JP2020154029A - Image formation device, sheet transfer device, and detection method of transfer speed - Google Patents

Abstract

To provide an image formation device that can correctly detect a transfer speed of a sheet and correct misalignment of a printing position with high accuracy.SOLUTION: An image formation device 10 comprises a scanner 200 for reading an image from a sheet transferred by an ADF 280. The image formation device 10 detects a transfer speed of the sheet based on a reading result by the scanner 200 of a speed detection chart for detecting the transfer speed of the sheet transferred by the ADF 280. The speed detection chart includes an image of a straight line having a predetermined slope with respect to the transfer direction of the sheet transferred by the ADF 280. The image formation device 10 detects the transfer speed based on a reading result of the straight line and a reading result of a reference for detecting a correct transfer speed by the scanner 200. The image formation device 10 generates a correction parameter for correcting a printing position based on the transfer speed.SELECTED DRAWING: Figure 1

Description

The present invention relates to a technique for accurately detecting the transport speed of a sheet.

The image forming apparatus generally has a double-sided printing function for forming an image on both sides of the sheet. When double-sided printing is performed, the position, magnification, and inclination of the formed image may change depending on the type of sheet such as sheet size, basis weight, and material. This causes a shift in the position (printing position) of the image formed on each of the front and back surfaces of the sheet. Such deviation of the printing position is corrected based on the distance from the sheet edge of the reference image, which is the reference of the printing position formed on the sheet. As a method of measuring the distance of the reference image from the sheet edge, there is a method of directly measuring by the user with a ruler or the like, or a method of measuring based on a reading result by an image reading device such as a scanner. Patent Document 1 discloses a technique for correcting a print position based on a reading result of a reference image by an image reading device. In this image reading device, for example, a reading unit for reading an image is provided in a transport path on which a sheet is transported, and a reference image is read from the sheet being transported.

When the length of the reference image (image length) with respect to the transport direction of the sheet is detected by using the image reading device, the image length is the time when the reading unit reads the reference image and the sheet passes through the reading position of the reading unit. It is calculated from the transport speed at the time. An accurate image length cannot be obtained unless the transfer speed of the sheet is kept constant or the transfer speed is detected with high accuracy. If the image length is inaccurate, a magnification error of the formed image will occur, and the deviation of the printing position will not be corrected accurately. Patent Document 2 discloses a method of detecting a sheet transport speed by forming predetermined images on a sheet at equal intervals and measuring the interval of reading time of the images.

Japanese Unexamined Patent Publication No. 2003-173109 Japanese Unexamined Patent Publication No. 2006-30451

If an image for detecting the transfer speed of the sheet is not accurately formed on the sheet in a predetermined shape, it becomes difficult to detect the transfer speed with high accuracy. However, the image may be deformed due to environmental conditions at the time of image formation, aging of the device, and the like. Therefore, a technique for accurately detecting the sheet transfer speed is required even when the image for detecting the sheet transfer speed is deformed.

Further, even when an image for detecting the conveying speed of the sheet is accurately formed at a predetermined position on the sheet, if the sheet is skewed when passing through the reading position of the reading unit, It becomes difficult to detect the transfer speed of the sheet with high accuracy. Therefore, a technique for accurately detecting the transport speed of the sheet is required even when the sheet is skewed.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of accurately detecting a sheet transport speed and correcting a deviation of a printing position with high accuracy.

The image forming apparatus of the present invention includes an image forming means for forming an image on a sheet, a conveying means for conveying the sheet on which an image is formed, and a reading means for reading an image from the sheet conveyed by the conveying means. The image forming means is formed with a detection chart for detecting the transfer speed of the sheet by the transfer means and a measurement chart for measuring the printing position of an image formed on the sheet on the sheet. The transport speed of the sheet is detected based on the reading result of the detection chart by the reading means, and the image is printed on the sheet based on the reading result of the reading means of the measurement chart and the transport speed. The control means includes a control means for controlling the position, and the control means forms a linear image having a predetermined gradient with respect to the transport direction of the sheet by the transport means on the image forming means as the detection chart. It is characterized by letting it.

According to the present invention, the sheet conveying speed can be accurately detected, and a correction parameter for correcting the deviation of the printing position with high accuracy can be generated.

The configuration explanatory view of the image forming apparatus. (A) and (b) are block diagrams of a controller. Explanatory drawing of the chart for printing position measurement. Explanatory drawing of the chart for speed detection. Explanatory drawing of reading result of chart for speed detection. (A) and (b) are explanatory views when an image is deformed by a secondary transfer part. An exemplary diagram of the original speed detection chart. An example diagram of a deformed speed detection chart. Another exemplary diagram of the deformed velocity detection chart. Explanatory drawing of the detection method of the sheet transport speed. Explanatory drawing of the detection method of the sheet transport speed. A flowchart showing a calculation process of a sheet transport speed. (A) and (b) are explanatory views of the reading result when the sheet is skewed. (A) and (b) are explanatory views of the method of detecting the transport speed when a sheet is skewed. A flowchart showing a correction value calculation process of a sheet transport speed. (A) and (b) are explanatory views of the method of detecting the transport speed when a sheet is skewed. A flowchart showing a correction value calculation process of a sheet transport speed. Explanatory drawing of the chart for speed detection. Explanatory drawing of reading result of chart for speed detection. Explanatory drawing of the chart for speed detection at the time of skewing. (A) and (b) are explanatory views of the reading result when the sheet is skewed. A flowchart showing a correction value calculation process of a sheet transport speed. The explanatory view of the reading result when the fluctuation of ΔSn becomes a curve. The configuration explanatory view of the image forming apparatus.

Hereinafter, embodiments will be described in detail with reference to the drawings.

(overall structure)
FIG. 1 is a configuration explanatory view of the image forming apparatus of the present embodiment. The image forming apparatus 10 of the present embodiment includes an image reading device (scanner 200) at the top. The scanner 200 reads an image from the sheet S and generates image data representing the read image. The scanner 200 transmits the generated image data to the image forming apparatus 10. The image forming apparatus 10 forms an image on a sheet based on a print job (including image data) acquired from an external device such as a personal computer and image data acquired from the scanner 200.

(Image forming device)
The image forming apparatus 10 includes a plurality of image forming units 101y, 101m, 101c, 101k and an exposure device 103 for image forming. The image forming unit 101y forms a yellow image. The image forming unit 101m forms a magenta image. The image forming unit 101c forms a cyan image. The image forming unit 101k forms a black image. The image forming portions 101y, 101m, 101c, 101k include photosensitive drums 102y, 102m, 102c, 102k on which an image is formed.

