Patent Publication Number: US-3874790-A

Title: Fail-safe mechanism for stopping movement of the photoconductive belt in an electrostatic reproduction machine when tracking of the belt becomes irregular and uncontrollable

Description:
United States Patent [191 Jordan 1 FAIL-SAFE MECHANISM FOR STOPPING MOVEMENT OF THE PHOTOCONDUCTIVE BELT IN AN ELECTROSTATIC REPRODUCTION MACHINE WHEN TRACKING OF THE BELT BECOMES IRREGULAR AND UNCONTROLLABLE [75] Inventor: William E. Jordan, Penfield. NY.  
 173] Assignee: Xerox Corporation, Stamford,  
 Conn.  
 [22] Filed: Nov. 23, 1973 [21] Appl. No.: 418,718  
 [52] US. Cl 355/16, 192/129 A, 198/232, 340/259 I51] Int. Cl 603g 15/00 Field ol Search 355/16, 3 R; 198/232; 226/16; 192/129 A; 340/259 [56] References Cited UNITED STATES PATENTS 2.933.382 4/1960 James 340/259 3.698.540 10/1972 Jordan 198/202 [4 1 Apr. 1,1975  
 3,820.888 6/1974 Jordon 355/16 X Primary Examiner-Richard L. Moses Atlorney, Agent, or Firm-James J. Ralabate; Earl T. Reichert [57] ABSTRACT An electrostatic reproduction machine has a belt assembly having an endless photoconductive belt mounted thereon for movement around a closed path. The machine also has a fail-safe mechanism for stopping the movement of the belt in the event the tracking thereof becomes irregular and uncontrollable. This mechanism converts lateral movement of the belt into rotary movement so as to open (or close) either of two mercury switches to stop the belt movement, the switches being mounted so that their positions with respect to the remainder of the mechanism and the belt assembly can be adjusted in accordance with position of a sensing rod with respect to the remainder of the mechanism after the belt assembly is initially moved into its operative position.  
 2 Claims, 3 Drawing Figures jf&#39;ENIEU APR NETS sum 1 of &#39;3 JATENTEDAPR uszs 3.874.790  
 sum 3 p 3 FIG 3 FAIL-SAFE MECHANISM FOR STOPPING MOVEMENT OF THE PHOTOCONDUCTIVE BELT IN AN ELECTROSTATIC REPRODUCTION MACHINE WHEN TRACKING OF THE BELT BECOMES IRREGULAR ANI) UNCONTROLLABLE BACKGROUND OF THE INVENTION This invention relates to an electrostatic reproduction machine having an endless belt assembly, but more particularly to means for tracking the movement of an endless photoconductive belt within the machine, and means for sensing when the lateral deviation of a belt reaches a predetermined position on one side or the other of the normal course of the belt, and for causing the movement of the belt to cease in response thereto. The invention also includes means for easily adjusting the sensing means when the belt assembly is initially moved into the machine cabinet.  
  In the practice of xerography as described in US. Pat No.2.297.(19l to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulting material affixed to a conductive backing is used to sup port electrostatic images. In the usual method ofcarrying out the process. the xerographic plate is electrostatically charged uniformly over it 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 may then be developed by contacting it with a finely divided electrostatically attractahle material. such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited; and where the field is least. little or not material is deposited. Thus, a powder image is produced in conformity with the light image of the copy being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably fixed to thereby form a permanent print.  
  The latest machine concept for copiers utilizes high speed flash exposure of a document and an endless belt having a photoconductive area thereon. the belt being mounted for movement around a closed path past various processing stations.  
  Photoconductor belts ar very delicate. are easily damaged. and the movement thereof through processing stations in the reproduction machine must be accomplished with high precision and with as little irregular movement as possible. Additionally. should the tracking of the photoconductive belt become irregular and uncorreetable by the tracking mechanism of the machine. must be placed in an inoperative mode as quickly as possible to prevent irreparable damage to the photoconduetive belt as well as the machine.  
