JP2008270955A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect position data on a paper end and a reference mark without using a large-capacity memory. <P>SOLUTION: The image forming apparatus which detects a write-out position for image formation of image data of a read document on a form based upon line data read by a CIS 14 and performs the image formation according to the detected write-out position, includes a RAM 21A in which line data are updated by lines and stored, and a control unit 21 which reads the line data out of the RAM 21A in predetermined timing, computes a paper end threshold Sp for detecting a paper end of the form and a mark threshold Sm for detecting the reference mark on which the write-out position is based on the basis of the read line data, and acquires the position data on the paper end and the position data on the reference mark based upon the computed paper end threshold Sp and mark threshold Sm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an image forming apparatus that forms an image of image data of a document to be read on a sheet is known.

For example, an image forming apparatus that stores image data read by a line image sensor in a memory and extracts an edge portion of the image data to correct the inclination of the document is known (see, for example, Patent Document 1).
JP 2002-142084 A

  However, the above-described technique is a technique for storing image data read by the line image sensor in a memory (storage unit) as multi-value data. For this reason, it is necessary to prepare a large-capacity memory.

In addition, when image data on both the front and back sides of a document is formed on a sheet, the position data of the paper edge and the reference mark is acquired in order to correct the position where the back side image data is written. In this case, there has been a demand for realizing an image forming apparatus that acquires the position data of the paper edge and the reference mark without using a large-capacity memory.
FIG. 8 shows position data (X1, Y1), (X2, Y2), (X3) used for correcting the writing position of the image data on the back side when image data on both sides of the document is formed on the paper P. , Y3). (X1, Y1) indicates the position data of the leading edge of the paper P. (X2, Y2) indicates the position data of the lateral edge of the paper P. (X3, Y3) indicates the position data of the intersection of the reference marks (register mark). The registration mark is a reference mark used to correct the writing position of the image data on the back side when the image data of the document is formed on the back side of the paper P. The registration mark is formed on the surface of the paper P when image data on the surface of the document is formed on the paper P.
The backside image data write position is adjusted for front and back magnification (ie, the amount of deviation between the distance from the paper edge to the registration mark on the front surface of the paper P and the distance from the paper edge to the registration mark distance on the back surface of the paper P is corrected). Is required. The front / back magnification matching is performed by acquiring position data (X1, Y1), (X2, Y2), (X3, Y3). The position data is acquired by reading the image data of the paper P by a CIS (Contact Image Sensor) and storing the read image data in a memory. At this time, if the amount of data read by the CIS is small, it is not necessary to facilitate a large-capacity memory. Therefore, there has been a request for acquiring the paper edge and reference mark position data without using a large-capacity memory.

  An object of the present invention is to detect the position data of a paper edge and a reference mark without using a large-capacity memory.

In order to solve the above-described problem, an image forming apparatus according to a first aspect of the present invention provides:
An image forming apparatus that detects a writing position when image data of a read original is formed on a sheet based on line data read by a line image sensor, and performs image formation according to the detected writing position.
A storage unit for sequentially updating and storing the line data for each line;
Line data is read from the storage unit at a predetermined timing, and based on the read line data, a first threshold for detecting a paper edge of the paper and a reference mark serving as a reference for the writing position are detected. And a control unit that obtains the position data of the paper edge and the position data of the reference mark based on the calculated first threshold value and the second threshold value.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
As the predetermined timing, an input unit is provided for receiving an input of timing for calculating the first threshold value and the second threshold value set by the user.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
The controller is
First line data, which is line data of a line read by the line image sensor at a portion outside the sheet, is read, and a value obtained by multiplying the read first line data by an arbitrary value is used as the first threshold value. Operate,
Second line data that is line data of a line read by the line image sensor at a portion other than the reference mark on the paper is read, and a value obtained by multiplying the read second line data by an arbitrary value is obtained. Calculate as the second threshold.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect,
The controller is
An average value of line data of a predetermined area of a line read by the line image sensor at a portion outside the paper is calculated as the first line data,
An average value of line data of a predetermined area of a line read by a part other than the reference mark on the paper by the line image sensor is calculated as the second line data.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects,
The controller is
The first threshold value is calculated, the paper edge position data is acquired based on the calculated first threshold value, the second edge value is calculated after acquiring the paper edge position data, and the calculation is performed. The reference mark position data is obtained based on the second threshold value.

