JPH11101947A - Laser driving system and adjusting method and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten first printing time by fixing a current impressed to each light emitting spot of a semiconductor laser in a hold mode at the time of detecting a laser beam and individually performing automatic light quantity control in a sample mode. SOLUTION: In order to expose a photoreceptor drum by making the light emission of a laser at each light emitting spot in a specified light quantity, a current is impressed to all the light emitting spots of the laser at a first time t0. At the time of impressing the laser to all the light emitting spots, the automatic light quantity control of each laser is started in a sample mode. At the point of a time t1 when a BD signal by a reference position photodetecting means detects the laser beam, the current impressed to each light emitting spot of a semiconductor laser is fixed in a hold mode. Thereafter, the automatic light quantity control is individually performed to each light emitting spot in the sample mode at a time t2. Thus, the time when the light quantity at each light emitting point of the laser is made to a specified light quantity is shortened and the first printing time of a recorder is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser scanner unit using a multi-beam laser having a plurality of light emitting units,
The present invention relates to an image recording device such as a laser printer.

[0002]

2. Description of the Related Art Conventionally, a laser scanner unit having a polygon mirror which is used in an image recording apparatus such as a laser printer and scans in a main scanning direction when forming an image by irradiating and exposing a rotating photosensitive drum with a laser beam. , A single semiconductor laser has been used. In addition, 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 system, a plurality of rows of images 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 multiple of the speed.

[0003]

A commercially available semiconductor multi-beam laser has one or more laser emission points.
It has two laser light monitoring photodiodes. Therefore, automatic light quantity control (APC: Automatic Positive
wer Control), it was necessary to increase the current individually for each laser emission point. 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.

Therefore, in a multi-beam laser having a large number of firing points, it takes a lot of time to set the laser light amount at each light emitting point to a specified value. As a result, in a laser printer using a multi-beam laser, an AP that sets the laser light amount at each light emitting point to a specified value at the start of printing
Since the C operation is performed, the time for shifting to the printing operation is long, and the first print time is long.

Further, in a recording apparatus using a multi-beam laser, an adjusting variable resistor for determining a prescribed value of a laser light amount at the time of manufacturing (this adjusting variable resistor converts a current of a photodiode for laser light monitoring into a voltage, The target voltage at the time of APC is adjusted for only one light emitting point,
One adjusted result was used for the other light emitting points. This is because the relation 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 monitor photodiode for detecting the back beam is sufficient to be performed only at one light emitting point. . However, the front beam at each laser emission point,
Due to variations in the end face coating of the laser resonator that determines the ratio of the back beam, the relationship between the front beam and the back beam at each laser emission point is slightly different, and in a recording device that prints high-definition images, There was a possibility of uneven density.

A first object of the present invention is to provide a recording apparatus using a multi-beam laser, in which the time required to set each laser emission point to a prescribed light amount is shortened and the first print time is short. Is what you do.

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]

In order to achieve the first object, a laser driving method according to the present invention comprises a semiconductor laser having a plurality of light-emitting portions and an individual back beam of the semiconductor laser. A laser drive circuit having an automatic light intensity control of a sample-and-hold method for setting the output of the photodetector to a specified value; In a laser scanner unit having a rotating polygon mirror that performs raster scanning of light and a reference position light detecting unit that detects the position of the scanned laser light, first, in order to make the laser light emission at each light emitting point to a specified light amount, A current is applied to the laser emission point of the laser beam, automatic light quantity control is started in the sample mode at the time of the application, and the reference position light detecting means At the time when light is detected, the current applied to each light emitting point of the semiconductor laser is fixed in the hold mode, and then the individual light emitting points are individually subjected to the automatic light intensity control in the sample mode, whereby each laser light is emitted. A feature of the present invention is to shorten the time for setting the light quantity at a point to the specified light quantity and shorten the first print time of the recording apparatus.

In order to achieve the first object, a laser driving method according to the present invention comprises 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 of the photodetector to a specified value, and raster-scanning the laser light In a laser scanner unit having a rotating polygon mirror and reference position light detecting means for detecting the position of the scanned laser light, first, in order to set the laser light emission at each light emission point to a specified amount, all laser light emission points An automatic light amount control is started in a sample mode at the time of the main application, and the detected light amount information of the photodetector is transmitted to the automatic light amount control. In a state that does not feedback to,
At the time 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 detection device is fed back to the automatic light amount control. By automatically controlling the amount of light at each laser emission point in the sample mode individually, the time required to set the amount of light at each laser emission point to the specified amount is shortened, and the first print time of the recording apparatus is shortened. I do.

