JPH0511646A - Image forming device - Google Patents

Abstract

PURPOSE:To secure high transfer efficiency without being influenced by fluctuations in the resistance of a transfer roller, and to improve a using latitude by converging on one point of a voltage-current characteristic set in advance with respect to the image carrier of the transfer roller by the use of PWM control. CONSTITUTION:On the voltage-current characteristic curves of the transfer rollers A-D having prescribed resistance, a transfer bias setting line N is obtained by plotting a point that the transfer efficiency is maximum on each transfer roller when the resistance of the transfer roller is changed and actual printing is executed. The intersection of the voltage-current characteristic curve and the transfer bias setting line N is obtained, and the transfer bias of the transfer roller is set. In other words, a voltage applied to the transfer roller is sequentially increased by using a PWM(pulse width modulating) system, and at this time, a current flowing on a photosensitive body is monitored to obtain a point that the monitored voltage is made coincident with the transfer bias setting line, as the voltage-current characteristic. This monitored voltage is held and applied when a transfer material passes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a toner image or the like on an image bearing member such as a photoconductive photosensitive member, a dielectric member or a magnetic member by an appropriate image forming process means such as electrophotography, electrostatic recording or magnetic recording. Of a transferable image is formed and carried, and the transfer material is passed through a transfer site between the image carrier and a contact transfer means such as a roller body or a belt body which is brought into contact with the image carrier to apply a transfer bias to the image carrier side. The present invention relates to a transfer type image forming apparatus such as a copying machine or a printer, which transfers a transferable image to a transfer material side to obtain an image formed product.

[0002]

2. Description of the Related Art In an image forming apparatus having a contact type transfer means, a transfer bias applied to the transfer means is usually controlled by a constant voltage or a constant current.

A transfer roller or the like used as the contact transfer means is usually one in which conductive particles are dispersed in rubber and the volume resistance is appropriately adjusted, but this kind of material is well known. Since the resistance value changes over several digits depending on the environment, it is difficult to always apply a stable transfer bias regardless of the environment.

[0004] To briefly describe this, when a transfer bias is set appropriately in a normal temperature and normal humidity environment (23 ° C, 60% RH, hereinafter referred to as N / N environment), a low temperature and low humidity environment (15 ° C, 10%). In RH (hereinafter, referred to as L / L environment), a transfer failure occurs because the resistance value of the transfer unit / transfer material is large.

On the contrary, a high temperature and high humidity environment (32 ° C., 85%
In RH (hereinafter, referred to as H / H environment), the resistance value of the transfer unit becomes small, so that an excessive bias is applied, and excess transfer charges caused by this cause punch-through of the transfer material. Part of the transfer bias changes to the same polarity as the transfer bias and does not transfer to the transfer material, resulting in transfer omission, or excessive current flowing into the image bearing member (hereinafter referred to as the photoconductor drum) to generate transfer memory. To do.

On the other hand, according to the constant current control, the inconvenience due to the change of the resistance value of the transfer means is solved and the charge amount required for the continuous transfer can be secured, but this type of image forming apparatus is large or small. Since various transfer materials can be used normally, when a small-sized transfer material is used, naturally, there is an area where the image carrier and the transfer means come into direct contact with each other. Therefore, if this direct contact area is large, most of the current will flow through this area, and especially under the L / L environment, the transfer charge will be insufficient and transfer failure will occur.

In order to avoid the above-mentioned inconvenience, constant current control is performed when the transfer material does not exist at the transfer portion, and the voltage at this time is held, and the voltage is fixed at this voltage when the paper is passed. A control system (Active Transfer Voltage Control, hereinafter referred to as ATVC control system) adapted to perform voltage control has been proposed (Japanese Patent Application No. 1-85189).

