US3867026A

US3867026A - Electrophotographic copier of transfer type

Info

Publication number: US3867026A
Application number: US319096A
Authority: US
Inventors: Masaya Ogawa
Original assignee: Minolta Co Ltd
Current assignee: Minolta Co Ltd
Priority date: 1970-08-03
Filing date: 1972-12-27
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18

Abstract

An exposure optical system for continuously projecting the image of an original on a document table onto a moving photoreceptor includes a first carriage equipped with document illuminating means moved in synchronism with the photoreceptor and a second carriage moved at half the speed of the first carriage in operative relation thereto by a rotary member and equipped with a reflecting optical system. Paper feed means includes a mechanism for temporarily interrupting the feed of paper and then intermittently sending out the paper to an image transfer station in synchronism with the movement of the photoreceptor. In order to rotate an endless support of the photoreceptor one turn more than the preset number of copies to be made, the switches of a program circuit for controlling the respective operations are opened and closed by a control member rotated in synchronism with the endless support. Air blasts or jets or a suction pick-up head separates the copy paper from the photoreceptor. The endless suport includes a drum having a narrow longitudinal slot, and copy paper is transferred to the photoreceptor with the paper leading edge overlying the recess. The paper is peeled from the receptor by a continuous flow of air directed tangentially at the drum or outward through apertures in the drum to separate the paper leading edge and the complete sheet.

Description

[111 3,867,026 [45 Feb. 18,1975

1 ELECTROPHOTOGRAPHIC COPIER OF TRANSFER TYPE [75] Inventor: Masaya Ogawa, Osaka, Japan [73] Assignee: Minolta Camera Kabushiki Kaisha,

Osaka, Japan [22] Filed: Dec. 27, 1972 [21] Appl. No.: 319,096

Related US. Application Data [62] Division of Ser. No. 167,398, July 29, 1971,

abandoned.

[52] US. Cl 355/8, 29/118, 242/74.1, 27l/DIG. 2, 355/16 [51] Int. Cl G03g 15/22 [58] Field of Search 355/3 R, 8, 11, 14, 16; 271/DIG. 2, 51, 80; 242/741, 74.2; 29/118; 96/1.5

[56] References Cited UNITED STATES PATENTS 3,062,110 11/1962 Shcpardson cl a1. 355/15 X 3,202,421 8/1965 (1am 271/51 3,380,733 4/1968 Draugelis 355/3 R UX 3,480,361 11/1969 Tatsumi Doi et a1. 355/1-6 3,502,407 3/1970 Granzow et a1 355/16 X 3,552,957 1/1971 Hodges 96/l.5 3,588,242 6/1971 Berlier et a1. 355/16 3,649,115 3/1972 Hodges 355/11 3,695,756 10/1972 Smith 355/3 R 3,700,327 10/1972 Murgas et a1. 355/14 3,720,466 3/1973 Koizumi 355/8 3,732,005 5/1973 Lloyd 355/14 3,744,900 7/1973 Reesen 355/16 Primary Examiner-Samuel S. Matthews Assistant Examinerl(enneth C. Hutchison Attorney, Agent, or Firm-Wolder & Gross [5 7] ABSTRACT An exposure optical system for continuously project ing the image of an original on a document table onto a moving photoreceptor includes a first carriage equipped with document illuminating means moved in synchronism with the photoreceptor and a second carriage moved at half the speed of the first carriage in operative relation thereto by a rotary member and equipped with a reflecting optical system. Paper feed means includes a mechanism for temporarily interrupting the feed of paper and then intermittently sending out the paper to an image transfer station in synchronism with the movement of the photoreceptor. In order to rotate an endless support of the photoreceptor one turn more than the preset number of copies to be made, the switches ofa program circuit for controlling the respective operations are opened and closed by a control member rotated in synchronism with the endless support. Air blasts or jets or asuction pick-up head separates the copy paper from the photoreceptor. The endless support includes a drum having a narrow longitudinal slot, and copy paper is transferred to the photoreceptor with the paper leading edge overlying the recess. The paper is peeled from the receptor by a continuous flow of air directed tangentially at the drum or outward through apertures I in the drum to separate the paper leading edge and the complete sheet.

6 Claims, 28 Drawing Figures PATENTED 8W5 3,887. 026

' SHEET 01 0F 12 PATENTED FEB I 8 I975 SHEET OEUF 12 PATENTED 3 sum 03 [1F 12 Fig.9

PATENTED 8W5 3 867, 026

" SHEET sum 12 sum as or 12 PATENTED FEB 1 81975 PMENTED W 3.867.026

sum D'IUF 12 PATENTED EBI 8191s 3, 867. 026

sum 08 [1F 12 P-ATENTEU FEB 1 8 1915 sum 09111 12 Fig .22

1:41 Fig.25

SHEET 1.0 HF 12 PATENTEB FEB] 8 I975 PAIENIEB E B sum MM 12 PATENTEB FEB I 8|975 SHEET lZUF 12 ELECTROPHOTOGRAPHIC COPIER F TRANSFER TYPE This is a division of application Ser. No. 167,398 filed July 29, 1971, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to electrophotographic copiers for copying books, sheets of documents and the like, and more particularly to an electrophotographi c copier of the transfer type which employs the Carlson system for formation of the image, and in which the image of an original document placed on a transparent document table is continuously projected onto a photoreceptor on a rotating or moving endless support by an exposure optical system of the slit scanning type and the latent image of the document thus formed is then rendered visible with a toner and transferred onto ordinary paper.

The copier of this type is known by the trade name of Xerox 914, etc. However, the copiers heretofore known have the following drawback;

1. Since the photoreceptor is integrally formed on the surface of a drum by vacuum evaporation, the photoreceptor has to be replaced, together with the drum, when the photoreceptor becomes deteriorated; hence the replacement of the photoreceptor is expensive.

2. With the exposure optical system of the slit scanning type, the document illuminating system and projecting lens must advance in parallel with the document at a speed proportional to the peripheral speed of the photoreceptor on the drum. Consequently, the exposure is not always effected with principal rays from the lens, and the varying length of the light path from the original to the photoreceptor requires an exposure optical system which occupies a large space relative to the length of the original. Thus the copier becomes inevitably large.

Further when employing a system of the foregoing type, it is generally difficult to provide copiers capable of copying documents of a large size, for example, those measuring 1 1" X 14" or 14- X17 and to make copies with a clear image.

