JP2021186974A - Image formation device - Google Patents

Abstract

To improve writing start timing accuracy to a photosensitive drum.SOLUTION: An image formation device for scanning a photosensitive drum with light from a light source and forming an image includes: a drive control part for controlling drive of the light source; a light detection part for detecting the light from the light source, and outputting a signal; and a control part for controlling writing start timing to the photosensitive drum on the basis of the signal output from the light detection part, and controlling the drive control part so as to cause the light source to emit light in a light quantity according to a light quantity indication value. The light detection part has a gain change circuit having a plurality of gains. The gain change circuit has a first gain usable in a first light quantity region and a second gain usable in a second light quantity region including a lower light quantity region than the first light quantity region. The control part outputs a signal of selecting the first gain or the second gain of the gain change circuit to the light detection part on the basis of the light quantity indication value so as to output a signal by a target time after the light is incident on a sensor, and changes the gain change circuit to the first gain or the second gain.SELECTED DRAWING: Figure 9

Description

The present invention relates to an image forming apparatus having an optical scanning apparatus.

Conventionally, an electrophotographic image forming apparatus has an optical scanning apparatus. The optical scanning device deflects and scans the light from the light source with a rotating polymorphic mirror, and focuses the light on the surface of the photosensitive drum by the imaging optical system. The light focused on the photosensitive drum forms an electrostatic latent image on the photosensitive drum as the main scan is performed by the rotation of the rotating polymorphic mirror and the sub-scanning is performed by the rotation of the photosensitive drum.

In addition, a part of the light deflected by the rotating polymorphic mirror is input to the BD (Beam Detector) sensor, and the output signal from the BD sensor is generally used to determine the timing to start writing the electrostatic latent image to the photosensitive drum. Used. However, since the delay time of the output signal (BD signal) from the BD sensor varies depending on the amount of incident light on the BD sensor, there is a problem that a desired write start timing cannot be obtained.

Therefore, in order to suppress the delay of the BD signal within a predetermined range, Patent Document 1 detects the amount of light incident on the BD sensor and changes either the amount of light incident on the BD sensor or the sensitivity of the BD sensor. It is disclosed to perform control.

Japanese Unexamined Patent Publication No. 2007-320130

However, in order for the image forming apparatus to be able to cope with a wide range of productivity, it is required that the light amount correction range of the laser diode as a light source for emitting the laser beam in the optical scanning apparatus can be controlled over a wide range. In the case of a configuration in which light emission is performed in the image region with the light amount adjusted during the laser light amount control operation, the light amount of the laser light incident on the BD sensor that outputs the scanning timing signal in the non-image area is also corrected by the light amount of the laser diode. It is necessary to be able to detect in the light amount range corresponding to the range.

However, depending on the internal environment (temperature and humidity) of the image forming apparatus, the amount of laser light required in the image region may be less than the light amount range that can be detected by the BD sensor. In such a case, the BD sensor cannot detect the laser beam emitted from the laser diode. Therefore, the scanning timing signal is not output from the BD sensor, and the accuracy of writing start timing to the photosensitive drum may deteriorate.

Therefore, an object of the present invention is to improve the accuracy of writing start timing to the photosensitive drum without falling below the detectable region of the BD sensor, even when the productivity is wide.

In order to achieve the above object, the present invention has a light source capable of emitting light according to an image signal and a light deflection unit that deflects and scans the light from the light source with respect to the photosensitive drum, and the photosensitive drum has an image. In an image forming apparatus that scans light corresponding to a signal to form an image, the drive control unit that controls the drive of the light source and the light from the light source that has been deflected and scanned by the light deflection unit are detected to generate a signal. The drive control is performed so that the light detection unit to be output and the write start timing to the photosensitive drum are controlled based on the signal output from the light detection unit, and the light source emits light with a light amount according to the light amount indicated value. The light detection unit includes a control unit that controls the unit, and the light detection unit includes a sensor that detects light incident from the light source and a light amount region that outputs a signal by the target time after the light is incident on the sensor. It has a gain changing circuit having a plurality of usable gains, and the gain changing circuit includes a first gain that can be used in the first light amount region and a light amount region lower than the first light amount region. It has a second gain that can be used in the light amount region of 2, and the control unit instructs the light amount so that the light detection unit outputs a signal by the target time after the light is incident on the sensor. It is characterized in that a signal for selecting the first gain or the second gain of the gain changing circuit based on the value is output to the light detection unit, and the gain changing circuit is changed to the first gain or the second gain. do.

According to the present invention, it is possible to improve the accuracy of writing start timing to the photosensitive drum and improve the image reproducibility.

Cross-sectional view showing the overall configuration of the image forming apparatus Perspective view showing the configuration of LD in an optical scanning device A perspective view showing the overall configuration of the optical scanning apparatus in the image forming apparatus. Schematic diagram of the response of the BD sensor to the amount of light The figure which shows the relationship between the incident light amount and the delay time in a predetermined BD gain. The block diagram which shows the control circuit of the optical scanning apparatus of 1st Embodiment A flowchart showing a control sequence for calculating the amount of laser light of a target density. (A) (b) (c) (d) are diagrams showing an example of a table for calculating the amount of laser light at the time of image formation and a toner check pattern image. The block diagram which shows the circuit of the BD sensor part of 1st Embodiment The figure which shows the gain switching table of the BD sensor of 1st Example (A) (b) is a timing chart of the BD signal with respect to the BD gain of the first embodiment. Flow chart of BD gain selection of the first embodiment The block diagram which shows the control circuit of the optical scanning apparatus of 2nd Embodiment The block diagram which shows the circuit of the BD sensor part of 2nd Embodiment The figure which shows the gain switching table of the BD sensor of 2nd Example The figure which shows the relationship between the incident light amount and the delay time in the BD gain of 2nd Example. Flow chart of BD gain selection of the second embodiment

Hereinafter, preferred embodiments of the present invention will be exemplified in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments should be appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions. It is not intended to limit the scope of the invention to those alone.

[Example 1]
(Structure of the entire image forming apparatus)
The image forming apparatus 1 in this embodiment will be described. FIG. 1 shows the overall configuration of the image forming apparatus 1. The image forming apparatus 1 includes an optical scanning apparatus 2 (2a, 2b, 2c, 2d), an image control unit 5, a reader scanner unit 500 as an image reading unit, and an image forming unit 503 including a photosensitive drum 25 as a photoconductor. It is composed of a fixing unit 504 and a feeding / transporting unit 505.

