JP4032669B2 - Image forming apparatus and transfer unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transfer unit incorporated in an image forming apparatus such as a color laser printer, and in particular, can swing around a frame, a transfer roller rotating around a central axis, and a support shaft parallel to the central axis of the transfer roller. The present invention relates to a transfer unit for an image forming apparatus that includes a swing member that is supported by a frame and holds a rotation shaft of a transfer roller.
[0002]
[Prior art]
In the transfer unit, a winding spring is sandwiched between the fixed frame and the swing member. Based on the contraction force of the winding spring, the transfer roller can be pressed against the photosensitive drum during printing. By this pressing operation, an accurate toner image can be transferred from the photosensitive drum to the printing paper or transfer belt sandwiched between the photosensitive drum and the transfer roller.
[0003]
[Problems to be solved by the invention]
When the printer is stopped, it is desirable that the transfer roller be separated from the photosensitive drum. In this separation, the coil spring is stretched against the contraction force. So far, a considerable driving force has been required for the extension of such a spring.
[0004]
For example, in a color laser printer, a color image is drawn in black in addition to the three primary colors cyan, magenta, and yellow. A photosensitive drum and a transfer roller are prepared for each color. During color printing, the corresponding transfer rollers are pressed against all four photosensitive drums. During monochrome printing, the transfer roller is pulled away from the three photosensitive drums corresponding to the three primary colors. The three springs are stretched against the contraction force. Further, when the printer is stopped, the transfer rollers are pulled away from all four photosensitive drums. At this time, the above-described three winding springs must be further stretched. Therefore, when the printer is stopped, a considerably large driving force is required to separate the transfer roller.
[0005]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a transfer unit for an image forming apparatus capable of realizing the pressing and separating of the transfer roller with the smallest possible driving force.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first invention, the frame, the first and second transfer rollers rotating around the central axis extending in parallel with each other, and the support shaft parallel to the central axis of the first transfer roller A first swinging member that is supported by the frame so as to be swingable around, and supported by the frame so as to be swingable about a support shaft parallel to the central axis of the second transfer roller, and a first swinging member that holds the rotation shaft of the first transfer roller. And a second swinging member that holds the rotation shaft of the second transfer roller, a first drive rail that is supported by the frame so as to be relatively displaceable, and transmits a driving force to the first swinging member, and is relatively displaceable. A second drive rail that is supported by the frame and transmits a driving force to the second swing member; One end is connected to the first swing member, the other end is connected to the first drive rail, one end is connected to the second swing member, and the other end is connected to the second drive rail. A second spring member, a first profile surface for moving the first drive rail in contact with a first cam receiving surface provided on the first drive rail, and a second cam receiving surface provided on the second drive rail A cam member comprising: a second profile surface that contacts and moves the second drive rail; A transfer unit for an image forming apparatus is provided.
[0007]
When the first drive rail is displaced on the frame, the driving force is transmitted to the first swing member. The first swing member swings. Thus, the movement of the first transfer roller is realized. On the other hand, when the second drive rail is displaced on the frame, the driving force is transmitted to the second swing member. The second swing member swings. Thus, the movement of the second transfer roller is realized. In such a transfer unit, for example, it is not always necessary to transmit the driving force to the second swing member when the first transfer roller moves. The first drive rail receives a repulsive force from the first swing member, but does not receive a repulsive force from the second swing member at all. Accordingly, the displacement of the first drive rail can be caused with a relatively small driving force.
[0008]
The transfer unit is connected to the first swing member at one end and connected to the first drive rail at the other end, and connected to the second swing member at one end and the second drive rail at the other end. And a second spring member connected to the second spring member.
[0009]
In this transfer unit, the expansion and contraction force of the first spring member acts between the first swing member and the first drive rail. The expansion and contraction force of the second spring member acts between the second swing member and the second drive rail. The swing of each swing member is urged in one direction by the action of these expansion and contraction forces. Based on the urging force applied to each swing member, the first and second transfer rollers can be pressed against the corresponding object. On the other hand, the first and second swing members can be released from the expansion and contraction forces of the first and second spring members based on the displacement of the first and second drive rails. Thus, if each swinging member is released from the expansion and contraction force, the first and second transfer rollers can be separated from the object relatively easily. For such separation, it is not necessary to apply any driving force to each swing member or each drive rail. Since excess driving force is eliminated, the rigidity of each swing member and each drive rail can be weakened. Each member can be reduced in weight and thickness.
[0010]
Moreover, in such a transfer unit, when the first and second transfer rollers are pressed, the first and second spring members can exhibit sufficient stretching force with a minimum displacement from the original shape. The driving force transmitted from the first and second drive rails to each swinging member during pressing can be minimized. Such a decrease in driving force can greatly contribute to miniaturization and power saving of a driving source such as an electric motor.
[0011]
Such a transfer unit can be used by being incorporated in an image forming apparatus such as a laser color printer. At this time, the first transfer roller only needs to face the photosensitive drum in the first print unit. The second transfer roller only needs to face the photosensitive drum in the second print unit. The first and second transfer rollers may be moved between a contact position pressed against the corresponding photosensitive drum and a retracted position separated from the corresponding photosensitive drum.
[0012]
In such an image forming apparatus, the first transfer roller can move between the contact position and the retracted position based on the displacement of the first drive rail. Based on the displacement of the second drive rail, the second transfer roller can move between the contact position and the retracted position. As described above, for example, the driving force is not necessarily transmitted to the second swing member when the first transfer roller is moved. The first drive rail receives a repulsive force from the first swing member, but does not receive a repulsive force from the second swing member at all. Accordingly, the displacement of the first drive rail can be caused with a relatively small driving force.
