JP2021074957A - Image formation apparatus - Google Patents

Abstract

To suppress the reduction in the service life of a photoreceptor drum by switching to unblanking control as quickly as possible since the service life of the photoreceptor drum becomes short if an image region is scanned with the laser.SOLUTION: The capacity of a first capacitor and the capacity of a second capacitor are smaller than the capacity of a third capacitor and the capacity of a fourth capacitor. Control means causes adjustment means to perform adjustment of a first light emission amount and a second light emission amount of a first light emitting unit in a state of controlling the first light emitting unit so as to be the first light emission for scanning an image region and a non-image region with the light emitted by the first light emitting unit in a start-up period of controlling the rotational speed such that a rotary polygon mirror rotates at a prescribed rotational speed, and controls the first light emitting unit so as to be the second light emission for scanning the non-image region with the light emitted by the first light emitting unit when the adjustment of the first light emission amount and the second light emission amount of the first light emitting unit is completed by the adjustment means.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus such as a laser printer, a copying machine, and a facsimile.

Conventionally, Patent Document 1 discloses that the potential of a non-image portion (a region where toner does not adhere) of a photosensitive drum is optimized in order to further improve the image quality of an electrophotographic image forming apparatus. Specifically, the image portion (region to which the toner is attached) of the photosensitive drum is irradiated with the light emitted at the first emission amount for setting the potential for attaching the toner. Then, the non-image portion of the photosensitive drum is irradiated with light emitted with a second emission amount smaller than the first emission amount for setting a potential at which toner does not adhere. Then, for the purpose of stabilizing the first light emission amount and the second light emission amount, APC (Auto Power Control) control for adjusting the two levels of light emission amount of the first light emission amount and the second light emission amount can be performed. It is disclosed.

Further, Patent Document 2 describes that when the scanner motor is started up, the laser is emitted (ambranking control) outside the image region to control the scanner motor. That is, based on the result of detecting the cycle of the detection signal by the detection means one scan before, the cycle of the detection signal when the next scan is performed is predicted. By performing the unbranking control, it is possible to obtain a detection signal of the laser beam without continuously lighting the laser and control the start-up of the scanner motor.

Japanese Unexamined Patent Publication No. 2012-137734 Japanese Unexamined Patent Publication No. 8-183198

When the scanner motor is started up, the scanner motor is started up by forcibly emitting a laser including the image area. By performing APC at the time of this forced light emission, the amount of light is appropriately set. On the other hand, since the life of the photosensitive drum is shortened when the image region is scanned by the laser, it is also desired to suppress the decrease in the life of the photosensitive drum by switching to the ambranking control as soon as possible.

The invention according to the present application has been made in view of the above circumstances, and an object of the present invention is to suppress a decrease in the life of the photosensitive drum while performing APC.

In order to achieve the above object, the first light emitting unit and the second light emitting unit are provided, and the first light emitting amount for forming an electrostatic latent image in the image unit from each light emitting unit, and the first light emitting amount The light emission amount is also small, and the irradiation means for irradiating the light with the second light emission amount for controlling the potential of the non-image part and the first light emission amount for adjusting the first light emission amount of the first light emitting part. A capacitor, a second capacitor for adjusting the second light emitting amount of the first light emitting unit, a third capacitor for adjusting the first light emitting amount of the second light emitting unit, and the second light emitting unit. The fourth capacitor for adjusting the second light emission amount of the light emitting unit and the drive current supplied to the light irradiation means are adjusted in order to adjust the light emission amount of the light emitted from the light irradiation means. The adjusting means, the rotating multi-sided mirror that reflects the light emitted from the irradiating means and can scan the image region and the non-image region on the photoconductor, and the first light emitting unit emits light and is reflected by the rotating multi-sided mirror. A detection means for detecting the emitted light and a control means for controlling the light emission of the first light emitting unit and the second light emitting unit are provided, and the capacity of the first capacitor and the capacity of the second capacitor are determined. The first is smaller than the capacity of the third capacitor and the capacity of the fourth capacitor, and the control means controls the rotation speed so that the rotating polymorphic mirror rotates at a predetermined rotation speed. In a state where the first light emitting unit is controlled so that the light emitted from the light emitting unit causes the first light emission to scan the image region and the non-image region, the first light emitting unit is controlled by the adjusting means. When the adjustment of the first light emitting amount and the second light emitting amount is completed and the adjustment of the first light emitting amount and the second light emitting amount of the first light emitting unit is completed by the adjusting means, the first light emitting unit It is characterized in that the first light emitting unit is controlled so as to be the second light emitted to scan the non-image region by the light emitted from the light.

According to the configuration of the present invention, it is possible to suppress a decrease in the life of the photosensitive drum while performing APC.

Schematic configuration diagram of the image forming apparatus Schematic perspective view of the optical scanning device Laser drive circuit The figure which shows the relationship between the current flowing through a laser diode and the emission intensity. The figure which shows the potential change of a photosensitive drum The figure which shows the change of the rotation speed from the start of a polygon motor Timing chart showing signals related to activation control of the optical scanning device Timing chart showing APC timing The figure which shows the relationship between minute light emission and PWM light emission Timing chart showing APC timing The figure which shows the relationship between the current flowing through a laser diode and the emission intensity by the film thickness of a photosensitive drum. Timing chart showing APC timing

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

(First Embodiment)
[Image forming device]
FIG. 1 shows a schematic configuration of an image forming apparatus that uses an electrophotographic process to form a color image in which four color images of yellow (Y), magenta (M), cyan (C), and black (K) are superimposed. It is a figure. In the following description, particularly for members that do not need to distinguish between yellow, magenta, cyan, and black, the subscripts Y, M, C, and K of the symbols may be omitted for convenience of description. In the following description, a color image forming apparatus will be used, but the description is not limited thereto. The micro-emission of the non-image portion can also be applied to, for example, a monochromatic image forming apparatus. Further, although the in-line type color image forming apparatus will be described as an example, a rotary type color image forming apparatus may be used, for example. Further, although the image forming apparatus having the intermediate transfer belt 3 will be described, an image forming apparatus adopting a method of directly transferring the toner image developed on the photosensitive drum 5 to the recording material may be used.

The image forming apparatus 50 has a photosensitive drum 5 (5Y, 5M, 5C, 5K) as a photoconductor, and sequentially multiplexes toner images formed on the photosensitive drum 5 (on the photoconductor) on the intermediate transfer belt 3. It is a printer that transfers and obtains a full-color image. The intermediate transfer belt 3 is suspended by a drive roller 12, a tension roller 13, an idler roller 17, and a secondary transfer opposed roller 18, and rotates in the direction of the arrow in the drawing. Four photosensitive drums 5 are arranged in series in the moving direction of the intermediate transfer belt 3. The photosensitive drum 5 is uniformly charged with a predetermined polarity and potential by the charging roller 7, and then the laser beam 4 is irradiated from the optical scanning device 9 as the light irradiation means. As a result, an electrostatic latent image is formed. Then, toner is attached to the electrostatic latent image by a developing roller 8 (also referred to as a developing device 8), and the image is developed as a toner image. As a result, the image is visualized.

Although not shown, the charging high-voltage power supply that supplies the charging bias to the charging rollers 7Y, 7M, 7C, and 7K is common. Further, a developing high-voltage power supply that supplies a developing bias to the developing rollers 8Y, 8M, 8C, and 8K is also standardized. As described above, since the high-voltage power supply is shared with respect to the plurality of charging rollers 7 and the developing rollers 8, further miniaturization of the apparatus can be realized. Further, a transformer having a variable output voltage for each color is provided, and the cost can be suppressed as compared with the case where the input voltage to each charging roller 7 and each developing roller 8 is individually controlled. Further, when a DC-DC converter (variable regulator) is provided for each charging roller 7 and each developing roller 8, the output from one transformer is individually controlled for each charging roller 7 and the developing roller 8. Even if compared, the cost can be suppressed.

The image formed on the photosensitive drum 5 enters the primary transfer portion with the intermediate transfer belt 3. In the primary transfer section, the primary transfer roller 10 is brought into contact contact with the back side of the intermediate transfer belt 3. A primary transfer bias power supply (not shown) is connected to the primary transfer roller 10 to enable the application of a bias. The yellow image is first transferred from the photosensitive drum 5Y to the intermediate transfer belt 3. Then, similarly, the magenta image from the photosensitive drum 5M, the cyan image from the photosensitive drum 5C, and the black image from the photosensitive drum 5K are primarily transferred. As a result, a color image is formed on the intermediate transfer belt 3.

