DE2646076A1 - ELECTROPHOTOGRAPHIC COPY DEVICE - Google Patents

Description

PATENT LAWYERS

H. Bartels

Dipt.-Chem. Dr, Brandes Dr .-! Ng. hero Dipl.-Phys. Wolff

D - 7 Stuttgart 1, Lange Strasse

Tel. (07 11) 29 63 10 and 23 72

Telex 07 22312 (patwo cf)

Telegram address:

tlx 07 223 12 woiff Stuttgart

PA Dr. Brandes: Headquarters Munich

Postal check. Stuttgart 7211-700 bank code 60010070

Deutsche Bank AG, 14/28630 BLZ 60070070

Office hours:

9-11.30 a.m., 1.30 p.m.-4 p.m.

except saturdays

October 8, 1976

Our ref .: 125 115/487333 kdk

Eastman Kodak Company, Rochester, New York State,
United States of America

Electrophotographic copier

Telephone information and orders are only possible after written Confirmation binding

ORIGINAL INSPECTED

26 ^ 6076

The invention relates to an electrophotographic copier with a charging station for uniform electrostatic charging of a reusable image carrier having a photoconductor, with an exposure station for image-wise exposure of the image carrier to the image a latent electrostatic corresponding to a master copy To create an image, a development station for developing the latent electrostatic image and with a controller for influencing the activity of these workstations.

While the reusable image carrier is moved past the individual work stations of such copier devices in order to produce copy after copy, changes in the "sensitivity" of the photoconductor occur, ie there are changes in the extent _/ χ _{η of} the charge reduction due to a given exposure The invention is based on the knowledge that these changes in sensitivity can basically be broken down into two types, namely, first, a temporary or temporary decrease in sensitivity that occurs after periods of non-use of the photoconductor, with the sensitivity of the photoconductor after a period of use again increases to a predictable sensitivity z. and secondly a progressive decrease in sensitivity, which results from increasing gas office usage (cumulative). The cause of the temporary change in sensitivity is not fully known. D The progressive decrease in sensitivity seems to be due to the fact that a film of accumulated toner particles builds up increasingly on the surface of the image carrier and that photochemical changes in the photoconductor add to this phenomenon.

In the known copying devices of the type mentioned, the disadvantage arises that the above discussed Changes in the sensitivity of the photoconductor during ejection of the copies made, fluctuations in quality become apparent.

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The invention relates to an electrophotographic copier with a charging station for uniform electrostatic charging of a reusable photoconductor having image carrier, with an exposure station for imagewise exposing the image carrier to the image to generate a copy master corresponding, latent electrostatic image, with a development station for Developing the electrostatic latent image and having a controller to affect the operation of these workstations.

As the reusable image carrier is moved past the individual workstations of such copier devices in order to produce copy after copy, changes in the "sensitivity" of the photoconductor occur, that is to say, they result. Changes in the extent χ _{η to} which the charge is reduced due to a given exposure. The invention is based on the knowledge that these changes in sensitivity can basically be broken down into two types, namely, first, into a temporary or temporary decrease in sensitivity that occurs after periods of non-use of the photoconductor, with the sensitivity of the photoconductor on again after a period of use a predictable sensitivity value increases and, secondly, a progressive decrease in sensitivity resulting from increasing total usage time (cumulative). The cause of the transient change in sensitivity is not fully known. The progressive decrease in sensitivity appears to be due to the fact that a film of deposited toner particles builds up on the surface of the image carrier and that photochemical changes in the photoconductor add to this phenomenon.

In the known copying devices of the type mentioned, the disadvantage arises that the above discussed Changes in the sensitivity of the photoconductor during ejection of the copies made, fluctuations in goods become apparent.

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The invention has for its object to provide a device of the type mentioned, which is designed so that despite the occurrence of the sensitivity fluctuations mentioned of the photoconductor copies of constant quality can be produced.

