JP2004347842A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deviation between images on both surfaces due to the thermal contraction of paper, and to detect a difference in the local contraction. <P>SOLUTION: The sizes of the paper in main and sub scanning directions are detected by a line sensor on a carrying path. Parts to be detected are previously divided to areas, and the contraction is calculated for every area. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, and more particularly, to an image forming apparatus configured to be capable of forming a two-sided image on the same sheet.
[0002]
[Prior art]
In the conventional copying machine shown in FIG. 1, when performing double-sided copying on the same sheet, the transferred sheet conveyed through the image forming unit 110 and the fixing unit 32 is transferred to a sheet re-feeding unit using a flapper or the like. The sheet is again introduced into the image forming section via the sheet conveying section.
[0003]
When performing double-sided copying, regarding the positioning of the paper in the main scanning direction and the positioning in the sub-scanning direction, one lateral end of the paper and the leading end of the paper are aligned to prescribed positions by a lateral registration unit and a pair of registration rollers, respectively. It is configured to be performed by. Regarding image reduction, the main and secondary data are thinned out and read from the image memory, or the speed of the polygon motor or the operating frequency of the laser CLK is changed to control the scanning line width on the original corresponding to one pixel. There is a method. (See Patent Document 1).
[0004]
[Patent Document 1]
JP-A-2000-255124
[0005]
[Problems to be solved by the invention]
By the way, after the toner image is transferred in the copying section of the above-described copying apparatus, the sheet is subjected to a fixing action in the fixing section 32. At this time, if the sheet is of a heat fixing type, moisture in the sheet is removed by the fixing section 32. As a result, the vertical and horizontal dimensions of the sheet change in the shrinking direction. The amount of paper shrinkage varies depending on the type of material, the size of the paper, and the direction of the fiber in the paper, and the amount of water in the paper also changes depending on the environment (humidity and temperature) when the paper was stored. Accordingly, the amount of shrinkage also changes. In a conventional copying apparatus, when performing double-sided copying on the same sheet, an image is placed at a specified position from one lateral end of the sheet and the leading end of the sheet without considering the shrinkage amount of the sheet as described above. Since the positioning of the laser emission reference is performed so as to be formed, the positional deviation between the image and the paper is generated on the two-sided paper as the distance from the specified position increases with the dimensional change of the paper described above. There were drawbacks.
[0006]
This will be described in more detail with reference to FIG. At the time of image formation on the front surface, since there is no shrinkage of the sheet, it is possible to form a frame as shown in FIG. 23A as desired. The above-described frame is formed as an image writing reference position with a distance b in the sub-scanning direction and a distance a in the main scanning direction from one end of the sheet. Here, it is assumed that the paper shrinks due to the fixing action of the fixing unit 32, for example, and the outer dimensions of the paper are reduced to 9/10. If shrinkage by the fixing unit is not taken into account when forming the image of the back side, the size of the frame is the same outer size as the front side, and the writing position of the image is the distance a, Since writing is started from the position b, the positional relationship of the frame with respect to the sheet is shifted as shown in FIG. At that time, since the entire surface of the sheet shrinks, the positional relationship between the frame and the sheet is the same as that in FIG. (FIG. 23-c. However, the size of the frame is reduced by shrinkage.) Then, when the images on the front and back are seen through, as shown in FIG. It will be very unsightly.
[0007]
Also, in the case of a double-page spread as in the bookbinding mode, for the same reason, the image size is different between the right page and the left page, making it difficult to see, and further reducing the value of the image formed product when it becomes a product. Will be lost.
[0008]
The first means for solving the above-mentioned disadvantages is to set the reference position of the transfer paper on the front surface in order to cope with the amount of change in the vertical and horizontal dimensions occurring in the fixing unit when performing double-sided copying. Has been proposed to be displaced by a predetermined amount with respect to a reference position in the copying process. However, although it has the effect of making image misalignment less noticeable, the size of the front side frame and the size of the back side frame are not a little different, and when the paper type (material) or paper size is changed, the actual There is a drawback that it is difficult to obtain a desired effect because the shrinkage of the paper does not match the amount of change in the preset reference position. Further, the image shrinkage greatly depends on the environment (humidity and temperature) in which the paper is stored, and there is also a disadvantage that it is difficult to obtain a desired effect. That is, as shown in FIG. 24, although the positional relationship between the sheet and the frame is improved, the size of the frame on the front surface and the size of the frame on the back surface are different from each other.
[0009]
Further, in addition to the control for displacing the reference position of the transfer sheet by a preset amount as described above, the contraction amount of the sheet is determined in advance, and the image on the back side is reduced according to the set contraction amount, There is also a method of displacing the reference position. However, it is difficult to obtain a desired effect because the amount of shrinkage is not constant depending on the type (material) of the paper, the size of the paper, the clearance direction of the fiber, and the environment. was there.
[0010]
As a second means for solving the above-mentioned drawbacks, a change in the sub-scanning dimension of the sheet is detected by a mechanical sensing lever type sensor (flag type sensor) as shown in FIG. For example, a method of finely adjusting the latent image speed (process speed) to correct the dimensional contraction in the sub-scanning direction can be considered.
[0011]
FIG. 13 shows a possible mechanical sensing lever type. The lever 201 is disposed so as to block the paper path, and when a part of the lever 201 is pressed by the leading end portion 30 of the paper passing through the paper path, the lever rotates clockwise, and the photocoupler 202 disposed near the lever is rotated. A signal is generated by shielding the light beam (the signal generating portion is not shown). When the trailing edge of the sheet is detected, the lever is rotated to the left by its own weight or a spring when the sheet passes, and the absence of the sheet is detected by receiving the light flux of the photocoupler 202 again. Here, when detecting the rear end, since the rotation of the lever is operated by its own weight or a spring in addition to the movement time of the lever, a bounce occurs, and for a certain period of time so that there is no erroneous detection due to the effect, Continue detection. This causes a problem that the detection time of the rear end detection is longer than that of the front end detection.
[0012]
Specifically, the processing time for detecting the trailing edge is empirically required to be about 20 ms, and when converted to a distance (assuming the paper transport speed is 500 mm / s), 20 ms × 500 mm / s = 10 mm. It is clear that although there is an effect on the configuration in which the gap is 10 mm or more, there is a problem in the accuracy of correction.
[0013]
Because, in recent years, demands for products that are required in the POD (print-on-demand) market are increasing, and requirements for printing accuracy on the front and back sides are also very high. The requirement for the amount of displacement between the front surface and the back surface described in FIGS. A and B is said to be within 0.5 mm or within 0.3 mm.
[0014]
Therefore, if it is assumed that the displacement caused by the heat shrinkage due to the fixing is corrected to be within 0.3 mm, the detection accuracy needs to be higher. As described above, the mechanical flag sensor requires a lot of processing time to prevent erroneous detection due to flag movement time and chattering, and does not involve detection capability, so that an accurate shrinkage ratio cannot be obtained. That is, it is far below the detection accuracy target of 0.3 mm. In recent years, an optical sensor may be used instead of the flag sensor. However, the detection accuracy of the optical sensor at the present time is about several mm in terms of distance (main causes such as spot diameter and the like). Although it is a restriction, details are omitted), although the detection accuracy is improved as compared with the flag type sensor, the detection capability is not finally accompanied.
[0015]
Further, even if the measurement of the amount of contraction in the sub-scanning direction is realized to some extent by the above method, it is difficult to detect the dimensional contraction in the main scanning direction by the same method. , The image may be uniquely predicted or determined from the change of the image, and the image may be reduced by performing image processing such as thinning out the pixels of the main scan. Even in this case, since the shrinkage rate in the main scanning direction is predicted from the dimension in the sub-scanning direction, there is a disadvantage that accurate shrinkage correction cannot be performed depending on the paper type, environment (humidity and temperature), and the like.
