Patent Grant
7391431
The present document incorporates by reference the entire contents of Japanese priority document, 2004-270049 filed in Japan on Sep. 16, 2004.
1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
In laser printers, which are image forming apparatuses, a photoconductor, which is an image carrier, is scanned in a horizontal scanning direction (i.e., main scanning direction) by optical beams (laser beams) deflected by a deflector to write an image on the surface of the photoconductor. The deflector can be, for example, a rotating polygon mirror.
Optical beams are deflected at an isometric velocity in the horizontal scanning direction by the deflector, and the optical beams are corrected from deflection at the isometric velocity to deflection at a uniform velocity by a fθ lens.
The fθ lenses can be made from different material including plastic. However, if an fθ lens made of plastic is used, its shape and/or refractive index can change with the surrounding temperature. If the shape or the refractive index changes, a scanning position on the photoconductor deviates, which results in a magnification error in the horizontal scanning direction. The magnification error leads to a degraded image. The refractive index also changes with the wavelength of the laser beam.
Various technologies have been proposed to correct the magnification error. In one approach, laser beams scanned in the horizontal scanning direction are respectively detected by laser beam detectors provided at two positions in the horizontal scanning direction, the time difference between detections of the laser beams in the two detectors is measured, and the magnification in the horizontal scanning direction is corrected based on this time difference.
Laser printers are disclosed in Japanese Patent Application Laid-open No. 2003-279873. In one of these laser printers, a scanning target surface is scanned in the horizontal scanning direction by beams of light deflected by a deflector, the beams of light are respectively detected on a write start position side and a write end position side, to correct the phase data based on the fluctuation amount of time required for scanning between the two positions, and the phase of respective signals of an image clock that performs image formation based on the phase data is shifted (phase modulation), thereby correcting the magnification of the image in the horizontal scanning direction on the image carrier.
In other laser printer disclosed in Japanese Patent Application Laid-open No. 2003-279873, the whole misregistration of dots in the horizontal scanning direction is shifted by changing the frequency of the image clock (frequency modulation), to correct the magnification of the image in the horizontal scanning direction on the image carrier.
The laser printer that corrects the magnification of the image by phase modulation in which the phase of the image clock signal is shifted can change the correction amount in a short period of time, and hence, correction can be performed in between sheets of paper (at the timing when image formation is not performed), when images are continuously formed. However, since image degradation occurs more or less as compared with the magnification correction of the image by frequency modulation, there is a problem in that when the phase shift amount of the image clock signal increases, degradation in the formed image increases.
On the other hand, when magnification correction of the image is performed by frequency modulation in which the whole misregistration amount of dots is shifted, a better image can be obtained as compared to the one obtained by phase modulation. In the case of frequency modulation, however, a phase-locked loop (PLL) circuit is normally used for generating a pixel clock for modulating the laser beams corresponding to an image signal. The PLL circuit includes a voltage-controlled oscillator that changes the frequency according to the applied voltage, and it is necessary to stop the printing operation until the PLL oscillating frequency is stabilized after having started a change in the oscillating frequency of the PLL.
That is, in the case of a method of correcting the frequency of the image signal, for example, number of prints and time are counted, and magnification correction of the image by frequency modulation is performed at an interval of certain time that is considered not to cause a side effect such as image degradation. In this case, however, image forming operation is suspended in order to correct the frequency of the image signal. As a result, the number of suspensions increases, and the overall print speed (number of image formations per unit time) as an image forming apparatus decreases drastically.
Further, when magnification correction of an image is performed by frequency modulation, if the timing for performing the frequency correction is previously set, then even when the magnification error in the horizontal scanning direction increases in the period after frequency correction of the image signal until the next frequency correction is performed, frequency correction is not performed until the timing for the next frequency correction, and hence, a degraded image is formed during this time.
It is an object of the present invention to at least solve the problems in the conventional technology.
According to an embodiment of the present invention, an image forming apparatus includes a deflector configured to deflect optical beams modulated according to an image signal to thereby scan a surface of an image carrier in a horizontal scanning direction to form an image on the image carrier; an optical beam detector arranged on either side of the image carrier along the horizontal scanning direction, wherein the optical beam detectors are configured to detect an optical beams deflected by the deflector; a time difference measuring unit configured to measure a time difference between detections of the optical beams by optical beam detectors; and a magnification correcting unit configured to correct, based on the time difference, a magnification in the horizontal scanning direction of the image on the image carrier. The magnification correcting unit includes a main position correcting unit configured to perform magnification correction of the image by changing a beam spot position interval on a scanning line in units of a line or lines; a sub position correcting unit configured to perform magnification correction of the image by changing a beam spot position interval on a scanning line in units of pixel; and a position adjustment amount-determining unit that determines whether a beam spot position adjustment amount corresponding to each of a plurality of developing colors preset by the sub position correcting unit exceeds a threshold preset for each of the plurality of developing colors, wherein the magnification correction of the image by the sub position correcting unit is changed over to the magnification correction of the image by the main position correcting unit based on a determination result of the position adjustment amount-determining unit.
According to another embodiment of the present invention, an image forming apparatus includes a deflector configured to deflect optical beams modulated according to an image signal to thereby scan a surface of an image carrier in a horizontal scanning direction to form an image on the image carrier; an optical beam detector arranged on either side of the image carrier along the horizontal scanning direction, wherein the optical beam detectors are configured to detect an optical beams deflected by the deflector; a time difference measuring unit configured to measure a time difference between detections of the optical beams by optical beam detectors; and a magnification correcting unit configured to correct, based on the time difference, a magnification in the horizontal scanning direction of the image on the image carrier. The magnification correcting unit includes a main position correcting unit configured to perform magnification correction of the image by changing a beam spot position interval on a scanning line in units of a line or lines; a sub position correcting unit configured to perform magnification correction of the image by changing a beam spot position interval on a scanning line in units of pixel; and a position adjustment amount-determining unit that determines whether a beam spot position adjustment amount by the sub position correcting unit, in a predetermined region in the horizontal scanning direction set for each of a plurality of colors, exceeds a threshold preset for each of the colors, wherein the magnification correction of the image by the sub position correcting unit is changed over to the magnification correction of the image by the main position correcting unit based on a determination result of the position adjustment amount-determining unit.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Exemplary embodiments of the present invention will be explained below in detail with reference to the accompanying drawings.
