Image forming apparatus and image forming method

Abstract

To correct the absolute position deviation of an image with respect to a recording medium.SOLUTION: An image forming apparatus according to an aspect of the present invention has: an image forming unit that forms an image on a recording medium based on an image forming condition; an image position determination unit that, based on a detection signal of predetermined patterns on the recording medium formed by the image forming unit and information on reference positions of the predetermined patterns on the recording medium, determines the position of the image on the recording medium formed by the image forming unit; and a reference position determination unit that determines the reference positions of the predetermined patterns so that the positions are made different depending on the image forming condition.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and an image forming method.

Background Art

[0002] Conventionally, in an image forming apparatus, there is known one that corrects an image forming position on a recording medium based on a detection signal of a predetermined pattern formed at a predetermined position of the recording medium.

[0003] Also, there is disclosed a technique of forming a predetermined pattern such as an image position shift correction pattern at the four corners of a recording paper, comparing the pattern detection result with an ideal pattern position, calculating a correction value from the shift amount, and correcting the image position (see, for example, Patent Document 1).

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, conventional techniques such as the technique described in Patent Document 1 cannot correct the absolute position shift of an image with respect to a recording medium with high accuracy under various image forming conditions. These days, with the demand for further higher image quality, the absolute position shift of an image with respect to a recording medium has become non-ignorable, and a correction technique therefor is required.

[0005] An object of the present invention is to correct the absolute position shift of an image with respect to a recording medium.

Means for Solving the Problems

[0006] An image forming apparatus according to an aspect of the present invention includes an image forming unit that forms an image on a recording medium based on image forming conditions, an image position determination unit that determines a position of the image formed by the image forming unit on the recording medium based on a detection signal of a predetermined pattern formed by the image forming unit on the recording medium and reference position information of the predetermined pattern on the recording medium, and a reference position determination unit that determines a reference position for forming the predetermined pattern to be different according to the image forming conditions. The image forming unit forms the predetermined pattern for each page of the recording medium, and the image positioning unit determines the position of the image based on the position of the predetermined pattern formed by the image forming unit for each page of the recording medium. Do it.

Advantages of the Invention

[0007] According to the present invention, it is possible to correct the absolute positional deviation of an image with respect to a recording medium.

Brief Description of the Drawings

[0008]

Figure 1

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Figure 11

Figure 12

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Figure 15

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are assigned to the same components, and duplicate descriptions will be omitted as appropriate.

[0010] The image forming apparatus according to the embodiment forms an image on a recording medium by an electrophotographic method. Hereinafter, the embodiment will be described in detail by taking a so-called tandem type image forming apparatus using an intermediate transfer belt as an example.

[0011] [Embodiment] [Configuration Example of Image Forming Apparatus 100] With reference to FIGS. 1 to 3, the configuration of the image forming apparatus 100 will be described. FIG. 1 is a diagram showing an example of the overall configuration of the image forming apparatus 100 according to the embodiment. FIG. 2 is a diagram showing an example of the configuration of the image forming unit 110 included in the image forming apparatus 100, and is a schematic view seen from the rotation axis direction of the photosensitive drum 40 of the image forming unit 110. FIG. 3 is a partially enlarged view showing a configuration example around the fixing unit 25 included in the image forming apparatus 100, and is a schematic view seen from the rotation axis direction of the fixing roller 26 around the fixing unit 25.

[0012] As shown in FIGS. 1 to 3, the image forming apparatus 100 includes an intermediate transfer belt 10, support rollers 64 to 66, a light beam scanning device 21, an image forming device 20, a belt cleaning unit 17, a secondary transfer unit 22, and a fixing unit 25. The image forming apparatus 100 also includes a paper reversing unit 28, a paper feed table 200, an image reading unit 300, and an automatic document feeder (ADF) 400.

[0013] As shown in FIG. 2, the image forming unit 110 includes an intermediate transfer belt 10, three support rollers 64 to 66, a light beam scanning device 21, an image forming device 20, a belt cleaning unit 17, and a secondary transfer unit 22. The image forming unit 110 forms an image on a sheet P, which is an example of a recording medium, based on image forming conditions.

[0014] The intermediate transfer belt 10 is an endless belt that is driven to run in the clockwise direction, and is provided so as to be wound around three support rollers 64 to 66 at approximately the center of the image forming apparatus 100. The running direction 5 indicated by the arrow in FIG. 2 represents the direction in which the intermediate transfer belt 10 runs.

[0015] Above the image forming device 20 in the vertical direction, an optical beam scanning device 21 is provided. The optical beam scanning device 21 includes four sets of optical beam scanning devices for each of the colors yellow, magenta, cyan, and black. Note that the optical beam scanning device 21 is a general term for the four-color optical beam scanning devices 21.

[0016] The optical beam scanning device 21 forms an electrostatic latent image based on image data on each photosensitive drum 40 by irradiating the photosensitive drums 40 of each color while scanning the optical beam of the laser light emitted from an LD (Laser Diode).

[0017] The image forming device 20 is detachably provided to the image forming apparatus 100 at a position facing the intermediate transfer belt 10 between the support roller 64 and the support roller 65. The image forming devices 20 of each color are juxtaposed along the running direction 5 of the intermediate transfer belt 10. The image forming device 20 is a general term for the four-color image forming devices.

[0018] Each of the four-color image forming devices 20 has a photosensitive drum 40, and around the photosensitive drum 40, there are a charging unit 18, a developing unit 29, a transfer unit 62, a drum cleaning unit 63, and a discharger 19.

[0019] The image forming device 20 develops (visualizes) the electrostatic latent image on the photosensitive drum 40, and transfers the developed toner image to the intermediate transfer belt 10, thereby forming toner images of each color on the intermediate transfer belt 10. The drum cleaning unit 63 removes the residual toner remaining on the photosensitive drum 40 after the toner image is transferred from the photosensitive drum 40 to the intermediate transfer belt 10.

[0020] On the upstream side of the support roller 65 in the traveling direction 5, a belt cleaning unit 17 is provided. The belt cleaning unit 17 removes the residual toner remaining on the intermediate transfer belt 10 after the toner image is secondarily transferred from the intermediate transfer belt 10 to the paper P.

[0021] Below the intermediate transfer belt 10 vertically, that is, on the opposite side of the image forming apparatus 20 across the intermediate transfer belt 10, a secondary transfer unit 22 is provided. As shown in FIG. 1, the secondary transfer unit 22 includes two rollers 23 and a secondary transfer belt 24.

