JPH0591272A - Image exposure device - Google Patents

Abstract

PURPOSE:To quickly reach prescribed light intensity and to make the exposure of a stable image by enabling switching a gain for a control means before and after a prescribed lapse of time of actuating a semiconductor laser element. CONSTITUTION:Within the prescribed period of time after starting the light-up of a laser element 1, a signal processing circuit 13 outputs a PC signal to a control circuit 10, a control operation at a high gain control mode is repeated for each scanning and the driving current of the element 1 is quickly changed. After the lapse of the prescribed time and a low gain mode is activated, the counted value of a counter 9 reaches a value corresponding to a required offset current. Since the counted value of the counter circuit 9 is set low at the time of starting the light-up and the gain is set large with a GH signal in order to avoid the risk of destruction at the time of starting the light-up of the element 1, the driving current can quickly be changed and immediately reach the prescribed light intensity. Since the change of the counted value is large by a single control operation after the lapse of the prescribed time, the control of the driving current can be stabilized without being affected by noise and thus, the high quality image is exposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image exposure apparatus,
More specifically, the present invention relates to a semiconductor laser drive circuit that stabilizes the optical output of a semiconductor laser device.

[0002]

2. Description of the Related Art Usually, in a laser printer or the like, an image is exposed by scanning and exposing a photosensitive member with a laser beam emitted from a semiconductor laser element and modulated based on an image signal. As is well known, a semiconductor laser device has a characteristic of emitting a laser beam when driven by a current exceeding a current value called a threshold current, and this threshold current is also operated by individual devices. As shown in FIG. 8, since the light intensity output from the semiconductor laser element varies greatly depending on the individual elements, even if the driving current is the same, as shown in FIG. is there.

When an image is formed by exposing with such an unstable laser beam, the output image is crushed or blurred, and the image quality is significantly impaired. Therefore, in an environment where the ambient temperature of the semiconductor laser element changes, it is necessary to stabilize the intensity of the laser light output from the semiconductor laser element by an output control device of the semiconductor laser element or the like.

Therefore, conventionally, a semiconductor laser device is current-driven by a drive circuit after adding a current corresponding to a threshold current as an offset current to a modulation signal, and the semiconductor laser is scanned while the laser beam is not scanning the photoconductor. The intensity of the laser light of the semiconductor laser device is stabilized by providing a control loop in which the optical output of the device is monitored by an optical monitor circuit and fed back to the drive circuit to control the offset current.

[0005]

However, the semiconductor laser device also has the above-mentioned characteristics, that is, it is very vulnerable to overcurrent and easily deteriorates. For this reason, in the conventional device, when starting the lighting of the semiconductor laser element, the starting is started with a sufficiently small current in consideration of the variation of the semiconductor laser element and the range of the environmental temperature, and the driving current is gradually increased to a predetermined value. Was controlled to reach the light intensity of. Therefore, in some cases, it takes a long time for the light intensity to stabilize, and there is a problem in that the lighting must be started considerably before the exposure of the image. Further, if the gain of the control loop is increased, the above problem can be solved, but the control in the image exposure area becomes unstable due to the influence of droop (transient thermal characteristics), etc., and thus the image quality is impaired. Therefore, it is impossible to unnecessarily increase the gain of the control loop, and it is very difficult to determine the gain of the control loop.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to quickly reach a predetermined light intensity after the semiconductor laser device is turned on and to stably expose an image. It is an object of the present invention to provide an image exposure apparatus that can be used.

[0007]

To achieve this object, an image exposure apparatus according to the present invention comprises a semiconductor laser element, drive means for modulating and driving the semiconductor laser element based on an image signal, and the semiconductor laser element. And a photoconductor on which an image corresponding to the image signal is exposed by scanning a modulated laser beam emitted from the semiconductor laser device, and the laser beam emitted from the semiconductor laser device while the image region of the photoconductor is not being scanned. An optical exposure device that detects an optical output of a laser beam generated by the laser light source, and controls the drive of the semiconductor laser element by the drive means based on the detection result, wherein the control means is the semiconductor laser element. Gain control means is provided which can switch the gain of the control means before and after a lapse of a predetermined time from when is turned on.

[0008]

In the image exposure apparatus of the present invention having the above-mentioned structure, the laser beam emitted from the semiconductor laser element driven by the drive means and modulated according to the image signal scans the photoconductor, whereby the photoconductor is The image is exposed to light. Further, the gain of the control means for controlling the drive current of the semiconductor laser element is different before and after the predetermined time has elapsed since the semiconductor laser element was turned on.

