JP4359048B2 - Laser diode drive control device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser diode drive control device and an image forming apparatus for controlling the amount of laser light emitted from a laser diode in order to write an image with a light beam, particularly in a digital copying machine, a laser beam printer, a facsimile machine or the like .
[0002]
[Prior art]
A detection circuit for detecting deterioration of a laser diode (LD) is conventionally known (see, for example, Patent Document 1 and Patent Document 2).
[Patent Document 1]
Japanese Patent Laid-Open No. 05-187964 [Patent Document 2]
Japanese Patent Laid-Open No. 11-204890
[Problems to be solved by the invention]
An LD is an element that easily deteriorates, and when the LD deteriorates, a desired amount of light cannot be obtained, or an abnormality (such as an image abnormality in a laser printer) often occurs due to a change in divergence angle.
For this reason , the LD control device usually monitors the drive current value of the LD to determine whether the LD has deteriorated and to stop the operation of the machine to cause a malfunction such as an image abnormality. It has been prevented. Further, in order to check the progress of the LD degradation at the time of shipment from the factory, the determination may be made by measuring the drive current value of the LD.
If there cow this, the interior of the laser driver (integrated circuit having a LD control circuit), it is considered that a built-in circuit for measuring the LD drive current value.
However, in this type of conventional technology, in the case of an integrated circuit capable of driving a plurality of LDs, it is necessary to provide a terminal for reading a drive current value corresponding to the number of channels in the package of the integrated circuit. With the increase in the number of terminals, it is inevitable that the cost will increase due to the need to use a larger package.
Furthermore, since the LD control device is often arranged at a position away from the main body control device, a signal line corresponding to the number of LDs is required to transmit the drive current value signal to the main body control device. Cost increases due to an increase in the number of connectors and pins are inevitable.
Moreover, even if the signal lines are gathered together by using an adder circuit, etc., as the current value is measured by lighting in order for each channel, the LD control circuit normally sets the bias current for the purpose of high-speed modulation. Since it is always flowing, a signal line that cuts off the bias current for each channel is required in addition to turning off the LD lighting signals of other channels. For this reason, even in this method, the number of connectors and pins increases due to an increase in signal lines, and an increase in cost is inevitable.
In addition, with this type of conventional technology, there is a problem that it takes time to determine deterioration of each channel one by one even though the cost can be reduced.
Therefore, the technical problem of the present invention is that even when a plurality of LDs are driven, a drive current value signal can be transmitted without increasing the number of external terminals, and a drive current that maintains a certain degree of LD degradation determination speed. It is an object of the present invention to provide a small and low-cost laser diode drive control device and an image forming apparatus incorporating a measurement device.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the invention described in claim 1, the amount of laser light emitted from the plurality of laser diodes is driven and controlled, and connected to an external device for determining deterioration of the plurality of laser diodes. In the laser diode drive control device, a plurality of laser diode drivers responsible for drive control for sequentially turning on the plurality of laser diodes without interrupting a bias current, and the plurality of laser diodes corresponding to each of the plurality of laser diodes A plurality of drive current measuring devices provided in a plurality of laser diode drivers and a plurality of drive current measurement values output from the plurality of drive current measurement devices are input in parallel, and the plurality of drive current measurement values An analog OR circuit that outputs the maximum value, and an output signal from the analog OR circuit Characterized by comprising a comprising output means for outputting the location, the.
According to a second aspect of the present invention, in the laser diode drive control device according to the first aspect, the analog OR circuit divides the plurality of drive current measurement values output from the plurality of drive current measuring devices into a predetermined number of groups. A plurality of systems are input in parallel, and a plurality of systems are provided to output the maximum value of the plurality of drive current measurement values for each of the plurality of systems, and the output means is the plurality of systems in the plurality of analog OR circuits. A plurality of the maximum values output every time are provided so as to be output individually.
According to a third aspect of the present invention, in the laser diode drive control device according to the first or second aspect, the laser diode drive control device includes a plurality of current / voltage converters that convert the plurality of drive current measurement values into voltage values, and the analog OR circuit includes: The maximum value among the plurality of voltage values from the plurality of current / voltage converters is output.
According to a fourth aspect of the present invention , there is provided an image forming apparatus comprising the laser diode drive control device according to any one of the first to third aspects.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing a configuration of a multi-beam laser printer as an example of an image forming apparatus to which a laser diode drive control device of the present invention is applied . This first embodiment shows an embodiment of a multi-beam laser printer that performs image writing simultaneously with a plurality of laser beams, among laser printers.
In the multi-beam laser printer, as shown in FIG. 1, a plurality of laser beams emitted individually from a plurality of laser diodes (LD) which are individually controlled and are adjacent to each other in the laser diode unit (LDU) 1 are LDU1. Parallel rays are generated by the internal collimating lens.
