Sheet feeder

Abstract

To solve a problem that when a printing job continues for a long time in an imaging device, temperature inside the imaging device rises, causing output of an ultrasonic sensor to fluctuate, which results in lower accuracy of double feed detection.SOLUTION: Decrease of accuracy of double feed detection is prevented by setting a threshold value according to temperature.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a sheet transport device that transports a sheet. [Background technology]

[0002] A technology has been disclosed in the past that detects whether or not multiple sheets are being conveyed in an overlapping state (multiple feed) based on an ultrasonic sensor (Patent Document 1). In Patent Document 1, when a signal obtained by receiving ultrasonic waves output from an output section of the ultrasonic sensor and received by a receiving section is smaller than a threshold value, it is determined that multiple feed has occurred. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-095390 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an image forming apparatus, when a print job continues for a long time, the temperature inside the apparatus increases and the output of the ultrasonic sensor may fluctuate, resulting in a decrease in the accuracy of detecting double feed.

[0005] In view of the above-mentioned problems, an object of the present invention is to suppress a decrease in accuracy of detecting double feeding by an ultrasonic sensor. [Means for solving the problem]

[0006] In order to solve the above problems, an image forming apparatus according to the present invention comprises: a multi-feed detection sensor including an output unit that outputs ultrasonic waves and a receiving unit that receives the ultrasonic waves output from the output unit and outputs a signal indicating a reception result; a determining unit that determines that a plurality of sheets are being conveyed in an overlapping state when the signal output from the receiving unit is smaller than a first value as a threshold value; A temperature sensor that detects a temperature; a first control means for controlling conveyance of the sheet so that, when a temperature detected by the temperature sensor rises to a predetermined temperature during execution of an image forming job for forming an image on the sheet, a distance between a rear end in a conveyance direction of a preceding first sheet and a front end in the conveyance direction of a second sheet following the preceding sheet increases; a second control means for causing the output section to output the ultrasonic wave during a period from when a trailing end of the first sheet in the transport direction passes a detection position of the double feed detection sensor until a leading end of the second sheet in the transport direction reaches the detection position; a setting means for setting the threshold value to a second value that is greater than the first value based on the signal output from the receiving unit during the period; The present invention is characterized by having the following. Effect of the Invention

[0007] According to the present invention, it is possible to suppress a decrease in the accuracy of detecting double feeding by an ultrasonic sensor. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an image forming apparatus. [Diagram 2] FIG. 2 is a block diagram showing an example of a control configuration of the image forming apparatus. [Diagram 3] 13A and 13B are diagrams illustrating signals received by the double feed detection sensor T2. [Figure 4] 13 is a diagram showing the relationship between the temperature of the double-feed detection sensor T2 and the amplitude (sensor sensitivity) of the signal output from the double-feed detection sensor T2. FIG. [Diagram 5] 13 is a diagram showing the relationship between the temperature detected by the temperature sensor and the amplitude of the signal output from the double feed detection sensor T2. FIG. [Figure 6] FIG. 11 is a diagram illustrating a method for setting a threshold value. [Figure 7] FIG. 13 is a diagram illustrating a set threshold value. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Preferred embodiments of the present invention will be described below with reference to the drawings. However, the shapes of the components and their relative positions described in the embodiments may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and the scope of the present invention is not intended to be limited to the following embodiments.

[0010] [First embodiment] [Image forming device] 1 is a cross-sectional view showing the configuration of a color electrophotographic copying machine (hereinafter referred to as an image forming apparatus) 100 used in this embodiment. Note that the image forming apparatus is not limited to a copying machine, and may be, for example, a facsimile machine, a printing machine, a printer, etc. Furthermore, the recording method is not limited to an electrophotographic method, and may be, for example, an inkjet method, etc. Furthermore, the type of the image forming apparatus may be either a monochrome type or a color type.

[0011] The configuration and functions of the image forming apparatus 100 will be described below with reference to Fig. 1. As shown in Fig. 1, the image forming apparatus 100 has an original feeding device 201 as a sheet transport device, an original reading device 200 including a reading device 202, and an image printing device 301.