Each of the photosensitive drums 102y, 102m, 102c, and 102k is rotationally driven at a predetermined speed by a motor (not shown). The rotating photosensitive drums 102y, 102m, 102c, 102k are uniformly charged. The exposure device 103 irradiates the charged surfaces of the photosensitive drums 102y, 102m, 102c, and 102k with a laser beam modulated based on the image data, so that the photosensitive drums 102y, 102m, 102c, and 102k are electrostatically latent. To form. The electrostatic latent image is developed with a developer (eg, toner) of the corresponding color. A yellow toner image is formed on the photosensitive drum 102y. A magenta toner image is formed on the photosensitive drum 102 m. A cyan toner image is formed on the photosensitive drum 102c. A black toner image is formed on the photosensitive drum 102k.

An annular intermediate transfer belt 104 is arranged above the photosensitive drums 102y, 102m, 102c, and 102k. Primary transfer rollers 105y, 105c, 105m, 105k are provided at positions facing the photosensitive drums 102y, 102m, 102c, 102k with the intermediate transfer belt 104 interposed therebetween. The toner images of each color formed on the photosensitive drums 102y, 102m, 102c, and 102k are sequentially transferred to the intermediate transfer belt 104 by the primary transfer rollers 105y, 105c, 105m, and 105k. The photosensitive drums 102y, 102m, 102c, and 102k are arranged at predetermined intervals with respect to the surface on which the toner image of the intermediate transfer belt 104 is transferred. The intermediate transfer belt 104 rotates counterclockwise in the figure. By transferring the toner image of each color at the timing corresponding to the arrangement of the photosensitive drums 102y, 102m, 102c, 102k and the rotation speed of the intermediate transfer belt 104, the toner image of each color is the same on the intermediate transfer belt 104. It is formed so as to overlap the position. As a result, a full-color image (toner image) is formed on the intermediate transfer belt 104. The intermediate transfer belt 104 functions as an image carrier that carries an image.

Below the exposure device 103, accommodating portions 110a and 110b for accommodating sheets on which an image is formed are provided. The sheets accommodated in the accommodating portions 110a and 110b are fed by the paper feed rollers and conveyed along the conveying path. A registration roller 111, a secondary transfer unit 106, a fixing device 107, and a paper ejection roller 112 are provided on the transport path. The registration roller 111 conveys the conveyed sheet to the secondary transfer unit 106. The secondary transfer unit 106 transfers the image (toner image) supported on the intermediate transfer belt 104 to the sheet. Therefore, the registration roller 111 controls the transfer timing and transfer speed of the sheet to the secondary transfer unit 106 in accordance with the timing at which the image is transferred to the secondary transfer unit 106 by rotating the intermediate transfer belt 104.

When the image on the intermediate transfer belt 104 and the sheet pass through the secondary transfer unit 106, the voltage applied to the secondary transfer unit 106 from the power supply unit (not shown) causes the image on the intermediate transfer belt 104 to be transferred to the sheet. Transferred. A belt cleaner 108 is provided in the vicinity of the intermediate transfer belt 104. The belt cleaner 108 cleans the toner remaining on the intermediate transfer belt 104 after being transferred to the sheet.

The secondary transfer unit 106 conveys the sheet on which the image is transferred to the fixing device 107. The fuser 107 has a plurality of rollers and heaters. The fixing device 107 heats and pressurizes the image on the sheet to fix the image on the sheet. The sheet on which the image is fixed by the fixing device 107 is discharged from the image forming apparatus 10 by the paper ejection roller 112 as a deliverable.

When operating in the double-sided printing mode in which an image is formed on both sides of a sheet, the image forming apparatus 10 conveys the sheet on which an image is formed on one side (first side) to the registration roller 111 again. Therefore, the image forming apparatus 10 includes a double-sided path 114. The sheet on which the image is formed on the first surface is discharged to the outside of the machine halfway by the paper ejection roller 112, and then is guided to the double-sided path 114 by the reverse rotation of the paper ejection roller 112. As a result, the surface on which the image is formed is inverted from the first surface to the other surface (second surface) of the sheet. The sheet is conveyed to the registration roller 111 through the double-sided pass 114. After that, the sheet is discharged to the outside of the machine after the image is formed on the second surface by the same process as when the image is formed on the first surface. As a result, a product in which images are formed on both sides of the sheet can be obtained.

(Scanner)
The scanner 200 is provided with an ADF (Auto Document Feeder) 280 that conveys the sheet S above. The scanner 200 includes a scanning glass 230 on the surface on which the ADF 280 is provided. The scanner 200 includes a scanner unit 404 having a lamp 402 as a light emitting unit, mirrors 405 and 406, a lens 407, and an image sensor 408 in order to read an image. When reading an image from the sheet S, the scanner unit 404 irradiates the sheet S with light. The reflected light from the sheet S is guided to the image sensor 408 via the mirrors 405 and 406 and the lens 407. The image sensor 408 outputs image data representing the image of the sheet S based on the received reflected light.

The scanner 200 can stop the scanner unit 404 directly under the scanning glass 230 and read the image of the sheet S when the sheet S conveyed by the ADF 280 passes through the scanning glass 230. The process of stopping the scanner unit 404 and reading the image of the sheet S conveyed by the ADF280 is called "scanning". In the present embodiment, the scanner 200 reads a reference image described later formed on the sheet S by scanning. Further, the scanner unit 404 can read an image while moving in the direction of the arrow in the drawing.

The ADF280 includes a seat tray 211 on which one or more sheets S can be loaded, a transport path, and a discharge tray 219. The ADF280 is a sheet transport device that transports a sheet placed on the sheet tray 211 to the discharge tray 219 via a transport path. A paper feed roller 201, a separation roller 203, a separation pad 204, a transport roller pair 224, and a discharge roller pair 216 are arranged in the transport path for transporting the sheet S. A sensor flag 225 is provided on the downstream side of the transfer roller pair 224 in the transfer direction of the sheet S. Further, a flapper 215 is provided on the upstream side of the discharge roller pair 216.

When the user places the sheet S on the sheet tray 211 and instructs the start of execution of the copy or scan process, the sheet S is taken into the transport path by the paper feed roller 201. When a plurality of sheets S are loaded, the paper feed roller 201 sequentially takes in the sheets S from the top. The separation roller 203 and the separation pad 204 cooperate to separate and feed the captured sheets S one by one. The sheet S separated into one sheet is conveyed to the transfer roller pair 224 by the separation roller 203. The transport roller pair 224 transports the sheet S to the discharge roller pair 216 via the upper part of the scanning glass 230. When the sheet S passes over the scanning glass 230, the image is read by the scanner 200. The sheet S from which the image is read is discharged to the discharge tray 219 by the discharge roller pair 216.

