JP4391356B2 - LD control apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an LD control apparatus and an image forming apparatus that can accurately detect even a slight degradation of an LD by a simple technique.

2. Description of the Related Art Conventionally, an image forming apparatus using a method in which a modulated laser beam is scanned on a charged image carrier to form an electrostatic charge image (electrostatic latent image) is known. An LD (laser diode) is often used as one means of the light beam of the writing device.
The LD has the property that the light emission amount varies depending on the environment in which the LD is placed or the temperature variation caused by the heat generated by the LD itself. On the other hand, in an apparatus such as a laser printer, it is desired that the LD light quantity is constant. For this reason, control is generally performed in which the amount of light emitted from the LD is detected by a PD (photodiode) attached to the LD and the amount of light is adjusted to be constant by feeding back to the control portion (see FIG. 13). .
As this control method, for example, there is a method of intermittently performing APC based on a sample and hold signal (S / H signal) (see FIG. 14). In this control method, in the standby state, the mode is shifted to the sample mode based on the sample signal and the light amount is adjusted by APC. Constant current drive is performed.
In this type of conventional technology, an LD lighting signal is sent simultaneously with a sample signal as a control signal from the LD control device during APC operation. The sample signal switches the S / H switch of FIG. 13, and the LD lighting signal lights the LD. The LD light amount is controlled to be constant by converting the PD current value proportional to the light intensity of the LD into a voltage, and comparing the voltage with a reference voltage serving as a reference for the light amount by a comparator.
As described above, when the LD is deteriorated when the output light quantity of the LD is kept constant by the APC control, the drive current increases due to an increase in threshold current, a decrease in differential efficiency, or the like. Is caused. Therefore, in this type of conventional technology, in order to prevent problems due to LD degradation, the magnitude of the LD drive current is monitored in the operating state of the LD, and when the LD drive current flows above a specified value, Control is performed to determine that the machine has deteriorated and stop the machine, or to report information that the LD has deteriorated to the outside of the machine.

For example, in the technique of Patent Document 1, a power source, a resistor, and a thermistor are used to generate a reference voltage that changes following a temperature change, and this is compared with a voltage that is generated by detecting a bias current. It is said that the degradation of the LD is detected stably and with high sensitivity in a wide temperature range, thereby facilitating maintenance and inspection of the optical transmitter and grasping the secular change of the optical transmitter in the actual operation state. In Patent Document 2, the laser diode drive current value is measured, and the measured value is compared with a preset threshold value, so that the laser diode lifetime warning and the emission lifetime can be accurately detected. . In Patent Document 3, the current of the laser light source is detected, and the deterioration of the laser light source is notified when the current of the laser light source exceeds a predetermined value, so that the laser light source can be replaced before the laser breaks in advance. The preparation period can be secured.
Further, in Patent Document 4, the deterioration state of the laser light emitting unit is determined based on a plurality of light amount values each having a different size detected when a plurality of drive currents having different sizes are supplied to the laser light emitting unit. The differential efficiency or the ratio of the differential efficiency is calculated, so that it is possible to detect an accurate deterioration state that eliminates the influence of individual variations of the individual image forming apparatuses of the laser light emission unit and the temperature of the installation location. . Further, in Patent Document 5, the ratio between the current value of the drive current of the semiconductor laser and the output light amount is calculated, and the deterioration of the semiconductor laser is determined based on whether or not the ratio exceeds the reference value. Instead of setting individual reference values according to variations, a fixed reference value can be used.
Patent Document 6 discloses a technique for determining an abnormality when the ratio between the laser operating current and the output light amount reaches a predetermined value in laser driving. Further, Patent Document 7 discloses a technique for causing a laser output unit abnormality when an error current exceeds a preset threshold value by laser driving. Further, Patent Document 8 discloses a technique for reporting, stopping the machine when LD deterioration is detected, and performing thinning control to suppress the deterioration.
Japanese Patent Laid-Open No. 5-190950 JP-A-5-187964 JP 2000-280522 A JP-A-11-204890 Japanese Patent No. 2539358 JP-A-6-166207 JP-A-8-295048 JP 2002-329924 A

