JPS62279779A - Writing device for laser printer - Google Patents

Abstract

PURPOSE:To obtain a writing device for a laser printer with low cost, and easy to control, by changing the duty of modulation corresponding to write density. CONSTITUTION:The on/off time of a laser LD can be selected, and the duty of the modulation can be changed by controlling the charge/discharge time of a capacitance C by a transistor(TR)Q2. In other words, a modulation signal is supplied to the base of the TRQ2, and the laser LD is turned on and off by the terminal voltage of the capacitance C. Also, an image frequency is changed according to the write density, and the value of the capacitance C is changed according to the image frequency. Therefore, correspondence to the write density can be performed by providing a switch SW between the anode and the cathode of the laser LD, and switching arbitrarily capacitances C1-C3. The writing device for the laser printer constituted in such way can be manufactured at low cost, and is easy to be controlled.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Technical Field) The present invention relates to a writing device for a laser printer, and more specifically can be applied to a recording device that records an image by modulating a semiconductor laser. The present invention relates to a writing device for a laser printer.

(Prior Art) Conventionally, writing system modulators for laser printers, laser copying machines, and the like are generally configured to have a fixed modulation waveform and a constant modulation duty. An example of such a conventional device will be explained based on the circuit shown in FIG. In the figure, 1 is a digital/analog (D/A) converter, 2
is an amplifier, Ql and Q2 are transistors, LD is a semiconductor laser, PD is a photodiode, 3 is an amplifier, 4 is a comparator, and 5 is a control section.

In the above configuration, the control section 5 outputs a power set signal to set the power of the semiconductor laser LD, and turns on the semiconductor laser LD. After turning on the semiconductor laser LD, the 8-bit digital output is counted up and the D/D output is counted up.
Output to A converter 1. The analog output of the D/A converter 1 changes depending on the value of the digital input, and the base current of the transistor Q1 increases via the amplifier 2. When the base current increases, the operating current of the semiconductor laser LD increases. p
increases, and the power of the semiconductor laser LD increases.

The laser light from the semiconductor laser LD is transferred to the photodiode P.
D, and this signal is amplified by amplifier 3. The amplifier 3
When the output reaches the set voltage of the comparator 4, a signal is input to the control unit 5, indicating that the semiconductor relay IJ''LD has the predetermined power, and this stops the count of the 8-bit digital output and completes the power set. After this, the printer becomes ready and can perform recording by exposing the photoreceptor with laser light according to the modulation signal.

The relationship between the modulation signal and the lighting time of the semiconductor laser in such a conventional device is shown in a waveform diagram as shown in FIG. In the figure, ■ is the waveform of the modulation signal of the transistor Q2 in FIG. 7, and ■ is a waveform showing the on-off state of the semiconductor laser LD. As is clear from the figure, the modulation signal and the lighting time of the semiconductor laser LD are the same. In this way, in conventional devices, the modulation waveform is generally fixed, so if the writing density of the laser beam on the recording medium differs, a different unit must be provided for each writing density, which reduces costs. It has the disadvantage that it increases in size and is difficult to manage.

(Purpose) The present invention was made to eliminate the above-mentioned drawbacks of conventional devices, and its purpose is to make it possible to change the modulation duty in the same unit according to the writing density even if the writing density is different. An object of the present invention is to provide a writing device for a laser printer.

(Structure) In order to achieve the above object, the present invention provides a writing device for a laser printer that uses a transistor that turns on and off between the anode and cathode of a semiconductor laser, in which the duty of modulation is made variable according to the writing density. This is a characteristic feature.

Hereinafter, a detailed description will be given based on an embodiment of the present invention.

First, the overall configuration of a printer to which the laser printer writing device of the present invention is applied will be briefly described with reference to FIG. In the figure, 6 is a paper feed tray, 7 is a paper feed section, 8 is a photoreceptor belt magazine, 9 is a charging section, 10 is an optical writing section, 11 is a toner cartridge, 12 is a developing section, 13 is a transfer section, 1
4 is a fixing section, 15 is a static eliminating section, 16 is a cleaning section, 1
Reference numeral 7 designates a paper discharge section, 18 a paper discharge stacker, 19 a power supply (main body controller), 20 a fan, 21 a sequence printer circuit board, 22 a controller printed circuit board, and 23 a photoreceptor mark sensor. The printer with the above configuration has a so-called face-down configuration in which paper is ejected with the printed side facing downward, and the photoreceptor belt magazine 8, which has been charged and made photosensitive, is ejected with an optical image from the optical writing unit 10. An electrostatic latent image is formed by exposure, and this electrostatic latent image is developed in a developing section 2. The developed image is transferred by the transfer section 13 to paper fed from the paper feed section 7, and the transferred image is fixed in the fixing section 14. Thereafter, the transferred and fixed paper is discharged to the upper part of the printer by the paper discharge section 17 and stacked on the paper discharge stacker 18.

Next, the principle of the present invention will be explained with reference to the circuit shown in FIG. Figure 2 is a circuit diagram showing only the main parts of the modulation system, where Q is a transistor, LD is a semiconductor laser, 2 is an amplifier, Q,
C is a transistor that turns on and off between the anode and cathode of the semiconductor laser LD, and C is a capacitor. In this method, the duty of the light emitting time of the semiconductor laser LD is changed depending on whether it is on or off. In this method, the operating voltage V of the semiconductor laser. , is about 2 volts,
The semiconductor laser LD is turned on or off at the operating voltage VOP depending on the charging/discharging time of the capacitor C. In Fig. 2, ■ indicates the modulation signal, and ■ indicates the operating voltage V6F. In this case, the relationship between the modulation signal ■, the operating voltage ■, and the on/off of the semiconductor laser is as shown in the waveform diagram shown in Fig. 3. , L.D.
The on and off waveforms of the semiconductor laser are shown.