More specifically, a constant current is passed through the dark potential (V _D portion) of the photosensitive drum, the generated voltage is monitored, and the voltage is changed to. 1x ,. Coefficient times ,. Apply a constant voltage ,. In addition, the applied bias is controlled by performing other combinations, etc., and has a certain effect in preventing the occurrence of transferability variations due to environmental changes and transfer material size differences.

[0009]

However, this A
When the TVC control method is applied to the contact transfer means, there are drawbacks as described below.

That is, in the ATVC, a current is made to flow on the photosensitive drum as an image carrier before transfer, the resistance of the contact transfer means is detected from the generated voltage, and the current value controlled during transfer is 1
Therefore, there is a problem that the estimation becomes unacceptable and the accuracy is low.

Further, since there is a secular change of the contact transfer means and a resistance change due to voltage application, ATVC cannot perform sufficient estimation and bias control, and there is a problem that the latitude of the resistance value suitable for use is narrow.

According to the present invention, the resistance latitude of the contact transfer means is widened so that the transfer voltage most suitable for the resistance value can be applied so that the resistance value of the contact transfer means is not affected by the fluctuation. The objective is to ensure high transfer efficiency, improve the latitude in use, improve the manufacturing yield, and reduce the cost due to its ripple effect.

[0013]

The present invention is an image forming apparatus having the following configuration.

(1) A transferable image is formed and carried on the image carrier by an image forming process means, and a transfer material is passed between the image carrier and the contact transfer means to which a transfer bias is applied. In a transfer type image forming apparatus for transferring a transferable image on the image carrier side to a transfer material side, the voltage applied to the contact transfer means is sequentially increased before the transfer operation, and the voltage of the contact transfer means on the image carrier is increased. An image forming apparatus characterized by having means for converging current characteristics to a preset point on a voltage-current curve, and using PWM control as the converging means.

(2) The image forming method according to (1), characterized in that the means for sequentially increasing the voltage applied to the contact transfer means by the PWM control is carried out at the start-up of the image forming apparatus or before the start of the transfer operation. apparatus.

(3) The image forming apparatus according to (1) or (2), wherein the means for sequentially increasing the voltage applied to the contact transfer means by the PWM control is repeated a plurality of times.

[0017]

In other words, in the image forming sequence of the image forming apparatus,
For example, the voltage applied to the contact transfer means such as a transfer roller before the transfer operation is sequentially increased by using the PWM control method,
By implementing a means for converging the voltage-current characteristic curve of the contact transfer means with respect to the image carrier to one point on the transfer bias setting line represented by a preset voltage-current curve, a contact having a relatively low resistance can be obtained. It is possible to set a bias that allows a large amount of current to flow to the transfer unit when the paper is passed, and a bias that allows a small amount of current to flow to the contact transfer unit having a relatively high resistance when the paper is passed. Become.

As a result, when the transfer material is passed, almost the same amount of current always flows into the transfer material irrespective of the resistance value state of the contact transfer means. High transfer efficiency and good transferability are always ensured without being affected by aging due to use, environmental changes, voltage changes, and the like.

In other words, it becomes possible to realize the transfer bias control which sufficiently copes with the manufacturing variation of the resistance value of the contact transfer means, the environmental variation / durability variation and the voltage variation, and it is possible to realize the L / L environment, the H / H environment, etc. Transfer failure can be solved and the transfer bias can be controlled to the bias most suitable for use of the transfer means, so that the latitude (margin) of the resistance value of the transfer means is widened, the yield at the time of manufacturing the transfer means is improved, and the cost is reduced. As a result, good transferability can be obtained in a wider resistance value range than before.

[0020]

【Example】

<Example 1> (Figs. 1 to 9) (1) Example of image forming apparatus Fig. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser printer using an electrophotographic process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member. The photoconductor drum of this example has an OPC photoconductor layer (organic photoconductor layer) formed on the outer peripheral surface of a conductive drum substrate made of Al or the like, and has a process speed of 50 mm / sec (clockwise direction). It is driven to rotate at a peripheral speed). The maximum throughput of the printer is 8 sheets in A4 size.

