JP2001036188A - Device and method for detecting fault of light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect faults of a light source that an electro-photographic image forming device, etc., is equipped with, regardless of temperature and to detect end surface break. SOLUTION: A constant-current source controls the drive current of a laser diode, according to a drive current setting signal so that it increases continuously at a certain time variation ratio, and when a monitor current reaches a prescribed value S1, a timer starts counting. The moment the timer is stopped when the monitor current increases to reach a prescribed value S2, the timer count value is saved in a memory. The gradient of the monitor current is found from the prescribed value S1, a prescribed value S2, and a timer count value. It is compared with the gradient which is stored previously in the memory to decide on a fault of the laser diode from the comparison result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for detecting a failure of a light source, and more particularly to an image forming apparatus (laser beam printer), a copying machine, a facsimile, etc. using an electrophotographic system, as well as an optical card and a magneto-optical device. The present invention relates to a light source failure detection device and a light source failure detection method included in a disk, an optical communication device, and the like.

[0002]

2. Description of the Related Art A laser beam printer will be described below as an example. The semiconductor laser element has a built-in light receiving element for receiving a part of the optical output, and the output is input to the semiconductor laser driving device. In the semiconductor laser driving device, APC (Automatic Power Control) control is performed based on an output from the light receiving element so that the semiconductor laser has a target light amount.

FIG. 9 shows an example of a conventional light source driving circuit (APC control block) including a semiconductor laser.

The monitor current Ipd output from the light receiving element PD in the semiconductor laser 90 is converted into a voltage by the variable resistor Rm and is input to the non-inverting input terminal of the comparator 91. The comparison reference voltage Vr is input to the inverting input terminal, and the comparator 91 outputs I _pd × Rm = V during the APC operation.
Control is performed so as to be r.

A sample and hold circuit 92 charges and discharges a hold capacitor Ch so as to realize a light amount set by an output from a comparator 91, and adjusts a potential Vch across the hold capacitor Ch. The constant current source 93 in accordance with the adjusted Vch performs constant current drive to the laser driving current I _LD and Vch / Rs.

At the time of image formation, the laser diode L in the semiconductor laser 90 is formed at the pixel formation timing in accordance with the switching operation of the switching circuit 94 according to the image signal.
Light D. During this lighting, the constant current source 93 is driven by the adjusted Vch. The resistance value of the variable resistor Rm is adjusted at the time of manufacture so as to obtain a required light amount in consideration of variations in the semiconductor laser 90 and the like.

FIG. 10 is a characteristic diagram showing the deterioration of the light emission characteristics of the semiconductor laser. A conventional semiconductor laser failure detection method will be described with reference to FIG.

The semiconductor laser starts to emit light at a certain threshold, and thereafter has an emission characteristic in which the amount of light emission increases in accordance with an increase in drive current. The emission characteristics of a normal semiconductor laser are shown by curves 100 to 102, each of which is due to temperature dependence. Curve 100 shows the characteristic at low temperature, and curve 102 shows the characteristic at high temperature. At a standard temperature, the threshold current Ith
1. With respect to the drive current I _D1 for obtaining the target light quantity (curve 101), when the deterioration starts, both currents increase as shown by the curve 103. As the deterioration progresses, the target light quantity cannot be finally reached, resulting in a failure (curve 104).

Conventionally, Vch is detected in accordance with the characteristics described above, and the laser drive current I at a target light quantity or a set light quantity under the target light quantity or the set light quantity is determined from Vch and Rs using the relationship at the time of constant current drive.
_{The LD} was calculated and the failure was determined based on the calculated value.
That is, when the calculated laser drive current has increased by a certain ratio with respect to the initial value and when the calculated laser drive current has exceeded the upper limit, the deterioration of the semiconductor laser has been detected, and a failure has been determined.

[0010]

As shown in FIG. 10, the threshold current and drive current of a semiconductor laser have a large positive temperature dependence. Further, the threshold current and the drive current themselves change over time due to the variation of the element alone.

[0011] The influence of the variation of the element itself can be avoided by storing the initial value and comparing it with the changed value. However, as for the influence of the temperature dependency, for example, it is impossible to distinguish between a rise in the ambient temperature and a rise in the element temperature during continuous operation, so that it is difficult to detect the original failure of the element when the temperature changes. there were.

