JP2013173618A - Conveying device, image forming apparatus, and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for detecting and correcting a lateral shift of a recording sheet with high accuracy.SOLUTION: A conveying device includes: a line sensor receiving reflected light from a conveyance path and a recording sheet; a generation means for generating a control signal for outputting a signal from the line sensor a plurality of times during conveyance of the recording sheet; and a detection means for determining, as a threshold, an intermediate level between an output level of the signal from the line sensor by the reflected light from the conveyance path and an output level of the signal from the line sensor by the reflected light from the recording sheet, binarizing the signal from the line sensor by the determined threshold, and detecting an edge position in a width direction on the basis of the position of the pixel having the varying value. The detection means detects the edge position corresponding to each of the control signals generated a plurality of times during the conveyance of one recording sheet, and determines the threshold for binarizing the signal from the line sensor on the basis of the output level of the signal by the reflected light from the recording sheet, out of the signals from the line sensor in response to the generation of the control signals.

Description

  The present invention relates to a conveyance device, an image forming apparatus, and a control method.

  With the widespread use of image forming apparatuses such as copying machines, such image forming apparatuses are increasingly required to have higher speed and higher image quality. In order to satisfy these requirements, a conveyance device for correcting skew and lateral registration deviation of the recording sheet (recording paper) is provided, and the recording sheet is accurately applied to the toner image formed on the photosensitive member or the transfer member. An image forming apparatus capable of aligning has been proposed.

  For example, a conveyance device using an active registration method does not stop conveyance of a recording sheet, and can correct skew and lateral registration deviation without reducing productivity (see Patent Document 1). In the active registration method, first, when the leading end of the recording sheet passes through two sensors that are spaced apart from each other in the width direction perpendicular to the conveyance direction of the recording sheet, the two sensors output the two. The skew of the recording sheet is detected based on the detection signal. Then, the respective conveying speeds of the two correction rollers arranged in the width direction and spaced apart on the same axis and rotated (driven) independently of each other are made different according to the skew amount of the recording sheet. Correct the skew of the recording sheet. In other words, the rotation speed of the motor that drives each of the two correction rollers is controlled based on the skew amount of the recording sheet, so that the conveyance speed of one correction roller is slower than the conveyance speed of the other correction roller. Alternatively, the skew of the recording sheet is corrected by increasing the speed.

  As described above, since the active registration method can correct the skew of the recording sheet without stopping the recording sheet conveyance, the recording sheet conveyance efficiency is reduced by making the recording sheet interval narrower than other methods. Can be improved. Therefore, the conveying apparatus using the active registration method can substantially improve the printing speed without increasing the image forming process speed in the image forming apparatus.

  In the recording sheet in which the skew feeding is corrected, the deviation in the width direction (lateral registration deviation) is further corrected. In correcting the lateral misregistration, the output from the line sensor for detecting the edge of the sheet in the width direction is binarized using a predetermined threshold. The change point of the binarized value (change from 1 to 0 or 0 to 1) is determined as the edge of the recording sheet. Further, the difference between the edge position and the lateral registration target position (lateral registration deviation amount) is calculated, the direction of the lateral registration deviation is judged, and the lateral registration deviation is shifted by shifting the roller for conveying the recording sheet. to correct.

  Hereinafter, a conventional transfer apparatus will be described in detail with reference to FIG. FIG. 5 is a schematic block diagram showing a conventional transfer apparatus 1000 using the active registration method. The transport apparatus 1000 includes a pre-registration correction roller 1010, skew detection sensors 1020L and 1020R, a skew detection unit 1030, skew correction rollers 1040L and 1040R, and a skew control unit 1050. Further, the transport apparatus 1000 includes an edge detection timing sensor 1060, a lateral registration deviation amount detection unit 1070, a line sensor 1080, a shift roller 1090, a timing sensor 1100, and a shift control unit 1110.

  In the transport apparatus 1000, the leading edge of the recording sheet PS is detected by the skew detection sensors 1020L and 1020R while the pre-registration correction roller 1010 is transporting the recording sheet PS. The skew detection unit 1030 calculates the skew amount from the detection time difference between the two skew detection sensors 1020L and 1020R, and which of the skew detection sensors 1020L and 1020R detects the leading edge of the recording sheet PS first. Determine the skew direction. When the skew correction rollers 1040L and 1040R sandwich the recording sheet PS, the skew control unit 1050 determines whether the skew correction roller 1040L or the skew correction roller 1040L or the skew direction is based on the skew amount and the skew direction calculated by the skew detection unit 1030. Decelerate 1040R. Thereby, the skew of the recording sheet PS is corrected.