Reference numeral 2 denotes a primary charging roller as a charging processing means for the photosensitive drum 1, which is brought into pressure contact with the photosensitive drum 1 with a predetermined pressing force and rotates following the rotation of the photosensitive drum 1. A bias voltage is applied to the charging roller 2 from the power source 3 to uniformly negatively charge the peripheral surface of the rotating photosensitive drum 1. The power supply 3 is controlled by a DC controller 9 having a CPU via a low pass filter 10a and an AD converter 10b.

Scanning by a laser beam 4 image-modulated and output from a laser scanner (not shown) corresponding to target image information on the surface of the rotary photosensitive drum 1 which is uniformly negatively charged by the charging roller 2. Upon exposure, the potential of the scanning exposed portion is attenuated and an electrostatic latent image corresponding to the target image information is formed on the surface of the rotary photosensitive drum 1. The electrostatic latent image is developed as a toner image by the negative toner of the reversal developing device 5.

Then, the toner image is transferred from a sheet feeding section (not shown) to a transfer portion between the photosensitive drum 1 and a transfer roller 6 as a contact transfer means through a conveying path 7 at the same timing as the rotation of the photosensitive drum 1. The transfer material P that has been fed is sequentially transferred. The transfer roller 6 is brought into pressure contact with the photosensitive drum 1 with a predetermined pressing force, is rotated in the forward direction of the rotation of the photosensitive drum 1 at substantially the same peripheral speed as the photosensitive drum 1, and the power source 3 The transfer bias is applied from.

The transfer material P that has passed through the transfer portion is sequentially separated from the rotary photosensitive drum 1 and conveyed to a fixing device (not shown) to undergo a fixing process of the transferred toner image.

After the toner image is transferred onto the transfer material P, the surface of the photosensitive drum 1 is cleaned by a cleaner 8 to remove adhering residual contaminants such as untransferred toner, and is repeatedly used for image formation.

The material of the transfer roller 6 as the contact transfer means used in this embodiment is urethane rubber, silicone rubber, EPR (ethylene propylene rubber), EPDM (terpolymer of ethylene propylene diene), IR (isoprene). Although a rubber material such as rubber) is used, EPDM is used in this embodiment. Examples of the conductive material dispersed in EPDM include carbon, zinc oxide, tin oxide, and the like. In this example, zinc oxide having a relatively high specific resistance was used. Then, EPDM in which zinc oxide is dispersed is foamed and formed in a roller shape with a thickness of 6 mm on a core metal 6a made of SUS φ8,
The foamed EPDM transfer roller 6 having an outer diameter of φ20 was used.

The resistance value of the transfer roller is determined from the relationship between the current measured under a load of about 300 g and at a peripheral speed of about 50 mm / sec with respect to the ground, and under a voltage of 1.0 KV. When the resistance value was measured, it was about 5 × 10 ^{7 to} 5 ×
Lot variation occurred at 10 ⁹ Ω. The primary charging potential on the photosensitive drum 1 is a dark potential VD = -600V and an exposure potential (bright potential) _VL = -100V.

(2) Transfer Bias Control Method FIG. 2 shows each VI of the transfer rollers A to D having the following resistance values.
It is a characteristic curve. This VI characteristic is due to the dark potential portion V on the photoconductor.
_{This is for D} (= -600V). The measuring method of the resistance value is the above-mentioned measuring method.

Roller A = 1.0 × 10 ⁸ Ω Roller B = 5.0 × 10 ⁸ Ω Roller C = 1.0 × 10 ⁹ Ω Roller D = 5.0 × 10 ⁹ Ω The solid straight line in FIG. Graph N is a preset voltage-current curve for transfer bias setting (hereinafter referred to as transfer bias setting line). The transfer bias setting line is obtained by plotting the points at which the transfer efficiency is maximized at each transfer roller when actually printing by changing the resistance value of the transfer roller. The relational expression between the voltage and the current on the transfer bias setting line in FIG. 2 is I _T = −0.85V _T +7, where I _T is [μA] and V _T is a unit of [KV].

