JPH0411864B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus having a switching regulator type high pressure generating device.

Generally, a self-excited inverter as shown in FIG. 1 is often used in a switching regulator type high voltage power supply. This method has features such as a simple circuit configuration, good starting characteristics, and the ability to omit the base winding, but since it is a self-excitation type, the oscillation frequency depends on various conditions such as the transformer core, windings, and saturation magnetic flux. If the device coexists with a digital device, the digital control clock pulse and the oscillation pulse of the inverter will coexist. In particular, spike voltage is a cause of pulse noise, and when multiple such switching regulators are operated at the same time, pulse nozzles with miscellaneous frequencies are generated due to changes in the oscillation frequency of each one, which can cause malfunctions. Become.

An image forming apparatus such as a copying machine is known as an apparatus using such a switching type high voltage power supply. Among such devices, one is known that detects the amount of charge such as the surface potential of a photoreceptor and controls the charging output.

However, in such a case, the detection output signal is weak, so if the above-mentioned noise occurs when detecting the amount of charge, accurate detection of the amount of charge and charge output control cannot be performed.

The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus equipped with a switching type high-voltage power supply, in which noise countermeasures can be easily taken. Specifically, the present invention includes a plurality of high voltage generating means including a transformer and generating a high voltage output on the secondary side of the transformer by switching the primary side of the transformer, and a plurality of high voltage generating means generating high voltage output from one of the high voltage generating means. In an image forming apparatus, the image forming apparatus includes a charging means that charges a photoreceptor by being supplied with a high voltage output, and a developing means that is biased by being supplied with a high voltage output generated from another high voltage generating means, wherein charging by the charging means is performed. A detection means for detecting the amount as a potential, an A/D conversion means for converting the output of the detection means into a digital signal, and a predetermined calculation based on the digital signal from the A/D conversion means to determine the amount of charge appropriately. a microcomputer that obtains control data for converting into an analog signal; a D/A converter that converts the control data outputted from the microcomputer into an analog signal; based on the analog signal output from the D/A converter,
a driving means for driving the high voltage generating means for the charging means and the developing means, and the microcomputer performs a control operation based on a first clock signal, and is further synchronized with the first clock signal. A second clock signal having a lower frequency than the first clock signal is output to the high voltage generating means, and the high voltage generating means switches the primary side of the transformer based on the second clock signal. The purpose is to provide an image forming apparatus that

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. The latent image surface potential measured by the surface electrometer 1 and the potential measuring circuit 2 is converted into a digital value by the A/D converter 3, and a predetermined calculation is performed by the microcomputer (hereinafter referred to as microcomputer) 4 to determine the bright area potential. , calculate the primary, secondary and charging current values and the optimum developing bias value for the light potential of standard white light in order to bring the dark potential closer to a predetermined target value, respectively, and perform D/A conversion for each with the D/A converter 5. Regarding primary and secondary charging, the high voltage drive circuits 6 and 8 drive the high voltage transformers of the primary high voltage power source 7 and secondary high voltage power source 9, and charge the primary charger 16 and secondary charger 17. Pass current. Regarding the development bias, the development bias drive circuit 10 drives the development bias high-voltage power supply 11 to apply a predetermined bias to the development roller 18 for control. Also, as shown in Figure 3, the microcomputer's crystal oscillation clock CLK ₁
For example, the inverter oscillation clock pulse CLK ₂ , which is generated by processing on software, is output from the microcomputer 4 to the buffer circuit 12 so as to alternately repeat the "H" level and "L" level by counting a predetermined number of times. , the clock pulse _CLK2 is sent to the subsequent drives 13-15. Drive circuits 13 to 15 are high voltage power supplies 7, 9, and 1, respectively.
A base current sufficient to turn on one oscillation transistor is supplied to the high voltage power supply.

The detailed configuration will be explained by taking the high voltage primary power supply section shown in FIG. 4 as an example. The oscillation clock _CLK from the microcomputer 4 is buffered by the buffer circuit 12 and the transistor in the drive circuit 13.
Turns Tr ₁ and Tr ₂ on and off alternately. transistor
A drive pulse having sufficient drive power to drive the switching transistors Tr ₃ and Tr ₄ of the high voltage power supply 7 can be obtained as the output of the drive pulse generating inverter composed of Tr ₁ , Tr ₂ and transformer T ₁ . The voltage induced on the primary side of the transformer T ₂ in response to the high-voltage primary control voltage applied to the transformer T ₂ is boosted to the secondary side voltage determined by the turns ratio of the transformer T ₂ and then the voltage is applied to the diode D ₁ and the capacitor. It is rectified and smoothed by C ₁ and supplied to the primary corona charger 16 . High pressure 2
Next, a similar configuration is used for the developing bias.

Note that it is conceivable that transistors Tr _{3 and Tr 4 may} become conductive at the same time due to the difference in speed when switching from on to off or from off to on, but according to the present invention, For example, since the timing at which the inverter oscillation clock pulse is output can be changed by a program, the duty ratio can be controlled very easily and this problem can be prevented.

Furthermore, the oscillation of the inverter itself can be controlled by turning on and off the inverter oscillation clock on the microcomputer side.

As described above, according to the present invention, a high voltage output is supplied to the charging means using a low frequency clock signal that is synchronized with a clock signal for operating the microcomputer that controls the charging means based on the detected output of the amount of charge. Since the primary side of the transformer of the high voltage generating means is switched, the frequency component of the spike noise is synchronized with the clock signal of the microcomputer, making it easier to take measures against noise. Furthermore, the timing of switching can be changed as desired by the program.

[Brief explanation of drawings]

Fig. 1 is a high voltage power supply circuit diagram having a self-excited inverter, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 shows the relationship between the microcomputer driving clock CLK ₁ and the inverter oscillation clock CLK ₂ . The time chart, FIG. 4, is a detailed configuration diagram of a part of FIG. 2. 1 is a surface electrometer, 2 is a potential measurement circuit, and 3 is an A/
D converter, 4 is a microcomputer, 5 is a D/A converter,
6 and 8 are high voltage drive circuits, 7 is a primary high voltage power supply,
9 is a secondary high-voltage power supply, 10 is a developing bias drive circuit, 11 is a high-voltage power supply for developing bias, 12 is a buffer circuit, 13 to 15 are drive circuits, 16 is a primary charger, 17 is a secondary charger, and 18 is a It is a developing roller.

Claims (1)

[Scope of Claims] 1. A plurality of high voltage generating means including a transformer and generating high voltage output on the secondary side of the transformer by switching the primary side of the transformer, a high voltage output generated from one of the high voltage generating means. In an image forming apparatus, the image forming apparatus includes: a charging means that charges a photoreceptor by being supplied with electricity; a developing means that is biased by being supplied with a high voltage output generated from another high voltage generating means; A/D conversion means for converting the output of the detection means into a digital signal; and for optimizing the amount of charge by performing a predetermined calculation based on the digital signal from the A/D conversion means. a microcomputer that obtains control data for the charging means; D/A conversion means for converting the control data outputted from the microcomputer into an analog signal; a drive means for driving a high-pressure generating means for a developing means, the microcomputer performs a control operation based on a first clock signal, and is further synchronized with the first clock signal and configured to control the microcomputer based on the first clock signal. An image forming apparatus characterized in that a second clock signal having a lower frequency than the second clock signal is output to the high voltage generating means, and the high voltage generating means switches the primary side of the transformer based on the second clock signal.