Electrophotographic apparatus

Abstract

An electrophotographic apparatus for producing single or multiple copies of an original makes use of a photoconductive belt having thereon detectable marks defining between them equally sized belt sections each suitable for the formation thereon of an image transferable to a copy sheet, together with means for driving a flight of the belt through a processing path at constant speed, several means respectively operable at locations spaced along said path for forming said image and transferring and fixing it to a copy sheet fed to and then from the belt, and a control combination including a pulse emittor, copies selector, run starter, pulse counter, mark sensor, shift register, and combinative circuit, for activating and inactivating the said means, respectively, at moments precisely related to the locations and movement in said path of the belt section or sections used for any copying run.

Description

The present invention relates to an electrophotographic apparatus and, more particularly, to a type of such apparatus in which the photoconductive medium has the form of an endless belt that is transported along a processing path in which it passes through a plurality of electrophotographic processing stations including a charging station, an exposing station, a developing station and a transfer station.

For the efficient utilization of such an apparatus it is desirable that each of the different processing stations be brought into active condition only when that portion of the belt which at the moment is being used for image formation is passing through the respective station. If the processing stations were active continuously, the belt would be exposed uninterruptedly to their operation, which would give rise to detrimented effects including undue wear.

Since the different processing stations are located at certain distances from each other along the transport path of the belt, it is important, in order to achieve the desired manner of operation, that the processing stations be activated in a certain order and at certain moments in relation to the start of each printing run. The activations, moreover, need to be effectual for making either a single copy or multiple copies in any printing run as desired.

A further important consideration is that the activations of the several processing stations for the formation of an image on any particular portion of the length of the belt be brought about in a certain relationship to the changing locations of that belt portion as it is being transported through the processing path of the apparatus, without dependence upon the position or movement of portions of the endless belt outside that path; also, that the activations so brought about be effected in a manner enabling successively following portions of the belt in the processing path to be utilized for the quick, successive production of multiple copies of an original to be reproduced.

The object of the present invention is to provide a control system for an electrophotographic apparatus of the type above mentioned whereby the desired manner of operation is achieved in a reliable and efficient way, both for making a single copy and for making multiple copies per printing run.

The electrophotographic apparatus for which the present invention is provided is one of the type above mentioned which makes use of a photoconductive belt provided with a plurality of detectable marks equally spaced apart on the belt over its length at intervals which divide the belt into a multiplicity of successive portions, or belt sections, of equal length, together with means for transporting a part of the length of the belt continuously along a processing path in which it is moved through the requisite image forming and image transfer stations and in which, at certain location, a sensor is provided for detecting the belt marks that pass that location and generating a pulse each time a mark passes the sensor. In order to form a transferable visible image, the image forming stations include charging, exposing and developing stations. The image transfer station then includes means for transferring the developed image to a copy sheet and means for feeding copy sheets successively into and away from engagement with successive image bearing portions of the belt at the transfer station. Also, a fixing station is provided in the path of movement of the copy sheets away from the transfer station, for fixing each transferred image on the copy sheet.

According to the invention, the respective means for driving the belt along the processing path, forming a transferable image on a portion of the belt, feeding a copy sheet to the image bearing belt portion, transfering the image to the copy sheet, and fixing the transferred image, can each be activated and inactivated for the initiation and the interruption of its own operating function; a pulse emittor is connected with the belt driving means for generating electric pulses at a frequency proportional to the speed of the belt when the belt is being driven; and the control system further comprises a manually operable print button for starting a printing run, a selector for selecting the number of copies to be made during the printing run, and a special combination of a pulse counter, a shift register and a combinative circuit.

The pulse counter is actuated in response to each sensing of a belt mark by the sensor, so as to count the number of pulses generated by the pulse emittor after the particular mark has been sensed, and it has a plurality of outputs which are energized in groups so that the respective output combinations correspond to different aggregate numbers of counted pulses.

The shift register provides a plurality of successively energized outputs. The first of these is activated upon the coincidence of a signal from either the print button ("print knob") or the selector and a pulse signal from the sensor, after which the other outputs are activated in succession, respectively, in response to succeeding pulse signals from the sensor.

