JPH0664220A - Image recording apparatus - Google Patents

Abstract

PURPOSE:To obtain image quality free from density irregularity and color irregularity by controlling the supply of a current to semiconductor laser on the basis of the detected value of the output of laser beam when a photosensitive material is irradiated with laser beam so that the output of laser beam becomes a predetermined value. CONSTITUTION:In a laser driving circuit, the beam output of a laser diode 13c detected by a photodiode 15c is inputted to a droop correction circuit 320 and an operational amplifier 378 through an I/V circuit 314 and subjected not only to amplifying and integrating processing by resistors 379, 383 and a condenser 384 but also to attenuation processing by resistors 381, 382 to be inputted to a constant current circuit 304. This inputted current is added to the current flowing to a resistor 332 and a Zener diode 344 and the added value is subtracted from the control current for a constant current inputted through a D/A converter 306. Then, the current after subtraction is applied to semiconductor laser. That is, a current wherein the beam output due to self-generation of heat is corrected is supplied to the laser beam output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus, and more particularly to an image recording apparatus for recording an image by exposing a photosensitive material with a light beam containing a plurality of wavelengths.

[0002]

2. Description of the Related Art Conventionally, there is known an image recording apparatus such as a laser beam printer which records an image by exposing a photosensitive material with a laser beam which is a mixture of a plurality of laser beams having different wavelengths.

As a light source of this image recording apparatus, a gas laser or the like which can obtain light (laser beam) in a predetermined wavelength band has been used, but the apparatus becomes large,
Moreover, since it is necessary to use a complicated structure to modulate the light output, recently, a semiconductor laser that is small and can easily modulate the light output has been used.

The image exposure apparatus is provided with a polygon mirror (rotary polygon mirror). The main surface of the laser beam is irradiated by irradiating the laser beam on the reflecting surface provided on the polygon mirror and rotating the polygon mirror. It is scanning. The sub-scanning is performed by moving the photosensitive material. In this way, a two-dimensional image is recorded on the photosensitive material by performing the main scanning and the sub scanning of the laser beam. The sub-scanning may be performed by irradiating the photosensitive material with the laser beam reflected from the polygon mirror through the deflector and deflecting the laser beam in the sub-scanning direction by the deflector.

When an image is recorded on a photosensitive material by an image recording apparatus using the above semiconductor laser, the semiconductor laser is optimally pulse-width modulated according to the density so that the color density of the photosensitive material becomes appropriate. The photosensitive material is irradiated with an exposure laser beam.

[0006]

However, as is well known, the semiconductor laser has a droop characteristic that the light output changes due to self-heating. That is, the semiconductor laser tends to decrease in light output as it generates heat. For example, as shown in FIG. 16, frequency 1000H
When the semiconductor laser is pulse-modulated with a pulse signal of z (1 ms repetition period) and a duty of 50%, the optical output near the falling edge is lower than the optical output near the rising edge of the pulse signal. This is because the amount of self-heating is larger near the fall of the pulse signal than when the pulse signal rises. Therefore, when the image recording apparatus is continuously operated, there is a problem that the finished state changes with time.

In order to solve this problem, temperature adjustment control may be performed to suppress the temperature change of the semiconductor laser, but it takes a long time for the effect of the temperature adjustment performed on the semiconductor laser to appear in the optical output. Since it takes time, it is not possible to adjust a subtle change in light output that occurs within a short time.

For example, when the main scanning of the laser beam is performed by rotating the polygon mirror as described above, if the semiconductor laser is modulated by exposing the photosensitive material with the same image data in one scanning, The temperature of the semiconductor laser rises due to self-heating in response to the pulse modulation in accordance with the image data, and the light output of the trailing edge of the photosensitive material after a predetermined time has elapsed compared to the leading edge of the photosensitive material in the main scanning direction decreases.
When an image is formed by exposing a photosensitive material that develops a low density when the exposure amount is small and a high density when the exposure amount is large to form an image, as shown in FIG. 17, one medium density (for example, gray) recording is performed. High density (for example, black) in the center of the image
When the image is recorded, the density of the area A ₁ recorded only with the gray image data in the main scanning direction and the density of the area A ₂ recorded with the gray image data after the black image data are recorded with the same image data. Nevertheless, the density is different, and the gray after black is lower. As described above, even if recording is performed with the same image data, there is a problem in that the optical output is different due to the self-heating of the semiconductor laser within one scan, and the image density is not optimal.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an image recording apparatus capable of obtaining stable image quality without density unevenness or color unevenness.

[0010]

In order to achieve the above object, the invention according to claim 1 is to provide a semiconductor laser for emitting a laser beam having an output according to a supply current, and a laser beam emitted from the semiconductor laser. Detecting means for detecting the output of, a scanning means for scanning a photosensitive material with a laser beam emitted from the semiconductor laser, and a pulse having a pulse width corresponding to image data representing the density of an image to be recorded on the photosensitive material. A pulse width modulation means for forming a signal and pulse width modulating a current flowing through the semiconductor laser based on the pulse signal; and based on the detected output when the photosensitive material is irradiated with a laser beam. Current supply means for supplying a current to the semiconductor laser so that the output of the laser beam applied to the photosensitive material becomes a predetermined value. It is equipped with a.

According to a second aspect of the present invention, a semiconductor laser for emitting a laser beam having an output according to a supply current,
Detection means for detecting an output of a laser beam emitted from the semiconductor laser, scanning means for performing main scanning of the laser beam emitted from the semiconductor laser and sub-scanning in a direction intersecting with the main scanning, and a photosensitive material. Based on the pulse signal, pulse signal forming means for forming a pulse signal having a pulse width corresponding to image data representing the density of an image to be recorded, current supplying means for supplying a constant current for energizing the semiconductor laser, And a modulation means for pulse-width-modulating the constant current supplied from the current supply means to the semiconductor laser, and the output of the laser beam applied to the photosensitive material based on the detected output reaches a predetermined value. And a correction unit that corrects the magnitude of the constant current supplied from the current supply unit.

According to a third aspect of the present invention, in the image recording apparatus according to the second aspect, the correcting means irradiates the photosensitive material based on the detected output before or after the start of the main scanning. A first correction unit that corrects the current supply unit so that the output of the laser beam is a predetermined value, and the photosensitive material is irradiated based on the detected output during one main scanning. Second correction means for correcting the current supply means so that the output of the laser beam becomes the predetermined value.

