Sheet feed device and image formation apparatus

Abstract

To prolong the service life of overlapping feed detection means and to suppress a service cost by suppressing the operation time per sheet of the overlapping feed detection means.SOLUTION: A sheet feed device 101 comprises an overlapping feed detector 233a, an overlapping feed detector 233b and an overlapping feed detector 233c provided with: an ultrasonic oscillation sensor 2331 for oscillating ultrasonic waves corresponding to the type of a sheet fed by a feed part 120a, a feed part 120b or a feed part 120c; and an ultrasonic reception sensor 2332 for receiving the ultrasonic waves oscillated by the ultrasonic oscillation sensor 2331 via the sheet fed by the feed part 120a, the feed part 120b or the feed pat 120c.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying device that conveys a sheet and an image forming apparatus that includes the sheet conveying device. [Background technology]

[0002] In an image forming apparatus that forms an image on a sheet of paper or the like, a multi-feed may occur, in which multiple sheets are transported in a stacked state. When a multi-feed occurs, an image is not formed on the stacked sheets (hereinafter referred to as "multi-fed sheets"), and blank sheets without images are mixed in with the finished product. In particular, when sheets with images formed on them are bound or stapled, there is a problem that blank sheets end up being mixed in with the finished product after the binding or stapling process.

[0003] In response to this, Patent Document 1 discloses a conveying device that, when a multi-fed sheet is detected by a multi-feed detecting means, discharges the multi-fed sheet into an escape conveying path that is branched off from a normal conveying path.

[0004] One such double feed detection means is an ultrasonic method using an ultrasonic sensor. The ultrasonic sensor is composed of an ultrasonic oscillator that vibrates when a voltage of a predetermined frequency is applied to radiate ultrasonic waves to the sheets, and an ultrasonic receiver that receives the ultrasonic waves and outputs a voltage in response to the received ultrasonic waves. In the ultrasonic method, the ultrasonic waves radiated by the ultrasonic oscillator and attenuated through the sheets are received by the ultrasonic receiver, and double feed is detected based on the magnitude of the signal received by the ultrasonic receiver.

[0005] Multi-feed detection means are often used in the paper feed section of commercial printing machines that print product deliverables such as pamphlets, books, and advertisements, because the quality and productivity requirements for commercial printing machines that print product deliverables are higher than the quality and productivity requirements for office printers.

[0006] In recent years, commercial printing machines have become longer in lifespan, and the total number of prints they can produce over their lifetime has increased. This has led to demand for longer lifespans for the various parts installed in the machines in order to reduce replacement costs and time. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-42077 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the past, as printing presses have become longer in life, ultrasonic sensors have deteriorated over time while the printing press is in use. In particular, when ultrasonic sensors are used in the sheet feed deck device of a commercial printing press, the total number of sheets output increases as the product life of the commercial printing press becomes longer, which can cause the ultrasonic sensor's life to be exceeded. Therefore, in the past, when ultrasonic sensors deteriorate over time, the sensitivity of the ultrasonic sensor changes due to deterioration over time, and the signal received by the ultrasonic receiving unit also changes. Therefore, there was a problem in that it was necessary to take such changes in the received signal into consideration.

[0009] Furthermore, in order to solve this problem, it is necessary to replace the ultrasonic sensor when it has deteriorated over time to a certain extent, which leads to an increase in service costs.

[0010] The object of the present invention is to provide a sheet conveying device and an image forming device that can extend the life of the multi-feed detection means and reduce service costs by reducing the operating time of the multi-feed detection means per sheet. [Means for solving the problem]

[0011] The sheet conveying device of the present invention is a sheet conveying device that conveys sheets, and has a sheet stacking section for stacking sheets, a sheet feeding means for feeding the sheets stacked on the sheet stacking section, and a double feed detection means for detecting double feed of sheets fed by the sheet feeding means, characterized in that the double feed detection means comprises an ultrasonic oscillator section that emits ultrasonic waves according to the type of sheets fed by the sheet feeding means, and an ultrasonic receiving section that receives the ultrasonic waves emitted by the ultrasonic oscillator section through the sheets fed by the sheet feeding means. [Effects of the Invention]

[0012] According to the present invention, by reducing the operation time per sheet of the multi-feed detection means, the life of the multi-feed detection means can be extended and service costs can be reduced. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 2 is a block diagram showing a configuration of a double feed detector of the sheet conveying device according to the embodiment of the present invention; FIG. [Figure 3] 1 is a block diagram showing a configuration of a sheet conveying device according to an embodiment of the present invention; [Figure 4] 10 is a diagram showing the reception level of an ultrasonic signal that is emitted from an ultrasonic oscillation sensor of the sheet conveying device according to the embodiment of the present invention and is received by an ultrasonic reception sensor via sheet A. FIG. [Figure 5] 6A to 6C are diagrams illustrating an operation of a double feed detector of the sheet conveying device according to the embodiment of the present invention. [Figure 6] 10 is a diagram comparing reception levels of ultrasonic signals emitted from an ultrasonic oscillation sensor of the sheet conveying device according to the embodiment of the present invention and received by an ultrasonic reception sensor via sheet A or sheet B. FIG. [Figure 7] FIG. 10 is a flowchart of a multi-feed detection process executed by the sheet conveying device according to the embodiment of the present invention. [Figure 8] FIG. 10 is a flowchart of a multi-feed process executed by the sheet conveying device according to the embodiment of the present invention. [Figure 9] 5 is a diagram showing an example of a table stored in a ROM of the sheet conveying device according to the embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments will be described in detail with reference to the drawings.