On the other hand, the recording material P loaded and stored in the paper feed cassette 1 is fed by the paper feed roller 2, transported to the nip portion of the resist roller pair 6, and temporarily stopped. The recording material P once stopped is conveyed to the secondary transfer section by the resist roller pair 6 in synchronization with the timing when the image formed on the intermediate transfer belt 3 reaches the secondary transfer section. Then, by applying the secondary transfer bias to the secondary transfer roller 11, the image on the intermediate transfer belt 3 is secondarily transferred onto the recording material P. The recording material P on which the image is secondarily transferred is separated from the intermediate transfer belt 3 and sent to the fixing device 14 via the transfer guide 19. Here, the image is melted and fixed by being heated and pressurized by the fixing roller 15 and the pressure roller 16 to be fixed to the recording material P. After that, the recording material P is discharged from the paper ejection roller pair 20 to the outside of the machine. On the other hand, the toner remaining on the intermediate transfer belt 3 without being transferred to the recording material P in the secondary transfer unit is removed by the cleaning unit 21 arranged on the downstream side of the secondary transfer unit.

[Optical scanning device]
FIG. 2 is a schematic perspective view of the optical scanning device 9. A drive current based on the operation of the laser drive system circuit 130 flows through the laser diode 107 (hereinafter, also referred to as LD107) which is a light emitting element. The LD107 emits a laser beam at an intensity level corresponding to the drive current. The laser drive system circuit 130 is a circuit for driving the LD 107 that is electrically connected to the engine controller 122 and the video controller 123, which will be described later.

The laser beam emitted by the LD 107 is shaped into a beam shape by the collimator lens 134, formed into a parallel beam, and then scanned in the main scanning direction of the photosensitive drum 5 by the polygon mirror 133 as a rotating multifaceted mirror. The scanned laser beam is imaged on the surface of the rotating photosensitive drum 5 by the fθ lens 132 to form a dot-shaped spot. Then, the laser beam in the main scanning direction (direction parallel to the rotation axis direction of the photosensitive drum 5) can be scanned, and the scanning line is formed by scanning the laser beam to expose the photosensitive drum 5.

On the other hand, a reflection mirror 131 on which the laser beam is incident is provided at a position upstream of the scanning start position of the scanning line on the photosensitive drum 5 in the main scanning direction. The laser beam incident on the reflection mirror 131 is incident on the BD (Beam Detector) sensor 121. The BD sensor 121 outputs a horizontal synchronization signal as a signal corresponding to the laser beam in response to the incident of the laser beam. Based on the signal from the BD sensor 121, the scanning start timing of the laser beam is determined so that the laser beam can be scanned from the scanning start position. Further, after scanning the photosensitive drum 5 for one line and then scanning the photosensitive drum 5 again, APC (Auto Power Control), which is an automatic light amount control of the laser light amount, is performed, and LD107 is performed for the next scanning. The emission level (emission intensity) of is adjusted.

When the optical scanning device 9 forms an image based on the image data, the optical scanning device 9 normally emits light (emission intensity) at a light emission level (emission intensity) that allows toner to adhere to the image portion in the image formable region of the photosensitive drum 5. Normal exposure). Further, in the image-formable region of the photosensitive drum 5, minute light emission (micro exposure) is performed on the non-image portion at a light emission level (light emission intensity) that does not allow toner to adhere. Such micro-emission is performed in order to optimize the potential of the non-image portion of the photosensitive drum 5 after charging. Image defects such as fog phenomenon in which positively charged toner adheres to the photosensitive drum 5 more than necessary due to minute light emission, and inversion fog phenomenon in which negatively charged toner adheres to the photosensitive drum 5 more than necessary. Can be suppressed.

[Laser drive circuit]
Next, a laser drive circuit for causing the light source of the optical scanning device 9 to emit light will be described. FIG. 3 shows a laser drive circuit that automatically adjusts the light intensity level of the LD107 in order to prevent toner from adhering to the photosensitive drum in the non-image area and to emit a small amount of light so as not to cause positive or inverted fog. Is. In the following description, a configuration related to the control of the LD107a will be described in order to avoid complication of the description. As the number of light emitting elements increases, it becomes LD107X (X is b, c, d, ...), And the same configuration as LD107a will be omitted from the description, and a configuration different from LD107a will be described. In the present embodiment, it is assumed that the light emitting element has two light emitting elements, that is, LD107a and LD107b, and the BD signal is acquired by the BD sensor 121 by the LD107a.

In FIG. 3, the laser drive system circuit 130 shown in FIG. 2 corresponds to a portion surrounded by a dotted line frame. 101 and 111 are comparator circuits, 102 and 112 are sample / hold circuits, and 103 and 113 are hold capacitors. 104 and 114 are current amplifier circuits, 105 and 115 are reference current sources (constant current circuits), and 106 and 116 are switching circuits. 107a is a laser diode, 108 is a photodiode (hereinafter, also referred to as PD), and receives light emitted from a plurality of laser diodes including 107a and 107b, respectively. Reference numeral 109 is a current-voltage conversion circuit, and reference numeral 121 denotes a BD sensor. As will be described in detail later, with respect to the LD107a, the portions 101 to 106 correspond to the first light quantity adjusting means, and the portions 111 to 116 correspond to the second light quantity adjusting means. The adjustment circuits corresponding to each of the plurality of LDs can also be collectively referred to as the adjustment means.

Reference numeral 122 denotes an engine controller, which includes an ASIC, a CPU, RAM, and EEPROM. Further, the engine controller 122 not only controls the printer engine, but also controls communication with the video controller 123. Reference numeral 124 denotes an OR circuit, in which the Ldrv signal of the engine controller 122 and the VIDEO1 signal from the video controller 123 are connected to the input, and the Data1 signal is connected to the switching circuit 106 described later. The VIDEO1 signal is a signal based on print data sent from an external device such as a reader scanner or a host computer connected to the outside.

The VIDEO1 signal output from the video controller 123 is input to the buffer with the enable terminal of 125, and the output of the buffer is connected to the OR circuit 124 described above. At this time, the enable terminal is connected to the line from which the Vemb1 signal from the engine controller 122 is output.

Further, the engine controller 122 is connected so as to output an SH11 signal, an SH12 signal, a BASE1 signal, an Ldrv1 signal, and a Vemb1 signal, which will be described later. The Vemb1 signal is for masking the Data1 signal based on the VIDEO1 signal, and the timing (image mask period) of the image mask region can be created by putting the Vemb1 signal in the disable state (OFF state).

The first reference voltage Vref111 and the second reference voltage Vref121 are input to the positive electrode terminals of the comparator circuits 101 and 111, respectively, and the outputs are input to the sample / hold circuits 102 and 112, respectively. This reference voltage Vref111 is set as a target voltage for causing the LD107a to emit light at a normal printing emission level (first emission level or first light amount). Further, the reference voltage Vref 121 is set as a target voltage of a light emission level (second light emission level or second light amount) for minute emission. Hold capacitors 103 and 113 are connected to the sample / hold circuits 102 and 112, respectively. The outputs of the hold capacitors 103 and 113 are input to the positive electrode terminals of the current amplifier circuits 104 and 114, respectively.

As will be described in detail later, the reference voltages Vref111 and Vref121 do not necessarily have to correspond to the light emission level for normal printing and the light emission level itself for minute light emission. The reference voltages Vref111 and Vref121 may be any information that can realize the emission level for normal printing and the emission level for minute emission in the laser drive circuit.

Reference current sources 105 and 115 are connected to the current amplifier circuits 104 and 114, respectively, and the output is input to the switching circuits 106 and 116, respectively. On the other hand, a third reference voltage Vref 112 and a fourth reference voltage Vref 122 are input to the negative electrode terminals of the current amplifier circuits 104 and 114, respectively. The currents Io1 (first drive current) and Io2 depend on the difference between the output voltage of the sample / hold circuit 102 and the reference voltage Vref 112 and the difference between the output voltage of the sample / hold circuit 112 and the reference voltage Vref 122 described above. (Second drive current) is determined respectively. That is, Vref112 and Vref122 are voltage settings for determining the drive current.

The switching circuit 106 operates on and off by the Data1 signal which is a pulse modulation data signal. The switching circuit 116 operates on and off by the input signal Base1. The output ends of the switching circuits 106 and 116 are connected to the cathode of the LD107a and supply the drive currents Idrv1 and Ib1. The drive current Idrv1 corresponds to the current Io11, and the drive current Ib1 corresponds to the current Io12. The drive current Idrv1 is a current for realizing a light emission level for normal printing, and the drive current Ib1 is a current for realizing a light emission level for minute emission. Therefore, each of the drive current Idrv1 and the drive current Ib1 can be made to correspond to the first drive current and the second drive current.

The anode of LD107a is connected to the power supply Vcc. The cathode of PD108 that monitors the amount of light of LD107a is connected to the power supply Vcc, and the anode of PD108 is connected to the current-voltage conversion circuit 109 to pass the monitor current Im through the current-voltage conversion circuit 109. As a result, the monitor voltage Vm is generated. This monitor voltage is non-feedback input to the negative electrode terminals of the comparator circuits 101 and 111.