A white plate 223 is provided above the scanning glass 230 in order to stabilize the transportability of the sheet S on the scanning glass 230. The white plate 223 is arranged with a predetermined gap with respect to the scanning glass 230. The sheet S is conveyed between the white plate 223 and the scanning glass 230 when the image is read.

When the image is read from both sides of the sheet S, the front and back surfaces of the sheet S are reversed after passing over the scanning glass 230. Therefore, the discharge roller pair 216 temporarily stops and rotates in the reverse direction when the rear end of the seat S passes the position of the flapper 215. When the discharge roller pair 216 rotates in the reverse direction, the sheet S is transported to the transport roller pair 224 via the reversing transport path 217. As a result, the surface of the sheet S that is read by the scanner 200 is inverted.

The transport roller pair 224 always rotates in the direction of transporting the sheet S to the scanning glass 230 (forward feed direction) regardless of the rotation direction of the discharge roller pair 216. The sensor flag 225 provided on the downstream side of the transport roller pair 224 detects that the tip of the sheet S has reached the transport roller pair 224 by discriminating the signal of the sensor. After the sheet S is sandwiched between the transport rollers pair 224, the two rollers constituting the discharge roller pair 216 are separated from each other.

The transport roller pair 224 transports the sheet S transported through the reversing transport path 217 to the discharge roller pair 216 again via the scan glass 230. At this time, the image of the back surface of the sheet S is read by the scanner 200. The repressurization of the discharge roller pair 216 is performed when the rear end of the sheet S in the reversing transport path 217 has passed through the discharge roller pair 216. As a result, in the discharge roller pair 216, it is prevented that the transport direction of the long sheet and the transport direction of the discharge roller pair 216 are different from each other. The sheet S whose back surface has been read passes through the reverse transfer path 217 again in order to align the page order, and is discharged to the discharge tray 219 by the discharge roller pair 216 via the transport roller pair 224 and the scanning glass 230. To.

(controller)
FIG. 2 is a configuration diagram of a controller that controls the operation of the image forming apparatus 10. FIG. 2A shows the hardware configuration of the controller 1. FIG. 2B shows a functional block of the controller 1.

The controller 1 is an information processing device including a CPU (Central Processing Unit) 301, a ROM (Read Only Memory) 302, a RAM (Random Access Memory) 303, and a storage 304. The CPU 301, ROM 302, RAM 303, and storage 304 communicate with each other via a bus. The CPU 301 controls the operations of the image forming apparatus 10, the scanner 200, and the ADF 280 by executing a computer program stored in the ROM 302 or the storage 304 using the RAM 303 as a work area. The storage 304 stores image data acquired from the scanner 200 or an external device, and various setting information.

By executing a computer program, the CPU 301 functions as an image processing unit 210, a sheet management table 400, a print position calculation unit 213, and a pattern generator 70 in cooperation with the RAM 303 and the storage 304. The image processing unit 210 includes a print position correction unit 311. The operation unit 20 and the scanner 200 are connected to the controller 1 to control the operation of the printer engine 150. The printer engine 150 includes an image forming unit 101y, 101m, 101c, 101k, an exposure device 103, a secondary transfer unit 106, and a fixing device 107.

The operation unit 20 is a user interface having an input device and an output device. The input device is, for example, a key button, a touch panel, or the like. The key buttons are, for example, a start key for instructing the start of execution of processing such as scanning and copying, a stop key for instructing stopping of processing such as scanning and copying, and a numeric keypad. The output device is a display, a speaker, or the like. The operation unit 20 receives an input such as an instruction or setting information operated by the user and inputs the input to the controller 1. The operation unit 20 provides information to the user on the display based on the control of the controller 1.

The image processing unit 210 corrects the image data by performing various image processing. In the present embodiment, the image processing unit 210 is realized by the CPU 301, but may be realized by a semiconductor device such as an ASIC (Application Specific Integrated Circuit). The image data corrected by the image processing unit 210 is transmitted to the exposure device 103 of the printer engine 150. The exposure device 103 irradiates the photosensitive drums 102y, 102m, 102c, and 102k with laser light based on the image data corrected by the image processing unit 210 at the time of image formation.

The print position correction unit 311 corrects the image data so that the image formation position (print position) with respect to the sheet becomes the target position. The print position of the image formed on the sheet may not be the target position. For example, when the sheet conveyed by the registration roller 111 is skewed, the skewed sheet passes through the secondary transfer unit 106, so that the image is formed at an angle with respect to the sheet. Further, for example, if the pressure distribution of the rollers of the fixing device 107 is not uniform, the sheet passing through the fixing device 107 may be deformed and the image on the sheet may be tilted. Further, for example, in double-sided printing, when an image is formed on the first surface, the sheet expands and contracts due to the heat and pressure of the fixing device 107, and the size of the image formed on the first surface of the sheet and the second surface of the sheet. The size of the image formed in may be different. In this case, the printing position of the image printed on the first surface of the sheet and the printing position of the image printed on the second surface of the sheet are different.

The inclination of the sheet passing through the secondary transfer unit 106 and the amount of deformation of the sheet by the fixing device 107 are highly reproducible if the types of sheets such as size, basis weight, and material are the same. Therefore, the image forming apparatus 10 of the present embodiment corrects the image data formed according to the amount of deformation so that the printing position of the image on the sheet becomes the ideal printing position (target position).

Therefore, the print position correction unit 311 corrects the image data based on the conversion formula for correcting the deviation of the print position of the image with respect to the sheet stored in the sheet management table 400. The sheet management table 400 stores the amount of deviation of the print position generated by the print position calculation unit 213, which will be described later, and the conversion formula for correcting the amount of deviation for each type of sheet. The printer engine 150 forms an image based on the image data converted by the print position correction unit 311. As a result, an image that offsets the deviation of the image formation position with respect to the sheet is formed on the intermediate transfer belt 104.

The pattern generator 70 generates image data (print position measurement image data) of a print position measurement chart for measuring the amount of deviation of the print position from the target position. When the print position adjustment is executed to measure the amount of deviation of the print position from the target position, the image data for print position measurement is transmitted from the pattern generator 70 to the printer engine 150. The printer engine 150 that has acquired the image data for print position measurement outputs a sheet on which the chart for print position measurement is formed as a deliverable. An image in which a reference image is combined is formed on this sheet as a chart for measuring the printing position. The print position measurement chart formed on the sheet is read by the scanner 200 in order to detect the print position of the reference image. The scanner 200 transmits the reading result of the print position measurement chart to the print position calculation unit 213.

The sheet on which the print position measurement chart is formed is read by the scanner 200 while being conveyed by the ADF280. At this time, in the present embodiment, the transport speed of the sheet S is calculated with high accuracy. The high-precision detection process of the transport speed will be described later.

