DE2603366A1 - CONTROL SYSTEM FOR AN ELECTROPHOTOGRAPHIC COPY DEVICE - Google Patents

Description

DR. BERG DiPL.-iNG. STAPF DIPL.-ING. SCHWABE DR. DR. SANDMAIR

PATENT LAWYERS
8 MUNICH 86, POST BOX 860245

260336b

Attorney's file: 26 796

2 9th M.

Ricoh Company Ltd Tokyo / Japan

Control system for an electrophotographic copier

The invention relates to a control system for an electrophotographic A copier, and particularly a copier employing a wet developer method is used to convert an electrostatic latent image into a visible image which is then transferred to a copy sheet will. The various steps, such as loading, exposure and development, are carried out one after the other in the copier, to create a visible image on a photoconductive member which is transferred to a copy sheet.

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t (089) 988272 8 Manchen 80, Mauerkircherstraße 45 Banks: Bayerische Vereinsbanlc Manchen 453100

98 70 43 Telegrams: BERGSTAPFPATENT Munich Hypo-Banlc Munich 389 2623

983310 TELEX: 0S24560 BERG d Postscheck Munich 65343-808

ORIGINAL INSPECTED

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With reference to Fig. 1, an embodiment of a copier will now be described, in which the invention is used or can be used. In Fig. 1, a photoconductive part 1 is shown in the form of a drum, which has a layer of photoconductive material on its periphery. The drum Λ is driven and thereby rotated in the direction indicated by an arrow, thereby continuously performing electrophotographic copying. When the drum 1 rotates, the layer of photoconductive material, which forms a photoconductive surface on which an electrostatic latent image is to be formed, is uniformly charged by means of a primary corona charger 2 which is connected to a high voltage source, not shown.

The charged, photoconductive surface then passes through an exposure station in which an optical system is arranged is to project an image of an original, not shown, onto the photoconductive surface. The electric charge on the photoconductive surface is thereby selectively eliminated imagewise, in order to thereby produce an electrostatic, to apply latent image. The latent image on the drum 1 is then developed by means of a developing device 4, a visible image being obtained with the aid of toner. The developing device 4 has a container 4a with a certain supply of developer solution containing the toner, and a curved developer plate 4b, which runs along one

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Part of the circumference of the drum is arranged close to this. The developing device further includes one not shown Pump, by means of which, when switched on, the developer solution into the space between the drum surface and the domed plate 4b is pumped. This is how the scope is the drum 1 is partially immersed in developer solution during operation of the copier.

After the latent image has been converted into a visible image, it is conveyed by the rotation of the drum 1 to a transfer station, where the toner image is then transferred from the surface of the drum to a copy sheet, which by means of a feed device (not shown) along a paper path P brought into full contact with the drum surface _; is fed at the same linear speed which corresponds to the peripheral speed of the drum 1. On the other side of the copy sheet, which is held in contact with the drum surface, a corona discharge device 5 is provided for transfer, which is designed similar to the primary corona discharge device 2 and generates a discharge of the same polarity as this, so that the toner image is electrostatically away from the drum surface is pulled to the leaf surface. After the transfer, the sheet carrying the toner image is conveyed through a fixing device (not shown) before it is ejected from the device to the outside.

When the transfer step is finished, a certain amount remains Amount of toner left on the drum surface, which when

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would be left there with the copy sheet during the the next copying cycle (i.e. it would contaminate it) or which would adhere firmly to the drum surface, which would prevent proper functioning. In order to avoid these disadvantages, a cleaning device provided, which has a roller 6 soaked with a cleaning liquid for wetting the toner on the drum surface, so that it comes free from her and can be removed, and has a scraping or scraping part 7 around the freed Scraping off toner; here both the roller 6 and the scraping or wiping off part 7 are normally held in contact with the drum surface. The cleaning liquid can either be the developer solution or one for this purpose have suitable means. After cleaning, a Charge left on the drum surface

can, by means of a charge-removing corona discharge device V, eliminated, which is connected to an AC voltage source; in this way a substantially uniform potential is then again established over the entire drum surface. The drive of the drum can then be interrupted or continued in order to repeat the above-described copying sequence.

As is known, the primary corona discharge device 2 charges the drum surface on a surface area which is wider than the area of the drum surface, which is exposed imagewise with an original to be copied, which

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is projected over the optical system 3. This means that the drum surface has a part which remains unexposed after exposure, and an electrical charge then remains on this part of the drum surface, where toner is then attracted during development. Of the toner which is attracted to the edge areas of the drum surface which protrudes beyond its exposed area, the part which lies in front of the exposed area is always removed by means of the cleaning device 6, 7. However, if the copy cycle in question is run through only once and then the device is stopped or switched off , the part of the toner attracted in the edge area outside the exposed area, which, as seen in the direction of rotation of the drum 1, lies behind the exposed area, is not cleaned or removed and remains on the drum surface.

