MXPA99008349A - Electronic solution for the defective, non-linear recording of tr exit device devices - Google Patents

Abstract

An electronic circuit is used to correct a defective register of a frame output scanning device. The circuit uses a main clock generator, to generate a main clock. Only during the time that a scan line is scanned, the frequency of the main clock is modulated, according to a correction curve. Between every two consecutive scan lines, the frequency of the main clock is calibrated at a reference frequency. This allows each scan line to receive a main clock, with the same frequency, at the beginning of the scan line.

Description

ELECTRONIC SOLUTION FOR THE DEFECTIVE, NON-LINEAR RECORD OF SCREEN EXPLORATION DEVICES BACKGROUND OF THE INVENTION This invention relates to a process for recording in a color xerographic printing system, and more particularly, to a system, which uses electronic devices to correct the defective records between the same pixels of different colors. It should be noted that from here on, for the purpose of simplification, that "xerographic color printing system" refers to the "color printing system". Typically, a color printing system comprises a photoreceptor and four color stations. Each color station, which is dedicated to a single color, comprises a frame output scan (ROS) device. With reference to Figure 1, a tangential view (fast scan) of a prior art screen scanning device 10 of a printing system is shown. The frame scanning system 10 utilizes a laser light source 12, a collimator 14, prepolygonal optical devices 16, a multi-faceted rotating polygonal mirror 18 as the scanning element, optical devices posterior to the polygon 20, and a photosensitive medium 22. REF .: 30872 The laser light source 12 sends a beam of light 24 to the rotating polygonal mirror 18, through the collimator 14 and the optical devices subsequent to the polygon 16. The collimator 14, collimates the light beam 24 and the optical devices prior to the polygon 16 focus the light beam 16 in the sagittal or transverse plane in the rotating polygonal mirror 18. The facets 26 of the rotating polygonal mirror 18, reflect the light beam 24, and also make the reflected light beam rotate around an axis near the reflection point of facet 26. The reflected light beam 24 is used through the optical devices posterior to the polygon 20 to explore a ed photosensitive 22, such as a xerographic drum (photoreceptor). Since the photoreceptor 22 moves, the light beam scans all scan lines of a document in the photoreceptor and generates a latent image. Typically, in a color printing system, a latent image is generated for each basic color and each latent image is placed on the previous latent images. After the first latent image has been generated and developed, the modulated light beam of the next ROS will begin to generate a new latent image on the first latent image. In this way, each of the following stations generates and reveals a latent image on the previous latent images. The process of generating and revealing a latent image is repeated four times, one for each of the stations, for four different colors (usually cyan (greenish blue), yellow, magenta and black). After the four different colors of organic pigment have been placed one on top of the other, the organic pigments will be transferred to a sheet of paper. Since each latent image is generated on the previous latent image, the placement of each pixel of each latent image on the same pixel of the previous latent image / images is too critical. However, due to the movement of the photoreceptor band and the tolerances of the optical elements of each ROS system, the location of the pixels of each latent image may be slightly different from the location of the pixels of the first latent image. This causes a problem known as a faulty registry. Faulty registration can occur in two ways: linear and non-linear. The linear faulty registration occurs when the distances between the adjacent pixels are equal, but the pixels are not placed precisely on the pixels of the previous latent image. Non-linear faulty registration occurs when the distances between the adjacent pixels of each scanning line of a latent image, it varies. The degree of variation of the distances between the adjacent pixels may be different for each latent image. This, in turn, can magnify the problem of defective registration. The defective, non-linear registration, in the fast scan or the direction of the scan, is difficult to correct by optical solutions. Due to the tolerances of the different elements, the four ROS systems of each printing system may not be identical. Therefore, each ROS system produces a different non-linear error. The correction of the four different errors, non-linear, through optical solutions is not feasible. Typically, optical solutions minimize non-linear faulty registration to approximately 100 microns, but do not reduce errors sufficiently. The electronic solutions provide a more precise correction, since an individual correction curve is applied to each scan line of each ROS system. In order to electronically correct the non-linearity of the defective register in the direction of the rapid scan,. it is necessary to vary the synchronization between the pulses of the pixel clock. The pixel clock pulses, which indicate the location of each pixel, are used to modulate the pixel information in the laser light beam.

