JPH05249770A - Image forming device - Google Patents

Abstract

PURPOSE:To simplify control for changing linear velocity and to miniaturize a device by constituting an image forming device in which an image is formed by switching the linear velocity of an image carrier in the midst of forming the image so that it may not perform image forming actions at the time of switching the linear velocity. CONSTITUTION:In this image forming device, processing velocity and fixing velocity are switched to be low in the case of forming the image for an OHP paper or the glossy image. Namely, when an OHP mode or a glossing mode is selected, a control part allows a speed control means to drastically decrease the processing velocity when the final development and the irradiation of PTL are finished, and duty ratio is switched to a small one side by a duty ratio changing circuit 32 for the transfer voltage of a constant-voltage power source 30. Since the image forming actions are not performed until the velocity becomes normal at the time of changing the processing velocity, the complicated control for changing the linear velocity in the midst of forming the image need not be performed, and the circuit is simplified.

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,
In particular, the present invention relates to an image forming apparatus capable of forming a toner image on a recording material (hereinafter referred to as OHP paper) made of a transparent member for an overhead projector (hereinafter referred to as OHP) or thick paper.

[0002]

2. Description of the Related Art Conventionally, when forming a glossy image on OHP paper or ordinary recording paper, the toner of each color is sufficiently melted so that reflection at the boundary surface of the toner does not occur and the color becomes cloudy. In order to obtain a vivid color image for prevention, there are those in which the linear velocity of the recording paper conveyance is reduced to increase the fixing nip time (JP-A-60-80885, JP-A-60-86574).
issue).

In these prior arts, when an image is formed on a photoconductor, it is executed at a normal speed as in the case of normal paper, and the linear speed is reduced after the rear end of the OHP paper passes through the transfer section. Has been switched to. When the linear velocity changes, the charge amount of the charged member changes. Therefore, in order to control the charge amount of the charged member that is conventionally moved, the output voltage of the high-voltage power source connected to the corona charger is changed or the charged member and the corona electrode are controlled according to the moving speed of the charged member. It was done by changing the distance from.

[0004]

However, it is difficult to charge the charged member to a desired potential by the conventional method when the charged member moves at a low speed or moves at an irregular speed.

For example, in the case of low speed movement, in this case, the charge amount of the charged member is the corona charge amount, in other words, the value of the time integration of the corona current. The amount of electrification is large. Therefore, it is necessary to reduce the output of the high-voltage power supply or to increase the distance between the member to be charged and the corona electrode in order to reduce the charge amount to a desired value. However, in any case, it is difficult to perform stable charging. That is, in the former case, unstable corona discharge occurs when the output voltage of the high-voltage power supply is lowered to near the corona discharge start voltage, and in the latter case, the atmosphere is easily affected.

Further, when the member to be charged moves irregularly, it is difficult to control stable constant charging by controlling the output of the high-voltage power source or by changing the distance between the electrodes and charging is difficult. Therefore, if charging is performed while changing the moving speed of the member to be charged or moving at a low speed, it is difficult to charge to a desired potential, and the charging at a low speed becomes an unnecessarily high potential, and the photoreceptor due to overcharging of the image bearing member Problems such as layer damage and toner scattering during transfer occur. Further, if the image forming operation is performed while the linear velocity of the image carrier is changed, problems such as exposure, development, irradiation by the pre-transfer illumination lamp (PTL), and illumination by the pre-charge illumination lamp (PCL) occur, and the speed is increased. Light fatigue when too low
There are problems such as problems such as excessive development. or,
If the speed of the image carrier is changed during transfer, problems such as transfer deviation and defective magnification occur.

Further, in the above-mentioned conventional technique, it is not suitable to change the linear velocity during the exposure or development process, because it tends to cause image irregularity and unevenness. Therefore, after the image transfer onto the recording paper is completed. Speed switching is being performed. Therefore, a distance longer than the length of OHP paper (not only OHP paper but also ordinary recording paper) must be provided between the transfer unit and the fixing unit, which leads to an increase in size of the apparatus and an increase in cost. Becomes

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide a compact and stable image formation capable of expressing vivid full color on OHP paper or ordinary recording paper. Another object is to provide an image forming apparatus.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent an image forming operation from being performed at the time of switching the linear velocity in an image forming apparatus which performs image formation by switching the linear velocity of an image carrier during image formation. This is achieved by a characteristic image forming apparatus.

