JP2004262584A - Image forming apparatus and image forming control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect a paper sheet position in a paper sheet feed direction and position an accurate printing-position even when transporting a paper sheet at a high speed without increasing cost. <P>SOLUTION: This image forming apparatus includes a plurality readable pixels reading an image, and includes an image reading means arranged in a passing zone where a plurality of the readable pixels can read a lateral end of the paper sheet transported to be aligned in a perpendicular direction to the paper sheet feed direction, a lateral end detecting means detecting the lateral end of the transported paper sheet by repeatedly reading at least a part of a plurality of the readable pixels at a predetermined cycle and a lateral end oblique travel amount detecting means detecting oblique travel amount of the paper sheet based on at least two positions of the lateral end position of the transported paper sheet detected by the lateral end detecting means. The image forming apparatus is provided with a difference calculating means detecting a plurality of lateral end oblique travel amounts detected by the lateral end oblique travel amount detecting means and calculating difference of a plurality of the oblique travel amounts. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as an LBP (laser beam printer) and a copying machine using electrophotography, and an image forming control method.
[0002]
[Prior art]
FIG. 29 is a side view showing a print position adjusting mechanism in a conventional image forming apparatus, and FIG. 30 is a plan view showing a part of the print position adjusting mechanism in FIG.
[0003]
29 and 30, reference numeral 1301 denotes a photosensitive drum; 1302, a laser for forming a latent image on the photosensitive drum 1301; 1303, a registration clutch (registration roller) for determining sheet feeding timing; 1304, a paper sensor for detecting a sheet to be conveyed; Reference numeral 1401 denotes a shift amount detection sensor for detecting a shift amount of a horizontal end in a direction perpendicular to the sheet feeding direction, and 1401 denotes an output sheet. Reference numeral 1403 denotes a sheet feeding direction.
[0004]
In the conventional print position adjusting mechanism having the above-described configuration, a CPU (not shown) obtains the shift amount of the lateral edge of the sheet detected by the shift amount detection sensor 1305 and the paper feed detected by the sheet sensor 1304. The paper position in the direction is obtained, and these information are transmitted to an image control circuit (not shown). Then, the image control circuit adjusts the transfer timing of the image data transferred to the laser control circuit (not shown) for driving the laser 1302 based on the obtained information.
[0005]
Furthermore, after setting the image writing position by the laser, the skew of the sheet is determined based on at least two lateral edge positions of the sheet detected by the shift amount detection sensor 1305, and an error display or the like is performed. See JP-A-9-219776).
[0006]
[Problems to be solved by the invention]
However, the above-described conventional print position adjusting mechanism of the image forming apparatus has the following problems, and improvement thereof has been demanded.
[0007]
That is, when the paper is transported at a high speed in order to improve the printing speed, the reading performance of the paper sensor in the paper feeding direction has become a problem. In particular, when an inexpensive mechanical sensor is used as the paper sensor, a reading error is large, and the reading error appears as an image position shift as it is.
[0008]
In addition, in the skew detection of the sheet, since the determination is made based on the lateral end position of the sheet detected by the shift amount detection sensor during the sheet conveyance, the image has already been formed at the time of the detection, and an error is notified to the operator. There was no alternative but to do.
[0009]
Therefore, the present invention provides an image forming apparatus and an image forming control method capable of detecting a sheet position in a sheet feeding direction with high accuracy without increasing costs even under high-speed conveyance of a sheet and realizing an accurate printing position. The purpose is to:
[0010]
The present invention also provides an image forming apparatus and an image forming apparatus capable of accurately detecting skew before an image is formed on a sheet, and eliminating the need to output a sheet on which an image of low print quality is formed due to the skew. It is another object to provide a control method.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus of the present invention has a plurality of read pixels for reading an image, and the plurality of read pixels are conveyed so as to be arranged in a direction perpendicular to a conveying direction of a sheet. Image reading means arranged in a pass area from which a lateral edge of a sheet can be read, and lateral edge detecting means for detecting a lateral edge of the conveyed sheet by repeatedly reading at least a part of the plurality of read pixels at a predetermined cycle An image forming apparatus comprising: a side edge skew amount detection unit configured to detect a side edge skew amount of the sheet based on at least two side edge positions of the conveyed sheet detected by the side edge detection unit. The apparatus further comprises a difference calculating means for detecting a plurality of skew amounts obtained by the skew amount detecting means and calculating a difference between the plurality of skew amounts.
[0012]
Further, a difference determining means for determining whether the difference between the plurality of lateral end skew amounts calculated by the difference calculating means is equal to or more than a predetermined amount or less than a predetermined amount is provided.
[0013]
Further, a leading edge detecting means for detecting a leading edge of the conveyed sheet by repeatedly reading a part of the plurality of read pixels at a cycle shorter than the predetermined cycle; A leading edge skew amount detecting means for detecting the leading edge skew amount of the sheet based on the data representing the leading edge of the sheet read from the unit, and the detected lateral edge skew amount and the detected leading edge skew. A mounting angle degree calculating means for calculating the mounting angle degree of the image reading means based on the line amount; and a tip skew amount detected by the tip skew amount detecting means based on the calculated mounting angle degree. And a tip skew amount correcting means.