[0013]
Generally, a color laser printer incorporates four print units, that is, first to fourth print units, in association with cyan toner, magenta toner, yellow toner, and black toner. For example, when a transfer unit is incorporated in such a color laser printer, the transfer unit includes third and fourth transfer rollers that rotate around a central axis that extends parallel to the central axis of the second transfer roller, and a third transfer roller. A third swinging member that is supported by the frame so as to be swingable about a support shaft parallel to the center axis of the transfer roller, and that supports the rotation shaft of the third transfer roller, and a support parallel to the center axis of the fourth transfer roller. A fourth swing member that is supported by the frame so as to be swingable about the axis and that holds the rotation shaft of the fourth transfer roller may be further provided. The third transfer roller only needs to face the photosensitive drum in the third print unit. Similarly, the fourth transfer roller only needs to face the photosensitive drum in the fourth print unit. The second drive rail described above may transmit the driving force to the third and fourth swing members in addition to the second swing member described above. Thus, in relation to the three primary colors, that is, cyan toner, magenta toner and yellow toner, the second to fourth swing members can be operated based on the displacement of the single second drive rail. In addition to the first and second spring members described above, the transfer unit includes a third spring member connected at one end to the third swing member and connected to the second drive rail at the other end, and a fourth at the one end. A fourth spring member connected to the swing member and connected to the second drive rail at the other end may be further incorporated.
[0014]
In such a transfer unit, a single cam member may be further incorporated to realize the displacement of the first and second drive rails. At this time, a first cam receiving surface may be formed on the first drive rail, and a second cam receiving surface may be formed on the second driving rail. The cam member may be defined with a first profile surface that receives the first cam receiving surface and a second profile surface that receives the second cam receiving surface. According to such a function of the cam member, the displacement of the first and second drive rails can be individually controlled for each of the first and second profile surfaces.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0020]
FIG. 1 schematically shows a color laser printer 11 according to a specific example of an image forming apparatus. A housing 12 of the color laser printer 11 is formed in a substantially rectangular parallelepiped shape, and is connected to the housing main body 12a that divides a housing space inside, and opens and closes an opening on one side surface of the housing main body 12a. And an opening / closing cover 12b. The housing main body 12a is installed on the paper feed cassette 13, for example. The paper feed cassette 13 stores print media such as a plurality of print sheets. A paper discharge receiver 14 is formed on the upper surface of the housing body 12a. The printed paper after printing is discharged from the paper discharge port 15 toward the paper discharge receptacle 14. Such a color laser printer 11 can be used by being connected to a computer terminal (not shown), for example.
[0021]
As shown in FIG. 2, four print units 16 are incorporated in the accommodating space in the housing body 12a. Each print unit 16 includes a developing drum, that is, a photosensitive drum 17 that rotates about a central axis. The four photosensitive drums 17 can rotate while being synchronized around the central axes arranged in parallel with each other in one plane. In each print unit 16, cyan toner C, magenta toner M, yellow toner Y, and black toner K are individually stored.
[0022]
The optical unit 18 is fixed above the four print units 16 in the housing space in the housing body 12a. As is well known, the optical unit 18 individually irradiates a laser beam 19 toward the cylindrical surface of each photosensitive drum 17. The laser beam 19 draws an electrostatic latent image on the cylindrical surface of each photosensitive drum 17. When the cylindrical surface is thus exposed based on the laser beam 19, toner C, M, Y, and K are supplied to each photosensitive drum 17. Each color toner C, M, Y, and K visualizes an electrostatic latent image on the cylindrical surface of each photosensitive drum 17.
[0023]
Further, a transfer unit 21 is disposed below the four print units 16 in the housing space in the housing body 12a. The transfer unit 21 is rotated about a central axis parallel to the central axis of each of the photosensitive drums 17 and rotated about a central axis parallel to the central axis of the front rotational rollers 22a and 22b. Side rotation roller 23. An intermediate transfer belt 24 that circulates between at least two rotation rollers 22a and 23 is wound around the front and rear rotation rollers 22a, 22b, and 23. The intermediate transfer belt 24 defines one horizontal plane from at least one front rotation roller 22 b toward the rear rotation roller 23. This one horizontal plane is defined at a position separated from the cylindrical surface of each photosensitive drum 17.
[0024]
Between the front and rear rotating rollers 22b and 23, four primary transfer rollers 25a to 25d facing each photosensitive drum 17 are arranged. Each of the primary transfer rollers 25 a to 25 d can rotate around a central axis parallel to the central axis of the photosensitive drum 17. As will be described later, each primary transfer roller 25 a to 25 d is completely separated from the contact position where the intermediate transfer belt 24 is sandwiched between the primary transfer rollers 25 a to 25 d and the cylindrical surface of the corresponding photosensitive drum 17. It can be displaced between the retracted position. As apparent from FIG. 2, when the intermediate transfer belt 24 is pressed against the cylindrical surface of each photosensitive drum 17 by the action of the primary transfer rollers 25 a to 25 d, each color toner C drawn on the cylindrical surface of each photosensitive drum 17. , M, Y, K visible images can be transferred to the intermediate transfer belt 24. Based on the toners C, M, Y, and K, for example, a multicolored visible image is drawn on the surface of the intermediate transfer belt 24 that successively contacts the four photosensitive drums 17. The tension of the intermediate transfer belt 24 can be adjusted by the action of the tension roller 26, for example.
