Sheet thickness detection device, sheet transport device, and image forming apparatus

Abstract

The present invention provides a sheet thickness detection device, a sheet transport device, and an image forming device that can accurately detect the thickness of a sheet. [Solution] A sheet thickness detection device such as the paper thickness detection device 100 is equipped with a separation mechanism that separates the detection roller 52b from the drive roller 52a, which is a transport roller. When the detection roller 52b is in the contact position, which is the initial position in which it contacts the drive roller 52a, a gap is formed between the fixed shaft 151b of the detection roller 52b and the through hole 69a of the contact / separation arm 69 of the separation mechanism. The minimum gap D from the fixed shaft 151b to the top of the through hole 69a is greater than or equal to the maximum paper thickness that the image forming apparatus can transport, so that the fixed shaft 151b and the contact / separation arm 69 do not come into contact when detecting the paper thickness, and the separation mechanism is configured to be separated from the detection roller 52b when detecting the paper thickness.

Description

Technical Field

[0001] The present invention relates to a sheet thickness detection device, a sheet conveyance device, and an image forming apparatus.

Background Art

[0002] Conventionally, a pair of conveyance rollers including a conveyance roller for conveying a sheet and a detection roller supported so as to be able to approach and separate in an approach and separation direction orthogonal to both the sheet conveyance direction and the rotation axis direction of the conveyance roller, a pressing means for pressing the detection roller toward the conveyance roller, a separation mechanism for separating the detection roller from the conveyance roller, and a displacement detection means for detecting a displacement in the approach and separation direction of the detection roller from an initial position in a state where the detection roller is in contact with the conveyance roller are known as a sheet thickness detection device. Sheet thickness detection is performed based on the displacement of the detection roller detected by the displacement detection means when the sheet is sandwiched by the pair of conveyance rollers.

[0003] In Patent Document 1, as the above sheet thickness detection device, until the leading end of a sheet-like passbook enters the conveyance roller, the detection roller is positioned at a separation position separated from the conveyance roller by a separation mechanism. When the leading end of the passbook enters the conveyance roller, the separation mechanism moves the detection roller from the separation position to a contact position which is an initial position where the detection roller contacts the conveyance roller, and the detection roller is brought into contact with the passbook, and the passbook is sandwiched and conveyed by the conveyance roller and the detection roller. It is described that by positioning the detection roller at the separation position when the leading end of the passbook enters the conveyance roller, the resistance force when the passbook enters the conveyance roller can be prevented from acting on the passbook. Then, when the passbook is sandwiched between the conveyance roller and the detection roller, the displacement of the detection roller is detected by a sensor which is a displacement detection means to detect the thickness of the passbook.

[0004] Patent Document 1 describes a separation mechanism comprising a solenoid, an arm member, and a torsion spring as a pressurizing means. The solenoid is connected to one end of the arm member, and the coil portion of the torsion spring is attached to the other end. One end of the torsion spring is hook-shaped and is attached to the shaft of the detection roller. The other end of the torsion spring is attached to the arm member so that the detection roller is biased toward the transport roller. In the above-mentioned approach-apartmental direction, when one end of the arm member is pushed toward the transport roller by the solenoid, the arm member rotates, and the other end of the arm member moves toward the transport roller. As a result, the torsion spring, which is the pressurizing means attached to the other end of the arm member, moves toward the transport roller, and the detection roller moves toward the transport roller. When moving the detection roller from a position away from the transport roller towards the contact position, a solenoid moves one end of the arm member away from the transport roller, and the arm member is rotated in the opposite direction, thereby moving the torsion spring toward the transport roller along with the other end of the arm member. As a result, the detection roller moves toward the initial position where it contacts the transport roller. [Overview of the project] [Problems that the invention aims to solve]

[0005] However, there was a risk that accurate thickness detection would not be possible. [Means for solving the problem]

[0006] To solve the above-mentioned problems, the present invention provides a sheet thickness detection device comprising: a pair of conveying rollers comprising a conveying roller for conveying a sheet and a detection roller supported so as to be able to move toward and toward the conveying roller in a direction perpendicular to both the sheet conveying direction and the rotation axis direction of the conveying roller; a pressurizing means for pressurizing the detection roller toward the conveying roller; a separation mechanism for separating the detection roller from the conveying roller; and a displacement detection means for detecting the displacement of the detection roller in the direction of contact or separation from an initial position when the detection roller is in contact with the conveying roller, wherein the thickness of the sheet is detected based on the displacement of the detection roller detected by the displacement detection means when the sheet is being held between the pair of conveying rollers, characterized in that when the thickness of the sheet is detected, the separation mechanism is separated from the detection roller. [Effects of the Invention]

[0007] According to the present invention, the thickness of a sheet can be detected with high accuracy. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram showing the general configuration of the image forming apparatus according to this embodiment. [Figure 2] A perspective view showing the schematic configuration of the paper thickness detection device in this embodiment. [Figure 3] A schematic cross-sectional view of a pair of transport rollers in a paper thickness detection device. [Figure 4] A schematic diagram showing the relationship between the pressure arm and the fixed axis of the paper thickness detection device. [Figure 5] A schematic perspective view of the separation mechanism of the paper thickness detection device. [Figure 6] Block diagram of the paper thickness detection device. [Figure 7] (a) is a control flowchart for separation, and (b) is a control flowchart for contact. [Figure 8] A schematic diagram showing the relationship between the connecting / separating arm and the fixed shaft. [Modes for carrying out the invention]

[0009] The following describes one embodiment in which the present invention is applied to an electrophotographic image forming apparatus. Figure 1 is a schematic diagram showing the general configuration of the image forming apparatus according to this embodiment. As shown in Figure 1, the image forming apparatus according to this embodiment includes a toner image forming unit 20 equipped with four image forming devices, each forming toner images of yellow (Y), cyan (C), magenta (M), and black (K). Each image forming device consists of a photoreceptor unit 40 as a latent image carrier, a charger unit 18 as a charging means, a developing unit as a developing means, a cleaning unit as a cleaning means, and so on. Each image forming device is equipped with an IC tag and is detachably attached to the main body of the image forming apparatus.

