JPH02194975A - Semiconductor laser deterioration detector for image forming apparatus - Google Patents

Abstract

PURPOSE:To prevent the quality of printing from deteriorating and an irretrievable accident from occurring by detecting the driving current of a laser diode when the driving current exceeds a maximum rated driving current even if an image forming apparatus is operating, or further warning to display the deterioration of a semiconductor laser at the time of detection. CONSTITUTION:When a laser diode 5 is deteriorated so that a driving current Id exceeds a maximum rated driving current, an analog voltage Vo is reduced to be lower than a reference voltage Vr. Accordingly, the output of a comparator 11 becomes 'H', and a deterioration signal is output. Warning and display means has, for example, a controller 12 for controlling a display and a display unit 13. The controller 12 outputs a display signal to the display unit 13 if the output of the comparator 11 becomes 'H'. The display unit 13 displays the deterioration of the laser diode 5 during a period in which a display signal is being inputted to warn an operator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser deterioration detection device in an image forming apparatus.

[Conventional technology]

Recently, there have been an increase in the number of image forming apparatuses that use semiconductor lasers as light sources, such as laser printers, digital copying machines, high-speed facsimile machines, color copying machines, and color printers.

Generally, in a semiconductor laser, as shown in FIG. 4, the driving current Id for obtaining the same optical output varies greatly depending on the temperature, so an active circuit is used to stabilize the optical output.

FIG. 5 is a block diagram showing a conventional example of an optical output stabilizing circuit for the semiconductor laser.

The U/D counter (up/down counter) 1 is initially set to the maximum value, eg, IF FJ (hexadecimal) if it is an 8-bit counter, when the power is turned on.

I) / A converter (digital/analog converter) 2 inputs the contents (digital data) of U/D counter 1, converts it into analog voltage Vo, and converts it to V/D converter (voltage/current converter) 3. Output to.

The V/I converter 3 converts the input analog voltage ■0 into an analog current Io proportional to the voltage, and converts it into an analog current Io proportional to the voltage, and converts it into a laser diode driver (hereinafter referred to as rLD), which is a semiconductor laser.
4 (referred to as "driver").

The LD driver 4 does not output when the video signal is °L, and when the video signal is H°, it outputs a drive current Id corresponding to the input analog current Io to the laser diode (LD) 5. The drive current 1d is analog. When the current Io is large, it is small, and when the analog current Io is small, it becomes large. When the content of U/D counter 1 is rFFJ, that is, when the analog current Io is maximum, the corresponding drive current Jd
is set smaller than the threshold value, so the laser diode 5 hardly emits light.

A part of the optical output of the laser diode 5 is detected by a photodiode 6 built in the same case, and amplified by an amplifier (not shown) to generate a voltage signal Ep proportional to the optical output.
It is output to the comparison port 17 as.

A reference voltage Er, which is equal to the voltage signal when the optical output is at a predetermined level, is connected to the other input terminal of the comparator circuit 7.

The comparator circuit 7 compares the voltage signal Ep and the reference voltage Er, and if the voltage signal Ep is larger than the reference voltage Er, the comparison circuit 7 determines °H°;
If it is small, a L'' U/D signal is output to the U/D counter 1.

U/D counter 1 is 1 when the enable signal from the sequence controller (not shown) is °H°, the U/D signal is I
(If it is “up mode, ゛L.

If it is in the down mode, the clock input from the oscillation circuit 8 is counted down and its contents are changed, and when the enable signal is L'', it is disabled and its contents are maintained.

During the optical output adjustment cycle, since the enable signal and the video signal become H° at the same time, a drive current Id corresponding to the contents of the U/D counter 1 flows to the laser diode 5.
Emits light.

When the optical output is lower than the predetermined L novel (the initial setting is an extreme example), the voltage signal EP becomes the reference voltage Er.
Since it is smaller, the U/D signal becomes °L°, and U/D
Counter 1 enters down mode and counts down,
Along with this, analog voltage Vo, analog current IO
decreases, and drive current Id and optical output increase.

Conversely, when the optical output is higher than the predetermined level, the U/D signal becomes H°, the U/D counter 1 goes into up mode and counts up, the analog voltage Vo and analog current Io increase, and the drive current increases. d, the light output decreases.

Therefore, in the end, the contents of the U/D counter 1 will increase/decrease in a width of one count above and below the value corresponding to the drive current Id that obtains a predetermined level of optical output at the temperature of the laser diode 5 at that time. Repeat.

When the enable signal returns to L, the tJ/D counter 1 retains its contents, and at the same time the video signal also goes to L, completing the optical output adjustment cycle.

