JPH0820815B2 - Toner image transfer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A toner image transfer device used in an electrostatic recording device using a photosensitive drum or a dielectric drum as an endless image bearing member carrying a charged toner. Regarding a toner image transfer device for electrostatically transferring a toner image formed on a recording medium, a toner image capable of reducing the electrostatic attraction force at the leading edge of recording paper that is passed through the image transfer device. To provide a transfer device, a transfer charger arranged to face an endless image bearing member carrying a charged toner, and a transfer charger so as to emit a charge having a polarity opposite to that of the charged toner. A first charge amount that does not discharge charges when the recording medium is not interposed between the power supply that supplies electric energy to the transfer charger and the image carrier, and a second charge that attracts the charged toner when the recording medium is present. amount A control means for controlling the electric energy so that when the leading edge portion of the recording medium is present, the electrostatic charge between the recording medium and the image carrier is reduced so that the third charge amount is smaller than the second electric amount. And a toner image transfer device including.

[Industrial applications]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner image transfer device used in an electrostatic recording device using a photosensitive drum or a dielectric drum as an endless image carrier for carrying charged toner, and more specifically, it is formed on such an image carrier. The present invention relates to a toner image transfer device that electrostatically transfers a toner image onto a recording medium.

[Conventional technology]

To explain the recording principle of the electrostatic recording apparatus, an electrostatic latent image is formed on the surface of a photosensitive drum or a dielectric drum, which is an endless image carrier, and this electrostatic latent image can be developed with charged toner. It is a visual image. Then, a recording medium, that is, a recording paper is applied to such a toner image, and a charge having a polarity opposite to that of the charged toner is applied to the recording paper from the back surface thereof, whereby the toner image is electrostatically transferred to the recording paper. It The recording paper having such a transferred toner image is separated from the drum and sent to a heat roller fixing device or the like, where the transferred toner image is thermally fixed on the recording paper.

Referring to FIG. 6, as an example of the electrostatic recording apparatus, the principle configuration of a laser printer adopting an electrophotographic system is schematically shown. In the electrophotographic system, a photosensitive drum 10 is used, and this photosensitive drum 10 is one in which a photosensitive material layer is formed on the surface of a cylindrical body made of Al, for example, and such a photosensitive material is known as a photoconductive substance. For example, a-Si
Is used. During the recording operation of the laser printer, the photosensitive drum 10 is rotationally driven in the direction indicated by the arrow a. The laser printer includes a charging device 12, a developing device 14, a transfer charging device 16 and a cleaner 18 which are sequentially arranged around the photosensitive drum 10 along the rotation direction thereof. The recording paper P is introduced between the photosensitive drum 10 and the transfer charger 16 in the direction of the arrow b, and the fixing device 20 is provided on the downstream side in the traveling direction of the recording paper P.

The charger 12 is composed of, for example, a corona discharger, and is configured to charge the photosensitive material layer of the photosensitive drum 10, that is, the a-Si layer, with a positive charge (indicated by + in the figure).
When the a-Si layer is positively charged, the Al inside
Negative charges appear in the layer. An electrostatic latent image is written in the charged area of the photosensitive drum 10 by a laser beam 22 based on image data from a word processor or a microcomputer, and the electrostatic latent image area (so-called charge well) 24 is an uncharged area. It is said that

The developing device 14 is a hopper that holds toner that is colored fine particles.
14a and a toner supply roller 14b for supplying toner to the surface of the photosensitive drum 10, and the toner in the hopper 14a is charged with a positive electric charge by frictional action or charge injection. In the figure, the charged toner charged with the electric charge on the front side is indicated by. When the electrostatic latent image area on the photosensitive drum 10 passes the developing device 14, the charged toner is charged inside the photosensitive drum 10.
The negative charge of the Al layer attracts and attaches to the electrostatic latent image area, which develops the electrostatic latent image as a visible or toner image.

