JP5717402B2 - Image forming apparatus - Google Patents

Description

The present invention is related to an electrophotographic image forming apparatus.

  A scanning optical device included in an electrophotographic image forming apparatus drives a semiconductor laser in accordance with input image data, and forms an electrostatic latent image in accordance with the image data on a photoreceptor. With the recent increase in speed and image quality of printers and copiers, the productivity of scanning optical devices is regarded as important. The productivity of the scanning optical device is determined by the number of exposure lines per unit time. In order to increase the productivity, the rotation speed of the laser scanner motor is increased, the number of surfaces of the rotary polygon mirror is increased, and exposure is performed for one scan. A method such as increasing the number of beams can be considered. However, the rotational speed of the laser scanner motor is approaching its limit, and problems such as temperature rise, noise, and cost increase have occurred. Further, since the scanning angle is reduced by increasing the number of surfaces of the rotary polygon mirror, it is necessary to increase the optical path length in order to obtain the same exposure width, resulting in an increase in size and cost of the apparatus. Therefore, in recent years, multi-beam laser diodes have been developed, and further multi-beams have been developed from 2 to 4 beams. For example, Patent Document 1 proposes a multi-beam technique, and a surface-emitting laser diode suitable for multi-beam development has been developed from an edge-emitting laser diode that is a conventional laser. Has been put to practical use.

  By the way, since the optical output characteristics of a semiconductor laser (laser element) are sensitive to ambient temperature changes, even if it is driven at a constant current value, its optical output varies greatly due to ambient temperature changes and self-heating. End up. Therefore, in response to the temperature dependence of the light output, the light amount control of the semiconductor laser is performed in order to keep the light output constant, and this control is called auto power control (hereinafter referred to as “APC”) control. In the APC control, the laser beam output is detected once in one horizontal scan in the vicinity of the laser, and this detection signal is fed back to the laser drive circuit to drive the semiconductor laser so that the laser beam output is always equal to a predetermined set value. Set the current and control the laser beam intensity. This stabilizes the light output against temperature changes. In general, it is known that a semiconductor laser is lit with a constant light amount when driven with the same current value in the same environment, and the semiconductor laser is controlled with a driving current set by APC control at the time of image formation. Thus, it is possible to turn on the light with a constant light amount equivalent to that during APC control.

  FIGS. 5A and 5B are sequence diagrams showing the operation timing of APC control of the laser diode converted into a multi-beam during the printing operation of the image forming apparatus. 5A and 5B, each row of LD1 to LD8 shows a control sequence in the laser diodes LD1 to LD8. “APC” in the figure indicates the operation period of the APC mode in which the APC control described above is performed, “printing” indicates the operation period of the printing mode in which the image forming apparatus performs printing, and “OFF” indicates that the laser diode is turned on. Indicates the period not to be allowed. FIG. 5A is a diagram showing a sequence in a case where APC control of all laser diodes is performed during one scan. In FIG. 5A, after the previous print scan is completed, each of the laser diodes LD1 to LD8 is once in the “OFF” mode, and then the laser diode LD1 is in the “APC” mode. The driver circuit turns on the laser diode LD1, adjusts the drive current of the laser diode LD1 so that the light amount becomes a constant light amount, and performs light amount control. Therefore, in the “APC” mode, a certain amount of time is required to make the light quantity control value constant. When the light amount control of the laser diode LD1 is completed and the “OFF” mode is set, the laser diode LD2 is subsequently set to the “APC” mode. As described above, the “APC” mode operation of the laser diodes LD1 to LD8 is sequentially performed, and after the “APC” mode up to the laser diode LD8 is finished, all the laser diodes are set to the “OFF” mode. Next, since the laser scanning enters the image printing area, the “printing” mode is set to expose the photosensitive member to form a latent image. Then, after the formation of one line of latent image in the main scanning direction is completed, the “OFF” mode is set again, and the execution of the series of “APC” modes described above is started for the next scanning line.