The laser printer includes an optical scanner 2. As shown in
The write clock generator 58 includes a PLL transmitter 58a and the phase controller 58b. The PLL transmitter 58a functions as a main position correcting unit (horizontal position correcting unit) that performs magnification correction of an image on the photoconductor 11 by changing a beam spot position interval on a scanning line in the unit of a line or in the unit of a plurality of lines. The phase controller 58b functions as a sub position correcting unit that performs magnification correction of an image by changing a beam spot position interval on a scanning line in the unit of pixel.
In the first embodiment, the magnification correction controller 61 also functions as a main position correcting unit and a sub position correcting unit.
The magnification correction controller 61 functions as a position adjustment amount-determining unit that determines the magnitude correlation between a beam spot position adjustment amount corresponding to each of a plurality of developing colors set by the sub position correcting unit (PLL transmitter 58a) and a threshold set for each of the developing colors. Further, the laser printer causes a controller 250, which is a microcomputer, to control so as to change over from the magnification correction of an image by the sub position correcting unit (phase controller 58b) to the magnification correction of the image by the main position correcting unit.
The laser printer shown in
The optical scanner 2 is situated above the four photoconductors 11. Paper feed cassettes 3 and 4 are provided in the lower part of an apparatus body 1 of the laser printer, and a pair of resist rollers 5 and the belt drive 6 are also provided. The belt drive 6, in the state with transfer paper (sheet) P carried thereon, sequentially carries the transfer paper P to toner image forming units (1Y, 1M, 1C, and 1K) where the photoconductors 11 are respectively provided, and carries the transfer paper P to a fixing unit 7. In the first embodiment, the belt drive 6 functions as a transfer unit.
Further, the laser printer includes a paper ejection tray 8, a manual feed tray 14, a toner supply container 22, and the like.
The transfer paper P is carried on a transport route shown by one-dot chain line in
When starting the image forming operation, the transfer paper P fed from the paper feed cassettes 3, 4, or the manual feed tray 14 is carried to the resist rollers 5, while being guided by a transport guide plate and stopped there temporarily.
The resist rollers 5 rotate at a predetermined timing. As a result, the resist rollers 5 carry the transfer paper P onto the transfer carrier belt 60. The transfer paper P gets electrostatically attracted onto the belt surface. The transfer paper P is then carried to the toner image forming unit, where the photoconductor 11 is present, by the transfer carrier belt 60 that is rotating in the direction shown by the arrow A.
Toner images of the respective colors formed on the respective photosensitive drums 11Y, 11M, 11C, and 11K are sequentially transferred and superposed on the transfer paper P by an action of transfer electric field and a nip pressure in the toner image forming unit. Accordingly, a full colored toner image is formed on the transfer paper P.
After the toner image is transferred onto the transfer paper P, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K are cleaned by respective cleaning units and the electricity is removed therefrom. Thus, the photosensitive drums 11Y, 11M, 11C, and 11K become ready for formation of next image.
The fixing unit 7 fixes the full-color toner image onto the transfer paper P. The transfer paper P with the fixed full-color toner image is then carried in a first paper ejection direction shown by an arrow B or a second paper ejection direction shown by an arrow C. In which direction the transfer paper P is carried depends on a switching position of a switching guide 21.
When the transfer paper P is carried in the first paper ejection direction and ejected onto the paper ejection tray 8, the transfer paper P is ejected in the paper ejection tray 8 in a so-called face down state, with the image surface facing down. When the transfer paper P is carried in the second paper ejection direction, the transfer paper P is carried toward a post-processor (not shown). The post-processor can be a sorter, a stapler, or the like.
In the optical scanner 2, a laser diode (LD) 29 that functions as an optical beam generator emits optical beams (laser beams) equivalent of image signals. Although not shown in the drawings, the optical beams pass through a collimate lens and a cylindrical lens, and finally fall on the rotating polygon mirror 32. The polygon mirror 32 deflects the optical beams so that optical beams pass through an fθ lens 23 and a toroidal lens (hereinafter, “BTL”) (not shown), and fall on the photoconductor 11. As the polygon mirror 32 rotates, the photoconductor 11 is scanned in the scanning direction with the optical beams. The BTL performs focusing mainly in a vertical scanning direction (i.e., sub scanning direction), that is, performs condensing function and position correction (cross-scan error compensation and the like) in the vertical scanning direction.
In
A driving unit, a motor, for example, rotates the polygon mirror 32. The fθ lens mainly performs velocity transformation. In other words, when optical beams of an isometric velocity that are deflected from the polygon mirror 32 enter into the fθ lens 23, they are converted into optical beams of a constant velocity.
When an optical beam scans the photoconductor 11, the optical beam first falls on the sensor 25, scans the photoconductor 11 in the direction shown by an arrow E, and finally falls on the sensor 26. Thus, there is a time lag, or a time difference, between when the optical beam falls on and it is detected in the sensor 25 and when the optical beam falls on and it is detected in the sensor 26. The sensor 25 also serves as a synchronism detection sensor for detecting a laser beam-scanning synchronization signal, which becomes a synchronism detection signal.
When an optical beam is detected, the sensor 25 outputs a laser beam detection signal DETP1, and the sensor 26 outputs a laser beam detection signal DETP2. The laser beam detection signals DETP1 and DETP2 are transmitted to the time difference measuring unit 57. The time difference measuring unit 57 measures a difference between the time of arrival of the laser beam detection signals DETP1 and DETP2. As the polygon mirror 32 rotates, the laser beam detection signals DETP1 and DETP2 arrive one after the other. The time difference measuring unit 57 calculates an average of a plurality of measured times as a time difference. The time difference measuring unit 57 measures the time of arrival of the laser beam detection signals DETP1 and DETP2 by using timing set by the controller (CPU) 250. The time difference measuring unit 57 transmits the time difference to the magnification correction controller 61.