[0025]
The transfer unit 21 further includes a secondary transfer roller 27 that faces the front rotating roller 22a. The secondary transfer roller 27 sandwiches the printing paper with the front rotation roller 22a. When the front rotation roller 22a and the secondary transfer roller 27 rotate in synchronization, the multicolor visible image on the intermediate transfer belt 24 is transferred to the printing paper passing between the front rotation roller 22a and the secondary transfer roller 27. The The secondary transfer roller 27 may be rotated around a central axis parallel to the central axis of the front rotation roller 22a.
[0026]
A drive unit 28 is disposed adjacent to the four print units 16 and the transfer unit 21 in the accommodating space in the housing body 12a. As will be described later, the driving unit 28 transmits a predetermined driving force to the photosensitive drum 17 incorporated in the four print units 16 and the rear rotation roller 23 of the transfer unit 21. Based on this driving force, each photosensitive drum 17 and the rear rotating roller 23 can rotate.
[0027]
A fixing unit 29 is further fixed above the front rotating roller 22a and the secondary transfer roller 27 in the housing space in the housing body 12a. The fixing unit 29 includes a pair of heat rollers 31, 31 that rotate about a central axis parallel to the central axis of the front rotation roller 22 a and the secondary transfer roller 27. The heat rollers 31, 31 sandwich the print paper fed from the front rotation roller 22 a and the secondary transfer roller 27. The heat of the heat rollers 31, 31 melts the toners C, M, Y, K on the print paper. As a result, the toners C, M, Y, and K soak into the print paper. In this way, visible images of toners C, M, Y, and K can be fixed on the surface of the printing paper. The print paper sent out from the fixing unit 29 is guided toward the paper discharge port 15.
[0028]
A paper feed mechanism 32 is disposed below the front rotating roller 22 a and the secondary transfer roller 27. The paper feed mechanism 32 is a feed roller 33 that feeds print paper from the paper feed cassette 13 one by one, and a feed that feeds the print paper delivered from the pickup roller 33 between the front rotation roller 22 a and the secondary transfer roller 27. Rollers 34, 34. The pickup roller 33 and the feed roller 34 may be rotated around a central axis parallel to the central axes of the front rotation roller 22 a and the secondary transfer roller 27.
[0029]
Here, the structure of the transfer unit 21 according to the present invention will be described in detail. As shown in FIG. 3, the transfer unit 21 includes a frame 35 fixed in the housing body 12a. The frame 35 includes a pair of side frame members 36a, 36b that rotatably support at least the rotation shafts of the front and rear rotation rollers 22a, 22b, 23. The intermediate transfer belt 24 is wound around the front and rear rotating rollers 22a, 22b, and 23 in a space between the side frame members 36a and 36b.
[0030]
A first swinging member 37 that holds the rotation shaft of the primary transfer roller related to the black toner K, that is, the first transfer roller 25a, is attached to each side frame member 36a, 36b. These first swing members 37 can swing around a support shaft 38 extending along a straight line parallel to the central axis of the first transfer roller 25a. These first swing members 37 are formed with first and second arms 37a and 37b extending from the support shaft 38 in different directions. A first transfer roller 25a is rotatably supported at the tip of the first arm. For example, the second arm 37b may intersect the first arm 37a on the support shaft 38 at an angle of about 90 °. Through the swinging of the swinging member 37, the first transfer roller 25a can move between the contact position and the retracted position as described above.
[0031]
Similarly, the side frame members 36a and 36b hold the rotation shafts of the primary transfer rollers related to the yellow toner Y, magenta toner M and cyan toner C, that is, the second to fourth transfer rollers 25b, 25c and 25d. Second to fourth swing members 39, 40, 41 are attached. The second swing member 39 can swing around a support shaft 42 extending along a straight line parallel to the central axis of the second transfer roller 25b. The third swing member 40 can swing around a support shaft 43 extending along a straight line parallel to the central axis of the third transfer roller 25c. The fourth swing member 41 can swing around a support shaft 44 extending along a straight line parallel to the central axis of the fourth transfer roller 25d. These second to fourth swing members 39, 40, 41 have first and second arms 39 a extending in different directions from the support shafts 42 to 44, similarly to the first swing member 37 described above. 39b, 40a, 40b, 41a, 41b are formed. Through the swinging of these swinging members 39, 40, 41, the second to fourth transfer rollers 25b to 25d can move between the contact position and the retracted position as described above.
[0032]
As shown in FIG. 4, the first and second drive rails 45 and 46 are supported on the side frame member 36 a so as to be relatively displaceable with respect to the frame 35. In this support, elastic hook pieces 47 and 48 are formed on the first and second drive rails 45 and 46. Each elastic hook piece 47, 48 is detachably received in a slot 49, 50 formed in the side frame member 36a. As shown in FIG. 5, flanges 47 a and 48 a are formed at the tips of the elastic hook pieces 47 and 48. When the elastic hook pieces 47 and 48 are fitted into the corresponding slots 49 and 50, the flanges 47 a and 48 a of the elastic hook pieces 47 and 48 engage with the edges of the slots 49 and 50. As is apparent from FIG. 4, each slot 49, 50 extends parallel to one horizontal plane including the axis of the support shafts 38, 42-44. Therefore, the first and second drive rails 45 and 46 can reciprocate on the side frame member 36a in parallel with one plane including the central axes of the four support shafts 38 and 42 to 44.
