Sheet conveying device and image forming apparatus

Abstract

To appropriately set the timing and period for removing rust generated on a connection surface of a rotor and an armature of an electromagnetic clutch.SOLUTION: In a sheet conveying device 30, a control unit 71 connects an electromagnetic clutch 54 to form a second driving force transmission path, determines a time interval T required for conveying recording paper P by a constant distance on the basis of detection output from a first sensor 37 and detection output from a second sensor 38 when accelerating a rotation speed of the first conveying roller 31, connects the electromagnetic clutch 54 to form the second driving force transmission path in a period during which the recording paper P is not conveyed when the time interval T is equal to or less than a second time interval t2, and increases a time to bring a rotor and an armature of the electromagnetic clutch 54 into pressure contact with each other.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a paper transport device and an image forming apparatus that have a roller for transporting paper and that accelerates the rotation speed of the roller to switch the paper transport speed, and in particular to a technique for performing maintenance on an electromagnetic clutch used to switch the rotation speed of the roller. [Background technology]

[0002] An image forming apparatus includes a paper transport device that transports paper and an image forming unit that forms an image on the transported paper. The paper transport device may adjust the paper transport speed by switching the rotation speed of a transport roller that transports the paper.

[0003] The drive transmission device described in Patent Document 1 includes a first drive train and a second drive train. The first drive train includes a first gear, a second gear, a rotating shaft, and a one-way clutch. The second drive train includes a third gear, a fourth gear, a rotating shaft, and an electric clutch. The third gear meshes with the first gear, and the fourth gear meshes with the second gear. By switching the electromagnetic clutch on and off, the drive force transmission path is changed, and the rotation speed of the pickup roller is changed.

[0004] Furthermore, in the gear device described in Patent Document 2, in normal mode, the rotation of the motor is transmitted to the roller via a clutch and multiple gears, causing the roller to rotate, and in cleaning mode, the rotation of each gear is not transmitted to the roller, and a connecting force is applied to the rotor and armature that make up the clutch, causing the rotor to stop rotating and the armature to rotate, causing the rotor and armature to slide and removing rust that has formed on the connecting surface between the rotor and armature. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Patent Publication No. 2016 / 163203 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-109281 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, multiple gears, a one-way clutch, and an electric clutch are combined, and the rotation speed of the pickup roller is switched by changing the transmission path of the driving force by turning the electromagnetic clutch on and off. However, if rust occurs on the connecting surface between the rotor and armature that make up the electromagnetic clutch, slippage occurs between the rotor and armature even when the rotor and armature are connected, causing the rotation speed of the armature to decrease.

[0007] In Patent Document 2, in cleaning mode, the rotation of each gear is not transmitted to the roller, and a connecting force is applied to the rotor and armature that make up the clutch, causing the rotor and armature to slide, removing rust that has formed on the connecting surface between the rotor and armature and preventing slippage between the rotor and armature. However, if the cleaning mode is set for a long period of time, wear on the rotor and armature will increase, which may impair the function of the clutch.

[0008] The present invention has been developed in consideration of the above circumstances, and aims to prevent slippage between the rotor and armature and maintain the function of the clutch by appropriately setting the timing and period for removing rust that has formed on the connecting surface between the rotor and armature of an electromagnetic clutch. [Means for solving the problem]

[0009] A paper transport device according to one aspect of the present invention includes a motor, a roller that is rotated by the driving force of the motor and transports multiple papers in sequence, a switching gear, and an electromagnetic clutch that transmits or disconnects the driving force of the motor received by the switching gear via a rotor and an armature, and when the rotor and the armature of the electromagnetic clutch are disconnected, the driving force is disconnected by the switching gear and the driving force is transmitted to the roller without passing through the switching gear, thereby forming a first driving force transmission path that rotates the roller, and when the rotor and the armature of the electromagnetic clutch are connected, the driving force is transmitted to the roller via the switching gear, thereby accelerating the rotation speed of the roller; a gear unit that detects the papers being transported by the roller in sequence, and a second sensor that is positioned differently from the first sensor in the paper transport direction; and a second sensor that detects the papers being transported by the roller in sequence when the electromagnetic clutch is disconnected, thereby forming the first driving force transmission path and transmitting the driving force to the roller. and a control unit that sequentially transports each sheet of paper by the first sensor, determines the distance between each sheet of paper based on the detection output of the first sensor, and if the determined distance is longer than a predetermined specified distance, connects the electromagnetic clutch to form the second driving force transmission path and accelerates the rotational speed of the roller.When the control unit connects the electromagnetic clutch to form the second driving force transmission path and accelerates the rotational speed of the roller, it determines the time required to transport the sheet of paper a certain distance between the first sensor and the second sensor based on the detection output of the first sensor and the detection output of the second sensor, and if the determined time exceeds a predetermined first threshold that is longer than a specified normal time for the sheet of paper to move the certain distance, it connects the electromagnetic clutch to form the second driving force transmission path during a period when the roller is not transporting the sheet of paper and drives the roller to rotate for a predetermined connection time, and then transports the next sheet of paper with the second driving force transmission path formed.

