JPH09183248A - Image forming device - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To maximize the characteristics of a semiconductor laser to improve the operation speed and to improve the definition of an image. A semiconductor laser (20) and a semiconductor laser (20)
A bias current source Jb for biasing the laser diode, a pulse current source Jp for driving the semiconductor laser 20 based on the image signal,
A feedback loop by feeding back the photodiode 60 that detects the laser beam L from the semiconductor laser 20 and the control signals Cb and Cp based on the detection current Ipd from the photodiode 60 to the bias current source Jb and the pulse current source Jp. Is configured. The selection switch Ss outputs the output current I.
By outputting pd to either the terminal T1 or T2, both the bias current source Jb and the pulse current source Jp are independently controlled in time by the two independent control signals Cb and Cp. The photoconductor is exposed by the laser beam L from the semiconductor laser 20 to form a latent image.

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, and in particular, it drives and controls a laser light source based on a detection signal obtained by detecting laser light from a laser light source to expose a photoconductor,
The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine that forms a latent image on a photosensitive surface.

[0002]

2. Description of the Related Art Conventionally, an exposure control section using a semiconductor laser optical system has been widely used in digital recording type copying machines, printers, facsimile machines and the like.

FIG. 6 is a diagram showing an example of a drive circuit of an exposure control section using a conventional semiconductor laser optical system. In FIG. 6, the semiconductor laser 20 is made of, for example, a GaAs pn junction, and the anode side is connected to the power supply Vcc and is forward biased. The cathode side is connected to a bias current source Jb for stabilizing the light emission of the semiconductor laser 20, and is also connected to a pulse current source Jp via a switch S. These two current sources Jb and Jp are configured so that the amount of current can be varied. By providing the current sources Jb and Jp, the emission characteristics of the semiconductor laser 20 are improved.

By the switch S being switched by the image pulse Vp based on the image signal to be recorded,
Pulse current Ip based on the current from the pulse current source Jp
Are supplied to the semiconductor laser 20, and the semiconductor laser 20 emits light according to the image signal. The semiconductor laser 20 has a cathode connected to the power supply Vcc and an anode side of the current amplifier 6
The laser chip 61 is formed by pairing with the reverse biased photodiode 60 by being connected to the second input terminal.

The photodiode 60 receives the laser beam L from the semiconductor laser and outputs a detection current Ipd according to the amount of received light. The detection current Ipd from the photodiode 60 is amplified by the current amplifier 62, the amplified output of the current amplifier 62 is sampled and held by the sample hold circuit 63 based on the sampling pulse Ps at a predetermined timing, and the sample hold output is fed back to the bias current source Jb. By doing so, the value of the bias current Ib is automatically controlled.

That is, a feedback loop is provided to keep the light quantity of the laser beam L constant, and automatic power control (APC;
Performing Automatic Power Control). At this time, in order to adjust the gain in the feedback loop, the current amplifier 62 is configured to be adjustable in gain.

[0007]

However, in the configuration of the exposure control section of FIG. 6 which performs the APC control as described above,
Only the amount of bias current is controlled based on the output of the photodiode 60 at the time of laser emission, not at the time of bias emission.
Alternatively, it may be possible to automatically control only the pulse current amount by configuring as shown by the broken line.

In the meanwhile, with the progress of higher speeds of devices and higher definition of images, it is demanded to maximize the characteristics of semiconductor lasers capable of high speed operation by controlling the semiconductor lasers at higher speeds. In order to maximize the characteristics of the semiconductor laser, it is generally desirable to set the bias current amount for stabilizing the light emission of the semiconductor laser to be slightly smaller in the vicinity of the oscillation start current Ith (threshold current). It is known. The oscillation start current Ith is a value unique to each semiconductor laser and changes depending on the environmental temperature.

Therefore, even if the bias current is set so that the bias light is emitted with a constant value near the standard value of the oscillation start current Ith of the semiconductor laser, the variation of the oscillation characteristics of the semiconductor laser and the change of the environmental temperature are accompanied. In some cases, the laser may be emitted. Therefore, in order to prevent unnecessary laser light emission due to such variations and temperature changes, it is necessary to set the bias current amount to a value sufficiently smaller than the oscillation start current Ith of the semiconductor laser. . Further, if the amplitude of the pulse current is small, there is a possibility that the laser will not emit light, and it was necessary to set the amplitude of the pulse current sufficiently large. Therefore, there is a problem that the characteristics of the semiconductor laser capable of high-speed operation cannot be maximized.

The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus capable of maximizing the characteristics of a semiconductor laser and improving the operating speed. is there.

[0011]

In order to achieve the above object, the apparatus of the present invention comprises a light source, biasing means for biasing the light source, driving means for driving the light source based on an image signal, and A feedback loop composed of a detection means for detecting the light from the light source, a control means for returning a control signal based on the detection signal from the detection means to the bias means and the driving means, and a feedback loop from the light source. An image forming apparatus comprising: a photoconductor that is exposed to light to form a latent image, and controls the exposure amount by controlling the light amount of the light source to a predetermined amount, wherein the control unit includes the bias unit and the bias unit. Two independent control signals are generated to control both drive means independently.