Another problem is that when the end face of the semiconductor laser on the photodiode side is destroyed, the amount of laser light is reduced by the APC control loop. That is,
Since the monitor current increases due to the end face breakdown and the threshold current and drive current on the laser diode side do not change, this failure mode cannot be detected by the conventional failure detection method. Therefore, when the APC control is performed as it is, there is a problem that the amount of laser light decreases because the monitor current increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to solve the problem of a light source failure which can solve the problem that it is difficult to detect a failure inherent in a semiconductor laser device due to a rise in temperature. It is an object of the present invention to provide a detection device and method.

Another object of the present invention is to provide an apparatus and a method for detecting a failure of a light source which can detect a failure due to end face destruction.

[0015]

According to a first aspect of the present invention, there is provided a light receiving element and a light source optically coupled to each other, and a light source for driving the light source by varying a driving current value by an external signal. In the failure detection device for a light source provided with a drive unit, a light source control unit that controls the light source drive unit to drive the light source by increasing a drive current at a constant time change rate; and Monitoring means for monitoring an output, a monitoring output from the monitoring means, a change monitoring means for obtaining a time change rate of the output based on the monitor output during which the drive current is increasing, and an initial value of the time change rate. A storage unit that stores a value in advance, and reads out the stored initial value and compares it with the time change ratio obtained by the change monitoring unit. When also small to provide a malfunction determining apparatus of a light source and a determination means that a failure of the light source.

According to a second aspect of the present invention, in the first aspect, the monitor means includes a conversion means for converting an output current of the light receiving element into a voltage to output the monitor output, and the change monitoring means comprises: Timer means for measuring time while the drive current is increasing, monitoring a value corresponding to the converted voltage and increasing to a predetermined value, and increasing to another value larger than the predetermined value. Monitoring means for detecting, a difference between the predetermined value and the another value, and a time change from a measurement value of the timer means when the voltage value is the predetermined value and another measurement value when the voltage value is the another value. Provided is a device for determining a failure of a light source, the device including a calculating means for calculating a ratio.

According to a third aspect of the present invention, in the first aspect, the monitor means includes a conversion means for converting an output current of the light receiving element into a voltage to output the monitor output, and the change monitoring means is provided with a differential monitor. Means for determining a time change ratio by differentiating the monitor output by the differentiating means.

According to a fourth aspect of the present invention, in the second or third aspect, the change monitoring means further performs analog-to-digital conversion of the converted voltage or analog-to-digital conversion of the differential output of the differentiating means. A / Digital conversion
A D / A converter, wherein the light source controller includes an A / D converter for digital-to-analog conversion of a set value stored in the storage unit, and controls the drive current according to the set value. Provided is a failure determination device.

According to a fifth aspect of the present invention, there is provided a light source failure detecting apparatus comprising: a light receiving element and a light source optically coupled to each other; and a light source driving means for supplying a driving current to the light source to drive the light source. A control means for controlling the light source driving means to start supplying the driving current, and for starting a time measurement by a timer means simultaneously with the start of the driving current supply, and monitoring an output from the light receiving element. Monitoring means, inputting a monitor output from the monitoring means, monitoring a value corresponding to the monitor output, and detecting that the drive current has increased to a predetermined value, and the timer at the time of the detection. A time measuring means for acquiring the measuring time by the means, and a rise required for the monitor output to increase to a predetermined value after starting to supply the driving current. A storage unit that stores an initial value of time in advance, and compares the stored initial value with a measurement time acquired by the time measurement unit. When the measurement time is smaller than the initial value, it is determined that the light source has failed. A light source failure determination device including:

According to a sixth aspect of the present invention, in the fifth aspect, the monitor means includes a conversion means for converting an output current of the light receiving element into a voltage to output the monitor output, and the monitoring means comprises a monitor. A / D conversion means for performing an analog-to-digital conversion of an output, and the control means includes A / D conversion means for performing a digital-to-analog conversion of a set value stored in the storage means, and according to the set value. A light source failure determination device that controls the drive current is provided.

In order to solve the former problem, a seventh aspect of the present invention provides a light source driving step of supplying a driving current to a light source optically coupled to a light receiving element and increasing the driving current at a constant time change rate. Monitoring the output from the light receiving element during the light source driving step, and determining a time change ratio of the output, and comparing the time change ratio with an initial value before the light source driving step. A determination step of determining that the light source has failed when the ratio is smaller than the initial value.