Typically, the clock pulses have an equal timing, and therefore, they modulate the information in the laser light beam at fixed intervals. However, due to the errors of the non-linear faulty registers, the pixels of a scan line are not placed at equal distances in a photoreceptor. Therefore, in order to match the pixels of the following latent images, the clock frequency will vary according to the pixel placement of the same scanning line of the previous latent image. This causes the pixel information to be modulated in the laser light beam at different intervals. Therefore, by varying the synchronization between the pulses (frequency modulation), the pixels can be placed in the desired places. The electronic correction of defective, non-linear records has several obstacles. With high resolutions, such as 600 pixels per inch, it is extremely difficult to vary the frequency of the clock generator at such a high speed. Also, due to clock generator tolerances, in addition to frequency modulation, the clock output of the pixel will deviate from the reference frequency, and therefore, it will introduce an error in the placement of the pixels. It is an object of this invention to provide an electronic solution to substantially reduce the problem of defective registration to less than 20 microns. Another object of this invention is to provide an electronic solution, which is capable of varying the high frequency (54 MHz), by increments of about 10 kHz, for a total peak-to-peak variation of about 3 MHz.

BRIEF DESCRIPTION OF THE INVENTION According to the present invention, an electronic circuit is described to correct the defective, non-linear register. The electronic circuit comprises a clock generator, a calibration means and a correction means. The calibration means is electrically connected to the clock generator to calibrate the clock frequency at a given frequency. The correction means is electrically connected to the clock generator to provide an individual correction curve for each scan line to modulate the frequency of the clock generating medium, for each scan line, according to a respective correction curve. The clock generator means, the calibration means and the correction means are connected to each other in such a way that the clock frequency is modulated during the time that a scan line is scanned and calibrated to the frequency given between two consecutive scan lines. In accordance with another aspect of this invention, a method for correcting the nonlinear defective registration of a scan line of a frame output scanning device is described. The method comprises the steps of generating a clock frequency, modulating the clock frequency for each scanning line, according to a respective correction curve, stopping the modulation at the end of each scan line, calibrating the clock frequency to a given frequency, before the start of the next scan line, and repeat the modulation and calibration for all scan lines of a page.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a tangential view (fast scan) of a prior art screen output scanning device, of a printing system; Figure 2 shows a block diagram of a ROS interface or interconnect module board of this invention, and Figure 3 shows a correction curve, which is used to modulate the frequency of the Mclk main clock.