Further, as one form of the apparatus of the present invention, the light source is composed of a plurality of light sources, and the control means is provided in a plurality corresponding to the plurality of light sources, and each horizontal period of the image signal. During the period other than the image signal period, the bias means and the driving means are independently controlled to sequentially control the plurality of light sources one by one to control the light amount of all the light sources to the predetermined amount. It is supposed to be.

In another form, the device of the present invention is
The control means includes a bias control means for variably controlling a bias amount by the bias means, a switching means for switching based on the image signal, and a signal amount for the driving means including a power source connected to the switching means. The bias means and the driving means are temporally constituted by a signal control means for controlling and a selection output means for selectively outputting the detection signal to either the signal control means or the bias control means. Control independently.

As another form of the apparatus of the present invention,
The bias control means has a first gain adjusting means whose gain is adjusted according to the level of the detection signal, and the signal control means has a second gain whose gain is adjusted according to the level of the detection signal. By including the adjusting means, the gain of the feedback loop is adjusted to a predetermined gain.

In another form, the apparatus of the present invention is
The period other than the image signal period is a horizontal synchronization period, and further includes a unit for sequentially operating the plurality of control units for each horizontal synchronization period.

In another form, the device of the present invention is
A light source, a first current control means for controlling the light source to a first light quantity, a second current control means for controlling the light source to a second light quantity, and a drive for driving the light source based on an image signal Means, detecting means for detecting light from the light source, and control means for feeding back a control signal based on the detection signal from the detecting means to the first current control means and the second current control means. An image forming apparatus comprising a configured feedback loop and a photoconductor that is exposed to light from the light source to form a latent image, and controls the light amount of the light source to a predetermined amount to control the exposure amount. Thus, the control means is configured to generate two independent control signals for independently controlling both the first current control means and the second current control means.

In another form, the device of the present invention is
The light source is composed of a plurality of light sources, a plurality of the control means are provided corresponding to the plurality of light sources, and the first light amount is controlled outside the image signal period of each horizontal period of the image signal. One current control means and a second current control means for controlling to the second light quantity are independently controlled to sequentially control the plurality of light sources one by one to control the light quantity of all the light sources to the predetermined amount. It is configured to be controlled to.

In another form, the device of the present invention is
The first current control means has first gain adjustment means whose gain is adjusted according to the level of the detection signal, and the second current control means adjusts gain according to the level of the detection signal. By including the second gain adjusting means, the gain of the feedback loop is adjusted to a predetermined gain.

According to the present invention, the control means for feeding back the detection signal from the detection means for detecting the light from the light source to the bias means and the drive means is replaced with the bias control means for variably controlling the bias amount by the bias means and the image signal. Signal control means for variably controlling a signal amount by a driving means composed of a switching means switched based on the switching means and a power supply connected to the switching means, and the detection signal is selectively output to either the signal control means or the bias control means. Since two independent control signals for controlling the bias means and the driving means independently in terms of time are applied by being constituted by the selective output means, the bias amount and the driving signal amount of the light source are relatively simple in structure. Can be controlled accurately.

Further, in the present invention, the bias control means has a first gain adjusting means whose gain is adjusted according to the level of the detection signal, and the signal control means adjusts the gain according to the level of the detection signal. Since the gain of the feedback loop is adjusted to a predetermined gain by including the second gain adjusting means, the feedback loop becomes stable.

Further, in the present invention, the period outside the image signal period is a horizontal synchronizing period, and means for sequentially operating a plurality of control means is applied for each horizontal synchronizing period, so that a semiconductor laser is used as a light source. Even in this case, the droop phenomenon can be suppressed.

[0022]

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

(First Embodiment) FIG. 1 is a side perspective view showing an image forming apparatus according to a first embodiment of the present invention.

The copying machine 1 shown in FIG. 1 is a kind of image forming apparatus, and the originals stacked on the original feeding device 2 are sequentially conveyed one by one onto the original glass platen surface 3. When the document is conveyed onto the platen glass surface 3, the lamp 5 in the scanner unit 4 is turned on, and the scanner unit 4 moves in the X direction in the drawing to illuminate the entire document surface.

Reflected light from the original is reflected by mirrors 6a, 6b, 6
The image described on the original is formed on the image pickup surface of the linear image sensor 8 that extends through the lens system 7 in the Z direction in FIG. The linear image sensor 8 photoelectrically converts the formed image and outputs an image signal. This image signal is subjected to processing such as correlated double sampling and waveform shaping by a signal processing circuit (not shown), and then, for example, DRA
It is once stored in an image memory (not shown) composed of M and then read again. The read image signal is input to the exposure control unit 9.

