Digital controlled document feeder

Abstract

A document sheet feeder for use with a recycling electrostatic copier having a moving photoreceptor, provides means to insure the imaging of the document on the photoreceptor in registration with a desired pitch frame of the photoreceptor, by comparing and correcting the position of the leading edge of each document sheet relative to the appropriate pitch line of the photoreceptor. A pulse generator is keyed to the movement of the photoreceptor and provides a pulse train output that is a digital reference of the position of the photoreceptor. As a document sheet passes a reference point in its feed path, its leading edge is detected and compared to the position of the photoreceptor. The document sheet is then accelerated or retarded relative to normal feed velocity by an amount which properly relates the document to the appropriate pitch frame of the photoreceptor.

Description

SUMMARY AND BACKGROUND OF INVENTION

The present invention relates to sheet feeders, and more particularly to the registration of documents along a feed path therefor relative to the operational cycle of a document processing machine, such as an electrostatic document copying machine.

In one form of electrostatic copying machine, for example, a document sheet to be copied is moved past a scanning slit, and an image of the document is focused on a photoreceptor drum or endless belt that is rotated at an angular velocity which provides a linear speed for the photoreceptor surface that is equal to the linear speed of the document. The electrostatic image thus formed on the photoreceptor may be developed with electroscopic toner powder, and the toner image transferred to a receiving sheet. The photoreceptor surface is then cleaned of any residual toner, the residual electrostatic image is discharged from the photoreceptor, and the photoreceptor is prepared to be recycled for copying another document sheet fed past the scanning slit. The photoreceptor may be sufficiently large to hold several document sheet images simultaneously on its surface. In automatic copying machines, a plurality of document sheets may be fed automatically for successive imaging on the photoreceptor, and for certain purposes it is important that the image of each sheet appear at a particular pitch frame or angular location on the photoreceptor.

In accordance with the present invention, document sheets to be copied are fed one by one from a document holding station or magazine to a pitch frame registration station, and thence to the document scanning and imaging station where an image of the document sheet is focused on the moving photoreceptor drum or belt. The speed of travel of the document sheet at the scanning station is predetermined and must correspond to the photoreceptor speed for proper imaging of the document sheet. However, before the document sheet reaches the scanning and imaging station, its speed of travel may be varied, and this is done at the pitch frame registration station to locate the leading edge of the document sheet at a proper reference point in its path of travel relative to the position of the photoreceptor. When this is accomplished, the document sheet leading edge will reach the document scan station in coincidence with the arrival of the pitch line of the pitch frame in which the document sheet is to be imaged.

To accomplish this registration of the document in its path of travel, the present invention utilizes an electrical pulse generator that is keyed to the movement of the photoreceptor, to establish a digital reference of the position of the photoreceptor. The passage of the document sheet leading edge over a reference point in its path of travel is sensed to produce an electrical signal. The time of occurrence of this document signal is compared with the pulse train indication of the position of the photoreceptor. If said document signal coincides with the appropriate pulse of said pulse train, the document is in proper position relative to that of the photoreceptor to arrive at the scan station in coincidence with the desired pitch frame of the photoreceptor, utilizing the established rate of advance for the document feed conveyor. However, if the document signal lags or precedes the appropriate pulse of the pulse train, the document sheet is accelerated or retarded an increment corresponding to the number of pulses in the pulse train by which the document signal is out of synchronism with the appropriate pulse of the pulse train. This action places the document sheet at the appropriate point in its feed path to bring it to the scan station in coincidence with the appropriate pitch frame of the photoreceptor.

It is therefore one object of the present invention to provide for the registration of a sheet along a feed path therefor relative to the operational cycle of a machine to which the sheet is being fed.

Another object of the present invention is to provide for the registration of a sheet along a feed path therefor relative to a reference indication.

Another object of the present invention is to provide for the registration of a sheet along a feed path therefor relative to a reference indication, by accelerating or retarding said sheet in its path of travel by an increment corresponding to the discrepancy between sheet location and said reference indication.

Still another object of the present invention is to provide for the foregoing registration of a sheet along a feed path therefor, wherein said sheet is a document sheet being fed to a document copier.

Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one exemplary embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of the invention is had in conjunction with the accompanying drawings, in which like reference characters refer to the same or corresponding parts, and wherein:

FIG. 1 is a schematic illustration of a sheet feeder for delivering successive document sheets to an electrostatic document copier; and

FIG. 2 is a schematic illustration of an apparatus for controlling the sheet feeder of FIG. 1 to accomplish registration of the document sheets along their feed path relative to the operational cycle of the document copier.

DETAILED DESCRIPTION

The document sheet feeder and copier illustrated in FIG. 1 comprises a magazine 11 for holding a stack of document sheets 12. A pressure pad 13 bears on top of the stack 12 enabling the belt 14 to feed sheets one by one from the bottom of the stack toward a sheet separator 15. If more than one sheet is fed to the separator 15, the upper sheet or sheets are held from further advance by the upper retard roll 16, while the bottom sheet is fed by the bottom roll 17 to the nip of drive rolls 18, and thence to the feed belt 19 which delivers each document sheet to and past the scanning sperture 20 of the electrostatic copier 50. Each sheet leaving feed belt 19 is conveyed by guide chute 21 to the pair of endless conveyor belts 22 and 23 which return the sheets to the top of the stack 12 in magazine 11 in readiness for recycling, if desired. Endless belts 22 and 23 are driven in synchronism by drums 24 and 25, whose shafts are keyed together by drive chain 26.

A tacking corona discharge device 27 is utilized at the input side of feed belt 19, to cause each sheet to adhere to the belt 19 by electrostatic attraction, and a detacking corona discharge device 28 is provided at the output side of belt 19 to facilitate the removal of sheets from the belt and their delivery to the chute 21.