[0015] <Configuration of image forming device> The configuration of an image forming apparatus 1 according to an embodiment of the present invention will be described in detail with reference to FIG.

[0016] Here, a printer is shown as an example of the image forming apparatus 1. The image forming apparatus 1 has an apparatus main body 100 and a sheet conveying apparatus 101.

[0017] The apparatus main body 100 forms an image on a sheet fed by a sheet conveying device 101 .

[0018] The sheet transport device 101 is connected to the device main body 100 and is a large-capacity stacker that can hold a larger number of sheets than the sheet cassettes 61, 62, 63, and 64 in the device main body 100. A paper deck is shown as an example here. The sheet transport device 101 transports sheets to the device main body 100.

[0019] <Device configuration> The configuration of the apparatus main body 100 of the image forming apparatus 1 according to the embodiment of the present invention will be described in detail with reference to FIG.

[0020] The apparatus main body 100 has a fixing device 5, an image reading unit 21, an image forming unit 22, an intermediate transfer belt 31, a secondary transfer inner roller 32, and a secondary transfer outer roller 41. The apparatus main body 100 also has a reversing path 52, a sheet cassette 61, a sheet cassette 62, a sheet cassette 63, a sheet cassette 64, and a duplex path 85.

[0021] The fixing device 5 is provided downstream of the secondary transfer portion T2 in the sheet transport direction. The fixing device 5 applies pressure and heat to the sheet on which an unfixed toner image is formed and which is transported from the secondary transfer portion T2, thereby fusing and fixing the toner image to the sheet. The fixing device 5 transports the sheet on which the toner image has been fixed toward the discharge port 50 or the reversing path 52.

[0022] The image reading unit 21 is provided on the upper part of the apparatus main body 100. The image reading unit 21 has a scanning optical system for reading an image of a document. The image reading unit 21 photoelectrically converts the image information of the document image read by the scanning optical system, and outputs the photoelectrically converted electrical signal to the image forming unit 22.

[0023] The image forming unit 22 forms an image based on an electrical signal input from the image reading unit 21. The image forming unit 22 includes image forming stations 23Y, 23M, 23C, and 23K that form images of the respective colors of yellow (Y), magenta (M), cyan (C), and black (K).

[0024] The image forming stations 23Y, 23M, 23C, and 23K are arranged in tandem along the intermediate transfer belt 31. The image forming station 23Y forms a yellow Y image based on an electrical signal input from the image reading unit 21. The image forming station 23M forms a magenta M image based on an electrical signal input from the image reading unit 21. The image forming station 23C forms a cyan C image based on an electrical signal input from the image reading unit 21. The image forming station 23K forms a black K image based on an electrical signal input from the image reading unit 21.

[0025] The image forming station 23Y includes a photosensitive drum 11Y, a charging device 12Y, an exposure device 13Y, a developing device 14Y, a cleaning blade 15Y, and a primary transfer roller 35Y.

[0026] The photosensitive drum 11Y is rotated by a driving force transmitted from a driving source (not shown).

[0027] The charging device 12Y charges the surface of the photosensitive drum 11Y to a predetermined potential.

[0028] The exposure device 13Y forms an electrostatic latent image on the surface of the photosensitive drum 11Y that has been uniformly charged by the charging device 12Y.

[0029] The developing device 14Y develops the electrostatic latent image formed on the photosensitive drum 11Y by the exposure device 13Y with toner to form a toner image.

[0030] The cleaning blade 15Y comes into contact with the photosensitive drum 11Y downstream of the primary transfer nip in the transport direction of the intermediate transfer belt 31, and removes residual toner remaining on the photosensitive drum 11Y after the primary transfer.

[0031] The primary transfer roller 35Y is pressed against the photosensitive drum 11Y via the intermediate transfer belt 31, thereby forming a primary transfer nip between the photosensitive drum 11Y and the intermediate transfer belt 31. When a transfer bias is applied to the primary transfer roller 35Y, the toner image on the photosensitive drum 11Y is transferred onto the intermediate transfer belt 31 at the primary transfer nip.

[0032] The image forming station 23M includes a photosensitive drum 11M, a charging device 12M, an exposure device 13M, a developing device 14M, a cleaning blade 15M, and a primary transfer roller 35M.

[0033] The image forming station 23C includes a photosensitive drum 11C, a charging device 12C, an exposure device 13C, a developing device 14C, a cleaning blade 15C, and a primary transfer roller 35C.

[0034] The image forming station 23K includes a photosensitive drum 11K, a charging device 12K, an exposure device 13K, a developing device 14K, a cleaning blade 15K, and a primary transfer roller 35K.

