US3627311A - Sheet sensor - Google Patents

Abstract

Apparatus which inactivates a xerographic machine in response to a copy sheet miss-puff. A sheet of paper remaining on the xerographic drum beyond the stripping station will move beneath a pneumatic sensor head. A second pneumatic sensor head adjacent the edge of the drum at an area beneath which misfed sheets will not pass is pneumatically coupled with the first sensor so that a change of pressure between the two sensors, as caused by a misspuffed sheet, will cause the tripping of a fluidic switch to energize a control relay and stop the machine.

Description

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Primary Examiner-Joseph Wegbreit Assistant Examiner-Bruce H. Stoner, Jr.

AnorneysNorman E. Schradcr, James J. Ralabate and Michael J. Colitz. Jr.

[54] SHEET SENSOR $Clalms,6Drawlng Figs. ABSTRACT: Apparatus which inactivates a xerographic machine in response to a copy sheet miss-puff. A sheet of paper remaining on the xerographic drum beyond the stripping station will move beneath a pneumatic sensor head. A second pneumatic sensor head adjacent the edge of the drum at an area beneath which misfed sheets will not pass is pneumatically coupled with the first sensor so that a change of pressure between the two sensors, as caused by a miss-puffed sheet, will cause the tripping of a fluidic switch to energize a control relay and stop the machine.

66 4 X 17. 7 H 5/ 7 mm 2 2 m: m "n" N" m: m mmm w m nu n an .IPL mmm M a "n" I m: cTe nu" Aw m: "T "n" SM nu" QDK m: mTm n3 2 N a U9 Ia H L 9 u 0 h UhF m m 2 0 6 in UB5 U 3 PATENTED DEC 1 4 Ian SHEET 1 [IF 2 INVENTOR. THOMAS S. SPINELLI BY V SHEET SENSOR This invention relates to a sensing device for detecting sheet material. More particularly, this invention relates to a device for monitoring a moving photoconductive surface and for inactivating its movement upon the detection of a sheet moved into proximity to detection apparatus.

In the practice of xerography, as described in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic photoconductive surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic surface is electrostatically charged unifonnly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.

The latent electrostatic image can then be developed by contacting it with a finely divided electrostatically attractable material such as toner powder. The powder is held in image areas by the electrostatic charge pattern on the layer. Where the charge field is greatest, the greatest amount of material is deposited; where the charge field is least, little or no material is deposited. Thus a powder image is produced in conformity with the light image of copy being reproduced.

A sheet of paper or other suitable support material may then be brought into contact with the photoconductive surface in registration with the image thereon. The powder may be transferred to the support material by electrostatic means behind the support material. The electrostatic means will electrostatically transfer the toner material from the photoconductive surface to the support material. The electrostatic force concurrently induces a charge into the support material tending to electrostatically tack the support material to the photoconductive surface. The support material may then be stripped from the photoconductive surface, as by a pneumatic puffer which blows a sharp stream of air between the paper and drum and physically forces the backing sheet away from the photoconductive surface. The toner image may then be fixed to the support material to form a pennanent copy of the original document being reproduced.

Occasionally, a sheet of paper will adhere to the drum surface past the position at which it should have been removed. This occurs when the puffer mechanism fails to operate, the paper is not aligned in the proper position on the photoconductive surface, when a double sheet is fed into the transfer station, or the like. When this situation occurs, it is desirable to detect or sense the misfed sheet on the photoconductor and immediately inactivate the machine. If the machine does not shut down immediately, the jamming of paper within the machine or the dumping of developer from the developer housing may occur. These cause downtime or damage to the machine.