Here, the configuration related to the control of the LD107a has been described. Since the configuration related to the control of the LD107b is the same as that of the LD107a, the description thereof is omitted here. Further, although the engine controller 122 and the video controller have been described as separate bodies here, the present invention is not limited to this. For example, a part or all of the engine controller 122 and the video controller may be constructed as the same control unit. Further, the laser drive circuit surrounded by the dotted line frame in the drawing may be partially or completely built in, for example, the engine controller 122.

[Explanation of APC of P (Idrv1)]
The engine controller 122 sets the sample / hold circuit 112 to the hold state (during the non-sampling period) according to the instruction of the SH12 signal, and sets the switching circuit 116 to the off operation state by the input signal Base1. Further, the engine controller 122 sets the sample / hold circuit 102 to the sampling state according to the instruction of the SH11 signal, and turns on the switching circuit 106 by the Data1 signal.

More specifically, the engine controller 122 sets the Data1 signal to be in the light emitting state of the LD107a by controlling the Ldrv1 signal. The period in which the sample / hold circuit 102 is in the sampling state corresponds to the period during APC operation. Although details will be described later, in the present embodiment, the BD signal is acquired by the laser emitted from the LD107a, and the capacity of the hold capacitor 103 is made smaller than the capacity of the hold capacitor 203. Specifically, the capacitance of the hold capacitor 103 is set to 4700 pF, and the capacitance of the hold capacitor 203 is set to 0.1 μF. By reducing the capacitance of the hold capacitor 103 of the LD107a in this way, the APC time of the LD107a can be shortened.

When the LD107a is in the full light emitting state, the PD108 monitors the light emitting amount of the LD107a and outputs a monitor current Im1 proportional to the light emitting amount. Then, the monitor voltage Vm1 is generated by passing the monitor current Im1 through the current-voltage conversion circuit 109. The current amplifier circuit 104 controls the drive current Idrv1 based on Io11 flowing through the reference current source 105 so that the monitor voltage Vm1 matches the target value of the first reference voltage Vref111. The reference voltage Vref111 is a voltage value corresponding to P (Idrv1). Such APC operation at a strong emission level in LD107a is also referred to as APC_Pa.

As will be described in detail later, when the LD107a is made to emit light at a normal light emission level for printing, the circuit of FIG. 3 operates as follows. First, the sample / hold circuit 112 is set to the hold period, the switching circuit 116 is turned on, and the sample / hold circuit 102 is set to the hold period. Then, during normal image formation during non-APC operation, the sample / hold circuit 102 is in the hold period (during the non-sampling period), the switching circuit 106 is turned on / off in response to the Data1 signal, and the drive current Idrv1 Is given pulse width modulation. Therefore, the above-mentioned control of the drive current Idrv1 (APC operation) adjusts the drive current that is superimposed or added to the drive current Ib1 corresponding to the minute emission level.

For example, the LD107b is also subjected to APC by the same control as described above, and the drive current Idrv2 is controlled respectively. That is, the engine controller 122 controls the SH21 signal and the Idrv2 signal in the same manner as described above to perform the APC operation of the LD107b. The APC operation of the strong emission level in this LD107b is also referred to as APC_Pb. The time required for this APC_Pb is a function inversely proportional to the capacitance of the hold capacitor 203, and is longer than the time required for APC_Pa due to the relationship of hold capacitor 203> hold capacitor 103.

[Explanation of APC of P (Ib1)]
On the other hand, the engine controller 122 sets the sample / hold circuit 102 to the hold state (during the non-sampling period) according to the instruction of the SH11 signal, and sets the switching circuit 106 to the off operation state by the Data1 signal. With respect to this Data1 signal, the engine controller 122 disables the Vemb1 signal connected to the enable terminal of the buffer 125 with an enable terminal, controls the Ldrv1 signal, and turns the Data1 signal into an off state. Further, the engine controller 122 sets the sample / hold circuit 112 during the APC operation according to the instruction of the SH12 signal, turns on the switching circuit 116 by the input signal Base1, and sets the LD107a to be in a minute light emitting state.

Although details will be described later, in the present embodiment, the BD signal is acquired by the laser emitted from the LD107a, and the capacity of the hold capacitor 113 is made smaller than the capacity of the hold capacitor 213. Specifically, the capacitance of the hold capacitor 113 is set to 4700 pF, and the capacitance of the hold capacitor 213 is set to 0.1 μF. By reducing the capacity of the hold capacitor 113 of the LD107a in this way, the APC time of the LD107a can be shortened.

When the LD107a is in the micro-emission state (lighting maintenance state) on the entire surface, the PD108 monitors the light emission amount of the LD107a and outputs a monitor current Im2 (Im1> Im2) proportional to the light emission amount. Then, the monitor voltage Vm2 is generated by passing the monitor current Im2 through the current-voltage conversion circuit 109. The current amplifier circuit 114 controls the drive current Ib1 based on Io12 flowing through the reference current source 115 so that the monitor voltage Vm2 matches the target value of the second reference voltage Vref121. The reference voltage Vref121 is a voltage value corresponding to P (Ib1). Such APC operation at a minute emission level in LD107a is also referred to as APC_Ba.

Based on the drive current Ib1 adjusted in this way, during normal image formation during non-APC operation, the sample / hold circuit 112 is in the hold period (during the non-sampling period), and the entire micro-emission state is maintained. ..

For example, the LD107b is also subjected to APC by the same control as described above, and the drive current Ib2 is controlled respectively. That is, the engine controller 122 controls the SH22 signal and the Base2 signal in the same manner as described above to perform the APC operation of the LD107b. The APC operation of the strong emission level in this LD107b is also referred to as APC_Bb.

If the toner fog / inversion fog and the like are ignored, the amount of laser emission light in the minute emission may be set to an appropriate intensity so that the charging potential does not fall below the developing potential. However, in order to suppress the occurrence of toner fog / reverse fog, it is necessary to stabilize the amount of light of P (Ib1) during image formation.

[Explanation of minute emission level]
The drive current Ib1 in the full-face micro-emission state is set so as to exceed the threshold current Is of LD107a shown in FIG. 4 and reach the micro-emission level P (Ib1). The minute emission level is an emission intensity level at which toner does not substantially adhere to the photosensitive drum 5 even when irradiated with a laser. Further, it means a light emission intensity level capable of suppressing the occurrence of toner fog and inversion fog. Further, the emission intensity of the emission level P (Ib1) is defined as a laser emission region. If the emission level P (Ib1) at this time is an LED emission region that is less than the laser emission region, the wavelength distribution of the spectrum is widened, and the wavelength distribution is wider than the rated wavelength of the laser. Therefore, the sensitivity of the photosensitive drum 5 is disturbed, and the surface potential becomes unstable. Therefore, the emission level P (Ib1) is set to a laser emission region that exceeds the LED emission region.

On the other hand, during normal image formation, the drive current Idrv1 + Ib1 is set to a light emission level that is the intensity of the print level P (Idrv1 + Ib1). The print level means a light emission intensity level at which the adhesion of toner to the photosensitive drum is saturated.

This emission level will be described with reference to FIG. The Vcdc applied to the photosensitive drum 5 from the charged high-voltage power supply (not shown) via the primary charging roller 7 appears as a charging potential Vd on the surface of the photosensitive drum 5. That is, the surface of the photosensitive drum 5 is charged with the potential Vd. At this time, the charging potential Vd is set to a potential higher than the charging potential of the non-image portion during toner development.

Then, the charging potential Vd is attenuated to the charging potential Vd_bg by the laser emission of the minute emission level Ebg1 (second emission level). The reason for the attenuation is that after the charging voltage is applied, a potential higher than the convergence potential may be generated in some places on the surface of the photosensitive drum 5, which increases Vback and induces inversion fog. Because there is. On the other hand, when the charging potential Vd is attenuated to the charging potential Vd_bg by the laser emission of the minute emission level Ebg1, it is possible to reduce the remaining potential higher than the convergence potential and suppress the inversion fog. it can. It is also well known that the transfer memory appears at the charging potential Vd. On the other hand, by performing laser emission at a minute emission level Ebg1, the transfer memory can be reduced, and the generation of a ghost image due to the transfer memory can be suppressed.

Further, the laser emission of the minute emission level Ebg1 can make the back contrast Vback, which is the potential difference from the development potential Vdc, appropriate. From this point of view, it is possible to suppress the occurrence of positive fog and reverse fog of the toner. Further, the development contrast Vcont (= Vdc-Vl), which is the difference value between the development potential Vdc and the exposure potential Vl, can be made appropriate at the same time. As a result, it is possible to suppress a decrease in development efficiency, suppress the occurrence of sweeping, or secure a transfer / retransfer margin.

