JPH0420983A - Transfer device for 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 (1) Purpose of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus that uses an electrostatic transfer process, such as an electrostatic copying machine or a printer, and particularly to a transfer apparatus thereof. be.

(Prior art and problems to be solved) A moving image carrier is provided with a contact transfer member such as a transfer roller that is in pressure contact with the image carrier, and a transfer material is passed through the pressure nip between the two as a transfer site. An image forming apparatus has already been proposed in which a toner image previously formed on the surface of an image carrier is transferred to a transfer material by applying a transfer bias to a transfer member.

However, in such image forming apparatuses, the resistivity of the transfer member, such as the transfer roller, changes significantly depending on the environment, especially humidity, and the transfer current also fluctuates due to this, and the transfer current also changes depending on the size of the transfer material. The change in image quality was significant, and it was therefore difficult to obtain stable images at all times.

In order to avoid such drawbacks, a method is used in which the transfer roller is controlled with a constant current when the transfer material is not present in the transfer area and the paper is not passing, the voltage at that time is held, and the voltage is controlled at this voltage when the paper is passing. is proposed.

FIG. 4 shows an example of such a control system, which will be briefly described.

Regarding the image forming section, reference numeral 1 denotes a photoreceptor having an axis perpendicular to the plane of the paper and rotating and traveling in the direction of the arrow in the drawing. The image signal 2 is applied to the electrostatic latent image to form an electrostatic latent image, and when the latent image reaches the developing area facing the developing device 7, a developing bias is applied by the developing high-voltage power source 8. The charged toner is attracted to the latent image by the sleeve 7a to form a toner image.

Furthermore, when this toner image arrives at the transfer site where the photoconductor 1 and transfer roller 3 are formed in pressure contact, a transfer bias is applied to the roller 3 by the transfer high voltage power source 4, and the toner image on the photoconductor side is transferred. It is assumed that the transfer material P is transferred to the material P, and then the transfer material P is conveyed to a fixing site (not shown).

Next, control of the bias applied to the transfer roller 3 will be explained.

The transfer high-voltage power supply 4 outputs a voltage proportional to the analog level of the input signal, as shown in FIG. 6, and the resistor 47 is a transfer current detection resistor.

Assuming that the transfer current is {circle around (2)}, the positive-phase input potential v3 of the operational amplifier 41 can be expressed as vx = Vss - (resistance value of the resistor 47): xrt.

Therefore, when the CPU output signal CNTON is high, the analog switch 42 is turned on, and the operational amplifier 41 is
(2) The input signal of the transfer high-voltage power supply 4 is changed so that the potential of the CPU becomes equal to the CCNT of the D/A output of the CPU.

That is, the operational amplifier 41, the resistors 47, 48, 49, and the capacitor 51 form a constant current control circuit.

Also, when CNTON is high, analog switch 4
Since 3 is also on, the output of operational amplifier 41 is connected to resistor 5.
0 to charge the capacitor 52.

Then, when CNTON goes low, analog switch 4
2.43 is turned off and the analog switch 44 is turned on, so that the voltage charged in the capacitor 52 is applied to the transfer high voltage power supply 4.

Since the input impedance of the transfer high voltage source 4 is sufficiently high, the voltage drop across the capacitor 52 is small, and the capacitor 52 serves as a constant voltage control circuit for the transfer roller.

FIG. 5 is a sequence showing the above-mentioned operation, and the figure shows the case where the photoreceptor starts printing and then stops after printing three sheets.

As the photoconductor starts, HVPON, HV
DON is set high to start up the temporary high voltage power supply 6 and the developing high voltage power supply 8, and the low current control analog level CCNT is set to a predetermined value.

As a result, the transfer roller is controlled with constant current according to the value of CCNT. In this case, the input voltage V to the transfer high voltage power supply 4
l fluctuates sharply, but the capacitor 5 for constant voltage control
2 is charged and discharged via the resistor 50, and the voltage Vφ becomes approximately the average value.

When printing starts, CNTON goes low and
The transfer roller 3 is controlled at a constant voltage by the voltage of the capacitor 52.

However, in the above-mentioned devices, constant voltage control depends on the capacity of the capacitor, so it gradually discharges, and constant current control is performed every time the capacitor is printed or every 2 to 3 sheets. Needs to be charged.

However, when constant current control is performed when no transfer material is present at the transfer site, a high voltage is applied directly to the photoreceptor, and even with subsequent primary charging, the uniformity of the photoreceptor surface potential cannot be maintained, resulting in uneven images. This results in deterioration of image quality.

In order to avoid such drawbacks, printing should not begin until the photoreceptor surface potential stabilizes after constant current control, but this reduces the number of prints per unit time and reduces efficiency. (Become.

In addition, the voltage during constant current control is averaged by a smoothing circuit, and that value is used as the voltage during constant voltage control, but since the voltage changes significantly during constant current control, it is difficult to obtain an accurate average value. There are some difficulties.