The combinative circuit is connected to receive and be activated by the output signals of the counter and the output signals of the shift register. It has a plurality of outputs connected with respective control systems for activating or inactivating the various means for driving the belt, forming a transferable image on a portion of the belt, feeding a copy sheet to that belt portion and transferring the image, and fixing the transferred image on the copy sheet.

The above mentioned and objects, features and advantages of the invention will become apparent from the following description and the accompanying drawings of an illustrative embodiment of the invention. In the drawings:

FIG. 1 is a schematic section of an electrophotographic apparatus embodying and for which the present invention is suited;

FIG. 2 is a section along the line II--II' of FIG. 1;

FIG. 3 is a block diagram of an electric circuit controlling the operations of the apparatus;

FIG. 4 is a diagram of an actuation schedule of the processing stations when making one copy per printing run;

FIG. 5 is a diagram similar to that of FIG. 4, but for making three copies per printing run;

FIG. 6 is a schematic cross sectional view of a pulse emittor used in the control system; and

FIG. 7 is a front view of the rotary disk of the pulse emittor of FIG. 6.

The electrophotographic apparatus illustrated in FIGS. 1 and 2 makes use of an endless, zigzag folded photoconductive belt medium in a process according to the invention disclosed in Netherlands patent application No. 7,105,941. A large part of the length of the belt is stored in a magazine 30 which corresponds substantially to the magazine disclosed in U.S. Pat. No. 3,756,488.

The magazine contains a stack of superimposed zigzag folded sections of a photoconductive belt 27 which, for instance, is an endless belt of paper coated with a layer of photoconductive zinc oxide-binder composition. The stacked belt sections are bowed upwardly in the magazine. The belt extends from the lower end of the stack through a delivery opening 30a in the bottom of the magazine and thence along a path extending through the electrophotographic processing stations, from which path it extends back to the magazine in connection with the section of the belt at the top of the stack.

The belt may be transported continuously through the processing path, and be deposited in the magazine, by the action of the belt driving rollers 28 and 29. It is guided into and through the processing path by a guide plate 31 located beneath the magazine and by rollers 32, 33, 34, 35, 36, 37, 38, 39, 40 and 41 which determine the path of movement of the belt from the curved surface of plate 31 to the driving rollers 28, 29.

When the belt is transported by actuation of the driving means, the part of the belt drawn from the magazine first passes a charging station at roller 32, where an electrostatic charge is applied to it, for instance, by a corona discharge unit 42 located opposite to roller 32. Then the charged part of the belt passes over a flat exposing table 43, upon which a length of the belt at least as large as a section of it between two fold lines is stretched out flat between the rollers 33 and 34 situated at the ends of the table. By means of flash lamps 46, a lens 47, and mirrors 48 and 49 the image of an original that has been placed between a glass plate 50 and a cover 51 is projected onto the charged section of the belt extending over the exposing table. This belt section is thus exposed so that the charge on its surface disappears imagewise and a charge pattern of the original is formed as a latent image thereon.

Upon further movement of the belt, the section thereof carrying the latent image passes through a developing station at rollers 36 and 37, where toner is applied to it by means of a device 52, for instance a magnetic brush. The charge pattern of the latent image is thus converted into a powder image.

Then the section carrying the powder image is transported to a transfer station at the roller 39, where the powder image and a copy sheet run together around the roller 39. During this movement the powder image is transferred to the copy sheet under the influence of an electric field generated by a corona discharge unit 58. The copy sheet is fed into face to face engagement with the belt at roller 39 by rollers 56, 57 to which the copy sheet has been delivered from a sheet supply holder comprising, for instance, a sheet separating roller 54 acting on the top of a pile 55 of plan paper copy sheets.

After traversing the transfer station the belt and the copy sheet are separated by the belt being drawn off around guide roller 40 while the copy sheet, which now carries the powder image, moves straight onward into the nip between heated rollers 59 and 60 which constitute a heat fixing station of known type. The copy sheet bearing the fixed powder image is then gripped by rollers 61 and 62 which deliver it onto a tray 63.

