Method And Apparatus For Making Composite Electrophotographic Prints

Abstract

A method and device for making electrophotographic multiple color prints is provided wherein photoconductive sheets or chips of separate stacks or sets are charged and exposed to each of a plurality of color separation images projected from an original. An electrostatic latent image thus formed on each of the exposed chips is developed and transferred to a receiver in a predetermined cycle with respect to the other chips, wherein the the separate images are placed thereon in registry to form a composite color print. In one embodiment, three sets of chips are moved through separate charging stations and sequentially cycled through a single exposure station. After exposure the electrostatic image on each chip is developed by different color toners at separate development stations and transfer of the toner images is made sequentially to a receiver at a single transfer station to make a composite color print. In another embodiment, three separate exposure stations are used to expose the respective chips to color separation images to form three separate electrostatic images, one on each chip. These electrostatic images are developed and transferred at separate transfer stations onto a single receiver which is moved sequentially past each transfer station to form a composite color print. In a further embodiment each chip is exposed sequentially at a single exposure station to form electrostatic images which are developed and then are transferred at separate transfer stations to a receiver which is moved sequentially past each transfer station to form a composite color print. In each embodiment, the chips are cycled so that color prints are made substantially continuously.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for making electrophotographic prints and more particularly to an apparatus for placing several electrophotographically formed toner images in registry on a receiver, such as to form a color print, each image representing a color separation image from the original being copied.

2. Description of the Prior Art

Prior to this invention, color electrophotographic processes have been developed, such as that disclosed in U.S. Pat. No. 2,986,466 to Kaprelian. However, some of these systems have been continuous wherein the film or other document to be copied is scanned and the projected color separation images are each placed on a moving photoconductor in synchronism. These latent images are then developed and sequentially transferred to a moving receiver or web in registry. In practice, such a system is extremely difficult to utilize. In the first place, it is extremely difficult to get the optical systems for the three color separation images aligned so that the images will be placed in exactly the same relationship on each moving photoconductive surface so that the developed images can be transferred in registry onto a receiver. In addition, a difference in exposure is sometimes desirable for the different colors making it impossible to use a synchronous scanning system for projecting a plurality of color separation images to separate photoconductors. This is necessary to provide proper color balance in the print. This color balance must be within certain defined limits regardless of the color balance or light level of the original scene to provide a salable print. Also, the sensitivity of a photoconductor to different colors of light varies since no known photoconductor is entirely panchromatic. Thus, different exposure times are necessary to provide prints having a satisfactory color balance. The use of separate photoconductive plates has been contemplated, as disclosed in U.S. Pat. No. 3,009,402, but the use of the separate photoconductive plates or chips has not been utilized in a system wherein a plurality of separate images must be superimposed in registry on a receiver nor where varying exposure times are necessary and desirable.

SUMMARY OF THE INVENTION

In the present invention, apparatus is disclosed which utilizes separate photoconductive elements that may be cycled or programmed to move through the various stations of the apparatus to provide composite prints comprising a plurality of superimposed images on a substantially continuous basis which are in substantially perfect register and of high quality. These elements may be in the form of flat rectangular chips. In one embodiment, several sets of photoconductive chips are provided which are sequentially moved from a storage position through a charging station, an exposure station, a developing station, a transfer station, a cleaning station, and then back to the storage position. Each of these sets utilizes the same exposure station and transfer station and each chip is aligned by the same aligning means thereby simplifying the registration problems both for exposure and transfer. Original images to be copied are projected onto separate photoconductive chips to form latent electrostatic images which may be toned and then transferred in registry to form the composite print. These original images may be any radiation patterns such as color separation images formed from a color transparency. In this latter case, the entire transparency can be exposed at one time so that a photocell (not shown) may sense the total light coming therethrough to adjust the exposure over a wide range of time in response to the image brightness, the sensitivity of the photoconductor to the particular color of light, and to provide the proper color balance. The chips are cycled so that chips which are not at an "active" station, i.e. one at which work is being done on the chip, may be held momentarily in either a passive "hold" or "escape" station until they can be cycled to the next station. This holding procedure can occur both before and after the exposure and transfer stations. However, since the chips are not interconnected in any way, they can be moved at different relative speeds dependent upon the position of other chips in the apparatus.

In another embodiment, which enhances productivity, a separate exposure and transfer station is provided for each set of chips. Thus, separate photoconductors may be exposed simultaneously to different radiation patterns or original images. The receiver is moved past each transfer station sequentially to pick up each toned image in registry with the last toned image so as to provide a composite print. Again, because of the desirability of different exposure times for different photographic characteristics, such as different colors and different exposure times for originals of different densities, the chip system provides the flexibility of movement needed to assure that all developed chips are at their respective transfer stations at the appropriate time even though the exposure of these chips may occur over different time increments or periods.

In still another embodiment, exposure of the different chips may be done sequentially whereas the transfer may be made substantially simultaneously, i.e., in rapid sequence across multiple transfer station. This structure avoids the problems of maintaining color separation images in optical alignment encountered with simultaneous exposure of three photoconductors but retains much of the productivity advantages of multiples station transfer.

The use of separate chips makes replacement easy when the chips wear out. Also, if a chip is damaged it may be replaced quickly and inexpensively by substituting a new chip for the damaged one.

Additional novel features of this invention will become apparent from the description which follows, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the electrophotographic apparatus of this invention in a color print system;

FIGS. 2, 2a and 2b are perspective views of photoconductive chips which may be utilized in this invention;

FIG. 3 is a schematic perspective view of one embodiment of this invention wherein sets of photoconductive chips are cycled sequentially through a single exposure station and a single transfer station;

FIGS. 4, 4a, 4b and 4c are logic diagrams for the charging and sequential exposure stations of FIG. 3;

FIGS. 5 and 5a are logic diagrams for the transfer station of FIG. 3;

FIG. 6 is a schematic perspective view of another embodiment wherein sets of photoconductive chips are cycled through separate exposure and transfer stations;

FIG. 6a is a fragmentary section, on an enlarged scale, showing a means for moving a chip from an exposure station to a developing station;

FIG. 7 is a logic diagram for the simultaneous exposure stations of FIG. 6;

FIGS. 8 and 8a are logic diagrams for the transfer stations of FIG. 6; and

FIG. 9 is a schematic perspective view of a further embodiment wherein sets of photoconductive chips are cycled sequentially through a single exposure station and are cycled through separate transfer stations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with this invention, an electrophotographic apparatus A is illustrated in FIG. 1 which includes a charging station, an exposure station, a developing station, a transfer station, and a cleaning station. This apparatus has particular application as a color processor for making color reflective prints from color negatives. However, it should be understood that the invention would have application in any embodiment wherein it was desired to superimpose in aligned relationship two or more images, whether of the same color or different colors. In a color system, an image, such as from a color negative 10 can be projected by means of a light source 11 through heat absorber and color balancing filters 12, as shown. The image from negative 10 is projected by a lens 13 past a shutter 14 and through color filters 15 onto a photoconductive chip at the exposure station. In a color system, the electrostatic image on the chip is developed with a toner having a color complementary to the originally projected image at the developing station. The resulting tone image is transferred to a receiver 16 fed from a roll 17. After transfer, the receiver may pass through a lacquering station 18 and a drying station 19 to a cutting mechanism 20 to provide finished prints 21.