[0033]
As shown in FIG. 4, a first spring member, that is, a first winding spring 52 is disposed between the first swing member 37 and the first drive rail 45. One end of the first winding spring 52 is connected to the tip of the second arm 37 b of the first swing member 37. The other end of the first winding spring 52 is connected to the mounting protrusion 45 a of the first drive rail 45. The first winding spring 52 exerts a contracting force that brings the second arm 37 b of the first swing member 37 and the mounting protrusion 45 a of the first drive rail 45 close to each other. When the first drive rail 45 is positioned at the foremost position closest to the front rotation rollers 22a and 22b, the first winding spring 52 contracts to its minimum length. Accordingly, the contraction force of the first winding spring 52 does not act between the first swing member 37 and the first drive rail 45. On the other hand, when the first drive rail 45 moves backward toward the rear roller 23, the contraction force of the first winding spring 52 acts on the second arm 37 b of the first swing member 37. Accordingly, the second arm 37b of the first swing member 37 moves backward following the backward movement of the first drive rail. The first swing member 37 swings.
[0034]
Similarly, second to fourth spring members, that is, second to fourth winding springs 53, 54, 55 are arranged between the second to fourth swing members 39, 40, 41 and the second drive rail 46. The One ends of the second to fourth winding springs 53 to 55 are connected to the tips of the second arms 39b, 40b, and 41b of the second to fourth swing members 39, 40, and 41, respectively. The other ends of the second to fourth winding springs 53 to 55 are connected to the mounting protrusions 46 a, 46 b and 46 c of the second drive rail 46. The second to fourth winding springs 53 to 55 are attached to the second arms 39b, 40b, 41b of the second to fourth swing members 39, 40, 41 and the mounting protrusions 46a, 46b, 46c of the second drive rail 46, respectively. Demonstrate the shrinkage force that brings them closer together. When the second drive rail 46 is positioned at the foremost position closest to the front rotation rollers 22a and 22b, the second to fourth springs 53 to 55 contract to their minimum lengths. Therefore, the contraction force of the second to fourth winding springs 53 to 55 does not act between the second to fourth swing members 39, 40, 41 and the second drive rail 46. On the other hand, when the second drive rail 46 moves backward toward the rear roller 23, the second arms 39b, 40b, 41b of the second to fourth swing members 39, 40, 41 have second to second The contraction force of the fourth winding springs 53 to 55 acts. Accordingly, the second arms 39 b, 40 b, 41 c of the second to fourth swing members 39, 40, 41 move backward following the backward movement of the second drive rail 46. The second to fourth swing members 39, 40, 41 swing.
[0035]
A cam member 56 that contacts the first and second drive rails 45 and 46 is attached to the side frame member 36a. The cam member 56 can rotate around a support shaft 57 extending in parallel with the axes of the four support shafts 38, 42 to 44. As is apparent from FIG. 6, the cam member 56 includes a first profile surface 56a that continues to contact the first drive rail 45 during one rotation of the cam member 56, and similarly, during one rotation of the cam member 56. A second profile surface 56b that continues to contact the second drive rail 46 is formed. The first and second profile surfaces 56 a and 56 b may be formed adjacent to each other in the direction defined by the axis of the support shaft 57. The first and second profile surfaces 56 a and 56 b are in contact with the cam receiving surfaces 58 and 59 of the first and second drive rails 45 and 46 between the rear rotating roller 23 and the support shaft 57. In establishing such contact between the second profile surface 56 b and the second drive rail 46, the cam receiving surface 59 of the second drive rail 46 straddles the support shaft 57 of the cam member 56 and is opposed toward the rear rotation roller 23. It is prescribed | regulated at the front-end | tip of the contact arm 61 extended in the side.
[0036]
As shown in FIG. 7, the cam member 56 has a first virtual cylindrical surface 62 drawn from the axis of the support shaft 57 with the first radius D <b> 1, and similarly, from the axis of the support shaft 57 with the second radius D <b> 2. A second virtual cylindrical surface 63 to be drawn can be defined. The difference between the first and second radii D1 and D2 corresponds to the amount of movement of the first and second drive rails 45 and 46 in the front-rear direction.
[0037]
The first profile surface 56a includes, for example, a flat surface 64 that spreads from a central angle position of 0 degrees to a central angle position of 80 degrees, and an actual cylindrical surface 65 that continues to the flat surface 64. The flat surface 64 extends along one plane in contact with the first virtual cylindrical surface 62 along the generatrix of the first virtual cylindrical surface 62 at the central angle of 0 degree. The actual cylindrical surface 65 extends along the second virtual cylindrical surface 63, for example, between the central angle position of 80 degrees and at least the central angle position of 190 degrees. For example, the flat surface 64 and the actual cylindrical surface 65 may be connected to each other along a smooth curved surface 66 at a central angle of 80 degrees. A curved surface 67 drawn with a radius that gradually decreases from the second radius D2 to the first radius D1 may be formed between the center angle position of 190 degrees and the center angle position of 360 degrees. The two curved surfaces 66 and 67 maintain a generatrix parallel to the axis of the support shaft 57.
[0038]
The second profile surface 56b includes a first real cylindrical surface 71 that extends along the first virtual cylindrical surface 62 between the central angle 0 degree position and the central angle 90 degree position. The first actual cylindrical surface 71 is continuous with a first flat surface 72 extending from a central angle position of 90 degrees to a central angle position of 170 degrees. The first flat surface 72 extends along one plane in contact with the first virtual cylindrical surface 62 along the generatrix of the first virtual cylindrical surface 62 at a central angle of 90 degrees. As described above, this one plane is orthogonal to one plane including the flat surface 64 of the first profile surface 56a.