[0010] Above the toner image forming unit 20, there is a writing unit 21 that irradiates the surface of the photoreceptor drum in the photoreceptor unit 40 of each imaging device with laser light corresponding to the image information to form an electrostatic latent image. Below the toner image forming unit 20, there is an intermediate transfer unit, which is equipped with an endless belt, the intermediate transfer belt 10. The intermediate transfer belt 10 can be a multi-layer belt in which an elastic layer is provided on a base layer made of a material that does not stretch easily, such as canvas, on top of a fluororesin with low elongation or a rubber material with high elongation. For example, the elastic layer can be made by coating the surface of a fluororubber or acrylonitrile-butadiene copolymer rubber with a fluororesin to form a smooth coating layer.

[0011] The intermediate transfer belt 10 is stretched across three support rollers 14, 15, and 16 and rotates clockwise in Figure 1. An intermediate transfer cleaning unit 17, which removes unwanted toner from the intermediate transfer belt 10, is located to the right of the second support roller 15 in Figure 1. A secondary transfer unit 22 is provided below the intermediate transfer belt 10. The secondary transfer unit 22 consists of an endless belt, the secondary transfer belt 24, stretched between two rollers 23, and is biased to press the secondary transfer belt 24 against the third support roller (secondary transfer roller) 16 that supports the intermediate transfer belt 10. The secondary transfer belt 24 performs a transfer process to transfer the toner image that was primarily transferred onto the intermediate transfer belt 10 onto the paper.

[0012] To the left of the secondary transfer unit 22 in the diagram is a fixing unit 25 that fixes the toner image, which has been secondarily transferred onto the sheet of paper, to the paper. The fixing unit 25 has a configuration in which a pressure roller 27 is pressed against a fixing belt 26, which is an endless belt. Below the secondary transfer unit 22 and the fixing unit 25 is a sheet reversal unit 28 that feeds the paper inverted so that the toner image can be recorded on the back side of the paper where the toner image has been fixed.

[0013] When the start switch on the control unit is pressed, if there is a document on the document feed tray 30 of the Automatic Document Feeder (ADF) 400, it is transported onto the contact glass 32. If there is no document in the ADF 400, the scanner of the image reading unit 300 is driven to read a manually placed document on the contact glass 32, and the first carriage 33 and the second carriage 34 are driven to read and scan. Light is emitted from the light source on the first carriage 33 onto the contact glass. The reflected light from the document surface is directed towards the second carriage 34 and reflected by the first mirror on the first carriage 33. The reflected light reflected by the mirror on the second carriage 34 is imaged through the imaging lens 35 onto the reading sensor 36, which is made of a CCD. Based on the image signal obtained by the reading sensor 36, K, Y, M, and C color recording data is generated.

[0014] Furthermore, when the start switch is pressed, the rotational drive of the intermediate transfer belt 10 begins, and the imaging preparation of each unit in each imaging device begins, and the imaging sequence for each color is executed. Then, an exposure laser modulated based on the recording data for each color is irradiated onto each color photoreceptor drum by the writing unit 21, and through the imaging process for each color, each color toner image is superimposed onto the intermediate transfer belt 10 as a single image. In this way, the paper is fed into the secondary transfer area at the same time that the leading edge of the toner image formed on the intermediate transfer belt 10 enters the secondary transfer area facing the secondary transfer unit 22. As a result, the toner image on the intermediate transfer belt 10 is secondary transferred onto the paper. The paper with the transferred toner image is fed into the fixing unit 25, where the toner image is fixed to the paper.

[0015] The paper that has been fixed in the fixing unit 25 and discharged is guided by the switching claw 55 to the discharge roller 56 and stacked on the output tray 57. Alternatively, the switching claw 55 guides it to the sheet reversal unit 28, where it is reversed and led back to the secondary transfer area, where an image is recorded on the back side as well, before being discharged onto the output tray 57 by the discharge roller 56. Meanwhile, residual toner remaining on the intermediate transfer belt 10 after secondary transfer is removed by the intermediate transfer body cleaning unit 17 in preparation for further image formation.

[0016] The aforementioned paper is fed from one of the multi-stage paper trays 44 in the paper feeding unit 43 by selectively rotating one of the paper feed rollers 42 on the paper feed table 200. Then, one sheet is separated by the separation roller 45 and placed into the transport roller unit 46, which is then transported by the transport roller pair 47 to the transport roller unit 48 in the image forming apparatus, where it is stopped by the register roller pair 49 of the transport roller unit 48. After that, the register roller pair 49 is driven in accordance with the aforementioned timing to feed the paper to the secondary transfer area.

[0017] It is also possible to insert and feed paper onto the manual feed tray 51. When the user inserts paper onto the manual feed tray 51, the manual feed roller 50 is rotationally driven to separate one sheet of paper on the manual feed tray 51 and draw it into the manual feed path 53, and it is conveyed by the pair of conveyance rollers 52 and is also abutted against and stopped by the registration roller pair 49.

[0018] The paper feed table 200 is equipped with various sensors such as, for example, a photosensor. Specifically, there are a paper end sensor that detects the remaining amount and presence or absence of paper stored in the paper feed tray 44, a size detection sensor that detects the size and orientation of the paper, a tray set detection sensor that detects whether each tray is attached to the image forming apparatus main body, and the like. Also, a paper conveyance sensor that detects whether the paper is being properly conveyed during paper conveyance and the presence or absence of a conveyance jam (paper jam) is provided in each paper feed tray.

[0019] The registration roller pair 49, which is a pair of conveyance rollers, is generally used while being grounded, but it is also possible to apply a bias voltage for removing paper dust from the paper. Specifically, for example, when using a conductive rubber roller and applying a bias, it has a diameter of 18 [mm], the surface is made of conductive NBR rubber with a thickness of 1 [mm], and the volume resistivity of the rubber material is 10 9 [Ωcm] so as to have an electrical resistance of about that value. The surface (image recording surface) of the paper after passing through the registration roller pair 49 to which a bias is applied is slightly negatively charged. Therefore, in the secondary transfer process from the intermediate transfer belt 10 to the paper, the transfer conditions change compared to the case where no voltage is applied to the registration roller pair 49. In this embodiment, a bias is applied to the registration roller pair 49. Also, as transfer conditions, for example, a voltage of about -800 [V] is applied to the secondary transfer roller 16 that supports the intermediate transfer belt 10. A voltage of about +200 [V] is applied to one of the secondary transfer opposing rollers 23 that stretches the secondary transfer belt 24 of the secondary transfer unit 22.

