JP5887781B2 - Driving device and image forming apparatus - Google Patents

Description

  The present invention relates to a drive device and an image forming apparatus.

  For example, it is known that wrinkles occur when an image is formed on a recording medium in which a plurality of parts such as envelopes are connected and overlapped.

  Patent Document 1 proposes that the pressure applied in a fixing device that heats and pressurizes a recording medium holding an unfixed toner image to fix the toner image on the recording medium is weakened in the envelope mode as compared to plain paper. Has been.

  Patent Document 2 proposes that the recording medium is transported at a transport speed faster than the transport speed in the fixing device by the transport roller immediately after the fixing device.

  Further, Patent Document 3 proposes to suppress the generation of wrinkles by devising the material of the fixing device and the length in the recording medium passing direction of the portion in contact with the recording medium front and back surfaces.

JP 2004-279702 A JP 2010-145620 A JP 2010-262137 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a driving device and an image forming apparatus that suppress the occurrence of image rubbing that becomes noticeable in an envelope or the like.

Claim 1
The recording medium conveyance path is sandwiched downstream of the recording medium in the conveyance direction from the fixing device that fixes the toner image on the recording medium by heating and pressurizing the recording medium on which the toner image is formed and conveyed. First and second rotating shafts arranged parallel to each other and driven to rotate;
The first and second rotation axis, the rotation axis extends, respectively it in a position to avoid overlapping each other in the direction fixed by the fixing unit was in first and second feeding the recording medium to further downstream has passed A driving roll;
Of the first and second drive rolls, the peripheral speed of one drive roll in contact with the first surface of the recording medium when the thickness of the recording medium is taken into consideration, where the length of the conveyance path in the fixing device is relatively long The first and second rotating shafts are rotated so that the peripheral surface speed of the other drive roll in contact with the second surface having a relatively short conveying path in the fixing device is relatively high. A driving device comprising a driving unit for driving.

  The drive device according to claim 1 further includes a receiving unit that receives a mode switching signal, and the drive unit has different circumferential speeds in which the first and second drive rolls are different from each other in the first mode. The first and second rotary shafts are rotationally driven so that the first and second rotary shafts have the same peripheral surface speed in the second mode, and the first and second rotary shafts are rotated. It is characterized by being driven.

According to a third aspect of the present invention, in the driving device according to the first or second aspect , the recording medium is supported by the first and second rotating shafts so as to be relatively rotatable, and the recording medium is one of the first and second driving rolls. A driven roll is provided that is sandwiched between the driven rolls and fed further downstream.

According to a fourth aspect of the present invention, in the drive device according to any one of the first to third aspects, the first and second drive rolls include a plurality of at least one of the first and second drive rolls. The drive roll is fixed to a position symmetrical to the left and right of the first and second rotating shafts in the direction in which the rotating shaft extends.

Claim 5
A toner image forming unit for forming a toner image on a recording medium being conveyed;
A fixing device that fixes the toner image on the recording medium by heating and pressurizing the recording medium on which the toner image is formed and conveyed; and
First and second rotating shafts that are arranged in parallel to each other at a position sandwiching the recording medium conveyance path on the downstream side in the recording medium conveyance direction from the fixing device and are driven to rotate;
The first and second rotation axis, the rotation axis extends, respectively it in a position to avoid overlapping each other in the direction fixed by the fixing unit was in first and second feeding the recording medium to further downstream has passed A driving roll;
Of the first and second drive rolls, the peripheral speed of one drive roll in contact with the first surface of the recording medium when the thickness of the recording medium is taken into consideration, where the length of the conveyance path in the fixing device is relatively long The first and second rotating shafts are rotated so that the peripheral surface speed of the other drive roll in contact with the second surface having a relatively short conveying path in the fixing device is relatively high. An image forming apparatus including a driving unit for driving.

According to the drive device of the first aspect and the image forming apparatus of the fifth aspect , the occurrence of image rubbing in the envelope or the like can be suppressed as compared with the case where the present configuration is not provided.
According to the drive device of claim 1 and the image forming apparatus of claim 5, the first drive roll due to the difference in peripheral surface speed when no recording medium is present between the first and second rotation shafts. And interference with the second drive roll can be avoided.