[0010] In addition, an image forming apparatus according to one aspect of the present invention includes a paper transporting device according to the above-described one aspect of the present invention, and an image forming section that forms an image on paper transported by the paper transporting device. [Effects of the Invention]

[0011] According to the present invention, by appropriately setting the timing and duration for removing rust that has developed on the connecting surface between the rotor and armature of an electromagnetic clutch, slippage between the rotor and armature can be prevented and the function of the clutch can be maintained. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing an image forming apparatus to which a paper transport device according to an embodiment of the present invention is applied; [Figure 2] 2 is a cross-sectional view showing a paper feed device and a paper transport device in the image forming apparatus of the present embodiment. FIG. [Figure 3] FIG. 2 is a perspective view showing the entire gear unit for driving the paper feeder and the paper transport device. [Figure 4] FIG. 2 is a perspective view mainly showing a gear unit of the paper transport device. [Figure 5] FIG. 2 is an enlarged perspective view showing a part of a gear unit of the paper transport device. [Figure 6] 1A and 1B are a side view and a front view, respectively, schematically showing a gear unit of a paper transport device. [Figure 7] 10A and 10B are a side view and a front view showing a first driving force transport path in a gear unit of the paper transport device. [Figure 8] 10A and 10B are a side view and a front view showing a second driving force transport path in a gear unit of the paper transport device. [Figure 9] FIG. 2 is a block diagram showing the configuration of a control system of the paper transport device. [Figure 10]This is a flowchart showing a control procedure for appropriately setting the timing and period for connecting the electromagnetic clutch of a paper transport device, removing rust and dirt that has formed on the connecting surface between the rotor and armature of the electromagnetic clutch, and maintaining the function of the electromagnetic clutch. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a cross-sectional view showing an image forming apparatus to which a paper transport device according to an embodiment of the present invention is applied. As shown in Fig. 1, the image forming apparatus 10 of this embodiment is, for example, a multifunction machine, and includes an image reading unit 11, an image forming unit 12, a paper feeder 20, and a paper transport device 30.

[0014] The image reading unit 11 has an imaging element (CCD sensor, contact image sensor) that optically reads the image of the document, and the analog output of this imaging element is converted into a digital signal to generate image data representing the image of the document.

[0015] The image forming unit 12 prints an image represented by the image data on recording paper and includes a magenta image forming unit 3M, a cyan image forming unit 3C, a yellow image forming unit 3Y, and a black image forming unit 3Bk. Each of the image forming units 3M, 3C, 3Y, and 3Bk uniformly charges the surface of the photosensitive drum 4, exposes the surface of the photosensitive drum 4 to light, forms an electrostatic latent image on the surface of the photosensitive drum 4, develops the electrostatic latent image on the surface of the photosensitive drum 4 into a toner image, and transfers the toner image on the surface of the photosensitive drum 4 to the intermediate transfer belt 5. This forms a color toner image on the intermediate transfer belt 5. This color toner image is secondarily transferred to the recording paper P transported through the transport path 8 at the nip region N between the intermediate transfer belt 5 and the secondary transfer roller 6.

[0016] Thereafter, the recording paper P is heated and pressed in the fixing unit 15 to fix the toner image on the recording paper P by thermocompression, and the recording paper P is then discharged onto a paper discharge tray 17 via a discharge roller 16 .

[0017] A paper feeder 20 and a paper transport device 30 are provided below the image forming unit 12. The recording paper P is drawn from the paper feeder 20 and transported through a transport path 8 of the paper transport device 30 to reach a nip area N between the intermediate transfer belt 5 and the secondary transfer roller 6.

