JP7183785B2 - SHEET SKEW DETECTION DEVICE, SHEET CONVEYING DEVICE INCLUDING THE SAME, AND IMAGE FORMING APPARATUS - Google Patents

Description

The present invention relates to a sheet skew amount detecting device mounted in an image forming apparatus such as a facsimile machine, a copying machine, a printer, etc., for detecting the skew amount of a sheet-like recording medium, a sheet conveying device having the same, and an image forming apparatus. be.

Image forming apparatuses such as facsimiles, copiers, and printers are configured to record images on recording media such as paper, cloth, and OHP sheets. These image forming apparatuses can be classified into an electrophotographic system, an ink jet system, and the like according to the recording system.

When printing on a recording medium using an image forming apparatus, if the recording medium is skewed with respect to the conveying direction, or if the position is shifted in the direction perpendicular to the conveying direction (the width direction of the recording medium). If so, the print position for each recording medium will be misaligned. In particular, when an inkjet recording apparatus is used, the ink is likely to soak into the recording medium and show through, so very high printing position accuracy (for example, 0.3 mm or less) is required during double-sided printing.

Conventionally, a CIS (contact image sensor) is arranged to detect the position of the edge in the width direction of a sheet (recording medium), and the position of the edge in the width direction of the sheet S is detected based on the difference in the intensity of light received by the CIS. method is known.

For example, Japanese Patent Application Laid-Open No. 2002-200001 discloses a displacement amount detecting means for detecting the lateral displacement amount and the skew amount of a sheet S by CIS, and a sheet as an error sheet when the detected positional displacement amount of the sheet is larger than a predetermined threshold value. error sheet detection means for detecting occurrence; double-sided path sheet detection means for detecting whether or not a sheet exists in the double-sided path when an error sheet occurs; A conveying source discriminating means for discriminating whether a sheet is a sheet conveyed from a sheet storage portion or a sheet conveyed through a double-sided path, and a sheet to be discharged is determined based on the discrimination result, and the determined sheet is determined. and a sheet discharging means for discharging the sheet.

In addition, in Patent Document 2, the output value of a CIS arranged in the transport path of the transported object (paper) is binarized, and the position at which the binarized value is switched is stored for each size of the transported object. An edge detection device is disclosed that determines an edge position of a conveyed object when it is within an edge detection range. It also describes shifting the transported object in the width direction based on the amount of deviation between the detected edge position and the reference position.

JP-A-2003-327345 JP 2016-145814 A

In the conventional skew amount detection mechanism using CIS, the paper transport speed is calculated by the CPU from the set speed of the transport motor and the mechanical parameters that transmit the drive to the transport roller, and the amount of paper movement per CIS scanning time is calculated. calculate. Then, the amount of skew (skew amount) of the paper is calculated from the number of reading scans of the CIS from when the paper passes a certain point of the CIS to when it passes another point.

However, with the above method, variations in the internal frequency of the CPU, variations in mechanical parameters, slippage in paper transport during paper edge detection by CIS, etc. can cause speed differences between the theoretical paper transport speed and the actual paper transport speed. occurs. Therefore, it is difficult to accurately detect the skew amount.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a sheet skew amount detection device capable of accurately detecting the skew amount of a sheet with a simple configuration regardless of fluctuations in the sheet conveying speed, a sheet conveying apparatus and an image forming apparatus having the same. intended to provide

A first configuration of the present invention to achieve the above object is a sheet skew amount detection device that includes an edge detection sensor, a sheet speed detection sensor, and a control section. The edge detection sensor has a detection area in which a plurality of photoelectric conversion elements are arranged in correspondence with pixels, which are the minimum units of an image, along the width direction perpendicular to the conveying direction of the sheet. By scanning in the main scanning direction, the pixel positions where the output signals of the photoelectric conversion elements are switched are detected as the leading edge in the transport direction and the side edge positions on both sides in the width direction. The sheet speed detection sensor detects the conveying speed of the sheet passing through the edge detection sensor. The controller controls the sheet conveying speed detected by the sheet speed detection sensor, the scanning time per line of the photoelectric conversion element of the edge detection sensor, and the first pixel position after passing the first pixel position of the edge detection sensor. and the distance between the first pixel position and the second pixel position are used to calculate the skew amount of the sheet.