  When the conveyance of the recording sheet PS advances and the leading edge of the recording sheet passes the edge detection timing sensor 1060, the lateral registration deviation amount detection unit 1070 outputs the output level (sensitivity) of the line sensor 1080 near the center of the recording sheet PS. ) Is meeting the target level. For example, when the line sensor 1080 has red (R), green (G), and blue (B) LEDs, these LEDs emit light alone, emit two colors, or all The output level of the line sensor 1080 changes depending on whether the color is emitted. Accordingly, the light emission pattern of the LED is set (determined) to an appropriate light emission pattern in which the output level of the line sensor 1080 achieves the target level. Further, the intermediate level of each output level of the line sensor 1080 between the state where the recording sheet PS is not conveyed to the position of the line sensor 1080 and the state where the recording sheet PS is conveyed is binary with respect to the output of the line sensor 1080. It becomes the threshold value of the conversion. In the state where the recording sheet PS is not conveyed to the position of the line sensor 1080, the line sensor 1080 detects the conveyance path (background) of the recording sheet PS.

  Further, when the conveyance of the recording sheet PS proceeds and the shift roller 1090 sandwiches the recording sheet PS, the edge detection of the recording sheet PS using the threshold value described above is executed a plurality of times. The lateral registration deviation amount detection unit 1070 calculates a difference (horizontal registration deviation amount) between the average value of the plurality of edge detections and the lateral registration target position, and determines the direction of lateral registration deviation. When the recording sheet PS passes the timing sensor 1100, the shift control unit 1110 shifts the shift roller 1090 based on the lateral registration deviation amount and the lateral registration deviation direction calculated by the lateral registration deviation amount detection unit 1070. Let Thereby, the lateral registration deviation of the recording sheet PS is corrected.

Japanese Patent Laid-Open No. 10-032682

  However, if the binarization threshold for the output of the line sensor is set (fixed) to an intermediate level of the output level of the line sensor when the conveyance path is detected and the recording sheet conveyed to the position of the line sensor is detected (fixed) This causes a problem when detecting the edge of the recording sheet.

  For example, as shown in FIG. 6A, when the recording sheet is conveyed so as to be positioned at the focal position of the line sensor, the edge of the recording sheet can be detected without error. However, as shown in FIG. 6B, when the recording sheet is conveyed out of the focus position of the line sensor, the output waveform from the line sensor becomes dull and the output level also decreases. Accordingly, when the recording sheet is conveyed out of the focus position of the line sensor, if the edge of the recording sheet is detected with the above-described threshold, an error (detection error) occurs in the detection result. That is, the detected edge position of the recording sheet is deviated from the actual edge position. 6A and 6B show the positional relationship between the recording sheet and the line sensor (the focal position thereof) as viewed from the recording sheet conveyance direction.

  Also, in correcting lateral misregistration, the shift roller must be shifted immediately after detecting the edge of the recording sheet in order to achieve high speed. Therefore, the skew correction roller and the shift roller have a certain distance. Need to be placed apart. Therefore, when the recording sheet is a small size (for example, letter size), the only roller that sandwiches the recording sheet at the time of edge detection is the shift roller. For this reason, the amount of deviation of the recording sheet from the focal position of the line sensor differs for each of a plurality of edge detections depending on the wind pressure during conveyance and the characteristics of the recording sheet. For example, as shown in FIGS. 7A to 7D, as the recording sheet is conveyed (as the line sensor detects the trailing edge of the recording sheet), the recording sheet moves from the focal position of the line sensor. As a result, the detection error gradually increases. 7A to 7D show the positional relationship between the recording sheet and the line sensor (the focal position thereof) viewed from the direction orthogonal to the recording sheet conveyance direction.

  In view of the above-described problems of the related art, an object of the present invention is to provide a technique capable of detecting and correcting a lateral registration shift of a recording sheet with high accuracy.

