Patent Grant
8570587
The field of the present invention relates generally to sensing the velocity of a moving surface and, more particular, to a motion sensor to detect the passage of registration marks formed around the circumference of a photoreceptor belt in a xerographic printing apparatus to measure the speed of the belt.
In printing systems that utilize an elongate image receiving surface, such as a paper web or a belt, the receiving surface reaches a first marking station where a marking material of a first color is applied to the surface, e.g., by firing ink jets, exposing an image on a photoconductive material, or applying toner particles to a selectively imaged photoconductive member. The receiving surface then moves on to a second marking station, where an image or marking material of a second color is applied, and so forth, depending on the number of colors. The timing of the actuation of the second marking station is controlled as a function of the speed of the image receiving surface so that the images applied by the two marking stations are registered one on top of the other to form a composite, multicolor image. A high degree of process direction alignment can be achieved by knowing the speed or position of the image receiving surface. Currently the speed is measured with an encoder at a certain location and then the images are timed accordingly. For example, an encoder is associated with a drive nip roller. The rotational speed of the roller is used to calculate the speed of the image receiving surface passing through the nip. The time for actuating the first, second, and subsequent marking stations is then calculated, based on their respective distances from the drive nip roller and the determined speed of the image receiving surface.
In the case of an electrophotographic printer, an encoder may be placed on the photoreceptor belt to measure the exact speed of the belt at each instant of time. Additional techniques for determining photoreceptor speed include calculation based on belt module encoder frequency, encoder roll diameter, and photoreceptor belt thickness. The photoreceptor speed can then be used to time the firing of the laser raster output scanner (ROS) or light emitting diode (LED) bar so that an even spacing of lines is imaged on the photoreceptor. The surface speed calculation is also used for sensor timing, image sync generation, calculations for image on paper setup, and speed matching with the media path. While adequate for current printing process speeds, the current techniques would not be adequate for designs that need an increase in process speed. Because current speed calculations are based on nominal values, they tend to produce photoreceptor speed calculations with variability or tolerances that are not within an acceptable range.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a more accurate measurement of photoreceptor speed.
The disclosure relates to method and apparatus for sensing the movement of a moving surface by utilizing a plurality of reference patterns positioned on the surface, using the precision of the ROS Start of Scan Clock, an encoder and an MOB sensor. The plurality of reference patterns are placed a known number of scanlines apart. The MOB sensor and encoder measure the distance between reference patterns. Increased accuracy is achieved by sampling the encoder signal with the ROS Master Clock and calculating a fractional encoder count at the first and last encoder counts of the measurement. The use of fractional encoder counts provides a speed measurement with greater tolerance for variations in encoder dimensions and belt thickness.
While the present invention will be described in connection with preferred embodiments thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
Aspects of the disclosed embodiments relate to method and apparatus to measure the speed of a moving surface having a primary movement direction. The apparatus comprises a plurality of reference patterns formed of slant lines provided on the moving surface, wherein the plurality of reference patterns are placed a predetermined distance apart on the moving surface; a sensor to detect the plurality of reference patterns being moved on the moving surface, wherein the sensor produces a timestamp when it detects a reference pattern; an encoder coupled to a drive system of the moving surface, the encoder generating encoder pulses; an ROS master clock to generate discrete clock pulses; and a logic circuit coupled to the sensor, the encoder, and the master clock to determine the speed of the moving surface by: counting the number of encoder pulses generated by the encoder between a first timestamp and a second timestamp; determining a leading fractional encoder count relative to the first time stamp; determining a trailing fractional encoder count relative to the second time stamp; and determining an elapsed interval of time between the first timestamp and the second timestamp.
In yet another aspect, the disclosed embodiment the apparatus uses a logic circuit such as field programmable gate array (FPGA), application specific integrated circuit (ASIC), or complex programmable logic device (CPLD) to determine the speed of the moving surface.
In still another embodiment, the plurality of reference patterns are arranged in a chevron pattern of regularly spaced stripes.