According to the first configuration of the present invention, in order to calculate the skew amount of the sheet using the actual conveying speed of the sheet detected by the sheet speed detection sensor, the set speed of the conveying motor and the driving force are transmitted to the pair of conveying rollers. Detects the skew amount of the sheet with high accuracy without being affected by variations in CPU internal frequency and mechanical parameters, etc. can do.

1 is a cross-sectional side view showing a schematic structure of a printer 100 having a sheet skew amount detection device 21 according to an embodiment of the present invention; FIG. 3 is an external perspective view of the sensor unit 30 mounted on the printer 100 of the present embodiment; FIG. Side sectional view of the sensor unit 30 Plan view of the correction unit 31 viewed from above A side view of the correction unit 31 viewed from the upstream side in the paper transport direction. A block diagram showing a control path of the printer 100 of this embodiment. 4 is a plan view of the printer 100 according to the present embodiment in which the state immediately before the sheet S passes through the CIS 40 is viewed from above; FIG. Flowchart showing an example of skew correction control in the printer 100 of the present embodiment

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side cross-sectional view showing a schematic structure of an inkjet recording printer 100 having a sheet skew amount detection device 21 according to an embodiment of the present invention.

As shown in FIG. 1, the printer 100 has a paper feed cassette 2a, which is a paper storage section, arranged in the lower part of the printer main body 1, and a manual paper feed tray 2b outside the right side of the printer main body 1. ing. A paper feeding device 3a is arranged above the downstream side of the paper feeding cassette 2a in the paper conveying direction (the right side of the paper feeding cassette 2a in FIG. 1). Further, a paper feeding device 3b is arranged downstream of the manual paper feed tray 2b in the paper transport direction (on the left side of the manual paper feed tray 2b in FIG. 1). Sheets S are separated one by one and sent out by the sheet feeding devices 3a and 3b.

A first paper transport path 4 a is provided inside the printer 100 . The first paper transport path 4a is located on the upper right side of the paper feed cassette 2a and on the left side of the manual paper feed tray 2b. The paper S fed from the paper feed cassette 2a passes through the first paper feed path 4a and is transported vertically upward along the side surface of the printer main body 1. The paper S fed from the manual paper feed tray 2b is transported vertically upward. The sheet is conveyed substantially horizontally to the left through the sheet conveying path 4a.

At the downstream end of the first paper transport path 4a with respect to the paper transport direction, a sensor unit 30 for detecting the position (edge position) of the end of the paper S in the width direction (perpendicular to the paper transport direction) is provided. are placed.

A correction unit 31 is provided immediately downstream of the sensor unit 30 . The correction unit 31 feeds the sheet S toward the first belt conveying section 5 while correcting the skew of the sheet S and the misalignment in the width direction. Detailed structures of the sensor unit 30 and the correction unit 31 will be described later.

A paper speed detection sensor 60 is arranged immediately upstream of the sensor unit 30 . The paper speed detection sensor 60 is, for example, a laser Doppler speed meter that utilizes the coherence of laser light. When a laser beam is split into two parallel beams of equal intensity and then crossed by a converging lens, bright and dark fringes (interference fringes) appear. When the object (paper) passes through these interference fringes, the change in intensity of the scattered light from the object is detected as a Doppler signal by a CCD (photoelectric conversion device), and the velocity is obtained from the frequency of the Doppler signal and the interval between the interference fringes. be able to. Alternatively, a non-contact LED velocimeter can be used that irradiates an object to be measured with an LED, performs signal processing on reflected light received by a CCD, and outputs a pulse signal. The sensor unit 30 and the paper speed detection sensor 60 constitute the sheet skew amount detection device 21 of the present invention together with a CPU 70 which will be described later.

A first belt conveying section 5 and a recording section 9 are arranged immediately downstream of the correction unit 31 . The first belt conveying section 5 includes an endless first conveying belt 8 wound around a first driving roller 6 and a first driven roller 7 . The first conveying belt 8 is provided with a large number of ventilation holes (not shown) for air suction. The paper S sent from the paper feed cassette 2a or the manual paper feed tray 2b is sucked and held by the first conveyor belt 8 by the paper suction unit 20 provided inside the first conveyor belt 8, and is transferred to the recording unit 9. pass below.