After the parallel rays are deflected and scanned by a rotating polygon mirror (hereinafter referred to as a polygon mirror) 2, an image is formed on the charged surface of the drum-shaped photoconductor 5 by an imaging lens composed of an fθ lens 3, a reflection mirror 4, and the like. Image.
At this time, each laser beam is modulated on the basis of the image signal and repeatedly turned on and off, and is repeatedly scanned in the main scanning direction indicated by the arrow in the drawing according to the rotation of the polygon mirror 2. An electrostatic latent image is formed on the photoreceptor 5 by rotating and performing sub-scanning.
The formed electrostatic latent image is developed with a charged developer (toner), and a transfer material (not shown) such as transfer paper to which a charge opposite to that of the developer is applied is brought into close contact with the photoreceptor 1. As a result, the developer is transferred onto the transfer material. Then, after the transfer material is separated from the photoreceptor 1, the developer is fused on the transfer material by heating, and fixing is performed.
Here, the light receiving element 6 arranged outside the scanning region on the photosensitive member 1 detects the laser beam, and the LD control unit detects the image on the photosensitive member 1 based on the detection signal obtained by the light receiving element 6. An effective scanning period, which is a writing period, is determined. In the figure, reference numeral 7 denotes a synchronization detection mirror.
[0006]
FIG. 2 is a block diagram showing a circuit configuration of the laser diode (LD) drive control apparatus according to the first embodiment of the present invention . Here, it is assumed that n (plurality) of LD drivers 11 are provided to drive n (plurality) of LDs 12 and 13 (that is, the LD driver 11 is provided for each LD12 and 13 ). shall have) found for each LD 12, 13 is shall be controlled in exactly the same manner, the in FIG. 2 shows only the configuration of the LD driver 11 and LD12,13 of one system, one system of Only the control method of the LDs 12 and 13 will be described.
The central processing unit 2 (hereinafter referred to as CPU) 8 controls the whole laser printer. The image processing unit (hereinafter referred to as IPU) 9 is synchronization based on the detection signal electrically processes the image data, pixel clock and image data (Fig. In parallel to the configured writing unit in LD driver or the like from the outside 2 is collectively shown as DATA) , an LD lighting signal as a control signal, a sample and hold signal (S / H signal) , and the like.
Image data transmitted to the write section includes a pulse width modulation is modulated by the unit 10 (hereinafter referred to as PWM), is sent to the LD driver 11.
L D driver 11, a signal transmitted by driving the LD12 based, as well as light the LD12 for APC control outside effective scanning period, the sample-and-hold signal (S / H signal) to the sample state Thus, APC is performed by feeding back the monitor current generated in the photodiode (PD) 13 built in the LD package to the LD driver 11 built in the APC circuit. During the effective scanning period , the sample and hold signal (S / H signal) is held and the output current of the LD driver 11 is fixed to a constant value.
[0007]
FIG. 3 is a block diagram showing an APC (automatic light output adjustment) circuit built in the LD driver 11 described above . The operation of the APC circuit will be described. Here, an APC circuit is built in each of the LDs 12 and 13 , but the configuration of each APC circuit is completely the same, so only one APC circuit 14 will be described.
The LD 12 is supplied with a bias current that does not always cause LD light emission. During the APC operation, an LD lighting signal and a sample signal following the LD lighting signal are sent out as a control signal from the image processing unit 9 which is an LD controller.
The LD lighting signal switches the switch circuit 15 of FIG. 3 on, and the sample signal switches the S / H switch 16 on. Then, a current based on the voltage value of the hold capacitor 21 flows from the signal current generation circuit 17 to the LD 12 via the switch circuit 15 , and this current is added to the bias current from the bias electricity generation circuit 18, thereby causing the LD 12 to emit light. and a current proportional to the light intensity of the LD12 flows into the L D13.
Then, the current value flowing through the L D 13 is converted into a voltage in the I / V conversion circuit 19. As the voltage with a reference voltage after conversion hold capacitor 21 is charged or discharged based on the comparison result by the comparator 20 with voltage values are changed. This ensures that the output current of the signal current generating circuit 17 is controlled, the amount of LD 12 is controlled to be constant.
When writes, the sample-and-hold signal (S / H signal) is turned into the hold signal, S / H switch 16 is switched off. As a result, since the value of the hold capacitor 21 is fixed to a constant value, the current flowing from the signal current generating circuit 17 to the LD 12 is fixed to a constant value.
Then, based on the image data signal sent from the PWM unit 10 shown in FIG. 2, the LD modulation switch circuit inside the LD driver 11 is switched, and the LD 12 modulates the light source 1 to write an image on the photosensitive member 5. Is done.