[0039]
The first flat surface 72 is continuous with, for example, a second real cylindrical surface 73 extending along the second virtual cylindrical surface 63 between a central angle position of 170 degrees and a central angle position of 190 degrees. The second actual cylindrical surface 73 and the first flat surface 72 may be connected to each other along, for example, a smooth curved surface 74 at a central angle of 170 degrees. A curved surface 75 drawn with a radius that gradually decreases from the second radius D2 to the first radius D1 may be formed between the central angle position of 190 degrees and the central angle position of 360 degrees. The two curved surfaces 74 and 75 maintain a generatrix parallel to the axis of the support shaft 57. However, it is desirable that the second flat surface 76 be formed between the curved surface 75 and the first actual cylindrical surface 71 at least in the range from the central angle position of 315 degrees to the central angle position of 360 degrees. As described above, the second flat surface 76 extends along one plane including the flat surface 64 of the first profile surface 56a.
[0040]
Similar to the side frame member 36a, the first and second drive rails 45 and 46, the first to fourth winding springs 52 to 55, and the cam member 56 may be attached to the side frame member 36b. At this time, the pair of cam members 56 of the side frame members 36a and 36b may share the support shaft 57. That is, for example, if a rotational driving force is applied to one cam member 56, the two cam members 56, 56 can rotate around the support shaft 57 while being synchronized.
[0041]
As is apparent from FIG. 8, two drive sources, that is, first and second electric motors 81 and 82 are incorporated in the drive unit 28. A first gear mechanism 86 that transmits the rotation of the first electric motor 81 at a predetermined gear ratio is connected to the drive shaft of the first electric motor 81 along the three transmission paths 83, 84, and 85. The first gear mechanism 86 includes first, second, and third output gears 87, 88, 89 connected to the print unit 16 related to cyan toner C, magenta toner M, and yellow toner Y, respectively. The first, second, and third output gears 87 to 89 may be coupled to the rotation shaft of the photosensitive drum 17 related to the toners C, M, and Y. When the drive shaft of the first electric motor 81 rotates, the photosensitive drum 17 of the print unit 16 related to the cyan toner C, magenta toner M, and yellow toner Y can rotate in synchronization.
[0042]
Similarly, the drive shaft of the second electric motor 82 rotates the second electric motor 82 at a predetermined gear ratio along the three transmission paths, that is, the first, second, and third transmission paths 91, 92, 93. Is connected to the second gear mechanism 94. The second gear mechanism 94 is incorporated in the first transmission path 91 and is connected to the print unit 16 related to the black toner K. The second gear mechanism 94 is incorporated in the second transmission path 92 and the transfer unit 21. A fifth output gear 96 connected to the rear rotation roller 23 and a sixth output gear 97 incorporated in the third transmission path 93 and connected to the cam member 56 of the transfer unit 21 are provided. The fourth output gear 95 may be coupled to the rotating shaft of the photosensitive drum 17 related to the black toner K. When the drive shafts of the first and second electric motors 81 and 82 rotate at the same speed, the photosensitive drums 17 of all four print units 16 can rotate in synchronization.
[0043]
The second gear mechanism 94 includes a distribution gear 98 that meshes with the drive shaft of the second electric motor 82 and distributes the rotation of the second electric motor 82 to the second and third transmission paths 92 and 93. The distribution gear 98 includes a first intermediate gear 99 that transmits the rotation of the second electric motor 82 at a predetermined gear ratio toward the fifth output gear 92, and a predetermined gear toward the sixth output gear 97. The second intermediate gear 101 that transmits the rotation of the second electric motor 82 by the ratio is individually meshed. The fifth output gear 96 may be coupled to the rotating shaft of the rear rotating roller 23. Thus, the rotation of the second electric motor 82 is transmitted to the rear rotation roller 23 at a predetermined gear ratio. When the drive shaft of the second electric motor 82 rotates, the rear rotation roller 23 can rotate in synchronization with at least the photosensitive drum 17 related to the black toner K.
[0044]
Further, in the second gear mechanism 94, the clutch 102 is incorporated in the third transmission path 93 from the second intermediate gear 101 to the sixth output gear 97. The clutch 102 includes an input side gear 103 that receives the rotation transmitted from the second intermediate gear 101, and an output side gear 105 that meshes with the sixth output gear 93 via the one transmission gear 104. The clutch 102 can be switched between a connected state in which the input side gear 103 and the output side gear 105 are rotated at the same rotational speed and a disconnected state in which the input side gear 103 is idled to prevent the output side gear 105 from rotating. it can. When the third transmission path 93 is established with the clutch 102 connected, the rotation of the second electric motor 82 is transmitted to the sixth output gear 93 at a predetermined gear ratio. As a result, the cam member 56 rotates. In the disconnected state of the clutch 102, the third transmission path 93 is disconnected between the input side gear 103 and the output side gear 105. In this case, the rotation of the cam member 56 is prevented regardless of the rotation of the second electric motor 82. The sixth output gear 93 may be coupled to the support shaft 57 of the cam member 56, for example.
[0045]
When the color laser printer 11 is turned off or on standby, the cam member 56 is maintained in the reference posture as shown in FIG. The cam receiving surface 58 of the first drive rail 45 is received by the flat surface 64 of the first profile surface 56a. At the same time, the cam receiving surface 59 of the second drive rail 46 is received by the second flat surface 76 of the second profile surface 56b. The first and second drive rails 45 and 46 are positioned at the foremost position, that is, the home position.
[0046]
At this time, the contraction force of the first to fourth winding springs 52 to 55 does not act on the first to fourth swing members 37 and 39 to 41. No pressing force is generated by the first to fourth transfer rollers 25a to 25d. Therefore, for example, the first to fourth transfer rollers 25 a to 25 d are pushed back to the retracted position based on the tension of the intermediate transfer belt 24. The first to fourth transfer rollers 25 a to 25 d are separated from the corresponding photosensitive drums 17. The intermediate transfer belt 24 defines one horizontal plane at a position away from all the photosensitive drums 17. The first to fourth winding springs 52 to 55 can be maintained at a minimum length, and therefore no driving force needs to be applied to maintain the foremost position of the first and second drive rails 45, 46. . Since the excessive driving force is eliminated, the rigidity of the swing members 37 and 39 to 41 and the first and second drive rails 45 and 46 can be weakened. Each member can be reduced in weight and thickness.
[0047]
Assume that a color print command is supplied to the color laser printer 11. The connection state of the clutch 102 is established. The first and second electric motors 81 and 82 are started. The cam member 56 rotates. According to the rotation, the contact position between the cam receiving surface 58 of the first drive rail 45 and the first profile surface 56a moves. The curved surface 66 of the first profile surface 56a applies a pressing force to the cam receiving surface 58. The first drive rail 45 moves backward from the foremost position. When contact is established between the cam receiving surface 58 and the actual cylindrical surface 65, the first drive rail 45 is positioned at the last retracted position, as shown in FIG.
[0048]
As the first drive rail 45 moves backward toward the last retracted position, the contraction force of the first winding spring 52 sufficiently acts between the first swing member 37 and the first drive rail 45. Therefore, the second arm 37 b of the first swing member 37 is attracted to the mounting protrusion 45 a of the first drive rail 45. Following the retreat of the first drive rail 45, the first swing member 37 swings. The first swinging member 37 lifts the first transfer roller 25a toward the contact position against the tension of the intermediate transfer belt 24. When the first transfer roller 25a reaches the contact position according to the swing, the first transfer roller 25a is pressed against the photosensitive drum 17 related to the black toner K. Thus, a nip of the intermediate transfer belt 24 is established between the first transfer roller 25a and the photosensitive drum 17. When the rotation angle of the cam member 56 reaches 190 degrees, the rotation of the cam member 56 is stopped.
[0049]
During such rotation of the cam member 56, the contact position between the cam receiving surface 59 of the second drive rail 46 and the second profile surface 56b is similarly moved. Such a contact position extends from the second flat surface 76 of the second profile surface 56 a to the curved surface 74 through the first actual cylindrical surface 71 and the first flat surface 72. As the cam member 56 rotates, the curved surface 74 applies a pressing force to the cam receiving surface 59. The second drive rail 46 moves backward from the foremost position. When contact is established between the cam receiving surface 59 and the second actual cylindrical surface 73, the second drive rail 46 is positioned at the last retracted position, as is apparent from FIG.
[0050]
As the second drive rail 46 retracts toward the last retracted position, the contraction force of the second to fourth winding springs 53 to 55 is between the second to fourth swing members 39 to 41 and the second drive rail 46. Works well. Therefore, the second arms 39b, 40b, 41b of the second to fourth swing members 39-41 are attracted to the corresponding mounting protrusions 46a, 46b, 46c by the second drive rail 45. Following the retreat of the second drive rail 46, the second to fourth swing members 39 to 41 swing. The second to fourth swinging members 39 to 41 lift the second to fourth transfer rollers 25b, 25c, and 25d toward the contact position against the tension of the intermediate transfer belt 24. When the second to fourth transfer rollers 25b, 25c, and 25d reach the contact position according to the swing, the second to fourth transfer rollers 25b, 25c, and 25d correspond to the corresponding yellow toner Y, magenta toner M, and cyan toner. C is pressed against the photosensitive drum 17 related to C. Thus, the nip of the intermediate transfer belt 24 is established between the second to fourth transfer rollers 25b, 25c, 25d and the photosensitive drum 17.
[0051]
During the operation as described above, the first to fourth winding springs 52 to 55 may generate a minimum contraction force necessary for the nip of the intermediate transfer belt 24. Therefore, the driving force applied to the first and second drive rails 45 and 46 can be minimized. Therefore, a dedicated drive motor that exhibits a large driving force when moving the first and second drive rails 45 and 46 is not required. The driving force distributed from the second driving motor 82 can cause the movement of the first and second driving rails 45 and 46 to be sufficiently performed.
[0052]
Next, assume that a monochrome print command is supplied to the color laser printer 11. The connection state of the clutch 102 is established. The second electric motor 82 starts. The cam member 56 rotates. According to the rotation, the contact position between the cam receiving surface 58 of the first drive rail 45 and the first profile surface 56a moves. As described above, when contact is established between the cam receiving surface 58 and the actual cylindrical surface 65, the first drive rail 45 is positioned at the last retracted position, as shown in FIG. The first transfer roller 25 a is pressed against the photosensitive drum 17 related to the black toner K. Thus, a nip of the intermediate transfer belt 24 is established between the first transfer roller 25a and the photosensitive drum 17.
[0053]
Here, when the rotation angle of the cam member 56 reaches 90 degrees, the rotation of the cam member 56 is stopped. During such rotation of the cam member 56, the contact position between the cam receiving surface 59 of the second drive rail 46 and the second profile surface 56b is similarly moved. However, the contact position is maintained on the first actual cylindrical surface 71 of the second profile surface 56a. Therefore, as is apparent from FIG. 11, the second drive rail 46 is held at the foremost position. The contraction force of the second to fourth winding springs 53 to 55 does not act on the second to fourth swing members 39 to 41. As described above, the second to fourth transfer rollers 25b, 25c, and 25d are pushed back to the retracted position. The second to fourth transfer rollers 25b, 25c, and 25d are separated from the corresponding photosensitive drums 17.