According to a fourth aspect of the invention, in the image recording apparatus according to the third aspect, the second correction means corrects the inside of the image recording area.

[0014]

In the image recording apparatus according to the first aspect of the invention, the scanning means scans the photosensitive material with a laser beam emitted from a semiconductor laser. This semiconductor laser outputs a laser beam according to the supply current, and the output of this laser beam is detected by the detection means.
The pulse width modulation means forms a pulse signal having a pulse width corresponding to image data representing the density of the image recorded on the photosensitive material. In addition, the pulse width modulation means performs pulse width modulation on the current flowing through the semiconductor laser based on the formed pulse signal. In this semiconductor laser, when the laser beam is applied to the photosensitive material by the current supply means, the output of the laser beam applied to the photosensitive material becomes a predetermined value based on the output detected by the detection means. Is supplied with current. Therefore, the light output of the laser beam emitted from the semiconductor laser is controlled to be constant, and the self-heating of the pulse width modulation of the semiconductor laser in order to develop the color of the photosensitive material at the density according to the image data causes self-heating Even if there is fluctuation, the light output of the laser beam is corrected to a predetermined value, so that the photosensitive material is irradiated with the laser beam having a stable light output.

The image recording apparatus according to the second aspect of the present invention comprises a scanning means, and the scanning means performs main scanning of the laser beam emitted from the semiconductor laser and sub-scanning in a direction intersecting with the main scanning. To do. The semiconductor laser is
A laser beam is output according to the supply current, and the output of this laser beam is detected by the detection means. A constant current flowing through the semiconductor laser is supplied to the semiconductor laser by the current supply means. The pulse signal forming means forms a pulse signal according to image data representing the density of the image recorded on the photosensitive material. Based on this pulse signal, the modulation means pulse-width modulates the constant current generated by the current supply means. Therefore, a constant current whose pulse width is modulated by the modulating means flows through the semiconductor laser, and the semiconductor laser emits a laser beam with an output according to the image data. The correction unit corrects the magnitude of the constant current supplied from the current supply unit so that the optical output of the laser beam applied to the photosensitive material becomes a predetermined value based on the output detected by the detection unit. Therefore, even if the optical output of the laser beam fluctuates by pulse-width-modulating the semiconductor laser in order to develop the color of the photosensitive material at a density according to the image data, the optical output of the laser beam emitted from the semiconductor laser is The photosensitive material is irradiated with a laser beam having a stable optical output because the photosensitive material is corrected to have a predetermined value.

Further, as in the invention described in claim 3, the first correcting means irradiates the photosensitive material on the basis of the detected output before or after the start of the scanning in the main scanning direction. The current supply means is corrected so that the output of the laser beam generated becomes a predetermined value, and the second correction means irradiates the photosensitive material based on the detected light output during one scanning in the main scanning direction. It is also possible to correct the current supply means so that the output of the laser beam becomes a predetermined value.
Further, the second correction means can also perform correction within the image recording area as in the invention described in claim 4. By doing so, the output of the laser beam emitted from the semiconductor laser is corrected for each main scanning and is also corrected to be a predetermined value even during one scanning in the main scanning direction. The photosensitive material is irradiated with a laser beam having a stable light output.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an image exposure apparatus 10 to which the present invention is applied.

The image exposure apparatus 10 includes a semiconductor laser 14
a, 14b and 14c. Each of the semiconductor lasers 14a, 14b and 14c is driven by a control device 40 (see FIG. 2) described later, and the semiconductor laser 1
4a emits a laser beam L1 in the infrared region having a wavelength of, for example, 670 nm, and semiconductor lasers 14b and 14c.
Is a laser beam L with wavelengths of 810 nm and 750 nm, respectively.
Inject 2, L3. Also, the laser beams L1 and L2
The wavelengths of L3 and L3 correspond to each color of magenta, yellow, and cyan that develops when the photosensitive material 36 is exposed. The laser beam L of these wavelengths
The semiconductor laser 14 which emits 1, L2 and L3 is very easily available.

A collimator lens 16a for converting the laser beam L1 into a parallel light beam is arranged on the laser beam emitting side of the semiconductor laser 14a, and the cylindrical lens 1 is spaced from the collimator lens 16a by a predetermined distance.
8a and a reflection mirror 20 are provided. Similarly, collimator lenses 16b and 16c are provided on the laser beam emitting sides of the semiconductor lasers 14b and 14c, respectively.
Cylindrical lenses 18b and 18c are provided at a predetermined distance from the collimator lenses 16b and 16c.

Dichroic mirrors 22a and 22b are arranged on the optical paths of the laser beams L2 and L3 which pass through the cylindrical lenses 18b and 18c. The reflection mirror 20 and the dichroic mirrors 22a and 22b have the same inclination angle, and the respective laser beams L1 and L2.
And L3 are guided to the same optical path 24. The dichroic mirror 22a transmits the laser beam L1 and reflects the laser beam L2. On the other hand, the dichroic mirror 22b has a function of transmitting the laser beams L1 and L2 and reflecting the laser beam L3.

Laser beam L reaching the same optical path 24
1, L2 and L3 are reflected by the reflection mirrors 26 and 28, and then enter the polygon mirror 30. The polygon mirror 30 rotates in the direction of the arrow, and the polygon mirror 30
The laser beams L1, L2, and L3 reflected by the laser beam pass through the fθ lens 32 and are reflected by the cylindrical mirror 34 for correcting the surface tilt, and are reflected on the photosensitive material 36 by the arrow A.
The main scanning is performed in the direction. The photosensitive material 36 is conveyed by a sub-scanning unit (not shown) so as to be conveyed in a sub-scanning direction (direction of arrow B) substantially orthogonal to the main scanning direction. As a result, an image is formed on the photosensitive material 36.

The semiconductor laser 14a is an anode common type semiconductor laser composed of a laser diode 13a and a photodiode 15a (see FIG. 2), and the laser diode 13a responds to a control signal from the control device 40 by a laser beam L1. And the photodiode 15a detects the optical output of the laser beam L1 emitted from the laser diode 13a. The semiconductor laser 14b is a cathode common type semiconductor laser including a laser diode 13b and a photodiode 15b, and the semiconductor laser 14c is a cathode common type semiconductor laser including a laser diode 13c and a photodiode 15c. These semiconductor lasers 14a, 14b, 14c,
That is, the laser diodes 13a, 13b, 13c and the photodiodes 15a, 15b, 15c are connected to the control device 40.

