Detection device and image forming apparatus

Abstract

To perform detection by distinguishing the cause at a time when no sheet is normally conveyed.SOLUTION: A detection device for detecting whether or not a sheet P is normally conveyed comprises a size detection sensor 61 (size detection means) for detecting size in a conveyance direction of the conveyed sheet P, and a thickness detection sensor 62 (thickness detection means) for detecting thickness H of the conveyed sheet P. Then, when previously obtained information about the size in the conveyance direction of the conveyed sheet P, and the size detected by the size detection sensor 61 are different from each other, the detection device distinguishes determination for distinguishing whether or not size mismatching is generated to the conveyed sheet P from whether or not continuous feed is generated is carried out based on a detection result of the thickness detection sensor 62.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This invention relates to a detection device for detecting whether a sheet is being normally conveyed, and an image forming apparatus such as a copier, a printer, a facsimile machine, or a multifunction machine or a printing machine incorporating these devices that includes such a detection device.

Background Art

[0002] Conventionally, in image forming apparatuses such as copiers, printers, and printing machines, there has been known a device for detecting whether a sheet such as paper is being normally conveyed (see, for example, Patent Document 1).

[0003] On the other hand, Patent Document 1 discloses a technique for detecting the presence or absence of double feeding of a sheet based on the detection result of a sensor that detects the paper thickness (thickness) of the conveyed sheet (paper).

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional techniques have been unable to distinguish and detect the causes when a sheet is not being normally conveyed, even though there are multiple causes. Therefore, when a sheet is not being normally conveyed, it has been impossible to present an appropriate countermeasure method based on the cause to the user.

[0005] This invention has been made to solve the above-described problems, and an object thereof is to provide a detection device and an image forming apparatus that can distinguish and detect the causes when a sheet is not being normally conveyed.

Means for Solving the Problems

[0006] The detection device in this invention is a detection device for detecting whether or not a sheet is being transported normally, and comprises a size detection means for detecting the size of the sheet being transported in the transport direction, and a thickness detection means for detecting the thickness of the sheet being transported, and when the size detected by the size detection means differs from information obtained in advance regarding the size of the sheet being transported in the transport direction, a distinction determination is made based on the detection result of the thickness detection means to distinguish whether a size mismatch has occurred in the sheet being transported or whether continuous transport is occurring. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a detection device and an image forming apparatus that can distinguish and detect the cause when a sheet is not transported normally. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a schematic diagram showing the feed supply device. [Figure 3] This figure shows the manner in which the sheet is transported as detected by the detection device. [Figure 4] This figure shows the detection method used by the thickness detection sensor. [Figure 5] This flowchart shows an example of control performed by a detection device. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments for carrying out this invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be simplified or omitted as appropriate.

[0010] First, Figure 1 will explain the overall configuration and operation of the image forming apparatus 1. In Figure 1, 1 is a copier as an image forming apparatus, 2 is a document reading unit that optically reads image information from the original document D, 3 is an exposure unit that irradiates exposure light L based on the image information read by the document reading unit 2 onto the photoreceptor drum 5, 4 is an imaging unit that forms a toner image (image) on the photoreceptor drum 5, and 7 is a transfer unit (image forming unit) that transfers the toner image formed on the photoreceptor drum 5 onto the sheet P. Furthermore, 10 indicates a document transport unit (automatic document transport device) that transports the set document D to the document reading unit 2, and 12 and 13 indicate a feeding device that feeds the sheet P contained in the paper feed cassette. Furthermore, 17 is a pair of registration rollers (a pair of timing rollers) that transport the sheet P toward the transfer section 7, 20 is a fixing device that fixes the toner image (unfixed image) supported on the sheet P, 21 is a fixing roller installed in the fixing device 20, 22 is a pressure roller installed in the fixing device 20, and 31 is a paper output tray on which the sheets P discharged from the main body of the device 1 are loaded. Furthermore, 42 and 43 indicate mounting sections (lifting plates) that are configured to be vertically movable in each feeding device 12 and 13, and 51 indicates a feeding mechanism as a feeding means installed in each feeding device 12 and 13. Furthermore, 61 indicates a size detection sensor as a size detection means in the detection device, 62 indicates a thickness detection sensor as a thickness detection means in the detection device, and 100 indicates an operation display panel for inputting the content of printing operations to be performed in the image forming apparatus 1 and displaying the status of the image forming apparatus 1.

