1. Field of the Invention
The present invention relates to an optical scanning device for performing optical writing in accordance with input image signals and to image forming apparatuses, such as copiers, printers, facsimile apparatuses, and printers (for both color and black-and-white) that include such optical scanning device.
2. Description of the Related Art
In a known image forming apparatus using light-beams scanning device, light beams are modulated with image data and are deflected at a constant angular velocity in a main-scanning direction by rotation of deflecting means (hereinafter referred to as a “polygon mirror”), the constant angular-velocity deflection is corrected to constant velocity deflection by an fθ lens, and the resulting beams scan on an image holder (hereinafter referred to a “photoreceptor”). However, the known apparatus has a problem in that the image magnification varies from apparatus to apparatus due to variations in the lens characteristics. In particular, when a plastic lens is used, the shape and the refractive index of the plastic lens change due to changes in ambient temperature and changes in the temperature inside the apparatus. Thus, the scanning position on an image surface of the photoreceptor shifts, and a magnification error in the main-scanning direction occurs; thus, it is impossible produce a high-quality image. In an apparatus that uses multiple laser beams and multiple lenses to produce an image of multiple colors, magnification errors thereof cause color shifting; thus, it is impossible to produce a high-quality image. Accordingly, the image magnifications of the respective colors must be made to match each other as much as possible.
In light of such situations, for an image forming apparatus for forming an image by scanning light beams, Japanese Unexamined Patent Application Publication No. 2002-96502 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 9-58053 (Patent Document 2) disclose technologies for correcting image magnification errors in the main-scanning direction which are generated due to various factors, such as changes in ambient temperature and changes in the temperature inside the apparatus. In Patent Documents 1 and 2, two light-beam detecting means are provided, and a time from when one of them detects a light beam until the other one detects a light beam is measured. Based on the result of this measurement, a pixel clock frequency is changed to correct the image magnification.
In Patent Documents 1 and 2, the light beams that are incident on the light-beam detecting means are transmitted through an fθ lens. As described above, the shape and the refractive index of the lens change due to changes in ambient temperature, changes in the temperature inside the apparatus, and so on, and thus the image magnification changes. With respect to an image position, the position at the scanning-start side does not substantially change, but the position at the scanning-end side changes significantly. In order to maintain the image quality in such a situation, it is necessary to frequently perform measurement between two points and perform correction, but it is difficult to change the pixel clock frequency during continuous printing. In a color-image forming apparatus, particularly, an apparatus in which the scanning direction of at least one light beam is opposite to that of other light beams, the magnification error directly leads to color shifting. In the color-image forming apparatus, it is more important to reduce color shifting than a magnification error, and it is also necessary to maintain a state in which there is color shifting.
An optical scanning apparatus includes a light source, deflecting means, an fθ lens, and first and second light-beam detecting means. The light source outputs light beams, and is turned on and is controlled in accordance with image data. The deflecting means deflects the output light beams in a main-scanning direction. The fθ lens corrects the deflected light beams from constant-angular-velocity scanning to constant-velocity scanning. The first and second light-beam detecting means detect the light beams, deflected by the deflecting means, at two spots along the main-scanning direction. The first light-beam detecting means is located at a scanning-start side, and the second light-beam detecting means is located at a scanning-end side. The light beam that is incident on the first light-beam detecting means is not transmitted through the fθ lens, and the light beam that is incident on the second light-beam detecting means is transmitted through the fθ lens.
Further, an image forming apparatus includes a light source, deflecting means, an fθ lens, first and second light-beam detecting means, and image forming means.
The light source outputs light beams, and is turned on and is controlled in accordance with image data. The deflecting means deflects the output light beams in a main-scanning direction. The fθ lens corrects the deflected light beams from constant-angular-velocity scanning to constant-velocity scanning. The first and second light-beam detecting means detect the light beams, deflected by the deflecting means, at two spots along the main-scanning direction. The first light-beam detecting means is located at a scanning-start side, and the second light-beam detecting means is located at a scanning-end side. The light beam that is incident on the first light-beam detecting means is not transmitted through the fθ lens, and the light beam that is incident on the second light-beam detecting means is transmitted through the fθ lens. The image forming means forms a visible image by forming a latent image through illuminating a rotating or moving image holder with the light beams output from the light source and by developing the latent image. In this apparatus, the light beam that is incident on the first light-beam detecting means is not transmitted through the fθ lens, and the light beam that is incident on the second light-beam detecting means is transmitted through the fθ lens.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to” or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to” or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers referred to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements describes as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors herein interpreted accordingly.