[0014]
Also, when the attachment angle is calculated by the attachment angle calculation means, it is determined whether the difference between the plurality of lateral end skew amounts determined by the difference determination means is equal to or greater than a predetermined amount, and is determined to be equal to or greater than the predetermined amount. In this case, a mounting angle degree invalidating means for invalidating the calculated mounting angle degree is provided.
[0015]
The image forming control method according to the present invention has a plurality of read pixels for reading an image, and a pass through which a lateral edge of the conveyed sheet can be read such that the plurality of read pixels are arranged in a direction perpendicular to a sheet conveying direction. An image reading step arranged in an area, a side edge detection step of detecting a side edge of the conveyed sheet by repeatedly reading at least a part of the plurality of read pixels at a predetermined cycle, and the side edge detection step A lateral edge skew amount detecting step of detecting a lateral edge skew amount of the sheet based on at least two lateral edge positions of the conveyed sheet detected by the image forming apparatus. The method further comprises a difference calculating step of detecting a plurality of side edge skew amounts obtained in the skew amount detecting step and calculating a difference between the plurality of skew amounts.
[0016]
Further, a difference determination step of determining whether the difference between the plurality of lateral end skew amounts calculated in the difference calculation step is equal to or more than a predetermined amount or less than a predetermined amount is provided.
[0017]
Further, a leading edge detecting step of detecting a leading edge of the conveyed sheet by repeatedly reading out a part of the plurality of read pixels at a cycle shorter than the predetermined cycle; A leading edge skew amount detecting step of detecting the leading edge skew amount of the sheet based on the data representing the leading edge of the sheet read from the unit, and the detected lateral edge skew amount and the detected leading edge skew. A mounting angle degree calculating step of calculating the mounting angle degree of the image reading means based on the line amount, and correcting a tip skew amount detected by the tip skew amount detecting step based on the calculated mounting angle degree. And a tip skew amount correcting step.
[0018]
In addition, when the attachment angle is calculated in the attachment angle calculation step, it is determined whether the difference between the plurality of lateral end skew amounts obtained in the difference determination step is equal to or larger than a predetermined amount, and is determined to be equal to or larger than the predetermined amount. The method further comprises a mounting angle degree invalidating step of invalidating the calculated mounting angle degree when performed.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of an image forming apparatus and an image forming control method of the present invention will be described with reference to the drawings.
[0020]
[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.
[0021]
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.
[0022]
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 the mirrors 22, 23, and 24. The light passing through the lens 25 forms an image on the imaging surface of the image sensor 26.
[0023]
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 transporting the scanner unit 21 in the 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.
[0024]
The exposure control unit of the printer 13 modulates a laser beam output from a laser element (not shown) based on the input video signal, 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.
[0025]
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, paper is fed from each of the cassettes 34, 35, 36, 37, the manual paper feed unit 38 or the double-sided conveyance path at a timing synchronized with the start of laser beam irradiation, and the paper is fed between the photosensitive drum 31 and the transfer unit. Conveyed in between. The developer image formed on the photosensitive drum 31 is transferred onto a sheet fed by a transfer unit.
[0026]
The sheet on which the developer image has been transferred is conveyed to a fixing unit 32, and the fixing unit 32 fixes the developer image on the sheet by heat-pressing the sheet. The paper that has passed through the fixing unit 32 is discharged from the printer 13 to the outside (the folding device 40) via the flapper and the discharge roller.
[0027]
Here, when the sheet is discharged with the image forming surface facing downward (face down state), the sheet that has passed through the fixing unit 32 is once guided into the reversing path by the 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.
[0028]
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, a state in which the image forming surface faces upward without leading the sheet to a reversing path (face-up state). Is discharged by the discharge roller.
[0029]
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.
[0030]
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 or B4 size sheet, the folding device 40 performs the folding process. Otherwise, the sheet discharged from the printer 13 passes through the folding device 40. 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.
[0031]
[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 FIG. 2, reference numeral 205 denotes a paper transport path, 31 denotes the above-described photosensitive drum, and 202 denotes 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.
[0032]
Reference numeral 203 denotes a paper transport roller (registration roller), which temporarily stops the paper sent along the paper transport path 205 and then sends it out to the photosensitive drum 31 side at a predetermined paper feed timing. Reference numeral 204 denotes an image reading sensor (image sensor) that reads an image to detect a sheet position, and is configured by a photoelectric conversion element array such as a CCD or a CIS. In the present embodiment, a CIS (contact image sensor) is used. The CIS 204 is disposed on the photosensitive drum side at a distance L1 (see FIG. 3) from the registration roller 203.
[0033]
FIG. 3 is a diagram showing the relationship between the paper feed timing and the image forming timing.