The exposure control unit 9 includes a semiconductor laser corresponding to a light source, and the emission timing of this semiconductor laser is controlled according to the image signal read from the image memory. The laser beam from the semiconductor laser is a rotating polygon mirror 1.
It is irradiated to 0. The cylindrical photosensitive drum 11 rotates in the clockwise direction (CW) in the figure, and the photosensitive surface thereof is uniformly charged by the charger 12. The reflected light from the rotary polygonal mirror 10 is reflected by the mirror 6d and then radiated to the photosensitive surface of the photosensitive drum 11 to remove a part of the charged electric charge, thereby forming an electrostatic latent image on the photosensitive surface. It is conceivable to use, for example, a gas laser as a light source instead of the semiconductor laser, but in this case, an optical modulator for performing optical modulation at high speed is required.

Here, FIG. 2 is a diagram showing a configuration of a main part in FIG. 2, the same components as those of FIG. 1 are designated by the same reference numerals, and the mirror 6a is omitted.

Laser beam L from the semiconductor laser 20
Is converted into substantially parallel light by the collimator lens 21 and the diaphragm 22 and is incident on the rotary polygon mirror 10 through a predetermined beam. The rotary polygon mirror 10 is rotated in the counterclockwise direction (CC
W) is rotating at a constant angular velocity. By this rotation, the laser beam L incident on the rotary polygon mirror 10 is reflected as a deflected beam Ld whose reflection angle is continuously changed.

The deflected beam Ld, which is a circular-arc scanning light, is f-θ.
The lens 23 receives a condensing function to focus on a straight line on the photosensitive surface of the photosensitive drum 11. At the same time, since the f-θ lens 23 corrects the distortion aberration that guarantees the linearity of the scanning in time, the deflected beam Ld scans the photosensitive surface of the photosensitive drum 11 at a constant speed in the direction of the arrow in the figure. Photosensitive drum 1
The electrostatic latent image is formed on No. 1 by variably controlling the light emission timing of the semiconductor laser 20 according to the image signal from the image memory.

The beam detector 24 detects the deflected beam Ld from the rotary polygon mirror 10, and the driving timing of the semiconductor laser 20 is set so as to start the modulation of the laser beam L based on the image signal after a fixed time corresponding to the distance d. Controlled. As a result, the recording start position of the image on the photosensitive surface of the photosensitive drum 11 can be made constant.

Returning to FIG. 1, the deflected beam Ld will be described.
By removing the charges on the photosensitive surface according to the image signal and exposing the photosensitive drum 11, an electrostatic latent image is formed on the photosensitive drum 11. This electrostatic latent image is developed by applying toner by the developing device 13. At the timing when the electrostatic latent image formed on the photosensitive drum 11 is developed, the transfer target paper is conveyed from the transfer target paper stacking section 14a or 14b to a position near the photosensitive drum 11 by a transfer mechanism.

Then, the transferred paper passes between the transfer device 15 disposed below the photosensitive drum 11 and the photosensitive drum 11, so that the developed image is transferred to the transferred paper. After that, the image on the transfer paper is heated by the fixing device 16,
It is fixed on the transfer paper. The transfer paper on which the image is fixed and printing is completed is discharged by the paper discharge roller 17 to a predetermined tray of the multi-tray device 18.

FIG. 3 is a diagram showing a drive circuit of the exposure control section of the copying machine 1 shown in FIG. 1 to which the present invention is applied. In FIG. 3, the same components as those in FIG. 6 are designated by the same reference numerals, and the description thereof will be omitted.

The drive circuit 30 is an exposure control unit (9) in FIG.
The image signal Vs included in the image memory is input to the image processing board 31. On the image processing board 31, a timer for timing the recording start time based on the detection output Id from the beam detector (24) in FIG. 2, and a horizontal synchronizing signal is generated based on the timing result of the timer to generate the image signal Vs.
A synchronizing circuit for synchronizing the image pulse Vp based on the above is provided. Further, a signal generation circuit that generates the selection signal Se and also generates the power control signals Pob and Pop, a CPU that controls the operation of the entire circuits, and the like are provided.

The anode of the photodiode 60 is connected to the input terminal of the selection switch Ss. A series circuit of a current amplifier 32 and an APC circuit 33 is connected to the output terminal T1 of the selection switch Ss, and a series circuit of a current amplifier 34 and an APC circuit 35 is connected to the output terminal T2.

The current amplifier 32 and the current amplifier 34 are
The gain is automatically and variably adjusted according to the level of the detection current Ipd of the photodiode 60. The APC circuit 33 is controlled by the power control signal Pob and outputs the bias control signal Cb. Also, A
The PC circuit 35 is controlled by the power control signal Pop and outputs the pulse control signal Cp.

That is, the bias current source Jb, the pulse current source Jp, the semiconductor laser 20, the photodiode 60, the selection switch Ss, the current amplifiers 32, 34 and A.
A feedback loop is composed of the PC circuits 33 and 35. Instead of each current source, a series circuit of a voltage source and a high impedance resistor whose resistance value is known can be used.