Therefore, after the lighting is started, the control loop operates with a high gain and reaches a predetermined light intensity in a short time. Also,
Since the control loop operates with a low gain after a predetermined time, modulated light with stable light intensity can be obtained when the photoreceptor is exposed to record an image.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied and applied to a laser beam printer will be described below with reference to FIGS.

The laser beam printer of this embodiment is shown in FIG.
As shown in FIG. 1, a well-known semiconductor laser device 1 is provided as a light source, and a drive circuit 2 for driving the semiconductor laser 1 is connected to the semiconductor laser device 1. On the optical path of the laser beam emitted from the semiconductor laser device 1, a collimator lens (not shown), a rotary polygon mirror 3 rotating in the direction of arrow A, and the laser beam are coupled to the surface of the photosensitive drum 5. The f-θ lens 4 for imaging is arranged in that order. A rotary polygon mirror 3 is provided outside the image information writing area.
A beam detection device 6 is provided which detects the laser beam deflected in step 1 for each scan prior to image exposure and generates a synchronization signal (BD signal). The beam detector 6 has a built-in oscillation circuit, and is configured to output the signal of the oscillation circuit as a BD signal when the light intensity of the laser beam is weak and the laser beam cannot be detected immediately after the start of lighting.

Further, a well-known D / A conversion circuit 7, an addition circuit 8, a counter circuit 9, and a monitor diode 111, which is held in the same container as the semiconductor laser device 1 and receives a laser beam emitted backward, outputs the laser beam. An optical monitor circuit 11 including an amplifier circuit 112 that amplifies a photocurrent and outputs the voltage as a voltage, a comparison circuit 113 that compares the amplified voltage with a reference voltage, and a known one-shot multivibrator. When a (LON signal) is input, the timer circuit 12 outputs a high gain signal (GH signal) for a predetermined constant time T, and a control circuit 10 and a signal processing circuit 13 described later.

The signal processing circuit 13 includes a photosensitive drum 5
BD generated from the beam detecting device 6 at the time of scanning a photosensitive member (hereinafter, referred to as an exposure mode) in which a laser beam is scanned
In the exposure mode, the image signal is timing-controlled and sent as a modulation signal to the addition circuit 8, and in the control mode, the light intensity setting signal is sent to the addition circuit 8 as a modulation signal. In the control mode, the control circuit 10 outputs a light intensity control signal (PC signal) for instructing the start of the light intensity control operation.

That is, as shown in FIG. 7, the exposure mode and the control mode are set alternately for each scan.

The control mode is further divided into a high gain control mode while the GH signal is being input and a low gain control mode while the GH signal is not being input.

The count value of the count circuit 9 corresponds to the above-mentioned offset current, and the adder circuit 8 performs an addition operation on the count value of the counter circuit 9 and the modulation signal or the light intensity setting signal to obtain D / A. Output to the conversion circuit 7. The drive circuit 2 current-drives the semiconductor laser element 1 based on the signal converted by the D / A conversion circuit 7.

Further, in the optical monitor circuit 11, FIG.
As shown in, the laser beam emitted rearward from the semiconductor laser device 1 enters the monitor diode 111, and the monitor diode 111 outputs a current proportional to the light intensity of the laser beam. The current is converted into a monitor voltage by the amplification circuit 112 and amplified, and then compared with the reference voltage Vref by the comparison circuit 113. The comparison circuit 113 has a reference voltage Vr.
When the monitor voltage by the laser light is larger than ef, the monitor signal (MON signal) is output to the control circuit 10 to notify that the light intensity of the laser beam has reached the light intensity corresponding to the light intensity setting signal.

The control circuit 10 functions to keep the relationship between the image signal and the light intensity constant, and as shown in FIG. 2, a well-known clock circuit 1 for outputting a clock signal.
01, a known frequency dividing circuit 102 that divides the clock signal by 8 to output a divided signal, and a switch circuit 103 that outputs either one of the clock signal and the divided signal.
The output of the switch circuit 103 is counted, the count is decoded, and a countdown signal (C
The state circuit 104 outputs a D signal) or a count-up signal (CU signal). The switch circuit 103 outputs the G output from the timer circuit 12.
If the GH signal is input (high gain control mode), the trigger of the state circuit 104 is the frequency-divided signal of the frequency-dividing circuit 102, and G is switched by the H-signal.
If no H signal is input (low gain control mode),
The trigger of the state circuit 104 is the clock signal of the clock circuit 101.