  According to the first aspect of the present invention, the line data is read at a predetermined timing from the storage unit in which the line data sequentially updated for each line is stored, and based on the read line data, the first threshold value, And the second threshold value is calculated, and the position data of the paper edge and the position data of the reference mark can be obtained based on the calculated first threshold value and second threshold value. Accordingly, since it is not necessary to store all of the read line data in the storage unit, it is possible to detect the position data of the paper edge and the reference mark without using a large-capacity memory. Further, since the first threshold value and the second threshold value are calculated based on the line data read out at a predetermined timing, the first threshold value and the second threshold value can be calculated with a small amount of data. That is, the position data of the paper edge and the reference mark can be detected at high speed.

  According to the second aspect of the present invention, the input unit can accept an input of timing for calculating the first threshold value and the second threshold value set by the user. Thereby, the user can freely set and input the timing for calculating the first threshold value and the second threshold value.

  According to the third aspect of the present invention, a value obtained by multiplying the first line data by an arbitrary value can be calculated as the first threshold value. A value obtained by multiplying the second line data by an arbitrary value can be calculated as the second threshold value.

  According to the fourth aspect of the present invention, the average value of the line data of a predetermined area of the line read by the line image sensor at the portion outside the sheet can be calculated as the first line data. Further, the average value of the line data of a predetermined area of the line read by the line image sensor at a portion other than the reference mark on the paper can be calculated as the second line data. Thus, the first threshold value and the second threshold value can be calculated as values that are not affected by the sheet passing state. That is, the position data of the paper edge and the reference mark can be detected with high accuracy.

  According to the fifth aspect of the invention, the first threshold value is calculated, the paper edge position data is acquired based on the calculated first threshold value, and the paper edge position data is acquired. The reference mark position data can be acquired based on the calculated second threshold value.

  Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings. However, the scope of the invention is not limited to the illustrated examples.

  FIG. 1 shows a schematic example of the overall configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is, for example, a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions.

  The image forming apparatus 1 includes a control unit 11, a laser unit 12, a photosensitive drum 13, a CIS 14 as a line image sensor, a registration roller 15, and a fixing roller 16.

  The control unit 11 performs an instruction and threshold calculation for each unit constituting the image forming apparatus 1. Details will be described later.

  The laser unit 12 is configured by an LD (Laser Diode) or the like, and emits laser light by pulse width modulating image data of a scanned original to be read by a pulse width modulator (not shown).

  The photosensitive drum 13 forms an electrostatic latent image on the surface by the laser light irradiated by the laser unit 12. Toner is attached to the electrostatic latent image by a developing device (not shown).

  The CIS 14 is constituted by a reflection type optical sensor, and detects an end of the paper P and a reference mark (register mark) on the paper P.

  The registration roller 15 and the fixing roller 16 convey the paper P fed from a paper feed tray (not shown).

  Next, the internal configuration of the image forming apparatus 1 will be described with reference to FIG. The image forming apparatus 1 illustrated in FIG. 2 includes a control unit 21, an operation display unit 22 as an input unit, an image reading unit 23, an image processing unit 24, a printer unit 25, a detection unit 26, and a conveyance unit 27. And configured.

  The control unit 21 corresponds to the control unit 11 in FIG. The control unit 21 includes a CPU (Central Processing Unit), a ROM (Read Only Memory) (not shown), and a RAM (Random Access Memory) 21A serving as a storage unit, and corresponds to each function constituting the image forming apparatus 1. Controls instructions and data communication between the functional units.

  Specifically, the control unit 21 develops a program designated in the system program and various application programs stored in the ROM in the RAM 21A, and performs various processes in cooperation with the program expanded in the RAM 21A and the CPU. Execute. The RAM 21A sequentially updates and stores the line data read by the CIS 14 for each line. Updating the line data sequentially for each line means that the line data read by the CIS 14 is overwritten and stored for each line. The ROM stores a mark detection program described later.

