JP2000226138A - Skew detecting method and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately discriminate presence or absence of skew of cut paper of various kinds of tip shapes by comparing a difference of skew amount of cut paper to be carried and an average value of skew amount of plural sheets of cut paper carried preliminarily before the cut paper with preliminarily fixed allowable amount. SOLUTION: As for a judgment of the presence or absence of skew of the second paper 128, data of the first paper 128 is compared after data is detected in tip detection sensors 214, 216 because a comparison object is the first paper 128. In this case, when a difference is larger than a prescribed value, skew to either one side is judged. When the difference is smaller than the prescribed value, both of first and second paper 128 are judged to be skewed, predicting that two sheets of paper 128 are not succeedingly slanted. As a result, judgment of skew of the first and second paper 128 is made possible. When the first and second paper 128 are judged to be normal (absence of skew), an average value of data of two sheets of paper 128 is calculated and is made a comparison object reference value for detecting succeeding skew.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a skew of cut sheets during the transfer when the cut sheets stacked and accommodated in a sheet feed tray are fed one by one to the apparatus main body and conveyed. And a device for detecting skew.

[0002]

2. Description of the Related Art In an apparatus having a conveying path for conveying a sheet cut to a predetermined size (hereinafter referred to as a cut sheet), for example, an image forming apparatus such as a copying machine or a printer. Is designed to transport cut sheets one by one from a paper feed tray and form an image on the cut sheets. At this time, if the skew occurs while the cut sheet is conveyed from the paper feed tray until the image is formed, the relative position between the cut sheet and the image is shifted,
It will look bad. Also, if there is an extreme skew,
A part of the image deviates from the cut sheet surface, and an image is not properly formed, that is, a defective image is generated.

For this reason, it has been proposed and implemented to provide a skew detection device for detecting the presence or absence of skew of cut paper on the transport path (see, for example, Japanese Patent Application Laid-Open No. 4-148775).
Reference).

In a general skew feeding detecting device, leading end detecting sensors are arranged at positions near both ends in the cut sheet width direction on a cut sheet conveying path, and based on leading end detecting signals from the respective leading end detecting sensors. Skew is determined. That is, when the detection timings of the leading edge by the pair of leading edge detection sensors are almost the same, it can be determined that the cut sheet is being transported straight and in a normal state, and the difference between the leading edge detection timings by the pair of leading edge detection sensors (the predetermined time In the case where the above is present, it can be determined that the cut sheet is conveyed diagonally.

However, in the above-described general skew detecting device, when a cut sheet having a specially shaped tip, for example, a cut sheet having a heading piece integrally formed at one end in the width direction is transported, a pair of cut sheets are used. The detection timing of the leading edge detection sensor is shifted, and a time difference corresponding to the protruding length (offset amount) of the heading piece is generated, and it is determined that the heading is skew.
In order to solve this problem, the shape of the cut sheet to be conveyed (especially the tip shape) may be recognized and the offset value in the conveyance direction may be stored in advance. The amount of offset must be measured and stored for each cut sheet.

In Japanese Patent Application Laid-Open No. 6-9105, the pair of leading edge detection sensors are disposed at two locations on the upstream and downstream sides of the transport path, and the leading edge is detected at each of the two locations, and the same width is detected. It has been proposed to determine the presence or absence of skew based on the amount of change in the skew. According to this, it is possible to determine the presence or absence of skew regardless of the shape of the leading end of the cut sheet.

However, since the presence or absence of the skew is limited between the two leading edge detection sensors in the transport direction, if the skew occurs in other transport paths, it cannot be determined whether the skew exists. . For this reason, in consideration of accuracy, the mounting position of the front end detection sensor is limited immediately after the sheet feeding tray or immediately before the image transfer unit. In addition, a tip detection sensor that is at least twice as large as a general skew detection device is required, which increases the number of components and complicates the assembling work.

In view of the above facts, the present invention can cut various tip shapes without changing the general structure of skew detection and without knowing in advance the offset amount between both ends in the width direction due to different shapes. An object of the present invention is to provide a skew detection method and apparatus capable of accurately determining the presence or absence of skew of a sheet.