  To place the machine in this inoperative mode, a failsafe mechanism utilizing switches is normally used, a portion of the mechanism being in contact with the belt or a sensing ring during its movement. One of the problems with such arrangements is that of initially adjusting the mechanism when the belt assembly or module is moved into the cabinet of the reproduction machine. The belt assembly is mounted on at least one shaft so that it can be moved into and out of the cabinet. Because of mechanical tolerances within the belt assembly and the other parts ofthe machine, it may be neces sary to make some initial adjustments on the fail-safe mechanism. Because the rear interior of the cabinet is relatively dark and inaccessible. however, it is very difficult to make any major adjustments. Thus, what is needed is an accurate fail-safe mechanism which will shut the machine off as quickly as possible should the tracking of the belt become irregular and uncorrectable, but one which also can be easily adjusted while mounted on the rear of the machine cabinet. The switches are mounted on the rear of the cabinet as opposed to the belt module so as to eliminate the need to make or disconnect electrical connections each time the belt module is moved into or out of the cabinet.  
 SUMMARY OF THE INVENTION The present invention is directed to a fail-safe mechanism for stopping the movement of an endless photoconductive belt in an electrostatic reproduction machine in the event that the tracking of the belt becomes irregular and uncontrollable. The fail-safe mechanism has two mercury swithches, and mounted to the rear wall of the machine cabinet so as to be contacted by the sensing ring of the belt module as the latter is moved into the cabinet. When contacted, the mechanism has a rod having indicia which rod is movable with respect to the remainder of the mechanism for registering the position of the mechanism when the belt is at one extreme limit of the permissible deviation from its normal course. When the belt module is pulled out from the cabinet. at reading can be taken from the rod indicia, and a pointer on the mechanism then can be set at a corresponding reading on a second indicia on the mechanism. This operation sets the attitude of the switches with respect to the photoconductive belt for two extreme positions of the belt from its normal course. When the belt module is pushed back into the machine cabinet so as to once again contact the failsafe mechanism, the mechanism is ready for operation.  
 BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the present invention as well as other objects and further features thereof will become apparent upon consideration of the following detailed disclosure thereof, especially when taken with the accompanying drawings, wherein like numerals designate like parts throughtout.  
  FIG. I is a schematic sectional view of an electrostatic reproduction machine cmbodying the principles of the invention; and  
  FIG. 2 is a top view of a portion of the belt assembly, and of the fail-safe mechanism;  
  FIG. 3 is an isometric view showing the fail-safe mechanism mounted to the rear wall of the machine cabinet.  
 DETAILED DESCRIPTION OF THE INVENTION For a general understanding of the illustrated copier reproduction machine in which the invention may be incorporated. reference is bad to FIG. I in which the various system components for the machine are schematically illustrated. A document to be copied is placed upon a transparent support platen P fixedly arranged in an illumination assembly, generally indicated by the reference numeral I0, positioned at the left end of the machine. Light rays from an illumination system are flashed upon the document to produce image rays corresponding to the inforimttional areas. The image rays are projected by means of an optical system onto the photosensitive surface of a xerographic plate in the form of a flexible photoconductive belt 12 arranged on a belt assembly, generally indicated by the reference numeral 14.  
  The belt is comprised of a photoconductive layer of selenium which is the light receiving surface and imaging medium for the apparatus formed on a conductive backing. The surface of the photoconductive belt is made photosensitive by a previous step of uniformly charging the same by means of a corona generating device or corotron [3.  
  The belt is journaled for continuous movement upon three rollers 20, 21, and 22 positioned with their axes in parallel. The photoconductive belt assembly [4 is slidably mounted upon two support shafts 23 and 24 with the roller 22 rotatably supported on the shaft 23 which is secured to the frame of the apparatus and is rotatably driven by a suitable motor and drive assembly (not shown) in the direction of the arrow at a constant rate. During exposure of the belt 12, the portion exposed is that portion of the belt running between rollers and 2]. During movement of the belt 12 the reflected light image of the original document positioned on the platen on the surface of the belt to produce an electrostatic latent image thereon at exposure station A.  