[0022] The secondary transfer belt 24, which is an endless belt, is looped between the two rollers 23 and is arranged to push up the intermediate transfer belt 10 and press against the support roller 16. The secondary transfer unit 22 secondarily transfers the image formed on the intermediate transfer belt 10 onto the paper P.

[0023] On the side of the secondary transfer unit 22, that is, on the downstream side of the secondary transfer unit 22 in the direction in which the paper P is conveyed, a fixing unit 25 is provided. The fixing unit 25 includes a fixing roller 26, which is an endless belt, and a heating roller 27 provided so as to press against the fixing roller 26. The fixing unit 25 fixes the toner image formed on the paper P sent from the secondary transfer unit 22 to the paper P by heating and pressurizing.

[0024] As shown in FIG. 3, near the outlet of the paper P in the fixing unit 25, correction sensors IS1 and IS2 are provided. The correction sensors IS1 and IS2 output detection signals of a correction pattern formed by the image forming unit 110 on the paper P.

[0025] The correction pattern is formed at the four corners etc. of the paper P and is an example of a predetermined pattern used to correct the positional deviation of the image formed on the paper P. This positional deviation of the image includes the relative positional deviation between the image on the first page and the image on the second page, the absolute positional deviation of the images of each color with respect to the paper P, and the positional deviation of the image on the back surface with respect to the image on the front surface.

[0026] The correction sensors IS1 and IS2 are image reading sensors such as a CCD (Charge Coupled Device) or a CIS (Contact Image Sensor), and are provided at positions where correction patterns can be detected. The image forming apparatus 100 can correct the positional deviation of an image based on the detection signals of the correction patterns by the respective correction sensors IS1 and IS2.

[0027] In FIG. 3, the direction A indicated by the arrow shows the direction in which the sheet P after image formation is discharged when an image is formed only on the front surface of the sheet P. Further, the direction B indicated by the arrow shows the direction in which the sheet P after image formation is conveyed to the sheet reversing unit 28 when an image is formed on both sides of the sheet P.

[0028] In FIG. 1, a sheet reversing unit 28 is provided vertically below the secondary transfer unit 22 and the fixing unit 25. The sheet reversing unit 28 reverses and feeds out the sheet P after an image is formed on its front surface so that an image is also formed on the back surface.

[0029] <Example of the image forming operation of the image forming apparatus 100> Continuing to refer to FIGS. 1 to 3, the image forming operation by the image forming apparatus 100 will be described.

[0030] When the start switch of the operation unit unit in the image forming apparatus 100 is pressed by the user of the image forming apparatus 100, if there is a document on the document feeder 30 of the automatic document feeder (ADF) 400, the image forming apparatus 100 conveys the document onto the contact glass 32. On the other hand, when there is no document in the automatic document feeder 400, the image forming apparatus 100 drives the scanner of the image reading unit 300 to read the document placed by hand on the contact glass 32, and moves the first carriage 33 and the second carriage 34 for reading. Then, the image forming apparatus 100 irradiates light from the light source on the first carriage 33 onto the contact glass 32.

[0031] The light reflected by the original surface from the irradiation light is reflected by the mirror on the first carriage 33 toward the second carriage 34, and after being further reflected by the mirror on the second carriage 34, it is approximately imaged on the imaging surface of the CCD 36, which is a reading sensor, by the imaging lens 35. Based on the image signal obtained by the CCD 36, image data for each color of Y, M, C, and K is generated.

[0032] When the start switch is pressed, or when there is a printing instruction from an external device such as a PC (Personal Computer), or when there is a printing instruction for FAX, the running drive of the intermediate transfer belt 10 is started. Also, each unit included in the image forming device 20 starts image forming preparation. Thereafter, the image forming process for each color is started. After the photosensitive drum 40 for each color is irradiated with laser light modulated based on the image data for each color, the toner images for each color are transferred onto the intermediate transfer belt 10 as a single toner image by being overlapped.

[0033] The image forming apparatus 100 selectively rotationally drives one of the plurality of paper feed rollers 42 on the paper feed table 200, and feeds out the paper P from one of the plurality of paper feed trays 44 stacked in multiple stages in the paper feed unit 43. Thereafter, the image forming apparatus 100 separates only one sheet of the paper P by the separation roller 45, puts it into the conveyance roller unit 46, conveys it by the conveyance roller 47, and guides it to the conveyance roller unit 48 inside the image forming apparatus 100. Thereafter, the image forming apparatus 100 stops the paper P by abutting it against the registration roller 49 of the conveyance roller unit 48, and then feeds the paper P into the secondary transfer unit 22 so that the leading edge of the paper P enters the secondary transfer unit 22 at the timing when the leading edge of the toner image enters the secondary transfer unit 22.

[0034] Thereafter, after the image forming apparatus 100 transfers the toner image on the intermediate transfer belt 10 to the sheet P fed into the secondary transfer unit 22, the image forming apparatus 100 feeds the sheet P onto which the toner image has been transferred into the fixing unit 25, and the fixing unit 25 fixes the toner image on the sheet P. In this way, the image forming apparatus 100 can form an image on the sheet P.

[0035] The feeding of the sheet P to the secondary transfer unit 22 can also be performed by the user of the image forming apparatus 100 inserting the sheet P into the manual tray 51. In this case, when the user inserts the sheet P into the manual tray 51, the image forming apparatus 100 rotationally drives the paper feed roller 50, separates one sheet of the sheet P on the manual tray 51, and draws it into the manual paper feed path 53. Thereafter, after the image forming apparatus 100 abuts the sheet P against the registration roller 49 to stop the sheet P, the image forming apparatus 100 feeds the sheet P into the secondary transfer unit 22 in the same manner as described above, transfers the toner image, and fixes it, thereby forming an image on the sheet P.

[0036] The image forming apparatus 100 guides the sheet P after image formation discharged from the fixing unit 25 to the discharge roller 56 with the switching claw 55 and stacks it on the paper discharge tray 57. Alternatively, the image forming apparatus 100 guides the sheet P to the sheet reversing unit 28 with the switching claw 55, reverses the sheet P by the sheet reversing unit 28, guides it back to the transfer position again, forms an image on the back side as well, and then discharges it onto the paper discharge tray 57 with the discharge roller 56. Further, the image forming apparatus 100 removes the residual toner remaining on the intermediate transfer belt 10 after image transfer of the toner image with the belt cleaning unit 17 to prepare for another image formation.

[0037] <Configuration Example of the Light Beam Scanning Device 21> FIG. 4 is a diagram showing an example of the configuration of the light beam scanning device 21 included in the image forming apparatus 100, and is a view of the light beam scanning device 21 in FIG. 2 viewed from vertically above (the side opposite to the photosensitive drum 40 side). FIG. 4 shows only one of the four light beam scanning devices 21 provided for each color, but the configurations of the four light beam scanning devices 21 are all the same.