[Control Device] As shown in FIG. 2, the control device 40 includes a main control board (VEC board) 42 composed of a microcomputer having a central processing unit (CPU). The VEC substrate 42 is connected to a semiconductor laser drive substrate (LD substrate) 44 via a plurality of bus lines 62, 64, 66, 68 for inputting and outputting data and commands between each other. .
The VEC board 42 includes a storage device (not shown), and the storage device (not shown) stores image data corresponding to the density of an image supplied from another device, such as a host computer. . Also, VE
The C substrate 42 has semiconductor lasers 14a, 14b, 14
A thermistor (not shown) that measures the temperature of each of c and the receiver 202 of the ECL described later is connected via an analog-digital converter (not shown).

The LD substrate 44 is a gate array circuit (G /
A) 46, pulse width modulation circuits (PWM) 50, 52, 5
4, a laser drive circuit (LDD) 56, 58, 60, and a temperature control circuit (TEM) 48. PWM
50, 52, 54 and LDDs 56, 58, 60 are provided corresponding to the semiconductor lasers 14a, 14b, 14c. This PWM50 is LDD5 via the signal line 70.
6 and the PWM 52 is LDD via the signal line 72.
58 is connected to the PWM 54, and the LD 54 is connected to the LD via the signal line 74.
It is connected to D60. In addition, PWM50, 52, 5
4 and LDDs 56, 58, 60 are each G / A 46
In addition, a plurality of bus lines 76, 78, 80, 82, 84, 8 for inputting / outputting data and commands between each other.
It is connected via 6. Further, the temperature control circuit 48 is G
/ A46 via a bus line 88.

(G / A) As shown in FIG. 3, the gate array circuit (G / A) 46 is a laser power control for generating a control signal for controlling the output of the white signal processing circuit 102 and the semiconductor laser. It has a signal generation circuit 104 and a decoder circuit 106. The decoder circuit 106 includes an address decoder for performing address decoding, a data latch circuit for latching input / output laser power digital data, an input port and an output port.

The white signal processing circuit 102 is a synchronous processing circuit 12 corresponding to the semiconductor lasers 14a, 14b and 14c.
0, 122, 124, and each synchronous processing circuit 120, 122, 124 is composed of a logic circuit. Each of the synchronous processing circuits 120, 122, and 124 has a raster gate signal (signal name, RG1, RG2,
The VEC board 42 is connected so that RG3) is input. Further, the synchronization processing circuits 120, 122, 124
Are connected to PWMs 50, 52, 54 corresponding to the semiconductor lasers 14a, 14b, 14c, respectively.

Laser power control signal generation circuit 104
Is a signal (signal name, AP) according to the logic when controlling the output of one of the semiconductor lasers 14a, 14b, 14c.
1, AP2) are connected to the VEC board 42. This laser power control signal generation circuit 1
04 outputs the input signals (AP1, AP2) as signals (signal names, AP01, AP02, AP03) synchronized with the corresponding pixel clocks (GC1, GC2, GC3). The laser power control signal generation circuit 104 also generates the generated control signal (AP01, A
P02, AP03) are semiconductor lasers 14a, 14b,
14c is connected so as to be output to the PWM 50, 52, 54 corresponding to 14c.

The decoder circuit 106 is connected to the VEC board 42. In addition, the decoder circuit 106 is an LDD.
56, 58, 60 and the temperature control circuit 48 are connected.
The decoder circuit 106 includes semiconductor laser drive current control data and a semiconductor laser (photodiode).
Optical output data (signal name, DB) of the decoder circuit 106
A control command (signal name, CM) for controlling is input / output.

FIG. 7 shows a circuit example of the synchronization processing circuit 120 corresponding to the semiconductor laser 14a. The synchronization processing circuit 120 includes the VEC 42 and the PWM 50 as described above.
Connected with. It should be noted that PWM is applied to the synchronization processing circuit 120.
Details of the signal input from 50 will be described later, and the signal name is described in ().

The synchronization processing circuit 120 includes flip-flop circuits 130 and 132, and the flip-flop circuit 130 is connected to the AND circuit 136. The flip-flop circuit 132 receives the A signal via the OR circuit 134.
It is connected to the ND circuit 136. This AND circuit 13
6 is a signal output via the buffer (signal name, RG
01) is connected so as to be input to the PWM 50. As will be described later in detail, the signal RG01 is a signal including a pulse width portion for removing the pulse width corresponding to the white pixel. In addition, the flip-flop circuit 130
Is connected to the VEC 42 so that the raster gate signal (RG1) is input as input data via the buffer, and is connected to the PWM 50 so that the pixel clock (GC1) is input as a synchronization signal. This pixel clock (GC1) is also input to the flip-flop circuit 132 as a synchronization signal. Flip-flop circuit 13
Reference numeral 2 is connected to the PWM 50 so that a signal (/ FF1) corresponding to white image data is input as input data via a buffer. This AND circuit 134
Displays the pixel clock delay signal (GCS
1) is connected so as to be input.

Since the synchronization processing circuits 122 and 124 have the same structure as the synchronization processing circuit 120, their description is omitted.

(PWM) As shown in FIG.
0 includes a digital-analog (D / A) converter 216. The D / A converter 216 converts the 10-bit image data input from the VEC 42 into an analog signal. Further, the PWM 50 has a NAND circuit 218, and the D / A converter 216 is connected so that the image data input thereto is output to the G / A 46 via the NAND circuit 218. The NAND circuit 218 outputs a signal corresponding to white image data, that is, a low level signal when all the bits of the input image data are at a high level (signal name, / FF).
1) is output.

The D / A converter 216 includes a receiver 202.
The converter 212 for converting the ECL signal connected to the TTL signal to the TTL signal is connected, and the VEC 42 is connected to the receiver 202 so that the clock signal (pixel clock, signal name GC1) for each pixel which is the ECL signal is input. It is connected. Pixel clock (GC
1) is D through the receiver 202 and the converter 212.
It is used as a synchronization signal for the / A converter 216. Also,
The delay circuit 210 is connected to the G / A 46 via the converter 212, and the pixel clock (G
The TTL signal of C1) is delayed (signal name, GCS1) for a predetermined time in the delay circuit 210 and output to the G / A 46.

