Medium conveying device and image forming device

Abstract

To stably convey a medium.SOLUTION: A medium conveyance device has a plurality of guide members that guide a medium fed from a paper feed part, a paper feed passage formed between the guide members for conveying a medium, a medium detection part that is arranged in the paper feed passage and detects the presence or absence of the medium, and a film member supported by the guide member so that a front edge ef is displaceable in the paper feed passage, By separating the front edge ef of the film member and a front edge Mge of the guide member, a gap δ having a width sufficient to allow the medium to pass is formed. When the medium passes through the gap δ, an energizing force with which the film member energizes the medium is extremely small. Since a load caused by a conveyance of the medium is reduced, the medium can be stably conveyed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a medium transport device and an image forming apparatus. [Background technology]

[0002] BACKGROUND ART Conventionally, in image forming devices such as printers, copiers, facsimile machines, and multifunction machines, for example, in a printer, a toner image is formed on the surface of a photosensitive drum in an image forming section, the toner image is transferred to paper as a medium, the paper onto which the toner image has been transferred is sent to a fixing device, and the toner image is fixed to the paper in the fixing device.

[0003] In the printer, paper fed from a paper cassette or the like is transported along a paper transport path by a paper transport device serving as a medium transport device, and the presence or absence of paper is detected by a paper detection unit in the paper transport path.The paper is then sent to the image forming unit.

[0004] Incidentally, in order to stabilize the position of the paper in the paper transport path, a printer is provided in which a pressing member is arranged in the paper transport path, and the pressing member urges the paper toward the transport guide of the paper transport path (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-75043 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional printers described above, the paper is urged toward the transport guide, which places a load on the paper, causing transport delays, or the urging force becomes unbalanced, causing skew, making it impossible to transport the paper stably.

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a medium transport device and an image forming apparatus that can solve the problems of the conventional printers and transport a medium stably. [Means for solving the problem]

[0008] To this end, the media transport device of the present invention has a plurality of guide members that guide the media fed from the paper feed section, a paper feed path formed between the guide members for transporting the media, a media detection section disposed in the paper feed path that detects the presence or absence of media, and a film member supported by the guide members in the paper feed path so that its leading edge can be displaced freely.

[0009] The leading edge of the film member and the leading edge of the guide member are then spaced apart to form a gap wide enough to allow the medium to pass through. [Effects of the Invention]

[0010] According to the present invention, the media transport device includes a plurality of guide members that guide media fed from a paper feed section, a paper feed path formed between the guide members for transporting the media, a media detection section disposed in the paper feed path that detects the presence or absence of media, and a film member supported by the guide members in the paper feed path so that its leading edge is freely displaceable.

[0011] The leading edge of the film member and the leading edge of the guide member are then spaced apart to form a gap wide enough to allow the medium to pass through.

[0012] In this case, by separating the leading edge of the film member from the leading edge of the guide member, a gap wide enough to allow the media to pass through is formed, so that the leading edge of the film member is only slightly displaced as the media passes through the gap, and the force with which the film member urges the media is extremely small.

[0013] Therefore, the load generated in association with the transport of the medium is reduced, so that the medium can be transported stably without delay in transporting the medium or without the balance of the displacement of the leading edge of the medium being lost and causing skew. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 4 is a detailed view showing a junction of a lower conveying path and an upper conveying path in the embodiment of the present invention. [Figure 2] 1 is a first perspective view of a printer according to an embodiment of the present invention. [Figure 3] FIG. 2 is a second perspective view of the printer according to the embodiment of the present invention. [Figure 4] 1 is a conceptual diagram of a printer according to an embodiment of the present invention. [Figure 5] 1 is a cross-sectional view showing a main part of a paper transport device according to an embodiment of the present invention. [Figure 6] 1 is a perspective view showing a main part of a paper transport device according to an embodiment of the present invention; [Figure 7] 1 is a plan view showing a main part of a paper transport device according to an embodiment of the present invention; [Figure 8] 10A and 10B are diagrams illustrating detection positions for the rear end of a sheet fed from a sheet cassette according to an embodiment of the present invention. [Figure 9] 10A and 10B are diagrams illustrating detection positions for the rear end of a sheet fed from a manual feed tray according to an embodiment of the present invention. [Figure 10] 10A and 10B are diagrams illustrating an example of variation in the position of the tip of the sensor lever when detecting the rear end of a sheet of paper fed from a paper cassette in the printer of the reference example. [Figure 11] 10A and 10B are diagrams illustrating an example of variations in the position of the tip of the sensor lever when detecting the rear edge of a sheet fed from a manual feed tray in the printer of the reference example. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings, in which a paper transport device as a medium transport device and a printer as an image forming device will be described.