The magnification correction controller 61 includes a storage unit that stores initial set values and current set values of the set write clock frequency and phase shift value which is indicative of beam spot position amount. The controller 250 sends the initial set values and the current set values to the magnification correction controller 61. The magnification correction controller 61 calculates the phase shift value when an optimum write clock frequency is set, by using the fact that the image magnification in the horizontal scanning direction is changed by the frequency of the write clock, and by using the fact that the image magnification is changed by shifting the phase in the case of such a short time that cannot be adjusted by adjusting a write clock.
The write clock generator 58 includes a PLL transmitter 58a and a phase controller 58b. The PLL transmitter 58a generates a clock n times as large as a write clock VCLK upon reception of a clock from an oscillator (not shown). The phase controller 58b divides the frequency of a PLL transmission clock by n, synchronized with the laser beam detection signal DETP1 as a synchronism detection signal to generate the write clock VCLK synchronized with the laser beam detection signal DETP1 and having a function of shifting (changing) the write clock cycle time of an optional pixel in the unit of pixel by adding or subtracting an integral multiple of the half cycle of the PLL transmission clock to or from a special cycle of the write clock.
In
The write clock VCLK subjected to the image magnification correction in the horizontal scanning due to changeability of the write clock frequency and the phase shift value by the write clock generator 58 is transmitted to the LD modulator 59 that functions as the optical beam generator actuator.
The LD modulator 59 controls lighting of the laser diode 29 in the LD unit according to the image signal synchronized with the write clock PCLK from the write clock generator 58. Accordingly, laser beams modulated according to the image signal are emitted from the laser diode 29, and the laser beams are deflected by the rotating polygon mirror 32 to scan across the photoconductor 11 via the fθ lens 23 in the direction of the arrow E in
In
The controller 250 can communicate with storage units that store comparison determination results in the image writing units through serial communications, and can simultaneously monitor determination results of comparing the phase shift value (beam spot position adjustment amount) with the threshold.
The magnification correction of an image performed by the control system in the image forming apparatus according to the first embodiment will be explained below with reference to
When the routine in
At next step S2, at the timing when the polygon mirror 32 is rotating between sheets or during printing, and when the laser diode 29 is in the state capable of lighting, the controller 250 outputs an instruction to calculate a magnification adjustment value to the time difference measuring unit 57 and the magnification correction controller 61, respectively.
At step S3, the controller 250 allows the time difference measuring unit 57 to measure the time difference since the sensor 25 has detected the laser beam at specified timing until the sensor 26 detects the laser beam for the specified number of measurements, to calculate a mean value of the measurement result. As a result, the time difference measuring unit 57 outputs the mean value or the like of the measurement result of the time difference to the magnification correction controller 61.
The measurement of the time difference is performed for each of the image writing units which handle the four developing colors, respectively.
At next step S4, the controller 250 allows the magnification correction controller 61 to calculate a phase shift value (beam spot position adjustment amount corresponding to each of the four developing colors) when the write clock frequency is fixed, from the mean value or the like of the measurement result of the time difference. At step S5, substantially at the same timing as at step S4 in parallel, the controller 250 allows the magnification correction controller 61 to calculate a write clock frequency (write clock value) and a phase shift value when an optimum write clock frequency is set, from the mean value or the like of the measurement result of the time difference.
At step S6a, the controller 250 determines the magnitude correlation between the phase shift value (beam spot position adjustment amount) calculated for each of the four developing colors at step S4 and the threshold preset in the controller 250. That is, the controller 250 determines whether the phase shift value is larger than the threshold for each image writing unit corresponding to each developing color to determine whether the phase shift value is larger than the threshold in at least one of the determinations corresponding to the four developing colors (another way to determine the magnitude correlation is explained later), and stores the comparison result (magnitude correlation) in the storage unit.
According to the determinations corresponding to the four developing colors, when the phase shift value is larger than the threshold in at least one of the determinations, control proceeds to step S10. When all the phase shift values corresponding to the four developing colors do not exceed respective thresholds (phase shift value≦threshold) (NO), at step S7, the controller 250 transmits the determination result such that magnification correction of an image (magnification correction of an image by the sub position correcting unit) is to be executed by phase modulation that can perform magnification correction of the image without expanding the interval between sheets even during continuous printing, to the write clock generator 58.
At step S8, the controller 250 issues a magnification adjustment instruction to the magnification correction controller 61 at the timing effective for printing after having calculated the phase shift value. Accordingly, the magnification correction controller 61 stores the instruction. At step S9, the magnification correction controller 61 transmits a control signal for performing the magnification correction of the image by using the determined phase shift value to the write clock generator 58. Accordingly, the magnification correction of the image is performed by changing the beam spot position interval on the scanning line in the unit of pixel.
According to the determination at step S6a, when the phase shift value is larger than the threshold in at least one of the determinations, and at least one of the phase shift values exceeds the threshold, control proceeds to step S10, where a determination result of magnification correction by the main position correcting unit (magnification correction by frequency modulation) is transmitted to the write clock generator 58. The main position correcting unit performs magnification correction of an image by changing the beam spot position interval on the scanning line in the unit of a line or in the unit of a plurality of lines.
The magnification correction by the frequency modulation cannot be performed at any timing during image formation, and a certain period of time is necessary for the magnification correction. Therefore, it is necessary to have an interval between sheets during continuous printing. Accordingly, continuous printing is temporarily suspended, and at step S11, a magnification adjustment instruction is sent to the magnification correction controller 61 at a convenient timing.
Accordingly, the magnification correction controller 61 stores the instruction. At step S12, the controller 250 allows the magnification correction controller 61 to transmit a control signal for performing the magnification correction of the image with optimum write clock frequency and phase shift value calculated at step S5 to the write clock generator 58. Accordingly, magnification correction of the image (magnification correction of the image by the main position correcting unit) is performed by the frequency modulation in which the frequency of the image signal is changed in the unit of a line or in the unit of a plurality of lines.
