JPH0117583B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transfer/separation device for an electrophotographic copying machine.

A transfer-type electrophotographic copying machine applies a transfer electric field to attract the toner adsorbed to the electrostatic latent image formed on the photoreceptor to the copy paper side, and performs the transfer. Copy paper sticks to the photoconductor. A separating device separates the copy paper from the photoreceptor, and in order to electrostatically apply the force for this separation, an electric charge is injected into the copy paper during transfer, and the copy paper is made into a conductor after transfer. It has been proposed to utilize the electrostatic attractive force between the charges and the induced charges generated in the conductor by bringing the charges close to each other.

FIG. 1 shows the principle of the transfer/separation device, which is the object of the present invention. Reference numeral 1 denotes a photoreceptor, which rotates in the direction of arrow A. The photoreceptor 1 carries an electrostatic latent image 2 of negative polarity, to which toner 3 of positive polarity is adsorbed. Copy paper 4, which is fed toward the circumferential surface of photoreceptor 1 as shown by arrow B, is injected with a negative charge by corona discharger 5 to which DC voltage is applied. As a result, the toner 3 is attracted to the copy paper 4 and transferred. The copy paper 4 that has been transferred is attracted to the circumferential surface of the photoreceptor 1 and advances to a position where the conductive belt 6 is installed. The conductive belt 6 is running as shown by arrow C. Copy paper 4 is placed on the conductive belt 6.
Electrostatic induction occurs due to the negative charge inside the copy paper 4.
A positive charge is induced in the area facing the And, due to the electrostatic attraction force that acts between these two charges,
The copy paper 4 is attracted to the conductive belt 6 and separated.

Incidentally, the potential of the conductive belt 6 has a great influence on transfer and separation performance. conductive belt 6
When the conductive belt 6 is grounded, the negative charges generated in pairs with the positive charges due to the electrostatic induction immediately escape to the ground, so that the potential of the conductive belt 6 is maintained at zero. In this state, the separation performance is sufficient, but on the other hand, the suction force of the toner 3 to the copy paper 4 side is insufficient, and the toner 3 is re-transferred to the photoreceptor 1 side, resulting in insufficient transfer performance. do. If the conductive belt 6 is not grounded but left floating,
Since the negative charge generated by the electrostatic induction has nowhere to escape, the potential of the conductive belt 6 is thereby increased to a negative polarity. In this state, the transfer performance is sufficient, but the separation performance is insufficient.

In order to solve this problem, the present inventor invented and separately applied for a method of connecting an external DC power source to the conductive conveying member and controlling the potential so that it is low at the start of separation and becomes high thereafter. . According to this invention, at the time of starting separation, although the transfer is temporarily insufficient and white spots appear at the leading edge of the copy paper, a reliable separation force is obtained, so the start of separation is reliably performed, and thereafter, Even if the separation force decreases,
Since the separation action once started can be maintained as it is, it is possible to achieve both separation performance and transfer performance.

However, in the above invention, since white spots occur at the leading edge of the copy paper, it is necessary to reduce these spots to a level that does not cause any practical problems.

In order to meet this demand, the present invention is an improvement of the above-mentioned invention, and the timing of voltage application to the conductive conveying member is determined based on the properties of the copy paper, environmental conditions, or use conditions such as changing the magnification. It is characterized in that it can be changed depending on the situation, etc., and the blank width can be kept to the necessary minimum.

Next, the invention before the improvement, which is the premise of the present invention, will be explained with reference to the embodiments shown in FIGS. 2 to 5.

Transfer from the photoreceptor 1 to the copy paper 4 is performed by charging the copy paper 4 with the corona discharger 5 in accordance with the principle described above. Feeding of copy paper 4 onto the circumferential surface of photoreceptor 1 is controlled by registration rollers 7 . That is, the registration roller 7
is waiting in a stopped state, and starts rotating when a resist clutch signal is applied as part of the copy cycle, and feeds the copy paper 4 to the circumferential surface of the photoreceptor 1 at a predetermined timing.

