JPH0743960A - Image forming device - Google Patents

Abstract

(57) [Summary] [Purpose] Whether the transfer paper is plain paper, cardboard or OHP paper,
Make it detectable by low cost means. [Structure] A current I1 flowing through a photoconductor in a transfer process is controlled to be constant. Since the output voltage Vf of the transfer bias power source changes according to the type and thickness of the transfer sheet, this voltage Vf is detected and the type of the transfer sheet is automatically identified by the level of Vf. When thick paper or OHP paper is used, the linearity of the fixing process is automatically reduced because its fixing property is poor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, etc.
This relates to image transfer, transfer paper conveyance, and fixing.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus, after a toner image corresponding to a recorded image is formed on a photoconductor, the toner image is transferred onto a transfer paper and the transfer paper is conveyed to a predetermined fixing device. And fix the toner image on the transfer paper. Normally, a fixing device of a copying machine passes a toner image transferred onto a transfer paper (including OHP paper) through a nip portion between a fixing roller and a pressure roller, and a toner image is transferred onto the transfer paper by heat and pressure. Fix it.

[0003]

By the way, in general, OHP paper or thick paper has a lower fixing property than plain paper.
Therefore, depending on the device, there is a device provided with an OHP mode or a cardboard mode. That is, these modes are intended to improve the fixability by lowering the linear velocity of the fixing roller or raising the temperature of the fixing roller.

However, in order to provide these modes, a sensor is provided for detecting whether the type of transfer paper is plain paper, OHP paper or thick paper having poor fixing property, or manual operation. Requires a switch to switch modes. Therefore, these modes
The provision of the cord inevitably increases the cost of the device. Further, when the mode is changed by manual operation, an operation error is likely to occur and a preferable fixing property may not be obtained.

Therefore, the present invention realizes the function of detecting whether the type of transfer paper is plain paper, OHP paper or thick paper having poor fixing properties by an inexpensive means, and regardless of the type of transfer paper. The challenge is to always obtain stable fixability.

[0006]

In order to solve the above-mentioned problems, in the present invention, a transfer paper is electrostatically adsorbed on a dielectric belt (B) and the transfer paper is formed on a photoconductor (PC). And a transfer electrode that applies a charge directly to the dielectric belt of the transfer device, a transfer bias power supply that applies a voltage to the contact electrode, and a current that flows through the photosensitive member of the transfer bias power supply. Detecting means (r1), a current value thereof is fed back to the control calculation section to control the electric charge applied to the dielectric belt constant, a storage means for holding the calculation result, and a transfer sheet. In an image forming apparatus having means (F) for fixing the transferred toner image: voltage detecting means (R, r, 11, 33, 34) for detecting the output voltage of the transfer bias power source, and the voltage detecting means Detected voltage value Based automatically providing the fixing rate identifying means (35) for identifying the height of the fixing rate of the transfer paper.
Further, in a preferred aspect of the present invention, it is provided with means for varying a rotation speed of a motor for driving the fixing roller (RF) and the pressure roller (RP) of the fixing device, and the fixing rate identifying means is
It includes means (36) for adjusting the driving speed of the motor according to the identified high or low fixing rate of the transfer paper and automatically adjusting the linear speed in the fixing process.

The symbols shown in parentheses are reference numerals of corresponding elements in the embodiments described later, but each constituent element of the present invention is a concrete element in the embodiments. It is not limited to only.

[0008]

In the image forming apparatus of the present invention, the transfer paper is
It is electrostatically attracted to the dielectric belt and is conveyed by the dielectric belt. The toner image formed on the photoconductor is superposed on the transfer paper on the dielectric belt. A bias voltage is applied to the dielectric belt from the transfer bias power source via the contact electrodes at a predetermined timing, and thus the toner image is transferred to the transfer paper on the dielectric belt by the bias voltage. At this time, the current flowing from the dielectric belt to the photoconductor through the transfer paper is detected by a predetermined detection means and fed back to the control calculation section. Then, the constant current control means controls the electric charge applied to the dielectric belt to be constant. In such a device, the output voltage of the transfer bias power source changes according to the type and thickness of the transfer paper. That is, the transfer bias voltage changes depending on whether the transfer paper is plain paper or paper with poor fixability such as OHP paper or thick paper.
Therefore, the voltage detecting means detects the output voltage of the transfer bias power source, and the fixing rate identifying means can automatically identify the level of the fixing rate of the transfer sheet based on the voltage value detected by the voltage detecting means. .