Several devices have been employed to detect a copy sheet on the photoconductive surface beyond the point at which it should have been removed. In one approach to the problem, as defined in U.S. Pat. No. 3,360,652, to Tayeb Bemous, apparatus is disclosed for reflecting light from a source of illumination onto the photoconductive surface beyond the sheet stripping means. The light reflecting from the photoconductive surface will enter a photocell to retain the machine in an operative state. If, however, a sheet is misfed and moves into a position beneath the light source and photocell, the photocell will sense a variation in the reflected light and inactivate the machine in response thereto.

ln another approach to the problem, as for example, described in U.S. Pat. No. 3,30l,975, to Raymond H. Camp, et al., a mechanical finger is positioned to ride against the photoconductive surface. If a sheet of paper is not removed from the drum by the pufier, the sheet of paper will strike the finger, pivoting it, to thereby trip a switch to thus inactivate the device.

While devices of these types operate satisfactorily and are in commercial use today, neither may be considered a universal type detector for misfed sheets. By way of example, the mechanical finger of the Camp et al. device requires an element to be in physical contact with the photoconductive surface at all times. If this device were used with a photoconductive surface of insufficient hardness, it would result in the creation of a circumferential groove in the photoconductor after extended use. This is undesirable since it would result in a linear imperfection in the drum as well as to copies transferred therefrom.

The optical misspuff detector of the type described in the Bemous patent, which relies on light energy reflected from the drum, may result in a light fatiguing of photoconductors having high spectral responsiveness. Thus, if the optical miss-puff detector were used in combination with certain photoconductors it would result in the changing of the spectral characteristics of the photoconductive surface along a circumferential line in a manner analogous to that described with respect to the mechanical miss-puff detector of Camp et al. and result in similar deficiencies.

To present invention is directed to a device for sensing misfed sheets of copy which has not been removed from the photoconductive surface at the sheet-stripping station. The present invention employs laterally displaced pneumatic sensor elements coupled together so that a change of pressure therebetween may be registered as a result of a sensed misfed sheet beneath one of the sensors to inactivate the machine.

It is therefore an object of the instant invention to overcome the above-noted prior art deficiencies.

It is a further object of the instant invention to control a machine in response to a change in pneumatic conditions as registered by monitoring devices.

It is a further object of the instant invention to detect sheets of paper which improperly adhere to a rotating xerographic drum.

lt is a further object of the instant invention to detect sheets being transported adjacent sensor members.

These and other objects of the instant invention are attained by pneumatic sensor heads adjacent an area to be sensed with one of the sensor heads positioned beneath the path past which a misfed sheet would move and the second laterally displaced therefrom adjacent an area beneath which a misspuffed sheet would not pass. The occurrence of a misfed sheet beneath the first sensor head causes a pneumatic imbalance between a pneumatic switching means coupling the sensor heads to register the misfed sheets and to inactivate the sheet beneath the mechanism.

For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 is an isometric view of a part of a xerographic machine including a xerographic drum with pneumatic sensor heads positioned thereat;

FIG. 2 is a schematic illustration of the xerographic drum and sensor heads in association with the pneumatic control devices therefor;

FIG. 3 is a side sectional view of a sensor head of HG. 2;

HO. 4 is a schematic illustration of the xerographic drum and sensor heads in association with the pneumatic control devices therefor but employing an alternate sensor head assembly;

HO. 5 is a sectional view of a sensor head of FIG. 4 taken along line 55 thereof; and FIG. 6 is a sectional view taken along line 6-6 of FIG. 5.

As shown in the drawings, a xerographic member in the shape of a drum 10 is shown in the position that it would be mounted in an automatic xerographic machine. The drum is rotatably mounted on shaft, not shown, extending through bearing 12 in the middle of the drum. The drum is held on the shaft by means of a hand nut 14, which cooperates with threads on the end of the shaft to secure the drum in place.

Sheets of paper are fed by the conveyor 16 into surface contact with the drum and electrostatically tacked to the drum surface by transfer corotron 18. At this point, xerographic powder images which have previously been developed on the drum surface are transferred to the surface of the sheet of paper by the transfer corotron 18. As the drum continues to rotate the sheet of paper is carried by the drum towards the conveyor belt 20. The conveyor 20 is a vacuum conveyor which will hold the paper on the surface of the belt and draws the paper away from the drum surface after the sheet has contacted the surface of the conveyor.