In order to achieve the above object, a transport apparatus according to a first aspect of the present invention is a transport apparatus that transports a recording sheet, and is disposed in a transport path of the recording sheet, from the transport path and the recording sheet. A line sensor that receives the reflected light of the line, a generating means for generating a control signal for outputting a signal from the line sensor a plurality of times during the conveyance of one recording sheet, and the line by the reflected light from the conveyance path An intermediate level between the output level of the signal from the sensor and the output level of the signal from the line sensor due to the reflected light from the recording sheet is determined as a threshold value, and the signal from the line sensor is binarized with the determined threshold value. , based on the position of the pixel of the line sensor binarized value changes, the recording sheet edges in the width direction perpendicular to the conveying direction of the recording sheet A detecting means for detecting a location, and the detecting device, the position of the edge of the recording sheet corresponding to each of the plurality of times the emitted control signal from said generating means during conveyance of one recording sheet detects, among the signals from the line sensor in response to said control signal is generated in each of the detection, the next control signal is generated based on the output level of the signal due to reflected light from said recording sheet The threshold value for binarizing the signal from the line sensor according to is determined.

  Further objects and other aspects of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, for example, it is possible to provide a conveyance device that detects and corrects a lateral registration deviation (a deviation in a direction perpendicular to the conveyance direction of the recording sheet) of the recording sheet with high accuracy.

It is a schematic block diagram which shows the conveying apparatus as 1 side surface of this invention. It is a schematic block diagram which shows the conveying apparatus as 1 side surface of this invention. It is a flowchart for demonstrating the conveyance operation of the conveying apparatus shown in FIG. It is a figure which shows an example of the relationship (timing chart) of the output of a synchronizing signal, an enable signal, and a line sensor. FIG. 10 is a diagram illustrating a state in which a threshold value when binarizing the output of a line sensor in each of a plurality of edge detections is changed in accordance with the output of the line sensor when performing edge detection of the recording sheet a plurality of times. . It is a schematic block diagram which shows the conventional conveying apparatus using an active registration system. It is a figure for demonstrating the problem of the conventional conveying apparatus. It is a figure for demonstrating the problem of the conventional conveying apparatus.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

  1A and 1B are schematic block diagrams showing a transport apparatus 1 as one aspect of the present invention. The conveyance device 1 is a device that conveys a recording sheet PS, and is a conveyance device of an image forming apparatus (for example, a copier, a facsimile, a printer, a multifunction machine, etc.) that includes an image forming unit that forms an image on the recording sheet PS. Can be applied.

  As shown in FIG. 1A, the conveyance device 1 includes a line sensor 101, a shift roller 102, a sensor 103, a delay unit 104, a control signal generation unit 105, an A / D conversion unit 106, and a provisional threshold calculation unit. 107. Further, the transport device 1 includes a threshold value calculation unit 108, an edge position detection unit 109, a shift calculation unit 110, a sensor 111, a shift control unit 112, a driver 113, and an LED driver 120. FIG. 1A shows only the configuration related to the correction of the lateral registration deviation of the recording sheet PS (deviation in the width direction perpendicular to the conveyance direction of the recording sheet PS). However, as shown in FIG. 1B, the conveyance device 1 includes the pre-registration correction roller 131, the skew detection sensors 132L and 132R, the skew detection unit 133, and the skew correction roller 134L related to the skew correction of the recording sheet PS. And 134R, and a skew control unit 135.

  The functions and configurations of the pre-registration correction roller 131, the skew detection sensors 132L and 132R, the skew detection unit 133, the skew correction rollers 134L and 134R, and the skew control unit 135 are the same as those in the related art (FIG. 5). The skew detection sensors 132L and 132R detect the leading end of the recording sheet PS while the pre-registration correction roller 131 is transporting the recording sheet PS. Further, the skew detection unit 133 calculates the skew amount of the recording sheet PS and determines the skew direction of the recording sheet PS based on the detection results of the skew detection sensors 132L and 132R. Then, based on the skew amount and skew direction calculated by the skew detection unit 133, the skew control unit 135 decelerates the skew correction rollers 134L and 134R that sandwich the recording sheet PS, and thereby records the recording sheet PS. Correct the skew.

