Belt edge steering sensor

Abstract: A sensor having a shutter (40) mounted upon a shaft (48) for rotation within a housing (36) in opposition to a light path between an LED (42) and photodetector (44). A portion of the shaft (48) extends outside the housing connected to an elongated arm (28). A runner (52), secured to the elongated arm (28), engages a moving photosensitive surface (12) and deviations of the edge position of the photosensitive surface rotate the shutter (40) in relation to the light path between the LED (42) and photodetector (44), for tracking the edge position of the moving photosensitive surface (12) by providing signals representing shutter position.

Description: This invention relates generally to an apparatus and method for tracking the position of a moving photoconductive belt, and more particularly concerns a contact sensor to measure belt edge deviation from a reference position. One of the many challenges to be overcome in the successful introduction of color reprographic machines is the relative registration of colors such as magenta, cyan, yellow, and black, on the output copy sheet. Registration requirements for new color reprographic machines are now far more stringent than the prior art registration requirements which were generally within a 125 µm range. Three techniques are known to have been previously used for measuring the position of a photoreceptor such as a belt. The first employed a series of three holes punched in the edge of the P/R placed in a "Z" pattern, the second involved placing xerographically developed marks on the belt, and the third involves measurement of the position of the edge of the belt. The latter has been deemed preferable, as it enables continuous monitoring of the belt position even when the belt is stopped, and eliminates the need for additional holes in the photoreceptor. Belt edge sensing is presently implemented using an open slotted, interruptive sensor, and appears to operate satisfactorily when the sensor is clean. However, experience has shown performance deteriorates during printing, as the optical surfaces of these sensors become coated with toner, and sensor cleaning intervals of 500 - 4000 copies are common. In addition, output of the devices is strongly affected by the optical transmissivity of the belt, and by the presence of holes in the belt edge required for seam sensing and belt registration. Both of these factors generate spurious signals, which may be interpreted by the control system as misregistration, when in fact the belt is well registered. Also, current edge sensors are relatively expensive. In addition to the above mentioned prior art, US-A-5,291,245 discloses an electro-optic sensor for recognizing a photoreceptor belt seam and US-A-4,864,124 discloses an electro-optic sensor having a mechanical arm disposed for engagement with a moving copy sheet to rotate a sleeve within the light path of the sensor. Suitable rotation of the sleeve interrupts the light path to manifest the presence of a copy sheet. It would be desirable, therefore, to be able to provide a relatively inexpensive sensor to measure photoreceptor lateral position as well as a sensor that minimizes the need for holes in the belt. In addition, it would be desirable to provide a lateral position measurement sensor that is very precise and does not exhibit deteriorating performance during extended machine operation. It is an object of the present invention, therefore, to provide a low cost sensor to measure a belt edge location within 5 µm. It is another object of the present invention to be able to measure belt edge position independent of the optical transmissivity of the belt material and of the presence of holes in the belt. It is still another object of the present invention to minimize the effects of optical contamination on the performance of the sensor. The present invention provides a sensor for tracking the position of an edge of a moving surface, according to claim 1 of the appended claims. According to one aspect of the invention, there is provided a sensor having a shutter mounted upon a shaft for rotation within a housing in opposition to a light path between an LED and phototransistor. A portion of the shaft extends outside the housing connected to an elongated arm. A runner secured to the elongated arm engages a moving photosensitive surface and deviations of the edge position of the photosensitive surface rotate the shutter in relation to the light path between the LED and phototransistor. This enables the tracking of the edge position of the moving photosensitive surface by providing signals representing shutter position. For a better understanding of the present invention, reference may be had to the accompanying drawings wherein the same reference numerals have been applied to like parts and wherein: Figure 1 is a block diagram depicting the the system incorporating the present invention; Figure 2 is a side view of the sensor in accordance with the present invention; Figure 3 is a top view of the sensor in accordance with the present invention; Figures 4A, 4B, and 4C illustrate operation of the sensor in accordance with the present invention; Figure 5 illustrates the relationship of photoreceptor belt position to sensor photocurrent and Figure 5 illustrates a typical photodetector and circuit diagram for use with the present invention. With reference to Figure 1, there is generally disclosed a photosensitive surface 12 suitably driven by drive roll 22 in the direction of arrow 14 in relation to an imaging zone 16 where latent images are projected upon the photosensitive surface 12 by well known imaging techniques