[0011] Referring to Figure 1, the operation of the image forming apparatus main unit 1 during normal image forming (printing) will be explained. First, the original document D is transported (fed) from the document table in the direction of the arrow in the diagram by the transport rollers of the document transport unit 10 and passes over the document reading unit 2. At this time, the image information of the original document D passing over it is optically read by the document reading unit 2. The optical image information read by the document reading unit 2 is then converted into an electrical signal and transmitted to the exposure unit 3 (writing unit). The exposure unit 3 then emits exposure light L, such as laser light, based on the image information in the electrical signal, onto the photosensitive drum 5 of the image formation unit 4.

[0012] Meanwhile, in the image-forming unit 4, the photoreceptor drum 5 rotates clockwise as shown in Figure 1, and after a predetermined image-forming process (charging process, exposure process, and development process), an image (toner image) corresponding to the image information is formed on the photoreceptor drum 5. Subsequently, the image formed on the photoreceptor drum 5 is transferred to the sheet P, which is transported by the resist roller pair 17, in the transfer unit 7, which acts as the image forming unit.

[0013] Meanwhile, the sheet P transported to the transfer unit 7 (image forming unit) operates as follows. First, one of the multiple feeding devices 12 and 13 of the image forming apparatus body 1 is automatically or manually selected (for example, the lower feeding device 13 is selected). Then, the uppermost sheet P stored in the feeding device 13 is fed by the feeding mechanism 51 and transported toward the transport path K. After that, the sheet P passes through the transport path K, which is equipped with multiple transport rollers (size detection sensor 61 and thickness detection sensor 62 are installed), and reaches the position of the registration roller pair 17. At this time, the registration roller pair 17 is in a stopped state, and the leading edge of the sheet P abuts against its nip, thereby correcting the skew of the sheet P.

[0014] Then, the rotation of the registration roller pair 17 begins, and the sheet P is transported toward the transfer unit 7 (image forming unit) in time to align with the image formed on the photoreceptor drum 5. In the transfer unit 7, the image on the photoreceptor drum 5 is transferred onto the sheet P (this is the transfer process). After that, after the sheet P passes through the position of the transfer unit 7, it reaches the fixing device 20 through the conveyance path. The sheet P that has reached the fixing device 20 is fed between the fixing roller 21 and the pressure roller 22, and the toner image is fixed by the heat received from the fixing roller 21 and the pressure received from both members 21 and 22 (this is the fixing process). After the fixing process in which the toner image is fixed, the sheet P is sent out from between the fixing roller 21 and the pressure roller 22 (this is the fixing nip), and then discharged from the image forming apparatus main body 1 and stacked on the paper discharge tray 31 as an output image. In this way, a series of image forming processes (printing operations) are completed.

[0015] Next, the feeding device in the present embodiment will be described in detail with reference to FIG. 2 and the like. Hereinafter, among the plurality of feeding devices 12 and 13 incorporated in the apparatus main body 1, the lower feeding device 13 will be described. However, since the upper feeding device 12 has substantially the same configuration as the lower feeding device 13 except for the different installation positions, the description thereof will be omitted.

[0016] Referring to FIG. 2 and the like, the feeding device 13 is provided with a placement portion 43 formed so as to be able to stack a plurality of sheets P, a feeding mechanism 51 for feeding the sheet P placed on the placement portion 43, and the like. A part of the placement portion 43 is configured to be able to move up and down so that the downstream side in the feeding direction of the uppermost sheet P placed thereon (the right side in FIG. 2) reaches a predetermined height position (the position of the pickup roller 52). Specifically, the placement portion 43 is composed of a lifting plate that is rotatable about a rotation center axis 43a and a fixed plate that does not move up and down. The lifting plate is disposed on the downstream side in the feeding direction with respect to the fixed plate, and is configured to move up and down by rotating in the forward and reverse directions about the rotation center axis 43a. Also, referring to FIG. 2, the feeding mechanism 51 is composed of a feed roller 53, a pickup roller 52, a separation roller 54, and the like.