[0008]
Figure 4 is a characteristic diagram showing the relationship between the light output P indicating the input current I and output light amount of the LD 12. Here, we show that the LD12 is not the current value Ith or in light emission called threshold value current has a first emission characteristics beyond the threshold current Ith.
For this reason , in order to operate the LD 12 at a high speed, a current value of about a threshold current called a bias current is always passed through the LD 12 and only when the LD is turned on, a current called a signal current is added to the bias current. LD control is performed.
Here, the operation has been described on the premise that a plurality of single LDs 12 are used as a multi-beam light source. Of course, as a multi-beam light source, a plurality of LDs that can be individually driven are incorporated in one element. An LDA (laser diode array) may be used.
FIG. 5 is a circuit diagram showing an I / V (current / voltage) conversion circuit 19 that converts the amount of current driving the LD 12 . Here, as an LD driving method, as shown in FIG. 5, the amount of current that drives each LD current the LD drive current amount for each LD - indicates the conversion constant to the voltage value by the voltage conversion circuit ing.
By the way, the current value converted into a voltage for each LD here is calculated by an analog OR circuit 22 shown in FIG. 6, and its output is sent to a main body control device (external device) different from the LD driver 11. It is configured to be sent out.
FIG. 7 is a circuit diagram showing a schematic configuration of the entire measurement detection circuit for the external device . Here, a drive current measurement value (supplied to the LD 12) based on the bias current from each LD driver 11 is converted into a voltage value by each I / V conversion circuit 19 ′ and output to the analog OR circuit 22. The analog OR circuit 22 will be briefly described. The analog OR circuit 22 is a multi-input one-output analog circuit as shown in FIG. 6, and is a circuit that outputs a voltage equal to the highest input voltage among a plurality of inputs. Therefore the analog OR circuit 22, also known as the maximum value detection circuit aliases.
Figure 8 is a diagram showing the relationship between the current amount and the channel of the bias current generating circuit 18. The non-lighting state for LD 12, the bias current of slightly different values for each channel is flowing, a large bias current value most of the channels are output.
Therefore , referring to FIG. 8, when the LD 12 is APC-lit only for an arbitrary channel (1ch) 23, a signal current flows in addition to the bias current only for that channel, so there is a slight variation in the bias current value of each channel. even if, ing to the largest current flows through the lighting channel. For this reason, the voltage of the analog OR circuit 22 indicates the value of the current flowing through the lit channel. When the output voltage of the analog OR circuit 22 output to the external terminal is read by a DAC or the like, the value can be regarded as the current value of the lighted channel.
[0009]
Figure 9 is a flowchart for explaining the operation process of the channel lighting. As shown in the flowchart of FIG. 9, the operating currents of the individual LDs 12 can be measured by sequentially lighting the channels and reading the output voltage of the external terminal with the DAC each time.
In the channel lighting operation process, the channel 1ch23 is turned on to read the DAC (D / A conversion value by the digital-analog conversion circuit) ( step S1), and then the channel 2ch24 is turned on to read the DAC ( step S2). The channel 3ch25 is turned on to read the DAC ( step S3), the channel 4ch26 is turned on to read the DAC ( step S4), and finally the channel nch27 is turned on to read the DAC ( step S5).
Figure 10 is a diagram showing the relationship between the optical output and the current due to the channel lighting the LD 12 (the drive control). The optical output P indicating the LD output light amount is known to increase with a slope called differential quantum efficiency when the input current I exceeds the threshold current Ith of the LD 12 as shown in FIG. When 12 deteriorates, it is known that the differential quantum efficiency decreases as shown in FIG. For this reason , in order to make the deteriorated LD 12 emit a predetermined amount of light by APC, a driving current larger than usual is required. Therefore, here, the amount of current flowing through the LD 12 when the APC is turned on is examined, and the LD 12 deteriorates. It is possible to check the progress of deterioration.
Figure 11 is a drawing showing the essential components of the measurement detection circuit according to a second embodiment of the present invention. It is assumed that the present invention is applied to a multi-beam laser printer as in the first embodiment, but the description of the same parts as those in the first embodiment is omitted.
In the second embodiment, divided into several groups 28, 29 a current value converted into a voltage for each LD, calculated by the analog OR circuits 30 and 31 concurrently independently for each the group 28, 29 Thus, this embodiment is exactly the same as the first embodiment except that the signal is output to the external terminal and the current is measured. Therefore, in the second embodiment the optical system and described in the first embodiment is to use the equivalent of a development process. Of course, the drive current measurement values (current values 1 to 4) based on the bias currents from the respective LD drivers 11 are converted into voltage values by the respective I / V conversion circuits 19 ′, and then to the analog OR circuits 30 and 31. It is good also as a structure which outputs each.
That is, in the second embodiment, by calculating the analog OR circuits 30 and 31 each measurement signal for each group as shown in FIG. 11, and transmits the result, whether LD 12 has deteriorated, It is judged whether the deterioration is progressing.