[0020] FIG. 2 is a perspective view showing a schematic configuration of the paper thickness detection device 100 in the present embodiment, and FIG. 3 is a schematic cross-sectional view of the transport roller pair 52 included in the paper thickness detection device 100. In the present embodiment, the transport roller pair 52 that transports the paper on the manual feed tray 51 is used as the paper thickness detection device 100. The paper thickness detection device 100 includes a transport roller pair 52. The transport roller pair 52 includes a driving roller 52a that rotates as a driving transport roller and a detection roller 52b.

[0021] The driving roller 52a has two driving rollers 152a arranged at a predetermined interval in the axial direction and a driving shaft 151a. The driving rollers 152a are attached to the driving shaft 151a so as to rotate integrally with the driving shaft 151a. At one end (the right end in the figure) of the driving shaft 151a, a driven coupling 153 that is connected to a driving coupling of a driving device including a transport motor 91 (see FIG. 6) provided in the image forming apparatus main body is attached. The driving shaft 151a is rotatably supported by a side plate of the image forming apparatus main body and is immovable in the vertical direction (a direction orthogonal to both the paper transport direction and the axial direction).

[0022] The detection roller 52b has two driven rollers 152b arranged at a predetermined interval in the axial direction and a fixed shaft 151b that is supported non-rotatably. Each driven roller 152b is rotatably supported by the fixed shaft 151b via a bearing 154 as shown in FIG. 3. Both ends of the fixed shaft 151b are supported by a pressing arm 72 that is a support member.

[0023] The other end side (the left end side in FIG. 3) of the fixed shaft 151b has a D-shaped cross-section cut shape, and the shaft support hole 72a of the pressing arm 72 that supports the other end side of the fixed shaft 151b is a hole having a D-shaped cross-section. By inserting the D-shaped cross-section cut portion of the other end side of the fixed shaft 151b into the shaft support hole 72a having a D-shaped cross-section, the pressing arm 72 on the other end side supports the other end side of the fixed shaft 151b in a non-rotatable manner.

[0024] On the other hand, the shaft support hole 72a of the pressure arm 72, which supports one end of the fixed shaft 151b (the right end in Figure 3), is a circular hole through which the fixed shaft 151b passes. The diameter of the fixed shaft 151b is approximately the same as that of the fixed shaft 151b. Furthermore, the one end of the fixed shaft 151b also has a circular cross-section, and the pressure arm 72 at that end supports one end of the fixed shaft 151b so that it can rotate relative to the fixed shaft 151b.

[0025] If one end of the fixed shaft 151b is also given a D-cut shape, similar to the other end, and is inserted into the D-shaped cross-section hole of the shaft support hole 72a to support the pressure arm 72 in a way that prevents rotation, the following problems may occur. Specifically, due to manufacturing tolerances, the straight section of the D-cut shape on the other end of the fixed shaft 151b may be tilted relative to the straight section of the D-cut shape on one end. Also, due to manufacturing tolerances, the straight section of the D-shaped cross-section shaft support hole 72a of the pressure arm 72 on the other end may be tilted relative to the straight section of the D-shaped cross-section shaft support hole 72a of the pressure arm 72 on one end. In this case, when each pressure arm 72 is assembled to the fixed shaft 151b, the other pressure arm will be tilted relative to one pressure arm, and the support shaft 72b of one pressure arm 72 (see Figure 4) will be shifted in the rotational direction around the fixed shaft 151b relative to the support shaft 72b of the other pressure arm.

[0026] As a result, when the detection roller 52b is assembled to the side plate of the image forming apparatus via a pair of pressure arms 72, the fixed shaft 151b and the pressure arms 72 become tilted. The tilting of the fixed shaft 151b may cause the contact pressure of each driven roller 152b against the drive roller 152a to be different from each other, or one of the two driven rollers 152b to be separated from the drive roller 152a.

[0027] Furthermore, the tilting of the pressure arm 72 may cause the support shaft 72b of the pressure arm 72 (see Figure 4) to come into strong contact with the supported portion of the side plate of the image forming apparatus that rotatably supports the support shaft 72b, potentially hindering the smooth rotation of the pressure arm 72. In some cases, this may also cause twisting of the fixed shaft 151b or deformation of the pressure arm 72.

[0028] In contrast, as in this embodiment, the shaft support hole 72a of one of the pair of pressure arms 72 is a round hole, and the fixed shaft 151b is rotatably supported. This allows one of the pressure arms 72 to rotate relative to the fixed shaft 151b, thereby aligning the position of the support shaft 72b of one of the pressure arms 72 with the position of the support shaft 72b of the other pressure arm 72. This prevents the fixed shaft 151b and the pressure arms 72 from being tilted when assembled to the image forming apparatus. This prevents differences in the contact pressure between each driven roller 152b and the drive roller 152a, and prevents one of the two driven rollers 152b from separating from the drive roller 152a. Furthermore, it prevents the support shaft 72b of the pressure arm 72 from strongly contacting the supported portion of the side plate of the image forming apparatus that rotatably supports the support shaft 72b, allowing the pressure arm 72 to rotate smoothly. Furthermore, it is possible to suppress twisting of the fixed shaft 151b and deformation of the pressure arm 72. In addition, it is possible to easily assemble the detection roller 52b into the image forming apparatus.

[0029] The pair of pressure arms 72 are biased toward the drive roller 52a by a compression spring 73, which acts as a pressurizing means. The biasing force of the compression spring 73 pressurizes the detection roller 52b toward the drive roller 52a via the pair of pressure arms 72, causing the driven roller 152b to come into contact with the drive roller 152a at a predetermined contact pressure.

[0030] As shown in Figure 4, the pressure arm 72 is equipped with a support shaft 72b, which is rotatably supported on the side plate of the image forming apparatus. The support shaft 72b is supported on the side plate of the image forming apparatus via bearings or the like so that the pressure arm 72 rotates smoothly around the support shaft 72b as a pivot point.

[0031] The support shaft 72b is located upstream of the detection roller 52b in the paper transport direction. When the detection roller 52b is in contact with the drive roller 52a, the axial center of the support shaft 72b and the axial center of the fixed shaft 151b are at the same position in the direction of contact and separation of the detection roller 52b with respect to the drive roller 52a (an orthogonal direction perpendicular to both the paper transport direction and the axial direction).

