JP2000168137A - Driving circuit for semiconductor laser diode and image- forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a failure mode that a quantity of light of a semiconductor laser diode decreases slightly or the like by monitoring the quantity of light of the semiconductor laser diode, judging whether or not the quantity of light is within a specified range, and outputting the judgment result as a logic value signal. SOLUTION: When the image-forming apparatus receives a printing request, a scanner motor 107 and a polygon mirror 108 are rotated and a semiconductor laser diode 121 is driven. At this time, a photodiode 122 feeds back a quantity of light of the semiconductor laser diode 121 to a semiconductor laser diode- driving circuit 102. A quantity of light of a semiconductor laser diode 103 is controlled so that the quantity of light becomes a target value. At the same time, whether or not the quantity of light is within a predetermined range is monitored, and the result is output as a logic value signal. The output logic value signal is fed back to a control part 101, where it is judged whether the quantity of light of the semiconductor laser diode 103 is normally controlled or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser diode driving circuit and an image forming apparatus such as a laser beam printer having the semiconductor laser diode driving circuit and forming an image by an electrophotographic process.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a laser beam printer having a semiconductor laser diode as a light source, there are roughly two types of light amount control (hereinafter, referred to as APC) of a semiconductor laser diode as a light source.

One type of external control type APC is as follows. In other words, a voltage proportional to the current obtained by photoelectrically converting the amount of light of the semiconductor laser diode with a photodiode built in the same package as the semiconductor laser diode is used to control a control circuit provided separately from the drive circuit of the semiconductor laser diode. CPU
To the A / D converter. The CPU outputs the voltage from the D / A converter to the drive circuit of the semiconductor laser diode so that the value of the fed back voltage (corresponding to the light amount of the semiconductor laser diode) becomes the target value.
The drive circuit of the semiconductor laser diode controls the light amount of the semiconductor laser diode by increasing or decreasing the drive current of the semiconductor laser diode according to the voltage received from the CPU.

Another type of self-control APC is as follows. That is, the current obtained by photoelectrically converting the amount of light of the semiconductor laser diode with a photodiode contained in the same package as the semiconductor laser diode is fed back to the semiconductor laser diode drive circuit, and the semiconductor laser diode drive circuit is The drive current of the semiconductor laser diode is increased or decreased so that the light amount of the semiconductor laser diode becomes the target value.

In recent years, a self-control type APC is generally used. In an image forming apparatus employing the self-control type APC, a sensor for generating a horizontal synchronization signal (hereinafter, referred to as a BD sensor) is used for detecting a failure of a semiconductor laser diode. However, when a horizontal synchronizing signal cannot be obtained from the BD sensor, detection is performed as a failure. In this case, in order to obtain a good and stable horizontal synchronizing signal in the BD sensor, the normal incident light amount of 50 is used.
A comparative value for detecting laser light is set to around%.

[0006]

However, the above-mentioned prior art has the following problems.

The first problem is that in order to obtain a good and stable horizontal synchronizing signal, 50% of the amount of light incident on the BD sensor is required.
Since the horizontal synchronizing signal is generated by setting the comparison value before and after, when the failure detection of the semiconductor laser diode is performed using the BD sensor in the image forming apparatus adopting the self-control APC, There is a problem in that a failure mode such as a slight decrease in light quantity (for example, about 10% decrease) cannot be detected. Further, a BD sensor having a function of automatically setting a comparison value for generating a horizontal synchronization signal always around 50% of the incident light amount in accordance with a change in the incident light amount may be used. In this case, even if the light amount of the semiconductor laser diode is significantly reduced (for example, reduced by 60% or more), the comparison value changes accordingly, so that a horizontal synchronization signal is generated, and as a result, failure detection cannot be performed. It is.

The second problem is that in the image forming apparatus employing the self-control type APC, the failure of the semiconductor laser diode is detected by using the BD sensor. The problem is that it cannot be determined whether the failure is a semiconductor laser diode failure or a BD sensor failure. Further, if a configuration is used in which a horizontal synchronizing signal is used to detect the speed of the scanner motor for optical scanning, is it possible that the semiconductor laser diode is malfunctioning?
This is a problem in that it cannot be determined whether the D sensor has failed or the scanner motor has failed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a driving circuit for a semiconductor laser diode which can detect that a light amount of a semiconductor laser has fluctuated by a predetermined amount.

Another object of the present invention is to provide a semiconductor laser drive circuit which can determine whether a semiconductor laser has failed or a BD sensor has failed.

[0011]

SUMMARY OF THE INVENTION A semiconductor laser diode driving circuit according to the present invention drives a semiconductor laser diode and monitors the amount of light of the semiconductor laser diode fed back from a monitoring photodiode. In a semiconductor laser diode drive circuit incorporating means for controlling the light amount of the semiconductor laser diode to be constant, the light amount of the semiconductor laser diode fed back from the monitoring photodiode is monitored so that the light amount of the semiconductor laser diode falls within a specified range. It is characterized by comprising monitoring means for making a determination as to whether or not there is a value, and outputting a result of the determination as a logical value signal.

In the image forming apparatus according to the present invention, in the image forming apparatus having the semiconductor laser diode drive circuit and the horizontal synchronizing signal generating means, the specified range used by the monitoring means is the horizontal synchronizing signal generation of the generating means. It is characterized by being a range narrower than the possible range.