The print position calculation unit 213 calculates the correction parameters stored in the sheet management table 400 from the coordinate data of the reference image included in the print position measurement chart read by the scanner 200. The print position calculation unit 213 stores the calculated correction parameters in the sheet management table 400. The print position correction unit 311 determines the print position based on the correction parameters.

(Print position adjustment)
FIG. 3 is an explanatory diagram of a chart for measuring the printing position. The image forming apparatus 10 forms a print position measurement chart on the sheet in response to an instruction from the operation unit 20 by the user. The print position measurement chart includes a measurement test pattern 802 for the front surface and a measurement test pattern 803 for the back surface. In the measurement test patterns 802 and 803, a plurality of reference images are composed of 820. The reference image 820 is formed near the four corners on both sides of the sheet.

In the print position measurement chart, the measurement test patterns 802 and 803 formed on both sides of the sheet are read by the scanner 200. The print position calculation unit 213 detects the coordinates of the four corners of the front surface and the back surface of the sheet and the coordinates (positions) of the reference image 820 of the front surface and the back surface based on the reading result of the scanner 200.
Coordinates of the four corners of the front side of the sheet: (X01, Y01) to (X31, Y31)
Coordinates of the reference image 820 on the front surface: (X41, Y41) to (X71, Y71)
Coordinates of the four corners of the back surface of the sheet: (X02, Y02) to (X32, Y32)
Coordinates of the reference image 820 of the back surface: (X42, Y42) to (X72, Y72)

The print position calculation unit 213 measures the amount of distortion of the image and the amount of deviation of the position of the reference image 820 with respect to the sheet based on these coordinates. The print position calculation unit 213 calculates correction parameters (lead position, side position, magnification, right angle, rotation amount, etc.) based on these measurement results. The print position calculation unit 213 stores the calculated correction parameter in the sheet management table 400 as a geometric adjustment amount. The correction parameters include a front surface parameter and a back surface parameter, which are stored in the sheet management table 400, respectively. The print position correction unit 311 corrects the image data using the correction parameters. As a result, the geometrical features (printing position, shape) of the image formed according to the image data are corrected (printing position adjustment).

The sheet transfer speed by the scanner 200 when reading the print position measurement chart for calculating the correction parameter varies depending on the paper type, the aging of the transfer roller pair 224, the temperature and humidity, and other environmental conditions. The print position calculation unit 213 analyzes the reading result of the print position measurement chart in consideration of the sheet transport speed, and generates a correction parameter. Therefore, it is necessary to accurately detect the transport speed of the sheet.

(Sheet transfer speed)
FIG. 4 is an explanatory diagram of a speed detection chart used for detecting the transport speed at the time of reading a sheet by the scanner 200. The speed detection chart 850 is an image of a straight line 851 having a predetermined gradient θ with respect to the sheet conveying direction. The scanner 200 (scanner unit 404) reads the speed detection chart 850 from the sheet conveyed by the ADF 280. The scanner 200 is a line sensor that reads the speed detection chart 850 line by line. The direction of reading line by line is the main scanning direction, and the transport direction of the speed detection chart 850 is the sub-scanning direction.

FIG. 5 is an explanatory diagram of the reading result of the speed detection chart 850. In FIG. 5, the reading results 861 and 862 of the speed detection chart 850 are represented as Y-t graphs in which the horizontal axis is time and the vertical axis is the distance in the main scanning direction. The Yt graph represents the position of the straight line 851 for each reading time. The reading result 861 and the reading result 862 are different in the carrying speed of the speed detection chart 850 at the time of reading. Since the reading result 861 has a higher transport speed than the reading result 862, the reading time (elapsed time from the start of reading) is shorter.

The reading result of the straight line 851 of the speed detection chart 850 differs in the reading time T at the same position in the main scanning direction of the straight line 851 depending on the gradient θ of the straight line 851 and the sheet transport speed. The reading result 861 is a straight line having an angle θH with respect to the time axis because the transport speed is high. The reading result 862 is a straight line with a θL smaller than the angle θH with respect to the time axis because the transport speed is slow. That is, assuming that the speed when the sheet transport speed is high is VH and the speed when the sheet is slow is VL, the following equation holds.
When θH> θL VH> VL

This equation indicates that the transport speed can be obtained by measuring the angle θ of a straight line representing the reading result with respect to the time axis. In the present embodiment, the transport speed is calculated based on this. The print position calculation unit 213 records the difference between the calculated transfer speed and the ideal transfer speed as an adjustment value, and corrects the reading result of the print position measurement chart based on the adjustment value to adjust the print position. Do it accurately. The calculation of the sheet transport speed is not limited to the speed detection chart 850, and for example, the reference image 820 of the print position measurement chart and the straight line 851 of the speed detection chart 850 are formed on one sheet for measurement. It may be done using a chart. By using such a measurement chart, it is possible to adjust the printing position and calculate the transport speed at the same time.

(Image transformation)
The straight line 851 of the speed detection chart 850 may be distorted in shape or deformed in size at the stage of image formation. In this case, the sheet transport speed is not accurately detected. For example, when the image is transferred by the secondary transfer unit 106, the sheet is skewed, so that the straight line 851 is distorted. FIG. 6 is an explanatory diagram when the image is deformed by the secondary transfer unit 106. As shown in FIG. 6A, in the secondary transfer unit 106, the sheet transport speed is slower on the left side in the sheet transport direction than on the right side. Therefore, the seat turns counterclockwise. FIG. 6B illustrates a straight line formed on a swivel seat. In contrast to the straight line 641 that should be originally formed as shown by the dotted line, the curve 651 shown by the solid line is actually formed on the sheet.

With the above method for detecting the transport speed of the sheet, it is difficult to detect the transport speed based on the curve 651. In the present embodiment, a technique for detecting the transport speed of the sheet even when the curve 651 is formed on the sheet will be described.

FIG. 7 is an example diagram of an original speed detection chart without deformation, which is used when actually calculating the sheet transfer speed of the present embodiment. As for the speed detection chart, the image data of the speed detection chart is generated by the pattern generator 70 in the same manner as the print position measurement chart. The printer engine 150 acquires this image data from the pattern generator 70 and performs an image forming process to generate a speed detection chart.

The deformation-free speed detection chart is composed of a plurality of straight lines having different gradients (two straight lines 641 and 642 in this embodiment). However, when the seat turns as described above, the straight lines 641 and 642 are deformed into a curved line. FIG. 8 is an example diagram of a deformed speed detection chart when the seat turns. Here, the straight lines 641 and 642 that should be originally formed are transformed into curves 651 and 652. The two straight lines 641 and 642 are similarly deformed to form curves 651 and 652. Therefore, the relative positional relationship between the straight line 641 and the straight line 642 and the relative positional relationship between the curve 651 and the curve 652 are not affected by the turning of the seat. This means that the difference in gradient between the curve 651 and the curve 652 is canceled and coincides with the difference in the gradient between the straight line 641 and the straight line 642.