[0009]

FIG. 1 shows an example of the configuration of an image forming apparatus for carrying out the present invention. This will be described with reference to FIG. In the image forming unit,
A grounded drum-shaped photoconductor PC is arranged and rotates in the direction of the arrow. Around the photoconductor PC, a charging corona discharger CH, a developing device D, a transfer / conveyance device, a cleaning device C, a charge eliminator QL and the like are arranged. The transfer / conveyance device comprises a dielectric belt B, a transfer roller RB also serving as a contact electrode for supplying electric charges to the dielectric belt B, and a grounding roller RA. A fixing device F is provided behind the dielectric belt B. Further, a bias power supply PP is connected to the transfer roller RB of the transfer / transport device.

First, the photoconductor PC is a charged corona discharger CH.
Due to corona discharge due to, negatively charged (about -800 to -900
V) Next, the surface of the photoconductor PC is irradiated with light according to the image information to be recorded, whereby an electrostatic latent image is formed on the photoconductor PC. Then, the electrostatic attraction between the toner and the photoconductor PC is weakened by a pre-transfer charge eliminator (not shown).
Next, the transfer paper is sent out from the feed roller, and the transfer paper is electrostatically attracted to the dielectric belt B to which the bias is applied.
This transfer paper is superposed on the toner image on the photoconductor PC. Then, a charge having a polarity opposite to that of the toner is applied from the back surface of the transfer paper via the dielectric belt B, and the toner image is transferred to the transfer paper. After the transfer, the paper dust adhering to the photoconductor PC and the untransferred residual toner are removed by the cleaning device C.
Are removed and discharged. Next, the surface of the photoconductor PC is photo-erased by the static eliminator QL, and the photoconductor PC returns to the initial state.
The transfer paper on which the toner image has been transferred is sent to the fixing device F, where it is fixed, and is discharged to the outside of the device. This completes a series of copying operations.

An electrostatic latent image of image information and a toner image electrostatically adsorbed to the electrostatic latent image are formed on the photosensitive layer on the surface of the photoconductor PC on which the conductive substrate is installed. On the other hand, from the back surface of the transfer paper, electric charges are applied to the dielectric belt B from the bias power source PP via the first roller RB. Therefore, the photoconductor PC
An electric charge is induced on the surface of the transfer paper interposed between the contact portion (nip) of the dielectric belt B and the dielectric belt B, and the electric charge transfers the toner to the transfer paper at the contact surface with the toner image. The transfer paper on which the toner image is transferred passes through the separation point of the photoconductor while being attracted to the dielectric belt B due to the strong electric field on the dielectric belt B side, and is conveyed to the next step. The potential of the dielectric belt B gradually decreases from the biased contact electrode RB toward the grounding roller RA, and the roller R
The voltage at the contact point with A is almost 0V. Therefore, the electrostatic attraction between the transfer belt B and the transfer paper is almost eliminated in the vicinity of the roller RA, so that the transfer paper is separated from the dielectric belt B due to the rigidity and waist of the transfer paper itself, and the next fixing device. Enter. After that, the untransferred toner and paper dust adhered on the dielectric belt B are scraped off by the blade TB. The fixing device F includes a fixing roller RF and a pressure roller R.
The fixing roller RF includes a heater for increasing the temperature of the fixing roller RF. The motor that drives the fixing roller RF and the pressure roller RP is a motor whose rotation speed is variable.

FIG. 2 shows the configuration of an electric system centered on the transfer bias power source PP shown in FIG. This will be described with reference to FIG.
Although the process conditions around the photoconductor PC vary depending on the type of transfer paper and the environmental conditions, in order to obtain stable transferability under those conditions, the transfer output drum current I1 in FIG. 2 is constant. Need to be controlled. Therefore, in this embodiment, the terminal voltage of the detection resistor r1 provided in the current path of the transfer output drum current I1 is fed back to the control arithmetic circuit 13 via the A / D conversion circuit 11,
The PWM control is executed so that the feedback value obtained by AD conversion is always equal to the target value.

That is, the fed back value of I1 is A
When the D-converted and AD-converted value is larger than the target value, the PWM (pulse width modulation signal) duty is reduced, and when it is smaller than the target value, the PWM duty is increased. The duty of the PWM waveform is limited to a level at which the transformer T does not saturate with energy.

Further, a voltage obtained by dividing the transfer output voltage by the resistors R and r is detected, and this voltage value is A / D conversion circuit 1
It is input to the control arithmetic circuit 13 via 1 and the output voltage of the transfer bias power source is detected.