. SUMMARY OF THE INVENTION An object of this invention is to provide a copier which is extremely compact relative to the size of the original document and is therefore usable on the table even when copying a document of a large size and which is capable of making copies with a clear image.

Another object of this invention is to provide a copier capable of making a great number of copies from an original document rapidly and successively.

Another object of this invention is to provide an efficient copier in which the operations of forming the image and making the copy are carried out systematically so as to eliminate unnecessary operations when a trouble such as clogging with paper takes place during paper feeding operation.

Another object of this invention is to provide a copier which employs a photoreceptor made of a flexible material and supported on an endless support so that the photoreceptor alone can be replaced when the photoreceptor gets deteriorated.

Another object of this invention is to provide a device by which the paper electrostatically adhering to the photoreceptor for the transference of the image can be peeled off the surface of the photoreceptor smoothly and easily.

Still another object of this invention is to provide a device by which the image of the original transferred onto the paper can be heat-fixed rapidly with a maximum thermal efficiency without causing overheating around the device.

In accordance with a first feature of this invention, there are provided a first carriage and a second carriage under a flat transparent document table fixed to the top of a copier, the first carriage being equipped with a document illuminating system and a plane mirror, the second carriage carrying one or a plurality of plane mirrors. These carriages are respectively mounted on guide rails parallel to the document table, and the first carriage is placed on rollers rotatably attached to the second carriage and adapted to roll on the rails supporting the second carriage. One of the carriages is connected to a drive mechanism for a photoreceptor support. The first and. second carriages are moved at speeds proportional to that of the photoreceptor and are in such relation that the second carriage travels at half the speed of the first carriage. To project the image of the original there is provided a lens in the path of the rays reflected by the plane mirrors on both the carriages. The projector for projecting the image of the original document of the slit type thus constructed occupies a markedly reduced space, ensures travel of the carriages at a given speed ratio, and gives clear copres.

In accordance with a second feature of this invention, a wheel for driving the first carriage having an outer peripheral length equal to the entire periphery of the photoreceptor support in an endless form is connected by way of a clutch to the drive mechanism for the support so as to be rotated at the same peripheral speed as the support, and the first carriage is connected to the wheel by separate pulling strip members such as belts which extend from the outer periphery. of the wheel in opposite directions. The wheel is rotatably mounted on a stationary shaft, with a spiral spring interconnecting the wheel and the shaft, the arrangement being such that, when the clutch is engaged, the first carriage travels forward in operative relation to the photoreceptor support while the spring is wound up.'D.uring this movement, the second carriage follows the first carriage at half the speed of the latter. When both the carriages have completed forward travel, the clutch is disengaged, whereupon the first carriage returns under the action of the wound-up spring, accompanied by the second carriage during the backward travel.

Further it is possible to provide a wheel for driving the second carriage which has an outer peripheral length half the length of the entire periphery of the photoreceptor support and which is connected, through a reduction gear and a clutch, to the support so as to be driven at half the peripheral speed of the support, the wheel being connected to the second carriage by separate belts extending from the wheel in opposite directions.

In this way it is assured that both the carriages travel forward in a given synchronized relation to the moving speed of the photoreceptor support, while the rapid backward travel of the carriages effected by the spiral spring ensures high speed copying operation.

In accordance with a third feature of this invention, an endless support for the photoreceptor has a length suitably greater than the entire length of the photoreceptor to be provided around the surface thereof. For example, for documents having miximum dimensions of 14'' X 17", the support may be about 560 mm in its entire peripheral length. Further the photoreceptor support is controlled by a program circuit including switches for initiating various operations in the image forming and copying process which are opened and closed by one or plurality of cams or a control member to be driven in a given relation to the support in synchronism therewith. Thus disposed around the cam or the control member are a switch for operating charging means, switch for operating an exposure optical system of the slit scanning type, switch for operating developing means, switch for initiating transport of paper and switch for operating transfer means. When a single copy is to be made, a start switch is depressed to effect charging of the photoreceptor, exposure, development, feed of paper, transfer of the image (and separation) in succession during the first one cycle of operation of the photoreceptor support. The photoreceptor support thereafter performs another cycle of operation for separation and transport of the paper and cleaning of the photoreceptor and is brought to a halt at a given starting position.

On the other hand, when a plurality of copies are to be made in succession, the start switch is depressed to effect, during the first cycle of operation, the same image forming and copying operation as in making a single copy. During eachof the subsequent cycles of operation, separation and transport of the paper and cleaning of the photoreceptor for the preceding sheet of paper as well as the image forming and copy operation for the next sheet of paper are performed continually. Upon completion of the final image forming and copying operation, the photoreceptor support conducts another cycle of operation, during which the separation and transport for the last copy and cleaning of the photoreceptor are performed and the support is then stopped at the predetermined position.

Thus, the program circuit enables the copier to perform the steps of image forming and copying operation systematically, rapidly and efficiently and contributes a great deal in providing a compacter copier than conventional devices.

In accordance with another feature of this invention, a flexible photoreceptor having approximately the same size as the document to be copied is detachably provided on an endless support so that the photoreceptor, when deteriorated, can be replaced, the support thereby being rendered serviceable for a prolonged period of use.

In accordance with another feature of this invention, there is provided between the paper feeding position and image transferring position an abutting plate (stopper lugs) for temporarily interrupting the transport of paper in the path thereof. Further just in front of the abutting plate there is disposed a detecting switch to be actuated by the leading edge of the paper and incorporated in the program circuit. The switch serves as a safety device in that insofar as the switch does not function, the photoreceptor support or the switches for initiating the image forming and copying operation will not be operated. This serves to prevent troubles such as incorrect positioning of paper and clogging with paper, to systematically effect various steps of image forming and copying operation and to stop such operation when a trouble occurs during paper feeding operation.

In accordance with another feature of this invention, paper loading means is provided in a magazine which is separate from the copier and which can be detachably mounted on the copier as desired, this also rendering the copier compact.

In accordance with another feature of this invention, there is provided a paper peeling device by which the paper electrostatically attracted to the photoreceptor during transfer operation can be peeled off the photoreceptor readily.

An embodiment of such device includes a recess formed in a suitable portion of the photoreceptor support and extending in the direction of the generating line thereof, that is longitudinally, in combination with an air duct for injecting air into the recess. The timing of operation of the abutting plate of the paper feed means is so determined that the leading edge of the paper will project slightly over the recess.