[0018] Fig. 2 is a cross-sectional view showing the paper feeder 20 and paper transport device 30 of this embodiment. As shown in Fig. 2, the paper feeder 20 includes a paper feed cassette 21, which is provided with a paper feed tray 22 on which a plurality of recording sheets P are stacked. The paper feeder 20 also includes a pick-up roller 23 that pulls out the recording sheets P from the paper feed tray 22, a feed roller 24 that transports the recording sheets P, and a retard roller 25 that contacts the underside of the circumferential surface of the feed roller 24.

[0019] The recording paper P is pulled out from the paper feed tray 22 by the pick-up roller 23, passes between the feed roller 24 and the retard roller 25, and is guided to the conveying path 8 of the paper conveying device 30 and supplied.

[0020] In the paper transport device 30, a first transport roller 31 and a driven roller 35, a second transport roller 32 and a driven roller 36, a first sensor 37, and a second sensor 38 are arranged along the transport path 8. The first sensor 37 and the second sensor 38 are, for example, optical sensors having a light-emitting unit and a light-receiving unit, and the light-emitting unit is installed on one inner wall of the transport path 8 and the light-receiving unit is installed on the other inner wall opposite the one inner wall. The first sensor 37 and the second sensor 38 detect that paper is present at the sensor location when the light-receiving unit can no longer receive light from the light-emitting unit.

[0021] The recording paper P pulled out from the paper feed device 20 is transported between the first transport roller 31 and the driven roller 35, and then transported between the second transport roller 32 and the driven roller 36, and is led to the nip area N between the intermediate transfer belt 5 and the secondary transfer roller 6.

[0022] The first sensor 37 is positioned upstream of the first transport roller 31 in the transport direction of the recording paper P, and detects the leading and trailing ends of the recording paper P being transported through the transport path 8 based on whether or not the light receiving unit receives light from the light emitting unit.

[0023] The second sensor 38 is positioned downstream in the transport direction of the recording paper P from the first transport roller 31, and detects the leading edge of the recording paper P being transported through the transport path 8 based on whether or not the light receiving unit receives light from the light emitting unit.

[0024] As will be described later, the control unit 71 (Figure 9) calculates the distance Xp between the rear end of the previous recording sheet P and the front end of the next recording sheet P based on the time interval T from the detection of the rear end of the previous recording sheet P by the first sensor 37 to the detection of the front end of the next recording sheet P, and the predetermined normal transport speed V of the recording sheet P through the transport path 8.

[0025] Here, when multiple recording sheets P are successively drawn out from the paper feed device 20 and transported one by one by the paper transport device 30, and an image is formed on each recording sheet P by the image forming unit 12, it is desirable to maintain the separation distance Xp between the rear end of the previous recording sheet P and the front end of the next recording sheet P at the specified separation distance x, which is the ideal reference value.

[0026] However, the separation distance Xp may become longer than the specified separation distance x due to factors such as the pickup roller 23 of the paper feeder 20 slipping on the surface of the next recording paper P. In this case, in this embodiment, the rotation speed of the first transport roller 31 is temporarily accelerated while the rotation speed of the second transport roller 32 is maintained constant, thereby increasing the transport speed of the next recording paper P by the first transport roller 31 and controlling the separation distance Xp to approach the specified separation distance x.

[0027] Next, a mechanism for temporarily accelerating the rotation speed of the first transport roller 31 will be described.

[0028] Fig. 3 is a perspective view showing the entire gear unit for driving the paper feeder 20 and the paper transport device 30. Fig. 4 is a perspective view mainly showing the gear unit of the paper transport device 30. Fig. 5 is a perspective view showing an enlarged portion of the gear unit of the paper transport device 30. Figs. 6(A) and 6(B) are a side view and a front view schematically showing the gear unit of the paper transport device 30.

[0029] As shown in Figures 3 to 6(A) and (B), the gear unit 40 of the paper transport device 30 includes an output gear 42 fixed to the shaft of a motor 41, a gear 43 meshing with the output gear 42, a gear 45 rotating together with a shaft 44 of the gear 43, a second gear 46 meshing with the gear 45, a first gear 49 provided around a shaft 47 of the second gear 46 via a one-way clutch 48, an intermediate gear 51 meshing with the first gear 49, a switching gear 52 meshing with the second gear 46, and a switching gear 53. The intermediate gear 52 is connected to or disconnected from the shaft 53 of the intermediate gear 51, a third gear 55 meshed with the intermediate gear 51, a gear 57 rotating with the shaft 56 of the third gear 55, a gear 58 meshed with the gear 57, a gear 61 rotating with the shaft 59 of the gear 58, and a roller gear 62 meshed with the gear 61. The driving force of the motor 41 is transmitted to the shaft 63 of the roller gear 62 to rotate the first conveying roller 31 provided on the shaft 63.