[0009]

According to the first aspect of the present invention, when the cut sheets stacked and accommodated in the paper feed tray are fed one by one to the apparatus main body and conveyed, the cutting at the time of the conveyance is performed. A skew detection method for detecting skew of a sheet, wherein a time difference between the vicinity of both ends in the width direction of the cut sheet until reaching a predetermined position is defined as a skew amount, and the cut sheet is conveyed. The skew of the cut sheet is determined by comparing a difference between the skew amount and the average value of the skew amounts of the plurality of cut sheets conveyed before the cut sheet in advance with a predetermined allowable value. It is characterized by:

According to the first aspect of the present invention, when determining whether or not the cut sheet is skewed, the amount of skew is not determined by the size, and the sheet is conveyed before the cut sheet to be inspected. A difference from the average value of the skew amount of the cut sheet thus obtained is obtained, and the difference is compared with a predetermined allowable value, so that the presence or absence of skew can be determined based on a relative difference. That is, regardless of the shape of the cut sheet stored in the sheet feed tray (for example, a cut sheet having a heading piece provided at one end in the width direction), most of the cut sheet is transported in a normal state. If it does not match the whole (cut sheet to be inspected), it can be determined that there is skew.

According to a second aspect of the present invention, in the first aspect, the average value is stored for each sheet feed tray.

According to the second aspect of the present invention, since the average value is meaningless unless cut sheets of the same type are used, if the average value is stored for each paper feed tray, the selected feeding value can be selected. The average value corresponding to the paper tray may be read.

According to a third aspect of the present invention, in the first or second aspect of the invention, the average value is at least the attachment / detachment and replacement of the paper feed tray, the detection of empty cut paper in the paper feed tray, It is characterized in that it is cleared when one of the supply and replacement of cut sheets to the sheet feed tray is performed.

According to the third aspect of the present invention, it is a condition that an average value is obtained within the range of cut sheets of the same type, at least having the same tip shape, and if this is neglected, the average value is applied. It will not be possible. Therefore, when there is an operation in which different types of cut sheets are mixed, that is, when there is attachment / detachment / replacement of the sheet feed tray, empty sheet detection in the sheet feed tray, supply / replacement of cut sheets to the sheet feed tray, etc. The currently stored average value is cleared, and the average value is taken again from the beginning.

Thus, an accurate average value can always be obtained, and accurate skew detection can be performed.

According to a fourth aspect of the present invention, a skew detection method according to any one of the first to third aspects is provided.
When determining the presence or absence of skew of the first and second cut sheets, the amount of skew of the cut sheet conveyed to the first sheet is stored.
The amount of skew of the cut sheet conveyed to the sheet is stored, and the difference between the amount of skew of the first sheet and the amount of skew of the second sheet is compared with a predetermined allowable value. It is characterized in that it is determined whether any one of the first and second cut sheets is skewed.

According to a fourth aspect of the present invention, there is provided a case where the first or second cut sheet is taken out of the paper feed tray and transported. Is considered.

That is, since the first cut sheet has no past (previous) result, it cannot be compared. Therefore, the determination of the presence or absence of skew is held until the second sheet is conveyed. When the second cut sheet is conveyed and the skew amount is obtained, the difference between the skew amount of the first sheet and the second cut sheet is compared with an allowable value. In this case, although not absolute, the probability of skew is low,
Further, assuming that the probability of two consecutive skews is low, if any one of them is skewed, it is determined that there is skew in the comparison result of the first or second cut sheet. If neither of them is skewed, it is determined that there is no skew in both the first and second sheets.

Therefore, the presence or absence of skew of the first and second cut sheets can be accurately determined with a considerable probability.