Another embodiment of the paper peeling device includes air injection apertures formed at a portion of the photoreceptor support where the leading edge of the paper is .to be positioned. Air supplied by a duct is discharged. from the apertures to peel off the front edge of the paper. At a suitable position near the photoreceptor support, another blast duct is provided from which air is forced into a clearance between the photoreceptor and peeled-off-edge of the paper to continuously separate the paper from the photoreceptor.

Still another embodiment of the paper peeling device includes a suction disk orhand for attracting the leading edge of paper so as to remove the paper when desired. The paper whose leading edge has been peeled off is further progressively peeled off the photoreceptor with a blast supplied from a blast duct positioned near the photoreceptor support.

The peeling devices described above require only a small amount of air with a low pressure, so that the fan to be used for the devices may be a sirocco fan of simple construction.

In the case where an endless belt is used for the support of the photoreceptor, the support may be bent at an acute angle about a guide roller of a small diameter. This provides another mode of peeling means. The inherent rigidity of the paper will then .overcome the electrostatic attraction of the photoreceptor at the bent portion, permitting the paper to be peeled off automatically.

The paper peeled off by the devices described above is immediately delivered onto a conveyor means and sent forward for 'the subsequent operation.

In accordance with anotherfeature of this invention, there is provided an air passage around the heat-fixing means for preventing the machine from overheating which enables the heat-fixing means to effect an efficient and rapid heat-fixing operation with the heat thus accumulated. 7

In accordance with another feature of this invention, paper suction means is provided beneath the paper conveyor means under the heat-frxing means. Due to the provision of this means, the distance between the conveyor means and the fixing means can be reduced to achieve heat-fixing operation more effectively and rapidly.

In accordance with another feature of this invention, an air drawer for cleaner means for the photoreceptor is disposed between a cleaning brush and a collector. This arrangement makes it possible to use a compact fan of small capacity such as a sirocco fan for the air drawer and to thereby provide a compact cleaner.

Other objects and features of the present invention will become more apparent from the detailed description of the embodiments of this invention to follow.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of an electrophotographic copier of the transfer type embodying the present invention;

FIG. 2 is a side elevation showing the principal parts of the copier of the present invention, the view being a longitudinal section taken along the path of travel of paper;

FIGS. 3 and 4 are views respectively illustrating the principle of travel of a first carriage and a second car- FIG. 8 is a view showing the construction ofa mounting for securing the flexible photoreceptor to a drumlike support therefor;

FIG. 9 is a view showing the operative relation between the photoreceptor support and the first or second carriage as the parts are seen from behind FIG. 2;

FIGS. 10 and 11 are views showing the construction and operation of shock absorbing means as the first carriage comes to a halt during its return travel;

FIG. 12 is a view showing the construction of drive means for returning the first carriage or the second carrrage;

FIG. 13 is a view showing an embodiment of means for peeling off paper from the photoreceptor to which it is electrostatically stuck;

FIG. 14 is a view showing another embodiment of the peeling means;

FIG. 15 is a view showing an air duct for the peeling means;

FIG. 16 is a view showing another embodiment of the peeling means;

FIG. 17 is a view showing another embodiment of the peeling means; I

FIG. 18 is a view showing another embodiment of the peeling means;

FIG. 19 is a perspective view showing an embodiment of the magazine to be used for paper loading means;

FIG. 20 is a perspective view showing part of frame of the copier where the magazine is to be inserted;

FIG. 21 is a perspective view showing the principal construction of paper feed means for temporarily stopping the paper at the feeding station;

FIG. 22 is a side elevation in longitudinal section taken along the path for transporting the paper and showing heat-fixing means and paper conveyor means positioned beneath the fixing means;

FIG. 23 is a view showing the heat-fixing means and the paper conveyor means illustrated in FIG. 22, the

View being in cross section taken transversely of the path for transporting the paper;

FIG. 24 is a view in cross section showing the conveyor'means positioned beneath the heat-fixing means;

FIG. 25 is a view showing an example of a cam for opening and closing various operation switches of a program circuit in operative relation to the photoreceptor support;

FIG. 26 is a view showing another embodiment of the copier in accordance with the present invention;

FIG. 27 is a diagram showing an example of the program circuit for controlling the image forming and copying operation; and

FIG. 28 is a diagram showing another example of the program circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown the frame I of a copier, the panel 1a of which is provided with a main switch S and a start switch S The frame has a detachable magazine 2 for containing transfer or copy paper at its one side and a copy receiver at the other side thereof.

FIG. 2, a vertical section taken along the direction of traVeLof-the paper, shows the principal mechanisms within the framef At the top of the frame 1 a document table 4 made ofa transparent plate such as a glass plate is fixedly mounted. Disposed under the table 4 is a projector 5 of the slit-scanning type for projecting the image of an original document on a photoreceptor 6 on the surface of which the image of the original is to be produced. Disposed around the photoreceptor 6 are charging means 7 such as a corona discharger, an exposure station 8 at which the image of the original from the projector 5 is projected onto the surface ofthe photoreceptor 6, developing means 9 for supplying toner powder to the surface of the photoreceptor to visualize the latent electrostatic image of the original produced when the photoreceptor 6 is exposed, transfer means 10 comprising a corona discharger or the like for transferring the image onto a sheet of copy paper, and cleaner means 11 for cleaning the surface of the photoreceptor after transference.

On the other hand, disposed in series with the magazine 2 are paper feed means 12 for dispensing paper from the magazine, interrupting the travel of the paper during transport and forwarding the paper to the transfer means 10 in synchronism with the operation of the photoreceptor 6, guide

rollers

13, 14 for bringing the paper into fitting contact with the surface of the photoreceptor 6 at the transfer station 10, peeling means 15 for removing the paper from the surface of the photoreceptor to which it has beenattracted electrostatically upon passage through the transfer means 10, conveyor means 16 for carrying the paper to a heat-fixing station and further toward the copy receiver 3, heat-fixing means 17 disposed in the path of the conveyormeans 16 for heat-fixing the image of the original on the copy paper, and suction means 18 disposed under'the heatfixing means 17 with the conveyor means 16 interposed therebetween.