[0034]
When the image forming operation is performed, as described above, the sheet sent from the registration roller 203 is transported along the paper transport path 205 to the photosensitive drum 31 side. At this time, in order to adjust the writing start position, the timing in the paper feeding direction (for convenience, referred to as a sub-scanning direction) and the timing in the direction perpendicular to this paper feeding direction (for convenience, referred to as a main scanning direction) are detected. Then, it is necessary to control the writing by the laser beam.
[0035]
That is, by starting writing by the laser when the sheet advances by the distance L2 after the leading edge position of the sheet is detected by the CIS 204, the writing position of the image in the sub-scanning direction can be adjusted. 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 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.
[0036]
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 write start timing to the laser control circuit 14 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 14 drives the laser element 202 based on an image signal sent from an image processing circuit (not shown) in synchronization with the writing start timing output from the TCU 105.
[0037]
[Configuration of CIS]
FIG. 4 is a diagram showing the configuration of the CIS 204.
[0038]
The CIS 204 includes an image reading unit 206 and an LED light emitting unit 207. The image reading unit 206 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 218, and an output unit 219. 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.
[0039]
Of the 7000 effective pixels in the entire CIS, 1000 read pixels in the chip (1) 211 located at the head are used for reading in the sub-scanning direction (detection of leading edge and skew described later). You.
[0040]
On the other hand, 6000 read pixels in the remaining six chips (2 to 6) 212 to 216 are used for reading in the main scanning direction (lateral edge detection described later). The number of effective pixels, which is the sum 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.
[0041]
In the image reading unit 206, when the selector 218 effectively selects only a specific chip, for example, only the chip 211 used for tip and skew detection by the selector signal from the TCU 105, the image signal detected by the light receiving element unit 211a is: After being temporarily read to the shift register 211b by the load signal (CIS-SH) from the TCU 105, the data is sequentially transferred from the shift register 211b to the output unit 219 via the selector 218 according to the clock (CLK) from the TCU 105. The output unit 219 converts the transferred serial image signal into parallel data and outputs it as CIS data.
[0042]
Further, when the selector 218 effectively selects the chips 212 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 212a to 217a is once determined by the load signal from the TCU 105. , And are sequentially transferred from the shift registers 212 b to 217 b to the output unit 219 via the selector 218 according to the clock (CLK) from the TCU 105. The output unit 219 converts the transferred serial image signal into parallel data and outputs it as CIS data.
[0043]
On the other hand, the LED light emitting unit 207 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 222 connected to the cathode side of each LED group to adjust a current flowing through each LED group. Consists of The LED current adjustment circuit 222 adjusts the entire LED light emission amount of the LED unit 221 according to the light amount control data from the TCU 105.
[0044]
FIG. 5 is a timing chart showing changes in the clock (CLK) of the CIS 204, the load signal (CIS-SH), and the image signal when the leading edge detection, the skew detection, and the side edge detection are performed.
[0045]
In the case of the front end detection and the skew detection (A and C in the figure), the number of the used light receiving element units 211a is one chip, and the charge accumulation time repeatedly read out by the load signal is shortened. In this case, the LED current value is set high by the LED current adjustment circuit 222 based on the light amount control data from the TCU 105 and the LED light emission amount is increased, thereby preventing a reduction in the S / N ratio of the read image.
[0046]
On the other hand, in the case of the horizontal edge detection (B in the figure), the number of the light receiving element units 212a to 217a used is six, and the charge accumulation time repeatedly read out by the load signal is relatively long. In this case, the S / N ratio of the read image can be maintained even if the LED current value by the LED current adjustment circuit 222 is set low by the light amount control data from the TCU 105 and the LED light emission amount is reduced.
[0047]
FIG. 6 is a diagram showing the arrangement of the CIS 204 with respect to the paper passage area.
[0048]
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 such that one end of the CIS 204 is located substantially at the center of the passing sheet 107 and the other end is located beyond the lateral end of the passing sheet 107. The chip (1) 211 is located substantially on the center side of the paper 107 of the CIS 204, and the chip (7) 217 is located beyond the lateral end.
[0049]
FIG. 7 is a diagram showing a leading end detection area and a side end detection area in the CIS 204.
[0050]
As described above, the leading edge (skew) detection area corresponds to 1000 pixels included in the light receiving element 211a in the CIS 204 located substantially at the center of the sheet 107, and performs leading edge (skew) detection. During this time, the remaining read pixels in the CIS are not used (indicated by x in the figure).
[0051]
On the other hand, the horizontal edge detection area corresponds to 6000 pixels included in the remaining light receiving element units 212a to 217a in the CIS 204, and is used to detect 1000 of the light receiving element unit 211a used for the front end detection while performing the horizontal edge detection. While the horizontal edge detection is not performed, 1000 pixels of the light receiving element unit 211a used for the front end detection are not used (indicated by X in the figure).
[0052]
FIG. 8 is a diagram showing the maximum detection width of the CIS 204. Assuming that the maximum paper width used in the image forming apparatus is Lmax and the minimum paper width is Lmin, the maximum detection width X is approximately （(Lmax−Lmin), and the CIS 204 having such a maximum detection width X It turns out that it is good to use.
[0053]
Here, usefulness when the CIS is used for tip (skew) detection will be described.
[0054]
For example, when the paper feeding speed (PS) is 800 mm / s, the maximum detection width (X) is 100 mm, and the main scanning / sub-scanning resolutions Ph and Pv are each 0.05 mm, the reading cycle of one sensor line = PS / Pv = 16 kHz, the number of sensor pixels = X / Ph = 2000 dots, VCLK = 16 kHz x 2000 dots in a normal sensor usage method, and VCLK = 16 kHz x 2000 dots = 32 MHz in a normal sensor usage method. That is, a sensor that can operate at 32 MHz is required.
[0055]
However, in the method described in the present embodiment, if the number of pixels used for reading in the sub-scanning direction is 1/10 of 200 dots, VCLK = 16 kHz × 200 dots = 3.2 MHz. That is, a sensor operable at 3.2 MHz can be used, and an inexpensive CIS can be employed. In reading in the main scanning direction, the clock VCLK is set to 3.2 MHz, so that detection can be performed only once while the distance of 10 lines is advanced.
[0056]
[Configuration of control circuit]
FIG. 9 is a block diagram showing the configuration of the control circuit.
[0057]
The control circuit 51 includes an image processing circuit 52, a laser control circuit (V-CNT) 14, 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.
[0058]
The laser control circuit 14 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 14 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.
[0059]
FIG. 10 is a block diagram showing the configuration of the TCU 105.
[0060]
The TCU 105 includes a counter 61, a registration ON section 62, a leading end detecting section 63, a side end detecting section 64, a CIS controller 65, a short cycle setting section 66 for CIS leading end detection, a leading end error detecting section 67, and a CIS side end detecting section. It has a long cycle setting section 68, a side edge error detection section 69 and a sequence end setting section (SEQ END) 70.
[0061]
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 leading edge detection unit 63 detects the leading edge position of the sheet based on the CIS data input from the CIS 204. The side edge detection unit 64 similarly detects the side edge position of the sheet based on the CIS data input from the CIS 204.
[0062]
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. In the CIS leading edge detection short cycle setting unit 66, the short cycle TS of the load signal (CIS-SH) input to the CIS 204 when the leading edge of the sheet is detected is set.
[0063]
On the other hand, the long cycle TL of the load signal (CIS-SH) input to the CIS 204 is set in the long cycle setting section 68 for CIS horizontal edge detection when the horizontal edge of the sheet is detected. In the present embodiment, the long period TL is six times as long as the short period TS.
[0064]
The leading edge error detecting section 67 generates an error signal (ERR) when the leading edge position of the sheet detected by the stopper end detecting section 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.
[0065]
FIG. 11 is a block diagram showing the configuration of the leading end detection unit 63.
[0066]
The leading edge detection 63 has a plurality of edge circuits (EDDGE) 81, a timing generation circuit 82, a counter 83, and a skew amount setting unit 84. To each edge circuit (EDDGE) 81, register signals (REG1 to REGn) specifying a pixel position in the light receiving element portion 211a 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 (TIMIMG) 82 performs an averaging process on the plurality of generated edges (EDDGE1 to EDNG) to output a leading end detection signal (VREQ), and also generates the plurality of generated edges (EDDGE1 to EDDG1 to n). The skew amount is detected using the signal, and if the detected skew amount is larger than the skew amount (REG) preset in the skew amount setting unit 84, a skew error signal (skew ERR) Is output. Details of the skew amount detection will be described later. Note that 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.
[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. 12 is a timing chart showing the operation of the TCU 105.
[0070]
The paper feeding / image forming sequence according to the present embodiment starts 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.
[0071]
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, the TCU 105 outputs a load signal (CIS-SH) to the CIS 204 with the short cycle TS set in the short cycle setting unit 66 for CIS leading edge detection. As a result, the leading end detection unit 63 reads only the CIS data from the light receiving element unit 211a in the CIS 204.
[0072]
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 edge detection signal VREQ to the laser control circuit 14, the laser control circuit 14 uses the laser in consideration of the vertical margin based on the vertical synchronization signal VSYNC from the CIS controller 65. Adjust the writing position in the sub-scanning direction.
[0073]
FIG. 13 is a diagram showing the writing start position adjustment by 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).
[0074]
In the side edge detection mode, the TCU 105 outputs the load signal (CIS-SH) with the long cycle TL set in the short cycle setting section 68 for CIS side edge detection. As a result, the lateral end detection unit 64 reads only the CIS data from the light receiving element units 212a to 217a in the specific area in the CIS 204.
[0075]
When the horizontal position of the sheet is detected when the count value reaches timing d, the CIS controller 65 stops the operation of the CIS 204 and outputs the horizontal synchronization signal HSYNC and the clock VCLK to the laser control circuit 14. The laser control circuit 14 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. 13). 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.
[0076]
[Skew detection]
A case where skew detection is performed at the same time as detecting the leading edge of a sheet conveyed by the CIS 204 is shown. In the detection of the skew amount of the sheet, only the light receiving element 211a in one chip of the CIS 204 is used as in the detection of the leading edge of the sheet. That is, of the 7,000 pixels included in the entire detection area of the CIS 204, the skew amount detection and the tip detection are performed for 1000 pixels in the specific area. Hereinafter, the amount of skew caused by such detection of the leading edge is referred to as the amount of skew of the leading edge.