[0010]

First, the outline of the present invention will be described.

Image exposure is performed on a image carrier (hereinafter referred to as a photoconductor drum) in the order of yellow (Y), magenta (M), cyan (C) and black (Bk) at a normal linear velocity (process velocity). , Develop and enter the 5th rotation
After the TL (pre-transfer illumination lamp) irradiation is finished, the process speed is switched to a speed much lower than the normal time, and the transit time of the fixing unit is increased to improve the smoothness and the transparency of the toner.

When the process speed is changed, the image forming operation is not performed until the speed reaches a steady state. As a result, it is not necessary to perform complicated control during linear velocity change for image formation. That is, basically, the process control only needs to change the voltage applied to the transfer device to the condition that the transfer can be surely performed on the OHP paper or the normal recording paper at a low speed. Therefore, the fixing performance can be improved by the simple process control. it can.

Although it is not always necessary to change the control of the fixing conditions, if they are performed at the same time, the temperature of the heat roller is switched to a temperature suitable for the fixing nip time to accelerate the deformation of the toner and prevent the occurrence of offset. .. It is preferable that the switching of the fixing temperature is performed at the time when the operation is started in the OHP or the gloss mode, or before the operation. That is,
Since the fixing roller has a large heat capacity, it takes some time after the switching to reach the desired roller temperature range. Therefore, after switching the roller temperature,
Most preferably, printing is started after the area of the desired controlled temperature is reached.

Further, by switching the duty ratio of the transfer voltage to an appropriate value according to the linear velocity, it is possible to improve the stability of transfer.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a main part of an embodiment of an image forming apparatus of the present invention.

The present embodiment is a color copying machine equipped with a non-contact developing type laser writing device for four colors of Y, M, C and Bk.

In this embodiment, when forming a glossy image on OHP paper or ordinary recording paper, the process speed and the fixing speed are switched by the control of a control unit (not shown). When selecting OHP paper or paper on which a glossy image is to be formed as the recording paper,
The operator presses the OHP / glossy mode selection key on the operation unit to switch from the normal mode to the OHP / glossy mode.

First, the basic structure of the color copying machine main body and the basic operation in the normal mode will be described.

Before being exposed by the laser writing unit 2, the photosensitive drum 1, which is an image carrier, is subjected to static elimination by the PCL 12 and then uniformly charged to a predetermined potential by the charger 13. The charger 13 is a scorotron charger,
The grit voltage is −550 V and the charging potential of the photoconductor is −600 V, and this condition does not change in the normal mode / OHP and the gloss mode.

On the photosensitive drum 1 which has been primary charged,
An electrostatic latent image is sequentially formed by the laser writing unit 2, and the latent image is subjected to non-contact reversal development Y, M, C, Bk.
The developing devices 3, 4, 5 and 6 are sequentially developed. In the case of full color, the photosensitive drum 1 rotates once for each color development, and a total of four rotations are performed, so that toner images of a plurality of colors are overlapped and formed on the photosensitive drum 1.

Reference numeral 8 is a transfer belt device which is a belt-shaped transfer / conveying device, 81 is a transfer belt which holds an electric charge and adsorbs the recording paper P, and 83 and 84 are provided at both ends of a support member 82 to support the transfer belt 81. A holding roller for extending and rotating, 85 is a paper charger that discharges the recording paper P to the transfer belt 81 by electrostatic force with a conductive brush, and 86 is a toner image on the photosensitive drum 1. The transfer device is a transfer charging device for transferring from the recording medium to the recording paper P. With this configuration, the recording paper P can be firmly attached to the transfer belt 81 and reliably transported, and excellent transfer efficiency and separation efficiency can be obtained in the transfer section.