The recording unit 9 includes line heads 10C, 10M, 10Y and 10K. The line heads 10C to 10K record an image on the sheet S conveyed while being attracted to the conveying surface of the first conveying belt 8 . Each of the line heads 10C-10K is supplied with ink of four colors (cyan, magenta, yellow and black) stored in ink tanks (not shown) for each color of the line heads 10C-10K.

By sequentially ejecting respective inks from the line heads 10C to 10K toward the sheet S attracted to the first conveying belt 8, four colors of yellow, magenta, cyan, and black inks are superimposed on the sheet S. A full-color image is recorded. Note that the printer 100 can also record a monochrome image.

A second belt conveying section 11 is arranged downstream of the first belt conveying section 5 (on the left side in FIG. 1) with respect to the sheet conveying direction. The paper S on which an image has been recorded in the recording unit 9 is sent to the second belt conveying unit 11, and the ink ejected onto the surface of the paper S is dried while passing through the second belt conveying unit 11. FIG. Since the configuration of the second belt conveying section 11 is the same as that of the first belt conveying section 5, the description thereof is omitted.

A decurler section 14 is provided in the vicinity of the left side surface of the printer main body 1 on the downstream side of the second belt conveying section 11 with respect to the sheet conveying direction. The paper S, the ink of which has been dried by the second belt conveying section 11, is sent to the decurler section 14, and the curl of the paper S is corrected.

A second paper transport path 4b is provided downstream of the decurler section 14 (upper in FIG. 1) with respect to the paper transport direction. The paper S that has passed through the decurler section 14 is discharged from the second paper transport path 4b via a pair of discharge rollers to a paper discharge tray 15 provided outside the left side of the printer 100 when double-sided recording is not performed. When printing on both sides of the paper S, the paper S that has finished printing on one side and passed through the second belt conveying section 12 and the decurler section 14 passes through the second paper conveying path 4b and onto the reversing conveying path 16. be transported. The sheet S sent to the reversing conveying path 16 has its conveying direction switched so as to be turned upside down, and is conveyed to the registration roller pair 13 through the upper portion of the printer 100 . Thereafter, the sheet is conveyed again to the first belt conveying section 5 with the surface on which no image is recorded facing upward.

A maintenance unit 19 is arranged below the second belt conveying section 12 . The maintenance unit 19 moves below the recording unit 9 when performing maintenance on the recording heads of the line heads 10C to 10K, and wipes off the ink ejected (purged) from the ink ejection nozzles of the recording heads. collect the ink.

Next, the detailed structure of the sensor unit 30 will be described. 2 is an external perspective view of the sensor unit 30 mounted on the printer 100, and FIG. 3 is a side sectional view of the sensor unit 30. As shown in FIG. 2 and 3, the direction of paper width is indicated by arrow XX', and the direction of paper transport is indicated by arrow Y. As shown in FIG.

The sensor unit 30 includes a unit housing 32 , a conveying roller pair 33 , a CIS 40 and a light source section 41 . The unit housing 32 rotatably supports the transport roller pair 33 and houses the CIS 40 and the light source section 41 . An entrance guide 35 that guides the sheet S to the nip portion of the pair of transport rollers 33 is provided at the upstream end of the unit housing 31 with respect to the sheet transport direction (arrow Y direction).

The CIS 40 and the light source section 41 are accommodated in the lower and upper parts of the unit housing 32, respectively. , edge positions of the paper S in the transport direction and width direction are detected. The light source unit 41 has an LED 41 a arranged at one end in the paper width direction, and a light guide plate 41 b that diffuses the light emitted from the LED 41 a over the entire paper width direction and guides the light to the CIS 40 . Between the CIS 40 and the light source section 41, two contact glasses 42a and 42b are arranged to face each other. A part of the paper transport path is formed by the upper surface of the contact glass 42a and the lower surface of the contact glass 42b.