[0038] The light beam emitted from the LD provided on the LD control board 211 passes through the CYL (cylindrical lens) 212 and enters the polygon mirror 213.

[0039] The polygon mirror 213 is a polygonal member having a mirror surface formed on its side surface, and is a rotating polygon mirror that can rotate around the axis at the center of the plane. In FIG. 4, a polygon mirror 213 having a hexagonal outer shape and six mirror surfaces is illustrated, but the configuration is not limited to this. For example, a configuration having a triangular outer shape and three mirror surfaces or a configuration having a pentagonal outer shape and five mirror surfaces may be used.

[0040] By rotating, the polygon mirror 213 can continuously change the angle of the mirror surface, continuously change the reflection angle of the incident light beam, and scan the light beam. The main scanning direction D indicated by the arrow in FIG. 4 represents the direction in which the light beam is scanned by the rotation of the polygon mirror 213 in the rotation direction 213a.

[0041] The scanning light beam Lb by the polygon mirror 213 passes through the fθ lens 214 and the second lens 219 that corrects the beam position and the like in the sub-scanning direction orthogonal to the main scanning direction D, and then is folded by the folding mirror 215 toward the photosensitive drum 40. The scanning light beam Lb is scanned along the main scanning direction D on the photosensitive drum 40.

[0042] Near the writing-side end in the main scanning direction D, that is, near the exposure start position of the photosensitive drum 40 by the light beam, a synchronization mirror 216, a synchronization lens 217, a synchronization sensor 218, etc. are provided. The scanning light beam Lb near the writing-side end enters the synchronization mirror 216 and is reflected by the synchronization mirror 216. The reflected light beam is condensed by the synchronization lens 217 and enters the synchronization sensor 218.

[0043] The synchronization sensor 218 is, for example, a PD (Photo Diode) that outputs an electrical signal according to the light intensity of incident light. The image forming apparatus 100 can determine the writing timing (the exposure start timing of the light beam) in the main scanning direction D using the electrical signal output by the synchronization sensor 218.

[0044] <Example of the hardware configuration of the image forming apparatus 100> Next, with reference to FIGS. 5 to 7, the electrical hardware configuration of the image forming apparatus 100 will be described.

[0045] FIG. 5 is a block diagram showing an example of the electrical hardware configuration of the image forming apparatus 100. FIG. 6 is a block diagram showing an example of the configuration of the VCO (Voltage-controlled oscillator) clock generation unit 227. FIG. 7 is a block diagram showing an example of the configuration of the write start position control unit 222. FIGS. 5 to 7 show only the configuration of one of the four color formation control units 120 included in the image forming unit 110, but the configurations of the formation control units 120 for each color are the same.

[0046] As shown in FIG. 5, the image forming apparatus 100 includes a printer control unit 1, a line memory 235, a formation control unit 120 included in the image forming unit 110, and a correction data storage unit 230.

[0047] The printer control unit 1 is a processor such as a CPU (Central Processing Unit) that corrects the positional deviation of the image formed on the paper P by the image forming apparatus 100.

[0048] The line memory 235 is provided in front of the write start position control unit 222 included in the formation control unit 120, and is a buffer memory that stores information such as image data used by the image forming unit 110 for image formation.

[0049] The formation control unit 120 includes a polygon mirror control unit 221, a writing start position control unit 222, an LD control unit 223, a synchronization detection lighting control unit 224, and a pixel clock generation unit 225. The pixel clock generation unit 225 includes a phase synchronization clock generation unit 226, a VCO clock generation unit 227, and a reference clock generation unit 228.

[0050] In FIG. 5, when the scanning light beam Lb reaches the synchronization sensor 218 on the image writing side at the end in the main scanning direction D, the synchronization detection signal XDETP is output from the synchronization sensor 218 to each of the pixel clock generation unit 225, the synchronization detection lighting control unit 224, and the writing start position control unit 222.

[0051] The pixel clock generation unit 225 generates a pixel clock PCLK synchronized with the synchronization detection signal XDETP and outputs it to each of the writing start position control unit 222 and the synchronization detection lighting control unit 224.

[0052] The synchronization detection lighting control unit 224 turns on the LD forced lighting signal BD to forcibly light the LD in order to detect the synchronization detection signal XDETP for the first time. After detecting the synchronization detection signal XDETP, the synchronization detection lighting control unit 224 lights the LD at a timing such that the synchronization detection signal XDETP can be surely detected without generating flare light, using the synchronization detection signal XDETP and the pixel clock PCLK.

[0053] When the synchronization detection lighting control unit 224 detects the synchronization detection signal XDETP, it generates an LD forced lighting signal BD for turning off the LD and outputs it to the LD control unit 223. Further, the synchronization detection lighting control unit 224 generates a light amount control timing signal APC for each LD using the synchronization detection signal XDETP and the pixel clock PCLK and outputs it to the LD control unit 223. This signal needs to be output outside the image writing area, and the LD control unit 223 controls the light amount of the laser light emitted by the LD to the target value at the timing when the light amount control timing signal APC is input.

[0054] The LD control unit 223 controls the lighting (emission) of the laser beam by the LD based on the LD forced lighting signal BD, the light quantity control timing signal APC, and the image data synchronized with the pixel clock PCLK. Under the control of the LD control unit 223, a light beam, which is a laser beam, is emitted from the LD provided on the LD control board 211 and scanned by the polygon mirror 213.

[0055] The polygon mirror control unit 221 controls, in response to the print start signal St from the printer control unit 1, the motor for rotationally driving the polygon mirror 213 so that it rotates at a predetermined rotational speed. For example, the polygon mirror control unit 221 can increase the image magnification in the sub-scanning direction by reducing the rotational speed.

[0056] The write start position control unit 222 generates the main scanning control signal XLGATE and the sub-scanning control signal XFGATE that determine the image write start timing and the image width in response to the synchronization detection signal XDETP, the pixel clock PCLK, the print start signal St from the printer control unit 1, and the like.

[0057] The correction sensors IS1 and IS2 output the detection signals Dt of the correction patterns by each of them to the printer control unit 1.

[0058] The printer control unit 1 generates correction data Ps1 for correcting the image misalignment based on the detection signals Dt of the correction patterns input from the correction sensors IS1 and IS2 and the reference position information of the correction patterns on the paper P. The correction data Ps1 is data for correcting the position and image magnification of the image in the main scanning direction, the position and image magnification of the image in the sub-scanning direction, and the like.

