JPH0222680A - Developing bias circuit - Google Patents

Abstract

PURPOSE:To detect an abnormal output voltage by means of the simple configuration of a circuit by comparing a voltage detected by means of a voltage detecting means with a duty instructed by means of a control means. CONSTITUTION:A voltage Vd divided by registers 26 and 27 is fed back to the voltage input terminal 20b of a CPU 20. The CPU 120 compares the feedback voltage Vd with the duty instruction outputted from the terminal 20a; when the device is normal, a pulse width and bias voltage Vb are regularly accorded with each other; when they are not accorded with each other, the CPU judges that the bias voltage is abnormal because of some reason, and turns off the bias voltage; on a display part it then displays the information about abnormality. A circuit abnormality is detected through the comparison of the bias voltage with the duty given to a pulse circuit; therefore, a developing bias circuit capable of detecting an abnormal bias voltage is obtained by means of the simple configuration of the circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a developing bias circuit for an electrophotographic copying machine, etc., and more particularly to a developing bias circuit that can easily detect abnormalities in the bias voltage of the developing bias circuit. .

(Background of the Invention) FIG. 2 is a block diagram schematically showing the structure of an electrophotographic copying machine. In this figure, 1 is a drum on which a toner image is formed;
2 is a charging electrode that uniformly charges the drum 1 by corona discharge; 3 is a charge erasing unit (CEL) that erases the 10 charges with light to prevent toner from adhering to the non-image area of the drum 1;
Reference numeral 4 denotes an exposure means for irradiating the drum 1 with light according to the original to form an electrostatic latent image corresponding to the density of the original. 5
6 is a developing device for forming a visible toner image on the electrostatic image formed on the surface of the drum 1, and 6 is a developing device that irradiates light onto the drum 1 to improve toner transfer efficiency and paper separation efficiency. The pre-transfer exposure area (PTL) lowers the surface potential by
), 7 is a transfer pole that transfers the toner on the drum to paper by corona discharge, 8 is a separation pole that separates the paper that is in close contact with drum 1 by AC discharge, and 9 is drum 1
a transfer paper conveying section for conveying the paper separated from the paper;
is a fixing section that fuses the toner to the paper using heat and pressure. 11 is a sensor for detecting paper wrapping around the drum 1 (jam), and 1 to toner control chart reading sensor for reading the image density of the toner control chart developed on the drum 1 and keeping the toner density constant. This is a tonacon/jam detection sensor section consisting of the following.

Reference numeral 12 denotes a cleaning section that removes residual toner on the drum 1 with a blade, and reference numeral 13 denotes a pre-charging exposure device (PCL) that irradiates the entire surface of the drum 1 with light to erase residual potential in preparation for the next copy.

On the drum 1, the portion corresponding to the blank paper (white background) of the original should have an electric charge of O due to exposure. However, in reality, some positive charge remains. As a result, toner adheres to portions of the document that correspond to blank pages, causing so-called fogging. In order to prevent this fogging, a positive voltage having a characteristic opposite to that of the toner is applied between the drum 1 and the developing sleeve of the developing device 2. This positive voltage is called a developing bias voltage (or simply a bias voltage). Depending on the level of this bias voltage, it is possible to control the crushing of toner adhering to the drum surface. Therefore, when the bias voltage is high, the amount of toner adhering to the drum surface decreases, and the toner becomes lighter. Conversely, when the bias voltage is low, the amount of toner adhering to the drum surface increases, and the amount of toner becomes dense.

This bias voltage varies depending on the model, but it is around +400V DC for light copying, around +280V DC for dark copying, and around +180V DC for dark copying.

Such a bias voltage is obtained by rectifying and smoothing an alternating current voltage produced by an inverter.

(Problems to be Solved by the Invention) There are many parts at ground potential near the developing bias voltage output, and there is a risk that the bias voltage may cause a ground fault. This causes a problem that the bias voltage fluctuates and the copy density changes.

In conventional devices, an abnormality in the output voltage is detected by detecting the output voltage and comparing it with a reference voltage. This conventional method requires a circuit to create a reference voltage. Therefore, the circuit configuration becomes complicated and the mounting space also increases.

The present invention has been made in view of the above-mentioned problems, and its purpose is to solve the problems described above. An object of the present invention is to realize a developing bias circuit capable of detecting an abnormality in the output voltage with a simple circuit configuration.

