JP3533018B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus using a laser diode array.

[0002]

2. Description of the Related Art Conventionally, a laser beam is generally used for image formation in an image forming apparatus such as a copying machine or a laser printer. In recent years, this image forming apparatus tends to have higher speed and higher functionality. In such a tendency, for example, when the copying speed of the copying machine is increased, the video clock frequency is increased, and the pulse width modulator IC (PWMIC) and the laser diode (hereinafter also referred to as LD) driver cannot respond. .

In order to cope with the above, a method has been used in which an LD array is used to simultaneously write a plurality of lines of two or more lines to halve the pixel frequency. For example,
An LD array of 2 laser diodes and 2 detectors (hereinafter also referred to as 2LD2PD) has a problem of crosstalk of LD light and is difficult to manufacture. The LD array that can be practically manufactured is
2LD1PD. The same applies to arrays having three or more LDs. Calibration is performed once for each line or once for each page in order to adjust the light amount of each LD that constitutes this LD array. Therefore, since the LD array is 1 PD (detector), a plurality of LDs are calibrated alternately.

Conventionally, in order to correct the variation in the coupling efficiency between the PD and the LD in the LD, the volume is adjusted by adjusting the volume while monitoring the PD current and the LD light quantity, and the PD monitor voltage at a constant light quantity is adjusted. Auto power control (APC) is performed by the CPU with a constant value. In recent copying machines, pixel density switching (VR) is generally supported, and the pixel clock frequency and polygon motor rotation speed are switched according to the pixel density. Naturally, if the pixel density changes, the synchronization detection cycle also changes.

As a conventional example 2 similar to the above-mentioned conventional example 1, there is JP-A-63-27162, "Semiconductor Laser Array Output Controller". The purpose of the second conventional example is to use a common output control comparator, a counter, and the like to simplify the circuit configuration and reduce the cost, and to commonize and simplify the output of each semiconductor laser. .

[0006]

However, in the above-mentioned conventional example 1, the switching of the calibration input to the LD driver and the switching of the PD monitor current input are performed at the same time. Therefore, when the calibration signal is input, the monitor current of the PD may not be input and the calibration may not be performed correctly depending on variations in the time delay of the selector. Further, it takes a lot of time to correct the variation.

In the conventional example 2, when the LD driver is calibrated once for each line by using the synchronization detection signal, since there is only one LD current setting holding element, the synchronization detection cycle becomes long. , With a problem that the LD current setting value may decrease.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of easily correcting variations in coupling efficiency between a laser diode and a detector.

[0009]

To achieve Means for Solving the Problems] Such objects, an image forming apparatus of the present invention includes a laser diode array having a plurality of laser diodes and one light receiving element in a single package, the laser diode An image forming apparatus having means for maintaining the load current of the laser diode at a predetermined value by holding the current setting value and monitoring the current of the light receiving element to perform calibration of automatic light amount adjustment. And a switching means for alternately calibrating a plurality of laser diodes using one light receiving element, and a timing means for deciding the timing of alternately performing the calibration.
The calibration is performed by delaying the output of the current from the means for performing the calibration to the laser diode rather than the current input for the monitor, which is the current input to the means for performing the calibration.

Further, the above-mentioned image forming apparatus preferably has a variable resistor for converting a monitoring current into a voltage, and the variation of the light emitting characteristic of the laser diode may be corrected by adjusting the resistance value of the variable resistor.

Further, the above-mentioned image forming apparatus has a current set value holding means for keeping the load current of the laser diode at a predetermined value, and the load current held by the current set value holding means causes the plurality of laser diodes to operate. The amount of light emission may be set to a predetermined amount. A capacitor may be used as the current setting value holding means.

Further, the above-mentioned image forming apparatus has a plurality of the current setting value holding means and a selecting means for selecting the plurality of current setting value holding means and switching the connection, and the plurality of current setting value holding means. It is advisable that the load current held by is set to a plurality of types and the amount of light emitted from the laser diode is switched to a plurality of types to allow setting.