However, in the above-described technique, the increase amount of the drive current is small depending on how the LD is degraded, and the drive current may not increase up to a predetermined value. Further, if the predetermined value is decreased, a malfunction may be caused due to an increase in driving current due to a temperature rise or variation in LD characteristics. Therefore, even if it is possible to detect that the LD is completely deteriorated with the conventional technology, it is not possible to detect even the subtle LD deterioration. For example, in the image forming apparatus, the LD deterioration is detected without detecting the LD deterioration. There is a problem that the image quality is affected by the collapse of the beam profile.
Therefore, the present invention has been made in consideration of the above-described circumstances, and can detect a slight degradation of the LD with a simple method and accurately prevent a problem caused by the inability to accurately detect the LD degradation. It is an object of the present invention to provide an LD control device and an image forming apparatus that can perform the same.

In order to solve the above problem, an invention according to claim 1, wherein, by feeding back the output current from the light receiving element, an LD controller for automatic power control with respect to LD, light Ryomoto of the LD and varying means for varying the light amount of the L D by a reference voltage as a quasi, at times other than normal operation, setting means for setting the reference voltage higher than the normal operation, the reference voltage by said setting means a light quantity detecting means at the time when the LD is lit when high is set to detect the amount of light output from the LD, and limiting means for limiting the LD drive current supplied to the LD at a predetermined current value, the A deterioration state detection means for detecting that the deterioration state of the LD is progressing based on a result of comparing the detection value of the light amount obtained by the light amount detection means with a predetermined value , The limiting means starts the automatic power control using a predetermined voltage lower than the reference voltage obtained by dividing the reference voltage, and the LD driving current is set to a predetermined light amount set in advance. After the predetermined time has elapsed, the automatic power control is shifted to the constant current control, and the LD drive current during the constant current control is converted into the V / I conversion based on the predetermined voltage along with the counter operation. The deterioration state detecting means determines that an abnormal current has flowed through the LD when the counter value of the counter operation overflows , and gradually adds the current value of the determined ratio obtained as described above. It is characterized by detecting the degradation state of the LD .
The invention described in claim 2 is characterized in that the LD control device further comprises a notification means for notifying the outside that the LD deterioration detected by the deterioration state detection means is in progress .
Furthermore, the invention described in claim 3 is characterized in that the LD control device further comprises stop means for stopping the machine when the LD deterioration detected by the deterioration state detection means is progressing .
In addition, the invention according to claim 4 is characterized in that, in the LD control device, when the LD deterioration detected by the deterioration state detecting means is proceeding, thinning means for thinning out data for modulating and driving the LD. It is characterized by having.
The invention described in claim 5 is an image forming apparatus including any one of the LD control devices described above .

According to the present invention, the LD drive current is limited when detecting the LD degradation after the LD is made to emit as much light as possible except during normal operation such as print processing , and gradually with the counter operation. Since the LD deterioration is detected when the counter value of the counter operation for the increasing LD drive current value overflows, it is possible to measure with a simple configuration, and at the same time, the LD drive current is simply during normal operation such as print processing. The subtle degradation of the LD can be detected with higher accuracy than in the case of measuring the above. In addition, it is possible to prevent problems that occur due to the inability to accurately detect LD degradation . In addition, since the data for driving the modulation of the LD is thinned out to reduce the light emission time of the LD so that the further progress of the LD deterioration is delayed, the LD deterioration proceeds and causes the LD deterioration. It is possible to delay the occurrence of the problem. Further , by stopping the LD control device, it is possible to prevent problems caused by LD degradation.