Thus, this remaining toner must be removed from the drum surface before a new copying process can be initiated will. In a conventional copier, therefore, cleaning is first carried out before the drum surface is charged evenly. Therefore, when a main switch of the apparatus is turned on, the drum 1 only rotated before loading and exposure are started in the copying sequence. A copy holder for introducing the The actual copying process is only switched on after the so-called pre-cleaning has been carried out for a specified period of time has been. So that such a way of working

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table expires, the device has a circuit which has the main switch and a timer, and the so-called Pre-cleaning is started and carried out as soon as the main switch is switched on, and a circuit is started with the copy switch is closed as soon as the timer has expired.

However, when this point is examined more closely, it is found that the remaining toner on the drum 1 is stuck can adhere to this if the device has been switched off for a long time and not in operation, so that the implementation the so-called pre-cleaning becomes difficult or is very difficult. Another difficulty that must be noted is posed the difference in charge density, which remains on the drum surface after cleaning, because the electrical Charge on the drum surface caused by the initial uniform charging by means of the primary corona discharge device 2, which selectively removes imagewise exposure, thereby removing charge on selected areas leaving behind which toner of opposite polarity is attracted to thereby create a toner image which is then transferred to the copy sheet, as stated above; consequently, an electric charge remains in the image areas of the surface, and there is also an electrical charge on the unexposed areas of the The drum surface is present, as already stated above. If the copier is operated repeatedly, that is the charge

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eliminating corona discharger 8 is effective to evenly charge different density charges from the drum surface removed by energizing it from an AC power source. However, if the device is not used for a long period of time it is difficult, if not impossible, to evenly remove the charge from the entire drum surface.

The invention is therefore intended to provide a control system for an electrophotographic Create copier or method in which the electric charge is removed evenly, which may remain on the drum surface of a copier, after this has been out of operation for a long time, in order to achieve uniform and consistent characteristics for an image-like To guarantee exposure over the entire effective surface of the photoconductive part and to ensure that it adheres firmly of the toner on the surface of the photoconductive member, thus making a copy with better reproduction to maintain equality that is also not smeared.

Here, in the copying process according to the invention, the The quality of a copy obtained is improved by a simple control of the work steps at the beginning and end of a copying process which are determined to remove toner adhering to the surface of the photoconductive member, and that uniform image-wise exposure characteristics are ensured without any particular Facility must be used in addition.

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The invention thus provides a control system for an electrophotographic Copier which works with wet developer and has a rotatable intermediate image carrier, and in which in addition to a copier circuit for operating and switching on the various devices which relate to a normal copying process, a circuit for prior cleaning i.e. for cleaning before the actual copying process and a circuit for subsequent cleaning i.e., for cleaning to be performed after copying has been performed, these circuits operate devices for cleaning the intermediate image carrier and switch on. When a main switch of the device is turned on, the circuit for the previous one, i.e. switched on for the cleaning that takes place before copying in order to initiate the so-called pre-cleaning of the intermediate image carrier, and after a predetermined time has elapsed, the circuit assigned to the precleaning is then switched on by means of a first timer opened, which can be an RC circuit, and then, as long as a copy switch is switched on, the copy process associated circuit closed in order to initiate and carry out the normal copying operation. Immediately after the required number of copying processes has been completed, the circuit provided for subsequent cleaning is switched on, in order to carry out the so-called post-cleaning of the intermediate image carrier during a predetermined period of time, which by a second timer is set. Before starting the normal copying process, the intermediate image carrier can with regard to the parameters for an imagewise exposure in a good condition

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be brought, i.e. the residual charge is distributed over its surface during a certain time interval. this can be achieved in that a further circuit is provided, which some corona discharge devices in the Turns on the device and another timer or switch.

The invention is described below on the basis of a preferred embodiment explained in detail with reference to the accompanying drawings; Show it:

Fig. 1 is a schematic representation of an electrophotographic Copier into which the invention can be built; and

Fig. 2 shows a circuit of an embodiment of the invention.

The invention will now be described in detail with reference to FIG. An electrophotographic copier in which the invention is applied comprises a main switch SW1 connected in series with a timer Ti which are connected in parallel to terminals of a voltage source E marked with plus and minus signs. With the Time switch or element Ti is the operation of a so-called Pre-cleaning controlling circuit A controlled for a predetermined time interval; the device also has a copy switch SW2, which can only be actuated after the pre-cleaning controlled by circuit A has ended.

