A method for determining cleaner retraction timing faults

Abstract: A method for determining cleaner retraction timing faults in an electrostatographic printer is described. A toner image (M to J) is developed on a moving photoreceptor surface during a non-printing mode of the printer. A retractable cleaner is operated to remove a portion (M to L, K to J) of the toner image and the remaining portion thereof is measured and compared to a predetermined length in order to determine timing faults associated with the cleaner subsystem of the electrostatographic printer.

Description: This invention relates to a method for determining cleaner retraction timing faults, particularly although not exclusively in an electrostatographic printer or copier. Cleaning systems consist in large part of two general types of cleaners. For low volume applications, blade cleaners are frequently used due to their low cost. For high volume applications, brush cleaners, either mechanical or biased electrostatic, are frequently used due to their reliability and life. In multi-pass color xerographic systems, retraction of these cleaners, from the photoreceptor, is required while the color images are being developed. These cleaners (e.g. brushes and blades) rely on mechanical mechanisms such as cams, linkages or slides to move the cleaning elements into and out of contact with the photoreceptor. The operating force for these mechanisms is normally supplied by electric motors and gear trains or solenoids. These mechanisms or devices can fail due to breakage or binding causing the cleaning elements to remain in either a retracted, or engaged position until repaired. The failure of these mechanisms can also cause the speed of the retraction and engagement motions to be reduced as a result of added frictional drag in the bearings, sliders, cams or seals due to contamination by toner, dirt or other debris. Furthermore, contamination can cause a change in the actuation speed generated by the electromechanical drive components. An example of this change in actuation speed, includes overheating a solenoid or motor which changes the force or torque output of the device or mechanism. Failures due to reduced actuation speed are more difficult to diagnose than failures that stop the cleaning elements completely. US-A-4 977 437 discloses an image recording apparatus for recording an image of an original on a developer sheet with the use of a microcapsule sheet, in which the developer sheet and the microcapsule sheet having a surface coated with immense number of photosensitive and pressure-rupturable microcapsules are subjected to pressure development by a pair of pressurizing rollers. To ensure that the pressure development is performed under the condition where the developer sheet and the microcapsule sheet are superposed one on the other, the nip and retract timings of the pressurizing rollers are determined. For example, the developer sheet is conveyed at a speed asynchronous with the microcapsule sheet conveying speed and the conveyance of the developer sheet is stopped after its leading edge is introduced between the rollers held in spaced apart condition. The rollers are brought to the nip position to thereby start the pressure development when the exposure start line on the microcapsule sheet is in alignment with the leading end of the developer sheet. The retract timing is determined, for example, depending upon the size of the developer sheet. In accordance with one aspect of the present invention, there is provided a method of removing particles from a moving photoreceptor surface with a retractable cleaner to determine the cycle timing for the engagement and retraction thereof, the method comprising the steps of: developing a toner image on the moving surface of a predetermined length; engaging the cleaner with the surface for a predetermined time at a predetermined position on the toner image to remove a portion thereof, the predetermined time being related to a distance of travel of the surface with the toner image thereon; retracting the cleaner from the surface; measuring the length of toner image remaining on the surface; and determining the cycle time from the measured length of toner image remaining on the surface. In another aspect of the present invention, there is provided a method for removing particles from a moving photoreceptor surface with a retractable cleaner to determine the engagement and retraction timing thereof the method comprising the steps of: retracting the cleaner from the surface while developing a toner image thereon, the toner image having a predetermined length; engaging the cleaner with the surface to remove a first predetermined measurable portion of the toner image; retracting and maintaining the cleaner in a retracted state over a distance equivalent to a second predetermined measurable portion of the toner image remaining on the surface; re-engaging the cleaner to remove the particles remaining on the surface from a third measurable portion of the toner image after passing the distance equivalent to the second predetermined measurable portion; and measuring a length of the toner image remaining on the surface which comprises the second predetermined measurable portion plus a length of the toner image remaining on the surface that occurs as the cleaner retracts away from and engages with the surface. In a further aspect of the present invention, there is provided a method for removing particles from a moving photoreceptor surface with a retractable cleaner to determine the engagement and retraction timing thereof, the method comprising the steps of: retracting the cleaner from the surface while developing a toner image thereon which has a predetermined length; maintaining full retraction of the cleaner over a distance equivalent to a first predetermined measurable portion of the toner image; engaging the cleaner with the surface to remove a second predetermined measurable portion of the toner image; retracting and maintaining