[0016]
Further, there are the following problems. This will be described with reference to FIG. In the figure, reference numeral 3001 enclosed by a broken line denotes a sheet before shrinking, and 3002 enclosed by a solid line denotes a sheet after shrinking. I have. Even if the amount of dimensional change is obtained with high accuracy, the amount of paper shrinkage varies locally even in the same direction as shown in FIG. In particular, it is said that the corners of the sheet have a large amount of water evaporation and are likely to shrink. Therefore, if only one value ((2) a in the figure) of the dimensional change is detected in one direction, even if the above-described scaling processing is performed, the change in the part ((2) b) in the figure is different. As shown in FIG. 27C, a defect such as a missing image occurs for an image. (The same applies to c and d in the vertical direction)
[0017]
[Means for Solving the Problems]
Therefore, in this embodiment, in order to solve the above-mentioned problem, the use of a line sensor as the heat shrinkage detecting means in the sub-scanning direction makes it possible to detect the heat shrinkage rate with higher accuracy than ever before, Can be obtained by the same line sensor, so that the main scanning direction and the sub-scanning direction can be independently corrected in accordance with the reduction rates of the main scanning and the sub-scanning. The point can be solved. Here, in this embodiment, a contact sensor (CIS) is taken as a representative line sensor. The accuracy of the contact sensor (CIS) is 600 dpi, which is typical, and can be detected at 0.042 mm in theory. / The contraction rate of the paper can be detected with very high accuracy in each of the sub-scanning directions. Actually, the accuracy is reduced due to other factors such as the transfer accuracy, but the accuracy is still as high as several commas.
[0018]
As a feature of the present embodiment, a single line sensor performs detection in both main and sub-scanning directions, which is very advantageous in terms of cost and mounting.
[0019]
Further, by detecting a plurality of contraction rates for each area, accurate detection can be performed even if the contraction method is locally different as described above.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of an image forming apparatus and an image forming control method according to the present invention will be described with reference to the drawings.
[0021]
[overall structure]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment. This image forming apparatus includes an image forming apparatus main body 10, a folding device 40, and a finisher 50. The image forming apparatus main body 10 includes an image reader 11 for reading a document image and a printer 13.
[0022]
A document feeder 12 is mounted on the image reader 11. The document feeder 12 feeds the documents set upward on the document tray 12a one by one from the top page one by one to the left in the drawing, and transports the documents onto the platen glass via a curved path to a predetermined position. The original is read by stopping at the position and scanning the scanner unit 21 from left to right in this state. After reading, the original is discharged toward the external discharge tray 12b.
[0023]
The reading surface of the document is irradiated with light from the lamp of the scanner unit 21, and the reflected light from the document is guided to the lens 25 via mirrors 22, 23, and 24. The light passing through the lens 25 forms an image on the imaging surface of the image sensor 26.
[0024]
Then, while reading the image of the document by the image sensor 26 line by line in the main scanning direction, the entire image of the document is read by conveying the scanner unit 21 in the sub-scanning direction. The optically read image is converted into image data by the image sensor 26 and output. The image data output from the image sensor 26 is subjected to predetermined processing in an image signal control unit (image processing circuit) not shown, and then input as a video signal to an exposure control unit (laser control circuit) not shown in the printer 13. I do.
[0025]
The exposure control unit of the printer 13 modulates a laser beam output from a laser element (not shown) based on the input image data, and the modulated laser beam is scanned by a polygon mirror 27 while a lens 28 is scanned. , 29 and the mirror 30 onto the photosensitive drum 31.
[0026]
On the photosensitive drum 31, an electrostatic latent image corresponding to the scanned laser beam is formed. The electrostatic latent image on the photosensitive drum 31 is visualized as a developer image by the developer supplied from the developing device 33. Further, at the timing synchronized with the start of the laser beam irradiation, paper is fed from each of the cassettes 34, 35, 36, 37, the manual paper feeding unit 38 or the double-sided conveyance path, and is conveyed to the image forming unit via a registration roller. Is done.
[0027]
The sheet is conveyed between the photosensitive drum 31 and the transfer roller 39, and the developer image formed on the photosensitive drum 31 is transferred onto the sheet fed by the transfer roller 39. The sheet on which the developer image has been transferred is conveyed to the fixing unit 32, and the fixing unit 32 fixes the developer image on the sheet by heat-pressing the sheet. The sheet that has passed through the fixing unit 32 is discharged from the printer 13 to the outside (folding device 40) via a flapper and a discharge roller.
[0028]
Here, when the sheet is discharged with its image forming surface facing downward (face down state), the sheet that has passed through the fixing unit 32 is once guided into a reversing path by a flapper switching operation, and the trailing edge of the sheet is discharged. After passing through the flapper, the sheet is switched back and discharged from the printer 13 by the discharge roller.
[0029]
When a hard sheet such as an OHP sheet is fed from the manual feed unit 38 and an image is formed on the sheet, the image forming surface is turned upward without leading the sheet to a reverse path (face-up state). ) To discharge by the discharge roller.
[0030]
Further, when double-sided recording in which image formation is performed on both sides of a sheet is set, the sheet is guided to a reversing path by a flapper switching operation, and then is conveyed to a two-sided conveyance path. Then, the paper is fed again between the photosensitive drum 31 and the transfer unit at the timing described above.
[0031]
The sheet discharged from the printer 13 is sent to the folding device 40. The folding device 40 performs a process of folding a sheet into a Z shape. For example, when a folding process is designated for an A3 size or B4 size sheet, the folding device 40 performs the folding process. Otherwise, the paper discharged from the printer 13 passes through the folding device 40 and passes through the folding device 40. It is sent to the finisher 50. The finisher 50 is provided with an inserter 90 for feeding a special sheet such as a cover sheet or a slip sheet to be inserted into a sheet on which an image is formed. In the finisher 50, various processes such as bookbinding, binding, and punching are performed.
[0032]
Here, the photosensitive drum is used as the image carrier of the image forming apparatus, but may be a photosensitive belt.
[0033]
[Mechanism of heat shrinkage in fixing section]
The paper stacked in each of the cassettes 34, 35, 36, and 37 contains a considerable amount of moisture, and the moisture varies depending on the environment in which the apparatus is arranged, such as temperature and humidity. The paper containing these moistures is fed from each cassette, and the developer image is first transferred to the front surface (first surface) by the photosensitive drum unit and the transfer roller unit. At this point, no shrinkage of the paper is observed, but after that, when the paper is conveyed to the fixing unit 32 and the fixing operation is performed by heat and pressure, the moisture contained in the paper evaporates at a stretch, and as a result, the distance between the fibers in the paper is reduced. As a result, the entire sheet contracts. Thereafter, in order to form an image on the back surface, the sheet is conveyed to a double-sided conveyance unit, and further conveyed to a photosensitive drum unit and a transfer roller unit. Although the shrinkage due to heat is said to gradually return to the original over time, it does not return to the original sheet length before image formation on the back surface. If an image on the back side is formed under the same control as the front side in this state of the sheet, a product having different front and back magnifications will be produced. In the present embodiment, by controlling the laser in accordance with the reduced paper magnification and reducing the image, it is possible to correct the apparent size and positional relationship between the front and back images. Further, since the magnification of the sheet is detected for each area, it is possible to cope with local shrinkage. Details of the reduction ratio detection method and the laser control method will be described later.
[0034]
[CIS arrangement, paper feed timing and image writing timing]
FIG. 2 is a diagram showing a print position adjusting mechanism arranged in a paper transport path leading to the photosensitive drum. In the figure, reference numeral 205 denotes a paper transport path. 206 is a circulation path. Reference numeral 31 denotes the above-described photosensitive drum. 202 is a laser element for forming a latent image on the photosensitive drum 31. Note that the arrangement of the laser elements 202 is drawn for convenience and differs from the actual arrangement. Reference numeral 203 denotes a paper transport roller (registration roller), which temporarily stops the paper sent along the paper transport path 205 and stays there, and then sends out the paper to the photosensitive drum 31 at a predetermined paper feed timing. .