The best mode for carrying out the invention will be described below in detail with reference to the drawings.
(First embodiment)
In the first embodiment, a laser printer (image forming apparatus) which is the best mode for carrying out the LD control apparatus and the image forming apparatus of the present invention will be described with reference to FIGS. This laser printer includes an LD controller that feeds back an output current from a PD (photodiode) as a light receiving element and performs APC (automatic power control) on the LD (laser diode). As will be described later, a variable means for changing the LD light amount according to a reference voltage that serves as a reference for the LD light amount, a setting means for setting the reference voltage higher than that in the normal operation at a time other than the normal operation such as print processing, and the reference voltage Current detection means for detecting the current output from the LD driving device at that time, and a current detection value by the current detection means in a state where the reference voltage is set high; Deterioration state detecting means for detecting that the deterioration is progressing by comparison with a predetermined value is provided.
A configuration example of a laser printer is shown in FIG. In the laser printer, as shown in FIG. 1, the laser beam emitted from the LD is converted into parallel rays by the collimating lens inside the LDU 1 and is rotated by a rotating polygon mirror (hereinafter referred to as a polygon mirror) 2. After being deflected and scanned, an image is formed on the charged surface of the drum-shaped photoconductor 4 via the imaging lens 3 including the f-θ lens and the reflection mirror 7. At this time, the laser beam is modulated on the basis of the image signal, repeatedly turned on and off, and repeatedly scanned in the main scanning direction according to the rotation of the polygon mirror 2, and at the same time, the photosensitive member 4 rotates to perform sub-scanning. As a result, an electrostatic latent image is formed on the photoreceptor 4.
The formed electrostatic latent image is developed with a charged developer (toner), and a transfer material such as transfer paper to which a charge opposite to that of the developer is applied is brought into close contact with the photosensitive member 4 so that the developer is removed. It is transferred to the transfer material. Then, after the transfer material is separated from the photoreceptor 4, the developer is fused to the transfer material by being heated, and fixing is performed. Here, the synchronization detection light-receiving unit 5 arranged outside the scanning region on the photosensitive member 4 detects the laser beam reflected by the synchronization detection mirror 6, and the LD control unit is obtained by the synchronization detection light-receiving unit 5. Based on the detection signal, an effective scanning period, which is a period during which an image is written on the photoreceptor 4, is determined.

FIG. 2 is a block diagram showing a circuit configuration of the write control unit. In FIG. 2, a central processing unit (hereinafter referred to as CPU) 11 controls the entire laser printer. An image processing unit (hereinafter referred to as IPU) 12 electrically processes image data, and in parallel to a writing unit constituted by an LD driver 13 or the like, a pixel clock, image data (collectively referred to as DATA in the figure), and a control signal Is sending. The image data transmitted to the writing unit is modulated by a pulse width modulation (hereinafter referred to as PWM) unit and transmitted to the LD driver 13. The LD driver 13 drives the LD based on the transmitted signal.
Then, by turning on the LD for APC control outside the effective scanning period and setting the sample and hold signal (S / H signal) to the sample state, the monitor current generated by the PD built in the LD package is built in the APC circuit. APC is performed by feeding back to the LD driver 13. During the effective scanning period, the S / H signal is held and the output current of the driver is fixed to a constant value.

A circuit block diagram of the APC circuit built in the LD driver 13 is shown in FIG. 3, and the operation of the APC circuit will be described. During the APC operation, an LD lighting signal and a sample signal following the LD lighting signal are sent out as control signals from the IPU 12 which is an LD controller. The LD lighting signal switches the switch circuit 14 of FIG. 3 ON, and the sample signal switches the S / H switch ON. Then, a current based on the voltage value of the hold capacitor 18 flows from the current generation circuit 15 into the LD via the switch circuit 14, the LD emits light, and a current proportional to the light intensity of the LD flows into the PD.
Then, the current value flowing through the PD is converted into a voltage in the I / V conversion circuit 16. The hold capacitor 18 is charged or discharged based on a result of comparison between the converted voltage and a reference voltage that is a reference of the light amount by the comparator 17, and the voltage value of the capacitor changes, so that the current generation circuit 15 The output current is controlled, and the LD light quantity is controlled to be constant. At the time of image writing, the S / H signal is changed to a hold signal, and the S / H switch is turned off. As a result, since the value of the hold capacitor 18 is fixed to a constant value, the current flowing from the current generation circuit 15 to the LD is fixed to a constant value.
Based on the image data signal sent from the pulse width modulation (hereinafter referred to as PWM) unit, the LD modulation switch circuit inside the LD driver is switched, and the LD light source is modulated to write an image on the photosensitive member 4 (FIG. 1). Is done. In this way, variable means for varying the LD light quantity is realized. Here, the light quantity reference voltage to be compared by the comparator 17 is controlled by a digital control signal from the IPU 12, and the output voltage value of the DAC (DA converter) 19 that outputs an analog voltage value of 8 bits 256 steps is divided. It is assumed that the voltage is generated by dividing by a resistor.