The receiver 202 is connected to one input side of a comparator 206 via an integrating circuit 204, and the comparator 206 receives a triangular wave signal waveform obtained by integrating the pixel clock (GC1). The D / A converter 218 is connected to the other input side of the comparator 206.
Is connected so that the output of is input.

The output side of the comparator 206 is connected to the gate circuit 208. The G / A 46 is connected to the gate circuit 208, and the signals RG01 and AP01 generated by the G / A 46 are input. Gate 20
The output side of 8 is connected to the LDD 56. Therefore, P
The pulse signal modulated according to the image data in the WM 50 is input to the LDD 56.

Since the PWMs 52 and 54 have the same structure, detailed description will be omitted. (LDD) As shown in FIG. 5, the LDD 56 includes a modulation circuit 302. The modulation circuit 302 is connected via a signal line 70 to the PWM 50 and the cathode of the laser diode 13a included in the semiconductor laser 14a. The modulation circuit 302 is a circuit (see FIG. 14) that switches and modulates the supply current to the laser diode 13a of the semiconductor laser 14a by a pulse signal input from the PWM 50 via the signal line 70.

The modulation circuit 302 includes a constant current circuit 304.
And via a digital-analog converter (D / A) 306 to the G / A 46. A current control signal (signal name, DATA1) of the semiconductor laser 14a is input to the D / A 306 from the G / A 46. The constant current circuit 304 and the D / A converter 306 include an off-surge countermeasure circuit 310 for suppressing a surge current when the power is cut off.
Are connected.

The constant current circuit 304 is a semiconductor laser 14a for automatic power control (APC control) so that a laser beam having a predetermined light output is emitted.
This is a circuit for supplying a constant current to the laser diode 13a (see FIG. 8). As is well known, the APC control is to drive the semiconductor laser 14a so that the standard optical output is obtained while monitoring the optical output by the photodiode 15a built in the semiconductor laser 14a.

A bias circuit 312 is connected to the output side of the modulation circuit 302.
A predetermined bias current generated by 12 is supplied. This bias current is for reducing a change in optical output (droop) due to self-heating of the semiconductor laser, and is adjusted to a predetermined current value regardless of the image recording area and the non-recording area.

The anode of the laser diode 13a is
It is connected to a 12V power line via an on-surge countermeasure circuit 308. The on-surge countermeasure circuit 308 is composed of a slow starter circuit having a predetermined time constant with a resistor and a capacitor and a three-terminal regulator (for example, 12 V is set to 5 V), and is supplied via the on-surge countermeasure circuit 308 when the power is turned on. The power supply is delayed by the time corresponding to the above time constant. Therefore, when the power of 12 V is turned on, the power supplied to the anode of the laser diode 13a (5 V in this embodiment) is delayed, which prevents a surge current from flowing through the semiconductor laser 14a. The anode of the laser diode 13a is connected to the cathode of the photodiode 15a.

The 12V power line is connected to the photocoupler 3
The photocoupler 318 is connected to the G / A 46 via 18, and outputs a high-level signal (signal name, LDSTS) to the G / A 46 when the 12V power is supplied.

The anode of the photodiode 15a is connected to an analog-digital converter (A / D) 316 via a current-voltage (I / V) conversion circuit 314 which converts an input current into a voltage and outputs the voltage. There is. This A / D3
16 is a control signal such as a control command or a flag (signal name,
Digital data signal (signal name, ADD1) for input / output of ADC1) and converted by A / D 316
Is connected to the G / A 46 so as to output.

Since the LDD 58 has a similar structure, a detailed description thereof will be omitted. Since the LDD 60 has a substantially similar structure, only different parts will be described below. The cathode of the photodiode 15b is connected to the cathode of the laser diode 13b, and the cathode of the photodiode 15c is connected to the cathode of the laser diode 13c.

As shown in FIG. 6, the modulation circuit 302 of the LDD 60 is connected via a signal line 74 to the PWM 54 and the cathode of the laser diode 13c of the semiconductor laser 14c. This laser diode 1
The cathode of the photodiode 15c is connected to the anode of 3c.

The anode of the photodiode 15c is I
It is connected to the A / D 316 via the / V conversion circuit 314. The A / D 316 is arranged to input / output control signals (signal name, ADC3) such as control commands and flags and output digital data signals (signal name, ADD3) converted by the A / D 316. It is connected to A46.

The semiconductor laser 14c used in this embodiment
In consideration of the large amount of droop (wavelength 750 nm), the LDD 60 includes a droop correction circuit 320 for correcting a change in optical output due to self-heating. The droop correction circuit 320 is connected so that the output signal of the I / V conversion circuit 314 is input, and the droop correction circuit 320 is connected so that the output signal is input to the constant current circuit 304. There is.

The droop correction circuit 320 is used for the LDD5 of all the semiconductor lasers 14a and 14b14c.
6, 58, 60 may be provided.

FIG. 14 shows a circuit example of the modulation circuit 302. The cathode of the laser diode 13a has a resistance of 1
It is connected to the collector of the transistor 150 via 57, and the emitter is connected to the constant current circuit 304 via the resistor 160. The base of the transistor 150 is connected to the PWM 50 so that a pulse signal for pulse-modulating the semiconductor laser is input, and is also connected to −5V via the resistor 162. Laser diode 13
The anode of a is connected to the on-surge countermeasure circuit 308 and is also connected to the collector of the transistor 152 via the resistor 156. The base of the transistor 152 is connected to −5V through the resistor 158, and the emitter is connected to the emitter of the transistor 150. The base of the transistor 152 is the base of the transistor 150.
The PWM 50 is connected so that the pulse signal, which is the inverted pulse signal supplied to the base of, is input. A condenser 154 is connected in parallel with the laser diode 13a. Therefore, the modulation circuit 302 can pulse-modulate the semiconductor laser by alternately switching the transistors 150 and 152 according to the pulse signal from the PWM 50.