Further, the image forming apparatus according to the present invention is characterized in that in the above-mentioned image forming apparatus, there is provided means for detecting a failure of the semiconductor laser diode based on a logical value signal output from the semiconductor laser diode driving circuit. And

[0014]

An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram illustrating a basic configuration of an image forming apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 101 denotes a control unit for performing sequence control and the like of the apparatus, 102 denotes a semiconductor laser diode driving circuit, and 103 denotes a semiconductor laser diode 121 as a light emitting element and a photodiode 122 for monitoring the amount of light. Package. 107, 106, 10
Reference numeral 8 denotes a scanner motor for scanning a laser beam, a driving circuit thereof, and a polygon mirror. 104,1
05, 109 and 110 are optical lenses, 111 and 112 are BD mirrors and BD lenses, and 113 is a BD sensor for generating a horizontal synchronization signal.

The semiconductor laser diode driving circuit includes a resistor 123 for converting a current generated by the photodiode 122 into a voltage, and a voltage generated at one end of the resistor 123 as a comparison value A.
APC that outputs a difference from PC_Ref
, An operational amplifier 126 for converting the output voltage of the APC section into a current, a transistor 127, a transistor 128 for switching the current drawn from the transistor 127 in accordance with an image signal, and a voltage at one end of the resistor 123 with a voltage L_Limit. Comparator 12
9. A comparator 130 that compares the voltage at one end of the resistor 123 with the voltage U_Limit; the output of the comparator 129 and the comparator 130 is combined to change the voltage at one end of the resistor 123 to the voltage L_L.
a logic circuit 131 that outputs a logic value signal indicating that the voltage is higher than the threshold voltage U_Limit and lower than the voltage U_Limit;
The BD sensor 113 includes a photodiode 131 that converts incident laser light into a current, an amplifier 132 that converts a current generated by the photodiode into a voltage, and a comparison that generates a horizontal synchronization signal by comparing an output voltage of the amplifier with a comparison value. Vessel 1
33 is provided.

Upon receiving a print request, the apparatus rotates the scanner motor 107 and the polygon mirror 108 to drive the semiconductor laser diode 121. At this time, the photodiode 122 photoelectrically converts the amount of light of the semiconductor laser diode 121 and
02, the semiconductor laser diode drive circuit 102 performs APC by increasing or decreasing the drive current of the semiconductor laser diode 103 so that the feedback value becomes a target value (APC_Ref in the figure). At the same time, it monitors whether or not the value fed back is within a range between a predetermined upper limit value and lower limit value (U_Limit, L_Limit in the figure), and outputs the result as a logical value signal. The output logical value signal is fed back to the control unit 101, and the control unit 101 determines whether the semiconductor laser diode 103 is normally driven by the APC.

For example, in the present embodiment, by setting the upper and lower limits to ± 5% of the target value, for example,
When the light amount of the semiconductor laser diode 103 decreases by 5% or more for some reason such as deterioration of the semiconductor laser diode 103, the failure of the semiconductor laser diode 103 is detected.

The control unit 101 determines the failure of the semiconductor laser diode 103 and the failure of the BD sensor 113 based on both the logical value signal input from the semiconductor laser diode drive circuit 102 and the horizontal synchronization signal input from the BD sensor 113. judge. If the logical value signal indicates true, the semiconductor laser diode 103 is determined to be normal, and if the logical value signal indicates false, the semiconductor laser diode 103 is determined to be faulty. If the semiconductor laser diode 103 is normal and the horizontal synchronizing signal does not become active, it is determined that the BD sensor 113 has failed.

[0020]

As described in detail above, according to the present invention,
In an image forming apparatus having a self-APC laser drive circuit using an electrophotographic process, the light amount of the semiconductor laser diode fed back to the drive circuit of the semiconductor laser diode falls within a predetermined range (for example, within ± 5% of a target value). By providing a means for determining whether or not there is, and outputting the determination result as a logical value signal, it is possible to detect a failure mode in which the light amount of the semiconductor laser diode is slightly reduced (for example, reduced by about 10%).

On the other hand, when a failure is actually detected, it is possible to determine whether the failure is a semiconductor laser diode failure or a BD sensor failure. Further, in the case where the horizontal synchronization signal is used for detecting the speed of the scanner motor for optical scanning, it is possible to determine whether the failure is a semiconductor laser diode failure, a BD sensor failure, or a scanner motor failure. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a basic configuration of an image forming apparatus according to an embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 101 control unit 102 semiconductor laser diode drive circuit 103 semiconductor laser diode 104, 105, 109, 110, 112 optical lens 106 scanner motor drive circuit 107 scanner motor 108 polygon mirror 111 BD mirror 113 BD sensor

Claims (3)

[Claims] 1. A built-in means for driving a semiconductor laser diode, monitoring a light amount of the semiconductor laser diode fed back from a monitoring photodiode, and controlling the light amount of the semiconductor laser diode to be constant. In the semiconductor laser diode driving circuit, the amount of light of the semiconductor laser diode fed back from the monitoring photodiode is monitored to determine whether the amount of light of the semiconductor laser diode is within a specified range, and the determination result is expressed as a logical value. A driving circuit for a semiconductor laser diode, comprising a monitoring means for outputting a signal. 2. The image forming apparatus according to claim 1, wherein the monitor uses the horizontal synchronizing signal generated by the horizontal synchronizing signal. An image forming apparatus, wherein the range is narrower than the range. 3. The image forming apparatus according to claim 2, further comprising: means for detecting a failure of the semiconductor laser diode based on a logical value signal output from the semiconductor laser diode driving circuit. apparatus.