4 is a plan view of the correction unit 31 viewed from above, and FIG. 5 is a side view of the correction unit 31 viewed from the upstream side in the paper transport direction (downward in FIG. 4). The correction unit 31 includes a correction roller pair 50 , a roller holder 51 , a carriage 53 , a roller drive motor 55 , a skew correction motor 57 and a lateral deviation correction motor 59 .

A plurality of correction roller pairs 50 (here, four pairs) are arranged in the paper width direction. Each correction roller pair 50 is composed of a driving roller 50a and a driven roller 50b. The roller holder 51 rotatably supports the rotating shaft 52 of the driving roller 50a. A rocking fulcrum 51a is provided on one end side (the left end side in FIGS. 4 and 5) of the roller holder 51 in the paper width direction, and the other end side (FIG. 4) of the carriage 53 is provided around the rocking fulcrum 51a. , right end in FIG. 5) can swing in the paper transport direction. The carriage 53 is supported by frames 101a and 101b on the front side and the back side of the printer 100 so as to be movable in the paper width direction.

The roller drive motor 55 is connected to the rotating shaft 52 via a plurality of gears, and rotates and stops the rotating shaft 52 . The skew correction motor 57 is connected via a plurality of gears to a rack 51b provided at the swing end of the roller holder 51, and changes the inclination of the roller holder 51 with respect to the paper transport direction. The lateral deviation correction motor 59 is connected to rack teeth (not shown) formed on the edge of the carriage 53 and reciprocates the carriage 53 in the paper width direction. As the roller drive motor 55, the skew correction motor 57, and the lateral deviation correction motor 59, stepping motors are used that can precisely control the rotation direction and rotation amount (rotation angle) by pulse control.

FIG. 6 is a block diagram showing control paths of the printer 100 of this embodiment. The CPU 70 centrally controls the printer 100 as a whole. When the printer 100 starts printing on the paper S in response to print data received from an external computer or the like, the CPU 70 performs various settings for the CIS control circuit 71 to read signals from the CIS 40 . .

The CIS control circuit 71 sends to the CIS 40 a reference clock signal for reading signals from the CIS 40 and an accumulation time determination signal for determining the charge accumulation time in the CIS 40 according to the contents set by the CPU 70 . Further, the CIS control circuit 71 sends out a PWM signal to the LED drive circuit 73 to set the current value to flow through the LED 41a. The LED drive circuit 73 generates a DC voltage according to the PWM signal from the CIS control circuit 71, and uses it as a reference voltage for the current flowing through the LED 41a. The CIS control circuit 71 also generates a comparison reference voltage (threshold voltage) for binarizing the analog signal (output signal) from the CIS 40 by the binarization circuit 75 .

At the timing when the sheet S is conveyed toward the recording section 9 (see FIG. 1), the CPU 70 instructs the CIS control circuit 71 to detect the edge position. The CIS control circuit 71, which has received the edge position detection instruction from the CPU 70, sends a control signal for lighting the LED 41a to the LED driving circuit 73 in synchronization with the accumulation time determination signal. The LED drive circuit 73 illuminates the LED 41 a for a certain period of time according to the control signal from the CIS control circuit 71 .

The CIS 40 has a detection area 40a (see FIG. 7) in which a plurality of photoelectric conversion elements are arranged corresponding to pixels, which are the minimum units of an image, along the width direction perpendicular to the paper transport direction. Then, the voltage corresponding to the amount of light accumulated in each pixel (photoelectric conversion element) of the pixel group (pixel group) of the detection area 40a is output as an output signal for each pixel by the following accumulation time determination signal and reference clock signal. Output. An output signal (analog signal) output from the CIS 40 is binarized by comparison with a comparison reference voltage (threshold voltage) in a binarization circuit (comparator) 75, and converted into a GPIO (general-purpose input/output signal) as a digital signal. output) port to the CIS control circuit 71 . Alternatively, the analog signal may be received at an AD (Analog/Digital) port and internally provided with a threshold value.

The CIS control circuit 71 sequentially confirms the 0/1 value of the digital signal binarized by the binarization circuit 75 for each output signal output from the CIS 40 pixel by pixel. Then, the CIS control circuit 71 detects the pixel position (the position of the photoelectric conversion element) in the detection area 40a where the value of the digital signal switches from 0 to 1 or from 1 to 0.