As the leading edge of the sheet of paper rotates to a position just over the conveyor belt 20, a puffer tube 22 directs a series of sharp streams of air through nozzles 24 between the drum surface and the sheet of paper. The nozzles 24 extend across the length of the drum and efiectively deflect the sheet of paper from the surface of the drum down against the surface of the belt 20. The stream of air in the puffer tube 22 emerging from the nozzles 24, is produced by a small air pump, not shown, and controlled and timed by electrical circuitry, not shown, to puff at the proper time to deflect the sheet of paper onto the conveyor belt. Further details of the pufi'er and other portions of the xerographic machine may be had by reference to US. Pat. No. 3,301,126, issued to Osborne et al.

if for any reason the puffer mechanism fails to strip the sheet of paper from the surface of the drum, the sheet of paper would otherwise continue to rotate around the drum surface interfering with the operation of other mechanisms about the periphery of the drum and causing leakage of developer from its housing. Also, with the sheet of paper on the surface of the drum, further xerographic images cannot be produced or developed. It is, therefore, desirable to immediately stop the machine and manually remove the sheet of paper from the drum surface.

For the purpose of detecting sheets not removed from the xerographic drum by the puffer 22, detector elements in the form of pneumatic sensing heads 30 and 32 as shown in FIGS. 1 and 2 are provided adjacent the xerographic drum in a location whereby an unpuffed sheet would pass beneath sensor 30. The view of FIG. 2 shows a section of the photoreceptive plate l0'with the sheet of unpuffed copy paper 28 attached thereto in a location beneath the sensor heads. During normal operating procedures, the copy sheet would not be there and the sensor heads would be the same distance from the photoconductive plate.

The showing of FIG. 2 is also a schematic illustration of the control logic to sense the presence of a misspuffed sheet. These elements, except for the sensor heads and pneumatic lines thereto are preferably mounted at a location remote from the xerographic surface whereat space is at a premium. The pneumatic sensor heads are adapted to be supplied with a source of fluid, preferably air, from a pressure source 34, as for example, the accumulator tank of the xerographic machine. Line 36 takes this source of high pressure and distributes it along three major channels 38, 40 and 42. Line 38 brings a flow of fluid to the first sensor head 30 while line 40 directs a flow of fluid to the second pressure head 32. The third branch line from the source of fluid is line 42 which brings air into orifice PS of a pneumatic control device 44 as shown in the form of a Schmitt-Trigger. Schmitt-Triggers are commercially available devices. Ones employable herein are sold by the Corning Corporation, Corning, New York as part No. 191,448 or 191,456. Also being fed into the Schmitt-Triggers at orifices Cl and C2 is a source of pressure from lines 46 and 48 which draw their pressures as an offshoot from line 38 and 40 respectively to monitor the flow of fluid therethrough.

In normal operations, the airflow from the pressure source is adjusted so that sensor heads 30 and 32 are exhausting air through orifices 58 at a common rate with the resulting pressure between C1 and C2 as received from lines 46 and 48 being equal. In this normal state, the fluid is exhausted from the Schmitt-Trigger 44 through exit orifice 02. Adjusting nuts 50 and 52 on lines 38 and 40 permit the adjustment of the airflow to the sensor heads so that the balanced state of the control device 44 may be attained. Brackets 60 and 62 support the heads in their proper orientation.

When a miss-puff has occurred and a piece of sheet material is fed beneath one of the sensor heads 30 by the drum, the airflow therefrom meets a change of resistance due to the change of condition beneath the sensor head. This is registered as an increase of air pressure to the Schmitt-Trigger 44 through line 46 and orifice C1. Sensor head 32 does not sense the sheet due to its location to the side of the misfed sheet and this portion of the xerographic drum acts as a reference surface. In this state, the pneumatic imbalance in the Schmitt-Trigger between points Cl and C2 causes pressure to switch its flow and flow from orifice 01 through line 54. This reverses the state of the control device to trip or trigger the pressure switch 56. This, in turn, reverses the state of contact relay CR1 to trigger it and inactivate the machine.

