JPH0630197A - Picture forming device - Google Patents

Abstract

PURPOSE:To decrease the variation of laser power by letting a laser turn on by a first control means, and letting a sample hold means be in a sample state, and rotating a motor stationarily at the time of adjusting the laser power. CONSTITUTION:A laser driver prevents a current stipulated by a constant current source 128 from flowing in resistance 150 when the level of the port p1 of an MPU 110 becomes L, but allows the current to flow in a laser diode 190a so as to emit laser light, and on the contrary, when the level of the port p1 of the MPU 110 becomes H, it allows the current to flow in the resistance 150, but prevents the current from flowing in the laser diode 190a so as to stop the emission of the laser light. Besides, a sample hold circuit is turned into a sample mode when the level of the port p2 of the MPU 110 is L, and it is turned into a hold mode at the time of H. Then, a polygon motor driver 130 drives and controls a polygon motor 170 in response to a clock when the level of the port p3 of the MPU 110 is made to be L by the MPU 110 or a switch 100.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art (a) Conventionally, as an image forming apparatus for scanning a photosensitive surface with a laser beam to form an image, a laser drive circuit for driving a laser and a polygon motor drive circuit are formed on separate chips. It is known that the laser power is adjusted only by the laser drive circuit to eliminate the fluctuation of the laser power due to the variation of the laser element.

However, since the laser drive circuit and the polygon motor drive circuit are formed on separate chips as described above, there is a problem that the cost of the apparatus increases.

As a method of solving such a problem, for example, as proposed in Japanese Patent Application No. 3-71699, there is a method of forming a laser drive circuit and a polygon motor drive circuit on the same chip. .

In this laser drive circuit, it is desirable that the laser power control circuit includes a sample and hold circuit, and the sample and hold circuit needs a reference voltage when sampling the laser power.

(B) The laser drive circuit is an automatic light amount adjusting circuit (au) for automatically adjusting the laser light amount to a specified light amount.
tomatic power control circuit;
Hereinafter, referred to as an APC circuit). The APC circuit includes a soft APC circuit via a CPU and the like, and a hard APC circuit using only electric elements without intervention of the CPU.

The APC circuit controls the current of the laser diode so that the photocurrent of the photodiode that receives the laser light is kept constant. At the time of image printing, in order to keep the current value of the controlled laser diode constant, a means for storing the set value is necessary. As a means for storing the set value, a CPU is generally used in the case of software APC, In the case of hard APC, a holding capacitor is generally used.

In a hard APC, a holding capacitor is generally used as a means for storing a set value, but the holding capacitor is used in a sample and hold circuit, and is operated in a sampled state during APC and regulated. The holding capacitor is charged with a value corresponding to the amount of light. At the time of image printing, the sample hold circuit is put in the hold state, and the laser is caused to emit light with a specified light amount based on the voltage value of the hold capacitor. Normally, in the APC using this sample hold circuit, the holding time of the holding capacitor is short, and the limit is several milliseconds although it depends on the capacity of the capacitor. Therefore, in a laser printer that performs raster scanning to form an image,
It is more common to perform APC for each scan.

A sample and hold amplifier and an analog switch are used as a structure for performing sample and hold, but since electric parts are used, a leakage current is generated at the time of hold. Therefore, normally, a reset means is provided for discharging the hold capacitor when APC is not performed.

(C) FIG. 11 shows a conventional laser driver IC.
Shows the configuration of.

The laser power control circuit converts the output current from the photodiode 313, which generates a current proportional to the power of the laser element 312, into a voltage by the resistor 304. The operational amplifier 305 receives this voltage and lowers the output impedance. The voltage output from the operational amplifier 305 is compared with the voltage of the reference power supply 307 by the comparison circuit 306. At this time, when the sample hold circuit 308 is in the sample mode, the output voltage of the comparison circuit 306 is the sample hold capacitor 310. It will take both ends. Then, the voltage across the sample-hold capacitor is converted into a laser current by the voltage-current conversion circuit 309. Pre-driver 301, transistors 302, 3
A laser switching circuit is constituted by 03 and the resistor 311.

