JPH07299930A - Electrophotographic recording apparatus - Google Patents

Abstract

PURPOSE:To sharply print a high-grade highly detailed image. CONSTITUTION:Power supply voltages V1, V2 (V1>V2) are provided and V1 is connected to the collector part C of a transistor 12 while V2 is connected to the anode part A of a diode 14. The base part B of the transistor 12 is connected to the output part of an one-shot pulse circuit 11. The one-shot pulse circuit 11 turns the transistor 12 ON for a definite time by the input of image data (0V in the presence of data). By this constitution, since the rising of the current I1 flowing to a laser diode main body 2 becomes one wherein the base current I1 of a transistor 13 is amplified by the current mu-factor (hFE) at the time of collector voltage V1, rising characteristics are enhanced as compared with a method wherein collector voltage V2 is fixed to be supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a semiconductor laser as a light source, scans a photosensitive recording medium with a laser beam modulated based on image information to form a latent image, and develops the latent image. The present invention relates to an electrophotographic recording device that forms a visible image by means of the above.

[0002]

2. Description of the Related Art FIG. 3 shows the structure of an optical system of a general electrophotographic recording apparatus. This type of electrophotographic recording apparatus includes a laser light emitting element that oscillates according to image information to be recorded, for example, a laser diode element 101, a collimator lens 102 that converts laser light from the laser diode element 101 into parallel beam light, A high-speed rotating polygon mirror (polygonal mirror) 103 for scanning, a laser beam scanned at a constant angular velocity by the polygon mirror 103 is converted into a laser beam scanning at a constant velocity on a photosensitive recording medium (hereinafter referred to as a photoconductor) 105. An F-θ lens 104 for conversion, a photoconductor 105 rotating at a constant speed, a reflecting mirror MR arranged in a scanning path of laser light, and a synchronizing member arranged at a position for receiving the laser light reflected by the reflecting mirror MR. It has a pin diode 106 and the like.

The image information is supplied as a signal in which the minimum unit pixel is converted into a binary signal of "white" and "black" and arranged in time. The laser diode element 101 is oscillated according to the image signal and generates an optical signal. This optical signal consists of an output signal for irradiating laser light and a non-signal without laser light. The laser light output from the laser diode element 101 based on the image signal is reflected by the polygon mirror 103 and scans the photoconductor 105 in the H direction (hereinafter referred to as the main scanning direction). On the other hand, since the photoconductor 105 rotates in the V direction (hereinafter, referred to as the sub-scanning direction), the surface of the photoconductor 105 is eventually scanned by the laser light one after another, and the latent image is formed on the surface of the photoconductor 105. An image is formed. That is, the photosensitive member 105 is uniformly charged by a charging unit (not shown) before scanning with the laser light, and the surface charge is removed only at the portion irradiated with the laser light, and the electrostatic latent image is removed. An image is formed. This latent image is developed by developing means (not shown),
Then, it is transferred onto a sheet of paper supplied so as to come into contact with the photoconductor 105, and the sheet becomes a sheet on which an image is printed through a fixing process.

In the above-mentioned latent image formation by laser light scanning, if the writing start position in the main scanning direction differs for each scan, it adversely affects image recording. Therefore, in order to prevent this influence, a pin diode 106 for synchronization is provided. ing. That is, the write start position for each main scan is determined from the output of the pin diode 106 for each scan by an electrical method with a certain delay. Here, the laser light output of the laser diode element 101 varies and is unstable even if the laser diode element 101 is driven by the same drive current due to variations in the temperature of the element itself or variations in the manufacturing stage. Therefore, in order to obtain a good print output, it is necessary to constantly monitor the laser light output of the laser diode element 101 and perform control so that the laser light output becomes constant. For this reason, a control means is conventionally provided. .