In order to achieve the second object, a method for adjusting the amount of laser light according to the present invention comprises the steps of:
A semiconductor multi-beam laser having a laser emission point, and a first adjusting variable resistor for converting a detection current of a photodiode as the photodetector into a voltage, and converting the voltage by the first adjusting variable resistor. And a second adjusting variable resistor for adjusting the reference voltage, and adjusting the laser light amount at the first light emitting portion to the first adjusting value. The adjustment is performed by a variable resistor, and the laser light amount at the second light emitting point is adjusted by the second adjustment variable resistor.

Further, according to the present invention, there is provided a semiconductor laser having a plurality of light emitting portions, one photodetector for detecting individual back beams of the semiconductor laser, and the semiconductor laser and the photodetector integrated. A semiconductor laser unit, a laser driving circuit having automatic light intensity control of a sample hold system for setting the output of the photodetector to a specified value, a rotating polygon mirror for raster-scanning laser light, and scanning with the rotating polygon mirror In the image forming apparatus having reference synchronization detecting means for detecting a synchronization signal of the laser light, the amount of emitted light is stabilized for each of the semiconductor lasers in order to make the amount of laser emission at each of the light emitting portions a prescribed amount. A
A PC circuit is provided, and all the APC circuits are first operated, and when the photodetection device detects the laser emission, the APC circuit is set as a sample mode for each of the APC circuits.
Operating the other APC circuit in the hold mode.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

(First 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.
For multi-beam lasers with more than two emission points,
The description can be omitted because it can be inferred from FIG.

In FIG. 1, LD1 and LD2 are laser diodes (hereinafter, also referred to as LDs) representing respective light emitting points of a multi-beam laser, and the anodes thereof are connected to a power supply V1.
It is connected to the. PD is each laser diode LD1,
A photodiode (hereinafter, also referred to as PD) for detecting the back beam laser light of the LD 2. Reference numerals 1 and 2 denote variable resistances VR1 and V for adjusting the detection current of the photodiode PD.
An analog switch for controlling whether or not to flow into R2 is 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 flowing through 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 convert the detection currents of the photodiodes PD into voltages by the variable resistors VR1 and VR2 for adjustment, and the reference voltage Vref. The sample and hold capacitors 15 and 16 are charged and discharged according to the difference. 13 and 14 are sample and hold capacitors 15,
A switch circuit for controlling the 16 sample and hold states, the state of which is controlled by a control signal (not shown).

FIG. 2 shows each of the laser diodes LD1 and LD2.
FIG. 4 is a conceptual perspective view in a case where a photodiode PD and a photodiode PD are integrated. On one surface of the stem 33, a base 34 is provided perpendicular to the base of the stem 33.
A laser chip 35 having a and 35b and a photodiode 36 are fixed. These laser chips 3
A cap 37 is attached to the stem 33 so as to cover the base 34 on which the photodiode 5 and the photodiode 36 are mounted.
A window 38 passing through a and Lb is provided. Further, the back beams La ′ and Lb ′ are transferred to the photodiode PD.
36 is receiving light. On the other hand, on the surface on the opposite side of the stem 33, there are energized terminals 3 for connecting the laser chip 35 and the photodiode 36 to a laser drive control system (not shown).
9 are provided. It is needless to say that the laser transceiver 35 and the light transmitting / receiving unit 30 of the photodiode 36 may be configured as one chip.

FIG. 3 is a functional explanatory view of a laser scanner unit according to a 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 compound lens combining an fθ lens and a tilt correction lens, which determines the laser spot diameter and the scanning speed on the photosensitive drum 24. Reference numeral 21 denotes a folding mirror, and reference numeral 22 denotes an imaging lens. 23 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,
It is a light detection sensor (hereinafter referred to as a BD sensor) for detecting a reference position. 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.

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 enter a sample state. At this point, the polygon mirror 19 has reached the specified rotation speed. The currents of the laser diodes LD1 and LD2 gradually increase, the amount of emitted light increases, and the current of the photodiode PD increases. At this time, the back beam of the laser diodes LD1 and LD2 is
To detect the amount of laser light. However, since the response speed of the photodiode PD is slow, for example, at most several hundred K
When the laser current is sharply increased in response to the Hz, even if the laser emits excessive light, the photodiode PD
Will not respond yet. 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).

In this sample mode, LD1,
2, the current of the photodiode PD increases, the terminal voltages of the adjustment resistors VR1 and VR2 increase, the voltages of the inverting terminals of the error detection amplifiers 11 and 12 increase, and the reference voltage Vref Near the error detection amplifier 11,
12 decreases, the error detection amplifiers 11, 12
The current values of the variable constant current sources 7 and 8 decrease according to the output of
The currents of LD1 and LD2 decrease, and the light emission amounts of LD1 and LD2 decrease, and the light emission amounts of LD1 and LD2 are kept constant by the loop circuit of the APC circuit.