In the circuit described above, when considering the writing density, the writing density is 240DPI and 300DPI.

There are 400 DPI, etc., and the image frequency differs depending on each of these writing densities, and the value of the capacitor C in FIG. 2 changes accordingly.

In order to cope with these changes in writing density, the circuit shown in FIG. 4 will be described. Similar to the circuit shown in FIG. 2, 2 is an amplifier, Q is a transistor, LD is a semiconductor laser, and Q! is a transistor that turns on and off between the anode and cathode of the semiconductor laser LD. Note that ■ in the figure indicates a modulation signal.

Three capacitors CI, Cz, and C3 are arranged between the anode and cathode of the semiconductor laser LD and can be arbitrarily switched by a changeover switch SW. According to this circuit, the value of the capacitor can be changed according to the image frequency, which differs depending on the above-mentioned writing densities, so that one unit can correspond to any of the three writing densities. For example, writing density 240DPI
So the capacitor value is 2200PF and the image frequency is 2.
At 6MHz and writing density of 300DPI, the capacitor value is 1500PF and the image frequency is 4.0MHz.

Similarly, at a writing density of 4000 PI, the capacitor value is 1000 PF and the image frequency is 7.2 MHz, so the capacitors C1, C2, and C3 in the circuit of Figure 4 are replaced by C+-2200 PF, , c, -1500 PF, and C.
If set to s-1000PF', capacitors 01 to C3 are changed by switch SW according to the change in writing density.
The on/off time of the semiconductor laser LD can be selected by switching, and the duty of modulation can be changed.

In the modulation method using the circuit described above, the image is where the semiconductor laser LD is off, but there is no problem even if the image is where the semiconductor laser is on.

Next, another embodiment of the writing device for a laser printer according to the present invention will be described with reference to FIG. In the figure, Q is a transistor, C2 is a transistor that turns on and off between the anode and cathode of the semiconductor laser LD, ■ is a modulation signal, C4 and R are a capacitor and a resistor that constitute the CR time constant circuit, 6 is a comparator, and A -C are DPI setting circuits each consisting of a transistor and a resistor.

The method of changing the duty in this embodiment is as follows:
A CR time constant circuit is inserted into the circuit, and the output thereof is compared with a comparator 6 having an arbitrarily set value, thereby controlling the time for controlling the transistor Q2. According to this embodiment, the on/off time of the semiconductor laser LD can be freely controlled by simply electrically setting the setting signals of the DPI setting circuits A to C.

FIG. 6 shows the turning on of the semiconductor laser LD by the circuit of FIG.
It is a waveform diagram showing the relationship between the off time and the setting signals of the DPI setting circuits A-C, and in the figure, A and B.

C indicates a DPI setting signal.

In this embodiment as well, like the embodiment shown in FIG. 4, the on/off state of the semiconductor laser LD can be freely controlled by the signal from the DPI setting circuit, so the duty can be changed with one unit.

(Effects) As described above, according to the present invention, the duty of modulation is made variable according to the writing density, thereby eliminating the inconvenience of having to provide a separate unit for each different writing density as in the past. It is possible to provide a writing device for a laser printer that is low in cost and easy to manage, even though the performance of the writing device is greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the overall configuration of a printer to which a writing device for a laser printer according to the present invention is applied, FIG. 2 is a circuit diagram of main parts showing the principle of the present invention, and FIG. 3 is the circuit of FIG. 2. FIG. 4 is a schematic circuit diagram showing an embodiment of the writing 'AX' of the laser printer according to the present invention, and FIG. 5 is a waveform diagram showing the relationship between the modulation signal and the lighting time of the semiconductor laser in accordance with the present invention. 6 is a waveform diagram showing the relationship between the on/off time of the semiconductor laser and the setting signal of the DPI setting circuit according to the circuit shown in FIG. 5, FIG. 7 is a circuit explaining the conventional device, and FIG. 7 is a waveform diagram showing the relationship between the modulation signal and the on/off time of the semiconductor laser in the circuit of FIG. 7. FIG. LD...Semiconductor laser, Qt...Transistor, C
2C+, Cz, C3... Capacitor, C4...
Capacitor, R...Resistor, 6...Comparator. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 0 Figure 6 ABCCBA ABC

Claims (3)

[Claims] (1) A writing device for a laser printer using a transistor that turns on and off between the anode and cathode of a semiconductor laser, characterized in that the duty of modulation is made variable according to the writing density. (2) The modulation duty is changed by a plurality of capacitors inserted between the cathode and anode of the semiconductor laser, and the on-off time of the semiconductor laser is changed by selecting these capacitors. A writing device for a laser printer according to claim (1). (3) The change in the modulation duty is controlled by a CR time constant circuit and a comparator that compares the output of this CR time constant circuit to control the time that controls the transistor that turns on and off between the anode and cathode of the semiconductor laser. A writing device for a laser printer as set forth in claim (1), wherein