FIG. 9 is another exemplary diagram of the deformed velocity detection chart. In FIG. 9, the original straight lines 641 and 642 are transformed into straight lines 661 and 662 by changing the magnification. In this case as well, the two straight lines 641 and 642 are transformed into straight lines 661 and 662 in the same manner. Therefore, the relative positional relationship between the straight line 641 and the straight line 642 and the relative positional relationship between the straight line 661 and the straight line 662 are not affected by the change in magnification. This means that the difference in slope between the straight line 661 and 662 coincides with the difference in slope between the straight line 641 and the straight line 642, with the deformation component canceled.

From the above, even when the image formed on the sheet is deformed, the deformation component is canceled by detecting the transport speed of the sheet based on the difference between the gradients of at least two images. Therefore, the sheet transfer speed can be detected with high accuracy by the difference in gradient. 10 and 11 are explanatory views of a method of detecting the transport speed of the sheet in this case.

As shown in FIG. 10, the original speed detection chart includes straight lines 641 and 642 having a length of X in the sub-scanning direction (conveying direction). The length of the straight line 641 in the main scanning direction is Y2, and the length of the straight line 642 in the main scanning direction is Y1. The transport speed V at the time of scanning the speed detection chart is expressed by the formula “V = X / t”, where t is the time for the straight lines 641 and 642 to pass through the reading position of the scanner 200.

The difference in the gradients of the two straight lines 641 and 642 is the difference ΔY between the lengths Y1 and Y2 of the two straight lines 641 and 642 in the main scanning direction. The angle θ formed by the difference ΔY and the length X in the sub-scanning direction as shown in FIG. 11 is expressed by the equation “tan θ = ΔY / X”. Since tan θ is the difference between the gradients of the two straight lines 641 and 642, the deformation component of the image at the time of image formation is cancelled. Therefore, the value of tan θ is constant regardless of the presence or absence of deformation during image formation. That is, at any timing when the straight lines 641 and 642 pass through the reading position of the scanner 200, it is calculated from the difference in length in the main scanning direction and the length in the sub-scanning direction of the straight lines 641 and 642 read at that time. The tan θ produced does not change.

From the equation of tanθ, the length X in the sub-scanning direction is “X = ΔY / tanθ”. Substituting the equation of the length X in the sub-scanning direction into the equation of the transport speed V, it becomes “V = ΔY / tan θ / t”. This equation is transformed as "ΔY = V × tan θ × t". In this modification, the vertical axis of the Yt graph of FIG. 5 is ΔY, and the slope α of the reading result is a value obtained by multiplying the transport speed V by the constant tan θ. That is, “α = V × tan θ”. This equation is transformed as "V = α / tan θ". That is, the transport speed V is a value obtained by dividing the slope α of the Yt graph by the constant tan θ (tangent of θ).

FIG. 12 is a flowchart showing a sheet transport speed calculation process performed using the formula for calculating the transport speed. This process is executed when the image position adjustment process is performed.

When the CPU 301 receives an image position adjustment instruction from the operation unit 20 (S101), the printer engine 150 performs an image forming process of the speed detection chart illustrated in FIG. 7. The image forming process of the speed detection chart is performed by transmitting the image data of the speed detection chart from the pattern generator 70 to the printer engine 150. The printer engine 150 generates a speed detection chart by forming an image corresponding to the image data of the speed detection chart on the sheet. The image forming apparatus 10 outputs the generated speed detection chart (S102).

The output speed detection chart is manually placed on the seat tray 211 of the ADF280 by the user. The user instructs the CPU 301 to perform image reading processing using the ADF 280 by the operation unit 20. Upon receiving this instruction, the CPU 301 controls the operations of the ADF 280 and the scanner 200 to scan the speed detection chart mounted on the sheet tray 211. The reading result of the speed detection chart is transmitted from the scanner 200 to the print position calculation unit 213 (S103).

The print position calculation unit 213 acquires a Yt graph from the reading result of the speed detection chart. The print position calculation unit 213 calculates the difference ΔY of the lengths in the main scanning direction, and calculates the slope α of the ΔY−t graph. The print position calculation unit 213 calculates the sheet transfer speed by the formula “V = α / tan θ” based on the calculated inclination α (S104). The print position calculation unit 213 stores the calculated transfer speed in the sheet management table 400 (S105).

By the above processing, the sheet conveying speed is detected with high accuracy even when the speed detection chart is deformed. The print position calculation unit 213 acquires the reading result of the print position measurement chart after detecting the transport speed. The print position calculation unit 213 generates a print position correction parameter based on the reading result of the print position measurement chart and the transport speed, and stores it in the sheet management table 400. The image processing unit 210 can adjust the printing position with high accuracy by correcting the image data using the correction parameters stored in the sheet management table 400 and causing the printer engine 150 to form an image.

(Slanting of the sheet when reading)
When the sheet on which the speed detection chart is formed is read by the scanner 200, the reading position may be skewed. In this case, even if the speed detection chart is not deformed, the sheet transfer speed is not accurately detected. An embodiment of the transport speed detection process when the sheet is skewed will be described below.

・ Example 1
FIG. 13 is an explanatory diagram of the reading result of the speed detection chart 850 when the sheet is skewed. Let VR be the transport speed of the sheet. The angle of the straight line 851 with respect to the transport direction obtained from the reading result when the sheet is not skewed is θR (dotted line). When the sheet is skewed, the length Y in the main scanning direction and the time T required for detection deviate from the case where the sheet is not skewed. The angle of the straight line 851 obtained from the reading result when the sheet is skewed with respect to the transport direction is θS (solid line). That is, even if the transport speed VR is the same, the angle of the reading result of the straight line 851 with respect to the transport direction changes due to skewing, which makes it difficult to accurately detect the transport speed.

FIG. 13A illustrates a case where the sheet is skewed counterclockwise. Therefore, as shown in FIG. 13B, the angle of the straight line 851 with respect to the transport direction has a relationship of θS> θR. When the sheet is skewed clockwise, θS <θR. If it is not skewed, θS = θR.

FIG. 14 is an explanatory diagram of a method of detecting a transport speed when the sheet is skewed. In FIG. 14A, the angle θS of the straight line 851 is detected from the reading result of the speed detection chart, and the angle θE with respect to the transport direction of the edge 850a of the sheet on which the speed detection chart 850 is formed is detected. .. As shown in FIG. 14B, the angle θE of the sheet edge 850a is the skew angle of the sheet. Therefore, “θS−θE = θR”. That is, by detecting the angle θS and the angle θE, the original angle θR can be detected and the accurate transfer speed can be detected.

