JPH04122968A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain good transferring performance and the image of good quality by providing an impedance detecting means on the upstream side of a transferring part with respect to the traveling direction of a transfer material and correcting a stored voltage by it. CONSTITUTION:A toner image formed by the action of an image forming member is formed on the surface of an image carrier 10 rotating and traveling in a direction shown by an arrow. The toner image is transferred to the transfer material by carrying the transfer material to the transferring part formed as the press-contact nipping part of the image carrier 10 with a transferring roller 15 which is made to press-contact with the image carrier 10 and along the arrow (p) and impressing transfer bias on the material. In such a device, the transfer material takenout from a cassette, etc., passes a sensor 17 for detecting the impedance of the transfer material at a position where it does not reach the transferring part yet. The impedance of the transferring roller is detected by closing switches SW-1 and SW-2 in specified timing when the transfer material reaches between rollers 61 and 62, and the respective switches are opened to make the rollers 61 and 62 in an electrically open-state before the transfer material reaches the transferring part.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention The present invention relates to an image forming apparatus that utilizes a transfer process.

(Prior art and issues to be solved) In an image forming apparatus that electrostatically transfers a toner image electrostatically formed on the surface of an image carrier to a transfer material such as paper, a moving image carrier is coated with rubber or the like. A transfer roller made of an elastic material is caused to contact and run synchronously, and the pressure nip between the two is used as a transfer site, and the transfer material is supplied to the transfer site in synchronization with the toner image on the image carrier side. A structure has already been proposed in which a transfer bias is applied and the toner image on the image carrier side is transferred to the transfer material by the action of the electric field formed.

In such an image forming apparatus, constant voltage control and constant current control have conventionally been used as means for controlling the bias applied to contact transfer means such as a transfer roller in order to obtain a desired electric field strength.

However, in the case of constant voltage control, for example, it is well known that even if the voltage is set to be applied appropriately in a certain environment, the resistance value of the transfer roller, which is the transfer means, changes widely, especially depending on humidity. For this reason, if the transfer roller has high resistance in a low humidity environment, the transfer current will be insufficient and transfer defects will occur, and if the transfer roller has low resistance in a high temperature environment, the excess current will cause charge penetration and the image will be damaged. There is a risk of damaging the carrier.

In addition, when using constant current control, when using a small transfer material, the transfer current is concentrated in the area where there is no transfer material and the image bearing member and the transfer roller directly oppose each other, causing the transfer material to There is a problem in that transfer defects occur due to insufficient transfer current in the portion where the transfer current exists.

In order to avoid such drawbacks, constant current control is performed when no transfer material is present at the transfer site and the paper is not passing, the voltage at that time is memorized, and the current voltage is maintained at that voltage (constant voltage control is performed when paper is passing). Several measures have been proposed and have had some success.

However, such means requires a hardware switching circuit such as an analog switch, which is undesirable because it generates heat, causes malfunctions, causes failures, and has a limited lifespan.

Furthermore, even if we correct for changes in the characteristics of the transfer roller, which is the transfer means, due to the environment, if there is a transfer material at the transfer site, paper, which is most often used as a transfer material, will still be affected by the environment, especially temperature. Since the resistance value changes greatly, it is not always possible to obtain good transfer performance even if we focus only on changes in the characteristics of the transfer roller.
The reality is that it has not been possible to reliably prevent the occurrence of transfer defects, fogging, etc.

The present invention has been made to deal with such a situation, and is applicable to an image forming apparatus in which constant current control is applied to the transfer means when paper is not passing, and constant voltage control is carried out when paper is passing. By switching the control using electrical means, it is possible to solve the above-mentioned drawbacks caused by switching, and also to be able to respond to changes in the characteristics of the transfer material, thereby achieving stable, high-quality transfer at all times. The purpose is to provide a device.

