JP2007216460A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus decreasing the number of correcting frequency of image signal. <P>SOLUTION: The image forming apparatus has a main position controlling means which changes density of intervals of beam spot positions on a scanning line, by one line unit or a unit not smaller than the one line unit, to perform correction of magnification, a sub-position controlling means which changes the density of the intervals of the beam spot positions on the scanning line by one pixel unit to correct the magnification, a sub-correction time calculating means which calculates a difference between a reference time which can be set by operating only the main position controlling means and the time measured by a time difference measuring means, and a judging means for judging a size between the amount of the corrected time calculated by the sub-correction calculating means and the amount of a regulating time set in advance. As a result of the judgement by the judging means, until the amount of the corrected time exceeds the amount of the regulating time, the correction of magnification is performed by the sub-position controlling means without operating the main position controlling means. As a result of the judgement by the judging means, at the time when the amount of the corrected time exceeds the amount of the regulating time, the main position controlling means is operated to perform the correction of magnification. <P>COPYRIGHT: (C)2007,JPO&INPIT

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. .

Conventional image forming apparatuses include those that perform frequency modulation for image magnification adjustment (for example, see Patent Documents 1 and 2) and those that perform phase modulation (for example, see Patent Document 3). No magnification correction is performed by the phase modulation means until the phase modulation amount exceeds the specified value, and no magnification correction is performed again by the frequency modulation means when the phase modulation amount exceeds the specified value.
Japanese Patent No. 3704997 Japanese Patent No. 3648786 JP 2003-279873 A

  2. Description of the Related Art Conventionally, an image forming apparatus using a light beam scanning device modulates a light beam (laser beam) with an image signal, deflects it at a constant angular velocity in a main scanning direction by a deflecting means (for example, a polygon motor), and converts it at a constant angular velocity by an fθ lens. Correction is made from deflection to constant velocity deflection, and scanning is performed on a photoconductor as an image carrier.

  However, in this image forming apparatus, particularly when a plastic lens is used as the fθ lens, the shape and refractive index of the plastic lens change due to a change in environmental temperature, a change in temperature in the apparatus, and the like. Similarly, the refractive index changes due to a change in the wavelength of the laser beam. For this reason, the scanning position on the image surface of the photoconductor changes, a magnification error occurs in the main scanning direction, and a high-quality image cannot be obtained.

  For this reason, in order to correct image magnification error and color misregistration caused by changes in the environmental temperature, changes in the internal temperature, etc., the laser beam is detected by the laser beam detection means at two locations in the main scan, Measures the time from detection by one laser beam detection means to detection by another laser beam detection means, corrects the frequency and phase of the image signal according to the measurement result, and corrects the scanning magnification of each laser beam is doing.

  Among the above corrections, the correction method for controlling the phase of the image signal can change the correction amount in a short time, and thus can be corrected between pages of normal printing. Since a PLL circuit is normally used as the correction method to be controlled, it is necessary to stop the printing operation until the PLL oscillation frequency is stabilized after the PLL oscillation frequency is changed.

  Normally, when correcting the frequency of the above image signal, the number of prints and time are counted, and correction is performed at regular intervals that are considered to have no side effects on image degradation due to phase correction. The number of stops for correcting the frequency of the image signal is increased, and the overall printing speed of the image forming apparatus is greatly reduced. At the same time, even if the amount of correction for phase correction increases and the side effects of image deterioration due to phase correction increase, the frequency is not corrected until the next frequency correction, so image deterioration due to phase correction may occur. There is.

  The present invention has been made in order to prevent the above-described decrease in printing speed and the possibility of image deterioration, and an object of the present invention is to provide an image forming apparatus that reduces the number of frequency corrections of image signals.