The reason why the transfer bias setting line has such a shape will be described with reference to FIG. FIG. 3 shows VI characteristics of the transfer roller B and the transfer roller D. The solid line is for the V _D portion (−600 v) when the paper is not passed, and the broken line is for the transfer material when the paper is passed.

What can be seen from FIG. 3 is that the transfer roller B,
Comparing D, the difference ΔI = I _P between the current I _vd flowing when the paper is not passed and the current I _P flowing when the paper is passed is different. This is because when the resistance of the transfer roller is relatively low, the load from the core metal of the transfer roller to the photoconductor largely changes depending on the presence or absence of the transfer material. Is smaller. Therefore, in order to obtain the voltage required to flow the same amount of current when the transfer material passes through the transfer roller having a resistance different from that before the transfer operation, the roller B having a relatively low resistance increases the current flowing in the V _D portion. On the contrary, it is desirable to set the current flowing through the V _D portion of the roller D, which is relatively high, to be smaller than that of the roller B. For that reason, the transfer bias setting line is sloping down to the right on the graph of the VI characteristic of FIG.

In the present invention, the intersection between the VI characteristic curve of the transfer roller and the transfer bias setting line is found to set the transfer bias of the transfer roller. The means and features will be described below. .

In this embodiment, the voltage applied to the transfer roller is sequentially increased before the transfer operation, and at that time, the current flowing on the photosensitive member is monitored to obtain the VI characteristic, and the transfer bias setting line IT ₌₌ A point corresponding to 0.85V _T +7 is obtained, and the voltage V _T at that time is held,
It is applied when the transfer material passes.

In FIG. 3, the holding voltage V of the transfer roller B is
_When printing is performed on each of the rollers by the holding voltage V _TD of _TB and the transfer roller D, I _TB of each of the rollers B and D,
The current I _TD will flow through the transfer material.

As a means for changing the voltage applied to the transfer roller, there is a method of increasing the signal from the DC controller through a DA converter in an analog manner. However, in the present invention, PWM (Pulse Width Modulation) is used.
method)) was used.

FIG. 6 shows an example of the transfer high voltage control circuit. D
The PWM signal output from the C controller 9 is converted into a signal having a level of 0 to 5 V by passing through the low-pass filter 10a on the primary side of the high-voltage transformer 41, and then transformed into a transfer bias.

That is, the Dut of the pulse signal is controlled by the RWM control.
LPF by modulating y (duty) ratio
The voltage after (low-pass filter) 10 changes, and the generated voltage also changes accordingly.

Schematic diagrams are shown in FIGS. Figure 4 shows PWM
The relationship of the (hard) generated (output) voltage to the control duty ratio (soft) is shown.

Since the maximum output voltage of the transfer high voltage transformer of the laser printer used in this embodiment is 5.0 kv,
When the PWM duty ratio is 100%, a voltage of 5.0 kv is output. Duty ratio of PWM is 25
It has a resolution of 6 bits and is increased by 1 bit. The ratio of the increasing voltage when divided by 256 bits is ≈20 v / bit, which is a sufficient value as the resolution of the transfer high voltage. A characteristic of PWM control is that such high resolution can be obtained.

FIG. 5 shows how to increase the voltage by sequentially increasing the duty ratio of PWM as a model. In FIG. 5, a: b is the duty ratio, and the duty ratio is gradually increased from the state of, that is, the number of bits is increased, and finally the voltage is increased to the voltage of the transfer bias setting line described above. This PWM-controlled signal is performed on the DC controller 9 in FIG. 1, and this signal is input to the high voltage control circuit shown in FIG.

The output voltage changes with the change of the PWM signal, and the current i flowing through the load 11 such as the transfer roller and the photoconductor also changes. The current i is converted into a voltage by the voltage conversion circuit 12 and fed back to the DC controller 9 via the A / D converter 10b.

