JP3542472B2 - Laser driving method and adjustment method, and image forming apparatus using the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image recording apparatus such as a laser scanner unit and a laser printer using a multi-beam laser having a plurality of light emitting units.
[0002]
[Prior art]
Conventionally, a laser scanner unit having a polygon mirror that scans in the main scanning direction when forming an image by irradiating and exposing a rotating photosensitive drum with laser light, which is used in an image recording apparatus such as a laser printer, has a single unit. Semiconductor lasers have been used. In recent years, as the speed and definition of laser printers have been increased, the use of a multi-beam laser having a plurality of laser emission points has been studied. By using the multi-beam laser method, an image of a plurality of rows can be formed by one scan, so that when the number of rotations of the polygon mirror is the same, it is possible to print out at a speed that is a plurality of times faster than that.
[0003]
[Problems to be solved by the invention]
A commercially available semiconductor multi-beam laser has one laser light monitoring photodiode for a plurality of laser emission points. Therefore, in automatic power control (APC) for setting the laser light amount of each laser emission point to a predetermined light amount, it is necessary to individually increase the current for each laser emission point. Was. Therefore, during the period in which a current is applied to one laser emission point and the APC operation is performed, the other laser emission points need to be turned off.
[0004]
Therefore, in a multi-beam laser having a large number of firing points, it takes a lot of time to set the laser light quantity at each light emitting point to a specified value. As a result, in the laser printer using the multi-beam laser, since the APC operation for setting the laser light amount of each light emitting point to the specified value at the start of printing is performed, the time to shift to the printing operation becomes longer, and the first print time becomes longer. Was.
[0005]
Also, in a recording apparatus using a multi-beam laser, an adjustment variable resistor for determining a prescribed value of a laser light amount at the time of manufacturing (this adjustment variable resistor converts a current of a photodiode for monitoring a laser beam into a voltage, The target voltage is adjusted only for one light emitting point, and one adjusted result is used for other light emitting points. This is because the relationship between the front beam and the back beam from each light emitting point of the multi-beam laser is almost equal, and the current-voltage conversion adjustment of the monitoring photodiode for detecting the back beam is sufficient to be performed at only one light emitting point. . However, the relationship between the front beam and back beam at each laser emission point is slightly different due to variations in the end face coating of the laser resonator that determines the ratio of the front beam and back beam at each laser emission point. In a recording apparatus that prints, there is a possibility that image density unevenness may occur.
[0006]
A first object of the present invention is to provide a recording apparatus using a multi-beam laser, in which the time for setting each laser emission point to a specified light amount is reduced, and the first print time is short. is there.
[0007]
A second object of the present invention is to provide a means for accurately and safely adjusting the amount of laser light at each laser emission point in a recording apparatus using a multi-beam.
[0008]
[Means for Solving the Problems]
In order to achieve the first object, a laser driving method according to the present invention includes a semiconductor laser having a plurality of light emitting points, one photodetector for detecting individual back beams of the semiconductor laser, and the semiconductor laser. Semiconductor laser unit with integrated photodetector, laser drive circuit with sample-and-hold type automatic light intensity control for setting output of photodetector to specified value, and rotating polygon mirror for raster-scanning laser light And a reference position light detecting means for detecting the position of the scanned laser light.In the laser scanner unit, a current is first applied to all the laser light emitting points in order to make the laser light emitted from each light emitting point a prescribed light amount. Automatic light amount control is started in the sample mode at the time of the main application, and when the reference position light detecting means detects the laser light, the semiconductor light is controlled. The current applied to each light emitting point of the laser is fixed in the hold mode, and then the light amount of each laser light emitting point is set to the specified light amount by automatically controlling the light amount individually in the sample mode for each light emitting point. It is characterized in that the time is shortened and the first print time of the recording apparatus is shortened.
