Paper property sensing system

Abstract: A sensor system (100a) for measuring physical properties of a sheet (116). In one embodiment, the sensor system measures paper curl and thickness using two sensors, each of which includes a member (112), a base (114), and measurement circuit. The two members (112) are positioned in opposition to each other and both contact the sheet (116) as it passes between them. Each member is coupled to a base (114), which includes a measurement circuit. Each measurement circuit measures the displacement of its associated member (112). In another embodiment (Fig. 4), the sensor system measures stiffness and curl using two pairs of opposed sensors. In yet another embodiment, the sensor system measures thermal diffusivity of a sheet using three sensors, one of which includes a heater for heating the sheet of paper and the other two sensors include thermocouples in contact with the sheet of paper for sensing the heat of the paper.

Description: The present invention relates to a sensor system for paper handling devices in a xerographic copier, according to the preamble of claim 1. The disclosed sensor system is suitable for determining paper properties such as paper mass. A need exists for a sensor system that provides information concerning paper properties to allow for optimizing adjustments in an image transfer mechanism in a copier. If paper properties are known prior to image transfer, the image transfer mechanism can be suitably optimized to ensure the best A paper mass sensor using spring biased scales is known from US-A-4348102. A paper thickness sensor using an optical detection arrangement is known from DE-4411957A1. An object of the present invention is to enable automatic adjustment of sheet handling in response to physical properties of a sheet of a markable medium, like paper. Another object of the present invention is to enable optimization of sheet transport mechanisms to permit use of a wide range of markable mediums, like paper and transparencies. A still further object of the present invention is to reduce paper wastage by reducing jams in sheet transport mechanisms. The present invention provides a sensor system for measuring physical properties of a sheet in a xerographic copier, the sensor system comprising the features as set out in claim 1. The invention further provides a sheet handling machine according to claim 5 of the appended claims. Other objects, features, and advantages of the present invention will be apparent from the following detailed description in conjunction with the accompanying drawings, in which: Figure 1 illustrates a reproductive machine incorporating the paper property sensor system according to an embodiment of the present invention; Figure 3 illustrates a further embodiment of a paper property sensor according to the invention; Figure 2 illustrates an embodiment of the paper property sensor system for measuring paper mass according to the invention. Figure 1 illustrates a reproductive machine 9 incorporating paper property sensor system 100 of the present invention. Paper property sensor system 100 enables reproductive machine 9 to alter its handling of sheets of a markable medium in response to properties of the markable medium currently within machine 9. Paper property sensor system 100 may also be used in conjunction with any machine that materials such as transparencies, metal, plastic, and silicon wafers. Briefly described, each embodiment of paper property sensor system 100 includes one or more paper property sensors, each of which includes a member coupled to a base and a measurement unit. Various properties of the medium being transported can be determined by measuring the displacement of the member relative to the base. Paper property sensor system 100 will be described in detail with respect to Figures 2-7. A. The Reproduction Machine Prior to a more detailed discussion of the paper property sensor system 100 according to an embodiment of the present invention, consider reproduction device 9, illustrated in Figure 1. Reproduction machine 9 includes a belt 10 having a photoconductive surface. After development of an electrostatic latent image thereon, belt 10 advances to the transfer station. At the transfer station a copy sheet is moved into contact with the toner powder image on belt 10. The copy sheet is fed from either tray 34 or 36 to the transfer station. After transfer, conveyor 32 advances the sheet to fusing station 40. Paper property sensor system 100 is disposed between copy paper trays 34 and 36 and conveyor 32 at any convenient location, or locations, within the copy paper transport path. Preferably, paper property sensor system 100 is located close to copy paper trays 34 and 36. Information provided by paper property sensor system 100 allows controller 38 to prevent jams by adjusting the speed of conveyors 32, 37 and 46, and the spacing between nips 39 and 41, between rollers 42 and 44, gates 48 and 52, and decision gate 52. Controller 38 includes a processor and memory. The processor controls and coordinates the operations of reproductive machine 9 by executing instructions stored electronically in memory, including instructions for controlling paper property sensor system 100. Instructions representing the methods discussed herein may be realized in any appropriate machine language. Semiconductor logic devices that can be used to realize memory include read only memories (ROM), random access memories (RAM), dynamic random access memories (DRAM), programmable read only memories (PROM), erasable programmable read only memories (EPROM), and electrically erasable programmable read only memories (EEPROM), such as flash memories. Figure 3 illustrates an embodiment 100b of a paper property sensor system 100 for measuring sheet mass according to the invention. System 100 includes paper property sensors to allow control of the positioning of sensor arms 112. Figure 2 illustrates one type of paper property sensor 100. which includes vertical actuator 126 coupled between sensor arm 112 and base 114. Vertical actuator 126 may be used in conjunction with a measurement circuit. The mechanisms that may be used to realize vertical actuator 126 include piezoelectric bimorph elements, linear piezo-elements with mechanical amplifiers, and bubble driven micro-pistons, for example. Alternatively, paper property sensor system 100 may include the paper property sensor shown in Figure 3. In this embodiment, vertical actuator 126 is replaced with linear actuator 119 for moving arm 112. Paper property sensor system 100 includes circuit 140 to sense the movement of sensor arms 112. Circuit 140 takes the outputs of strain gauges 124 and feeds them to opamp 142, which functions as a differential amplifier. Low pass filter 144 separates high frequency components of the difference signal output by opamp 142, thereby allowing faithful feedback tracking. The analog output from filter 144 is then converted to a digital signal by an A/D converter prior to being coupled to controller 38. Alternatively, the A/D converter may be incorporated into controller 38. Paper mass measurement with paper property sensor system 100 begins with a signal from controller 38, applied to actuators 126, that causes application of a vertical impulsive force of fixed amplitude to sensor arms 112 without sheet 116 therebetween. The differential displacement,  base , is then sensed by the measurement circuits and coupled to controller 38, providing a baseline for comparison. Afterward, with sheet 116 between sensor arms 112, a vertical impulsive force of the same magnitude is applied to sensor arms 112 and the differential displacement  load , is sensed. Controller 38 can estimate the mass of paper 116 by taking the difference between  load and  base .