[0059] The printer control unit 1 outputs the generated correction data Ps1 to each of the write start position control unit 222, the pixel clock generation unit 225, the polygon mirror control unit 221, and the correction data storage unit 230.

[0060] When the image forming apparatus 100 performs an image forming operation, the printer control unit 1 reads out correction data Ps1 stored in the correction data storage unit 230. The read correction data Ps1 is output to each of the write start position control unit 222, the pixel clock generation unit 225, and the polygon mirror control unit 221.

[0061] As shown in FIG. 6, the VCO clock generation unit 227 includes a phase comparator 231, a LPF (Low Pass Filter) 232, a VCO 233, and a 1 / N frequency divider 234.

[0062] The phase comparator 231 inputs a reference clock signal FREF from the reference clock generation unit 228 and a signal obtained by dividing the signal VCLK by N using the 1 / N frequency divider 234, compares the phases of the rising edges of these signals, and outputs a constant current as an error component.

[0063] The LPF 232 removes unnecessary high-frequency components and noise and outputs them to the VCO 233. The VCO 233 outputs an oscillation frequency depending on the output of the LPF 232. Therefore, the frequency of the signal VCLK can be varied by varying the frequency of the reference clock signal FREF and the division ratio N from the printer control unit 1. When the frequency of the signal VCLK changes, the frequency of the pixel clock PCLK also changes.

[0064] For example, the VCO clock generation unit 227 can increase the image magnification in the main scanning direction D by decreasing the frequency of the pixel clock PCLK.

[0065] As shown in FIG. 7, the write start position control unit 222 includes a main scanning line synchronization signal generation unit 240, a main scanning gate signal generation unit 250, and a sub-scanning gate signal generation unit 260. The main scanning gate signal generation unit 250 includes a main scanning counter 251, a comparator 252, and a gate signal generation unit 253. The sub-scanning gate signal generation unit 260 includes a sub-scanning counter 261, a comparator 262, and a gate signal generation unit 263.

[0066] The main scanning line synchronization signal generation unit 240 generates a signal XLSYNC for operating the main scanning counter in the main scanning gate signal generation unit and the sub-scanning counter in the sub-scanning gate signal generation unit. The main scanning gate signal generation unit generates a signal XLGATE that determines the capture timing of the image signal (image writing timing in the main scanning direction). The sub-scanning gate signal generation unit generates a signal XFGATE that determines the capture timing of the image signal (image writing timing in the sub-scanning direction).

[0067] The main scanning counter 251 operates based on the signal XLSYNC and the pixel clock PCLK. The comparator 252 compares the counter value with the set value STx from the printer control unit 1 and outputs the comparison result. The set value STx is data in the correction data Ps1 that corrects the positional shift of the image in the main scanning direction D.

[0068] The sub-scanning counter 261 operates based on the print start signal St from the printer control unit 1, the signal XLSYNC, and the pixel clock PCLK. The comparator 262 compares the counter value with the set value STy from the printer control unit 1 and outputs the comparison result. The set value STy is data in the correction data Ps1 that corrects the positional shift of the image in the sub-scanning direction E. The gate signal generation unit 263 generates the signal XFGATE from the comparison result by the comparator 262.

[0069] The write start position control unit 222 can correct the write position in units of one cycle of the pixel clock PCLK, that is, one dot unit, in the main scanning direction, and in units of one cycle of the signal XLSYNC, that is, one line unit, in the sub-scanning direction. In both the main scanning direction and the sub-scanning direction, the correction data Ps1 is stored in the correction data storage unit 230.

[0070] <An example of write start control> Next, with reference to FIGS. 8 and 9, the control by the write start position control unit 222 will be described. FIG. 8 is a timing chart showing an example of the main scanning direction write start control by the write start position control unit 222. FIG. 9 is a timing chart showing an example of the sub-scanning direction write start control by the write start position control unit 222.

[0071] As shown in FIG. 8, the write start position control unit 222 resets the main scanning counter 251 in response to the signal XLSYNC, and counts up in response to the pixel clock PCLK. At the timing when the counter value becomes the set value STx (X in this case) set by the printer control unit 1, the comparator 252 outputs the comparison result, and the gate signal generation unit 253 sets the signal XLGATE to the Low level (valid). The signal XLGATE is a signal that becomes Low level for the image width in the main scanning direction.

[0072] As shown in FIG. 9, the write start position control unit 222 resets the sub-scanning counter 261 in response to the print start signal St from the printer control unit 1, and counts up with the signal XLSYNC. At the timing when the counter value becomes the set value STy (Y in this case) set by the printer control unit 1, the comparator 262 outputs the comparison result, and the gate signal generation unit 263 sets the signal XFGATE to the Low level (valid). The signal XFGATE is a signal that becomes Low level for the image length in the sub-scanning direction.

[0073] FIG. 10 is a diagram showing an example of the operation of the line memory 235. The line memory 235 outputs an image signal by synchronizing the pixel clock PCLK with the image data captured from the printer controller, the frame memory, the scanner, etc. at the timings of the signals XFGATE and XLGATE. The output image data is output to the LD control unit 223, and the LD in each color light beam scanning device 21 lights up at the output timing.

[0074] <Functional configuration example of the printer control unit 1> FIG. 11 is a block diagram showing an example of the functional configuration of the printer control unit 1. As shown in FIG. 11, the printer control unit 1 includes an input / output unit 101, a reference position determination unit 102, and an image position determination unit 103.

[0075] The input / output unit 101 controls the input / output of signals or data between the printer control unit 1 and an external component.

[0076] The reference position determination unit 102 determines the reference position of the correction pattern on the sheet P to be different according to the image formation condition Cd, and outputs the reference position information Ps2 to the image formation unit 110 via the input / output unit 101.

[0077] The image formation condition Cd is information indicating various conditions used for the image formation apparatus 100 to form an image on the sheet P or information related to various conditions. For example, the image formation condition Cd includes information such as the minimum formation position resolution (hereinafter simply referred to as the minimum formation position resolution) of the image formed on the sheet P by the image formation unit 110, the resolution (hereinafter simply referred to as the resolution) of the image formed on the sheet P by the image formation unit 110, or the size of the sheet P. The minimum formation position resolution, for example, coincides with the resolution.

[0078] The reference position determination unit 102 can input the image formation condition Cd set by the user using the operation panel of the image formation apparatus 100 or an external device such as a PC from the operation panel or the PC.