Now, in this machine, at a predetermined time other than during the printing operation such as when the machine is started, a DA converter control signal is transmitted from the CPU 11 as shown in FIG. 2, and the output voltage of the DAC 19 is transmitted via the IPU 12. Control is performed so that the value is maximized and the light amount setting value of the LD is maximized. In this case, the CPU 11 also functions as setting means for setting the reference voltage higher than that during normal operation. The effect of setting the light amount high will be described later.
Further, a data signal for forcibly lighting the LD or a forcible lighting signal and a sample signal for turning on the S / H switch for APC control are transmitted to the LD driver 13 via the IPU 12 by the control signal from the CPU 11. Assume that the APC operation of the LD driver 13 is performed. Thereafter, the current output from the LD driver 13 during APC driving is monitored by the current detection means, and the deterioration of the LD is determined by comparing the converted voltage value with the voltage value set in advance for deterioration determination. Shall. Thereby, a deterioration state detection means is realized. Specifically, the method shown in FIG. 4 is used as a method for monitoring the output current of the LD driver 13.
In FIG. 4, the current output from the LD driver 13 is converted into a voltage value by a current-voltage conversion circuit. By comparing this voltage value with a predetermined voltage value by the comparator 17 (FIG. 3), the degradation state of the LD is determined. When the degradation is recognized, the CPU 11 (via the IPU 12 (FIG. 2)). Assume that a signal is sent to FIG. The CPU 11 displays the LD degradation on the operation display unit 20 based on the LD degradation signal to notify the outside of the LD degradation and send it from the IPU to prevent further LD degradation. It is assumed that the machine is operated with thinned image signals.
FIG. 5 is a flowchart showing the series of deterioration determination operations. In this flow, first, in step S1, the DAC setting is maximized, the light amount setting value is maximized, the process proceeds to step S2, an APC control signal is given to the LD driver, the APC operation is started, and the process proceeds to step S3. The deterioration determination signal generated from the monitor value of the drive current is read, and then the process proceeds to step S4. In step S4, it is confirmed whether or not the LD has deteriorated. If not, the process proceeds to step S5, the DAC setting value is returned to the original value, the light amount setting value is returned to the original value, and the operation flow is ended. If it is determined in step S5 that the battery has deteriorated, the process proceeds to step S6, the operation display unit 20 (FIG. 2) is notified of the deterioration, and the machine is stopped.

The reason why the LD degradation can be accurately determined by measuring the LD driving current with the maximum light amount is as follows. The LD normally has characteristics as shown in FIG. 6. Even if a drive current is passed through the LD, the LD does not emit light up to a value called a threshold current, and the threshold current is exceeded when the threshold current is exceeded. It is known that the amount of light increases almost linearly in proportion to the current increment. This LD drive current-light output characteristic is called an IL curve. Further, the slope of the straight line where the amount of light increases linearly is called differential efficiency.
However, when the LD deteriorates, as shown in FIG. 6, this characteristic changes, the threshold current increases, and the slope of the differential efficiency decreases, so that it is the same as the LD in which deterioration has not progressed. The amount of LD drive current required to increase the amount of light will increase. In addition, as shown in FIG. 6, it is also known that when the deterioration progresses, the linearity of the IL curve becomes dull and a curve is drawn.
For this reason, in the conventional deterioration determination method, if the image forming apparatus is an image forming apparatus, the LD drive current value is constantly monitored in the print state, and it is determined that the LD drive current has increased, thereby determining deterioration. Each light quantity is detected by a plurality of current values, converted into digital values by an AD converter, recorded in a recording device, and the difference between currents is calculated in a software / program manner. A method is adopted in which the differential efficiency is calculated, and the differential efficiencies are compared in a software / program manner to determine deterioration. In the LD deterioration determination in the laser printer which is the best mode for carrying out the LD control device and the image forming apparatus of the present invention, two characteristics at the time of LD deterioration are:
(1) The characteristic that the threshold current increases and the slope of the differential efficiency decreases when the LD deteriorates, and the LD drive current amount increases. (2) The linearity of the IL curve becomes dull and the curve is drawn when the LD deteriorates. It uses the property of becoming like at the same time.