The control unit 21 detects the paper edge and the registration mark of the paper P by the mark position acquisition program. The paper edge of the paper P refers to the leading edge and the horizontal edge of the paper P. The registration mark is a mark used as a reference for correcting the writing position of the image data on the back side when the image data of the document is formed on the back side of the paper P.
Specifically, the control unit 21 reads line data from the RAM 21A at a predetermined timing, and based on the read line data, the paper edge threshold Sp as the first threshold and the mark threshold Sm as the second threshold. Is calculated. Then, based on the calculated paper edge threshold Sp and mark threshold Sm, paper edge position data and registration mark mark position data are acquired.
The predetermined timing refers to timing for calculating the paper edge threshold Sp and the mark threshold Sm. The timing is set and input by the user via the operation display unit 22. The paper edge threshold value Sp is a threshold value for detecting the paper edge of the paper P. The mark threshold value Sm is a threshold value for detecting a registration mark serving as a reference for the writing position of the back side image data. The paper edge position data refers to the position data of the leading edge and the horizontal edge of the paper P. The registration mark position data refers to position data indicating the intersection of registration marks.

  The operation display unit 22 is configured by an LCD (Liquid Crystal Display) or the like, and displays various operation buttons, device statuses, operation statuses of functions, and the like on the display screen according to instructions of display signals input from the control unit 21. I do. On the LCD display screen, a pressure-sensitive (resistive film pressure type) touch panel with transparent electrodes arranged in a grid is configured, and the XY coordinates of the force point pressed by a finger or a touch pen are detected by voltage values. The detected position signal is output to the control unit 21 as an operation signal.

  The image reading unit 23 includes a scanner and reads image data of a document. The scanner includes a light source, a CCD (Charge Coupled Device), and the like, and reads an image of a document by forming an image of reflected light of light scanned from the light source to the document and performing photoelectric conversion. Then, the read image is converted into digital image data by an A / D converter and output to the image processing unit 24. The image processing unit 24 performs image processing such as gradation correction processing on the document image data input from the image reading unit 23. Then, the image data is output to the printer unit 25.

  The printer unit 25 includes the laser unit 12 and the photosensitive drum 13 in FIG. 1, and forms image data of the original on the paper P. In addition to the laser unit 12 and the photosensitive drum 13, the printer unit 25 includes a pulse width modulator, a charger, a developing unit, a fixing unit (all not shown), and the like.

  The detection unit 26 corresponds to the CIS 14 in FIG. 1 and detects the end of the paper P and the mark on the paper P. The transport unit 27 corresponds to the registration roller 15 and the fixing roller 16 in FIG. 1 and transports the paper P fed from a paper feed tray (not shown).

Next, detection examples of the position data (X1, Y1), (X2, Y2), (X3, Y3) will be described with reference to FIG. In addition, description of position data uses the description of FIG. FIG. 3 is a diagram showing output values of the CIS 14 when detecting the position data of the paper edge and the position data of the intersection of the registration mark. A part A of FIG. A1 shows a graph when the A part is read by the CIS14. Part B indicates the lateral end of the paper P. B1 shows a graph when the B part is read by the CIS14. Part C indicates a registration mark. C1 shows a graph when C part is read by CIS14.

  Here, an example of detecting the position data (X1, Y1) of the leading edge of the paper P will be described on behalf of the graph A1. The vertical axis of graph A1 shows the output value of CIS14. The horizontal axis of the graph A1 indicates the pixel number of CIS. One pixel of the CIS 14 indicates a distance. Here, the position data (X1, Y1) of the leading edge of the paper P is obtained based on the paper edge threshold Sp. For example, it is assumed that the position data (X1, Y1) of the leading edge of the paper P is detected while the paper edge threshold Sp is fixed. In this case, the position data (X1, Y1) of the leading edge of the paper P can be obtained by obtaining the CIS pixel number when the paper edge threshold Sp is exceeded. The position data (X2, Y2) of the paper lateral edge of the paper P is similarly obtained based on the paper edge threshold Sp. The position data (X3, Y3) of the intersection of the registration mark is obtained based on the mark threshold value Sm.