According to an eighth aspect of the present invention, in the seventh aspect, the change monitoring step includes detecting that an output from the light receiving element has reached a predetermined value and measuring a time at the time of the detection. Detecting that the output from the element has become another value larger than the predetermined value and measuring the time at the time of detection, the difference between the predetermined value and the another value,
A light source failure determination method for obtaining the time change ratio from the measured time is provided.

According to a ninth aspect of the present invention, in the seventh aspect, there is provided a light source failure determination method for obtaining the time change ratio by differentiating an output from the light receiving element in the change monitoring step.

The invention according to a tenth aspect is the invention according to any one of the seventh to ninth aspects, further comprising, before the light source driving step, a step of obtaining the initial value of the time change ratio of the output; Storing the light source.

[0025] In order to solve the latter problem, claim 1 is provided.
According to a first aspect of the present invention, a start step of starting supply of a driving current to a light source optically coupled to a light receiving element and simultaneously starting time measurement, and monitoring an output from the light receiving element, wherein the output is determined by the driving current Value is detected, and the time measurement step of measuring the time measured at the time of the detection and the measured time are compared with the initial value before the start step, and the measured time is the initial value. And a determining step of determining that the light source has failed when the value is smaller than the threshold value.

According to a twelfth aspect of the present invention, in addition to the eleventh aspect, prior to the starting step, the initial time, which is a rising time required for the output to increase to a predetermined value after the supply of the driving current is started, is further improved. A method for determining a failure of a light source includes a step of obtaining a value and a step of storing the initial value.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of failure detection according to the present invention will be described.

The absolute value of the monitor current of the photodiode output fluctuates depending on the laser light amount and thus is affected by the temperature. However, the rate of increase of the monitor current, that is, the differential value does not change with the temperature. When this value changes,
A failure can be determined regardless of the temperature dependency. Therefore, a failure determination is made in accordance with a change in the value of the increase (differential value) of the monitor current from the photodiode for APC control.

FIG. 1 shows how the slope of the monitor current decreases when the semiconductor laser deteriorates. Hereinafter, the laser failure detection method according to the present invention will be described with reference to this characteristic diagram.

The constant current source controls the drive current (horizontal axis) of the laser diode in accordance with the drive current setting signal so as to continuously increase at a constant rate of change with time. Data relating to the drive current setting signal is stored in a memory in advance. The monitor current output from the photodiode is converted into a voltage, and the converted monitor signal is subjected to analog-to-digital conversion. When the laser diode starts to be driven, the monitor signal reaches the specified value S1 while the drive current is increasing, and furthermore, the specified value S1
2 (S2> S1). During this increase, the timer is operated to measure the time until the value increases from the specified value S1 to the specified value S2.

For example, when the count reaches the specified value S1, counting by the timer is started. Thereafter, when the monitor current increases and reaches the specified value S2, the timer is stopped, and at the same time, the timer count value T (measured increase time) is stored in the memory. The specified value S1, the specified value S2, and the timer count value T are calculated to determine the monitor current slope (time change ratio). The laser diode is compared with a gradient (initial value Ao of the time change ratio) stored in the memory in advance, and a failure of the laser diode is determined from the comparison result.

The value of the initial value is a normal inclination a ≧ Ao> a failure inclination b.

(First Embodiment) In the first embodiment of the present invention, an example in which the light source failure detecting device of the present invention is applied to light source failure detection of an image forming apparatus will be described.

FIG. 2 is a sectional view showing a light source failure detecting apparatus (image forming apparatus) according to the first embodiment of the present invention, in which the image forming apparatus is a laser beam printer. Hereinafter, the configuration and operation will be described.

A laser beam printer main body 1 serving as an image forming apparatus can mount a paper feed cassette 2 for setting a recording paper P, and a paper presence / absence sensor 3 for detecting the presence or absence of the recording paper P in the paper feed cassette 2. The paper feed roller 4 for taking out the recording paper P from the paper feed cassette 2, and the recording paper P
And a TOP sensor 7 for detecting that the recording paper P aligned by the registration rollers 5 has reached the image writing position.