The setting for switching the light emission amount of the laser diode to a plurality of types may be performed in conjunction with at least one of switching the resolution of the image formed by the image forming apparatus and switching the image forming speed.

[0014]

Therefore, according to the image forming apparatus of the present invention,
Determine the timing for alternately calibrating multiple laser diodes using one light receiving element, and input the current from the light receiving element to the means for performing calibration.
Than the current input for monitoring is, calibration
The current to the laser diode from the means
Perform calibration by delaying. Therefore, the current input value for monitoring can be fixed when the calibration is executed.

[0015]

Embodiments of the image forming apparatus according to the present invention will now be described in detail with reference to the accompanying drawings. 1 to 6, there is shown an embodiment of the image forming apparatus of the present invention.
FIG. 1 is a block diagram of the optical system of the embodiment, and FIG. 2 is a conceptual view of the optical system of FIG. 1 as seen from the horizontal direction. FIG. 3 is a circuit configuration block diagram of the LD drive unit. 4 shows an example of a drive circuit configuration of a diode array, FIG. 5 shows an example of a calibration timing circuit, and FIG. 6 shows an example of a timing waveform.

1 and 2, the LD array 11 is shown.
Is controlled by the LD control plate 15, the LD light 21 is collimated by the collimator lens 12, and the beam is narrowed by the beam compressor 13. This LD light is a polygon scanner 16
The image is scanned by, reaches the photoconductor 20 through the fθ lens 17, and forms a latent image. LD light 2 by the synchronization detection element 18
While 1 is received, the synchronization detection signal (DETP) becomes active. It should be noted that while the LD light 21 is being received, the time is usually several μs.

FIG. 2 is a conceptual view of the optical system of FIG. 1 as seen from the horizontal direction. This figure shows the case of an LD array in which two LDs are included in one package, and two beams are scanned by the polygon scanner 16 once. That is, two lines are simultaneously irradiated on the photoconductor 20. L in one package
In an LD array containing 3 D's, 3 lines are illuminated at the same time.

FIG. 3 shows a block diagram of an LD driver 30 for driving the LD of this embodiment. PULSE input is L
This is a signal for turning D on and off. CAL is an input signal for performing calibration (light amount adjustment).
When CAL is L and PULSE is H, the LD is lit while PULSE is H. SENSE IN is PD in LD
It is a current input terminal of. When the LD emits light, a current I1 proportional to the amount of light flows through the PD. The amplifier 1 is an operational amplifier amplifier circuit. Therefore, the potential V3 is the reference potential Vref.
Is equal to Therefore, the output potential V1 of the amplifier 1 is V1 = V
ref-I1 (R1 + VR1).

The amplifier 2 is a differential input amplifier circuit. Therefore, when the input potential V1 is smaller than the level input voltage LVL1, the output current I2 is in the discharge direction, and as the difference between the input potential V1 and the level input voltage LVL1 is larger, the output current I2 is larger.
The value of increases. Further, when the input potential V1 is higher than the level input voltage LVL1, the output current I2 is in the sinking direction, and the value of the output current I2 increases as the difference between the input potential V1 and the level input voltage LVL1 increases. When the dpi1 select is selected, the capacitor C2 is connected and the dpi2 is selected.
When select is selected, C3 is connected.

The case where the capacitor C2 is connected will be described below. SW1 when CAL is H and PULSE is H
Closes. When the input potential V1 of the amplifier 2 is smaller than the level input voltage LVL1, the output current I2 is in the discharge direction and the capacitors C1 and C2 are charged by the output current I2, so that the voltage V2 rises. When the voltage V2 rises, the output current I3 of the V / I converter increases. PUL
When SE is H, SW2 is switched to the LD OUT side, so a current I3 flows through the LD.

When the input potential V1 of the amplifier 2 is larger than the level input voltage LVL1, the output current I2 is in the absorbing direction, the electric charges stored in the capacitors C1 and C2 are discharged, and the voltage V2 is lowered. When the voltage V2 drops, V / I
The output current I3 of the converter decreases, and the current I3 that becomes the LD load current decreases.