According to a fifth aspect of the present invention, when the cut sheets stacked and housed in the paper feed tray are fed one by one to the apparatus main body and conveyed, the skew of the cut sheets during the conveyance is detected. A skew detection device for detecting the leading edge of the cut sheet in the transport direction at least at two locations in the width direction, and a difference between output timings of leading edge detection signals from the plurality of leading edge detection sensors. Skew amount calculating means for calculating the skew amount of the detection tip portion based on the skewing amount; average value calculating means for calculating an average value of the skew amounts calculated by the skew amount calculating means; Storage means for updating and storing the average value calculated by the calculation means; and a predetermined allowable value representing a difference between the skew amount calculated by the skew amount calculation means and the average value stored in the storage means. Comparison means for comparing with the comparison means; It has a discriminating means for discriminating whether the skew of the cut sheet, the based on.

According to the fifth aspect of the present invention, the skew amount is calculated by the leading edge detection sensor based on the difference between the output timings of the leading edge detection signal at two places in the width direction when the cut sheet is transported. For example, the skew amount may be a time difference.

Next, an average value of the calculated skew amount up to the present is obtained. That is, instead of directly using the skew amount as a reference, the average value of the skew amount of the same type of cut paper as a whole is calculated, and the difference between the current skew amount and the average value is obtained and compared with an allowable value. That is, if there is no difference from the average value even if the skew amount is numerically large, the skew is actually skewed even if there is a large skew amount for some reason in the range of the same type of cut paper. It is determined that there is no skew, and it is determined that there is skew only when the value is equal to or larger than the allowable value.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the front end surface of the cut sheet is non-perpendicular to the conveying direction or non-linear in the width direction. Features.

According to the sixth aspect of the present invention, even if there is a skew amount in the fifth aspect, the cut sheet that is normally transported is not perpendicular to the transport direction or extends in the width direction. It is a non-linear shape, and an example of such a shape is cut paper in which a heading piece is integrally formed at one end in the width direction at the leading end in the transport direction. In the case of such a cut sheet, since one of the leading edge detection sensors is disposed on the conveyance path at the position of the heading piece, there is naturally a time difference between the leading edge detection signals from the two leading edge detection sensors. Therefore,
In such a case, by judging the relative difference between the front and rear cut sheets, it is possible to determine whether the sheet is transported normally or skewed.

Since the average value cannot be obtained for the conveyance of the first and second cut sheets, the amount of skew is calculated for the first cut sheet to determine the presence or absence of skew. Is reserved. Next, the skew amount of the second cut sheet is calculated, and 1
By comparing the difference with the skew amount of the sheet with the allowable value, it is possible to determine whether both are OK or either one is NG. The determination may be made based on the average value of the skew amount of the cut sheet conveyed thereafter, or the operator may determine the first sheet and the second sheet.

[0026]

FIG. 1 shows units (an image information supply device 102 as a high-order device and a printing device 104 as a low-order device) constituting an image forming apparatus 100 according to the present embodiment. I have. This image information supply device 10
2 and the printing device 104 are provided with control units 106 and 108 for controlling the respective devices, and these are connected by a communication path 109. In addition, for example, LA
Networking may be performed by N (local area network) or the like. The image information supply device 102 includes a print data creation unit 110, a print information transmission unit 112, and a paper supply unit selection unit 111. The print data creation unit 110 includes a scanner, an information reading device for loading various recording media (for example, a floppy disk, an MO, a CD-ROM, etc.) and reading information, and data for obtaining image information using a telephone line or the like. A communication unit and a personal computer on which image creation software for directly recording an image are installed are provided as necessary. Of course, the above may be added.

The print data created by the print data creation unit 110 is sent to the print information transmission unit 112 together with the paper size selected by the paper feed selection unit 111, and the printing device 104 is sent by the transmission instruction from the control unit 106. The print data is transmitted to the printer.

The transmission instruction from the control unit 106 is a page sync (synchronization signal) output from the control unit 108 of the printing device 104.

The printing device 104 includes a job determining unit 114,
Non-volatile memory module 116, paper feed tray determination section 118,
It comprises a sheet skew amount detection unit 120, a paper presence / absence detection unit 122 provided in the paper supply unit 121, a detachment determination unit 124, and a print information reception unit 126.

The function of each part of the printing device 104 will be described with reference to the schematic configuration diagram of the printing device 104 in FIG.
A description will be given along the flow of 28.