[0030] The first gear 49, second gear 46, one-way clutch 48, intermediate gear 51, switching gear 52, electromagnetic clutch 54, and third gear 55 correspond to the first gear, second gear, one-way clutch, intermediate gear, switching gear, electromagnetic clutch, and third gear in the claims. The electromagnetic clutch 54 includes a rotor and an armature, and interrupts or transmits the driving force of the motor 41 received by the switching gear 52 by contacting or separating the rotor and the armature.

[0031] 3, gear unit 65 of paper feeder 20 is provided below gear unit 40 of paper transport device 30. Gear unit 65 of paper feeder 20 includes gear 66 that meshes with first gear 49 of gear unit 40 of paper transport device 30, and multiple gears and multiple electromagnetic clutches for transmitting or blocking the driving force of gear 66 to pick-up roller 23, feed roller 24, etc., and is driven by motor 41, just like paper transport device 30.

[0032] Furthermore, the gear unit 40 of the paper transport device 30 transmits the driving force of the motor 41 to the second transport roller 32 via a plurality of gears, causing the second transport roller 32 to rotate at a constant rotational speed.

[0033] Here, upstream of the second gear 46 in the driving force transmission direction, the driving force is transmitted through the transmission path of the output gear 42 of the shaft of the motor 41 → gear 43 → shaft 44 → gear 45 → second gear 46.

[0034] Further, downstream of the third gear 55 in the driving force transmission direction, the driving force is transmitted through the transmission path of the third gear 55 → shaft 56 → gear 57 → gear 58 → shaft 59 → gear 61 → roller gear 62.

[0035] Then, the driving force is transmitted between the second gear 46 and the third gear 55 via the first driving force transmission path or the second driving force transmission path depending on whether the electromagnetic clutch 54 is disengaged or engaged. In other words, the driving force of the first driving force transmission path or the second driving force transmission path is switched depending on whether the electromagnetic clutch 54 is disengaged or engaged. The electromagnetic clutch 54 is disengaged by separating the rotor and the armature, and is engaged by connecting the rotor and the armature.

[0036] When the electromagnetic clutch 54 is disengaged (off), the switching gear 52 is disconnected from the shaft 53 of the intermediate gear 51, and the switching gear 52 rotates freely around the shaft 53. In this case, as shown in Figures 7(A) and (B), a first driving force transmission path is formed, which is the gear 45 → second gear 46 → shaft 47 → one-way clutch 48 → first gear 49 → intermediate gear 51 → third gear 55. In the first driving force transmission path, because the electromagnetic clutch 54 is disengaged, even if driving force is transmitted from the second gear 46 to the switching gear 52, the switching gear 52 rotates freely around the shaft 53, and the driving force of the switching gear 52 is interrupted. Furthermore, the driving force of the second gear 46 is transmitted to the first gear 49 via the one-way clutch 48 of the shaft 47, and the driving force of the first gear 49 is transmitted to the intermediate gear 51, and the driving force is transmitted from the intermediate gear 51 to the third gear 55.

[0037] Furthermore, when the electromagnetic clutch 54 is engaged (ON), the switching gear 52 is connected to the shaft 53 of the intermediate gear 51, and the driving force of the switching gear 52 is transmitted to the intermediate gear 51 via the shaft 53. In this case, as shown in Figures 8(A) and 8(B), a second driving force transmission path is formed, which is the gear 45 → second gear 46 → switching gear 52 → shaft 53 → intermediate gear 51 → third gear 55. Since the electromagnetic clutch 54 is engaged in the second driving force transmission path, when the driving force is transmitted from the second gear 46 to the switching gear 52, the driving force of the switching gear 52 is transmitted to the intermediate gear 51 via the shaft 53, and then the driving force is transmitted from the intermediate gear 51 to the third gear 55. At the same time, the first gear 49 is disconnected from the shaft 47 of the second gear 46 by the one-way clutch 48, and the first gear 49 rotates freely.