[0035]
Reference numeral 204 denotes an image reading sensor (image sensor) that reads an image to detect an edge of the sheet, and includes an array of photoelectric conversion elements such as a CCD and a CIS. In the present embodiment, a CIS (contact image sensor) is used.
[0036]
The CIS 204 is arranged in such a manner that, in order to determine the thermal shrinkage of the sheet at the fixing unit, the size of the sheet is twice before and after the image is formed on the front surface (first surface) and after the sheet has passed the fixing unit. Need to be measured. Therefore, they are arranged as shown in FIG.
[0037]
In this embodiment, the CIS has not only the purpose of measuring the paper reduction ratio due to heat, but also the purpose of detecting the position of the paper with high accuracy and thereby controlling the laser writing start position. Because of the configuration, it was arranged at a position satisfying the following conditions. However, when the CIS 204 is dedicated to the reduction ratio detection and is not used for detecting the position of the sheet, it goes without saying that this condition need not be satisfied.
[0038]
The CIS 204 is disposed on the side of the registration roller 203 that is separated from the photosensitive drum 31 by a distance L1, and is disposed on the side of the registration roller 203 that is separated by a distance L2 from an image forming point (point a) described later. Further, the CIS 204 is arranged at a distance L3 from a BD detector 108 described later in a direction perpendicular to the paper feeding direction.
[0039]
Reference numeral 108 denotes a beam detector (BD) detector for detecting the irradiation timing of a laser element (hereinafter simply referred to as a laser) 202. The laser light is irradiated to the BD detector 108 by the polygon mirror, and then is shaken and irradiated on the photosensitive drum 31 to form a latent image on the photosensitive drum 31.
[0040]
In the figure, point a indicates an image forming point. For example, when an image is formed by the laser 202 at a point 5 mm after the point a of the sheet a, the rotation of the photosensitive drum 31 and the conveyance of the sheet 107 are performed in synchronization, and as a result, the output image is 5 mm from the leading end of the sheet. Formed in position.
[0041]
In the drawing, point b indicates a transfer point, and point c indicates a laser writing point. When a latent image is formed on the photosensitive drum 31 by the laser 102 at the laser writing point c, the toner is transferred to the paper at the transfer point b via the developing unit, and an image is formed.
[0042]
At the time of this image formation, the sheet 107 sent from the registration roller 203 is conveyed to the photosensitive drum 31 side along the sheet conveying path 205, and when the leading end is detected by the CIS 204 and then advances by a distance L2, the photosensitive drum 31 Is controlled so as to irradiate the laser beam to the. Specifically, the timer counts the time that the sheet 107 travels the distance L2, and irradiates the photosensitive drum 31 with laser light when the time has elapsed.
[0043]
To adjust the laser writing position with higher precision, the timing in the paper feed direction (for convenience, referred to as the sub-scanning direction) and the timing in the direction perpendicular to this paper feed direction (for convenience, referred to as the main scanning direction) It is necessary to control the writing by the laser beam according to this detection information.
[0044]
That is, the start time of image formation is determined after the leading edge position of the sheet is detected by the CIS 204, and writing is started by laser when the sheet advances by the distance L2, thereby adjusting the image writing position in the sub-scanning direction. can do. Therefore, the distance L2 is from when the CIS 204 detects the leading edge of the sheet 107 to when the CIS 204 detects a deviation in the direction perpendicular to the sheet feeding direction and sets the timing of writing the laser beam in each direction. It is necessary to have at least a distance corresponding to time.
[0045]
In a normal image forming apparatus, the sheet conveyance speed and the rotation speed of the photosensitive drum 31 are set to be equal. This is the distance L1-L2 from the position (image forming point a) advanced from the CIS 204 by the distance L2 to the transfer position to the sheet (transfer point b) which is the nip position between the transfer roller 39 and the photosensitive drum 31. Means that the circumferential (circular) distance on the photosensitive drum 31 from the laser writing position (writing start point c) to the transfer position to the sheet (transfer point b) is equal.
[0046]
When the horizontal edge position (horizontal registration) of the paper is detected by the CIS 204, the distance x from the lower edge of the CIS 204 to the horizontal edge position of the paper is added to the distance L3 from the beam detector (BD) 108 to the lower edge of the CIS 204. The calculated distance (x + L3) is calculated, and after the laser beam is detected by the beam detector 108, the laser beam is swung in the main scanning direction by the calculated distance, and then writing by the laser is started. The writing position of the image can be adjusted.
[0047]
The adjustment of the writing position of the image in the sub-scanning direction and the main scanning direction by the laser light is performed by a timing control unit (TCU) 105 described later. That is, the TCU 105 outputs the writing start timing to the laser control circuit 27 based on the detection signal from the CIS 204 after turning on the registration roller 203 to start the conveyance of the sheet. The laser control circuit 27 drives the laser element 202 based on image data sent from an image processing circuit (not shown) in synchronization with the write start timing output from the TCU 105.
[0048]
By having the above configuration, it is also possible to control the writing position of the image after the shrinkage ratio of the sheet due to heat is determined.
[0049]
[Configuration of CIS]
FIG. 3 is a diagram showing the configuration of the CIS 204. The CIS 204 includes an image reading unit 205 and an LED light emitting unit 206. The image reading unit 205 includes a plurality of chips (1 to n) 211 to 217 each containing a light receiving element unit and a shift register in one chip, a selector 215, and an output unit 216. In the present embodiment, the number of chips is seven (n = 7). Each light receiving element portion in each chip is provided with 1000 read pixels.
[0050]
Of the 7,000 effective pixels in the entire CIS, 1000 pixels in 213, which is one of the seven chips, are used for reading in the sub-scanning direction (the leading end described later). In this embodiment, the chip 213 is used for reading in the sub-scanning direction. However, any one of the chips 211 to 217 may be selected. On the other hand, 6000 read pixels in the remaining six chips 211 to 217 are used for reading in the main scanning direction (lateral edge detection described later). Note that the number of effective pixels, which is the total of the plurality of chips, is an example, and is not particularly limited, and may be an arbitrary number. Also, the chip division is not limited to 1: (n-1) in the present embodiment, but may be any division number. Moreover, you may use it without dividing.
[0051]
In the image reading unit 205, when the selector 215 effectively selects only a specific chip, for example, only the chip 213 used at the tip, based on a selector signal from the TCU 105, the image signal detected by the light receiving element unit 213a is loaded from the TCU 105. The signal is temporarily read out to the shift register 213b by the signal (CIS-SH), and is sequentially transferred from the shift register 213b to the output unit 216 via the selector 215 in accordance with the clock (CLK) from the TCU 105. The output unit 216 converts the transferred serial image signal into parallel data and outputs it as CIS data.
[0052]
Further, when the selector 215 effectively selects the chips 211 to 217 used for the side edge detection by the selector signal from the TCU 105, the image signal detected by each of the light receiving element units 211a to 217a is once determined by the load signal from the TCU 105. , And are sequentially transferred from the shift registers 211b to 217b to the output unit 216 via the selector 215 according to the clock (CLK) from the TCU 105. The output unit 216 converts the transferred serial image signal into parallel data and outputs it as CIS data.
[0053]
On the other hand, the LED light emitting unit 206 includes an LED unit 221 in which a plurality of LED groups connected in series are connected in parallel, and an LED current adjusting circuit connected to the cathode side of each LED group and adjusting a current flowing through each LED group. 222. The LED current adjustment circuit 222 adjusts the overall LED light emission amount of the LED unit 221 according to the light amount control data from the TCU 105.
[0054]
FIG. 5 is a diagram showing the arrangement of the CIS 204 with respect to the paper passage area. The CIS 204 is arranged such that read pixels are arranged in a direction perpendicular to the transport direction of the sheet 107. In addition, the CIS 204 is arranged so that both ends of the sheet to be detected in the main scanning direction can be detected. In the present embodiment, the number of pixels is described as 7000, but the number of pixels is configured to be sufficient for detecting both ends of the maximum sheet to be conveyed in accordance with the resolution of the CIS 204. Should.