The transfer belt device 8 includes the photosensitive drum 1
This is a preferable apparatus in a color image forming apparatus in which toner images are formed on top of each other and transferred onto the recording paper P at one time. In the color copying machine, a plurality of developing devices are provided on the photosensitive drum 1 in order to superimpose a toner image on the photosensitive drum 1.
Since the drum diameter is larger in preparation for the peripheral portion and sufficient separation performance cannot be obtained with the conventional electrostatic transfer separation method, more reliable separation performance is required, and the toner adhesion amount is large in the method of superposing toner images. Therefore, the transfer belt device is excellent in two respects that a large transfer charge amount is required and therefore a large transfer charge holding capability is required.

The holding rollers 83, 84 of the transfer belt device 8 are rollers made of a conductive metal material, and the holding roller 83 on the upstream side is grounded or at a predetermined potential close to the grounded state. The supporting member 82 uses the axis of the holding roller 84 as a fixed shaft, and is normally urged by an elastic member (not shown) so that the holding roller 83 is located below the transfer belt 81.
Retreat away from the surface.

At the time of transfer, the support member 82 is rotated in the clockwise direction against the force of the elastic member by, for example, a solenoid which operates under the control of the control unit of the apparatus main body, and the transfer belt is rotated.
Reference numeral 81 is adapted to contact the photosensitive drum 1 with a predetermined pressure.

In the transfer belt device 8, the photosensitive drum 1 of the transfer belt 81 is rotationally driven at the same time when the second paper feed roller 9 starts to rotate and at the same time when the copying operation starts.
And a bias voltage for attracting the recording paper P before transfer is applied by the paper charger 86 and the paper charger 86. The leading edge of the recording paper P is the second
The sheet is fed to the transfer belt 81 by the sheet feeding roller 9. The recording paper P is attracted to the transfer belt 81 and is conveyed to the transfer section. The leading edge of the recording paper P has a certain length of the transfer portion (for example, 5 to 7 m).
m) When passing, the transfer power source of the transfer device 86 is turned on to start the transfer of the toner image. When the transfer is completed, the transfer belt 81 is separated from the photosensitive drum 1.

The recording paper P set in the paper feed tray 20
As shown in FIG. 4, the sheets are fed one by one by the feeding roller 16 and fed to the second feeding roller 9 via the first feeding roller 17 and the intermediate conveying roller 18. When the leading edge of the recording paper P comes into contact with the second paper feed roller 9, the paper sensor 91 causes the recording paper P to move.
It detects the arrival of the and emits a detection signal. By this signal, the first paper feed roller 17 and the intermediate conveyance roller 18 are stopped, and the recording paper P
Stands by for the transfer of the toner image while being in contact with the second paper feed roller 9. The rotation speeds of the first paper feed roller 17 and the intermediate conveyance roller 18 that feed the recording paper P in the standby state are the same in any mode, and the operation is performed at the process speed in the normal mode. As a result, the recording paper P always contacts the second paper feed roller 9 at the same speed and stands by, and the synchronous rotation of the second paper feed roller 9 ensures that the recording paper P is synchronized with the toner image on the photosensitive drum 1 and is transferred to the transfer portion. Will be delivered.

Numeral 21 is a tray for manual feeding, and the manually feeding recording paper is fed to the second paper feeding roller 9 by the feeding roller 16, and the recording paper is fed secondly by the detection signal issued by the paper sensor 91 as described above. It contacts the roller 9 and stands by for transfer.

When the recording paper P passes over the transfer device 86, the multicolor toner images formed in an overlapping manner are transferred at one time. The applied voltage for transfer is the normal paper mode and the OH, as described later.
The duty ratio is switched between P and gloss mode, and the same transfer voltage is always maintained.

The recording paper P on which the multicolor toner image has been transferred is neutralized by the static eliminator 87 and then fixed by the conveying roller 19 to the fixing device.
It is fed to 14 and the fixing process is performed. The fixing process is performed using the pair of heat rollers 14a and 14b. A heater is built in the heat roller 14a, and the fixing temperature is controlled by switching the operation time of the heater. This temperature control is performed by two types of uniform switching according to the recording paper mode and negative feedback control based on the environmental temperature measurement result by a temperature sensor (not shown).

After the fixing process, the recording paper P is sent to the external copy tray via the paper discharge roller 15 and discharged.