As shown in FIG. 2, the papers 128 are stacked and accommodated in paper feed trays 130 and 132 for different sizes. The paper feed trays 130 and 132 are detachable from the apparatus main body, and sheets 128 of different sizes are stored in advance for each paper feed tray, and can be replaced as needed.

Tray attachment / detachment sensors 200 and 202 are provided at the loading positions of the paper supply trays 130 and 132, respectively, so that the attachment / detachment state of the paper supply trays 130 or 132 can be electrically recognized. Tray sheet detection sensors 204 and 206 are provided at the loading positions of the paper feed trays 130 and 132,
2, the presence or absence of the paper 128 is detected. Further, sheet feed sensors 208 and 210 are provided in the transport path near the outlet for taking out the paper 128 from the paper feed trays 130 and 132.
Is provided to detect that the paper 128 has been taken out of the paper feed trays 130 and 132.

In FIG. 2, the paper feed trays 128, 13
0 (the capacity of the paper 128) is different,
Generally used paper size (for example, A4 size)
Is set to the large paper feed tray 130 side, it is possible to reduce the trouble of paper supply. A manual feed tray 134 is provided above the paper feed tray 130 and is used when a special size or type of paper 128 is used. A sheet feed sensor 135 is also provided near the cut sheet take-out port of the manual feed tray 134.

Each of the paper feed trays 130 and 132 is provided with a paper feed device 138 constituting a part of the transport device 136.
Each sheet can be taken out.

The paper feed tray 130 (or the paper feed tray 13)
The paper 128 taken out from 2) is hung down by the transport belt 140 whose transport direction is vertical, and is then transferred to the transport belt 142 whose transport direction is horizontal, and the exposure unit 144 is arranged in a horizontal state. Set direction (Fig. 2
To the left).

A sheet skew amount detection unit 212 is provided on the conveyance path by the conveyance belt 142. Specifically, leading edge detection sensors 214 and 21 for detecting the leading edge of the paper 128 at both ends in the width direction of the transport path.
6 are provided. This pair of tip detection sensors 21
The lines connecting the detection positions 4 and 216 are arranged so as to be orthogonal to the normal conveyance direction of the paper 128.

Here, in the case of general paper 128, if the pair of leading edge detection sensors 214 and 216 detect the leading edge of the paper 128 at the same time, it can be determined that the paper 128 is being conveyed normally. Conversely, when the pair of leading edge detection sensors 214 and 216 detects the leading edge of the adopted child 28 with a time difference, it is determined that the transport is skewed, and it is determined that the transport is abnormal.

The exposing section 144 includes an endless photosensitive belt 152 wound around a plurality of rollers (in the present embodiment, two large-diameter rollers 146 and 148 and one small-diameter roller 150). Exposure unit (hereinafter referred to as ROS) 15
4.

A large-diameter roller 148 on the right side of FIG. 2 of the photoreceptor belt 152 has a function as a driving roller that rotates with a driving force from a driving unit (not shown), and is further provided with an encoder 156. Photoreceptor belt 152
Is transported counterclockwise in FIG. 2 (in the direction of arrow A in FIG. 2) by the driving force of the driving roller 148.

The number of rotations of the driving roller 148 is
It can be recognized by an output signal from the encoder 156.

A hole 152A is provided in a part (preferably near the end in the width direction) of the photoreceptor belt 152, and the optical axis of the belt hole sensor 158 is provided on the movement locus of the hole 152A. Intersect. The belt hole sensor 158 has a hole 15 for each rotation of the photoreceptor belt 152.
2A, and outputs a signal different from that when the hole 152A is not opposed.

Further, on the outer periphery of the photosensitive belt 152,
A cleaner 160 and a developing device 162 are provided with the exposure unit 154 interposed therebetween. For this reason, the outer peripheral surface (electrostatic exposure surface) of the photoreceptor belt 152 is
After the cleaning, the image is exposed by the exposure unit 154, and the toner is adhered by the developing unit 162 to be visualized. The photoreceptor belt 152 corresponding to a visualized image area is sent to a transfer unit 164 that comes into contact with the conveyance path of the paper 128.