  The sensor 103 is arranged so as to be able to detect the vicinity of the central portion of the recording sheet PS and the conveyance path of the recording sheet PS, and detects the leading end of the recording sheet PS. When the sensor 103 detects the leading edge of the recording sheet PS, the lateral registration deviation of the recording sheet PS is corrected by the line sensor 101, the lateral registration deviation amount detection unit, the sensor 111, the shift control unit 112, the shift roller 102, and the like. Here, the lateral registration deviation amount detection unit includes a provisional threshold calculation unit 107, a threshold calculation unit 108, an edge position detection unit 109, a shift calculation unit 110, and the like, and the difference between the edge of the recording sheet PS in the width direction and the target position. While calculating (lateral registration deviation amount), the direction of lateral registration deviation is determined. Note that the specific operation of correcting the lateral registration deviation of the recording sheet PS will be described in detail in the transport operation of the transport device 1 described later.

  The line sensor 101 also includes an LED that emits light to the recording sheet PS, and a plurality of pixels (sensor elements) that receive the light reflected by the recording sheet PS or the conveyance path (base) of the recording sheet PS. It consists of. The line sensor 101 is arranged so that at least a region from one edge of the recording sheet PS in the width direction to the vicinity of the center of the recording sheet PS can be detected. Accordingly, the line sensor 101 detects the recording sheet PS in a state where the recording sheet PS is conveyed to the position of the line sensor 101, and detects the recording sheet PS in a state where the recording sheet PS is not conveyed to the position of the line sensor 101. A conveyance path (base) is detected. In the present embodiment, the edge of the recording sheet PS in the width direction is binarized using a threshold value described later, and is used as a change point of the binarized value. In the line sensor 101, the light emission pattern of the LEDs is set so that the output level (sensitivity) near the center of the recording sheet PS achieves the target level.

  Hereinafter, with reference to FIG. 1A and FIG. 2, the conveying operation of the conveying device 1 will be described together with each part constituting the conveying device 1. FIG. 2 is a flowchart for explaining the transport operation of the transport apparatus 1. The transport operation of the transport device 1 is started after the power is turned on and the system is reset. Such a conveyance process is executed when the control signal generation unit 105 outputs a control signal to each part of the conveyance apparatus 1 (that is, comprehensively controls each part of the conveyance apparatus 1). However, as described above, the conveyance device 1 is similar to the conventional conveyance operation related to the correction of the skew of the recording sheet PS, and here, the conveyance operation related to the correction of the lateral registration deviation of the recording sheet PS is performed. Only the operation will be described.

  Referring to FIG. 2, the control signal generation unit 105 determines whether or not an initializing trigger (initial trigger) has been input (S202). If the initial trigger is not input, it waits until the initial trigger is input.

  When the initial trigger is input, the control signal generation unit 105 generates (outputs) a synchronization signal and an enable signal for causing the LED built in the line sensor 101 to emit light (S204). The synchronization signal is directly input to the line sensor 101. The enable signal is input to the line sensor 101 via the LED driver 120.

  The line sensor 101 to which the synchronization signal and the enable signal are input causes the LED to emit light based on the synchronization signal and the enable signal (S206). As a result, the line sensor 101 outputs a detection signal corresponding to the conveyance path (base) of the recording sheet PS.

  FIG. 3 is a diagram illustrating an example of a relationship (timing chart) between the synchronization signal, the enable signal, and the output of the line sensor 101. As shown in FIG. 3, the line sensor 101 causes the LED to emit light corresponding to each of the enable signals ES1 and ES2, executes charge storage of the pixels (sensor elements), and outputs detection signals DS1 and DS2.

  After the light emission of the LED of the line sensor 101 is completed, the control signal generation unit 105 generates (outputs) the synchronization signal again (S208).

  The A / D converter 106 converts the detection signal from the line sensor 101 into digital data, and stacks a predetermined number of digital data on the output level calculator 121. The output level calculation unit 121 calculates (outputs) the average value of a predetermined number of digital data stacked from the A / D conversion unit 106 as the output level when the line sensor 101 detects the conveyance path (S210).

  The control signal generator 105 determines whether the sensor 103 has detected the leading edge of the recording sheet PS (S212). If the sensor 103 has not detected the leading edge of the recording sheet PS, the process waits until the sensor 103 detects the leading edge of the recording sheet PS. When the sensor 103 detects the leading edge of the recording sheet PS, the sensor 103 transmits a signal indicating that the leading edge of the recording sheet PS has been detected to the control signal generation unit 105 and the temporary threshold calculation unit 107.