[0038] Here, the number of teeth of first gear 49 is fewer than the number of teeth of intermediate gear 51, and the number of teeth of second gear 46 is greater than the number of teeth of switching gear 52. In the second driving force transmission path, electromagnetic clutch 54 is connected, switching gear 52 rotates together with intermediate gear 51, and due to the relationship in the number of teeth of the two sets of gears, the rotational speed of first gear 49 meshing with intermediate gear 51 becomes faster than the rotational speed of shaft 47 of second gear 46, and first gear 49 is disconnected from shaft 47 of second gear 46 by one-way clutch 48, causing first gear 49 to rotate freely.

[0039] Furthermore, due to the relationship between the two gear ratios, the rotation speed of the switching gear 52 and the intermediate gear 51, which rotate upon receiving the driving force from the second gear 46 in the second driving force transmission path, is faster than the rotation speed of the intermediate gear 51, which rotates upon receiving the driving force from the first gear 49 in the first driving force transmission path, and the rotation speed of the first conveyance roller 31 is also faster in the second driving force transmission path than in the first driving force transmission path. Therefore, when the electromagnetic clutch 54 is switched from a disengaged state to a connected state and the driving force transmission path is switched from the first driving force transmission path to the second driving force transmission path, the rotation speed of the first conveying roller 31 increases and is accelerated.

[0040] As described above, when the separation distance Xp between the rear end of the previous recording sheet P and the leading end of the next recording sheet P becomes longer than the specified separation distance x due to reasons such as the pickup roller 23 of the paper feeder 20 slipping on the surface of the next recording sheet P, the rotation speed of the first transport roller 31 is temporarily accelerated while maintaining a constant rotation speed of the second transport roller 32, thereby increasing the transport speed of the next recording sheet P and bringing the separation distance Xp closer to the specified separation distance x. Therefore, the electromagnetic clutch 54 is not frequently engaged.

[0041] Meanwhile, as described above, the electromagnetic clutch 54 can be in a disengaged state where the rotor and armature are separated, or in a connected state where the rotor and armature are pressed against each other. If the electromagnetic clutch 54 is not engaged and the rotor and armature remain in a separated and disconnected state, rust and dirt will form on the connecting surface between the rotor and armature. Even if the rotor and armature are connected, if rust and dirt are present on the connecting surface, slippage will occur between the rotor and armature, causing the rotational speed of the armature to decrease. In this case, even if the drive force transmission path is switched from the first to the second drive force transmission path, the rotational speed of the first transport roller 31 will not be sufficiently accelerated.

[0042] For this reason, the rotor and armature of the electromagnetic clutch 54 are allowed to slide while pressed against each other, removing rust and dirt that has formed on the connecting surfaces of the rotor and armature and preventing slippage between the rotor and armature. However, if the rotor and armature are kept pressed against each other for a long period of time, wear between the rotor and armature will increase, and there is a risk that the function of the electromagnetic clutch 54 will be impaired.

[0043] Therefore, in this embodiment, the timing and period for connecting the electromagnetic clutch 54 are limited, so that the function of the electromagnetic clutch 54 is maintained while removing rust and dirt that has formed on the connecting surface between the rotor and armature of the electromagnetic clutch 54.

[0044] Fig. 9 is a block diagram showing the configuration of a control system for paper transport device 30. As shown in Fig. 9, control unit 71 controls motor 41 to rotate output gear 42 fixed to the shaft of motor 41, turns off (disconnects) electromagnetic clutch 54 of gear unit 40 to form a first driving force transmission path, and turns on (connects) electromagnetic clutch 54 to form a second driving force transmission path.

[0045] Furthermore, the control unit 71 acquires the detection output of the first sensor 37 and the detection output of the second sensor 38, and determines the detection timing of the leading edge and trailing edge of the recording paper P based on each detection output. For example, as described above, if the first sensor 37 and the second sensor 38 are equipped with a light-emitting unit (light-emitting element) that emits light toward the transport path 8 of the recording paper P and a light-receiving unit (light-receiving element) that receives light reflected by the recording paper P, the timing when the light-receiving unit starts receiving light is the detection timing of the leading edge of the recording paper P, and the subsequent timing when the light-receiving unit stops receiving light is the detection timing of the trailing edge of the recording paper P.

[0046] Next, a control procedure for appropriately setting the timing and period for connecting the electromagnetic clutch 54 will be described with reference to the flowchart shown in FIG.