[0032] By positioning the axis center of the support shaft 72b at the same location as the axis center of the fixed shaft 151b in the aforementioned approach-to-across direction, the direction of movement of the shaft support hole 72a when the pressure arm 72 rotates counterclockwise in the figure from the state shown in Figure 4 can be made to be approximately the same as the direction of the paper thickness. This suppresses the effect of the rotation of the pressure arm 72 on the displacement of the detection roller 52b when the detection roller 52b is displaced according to the thickness of the sheet, and enables accurate detection of the paper thickness.

[0033] Furthermore, in this embodiment, there are two drive rollers 152a and two driven rollers 152b. If there are three or more drive rollers 152a and driven rollers 152b, variations in the diameters of the drive rollers 152a and driven rollers 152b may cause a gap to form between one of the multiple driven rollers 152b and the drive roller 152a. As a result, as described above, when the paper enters the transport roller pair 52, the detection roller 52b will not be displaced by the amount of that gap, and accurate detection of the paper thickness may not be possible.

[0034] On the other hand, in this embodiment, where there are two drive rollers 152a and two driven rollers 152b, even if there is variation in the diameters of the drive rollers 152a and the driven rollers 152b, the fixed shaft 151b tilts, allowing all the driven rollers 152b to come into contact with the drive roller 152a. This allows the detection roller 52b to be displaced by the thickness of the paper, enabling accurate detection of the paper thickness.

[0035] Furthermore, as shown in Figure 2, the detection roller 52b can move from a position in contact with the drive roller 52a to a separated position separated from the drive roller 52a by the separation mechanism 60.

[0036] Upstream of the transport roller pair 52 in the paper transport direction, a paper detection sensor 81, which is a sheet detection means for detecting paper, is positioned. As will be described later, the separation mechanism 60 moves the detection roller 52b toward and toward the drive roller 52a based on the detection result of this paper detection sensor 81.

[0037] Furthermore, the paper thickness detection device 100 is equipped with a displacement sensor 71 as a displacement detection means for detecting the displacement of the detection roller 52b. The displacement sensor 71 can be a known type such as a distance measuring sensor. The displacement sensor 71 is positioned opposite the fixed shaft 151b of the detection roller 52b and detects the displacement of the fixed shaft 151b from the initial contact position where the detection roller 52b is in contact with the drive roller 52a. Based on the detection result of this displacement sensor 71, the thickness of the conveyed paper is detected.

[0038] Specifically, when the paper enters the transport roller pair 52, the pressure arm 72 rotates counterclockwise in Figure 4 with the support shaft 72b as the pivot point, causing the detection roller 52b to be displaced in a direction away from the drive roller 52a. The displacement sensor 71 detects the displacement of the fixed shaft 151b at this time, thereby detecting the thickness of the paper.

[0039] In this embodiment, as described above, the pressure arm 72 is supported on the side plate of the image forming apparatus via bearings or the like so that it rotates smoothly with the support shaft 72b as a fulcrum. As a result, when the paper enters the transport roller pair 52, the detection roller 52b can be smoothly displaced in a direction away from the drive roller 52a according to the thickness of the paper, enabling highly accurate paper thickness detection.

[0040] Next, the separation mechanism 60 will be explained using Figures 2 and 5. Figure 5 is a schematic perspective view of the separation mechanism 60. The separation mechanism 60 is equipped with an approach / separation motor 61. A motor pulley 61a is attached to the motor shaft of the approach / separation motor 61, and a first timing belt 62a is stretched between this motor pulley and a two-stage pulley 63. In addition, a second timing belt 62b is stretched between the two-stage pulley 63 and a cam pulley 64 attached to one end of the camshaft 65a (the right end in Figure 2).

[0041] A cam 65 and a detection filler 67 detected by a home position sensor 66 are attached to one end of the cam shaft 65a so as to be rotatable integrally with the cam shaft 65a. The cam shaft 65a is rotatably supported on the side plate of the image forming apparatus. The cam contact portion 68b of the cam follower 68 contacts the cam 65 from above. The cam contact portion 68b is provided at one end of the cam follower 68. The other end of the cam follower 68 is attached to one end of the cam follower shaft 68a so as to be rotatable integrally with the cam follower shaft 68a. The cam follower shaft 68a is rotatably supported on the side plate of the main body of the image forming apparatus.

[0042] On both sides of the cam follower shaft 68a, one end of each connecting / separating arm 69 is attached so as to be rotatable integrally with the cam follower shaft 68a. The other end of the contact / separation arm 69 is provided with a through hole 69a through which the fixed shaft 151b passes. In this embodiment, as will be described later, when the detection roller 52b is in a contact position that contacts the drive roller 52a, the fixed shaft 151b is not in contact with the through hole 69a.

[0043] Next, the movement of the detection roller 52b by the separation mechanism 60 will be described. When the detection roller 52b is in contact with the drive roller 52a and is in the initial home position, the home position sensor 66 does not detect the detection filler 67. Also, when in the home position, the bottom dead center of the cam 65 is in contact with the cam contact portion 68b of the cam follower 68. Specifically, due to the weight of the cam follower 68 and the weight of the contact / separation arm 69, a force acts on the cam follower 68 to cause it to rotate in the opposite direction to arrow A in Figure 5, and this force causes the cam contact portion 68b to contact the cam 65. The contact / separation motor 61 is a stepping motor, and it performs separation by managing the rotation angle based on the number of pulses, starting from the home position described above. The contact / separation motor 61 does not have to be a stepping motor as long as the rotation angle can be managed; for example, a combination of a DC motor and an encoder may be used, or a solenoid may be used as the drive source.

[0044] When the contact / disconnection motor 61 is driven, the driving force of the contact / disconnection motor 61 is transmitted to the cam pulley 64 via the first timing belt 62a and the second timing belt 62b, causing the camshaft 65a to rotate. As the camshaft 65a rotates, the detection filler 67 and the cam 65 attached to the camshaft 65a also rotate.

[0045] As the detection filler 67 rotates, it is detected by the home position sensor 66. Also, as the cam 65 rotates, the cam contact portion 68b of the cam follower 68 is lifted. As the cam contact portion 68b is lifted, the cam follower 68 rotates in the direction of arrow A in Figure 5, pivoting on the cam follower shaft 68a. At this time, since the cam follower 68 is mounted on the cam follower shaft 68a so as to be rotatable integrally with the cam follower shaft 68a, the cam follower shaft 68a rotates together with the cam follower 68 in the direction of arrow B in Figure 5.

[0046] As the cam follower shaft 68a rotates in the direction of arrow B in Figure 5, the contact / separation arm 69, which is attached to the cam follower shaft 68a so as to be rotatable together with the cam follower shaft 68a, rotates in the direction of arrow C in Figure 5. This rotation of the contact / separation arm 69 in the direction of arrow C causes the inner circumferential surface of the through hole 69a of the contact / separation arm 69 to come into contact with the fixed shaft 151b, and against the pressure applied by the pressurizing arm 72, moves the detection roller 52b in a direction away from the drive roller 52a.

[0047] When the top dead center of the cam 65 reaches the contact position with the cam contact portion 68b, the detection roller 52b reaches the separated position, and the drive of the contact / separation motor 61 stops.

[0048] When moving the detection roller 52b from a separated position to a contact position, the contact / separation motor 61 is rotated in the reverse direction. When the detection roller 52b is in the separated position, the pressure of the pressure arm 72 is applied to the contact / separation arm 69 via the detection roller 52b. This pressure from the pressure arm 72 causes the cam follower 68 to rotate in the opposite direction to arrow A in Figure 5, and the cam contact portion 68b descends following the outer surface of the cam 65. As a result, the contact / separation arm 69 rotates in the opposite direction to arrow C in Figure 5, and the detection roller 52b approaches the drive roller 52a due to the pressure from the pressure arm 72.

[0049] Even after the detection roller 52b contacts the drive roller 52a, the contact / separation motor 61 continues to drive, causing the contact / separation arm 69 to rotate in the opposite direction to arrow C in Figure 5. When the fixed shaft 151b of the detection roller 52b separates from the through hole 69a of the contact / separation arm 69, and the separation mechanism 60 and the detection roller 52b become non-contacting, the bottom dead center of the cam 65 reaches the contact position with the cam contact portion 68b. Furthermore, once the bottom dead center of the cam 65 reaches the contact position with the cam contact portion 68b and the home position sensor 66 stops detecting the detection filler 67, the contact / separation motor 61 begins to decelerate. Then, at a certain angle from the point when the home position sensor 66 stops detecting the detection filler 67, the drive of the contact / separation motor 61 is stopped, and this position is set as the home position.

[0050] Figure 6 is a block diagram of the paper thickness detection device 100 in this embodiment. The control unit 90, which is a control means, is responsible for controlling the entire image forming apparatus and includes a CPU 90a, which is a calculation means, and RAM 90c, ROM 90b, etc., which are information storage units.

[0051] The control unit 90 is electrically connected to the separation mechanism 60's connecting / separating motor 61, the separation mechanism 60's home position sensor 66, the paper detection sensor 81, the displacement sensor 71, and the transport motor 91 that rotates the drive roller 52a, and the control unit 90 controls the operation of each of them.

[0052] Specifically, as will be described later, the control unit 90 controls the drive of the contact / separation motor 61 based on the detection result of the paper detection sensor 81 and the detection result of the home position sensor 66.

[0053] The displacement of the detection roller 52b (fixed shaft 151b) is detected by the displacement sensor 71, for example, as follows: When the paper detection sensor 81 detects the leading edge of the paper, the control unit 90 starts measuring time. When the measurement time has elapsed for a predetermined amount of time and the paper has entered the transport roller pair 52 and been transported by a predetermined amount, the displacement sensor 71 detects a displacement of the detection roller 52b (fixed shaft 151b) in the direction away from the drive roller 52a.

[0054] For example, if the displacement sensor 71 is a distance measuring sensor, the displacement (amount of displacement) of the detection roller 52b (fixed shaft 151b) from the contact position is detected as follows. That is, the distance from the detection roller 52b (fixed shaft 151b) at the contact position is measured by the distance measuring sensor, and this measured value (distance) is stored as a reference distance in the RAM 90c of the control unit 90. Based on the distance from the detection roller 52b (fixed shaft 151b) measured when the paper enters and the stored reference distance, the displacement (amount of displacement) of the detection roller 52b (fixed shaft 151b) is detected.

[0055] It is preferable to detect the displacement using the displacement sensor 71 multiple times and average the multiple detected displacements (amount of displacement) over a time period equal to the number of rotations of the driven roller 152b. This eliminates the influence of eccentricity of the driven roller 152b or the drive roller 152a, enabling highly accurate paper thickness detection.

[0056] The control unit 90 determines the paper thickness based on the detected displacement (amount of displacement). Then, according to the determined paper thickness, it changes sheet material transport operations such as the paper transport speed and the nip pressure of the transport roller pair, or changes image formation operations such as secondary transfer conditions (secondary transfer bias value) and fixing temperature. By detecting the paper thickness upstream of the registration roller pair 49 in the paper transport direction, the secondary transfer conditions (secondary transfer bias value) can be set according to the paper thickness.

[0057] In this embodiment, when the register roller pair 49 transports the paper to the secondary transfer nip, the detection roller 52b is separated from the drive roller 52a so that the transport of the paper to the secondary transfer nip is performed solely by the register roller pair 49. This is because, due to component tolerances, the installation status of peripheral machines, etc., the transport roller pair 52 may be tilted in the paper transport direction relative to the register roller pair 49. In this case, if the paper is transported toward the secondary transfer nip by the transport roller pair 52 and the register roller pair 49, the paper may skew due to the influence of the transport by the transport roller pair 52, and there is a risk that the paper will enter the secondary transfer nip in a skewed state. As a result, the toner image may not be transferred to the desired position on the paper, and the toner image may be tilted relative to the paper. In addition, if the paper is transported in a skewed state, the paper may get caught downstream of the register roller pair 49 in the paper transport direction, which may cause a paper jam.

[0058] Therefore, in this embodiment, after paper transport by the registration roller pair 49 begins, the detection roller 52b is quickly separated from the drive roller 52a, and once the trailing edge of the paper has passed the transport roller pair 52, the detection roller 52b is brought into contact with the drive roller.

[0059] Figure 7(a) is a control flowchart for the separation operation, which separates the detection roller 52b from the drive roller 52a, and Figure 7(b) is a control flowchart for the contact operation, which brings the detection roller 52b into contact with the drive roller 52a. As shown in Figure 7(a), after a certain period of time has elapsed since the image creation sequence operation timing for each color, the drive of the contact / separation motor 61 is started when the leading edge of the paper fed from the manual feed tray 51 is gripped by the registration roller pair 49 (S1~S3).

[0060] When the contact / disconnection motor 61 is started to operate, as described above, the cam 65 rotates and the cam contact portion 68b of the cam follower 68 is lifted. As the cam contact portion 68b is lifted, the cam follower 68 rotates around the cam follower shaft 68a as a pivot point, and the contact / disconnection arm 69 rotates, causing the detection roller 52b to move away from the drive roller 52a.

[0061] Then, when the top dead center of the cam 65 reaches the contact position with the cam contact portion 68b (S4), and the detection roller 52b reaches the separated position (when the contact / separation motor 61 rotates by a certain angle), the drive of the contact / separation motor 61 is stopped (S5). As a result, the separation operation is completed immediately after the paper transport is started by the registration roller pair 49.

[0062] As shown in Figure 7(b), when the registration roller pair 49 starts paper transport and the paper detection sensor 81 detects the trailing edge of the paper (S11), the control unit 90 starts measuring time. When the measured time reaches the specified time and the paper has moved the distance from the paper detection sensor 81 to the transport roller pair 52 (S12), and the trailing edge of the paper has passed the transport roller pair 52, the reverse rotation drive of the contact / separation motor 61 is started (S13).

[0063] Then, when the bottom dead center of the cam 65 reaches the contact position with the cam contact portion 68b (S14), and the detection roller 52b reaches the contact position with the drive roller 52a (when the home position sensor 66 no longer detects the detection filler 67 and the home position is detected), the drive of the contact / separation motor 61 is stopped (S15). This makes it possible to detect the thickness of the paper to be fed from the manual feed tray 51 next.

[0064] Next, the distinctive features of this embodiment will be described. Figure 8 is a schematic diagram showing the relationship between the contact / separation arm 69 and the fixed shaft 151b. As shown in Figure 8, the through-hole 69a through which the fixed shaft 151b passes in the connecting / separating arm 69 is rectangular in shape, and the lengths of the long and short sides of the through-hole 69a are greater than the diameter of the fixed shaft 151b. When the detection roller 52b is in the contact position, which is the initial position in which it contacts the drive roller 52a, as shown in Figure 8, a gap is formed between the fixed shaft 151b and the through-hole 69a. In the contact position, the fixed shaft 151b is not in contact with the connecting / separating arm 69, and the separation mechanism 60 is physically separated from the detection roller 52b (see also Figure 3). In this embodiment, the cam contact portion 68b of the cam follower 68 contacts the bottom dead center of the cam 65 due to the weight of the cam follower 68, so that the posture of the connecting / separating arm 69 is as shown in Figure 8, and the fixed shaft 151b is not in contact with the connecting / separating arm 69.

[0065] The minimum gap D from the fixed shaft 151b to the top of the through hole 69a is greater than or equal to the maximum paper thickness that the image forming apparatus of this embodiment can transport. As a result, even when the image forming apparatus detects the thickness of paper that is the maximum paper thickness it can transport, the fixed shaft 151b and the contact arm 69 do not come into contact.

[0066] In a conventional configuration where the length of the shorter side of the through-hole 69a of the contact / separation arm 69 is equal to the diameter of the fixed shaft 151b, and the fixed shaft 151b is in constant contact with the through-hole 69a, the following problem may occur. Specifically, the fixed shaft 151b may bend, resulting in an inability to accurately detect the paper thickness.

[0067] As shown in Figure 3, the pressure applied by the pressurizing arm 72 pressurizes both ends of the fixed shaft 151b toward the drive roller 52a. On the other hand, the counterclockwise rotation of the contact / separation arm 69 in Figure 8 is restricted by the contact between the cam contact portion 68b of the cam follower 68 and the cam 65. In the conventional configuration, the pressure applied by the pressurizing arm 72 to the fixed shaft 151b is received by the cam 65. As a result, when the detection roller 52b is in contact with the drive roller 52a, the fixed shaft 151b bends due to the pressure applied by the pressurizing arm 72, with the contact / separation arm 69 acting as a fulcrum, so that both ends are positioned toward the drive roller 52a side rather than the center.

[0068] On the other hand, the clockwise rotation of the contact / separation arm 69 in Figure 8 is not restricted by the cam 65 and is free to rotate. Therefore, in the conventional configuration, when paper enters the transport roller pair 52 and the detection roller 52b moves away from the drive roller 52a according to the thickness of the paper, the contact / separation arm 69 rotates together with the cam follower shaft 68a and the cam follower 68, with the cam follower shaft 68a as the pivot point. As a result, the cam contact portion 68b of the cam follower 68 separates from the cam 65. When the cam contact portion 68b separates from the cam 65, the cam 65 is no longer subjected to the pressure of the pressurizing arm 72, and the reaction force of the pressure from the pressurizing arm 72 from the contact / separation arm 69 is no longer applied to the fixed shaft 151b. As a result, the deflection of the fixed shaft 151b is reduced. As the deflection of the fixed shaft 151b decreases, the displacement of the fixed shaft 151b becomes less than the displacement of the driven roller 152b, and the displacement of the fixed shaft 151b no longer corresponds to the paper thickness. Therefore, in the conventional configuration, there is a risk that paper thickness detection cannot be performed accurately.

[0069] Furthermore, in conventional configurations, if the position of the contact / separation arm 69 when the detection roller 52b is in contact position deviates from the target position due to manufacturing errors or assembly errors, the fixed shaft 151b receives a force from the contact / separation arm 69. This can cause the fixed shaft 151b to bend.

[0070] Furthermore, in the conventional configuration, when paper thickness is detected (when the displacement of the fixed shaft 151b is detected), vibrations are transmitted to the cam follower shaft 68a via the side plate of the image forming apparatus, causing the movable parts consisting of the contact / separation arm 69, the cam follower shaft 68a, and the cam follower 68 to vibrate. This vibration causes the fixed shaft 151b to vibrate slightly in the contact / separation direction relative to the drive roller 25a, which may prevent highly accurate paper thickness detection (displacement detection of the fixed shaft 151b).

[0071] In contrast, in this embodiment, as shown in Figure 8, when the detection roller 52b is in contact position and when detecting the paper thickness, the fixed shaft 151b and the contact / separation arm 69 are not in contact. This allows the separation mechanism 60 to be physically separated from the detection roller 52b when the detection roller 52b is in contact position and when detecting the paper thickness.

[0072] Therefore, when the detection roller 52b is in contact position, the force of the separation mechanism 60 does not act on the fixed shaft 151b, and the deflection of the fixed shaft 151b is suppressed. In addition, vibrations of the movable parts consisting of the contact / separation arm 69 of the separation mechanism 60, the cam follower shaft 68a, and the cam follower 68 are not transmitted to the fixed shaft 151b, enabling high-precision detection of paper thickness.

[0073] In this embodiment, the manual feed tray 51 can be removed and an optional paper feed bank can be attached to the main body of the image forming apparatus to feed a large amount of paper. When attaching the paper feed bank, the transport unit equipped with the manual feed roller 50, transport roller pair 52, and manual feed path 53 is removed from the image forming apparatus and replaced with a transport unit equipped with an entrance roller pair and a transport roller pair.

[0074] By installing the paper thickness detection device of the present invention in this paper feed bank, the thickness of the paper fed from the paper feed bank can be accurately detected, and the secondary transfer conditions, etc., can be changed based on the detected thickness. Alternatively, if the paper thickness detection device of the present invention is not installed in this paper feed bank, a connection unit equipped with the paper thickness detection device of the present invention may be connected between the image forming apparatus and this paper feed bank.

[0075] Alternatively, the transport roller pair 47 located furthest downstream in the paper transport direction among the multiple transport roller pairs 47 that transport the paper fed from the paper feed tray 44 shown in Figure 1 may be used as a paper thickness detection device to detect the thickness of the paper fed from the paper feed tray 44.

[0076] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the spirit of the present invention as described in the claims, unless otherwise specifically limited in the above description.

[0077] The above is just one example; each of the following embodiments produces its own unique effects. (Aspect 1) A sheet thickness detection device such as a paper thickness detection device 100 comprises a transport roller pair 52, which consists of a transport roller such as a drive roller 52a that transports a sheet of paper, and a detection roller 52b that is supported so as to be able to move toward and away from the transport roller in an orthogonal direction perpendicular to both the sheet transport direction and the rotation axis direction of the transport roller; a pressurizing means such as a compression spring 73 that pressurizes the detection roller 52b toward the transport roller; a separation mechanism 60 that separates the detection roller 52b from the transport roller; and a displacement detection means such as a displacement sensor 71 that detects the orthogonal displacement of the detection roller 52b from an initial position such as the contact position when the detection roller 52b is in contact with the transport roller, and detects the thickness of a sheet based on the displacement of the detection roller 52b detected by the displacement detection means when the sheet is being transported while being held between the transport roller pair 52, wherein when the sheet thickness is detected, the separation mechanism is separated from the detection roller. In Patent Document 1, when detecting the thickness of a sheet, vibrations from movable parts such as the arm members of the separation mechanism may be transmitted to the detection roller via a pressurizing means such as a torsion spring, potentially causing the detection roller to vibrate. When vibrations from the movable parts of the separation mechanism are transmitted to the detection roller and cause it to vibrate, the vibration of the detection roller may prevent the displacement detection means from accurately detecting the displacement of the detection roller, potentially resulting in an inability to accurately detect the thickness of the sheet. In contrast, in Embodiment 1, when detecting the sheet thickness, the separation mechanism is separated from the detection roller, so that vibrations of the separation mechanism are not transmitted to the detection roller, the displacement of the detection roller can be detected accurately, and the sheet thickness can be detected accurately. Furthermore, by providing a pressurizing means, such as a compression spring 73, that pressurizes the detection roller toward the conveyor roller, separately from the separation mechanism, the detection roller can be pressed toward the conveyor roller even when the separation mechanism is disconnected from the detection roller when detecting the thickness of the sheet.

[0078] (Aspect 2) In embodiment 1, the separation mechanism 60 moves the detection roller 52b to a separated position away from the transport rollers such as the drive roller 52a when the transport roller pair downstream in the sheet transport direction from the transport roller pair 52, such as the resist roller pair 49, grips the leading edge of the sheet, and after the rear end of the sheet has passed the transport roller pair 52, the detection roller 52b moves from the separated position to an initial position such as the contact position. According to this, it is possible to suppress the conveying of the sheet by the downstream conveying roller pair, such as the resist roller pair 49, and the conveying roller pair 52. This prevents the sheet from skewing due to the sheet conveying force of the conveying roller pair 52. Furthermore, by moving the detection roller 52b from a separated position to an initial position such as a contact position after the rear end of the sheet has passed the transport roller pair 52, the detection roller 52b can be positioned at its initial position before the next sheet enters the transport roller pair 52, thereby enabling the detection of the next sheet thickness.

[0079] (Aspect 3) In embodiment 2, the device has a sheet detection means, such as a paper detection sensor 81, that detects a sheet upstream of the transport roller pair 52 in the sheet transport direction, and the separation mechanism 60 moves the detection roller 52b from the separation position to an initial position such as the contact position based on the sheet detection result of the sheet detection means. According to this, as described in the embodiment, a sheet detection means such as a paper detection sensor 81 can detect the rear end of the sheet, and after a predetermined time has elapsed, the detection roller 52b can be moved from a separated position to an initial position such as a contact position. This ensures that the detection roller 52b is moved to the initial position only after the rear end of the sheet has cleared the transport roller pair.