A photoconductive chip may have a relatively rigid base, such as base 24 of chip C in FIG. 2. To one side of base 24 is attached a layer of photoconductive material 25. Base 24 can be made of glass or metal or some other rigid material or could be made of a plastic material and could be bendable but should be rigid enough to be easily handled. Base 24 has three bosses 26, 27, and 28 which are adapted to engage alignment pins at the exposure and transfer stations to assure that the chip is in proper position. In FIG. 2a, a chip C' is shown having a base 29 to which a photoconductor 30 is attached. Base 29 has a hole 31 adjacent one edge thereof and a slot 32 adjacent the same edge but spaced from hole 31 so that chip C' may be dropped down over a pair of pins at the exposure and transfer stations. In FIG. 2b, a photoconductive chip C" is shown which has a base 33 having a photoconductor 34 attached to one side of two rows of sprocket holes 35 adjacent opposite edges thereof to provide registry means at exposure and transfer stations, respectively, and for engagement with suitable teeth on drive means for advancing the chips from one station to another.

SEQUENTIAL EXPOSURE AND SINGLE-STATION TRANSFER

In the embodiment of FIG. 3, electrophotographic apparatus A is provided with three stacks or sets of photoconductive chips supplied from storage stations 40, 40' and 40", respectively. The chips are fed sequentially from the bottom of their respective storage positions by intermittently driven belts 41, 41' and 41" which have spaced dogs, such as dogs 42, 42' and 42". The chips are then engaged by similar dogs on continuously running belts 43, 43' and 43" which drive the chips past charging stations 44, 44' and 44", respectively wherein an electrostatic charge is placed on the photoconductive surface of each chip. Drive belts 43, 43' and 43" move the respective chips into holding stations or hold-to-expose stations 45, 45' and 45" where they are held until each chip can be sequentially moved to a stationary exposure station by an elevator to be described. The chips are sequentially moved from the hold-to-expose stations by intermittently driven belts 46, 46' and 46", each having dogs which engage the chips. Upon reaching the top of the elevator, each chip is moved down to the exposure station, as by endless belt 47 to exposure station 48.

The time that each chip is at the exposure station will depend on the color of the light image to which it is exposed and also the density of that image. Thus, cycling time for each chip will be different at the exposure station. This difference in time is compensated for at hold-to-expose stations 45, 45' and 45" and at escape-to-develop stations 49, 49' and 49" to which the respective chips are driven by intermittently driven endless belts 50, 50' and 50". Each of these belts has spaced dogs, such as dogs 51, 51' and 51" which are adapted to engage openings in the respective chips so that they are moved to the appropriate development station. Thus, the chips from storage station 40 have an opening 52 located in one corner adjacent the marginal edge thereof which is adapted to be engaged by dog 51 of drive belt 50 so that when a chip from this set is in the exposure station it will be driven from the exposure station to escape-to-develop station 49, as shown. Similarly, the set of chips from storage station 40' are provided with an opening 53 in a center portion of the marginal edge, as shown, for engagement by dogs 51 of intermittent drive 50' so that when one of these chips is in the exposure station it will be driven to escape-for-transfer station 49'. Likewise, the chips from storage station 40" have an opening 54 in a corner adjacent the marginal edge thereof which is engageable by dogs 51" of intermittent drive 50" to move those chips from the exposure station to escape-for-develop station 49. The chips then are driven by motors 55, 55' and 55', respectively, from their respective escape-to-develop stations by continuously driven belts 56, 56' and 56", having spaced dogs thereon which engage the chips, across development stations 57, 57' and 57", respectively, where the latent electrostatic image thereon is toned. The same continuously driven belts move the chips into hold-for-transfer stations 58, 58' and 58". In the hold-for-transfer stations, the chips await their turn in the cycling sequence in which each chip is moved to transfer station 59 by means of a transfer roller 61 moved across the receiver by endless belt 62. After transfer, the chips are moved by intermittently driven belt 63 into an intermittently running elevator 64 having means 65 for engaging the chips and raising them as shown.

From the top of the elevator, the chips are moved by continuously running belts 66, 67, or 68 each of which has spaced dogs 69, 71, and 72, respectively, for engaging holes 52, 53 and 54 of the respective chips to move them in the appropriate direction. The chips which are engaged by dogs 69 are moved to a hold-for-clean station 73 where they are engaged by dogs on a continuously running belt 74 which moves them past a cleaning station 75 and back to the top of storage station 40. If a chip is engaged by dogs 71, it is moved directly to cleaning station 75' and back to the top of storage station 40'. The chips which are engaged by dog 72 are moved to a hold-to-clean station 77 where they are engaged by dogs on a continuously running belt 79 which moves the chips past a cleaning station 75" and back to the top of storage station 40".

Although many motors have been shown for driving the various means for moving the chip from station to station, it should be readily apparent that a lesser number of motors could be used with proper gearing and interconnection between the various drive belts. Also, the cleaning stations have been illustrated as brushes but it should be understood that this is a purely schematic representation and that any suitable cleaning apparatus may be used.

Each of the holding and escape stations has been shown in FIG. 3 to be stationary to simplify the illustration thereof but it will be understood that these passive stations may be part of the conveying system which transports the chips from one active station to another. The "passive" stations are those at which no work is done on the chips and the "active" stations are those at which work is done on the chips. The important thing is that the length of time that a given photoconductive chip spends at any one of the escape or hold stations may be varied. Also, it should be evident that the chips move continuously through all the processing stations with the exception of the exposure station and the transfer station in which they are held stationary during the exposure and print cycles, respectively. Thus, with the electrophotographic apparatus A illustrated in FIG. 3, the cycling can be adjusted so that as soon as one chip leaves the transfer station another chip is ready to take its place, providing a substantially continuous transfer operation. Thus, printing of successive images can take place at a very rapid rate.

The times necessary for charging, exposing, developing, transferring and cleaning for all colors must be compatible to the extent that at least one chip will be in each hold station at any time when exposure times vary randomly about normal. If a lot of short exposure times occur in succession, the number of chips will build up on the hold-to-transfer stations until they reach some predetermined arbitrary number, at which time an interlock (not shown) will prevent more exposures from being made until the number of chips in this hold station drops below the predetermined number. When a hold-for-transfer station runs out of chips, because of a succession of long exposures, no transfers will be made, but the rest of the operations will continue. When a chip is again in this hold station, the transfer operation will continue again.