(I) Construction of the Projector Referring to FIG. 2, a pair of guide rails 19 and another pair of guide rails 20 positioned under the glass plate 4 serving as a document table are fixed to the frame 1, the guide faces of the

rails

19 and 20 being parallel to the glass plate 4. I

A first carriage 21 is slidably mounted on the guide rails 13 by means of sleeves 22, and friction rollers 24 fixed to a second carriage 23 are mounted on the guide rails 20, the guide rails 20 thus guiding the movement of the second carriage 23. The first carriage 21 is mounted on the friction rollers 24 so that friction guides 25 on the bottom of the support 21 come into contact with the friction rollers 24 without slippage, the arrangement being such that the first carriage 21 and the second carriage 23 move in the same direction in synchronism at a constant speed ratio of l /2.

The principle of the above-mentioned movement is that, as shown in FIG. 3, when the first carriage 21 moves at a speed of v,, the friction rollers 24 roll on the guide rails 20, with the result that the second carriage 23 with the friction rollers 24 moves at a speed of v half the speed v The present invention applies this principle to the first and second carriages.

The foregoing structure may alternatively comprise

racks

25R and 20R formed in the lower face of the first carriage 21 and in the upper face of the guide rail 20 and a pinion 24F in place of the roller, whereby the same result as above will be achieved.

The first carriage 21 carries a document illuminating system and a mirror 29, the illuminating system comprising a light source 27 for illuminating the surface to be copied of the original document 26 and a reflector 28 for directing the illuminating light to the face of the original to be copied. The mirror 29 serves to reflect the projected light from the original at a right angle. The second carriage 23 is provided with two

mirrors

30 and 31 for turning 180 the rays from the original reflected by the mirror 29.

A projecting lens 32 is mounted at such position that the rays from the original and reflected by the mirror 31 coincide with the optical axis of the lens. A stationary mirror 33 is located at such position that the rays coming from the original and passing through the lens 32 will strike the face of the photoreceptor 6 at a right angle therewith and that the length of the light path from the original 26 to the lens 32 and that of the light path from the lens 32 to the face of the photoreceptor 6 are equal. Disposed along the light path from the lens 32 to the photoreceptor 6 is a shield plate 34.

The speed ratio between the first carriage 21 and the second carriage 23 has already been described. This will further be described with reference to FIG. in respect of the case wherein both

carriage

21 and 23 travel from the positions indicated in FIG. 2 by solid line at 21 and 23 toward the positions 21' and 23 indicated in phantom line.

When the first carriage 21 moves in the direction of an arrow in the figure, the second carriage 23 moves in the same direction at half the speed of the former. The carriages are of course guided by the guide rails 19 and 20 during this movement. The illuminating means 27 and 28 on the first carriage 21 illuminate the face of the original, and the image of the original is reflected on the mirror 29 toward the mirror 30. Since the displacement of the first carriage 21 is always twice that of the second carriage 21 which has started to move at the same time, the distance between the mirror 29 and the mirror 30 increases as the distance between the mirror 31 and the projecting lens 32 decreases, with the result that the length of the light path from the face of the original to the lens 32 is kept constant all the time in spite of the movement of the first and

second carriages

21 and 23 for the projection of the image of the original onto the surface of the photoreceptor 6. Since the speed of travel of the first carriage 21 is in synchronism with the speed of movement ofthe photoreceptor 6 and since the photoreceptor 6 is charged by the charging means 7, the exposure effected in the abovementioned manner continuously produces an electrostatic latent image on the surface of the photoreceptor 6.

In the embodiment shown, the projecting lens 32 has a magnification of l. A mirror image is formed on the surface of the photoreceptor 6 indicated by a solid arrow, so that such structure is applied to a copier of the transfer type as in the case of this invention. If the mirror 33 is eliminated, a normal image will be formed on the surface 6' of the photoreceptor. Accordingly such structure will be embodied in a copier in which the image of the original is directly formed on sensitive paper.

FIG. 6 shows a construction including only one upright mirror on the second carriage 23. In this case the length of the light path from the surface of the original to the lens 32 can also be kept constant all the time despite the movement of the first and

second carriages

21 and 23 at the aforementioned speed ratio. If the mirror 33 is eliminated in this construction, a mirror, image will be formed on the surface of the photoreceptor 6. This construction will then be employed in a copier of the transfer type, whereas the provision of the mirror 33 will permit a normal image to be produced on the surface of the photoreceptor 6'.

Means for operating the first and

second carriages

21 and 23 and the photoreceptor 6 will be described later.

(ll) Construction of the Photoreceptor and the Support therefor The photoreceptor 6 in accordance with this invention is made of a flexible sheet which comprises a laminate of a film of inorganic semi-photoconductor formed by vacuum evaporation and a' layer of organic semiphotoconductor containing a very small amount of silicone which are laid on a flexible base sheet of electrically conductive material. As shown in FIG. 7(A), for example, the photoreceptor comprises a flexible base a having a thickness of microns and image of a polyester film, a thin aluminum film b deposited on the base by vacuum evaporation and serving as an electrode, a very thin film 0 of amorphous selenium formed on the film b by vacuum evaporation (which may contain not more than 7 percent by weight of tellurium) and a coating d on the film that made of organic semiconductor comprising polyvinylcarbazole and a very small amount of silicone (the amount of silicone being such that it is serviceable as a binder or tht it will not form a coating about several microns in thickness). The uppermost layer d of polyvinylcarbazole containing a very small amount of silicone serves to satisfactorily retain charges and to provide a passage for holes, while the thin selenium film 0 produces charge carriers upon absorption of the light. The aluminum film b forms a high rectification barrier at the boundary between the film b and selenium film c to completely prevent hole injection into the latter. When the photoreceptor is exposed with negative charges on its surface, the holes produced on the thin selenium film c are injected into the polyvinylcarbazole film and move to the surface to neutralize the charges on the surface to form an electrostatic latent image. Thus a useful photoreceptor capable of providing images of improved density and contrast is obtained.