On the DC controller 9, it is judged whether or not the relationship between the PWM signal and the above voltage, that is, the transfer roller applied voltage and the photosensitive member inflow current matches the VI relationship of the transfer bias setting line described above, and the PWM is performed until they match. Signal Du
Keep increasing the ty ratio.

Then, the voltage (P
The WM signal level) is held and is applied when the transfer material passes.

FIG. 7 is a diagram showing an algorithm of the above bias control.

8 and 9 are timing charts for implementing the present invention. In carrying out the present invention, it is necessary to carry out before the transfer operation. After turning on the power of the laser printer, the fixing device is first heated. Then, the photosensitive drum drive called pre-multi-rotation is executed before or after the warm-up. This is carried out for a certain period of time for the purpose of cleaning the surface of the photoconductor and making the surface potential uniform when the laser printer is started up. FIG. 8 is a timing chart when the present invention is carried out during the multi revolution before that. FIG. 9 is a timing chart when the present invention is carried out in a state called pre-rotation, which is carried out for a period of time after the transfer of the print signal until the transfer material reaches the transfer position.

In FIGS. 8 and 9, the transfer bias PWM control is carried out during the pre-multi-rotation and the pre-rotation respectively. During the time period other than printing, the transfer roller is cleaned by applying a bias having the same polarity as the toner to the transfer roller.

In order to carry out the present invention, either pre-multi-rotation or pre-multi-rotation is possible, but if it is carried out during pre-multi-rotation, it is not necessary to lengthen the pre-rotation for control, and a decrease in throughput is achieved. Can be prevented. Further, if it is performed during the pre-rotation, a new transfer bias is set each time the printing operation is performed, so that accurate transfer bias control is possible.

In this embodiment, the purpose is for better transfer bias control, and therefore the timing chart shown in FIG. 9 is used.

The transfer rollers A to D shown in FIG. 2 were incorporated into the laser printer shown in FIG. 1, respectively, and the images were output under the control method described above. 2.2KV, 2.95K
V and a voltage of 4.25 KV were obtained, the current when the transfer material was passed was within a range of approximately 1.2 to 1.8 μA, and good image quality could be obtained with high transfer efficiency.

Even if the resistance value of the transfer roller changes due to aging or environmental change, the tendency of the VI characteristic does not change. Therefore, the amount of current flowing through the transfer material is always controlled regardless of the resistance value. Therefore, highly accurate transfer bias control can be realized.

<Second Embodiment> (FIGS. 10 to 12) A second embodiment of the present invention will be described with reference to FIG. A transfer roller or the like as the contact transfer means does not reach a state in which the foamed rubber and the dispersed filler are uniformly mixed due to manufacturing problems. As a result, the longitudinal direction of the transfer roller
Variation and unevenness of the transfer roller resistance occur in the circumferential direction.

FIG. 10 is a graph of VI characteristics when such a transfer roller is used. Due to the variation in resistance of the transfer roller, the current flowing into the photosensitive member fluctuates as shown in FIG. 10 even if a constant voltage is applied. In the transfer roller E, there is a variation of about ± 20% in the central value of the current flowing in, and in the transfer roller F, there is a variation of ± 10%.

When the above transfer roller is incorporated into the laser printer of FIG. 1 and the transfer bias control described in the first embodiment is performed, the transfer voltage V _TE required for the transfer roller E is not determined and V _TEmin. It swings between V _TE ≤ V _{TE max} .

[0055] swings between _{V TFmin. ≦ V TF ≦ V} TFmax. In the same time the transfer roller F. In this way, when the transfer voltage fluctuates, particularly when printing is performed with a transfer roller having a relatively low resistance such as the transfer roller E, the current flowing through the transfer material also fluctuates during printing as shown by the dotted line in FIG.