The state circuit 104 starts its operation after being reset by the input of the PC signal.

That is, when the GH signal is input (high gain control mode), the frequency division signal of the frequency division circuit 102 is input as the trigger of the state circuit 104, and FIG.
As shown in, a countdown signal (CD signal) is output from the state circuit 104 to the counter circuit 9 for 8 clocks (1 divided signal) after the PC signal is input, and the counter circuit 9 outputs the clock signal of the clock circuit 101. Is used as a trigger to count down by 8 counts. And
MON for the subsequent 16 clocks (during the frequency-divided signal)
A count-up signal (CU signal) is output from the state circuit 104 to the counter circuit 9 until a signal is detected,
In the counter circuit 9, the clock signal of the clock circuit 101 is used as a trigger to count up to 16 counts.

When the GH signal is not input (low gain control mode), the clock signal of the clock circuit 101 is input as the trigger of the state circuit 104. As shown in FIG. A countdown signal (CD signal) is output from the state circuit 104 to the counter circuit 9 for one clock, and the counter circuit 9 downcounts using the clock signal of the clock circuit 101 as a trigger.

After that, during the following two clocks, MO
A count-up signal (CU signal) is output from the state circuit 104 to the counter circuit 9 until the N signal is detected, and the counter circuit 9 is up-counted up to 2 counts by using the clock signal of the clock circuit 101 as a trigger.

Next, the operation of the laser beam printer having the above structure will be described.

When an image signal is input from a terminal device (not shown), a LON signal is issued from a controller (not shown). The LON signal is input to the drive circuit 2 so that the semiconductor laser device 1 is turned on, and is also input to the timer circuit 12 so that the G laser signal G
The H signal is output to the control circuit 10.

The control mode within a predetermined time T after turning on the laser is a high gain control mode, and the control mode after a predetermined time T has passed is a low gain control mode.

The control mode within a predetermined time T from the start of laser lighting is a high gain control mode, and its operation will be described below.

The signal processing circuit 13 controls the PC signal by the control circuit 1.
Then, the control operation in the high gain control mode is started. As described above, the divided signal of the frequency dividing circuit 102 is input as a trigger of the state circuit 104, and the CD signal is output from the state circuit 104 to the counter circuit 9 for 8 clocks. Then, in the counter circuit 9, the output count value of the counter circuit 9 is counted down by 8 using the clock signal of the clock circuit 101 as a trigger. Then, thereafter, the CU signal is output from the state circuit 104 to the counter circuit 9 within a limit of 16 clocks until the MON signal is detected. Then, the counter circuit 9 uses the clock signal of the clock circuit 101 as a trigger to increase the output count value of the counter circuit 9 up to 16 counts until the MON signal is detected. Therefore, as shown in FIG. 4, the output count value of the counter circuit 9 is 1
Since it can be changed within ± 8 counts by one control operation, the drive current for driving the semiconductor laser device 1 changes greatly.

Since the control operation in the high gain control mode as described above is repeatedly performed for each scan for the predetermined time T, the drive current changes rapidly.

At the start of lighting, the count value of the counter 9 is a sufficiently small value (for example, zero), but thereafter the count value rapidly increases. Further, since the predetermined time T is appropriately selected, the count value of the counter 9 is roughly the required offset current when the predetermined time T has passed after the laser is turned on and the control mode shifts from the high gain control mode to the low gain control mode. The value corresponds to.

Next, the control operation in the low gain control mode will be described.

The signal processing circuit 13 controls the PC signal by the control circuit 1.
0 is output to start the control operation in the low gain control mode. As described above, the clock signal of the clock circuit 101 is input as a trigger of the state circuit 104, and the CD signal is output from the state circuit 104 to the counter circuit 9 for one clock. Then, in the counter circuit 9, the output count value of the counter circuit 9 is counted down by 1 using the clock signal of the clock circuit 101 as a trigger. Then, thereafter, the CU signal is output from the state circuit 104 to the counter circuit 9 within a period of two clocks until the MON signal is detected. Then, the counter circuit 9 uses the clock signal of the clock circuit 101 as a trigger to increase the output count value of the counter circuit 9 up to 2 counts until the MON signal is detected. Therefore, as shown in FIG. 5, since the output count value of the counter circuit 9 can be changed within ± 1 count by one control operation, the drive current for driving the semiconductor laser device 1 changes by a small amount. To do.

The control operation in the low gain control mode as described above is repeated for each scan, but the drive current cannot change promptly, but only slowly.

