Method and apparatus for detecting holes in copy media

Abstract: A copy media registration module for positioning paper (170) in a feed path is disclosed. More specifically, the present invention is directed to a method and apparatus for detecting pre-drilled holes in copy media. A sensor (310,312,314) detects the presence and absence of copy media in the feed path. Once a transition from paper to no-paper, or from no-paper to paper occurs, subsequent signals from the sensor are ignored for a designated period of time. At the leading edge of the sheet, this designated time period is chosen such that any possible holes will have moved past the sensor. At the trailing edge of the sheet, the designated time period is chosen based upon the maximum possible size of any holes that may be present.

Description: The present invention is directed to a method and apparatus for positioning paper in a feed path. More specifically, the present invention is directed to a method and apparatus for detecting holes in copy media. The invention allows a registration system to distinguish between a hole and the leading or trailing edge of a copy sheet, to facilitate proper registration of the copy media onto a photoreceptor. BACKGROUND OF THE INVENTION The xerographic imaging process begins by charging a photoconductive member to a uniform potential, and then exposing a light image of an original document onto the surface of the photoconductor, either directly or via a digital image driven laser. Exposing the charged photoconductor to light selectively discharges areas of the surface while allowing other areas to remain unchanged, thereby producing an electrostatic latent image of the document on the surface of the photoconductive member. A developer material is then brought into contact with the surface of the photoconductor to transform the latent image into a visible reproduction. The developer material includes toner particles with an electrical polarity opposite that of the photoconductive member, causing them to be naturally drawn to it. A blank copy sheet or other type of copying media is brought into contact with the photoreceptor and the toner particles are transferred thereto by electrostatic charging the media. The copy media is subsequently heated, for permanent affixing of the reproduced image thereto to produce a "hard copy" reproduction of the document or image. The photoconductive member is then cleaned to remove any charge and/or residual developing material from its surface to prepare it for subsequent imaging cycles. Blank copy media of a variety of sizes are typically stored in trays that are mounted at the side of the machine. In order to duplicate a document, copy media having the appropriate dimensions is transported from the tray into the paper path just ahead of the photoreceptor. The copy media is then brought in contact with the toner image that is present on the surface of the photoreceptor prior to transfer. If the copy media has not been oriented or registered properly before it is brought in contact with the toner image, the toner image may be fused at an improper location on the copy media, causing it to be skewed or too far up, down, front or back on the page. Devices are presently available which provide for accurate copy media registration. For example, sensors may be strategically placed at the end the feed path, and their sequence of engagement used to determine whether a transporting copy sheet is skewed and/or laterally mis-aligned. If the sheet is skewed, the velocity of one side of the copy sheet is increased relative to the other side to return the sheet to proper alignment. If the sheet is laterally mis-aligned, the sheet is shifted to the proper lateral position. A device such as this is disclosed in US-A 5,094,442 to Kamprath et al. issued March 10, 1992, which discloses a translational electronic registration (TELER) system. This system generally includes three optical sensors, a pair of coaxial independently driven drive rolls, a carriage with a linear drive on which paper drive rolls are mounted, and a microprocessor controller. A blank copy media is driven into the nip rolls and moved through the paper path for placement and fusing of an image thereon. The speed of both nip rolls can be controlled to effect skew alignment and longitudinal registration. The nip rollers are mounted on a carriage movable transversely with respect to the feed path. A sensor system controls positioning of the carriage to achieve the desired top edge or a lateral positioning of the copy media. Independent control of nip roll drive and carriage translation provides simultaneous alignment in lateral and longitudinal directions. Copending application Ser. No. (concurrently filed, not yet assigned, our ref. D/97253) to Milillo et al. is another device that may be enhanced with the present invention. It is often advantageous to feed copy media with pre-drilled holes through the path. Copy media of this type is useful when it is desired to place the printed copies into a looseleaf binder, or at other times when it becomes necessary to have output with punched holes. Problems arise, when copy media is transported through a system such as the one described above, because a hole passing over one of the sensors, causes the system to act as though the edge of the sheet is being detected. More specifically, the front edge of a hole appears to the system as the trailing edge (TE) of a sheet, and the back of a hole appears to be the leading edge (LE) of a sheet. This improper recognition of a hole as the edge of a sheet causes the system to correct misalignments that are not actually present, resulting in paper jams, and malfunctioning of the printing system. It is therefore advantageous to develop a way to detect pre-existing holes in copy media, and