[0047] When multiple sheets of recording paper P are successively pulled out from the paper feed device 20 and transported one by one by the paper transport device 30, and an image is formed on each sheet of recording paper P by the image forming unit 12, the control unit 71 rotates the motor 41 and controls the electromagnetic clutch of the gear unit 65 (shown in Figure 3) of the paper feed device 20 to intermittently rotate the pick-up roller 23, the feed roller 24, etc., to supply the recording paper P one sheet at a time from the paper feed cassette 21, and also turns off (disconnects) the electromagnetic clutch 54 of the gear unit 40 of the paper transport device 30 to form a first driving force transmission path in the gear unit 40, and transports the recording paper P one sheet at a time by the first transport roller 31 at the normal transport speed V (S101).

[0048] The control unit 71 determines the detection timing of the rear end of the previous (N-1th) sheet of recording paper P by the first sensor 37, and then when the next (Nth) sheet of recording paper P is pulled out, determines the detection timing of the front end of the Nth sheet of recording paper P by the first sensor 37 (S102), calculates the time interval T between the detection timing of the rear end of the N-1th sheet of recording paper P and the detection timing of the front end of the Nth sheet of recording paper P, and calculates the separation distance Xp between the rear end of the N-1th sheet of recording paper P and the front end of the Nth sheet of recording paper P based on this calculated time interval T and the normal transport speed V of the recording paper P by the first transport roller 31 (S103).

[0049] The control unit 71 compares the separation distance Xp calculated in S103 with a preset specified separation distance x (for example, 30 mm) and determines whether the separation distance Xp is equal to or less than the specified separation distance x (S104), and if the separation distance Xp is equal to or less than the specified separation distance x (S104 "Yes"), the process returns to S101 and the (N+1)th sheet of recording paper P is pulled out from the paper feed device 20 and conveyed by the paper conveying device 30. This means that the distance between the (N-1)th sheet of recording paper P and the Nth sheet of recording paper P is maintained accurately.

[0050] Furthermore, if the separation distance Xp exceeds the specified separation distance x (S104 "No"), the control unit 71 turns on (connects) the electromagnetic clutch 54 of the gear unit 40 of the paper transport device 30 to form a second driving force transmission path in the gear unit 40, accelerates the rotational speed of the first transport roller 31, and makes the transport speed of the Nth sheet of recording paper P by the first transport roller 31 higher than the normal transport speed V (S105). By transporting the Nth sheet of recording paper P in this manner, the gap between the N-1th sheet of recording paper P and the Nth sheet of recording paper P is narrowed. This control is performed because the gap between the N-1th sheet of recording paper P and the Nth sheet of recording paper P is too wide.

[0051] Next, the control unit 71 determines the detection timing of the leading edge of the Nth sheet of recording paper P by the first sensor 37 and the detection timing of the leading edge of the Nth sheet of recording paper P by the second sensor 38 (S107), and calculates the time interval T between each detection timing (S108).

[0052] The time interval T is the time required for the recording paper P to be transported (for the recording paper P to move) a certain distance between the first sensor 37 and the second sensor 38. The time interval T also corresponds to the average value of the transport speed of the recording paper P accelerated from the position where the leading edge of the recording paper P is detected by the first sensor 37 to the position where the leading edge of the recording paper P is detected by the second sensor 38. Here, when the electromagnetic clutch 54 is turned on (connected) in S105 and the rotational speed of the first transport roller 31 is accelerated, if no slippage occurs between the rotor and armature of the electromagnetic clutch 54, the time interval T will become the predetermined normal time, time interval t.

[0053] The control unit 71 compares the time interval T calculated in S108 with a preset first time interval t1 (second threshold) and a preset second time interval t2 (first threshold) (S109). Here, as an example, it is assumed that the first time interval t1 is set to the specified time interval t×1.1 (10% more than the specified time interval t), and the second time interval t2 is set to the specified time interval t×1.2 (20% more than the specified time interval t).

[0054] When the time interval T exceeds the second time interval t2, it is assumed that the average value of the accelerated conveyance speed of the Nth recording paper P is low, and the slip between the rotor and the armature of the electromagnetic clutch 54 is large.

[0055] Also, when the time interval T exceeds the first time interval t1 but is less than or equal to the second time interval t2, it is assumed that the average value of the accelerated conveyance speed of the Nth recording paper P is not sufficiently high, and there is a slip between the rotor and the armature of the electromagnetic clutch 54.