[0012]

However, in the above (a), when the reference voltage generating circuit for generating the reference voltage is also formed on the same chip, the reference voltage fluctuates depending on the chip temperature. When adjusting the power,
If only the laser drive circuit is operated, the difference between the temperature of the chip when adjusting the laser power and the temperature when the polygon motor is rotating becomes large, and the reference voltage generated by the reference voltage generating circuit becomes the laser power. There is a problem in that the laser power differs between the time of adjustment and the time of actual use, and as a result, the laser power differs between the time of laser power adjustment and the time of actual use.

Further, in the above (b), there is a problem that the laser emits abnormally due to the abnormal charging of the holding capacitor.

Further, in the above (c), when the chip temperature of the laser driver IC changes, the reference power supply voltage of the operational amplifier 306 also changes, and thus the laser power changes.

An object of the present invention is to solve the above problems, (1) prevent the laser power from being different between when the laser power is adjusted and when it is actually used, and (2) due to abnormal charging of the holding capacitor. Prevents abnormal laser emission
(3) It is an object of the present invention to provide an image forming apparatus capable of reducing fluctuations in laser power caused by fluctuations in chip temperature.

[0016]

In order to achieve such an object, the present invention provides a laser, a laser driving means for driving the laser, and a polygon mirror for scanning a laser beam from the laser on a photosensitive surface. A motor for driving the polygon mirror, and a motor driving means for driving the motor,
It has a sample and hold means for sampling and holding the laser power, and an adjusting means for adjusting the laser power based on the laser power sampled and held by the sample and hold means, and the motor driving means and the laser driving means are provided on the same chip. In the integrated image forming apparatus, when the laser power is adjusted by the adjusting means, the laser is turned on, the sample-holding means is brought into a sample state, and the first control means is provided to rotate the motor steadily. .

Further, the present invention provides a laser, a laser driving means for driving the laser, a polygon mirror for scanning the laser beam from the laser on a photosensitive surface, a motor for driving the polygon mirror, and the motor. In the image forming apparatus, there is provided a motor drive unit for driving the laser power source, a sample and hold unit for sampling and holding the laser power, and an adjusting unit for adjusting the laser power based on the laser power sampled and held by the sample and hold unit.
Resetting means for discharging the holding capacitor of the sample-holding means; timing detecting means for detecting the timing at which the sample-holding means changes to the sample state when the motor is driven by the motor driving means; Reset release means for releasing the reset state by the reset means when the detection means detects the timing at which the sample and hold means changes to the sampled state.

Further, according to the present invention, a laser, a laser driving means for driving the laser, a polygon mirror for scanning a laser beam from the laser onto a photosensitive surface, a motor for driving the polygon mirror, and the motor. In the image forming apparatus, there is provided an image forming apparatus including: a motor driving unit that drives the motor, a sample-hold unit that samples and holds the laser power, and an adjusting unit that adjusts the laser power based on the laser power sample-held by the sample-holding unit. Signal generating means for generating a reset signal for the holding capacitor by a drive signal for starting driving and a sample and hold signal, and reset means for discharging the holding capacitor of the sample and hold means based on the signal from the signal generating means. And the motor drive means If the serial motor is driven,
Reset release means for releasing the reset state by the reset means in synchronization with the laser drive by the laser drive means.

Furthermore, the present invention comprises a laser, sample-hold means for sampling and holding the laser power, and control means for controlling the laser power based on the laser power sample-held by the sample-hold means. In the image forming apparatus in which the control means is integrated on the same chip, the control means includes a current generating means for generating a current proportional to the laser power, and a current-voltage converter for converting the current generated by the current generating means into a voltage. A circuit, a reference voltage generation circuit that generates a voltage that is a reference of laser power, a first reference voltage generation circuit that generates a first reference voltage from the reference voltage generated by the reference voltage generation circuit, and Adder circuit for adding the first reference voltage from the first voltage generation circuit and the voltage from the current-voltage conversion circuit; A second reference voltage generation circuit for generating a second reference voltage from the reference voltage generated by the voltage conversion circuit, a second reference voltage from the second voltage generation circuit and an output voltage of the addition circuit. A comparison circuit for comparison, a sample hold circuit for sampling and holding the voltage from the comparison circuit, and a control circuit for controlling the laser power based on the output voltage of the sample hold circuit are provided.