  As described above, in APC control, a certain amount of time is required to adjust the laser diode drive current to set the laser beam output to a predetermined set value. However, with the recent increase in the speed and resolution of image forming apparatuses, when the laser emission point is constant, the speed of the laser scanner motor and the rotation of the polygon mirror are increased in order to increase the speed and resolution. Accordingly, the time required for one scan is also shortened. The APC control needs to be performed during a non-image period in which the surface of the photoconductor is not scanned. However, this non-image period is further shortened by increasing the speed of the laser scanner motor and increasing the number of polygons of the rotary polygon mirror. The issue of lack of time has become apparent. As a solution to such a problem, there is a method of performing APC control in a plurality of scanning periods instead of performing APC control of all lasers in one scanning period. With this method, the time required for APC control in one scanning period is shortened, so that the scanning cycle of one scanning can be shortened.

  FIG. 5B is a diagram showing a sequence when APC control of all laser diodes is performed in a plurality of scanning periods. In FIG. 5B, after the previous print scan is finished, the laser diodes LD1 to LD8 are in the “OFF” mode. Next, the laser diode LD1 enters the “APC” mode. When the APC control of the laser diode LD1 ends, the laser diode LD1 enters the “OFF” mode, and then the laser diode LD2 enters the “APC” mode. As described above, the “APC mode” operation from the laser diodes LD1 to LD4 is sequentially performed, and after the “APC” mode to the laser diode LD4 is completed, all the laser diodes are in the “OFF” mode. Next, since the laser scanning enters the image printing area, the “printing” mode is entered, and the photosensitive member is exposed to form a latent image. After the formation of the latent image for one line in the main scanning direction, the “OFF” mode is set again, and the APC control for the next scanning line is performed, so that the laser diode LD5 is set in the “APC” mode. When the APC control of the laser diode LD5 is completed, the laser diode LD5 is in the “OFF” mode, and then the laser diode LD6 is in the “APC” mode. As described above, the “APC” mode operation from the laser diodes LD5 to LD8 is sequentially performed, and when the “APC” mode to the laser diode LD8 is completed, all the laser diodes are in the “OFF” mode, and then image formation is performed. Therefore, the “printing” mode is set. In this way, one laser diode performs APC control once every two scans, thereby performing one cycle of APC operation, and the time required for APC control per scan can be shortened.

JP 2006-116716 A

  As described above, when the semiconductor laser is driven with the same current value in the same environment, it is lit with a constant light amount. In the print mode, the semiconductor laser is driven with the current value set by the APC control. Conventionally, constant current control has been performed on semiconductor lasers. By the way, even if the semiconductor laser is driven with the same current value, it has a temperature dependency in which the amount of light varies due to the variation of the ambient temperature. For this reason, the amount of light is corrected by performing APC control in a short cycle, and the ambient temperature Even if fluctuated, a predetermined image density was obtained. However, in the method of performing APC control in a plurality of scanning periods, the cycle for performing APC control becomes longer and the cycle for performing light amount correction also becomes longer. In the meantime, if the temperature of the semiconductor laser, which is the light emitting point, rises, or if the environmental temperature in the image forming apparatus rises, the constant current control causes the amount of light of the semiconductor laser to fluctuate, making it impossible to obtain a predetermined image density Occurred.

  The present invention has been made under such circumstances, and in a scanning optical apparatus in which the APC control cycle of each light emitting point must be set to be long, the light beam generated by the temperature rise of the light emitting point or the ambient temperature fluctuation can be obtained. An object is to suppress fluctuations in the amount of light and prevent image deterioration.

  In order to solve the above-described problems, the present invention is configured as follows.

(1) A semiconductor laser including a photoconductor and a light emitting unit that emits laser light for exposing the photoconductor, wherein the light emitting unit emits laser light when current is supplied; The light emitting unit, comprising: a deflecting unit that deflects the laser light so that the laser light emitted from the light emitting unit scans the photoconductor; and a light receiving element that receives the laser light emitted from the light emitting unit. In the image forming apparatus in which the cathode is set to a voltage lower than the anode, the current source is connected to the anode of the light emitting unit and outputs current, and the anode of the light emitting unit is connected to hold the voltage of the anode. A capacitor, a voltage control circuit connected to the anode of the light emitting unit, and controlling the voltage of the anode based on the voltage of the capacitor; an anode of the light emitting unit; And a control means for controlling an electrical connection state between the current source, the voltage control circuit, and the capacitor. The control means scans the photosensitive member with the laser light within the scanning period of the laser light. In the non-period, the electrical connection state is such that the anode of the light emitting unit and the current source, the anode of the light emitting unit and the capacitor are connected, and the anode of the light emitting unit and the voltage control circuit are not connected. The current source is controlled so as to be in a connected state, and the current source is output so that a light amount of the laser light emitted from the light emitting unit and incident on the light receiving element in the first state becomes a target light amount. The capacitor controls the current of the anode of the light emitting unit when the light amount of the laser light incident on the light receiving element in the first state is controlled to a target light amount. The control unit is configured to change the electrical connection state between the anode of the light emitting unit and the current source in a period during which the laser light scans the photosensitive member within the scanning period of the laser light. The anode of the light emitting unit and the capacitor are controlled to be in a non-connected state, and the anode of the light emitting unit and the voltage control circuit are connected to the second state. In the state, the voltage of the anode of the light emitting unit is controlled based on the voltage of the capacitor. In the second state, the current of the value based on the potential difference between the anode and the cathode of the light emitting unit is supplied to the light emitting unit as image data. The image forming apparatus is supplied on the basis of the above .