Specifically, in the transfer roller E, if the desired transfer voltage is V _TE = 2.05 KV, the voltage value deviated by the resistance unevenness in the circumferential direction of the transfer roller is ± 2.
A 00V, the V _TEmin. = 1.88KV in V _TEmax. = 2.28KV, the minimum voltage is the maximum voltage. The current flowing through the transfer material is 1.0 to _1.8 μA at the optimum transfer voltage V _TE , whereas it is 0.8 to _1.4 μA at V _{TE min.} , _And 1.6 to _2.6 μA at V _{TE max.} An electric current flows.

Looking at the minimum and maximum values of these current values, the values fluctuate from 0.8 to 2.6 μA. In the case of 0.8 μA, insufficient current causes transfer failure, resulting in 2.6 μA
In the case of, the current becomes excessive, resulting in popping and blurring, which lowers the transfer efficiency.

In order to solve these problems, it is necessary to make the point of convergence as close as possible to V _TE .

In the present embodiment, this converging means is realized as follows. That is, the operation of the means for sequentially increasing the voltage applied to the transfer roller before the transfer operation and converging the VI characteristic of the transfer roller with respect to the photoconductor to one point on the preset transfer bias setting line is performed a plurality of times. It was attempted to obtain the desired bias by executing and averaging the held voltages.

The transfer bias control method will be described with reference to FIG. Although this control is executed during the pre-rotation before the transfer operation, it may be executed a certain number of times or as many times as possible within the unit time. In this embodiment, the control time is set to 1.26 sec for one rotation of the transfer roller, and the control means specifically described in the first embodiment is implemented. The time required for the control means to raise the voltage once to 0 to V _T [KV] is about 50 to 100 msec. Therefore, sampling can be performed at least 10 times or more. The voltages V _{T1 to} V _Tn obtained by this control are averaged to obtain a transfer voltage V _T [KV]. The algorithm of the above sequence is shown in FIG.

FIG. 1 shows the transfer rollers E and F of FIG.
Was installed in the laser printer of the above, and the printing was executed by controlling the transfer bias described above.
A bias of 2.2 KV was obtained with the transfer roller E and a bias of 3.75 KV was obtained with the transfer roller F with respect to _TE = 2.08 KV.

By carrying out the control according to the present invention, the deviation of the control value of the transfer bias when it is not carried out is ± 5.
What was 10% came to fall within ± 3 to 5%. The result of printing with each of the transfer rollers is
Good quality with no transfer defects, pops, blurring, etc.
More precise control is possible.

<Embodiment 3> (FIGS. 13 and 14) A feature of this embodiment is that the VI characteristic of the transfer roller with respect to the photoconductor is accurately converged at one point on the transfer bias setting line. It is always raised from the applied voltage V _t = 0 [V] when performed multiple times V-I characteristics of the transfer roller in the second embodiment described above. However, once PW
The voltage V _tn raised by the M control is dropped to 0 [V] again,
It can be said that raising V _{tn + 1} again is a waste of time.

In the present embodiment, the dead time of the PWM control is omitted, and the convergence means is implemented as many as possible to achieve the convergence with higher accuracy. FIG. 13 shows a model when this control is executed. Together with the V _t1 When Motoma' the first intersection V _t1 of the transfer bias setting line and V-I characteristic curve in the present embodiment, the value 3 of its 3/4
V _t1 / 4 is held, and in the control of the next stage, the voltage is gradually increased from 3 V _t1 / 4 instead of from 0 [V].

The value of 3/4 is a value arbitrarily set by the present inventor, but if this value is small, the characteristics of this embodiment cannot be utilized and only the same effect as that of the second embodiment can be obtained. Absent. Further, when the value approaches 1, the current value on the transfer bias setting line exceeds the current value when the initially converged voltage becomes higher than the average, and then the voltage does not converge.

