JP2006076114A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus making correction of a magnification in a main scanning direction by considering variation of each face of a polygon mirror. <P>SOLUTION: This image forming apparatus comprises: the polygon mirror 102 for deflecting in the main scanning direction a light beam modulated according to an image signal; a preceding synchronism detection sensor 105 and a following synchronism detection sensor 106 for detecting the light beam deflected by the polygon mirror 102 at two positions on the main scanning line, a time difference measurement section 107 for measuring a time difference from when one of the sensors 105, 106 detects the light beam until the other detects the light beam, and a magnification correction control section 110 for correcting a magnification of an image on a photosensitive body 104 in the main scanning direction according to the time difference measured by the time difference measurement section 107. The time difference measurement section 107 measures the time difference on each of the faces of the polygon mirror 102. The magnification correction control section 110 calculates a correction value on the basis of the time difference on each of faces of the polygon mirror 102 to make the correction according to the correction value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus for correcting an image magnification in a main scanning direction of a copying machine, a printer, a facsimile, a printing machine, or the like that forms a color image or an image in which a plurality of colors are superimposed on an image carrier using a light beam. .

In the prior art disclosed in Patent Documents 1 and 2 and the like, in order to improve the color correction accuracy of an image, two light detection means are prepared for an arbitrary surface of a polygon mirror, and measurement is performed thereby. A method has been adopted in which a time difference is measured and reflected on all polygon surfaces based on the time difference. However, since this method does not take into account variations on each surface of the polygon mirror, there is a risk of erroneous magnification correction. In addition, since the variation in reading the time difference is not taken into account, there is a problem that accurate magnification correction cannot be performed.
JP 2001-108921 A JP-A-8-136838

  In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus that performs magnification correction in the main scanning direction in consideration of variations on each surface of a polygon mirror.

  According to an aspect of the present invention for solving the above-described problems, an image forming apparatus that forms an image on an image carrier by scanning a light beam modulated according to an image signal. One of the two light beam detecting means, a deflecting means for deflecting the light beam in the main scanning direction, two light beam detecting means for detecting the light beam deflected by the deflecting means at two locations on the main scanning line, respectively. A time difference measuring means for measuring a time difference from when the light beam is detected until the other of the two light beam detecting means detects the light beam, and the time difference measured by the time difference measuring means in the main scanning direction. A magnification correction unit configured to correct a magnification of an image on the image carrier, wherein the time difference measurement unit measures a time difference on each surface of the deflection unit, and the magnification correction unit includes the deflection Based on the time difference in the stage of each side calculates a correction value, performs a correction by the correction value.

  Here, the magnification correction unit calculates a correction value for each surface of the deflection unit based on a time difference in each surface of the deflection unit, and performs correction using the correction value on each surface of the deflection unit. It is characterized by. Then, even if there are variations in each surface of the deflecting means, it can be corrected to the same scanning time.

  The time difference measuring means calculates an average value for one rotation of the deflecting means based on a time difference on each surface of the deflecting means, and the magnification correcting means calculates a correction value based on the average value. The correction is performed using the correction value. As a result, it is possible to reduce the burden when calculating and processing the time difference, such as when the total value of the scanning time of each surface of the deflecting means becomes large.

  On the other hand, when the time difference measuring unit measures the time difference on each surface of the deflection unit a plurality of times, the time difference measuring unit calculates a weighted average value on each surface of the deflection unit of the time difference measured a plurality of times, and the magnification correction unit A correction value for each surface of the deflecting unit is calculated based on a weighted average value on each surface of the deflecting unit, and correction using the correction value is performed on each surface of the deflecting unit.

  In addition, when the time difference measuring unit measures the time difference on each surface of the deflecting unit a plurality of times, the time difference measuring unit calculates a sum of the time difference measured a plurality of times for one rotation of the deflecting unit, A weighted average value based on the total sum is calculated, and the magnification correction means calculates a correction value based on the weighted average value based on the total sum of the deflection means for one rotation, and performs correction using the correction value. It is characterized by that.

  Further, when the time difference measuring means measures the time difference on each surface of the deflecting means a plurality of times, an average value for one rotation of the deflecting means based on the time difference on each surface of the deflecting means measured a plurality of times is obtained. And calculating a weighted average value based on the average value for one rotation of the deflection means, and the magnification correction means corrects based on the weighted average value based on the average value for one rotation of the deflection means. A value is calculated, and correction using the correction value is performed.