FIG. 4 is a diagram showing a main part of a conventional light output control circuit for stabilizing the laser light output of the laser diode element 101. In the figure, a laser diode element 101 is composed of a laser diode body 107 and a pin diode 108, and the pin diode 108 receives a laser beam from the laser diode body 107 and generates a current according to the laser light, thereby changing the voltage. Then, the laser light output is detected. The output from the pin diode 108 is input to the voltage comparator 109 and compared with the reference voltage V _S. The result of comparison by the voltage comparator 109 is
Input to the input port P2 of the CPU 110, and the CPU 11
0 recognizes the current laser light output. CPU 110
Based on the comparison result, the pulse width modulation (PWM) output output from the output port P1 is varied to control the laser light output to be constant. Pulse width modulation output is AND
The gate 113 performs a logical product with the image information, and the integrating circuit 111 converts the logical product into a voltage according to the pulse width modulation output.
According to this voltage, I ₁ ′ flows into the base portion of the transistor 112, and the collector current I ₁ amplified by the current amplification factor (h _FE ) of the transistor 112 flows into the laser diode main body 107, causing it to emit light. The laser light output of the laser diode body 107 is the pin diode 10
8, the laser light output is kept constant by the same control procedure.

[0006]

However, conventionally, the optical system means such as the laser diode element 101 and the polygon mirror 103 are often combined into one unit, and are not connected to the circuit board such as the optical output control circuit. In most cases, they are connected by wiring using the above. Therefore, a resistance component, a capacitance component, and an inductance component are generated in the laser diode light emission signal in the wiring or in the connection portion of the connector, and a rising phenomenon of the rising characteristic of the laser diode light emission signal occurs. This blunt phenomenon is caused by the laser diode body 1
This causes a delay in the time required for 07 to reach the threshold current value at which light emission starts. That is, the light emission timing of the laser diode body 107 is delayed due to the rounding phenomenon described above. By this, 1 pixel (dot)
The minute pixel data is reduced, and the print density of a high-definition image such as a thin line or a halftone becomes thin, or image blurring occurs. In addition, the edges of the image are blurred, and an image having no so-called edge effect is printed.

The present invention has been made to solve such a problem, and an object of the present invention is to clearly print a high-definition image such as a fine line or a halftone to print a high-quality image. It is to provide an electrophotographic recording device capable of

[0008]

In order to achieve such an object, a first invention (an invention according to claim 1) of the invention is to provide a laser light emission corresponding to one pixel of image information in the above-mentioned electrophotographic recording apparatus. When power is supplied to the means, a large amount of power is supplied until a predetermined time elapses from the start of the power supply. The second invention (the invention according to claim 2) is, in the electrophotographic recording apparatus described above, when supplying power to the laser emitting means corresponding to one pixel of image information, a predetermined time elapses from the start of the power supply. Until then, the first power supply voltage is applied to the laser emitting means, and when the predetermined time elapses, the application is switched to the second power supply voltage lower than the first power supply voltage. A third aspect of the invention (the invention according to claim 3) is that, in the electrophotographic recording apparatus described above, when power is supplied to the laser emitting means corresponding to one pixel of image information, a predetermined time has elapsed from the start of the power supply. Until then, a large current is supplied to the laser emitting means, and when the above-mentioned predetermined time elapses, the supply of the drive current is switched to the normal one.

[0009]

Therefore, according to the first aspect of the present invention, when power is supplied to the laser emitting means corresponding to one pixel of image information, a large amount of power is supplied until a predetermined time elapses from the start of the power supply, The light emission timing of the laser light from the laser light emitting means is advanced. Further, in the second invention, when power is supplied to the laser emitting means corresponding to one pixel of image information, a large voltage (first power supply voltage) is applied to the laser emitting means until a predetermined time elapses from the start of the supply of the power. When applied, the laser light emission timing of the laser light from the laser light emitting means is advanced. According to the third aspect of the invention, when power is supplied to the laser light emitting means corresponding to one pixel of image information, a large current is supplied to the laser light emitting means until a predetermined time elapses from the start of the power supply, and the laser light emitting means The light emission timing of the laser light becomes faster.

[0010]

EXAMPLES The present invention will now be described in detail based on examples. FIG. 1 is a diagram showing a main part of a light output control circuit in an electrophotographic recording apparatus showing an embodiment of the present invention. In this embodiment, the power supply voltages V ₁ and V having two different magnitudes are used.
₂ is provided (V ₁ > V ₂ ), V ₁ is connected to the collector portion C of the transistor 12, and V ₂ is connected to the anode portion A of the diode 14. The cathode portion K of the diode 14 is connected to the emitter portion E of the transistor 12, the collector portion C of the transistor 13 and one end of the resistor R ₂ . Since the power supply voltage V ₂ is lower than V ₁ , the diode 14 is inserted for the purpose of preventing reverse bias from V ₁ .