  As the belt surface continues its movement, the elec trostatic image is passes through a developing station B in which there is positioned a developer assembly, generally indicated by the reference numeral l5, and which effects development of the electrostatic image by means of multiple magnetic brushes l6 as the image moves through the development zone.  
  The developed electrostatic image is transported by the belt to a transfer station C where a sheet of copy paper is moved between a transfer roller 29 and the belt at a speed in synchronism with the moving belt in order to accomplish transfer ofthe developed image by an electrical bias on the transfer roller. There is pro&#39; vided at this station a sheet transport mechanism, generally indicated at 17. adapted to transport sheets of paper from a paper handling mechanism, generally in dicated by the reference numeral 18. to the developed image on the belt at the station C.  
  After the sheet is stripped front the belt 12, it is conveyed into a fuser assembly, generally indicated by 19, wherein the developed and transferred xerographic powser image on the sheet material is permanently fixed thereto. After fusing, the finished copy is dis charged from the apparatus at a suitable point for col leetion externally of the apparatus. The toner particles remaining as residue on the developed image, background particles and those particles otherwise not transferred are carried by the belt l2 to a clearing apparatus 26 positioned on a course of the belt between rollers 20 and 22 adjacent to charge device 25.  
  Further details regarding the structure of the belt assembly I4 and its relationship with the machine and support therefor may be found in the copending application Ser. No. 102.312 assigned to the same assignee.  
  Referring now to FIG. 2. there is illustrated a tracking assembly, generally indicated as 30 including the upper roller 20 and the tracking roller 21. The upper roller 20 is rotatably supported on a hollow shaft jounaled for rotation in bearing disposed in side plates (ill such as described in corresponding application Ser. No. lll&#39;lfill to David Roth Stokes, et al. entitled Belt Tracking System,&#34; assigned to the same assignee. The tracking roller 2| is secured to a shaft journaled for rotation in bearings secured to the ends of the parallel legs of a yoke member. The tracking mechanism is described in US. application Ser. No. 3ll,345 filed on Dec. l, I972.  
  It is sufficient for present purposes to say that the tracking mechanism includes a flat plastic sensing ring 32 which contacts the belt 12 during movement of the latter over the roller 20. The sensing ring is mounted for rotation about a bearing, and is supported on a support plate 34. Thus, lateral movement of the belt 12 results in lateral movement of both the sensing ring 32 and support plate 34 which in turn causes rotation of a shaft 36 about its axis to effect the correction neces sary to move the belt back to its normal course of movement. It is only when the tracking mechansim 30 does not satisfactorily correct the movement of the belt that the fail-safe mechanism 38 (FIG. 2) ofthe present invention operates to stop the movement of the belt.  
  Referring to FIGS. 2 and 3, the operation of the mechanism 38 will be described in more detail. When on its normal course. the belt 12 overlaps each end of roller 20 by a distance a, which in the present example is 1/8 inchv lfthe belt deviates 1/8 inch in either diireetion during operation of the machine, the mechansim operates to stop the movement of the belt to prevent damage to the machine and the belt. It does this by opening [or closing] one of two mercury switches 40 or 42 depending upon the direction of the deviation of the belt.  
  To set the mechanism up for operation, the belt as sembly 14 (without a belt) is moved into the machine cabinet (away from the reader as viewed in FIG. I. and to the left as viewed in FIG. 2) until the sensing pin 44 of the mechanism 38 is contacted by either the sensing ring 32 or the support plate 34 of the belt assembly as shownv As can be seen, the mechanism 38 is mounted to the rear wall 46 of the machine cabinet. The mechanism 38 has a setting rod 48 which is slidably mounted in an opening 50, the setting rod contacting the rear wall 46 prior to the time the sensing pin 44 is contacted by the belt assembly T4. The setting rod has color coded markings 46 on one end thereof, and as the belt assembly applies a linear force against the sensing pin 44, the housing 52 moves inwardly toward the rear wall 46 while simultaneously rotating in a countclockwise direction via the action of flexure legs 49. As the housing 52 moves inwardly, more of the setting rod 48 is exposed. Thus. when the belt assembly 14 (without the belt) is initially moved completely into the cabinet, the setting rod 48 will indicate via the color coded markings 46 how the mechansim 38 should be adjusted. This inward position of the mechanism will correspond to one of the limits of the permissible deviation of the belt [2, because without a belt on the belt assembly 14. the sensing ring will be resting against the end of the roller 20.  