Further as shown in FIG. 7(B), a thin seleniumtellurium alloy film e formed by vacuum evaporation may be interposed between the polyvinylcarbazole film d and the selenium film c. In this arrangement, the selenium film c does not absorb light but merely serves to form a high rectification barrier at the boundary between the films c and b and thereby prevent hole injection. Thus it becomes possible to use about 10 to 60 percent by weight of tellurium in forming the seleniumtellurium alloy film e to thereby provide a photoreceptor having a remarkably improved sensitivity. The selenium film and the selenium-tellurium alloy film in these photoreceptors have a thickness of not more than 1 micron and the polyvinylcarbazole film is made of a high molecular weight material. The aluminum film and selenium film are adhered to each other firmly by exposing the aluminum film to glow discharge, forcibly oxidizing the same by ion impact and then depositing selenium thereon by vacuum evaporation. For these reasons, the selenium film will not be peeled off the aluminum film even when the photoreceptor is used in the form of a belt which is passed around two rollers having a diameter of 30 mm and driven at a speed of lm/sec for 1000 hours without interruption. In fact, the present photoreceptor is very useful even when used in the form ofa belt, has high mechanical strength and excellent flexibility, can be charged to a potential as high as 1000 volts. The photoreceptor has such high sensitivity that exposure to the image of an original can be effectedat several lux. see. In addition, the photoreceptor permits very low pre-exposure effect and is capable of forming an electrostatic latent image having high contrast and resolution and serviceable for repeated use with good results.

The photoreceptor to be used in accordance with this invention is limited to those of the foregoing construction but also employable are flexible photoreceptors of the prior art made of a zinc oxide-resin dispersion.

A support for the photoreceptor 6 comprises a drum 35 of which the circular peripheral portion includes a flat portion 36 serving as a mounting for the photoreceptor 37. The flat portion 36 is provided with a cover 38 having a smaller radius of its curvature than the radius defining the periphery of the drum 35 and disposed substantially along the circumference defining the periphery of the drum 35. The cover 38 serves to eliminate troubles to be caused to the portions where the photoreceptor is fixed to the drum 35, namely the deterioration of the material resulting from ion discharges during charging operation, smudging due to invasion of carrier and toner at the developing station, or damage caused by a cleaner brush.

The circumferential length of the circular face of the drum on which the photoreceptor is positioned is approximately equal to the length of the document table, namely the glass plate 4. (In the case where the maximum dimensions of the original document are 14" X l7", the circumferential length of the drum is about 420 mm and the entire periphery of the drum including the outer periphery of the cover is about 560 mm.)

FIG. 8 shows the photoreceptor 6 as it is mounted on the drum 35. One end of the photoreceptor 6 is secured to a chuck 39 on the mounting 37 and the other end is secured to another chuck 40, with a spring '41 provided between the

chucks

39 and 40 to tension the photoreceptor 6 and thereby fit the photoreceptor 6 tightly to the peripheral surface of the drum 35. Although these

chucks

39 and 40 are slidably mounted on the flat portion 36, it will be seen from FIG. 2 that one end of the photoreceptor 6 may be directly secured to the mounting 37, with the other end secured to a chuck and tensioned by a spring. Thus, the photoreceptor 6, when deteriorated due to a long use, can be replaced with a new one.

As shown in FIG. 8, the cover 38 is smaller in the radius defining the curvature than the drum 35. Thus when secured to the drum 35, the cover 38 forms at its end a recess 42 inwardly of the peripheral face of the drum 35. The recess 42 extends from one end of the drum 35 to the other end thereof along the direction of its generating line and aids in peeling off the paper as will be described later.

The drum 35 may not be limited to the one describe above in respect of its shape and construction, but may be of any shape described with reference to the embodiments to be given later. Further the photoreceptor 6 may alternatively be mounted on a support in the form of a belt as will be described with reference to FIG. 26.

(III) Mechanism for Interlocking Photoreceptor Support and Image Projector Referring to FIG. 9, the drum 35 carrying the flexible photoreceptor 6 is rotatably mounted on a stationary shaft 43 within the frame and connected to a drivegear 44 on the same shaft 43 by a pin 45 so as to rotate integrally therewith. A scanning wheel 46 having the same diameter as the support 6 is mounted on the stationary shaft 43 and provided with a belt47 to be driven in a normal direction and another belt 48 to be driven in a reverse direction which are disposed side by side. One end of each of the

belts

47 and 48 is fixed to the outer peripheral surface of the wheel 46 and the belts are adapted to be wound on the wheel 46 in directions opposite to each other. The other end of each of the

belts

47 and 48 is joined to the first carriage 21. The scanning wheel 46 is connected to a drive gear 49 on the stationary shaft 43 by pins 50 or the like for rotation with the gear 49.

As shown in FIG. 12 the scanning wheel 46 has a spiral spring 52 for returning the carriage having one end fixed to the inner surface of the wheel 46 and the other end fixed to sleeve 51 which is adapted to be fixed to a suitable portion, in the circumferential direction, of the stationary shaft 43. The spring 52 is wound up by the rotation of the wheel 46 in a normal direction.

To provide means for absorbing shock at the time when the carriage is returned, the drive gear 49 has a pin 53 and a rotary plate formed with a recessed portion 54 for engatement with engagement pin 53 and pivoted to the frame 1 at 56. Further pivoted at 59 to the rotary plate 55 is the end of an arm 58 on a support pin 57 fixed to the frame 1, the support pin 57 being spaced from the pivot 56 by a suitable distance. The arm 58 has at its base end a slot 60 in which the pin 57 engages, and a spring 61 acting on the pin 57 and the arm 58 urges the rotary plate 55 in a counter-clockwise direction in the drawing (see FIGS. 9 to 11). Indicated at 62 is a stopper for the rotary plate 55.

The drive gears 44 and 49 are supplied with torque from a drive shaft 65 through

gear system

63 and 64, and electromagnetic clutches CL, and CL,; effect or interrupts the supply of the torque. The drive shaft 65 is associated with a main motor M by way of a sprocket transmission system 66.

The clutch CL is operated by the start switch S; on the operation panel laof the copier to deliver the torque of the drive shaft 65 to the drive gear 44 through the gear system 63 and thereby rotates the drum 35. The clutch CL is disengaged by a microswitch SW which is operated by the control cam- 67 of various image reproducing copying devices to be described later. The cam 67 is coupled to the drum 35.

The clutch CL is actuated by a microswitch SW to be operated by the control cam 67 and delivers the torque of the drive shaft 65 to the drive gear 49 through the gear system 64 and thereby rotates the scanning wheel 46 in a normal direction. The clutch CL is disengaged by the operation of a return switch SW mounted at a position where the forward travel (in the direction of an arrow a in FIG. 9) of the first carriage 2'1 terminates.

Thus the depression of the start switch S rotates the drum 35 in the (normal) direction indicated by an arrow b in FIG. 9 and the microswitch SW then operates to rotate the scanning wheel 46 in the same direction and at the same peripheral speed as the drum 35 to wind up the belt 47 and thereby draw the first carriage 21 in the direction of the arrow a in the figure for the scanning of the surface of the original document. The image of the original document is therefore projected on the photoreceptor 6 on the drum 35. During this movement, the spiral spring 52 within the wheel 46 is wound up.