At step S13, printing is executed according to the control signal set and transmitted to the write clock generator 58 at step S9, or the control signal set and transmitted to the write clock generator 58 at step S12.
At step S14, it is determined whether the all set image formation has finished, and if the image formation has finished, the processing in this routine is finished. If all image formation has not finished yet, with returning to step S2, to repeat the processing and determination at step S2 and following steps at a predetermined timing.
Thus, in the image forming apparatus (laser printer) according to the first embodiment, the magnification correction of the image (magnification correction of an image by the sub position correcting unit) is performed by changing the beam spot position interval on the scanning line in the unit of pixel until at least one of the beam spot position adjustment amounts (phase shift values) corresponding to the four developing colors exceeds a preset threshold, and after at least the one thereof exceeds the preset threshold, magnification correction of the image (magnification correction of the image by the main position correcting unit) is performed by changing the beam spot position interval on the scanning line in the unit of line or in the unit of a plurality of lines.
Since the interval between sheets has to be enlarged in the latter case, it is necessary to suspend continuous printing. However, the execution times of magnification correction (frequency modulation) of an image by the main position correcting unit can be decreased. Therefore, productivity of image formation can be improved.
Furthermore, the threshold can be set to an optimum value for each developing color. Therefore, the changeover from the magnification correction of an image by the sub position correcting unit to the magnification correction of an image by the main position correcting unit can be performed at more appropriate timing.
In the image forming apparatus according to the second embodiment, when the routine shown in
Thereafter, control proceeds to step S6a, where the controller 250 determines the magnitude correlation between the phase shift value (beam spot position adjustment amount) calculated for each of the four developing colors at step S4 and the threshold preset in the controller 250, that is, whether the phase shift value is larger than the threshold for each of the image writing units corresponding to the developing colors. The controller 250 further determines whether the phase shift value is larger than the threshold in least one of the determinations corresponding to the four developing colors, and stores the comparison result (magnitude correlation) in the storage unit.
According to the determinations corresponding to the four developing colors, when the phase shift value is larger than the threshold in at least one of the determinations, control proceeds to step S5. When all the phase shift values corresponding to the four developing colors do not exceed respective thresholds (phase shift value≦threshold) (NO), at step S7, the controller 250 transmits the determination result such that magnification correction of an image is to be executed by phase modulation (magnification correction of an image by the sub position correcting unit), by which magnification correction of the image can be performed without expanding the interval between sheets even during continuous printing, to the write clock generator 58.
According to the determination at step S6a, when the phase shift value is larger than the threshold in at least one of the determinations, and at least one of the phase shift values exceeds the threshold, control proceeds to step S5, where the same processing as that explained at step S5 of
That is, in the second embodiment, only when the phase shift value (beam spot position adjustment amount) at least one of the four developing colors when the write clock is fixed is larger than the threshold, the controller 250 allows the main position correcting unit to calculate the write clock value and the phase shift value when the optimum write clock frequency is set, that is, to perform magnification correction.
In this manner, the same effect as in the first embodiment can be obtained in the second embodiment.
The configuration of the image forming apparatus according to the third embodiment is the same as that in
The image forming apparatus according to the third embodiment is different from the image forming apparatus according to the first embodiment in that a controller (CPU) 250′ performs the function of the magnification correction controller 61. The controller 250′ includes a microcomputer similar to that of the controller 250, and only the content of the control is different from the controller 250.
In the third embodiment, the time difference measuring unit 57 performs time difference measurement and calculation between the laser beam detection signals DETP1 and DETP2, and transmits the measurement result and the calculation result to the controller 250′. The controller 250′ has a storage unit that stores the initial set values and the current set values of the write clock frequency and the phase shift value (beam spot position adjustment amount), and has a function of calculating an optimum write clock frequency and a phase shift value by using the fact that the image magnification in the horizontal scanning direction is changed by the frequency of the optimum write clock, and by using the fact that the image magnification is changed by shifting the phase in the case of such a short time that cannot be adjusted by adjusting a write clock.
The controller 250′ has a function of calculating the optimum phase shift value (beam spot position adjustment amount) by fixing the write clock frequency, and also has a function of comparing the phase shift value calculated with a preset threshold. The controller 250′ transmits a write clock setting signal and a control signal for executing the phase shift to the write clock generator 58 at a predetermined timing, respectively.
That is, in the third embodiment, the controller 250′ functions as the phase adjustment amount-determining unit. The controller 250′ also functions as the frequency modulator (main position correcting unit) together with the PLL transmitter 58a, and as the phase modulator (sub position correcting unit) together with the phase controller 58b.
In
The controller 250′ in the third embodiment starts the routine of magnification correction of an image shown in
That is, at first step S21, the controller 250′ sets a write clock initial value and a phase shift initial value in the write clock generator 58, at a predetermined timing such as after turning the power on or restarting after having stopped the machine, and makes the optical scanner printable corresponding to the set write clock initial value and phase shift initial value. In this state, since the printing is possible, printing can be performed.
At next step S22, at the timing when the polygon mirror 32 is rotating between sheets or during printing, and when the laser diode 29 is in the state capable of lighting, the controller 250′ outputs an instruction to calculate a magnification adjustment value to the time difference measuring unit 57.
At step S23, the controller 250′ allows the time difference measuring unit 57 to measure the time difference since the sensor 25 has detected the laser beam at specified timing until the sensor 26 detects the laser beam, for the specified number of measurements. The controller 250′ inputs the measurement result to calculate a mean value or the like of the measurement result.