FIG. 15 is a flowchart showing a correction value calculation process for the sheet transport speed. This process is executed when the image position adjustment process is performed.

When the CPU 301 receives an image position adjustment instruction from the operation unit 20, the printer engine 150 performs an image forming process of the speed detection chart 850 as illustrated in FIG. 14A. The image forming process of the speed detection chart 850 is performed by transmitting the image data of the speed detection chart from the pattern generator 70 to the printer engine 150. The printer engine 150 generates a speed detection chart 850 by forming an image corresponding to the image data of the speed detection chart on the sheet. The image forming apparatus 10 outputs the generated speed detection chart 850 (S201). A speed detection chart 850 is generated by forming a straight line 851 having a gradient θR with respect to the sheet conveying direction on the sheet.

The output speed detection chart 850 is manually placed on the seat tray 211 of the ADF280 by the user. The user instructs the CPU 301 to perform image reading processing using the ADF 280 by the operation unit 20. Upon receiving this instruction, the CPU 301 controls the operations of the ADF 280 and the scanner 200 to scan the speed detection chart 850 mounted on the sheet tray 211. The reading result of the speed detection chart 850 is transmitted from the scanner 200 to the print position calculation unit 213.

The print position calculation unit 213 detects the angle θS of the straight line and the angle θE of the edge 850a of the sheet from the reading result of the speed detection chart 850 (S202, S203). The print position calculation unit 213 compares the value obtained by subtracting the angle θE from the detected angle θS with the gradient θR (S204, S205). The print position calculation unit 213 determines the correction value of the transport speed according to the comparison result. When (θS−θE) −θR> 0, the print position calculation unit 213 stores the positive correction value in the sheet management table 400 and ends the process (S206). When (θS−θE) −θR = 0, the print position calculation unit 213 ends the process without storing the correction value. When (θS−θE) −θR <0, the print position calculation unit 213 stores the negative correction value in the sheet management table 400 and ends the process (S207). The sheet transport speed is corrected and detected according to the correction value.

-Example 2
FIG. 16 is an explanatory diagram of a method of detecting a transport speed when the sheet is skewed. In FIG. 16A, the angle θES of the straight line 851 with respect to the edge 850a of the sheet on which the speed detection chart is formed is detected from the reading result of the speed detection chart. As shown in FIG. 16B, the angle θES representing the relative position between the straight line 851 and the edge 850a of the sheet is a fixed value regardless of the presence or absence of skew, and is “θES = θR”. That is, by detecting the relative position between the straight line 851 and the edge 850a of the sheet, the original angle θR can be detected and the accurate transfer speed can be detected.

FIG. 17 is a flowchart showing a correction value calculation process for the sheet transport speed. This process is executed when the image position adjustment process is performed.

When the CPU 301 receives an image position adjustment instruction from the operation unit 20, the printer engine 150 performs an image forming process of the speed detection chart 850 as illustrated in FIG. 14A. The image forming process of the speed detection chart 850 is performed by transmitting the image data of the speed detection chart from the pattern generator 70 to the printer engine 150. The printer engine 150 generates a speed detection chart 850 by forming an image corresponding to the image data of the speed detection chart on the sheet. The image forming apparatus 10 outputs the generated speed detection chart 850 (S301). A speed detection chart 850 is generated by forming a straight line 851 having a gradient θR with respect to the sheet conveying direction on the sheet.

The output speed detection chart 850 is manually placed on the seat tray 211 of the ADF280 by the user. The user instructs the CPU 301 to perform image reading processing using the ADF 280 by the operation unit 20. Upon receiving this instruction, the CPU 301 controls the operations of the ADF 280 and the scanner 200 to scan the speed detection chart 850 mounted on the sheet tray 211. The reading result of the speed detection chart 850 is transmitted from the scanner 200 to the print position calculation unit 213.

The print position calculation unit 213 detects the angle θES representing the relative position between the straight line 851 and the edge 850a of the sheet from the reading result of the speed detection chart 850 (S302). The print position calculation unit 213 compares the detected angle θES with the gradient θR (S303). The print position calculation unit 213 determines the correction value of the transport speed according to the comparison result. When θES−θR> 0, the print position calculation unit 213 stores the positive correction value in the sheet management table 400 and ends the process (S304). When θES−θR = 0, the print position calculation unit 213 ends the process without storing the correction value. When θES−θR <0, the print position calculation unit 213 stores the negative correction value in the sheet management table 400 and ends the process (S305). The sheet transport speed is corrected and detected according to the correction value.

・ Example 3
FIG. 18 is an explanatory diagram of a speed detection chart. A single scanner unit 404 or a plurality of scanner units 404 are arranged in the main scanning direction. The speed detection chart 850 is an image of straight lines 851 and 852 having a predetermined gradient θ with respect to the sheet transport direction (sub-scanning direction). The straight line 851 and the straight line 852 are arranged so as to be symmetrical with respect to the center line in the main scanning direction (direction orthogonal to the transport direction). Therefore, the straight line 851 and the straight line 852 have the same inclination with respect to the center line in the main scanning direction, but have different positive and negative signs.

The chart width H853, which is the length of the sheet in the main scanning direction, can be detected from the reading result of the speed detection chart 850 by scanning. The chart width H853 provides a center value h854 in the main scanning direction for each unit time of the speed detection chart 850. The number of measurements of the center value h854 is determined by the transport speed of the sheet on which the speed detection chart 850 is formed and the performance of the scanner 200. When the number of measurements is n (n is a natural number), "h1 to hn" is calculated as the center value h854 based on the chart width H853.

From the reading result of the speed detection chart 850 by scanning, the coordinates of the straight line 851 are read every unit time. The distance Ln between the coordinate ln in the main scanning direction of the straight line 851 and the center value h854 (hn) at that time is “Ln = ln−hn”. Similarly, the distance Rn between the coordinate rn in the main scanning direction of the straight line 852 and the center value h854 (hn) at that time is “Rn = rn−hn”.

FIG. 19 is an explanatory diagram of the reading result of such a speed detection chart 850. In FIG. 19, the distances L1 to Ln obtained from the reading result of the straight line 851 and the distances R1 to Rn obtained from the reading result of the straight line 852 are shown for each measurement time. When the sheet is read without skewing, the distance Ln and the distance Rn become equal at each measurement time. Assuming that the difference between the distance Ln and the distance Rn is ΔSn, ΔSn becomes “0” when the sheet is read without skewing.