[0056] Furthermore, when the time interval T is less than the first time interval t1, it is assumed that the average value of the accelerated conveyance speed of the Nth recording paper P is high, and the slip between the rotor and the armature of the electromagnetic clutch 54 is slight (small).

[0057] When the control unit 71 determines that the time interval T calculated in S108 is less than the first time interval t1 (S109 "T < t1"), it returns to S101 and causes the N+1th recording paper P to be pulled out from the paper feeding device 20 and conveyed by the paper conveyance device 30. This is because it can be assumed that the slip between the rotor and the armature of the electromagnetic clutch 54 is slight and the adverse effect is small.

[0058] Also, when the control unit 71 determines that the time interval T calculated in S108 exceeds the first time interval t1 and is less than or equal to the second time interval t2 (S109 "t1 ≤ T < t2"), it feeds and conveys the N+1th recording paper P (S110). At this time, the control unit 71 turns on (connects) the electromagnetic clutch 54 of the gear unit 40 of the paper conveyance device 30 to form the second driving force transmission path in the gear unit 40, and keeps the rotational speed of the first conveyance roller 31 accelerated. Thereby, the conveyance speed of the N+1th recording paper P by the first conveyance roller 31 is made higher than the normal conveyance speed V, and the N+1th recording paper P is conveyed. In this case, since it is assumed that there is a slip between the rotor and the armature of the electromagnetic clutch 54 and the paper conveyance speed is slow, the control to convey the next recording paper P at an accelerated speed is also performed. After this, the process returns to S107.

[0059] On the other hand, if the control unit 71 determines that the time interval T calculated in S108 exceeds the second time interval t2 (S109 "T≦t2"), it delays the timing of the feeding of the (N+1)th sheet of recording paper P by the paper feeder 20 by a fixed time (extending the time interval between feeding of the recording paper P), and turns on the electromagnetic clutch 54 of the gear unit 40 of the paper transport device 30 for a preset fixed connection period ST (e.g., 5 seconds) during the period when the roller 31 is not transporting the (N+1)th sheet of recording paper P before feeding the (N+1)th sheet of recording paper P from the paper feed cassette 21 (S113). At this time, the first transport roller 31 is driven to rotate, but does not transport the recording paper P and is in an idling state. In other words, by the control unit 71 turning on the electromagnetic clutch 54 in this way, the rotor and armature are in pressure contact for an additional connection period ST during the period when the recording paper P is not being transported.

[0060] If "T≦t2" in S109, it is assumed that there is a large amount of slippage between the rotor and armature of the electromagnetic clutch 54. For this reason, by turning on the electromagnetic clutch 54 for an extra fixed connection period ST, the contact time between the rotor and armature of the electromagnetic clutch 54 is increased, ensuring time for any rust that has formed on the connecting surface between the rotor and armature to be removed.

[0061] Then, the control unit 71 keeps the electromagnetic clutch 54 of the gear unit 40 of the paper transport device 30 turned on (connected) and feeds and transports the (N+1)th sheet of recording paper P (S110). That is, the second drive force transmission path in the gear unit 40 is formed, the rotation speed of the first transport roller 31 is accelerated, and the (N+1)th sheet of recording paper P is also transported in a state where the transport speed of the (N+1)th sheet of recording paper P by the first transport roller 31 is higher than the normal transport speed V. After this, the process returns to S107.

[0062] After that, when the processes after S107 are performed again and the time interval T after the process of S113 does not change, S113 and S110 are repeated. When "t1 ≦ T < t2" is satisfied in S109, S110 is performed without performing the process of S113. When "T < t1" is satisfied in S109, the process returns to S101, and the electromagnetic clutch 54 is turned off by the control unit 71, and the first driving force transmission path is formed. The recording paper P is conveyed one by one at the normal conveyance speed V by the first conveyance roller 31.

[0063] In the present embodiment, when the time interval T exceeds the second time interval t2, during the period in which the recording paper P is not being conveyed, the electromagnetic clutch 54 is connected for a preset connection period ST, and then the electromagnetic clutch 54 is connected to form the second driving force transmission path and rotate the first conveyance roller 31, thereby taking an extra contact time between the rotor and the armature of the electromagnetic clutch 54. According to this embodiment, it is possible to appropriately set the timing and period for connecting the electromagnetic clutch 54 to remove rust and dirt generated on the connecting surface between the rotor and the armature of the electromagnetic clutch 54 and maintain the function of the electromagnetic clutch 54.