The means for moving the chips through the various stations in timed sequence in accordance with the exposure time, may better be understood by reference to the logic diagrams of FIGS. 4--4c, 5 and 5a. To start the machine, a switch (not shown) may be closed by the operator which sends a signal to single shot generator 81 of FIG. 4 which in turn causes OR gate 82 to provide a signal to single shot generator 83, such as 1.0 second duration, which causes charge insertion motor 84 to drive belt 41 to move the bottommost chip out of storage station 40 into a position where it can be engaged by dogs on belt 43 which is continuously driven by motor 85. As the chip moves toward the charging station, it will close a microswitch 86, shown in FIG. 3, which generates a signal to single shot generator 87 of FIG. 4a which pulses chip insertion motor 88 for 1.0 second so that belt 41' drives a chip from the bottom of storage chamber 40' where it is picked up by dogs on belt 43' also driven by continuously running motor 85. The chips from storage chamber 40' will engage a microswitch 89, of FIG. 3, generating a signal to activate single shot generator 91 of FIG. 4b to pulse insertion motor 92 for approximately 1.0 second so a chip C is fed from the bottom of storage chamber 40" to a position where it can be engaged by dogs on belt 43", driven by continuously running motor 85.

When the chip being fed by drive belt 43 reaches hold-for-expose station 45, it will close microswitch 93 of FIG. 3 which will generate a signal to single shot generator 94, of FIG. 4c, for approximately 0.3 seconds to energize motor 95 which causes belt 46 to drive the chip to the top of elevator 47. Similarly, the chip which is fed to hold-for-expose station 45' will close microswitch 96 of FIG. 3 to generate a signal only after drive motor 95 is off to assure that two chips do not arrive at the elevator at the same time. When AND gate 97 generates a signal, it will activate single shot generator 98 for approximately 0.3 seconds to pulse motor 99 connected to drive belt 46' to drive the chip in hold station 45' into the elevator. A chip in hold-for-expose station 45" will close a microswitch 100 which will generate a signal to AND gate 101. When motor 99 has discontinued running, AND gate 101 will activate single shot generator 102 for approximately 0.3 seconds to energize motor 103 connected to drive belt 46" of FIG. 3 to drive chip to the elevator. Thus, the chips will be alternatingly received from each set so that subsequent color separation exposures may be made on one chip from each set.

A chip inserted in the top of elevator 47 will close a microswitch 104, generating a signal to AND gate 105, of FIG. 4. If no chip is in the exposure position, the AND gate will generate a signal to single shot generator 106 of a duration of say 0.3 seconds which will energize elevator motor 107 to move the chip from the top of the elevator to the exposure station 48 at the bottom. It will be understood that elevator 47 may contain a plurality of chips so that the chip which is inserted in the top of the elevator will not necessarily be the next chip to be inserted in the exposure station. If the chip received in the top of the elevator is the first one, the above-described operations will continue until the elevator is filled and a chip is in place in exposure station 48.

When the chip reaches the exposure station, it will close microswitch 108 which will generate a signal to AND gate 109. AND gate 109 will generate a signal when a signal is received by the closing of switch 108 and when elevator motor 107 has stopped running and when the exposure exit drive is not running, as described below. This signal from AND gate 109 activates an exposure registration clamp 111, which in FIG. 3 is illustrated as a solenoid which pushes the chip against registration pins 111a. This same signal also activates a negative gate clamp 112, FIG. 4, for clamping the film strip 10 of FIG. 3 in position for exposure. When the operator closes a "print" switch (not shown) an output signal will be given by clamp 112. The output signals from clamps 111 and 112 activate AND gate 113 which provides a signal to exposure monitoring station 114, and to AND gate 115. At this point a positive signal will be supplied to AND gate 115 from the "zero" output terminal of a flip-flop circuit 116. Thus, gate 115 will transmit a signal to OR gate 117 which will energize solenoid 118 to open a shutter (not shown) permitting exposure of the photoconductor to an image transmitted by lens 13 of FIG. 1 from negative 10. Also, solenoid 119 will be energized to interpose a filter, such as a red filter, (not shown) between negative 10 and photoconductive chip C in exposure station 48.

The signal from AND gate 115 will also provide a signal to AND gate 120 which will also receive a negative pulse of 1.1 seconds from single shot generator 121 which in turn receives an input signal from normally open microswitch 122 of FIG. 3 indicating that no chip is present in hold-for-development station 49. This will activate OR gate 82 through normally closed switch 123, single shot generator 83 and chip insertion motor 84 to start another chip through the charging station to assure a continuous operation.

The length of time that the shutter is opened is determined by the color of light being projected and the density of the negative. This may be controlled in a manner disclosed in commonly assigned U.S. Pat. No. 3,321,307, entitled "Exposure Control in Xerographic Printing" to Urbach or by other suitable means all of which form part of exposure monitoring station 114. When the exposure has continued for the proper duration, a signal will be generated by the exposure monitoring station 114 to AND gate 115 which becomes blocking so that solenoid 118 closes the shutter and solenoid 119 removes the filter. When AND gate 115 discontinues transmitting a signal, OR gate 124 will generate a signal to single shot generator 125 which generates a signal of say 0.4 seconds thereby activating AND gate 126 and exposure exit motor 127 which is connected to belt 50' in turn connected to belts 50 and 50" by the bevel gear arrangement shown so that all three belts are driven simultaneously. Since a chip from storage station 40 is in the exposure chamber, it will have an opening 52 in one corner thereof which will be engaged by an articulated dog 51 on endless belt 50 so that the chip will be moved from the exposure station to hold-for-development station 49.

Because of the sequence in which the chips are started, a chip from storage chamber 40' which has passed through charging station 44' and hold station 45" will be inserted into the top of the elevator so as to close switch 104 which begins the movement of the elevator and causes the chip to be properly registered in exposure station 48 and to be clamped as before. This time, however, a signal from AND gate 113 will not activate AND gate 115 since flip-flop circuit 116 will provide a signal from the "zero" output thereof. This is true because flip-flop circuit 116 is triggered by the input from switch 122 in hold-to-develop gate 49 which is now closed so a signal is provided from the "one" output to AND gate 128 which also receives an output signal from AND gate 113 and from the "zero" output of flip-flop circuit 129. Thus, AND gate 128 is activated to energize a second solenoid 130 to place a filter, such as a green filter (not shown) in front of negative 10 and provide a signal to OR gate 117 which again activates shutter solenoid 118 to open the shutter for exposure.

After the correct exposure time has elapsed, exposure monitoring station 114 will provide a signal to AND gate 128 which will cause it to terminate its output signal thereby causing solenoid 118 to close the shutter and removing the filter from in front of negative 10. The termination of this exposure will activate OR gate 124 which, as described above, will cause exit drive motor 127 to be energized. Since a chip from storage station 40' of FIG. 3 is in exposure station 48, which has an opening 53 in the center of the marginal edge thereof, this opening will be engaged by dog 51' on belt 50' thereby moving the chip from exposure station 48 to hold-to-develop station 49' closing microswitch 131. The closing of this switch will provide a signal to the trigger of flip-flop circuit 129, FIG. 4, thereby providing a signal out of the "one" output to AND gate 132 which will also receive a signal from AND gate 113 after a chip from the third storage chamber 40" has been properly registered in exposure station 48, as described with respect to the previous chips. The output signal from AND gate 132 will activate solenoid 133 which will place a color filter between the chip and negative 10, such as a blue filter, and the same signal will activate OR gate 117 to open the shutter operated by solenoid 118 to make the exposure.