The reader scanner unit 500 illuminates the document placed on the platen and optically reads the image of the document, converts the image into an electric signal, and generates an image signal. The image control unit 5 has an image processing unit 403 and an image signal output unit 404 (see FIG. 6), which will be described later, and controls light emission of the optical scanning device 2 (2a, 2b, 2c, 2d) and generates an image signal. ..

The image forming unit 503 rotates and drives the photosensitive drum 25, which is a photoconductor, and charges the surface of the photosensitive drum 25 by the charging device 513, which is a charging unit. In the optical scanning device 2 (2a, 2b, 2c, 2d), a light source emits light in response to the image signal to expose the surface of the charged photosensitive drum 25, thereby causing an electrostatic latent image on the surface of the photosensitive drum 25. To form. Then, the developing apparatus 512 supplies toner as a developing agent to make a latent image formed on the surface of the photosensitive drum 25 into a visualization image (toner image). The toner image formed on the surface of the photosensitive drum 25 is transferred to the intermediate transfer body 511 by the primary transfer unit 520. After that, the cleaning unit 522 performs cleaning to collect the toner remaining on the surface of the photosensitive drum without being transferred.

The image forming unit 503 realizes image forming by having four process units (image forming stations) of such a series of electrophotographic processes. The image forming unit 503 has four process units arranged in the order of yellow (Y), magenta (M), cyan (C), and black (K). The four process units sequentially execute magenta, cyan, and black image formation operations after a predetermined time has elapsed from the start of image formation at the yellow station. By this timing control, the full-color toner image is transferred to the intermediate transfer body 511. The toner image formed on the intermediate transfer body 511 is transferred by the secondary transfer unit 521 to the sheet 514 transferred from the feed / transfer unit 505. The fixing unit 504 fixes the toner image transferred to the sheet by the secondary transfer unit to the sheet 514 by heat and pressure.

The environment sensor 141 is a sensor for measuring the temperature and humidity inside the device, which is the internal environment of the image forming device 1. Further, the density sensor 142 detects the density of the toner check pattern (see FIG. 8D) formed on the intermediate transfer body 511 described later.

Further, the toner check pattern for density detection by the density sensor 142 is not limited to the one formed on the intermediate transfer body 511 which is an image carrier, but is formed on the sheet S which is a recording medium by the image forming apparatus 1. You may. When the reader scanner unit 500 reads the density detection toner check pattern formed on the sheet S by the image forming apparatus 1, the surface side on which the density detection toner check pattern of the sheet S is formed is the platen side. Install so that The toner check pattern for density detection (toner image for density detection) is composed of a plurality of toner images having different densities.

(Photosensitive drum and optical scanning device)
The optical scanning device 2 in this embodiment will be described. FIG. 2 is a perspective view showing LD201 and PD302 which are light sources in the optical scanning device 2. FIG. 3 is a perspective view showing an optical scanning device 2 as an exposure means and a photosensitive drum 25 as a photoconductor.

The optical scanning device 2 as an exposure means includes a laser diode (hereinafter referred to as LD) 201 as a light source, a collimator lens 202, an aperture 203, a cylindrical lens 204, a polygon mirror (rotating polymorphic mirror) 205 as an optical deflection unit, and an fθ lens 206. Consists of.

The LD201 used in the optical scanning device 2 in this embodiment is a light source capable of emitting light in order to form an electrostatic latent image on the photosensitive drum 25. The LD201 emits laser light a (front light) corresponding to the image data to one side (right side shown in FIG. 2). The laser beam a emitted by the LD 201 on one side is applied to the photosensitive drum 25, and a latent image corresponding to the image data is formed on the photosensitive drum 25. The LD 201 also emits laser light a'(rear light) at a constant ratio of front light (laser light a) to the other side (left side shown in FIG. 2) which is opposite to the one side. The laser beam a'emitted by the LD 201 to the other side is incident on the photodiode (hereinafter, PD) 302.

However, the configuration of LD201 is not limited to the above-mentioned configuration. For example, a part of the laser light (front light) emitted by the LD 201 on one side may be incident on the PD 302. In this case, the LD 201 is configured to emit laser light to one side and not to emit laser light to the other side.

In the optical scanning device 2, the laser light a (front light) emitted by the LD 201 is made parallel light by the collimator lens 202 and the aperture 203. Then, the laser beam a becomes an elliptical image long in the rotation axis direction of the photosensitive drum 25 by the cylindrical lens 204, and is incident on the polygon mirror 205 with a predetermined beam diameter.

The polygon mirror 205 is an optical deflection unit (rotating polymorphic mirror) that deflects and scans the laser beam a from the LD201 in the main scanning direction (the direction of the arrow shown by the dotted line in FIG. 3) with respect to the surface of the photosensitive drum 25. The polygon mirror 205 rotates at an equal angular velocity in the direction of the arrow shown in FIG. 3, and along with this rotation, the incident laser beam a (light beam) is continuously reflected at different angles. The reflected (deflected) laser beam a receives a light-collecting action by the fθ (F-theta) lens 206 and irradiates the photosensitive drum 25.

On the other hand, the fθ lens 206 corrects the distortion aberration so as to guarantee the temporal linearity of scanning in the direction of the rotation axis at the same time as focusing. Therefore, the laser beam a is coupled and scanned on the surface of the photosensitive drum 25 at a constant velocity in the direction of the rotation axis of the photosensitive drum 25 (the direction of the arrow shown by the dotted line in FIG. 3). The potential on the surface of the photosensitive drum 101 is displaced by the intensity of the irradiated laser beam.

The BD (Beam Detector) sensor 209 is a sensor that detects a part of the reflected light (laser beam a) from the polygon mirror 205 via the BD mirror 208. The detection signal (BD signal) of the laser beam a by the BD sensor 209 is used as a synchronization signal for synchronizing the rotation of the polygon mirror 205 and the writing of the image data to the photosensitive drum 25.