Beyond the guide roller 40 the used section of the belt passes a lamp 64 which irradiates the belt in order to remove any residual charge from the photoconductive layer, and subsequently the belt section passes through a cleaning station at guide roller 41, where a rotating brush 65 cooperating with that roller cleans the belt by brushing away any remaining toner powder. The brush 65 is enclosed by a shield 66 which by means of a pipe (not shown) is connected via an air pump 67 with a filter bag 68. The powder removed from the belt is thus sucked away from the brush 65 and collected in the bag 68.

From the cleaning station the used section of the belt, which is now free from electrostatic charges and toner particles, is transported between the rollers 28 and 29 and thence to the top of the magazine 30 so that it is deposited onto the top of the stack in the magazine. A rocking mechanism 10 in the magazine assists in laying the belt, folded on its preformed zigzag fold lines, section by section onto the top of the stack.

The part of the length of belt 37 being transported by the rollers 28 and 29 is driven with a constant linear velocity by means of a constant speed drive motor (not shown) acting on roller 29. A pulse emittor 100 (FIG. 6) is associated with the roller 29 so as to be operated in unison with it. For instance, on the shaft 29a of roller 29 is fitted a circular disc 101 which is provided with a circumferential series of radial slots 102. These slots have the same size and are equally spaced apart so that the angle included between vicinal slots 102 has the same constant magnitude for each pair of the slots. A lamp 103 is provided opposite the slots 102 at one side of the disc 101, and a photo-electric cell 104 at the other side. When the disc is rotated in unison with the roller 29, the photo-electric cell 104 generates a pulse every time a slot 102 passes between the lamp 103 and the photo-electric cell 104. Since the linear velocity of the driven part of the belt is directly proportional to the angular velocity of the disc 101, the number of pulses generated by the photo-electric cell 104 is directly proportional to the distance of travel of the driven part of the belt 27, or, in other words, to the belt length transported past a certain point from the moment when the driving of the belt commences.

The non-photoconductive, or rear, side of the belt is provided with detectable marks which are equally spaced thereon longitudinally of the belt. In the embodiment shown these marks substantially coincide with the preformed fold lines in the belt. The ratio of the belt length moved past a certain point to the number of pulses emitted by the pulse emittor 100 during the belt movement is so chosen that when, for instance, the length of a belt section between two successive marks on the belt amounts to 406.4 mm, the corresponding operation of the pulse emittor generates 406.4 pulses. Thus, for instance, one pulse is emitted for every millimeter of travel of a section of the belt through the processing path.

The pulses generated by the photo-electric cell 104 of the pulse emittor are conducted to a counter 110 (FIG. 3) of a type known per se, in which the number of these pulses is counted.

A belt mark sensor 53, or scanning element, is arranged in a fixed location at the rear side of the belt so that this sensor will generate a pulse signal whenever a mark on the belt moves past its location. The signal output of the sensor 53 is conducted to (1) a resetting input of the counter 110, whereby the counter is reset to a zero count condition whenever a mark on the belt moves past the sensors 53, (2) a gate circuit 112, and (3) a clock input of a shift register 114.

The gate circuit 112 is also connected to receive a signal from a manually operable switch 116, or "print knob", which is provided for starting each printing run of the apparatus, and a signal from a selector 118 which is settable by means of a manually operable selector knob 117 for selection of the number of copies to be made in any printing run. The selector 118 emits no signal, i.e. its output is zero, when only one copy is to be made or, in other words, when it is set to position "one". On the other hand, it emits a signal when it is set for more than one copy to be made in one printing run, and its output becomes zero after the initiation of the making of the final copy of the printing run, as will be further evident from the description below.

The gate circuit 112 emits a signal pulse whenever it receives a combination of either (1) a signal from the sensor 53 and a signal from the print knob 116 or (2) a signal from the sensor and a signal from the selector 118. Thus, the gate circuit 112 is activated to emit a signal pulse, and this pulse is conducted to an input of the shift register 114, upon the first movement of a belt mark past the sensor after actuation of the print knob, or of both the print knob and the selector, in order to initiate a printing run.