  When the sensor 103 detects the leading edge of the recording sheet PS, the control signal generation unit 105 generates (outputs) a synchronization signal, an enable signal, and a sensor clock using the signal from the sensor 103 as a trigger (S214). The synchronization signal and the sensor clock are directly input to the line sensor 101. The enable signal is input to the line sensor 101 via the LED driver 120.

  The line sensor 101 causes the LED to emit light while the enable signal is input from the control signal generation unit 105 (S216). Thereby, the line sensor 101 outputs a detection signal when the recording sheet PS is detected.

  After the light emission of the LED of the line sensor 101 is completed, the control signal generation unit 105 generates (outputs) the synchronization signal again (S218).

  The temporary threshold value calculation unit 107 is an area in which the presence of the recording sheet PS is determined in the digital data input from the line sensor 101 via the A / D conversion unit 106 (that is, the line sensor 101 detects the recording sheet PS). The output level is extracted (S220). Further, the temporary threshold calculation unit 107 calculates a temporary threshold (setting value) (S222). Specifically, the temporary threshold value calculation unit 107 calculates an intermediate level between the output level when the line sensor 101 detects the conveyance path and the output level when the line sensor 101 extracted in S220 detects the recording sheet PS. And calculated as a provisional threshold (set value).

  On the other hand, a delay amount is set in the delay unit 104 so that detection of the edge (position) of the recording sheet PS in the width direction is started after correcting the skew of the recording sheet PS. The delay unit 104 outputs the set delay amount to the control signal generation unit 105 and the threshold value calculation unit 108, and the control signal generation unit 105 determines whether the delay amount is input from the delay unit 104 (S224). If no delay amount is input from the delay unit 104, the process waits until a delay amount is input from the delay unit 104.

  When the delay amount is input from the delay unit 104, the control signal generation unit 105 generates (outputs) a synchronization signal, an enable signal, and a sensor clock (S226).

  The line sensor 101 causes the LED to emit light while the enable signal is input from the control signal generation unit 105 (S228). Thereby, the line sensor 101 outputs a detection signal.

  After the light emission of the LED of the line sensor 101 is completed, the control signal generation unit 105 generates (outputs) the synchronization signal again (S230).

  The threshold calculation unit 108 has digital data (output of the line sensor 101) input from the line sensor 101 via the A / D conversion unit 106 equal to or greater than the provisional threshold calculated by the provisional threshold calculation unit 107 (more than a set value). It is determined whether or not there is (S232). If the digital data is not greater than or equal to the provisional threshold, the process waits until the digital data exceeds the provisional threshold.

  If the digital data is greater than or equal to the provisional threshold, the threshold calculation unit 108 extracts the output level of the line sensor 101 at a position (pixel) that is a predetermined distance away from a position (pixel) that is greater than or equal to the provisional threshold (S234). ). Further, the threshold value calculation unit 108 calculates a threshold value when binarizing the output of the line sensor 101 (that is, when detecting the position of the edge of the recording sheet PS) (S236). Specifically, the threshold value calculation unit 108 calculates an intermediate level between the output level when the line sensor 101 detects the conveyance path and the output level when the line sensor 101 extracted in S236 detects the recording sheet PS, Calculate as the threshold. Further, the threshold value calculation unit 108 inputs the calculated threshold value to the edge position detection unit 109. The surface of the conveyance path has, for example, a color and surface property (roughness) such that the reflection level from the recording sheet PS and the reflection level from the conveyance path can be distinguished. Further, the wavelength of the LED light of the line sensor 101 is also set to a wavelength that allows the detection level of the recording sheet PS and the detection level of the conveyance path to be distinguished.

  When the threshold value is calculated, the control signal generation unit 105 generates (outputs) a synchronization signal, an enable signal, and a sensor clock (S238).

  The line sensor 101 causes the LED to emit light while the enable signal from the control signal generation unit 105 is input (S240). Thereby, the line sensor 101 outputs a detection signal.

  After the light emission of the LED of the line sensor 101 is completed, the control signal generation unit 105 generates (outputs) the synchronization signal again (S242).

  The edge position detection unit 109 determines whether the digital data (output of the line sensor 101) input from the line sensor 101 via the A / D conversion unit 106 is equal to or greater than the threshold calculated by the threshold calculation unit 108. (S244). If the digital data is not greater than or equal to the threshold, the process waits until the digital data exceeds the threshold.