(Response of the output signal to the amount of incident light on the BD sensor)
Here, the responsiveness of the output signal (BD signal) to the amount of light incident on the BD sensor 209 will be described. FIG. 4 is a diagram showing the responsiveness of the output signal (BD signal) to the amount of light incident on the BD sensor 209, where the horizontal axis shows the scanning time [μs] and the vertical axis shows the sensor output voltage [V]. FIG. 4 shows a state in which light of different light amounts (first light amount, second light amount, and third light amount) emitted from the LD201 is incident on the BD sensor 209. FIG. 4 exemplifies the first light amount, the second light amount, and the third light amount as the light amount of the light emitted from the LD201. However, it is assumed that the first light amount has the largest light output, the second light amount is the second largest, and the third light amount has the smallest light output (first light amount> second light amount> third light amount). Then, in the BD sensor 209, photoelectric conversion is performed according to the amount of incident light, and the voltage is converted into the sensor output voltage. Then, it is compared with the threshold value _{Vth of} the BD sensor 209, and a digital BD signal is output. At this time, since the response of the sensor output voltage differs depending on the amount of light incident on the BD sensor 209, the output timing of the BD signal differs. Specifically, in the second light amount, there is a delay of _{time t d1} as compared with the first light amount having the largest light output. Further, in the third light amount, there is a delay of _{time t d2 as compared with the first light amount.} That is, the smaller the amount of light incident on the BD sensor 209, the slower the responsiveness, and therefore the slower the output timing of the BD signal. As shown above, the output BD signal has a predetermined delay amount depending on the amount of light incident on the BD sensor 209.

(Relationship between BD gain and delay time)
Therefore, the BD sensor 209 sets the sensitivity of photoelectric conversion (BD gain) by using the BD gain change circuit 701 (see FIG. 9) described later. FIG. 5 shows the relationship between the incident light amount [μW] incident on the BD sensor and the delay time [ns] of the BD signal output from the BD sensor when a plurality of BD gains are used. FIG. 5 shows a case where a plurality of BD gains are set to a first gain that can be used in the first light amount region and a second gain that can be used in the second light amount region. However, for the same amount of incident light, the second gain can obtain a sensor output voltage larger than that of the first gain. Therefore, the second gain can be used in a lower light amount region than the first gain with respect to the delay time target value [ns] in which the correction accuracy of the writing position at the time of image formation is determined. On the other hand, the first gain can be used in a higher light intensity region than the second gain. That is, the second light amount region in which the second gain can be used includes a light amount region lower than the first light amount region of the first gain, and the first light amount region in which the first gain can be used is the second gain. It includes a higher light intensity region than the second light intensity region.

Further, as shown in FIG. 5, it is assumed that the used light amount range (light amount region) used for image formation is larger than the usable light amount region of the first gain and the usable light amount region of the second gain. In this case, the BD gain change circuit 701 is switched to the first gain or the second gain at the BD gain switching point shown in FIG. This makes it possible to control the time from when light is incident on the BD sensor 209 to when the BD signal is output, which is always less than the delay time target value (target time) [ns] within the light amount range used. be. In this way, by selecting an appropriate BD gain according to the amount of incident light, it is possible to realize the writing position accuracy required for image formation even for a wide range of light amounts used.

(Control circuit of optical scanning device)
The control circuit of the optical scanning apparatus in this embodiment will be described. FIG. 6 is a block diagram showing a control circuit of the optical scanning device in this embodiment. This control circuit performs laser light intensity control (auto power control, hereinafter referred to as APC) in a non-image region with reference to a BD signal, and performs light emission control according to the image signal in the image region.

The operation of the control circuit will be described with reference to FIG. First, the environment sensor 141 measures the temperature and humidity inside the device, which is the internal environment of the image forming device 1. Further, the density sensor 142 detects the density of the toner check pattern (see FIG. 8D) formed on the intermediate transfer body 511 described later. The environment sensor 141 inputs the measured temperature information and humidity information inside the image forming apparatus 1 to the light amount setting unit of the CPU 401, which is a control unit. Further, the density sensor 142 inputs the detected waveform signal to the light amount setting unit 407 of the CPU 401. The light amount setting unit 407 of the CPU 410 stores the light amount indicated value in the storage unit 408 of the CPU 401 as a target value of the light amount that becomes an appropriate toner density (target density at the time of image formation).

Here, the light amount indicated value stored in the CPU 401 will be described with reference to FIGS. 6, 7, and 8.

The CPU 401, which is a control unit, acquires a light amount indicated value (target light amount) emitted from the LD201 of the optical scanning device 2 from the storage unit 408 according to the target density at the time of image formation. The light amount indicated value stored in the storage unit 408 is a light amount PWM signal for making the light amount of the LD 201 variable, is calculated by the process of FIG. 8 described below, and is stored in the storage unit 408.

By the way, in a state where the light amount PWM signal (light amount indicated value) stored in the storage unit 408 is set to 100% in advance at the factory, the resistance value of a semi-fixed resistor (not shown) is adjusted while performing APC control described later. Thereby, the light amount of LD201 is adjusted. Then, at the time of printing (at the time of image formation), the amount of light corresponding to an appropriate density is set by controlling the pulse width of the light amount PWM signal.

In the image forming apparatus, the amount of laser light is set to an appropriate density when the image forming speed changes or the surrounding environment changes, when the power of the image forming apparatus is turned on, or when the user requests. By setting, the density of the image is set. At that time, a toner check pattern for density detection is formed on the photosensitive drum 25 and transferred onto the intermediate transfer body 511. Then, the density of the toner check pattern transferred on the intermediate transfer body 511 is detected by the density sensor 142, or the toner check pattern printed on the sheet S is read by the reader scanner unit 500 to acquire the density information. Concentration measurement is performed.

First, a method of calculating the target light amount according to the environment (temperature, humidity) will be described. FIG. 7 is a flowchart showing a control sequence for calculating a target light amount according to the environment (temperature, humidity). The process shown in FIG. 7 is a request from the user when the image forming speed changes or the surrounding environment changes, the power of the image forming apparatus is turned on, or the number of printed sheets reaches a predetermined number. It is started when there is, etc., and is executed by the CPU 401.

When the process shown in FIG. 7 is activated, in step 901 (hereinafter referred to as S), the CPU 401 acquires the temperature information and the humidity information inside the image forming apparatus 1 detected by the environment sensor 141. In S902, the CPU 401 determines the environment classification inside the image forming apparatus 1 based on the temperature information and the humidity information acquired in S901. The table shown in FIG. 8A is an environment classification table in which the environment classification is divided into five stages according to the temperature and humidity inside the image forming apparatus 1, and the vertical axis of the table shows the temperature [° C.] and the horizontal axis shows the temperature [° C.]. Indicates humidity [%]. The environment classification is divided into environment classification 1 to environment classification 5 from the lower temperature to the higher temperature and from the lower humidity to the higher humidity. The CPU 401 determines the environment classification of the image forming apparatus 1 based on the temperature information and the humidity information acquired in S901 and the environment classification table. For example, assuming that the temperature detected by the environment sensor 141 in S901 is 25 ° C. and the humidity is 45%, the CPU 401 determines from the environment classification table that the environment classification is environment classification 3.