The forward travel of the first carriage 21 is followed by the movement of the second carriage 23 at half the speed of the former. When both the

carriages

21 and 23 reach the terminal position of the forward travel, the first carriage 21 actuates the return switch SW to disengage the clutch CL whereupon the scanning wheel 46 is rapidly rotated in the (reverse) direction indicated by the arrow c under the restoring action of the spiral spring 52, winding up the belt 48 to return both the

carriages

21 and 23.

In order stop the carriages smoothly upon termination of the return movement, the shock absorbing means acts on the scanning wheel 46 through the drive gear 49 as already described. With reference to FIG. showing the shock absorbing means, the pin 53 moves out of the recess 54 of the rotary plate 55 when the drive gear 49 is initiated into rotation in a normal direction, whereupon the rotary plate 55 is driven in a counterclocltwise direction about the pivot 56 and remains inclined under the action of the stopper 62 and the spring 61. Accordingly, during the rotation of the drive gear 49 in the reverse direction, the recess 54 is positioned in the path of the pin 53 and is ready to receive the pin 53. Consequently, when the drive gear 49 is urged toward the direction of the arrow c by the rapid return movement of the

carriages

21 and 23, the pin 53 is urged into engagement with the recess 54, thereby rotating the rotary plate 55 in a clockwise direction against the action of the spring 61 as seen in FIG. 11. The resilient action of the spring 61 therefore absorbs the impact ofreturn movement of the carriages to bring the same to a halt.

The same result will be obtained if the shock absorbing means is so provided as to directly act on the scanning wheel 46.

The nearer the support pin 57 supporting the arm 58 to the pivot 56, the smaller will be the force required for disengaging the pin 53 from the recess 54 during the rotation of the drive gear in a normal direction and the greater will be the resilient force for absorbing the returning force of the scanning wheel 46, whereby the

carriages

21 and 23 can be brought to a halt smoothly,

The restoring force of the spiral spring 52 acting on the scanning wheel 46 may be controlled as desired by shifting the sleeve 51 in the circumferential direction as it is secured to the stationary shaft 43.

Even after the completion of rotation of the scanning wheel 46, the drum 35 rotates to make a required number of turns of rotation (i.e. two turns if a single copy is to be made, the number of the turns being the desired number of the copies plus one, if many copies are to be made in succession), whereupon the control cam 67 actuates the microswitch SW which in turn disengages the clutch CL to stop the drum.

(IY) Construction of Image Forming and Copying Assembly As'shown in FIG. 2, disposed around the support or drum 35 equipped with the flexible photoreceptor 6 are charging means 7 comprising a corona discharger; developing means of the dry type such as a developing device 9 including a magnetic roller 69 magnetized as a specific magnetic pole and to be driven by a motor M by means ofa belt 68 and a magnetic brush, the device containing a powder mixture of iron powder carrier and toner to be supplied to the photoreceptor 6; transfer means 10 comprising a corona discharger; guide

rollers

13 and 14 for guiding and pressing the paper disposed on the both sides of the transfer means 10 and driven in contact with the photoreceptor 6; peeling means 15 comprising, for example, a sirocco fan 71 and an air duct 72 for removing the paper from the surface of the photoreceptor 6 after it has passed through the transfer means 10; and cleaner means 11 for removing toner remaining on the surface of the photoreceptor 6 from which the paper has been peeled off.

As already known, the charging means 7 charges the I photoreceptor 6 by corona discharge. The developing means 9 supplies carrier and toner to the photoreceptor 6 on which the image of the original is projected through the exposure window 8 and electrostatic latent image is thereby formed, whereby the latent image is visualized. The

guide rollers

13 and 14 press the trans fer paper from the paper supply station against the surface of photoreceptor formed with the visualized image and guide the same for transport. The transfer means 10 transfers the image of the original on the photoreceptor 6 onto the paper.

Referring to FIG. 13 showing the peeling means 15, the air injection slit 73 of the air duct 72 is directed to the peripheral surface of the photoreceptor 6 along its generating line so as to force the air from a blower such as the fan 71 to the peripheral surface of the photoreceptor 6 substantially in the tangential direction.

The paper A, with its leading end positioned at the recess 42 formed by the cover 38, is guided by the

guide rollers

13 and 14 and advanced in snug-fit contact with the peripheral surface of the photoreceptor 6 as the photoreceptor 6 rotates. Since the air is forced into the recess 42 formed along the cover 38, the paper whose leading end is positioned at the recess 42 is readily peeled off the photoreceptor 6 at its leading end. As the drum 35 further rotates, air is forced into a V-shaped clearance formed between the photoreceptor 6 and the paper A with its leading end peeled off. Thus the paper becomes progressively peeled off and is then delivered onto the conveyor means 16.

Peeling of the paper thus effected with extreme ease and smoothness requires much smaller amount of air with lower pressure as compaired with conventional devices. Accordingly a very simple and compact fan will serve the purpose satisfactorily.

Although the paper is electrostatically attracted to the surface of the photoreceptor 6, the conductive cover 38 with the recess 42 free of charging will not cause the leading edge of the paper to bend into the recess 42. Even in the case where the cover 38 is made of synthetic resin or the like and is therefore charged on its surface, the leading end of the paper, with its own strength, will not be bent by attraction, since the leading end of the paper is projected over the recess 42 only 3 or 5 mm. It is therefore assured that the air will be forced into the recess 42 underneath the front edge of the paper.

The peeling means may further be somewhat modifled as shown in FIGS. 14, 16, 17 and 18, whereby equivalent or greater efficiency will be achieved for peeling operation.

FIG. 14 shows a drum a formed in its peripheral surface with a groove 42a extending along the generating line thereof to thereby provide an identical effect with the recess 42 shown in FIG. 13. The air from the duct 72 is injected into the groove 42a. The drum 35a is of course equipped with the photoreceptor 6 on its periphery, with the groove 42a left uncovered with the photoreceptor 6. Exactly the same action takes place in this portion as with the embodiment of FIG. 13. The shape of the groove 42a may not be limited to that shown in the drawing but may be of any suitable shape.

The air duct to be used in the embodiments of FIGS. 13 and 14 may have an elongated slit 73 at its front end as illustrated in FIG. 15 and include a suitable member of blades 74 disposed within the duct for uniform discharge of air from the slit 73.