  Next, it will be described that the position data (X1, Y1) of the leading edge of the paper P is shifted when the output value of the CIS 14 differs using the graph A1. A2 indicates the output value of the CIS 14 when the distance between the paper P and the CIS 14 is 0 mm. A3 indicates an output value of the CIS 14 when the distance between the paper P and the CIS 14 is 2.5 mm. As shown in A2 and A3, the output value of the CIS 14 varies depending on the distance between the paper P and the CIS 14. That is, the output value of the CIS 14 varies depending on the paper P passing state. In this case, the position data (X1, Y1) of the leading edge of the paper P is displaced. For example, in A2 and A3, the position data (X1, Y1) of the leading edge of the paper P is shifted by the difference between A5 and A6. Then, when the image data of the back side is formed on the paper P, the image data writing position is shifted. Therefore, it is necessary to calculate the paper edge threshold value Sp and the mark threshold value Sm according to the paper passing state.

  Next, with reference to FIG. 4, a method for calculating the paper edge threshold Sp and the mark threshold Sm executed by the control unit 21 will be described. FIG. 4 shows the distribution of output data of the CIS 14 outside and on the paper P. The output value of the CIS 14 shows a low value when the reading portion is black (that is, when the reading portion is outside the paper P). When the reading portion is white (that is, when the reading portion is on a sheet), a high value is indicated.

A1 to An indicate output data of the CIS 14 in a predetermined area of a line read by a portion outside the paper P by the CIS 14. The predetermined area refers to an arbitrary range (distance) on the line read by the CIS 14. For example, a range C from A1 to An in FIG. 4 corresponds to a predetermined region.
B1 to Bn indicate output values of the CIS 14 in a predetermined area of the line read by the CIS 14 at portions other than the registration mark on the paper P. The predetermined area refers to an arbitrary range (distance) on the line read by the CIS 14. For example, a range D from B1 to Bn in FIG. 4 corresponds to a predetermined region.

Next, a method for calculating the paper edge threshold Sp and the mark threshold Sm will be described.
The paper edge threshold value Sp is obtained by the following equation (1).
Sp = Kp × (A1 + A2 +... + An-1 + An) / n (1)
(A1 + A2 +... + An-1 + An) / n represents an average value of line data in a predetermined area of the line read by the CIS 14. A1 + A2 +... + An-1 + An) / n corresponds to the first line data. n represents the number of measurement points A1 to An. Kp as an arbitrary value indicates a predetermined magnification. Kp may be a value set and input by the user every time the paper edge threshold Sp is calculated, or may be a fixed value set in advance.

  The paper edge position data (X1, Y1) or (X2, Y2) is acquired using the paper edge threshold Sp obtained by the above equation (1). For example, when the output value of the CIS 14 exceeds the paper edge threshold Sp, the position exceeding the paper edge threshold Sp is acquired as paper edge position data (X1, Y1) or (X2, Y2). Further, as shown in the above equation (1), the paper edge threshold Sp is calculated based on the average value of the line data read by the CIS 14. Therefore, it is possible to calculate the paper edge threshold value Sp corresponding to the paper passing state.

The mark threshold value Sm is obtained by the following equation (2).
Sm = Km × (B1 + B2 +... + Bn-1 + Bn) / n (2)
(B1 + B2 +... + Bn-1 + Bn) / n represents an average value of line data in a predetermined region of the line read by the CIS 14. (B1 + B2 +... + Bn-1 + Bn) / n corresponds to the second line data. n represents the number of measurement points B1 to Bn. Km as an arbitrary value indicates a predetermined magnification. Km may be a value set and input by the user every time the mark threshold value Sm is calculated, or may be a fixed value set in advance.

  The registration mark position data (X3, Y3) is acquired using the mark threshold value Sm obtained by the above equation (2). For example, when the output value of the CIS 14 falls below the mark threshold value Sm, the position is acquired as registration mark mark position data (X3, Y3). Further, as shown in the above equation (2), the mark Sm is calculated based on the average value of the line data read by the CIS 14. Accordingly, it is possible to calculate the paper edge threshold value Sm according to the paper passing state.