[0016] Figure 2 is a first perspective view of a printer according to an embodiment of the present invention, Figure 3 is a second perspective view of the printer according to an embodiment of the present invention, and Figure 4 is a conceptual diagram of the printer according to an embodiment of the present invention. In the figures, the positive X-axis direction is the rear direction of the printer 11, the negative X-axis direction is the front direction of the printer 11, the positive Y-axis direction is the left direction of the printer 11, the negative Y-axis direction is the right direction of the printer 11, the positive Z-axis direction is the upward direction of the printer 11, and the negative Z-axis direction is the downward direction of the printer 11.

[0017] In the figure, 11 is a printer, Cs is a housing as an exterior of the printer 11, and Bd is the main body of the printer 11, that is, the main body of the device.

[0018] The housing Cs includes a front wall Wf, a back wall Wr, a side wall Ws1 on the left side as viewed from the front wall Wf, a side wall Ws2 on the right side as viewed from the front wall Wf, and a top wall Wt.

[0019] A front cover Pf as a first opening / closing member is provided in the upper half of the front wall Wf so as to be able to open and close freely, and an operator can access the inside of the device body Bd by opening the front cover Pf. In addition, a manual feed cover Cv as a second opening / closing member is provided in the front cover Pf so as to be able to open and close freely.

[0020] An operation panel 13 is disposed on the top wall Wt adjacent to the front wall Wf. The operation panel 13 includes a display unit 13a, such as an LED screen, for displaying the status of the printer 11, and an operation unit 13b, such as switches and keys, for an operator to input instructions to the printer 11. A stacker Sk serving as a medium stacking unit is formed from the center of the top wall Wt to ​​the spine wall Wr. A discharge opening Hd is formed facing the stacker Sk and for discharging paper P, which serves as a medium on which an image has been formed, and a pair of discharge rollers md serving as a discharge member are rotatably disposed at the discharge opening Hd.

[0021] An image forming unit 12 is disposed in the upper part of the apparatus main body Bd, and a toner image is formed as a developer image in the image forming unit 12.

[0022] The image forming unit 12 includes a photosensitive drum 13 as an image carrier formed in a drum shape and equipped with an organic photosensitive material on its surface, a charging roller 14 as a charging device arranged in contact with the photosensitive drum 13 and for uniformly charging the surface of the photosensitive drum 13, a developing roller 16 as a developer carrier arranged in contact with the photosensitive drum 13 and for causing toner as a developer to adhere to an electrostatic latent image as a latent image formed on the surface of the photosensitive drum 13, thereby forming a toner image of each color, a supply roller 18 as a developer supply member arranged in pressure contact with the developing roller 16 and for supplying toner supplied from a toner cartridge (not shown) as a developer storage section to the developing roller 16, a developing blade (not shown) as a developer regulating member arranged with its tip in pressure contact with the developing roller 16 and for thinning the toner supplied from the supply roller 18, and a cleaning device 19 for removing and collecting toner remaining on the surface of the photosensitive drum 13 after transfer.

[0023] The developing roller 16 and the supply roller 18 are arranged in pressure contact with each other and rotated in the same direction, and at the contact point between the developing roller 16 and the supply roller 18, the surface of the developing roller 16 and the surface of the supply roller 18 are moved in opposite directions.

[0024] Above the photosensitive drum 13 in the image forming unit 12, an LED head 15 serving as an exposure device is disposed facing the photosensitive drum 13. Each LED head 15 includes a plurality of LEDs serving as light-emitting elements, a lens array, etc., and irradiates the photosensitive drum 13 with light in print dot units according to image data for each color, exposing the surface of the photosensitive drum 13, and forms an electrostatic latent image by attenuating the potential of the irradiated area.