First, the APC control during bias light emission will be described. At this time, the switch S is turned off according to the image pulse Vp. Further, the selection switch Ss is switching-controlled by the selection signal Se so as to be electrically connected to the output terminal T1. Therefore, the detection current Ipd of the photodiode 60 is input to the current amplifier 32, and the gain is variably adjusted according to the level of the detection current Ipd so as to obtain an in-loop gain that stabilizes the feedback loop, and then amplified and output. It

The output of the current amplifier 32 is input to the APC circuit 33. The APC circuit 33 is controlled by the power control signal Pob and outputs the bias control signal Cb that supplies the semiconductor laser 20 with the bias current Ib of a constant level to control the bias current source Jb. At this time, the bias current Ib is the oscillation start current It of the semiconductor laser 20.
The value is set to be smaller than Ith in the vicinity of the standard value of h (threshold current), and the value does not exceed Ith even if the emission characteristics of the semiconductor laser 20 vary or the environmental temperature changes. This value can be set closer to Ith than before.

Next, the APC control during laser emission will be described. At this time, the switch S is turned on according to the image pulse Vp. Further, the selection switch Ss is switching-controlled by the selection signal Se so as to be electrically connected to the output terminal T2. Therefore, the detection current Ipd of the photodiode 60 is input to the current amplifier 34, and the gain is variably adjusted according to the level of the detection current Ipd so as to obtain an in-loop gain that stabilizes the feedback loop, and then amplified and output. It

The output of the current amplifier 34 is input to the APC circuit 35. The APC circuit 35 is controlled by the power control signal Pop and outputs a pulse control signal Cp that supplies the semiconductor laser 20 with a constant level pulse current Ip to control the pulse current source Jp. At this time, the pulse current Ip is set to be necessary and sufficiently larger than the standard value of the oscillation start current Ith (threshold current) of the semiconductor laser 20, and a pulse having a smaller amplitude than the conventional pulse can be obtained. Of course, even if the emission characteristics of the semiconductor laser 20 are varied or the environmental temperature is changed, the value does not become Ith or less, and the value is set to a value that allows stable laser emission.

As described above, according to the present embodiment, by switching the selection switch Ss in accordance with the selection signal Se, the detection current Ipd is changed to the bias control side (current amplifier 32).
And the APC circuit 33) or the pulse control side (series circuit of the current amplifier 33 and the APC circuit 34), so that both the bias current source Jb and the pulse current source Jp are output in time. Can be independently controlled.

As described above, since the bias current Ib and the pulse current Ip can be accurately controlled with a relatively simple structure, the bias current Ib can be controlled by I compared with the conventional one.
It can be near th, and the pulse current Ip can be a pulse having a smaller amplitude than before. Therefore, the responsiveness of light emission to the drive current of the semiconductor laser 20 is improved, and a higher definition image can be formed. Further, since the light amount of the laser beam L at the time of image formation can be stabilized even if the emission characteristics of the semiconductor laser 20 vary or the environmental temperature changes, stable image formation can be performed.

Although the switch S and the pulse current source Jp are connected in series, the semiconductor laser 20 can be driven with a pulse current corresponding to the image pulse Vp even if they are connected in parallel. Further, instead of the photodiode 60, a phototransistor in which the pn junction of the base emitter is reverse-biased may be used.

(Second Embodiment) FIG. 4 shows a second embodiment of the image forming apparatus to which the present invention is applied. In FIG. 3, the drive circuit 40 of the exposure control unit, which is the main part of the copying machine.
It is shown. The overall construction of the copying machine is similar to that shown in FIG.

The copying machine of the present embodiment can operate at a higher speed than the copying machine (1) of the first embodiment, and is provided with the twin laser chip 41 so as to realize high definition of the image. It is said that. The twin laser chip 41 includes the semiconductor lasers 20a whose cathodes are commonly connected,
20b and a photodiode 60a whose anode is connected to this common cathode. It is assumed that the semiconductor lasers 20a and 20b have the same characteristics as the semiconductor laser (20) in the first embodiment.

The image signal Vs from the linear image sensor (8) and the detection output Id from the beam detector (24) are input to the image processing board 31a. The image processing board 31a has an image pulse generation circuit that generates time-division image pulses Vp1 and Vp2 based on the image signal Vs, a timer that counts a recording start time based on the detection output Id, and a horizontal position based on a timing result of the timer. A synchronizing circuit and the like for generating a synchronizing signal and synchronizing the time-division image pulses Vp1 and Vp2 are provided. Time division image pulses Vp1 and Vp
2 is output alternately in an extremely short cycle.

Further, the selection signals Se1 and Se2 and the current control signals Cs1 and Cs2 are generated, and the sampling pulse Ps1 is generated at a timing based on the detection output Id.
A signal generation circuit for generating Ps4 to Ps4, a CPU for controlling the operation of all of these circuits, and the like are provided.