(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 bearing member and a transfer means that comes into contact with the image bearing member, and a contact portion between the two. In an image forming apparatus that performs transfer by inserting a transfer material into a transfer site,
An impedance detection means for the transfer material is disposed upstream of the transfer site when viewed in the traveling direction of the transfer material, and further,
The transfer bias is controlled at a constant current when no transfer material is present at the transfer site and paper is not passing, the voltage at this constant current control is memorized, and the stored voltage value is used as a constant voltage when paper is passing when there is a transfer material at the transfer site. The image forming apparatus to be controlled is characterized in that a transfer material impedance detection means is provided upstream of the transfer site when viewed in the traveling direction of the transfer material, and the storage voltage is corrected based on the detected impedance of the transfer material. .

With this configuration, it is possible to control the bias for both the transfer material and the transfer means such as the transfer roller, which are often influenced by the environment, and it is possible to obtain good transfer performance and obtain a high-quality image.

(Description of Embodiment) FIG. 1 shows an embodiment of a circuit for applying a transfer bias according to the present invention, in which reference numeral 1 is an oscillation circuit, 2.3 is a differential amplifier, and 4.5 is a D/ A converter, 6 an A/D converter, 7 a CPU, and T a converter transformer.

When paper is not being passed, zero is input for (2), and a positive value corresponding to a predetermined current is input for (1).

At this time, the diode D3 becomes conductive and the diode D4 becomes conductive, thereby establishing a servo system using the differential amplifier 2 as an error amplifier.

Output voltage at this time■. is ■ by Rs, R7. 7
m, and is input to the CPU 7 via the converter 6.

Then, when passing the paper, ■1 becomes zero, and as V2,
The stored voltage V0/m (or A
Vo/m+B: A and B are constants (to be described later) are input, the diode D4 becomes conductive, and the diode D3 is cut off, establishing a servo system using the differential amplifier 3 as an error amplifier.

In the case of Kono, R4 and Rli are m = (R4+ Rs)
/R4, and R8 as shown in the figure.
, R, , C3 are phase correction circuits during constant current control.

FIG. 2 shows another embodiment of the transfer bias applying circuit, in which a PWMm is used in place of the ejection circuit 1 in the circuit shown in FIG. It is suitable for use in cases of large-capacity output where heat generation increases over time.

The third section shows still another embodiment of the transfer bias circuit, in which the output voltage is divided into voltage dividing circuits R6 and R7.
This detection output is manually input to the CPU 7 via the A/D converter 6, and during constant voltage control, the output is sent from the CPtj7 to the negative phase input of the differential amplifier 3 via the D/A converter 5. The stored value of the pressure detection output is applied to the transfer means.

In the figure, R31, R3□, and C31 are phase correction circuits during constant voltage control.

In FIG. 4, the current detection voltage VFI in the third section is canceled out by operational amplifiers 41 and 42.

R4,=R4□, R43"R44" R46, so the output of amplifier 41 is -■, 1, amplifier 42
V-1V2 appears in the output of amplifier 3, and the in-phase human power V of amplifier 3
It is possible to cancel the V F l of , , +Vo/m.

Next, a description will be given of means for responding to changes in the characteristics of the transfer material.

Toner is formed on the surface of the image carrier 10, which has an axis perpendicular to the plane of the paper and rotates in the direction of the arrow shown, by the action of image forming members such as a primary charger, an image signal applying means, and a developer (not shown). An image is formed, and the transfer material is conveyed along the arrow p to a transfer site formed as a pressure nip between the image carrier 10 and the transfer roller 15 that is in pressure contact with the image carrier 10,
The toner image is supplied to the transfer site in synchronization with the toner image, and at the same time, a transfer bias is applied to the transfer roller 15, so that the toner image on the image carrier side is transferred to the transfer material.

After that, the transfer material passes through the fixing section, the print is completed, and the transfer material is discharged outside the machine.

In such an apparatus, in the case shown in the figure, at a position before the transfer material taken out from the cassette etc. reaches the transfer site,
It passes through a sensor 17 that detects the impedance of the transfer material.