[0055]
In addition, since multiple pixels are used in the main scanning direction as pixel data used for leading edge detection, a sensor for leading edge detection is required compared to conventional single optical sensors and mechanical paper detection sensors. Therefore, the image forming apparatus can be made more compact by reducing the number of components.
[0056]
By detecting the side edge and then the rear edge after the detection of the front edge, it is possible to use different methods as the respective detection methods, and it is possible to improve the detection accuracy by adopting a detection method suitable for each detection. Will be possible. In particular, the use of a plurality of pieces of pixel data in the main scanning direction in the front / rear end detection contributes to an improvement in detection accuracy.
[0057]
Further, by separately performing the front / rear end detection and the lateral end detection, it is possible to set the detection processing to the shortest time at the optimum detection cycle.
[0058]
[Paper edge detection method using CIS]
FIG. 4 is a conceptual diagram for detecting the size of a sheet in the main scanning direction and the sub scanning direction using a single CIS. First, the leading edge of the conveyed paper is detected by passing through the CHIPn in the CIS. Thereafter, the sheet is conveyed, and both ends of the sheet in the main scanning direction are detected by at least two or more CHIPs (Chip n + x and Chip n-y in the figure) at a predetermined timing, so that the sheet size in the main scanning direction is determined. You can ask. Further, by detecting that the sheet is conveyed and the trailing edge of the sheet passes through the CIS, it is possible to determine the dimension of the sheet in the sub-scanning direction together with the result of the leading edge detection previously obtained. As described above, by using one line sensor, the sheet size in both the main scanning and sub-scanning directions can be obtained. The above-described paper size detection processing is performed for each of the plurality of divided areas.
[0059]
[Configuration of control circuit]
FIG. 6 is a block diagram showing the configuration of the control circuit. The control circuit 51 includes an image processing circuit 52, a laser control circuit (V-CNT) 27, and a timing control unit (TCU) 105. The image processing circuit 52 includes an image memory (P-MEM) 56 for storing image data read by the image sensor 26, and a CPU 57 for processing the image data stored in the image memory 56.
[0060]
The laser control circuit 27 outputs a drive signal to the laser element 202 based on a signal output from the image processing circuit 52 according to the image data. The output of the drive signal to the laser element 202 is performed in synchronization with the timing signal from the TCU 105. The TCU 105 outputs a CIS control signal to the CIS 204, inputs the CIS data read by the CIS 204, and outputs a timing signal to the laser control circuit 27 based on the CIS data. The timing signal includes a vertical synchronizing signal VSYNC, a clock VCLK, a laser writing signal of a horizontal synchronizing signal HSYNC, a signal for driving the registration roller 203 (registration ON signal), and the like.
[0061]
[Configuration of reduction ratio detection circuit]
FIG. 7 is a block diagram showing the configuration of the TCU 105. The TCU 105 includes a counter 61, a registration ON section 62, a front / rear end detection section 63, a side end detection section 64, a CIS controller 65, a front / rear end error detection section 67, a side end error detection section 69, and a sequence end. A setting unit (SEQ END) 70 and a correction parameter storage unit 71 are provided.
[0062]
The counter (counter) 61 is started by a sequence start signal (SEQ START) and counts a clock of a fixed cycle. The registration ON unit 62 turns on / off the driving of the registration roller 203. The paper length in the sub-scanning direction is calculated based on the data of the leading edge position and the trailing edge position of the paper, and the leading edge / rear edge detecting unit 63 determines the leading edge position / the trailing edge of the paper based on the CIS data input from the CIS 204. Detect the rear end position. The side edge detection unit 64 detects the side edge position of the sheet based on the CIS data similarly input from the CIS 204. The sheet length in the main scanning direction is calculated based on the lateral end positions of both ends of the sheet. The detection of the front end position / rear end position and the lateral end position is performed for each divided area. This area division will be described with reference to FIG. The leading end position / rear end position is divided as a, b, and c at the detection element position of the CIS 204 as shown in (1) in the figure, and the leading end position / rear end position is detected in each area to detect the sheet length. . In the drawing, the sub-scanning direction paper length of dimension Va is detected in area a, Vb is detected in b, and Vc is detected in c. The horizontal end position is divided according to the value of the counter 61 after the front end is detected. In the figure, the range of the counter 61 is divided into the range of n0 to n1 as area d, the range of n1 to n2 as area e, and the range of n2 to n3 as area f. The sheet length in the main scanning direction is determined as Hd, He, and Hf.
[0063]
In the above example, the area is divided into three in both the main scanning and sub-scanning directions, but the number of divisions is not limited to this.
[0064]
The CIS controller 65 outputs a CIS control signal such as a load signal (CIS-SH), a clock (CIS-CLK), a selector signal, and light amount control data to the CIS 204.
[0065]
The leading edge error detecting unit 67 generates an error signal (ERR) when the leading edge position of the sheet detected by the leading edge detecting unit 63 is out of a predetermined range. Similarly, the horizontal edge error detecting section 69 generates an error signal (ERR) when the horizontal edge position of the sheet detected by the horizontal edge detecting section 64 is out of a predetermined range. In the sequence end setting unit 70, a count value of a sequence for ending printing of one sheet is set. The correction parameter storage unit 71 may store a correction value of the laser writing position in the main scanning and sub-scanning directions obtained by the adjustment process at the time of installing the CIS.
[0066]
FIG. 8 is a block diagram showing the configuration of the leading end detection unit 63. The leading end detection unit 63 has a plurality of edge circuits (EDDGE) 81, a timing generation circuit 82, and a counter 83. To each edge circuit (EDDGE) 81, register signals (REG1 to REGn) specifying the pixel positions in the light receiving element units 211 to 7a of the CIS 204 are input together with the CIS data. Then, when “paper out → paper present” is detected at the designated pixel position in synchronization with the count signal from the counter 83, the edge circuit (EDDGE) 81 generates edge (EDDGE1 to EDDGE) signals.
[0067]
The timing generation circuit (TIMING) 82 averages the plurality of generated edge (EDDGE1 to EDDGE) signals and outputs a leading edge detection signal (VREQ). Further, when performing the tip detection, only a specific pixel alone may be used. However, in the present embodiment, the influence of noise or the like is removed by using a plurality of pixels. Further, in the tip detection, since a plurality of pixels are used, the tip detection accuracy is further improved as compared with a conventional single optical sensor or mechanical sensor.
[0068]
The counter 83 outputs a count signal to a plurality of edge circuits (EDDGE) 81 based on the load signal (CIS-SH) and the clock (CIS-CLK).
[0069]
[Paper feed / image forming sequence]
FIG. 9 is a timing chart showing the operation of the TCU 105. The paper feed / image forming sequence according to the present embodiment is started in a state where the paper 107 is transported to the registration roller 203 along the paper transport path 205 and the paper 107 stays at the registration roller 203. When the sequence start signal (SEQ START) is input to the counter 61, the counter 61 starts measuring a clock having a constant cycle. When the count value of the counter 61 reaches the timing a, the registration ON unit 62 sets the registration signal to the H level and drives the registration roller 203 to turn on.
Then, when the count value reaches timing b, the operation in the leading end detection mode in the CIS 204 is started. In the leading edge detection mode, a plurality of edges are detected as described above, and an averaging process is performed to accurately detect the leading edge of the sheet.