The drive unit A for the semiconductor laser 20a and the drive unit B for the semiconductor laser 20b have the same structure. Therefore, only the configuration of the drive unit A will be described here.
The other end of the series circuit of the constant current source J1 whose one end is connected to the power supply Vcc and the current control switch Sc1 has the other end of the semiconductor laser 20.
It is connected to the anode of a. In addition, the semiconductor laser 2
The cathode of 0a is grounded, and the current control signal Cs1
When the current control switch Sc1 is turned on by being controlled by, the pn junction of the semiconductor laser 20a is forward biased.

On the other hand, the anode of the photodiode 60a is grounded, and its cathode is the selection switch Ss1.
It is reverse biased by being connected to the input terminal of the current amplifier 42 or the current amplifier 44 via. Selection switch S
The output terminal T3 of s1 is connected to the series circuit of the current amplifier 42 and the sample hold circuit 43, and the output terminal T4 is connected to the series circuit of the current amplifier 44 and the sample hold circuit 45.

The current amplifier 42 and the current amplifier 44 are
The gain is automatically and variably adjusted according to the level of the detection current Ipd of the photodiode 60a. The amplified output of the current amplifier 42 is sampled and held by the sample and hold circuit 43 based on the sampling pulse Ps1 at a predetermined timing, and the bias current source Jb is supplied by the sample and hold output control signal Cb1.
The value of the bias current Ib1 of 1 is automatically controlled.

The amplified output of the current amplifier 44 is sampled and held by the sample and hold circuit 45 based on the sampling pulse Ps2 at a predetermined timing, and the pulse current source Jp1 is automatically controlled by the sample and hold output pulse control signal Cp1. The switch S1 connected to the pulse current source Jp1 is switching-controlled according to the time-division image signal Vp1 to generate the pulse current Ip1.

Next, FIG. 5 is a timing chart showing the waveform of each part in FIG. In FIG. 5, (A) is a time-division image pulse Vp1, (B) is a time-division image pulse Vp.
2, (C) is the selection signal Se1, and (D) is the selection signal Se
2, (E) is a sample hold pulse Ps2, (F) is a sample hold pulse Ps1, (G) is a sample hold pulse Ps4, (H) is a sample hold pulse P
s3, (I) shows the current control signal Cs1, and (J) shows the current control signal Cs2, respectively.

The operation of this embodiment will be described below with reference to FIGS. 3 and 4. In the present embodiment, in order to suppress the droop phenomenon (pulse waveform distortion tilt), which is one of the characteristics of the semiconductor laser, as shown in FIG. 4, every horizontal period of the image signal within a period other than the image signal period. APC control is performed.

In FIG. 4, a period from time t1 to time t8 is one horizontal period (1H), and a period from time t6 to time t7 is an image signal period Ts. The front porch is from time t5 to time t6, and the back porch is from time t7 to time t8.

At time t1, the image processing board 31a
The current control switch Sc2 is turned off by the current control signal Cs2 becoming low level in synchronization with the above-mentioned horizontal synchronizing signal (not shown) generated therein becoming low level. At this time, the selection signal Se2 becomes low level, the selection switch Ss2 becomes conductive with the output terminal T6, and since the time-division image pulse Vp2 is low level, the switch S2 is off, so the semiconductor laser 20b is completely turned off.
At this time, the current control signal Cs1 is at a high level and the current control switch Sc1 is on, so the constant current I1 is supplied to the semiconductor laser 20a.

At the same time that the current control signal Cs2 becomes low level, the time-division image pulse Vp1 becomes high level and the switch S1 is turned on.
1 flows, AP of the laser emission current of the semiconductor laser 20a
C control is performed. At this time, the selection signal Se1 is at a low level, and the selection switch Ss1 has an output terminal T4.
It is conducting.

Therefore, the photodiode 60a receives the laser beam La from the semiconductor laser 20a driven based on the constant current I1 and the pulse current Ip1 and outputs the detection current Ipd according to the amount of received light. The detection current Ipd from the photodiode 60a is input to the current amplifier 44 and amplified. At this time, the detection current Ipd is adjusted so as to obtain an in-loop gain that stabilizes the feedback loop.
The gain is variably adjusted according to the level of and the output is amplified.

The amplified output from the current amplifier 44 is sampled and held by the sample hold circuit 45 for a certain period of time based on the sampling pulse Ps2 generated at a predetermined timing from time t1 to time t2, and the pulse control signal output from the sample hold circuit 45. The value of the pulse current Ip1 is automatically controlled by feeding back Cp1 to the pulse current source Jp1.

At this time, the pulse current Ip1 is set so that the current (I1-Ip1) flowing through the semiconductor laser 20a becomes necessary and sufficiently larger than the standard value of the oscillation start current Ith (threshold current). The pulse having a smaller amplitude than the conventional one can be used. Of course, even if the emission characteristics of the semiconductor laser 20a vary or the environmental temperature changes, the current (I1−Ip1) does not become less than Ith and the laser emission is stable.