Further, the charging voltage Vcdc is variably set according to the environment, changes with time of the photosensitive drum 5, and the like when trying to control the charging potential Vd to a constant value. Then, from the viewpoint of maintaining the image quality, it is necessary to set the amount of light of the target minute emission level variably accordingly. For example, when the value of the charging voltage Vcdc becomes large as an integer value (when it becomes small as an absolute value), the amount of light at the minute emission level Ebg1 is also increased. Further, when the value of the charging voltage Vcdc becomes small as an integer value (when it becomes large as an absolute value), the amount of light of the minute emission level Ebg1 is also reduced. Specifically, it is preferable to set the charging potential Vd to -700 to -600V, the charging potential Vd_bg to -550V to -400V, the developing potential Vdc to -350V, and the exposure potential Vl to -150V.

Further, when the charging voltage Vcdc is set to a fixed value, it is necessary to adjust the minute emission level as follows. When the charging voltage Vcdc is constant, for example, as the deterioration (usage status) of the photosensitive drum 5 progresses, the charging potential Vd rises. Therefore, when the charging potential Vd rises, it is necessary to increase the amount of light at the minute emission level Ebg1. On the contrary, the charging potential Vd before the deterioration of the photosensitive drum 5 progresses is smaller than the charging potential Vd when the deterioration progresses. Therefore, the amount of light of the minute emission level Ebg1 before the deterioration of the photosensitive drum 5 is smaller than that of the minute emission level Ebg1 when the deterioration of the photosensitive drum 5 progresses. In this way, the minute emission level can be made variable according to the change in the charging potential Vcdc.

[Explanation of P (Ib1 + Idrv1) emission]
When the LD107a is made to emit light at a normal light emission level for printing, the circuit of FIG. 3 is operated as follows. That is, the sample / hold circuit 112 is set to the hold period and the switching circuit 116 is turned on, the sample / hold circuit 102 is set to the hold period, and the switching circuit 106 is turned on. As a result, the drive current Idrv1 + Ib1 is supplied. Further, the LD107a can have a minute emission level emission intensity P (Ib1) of the drive current Ib1 in the off state of the switching circuit 106.

As will be described in detail later, the print level P (Idrv1 + Ib1) is an emission amount (emission intensity) obtained by superimposing the PWM emission level P (Idrv1) by pulse width modulation on the minute emission level P (Ib1). More specifically, when the SH12, SH11 and Base1 signals are in the above-mentioned setting state and the engine controller 122 is in the Vemb1 signal enabled state, the switching circuit 106 is turned on / off by the Data1 signal (VIDEO1 signal). This enables two levels of light emission between Ib1 to Idrv1 + Ib1 in terms of drive current, that is, between P (Ib1) and P (Idrv1 + Ib1) in terms of emission intensity. Further, in the light amount of P (Idrv1 + Ib1), the laser emission at the time according to the pulse duty is performed based on P (Ib1).

By operating the circuit of FIG. 3 in this way, the engine controller 122 can perform APC on the LD107a at a minute emission level. Further, the LD107a can be made to emit light at a minute emission level P (Ib). Further, the Data1 signal by the VIDEO1 signal transmitted from the video controller 123 enables light emission of the print level P (Idrv1 + Ib1) which is the first level in the laser light emitting region, and has two levels of light emission level. It will be possible.

Here, the configuration related to the control of the LD107a has been described, but the same applies to the configuration related to the control of the LD107b. It is possible to emit light at two levels of light emission level, that is, a minute light emission level P (Ib2) that does not adhere toner and a print level P (Idrv2 + Ib2) that adheres toner.

FIG. 9C is a diagram showing a light emitting state of the LD 107 when a VIDEO signal is output from the video controller 123. In the conventional PWM method, light emission of the same print level P (drv + b) is added to the light emission amount of the minute light emission level in one pixel described in FIG. 9A. On the other hand, in the present embodiment, PWM light emission by pulse width modulation is superimposed on the minute light emission level Pb that is constantly emitting light. The shaded area in the figure corresponds to the amount of light emitted at the print level. According to FIG. 9 (c), the radiated noise generated can be suppressed to a low level as compared with the case where the minute light emission is performed by the PWM method as shown in FIG. 9 (b).

[Two-level APC sequence]
Next, the execution timing of the APC that maintains the laser emission level will be described. In the present embodiment, the optical scanning device 9 is configured to include a plurality of light emitting units, LD107a and LD107b. Therefore, in each of the LD107a and LD107b, it is preferable to perform the normal APC for printing and the APC for minute light emission within one scan (within the BD cycle). However, if one cycle of the BD signal is shortened due to the miniaturization of the image forming apparatus and the optical scanning apparatus and the increase in the rotation speed of the polygon mirror 133, it may be difficult to secure the time for performing APC. .. That is, it may not be possible to carry out all of the above-mentioned four types of APCs in one cycle of the BD signal.

Therefore, in the present embodiment, the APC of the LD107a is controlled to perform both of the four types of APCs in one cycle of the BD signal, and the APC of the LD107b is controlled to perform one of the four types of APCs in each BD cycle. Specifically, in the odd-numbered BD cycle in one job, the first adjustment step of executing APC_Ba, APC_Pa, and APC_Bb is performed without executing APC_Pb of LD107b in one cycle of the BD signal. Further, in the even-numbered BD cycle in one job, the second adjustment step of executing APC_Ba, APC_Pa, and APC_Pb is performed without executing APC_Bb of LD107b in one cycle of the BD signal.

In this way, either one of APC_Pb and APC_Bb, which are APCs for micro-emission, is thinned out alternately at each BD cycle. That is, the first adjustment step and the second adjustment step are alternately executed for each BD cycle. FIG. 8 is a timing chart showing the timing of the APC in the present embodiment.

[First adjustment step]
FIG. 8A is a diagram showing the first adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. At the timing t7', the engine controller 122 turns on the SH12 signal and the BASE1 signal, and turns on the switching circuit 116. In addition, the notation such as timing t7'is also referred to as t7'hereinafter. After that, at t8', the engine controller 122 turns off the SH12 signal, turns off the BASE1 signal, and turns off the switching circuit 116. As a result, the APC having a minute emission level for LD107a is terminated.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. At t8', the engine controller 122 turns on the SH11 signal and the Ldrv1 signal, and turns on the switching circuit 106. At t0, after the BD signal is detected by the engine controller 122, at t1, the engine controller 122 turns off the SH11 signal, turns off the Ldrv1 signal, and turns off the switching circuit 106. As a result, the APC having a strong emission level for LD107a is terminated.

Next, APC (APC_Bb) with a minute emission level is performed on the LD107b. At t1, the engine controller 122 turns on the SH22 signal and the BASE2 signal, and turns on the switching circuit 216. As a result, the engine controller 122 starts the APC of the minute emission level. Then, at t2, the engine controller 122 turns off the SH22 signal and the BASE2 signal to terminate the APC having a minute light emission level.

Next, the timing at which the laser beam scanned on the photosensitive drum 5 reaches the position corresponding to the end portion on the photosensitive drum 5 is t3. In order to suppress inversion fog, minute light emission is performed on the LD107a and LD107b from the end to the end of the photosensitive drum 5. Therefore, at the timing t3, the engine controller 122 turns on the BASE1 signal and the BASE2 signal, and turns on the switching circuits 116 and 216. As a result, micro-emission is started.

Next, light emission (hereinafter, also referred to as VIDEO light emission) for image formation of LD107a and LD107b is started. The engine controller 122 inputs an enable signal instruction to the enable terminals of the buffer 125 and the buffer 225 by the Vemb1 signal and the Vemb2 signal from t4 after a lapse of a predetermined time with reference to t0 or t1 which is the output timing of the BD signal. To do. Further, in response to an enable signal instruction to the enable terminal, the video controller 123 outputs a VIDEO1 signal and a VIDEO2 signal from t4 after a lapse of a predetermined time with reference to t0 or t1 which is the output timing of the BD signal. Then, the LD 107 emits light at a light emission level P (Ib + Idrv) for printing, and the laser light is scanned by the optical scanning apparatus described with reference to FIG. The image region on the photosensitive drum 5 is scanned with a laser beam according to the VIDEO signal.

Then, the light emission for image formation of LD107a and LD107b is terminated. The engine controller 122 gives a disable signal instruction to the buffer 125 and the enable terminal of the buffer 225 by the Vemb1 signal and the Vemb2 signal at t5 after a predetermined time elapses with reference to t0 or t1 which is the output timing of the BD signal. input. Then, the light emission for image formation is terminated. In addition, minute light emission is also performed in the non-image portion in the region of the VIDEO1 signal and the VIDEO2 signal.

Next, at the timing t6 when the scanned laser beam reaches the position corresponding to the end portion on the photosensitive drum 5, the minute light emission of the LD107a and LD107b is terminated. The engine controller 122 turns off the switching circuit 116 and the switching circuit 216 by the BASE1 signal and the BASE2 signal at t6 after a lapse of a predetermined time based on t0 or t1 which is the output timing of the BD signal, and emits a minute amount of light. finish.