FIG. 8 shows a circuit example of the constant current circuit 304 and the off-surge countermeasure circuit 310. Constant current circuit 304
Has a circuit for generating a constant current formed by the operational amplifier 340, the transistor 342, and the resistor 336. Further, the constant current circuit 304 is the subtraction operational amplifier 3
38 and a voltage-current (V / I) conversion operational amplifier 340. The signal output from the D / A 306 is input to the one input side of the subtraction operational amplifier 338 via the resistor 330. One input side of the subtracting operational amplifier 338 is connected to the output side via the resistor 331. The other input side of the subtraction operational amplifier 338 is grounded via the resistor 333 and also grounded via the resistor 332 and the Zener diode 344. Also, the resistor 332
The connection point between the zener diode 344 and the zener diode 344 is a resistor 335.
Is connected to a power source (-12V) not shown.

The output side of the subtracting operational amplifier 338 is V /
It is connected to one input side of the I conversion operational amplifier 340, and the other input side of the V / I conversion operational amplifier 340 is connected to the emitter of the transistor 342. The emitter of the transistor 342 is connected to the terminal TP1, and the terminal TP1 is connected to the terminal TP2 via the resistor 336. The base of the transistor 342 is connected to the output side of the V / I conversion operational amplifier 340 via the resistor 334, and the collector is connected to the modulation circuit 302. The base of the transistor 342 and the other input side of the V / I conversion operational amplifier 340 are connected via a diode 346.

The off-surge countermeasure circuit 310 includes a constant current shutdown circuit 322 and a DA shutdown circuit 32.
It is equipped with 4. The constant current shutdown circuit 322 is
The regulator 359 has a regulator 359.
The output side of is connected to the terminal TP2 of the constant current circuit 304. The input side of the regulator 359 is connected to the collector of the transistor 356. The base of the transistor 356 is connected to the transistor 35 via the resistor 355.
It is connected to 7 collectors. The emitter of the transistor 356 is connected to the base via the resistor 354, and is also grounded via the resistor 350 and the Zener diode 358. The emitter of the transistor 356 is connected to the base of the transistor 357 via the resistors 351 and 353, and the connection point of the resistors 351 and 353 is grounded via the resistor 352. Transistor 357
The emitter of is connected to the anode of the Zener diode 358. The emitter of the transistor 356 is connected to a power source (not shown) so that a negative power source of -12V is supplied.

The DA shutdown circuit 324 has a regulator 360, and the output side of the regulator 360 is connected to the D / A 306. Since the configuration is the same as that of the constant current shutdown circuit 322, the description is omitted.

FIG. 9 shows a circuit example of the I / V conversion circuit 314 and the droop correction circuit 320 shown in FIG. The I / V conversion circuit 314 has an operational amplifier 372 to form a current-voltage conversion circuit. The negative input side of the operational amplifier 372 is connected to the photodiode 15c, and a resistor 374 is connected to the input side and the output side of the operational amplifier 372. And a capacitor 373 are connected in parallel. This operational amplifier 37
The positive input side of 2 is grounded. The output side of the operational amplifier 372 is connected to the A / D 316 via the resistor 375.

The droop correction circuit 320 includes the operational amplifier 3
78, and the output signal from the I / V conversion circuit 314 is applied to the resistor 3 on the negative input side of the operational amplifier 378.
The analog switch 38 is connected to the input side and the output side of the operational amplifier 378.
5, resistor 383 and capacitor 384 are connected in parallel. The positive input side of the operational amplifier 378 is grounded via the resistor 380. In addition, the operational amplifier 37
The output side of 8 is a resistor 382, a variable resistor 381 and a resistor 32.
8 through the subtraction operational amplifier 338 of the constant current circuit 304
Is connected to the positive side of. Analog switch 3 above
Reference numeral 85 is connected to the output side of the AND circuit 386 so as to be controlled by the logical product of the signal (RG3) output from the VEC 42 and G / A (AP03).

(TEM) FIG. 10 shows a temperature control circuit (TE).
An example of the circuit configuration of M) is shown. This TEM controls the temperature by turning on and off the power transistor by utilizing the heat generated when the power transistor is energized. In this embodiment, a circuit for heating and stopping heating for adjusting the temperature of the receiver 202. TEM48 (Fig. 1
0 (1)), and the semiconductor lasers 14a, 1a
A circuit TEM49 (see FIG. 10 (2)) for applying strong heating, weak heating and stopping heating is applied to the temperature adjustment of 4b and 14c.

The TEM 48 includes a photocoupler 402, and one of the input sides of the photocoupler 402 has a resistor 40.
It is connected to a 5V power source through 1, and the other is connected so that a signal from the G / A 46 is input. One of the output sides of the photocoupler 402 is grounded, and the other is input to the plus side of the operational amplifier 404. This operational amplifier 404
The positive side of is connected to the analog 5V power source via the resistor 403. The output side of the operational amplifier 404 is a resistor 4
It is connected to the base of the power transistor 408 via 06, and the emitter of this power transistor 408 is connected so as to be input to the negative side of the operational amplifier 404. The emitter of the power transistor 408 is grounded via the resistor 410, and the power transistor 40
The collector of 8 is connected to the 24V power supply.

Therefore, from the G / A 46, this TEM48
When a high level signal is input to the photo coupler 40,
2 is turned off, and the input of the operational amplifier 404 becomes 5V. Therefore, due to the configuration of the operational amplifier, the power transistor 408, and the resistor 410, a constant current flows through the power transistor 408, and the power transistor 408 generates heat.

The TEM 49 is equipped with a photocoupler 412 composed of two elements. One of the input sides of each element is connected to a 5V power source via resistors 423 and 425, and the other end has an H terminal and an L terminal. Are connected so that different signals from the G / A 46 are input. This photo coupler 41
One of the two output sides is grounded, and the other one is a resistor 415,
It is connected to the analog 5V power source through 417.
The other output side of the photocoupler 412 has a resistor 4
It is connected so as to be input to the adding circuit 420 via 13 and 414 (plus side). A resistor 418 is connected in parallel to the output side and the minus input side of the adder circuit 420, and the minus input side is grounded via the resistor 416. The output side of the adder circuit 420 is the operational amplifier 42.
It is connected to the minus side of 2. The output side of the operational amplifier 422 is connected to the power transistor 426 via the resistor 424.
Of the power transistor 426, and the emitter of the power transistor 426 is connected to the negative side of the operational amplifier 422. In addition, the power transistor 42
The emitter of 6 is grounded through a resistor 428, and the collector of the power transistor 426 is connected to the 24V power source.