The transfer charger 16 can be composed of a corona discharger like the charger 12, and is configured to charge the recording paper P with a negative charge (indicated by-in the figure) having a polarity opposite to that of the charged toner. It Therefore, when the toner image on the photosensitive drum 10 passes through the transfer charger 16, the toner image is electrostatically attracted from the photosensitive drum 10 side to the recording paper P side, whereby the toner image is transferred to the recording paper P. To be done.

The transfer efficiency of the toner image by the transfer charger 16 is determined by the charge amount of the recording paper P, and a part of the charged toner is on the photosensitive drum 10.
Will remain. Such residual toner is
The photosensitive area 10 is cleaned by the cleaner 18, and the cleaning area is charged with a positive charge again by the charger 12.
In preparation for writing the next electrostatic latent image. The cleaner 18 may be configured by, for example, a fur brush 18a. On the other hand, the transferred toner image is sent to the heat fixing device 20, for example, together with the recording paper P, and is thermally fixed as a fixed image 26 on the recording paper P. The heat bonder 20 may include a heat roller 20a and a pressure roller 20b.

Incidentally, as described above, the transfer efficiency of the toner image is determined by the charge amount of the recording paper P, but in order to increase the transfer efficiency, a relatively large predetermined charge amount, for example, about 320 μC / m ²
It is necessary to give a certain degree to the recording paper P.
The 16 is naturally designed to accommodate its charge supply.
However, when such a charge amount is applied to the recording paper P, the recording paper P receives an electrostatic attraction force that attracts it toward the photosensitive drum 10, and as a result, the recording paper P is
When the recording paper P is introduced between the transfer charger 10 and the transfer charger 16 and discharged from between the transfer charger 16 and the transfer charger 16, the leading edge portion of the recording paper P is wound around the photosensitive drum 10 without being separated from the photosensitive drum 10.

Therefore, conventionally, the separation claw member 28 as shown in FIG. 7 is used.
Is applied to the photosensitive drum 10, so that the recording paper P is separated from the photosensitive drum 10 after the toner image is transferred. More specifically, the separating claw member 28 includes a claw element 28a made of an elastic rubber material and an arm portion 28b holding the claw element 28a, and the arm portion 28b is pivotally attached to the shaft portion 28c,
Moreover, a torsion spring is provided on the shaft portion 28c so as to elastically bias the arm portion 28b counterclockwise (in FIG. 7).
28d is provided so that the pawl element 28a is elastically pressed against the surface of the photosensitive drum 10. In short, by interposing a claw element between the front edge of the recording paper P that has passed through the transfer charger 16 and the surface of the photosensitive drum 10,
The recording paper P is peeled off from the photosensitive drum 10. In FIG. 7, reference numerals 30 and 32 respectively denote guide plates for the recording paper P, and the guide plate 30 denotes the recording paper P.
The guide plate 32 is arranged on the introduction side of the recording paper P and the guide plate 32 is arranged on the discharge side of the recording paper P.

[Problems to be Solved by the Invention]

As described above, in the conventional electrostatic recording device, the separation claw member is used to separate the recording paper from the photosensitive drum after the toner image transfer. The problem is that the separation of the paper cannot be achieved sufficiently. Separation performance with only the separation claw member varies depending on various conditions such as the type of recording paper, but normally only about 80% can be obtained. That is, two of the ten recording sheets may be caught on the photosensitive drum without being peeled off from the photosensitive drum. One of the reasons is that the separation claw member can be provided only on the side of the recording sheet (that is, when the separation claw member is provided at the center of the recording sheet, the claw element is The biggest reason is that when the recording paper is passed through the transfer charger, the leading edge of the recording paper is charged with an abnormally high amount of electric charge, which causes This is because the leading edge of the paper is attracted to the photosensitive drum side with a large electrostatic attraction force.