When the type and thickness of the transfer paper are different, the resistance of the transfer paper is different, so that the resistance of the path of the current I1 passing through the dielectric belt B-transfer paper-photoreceptor changes. Actually, since the resistance value of OHP paper or thick paper is higher than that of transfer paper generally used, the resistance value of this current path is also high, but in this embodiment, the value of the current I1 is always constant. Since the constant current control is performed, good transfer can always be obtained.

On the other hand, since the transfer output voltage is adjusted so that the value of the current I1 becomes constant regardless of the change in the resistance value of the current path, in this example, the transfer output voltage depends on the resistance of the transfer paper. Change. That is, if the load other than the transfer paper is stable, the type and thickness of the transfer paper can be identified by the change in the transfer output voltage.

Further, OHP paper and thick paper have lower fixability than ordinary transfer paper. Therefore, in order to fix the toner image on the OHP paper or the thick paper, the characteristics of the fixing device must be improved. To obtain high fixability, the fixing device F
Since it is effective to reduce the linear velocity of No. 3, it is desirable to reduce the linear velocity of the fixing device to improve the fixability when OHP paper or thick paper is detected. However, if the linear velocity of the fixing device is slowed down more than necessary, the time required for image formation becomes long. Therefore, in this embodiment, when plain paper is used as the transfer paper, a relatively high (normal) linear velocity is set, and the linear velocity of the fixing device is reduced only when OHP paper or thick paper is detected. Control.

An outline of the control of the control arithmetic circuit 13 is shown in FIG. This will be described with reference to FIG. When the predetermined transfer timing is reached, the process proceeds from step 31 to 32, the voltage output of the transfer bias power supply PP is turned on, and the transfer bias voltage is applied to the roller RB. Then, in the next step 33, the transfer bias voltage Vf divided by the two resistors R and r.
Is sampled, and this voltage Vf is A / D converted and read in the next step 34. In the next step 35, A / D
The value of the converted voltage Vf is compared with a predetermined threshold value M. When Vf ≧ M, the transfer paper is thick paper or OH.
It is determined that the fixing property is poor such as P paper, and the process proceeds to the next step 36. In step 36, a deceleration signal is applied to the motor driver 16 shown in FIG. 2 to reduce the speed of the electric motor 17 which drives the fixing device. When Vf <M, the transfer paper is regarded as plain paper and the fixing device is not decelerated.

[0019]

As described above, according to the present invention, it is possible to surely discriminate whether the transfer paper is plain paper or OHP paper or thick paper having a poor fixing property by a very inexpensive means. . In addition, by automatically adjusting the linear speed of the fixing device according to the identified type of transfer paper,
Stable fixability can be obtained even when using HP paper.

[Brief description of drawings]

FIG. 1 is a front view showing a main part of an image forming apparatus according to an embodiment.

FIG. 2 is a block diagram showing a configuration of an electric system of the apparatus shown in FIG.

FIG. 3 is a flowchart showing the operation of the control arithmetic circuit of FIG.

[Explanation of symbols]

11: A / D conversion circuit 12: Storage device 13: Control arithmetic circuit 14: I / O port
15: PWM generator 16: Motor driver 17: Electric motor B: Dielectric belt RA: Roller RB: Transfer roller PP: Transfer bias power supply PC: Photoconductor CH: Charging corona discharger D: Development device C : Cleaning device QL: Static eliminator F: Fixing device

Claims (2)

[Claims] 1. A transfer unit that electrostatically attracts a transfer sheet to a dielectric belt and transfers the transfer sheet by superposing the transfer sheet on a toner image formed on a photosensitive member, and a charge is directly applied to the dielectric belt of the transfer unit. Contact electrode, a transfer bias power supply for applying a voltage to the contact electrode, a means for detecting the current flowing through the photosensitive member of the transfer bias power supply, and the current value is returned to the control calculation unit to keep the charge applied to the dielectric belt constant. In an image forming apparatus having a constant current control means for controlling, a storage means for holding a calculation result, and a means for fixing a toner image transferred on a transfer sheet: a voltage for detecting an output voltage of the transfer bias power source An image forming apparatus comprising: a detecting unit; and a fixing rate identifying unit that automatically identifies the level of the fixing rate of a transfer sheet based on the voltage value detected by the voltage detecting unit. 2. A fixing means for varying the rotation speed of a motor for driving a fixing roller and a pressure roller of a fixing device, wherein the fixing rate identifying means determines the mode depending on whether the identified fixing rate of the transfer sheet is high or low. The image forming apparatus according to claim 1, further comprising means for adjusting a drive speed of the printer and automatically adjusting a linear velocity in a fixing process.