[0054]
Thus, the second to fourth winding springs 53 to 55 are maintained at the minimum length. The cam member 56 requires only a driving force that causes the first driving rail 45 to retract against the contraction force of the first winding spring 52. Therefore, the driving force required for driving the cam member 56 can be minimized. The burden on the second drive motor 82 can be further reduced.
[0055]
In the color laser printer 11 as described above, the foremost positions of the first and second drive rails 45 and 46 may be detected, for example, when the power is turned on. In such detection, the first and second electric motors 81 and 82 rotate after the connection state of the clutch 102 is established. The positions of the first and second drive rails 45 and 46 may be continuously monitored during at least one rotation of the cam member 56. When the positions of the first and second drive rails 45 and 46 are monitored in this manner, the posture of the cam member 56, that is, the rotation amount of the support shaft 57 can be specified, as is apparent from FIG. The rotational position of the second drive motor 82 that establishes the cam member 56 reference posture can be specified.
[0056]
In addition, in the transfer unit 21 as described above, as shown in FIG. 13, for example, a fall prevention mechanism 106 may be incorporated between the first drive rail 45 and the cam member 56. The fall prevention mechanism 106 may include a guide rail 107 that is integrally formed around the cam member 56 and a guide groove 108 that is formed in the first drive rail 45 and receives the guide rail 107. As long as the cam receiving surface 58 of the first drive rail 45 contacts the first profile surface 56 a of the cam member 56, the guide groove 108 continues to receive the guide rail 107 during one rotation of the cam member 56. The guide rail 107 only has to rise from the first profile surface 56a along the boundary between the first and second profile surfaces 56a and 56b. According to such a fall prevention mechanism 106, for example, when the first drive rail 45 tries to move away from the side frame member 36a, the guide rail 107 receives the inner wall of the guide groove 108. The guide rail 107 can restrict the movement of the first drive rail 45. Therefore, the overturn of the first drive rail 45 can be reliably prevented. As is apparent from FIG. 14, the guide rail 107 only has to rise from the first profile surface 56a at a uniform height.
[0057]
(Supplementary Note 1) A frame, first and second transfer rollers rotating around a central axis extending in parallel to each other, and a frame supported by the frame so as to be swingable around a support shaft parallel to the central axis of the first transfer roller. A first swinging member that holds the rotation shaft of the first transfer roller, and a frame that is swingably supported about a support shaft parallel to the central axis of the second transfer roller. A second swing member to be held, a first drive rail that is supported by the frame so as to be relatively displaceable, and a driving force that is transmitted to the first swing member, and a second swing that is supported by the frame so as to be relatively displaceable. A transfer unit for an image forming apparatus, comprising: a second drive rail that transmits a driving force to the member.
[0058]
(Supplementary Note 2) In the transfer unit for an image forming apparatus according to Supplementary Note 1, one end is connected to the first swing member and the other end is connected to the first drive rail, and the one end is the first spring member. A transfer unit for an image forming apparatus, further comprising a second spring member connected to the second swing member and connected to the second drive rail at the other end.
[0059]
(Supplementary Note 3) In the transfer unit for an image forming apparatus according to Supplementary Note 1, third and fourth transfer rollers rotating around a central axis extending in parallel with a central axis of the second transfer roller, and a center of the third transfer roller A third swinging member that is supported by the frame so as to be swingable about a support shaft parallel to the shaft, and that holds the rotation shaft of the third transfer roller, and swings about a support shaft parallel to the central axis of the fourth transfer roller. And a fourth swinging member supported by the frame so as to hold the rotation shaft of the fourth transfer roller. The second drive rail includes third and fourth in addition to the second swinging member. A transfer unit for an image forming apparatus, wherein a driving force is transmitted to a swing member.
[0060]
(Supplementary Note 4) In the transfer unit for an image forming apparatus according to Supplementary Note 3, one end is connected to the first swing member, and the other end is connected to the first drive rail. A second spring member connected to the second swing member and connected to the second drive rail at the other end, connected to the third swing member at one end, and connected to the second drive rail at the other end. A transfer unit for an image forming apparatus, further comprising: a third spring member connected to the fourth swing member at one end, and a fourth spring member connected to the second drive rail at the other end. .
[0061]
(Supplementary Note 5) In the transfer unit for an image forming apparatus according to any one of Supplementary Notes 1 to 4, a first cam receiving surface formed on the first drive rail and a second cam formed on the second drive rail. A transfer unit for an image forming apparatus, further comprising: a receiving surface; and a cam member that individually receives the first and second cam receiving surfaces by the first and second profile surfaces.
[0062]
(Appendix 6) A housing, a frame fixed in the housing, first and second print units incorporated in the housing, and a first transfer that rotates around the central axis and faces the photosensitive drum in the first print unit A roller, a first swinging member supported by the frame so as to be swingable about a support shaft parallel to the central axis of the first transfer roller, and holding the rotation shaft of the first transfer roller; and the center of the first transfer roller A second transfer roller that rotates about a central axis parallel to the shaft and faces the photosensitive drum in the second print unit, and is supported by the frame so as to be swingable about a support shaft parallel to the central axis of the second transfer roller. A second swing member that holds the rotation shaft of the second transfer roller, a first drive rail that is supported by the frame so as to be relatively displaceable, and that transmits a driving force to the first swing member, and is relatively displaceable. And a second drive rail that is supported by the frame and transmits a driving force to the second swing member.
[0063]
(Supplementary note 7) In the image forming apparatus according to supplementary note 6, one end is connected to the first swing member and the other end is connected to the first drive rail, and the other end is connected to the second swing member. An image forming apparatus, further comprising: a second spring member connected to the moving member and connected to the second drive rail at the other end.