In a device of the type mentioned at the outset, this object is achieved according to the invention in that the control has a circuit part for generating a control signal which is responsive to the control signal via a second circuit part acts in a controlling manner on at least one of the workstations of the device that both a progressive reduction in sensitivity due to the increasing total service life of the photoconductor the same as well as changes in sensitivity of the photoconductor is counteracted, which are due to previous Rest periods or operating times of the same result. As in the following with the help of the drawing, detailed description is set forth, is provided by means of the additional circuit parts provided according to the invention both the rest time and work time history immediately preceding a copy cycle to be carried out determined as well as a determination of the cumulative total operating time of the photoconductor in question is carried out. On the basis of these determinations, a combined compensation is then made for both the intermittent ones Changes in sensitivity as well as those with increasing operating time progressive decrease in sensitivity of the photoconductor, this compensation by influencing a or more of the work stations of the copying device, preferably by influencing the activity of the exposure station.

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The invention is explained in detail below with reference to the drawing.

Show it:

Fig. 1 is a schematic block diagram of an embodiment of the invention Contraption;

Fig. 2 is an exaggerated cross-section of a photoconductor having the image carrier tape of the device according to FIG. 1;

3 shows a representation of part of the electrical circuit of the exemplary embodiment according to Fig. 1 and

4 shows a schematic representation of a modified exemplary embodiment, similar to FIG. 1 the device.

1 shows an exemplary embodiment of one to be shown here Electrophotographic device 1 with a flexible image carrier belt 2, which is attached along an endless path to the individual workstations of the device can be moved past. As can be seen more clearly from FIG the image carrier tape 2 has an insulating, photoconductive layer 3 (as shown, for example, in US Pat. No. 3,615,414 is), which is overlaid by a thin, electrically conductive layer 4. The photoconductive layer 3 and the electrically conductive layer 4 are both supported on a film 5 serving as a carrier. The conductive layer is with earth or with electrically connected to another source for a selected reference potential in that contact rollers of the device

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device 1 touch the side edge of the layer 4 or that other known devices are provided for this purpose.

The work stations of the device 1 include a charging station for primary charging in which a corona device 7 causes the outer surface of the photoconductive layer 3 to be uniformly charged. After receiving the primary Charging moves an image portion of the image carrier tape 2 past an exposure station 8, in which this image section an imagewise exposure with one of the original to be copied, by xenon flash lamps or received light patterns generated by other known imaging devices. The latent electrostatic image that is now on the Image section is present next via a development station 9 moves, in which a tonar development is carried out by means of magnetic brushes or other known devices the toner is attracted to the charge pattern corresponding to the dark image areas of the original. The developed image now becomes a transfer station 10 moved, in which the toner image is transferred by means of a corona device 12 to paper that is supplied from a supply 11 will.

The paper carrying the toner image is now through a Fixing station 13, which is designed, for example, as a roller melting device, to a container 14 transported. Meanwhile, the portion of the image from which the toner was transferred is moving in preparation another copy cycle past a cleaning station 15. A light source 16 provided for deletion is in the exemplary embodiment arranged behind the cleaning station, to dissipate any remaining charge, before the next copy cycle of the relevant image section is initiated.

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As indicated schematically in FIG. 1, the cyclical operation of the individual work stations of the device 1 in the desired time coordination with the moving past of the image sections of the image carrier tape 2 by means of a Control logic 20 controlled. The details of a control logic suitable for this and its interaction with the work stations, for example with the corona device 12, are known per se, see, for example, German OS 2 446 919. The control logic 20 has a central data processing unit 21 of the kind used in commercially available, programmable mini computers and microprocessors finds and operates the electromechanical workstations of the device 1 as a function of a control program 23 controls. The control logic 20 is also one the total number of copies cumulatively ascertaining memory 25, which will be discussed in more detail below.

As already indicated above, the sensitivity of the photoconductive image carrier decreases progressively during the service life the same from. to compensate for this progressive loss of sensitivity, the overall utilization of a photoconductor is made by the central data processing unit 21 every time a controlled by the data processing unit Copy cycle is performed, determined and the total cumulative usage time of the photoconductor in question is in the memory 25 held. In the operation carried out under the influence of the control program 23, the commands central data processing unit a signal of the memory 25, which for the cumulative total usage of a given Photoconductor is indicative, and when the cumulative total usage signals correspond to predetermined levels of use, which are defined in the control program 23 as levels of use, for which compensation is required are marked, then the data processing unit 21 sends in Signal to a programmable energy source 4O, -um

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cause a change in the illuminance level, which is used to expose the photoconductor with the image of the original.