  According to the present invention, in a scanning optical apparatus in which the APC control cycle of each light emitting point must be set long, the light amount fluctuation of the light beam due to the temperature rise of the light emitting point and the ambient temperature fluctuation is suppressed, thereby preventing image deterioration. be able to.

Configuration of Main Part of Image Forming Apparatus of Embodiment The figure which showed the ILV characteristic of the laser diode of an Example The figure which showed the temperature characteristic of the laser diode of the Example The figure which shows the semiconductor laser of the multi-beam of an Example, and its driver circuit The figure which shows the operation sequence of the laser diode at the time of image formation of the conventional example

  Hereinafter, the form for implementing this invention is demonstrated in detail by an Example.

[Overview of image forming apparatus]
FIG. 1 is a configuration diagram of a main part of an image forming apparatus using a multi-beam semiconductor laser (laser element) according to the present embodiment. In FIG. 1, a laser scanner motor 1016 drives a rotary polygon mirror 1015 to rotate. A laser diode 1017 serving as an exposure light source is turned on or off according to an image signal by a laser driver 1029, and modulated laser light from the laser diode 1017 is emitted toward the rotary polygon mirror 1015. The laser light emitted from the laser diode 1017 is reflected as a deflected beam that continuously changes its angle on the reflecting surface as the rotary polygon mirror 1015 rotates. The reflected light is subjected to correction of distortion and the like by a lens group (not shown), and scans in the main scanning direction (perpendicular to the drawing) of the photosensitive drum 1010 through the reflecting mirror 1018. One surface of the rotating polygon mirror 1015 corresponds to one scan, and the rotation of the rotating polygon mirror 1015 causes the laser light from the laser diode 1017 to be line by line in the main scanning direction of the photosensitive drum 1010 that is a photosensitive member. Scan. The photosensitive drum 1010 is charged in advance by a charger 1011 and sequentially exposed by scanning with a laser beam to form an electrostatic latent image. Further, the photosensitive drum 1010 rotates in the direction of the arrow, and the formed electrostatic latent image is developed by the toner of the developing device 1012. The visualized toner image is transferred to a transfer paper (not shown) by the transfer charger 1013. Is done. The transfer paper onto which the toner image has been transferred is conveyed to a fixing device 1014, and after being fixed, is discharged outside the apparatus.

  A beam detect sensor (hereinafter, referred to as “BD sensor”) 1019 is disposed in the vicinity of the scanning start position in the main scanning direction on the side of the photosensitive drum 1010 or a corresponding position. The laser beam reflected by each reflecting surface of the rotary polygon mirror 1015 is detected by the BD sensor 1019 prior to scanning each line. The BD sensor 1019 outputs a beam detect signal (hereinafter referred to as “BD signal”) that is a scanning start reference signal in the main scanning direction, and the BD signal is input to the controller 1027. The controller 1027 generates a timing signal so that the writing start position of each line in the main scanning direction can be synchronized based on the BD signal, and supplies the timing signal to the FIFO memory 1028 and the laser driver 1029. The FIFO memory 1028 outputs the image signal by synchronizing the input image data with the timing signal from the controller 1027. The laser driver 1029 generates an optical pulse signal that controls blinking driving of the laser diode 1017 from the image signal from the FIFO memory 1028 and the timing signal from the controller 1027. In this manner, the semiconductor laser driving circuit generates an optical pulse signal of the semiconductor laser based on the electrical image signal, thereby performing image exposure on the photosensitive drum 1010 and image formation.