[0035] The photosensitive drums 11M, 11C, and 11K have the same configuration as the photosensitive drum 11Y, and therefore their description will be omitted. The charging devices 12M, 12C, and 12K have the same configuration as the charging device 12Y, and therefore their description will be omitted. The exposure devices 13M, 13C, and 13K have the same configuration as the exposure device 13Y, and therefore their description will be omitted.

[0036] Furthermore, the configurations of developing devices 14M, 14C, and 14K are the same as that of developing device 14Y, and therefore their description will be omitted. The configurations of cleaning blades 15M, 15C, and 15K are the same as that of cleaning blade 15Y, and therefore their description will be omitted. The configurations of primary transfer rollers 35M, 35C, and 35K are the same as that of primary transfer roller 35Y, and therefore their description will be omitted.

[0037] The intermediate transfer belt 31 conveys the toner images transferred from the photosensitive drums 11Y, 11M, 11C, and 11K by the primary transfer rollers 35Y, 35M, 35C, and 35K to the secondary transfer portion T2.

[0038] The inner secondary transfer roller 32 and the outer secondary transfer roller 41 are provided downstream of the image forming station 23K in the conveying direction of the intermediate transfer belt. The inner secondary transfer roller 32 and the outer secondary transfer roller 41 form a secondary transfer portion T2. The inner secondary transfer roller 32 and the outer secondary transfer roller 41 transfer the toner image transferred onto the intermediate transfer belt 31 onto a sheet conveyed by a sheet cassette 62, 63, 64 or a sheet conveying device 101 at the secondary transfer portion T2.

[0039] The inner secondary transfer roller 32 and the outer secondary transfer roller 41 transfer the toner image transferred onto the intermediate transfer belt 31 to the back side of the sheet transported from the double-sided path 85 at the secondary transfer section T2. The inner secondary transfer roller 32 and the outer secondary transfer roller 41 transport the sheet onto which the toner image has been transferred to the fixing device 5.

[0040] The reversing path 52 is a conveying path for switching back and conveying the sheet conveyed by the fixing device 5 to the double-sided path 85 when images are formed on both sides of the sheet.

[0041] The sheet cassettes 61, 62, 63, and 64 are provided below the image forming unit 22. The sheet cassettes 61, 62, 63, and 64 store sheets and are front-loading sheet cassettes that are attached to the apparatus main body 100 so as to be removable from the front side.

[0042] The double-sided path 85 is a conveying path for conveying the sheet conveyed from the reversing path 52 to the secondary transfer portion T2.

[0043] In the apparatus main body 100 having the above configuration, the image reading unit 21 reads an image of an original, photoelectrically converts the image information of the read image, and outputs the photoelectrically converted electrical signals to the image forming stations 23Y, 23M, 23C, and 23K. The image forming stations 23Y, 23M, 23C, and 23K form toner images of each color based on the electrical signals input from the image reading unit 21, and perform primary transfer onto the intermediate transfer belt 31 in a superimposed state.

[0044] The secondary transfer unit T2 performs second transfer of the toner image that has been primarily transferred onto the intermediate transfer belt 31 onto a sheet transported by the sheet cassettes 61, 62, 63, and 64 or the sheet transport device 101. The fixing unit 5 applies heat and pressure to the sheet onto which the toner image has been secondarily transferred by the secondary transfer unit T2, thereby fusing the toner image to the sheet.

[0045] When the user has specified a single-sided image forming mode, the sheet on which the toner image has been fused by the fixing device 5 is discharged from the device main body 100 through the discharge port 50. When the user has specified a double-sided image forming mode, the sheet on which the toner image has been fused by the fixing device 5 is transported to the reversing path 52 and the double-sided path 85, and then transported again to the image forming unit 22.

[0046] <Configuration of the sheet conveying device> The configuration of a sheet conveying device 101 according to an embodiment of the present invention will be described in detail with reference to FIGS.

[0047] The sheet conveying device 101 includes a sheet stacking unit 110a, a sheet stacking unit 110b, a sheet stacking unit 110c, a feeding unit 120a, a feeding unit 120b, and a feeding unit 120c. The sheet conveying device 101 also includes pairs of conveying rollers 205, 206, 207, 208, 209, 210, 211, 212, 213, and 214, a pair of conveying rollers 215, pairs of conveying rollers 216, 217, 218, 219, and 220, and a branching unit 231.

[0048] The sheet transport device 101 also has an escape tray 232, a double feed detector 233a, a double feed detector 233b, a double feed detector 233c, a first drive motor 234a, a second drive motor 234b, a third drive motor 234c, and a transport switch 235. The sheet transport device 101 also has a first paper feed fan 236a, a second paper feed fan 236b, a third paper feed fan 236c, a sheet trailing edge detection sensor 240, a sheet transport path 250, an escape transport path 251, and a control unit 300. The double feed detectors 233a, 233b, and 233c, and the control unit 300, together, constitute a double feed detection means.

[0049] The sheet stacking portion 110a, the sheet stacking portion 110b, and the sheet stacking portion 110c have a larger capacity than the sheet cassettes 61, 62, 63, and 64. The sheet stacking portion 110a, the sheet stacking portion 110b, and the sheet stacking portion 110c store sheets in a stacked state.