[0009]
In order to achieve the first object, a laser driving method according to the present invention includes a semiconductor laser having a plurality of light emitting points, one photodetector for detecting individual back beams of the semiconductor laser, and the semiconductor laser. Semiconductor laser unit with integrated photodetector, laser drive circuit with sample-and-hold type automatic light intensity control for setting output of photodetector to specified value, and rotating polygon mirror for raster-scanning laser light And a reference position light detecting means for detecting the position of the scanned laser light, in order to set the laser light emission at each light emission point to a prescribed light amount, first, current is applied to all laser light emission points. To start automatic light intensity control in the sample mode at the time of this application, and feed the detection amount information of the photodetector to the automatic light intensity control. When the reference position light detecting means detects the laser light, the current applied to each light emitting portion of the semiconductor laser is fixed in the hold mode, and thereafter, the detection amount information of the detecting device is used as the information. By feeding back to the automatic light intensity control and performing automatic light intensity control in the sample mode individually for each light emitting point, the time for setting the light intensity of each laser emission point to the specified light intensity is reduced, and the first print time of the recording device is shortened. It is characterized by shortening.
[0010]
In order to achieve the second object, a laser light amount adjusting method according to the present invention comprises a semiconductor multi-beam laser having a first laser light emitting portion and a second laser light emitting portion, and a photodiode as the photodetector. A first adjusting variable resistor for converting the detected current into a voltage, and a comparing means for comparing the voltage converted by the first adjusting variable resistor with a reference voltage, for adjusting the reference voltage. A second adjusting variable resistor for adjusting the laser light amount at the first light emitting point by the first adjusting variable resistor, and adjusting the laser light amount at the second light emitting point by the second adjusting. It is characterized in that it is adjusted by a variable resistor.
[0011]
Further, the present invention provides a semiconductor laser having a plurality of light-emitting portions, one photodetector for detecting individual back beams of the semiconductor laser, and a semiconductor laser unit in which the semiconductor laser and the photodetector are integrated. A laser driving circuit having a sample-and-hold type automatic light amount control for setting the output of the photodetector to a specified value, a rotating polygon mirror for raster-scanning laser light, and a laser scanned by the rotating polygon mirror In an image forming apparatus having reference synchronization detection means for detecting a light synchronization signal, an APC circuit for stabilizing the light emission amount of each of the semiconductor lasers is provided for each of the semiconductor lasers in order to set the laser light emission at each of the light emitting portions to a specified light amount. And all the APC circuits are operated first, and after the photodetection device detects the laser emission, a sample is provided for each of the APC circuits. And other APC circuit is APC operation is characterized in that to operate as a hold mode as Rumodo.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
FIG. 1 is an explanatory diagram of a drive circuit function of a multi-beam laser according to a first embodiment of the present invention. In this embodiment, a semiconductor multi-laser having two light-emitting points is described as a multi-beam laser. However, a multi-beam laser having three or more light-emitting points can be inferred from FIG. I do.
[0013]
In FIG. 1, LD1 and LD2 are laser diodes (hereinafter, also referred to as LDs) representing respective light emitting points of the multi-beam laser, and their anodes are connected to a power supply V1. PD is a photodiode (hereinafter also referred to as PD) for detecting the back beam laser light of each of the laser diodes LD1 and LD2. Reference numerals 1 and 2 denote analog switches for controlling the detection current of the photodiode PD to flow through the adjustment variable resistors VR1 and VR2 and not to flow the current, and are controlled by signals 9 and 10. Reference numerals 3 and 4 denote transistors for switching whether or not to turn on the laser diodes LD1 and LD2 based on the image data. The image data is applied from signals 5 and 6. Reference numerals 7 and 8 denote variable constant current sources, which determine voltage to be supplied to the laser diodes LD1 and LD2 based on voltage information of the sample and hold capacitors 15 and 16. Reference numerals 11 and 12 denote error detection amplifiers for detecting and comparing voltages according to the currents of the PDs. The error detection amplifiers 11 and 12 convert the detection currents of the photodiodes PD into voltages by the adjustment variable resistors VR1 and VR2, and the reference voltage Vref. The sample and hold capacitors 15 and 16 are charged and discharged according to the difference. Reference numerals 13 and 14 denote switch circuits for controlling the sample and hold states of the sample and hold capacitors 15 and 16, the states of which are controlled by control signals (not shown).