In a particular embodiment, more specifically, 8 bits of permanent memory may be used Control logic 20 may be provided as memory 25 to keep track of the total number of copy cycles of a given photoconductor s, from its insertion into the device, cumulative save. The least significant bit is 256 copies, and you can get a total number of more than 65,000 copies in increments of 256. During the operation of the device, the (ie not only temporarily) storing memory 25 from a DC voltage source of the device with energy provided. However, a battery is also provided to power this part of the memory in order to prevent that memory contents can be lost if the main switch of the device is switched off. Separate Copy cycle counts, up to 256 steps, are in a part of the central data processing unit provided for temporary storage. this part is cleared whenever the memory 25 is supplied with a signal which is "indicative of 256 cumulative copies" and as often as the main switch of the device is switched off. The control program 23 is designed so that the memory is reset to zero when a new photoconductor is installed in the device.

Depending on a comparison between the content of the cumulative, indicating the need for compensation The central data processing unit 21 provides a suitable memory 25 and the stored control program 23 digital 4-bit signal under the influence of the control program

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23 from. A non-illustrated digital / analog converter converts this digital signal into an analog signal V, which is supplied to one input of a summing amplifier 39 to which belongs a programmable power source 40th _{The latter controls the voltage f} supplied to the light source (the exposure station 8), for example the voltage which is supplied to the charging capacitor of a conventional xenon flash unit.

The special program for adjusting the exposure over the life of a certain type of photoconductor can be determined empirically, and the performance of the photoconductor, for example a photoconductor, such as it is shown in US Pat. No. 3,615,414, can be significantly improved by the fact that the exposure according to a predetermined Plan is modified in the manner shown here. In a preferred embodiment, a photoconductor used, which has a multiphase, aggregate-forming photoconductor terrace with a continuous Phase with a solid solution of an organic photoconductor, i.e. 4,4'-bis (diethylamino) -2,2'-dimethyltriphenylmethane, and an electrically insulating polymer-binder phase, i.e. a polycarbonate (Lexan 145, manufacturer Genral Electric Corporation, USA), with a discontinuous phase dispersed therein composed of a finely divided co-crystalline complex of at least one polymer with an alkylidene diarylene group in repeating units, i.e. a polycarbonate (Lexan 145) and at least one Pyrylium type dye salt i.e. 4- (4-dimethylaminophenyl) -2,6-diphenylthiapyrylium fluoroborate. The device designed essentially according to the description of FIGS. 1 to 3 was programmed in this case so that at 15,000, at -35,000 and 60,000 copy cycles of the service life of the photoconductor, the energy supplied to the flash lamps was increased so that an increase in the exposure

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-beum 0.03 log E has been reached. The strength of the original The exposure was chosen so that the best copies were obtained, for example with regard to the background density for copies of different colored originals and for the reproduction of details in shadow areas from. Halftone templates. It has been shown that the evenness of the copies produced (i.e. keeping the copies constant, for example with regard to the background density and the reproduction of details) with a lifetime of 60,000 copies using the above compensation technique was significantly better than it was with the same lifetime can be achieved without this compensation. Corresponding increases in exposure were made in another case at 500 copies, 2,000 copies, 7,000 copies, 15,000 copies and 60,000 copies made. Here, too, when the same photoconductor was used (see US Pat. No. 3,615,414), there was one improved uniformity of copies.

The above description relates to the fact that the device has been made able to compensate for the progressive reduction in sensitivity which results from the total period of use. However, the device also has a device to compensate for the temporary loss of sensitivity which occurs following periods of non-use of the image carrier. It has been found that a sensitivity fall occurs after a period in which the photoconductor has not been used, that is subsequent to "rest" for certain electrophotographic image carriers, the _/ back again after a period of use, that is after a "working time", so that the sensitivity again corresponds to a predictable value. It is not entirely clear whether this temporary shift in sensitivity between "idle times" and "work times" in the device results solely from sensisometric changes in the photoconductor or from these changes in combination with other changes occurring in the operation of the device

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occur at the transition between rest and working hours. It has been found, however, that these are temporary Changes take place in a predeterminable manner and that raan can compensate for these changes in such a way that that an improved quality of the copies is achieved.