  In order to achieve this object, the invention described in claim 1 is an image forming apparatus for forming an image on an image carrier by scanning a light beam modulated in accordance with an image signal, A deflecting means for deflecting the light beam modulated accordingly 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, and two light beam detections, respectively. The time difference measuring means for measuring the time difference from when one of the means detects the light beam 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, A magnification correction unit that corrects the magnification of the image on the image carrier in the scanning direction. The magnification correction unit is a beam spot on the scanning line in units of one line or more than one line. A main position control unit that performs magnification correction by changing the density of position intervals, and a sub-position control unit that corrects magnification by changing the density of beam spot position intervals on a scanning line in units of pixels. A sub correction time calculating means for calculating a difference between a reference time that can be set only by the operation of the main position control means and a time measured by the time difference measuring means; a correction time amount calculated by the sub correction calculating means; And a sub-position control without operating the main position control means until the correction time amount exceeds the specified time amount as a result of the determination by the determining means. When the correction time amount exceeds the specified time amount as a result of the determination by the determination unit, the main position control unit is operated to perform the magnification correction. And wherein the door.

  According to a second aspect of the present invention, in the first aspect of the invention, the reference time that can be set only by the operation of the main position control means depends on the set value of the main position control means, and there are a plurality of reference time amounts. It is set according to the time difference of time.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the main position control means is operated and set when the reference time and the specified time amount before the change and the correction time amount exceed the specified time amount. The reference time and the specified time amount after the change have a relationship of | reference time before change−reference time after change | <(specified time amount before change + specified time amount after change).

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, further comprising specified value changing means for changing the specified time amount.

  The invention described in claim 5 is the invention described in any one of claims 1 to 4, further comprising specified value changing means for changing the specified time amount according to the transfer paper size.

  The invention described in claim 6 is characterized in that in the invention described in any one of claims 1 to 4, there is further provided a specified value changing means for changing the specified time amount in accordance with the main scanning registration position.

  The invention according to claim 7 is the invention according to any one of claims 1 to 4, further comprising specified value changing means for changing the specified time amount according to the development color at the time of color printing. To do.

  The invention described in claim 8 is characterized in that in the invention described in any one of claims 1 to 4, the apparatus further comprises specified value changing means for changing the specified time amount according to the color type.

  The invention according to claim 9 is the invention according to any one of claims 1 to 4, further comprising specified value changing means for changing the specified time amount according to the image type.

  The invention described in claim 10 is the invention described in any one of claims 1 to 4, further comprising specified value changing means for changing the specified time amount according to the application function.

  According to an eleventh aspect of the present invention, in the invention according to any one of the first to fourth aspects, the input pixel density, the write pixel density, the input gradation number, or the write gradation number is specified. It further has a specified value changing means for changing the amount of time.

  The invention according to claim 12 is the invention according to any one of claims 1 to 4, wherein the transfer paper size, the main scanning registration position, the development color at the time of color printing, the color type, the image type, the application function, the input It further has a specified value changing means for changing the specified time amount according to a predetermined combination among the pixel density, the writing pixel density, the number of input gradations, and the number of writing gradations.

  According to the present invention, since the frequency change frequency of the frequency modulation means can be reduced, the print stop time due to the frequency change can be shortened, and the productivity of the image forming apparatus can be improved.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

  An image forming apparatus according to an embodiment of the present invention is intended to reduce the number of frequency corrections of an image signal in order to prevent a decrease in printing speed and a possibility of image deterioration.

  In addition, the image forming apparatus according to the present exemplary embodiment aims to improve image quality by performing frequency correction according to the discreteness of PLL oscillation.

  In addition, the image forming apparatus according to the present exemplary embodiment is configured to have a configuration in which a change in the reference time does not occur frequently by overlapping the specified times to form a hysteresis.

  In addition, the image forming apparatus of the present embodiment is intended to provide adaptability by changing the specified time.

  In addition, the image forming apparatus according to the present embodiment aims to further reduce the number of times of frequency correction of the image signal by changing the specified time according to the print size.

  In addition, the image forming apparatus according to the present exemplary embodiment is intended to further reduce the number of times of frequency correction of the image signal by changing the specified time according to the image start position.