When exposure monitoring station 114 senses that an appropriate exposure time has elapsed, as described above, an output signal therefrom will terminate the signal from AND gate 132 thereby deactivating solenoid 133 and shutter solenoid 118. The termination of this signal will again activate OR gate 124 which will cause motor 127 to be energized, as described previously. This time, a chip from storage station 40" will be present in exposure station 48' and will have an opening 54 in one corner thereof which will be engaged by a dog 51" of belt 50" and driven from exposure station 48 to a hold-to-develop station 49". When the chip reaches this station, it will close microswitch 134 which provides a signal to the "clear" inputs of flip-flop circuits 116 and 129 to reset them to their initial position so that the cycles described above may be repeated.

To terminate the operation of the machine for any purpose, normally closed switch 123 between AND gate 120 and OR gate 82 may be opened and the operator may close the negative ready-to-print switch so that an input is provided to negative gate clamp 112 even when no negative is in place so that the chips which are in intermediate positions throughout the machine may be run through exposure station 48 and subsequentially returned to their storage stations.

A chip in hold-to-develop station 49 will be moved through development station 57 by dogs on endless belt 56 to a hold-for-transfer station 58, as shown in FIG. 3, closing microswitch 135 to provide a signal to AND gate 136 of FIG. 5. If transfer station 59 does not have a chip therein, an output signal from AND gate 136 will cause single shot generator 137 to generate a signal 0.3 seconds, to motor 138 which drives belt 60 to move a chip from hold station 58 to transfer station 59. When the chip reaches transfer station 59, it will close a microswitch 139 which will terminate the signal from AND gate 136 and stop motor 138. This same signal will also trigger AND gate 141, of FIG. 5, to cause the transfer registration clamp solenoid 142 to urge the chip against registration pins 143 as in FIG. 3. An output signal from solenoid 142 will trigger AND gate 144 when a signal is also received from microswitch 145, FIG. 3, indicating that transfer roller 61 is in the ready position, as shown, to make a transfer. AND gate 144 will energize transfer roller drive motor 146 to drive transfer roller 61 across receiver 16 by means of endless belt 62. The transfer roller brings the receiver into contact or in the close proximity with the toned image on the photoconductive chip so that a transfer is made. This transfer may be made by any suitable mechanism, such as that shown in commonly assigned U.S. Pat. application Ser. No. 741,387, filed on even date herewith entitled "Image Transfer Mechanism," to Oliver W. Gnage. When transfer roller 61 reaches the end of its path, it will close microswitch 148 providing a signal to AND gate 149, FIG. 5, which together with the signal from switch 139 will cause the AND gate to generate a signal to single shot generator 151. Single shot generator 151 will generate a signal, such as 0.5 seconds, to AND gate 152 which will cause transfer station exit drive motor 153 to be energized so that belt 63 is driven. Dogs thereon engage the chip and move it to elevator 64 where it will be raised, as described below. Looking at the left-hand side of FIG. 5, it will be noted that when single shot generator 137 puts out an output signal to motor 138 to drive the ship from hold station 58 to transfer station 59, a signal is also generated to several other single shot generators including single shot generator 154 which generates the signal from its "zero" output for a period of say 1.6 seconds so that when the signal goes positive again it provides a signal to AND gate 155. This delay of 1.6 seconds is sufficient for the image on the first chip to be transferred and for the chip to be moved out of the transfer station to the elevator. Thus, when the AND gate 155 receives a signal from single shot generator 154 and a signal from microswitch 156 in hold station 58' indicating that a chip with a developed image thereon is ready for transfer and when microswitch 139 in transfer station 59 is open indicating that no chip is present in the transfer station, a signal will be generated by AND gate 155 to single shot generator 157 which will generate a signal of 0.3 seconds to energize chip insertion motor 158. Motor 158 then drives endless belt 60' so that the dogs thereon move the chip from hold station 58' into transfer station 59. When switch 139 is again closed by the chip moving into position, the chip will be registered and transfer made as described above. At the end of transfer, a signal from switch 148 will cause motor 153, as described above, to drive a chip from the transfer station 59 into elevator 64.

Again looking at the left-hand side of FIG. 5, the signal from single shot generator 137 will also provide a signal to single shot generator 159 which will generate a signal from its "zero" output of a duration of say 3.2 seconds which gives time for the transfer from both of the first two chips to be made and for the chips to be driven to the elevator. When this signal finally goes positive, AND gate 161 will generate a signal if a signal has been received from microswitch 162 in hold station 58" of FIG. 3, indicating that a developed chip is ready for transfer, and if no signal is received from switch 139 indicating the transfer station 59 is empty. This generated signal will cause signal shot generator 163 to provide a signal of 0.3 seconds to motor 164 to cause endless belt 61", of FIG. 3, to drive a chip from hold station 58" into transfer station 59. When the chip from hold station 58" is in transfer station 59, a signal from the closing of microswitch 139 will cause the chip to be registered and transfer made as described above.

It will be noted that the signal from single shot generator 137 also provides a signal to another single shot generator 165 which generates a signal from its "zero" output of a duration of say 4.8 seconds to give time for registration, transfer and removal of chips from all three sectors of the machine before the signal again goes positive to provide a signal to AND gate 136 permitting the cycle to start all over again with a new chip from hold station 58.

As a chip is driven into position into engaging means 65 of elevator 64, as shown in FIG. 3, it will close a microswitch 166 to energize single shot generator 167 of FIG. 5a in turn providing a signal to elevator motor 168 which causes the chip in the elevator to be driven to the top thereof. It will be understood that the elevator may have the capacity to hold more than one chip at a time. The important thing is that when a chip is inserted in the bottom of the elevator, it will be raised immediately to provide room for the next chip. When a chip reaches the top of the elevator, it will be engaged by articulated dogs on one of endless belts 66, 67 and 68 which are continuously driven as by motor 169, 171 and 172, respectively.

Because of the location of the openings in the marginal edge of the chips, a dog from one of the belts will engage the chip and move it to the appropriate hold-to-clean station and/or cleaning station so that any residue toner material may be cleaned from the chip and they will then be returned to their respective storage stations 40, 40' and 40". Thus, a chip which originated from storage station 40 will be moved by belt 66 to hold-to-clean station 73 where it will be moved through cleaning station 75 back to storage station 40, as described above. A chip which originated from storage station 40' will be moved by belt 67 directly into cleaning station 75' and back to storage station 40'. A chip which originated from storage station 40" will be moved by belt 68 to hold-to-clean station 77 where it will be moved through cleaning station 75" back to storage station 40".

Of course, it will be understood that suitable rails and guides for supporting the chips as they are moved from station to station may be provided as will be apparent to one skilled in the art. Also, the endless belts and drive means will be provided with suitable bearings and mounting supports as needed. If desired, some suitable means other than the belts shown may be used to advance the chips. Furthermore, the time periods given for the various operating signals are purely arbitrary and could be varied considerably as required for a particular requirement.