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Before the structure of the arrangement is described in detail, it should be briefly described in general. When the main switch SW1 is closed, the circuit A for a predetermined time interval to carry out the so-called Pre-cleaning, i.e. cleaning that is carried out before the actual copying process, is actuated by the copy switch SW2 can only be operated after this pre-cleaning has been completed. When the main switch SW1 is closed, the development device 4 starts to work continuously, as long as the switch is open. Then, when the copy switch SW2 is operated, a circuit B by means of which the corresponding characteristic values for a subsequent imagewise exposure are created for a predetermined time interval, which is controlled by a timer 3) 2, connected to the circuit. When the operation of circuit B is finished, a copying circuit G is excited, when the copying process is then also finished, a switch SW3 is switched over, whereby a time switch or -g! dedT3 a predetermined time interval long actuated a circuit D, by means of which sticking (of toner) is prevented.

The copier will now be described in detail; it has an energy source E represented by plus and minus signs and a main switch SW1 is in series with a CR timer or timing element T1 and these in turn are connected in parallel to the energy source. The time switch or the timer T1 has a series connection of a resistor R1,

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a diode Z1 creating a constant voltage and a capacitor C1, a switching element or a transistor relay circuit Tr1 being connected in parallel to the series circuit of the diode Z1 and the capacitor C1. When the main switch SW1 is closed, the timer or timer T1 begins to work, and the circuit A associated with the cleaning device, which is shunted or connected in parallel via a pair of relay contacts RA1, is closed to carry out the so-called pre-cleaning (i.e. the Cleaning, which is carried out before the actual copying) *, the remaining toner being removed from the drum surface by means of the roller 6 and the stripping device 7 when the drum 1 rotates. The duration ti of the so-called pre-cleaning is controlled by the timer or the timing element T1 and depends on the off time of the main switch SVM. Then, if the main switch is turned off for a longer period of time, the length of the period ti is increased. During the pre-cleaning, the various corona discharge devices remain switched off.

When the period ti is over, the timer or the timer T1 opens the pair of relay contacts RA1 and a pair of normally open contacts RA1-1 is opened, whereby the actual copying process is then initiated in the device. When the copy switch SW2 is closed, a relay K1-1 energizes, making a pair normally open Contacts KI-1 is closed, which in turn creates a timer or timer T2 is actuated to initiate the process at

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which the corresponding parameters for the subsequent imagewise exposure are created. In Fig. 1 concerns this process ensures an even, saturated charge of the drum 1 over its entire surface by means of the transfer or Corona discharge device assigned to the transfer process 5 » whereupon a discharge by means of the charge eliminating corona discharge device 8 follows, so that in this way the electric charge is evenly removed from the entire drum surface. In this way are the characteristics and requirements equalized for imagewise exposure of the drum over its entire surface. The period t2 during which the same conditions for a subsequent imagewise exposure are created, by means of the timer or member T2 controlled, which or which is a series circuit of a resistor R2, a constant voltage creating diode Z2 and a capacitor C2, in turn to the series connection of the diode Z2 and the capacitor 02 a transistor relay circuit Tr2 in shunt or is connected in parallel.

When the period t2 is over, the timer T2 energizes the relay circuit Tr2 which opens a pair of normally closed relay contacts RA 2, causing the circuit B to create equal conditions for an imagewise exposure, and which also a pair normally open contacts RA2-1 open in order to close the circuit C associated with the actual copying process; to this Way is then the copying process initiated and it becomes a

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required number of copies created. Of course, the drum surface is first used in the copying process by means of the primary corona discharge device 2 is loaded, an image of an original to be copied is then loaded by means of the optical system 3 projected onto the drum surface to generate an electrostatic, to form a latent image, then the latent image is converted into a visible one by means of the developing device 4 · Image converted which is then transferred to a copy sheet; thereafter the drum surface is covered by the toner cleaned and a residual charge is removed from the drum surface by means of the corona discharge device 8.

After completion of the copying process, a switch SW3 is in the other switch position shown by dashed lines are switched, whereby the circuit D, which is provided to prevent adhesion of toner, and a timer or a timer T3 are excited. Circuit D is provided to remove any remaining toner from the drum surface, thereby preventing it from settling Firmly bonds toner to the drum surface. To this end, after the transfer is carried out, the drum is 1 µm turned more than half a turn before turning is stopped so that any part of the drum 1 on which toner may be present is among the cleaning means has gone through; in this way it is avoided that any residual toner remains on the drum surface are. The period or the time segment t3, during which adhesion of toner is prevented, is determined by means of the time

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controlled switch or member T3, which has a series circuit of a resistor R3, a constant voltage creating diode Z3 and a capacitor C3, again in parallel to the diode Z3 and the capacitor C3, a transistor relay circuit Tr3 is connected. When the time period t3 is over, the relay circuit Tr3 is energized by means of the timer Ί? 3, through which a pair of normally closed contacts RA3M is then opened. Then all circuits A, B, C and D as well as the timer T2 are reset to their initial state, then the timer 13 is also reset, whereby the contact pair RA3-1 is closed. This then ends a cycle.