The shift register 114 is provided with five outputs, the first of which is excited when the gate circuit emits a signal pulse. Since the sensor 53 is also connected with the clock input of the shift register, the shift register receives a clock signal from the sensor upon each movement of a belt mark past the active sensor. The sensor signals so received cause the shift register to shift its output conditions progressively from one to the next of its five outputs. More particularly, when the sensor has emitted the next signal after the one passed through the gate circuit to activate the shift register, the existence or non-existence of a signal in the first output of the shift register is converted into the existence or non-existence of a signal in the second output of the shift register; the existence or non-existence of a signal in the second output, when the sensor has again emitted a signal, is converted into the existence or non-existence of a signal in the third output; etc.

The output signals of the shift register 114 and of the counter 110 are combined in a combinative circuit 120. This circuit has a plurality of outputs which are connected respectively with control systems for starting and stopping the various operations that are to be performed in the apparatus in order to make one or more copies. The several outputs of the combinative circuit are excited in response to respective combinations of signals received in this circuit from the counter 110 and the shift register 114, and the output signals thus generated activate or inactivate respective operating components of the apparatus in the manner more fully described below.

I. For making only one copy the operation of the apparatus from start to finish is as follows (see FIGS. 1 and 4):

a. When a main switch is closed to energize the apparatus:

1. a main driving motor (not shown) is energized;

2. the magnetic brush 52 is driven;

3. an electric field for suppressing the background on the belt after exposure is applied between the magnetic brush and the rollers 36, 37;

4. an electric field is applied at unit 58, with a polarity (cleaning polarity) required for transferring a powder image on the belt to a copy sheet; and

5. the heating elements of the fixing device 59, 60 are partially energized.

b. When the print knob 116 is actuated, it emits a signal into the combinative circuit 120, as a result of which the rollers 28 and 29 ("belt drive" 130 of FIG. 3) are coupled to the main motor, so that the belt is now driven at a constant linear velocity, and at the same time the rocking device 10 (FIG. 1) is activated for laying the leading moving sections of the belt onto the top of the stack in the magazine 30.

c. By the rotation of the belt driving rollers, which are coupled to the pulse emitter 100 (FIG. 6) as described above, pulses are emitted which are counted in the counter. Then, as soon as the first belt mark arrives opposite to the sensor 53, a signal is generated which on the one hand resets the counter 110 to zero, and on the other hand is combined in the gate circuit 112 with the signal emitted by the print knob. As a result, the gate circuit emits a signal pulse, and a signal is thus created in the first output of the shift register 114. The counter now restarts, counting the number of pulses from zero, and in the counter a certain combination of output signals is created for any number of pulses counted. These counter outputs are combined with the outputs of the shift register in the combinative circuit.

When a signal exists in the first output of the shift register and output signals corresponding with 64 pulses have occurred in the counter, when a signal is created in an output of the combinative circuit that is connected with the control system 142 of the corona device 42. Consequently, the corona 42 is excited and as a result the photoconductive layer on the portion of the endless belt passing guide roller 32 is charged. At the same time a signal is generated in an output of the combinative circuit connected with the control system 143 for the current supply to the capacitors of the flash lamps 46, as a result of which this supply is switched on and the capacitors are charged.

d. When the next belt mark arrives at the sensor 53, this causes the emission of a signal which on the one hand resets the counter to zero, and on the other hand shifts the shift register to its second output stage where a signal now occurs. Since the signal from the print knob 116 no longer exists and the selector 118 emits no signal, the gate circuit is blocked and no new signal pulse passes to the shift register; so the first output of the shift register becomes inactive, or at zero signal.

The resetting of the counter starts a new counting of the number of pulses from zero. Then, there now being a signal in the second output of the shift register, when signals corresponding with 32 pulses have occurred in the outputs of the counter, a signal is created in an output of the combinative circuit that is connected with the control system 142 of the corona device 42, by which signal this device is switched off. A signal in the second output of the shift register, combined with counter output signals that correspond with 108 pulses, generates a signal in an output of the combinative circuit connected with the control system 143 for the current supply to the capacitors of the flash lamps, this supply thus being switched off. The same combinative circuit output is also connected with a control system 144 controlling the switching-on of the flash lamps, so that the flash lamps 46 are momentarily energized and an image of the original previously placed on exposure plate 50 is thus projected on the photoconductive layer of a section of the belt located at that moment on exposing table 40.