[0079] The image position determination unit 103 generates correction data Ps1 based on the detection signal Dt of the correction pattern input from the correction sensors IS1 and IS2 and the reference position information Ps2, thereby determining the position of the image formed by the image formation unit 110 on the sheet P. The image position determination unit 103 outputs the generated correction data Ps1 to each of the image formation unit 110 and the correction data storage unit 230.

[0080] When the image forming apparatus 100 performs image formation, the image position determination unit 103 can read the correction data Ps1 stored in the correction data storage unit 230 and output the read correction data Ps1 to the image forming unit 110.

[0081] <An example of the correction pattern 150> FIG. 12 is a diagram showing an example of the correction pattern 150 formed on the sheet P by the image forming unit 110. In FIG. 12, the side in the direction of the arrow indicating the main scanning direction D is the +D side, the side opposite to the +D side is the -D side, the side in the direction of the arrow indicating the sub-scanning direction E is the +E side, and the side opposite to the +E side is the -E side. The image forming apparatus 100 conveys the sheet P with the +E side facing.

[0082] As shown in FIG. 12, the correction pattern 150 includes patterns 151 to 158 formed near the end portions at the four corners of the sheet P. The patterns 151 to 158 are rectangular patterns having either the main scanning direction D or the sub-scanning direction E as the longitudinal direction.

[0083] On the end portion on the +E direction side on the -D direction side of the sheet P, a pattern 151 having the main scanning direction D as the longitudinal direction and a pattern 152 having the sub-scanning direction E as the longitudinal direction are formed. On the end portion on the +E direction side on the +D direction side of the sheet P, a pattern 153 having the main scanning direction D as the longitudinal direction and a pattern 154 having the sub-scanning direction E as the longitudinal direction are formed.

[0084] On the end portion on the -E direction side on the -D direction side of the sheet P, a pattern 155 having the main scanning direction D as the longitudinal direction and a pattern 156 having the sub-scanning direction E as the longitudinal direction are formed. On the end portion on the -E direction side on the +D direction side of the sheet P, a pattern 157 having the main scanning direction D as the longitudinal direction and a pattern 158 having the sub-scanning direction E as the longitudinal direction are formed.

[0085] Here, the reference position 150c of the correction pattern 150 determined by the reference position determination unit 102 will be described.

[0086] In FIG. 12, the paper width W represents the length of the paper P in the main scanning direction D, and the paper length L represents the length of the paper P in the sub-scanning direction E. The distance X represents the distance between each of the patterns 152, 154, 156, and 158 and the end portion of the paper P closest to each in the main scanning direction D. The distance Y represents the distance between each of the patterns 151, 153, 155, and 157 and the end portion of the paper P closest to each in the sub-scanning direction E. The pattern width T represents the length in the short side of each of the patterns 151 to 158.

[0087] For example, assume that the paper width W is 297 [mm], the paper length L is 420 [mm], the distance X is 5 [mm], the distance Y is 5 [mm], and the pattern width T is 2 [mm]. Also, when the reference is made to the origin position O of the paper P, in the case where the resolution is 1200 [dpi], the reference position determination unit 102 determines the center positions of each of the patterns 151 to 158 with respect to the origin position O as the reference positions 151c to 158c corresponding to each of the patterns 151 to 158 as follows.

[0088] Reference position 151c of pattern 151: 5.990 [mm] Reference position 152c of pattern 152: 5.990 [mm] Reference position 153c of pattern 153: 5.990 [mm] Reference position 154c of pattern 154: 290.990 [mm] Reference position 155c of pattern 155: 413.990 [mm] Reference position 156c of pattern 156: 5.990 [mm] Reference position 157c of pattern 157: 413.999 [mm] Reference position 158c of pattern 158: 290.999 [mm]

[0089] The reference positions of patterns 151, 153, 155, and 157 correspond to the distance from the origin position O in the sub-scanning direction E to the center position, and the reference positions of patterns 152, 154, 156, and 158 correspond to the distance from the origin position O in the main scanning direction D to the center position.

[0090] When the resolution is 600 [dpi], the reference position determination unit 102 determines the center position of each of the patterns 151 to 158 with respect to the origin position O as the reference positions 151c to 158c corresponding to each of the patterns 151 to 158 as follows.

[0091] Reference position 151c of pattern 151: 6.011 [mm] Reference position 152c of pattern 152: 6.011 [mm] Reference position 153c of pattern 153: 6.011 [mm] Reference position 154c of pattern 154: 290.999 [mm] Reference position 155c of pattern 155: 414.020 [mm] Reference position 156c of pattern 156: 6.011 [mm] Reference position 157c of pattern 157: 414.020 [mm] Reference position 158c of pattern 158: 290.999 [mm]

[0092] That is, the reference position determination unit 102 can determine the reference positions 151c to 158c that are different in position according to the resolution.

[0093] In FIG. 12, the correction sensors IS1 and IS2 provided on the +E side of the paper P detect each of the patterns 151 to 158 formed on the conveyed paper P, and output the respective detection signals Dt to the image position determination unit 103 in the printer control unit 1.

[0094] The image position determination unit 103 calculates the position of each of the patterns 151 to 158 with respect to the edge of the paper P based on the detection signal Dt. Then, the image position determination unit 103 generates correction data Ps1 based on the amount by which the calculated positions of each of the patterns 151 to 158 deviate from the respective reference positions 151c to 158c, so that each of the patterns 151 to 158 is formed at the corresponding reference positions 151c to 158c, or so that the position of the image formed on the front surface of the paper P and the position of the image formed on the back surface are aligned.

[0095] In image position correction, when correcting the image position on the front surface of the sheet P, the images formed on the sheets subsequent to the sheet P on which the correction pattern 150 is detected are corrected. When correcting the image position on the back surface with respect to the image position on the front surface of the sheet P, the image formed on the back surface of the sheet P on which the correction pattern 150 is detected is corrected.

[0096] Here, the reference position 150c will be further described. When the conditions such as the sheet width W, the distance X, the distance Y, and the pattern width T are set as described above, the center position of each of the patterns 151 to 158 with respect to the origin position O is as follows as a general target position.

[0097] Pattern 151: 6.000 [mm] Pattern 152: 6.000 [mm] Pattern 153: 5.990 [mm] Pattern 154: 291.000 [mm] Pattern 155: 414.000 [mm] Pattern 156: 6.000 [mm] Pattern 157: 414.000 [mm] Pattern 158: 291.000 [mm]

[0098] However, since the image forming apparatus 100 cannot form the patterns 151 to 158 with a positional resolution less than the minimum forming positional resolution, the positions of each of the patterns 151 to 158 actually formed on the sheet P are slightly deviated from the target positions. Therefore, when correction data Ps1 is generated with the target position as the reference position and the image position is corrected, the absolute position of the image formed on the sheet P is deviated according to the deviation of the actually formed patterns 151 to 158 with respect to the target position.