[0020]

In the present invention, when the laser power is adjusted by the adjusting means, the laser is turned on by the first control means, the sample hold means is put in the sample state, and the motor is steadily rotated.

Further, in the present invention, when the motor is driven by the motor driving means, the timing detecting means detects the timing at which the sample hold means changes to the sample state, and the timing detecting means puts the sample hold means in the sample state. When the changing timing is detected, the reset release means releases the reset state by the reset means.

Further, according to the present invention, the reset signal for the holding capacitor is generated by the signal generating means by the drive signal for starting the driving of the motor and the sample hold signal, and the sample holding means is generated based on the signal from the signal generating means. When the hold driving capacitor is discharged by the reset means and the motor is driven by the motor driving means, the reset release means releases the reset state by the reset means in synchronization with the laser driving by the laser driving means.

Furthermore, in the present invention, the control means causes the current generation means to generate a current proportional to the laser power, and the current generated by the current generation means is converted into a voltage by the current-voltage conversion circuit. A reference voltage is generated by the reference voltage generation circuit, a first reference voltage is generated by the first reference voltage generation circuit from the reference voltage generated by the reference voltage generation circuit, and a first reference voltage generated by the first voltage generation circuit is generated. The reference voltage of 1 and the voltage from the current-voltage conversion circuit are added by the addition circuit, and the second reference voltage is generated by the second reference voltage generation circuit from the reference voltage generated by the current-voltage conversion circuit. The second reference voltage from the voltage generation circuit of No. 2 and the output voltage of the adder circuit are compared by the comparison circuit, and the voltage from the comparison circuit is sample-held by the sample-hold circuit. Controls the laser power by the control circuit based on the output voltage of the sample-and-hold circuit.

[0024]

Embodiments of the present invention will now be described in detail with reference to the drawings.

First Embodiment FIG. 1 shows a first embodiment of the present invention.

In FIG. 1, a monolithic driver IC 120 is a polygon motor driver 130 in which main parts of a laser driver are integrated and a resistor 180 is excluded.
Are accumulated.

Reference numeral 110 denotes an MPU, which controls the monolithic driver IC 120. The port p3 of the MPU 110 is at high level (H) while the device is in standby,
It is in the input mode, becomes low level (L) at the start of printing, and becomes the output mode.

Reference numeral 100 denotes a switch for switching to a laser power adjustment mode.

The laser driver is composed of a resistor 150, transistors 121 and 122, a constant current source 128, and a reference power source. When the level of the port p1 of the MPU 110 becomes L, the transistor 121 is turned off and the transistor 1 is turned on.
22 is turned on to stop the current defined by the constant current source 128 from flowing through the resistor 150, but a current is passed through the laser diode 190a to emit laser light, and conversely, M
When the level of the port p1 of the PU 110 becomes H, the transistor 121 is turned on and the transistor 1
22 is turned off, and the current defined by the constant current source 128 is made to flow through the resistor 150, but is not made to flow in the laser diode 190a, and the emission of laser light is stopped.

The sample-hold circuit is composed of a voltage follower 127, a sample capacitor 160, an analog switch 125, an operational amplifier 124, a reference power source 200 and a buffer 123, and a port p of the MPU 110.
When the level of 2 is L, the sample mode is set, and when it is H, the hold mode is set. That is, when the level of the port p2 of the MPU 110 is L, the analog switch 125 is turned on, the voltage output from the buffer 123, that is, the divided voltage of the variable resistor 140 is compared with the voltage of the reference power supply 200, and both voltages are compared. The constant current source 128 is controlled via the voltage follower 127 to control the laser power to be equal. On the other hand, when the level of the port p2 of the MPU 110 is H, the analog switch 125 is turned off and the constant current source 128 is controlled via the voltage follower 127 according to the voltage of the sample capacitor 160.