This light output adjustment cycle is executed when the power is turned on and every time one page is printed, to maintain the light output at a predetermined level even if there are temperature changes such as ambient temperature or temperature rise due to continuous use.

[Problem to be solved by the invention]

However, as the laser diode deteriorates over time or due to instantaneous surge current, the light emitting efficiency decreases and the driving current required to obtain a predetermined level of optical output increases.

When the drive current exceeds the maximum rated drive current, the internal loss, that is, the amount of heat generated, of the laser diode suddenly increases and the temperature rises rapidly, resulting in a repeated vicious cycle in which the drive current increases further.

As a result, a difference in density occurs between the beginning and end of one page of printing, or in extreme cases, a fatal accident occurs such as failure of printing due to a laser diode going down during printing.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to prevent deterioration in print quality and the occurrence of unrecoverable fatal accidents while an image forming apparatus is in operation.

[Means to solve the problem]

In order to achieve the above object, the present invention detects the optical output of a semiconductor laser, stores data corresponding to the drive current of the semiconductor laser that provides a predetermined level of optical output according to the detection signal, and In an image forming apparatus equipped with means for causing a semiconductor laser to emit light with a drive current based on the data, the data corresponding to the maximum rated drive current of the semiconductor laser is compared with the stored data to determine the magnitude thereof; Provided is a deterioration detection device for a semiconductor laser that is equipped with a comparison means that outputs a deterioration signal when the drive current that provides a predetermined level of optical output exceeds the maximum rated drive current, and furthermore, when the deterioration signal is output, the semiconductor laser The present invention also provides a device equipped with a warning display means for indicating deterioration of the product.

[For production]

By configuring as described above, the present invention outputs a deterioration signal when the semiconductor laser deteriorates and the drive current for obtaining a predetermined level of optical output exceeds the maximum rated drive current, or further outputs the deterioration signal. By displaying the deterioration of the semiconductor laser and warning the operator, it is possible to prevent accidents.

〔Example〕

Hereinafter, this invention will be specifically explained based on Examples.

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
The figure is also a circuit diagram showing a part thereof, and the same parts as in the conventional example shown in FIG. 5 are given the same reference numerals.

In this first embodiment, the D/A converter 2 converts the contents (digital data) of the U/D counter 1 into analog and outputs an analog voltage Vo, and an analog voltage corresponding to the maximum rated drive current of the laser diode 5. Equal reference voltage V
An analog comparison method in which r is compared by a comparison circuit 11 which is a comparison means.The comparison circuit 11 consists of a comparator (analog) as shown in FIG. 2, for example, and a D/A converter that outputs an analog voltage Vo. The output terminal of 2 is the comparator 11
It is connected to one input terminal of the V/I converter 3 and an input terminal of the V/I converter 3.

A resistor R1, one end of which is grounded, and a variable resistor R2, one end of which is connected to a DC constant voltage power supply Vcc, are connected in series to form a voltage divider. is also connected.

By adjusting the resistance value of the variable resistor R2, the middle terminal of the comparator 11 is set to the reference voltage Vr.

When the alligator dynamic current Id is smaller than the maximum rated drive current, the analog voltage Vo is higher than the reference voltage Vr, so the output of the comparator 11 is °L°, that is, no deterioration signal is output.

When the laser diode 5 deteriorates and the drive current Id exceeds the maximum rated drive current, the analog voltage Vo becomes lower than the reference voltage Vr, so the output of the comparator 11 becomes °H°, and the deterioration signal increases. Output.

The warning display means is 1, for example, a controller 1 that controls the display.
2, and a display device 1!1 (not shown) provided on the panel surface of the image forming apparatus.

The controller 12 outputs a display signal to the display device 13 when the output of the comparison circuit 11 becomes 'H-.

The display device 13 displays deterioration of the laser diode 5 and warns the operator while the display signal is being input.

FIG. 3 is a block diagram showing a second embodiment of the invention, in which the same parts as in the first embodiment shown in FIG. 1 are given the same reference numerals.

In this second embodiment, digital data, which is the content of the U/D counter 1, and data (digital value) corresponding to the maximum rated instant current of the laser diode 5 are compared by a data selector 21, which is a comparing means. This is an example of a comparison method.

The digital value corresponding to the maximum rated drive current is set in advance in a nonvolatile memory built into the data selector 21, or is set by a jumper or dip switch corresponding to the number of bits of the U/D counter 1.

The data selector 21 inputs the content of the U/D counter 1 and compares it with preset data, and if the content of the U/D counter 1 is greater than the set data, the output is °L°, If it is less than the set data, the output becomes H'' and a degraded 4W signal is output to the controller 12.