The process cartridge 8 includes a photosensitive drum 9, a primary charging roller 10, a developing unit 11, and a cleaner 12 necessary for an electrophotographic system. Laser light from a laser unit 14 in the laser scanner unit 13 is irradiated on a polygon mirror 15, and a latent image is formed on the photosensitive drum 9 via an imaging lens 16 and a return mirror 17. This latent image is developed by a toner in a developing device 11 to be visualized on the photosensitive drum 9, and the toner image is transferred onto the recording paper P by the transfer roller 18.

Downstream of the transfer roller 18, a fixing device 19 for thermally fixing the toner image formed on the recording paper P is provided. The fixing device 19 fixes a toner image on the recording paper P by a heating source 21 and a pressure roller 22 provided in a polyimide film 20 that rotates together with the recording paper P. Further, downstream of the fixing device 19, there are provided a paper discharge sensor 23 for detecting the paper conveyance state and a paper discharge roller 24 for discharging the recording paper P. Also, the fan motor 25
Plays a role in lowering the temperature inside the laser beam printer body 1.

FIG. 3 is a detailed schematic diagram of a laser scanner unit using a semiconductor laser in the apparatus of FIG.

The semiconductor laser 26 (90) includes a laser diode (not shown) and a photo diode (not shown).
Are built in so that they can be optically coupled, and the collimator lens 27
Is irradiated with laser beam light. This laser beam is made parallel by a collimator lens 27 and contracted only in the vertical direction by a cylindrical lens 28. Thereafter, the laser beam reflected by the polygon mirror 15 is returned to parallel light again by the toric lens 29, fθ corrected by the fθ lens 30, and formed on the photosensitive drum 9 via the folding mirror 17. . The polygon mirror 15 is fixed to a scanner motor 35.

Further, a laser beam is incident on a BD sensor 32 via a BD mirror 31 arranged at a predetermined position outside the image area, thereby generating a horizontal synchronizing signal 34. The horizontal synchronization signal 34 is used for horizontal synchronization of the image information signal 39.

The horizontal synchronizing signal 34 is input to the control unit 33, where the number of rotations of the scanner motor 35 is detected from the edge period of the horizontal synchronizing signal 34, and the detected number is determined via the scanner motor driving circuit 36. The rotation of the scanner motor 35 is controlled. The control unit 33 includes a sequence controller 331, a memory 332, an A / D conversion unit 333,
It comprises a D / A converter 334, a timer 335, a calculator 336, a comparator 337, etc., and controls the laser beam printer main body 1. The memory 332 is a nonvolatile memory that can hold data even when the power is turned off.

The laser driving section 37 is a monitor current conversion circuit 3
71, laser drive circuit 372, image signal receiver 373
And so on. In the laser driving unit 37, the image signal receiver 373 outputs the horizontal synchronization signal 3 from the image forming unit 38.
Receiving the image information signal 39 synchronized with 4, the laser drive circuit 372 drives the semiconductor laser 26. Laser driver 3
In 7, the monitor current conversion circuit 371 monitors the current flowing through the photodiode built in the semiconductor laser 26, and performs APC control between sheets and between lines during the initial operation.

The image forming section 38 comprises an image developing section 381, a communication control section 382 and the like. The image information from the host computer or the like is expanded by the image expanding unit 381 and converted into an image information signal 39.

FIG. 4 is a detailed block diagram of a configuration for detecting a laser failure in the light source failure detection device according to the first embodiment. Hereinafter, the laser failure detection method according to the present embodiment will be described.

The present embodiment is different from the first embodiment in that the switching circuit 41 is provided between the sample-and-hold circuit 92 and the constant current source 93, and that the monitor voltage detector 44 for detecting the voltage at the end of the variable resistor Rm is provided. This is different from the conventional example. Further, as will be described later, the present embodiment is characterized by the control by the sequence controller 331.

The switching circuit 41 can switch between the APC mode and the laser failure detection mode in accordance with the mode setting signal MS from the control unit 33. In the laser failure detection mode, the switching circuit 41 receives the drive current setting signal VD from the control unit 33. The driving current value can be changed by inputting to the constant current source 93. The monitor voltage detector 44 detects the voltage at the end of the variable resistor Rm, which is a voltage conversion value of the monitor output current I _PD , and
3 to the A / D converter 333 for analog-to-digital conversion.

FIG. 5 is a flowchart of the sequence control by the control unit for explaining the first embodiment of the present invention. Hereinafter, description will be made according to this flowchart.

