JP4349024B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of forming images at a plurality of resolutions.

  In order to meet the demands for colorization and high-speed image forming apparatuses, each of the four colors of yellow (Y), magenta (M), cyan (C), and black (K) is provided with an image forming unit. A so-called tandem type image forming apparatus including an optical scanning device that performs optical scanning exposure on a part has been proposed.

  This type of image forming apparatus can form color images at high speed by forming images of the respective colors by respective image forming units and sequentially superimposing them.

  An image forming apparatus capable of forming images with a plurality of resolutions has also been proposed. In an image forming apparatus capable of forming images at a plurality of resolutions, image formation is performed using a main scanning synchronization signal having a unique period for each resolution.

  For example, in the case of having a high resolution mode and a low resolution mode that is half the resolution of the high resolution mode, as shown in FIG. 21, the main scanning synchronization signal for the high resolution mode and the low resolution mode are used. An image is formed using each main scanning synchronization signal, and the resolution is changed.

  On the other hand, in the color image forming apparatus, since the images of the respective colors are superposed, the relative positional relationship between the respective color images is a very important factor for improving the image quality.

  For example, adjustment of the relative position of each color image enables image position control of each color in the sub-scanning direction by moving a main scanning synchronization signal as a reference of the writing position of each line.

In addition, in the invention described in Patent Document 1, in the invention described in Patent Document 1, the first laser beam scanned horizontally with respect to the recording medium from the first optical scanning system is detected and the first laser beam is detected. A first beam detector for outputting a first horizontal synchronizing signal for determining an image writing start position of the recording medium based on the image signal of the recording medium to a host is provided at a predetermined position, and the image writing of the recording medium based on the second image signal is performed. A second beam detector for determining the start position is provided at a position preceding the arrangement position of the first beam detector by a predetermined amount with respect to the scanning direction of the recording medium, and a second beam detector output from the second beam detector is provided. Mounting position with respect to the arrangement positions of the first and second beam detectors by providing timing adjustment means for adjusting the transmission timing of the horizontal synchronization signal to the host by a predetermined time delay The first and second optical scanning systems record the first and second horizontal synchronizing signals output from the first and second beam detectors with high accuracy in synchronization. Image displacement is prevented.
JP 63-261279 (pages 22-24, FIG. 3)

  In a conventional image forming apparatus, when adjusting the relative position of each color image in an image forming apparatus having a plurality of resolutions, for example, in a high resolution mode (for example, 1200 dpi), main scanning synchronization signals are output at intervals of 1200 dpi. Therefore, the writing position of each color image can be adjusted at an interval of 1200 dpi. However, in the low resolution mode (for example, 600 dpi), since the main scanning synchronization signal is output at an interval of 600 dpi, there is a problem that the writing position of each color image can be adjusted only at an interval of 600 dpi.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image forming apparatus capable of correcting each color image position with high accuracy.

In order to achieve the above object, the invention described in claim 1 has a plurality of predetermined resolution modes and is set by a setting means for setting a resolution mode for forming an image, and the setting means. Generation means for generating a main scanning synchronization signal for performing main scanning according to the resolution mode, and sub-generation means for generating a sub-scanning synchronization signal for performing sub-scanning according to the resolution mode set by the setting means A plurality of image forming units that form images based on the main scanning synchronization signal and the sub-scanning synchronization signal, and absolute positions of images that the plurality of image forming units form on a recording medium in all resolution modes, and a correcting means for correcting, based on the main scanning synchronization signal corresponding to the highest resolution resolution mode of the plurality of resolution mode, the correction means, said plurality of image forming After correcting the relative position of the image formed by, it is characterized by correcting the absolute position.

  According to the first aspect of the present invention, the main scanning is performed by the generation unit according to the set resolution mode by setting the resolution mode for image formation from the plurality of resolution modes predetermined by the setting unit. A main scanning synchronization signal for performing sub-scanning is generated, and a sub-scanning synchronizing signal for performing sub-scanning is generated by the sub-generating unit. An image is formed based on the main scanning synchronization signal and the sub-scanning synchronization signal generated by the plurality of image forming units. That is, an image is formed by each image forming unit, and one image can be formed by overlapping each image formed by each image forming unit. For example, a color image can be formed by forming an image with a different color by each image forming unit.

  By the way, when a color image is formed, color misregistration and absolute positional deviation of image formation on a recording medium become problems. Therefore, the correction means corrects the absolute position of the image formed on the recording medium by the plurality of image forming units in all resolution modes based on the main scanning synchronization signal corresponding to the highest resolution mode among the plurality of resolution modes. Is done. That is, when the resolution is lowered, the interval of the main scanning synchronization signal is also increased, and the resolution for correcting the image misalignment is lowered. However, in all resolution modes, the main scanning synchronization signal corresponding to the highest resolution mode is used. By correcting the absolute position of the image using the image position, the image position can be adjusted with the highest resolution, so that the image position can be corrected with high accuracy, color misregistration can be prevented, and recording can be performed. It is also possible to prevent an absolute position shift of the image with respect to the medium.

The correcting unit corrects the absolute position after correcting the relative position of the image formed by the plurality of image forming units. That is, by correcting the relative position of image formation by each image forming unit and then correcting the absolute position of image formation on the recording medium, it is possible to correct the displacement of each image and the displacement of the recording medium.

For example, as in the invention described in claim 2 , the correction means matches the relative positions of the image formation on the recording medium by the plurality of image forming units based on the main scanning synchronization signal whose maximum resolution corresponds to the resolution mode. The relative position of image formation by each image forming unit can be corrected by controlling the sub-generation means so as to generate the sub-scanning synchronization signal at the timing to be performed.