[0070]
When the leading edge of the sheet is detected when the count value reaches timing c, the leading edge detection unit 63 outputs the leading edge detection signal VREQ to the CIS controller 65 and starts the operation of the CIS 204 in the side edge detection mode. When the CIS controller 65 outputs a vertical synchronization signal VSYNC corresponding to the leading end detection signal VREQ to the laser control circuit 27, the laser control circuit 27 takes the vertical synchronization signal VSYNC from the CIS controller 65 into account by taking into account the vertical margin. To adjust the writing start position in the sub-scanning direction. FIG. 10 is a diagram showing the writing start position adjustment by the laser. Even if the count value reaches timing c ′ (c ′> c), if the leading edge position of the sheet is not detected, the CIS controller 65 outputs a leading edge error signal (leading edge ERR).
[0071]
When the horizontal end position of the sheet is detected when the count value reaches timing d, the horizontal synchronization signal HSYNC and the clock VCLK are output to the laser control circuit 27. The laser control circuit 27 sets a write start position in the main scanning direction by the laser based on the horizontal synchronization signal HSYNC and the clock VCLK (see FIG. 10). If the horizontal end position is not detected even when the count value reaches the timing d ', a horizontal end error signal (horizontal end ERR) is output. At this time, the operation of the rear end detection mode in the CIS 204 is started. The control is the same as that at the time of detecting the front end.
[0072]
When the trailing edge of the sheet is detected when the count value reaches timing e, the CIS controller 65 stops the operation of the CIS 204.
[0073]
[Heat shrinkage measurement mode]
FIG. 11 is a flowchart showing a procedure for obtaining the paper shrinkage in the thermal shrinkage measurement mode. When the thermal contraction rate measurement mode is started by an operator's operation, the TCU 105 outputs the above-described timing signal, causes the paper 107 to be transported from a paper supply unit such as the cassette 34 or 35, and passes through the paper transport path 205 to register. The paper 107 is temporarily retained in the clutch 203. Then, the registration clutch 203 is turned on, and the sheet 107 is transported to the developing unit side (step S1).
[0074]
The TCU 105 acquires the position of the leading edge of the sheet detected by the CIS 204 for each of the divided areas (a, b, and c in the example) as shown in FIG. 27 (step S2), and stores the value in the memory. (Step S3). When the front end detection is completed, the side end detection is performed at a predetermined timing (step S13). At this time, the positions of both ends of the sheet are acquired (step S4), and the values are stored in the memory (step S5). The processing of the side edge detection is repeated by the value of the counter 61 to perform the side edge detection for each area (step S13 → S4 → S5 → S14 → S13). In the example of FIG. 27, the case of “the value of the counter 61 = n0, n1, n2” corresponds to Yes in step S13, and after the third horizontal edge detection, the value of the counter 61> n2 in step S14. The process shifts to the rear end detection mode (step S14 / Yes). In step 6, the position of the paper at the rear end is acquired for each area in the same manner as when the front end is detected, and stored in the memory. Thereafter, the length of the paper in the main scanning direction is obtained by converting the positions of both ends of the paper as a result of the detection of the horizontal edge into a distance, and the length of the paper in the sub-scanning direction is obtained by converting the front end position and the rear end position into the distance. . In this way, the paper outer size of the first side is determined for each of the above-mentioned areas from the data from step 2 to step 7. (Step 8). In step 9, the sheet whose outer size has been measured is conveyed to the fixing unit and heated and pressed. At this time, it is assumed that a predetermined developed image may be formed on the sheet, or the image may not be present. If it is determined in step 10 that the sheet conveyed through the fixing unit is the front side (first side), the sheet is conveyed to the double-sided conveying unit to measure the shrinkage of the sheet, and is re-fed to the registration clutch unit. Steps 1 to 9 are repeated. As in the case of the front side, the outer size of the back side is obtained, and the amount of contraction (thermal shrinkage) of the sheet generated by the fixing unit is calculated for each main scanning / sub-scanning area from the ratio of the outer size.
[0075]
In the above, the embodiment in which the outer size of the first side paper is measured has been described. However, the outer size of the first side (front side) is not measured, and the value of the standard size of the paper (297 × 210 mm for A4) is substituted. Is also good.
[0076]
[Normal mode]
FIG. 12 is a flowchart illustrating an image forming process procedure in the paper passing mode. When an image forming operation in the paper passing mode is started by an operator's operation, the TCU 105 outputs the above-described timing signal, causes the paper 107 to be transported from a paper feeding unit such as the cassette 34 or 35, and passes through the paper transport path 205 to register. The paper 107 is temporarily retained in the clutch 203. Then, the registration clutch 203 is turned on, and the sheet 107 is transported to the developing unit side (step S21).
[0077]
When the TCU 105 acquires the leading edge and the lateral edge position of the sheet detected by the CIS 204 (step S22), the TCU 105 determines the laser writing timing in the paper feed (sub-scanning) direction based on the distance L2 between the CIS 204 and the image forming point a. It notifies the laser control circuit 27 (step S23). At the time of image formation of the back surface (determined in step 29), the shrinkage rate for each area obtained in the previous heat shrinkage measurement mode is read (step 24), and writing control is performed in accordance with the value, and the image in the sub-scanning direction is obtained. Reduction is performed (step 25). Here, in S25, the reduction correction method in the sub-scanning direction is performed by a method described in a flow B or B ′ in FIG. 15 described later.
[0078]
Further, based on the distance (x + L3) obtained by adding the distance x from the lower end of the CIS 204 to the lateral end position of the sheet to the distance L3 between the CIS 204 and the BD detector 108, the laser control circuit 27 determines the laser writing timing in the main scanning direction. Notify (step S26). At the time of image formation on the back side (determined in step 29), writing control is performed in accordance with the shrinkage ratio obtained in the previous heat shrinkage measurement mode, and image reduction in the main scanning direction is performed (step 27). Here, in S27, the reduction correction method in the main scanning direction is performed by a method described later in a flow C or C ′ of FIG.
[0079]
Based on the laser writing timing signals in the main scanning and sub-scanning directions from the TCU 105, the writing control circuit 27 outputs a driving signal based on the job on the sheet 107 to the laser element 202 to form an image (step S28). In the one-sided mode, when the image formation on the front side is completed, the TCU 105 discharges the sheet 107 to the finisher side (step S30), and ends this processing. In the duplex mode, when forming an image on the back side (step 29), S21 to S28 are performed again, and then the sheet 107 is discharged to the finisher side (step S30), and this processing ends.
[0080]
Here, in the above flowchart, the writing system control is described in S25 and S27, and the details of the main / sub control method will be described below.
[0081]
The latent image forming method according to the present embodiment modulates a laser beam emitted by a laser beam emitting circuit by an image signal, and performs a raster scan of the laser beam on a photosensitive drum by a polygon motor 1337. The following describes two examples of a method of correcting (changing) the image size.
[0082]
(First magnification example)
FIG. 14 is a schematic diagram of a motor driving device, FIG. 15 is a block diagram of a polygon motor (also called a polyhedral mirror) control circuit, and FIG. 16 is a timing chart of a motor control circuit / main part. A beam detection signal 1304 detected by the beam detector 1338 is a horizontal synchronization signal obtained by detecting a laser beam raster-scanned by the polygon motor 1337 at a predetermined position. At 1307, the frequency is divided by 2 and input to the rising edge detection circuit 1309 and the falling detection circuit 1315, respectively. The counter a1313 counts with a scanner clock (SCNCLK) 1310 input from the image forming control circuit starting from the rising edge 1312. The discrimination value 1311 is a value obtained by converting a predetermined rotation speed input from the image forming control circuit into time. The counter a1313 starts counting from the rising edge 1312 and continues counting up to the discrimination value 1311. For example, the counter a output signal 1314 is set so as to rise in synchronization with the rising edge 1312 and to fall at the point where it coincides with the discrete value 1311. Similarly, the counter b 1317 counts from the falling edge 1316 using the scanner clock (SCNCLK) 1310. The counter b1317 starts counting from the falling edge 1316 and continues counting up to the discrete value 1311. The counter b output signal 1317 is set so as to rise in synchronization with the falling edge 1316 and to fall at a point where the counter b coincides with the discrete value 1311. The OR gate 1319 and the NAND gate 1321 generate an acceleration signal 1320 and a deceleration signal 1322 from the counter a output signal 1314 and the counter b output signal 1317 (both are negative logic).