[0025] A transfer roller 27 as a transfer member is rotatably disposed below the photosensitive drum 13, facing the photosensitive drum 13. By applying a voltage to the transfer roller 27, the paper P is charged to a polarity opposite to that of the toner, and the toner image is transferred onto the paper P.

[0026] The image forming unit 12, the LED head 15, and the transfer roller 27 form an image forming section Q1.

[0027] A first paper feed mechanism is disposed in the lower portion of the device body Bd, and includes a paper cassette Ca as a first paper feed section and medium storage section, a tray Tr as a first medium loading section, a feed roller 20 as a first feed member, a pair of paper feed rollers 21 as a first paper feed member, a pair of paper feed rollers 22 as a second paper feed member, and a pair of paper feed rollers 23 as a third paper feed member, and the paper P is loaded on the tray Tr.

[0028] The feed roller 20 is disposed at the front end of the paper cassette Ca, and the paper P is fed by the feed roller 20 to a paper transport path Rt serving as a medium transport path, and is fed by paper feed roller pairs 21 to 23 and transported along the paper transport path Rt.

[0029] A second paper feed mechanism is also provided on the side (right end in FIG. 4) of printer 11. The second paper feed mechanism includes a manual feed tray (multipurpose tray: MPT) 24 as a second paper feed unit and a second medium loading unit that is set by opening the manual feed cover Cv of printer 11, a feed roller 25 as a second feed member, and a pair of paper feed rollers 26 as a fourth paper feed member, and paper P is loaded on manual feed tray 24.

[0030] The feed roller 25 is disposed at the front end of the manual feed tray 24, and the paper P is fed to the paper transport path Rt by the feed roller 25, fed by a pair of paper feed rollers 26, and transported along the paper transport path Rt.

[0031] A pair of registration rollers 29 is arranged upstream of the image forming unit 12 on the paper transport path Rt as a first transport member for temporarily stopping the paper P fed from the first and second paper feed mechanisms and correcting any skew of the paper P.

[0032] The paper transport device is made up of the first and second paper feed mechanisms, the paper transport path Rt, the pair of registration rollers 29, etc. In the present embodiment, plain paper is used as the paper P, but other types of paper such as overhead projector paper, envelopes, copy paper, and special paper can also be used.

[0033] Further, a fixing device 37 is disposed downstream of the image forming unit Q1 on the paper transport path Rt. The fixing device 37 includes a heating roller 38 as a first fixing member and a pressure roller 39 as a second fixing member.

[0034] Further, a pair of conveying rollers m1 and m2 as second and third conveying members are arranged downstream of the fixing unit 37 on the paper conveying path Rt, and the pair of discharge rollers md is arranged downstream of the pair of conveying rollers m2.

[0035] Next, the operation of the printer 11 will be described.

[0036] In the image forming unit 12, the surface of the photosensitive drum 13 is uniformly charged by the charging roller 14, and light is irradiated onto the surface of the photosensitive drum 13 by the LED head 15, forming an electrostatic latent image corresponding to the image data.

[0037] The toner on the supply roller 18 is supplied to the developing roller 16, and at this time, the toner is charged by friction with the supply roller 18, friction with the developing roller 16, and the voltage difference between the supply roller 18 and the developing roller 16. The toner supplied from the supply roller 18 to the developing roller 16 is then thinned by the developing blade, forming a toner layer on the surface of the developing roller 16. Next, as the developing roller 16 rotates, the toner is sent to the contact point between the developing roller 16 and the photosensitive drum 13.

[0038] At the contact point, toner is attached to the photosensitive drum 13, and the electrostatic latent image formed on the surface of the photosensitive drum 13 is developed to form a toner image.

[0039] In addition, the paper P placed on the tray Tr of the paper cassette Ca is fed into the media transport path Rt by the feed roller 20, fed by the paper feed roller pairs 21 to 23, and after the skew is corrected by the registration roller pair 29, it is supplied to the transfer section between the photosensitive drum 13 and the transfer roller 27 of the image forming unit 12.

[0040] Furthermore, the paper P placed on the manual feed tray 24 is similarly fed to the media transport path Rt by the feed roller 25, transported by the paper feed roller pair 26, and after the skew is corrected by the registration roller pair 29, is supplied to the transfer section.