and a developer housing 18 at which suitable toner is applied to develop the latent image for transfer to a copy sheet (not shown). Various document image areas are shown by the dotted rectangular areas and illustrated at 20 along the photosensitive surface 12. The well known xerographic process for projecting images, developing the images, transferring to copy sheets, fusing the images to the copy sheets, and transporting to a suitable output station forms no part of the present invention, and details thereof have therefore been omitted. In accordance with the present invention, a belt edge steering sensor 26 with a suitable actuating arm 28 is positioned adjacent the photosensitive surface 12 for the actuating arm 28 to engage an edge of the photosensitive surface 12. Suitable signals generated by the movement of the actuating arm 28 are provided by the steering sensor 26 to a microcontroller 30. In turn, the microcontroller 30 converts the arm position signals from the sensor 26 into driver signals to operate motor driver 32. The motor driver 32 provides motor signals to the steering motor 34 which in turn operates the steering roll 37 to provide suitable steering adjustments to adjust the edge position of the photosensitive surface 12. With reference to Figures 2 and 3, there is illustrated one embodiment of the sensor 26 employing a flag switch architecture. In particular, the sensor 26 is primarily affected by the position of the actuator arm 28 in contact with the photosensitive surface 12. Preferably, the actuator arm 28 is lightly spring loaded and, at one end 54, runner 52 bears against the edge of the photosensitive surface 12. The other end of the arm is in the shape of the shutter 40 (or flag) which is disposed to gradually interrupt a beam of light from striking a detector as the photosensitive surface or belt edge moves progressively outward and rotates the arm 28 and shutter 40. The sensor 26 includes a housing 36 suitably mounted by a bracket 38 to a frame in close proximity to the photosensitive surface 12. An LED 42 projects a beam of light in the direction of photodetector 44 with shutter 40 mounted at one end of the arm 28 for interrupting or blocking the light from striking photo detector 44 depending upon the relative position or rotation of the arm 28 with respect to the photosensitive surface edge 50. The actuating arm 28 is secured to shaft 48 outside of the housing 36 and the shutter 40 is secured to a portion of the shaft 48 extending inside the housing 36. As the actuating arm moves or rotates about the point of the shaft 48 in relation to the position of the edge 50 of the photosensitive surface, the actuating arm 28 traces an arc about the shaft 48. This movement of the actuating arm 28 in turn rotates the shutter 40 to a position of more or less blocking of the light from the LED 42 striking the photo detector 44. A suitable skid or the runner 52 attached to the end 54 of the actuating arm 28 provides a suitable contact surface that tracks the edge 50 of the photosensitive surface with a minimum amount of edge wear or deterioration. Figures 4A, 4B, and 4C illustrate the belt edge steering sensor 26 in operation. In particular, Figure 4A illustrates the shutter 40 completely blocking the light path between the LED 42 and the photodetector 44 with the arm 28 at a very narrow angle a with respect to the edge 50 of the photosensitive surface 12 moving in the direction of arrow 14. This represents the edge 50 of the photoreceptor 12 at a given outward position or edge position in close proximity to the sensor 26. The complete blocking of the flux or light path of the LED 42 to the photodetector 44 results in a relatively low photodetector current. Figure 4C illustrates the position of the edge 50 of the photosensitive 12 at a relatively large angle α 2 with respect to the arm 28. In this position the shutter 40 is completely outside of the light path between the LED 42 and photodetector 44 and the edge 50 of the photosensitive surface is at an extreme inward position or relatively greater distance from the sensor 26. In this position the light emitted from LED 42 is completely received by the photodetector 44 and there is produced thereby a relatively large photodetector current. Figure 4B illustrates a nominal operating position wherein the arm 28 is at a position, angle α 1 , midway between the position shown in Figures 4A and 4C. This is a reference position or normal operating position with the shutter 40 part way between the light path from the LED 42 to the photodetector 44. From this position, it can be seen that movement of the edge 50 of the photosensitive surface 12 toward the sensor 26 will pivot the shutter 44 into a further blocking alignment between the LED 42 and shutter 44 and a movement of the edge 50 of the photosensitive surface away from the sensor 26 will result in less blockage of the light path as the shutter 40 moves or pivots away from the edge 50. The relationship of the photoreceptor surface edge 50 or photoreceptor position in relation to the photodetector 44 current is shown in Figure 5. The relatively low current is shown at A in relation to Figure 4A with the edge 50 in an extreme outer position or near position (α) to the sensor 26. High current as illustrated at C is equivalent to the large angle α 2 as illustrated in Figure 4C or an extreme innermost position of the edge 50 away from the sensor 26. The nominal operating position is generally illustrated at B as being generally a mid point or level of current between the two extreme positions. It will be understood that there is a relationship of the photodetector 44 current to