[0064] In the above embodiment, the one-way clutch 48 is used to connect or disconnect the first gear 49 with respect to the shaft 47 of the second gear 46. However, instead of the one-way clutch 48, an electromagnetic clutch for connecting or disconnecting the first gear 49 with respect to the shaft 47 of the second gear 46 may be applied.

[0065] In the above embodiment, a multifunction peripheral is exemplified as one embodiment of the image forming apparatus of the present invention, but this is merely an example, and it may be a printer, a copier, a facsimile apparatus, or the like.

[0066] The configuration of the above embodiment described using FIGS. 1 to 10 is merely an example of the present invention, and the present invention is not intended to be limited to such a configuration.

Explanation of Reference Numerals

[0067] 10 Image forming apparatus 12 Image forming unit 20 Paper feeder 30 Paper transport device 31 First conveyor roller 32 Second conveyor roller 37 First Sensor 38 Second Sensor 40 Gear Unit 41 Motor 46 2nd Gear 48 One-way clutch 49 First Gear 51 Intermediate gear 52 Switching gear 54 Electromagnetic clutch 55 3rd Gear 65 Gear Unit

Claims

1. A motor and a roller that is rotated by the driving force of the motor and sequentially transports a plurality of sheets of paper; a gear unit including a switching gear and an electromagnetic clutch that transmits or interrupts the driving force of the motor received by the switching gear through a rotor and an armature, wherein when the rotor and the armature of the electromagnetic clutch are disconnected, the driving force is interrupted by the switching gear and transmitted to the roller without passing through the switching gear, thereby forming a first driving force transmission path that rotates the roller, and when the rotor and the armature of the electromagnetic clutch are connected, the driving force is transmitted to the roller via the switching gear, thereby accelerating the rotational speed of the roller; a first sensor that sequentially detects the paper being transported by the roller; a second sensor disposed at a position different from the first sensor in the paper transport direction; a control unit that disengages the electromagnetic clutch to form the first driving force transmission path, sequentially transports each sheet of paper by the roller, determines the separation distance between each sheet of paper based on the detection output of the first sensor, and when the determined separation distance is longer than a predetermined separation distance, connects the electromagnetic clutch to form the second driving force transmission path and accelerates the rotation speed of the roller; The control unit connects the electromagnetic clutch to form the second driving force transmission path and accelerates the rotational speed of the roller, and determines the time required to transport paper a certain distance between the first sensor and the second sensor based on the detection output of the first sensor and the detection output of the second sensor.If the determined time exceeds a predetermined first threshold that is longer than the specified normal time for paper to move the certain distance, the control unit connects the electromagnetic clutch to form the second driving force transmission path during a period when paper is not being transported by the roller and drives the roller to rotate for a predetermined connection time, and then transports the next paper while the second driving force transmission path is formed.This is a paper transport device.

2. The control unit compares the determined time with the first threshold value and a predetermined second threshold value that is smaller than the first threshold value, and if the determined time exceeds the second threshold value and is less than or equal to the first threshold value, does not control the roller to rotate for the connection time, and instead transports the next sheet of paper while the second driving force transmission path is formed.

3. The paper transport device described in claim 2, wherein the control unit, when the determined time is less than or equal to the second threshold value, disengages the electromagnetic clutch and causes the roller to transport the next paper while forming the first driving force transmission path.

4. the gear unit includes an intermediate gear fixed to a shaft that rotatably supports the switching gear, a first gear and a second gear that are on the upstream side in the driving force transmission direction and mesh with the intermediate gear and the switching gear, a third gear that is on the downstream side in the driving force transmission direction and meshes with the intermediate gear, and a one-way clutch that transmits rotation of the first gear in one direction to the intermediate gear, the electromagnetic clutch connects or disconnects the switching gear from or to the shaft, causing the switching gear to rotate freely around the axis of the shaft or transmitting the driving force of the switching gear to the shaft; A paper transport device as described in claim 1, wherein when the electromagnetic clutch is disengaged, the driving force is transmitted through the first driving force transmission path in the order of the first gear, the intermediate gear, and the third gear, and when the electromagnetic clutch is engaged, the driving force is transmitted through the second driving force transmission path in the order of the second gear, the switching gear, the shaft, the intermediate gear, and the third gear, and the one-way clutch causes the first gear to rotate freely.

5. A paper transport device according to any one of claims 1 to 4; an image forming unit that forms an image on a sheet of paper transported by a sheet transport device.

Images