[0014]
FIG. 2 is a conceptual perspective view in a case where the laser diodes LD1, LD2 and the photodiode PD are integrated. On one surface of the stem 33, a base 34 is provided perpendicular to the base of the stem 33, and a laser chip 35 having light emitting points 35a and 35b and a photodiode 36 are fixed on the base 34. A cap 37 is attached to the stem 33 so as to cover the base 34 on which the laser chip 35 and the photodiode 36 are mounted, and a window 38 through which the laser front beams La and Lb pass is provided on the tip surface of the cap 37. Have been. The photodiodes PD36 receive the back beams La 'and Lb'. On the other hand, on the surface on the opposite side of the stem 33, an energization terminal 39 for connecting the laser chip 35 and the photodiode 36 to a laser drive control system (not shown) is provided. It is needless to say that the laser transceiver 35 and the light transmitting / receiving section 30 of the photodiode 36 may be constituted by one chip.
[0015]
FIG. 3 is a functional explanatory view of a laser scanner unit according to the first embodiment of the present invention. LD represents a multi-beam laser diode. Laser radiation light from the multi-beam laser diode LD is converted into parallel light by a collimator lens 17 and is incident on a cylindrical lens 18. A polygon mirror 19 is rotated by a spindle motor (not shown) in the direction of arrow M. Reference numeral 20 denotes a composite lens in which an fθ lens and a tilt correction lens are combined, and determines a laser spot diameter and a scanning speed on the photosensitive drum 24. Further, 21 is a folding mirror, and 22 is an imaging lens. Reference numeral 23 denotes a light detection sensor (hereinafter referred to as a BD sensor) which detects a laser beam before the start of scanning in the main scanning direction of image formation, detects a synchronization signal synchronized with the rotation speed of the polygon mirror 19, and detects a reference position. It is. Here, the laser beam incident through the folding mirror 21 and the imaging lens 22 is detected, and an image writing signal in the main scanning direction is generated.
[0016]
Hereinafter, the operation of the first embodiment of the present invention will be described with reference to the timing chart of FIG. At time t0, the analog switches 1 and 2 are turned on by the signals 9 and 10. The transistors 3 and 4 are turned on by the laser-on signals 5 and 6. The switch circuits 13 and 14 are turned on at a high level indicating the sample mode (S), and the output voltages of the error detection amplifiers 11 and 12 are accumulated in the sample and hold capacitors 15 and 16 to be in a sample state. At this point, the polygon mirror 19 has reached the specified rotation speed. The current of the laser diodes LD1 and LD2 gradually increases, the amount of emitted light increases, and the current of the photodiode PD increases. At this time, the photodiode PD detects the back beam of the laser diodes LD1 and LD2, and the amount of laser light can be determined. However, since the response speed of the photodiode PD is low, for example, when the laser current is rapidly increased with a response of at most several hundred KHz, even if the laser emits excessive light, the photodiode PD has not yet responded. A state occurs. This contributes to laser destruction. Therefore, in APC, it is necessary to gradually increase the current flowing through the laser diode LD. In this embodiment, the sample and hold capacitor circuit suppresses a rise in the current of the laser diode LD. At the time of high-speed switching at the time of printing, there is no problem because the mode is the constant current mode (hold mode).
[0017]
In this sample mode, if the light amounts of the LDs 1 and 2 increase and the current of the photodiode PD increases, the terminal voltages of the adjustment resistors VR1 and VR2 increase, and the inverting terminals of the error detection amplifiers 11 and 12 increase. The voltage increases, the outputs of the error detection amplifiers 11 and 12 decrease near the reference voltage Vref, and the current values of the variable constant current sources 7 and 8 decrease in accordance with the outputs of the error detection amplifiers 11 and 12; The current of LD2 decreases, and the light emission amount of LD1 and LD2 decreases, and the light emission amount of LD1 and LD2 is kept constant by the loop circuit of the APC circuit.