Of course, the timer T1 is also provided in order to carry out a so-called pre-cleaning of the drum, if the copier is put into operation, and normal cleaning is then carried out after the lapse of the period ti.

In the copying method according to the invention thus enables the Linking of the so-called pre-cleaning of the drum, which takes place when the main switch is switched on and which must be completed so that the copy switch can be operated, with the process in which the same good conditions for the subsequent imagewise exposure are created and which takes place in accordance with the actuation of the copy switch before the copier starts the actual copying process in order to completely eliminate any residual potential,

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which is not evenly distributed on the drum surface can remain, a subsequent uniform charge of the drum surface by means of the primary corona discharge device 2, which ensures a faithful reproduction of the image of an original. By rotating the drum around more than half a turn after the end of the copying process, with all corona discharge devices switched off, the part of the drum which can be contaminated with toner can pass through the cleaning station, so that a sticking of residual toner to the drum surface is minimized, so that on this This means that the copy sheet is smeared in the background and the drum surface is damaged by such residual toner is prevented. In addition, by removing the remaining toner, the time for the previous cleaning can be reduced effectively shortened, which is carried out as soon as the copier is in operation, so that in this way the The total time required to perform copying is shortened. It should also be mentioned again in particular, that during the so-called pre-cleaning the individual corona discharge devices are switched off, thereby a to avoid greater stress in the cleaning station and fatigue or consumption of the developer solution, which otherwise could be due to a larger amount of toner being supplied to the cleaning station when the drum surface loading in the dark.

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Claims (3)

Claims Λ η control system for an electrophotographic copier with a one-way periodically movable intermediate image carrier with an endless photoconductive surface and arranged around the intermediate image carrier means to sequentially charge the moving surface uniformly, the charged surface by means of an optical system image-wise with a to expose copying original to apply an electrostatic latent image to it, to develop the latent image with toner contained in a developer solution, to transfer the toner image to a copy sheet, to clean the moving surface following the transfer and finally to removing any charge left on the surface prior to uniform charging, indicated by a) a circuit (A) assigned to an upstream cleaning system for actuating the cleaning device (6, 7); b) a copy circuit (0) for actuating the at one facilities required for normal copying; c) a circuit (D) provided for downstream cleaning for actuating the cleaning device (6, 7); d) a main switch (SW1), by means of which when it is closed is, all devices required for a normal copying process are connected to a power source (E) are; - 17 - 609834 / UÖ8 1 -, 7- $ 280,336 e) a copy switch (SW2); f) a first timer (T1) with a first timer device (R1, C1) for switching off an energy supply from the voltage source (E) to the circuit (A) _# provided for an upstream cleaning after a predetermined time has elapsed from the point in time to which the main switch (SWi ") is closed to open; g) a device for supplying voltage across the closed main switch (SW1) to the copy circuit (B) to start its operation after the copy switch (SW2) closed and the circuit (A) provided for the upstream cleaning has been opened; h) a changeover switch (SW3) to switch the energy source (E) to the Switch off the copier circuit (B) and at the same time connect the voltage source (E) to the downstream cleaning unit to turn on the provided circuit (D) in order to initiate their operation as soon as a required number of copying processes has been carried out has been; and i) a second timer (TJ) with a second timer (RJ, C3), which ^ parallel to that for the downstream cleaning provided circuit (D) is connected to the connection of the voltage source (E) with the copy circuit (C ^ the for a downstream cleaning provided circuit (D) and the second timer (T3) to turn off this thereby after a specified time has elapsed, which is calculated from the point in time at which the for the downstream Cleaning process provided circuit (D) by means of the - 18- 6098 3 4/0881 2S0336B switch (SV / 3) is energized. 2. Control system according to claim 1, characterized in that that the first timer (T1) is an RC time constant circuit (R1, C1), which is connected to the power source (E) via the main switch (SW1). . 3. Control system according to claim 1, characterized in that the transmission device comprises a corona discharge device (5), that a device for removing charge comprises a corona discharge device (8), and that the system further comprises a circuit (B) by means of which equal conditions and conditions for an imagewise exposure are created, and which has both the discharge device (5, 8) and a third timer (T2) with a third timer (R ² , c ² ) to supply an energy from the source (E) switch off the circuit (B) after a preset time has elapsed, which is calculated from the point in time at which the copy switch (SW2) is closed and the circuit (A) provided for the upstream cleaning is open, and at the same time the power supply from the source (E) to enable the copy circuit (B) to thereby initiate its operation. 609834/0881