[0017] The feed roller 53 is installed on the front end side (downstream side) in the feeding direction (the direction of the white arrow in FIG. 2) with respect to the sheet P placed on the placement portion 43, contacts the upper surface of the uppermost sheet P, and rotates (rotates counterclockwise in FIG. 2) along the feeding direction of the sheet P to feed the sheet P in the feeding direction indicated by the dashed-dotted arrow. The pickup roller 52 rotates counterclockwise in FIG. 2 along the traveling direction while contacting the surface (upper surface) of the uppermost sheet P placed on the placement portion 43, and conveys the sheet P toward the position of the feed roller 53. The pickup roller 52 is configured to be able to contact and separate from the sheet P (the uppermost sheet P) placed on the placement portion 43 (lifting plate). That is, the pickup roller 52 is formed to be movable between a retracted position where it does not contact the sheet P placed on the placement portion 43 and a contact position where it contacts (the position shown in FIG. 2). The separation roller 54 is installed so as to form a nip portion with the feed roller 53. When one sheet P is sandwiched in the nip portion and when no sheet P is sandwiched in the nip portion, the separation roller 54 rotates in the forward direction (the direction of the dashed arrow in FIG. 2, which is the clockwise direction) along the feeding direction. In contrast, when a plurality of sheets are sandwiched in the nip portion, the separation roller 54 rotates in the reverse direction (the direction of the solid arrow in FIG. 2, which is the counterclockwise direction) with respect to the above-mentioned forward direction. As a result, the uppermost sheet P among the plurality of sheets P sandwiched in the nip portion is fed in the feeding direction along the rotation of the feed roller 53, and the lower sheet P is conveyed in the direction opposite to the feeding direction (forward direction), reducing double feeding and continuous feeding of the sheet P. In this embodiment, a plate-shaped separation pad may be used instead of the separation roller 54.

[0018] In this embodiment, the feeding device 13 raises and lowers the loading section 43 (lifting plate) vertically according to the number of sheets P loaded on the loading section 43, so that the pickup roller 52 can contact the uppermost sheet P loaded on the loading section 43 (lifting plate). The sheet feeding operation is performed after the pickup roller 52 has descended to a position where it contacts the upper surface of the sheet P placed on the loading section 43 (lifting plate), which has been adjusted to its vertical position. Furthermore, the feeding device 13 in this embodiment is provided with a pair of side fences (not shown) that restrict the position of the sheet P placed on the mounting section 43 in the width direction (the direction perpendicular to the plane of the paper in Figure 2). The side fences are installed at both ends in the width direction so as to sandwich the sheet P, and are configured to move in conjunction with each other in the width direction according to the width size of the sheet P by a manual moving mechanism (the spacing in the width direction can be increased or decreased). Furthermore, the feeding device 13 in this embodiment is provided with a reference fence 107 and an end fence 103 that regulate the position of the sheet P placed on the mounting section 43 in the feeding direction (left-right direction in Figure 2). The reference fence 107 is installed so that the downstream side (front end) of the sheet P in the feeding direction abuts against it. The end fence 103 is installed so as to abut the upstream side (rear end) of the sheet P in the feeding direction and is configured to be movable in the feeding direction according to the size of the sheet P in the feeding direction by a manual movement mechanism.

[0019] In the feeding device 13 configured in this way, when the sheet P is not set on the mounting section 43, this state is detected by an end detection sensor (not shown), and the pickup roller 52 is retracted to the retracted position. Then, when the sheet P is set on the mounting section 43, this state is detected by the end detection sensor, and the pickup roller 52 moves from the retracted position toward the contact position (the position shown in Figure 2). Then, as shown in Figure 2, with the pickup roller 52 in contact with the upper surface of the uppermost sheet P placed on the mounting section 43, the counterclockwise rotation drive of the pickup roller 52 is started, and at the same time, the rotation of the feed roller 53 and the separation roller 54 is started. As a result, the uppermost sheet P of the sheet bundle PT placed on the mounting section 43 is transported by the pickup roller 52 toward the nip between the feed roller 53 and the separation roller 54, and then one sheet P is separated from that nip and transported toward the image forming section. Furthermore, when all the sheets P placed on the mounting section 43 have been fed and there are no sheets P set on the mounting section 43, this state is detected by the end detection sensor, and the pickup roller 52 moves back to the retracted position.

[0020] The detection device 60 (image forming apparatus 1), which is characteristic of this embodiment, will be described below with reference to Figures 3 to 5, etc. In this embodiment, the detection device 60 (see Figure 3) is a device that detects whether or not the sheet P is being transported normally, and is installed in the transport path K from the feeding devices 12 and 13 to the pair of register rollers 17. Specifically, the detection device 60 distinguishes and determines (detects) the following: (1) a state in which sheet P is transported normally (see Figure 3(A)), (2) a state in which sheet P of a different size than the planned size is transported (hereinafter referred to as "size mismatch"; see Figure 3(B)), (3) a state in which multiple sheets P1 and P2 are transported with parts of them overlapping each other (hereinafter referred to as "continuous transport"; see Figure 3(C)), and (4) a state in which multiple sheets P1 and P2 are transported with all of them overlapping each other (hereinafter referred to as "double transport"; see Figure 3(D)). "Size mismatch" can occur, for example, if a user sets a sheet P of a different size into the feeding devices 12 and 13.

[0021] As shown in Figure 3 (and Figure 1), in this embodiment, the detection device 60 is provided with a size detection sensor 61 as a size detection means and a thickness detection sensor 62 as a thickness detection means. The size detection sensor 61 (size detection means) detects the size of the sheet P being transported in the transport direction. The size detection sensor 61 is a known type, and for example, a reflective photosensor that optically detects the presence or absence of the sheet P at that location can be used. Based on the detection result detected by the size detection sensor 61, the control unit 70, which is a processor made of an integrated circuit, converts the size of the sheet P in the transport direction. The thickness detection sensor 62 (thickness detection means) detects the thickness H of the sheet P being transported. The thickness detection sensor 62 can be a known type, for example, a distance measuring sensor that optically detects the distance to the surface of the sheet P at that location can be used. Based on the detection result detected by the thickness detection sensor 62, the control unit 70 calculates the thickness of the sheet P. Furthermore, the thickness detection sensor 62 (thickness detection means) is installed downstream of the size detection sensor 61 (size detection means) in the transport direction (left side in Figure 3). In Figure 3, the white arrow indicates the direction in which the sheet P is transported (transport direction).

[0022] In this embodiment, the detection device 60 makes a determination (hereinafter referred to as "distinction determination") based on the detection result of the thickness detection sensor 62 to distinguish whether a size mismatch has occurred or whether continuous feeding has occurred in the sheet P being transported, when the size detected by the size detection sensor 61 (size in the transport direction) differs from the size information acquired in advance regarding the size of the sheet P being transported in the transport direction. In this embodiment, the control unit 70 acquires and stores size information based on information about the printout (sheet P) that has been pre-entered by the user through the operation of the operation display panel 100. Alternatively, size information can be directly obtained based on the detection results of sensors that detect the position of the end fences 103 (see Figure 2) of the feeding devices 12 and 13. In this case, "size mismatch" would be caused by improper operation (incorrect positioning) of the end fences 103 by the user.

[0023] More specifically, the "distinction determination" is performed based on the variation in the detection result of the thickness detection sensor 62 over a predetermined time T determined by the information (size information) acquired by the control unit 70. Specifically, the predetermined time T mentioned above is roughly the time from when the leading edge of the sheet P (which is normal and conforms to the size information) passes the position of the thickness detection sensor 62 until the trailing edge exits, and it increases or decreases depending on the size of the sheet P in the transport direction. In other words, the predetermined time T set when an A3-sized sheet P is fed through is longer than the time set when an A3-sized sheet P is fed through.