When the CIS control circuit 71 detects the pixel position where the value of the digital signal is switched, the switched pixel position is determined as the position of the leading edge of the sheet S in the conveying direction and the lateral edge positions on both sides in the width direction. Based on the side edge positions determined by the CIS control circuit 71, the CPU 70 determines the edge positions ( A deviation amount (amount of deviation in the width direction) from the reference edge position) is calculated.

The CPU 70 also calculates the amount of skew (skew angle) of the sheet S based on the timing at which the leading edge of the sheet S passes through a predetermined area of the CIS 40, the number of times the CIS 40 scans, and the sheet transport speed. The calculated width direction deviation amount and skew amount are transmitted to the correction unit control section 77 . The correction unit control section 77 transmits a control signal to the correction unit 31 according to the transmitted width direction shift amount and skew amount, and corrects the lateral shift and skew of the sheet S. FIG.

Next, detection control of the amount of skew of the paper S in the printer 100 of this embodiment will be described. FIG. 7 is a top plan view of the printer 100 of the present embodiment, just before the sheet S passes through the CIS 40. As shown in FIG. In this embodiment, the CIS 40 having a detection width larger than the paper width (279 mm) of the maximum size paper S (A4 landscape size) that can be passed through the printer 100 is used.

In the conventional method of calculating the amount of skew, the paper S theoretically is calculated. Next, using the calculated theoretical transport speed vr and the scanning time t per scan of the CIS 40, the amount of movement Δd (=vr×t) in the transport direction of the sheet S per scan of the CIS 40 is calculated. .

Then, after the paper S passes a certain point (point A in FIG. 7, first pixel position) of the CIS 40 (dotted line position in FIG. 7), another point (point B in FIG. 7, second pixel position) is The movement amount ΣΔdn (=vr×t×n) of the paper S in the conveying direction calculated from the number n of scans of the CIS 40 until it passes (solid line position in FIG. 7), and the distance D between the point A and the point B is used to calculate the amount of skew (skew angle) θ of the paper from θ=tan ⁻¹ (ΣΔdn/D).

In the above method, a speed difference occurs between the theoretical transport speed vr of the paper S and the actual transport speed due to variations in the internal frequency of the CPU 70, variations in mechanical parameters, and the like. In addition, it is difficult to avoid erroneous detection of the skew amount due to variations in paper speed caused by slipping of the paper during scanning by the CIS 40 . Therefore, in the printer 100 of the present embodiment, the paper speed detection sensor 60 is used to measure the actual transport speed of the paper S, and the measured transport speed is used as a calculated value to improve the skew amount detection accuracy. there is

FIG. 8 is a flowchart showing an example of skew correction control in the printer 100 of this embodiment. The procedure for detecting the skew amount of the paper S will be described in detail along the steps of FIG. 8 while referring to FIGS. 1 to 7 as necessary.

When the paper S starts to be transported from the paper feed cassette 2a (or the manual paper feed tray 2b) (step S1), the CIS control circuit 71 controls that the leading edge of the paper S is positioned at an arbitrary point of the CIS 40 (point A in this case). ) is passed (step S2). When the leading edge of the sheet S has passed point A of the CIS 40 (Yes in step S2), the CIS 40 starts counting the number of times of scanning (step S3). Further, the sheet speed detection sensor 60 detects the transport speed of the sheet S for each scanning of the CIS 40 (step S4).

Since the output of the paper speed detection sensor 60 may fluctuate due to noise components, the scanning speed of the CIS 40 may be considered and the average (moving average) of multiple detection results may be taken within a range that does not affect the skew amount detection. .

Next, the CIS control circuit 71 determines whether or not the leading edge of the sheet S has passed through a different point (here, point B) of the CIS 40 (step S5). When the leading edge of the sheet S has passed the B point of the CIS 40 (Yes in step S5), the counting of the number of scans of the CIS 40 is stopped (step S6).

Then, the CPU 70 determines the paper transport speed detected by the paper speed detection sensor 60, the scanning time per line (one scan) of the CIS 40, the count value of the number of times of scanning of the CIS 40, and the point A through which the leading edge of the paper S has passed. A skew amount θ is calculated from the distance to the B point (step S7).