[0083]
For example, when the rotation speed is low, the cycle of the beam detection signal 4 is longer than the discrete value 11, and the difference between the counter a output signal 1314 and the counter b output signal 1317 becomes the acceleration signal 1320. As the rotation speed of the motor 1337 increases, the cycle of the beam detection signal 1304 becomes shorter, and the difference from the discrete value 11 becomes smaller. The output signal cycle of the acceleration signal 1320 is shortened according to the rotation speed of the motor 37. When the rotation speed of the motor 1337 exceeds a predetermined rotation speed, the counter a output signal 1314 and the counter b output signal 1317 overlap. This overlapping portion is an excess of the rotation speed of the motor 1337, and is a deceleration signal 1322. As described above, the speed of the polygon motor is controlled to be accurately stabilized at the target speed (discrete value 1311). The image data synchronized with the data clock (DCLK) 1350 is stored in a line buffer (eg, a plurality of lines) 1352 such as a FIFO and the like in the laser driver (LASERCLK) 1353 as shown in FIG. The synchronization is reestablished and sent to the laser driver 1354. The laser driver 1354 controls light emission / extinguishment of the laser 1356 based on image data in synchronization with the laser clock (LASERCLK) 1353. The beam is reflected by the surface of a polygon mirror 1355 driven to rotate by a polygon motor 1337, and scans an image for one line repeatedly. Thus, a latent image is formed. Although the buffer 1352 for the speed conversion is FIFO in the above example, it goes without saying that LIFO or the like can be selected according to the specifications of the laser.
[0084]
The overall flow of the image size reduction correction method will be described with reference to flow Y in FIG. In S41, the main-scanning reduction ratio Sh and the sub-scanning reduction ratio Sv that have been calculated are acquired. The reduction ratios Sh and Sv are 1 or less. Next, in step S42, the magnification of the sub-scan is set, and then in step S43, the magnification of the main scan is set.
[0085]
The reason why the magnification of the sub-scan is performed prior to the magnification of the main scan is that the magnification of the sub-scan in the sub-scan magnification method in this embodiment affects the main-scan direction and is simultaneously enlarged in the main-scan. The main scanning setting which does not affect the zooming in the other direction is performed later and adjusted so that the main scanning / sub-scanning direction can be zoomed independently. Details will be described later.
[0086]
A reduction method in the sub-scanning direction will be described with reference to a flow B. In S51, the discrimination value 1311 is divided by the sub-scanning reduction ratio Sv from the default value (100% in the sub-scanning direction) Vini.
Vini × Sv (Sv is 1 or less)
Set to. With this setting, the speed of the polygon motor 37 is accelerated 1 / Sv times in S52, and the cycle of the beam detection signal 1304 is shortened Sv times in S53. As a result, in S54, the image is reduced by Sv times in the sub-scanning direction, and the scanning speed of the main scanning is increased by 1 / Sv times, so that the image is enlarged by 1 / Sv times in the main scanning direction. It becomes.
[0087]
A method of reducing in the main scanning direction will be described with reference to a flow C. In order to reduce the image width in the main scanning direction, the frequency of the laser clock (LASERCLK) 13 is increased in consideration of the acceleration of the polygon motor due to the sub-scanning magnification setting as described above. In S55, the modulating circuit divides the frequency of the laser clock by a default clock (DEFCLK) value (fini in the main scanning direction) of fini (100% in the main scanning direction) by the main scanning enlargement ratio 1 / Sv by polygon motor acceleration in S42 (= Sv times). Multiplied by the main scanning reduction ratio Sh
fini × Sv × Sh
And the laser scanning speed per pixel is multiplied by (1 / Sv × 1 / Sh) in S56. As a result, since the scanning cycle in the sub-scanning direction does not change in S57, the magnification of the sub-scanning image is not changed, and the image is reduced by (Sv × Sh) times only in the main scanning direction in S43.
[0088]
By the method of S41 to S43 of the flow Y described above, finally in S44
Main scan: Sv times
Sub-scan: Sh times (= 1 / Sv × Sv × Sh)
Independent image scaling is performed.
[0089]
A specific example will be described. When the first side or the default paper size is “A (7000 pixels) × B (3500 pixels)” (= main × sub), the laser clock (LASERCLK) 13 has a default frequency fini and a discrimination value 1311. Is set to the default motor speed Vini. Here, it is assumed that the paper size after fixing the first side image detected by the CIS is “C × D”, and the paper shrinkage ratio is as follows. Hereinafter, “Adata”, “Bdata”, “Cdata”, and “Ddata” in the drawing indicate that they correspond to the effective image sizes of the paper sizes A, B, C, and D, respectively.
[0090]
Main scanning direction 95%: C = A × 0.95
97% in the sub-scanning direction: D = B × 0.97
FIG. 19 (i) shows a schematic diagram of correction in the sub-scanning direction at this time, where (A) shows before correction and (A) shows after correction. By setting the discrete value = Vini × 0.97 from the sub-scanning reduction ratio Sv = 0.97, the sub-scanning is reduced by 97% as shown in FIG. In the main scanning direction, as shown in (ii), the reflection angle θ per data (pixel) is increased by the acceleration ratio, that is, the main scanning pixel width WidH is increased by the acceleration ratio. % Expansion. It is assumed that the sub-scanning reduction ratio is a value in a range where the end data of the main scanning effective image is not lost.
[0091]
Next, correction in the main scanning direction is performed. FIG. 20 is a schematic diagram showing the state before the correction (after the sub-scanning correction = A) and the state after the correction (E). By modulating the frequency of the laser clock (LASERCLK) 13 = fini × 0.97 × 0.95 from the main scanning reduction ratio Sv = 0.95, as shown in (E), only main scanning is performed for (C) as shown in (E). 97% × 95%). (D) in the figure means that the main scanning enlargement in the sub-scanning correction is canceled (reduced) by multiplying by the sub-scanning magnification of 0.97.
[0092]
That is, reduction of 95% in the main scanning and 97% in the sub-scanning are performed as a series of corrections from the sub-scanning to the main scanning. In this way, scaling correction is performed independently of main scanning and sub-scanning at the target reduction ratio.
[0093]
The method described above is performed for each predetermined area. As shown in FIG. 26C, when the reduction ratios a and b are different in the sub-scanning direction and the reduction ratios c and d are different in the main scanning direction depending on the area, the processing of the previous example is performed for each area. This will be described with reference to FIG. For example, it is assumed that the sub-scanning is divided into areas A and B and the reduction ratio is detected as Sva and Svb, respectively, and the main scanning is divided into areas C and D and the reduction ratio is detected as Shc and Shd. Areas are divided as shown in the matrix in the figure. The processing for each area is as follows.
[0094]
★ Area (1): Reduction rate (Sva, Shd)
⇒ Discrete value = Vini x Sva, Clock frequency = fini x Sva x Shd
★ Area (2): Reduction rate (Svb, Shd)
⇒ Discrete value = Vini x Svb, Clock frequency = fini x Svb x Shd
★ Area (3): Reduction rate (Sva, Shc)
⇒ Discrete value = Vini x Sva, Clock frequency = fini x Sva x Shc
★ Area (4): Reduction rate (Svb, Shc)
⇒ Discrete value = Vini x Svb, Clock frequency = fini x Svb x Shc
By detecting and correcting a different reduction ratio for each area by the above processing, it is possible to cope with a difference in a local reduction method.
[0095]
(2nd magnification example)
In addition to the first example, FIG. 21 shows a flow of digital scaling for thinning out and reducing predetermined image data in both the main scanning and sub-scanning directions. The reduction method in the main scanning is shown in a flow C 'and the reduction method in the sub-scanning is shown in a flow B'.
[0096]
Hereinafter, the parameter values in parentheses indicate (primary, secondary).