The base portion B of the transistor 12 has a resistor R
Delay circuit consisting of ₁ , capacitor C ₁ and buffer B ₁ ,
OR gate 9, AND gate 10 and NOT gate 8
Is connected to the output section of the one-shot pulse circuit 11. The one-shot pulse circuit 11 receives the image information (0 V with data) to input the transistor 1
It is a circuit that generates a pulse that turns on 2 for a certain time,
This fixed time is determined by the time delayed by the resistor R ₁ and the capacitor C ₁ . On the other hand, the transistor 13
The base portion B of is connected to the output portion of the integrating circuit 7 and receives the base current I ₁ ′ for controlling the laser light output constant from the integrating circuit 7. The input part of this integrating circuit 7 is
The output port P1 of the CPU 5 and the output portion of the AND gate 6 which performs a logical product of the image information inverted by the NOT gate 8 are connected.

[Basic Operation] In this optical output control circuit, the pulse width modulation output output from the output port P1 of the CPU 5 is effective only when there is image information (0V).
The integrating circuit 7 converts this pulse width modulation output into a voltage corresponding to the output, and changes the base current I ₁ ′ to the transistor 13 according to this voltage. The emitter portion E of the transistor 13 is connected to the anode of the laser diode body 2 of the laser diode element 1, and the collector current I ₁ is amplified by the current amplification factor (h _FE ) of the transistor 13.
Flow into the laser diode body 2 and cause it to emit light.
Here, the laser light output of the laser diode body 2 fluctuates even if the laser diode body 2 is driven with the same drive current due to the temperature of the element itself or variations in the manufacturing stage, and is unstable. Therefore, in order to obtain a good print output, it is necessary to monitor the laser light output of the laser diode body 2 and control the laser light output to be constant.

The control of the laser light output is performed as follows. The laser diode element 1 comprises a laser diode body 2 and a pin diode 3, and the pin diode 3 receives laser light from the laser diode body 2,
A current corresponding thereto is generated, and an optical output voltage is generated by the voltage division with the resistor R ₂ . This voltage is input to the voltage comparator 4 and compared with the reference voltage V _S. The comparison result is input to the input port P2 of the CPU 5, and the CPU 5 recognizes the current laser light output of the laser diode body 2. If the CPU 5 obtains the comparison result that the optical output voltage is lower than the reference voltage V _S, it recognizes that the laser light output is insufficient and increases the pulse width modulation output output from the output port P1. Thereafter, the laser light output is kept constant by the same control procedure.

[Characteristic Operation] Next, a characteristic operation of the light output control circuit will be described with reference to FIG. 2 showing voltage waveforms and current waveforms at main points. FIG. 2A is a voltage waveform diagram when there is data of one pixel (dot) of image information, and the data of one pixel is T _W.
It is given as a low pulse with the following time width. Figure 2
(A) is a high-voltage (V ₁ ) drive pulse input to the base portion B of the transistor 12, which is triggered by the falling of the low pulse shown in FIG. It is generated as a high pulse (+ 5V) having a time width of _d . Here, the time width T _d is the resistance R ₁ and the capacitor C ₁ of the one-shot pulse circuit 11.
The transistor 12 is turned on during this time width T _d , which is determined by the delay time due to As a result, the collector voltage of the transistor 13, which is the power supply voltage supplied to the laser diode body 2, has a voltage waveform as shown in FIG.