In S903, the CPU 401 determines the charging voltage of the charger 513 that charges the photosensitive drum 25, which is one of the image forming conditions, based on the environment classification determined in S902. The table shown in FIG. 8B is a charging voltage setting table showing the correspondence between the environment classification and the charging voltage of the charging device 513 that charges the photosensitive drum 25. In the charging voltage setting table of FIG. 8B, the numbers 1 to 5 shown in the environment category column correspond to the environment categories 1 to 5, respectively. Further, in the figure, Y, M, C, and K correspond to a charger 513 that charges the photosensitive drums 25 having a yellow color, a magenta color, a cyan color, and a black color, respectively. Further, the numbers 50, 100, 200, 300, and 400 in the table indicate the charging voltage (unit: volt) applied to the photosensitive drum 25 by the charger 513. The charging voltage applied to the photosensitive drum 25 by the charger 513 is a negative potential. Therefore, 50 means -50 volts and 400 means -400 volts. The CPU 401 determines the charging voltage of the charger 513 based on the environment classification determined in S902 and the charging voltage setting table. For example, assuming that the temperature detected by the environment sensor 141 in S901 is 25 ° C. and the humidity is 45%, the environment category is environment category 3, and the charging voltage applied to the photosensitive drum 25 from the charger 513 is −200 volts. Become.

In S904, the CPU 401 calculates the maximum laser light amount value that can be applied to the photosensitive drum 25 from the LD201 of the optical scanning device 2 based on the charging voltage determined in S903. The table shown in FIG. 8C is a maximum laser light amount value table showing the correspondence between the charging voltage applied to the photosensitive drum 25 from the charger 513 and the laser light amount set value (maximum light amount) that can irradiate the photosensitive drum 25. be. 50 to 400 shown in the column of charging voltage indicates the charging voltage of -50 to -400 volts applied to the photosensitive drum 25 by the charger 513, respectively. The laser light amount setting value is the value of the light amount PWM signal 320 output by the CPU 401 to the LD drive control unit 405. The light amount PWM signal 320 is represented by 8-bit data, and its value is represented by 0 to 255. The CPU 401 calculates the maximum laser light amount value based on the charging voltage of the charger 513 determined in S903 and the maximum laser light amount value table. For example, assuming that the temperature detected by the environment sensor 141 in S901 is 25 ° C. and the humidity is 45%, the high voltage of the charger 513 is −200 volts, and the maximum laser beam amount value in this case is 180.

In S905, the CPU 401 forms an image of the toner check pattern as shown in FIG. 8D on the photosensitive drum 25 to which the charging voltage determined from the charger 513 is applied. FIG. 8D is an example of a patch image for density detection in which the maximum laser light amount value 180 is set to 100% and the laser light amount is gradually reduced. In the figure, (Y), (M), (C), and (K) refer to pattern data of yellow color, magenta color, cyan color, and black color, respectively. Further, the numbers 20, 74, 127, and 180 in the figure indicate the laser light amount setting values corresponding to the toner check pattern, with the maximum laser light amount value 180 calculated in S904 as 100%. Here, in order to form a patch in which the laser light amount is changed in four stages up to the minimum value 20 of the laser light amount set value, the set value of the light amount PWM signal 320 of (180-20) ÷ 3 = 53 is changed by 53. A toner check pattern (density patch) is formed.

In S906, the CPU 401 detects the density of the toner check pattern formed on each photosensitive drum 25 and transferred onto the intermediate transfer body 511 by the density sensor 142, and acquires the detection result. In S907, the CPU 401 calculates the laser light amount (target light amount) according to the target density by the above-mentioned method based on the duty of the PWM signal and the density detection result of the density sensor 142. Here, the maximum laser light amount value 180 is set as 100%, and the laser light amount (target light amount) according to the target density, that is, the light amount indicated value (%) is calculated. The CPU 401 stores the calculated laser light amount value (light amount indicated value) in the storage unit 408, and ends the process.

In the process shown in FIG. 7, an example in which the density of the toner check pattern transferred on the intermediate transfer body 511 is detected by the density sensor 142 has been described, but the present embodiment is not limited to this. For example, a method may be used in which the toner check pattern is printed on the sheet S, the sheet S on which the toner check pattern is printed is read by the reader scanner unit 500, and the density of the toner check pattern is detected. That is, the reader scanner unit 500, which is an image reading unit, may be configured to function as a density sensor.

Next, the APC operation will be described with reference to FIG. The APC operation is performed in a non-image region outside the image region of the photosensitive drum 25 in the direction of the rotation axis of the photosensitive drum 25 (see FIGS. 3 and 5). The CPU 401 issues an instruction to execute the APC operation to the APC control unit 406. The APC control unit 406 inputs the drive current of the LD 201 to the LD drive control unit 405. _{The LD drive control unit 405 determines the drive current ILD of the LD} 201 according to the target light amount, and the LD 201 emits a laser beam. The amount of laser light from the LD201 is detected by the PD 302 and input to the APC control unit 406. The LD drive control unit 405 adjusts the drive current of the LD 201 so that the detected light amount becomes a predetermined light amount instruction value notified from the light amount setting unit 407 to the CPU 401. The details will be described below.

The PD 302 generates a monitor current according to the amount of light of the LD 201, and the monitor current is input to the APC control unit 406. Inside the APC control unit 406, the monitor current is converted into a voltage value (monitor voltage) by current-voltage conversion. The monitor voltage is compared with the APC reference voltage set in advance by the CPU 401. Here, the APC voltage to be compared with the monitor voltage is a predetermined value notified from the light amount setting unit 407 to the CPU 401, as described above. The APC control unit 406 controls the APC control voltage V _apc according to the comparison result, and adjusts the monitor voltage so as to be the APC reference voltage. The LD drive control unit 405 generates _{the drive current ILD of the LD 201.} At this time, LD201 and PD302 are connected to a common power supply 409.

By the APC operation described above, the drive current ILD of the _LD 201 is automatically adjusted so that the amount of light emitted from the laser beam from the LD 201 becomes a predetermined light amount indicated value. The amount of laser light at the time of adjusting the amount of light adjusts the maximum amount of light required at the time of image formation. The timing of the APC operation is controlled by the APC control unit 406. The CPU 401 sets the timing of the APC operation for the APC control unit 406. The APC control unit 406 performs an internal clock counting operation based on the input timing of the BD signal, and controls the timing of the APC operation based on the count value set by the CPU 401. The timing of the APC operation is set so that it is performed in the non-image area.