At time t1, the BD sensor 23 detects the laser beam from 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 this embodiment, the BD sensor 23 includes a portion for detecting the laser beam of the LD 1,
There are two laser beam detecting portions and two portions. Further, in this embodiment, the laser beam of 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. LD1, LD
A configuration in which two light beams are simultaneously detected by one light detection unit of the BD sensor 23 can be easily analogized.

At time t1, the switch circuit 14 is used to set the current applied to the laser diode LD2 to the hold mode.
Turns off at a low level indicating the hold mode (H), and turns off the laser diode LD2 by turning off the transistor 4 by the signal 6 for turning on the LD2. At time t2 after the lapse of the specified time, the switch circuit 13 is switched to set the applied current of the laser diode LD1 to the hold mode.
Is turned off, the LD1 on signal 5 is turned off, and the transistor 3
Is turned off and the laser LD1 is turned off,
2 ON signal 6 is turned on and switch circuit 14 is turned on,
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.

Thereafter, each of the laser diodes LD1, LD
2 is alternately turned on and off, and the laser diode L
The amount of light emitted from D1 and LD2 reaches the specified amount. that 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,
From the threshold current Ith to the supply current IB when the BD detection light amount PB, the light amount also increases with the current sharply, and also from the supply current IB to the supply current IS when the specified light amount PS, the light amount also increases rapidly according to the current. Increase but the supply current from zero to I
The current values from B to IB and from B to IS are obviously linearly larger in the former. Therefore, multiple lasers can be individually
Is performed, it is generally necessary to multiply the time when the supply current is from zero to IS by the number of lasers. In the present embodiment, however, the time from when the supply current is zero to IB, the time from when IB to IS The number of lasers multiplied by the time until
Obviously, the time can be reduced, which contributes to the reduction of the first print time.

In the above operation, in order to expose the photosensitive 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 total light emission is performed. At the time of application of the laser at each point, the automatic light intensity control of each laser is started in the sample mode, and the current applied to each light emitting point of the semiconductor laser at the time t1 when the BD signal is detected by the reference position light detecting means. Is fixed in the hold mode, and then at time t2, the individual light emitting points are individually subjected to automatic light amount control in the sample mode, thereby shortening the time required for setting the light amount of each laser light emitting point to the specified light amount. This makes it possible to shorten the first print time of the recording apparatus.

In other words, at the first time t0, a current is applied to all the laser light emitting points so that the laser light emitted from each light emitting point has a prescribed light amount necessary for exposing the photosensitive drum. At the time of application of the laser at the light emitting point, 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 detecting means detects the laser light,
The current applied to each light emitting point of the semiconductor laser is fixed in the hold mode, and then the detected amount information of the detector is fed back to the automatic light amount control, and the individual light emitting points are individually controlled in the sample mode for the automatic light amount control. By performing the above, 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.

(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.

In FIG. 5, the analog switches 1 and 2 are turned off at time t0, and thereafter turned on by the laser on signals 5 and 6, as in the first embodiment. 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.

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 laser diode L
In order to set the applied current of D2 to the hold mode, the switch circuit 14 is turned off and the laser diode LD2 is turned off by the signal 6. Furthermore, a laser diode LD
1 is the sample mode continuously, and the analog switch 1
The analog switch 1 is turned on by the ON signal 9 of, and the detection current of the photodiode PD is adjusted by the current-voltage conversion adjusting resistor V.
Then, the laser beam is supplied to the error detection amplifier 11. Error detection amplifier 1
1 is compared with the reference voltage Vref, and when the voltage of the adjustment resistor VR1 increases, the output of the error detection amplifier 11 becomes low level. 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.

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 LD2, turn on the analog switch 2, and enter the sample mode. 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 and enters the hold mode. Thereafter, the laser diodes LD1 and LD2 are alternately turned on and off alternately,
The specified amount of light is reached. 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.

In the second embodiment, the analog switches 1 and 2 are initially turned off, and the laser diodes LD1 and LD1 are turned off.
2 is not transmitted to the error detection amplifiers 11 and 12, the gains of the error detection amplifiers 11 and 12 are maintained at the maximum, the initial current rises faster, and the LD1 and LD2 of the LD1 and LD2 are faster than in the first embodiment. The laser light amount reaches the specified value quickly.

(Third Embodiment) FIG. 6 shows a drive circuit diagram for driving a plurality of semiconductor lasers of an image forming apparatus according to a third embodiment of the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

Normally, 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 characteristics 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. With this standard light sensor,
At the time when the laser light reaches the specified light amount, control is performed to make the laser light constant.

When the laser beam 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 at 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.

A method for adjusting the adjusting variable resistor will be described below with respect to a semiconductor multi-beam laser having a plurality of light emitting points.