[0012] <Document reader> The position in the width direction (a direction intersecting the feeding direction in which the document P is fed) of the document P loaded on the document loading section 2 of the document feeding device 201 is regulated by a pair of regulating sections 1 provided on the document loading section 2. The pair of regulating sections 1 are configured to be movable in accordance with the width of the document.

[0013] The originals P are fed one by one by the pickup roller 3, and then transported further downstream by the feed roller 4. A separation roller 5 that is in pressure contact with the feed roller 4 is provided at a position opposite to the feed roller 4. The separation roller 5 is configured to rotate when a load torque equal to or greater than a predetermined torque is applied to the separation roller 5, and has the function of separating the originals that are fed in a two-sheet overlapping state.

[0014] The pickup roller 3 and the feed roller 4 are connected by a swing arm 12. The swing arm 12 is supported by the rotation shaft of the feed roller 4 so as to be rotatable around the rotation shaft of the feed roller 4.

[0015] The document P fed by the feed roller 4 is transported further downstream by the transport roller 6. The document P is discharged onto the discharge tray 10 by the discharge roller 11.

[0016] The reading device 202 is provided with a reading unit 16 that reads an image of the first side of a document being conveyed. The reading unit 16 has an LED 110, an image sensor 111, and an optical component group 112. The image sensor 111 has a plurality of light receiving elements that receive R (red), G (green), and B (blue) light in the main scanning direction (corresponding to the width direction perpendicular to the conveying direction of the document). The reading unit 16 reads an image of the front side (first side) of the document as follows. Specifically, the LED 110 as a light source irradiates (emits) light onto the front side of the document being conveyed through the reading glass 108. The optical component group 112 guides the reflected light from the document received through the reading glass 108 to the image sensor 111. The image sensor 111 outputs analog image data based on the received light. The image sensor 111 simultaneously reads one line of the image in the main scanning direction. Therefore, by reading one line of image multiple times by the image sensor 111 while conveying the document, the image sensor 111 can output image data including the entire document.

[0017] Further, the document feeder 201 is provided with a reading unit 17 that reads an image on the second side of the document being conveyed. The configuration of the reading unit 17 is similar to that of the reading unit 16, and therefore a description thereof will be omitted.

[0018] Methods for reading an original include a skimming method and a pressure plate reading method. The skimming method is a method for reading an image of an original transported by the above-mentioned method. The pressure plate reading method is a method for reading an image of an original placed on the original table glass 214 of the reading device 202 by the reading unit 16 moving at a constant speed in the sub-scanning direction (rightward in FIG. 1) corresponding to the transport direction in which the original is transported. Usually, images of sheet-like originals are read by the skimming method, and images of bound originals such as books and pamphlets are read by the pressure plate reading method.

[0019] The document feeder 201 is rotatable relative to the reader 202 between an open position where the document glass 214 is exposed and a closed position where the document glass 214 is covered by a pressure plate 18. The document feeder 201 has a pressure plate that presses the document placed on the document glass 214 toward the document glass 214 in the closed position. In the pressure plate reading method, the document placed on the document glass 214 is read by the reader 16 that moves in the sub-scanning direction.

[0020] <Image printing device> A sheet storage tray 18 for storing recording media is provided inside the image printing device 301. Note that the recording media are those on which an image is formed by the image forming device, and include, for example, paper, resin sheets, cloth, OHP sheets, labels, etc.

[0021] The recording medium stored in the sheet storage tray 18 is sent out by a pickup roller 19, and is sent to a registration roller 20 by conveyance rollers 39, 40, 41, 42, etc.

[0022] The image printing device 301 is also provided with a manual feed tray 44 on which recording media are stacked. The recording media stacked on the manual feed tray 44 are sent out by a pickup roller 43, and are then sent to the registration rollers 20 by a transport roller 42 and the like.

[0023] A double-feed detection sensor is provided downstream of the transport roller 42 to detect whether or not two or more documents are transported overlapping each other (double-feed). The double-feed detection sensor is, for example, an ultrasonic sensor, and an ultrasonic transmission sensor T1 serving as an output section transmits ultrasonic waves, and an ultrasonic reception sensor T2 serving as a reception section receives the ultrasonic waves. Although not shown in FIG. 1, a temperature sensor 162 is provided near the double-feed detection sensor to detect the temperature near the double-feed detection sensor.