Next, at time t2, the time-division image pulse Vp1 becomes low level, the switch S1 is turned off, and the APC control of the laser emission current is completed. At the time t2, the APC control of the laser emission current is finished, and at the same time, the selection signal Se1 becomes high level, and the selection switch Ss1.
Is electrically connected to the output terminal T3.

Therefore, the photodiode 60a receives the laser beam La from the semiconductor laser 20a driven based on the constant current I1 and the bias current Ib1,
The detection current Ipd corresponding to the amount of received light is output. The detection current Ipd from the photodiode 60a is input to the current amplifier 42 and amplified. At this time, the detection current Ip is adjusted so as to obtain an in-loop gain that stabilizes the feedback loop.
The gain is variably adjusted according to the level of d and amplified and output.

The amplified output from the current amplifier 42 is sampled and held by the sample hold circuit 43 for a certain period of time based on the sampling pulse Ps1 generated at a predetermined timing from time t2 to time t3, and the bias control signal output from the sample hold circuit 43. By feeding back Cb1 to the bias current source Jb1, the bias current I
The value of b1 is automatically controlled.

At this time, the bias current Ib1 is such that the current (I1-Ib1) flowing through the semiconductor laser 20a is near the standard value of the oscillation start current Ith (threshold current) Ith.
The semiconductor laser 20a is set to be smaller than
The current (I1−Ib1) does not exceed Ith even if the light emission characteristics of the device vary or the environmental temperature changes. This value can be set closer to Ith than before. In this way, the bias current APC
Control ends.

When the APC control of the laser oscillation current and the bias current of the drive section A is completed, the current control signal Cs1 becomes low level at time t3, and the current control switch Sc1 is turned off. At this time, the selection signal Se
1 becomes low level, and the selection switch Ss1 has an output terminal T.
4 and the time-division image pulse Vp1 is at the low level, the switch S1 is turned off, so that the semiconductor laser 20a is completely turned off. At the same time, the current control signal Cs2 becomes high level, and the current control switch Sc2 is turned on to supply the constant current I2 to the semiconductor laser 20b, and the APC control of the drive section B is started.

At the same time that the current control signal Cs1 becomes low level, the time-division image pulse Vp2 becomes high level and the switch S2 is turned on.
2 flows, AP of the laser emission current of the semiconductor laser 20b
C control is performed. At this time, the selection signal Se2 is at a low level, and the selection switch Ss2 has an output terminal T6.
It is conducting.

Therefore, the photodiode 60a receives the laser beam Lb from the semiconductor laser 20b,
The detection current Ipd corresponding to the amount of received light is output. The detection current Ipd from the photodiode 60a is input to the current amplifier 48 and amplified. At this time, the detection current Ip is adjusted so as to obtain an in-loop gain that stabilizes the feedback loop.
The gain is variably adjusted according to the level of d and amplified and output.

The amplified output from the current amplifier 48 is sampled and held by the sample hold circuit 49 for a certain period of time based on the sampling pulse Ps4 generated at a predetermined timing from time t3 to time t4, and the pulse control signal output from the sample hold circuit 49. The value of the pulse current Ip2 is automatically controlled by feeding back Cp2 to the pulse current source Jp2.

At this time, the pulse current Ip2 is set so that the current (I2-Ip2) flowing through the semiconductor laser 20b becomes necessary and sufficiently larger than the standard value of the oscillation start current Ith (threshold current). The pulse having a smaller amplitude than the conventional one can be used. Of course, even if the emission characteristics of the semiconductor laser 20b are varied or the environmental temperature is changed, the current (I2-Ip2) is not likely to be less than Ith and stable laser emission is possible. ) Is almost equal to the value.

Next, at time t4, the time-division image pulse Vp2 becomes low level, the switch S2 is turned off, and the APC control of the laser emission current is completed. At the time t4, the APC control of the laser emission current is completed, and at the same time, the selection signal Se2 becomes high level and the selection switch Ss2.
Is electrically connected to the output terminal T5.

Therefore, the photodiode 60a receives the laser beam Lb from the semiconductor laser 20b driven based on the constant current I2 and the bias current Ib2,
The detection current Ipd corresponding to the amount of received light is output. The detection current Ipd from the photodiode 60a is input to the current amplifier 46 and amplified. At this time, the detection current Ip is adjusted so as to obtain an in-loop gain that stabilizes the feedback loop.
The gain is variably adjusted according to the level of d and amplified and output.

The amplified output from the current amplifier 46 is sampled and held by the sample hold circuit 47 for a certain period of time based on the sampling pulse Ps3 generated at a predetermined timing from time t4 to time t5, and the bias control signal output from the sample hold circuit 47. By feeding back Cb2 to the bias current source Jb2, the bias current I
The value of b2 is automatically controlled.