In the exposure and development process, the transfer belt
81 and the cleaning blade 11 of the cleaning device 11
A is retracted and in a non-contact state, and the photosensitive drum 1
In the fifth rotation, the transfer belt device 8 and the cleaning device 11 are pressed against each other. The reason why the transfer belt or the like is pressure-bonded after the multicolor toner image is completely formed is to prevent image fluctuation due to an increase in load during image formation.

The control section (not shown) is a fixing temperature control means,
A process speed control unit, a transfer / cleaning pressure bonding control unit, a transfer voltage duty ratio switching unit, and the like are provided, and the process speed switching, the transfer voltage duty ratio switching, and the like are comprehensively controlled.

Further, as the drive system block, for example, a three-phase stepping motor is used, and the photosensitive drum 1, the developing devices 3 to 6, the first paper feeding roller 17, the intermediate carrying roller 18, the second paper feeding roller 9, and the carrying device are carried. Belt 19, heat roller pair 14 of fixing device 14
Drive a, 14b, etc. This driving is performed, for example, by turning on the electromagnetic spring clutch of the first paper feed roller 9, and the electromagnetic clutches of the developing devices 3 to 6, the first paper feed roller 17, the intermediate conveyance roller 18, etc. by a command from the control unit.

Further, in order to supply the transfer voltage to the transfer device 86, a constant voltage power source 30 having a duty ratio switching means for switching the duty ratio of the transfer voltage according to the process speed shown in FIG. 2 is provided. The constant voltage power supply 30 includes a reference pulse generating circuit 31, a duty ratio changing circuit 32, a high frequency generating circuit 33 that is a high frequency constant voltage source, a switching circuit 34, a step-up transformer 35, and a rectifying / smoothing circuit 36 (a rectifier is connected in a bridge shape. Rectifier circuit 37 and smoothing capacitor 38), and a reference from the reference pulse generator circuit 31 based on a duty ratio command corresponding to the process speed (linear velocity) from the control unit, which is input to the duty ratio changing circuit 32. The duty ratio of the pulse is changed and sent to the switching circuit 34.
The switching circuit 34 chops (intermits) the high frequency from the high frequency generation circuit 33 based on the pulse having the duty ratio. This intermittent high frequency is a step-up transformer
The voltage is boosted to a predetermined voltage by 35, rectified and smoothed by the rectifying / smoothing circuit 36, and supplied to the charger 86. The charging state by the supplied voltage is shown in FIG. 3 with the vertical axis and the horizontal axis representing time, and the duty ratio changes as the process speed changes. The time for the charged body to pass through the opening of the transfer device 86 becomes longer as the process speed decreases and the number of applied voltage pulses increases, so if the duty ratio is changed in proportion to the process speed, regardless of the change in the process speed. It is possible to always maintain a constant charge amount. The constant voltage power supply 30 has been described as being used for the transfer device 86, but it can be used as an AC high voltage power supply such as a static eliminator if the rectifying and smoothing circuit 36 is removed as well as being used as another DC high voltage power supply. Even if the process speed changes, the member to be charged can always be maintained at a constant charge.

When the OHP or gloss mode is selected, the control section detects this and notifies the process speed switching means and the fixing temperature control means.

When the OHP and gloss modes are notified, the control section instructs the speed control means to significantly reduce the process speed and to keep the constant voltage at the time when the final development and irradiation of the PTL7 are completed. The power supply 30 is instructed to switch the duty ratio of the transfer voltage to the smaller side. As a result, the transfer adapted to the decrease in the process speed is performed.

When the fixing temperature is also controlled, the fixing temperature control means is instructed to switch the fixing temperature and the optimum fixing temperature condition is set. This switching is performed before the start of copying (printing) and the heat roller pair 14
Printing is started after the temperatures of a and 14b reach a desired area.

An example of the process speed and transfer condition switching in this embodiment is as follows.

Example of switching process speed (linear velocity) Normal paper mode From the first rotation to the end of printing: 140 mm / sec, OHP and gloss mode: Full color From the first rotation to the end of four revolutions: 140 mm / sec , From the 5th rotation to the end of printing… Switch to 20mm / sec.

Example of transfer condition switching Normal mode ... Duty ratio 84% OHP, gloss mode ... Duty ratio 12% The above description is for two modes, but for two or more modes respectively. It goes without saying that it is possible to control so that the process speeds of (1) and (2) are set and the duty ratio suitable for each process speed is selected.

Next, the operation in the OHP and gloss modes will be described with reference to the timing chart of FIG. 5 (the low speed portion is shown a little short because the chart becomes long).

When the mode selection key is pressed to select the OHP or gloss mode and the copy key (not shown) is pressed to issue a start command, control including switching of process conditions is started. That is, first, the fixing temperature control by the fixing temperature control means is started at time t ₀ , and the optimum fixing temperature is set. Since the fixing roller pair 14a, 14b has a considerable heat capacity, even if the fixing temperature is switched, the desired temperature range cannot be reached immediately. Therefore, at time t ₁ when the temperature reaches the desired temperature range, a start command is issued and the printing operation is started.

At time t ₁ , the photosensitive drum 1 starts to rotate at a linear velocity of 140 mm / sec. Image exposure and development of Y, M, C, and Bk are sequentially performed each time the photosensitive drum 1 makes one rotation, and when four rotations are completed and five rotations are completed, a superposed multicolor image is formed. Formed on.

The photosensitive drum 1 further rotates, and at the time t when the development of Bk of the fifth rotation is completed and the image forming operation is not performed.
₂ , the control unit issues a speed switching command to the speed control means,
The process speed can be switched to 20 mm / sec. Simultaneously with this control, the control unit controls the duty ratio changing circuit 32 of the constant voltage power supply 30.
Is output to the transfer device 81, and as a result, a transfer voltage with a duty ratio of 12% is applied to the transfer device 81 during transfer.

The peripheral surface of the photosensitive drum 1 to which the toner image has been transferred is neutralized by the pre-cleaning static eliminator 10 and then at a time t ₃ shortly before reaching the cleaning device 11, the cleaning device 11 is released and the cleaning blade 11A is removed. The photosensitive drum 1 is pressed and cleaning is started. The pre-cleaning static eliminator 10 and the static eliminator 87 are supplied with a constant voltage power source having a configuration in which the pulse of the neutralization voltage having a duty ratio adapted to the linear velocity of the photosensitive drum 1 is excluded from the rectifying and smoothing circuit 36 of the constant voltage source 30. Is applied.

Although the embodiments of the present invention have been described above, the control of the fixing roller temperature is not necessarily required for switching the fixing conditions, that is, the smoothness of the toner is changed only by changing the fixing nip time by changing the process speed. In addition, the transparency can be improved.

[0048]

As described above, in the image forming apparatus of the present invention, in the case of the OHP and gloss modes, the process speed is normally set at the time when the image forming operation is not performed after the last toner images are superposed. Since it is set to be much slower than the speed, the overall printing speed is much faster than conventional devices while keeping the device small, and it is possible to obtain vivid color images without requiring complicated control. The forming device was realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a main configuration of an embodiment of a color image forming apparatus of the present invention.

FIG. 2 is a block diagram showing an example of a constant voltage power supply used in the present invention.

FIG. 3 is a diagram showing a change of a duty ratio of an applied voltage by the constant voltage power supply of FIG.

FIG. 4 is a diagram showing a recording paper path from the paper feed tray of FIG. 1 to a second paper feed roller.

5 is a timing chart showing the operation of the apparatus of FIG. 1 in OHP and gloss modes.

[Explanation of symbols]

 1 image carrier (photosensitive drum) 2 laser writing unit 3, 4, 5, 6 developing device 7 PTL 8 transfer belt device 9 second paper feeding roller 10 pre-cleaning static eliminator 11 cleaning device 12 PCL 13 charger (scorotron charging) 14 Fixing device 16 Feeding roller 17 First paper feeding roller 18 Intermediate feeding roller 30 Constant voltage power supply

Claims (1)

[Claims] 1. An image forming apparatus for performing image formation by switching the linear velocity of an image carrier during image formation, wherein the image forming operation is not performed at the time of switching the linear velocity.