To these temporary changes in sensitivity mentioned above To compensate for the photoconductor, the device also has a previous use responsive Storage and control circuit 30, which is used by a suitable work station of the device, in the embodiment of the serving as a charging station for primary charging Corona device 7, receives signals and a control signal to the programmable energy source 40 for the Xenon flash system of the exposure station 8 emits. As discussed above, the memory and control circuit 30 serves this purpose Zwack, the way one or more of the workstations work of the device so that the differences in the performance of the device are compensated for result when the device is put into operation after a previous rest period or when the device was previously in operation.

In the embodiment shown in Fig. 1, the above-mentioned "changes in the sensitivity of the photoconductor compensated for between rest times and working hours by making a determination, whether or not the primary charging station's corona device 7 is in operation. It goes without saying that the Operating period of the corona device 7 indicates a period of use of the electrophotographic image carrier is. Determining the operating time while whose corona device is switched on can be through a conventional circuit, a relay or another electromechanical transducer operated when the corona device is turned on and off, accomplished

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will. Such a converter can be used to switch a two-pole changeover switch 31, as shown in FIG is, between a switching position shown in Fig. 3 with a solid line and one shown with a dashed line To switch the switching position, the holding position shown with a solid line being the switched-off state of the corona device 7 is assigned and the switch position indicated by the dashed line is the switched-on state of the Corona device 7 is assigned to the charging station.

From Fig. 3 it can be seen that when the changeover switch 31 is in the switching position shown with a dashed line, the corresponds to the operating state of use of the device 1, a potential V via contact pieces 33 and 34 and a resistor Rl is fed to a capacitor 32 to charge it. If, on the other hand, the switch 31 is in the switching position shown with a solid line, which is the Corresponds to the idle state of the device 1, then the capacitor 32 discharges to earth via a resistor R2 and Contacts 35 and 36. It can therefore be seen that the voltage V across the terminals of the capacitor 32 at any point in time of the time constant of the capacitor 32 and the resistor Rl or the time constant of the capacitor 32 and the Resistor R2 depends. This voltage V becomes an input of a differential amplifier via a one-way diode 37

38 supplied. A reference voltage V is applied to the other input of the differential amplifier 38, and an output signal, which is determined by the difference between the voltage V and the reference voltage V, becomes a summing amplifier

39 supplied, which by combination with the output signal of the differential amplifier 38, the analog signal V. for the Modified exposure. The output signal of the summing amplifier 39 forms the energy supply for the light source, so it provides, for example, the energy supply for the charging capacitor a xenon flashlight device of the usual type. As mentioned above, the analog signal V.

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clearing from time to time due to the control program of the Control logic 20 adjusted so that the length of the usage period progressive decrease in the sensitivity of the photoconductor is compensated.

It can be seen that after a long period of rest, for example, overnight, the capacitor 32 is completely is discharged. The next time the device is started up, a charge begins to accumulate in the capacitor again, namely at a speed which depends on the values chosen for the voltage V and the resistance Rl is. With continued operation of the device, the exposure caused by the lamps of the exposure station 8 becomes progressive decreases as the voltage values increase (as the device continues to operate) V can be subtracted from the reference voltage V, which the exposure had determined during the initial operating time following the rest period. In a similar way it can be seen that if the device is taken out of service for a shorter or longer period of time, the voltage V progressively decreases due to the discharge of the capacitor 32, the rate of discharge of depends on the selected resistance value of the resistor R2. The overall decrease in the value of the voltage V during a period of rest may lead to an increase in the signal value at the output of the differential amplifier 38 and to a correspondingly increased illuminance value, that of the photoconductor exposed during exposure.