SIMULTANEOUS EXPOSURE AND MULTIPLE-STATION TRANSFER

An alternative electrophotographic apparatus A' is shown in FIG. 6 wherein separate exposure and transfer stations are used for each stack or set of chips. Thus, the chips may be fed sequentially from each of storage stations or storage positions 175, 175' and 175", respectively, by means, such as articulated dogs, on endless belts 176, 176' and 176" to a position where they are engaged by dogs on continuously moving endless belts 177, 177' and 177". Then the chips are driven past charging stations 178, 178' and 178", respectively, where an electrostatic charge is placed on the photoconductive surface of each chip. The charged chips are fed into respective elevators 179, 179' and 179" where they are lowered onto intermittently driven belts 181, 181' and 181" which move the respective chips to exposure stations 182, 182' and 182". Light from a light source 183 is directed through negative 10 and lens 13 and through a color separation system, such as a dichoric beam splitter 184 which reflects light at one frequency, such as blue light, to a mirror 185 to form an image on a photoconductive chip at exposure station 182". The rest of the light passes through beam splitter 184 to a beam splitter 186 where light of another frequency, such as green light, is reflected onto mirror 187 to form another image on the photoconductive chip at exposure station 182'. The remainder of the light, i.e. the red light passes through beam splitter 186 to form a third image on the photoconductive chip at station 182. Thus, electrostatic images are formed on each chip corresponding to the color separation originals from negative 10. Conveniently, the beam splitters and mirrors are so arranged that the length of the optical path for each color of light is the same. The exposure time at each exposure station will be controlled by the density of the image being projected and by the color projected onto each photoconductive chip. This may be controlled by individually actuated shutter (not shown) interposed between beam splitter 186 and exposure station 182 and 182', respectively, and a shutter interposed between beam splitter 184 and exposure station 182". This may be accomplished by use of an exposure control, such as that disclosed in U.S. Pat. No. 3,321,307, discussed above with respect to the embodiment of FIG. 3.

After exposure, intermittently driven belts 181, 181' and 181" are again energized to move the chips toward development stations 188, 188' and 188", respectively, as a second set of chips is moved from the bottom of the elevators to the respective exposure stations. The first set of chips are engaged by articulated dogs 189 on continuously moving endless belts 191, 191' and 191", respectively, as best shown in FIG. 6a, which moves them across the development station, wherein the electrostatic image thereon is toned, and then are moved into transfer stations 192, 192' and 192". The developed image on each of these chips is then transferred to a receiver, such as receiver 193 on roller 194 which is driven across the chips by endless belt 195 for transfer, in a manner such as that disclosed in commonly assigned U.S. Pat. application Ser. No. 741,387, filed on even date herewith, entitled "Image Transfer Mechanism" to Oliver W. Gnage. Thus, the images on each of the chips is transferred to the receiver in succession and in registry as the roller moves across the chips.

After transfer, the chips are moved by endless belts 196, 196' and 196" to elevators 197, 197' and 197", respectively. The elevators are intermittently driven to move the chips upwardly whenever a chip is received in the bottom of the elevator. When the chips reach the top, they are picked off by dogs on continuously driven endless belts 198, 198' and 198" through cleaning stations 199, 199' and 199", respectively, back to the top of storage stations 175, 175' and 175".

It is apparent that no hold or escape stations are required with electrophotographic apparatus A' since separate exposure and transfer stations are provided for each set of chips. The chips are stationary at both the exposure and transfer stations but move through the charging, development, and cleaning stations. With the arrangement shown, the chips may be cycled so that they arrive at all three transfer stations substantially simultaneously so that transfer may take place immediately. Also, the cycling between chips of the same set is such that as soon as the image has been transferred from a chip and it has been moved out of the transfer station, the next chip is ready to move into the transfer station. Also, to shorten the transfer time even more, the chips may be cycled so that a chip is received in the exposure station closest to the transfer means (transfer station 192" in FIG. 6) so that transfer may begin while chips are still moving into each of the other transfer stations. In other words, transfer of the first image can commence as soon as the other chips have reached a position in the developing station which assures that they will be in the transfer station in time to be transferred.

The number of chips in each set depends on the charge, exposing, developing, transferring, and cleaning times. The minimum number of chips in each set required for the cycle to be repeated continuously can be calculated by assuming minimum exposure time for every exposure. Of course, additional chips may be added to each set to decrease the frequency of exposure of any one chip so that the number of prints that can be made from a given set of chips corresponds to a convenient interval at which all the chips can be changed, such as once a day or once a week.

With the above general discussion, the more detailed explanation of the machine will be given. When the operator is ready to start the machine, a starting switch (not shown) is depressed providing a signal to single shot generators 200, 201, and 202, as shown in FIG. 7. Conveniently, single shot generator 200 is adapted to produce an output having a duration of approximately 0.1 seconds from its "one" output whereas single shot generator 201 will give a signal from its "zero" output of approximately a 1 second duration before the signal goes back to the positive state and single shot generator 202 will give a signal from its "zero" output for a period of approximately 2 seconds before it goes positive providing three distinct impulses to OR gate 203 which are spaced approximately 1 second apart. OR gate 203 will generate a signal to a single shot generator 204 which will provide a signal of slightly less than 1 second to charge insertion motor 205 which drives belts 176, 176' and 176" incrementally to successively move chips from storage chambers 175, 175' and 175" of FIG. 6. Thus, the closing of the starting switch will cause a chip to be ejected simultaneous from each of the three storage chambers to begin the continuous operation of the machine. As the chips are driven out of the storage stations, they will be picked up by articulated dogs on endless belts 177, 177' and 177" continuously driven by motor 206 which moves the chips past charging stations 178, 178' and 178", wherein an electrostatic charge is placed on the photoconductive surface of each chip, and into elevators 179, 179' and 179". These elevators are illustrated as endless belts 207, 207' and 207" having chip engaging means 208, 208' and 208" which support the chips for movement to the exposure station. It will be understood that the elevators may take any suitable form known in the art and that the means shown in FIG. 6 is schematic only. When the chips are positioned in the elevator, the chip in one of the elevators, such as elevator 179, will close a microswitch 209, as shown in FIG. 6, to provide a signal to AND gate 211 of FIG. 7 which will provide an output signal if no chip is present in the exposure chamber and if no chip is being driven out of the storage chamber. Since this is the first cycle, this condition will be met and AND gate 211 will transmit a signal to single shot generator 212 which will provide an output signal of say 0.25 seconds to elevator drive motor 213 which will move the chips in the elevators down to the exposure station level. Of course, it will be understood that other chips may be stored in the elevator intermediate the top and the bottom so that each time the elevator is energized a chip does not necessarily go all the way from the top to the bottom. When the chips reach the bottom of the elevator, they will close a switch, such as switch 214, see FIG. 6, which provides a signal to AND gate 215 of FIG. 7 which in turn provides an output signal to single shot generator 216. Single shot generator 216 then generates a signal of approximately 0.5 seconds duration to AND gate 217 which energizes drive motor 218 connected to endless belts 181, 181' and 181" which moves the chips from the elevator to exposure stations 182, 182' and 182", respectively. When the chips reach the exposure stations, one of the chips will engage a microswitch, such as switch 219 in exposure station 182, FIG. 6, which provides a signal to AND gate 221, see FIG. 7. An output signal will be received from AND gate 221 when the signal from single shot generator 216 has ceased. This output signal energizes solenoids 222, 222' and 222", of FIG. 6 to register the respective chips against registration pins 223, 223' and 223" as shown in FIG. 6. For convenience of illustration, only solenoid 222 has been shown in FIG. 7. The same signal will cause a negative gate clamp 224 to register the negative and upon the closing of a switch (not shown) by an operator indicating that the negative is ready to print, an output signal will be generated from this clamp. This signal together with a signal from solenoid 222 will cause AND gate 225 to provide signals to AND gates 226, 227 and 228, respectively, as well as to exposure monitoring station 229. The output signals from AND gates 226, 227, and 228 will energize solenoids 231, 232 and 233 to open shutters (not shown) to expose the charged photoconductive surfaces of the chips in the respective exposure stations to color separation images from negative 10 to form corresponding electrostatic images thereon. The length of time each chip is illuminated by energization of the respective solenoids is controlled by an exposure control system, such as that disclosed in U.S. Pat. No. 3,321,307, discussed above, which forms a part of exposure monitoring station 229. Thus, as the proper exposure level of each chip is reached, a signal will be generated by exposure monitoring station 229 to the respective AND gates 226, 227 and 228 terminating the signals to the respective shutter solenoids. Of course, this will not necessarily happen simultaneously but will happen as each exposure reaches the proper level. The termination of signals from AND gates 226, 227 and 228 will be sensed by AND gate 215. In addition, the output from AND gate 225 will cause single shot generator 234 to generate a negative pulse from the "zero" output thereof for a period of say 3.0 seconds which period is longer than any of the exposure times. At the end of this 3.0 second period, the generated signal will again go positive to trigger AND gate 215. When a subsequent set of chips have reached the bottom of the respective elevators, switch 214 of FIG. 6 will be closed thereby pulsing AND gate 215 to generate the proper signals to motor 218 so that the exposed chips are driven from the exposure stations and the next set of charged chips are driven into the exposure station. It will be noted that the signal from AND gate 225 of FIG. 7 also provides a signal to OR gate 203 so that motor 205 is energized to eject another set of chips from storage stations 175, 175' and 175" so that the cycle may run continuously.