the cleaner in the retracted state over a distance equivalent to a third measurable portion of the toner image remaining on the surface; and measuring a length of the toner image removed from the surface which comprises the second predetermined measurable portion plus a length of removed toner image from the surface that occurs as the cleaner engages with and retracts from the surface. In accordance with a second aspect of the present invention, there is provided a printing machine for carrying out the method as recited in any one of the preceding claims, the printing machine including: a moving photoreceptor surface; means for forming a toner image of a predetermined length on the photoreceptor surface; developer means for developing the toner image; a retractable cleaner for cleaning the photoreceptor surface; means for controlling the engagement and retraction of the retractable cleaner with respect to the photoreceptor surface to remove a portion of the toner image formed thereon; and measuring means for measuring the length of toner image remaining on the photoreceptor surface. For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure 1 is a schematic of the retracting and engaging cleaning motion of a cleaner in a multi-pass xerographic system; Figure 2A is a schematic of a retraction and engagement cycle time measurement in the present invention using a line image; Figure 2B is a schematic of a retraction and engagement cycle time measurement of the present invention using a band image; Figure 2C is a schematic of a retraction and engagement cycle time measurement of the present invention using a stripe image; Figures 3A to 3C show another embodiment of the retraction and engagement cycle time measurement by measuring the area cleaned of: the line image (3A), the band image (3B), or the stripe image (3C). Figures 4A to 4H are schematic representations of retraction and engagement measurements of developed images before cleaning and after cleaning; and Figure 5 is a schematic illustration of a printing apparatus incorporating the present invention. For a general understanding of a color electrostatographic printing or copying machine in which the present invention may be incorporated, reference is made to US-A-4 599 285 and US-A-4 679 929, which describe the image-on-image process having multi-pass development with single pass transfer. Although the cleaning method and apparatus of the present invention is particularly well adapted for use in a color electrostatographic printing or copying machine, it should become evident from the following discussion, that it is equally well suited for use in a wide variety of devices and is not necessarily limited to the particular embodiments shown and described herein. Referring now to the drawings, where the showings are for the purpose of describing a preferred embodiment of the invention and not for limiting same, the various processing stations employed in the reproduction machine illustrated in Figure 5 will be briefly described. A reproduction machine, from which the present invention finds advantageous use, utilizes a charge retentive member in the form of the photoconductive or photoreceptor belt 10 consisting of a photoconductive surface and an electrically conductive, light transmissive substrate mounted for movement past charging station A, and exposure station B, developer stations C, transfer station D, fusing station E and cleaning station F. Belt 10 moves in the direction of arrow 16 to advance successive portions thereof sequentially through the various processing stations disposed about the path of movement thereof. Belt 10 is entrained about a plurality of rollers 18, 20 and 22, the former of which can be used to provide suitable tensioning of the photoreceptor belt 10. Motor 23 rotates roller 18 to advance belt 10 in the direction of arrow 16. Roller 20 is coupled to motor 23 by suitable means such as a belt drive (not shown). As can be seen by further reference to Figure 5, initially successive portions of belt 10 pass through charging station A. At charging station A, a corona device such as a scorotron, corotron or dicorotron indicated generally by the reference numeral 24, charges the belt 10 to a selectively high uniform positive or negative potential. Any suitable control, well known in the art, may be employed for controlling the corona device 24. Next, the charged portions of the photoreceptor surface are advanced through exposure station B. At exposure station B, the uniformly charged photoreceptor or charge retentive surface 10 is exposed to a laser based input and/or output scanning device 25 which causes the charge retentive surface to be discharged in accordance with the output from the scanning device (for example, a two level Raster Output Scanner (ROS)). The photoreceptor, which is initially charged to a voltage, undergoes dark decay to a voltage level. When exposed at the exposure station B, it is discharged to near zero or ground potential for the image area in all colors. At development station C, a development system, indicated generally by the reference numeral 30, advances development materials into contact with the electrostatic latent images. The development system 30 comprises first 42, second 40, third 34 and fourth 32 developer apparatuses. (However, this number may increase or decrease depending upon the number of colors, i.e. here four colors are referred to, thus, there are four developer housings.) The first developer apparatus 42 comprises a housing'containing a donor roll 47, a magnetic roller 48, and developer material 46. The second developer apparatus 40 comprises a housing containing a donor roll 43, a magnetic roller 44, and developer material 45. The third developer apparatus 34 comprises a housing containing a donor roll 37, a magnetic roller 38, and developer material 39. The fourth developer apparatus 32 comprises a housing containing a donor roll 35, a magnetic roller 36, and developer material 33. The magnetic rollers 