(Means for Solving the Problems) The present invention for solving the above problems is a developing bias circuit that applies a bias voltage between a photosensitive drum of a copying machine and a developing sleeve of a developing device, and generates a pulse signal. a control means for instructing the pulse duty to the pulse generating means, a boosting means for boosting the pulse signal from the pulse generating means, and a boosting means for rectifying the boosted pulse signal to generate high voltage DC. An abnormality in the output voltage is detected by comparing the output rectifying means, the voltage detecting means detecting the output voltage of the rectifying means, and the voltage detected by the voltage detecting means with the duty instructed by the control means. The present invention is characterized in that it includes an abnormality detection means for detecting an abnormality.

(Operation) The abnormality detection means detects an abnormality in the bias voltage by comparing the output voltage of the rectification means and the duty instructed by the control means.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of an embodiment of the present invention.

In the figure, reference numeral 20 denotes a CPU for controlling all parts of the copying machine as well as instructing the bias voltage and detecting malfunctions in the developing bias circuit. 21 is a pulse circuit that generates pulses with different duty ratios based on the signal given from the terminal 20a of the CPU 20; 22 is a transistor for amplifying the pulse from the pulse circuit 21; 23;
2 is a transformer for boosting the pulse signal amplified by the transistor 22, 24 is a rectifier for rectifying the pulse signal boosted by the lance 23, and 25 is a location where a bias voltage is applied between the developing sleeve and the drum. . 26 and 27 are resistors connected in series between the output of the bias voltage and the reference (earth) potential, and their midpoint is
is connected to the voltage input terminal terminal 20b.

The operation of the apparatus of the present invention will be explained below using FIG.

The CPU 20 has a duty ratio instruction outputted from a terminal 20a. The pulse circuit 21 oscillates pulses with a predetermined duty ratio based on instructions from the CPU 20. This pulse causes the transistor 22 to repeatedly turn on and off, causing a pulse current to flow through the primary winding of the transformer 23. A boosted high voltage pulse signal is generated in the secondary winding of the transformer, and this high voltage pulse signal is rectified by a rectifier 24. This rectified high voltage is the developing bias voltage. This bias voltage is applied between the developing sleeve and the drum.

As described above, this bias voltage needs to be set to a different value depending on the copy density. For this purpose, C.P.
U20 changes the duty (pulse width) instruction supplied to the pulse circuit 21. Due to this change in pulse width, the developing bias voltage also changes.

The voltage input terminal 20b of the CPU 20 has a voltage divided by the resistors 26 and 27 (hereinafter referred to as the "return 3g voltage") Vd.
has been returned. CPLI20 is this return)! Voltage Vd
and the duty instruction output from the terminal 20a. If there is no abnormality in the equipment, there is a certain correspondence between the pulse width and the bias voltage vb. Therefore, there should be a corresponding relationship between the feedback voltage Vd and the pulse duty. If the duty instructed to the pulse circuit 21 and the feedback voltage Vd do not correspond, the CPU 20 determines that the bias voltage is not normal for some reason. Then, the bias voltage is turned off and an abnormality is displayed on the display section.

By doing so, short circuits of the bias voltage to ground can also be detected.

As described above, since the developing bias voltage is compared with the duty applied to the pulse circuit, there is no need to create a reference voltage, and the circuit configuration can be simplified.

In the above embodiment, the voltage divided by the resistors is directly applied to the CPU 2.
Although the voltage is applied to the terminal 20a of 0, other configurations may be used. For example, a voltage value may be input via an A/D converter.

(Effects of the Invention) As described in detail above, in the present invention, abnormality in the circuit is detected by comparing the bias voltage with the duty applied to the pulse circuit. Therefore, a developing bias circuit capable of detecting an abnormality in bias voltage can be realized with a simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the structure of an embodiment of the present invention, and FIG. 2 is a block diagram showing the schematic structure of a copying machine. 20...CPU 21...Pulse circuit 2
2...Transistor 23...Transformer 24...
・Rectifier patent applicant Konica Co., Ltd.
Company representative Patent attorney Ijima
Fuji Jigai 1 person

Claims (1)

[Scope of Claims] A developing bias circuit that applies a bias voltage between a photosensitive drum of a copying machine and a developing sleeve of a developing device, comprising: a pulse generating means for generating a pulse signal; and a pulse generating means for generating a pulse signal. a control means for instructing the duty of the pulse generator; a booster for boosting the pulse signal from the pulse generator; a rectifier for rectifying the boosted pulse signal to output high voltage DC; A developing device comprising: a voltage detecting means for detecting; and an abnormality detecting means for detecting an abnormality in the output voltage by comparing the voltage detected by the voltage detecting means with the duty instructed by the control means. bias circuit.