When the paper 128 is horizontally conveyed by the conveyor belt 152 and approaches the photosensitive belt 152, the sheet 128 is turned upward in FIG. 2 and reaches the transfer section 164. A sheet detection sensor 166 is provided immediately before the transfer unit 164, and the sheet 128 is transferred to the transfer unit 164.
The presence or absence of a sheet can be detected immediately before the operation.

In the transfer section 164, the paper 128 is bonded to the photoreceptor belt 152, and the image is transferred. The paper 128 on which the image has been transferred is transported by the transport belt 152.
The sheet is conveyed substantially vertically upward in FIG. 2 and sent to a fixing section 170 including a pair of rollers 168. In the fixing unit 170, the pair of rollers 168 is heated to a predetermined temperature, and the sheet 128 is heated and fixed to the transferred image by being sandwiched between the heated pair of rollers 168. As a heating source of the fixing unit 170, one or both of the pair of rollers 168 may be a heat roller, or hot air may be sent and heated using a separate hot air generating unit.

The paper 128 that has passed through the fixing unit 170 is guided to a plurality of transport rollers 172 and guide plates 174, and is sent to a stacker unit 176.

The stacker section 176 is provided with a plurality of discharge trays 172 and 174, which can discharge to a predetermined discharge tray 172 (or discharge tray 174). In this embodiment, the discharge trays 172, 1
74 corresponds to the paper feed trays 130 and 132, and the paper feed trays 130 and 132 from which the paper 128 is taken out.
Are automatically selected, and the point switching unit 176 is guided so as to be guided by the selected discharge tray 172 (or the discharge tray 174).
Is controlled.

The above is the outline of the printing apparatus 104, and FIG.
Of the sheet feed sensor 13
5 and a processing unit (not shown) for processing signals from the sheet feed sensors 208 and 210.

The attachment / detachment determination unit 124 includes tray sheet detection sensors 204 and 206 and the sheet detection sensors 204 and
And a processing unit (not shown) for processing the signal from the control unit 206.

The paper feed tray judging section 118 selects the paper feed tray 130 (or 132) containing the paper 128 of the size selected by the paper feed selecting section 111, and drives the corresponding paper feeder 138. It has a function to make it work.

In the job determination section 114, the paper 12 taken out of the paper feed trays 130 and 132 and conveyed is
8 and the exposure unit 154 performs synchronization control between the photosensitive belt 152 on which an image is formed based on image information.

In the sheet skew detecting section 120, a pair of leading edge detecting sensors 214 and 21 provided on the transport belt 142 are provided.
6 has a function of judging the skew of the cut sheet 128 based on the detection result from Step 6.

By the way, depending on the presence or absence of skew detected on the conveyor belt 142, a pair of tip detection sensors 214,
General skew detection at 214 (a pair of the tip sensor 21
4 and 216, the skew is determined based on the difference in the leading edge detection time).
An irregularly shaped sheet (for example, as shown in FIG. 3A, a heading piece 1
FIG. 4 shows a sheet 128A integrally formed with the sheet 28B.
In the case of a sheet 128C or the like having a chamfered 128D at one corner as shown in FIG. 7A), the pair of leading edge detection sensors 214 and 216 have a time lag in detection despite the normal conveyance state. (See FIGS. 3B and 4B).

Therefore, in this embodiment, the sheet 128 to be conveyed before and after the sheet 128 for detecting the skew
The presence / absence of skew is determined by comparing the detected state with the detection states of the leading edge detection sensors 214 and 216 at 28.

In this case, the determination of the presence or absence of skew of the first sheet of paper 128 is not made because there is no comparison object.
Only the detection data according to 14, 216 will be taken.

The determination of the presence or absence of skew of the second sheet of paper 128 is made after the data is detected by the leading edge detection sensors 214 and 216 because the comparison object is the first sheet of paper 128. Compare. In this case, there is a case where the difference is larger than a predetermined value and a case where it is smaller. When the difference is larger than the predetermined value, it is determined that one of them is skewed, and when the difference is smaller than the predetermined value, Predicts that two sheets will not be skewed in succession, and determines that both are not skewed.