[0050] The sheet feeding unit 120a includes a belt that is driven to rotate by a first drive motor 234a. The sheet feeding unit 120a attracts the topmost sheet of the sheets stacked on the sheet stacking unit 110a and separated by a first sheet feed fan 236a onto the belt and feeds the sheet to a pair of conveying rollers 205.

[0051] The sheet feeding unit 120b includes a belt that is driven to rotate by the first drive motor 234a. The sheet feeding unit 120b attracts the topmost sheet of the sheets stacked on the sheet stacking unit 110b, which has been separated by the second sheet feed fan 236b, onto the belt and feeds the sheet to the conveying roller pair 206.

[0052] The sheet feeding unit 120c includes a belt that is driven to rotate by the first drive motor 234a. The sheet feeding unit 120c attracts the topmost sheet of the sheets stacked in the sheet stacking unit 110c, which has been separated by the third sheet feed fan 236c, onto the belt and feeds the sheet to the conveying roller pair 207.

[0053] Conveying roller pairs 205, 206, 207, 208, 209, 210, 211, 212, 213, and 214 are provided on sheet conveying path 250. Conveying roller pairs 205, 206, 207, 208, 209, 210, 211, 212, 213, and 214 convey the sheet fed from feeding unit 120a, feeding unit 120b, or feeding unit 120c toward apparatus main body 100.

[0054] The conveying roller pair 215 is provided on the escape conveying path 251. The conveying roller pair 215 conveys the sheet on the escape conveying path 251 toward the escape tray 232.

[0055] When another paper deck is extended and provided on the right side of the sheet conveying device 101 in FIG. 1, the conveying roller pairs 216, 217, 218, 219, and 220 convey the sheet fed from the extended paper deck to the conveying roller pair 213.

[0056] The branching portion 231 is provided on the upstream side of the conveying roller pair 214 in the sheet conveying direction, and is provided at a position where the sheet conveying path 250 and the escape conveying path 251 branch off.

[0057] The escape tray 232 is provided on the upper surface of the sheet conveying device 101 and at the end of the sheet conveying direction of the escape conveying path 251. Multi-fed sheets conveyed by the conveying roller pair 215 are discharged to the escape tray 232. The escape tray 232 is a multi-fed sheet discharge portion where multi-fed sheets detected by the multi-feed detector 233a, the multi-feed detector 233b, or the multi-feed detector 233c are discharged from the escape conveying path 251.

[0058] The double feed detector 233a is provided downstream in the sheet conveying direction of the conveying roller pair 205. The double feed detector 233a outputs a signal of a level corresponding to single feeding or double feeding of the sheets fed from the sheet stacking unit 110a and conveyed by the conveying roller pair 205 to the control unit 300. Here, single feeding means that one sheet is conveyed.

[0059] The double feed detector 233b is provided downstream in the sheet conveying direction of the conveying roller pair 206. The double feed detector 233b outputs a signal of a level corresponding to single feeding or double feeding of the sheet fed from the sheet stacking unit 110b and conveyed by the conveying roller pair 206 to the control unit 300.

[0060] The double feed detector 233c is provided downstream in the sheet conveying direction of the conveying roller pair 207. The double feed detector 233c outputs a signal of a level corresponding to single feeding or double feeding of the sheet fed from the sheet stacking unit 110c and conveyed by the conveying roller pair 207 to the control unit 300.

[0061] Each of the double feed detectors 233 a , 233 b , and 233 c includes an ultrasonic oscillation sensor 2331 and an ultrasonic reception sensor 2332 .

[0062] The ultrasonic oscillation sensor 2331 as an ultrasonic oscillator includes a piezoelectric element (not shown), which vibrates and emits ultrasonic waves when a voltage of a predetermined frequency is applied to the piezoelectric element. The ultrasonic oscillation sensor 2331 emits ultrasonic waves to the sheet fed from the feeding unit 120a, the feeding unit 120b, or the feeding unit 120c and conveyed by the conveying roller pair 205, the conveying roller pair 206, or the conveying roller pair 207.

[0063] The ultrasonic receiving sensor 2332 as an ultrasonic receiving unit receives the ultrasonic waves oscillated by the ultrasonic oscillating sensor 2331 through the sheet fed from the feeding units 120a, 120b, and 120c and conveyed by the conveying roller pairs 205, 206, and 207. The ultrasonic receiving sensor 2332 outputs an ultrasonic signal having a voltage corresponding to the reception level of the received ultrasonic waves to the control unit 300.

[0064] The first drive motor 234a is driven under the control of the control unit 300 to rotate the conveying roller pairs 205, 206, 207, 208, 209, 210, 211, 212, 213, and 214. The first drive motor 234a is driven under the control of the control unit 300 to rotate the belt of the feeding unit 120a, the feeding unit 120b, or the feeding unit 120c.

[0065] The second drive motor 234b is driven under the control of the control unit 300 to rotate the conveying roller pairs 216, 217, 218, 219, and 220.

[0066] The third drive motor 234c is driven under the control of the control unit 300 to rotate the pair of conveying rollers 215.