Fig. 8 shows the result of measuring the electric potential of the recording paper discharged from the transfer charger by a surface electrometer (Model 360 manufactured by Trek). The horizontal axis of this graph indicates the surface electric potential of the recording paper. (T) when the recording paper passes through, and the vertical axis thereof represents the potential (V) of the passing portion when the recording paper passes through the surface electrometer. That is, from t = 0 to t≈1250ms
The potential distribution up to shows the potential distribution from the leading edge to the trailing edge of the recording paper. As is clear from the graph in FIG. 8, the leading edge portion and the trailing edge portion of the recording paper are maintained even though the corona current is kept constant while the recording paper passes through the transfer charger, that is, the corona discharger. It can be seen that the electric potential becomes abnormally high between the parts. This phenomenon is caused by a large difference between the electrostatic capacity of the photosensitive drum only and the electrostatic capacity of the recording sheet applied to the photosensitive drum. To be more specific, when viewed from the transfer charger, that is, the corona discharger, when the photosensitive drum alone is used, the electrostatic capacity of 5 μF / m ² is the charged object, whereas when the recording paper is applied to the photosensitive drum, 0.5 μF / m ² represented by the composition of the recording paper and the photosensitive drum is the object to be charged, and as a result, a large amount of charge is given to the surface of the a-Si photosensitive layer having a large electrostatic capacity. When the leading edge of the recording paper is introduced into the transfer charger and when the trailing edge is discharged from the transfer charger, a part of the large amount of charges to be applied to the surface of the a-Si photosensitive layer is part of the leading edge of the recording paper. And the trailing edge portion thereof, and as a result, the potential distribution of the recording paper becomes as shown in FIG.

For the above reasons, the charge amount between the leading edge portion and the trailing edge portion of the recording paper is the optimum transfer charge amount (320
μC / m ² ), which makes the electrostatic attraction force at the leading edge of the recording paper extraordinarily important for separating the recording paper abnormally large. It is not possible to sufficiently separate the recording paper only by itself.

Therefore, an object of the present invention is to provide a toner image transfer device capable of reducing the electrostatic attraction force at the leading edge of recording paper that is passed through the toner image transfer device.

[Means for solving the problem]

Then, as shown in FIG. 1, such an object is to provide a transfer charger 16 arranged to face an endless image carrier carrying a charged toner, and the transfer charger 16 is opposite to the charged toner. In the state where the recording medium is not interposed between the image carrier 10 and the power source 34 for supplying electric energy to the transfer charger 16 so as to discharge the polar charge, the charge is not discharged. The first charge amount, when the recording medium is present (FIG. 1 (c)), the second charge amount for adsorbing the charged toner, and when the leading edge portion of the recording medium is present (FIG. 1 (d)) In order to reduce the electrostatic attraction force between the recording medium and the image carrier and to make the electric potentials at the leading edge portion and the central portion of the recording medium the same,
It is achieved by providing a toner image transfer device including a control means 36 for controlling electric energy so that the third charge amount is smaller than the third charge amount.

[Action]

As described above, in the toner image transfer device according to the present invention, the electric energy to the transfer charger is controlled by the control means so as to reduce the charge amount at the leading edge portion of the recording paper. The electrostatic attraction force that acts to draw the leading edge toward the image carrier is reduced.

〔Example〕

Next, referring to FIG. 2A, FIG. 2B, FIG. 3A, FIG. 3B, FIG. 4A and FIG. 4B of the attached drawings, an embodiment of a toner image transfer device according to the present invention Will be described.

FIG. 2A shows an embodiment of the toner image transfer device according to the present invention, which is used in the electrophotographic laser printer as described with reference to FIGS. 6 and 7. It will be described as being incorporated. In addition,
In FIG. 2A, the same reference numerals are used for the same components as in FIGS. 6 and 7, and those components have the same function.

In the embodiment shown in FIG. 2A, the toner image transfer device comprises a transfer charger 16 configured as a corona discharger, and a DC power supply 34 for supplying electric energy to the transfer charger 16. The transfer charger 16 is arranged close to the photosensitive drum 10 so as to transfer the toner image on the photosensitive drum 10 onto the recording paper introduced in the direction of the arrow b. As described with reference to FIG. 6 and FIG. 7, since the toner image on the photosensitive drum 10 is given a positive charge, the DC power source 34 controls the recording paper P.
Transfer charger 16 corona wire to give negative charge to
By supplying electric energy to 16a, the toner image is electrostatically transferred from the photosensitive drum 10 to the recording paper P.