Although the terms first, second, etc. may be used herein to described various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layer and/or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, example embodiments of the present patent application are described.
Referring to
A charger 107, a developing unit 108, a transfer unit 109, a cleaning unit 110, and a discharger 111 are disposed around the photoreceptor 106 to constitute image-forming means. The image-forming means performs charging, exposure, developing, and transferring, which are typical electrophotographic processes, to form an image on recording paper P. A fixing device (not shown) fixes the image on the recording paper P.
In this configuration, when the light beam L is incident on the first synchronization detecting sensor 123a, the start-side synchronization detection signal XDETP is output, and when the light beam L is incident on the second synchronization detecting sensor 123b, an end-side synchronization detection signal XEDETP is output. These signals XDETP and XEDETP are input to the magnification error detector 203. The magnification error detector 203 measures a time from the falling edge of the start-side synchronization detection signal XDETP to the falling edge of the end-side synchronization detection signal XEDETP, and compares the measured time with a reference time to determine the time difference therebetween. The magnification error detector 203 then generates an amount of correction corresponding to the time difference, that is, correction data for changing the pixel clock frequency. The magnification error detector 203 then sends the generated correction data to the pixel-clock generator 202 to correct the image magnification.
The correction data indicates one or both of the frequency setting value of a reference clock FREF output from the reference clock generator 2021 and the setting value of a division ratio N of the PLL circuit.
The start-side synchronization detection signal XDETP output from the first synchronization detecting sensor 123a is also sent to the pixel-clock generator 202. In the pixel-clock generator 202, the phase-synchronization clock generator 2023 generates pixel clocks PCLK that are synchronized with the start-side synchronization detection signal XDETP and sends the pixel clocks PCLK to the LD controller 205 and the synchronization-detection illumination controller 204. In order to first detect the start-side synchronization detection signal XDETP, the synchronization-detection illumination controller 204 forcibly turn on the LD by turning on an LD forced-illumination signal BD. In scanning after the start-side synchronization detection signal XDETP is detected, the synchronization-detection illumination controller 204 generates an LD forced-illumination signal BD at a timing at which the start-side detection signal XDETP can be reliably detected without generating flare, in accordance with the start-side synchronization detection signal XDETP and the pixel clock PCLK. The synchronization-detection illumination controller 204 then sends the generated LD forced-illumination signal BD to the LD controller 205. Similarly, when the end-side synchronization detection signal XEDETP is to be detected, the synchronization-detection illumination controller 204 generates an LD forced-illumination signal BD for turning on the LD at a timing at which the end-side detection signal XEDETP can be reliably detected without generating flare, in accordance with the start-side synchronization detection signal XDETP and the pixel clock PCLK. The synchronization-detection illumination controller 204 then sends the generated LD forced-illumination signal BD to the LD controller 205.
The LD controller 205 controls the illumination of the LD in accordance with an image signal that is synchronized with the synchronization-detection forced-illumination signal BD output from the synchronization-detection illumination controller 204 and the pixel clock PCLK output from the phase-synchronization clock generator 2023. The light beams L emitted from the LD unit 120 are deflected by the polygon mirror 101, pass through the fθ lens 103, and scan on the photoreceptor 106. In accordance with a control signal sent from the printer controller 201, the polygon-motor drive controller 206 controls the rotation of the polygon motor 102 at a predetermined rotation speed.
The transfer belt B is provided between rollers R in a tensioned state and is driven by a conveying motor M. As each of the four optical units, the optical unit shown in
The main-scanning-line synchronization-signal generator 2091 generates a signal XLSYNC for operating the main-scanning counter 20921 in the main-scanning gate-signal generator 2092 and the sub-scanning counter 20931 in the sub-scanning gate-signal generator 2093. The main-scanning gate-signal generator 2092 generates a signal XLGATE for determining an image write timing in the main scanning direction. The sub-scanning gate-signal generator 2093 generates a signal XFGATE for determining an image write timing in the sub-scanning direction.
The main-scanning counter 20921 operates in accordance with the signal XLSYNC and the pixel clock PCLK. The comparator 20922 compares the value of the main-scanning counter 20921 with first correction data supplied from the printer controller 201 and outputs the comparison result. The gate-signal generator 20923 generates a signal XLGATE based on the comparison result of the comparator 20922. The sub-scanning counter 20931 operates in accordance with a control signal from the printer controller 201, the signal XLSYNC, and the pixel clock PCLK. The comparator 20932 compares the value of the sub-scanning counter 20931 with second correction data supplied from the printer controller 201 and outputs the comparison result. The gate-signal generator 20933 generates a signal XFGATE based on the comparison result of the comparator 20932. With respect to the main scanning, the write-start-position controller 209 can correct a write position for each period of the pixel clock PCLK, that is, for each dot. With respect to the sub scanning, the write-start-position controller 209 can correct a write position for each period of the signal XLSYNC, that is, for each line.