[0024] Then, if there is no fluctuation in the detection result of the thickness detection sensor 62 exceeding a predetermined value α within a predetermined time T (H2 ≤ H1 × α), it is determined that a "size mismatch" has occurred. Conversely, if there is a fluctuation in the detection result of the thickness detection sensor 62 exceeding a predetermined value α within a predetermined time T (H2 > H1 × α), it is determined that a "continuous transmission" has occurred. These points will be explained later in steps S11 to S13 of Figure 5. Furthermore, when the information (size information) matches the transport direction size detected by the size detection sensor 61, the system determines whether or not "double feeding" is occurring in the transported sheet P based on the detection result of the thickness detection sensor 62. This will be explained later in steps S6 to S8 of Figure 5.

[0025] The reason why this type of control works will be explained below using Figures 3 to 5. First, in Figure 3, the size information of sheet P entered into the operation display panel 100 is assumed to be X (for example, A4 size). The sheet P fed from the feeding device (for example, the lower feeding device 13) is transported along the transport path K in the direction of the white arrow in Figure 3, passing the position of the size detection sensor 61 and then passing the position of the thickness detection sensor 62. Figure 3(A) shows the operation in which a sheet P of size X according to pre-set size information is fed through the machine. At this time, the control unit 70 detects the size X of the sheet P in the transport direction from the time it takes for the output of the size detection sensor 61 to turn on and off (the time from when the leading edge of the sheet P passes through until the trailing edge exits).

[0026] In Figure 3, the dashed line indicates sheet P' when the tip has reached the size detection sensor 61 (when the sensor output switches from off to on), and the solid line indicates sheet P when the rear end has passed the size detection sensor 61 (when the sensor output switches from on to off). Furthermore, in Figure 3, the distance from the size detection sensor 61 to the thickness detection sensor 62 is approximately X, but this distance is not limited to this. Also, different size detection sensors 61 (see Figure 1) can be used depending on the feeding devices 12 and 13 (feeding paths) used.

[0027] As shown in Figure 3(A), when a sheet P of the preset size X is fed through the machine, the size detection sensor 61 will turn on and off at the intended timing (time) (it will turn on and off within the time obtained by dividing the distance the sheet P is transported by the transport speed of the sheet P, plus a buffer). Therefore, if the size detection sensor 61 does not turn on and off at the intended timing (time), it is possible that the transported sheet P is not of the preset size X. Figure 3(B) shows the operation when a sheet P of a different size from the pre-set size X (size information) (for example, twice the size, 2X) is fed through the machine (operation in case of size mismatch). In this case, the timing at which the output of the size detection sensor 61 switches from on to off will be later than that for the target size X. Figure 3(C) shows the operation when multiple sheets P1 and P2 of a predetermined size X are sent in succession. Even in this case, the timing at which the output of the size detection sensor 61 switches from on to off is later than that of the target size X. Therefore, the size detection sensor 61 has difficulty distinguishing between a size mismatch, as shown in Figure 3(B), and a continuous feed, as shown in Figure 3(C). In particular, during continuous feed, the shorter the overlapping portion between sheet P1 and sheet P2, the more difficult it is to distinguish it from a size mismatch.

[0028] In this embodiment, in order to solve such problems (the inability to distinguish between "size mismatch" and "continuous feeding"), the thickness of sheets P1 and P2 (sheet thickness) is detected by a thickness detection sensor 62 located downstream of the size detection sensor 61. First, as shown in Figure 4(A), when a sheet P of a preset size X is fed through the machine (the feeding state shown in Figure 3(A)), the thickness detection sensor 62 outputs a value equal to the sheet thickness H for a length of X. In contrast, as shown in Figure 4(B), if a sheet P of mismatched size is fed through (the feeding state in Figure 3(B)), the thickness detection sensor 62 outputs a value equal to the sheet thickness H for a length of 2X.

[0029] In this embodiment, the thickness detection sensor 62 detects the thickness H1 at the leading edge and the thickness H2 at the trailing edge of a sheet P of a preset size X. In other words, it obtains two detection results from the thickness detection sensor 62 during the "predetermined time T" described earlier. Therefore, in the cases of Figures 4(A) and (B), the thickness H1 at the leading edge and the thickness H2 at the trailing edge coincide to the thickness H of one sheet (H1=H2=H). Alternatively, it is also possible to obtain continuous detection results from the thickness detection sensor 62 over a predetermined time T.