By the above operation, the APC operation is executed in the non-image region, and the amount of emitted light of the laser beam is controlled to the amount of light according to the APC reference voltage. Further, in this embodiment, the amount of light determined by the APC operation is the amount of light incident on the BD sensor unit 410, which is a photodetection unit having the BD sensor 209.

Next, in the image region of the photosensitive drum 25, the light emission control of the LD201 according to the image signal will be described. Emission control LD201 is the drive current _{I LD,} which is determined by the APC operation, the image signal is driven only LD201 period on to emit LD201, image signal is off in the non-emission does not emit LD201 , LD201 is a control to blink. The details will be described below.

First, the PC 400 or the reader scanner unit 500 inputs image data to the image processing unit 403. The image data is data represented by the RGB color space. The image processing unit 403 converts the image data from the RGB color space to the YMCK color space. Further, the image processing unit 403 performs screen processing on the image data converted into the color space of YMCK. The screen processing is a processing for expressing gradation by adjusting the number and density of dots and lines. By performing this screen processing, even if the gradation expression by the light emission control of LD201 is binary, it is possible to express the full color of 256 gradations of each color.

Next, the image processing unit 403 inputs the screen-processed image data to the image signal output unit 404. The image signal output unit 404 converts the image data of each color of YMCK into an image signal having a predetermined frequency that blinks (lights or does not emit) the LD201. Next, the image signal output unit 404 outputs an image signal to the LD drive control unit 405 at a predetermined timing based on the BD signal. At this time, the image signal output unit 404 performs PWM control for the image signal according to the image data, and the pulse width (Duty) is determined for each gradation. The LD drive control unit 405 controls the light emission of the LD 201 according to the image signal. When the image signal is in the ON state drives the LD201 in drive current _{I LD,} which is determined by the APC operation, when the image signal is OFF drives the LD201 in bias current _{I BIAS.} Bias current _{I BIAS,} it is possible to suppress desirable to LD201 is adjusted to the threshold current _{I TH} immediately before the emission start, emission delay time closer to the threshold current _{I TH} LD201. In the image region, as described above, the BD signal is used as a reference timing, and _{the light emission control of the LD} 201 is performed based on the drive current ILD determined by the APC operation and the blinking pattern of the image signal.

Therefore, the image formation position differs because the delay time of the BD signal differs depending on the amount of light determined by the APC operation.

Therefore, the BD sensor unit 410, which is an optical detection unit, has a BD gain changing circuit in order to reduce the delay time of the BD signal.

(BD gain change circuit of BD sensor)
Next, the BD sensor unit 410 will be described with reference to FIG. FIG. 9 is a diagram showing a circuit of the BD sensor unit 410 in this embodiment.

The BD sensor unit 410, which is an optical detection unit in this embodiment, has a BD gain changing circuit 701 and a BD sensor 209. The BD gain change circuit 701 has a gain change unit 704, a first gain resistor 702, and a second gain resistor 703. A gain change signal is input to the BD gain change circuit 701 from the CPU 401 shown in FIG. The gain change signal controls the gain change unit 704, controls whether or not the first gain resistor 702 and the second gain resistor 703 are used, and changes the sensitivity (BD gain) of the photoelectric conversion of the BD sensor 209. Here, as described with reference to FIG. 5, by switching between the first gain and the second gain at the BD gain switching point, control below the delay time target value is performed within the used light amount range. The second gain has a higher sensitivity (BD gain) for photoelectric conversion than the first gain, and the second BD gain can be used in a lower light amount region than the first BD gain. In this embodiment, when a gain change signal is input from the CPU 401 to the BD gain change circuit 701 and the gain change unit 704 is turned on, the first gain resistance 702 and the second gain resistance 703 are connected in parallel to obtain the first gain. Be selected. Further, when the gain change signal is input from the CPU 401 to the BD gain change circuit 701 and the gain change unit 704 is turned off, the second gain is selected by using the second gain resistor 703. That is, when the first gain is used, the gain changing unit 704 is turned on, and when the second gain is used, the gain changing unit 704 is turned off.

The BD sensor 209 includes a PDBD705 which is a photodiode of the BD sensor, a current amplifier 706, and a comparator 707. The PDBD705 photoelectrically converts the input light and outputs the converted current to the current amplifier 706. The current amplifier 706 amplifies the current from the PDBD 705 with a predetermined gain, and outputs the amplified current to the gain change circuit 701. The current input to the gain change circuit 701 is current-voltage converted according to the first gain or the second gain controlled by the gain change signal, and is converted into the sensor output voltage. The sensor output voltage converted into current and voltage by the gain change circuit 701 is input to the comparator 707. Comparator 707 compares the threshold value V _th and the sensor output voltage, when the sensor output voltage is greater than the threshold V _th and outputs a Lo voltage, when the sensor output voltage is the threshold value V _th is smaller than the outputs a Hi voltage. At this time, the digital signals of Hi voltage and Lo voltage output from the comparator 707 are BD signals output from the BD sensor 209.

FIG. 10 shows a selection table of BD gain with respect to the BD light amount indicated value in this embodiment. In this embodiment, the amount of light incident on the BD sensor is determined by the above-mentioned APC operation. Therefore, the ratio of the light output transmitted from the CPU 401 to the APC control unit 406 shown in FIG. 6 and the ratio of the amount of incident light to the BD sensor are equal. Further, in the light amount range used in a predetermined image forming apparatus, the light amount indicated value when outputting the maximum light amount is set to 100%. In the selection table shown in FIG. 10, it is assumed that image formation is not performed when the light intensity indicated value is less than 30%. Therefore, if the light intensity indicated value is less than 30%, it is out of the range of use, and the BD gain is Don't care. However, since there is a concern that the element is thermally destroyed by the intermediate potential, the first gain or the second gain is selected. Next, in the selection table shown in FIG. 10, the second gain is selected when the light amount indicated value is 30% or more and less than 65%, and the first gain is selected when the light amount indicated value is 65% or more. In the selection table shown in FIG. 10, the light intensity indicated value of 65% is set as the boundary value between the first gain and the second gain. A method of determining the amount of incident light at the BD gain switching point shown in FIG. 5 will be described. The variation in the transmittance and reflectance of the optical system of the optical scanning device 2 and the variation in the output light amount with respect to the input current of the LD201 are calculated and determined by the central light amount indicated value. Therefore, the light intensity indicated value of 65% does not always coincide with the BD gain switching point shown in FIG. As described above, it has a BD gain selection table based on the light amount indicated value to the BD sensor, aiming at an appropriate BD gain switching point.