Further, the correction means includes a phase control means for controlling the phase of the main scanning synchronization signal generated by the generation means as in the third aspect of the invention, and the phase control means adjusts the phase of the main scanning synchronization signal. By controlling, the absolute position of the image formed on the recording medium can be corrected by the phase control amount. For example, as in the invention described in claim 4 , the phase control means has a plurality of predetermined phase control amounts, and is based on the resolution mode set by the setting means and a preset image margin. The absolute position of the image may be corrected by selecting a plurality of phase control amounts.

Further, since the correction means uses the main scanning synchronization signal corresponding to the resolution mode of the highest resolution, the resolution mode for performing the highest resolution and the fastest image formation is set by the setting means as in the invention described in claim 5. In the case of failure, phase control by the phase control means is prohibited. In other words, the absolute value of the image is obtained by performing phase control by the phase control means when a mode other than the resolution mode for performing the highest resolution and fastest image formation is set as in the invention described in claim 6. Can be corrected.

The resolution mode that can be set by the setting means is the high-speed high-resolution mode that is the standard for all resolution modes, the half-speed high-resolution mode that forms images at half the speed of the high-speed high-resolution mode, and the high-speed high-resolution mode. when the high-speed low-resolution mode imaging at half resolution, and with respect to high-speed and high-resolution modes consisting half resolution and half speed low-resolution mode for forming an image at half the speed, the invention described in claim 7 As described above, when the phase control means sets any one of the half-speed high-resolution mode, the high-speed low-resolution mode, and the half-speed low-resolution mode by the setting means, one line is output after the sub-scanning synchronization signal is output in the high-speed high-resolution mode. By determining the phase control amount of the main scanning synchronization signal based on the number N of blank lines until the eye image is sent out, the image recording medium is recorded. It is possible to correct the absolute position.

At this time, when the resolution mode set by the setting means is the half-speed high-resolution mode or the high-speed low-resolution mode and the number of margin lines N is an even number as in the invention described in claim 8 , the phase control means The phase control amount can be a predetermined positive number A.

Further, as in the ninth aspect of the invention, when the resolution mode set by the setting means is the half speed low resolution mode and the number N of blank lines is an even number, the phase control means sets the phase control amount to a predetermined value. It is possible to use a positive number B.

It is preferable as defined in claim 1 0, when the resolution mode is the case of the half speed high-resolution mode or a high-speed low-resolution mode and the number of blank lines N is an odd number that is set by the setting means, the phase control means The phase control amount can be a predetermined positive number C or D. In this case, as in the invention of claim 1 1, the margin to the number of blank lines N, the image of the first line after the sub-scanning synchronization signal output at half speed high-resolution mode or a high-speed low-resolution mode is sent If the relation of M <N / 2 is established between the line number M, the phase control means, it is possible to the phase control amount and a predetermined positive number C, according to claim 1 2 When the relationship of M> N / 2 is established between the number of blank lines N and the number of blank lines M as in the invention, the phase control means sets the phase control amount to a predetermined positive number D. It is possible.

The invention of claim 1 0, as in the embodiment described in claims 1 to 3, the number of blank lines N, until the image of the first line in the half speed low-resolution mode after the sub-scanning synchronization signal output is sent between the blank line number M, when the relation of M <N / 2 is satisfied, the phase control means, it is possible to the phase control amount and a predetermined positive number E, to claim 1 4 When the relationship of M> N / 2 is established between the number of blank lines N and the number of blank lines M as in the described invention, the phase control means sets the phase control amount to a predetermined positive number F. Is possible.

As described above, according to the present invention, in all resolution modes, the highest resolution is obtained by correcting the absolute position after correcting the relative position of the image using the main scanning synchronization signal corresponding to the highest resolution mode. Since the image forming position can be adjusted, the image position can be corrected with high accuracy, color misregistration can be prevented, and absolute image misregistration with respect to the recording medium can also be prevented. There is an effect that.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a tandem color image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing an optical scanning device mounted on the color image forming apparatus.

  As shown in the figure, the color image forming apparatus 10 includes an optical scanning device 12 that is arranged upright in the center of the apparatus. From the optical scanning device 12, yellow (Y), magenta (M), cyan ( C) Light beams (hereinafter also referred to as scanning beams) AY, AM, AC, and AK corresponding to the respective colors of black (K) are output in the left direction. Photosensitive drums 14Y, 14M, 14C, and 14K are arranged in series from the top along the vertical direction on the left side of the optical scanning device 12, and in the vicinity of each photosensitive drum 14, a corresponding charger 16Y, 16M, 16C, 16K and developing units 18Y, 18M, 18C, 18K are arranged. The photosensitive drum 14, the charger 16, and the developing unit 18 constitute an image forming unit for each color.

  The photosensitive drum 14 is charged by a charger 16, and the drum surface is scanned and exposed by a light beam from the optical scanning device 12 to form an electrostatic latent image. The electrostatic latent image is developed by the developing unit 18 to become a toner image of each color, and is transferred to the primary intermediate transfer bodies 20YM and 20CK in a combination of Y color, M color, C color, and K color, and primary intermediate transfer. It is transferred from the bodies 20YM and 20CK to the secondary intermediate transfer body 22 and superimposed. In the vicinity of the secondary intermediate transfer member 22, a transfer charger 24 that charges the secondary intermediate transfer member 22 and a cleaner 26 that collects waste toner from the secondary intermediate transfer member 22 are disposed. The primary intermediate transfer members 20YM and 20CK, the secondary intermediate transfer member 22, and the drive motor (MOT) 27 for driving each of the image forming units are disposed in the vicinity thereof.