When it is desired to clear the machine of chips for cleaning, changing the chips, or maintenance, switch 209 at the top of elevator 179 may be closed by manual means (not shown) and the negative ready-to-print switch (not shown) may be held closed so that the sets of chips dispersed through the machine may be fed through the rest of the cycle and back to their respective storage stations.

As the exposed set of chips are moved from their respective exposure stations, they will be engaged by articulated dogs 189, of FIG. 6a, on endless belts 191, 191' and 191" driven by continuously running motor 230, of FIG. 6, to transport them through development stations 188, 188' and 188" where the electrostatic images thereon are toned, and finally to transfer stations 192, 192' and 192", respectively. Upon reaching the transfer stations, one of the chips, such as the chip in transfer station 192, will close a microswitch 236 which energizes AND gate 237, of FIG. 8, which in turn generates a signal to solenoids or registration clamps 238, 238' and 238" of FIG. 6 which force the chips against their respective registration pins 239, 239' and 239". For convenience of illustration, only solenoid 238 has been shown in FIG. 8. The output signal from solenoid 238 will be supplied to AND gate 241 which will also receive an input signal from microswitch 242 of FIG. 6 which is closed by transfer roller 194 when the transfer roller is in starting position as shown in FIG. 6. A signal from AND gate 241 will energize transfer roller motor 243 which, through belt 195, will move the transfer roller across the respective transfer stations so that the toner images are sequentially transferred onto receiver 193 in registry.

When the transfer roller has moved past all the transfer stations, it will close microswitch 244 providing a signal to AND gate 245 of FIG. 8 which now energizes single shot generator 246 of a duration of say 0.5 seconds. This signal causes AND gate 237 to discontinue the signal to transfer registration clamp 238 so that it is released and causes AND gate 247 to provide a signal to transfer station exit motor 248 which through endless belts 196, 196' and 196" drives the respective chips into elevators 197, 197' and 197" as shown in FIG. 6.

When the chips reach the respective elevators, one of the chips will close a microswitch, such as microswitch 249, in elevator 197 to energize single shot generator 251 of FIG. 8a for approximately 1.0 seconds causing elevator transfer motor 252 to lift the chips to the top of the elevator by means of endless belts 253, 253' and 253" which each have chip gripping means 254, 254' and 254" thereon for engaging the chips. Of course, it will be understood that this FIG. 6 is purely schematic and that any type of suitable elevator means may be used for raising the chips. Also, the elevators may hold a plurality of chips at one time. The important thing is that as soon as a set of chips are received in the bottom of the elevators, motor 252 is energized to raise the chips so that another set of chips may be inserted therein.

As the chips reach the top of their respective elevators, they will be engaged by dogs on endless belts 198, 198' and 198", respectively, driven by continuously running motor 255 which will move the chips past cleaning stations 199, 199' and 199", respectively, to remove any residual toner therefrom. Finally the chips will come to rest at the top of their respective storage stations 175, 175' and 175".

As in the previous embodiment, suitable rails and guides may be provided for supporting the chips as they are moved from station to station as will be apparent to one skilled in the art. Also, the endless belts and drive means may be provided with suitable bearings and mounting supports as needed. If desired, some suitable means other than the belts shown may be used to advance the chips from one station to another. In addition, the time periods given for the various operating signals are purely arbitrary and could be varied as needed for a particular application.

SEQUENTIAL EXPOSURE AND MULTIPLE-STATION TRANSFER

A further alternative, electrophotographic apparatus A" as shown in FIG. 9 wherein a single exposure station is used for all of the chips but separate transfer stations are used for each set of chips. Thus, the chips are fed sequentially from the bottom of each of storage stations 256, 256' and 256", respectively, by belts 257, 257' and 257" driven intermittently by motors 258, 258' and 258". The belts have spaced dogs, such as dogs 259, 259' and 259" which engage the edge of the chips to advance them. The chips are then engaged by similar dogs on continuously running belts 260, 260' and 260" all driven by motor 261, which drives the chips past charging stations 262, 262' and 262", respectively, wherein an electrostatic charge is placed on the photoconductive surface of each chip. Thus, upon closing a starting switch, such as switch 81 of FIG. 4, motor 258 is energized. A chip from storage station 256 will close a microswitch 263 to energize motor 258' to feed a chip from storage chamber 256'. Similarly, the chip from storage chamber 256' will close a microswitch 263'. Belts 260, 260' and 260" move the respective chips into holding stations or hold-to-expose station 264, 264' and 264" where they are held until each chip can be sequentially moved to a stationary exposure station by an elevator to be described. The chips are sequentially moved from the hold-to-expose stations by intermittently driven belts 265, 265' and 265" each having dogs which engage the chips and each being driven by motors 266, 266' and 266". When a chip reaches holding station 264, it will close microswitch 267 energizing motor 266 to move the chip to the top of elevator 268. Similarly, when a chip reaches holding station 264', microswitch 267' is closed to energize motor 266' to move the chip to the top of the elevator. Likewise, when a chip is received in holding station 264", microswitch 267" is closed thereby energizing motor 266" so that the chip is moved to the top of elevator 268. Upon reaching the top of the elevator, each chip is moved down to exposure station 269 where it is exposed to a light image projected from film 10 through lens 13. Upon reaching the exposure station, the chip will close microswitch 270 which will energize solenoid 271 to register the chip against pins 272.