[0067] The conveyance switch 235 is moved by a solenoid (not shown) between a first position where the sheet is guided to the sheet conveyance path 250 in the branching portion 231 and a second position where the sheet is guided to the escape conveyance path 251.

[0068] The first sheet feed fan 236a is driven under the control of the control unit 300 to blow air onto the sheets stacked on the sheet stacking unit 110a, thereby separating the sheets.

[0069] The second sheet feed fan 236b is driven under the control of the control unit 300 to blow air onto the sheets stacked on the sheet stacking unit 110b, thereby separating the sheets.

[0070] The third sheet feed fan 236c is driven under the control of the control unit 300 to blow air onto the sheets stacked on the sheet stacking unit 110c to separate the sheets.

[0071] The sheet trailing edge detection sensor 240 is provided downstream in the sheet conveying direction of the conveying roller pair 215. The sheet trailing edge detection sensor 240 outputs an electric signal to the CPU 301 according to the detection result of the trailing edge of the sheet.

[0072] The sheet transport path 250 is a transport path for transporting and guiding the sheets transported by the transport roller pairs 205, 206, 207, 208, 209, 210, 211, 212, 213, and 214 toward the apparatus main body 100. Here, the sheet transport path is a route along which the sheets pass from the sheet cassettes 61, 62, 63, and 64 or the sheet stacking units 110a, 110b, and 110c until they are discharged from the discharge port 50 to the outside of the apparatus main body 100 after an image is formed on the sheets.

[0073] The escape conveying path 251 branches upward from the sheet conveying path 250 at the branching portion 231 , and guides the sheet conveyed by the conveying roller pair 215 to the escape tray 232 .

[0074] The control unit 300 controls the overall operation of the image forming apparatus 1. The control unit 300 includes a CPU 301, a ROM 302, and a RAM 303.

[0075] The CPU 301 executes various calculations. The CPU 301 reads and executes various programs stored in the ROM 302, thereby controlling the operation of the image forming apparatus 1 while using the RAM 303. The CPU 301 reads and executes a multi-feed processing program P1 stored in the ROM 302, thereby performing the multi-feed detection processing described below.

[0076] The ROM 302 stores various programs including a multiple feed processing program P1 used to control the sheet conveying device 101.

[0077] The RAM 303 functions as a working area for the CPU 300 .

[0078] <Operation of the sheet conveying device> The operation of the sheet conveying device 101 according to the embodiment of the present invention will be described in detail with reference to FIGS.

[0079] Fig. 4 shows, in voltage, the reception level of the ultrasonic signal that is the output of the ultrasonic receiving sensor 2332. Fig. 4 also shows the reception level of the ultrasonic signal in the case of, for example, a double feed state and a single feed state for A4 size and 80g sheets.

[0080] By starting the execution of the double feed detection control process, the control unit 300 causes an oscillator (not shown), such as a piezoelectric element, of the ultrasonic oscillation sensor 2331 to perform burst oscillation a number of times Nb for each sheet. As shown in FIG. 5, the control unit 300 drives the ultrasonic oscillation sensor 2331 with a pulse signal having a predetermined number of pulses Np and a predetermined period Tp during each burst oscillation. Here, the predetermined number of pulses Np is exemplified as 8 (Np=8). Also, the predetermined period Tp is exemplified as 100 kHz. The ultrasonic oscillation sensor 2331 intermittently emits ultrasonic waves by performing burst oscillation under the control of the control unit 300.

[0081] The ultrasonic receiving sensor 2332 receives the ultrasonic waves emitted by the ultrasonic oscillation sensor 2331 through the sheet fed from the feed units 120a, 120b, and 120c and conveyed by the conveyance roller pairs 205, 206, and 207. The ultrasonic waves received by the ultrasonic receiving sensor 2332 have a waveform that vibrates like a sine wave. The ultrasonic receiving sensor 2332 outputs the received ultrasonic signal to the control unit 300.

[0082] The control unit 300 detects the maximum peak value Vp of the ultrasonic signal input from the ultrasonic receiving sensor 2332 .

[0083] The control unit 300 performs the above-mentioned burst oscillation multiple times Nb for each sheet, calculates the average value of the maximum crest value Vp during each burst oscillation, and determines whether the sheets are being fed in multiples based on the average value of the calculated maximum crest values Vp.

[0084] Specifically, when sheets are fed individually, the ultrasonic waves emitted from the ultrasonic oscillation sensor 2331 and received by the ultrasonic reception sensor 2332 are not significantly attenuated by the sheets. Therefore, in this case, the reception level Vs1 of the ultrasonic signal obtained based on the average value of the maximum crest value Vp calculated by the control unit 300 is high. Furthermore, when sheets are fed in a double state, the ultrasonic waves emitted from the ultrasonic oscillation sensor 2331 and received by the ultrasonic reception sensor 2332 are attenuated by the sheets. Therefore, in this case, the reception level Vd1 of the ultrasonic signal obtained based on the average value of the maximum crest value Vp calculated by the control unit 300 is lower than when sheets are fed individually (Vs1>Vd1).