allow for continuous, accurate copy media registration. EP-A-0363153 discloses an apparatus which determines the location of an edge of an advancing sheet and discriminates between the edge and a hole in the sheet. After the leading edge of the sheet is detected by a sensor (108) and the sheet has moved a first predetermined distance, the absence or presence of the sheet is sensed for a second predetermined distance. US 4540170 discloses a paper feed control device having paper feed rollers for feeding a paper sheet such as an original to a predetermined position, a first sensor for detecting the paper sheet, a second sensor for detecting leading edge and trailing ends of the paper sheet, a microcomputer for controlling the rollers in response to the output signals from the sensors, and a compensating circuit for compensating the level of the output signal from a second sensor which is maintained in a non-detecting state until the paper sheet completely passes through the second sensor. Anonymous, "Prepunched Paper Feed," IBM Technical Disclosure Bulletin, Vol. 25, No. 12, p. 6524-6526, discloses a device to prevent false trailing-edge indications caused by the existence of prepunched holes in proximity to paper sensors by controls which ignore sensor output for a predetermined time period after the leading edge is sensed, where the time period is adequate to insure that any prepunched holes will pass before reenabling the sensor. SUMMARY OF THE INVENTION It is the object of the invention to provide a method and an apparatus for detecting holes in copy media thereby allowing a registration system to distinguish between a hole and a leading or trailing edge of the copy sheet. This object is achieved by an apparatus according to claim 1. In accordance with another aspect of the invention, there is provided a method according to claim 10. The present invention has a significant advantages over current methods of aligning copy media in a feed path in that it allows the presence of pre-drilled holes in copy media to be detected and insures more accurate alignment of such a copy sheet. In addition, it enables the imaging system to be able to track the presence of holes, to avoid printing over undesirable locations. According to a further aspect of the invention, said first signal is generated when the copy media blocks light emitted from said light source and prevents said emitted light from reaching said light sensing device, and said second signal is generated when the copy media is not located between said light source and said light sensing device. According to a further aspect of the invention, said designated time period is dependent upon a speed of a leading edge of the copy media as it passes a light sensor, and a distance from a leading edge of the copy media for which it is known that no more holes will be present. Preferably, said designated time period is determined by dividing said leading edge distance by said copy media velocity. It may also be preferable that said designated time period is dependent upon a speed of a trailing edge of the copy media as passes a light sensor, and a diameter of a largest hole that can be defined by the copy media. According to a further aspect, said designated time period is determined by dividing said diameter by copy media velocity over said designated distance said diameter. Preferably, said registration is an electronic registration system. It may be of advantage if said electronic registration system is a translating electronic registration system. Preferably, said light source is an LED disposed near said feed path for projecting light toward said feed path. Said light sensing device may be a phototransistor. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 depicts an isometric view of a possible layout of the interior of a xerographic copy machine. Relative positions of the platen glass, document, light source, lens, and photoreceptor are shown. FIG. 2 shows a front view of an interior cavity of a photocopy machine. A photoreceptor is shown with latent and developed images shown thereon. The relative positions of the registration, development, transfer, and fusing stations are also shown. The paper path and media storage trays are also shown. FIG. 3 contains an isometric view of a TELER system, one type of electronic drive roll system that may be used with the present invention. FIG. 4 depicts an example sheet of pre-drilled copy media that may be transported through the present invention. FIG. 5 contains a flow chart describing operation of a pre-drilled media algorithm that may be incorporated into the copy registration module of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is directed to a method and apparatus for positioning paper in a feed path. Specifically the present invention relates to a method and apparatus detecting holes in copy media thereby allowing a registration system to distinguish between a hole and the leading or trailing edge of a copy sheet, to facilitate proper registration of the copy media onto a photoreceptor. Referring now to the drawings where the showings are for the purpose of describing an embodiment of the invention and not for limiting same, FIG. 1 is used to illustrate an example light lens copying operation which begins by placing the document 60 face down upon the platen glass 62, such that the right edge of the original image is lined up with axis A. Axis B corresponds to the location at which the left edge of document 60 comes in contact with platen glass 62. It should be noted that the left edge of the image will rest at locations further away from or closer to axis A to axes B', B", etc. as documents with differing widths are used. With continued reference to FIG. 1, document 60 is exposed to a light source 64, which causes the image thereon to be