[Characteristics of semiconductor laser]
FIG. 2 is a diagram showing current-light output-voltage characteristics (hereinafter referred to as “ILV characteristics”) of a semiconductor laser used in the scanning optical device of the image forming apparatus. 2A is an edge-emitting laser diode, FIG. 2B is a current-light output characteristic (hereinafter referred to as “IL characteristic”), and a current-voltage characteristic (hereinafter referred to as “IL characteristic”). , “IV characteristics”). The IL characteristics and IV characteristics in FIG. 2A indicate characteristics measured at intervals of 10 ° C. from 10 ° C. to 40 ° C., and the IL characteristics and IV in FIG. A characteristic shows the characteristic measured at 10 degreeC intervals from environmental temperature 20 degreeC-50 degreeC.

  As shown in FIG. 2A, the edge-emitting laser diode has a light amount output-voltage characteristic (hereinafter referred to as “LV characteristic”) that has a very large light amount change rate with respect to a voltage in a current region equal to or higher than a threshold current. ). That is, according to the IV characteristic graph of FIG. 2A, when the environmental temperature is 20 ° C., when the voltage fluctuates by 0.1 V from 1.75 V to 1.85 V, the current value changes from 12.5 mA to 22 It will be 5 mA and will change by 10 mA. Then, from the IL characteristic graph of FIG. 2A, when the environmental temperature is 20 ° C., the change in the light output when the current value changes by 10 mA from 12.5 mA to 22.5 mA is 0.4 mW. 8.4 mW to about 8 mW. Therefore, the change rate of the light quantity with respect to the voltage of the edge-emitting laser diode is about 80 mW per 1 V from about 8 mW / 0.1 V.

  Next, the change rate of the light amount with respect to the voltage in the current region equal to or higher than the threshold current of the surface emitting laser diode is obtained. From the IV characteristic graph of FIG. 2 (b), when the environmental temperature is 20 ° C., the current value when the voltage changes 0.7V from 2.4V to 3.1V is changed from 1 mA to 4 mA, and the fluctuation is 3 mA. To do. From the IL characteristic graph of FIG. 2 (b), when the environmental temperature is 20 ° C., the variation in the light output when the current value varies by 3 mA from 1 mA to 4 mA is 1.3 mW to 4.8 mW. Of about 3.5 mW. Therefore, the rate of change in the amount of light with respect to the voltage of the surface emitting laser diode is about 5 mW per 1 V from about 3.5 mW / 0.7V. Compared to the edge-emitting laser diode described above, it can be seen that the surface-emitting laser diode has a very small change rate of light quantity with respect to the voltage in the current region equal to or higher than the threshold current.

  Further, when the light amount change rate with respect to the current of the surface emitting laser diode is obtained from the IL characteristic of FIG. 2B, the current value varies by 1 mA from 1.0 mA to 2.0 mA, and the light amount change rate is large. However, it is about 2 mW / mA, which is sufficiently small. For this reason, when performing feedback control in the APC mode, by performing constant current control, the control gain can be reduced and the control becomes more stable.

  Furthermore, from the graph of the IL characteristic in FIG. 2B, the light output is smaller as the environmental temperature is higher at the same current value. In the surface emitting laser diode, the light intensity increases as the environmental temperature increases. It turns out that it has the characteristic which falls.

[Temperature characteristics of surface emitting laser diode]
Next, temperature characteristics when a surface emitting laser diode is driven by constant current control will be described with reference to FIG. Fig. 3 (a) shows a case where constant current control is performed with a current value adjusted at intervals of 0.5 mW from 1 mW to 3 mW at 20 ° C, and the ambient temperature is increased from 20 ° C to 60 ° C at 10 ° C intervals. Temperature characteristics are shown. From FIG. 3A, for example, when APC control is performed at 20 ° C. and 3 mW, when the ambient temperature rises by 10 ° C. to 30 ° C. by the next APC cycle, it is compared with that at 20 ° C. The light output is reduced by 7.7%. Further, when the ambient temperature rises by 40 ° C. to 60 ° C., the light output is reduced by 41% compared to 20 ° C.