[0041] In the transfer section, the toner image is transferred onto the paper P by a voltage applied to a transfer roller 27 .

[0042] Next, the paper P is sent to the fixing device 37, where the toner image on the paper P is heated by a heating roller 38 and pressed by a pressure roller 39 to penetrate between the fibers of the paper P, thereby being fixed to the paper P. In this way, an image is formed on the paper P.

[0043] Then, the paper P on which the image has been formed is conveyed by the conveyance roller pair m1, m2, and then discharged to the outside of the apparatus main body Bd by the discharge roller pair md, and stacked on the stacker Sk.

[0044] Next, the main parts of the paper transport device will be described.

[0045] Fig. 1 is a detailed view showing the junction of the lower transport path and the upper transport path in an embodiment of the present invention, Fig. 5 is a cross-sectional view showing the main parts of the paper transport device in an embodiment of the present invention, Fig. 6 is a perspective view showing the main parts of the paper transport device in an embodiment of the present invention, and Fig. 7 is a plan view showing the main parts of the paper transport device in an embodiment of the present invention. Note that in Figs. 1, 5, and 7, the positive X-axis direction is the rear direction in the printer 11 (Fig. 2), the negative X-axis direction is the front direction in the printer 11, the positive Y-axis direction is the left direction in the printer 11, the negative Y-axis direction is the right direction in the printer 11, the positive Z-axis direction is the upward direction in the printer 11, and the negative Z-axis direction is the downward direction in the printer 11.

[0046] In the figure, reference numerals 23 and 26 denote a pair of paper feed rollers, 29 a pair of registration rollers, Rt a paper transport path, and arrow D the transport direction of paper P. Paper feed roller pair 23 includes a paper feed roller 23a and a pressure roller 23b arranged to press against paper feed roller 23a, paper feed roller pair 26 includes a paper feed roller 26a and a pressure roller 26b arranged to press against paper feed roller 26a, and registration roller pair 29 includes a registration roller 29a and a pressure roller 29b arranged to press against registration roller 29a. A nip portion Nr is formed between registration roller 29a and pressure roller 29b.

[0047] Furthermore, Lg is a lower guide serving as a first guide member (guide) that guides the paper P from below in the paper transport path Rt, Mg is a middle guide serving as a second guide member that guides the paper P in the center in the paper transport path Rt, and Ug is an upper guide serving as a third guide member that guides the paper P from above in the paper transport path Rt. The lower guide Lg is formed in an arc-like shape rising from the paper feed roller 23a downstream of the paper transport path Rt, the middle guide Mg is formed in an arc-like shape rising from the pressure roller 23b downstream of the paper transport path Rt, and the upper guide Ug is formed by protruding obliquely downward from the paper feed roller 26a downstream of the paper transport path Rt. Sheet P fed from paper cassette Ca is transported by paper feed roller pair 23 in the direction of arrow B along lower paper feed path LR, which serves as a first paper feed path formed between lower guide Lg and intermediate guide Mg, and sheet P fed from manual feed tray 24 is transported in the direction of arrow C along upper paper feed path UR, which serves as a second paper feed path formed between intermediate guide Mg and upper guide Ug. Sheet P fed from paper cassette Ca and sheet P fed from manual feed tray 24 are joined at a joining point pt and guided to nip portion Nr of registration roller pair 29 disposed downstream of lower paper feed path LR and upper paper feed path UR.

[0048] Near the downstream ends of the lower paper feed path LR and the upper paper feed path UR, a paper sensor 50 is disposed as a medium detection unit that detects the presence or absence of paper P being transported toward the registration roller pair 29. The paper sensor 50 includes a sensor lever 51 as a swinging member disposed at the downstream ends of the lower paper feed path LR and the upper paper feed path UR so as to be able to swing freely around a rotation axis sh1 disposed at a predetermined position on the lower guide Lg, a photosensor 52 as a sensor that generates a sensor output in response to the swing of the sensor lever 51, and a torsion spring (not shown) as a biasing member that biases the sensor lever 51 in the clockwise direction in FIG. 5 with a predetermined biasing force.