FIG. 20 is an explanatory diagram of a speed detection chart at the time of skewing. When the sheet is skewed, the position of the speed detection chart 850 (solid line) is swiveled in the main scanning direction as compared with the speed detection chart 850 (dotted line) when the sheet is not skewed. As a result, the distance Ln and the distance Rn at each measurement time are not equal, and ΔSn is not “0”. That is, when the sheet is read while skewing, the coordinates of the straight lines 851 and 852 obtained from the reading result of the speed detection chart 850 change from the case where the sheet is not skewed, and accurate sheet transport speed detection can be performed. It will be difficult. When the sheet rotates clockwise and skews, the distance Ln becomes larger than the distance Rn and ΔSn <0. When the sheet rotates counterclockwise and skews, the distance Ln becomes smaller than the distance Rn and ΔSn> 0.

FIG. 21 is an explanatory diagram of the reading result of the speed detection chart 850 when the sheet is skewed. FIG. 21A illustrates the distances Ln and Rn when the sheet rotates counterclockwise and skews. Due to the skew, the original distances Ln and Rn (dotted line) change to the distances Ln and Rn (solid line). FIG. 21B illustrates ΔSn when the sheet is skewed. As described above, when the sheet rotates clockwise and skews, ΔSn <0. When the sheet rotates counterclockwise and skews, ΔSn> 0. In order to detect the transport speed according to the skew, ΔSn is used as a correction value of the reading result (coordinates) of the straight lines 851 and 852, respectively. For example, when the sheet rotates counterclockwise and skews, ΔSn is added to the reading result (distance Ln) of the straight line 851, and ΔSn is subtracted from the reading result (distance Rn) of the straight line 852. The sheet conveying speed is detected based on the reading result of the straight lines 851 and 852 after the calculation. As a result, the effect of skewing is suppressed, and the sheet transport speed is accurately detected.

FIG. 22 is a flowchart showing a correction value calculation process for the sheet transport speed. This process is executed when the image position adjustment process is performed.

When the CPU 301 receives the image position adjustment instruction from the operation unit 20, the printer engine 150 performs the image formation process of the speed detection chart 850 illustrated in FIG. The image forming process of the speed detection chart is performed by transmitting the image data of the speed detection chart from the pattern generator 70 to the printer engine 150. The printer engine 150 generates a speed detection chart 850 by forming an image corresponding to the image data of the speed detection chart on the sheet. The image forming apparatus 10 outputs the generated speed detection chart 850 (S401). The speed detection chart 850 is generated by forming straight lines 851 and 852 having a gradient θ with respect to the sheet conveying direction on the sheet.

The output speed detection chart 850 is manually placed on the seat tray 211 of the ADF280 by the user. The user instructs the CPU 301 to perform image reading processing using the ADF 280 by the operation unit 20. Upon receiving this instruction, the CPU 301 controls the operations of the ADF 280 and the scanner 200 to scan the speed detection chart 850 mounted on the sheet tray 211. The reading result of the speed detection chart is transmitted from the scanner 200 to the print position calculation unit 213 (S402).

The print position calculation unit 213 detects the distances Rn and Ln of the straight lines 851 and 852 from the reading result of the speed detection chart 850 (S403). The print position calculation unit 213 calculates ΔSn based on the detected distances Rn and Ln (S404). The print position calculation unit 213 determines whether or not the calculated ΔSn is equal to “0” (S405). When ΔSn is not equal to “0” (S405: N), the print position calculation unit 213 calculates the correction value (S406). The print position calculation unit 213 calculates a positive value ΔSn as a correction value when ΔSn> 0, and calculates a negative value ΔSn as a correction value when ΔSn <0. The print position calculation unit 213 stores the calculated correction value in the sheet management table 400 and ends the process (S407). When ΔSn is equal to “0” (S405: Y), the print position calculation unit 213 determines that the sheet is not skewed. In this case, the print position calculation unit 213 ends the process without calculating and storing the correction value.

FIG. 23 is an explanatory diagram of the reading result of the speed detection chart 850 when the fluctuation of ΔSn becomes a curve. Even when the reading result within a predetermined range in the sub-scanning direction fluctuates in this way, the print position calculation unit 213 can generate a correction value by the process described with reference to FIG.

By the processing of Examples 1, 2 and 3 as described above, the sheet conveying speed is detected with high accuracy even when the sheet on which the speed detection chart is formed is obliquely read. The print position calculation unit 213 acquires the reading result of the print position measurement chart after detecting the transport speed. The print position calculation unit 213 generates a print position correction parameter based on the reading result of the print position measurement chart and the transport speed, and stores it in the sheet management table 400. The image processing unit 210 can adjust the printing position with high accuracy by correcting the image data using the correction parameters stored in the sheet management table 400 and causing the printer engine 150 to form an image. Further, in Examples 1, 2 and 3, the speed detection chart and the print position measurement chart are formed on separate sheets. For example, a straight line of the speed detection chart is formed in the margin portion of the print position measurement chart. It may be a single chart formed. According to this configuration, it is possible to realize highly accurate printing position adjustment in which the influence of the conveying speed and the skew is suppressed based on the reading result of the straight line with a small amount of sheets.

(Modification example)
In the above description, the user manually causes the scanner 200 to read the speed detection chart, which can be automated. FIG. 24 is a configuration explanatory view of an image forming apparatus 10 having a configuration for automatically reading a speed detection chart. In addition to the configuration shown in FIG. 1, the image forming apparatus 10 is a front and back registering apparatus provided with an adjustment unit 600 at a sheet ejection destination after image formation. The adjustment unit 600 eliminates the need for the user to manually read the speed detection chart.

The image forming apparatus 10 has a configuration in which the sheet is not discharged from the paper ejection roller 112 to the outside of the machine, but is delivered to the adjusting unit 600 via a transport path. The adjustment unit 600 is a sheet transport device including a through pass 630 that receives and transports a sheet from the image forming apparatus 10, a measurement path 631 that serves as a detour for the through pass 630, and a discharge path 632 that discharges the sheet to an external device. A flapper 621 is provided at the branch of the through path 630 and the measurement path 631.

The through pass 630 is provided with a first transport roller pair 601. The discharge path 632 is provided with a second transport roller pair 602 and a third transport roller pair 603. When not passing through the measurement path 631, the sheet guided to the through path 630 by the flapper 621 is conveyed in the order of the first transfer roller pair 601, the second transfer roller pair 602, and the third transfer roller pair 603, and the adjustment unit 600 It is discharged to the outside. For example, the sheet on which the normal image is formed is discharged from the adjustment unit 600 via the through pass 630 and the discharge path 632.

The front and back register portion 700 is provided on the measurement path 631. The front and back register portion 700 measures the shape of the sheet and the shape and position of the image printed on the sheet. In order to obtain highly accurate measurement results, it is necessary to average the variations in shape and printing position for each sheet. Therefore, the front and back register unit 700 measures a plurality of sheets. The front and back register portion 700 is composed of, for example, a contact image sensor (CIS). As a result, the adjustment time can be shortened and the device size can be reduced by performing the measurement while transporting the sheet.