The conductive belt 6 is grounded via a power supply circuit 8, and its potential is controlled by the power supply circuit 8. The power supply circuit 8 is controlled by a timing control circuit 9 which starts operating when the registration roller 7 starts rotating.

FIG. 3 shows a power supply circuit 8 and a timing control circuit 9.
This is an example. When a resist clutch signal A (see Fig. 4, hereinafter the same) for starting the resist roller 7 is applied to the input terminal T, the transistor Tr ₁ is turned on, the electromagnetic clutch CL is connected, and the resist roller 7 is turned on. Rotation is started, and feeding of the copy paper 4 is started. When transistor Tr ₁ turns on, transistors Tr ₂ and Tr ₃ also turn on, and transistor Tr ₃ turns on.
The collector of changes from high level to low level as shown by b. This change causes capacitor C ₁
A differentiator circuit containing the trigger signal becomes the trigger signal and starts timer IC ₁ . Timer IC ₁ produces an output signal C for time t ₁ and connects it to capacitor C ₂
is applied to a second differentiating circuit including This second differentiating circuit generates a trigger signal T at the rising edge of signal I and supplies it to the second timer IC ₂ to start it. The second timer IC ₂ produces an output D, turning on the transistor Tr ₄ for a time t ₂ and energizing the relay RA.

A normally closed contact S of the relay RA is connected between the output terminal 10 of the power supply circuit 8 and the ground terminal via a resistor _R2 . The output terminal 10 is connected to a -600V DC power supply via a resistor _R1 . Further, between the output terminal 10 and the ground terminal, there is a constant voltage element Z and a series circuit of a resistor R ₃ and a capacitor C ₃ .
each connected. Since the contact S is closed until the relay _R4 is energized, the potential at the output terminal 10 of the power supply circuit 8 exhibits a value close to zero. When relay RA is energized and contact S is opened, capacitor _C3 is charged from the -600V DC power supply via resistors _R1 and _R3 , so output terminal 1
The potential at 0 gradually increases as shown by E, and -
It becomes constant at 600V. Since the conductive belt 6 is connected to the output terminal 10 of this power supply circuit 8,
Its potential will also be the same.

FIG. 5 shows temporal changes in the potential of the conductive belt 6, and also shows the conveyance position of the copy paper 4. In FIG.

At time 0, the resist clutch signal A is given,
When the registration rollers 7 start rotating, the leading edge of the copy paper 4 starts running from a point _P1 on the registration rollers 7. At time _t3 , the leading edge of the copy paper 4 reaches the contact point _P2 between the conductive belt 6 and the photoreceptor 1.
However, since the power supply circuit 8 does not yet produce an output, the potential of the conductive belt 6 exhibits a value close to zero.
When time t ₁ , that is, the time t ₁ set by timer IC ₁ has elapsed since the start, relay RA is energized and its contact S opens, so power supply circuit 8
generates an output, and the potential of the conductive belt 6 gradually increases as shown in graph ho, reaching -600V.
When the time _t2 set by the timer IC ₂ has elapsed from the time _t1 , the copy paper 4 completes passing, and the power supply circuit 8 returns to the original zero potential state again to prepare for the next start.

By the way, when the leading edge of the copy paper 4 reaches point _P2 , the potential of the conductive belt 6 is still zero, so sufficient separation performance is obtained, and the copy paper 4
The tip of the conductive belt 6 is separated from the photoreceptor 1.
, and is thereby conveyed in the direction of arrow C.
At this time, the transfer performance is degraded and white spots occur at the leading edge of the copy paper 4, but since it is at the edge, there is no practical problem.

Since the potential of the conductive belt 6 begins to rise (in the negative direction) when the leading edge of the copy paper 4 reaches the _P3 point, the resulting suction force gradually decreases and the transfer performance recovers. Once the copy paper 4 is attracted to the conductive belt 6, it moves away from the photoreceptor 1, so even if the suction force decreases, the separation performance does not deteriorate, and the copy paper 4 continues to be attracted to the conductive belt 6. transported.

The above is the invention before improvement, but in the present invention, the timing _t1 is changed according to variable factors such as the properties of copy paper, environmental conditions such as temperature and humidity, or usage conditions such as copying magnification. do.