  If the digital data is equal to or greater than the threshold value, the edge position detection unit 109 detects the edge position (edge detection) of the recording sheet PS in the width direction when the digital data exceeds the threshold value (S246). Specifically, the edge position detection unit 109 binarizes the output of the line sensor 101 using the threshold value calculated in S236, and uses the position where the binarized value changes as the edge position of the recording sheet PS. To detect.

  Further, the edge position detection unit 109 determines whether or not the detection of the edge position (edge detection) of the recording sheet PS has been performed a plurality of times (that is, whether the detection has been performed a predetermined number of times) (S248). The recording sheet PS tends to gradually increase the deviation amount of the recording sheet PS from the focal position of the line sensor 101 according to the conveyance of the conveyance sheet PS due to the wind pressure during conveyance and the characteristics of the recording sheet. Therefore, it is necessary to detect the edge of the recording sheet PS with high accuracy by executing edge detection a plurality of times while changing the threshold value.

  If the detection of the edge position of the recording sheet PS (edge detection) has not been performed a plurality of times, the edge position detection unit 109 temporarily detects the edge position (edge position information) of the recording sheet PS detected so far. Store (S250). Then, the edge position detection unit 109 generates an edge detection continuation signal (S252), returns to S234, and continues the edge detection while calculating a new threshold (that is, changing the threshold). The edge detection continuation signal is input to the threshold value calculation unit 108.

  If the detection of the edge position (edge detection) of the recording sheet PS is performed a plurality of times, the edge position detection unit 109 calculates the average of the edge positions of the recording sheet PS detected by the plurality of edge detections as the edge position. Information is output to the shift calculation unit 110 (S254). Further, the edge position detection unit 109 generates an edge detection completion signal (S256). The edge detection completion signal is input to the control signal generation unit 105.

  Based on the edge position information from the edge position detection unit 109, the shift calculation unit 110 calculates a shift amount and a shift direction indicating a deviation of the edge of the recording sheet PS in the width direction from the target position (S258). In addition, the shift calculation unit 110 inputs the calculated shift amount and shift direction to the shift control unit 112.

  The shift control unit 112 generates (outputs) control pulses and CW / CCW signals corresponding to the shift amount and the shift direction calculated by the shift calculation unit 110 when the sensor 111 detects the leading edge of the recording sheet PS. (S260). In other words, the shift control unit 112 controls the position of the recording sheet PS based on the shift amount and the shift direction calculated by the shift calculation unit 110 so that the edge of the recording sheet PS matches the target position. Is generated (output).

  The driver 113 drives the motor based on the control pulse and the CW / CCW signal from the shift control unit 112 to shift the shift roller 102 (drive shaft thereof) in the direction perpendicular to the transport direction (S262). Thereby, the lateral registration deviation of the recording sheet PS is corrected.

  4A to 4D show the output of the line sensor 101 in each of the plurality of edge detections in accordance with the output of the line sensor 101 when the edge detection of the recording sheet PS is executed a plurality of times. It is a figure which shows a mode that the threshold value at the time of binarization is changed. 4A to 4D correspond to the states shown in FIGS. 7A to 7D.

In the state shown in FIG. 4A, the output level when the line sensor 101 detects the conveyance path is G, and the output level when the line sensor 101 detects the recording sheet PS positioned at the focal position of the line sensor 101 is G. a, the threshold is assumed to be TH _1.

When edge detection is performed in the state shown in FIG. 4B, the threshold TH ₁ is set to the output level A and the output level G when the line sensor 101 detects the recording sheet PS in the state shown in FIG. Is changed to a threshold value TH ₂ ((A + G) / 2) which is an intermediate level. Threshold TH ₂ is substantially the same as the threshold value TH _1, has a value of slightly more recording sheet PS for output level B.

Further, at the edge detection in the state shown in FIG. 4 (c), the threshold value TH ₂ is, and FIG. 4 (b) and the output level B at which the line sensor 101 has detected the recording sheet PS in the state shown in the output level G Is changed to a threshold value TH ₃ ((B + G) / 2) which is an intermediate level. Threshold TH ₃ is smaller than the threshold value TH _2, since the falling output level C, it is possible to reduce the detection error in detecting the position of an edge of the recording sheet PS. On the other hand, if the threshold value TH ₁ or TH ₂ is used in the edge detection in the state shown in FIG. 4C, the detection error when detecting the position of the edge of the recording sheet PS becomes large.