The operations after the controller 12 are the same as in the first embodiment (FIG. 1), and the effects are also the same as in the analog comparison method.

The two embodiments of the analog comparison method and the digital comparison method have been described above. Once a degraded signal is input, the controller 12 outputs a display signal, but if the degraded signal disappears after a certain period of time, the display signal is canceled. Alternatively, once the -degree display signal is output, it may not be canceled until the power is turned off or a recheck button (not shown) is pressed by the operator.

This is because even if the laser diode deteriorates to some extent and the drive current exceeds the maximum rated drive current during the job, it will not immediately cause a vicious cycle and lead to rapid deterioration or shutdown, but rather will be stopped for a while. If the temperature drops, you can continue working until the job is finished.

Alternatively, even if the laser diode has not deteriorated, the drive current may increase due to an abnormally high ambient temperature due to other causes, and a warning may be displayed, in which case you may continue work without noticing. This has the effect of preventing the laser diode from deteriorating.

Furthermore, an alarm sound can be emitted along with the deterioration display to prevent the operator from continuing the work without noticing the display.

Furthermore, in many cases, the deterioration signal is output when the optical output ll4fi cycle is executed between pages during continuous work, so when the deterioration signal from the comparison means is manually input, the next You can also choose to stop working on a page.

Therefore, after a certain period of time after the degradation signal is output,
Alternatively, when the operator presses the check button again, the optical output adjustment cycle is executed, and if the drive current has fallen below the maximum rated drive current and no deterioration signal has been output, the 1st. Ba,
The warning display may disappear and you can start working.

Furthermore, in both the first and second embodiments, the increase/decrease relationship between the analog current Io obtained by converting the contents of the UZD counter 1 and the drive current Id of the laser diode 5 is reversed. As explained above, this invention uses an analog current I.

This can also be applied to the case of an LD driver in which the drive current Id and the drive current Id have the same proportional or increasing/decreasing relationship.

That is, the contents of the U/D counter 1 are cleared when 1tiIIIX' is turned on, and the output of the comparison circuit 11 or data selector 21 which is the comparison means and the comparison circuit 7
The polarity of the output may be reversed between "H" and "L" by, for example, inserting a knot circuit, respectively.

Furthermore, when the optical output beam of the laser diode is scanned to form a latent image of an image, means is provided for changing the optical output in accordance with the scanning speed, that is, the position of the spot on the latent image forming surface, to keep the density constant. Although there are image forming apparatuses equipped with such an image forming apparatus, the present invention was developed by comparing the data corresponding to the drive current that obtains the maximum optical output (generally, the optical output is maximum at both ends of the scanning area) and the maximum rated driving current. can be applied.

〔Effect of the invention〕

As described above, according to the present invention, even when the image forming apparatus is in operation, it is detected when the drive current of the laser diode exceeds the maximum rated drive current, or furthermore, when this is detected, the semiconductor laser Displays a warning about the deterioration of the
It is possible to prevent deterioration in print quality and irrecoverable fatal accidents.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
FIG. 3 is a block diagram showing a second embodiment of the same, FIG. 4 is a characteristic diagram showing an example of temperature change in drive current versus optical output of a semiconductor laser, and FIG. The figure is a block diagram showing a conventional example of an optical output stabilizing circuit for a semiconductor laser. 1... U/D counter 2... D/A converter 3... V/I converter 4... LD driver 5... Laser diode (semiconductor laser) 6... Photodiode 7... Comparison circuit 8... Oscillation circuit 11... Comparison circuit (comparison means) 12... Controller 13... Display device 21
...Data selector (comparison means) Fig. 3 s4 Fig. □ Drive current Id Fig. 1 Fig. 2 Fig. 5

Claims (1)

[Scope of Claims] 1. Detecting the optical output of a semiconductor laser, storing data corresponding to a driving power source for the semiconductor laser that provides a predetermined level of optical output according to the detection signal, and In the image forming apparatus, the image forming apparatus includes means for causing the semiconductor laser to emit light with a drive current based on the drive current, the data corresponding to the maximum rated drive current of the semiconductor laser is compared with the stored data to determine the magnitude thereof; 1. A semiconductor laser deterioration detection device for an image forming apparatus, comprising comparison means for outputting a deterioration signal when a drive current that provides a predetermined level of optical output exceeds the maximum rated drive current. 2. The semiconductor laser deterioration detection device for an image forming apparatus according to claim 1, further comprising warning display means for displaying deterioration of the semiconductor laser when the comparison means outputs a deterioration signal.