The initial value setting mode is executed at the time of product inspection before shipment from the factory, and the initial value A0 of the monitor current gradient is calculated. The calculation method is the same as in the laser failure detection mode described below, and according to the failure detection principle of the present invention described above,
The monitor current gradient A0 during the drive current increase is calculated according to the timer count (S502 to S518). Then, compared with the lower limit value A _min gradient stored the gradient A0 the calculated in advance in the memory 332, detects the failure of the semiconductor laser due to stress or the like during manufacture (S520).

[0049] Here, A0 is determined if the laser failure less than A _min (S570), and notifies the laser failure in the image forming unit 38 (S580). Meanwhile, A0 is stored in the memory 332 in the control unit 33 to A0 is larger than A _min (S530), and shipped as normal.

After shipment, the laser failure detection mode started in S540 is executed. In the laser failure detection mode, the control unit 33 outputs the mode setting signal MS, switches the switching circuit 41 so that the control unit 33 can set the driving current I _LD of the constant current source 93, and outputs the driving current setting start signal. Is performed (S542).

After that, the drive current setting signal VD is exchanged via the D / A converter 334 according to a preset value, and the drive current is continuously increased at a constant time change rate according to the set value. Let it. The set value is stored in the memory 332 in the control unit 33 in advance. When the drive current exceeds the threshold, the laser diode starts emitting light. laser·
The monitor current I _PD also starts to increase according to the light emission of the diode. The monitor current value is converted into a voltage value at the end of the variable resistor Rm, and is converted from analog to digital via the monitor voltage detection unit 44. The control unit 33 monitors the digital value.

First, it is detected whether the monitor current value has reached the specified value S1 (S544).
At 3, the timer 335 starts counting (S54).
6). Thereafter, it is detected whether or not the monitor current value has reached the specified value S2 set lower than the monitor current at the time of the target light amount (S2).
548) When the monitor current reaches the specified value S2, the timer 3
35 stops counting (S550), reversely switches the switching circuit 41 to stop outputting the drive current setting start signal (S552), and the count value T at this time is stored in the memory 332 in the control unit 33. (S554). When the count value is saved, the timer count value is cleared (S55).
6).

The rising slope A of the monitor current is calculated from the specified value S1, the specified value S2, and the count value T of the timer 335 by the arithmetic unit 336 in the control unit 33.
(S558).

The operation period of the timer is not limited to the above, and at least the monitor current is changed from the specified value S1 to the specified value S2.
It is also possible to operate while increasing, and use the difference between the two count values at each specified value.

By the way, the memory 332 in the control section 33 stores the slope data A0 of the monitor current calculated at the time of the initial operation (initial value setting mode). When the slope A is calculated, the data A0 at the time of the initial operation is read out, and the comparator 337 compares the data A0 with the operation value A (S5).
60) The laser failure is determined according to the comparison result. That is, the calculated inclination A is equal to the preset inclination data A0.
If it is smaller than (A <A0), it is determined that the laser diode has failed (S570). If it is determined that the laser diode has failed, the image forming unit 38 is notified of the laser failure (S580).

(Second Embodiment) In a second embodiment of the present invention, instead of calculating the slope of the monitor current from the specified value S1, the specified value S2, and the timer count value as in the first embodiment, the monitor current The converted monitor signal is input to the differentiation circuit,
The differential value obtained by the differentiating circuit is subjected to analog-to-digital conversion, and 2 of this differential value indicating the rate of increase of the monitor current
The configuration is such that the value data is compared with an initial value stored in advance, and a laser failure is determined from the comparison result.

FIG. 6 is a block diagram of a main part of a configuration for detecting a laser failure in the light source failure detection device according to the second embodiment of the present invention.

The apparatus according to the present embodiment uses the differentiating circuit 60 shown in FIG. 6 together with the monitor voltage detecting unit 44 in FIG. The difference from the first embodiment is that the differential value is output to the unit 333.

The monitor current IPD from the photo diode incorporated in the laser 90 is a resistor R for APC control.
The voltage is converted by m and input to the comparator 91. The voltage generated at the m end of the resistor for APC control is input to the differentiating circuit 60 via the monitor voltage detecting unit 44, and the differential output thereof is input to the A / D converter 333, so that the differential value of the monitor current is binary. It is stored in the memory 332 as data. The calculation unit 336 is unnecessary, and the other parts may be the same as in the first embodiment.