[0030] On the other hand, as shown in Figure 4(C), when multiple sheets P1 and P2 are fed in a continuous stream (the feeding state in Figure 3(C)), the thickness detection sensor 62 outputs multiple sheet thicknesses H and 2H over a length of approximately 2X of the two sheets P1 and P2. Specifically, the sheet thickness 2H of the overlapping portion of the two sheets P1 and P2 becomes twice the sheet thickness H of the other portions. Therefore, it is possible to distinguish between "size mismatch" and "continuous feeding" based on the presence or absence of such fluctuations in sheet thickness H. In other words, if there is no fluctuation in sheet thickness H, a "size mismatch" has occurred, and if there is a fluctuation in sheet thickness H, a "continuous feeding" has occurred.

[0031] More specifically, in this embodiment, the sheet thickness H1 at the leading edge (sheet thickness at the start of a predetermined time T) and the sheet thickness H2 at the trailing edge (sheet thickness at the end of a predetermined time T) are obtained, and if the condition H2 > H1 × α (where α is a predetermined value (coefficient) that takes into account a margin, for example, 1.5) is satisfied, it is assumed that "continuous feeding" has occurred, and if the above condition is not satisfied, it is assumed that "size mismatch" has occurred. Although Figures 3(C) and 4(C) illustrate the case where two sheets P1 and P2 are fed in succession, even when three or more sheets are fed in succession, the sheet thicknesses H1 and H2 detected by the thickness detection sensor 62 will always be different, so the same distinction can be made.

[0032] Here, Figure 3(D) shows the operation when multiple sheets P1 and P2 of a predetermined size X are fed in a double feed. In this case, the timing at which the output of the size detection sensor 61 switches from on to off is the same as that of the target size X (as shown in Figure 3(A)). Therefore, in this case, it is not possible to distinguish whether sheet P is being transported normally or whether a "double feed" is occurring. However, as shown in Figure 4(D), if multiple sheets P1 and P2 are fed together, the thickness detection sensor 62 outputs a sheet thickness 2H that is thicker than normal for the length X of sheets P1 and P2. Specifically, the sheet thickness 2H becomes twice the thickness of the two sheets P1 and P2. Therefore, it is possible to determine whether it is "normal" or "double-feed" (hereinafter referred to as "double-feed determination") from the size of this sheet thickness. More specifically, in this embodiment, the thickness H1 of the leading sheet is compared with the thickness H1' of the leading sheet P that was fed immediately before it. If the condition H1 > H1' × α is met, it is assumed that a "double feed" has occurred. If the above condition is not met, it is assumed that "normal" conveyance is taking place. In contrast, the information about the sheet P input via the operation display panel 100 includes not only size information but also thickness information, and double feeding can be determined by comparing this thickness information with the sheet thickness H detected by the thickness detection sensor 62.

[0033] Thus, the detection device 60 in this embodiment can distinguish and detect "size mismatch," "continuous feeding," and even "double feeding." In other words, even if there are multiple reasons why sheet P is not transported normally, it can distinguish and detect those reasons. Therefore, when sheet P is not transported normally, it becomes possible to present the user with an appropriate countermeasure based on the cause.

[0034] In particular, in this embodiment, when it is determined that the sheet P is not being transported normally, the system notifies the system of the transport abnormality and controls the system to interrupt the transport of the sheet P. Specifically, when a "size mismatch" occurs, the operation display panel 100 will display a message such as, "There is a possibility that a sheet of the wrong size is set in the feeder, so printing has been interrupted. Follow the next steps to remove the sheet in the transport path (jam removal) and set a sheet of the correct size." Similarly, when "continuous feeding" or "double feeding" occurs, the operation display panel 100 will display a message such as, "More than one sheet has been fed from the feeder, so printing has been interrupted. Follow the next steps to remove the sheet in the transport path (jam removal)." In either case, printing will resume after the jam removal is properly performed. Therefore, when sheet P is not transported properly, the user can take appropriate action based on the cause.