At next step S24, a phase shift value (beam spot position adjustment amount) when the write clock frequency is fixed is calculated from the mean value or the like of the measurement result of the time difference. At step S25′, the controller 250′ determines the magnitude correlation between the phase shift value (beam spot position adjustment amount) calculated for each of the four developing colors at step S24 and the threshold preset in the controller 250′. That is, the controller 250′ determines whether the phase shift value is larger than the threshold for each of the image writing units corresponding to the developing colors, to further determine whether the phase shift value is larger than the threshold in at least one of the determinations corresponding to the four developing colors, and stores the comparison result (magnitude correlation) in the storage unit.
According to the determinations corresponding to the four developing colors, when the phase shift value is larger than the threshold in at least one of the determinations, control proceeds to step S27. When all the phase shift values corresponding to the four developing colors do not exceed respective thresholds (phase shift value≦threshold) (NO), at step S26, the controller 250′ transmits a control signal for performing the magnification correction of the image based on the phase shift value determined to the write clock generator 58, so as to perform magnification correction of the image by changing the cycle time of an optional pixel in the unit of pixel. That is, the magnification correction of the image is performed by the sub position correcting unit that performs magnification correction of the image by changing the beam spot position interval on the scanning line in the unit of pixel.
According to the determination at step S25′, when the phase shift value of at least one of the four developing colors is larger than the threshold, and the phase shift value exceeds the threshold, control proceeds to step S27, where a write clock value and a phase shift value when an optimum write clock frequency is set is calculated from the measurement and calculation results at step S23. That is, the write clock frequency and the phase shift value (beam spot position adjustment amount) when executing the frequency modulation are calculated. The frequency modulation is executed in such a manner that magnification correction of an image (magnification correction of an image by the main position correcting unit) is performed by changing the beam spot position interval on the scanning line in the unit of a line or in the unit of a plurality of lines.
At next step S28, a control signal for performing magnification correction of an image based on the write clock frequency and the phase shift value calculated at step S27 is transmitted to the write clock generator 58, and at step S29, a control signal for performing magnification correction of an image based on the write clock frequency and the phase shift value calculated at step S27 is transmitted to the write clock generator 58. Accordingly, magnification correction of the image (magnification correction of an image by the main position correcting unit) is performed by changing the beam spot position interval on the scanning line in the unit of a line or in the unit of a plurality of lines.
In the case of the magnification correction by the frequency modulation, since the write clock is changed, magnification correction cannot be performed at any timing during image formation. Further, since a certain period of time is necessary for the processing of the magnification correction, it is necessary to have an interval between sheets during continuous printing. Accordingly, continuous printing is temporarily suspended, and the control signal is sent to the write clock generator 58 at a convenient timing.
At next step S30, printing is executed at the write clock frequency, with the write clock frequency changed according to the control signal set and transmitted to the write clock generator 58 at step S26, or the control signal set and transmitted to the write clock generator 58 at step S29.
At step S31, it is determined whether the all set image formation has finished, and if the image formation has finished, the processing in this routine is finished. However, if all image formation has not finished yet, control returns to step S22, to repeat the processing and determination at step S22 and following steps at a predetermined timing.
The first embodiment to the third embodiment indicate respective examples, each in which it is determined whether the phase shift value (beam spot position adjustment amount) calculated for each of the four developing colors exceeds the threshold, and in which when the phase shift value exceeds the threshold in at least one of four determination results, the main position correcting unit performs magnification correction. However, determination of a timing of changing over to the magnification correction by the main position correcting unit may be performed when the phase shift values exceed the respective thresholds in determination results corresponding to a plurality (the number can be arbitrarily set) of developing colors.
Alternatively, when a total amount obtained by adding up all of the four phase shift values (beam spot position adjustment amounts) corresponding to the four developing colors exceeds a corresponding threshold, the magnification correction may be performed by the main position correcting unit.
The configuration of the image forming apparatus according to the fourth embodiment is the same as that in
The image forming apparatus according to the fourth embodiment is different from the image forming apparatus explained with reference to
When all the four determination results are in the respective thresholds, the magnification correction of the image (magnification correction of the image by the sub position correcting unit) is performed by changing the beam spot position interval (changing the phase shift amount) on the scanning line in the unit of pixel.
Thus, in the configuration in which optimum phase adjustment (phase shift) is performed by changing the cycle time of an optional pixel per unit of pixel, that is, when correction of the optimum write start position Ps in the horizontal scanning direction and correction of the magnification in the horizontal scanning direction are respectively performed based on the write position-correcting phase shift value and the magnification-correcting phase shift value calculated by fixing the write clock frequency, the magnification correction controller 61′ has a storage unit that stores initial set values of the write clock frequency, the write position-correcting phase shift value in the horizontal scanning direction, and of the magnification-correcting phase shift value, transmitted from a controller (CPU) 250″, as well as the current set values thereof.
The controller (CPU) 250″ is a microcomputer and it starts the routine for a magnification correction of an image shown in
At first step S1′, the controller 250″ sets an initial value of the write clock frequency, an initial value of the write position-correcting phase shift value (write position-correcting phase shift initial value), and an initial value of the magnification-correcting phase shift value (magnification-correcting phase shift initial value) in the magnification correction controller 61′, at a predetermined timing such as after turning the power on or restarting after having stopped the machine, and makes the optical scanner printable corresponding to the set initial value of the write clock frequency and phase shift initial values. In this state, since the printing is possible, printing can be performed.
At steps S2 and S3, the same processing as those explained at the steps S2 and S3 shown in
At step S5′, the magnification correction controller 61′ calculates a write clock value (frequency) and a magnification-correcting phase shift value when an optimum write clock frequency is set, corresponding to each of the developing colors, from the mean value or the like of the measurement result of the time difference.
At next step S6a′, the controller 250″ determines the magnitude correlation between the magnification-correcting phase shift value calculated at step S4′ and a threshold preset in the controller 250″, that is, whether the magnification-correcting phase shift value is larger than the threshold for each of the image writing units. The controller 250″ further determines whether the magnification-correcting phase shift value is larger than the threshold in at least one of the determinations corresponding to the four developing colors, and stores the comparison result (magnitude correlation) in the storage unit.