  Then, the color toner image on the secondary intermediate transfer body 22 is batch-transferred from the secondary intermediate transfer body 22 onto the recording paper 30 delivered from the paper feed cassette 28 at the lower part of the apparatus, and the recording paper 30 is fixed on the upper fixing device. 32, the transferred image becomes a fixed image. Through the above process, a color image is formed on the recording paper 30 by the color image forming apparatus 10, and the recording paper 30 is discharged to a paper discharge tray 34 at the top of the apparatus.

  Next, the optical scanning device 12 will be described.

  As shown in FIG. 2, the optical scanning device 12 includes a single optical box 36, and four light sources 38 </ b> Y, 38 </ b> M, 38 </ b> C, and 38 </ b> K are provided on one side of the optical box 36. The light beams AY, AM, AC, and AK modulated according to image information are emitted from the semiconductor lasers of the respective light sources, and the light beams AY and AM are disposed on the upper side in the optical box 36. Reflected by 40YM and 42YM, the light beams AY and AM are reflected by the common reflecting mirrors 40CK and 42CK disposed on the lower side in the optical box 36, and reflected by 12 surfaces disposed in the center of the bottom surface of the optical box 36. The light enters a polygon mirror 44 having a surface, and is deflected and scanned in two directions two by two (bidirectional spray paint method).

  Each deflected beam is transmitted through an fθ lens 46 (46A, 46B), 46 ′ (46A ′, 46B ′) as an imaging optical system, the scanning speed is corrected, and a reflection provided on the optical path of each beam. The mirrors 48YM and 48CK and a plurality of reflection mirrors (not shown) are guided to the photosensitive drums 14Y, 14M, 14C, and 14K to form an image, and the photosensitive drums are scanned at a substantially constant speed.

  In the optical box 36, the main scanning start by the light beams AC and AK is started in the vicinity of the scanning start position in the light beam main scanning direction (arrows C and K in FIG. 2) on the optical paths of the light beams AC and AK. The SOS sensor 50CK (SOS2) for detecting each light beam is arranged in order to synchronize the timing of of scan (SOS). Similarly, SOS sensors 50YM (SOS1) are arranged in the vicinity of the scanning start position in the light beam main scanning direction (arrows Y and M in FIG. 2) on the optical paths of the light beams AY and AM. The control circuit 60 is connected. The drawing circuit 62 is connected to an input device (INPUT UNIT) 56 for inputting various settings relating to the operation of the color image forming apparatus 10 and a print start command.

  The SOS sensors 50YM and 50CK output detection signals to the control circuit 60 each time each light beam passes over the sensor (detector). The control circuit 60 generates a horizontal synchronization signal that determines the writing position of the image information based on the output signal from each sensor, and supplies it to the drawing circuit 62. The drawing circuit 62 outputs an image information signal to the optical scanning device 12 after a predetermined time has elapsed from the horizontal synchronization signal. Based on this image information signal, the semiconductor laser of each light source is modulated, and light beams AY, AM, AC, and AK are emitted from the light sources 38Y, 38M, 38C, and 38K.

  The SOS sensors 50CK and 50YM are configured to detect the light beams AC and AK or the light beams AY and AM with one sensor. However, an SOS sensor may be provided for each light beam.

  Subsequently, a detailed configuration of the color image forming apparatus 10 including the control circuit 60 and the drawing circuit 62 described above will be described.

  FIG. 3 is a block diagram showing the configuration of the control system of the color image forming apparatus 10 according to the embodiment of the present invention.

  As shown in FIG. 3, the controller 54 that controls the printer includes a control circuit 60 that controls the mechanical control of the printer, image drawing timing, and the like, a drawing circuit 62 that controls image drawing, and an I / O interface 58. ing.

  The I / O interface 58 includes a polygon motor 64 for rotationally driving the polygon mirror 44, primary intermediate transfer members 20YM and 20CK and the secondary intermediate transfer member 22, and drive motors for driving the image forming units described above. (MOT) 27, LD driver 66 for driving the light source 38 (38Y, 38M, 38C, 38K), SOS sensor 50 (50CK, 50YM), various settings relating to the operation of the color image forming apparatus 10, a print start command, etc. An input device (INPUT UNIT) 56 for inputting and a recording medium leading end detection sensor 68 are connected.

  The I / O interface 58 is configured to receive image data 70 including an image formation request from an external device (for example, a personal computer).

  When an image formation request is made from the input device 56 or an external device via the I / O interface 58, the control circuit 60 drives and controls the polygon motor 64 so that the polygon mirror 44 rotates. At this time, the control circuit 60 drives the polygon motor 64 so that the rotation speed of the polygon mirror 44 rotates at a constant rotation speed regardless of the image formation request from the external device or the resolution mode set by the input device 56. Take control.

  Further, the control circuit 60 has a function of changing the resolution for recording an image in accordance with the resolution included in the image formation request from the external device or the resolution set in the input device 56. In this case, there are four types of resolution modes.

  Specifically, high-speed high-resolution mode, half-speed high-resolution mode (recording at half the speed of high-speed high-resolution mode), high-speed low-resolution mode (recording at half the resolution of high-speed high-resolution mode), half-speed low-resolution mode ( 4 types of resolution modes (recording at half the speed of the high-speed low-resolution mode). The control circuit 60 has a function of changing the rotation speed of the drive motor 27 in accordance with each mode, and a main scanning synchronization signal from the SOS sensor 50 provided in the optical scanning device 12 is synchronized with the main scanning in accordance with the resolution mode. It has a function to generate a signal. That is, the control circuit 60 controls the rotation speed of the drive motor 27 to control the conveyance speed of the recording medium in the sub-scanning direction, and the control circuit 60 controls the light emission of the light source 38 via the LD driver 66. A scan synchronization signal is generated. As a result, the mode can be switched to the above-described resolution modes.