[0049] The photosensor 52 includes a light-emitting element and a light-receiving element (not shown), and as the transported paper P rotates the sensor lever 51 in a predetermined direction, in this embodiment counterclockwise, against the biasing force of the torsion spring, the light emitted by the light-emitting element is received by the light-receiving element to generate a sensor output. This allows the paper sensor 50 to detect the leading edge of the paper P and determine whether paper is present.

[0050] Furthermore, when the paper P passes the downstream end of the lower paper feed path LR or the upper paper feed path UR, the sensor lever 51 is rotated in the opposite direction by the biasing force of the torsion spring, in the clockwise direction in this embodiment, and the photosensor 52 no longer receives the light emitted by the light-emitting portion at the light-receiving portion and no longer generates a sensor output. As a result, the paper sensor 50 detects the rear end of the paper P and determines that no paper is present.

[0051] However, when the front end of the paper P being transported through the lower paper feed path LR and the upper paper feed path UR hits the sensor lever 51, and when the paper P passes the paper detection point and the rear end of the paper P moves away from the sensor lever 51, if the front end or rear end of the paper P flaps up and down, it is not possible to accurately detect whether the paper P is present or not.

[0052] Therefore, in this embodiment, a lower film 55, which serves as a first film member and a first guide member, is arranged diagonally upward along the lower guide Lg on the upper surface of the lower guide Lg in the lower paper feed path LR, and an upper film 56, which serves as a second film member and a second guide member, is arranged diagonally downward along the upper guide Ug on the lower surface of the upper guide Ug in the upper paper feed path UR, so that the lower film 55 and the upper film 56 guide the paper P transported through the lower paper feed path LR and the upper paper feed path UR toward the nip portion Nr of the registration roller pair 29.

[0053] The lower film 55 and the upper film 56 are made of a flexible material, such as a resin material, and have the same shape.

[0054] The lower film 55 is supported in a cantilever manner by the lower guide Lg so that its leading edge ef, which is the edge on the downstream side in the transport direction of the paper P, faces the junction point pt, and its trailing edge er, which is the edge on the upstream side in the transport direction of the paper P, is attached with double-sided tape (not shown) to a surface Sa set at a predetermined location on the upper surface of the lower guide Lg, so that the leading edge ef is freely displaceable in the vertical direction (Z-axis direction).The upper film 56 is supported in a cantilever manner by the upper guide Ug so that its leading edge ef, which is the edge on the downstream side in the transport direction of the paper P, faces the junction point pt, and its trailing edge er, which is the edge on the upstream side in the transport direction of the paper P, is attached with double-sided tape to a surface Sb set at a predetermined location on the upper guide Ug.

[0055] 6 and 7, the lower film 55 and the upper film 56 are formed by integrally connecting a trapezoidal front half 58 and a rectangular rear half 59, the front half 58 having the leading edge ef and side edges es1 extending diagonally rearward from both ends of the leading edge ef, and the rear half 59 having side edges es2 extending parallel to each other rearward from the rear ends of the side edges es1, and the rear edge er connecting the side edges es2. A groove m1 having a predetermined width is formed in the center of the width direction of the lower film 55 and the upper film 56, extending from the leading edge ef to the vicinity of the rear edge er, so that the sensor lever 51 can be sandwiched from the left and right.

[0056] In addition, a groove m2 having a predetermined width is formed in the corresponding central portion of the intermediate guide Mg from the front edge Mge to the rear, and the sensor lever 51 is made to protrude upward within the grooves m1 and m2 and is made to swing within the grooves m1 and m2.

[0057] By separating the leading edge ef of the lower film 55 from the leading edge Mge of the lower surface S1 of the intermediate guide Mg, a gap δ is formed between the leading edges ef and Mge that is wide enough to allow paper P to pass through, and by separating the leading edge ef of the upper film 56 from the leading edge Mge on the upper surface S2 of the intermediate guide Mg, a gap δ is formed between the leading edges ef and Mge that is wide enough to allow paper P to pass through.