  According to the drive device of the second aspect, the occurrence of image rubbing in the envelope or the like is suppressed, and the recording medium other than the envelope or the like is appropriately conveyed.

According to the driving device of the third aspect , the recording medium can be more reliably conveyed as compared with the case where this configuration is not provided.

According to the drive device of the fourth aspect , the left and right balance of the conveyance force during conveyance of the recording medium is maintained as compared with the case where this configuration is not provided.

1 is an internal configuration diagram of a copying machine as an example of an image forming apparatus. FIG. 2 is a diagram illustrating a sheet conveyance path after a fixing unit in the image forming unit of the copier illustrated in FIG. 1. It is the schematic diagram which showed the structure of decurler. It is the figure which showed an example of the curved conveyance path.

  Embodiments of the present invention will be described below.

  FIG. 1 is an internal configuration diagram of a copying machine as an example of an image forming apparatus.

  The copying machine 1 has a document reading unit 1A and an image forming unit 1B. Further, below the image forming unit 1B, a wheel 1C that enables the copying machine 1 to move and a wheel 1C that does not move easily. A fixed foot 1D is attached.

  The document reading unit 1A is provided with a document feed table 11 on which documents are stacked. The documents S placed on the document feeder 11 are sent out one by one, and characters and images recorded on the document S are read and discharged onto the document discharge tray 12.

  Further, the document reading unit 1A has a hinge extending left and right on the back side, and the document feeding table 11 and the document discharging table 12 can be lifted integrally around the hinge as a center of rotation. The document reading plate 13 made of transparent glass is spread. In this document reading unit 1A, instead of placing a document on the document feeding table 11, only one document is placed on the document reading plate 13 downward, and characters and images are read from the document on the document reading plate 13. You can also.

  On the front side of the document reading plate 13, various messages are displayed for the user, and various operation buttons are displayed so that the user can perform operations such as document reading and image formation instructions. Part (not shown).

  A document reading optical system 30 is provided under the document reading plate 13. The document reading optical system 30 includes a first block 31 having a lamp 311 and a mirror 312, a second block 32 having two mirrors 321 and 322, and a photoelectric that reads light representing an image and generates an image signal. Sensor 33.

  The first block 31 and the second block 32 are movable in the direction of the arrow A-A ′ along the original reading plate 13, and are in the position on the left side shown in FIG. 1 in the initial state.

  The documents S placed on the document feeding table 11 are fed one by one and conveyed on a conveyance path 17 in contact with the document reading plate 13 by a conveyance roller 16. When the document S is conveyed in contact with the document reading plate 13, it is irradiated by the lamp 311, the reflected light from the document S is reflected by the mirrors 312, 321, 322, read by the photoelectric sensor 33, and the document S An image signal representing the recorded character or image is generated. The document S irradiated by the lamp 311 is further conveyed and sent out onto the document discharge table 12.

  When the original is placed on the original reading plate 13, the first block 31 and the second block 32 always have the same optical distance between the original reading position on the original reading plate 13 and the photoelectric sensor 33. Move in the direction of arrow A to keep During this time, the lamp 311 irradiates the original, and the photoelectric sensor 33 reads characters and images on the original and converts them into image signals.

  An image signal obtained by the photoelectric sensor 33 is input to the image processing unit 34. The image signal obtained by the photoelectric sensor 33 is an image signal representing each color of R (red), G (green), and B (blue), and the image processing unit 34 converts the RGB image signal into Y (yellow). , M (magenta), C (cyan), and K (black) are converted into image data for four colors and temporarily stored. Then, it is transmitted to the exposure control unit 41 provided in the image forming unit 1B in accordance with the exposure time for forming a latent image, which will be described later.

  In the upper part of the image forming unit 1B, there are provided two paper trays 21_1 and 21_2 for discharging the paper after the image is formed. The discharge trays 21_1 and 21_2 are configured in two stages because, depending on the use of the user, for example, a post-processing machine such as a stapler may be disposed on one of the discharge trays. is there. Alternatively, the two-stage discharge trays 21_1 and 21_2 can be used as the discharge trays as they are, for example, for separately discharging sheets on which different images are formed.