Figure 11 (a), the time of the setting of the first gain and second gain, showing the relationship between the delay time of the BD signal when a predetermined amount of incident light P ₁ or P ₂ is input to the BD sensor. FIG. 11B shows a timing chart of the BD signal when a _{predetermined incident light amount P 1} or P ₂ is input to the BD sensor when the first gain and the second gain are set. At this time, it is assumed that the _{incident light amount P 1} is sufficiently larger than the incident light amount P _2.

The timing chart (1) shown in FIG. 11B shows an ideal timing chart without delay of the BD signal. Timing chart shown in FIG. 11 (b) (2), when the first gain is selected, showing a state where the amount of incident light P ₁ is incident on the BD sensor. The first gain is an appropriate gain for a high amount of light, and the BD signal is output after the _{delay time tg11 elapses, as compared with the case of the BD signal without delay.} Timing chart shown in FIG. 11 (b) (3), when the second gain is selected, showing a state where the amount of incident light P ₁ is incident on the BD sensor. The second gain is an appropriate gain for a low amount of light, but the sensor output voltage itself is large, and a BD signal is output after the _{delay time tg21 has elapsed.} However, since the gain is excessive with respect to the amount of incident light, the sensor output voltage due to stray light generated in the lead frame or package of the BD sensor, the housing of the optical scanning device, or the like also increases, which may cause erroneous detection. The timing chart (4) shown in FIG. 11B shows _{a state in which the incident light amount P 2} is incident on the BD sensor when the first gain is selected. The first gain is an appropriate gain for a high amount of light, and a BD signal is output after the _{delay time tg12 has elapsed.} The timing chart (5) shown in FIG. 11B shows _{a state in which the incident light amount P 2} is incident on the BD sensor when the second gain is selected. The second gain is an appropriate gain for a low amount of light, and a BD signal is output after the _{delay time tg22 has elapsed.}

From the above, the magnitude relationship of the delay time is the relationship of t _g11 ≈ t _g21 <t _g22 <t _g12 . However, in a state where the delay time is t _g21 , the BD sensor may cause a false detection, and there is a high possibility that the writing position control cannot be performed as expected. _{Further, in} the case of the delay time t g12, the delay time of the BD signal is larger than that of other delay times, and it is assumed that the accuracy of the writing position control cannot be satisfied.

Therefore, by changing the gain change circuit 701 shown in FIG. 9 with the selection table shown in FIG. 10, the delay time can be suppressed within a predetermined range from t _{g 11 to t g 22.}

Next, a flow of selecting the BD gain will be described with reference to FIG. FIG. 12 shows a flowchart for performing BD gain selection. The CPU 401 starts BD gain selection based on the light amount indicated value notified to the light amount setting unit 407 (S1001). When the light amount indicated value set in the APC control unit 406 is equal to or greater than the threshold value (S1002: Yes), the CPU 401 selects the first gain based on the selection table shown in FIG. 10 (S1004). The BD gain selection is completed (S1005). As a result, the CPU 401 inputs a gain change signal for selecting the first gain to the BD sensor unit 410. On the other hand, when the light amount indicated value set in the APC control unit 406 is less than the threshold value (less than 65%) (S1002: No), the CPU 401 selects the second gain based on the selection table shown in FIG. 10 (S1003). ), BD gain selection is completed (S1005). As a result, the CPU 401 inputs a gain change signal for selecting the second gain to the BD sensor unit 410.

As described above, in this embodiment, in order to reduce the delay time of the BD signal from the BD sensor, the BD gain is selected based on the light amount indicated value. As a result, the accuracy of the timing of starting writing to the photosensitive drum at the time of image formation can be improved, and the accuracy of image misalignment correction can be improved.

However, in this embodiment, the APC light amount and the BD incident light amount used for image formation are the same, but since an appropriate BD gain may be selected for the BD incident light amount, the APC light amount and the BD incident light amount are different. It doesn't have to match.

Further, although the configuration in which the BD gain change signal is output from the CPU 401 is illustrated, since the BD gain change signal may be input based on the light intensity indicated value, it may be output from an IC other than the CPU 401. Further, in this embodiment, a configuration having a plurality of resistors and a circuit for selecting whether or not to use each resistor is illustrated in the BD gain switching circuit (gain changing circuit) is exemplified, but the present invention is not limited to this, and the electronic volume (electronic volume) ( A circuit that can select the resistance value such as electronic VR) may be used. In addition, in this embodiment, the boundary value for BD gain switching is set to the light amount indicated value of 65%, but this is not the case because it may be selected according to the characteristics of the optical system and LD. Further, in this embodiment, a configuration having two BD gain selections has been exemplified, but the present invention is not limited to this, and the target delay time (the target from the time when the light is incident on the sensor to the time when the signal is output) is used. You may perform three or more gain selections based on time).

[Example 2]
Next, the image forming apparatus according to the second embodiment will be described. In the first embodiment described above, the gain change is realized by inputting the gain change signal based on the light amount indicated value from the CPU 401 to the BD sensor unit 410. Therefore, it is necessary to secure a port for outputting the gain change signal in the CPU 401, which has a small influence on the limitation of the number of IO ports of the CPU 401.

In the second embodiment, the light amount indicated value itself is input from the CPU 401 to the BD sensor unit 410 to change the gain in the BD sensor unit 410. By using the light amount indicated value (light amount PWM signal), which is a signal that has been used conventionally, BD gain switching is performed while reducing the increase in the number of signals as an image forming apparatus, and the timing of starting writing to the photosensitive drum is set. Improve accuracy.

Since the configuration of the image forming apparatus in the second embodiment is the same as the configuration of the image forming apparatus in the first embodiment, the description thereof will be omitted.