[0024] The leading edge of the recording medium conveyed by the pre-registration roller 37 hits the registration roller 20. As a result, a loop is formed in the recording medium between the registration roller 20 and the pre-registration roller 37, and the skew of the recording medium is corrected (reduced).

[0025] The image signal output from the document reading device 200 is input for each color component to optical scanning devices 21Y, 21M, 21C, and 21K including a semiconductor laser and a polygon mirror. Specifically, the image signal for yellow output from the document reading device 200 is input to optical scanning device 3Y, and the image signal for magenta output from the document reading device 200 is input to optical scanning device 3M. In addition, the image signal for cyan output from the document reading device 200 is input to optical scanning device 3C, and the image signal for black output from the document reading device 200 is input to optical scanning device 3K. In the following description, a configuration for forming a yellow image will be described, but the same configuration applies to magenta, cyan, and black.

[0026] The outer peripheral surface of the photosensitive drum 22Y is charged by the charger 23Y. After the outer peripheral surface of the photosensitive drum 22Y is charged, a laser beam corresponding to an image signal input from the document reading device 200 to the optical scanning device 21Y is irradiated onto the outer peripheral surface of the photosensitive drum 22Y from the optical scanning device 21Y via an optical system including a polygon mirror and a mirror. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 22Y.

[0027] Next, the electrostatic latent image is developed by toner in a developing device 24Y as a developing unit, and a toner image is formed on the outer peripheral surface of the photosensitive drum 22Y. The toner image formed on the photosensitive drum 22Y is transferred to a transfer belt 27 as an intermediate transfer body by a transfer roller 25Y provided at a position facing the photosensitive drum 22Y. Note that the toner remaining on the outer peripheral surface of the photosensitive drum 22Y after the toner image is transferred to the transfer belt 27 is collected by a cleaning unit 26Y.

[0028] The yellow, magenta, cyan, and black toner images transferred onto the transfer belt 27 are transferred onto the recording medium by the pair of transfer rollers 28. A high voltage is applied to the pair of transfer rollers 28, and the toner images are transferred onto the recording medium due to the high voltage. The registration rollers 20 feed the recording medium into the pair of transfer rollers 28 in accordance with the timing of this transfer.

[0029] As described above, the recording medium onto which the toner image has been transferred is sent to the fixing device 29 as a fixing section, and the toner image is fixed to the recording medium by heating and pressurizing the recording medium by the fixing device 29. In this manner, an image is formed on the recording medium by the image forming apparatus 100.

[0030] When an image is formed in a single-sided printing mode, the recording medium that has passed through the fixing device 29 is discharged to a discharge tray 31 by a paper discharge roller 30. When an image is formed in a double-sided printing mode, the fixing device 29 performs a fixing process on the first side of the recording medium, and then the recording medium is conveyed to a reversing path 32 by a reversing roller 38. The recording medium conveyed to the reversing path 32 is reversed between the first side and the second side by the reversing roller 38 and conveyed to a conveying guide provided with conveying rollers 33, 34, 35, and 36. The recording medium is conveyed again to the registration roller 20 by the conveying rollers 33, 34, 35, and 36, and an image is formed on the second side of the recording medium by the method described above. Thereafter, the recording medium is discharged to a paper discharge tray 31 by a paper discharge roller 30.

[0031] The configuration and functions of image forming apparatus 100 have been described above.

[0032] [Control configuration] <Control configuration of image printing device> 2 is a block diagram showing an example of a control configuration of the image forming apparatus 100. First, the control configuration of the image printing apparatus 301 will be described.

[0033] 2, the system controller 151 includes a CPU 151a, a ROM 151b, and a RAM 151c. The system controller 151 is also connected to an analog-to-digital (A / D) converter 153, a high voltage control unit 155, a motor control device 600, sensors 159, and an AC driver 160. The system controller 151 is capable of transmitting and receiving data and commands to and from each of the connected units.

[0034] The CPU 151a reads out and executes various programs stored in the ROM 151b to execute various sequences related to a predetermined image formation sequence.

[0035] The RAM 151c is a storage device and stores various data such as set values ​​for the high voltage control unit 155, command values ​​for the motor control device 600, and the like.