reflected back toward the copy machine and onto photoreceptor 66. Passage of the light reflected from document 60 through lens 72 causes latent image 68 projected onto photoreceptor 66 to be reversed such that the left edge of document 60 at axis A will be reflected at axis C on the photoreceptor belt. Thus, the left edge axis A of document 60 will become the trailing edge axis B of latent image 68, and will remain so throughout processing. As shown in FIG. 2, once the latent image is generated, photoreceptor 66 will move latent image 68 in the direction of arrow G. Toner particles are deposited onto it at development station 182, thereby transforming latent image 68 into a developed image 174. Photoreceptor 66 and developed image 174 will then proceed toward transfer station 184. Before developed image 174 reaches transfer station 184, a blank copy media 170 will be removed from one of paper trays 176 and transported along paper path 178. Copy media 170 will pass through nip 180 between two rolls included in registration system 200 end of paper path 178, to be placed in contact with developed image 174 just as it reaches transfer station 184. Copy media 170 with developed image 174 thereon will then move through a pre-fuser transport 186 (not shown) to fusing station 188 (not shown) where the toner image will be permanently affixed to copy media 70. While registration module 200 will operate successfully using a variety of types of drive roll systems, it will often include an electronic drive roll system, which is controlled by electronic signals that are transmitted from a microprocessor. One type of electronic drive roll system known to be very effective in accurately registering copy sheets is a translating electronic registration (TELER) system 300, illustrated in detail in FIG. 3. In the embodiment shown, TELER system 300 includes a carriage 306 having two drive rolls 202 and 204 which are mounted thereon in rotatable fashion, and are driven by drive motors 206. The roll pairs 202 and 302 engage copy media 170 and drive it through TELER system 300. The system includes optical sensors 312, 314 and 310 which will detect the presence of the edges of copy media 170. Two sensors 312 and 314 are mounted on the carriage 306 adjacent the drive rolls 202 for lead edge detection of the copy media and control of motors 206. The sequence of engagement of the sensors 312 and 314 and the amount of time between each detection is utilized to generate control signals for correcting skew (rotational mis-positioning of the copy media about an axis perpendicular to the copy media) of the copy media by variation in the speed of drive rolls 202. Sensor 310 is arranged to detect the top edge of the copy media and the output therefrom is used to control transverse drive motor 308. According to the further aspect of the invention said first signal is generated when the copy media blocks light emitted from said light source and prevents said emitted light from reaching said light sensing device, and said second signal is generated when the copy media is not located between said light source and said light sensing device. According to the further aspect of the invention said designated time period is dependent upon a speed of copy media as it enters said registration system, and a distance from a leading edge of the copy media for which it is known that holes will be present. Preferably, said designated time period is determined by dividing said leading edge distance by said copy media velocity. It may also be preferable that said designated time period is dependent upon a speed of copy media as it exits said registration system, and a diameter of a largest hole that will potentially be present upon the copy media. According to the further aspect said designated time period is determined by dividing said diameter by copy media velocity over said designated distance said diameter. Preferably, said registration is an electronic registration system. It may be an advantage if said electronic registration system is a translating electronic registration system. Preferably, said light source is an LED disposed near said feed path for projecting light toward said feed path. Said light sensing device may be a phototransistor. With reference now to FIG. 2, it is often advantageous to fill paper trays 176 with copy media 170 that has pre-drilled holes. The present invention includes a pre-drilled media algorithm which can be used to ensure proper registration of copy media 170 that has pre-drilled holes 402, best illustrated in FIG. 4. As stated above, sensors can be used to detect the presence of copy media 170 in paper path 178 by measuring the amount of light that reaches a photodetector. These devices can also be used to detect the presence or absence of holes or slots in copy media 170. Referring now to FIG. 4, sensor 404 should be placed in paper path 178 such that copy media 170 moving through the paper path in the direction of arrow J can be detected. As copy media moves past sensor 404, electronic signals 416 are generated in response to the amount of light measured at the photodetector. A "no paper" signal (which may be either an ON/HI/ 1 signal or an OFF/LOW/0 signal depending upon the chosen configuration) is generated when light is being measured at the photodetector, indicating that a hole has been detected, while a "paper" signal (the signal opposite that chosen for the "no paper" signal) is generated while the solid portion of copy media 170 is being transported past sensor 404. However, a "no paper" signal will also be generated when there is no copy media moving past sensor 404, while an OFF signal will be generated when copy media is moving past sensor 404. Thus, capability which enables sensor 404 to discriminate between the leading edge 412 of a sheet and the