As described above, the pixel-clock generator 202 includes the reference-clock generator 2021, the VCO (voltage-controlled oscillator) clock generator 2022, and the phase-synchronization clock generator 2023.
The phase-synchronization clock generator 2023 generates a pixel clock PCLK from VCLK, which has a frequency set to eight times the pixel clock frequency, and further generates a pixel clock PCLK that is synchronized with the start-side synchronization detection signal XDETP.
The corrected frequency f′ can be determined by:
f′=fo×T0/(2T−T0),
where fo indicates the frequency before the correction. In this embodiment, the change is simply doubled based on the assumption that the characteristics of the left half and right half of the fθ lens 103 are the same and the temperature changes are also the same. Needless to say, it is also possible to perform correction using the values of pre-measured characteristics.
In a second embodiment, with respect to the pixel clock PCLK described in the first embodiment, the phase at the rising edge is further advanced or delayed by an amount corresponding to a half period of VCLK, in accordance with the correction data supplied from the printer controller 201.
In the case of the present embodiment, the magnification error detector 203 determines the magnification error data and sends the data to the printer controller 201, as in the first embodiment described above. Based on magnification error data, the printer controller 201 determines the number of pixels to which a period change is made, determines whether or not to advance or delay the phase, and sends, as correction data, the determined information to the phase-synchronization clock generator 2023. As indicated in the timing chart shown in
(20005−20000)×2=10VCLK.
Thus, the phase is delayed (the frequency is extended) by an amount corresponding to 1/16 PCLK×20.
Consequently, pixels to which a period change is made can be equally distributed over the width of the image. Needless to say, the equation for determining the period is not particularly limited to the above-noted equation and thus may be any equation that can distribute pixels over the image area.
In the present embodiment, the magnification may also be corrected in combination with the change of the pixel clock frequency. In such a case, when the period for each pixel is changed to compensate for periods between the steps of changing the pixel clock frequency, the accuracy (the resolution) can be improved.
In the present embodiment, the arrangement may also be such that pixels to which a period change is made are equally distributed over the width of the image and the positions thereof are changed for each main-scanning line so that the pixels to which the period change is made are not located at the same position in the sub-scanning direction.
When the amount of change exceeds the period at which the pixel change is made, a change corresponding to the exceeded amount is made to the first line. Specifically, for the first line, counting is started from “1”, but for the second line, the position is shifted by an amount corresponding to three dots and the start value of the counter is thus set to 1+3=4. As a result, the positions of pixels to which a period change is made are shifted (i.e., advanced) by an amount corresponding to three dots. For the third line, the position is further shifted by an amount corresponding to three dots and thus the start value of the counter is set to 4+3=7. As a result, the positions of pixels to which a period change is made are shifted (i.e., advanced) by an amount corresponding to three dots. For the fourth line, the start value of the counter is set to 7+3=10. However, it exceeds the period of the pixels to which a change is made, i.e., eight dots, the start value of the counter is set to an amount corresponding to the exceeded amount “10−8=2”.
The start value of the counter is changed for each line, as described above, to thereby change the positions of pixels to which a period change is made. The expression for determining the amount of position change is not particularly limited to the above-noted expression, and any expression that allows the positions to be randomly changed may be used.
Other units and elements for which descriptions have not been particularly given are configured in the same manner as those in the first embodiment and function in the same manner.
The light-beam scanning device and the image-formation control system in the color-image forming apparatus are analogous to those in the first embodiment. However, as shown in
In the color image forming apparatus having such a configuration, signals of the image-position shift correction patterns BK1, C1, M1, Y1, BK2, C2, M2, Y2, BK3, C3, M3, Y3, BK4, C4, M4, and Y4 detected by the first and second sensors 126a and 126b are sent to the printer controller 201, and the amount (time) of shift of each color relative to BK is determined. The detection timings of the oblique-line patterns BK2, C2, M2, Y2, BK4, C4, M4, and Y4 vary when the image position or the image magnification in the main-scanning direction changes. The detection timings of the lateral-line patterns vary when the image position in the sub-scanning direction shifts.