[0036] A high voltage control unit 155 supplies a necessary voltage to a high voltage unit 156 (charger 310, developer 314, transfer charger 315, etc.) in accordance with a set value set by the system controller 151.

[0037] The motor control device 600 controls the motor 509 that drives a load provided in the image printing device 301 in response to a command output from the CPU 151a.

[0038] The A / D converter 153 receives a detection signal detected by a thermistor 154 for detecting the temperature of the fixing heater 161, converts the detection signal from an analog signal to a digital signal, and transmits the digital signal to the system controller 151. The system controller 151 controls the AC driver 160 based on the digital signal received from the A / D converter 153. The AC driver 160 controls the fixing heater 161 so that the temperature of the fixing heater 161 becomes a temperature required for performing the fixing process. The fixing heater 161 is a heater used in the fixing process, and is included in the fixing unit 318.

[0039] Moreover, the CPU 151 determines whether or not the sheets are being fed in multiple feeds based on the multiple feed detection sensors T1 and T2. The CPU 151 also controls the multiple feed detection sensors T1 and T2 based on the detection result of the temperature sensor 162. Details will be described later.

[0040] As described above, the system controller 151 controls the operation sequence of the image forming apparatus 100 .

[0041] <Control configuration of document reading device> Next, a description will be given of a control configuration of the document reading device 200. The CPU 401 controls the document reading device 200 by executing a program stored in the non-volatile memory 402.

[0042] The operation unit 403 provides a user interface. The CPU 401 controls the operation unit 403 so as to display, on a display unit provided in the operation unit 403, an operation screen for a user to perform reading settings when reading an image of a document by the document reading device 200. The CPU 401 receives information set by the user from the operation unit 403, and controls the document reading device 20 based on the information.

[0043] The system controller 151 transmits information indicating the status of the image forming apparatus to the operation unit 403. The information indicating the status of the image forming apparatus is, for example, information regarding the number of images formed, the progress of the image forming operation, and information regarding sheet jams and multiple feeds in the image printing device 301 and the document feeding device 201. The operation unit 403 displays the information received from the system controller 151 on the display unit.

[0044] The image data output by the reading units 16 and 17 is input to the image processing unit 404. The image processing unit 404 converts the analog image data into digital image data. The digital image data has a higher numerical value as the intensity of the reflected light increases. This numerical level is hereinafter referred to as a luminance value. The image processing unit 404 performs corrections such as known shading corrections on the image data.

[0045] <Double feed detection sensor> Fig. 3 is a diagram showing signals indicating the reception results of the multi-feed detection sensor T2. Fig. 3(a) is a diagram showing a signal received by the multi-feed detection sensor T2 when there is no document. Fig. 3(b) is a diagram showing a signal received by the multi-feed detection sensor T2 when one document is being conveyed. Fig. 3(c) is a diagram showing a signal received by the multi-feed detection sensor T2 when two documents are being fed in a overlapping manner.

[0046] As shown in Fig. 3(b), the amplitude of the signal received by the multi-feed detection sensor T2 when one document is being conveyed is smaller than the amplitude of the signal received by the multi-feed detection sensor T2 when no document is being conveyed. This is because the signal (ultrasound) output from the multi-feed detection sensor T1 is attenuated by the document. Also, as shown in Fig. 3(c), the amplitude of the signal received by the multi-feed detection sensor T2 when two documents are being conveyed is smaller than the amplitude of the signal received by the multi-feed detection sensor T2 when one document is being conveyed. This is because the signal (ultrasound) output from the multi-feed detection sensor T1 is further attenuated by the two documents.

[0047] 4 is a diagram showing the relationship between the temperature of the double-feed detection sensor T2 and the amplitude (sensor sensitivity) of the signal output from the double-feed detection sensor T2. As shown in FIG 4, as the temperature of the double-feed detection sensor T2 rises, the amplitude of the signal output from the double-feed detection sensor T2 increases.