  Further, the control circuit 60 generates an image start signal at the time of image formation, detects a signal from the recording medium leading edge detection sensor 68, and then generates a sub-scanning synchronization signal based on the image start signal. The image start signal is generated, for example, at a timing when an image formation start is instructed by an operation of the input device 56, or when image data for image formation from an external device or the like is transmitted to the image forming device 10. Is done.

  At this time, the main scanning synchronization signal for the high-speed resolution mode is used to generate the sub-scanning synchronization signal at a timing at which the relative positional deviation (color registration) between the colors is minimized. That is, the control circuit 60 controls the LD driver 66 so that the main scanning synchronization signal for the high-speed and high-resolution mode is output from the SOS sensor 50 until the sub-scanning synchronization signal is generated.

  Further, the control circuit 60 controls the LD driver 66 so that it becomes the main scanning synchronization signal in the resolution mode at the time of image formation after generating the sub-scanning synchronization signal, and the main scanning synchronization signal according to the resolution mode. The phase is controlled so that the absolute positions of the respective color images with respect to the recording medium coincide with each other.

  The drawing circuit 62 is based on a main scanning synchronization signal generated by the control circuit 60 controlling the LD driver 66, a sub-scanning synchronization signal generated by the control circuit 60, and image data input from an external device or the like. The LD driver 66 is controlled to control the light emission of the light source 38 and the image is recorded on the recording medium.

  Here, generation of a sub-scanning synchronization signal performed by the control circuit 60 in order to align the relative positions of the color images in the sub-scanning direction will be described.

  First, after receiving the sub-scanning synchronization signal generated by the control circuit 60, the drawing circuit 62 measures the number of pulses of the main scanning synchronization signal and reaches a specified value (for example, the count number n) as shown in FIG. In this case, image formation is started by outputting image data of the first line of the page. Thereafter, image data is formed by outputting the image data of the second line with the count number n + 1 lines and repeating this in the page. Note that image formation is similarly performed for each color.

  That is, the recording timing in the sub-scanning direction can be controlled by the timing of the sub-scanning synchronization signal generated by the control circuit 60, and the color misregistration of each color can be matched.

  For example, as shown in FIG. 5, due to a mechanical error of the image forming apparatus 10, the Y single color image “F” has a color shift of about 20 μm in the sub-scanning direction with respect to the M single color image “F”. Think about the case.

  This becomes prominent when the error between the Y color and the M color becomes large with respect to the distance between the optical scanning device 12 and the image transfer position.

  FIG. 6 shows a state in which the image of FIG. 5 is separated into a Y monochromatic image and an M monochromatic image. 6A shows a Y-color image, and FIG. 6B shows an M-color image.

  The reason why the M color image is delayed with respect to the Y color image is that the distance between the M color optical scanning device 12 and the image transfer position is larger than the distance between the Y color optical scanning device and the image transfer position. Caused by The causes of errors include differences in the thermal expansion coefficient of each member due to component accuracy, assembly accuracy, temperature rise in the machine, and the like.

  Since it is difficult to correct such a mechanical error, an image from the apparent M color optical scanning device 12 is electrically controlled to match the M color image with the Y color image position. It is only necessary to shorten the distance between the transfer positions. In the case shown in FIG. 5, a specific measure for correcting the color misregistration is that when the Y color image writing timing is set to the count value n of the main scanning synchronization signal, the M color image writing timing is set to the main scanning synchronization. By setting the signal count value n−1, the relative image position can be adjusted. That is, the relative positions of the images can be matched by setting the timing at which the control circuit 60 generates the sub-scanning synchronization signal according to the image position shift.

  However, since the output interval of the main scanning synchronization signal is longer in the low resolution mode than in the high resolution mode, the correction of the writing timing in the sub-scanning direction has a larger correction amount than the high resolution mode, and the Correction can only be made within the resolution range of the resolution mode.

  Therefore, in the present embodiment, the polygon motor 64 of the optical scanning device 12 is always driven at a rotational speed equivalent to the high resolution mode (for example, equivalent to 1200 dpi) to generate a main scanning synchronization signal having a high resolution mode period. When an image is formed in the low resolution mode (for example, 600 dpi), the main scanning synchronization signal is thinned out by the control circuit 60 to generate a main scanning synchronization signal having a period corresponding to the low resolution mode (for example, 600 dpi). Thus, image formation is performed.

  Here, color misregistration correction using a main scanning synchronization signal corresponding to the high resolution mode will be described. When an image is formed at half the resolution (for example, 600 dpi) with respect to the high resolution mode (for example, 1200 dpi), the M monochrome image “F” is changed to the Y monochrome image “F” due to a mechanical error of the image forming apparatus 10. The case where the position is shifted by about 20 μm in the sub-scanning direction will be described as an example.

  As described above, the writing timing of the Y color image is set to the count value n of the main scanning synchronization signal corresponding to the low resolution mode, and the writing timing of the M color image is set to the count value of the main scanning synchronization signal corresponding to the low resolution mode. When n-1 is set, as shown in FIGS. 7A and 7B, the M color image jumps over the Y color image, and color misregistration cannot be corrected. FIG. 7A shows an image before correction, and FIG. 7B shows an image after correction.

  Therefore, in order to correct color misregistration, a main scanning synchronization signal corresponding to the high resolution mode is used. That is, the main scanning synchronization signal corresponding to the high resolution mode (for example, 1200 dpi) should be generated in the middle of the main scanning synchronization signal corresponding to the low resolution mode (for example, 600 dpi). By drawing the M color image using the synchronization signal, it is possible to correct the image misalignment with a resolution equivalent to the high resolution mode. That is, the control circuit 60 can correct the relative position of the image with the resolution equivalent to the high resolution mode by generating the sub-scanning synchronization signal based on the main scanning synchronization signal equivalent to the high resolution mode.