The seventh section shows the configuration of the sensor 17, in which the transfer material is conveyed by a pair of rollers 61 and 62 within the sensor, and the roller 61 is supplied with a constant voltage of 50 to IKV.
3 is applied, and the roller 62 is grounded via the current detection resistor R1.

Output of operational amplifier Q61■. is v o = Rl i x (1+ Rz / R2
) = R + VR / Rx X (R2 + R3)
/ R2 (Rx > R,) R, is the resistance between the rollers 61, 62 in the presence of transfer material, l = V PI / Rx.

8 power ■ of this operational amplifier Q61. is digitally converted by the A/D converter 18 and input to the CPU 12.

After the CPU converts R,=F/Vo [here T'F=
R+V*f R2+Ri)/R2], a predetermined discriminant, f fR, l, g (The constants A and B in the embodiment of FIG. 1 are set by R, i, A = f fR,) B = g fR,)■2
=Ax(■o/m)×B The bias voltage vo of the transfer roller during paper passing is determined by:

Section 7 shows a circuit for calculating the S ratio of the impedance of the transfer material, and at a predetermined timing when the transfer material reaches between the rollers 61 and 62, the switch sw-1.5W-2 is closed and the transfer roller Detects the impedance of the roller 6 and opens each switch before the transfer material reaches the transfer site.
1.62 is electrically opened.

FIG. 8 shows the above circuit for detecting the impedance of the transfer material, so that when the switches 5W-1 and 5W-2 are opened, the rollers 61 and 62 are not charged to a high voltage higher than a predetermined value due to frictional charging or the like. , a varistor D with a predetermined rating
81 and D82 are arranged.

(3) Detailed Description of the Invention As described above, the present invention is an image forming apparatus using a contact type transfer means such as a transfer roller, and the transfer bias is controlled at a constant current when paper is not passing through. In a transfer device configured to hold a voltage and use this held voltage to control the constant voltage during paper feeding, there is no need to use hardware such as an analog switch in the control bias switching circuit, and it is possible to switch between constant current and constant voltage. It is possible to switch between constant current mode and constant voltage mode by simply switching the level of each control value, and it operates quickly and reliably, with little risk of failure and can withstand long-term use. Since it can respond to changes in impedance, stable and good transfer performance can be obtained at all times, which has a remarkable effect on obtaining high-quality images.

[Brief explanation of drawings]

FIG. 1 is a transfer bias generation switching circuit diagram showing an embodiment of the present invention. FIGS. 2 to 4 are diagrams showing other embodiments of the transfer bias generation switching circuit. FIG. 5 is impedance detection of a transfer material. 6 to 8 are schematic side views of the image forming apparatus including the means, shown along the transfer material conveyance path, and FIG. 5 is a circuit diagram showing the configuration of the impedance detection means. 1... Oscillation circuit, 2.3... Differential amplifier, 4, 5. 6... Converter, 7... CPv, 10... Image carrier, 17... Impedance detection circuit, 61.62... Conveyance roller. Figure Figure Figure Figure Figure] 6 Figure Figure Figure Figure

Claims (2)

[Claims] (1) In an image forming apparatus that includes an image carrier and a transfer means that comes into contact with the image carrier, and performs transfer by inserting the transfer material into the transfer portion that is the abutment area between the two, when viewed in the running direction of the transfer material, An image forming apparatus comprising a transfer material impedance detection means disposed upstream of a transfer site. (2) When the transfer material is not present at the transfer site and the paper is not passing, the transfer bias is controlled at a constant current, the voltage during this constant current control is memorized, and the paper is being passed when the transfer material is present at the transfer site at the memorized voltage value. An image forming apparatus that sometimes performs constant voltage control is characterized in that a transfer material impedance detection means is provided upstream of a transfer site when viewed in the traveling direction of the transfer material, and the storage voltage is corrected based on the detected impedance of the transfer material. Image forming device.