  In addition, four paper feed tables 23_1, 23_2, 23_3, and 23_4 are supported and accommodated by the left and right guide rails 24_1, 24_2, 24_3, and 24_4 in the lower portion of the image forming unit 1B. The sheets P are stored in a stacked state on each of the sheet feeding tables 23_1, 23_2, 23_3, and 23_4. Each of the sheet feeding bases 23_1, 23_2, 23_3, and 23_4 is guided by guide rails 24_1, 24_2, 24_3, and 24_4 so that the paper P can be replenished.

  Of these four paper feed tables 23_1, 23_2, 23_3, and 23_4, for example, a paper feed table that accommodates a sheet P having a size that conforms to the size of the document S (here, the paper feed table 23_1 is taken as an example). The paper P is fed out by the pick-up roll 25, separated one by one by the separating roll 26, the one paper P is transported upward by the transport roll 27, and the subsequent transport timing by the standby roll 28 Is adjusted and further conveyed upward. The conveyance of the sheet after the standby roll 28 will be described later.

  As described above, the image signal obtained by the document reading unit 1A is transmitted to the exposure control unit 41 of the image forming unit 1B.

  The image forming unit 1B is provided with exposure units 42Y, 42M, 42C, and 42K. In the latent image format, the exposure control unit 41 sends Y, M, C, and Y to the exposure units 42Y, 42M, 42C, and 42K. K image data is sent in, and each exposure light modulated by each Y, M, C, K image data is emitted from the exposure devices 42Y, 42M, 42C, 42K.

  In the image forming unit 1B, a main control unit 40 is shown at a position adjacent to the exposure control unit 41. The main control unit 40 includes a microcomputer and a program executed by the microcomputer. The exposure control unit 41, a display operation unit (not shown), an image processing unit 34, and other various power sources (not shown). It is connected to a circuit, a drive circuit, etc., and is responsible for overall control of the copying machine 1.

  Four image forming units 50Y, 50M, 50C, and 50K that form toner images with toners of colors Y, M, C, and K are disposed in the central portion of the image forming unit 1B. Since these four image forming units 50Y, 50M, 50C, and 50K have the same configuration except that the colors of the toners to be used are different, the configuration of the image forming unit 50Y will be described here.

  The image forming unit 50Y has a photoconductor 51Y that rotates in the direction indicated by an arrow R in FIG. 1, and around the photoconductor 51Y, a charger 52Y, a developing device 53Y, the above-described exposure device 42Y, and a cleaner 55Y. Is arranged. A transfer unit 54Y is placed at a position where an intermediate transfer belt 61 described later is sandwiched between the photoreceptor 51Y.

  The photoreceptor 51 </ b> Y has a roll shape, holds charges by charging, releases the charges by exposure, and holds an electrostatic latent image on the surface thereof.

  The charger 52Y charges the surface of the photoreceptor 51Y to a certain charging potential.

  Further, as described above, image data corresponding to the Y color is input from the exposure control unit 41 to the exposure device 42Y, and exposure light modulated in accordance with the input image data is output from the exposure device 42Y. Is done. After the photoreceptor 51Y is charged by the charger 52Y, it is irradiated with exposure light from the exposure device 42Y, and an electrostatic latent image is formed on the surface of the photoreceptor 51Y.

  The photosensitive member 51Y is exposed to exposure light to form an electrostatic latent image on the surface, and then developed by the developing unit 53Y. A toner image (yellow (Y in this image forming unit 50Y) is formed on the surface of the photosensitive member 51Y. ) Is formed.

  The developing device 53Y has two augers 532_1 and 532_2 that stir the developer in a case 531 that contains a developer composed of toner and a carrier, and a developer that transports the developer to a position facing the photoreceptor 51Y. A roll 533. In developing the electrostatic latent image formed on the photoreceptor 51Y, a bias voltage is applied to the developing roll 533, and the toner in the developer is formed on the photoreceptor 51Y by the action of the bias voltage. The toner image is formed on the photoreceptor 51Y according to the electrostatic latent image.