Therefore, from the G / A 46, this TEM49
The current output from the photocoupler 412 and input to the adder circuit 420 changes according to the signals input to the H and L ends of the, and the signal input to the adder circuit 420 increases or decreases. For example, when a high level signal is input to the H terminal of the TEM 49 and a low level signal is input to the L terminal, one of the photocouplers 412 turns on and the other turns off, and the operational amplifier 4
The voltage divided by the resistors 417 and 413 and the resistor 414 is input to the circuit 20. On the other hand, when a low level signal is input to the H terminal and a high level signal is input to the L terminal, the voltage division by the resistors 415, 414 and the resistor 413 is input to the operational amplifier 420. Therefore, due to the configuration of the operational amplifier 422, the power transistor 426, and the resistor 428, a constant current corresponding to the signal output from the adder circuit 420 flows in the power transistor 426, and the power transistor 408 heats strongly and weakly. Become.

(Operation of Embodiment) The operation of this embodiment will be described below. A power switch (not shown) is turned on,
Power is supplied to the control device 40. At this time, since power is supplied to each semiconductor laser via the on-surge 308, surge current is suppressed, and deterioration and destruction of the semiconductor laser are suppressed (see FIG. 5). Next, although details will be described later, a pulse signal having a pulse width corresponding to the image density is generated in the PWM 50 based on image data supplied from a storage device (not shown), and a signal modulated by this pulse signal is generated in the LDD 56. Semiconductor laser 1
4a is driven, and the laser beam L1 with a predetermined exposure amount is emitted from the semiconductor laser 14a. Similarly, PWM
LDD5 is generated by the pulse signals generated by 52 and 54.
The corresponding semiconductor lasers 14b and 14c are driven by the signals modulated by 8 and 60, and laser beams L2 and L3 having a predetermined exposure amount are emitted (see FIG. 2).
The laser beams L1, L2, L3 emitted from the semiconductor lasers 14a, 14b, 14c are mixed in the optical path 24, and the reflection mirrors 26, 28, the polygon mirror 30,
The photosensitive material 36 is irradiated with light through the fθ lens 32 and the cylindrical mirror 34. As a result, the photosensitive material 36
Is irradiated with a laser beam having an exposure amount corresponding to the image data, and a predetermined color density is obtained, whereby an image is formed (see FIG. 1).

Here, the control device 40 of this embodiment has an off-surge countermeasure circuit 310 in the laser drive circuit (LDD) for suppressing a surge current when the power is cut off.

As shown in FIG. 8, when the control device 40 is powered on, the constant current shutdown circuit 3 is provided.
At 22, the resistance 351 to the base of the transistor 357,
Current is supplied through the transistor 353, and the transistor 357 is turned on. Therefore, the resistor 355 is energized, the transistor 355 is turned on, and the power of -12 V is supplied to the regulator 359. The regulator 359 converts the input voltage of -12V into -8V and outputs it. Therefore, the voltage of the terminal TP2 becomes -8V. Similarly, in the DA shutdown circuit 324, a current is supplied to the base of the transistor 362 via the resistors 365 and 368, the transistor 362 is turned on, and the transistor 361 is turned on by energizing the resistor 369, so that the regulator 360
Power of 2V is supplied. Therefore, D / A306
A voltage of 8V is input.

In the constant current circuit 304, the APC control current data, which is the current value flowing from the VEC substrate 42 to the preset semiconductor laser, is converted into an analog value (for example, a voltage value) by the D / A 306. The converted output voltage and the Zener voltage (for example, -6.9 V) of the Zener diode 344 are input to the subtraction operational amplifier 338. The output voltage of the subtraction operational amplifier 338 is input to the operational amplifier 340, and the operational amplifier 3
A constant current circuit composed of 40, a transistor 342, and a resistor 336 converts the constant current. This constant current is supplied to the modulation circuit 302. Therefore, the terminal TP1 becomes the same level as the output voltage of the subtraction operational amplifier 338, and the terminal T1
Since the voltage of P2 is −8V, the current flowing through the resistor 336 is supplied to the modulation circuit 302 due to this potential difference.

The power supply of -12 V supplied to the constant current shutdown circuit 322 is lowered (for example, -10
V) Then, the resistances 351 and 353 of the transistor 357.
The bias condition due to is broken, and the transistor 357 is turned off. As a result, no voltage is output from the regulator 359, and the voltage of the terminal TP2 becomes indefinite. However, since the voltage of the terminal TP2 is connected to the terminal TP1 via the resistor 336, the voltage of the terminal TP2 becomes the terminal TP1. It fluctuates as it approaches. Therefore, the current supplied to the modulation circuit 302 decreases and fluctuates, so that the optical output of the semiconductor laser 14a does not exceed the rated value.

In this embodiment, the D / A 306 has
D having the same configuration as the constant current shutdown circuit 322
A voltage is supplied by the A shutdown circuit 324. Therefore, when the −12V power supplied to the DA shutdown circuit 324 drops, the voltage is not supplied to the D / A 306 and the output of the D / A 306 is stopped. Therefore, as for the voltage of the terminal TP1,
The voltage fluctuates in the voltage direction of 2. Therefore, the terminal TP
Since the voltage fluctuates in the direction in which the potential difference between 1 and the terminal TP2 decreases, the optical output of the semiconductor laser 14a does not exceed the rated value.

Therefore, a surge current does not flow through the semiconductor laser even when the power is turned off, such as when a power failure occurs or when the power switch of the control device is turned on and the power plug is removed. This makes it possible to suppress deterioration and destruction of the semiconductor laser. Therefore, in the image exposure apparatus, a slight fluctuation of the light output due to the deterioration of the semiconductor laser causes color unevenness and density unevenness, which makes it difficult to form a high-quality image. Since the deterioration can be suppressed, it is possible to continuously provide an image exposure apparatus having high image quality.

As the off-surge countermeasure circuit 310, the constant current shutdown circuit 322 and the DA shutdown circuit 324 are used to cut off the supply current to the semiconductor laser.
Even when either one of the D.22 and the DA shutdown circuit 324 is used, a sufficient effect can be obtained.