[0018]
At time t1, the BD sensor 23 detects the laser beam of the LD1. In a recording apparatus using laser light, a relational expression of laser light quantity at the time of recording> laser light quantity capable of BD detection is normally established. In the present embodiment, the BD sensor 23 has a configuration in which a portion for detecting the laser beam of the LD 1 and a portion for detecting the laser beam of the LD 2 exist at two locations. In the present embodiment, the laser beam from the LD 1 has the reference BD sensor detection level earlier. From FIG. 4, an example in which the laser beam of the LD 2 is detected by the BD sensor first can be easily analogized. Further, a configuration in which the laser beams of LD1 and LD2 are simultaneously detected by one photodetector of the BD sensor 23 can be easily analogized.
[0019]
At time t1, in order to set the applied current of the laser diode LD2 to the hold mode, the switch circuit 14 is turned off at the low level indicating the hold mode (H), and the transistor 4 is turned off by the signal 6 for turning on the LD2. LD2 is turned off. At time t2 after the lapse of the specified time, the switch circuit 13 is turned off, the LD1 on signal 5 is turned off, the transistor 3 is turned off to turn off the laser LD1, and the laser LD1 is turned off in order to set the applied current of the laser diode LD1 to the hold mode. , The LD2 on signal 6 is turned on, the switch circuit 14 is turned on, and the laser diode LD2 is turned on to enter the sample mode. Then, when the laser light of LD2 increases and reaches the BD sensor detection level, at time t3, the laser diode LD2 is turned off and the laser diode LD2 is set to the hold mode.
[0020]
Thereafter, the laser diodes LD1 and LD2 are alternately turned on and off alternately, and the light emission amount of the laser diodes LD1 and LD2 reaches the specified light amount. At this time, when the LD1 is on, only the analog switch 1 is on, and when the LD2 is on, only the analog switch 2 is on. At this time, the relationship between the supply current and the light amount of the laser diode is such that the supply current IL does not emit light until the threshold current Ith, and the current suddenly changes from the threshold current Ith to the supply current IB when the BD detection light amount PB. The light amount also increases with the increase, and the light amount also increases rapidly according to the current from the supply current IB to the supply current IS at the specified light amount PS, but the supply current ranges from zero to IB and the current value from IB to IS. Is obviously linear in the former. Therefore, when APC is performed on a plurality of lasers individually, generally, a time period is required in which the supply current is multiplied by the number of lasers from zero to IS, but in the present embodiment, the supply current is reduced from zero. The time from IB to the time from IB to IS is multiplied by the number of lasers, so that the time can be clearly reduced, and this obviously contributes to the reduction in the first print time.
[0021]
In this operation, in order to expose the photoconductive drum 24 with the specified amount of laser light at each light emitting point, a current is applied to all the laser light emitting points at the first time t0, and the laser light at all the light emitting points is applied. At the time of application, the automatic light intensity control of each laser is started in the sample mode, and at time t1 when the BD signal is detected by the reference position light detecting means, the current applied to each light emitting portion of the semiconductor laser is held in the hold mode. Then, at time t2, by performing automatic light amount control in the sample mode individually for each light emitting portion, it is possible to shorten the time for setting the light amount of each laser light emitting point to the specified light amount, The first print time of the recording device can be shortened.
[0022]
In other words, in order to set the laser light emission at each light emission point to a specified light amount required for exposure of the photosensitive drum, at the first time t0, a current is applied to all laser light emission points, and all the light emission points are applied. When the laser is applied, the automatic light amount control is started in the sample mode, the detection amount information of the photodetector is not fed back to the automatic light amount control, and when the reference position light detection means detects the laser light, each of the semiconductor lasers By fixing the current applied to the light emitting point in the hold mode, and then feeding back the detection amount information of the detection device to the automatic light quantity control, and performing the automatic light quantity control in the sample mode individually for each light emitting point. Further, it is possible to shorten the time for setting the light amount of each laser emission point to the specified light amount, and to shorten the first print time of the recording apparatus.
[0023]
(Second embodiment)
FIG. 5 is a timing chart showing a second embodiment according to the present invention. The configuration of the image forming apparatus is the same as in FIGS. 1 and 3 described in the first embodiment.