[0085] Then, the control unit 300 determines that a single feed has occurred and not a double feed, when the reception level of the ultrasonic signal obtained based on the average value of the maximum crest values Vp is equal to or greater than a predetermined determination threshold pre-stored in ROM 302. The control unit 300 also determines that a double feed has occurred when the reception level of the ultrasonic signal obtained based on the calculated average value of the maximum crest values Vp is less than a predetermined determination threshold pre-stored in ROM 302. In this way, the control unit 300 determines whether a double feed has occurred based on the degree of attenuation of the ultrasonic signal input from the ultrasonic receiving sensor 2332 of the double feed detector 233a, double feed detector 233b, or double feed detector 233c.

[0086] Here, the lifespan of the double feed detectors 233a, 233b, and 233c is shortened by performing burst oscillation. This shortening of the lifespan is thought to be caused by deterioration of the piezoelectric elements that are the vibrators of the ultrasonic oscillation sensor 2331 and the ultrasonic reception sensor 2332.

[0087] The ultrasonic oscillation sensor 2331 and the ultrasonic reception sensor 2332 change in sensitivity as their cumulative driving time increases and their lifespan shortens. In addition, the reception level of the ultrasonic signal received by the ultrasonic reception sensor 2332 fluctuates due to changes in the sensitivity of the ultrasonic oscillation sensor 2331 and the ultrasonic reception sensor 2332.

[0088] If the sensitivity of the ultrasonic oscillation sensor 2331 and the ultrasonic reception sensor 2332 decreases, the reception level Vs1 of the ultrasonic signal in the case of single feeding may decrease and fall below the determination threshold. On the other hand, if the sensitivity of the ultrasonic oscillation sensor 2331 and the ultrasonic reception sensor 2332 increases, the reception level Vd1 of the ultrasonic signal in the case of multiple feeding may increase and exceed the determination threshold.

[0089] In response to this, the control unit 300 performs drive control to suppress changes in sensitivity of the ultrasonic oscillation sensor 2331 and the ultrasonic reception sensor 2332, taking into consideration the lifespan of the sheet conveying device 101 and the lifespan of the ultrasonic oscillation sensor 2331 and the ultrasonic reception sensor 2332.

[0090] The reception level of the ultrasonic signal at the ultrasonic receiving sensor 2332 depends on the type of sheet, such as the sheet basis weight or surface characteristics, and therefore varies depending on the type of sheet. Therefore, there are paper types for which the reception level of the ultrasonic signal at the ultrasonic receiving sensor 2332 has a large difference from the determination threshold and paper types for which the difference is small. Here, the surface characteristics include the degree of surface irregularities, etc.

[0091] Therefore, the CPU 301 causes the ultrasonic oscillation sensor 2331 to emit ultrasonic waves in accordance with the type of sheet fed from the feeding unit 120a, the feeding unit 120b, or the feeding unit 120c.

[0092] For example, when the 80 g sheet A is sent singly, the ultrasonic reception level is Vs1, and when it is sent repeatedly, the reception level of the ultrasonic signal is Vd1. Also, when the 150 g sheet B is sent singly, the reception level of the ultrasonic signal is Vs2 (Vs1 > Vs2), and when it is sent repeatedly, the reception level of the ultrasonic signal is Vd2 (Vd1 < Vd2). From this, the difference in the reception levels between the case of repeated sending and the case of single sending with respect to the determination threshold of sheet A is larger than the difference in the reception levels between the case of repeated sending and the case of single sending with respect to the determination threshold of sheet B.

[0093] In this case, the CPU 301 optimizes the burst oscillation count Nb of sheet A and the burst oscillation count Nb of sheet B respectively. Specifically, in sheet A where the difference in the reception levels between the case of repeated sending and the case of single sending with respect to the determination threshold is large, since it is easy to distinguish between the repeated sending state and the single sending state, the burst oscillation count Nb is made less than before. On the other hand, in sheet B where the difference in the reception levels between the case of repeated sending and the case of single sending with respect to the determination threshold is small, since the risk of false detection becomes high when the burst oscillation count Nb is small, the burst oscillation count Nb is kept as before.

[0094] Thus, since burst oscillation is not executed unnecessarily, the lifetimes of the double - feed detectors 233a, 233b, and 233c can be substantially extended. Also, by optimizing the burst oscillation count Nb, the detection accuracy required for the double - feed detectors 233a, 233b, and 233c can be maintained.

[0095] Alternatively, CPU 301 optimizes the number of pulses Np for sheet A and the number of pulses Np for sheet B. Specifically, for sheet A, where the difference in reception level between the double feed and single feed cases is large relative to the determination threshold, it is easy to distinguish between the double feed state and the single feed state, so the number of pulses Np is made smaller than before. On the other hand, for sheet B, where the difference in reception level between the double feed and single feed cases is small relative to the determination threshold, a small number of pulses Np increases the risk of false detection, so the number of pulses Np remains the same as before.

[0096] In this way, the number of pulses Np is not unnecessarily increased, which effectively extends the lifespan of double feed detector 233a, double feed detector 233b, and double feed detector 233c. Also, by optimizing the number of pulses Np, it is possible to maintain the detection accuracy required for double feed detector 233a, double feed detector 233b, and double feed detector 233c.