  In addition, the image forming apparatus according to the present embodiment is intended to further reduce the number of times of frequency correction of the image signal by changing the specified time according to the development color.

  In addition, the image forming apparatus according to the present embodiment is intended to further reduce the number of times of frequency correction of the image signal by changing the specified time according to the color type.

  In addition, the image forming apparatus according to the present exemplary embodiment is intended to further reduce the number of times of frequency correction of the image signal by changing the specified time according to the image type.

  In addition, the image forming apparatus of the present embodiment is intended to further reduce the number of times of frequency correction of an image signal by changing the specified time according to the application type.

  Further, the image forming apparatus according to the present embodiment further corrects the frequency of the image signal by changing the specified time according to the input pixel density, the writing pixel density, the number of input gradations, the number of writing gradations, and the combination thereof. The purpose is to reduce the number of times to perform.

  The image forming apparatus according to the present embodiment includes (1) transfer paper size, (2) main scanning registration position, (3) development color at the time of color printing, (4) color type, (5) image type, (6 ) By changing the specified time according to any one of the seven types of application functions, (7) input pixel density, writing pixel density, number of input gradations, number of writing gradations and combinations thereof, Furthermore, it aims at reducing the frequency | count of performing the frequency correction of an image signal.

  Hereinafter, an image forming apparatus having a laser beam scanning apparatus as a light beam scanning apparatus will be described as the image forming apparatus of the present embodiment.

  In the laser beam scanning apparatus of the present embodiment, a light beam (laser beam) emitted from an LD in a laser diode (hereinafter referred to as LD) unit as a light beam generating means that is turned on in accordance with an image signal is transmitted by a collimating lens. The light beam is converted into a parallel light beam, passes through a cylinder lens, is deflected by a polygon mirror as a deflecting unit, passes through an fθ lens and a BTL, and scans on a photoconductor as an image carrier.

  Here, the polygon mirror is rotationally driven by a polygon motor as driving means, and a drum-like photoreceptor or a belt-like photoreceptor is used as the photoreceptor. The fθ lens performs speed conversion so that a laser beam scanned at a constant angular velocity mainly by a polygon mirror is scanned at a constant speed on the photosensitive member. BTL mainly performs focusing in the sub-scanning direction (condensing function and position correction in the sub-scanning direction (surface tilt, etc.)). Around the photosensitive member, a developing device as a developing means as a charging means, a transfer device as a transfer means, a cleaning device as a cleaning means, a static eliminator as a static elimination means, and the like are arranged. As a result, an image is formed on a recording sheet as a transfer material.

  That is, the photosensitive member is rotated by a driving mechanism, uniformly charged by a charger, and then exposed by scanning with a laser beam from a laser beam scanning device to form an electrostatic latent image. The electrostatic latent image on the photosensitive member is developed (visualized) by a developing device to become a toner image, and recording paper as a transfer material is fed from a paper feeding device. A toner image on the photosensitive member is transferred to the recording paper by a transfer device, and the toner image is fixed by a fixing device and discharged to the outside. The photosensitive member is cleaned by a cleaning device after the toner image is transferred to remove residual toner, and is neutralized by a static eliminator to prepare for the next electrophotographic process.

FIG. 1 shows a laser beam scanning device as an image writing unit and its surrounding control system.
The laser beam scanning device is provided with sensors 105 and 106 as light beam detecting means for detecting a light beam (laser beam) at both ends in the main scanning direction, and the laser beam transmitted through the fθ lens 103 is detected by the sensors 105 and 106. It is configured to be incident on and detected. In FIG. 1, only the fθ lens 103 is shown as a representative of a plurality of lenses. The sensor 105 also serves as a synchronization detection sensor for detecting a laser beam scanning synchronization signal that is a synchronization detection signal.