[Second adjustment process]
FIG. 8B is a diagram showing a second adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. Since the processing at the timings t7'to t8'is the same as that of the first adjustment step described above, detailed description here will be omitted.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. Since the processing at the timings t8'to t1 is the same as that of the first adjustment step described above, detailed description here will be omitted. At t0 to t1, the BD signal is detected by the engine controller 122.

Next, a strong emission level APC (APC_Pb) is performed on the LD107b. The engine controller 122 turns on the SH21 signal and the Ldrv2 signal at t1, and turns on the switching circuit 206. As a result, the engine controller 122 starts the APC of the strong emission level. Then, the engine controller 122 turns off the SH21 signal and the Ldrv2 signal at t2, and ends the APC having a strong light emission level. Since the subsequent processing is the same as that of the first adjustment step described above, detailed description here will be omitted.

As described above, the time related to APC can be shortened by alternately performing APC with a strong emission level and APC with a minute emission level of LD107b every BD cycle. On the other hand, the frequency of APC of LD107b is lower than that of LD107a. As the frequency of APC decreases, the amount of light of LD107b tends to decrease as compared with LD107a due to a minute discharge from the hold capacitor. Therefore, while the capacitances of the hold capacitors 103 and 113 are 4700 pF, the decrease in the amount of light can be suppressed by increasing the capacitance of the hold capacitors 203 and 213 to 0.1 μF. Here, as an example, an example of switching the target of the APC for each scanning line has been described, but the present invention is not limited to this, and the target of the APC may be controlled to be switched, for example, by several lines. ..

[Startup control of optical scanning device 9]
FIG. 6 is a characteristic diagram showing a change in the rotation speed of the polygon motor that drives the polygon mirror 133 from the start of startup, with the horizontal axis showing time and the vertical axis showing the rotation speed of the polygon motor. It also shows the control states of the polygon motors, LD107a and 107b, and the developer 8 controlled by the engine controller 122.

FIG. 7 is a timing chart of a signal related to activation control of the optical scanning device 9, and shows a BD signal output from the BD sensor 121, a strong light emitting state of LD107a and LD107b, and a minute light emitting state. In FIG. 7, the BD signal is a signal that becomes High level (hereinafter, also referred to as H level) when the BD sensor 121 does not receive the laser light, and Low level (hereinafter, also referred to as L level) when the BD sensor 121 receives the laser light. is there. In the present embodiment, the BD signal is acquired by detecting the laser beam from the LD107a with the BD sensor 121. Further, the strong light emitting state and the minute light emitting state of the LD107 are signals in which the extinguished state is the L level and the state in which the laser light is emitted to perform APC is the H level.

Upon receiving the print start instruction, the engine controller 122 starts the polygon motor start control by the polygon motor drive signal at a predetermined timing after the print start instruction is generated. At this time, the developer 8 is in a separated position away from the photosensitive drum 5. The polygon motor operates according to the set target rotation speed and the speed control instruction by the engine controller 122, and the polygon mirror 133 also starts rotating with the rotation of the polygon motor. At this time, since the LD 107 is in the extinguished state and the BD signal is not generated, the polygon motor is instructed to accelerate.

Next, the engine controller 122 performs a first light emission that forcibly emits light over the entire scanning region at a timing (first timing) when a predetermined time has elapsed. Here, when the first light emission is performed immediately after the polygon motor is started, the rotation speed of the polygon motor is slow, so that the laser beam has a larger energy than the energy emitted when forming a normal image. Is irradiated to the photosensitive drum 5. As a result, the photosensitive drum 5 is deteriorated, which may be a factor of shortening the life. Therefore, the LD107 is turned off from the start of the polygon motor to the first timing, and the LD107a is started to emit light after the polygon motor is in a stable acceleration state. If an attempt is made to carry out an APC having a strong emission level in the first emission, the amount of light of the LD107a increases momentarily, and the LD107a may be destroyed beyond the permissible range of the LD107a. Therefore, when the first light emission is performed, the APC at the minute light emission level is first performed, and then the APC at the minute light emission level and the APC at the strong light emission level are alternately repeated.

As the amount of laser light of the LD107a increases due to the APC generated by the first light emission, a BD signal corresponding to the laser light received by the BD sensor 121 is eventually generated at the timing of the APC having a strong light emission level of the LD107a. Then, the engine controller 122 stores the most recently updated BD cycle value each time a BD signal is generated. That is, when the BD signal is generated twice by the first light emission in FIG. 7, the engine controller 122 stores the BD period P1. Then, the engine controller 122 starts the unbranking control after the timing (second timing) when the BD signal is generated twice in order to switch the LD107a to the unbranking control in which the LD107a emits light only in the non-image region. In the present embodiment, as described above, the capacitances of the hold capacitors 203 and 213 are 0.1 μF, and the capacitances of the hold capacitors 103 and 113 are 4700 pF. That is, by reducing the capacitance of the capacitor related to the LD107a, the time related to the APC is shortened, and the time until switching to the unblanking control is shortened. As a result, it is possible to prevent the life of the photosensitive drum 5 from being shortened.

First, at the second timing, the engine controller 122 calculates a value P1 × Md1 [%] obtained by multiplying the most recently updated BD period P1 by a preset set value Md1. Then, at the timing when P1 × Md1 [%] elapses from the timing at which the BD signal is acquired, APC at a strong emission level is performed in order to acquire the next BD signal. When the next BD signal is acquired by the APC having this strong emission level, the LD107a is turned off.

Similarly, the engine controller 122 calculates a value P1 × Mbs1 [%] obtained by multiplying the recently updated BD period P1 by a preset set value Mbs1. Then, APC of a minute emission level is performed at the timing when P1 × Mbs1 [%] elapses from the timing at which the BD signal is acquired. The timing for ending the micro-emission level APC is determined by using the most recently updated BD cycle P1 as in the case of the micro-emission start timing. Based on the value P1 × Mbe1 [%] obtained by multiplying the BD cycle P1 by the preset value Mbe1, the process ends when P1 × Mbe1 [%] elapses from the timing at which the BD signal is acquired.

Further, in the second light emission, the APC having a strong light emission level and the APC having a minute light emission level of LD107b are performed by performing unbranking control in a non-image region in the same manner as LD107a. Therefore, the start timing of the strong emission level APC of LD107b is P1 × Mds2 [%], and the end timing is P1 × Mde2 [%]. Further, the start timing of the minute emission level APC is P1 × Mbs2 [%], and the end timing is P1 × Mbe2 [%] (second emission).

This second light emission is performed while sequentially determining the light emission timing as the BD cycles P1, P2, P3, ... Stored in the engine controller 122 are updated. Here, since the speed control of the polygon motor is accelerating toward the target rotation speed, the BD period tends to be gradually shortened, but the rate of change of the adjacent BD periods is small. Therefore, the next BD signal can be acquired by determining the light emission timing in the next scan from the previously stored BD cycle and emitting light in the non-image region. That is, the set value Md1 is set based on the timing of acquiring the next BD signal in the non-image region. Similarly, the set values Mbs1, Mbe1, Mds2, Mde2, Mbs2, and Mbe2 are set based on the timing at which the LD emits light in the non-image region.

Next, the engine controller 122 controls the developer 8 to come into contact with the photosensitive drum 5 during the start-up period of the polygon motor in order to shorten the first printout time. Generally, in the control of bringing the developer 8 into contact with the photosensitive drum 5, the time from the instruction of contact from the engine controller 122 to the actual contact of the developer 8 with the photosensitive drum 5 is mechanical. There is a lot of variation. Therefore, in consideration of the time of this variation, it is desirable to complete the contact operation for switching the developer 8 from the separated position to the contact position for contacting the lower photosensitive drum 5. On the other hand, as described above, when the developer 8 is brought into contact with the photosensitive drum 5, the image region on the photosensitive drum 5 is emitted with a small amount of light to generate toner. It is necessary to suppress the occurrence of positive fog and inverted fog.

Therefore, the engine controller 122 emits a minute amount of light from the state in which the APC having a strong light emission level or the APC having a minute light emission level is performed in the non-image area by the second light emission before the developer 8 is brought into contact with the developer 8. Take control. The engine controller 122 estimates the amount of minute emission energy when minute emission is performed in the image region based on the cumulative time when the LD 107 is subjected to APC at the minute emission level and the current rotation speed of the polygon motor.

That is, the engine controller 122 determines the current minute emission level obtained from the cumulative time when the LD 107 is subjected to the minute emission level APC, and the scanning speed when the image region corresponding to the current rotation speed of the polygon motor is minutely emitted. The amount of minute emission energy is estimated based on. Then, the back contrast Vback defined by the minute amount of light emission energy is within a predetermined threshold range, and control is performed so that positive fog and reverse fog of the toner can be suppressed.