(Control circuit of optical scanning device)
The control circuit of the optical scanning apparatus in this embodiment will be described. FIG. 13 is a block diagram showing a control circuit of the optical scanning device in this embodiment. The control circuit of this embodiment is different from the control circuit of the first embodiment described with reference to FIG. 6, and the light amount indicated value instructed from the CPU 401 to the APC control unit 406 is also input to the BD sensor unit 410. .. As a result, in this embodiment, the number of IO ports of the CPU 401 can be reduced as compared with the first embodiment. In this embodiment, it is assumed that the light amount indicated value to the APC control unit 406 is expressed by the DUTY of the PWM signal. Further, also in this embodiment, the amount of light determined by the APC operation is the amount of light incident on the BD sensor 209 of the BD sensor unit 410. The other configurations of the control circuit are the same as those of the control circuit of the first embodiment described with reference to FIG. 6, except for the configuration of the BD sensor unit 410 including the BD gain switching circuit described below. The explanation is omitted.

(BD gain switching circuit using light intensity indicated value)
Next, the BD sensor unit 410 will be described with reference to FIG. FIG. 14 is a diagram showing a circuit of the BD sensor unit 410 in this embodiment.

The BD sensor unit 410 in this embodiment includes a BD gain switching circuit 1201 and a BD sensor 209. The BD gain switching circuit 1201 includes a filter unit 1202, a hysteresis comparator 1203, and a BD gain changing circuit 701. A PWM signal, which is a light amount instruction value from the CPU 401 shown in FIG. 13, is input to the BD gain switching circuit 1201. The PWM signal is input to the filter unit 1202 and converted into a DC signal having a predetermined voltage by the filter unit 1202. The DC signal converted by the filter unit 1202 is input to the hysteresis comparator 1203. The hysteresis comparator 1203 has resistors R ₁ , R ₂ , R ₃ , R _p , a pull-up voltage V _p , and a voltage V _ref, and has a threshold value V _{thH of the following} equation 1 and the following equation 2 for the DC signal. It has a threshold V _thL . In addition, a in the following formulas 1 and 2 is as shown in the following formula 3.

(Equation 1)

(Equation 2)

(Equation 3)

In the above equations 1 and 2, V _OH is a Hi level output voltage and _VOL is a Lo level output voltage. Further, the threshold value V _thH is a threshold value when the output voltage is V _OH , and is a threshold value for switching from the Hi level output voltage to the Lo level output voltage. Similarly, the threshold V _thL is a threshold in the case where the output voltage is V _OL, a threshold value from the Lo level output voltage is switched to the Hi level output voltage. In other words, the threshold value V _thH is the first threshold value for switching from the second gain to the first gain, and the threshold value V _thL is the second threshold value for switching from the first gain to the second gain.

Therefore, when the light amount indicated value becomes high, that is, when the DUTY of the PWM signal becomes large, the threshold value _VthH is exceeded and the Lo level output voltage is output from the hysteresis comparator 1203. The Lo level output voltage output from the hysteresis comparator 1203 is a signal for selecting the gain. Since the inverted output of the hysteresis comparator 1203 is input to the BD gain change circuit 701, the first gain is selected by connecting the first gain resistor 702 and the second gain resistor 703 in parallel.

Further, when the light amount indicated value becomes low, that is, when the DUTY of the PWM signal becomes small, the threshold value _VthL is lowered and the Hi level output voltage is output from the hysteresis comparator 1203. The Hi level output voltage output from the hysteresis comparator 1203 is a signal for selecting the gain. Since the inverted output of the hysteresis comparator 1203 is input to the BD gain changing circuit 701, the second gain is selected by the first resistance.

By using the circuit of the BD sensor unit 410 of FIG. 14 as described above, it is possible to change the BD gain by using the light amount indicated value itself.

FIG. 15 shows an example of the set value of the hysteresis comparator 1203 shown in FIG. In FIG. 15, it is assumed that the voltage amplitude of the PWM signal is 3.3 V. _V ref shown in FIG. _15, by setting such that _{R 1, R 2, R 3} , V OH, and _{V OL,} 10% to the threshold _{V thH} and the threshold _{V thL} the PWM signal DUTY (light amount instruction value) It has the hysteresis of.

FIG. 16 shows a graph showing the operation of the BD sensor unit 410 set in FIG. The maximum amount of light used in the image forming apparatus is P _1, and the minimum amount of light used is up to 30% _{of P 1.} The range from the maximum light amount P ₁ to the minimum light amount 0.3 × P ₁ is defined as the light amount range used in the image forming apparatus. In this case, the transition from low light intensity to high light intensity is represented by a solid line graph.

Specifically, the minimum light amount of 0.3 × P ₁ uses the second gain, which is appropriate for a low light amount, and when the light amount is increased from _{0.3 × P 1, 0.7 ×} At P ₁ , the BD sensor unit 410 switches to the first gain. That is, in the example shown in FIG. 16, 0.7 × P ₁ that switches to the first gain is the above-mentioned threshold value V _thH . Then, the first gain is used while the amount of light is increased to _{P 1,} which is the maximum amount of light.

On the contrary, when the amount of light is reduced from _{P 1} which is the maximum amount of light, the gain is switched to the second gain at _{0.6 × P 1.} That is, in the example shown in FIG. 16, 0.6 × P ₁ that switches to the second gain is the above-mentioned threshold value _VthL . Then, the second gain is used up to the minimum amount of light of 0.3 × P _1.

BD sensor unit shown thus in Figure 14 410 10% at a light quantity indicated value to the threshold _{V thL} when the threshold _{V thH} a first gain when the second gain switched to the first gain switched to the second gain The BD gain is switched with the hysteresis of.

FIG. 17 shows a flowchart of BD gain selection in this embodiment. The CPU 401 starts BD gain selection based on the light amount indicated value notified to the light amount setting unit 407 (S1501). The CPU 401 notifies the light amount indicated value set in the APC control unit 406 (S1502). Based on the light amount instruction set in the APC control unit 406, the BD sensor unit 410 shown in FIG. 14 performs BD gain selection as a circuit operation (S1503) and ends BD gain selection (S1504). The specific gain switching is as described above with reference to FIGS. 15 and 16.

As described above, in this embodiment, the light amount indicated value is also input to the BD sensor unit 410 through the port input by the CPU 401 to the APC control unit 406, and an appropriate gain is hard-selected by the BD sensor unit 410. It was configured. As a result, the accuracy of the writing start timing to the photosensitive drum at the time of image formation can be improved, and the configuration can be configured so as not to affect the limitation of the number of IO ports of the CPU 401. Then, the delay time of the BD signal from the BD sensor can be reduced, and the position shift correction accuracy of the image can be improved.

[Other Examples]
In the above-described embodiment, the APC light amount and the BD incident light amount used for image formation are the same, but since an appropriate BD gain may be selected for the BD incident light amount, the APC light amount and the BD incident light amount may be selected. The amount of light does not have to match.