Further, at the edge detection in the state shown in FIG. 4 (d), the threshold value TH ₃ is, and FIG. 4 (c) in the line sensor 101 in a state indicated by the output level C at the time of detection of the recording sheet PS output level G Is changed to a threshold value TH ₄ ((C + G) / 2) which is an intermediate level.

  As described above, in the conveyance apparatus 1 of the present embodiment, when the edge detection of the recording sheet PS is performed a plurality of times, the threshold value is changed according to the output level of the line sensor 101 in each of the plurality of edge detections. Specifically, an intermediate level between the output level when the line sensor 101 detects the conveyance path and the output level of the line sensor 101 in an arbitrary edge detection among a plurality of edge detections is determined by the arbitrary edge detection. It is set as a threshold in the next edge detection. Therefore, even if the recording sheet PS is not positioned at the focal position of the line sensor 101, the conveying device 1 detects the lateral registration deviation (deviation in the direction orthogonal to the recording sheet conveyance direction) of the recording sheet with high accuracy. And can be corrected.

  As mentioned above, although preferable embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

Claims (6)

A conveying device for conveying a recording sheet,
A line sensor that is disposed in the conveyance path of the recording sheet and receives reflected light from the conveyance path and the recording sheet ;
Generating means for generating a control signal for outputting a signal from the line sensor a plurality of times during conveyance of one recording sheet;
An intermediate level between the output level of the signal from the line sensor due to the reflected light from the conveyance path and the output level of the signal from the line sensor due to the reflected light from the recording sheet is determined as a threshold, and the determined threshold is used as the threshold. The signal from the line sensor is binarized, and the position of the edge of the recording sheet in the width direction orthogonal to the conveyance direction of the recording sheet is determined based on the position of the pixel of the line sensor where the binarized value changes. Detecting means for detecting;
Have,
It said detecting means, corresponding to each of said generating means during conveyance of one recording sheet of a plurality of times the emitted control signal detects the position of the edge of the recording sheet, wherein the control signal is in each of the detection Among the signals from the line sensor in response to the generation, the signal from the line sensor in response to the generation of the next control signal based on the output level of the signal by the reflected light from the recording sheet is binary. A transport apparatus characterized by determining a threshold value for conversion into a threshold. The detection means is based on an output level of a signal from the line sensor at a pixel position separated by a predetermined distance from a pixel in the width direction where the binarized value changes in each detection. The transport apparatus according to claim 1, wherein a threshold for binarizing a signal from the line sensor in response to generation of the next control signal is determined . Shift means for shifting the recording sheet in the width direction;
Control means for controlling the shift means so that the edge of the recording sheet in the width direction is shifted to a target position based on the position of the edge of the recording sheet detected by the detection means;
The transport apparatus according to claim 1 , further comprising: 4. The conveying apparatus according to claim 3, wherein the control unit controls the shift unit based on an average value of edge positions detected a plurality of times on one recording sheet . An image forming apparatus for forming an image on a recording sheet,
A conveying device according to any one of claims 1 to 4, which conveys the recording sheet;
Image forming means for forming an image on a recording sheet conveyed by the conveying device;
An image forming apparatus comprising: A control method for a transport device that is disposed in a transport path of a recording sheet , includes a line sensor that receives reflected light from the transport path and the recording sheet, and transports the recording sheet,
A generation step of generating a control signal for outputting a signal from the line sensor a plurality of times during conveyance of one recording sheet;
An intermediate level between the output level of the signal from the line sensor due to the reflected light from the conveyance path and the output level of the signal from the line sensor due to the reflected light from the recording sheet is determined as a threshold, and the determined threshold is used as the threshold. The signal from the line sensor is binarized, and the position of the edge of the recording sheet in the width direction orthogonal to the conveyance direction of the recording sheet is determined based on the position of the pixel of the line sensor where the binarized value changes. A detection step to detect;
Have,
In the detecting step, the position of the edge of the recording sheet is detected corresponding to each of the control signals generated a plurality of times in the generating step during conveyance of one recording sheet, and the control signal is detected in each detection. Among the signals from the line sensor in response to the generation, the signal from the line sensor in response to the generation of the next control signal based on the output level of the signal by the reflected light from the recording sheet is binary. A control method characterized by determining a threshold value for conversion into a threshold.

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