[0097]
"S61, 71": Obtain the number of pixels of the selected paper size (Nh, NV).
[0098]
"S62, 72": A reduction ratio is obtained (Sh, SV).
[0099]
“S63, 73”: The number of thinned pixels is calculated from the number N of pixels and the reduction ratio S (Ph, Pv).
[0100]
"S64-65-66, 74-75-76": If there is a thinned pixel number P, the position of the pixel is determined. "S64-67, S74-77": When all the positions of the thinned pixels are determined, the designated pixels (Ph [Nh], Pv [Nv]) are thinned to reduce the image. Alternatively, if the reduction ratio is 1 in S64, P = 0 without pixel thinning, and the thinning process is performed in S67 because there is no designated pixel (Ph [Nh], Pv [Nv]) in S67. Absent.
[0101]
A specific example is shown in FIG. In the figure, (1) indicates the sheet size “A × B” (image: 7000 × 3500) before the first side is fixed, and (2) indicates the sheet size “C × D” after the first side is fixed by heat. . The arrow line is an example showing the position of the pixel to be thinned out, and an enlarged one point is described on the right side, and the number represents the pixel number. In this case, it means that the 1000th pixel is thinned out.
[0102]
Assuming that the contraction rate is the same as the previous example, the image size corresponding to the “C × D” paper size is corrected by thinning out the following number of pixels.
[0103]
350 pixels in main scanning direction (= 7000 pixels x {1-0.95})
305 pixels in the sub-scanning direction (= 3500 pixels x {1-0.97})
The positions of the pixels to be decimated are arbitrary, and are shown at equal intervals in the figure, but are not limited thereto, and needless to say, they may be changed depending on the image.
[0104]
The main scanning / sub-scanning correction method described so far may be a combination of main scanning / sub-scanning methods such as main scanning: clock modulation and sub-scanning: image thinning, or a different method may be selected depending on the magnification. May be.
[0105]
"Time to execute heat shrink mode"
In the POD market, a test print called a proof print is generally performed before forming an image of job data sent from a scanner or a PC. The job here includes image data input from various input means and external devices and various settings. Various confirmations such as missing images are performed by the proof print. Measurement of heat shrinkage, which is a major feature of the present embodiment, is performed at the time of proof print. Since it is very effective to reduce the image based on the above, a control method thereof will be described with reference to FIG. Further, it is easy to measure the thermal shrinkage intention of all the pages, store all the pages, and reduce the image of the back side based on the data, but in FIG. 25, the shrinkage rate is stored for each cassette. The control to be performed will be described. This is because, in many cases, sheets of the same material, outer size, and direction are stacked in a cassette, and it is determined that storing data for each cassette is sufficient.
[0106]
Based on the start of the proof print, the sheet feeding operation is performed from the cassette stage designated by the job. Move to heat shrink mode. S120. In S121, the dimension of the front surface sheet is measured as a reference when determining the dimension change amount of the sheet. At this time, the paper size in each of the main scanning and sub-scanning directions is detected using the line sensor (CIS) as described above. After the detection, an image is formed on the front surface (S122), and the fixing operation in the process causes thermal contraction of the sheet. The shrunk paper is fed again to the image forming unit via the double-sided conveyance unit. This is performed for each area, and the rate of change is calculated and stored. S125. Thereafter, an image is formed on the back surface. Further, at the time of proof printing, the magnification of the image need not be corrected.
[0107]
Similarly, in a job in which the cassette 2 or the cassette n is designated, a change rate is obtained for each cassette, and the change rate is stored as data corresponding to each cassette, and is used at the time of job printing. These operations are repeatedly performed by the number of cassettes specified in the proof print.
[0108]
FIG. 26 is a diagram showing a typical flow in the case of job printing.
[0109]
When the image forming operation in the paper passing mode is started by an operator's operation, the TCU 105 outputs the above-described timing signal, and when the paper to be fed is the cassette 1,
The paper 107 is transported from the paper feed unit of the cassette 1, and temporarily stays in the registration clutch 203 through the paper transport path 205. Then, the registration clutch 203 is turned on, and the sheet 107 is transported to the developing unit side (step S141). In image formation on the front surface, since heat contraction due to the fixing operation has not yet occurred, magnification correction of the image is not performed, and normal image formation is performed. Thereafter, heat contraction occurs due to the fixing operation, but if it is determined that a two-sided image should be formed on the fed paper, the proof described above is performed before image formation after re-feeding. The change rate of the cassette 1 stored at the time of printing is read, and the image is scaled in the main / sub-scanning direction in accordance with the data. S148.
[0110]
Similarly, when paper is fed from the cassettes 2 and n, the main / sub image magnification is corrected in accordance with the previously determined change rates of the cassettes 2 and n. These steps are repeated until image formation on all sheets is completed.
[0111]
According to the above flow, the most suitable heat shrinkage correction can be performed according to the humidity and various materials. Here, the change rate is calculated for each cassette.However, when a material is specified by setting from the operation unit or the like, the change rate is obtained and stored at the time of proof printing for each set material, and the heat value is calculated based on the value. Needless to say, contraction correction may be performed.
[0112]
The above is the description of the embodiments of the present invention. However, the present invention is not limited to the configurations of these embodiments, and achieves the functions described in the claims or the functions of the configurations of the embodiments. Any configuration that can be applied is applicable.
[0113]
For example, in the above embodiment, after detecting the timings in the main scanning direction and the sub-scanning direction, the timings are notified to the TCU 105. However, the adjustment of the laser writing timing after the detection is not particularly limited. Any adjustment method may be used.
[0114]
Although the image forming timing in the sub-scanning direction is determined by detecting the leading edge of the paper, it may be determined by detecting the trailing edge of the paper by the CIS depending on the mechanical configuration of the apparatus.
[0115]
Further, in the above embodiment, the image formed in the heat shrink mode is not particularly limited.
[0116]
Further, in the above embodiment, the execution of the heat shrink mode may be performed at any timing.
[0117]
【The invention's effect】
According to the present invention, the use of a line sensor as a means for detecting the contraction rate in the main scanning direction and the thermal contraction rate in the sub-scanning direction enables highly accurate detection of the thermal contraction rate. It is possible to independently correct the main scanning direction and sub-scanning direction in accordance with the paper size, so that various shrinkage rates that vary greatly depending on the type and size of paper, environment (humidity and temperature), and the clearance direction of the fiber On the other hand, the image can be appropriately reduced. Further, since the shrinkage ratio is obtained for each area, it is possible to cope with a local difference in shrinkage as shown in FIG. 26, and more appropriate processing can be performed as compared with FIG. 25 in which the conventional method is used. Increasing the number of divisions of the area results in image correction that is almost linear in how the paper shrinks. As a result, it is possible to solve the problem that the image position is shifted between the front surface and the back surface or the image size is different, and it is possible to obtain a product with high commercial value and good appearance. In addition, since the detection in both the main scanning direction and the sub-scanning direction can be performed by a single line sensor, it is very advantageous in terms of cost and mounting.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment.
FIG. 2 is a diagram illustrating a print position adjusting mechanism arranged in a paper transport path leading to a photosensitive drum.
FIG. 3 is a diagram illustrating a configuration of a CIS 204.
FIG. 4 is a conceptual diagram of detecting a size of a sheet in a main scanning direction and a sub-scanning direction by a CIS 204.
FIG. 5 is a diagram showing an arrangement of a CIS 204 with respect to a paper passage area.
FIG. 6 is a block diagram illustrating a configuration of a control circuit.
FIG. 7 is a block diagram showing a configuration of the TCU 105.
FIG. 8 is a block diagram illustrating a configuration of a tip detection unit 63.
FIG. 9 is a timing chart showing the operation of the TCU 105.
FIG. 10 is a diagram showing a write start position adjustment by a laser.
FIG. 11 is a flowchart illustrating an image position adjustment processing procedure in an adjustment mode.