The analog switch 126 is the MPU 110.
When the level of the port p3 of the inverter is set to L by the MPU 110 or the switch 100, that is, the inverter 12
When the output level of 9 becomes H, it turns off.

The polygon motor driver 130 is an MPU.
When the level of the port p3 of 110 is set to L by the MPU 110 or the switch 100, the polygon motor 170 is driven and controlled according to the clock from the port p4.

FIG. 2 is a flow chart showing the control procedure by the MPU 110 shown in FIG.

In step S201, it is determined whether or not the device is in the standby state. If the result of determination is that the device is not in the standby state, the port p3 is set to the output mode in step S202, and the routine returns from this routine in step S203. .

On the other hand, if the result of determination in step S201 is that it is in standby, port p3 is placed in the input mode, and in step S205 it is determined whether switch 100 is in the on state or the off state. As a result of judgment,
If the switch 100 is off, step S2
At 15, the routine returns from this routine.

On the other hand, if the result of determination in step S205 is that switch 100 is in the on state, port p3 is set to the output mode in step S206, and the level of port p3 is set to L in step S207. Therefore, the reset of the sample hold circuit is released regardless of the state of the switch 100, and the rotation of the polygon motor 170 is started. Then, in step S208, the level of the port p1 is set to L to enable the emission of laser light, and in step S209, the port p2 is set to L and the sample mode is set.

In this state, the process stands by until a predetermined time elapses in step S210, during which the variable resistor 140 adjusts the laser power so that the required laser power is obtained. In addition, this laser power adjustment is performed by the switch 100.
It shall be performed after a predetermined time has passed after turning on. Then, after a predetermined time has passed, in step S211,
The level of the port p2 is set to H to enter the hold mode, and in step S212, the level of the port p1 is set to H to stop the emission of laser light. Further, in step S213, the level of the port p3 is set to H, and the polygon motor 17
Turn 0 off. Further, the sample capacitor 160 is discharged and reset. In step S214, the process returns from this routine.

The polygon motor 170 is forced to O
When turned on from the FF state, the laser power adjustment mode may be entered. In this case, polygon motor 1
By combining the signal for turning on / off 70 and the signal for entering the laser power adjustment mode, MPU 110
The number of ports can be reduced.

Second Embodiment FIG. 3 shows a second embodiment of the present invention.

In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals. Reference numeral 301 denotes a test print switch whose contact is connected to the port p5 and whose contact piece is connected to the ground. 302 is a pull-up resistor connected to the port p5.

Compared with the first embodiment, this embodiment is as follows.
The method of switching the laser power adjustment mode is different. In other words, in the first embodiment, the switch 100 is turned on to enter the laser power adjustment mode so that the laser power adjustment mode is set to exit after a lapse of a predetermined time.
Is turned on to enter the laser power adjustment mode so that the test print switch 301 comes out when it is pressed.

FIG. 4 is a flow chart showing the control procedure by the MPU 110 shown in FIG.

In FIG. 4, steps S201 to S209 and steps S211 to S215 show the same steps as in FIG.

In step S209, the port p2 is set to L to enter the sample mode, and in step S401, the process waits until the test print switch 301 is turned on. Then, when the test print switch 301 is turned on, in step S211, the level of the port p2 is set to H, and the hold mode is set.

In the present embodiment, an example of exiting the laser power adjustment mode when the test print switch 301 is pressed has been described. However, it is possible to exit the laser power adjustment mode using the level of the input port. Is also good.

In the first and second embodiments, the difference between the chip temperature during the laser power adjustment and the chip temperature during actual use is reduced to reduce the influence of the fluctuation of the sample reference voltage due to the temperature. The laser power does not change between actual use and adjustment.

Third Embodiment FIG. 5 shows a third embodiment of the present invention.