[0024]
In FIG. 5, at time t0, the analog switches 1 and 2 are turned off, and thereafter, as in the first embodiment, the laser switches are turned on by laser on signals 5 and 6. The switch circuits 13 and 14 are turned on to enter the sample mode state. At this point, the polygon mirror 19 has reached the specified rotation speed. The current of the laser diodes LD1 and LD2 gradually increases, the light amount of the laser diodes LD1 and LD2 increases, and the current of the photodiode PD increases.
[0025]
At time t1, the BD sensor 23 detects the laser beam of the LD1. At time t1 when the BD sensor 23 reaches the laser beam detection level of the LD1, the switch circuit 14 is turned off and the laser diode LD2 is turned off by the signal 6 in order to set the current applied to the laser diode LD2 to the hold mode. Further, the laser diode LD1 is continuously in the sample mode, and the analog switch 1 is turned on by the ON signal 9 of the analog switch 1, and the detection current of the photodiode PD flows to the current-voltage conversion adjusting resistor VR1. The laser light amount information is transmitted to the error detection amplifier 11. The error detection amplifier 11 is compared with the reference voltage Vref, and the output of the error detection amplifier 11 becomes low level when the voltage of the adjustment resistor VR1 increases. On the other hand, when the detection current of the photodiode PD is small, the voltage of the adjustment resistor VR1 is small, the output of the error detection amplifier 11 is at a high level, and even if the current absorption of the variable constant current source 7 is maximum, LD1 is The output light quantity does not immediately become high, and the detection current of the photodiode PD gradually increases.
[0026]
At the time t2 after the lapse of the prescribed time, the switch 13 of the laser diode LD1 is turned off to be in the hold mode, the on signal 5 of the laser LD1 is turned off, the analog switch 1 is turned off, and at the same time, the transistor 4 is turned on to turn on the laser diode LD1. LD2 is turned on, analog switch 2 is turned on, and the sample mode is set. When the laser beam of LD2 increases and reaches the BD sensor detection level, which is the reference voltage Vref, at time t3, the laser diode LD2 is turned off to enter the hold mode. Thereafter, the laser diodes LD1 and LD2 are alternately turned on and off alternately to reach the specified light amount. At this time, when the LD 1 is on, only the analog switch 1 is on, and when the LD 2 is on, only the analog switch 2 is on.
[0027]
In the second embodiment, since the analog switches 1 and 2 are initially turned off and the light amount information of the laser diodes LD1 and LD2 is not transmitted to the error detection amplifiers 11 and 12, the gain of the error detection amplifiers 11 and 12 is maximized. It is maintained, the rise of the initial current is earlier, and the laser light amounts of the LD1 and LD2 reach the specified value faster than in the first embodiment.
[0028]
(Third embodiment)
FIG. 6 shows a drive circuit diagram for driving a plurality of semiconductor lasers of the image forming apparatus according to the third embodiment of the present invention. The same members as those shown in FIG.
Description is omitted.
[0029]
Usually, in the image forming apparatus, it is necessary to set the value of the laser light amount to a specified light amount according to the sensitivity characteristic of the photosensitive drum. In order to set the laser light amount of the laser scanner unit to this specified light amount, first place the reference optical sensor a little before the photosensitive drum position or the photosensitive drum position where the laser spot does not focus. Is detected. The optical sensor serving as a reference controls the laser light to be constant when the laser light reaches the specified light amount.
[0030]
When the laser light has a specified light amount, the value of the adjusting variable resistor is determined so as to convert the photocurrent of the built-in photodiode into a specified voltage. Thereafter, in the image forming apparatus, the APC operation is performed with the specified voltage obtained by converting the photocurrent of the built-in photodiode, and the laser light amount is kept constant at the specified light amount.
[0031]
With respect to a semiconductor multi-beam laser having a plurality of light emitting points, a method of adjusting a variable resistor for adjustment will be described below.