Based on the above, it can be seen that the resistance values of the resistors Rl and R2 in connection with the values of the other circuit elements depending on the observed changes in performance are how they result after different periods of rest and operating times. In a special embodiment of the device constructed as shown in FIG

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when using the organic photoconductor described above an exposure for the steady-state operating state

provided by about 97 erg / cra. It has been found to be special it is desirable that the size of the resistor Rl (in conjunction with the values of the other circuit elements) so to choose that a decrease in exposure of about 0. OS log E Units occurs for approximately 8.2 minutes of operation and that the size of the resistor R2 (in connection with the values the other circuit elements) is chosen so that an increase of about 0.08 log Ε units for each 1.2 hours. Rest period comes about. The uniformity of the output of copies (for example with regard to the consistency of the Rendering of detail and the level of background density) was during transitional hours of operation following quiet periods significantly improved over similar devices in which none of the compensations shown here are carried out is, "after some operating time the device reaches a steady state in terms of power, and the capacitance value of the capacitor should (in connection with the Values of the other circuit elements) are chosen so that no further increase in voltage V occurs, after the capacitor has been charged continuously until. the device has reached the steady-state operating state.

It can also be seen that the values of the components are chosen in this way can be that the desired compensation of the power in the idle operating conditions between the limits of the complete discharge of the capacitor (long idle time) and the maximum charge of the capacitor (long operating time) reached with the charge and discharge cycles fully synchronized with the operation and rest cycles of the device.

Of course, it is understood that other circuit devices can be provided in order to carry out the compensation shown here * The signals for actuating such storage space that is responsive to the conditions of use

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and control circuits could be from other workstations the device can be derived, for example directly from the traffic jam logic 20. The compensating control can also be done by other work stations of the device 1, for example in such a way that the primary charge in direct proportion to the operating time of the device and in direct proportion is lowered at rest time or that the bias of the development station is reduced in direct proportion to the operating time and increased in direct proportion to the idle time. Such by other work stations of the device effected compensation could be provided alone or in combination with other compensation measures. For example the compensation mentioned above could be combined with the compensation shown above (in which the imagewise exposure for the compensation is influenced). Such examples are referenced below on Fig. 4 explained.

In Fig. 4 is an electrophotographic apparatus of the same type as was baschriaban with reference to Fig. 1, shown, with a control device for performing an idle operation compensation, this compensation in connection with which the cumulative total operating time of the photoconductor is taken into account compensation. More specifically, in this embodiment, the output signal becomes the one responsive to the recently used Storage and control circuit 30 is fed to a programmable energy source 5O, which in a similar manner for the cumulative total operating time characteristic of the compensating signal received from the control logic 20. The signals of the Control logic 20 and the storage and control circuit 30 are combined by conventional means, for example by means of operational amplifiers, and influence the power sources for the corona device 7 of the primary charging station and for the magnetic brushes of the development station 9, impure

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desired change in primary charge or development bias to be obtained in the compensating manner described above. As already stated, the compensating Control can be effected by one or more workstations or in various combinations, for example can compensate for the cumulative total operating time can be carried out in one station and the idle mode compensation in another station.

Figure 4 also shows another way of manipulating the imagewise exposure to compensate for the sleep mode sensitivity changes. In this embodiment, the saliva and control circuit 30 provides an output signal generated, not to change the exposure level, but by means of a conventional electronic shutter with timer circuit to change the exposure time. In this embodiment, the threshold voltage becomes the timer circuit of the shutter by means of an RC circuit in the manner as described with reference to Fig. was explained, lowered depending on the operating time and raised depending on the idle time by the Change the time-intensity product of the imagewise exposure as indicated.

As has been found, it has proven to be particularly advantageous if the image-wise exposure is adjusted for the purpose of the coitipensations shown here (and not, for example, the primary charge or _: the bias of the magnetic brushes is changed). The reason why the compensation is preferably done by changing the exposure can be seen by considering an illustrative example in which a fresh photoconductor, which has an initial total primary charge of 450 volts, is exposed through the background area (white ) a template