  However, it is also possible to correct the image position deviation with respect to the M color by drawing with respect to the Y color using a main scanning synchronization signal corresponding to the high resolution mode. However, as shown in FIG. 8, the image forming position on the recording medium is different between the former and the latter.

  Therefore, after generating the sub-scanning synchronization signal, the control circuit 60 controls the phase of the main scanning synchronization signal according to the resolution mode so that the absolute values of the images of the respective colors with respect to the recording medium match. It has become. The details of the phase control of the main scanning synchronization signal according to the resolution mode performed by the control circuit 60 will be described in the process performed by the controller 54 described later.

  Next, processing performed by the controller 54 when the resolution mode is changed in the image forming apparatus 10 configured as described above will be described.

  FIG. 9 is a flowchart showing the flow of processing performed by the controller 54 when changing the resolution mode.

  First, in step 100, it is determined whether or not the mode is a high-speed and high-resolution mode. This determination is made by determining whether the high-speed / high-resolution mode is set by the input device 56, or by determining whether an image formation request in the high-speed / high-resolution mode is made by an external device. If YES in step 102, the flow advances to step 102 to generate a main scanning synchronization signal for the high speed and high resolution mode. That is, when the light source 38 is controlled by the control circuit 60 via the LD driver 66, a main scanning synchronization signal for the high speed and high resolution mode is generated, and the main scanning synchronization signal is detected by the SOS sensor 50.

  In the processing for generating the main scanning synchronization signal for the high-speed and high-resolution mode, as shown in FIG. 10, the output timing of the sub-scanning synchronization signal is determined based on the output of the image start signal. At this time, by using the main scanning synchronization signal for the high-speed and high-resolution mode, the sub-scanning synchronization signal can be output at a timing at which the relative positional deviation (color registration) in the sub-scanning direction between the colors is minimized. After the sub-scan sync signal is output, it is necessary to output the main scan sync signal in the original image forming mode. However, in the high-speed and high-resolution mode, the period does not change before and after the sub-scan sync signal is output. One type of scanning synchronization signal is determined. As the control circuit 60 performs control in this way, the absolute position (paper registration) with respect to the recording medium in which each color is a prime color can be uniquely determined.

  If the determination in step 100 is negative, the process proceeds to step 104 to determine whether or not the mode is the half speed high resolution mode or the high speed low resolution mode. Similarly to step 100, the determination is also made as to whether the half-speed high-resolution mode or the high-speed low-resolution mode is set by the input device 56, or an image formation request in the half-speed high-resolution mode or the high-speed low-resolution mode by an external device. If the determination is affirmative, the process proceeds to step 106, and a main scanning synchronization signal for the half-speed high-resolution mode or the high-speed low-resolution mode is generated. That is, the control circuit 60 controls the light source 38 via the LD driver 66 to generate a main scanning synchronization signal for the half speed high resolution mode or the high speed low resolution mode, and the SOS sensor 50 generates the main scanning synchronization signal. Detected.

  In the process of generating the main scanning synchronization signal for the half-speed high-resolution mode or the high-speed low-resolution mode, as shown in FIG. 11, the output timing of the sub-scanning synchronization signal is determined based on the output of the image start signal. At this time, by using the main scanning synchronization signal for the high-speed and high-resolution mode, the sub-scanning synchronization signal is generated at the timing at which the color misregistration error between the colors in the sub-scanning direction is minimized even in the half-speed high-resolution or high-speed and low-resolution mode. Output is possible. After the sub-scan sync signal is output, it is necessary to output the main scan sync signal in the original image forming mode. In the case of the half-speed high-resolution mode or the high-speed low-resolution mode, the cycle changes before and after the sub-scan sync signal is output. To do. As a result, theoretically, two types of main scanning synchronization signals can be output, and even if any of the main scanning synchronization signals is used, the absolute positional deviation (color registration) in the sub-scanning direction between the colors is minimized. A difference occurs in the absolute position (paper registration) of each color pixel with respect to the recording medium between the image drawn by the main scanning synchronization signal 1 and the image drawn by the main scanning synchronization signal 2. Therefore, the process shown in FIG. 12 described later is performed.

  Here, the flowchart of FIG. 12 will be described. FIG. 12 is a diagram showing a subroutine of main scanning synchronization signal generation processing for the half-speed high-resolution mode or the high-speed low-resolution mode.

  First, in step 200, it is determined whether or not the number N of blank lines in the high-speed and high-resolution mode is an odd number. This determination is made by determining whether or not the number of blank lines N set in advance when forming an image in the high-speed and high-resolution mode is an odd number. If the determination is affirmative, the process proceeds to step 202.

  In step 202, the phase of the main scanning synchronization signal in the high-speed high-resolution mode is controlled with the number of blank lines M = TRUNC (N / 2) for the half-speed high-resolution mode or the high-speed low-resolution mode (the sub-scanning synchronization signal is output). Therefore, the phase of the main scanning synchronization signal in the high-speed and high-resolution mode is controlled (0 pulse skip after the sub-scanning synchronization signal is output) and M = ROUNDUP (N / 2). A main scanning synchronization signal in the resolution mode or the high-speed low-resolution mode is generated. The number of blank lines M = TRUNC (N / 2) indicates a value obtained by truncating the decimal point of the value calculated by M = N / 2, and M = ROUNDUP (N / 2) is M = N / 2. The numerical value rounded up after the decimal point of the value calculated in.