In this way, after the timing (third timing) when the engine controller 122 determines that the minute emission energy amount is within the predetermined threshold range, the image region is added to the second emission (ambling control). Starts micro-emission to. The minute light emission to this image region is performed based on the recently updated BD period P5, as in the second light emission. That is, it is performed at the timing when the value P5 × Mvs1 [%] obtained by multiplying the BD period P5 by the preset value Mvs1 elapses from the timing at which the BD signal is acquired.

The timing of ending the micro-emission is also performed based on the recently updated BD cycle P5, similarly to the start timing of the micro-emission. That is, it is performed at the timing when the value P5 × Mve1 [%] obtained by multiplying the BD period P5 by the preset set value Mve1 elapses from the timing at which the BD signal is acquired. Similarly, for LD107b, it starts at the timing when P5 × Mvs2 [%] elapses from the timing when the BD signal is acquired, and ends at the timing when P5 × Mve2 [%] elapses from the timing when the BD signal is acquired. .. When micro-emission is performed in the image region, the sample / hold circuit 112 may be put in a hold state to emit light while maintaining the emission level of the micro-emission so that the back contrast Vback is within a predetermined threshold range. desirable.

As for the third light emission, the light emission timing is sequentially determined as the BD cycles P5, P6, P7, ... Are updated. Then, the engine controller 122 abuts the developer 8 on the photosensitive drum 5 after the timing when the third light emission is started, the rotation of the photosensitive drum 5 makes one revolution, and the entire surface of the photosensitive drum 5 emits a minute amount of light. Let me. After that, when the polygon motor reaches within 1% of the target rotation speed, the engine controller 122 determines that the start of the polygon motor is completed. At this time, the LD 107 has completed APC with a desired strong emission level and minute emission level suitable for performing image formation.

As described above, when the optical scanning device 9 is started, the period during which the photosensitive drum 5 is forced to emit light is suppressed, and by switching to the unblanking control, it is possible to suppress the decrease in the life of the photosensitive drum 5. Further, by bringing the developing device 8 into contact with the photosensitive drum 5 after switching to the unbranking control, the image can be formed without downtime after the start-up of the optical scanning device 9 is completed, so that the FPOT is shortened. You can also do it.

(Second embodiment)
In the first embodiment described above, the light emission control in the configuration having two LDs has been described. In this embodiment, the light emission control in the configuration having four LDs will be described. The detailed description of the configuration similar to that of the first embodiment, such as the image forming apparatus, will be omitted here.

In this embodiment, it is assumed that the LD107a, LD107b, LD107c, and LD107d are provided, and the laser beam emitted from the LD107a is detected by the BD sensor 121. Further, in order to detect the laser beam emitted from the LD107a by the BD sensor 121, the hold capacitors 103 and 113 are made smaller than the hold capacitors 203, 303, 403, 213, 313, and 413. Specifically, the capacitances of the hold capacitors 103 and 113 are set to 3300 pF, and the capacitances of the hold capacitors 203, 303, 403, 213, 313, and 413 are set to 0.1 μF. Thereby, the time required for APC of LD107a can be suppressed. Hereinafter, the two-level APC sequence will be described with reference to FIG.

[Two-level APC sequence]
The execution timing of the APC that maintains the laser emission level will be described. The optical scanning device 9 has a configuration including a plurality of light emitting units LD107a, LD107b, LD107c, and LD107d. In the present embodiment, an example will be described in which, of the eight types of APCs, the APCs of the LD107a are both performed in one cycle of the BD signal, and the APCs of the LD107b, LD107c, and LD107d are performed for each BD cycle.

Specifically, in the Nth BD cycle in one job, the first adjustment step of executing APC_Ba, APC_Pa, APC_Bb, and APC_Pb without executing the APCs of LD107c and LD107d in one cycle of the BD signal is performed. Do. Further, in the (N + 1) th BD cycle in one job, the second adjustment step of executing APC_Ba, APC_Pa, APC_Bc, and APC_Pc is performed without executing the APCs of LD107b and LD107d in one cycle of the BD signal. .. Further, in the (N + 2) th BD cycle in one job, the third adjustment step of executing APC_Ba, APC_Pa, APC_Bd, and APC_Pd is performed without executing the APCs of LD107b and LD107c in one cycle of the BD signal. ..

[First adjustment step]
FIG. 10A is a diagram showing the first adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. Since the control of the minute emission level of APC in t8'to t9'is the same as that of the first embodiment, detailed description here will be omitted.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. Since the control of the strong emission level APC in t9'to t1 is the same as that of the first embodiment, detailed description here will be omitted. At t0 to t1, the BD signal is detected by the engine controller 122.

Next, APC (APC_Bb) with a minute emission level is performed on the LD107b. Since the control of the minute emission level APC in t1 to t2 is the same as that in the first embodiment, detailed description here will be omitted. Next, a strong emission level APC (APC_Pb) is performed on the LD107b. Since the control of the strong emission level APC at t2 to t3 is the same as that of the first embodiment, detailed description here will be omitted.

Next, the timing at which the laser beam scanned on the photosensitive drum 5 reaches the position corresponding to the end portion on the photosensitive drum 5 is t4. In order to suppress inversion fog, micro-emission is performed on the LD107a, LD107b, LD107c, and LD107d from one end to the other of the photosensitive drum 5. Therefore, at the timing t4, the engine controller 122 turns on the BASE1, BASE2, BASE3, and BASE4 signals, and turns on the switching circuits 116, 216, 316, and 416. As a result, micro-emission is started.

Next, light emission for image formation of LD107a, LD107b, LD107c, and LD107d is started. The engine controller 122 inputs the following signals from t5 after a lapse of a predetermined time with reference to t0 or t1 which is the output timing of the BD signal. That is, the enable signal instruction is input to the enable terminals of the buffers 125, 225, 325, and 425 by the Vemb1, Vemb2, Vemb3, and Vemb4 signals. Further, in response to the enable signal instruction to the enable terminal, the video controller 123 outputs the VIDEO1, VIDEO2, VIDEO3, and VIDEO4 signals from t5 after a predetermined time elapses, based on the BD signal output timing t0 or t1. Will be done. Then, the LD 107 emits light at a light emission level P (Ib + Idrv) for printing, and the laser light is scanned by the optical scanning apparatus described with reference to FIG. The image region on the photosensitive drum 5 is scanned with a laser beam according to the VIDEO signal.

Then, the light emission for image formation of LD107a, LD107b, LD107c, and LD107d is terminated. The engine controller 122 inputs the following instructions at t0, which is the output timing of the BD signal, or at t6 after a lapse of a predetermined time with reference to t1. That is, the disable signal instruction is input to the enable terminals of the buffers 125, 225, 325, and 425 by the Vemb1, Vemb2, Vemb3, and Vemb4 signals. Then, the light emission for image formation is terminated. It should be noted that even in the non-image portion in the region of the VIDEO1, VIDEO2, VIDEO3, and VIDEO4 signals, minute light emission is performed.

Next, at the timing t7 when the scanned laser beam reaches the position corresponding to the end portion on the photosensitive drum 5, the minute emission of the LD107a, LD107b, LD107c, and LD107d is terminated. The engine controller 122 turns off the switching circuits 116, 216, 316, and 416 by the BASE1, BASE2, BASE3, and BASE4 signals at t7 after the elapse of a predetermined time with reference to the output timing of the BD signal, t0 or t1. As a result, the minute light emission is terminated.

[Second adjustment process]
FIG. 10B is a diagram showing a second adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. Since the processing in t8'to t9'is the same as that of the first adjustment step described above, detailed description here will be omitted.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. Since the processing in t9'to t1 is the same as the first adjustment step described above, detailed description here will be omitted. At t0 to t1, the BD signal is detected by the engine controller 122.

Next, APC (APC_Bc) with a minute emission level is performed on the LD107c. The engine controller 122 turns on the SH32 signal and the BASE3 signal at t1, and turns on the switching circuit 316. As a result, the engine controller 122 starts the APC of the minute emission level. Then, the engine controller 122 turns off the SH32 signal and the BASE3 signal at t2, and ends the APC at the minute emission level.

Next, a strong emission level APC (APC_Pc) is performed on the LD107c. The engine controller 122 turns on the SH31 signal and the Ldrv3 signal at t2, and turns on the switching circuit 306. As a result, the engine controller 122 starts the APC of the strong emission level. Then, the engine controller 122 turns off the SH31 signal and the Ldrv3 signal at t3, and ends the APC having a strong light emission level. Since the subsequent processing is the same as that of the first adjustment step described above, detailed description here will be omitted.

[Third adjustment process]
FIG. 10C is a diagram showing a third adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. Since the processing in t8'to t9'is the same as that of the first adjustment step described above, detailed description here will be omitted.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. Since the processing in t9'to t1 is the same as the first adjustment step described above, detailed description here will be omitted. At t0 to t1, the BD signal is detected by the engine controller 122.