The timing for calculating the paper edge threshold value Sp and the mark threshold value Sm is input from the user via the operation display unit 22. For example, it is assumed that a predetermined timing is input by the user via the operation display unit 22. In this case, line data (that is, A1 to An, B1 to Bn) is read from the RAM 21 at the inputted predetermined timing. Based on the read line data, the paper edge threshold Sp and the mark threshold Sm are calculated. Arbitrary number of sheets, arbitrary job, or arbitrary time may be set and inputted as the timing for calculating the paper edge threshold Sp and mark threshold.
Further, the predetermined magnification Kp (Km), the number N of measurement points, the data acquisition interval of A1 to An (B1 to Bn), and the acquisition timing of A1 to An (B1 to Bn) are set by the user via the operation display unit 22. can do.

Next, an example of calculating the position data (X3, Y3) of the intersection of the registration marks executed by the control unit 21 will be described with reference to FIG. FIG. 5 is a diagram showing position data (X3, Y3) of the intersection of the registration mark. (X3, Y3) is obtained by acquiring four points of position data (Xa, Ya), (Xb, Yb), (Xc, Yc), (Xd, Yd) and using the acquired position data. Specifically, it is obtained by the following formulas (3) and (4).
X3 = (Xa + Xd) / 2 (3)
Y3 = (Yb + Yc) / 2 (4)

  Here, an example of acquiring position data of four points will be described. In the case of FIG. 4, reading of image data by the CIS 14 is performed in the Y direction for each line in the X direction. At this time, the data read by the CIS 14 is updated and stored in the RAM 21A for each line in the X direction. In the following description, it is assumed that the A line is set as the line for calculating the mark threshold value Sm.

  First, (Xa, Ya) of the A line is acquired. (Xa, Ya) is acquired by using the mark threshold value Sm described in FIG. Then, position data (Xe, Ye) on the A line is acquired. (Xe, Ye) is acquired by using the mark threshold value Sm in the same manner as (Xa, Ya). (Xe, Ye) may be acquired based on the design value of the registration mark. )

Next, (Xb, Yb) is acquired. Here, Xb is acquired by using an offset value that is several dots away from Xa in the X direction. For example, assume that a position 10 dots away from Xa in the X direction is set as the offset value. In this case, first, using the mark threshold value Sm, it is detected that the C line (that is, Yb) is the edge of the registration mark. Then, among the detected Yb lines, position data of Xb that is 10 dots away from Xa is acquired. Thereby, (Xb, Yb) is acquired.

  Then, (Xc, Yc) is acquired. Here, Xc is acquired by using an offset value separated from Xe by several dots (for example, 10 dots) in the X direction. The acquisition method is the same as the method of acquiring Xb from Xa.

Then, (Xd, Yd) is acquired. Here, Yd is acquired by using an offset value separated from Yc by several dots (for example, 10 dots) in the Y direction. The acquisition method is the same as the method of acquiring Xb from Xa.
As described above, the four position data (Xa, Ya), (Xb, Yb), (Xc, Yc), (Xd, Yd) are acquired, and (X3, Y3) is obtained using the acquired position data. Desired.

  Next, with reference to FIG. 6 and FIG. 7, the mark position acquisition process executed in the image forming apparatus 1 will be described. The mark position acquisition process is a process of acquiring the position data of the paper edge and the registration mark of the paper P. In the mark position acquisition process described below, after image formation is performed on the front surface of the paper P, a writing position when the image is formed on the back surface of the paper P is detected, and image formation is performed according to the detected writing position. It is a part of the operation when performing.

  For example, in the image forming apparatus 1, a mark position acquisition program that is read from the ROM and appropriately expanded in the RAM 21 </ b> A is triggered by the input of the execution instruction of the mark position acquisition process by the user via the operation display unit 22. The mark position acquisition process is executed in cooperation with the CPU.

  It is assumed that image data of a document and a registration mark are formed in advance on the surface of a sheet. In addition, it is assumed that an input of timing for calculating the paper edge threshold Sp and the mark threshold Sm is received by the user via the operation display unit 22. That is, it is assumed that the timing input for acquiring A1 to An and B1 to Bn is accepted. Similarly, it is assumed that the predetermined magnification Kp (Km), the number N of measurement points, the acquisition interval of A1 to An (B1 to Bn), and the acquisition timing of A1 to An (B1 to Bn) are set in advance.