back edge of a hole 402 upon receiving a transition from a no paper signal to a paper signal must be added. Similarly, sensor 404 must be able to distinguish the trailing edge 414 of copy media 170 from the front of a hole 402 when a transition from a paper signal to a no paper signal occurs. Referring now to FIG. 5, software can be incorporated into copy registration module 200 of the present invention in order to add this feature. As shown in the diagram, sensor 404 detects a transition from no paper to paper at block 502, indicating a leading edge (LE) of a sheet of new copy media 170, or the back of a hole 402 is passing sensor 404. After the no paper to paper signal is received, block 504 is active for a designated period of time. The length of this designated time period must be chosen by considering the speed of the copy machine, and the possible locations of any holes that might be present in copy media. Quite often, holes in copy media lie within 3/4 in from the leading edge. However, it is not unusual for holes to lie further from the leading edge, or for consecutive holes to be placed next to each other, such that there is at least one hole further than 3/4 inch from the leading edge. On the other hand, it is rare that a hole will lie in or near the middle of a page. Thus, the designated time period must simply be long enough to allow the leading edge of the copy media to pass a comfortable distance away from sensor 404, so that it will be clear that the sensor is reading light reflected from the center of the copy media. More specifically, the length of time that should elapse once a no paper to paper signal transition occurs should be determined by dividing the distance the copy media must travel to ensure that no holes will be present, by the velocity of the sheet as it passes over the sensing device. In one embodiment of the invention, the speed of copy media 170 as it enters nip 180 is known to be 1000 mm/s, while it is known that no holes will lie more than 100 mm from the leading edge of copy media 170. In this embodiment, the designated time period is approximately 100 ms. With continued reference to FIG. 5, if a paper to no paper signal transition has not occurred within the designated time period, a LE with no holes has been detected by sensor 404 as shown in block 506. On the other hand, a transition from a paper signal to a no paper signal within the designated time period X indicates that a hole lies within the allocated distance from the LE of copy media 170, as indicated in block 508. An electronic registration system cannot function properly without a mechanism which accurately detects the leading and trailing edges of copy media. Information about the location of pre-existing holes can also be used by the imaging system of the printing machine to shift the location of the image so information will not be printed over a hole in the copy media. Similarly, the presence of holes at the trailing edge (TE) of a copy sheet must also be detected, however the process for detecting holes at this end of the page must be slightly different. First, this consideration is being made while a paper signal is already being transmitted from sensor 404. Once a paper to no paper transition occurs as indicated in block 510, the sensor must determine whether or not subsequent no paper to paper transition occurs within a designated time period y as indicated in block 512. Again, this time period must be altered as print speed and hold diameter are changed. However, the length of the time period is chosen by considering the speed of the copy machine, and the largest possible diameter size for any holes that might be present in copy media. This is because it is impossible to simply select an appropriate distance for which it is certain that a no paper to paper transition which follows a paper to no paper transition will mean that the trailing edge of copy media 170 is being sensed, rather than the back of a hole on a subsequent copy sheet. Thus, the designated time period is chosen by considering the largest possible diameter of a hole that will lie near the trailing edge of the copy media. Once the speed at which the copy media 170 exits nip 180 is known, the designated time period should be equal to the amount of time that it will take for the diameter distance to move past the sensor at the known copy speed. In the embodiment described above, it is also known that no holes larger than 10 mm will ever be present on a page. It is also known that the speed of exiting speed of copy media 170 is 480 mm/s. Under these circumstances 20 ms is the approximate time period that will elapse. If a no paper to paper transition does not occur within the given time period, the TE of copy media 170 has been detected as indicated in block 514. the presence of a no paper to paper signal transition indicates that a hole lies in the margin next to the trailing edge of the page as shown in block 516. The system can automatically be reset as another sheet of copy media 170 is fed from paper tray 176. The information regarding the presence or absence of holes in the margins of copy media 170 can be used for many purposes, including transmitting signals to the imaging system in order to prevent the latent image from being generated in locations on photoreceptor 66 that will correspond to areas on copy media 170 that will contain holes. Also the use of sensors to accurately detect copy media edges is critical to the functioning of an electronic registration system. The above subsystems are merely examples of the types of enhancements that may be added to copy registration module 200 of the present invention. Any or all of them may be added or removed from the module at a single time. It will also be possible to add other enhancements which have not been mentioned here.