According to the determination, when all the magnification-correcting phase shift values corresponding to the four developing colors are equal to or smaller than the respective thresholds, that is, when the magnification-correcting phase shift values do not exceed the thresholds (NO), the same processing and determination as those in
According to the determination at step S6a′, when the magnification-correcting phase shift value is larger than the threshold in at least one of the determinations corresponding to the four developing colors, that is, the magnification-correcting phase shift value exceeds the threshold, the same processing and determination as those in
Thus, in the fourth embodiment, the phase adjustment amount (phase shift) at the time of fixing the write clock frequency is divided into the write position-correcting phase shift value for correcting the write start position and the magnification-correcting phase shift value for correcting the magnification in the horizontal scanning direction. Only the magnification-correcting phase shift value is compared with the threshold to determine the magnitude correlation therebetween, and magnification correction of the image by phase modulation and magnification correction of the image by frequency modulation are changed over according to the determination result. Even when the changeover of the image magnification correction method is determined based on only the magnification-correcting phase shift value, no problem will occur because the write position-correcting phase shift value affects little on image degradation in the image area.
Magnification correction of the image by the frequency modulation, in which the image forming operation needs to be suspended temporarily, is executed only when the magnification-correcting phase shift value exceeds the threshold. Therefore, the number of executing the magnification correction of the image by the frequency modulation can be reduced, thereby improving the overall print speed (productivity of image formation) accordingly, as the whole image forming apparatus.
As a fifth embodiment of the present invention that is a modification of the fourth embodiment, the magnification correction controller 61′ shown in
In this case, the time difference measuring unit 57 shown in
The controller 250″ has a configuration including a storage unit that stores respective initial set values and current set values of the write clock frequency, the magnification-correcting phase shift value, and the write position-correcting phase shift value.
Further, the controller 250″ has a function of calculating an optimum write clock frequency, and a magnification-correcting phase shift value and a write position-correcting phase shift value at the optimum frequency, a function of calculating an optimum magnification-correcting phase shift value by fixing the write clock frequency, and a function of comparing the magnification-correcting phase shift value calculated with a preset threshold, and transmits a write clock setting signal and a control signal for performing phase shift to the write clock generator 58 at a predetermined timing, respectively.
The configuration of the image forming apparatus according to the sixth embodiment is the same as that in
The phase modulator in the image forming apparatus according to the sixth embodiment can correct the write start position in the horizontal scanning direction by a write position-correcting phase shift value (write start position-correcting phase adjustment amount), and the magnification in the horizontal scanning direction by a magnification-correcting phase shift value (magnification-correcting phase adjustment amount in the horizontal scanning direction), respectively, as in the fourth embodiment explained with reference to
In the sixth embodiment, a phase adjustment amount-determining unit (corresponding to the magnification correction controller 61′ in
That it, when the routine in
At steps S2 and S3, the controller performs the same processing as those at steps S2 and S3 in
At step S5′, the magnification correction controller 61′ calculates a write clock value (frequency) and a magnification-correcting phase shift value when an optimum write clock frequency is set, from the mean value or the like of the measurement result of the time difference.
At next step S6a″, the controller 250″ determines the magnitude correlation between a phase adjustment amount, obtained by adding up the write position-correcting phase shift value and the magnification-correcting phase shift value when the write clock frequency calculated at step S4′ is fixed, and a threshold preset in the controller 250″. That is, the controller 250″ determines whether the total of the magnification-correcting phase shift values is larger than the threshold, for each of the image writing units corresponding to the developing colors. The controller 250″ further determines based on the determinations whether the magnification-correcting phase shift value is larger than the threshold in at least one of the determinations corresponding to the four developing colors, and stores the determination result (magnitude correlation) in the storage unit.
According to the determinations, when the total of the magnification-correcting phase shift values corresponding to the four developing colors is equal to or smaller than the threshold, that is, when the total of the phase shift values does not exceed the threshold for all the image writing units corresponding to the four developing colors (NO), the same processing and determination as those in
According to the determination at step S6a″, when the total of the magnification-correcting phase shift values is larger than the threshold in at least one of the determinations corresponding to the four developing colors, that is, the total of the magnification-correcting phase shift values exceeds the threshold, the same processing and determination as those in
Thus, in the sixth embodiment, magnification correction of an image (magnification correction of an image by the sub position correcting unit) by phase modulation (frequency fixed) and magnification correction of the image by frequency modulation (magnification correction of the image by the main position correcting unit) are changed over, according to whether the phase shift value exceeds the preset threshold, the phase shift value being obtained by adding up the write position-correcting phase shift value and the magnification-correcting phase shift value when the write clock frequency is fixed.
Therefore, as compared with the fourth embodiment explained with reference to
The fourth embodiment to the sixth embodiment indicate respective examples, each in which it is determined whether the phase shift value (beam spot position adjustment amount) calculated for each of the four developing colors exceeds the threshold, and in which when the phase shift value exceeds the threshold in at least one of four determination results, the main position correcting unit performs magnification correction. However, determination of a timing of changing over to the magnification correction by the main position correcting unit may be performed when the phase shift values exceed the respective thresholds in the determination results corresponding to a plurality (the number can be arbitrarily set) of developing colors.
Alternatively, when a total amount obtained by adding up all of the four phase shift values (beam spot position adjustment amounts) corresponding to the four developing colors exceeds a corresponding threshold, the magnification correction may be performed by the main position correcting unit.
The configuration of the image forming apparatus according to the seventh embodiment is the same as that in
The image forming apparatus according to the seventh embodiment is different from that of the first embodiment explained with reference to
In the seventh embodiment, the magnitude correlation between the magnification-correcting phase shift value corresponding to each of the developing colors and a set threshold is determined. When the magnification-correcting phase shift value is larger than the threshold in at least one of determination results corresponding to the four developing colors, the magnification correction of an image by the sub position correcting unit is changed over to the magnification correction of the image (magnification correction of an image by the main position correcting unit) by changing the beam spot position interval on the scanning line in the unit of a line or in the unit of a plurality of lines.