36, 38, 44, and 48 develop toner onto donor rolls 35, 37, 43 and 47 respectively. The donor rolls 35, 37, 43, and 47 then develop the toner onto imaging surface 11 of the photoreceptor belt 10. It is noted that development housings 32, 34, 40, 42, and any subsequent development housings must be scavengeless so as not to disturb the image formed by the previous development apparatus. All four housings contain developer material 33, 39, 45, 46 of selected colors. Electrical biasing is accomplished via power supply 41, electrically connected to developer apparatuses 32, 34, 40 and 42. Sheets of substrate or support material 58 are advanced to transfer D from a supply tray, not shown. Sheets are fed from the tray by a sheet feeder, also not shown, and advanced to transfer D through a corona charging device 60. After transfer, the sheet continues to move in the direction of arrow 62, to fusing station E. Fusing station E includes a fuser assembly, indicated generally by the reference numeral 64, which permanently affixes the transferred toner powder images to the sheets. Preferably, fuser assembly 64 includes a heated fuser roller 66 adapted to be pressure engaged with a back-up roller 68 with the toner powder images contacting fuser roller 66. In this manner, the toner powder image is permanently affixed to the sheet. After fusing, copy sheets are directed to a catch tray, not shown, or a finishing station for binding, stapling, collating, etc., (also not shown) and removal from the machine by the operator. Alternatively, the sheet may be advanced to a duplex tray (not shown) from which it will be returned to the processor for receiving a second side copy. A lead edge to trail edge reversal and an odd number of sheet inversions is generally required for presentation of the second side for copying. However, if overlay information in the form of additional or second color information is desirable on the first side of the sheet, no lead edge to trail edge reversal is required. Of course, the return of the sheets for duplex or overlay copying may also be accomplished manually. Residual toner and debris remaining on photoreceptor belt 10 after each copy is made, may be removed at cleaning station F with a brush or other type of cleaning system 70. The cleaning system is supported under the photoreceptive belt by two backers 160 and 170. Reference is now made to Figure 1, which shows the retracting and engaging cleaning motion of a cleaner. Multi-pass color xerographic systems require retraction of the cleaner (e.g. brush, blade) from the photoreceptor belt 10 while the color images are being developed. The dotted line 101 shows the cleaner motion in a multi-pass xerographic system. The dotted line 101 indicates retraction (by the distance away from the photoreceptor belt 10) of the cleaner over the image area 90 and the engagement of the cleaner with the photoreceptor belt 10 beginning in the interdocument zone 95 and remaining engaged to clean the residual image particles 91 after transfer of the image. The cleaner then retracts away from the photoreceptor belt 10 in the interdocument zone 95 as another image 90 is being developed with toner particles. In order to maintain a high level of productivity, the cleaning elements are required to engage and retract from the photoreceptor belt 10 within the normal interdocument zone 95. Since these interdocument zones 95 are fairly narrow in width, the engagement and retraction of the cleaning elements must occur rapidly and be timed so that all of the residual toner 91 left after transfer is removed and that none of the developed image 90 is removed before transfer. In the present invention, the cleaned length of the developed images are measured to verify the engagement and retraction timing of a retractable cleaner. This method is useful for dual as well as single element cleaners. The diagnostic measurements can be made manually by someone such as a technical representative or automatically by the copy machine through the use of an ESV (i.e. electrostatic voltmeter) or ETAC (i.e. electronic toner area coverage sensor). If the retraction timing is found to be in error, adjustments to the timing can be made either through input from the technical representative or automatically through the machine timing controller. Reference is now made to Figure 2, which shows a retraction and engagement cycle time measurement of the present invention. The present invention consists of developing a toner image on the photoreceptor belt, cleaning a portion of the image with a cleaner which is cycled through the retraction and engagement cycles and then examining the remaining image to determine if the retraction timing was correct. Combinations of several image types and several methods of examining the cleaner image are feasible. Examples of some of these images and methods are provided within this specification. Also, several options are available for use of the timing information once it has been measured. The toner image used must allow the measurement of distance along the photoreceptor belt in the process direction, which when the process speed is known can be converted to time (distance ÷ speed = time). The simplest image would be a line in the process direction, as shown in Figure 2A. As an example to determine if the retraction and engagement timing is working properly, the following test could be run. First, develop a line 50mm long (i.e. the original length of a developed line M to J). Next, engage the cleaning element to clean approximately the first 10mm of the line (M to L). Then, retract the cleaning element, and allow the cleaning element to remain retracted for a time equivalent to 10mm of photoreceptor belt travel (L to K). Next, engage the cleaning element and clean the end of the line (K to J). Then, measure the length of the line (L to K) which was not cleaned. Finally, the length of time required to perform the retraction and engagement cycles is equal to the remaining length of line