[0058] That is, the leading edge ef of the lower film 55 is placed on the first tangent L1 between the nip portion Nr of the pair of registration rollers 29 and the leading edge Mge of the lower surface S1 of the intermediate guide Mg, and the leading edge ef of the upper film 56 is placed on the second tangent L2 between the nip portion Nr and the leading edge Mge of the upper surface S2 of the intermediate guide Mg, and the gap δ between the leading edge ef of the lower film 55 and the leading edge Mge of the intermediate guide Mg on the first tangent L1, and the gap δ between the leading edge ef of the upper film 55 and the leading edge Mge of the intermediate guide Mg on the second tangent L2 are equal to each other and are narrowed to the extent that the paper P slightly abuts the lower film 55, the upper film 56 and the intermediate guide Mg when it passes through the gap δ, and in this embodiment, the width is 2 mm.

[0059] Therefore, when the front end of the paper P passing through the gap δ hits the sensor lever 51, and when the rear end of the paper P moves away from the sensor lever 51, the front end or rear end of the paper P does not flap up or down, so the paper sensor 50 can accurately detect whether or not the paper P is present.

[0060] Furthermore, when the paper P passes through the gap δ, the leading edges ef of the lower film 55 and the upper film 56 are only slightly displaced, and the force with which the lower film 55 and the upper film 56 urge the paper P is extremely small. Therefore, the load generated as the paper P is transported is caused only by the displacement of the leading edges ef of the lower film 55 and the upper film 56, and is small. As a result, there is no delay in the transport of the paper P, and the balance of the displacement of the leading edges ef is not disturbed in the width direction of the paper transport path Rt, causing skew, and the paper P can be transported stably.

[0061] Since the sensor lever 51 is rotated about the rotation axis sh1, the paper sensor 50 detects the presence or absence of paper P with the tip 51a of the sensor lever 51 placed on the locus Ck (FIGS. 6 and 8) described below. Therefore, the lower film 55 is disposed slightly downstream of the upper film 56, and the leading edge ef of the lower film 55 on the first tangent line L1 is positioned slightly downstream of the leading edge ef of the upper film 56 on the second tangent line L2. Furthermore, in order to equalize the gaps δ on the first and second tangent lines L1 and L2, the end of the first tangent line L1 on the lower surface S1 side of the leading edge Mge is positioned slightly downstream of the end of the second tangent line L2 on the upper surface S2.

[0062] Incidentally, if the width W1 (dimension in the Y-axis direction) of each leading edge ef of the lower film 55 and the upper film 56 is wide, when the paper P passes through the gap δ, the moment applied to the paper P by the lower film 55 and the upper film 56 increases in proportion to the width W1, causing skew. Therefore, in this embodiment, the width W1 is set to 30 mm, which is sufficiently shorter than the width of the paper P.

[0063] Furthermore, even if the width W1 of the leading edge ef is small, the front half 58 has a trapezoidal shape and the width becomes wider towards the rear, so that the lower film 55 and the upper film 56 can be prevented from being displaced by external forces as the paper P is transported.

[0064] Next, the detection position of the rear end of the paper P on the locus of the sensor lever 51 when the paper sensor 50 detects the presence or absence of the paper P will be described.

[0065] FIG. 8 is a diagram showing the detection position of the rear end of a sheet of paper fed from a paper cassette in an embodiment of the present invention, and FIG. 9 is a diagram showing the detection position of the rear end of a sheet of paper fed from a manual feed tray in an embodiment of the present invention.

[0066] In the figure, reference numeral 29 denotes a pair of registration rollers, 55 denotes a lower film, 56 denotes an upper film, 51 denotes a sensor lever, Nr denotes a nip portion, P denotes paper, Lg denotes a lower guide, Ug denotes an upper guide, Mg denotes an intermediate guide, LR denotes a lower paper feed path, and UR denotes an upper paper feed path. Also, Ck denotes the trajectory of the tip 51a of the sensor lever 51 when the sensor lever 51 rotates counterclockwise and clockwise.

[0067] When the sensor lever 51 moves away from the rear end Pr of the paper P fed from the paper cassette Ca (Figure 2) and the tip 51a of the sensor lever 51 is placed at the paper rear end detection point α1 as the first medium rear end detection point on the trajectory Ck, the paper P is brought into contact with the leading edge ef of the lower film 55 on the first tangent line L1 (Figure 1), thereby preventing the leading end of the paper P from flapping.