  By scanning the laser beam, the sensors 105 and 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 sent to the time difference measuring unit 107. The time difference measuring unit 107 has an arithmetic function such as measuring and averaging a time difference between the output signal DETP1 of the sensor 105 and the output signal DETP2 of the sensor 106, and according to a set timing from a control device (CPU) not shown. Measurement / calculation is performed, and the measurement / arithmetic result is sent to the sub correction amount determination unit 111. The sub correction amount determination unit 111 determines the sub correction time based on the reference time that stores the reference time that can be set only by the PLL oscillation unit 108-1 and the reference time and the specified time data from the specified time storage unit 112. . The sub correction amount determination unit 111 sends the determination result and the calculated sub correction time to the magnification correction control unit 110. The magnification correction control unit 110 calculates a phase shift value when the determination result is OK based on the determination result and the sub correction time, and when the determination result is NG, an optimum reference time (that is, a write clock frequency). And the phase shift value at that time is calculated and sent to the write clock generator 108.

  The write clock generation unit 108 receives a clock from an oscillator (not shown) and generates a PLL in synchronization with the PLL oscillation unit 108-1 that generates n times the write clock VCLK and the DETP1 as a synchronization detection signal. Write clock in units of one pixel by dividing the clock by n and generating a write clock VCLK synchronized with DETP1 and by adding or subtracting an integral multiple of the PLL transmission clock half cycle to a specific cycle of the write clock The phase control unit 108-2 has a function of shifting the cycle, and generates a write clock and performs phase shift under the control of the magnification correction control unit 110. The execution timing is set by a CPU or the like.

  The write clock VCLK subjected to the main scanning image magnification correction by the variable frequency and the variable phase in the write clock generation unit 108 is sent to the LD modulation device 101 as the light beam generating means driving 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 scanned on the photoconductor 104 via the fθ lens 103.

  In FIG. 1, the write clock generation unit 108, the time difference measurement unit 107, the magnification correction control unit 110, the sub correction amount determination unit 111, and the reference time / specified time storage unit 112 are illustrated as separate blocks. These may be configured as a write clock generation unit as one block.

  The reference time determined by the PLL oscillation unit 108-1 is a value determined by reference time = PLL oscillation frequency × number of pixels between the sensors 105 and 106. Here, the number of pixels between the sensors 105 and 106 is a constant value (the magnification is adjusted so as to be a constant value) and a large value. Since the PLL oscillation frequency is also a discrete value, the interval between the reference time and the adjacent reference time is a value sufficiently larger than the adjustment unit time of the phase control unit 108-2.

FIG. 2A shows the relationship between the reference time and the specified amount of time.
In FIG. 2A, reference times A to H indicate the respective reference times set in the above (actually, the time from the sensor 105). Moreover, the arrow in a figure has shown the magnitude | size of regulation time amount. The prescribed amount of time is one interval unit or a plurality of interval units as shown in FIG.

  FIGS. 2B and 2C show a case where the reference time unit is divided into two or three (division is indicated by a dotted line) with respect to FIG. The prescribed time is one interval unit or a plurality of interval units with dotted line intervals as shown in the figure.

FIG. 3A shows a change in the range of the prescribed time amount when the reference time is changed from D to E.
As shown in the figure, the specified time amount range overlaps from D to E. When the reference time exceeds the specified time amount and changes to E at the reference time D, the specified time amount exceeds the specified time amount of the reference time E. Unless it is, the original reference time D is not restored.

  FIG. 3B is a diagram showing a case where the specified time amounts in FIG. 3A are different. Moreover, FIG.3 (c) and FIG.3 (d) are figures which show the case where a regulation time amount is a dotted line interval.

FIG. 4 is a diagram illustrating an operation flow of phase shift value determination.
The control device (CPU) sets the PLL clock initial value and the phase shift initial value to the magnification correction control unit 110 after the power is turned on or the machine is restarted, and the initial value of the PLL clock or the phase shift is set. Then, the laser beam scanning device is operated (step S1). Although not instructed in the operation flow of FIG. 4, printing is possible because printing is possible at this stage.