Next, APC (APC_Bd) with a minute emission level is performed on the LD107d. The engine controller 122 turns on the SH42 signal and the BASE4 signal at t1, and turns on the switching circuit 416. As a result, the engine controller 122 starts the APC of the minute emission level. Then, the engine controller 122 turns off the SH42 signal and the BASE4 signal at t2, and ends the APC at the minute emission level.

Next, a strong emission level APC (APC_Pd) is performed on the LD107d. The engine controller 122 turns on the SH41 signal and the Ldrv4 signal at t2, and turns on the switching circuit 406. As a result, the engine controller 122 starts the APC of the strong emission level. Then, the engine controller 122 turns off the SH41 signal and the Ldrv4 signal at t3, and ends the APC at the minute emission level. Since the subsequent processing is the same as that of the first adjustment step described above, detailed description here will be omitted.

By repeating the first adjustment step to the third adjustment step in this way, the time required for the APC can be shortened by appropriately thinning out the APCs having a strong emission level and the APCs having a minute emission level of LD107b, LD107c, and LD107d. it can. On the other hand, the frequency of APCs of LD107b, LD107c, and LD107d is lower than that of LD107a. As the frequency of APC decreases, the amount of light of LD107b, LD107c, and LD107d tends to decrease as compared with LD107a due to a minute discharge from the hold capacitor. Therefore, while the capacitances of the hold capacitors 103 and 113 are 3300 pF, the decrease in the amount of light is suppressed by increasing the capacitances of the hold capacitors 203, 303, 403, 213, 313, and 413 to 0.1 μF. Can be done.

In this embodiment, each adjustment step is set as follows. In the first adjustment step, APC_Ba, APC_Pa, APC_Bb, and APC_Pb are carried out. In the second adjustment step, APC_Ba, APC_Pa, APC_Bc, and APC_Pc are carried out. In the third adjustment step, APC_Ba, APC_Pa, APC_Bd, and APC_Pd are carried out. However, the combination in which APC is performed is not limited to this, and the LD to be performed in APC can be set as appropriate. If the time for performing APC is short within one cycle of the BD signal, the first to sixth adjustment steps are provided, and APC_Bb, APC_Pb, APC_Bc and APC_Pc, APC_Bd, and APC_Pd are performed in each adjustment step. You may try to do it.

(Third Embodiment)
In this embodiment, a case where the two-level APC sequence is changed according to the film thickness of the photosensitive drum 5 will be described. As the configuration of the optical scanning device 9, a configuration having four LDs will be described as an example. Further, as in the previous embodiment, the BD sensor 121 detects the laser beam emitted from the LD107a. Further, in order to detect the laser beam emitted from the LD107a by the BD sensor 121, the hold capacitors 103 and 113 are made smaller than the hold capacitors 203, 303, 403, 213, 313, and 413. Specifically, the capacitances of the hold capacitors 103 and 113 are 3300 pF, and the capacitances of the hold capacitors 203, 303, 403, 213, 313, and 413 are 0.1 μF. Thereby, the time required for APC of LD107a can be suppressed.

FIG. 11 is a diagram showing the relationship between the current flowing through the laser diode and the emission intensity according to the film thickness of the photosensitive drum 5. FIG. 11A shows a case where the film thickness of the photosensitive drum 5 is thicker than a predetermined thickness, that is, the photosensitive drum 5 is in the initial state, and FIG. 11B shows that the film thickness of the photosensitive drum 5 is larger than the predetermined thickness. When it is thin, that is, it is a state after the photosensitive drum 5 has been durable. Here, when the film thickness of the photosensitive drum 5 is thick, the drive current Ib1 for minute light emission is close to the threshold current Is, so that when the frequency of APC decreases, the amount of light for minute light emission becomes unstable. Therefore, when the film thickness of the photosensitive drum 5 is thick, the frequency of APC at the minute emission level of LD107 is increased. That is, the control for changing the target of the APC performed in the two-level APC sequence is performed according to the film thickness condition of the photosensitive drum 5.

[Two-level APC sequence]
The execution timing of the APC that maintains the laser emission level will be described. In the present embodiment, an example will be described in which, of the eight types of APCs, the APCs of the LD107a are both performed in one cycle of the BD signal, and the APCs of the LD107b, LD107c, and LD107d are performed for each BD cycle.

Specifically, in the N, (N + 2), and (N + 4) th BD cycles in one job, the first adjustment step of executing APC_Ba, APC_Pa, APC_Bb, and APC_Bc is performed in one cycle of the BD signal. Further, in the (N + 1) th BD cycle in one job, the second adjustment step of executing APC_Ba, APC_Pa, APC_Bd, and APC_Pb is performed in one cycle of the BD signal. In the (N + 3) th BD cycle in one job, the third adjustment step of executing APC_Ba, APC_Pa, APC_Bd, and APC_Pc is performed in one cycle of the BD signal. In the (N + 5) th BD cycle in one job, the fourth adjustment step of executing APC_Ba, APC_Pa, APC_Bd, and APC_Pd is performed in one cycle of the BD signal.

[First adjustment step]
FIG. 12A is a diagram showing the first adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. Since the control of the minute emission level of APC in t8'to t9'is the same as that of the first embodiment, detailed description here will be omitted.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. Since the control of the strong emission level APC in t9'to t1 is the same as that of the first embodiment, detailed description here will be omitted. At t0 to t1, the BD signal is detected by the engine controller 122.

Next, APC (APC_Bb) with a minute emission level is performed on the LD107b. Since the control of the minute emission level APC in t1 to t2 is the same as that in the first embodiment, detailed description here will be omitted. Next, APC (APC_Bc) with a minute emission level is performed on the LD107c. Since the control of the strong emission level APC at t2 to t3 is the same as that of the first embodiment, detailed description here will be omitted.

Next, the timing at which the laser beam scanned on the photosensitive drum 5 reaches the position corresponding to the end portion on the photosensitive drum 5 is t4. In order to suppress inversion fog, micro-emission is performed on the LD107a, LD107b, LD107c, and LD107d from one end to the other of the photosensitive drum 5. Since the micro-emission is the same as that of the second embodiment, detailed description here will be omitted.

Next, light emission for image formation of LD107a, LD107b, LD107c, and LD107d is started. The engine controller 122 emits light from t5 after a lapse of a predetermined time with reference to t0 or t1 which is the output timing of the BD signal. Since the light emission for image formation is the same as that of the second embodiment, detailed description here will be omitted. Then, the light emission for image formation of LD107a, LD107b, LD107c, and LD107d is terminated. The engine controller 122 ends the light emission at t6 after a lapse of a predetermined time with reference to t0 or t1 which is the output timing of the BD signal. Since the termination process is the same as that of the second embodiment, detailed description here will be omitted.

Next, at the timing t7 when the scanned laser beam reaches the position corresponding to the end portion on the photosensitive drum 5, the minute emission of the LD107a, LD107b, LD107c, and LD107d is terminated. Since the termination process is the same as that of the second embodiment, detailed description here will be omitted.

[Second adjustment process]
FIG. 12B is a diagram showing a second adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. Since the processing in t8'to t9'is the same as that of the first adjustment step described above, detailed description here will be omitted.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. Since the processing in t9'to t1 is the same as the first adjustment step described above, detailed description here will be omitted. At t0 to t1, the BD signal is detected by the engine controller 122.

Next, APC (APC_Bd) with a minute emission level is performed on the LD107d. Since the processes in t1 to t2 are the same as those in the second embodiment, detailed description here will be omitted. Next, a strong emission level APC (APC_Pb) is performed on the LD107b. Since the processing in t2 to t3 is the same as that in the second embodiment, detailed description here will be omitted. Since the subsequent processing is the same as that of the first adjustment step described above, detailed description here will be omitted.

[Third adjustment process]
FIG. 12C is a diagram showing a third adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. Since the processing in t8'to t9'is the same as that of the first adjustment step described above, detailed description here will be omitted.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. Since the processing in t9'to t1 is the same as the first adjustment step described above, detailed description here will be omitted. At t0 to t1, the BD signal is detected by the engine controller 122.

Next, APC (APC_Bd) with a minute emission level is performed on the LD107d. Since the processes in t1 to t2 are the same as those in the second embodiment, detailed description here will be omitted. Next, a strong emission level APC (APC_Pc) is performed on the LD107c. Since the processing in t2 to t3 is the same as that in the second embodiment, detailed description here will be omitted. Since the subsequent processing is the same as that of the first adjustment step described above, detailed description here will be omitted.

[Fourth adjustment process]
FIG. 12D is a diagram showing a fourth adjustment step. First, APC (APC_Ba) at a minute emission level is performed on LD107a. Since the processing in t8'to t9'is the same as the first adjustment step described above, detailed processing here is omitted.

Next, APC (APC_Pa) with a strong emission level is performed on the LD107a. Since the processing in t9'to t1 is the same as the first adjustment step described above, detailed description here will be omitted. At t0 to t1, the BD signal is detected by the engine controller 122.