The time that each chip is at the exposure station will depend on the color of the light image to which it is exposed and also the density of that image. Thus, cycle time for each chip will be different at the exposure station. This difference in time is compensated for at hold-to-expose stations 264, 264' and 264" and at escape-to-develop stations 273, 273' and 273" to which the respective chips are driven by endless belts 274, 274' and 274" by intermittently driven motor 275. Each of these belts has spaced dogs, such as dogs 276, 276' and 276" which are adapted to engage openings in respective chips that they are moved to the appropriate development station. Thus, the chips from storage station 256 have an opening 277 located on one corner adjacent the marginal edge thereof which is adapted to be engaged by dog 276 of drive belt 274 so that when a chip from this set is in the exposure station, it will be driven from the exposure station to the escape-to-develop station 273, as shown in FIG. 9. Similarly, the set of chips from storage station 256' are provided with an opening 278 in a center portion of the marginal edge, as shown, for engagement by dogs 276' of intermittent drive 274 so that when one of these chips is in exposure station it will be driven to escape-for-transfer station 273'. Likewise, the chip from storage station 256" has an opening 279 in a corner adjacent the marginal edge thereof which is engageable by dogs 276" of intermittent drive 274" through those chips from the exposure station to escape-for-develop station 273".

When a chip reaches escape station 273", it will close a microswitch 281 energizing motor 282 which drives endless belts 283, 283' and 283" so that the respective chips in each escape station is engaged by articulating dogs 284, 284' and 284" to move each of them across development stations 285, 285' and 285", wherein the electrostatic image thereon is toned, and then to move them to respective transfer stations 286, 286' and 286". When microswitch 288 in transfer station 286 is closed by the presence of a chip in that station, solenoids 289, 289' and 289", respectively, will be energized to force the chips against registration pins 290, 290' and 290". The developed image on each of these chips is then transferred to a receiver, such as receiver 291 on roller 292 which is driven across the chips by endless belt 293 connected to motor 294. Such transfer may take place in a manner such as that disclosed in commonly assigned U.S. Pat. application Ser. No. 741,387, filed on even date herewith, entitled "Image Transfer Mechanism" to Oliver W. Gnage. Transfer will take place when microswitch 295 is closed indicating that a transfer roller is in position for transfer. Thus, the image is on each of the chips is transferred from the receiver in succession and in registry as the roller moves across the chips.

At the end of the transfer path, roller 292 will close a microswitch 296 energizing motor 297 so that the chips are driven by belts 298, 298' and 298", respectively, from the respective transfer stations to elevators 299, 299' and 299". The elevators are driven by motor 300 which is energized as by a chip engaging microswitch 301 at elevator 299. The elevators move the chips to the top, where they are picked up by dogs on endless belts 302, 302' and 302", which are driven continuously by motor 303. The chips are moved past cleaning stations 304, 304' and 304", so that any residual toner may be removed from the photoconductive surface thereof, and back to the top of storage stations 256, 256' and 256", respectively.

From the foregoing discussion, it can be seen that the circuit logic applicable to the charging and exposure mechanism disclosed in FIG. 9, is substantially identical to that shown in FIGS. 4, 4a, 4b and 4c, whereas the logic circuitry applicable to the transfer mechanism of FIG. 9 is substantially identical to that of FIGS. 8 and 8a. Therefore, a detailed discussion of the specific circuitry for this embodiment will not be given since the analogies to the other embodiments are obvious.

It is apparent that no hold or escape stations are required adjacent the transfer station of electrophotographic apparatus A" since separate transfer stations are provided for each set of chips. The chips are stationary in both the exposure and transfer stations while work is done on the chips but they move continuously through the charging, development and cleaning stations. With the arrangement shown, the chips may be cycled so that they arrive at all three transfer stations substantially simultaneously so that transfer may take place immediately. Also, the cycling between chips of the same set is such that as soon as the image has been transferred from a chip and it has been moved out of the transfer station, the next chip is ready to move into the transfer station. Also, to shorten the transfer time even more, the chips may be cycled so that a chip is received in the exposure station closest to the transfer means (transfer station 288" of FIG. 9) so that transfer may begin while chips are still moving into the other transfer stations. In this case, of course additional circuitry and microswitches are needed, as will be readily apparent to one skilled in the art, but transfer of the first image can commence as soon as the other chips have reached a position in the developing station in time to be transferred. In such a case, belts 283, 283' and 283" might be continuously driven.

SUMMARY

From the foregoing, the novel features and the advantages of this invention are readily apparent. An electrophotographic apparatus has been provided wherein a plurality of stacks or sets of photoconductive chips are provided which may be exposed to different images which are in turn transferred in registry to a receiver. This system contemplates both stations in which the chips are stationary and stations in which they are moving. In one embodiment, passive escape and hold stations are provided between the active stations wherein the photoconductive chip is stationary to permit efficient machining cycling so that the most prints may be made in the shortest time. In another embodiment, separate exposure and transfer stations are provided for each set of chips. With this arrangement, all stations may be active ones but at some the chips are stationary and at others the chips are in motion. In a third embodiment, a single exposure station is used in conjunction with passive hold and escape stations whereas transfer is made at separate transfer stations which require no hold stations. In this case there will be passive stations in the vicinity of the exposure station but not in the vicinity of the transfer stations.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

I claim:

1. An electrophotographic device for printing at least two toner images, from at least two radiation patterns, in registry with each other on a receiver, wherein said device includes:

image forming means including exposing means;

developing means; and

transfer means;

the improvement comprising:

first and second photoconductor means movable through each of said means in a time interval to form, tone and transfer said two toner images to said receiver; and

means for intermittently moving said photoconductor means to vary the time interval each of said photoconductor means is in said exposing means in accordance with photographic characteristics of each of said radiation patterns to transfer successively toner images from said first and second photoconductive means to said receiver substantially continuously.

2. A device, as claimed in claim 1, wherein:

said first and second photoconductive means includes first and second sets of separate photoconductive chips.

3. A device, as claimed in claim 2, wherein said improvement further comprises:

first and second storage stations intermediate said transfer means and said image forming means, respectively.

4. A device for printing at least two images, from at least two radiation patterns, in registry with each other on a receiver, said device including:

image forming means including exposing means;

at least one developing station;

transfer means;

first and second sets of photoconductive elements movable in time intervals through said exposing means, said developing station and said transfer means, respectively;

means for moving said photoconductive elements through said respective means and said station to transfer successive images from said elements to said receiver substantially continuously; and

means for moving said photoconductive elements through said exposing means intermittently for varying the time interval each of said elements is in said exposing means in accordance with photographic characteristics of each of said radiation patterns.