[0068] Furthermore, when the sensor lever 51 moves away from the rear end Pr of the paper P fed from the manual feed tray 24 and the tip 51a of the sensor lever 51 is placed at the paper rear end detection point β1 as the second medium rear end detection point on the trajectory Ck, the paper P is brought into contact with the leading edge ef of the upper film 56 on the second tangent line L2, thereby preventing the leading end of the paper P from flapping.

[0069] Therefore, the rear end Pr of the paper P can be detected with high accuracy by the paper sensor 50 (FIG. 5), and therefore the presence or absence of the paper P can be detected with high accuracy.

[0070] Furthermore, since the first and second tangent lines L1 and L2 are formed by the nip portion Nr of the registration roller pair 29 and the lower surface S1 and upper surface S2 at the leading edge Mge of the intermediate guide Mg, the paper trailing end detection points α1 and β1 can be brought close to each other on the locus Ck.

[0071] Therefore, the paper sensor 50 can detect the presence or absence of paper P with even greater accuracy.

[0072] Next, the detection error of the rear end of the paper P by the paper sensor 50 in the printer 11 of the reference example in which the lower paper feed path LR and the upper paper feed path UR do not have the lower film 55 and the upper film 56 will be described.

[0073] Figure 10 is a diagram showing an example of variation in the position of the tip of the sensor lever when detecting the rear end of paper fed from a paper cassette in the reference example printer, and Figure 11 is a diagram showing an example of variation in the position of the tip of the sensor lever when detecting the rear end of paper fed from a manual feed tray in the reference example printer.

[0074] In the figure, 29 is a pair of registration rollers, 51 is a sensor lever, Nr is a nip portion, Lg is a lower guide, Ug is an upper guide, Mg is an intermediate guide, LR is a lower paper feed path, and UR is an upper paper feed path.

[0075] In the reference example printer 11, when the paper P fed from the paper cassette Ca is guided along the lower guide Lg through the lower paper feed path LR, the paper trailing end detection point of the tip 51a of the sensor lever 51 is α2, and when the paper P is guided along the intermediate guide Mg through the lower paper feed path LR, the paper trailing end detection point of the tip 51a of the sensor lever 51 is α3. The distance Lα2 between the nip portion Nr of the registration roller pair 29 and the paper trailing end detection point α2 is minimum, and the distance Lα3 between the nip portion Nr of the registration roller pair 29 and the paper trailing end detection point α3 is maximum.

[0076] In this case, the difference Δα between the distance Lα3 and the distance Lα2 is Δα=0.5 [mm] becomes.

[0077] That is, in the printer 11 of the reference example, a detection error of 0.5 mm occurs when detecting the rear end Pr (FIG. 8) of the paper P fed from the paper cassette Ca. This shows that in the printer 11 of the reference example, variation occurs in the position of the tip 51a of the sensor lever 51 when detecting the rear end Pr of the paper P fed from the paper cassette Ca.

[0078] Furthermore, in the printer 11 of the reference example, when the paper P fed from the manual feed tray 24 is guided along the intermediate guide Mg through the upper paper feed path LR, the paper rear end detection point of the tip 51a of the sensor lever 51 is β2, and when the paper P is guided along the upper paper feed path UR along the upper guide Ug, the paper rear end detection point of the tip 51a of the sensor lever 51 is β3, the distance Lβ2 between the nip portion Nr of the registration roller pair 29 and the paper rear end detection point β2 is minimum, and the distance Lβ3 between the nip portion Nr of the registration roller pair 29 and the paper rear end detection point β3 is maximum.

[0079] In this case, the difference Δβ between the distance Lβ3 and the distance Lβ2 is Δβ=2.5 [mm] becomes.

[0080] That is, in the printer 11 of the reference example, a detection error of 2.5 mm occurs when detecting the rear end Pr of the paper P fed from the manual feed tray 24. This shows that in the printer 11 of the reference example, variation occurs in the position of the tip 51a of the sensor lever 51 when detecting the rear end Pr of the paper P fed from the manual feed tray 24.

[0081] In this manner, in the present embodiment, by separating the leading edges ef of the lower film 55 and the upper film 56 from the leading edge Mge of the intermediate guide Mg, a gap δ is formed that is wide enough to allow the paper P to pass through. Therefore, when the paper P passes through the gap δ, the leading edges ef of the lower film 55 and the upper film 56 are only slightly displaced, and the force with which the lower film 55 and the upper film 56 urge the paper P is extremely small.