The front and back register portion 700 can read the measurement test pattern 802 for the front side and the measurement test pattern 803 for the back side of the print position measurement chart substantially at the same time. Therefore, the front and back register portions 700 are provided with CIS701 for the front surface and CIS702 for the back surface which are arranged to face each other with the measurement path 631 in between. The front and back register portion 700 includes sheet transfer roller pairs 611, 612, 613, glass / transfer guide members 703, 704, and black backing / transfer guide members 705, 706.

The sheet transfer roller pairs 611, 612, and 613 transfer the sheet at a stable transfer speed inside the front and back register portion 700. The sheet transfer roller pairs 611, 612, and 613 are driven by a drive unit (not shown). The glass / transport guide member 703 stabilizes the position of the front surface CIS701 in the depth of focus direction. The glass / transport guide member 704 stabilizes the position of the back surface CIS702 in the depth of focus direction. The glass / transfer guide member 703 and the glass / transfer guide member 704 are arranged to face each other with respect to the measurement path 631. The black backing and transport guide members 705 and 706 clarify the contrast at the edge of the sheet. The black backing / transport guide member 705 and the black backing / transport guide member 706 are arranged to face each other with respect to the measurement path 631.

In the above configuration, the front / rear register unit 700 reads the speed detection chart to detect the transport positioning degree. The transport speed detection process is as described above. Therefore, when the speed detection chart is deformed or the sheet is skewed, the accurate sheet transfer speed can be detected.

In the present embodiment as described above, the straight line of the speed detection chart is read from the sheet being conveyed, and the transfer speed of the sheet is detected based on the reading result. The reading result includes, in addition to the reading result of the straight line for detecting the transport speed, the reading result of other straight lines and the edge of the sheet which is the reading result of the reference for detecting the accurate transport speed. By detecting the transfer speed of the sheet based on the reference reading result and the linear reading result, the detection accuracy of the transfer speed is lowered due to the deformation of the image formed on the sheet and the skewing of the sheet being conveyed. Can be prevented. By detecting the sheet transport speed with high accuracy, the image forming apparatus 10 can adjust the printing position with high accuracy.

Claims (15)

An image forming means for forming an image on a sheet and
A transport means for transporting the sheet on which an image is formed, and
A reading means for reading an image from the sheet conveyed by the conveying means, and
The sheet is formed with a detection chart for detecting the transfer speed of the sheet by the transfer means and a measurement chart for measuring the printing position of an image formed on the sheet. The transport speed of the sheet is detected based on the reading result of the detection chart by the reading means, and the image is printed on the sheet based on the reading result of the reading means of the measurement chart and the transport speed. With a control means to control the position,
The control means is characterized in that, as the detection chart, the image forming means forms a linear image having a predetermined gradient with respect to the conveying direction of the sheet by the conveying means.
Image forming device. As the detection chart, the control means causes the image forming means to form an image of a second straight line having a gradient different from the gradient of the straight line, and the reading result of the straight line and the reading result of the second straight line are obtained. The transport speed is detected based on the above.
The image forming apparatus according to claim 1. The control means is characterized in that the difference in gradient is acquired from the reading result of the straight line and the reading result of the second straight line, and the transport speed is detected based on the difference in gradient.
The image forming apparatus according to claim 2. The control means is characterized in that the transport speed is detected based on the reading result of the straight line and the reading result of the edge of the sheet.
The image forming apparatus according to claim 1. The control means detects the first angle with respect to the transport direction of the straight line from the reading result of the straight line, detects the second angle of the edge with respect to the transport direction from the reading result of the edge, and the first angle and the first angle. It is characterized in that the transport speed is detected based on two angles.
The image forming apparatus according to claim 4. The control means is characterized in that the transport speed is detected based on a comparison result between the difference between the first angle and the second angle and the gradient of the straight line.
The image forming apparatus according to claim 5. The control means is characterized in that the relative position between the straight line and the edge is detected from the reading result of the straight line and the reading result of the edge of the sheet, and the transport speed is detected based on the relative position. ,
The image forming apparatus according to claim 4. The control means detects the angle of the straight line with respect to the edge from the reading result of the straight line and the reading result of the edge of the sheet, and the transport is based on the comparison result between the detected angle and the gradient of the straight line. Characterized by detecting speed,
The image forming apparatus according to claim 4. As the detection chart, the control means makes the image forming means symmetrical with the straight line and the second straight line so as to be symmetrical with respect to the center line in the direction orthogonal to the transport direction with respect to the transport direction of the sheet. The image is formed with, and the transport speed is detected based on the reading result of the straight line and the reading result of the second straight line.
The image forming apparatus according to claim 1. The control means acquires the center value in the direction orthogonal to the transport direction from the reading result of the straight line and the reading result of the second straight line, and the coordinates in the direction orthogonal to the transport direction and the center of the straight line. The transport speed is detected based on the difference between the first distance to the value and the second distance between the coordinates in the direction orthogonal to the transport direction of the second straight line and the center value.
The image forming apparatus according to claim 9. The control means is characterized in that a correction value such that the difference becomes 0 is generated, and the transfer speed is detected based on the correction value.
The image forming apparatus according to claim 10. The reading means can read the images formed on both sides of the sheet substantially simultaneously.
The control means is characterized in that the image forming means forms the measurement chart on both sides of the sheet.
The image forming apparatus according to any one of claims 1 to 11. The control means causes the image forming means to form the detection chart and the measurement chart on one sheet, and detects the transport speed based on the reading result of the reading means of the sheet. It is characterized in that a correction parameter for controlling the print position is generated.
The image forming apparatus according to any one of claims 1 to 12. A transport path through which the sheet on which the image is formed is transported, and
A reading means for reading an image from the sheet transported along the transport path, and
A reference reading for detecting the reading result of the straight line included in the reading result by the reading means and an accurate transport speed of the sheet on which the image of the straight line having a predetermined gradient with respect to the transport direction of the sheet is formed. The transport speed is detected based on the result.
Sheet transfer device. An image forming means for forming an image on a sheet and
A transport means for transporting the sheet on which an image is formed, and
A method performed by a device comprising a reading means for reading an image from the sheet conveyed by the conveying means.
By the image forming means, a detection chart including an image of a straight line having a predetermined gradient with respect to the conveying direction of the sheet by the conveying means is formed on the sheet.
The detection chart is read by the reading means, and the transfer speed of the sheet is detected based on the reading result of the straight line included in the reading result and the reading result of the reference for detecting the accurate transfer speed. Characteristic,
How to detect the transport speed.

Images