  First, it is determined whether or not data for calculating the paper leading edge threshold Sp1 has been acquired (step S101). The paper leading edge threshold Sp1 refers to the paper leading edge threshold Sp in Expression (1). The data for calculating the paper leading edge threshold Sp1 refers to data A1 to An in Expression (1). If it is determined that the paper leading edge threshold Sp1 has not been determined (step S101; NO), data acquisition is executed (step S102). Data acquisition in this step refers to acquiring data of A1 to An in Expression (1). After execution of step S102, the process proceeds to step S101.

  If it is determined in step S101 that data for calculating the paper leading edge threshold Sp1 has been acquired (step S101; YES), the calculation of the paper leading edge threshold Sp1 is executed (step S103). The calculation of the paper leading edge threshold Sp1 is executed based on the above-described equation (1).

  After execution of step S103, it is determined whether it is time to detect the leading edge of the paper (step S104). That is, it is determined whether or not the leading edge of the paper is being detected. If it is determined that it is time to detect the leading edge of the paper (step S104; YES), position data of the leading edge of the paper is acquired (step S105). That is, (X1, Y1) described in FIG. 3 is acquired. If it is determined that it is not time to detect the leading edge of the paper (step S104; NO), the process proceeds to step S104.

  After execution of step S105, it is determined whether or not data for calculating the paper lateral edge threshold Sp2 has been acquired (step S106). The paper lateral edge threshold Sp2 refers to the paper edge threshold Sp in the formula (1). The data for calculating the paper leading edge threshold Sp2 refers to data A1 to An in Expression (1). If it is determined that the data for calculating the paper lateral edge threshold Sp2 has not been acquired (step S106; NO), the data is acquired (step S107). Data acquisition in this step refers to acquiring data of A1 to An in Expression (1). After execution of step S107, the process proceeds to step S106.

  If it is determined in step S106 that data for calculating the paper horizontal edge threshold Sp2 has been acquired (step S106; YES), the paper horizontal edge threshold Sp2 is calculated (step S108). The calculation of the paper lateral edge threshold Sp2 is executed based on the equation (1).

  After the execution of step S108, it is determined whether or not it is time to detect the lateral edge of the paper (step S109). That is, it is determined whether or not it is in a state of detecting the lateral edge of the paper. When it is determined that it is time to detect the paper lateral edge (step S109; YES), the position data of the paper lateral edge is acquired (step S110). That is, (X2, Y2) described in FIG. 3 is acquired. If it is determined that it is not time to detect the horizontal edge of the paper (step S109; NO), the process proceeds to step S109.

  After execution of step S110, it is determined whether or not data for calculating the mark threshold value Sm has been acquired (step S111). The mark threshold value Sm refers to the mark threshold value Sm of Expression (2). The data for calculating the mark threshold value Sm refers to the data of B1 to Bn in Expression (2). If it is determined that data for calculating the mark threshold value Sm has not been acquired (step S111; NO), data is acquired (step S112). Data acquisition in this step refers to acquiring B1 to Bn in Expression (2). After execution of step S112, the process proceeds to step S111.

  When it is determined in step S111 that data for calculating the mark threshold value Sm has been acquired (step S111; YES), the mark threshold value Sm is calculated (step S113). The calculation of the mark threshold value Sm is executed based on Expression (2).

  After execution of step S113, it is determined whether or not it is time to detect a mark (step S114). That is, it is determined whether or not the registration mark is being detected. If it is determined that it is time to detect the mark (step S114; YES), the mark position data is acquired (step S115). That is, (Xa, Ya) to (Xd, Yd) described in FIG. 5 are calculated, and (X3, Y3) is acquired. If it is determined that the mark is not detected (step S114; NO), the process proceeds to step S114. After execution of step S115, the mark position acquisition process ends.

  As described above, according to the present embodiment, the line data is read at a predetermined timing from the RAM 21A in which the line data sequentially updated for each line is stored, and the paper edge threshold Sp and the mark are determined based on the read line data. The threshold value Sm is calculated, and the paper edge position data and the reference mark position data can be acquired based on the calculated paper edge threshold value Sp and mark threshold value Sm. Thereby, since it is not necessary to store all of the read line data in the RAM 21A, it is possible to detect (acquire) the paper edge and reference mark position data without using a large-capacity memory. Further, since the paper edge threshold Sp and the mark threshold Sm are calculated based on the line data read at a predetermined timing, the paper edge threshold Sp and the mark threshold can be calculated with a small amount of data. That is, the position data of the paper edge and the reference mark can be acquired at high speed.