[0082] Therefore, the load generated in association with the transport of the paper P is reduced, so that the paper P can be transported stably without delay in transporting the paper P or without skew caused by imbalance in the displacement of the leading edge of the paper P.

[0083] In this embodiment, the width of the gap δ between the leading edge ef of the lower film 55 and the upper film 56 and the leading edge Mge of the intermediate guide Mg is set to 2 mm, but if the width is made smaller than 2 mm, it is possible to further reduce the detection error when detecting the rear end of the paper P. However, in that case, the load generated by the transport of the paper P increases, which may cause a delay in the transport of the paper P or cause the paper P to become skewed.

[0084] When the parameters of the lower film 55 and the upper film 56, such as the material, thickness, width W1 of the leading edge ef, elastic coefficient, and distance of the flexible portion from the leading edge ef to the trailing edge er, vary, the reaction force generated in the lower film 55 and the upper film 56 also varies, and therefore, in this embodiment, the width of the gap δ was set based on the results of experiments conducted with different parameters. Note that, since the appropriate range of the gap δ varies depending on the parameters, the width of the gap δ does not necessarily have to be 2 mm.

[0085] In this embodiment, the paper sensor 50 is configured to use a sensor lever 51 and a photosensor 52 that are supported so as to be able to swing freely, but a reflective or transmissive optical sensor can also be used.

[0086] Although the printer 11 has been described in this embodiment, the present invention can be applied to image forming devices such as copying machines, facsimile machines, and multifunction machines.

[0087] The present invention is not limited to the above-described embodiment, and various modifications can be made based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention. [Explanation of symbols]

[0088] 24 Manual feed tray 50 Paper sensor 55 Lower film 56 Upper film Ca Paper Cassette ef leading edge Lg bottom guide Mg intermediate guide Mge leading edge LR lower paper feed path P paper Ug Upper guide UR upper paper feed path β Gap

Claims

1. (a) a plurality of guide members that guide the media fed from the paper feed unit; (b) a paper feed path formed between the guide members for transporting a medium; (c) a medium detection unit disposed in the paper feed path and detecting the presence or absence of a medium; (d) a film member in the paper feed path, the film member being supported by the guide member so that the leading edge thereof is displaceable; (e) separating the leading edge of the film member from the leading edge of the guide member to form a gap having a width for allowing a medium to pass therethrough; (f) the paper feed path is formed between the first and second guide members, and includes a first paper feed path for transporting the medium fed from the first paper feed unit, and a second paper feed path formed between the second and third guide members, and for transporting the medium fed from the second paper feed unit; (g) a first film member supported by the first guide member is disposed in the first paper feed path; (h) a second film member supported by the third guide member is disposed in the second paper feed path; (i) a transport member that transports the medium fed from the first and second paper feed units is disposed downstream of the first and second paper feed paths; (j) a leading edge of the first film member is placed on a first tangent line between the nip portion of the conveying member and a surface of the leading edge of the second guide member facing the first guide member; (k) the leading edge of the second film member is placed on a second tangent line between the nip portion of the conveying member and the surface of the leading edge of the second guide member facing the third guide member; A medium transport device characterized by:

2. (a) the medium detection unit includes a swinging member that is swingably disposed in the first and second paper feed paths and that is rotated as the medium is transported, and a sensor that generates a sensor output as the swinging member rotates; (b) when the swinging member separates from the rear end of the medium fed from the first paper feed unit, the medium is brought into contact with the front edge of the first film member on the first tangent line, (c) A medium transport device as described in claim 1, wherein when the oscillating member moves away from the rear end of the medium fed from the second paper feed section, the medium is abutted against the leading edge of the first film member on the second tangent line.

3. 3. The medium transport device according to claim 2, wherein the swingable member is swung within a groove formed in a central portion in the width direction of the first and second film members.

4. (a) the medium detection unit detects the presence or absence of a medium when the tip of the swinging member is placed on the trajectory; 4. The medium transport device according to claim 2, wherein the leading edge of the first film member is positioned downstream in the medium transport direction from the leading edge of the second film member.

5. An image forming apparatus comprising the medium transport device according to any one of claims 1 to 4.

Images