[0099] In this embodiment, the reference position determination unit 102 determines positions slightly shifted from the above general positions as the reference positions 150c to 158c of the patterns 151 to 158 according to the image formation conditions Cd such as the resolution. Thereby, the image forming apparatus 100 eliminates the influence of the absolute position shift according to the image formation conditions Cd of the patterns 151 to 158 actually formed on the paper P, and can accurately generate the correction data Ps1.

[0100] There is no particular limitation on the position of the reference position 150c on the paper P, and the reference position determination unit 102 can determine any position on the paper P as the reference position 150c. However, when the position of the correction pattern 150 approaches the image formation possible range Im or the end Pe of the paper P according to the reference position 150c, the detection signals of the image and the end Pe of the paper P are included in the detection signals by the correction sensors IS1 and IS2, and the position of the correction pattern 150 may not be accurately detected.

[0101] Therefore, on the paper P, the reference position determination unit 102 is at a central position separated from the end Pe of the paper P by a distance that is half of the shortest distance s between the image formation possible range Im by the image forming unit 110 and the end Pe of the paper P, and along the direction in which the line connecting the central position and the end Pe extends, it is preferable to determine a position separated by a distance corresponding to a multiple of the minimum formation position resolution Δs by the image forming apparatus 100 as the reference position 150c.

[0102] For example, when the distance that is half of the above shortest distance s is 5.995 [mm] and the minimum formation position resolution Δs is 11 [μm], the reference position determination unit 102 is at a central position separated from the end Pe of the paper P by 5.995 [mm], and along the direction in which the line connecting the central position and the end Pe extends, it is preferable to set positions such as 5.995 [mm], 6.006 [mm], 6.017 [mm], etc., which are separated by a distance corresponding to a multiple of 11 [μm], as the reference position 150c.

[0103] Accordingly, the reference position 150c can be set at a position as far as possible from both the image formation possible range Im and the end Pe of the sheet P. As a result, it is possible to suppress the detection signals of the image and the end Pe of the sheet P from being included in the detection signals by the correction sensors IS1 and IS2, and it becomes possible to accurately detect the position of the correction pattern 150.

[0104] In the above-described example, the case where the image formation condition Cd is the resolution is illustrated, but the present invention is not limited to this. For example, the positions of the patterns 151 to 158 actually formed on the sheet P also vary depending on the size of the sheet P. Therefore, the reference position determination unit 102 can determine the reference positions 151c to 158c of the patterns 151 to 158 according to the size information of the sheet P.

[0105] <Operation example of the image forming apparatus 100> (Image position correction operation) FIG. 13 is a flowchart showing an example of an image position correction operation by the image forming apparatus 100.

[0106] FIG. 13 shows the operation of the image forming apparatus 100 triggered by an image formation start instruction given by the user of the image forming apparatus 100 via an operation panel or the like provided in the image forming apparatus 100.

[0107] First, in step S121, the polygon mirror control unit 221 starts the rotation of the polygon mirror 213 at a predetermined rotation speed based on the image formation condition Cd in response to the print start signal St from the printer control unit 1.

[0108] Subsequently, in step S122, the printer control unit 1 outputs correction data Ps1 to the polygon mirror control unit 221, the write start position control unit 222, the reference clock generation unit 228, and the like. The correction data Ps1 here is the one used at the previous correction or the initial value of the correction data Ps1.

[0109] Subsequently, in step S123, the LD control unit 223 turns on the LD to output a synchronization detection signal, and performs an APC operation to bring each LD into a state where it can emit light with a predetermined light amount.

[0110] Subsequently, in step S124, the image forming unit 110 forms a correction pattern 150 on the paper P under the control of the formation control unit 120. In this embodiment, it is assumed that the correction pattern 150 is formed in the K color.

[0111] Subsequently, in step S125, the correction sensors IS1 and IS2 detect the correction pattern 150 and output a detection signal Dt to the printer control unit 1.

[0112] Subsequently, in step S126, the image positioning unit 103 calculates the deviation amount of the position of the correction pattern 150 based on the detection signal Dt with respect to the reference position 150c.

[0113] Subsequently, in step S127, the image positioning unit 103 determines whether to perform correction. For example, when the deviation amount is equal to or greater than 1 / 2 of the correction resolution, the image positioning unit 103 determines to perform correction.

[0114] If it is determined to perform correction in step S127 (step S127, Yes), then in step S128, the image positioning unit 103 generates correction data Ps1 through calculation.

[0115] Subsequently, in step S129, the image positioning unit 103 updates the correction data Ps1 stored in the correction data storage unit 230 by outputting the generated correction data Ps1 to the correction data storage unit 230. For example, the image positioning unit 103 updates the correction data Ps1 by adding or subtracting from the correction data Ps1 used when forming the correction pattern 150 on the paper P.

[0116] The correction data Ps1 here includes the set value of the pixel clock frequency that determines the image magnification in the main scanning direction D, the set value of the XRGATE signal that determines the image position in the main scanning direction D, the set value of the XFGATE signal that determines the image position in the sub-scanning direction E, and the set value of the rotation speed of the polygon mirror 213 that determines the image magnification in the sub-scanning direction E, etc.

[0117] On the other hand, if it is determined not to correct in step S127 (step S127, No), the image forming apparatus 100 shifts the operation to step S130.

[0118] Subsequently, in step S130, the LD control unit 223 turns off the LD.

[0119] Subsequently, in step S131, the polygon mirror control unit 221 stops the polygon mirror 213.

[0120] In this way, the image forming apparatus 100 can correct the position of the image. Note that the correction is not only performed using the position information of the correction pattern 150 formed on a single sheet of paper P, but can also be performed using the average value information of the positions of the correction patterns 150 formed on a plurality of sheets of paper P. Using the average value information can reduce the influence of the detection error of the correction pattern 150 by the correction sensors IS1 and IS2, so it is more preferable.

[0121] (Image forming operation) FIG. 14 is a flowchart showing an example of the image forming operation by the image forming apparatus 100.

[0122] FIG. 14 shows the operation of the image forming apparatus 100 triggered by an image forming start instruction given by the user of the image forming apparatus 100 via an operation panel or the like provided in the image forming apparatus 100. The operations in steps S141 to S143 in FIG. 14 are the same as those in steps S121 to S123 in FIG. 13, and the operations in steps S146 and S147 in FIG. 14 are the same as those in steps S130 and S131 in FIG. 13. Therefore, overlapping explanations are omitted here, and only the differences from FIG. 13 are explained.