on the photoreceptor belt minus the 10mm when the cleaning element was in the fully retracted position divided by the photoreceptor speed; cycle time = (line length (L to K) - 10mm)/photoreceptor belt speed. In the example shown in Figure 2A, the length of line which is not cleaned, L to K, is 25mm, and the cycle time = 15mm/(photoreceptor belt speed). Other ways the image could be shown include a band in the process direction (see Figure 2B) or a series of parallel lines perpendicular to the process direction (see Figure 2C). The lines of Figure 2C may be convenient in that counting the number of lines remaining, subtracting the lines passing under the cleaning element during the retracted dwell time and multiplying by the time for the photoreceptor belt to travel the spacing between the lines yields the cycle time. If the measurement of the remaining portion of the image is to be made manually (e.g. by a technical representative), then counting lines would perhaps be easier than measuring the length of a band or line. With known dwell time and photoreceptor speeds, the tech rep would compare the number of lines counted to a specification range. The number of lines less than or greater than the specification value could also indicate the change required in timing NVM (i.e. non-volatile memory) parameters. A similar procedure could be followed if the length of a band or line is measured with a ruler. The length of the remaining portion of the image could also be measured by an ESV, and ETAC or some other type of sensor positioned above the photoreceptor surface. The machine software could compute the value and display the result to the tech rep for corrective action if required. Or, the machine could automatically make the measurement and automatically make any corrections to the cleaner retraction cycle timing in order to operate within specifications. This type of self-correcting measurement and action could be taken at infrequent intervals because of the expected slow changes in retraction performance. This would result in very small impacts on toner consumption and copy productivity. If only one end of the image is cleaned rather than both ends, then the retraction and engagement times can be determined separately. For example, in Figure 2A, instead of cleaning the image from J to K and then from L to M, the engagement would start at some predetermined time after the image had passed under the blade and only clean from L to M. The length of the remaining image minus the dwell length before the engagement cycle was started now represents the time for the cleaner to engage and clean the photoreceptor belt. A similar procedure could be used on the right side of the image in Figure 2A to determine the amount of time required to retract the cleaner. In both retraction and engagement cases, the length of the image remaining is determined by the cleaner motion speed and the accuracy with which the length of image developed can be coordinated with the retraction or engagement signal to the cleaner. If required, the needed accuracy can be obtained by storing a reference image length in the machine memory. When this test is performed under known conditions,, a reference image length of image developed can also be coordinated with the retraction or engagement signal to the cleaner. If required, the needed accuracy can also be obtained by storing a reference image length in the machine memory when this test is performed under known "in specification conditions" such as in final test in manufacturing. Registration requirements for color printing, however, make it likely that the timing of the cleaner motions to the position of the image under the cleaner can be controlled accurately enough. Another embodiment of the present invention is shown in Figures 3A to 3C. In Figures 3A to 3C, rather than measuring the length of toner remaining on the photoreceptor as in Figures 2A to 2C, the length of cleaned area on the photoreceptor belt is measured using the same method described with reference to Figures 2A to 2C. For example, the developed toner line M to J is still 50mm, but the cleaner is initially retracted for 10mm (M to L), engaged for a time equivalent to 10mm of photoreceptor belt travel (L to K), and then retracted for the remaining time (K to J). As before, in the example shown in Figure 3A, the cycle time is 15mm/(photoreceptor belt speed). If the image position to cleaner motion start can be controlled accurately, then even simpler measurements can be made. For example, rather than using the long length of the developed image shown in Figures 2A to 2C, a short segment of image developed around the engagement and retraction locations on the photoreceptor belt can be used. An example of this shorter length segment is shown by the series of Figures 4A to 4H. Figure 4A shows the engagement target band of lines after developing images before cleaning. Figure 4B shows the retraction target band before cleaning. When the engagement and retraction of the cleaner is within timing specifications, one set of long lines and one set of short set of lines remains on the photoreceptor after cleaning, as shown in Figures 4C and 4D. However, when the mechanisms for retraction and engagement are out of specification, the lines remaining either have two sets of long lines as in Figures 4E (i.e. engagement of the cleaner is too late) and 4F (i.e. retraction of the cleaner is too early), or have no short lines remaining as shown in Figure 4G (i.e. engagement of the cleaner is too early) and 4H (i.e. retraction of the cleaner is too late). As an automatic control method the lines could be counted by a sensor or the distance of a solid band could be measured. It is, therefore, apparent that there has been provided in accordance with the present invention, a method for identifying cleaner retraction timing faults that fully satisfies the aims and advantages hereinbefore set forth. While this invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art.