  Next, temperature characteristics when a surface emitting laser diode is driven by constant voltage control based on the present embodiment will be described with reference to FIG. FIG. 3 (b) shows the temperature when constant voltage control is performed with a voltage value adjusted at intervals of 0.5 mW from 1 mW to 3 mW at 20 ° C., and the ambient temperature is increased from 20 ° C. to 60 ° C. at intervals of 10 ° C. The characteristics are shown. From FIG. 3B, for example, when APC control is performed at 20 ° C. and 3 mW, when the ambient temperature rises by 10 ° C. and reaches 30 ° C. by the next APC cycle, compared to 20 ° C. The light output is increased by 2.0%. Further, when the ambient temperature rises by 40 ° C. to 60 ° C., the light output is reduced by 30% compared to 20 ° C. This indicates that the light amount change amount can be suppressed smaller in the constant voltage control of FIG. 3B than the light amount down rate in the constant current control described in FIG.

  When APC control is performed over a plurality of scanning periods and the APC control cycle is long, the light amount correction cycle is also long, during which the temperature of the laser diode as the light emitting point and the environmental temperature in the image forming apparatus rise. To do. In that case, in the constant current control, the light amount fluctuation of the semiconductor laser is larger than in the case of the constant voltage control, and it is difficult to obtain a predetermined image density in image formation. On the other hand, when the laser diode is driven by the constant voltage control, the change in the amount of light with respect to the environmental temperature fluctuation can be suppressed smaller than the constant current control, and the image deterioration can be prevented.

[Outline of driver circuit using surface emitting semiconductor laser]
Next, an embodiment in which a surface-emitting type multi-beam semiconductor laser is used in an image forming apparatus will be described with reference to FIG. FIG. 4 is a diagram showing an embodiment of a multi-beam semiconductor laser and its driver circuit in the scanning optical device of the image forming apparatus. 4, the driver circuit corresponds to the laser driver 1029 in FIG. 1, and the semiconductor laser LD100 corresponds to the laser diode 1017 in FIG. The semiconductor laser LD100 has a plurality of laser diodes LD1 to LD8 in a package, and the cathode terminals of the laser diodes LD1 to LD8 are grounded as a common terminal. The anode terminals of the laser diodes LD1 to LD8 are connected to the driver circuits 110 to 180, respectively, and a drive current is supplied from the corresponding driver circuit.

The driver circuits 110 to 180 are the same circuit, and the connection relationship of the circuits will be described below using the driver circuit 110 as an example. The photodiode PD 1 is installed at a position where the radiated light of the laser diodes LD1 to LD8 or a part thereof is irradiated in order to monitor the output light amount of each of the laser diodes LD1 to LD8. Convert and output. The anode terminal of the photodiode PD1 is grounded, and the cathode terminal is connected to the power supply Vcc via the resistor R1. The cathode terminal of the photodiode PD1 is connected to the + input terminal of the error amplifier OP111. The resistor R1 is a monitor current detection resistor that converts the monitor current output from the photodiode PD1 into a monitor voltage, and a voltage corresponding to the monitor current is applied to the + input terminal of the error amplifier OP111. The reference voltage Vref is applied to the negative input terminal of the error amplifier OP111. The output terminal of the error amplifier OP111 is connected to the control terminal of the constant current source Q111, and the constant current source Q111 outputs a current corresponding to the voltage applied to the control terminal. The output terminal of the constant current source Q111 is connected to the collector terminal of the NPN transistor Q112. The emitter terminal of the transistor Q112 is connected to the anode terminal of the laser diode LD1 as the output of the driver circuit 110. The cont1 signal generated by the controller 1027 in FIG. 1 is input to the base terminal of the transistor Q112. The emitter terminal of the transistor Q112 is also connected to the input terminal of the analog switch SW111, and the cont1 signal is input to the control terminal that controls the operation of the analog switch SW111. An output terminal of the analog switch SW111 has one end of the sample hold capacitor C11 1, is connected to a control terminal of the constant voltage source Q113. The other end of the sample hold capacitor C111 is grounded. The output terminal of the constant voltage source Q113 is connected to the collector terminal of the NPN transistor Q114. Similarly to the emitter terminal of the transistor Q112, the emitter terminal of the transistor Q114 is also connected to the anode terminal of the laser diode LD1 as an output of the driver circuit 110. A data1 signal that is an image signal is input to the base terminal of the transistor Q114 from the FIFO memory 1028 in FIG. The circuit configuration of the other driver circuits 120 to 180 is the same as that of the driver circuit 110.