[0077]
FIG. 14 is a diagram illustrating a tip skew amount obtained from a read image obtained by the tip detection of the CIS 204.
[0078]
In FIG. 14, the horizontal axis indicates the transport distance in the sub-scanning direction, and the vertical axis indicates the arrangement of pixels in the main scanning direction. Each read image divided into squares represents an average value of images read from read pixels of an arbitrary number of pixels (for example, 10 to 100 pixels). In the figure, a black image portion indicates that the paper is read. To indicate that The inclination of the boundary portion of the square indicated by the black image indicates the amount of skew at the front end, as described later, and its value is represented by dH / dV.
[0079]
Here, when the CIS 204 is attached so that the read pixels are lined up in the vertical direction with respect to the paper transport direction, the calculated tip skew amount is equal to the paper skew amount.
[0080]
However, in practice, the CIS 204 is not always accurately mounted. If the arrangement of the read pixels is slightly deviated from the above-described vertical direction, it is necessary to correct the CIS 204 and calculate the amount of skew at the tip. There is.
[0081]
Therefore, in the present embodiment, it is assumed that the skew amount (lateral end skew amount) detected by the horizontal edge is an accurate skew amount of the sheet (the reason will be described later). However, since it is an absolute condition that the straightness of the paper is good, the horizontal edge detection is performed in at least three places in order to confirm the straightness of the paper, and whether the skew amount of the horizontal edge is constant. to decide.
[0082]
FIG. 15 is a conceptual diagram when checking the straightness of a sheet.
[0083]
In FIG. 15, after determining the lateral end skew amount by calculating the lateral end position in (1) and (2), the lateral end skew amount is subsequently determined in (2) and (3). When the horizontal skew amount is constant, the paper straightness is good, and the front skew amount is corrected based on the horizontal skew amount. Then, after the correction value is obtained, an accurate skew amount of the sheet is calculated only by the skew amount of the leading end detected by the leading end. However, when the straightness is poor as shown by (3) in FIG. 15, the sheet is conveyed again, and the skew amount at the side edge when the straightness is good is determined.
[0084]
FIG. 16 is a diagram showing the skew amount of the side edge obtained by detecting the side edge of the CIS 204. If at least two horizontal edge positions are detected by the horizontal edge detection of the sheet, the horizontal edge skew amount is (X1−X2) using the horizontal edge positions X1 and X2 and the transport distance L between the horizontal edge detections. ) / L.
[0085]
Using this lateral end skew amount, a correction value of the tip skew amount due to the mounting angle error of the CIS is calculated, and if the calculated mounting angle error is equal to or larger than a predetermined value, the mounting of the CIS is adjusted again. As described above, the lateral end skew amount detection is performed when the mounting angle of the CIS is adjusted or in the adjustment mode.
[0086]
If the corrected tip skew amount obtained by detecting the leading edge of the sheet is equal to or more than a predetermined amount after the CIS mounting angle is adjusted, a warning is issued to the operator, and the subsequent image forming operation is stopped. .
[0087]
Next, the correction of the front-end skew amount using the horizontal-end skew amount will be considered.
[0088]
FIG. 17 is a diagram showing the correction of the skew amount of the front end. In the figure, a method of determining the skew amount of a sheet skewed by an angle β using a CIS that is conveyed in the x-axis direction and is shifted by an angle α with respect to the y-axis will be described below.
(1) At the time of paper conveyance, the skew determination amount β2 based on the leading edge and the skew determination amounts β1 and β1 ′ based on the lateral edges are measured at two locations, and the CIS mounting angle α1 is determined based on the obtained values of β1 and β2. Is calculated, and this is hereinafter referred to as a correction value. However, if β1 and β1 ′ are different from each other by a predetermined amount or more, the calculated α1 is invalidated, and β1, β1 ′, and β2 are measured again to calculate α1 when straightness is good.
(2) At the time of paper conveyance, the amount of skew determination γ1 by the leading edge is measured, and an accurate skew amount γ2 is derived by calculating this value and the correction value α1.
(3) When the CIS mounting angle α is sufficiently small, β1 becomes almost equal to β, and β2 becomes almost equal to α + β. Therefore, if β1 and β2 are assumed, α1 obtained by the calculation becomes CIS of CIS. When the inclination γ of the sheet is substantially equal to the inclination α, the subsequent detection of the inclination γ of the sheet can be performed only by detecting the leading edge.
[0089]
Hereinafter, the procedures (1) to (3) will be described more specifically.
[0090]
(Determining the amount of skew by the side edge)
FIG. 18 is a diagram illustrating the determination of the skew amount detected when a sheet skewed by the angle β has advanced by the distance x1 by a CIS (sensor) attached at an angle α. The true value of the skew amount due to the lateral end is tan (β) = c / x1, but since the sensor is inclined by α, an error occurs in the detection amount, and tan (β1) = L1 / x1. Is determined. Here, it is proved by calculation that β1 is almost equal to β.