FIG. 6 shows an embodiment thereof. The resist clutch signal A is applied to the CPU control circuit 12 together with the signal Q generated from the input circuit 11 in accordance with the fluctuation factor, and the timing control circuit 9' is controlled by the output signal I' of the CPU control circuit 12. Ru. The CPU control circuit 12 is provided not only to control the transfer/separation device but also to centrally control the inside of the copying machine, and performs various controls based on the signal input from the input circuit 11. Emit a signal. The input circuit 11 includes a paper quality changeover switch, a temperature and humidity detector, a magnification changeover switch, and the like.

The CPU control circuit 12 is the input circuit 11
The optimum timing t ₁ is determined based on the signal Q from the timing control circuit 9', and the output signal A' is given to the timing control circuit 9'. As shown by graph ho' in Figure 7, the start time of voltage application to the conductive belt 6
Lengthen t ₁ ′. As a result, the separation force is increased and the period at which transfer performance is sacrificed becomes longer, so the width of the white spot that occurs at the leading edge of the copy paper 4 becomes longer.
They are never inseparable. This width changes depending on the timing _t1 , but is usually about 3 mm and can be used as a binding margin for copies.

FIG. 8 shows a second embodiment. In this example, the timing control circuit 9 shown in FIG.
A timing switching circuit 13 is added.
The timing switching circuit 13 includes a resistor R ₄ inserted into a time constant circuit including a capacitor C ₄ that determines the set time t ₁ of the timer IC ₁ . The resistance R ₄ is
The relay RA ₂ is short-circuited by the normally closed contact S ₂ of the relay RA ₂ , which is connected to the transistor Tr ₅ which is turned on by the timing switching signal applied to the terminal T ₁ .
controlled by.

When there is a factor of separation uncertainty or when increasing the binding margin, a timing switching signal is applied to the terminal _T1 . As a result, relay RA ₂ is energized, contact S ₂ is opened, and resistor R ₄ is inserted into the time constant circuit, so timing t ₁ changes to t ₁ ', and conductive belt 6 is connected to the external power supply circuit. The timing at which the voltage from 8 is applied is delayed to ensure separation.

In the above embodiment, the registration clutch signal issued at the start of the registration rollers was used as a means for detecting the timing of conveyance of the copy paper. The timing of conveyance of copy paper can also be detected by detecting a passing point or by detecting that the potential of a conductive conveyance member changes due to electrostatic induction due to the approach of charged copy paper. This can be used as a resist clutch signal.

As described above, the present invention makes it possible to adjust the period when securing separation performance by temporarily sacrificing the transfer function at the start of separation, thereby reducing the white area to the minimum necessary value. It is possible to achieve both transcription and separation functions while suppressing

[Brief explanation of drawings]

Figure 1 is a front view showing the principle of the transfer/separation device;
Fig. 2 is a front view showing the invention before improvement, Fig. 3 is its circuit diagram, Fig. 4 is a timing chart, Fig. 5 is a graph showing potential changes, and Fig. 6 is a diagram showing an embodiment of the invention. 7 is a graph showing the potential change, and FIG. 8 is a circuit diagram of another embodiment. 1... Photoreceptor, 4... Copy paper, 5... Corona discharger, 6... Conductive belt, 8... Power supply circuit, 9, 9'... Timing control circuit, 11...
Input circuit, 13... timing switching circuit.

Claims (1)

[Claims] 1. Toner is attracted to the electrostatic latent image formed on the photoconductor, and the resulting toner image is transferred to copy paper in a transfer section under the application of a transfer electric field, and then the copy paper and conductive In a transfer/separation device of an electrophotographic copying machine that separates the copy paper from the photoreceptor by applying an electrostatic attraction force between the conveying members, an external DC power supply connected to the conveying member and , properties of copy paper, environmental conditions,
External variation factor input means such as usage conditions, and timing control means for controlling the timing of voltage application to the conveyance member by the DC power supply based on a copy paper conveyance timing signal and a signal from the external variation factor input means. A transfer/separation device for an electrophotographic copying machine, comprising: