JP3511627B2 - Image exposure equipment - Google Patents

Description

Description: 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 for stabilizing the optical output of a semiconductor laser device. 2. Description of the Related Art Generally, 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 element has a characteristic of emitting laser light when driven with a current exceeding a current value called a threshold current, and this threshold current is again operated by each element. As shown in FIG. 8, the light intensity output from the semiconductor laser device varies greatly depending on each device even with the same drive current, and is very unstable with respect to temperature. 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. For this reason, in an environment where the ambient temperature of the semiconductor laser device changes, it is necessary to stabilize the intensity of the laser light output from the semiconductor laser device by an output control device or the like of the semiconductor laser device. Conventionally, a current corresponding to a threshold current is added to a modulation signal as an offset current, and then a semiconductor laser element is driven by a drive circuit. By providing a control loop in which the optical output of the device is monitored by an optical monitor circuit and fed back to a drive circuit to control the offset current, the intensity of the laser light of the semiconductor laser device has been stabilized. [0005] However, the semiconductor laser device has a characteristic that it is very susceptible to overcurrent and easily deteriorates in addition to the above-mentioned characteristics. For this reason, in the conventional apparatus, when starting the lighting of the semiconductor laser device, the lighting is started with a sufficiently small current in consideration of the variation of the semiconductor laser device and the range of the environmental temperature, and the drive current is gradually increased to a predetermined value. Was controlled so as to reach the light intensity. For this reason, in some cases, a long time is required for the light intensity to stabilize, and there is a problem that the lighting must be started considerably before the exposure of the image. If the gain of the control loop is increased, the above problem is solved, but the control in the image exposure region becomes unstable due to the effect of droop (transient thermal characteristics) and the image quality is impaired. Therefore, the gain of the control loop cannot be increased unnecessarily, and it is very difficult to determine the gain of the control loop. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to quickly reach a predetermined light intensity after turning on a semiconductor laser element and stably perform image exposure. It is an object of the present invention to provide an image exposure apparatus capable of performing the above. In order to achieve this object, an image exposure apparatus according to the present invention comprises: a semiconductor laser element; a drive means for modulating and driving the semiconductor laser element based on an image signal; A photoconductor on which an image corresponding to the image signal is exposed by scanning a modulated laser beam emitted from a semiconductor laser element; and the semiconductor laser while the laser beam is not scanning an image area of the photoconductor. Control means for detecting the light output of laser light emitted from the element and controlling the driving of the semiconductor laser element by the drive means based on the detection result, wherein the semiconductor laser element is turned on. Signal is on
When pressed, the gain of the control means is determined for a predetermined period of time.
Timer means for outputting a signal obtained by the control means , wherein the control means is configured to output a signal based on the gain signal output from the timer means.
Te, the semiconductor in the laser element is turned and after a predetermined time has elapsed before a predetermined time, and a gain selection means capable of switching the gain of the control means. In the image exposure apparatus of the present invention having the above structure, the laser beam emitted from the semiconductor laser element driven by the drive means and modulated according to the image signal scans the photosensitive member. Then, the image is exposed to the photoconductor. Further, the gain of the control means for controlling the drive current of the semiconductor laser element differs before and after a predetermined time has elapsed since the semiconductor laser element was turned on. Therefore, after the start of lighting, the control loop operates with a high gain, and reaches a predetermined light intensity in a short time. Also,
After a predetermined time, the control loop operates with a low gain, so that when exposing the photosensitive member to record an image, modulated light having a stable light intensity can be obtained. An embodiment in which the present invention is embodied and applied to a laser beam printer will be described below with reference to FIGS. FIG. 1 shows a laser beam printer according to this embodiment.
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 element 1, a collimator lens (not shown), a rotary polygon mirror 3 rotating in the direction of arrow A, and the laser beam The imaging f-θ lens 4 is arranged in that order. Outside the image information writing area, the rotating polygon mirror 3
A beam detection device 6 is provided for detecting the laser beam deflected in the step before the image is exposed for each scan and generating a synchronization signal (BD signal). The beam detecting device 6 has a built-in oscillation circuit, and is configured to output a signal of the oscillation circuit as a BD signal when the light intensity of the laser beam is low immediately after the start of lighting and the laser beam cannot be detected. 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, output. A laser monitor signal comprising an amplifying circuit 112 for amplifying a photocurrent and outputting it as a voltage, a comparing circuit 113 for comparing the amplified voltage with a reference voltage, and a well-known one-shot multivibrator; It comprises a timer circuit 12 for outputting a high gain signal (GH signal) for a predetermined time T when a (LON signal) is input, and a control circuit 10 and a signal processing circuit 13 to be described later. The signal processing circuit 13 includes a photosensitive drum 5
The BD generated by the beam detection device 6 during the scanning of the photoconductor scanned by the laser beam (hereinafter referred to as an exposure mode) and the scanning of the other non-photoconductors (hereinafter referred to as a control mode).
In the exposure mode, the image signal is timing-controlled and sent to the addition circuit 8 as a modulation signal. 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 control circuit 10 to start a 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 modes are 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-described offset current, and the adder circuit 8 performs a D / A operation by adding the count value of the counter circuit 9 to the modulation signal or the light intensity setting signal. Output to the conversion circuit 7. The drive circuit 2 drives the semiconductor laser device 1 based on the signal converted by the D / A conversion circuit 7. In the optical monitor circuit 11, FIG.
As shown in (1), a laser beam emitted backward from the semiconductor laser element 1 enters the monitor diode 111, and the monitor diode 111 outputs a current proportional to the light intensity of the laser beam. After the current is converted and amplified into a monitor voltage by the amplifier circuit 112, the current is compared with the reference voltage Vref by the comparator circuit 113. The comparison circuit 113 outputs the reference voltage Vr
When the monitor voltage by the laser light is higher than ef, a 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 serves to keep the relationship between the image signal and the light intensity constant. As shown in FIG. 2, a well-known clock circuit 1 for outputting a clock signal is provided.
01, a known frequency dividing circuit 102 for dividing the clock signal by, for example, eight and outputting a frequency-divided signal, and a switch circuit 103 for outputting one of the clock signal and the frequency-divided signal
And the output of the switch circuit 103 is counted, the count is decoded, and a countdown signal (C
D signal) or a state circuit 104 that outputs a count-up signal (CU signal). The switch circuit 103 is connected to the G output from the timer circuit 12.
The signal is switched by the H signal, and when the GH signal is input (high gain control mode), the trigger of the state circuit 104 is used as the frequency-divided signal of the frequency divider 102, and
If no H signal is input (low gain control mode),
The trigger of the state circuit 104 is a clock signal of the clock circuit 101. After being reset by the input of the PC signal, the state circuit 104 starts its operation. That is, when the GH signal is input (high gain control mode), the frequency-divided signal of the frequency divider 102 is input as a trigger of the state circuit 104, and FIG.
As shown in the figure, a countdown signal (CD signal) is output from the state circuit 104 to the counter circuit 9 for eight clocks (during the frequency-divided signal) after the PC signal is input. Is counted down by 8 counts. And
MON during the subsequent 16 clocks (during the divide-by-2 signal)
A count-up signal (CU signal) is output from the state circuit 104 to the counter circuit 9 until a signal is detected,
The counter circuit 9 counts up to 16 counts using the clock signal of the clock circuit 101 as a trigger. When the GH signal is not input (low gain control mode), the clock signal of the clock circuit 101 is input as a trigger of the state circuit 104, and as shown in FIG. During one clock, a countdown signal (CD signal) is output from the state circuit 104 to the counter circuit 9, and the counter circuit 9 counts down using the clock signal of the clock circuit 101 as a trigger. Thereafter, the MO is kept for two clocks.
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 counts up to two counts using the clock signal of the clock circuit 101 as a trigger. Next, the operation of the laser beam printer having the above configuration will be described. When an image signal is input from a terminal device (not shown), an LON signal is issued from a controller (not shown). The LON signal is input to the drive circuit 2 to turn on the semiconductor laser device 1, and is input to the timer circuit 12 to output G for a predetermined time T.