That is, the collector C of the transistor 13
In the section, the transistor 12 is turned on by the high pulse of FIG. 2A (point t ₁ shown in FIG. 2), so that the voltage of V _{1 in} the time width T _d (more precisely, there is a loss voltage of the transistor 12). , Which is slightly lower than V ₁ ). After that, when the transistor 12 is turned off (t ₂ point shown in FIG. 2), this collector voltage drops to V ₂ and image information disappears (t ₃ point shown in FIG. 2).
It drops to 0V. Thus, that power supply voltage supplied to the laser diode body 2 by switching the timing of t _2, the waveform of the current flowing through the laser diode body 2 becomes a waveform as shown in FIG. 2 (d). As shown in this waveform, the rise of the current I ₁ flowing through the laser diode body 2 depends on the base current I of the transistor 13.
Current gain in time collector voltages V ₁ and ₁ '(h _FE)
Since it is amplified by the collector voltage V ₂
The rising characteristic is improved as compared with the conventional method of supplying the fixed voltage (see the characteristic of the dotted line shown in FIG. 2D). Therefore, when the threshold current at which the laser diode body 2 starts emitting light is I _th , the collector voltage V ₂
The laser diode body 2 starts to emit light earlier than the fixed time by T ₁ time, and the emission time of one pixel (dot) can be lengthened.

In the above embodiment, when supplying power to the laser diode body 2 corresponding to one pixel of image information,
Although a large voltage is applied to the laser diode main body 2 until the time T _d elapses from the start of the power supply, the emission timing of the laser light from the laser diode main body 2 is advanced, but instead of applying a large voltage, a large voltage is applied. A method of supplying an electric current may be used. For example, in FIG. 4, a current amplifier is provided between the integrating circuit 111 and the transistor 112, and the timing and time for amplifying the current are set by the CPU.
When the power is supplied to the laser diode main body 101 corresponding to one pixel of image information, a large current is supplied to the laser diode main body 101 until a predetermined time elapses from the start of the power supply. ,
When the predetermined time has elapsed, the supply of the normal drive current is switched to.

[0017]

As is apparent from the above description, according to the present invention, when power is supplied to the laser emitting means corresponding to one pixel of image information, a large amount of power is supplied until a predetermined time elapses from the start of the power supply. Since the laser light is supplied and the emission timing of the laser light from the laser emitting means is advanced, it is possible to clearly print a high-definition image such as a fine line or a halftone, and to print a high-quality image.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of a light output control circuit in an electrophotographic recording apparatus showing an embodiment of the present invention.

FIG. 2 is a diagram showing voltage waveforms and current waveforms at main points in this optical output control circuit.

FIG. 3 is a diagram showing a configuration of an optical system of a general electrophotographic recording apparatus.

FIG. 4 is a diagram showing a main part of a conventional light output control circuit.

[Explanation of symbols]

1 ... Laser diode element, 2 ... Laser diode body, 3 ... Pin diode, 4 ... Voltage comparator, 5 ... CP
U, 6 ... AND gate, 7 ... Integrator circuit, 8 ... NOT gate, 9 ... OR gate, 10 ... AND gate, 11 ... One-shot pulse circuit, 12, 13 ... Transistor, 14
…diode.

Claims (3)

[Claims] 1. A laser emitting means, a driving means for driving the laser emitting means by image information, a photosensitive recording medium on which a latent image is formed by laser light from the laser emitting means, and the laser light In an electrophotographic recording apparatus provided with a scanning means for scanning a photosensitive recording medium, when power is supplied to the laser emitting means corresponding to one pixel of image information, a large amount of power is supplied until a predetermined time elapses from the start of the power supply. An electrophotographic recording apparatus comprising a large power supply means for supplying power. 2. A laser emitting means, a driving means for driving the laser emitting means by image information, a photosensitive recording medium on which a latent image is formed by laser light from the laser emitting means, and the laser light In an electrophotographic recording apparatus provided with a scanning means for scanning on a photosensitive recording medium, when power is supplied to the laser emitting means corresponding to one pixel of image information, the power is supplied until a predetermined time elapses. A power supply voltage switching means is provided for applying a first power supply voltage to the laser emitting means and switching to application of a second power supply voltage lower than the first power supply voltage when the predetermined time has elapsed. Electrophotographic recording device. 3. A laser emitting means, a driving means for driving the laser emitting means by image information, a photosensitive recording medium on which a latent image is formed by laser light from the laser emitting means, and the laser light In an electrophotographic recording apparatus provided with a scanning means for scanning on a photosensitive recording medium, when power is supplied to the laser emitting means corresponding to one pixel of image information, the power is supplied until a predetermined time elapses. An electrophotographic recording apparatus comprising: a current switching unit that supplies a large current to a laser emitting unit and switches to a normal driving current when the predetermined time has elapsed.