DESCRIPTION OF THE PREFERRED MODE With reference to Figure 1, a block diagram 40 of a ROS interface or interconnect module board of this invention is shown. In Figure 2, a voltage controlled oscillator (VCO) 42 and a closed circuit are used per phase 44 to generate an exact Mclk master clock. Within the closed circuit by phase 44, a phase detector 46 receives the end of the scanning signal (EOS), and the end of the counting signal (EOC). On the basis of the difference in the synchronization of the received signals, the phase detector 46 generates a pulse and sends it to a charging pump 48. On the basis of the received pulse, the charging pump 48 sends a voltage Vd to the oscillator voltage controlled (VCO) 42, through a low pass filter 50. The low pass filter 50, reduces the noise level of the Vd voltage before supplying it to the VCO 42. The voltage level of the Vd controls the frequency of the VCO 42. On the basis of the voltage Vd, the VCO 42 (clock generator) generates a Mclk main clock. The Mclk is sent to a divisor 52, to divide the Mclk between M, to generate an end of the count (EOC). M is the total number of pixels per scan line. In this application, for a paper of 36.5 cm (14.4 inches) with 600 pixels per inch, M is 8640. The EOC, which indicates the end of the pixel information, is sent to the phase detector 46 through the block. alignment 54. Alignment block 54 aligns the EOC for any movement of the photoreceptor band in the direction of the scan or any faulty alignment between the SOS of each different ROS. In operation, the phase detector 46 compares the EOC with the EOS. The EOS is a signal generated within the ROS. Typically, there are two detectors placed within a ROS system, to detect the start of the SOS scan and the end of the EOS scan. As the laser light beam passes over a dedicated point on the scan line, immediately before the pixel is placed, the respective detector generates an SOS scan start. In the same way, as the scanning laser light beam passes over a dedicated point or point in the scanning line, immediately after the end of the pixel placement, the respective detector generates an end of the EOS scan. And the SOS and the EOS are generated for each scan line. Since the speed of the laser light beam is fixed, the time between the SOS and the EOS is the same for each scan line. The EOC has to match the EOS. If they do not match, it means that the frequency of the Mlk main clock needs to decrease or increase depending on whether the EOC was before or after the EOS, respectively. Therefore, depending on whether the EOC is before or after the EOS, the phase detector 46 generates either a positive or a negative pulse, respectively. The pulse width indicates the time difference between the EOS and the EOC. The phase detector 46 sends the generated pulse to the charge pump 48. Typically, the synchronization of the EOS and the EOC do not coincide. As a result, the phase detector 46 typically generates either a negative or a positive pulse. However, if the synchronization of the EOS and the EOC coincide, the phase detector 46 does not generate a pulse. In the absence of the pulse of the phase detector 46, the charge pump 48 generates a base voltage, and sends it as the voltage Vd, to the VCO 42. When the phase detector 46 generates a pulse, depending on whether the pulse is positive negative , the charge pump 48 subtracts or adds a voltage, proportional to the pulse width, from / to its base voltage, and sends the result as the voltage Vd to VCO 42. Initially, Vd is equal to the base voltage, since there is no EOC to compare with the EOS. Therefore, the first Vd causes the VCO 42 to calibrate the Mclk frequency to a reference frequency (54 MHz). Subsequently, at the end of each scan line, depending on whether the EOC deviates from, or matches the EOS, a new or same Vd is sent by the load pump 48 respectively.

If the same Vd is sent, the frequency of the Mclk does not change. However, if a new Vd is sent, the deviation of Vd from the base voltage causes the VCO 42 to recalibrate the deviated frequency of the Mclk back to the reference frequency. The recalibration of the Mclk frequency is done only at the end of each scan line, and only if the EOC synchronization does not match the EOS synchronization. After calibration or recalibration, the Mclk frequency remains constant until the next SOS, because the charge pump 48 provides a fixed voltage V to the VCO 42. Once the exploration of a scan line has begun and it is generated In the SOS signal, the Mclk main clock frequency has to be varied to correct the defective, non-linear registration of the pixels of each scan line. The frequency of this Mclk master clock will vary (modulated) based on a predetermined correction curve for each scan line. Correction curves are generated through a test. During the test, when the first image is generated in the photoreceptor, the placement of the pixels of each scan line is verified. In the following images, for each scan line, the placement of the pixel is compared to the pixel placement of the same scan line of the first image, and an error signal is generated. On the basis of the error signals, the correction curves are generated and stored in the search table 56. Referring to Figure 3, a correction curve 60 is shown, which is used to modulate the frequency of the main clock Mclk. The vertical axis represents the frequency and the horizontal axis represents the number of increments or corrections. The correction curve 60 is shown along a scan line for a 36.5 cm (14.4 inch) paper with 8640 pixels. Correction curve 60 has 86 increments (corrections), along the entire scan line. This means that for every 100 pixels, there is an error correction. The number of increments can be selected to be more or less than 86. However, 86 increments reduce the defective register to less than 20 microns. The peak-to-peak range of the correction curves is designed to be within ± 3% of the Mclk main clock frequency. This means that the frequency of the Mclk main clock can change by ± 1.62 (3% of 54 MHz). The frequency of the correction curve can be calculated as follows: ND of pariacts ar scan line by clock frequency _ 1.5 x 54 x I06"^ 10 KH? to. -te pixslf-8640 Therefore, the correction curves will modulate the high frequency (54 MHz) of the Mclk main clock by fine increments of approximately 10 kHz. Referring again to Figure 2, the Mclk is also sent to the clock generator of the pixel 62, which receives a synchronization signal generated by the SOS. The pixel clock generator 62 synchronizes the Mclk with the synchronization signal and sends it as a pixel clock Pclk to a counter 64. Therefore, the Pclk is a clock with the same frequency as the Mclk, except that it is synchronized to start with the SOS. Counter 64 counts the number of pixels and increases the count by receiving each Pclk. The count of the counter 64 is sent to the search table or query 56 to indicate which increment or which correction curve needs to be sent. During the time that a scan line is scanned, the lookup table 56 sends a respective correction curve to the VCO 42 through the V / A converter, which converts the digital correction curve to an analog correction voltage. . It should be noted that in this specification "during the time a scan line is scanned", it refers to "the time between SOS and EOS".