Specifically, in the main-scanning direction, a time from the pattern C1 to the pattern C2 is compared with a time from the pattern BK1 to the pattern BK2 to determine the amount of shift TBKC12. Further, a time from the pattern C3 to the pattern C4 is compared with a time from the pattern BK3 to the pattern BK4 to determine the amount of shift TBKC34. Thus, TBKC34-TBKC12 represents a magnification error of a cyan image relative to a black image, and the pixel clock frequency is changed by an amount corresponding to the magnification error. The corrected pixel clock is used to form the same pattern and TBKC12 and TBKC34 are similarly determined. The value TBKC34+TBKC12)/2 represents a main-scanning shift of a cyan image relative to a black image. Thus, for each period of a writing clock, the write-start timing is changed by an amount corresponding to the shift. While the description has been given of the case of a cyan image, similar operations are also performed on magenta and yellow images.
In the sub-scanning direction, the sub-scan shift of a cyan image relative to a black image is expressed by:
((TBKC3+TBKC1)/2)−Tc
where Tc indicates an ideal time interval when no shift occurs between the color positions, TBKC1 indicates a time from the pattern BK1 to the pattern C1, and TBKC3 indicates a time from the pattern BK3 to the pattern C3. Thus, for each line, the write-start timing is changed by an amount corresponding to the sub-scan shift. Similar operations are also performed on magenta and yellow images.
Although the description has been given of an example in which the detection of a magnification error and the detection of a main-scan shift are performed using different patterns, they can be performed using the same pattern by determining a change in time due to magnification error correction.
In the present embodiment, although the measurement between two points is performed for only one color (i.e., black in this case) to perform image-position correction, the light-beam scanning device 16 and the image-formation control system shown in
In a light-beam scanning device 1 of the present embodiment, one polygon mirror 1301 is used, and an upper portion and a lower portion on the polygon mirror 1301 deflect light beams L1 and L2, which are different colors, to perform scanning. The polygon mirror 1301 is driven and rotated by a polygon motor 1307. The light beams L1 and L2 are split in opposite directions by the polygon mirror 1301, so that the light beams L for four colors scan on photoreceptors 106BK, 106C, 106M, and 106Y (hereinafter, the relationships of units for the individual colors will be described using the color abbreviations, such as 106BKCMY). The light beams of the individual colors are deflected by the polygon mirror 1301, pass through fθ lenses 1302BKC and 1302MY, and are returned by a first mirror 1303BKCMY and a second mirror 1304BKCMY. The light beams then pass through a BTL 1305BKCMY, are returned by a third mirror 1306BKCMY, and scan on a photoreceptor 106BKCMY.
A charger 107BKCMY, a developing unit 108BKCMY, a transfer unit 109BKCMY, a cleaning unit 110BKCMY, and a discharger 111BKCMY are disposed around the photoreceptor BKCMY106.
When the image-formation control system is configured so that two light beams are incident on the same synchronization detecting sensor, it is necessary to provide a separation circuit for separating the start-side synchronization detection signal XDETP into synchronization detection signals for the respective colors. In such a case, in the image-formation control system shown in
In the image forming device having this configuration, when the image magnification of Y or M whose scanning direction is opposite to that of BK changes, an image position shift corresponding to the change occurs in the main-scanning direction. With respect to C, when the amount of magnification change is the same, no position shift occurs. Thus, the magnification correction accuracy directly affects the correction accuracy for a main-scanning position shift.
The correction scheme in the third embodiment can also be used in the present embodiment. In the third embodiment, when the measurement between two points is not properly performed for even one color due to some failure, no correction is performed on all the colors. In the present embodiment, however, only when the measurement between two points is not properly performed for color in the same scanning direction, no correction is performed, and correction based on the result of the measurement between two points is performed for color in the opposite direction.
The individual units for which descriptions have not been particularly given are configured in the same manner as those in the first and third embodiments and function in the same manner.
As described above, the first to fourth embodiments have the following advantages:
1) The frequency of image magnification correction can be reduced compared to the related art to maintain the image quality.
2) The frequency of color shift correction can be reduced compared to the related art to maintain the image quality.
3) The magnification correction can be easily performed.
4) The correction accuracies of the magnification error and the image position can be improved.
This invention may be conveniently implemented using a conventional general purpose digital computer programmed according to the teachings of the present specification, as will be apparent to those skilled in the computer art. Appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure, as will be apparent to those skilled in the software art. The present invention may also be implemented by the preparation of application specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as will be readily apparent to those skilled in the art.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
This patent specification is based on Japanese patent applications, No. JPAP2006-042800 filed on Feb. 20, 2006 and NO. JPAP2007-029230 filed on Feb. 8, 2007 in the Japan Patent Office, the entire contents of each of which are incorporated by reference herein.
Number | Date | Country | Kind |
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2006-042800 | Feb 2006 | JP | national |
2007-029230 | Feb 2007 | JP | national |