. The fact that the reference surface employed is an edge of the sheet-feeding surface with the pneumatic sensors laterally disposed adjacent the drum permits the sensing of sheet material on the drum even through the drum may not be of a perfect right circular cylinder. That is, the distance between the sensor heads and the sheet-feeding photoconductive surface will cause equal changes of pressure in the event that the photoreceptive surface is out of round.

1n the alternate embodiment as disclosed in the FIGS. 4-6 showing, the sensor heads 70, 72 are of a slightly modified design. The sensor heads are each constructed to receive two pneumatic lines on the side thereof remote from the sensing side. As in the first embodiment, a suitable source of fluid 74 provides fluid pressure through line 76 which is divided between lines 78 and 80 to provide a source of pressure to the sensor head monitoring the movement of sheets on the drum. These lines direct fluid into the sensor head which is directed into a swirling fashion to the path to the sensor head and adjacent the area to be sensed. A branch, line 82, from line 76 directs air to the Schmitt-Trigger 84 which may be of the same design as that described with respect to the FIG. 2 embodiment. Lines 86 and 88 couple an aperture through the center of the sensor heads back to orifices Cl and C2 of the Schmitt- Trigger. Details of the sensor heads will be described hereinafter. The end of these lines adjacent the sensor heads are directed to sense the pressure at the central portion of the sensor head between the sensor head and the area being sensed. This is at the vortex of the swirling air caused by lines 78 and 80. Adjusting nuts 90 and 92 may be provided on line 78 and 80 to adjust the pressures to the sensor heads so that the pressure sensed by C1 and C2 through lines 86 and 88 are equal. ln this normal operating state, air is exhausted from the control device 84 through orifice 02.

When, however, a foreign object such as a misfed copy sheet passes beneath one of the sensor heads, 70, this head senses the change of pressure thereat which is registered at a backup of pressure to C1 through line 86. This pneumatic imbalance across orifices Cl and C2 causes a flow of fluid through orifice 01 to trigger the pressure switch 96, trip the contact CR1 and inactivate the machine.

Details of the pneumatic sensor heads of the FIGS. 4-6 embodiment are shown in FIGS. 5 and 6. Air is adapted to be supplied through line 80 into hole 100. This air is channeled to a central circular chamber 102 through intermediate passage 104. Air entering the chamber 102 is spiraled due to its construction and relationship to passage 104. This air is then passed through connecting passage 106 to a circular exhaust chamber 108 communicating with exterior of the device and facing the area to be sensed. As the spiraling air passed from chamber 102 to chamber 108, its spiraling is continued. Venting hole 110 connects line 88 with the central portion of chamber 102 to monitor the vortex of the spiraling air in the chamber 102 during normal operation. Line 88 which is the input signal to the Schmitt-Trigger can react very sensitively to changes beneath the sensor head since it is the vortex of the air which is being monitored. Both sensor heads 70 and 72 are of this same construction.

In a normal operating state, the pressure source 34 of the first embodiment would be provided with about pounds per square inch of pressure while the pressure source of the second embodiment would be provided with the same pressure. The three lines from the pressure source would preferably receive about equal fluid flows. The pressure heads of the first embodiment would be positioned about 0.020 inch from the xerographic surface, while they would be located about 0.030 inch away from the xerographic surface in the second embodiment. A sheet of paper, nominally 0.003 inch, passed beneath the sensor heads would cause a change in pressure across the Schmitt-Trigger of about 0.25 inch of water in both embodiments. This pneumatic pressure difference would be sufficient to cause the flow of fluid to the pressure switch to inactivate the machine. The existence of miscellaneous foreign objects, as for example, toner particles in the drum which are merely a few microns in thickness, would be insufficient to cause an adequate pressure difference between the sensing portions of the Schmitt-Trigger to register it as a misfed sheet and would therefore not inactivate the machine.