  That is, when the number of blank lines M = TRUNC (N / 2), as shown in FIG. 13, the main scanning synchronization signal in the high-speed and high-resolution mode immediately after the sub-scanning synchronization signal is output is skipped by two pulses. A main scanning synchronization signal for the half-speed high-resolution mode or the high-speed low-resolution mode is generated with the first pulse as a reference. By counting the main scanning synchronization signal and controlling to start sending image data when the margin line M = TRUNC (N / 2) for the half-speed high-resolution mode or the high-speed low-resolution mode is reached, It becomes possible to form an image at exactly the same position as in the high-speed and high-resolution mode.

  On the other hand, when the number of margin lines is M = ROUNDUP (N / 2), as shown in FIG. 14, the half-speed high speed is based on the main scanning synchronization signal in the high-speed high-resolution mode immediately after the sub-scanning synchronization signal is output. A main scanning synchronization signal for the resolution mode or the high-speed low-resolution mode is generated. That is, the main scanning synchronization signal in the high-speed and high-resolution mode immediately after the sub-scanning synchronization signal is output is skipped by 0 pulses to generate the main-scanning synchronization signal for the half-speed high-resolution mode or the high-speed and low-resolution mode. The main scanning synchronization signal is counted, and when the margin line M = ROUNDUP (N / 2) for the half-speed high-resolution mode or the high-speed low-resolution mode is reached, control is performed so that image data is sent out, so that high-speed is achieved. An image can be formed at the same position as in the high resolution mode.

  Whether the number of margin lines M = TRUNC (N / 2) or M = ROUNDUP (N / 2) is set as appropriate according to the apparatus.

  If the determination in step 200 is negative, the process proceeds to step 204 where the number of blank lines M = N / 2 and the phase of the main scanning synchronization signal in the high-speed high-resolution mode is controlled (the sub-scanning synchronization signal is 1 pulse is skipped after output), and the main scanning synchronization signal in the half-speed high-resolution mode or the high-speed low-resolution mode is generated.

  That is, as shown in FIG. 15, the main scanning synchronization signal in the high-speed and high-resolution mode immediately after the sub-scanning synchronization signal is output is skipped by one pulse, and the half-speed high-resolution mode or the high-speed low-speed is set based on the second pulse. A main scanning synchronization signal for the resolution mode is generated. By counting this main scanning synchronization signal and controlling to start sending image data when the number of blank lines M = N / 2 for the half-speed high-resolution mode or the high-speed low-resolution mode is reached, high-speed and high-speed An image can be formed at exactly the same position as in the resolution mode.

  As described above, when the number of blank lines (the count value of the main scanning synchronization signal) N in the high-speed and high-resolution mode is an odd number, the number M of blank lines in the half-speed high-resolution mode or the high-speed and low-resolution mode is M = N / 2. In this case, the numerical value TRUNC (N / 2) obtained by rounding down the decimal point of the value calculated at M = N / 2 is M, and the decimal point of the value calculated at M = N / 2. There are two cases where the numerical value ROUNDUP (N / 2) rounded up is M. Therefore, when the number N of blank lines in the high-speed and high-resolution mode is an odd number, the algorithm for selecting the target main scanning synchronization signal is selected, so that the high-speed and high-resolution mode is selected in the half-speed high-resolution mode or the high-speed and low-resolution mode. An image can be formed at exactly the same position as when an image is formed, and the absolute position of each color image in each mode can be unified.

  Here, the description returns to step 104 of the flowchart of FIG.

  If the determination in step 104 is negative, the process proceeds to step 108, and a half-speed low-resolution mode main scanning synchronization signal is generated. That is, the control circuit 60 controls the light source 38 via the LD driver 66 to generate a main scanning synchronization signal for the half speed low resolution mode, and the SOS sensor 50 detects the main scanning synchronization signal.

  In the process of generating the main scanning synchronization signal for the half-speed low-resolution mode, as shown in FIG. 16, the output timing of the sub-scanning synchronization signal is determined based on the output of the image start signal. At this time, by using the main scanning synchronization signal for the high-speed and high-resolution mode, the sub-scanning synchronization signal can be output at the timing at which the color misregistration error between the colors in the sub-scanning direction is minimized even in the half-speed and low-resolution mode. After outputting the sub-scanning synchronization signal, it is necessary to output the main scanning synchronization signal in the original image forming mode, and the period changes before and after the output of the sub-scanning synchronization signal also in the half-speed low-resolution mode. As a result, theoretically, four types of half-speed low-resolution mode main scanning synchronization signals can be configured, and which main scanning synchronization signal is used to minimize the relative positional deviation (color registration) in the sub-scanning direction between the colors. However, between the image drawn by the main scanning synchronization signal 1, the image drawn by the main scanning synchronization signal 2, the image drawn by the main scanning synchronization signal 3, and the image drawn by the main scanning synchronization signal 4, each color pixel is changed. A difference occurs in the absolute position (paper registration) with respect to the recording medium. Therefore, the process shown in FIG. 17 described later is performed.

  Here, the flowchart of FIG. 17 will be described. FIG. 17 is a diagram showing a subroutine of main scanning synchronization signal generation processing for the half-speed low-resolution mode.

  First, in step 300, it is determined whether or not the number N of blank lines in the high-speed and high-resolution mode is an odd number. This determination is made by determining whether or not the preset number N of blank lines is odd when an image is formed in the high-speed and high-resolution mode. If the determination is affirmative, the routine proceeds to step 302.