In a further disclosed embodiment, the apparatus determines a leading fractional encoder by counting the discrete clock pulses that occur between the first time stamp and a next encoder pulse.
In another disclosed embodiment, the apparatus determines a trailing fractional encoder count by counting the discrete clock pulses that occur between the second time stamp and a next encoder pulse.
In another aspect, the disclosed embodiment, the apparatus further comprises a controller to control a printing system based on the determined speed of the moving surface.
In another aspect, the disclosed embodiment is a method to determine the speed of a moving surface having a primary movement direction. The method comprises receiving from a sensor a plurality of timestamps indicative of a plurality of reference patterns being moved on the moving surface; receiving encoder pulses from an encoder associated with the moving surface; receiving discrete clock pulses from an ROS master clock; and processing with a logic unit the received timestamps, encoder pulses, and discrete clock pulses to determine the speed of the moving surface by: counting the encoder pulses generated between a first timestamp and a second timestamp; determining a leading fractional encoder count relative to the first time stamp; determining a trailing fractional encoder count relative to the second time stamp; determining an elapsed interval of time between the first timestamp and the second timestamp.
In another aspect, the disclosed embodiment is a document processing system that comprises a photoreceptor that continuously moves along a closed path; at least one raster output scanner (ROS) located along the closed path of the photoreceptor, the ROS operable to generate a latent image on a portion of the photoreceptor based on a clock input; a clock providing a clock output signal to the ROS; a sensor to detect a plurality of reference patterns being moved on the photoreceptor, wherein the sensor produces a timestamp when it detects a reference pattern; an encoder coupled to the photoreceptor, wherein movement of the photoreceptor causes the encoder to generate encoder pulses; a controller coupled with the ROS to selectively operate the document processing system according to a photoreceptor speed; and logic circuit to determine photoreceptor speed from the encoder pulses, the timestamp, and the clock output signal by: counting the number of encoder pulses generated by the encoder between a first timestamp and a second timestamp; determining a leading fractional encoder count relative to the first time stamp; determining a trailing fractional encoder count relative to the second time stamp; and determining an elapsed interval of time between the first timestamp and the second timestamp.
Embodiments as disclosed herein may also include computer-readable media for carrying or having computer-executable instructions or data structures stored thereon for operating such devices as controllers, sensors, and eletromechanical devices. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code means in the form of computer-executable instructions or data structures. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or combination thereof) to a computer, the computer properly views the connection as a computer-readable medium. Thus, any such connection is properly termed a computer-readable medium. Combinations of the above should also be included within the scope of the computer-readable media.
The term “printing system” as used herein refers to a digital copier or printer, image printing machine, digital production press, image reproduction machine, bookmaking machine, facsimile machine, multi-function machine, or the like and can include several marking engines, feed mechanism, scanning assembly as well as other print media processing units, such as paper feeders, finishers, and the like.
The term “Print job” or “document” can include a plurality of digital pages or electronic pages to be rendered as one or more copies on a set of associated sheets of print media, each page, when rendered constituting the front or backside of a sheet. The pages of a print job may arrive from a common source and, when rendered, be assembled at a common output destination. The term “print media” generally refers to a usually flexible, sometimes curled, physical sheet of paper, plastic, or other suitable physical print media substrate for images, whether precut or web fed.
The printing system preferably uses a charge retentive surface in the form of an Active Matrix (AMAT) photoreceptor belt 410 supported for movement in the direction indicated by arrow 412, for advancing sequentially through the various xerographic process stations. The belt is entrained about a drive roller 414, tension roller 416 and fixed roller 418 and the drive roller 414 is operatively connected to a drive motor 420 for effecting movement of the belt through the xerographic stations. A portion of belt 410 passes through charging station A where a corona generating device, indicated generally by the reference numeral 422, charges the photoconductive surface of photoreceptor belt 410 to a relatively high, substantially uniform, preferably negative potential.