[0064]
(Supplementary note 8) In the image forming apparatus according to supplementary note 6 or 7, the first cam receiving surface formed on the first drive rail, the second cam receiving surface formed on the second drive rail, and the first And an cam member that individually receives the first and second cam receiving surfaces on the second profile surface.
[0065]
(Supplementary Note 9) Frame, transfer roller that rotates about the central axis, and a swinging member that is supported by the frame so as to be swingable about a support shaft that is parallel to the central axis of the transfer roller, and holds the rotational axis of the transfer roller And a drive rail supported by the frame so as to be relatively displaceable, and a spring member connected to the swing member at one end and connected to the drive rail at the other end.
[0066]
(Supplementary Note 10) A housing, a frame fixed in the housing, a print unit incorporated in the housing, a transfer roller that rotates around the central axis and faces the photosensitive drum in the print unit, and a central axis of the transfer roller A swinging member that is supported by the frame so as to be swingable about a parallel support shaft and that holds the rotation shaft of the transfer roller, a drive rail that is supported by the frame so as to be relatively displaceable, and a swinging member that is connected at one end. An image forming apparatus comprising: a spring member coupled to the drive rail at the other end.
[0067]
【The invention's effect】
As described above, according to the present invention, there is provided a transfer unit for an image forming apparatus capable of realizing the pressing and separating of the transfer roller with the smallest possible driving force.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating an appearance of a color laser printer according to a specific example of an image forming apparatus.
FIG. 2 is a vertical sectional view schematically showing an internal structure of a color laser printer.
FIG. 3 is a perspective view schematically showing a structure of a transfer unit.
FIG. 4 is an outward side view schematically showing a structure of a side frame member.
5 is an enlarged partial sectional view taken along line 5-5 of FIG.
FIG. 6 is a partial plan view of a side frame member observed from above.
FIG. 7 is a side view of a cam member schematically showing first and second profile surfaces.
FIG. 8 is a side view schematically showing the structure of a drive unit.
FIG. 9 is a side view schematically showing the relationship between the first and second drive rails and the swing members during standby of the color laser printer.
FIG. 10 is a side view schematically showing the relationship between the first and second drive rails and the swinging members when color printing is performed.
FIG. 11 is a side view schematically showing the relationship between the first and second drive rails and the swinging members when performing monochrome printing.
FIG. 12 is a graph showing the relationship between the displacement amount of the first and second drive rails and the rotation amount of the cam member.
FIG. 13 is a partial plan view of a side frame member schematically showing a configuration of a fall prevention mechanism.
FIG. 14 is a side view of the cam member schematically showing the shape of the guide rail.
[Explanation of symbols]
11 Color laser printer as electrophotographic apparatus, 12 housing, 16 first and second print unit, 17 photosensitive drum, 21 transfer unit, 25a to 25d first to fourth transfer roller, 35 frame, 37 first swing member, 38 Support shaft of the first swing member, 39 Second swing member, 40 Third swing member, 41 Fourth swing member, 42 Support shaft of the second swing member, 43 Support shaft of the third swing member , 44 Support shaft of the fourth swing member, 45 First drive rail, 46 Second drive rail, 52-55 First to fourth winding springs as first to fourth spring members, 58 First cam receiving surface, 59 Second cam receiving surface, 56 cam member, 56a first profile surface, 56b second profile surface.

Claims (2)

Frame,
First and second transfer rollers rotating around a central axis extending in parallel to each other;
A first swinging member supported by the frame so as to be swingable about a support shaft parallel to the central axis of the first transfer roller, and holding the rotation shaft of the first transfer roller;
A second swinging member that is supported by the frame so as to be swingable about a support shaft parallel to the central axis of the second transfer roller, and holds the rotation shaft of the second transfer roller;
A first drive rail supported by the frame so as to be relatively displaceable and transmitting a driving force to the first swing member;
A second drive rail supported by the frame so as to be relatively displaceable and transmitting a driving force to the second swing member;
A first spring member having one end connected to the first swing member and the other end connected to the first drive rail;
A second spring member having one end connected to the second swing member and the other end connected to the second drive rail;
A first profile surface for moving the first drive rail in contact with the first cam receiving surface provided on the first drive rail, and a second drive in contact with the second cam receiving surface provided on the second drive rail A cam member comprising: a second profile surface for moving the rail;
A transfer unit for an image forming apparatus. A housing;
A frame fixed in the housing;
First and second print units incorporated in the housing;
A first transfer roller that rotates about a central axis and faces a photosensitive drum in the first print unit;
A first swinging member supported by the frame so as to be swingable about a support shaft parallel to the central axis of the first transfer roller, and holding the rotation shaft of the first transfer roller;
A second transfer roller that rotates about a central axis parallel to the central axis of the first transfer roller and faces the photosensitive drum in the second print unit;
A second swinging member that is supported by the frame so as to be swingable about a support shaft parallel to the central axis of the second transfer roller, and holds the rotation shaft of the second transfer roller;
A first drive rail supported by the frame so as to be relatively displaceable and transmitting a driving force to the first swing member;
A second drive rail supported by the frame so as to be relatively displaceable and transmitting a driving force to the second swing member;
A first spring member having one end connected to the first swing member and the other end connected to the first drive rail;
A second spring member having one end connected to the second swing member and the other end connected to the second drive rail;
A first profile surface for moving the first drive rail in contact with the first cam receiving surface provided on the first drive rail, and a second drive in contact with the second cam receiving surface provided on the second drive rail A cam member comprising: a second profile surface for moving the rail;
An image forming apparatus comprising:

Images