Claims: An apparatus for detecting the presence of pre-existing holes in copy media (170), comprising: a) a copy media transport means for moving the copy media along a path (178); b) a registration system (200) for placing the copy media at a designated location at an end of said path; c) a microprocessor, communicating with said registration system to adjust a location at which the copy media is placed at said path end; d) a light source, situated along said path; e) a light sensing device (404) in a receiving relationship with said light source for sensing a light intensity from said light source, and generating signals (416) indicative of said sensed light intensity, said sensed light intensity including a first signal when no light is sensed and generated, when a copy medium blocks light emitted from the light source and a second signal when light is sensed and generated, when the copy medium is not located between the light source and the sensing device; and f) a detecting device for receiving said generated signals from said light sensing device, and for transmitting signals to a timing device at points at which a transition of the generated signals between said first signal and said second signal takes place; g) the timing device is adapted to count an amount of time that elapses after a transition corresponding to a leading edge of the copy medium has taken place, and to transmit a timing signal to said microprocessor when a designated time period has elapsed, whereby the designated time period starts, when the transition corresponding to a leading edge occurs, the light sensing device (404) and the detecting device being active during the designated period, whereby a hole is detected, if transitions are detected by the detecting device during the designated time period. An apparatus for detecting the presence of pre-existing holes as claimed in claims 1 wherein the microprocessor is adapted to determine the designated time period from a speed of a leading edge of the copy media as it passes said light sensing device, and a distance from said leading edge for which it is known that no more holes will be present. An apparatus for detecting the presence of pre-existing holes as claimed in claim 2, wherein the microprocessor is adapted to determine the designated time period by dividing said distance from said leading edge by said leading edge speed. An apparatus for detecting the presence of pre-existing holes as claimed in any of the claims 1 to 3, wherein the microprocessor is adapted to determine the designated time period from a speed of a trailing edge of the copy media passes said light sensing device, and a diameter of a largest hole that can be defined by the copy media. An apparatus for detecting the presence of pre-existing holes a claimed in any of the claims 1 to 4, wherein the microprocessor is adapted to determines the designated time period by dividing said diameter by said trailing edge speed. An apparatus for detecting the presence of pre-existing holes as claimed in any of the claims 1 to 5, wherein said registration (200) is an electronic registration system. An apparatus for detecting the presence of pre-existing holes as claimed in claim 6, wherein said electronic registration system is a translating electronic registration system (300). An apparatus for detecting the presence of pre-existing holes as claimed in any of the claims 1 to 7, wherein said light source is an LED disposed near said feed path for projecting light toward said feed path. An apparatus for detecting the presence of pre-existing holes as claimed in any of the claims 1 to 8, wherein said light sensing device is a phototransistor. A method for detecting pre-existing holes in copy media, comprising: a) measuring an amount of light, emitted from a light source which is adjacent to a copy medium path (178) and propagating along a way that can be interrupted by a copy medium, to determine when a copy medium is present; b) generating electronic signals (416) in response to an amount of light measured; c) detecting transitions between signals generated when light is detected indicating that no copy medium is located between the light source and a sensor device and signals generated when no light is detected, indicating that a copy medium (170) is located between the light source and a sensor device; and d) detecting the transitions for a designated time period, which starts after a transition corresponding to a leading edge of the copy medium is detected, whereby holes are detected, if transitions occur during the designated time period.

Inventors: MILILLO WILLIAM D, MILILLO, WILLIAM D.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1998
Main classification: G03G15
IPC codes: B65H9, G01B11, B65H7, G03G15