Next, the charged portion of photoconductive surface is advanced through an imaging/exposure station B. At imaging/exposure station B, a controller, indicated generally by reference numeral 490, receives the image signals from Print Controller 630 representing the desired output image and processes these signals to convert them to signals transmitted to a laser based output scanning device, which causes the charge retentive surface to be discharged in accordance with the output from the scanning device. Preferably, the scanning device is a laser Raster Output Scanner (ROS) 424. Alternatively, the ROS 424 could be replaced by other xerographic exposure devices such as LED arrays.
The photoreceptor belt 410, which is initially charged to a voltage V0, undergoes dark decay to a level equal to about −500 volts. When exposed at the exposure station B, it is discharged to a level equal to about −50 volts. Thus after exposure, the photoreceptor belt 410 contains a monopolar voltage profile of high and low voltages, the former corresponding to charged areas and the latter corresponding to discharged or developed areas.
At a first development station C, developer structure, indicated generally by the reference numeral 432 utilizing a hybrid development system, the developer roller, better known as the donor roller, is powered by two developer fields (potentials across an air gap). The first field is the AC field which is used for toner cloud generation. The second field is the DC developer field which is used to control the amount of developed toner mass on the photoreceptor belt 410. The toner cloud causes charged toner particles to be attracted to the electrostatic latent image. Appropriate developer biasing is accomplished via a power supply. This type of system is a non-contact type in which only toner particles (black, for example) are attracted to the latent image and there is no mechanical contact between the photoreceptor belt 410 and a toner delivery device to disturb a previously developed, but unfixed, image. A toner concentration sensor 200 senses the toner concentration in the developer structure 432.
The developed but unfixed image is then transported past a second charging device 436 where the photoreceptor belt 410 and previously developed toner image areas are recharged to a predetermined level.
A second exposure/imaging is performed by device 438 which comprises a laser based output structure is utilized for selectively discharging the photoreceptor belt 410 on toned areas and/or bare areas, pursuant to the image to be developed with the second color toner. At this point, the photoreceptor belt 410 contains toned and untoned areas at relatively high voltage levels, and toned and untoned areas at relatively low voltage levels. These low voltage areas represent image areas which are developed using discharged area development (DAD). To this end, a negatively charged, developer material 440 comprising color toner is employed. The toner, which by way of example may be yellow, is contained in a developer housing structure 442 disposed at a second developer station D and is presented to the latent images on the photoreceptor belt 410 by way of a second developer system. A power supply (not shown) serves to electrically bias the developer structure to a level effective to develop the discharged image areas with negatively charged yellow toner particles. Further, a toner concentration sensor 200 senses the toner concentration in the developer housing structure 442.
The above procedure is repeated for a third image for a third suitable color toner such as magenta (station E) and for a fourth image and suitable color toner such as cyan (station F). The exposure control scheme described below may be utilized for these subsequent imaging steps. In this manner a full color composite toner image is developed on the photoreceptor belt 410. In addition, a mass sensor 110 measures developed mass per unit area. Although only one mass sensor 110 is shown in
To the extent to which some toner charge is totally neutralized, or the polarity reversed, thereby causing the composite image developed on the photoreceptor belt 410 to consist of both positive and negative toner, a negative pre-transfer dicorotron member 450 is provided to condition the toner for effective transfer to a substrate using positive corona discharge.
Subsequent to image development a sheet of support material 452 is moved into contact with the toner images at transfer station G. The sheet of support material 452 is advanced to transfer station G by a sheet feeding apparatus 500, described in detail below. The sheet of support material 452 is then brought into contact with photoconductive surface of photoreceptor belt 410 in a timed sequence so that the toner powder image developed thereon contacts the advancing sheet of support material 452 at transfer station G.
Transfer station G includes a transfer dicorotron 454 which sprays positive ions onto the backside of sheet 452. This attracts the negatively charged toner powder images from the photoreceptor belt 410 to sheet 452. A detack dicorotron 456 is provided for facilitating stripping of the sheets from the photoreceptor belt 410.