In FIG. 5, the laser switching circuit comprises a resistor R1, transistors Q1 and Q2, and a current controller CC, the base of the transistor Q2 is connected to the power source V1, and a laser ON / OFF signal is sent to the base of the transistor Q1. Is a differential amplifier circuit to which is input,
The laser diode LD is ON / OFF controlled.

The current controller CC is composed of a constant current source and a g _m amplifier, and controls the value of the current flowing through the laser diode LD in proportion to the voltage held in the holding capacitor C1. Voltage control is converted to current control by the g _m amplifier.

PD is a photodiode, which generates a photocurrent according to the intensity of the laser beam from the laser diode LD. R2 and R3 are resistors for converting photocurrent into voltage.

OP1 is an operational amplifier, the voltage converted by the resistors R2 and R3 is input to the non-inverting input terminal, the output is input to the inverting input terminal via the resistor R5, and is connected to the ground via the resistor R4. Has been done. The DC gain is determined by the resistors R4 and R5.

OP2 is an operational amplifier, the output of the operational amplifier OP1 is input to the inverting input terminal, the non-inverting input terminal is connected to the ground via the reference power source, and the operational amplifier OP1 is provided.
Is compared with the reference voltage Vref, and the output is input to and held by the holding capacitor C1 based on the on / off state of the analog switch SW1. The analog switch SW1 is turned on / off based on the sample hold signal.

FF1 is a D flip-flop, and a sample hold signal is input to the clock terminal CK and a motor OFF / ON signal is input to the reset terminal R. S
W2 is an analog switch, D flip-flop FF1
It is turned on and off based on the output of. When the analog switch SW2 is turned on, the hold capacitor C1 is discharged.

Next, the operation will be described with reference to FIG.

The motor OFF / ON signal turns off the polygon scanner motor at a high level (H) and turns it on at a low level (L). When the sample hold signal is H, the switch SW1 is turned off to enter the hold state, and when the sample hold signal is L, the switch SW1 is turned on to enter the sample state. In addition, the laser blinking signal turns off the laser diode LD when H, and turns off when L
N

When the motor OFF / ON signal becomes L, the polygon scanner motor starts rotating, and when the number of rotations of the polygon scanner motor reaches the specified number of rotations, the APC operation is started. The laser diode LD is turned on, and the sample hold circuit is turned on. That is, the reset of the D flip-flop FF1 is released, and Q bar (hereinafter, / Q) is generated at the negative edge of the sample signal.
The output becomes L.

At time t1, the switch SW2 is turned off and charging of the holding capacitor C1 is started. Then, the current flowing through the laser diode LD is controlled by the current controller CC according to the potential of the holding capacitor C1. When the current flowing through the laser diode LD is controlled, the photocurrent of the photodiode PD increases according to the laser power from the laser diode LD. Then, when the voltage input to the inverting input terminal of the operational amplifier OP2 becomes equal to the voltage Vref applied to the non-inverting input terminal, the equilibrium state is reached and the hold capacitor C1.
Potential becomes Vo and becomes constant.

At time t2, the initial APC operation is completed, the switch SW1 is turned off by the sample hold signal,
Put the sample-hold circuit in the hold state. here,
Initial APC is the APC performed at the start of printing one page.
On the other hand, APC performed for each line scan is referred to as interline APC.

In the hold state, the laser diode LD is turned on / off based on the print data, and APC between lines is performed in the non-image area after one scan. When performing APC,
The laser diode LD is forcibly turned on.

At time t3, the polygon scanner motor is turned on.
By performing FF, the switch SW2 is turned on and the hold capacitor C1 is discharged.

In this embodiment, since it is configured in this way,
The holding capacitor can be set and reset at an appropriate timing. Therefore, the holding capacitor C1 does not become an excessive potential due to the leakage current of the g _m amplifier, the leakage current of the analog switch SW1, and the like. Therefore, there is no fear that an excessive current will flow when the laser is turned on.

Fourth Embodiment FIG. 7 shows a fourth embodiment of the present invention.

In comparison with the third embodiment, this embodiment is as follows.
The signal applied to the transistor Q1 is different from the signal input to the clock terminal CK of the D flip-flop FF1.