  After the belt assembly l4 has thus been moved into the machine cabinet, it is then pulled out of the cabinet, and a reading is taken of how far the setting rod 48 is protruding. It is apparent that as the housing 52 moves outwardly from the rear wall 46 as the belt assembly 14 is being withdrawn from the cabinet, the setting rod 48 will move along with it.  
  The sensing pin is normally held in a fixed position with respect to the housing 52 by a locking screw 54. After the belt assembly has been withdrawn from the cabinet. however the locking screw 54 is loosened so that the sensing pin 44 can be rotated so that its pointer 56 points to one of the color coded markings 58 which corresponds to the reading obtained on the markings 46 on the setting rod 48: as can be seen. when the sensing pin is rotated. both switches 40 and 42 are also rotated.  
  By the above procedure. the attitude of the switches 4t) and 42 has now been set. and when a belt is placed onto the rollers 20. 2!, and 22. and the belt assembly moved back into the machine cabinet. the mechanism 38 is properly adjusted and ready for operation.  
  As should now be apparent. the belt I2 is in its normal position in FIG. 2. each end of the belt overlapping the roller 20 by one-eight inch in the present example. Thus. the belt can deviate a total of one-fourth inch during its movement and one-eight inch in either direction from that shown in FIG. 2. If it does deviate oneeight inch in either direction. the mechanism 38 will act to stop the movement of the belt by opening the circuit to the motor driving the belt assembly 14. It does this by rotating either clockwise or counterclockwise from the position shown in FIG. 2 depending upon the direction of the deviation of the belt 12 from its normal course. The attitude of the switches having been initially adjusted. one of the switches will open (or close) to open the motor circuit driving the belt assembly. depending upon which direction the mechanism 38 rotates.  
  As can be seen. the above arrangement provides for a fail-safe mechanism which is very accurate, but yet provides for easy adjustment so as to accommodate itsell to belt assemblies or machines having varying toleranccs. In the present embodiment. a suitable mechanism was formed plastic. Other materials might also be used. however. the modules of the material and the cross-sectional area of the tlexure legs being taken into consideration to get the degree of movement desired.  
  While the invention has been described with reference to the structure disclosed. it is not confined to the details set forth, but is intended to cover such modifications or changes as may come within the scope of the following claims:  
 What is claimed is:  
  1. An improved electrostatic reproduction machine having framework, and an endless belt assembly mounted for movement between an operative position within the framework to an inoperative position remote from the framework, the belt assembly having a plurality of rollers adapted to support and move an endless belt having a photoconductive areas thereon, the improvement comprising means including switch means mounted to the framework for sensing a lateral deviation of the belt from its normal course of movement during operation and for opening a circuit in response to sensing a predetermined deviation, the sensing means having means for converting the lateral move ment of the belt into rotational movement in effecting the opening ofthe circuit, means for adjusting the position ofthe switch means with respect to the belt assembly comprising a first member mounted so as to be movable with respect to the remainder of the sensing means. means for indicating the position of the first member with respect to the remainder of the sensing means after the belt assembly has been moved into its operative position, and means for adjusting the position of the switch means to correspond to the position of the first member after the belt has been moved into its inoperative position.  
  2. An improved electrostatic reproduction machine having framework, and an endless belt assembly mounted for movement between an operative position within the framework to an inoperative position remote from the framework. the belt assembly having a plural ity of rollers adapted to support and move an endless belt having a photoconductive area thereon, the improvement comprising means including switch means mounted to the framework for sensing a lateral deviation of the belt from its normal course of movement during operation and for opening a circuit in response to sensing a predetermined dCViflllOH, means mounted so as to contact the belt assembly when the latter has been moved into its operative position for indicating how the position of the switch means with respect to the belt assembly should be adjusted, and means for adjusting the position of the switch means as indicated.