The ON / OFF control of the DC power supply 34 is performed by the control circuit 36, and this control circuit 36 is also the control circuit of the laser printer itself. The control circuit, that is, the mechanical controller 36, includes a central processing unit (CPU) 38, a read-only memory (ROM) 40 that stores an operation program of the laser printer itself, an ON / OFF control program of the DC power source 34, constants, and the like. Writable and readable memory (RAM) that stores specific data, etc. 4
2 and an input / output interface (I / O) 44.
The ON / OFF signal of the DC power supply 34 is sent via the I / O 44 to the DC power supply 34.
Is input to

In the embodiment shown in FIG. 2A, the DC power source 34 is turned on after the leading edge of the recording paper P has passed the transfer charger 16 for a predetermined length, whereby the leading edge of the recording paper P is turned on. Is not substantially given a negative charge. DC power supply 34
Regarding the timing of ON / OFF operation, the leading edge of the recording paper may be detected by an appropriate recording paper detector arranged near the recording paper introduction port of the transfer charger 16, and this detection time may be used as a reference. However, in this embodiment, the rise of the write timing signal when writing the electrostatic latent image on the photosensitive drum 10 with the laser beam is used as a reference. In the above laser printer, the feeding operation of the recording paper is synchronized with the rising of the writing timing signal, and the recording paper reaches a predetermined position with respect to the transfer charger 16 after a lapse of a predetermined time from the rising of the writing timing signal. Since the transfer start position of the toner image on the recording paper is always the same, the rising edge of the write timing signal can be used as a reference for the ON / OFF operation timing of the DC power supply 34. is there.

More specifically, as shown in FIG. 2A, the cart sheet-shaped recording paper P fed from the paper feeding hopper (not shown) by the pick roller (not shown) reaches the positions of the standby rollers 50a and 50b. , Both standby rollers 50a, 50b
It is pinched in between and stopped. This state is detected by the photo sensor 51, and a detection signal is sent to the mechanical controller 36 via the A / D converter 51a.

Since the recording paper P is in the standby state, the mechanical controller 36 sends a print data request signal to the host controller 61 via the I / O 44. The host controller 61 receives via the I / O 61a, the character code data sent from the host computer stored in the code buffer 61b,
The image signal is converted based on a CG (character generator) 61c and stored in the image memory 61d.

The host controller 61 sends a start signal to the mechanical controller 36 via the I / O 61e when the image data for one page is stored in the image memory 61d. After the mechanical controller 36 receives the start signal, the laser scanning optical system including the semiconductor laser 71a and the polygon mirror 71b.
Output of a beam detection signal (writing timing signal) from a start detection sensor 71d provided at the scanning start reference position of the laser beam 71c of 71 (this writes an electrostatic latent image on the photosensitive drum 10). At that time,
A drive command is output to the driver 50d to drive the standby rollers 50a and 50b, and the motor 50e is rotationally driven. The output signal of the start detection sensor 71d is read by the mechanical controller 36 via the A / D converter 71e and I / O 44.

On the other hand, the mechanical controller 36 issues such a drive command, and at the same time when the recording paper P reaches the position of the transfer charger 16, the start detection sensor is activated so that the toner image is transferred.
The host controller 6 synchronizes with the beam detection signal of 71d.
Outputs a horizontal sync signal for 1.

Therefore, each time the host controller 61 receives such a horizontal synchronizing signal, it sends the image data (video signal) for each line from the image memory 61d to the mechanical controller 36. The mechanical controller 36 turns on / off a drive circuit (not shown) of the semiconductor laser 71a based on the video signal to form an electrostatic latent image on the photosensitive drum 10.

By the way, the mechanical controller 36 counts the detection signals of the start detection sensor 71d in parallel with such an image forming operation. When the count value coincides with a predetermined value corresponding to the leading edge of the recording paper P passing through the transfer charger 16 for a predetermined length as described above, the DC power supply 34 is turned on. "It will be done.