At this time, the bias current Ib2 is such that the current (I2-Ib2) flowing through the semiconductor laser 20b is near the standard value of the oscillation start current Ith (threshold current) Ith.
The semiconductor laser 20b is set to be smaller than
The current (I2-Ib2) is unlikely to exceed Ith even if the light emission characteristics of No. 1 vary or the environmental temperature changes, and the current (I2-Ib2) is set to a value substantially equal to the current (I1-Ib1). This value can be set closer to Ith than before. In this way, the APC control of the bias current is completed.

In the period from time t5 when the horizontal synchronizing signal becomes high level and the horizontal synchronizing period ends and the front porch starts to time t8 when the back porch ends and the horizontal synchronizing period starts again, the current control signal Cs1 is generated. And the current control signal Cs2 are both at the high level, and the current control switches Sc1 and Sc2 are both turned on. Therefore, the constant currents I1 and I2 are supplied to the semiconductor laser 20a and the semiconductor laser 20b during this period.

During this period, the selection signal Se1 and the selection signal Se2 are at the low level, and the selection switch S
s1 is electrically connected to the output terminal T4, and the selection switch Ss2 is electrically connected to the output terminal T6. Therefore, the semiconductor laser 20a and the semiconductor laser 20b are biased at the current values set in the horizontal synchronization period other than the image signal period.

Further, in the image signal period Ts from time t6 to time t7, the time-division image pulse Vp1 and the time-division image pulse Vp2 generated based on the image signal Vs are output as described above. Therefore,
It is possible to form a high-definition image at a speed higher than the operable speed of the semiconductor lasers 20a and 20b.

As described above, according to the present embodiment, in the image forming apparatus having the configuration using the multi-laser type laser chip, the selection signal Se is selected during the synchronization period of one horizontal period.
By switching the selection switches Ss1 and Ss2 in accordance with 1 and Se2, the detection current Ipd is applied to the bias control side of each of the driving units A and B (the series circuit of the current amplifier 42 and the sample hold circuit 43, or the current amplifier 46 and the sample). Hold circuit 47 in series) or pulse control side (current amplifier 44 and sample hold circuit 45 in series, or current amplifier 48 and sample hold circuit 4)
9) (serial circuit with 9)
Bias current sources Jb1, Jb2 and pulse current sources Jp1,
Both Jp2 can be controlled independently in time.

As described above, since the bias currents Ib1 and Ib2 and the pulse currents Ip1 and Ib2 can be accurately controlled with a relatively simple structure, the bias currents Ib1 and Ib2 can be set closer to Ith than in the conventional case. In addition, the pulse currents Ip1 and Ib2 can be pulses having a smaller amplitude than before. Therefore, the responsivity of light emission to the drive current of the semiconductor lasers 20a and 20b is improved, and it is possible to form a higher definition image.

Further, even if the emission characteristics of the semiconductor lasers 20a and 20b vary or the environmental temperature changes, the light amounts of the laser beams La and Lb can be made substantially equal and stable at the time of image formation, so that a high-speed and high-definition image can be obtained. The formation can be performed stably. Further, since the APC control of each semiconductor laser is sequentially performed one by one in each period other than the image signal period of one horizontal period, the droop phenomenon of the semiconductor laser can be suppressed.

Although the switches S1 and S2 and the pulse current sources Jp1 and Jp2 are connected in series, even if they are connected in parallel, the semiconductor lasers 20a and 20b are driven by the pulse current corresponding to the image pulses Vp1 and Vp2. can do. Further, instead of the photodiode 60b, a phototransistor in which the pn junction of the base emitter is reverse biased may be used.

[0081]

As described above, according to the present invention, the light source is controlled by two independent control signals for independently controlling the bias means for biasing the light source and the driving means for driving the light source based on the image signal. Since the exposure amount is controlled by controlling the amount of light from the specified amount to a certain amount, the bias means and the driving means can be accurately controlled, and when a semiconductor laser is used as the light source, its characteristics are maximized and the operating speed is And an effect that a high-definition image can be formed can be obtained.

That is, in the present invention, the control means for feeding back the detection signal from the detection means for detecting the light from the light source to the bias means and the drive means, the bias control means for variably controlling the bias amount by the bias means, and the image. A signal control means for variably controlling a signal amount by a switching means that is switched based on a signal and a drive means that is connected to the switching means and the detection signal is selected as either the signal control means or the bias control means. Since two independent control signals for controlling the bias means and the driving means independently in terms of time are applied by being composed of the selective output means for outputting, the bias amount and the driving of the light source are relatively simple. The signal amount can be controlled accurately.

Further, in the present invention, the bias control means has the first gain adjusting means whose gain is adjusted according to the level of the detection signal, and the signal control means adjusts the gain according to the level of the detection signal. Since the gain of the feedback loop is adjusted to the predetermined gain by including the second gain adjusting means, the feedback loop can be stably operated.