FIG. 7 is a flowchart of the sequence control by the control unit for explaining the second embodiment of the present invention.

In the initial value setting mode, when the output of the drive current setting signal is started and the drive current is continuously increased at a constant rate of change (S702), the monitor current gradient A0 is controlled via the differentiating circuit 60 by the control unit 33. A / D converter 333
(S708). When the gradient A0 is input, the output of the drive current setting signal is stopped (S712).

[0062] slope A0 analog by the A / D conversion unit 333 - is a digitally converted by binary data, is compared with the lower limit value A _min gradient stored in advance in the memory 332 by the comparator 337 (S720) . Where A0
There is judged that the laser failure is smaller than A _min (S77
0), a laser failure is notified to the image forming unit 38 (S78).
0). Meanwhile, A0 is stored in the memory 332 in the control unit 33 to A0 is larger than A _min (S730), and shipped as normal.

In the laser failure detection mode, the control unit 3
A switching circuit 4 outputs a mode setting signal MS so that the control unit 33 can set the driving current I _LD of the constant current source 93.
1 and the output of the drive current setting start signal is started (S742).

Thereafter, the drive current setting signal VD is exchanged via the D / A converter 334 in accordance with a preset set value, and the drive current is continuously increased at a constant time change rate in accordance with the set value. Let it. The set value is stored in the memory 332 in the control unit 33 in advance. When the drive current exceeds the threshold, the laser diode starts emitting light. laser·
The monitor current I _PD also starts to increase according to the light emission of the diode.

The differential value A (slope) during the increase of the monitor current is input from the differentiating circuit 60 to the A / D converter 333 (S74).
8). When the slope value is input, the switching circuit 41 is switched in the opposite manner to stop outputting the drive current setting start signal (S75).
2). The slope value is converted from analog to digital and stored in the memory 332 as digital data.

The memory 332 in the control unit 33 stores the monitor current gradient data A0 calculated during the initial operation (initial value setting mode). When the slope A is calculated, the data A0 at the time of the initial operation is read out, and the comparator 337 compares the data A0 with the operation value A (S7).
60) The laser failure is determined according to the comparison result. That is, the calculated inclination A is equal to the preset inclination data A0.
If it is smaller than (A <A0), it is determined that the laser diode has failed (S770). If it is determined that the laser diode has failed, the image forming unit 38 is notified of the laser failure (S780).

(Third Embodiment) The third embodiment of the present invention is intended to detect laser edge destruction. Unlike the above embodiments, the third embodiment is not based on the slope of the monitor current but on the monitor current. It is configured to detect the failure in the end face destruction mode by the rise time. The calculation unit is unnecessary in the control unit 33 of FIG. 4, and the other parts can be implemented by the same configuration.

FIG. 8 is a flow chart of the sequence control by the control unit for explaining the third embodiment of the present invention.

In the initial value setting mode, an initial value T0 of the monitor current rising time is calculated. The calculation method is the same as that in the laser failure detection mode described later, by starting the supply of the drive current and simultaneously counting the timer to count the rise time until the monitor current reaches the specified value (S800 to S816). Subsequently, the calculated initial value T
0 compared with the lower limit value T _min of the rise time stored (the timer count value) in advance in the memory 332, detects the failure of the semiconductor laser due to stress or the like during manufacture (S
820).

[0070] Here, T0 is determined to be a laser failure less than T _min (S870), and notifies the laser failure in the image forming unit 38 (S880). On the other hand, T0 is stored T0 is greater than T _min in the memory 332 in the control unit 33 (S830), and shipped as normal.

In the laser failure detection mode, the control unit 3
A switching circuit 4 outputs a mode setting signal MS so that the control unit 33 can set the driving current I _LD of the constant current source 93.
1 and the output of the drive current setting start signal is started (S842).

Thereafter, the drive current setting signal VD is exchanged via the D / A converter 334 in accordance with a preset value, and the drive current is continuously increased in accordance with the set value. The set value is stored in the memory 332 in the control unit 33 in advance. When the drive current exceeds the threshold, the laser diode starts emitting light. The monitor current I _PD also begins to increase as the laser diode emits light. The monitor current value is converted to a voltage value at the end of the variable resistor Rm.
, And the control unit 33 monitors the digital value.