[Operation of driver circuit using surface emitting semiconductor laser]
Then, when APC mode is a period in which the APC control is performed, OFF mode without lighting the laser diode, the circuit operation of FIG. 4 at the time of printing mode will be described below. In this embodiment, APC control of four laser diodes is performed in one scanning period based on the operation sequence of FIG. 5B, and APC control of all laser diodes is performed in two scanning periods. It shall be done in

  First, in FIG. 4, in the APC mode, the controller 1027 outputs a high level signal for the cont1 signal and a low level signal for the data1 signal so that the laser diode LD1 is in the APC mode. For the laser diodes LD2 to LD8, the controller 1027 outputs a low level signal to the cont2 to cont8 signals and the data2 to data8 signals so as not to be in the APC mode. Since the cont1 signal is at a high level, the NPN transistor Q112 is turned on. Further, since the high level signal is input to the control terminal, the analog switch SW111 is also turned on. Since the data1 signal is at a low level, the NPN transistor Q114 is turned off. When the transistor Q112 is turned on, the laser diode LD1 is turned on by the current supplied from the constant current source Q111. As the amount of light from the laser diode LD1 increases, the output current of the photodiode PD1 increases and the voltage drop due to the resistor R1 increases, so the voltage input to the error amplifier OP111 decreases. The output of the photodiode PD1 is compared with the reference voltage Vref by the error amplifier OP111, and the output voltage of the error amplifier OP111 decreases. When the output voltage of the error amplifier OP111 decreases, the voltage applied to the control terminal of the constant current source Q111 decreases, and as a result, the output current of the constant current source Q111 also decreases. When the output current of the constant current source Q111 decreases, the light amount of the laser diode LD1 also decreases. As described above, the driver circuit 110 constitutes a negative feedback circuit, and the laser diode LD1 is lit and driven with a constant light amount so that the output of the photodiode PD1 and the reference voltage Vref are the same voltage. Further, the emitter voltage of the transistor Q112, that is, the output voltage of the driver circuit 110 is applied to the laser diode LD1, and is further input to the sample hold capacitor C111 and the control terminal of the constant voltage source Q113 via the analog switch SW111. The constant voltage source Q113 outputs a voltage having the same potential as the voltage input to the control terminal. Since the transistor Q114 to which the output voltage from the constant voltage source Q113 is applied is turned off by the data1 signal, the output of the constant voltage source Q113 is not output to the laser diode LD1. In addition, since low level signals are input to the cont2 to cont8 signals and the data2 to data8 signals, the outputs of the driver circuits 120 to 180 are not input to the laser diodes LD2 to LD8. Is off.

  Next, the cont1 signal output from the controller 1027 changes from high level to low level, the cont2 signal changes from low level to high level, and low level signals are output to the other cont3 to cont8 signals and data1 to data8 signals. . As a result, the laser diode LD2 shifts to the APC mode, and the APC operation similar to the laser diode LD1 described above is performed. The APC control is sequentially performed on the laser diodes LD3 and LD4.

  Next, when the APC control of the laser diodes LD1 to LD4 is completed, all the laser diodes LD1 to LD8 are in the OFF mode. In the OFF mode, since low level signals are input from the controller 1027 to the cont1 to cont8 signals and the data1 to data8 signals, all the laser diodes LD1 to LD8 are turned off.

  Next, the circuit operation in the print mode, which is a period in which the laser diode is driven to scan the photosensitive drum 1010 with the current value set so that the light amount is constant, will be described. In the print mode, the controller 1027 outputs low level signals to the cont1 to cont8 signals, and the image data to be printed is output to the data1 to data8 signals. In the driver circuit 110, since the cont1 signal is at a low level, the transistor Q112 and the analog switch SW111 are turned off. As a result, the output of the constant current source Q111 is cut off and is not output to the laser diode LD1. On the other hand, the voltage applied to the laser diode LD1 in the APC mode and held by the sample hold capacitor C111 is applied to the control terminal of the constant voltage source Q113. As a result, the constant voltage source Q113 outputs a voltage having the same potential as that in the APC mode and applies it to the collector terminal of the transistor Q114. When the data1 signal is at a high level, the transistor Q114 is turned on. Therefore, the voltage in the APC mode is applied to the laser diode LD1 by the constant voltage source Q113 via the emitter terminal of the transistor Q114, and the laser diode LD1 is turned on. . When the data1 signal is at a low level, the transistor Q114 is turned off, so that the laser diode LD1 is turned off. As a result, the laser can be driven to blink by the image data input as the data1 signal, and image exposure is performed. In the driver circuits 120 to 180, the laser diodes LD2 to LD8 are driven to blink on the basis of the data2 to data8 signals, and image exposure is performed.