Further, although the configuration in which the BD gain change signal (or the light amount indicated value) is output from the CPU 401 is shown, since the BD gain change signal may be input based on the light amount indicated value, it may be output from an IC other than the CPU 401. ..

Further, in this embodiment, the BD gain switching circuit is configured to have a plurality of resistors and a circuit for selecting whether or not to use each resistor, but the present invention is not limited to this, and a circuit capable of selecting the resistance value such as an electronic VR is used. You may.

In addition, in Example 1 described above, the boundary value for BD gain switching is set to 65%, but this is not the case because it may be selected depending on the characteristics of the optical system and LD.

Further, in the above-described embodiment, the configuration has two BD gain selections, but three or more gain selections may be performed based on the target delay time.

Further, in the above-described embodiment, four image forming stations are used in the image forming unit for forming an image, but the number of used is not limited and may be appropriately set as needed.

Further, in the above-described embodiment, the printer is exemplified as the image forming apparatus, but the present invention is not limited thereto. For example, it may be another image forming apparatus such as a copying machine or a facsimile apparatus, or another image forming apparatus such as a multifunction device combining these functions. Further, an image forming apparatus is exemplified in which an intermediate transfer body is used, toner images of each color are sequentially superimposed and transferred to the intermediate transfer body, and the toner images carried on the intermediate transfer body are collectively transferred to a sheet. , Not limited to this. An image forming apparatus may be used in which a sheet carrier is used and a toner image of each color is sequentially superimposed and transferred onto the sheet supported on the sheet carrier. Similar effects can be obtained by applying the present invention to these image forming devices.

a, a'... Laser light 1 ... Image forming device 2 ... Optical scanning device 5 ... Image control unit 25 ... Photosensitive drum 141 ... Environment sensor 142 ... Density sensor 201 ... LD
205 ... Polygon mirror 209 ... BD sensor 302 ... PD
401 ... CPU
405 ... LD drive control unit 406 ... APC control unit 407 ... Light amount setting unit 408 ... Storage unit 410 ... BD sensor unit 500 ... Reader scanner unit 503 ... Image drawing unit 504 ... Fixing unit 505 ... Feeding / transporting unit

Claims (8)

It has a light source capable of emitting light according to an image signal and a light deflection unit that deflects and scans the light from the light source with respect to the photosensitive drum, and scans the photosensitive drum with light corresponding to the image signal to obtain an image. In the image forming apparatus to be formed,
A drive control unit that controls the drive of the light source,
A photodetector that detects light from the light source that has been deflected and scanned by the photodetector and outputs a signal.
A control unit that controls the write start timing to the photosensitive drum based on the signal output from the photodetector, and controls the drive control unit so that the light source emits light with a light amount corresponding to the light amount indicated value. ,
Equipped with
The photodetector is a gain change circuit having a sensor that detects light incident from the light source and a plurality of gains that can be used in a light amount region that outputs a signal by the target time after the light is incident on the sensor. And have
The gain changing circuit has a first gain that can be used in the first light amount region and a second gain that can be used in a second light amount region including a light amount region lower than the first light amount region.
The control unit determines the first gain or the second gain of the gain changing circuit based on the light amount indicated value so that the light detection unit outputs a signal by the target time after the light is incident on the sensor. An image forming apparatus characterized in that a selected signal is output to the light detection unit to change the gain changing circuit to a first gain or a second gain. Claim 1 is characterized in that the control unit selects the first gain when the light amount indicated value is equal to or greater than a threshold value, and selects the second gain when the light amount indicated value is less than the threshold value. The image forming apparatus according to. It has a light source capable of emitting light according to an image signal and a light deflection unit that deflects and scans the light from the light source with respect to the photosensitive drum, and scans the photosensitive drum with light corresponding to the image signal to obtain an image. In the image forming apparatus to be formed,
A drive control unit that controls the drive of the light source,
A photodetector that detects light from the light source that has been deflected and scanned by the photodetector and outputs a signal.
A control unit that controls the write start timing to the photosensitive drum based on the signal output from the photodetector, and controls the drive control unit so that the light source emits light with a light amount corresponding to the light amount indicated value. ,
Equipped with
The light detection unit is a gain change circuit having a sensor that detects light incident from the light source and a plurality of gains that can be used in a light amount region that outputs a signal by the target time after the light is incident on the sensor. And a comparator that switches the first gain or the second gain of the gain changing circuit according to the light amount indicated value.
The gain changing circuit has a first gain that can be used in the first light amount region and a second gain that can be used in a second light amount region including a light amount region lower than the first light amount region.
The control unit inputs the light amount indicated value to the comparator and inputs the light amount indication value to the comparator.
The comparator outputs a signal for selecting the first gain or the second gain of the gain changing circuit according to the input light amount indicated value, and changes the gain changing circuit to the first gain or the second gain. An image forming apparatus characterized in that. When the light amount indicated value exceeds the first threshold value, the comparator outputs a first signal for selecting the first gain, changes the gain changing circuit to the first gain, and the light amount indicated value becomes the second. The image forming apparatus according to claim 3, wherein when the value falls below the threshold value of, a second signal for selecting the second gain is output, and the gain changing circuit is changed to the second gain. The image forming apparatus according to any one of claims 1 to 4, wherein the first light quantity region includes a higher light quantity region than the second light quantity region. An environment sensor for measuring the temperature and humidity inside the image forming device,
A density sensor that detects the density of the toner check pattern formed on the image carrier or recording medium, and
Equipped with
The one according to any one of claims 1 to 5, wherein the control unit sets a light amount indicated value based on the information obtained by the density sensor and the environment sensor and stores it in the storage unit. Image forming device. The image forming apparatus includes an image reading unit for reading an image formed on a sheet.
The image forming apparatus according to claim 6, wherein the image reading unit functions as the density sensor. The control unit determines the charging voltage of the charging unit that charges the photosensitive drum from the information obtained by the environment sensor, and calculates the maximum amount of light that can be emitted from the light source based on the determined charging voltage. The toner check pattern consisting of patch images for each amount of light gradually reduced from the maximum amount of light was formed on the photosensitive drum charged with a charging voltage, and the density of the toner check pattern was detected and detected by the density sensor. The image forming apparatus according to claim 6 or 7, wherein a light amount indicated value corresponding to a target density is calculated from the density and stored in a storage unit.

Images