5. A device for printing at least two images, from at least two radiation patterns, in registry with each other on a receiver, said device including:

image forming means including exposing means;

first and second developing stations;

transfer means;

first and second cleaning stations;

first and second sets of photoconductive elements, said first set being movable in time intervals through said exposing means, said first developing station, said transfer means, and said first cleaning station, said second set being movable in time intervals through said exposing means, said second developing station, said transfer means, and said second cleaning station;

means for moving said photoconductive elements through said respective means and said stations to transfer successive images from said elements to said receiver substantially continuously; and

means for moving said photoconductive elements through said exposing means intermittently to vary the time interval each of said elements is in said exposing means in accordance with photographic characteristics of each of said radiation patterns.

6. A device, as claimed in claim 5, wherein said image forming means further includes:

first and second charging stations; and

a single exposure station, said elements of said first and second sets being continuously movable through said first and second charging stations, respectively, and being intermittently movable through said single exposure station in alternating relationship.

7. A device, as claimed in claim 6, wherein said transfer means includes:

a single transfer station, said elements of said first and second sets being continuously movable through said first and second developing stations, respectively, and being intermittently movable through said single transfer station in alternating relationship to transfer developed images from said elements onto a receiver in registry.

8. A device, as claimed in claim 7, further including:

first and second hold-to-transfer stations between said single transfer station and said first and second developing stations, respectively, for holding a developed element of one set while an image on a developed element of the other set in said transfer station is transferred to said receiver.

9. A device, as claimed in claim 7, further including:

first and second escape-to-clean stations between said single transfer station and said first and second cleaning stations, respectively, for holding said elements from said first and second sets, respectively, after transfer prior to movement through said respective cleaning stations.

10. A device, as claimed in claim 6, wherein said transfer means includes:

first and second transfer stations, said elements of said first and second sets being intermittently movable through said first and second transfer stations, respectively.

11. A device, as claimed in claim 6, further including:

first and second hold-to-expose stations between said single exposure station and said first and second charging stations, respectively, for holding a charged element of one set while a charged element of the other set is in said exposure station.

12. A device, as claimed in claim 6, further including:

first and second escape-to-develop stations between said single exposure station and said first and second developing stations, respectively, for holding said elements of said first and second sets, respectively, after exposure prior to movement through said respective developing station.

13. A device, as claimed in claim 5, wherein said image forming means includes:

first and second charging stations; and

first and second exposure stations, said elements of said first and second sets being continuously movable through said first and second charging stations, respectively, and being intermittently movable through said first and second exposure stations, respectively; and

said transfer means includes:

first and second transfer stations, said elements of said first and second sets being intermittently movable through said first and second transfer stations, respectively.

14. A device for printing three images from three color separation images in registry with each other on a receiver to make a composite color print, said device comprising:

first, second and third storage stations;

first, second and third charging stations;

a single exposure station;

first, second and third developing stations;

a single transfer station;

first, second and third cleaning stations;

first, second and third sets of separate photoconductive chips movable seriatum through said respective stations;

means for moving said chips continuously through their respective charging, developing and cleaning stations and for moving said chips intermittently through said exposure station and said transfer station;

means for varying the time interval each of said chips are in said exposure station in accordance with the color and density of their respective color separation images;

first, second and third hold-for-expose stations intermediate said exposure station and said first, second and third charging stations, respectively, for holding charged chips, said chips being moved into said exposure station in turn from each of said hold-for-expose station; and

first, second and third hold-for-transfer stations intermediate said transfer station and said first, second and third developing stations, respectively, for holding developed chips, said chips being moved into said transfer station in turn from each of said hold-for-transfer stations so that transfer of successive images from said chips to said receiver occurs substantially continuously.

15. A device, as claimed in claim 14, wherein:

each of said chips is primarily photosensitive to one of said color separation images; and

each of said developing station tones electrostatic images formed from said color separation images with a toner having a color complementary to the color of said color separation images, respectively.

16. A device for printing three images from three color separation images in registry with each other on a receiver to make a composite color print, said device comprising:

first, second and third storage stations;

first, second and third charging stations;

first, second and third exposure stations;

first, second and third developing stations;

first, second and third transferring stations;

first, second and third cleaning stations;

first, second and third sets of separate photoconductive chips movable from their respective storage stations through the other respective stations;

means for moving said chips continuously through their respective charging, developing and cleaning stations and for moving said chips intermittently through said exposure station and said transfer station; and

means for varying the time interval each of said chips are in said exposure station in accordance with the color and density of said color separation images.

17. A device for printing three images from three color separation images in registry with each other on a receiver to make a composite color print, said device comprising:

first, second and third storage stations;

first, second and third charging stations;

a single exposure station;

first, second and third developing stations;

first, second and third transferring stations;

first, second and third cleaning stations;

first, second and third sets of separate photoconductive chips movable seriatum through said respective stations;

means for moving said chips continuously through their respective charging, developing and cleaning stations and for moving said chips intermittently through said exposure station and said respective transfer stations; and

means for varying the time interval each of said chips are in said exposure station in accordance with the color and density of their respective color separation images.

18. An electrophotographic apparatus having:

a plurality of active stations including a charging station, an exposure station, a developing station, a transfer station and a cleaning station; and

a plurality of separate photoconductive members movable relative to some of said active stations while work is performed thereon and stationary relative to other of said active stations while work is performed thereon, the improvement comprising:

at least one passive holding station serving as a buffer between adjacent active stations wherein the first of said adjacent active stations to do work on said photoconductive member is one of said relative moving stations and the other of said adjacent stations is one of said stationary stations.

19. An electrophotographic apparatus, as claimed in claim 18 wherein said one of said stationary stations works on each of said photoconductive members for different time periods.

20. An electrophotographic apparatus, as claimed in claim 18, wherein the improvement further includes:

a plurality of sets of said active stations, said sets having a common stationary station.

21. An electrophotographic apparatus for printing three images from three color separation original images in registry with each other on a receiver to make a composite color print, said apparatus having:

three sets of active stations, each set of stations including a charging station, an exposure station, a developing station, a transfer station, and a cleaning station; and

three sets of separate photoconductive chips, each set being sensitive primarily to one of said three color separation original images and movable relative to some of said active stations while work is performed thereon and stationary relative to other of said active stations while work is performed thereon;

the improvement wherein:

said stationary stations include a single exposure station common to all three sets of stations; and

first passive holding stations in each of said sets of stations, said first holding stations being between said respective charging stations and said single exposure station and holding the charged chips, respectively, of any two of said sets of chips while a chip of the third set is being exposed.

22. An electrophotographic apparatus, as claimed in claim 21, the improvement further including:

a single transfer station common to all three sets of stations; and

second passive holding stations in each of said sets of stations, said second holding station being between said respective developing stations and said single transfer station and holding the developed chips, respectively, of any two of said sets of chips while a toner image on a chip of said third set is being transferred.