  Next, the CPU estimates the timing when the polygon motor is rotating, such as between papers or during printing, and the LD can be turned on, and issues a magnification adjustment value calculation instruction to the time difference measuring unit 107, the magnification correction control unit 110, and the sub correction amount determination. It outputs to the part 111 (step S2).

  The time difference measurement unit 107 outputs a measurement result and / or a calculation result such as an average value to the sub correction amount determination unit 111 according to the designated timing and the number of measurements (step S3). The sub correction amount determination unit 111 calculates a sub correction time amount from the reference time and specified time data from the reference time and specified time storage unit 112 (step S4), and compares the sub correction time amount with the specified time amount. Determination is performed (step S5, step S6), and the determination result is output to the magnification correction control unit 110.

  When the determination result is OK (step S6 / OK), the magnification correction control unit 110 calculates a phase shift value from the determination result, and when the determination result is NG (step S6 / NG), the optimum reference time ( That is, the write clock frequency) and the phase shift value at that time are calculated and sent to the write clock generation unit 108 (step S10).

  If the determination result is OK (step S6 / OK), the CPU does not need to open a gap between sheets during continuous printing. Therefore, the CPU estimates the timing so that it is effective for printing after calculating the adjustment amount, and the phase shift. Is sent to the write clock generator 108 (step S8). If the determination result is NG (step S6 / NG), it is necessary to open a gap between sheets during continuous printing, etc., so the continuous printing is temporarily interrupted (step S11), and the CPU looks for a convenient timing, and the next A control signal for PLL clock setting and phase shift is sent to the write clock generation unit 108 so as to be effective for printing (step S12).

  The write clock generation unit 108 changes the write clock according to the above setting, and then performs printing (step S9).

FIG. 5A shows an example of magnification variation and print size.
The magnification variation is not constant between DETP1 and DETP2. In addition, since the range changes depending on the print size, the influence of the magnification fluctuation differs.

FIG. 5B shows an example in which the resist shown in FIG. 5A is changed.
Since the magnification variation is not constant as described above, the influence of the magnification variation differs depending on the print start position.

  Table 1 shows a look-up table when the specified time is selected according to the difference in development color.

The specified time stored in the reference time and specified time storage unit 112 in FIG. 1 is the table shown in Table 1, and the specified time is selected from the development color information instructed at the time of printing.
The same selection is made from Table 2 to Table 6 below.

  As an example in Table 6, lookup used when selecting a reference value by setting development color, application function, image type, number of input gradations, number of writing gradations, input pixel density, and writing pixel density An example of a table is shown.

  As described above, according to the image forming apparatus of the present embodiment, since the frequency change frequency of the frequency modulation unit can be reduced, the print stop time due to the frequency change can be reduced, and the image forming apparatus can be produced. Can be improved.

  Further, according to the image forming apparatus of the present embodiment, by setting the frequency change point according to the PLL oscillation frequency, in addition to shortening the print stop time due to the frequency change, it is possible to prevent the deterioration of the image quality. Can do.

  In addition, according to the image forming apparatus of the present embodiment, unnecessary change in the PLL oscillation frequency is reduced, so that a reduction in productivity can be prevented.

  In addition, according to the image forming apparatus of the present embodiment, the optimum specified time can be selected, so that the print stop time due to the frequency change can be further reduced, and the productivity of the image forming apparatus is improved. Can do.

  Further, according to the image forming apparatus of the present embodiment, the optimum specified time can be selected according to various modes, and therefore, the print stop time due to the frequency change can be further reduced. Productivity can be improved.

  As mentioned above, although the Example of this invention was described, it is not limited to the said Example, A various deformation | transformation is possible in the range which does not deviate from the summary.

  The present invention can be applied to all image forming apparatuses and image forming methods.