[0091]
In the drawing, assuming that auxiliary lines are drawn on the x-axis and the y-axis from the intersection and the lengths are a, b, and c, sin (α) = a / L1, cos (α) = (b + c) / L1, tan (Β) = (b + c) / (x1 + a). Then, when these are arranged, the tangent of the skew amount β1 detected by the sensor is expressed by Expression (1).
[0092]
tan (β1) = sin (β) / cos (α + β) (1)
FIG. 19 is a table showing values of β1 obtained from Expression (1) using α and β as variables. FIG. 20 is a table in which the value of β1 and the actual value of β in FIG. 18 are calculated, and the error is shown in units of%. As shown in FIG. 19, when the mounting angle of the sensor is within 5 degrees, when the skew amount of the sheet is within 4 degrees, the detection error is within 1%.
[0093]
(Determining the amount of skew by the tip)
FIG. 21 is a diagram showing the skew amount determination by the tip.
[0094]
FIG. 11 is a diagram illustrating a determination of a skew amount detected when a sheet skewed by β has advanced by a distance x2 to a sensor attached at an angle of α. In the figure, the true value of the skew amount due to the lateral end is tan (β) = c / a, but since the sensor is inclined, an error occurs in the detection amount, and tan (β2) = x2 / L2. Is determined.
[0095]
Here, it is proved by calculation that β2 is a function of β and α. In the drawing, assuming that auxiliary lines are drawn on the x-axis and the y-axis from the intersection and the lengths are a, b, and c, sin (α) = b / L2, cos (α) = a / L2, tan (β ) = C / a, x2 = b + c. When these are arranged, the tangent of the skew amount β2 detected by the sensor is as shown in Expression (2).
[0096]
tan (β2) = sin (α + β) / cos (β) (2)
FIG. 22 is a table showing the value of the skew amount β2 obtained by the tip detection obtained from Expression (2) when α and β are variables.
[0097]
(Calculation of correction value α1)
The inclination α of the sensor is calculated from the measured values β1 and β2 as α1 based on the following assumptions 1 and 2.
[0098]
(Premise 1): β1 is equal to β.
[0099]
(Premise 2): β2 is represented by Expression (2).
[0100]
That is, α1 is obtained by substituting the value of β1 into the term β in Expression (2) to obtain Expression (3).
[0101]
tan (β2) = sin (α1 + β1) / cos (β1) (3)
Here, since β1 and β2 are values known as the skew amounts obtained by the edge detection, solving for α1 yields Expression (4).
[0102]
α1 = asin (cos (β1) * tan (β2))-β1 (4)
FIG. 23 is a table showing values of α1 obtained from Expression (4) when α and β are variables. FIG. 24 is a table in which the ratio between the value of α1 in FIG. 23 and the actual value of α is calculated, and the error is expressed in units of%.
[0103]
Thereby, the mounting angle of the sensor can be obtained in the adjustment mode or the like.
[0104]
(Skew detection using correction value α1)
Next, the skew amount determination γ based on actual tip detection will be described. Here, the sensor inclination α is stored as the calculated value α1 in the above-described adjustment mode, and the actual skew amount is set to γ in the tip detection, and the detection amount is set to γ1.
[0105]
From equation (2), tan (γ) = sin (α1 + γ1) / cos (γ1), and solving for γ1 yields equation (5).
[0106]
γ1 = atan ((tan (γ) −sin (α1)) / cos (α1)) (5)
Here, tan (γ) is a measured value, and sin (α1) and cos (α1) are known from the correction value α1.
[0107]
FIG. 25 is a table showing the skew amount by the leading edge detection with respect to the sensor attachment angle α and the skew amount β of the sheet at the time of adjustment. FIG. 26 is a table showing an error with respect to the theoretical value in FIG. 25 in units of%.
[0108]
It can be seen that the greater the sensor attachment angle and the amount of skew of the sheet in the adjustment mode, the greater the final error. In other words, the following operation is performed in the adjustment mode depending on how much the skew detection accuracy is required.
[0109]
That is, if it is determined that the sensor mounting angle is inclined by a predetermined amount or more, the mounting of the sensor itself is adjusted. When it is determined that the skew amount of the sheet is inclined by a predetermined amount or more, the adjustment mode is performed again. If it is determined in the adjustment mode that the straightness of the sheet is poor, the calculated sensor attachment angle is invalidated, and the sheet is conveyed again to calculate the sensor attachment angle.
[0110]
FIG. 27 shows a flowchart until the CIS mounting angle α1 in the adjustment mode in this embodiment is calculated.
[0111]
In the adjustment mode, β1, β1 ′, and β2 are measured by transporting the sheet (S1) (S2). Here, if the difference between β1 and β1 ′ is less than the predetermined amount, that is, if the straightness is good, the process proceeds to S4, and if the difference between β1 and β1 ′ is more than the predetermined amount, that is, if the straightness is bad, the process is repeated from S1 (S3). If β1 = β1 ′, α1 is calculated from β1 and β2 (S4). This adjustment mode is performed at the time of factory adjustment or removal of the CIS.