The scanning slit 20 focuses the moving image of a document sheet carried by belt 19 onto the surface of photoreceptor drum 51 of conventional electrostatic copier 50. Drum 51 is rotated by shaft 52 past the scanning slit 20 in synchronism with the movement of a document sheet on belt 19 past said slit. Thus, the speed of belt 19 and the peripheral speed of drum 51 are made equal, and it is likewise desirable that feed rolls 18 deliver each document sheet to belt 19 at the same speed of travel.

The electrostatic copier 50 is shown as having a plurality of image processing stations positioned about its periphery. An electrostatic charging station 53 is located just in advance of the image exposure station formed by scanning slit 20, and an image developing station 54 is located immediately following the scanning slit. The developing station is followed by an image transfer station 55, which is followed by a residual image cleaning station 56, and an electrostatic image erasing station 57.

The document sheet feeding apparatus 10 and the electrostatic copier apparatus 50 as thus far described are composed of well known components, and the structure and operation of the components and of the system as a while will be readily understood by those skilled in the art.

The rate of peripheral speed of photoreceptor drum 51 and linear speed of feed belt 19 must be the same in order to obtain a clear image of the document sheets on the drum 51. Likewise the rate of feed of the document sheets by feed rolls 18 should preferably be the same as that obtained by feed belt 19. However, the speed at which a document sheet is fed by sheet separator 15 toward the feed rolls 18 can be varied, and this feature is used to bring each document sheet into registration which the appropriate pitch frame therefor on photoreceptor drum 51. For this purpose, a photodetector indicated at 31 is positioned between sheet separator 15 and feed rolls 18, and is used as the reference point in locating the leading edge of each sheet as it is fed toward the copying station.

The registration control system is schematically shown in FIG. 2. The angular position of photoreceptor drum 51 is constantly monitored by utilizing its drive shaft 52 to drive a pulse generator 32. The generator 32 may, for example, generate 360 pulses per revolution of shaft 52, and its pulse train output would therefore represent the angular position of the drum 51 to the nearest degree. The output of generator 32 is fed to a power amplifier, counter and discriminator circuit generally designated by the numeral 33. A second input to circuit 33 is obtained from the photodetector 31, which is used to identify the passage of the leading edge of each document sheet at the registration point in the sheet feed path.

Circuit 33 compares the time of occurrence of the leading edge of a document sheet at the registration point with the angular position of the photoreceptor drum 51. If the relationship is proper to relate the document sheet to its appropriate pitch frame on the drum 51, there is no registration correction output from the circuit 33, and the document feed continues in the manner above-described. However, if the relationship is not proper, the amount of correction is measured in circuit 33, and it operates a control drive to either accelerate or decelerate the document sheet by an appropriate amount, depending upon whether the sheet is lagging or leading its appropriate pitch frame location.

The registration control system operates on and is the drive for sheet separator roll 17. A first stepping motor 34 is driven by the circuit 33 in accordance with the pulse output of generator 32. The motor 34 thus drives separator feed roll 17 through differential 35 and a gear and belt drive train at a rate directly controlled by rotation of drum 51.

The differential 35 has a second drive input from stepping motor 36. Stepping motor 36 is driven an appropriate amount forward or backward as determined at circuit 33 by comparing the input from photodetector 31 with the angular position of the drum 51. This action either speeds up or slows down the drive of roll 17, and hence accelerates or decelerates the feed of the document sheet by that amount required to place it in proper relation to its appropriate pitch frame on the photoreceptor drum 51.

It will thus be appreciated, as each sheet passes from sheet separator 15 toward feed rolls 18, its leading edge is detected by photodetector 31. The occurrence of this signal is compared with the angular position of drum 51 by circuit 33, and its relation to an appropriate pitch frame on the drum is determined. Roll 17 of sheet separator 15 is operated through differential drive 35, and by means of a normal power input from stepping motor 34 and a correctional power input from stepping motor 36, roll 17 advances the document sheet at a rate that places it in registration with its appropriate pitch frame on photoreceptor drum 51.

While a drum type xerographic reproduction machine employing scan exposure has been illustrated and described, it should be understood that the invention may also be practiced with a reproduction machine employing a photoreceptor in the form of a belt utilizing a scan exposure, or, if the surface of the belt opposite the document is maintained in a planar condition, flash exposure might also be utilized without departing from the scope of the present invention.

Claims

What is claimed is:

1. Sheet feeding and processing apparatus comprising, first sheet conveyor means, second sheet conveyor means, cyclic processing means including an electrostatic photocopier having an endless and repetitively cycling photoreceptor cooperating with a sheet on said second conveyor means, means for identifying the cyclic position of said photoreceptor, means between said first and second conveyor means for detecting the presence of a sheet, means for relating the detection of a sheet by said detection means to the cyclic position of said photoreceptor as determined by said identifying means, and means responsive to said relating means for momentarily varying the speed of said first conveyor means to correct any deviation from a predetermined relationship between said cyclic position of said processing means and said detection of the presence of a sheet.

2. Sheet feeding and processing apparatus as set forth in claim 1, wherein said identifying means comprises a pulse generator means operated by said processing means.

3. Sheet feeding and processing apparatus as set forth in claim 2, wherein said first conveyor means includes a first drive means controlled by said pulse generator means.

4. Sheet feeding and processing apparatus as set forth in claim 3, wherein said means responsive to said relating means comprises a second drive means coupled to said first conveyor means.

5. Sheet feeding and processing apparatus as set forth in claim 4, and including a differential for combining said first and second drive means.