  In the above-described method for calculating the weighted average, since the measurement time is weighted and averaged closer to the present time, the scan time becomes closer to the current state, and a value with reduced variation can be measured.

  Since the variation of each surface of the polygon mirror is taken into account, the accuracy of magnification correction is improved.

  The best mode for carrying out the image forming apparatus of the present invention will be described below with reference to the drawings submitted at the same time as this specification.

  FIG. 1 shows a configuration of a color image forming apparatus called a tandem type in which image forming units are arranged along a conveying belt as an image forming apparatus of the present invention. First, an outline of the color image forming apparatus will be described.

  Image forming portions for forming images of different colors (yellow: Y, magenta: M, cyan: C, black: K) are arranged in a line along the conveyance belt 2 that conveys the transfer paper 1.

  The conveying belt 2 is constructed by conveying rollers 3 and 4, one of which is a driving roller that is driven and rotated, and the other is a driven roller that is driven and rotated, and is rotated in the direction of the arrow by the rotation of the conveying rollers 3 and 4. A paper feed tray 5 in which the transfer paper 1 is stored is provided below the transport belt.

  The transfer sheet 1 at the uppermost position among the transfer sheets 1 stored in the sheet feed tray 5 is fed at the time of image formation, and is timed with each unit by a registration sensor 14 on the way. To be adsorbed. The adsorbed transfer sheet 1 is conveyed to the first image forming unit (yellow), where yellow image formation is performed.

  The first image forming unit (yellow) includes a photosensitive drum 6Y, a charger 7Y, an exposure unit 8, a developing unit 9Y, and a photosensitive cleaner 10Y disposed around the photosensitive drum 6Y.

  The surface of the photosensitive drum 6Y is uniformly charged by the charger 7Y, and then exposed by the exposure device 8 with the laser beam 11Y corresponding to the yellow image, thereby forming an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 9Y, and a toner image is formed on the photosensitive drum 6Y. This toner image is transferred by the transfer device 12Y at a position (transfer position) where the photosensitive drum 6Y contacts the transfer paper 1 on the transport belt 2, and forms a single color (yellow) image on the transfer paper 1.

  After the transfer, the photoreceptor drum 6Y is cleaned with unnecessary toner remaining on the drum surface by the photoreceptor cleaner 10Y to prepare for the next image formation. As described above, the transfer sheet 1 on which the single color (yellow) is transferred by the first image forming unit (yellow) is transferred to the photosensitive drum 6M and the charger 7M disposed around the photosensitive drum 6M by the conveying belt 2. Then, it is conveyed to a second image forming unit (magenta) constituted by the exposure device 8, the developing device 9M, and the photoreceptor cleaner 10M.

  Here, similarly, the laser beam 11M is exposed, and the toner image (magenta) formed on the photosensitive drum 6M is transferred onto the transfer paper 1 in an overlapping manner. The transfer paper 1 further includes a photoconductor drum 6C and a third image forming unit (cyan) composed of a charger 7C, an exposure device 8, a developing device 9C, and a photoconductor cleaner 10C arranged around the photoconductor drum 6C. And a photosensitive drum 6K and a charging device 7K arranged around the photosensitive drum 6K, an exposure device 8, a developing device 9K, and a fourth image forming unit (black) composed of a photosensitive cleaner 10K. Similarly, the laser beams 11C and 11K are exposed, and the formed toner image is transferred to the transfer paper 1 to form a color image. The transfer paper 1 on which a color image has been formed by passing through the fourth image forming section is peeled off from the conveying belt 2, fixed by the fixing device 13, and then discharged.

  FIG. 2 shows a laser beam scanning apparatus having an image writing function, which is one of the components constituting the exposure unit 8 of FIG. 1, and its surrounding control system. The configuration and operation of the laser beam scanning apparatus and its surrounding control system will be described with reference to FIG.

  The laser beam scanning device includes a leading synchronization detection sensor 105 and a trailing synchronization detection sensor 106 as light beam detecting means for detecting a light beam (laser beam) at both ends in the main scanning direction, and transmits through the fθ lens 103. The laser beam thus incident on the preceding synchronization detection sensor 105 and the subsequent synchronization detection sensor 106 is detected. In FIG. 2, only the fθ lens 103 is shown as a representative of a plurality of lenses, and the other lenses are not shown. The preceding synchronization detection sensor 105 and the subsequent synchronization detection sensor 106 also play a role of synchronization detection for detecting a laser beam scanning synchronization signal that becomes a synchronization detection signal.