The laser diode drive control circuit according to the first embodiment and the second embodiment described above can be applied to a laser beam light source used in the information / communication field such as an optical disk or optical communication.
[0010]
【The invention's effect】
As described above , according to the configuration of the laser diode drive control device of claim 1 , the drive current measurement value obtained individually for each LD is calculated by one analog OR circuit, and the calculated signal is converted into one signal. Since it can be configured to output to an external terminal only by a line, an increase in the number of terminals that output a drive current measurement value can be suppressed, and a device configuration that incorporates a low-cost, small-sized drive current measurement device can be achieved.
According to the configuration of the laser diode drive control device of claim 2 , the drive current measurement values obtained individually for each LD are divided into several groups, and calculated by a plurality of analog OR circuits corresponding to each group. Therefore, even if a large number of LDs are used, an increase in cost due to an increase in the number of terminals can be suppressed, and at the same time, a certain degree of LD can be obtained. A device configuration with a built-in drive current measuring device that maintains the determination speed of deterioration can be achieved.
According to the configuration of the laser diode drive control device of claim 3, the drive current measurement value input to one analog OR circuit or a plurality of analog OR circuits in the laser diode drive control device of any of the above forms Since it is converted to a value, signal processing in the apparatus is simplified, and it is possible to accurately determine the LD degradation on the external apparatus side.
According to the configuration of the image forming apparatus of the fourth aspect, the laser diode drive control device according to any one of the above forms can be used as a light source, so that a light source capable of accurately determining the LD degradation can be used. The application of becomes effective.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of a multi-beam laser printer as an example of an image forming apparatus to which a laser diode drive control device of the present invention is applied .
FIG. 2 is a block diagram showing a circuit configuration of the laser diode (LD) drive control apparatus according to the first embodiment of the present invention .
3 is a block diagram showing an APC circuit built in an LD driver provided in the laser diode drive control device shown in FIG . 2. FIG.
4 is a characteristic diagram showing the relationship between the input current and output light amount of the LD provided in the laser diode drive controller shown in FIG.
5 is a circuit diagram showing an I / V conversion circuit for converting an amount of current driving an LD provided in the laser diode drive control device shown in FIG . 2 ;
6 is a circuit diagram showing an analog OR circuit of a measurement detection circuit attached to an LD driver provided in the laser diode drive control device shown in FIG . 2 ;
7 is a circuit diagram showing the configuration of the entire measurement detection circuit described in FIG . 6 ;
8 is a diagram showing the relationship between the current amount and the channel of the bias current generating circuit provided to the APC circuit explained in FIG.
FIG. 9 is a flowchart for explaining an operation process of channel lighting of the LD described in FIG . 8 ;
10 is a diagram showing the relationship between the light output and current associated with channel lighting (LD drive control) described in FIG.
FIG. 11 is a diagram showing a main part of a measurement detection circuit according to a second embodiment of the present invention.
[Explanation of symbols]
1 Light source (LD unit)
8 CPU
9 Image processing unit (IPU)
10 pulse width modulator (PWM)
11 laser diode (LD) driver 12 , 13 laser diode (LD)
22 , 30, 31 analog OR (OR) circuit

Claims (4)

In the laser diode drive control device connected to an external device for controlling the amount of laser light emitted from a plurality of laser diodes and determining the deterioration of the plurality of laser diodes,
A plurality of laser diode drivers responsible for driving control for sequentially turning on the plurality of laser diodes without interrupting a bias current, and a plurality of laser diode drivers in the plurality of laser diode drivers so as to correspond to each of the plurality of laser diodes A plurality of drive current measuring devices provided and a plurality of drive current measurement values output from the plurality of drive current measuring devices are input in parallel, and an analog OR that outputs a maximum value among the plurality of drive current measurement values is input. A laser diode drive control device comprising: a circuit; and output means for outputting an output signal from the analog OR circuit to the external device. 2. The laser diode drive control device according to claim 1, wherein the analog OR circuit divides the plurality of drive current measurement values output from the plurality of drive current measuring devices into a predetermined number of groups and inputs them in parallel in a plurality of systems. And a plurality of the drive current measurement values are provided for each of the plurality of systems, and the output means outputs the maximum value output for each of the plurality of systems in the plurality of analog OR circuits. A plurality of laser diode drive control devices are provided so as to individually output the laser diode. 3. The laser diode drive control device according to claim 1, further comprising a plurality of current / voltage converters for converting the plurality of drive current measurement values into voltage values, wherein the analog OR circuit includes the plurality of current / voltage conversions. A laser diode drive control device for outputting a maximum value among the plurality of voltage values from a detector. An image forming apparatus comprising the laser diode drive control device according to claim 1.

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