Specifically, the movement distance Δd (=v×t) in the transport direction per scan of the paper S is calculated from the paper transport speed v for each scan of the CIS 40 and the scanning time t per line of the CIS 40 . Then, the moving distance ΣΔdn of the paper S is calculated by adding the calculated moving distance Δd in each scan by the number of times of scanning (n times) of the CIS 40 from passing the A point to passing the B point. Then, the calculated ΣΔdn and the distance D between the A point and the B point are used to calculate the skew amount (skew angle) θ (=tan ⁻¹ (ΣΔdn/D)).

For example, if the CIS 40 scans five times before the leading edge of the sheet S passes point A of the CIS 40 and passes point B, and the scanning time t is 400 μsec, the sheet speed detection sensor 60 Using the detected paper transport speeds v1, v2, .

From Table 1, adding the calculated moving distances Δd1 to Δd5 of the paper S for five scans gives 788.8 μm. Assuming that the distance D between point A and point B through which the leading edge of sheet S passes is 300 mm, θ=tan ⁻¹ (788.8/300)=0.1507°.

On the other hand, when the theoretical transport speed vr (=400 mm/s) is used, the movement distance Σd of the paper S for five scans is 400 (mm/s)×400 (μs)×5 (times)=800 μm, θ=tan−1(800/300)=0.1528°. That is, a difference of 12.2 μm in the movement distance of the sheet S and a difference of 0.0014° in the amount of skew occurs compared to the present embodiment.

Then, the skew amount θ calculated in step S7 is converted into the number of motor pulses of the skew correction motor 57 required for correcting the right side skew of the paper S (step S8). The converted motor pulse number is transmitted from the CIS control circuit 71 to the skew correction motor 57, and the skew correction motor 57 is driven by the transmitted motor pulse number to correct the skew of the sheet S (step S9).

According to the control described above, since the skew amount of the paper S is calculated using the actual transport speed of the paper S detected by the paper speed detection sensor 60, the set speed of the transport motor and the driving of the transport roller pair 33 are adjusted. Detects the amount of skew accurately without being affected by variations in the internal frequency of the CPU 70, variations in mechanical parameters, etc., compared to the case of using the theoretical paper transport speed determined based on the mechanical parameters to be transmitted. can do. By performing skew correction using the correction unit 31 based on the detected skew amount, the print image can be printed on the paper S without being skewed.

Further, since it is not necessary to stop the paper S by the registration roller pair, the collision noise of the paper S against the registration roller pair can be reduced. In addition, since there is no restriction on the interval between sheets S (paper interval) in consideration of the sheet stop time between the pair of registration rollers in continuous printing, productivity (image forming efficiency) can be improved.

Here, the paper transport speed v for each scan of the CIS 40 detected by the paper speed detection sensor 60 and the scanning time t for one line of the CIS 40 are used to determine the transport direction of the paper S per scan. A moving distance Δd is calculated, and the sheet skew amount θ is calculated using a moving distance ΣΔdn obtained by adding the calculated moving distance Δd for n scans of the CIS 40 until passing a point B that is apart from the point A in the width direction. However, it is not limited to this.

For example, the paper transport speed is detected only once by the paper speed detection sensor 60, and the detected paper transport speed v, the scanning time t per line of the edge detection sensor, and the time after the paper S passes the A point , the number of scans n of the edge detection sensor until passing point B, and the distance D between point A and point B, θ=tan ⁻¹ {(v×t×n)/D} A skew amount (skew angle) θ may be calculated.

In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, an example using a transmissive CIS 40 having a detection region 40a that receives laser light from the light source unit 41 is shown. Using a reflective CIS 40 that detects the reflected light from the sheet S in the area 40a, the edge position of the sheet S is determined by the intensity difference between the reflected light from the sheet S and the reflected light from the non-passing area of the sheet S. can also In this case, a color different from the color of the paper S (white) is placed at a position facing the detection area 40a of the CIS 40 so that the intensity difference between the reflected light from the paper S and the reflected light from the non-passing area of the paper S increases. background member.