FIG. 2B shows another embodiment of the toner image transfer device according to the present invention. This toner image transfer device uses a DC power source 34 'of a type different from that in the case of FIG. 2A. Except for this, it is the same as the toner image transfer device shown in FIG. 2A. The DC power supply 34 'is provided with two output terminals, one of which outputs low electric energy and the other of which outputs high electric energy.
to supply to a. For example, DC power supply 34 '
Is a direct current source, the low electrical energy is 100
μA, and the electric energy of each is 200 μA. Second
Also in the embodiment of FIG. B, the ON / OFF operation timing of the DC power source 34 'is based on the rise of the write timing signal when writing the electrostatic latent image on the photosensitive drum 10 with the laser beam. An output switching signal as to whether to output low electric energy or high electric energy from 34 'is also referred to the rising edge of the write timing signal, and these signals are supplied via the I / O 44 to the DC power source 3
Entered in 4.

Next, the operation of the toner image transfer device shown in FIG. 2A will be described with reference to FIGS. 3A and 3B. FIG. 3A shows a power supply output control routine of the DC power supply 34, which is 4 ms.
The interrupt routine is executed every time, and FIG. 3B is a time chart for explaining the power output control routine of FIG. 3A. The operating conditions are as follows.

The photosensitive drum 10 was a drum having a diameter of 120 mm and having an a-Si photosensitive layer, and was rotated at a low speed so that the peripheral speed was 240 mm / s.

+70 for the photosensitive drum 10 with a charger, that is, a corona discharger
The surface potential of the electrostatic latent image area was lowered to about 100V by charging to 0V and writing an electrostatic latent image on the surface with a semiconductor laser beam.

Applying a bias voltage of + 450V to the magnetic brush developer,
The electrostatic latent image area was developed as a toner image.

DC power source 34 for transfer charger 16 or corona discharger
To 200 μA of direct current was applied.

The time required from the start of writing the electrostatic latent image to the photosensitive drum 10, that is, the rising edge of the write timing signal, until the leading edge of the recording paper P reaches the introduction port of the transfer charger 16 is 532 ms, and then 172 ms delay. The DC power supply 34 was turned on at the timing. That is, after 704 ms from the rising edge of the write timing signal, the transfer charger 16 sets 200 μA
Will be applied with a direct current of.

In step 301, it is determined whether the write timing signal for writing the electrostatic latent image on the photosensitive drum 10 is at the H level or the L level. When the write timing signal becomes H level (that is, at the rising time), the routine proceeds to step 302, where the counter C _H is incremented by 1. Then proceed to step 303, where the counter C _H
It is determined whether the count number of is greater than 176 (704 ms). When the count number of the counter C _H is 176 (704 ms) or less, the process goes beyond step 304 to proceed to step 305, where the counter C _L is cleared and then the process is returned. In the above operation, the count number of the counter C _H is 176 (704m
It is repeated every 4ms until the time reaches s). The counter C _H
When the number of counts reaches 133 (532 ms), the leading edge of the recording paper P reaches the transfer charger 16 up to the inlet (FIG. 3B). At this time, the DC power supply 34 is in the "off" state, and the transfer charger 16 is controlled to have the first charge amount that does not discharge the charges.

In step 303, the count number of the counter C _H is 176 (704m
s), go to step 304, where DC power source
34 is turned on, and at this time, the toner on the photosensitive drum 10 is controlled to the second charge amount for transferring the toner onto the recording paper P. Therefore, the count number is 133 (5
From 32 ms) to 176 (704 ms), the leading edge of the recording paper P is controlled to have a third charge amount (that is, the same as the first charge amount in this embodiment). It will be. Next, the routine proceeds to step 305, where the counter _CL is cleared and then the routine is returned. When the count number of the counter C _H becomes 176 (704 ms) or more, steps 301 to 305 are repeated every 4 ms, but this repetition is continued until the fall of the write timing signal. The electrostatic latent image written between the rising edge and the falling edge of the write timing signal should be recorded as a transfer toner image on one sheet of the recording paper P.