  By scanning the laser beam, the preceding synchronization detection sensor 105 and the subsequent synchronization detection sensor 106 detect the laser beam and output laser beam detection signals DETP1 and DETP2, respectively, and the laser beam detection signals DETP1 and DETP2 are It is sent to the time difference measuring unit 107.

  The time difference measuring unit 107 has an arithmetic function such as measuring and averaging the time difference between the output signal DETP1 of the preceding synchronization detection sensor 105 and the output signal DETP2 of the subsequent synchronization detection sensor 106, and is provided from the control device (CPU 111). The time difference measurement and the calculation based on the measurement are performed according to the set timing, and the measurement result and the calculation result are sent to the magnification correction control unit 110.

  The magnification correction control unit 110 has a storage unit (not shown) that stores the initial setting value of the write clock frequency and the phase shift value set by the CPU 111 and / or the current setting value. Then, using the fact that the image magnification in the main scanning direction changes according to the frequency of the write clock, or by shifting the phase for a minute time that cannot be adjusted in the write clock adjustment unit, the image magnification changes. By utilizing this, it has a function of calculating the optimum write clock frequency and phase shift value. It also has a function of calculating the optimum phase shift value with the write clock frequency fixed. It also has a function of comparing the phase shift value with a reference value set by the CPU 111. The above functions are exhibited by the setting of the CPU 111, and a control signal for executing the write clock setting and the phase shift is sent to the write clock generation unit 108.

The write clock generation unit 108 includes a PLL transmission device 108-1 and a phase control device 108-2, and generates a write clock and performs phase shift under the control of the magnification correction control unit 110. .
The PLL oscillator 108-1 has a function of receiving a clock from the oscillator 112 and generating a PLL oscillator clock having a frequency n times the write clock VCLK.
The phase control device 108-2 has a function of generating a write clock VCLK synchronized with DETP1 by dividing the PLL oscillation clock by n in synchronization with the DETP1, which is a synchronization detection signal. The write clock cycle is shifted by one pixel unit by adding or subtracting an integral multiple of the PLL transmission clock half cycle to the specific cycle of the write clock VCLK.

  The write clock VCLK that has been subjected to the main scanning image magnification correction by the variable frequency and phase in the write clock generator 108 is sent to an LD (Laser Diode) modulator 101 as a light beam generator drive unit. The LD modulation device 101 controls the lighting of the LD 109 in the LD unit in the laser beam scanning device in accordance with an image signal synchronized with the write clock VCLK from the write clock generation unit 108. Accordingly, a laser beam modulated in accordance with the image signal is emitted from the LD 109 in the LD unit, and this laser beam is deflected by the polygon mirror 102 and corresponds to 6Y, 6M, 6C, and 6K in FIG. The photosensitive member 104 to be scanned is scanned.

  Hereinafter, a time difference measurement according to the magnification correction performed in this embodiment and a calculation method based on the measurement will be described. First, in the polygon mirror 102 of FIG. 4, numbers m1 to m6 are assigned to the respective surfaces (in the case of six surfaces). The difference between the passage times of the preceding synchronization detection sensor 105 and the subsequent synchronization detection sensor 106 on each surface m1 to m6 is defined as t1 to t6, respectively (see the timing chart in FIG. 5). The time differences t1 to t6 are measured by the time difference measuring unit 107, and the data is sent to the CPU 111. In the CPU 111, if the time difference that is the reference (ideal) is T, the scanning error rate of each surface of the polygon mirror is (t1 / T) to (t6 / T), so that the magnification correction is performed so that it returns to the reference value T again. The processing by the control unit 110 corrects the scanning time for each surface of m1 to m6 at each magnification.

Another method of time difference measurement for magnification correction and calculation based on the measurement will be described.
A time difference measuring unit 107 measures the difference t1 to t6 in the passage times of the preceding synchronization detection sensor 105 and the subsequent synchronization detection sensor 106 on each surface m1 to m6 of the polygon mirror 102. However, the data sent to the CPU 111 is an average of t1 to t6 (t1 + t2 + t3 + t4 + t5 + t6) / 6. In the CPU 111, if the time difference that is the reference (ideal) of the polygon mirror 1 surface is T, (t1 + t2 + t3 + t4 + t5 + t6) / 6T is an average from the average time sent from the time difference measuring unit 107. Since the scanning error rate of each surface of the polygon mirror becomes a correct, the scanning time is corrected at the same magnification for each of the m1 to m6 surfaces by processing by the magnification correction control unit 110 based on this scanning error rate.