The light amount adjustment (calibration) of the LD is performed by the procedure described above. By adjusting the amount of light once for each line, an image with good image quality can be obtained. When SW1 opens, the potential V2 is held and the LD current becomes a constant value.

FIG. 4 is a circuit diagram showing an application example of the LD driver 30 shown in FIG. 3 to an LD array. In Figure 4,
An example of a circuit configuration corresponding to an LD array in which two LD1, LD2 and one PD are contained in one package is shown. Further, FIG. 5 shows a configuration example of a timing circuit that creates timings of CAL1 and CAL2 corresponding to the application example of FIG. Further, FIG. 6 shows the timing waveforms of these circuits.

In FIG. 4 and FIG. 5, LD is used as CAL1.
The driver 1 is calibrated. L at CAL2
The D driver 2 is calibrated. As shown in FIG. 4, the JK flip-flop is toggled at the rising edge of CAL1 or the rising edge of CAL2,
The selector is switched by the output Q of this JK flip-flop.

As shown in FIG. 6, when the synchronization detection signal DETP becomes active, the selector is on the LD driver 1 side. At this time, as shown in FIG. 4, the PD current is SENSE.
Input to IN1. CAL1 becomes H, and the LD driver 1 is calibrated. When the CAL1 becomes L, the output Q of the JKFF is inverted and becomes H at the rising edge thereof, so that the selector is switched to the LD driver 2 side. PD current is input to SENSE IN2. Then, CAL2 goes high after a delay of one clock period t1.
Then, the LD driver 2 is calibrated.

In FIG. 3, the monitor voltage V1 is compared with the level input voltage LVL1 to adjust the light amount. In this adjustment procedure, when the monitor voltage V1 is smaller than the level input voltage LVL1, the capacitors C1 and C2 are charged to increase the LD current and increase the light amount. When the monitor voltage V1 is higher than the level input voltage LVL1, the capacitor C1
And C2 are discharged to reduce the LD current and reduce the light quantity. By this operation, the light emission amount of the LD can be set to a predetermined constant value.

In a general LD, the LD emission amount and PD
The coupling efficiency with the current varies. That is,
In one LD, the PD current when emitting 3 mW is 1 mA, whereas in another LD, the PD current when emitting 3 mW is 0.5 mA. In the present embodiment, this variation is corrected by the volume VR1 shown in FIG. The correction procedure is as follows.

As described above, the monitor voltage V1 is V1 = Vre
It becomes f-I1 (R1 + VR1). The reference voltage Vref is a constant value. The resistor R1 is also a fixed value in the driver. Therefore, changing the value of the volume VR1 changes the value of the monitor voltage V1. In the calibration, the LD current is increased or decreased so that the value of the level input voltage LVL1 is equal to the value of the monitor voltage V1. Therefore, the level input voltage LVL1 is set to a constant voltage such as 2V, and the CAL input and the PULSE input are set to H for calibration. LD light quantity is a predetermined constant value (for example, 3 m
By changing the value of the volume VR1 so as to be W), it is possible to correct the characteristic variation of the LD.
According to this method, even if the LDs are different, the LD driver has an L level input voltage LVL1 when the input voltage is 2V.
It is possible to set the D light amount to 3 mW.

The LD current setting value holding element is a capacitor. In FIG. 3, when the dpi1 select is selected,
When the capacitor C2 is selected and the dpi2 select is selected, the capacitor C3 is selected. dpi1
Select 400dpi, dpi2 select 600d
Assuming pi, since the period of the sync detection signal is longer in the dpi1 select, the capacitance of the capacitor C2 is equal to that of the capacitor C3.
The value is larger than the capacity of. That is, an appropriate capacitor corresponding to each dpi select is selected.

Although FIG. 3 shows an example using two capacitors, the same idea can be applied when the number of capacitors is three or more.
The larger the capacitance value of the capacitor is, the longer the discharge time is, and the smaller the voltage drop of the potential V2 is, even if the time from the end of the calibration to the next calibration is long. That is, the amount of attenuation of the LD current value becomes small. The stepwise change setting of the LD current value is used along with the change of the resolution of the image formed by the image forming apparatus and the change of the image forming speed.