The signal applied to the transistor Q1 is the laser blinking OFF / ON signal in the third embodiment, but in the present embodiment, the laser forced lighting signal synchronized with the sample signal and the NOR calculation of the print data are performed. The result has been entered.

As the signal input to the clock terminal CK of the D flip-flop FF1, the sample hold signal is input in the third embodiment, but the forced lighting signal is input in the present embodiment.

Next, the operation of this embodiment will be described with reference to the timing chart shown in FIG.

When the print command is received, the polygon scanner motor is turned on, and when the rotation speed of the polygon scanner motor reaches the specified rotation speed, the initial APC operation is performed.
Turn on the laser compulsory lighting signal. By catching the first rising edge (time t4) of the forced lighting signal, the / Q output of the D flip-flop FF1 becomes L, and the reset of the hold capacitor C1 is released. The subsequent operation is similar to that of the third embodiment, and the hold capacitor is reset at the same time when the motor is turned off.

As described above in the third and fourth embodiments, while the polygon scanner motor is ON, the sample signal of the sample hold circuit or the laser compulsory lighting signal synchronized with the sample signal is ON. By generating the reset signal of the holding capacitor C1 at the timing of, the reset of the holding capacitor C1 can always be released at the optimum timing without using the reset signal by the control unit such as the CPU. Abnormal laser emission due to abnormal charging of the holding capacitor C1 can be prevented.

Fifth Embodiment FIG. 9 shows a fifth embodiment of the present invention.

In FIG. 9, 101 is a pre-driver. The laser switching circuit is an amplifier circuit including resistors 111, transistors 102 and 103, and a voltage / current circuit 108. The bases of the transistors 102 and 103 are connected to the pre-driver 101. The laser switching circuit controls ON / OFF of the laser diode 112. Is.

Reference numeral 113 denotes a photodiode, which generates a photocurrent proportional to the laser power from the laser diode 112. Reference numeral 104 denotes a resistance, which converts a photocurrent into a voltage.

Reference numeral 107 is a reference power source. An operational amplifier 114 outputs a voltage that is (1+ (resistance value of resistor 115 / resistance value of resistor 116)) times the voltage of the reference power source 107. An operational amplifier 117 outputs a voltage that is (1+ (resistance value of resistance 118 / resistance value of resistance 119)) times the voltage of the reference power supply 107.

Reference numeral 105 denotes an operational amplifier, to which the sum of the voltage across the resistor 104 and the output voltage of the operational amplifier 114 is input. Reference numeral 106 is a comparison circuit, which compares the output voltages of the operational amplifier 105 and the operational amplifier 117. 108
Is a sample hold circuit, which samples and holds the output voltage of the comparison circuit 106. Reference numeral 110 is a holding capacitor.

With this configuration, the operational amplifier 11
4 has an output voltage V ₁₁₄ of which the resistance value of the resistor 115 is R ₁₁₅ ,
When the resistance value of the resistor 116 is R ₁₁₆ and the output voltage of the reference power supply 107 is V ₁₀₇ , it is expressed by the following equation (1).

[0075]

## EQU1 ## V ₁₁₄ = (1+ (R ₁₁₅ / R ₁₁₆ )) V ₁₀₇ (1) Further, the output voltage V ₁₁₇ of the operational amplifier ₁₁₇ is the resistance 11
When the resistance value of _No. 8 is R ₁₁₈ , the resistance value of the resistor 119 is R _119, and the output voltage of the reference power supply 107 is V ₁₀₇ , it is expressed by the following equation (2).

[0076]

V ₁₁₇ = (1+ (R ₁₁₈ / R ₁₁₉ )) V ₁₀₇ (2) Therefore, the output voltage (= input voltage) of the operational amplifier 105 is expressed by the following equation (3).

[0077]

## EQU00003 ## V ₁₀₅ = (1+ (R ₁₁₅ / R ₁₁₆ )) V ₁₀₇ + R ₁₀₄ I _M (3) Therefore, the output voltage V ₁₀₆ of the comparison circuit ₁₀₆ is expressed by the following equation (4).