Another method of time difference measurement for magnification correction and calculation based on the measurement will be described.
A time difference measuring unit 107 measures the difference t1 to t6 in the passage times of the preceding synchronization detection sensor 105 and the subsequent synchronization detection sensor 106 on each surface m1 to m6 of the polygon mirror 102. The same measurement is repeated n times, and values t1 ′ to t6 ′ obtained by weighted averaging t1 to t6 are sent to the CPU 111. The weighted average method will be described by taking n = 3 as an example. Assuming that the time difference measurement results for one of the polygon mirror surfaces m1 are t11, t12, and t13, they are multiplied by different weighting coefficients ω1, ω2, and ω3 and averaged. At this time, if the weighting coefficient is in the relationship of ω1 + ω2 + ω3 = 1, the weighted average value t1 ′ of the time difference of the polygon mirror surface m1 is t1 ′ = (ω1 · t11 + ω2 · t12 + ω3 · t13). The method of determining the weighting coefficient is changed according to the condition, for example, if the weight is to be placed in the closest measured time, ω1 = 0.25, ω2 = 0.25, ω3 = 0.50. In the CPU 111, assuming that the reference (ideal) time difference is T, the scanning error rate of each surface of the polygon mirror is (t1 '/ T) to (t6' / T). By the processing by the magnification correction control unit 110, the scanning time of each surface of m1 to m6 is corrected at each magnification.

Another method of time difference measurement for magnification correction and calculation based on the measurement will be described.
A time difference measuring unit 107 measures a difference t1 to t6 in passing time between the preceding synchronization detection sensor 105 and the subsequent synchronization detection sensor 106 on each surface m1 to m6 of the polygon mirror 102, and sums them (t1 + t2 + t3 + t4). + t5 + t6) is calculated. Then, the same measurement and calculation are repeated n times, and a weighted average value (t1 + t2 + t3 + t4 + t5 + t6) ′ is calculated. The weighted average method is the same as that described above. The data sent to the CPU 111 is a weighted average value of the sum (t1 + t2 + t3 + t4 + t5 + t6) ′. In the CPU 111, if the time difference that is the reference (ideal) of the polygon mirror 1 surface is T, (t1 + t2 + t3 + t4 + t5 + t6) '/ 6T is an average from the total time sent from the time difference measuring unit 107 Thus, the scanning error rate of each surface of the polygon mirror is corrected. Based on this scanning error rate, the scanning time is corrected for each surface of m1 to m6 at the same magnification by the processing by the magnification correction control unit 110.

Another method of time difference measurement for magnification correction and calculation based on the measurement will be described.
The time difference measuring unit 107 measures the difference t1 to t6 in the passage time between the preceding synchronization detection sensor 105 and the subsequent synchronization detection sensor 106 on each surface m1 to m6 of the polygon mirror 102, and averages them (t1 + t2 + t3 + t4 + t5 + t6) / 6 is calculated. Then, the same measurement and calculation are repeated n times, and a weighted average value {(t1 + t2 + t3 + t4 + t5 + t6) / 6} ′ is calculated. The weighted average method is the same as that described above. The data sent to the CPU 111 is a weighted average value of average values {(t1 + t2 + t3 + t4 + t5 + t6) / 6} ′. In the CPU 111, if the time difference serving as the reference (ideal) of the polygon mirror 1 surface is T, {(t1 + t2 + t3 + t4 + t5 + t6) / 6} ′ from the average time sent from the time difference measuring unit 107. Since / T is the average scanning error rate of each surface of the polygon mirror, the scanning time is corrected at the same magnification for each of the m1 to m6 surfaces by processing by the magnification correction control unit 110 based on this scanning error rate.

  The above-described embodiment is the best mode for carrying out the present invention, but the present invention is not limited to this. Therefore, various modifications can be made without departing from the scope of the present invention.