[0123] After the LD is lit in step S143, in step S144, the image forming unit 110 forms an image on the sheet P.

[0124] Subsequently, in step S145, the image forming apparatus 100 determines whether there is a next image.

[0125] If it is determined in step S145 that there is a next image (step S145, Yes), the image forming apparatus 100 performs the operation in step S144 again. On the other hand, if it is determined that there is no next image (step S145, No), the image forming apparatus 100 proceeds to step S146.

[0126] In this way, the image forming apparatus 100 can form an image on the sheet P. Note that the correction data Ps1 used in the operation of FIG. 14 is the correction data stored in the correction data storage unit 230 after being generated in the operation shown in FIG. 13.

[0127] (Image position correction operation for image formation on the back side of the sheet P) FIG. 15 is a flowchart showing an example of the correction operation by the image forming apparatus 100 for image formation on the back side of the sheet P.

[0128] FIG. 15 shows an operation triggered by the timing at which the image forming apparatus 100 starts correction. That is, the operation shown in FIG. 15 is an operation performed during the image forming operation. The position correction of the image formed on the back surface of the sheet P with respect to the image formed on the front surface of the sheet P is performed during double-sided printing, but it may be performed always during double-sided printing, or it may be performed in response to an instruction by the user via the operation panel.

[0129] First, in step S151, the printer control unit 1 outputs correction data Ps1 to the polygon mirror control unit 221, the writing start position control unit 222, the reference clock generation unit 228, and the like. The correction data Ps1 here is the correction data generated in the correction operation of FIG. 13, the correction data stored in the correction data storage unit 230, or the correction data generated in this correction operation.

[0130] Subsequently, in step S152, the image forming unit 110 forms a correction pattern 150 on the sheet P under the control of the formation control unit 120. In the present embodiment, it is assumed that the correction pattern 150 is formed in the K color.

[0131] When the image formation starts, the image forming apparatus 100 forms the correction pattern 150 on the sheet P in parallel with the image formation on the front surface of the sheet P. In the colors in which the correction pattern 150 is not formed, only the image is formed.

[0132] Subsequently, in step S153, the correction sensors IS1 and IS2 detect the correction pattern 150 and output a detection signal Dt to the printer control unit 1.

[0133] Subsequently, in step S154, the image positioning unit 103 calculates the deviation amount of the position of the correction pattern 150 based on the detection signal Dt with respect to the reference position 150c.

[0134] Subsequently, in step S155, the image positioning unit 103 determines whether or not to perform correction. For example, when the deviation amount is equal to or more than 1 / 2 of the correction resolution, the image positioning unit 103 determines to perform correction.

[0135] If it is determined in step S155 that correction is to be performed (step S155, Yes), in step S156, the image positioning unit 103 generates correction data Ps1 through calculation.

[0136] Subsequently, in step S157, the image positioning unit 103 updates the correction data Ps1 stored in the correction data storage unit 230 by outputting the generated correction data Ps1 to the correction data storage unit 230. For example, the image positioning unit 103 updates the correction data Ps1 by adding or subtracting it from the correction data Ps1 used when forming the correction pattern 150 on the paper P.

[0137] The correction data storage unit 230 stores the correction data Ps1 for the front surface and the correction data Ps1 for the back surface, and the data is updated when correction is performed.

[0138] Subsequently, in step S158, the printer control unit 1 outputs the generated correction data Ps1 to each of the writing start position control unit 222, the pixel clock generation unit 225, the polygon mirror control unit 221, and the correction data storage unit 230.

[0139] On the other hand, if it is determined in step S155 that correction is not to be performed (step S127, No), the image forming apparatus 100 ends the correction operation.

[0140] In this way, the image forming apparatus 100 can correct the image position in forming an image on the back surface of the paper P.

[0141] Here, the correction operation for the image position formed on the front surface is the same as that shown in FIG. 15, but unlike the correction for the image position formed on the back surface, there may be cases where real-time correction is not possible. For example, when forming the second image while detecting the first pattern, real-time correction is not possible.

[0142] In this case, since the detection result of the correction pattern 150 formed on the first surface cannot be fed back to the image formation on the second surface, the correction data Ps1 will be fed back to the image formation several sheets later. In this case, in order to reduce the detection error, the average value information of the detection results of the correction pattern 150 formed on several sheets of paper P can also be used.

[0143] By storing the correction data Ps1 in the correction data storage unit 230, the latest correction data can always be used.

[0144] When the image formation conditions Cd such as the size and resolution of the paper P change for each page, the image forming apparatus 100 recalculates the position of the correction pattern 150 for each sheet of paper P on which the correction pattern 150 was generated under the image formation conditions Cd for each page. Then, the image forming apparatus 100 generates the correction data Ps1 and outputs it to the writing start position control unit 222, the pixel clock generation unit 225, and the polygon mirror control unit 221.

[0145] In other words, the image forming unit 110 forms the correction pattern 150 for each page of the paper P, and the image positioning unit 103 determines the position of the image based on the position of the correction pattern 150 formed by the image forming unit 110 for each page of the paper P. Thereby, even when the image formation conditions Cd change for each page, the image position can be accurately corrected.

[0146] <The operation and effect of the image forming apparatus 100> Next, the operation and effect of the image forming apparatus 100 will be described.

[0147] Since the image forming apparatus cannot form the correction pattern at a positional resolution lower than the minimum formation positional resolution, the position of the correction pattern actually formed on the paper is slightly deviated from the target position.

[0148] Therefore, when correction data is generated with the target position as the reference position and the image position is corrected, the absolute position of the image formed on the paper may shift according to the absolute position deviation of the actual correction pattern from the target position, and the quality of the image formed by the image forming apparatus may deteriorate.

[0149] These days, with the demand for further higher image quality, the absolute position deviation of the image with respect to the paper can no longer be ignored, and a correction technique therefor is required.

[0150] The image forming apparatus 100 according to the present embodiment includes an image forming unit 110 that forms an image on a paper P (recording medium) based on image forming conditions Cd, a detection signal Dt of a correction pattern 150 (predetermined pattern) formed by the image forming unit 110 on the paper P, and reference position information Ps2 of the correction pattern 150 on the paper P, and an image positioning unit 103 that determines the position of the image formed by the image forming unit 110 on the paper P based thereon. The image forming apparatus 100 also includes a reference position determination unit 102 that determines the reference position 150c of the correction pattern 150 to be different according to the image forming conditions Cd.

[0151] For example, the image forming conditions Cd include minimum formation position resolution information of the image formed by the image forming unit 110.