[0078]

Equation 4] _{V 106 = V 105 -V 117 =} (1+ (R 115 / R 116)) V 107 + R 104 I M - (1+ (R 118 / R 119)) V 107 = ((R 115 / R 116 _{) - (R 118 / R 119} )) V 107 -R 104 I M ... (4) Then, since it is controlled so that the output voltage V ₁₀₆ of the comparator circuit 106 becomes 0, for example, (R ₁₁₅ / R ₁₁₆ ) =
When 0.5, (R ₁₁₈ / R ₁₁₉ ) = 1, the formula (4)
Is expressed by the following equation (5).

[0079]

Equation 5 can be seen from _{-0.5V 107 + R 104 I M =} 0 ... (5) Equation (5), even if the reference voltage V ₁₀₇ varies due to the chip temperature, the variation is compared with the conventional 1 / 2.

Further, R ₁₁₅ / R ₁₁₆ , R ₁₁₈ / R ₁₁₉
By properly selecting, the fluctuation of the reference voltage V ₁₀₇ can be reduced.

Sixth Embodiment This embodiment is different from the fifth embodiment in the method of suppressing fluctuation of the reference power supply voltage V ₁₀₇ .

FIG. 10 shows a sixth embodiment of the present invention.

Output current I _M from the photodiode 113
Flows into the resistor 201, and at the same time, when the collector current of the transistor 202 flows into the resistor 201, the transistor 20
Since the current mirror circuit is composed of 2 and the transistor 203, the collector current of the transistor 202 is substantially equal to the collector current of the transistor 203.

The collector current of the transistor 203 is the collector current of the transistor 204, and is the voltage V _{107 of the} resistor 205, the operational amplifiers 206 and 207, and the reference power supply _107.
Determined by This current becomes V ₁₀₇ / R ₂₀₅ when the resistance value of the resistor 205 is R ₂₀₅ .

[0085] resistor 201 between voltage and the resistance value is _{R 201, R 201 (I M} + (V 107 / R 205)) is expressed as.

The comparator circuit 106 causes the voltage across the resistor R201 input via the operational amplifier 105 and the output voltage of the operational amplifier 208, that is, the reference power supply voltage V.
₁₀₇ is compared. The output voltage of the comparison circuit 106 is expressed as _R201 ( _IM + ( _V107 / _R205 ))- _V107 , so that the output voltage becomes 0, that is,

[0087]

## EQU6 ## Loop control is performed so that ((R ₂₀₁ / R ₂₀₅ ) -1) V ₁₀₇ + R ₂₀₁ I _M = 0.

Therefore, for example, R ₂₀₁ / R ₂₀₅ = 0.5
Then,

[0089]

[Equation 7] −0.5V ₁₀₇ 7 + R ₂₀₁ I _M = 0, and even if the reference power supply voltage V ₁₀₇ fluctuates depending on the chip temperature, the fluctuation can be halved as compared with the conventional one.
By properly selecting R ₂₀₁ / R ₂₀₅ , the fluctuation of the reference power supply voltage V ₁₀₇ can be further reduced.

[0090]

As described above, according to the present invention,
With the above configuration, the laser power does not differ between when adjusting the laser power and when actually used, and it is possible to prevent abnormal light emission of the laser due to abnormal charging of the hold capacitor, and fluctuations in the chip temperature. It is possible to reduce the fluctuation of the laser power caused by.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure by the MPU 110 shown in FIG.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

4 is a flowchart showing a control procedure by the MPU 110 shown in FIG.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

FIG. 6 is a timing chart showing an example of the timing of each unit shown in FIG.

FIG. 7 is a circuit diagram showing a fourth embodiment of the present invention.

8 is a timing chart showing an example of the timing of each part shown in FIG.

FIG. 9 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 10 is a circuit diagram showing a sixth embodiment of the present invention.

FIG. 11 is a circuit diagram showing a configuration of a conventional laser driver IC.