Thus, it is possible to determine the skew of the first and second sheets. In the first and second sheets,
If it is determined that the data is normal (no skew), the average value of the data of the two sheets of paper 128 is calculated and used as a reference value for comparison for detecting skew thereafter.

Next, for the third and subsequent sheets, the average value of past data is calculated, and the presence or absence of skew is determined based on the difference (absolute value) between this average value and the data of the third and subsequent sheets. .

Further, in this embodiment, the average value is stored or cleared based on the following conditions,
Processing is performed.

Condition 1: selected paper feed tray 130, 1
The average value data is stored for each of the sheets 32, and data suitable for the sheet feed trays 130 and 132 based on the selected sheet size is read.

Condition 2: The average value data is cleared each time the sheet is supplied to the paper feed tray, and the processing is started from the first sheet. In this case, the supply of the paper 128 to the paper feed trays 130 and 132 is limited to the case where the supply of the paper 128 is possible only when the apparatus power is off.
Therefore, in the power-on state, the paper feed trays 130, 132
It is not necessary to clear the stored data even if the paper 128 is replenished.

Condition 3: The paper feed trays 130 and 132 described in the present embodiment, but in the case of a device capable of loading more trays, they are grouped (sheets 128 of the same size (type)). Thus, even if the paper feed trays are different, data can be used mutually in the same group.

The operation of the present embodiment will be described below.

The cut sheet 128 taken out by the sheet feeding device 138 is hung down by the conveyor belt 140, and is then transferred to the conveyor belt 142 whose conveyance direction is horizontal, and the exposure unit 144 is disposed in a horizontal state. Is transported in the direction (left direction in FIG. 2).

In the transfer section 164 of the exposure section 144, the cut paper 128 is bonded to the photoreceptor belt 152, and the image is transferred. The cut sheet 128 on which the image has been transferred is directly conveyed by the conveyance belt 152 substantially vertically in the upward direction in FIG. 2, and the fixing unit 17 including a pair of rollers 168 is provided.
It is sent to 0. In the fixing unit 170, a pair of rollers 1
68, the cut paper 128
Is heated and the transferred image is fixed.

The cut paper 128 that has passed through the fixing unit 170
Is sent to the stacker unit 176 by being guided by the plurality of transport rollers 172 and the guide plate 174.

The skew detection procedure will now be described with reference to the flowcharts of FIGS.

First, the skew detection main routine of FIG. 5 will be described.

In step 300, it is determined whether or not a condition for clearing the average value Save (X) of the skew amount of the cut sheet has occurred. Note that (X) indicates the type of the paper feed tray, and in the present embodiment, indicates one of the paper feed trays 130 and 132.

The conditions for clearing are as follows:
0, 132, whether the paper tray 13
It is determined whether or not the cut sheets 0 and 132 have become empty and whether or not the cut sheets have been replenished. If at least one of these has been performed, the past average value cannot be used. To clear. This is because there is a possibility that cut sheets having different shapes (especially, the shape on the leading end side in the transport direction) may be mixed.

If an affirmative determination is made in step 300, the flow proceeds to step 302 to determine the paper feed tray 130 (or 132) that satisfies the condition, and then proceeds to step 304 to make a determination. Paper tray 1
Average value S stored corresponding to 30 (or 132)
ave is cleared and the process returns to step 300.

If a negative determination is made in step 300, the process proceeds to the next step 306, where it is determined whether or not there is a print instruction. If a negative determination is made, step 300 is performed.
Return to That is, when the apparatus is not performing the printing process, steps 300 and 306 are repeated.

If an affirmative determination is made in step 306, the flow advances to step 308 to specify the designated paper feed tray 132 (1).
32), and then read the allowable value DS of the skew amount difference corresponding to the paper feed tray 130 (or 132) selected in step 310.

In the next step 312, the process of detecting the presence or absence of skew shown in FIG. 6 is controlled.
Return to 0.

FIG. 6 shows a subroutine for detecting the presence or absence of skew in step 312 of FIG.