Another embodiment of the peeling means shown in FIG. 16 includes a guide plate 75 for conducting the paper A from the guide roller 14 to the conveyor means 16. The guide plate 75 is formed at a suitable portion with a window 76 having such size that a flaring suction disk cup or head 77 can be retracted or extended through the window.

The suction disk 77 is joined with the front end of a bent nozzle 78 which is secured at its base end to a duct 79 rotatably supported on an unillustrated bracket within the frame 1, the arrangement being such that the rotation of the duct 79 moves the suction disk 77 through the window 76 upwardly or downwardly of the guide plate 75. The nozzle 78 communicates with the inner passage of the duct 78. A suitable number of nozzles 78, each equipped with a suction disk 77, may be mounted on the duct 79. The duct 79 is disposed in parallel with the generating line of the drum 35b, and the inner passage 80 thereof communicates with an air chamber 82 of a cylinder 81 by way of a pipe 83. Fixed to the duct 79 is an arm 84 whose distal end is connected by a link 85 to the actuator 87 of a solenoid 86.

Accordingly, the solenoid '86, when energized, rotates the duct 79.

Disposed above the guide plate is a duct 89 for conducting air from a fan 88. The duct 89 has a suitable number of air injection holes 90 or slits in its under face.

In the rear of the solenoid 86, there is provided an other actuator 91 connected to a rod 93 whose movement is guided by pins 92. The tail end of the rod 93 is engaged with the driven portion of an actuating lever 95 pivoted at 94.

The cylinder 81 includes therein a piston 96 with a piston rod 97 formed with a rack 98 meshing with a gear 99.-The piston rod 97 is provided with a spring 100 for pulling the piston downward in the figure. The gear 99 is associated with unillustrated drive means by way ofa clutch and is rotatable in normal and reverse directions. The piston rod 97 is further provided with a pin 101 to be engaged by the book of a latch lever 103 pivoted at 102 so as to retain the piston rod 97 at the position where the spring 100 is tensioned. The tail end of the latch lever 103 is in engagement with the drive portion of the actuating lever 95. A spring 104 urges the latch lever 103 in a counterclockwise direction in the drawing to keep its hook in engagement with the piston rod 97.

When the leading edge of the paper A passes over the guide roller 14 and reaches the position of the suction disk 77 while the image of the original is being transferred onto the paper A, the control cam 67 rotating integrally with the drum 35b actuates a microswitch SW to feed a signal to the solenoid 86, whereupon one of the actuators indicated at 87 is pulled to rotate the duct 79 and thereby press the suction disk 77 against the rear face of the paper A as shown. At the same time, the solenoid pushes the other actuator 91 to bring the rod 93 to the illustrated position and thereby operate the actuating lever 95, which in turn rotates the latch lever 103 to the illustrated position to release the piston rod 97. The parts are therefore brought to the position as shown.

Due to the above movement, the piston is pulled down by the spring 100 to reduce the pressure within the air chamber 82, whereby the rear face of the paper A is forcibly fitted to the suction disk 77 under the suction acting by way of the duct 80 and nozzle 78. Subsequently, the signal to the microswitch SW is interrupted through the rotation of the control cam 67. The

actuators

87 and 91 are consequently moved leftward causing the duct 79 to rotate clockwise and thereby retract the suction disk 77 downwardly through the window of the guide plate 75, permitting the paper A to lie on the guide plate 75. Simultaneously with this movement of the suction disk 77, namely with the positioning of the paper A on the guide plate 75, the electromagnetic clutch for the gear 99 is actuated to rotate the gear 99 in a clockwise direction and return the piston 96 upward, with the result that the air in the chamber 82 is compressed to eliminate the suction of the suction disk 77.

The paper A on the guide plate 75 is then delivered to the conveyor means 16 by the guide roller 14 while being subjected to a weak wind supplied through the duct 89 from the fan 88 thereabove and is sent forward for the subsequent operation. On the other hand, the piston 96 returned to an upper position is retained in this position, with the spring 100 tensioned, the pin 101

Claims

1. An electrophotographic copier of the transfer type comprising: a document table fixed to the top of said copier and made of a transparent plate; an exposure optical system of the slit scanning type including a projecting lens and having means for scanning the surface of an original document, said optical system being disposed below said document table; an endless support disposed below said exposure optical system and movable at a constant peripheral speed, said support being detachably provided with a flexible photoreceptor having a size appproximately equal to the size of the image to be projected and said endless support having an entire peripheral length slightly greater than the length of said photoreceptor; an image forming and copying assembly disposed around said endless support including means for charging said photoreceptor composed of a corona discharger, and followed by an exposure station at the terminal end of the light path of said exposure optical system where said charged photoreceptor is exposed to light projected through said optical system, developing means for visualizing with a toner an electrostatic latent image formed on said photoreceptor at the exposure station to produce a powder image, transfer means for applying a sheet of copy paper to said photoreceptor and transferring the powder image onto said sheet of paper, cleaner means for cleaning the surface of said photoreceptor after the paper has been peeled off said photoreceptor, and peeling means following said transfer means for peeling the paper sheet off the surface of said photoreceptor; a paper supply station including paper supply roller means for dispensing sheets of said paper disposed adjacent to said developing means; paper feed means for feeding said dispensed sheets of paper to said transfer means; conveyor means disposed below said cleaner means for advancing said paper from said copier; means disposed proximate the transport path of said conveyor means for heat-fixing the transferred image on said paper; said photoreceptor support comprising a cylindrical drum having a depressed longitudinally extending portion and said peeling means comprising an arcuate cover member with a curvature of a smaller radius than said drum and an air duct for injecting a weak blast of air onto the outer periphery of said drum approximately in a tangential direction opposite to the direction of transport of the paper sheet, said cover defining a recess in the outer peripheral surface of said support and means for controlling said transfer means to apply a sheet of copy paper supplied by said transfer means to said photoreceptor with the leading edge of said paper overlapping said recess and leaving a part of said recess exposed.