When the write timing signal becomes L level (that is, at the falling time), steps 301 to 306
And the counter C _L is incremented by 1. Next, in step 307, it is determined whether or not the count number of the counter C _L is larger than 133 (532 ms).
When the count number of the counter C _L is 133 (532 ms) or less, the process goes beyond step 308 to proceed to step 309, where the counter C _H is cleared and then the process is returned. The above operation is repeated 4ms each until the count number of the counter C _L reaches 133 (532ms), when the count number of the counter C _L at step 307 reaches 133 (532ms), the process proceeds to step 309,
Then, the DC power supply 34 is turned off. That is, after the count number of the counter C _H reaches 176 (704 ms) in step 303, until the write timing signal becomes L level, and even after the write timing signal becomes L level, the count of the counter C _L is counted in step 307. The ON state of the DC power supply 34 is maintained until the number reaches 133 (532 ms), and thus the transfer of the one toner image from the photosensitive drum 10 to the recording paper P is completed.

When the DC power supply 34 is turned off in step 308, the process proceeds to step 309, where the counter C _H is cleared and then the process is returned. The count number of counter C _L is 133 (532ms)
When the above is reached, steps 301, 306 to 309 are repeated every 4 ms, and this repetition is continued until the rising of the write timing signal, while the counter C _H is maintained in the clear state and the write timing signal becomes H level again. The above-mentioned operation will be repeated.

As is clear from the above description, since the DC power supply 34 is turned on at a timing 172 ms after the leading edge of the recording paper P reaches the transfer charger 16, it corresponds to the delay time. The amount of electric charge applied to the leading edge of the recording paper P is substantially zero, and the electrostatic attraction force can be reduced.

Next, the operation of the toner image transfer device shown in FIG. 2B will be described with reference to FIGS. 4A and 4B. FIG. 4A shows a power supply output control routine of the DC power supply 34 ', which is an interrupt routine executed every 4 ms as in the case of FIG. 3A, and FIG. 4B shows that of FIG. The time chart for demonstrating a power supply output control routine is shown. The operating conditions are almost the same as those in FIGS. 3A and 3B, and only the differences will be described below.

DC power supply 3 for transfer charger 16 or corona discharger
A DC current of 100 μA or 200 μA from 4'is applied according to the power output switching signal.

The time required from the start of writing the electrostatic latent image to the photosensitive drum 10, that is, the rising edge of the write timing signal, until the leading edge of the recording paper P reaches the introduction port of the transfer charger 16 is 532 ms. Turn on the DC power supply 34 '
At the same time, a DC current of 100 μA was applied to the transfer charger 16, and then a DC current of 200 μA was applied to the transfer charger 16 at a timing delayed by 172 ms.

In step 401, it is determined whether the write timing signal for writing the electrostatic latent image on the photosensitive drum 10 is at H level or L level. When the write timing signal becomes H level (that is, at the rising edge), the process proceeds to step 402, where the output current from the DC power source 34 '(100 μA).
And 200 μA), the power supply output switching signal is judged to be at the H level or the L level.

When the power supply output switching signal is at the L level in step 402, the process proceeds to step 403, where the flag F ₁ is "1" or "0".
Is determined. When flag F ₁ is “1”, step
Proceed to 404, where the counter C _H is incremented by 1.

Next, in step 405, it is determined whether or not the count number of the counter C _H is greater than 133 (532 ms). When the count number of the counter C _H is 133 (532 ms) or less, the process goes beyond the steps 406 to 412 to the step 413, where the counter C _L is cleared and then the process is returned. In the above operation, the count number of the counter C _H is 133 (532m
It is repeated for 4 ms until it reaches (s).

In step 405, the count number of the counter C _H is 133 (532 m
s) (at this time, the leading edge of the recording paper P reaches the transfer charger 16 up to the introduction port), the process proceeds to step 406.
Therefore, the flag F ₁ is rewritten to “0”, and then step 407
Then, the DC power supply 34 'is turned on. At this time, the power supply output switching signal is at the L level, so the DC power supply
A current of 100 .mu.A is output from 34 ', and the transfer charger 16 is applied by the current of 100 .mu.A.