In step 320, step 30 in FIG.
It is determined whether the process is the first process (the first cut sheet) after the average value is cleared in step 4, and in the case of an affirmative determination, the process proceeds to step 322, where the cut sheet is first detected by conveyance. The skew amount Sx1 is obtained. The skew amount is the time difference between the rising edges of the tip detection signals from the pair of tip detection sensors 214 and 216. The time difference may be applied as it is, or may be a numerical value proportional to the time difference (for example, a numerical value with 0.1 second as one unit).

When the detection of the skew amount Sx1 is completed in step 322, the process proceeds to step 324, where the skew amount Sx1 is detected.
Is registered (stored) as aSave (X), and the process returns.

In the case of the present embodiment, in the first transport,
It is not determined whether or not the cut sheet is skewed, and the next processing is awaited for the moment.

That is, in the case of the processing of the second sheet, after the above processing is completed, the process proceeds to step 320. Therefore, a negative determination is made in this step 320, an affirmative determination is made in the next step 326, and the process proceeds to step 328. .

In step 328, the skew amount Sx2 detected by the conveyance of the cut sheet is obtained.

When the detection of the skew amount Sx2 is completed in step 328, the process proceeds to step 330, where the stored 1
The absolute value of the difference between the skew amount Sx1 of the sheet and the allowable value dDS is compared (| Sx2-Sx1 |: DS).

If it is determined that | Sx2−Sx1 |> DS as a result of the comparison (affirmative determination), the flow shifts to step 332 to determine the presence of skew. That is, when the difference between the two is greater than the allowable value, it can be determined that skew has occurred in any of the cut sheets. However, at this point, it is not possible to determine which cut sheet is skewed.

In the next step 334, processing after detecting skew is performed. For example, in this case, a display or the like notifying the operator that the skew has occurred on the first or second cut sheet is performed, and the process proceeds to step 336. In step 336, the average value Save (X) is cleared and the routine returns. The average value Save (X) at this time is the skew amount of the first sheet. Therefore, since there is no need to retain data suspected of skew, the data is cleared and the next print processing is executed as the first processing.

Next, a negative determination is made in step 330,
That is, if | Sx2−Sx1 | ≦ DS, the difference between the skew amounts of the first and second cut sheets 128 is small, and it is determined that there is no skew.
Move to 8. That is, even if the amount of skew is large, skew may not be a cause in the case of a special cut sheet as shown in FIGS. So 2
By comparing the sheets (or more),
By determining the presence or absence of skew, skew can be determined even for a special cut sheet having the above shape.

At step 338, the average value Save
As (X), the average value of the skew amounts of the two cut sheets is substituted, and the process returns.

When it is determined that there is skew in the first and second cut sheets 128, the operator may make a visual determination, and in order to obtain this determination, the normal discharge trays 172 and 174 are used. Other trays may be prepared.

In the case of the processing for the third and subsequent sheets, step 32
0 and 326 are both determined to be negative, and the process proceeds to step 340. In step 340, the skew amount SxN of the cut sheet (N-th sheet) is detected, and then in step 342, the detected skew amount SxN and the average value Save (X)
Is compared with the allowable value DS (| SxN-S
ave (X) |: DS).

As a result of this comparison, it is smaller than the allowable value (|
When it is determined that SxN-Save (X) |> DS (affirmative determination), the process proceeds from step 342 to step 344 to determine that the N-th cut sheet 128 has skew, and then proceeds to step 346. Then, skew detection processing (notification to the operator, stop of the apparatus, and the like) is performed, and the processing ends. After the skew detection process, the history (the average value) so far may be cleared.

On the other hand, in step 342, | SxN
If it is determined that −Save (X) | ≦ DS (negative determination), the process proceeds to step 350 to update the average value (the average value is calculated again including the current skew amount), and the processing is performed. finish.

In step 348, N has cleared the average value regardless of the numerical value. However, if N is larger than a predetermined value (for example, 100 to 1000 sheets), the current skew amount Instead of using only the average value, the average value up to the previous time may be used in the future.