[0152] The image forming apparatus 100 can generate accurate correction data Ps1 that is not affected by the absolute position deviation according to the image forming conditions Cd of the patterns 151 to 158 actually formed on the paper P by determining the positions shifted from the target position as the reference positions 150c to 158c of the patterns 151 to 158 according to the image forming conditions Cd such as the resolution. Thereby, the image forming apparatus 100 can correct the absolute position deviation of the image with respect to the paper P.

[0153] The reference position 150c of the correction pattern 150 also shifts depending on the resolution and the size of the paper P, but by including the resolution information and the size information of the paper P in the image forming conditions Cd, it becomes possible to correct the absolute position deviation of the image due to these shifts.

[0154] [Other Preferred Embodiments] In the above-described embodiment, as the correction pattern 150, an example is given of a rectangular shape having a longitudinal direction along the main scanning direction D or the sub-scanning direction E, but the present invention is not limited thereto. As long as the position of the correction pattern 150 with respect to the paper P in the main scanning direction D and the sub-scanning direction E can be detected, for example, the correction pattern 150 may have a bent shape or a square shape. From the viewpoint of making the correction pattern 150 formed on the paper P less conspicuous, the correction pattern 150 is preferably as small as possible as long as it can be detected by the correction sensors IS1 and IS2.

[0155] In the above-described embodiment, a configuration in which the correction pattern 150 is detected by two correction sensors IS1 and IS2 is exemplified. However, as long as all the correction patterns 150 can be detected even if the width of the paper P changes, the number of correction sensors may be one.

[0156] The minimum formation position resolution for generating the correction pattern 150 does not necessarily have to be the same as the resolution. For example, when it is twice the resolution, the image forming apparatus 100 can calculate the deviation amount of the correction pattern from the position of the correction pattern 150 calculated based on the twice resolution and generate the correction data Ps1.

[0157] As described above, examples of the embodiments of the present invention have been described. However, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

[0158] Furthermore, the embodiment also includes an image forming method. For example, the image forming method is an image forming method by an image forming apparatus, wherein the image forming apparatus forms an image on a recording medium by an image forming unit based on image forming conditions, and an image positioning unit determines, based on a detection signal of a predetermined pattern formed by the image forming unit on the recording medium and reference position information of the predetermined pattern on the recording medium, the position where the image forming unit forms the image on the recording medium, and a reference position determination unit determines the reference position of the predetermined pattern to be different according to the image forming conditions. By such an image forming method, the same effects as those of the above-described image forming apparatus can be obtained.

[0159] Moreover, each function of the embodiment described above can be realized by one or a plurality of processing circuits. Here, the "processing circuit" in this specification includes a processor programmed to execute each function by software like a processor implemented by an electronic circuit, an ASIC (Application Specific Integrated Circuit) designed to execute each function described above, a DSP (digital signal processor), an FPGA (field programmable gate array), and devices such as conventional circuit modules.

Explanation of Reference Numerals

[0160] 1 Printer control unit 100 Image forming apparatus 101 Input / output unit 102 Reference position determination unit 103 Image positioning unit 110 Image forming unit 120 Formation control unit 150 Correction pattern 151 to 158 Patterns 150c, 151c to 158c Reference positions 213 Polygon mirror 230 Correction data storage unit 235 Line memory D Main scanning direction E Sub-scanning direction Lb Scanning light beam L Paper length W Paper width T Pattern width P Paper (an example of a recording medium) Pe Edge of the paper s Shortest distance Cd Image formation conditions Dt Detection signal IS1, IS2 Correction sensors St Printing start signal Ps1 Correction data Ps2 Reference position information

Prior art documents

Patent documents

[0161]

Patent Document 1

Claims

1. An image forming unit that forms an image on a recording medium based on image forming conditions; An image positioning unit that determines the position of the image formed by the image forming unit on the recording medium based on a detection signal of a predetermined pattern formed by the image forming unit on the recording medium and reference position information of the predetermined pattern on the recording medium; A reference position determination unit that determines the reference position for forming the predetermined pattern to be different according to the image forming conditions, and having: The image forming unit forms the predetermined pattern for each page of the recording medium, The image positioning unit determines the position of the image based on the position of the predetermined pattern formed by the image forming unit for each page of the recording medium, and an image forming apparatus characterized by this.

2. An image forming unit that forms an image on a recording medium based on image forming conditions; An image positioning unit that determines the position of the image formed by the image forming unit on the recording medium based on a detection signal of a predetermined pattern formed by the image forming unit on the recording medium and reference position information of the predetermined pattern on the recording medium; A reference position determination unit that determines the reference position of the predetermined pattern to be different according to the image forming conditions, and having: The image forming conditions include resolution information of the image formed by the image forming unit, and an image forming apparatus characterized by this.

3. The image forming apparatus according to claim 1 or 2, wherein the image forming conditions include minimum formation position resolution information of the image formed by the image forming unit.

4. The reference position determination unit is a central position that is separated from the end of the recording medium by a distance that is 1 / 2 of the shortest distance between the image forming range by the image forming unit and the end of the recording medium on the recording medium, and along the direction in which the line connecting the central position and the end of the recording medium extends, the image forming apparatus according to claim 3, wherein a position separated by a distance corresponding to a multiple of the minimum formation position resolution of the image is determined as the reference position.

5. The image forming apparatus according to any one of claims 1 to 4, wherein the image forming conditions include size information of the recording medium.

6. An image forming method by an image forming apparatus, wherein the image forming apparatus forms an image on a recording medium by an image forming unit based on image forming conditions, Based on the detection signal of the predetermined pattern formed by the image forming unit on the recording medium and the reference position information of the predetermined pattern on the recording medium, the image position determination unit determines the position where the image forming unit forms the image on the recording medium. The reference position determination unit determines the reference position for forming the predetermined pattern to be different according to the image forming conditions. The image forming unit forms the predetermined pattern for each page of the recording medium. The image position determination unit determines the position of the image based on the position of the predetermined pattern formed by the image forming unit for each page of the recording medium. A method for forming an image is characterized by this. **Claim 7**: A method for forming an image by an image forming apparatus, wherein the image forming apparatus forms an image on a recording medium based on image forming conditions by an image forming unit. Based on the detection signal of the predetermined pattern formed by the image forming unit on the recording medium and the reference position information of the predetermined pattern on the recording medium, the image position determination unit determines the position of the image formed by the image forming unit on the recording medium. The reference position determination unit determines the reference position of the predetermined pattern to be different according to the image forming conditions. The image forming conditions include resolution information of the image formed by the image forming unit. A method for forming an image is characterized by this.

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