FIG. 12 is a flowchart illustrating an image forming processing procedure in a normal mode.
FIG. 13 is a diagram showing a mechanical sensing lever type sensor.
FIG. 14 is a main block diagram of a polygon motor driving device described in the present embodiment.
FIG. 15 is a block diagram of a motor control circuit in the polygon motor driving device according to the present embodiment.
FIG. 16 is a timing chart of a main block diagram of the polygon motor control circuit described in the present embodiment.
FIG. 17 is a main scanning / sub-scanning reduction / magnification flowchart (clock modulation / polygon motor shifting) described in the present embodiment.
FIG. 18 is a schematic diagram around a laser driver described in the present embodiment.
FIG. 19 is a schematic diagram of main scanning magnification change by clock modulation described in the present embodiment.
FIG. 20 is a schematic diagram of sub-scanning magnification change by polygon motor shift described in the present embodiment.
FIG. 21 is a main scanning / sub-scanning reduction / magnification flowchart (pixel thinning) described in the present embodiment.
FIG. 22 is a schematic diagram of main / sub-scanning magnification by pixel thinning described in the present embodiment.
FIG. 23 is a diagram showing a failure example 1 due to heat shrinkage described in the present embodiment.
FIG. 24 is a diagram illustrating a second example of a problem caused by heat shrinkage, which is described in the present example.
FIG. 25 is a control flowchart for storing a contraction rate for each cassette.
FIG. 26 is a typical flowchart for job printing.
FIG. 27 is a conceptual diagram of detection for each area in the main scanning / sub-scanning directions.
FIG. 28 is a diagram showing a problem in the conventional method (one reduction ratio).
FIG. 29 is a diagram showing an effect of the present invention (multiple values of reduction ratio).
FIG. 30 is a conceptual diagram in which a reduction ratio is calculated for each area.
[Explanation of symbols]
27 Laser control circuit
31 Photosensitive drum
52 Image processing circuit
62 Cash register ON section
63 Tip detector
64 Side edge detector
65 CIS controller
66 CIS tip detection short cycle setting unit
68 CIS side edge detection long cycle setting unit
71 Correction parameter storage unit
82 Timing Generation Circuit
105 Timing control unit (TCU)
107 paper
202 laser
203 Registration roller (registration clutch)
204 CIS (Contact Image Sensor)
211a to 217a Light receiving element section
1301 Motor control circuit
1302 Motor rotation instruction signal (/ SCNON)
1303 Rotation permission signal (SCNREADY)
1304 Beam detection signal (/ BD)
1305 Waveform shaping circuit
1306 Waveform shaping signal
1307 frequency divider (1/2)
1308 divider output signal
1309 rising edge detection circuit
1310 Scanner clock (SCCLK)
1311 Discrete value
1312 rising edge
1313 Counter a
1314 Counter a output
1315 falling edge detection circuit
1316 falling edge
1317 Counter b
1318 Counter b output
1319 OR gate
1320 Acceleration signal (/ ACC)
1321 NAND gate
1322 Deceleration signal (/ DEC)
1337 motor
1338 Beam detector
1339 Position detecting element
1340 Position detection signal
1350 Default laser clock (DEFCLK)
1351 Modulation circuit
1352 Buffer (FIFO)
1353 Laser clock (LASERCLK)
1354 Laser Driver
1355 polygon mirror
1356 laser

Claims (29)

In order to form a double-sided image on the same sheet, the image-formed sheet conveyed through the image forming unit is introduced again into the image forming unit via the sheet re-feeding unit and the sheet conveying unit. Image forming apparatus,
A change rate detecting unit that can detect each of the dimensional change amount of the sheet generated in the image forming in the main scanning direction and the dimensional change amount in the sub-scanning direction by the same detecting unit,
The change rate detecting means detects a sheet shrinkage rate for each of a plurality of divided areas in the same scanning direction. 2. The image forming apparatus according to claim 1, wherein the shrinkage ratio detecting unit is a line sensor. 2. The image forming apparatus according to claim 1, wherein the control of the writing means in the main scanning direction is changed for each main scanning division area in accordance with the detected dimensional change amount for each main scanning division area. Means,
A sub-scanning direction magnification correcting unit for changing the control of the writing unit in the sub-scanning direction for each of the sub-scanning divided areas in accordance with the detected dimensional change amount for each of the sub-scanning divided areas. 2. The image forming apparatus according to claim 1, wherein the change rate detecting means detects a change rate from a change in length between sheet edges. 2. The image forming apparatus according to claim 1, wherein the change rate detecting means detects a change rate from a change in length between lines printed on a sheet at a predetermined interval. 2. The image forming apparatus according to claim 1, wherein the change rate detecting unit detects a change rate from a change in length between a sheet end and a line printed at a predetermined interval from the sheet end. 4. The image forming apparatus according to claim 3, wherein the magnification changing means in the main scanning direction thins out pixels in a predetermined or random manner in one main scanning line. 4. The image forming apparatus according to claim 3, wherein the magnification changing means in the main scanning direction changes the laser reference CLK. 4. The image forming apparatus according to claim 3, wherein the magnification changing means in the sub-scanning direction controls the speed of the polyhedral mirror. 10. The image forming apparatus according to claim 9, wherein the reference interval of the section signal corresponding to one line in the main scanning direction is changed by controlling the speed of the polyhedral mirror. 4. The image forming apparatus according to claim 3, wherein the magnification changing means in the sub-scanning direction thins out predetermined or random sub-scanning lines. 4. The image forming apparatus according to claim 3, wherein the magnification changing means in the sub-scanning direction changes a latent image speed. In the image forming apparatus according to any one of claims 1, 8, 9, and 10, after changing the magnification in the sub-scanning direction by controlling the speed of the polyhedral mirror, changing the magnification in the main scanning direction by changing the laser reference CLK. It is characterized. 2. The image forming apparatus according to claim 1, wherein when the fixing method is a heat fixing method, the change rate detecting means is for detecting a contraction rate. 2. The image forming apparatus according to claim 1, wherein when the fixing method is a pressure fixing method, the change rate detecting means is for detecting an expansion rate. 4. The image forming apparatus according to claim 3, wherein the magnification changing means in the main scanning direction includes a writing start position changing means in the main scanning direction. 4. The image forming apparatus according to claim 3, wherein the magnification changing means in the sub-scanning direction includes a writing start position changing means in the sub-scanning direction. 4. The image forming apparatus according to claim 3, wherein the magnification changing means in the sub-scanning direction includes a paper transport timing changing means. In the image forming apparatus described in Item 3, the dimensional change amount is a dimensional change amount of the sheet before and after the fixing process. 20. The image forming apparatus according to claim 19, wherein the sheet size before fixing is data determined in advance. 20. The image forming apparatus according to claim 19, wherein the sheet size before fixing is obtained by detecting the change rate detecting unit. 2. The image forming apparatus according to claim 1, wherein the change rate detecting unit is disposed between a sheet storing unit on which sheets are stacked and the image forming unit, and is provided between the circulating transport path and the sheet storing unit and the image forming unit. It is characterized by being located downstream of the junction of the transport path. 2. The image forming apparatus according to claim 1, wherein the change rate is measured after a job is input from a scanner or an external device until image formation is started. 24. The image forming apparatus according to claim 23, wherein when a plurality of jobs are input, the change rate is measured for each job. 24. The image forming apparatus according to claim 23, wherein the change rate is measured according to a sheet storage unit used according to the job. 24. The image forming apparatus according to claim 23, further comprising a storage unit for storing the measured result, wherein an image is formed based on data in the storage unit when a job is executed. 24. The image forming apparatus according to claim 23, wherein the rate of change is measured according to the type of paper used according to the job. 28. The image forming apparatus according to claim 27, wherein the type of the sheet includes at least one of a material, a size, and a direction. 24. The image forming apparatus according to claim 23, wherein the measured result is stored for each page.

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