Next, APC (APC_Bd) with a minute emission level is performed on the LD107d. Since the processes in t1 to t2 are the same as those in the second embodiment, detailed description here will be omitted. Next, a strong emission level APC (APC_Pd) is performed on the LD107d. Since the processing in t2 to t3 is the same as that in the second embodiment, detailed description here will be omitted. Since the subsequent processing is the same as that of the first adjustment step described above, detailed description here will be omitted.

In this way, when the film thickness of the photosensitive drum 5 is thick, the APC is applied in the order of 1st adjustment step ⇒ 2nd adjustment step ⇒ 1st adjustment step ⇒ 3rd adjustment step ⇒ 1st adjustment step ⇒ 4th adjustment step. Do. This makes it possible to increase the frequency of APCs with minute emission levels of LD107b, LD107c, and LD107d. When the film thickness of the photosensitive drum 5 is thin, the two-level APC sequence described in the second embodiment is performed. In this way, by appropriately changing the target of APC according to the film thickness of the photosensitive drum 5, it is possible to perform APC at a minute emission level at a frequency according to the film thickness. In this embodiment, the frequency of APCs with minute emission levels of LD107b, LD107c, and LD107d was increased. However, the frequency of APCs with strong emission levels may be increased depending on the characteristics of the LD107. Further, in the present embodiment, the target of APC is changed according to the film thickness of the photosensitive drum 5. For example, the target of the APC may be changed according to the life of the LD 107 based on the light emission time.

103, 113, 203, 213 Hold capacitor 107 Laser diode 112 Engine controller

Claims (12)

It has a first light emitting part and a second light emitting part, and the first light emitting amount for forming an electrostatic latent image in the image part from each light emitting part is a light emitting amount smaller than the first light emitting amount, and is not. An irradiation means that irradiates light with a second emission amount for controlling the potential of the image unit, and
A first capacitor for adjusting the first light emitting amount of the first light emitting unit, and
A second capacitor for adjusting the second light emitting amount of the first light emitting unit, and
A third capacitor for adjusting the first light emission amount of the second light emitting unit, and
A fourth capacitor for adjusting the second light emitting amount of the second light emitting unit, and
In order to adjust the amount of light emitted from the light irradiating means, the adjusting means for adjusting the drive current supplied to the light irradiating means and the adjusting means.
A rotating multifaceted mirror that reflects the light emitted from the irradiation means and can scan the image area and the non-image area on the photoconductor.
A detection means for detecting light emitted from the first light emitting unit and reflected by the rotating multifaceted mirror, and
A control means for controlling the light emission of the first light emitting unit and the second light emitting unit is provided.
The capacity of the first capacitor and the capacity of the second capacitor are smaller than the capacity of the third capacitor and the capacity of the fourth capacitor.
The control means uses the light emitted from the first light emitting unit to cover the image region and the non-image region during a start-up period in which the rotation speed is controlled so that the rotary polyplane mirror rotates at a predetermined rotation speed. In a state where the first light emitting unit is controlled so as to obtain the first light emission to be scanned, the adjusting means is used to adjust the first light emitting amount and the second light emitting amount of the first light emitting unit.
When the adjustment of the first light emitting amount and the second light emitting amount of the first light emitting unit is completed by the adjusting means, the light emitted from the first light emitting unit scans the non-image region with the second light emitting. An image forming apparatus characterized in that the first light emitting unit is controlled so as to be. Photoreceptor and
A developing means capable of switching between a contact position in contact with the photoconductor and a separation position in distance from the photoconductor is provided.
The control means uses the developing means after the first light emitting unit emits the second light during the start-up period in which the rotation speed is controlled so that the rotating multifaceted mirror rotates at a predetermined rotation speed. The image forming apparatus according to claim 1, wherein the contact position is switched from the separated position. The image forming apparatus according to claim 1 or 2, wherein the detection means outputs a horizontal synchronization signal to the control means in response to detecting the light reflected by the rotating multifaceted mirror. The control means is said to have the first horizontal synchronization signal by the adjusting means during the first cycle from the output of the first horizontal synchronization signal to the next output of the second horizontal synchronization signal by the detection means. The first adjustment step of adjusting the first light emitting amount and the second light emitting amount of the light emitting unit and the first light emitting amount of the second light emitting unit is executed.
During the second cycle from the output of the third horizontal synchronization signal by the detection means to the next output of the fourth horizontal synchronization signal, the adjustment means said the first light emitting unit of the first light emitting unit. The image forming apparatus according to claim 3, further comprising performing a second adjusting step of adjusting one light emitting amount, the second light emitting amount, and the second light emitting amount of the second light emitting unit. The image forming apparatus according to claim 4, wherein the control means alternately executes the first adjustment step and the second adjustment step every cycle. The light irradiation means further includes a third light emitting unit and a fourth light emitting unit.
A fifth capacitor for adjusting the first light emission amount of the third light emitting unit, and
A sixth capacitor for adjusting the second light emitting amount of the third light emitting unit, and
A seventh capacitor for adjusting the first light emission amount of the fourth light emitting unit, and
An eighth capacitor for adjusting the second light emitting amount of the fourth light emitting unit is provided.
The capacity of the first capacitor and the capacity of the second capacitor are the capacity of the third capacitor, the capacity of the fourth capacitor, the capacity of the fifth capacitor, the capacity of the sixth capacitor, and the above. The image forming apparatus according to claim 1, wherein the capacity of the seventh capacitor is smaller than the capacity of the eighth capacitor. The image forming apparatus according to claim 6, wherein the detection means outputs a horizontal synchronization signal to the control means in response to detecting the light reflected by the rotating multifaceted mirror. The control means is said to have the first horizontal synchronization signal by the adjusting means during the first cycle from the output of the first horizontal synchronization signal to the next output of the second horizontal synchronization signal by the detection means. A first adjustment step of adjusting the first light emitting amount and the second light emitting amount of the light emitting unit and the first light emitting amount and the second light emitting amount of the second light emitting unit is executed.
During the second cycle from the output of the third horizontal synchronization signal by the detection means to the next output of the fourth horizontal synchronization signal, the adjustment means said the first light emitting unit of the first light emitting unit. The second adjustment step of adjusting the 1 light emission amount and the 2nd light emission amount and the 1st light emission amount and the 2nd light emission amount of the 3rd light emitting unit is executed.
During the third cycle from the output of the fifth horizontal synchronization signal by the detection means to the next output of the sixth horizontal synchronization signal, the adjustment means said the first light emitting unit of the first light emitting unit. The image formation according to claim 7, wherein a third adjustment step of adjusting the first light emission amount and the second light emission amount and the first light emission amount and the second light emission amount of the fourth light emitting unit is executed. apparatus. The image forming apparatus according to claim 8, wherein the control means repeatedly executes the first adjustment step, the second adjustment step, and the third adjustment step every cycle. The image forming apparatus according to claim 7, wherein the control means switches which light emission amount is adjusted during one cycle of the horizontal synchronization signal according to the film thickness of the photoconductor. When the film thickness of the photoconductor is thicker than a predetermined thickness, the control means
During the first cycle from the output of the first horizontal synchronization signal by the detection means to the next output of the second horizontal synchronization signal, the adjustment means said the first of the first light emitting unit. The first adjustment step of adjusting the 1 light emitting amount, the 2nd light emitting amount, the 2nd light emitting amount of the 2nd light emitting unit, and the 2nd light emitting amount of the 3rd light emitting unit is executed.
During the second cycle from the output of the third horizontal synchronization signal by the detection means to the next output of the fourth horizontal synchronization signal, the adjustment means said the first light emitting unit of the first light emitting unit. A second adjustment step of adjusting the first light emitting amount, the second light emitting amount, the first light emitting amount of the second light emitting unit, and the second light emitting amount of the fourth light emitting unit is executed.
During the third cycle from the output of the fifth horizontal synchronization signal by the detection means to the next output of the sixth horizontal synchronization signal, the adjustment means said the first light emitting unit of the first light emitting unit. A third adjustment step of adjusting the first light emitting amount, the second light emitting amount, the first light emitting amount of the third light emitting unit, and the second light emitting amount of the fourth light emitting unit is executed.
During the fourth cycle from the output of the seventh horizontal synchronization signal by the detection means to the next output of the eighth horizontal synchronization signal, the adjustment means said the first light emitting unit of the first light emitting unit. The image formation according to claim 10, wherein a fourth adjustment step of adjusting the first light emission amount and the second light emission amount and the first light emission amount and the second light emission amount of the fourth light emitting unit is executed. apparatus. The control means adjusts the amount of light emitted in the order of the first adjusting step, the second adjusting step, the first adjusting step, the third adjusting step, the first adjusting step, and the fourth adjusting step. The image forming apparatus according to claim 11.

Images