the position of the edge 50 in relation to the sensor 26. A voltage signal corresponding to this photodetector current is fed from sensor 26 (as illustrated in Figure 1) and received by controller 30 to drive the steering roll 36 via the motor driver 32 and steering motor 34. Figure 5 illustrates the changing photodetector current in response to the changing position or rotation of the arm 28 of the sensor 26 as the belt edge position changes. In operation, the shutter 40 interrupts the beam of light between the emitter 42 and the detector 44 to varying degrees as the photosensitive surface 12 moves inward and outward rotating the arm and shutter. In one embodiment, there is a five degree total rotation of the shutter from a nominal position to provide the minimum and maximum current readings. Preferably, the sensor 26 includes a phototransistor as the detector 44 to provide high level signals and eliminate the need for further manipulation and buffering of signals at the sensor head. Also, the shutter 40, LED 42 and detector 44 are preferably enclosed in a small molded plastic housing to prevent toner from being deposited on the optical surfaces and blocking the LED light from reaching the detector 44. Further, the housing 36 provides mechanical support, alignment, and general mechanical protection. Figure 6 illustrates a typical sensor circuit. In particular, a plus 5 volts to ground parallel circuit includes the LED 42 and the photo transistor 44 and 1500 ohm resistor R1 and 200 ohm resistor R2. The output (V OUT ) at the collector of the photo transistor 44 is a function of the photo detector current through R1, i.e. V OUT = 5 - R1.I ph , where I ph is the photocurrent. The minimal voltage drop across resistor R1 is the result of the maximum light interruption by the shutter 40. On the other hand, with the high current flowing from the photodetector 44 shown in Figure 4C, there is a maximum voltage drop across resistor R1 or maximum current flow, and V OUT is at its minimum.

Claims: A sensor for tracking the position of an edge of a moving surface (12), comprising: an elongated arm (28) mounted for rotation about an axis (48) perpendicular to said surface, a first end (54) of the arm (28) being spring loaded into contact with said edge; electronic sensing means (42,44) for generating a signal indicative of the deviation of the position of said edge from a pre-determined position; an adjustment member (40), mechanically coupled to said arm (28), at a second end, opposite the first end thereof cooperating, in use, with the electronic sensing means (42,44). The sensor of claim 1, wherein: the electronic sensing means (42,44) comprises a LED (42) and a photodetector (44); and the adjustment member (40) comprises a shutter movable into and out of the light path between said LED (42) and said photodetector (44). The sensor of claims 1 or 2, wherein: the arm (28) and adjustment member (40) are mechanically connected to a shaft (48). The sensor of claim 1, 2 or 3, wherein: a contact member (52) is mounted on said first end (54) of the arm (28), for engaging said edge of the surface (12). A sensor for tracking the position of an edge of a moving photosensitive surface (12) comprising: an electro-optic sensor including an LED (42) and a photodetector (44), a shutter (40) mounted upon a shaft (48) for rotation in a light path between the LED and photodetector, an elongated arm (28) having one end mechanically connected to said shaft, and a contact member (52) secured to the other end (54) of the elongated arm (28) engaging the edge of the moving photosensitive surface (12) whereby deviations of the edge position of the photosensitive surface rotate the shutter (40) in relation to the light path between the LED (42) and photodetector (44). The sensor of claim 5 wherein the elongated arm (28) is spring loaded into contact with the edge of the photosensitive surface (12). The sensor of claim 5 or 6 wherein the signals generated by the photodetector (44) are a function of the relative deviation of the position of the edge from a standard position. The sensor of any of claims 4 to 7 wherein the contact member (52) is a smooth, rounded element. The sensor of any of the preceding claims, further comprising: a housing (36), a substrate disposed within the housing (36), the substrate supporting the LED and a photodetector, the shutter (40) being mounted upon a shaft (48) for rotation within the housing (36), a portion of the shaft (48) extending outside the housing (36), the elongated arm (28) being disposed outside the housing and having one end mechanically connected to said portion of the shaft (48). A system for correcting the position of an edge of a surface (12), comprising; a sensor according to any of the preceding claims; a steering roll (37) mechanically coupled to the surface (12) and a steering motor (34) connected to the steering roll whereby the position of the edge of the surface is changed in response to signals generated by said sensor; the system preferably further including a motor driver (32) connected to the steering motor (34) and a controller (30) electrically interconnected between the sensor and the motor driver (32) where the controller provides signals to the motor driver (32) in response to the signals generated by the sensor, to determine the corrective action of the steering roll.

Inventors: COSTANZA DANIEL W, FURST MICHAEL R, HINTON EDWARD T, HUBBLE FRED F III, COSTANZA, DANIEL W., FURST, MICHAEL R., HINTON, EDWARD T., HUBBLE, FRED F., III
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1995
Main classification: G03G15
IPC codes: G03G21, B65H23, G01B5, B65H5, G03G15