After transfer, the sheet of support material 452 continues to move, in the direction of arrow 458, onto a conveyor (not shown) which advances the sheet to fusing station H. Fusing station H includes a fuser assembly, indicated generally by the reference numeral 460, which permanently affixes the transferred powder image to sheet 452. Preferably, fuser assembly 460 comprises a heated fuser roller 462 and a backup or pressure roller 464. Sheet 452 passes between fuser roller 462 and backup roller 464 with the toner powder image contacting fuser roller 462. In this manner, the toner powder images are permanently affixed to sheet 452. After fusing, a chute, not shown, guides the advancing sheet 452 to a catch tray, stacker, finisher or other output device (not shown), for subsequent removal from the printing machine by the operator.
After the sheet of support material 452 is separated from photoconductive surface of photoreceptor belt 410, the residual toner particles carried by the non-image areas on the photoconductive surface are removed therefrom. These particles are removed at cleaning station I using a cleaning brush or plural brush structure contained in a housing 466. The cleaning brushes 468 are engaged after the composite toner image is transferred to a sheet.
Controller 490 regulates the various printer functions. The controller 490 is preferably a programmable controller, which controls printer functions hereinbefore described. The controller 490 may provide a comparison count of the copy sheets, the number of documents being recirculated, the number of copy sheets selected by the operator, time delays, jam corrections, and the like. The control of all of the exemplary systems heretofore described may be accomplished by conventional control switch inputs from the printing machine consoles selected by an operator. Conventional sheet path sensors or switches may be utilized to keep track of the position of the document and the copy sheets.
FPGA Module 496 determines the speed of photoreceptor belt 410 from data provided primarily from an encoder, ROS master clock (RMC), and an MOB sensor. The Field Programmable Gate Array (FPGA) provides controller 490 with the calculated speed of the photoreceptor belt. The controller uses the calculated speed to generate a control parameter to influence the printing process.
In eight pitch mode, an FPGA generates eight (8) photoreceptor speed measurements around the belt circumference. The exemplary photoreceptor belt 410 includes a plurality of image panel zones 202, 206, 208 in which ROS 424 generates latent images, where two exemplary panel zones 202 and 208 are illustrated in partial views. Any number of panels may be defined along the circuitous length of the photoreceptor belt 410, and the number may change dynamically based on the size of the print media being fed to the transfer mechanism, where the illustrated photoreceptor belt 410 includes about eight (8) such zones to accommodate two chevron marks per panel, where the distance between the marks is one encoder roll circumference. The panel zones are separated from one another by inter panel zones, where two exemplary inter panel zones IDZ1 and IDZ2 are shown. In operation, the controller provides ROS 424 with one or more control signals through driver 255, including a control parameter associated with each upcoming image panel zone to indicate whether a latent image to be generated on the upcoming panel zone is to be fixed to a first side or to a second side. Based on this control parameter, the ROS 424 selects the clock output signals from RMC 235 for use in generating a latent image on the upcoming panel zone.
The exemplary photoreceptor belt 410 includes a plurality of image panel zones 202, 206, 208 in which ROS 424 generates latent images, where two exemplary panel zones 202 and 208 are illustrated in partial views. Any number of panels may be defined along the circuitous length of the photoreceptor belt 410, and the number may change dynamically based on the size of the print media being fed to the transfer mechanism, where the illustrated photoreceptor belt 410 includes about eight (8) such zones to accommodate two chevron marks per panel, where the distance between the marks is one encoder roll circumference. The panel zones are separated from one another by inter panel zones, where two exemplary inter panel zones IDZ1 and IDZ2 are shown. In operation, the controller provides ROS 424 with one or more control signals through driver 255, including a control parameter associated with each upcoming image panel zone to indicate whether a latent image to be generated on the upcoming panel zone is to be fixed to a first side or to a second side. Based on this control parameter, the ROS 424 selects the clock output signals from RMC 235 for use in generating a latent image on the upcoming panel zone.