The present invention was made to deal with this situation, and it converts the voltage during constant current control into an A/D converter, and accurately calculates the output voltage during constant voltage control based on the converted value. ,
It is an object of the present invention to provide a transfer device that can maintain stable transfer performance at all times by maintaining a control voltage for a long period of time.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention comprises an image carrier and a contact transfer member such as a transfer roller that comes into pressure contact with the image carrier, Means for passing a transfer material through a transfer site that is a pressure contact part, and controlling the transfer member at a constant voltage when paper is passing when there is a transfer material in the transfer site, and controlling the transfer member at a constant current when paper is not passing when no transfer material is present. In an image forming apparatus equipped with a means for controlling an output voltage during constant current control by a constant current control means,
This is a transfer device characterized by comprising means for performing D conversion, and means for controlling a transfer member at a constant voltage according to the output of the A/D conversion means.

With this configuration, it is possible to accurately calculate the output voltage during constant voltage control and maintain this value for a long period of time, making it possible to obtain good transfer characteristics.

(Description of Embodiments) FIG. 1 is a diagram showing an outline of an image forming apparatus and a transfer bias control section, showing an embodiment of the present invention, and the configuration of the image forming apparatus itself is as shown in the fourth section. There is no difference from the previous version, and corresponding parts are designated by the same reference numerals, and explanations thereof will be omitted unless necessary.

Reference numeral 11 is a CPU with built-in A/D and D/A, 12
．． 13 is an operational amplifier, 14.15 is a diode, 16.
17 and 18 are resistors, and 19 is a capacitor.

To explain the operation, the D/A output signal CCN of cputi is increased to set a target value for constant current control.

At this time, if the other output signal VCNT is set to zero,
Constant current control is performed by the operational amplifier 12, and the input signal VIN of the transfer high voltage power supply 4 at this time is input to the A/D boat of the CPU.

The CPU II inputs VIN multiple times during one rotation of the photoconductor.
For example, after reading 256 times and finding the average value, C
CNT is V. Keep it.

When printing starts, the CPU II outputs the average value of the VIN as the D/A output VCNT, and the operational amplifier 1
3 acts as a voltage follower, VCNT is input to the transfer high voltage power source 4, and the transfer roller 3 is controlled at a constant voltage with a voltage proportional to VCNT.

FIG. 2 shows the sequence when three sheets are passed by the above-mentioned apparatus.

By starting the photoreceptor, the primary high-voltage power supply 6 and the image high-voltage power supply 8 are turned on, and the CCNT is set to the target value for constant current control.

Next, after calculating the average value of VIN, CCNT is Vaml
When the non-uniform potential on the photoreceptor surface caused by constant current control becomes uniform, image formation is started.

The target value for constant voltage control is held by the cPU. When the transfer material is at the transfer site, this target voltage is output to VCN' to perform transfer.

At this time, the constant current control operation is not required at C, and image formation can be performed without reducing throughput even in the case of continuous printing.

It is convenient for the constant current control means to be of an analog type as in this embodiment. That is, in a digital system using a cPU, the response of constant current control is slow (and if the output voltage changes widely, such as constant current control of a transfer roller, there is a risk of oscillation).

The voltage obtained by constant current control changes mainly in response to changes in the environment, so even when printing a considerable number of sheets, if the environmental conditions inside the device do not seem to change much during that time, As can be seen from the sequence shown in Figure 3A, constant current control is performed immediately after the power switch is turned on, and thereafter transfer is performed at that voltage until the power switch is turned off, and as shown in Figure 3B, the number of printed sheets is counted. For example, constant current control is performed every 1000 sheets to set the transfer voltage, or as shown in Figure 3C, a timer is provided and constant current control is performed every hour, for example. It is easy to infer that similar effects can be obtained.

Furthermore, if the CPU has a built-in PWM output port, it can be used in the same way as a D/A converter by passing it through a low-pass filter, as shown in FIG. 3D.

(3) As described in detail, according to the present invention, an image carrier is provided with a contact transfer member such as a transfer roller that is in pressure contact with the image carrier, and a transfer material is passed through a transfer site where the two come into contact with each other, and
In a transfer device that controls the transfer member at a constant current when using non-traffic paper, and uses the voltage at that time to control the transfer member at a constant voltage when passing the paper, the output voltage during constant current control is A/D converted, and the output voltage during constant voltage control is calculated from that value. Since the output voltage is set, the voltage can be stably maintained for a long period of time, making it possible to obtain stable transfer performance at all times, which greatly contributes to obtaining high-quality images.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a transfer means of an image forming apparatus showing an embodiment of the present invention, FIGS. 3A to 3C are sequences showing other embodiments, and FIG. 3D is a circuit diagram showing another embodiment of a CPU. FIG. 5 is a sequence diagram of the same as the above, and FIG. 6 is a graph showing the input characteristics of the transfer high voltage power supply of the same as the above. Figure number country number number number number number number number number number VIN(-Tue)

Claims (3)

[Claims] (1) An image bearing member and a contact transfer member that is in pressure contact with the image carrier are provided, and the transfer material is passed through the transfer area that is the pressure contact area between the two, and when the transfer material is present in the transfer area and the sheet is being passed, the transfer member is applied with a constant voltage. In an image forming apparatus equipped with a means for controlling a transfer member and a means for controlling a transfer member with a constant current when no transfer material is present and no paper is passing, the output voltage during constant current control by the constant current control means is controlled by an A/D.
1. A transfer device for an image forming apparatus, comprising: converting means; and means for controlling a transfer member at a constant voltage according to the output of the A/D converting means. (2) The transfer device according to claim 1, wherein the constant current control means comprises an analog circuit. (3) The transfer device according to claim 1, wherein the constant voltage control means includes a calculation means.