  For example, the configuration relating to the laser beam scanning apparatus of FIG. 2 and its surrounding control system can also be realized by the configuration shown in FIG. That is, the magnification correction control unit 110 does not exist as an independent control unit, and the function related to magnification correction is performed by the CPU 111. At this time, the time difference measuring unit 107 sends the measurement result and the calculation result to the CPU 111, and the CPU 111 stores the initial setting value and / or the current setting value of the writing clock frequency and the phase shift value, and the optimum writing clock frequency. And a phase shift value is calculated. Also, the optimum phase shift value is calculated with the write clock frequency fixed. The phase shift value is compared with a reference value. Then, a control signal is sent to the write clock generation unit 108 as necessary. By entrusting the function of the magnification correction control unit 110 to an external CPU, the configuration of the laser beam scanning device itself can be simplified and the load can be reduced.

  2 and 3, the write clock generation unit 108, the time difference measurement unit 107, and the magnification correction control unit 110 are configured separately. However, these are combined into a single circuit to simplify the apparatus. You may plan to make it.

  Development of printers, color copiers, and MFPs (Multi Functional Products) equipped with the image forming apparatus of the present invention is desired.

1 is a diagram illustrating a configuration of a tandem type color image forming apparatus. It is drawing which described the structure of the laser beam scanning apparatus and its periphery control system. It is drawing which described the other structure of the laser beam scanning apparatus and its surrounding control system. A polygon mirror 102 is illustrated. It is a timing chart regarding DETP1 and DETP2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transfer paper 2 Conveyance belt 3 Conveyance roller 4 Conveyance roller 5 Feed tray 6Y, 6M, 6C, 6K Photosensitive drum 7Y, 7M, 7C, 7K Charger 8 Exposing device 9Y, 9M, 9C, 9K Developer 10Y, 10M 10C, 10K Photoconductor cleaner 11Y, 11M, 11C, 11K Laser light 12Y, 12M, 12C, 12K Transfer device 13 Fixing device 101 LD modulator 102 Polygon mirror 103 fθ lens 104 Photoconductor 105 Pre-synchronization detection sensor 106 Trailing synchronization Detection sensor 107 Time difference measurement unit 108 Write clock generation unit 108-1 PLL transmission device 108-2 Phase control device 109 LD
110 Magnification Correction Control Unit 111 Oscillator 112 CPU

Claims (6)

In an image forming apparatus for forming an image on an image carrier by scanning a light beam modulated according to an image signal,
Deflection means for deflecting a light beam modulated in accordance with an image signal in the main scanning direction;
Two light beam detecting means for detecting the light beam deflected by the deflecting means at two positions on the main scanning line, and
A time difference measuring means for measuring a time difference from when one of the two light beam detecting means detects a light beam until the other of the two light beam detecting means detects the light beam;
Magnification correction means for correcting the magnification of the image on the image carrier in the main scanning direction by the time difference measured by the time difference measurement means,
The time difference measuring means measures a time difference on each surface of the deflecting means,
The image forming apparatus according to claim 1, wherein the magnification correction unit calculates a correction value based on a time difference on each surface of the deflection unit and performs correction using the correction value.   The magnification correction unit calculates a correction value for each surface of the deflection unit based on a time difference in each surface of the deflection unit, and performs correction using the correction value on each surface of the deflection unit. The image forming apparatus according to claim 1. The time difference measuring means calculates an average value for one rotation of the deflecting means based on a time difference on each surface of the deflecting means,
The image forming apparatus according to claim 1, wherein the magnification correction unit calculates a correction value based on the average value and performs correction using the correction value. The time difference measuring means measures a time difference on each surface of the deflection means a plurality of times, calculates a weighted average value on each surface of the deflection means for the time difference measured a plurality of times,
The magnification correction unit calculates a correction value for each surface of the deflection unit based on a weighted average value on each surface of the deflection unit, and performs correction using the correction value on each surface of the deflection unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The time difference measuring means measures a time difference on each surface of the deflecting means a plurality of times, calculates a sum of the time difference measured a plurality of times for one rotation of the deflecting means, and based on the sum of the one rotation of the deflecting means. To calculate the weighted average
2. The image according to claim 1, wherein the magnification correction unit calculates a correction value based on a weighted average value based on a total sum of one rotation of the deflection unit, and performs correction using the correction value. Forming equipment. The time difference measuring means measures a time difference on each surface of the deflecting means a plurality of times, calculates an average value for one rotation of the deflecting means based on a time difference measured on each surface of the deflecting means a plurality of times, Calculating a weighted average value based on an average value for one rotation of the deflection means;
4. The magnification correction unit calculates a correction value based on a weighted average value based on an average value for one rotation of the deflection unit, and performs correction using the correction value. The image forming apparatus described.

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