[0035] Below, an example of the control performed by the detection device 60 will be explained using the flowchart in Figure 5. As shown in Figure 5, first, the size information of sheet P is acquired based on the input information regarding the print job entered by the user from the operation display panel 100 (step S1). At the same time, the control unit 70 sets a predetermined time T based on the size information. Then, when printing (job) starts (step S2), it is determined whether the output of the size detection sensor 61 has been turned on within a certain period of time (step S3). This "certain period of time" is the time it takes for the sheet P, which has been successfully transported from the selected feeding device (for example, the lower feeding device 13), to reach the position of the size detection sensor 61. Therefore, in step S3, if the output of the size detection sensor 61 has not been turned on within the certain period of time, it is determined that a jam has occurred in the sheet P, and this is displayed on the display panel 100, and the transport operation is interrupted (step S4). In contrast, in step S3, if the output of the size detection sensor 61 turns on within a certain time, it is determined that no jam has occurred in sheet P, and then it is determined whether the output of the size detection sensor 61 turned off within a predetermined time T after it turned on (step S5).

[0036] Then, in step S5, if the output of the size detection sensor 61 turns off within a predetermined time T, it is assumed that no "size mismatch" or "continuous feeding" occurred, and a "double feed determination" is performed (step S6). Specifically, as explained earlier using Figures 3(D) and 4(D), the thickness H1 of the leading sheet and the thickness H1' of the leading sheet P that was fed immediately before it are compared to determine if the condition H1 > H1' × α is met. If such a condition is met, it is assumed that a "double feed" has occurred, and this is displayed on the display panel 100, and the transport operation (printing operation) is interrupted (step S8). On the other hand, if such a condition is not met, it is assumed that no "double feed" has occurred and that normal sheet P transport is taking place, and the transport operation (printing operation) continues as is (step S7).

[0037] In contrast, in step S5, if the output of the size detection sensor 61 does not turn off within a predetermined time T, it is determined that a "size mismatch" or "continuous feeding" has occurred, and then it is determined whether the determination relates to the first sheet in continuous feeding (step S9). If it is determined to be related to the first sheet, a "distinction determination" is performed (step S11). Specifically, as explained earlier using Figures 3(B), (C), and 4(B), (C), the sheet thickness H1 at the leading edge and the sheet thickness H2 at the trailing edge are obtained, and it is determined whether the condition H2 > H1 × α is satisfied. If such a condition is met, it is determined that a "continuous feeding" has occurred, and this is displayed on the display panel 100, and the transport operation is interrupted (step S13). In contrast, if such a condition is not met, it is determined that a "size mismatch" has occurred, and this is displayed on the display panel 100, and the transport operation is interrupted (step S12).

[0038] On the other hand, if the determination in step S9 is not related to the first sheet in continuous feeding, the "distinction determination" is not performed, and it is determined that "continuous feeding" has occurred. This fact is displayed on the display panel 100 and the transport operation is interrupted (step S10). In other words, when multiple sheets are transported in succession, the "distinction determination" is performed only when the first sheet is transported. If the information (size information) for the second and subsequent sheets differs from the size detected by the size detection sensor 61, it is determined that "continuous transport" has occurred. This type of control is implemented because it is sufficient to check the first sheet to determine whether the size of the sheet set in the feeding device differs from the size information (pre-set size), and checking subsequent sheets is unnecessary. In other words, since multiple sheets P are set in bundles in the feeding devices 12 and 13, if the first sheet is of the intended size, it is not the case that the second and subsequent sheets are of the intended size. Therefore, the "distinction judgment" to distinguish between "size mismatch" and "continuous feeding" is performed only on the first sheet. For the second and subsequent sheets P, if the output of the size detection sensor 61 does not turn off within a predetermined time X, it is uniformly determined that continuous feeding has occurred.

[0039] As described above, the detection device 60 in this embodiment is a detection device that detects whether or not the sheet P is being transported normally, and is equipped with a size detection sensor 61 (size detection means) that detects the size of the sheet P being transported in the transport direction, and a thickness detection sensor 62 (thickness detection means) that detects the thickness H of the sheet P being transported. When the size of the sheet P being transported in the transport direction differs from the size detected by the size detection sensor 61, the detection result of the thickness detection sensor 62 is used to perform a distinction determination to distinguish whether there is a size mismatch or continuous transport in the sheet P being transported. This makes it possible to distinguish and detect the cause when sheet P is not being transported properly.