[0112]
FIG. 28 shows a flowchart up to skew detection during copying in the present embodiment.
[0113]
The sheet is conveyed (S5), and β2 is measured (S6). Since α1 has already been calculated in the adjustment mode, γ1 is obtained using α1 as a correction value (S7).
[0114]
The above is an explanation 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.
[0115]
For example, in the above-described embodiment, the image forming timing in the sub-scanning direction is acquired by detecting the leading edge of the paper by the CIS. However, depending on the configuration of the apparatus, instead of detecting the leading edge, the secondary edge may be detected by the CIS to detect the trailing edge of the paper. The image forming timing in the scanning direction may be obtained.
[0116]
Further, in the above-described embodiment, the entire detection area of the CIS is divided into 1: 6, and they are respectively used for the front end (slant line) detection area and the side end detection area. However, this division may be arbitrary. Instead of the division, the entire detection area may be used in the lateral end detection, and only a part of the detection area may be used in the front end (skew) detection.
[0117]
Further, the paper feed / image forming sequence is realized by a hardware circuit, but may be realized by software control by executing a program by a CPU instead of the hardware circuit.
[0118]
【The invention's effect】
As described above, according to the present invention, the reliability of the attachment angle correction value of the image reading unit when obtaining the amount of skew increases, and more accurate skew can be achieved before an image is formed on a sheet. Detection can be performed, and it is not necessary to output a sheet on which an image of low print quality is formed due to skew.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to the present invention.
FIG. 2 is a diagram illustrating a print position adjusting mechanism arranged in a paper transport path leading to a photosensitive drum of the image forming apparatus according to the present invention.
FIG. 3 is a diagram illustrating a relationship between a paper feed timing and an image forming timing of the image forming apparatus according to the present invention.
FIG. 4 is a diagram illustrating a configuration of a CIS of the image forming apparatus according to the present invention.
FIG. 5 is a timing chart illustrating changes in a CIS clock (CLK), a load signal (CIS-SH), and an image signal when the leading edge detection, the skew detection, and the lateral edge detection of the image forming apparatus according to the present invention are performed. is there.
FIG. 6 is a diagram illustrating an arrangement of CISs with respect to a paper passage area of the image forming apparatus according to the present invention.
FIG. 7 is a diagram illustrating a front end detection area and a side end detection area in the CIS of the image forming apparatus according to the present invention.
FIG. 8 is a diagram illustrating a maximum detection width of a CIS.
FIG. 9 is a block diagram illustrating a configuration of a control circuit.
FIG. 10 is a block diagram illustrating a configuration of a TCU.
FIG. 11 is a block diagram illustrating a configuration of a tip detection unit.
FIG. 12 is a timing chart showing the operation of the TCU.
FIG. 13 is a diagram illustrating writing start position adjustment using a laser.
FIG. 14 is a diagram illustrating a tip skew amount obtained from an image read by CIS tip detection.
FIG. 15 is a conceptual diagram when checking the straightness of a sheet.
FIG. 16 is a diagram illustrating a lateral end skew amount obtained by detecting a lateral end of the CIS.
FIG. 17 is a diagram illustrating correction of a front-end skew amount;
FIG. 18 is a diagram illustrating determination of a skew amount detected when a sheet skewed by an angle β advances by a distance x1 by a CIS (sensor) attached at an angle of an angle α.
FIG. 19 is a table showing β1 values obtained from Expression (1) using α and β as variables.
20 is a table showing the ratio between the value of β1 in FIG. 19 and the actual value of β, and showing the error in%.
FIG. 21 is a diagram illustrating a skew amount determination based on a tip.
FIG. 22 is a table showing the value of the skew amount β2 obtained by detecting the leading end obtained from Expression (2) when α and β are variables.
FIG. 23 is a table showing values of α1 obtained from Expression (4) when α and β are variables.
24 is a table in which the ratio between the value of α1 in FIG. 23 and the actual value of α is calculated, and the error is expressed in units of%.
FIG. 25 is a table showing a skew amount by leading edge detection with respect to a sensor attachment angle α and a sheet skew amount β at the time of adjustment.
FIG. 26 is a table showing an error with respect to the theoretical value in FIG. 25 in units of%.
FIG. 27 is a flowchart until α1 is calculated in the adjustment mode in the embodiment.
FIG. 28 is a flowchart illustrating a process up to skew detection during copying in the embodiment.
FIG. 29 is a side view showing a print position adjusting mechanism in a conventional image forming apparatus.
30 is a plan view showing a part of the printing position adjusting mechanism of FIG. 29.
