JPH03189660A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus having an electrophotographic process such as a copying machine or a laser printer, and particularly relates to control of the surface potential of a photoreceptor.

(Prior Art) In the image forming apparatus illustrated in FIG. 3, the surface potential of the photoreceptor 1 is measured with an electrometer probe 2 in order to prevent density variations in a developed image caused by variations in the surface potential of the photoreceptor 1. Then, the amount of charge by the charger 3 or the laser diode (LD) is adjusted so that the surface potential becomes a predetermined value.
) The exposure amount (laser light, ) by the unit 4 was controlled. In this case, the electrometer probe is usually prone to zero point fluctuations and gain fluctuations due to environmental changes such as temperature, and may not be able to accurately measure the photoreceptor surface potential.

Therefore, an image forming apparatus having a means for correcting the electrometer probe before measuring the surface potential of the photoreceptor has been proposed (Japanese Patent Laid-Open No. 133164/1983).

(Problem to be Solved by the Invention) When measuring the surface potential of the photoconductor 1 and controlling the surface potential of the photoconductor based on the measured value, generally the surface potential of the electrometer probe 2 is The amount of offset due to attached toner, etc. is measured using a correction electrode 5, and an accurate surface potential of the photoreceptor 1 is calculated from that value and the measured surface potential of the photoreceptor 1, and the above-mentioned potential control is performed using that value 6 The potential measuring means at this time uses a vibrating capacitance electrometer probe, and by feeding back the potential to be measured to the probe itself and making the potential to be measured and the probe itself the same potential, the surface to be detected and the electrometer are connected. A device equipped with a distance correction circuit that cancels the dependence on the distance from the probe is designed so that when the toner adheres to the probe surface during a process in which the surface potentials of the toner and the photoreceptor 1 are of the same polarity, the correction electrode changes to zero focal potential. When 0 pyroelectric potential is detected, the surface potential of the photoconductor 1 is in the opposite polarity compared to the probe itself, so that the detected offset amount is in the opposite polarity to the surface potential of the photoconductor 1.

In this case, there is no problem if the potential measuring means is capable of measuring bipolarity, but if it is unipolar, the offset amount of the opposite polarity to the surface potential to be measured cannot be measured and accurate offset amount correction cannot be performed. There was a drawback. Furthermore, bipolar potential measuring means has the disadvantage of being expensive.

(Object of the Invention) Therefore, the present invention adds a potential shifted by a certain value with respect to the ground level to the correction electrode on the same polarity side as the potential measured on the surface of the photoreceptor 1, and uses the detected value to perform an accurate offset in the CPU. By calculating the amount, it is an object of the present invention to make it possible to measure an offset potential of opposite polarity even if an inexpensive unipolar potential measuring means is used.

(Structure and operation) In order to achieve the above object, the present invention provides an image forming apparatus that measures the surface potential of a photoreceptor and controls the surface potential of the photoreceptor based on the result. The correction electrode is equipped with a means for detecting the offset amount of the potential measuring means to be measured using a reference correction electrode, and the correction electrode has a correction electrode shifted by a certain value with respect to the ground level on the same polarity side as the photoreceptor surface measurement potential. It is characterized by applying an electrode potential.

In a normal process state, after being charged by a charger, the surface potential of the exposed portion of the photoreceptor and the surface potential of the unexposed portion of the photoreceptor are measured by potential measuring means at predetermined timings. Detection is performed, offset correction is performed for each detected potential (the offset amount is detected at a different timing), and the charger voltage and LD current are controlled based on the corrected potential to ensure that the surface of the photoreceptor is at a predetermined level. Process control is performed to maintain the potential.

(Embodiment) FIGS. 1 and 2 show a mechanism diagram for explaining an embodiment of the present invention, and FIG. 1 is an enlarged side view of the main part of FIG. 3, and FIG.
1 is a plan view of the offset amount detection mechanism viewed from above in FIG. There is. Note that 7 is a developing roller, and other numbers and symbols that are the same as those in FIG. 3 indicate the same members. Further, the correction electrode potential V is not normally applied to the correction electrode 5.

Next, the operation of this embodiment will be explained. 1. In a normal process state, as shown in FIG.
is at position 2, and the detection port 2a of the electrometer probe 2 is at position 2, directly facing the photoreceptor 1 (see FIG. 1), performing normal process control. Then, when detecting the offset amount of the electrometer probe at a certain timing,
The correction electrode 5 is controlled along the guide member 6 by the pushing and pulling force of the solenoid so that its tip 5a is at the position ◎, and at the same time, the correction electrode 5 is controlled by a certain value with respect to the ground level on the same polarity side as the detected potential of the photoreceptor. Add the shifted correction electrode potential v0.

At this time, the detection port 2a of the electrometer probe 2 faces the correction electrode 5 at a position ◎, so a microcomputer (CPU, not shown) calculates an accurate offset potential from the correction electrode measurement potential vl and the correction electrode potential V. It can be calculated by

That is, the electrometer probe offset amount v,st is y,
, =V, -V,----(t).

When the calculation of equation (1) is completed, the CPU releases the energization of the solenoid of the correction electrode 5, returns the tip 5a to the original position (1), and cancels the correction electrode potential V.

Next, numerical examples of the offset amount detection and correction described above are shown in the table below.

In the above table, a potential of -50V is applied to the correction electrode 5, and the offset amount detection mechanism shown in FIG.
Assume that the correction electrode measurement potential v1 is -45V. At this time, the offset amount of the electrometer probe 2 is determined by equation (1). 1 is calculated to be +5v. Then, after that, the surface measurement potential V of the photoreceptor 1 (-950V)
Every time it is detected, the CPU calculates from the surface measurement potential v4,
By constantly subtracting V, .

(Effects of the Invention) As explained above, the present invention can measure one offset potential of opposite polarity even when using a unipolar potential measuring means, so it is possible to easily and accurately measure the offset amount of an electrometer probe. Detection can be performed with an inexpensive mechanism, and by offset-correcting the measured surface potential of the photoreceptor, the process control can be performed using accurate photoreceptor surface potential at any time.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 show a mechanism diagram in which the present invention is implemented,
Fig. 1 is a side view of the main parts of the photoreceptor, electrometer probe, correction electrode, etc., Fig. 2 is a plan view of the offset amount detection mechanism seen from above in Fig. 1, and Fig. 3 is an example to which the present invention is applied. FIG. 2 shows a side view of main parts of an image forming apparatus. 1... Photoreceptor, 2... Electrometer probe, 2a.
...detection port, 3 ...electrostatic charger, 4 ...
Laser diode (LD) unit, 5...
- Correction electrode, 5a... tip, 6... guide member, 7... developing roller. Figure 1

Claims (1)

[Scope of Claims] In an image creating apparatus that measures the surface potential of a photoreceptor and controls the surface potential of the photoreceptor based on the result, an offset amount of a potential measuring means for measuring the surface potential of the photoreceptor is provided. , comprising a means for detecting using a correction electrode serving as a reference, and is characterized in that a correction electrode potential shifted by a certain value with respect to the ground level is applied to the correction electrode on the same polarity side as the potential measured on the surface of the photoreceptor. Image creation device.