As shown in FIG. 7, when the LD deteriorates and the linearity of the IL curve becomes dull, the LD drive current amount required to emit a certain amount of light will be described. In FIG. 7, the IL curve at the time of LD degradation is shown by a solid line, and the normal IL curve is shown by a dotted line. As the LD light quantity used as a reference when measuring the LD drive current amount, two types of P1 and P2 are considered as shown in FIG. Here, P1 <P2. As can be seen from FIG. 7, when the LD deteriorates, the slope of the IL curve decreases as the amount of light increases. Therefore, the amount of drive current required to emit the same amount of light as normal and the amount of drive current during normal The difference increases as the amount of light increases (as can be seen by comparing the magnitudes of ΔI1 and ΔI2 in FIG. 7).
Therefore, in order to determine the deterioration of the LD based on the magnitude of the driving current amount, the measurement and the deterioration determination of the driving current amount can be performed with a large amount of light as much as possible. Furthermore, even if it is assumed that the slope of the differential efficiency is simply reduced due to the LD degradation, it can be seen from FIG. 8 that the difference from the normal driving current amount increases as the light amount increases. It can be seen that the greater the amount of light, the easier it is to determine the deterioration.
On the other hand, in general, in an image forming apparatus using an LD, when an actual printing operation is performed, the amount of image surface light on the surface of the photosensitive drum determined from the characteristics of the photosensitive member and the rotational speed of the photosensitive drum, and the photosensitive member. The LD emits light with an amount of light determined by the light utilization efficiency of the optical system that performs the image. For this reason, the LD light amount of the printing operation is very often a light amount having a considerable margin with respect to the absolute maximum rated light amount of the LD.
For this reason, in the LD deterioration determination in this embodiment, the LD drive current is measured after causing the LD to emit as much light as possible, except during the printing operation. As a result, the LD control apparatus according to the first embodiment which is the best mode for carrying out the present invention and the laser printer (image forming apparatus) using the LD control apparatus have the following two characteristics at the time of LD degradation,
(1) The characteristic that the threshold current increases and the slope of the differential efficiency decreases when the LD deteriorates, and the LD drive current amount increases. (2) The linearity of the IL curve becomes dull and the curve is drawn when the LD deteriorates. It can be used in combination with the characteristic that it is possible to measure with a simpler and simpler configuration than comparing differential efficiencies, and at the same time, it can simply measure drive current during normal operation such as printing operation. Rather than performing it, subtle degradation of the LD can be accurately detected. In addition, it is possible to prevent problems that occur due to the inability to accurately detect LD degradation. In addition, since the data for driving the modulation of the LD is thinned out to reduce the light emission time of the LD so that the further progress of the LD deterioration is delayed, the LD deterioration proceeds and causes the LD deterioration. It is possible to delay the occurrence of the problem.

(Second embodiment)
Here, a laser printer as a second embodiment will be described with reference to FIGS. The laser printer in this example includes an LD control device that feeds back an output current from a PD (photodiode) as a light receiving element and performs APC (automatic power control) on the LD (laser diode), and also performs LD control. The apparatus includes a variable unit that varies the LD light amount according to a reference voltage that serves as a reference for the LD light amount, a setting unit that sets the reference voltage higher than that during the normal operation, and a reference voltage that is higher than during normal operation, such as print processing. The LD is turned on when set, the light amount detecting means for detecting the light amount output from the LD at that time, the limiting means for limiting the LD drive current with a predetermined current value, and the reference voltage being set high A deterioration state detecting means for detecting that the deterioration is progressing by comparing the light amount detected value by the light amount detecting means with a predetermined value; It is provided.
In addition, about the part which description overlaps with 1st Example, it abbreviate | omits as much as possible and demonstrates. The optical system and the development process are exactly the same as those of the laser printer described in the first embodiment. For this reason, in the second embodiment, the description is omitted on the assumption that the optical system described in the first embodiment and the equivalent of the developing process are used. Further, the circuit configuration of the write control unit is basically the same as that of the first embodiment, so that the description thereof is omitted. In the second embodiment, as in the first embodiment, a DA converter control signal is transmitted from the CPU as shown in FIG. 9 at a predetermined time other than during the printing operation such as when the machine is started. Control is performed so that the output voltage value of the DA converter is maximized via the IPU, and the LD light amount setting value is maximized. Further, the limiting means provided in the LD driver used in the second embodiment limits the LD driving current when measuring the LD driving current in order to prevent the LD from deteriorating. Further, in the second embodiment, it is assumed that a circuit for automatically determining the LD degradation is incorporated inside the LD driver, triggered by inputting a specific signal to the LD driver.