[0097] Alternatively, CPU 301 optimizes the number of multi-feed detections for each sheet A and each sheet B. Specifically, for sheet A, where the difference in reception level between the case of multi-feed and the case of single feeding is large relative to the determination threshold, it is easy to distinguish between the multi-feed state and the single feeding state, so the number of multi-feed detections for each sheet is reduced compared to the conventional method. On the other hand, for sheet B, where the difference in reception level between the case of multi-feed and the case of single feeding is small relative to the determination threshold, the risk of false detection increases if the number of multi-feed detections for each sheet is small, so the number of multi-feed detections for each sheet is left unchanged.

[0098] In this way, the number of times multi-feed detection is performed for each sheet is not unnecessarily increased, and the lifespan of multi-feed detectors 233a, 233b, and 233c can be substantially extended. Also, by optimizing the number of times multi-feed detection is performed for each sheet, the detection accuracy required for multi-feed detectors 233a, 233b, and 233c can be maintained.

[0099] In the sheet conveying device 101 that performs the above operations, the CPU 301 optimizes any one, any two, or all of the number of burst oscillations Nb, the number of pulses Np, and the number of double feed detections for each sheet.

[0100] <Double feed detection processing> The multi-feed detection process executed by the sheet conveying apparatus 101 according to the embodiment of the present invention will be described in detail with reference to FIG.

[0101] The multi-feed detection process shown in Fig. 7 starts when the main power supply (not shown) of the image forming apparatus 1 is turned on, and is executed each time a sheet is fed from the sheet stacking unit 110a, the sheet stacking unit 110b, or the sheet stacking unit 110c. Fig. 7 explains the case where a sheet is fed from the sheet stacking unit 110a. Note that the multi-feed detection process shown in Fig. 7 uses the basis weight of the sheet as the type of sheet, and optimizes the number of burst oscillations Nb.

[0102] First, the CPU 301 acquires sheet information of the sheets stacked on the sheet stacking unit 110a set by the user. Specifically, the CPU 301 acquires the sheet information via an operation unit (not shown) of the image forming apparatus 1 that executes print settings or print instructions, or via a controller device (not shown) that controls the operation of the image forming apparatus 1 from a PC connected to the image forming apparatus 1 (S300).

[0103] Next, the CPU 301 sets the number of burst oscillations Nb of the double feed detector 233a based on the acquired sheet information (S301). Specifically, the CPU 301 sets the number of burst oscillations Nb associated with the basis weight of the sheet in the sheet information in a table that associates the basis weight with the number of burst oscillations Nb shown in Fig. 9 and that is stored in the ROM 302. Note that the number of burst oscillations Nb in the table that associates the basis weight with the number of burst oscillations Nb differs depending on the oscillation characteristics of the ultrasonic waves and the characteristics of the ultrasonic receiving sensor 2332, and is therefore a number determined from experimental results.

[0104] Next, the CPU 301 determines whether the sheet has been conveyed to a multi-feed detection position where multi-feed detection can be started (S302).

[0105] If the sheet has not been transported to the double feed detection position (step S302: No), the CPU 301 repeats the process of step S302 to wait until the sheet is transported to the double feed detection position.

[0106] On the other hand, when the sheet is transported to the double feed detection position (step S302: Yes), the CPU 301 causes the ultrasonic oscillation sensor 2331 of the double feed detector 233a to emit ultrasonic waves for the number of burst oscillations Nb set in step S301. Then, the CPU 301 starts reading the reception level of the ultrasonic signal received by the ultrasonic receiving sensor 2332 of the double feed detector 233a and input by the ultrasonic receiving sensor 2332 (S303).

[0107] Next, the CPU 301 determines whether or not a multiple feed has occurred based on the reception level read in the process of step S303 (S304).

[0108] If a multi-feed has occurred (step S304: Yes), CPU 301 executes a multi-feed process and then ends the multi-feed detection process. The multi-feed process will be described later.

[0109] On the other hand, if there is no double feed (step S304: No), CPU 301 skips the process of step S305 and ends the double feed detection process.

[0110] 7 uses the basis weight of the sheet as the type of sheet, but is not limited to this, and the type of sheet may be determined based on other factors than basis weight, such as the surface characteristics of the sheet. Also, the multi-feed detection process shown in Fig. 7 optimizes the number of burst oscillations Nb, but is not limited to this, and may optimize the number of pulses Np or the number of multi-feed detections per sheet.

[0111] <Multi-feed handling> The multiple feed processing executed by the sheet conveying apparatus 101 according to the embodiment of the present invention will be described in detail with reference to FIG.

[0112] The multi-feed processing shown in FIG. 8 is started at the timing when the determination in step S304 of the multi-feed detection processing shown in FIG. 7 is Yes.

[0113] First, the CPU 301 controls the conveyance switch 235 to switch the conveyance path at the branching section 231 from a first position where the sheet is guided to the sheet conveyance path 250 to a second position where the sheet is guided to the escape conveyance path 251 (S600). This makes it possible to convey the overlapped sheets from the middle of the sheet conveyance path 250 to the escape conveyance path 251.

[0114] Next, the CPU 301 controls the driving of the first drive motor 234a to drive the pair of conveying rollers 215 (S601). This makes it possible to discharge the multi-fed sheets from the escape conveying path 251 to the escape tray 232.