  After the formation of the latent image for one line in the main scanning direction, the OFF mode is set, and the laser diode LD5 is set to the APC mode for the next scanning line. When the APC control of the laser diode LD5 is completed, the laser diode LD5 enters the OFF mode, and then the laser diode LD6 enters the APC mode. As described above, the APC operations from the laser diodes LD5 to LD8 are sequentially performed, and after the APC control to the laser diode LD8 is completed, all the laser diodes are in the OFF mode. Subsequently, in order to perform image formation of this line, the print mode is set, and the operation in the print mode described above is executed.

  In general, high-speed driving of a constant voltage circuit, particularly switching operation at several tens of MHz for image formation is possible. Therefore, by selecting a transistor capable of high-speed switching as the transistor Q114, high-speed printing becomes possible.

  As described above, according to the present embodiment, in the scanning optical apparatus that must set a long APC control period for each light emitting point, the light amount variation of the light beam due to the temperature rise of the light emitting point and the ambient temperature variation is reduced. It is possible to suppress and prevent image deterioration.

  By the way, in the present embodiment, the circuit operation in the case where the APC control of all the laser diodes is performed in two scanning periods based on the operation sequence of FIG. That is, in the description of the above-described embodiment, the APC control of the laser diodes LD1 to LD4 is performed in the first scanning period, and the APC control of the laser diodes LD5 to LD8 is performed in the next scanning period. When the APC control is performed in one scanning period, the APC control of the laser diodes LD1 to LD8 is performed in the first scanning period, so that the present invention can perform the APC as shown in FIG. The present invention can also be applied to a case where the control is performed in one scanning period. As a result, the temperature rise of the light emitting point and the ambient temperature fluctuation are less likely to occur, and image deterioration can be prevented.

LD1 Laser diode PD1 Photodiode OP111 Error amplifier Q111 Constant current source Q113 Constant voltage source C111 Sample hold capacitor Q112 Transistor Q114 transistor

Claims (11)