  In step 302, the number of blank lines M = TRUNC (N / 2) and the phase of the main scanning synchronization signal in the high-speed and high-resolution mode is controlled (5 pulses skipped after the sub-scanning synchronization signal is output), or M = ROUNDUP ( N / 2), the phase of the main scanning synchronization signal in the high-speed and high-resolution mode is controlled (one pulse skip after the sub-scanning synchronization signal is output) to generate the main scanning synchronization signal in the half-speed low-resolution mode. The number of blank lines M = TRUNC (N / 2) indicates a value obtained by truncating the decimal point of the value calculated by M = N / 2, and M = ROUNDUP (N / 2) is M = N / 2. The numerical value rounded up after the decimal point of the value calculated in.

  That is, when the number of blank lines is M = TRUNC (N / 2), as shown in FIG. 18, the main scanning synchronization signal in the high-speed and high-resolution mode immediately after the sub-scanning synchronization signal is output is skipped by 5 pulses. A main scanning synchronization signal for the half-speed low-resolution mode is generated with reference to the pulse of the first pulse. The main scanning agreement signal is counted, and when the number of blank lines for half speed low resolution M = TRUNC (N / 2) is reached, control is performed so as to start sending image data. An image can be formed at the taste position.

  On the other hand, when the number of margin lines M = ROUNDUP (N / 2), as shown in FIG. 19, the main scanning synchronization signal in the high-speed and high-resolution mode immediately after the sub-scanning synchronization signal is output is skipped by 1 pulse. A main scanning synchronization signal for the half-speed low-resolution mode is generated with reference to the first pulse. The main scanning synchronization signal is counted, and when the blank line M = ROUNDUP (N / 2) for the half-speed low-resolution mode is reached, control is performed so that image data is sent out. Images can be formed at the same position.

  Whether the number of margin lines M = TRUNC (N / 2) or M = ROUNDUP (N / 2) is set as appropriate according to the apparatus.

  If the determination in step 300 is negative, the process proceeds to step 304 where the number of blank lines M = N / 2 and the phase of the main scanning synchronization signal in the high-speed high-resolution mode is controlled (the sub-scanning synchronization signal is 3 pulses are skipped after output), and the main scanning synchronization signal in the half speed low resolution mode is generated.

  That is, as shown in FIG. 20, the main scanning synchronization signal in the high-speed and high-resolution mode immediately after the sub-scanning synchronization signal is output is skipped by three pulses, and the main pulse for the half-speed low-resolution mode is used with the fourth pulse as a reference. A scan synchronization signal is generated. The main scanning synchronization signal is counted, and when the number of blank lines M = N / 2 for the half-speed low-resolution mode is reached, control is performed so as to start sending image data, so that it is exactly the same as the high-speed high-resolution mode. An image can be formed at the position.

  As described above, in the half-speed high resolution mode or the high-speed low-resolution mode, there are two types of main scanning synchronization signal generation timings, and in the half-speed low resolution mode, there are four types of main scanning synchronization signal generation timings. Will exist. Since there is only one type of main scanning synchronization signal that can match the absolute image position in the high-speed and high-resolution mode in each mode, there are two types of main-scanning synchronization signals in the half-speed high-resolution mode or the high-speed and low-resolution mode. In the half-speed low-resolution mode, the target main scanning synchronization signal is selected from four types of main scanning synchronization signals, and the image absolute position in each mode is selected by the control algorithm as described above. Can be matched.

  In addition, when the number N of blank lines in the high-speed and high-resolution mode is an even number, the number M of blank lines in the half-speed high-resolution mode or the high-speed and low-resolution mode and the half-speed and low-resolution mode can be calculated by M = N / 2. By determining one type of control algorithm for selecting the target main scanning synchronization signal, it is possible to match the absolute image position in each mode.

1 is a diagram illustrating a tandem color image forming apparatus according to an embodiment of the present invention. 1 is a diagram showing an optical scanning device mounted on a tandem color image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a control system of the color image forming apparatus according to the embodiment of the present invention. It is a figure for demonstrating the production | generation of a subscanning synchronizing signal. FIG. 10 is a diagram illustrating a state where a Y single color image “F” is color-shifted in the sub-scanning direction with respect to an M single color image “F”. It is a figure which shows the state at the time of isolate | separating the Y color image and M color image in FIG. It is a figure which shows the state at the time of correct | amending a color shift using the main scanning synchronizing signal of a low resolution mode, when the image formed in the low resolution mode has color shift. FIG. 6 is a diagram illustrating that when the color misregistration correction is performed using the main scanning synchronization signal in the high resolution mode and the reference image is different, the absolute position of the image on the recording medium is changed. It is a flowchart which shows the flow of the process performed by a controller when changing a resolution mode. It is a figure for demonstrating the process of the main scanning synchronizing signal for high-speed high-resolution modes. It is a figure for demonstrating the process of the main scanning synchronizing signal production | generation for half speed high resolution modes or high-speed low resolution modes. It is a figure which shows the subroutine of the process of the main scanning synchronizing signal production | generation for half speed high resolution modes or high speed low resolution modes. In the main scanning synchronization signal generation for the half-speed high-resolution mode or the high-speed low-resolution mode, the generation of the main scanning synchronization signal when the number of blank lines N is an odd number and the number of blank lines M = TRUNC (N / 2) is described. FIG. In main scanning synchronization signal generation for the half-speed high-resolution mode or high-speed low-resolution mode, main scanning synchronization signal generation when the number of blank lines N is an odd number and the number of blank lines M = ROUNDUP (N / 2) will be described. FIG. FIG. 10 is a diagram for explaining generation of a main scanning synchronization signal when the number of blank lines N is an even number in generation of a main scanning synchronization signal for a half-speed high-resolution mode or a high-speed low-resolution mode. It is a figure for demonstrating the process of the main scanning synchronizing signal generation for half speed low resolution modes. It is a figure which shows the subroutine of the process of the main scanning synchronizing signal production | generation for half speed low resolution modes. FIG. 10 is a diagram for explaining main scanning synchronization signal generation when the number of blank lines N is an odd number and the number of blank lines M = TRUNC (N / 2) in the generation of the main scanning synchronization signal for the half-speed low-resolution mode. FIG. 10 is a diagram for explaining main scanning synchronization signal generation when the number of blank lines N is odd and the number of blank lines M == ROUNDUP (N / 2) in the generation of the main scanning synchronization signal for the half-speed low-resolution mode. . FIG. 10 is a diagram for describing processing of generating a main scanning synchronization signal when the number of blank lines N is an even number in generating the main scanning synchronization signal for the half-speed low-resolution mode. It is a figure which shows the main scanning synchronizing signal for high resolution modes, and the main scanning synchronizing signal for low resolution modes in the case of having a high resolution mode and a low resolution mode that is half the resolution of the high resolution mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Optical scanning device 27 Drive motor 50 SOS sensor 54 Controller 56 Input device 60 Control circuit 62 Drawing circuit 68 Recording medium front-end | tip detection sensor 70 Image data