[0115] Next, the CPU 301 determines whether the trailing end of the overlapped sheets in the conveying direction has been detected based on the electrical signal input from the sheet trailing end detection sensor 240, thereby determining whether the overlapped sheets have been discharged to the escape tray 232 (S602).

[0116] If the multi-fed sheets have not been discharged onto the escape tray 232 (step S602: No), the CPU 301 waits until the multi-fed sheets are discharged onto the escape tray 232 by repeating the process of step S602.

[0117] On the other hand, if the multi-fed sheets are discharged onto the escape tray 232 (step S602: Yes), the CPU 301 controls the driving of the first driving motor 234a to stop the driving of the conveying roller pair 215 (S603).

[0118] Next, the CPU 301 controls the conveyance switch 235 to switch the conveyance path at the branching section 231 from the second position where the sheet is guided to the escape conveyance path 251 to the first position where the sheet is guided to the sheet conveyance path 250 (S604). Then, the CPU 301 ends the multiple feed processing.

[0119] After completing the multi-feed processing shown in FIG. 8, the CPU 301 completes the multi-feed detection processing shown in FIG.

[0120] According to this embodiment, the number of burst oscillations Nb, the number of pulses Np, or the number of times of multi-feed detection per sheet that drives multi-feed detector 233a, multi-feed detector 233b, or multi-feed detector 233c is changed depending on the type of sheet. This makes it possible to optimize the number of burst oscillations Nb, the number of pulses Np, or the number of times of multi-feed detection per sheet for each type of sheet, thereby extending the lifespan of multi-feed detector 233a, multi-feed detector 233b, and multi-feed detector 233c.

[0121] In this embodiment, ultrasonic oscillation sensor 2331 emits ultrasonic waves according to the type of sheet fed from feed unit 120a, feed unit 120b, or feed unit 120c. Furthermore, ultrasonic receiving sensor 2332 receives the ultrasonic waves emitted by ultrasonic oscillation sensor 2331 via the sheet fed by feed unit 120a, feed unit 120b, or feed unit 120c. In this manner, the operating time per sheet of double feed detector 233a, double feed detector 233b, and double feed detector 233c is reduced. This allows the lifespan of double feed detector 233a, double feed detector 233b, and double feed detector 233c to be extended, and service costs to be reduced.

[0122] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention.

[0123] Specifically, in the above embodiment, ultrasonic sensors are used for the double feed detectors 233a, 233b, and 233c, but this is not limited thereto, and optical sensors may also be used for the double feed detectors 233a, 233b, and 233c.

[0124] Furthermore, in the above embodiment, the type of sheet is determined by basis weight or surface characteristics, but this is not limiting, and the type of sheet may be determined by other characteristics than basis weight and surface characteristics. [Explanation of symbols]

[0125] 1. Image forming device 22 Image forming unit 100 Device body 101 sheet transport device 110a Sheet stacking area 110b Sheet stacking section 110c seat loading area 120a Feeding section 120b Feeding section 120c feeding section 231 Branch 232 Escape Tray 233a Double feed detector 233b Double feed detector 233c Double Feed Detector 240 Sheet rear end detection sensor 250 Sheet transport path 251 Escape conveyor 300 control section 301 CPU 302 ROM 303 RAM 2331 Ultrasonic oscillation sensor 2332 Ultrasonic receiving sensor

Claims

1. A sheet conveying device that conveys a sheet, a sheet stacking section for stacking sheets; a sheet feeding unit for feeding the sheets stacked in the sheet stacking unit; a double feed detection means for detecting double feed of the sheets fed by the sheet feeding means; and The double feed detection means an ultrasonic wave oscillator that emits ultrasonic waves in accordance with the type of sheet fed by the sheet feeding means; and an ultrasonic wave receiver that receives the ultrasonic waves emitted by the ultrasonic wave oscillator through the sheet fed by the sheet feeding means. A sheet conveying device characterized by:

2. The ultrasonic oscillator includes: ultrasonic waves are intermittently emitted a predetermined number of times, and the predetermined number of times is changed depending on the type of sheet fed by the sheet feeding means; 2. The sheet transport device according to claim 1.

3. The ultrasonic oscillator includes: an ultrasonic wave is generated using a pulse signal having a predetermined number of pulses, and the predetermined number of pulses is changed depending on the type of sheet fed by the sheet feeding means; 2. The sheet transport device according to claim 1.

4. A sheet conveying device that conveys a sheet, a sheet stacking section for stacking sheets; a sheet feeding unit for feeding the sheets stacked in the sheet stacking unit; a double feed detection means for detecting double feed of the sheets fed by the sheet feeding means; and The double feed detection means every time a sheet is fed from the sheet feeding means, detecting whether or not a sheet has been fed multiple times according to the type of the sheet fed from the sheet feeding means; A sheet conveying device characterized by:

5. The type of the sheet is: The basis weight or surface properties of the sheet.

5. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

6. The sheet conveying device according to any one of claims 1 to 4, an image forming unit that forms an image on the sheet conveyed by the sheet conveying device; An image forming apparatus comprising:

Images