After turning on the DC power supply 34 'in step 407, the process proceeds to step 408 where the counter C _H is cleared and then to step 409 where the counter C _H is incremented by 1 and then step 410. Then counter C _H
It is determined whether the count number of is greater than 43 (172 ms). If the count value of counter C _H is 43 (172ms) or less, step beyond steps 411 and 412
Proceed to 413 where the counter C _L is cleared and then returned. In the above operation, the count number of the counter C _H is 43
It is repeated every 4ms until it reaches (172ms).

In step 410, the count number of the counter C _H is 43 (172ms)
(At this time, the leading edge of the recording paper P is a transfer charger.
16 reaches the discharge port), the process proceeds to step 411, where the power supply output switching signal is changed from the L level to the H level. When the power supply output switching signal becomes H level, the current output from the DC power supply 34 'is switched from 100 μA to 200 μA, and the transfer charger 16 is applied by the current of 200 μA.

Next, in step 412, the flag F _{1 is set} to "1".
To the counter C _L.
It is returned after clearing.

When the power output control routine is executed again after 4 ms,
The process proceeds from step 401 to step 402. At this time, the power supply output switching signal is at the H level, so step 402
To Step 413, the counter C _L is cleared, and then the process is returned. Such an operation is performed until the write timing signal becomes L level (that is, the photosensitive drum 10
It is repeated every 4 ms until the writing of the electrostatic latent image to the end is completed.

When the write timing signal becomes L level, step
The routine proceeds from 401 to step 414, where it is determined whether the power supply output switching signal is at H level or L level. At this time, the power supply output switching signal is at the H level (Fig. 4B).
The process proceeds from step 414 to step 415 where the flag F ₂ is rewritten to “1” and then step 416 where the counter _CL
Is incremented by 1.

In step 417, the count number of the counter C _L is 133 (53
2 ms), and if the count value of the counter C _H is 133 (532 ms) or less, step
After passing 418 to 424, the process proceeds to step 425 where the counter C _M is cleared and then the process is returned. The above operation is 4m until the count number of the counter C _L reaches 133 (532ms)
Repeated every s.

In step 417, the count number of the counter C _L is 133 (532m
s) (at this time, the recording paper P from the photosensitive drum 10
Transfer of the toner image to the end is completed), the process proceeds to Step 418, where the flag F ₂ is rewritten to “0”, and then Step
Proceeding to 419, the power supply output switching signal is changed from the H level to the L level. At this time, the current output from the DC power supply 34 'is switched from 200 μA to 100 μA.
The transfer charger 16 is applied with a current of 0 μA.

Then, the process proceeds to step 420, where the counter C _L is cleared, in step 421 the counter C _L is incremented by one. Then, in step 422,
There, it is determined whether the count number of the counter C _L is larger than 55 (220 ms).

When the count number of the counter C _L is 55 (220 ms) or less, the process goes beyond the steps 423 and 424 to the step 425 where the counter C _H is cleared and then the process is returned. In this operation, the count number of the counter C _L is 55 (220ms)
Is repeated every 4 ms, and if the write timing signal becomes H level in the meantime, the operation described above is repeated.

On the other hand, when the write timing signal does not become the H level even when the count number of the counter C _L reaches 55 (220 ms), the routine proceeds to step 423, where the DC power supply 34 ′ is turned off, and then the flag F. _{After 2} is rewritten to "1", the process proceeds to step 425, where the counter _CM is cleared and then the process is returned. After that, when the power output switching control routine is executed every 4 ms, step 401 to step 4
When the routine proceeds to step 14 and then proceeds to step 415, steps 516 to 420 are skipped, and then steps 421 to 425 are successively proceeded to and then the routine is returned. In short, it waits for the next rise (H level) of the next write timing signal while the power supply output switching signal is at L level.

As is clear from the above description, the current applied to the transfer charger 16 is 100 μA to 200 μ at a timing 172 ms after the leading edge of the recording paper P reaches the transfer charger 16.
Since A switching is performed, the amount of electric charge applied to the leading edge of the recording paper P corresponding to the delay time is greatly reduced.

In the embodiment described above, a direct current source was used as a direct current power source for supplying electric energy to the transfer charger, but it will be apparent that a direct current voltage source may be used instead to perform the same control. .