As described above, in the present embodiment, the skew is not detected based on the time difference between the detection of the leading ends of both ends in the width direction of each cut sheet 128. In this case, if the time difference is a steady value, it is determined that the sheet is not a skew but a cut sheet having a special shape formed at the tip (for example, see FIGS. 3 and 4), and is regarded as a normal conveyance. You can judge.
In addition, since the presence or absence of skew is determined based on the difference from the average value of the skew amount of each identical unit, the presence or absence of skew can be accurately determined without erroneous determination.

[0091]

As described above, the skew detection method and apparatus according to the present invention can determine the offset amount between both ends in the width direction due to a different shape without changing the general skew detection structure. Without this, there is an excellent effect that the presence or absence of skew of cut paper having various leading end shapes can be accurately determined.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a printing device of the image forming apparatus according to the embodiment of the present invention.

3A is a front view of a cut sheet having a heading piece at a leading end in a conveying direction, and FIG. 3B is a signal characteristic of a leading end detection sensor when the cut sheet of FIG. 3A is conveyed normally; FIG.

4A is a front view of a cut sheet having a chamfered front end portion in the conveyance direction, and FIG. 4B is a signal characteristic of a front end detection sensor when the cut sheet of FIG. 4A is normally conveyed; FIG.

FIG. 5 is a control flowchart showing a main routine for skew detection.

FIG. 6 is a flowchart illustrating a subroutine for detecting the presence or absence of skew;

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 image forming device 102 image information supply device 104 printing device 106, 108 control unit 114 job determination unit 116 non-volatile memory 118 paper feed tray determination unit 120 sheet skew amount detection unit 122 paper presence / absence detection unit 124 detachment determination unit 128 paper 212 Sheet skew detection unit 214, 216 Edge detection sensor

Claims (6)

[Claims] 1. A skew detection method for detecting skew of cut sheets during conveyance when the cut sheets stacked and accommodated in a sheet feed tray are fed one by one to the apparatus main body and conveyed. The time difference between when the vicinity of both ends in the width direction of the cut sheet reaches a predetermined position is defined as a skew amount, and the skew amount of the cut sheet to be conveyed and the plurality of sheets previously conveyed before the cut sheet are determined. A skew detection method characterized by determining the skew of the cut sheet by comparing a difference between the average value of the skew amount of the cut sheets and a predetermined allowable value. 2. The skew detection method according to claim 1, wherein the average value is stored for each paper feed tray. 3. The average value is cleared when at least one of attachment / detachment and replacement of the paper feed tray, detection of empty cut paper in the paper feed tray, supply of cut paper to the paper feed tray and replacement is performed. The skew detection method according to claim 1 or 2, wherein 4. The skew detection method according to claim 1, wherein the skew detection of the first and second cut sheets is performed using the first skew detection method. The skew amount of the cut sheet conveyed to the second sheet is stored, the skew amount of the cut sheet conveyed to the second sheet is stored, and the difference between the skew amount of the first sheet and the skew amount of the second sheet is stored. Is compared with a predetermined allowable value to determine whether the first or second cut sheet is skewed,
A skew detection method characterized in that: 5. A skew detecting device for detecting skew of the cut sheets during the transfer when the cut sheets stacked and stored in the sheet feed tray are fed one by one to the apparatus main body and conveyed. Wherein the leading end of the cut sheet in the transport direction is at least two in the width direction.
A tip detection sensor that detects at a location; a skew amount calculating unit that calculates a skew amount of the detected tip based on a difference between output timings of tip detection signals from the plurality of tip detection sensors; Average value calculating means for calculating an average value of the skew amount calculated by the amount calculating means; storage means for updating and storing the average value calculated by the average value calculating means; Comparing means for comparing the difference between the skew amount and the average value stored in the storage means with a predetermined allowable value; and determining whether or not the cut sheet has skew based on a comparison result of the comparing means. A skew detection device having a determination unit that performs the determination. 6. The skew detection device according to claim 5, wherein a front end surface of the cut sheet is non-perpendicular to the transport direction or non-linear in the width direction.