The color density of the photosensitive material 36 will be described with reference to FIG. The photosensitive material 36 has the minimum color density Dmin and the maximum color density Dmax, and has the characteristic of the color density D with respect to the exposure amount logE between these densities (see FIG. 15 (3)). Therefore, even if the photosensitive material 36 is irradiated with an exposure amount less than the minimum exposure amount Emin corresponding to the minimum color density Dmin, a desired color density cannot be obtained. Therefore, even if a signal having a pulse width corresponding to image data is generated, a predetermined exposure amount (minimum exposure amount Emin) is generated.
Coloring by the image data up to is not properly performed (see FIG. 15 (1)). Therefore, in the present embodiment, the pulse width of the pulse signal is set to 0 when the image density of the image data is minimum (for example, the designated density is 0). Further, in this embodiment, the pulse width corresponding to the image data for developing the color to the minimum density is made to correspond to the minimum exposure amount Emin. That is, the pulse width is set to 0 when the indicated density of the image data is the minimum value, and the pulse width is set to 15 nsec when the indicated density of the image data exceeds the minimum value. Therefore, the relationship between the image data and the exposure amount can be made to correspond to the optimum exposure amount except when the indicated density is 0 (FIG. 15).
(See (2)). As a result, an image having an optimum color density based on the image data is formed on the photosensitive material.

The pulse signal formation for modulating the optical output of the semiconductor laser according to the image data will be described in detail.

FIG. 11 shows the waveforms of signals at various points of the PWM 50. As shown in FIG. 4, the receiver 20
2, the pixel clock GC1 (FIG. 11 (1)) is VEC.
It is input from the substrate 42. The integrating circuit 204 integrates the pixel clock GC1 and outputs a triangular waveform signal 230 (FIG. 11 (3)). Image data (FIG. 11 (2)) is input to the D / A 216, and the D / A 216 outputs a voltage signal (FIG. 11 (3)) corresponding to the image data. The comparator 206 compares the signal 230 and the signal 232. The triangular wave signal 230 is the signal 232.
High level signal (Fig. 11 (4)) 23
4 is output. This signal 234 is image data for forming a white pixel (for example, 3 for 10-bit D / A).
FF) is included in the signal 236.

As image data, a logical product signal (/ FF, FIG. 11 (5)) by the NAND 218 is output to the G / A 46, and the G / A 46 outputs a signal RG01 (FIG. 11) which will be described later.
(6)) is formed and input to the gate circuit 208.
The gate circuit 208 uses the signal RG01 and the signal AP0.
1 (FIG. 11 (7)), the signal 236
A signal 238 (FIG. 11 (8)) gated with is output. Therefore, the signal 238 becomes only the signal of the pulse width corrected by the white signal by removing the signal 236 of the pulse width corresponding to the white pixel. This signal 238 is output to the LDD 50 via the signal line 70.

Next, the formation of the pulse signal (RG01) for the white signal correction will be described.

FIG. 12 shows signal waveforms at various points in the synchronization processing circuit 120 of the white signal processing circuit 102 in the G / A 46. As shown in FIG. 7, the synchronization processing circuit 1
In the flip-flop circuit 130 of 20, the input raster gate signal RG1 (FIG. 12 (1)) is synchronized with the rising edge of the pixel clock GC1 (FIG. 12 (2)) to form a signal. The signal (/ FF, FIG. 12 (5)) input to the flip-flop circuit 132 is also synchronized with the rising edge of the pixel clock GC1. This signal (/ FF)
Synchronized signal (Fig. 12 (6)) and pixel clock GC
1 is delayed by a predetermined time and the signal (/ GCS1, FIG. 12 (4)) and the logical OR signal (FIG. 12 (7)) by the OR circuit 134 are synchronized with the raster gate signal by the AND circuit 136. The logical product with RG1 is obtained, and the logical product output (FIG. 12 (8)) is output to the PWM 50.

As described above, the signal RG01 in which the raster gate signal RG1 for instructing image recording is synchronized with the pixel clock GC1 and the pulse width signal 236 (see FIG. 11) corresponding to the white pixel is removed is obtained. It is formed.

Therefore, since the signal 236 having the pulse width corresponding to the white pixel is removed during the modulation of the semiconductor laser, the optimum color reproduction can be realized without generating a weak light output. Further, even in the case of performing multiple exposure such as overlapping exposure of a plurality of images, fogging due to weak light can be prevented.

Further, in the present pulse width modulation, gradation resolution can be improved without the need to control the pulse width to the minimum or less. That is, since the pulse width corresponding to the image data for developing the minimum density corresponds to the minimum exposure amount, it is not necessary to control the short pulse width which is the exposure amount that does not develop the color of the photosensitive material, and the gradation The resolution can be increased.

As described above, the semiconductor laser is modulated by the signal having the pulse width according to the image data. Generally, the semiconductor laser has the droop characteristic, and the self-heating of the semiconductor laser during the pulse width modulation. Causes the light output to change. This change in light output due to self-heating cannot be controlled by temperature adjustment because the time constant is on the order of 100 μs. For example, when one scan is modulated with the same image data, the light output of the trailing edge is lower than that of the leading edge (the history of the preceding image is received). Therefore, the control device 40 of this embodiment includes the droop correction circuit 320.

In the droop correction circuit 320, as shown in FIG. 9, the photodiode 15 which has detected the light output (FIG. 13 (1)) emitted from the laser diode 13c.
The current output of c is converted into a voltage ((2) in FIG. 13) in the I / V conversion circuit 314 and is input. When the analog switch 385 is off, the droop correction circuit 320 inverts and amplifies the input signal by the operational amplifier 378, and integrates it according to the time constants of the resistor 383 and the capacitor 384. The integrated signal is attenuated by the variable resistor 381 ((3) in FIG. 13), and the constant current circuit 30
4 is output to the plus input side of the subtraction operational amplifier 338. Therefore, the subtraction operational amplifier 33 of the constant current circuit 304
The voltage on the positive input side of 8 is the Zener diode 344
The signal (FIG. 13 (4)) is obtained by adding the signal shown in FIG. 13 (3) to the voltage (-6.9V) limited by.

The analog switch 385 is a logical product of the raster gate signal RG3 and the signal AP03, that is, turned off in the image recording area and turned on in the non-image recording area. Therefore, in the non-image recording area, the reset state in which 0V is output from the droop correction circuit 320 is set. Therefore, when the droop correction is performed in each scan, the droop correction in the previous scan is affected. There is no.