FIG. 11 is a block diagram of a circuit that automatically performs LD deterioration determination in the LD driver of FIG. 10. At the time of starting the machine, first, as in the first embodiment, a DAC control signal is transmitted from the CPU 11 as shown in FIG. 9, the output voltage value of the DAC 19 is maximized via the IPU 12, and the light intensity setting value of the LD is set. Control to maximize. Further, a signal serving as a trigger for determining the deterioration of the LD is transmitted to the LD driver 13 via the IPU 12 by the control signal from the CPU 11, and the following LD deterioration determination operation is performed inside the LD driver 13.
The LD driver has an internal configuration as shown in FIG. Inside the LD driver, a voltage lower than a predetermined reference voltage is always generated by a voltage dividing resistor inside the LD driver based on a reference voltage signal that is a light quantity reference input from the outside of the LD driver. When a signal serving as a trigger for determining deterioration is input from the outside, the LD driver has a predetermined voltage lower than a reference voltage generated inside the LD driver based on a signal generated by a control circuit built in the LD driver. By starting the APC control using the voltage, the LD driving current is caused to flow so as to have a predetermined light amount that is lower than the external reference voltage signal.
Further, the LD driver uses a control circuit built in the LD driver as a trigger for a signal that triggers the above-described deterioration determination input from the outside, and based on the clock signal generated by the internal clock 21 in the LD driver. By performing a counting operation using the circuit 22, when a predetermined time has elapsed and the APC operation has stabilized, a hold signal is automatically generated from the built-in control circuit and a constant current is generated from the APC control. Transition to control.

Here, when the control is shifted to the constant current control, the control circuit built in the LD driver counts up another counter existing in the LD driver bit by bit based on the clock signal in the LD driver, The DAC 19 built in the LD driver converts the counter value to generate an analog signal. Further, the analog signal converted by the DAC is converted into a current at a predetermined ratio using the V / I conversion circuit 23 incorporated in the LD driver, and is added to the LD drive current during the constant current control. Thus, the current value is gradually increased.
The current flowing into the PD in proportion to the LD light intensity is converted into a voltage by the I / V conversion circuit 16, and this signal is input from the outside as a light quantity reference in the comparator 17 built in the LD driver. When a predetermined amount of light is obtained based on the reference voltage signal as compared with the signal, the control circuit built in the LD driver based on the comparator output normally stops the LD driver after stopping the counter count-up. Move to operation. In this way, the light quantity detection means and the restriction means function.
Also, if the counter value overflows, the control circuit built in the LD driver determines that an abnormal current value has flowed through the LD, and informs the effect of LD degradation through the LD driver external terminal. And forcibly turning off the LD by generating an LD forced turn-off signal inside the LD driver. In this way, the deterioration state detecting means functions. On the other hand, when the CPU determines that the LD has deteriorated based on the deterioration signal, the CPU displays on the operation display unit 20 that the LD has deteriorated and stops the machine.

FIG. 11 is a flowchart showing the series of deterioration determination operations described above in the second embodiment. Referring to FIG. 11, first, in step S11, the DAC set value is maximized, the light amount set value is maximized, the process proceeds to step S12, a deterioration determination operation signal is given to the LD driver, and the deterioration determination operation is started. Moving to S13, the generated deterioration determination signal is read, and the process proceeds to Step S14. In step S14, it is confirmed whether or not the LD has deteriorated. If it has not deteriorated, the process proceeds to step S15, the DAC setting value is returned to the original value, the light amount setting value is returned to the original value, and the operation flow is ended. If it is determined in step S14 that the battery has deteriorated, the process proceeds to step S16, the operation display unit 20 (FIG. 9) is notified of the deterioration, and the operation flow ends.
FIG. 12 is a flowchart showing the deterioration determination operation performed based on the control signal automatically generated by hardware in the control circuit inside the LD driver in the second embodiment. In the operation of FIG. 12, first, when a deterioration determination operation signal is given, the light amount reference voltage is switched to the internally generated voltage in step S21, the process proceeds to step S22, the APC operation is started, and the SAMPLE signal is generated. Proceed to S23. In step S23, the confirmation operation is repeated until the predetermined number of clocks elapses, and when it elapses, the process proceeds to step S24 to shift to a constant current operation to generate a Hold signal and increase the counter by 1 bit.
Thereafter, the process proceeds to step S26 to check whether or not the PD generation voltage is larger than the reference voltage. If the PD generation voltage is smaller, the process proceeds to step S27 to stop the counter, and further proceeds to step S28 to determine the light amount reference voltage. Is switched to the external voltage, the normal operation is performed, and the operation flow is terminated. If the PD generation voltage is larger in step S26, the process proceeds to step S29 to check whether the counter value has overflowed. If it has not overflowed, the process returns to step S25, and if it has overflowed, the process proceeds to step S30. An LD deterioration detection signal is output, the LD is forcibly turned off, and the operation flow is terminated.
Therefore, the LD control device according to the second embodiment, which is the best mode for carrying out the present invention, and the laser printer (image forming apparatus) using the LD control device use a simple method and can accurately subtle degradation of the LD. Can be detected. In addition, it is possible to prevent problems that occur due to the inability to accurately detect LD degradation. Also, stopping the LD control device can prevent problems caused by LD degradation.