The H signal is output to the control circuit 10. The control mode within a predetermined time T after the laser is turned on is the high gain control mode, and the control mode after the predetermined time T has elapsed is the low gain control mode. The control mode within a predetermined time T after the start of laser lighting is the high gain control mode, and its operation will be described below. The signal processing circuit 13 outputs the PC signal to the control circuit 1
0 to start the control operation in the high gain control mode. As described above, the frequency-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 eight clocks. Then, in the counter circuit 9, the output count value of the counter circuit 9 counts down by 8 using the clock signal of the clock circuit 101 as a trigger. Thereafter, the CU signal is output from the state circuit 104 to the counter circuit 9 within a period 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
The driving current for driving the semiconductor laser device 1 greatly changes because it can be changed within ± 8 counts by the number of control operations. Since the control operation in such a high gain control mode is repeatedly performed for each scan during the predetermined time T, the drive current changes quickly. 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. Since the predetermined time T is appropriately selected, when the predetermined time T elapses after the laser is turned on, and the control mode shifts from the high gain control mode to the low gain control mode, the count value of the counter 9 generally includes the necessary offset current. Is a value corresponding to. Next, the control operation in the low gain control mode will be described. The signal processing circuit 13 outputs the PC signal to the control circuit 1
0 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 a CD signal is output from the state circuit 104 to the counter circuit 9 for one clock. Then, the counter circuit 9 counts down the output count value of the counter circuit 9 by the clock signal of the clock circuit 101 as a trigger. 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 two 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 in one control operation, the drive current for driving the semiconductor laser device 1 changes by a small amount. I do. The control operation in such a low gain control mode is repeatedly performed for each scan, but the drive current cannot be changed quickly, 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 adder 8 adds the count value of the counter 9 corresponding to the offset current of the semiconductor laser element 1 determined by the light intensity control operation described above and the input image signal. And the addition result is D
The driving signal is converted into an analog voltage by the / A conversion circuit 7. The drive circuit 2 drives the semiconductor laser element 1 based on the drive signal, and the laser beam emitted from the semiconductor laser element 1 is deflected by the rotation of the rotary polygon mirror 3 and is shown by the f-θ lens 4. An image is formed on the surface of the photosensitive drum 5 which is uniformly charged by a non-charger. Then, as shown in FIG. 1, the surface of the photosensitive drum 5 rotating at a predetermined speed is scanned and exposed by repeatedly moving the imaging spot in the direction of arrow B, and a static image corresponding to the input image signal is formed. An electrostatic latent image is formed. After the electrostatic latent image is developed by a well-known developing device (not shown), it is transferred to paper by a well-known transferring device (not shown) and discharged. As described in detail above, at the start of lighting of the semiconductor laser element 1, the count value of the counter circuit 9 at the start of lighting is low in order to avoid the risk of destruction of the semiconductor laser element 1. (For example, zero), the control gain is set large by the GH signal for a predetermined time T after lighting, and the count value can be changed by a maximum of ± 8 in one control operation, so that the drive current changes rapidly, A predetermined light intensity can be reached quickly. After the lapse of the predetermined time T, since the count value changes only within ± 1 count in one control operation, the control of the drive current becomes stable without being affected by noise or the like, and the exposure of a high-quality image is reduced. It is possible. FIG. 6 shows how the count value changes. The present invention is not limited to the embodiment 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 predetermined time after the start of lighting of the semiconductor laser element 1 is set by the timer circuit 12, the number of light intensity control signals (PC signals) may be counted. Further, in this embodiment, the gain is changed by changing the magnitude of the count number which can be changed in one control operation. However, the magnitude of the count number which can be changed is fixed and the control operation is performed. The frequency may be changed. As is apparent from the above, according to the image exposure apparatus of the present invention, the output from the timer means is provided.
Based on the gain signal obtained, the gain of the control means can be switched between a predetermined time after the start of lighting of the semiconductor laser element and thereafter, so that the predetermined light intensity is quickly obtained after the start of lighting of the semiconductor laser element. The image can be reached, and the image can be stably exposed at the time of image exposure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a configuration of a laser beam printer suitable for applying the present invention. FIG. 2 is a block diagram illustrating a configuration of a control circuit according to the present embodiment. FIG. 3 is a circuit diagram illustrating a configuration of an optical monitor circuit according to the present embodiment. FIG. 4 is an explanatory diagram showing a change in a count value of a counter circuit when a GH signal is output in the present embodiment. FIG. 5 is an explanatory diagram showing a change in a count value of a counter circuit when a GH signal is not output in the embodiment. FIG. 6 is an explanatory diagram showing a change in a count value of a counter circuit before and after a predetermined time elapses after the semiconductor laser element is turned on in the present embodiment. FIG. 7 is an explanatory diagram showing a relationship between an exposure mode and a control mode and a change in a count value of a counter circuit in the embodiment. FIG. 8 is an explanatory diagram showing characteristics of a semiconductor laser device. [Description of Signs] 1 Semiconductor laser element 2 Drive circuit 5 Photoconductor drum 7 D / A conversion circuit 8 Addition circuit 9 Counter circuit 10 Control circuit 11 Optical monitor circuit 12 Timer circuit 111 Monitor diode

Claims (1)

(57) [Claim 1] A semiconductor laser element, drive means for modulating and driving the semiconductor laser element based on an image signal, and scanning with a modulated laser beam emitted from the semiconductor laser element. A photoconductor on which an image corresponding to the image signal is exposed, and detecting a light output of a laser beam emitted from the semiconductor laser element while the laser beam is not scanning an image area of the photoconductor, Control means for controlling the drive of the semiconductor laser element by the drive means based on the detection result, wherein when a lighting signal of the semiconductor laser element is input, a predetermined
A signal for determining the gain of the control means is output for a fixed time.
Timer means, and the control means controls the gain signal output from the timer means.
An image exposure apparatus comprising: a gain selection unit that can switch a gain of a control unit before and after a predetermined time has elapsed after the semiconductor laser element is turned on based on the signal. .