Claims (14)

A setting unit having a plurality of predetermined resolution modes and setting a resolution mode for image formation;
Generating means for generating a main scanning synchronization signal for performing main scanning according to the resolution mode set by the setting means;
Sub-generation means for generating a sub-scanning synchronization signal for performing sub-scanning according to the resolution mode set by the setting means;
A plurality of image forming units for forming an image based on the main scanning synchronization signal and the sub-scanning synchronization signal;
Correction means for correcting an absolute position of an image formed on the recording medium by the plurality of image forming units in all resolution modes based on a main scanning synchronization signal corresponding to a resolution mode of the highest resolution among the plurality of resolution modes; ,
Equipped with a,
An image forming apparatus that corrects the absolute position after correcting the relative position of an image formed by the plurality of image forming units. The correction unit generates a sub-scanning synchronization signal at a timing at which relative positions of image formation on the recording medium by the plurality of image forming units match based on a main-scanning synchronization signal corresponding to the resolution mode of the highest resolution. The image forming apparatus according to claim 1, wherein the relative position is corrected by controlling the sub-generating unit . The correction means includes phase control means for controlling the phase of the main scanning synchronization signal generated by the generation means, and corrects the absolute position by controlling the phase of the main scanning synchronization signal by the phase control means. The image forming apparatus according to claim 2. The phase control unit has a plurality of predetermined phase control amounts, and selects the plurality of phase control amounts based on a resolution mode set by the setting unit and a preset image margin. The image forming apparatus according to claim 3, wherein the absolute position is corrected by: The correction means, when the resolution mode for highest resolution and fastest imaging is set by the setting means, according to claim 3 or claim 4, characterized that you prohibit the phase control by the phase control means The image forming apparatus described in 1. The said correction | amendment means performs phase control by the said phase control means, when the resolution modes other than the resolution mode which performs the highest resolution and the fastest image formation are set by the said setting means. Item 5. The image forming apparatus according to Item 4 . The resolution mode that can be set by the setting means is a high-speed high-resolution mode that is a reference for all resolution modes, a half-speed high-resolution mode that forms an image at half the speed of the high-speed high-resolution mode, and the high-speed high-resolution mode And a half-speed low-resolution mode that forms an image at half the resolution and half the speed of the high-speed resolution mode. When the half-speed high-resolution mode, the high-speed low-resolution mode, or the half-speed low-resolution mode is set, until the first line image is sent after the sub-scanning synchronization signal is output in the high-speed high-resolution mode 7. The phase control amount of the main scanning synchronization signal is determined based on the number N of blank lines. The image forming apparatus according to claim. When the resolution mode set by the setting means is the half speed high resolution mode or the high speed low resolution mode and the margin line N is an even number, the phase control means sets the phase control amount to a predetermined positive number. The image forming apparatus according to claim 7 , wherein the image forming apparatus is A. When the resolution mode set by the setting unit is the half speed low resolution mode and the number of blank lines N is an even number, the phase control unit sets the phase control amount to a predetermined positive number B. The image forming apparatus according to claim 7 . When the resolution mode set by the setting unit is the half-speed high-resolution mode or the high-speed low-resolution mode and the number of margin lines N is an odd number, the phase control unit sets the phase control amount to a predetermined positive value. The image forming apparatus according to claim 7 , wherein the number is C or D. Between the number N of blank lines and the number M of blank lines until the first line image is transmitted after the sub-scanning synchronization signal is output in the half-speed high-resolution mode or the high-speed low-resolution mode. The image forming apparatus according to claim 10, wherein when the relationship of 2 holds, the phase control unit sets the phase control amount to a predetermined positive number C. Between the number N of blank lines and the number M of blank lines until the first line image is transmitted after the sub-scanning synchronization signal is output in the half-speed high-resolution mode or the high-speed low-resolution mode. The image forming apparatus according to claim 10, wherein when the relationship of 2 holds, the phase control unit sets the phase control amount to a predetermined positive number D. A relationship of M <N / 2 is established between the number N of blank lines and the number M of blank lines until the first line image is transmitted after the sub-scanning synchronization signal is output in the half-speed low-resolution mode. The image forming apparatus according to claim 10, wherein the phase control unit sets the phase control amount to a predetermined positive number E. A relationship of M> N / 2 is established between the number N of blank lines and the number M of blank lines until the first line image is transmitted after the sub-scanning synchronization signal is output in the half-speed low-resolution mode. The image forming apparatus according to claim 10, wherein the phase control unit sets the phase control amount to a predetermined positive number F.

Images