In determining photoreceptor speed an MOB sensor signal, a PR Encoder 230 signal, and a ROS Master Clock (RMC) 235 signal is processed by an FPGA (Field Programmable Gate Array) module, ASIC circuit and the like. In the iGen family of printers the FPGA already exists on the MIOP Board. The RMC 235 is a high speed clock which is also used to drive the ROS motor polygon assembly (MPA). The MOB sensor 218 read the chevrons 212. The MOB sensor 218 produces a timestamp 220 as the centroid 222 of the chevron mark passes and this timestamp is sent to the FPGA module. MOB sensors used on belts are shown in U.S. Pat. No. 6,292,208, which is incorporated by reference. The FPGA module can now count the number of roll encoder 230 counts between the marks. During a calibration cycle the FPGA measures and stores the RMC counts in 18432 PRMC, which represents 18 revolutions of the photoreceptor (PR) encoder at 1024 PR Encoder lines/rev. Additionally, the FPGA module can count the number of RMC 236 counts from the first mark or first timestamp to the next encoder count and from the last mark or second timestamp to the next encoder count. Note that the FPGA also divides the ROS Master Clock (RMC) signal down by 256 in order to get units of 256RMC. From this a leading fractional encoder count relative to the first time stamp and a trailing fractional encoder fractional encoder count can be calculated. Accuracy in determining photoreceptor belt speed is increased by using chevrons placed one encoder circumference apart and by using the fractional encoder counts and ROS master clock.
In terms of the plurality of reference patterns the velocity of the belt is expressed as:
In order to perform the above calculation a lookup table (LUT) 10 is populated with values needed internally by the FPGA to perform the calculations. These values can be populated by controller 490 through line 15 or the values could be calculated on the FPGA from the received RMC, roll encoder, and MOB sensor signals.
Multiplier 40 calculates ChevronImageTime by multiplying the distance between chevron marks 214 (ChevronDistScanlines 42) and the TimeperScan. Divider 30 determines TimePerScan from the number of RMC counts in a scan (RMC/Scan) 11 and the number of RMC counts in a second (RMC/second) 12, which are both taken from LUT 10. TimePerScan is in the range of 150-200 Microseconds (μsecs). ChevronImageTime is roughly two thirds (⅔) of a second because there are roughly 7276 scanlines between the chevrons (ChevronDistScanlines 42).
Chevron distance is determined from the following relationship:
Where:
WholeEncoderCnt 72 is Number of whole encoder counts between the chevron marks (Timestamp1305 and Timestamp2315) detected by MOB Sensor 218. SPBeltEncoderResolution is the nominal roll encoder 230 resolution in MachineClocks/mm. PRMCScalingFactor is a Scaling factor calculated based on encoder measurement using the ROS Master clock (RMC 235) and the nominal value for RMC 235. The SP_BeltEncoderResolution and the PRMCScalingFactor is supplied by LUT 10 through line 79 as a composite value. By multiplying by this factor, any error due to the Belt Control board is removed.
The fractional encoder count is a sampling of the encoder signal so as to mitigate circumstances where the encoder pulses are only partially within the defined range. The fractional encoder count is calculated from the following mathematical relationship:
Where:
LFEC 22 is the Number of RMC Counts from the first mark 325 to the next Encoder Count.
TFEC 23 is the Number of RMC Counts from the second mark 327 to the next Encoder Count. Further, note that in the above equation this number is subtracted 24 from the average 62 of NVM23524_RmcBlockToPRmcRatio.
NVM23524_RmcBlockToPRmcRatio*256 is Total Number 21 of RMC in one encoder count. This is an average number 62 that is calculated in the printing system and stored in a non-volatile memory (NVM).
NVM23524_RmcBlockToPRmcRatio is the RMC count divided into 256*18432 PRMC slots.
Although the illustrated hardware embodiment, such as shown in
Although specific embodiments of the present technology have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the technology is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.
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