In FIG. 6, a resistor 25 and a variable resistor VR3
Divides the voltage of the reference voltage Vref 2 and uses it 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 amount of laser light from the laser diode LD2 is detected by an optical sensor (not shown), and when the amount of light reaches the specified amount, the variable resistor VR3 is adjusted to equalize the two inputs of the error detection amplifier 12.

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,
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.

Next, the variable resistor VR3 is set near the minimum value,
The laser diode LD1 is turned off, and the laser diode L
Turn on D2. The switch circuit 14 is turned on to start APC. The resistance 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.

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.

Thus, the first laser emission point LD1
And a first adjusting variable resistor VR1 for converting a detection current of a photodiode PD as a photodetector into a voltage by a semiconductor multi-beam laser having a second laser emission point LD2. A second adjusting variable resistor for adjusting the reference voltage, comprising comparing means for comparing the voltage converted by the variable resistor VR1 with the reference voltage Vref;
R3, the amount of laser light at the first light emitting point is adjusted by the first adjusting variable resistor VR1, and the amount of laser light at the second light emitting point is adjusted by the second adjusting variable resistor VR3. Then, the laser diodes LD1, L
The laser light amount of D2 can be accurately and safely adjusted to the specified light amount, and the light amount stability of each laser diode during the APC operation can be increased.

[0037]

As described above, according to the laser driving method of the present invention, in a recording apparatus using a multi-beam, the time required to set each laser emission point to a specified light amount is reduced, and the recording apparatus having a short first print time is used. Can be provided.

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 an explanatory diagram of functions 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 Adjustable variable resistor 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 Composite lens 21 Folding mirror 22 Imaging lens 23 BD sensor 24 Photoconductor drum 35 Laser chip 36 Photodiode 38 Irradiation window 39 I / O pin

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 1/23 103 H04N 1/04 104A

Claims (5)

[Claims] 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 of the light detection device to a specified value, a rotary polygon mirror for raster-scanning the laser light, and a reference for detecting the position of the scanned laser light In a laser scanner unit having position light detection means, in order to make the laser light emission at each of the light emission locations a prescribed light amount,
First, current is applied to all laser emission points,
Automatic light quantity control is started in the sample mode at the time of this application, and when the reference position light detecting means detects the laser light, the current applied to each of the light emitting points except for one light emitting point of the semiconductor laser. Is fixed in the hold mode, and thereafter, automatic light intensity control is individually performed in the sample mode for each light emitting portion. 2. The laser driving method according to claim 1, wherein a current is first applied to all the laser light emitting portions of the laser scanner unit so that the laser light emitted from each of the light emitting portions has the specified light amount. Then, the automatic light amount control is started in the sample mode at the time of the main application, and the detection amount information of the photodetector is set not to be fed back to the automatic light amount control, and at the time when the reference position light detection unit detects the laser light, The current applied to each light emitting point is fixed in a hold mode except for one light emitting point of the semiconductor laser, 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 A laser driving method wherein automatic light amount control is individually performed in the sample mode. 3. 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 of the light detection device to a specified value, a rotary polygon mirror for raster-scanning the laser light, and a reference for detecting the position of the scanned laser light In a laser scanner unit having position light detecting means, a detection current of a semiconductor multi-beam laser having a first laser light emission point, a second laser light emission point, and a photodiode serving as the light detection device is converted into a voltage. A first adjusting variable resistor, and a comparator for comparing a voltage converted by the first adjusting variable resistor with a reference voltage; A second adjusting variable resistor for adjusting the reference voltage; adjusting a laser light amount at the first light emitting point by the first adjusting variable resistor; A method for adjusting the amount of laser light, wherein the amount of laser light at a location is adjusted by the second variable resistor for adjustment. 4. 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 drive circuit having a sample-and-hold type automatic light amount control for setting the output of the photodetector to a specified value, a rotary polygon mirror for raster-scanning the laser beam, and a laser beam scanned by the rotary polygon mirror In the image forming apparatus having a reference synchronization detecting means for detecting the synchronization signal of, in order to make the laser emission of each light emitting location to a specified light amount,
APC for stabilizing the amount of emitted light for each of the semiconductor lasers
A circuit, and first operate all the APC circuits, and from the time when the photodetector detects the laser emission, perform the APC operation as a sample mode for each of the first detected APC circuits, and perform the other APC circuits. An image forming apparatus that operates in a hold mode. 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 quantity control for setting the output of the photodetector to a specified value, a rotary polygon mirror for raster-scanning the laser light, and detecting a synchronization signal of the scanned laser light An image forming apparatus having a reference synchronization detecting means, comprising: 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; first, all the APC circuits are operated; The APC operation is performed as a sample mode for each of the first detected APC circuits from when the light detection device detects the laser emission. And then adjusting the variable resistor by the image forming apparatus other APC circuit is characterized in that to operate as a hold mode.