It is necessary that the time from the completion of calibration to the next calibration and the capacitance value of the capacitor are matched. When the capacitance value of the capacitor is too small, the electric charge is discharged in a short time, so that the LD current value is attenuated. If the capacitance value of the capacitor is too large, it takes time to charge the capacitor.
The response becomes poor until the D current reaches an appropriate value. Therefore,
Calibration takes a lot of time.

In the above-described embodiment, the calibration current input of the LD is input later than the monitoring current input of the PD. Therefore, since the monitor current input value is fixed at the time of executing the calibration, the light amount can be adjusted with high accuracy.

Further, the characteristic gain of the LD is corrected by changing the gain of the voltage generated by the monitor current of the PD. Therefore, a stable constant light amount can be obtained even if the LD changes. In addition, the light amount adjustment work can be easily performed.

Further, since the LD current setting holding element is selected according to each pixel density, it is possible to obtain an image having a constant density and good image quality.

[0035]

As kana bright et than the above description, the image forming apparatus of the present invention determines the timing for alternately with one light receiving element to calibrate the plurality of laser diodes, the light receiving element Calibrate
Than the current input for the monitor which is the current input to the
From calibration means to laser diodes
Calibration is performed by delaying the output of current . Therefore, when the calibration is executed, it is possible to fix the current input value for the monitor and perform the accurate automatic light amount adjustment.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical system applied to an image forming apparatus of the present invention.

FIG. 2 is a conceptual diagram of the optical system of FIG. 1 viewed from the horizontal direction.

FIG. 3 is a block diagram showing a circuit configuration example of an LD drive section applied to the image forming apparatus of the present invention.

4 is a circuit configuration block diagram showing an embodiment in which the LD drive unit of FIG. 3 is applied to a diode array.

5 is an example of a calibration timing circuit applied to the circuit of FIG. 4;

6 is a timing waveform chart of the timing circuit of FIG.

[Explanation of symbols]

11 LD array 12 Collimating lens 13 Beam compressor 15 LD control board 16 polygon scanner 17 fθ lens 18 Synchronous detection element 20 photoconductor 21 LD light 30 LD driver

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Claims (6)

(57) [Claims] To 1. A single package a plurality of laser diodes and laser diode array comprising a single light receiving element, by holding the current setting value of the laser diode, the load current of the laser diode to a predetermined value An image forming apparatus having a means for keeping and monitoring the current of the light receiving element to perform calibration for automatic light amount adjustment, wherein the plurality of laser diodes are calibrated alternately using the one light receiving element. A means for performing the calibration and a means for performing the calibration from the light receiving element, the timing means for determining the timing for performing the alternation .
Than the current input for monitoring a current input to the key
An image forming apparatus, wherein the calibration is performed by delaying output of a current from the calibration means to the laser diode. 2. The image forming apparatus further includes a variable resistor for converting the current for monitoring into a voltage, and the variation of the emission characteristic of the laser diode is corrected by adjusting the resistance value of the variable resistor. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus further comprises a current set value holding means for holding the load current of the laser diode at a predetermined value, and the plurality of lasers are driven by the load current held by the current set value holding means. The image forming apparatus according to claim 1, wherein the amount of light emitted from the diode is set to a predetermined amount. 4. The image forming apparatus according to claim 3, wherein the current setting value holding means is a capacitor. 5. The image forming apparatus further includes a plurality of the current setting value holding means and a selection means for selecting the plurality of current setting value holding means and switching the connection, and the plurality of current setting value holding means. 4. The load current held by the means is set to a plurality of types, and the light emission amount of the laser diode can be switched to a plurality of types for setting.
Alternatively, the image forming apparatus according to item 4. 6. The setting for switching the light emission amount of the laser diode to a plurality of types is performed in conjunction with at least one of switching of resolution of an image formed by the image forming apparatus and switching of image forming speed. The image forming apparatus according to claim 5, which is characterized in that.