Further, in the above-mentioned embodiment, the corona discharger is used as the transfer charger, but it goes without saying that the charge can be applied to the recording paper by using another charger.

〔The invention's effect〕

As is clear from the above description, in the toner image transfer device according to the present invention, the charge amount to the leading edge portion of the recording paper can be reduced, so that the separation property of the recording paper from the recording medium drum after the toner image transfer can be reduced. As a result, the separating performance by the separating claw member was improved to almost 100%.

5A and 5B show the results of measuring the charge distribution of the recording paper when the toner image was transferred to the recording paper in the above-mentioned two examples by the same method as in FIG. Show. FIG. 5A shows the measurement result in the case of the embodiment of FIG. 2A, and FIG. 5B shows the measurement result in the case of the embodiment of FIG. 2B. As is clear from the comparison of FIGS. 8A and 8B, according to the present invention, the amount of charge at the leading edge of the recording paper can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of the present invention, FIG. 2A is a block diagram showing an embodiment of a toner image transfer device according to the present invention, and FIG. 2B is a block diagram showing another embodiment of the toner image transfer device according to the present invention. FIG. 3A is a power output control routine for explaining the operation of the toner image transfer device of FIG. 2A, FIG. 3B is a time chart for explaining the power output control routine of FIG. 3A, and FIG. FIG. A is a power output control routine for explaining the operation of the toner image transfer device of FIG. 2B, FIG. 4B is a time chart for explaining the power output control routine of FIG. 4A,
FIG. 5A is a graph showing the charge distribution of the recording paper when the toner image is transferred onto the recording paper by the toner image transfer device of FIG. 2A, and FIG. 5B is the toner image transfer device of FIG. 2B. 6 is a graph showing the charge distribution of a toner image when the toner image is transferred onto the recording paper, FIG. 6 is a schematic view for explaining the recording principle of a laser printer adopting an electrophotographic method, and FIG. 7 is a toner image transfer. FIG. 8 is a schematic diagram illustrating a conventional technique for separating a subsequent recording sheet from a photosensitive drum by a separation claw member, and FIG. 8 is a charge of the recording sheet when a toner image is transferred to the recording sheet by a conventional toner image transfer device. It is a graph which shows distribution. 10 ... Photosensitive drum, 16 ... Transfer charger, 34, 34 '... DC power supply, 36 ... Control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunihiko Sato, Kanahiko-ku, Nakagawa-ku, Kawasaki, Kanagawa 1015, Kamiodanaka, Fujitsu Limited (72) Inventor Masao Konishi, 1015, Kami-Odanaka, Nakahara-ku, Kawasaki, Kanagawa Prefecture, Fujitsu Limited ( 72) Inventor Akaken Iwamasa 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Toshio Toda 1015, Uedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (72) Inventor, Hiroshi Kano Kanagawa 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Fukuoka Within Fujitsu Limited (72) Inventor Osamu Utaka, 1015 Kamiotanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Kanagawa, Ltd. (72) Ryu Kitao, Nakahara-ku, Kawasaki-shi, Kanagawa 1015 Odanaka, Fujitsu Limited (56) Reference JP-A-52-43440 (JP, A) JP-A-57-506 9 (JP, A) JP-A-61-73170 (JP, A)

Claims (1)

[Claims] 1. A transfer charging device, which is arranged so as to face an endless image bearing member carrying a charged toner, and the transfer charging device so that the transfer charging device discharges a charge having a polarity opposite to that of the charged toner. The recording medium is not present between the power source for supplying electric energy to the container and the image carrier (first
In FIG. 1B, the first charge amount that does not release the charge, when the recording medium exists (FIG. 1C), the second charge amount that adsorbs the charged toner, and the presence of the leading edge portion of the recording medium (first At the time of FIG. 1 (d), the electrostatic charge between the recording medium and the image carrier is reduced, and the electric potentials of the leading edge portion and the central portion of the recording medium are made equal to each other so as to be smaller than the second charge amount. A toner image transfer device including: a control unit that controls the electric energy so as to have a third charge amount.