Therefore, it is desirable to set an optimum value based on the above two conditions. Normally, the transfer roller, which has a relatively low resistance, has a high probability of not converging on one point on the transfer bias setting line, so that the converged voltage is 0.5 to 0.8.
It is better to set it to double. In this embodiment, 3/4 = 0.75
Set to.

FIG. 14 shows the transfer bias control algorithm at this time. In this algorithm, the PWM control of the transfer bias is continued during the time required for one round of the transfer roller to be 1.26 sec. However, since the sampling time is simply 1/4 of the time to reach 0 [V], the number of times of sampling becomes four times and the accuracy becomes high. 0
Time required for [V] to V _Tn [V] 50 to 100 msec
Is possible in 15 to 25 msec, and the sampling frequency is 30 to 40 times. As a result, the accuracy with which the desired transfer bias is obtained is greatly increased, and when the transfer roller E used in Example 2 is tested, it converges to a desired set value within ± 1% to 2%, and higher accuracy is obtained. It became possible to control the transfer bias.

[0068]

As described above, according to the present invention, a transferable image is formed and carried on the image carrier by the image forming process means, and the image carrier is brought into contact with the contact transfer means to which a transfer bias is applied. Regarding a transfer type image forming apparatus that transfers a transferable image on the image carrier side to the transfer material side by passing a transfer material between them, the resistance latitude of the contact transfer means is wide,
Furthermore, it is possible to apply the optimum transfer voltage to the resistance value, and always ensure high transfer efficiency without being affected by the resistance fluctuation of the contact transfer means, the latitude used, the improvement of manufacturing yield, and the cost due to its ripple effect. Allow down.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a laser printer as an image forming apparatus according to an embodiment.

FIG. 2 is a voltage-current characteristic diagram of a transfer roller.

FIG. 3 is a diagram showing a current flowing when the voltage is the same when the paper is not fed and when the paper is fed

FIG. 4 is a diagram showing a relationship between a PWM duty ratio and a generated voltage.

FIG. 5 is a diagram showing how the duty ratio of PWM increases.

FIG. 6 is a schematic diagram of a transfer high voltage control circuit.

FIG. 7 is a diagram showing an algorithm for controlling a transfer bias according to the first embodiment.

FIG. 8 is a timing chart when the transfer bias is controlled during the previous multi-rotation.

FIG. 9 is a timing chart when the transfer bias is controlled during the previous rotation.

FIG. 10: Voltage when transfer roller has uneven resistance
Current characteristic diagram

FIG. 11 is a schematic view when the converging means of the second embodiment is carried out.

FIG. 12 is a diagram showing an algorithm of transfer bias control according to the second embodiment.

FIG. 13 is a schematic diagram when the sampling time is shortened in the third embodiment.

FIG. 14 is a diagram showing an algorithm of transfer bias control according to the third embodiment.

[Explanation of symbols]

1 Image carrier (photosensitive drum) 2 Contact transfer means (transfer roller) 3 Bias application power supply 4 laser light 5 Developer 6 Contact transfer means (transfer roller) 8 cleaner P transfer material 9 DC controller with CPU 10a low pass filter 10b ADA converter

Claims (3)

[Claims] 1. A transferable image is formed and carried on an image carrier by an image forming process means, and a transfer material is passed between the image carrier and the contact transfer means to which a transfer bias is applied. In a transfer type image forming apparatus that transfers a transferable image on the image carrier side to a transfer material side, the voltage applied to the contact transfer means is sequentially increased before the transfer operation, and the voltage applied to the image carrier by the contact transfer means- A means for converging the current characteristic to one point on a preset voltage-current curve,
An image forming apparatus using PWM control as the converging means. 2. The means for sequentially increasing the voltage applied to the contact transfer means by the PWM control is carried out when the image forming apparatus is started up or before the transfer operation is started. Image forming apparatus. 3. A means for sequentially increasing the voltage applied to the contact transfer means by the PWM control is repeated a plurality of times.
The image forming apparatus according to claim 1 or 2, characterized in that.