1 is a block diagram illustrating a laser beam scanning device as an image writing unit and a peripheral control system provided in an image forming apparatus according to an embodiment of the present invention. (A) is a figure which shows the relationship between reference | standard time and a regulation time amount, and FIG.2 (b) and (c) are the cases where a reference | standard time unit is divided into 2 or 3 with respect to Fig.2 (a). FIG. (A) is a figure which shows the change of the range of the regulation time amount when the reference time is changed from D to E, (b) is a figure which shows the case where the regulation time quantity of Fig.3 (a) differs. FIGS. 3C and 3D are diagrams showing a case where the specified amount of time is a dotted line interval. 6 is a flowchart illustrating an operation of phase shift value determination performed in the image forming apparatus according to the embodiment of the present invention. (A) is a figure which shows an example of a magnification fluctuation and printing size, (b) is a figure which shows an example which changed the resist of Fig.5 (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 LD modulator 102 Polygon scanner 103 f (theta) lens 104 Photoconductor 105 Leading synchronization detection sensor 106 Trailing synchronization detection sensor 107 Time difference measurement part 108 Write clock generation part 108-1 PLL oscillation apparatus 108-2 Phase control apparatus 109 LD
110 Magnification Correction Control Unit 111 Sub Correction Amount Determination Unit 112 Reference Time and Specified Time Storage Unit

Claims (12)

An image forming apparatus that forms 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 a light beam;
Magnification correction means for correcting the magnification of the image on the image carrier in the main scanning direction based on the time difference measured by the time difference measurement means,
The magnification correction means includes
Main position control means for performing magnification correction by changing the density of beam spot position intervals on the scanning line in units of one line or in units of one line or more;
Sub-position control means for correcting magnification by changing the density of beam spot position intervals on the scanning line in units of one pixel;
Sub correction time calculating means for calculating a difference between a reference time that can be set only by the operation of the main position control means and a time measured by the time difference measuring means;
Determination means for determining the magnitude of the correction time amount calculated by the sub correction calculation means and a preset specified time amount;
As a result of determination by the determination means, until the correction time amount exceeds the specified time amount, magnification correction is performed by the sub position control means without operating the main position control means, and the determination by the determination means is performed. As a result, when the correction time amount exceeds the specified time amount, magnification correction is performed by operating the main position control means.   The reference time that can be set only by the operation of the main position control means is in accordance with a set value of the main position control means, and the specified time amount is set corresponding to a time difference between the plurality of reference times. The image forming apparatus according to claim 1, wherein: The reference time and the specified time amount before the change, and the changed reference time and the specified time amount set by operating the main position control means when the correction time amount exceeds the specified time amount,
｜ Reference time before change-Reference time after change | <(Specified amount of time before change + Specified amount of time after change)
The image forming apparatus according to claim 1, wherein the relationship is as follows.   The image forming apparatus according to claim 1, further comprising a specified value changing unit that can change the specified amount of time.   5. The image forming apparatus according to claim 1, further comprising a specified value changing unit configured to change the specified amount of time in accordance with a transfer sheet size.   5. The image forming apparatus according to claim 1, further comprising a specified value changing unit configured to change the specified amount of time in accordance with a main scanning registration position.   5. The image forming apparatus according to claim 1, further comprising a specified value changing unit configured to change the specified amount of time in accordance with a development color at the time of color printing.   5. The image forming apparatus according to claim 1, further comprising a specified value changing unit configured to change the specified amount of time according to a color type.   5. The image forming apparatus according to claim 1, further comprising a specified value changing unit that changes the specified time amount according to an image type.   5. The image forming apparatus according to claim 1, further comprising a specified value changing unit configured to change the specified amount of time in accordance with an application function.   5. The specified value changing means for changing the specified time amount according to any one of an input pixel density, a writing pixel density, an input gradation number, and a writing gradation number. The image forming apparatus according to claim 1.   Transfer paper size, main scanning registration position, development color at color printing, color type, image type, application function, input pixel density, writing pixel density, input gradation number, and writing gradation number 5. The image forming apparatus according to claim 1, further comprising a specified value changing unit configured to change the specified amount of time according to a combination.

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