When the monitor current reaches the specified value, the control unit 33
Then, the count of the timer 335 is stopped (S850), the switching circuit 41 is switched in reverse to stop the output of the drive current setting start signal (S852), and the count value T at this time is stored in the memory 332 in the control unit 33. Is performed (S854).
When the count value is saved, the timer count value is cleared (S856).

By the way, the memory 332 in the control section 33 stores the rise time data T0 of the monitor current calculated at the time of the initial operation (initial value setting mode). When the rise time T is counted, the count data T0 at the time of the initial operation is read out, the comparator 337 compares the data T0 with the count value T (S860), and determines a laser failure according to the comparison result. That is, when the calculated rise time T becomes smaller than the preset rise time data T0 (T <T0), it is determined that the laser diode is in the failure in the end face breakdown mode (S8).
70). When it is determined that the laser diode has failed, the image forming unit 38 is notified of the laser failure (S880).

[0075]

According to the light source failure detecting device according to the present invention of claims 1 and 2 and the light source failure detecting method according to the present invention of claims 7 and 8, the time is measured while the drive current is increasing. Detecting that the converted voltage has increased to a predetermined value and having increased to another value greater than the predetermined value, and calculating a difference between the difference and a time measurement value when the voltage value is the predetermined value. By calculating the time change rate by calculating another time measurement value at the time of, the threshold current and drive current were used for laser failure detection, so the ambient temperature increased and the light source temperature increased due to continuous operation This solves the conventional problem that it is difficult to detect the original failure, and has the effect of detecting the failure of the light source regardless of the temperature.

According to the light source failure detecting device according to the third and fourth aspects of the present invention and the light source failure detecting method according to the ninth and tenth aspects of the present invention, the above-described time measurement and calculation are not performed, and the light source failure detecting method is simply performed. The same effects as above can be obtained.

According to the light source failure detecting device according to the fifth and sixth aspects of the present invention and the light source failure detecting method according to the eleventh and twelfth aspects of the present invention, not only a failure in a normal deterioration mode but also a failure in a normal deterioration mode is achieved. It is possible to detect the laser end surface destruction of the light source that could not be detected, which has the effect of enabling more accurate failure state detection.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a state in which a slope of a monitor current at the time of deterioration of a semiconductor laser is reduced, and shows a drive current-monitor current characteristic of the semiconductor laser.

FIG. 2 is a cross-sectional view showing a light source failure detection device (laser beam printer) according to the first embodiment of the present invention.

FIG. 3 is a detailed schematic diagram of a laser scanner unit using a semiconductor laser in the light source failure detection device according to the first embodiment of the present invention.

FIG. 4 is a detailed block diagram of a configuration for detecting a laser failure in the light source failure detection device according to the first embodiment of the present invention.

FIG. 5 is a flowchart of sequence control performed by a control unit according to the first embodiment of the present invention.

FIG. 6 is a main block diagram of a configuration for detecting a laser failure in the light source failure detection device according to the second embodiment of the present invention.

FIG. 7 is a flowchart of sequence control by a control unit for explaining a second embodiment of the present invention.

FIG. 8 is a flowchart of sequence control by a control unit for explaining a third embodiment of the present invention.

FIG. 9 shows a conventional light source driving circuit (AP) including a semiconductor laser.
FIG. 3 is a block diagram illustrating an example of a (C control block).

FIG. 10 is a characteristic diagram showing deterioration of light emission characteristics (drive current-light amount characteristics) of a semiconductor laser.

[Explanation of symbols]

60 Differentiating circuit 90 Semiconductor laser 44 Monitor voltage detector 332 Memory 335 Timer 336 Operation unit 337 Comparison unit A, AO, _Amin monitor current differential value LD Laser diode MS mode setting signal PD Photodiode T, TO, _Tmin monitor Current rise time VD Drive current setting signal

Claims (12)