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200 volts is discharged _r wherein at the development station, a bias voltage is applied, the urn the background voltage exceeds 50 volts. With an increase in the cumulative copy cycles, a change in the sensitometric properties of the photoconductor can result in the background area being only discharged to 250 volts under the same exposure conditions. This could be compensated for by changing the primary charge, for example by creating a primary charge of only about 400 volts, which would result in a background charge of 200 volts, as was the case with the fresh photoconductor. The bias voltage of the magnetic brush would be 250 volts as before. Instead of changing the primary charge, the bias voltage of the magnetic brush could also be increased, for example to 300 volts, in order to compensate for the aforementioned sensitometric change in the photoconductor. However, it should be noted that by changing both the primary charge and the bias voltage in the Development station the contrast of the electrophotographic system is reduced. This means that when the primary charge is changed, the difference between the image background voltage and the voltage of the maximum charge is 150 volts (400 volts minus 250), and when the bias voltage in the development station is changed, this difference is also 150 volts (450 volts minus 300 volts) for this purpose, a voltage of 200 volts (450 volts minus 250 volts) results as a contrast when changing the imagewise exposure. It is known that increased contrast is desirable, for example with a view to being able to reproduce more details in the copies, in particular in the case of copies of originals which contain information of low optical density to be reproduced.

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Claims (1)

Claims 1. Electrophotographic copier with a charging station for uniform electrostatic charging of a reusable, photoconductor having image carrier, with an exposure station sum imagewise exposing the 3image carrier in order to generate a latent electrostatic image corresponding to the image of a copy original, with a development station for developing the latent electrostatic Image and with a controller for influencing the activity of these workstations, characterized in that the controller has a circuit part (Vo, Rl, 31, 32) for generating a control signal, which via a second circuit part (38) responsive to the control signal is controlled in this way to at least one of the workstations (7 to 9) of the device (1) acts that both one due to the increasing total operating time of the photoconductor (3). progressive reduction in the sensitivity of the same as well as changes in sensitivity 'of the photoconductor (3) are counteracted, which result from previous idle times or operating times of the same. 2. Device according to claim 1, characterized in that the controller has a third circuit part (R2, 31, 32) to generate one of the duration of non-use of the Photoconductor (3) dependent, the change in sensitivity ' of the photoconductor (3) due to the non-use of the same representative second control signal and that the second circuit part (38) responsive to the second control signal to the imagewise exposure of the photoconductor (3) in the exposure station (8) and / or the uniform charging of the same in the charging station (7) and / or the amount of toner applied in the development station (9) to influence. 709816/0883 ORIGINAL INSPECTED -IK'S . Device according to Claim 1 or 2, characterized in that the first circuit part (Vo, Rl, 31, 32) is operatively coupled to the charging station (7) in order to determine the periods of use or non-use of the photoconductor (3). 4. Apparatus according to claim 2 or claims 2 and 3, characterized in that the first and the third Circuit part have an R-C circuit network. 5. Device according to one of claims 1 to 4, characterized in that the first circuit part has a capacitor (32), an electrical resistor (Rl) and a device (31, Vo) for charging the capacitor (32) via the resistor (Rl ) depending on the beginning of a use of the photoconductor (3) has ^{un <} i ^that the capacitance of the capacitor (32) and the resistance of the resistor (Rl) are chosen so that the instantaneous value of the charge on the capacitor (32) is related to the respective sensitivity resulting from the duration of use of the photoconductor (3). 6. Apparatus according to claim 5, characterized in that the third circuit part has the capacitor (32), a second electrical resistance (R2) and a device (31) for depending from! Beginning of a period of non-use of the photoconductor (3) taking place discharging of the capacitor (32) via the second resistor (R2) and that the The capacitance of the capacitor (32) and the resistance of the second resistor (R2) are chosen so that the Instantaneous value of the charge of the capacitor (32) with the respective sensitivity of the photoconductor (3), which due to the non-use of the same, is related. 709816/0883 - yr- 7. Device according to one of claims 1 to 6, characterized in that that a control logic (20) for determining the cumulative total usage time of the photoconductor {3) and to generate a third one from this total usage period dependent control signal is provided and that the second circuit part responds to the third control signal, the strength of the charging of the photoconductor (3) brought about by the charging station (7) and / or the imagewise, through the exposure station (8) effected exposure of the photoconductor (3) and / or to influence the amount of the toner applied in the development station (9). 8. Apparatus according to claim 7, characterized in that the control logic (20) for generating one production each a predetermined number of copies signaling signal a central data processing unit (21),. a control program (23), a memory (25). as well as a facility that based on the comparison the contents of the memory (25) representing the total number of copies made with the control program (23) generated for the cumulative total service life of the photoconductor {3) indicative signal. 709816/0883