Claims: A method of removing particles from a moving photoreceptor surface (10, 11) with a retractable cleaner (70) to determine the cycle timing for the engagement and retraction thereof, the method comprising the steps of: developing a toner image on the moving surface (10, 11) of a predetermined length; engaging the cleaner (70) with the surface for a predetermined time at a predetermined position on the toner image to remove a portion thereof, the predetermined time being related to a distance of travel of the surface (10, 11) with the toner image thereon; retracting the cleaner (70) from the surface (10, 11); measuring the length of toner image remaining on the surface (10, 11); and determining said cycle timing of said cleaner (70) from the measured length of toner image remaining on the surface (10, 11). A method for removing particles from a moving photoreceptor surface (10, 11) with a retractable cleaner (70) to determine the engagement and retraction timing thereof, the method comprising the steps of: retracting the cleaner (70) from the surface (10, 11) while developing a toner image thereon, the toner image having a predetermined length; engaging the cleaner (70) with the surface (10, 11) to remove a first predetermined measurable portion of the toner image; retracting and maintaining the cleaner (70) in a retracted state over a distance equivalent to a second predetermined measurable portion of the toner image remaining on the surface (10, 11); re-engaging the cleaner (70) to remove the particles remaining on the surface (10, 11) from a third measurable portion of the toner image after passing the distance equivalent to the second predetermined measurable portion; measuring a length of the toner image remaining on the surface (10, 11) which comprises the second predetermined measurable portion plus a length of the toner image remaining on the surface (10, 11) that occurs as the cleaner (70) retracts away from and engages with the surface (10, 11); and determining said engagement and retraction timing of said cleaner (70) from the measure of said length of toner image remaining on the surface (10, 11). A method as recited in claim 2, further comprising the step of determining the timing by setting a length of time required to perform retraction and engagement cycles equal to the length of the toner image remaining on the surface (10, 11) less the second predetermined measurable portion of the toner image after the cleaner (70) has been fully retracted divided by a speed of the moving surface (10, 11). A method for removing particles from a moving photoreceptor surface (10, 11) with a retractable cleaner (70) to determine the engagement and retraction timing thereof, the method comprising the steps of: retracting the cleaner (70) from the surface (10, 11) while developing a toner image thereon which has a predetermined length; maintaining full retraction of the cleaner (70) over a distance equivalent to a first predetermined measurable portion of the toner image; engaging the cleaner with the surface (10, 11) to remove a second predetermined measurable portion of the toner image; retracting and maintaining the cleaner (70) in the retracted state over a distance equivalent to a third measurable portion of the toner image remaining on the surface (10, 11); measuring a length of the toner image removed from the surface (10, 11) which comprises the second predetermined measurable portion plus a length of removed toner image from the surface (10, 11) that occurs as the cleaner (70) engages with and retracts from the surface (10, 11); and determining said engagement and retraction timing from the measure of said length of the toner image removed from the surface (10, 11). A method as recited in claim 4, further comprising the step of determining the timing by setting a length of time required to perform retraction and engagement cycles equal to the length of the toner image removed from the surface (10, 11) less the second predetermined measurable portion of the toner image after the cleaner (70) has been fully engaged divided by a speed of the surface (10, 11). A printing machine for carrying out the method as recited in any one of the preceding claims, the printing machine including: a moving photoreceptor surface (10, 11); means (25) for forming a toner image of a predetermined length on the photoreceptor surface (10, 11); developer means (30) for developing the toner image; a retractable cleaner (70) for cleaning the photoreceptor surface (10, 11); means for controlling the engagement and retraction of the retractable cleaner with respect to the photoreceptor surface (10, 11) to remove a portion of the toner image formed thereon; and measuring means for measuring the length of toner image remaining on the photoreceptor surface (10, 11). A printing machine as recited in claim 6, wherein the measuring means comprises a measurement sensor. A printing machine as recited in claim 7, wherein the measurement sensor enables calculation of retraction timing of the retractable cleaner by setting a length of time required to perform retraction and engagement cycles equal to the length of the toner image on the surface (10, 11) less the second predetermined measurable portion of the toner image after the cleaner (70) has been fully retracted divided by a speed of the photoreceptor surface (10,11). A printing machine as recited in any one of claims 6 to 8, wherein the retractable cleaner (70) comprises a brush. A printing machine as recited in any one of claims 6 to 8, wherein the retractable cleaner (70) comprises a blade.

Inventors: GERBASI DENNIS G, THAYER BRUCE E, GERBASI, DENNIS G., THAYER, BRUCE E.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1997
Main classification: G03G21
IPC codes: G03G21