[Claims] 1. A failure detection device for a light source, comprising: a light receiving element and a light source optically coupled to each other; and a light source driving means for driving a light source by varying a driving current value according to an external signal. Light source control means for controlling the drive of the light source by increasing the drive current at a constant rate of change over time, monitor means for monitoring the output from the light receiving element, and inputting the monitor output from the monitor means, Change monitoring means for calculating a time change rate of the output based on the monitor output during which the drive current is increasing; storage means for storing an initial value of the time change rate in advance; and reading the stored initial value to perform the change. Comparing the time change rate obtained by the monitoring means, and when the time change rate is smaller than the initial value, failure detection means for determining that the light source has failed; Failure detection device of the light source, characterized in that it comprises. 2. The monitor according to claim 1, wherein the monitor includes a converter that converts an output current of the light receiving element into a voltage and outputs the monitor output. Timer means for measuring time; monitoring means for monitoring a value corresponding to the converted voltage to increase to a predetermined value, and detecting that the value has increased to another value greater than the predetermined value; and A difference between a predetermined value and the another value, and a calculation means for calculating the time change ratio from a measurement value of the timer means when the voltage value is the predetermined value and another measurement value when the voltage value is the another value. A failure detection device for a light source, comprising: 3. The monitor according to claim 1, wherein the monitor includes a converter that converts an output current of the light receiving element into a voltage and outputs the monitor output, the change monitor includes a differentiator, and the monitor output includes The light source failure detection device is characterized in that the time change ratio is obtained by differentiating the time change ratio by the differentiating means. 4. The A / D converter according to claim 2, wherein the change monitoring means further converts the converted voltage from analog to digital, or converts the differential output of the differentiating means from analog to digital. Means, wherein the light source control means includes A / D conversion means for digital-to-analog conversion of a set value stored in the storage means, and controls the drive current according to the set value. Light source failure detection device. 5. A failure detecting device for a light source, comprising: a light receiving element and a light source optically coupled to each other; and a light source driving unit for supplying a driving current to the light source to drive the light source. And control means for starting time measurement by a timer means simultaneously with the start of the drive current supply, monitoring means for monitoring an output from the light receiving element, and inputting a monitor output from the monitoring means. Monitoring means for monitoring a value corresponding to the monitor output and detecting that the value has been increased to a predetermined value by the drive current; time measuring means for acquiring a time measured by the timer means at the time of the detection; Storage means for storing in advance an initial value of a rising time required for the monitor output to increase to a predetermined value after starting to supply the drive current, Failure detecting means for reading out the stored initial value and comparing it with the measured time acquired by the time measuring means, and determining that the light source has failed if the measured time is smaller than the initial value. Light source failure detection device. 6. The monitor according to claim 5, wherein the monitor includes a converter that converts an output current of the light receiving element into a voltage and outputs the monitor output, and the monitor performs analog-to-digital conversion of the monitor output. A / D conversion means, wherein the control means includes A / D conversion means for digital-to-analog conversion of a set value stored in the storage means,
A failure detection device for a light source, wherein the drive current is controlled according to the set value. 7. A light source driving step of supplying a driving current to a light source optically coupled to the light receiving element and increasing the driving current at a constant rate of change over time, and monitoring an output from the light receiving element during the light source driving step. A change monitoring step of calculating a time change ratio of the output; and comparing the time change ratio with an initial value before the light source driving step. When the time change ratio is smaller than the initial value, it is determined that the light source has failed. Detecting a failure of the light source. 8. The change monitoring step according to claim 7, wherein in the change monitoring step, an output from the light receiving element is detected to have a predetermined value, and a time at the time of detection is measured. Detecting that the value has reached another value larger than the value and measuring the time at the time of detection, and calculating the time change ratio from the difference between the predetermined value and the another value and the measured time. Light source failure detection method. 9. The light source failure detection method according to claim 7, wherein, in the change monitoring step, the time change ratio is obtained by differentiating an output from the light receiving element. 10. The method according to claim 7, further comprising, before the light source driving step, a step of obtaining the initial value of the temporal change ratio of the output, and a step of storing the initial value. A method for detecting a failure of a light source. 11. A start step of starting supply of a drive current to a light source optically coupled to the light receiving element and simultaneously starting time measurement, and monitoring an output from the light receiving element, wherein the output is determined by the drive current. Value is detected, and the time measurement step of measuring the time measured at the time of the detection and the measured time are compared with the initial value before the start step, and the measured time is the initial value. A failure detection step of determining that the failure of the light source is smaller than the failure. 12. The method according to claim 11, further comprising, before the starting step, obtaining the initial value that is a rising time required for the output to start to supply the driving current and increase to a predetermined value. Storing a default value.