Further, in the above embodiment, the CIS 40 is used as the sensor for detecting the edge position of the sheet S, but a sensor other than the CIS, such as a CCD, may be used.

Further, in the above embodiment, the inkjet recording type printer 100 that records an image by ejecting ink onto the paper S from the ink ejection nozzles of the line heads 10C to 10K has been described as an example. For example, an electrostatic latent image is formed by irradiating an image carrier such as a photosensitive drum with a laser, and toner is applied to the electrostatic latent image to form a toner image. The present invention can also be applied to an electrophotographic image forming apparatus that transfers an image onto a sheet of paper (recording medium) and heats and presses the transferred unfixed toner to form a permanent image.

5 first belt conveying unit 9 recording unit (image forming unit)
21 Sheet skew amount detection device 30 Sensor unit 31 Correction unit 33 Conveying roller pair (sheet conveying section)
40 CIS (edge detection sensor)
40a detection area 41 light source unit 60 paper speed detection sensor (sheet speed detection sensor)
70 CPU (control unit)
71 CIS control circuit (control unit)
100 printer (image forming device)
P paper (sheet)

Claims (7)

A plurality of photoelectric conversion elements have detection areas arranged corresponding to pixels, which are the minimum units of an image, along the width direction perpendicular to the conveying direction of the sheet. an edge detection sensor that detects pixel positions at which the output signals of the photoelectric conversion elements are switched by scanning in the scanning direction as leading edge positions in the transport direction and side edge positions on both sides in the width direction;
a sheet speed detection sensor that detects the conveying speed of the sheet passing through the edge detection sensor;
a control unit that calculates a skew amount of the sheet based on detection results of the edge detection sensor and the sheet speed detection sensor;
with
The control unit passes the conveying speed of the sheet detected by the sheet speed detection sensor, the scanning time per line of the photoelectric conversion element of the edge detection sensor, and the first pixel position of the edge detection sensor. and the number of scans of the edge detection sensor from the first pixel position until it passes a second pixel position away from the first pixel position in the main scanning direction, and the distance between the first pixel position and the second pixel position. and calculating the skew amount of the sheet using . 2. The sheet skew amount detection device according to claim 1, wherein the control unit detects the skew amount .theta.
θ=tan ⁻¹ {(v×t×n)/D} (1)
however,
v; conveying speed of the sheet detected by the sheet speed detection sensor;
t; scanning time per line of the edge detection sensor;
n; the number of scans of the edge detection sensor after the sheet passes the first pixel location until it passes the second pixel location;
D; the distance between the first pixel location and the second pixel location;
is. The control unit uses the sheet conveying speed v for each scanning of the edge detection sensor detected by the sheet speed detecting sensor and the scanning time t to determine the conveying direction per scanning of the sheet. and adding the calculated moving distance Δd for n scans of the edge detection sensor from the first pixel position to passing the second pixel position separated in the width direction, ΣΔdn 3. The sheet skew amount detecting device according to claim 2, wherein the sheet skew amount .theta.
θ=tan ⁻¹ (ΣΔdn/D) (2) a sheet conveying unit that conveys the sheet;
A sheet skew amount detection device according to any one of claims 1 to 3, which is arranged in the sheet conveying unit;
sheet conveying device. a correction unit disposed on the downstream side of the edge detection sensor in the sheet conveying direction for correcting skew and widthwise misalignment of the sheet;
5. The sheet conveying method according to claim 4, wherein the control unit uses the correction unit to perform the width direction misalignment correction and the skew correction of the sheet based on the width direction misalignment amount and the skew amount of the sheet. Device. The correction unit is
a pair of correction rollers for correcting skew and misalignment in the width direction of the sheet while conveying the sheet;
a skew correction motor that tilts a roller holder that supports the pair of correction rollers in the conveying direction;
a lateral displacement correction motor that moves the roller holder in the width direction;
has
6. The sheet conveying apparatus according to claim 5, wherein the skew correction motor and the lateral deviation correction motor are stepping motors capable of controlling the direction and amount of rotation by pulse control. a sheet conveying device according to any one of claims 4 to 6;
an image forming unit that forms an image on the sheet conveyed by the sheet conveying device;
image forming apparatus.

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