[0048] 5 is a diagram showing the relationship between the temperature detected by the temperature sensor 162 and the amplitude of the signal output from the multi-feed detection sensor T2. When the cumulative number of output sheets of paper increases during execution of a print job (image formation job), the temperatures of the ultrasonic sensors T1 and T2 rise due to the long drive of the ultrasonic sensors T1 and T2. As a result, as shown in FIG. 5, the amplitude of the signal output from the multi-feed detection sensor T2 increases. For example, when the threshold value Vth1 for determining whether or not a multi-feed has occurred is 130, even if a multi-feed of paper has occurred, it is determined that a multi-feed has not occurred because the amplitude of the signal output from the multi-feed detection sensor T2 is greater than the threshold value Vth1.

[0049] Therefore, in this embodiment, the following configuration is applied to prevent a decrease in the accuracy of detecting double feeding by the ultrasonic sensor.

[0050] FIG. 6 is a diagram for explaining a method for setting a threshold value in this embodiment.

[0051] As shown in FIG. 6(a), when an instruction to start a print job is input, the CPU 151 acquires the detected temperature of the temperature sensor 162. FIG. 6(a) shows a case where the detected temperature is 20° C. The CPU 151 also drives the multi-feed detection sensors T1 and T2 when the first paper in the print job has not yet reached the detection positions of the multi-feed detection sensors T1 and T2 (i.e., there is no paper). The CPU 151 then sets a value obtained by multiplying the amplitude of the signal output from the multi-feed detection sensor T2 by a predetermined value smaller than 1 as the threshold value Vth1. FIG. 6(a) shows a case where the threshold value Vth1 is 130. After that, the CPU 151 detects multi-feeding based on the threshold value Vth1.

[0052] As shown in FIG. 6(b), when the temperature detected by the temperature sensor 162 rises by a predetermined temperature (10° C. in this embodiment), the CPU 151 controls the image forming apparatus 100 so that the distance (paper gap) between the rear end of the preceding paper and the front end of the succeeding paper increases (widens the paper gap). Then, the CPU 151 drives the double feed detection sensors T1 and T2 during a period when the paper has not yet reached the detection position of the double feed detection sensors T1 and T2 (i.e., there is no paper). Then, the CPU 151 sets a value obtained by multiplying the amplitude of the signal output from the double feed detection sensor T2 by a predetermined value smaller than 1 as the threshold value Vth2. FIG. 6(b) shows a case where the threshold value Vth2 is 135. After that, the CPU 151 detects the double feed based on the threshold value Vth2.

[0053] Fig. 7 is a diagram showing threshold values ​​set by the method shown in Fig. 6. As shown in Fig. 7, by setting threshold values ​​according to temperature, a decrease in accuracy of double feeding detection is suppressed.

[0054] In this embodiment, the paper gap is increased based on the detection result of the temperature sensor 162, but this is not limited to the above. For example, the paper gap may be increased every time a predetermined number of sheets are output in a print job, and the above threshold value may be set. [Explanation of symbols]

[0055] 151 CPU 162 Temperature Sensor T1, T2 double feed detection sensor

Claims

1. a multi-feed detection sensor including an output unit that outputs ultrasonic waves and a receiving unit that receives the ultrasonic waves output from the output unit and outputs a signal indicating a reception result; a determining unit that determines that a plurality of sheets are being conveyed in an overlapping state when the signal output from the receiving unit is smaller than a first value serving as a threshold value; A temperature sensor that detects a temperature; a first control means for controlling conveyance of the sheet such that, when a temperature detected by the temperature sensor rises to a predetermined temperature during execution of an image forming job for forming an image on the sheet, a distance between a rear end in a conveyance direction of a preceding first sheet and a front end in the conveyance direction of a second sheet following the preceding sheet increases; a second control means for outputting the ultrasonic wave from the output unit during a period from when a trailing end of the first sheet in the transport direction passes a detection position of the double feed detection sensor until a leading end of the second sheet in the transport direction reaches the detection position; a setting means for setting the threshold value to a second value that is greater than the first value based on the signal output from the receiving unit during the period; An image forming apparatus comprising:

2. when an instruction to start the image forming job is input, the second control means outputs the ultrasonic wave from the output unit before a first sheet in the image forming job reaches the detection position; 2 . The image forming apparatus according to claim 1 , wherein the setting unit sets the first value as the threshold value based on a signal output from the receiving unit during the period.

Images