In the seventh embodiment, predetermined regions in the horizontal scanning direction, that is, the whole region between the detection positions PO1 and PO2 of the sensors 25 and 26, as shown in
Further, the magnification correction controller 61 and the controller 250 (see
Determination of the magnitude correlation between the phase shift value and the threshold is performed in the following manner.
At first, comparison is made between the phase shift values I to X for the regions of the divided first to the tenth regions and corresponding thresholds I to X, for each of the image writing units corresponding to the four developing colors. The regions are then divided into a region in which the phase shift value is equal to or smaller than the threshold, and a region in which the phase shift value is larger than the threshold. If there is even one region, (it may be set when the number becomes equal to or larger than a preset plurality number), in which the phase shift value is larger than the threshold, magnification correction of an image is performed by frequency modulation (magnification correction of an image by the main position correcting unit) in which the magnification correction is performed by changing the frequency of an image signal to an optimum write clock frequency in the unit of a line or in the unit of a plurality of lines.
In
The image forming apparatus according to the seventh embodiment starts the routine of magnification correction of an image shown in
At first step S41, the controller 250 sets a write clock frequency initial value (hereinafter, simply as write clock initial value) and a phase shift initial value in the magnification correction controller 61, at a predetermined timing such as after turning the power on or restarting after having stopped the machine. At this time, the phase shift value of the whole region between the detection positions PO1 and PO2 (also see
The optical scanner is made printable corresponding to the set write clock initial value and phase shift initial value.
At next step S42, the same processing as explained at step S2 in
At step S44, the phase shift value (beam spot position adjustment amount) is calculated for each region when the write clock frequency is fixed, from the mean value or the like of the measurement result of the time difference.
At step S45, substantially at the same timing as at step S44 in parallel, a write clock frequency (write clock value) when an optimum write clock frequency is set is calculated from the mean value or the like of the measurement result of the time difference. Further, the phase shift value (beam spot position adjustment amount) for each region when the frequency is changed to the optimum write clock frequency is calculated.
At step S46, the phase shift value (a value calculated by fixing the write clock frequency) is compared with each of the thresholds I to X (see Table 1) corresponding thereto for each region, to calculate the number of regions in which the phase shift value is larger than the threshold.
At step S47′, it is determined whether the number of regions in which the phase shift value calculated is larger than the threshold is equal to or smaller than a preset value (0 is set in this example), and if the number is equal to or smaller than the preset value (Yes), control proceeds to steps S48 and S49, to transmit a determination result such that magnification correction of an image is to be executed by phase modulation (magnification correction of an image by the sub position correcting unit), which can perform magnification correction of the image without expanding the interval between sheets even during continuous printing, as in the processing explained at steps S7 and S8 in
At step S50, the controller 250 issues an instruction for performing magnification correction of an image with the respective phase shift values when the write clock frequency is fixed, calculated for respective regions. Accordingly, magnification correction of the image is performed by changing the cycle time of an optional pixel in the unit of pixel.
According to the determination at step S47′, when control proceeds to step S51 since the number of regions in which the phase shift value is larger than the threshold is one or more and exceeds the preset value, the same processing as explained at steps S10 and S11 in
At step S53, the controller 250 issues an instruction for performing magnification correction of an image based on the optimum write clock frequency and the phase shift value for each region calculated at step S45. As a result, the magnification correction of an image is performed by frequency modulation, in which the frequency of an image signal is changed in the unit of a line or in the unit of a plurality of lines.
The processing and determination as those explained at step S13 and following steps in
Thus, in the seventh embodiment, it is determined whether a magnification-correcting phase shift value is larger than the threshold for each of predetermined regions (indicating any ones of the first to the tenth regions shown in
The comparison between the phase shift value and the threshold can be performed in such a manner that, as shown in Table 2, a threshold obtained by unifying a plurality of divided regions is provided, which is then compared with a phase shift value obtained in the above manner. For example, even when the phase shift value is set for each region of from the first to the tenth regions, as in the example shown in Table 2, the respective regions are unified into a group (region) of from the second to the fourth regions, a group (region) of from the fifth to the sixth regions, and a group (region) of from the seventh to the ninth regions, and total values II, III, and IV of the phase shift values are respectively set corresponding to the groups, and these can be compared with the respective thresholds II, III, and IV.
Each group (region) is obtained by unifying a plurality of regions, and the number of groups in which the phase shift value exceeds the corresponding threshold is calculated. When the number exceeds a preset value, magnification correction of an image is performed by frequency modulation, which is performed by changing the write clock frequency.
In this case, the magnification correction controller 61 (or the controller 250′ when applied to
The way to unify the first to the tenth regions into a plurality of groups (regions) is not limited to the one shown in Table 2.
The predetermined regions in the horizontal scanning direction can be positioned in a horizontal-scanning image area, as the second to the ninth regions shown in
The configuration of the image forming apparatus according to the eighth embodiment is the same as that in
The phase modulator (sub position correcting unit) in the image forming apparatus according to the eighth embodiment can correct the write start position in the horizontal scanning direction by a write position-correcting phase shift value (write start position-beam spot position adjustment amount) by phase modulation, and correct the magnification in the horizontal scanning direction by a magnification-correcting phase shift value (beam spot position adjustment amount in the horizontal scanning direction) by phase modulation, respectively, as in the fourth embodiment explained with reference to
When the routine in
At next step S64, a magnification-correcting phase shift value and a write position-correcting phase shift value, for each region (each predetermined region in 1 to 10 regions shown in
At step S65, substantially at the same timing as at step S64 in parallel, a write clock frequency (write clock value) when an optimum write clock frequency is set is calculated. Further, a magnification-correcting phase shift value for each region when the frequency is changed to the optimum write clock frequency is calculated.
At next step S66, the magnification-correcting phase shift value (a value calculated by fixing the write clock frequency) for each region for each of the image writing units respectively corresponding to the four developing colors is compared with each of the thresholds I to X corresponding thereto for each region (see Table 3), to calculate the number of regions in which the magnification-correcting phase shift value in each region is larger than the threshold in the region.