e. When the third belt mark arrives at the sensor, a signal is emitted causing on the one hand the counter to be reset to zero, and on the other hand the shift register to be again shifted; in other words, a signal now occurs in the third output stage of the shift register. The counter now restarts counting the number of pulses from zero. There now being a signal in the third output of the shift register, when signals corresponding with 240 pulses have occurred in the outputs of the counter, a signal is created in an output of the combinative circuit connected with the control system 145 of the sheet separator (feed roller 54) of the copy sheet holder, by which signal a copy sheet is fed from the sheet holder up to a limit stop constituted by the nip of rollers 56 and 57. Then, when the signal in the third output of the shift register has combined with counter output signals corresponding with 400 pulses, the combinative circuit generates a signal in an output thereof connected on the one hand with the control system 145 of the sheet separator, whereby the operation of roller 54 is stopped, and on the other hand with the control system 146 of the drive of the sheet feeding rollers 56 and 57, whereby this drive is activated and the copy sheet is passed onward to the transfer station at belt guide roller 39.

f. Upon arrival of the fourth belt mark at the sensor a signal is emitted by which on the one hand the counter is reset to zero, and on the other hand the shift register is again shifted; in other words, a signal now occurs in the fourth output stage of the shift register. The counter now restarts counting from zero. When the signal thus occurs in the fourth output of the shift register, with the counter output corresponding to zero pulses, a signal is created in an output of the combinative circuit connected with the control system 147 of the transfer field circuit, as a result of which the transfer voltage at unit 58 is switched on.

The combination of the signal in the fourth output of the shift register and counter output signals corresponding to 128 pulses generates a signal in an output of the combinative circuit connected with a control system 148 of the heating elements of the fixing device 59-60, causing them to be fully energized; whereas the combination of a signal in the fourth output of the shift register and counter output signals corresponding to 312 pulses generates a signal in an output of the combinative circuit connected with the control system 146 of the drive of the sheet feeding rollers 56 and 57, whereby the rotation of these rollers is stopped.

g. Upon arrival of the fifth belt mark at the sensor, the signal then emitted causes on the one hand the counter to reset to zero and on the other hand the shift register to shift again; in other words, a signal now occurs in the fifth output stage of the shift register. Then, when counter output signals corresponding with 160 pulses have occurred, the combination of these signals with the signal occurring in the fifth output of the shift register is converted in the combinative circuit into a signal in an output connected with a control system 147 by which the transfer voltage is switched off or, in some cases, is changed over to a reversed polarity.

h. The arrival of the sixth belt mark at the sensor results in the emission of a signal causing on the one hand the counter to be reset to zero and on the other hand the shift register again to shift. Since the shift register has only five output stages, all its outputs now become inactive, or are at zero signal. The counter output signals corresponding to zero pulses now cause a signal to be generated in an output of the combinative circuit connected with the control system 148 for the heating elements of the fixing device 59-60, as a result of which these heating elements are either switched off or switched to a reduced operating intensity.

All the operations necessary to make a copy now have been performed in the proper sequence and at the right moment. When the rocking mechanism 10 of the magazine 30 next reaches a certain position, it actuates a micro switch which is operative only when the printing run has been entirely completed, and that switch consequently deenergizes the drive of the belt; so the belt stops. The apparatus thus is brought to stand-by condition.

II. For making multiple copies in one printing run (see FIG. 5), the complete operation of the apparatus is as follows (the main switch having been closed previously with the effects described at I(a) above):

b. By means of the selector knob 117 the selector 118 is set, for instance, at a position to give three copies. A signal consequently occurs in the selector output connected with the gate circuit 112.