Claims: A sensor system for measuring physical properties of a sheet (116) in a xerographic copier, the sensor system comprising: a) a first member (112) positioned to contact the sheet; b) a first base (114) attached to the first member (112); characterized by c) a first actuator (126) for imparting force to the sheet (116) at a predetermined time; and d) a first measurement unit attached to the first base for measuring displacement of the first member relative to the first base both before the predetermined time and after the first actuator has imparted force to the sheet at the predetermined time. The sensor system of claim 1, wherein the first member (112) comprises a spring, or a linear actuator, or an arm. The sensor system of claims 1 or 2, further comprising a second member positioned in opposition to the first member to each respectively contact the sheet passing therebetween; and a second base coupled to the second member. The sensor system of any of claims 1 to 3, wherein the first measurement unit further comprises (A) a light source (120) and a light position detector (122), with light from the light source (120) being reflected from the first member to the light position detector, or (B) a strain gauge (124) coupled to the first member to measure a flexure of the first member. A sheet handling machine in a xerographic copier comprising: a) a sheet transport mechanism for moving a sheet in response to a control signal; b) a controller coupled to the sheet transport mechanism for generating the control signal in response to a first property signal; and c) a sensor system coupled to the sheet transport mechanism and generating the first property signal, the sensor system being in accordance with any of the preceding claims.

Inventors: BERLIN ANDREW A, BIEGELSEN DAVID K, CASS TODD A, JACKSON WARREN B, SPRAGUE ROBERT A, BERLIN, ANDREW A., BIEGELSEN, DAVID K., CASS, TODD A., JACKSON, WARREN B., SPRAGUE, ROBERT A.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1997
Main classification: G03G15
IPC codes: H04N1, B65H7, G03G15, G01N13, G01N33, B41J11