[Explanation of symbols]

 90,150,180 Resistance 100 Switch 110 MPU 120 Monolithic Driver IC 121,122 Transistor 123,124,127 Operational Amplifier 125,126 Analog Switch 128 Constant Current Source 129 Inverter 130 Polygon Motor Driver 140 Variable Resistor 160 Sample Capacitor 170 Polygon Motor 190a Laser diode 190b Photo diode 200 Reference power supply

Claims (7)

[Claims] 1. A laser, a laser driving means for driving the laser, a polygon mirror for scanning a laser beam from the laser on a photosensitive surface, a motor for driving the polygon mirror, and a motor for driving the motor. The motor drive means and the laser drive means include drive means, sample hold means for sampling and holding the laser power, and adjusting means for adjusting the laser power based on the laser power sampled and held by the sample hold means. In the image forming apparatus integrated on the same chip, at the time of adjusting the laser power by the adjusting means, the laser is turned on, the sample hold means is put into a sample state, and the first control means is provided to rotate the motor steadily An image forming apparatus characterized by. 2. The image forming apparatus according to claim 1, further comprising a second control unit that brings the adjustment unit into an adjustable state when the motor is forcibly turned on from the OFF state. . 3. The adjustment control means according to claim 1, further comprising: an adjustment control means for starting the adjustment by the adjusting means after a predetermined time has elapsed after the adjustment by the adjusting means is enabled. Image forming apparatus. 4. A laser, a laser driving means for driving the laser, a polygon mirror for scanning a laser beam from the laser onto a photosensitive surface, a motor for driving the polygon mirror, and a motor for driving the motor. An image forming apparatus comprising: a driving unit; a sample-holding unit that samples and holds the laser power; and an adjusting unit that adjusts the laser power based on the laser power sample-held by the sample-holding unit. Resetting means for discharging a capacitor; timing detecting means for detecting a timing at which the sample holding means changes to a sample state when the motor is being driven by the motor driving means; and the sample holding means by the timing detecting means. Is a sample An image forming apparatus, comprising: a reset canceling unit that cancels the reset state by the reset unit when the timing of changing to the state is detected. 5. A laser, a laser driving means for driving the laser, a polygon mirror for scanning a laser beam from the laser onto a photosensitive surface, a motor for driving the polygon mirror, and a motor for driving the motor. An image forming apparatus comprising: a driving unit, a sample-holding unit that samples and holds the laser power, and an adjusting unit that adjusts the laser power based on the laser power sample-held by the sample-holding unit, in order to start driving the motor. Signal generating means for generating a reset signal for the holding capacitor based on the drive signal and the sample-hold signal, reset means for discharging the holding capacitor of the sample-hold means based on the signal from the signal generating means, and the motor The motor is driven by drive means Image forming apparatus, the image forming apparatus further comprises a reset releasing unit that releases the reset state by the reset unit in synchronization with the laser driving by the laser driving unit. 6. The signal generating means according to claim 5, wherein a reset signal for the holding capacitor is generated by a signal having the same timing as the sample hold signal and a drive signal for starting driving of the motor. Image forming apparatus. 7. A laser, a sample and hold means for sample and hold the laser power, and a control means for controlling the laser power based on the laser power sampled and held by the sample and hold means, the control means being the same chip. In the image forming apparatus integrated above, the control means includes: current generation means for generating a current proportional to laser power; a current-voltage conversion circuit for converting the current generated by the current generation means into a voltage; A reference voltage generating circuit for generating a voltage serving as a reference of the first reference voltage and a reference voltage generated by the reference voltage generating circuit.
A reference voltage generating circuit for generating a reference voltage of the current voltage converting circuit, a summing circuit for adding the first reference voltage from the first voltage generating circuit and the voltage from the current voltage converting circuit, A second reference voltage generating circuit for generating a second reference voltage from a reference voltage generated by the comparator, and a comparison for comparing the second reference voltage from the second voltage generating circuit with the output voltage of the adding circuit. An image forming apparatus comprising: a circuit, a sample-hold circuit that samples and holds the voltage from the comparison circuit, and a control circuit that controls laser power based on the output voltage of the sample-hold circuit.