When the print knob 116 is pushed, it emits a signal into the combinative circuit 120, as a result of which the belt drive rollers 28 and 29 are coupled to the main motor so that the belt is driven with a constant linear velocity, and at the same time the rocking mechanism 10 is activated.

c. Rotation of the belt drive rollers causes the pulse emittor 100 to emit pulses which are counted in the counter 110. When the first belt mark then arrives opposite to the sensor 53, a sensor signal is generated which on the one hand resets the counter to zero and on the other hand is combined in the gate circuit 112 with the signal from the selector and/or the print knob, as a result of which the gate circuit emits a signal pulse and a signal is thus created in the first output of the shift register. The counter than restarts counting the number of pulses from zero, and, just as for making only one copy, when counter output signals corresponding with 64 pulses have occurred, there being a signal in the first output of the shift register, a signal is created in an output of the combinative circuit that is connected with the control system 142 of the corona device 42. Consequently, the corona is energized and the photoconductive layer on the portion of the belt being moved through the charging station at roller 32 is electrostatically charged. At the same time a signal is generated in an output of the combinative circuit connected with the control system 143 for the current supply to the capacitors of the flash lamps 46, as a result of which this supply is switched on and the capacitors are charged.

d. Upon arrival of the second belt mark at the sensor, the resulting sensor signal causes the counter to be reset to zero and the shift register to be shifted so that a signal now occurs in the second output of the shift register. Also, since the gate circuit 116 receives this sensor signal together with a signal from the selector 118, the gate circuit opens and delivers a new signal to the shift register so that the first output as well as the second output of the shift register emits a signal. The counter now restarts counting the number of pulses from zero. Normally the combination of a signal in the second output with counter output signals corresponding to 32 pulses would cause interruption of the current supply to the corona. This, however, does not occur, because a signal exists in the first output of the shift register; in other words, the corona is not switched off whenever a signal exists in the first output of the shift register, signifying that at least one copy still remains to be made in the printing run being carried out.

After 108 pulses have been counted, there being a signal in the second output of the shift register, a signal is generated in an output of the combinative circuit whereby the flash lamps are ignited. Again, however, as in the case of the corona, the current supply to the capacitors of the flash lamps is not switched off, because a signal still exists in the first output of the shift register.

The combination of counter output signals corresponding to 256 pulses with the existence of a signal in both the first and the second outputs of the shift register forms a signal in a counting output of the combinative circuit 120, which output is connected with the selector 118, whereby the selector is switched back by one step; in other words, the number of copies originally set in the selector is reduced by one.

e. Upon arrival of the third belt mark at the sensor, the resulting sensor signal causes the counter to be reset to zero and the shift register to be shifted so that signals now occur in the second and third outputs of the shift register. In addition, the sensor signal in combination with the signal of the selector causes the gate circuit to be opened again for emission of a signal by which the first output of the shift register is kept active. The operation of the corona, the current supply of the flash lamps, the ignition of the flash lamps, and the counter outputs then are effected as already described above. However, the sheet separator 54 is started after 240 pulses, and after 400 pulses that element is stopped and the rollers 56 and 57 are started. Also, after 256 pulses the selector is switched back one more step by the counting output signal of the combinative circuit so that, since the printing run was to make three copies, only one copy remains to be made and the output of the selector has now become zero.

f. When the fourth belt mark passes the sensor, the counter is reset to zero and the shift register again shifts, but no new signal is emitted into the shift register, because the gate circuit is blocked. The second, third and fourth outputs of the shift register are now active.

Then, at zero pulses, the transfer voltage at 58 is switched on; after 32 pulses the corona is switched off (the first output of the shift register being zero); after 108 pulses the current supply of the flash lamps is switched off and the flash lamps are switched on; after 128 pulses the heating elements of the fixing device are energized; after 240 pulses the sheet separator is started; after 320 pulses the feed rollers 56 and 57 are stopped; and after 400 pulses the sheet separator is stopped and the rollers 56 and 57 are driven again.

The control system 147 for the transfer voltage at 58 is so connected with the combinative circuit that the transfer voltage will not be switched off while a signal occurs in the fourth output of the shift register. The fixing device continues to be energized as long as a signal occurs in the fifth output of the shift register.

g. When the fifth belt mark passes the sensor, the counter is reset to zero and the shift register shifts so that signals occur in its third, fourth and fifth outputs.