At step S47′, it is determined whether the number of regions calculated is equal to or smaller than a preset value (0 is set in this example, but a numerical value may also be set to 1 or more), and if the number is equal to or smaller than the preset value (YES), control proceeds to steps S48 and S49, to transmit a determination result such that magnification correction of an image (magnification correction of an image by the sub position correcting unit) is to be executed by phase modulation that can perform magnification correction of the image without expanding the interval between sheets even during continuous printing, as in the processing explained at steps S7 and S8 in
At step S70, the controller 250″ issues an instruction for performing magnification correction of an image with the respective magnification-correcting phase shift values when the write clock frequency is fixed, calculated for respective regions. Accordingly, magnification correction of the image is performed by changing the cycle time of an optional pixel in the unit of pixel.
According to the determination at step S47′, when control proceeds to step S51 since the number of regions in which the phase shift value is larger than the threshold is one or more and exceeds the preset value, the same processing as explained at steps. S10 and S11 in
At step S73, the controller 250″ issues an instruction for performing magnification correction of an image based on the optimum write clock frequency and the magnification-correcting phase shift value for each region calculated at step S65. Accordingly, the magnification correction of the image is performed by frequency modulation, in which the frequency of an image signal is changed in the unit of a line or in the unit of a plurality of lines.
Thereafter, the same processing and determination as those explained at step S54 and following steps in
According to the eighth embodiment, determination to change over the magnification correction of an image from the one by phase modulation (magnification correction of an image by the sub position correcting unit) to the one by frequency modulation (magnification correction of an image by the main position correcting unit) is performed by comparing only the magnification-correcting phase shift value (beam spot position adjustment amount in the horizontal scanning direction) with the threshold set in the predetermined region in the horizontal scanning direction. The write position-correcting phase shift value is not used for the comparison because it has little influence on image degradation in the image area. Accordingly, the content of the control can be simplified.
The configuration of the image forming apparatus according to the ninth embodiment is the same as that in
The image forming apparatus according to the ninth embodiment is different from that of the eighth embodiment shown in
When the routine in
At step S66′, comparison is made between a phase shift value (beam spot position adjustment amount) and each of thresholds I to X for each region, the phase shift value being obtained by adding up the write position-correcting phase shift value and the magnification-correcting phase shift value (a value calculated with the write clock frequency being fixed) calculated for each of 1 to 10 regions shown in Table 3. The number of regions, each in which the total of phase shift values in a region is larger than the threshold in the region, is then calculated.
Thereafter, the determination and processing at step S47′ and following steps in
According to the determination at step S47′, when the number of regions, in which the total of the phase shift values in each region is larger than the threshold in the relevant region, is 1 or more and exceeds the preset value, the magnification correction of an image (magnification correction of an image by the main position correcting unit) is executed by frequency modulation in which magnification correction of the image is performed by changing the write clock frequency (frequency of an image signal) in the unit of a line or in the unit of a plurality of lines.
The processing at step S65 in
According to the ninth embodiment, determination to changeover the magnification correction of an image from the one by phase modulation to the one by frequency modulation is performed by comparing the phase shift value obtained by adding up the write position-correcting phase shift value and the magnification-correcting phase shift value with the threshold. Therefore, the phase shift amount in a region in which image degradation is desired to be prevented can be determined accurately.
According to the present invention, the magnitude correlation between the phase adjustment amount and the threshold is determined, and changeover to the magnification correction of an image by frequency modulation, at which image degradation does not occur, is performed based on the determination result. Therefore, the threshold is set to a value of allowable limit in image degradation, so that image degradation cannot occur. Since the number of suspending the image forming operation, due to magnification correction of an image by frequency modulation, can be reduced, a drop of the overall print speed (number of image formations per unit time) as an image forming apparatus can be prevented.
According to the image forming apparatus that includes the position adjustment amount-determining unit that determines the magnitude correlation between the beam spot position adjustment amount corresponding to each of a plurality of developing colors and the threshold set for each of the developing colors, the threshold can be optimized for each developing color. Therefore, changeover of magnification correction of an image can be performed from the one by the sub position correcting unit to the one by the main position correcting unit at more optimum timing. Therefore, productivity of image formation can be improved.
According to the present embodiments, the magnitude correlation between the phase shift value and the threshold is determined, and magnification correction of an image is changed over to the one by frequency modulation, in which image degradation does not occur, based on the determination result. Accordingly, degradation in an image can be prevented by setting the threshold to a value within a tolerance limit of image degradation. Further, the number of suspending the image forming operation, due to execution of the magnification correction of the image by frequency modulation, can be reduced, thereby preventing a drop in the overall sprint speed (number of image formations per unit time) as the image forming apparatus.
Further, according to the image forming apparatus including the frequency adjustment amount converter that converts the phase adjustment amount set by the phase modulator to the frequency adjustment amount for the frequency modulator, the phase adjustment amount set by the phase modulator is directly converted to the frequency adjustment amount for the frequency modulator without measurement of the amount or the like. Therefore, magnification correction of an image can be controlled only by calculation, without suspending continuous printing, thereby preventing a drop in sprint speed as the image forming apparatus.
Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-270049 | Sep 2004 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5610651 | Yamakawa et al. | Mar 1997 | A |
| 6157400 | Genovese | Dec 2000 | A |
| 6219085 | Hanna | Apr 2001 | B1 |
| 6236418 | Yamakawa | May 2001 | B1 |
| 6459520 | Takayama | Oct 2002 | B1 |
| 6833856 | Maeda | Dec 2004 | B2 |
| 6933957 | Omori et al. | Aug 2005 | B2 |
| 7050080 | Ema et al. | May 2006 | B2 |
| 20030067533 | Omori et al. | Apr 2003 | A1 |
| 20060055902 | Ohkawara et al. | Mar 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 2003-279873 | Oct 2003 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20060055902 A1 | Mar 2006 | US |