[0032]
In FIG. 6, the voltage of the reference voltage Vref 2 is divided by the resistor 25 and the variable resistor VR 3 to be used as the reference voltage of the error detection amplifier 12. First, the transistor 3 is turned on by the ON signal 5 of the laser LD1, and only the laser diode LD1 is turned on. The laser light amount of the laser diode LD1 is detected by an optical sensor (not shown), and when the light amount reaches a specified value, the variable resistor VR1 is adjusted to be equal to the reference voltage Vref of the error detection amplifier 11. Next, the laser diode LD1 is turned off, and the laser diode LD2 is turned on. The laser light amount of the laser diode LD2 is detected by an optical sensor (not shown), and when the light amount reaches a specified value, the variable resistor VR3 is adjusted to make the two inputs of the error detection amplifier 12 equal.
[0033]
As another adjustment method, the variable resistor VR1 is set near the maximum value, and only the laser diode LD1 is turned on. The switch circuit 13 is turned on to start APC. The resistance value of the variable resistor VR1 is gradually reduced, and the adjustment of the variable resistor VR1 is stopped when the laser light amount detection value of the optical sensor (not shown) reaches a specified value.
[0034]
Next, the variable resistor VR3 is set near the minimum value, the laser diode LD1 is turned off, and the laser diode LD2 is turned on. The switch circuit 14 is turned on to start APC. The resistance value of the variable resistor VR3 is gradually increased, and the adjustment of the variable resistor VR3 is stopped when the laser light amount detection value of the optical sensor (not shown) reaches a specified value.
[0035]
By performing this adjustment, the laser light amount of the laser diodes LD1 and LD2 can be accurately and safely adjusted to the specified light amount.
[0036]
Thus, the first adjusting variable resistor VR1 for converting the detection current of the photodiode PD, which is a photodetector, to a voltage by the semiconductor multi-beam laser having the first laser light emitting portion LD1 and the second laser light emitting portion LD2. A comparison means for comparing the voltage converted by the first adjustment variable resistor VR1 with the reference voltage Vref, and a second adjustment variable resistor VR3 for adjusting the reference voltage; The laser light amount at the first light emitting point is adjusted by the first adjusting variable resistor VR1, and the laser light amount at the second light emitting point is adjusted by the second adjusting variable resistor VR3. It is possible to accurately and safely adjust the laser light quantity of the LD1 and LD2 to the specified light quantity, and to increase the light quantity stability of each laser diode during the APC operation. Can.
[0037]
【The invention's effect】
As described above, according to the laser driving method of the present invention, in a recording apparatus using a multi-beam, it is possible to provide a recording apparatus in which the time for setting each laser emission point to a predetermined light amount is reduced and the first print time is short. It becomes possible.
[0038]
Further, according to the laser beam adjusting method of the present invention, in a recording apparatus using a multi-beam laser, it is possible to accurately and safely adjust the amount of laser light at each laser emission point.
[Brief description of the drawings]
FIG. 1 is a functional explanatory diagram of a laser drive circuit according to a first embodiment of the present invention.
FIG. 2 is an external view of a laser unit according to the first embodiment of the present invention.
FIG. 3 is a functional explanatory diagram of the laser scanner unit according to the first embodiment of the present invention.
FIG. 4 is a timing chart according to the first embodiment of the present invention.
FIG. 5 is a timing chart according to a second embodiment of the present invention.
FIG. 6 is a functional explanatory diagram of a laser drive circuit according to a third embodiment of the present invention.