2. An electrophotographic copier of the transfer type comprising: a document table fixed to the top of said copier and made of a transparent plate; an exposure optical system of the slit scanning type including a projecting lens and having means for scanning the surface of an original document, said optical system being disposed below said document table; an endless support disposed below said exposure optical system and movable at a constant peripheral speed, said support being detachably provided with a flexible photoreceptor having a size approximately equal to the size of the image to be projected and said endless Support having an entire peripheral length slightly greater than the length of said photoreceptor; an image forming and copying assembly disposed around said endless support including means for charging said photoreceptor composed of a corona discharger and followed by an exposure station at the terminal end of the light path of said exposure optical system where said charged photoreceptor is exposed to said light, developing means for visualizing with a toner an electrostatic latent image formed on said photoreceptor at the exposure station to produce a powder image, transfer means for applying a sheet of copy paper to said photoreceptor and transferring the powder image onto said sheet of paper, cleaner means for cleaning the surface of said photoreceptor after the paper has been peeled off said photoreceptor, and peeling means following said transfer means for peeling the paper sheet off the surface of said photoreceptor; a paper supply station including paper supply roller means for dispensing sheets of said paper disposed adjacent to said developing means; paper feed means for feeding dispensed sheets of paper to said transfer means; conveyor means disposed below said cleaner means for advancing said paper from said copier; means disposed proximate the transport path of said conveyor means for heat-fixing the transferred image on said paper; said photoreceptor support comprising a cylindrical drum having a peripheral face and an end face, said peeling means comprising a duct disposed within said drum and extending longitudinally thereof and having an air inlet open at said drum end face and a row of small apertures open at said drum peripheral face, an air conduit in hermetic sliding contact with said drum end face to supply air into said duct at a predetermined position of said drum, and an air duct for injecting a weak air stream onto the surface of said drum approximately in a tangential direction thereof opposite to the direction of transport of the copy paper.

3. An electrophotographic copier of the transfer type comprising: a document table fixed to the top of said copier and made of a transparent plate; an exposure optical system of the slit scanning type including a projecting lens and having means for scanning the surface of an original document, said optical system being disposed below said document table; an endless support disposed below said exposure optical system and movable at a constant peripheral speed, said support being detachably provided with a flexible photoreceptor having a size approximately equal to the size of the image to be projected and said endless support having an entire peripheral length slightly greater than the length of said photoreceptor; an image forming and copying assembly disposed around said endless support including means for charging said photoreceptor composed of a corona discharger and followed by an exposure station at the terminal end of the light path of said exposure optical system where said charged photoreceptor is exposed to light projected through said optical system, developing means for visualizing with a toner an electrostatic latent image formed on said photoreceptor at the exposure station to produce a powder image, transfer means for applying a sheet of copy paper to said photoreceptor and transferring the powder image onto said sheet of paper, cleaner means for cleaning the surface of said photoreceptor after the paper has been peeled off said photoreceptor, and peeling means following said transfer means for peeling the paper sheet off the surface of said photoreceptor; a paper supply station including paper supply roller means for dispensing sheets of said paper disposed adjacent to said developing means; paper feed means for feeding said dispensed sheets of paper to said transfer means; conveyor means disposed below said cleaner means for advancing said paper from said copier; means disposed proximate the transport path of said conveyor means for heat-fixing the transferred image on said paper; said photoreceptor support comprising an endless belt having a transverse row of apertures formed therein and means for controlling said transfer means to apply a copy paper sheet to said photoreceptor with the paper leading border overlying the apertures and said peeling means comprising a pressurized air duct disposed along the rear face of said belt and communicating with said apertures when registering with said duct to produce air jets through said apertures, and a plurality of fingers substantially extending between said belt and said conveyor.

4. An electrophotographic copier of the transfer type comprising: a transparent table for supporting an original, a rotatable cylindrical drum having a longitudinally extending recessed portion in the outer peripheral face thereof and a cylindrical arcuate cover plate of lesser radius than said drum registering with said recessed portion and having an outer peripheral face radially inwardly offset relative to the peripheral face of said drum; a flexible photosensitive member of a length less than the circumference of said drum detachably supported by and extending along the periphery of said drum and exposing said recess, means for charging said photosensitive member at a charging station; a scanning optical system for projecting an image of said original onto said photosensitive member at an image projection station following said charging station to produce an electrostatic latent image of said original on said photosensitive member, developing means following said projection station for developing said latent image with a toner to form a powder image, transfer means for superimposing a copy sheet on said powder image carrying photosensitive member to transfer said powder image to said copy sheet with the leading edge of said sheet partially overlapping said longitudinal recess and leaving part of said recess exposed, paper peeling means including means for directing a stream of air onto said support drum and to the underface of the leading edge of said sheet overlapping said recess, and means for heat fixing said transferred powder image on said sheet.

5. An electrophotographic copier of the transfer type comprising: a rotatable support drum having a peripheral face and an end face, peeling means including a duct disposed within said drum and extending longitudinally thereof and having an air inlet open at said drum end face and a row of small apertures open at said drum peripheral face, an air conduit in hermetic sliding contact with said drum end face to supply pressurized air into said duct at a predetermined position of said drum, and an air duct for injecting a weak air stream onto the peripheral face of said drum approximately in a tangential direction thereof opposite to the direction of movement of said drum peripheral face, a flexible photosensitive member supported by and extending along the peripheral face of said drum and leaving said apertures exposed, means for charging said photosensitive member at a charging station; a scanning optical system for projecting an image of said original onto said photosensitive member, at an image projection station following said charging station to produce an electrostatic latent image of said original on said photosensitive member, developing means following said projection station for developing said latent image with a toner to form a powder image, transfer means for superimposing a copy sheet on said powder image carrying photosensitive member to transfer said powder image to said copy sheet with the leading edge of said sheet overlapping said apertures, and means for heat fixing said transferred powder image on said sheet.

6. An electrophotographic copier of the transfer type comprising: a transparent table for supporting an original, an endless belt carrying a flexible photosensitive member and havIng a transverse row of apertures formed therein exposed by said photosensitive member, a paper sheet advancing conveyor following said belt, peeling means comprising a pressurized air duct disposed along the rear face of said belt and communicating with said apertures when registering with said duct to produce air jets through said apertures and a plurality of fingers substantially extending between said belt and said conveyor, means for charging said photosensitive member at a charging station; a scanning optical system for projecting an image of said original onto said photosensitive member at an image projection station following said charging station to produce an electrostatic latent image of said original on said photosensitive member, developing means following said projection station for developing said latent image with a toner to form a powder image, transfer means for superimposing a copy sheet on said powder image carrying photosensitive member to transfer said powder image to said copy sheet with the leading edge of said sheet overlapping said apertures, and means for heat fixing said transferred powder image on said sheet.