It is a perspective view which shows the optical system of a laser printer. It is a block diagram of the LD degradation determination circuit of the first embodiment. It is an internal block diagram of the LD driver of the first embodiment. It is a block diagram of a LD drive current detection circuit. 3 is a flowchart of a deterioration determination / notification method according to the first embodiment. It is a graph which shows the IL characteristic at the time of LD deterioration. FIG. 5 is a graph (No. 1) illustrating an LD drive current amount error when an LD is deteriorated. FIG. 10 is a graph (part 2) illustrating an LD drive current amount error when the LD is deteriorated. It is a block diagram of the LD degradation determination circuit of 2nd Example. It is a block diagram of a deterioration determination circuit inside the LD driver of the second embodiment. It is a flowchart which shows operation | movement of the deterioration determination / notification method of 2nd Example. It is a flowchart of the degradation determination operation inside the LD driver of the second embodiment. It is a block diagram of an APC circuit. It is an operation | movement time chart of an intermittent APC circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 LDU, 2 rotation polygon mirror (polygon mirror), 3 imaging lens, 4 photoconductor, 5 light reception part for synchronous detection, 6 synchronous detection mirror, 7 reflective mirror, 11 CPU, 12 IPU, 13 LD driver, 14 switch circuit , 15 Current generation circuit, 16 I / V conversion circuit, 17 Comparator, 18 Hold capacitor, 19 DAC, 20 Operation display section, 21 Internal clock, 22 Counter circuit, 23 V / I conversion circuit

Claims (5)

An LD control device that feeds back an output current from a light receiving element and performs automatic power control on the LD,
And varying means for varying the light amount of the L D by a reference voltage as a light Ryomoto quasi of the LD,
When other than normal operation, a setting unit set higher to than in the normal operation of the reference voltage,
Light quantity detecting means for detecting the amount of light output from the LD when is lit the LD when the reference voltage is set higher by the setting unit,
Limiting means for limiting an LD driving current supplied to the LD at a predetermined current value ;
A deterioration state detection means for detecting that the deterioration state of the LD is progressing as a result of comparing the detection value of the light amount obtained by the light amount detection means with a predetermined value ;
The limiting means starts the automatic power control using a predetermined voltage lower than the reference voltage obtained by dividing the reference voltage, and the LD driving current is set to a predetermined light amount set in advance. After the predetermined time has elapsed, the automatic power control is shifted to the constant current control, and the LD drive current during the constant current control is converted into the V / I conversion based on the predetermined voltage along with the counter operation. Gradually add the current value of the determined ratio obtained by
The LD control device according to claim 1, wherein the deterioration state detecting means determines that an abnormal current flows through the LD when the counter value of the counter operation overflows, and detects the deterioration state of the LD. The LD control device according to claim 1,
An LD control apparatus comprising a notification means for notifying the outside that the LD deterioration detected by the deterioration state detection means is in progress . The LD control device according to claim 1,
An LD control apparatus comprising: a stopping unit that stops the machine when the LD deterioration detected by the deterioration state detecting unit is in progress . The LD control device according to claim 1,
An LD control apparatus comprising thinning-out means for thinning out data for modulating and driving the LD when the LD deterioration detected by the deterioration state detecting means is in progress . An image forming apparatus comprising the LD control device according to claim 1.

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