherein it is determined whether or not the developer density of the electrostatic latent image is within a predetermined area. An image carrier that carries an electrostatic latent image, and a developer carrier that is disposed with a predetermined gap between the image carrier and a developer that applies a developing bias voltage to develop the electrostatic latent image. A method for controlling an image forming apparatus having a body,
A density detection step for detecting the density of the developer in the developed electrostatic latent image;
A current value detection step of detecting a current value flowing from the developer carrier to the image carrier when the development bias voltage is applied;
A correction table generating step for generating a correction table for correcting the developing bias voltage based on the detected current value;
A storing step for storing the generated correction table and a gain value having a predetermined control range;
A first correction step of correcting a developing bias voltage using the stored correction table and the stored gain value;
A density setting step for setting the density of the developer;
A developing step of developing the electrostatic latent image by applying a developing bias voltage corrected in the first correcting step corresponding to the set developer concentration to the developer carrying member;
A second correction step of correcting the development bias voltage again by changing the gain value used in the first correction step;
A determination step of determining whether or not the developer concentration of the electrostatic latent image developed in the development step is within a predetermined region;
In the second correction step, when the developer density of the developed electrostatic latent image deviates from a predetermined region, the gain value used in the first correction step is changed and the development is performed. A method for controlling an image forming apparatus, wherein the bias voltage is corrected again. An image carrier that carries an electrostatic latent image, and a developer carrier that is disposed with a predetermined gap between the image carrier and a developer that applies a developing bias voltage to develop the electrostatic latent image. A program for causing a computer to execute a control method of an image forming apparatus having a body,
The control method of the image forming apparatus is:
A density detection step for detecting the density of the developer in the developed electrostatic latent image;
A current value detection step of detecting a current value flowing from the developer carrier to the image carrier when the development bias voltage is applied;
A correction table generating step for generating a correction table for correcting the developing bias voltage based on the detected current value;
A storing step for storing the generated correction table and a gain value having a predetermined control range;
A first correction step of correcting a developing bias voltage using the stored correction table and the stored gain value;
A density setting step for setting the density of the developer;
A developing step of developing the electrostatic latent image by applying a developing bias voltage corrected in the first correcting step corresponding to the set developer concentration to the developer carrying member;
A second correction step of correcting the development bias voltage again by changing the gain value used in the first correction step;
A determination step of determining whether the concentration of the developer of the electrostatic latent image developed in the development step is within a predetermined region;
In the second correction step, when the developer density of the developed electrostatic latent image deviates from a predetermined region, the gain value used in the first correction step is changed and the development is performed. A program characterized by correcting the bias voltage again.