[Explanation of symbols]
1D1 laser diode
LD2 laser diode
PD photodiode
VR1 Adjustable variable resistor
VR2 Variable resistor for adjustment
VR3 Adjustable variable resistor
Vref reference voltage
Vref 2 reference voltage
1 Analog switch
2 Analog switch
3 Switching transistor
4 Switching transistor
7 Current source
8 Current source
11 Error detection amplifier
12 Error detection amplifier
13 Switch circuit
14 Switch circuit
15 Sample hold capacitor
16 Sample hold capacitor
17 Collimator lens
18 cylindrical lens
19 Polygon mirror
20 Compound lens
21 Folding mirror
22 Imaging lens
23 BD sensor
24 Photoconductor drum
35 Laser chip
36 Photodiode
38 Irradiation window
39 I / O pins

Claims (5)

A semiconductor laser having a plurality of light-emitting portions, one photodetector for detecting individual back beams of the semiconductor laser, a semiconductor laser unit in which the semiconductor laser and the photodetector are integrated, A laser driving circuit having a sample-and-hold type automatic light amount control for setting the output to a specified value, a rotating polygon mirror for raster-scanning the laser light, and a reference position light detecting means for detecting the position of the scanned laser light; In the laser scanner unit having, in order to make the laser light emission of each of the light emitting portions a prescribed light amount, first apply a current to all the laser light emitting portions, and start automatic light amount control in a sample mode at the time of this application, At the time when the reference position light detecting means detects the laser light, each of the light emitting devices except one light emitting portion of the semiconductor laser is used. Laser driving method which is characterized in that the auto light power control individually the sample mode current applied and fixed by the hold mode, for subsequent individual light emitting points against. In the laser driving method according to claim 1, for the laser scanner unit, a current is first applied to all the laser light emitting points in order to make the laser light emitted from each of the light emitting points to the specified light amount. Automatic light amount control is started in the sample mode, and the detection amount information of the photodetector is not fed back to the automatic light amount control. When the reference position light detecting means detects the laser light, one of the semiconductor lasers is detected. The current applied to each light emitting point except for one light emitting point is fixed in the hold mode, and thereafter, the detection amount information of the detection device is fed back to the automatic light amount control, and the individual light emitting points are individually A laser drive method characterized by performing automatic light intensity control in the sample mode. A semiconductor laser having a plurality of light-emitting portions, one photodetector for detecting individual back beams of the semiconductor laser, a semiconductor laser unit in which the semiconductor laser and the photodetector are integrated, A laser driving circuit having a sample-and-hold type automatic light amount control for setting the output to a specified value, a rotating polygon mirror for raster-scanning the laser light, and a reference position light detecting means for detecting the position of the scanned laser light; And a semiconductor multi-beam laser having a first laser emission point, a second laser emission point, and a first adjusting device for converting a detection current of a photodiode serving as the light detection device into a voltage. A variable resistor, and comparing means for comparing a voltage converted by the first adjustment variable resistor with a reference voltage, A second adjusting variable resistor for adjusting the quasi-voltage; adjusting a laser light amount at the first light emitting portion by the first adjusting variable resistor; and adjusting a laser light amount at the second light emitting portion. A method for adjusting the amount of laser light, wherein the adjustment is performed by the second variable resistor for adjustment. A semiconductor laser having a plurality of light-emitting portions, one photodetector for detecting individual back beams of the semiconductor laser, a semiconductor laser unit in which the semiconductor laser and the photodetector are integrated, and the photodetector A laser drive circuit having a sample-and-hold type automatic light amount control for setting the output of the laser beam to a specified value, a rotating polygon mirror for raster-scanning the laser beam, and detecting a synchronization signal of the laser beam scanned by the rotating polygon mirror In the image forming apparatus having a reference synchronization detecting means,
An APC circuit is provided for each of the semiconductor lasers to stabilize the amount of emitted light in order to make the laser emission of each of the light emitting portions a prescribed amount of light. An image forming apparatus comprising: an APC circuit that operates as a sample mode for each of the first detected APC circuits; A semiconductor laser having a plurality of light-emitting portions, one photodetector for detecting individual back beams of the semiconductor laser, a semiconductor laser unit in which the semiconductor laser and the photodetector are integrated, A laser driving circuit having a sample-and-hold type automatic light intensity control for setting the output to a specified value, a rotary polygon mirror for raster-scanning the laser light, and reference synchronization detecting means for detecting a synchronization signal of the scanned laser light; In the image forming apparatus having
An APC circuit having a variable resistor that stabilizes the amount of emitted light and adjusts a reference voltage for each of the semiconductor lasers, operates all the APC circuits first, and detects the laser emission by the photodetector. The image forming apparatus according to claim 1, wherein the APC operation is performed as a sample mode for each of the first detected APC circuits, the variable resistance is adjusted, and another APC circuit is operated as a hold mode.

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