Consequently, after 240 pulses the sheet separator 54 is started; after 320 pulses the drive of the rollers 56 and 57 is switched off; and after 400 pulses the sheet separator is stopped and the rollers 56 and 57 are restarted.

h. When the sixth belt mark has passed the sensor, signals remain in the fourth and fifth outputs of the shift register, so that after 320 pulses the drive of the rollers 56 and 57 is switched off. When the seventh mark has passed, a signal remains only in the fifth output of the shift register, so that after 160 pulses the transfer voltage is switched off or is reversed in polarity. When the eighth mark has passed, the shift register empties, whereupon at zero pulses the energy supply to the heating elements of the fixing rollers is switched off or reduced to a lower value. Then, as soon as the rocking mechanism 10 reaches the position above mentioned, the drive of the belt is interrupted and the printing run has been completed.

It is possible in the use of the apparatus that the sensor 53 may fail to respond to the presence of a mark on the belt. This might occur, for instance, due to a defect in the sensor itself, or due to failure of a lamp if a photoconductive cell is used to sense black spots used on the belt as the detectable marks. If no particular provisions were made for the absence of a sensor signal due to be emitted, this would cause the counter to count more than 407 pulses and the control would be disarranged. To avoid this, a limit signal is emitted in an output of the combinative circuit when the counter has reached, for instance, a count of 424 pulses. This limit signal takes over the task of the signal that should have been emitted by the sensor, so that the counter is now reset to zero, the shift register is shifted, and the next cycle can be started without more.

Claims

What is claimed is:

1. In an electrophotographic apparatus comprising

an elongate photoconductive belt providing a multiplicity of successive areas for image formation thereon,

means for driving a flight of said belt continuously through a processing path having image forming stations and an image transfer station spaced apart therealong,

means for feeding copy sheets individually to said belt at said transfer station;

means at said stations for, respectively, electrostatically charging said belt, imagewise exposing said belt to form a latent image thereon, developing the latent image into a transferable image, and transferring the transferable image from said belt to a copy sheet,

means for fixing the transferred image on the copy sheet,

and control means, respectively, for activating and inactivating said driving means, and charging means, said exposing means, and said sheet feeding means,

the combination which includes:

a multiplicity of detectable marks on and equally spaced apart along said belt so as to define between said marks equally sized belt sections for image formation,

sensor means for generating a pulse signal in response to movement of any of said marks past a fixed point in the path of said belt,

means connected with said driving means for generating electric pulses having a frequency proportional to the velocity of said belt,

manually operable switch means for energizing said driving means to start a printing run,

selector means settable according to the number of copies to be made in a printing run, and which generates a copy signal when demanding more than one copy to be so made,

counter means for counting said pulses and including means for resetting itself to zero count condition and renewing its count in responsive to any pulse signal of said sensor means, said counter means being operative to produce groups of output signals that differ for different counts of said pulses,

a shift register having a plurality of successively activatable outputs and being operative to shift the signal condition existing at any of its outputs to the next in its succession of outputs in response to a pulse signal of said sensor means,

means for activating the first of said outputs of said shift register in response to the combination of a pulse signal from said sensor means and either a signal from said switch means or a copy signal from said selector means,

and a combinative circuit having a plurality of outputs connected respectively with the respective control means aforesaid, said combinative circuit being responsive to respective combinations of the output signals of said counter means and the output signals of said shift register to produce respective signals to said control means whereby said driving means, said charging means, said exposing means and said sheet feeding means, respectively, are activated and inactivated, respectively, at moments precisely related to the movements past said sensor means of those of said marks on said belt which pass said sensor means after an actuation of said switch means.

2. An electrophotographic apparatus according to claim 1, said combination further including means for applying to said belt at said transfer station an electric field to aid the image transfer to a copy sheet, said combinative circuit being further responsive to certain combinations of said output signals to produce signals for activating and inactivating said field applying means at respective moments aforesaid.

3. An electrophotographic apparatus according to claim 1, said image fixing means including means for heating the transferred image on the copy sheet, said combinative circuit being further responsive to certain combinations of said output signals to produce signals for energizing and deenergizing said heating means at respective moments aforesaid.

4. An electrophotographic apparatus according to claim 1, said combinative circuit further including an output connected to the resetting means of said counter means and operative to emit a signal thereto, in the absence of a pulse signal due from said sensor means, in response to a limiting number of said pulses connected in said counter means, said limiting number being slightly greater than the number of said pulses generated during movement of said belt by said driving means over a distance equal to the length of one of said belt sections.