[0080] (Aspect 4) In any of embodiments 1 to 3, the detection roller 52b is composed of a fixed shaft 151b that is supported so as not to rotate, and a roller member such as a driven roller 152b that is rotatably supported with respect to the fixed shaft. According to this, as described in the embodiment, if the detection roller 52b is composed of a rotating shaft and a roller member that rotates integrally with the rotating shaft, when the sheet is being held and conveyed between the detection roller 52b and the conveying roller, the eccentricity of the rotating shaft and the eccentricity of the roller member may affect the displacement of the detection roller 52b in the direction away from the conveying roller such as the drive roller 52a, which may prevent accurate detection of the thickness of the sheet such as paper. In contrast, in embodiment 4, by making the axis supporting the roller member of the detection roller 52b a fixed axis, only the eccentricity of the roller member affects the displacement of the detection roller 52b. This allows for more accurate detection of the sheet thickness compared to a system where the eccentricity of both the roller member and the axis supporting the roller member affects the displacement of the detection roller 52b.

[0081] (Aspect 5) In embodiment 4, both ends of the fixed shaft 151b are supported by support members such as a pressure arm 72, the support member supporting one end of the fixed shaft 151b supports the fixed shaft 151b so that it cannot rotate, and the support member supporting the other end of the fixed shaft 151b supports the fixed shaft 151b so that it can rotate. According to this, as described in the embodiment, the fixed shaft 151b can be supported so as not to rotate, and each support member can be attached to the side plate of the image forming apparatus, etc., without the fixed shaft 151b tilting.

[0082] (Aspect 6) In any of embodiments 1 to 5, the separation mechanism 60 contacts both sides of the axis of the detection roller 52b to move the detection roller 52b toward and away from the transport roller, and the separation mechanism 60 is not in contact with the detection roller 52b when it is in an initial position such as the contact position, except when the separation operation is performed to move the detection roller 52b toward the transport roller such as the drive roller 52a. According to this, as described in the embodiment, the separation mechanism 60 can prevent the detection roller's shaft from bending due to manufacturing errors or the like by pressing on both sides of the shaft, such as the fixed shaft 151b of the detection roller, which is located at an initial position such as the contact position. As a result, when detecting the thickness of a sheet such as paper, if the detection roller is displaced in the direction away from the transport roller, the pressing force from the separation mechanism 60 will change, and the bending of the detection roller's shaft will not change. As a result, the displacement of the detection roller will correspond to the thickness of the sheet, and the sheet thickness can be detected with high accuracy.

[0083] (Aspect 7) In a sheet transport device equipped with a sheet thickness detection means for detecting the thickness of a sheet such as paper, any of the sheet thickness detection devices from embodiments 1 to 6 was used as the sheet thickness detection means. According to this, as described in the embodiment, the sheet thickness during transport can be detected with high accuracy.

[0084] (Pattern 8) In an image forming apparatus equipped with a sheet transport device, the sheet transport device of embodiment 7 was used as the sheet transport device. According to this method, the thickness of the sheet during transport can be detected with high accuracy. [Explanation of Symbols]

[0085] 49: Registrola vs. 50: Manual feed roller 51: Manual feed tray 52: Conveyor roller pair 52a: Drive roller 52b: Detection roller 60: Separation mechanism 61: Contact / Disconnection Motor 61a: Motor pulley 62a: First timing belt 62b: Second timing belt 64: Cam pulley 65: Cam 65a: Camshaft 66: Home position sensor 67: Detection filler 68: Come Follower 68a: Cam follower axis 68b: Cam contact area 69: Contact / separation arm 69a: Through hole 71: Displacement Sensor 72: Pressurized Arm 72a: Shaft support hole 72b: Support shaft 73: Compression spring 81: Paper detection sensor 90: Control Unit 91: Conveyor motor 100: Paper thickness detection device 151a: Drive shaft 151b: Fixed axis 152a: Drive roller 152b: Driven roller [Prior art documents] [Patent Documents]

[0086] [Patent Document 1] Patent No. 2568154

Claims

1. A pair of conveying rollers, each comprising a conveying roller for conveying a sheet and a detection roller supported so as to be able to move toward and toward the conveying roller in a direction perpendicular to both the sheet conveying direction and the rotation axis direction of the conveying roller, A pressurizing means for pressurizing the detection roller toward the conveying roller, A separation mechanism for separating the detection roller from the transport roller, A sheet thickness detection device comprising a displacement detection means for detecting the displacement of the detection roller in the contact-to-separation direction from an initial position when the detection roller is in contact with the conveyor roller, wherein the thickness of the sheet is detected based on the displacement of the detection roller detected by the displacement detection means when the sheet is being held between the conveyor rollers, A sheet thickness detection device characterized in that, when detecting the thickness of a sheet, the separation mechanism is detached from the detection roller.

2. A sheet thickness detection device according to claim 1, The separation mechanism is characterized in that, when the pair of transport rollers downstream of the transport roller pair in the sheet transport direction grips the leading edge of the sheet, the detection roller is moved to a separated position separated from the transport rollers, and after the rear end of the sheet has passed the transport roller pair, the detection roller is moved from the separated position back to the initial position.

3. In the sheet thickness detection device according to claim 2, The sheet detection means for detecting a sheet is located upstream of the aforementioned pair of conveying rollers in the sheet conveying direction. The separation mechanism is characterized by moving the detection roller from the separation position to the initial position based on the sheet detection result of the sheet detection means.

4. A sheet thickness detection device according to claim 1, The sheet thickness detection device is characterized in that the detection roller is composed of a fixed shaft that is supported so as not to rotate and a roller member that is rotatably supported with respect to the fixed shaft.

5. In the sheet thickness detection device according to claim 4, Both ends of the aforementioned fixed shaft are supported by support members, The support member that supports one end of the fixed shaft supports the fixed shaft so that it cannot rotate. A sheet thickness detection device characterized in that the support member supporting the other end of the fixed shaft rotatably supports the fixed shaft.

6. In the sheet thickness detection device according to claim 1, The separation mechanism contacts both sides of the axis of the detection roller, causing the detection roller to move relative to the transport roller. The sheet thickness detection device is characterized in that the separation mechanism is non-contact with the detection roller at its initial position, except during the separation operation that separates the detection roller from the transport roller.

7. In a sheet conveying device equipped with a sheet thickness detection means for detecting the thickness of a sheet, A sheet conveying device characterized in that the sheet thickness detection means uses the sheet thickness detection device described in claim 1.

8. In an image forming apparatus equipped with a sheet transport device, An image forming apparatus characterized in that the sheet conveying device described in claim 7 is used as the sheet conveying device.

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