At node 68, the correction voltage is added to the Vd supplied from the charge pump to VCO 42. The correction voltage modulates the frequency of the Mclk master clock as needed along a scan line. This process continues until the end of the EOS scan is generated. At the end of the exploration, a reset signal Rst generated by the EOC, will reset the counter 64. Therefore, the search or query table 56 ends sending correction curves that terminate the modulation of the Mclk frequency. Also, at the end of the scan, as previously described, if the Mclk frequency has deviated from the reference frequency, it will be recalibrated. The recalibration ensures that each scan line starts with an identical frequency (reference frequency). The disclosed embodiment of this invention provides fast and asynchronous modulation of a fast frequency. In addition, it reduces the nonlinear defective register to less than 20 microns. It should be noted that in this invention, for even finer corrections, the number of increments or corrections in the correction curves can be increased beyond 86. This requires a larger search or query table, and a digital-to-analog converter DAC more big. It should also be noted that numerous changes may occur in the details of the construction and the combination and arrangement of the elements, without departing from the true spirit and scope of the invention as claimed later. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (3)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property.

1. An electronic circuit for correcting the defective, non-linear registration of a frame output scanning device, characterized in that it comprises: means for generating a clock signal having a frequency; a calibration means electrically connected to the means for generating the clock; the means for generating the clock respond to the calibration means for calibrating the clock frequency at a given frequency; a correction means electrically connected to the means for generating the clock, to provide an individual correction curve for each scan line, to the means for generating the clock; the means for generating the clock respond to the correction means for modulating the clock frequency for each scan line, according to a respective correction curve; and the means for generating the clock, the calibration means and the correction means, are constructed and arranged to modulate the clock frequency, only during the time in which a scan line is scanned and calibrate the frequency of the clock to the frequency given between two consecutive scan lines. A printing system with an electronic circuit for correcting the defective, non-linear registration of a frame output scanning device, characterized in that it comprises: means for generating a clock signal having a frequency; a calibration means electrically connected to the means for generating the clock; the means for generating the clock respond to the calibration means for calibrating the clock frequency at a given frequency; a correction means electrically connected to the means for generating the clock, to provide an individual correction curve for each scan line, to the means for generating the clock; the means for generating the clock respond to the correction means for modulating the clock frequency for each scan line, according to a respective correction curve; and the means for generating the clock, the calibration means and the correction means, are constructed and arranged to modulate the clock frequency, only during the time in which a scan line is scanned and calibrate the frequency of the clock to the frequency given between two consecutive scan lines. 3. A method for electronically correcting a defective, non-linear record of a frame output scanning device, comprising the steps of: a. generate a clock frequency; b. modulating the clock frequency, for each scan line, according to a respective correction curve; c. stop the modulation at the end of each scan line; d. calibrate the clock frequency at a given frequency, before the start of the next scan line; and e. Repeat steps b through d for all the scan lines of a page.