While the instant invention has been described as carried out in the specific embodiments thereof, it is not intended to be limited thereby but it is intended to protect the invention broadly within the scope of the appended claims.

What is claimed is:

1. Apparatus for detecting misfed copysheets on a xerographic surface of a xerographic reproducing machine and to inactivate the machine in response thereto including a first sensor head positioned adjacent the xerographic surface to overlie a portion thereof beneath which misfed sheets may pass to direct a stream of fluid thereagainst,

a second sensor head positioned adjacent the xerographic surface to overlie a portion thereof beneath which misfed sheets may not pass to direct a stream of fluid thereagainst,

means coupling said sensor heads to detect a pneumatic balance of pressure between said sensor heads when no material to be detected is between said first sensor head and the xerographic surface, said coupling means being rendered imbalanced when sheet material is passed between said xerographic surface and said first sensor head and control means triggered by said coupling means to inactivate the machine in response to said imbalanced condition.

2. The apparatus as set forth in claim 1 wherein said sensor heads are adapted to be laterally disposed adjacent a xerographic drum with said second sensor head adjacent an edge thereof and said first sensor head adjacent a central portion thereof.

3. Apparatus for monitoring sheet material movement along a path of travel including first and second pneumatic sensor means each adapted to direct a stream of fluid against a reference surface,

means to position said first sensor means adjacent the path of travel so that sheet material may pass between said reference surface and said first sensor means means to position said second sensor means adjacent said first sensor means whereby said second sensor means continues to direct a stream of fluid against said reference surface as the sheet material passes between said first sensor means and said reference surface,

pneumatic switching means, and

means coupling said first and second sensor means with said pneumatic switching means and being adapted to normally retain said switching means in a first state and to reverse the state of said switching means upon a change of condition of sheet material between the reference surface and said first sensor means.

4. The apparatus as set forth in claim 3 wherein said pneumatic sensor means include means to supply flows of fluid against said sheet feeding surface and said reference surface.

5. The apparatus as set forth in claim 4 wherein said coupling means includes means to :nonitor the flows of fluid.

Claims (5)

1. Apparatus for detecting misfed copysheets on a xerographic surface of a xerographic reproducing machine and to inactivate the machine in response thereto including a first sensor head positioned adjacent the xerographic surface to overlie a portion thereof beneath which misfed sheets may pass to direct a stream of fluid thereagainst, a second sensor head positioned adjacent tHe xerographic surface to overlie a portion thereof beneath which misfed sheets may not pass to direct a stream of fluid thereagainst, means coupling said sensor heads to detect a pneumatic balance of pressure between said sensor heads when no material to be detected is between said first sensor head and the xerographic surface, said coupling means being rendered imbalanced when sheet material is passed between said xerographic surface and said first sensor head and control means triggered by said coupling means to inactivate the machine in response to said imbalanced condition.

2. The apparatus as set forth in claim 1 wherein said sensor heads are adapted to be laterally disposed adjacent a xerographic drum with said second sensor head adjacent an edge thereof and said first sensor head adjacent a central portion thereof.

3. Apparatus for monitoring sheet material movement along a path of travel including first and second pneumatic sensor means each adapted to direct a stream of fluid against a reference surface, means to position said first sensor means adjacent the path of travel so that sheet material may pass between said reference surface and said first sensor means, means to position said second sensor means adjacent said first sensor means whereby said second sensor means continues to direct a stream of fluid against said reference surface as the sheet material passes between said first sensor means and said reference surface, pneumatic switching means, and means coupling said first and second sensor means with said pneumatic switching means and being adapted to normally retain said switching means in a first state and to reverse the state of said switching means upon a change of condition of sheet material between the reference surface and said first sensor means.

4. The apparatus as set forth in claim 3 wherein said pneumatic sensor means include means to supply flows of fluid against said sheet feeding surface and said reference surface.

5. The apparatus as set forth in claim 4 wherein said coupling means includes means to monitor the flows of fluid.

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