As described above, since the current supplied to the semiconductor laser is corrected only for the time corresponding to the image recording area according to the optical output of the laser diode 13c detected by the photodiode 15c, 1 corresponding to the high level of the raster gate signal is obtained. During scanning, the light output of the semiconductor laser 14c can be corrected. Therefore, the image can be formed without deteriorating the image quality of the obtained image.

As a method of preventing image quality deterioration due to the influence of droop without adding a droop correction circuit, each semiconductor laser has a difference between the minimum pulse width and the maximum pulse width of the semiconductor laser for pulse width modulation. There is a method to change it depending on the amount of droop. That is, a semiconductor laser with a large amount of droop reduces the difference,
A semiconductor laser with a small amount of droop increases the difference. By doing so, the amount of droop can be made uniform, and an image with a small change in hue when forming a color image can be formed. Further, the semiconductor laser having a large difference between the minimum pulse width and the maximum pulse width has a large dynamic range.

In this embodiment, the case where an image is formed by using three semiconductor lasers has been described.
The number of semiconductor lasers is not limited, and the present invention may be applied to any one or more semiconductor lasers.

In the above embodiment, the case where an image is recorded as an image exposure device has been described, but it can be easily applied to a reading / reproducing device that obtains image information by using a photoelectric conversion element or the like.

Further, in the above embodiment, the optical output correction by the self-heating of the semiconductor laser is performed in an analog manner, but the pulse width for modulating the semiconductor laser may be changed and corrected. In this case, the pulse width can be changed by adding the correction amount based on the light output measured by the photodiode to the stored image data.

[0085]

As described above, according to the first aspect of the present invention, since the current is supplied to the semiconductor laser so that the output of the laser beam becomes a predetermined value, it is possible to stabilize the density and color. There is an effect that a captured image can be obtained.

According to the second aspect of the invention, during the main scanning and the sub-scanning crossing the photosensitive material, the output of the laser beam flows through the semiconductor laser so as to correspond to the image density recorded on the photosensitive material. Since the current is controlled, it is possible to irradiate the laser beam having a stable light output over the entire surface of the image to be recorded, and it is possible to obtain a stable image without density unevenness and color unevenness.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of an image exposure apparatus to which the present invention is applicable.

FIG. 2 is a block diagram showing an internal configuration of a control device of the image exposure apparatus of this embodiment.

FIG. 3 is a block diagram showing a configuration of a gate array circuit on an LD substrate.

FIG. 4 is a block diagram showing a configuration of a pulse width modulation circuit on an LD substrate.

FIG. 5 is a block diagram showing a configuration of a laser drive circuit for an LD substrate.

FIG. 6 is a block diagram showing a configuration of a laser drive circuit including a droop correction circuit of an LD substrate.

FIG. 7 is a block diagram showing an example of an internal configuration of a synchronization processing circuit.

8 is a circuit diagram showing an example of the configuration of the off-surge countermeasure circuit of FIG.

9 is a circuit diagram showing an example of the configuration of the droop correction circuit of FIG.

FIG. 10 is a circuit diagram showing an example of a configuration of a temperature control circuit of this embodiment.

11 is a diagram showing a time chart of each signal of the pulse width modulation circuit of FIG. 4. FIG.

12 is a diagram showing a time chart of each signal of the synchronization processing circuit of FIG.

13 is a diagram showing a time chart of each signal related to the droop correction circuit of FIG. 6. FIG.

14 is a circuit diagram showing an example of a configuration of the modulation circuit of FIG.

15 (1) is a diagram showing a relationship between image data and an exposure amount, FIG. 15 (2) is a diagram showing a relationship between image data and an exposure amount of this embodiment, and FIG. It is a diagram showing the relationship between the amount and the color density.

FIG. 16 is a diagram showing an optical output for explaining a droop characteristic of a semiconductor laser.

FIG. 17 is an image diagram showing a state of color density in a photosensitive material on which the same image data is recorded by a semiconductor laser having a droop characteristic.

[Explanation of symbols]

 10 image exposure device 14 semiconductor laser 13a laser diode 15a photo diode (detection means) 40 control device 50 pulse width modulation circuit 56 laser drive circuit 302 modulation circuit (pulse width modulation means) 304 constant current circuit (current supply means) 310 anti-surge measure Circuit 320 Droop correction circuit

Claims (4)

[Claims] 1. A semiconductor laser that emits a laser beam having an output according to a supply current, a detection unit that detects the output of the laser beam emitted from the semiconductor laser, and a laser beam emitted from the semiconductor laser. Scanning means for scanning the material, forming a pulse signal having a pulse width corresponding to the image data representing the density of the image to be recorded on the photosensitive material, the current flowing through the semiconductor laser based on the pulse signal pulse width A pulse width modulating means for modulating; and the semiconductor so that the output of the laser beam applied to the photosensitive material becomes a predetermined value based on the detected output when the laser beam is applied to the photosensitive material. An image recording apparatus comprising: a current supply unit that supplies a current to a laser. 2. A semiconductor laser that emits a laser beam having an output according to a supply current, a detection unit that detects an output of the laser beam emitted from the semiconductor laser, and a main of the laser beam emitted from the semiconductor laser. Scanning means for performing scanning and sub-scanning in a direction intersecting with the main scanning; pulse signal forming means for forming a pulse signal having a pulse width corresponding to image data representing the density of an image to be recorded on a photosensitive material; A current supply means for supplying a constant current for energizing the laser; a modulation means for pulse-width-modulating the constant current supplied from the current supply means based on the pulse signal to supply the semiconductor laser; From the current supply means so that the output of the laser beam applied to the photosensitive material based on the output thus obtained becomes a predetermined value. An image recording apparatus comprising: a correction unit that corrects the magnitude of a constant current supplied. 3. The correction means controls the current supply means so that the output of the laser beam applied to the photosensitive material becomes a predetermined value based on the detected output before or after the start of the main scanning. First correction means for correcting, and the current supply means so that the output of the laser beam applied to the photosensitive material on the basis of the detected output during one main scan becomes the predetermined value. The second correction means for correcting is provided.
The image recording device described in 1. 4. The image recording apparatus according to claim 3, wherein the second correction unit corrects the image recording area.