Further, in the present invention, the period other than the image signal period is the horizontal synchronizing period, and since the means for sequentially operating the plurality of control means for each horizontal synchronizing period is applied, the semiconductor laser is used as the light source. Even in this case, the droop phenomenon can be suppressed.

[Brief description of the drawings]

FIG. 1 is a side perspective view showing a first embodiment of an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram showing a configuration of a main part in FIG.

3 is a diagram showing a drive circuit of an exposure control unit of the copying machine 1 shown in FIG. 1 to which the present invention is applied.

FIG. 4 is a diagram showing a second embodiment of an image forming apparatus to which the invention is applied.

FIG. 5 is a timing chart showing waveforms of respective parts in FIG.

FIG. 6 is a diagram showing an example of a drive circuit of an exposure control unit by a conventional semiconductor laser optical system.

[Explanation of symbols]

 1 Copier 9 Exposure Control Unit 11 Photosensitive Drum 20, 20a, 20b Semiconductor Laser 30, 40 Drive Circuit 31, 31a Image Processing Board 32, 34, 42, 44, 46, 48 Current Amplifier 33, 35 APC Circuit 41 Laser Chip 43 , 45, 47, 49 Sample and hold circuit 60, 60a Photodiode Ipd Detection current Jb, Jb1, Jb2 Bias current source Jp, Jp1, Jp2 Pulse current source S, S1, S2 switch Sc1, Sc2 Current control switch Ss, Ss1, Ss2 Selection switch

Claims (9)

[Claims] 1. A light source, a biasing means for biasing the light source, a driving means for driving the light source based on an image signal, a detecting means for detecting light from the light source, and a detection signal from the detecting means. A feedback loop composed of a control means for returning a control signal based on the above to the bias means and the driving means, and a photoconductor that is exposed by the light from the light source to form a latent image, An image forming apparatus for controlling an exposure amount by controlling a light amount of the light source to a predetermined amount, wherein the control unit generates two independent control signals for independently controlling both the bias unit and the driving unit. An image forming apparatus comprising: 2. The light source comprises a plurality of light sources, a plurality of the control means are provided corresponding to the plurality of light sources, and the bias is provided in a period outside the image signal period of each horizontal period of the image signal. The light source of all the light sources is controlled to the predetermined amount by controlling the plurality of light sources one by one by independently controlling both the light source and the driving means. 1. The image forming apparatus according to 1. 3. The drive means, which comprises: bias control means for variably controlling the bias amount of the bias means; switching means for switching based on the image signal; and a power supply connected to the switching means. Signal control means for variably controlling the signal amount by
It is characterized in that the bias signal and the driving means are controlled independently in terms of time by being configured by selective output means for selectively outputting the detection signal to either the signal control means or the bias control means. The image forming apparatus according to claim 1 or 2. 4. The bias control means has a first gain adjusting means whose gain is adjusted according to the level of the detection signal, and the signal control means has a gain adjusted according to the level of the detection signal. The image forming apparatus according to claim 3, wherein the image forming apparatus includes a second gain adjusting unit that adjusts the gain of the feedback loop to a predetermined gain. 5. The period other than the image signal period is a horizontal synchronization period, and further comprises means for sequentially operating the plurality of control means for each horizontal synchronization period. The image forming apparatus described. 6. A light source, a first current control means for controlling the light source to a first light quantity, a second current control means for controlling the light source to a second light quantity, and the second current control means based on an image signal. Driving means for driving the light source, detection means for detecting light from the light source, and a control signal based on the detection signal from the detection means is fed back to the first current control means and the second current control means. And a photoconductor that is exposed to light from the light source to form a latent image, and controls the light amount of the light source to a predetermined amount to control the exposure amount. An image forming apparatus, wherein the control unit generates two independent control signals for independently controlling both the first current control unit and the second current control unit. apparatus. 7. The light source comprises a plurality of light sources, a plurality of the control means are provided corresponding to the plurality of light sources, and the first light source is provided outside the image signal period of each horizontal period of the image signal. A first current control unit for controlling the light amount and a second current control unit for controlling the second light amount are independently controlled to sequentially control the plurality of light sources one by one to control all the light sources. The image forming apparatus according to claim 6, wherein the light amount is controlled to the predetermined amount. 8. The first current control means for controlling the control means to the first light quantity, the second current control means for controlling the second light quantity, and the detection signal to the first light control means. By configuring the current control means and the selective output means for selectively outputting to either one of the second current control means, the first current control means and the second current control means are temporally independent of each other. It controls, It is characterized by the above-mentioned.
An image forming apparatus according to claim 1. 9. The first current control means has first gain adjustment means whose gain is adjusted according to the level of the detection signal, and the second current control means adjusts the level of the detection signal. 9. The image forming apparatus according to claim 8, wherein the image forming apparatus is configured to adjust the gain of the feedback loop to a predetermined gain by including a second gain adjusting unit that adjusts the gain accordingly.