A semiconductor laser comprising a photoconductor and a light emitting unit that emits laser light for exposing the photoconductor, wherein the light emitting unit emits laser light when supplied with current, and the light emitting unit A deflecting means for deflecting the laser light so that the laser light emitted from the light beam scans the photoconductor, and a light receiving element for receiving the laser light emitted from the light emitting part, and the cathode of the light emitting part is In the image forming apparatus set to a voltage lower than the anode,
A current source connected to the anode of the light emitting unit and outputting a current;
A capacitor connected to the anode of the light emitting unit and holding the voltage of the anode;
A voltage control circuit that is connected to the anode of the light emitting unit and controls the voltage of the anode based on the voltage of the capacitor;
A control means for controlling an electrical connection state between the anode of the light emitting unit, the current source, the voltage control circuit, and the capacitor;
The control means is configured to change the electrical connection state between the anode of the light emitting unit, the current source, and the anode of the light emitting unit during a period in which the laser light within the scanning period of the laser light does not scan the photoconductor. And the capacitor is connected, and the anode of the light emitting unit and the voltage control circuit are controlled to be in a first state,
The current source controls a current to be output so that a light amount of the laser light emitted from the light emitting unit and incident on the light receiving element in the first state becomes a target light amount;
The capacitor holds the voltage of the anode of the light emitting unit when the light amount of the laser light incident on the light receiving element in the first state is controlled to a target light amount,
The control means is configured to change the electrical connection state between the anode of the light emitting unit, the current source, and the anode of the light emitting unit during a period in which the laser light within the scanning period of the laser light scans on the photoconductor. And the capacitor is disconnected, and the anode of the light emitting unit and the voltage control circuit are controlled to be connected to a second state,
The voltage control circuit controls the voltage of the anode of the light emitting unit based on the voltage of the capacitor in the second state,
In the second state, the image forming apparatus and a current value based on the anode and cathode potential of the light emitting portion is provided on the basis of the image data to the light emitting portion. The semiconductor laser, the image forming apparatus according to claim 1, which is a surface-emitting laser diode. The semiconductor laser includes a plurality of the light emitting units,
The current source, the capacitor, and the voltage control circuit are individually provided for each of the plurality of light emitting units,
A switch is provided between each of the anodes of the plurality of light emitting units and the plurality of voltage control circuits corresponding to the plurality of light emitting units,
The control means includes
In a period in which the laser light within the scanning period of the laser light does not scan the photoconductor, the electrical connection state related to any one light emitting unit is controlled to the first state, and the other light emitting units related to Controlling the electrical connection state between the anode of the light emitting unit and the current source, the anode of the light emitting unit and the capacitor, and the anode of the light emitting unit and the voltage control circuit to a disconnected state;
In the period in which the laser light within the scanning period of the laser light scans the photoconductor, the electrical connection state of all the light emitting units is controlled to the second state, and the anodes of the plurality of light emitting units The image forming apparatus according to claim 1, wherein a switch provided between each of the plurality of voltage control circuits corresponding to the plurality of light emitting units is controlled to be turned off. The control unit controls the electrical connection state of the plurality of light emitting units to the first state at different timings within a period in which the laser light within one scanning period of the laser light does not scan the photoconductor. The image forming apparatus according to claim 3. The control unit is configured to control the electrical part of the plurality of light emitting units among the plurality of light emitting units at different timings within a period in which the laser light within one scanning period of the laser light does not scan the photoconductor. The image forming apparatus according to claim 3, wherein the connection state is controlled to the first state. The control means sets the electrical connection state of the plurality of light emitting units in a period in which the laser beam within the scanning cycle of the laser beam does not scan the photosensitive member at a frequency of once in a plurality of scanning cycles. The image forming apparatus according to claim 5, wherein the image forming apparatus is controlled to a first state. A switch provided between the front SL current source and the anode of the light emitting portion,
A switch provided between the front SL voltage control circuit and the anode of the light emitting portion,
A switch provided between the capacitor and the anode of the light emitting unit ;
With
The control means includes
The switch between the current source and the anode of the light emitting unit and the switch between the capacitor and the anode of the light emitting unit are turned on, and the switch between the voltage control circuit and the anode of the light emitting unit is turned off. Controlling the electrical connection state to the first state by controlling;
The switch between the current source and the anode of the light emitting unit and the switch between the capacitor and the anode of the light emitting unit are turned off, and the switch between the voltage control circuit and the anode of the light emitting unit is turned on. the image forming apparatus according to claim 1 or 2, wherein the controller controls the electrical connection to said second state by controlling. The switch provided between the current source and the anode of the light emitting unit , and the switch provided between the voltage control circuit and the anode of the light emitting unit are transistors, and the capacitor and the anode of the light emitting unit The image forming apparatus according to claim 7 , wherein the switch provided between the two is an analog switch. A switch is provided between each of the anodes of the plurality of light emitting units and the plurality of current sources corresponding to the plurality of light emitting units,
A switch is provided between each of the anodes of the plurality of light emitting units and the plurality of capacitors corresponding to the plurality of light emitting units,
The control means includes
The switch between the current source and the anode of the light emitting unit and the switch between the capacitor and the anode of the light emitting unit are turned on, and the switch between the voltage control circuit and the anode of the light emitting unit is turned off. Controlling the electrical connection state to the first state by controlling;
The switch between the current source and the anode of the light emitting unit and the switch between the capacitor and the anode of the light emitting unit are turned off, and the switch between the voltage control circuit and the anode of the light emitting unit is turned on. The image forming apparatus according to claim 3, wherein the electrical connection state is controlled to the second state by controlling. The switches provided between the plurality of current sources and the anodes of the plurality of light emitting units, and the switches provided between the plurality of voltage control circuits and the anodes of the plurality of light emitting units are transistors, The image forming apparatus according to claim 9, wherein the switch provided between the plurality of capacitors and the anodes of the plurality of light emitting units is an analog switch. The image forming apparatus according to claim 1, wherein a cathode of the light emitting unit is grounded.

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