  Further, it is possible to receive an input of timing for calculating the paper edge threshold Sp and the mark threshold Sm set by the user. Thereby, the user can freely set and input the timing for calculating the paper edge threshold value Sp and the mark threshold value Sm.

  Further, a value obtained by multiplying (A1 + A2 +... + An-1 + An) / N by Kp can be calculated as the paper edge threshold value Sm. Further, a value obtained by multiplying (B1 + B2 +... + Bn-1 + Bn) / N by Km can be calculated as the mark threshold value Sm.

  Further, the average value of the line data of a predetermined area of the line read by the CIS 14 at the portion outside the sheet can be calculated. Further, the average value of the line data of a predetermined area of the line read by the CIS 14 outside the reference mark on the sheet can be calculated. As a result, the paper edge threshold Sp and the mark threshold Sm can be calculated as values that are not affected by the paper passing state of the paper P. That is, the position data of the paper edge and the reference mark can be detected with high accuracy.

  Further, the paper edge threshold Sp is calculated, the paper edge position data is acquired based on the calculated paper edge threshold Sp, the mark threshold Sm is calculated after acquiring the paper edge position data, and the calculated mark The registration mark position data can be acquired based on the threshold value Sm.

  In addition, the detailed configuration and detailed operation of the image forming apparatus 1 in the above embodiment can be changed as appropriate without departing from the spirit of the present invention.

1 is a schematic configuration diagram of an image forming apparatus 1 according to the present invention. 2 is an internal configuration diagram of the image forming apparatus 1. FIG. It is a figure showing the output value of CIS14 at the time of detecting the position data of a paper edge part, and the position data of the intersection of a register mark. It is a figure which shows the calculation method of paper edge threshold value Sp and mark threshold value Sm. It is a figure which shows the positional data (X3, Y3) of the intersection of a registration mark. It is the figure which showed the flow of the mark position acquisition process. It is the figure which showed the flow of the mark position acquisition process. It is the figure which showed position data (X1, Y1), (X2, Y2), (X3, Y3).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11, 21 Control part 12 Laser part 13 Photosensitive drum 14 CIS
15 Registration roller 16 Fixing roller 21A RAM
22 Operation display unit 23 Image reading unit 24 Image processing unit 25 Printer unit 26 Detection unit 27 Conveying unit Sm Mark threshold Sp Paper edge threshold

Claims (5)

An image forming apparatus that detects a writing position when image data of a read original is formed on a sheet based on line data read by a line image sensor, and performs image formation according to the detected writing position.
A storage unit for sequentially updating and storing the line data for each line;
Line data is read from the storage unit at a predetermined timing, and based on the read line data, a first threshold for detecting a paper edge of the paper and a reference mark serving as a reference for the writing position are detected. A control unit that calculates a second threshold value for acquiring the position data of the paper edge and the position data of the reference mark based on the calculated first threshold value and the second threshold value;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, further comprising an input unit configured to receive an input of a timing for calculating the first threshold value and the second threshold value set by a user as the predetermined timing. The controller is
First line data, which is line data of a line read by the line image sensor at a portion outside the sheet, is read, and a value obtained by multiplying the read first line data by an arbitrary value is used as the first threshold value. Operate,
Second line data that is line data of a line read by the line image sensor at a portion other than the reference mark on the paper is read, and a value obtained by multiplying the read second line data by an arbitrary value is obtained. The image forming apparatus according to claim 1, wherein the image forming apparatus calculates the second threshold value. The controller is
An average value of line data of a predetermined area of a line read by the line image sensor at a portion outside the paper is calculated as the first line data,
4. The image forming apparatus according to claim 3, wherein an average value of line data of a predetermined area of a line read at a portion other than the reference mark on the paper by the line image sensor is calculated as the second line data. The controller is
The first threshold value is calculated, the paper edge position data is acquired based on the calculated first threshold value, the second edge value is calculated after acquiring the paper edge position data, and the calculation is performed. 5. The image forming apparatus according to claim 1, wherein position data of the reference mark is acquired based on the second threshold value.

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