[Explanation of symbols]
10 Image Forming Apparatus Main Body
11 Image reader
12 Document feeder
12a Document tray
12b paper output tray
13 Printer
14 Laser control circuit
21 Scanner unit
22-24 mirror
25 lenses
26 Image Sensor
27 Polygon mirror
28, 29 lenses
30 mirror
31 Photosensitive drum
32 Fixing unit
33 Developer
34-37 cassettes
38 Manual Feed Unit
40 folding device
50 Finisher
51 Control circuit
52 Image processing circuit
56 image memory
57 CPU
61 counter
62 Cash register ON section
63 Tip detector
64 Side edge detector
65 CIS controller
66 CIS tip detection short cycle setting unit
67 Tip error detector
68 CIS side edge detection long cycle setting unit
69 Horizontal edge error detector
70 Sequence end setting section
81 Edge Circuit
82 Timing Generation Circuit
83 counter
84 Skew amount setting section
105 Timing control unit (TCU)
107 paper
108 Beam Detector
202 Laser element
203 registration roller
204 CIS
205 Paper transport path
206 Image reading unit
207 LED light emitting unit
211-217 chips
211a to 217a Light receiving element section
211b-217b shift register
218 Selector
219 Output unit
221 LED section
222 LED current adjustment circuit
1301 Photosensitive drum
1302 laser
1303 Registration roller
1304 Paper sensor
1305 Misalignment detection sensor
1401 Output paper
1403 Paper feeding direction

Claims (8)

Image reading means having a plurality of read pixels for reading an image, and arranged in a pass area where a lateral end of the conveyed sheet can be read such that the plurality of read pixels are arranged in a direction perpendicular to a sheet conveying direction. A lateral edge detecting means for detecting a lateral edge of the conveyed sheet by repeatedly reading at least a part of the plurality of read pixels at a predetermined cycle; and at least two of the lateral edges detected by the lateral edge detecting means. A lateral end skew amount detecting unit for detecting a lateral end skew amount of the sheet based on a lateral end position of the conveyed sheet;
An image forming apparatus, comprising: a difference calculating means for detecting a plurality of skew amounts of the side edge obtained by the skew amount detecting means for the side ends and calculating a difference between the plurality of skew amounts. 2. The image forming apparatus according to claim 1, further comprising a difference determination unit configured to determine whether a difference between the plurality of lateral edge skew amounts calculated by the difference calculation unit is equal to or greater than a predetermined amount or less than a predetermined amount. apparatus. A leading edge detecting means for detecting a leading edge of the conveyed sheet by repeatedly reading a part of the plurality of read pixels at a cycle shorter than the predetermined cycle; and Tip skew amount detection means for detecting the skew amount of the leading edge of the sheet based on the read data representing the leading edge of the sheet; the detected skew amount of the lateral edge and the detected skew amount of the leading edge Mounting angle calculation means for calculating the mounting angle degree of the image reading means based on the image reading means, and a tip for correcting the tip skew amount detected by the tip skew amount detecting means based on the calculated mounting angle degree. An image forming apparatus comprising: a skew amount correcting unit. When the attachment angle is calculated by the attachment angle calculation means, it is determined whether the difference between the plurality of lateral end skew amounts obtained by the difference determination means is equal to or greater than a predetermined amount or less than a predetermined amount, and is determined to be equal to or greater than the predetermined amount The image forming apparatus according to claim 3, further comprising: a mounting angle degree invalidating unit that invalidates the calculated mounting angle degree. An image reading step having a plurality of read pixels for reading an image, wherein the plurality of read pixels are arranged in a pass area where a lateral end of the conveyed sheet can be read so as to be arranged in a direction perpendicular to a sheet conveying direction A lateral edge detecting step of detecting a lateral edge of the conveyed sheet by repeatedly reading at least a part of the plurality of read pixels at a predetermined cycle, and at least two of the lateral edges detected by the lateral edge detecting step. A side edge skew amount detecting step of detecting the side edge skew amount of the sheet based on the side edge position of the conveyed sheet,
An image forming control method, comprising: detecting a plurality of side edge skew amounts obtained by the side edge skew amount detection step and calculating a difference between the plurality of skew amounts. 6. The image forming control according to claim 5, further comprising a difference determination step of determining whether a difference between the plurality of lateral edge skew amounts calculated in the difference calculation step is equal to or more than a predetermined amount or less than a predetermined amount. Method. A leading edge detecting step of detecting a leading edge of the conveyed sheet by repeatedly reading a part of the plurality of read pixels at a cycle shorter than the predetermined cycle, and a part of the plurality of read pixels in the leading edge detecting step. A leading edge skew amount detecting step of detecting the leading edge skew amount of the sheet based on the read data representing the leading edge of the sheet; and the detected lateral edge skew amount and the detected leading edge skew amount. A mounting angle degree calculating step of calculating the mounting angle degree of the image reading means based on the image reading means; and a tip for correcting a tip skew amount detected by the tip skew amount detecting step based on the calculated mounting angle degree. An image forming control method, comprising: a skew amount correcting step. When the attachment angle is calculated by the attachment angle calculation step, it is determined whether the difference between the plurality of lateral end skew amounts determined by the difference determination step is equal to or greater than a predetermined amount or less than a predetermined amount, and is determined to be equal to or greater than the predetermined amount 8. The image forming control method according to claim 7, further comprising a step of invalidating the calculated angle of attachment in the case.

Images