After the control mode is changed to the low gain control mode, the laser beam is modulated by the input image signal (see FIG. 6).

In the modulation operation, the count value of the counter 9 corresponding to the offset current of the semiconductor laser device 1 determined by the light intensity control operation described in detail above and the input image signal are added by the adder circuit 8. And the addition result is D
The / A conversion circuit 7 converts the driving signal into an analog voltage. The drive circuit 2 current-drives the semiconductor laser element 1 based on the drive signal, and the laser beam emitted from the semiconductor laser element 1 is deflected as the rotary polygon mirror 3 rotates, and is illustrated by the f-θ lens 4. An image is formed on the surface of the photoconductor drum 5 that is uniformly charged by the charger. Then, as shown in FIG. 1, the imaging spot repeatedly moves in the direction of the arrow B to scan and expose the surface of the photoconductor drum 5 rotating at a predetermined speed, and a static image corresponding to the input image signal is obtained. Form a latent image.

The electrostatic latent image is developed by a well-known developing device (not shown), transferred to paper by a well-known transfer device (not shown), and discharged.

As described above in detail, at the start of lighting of the semiconductor laser device 1, the count value of the counter circuit 9 at the start of lighting is a low value in order to avoid the risk of destruction of the semiconductor laser device 1. (For example, zero), the control gain is set to be large by the GH signal for the predetermined time T after lighting, and the count value can be changed by a maximum of ± 8 in one control operation, so the drive current changes rapidly. The predetermined light intensity can be reached quickly. Then, after the lapse of the predetermined time T, the count value changes within ± 1 count in one control operation, so that the control of the drive current is stable without being affected by noise and the like, and the exposure of a high-quality image is performed. It is possible. The state of the change in the count value is shown in FIG.

The present invention is not limited to the embodiments described in detail above, and various modifications and improvements are possible.

For example, in the present embodiment, the frequency dividing number of the frequency dividing circuit 102 is set to 8, but other values may be used. Although the timer circuit 12 sets the predetermined time after the semiconductor laser device 1 is turned on, the number of light intensity control signals (PC signals) may be counted.

In this embodiment, the gain is changed by changing the size of the count number that can be changed in one control operation, but the size of the count number that can be changed is fixed and the control operation is performed. The frequency may be changed.

[0040]

As is apparent from the above detailed description, according to the image exposure apparatus of the present invention, the gain of the control means can be switched between a predetermined time after the start of lighting of the semiconductor laser device and thereafter. Therefore, the predetermined light intensity can be reached quickly after the semiconductor laser element starts to be turned on, and the image can be stably exposed during the image exposure.

[Brief description of drawings]

FIG. 1 is a schematic view showing a configuration of a laser beam printer to which the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a control circuit of this embodiment.

FIG. 3 is a circuit diagram showing a configuration of an optical monitor circuit of this embodiment.

FIG. 4 is an explanatory diagram showing changes in the count value of the counter circuit when a GH signal is output in the present embodiment.

FIG. 5 is an explanatory diagram showing changes in the count value of the counter circuit when the GH signal is not output in the present embodiment.

FIG. 6 is an explanatory diagram showing a change in the count value of the counter circuit before and after a predetermined time has passed after the semiconductor laser device is turned on in the present embodiment.

FIG. 7 is an explanatory diagram showing the relationship between the exposure mode and the control mode and the change in the count value of the counter circuit in the present embodiment.

FIG. 8 is an explanatory diagram showing characteristics of a semiconductor laser device.

[Explanation of symbols]

 1 Semiconductor Laser Element 2 Drive Circuit 5 Photosensitive Drum 7 D / A Conversion Circuit 8 Adder Circuit 9 Counter Circuit 10 Control Circuit 11 Optical Monitor Circuit 12 Timer Circuit 111 Monitor Diode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H01L 21/027 H01S 3/103 7131-4M H04N 1/04 104 A 7251-5C

Claims (1)

[Claims] 1. A semiconductor laser device, drive means for modulating and driving the semiconductor laser device based on an image signal, and scanning the modulated laser beam emitted from the semiconductor laser device to cope with the image signal. The photoconductor to which an image is exposed, and the light output of the laser light emitted from the semiconductor laser device while the laser light is not scanning the image area of the photoconductor, and the drive means is based on the detection result. In the image exposure apparatus having a control means for controlling the driving of the semiconductor laser element by the control means, the control means controls the control means before and after a predetermined time elapses after the semiconductor laser element is turned on. An image exposure apparatus comprising a gain selection means capable of switching a gain.