[0040] In this embodiment, the present invention was applied to a detection device 60 installed in a monochrome image forming apparatus 1, but the present invention can naturally also be applied to a detection device installed in a color image forming apparatus. Furthermore, although this embodiment applies the present invention to a detection device 60 installed in an electrophotographic image forming apparatus 1, the application of the present invention is not limited to this, and the present invention can also be applied to detection devices installed in other types of image forming apparatuses (for example, inkjet image forming apparatuses, stencil printing machines, etc.). Furthermore, in this embodiment, the present invention was applied to a detection device 60 that detects whether or not the sheets fed from the feeding devices 12 and 13 are being transported normally. However, the present invention can also be applied to a detection device that detects whether or not the original document D, as a sheet, fed from the document transport unit 10 (automatic document transport device) is being transported normally. Furthermore, in this embodiment, the positions and number of size detection sensors 61 and thickness detection sensors 62 are not limited to those shown in Figure 1, but can be appropriately changed within the scope of the technical concept of the present invention. Furthermore, even in such cases, the same effects as those of this embodiment can be obtained.

[0041] It is clear that the present invention is not limited to this embodiment, and that this embodiment can be modified as appropriate within the scope of the technical concept of the present invention, in addition to what is suggested here. Furthermore, the number, position, shape, etc. of the constituent members are not limited to this embodiment, and can be set to a number, position, shape, etc. that is suitable for carrying out the present invention.

[0042] In this specification, the term "sheet" is defined to include not only paper but also all sheet-like recording media such as coated paper, label paper, OHP sheets, and film sheets. [Explanation of symbols]

[0043] 1. Image forming apparatus (image forming apparatus main unit), 13 feeding device; 60 detection devices, 61 Size detection sensor (size detection means), 62 Thickness detection sensor (thickness detection means), 70 Control unit, 100 Operation display panel (notification means), P, P1, P2 seats. [Prior art documents] [Patent Documents]

[0044] [Patent Document 1] Japanese Patent Application Publication No. 6-40604

Claims

1. A detection device that detects whether a sheet is being conveyed normally, a size detection unit for detecting the size of the sheet in the conveying direction; a thickness detection means for detecting the thickness of the sheet being conveyed; Equipped with A detection device characterized in that, when information previously acquired regarding the size of the conveyed sheet in the conveying direction differs from the size detected by the size detection means, a discrimination judgment is made to determine whether there is a size mismatch or continuous feeding of the conveyed sheet based on the detection result of the thickness detection means.

2. 2. The detection device according to claim 1, wherein the thickness detection means is disposed downstream in the conveying direction relative to the size detection means.

3. 3. The detection device according to claim 1, wherein the discrimination is made based on a change in the detection result of the thickness detection means during a predetermined time period determined by the information.

4. If there is no fluctuation exceeding a predetermined value in the detection result of the thickness detection means within the predetermined time, it is determined that the size mismatch has occurred, 4. The detection device according to claim 3, wherein if the detection result of said thickness detection means fluctuates beyond said predetermined value within said predetermined time, it is determined that said continuous feeding has occurred.

5. A detection device as described in any one of claims 1 to 4, characterized in that when multiple sheets are transported continuously, the discrimination judgment is performed only when the first sheet is transported, and when the information for the second or subsequent sheets differs from the size detected by the size detection means, it is judged that continuous transport has occurred.

6. A detection device as described in any one of claims 1 to 5, characterized in that when the information matches the size detected by the size detection means, it determines whether or not double feeding is occurring in the transported sheet based on the detection result of the thickness detection means.

7. 7. The detection device according to claim 1, wherein when it is determined that the sheet is not being conveyed normally, the detection device notifies the abnormality in conveyance and suspends conveyance of the sheet.

8. An image forming apparatus comprising the detection device according to any one of claims 1 to 7.

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