  The toner image formed on the photoreceptor 51Y by development by the developing unit 53Y is transferred onto the intermediate transfer belt 61 by the action of the transfer unit 54Y.

  The toner remaining on the photoreceptor 51Y after this transfer is removed from the photoreceptor 51Y by the cleaner 55Y.

  The intermediate transfer belt 61 is an endless belt that is looped around the driving roll 62 and other plural rolls 63 and circulates in the arrow B direction.

  The toner images of the respective color toners formed by the image forming units 50Y, 50M, 50C, and 50K are transferred onto the intermediate transfer belt 61 so as to overlap one another, and conveyed to the secondary transfer position where the transfer device 64 is disposed. The In synchronization with this, the sheet that has been conveyed to the standby roll 28 is conveyed to the secondary transfer position, and the toner image on the intermediate transfer belt 61 is transferred onto the conveyed sheet by the action of the transfer unit 64. Transcribed. The sheet that has received the transfer of the toner image is further conveyed, the toner image on the sheet is fixed on the sheet by pressurization and heating by the fixing device 65, and an image composed of the fixed toner image is formed on the sheet. Is done. The paper on which the image is formed is decurled by the decurler 66 and further curled, and is transported to one of the two paper discharge trays 21_1 and 21_2, and one of the discharge rollers 67_1 and 67_2. Are discharged onto a paper discharge tray corresponding to the discharge roll.

  After the toner image is transferred onto the paper by the transfer device 64, the intermediate transfer belt 61 further circulates, and the toner remaining on the surface thereof is removed from the intermediate transfer belt 61 by the cleaner 68.

  In addition, container mounting portions 29Y, 29M, 29C, and 29K are provided above the intermediate transfer belt 61 in the image forming portion 1B. In these container mounting portions 29Y, 29M, 29C, and 29K, toner containers 69Y, 69M, 69C, and 69K that store toner of each color of yellow (Y), magenta (M), cyan (C), and black (K). Is installed. Each color toner contained in the toner containers 69Y, 69M, 69C, and 69K is consumed by each developing device provided in the corresponding image forming unit 50Y, 50M, 50C, and 50K, such as the developing device 53Y. Each developer is replenished accordingly.

  The copying machine 1 has a normal mode in which copying is performed only on one side of a normal sheet, and a duplex copying mode in which images are formed on both sides of a sheet. In this double-sided copy mode, a sheet on which an image is formed on only one side advances toward the upper output tray 21_1, the front edge of the paper advances above the output tray 21_1, and the rear edge of the paper is The rotation of the discharge roll 67_1 is reversed while being sandwiched between the discharge rolls 67_1, and the paper advances the conveyance path 294 and reaches the standby roll 28 again. Thereafter, the toner image is transferred to the transfer device 64 again at the same timing, and the transfer device 64 transfers the toner image to the other side of the paper. The sheet on which the toner image has been transferred is fixed on the sheet by the fixing device 65 and further conveyed, and is discharged onto one of the two-stage discharge trays 21_1 and 21_2.

  FIG. 2 is a diagram showing a sheet conveyance path after the fixing unit of the image forming unit of the copying machine shown in FIG.

  The fixing device 65 includes a pressure roll 651, a heater 652, and a sheet peeling member 653.

  The pressure roll 651 is a rubber roll that rotates in the direction of arrow C, and presses the receiving block 652b with a heating belt 652a described below interposed therebetween. On the other hand, the heater 652 includes a heating belt 652a, a receiving block 652b, and a heating coil 652c. The heating belt 652a is an endless belt, and rotates in the direction of arrow D along with the rotation of the pressure roll 651 in the arrow C direction while being pressed against the receiving block 652b by the pressure roll 651. The receiving block 652b is a member that receives pressure from the pressure roll 651. The heating belt 652a has a metal layer and is induction-heated by the magnetic force from the heating coil 652c.

  The sheet on which the toner image has been transferred by the action of the transfer device 64 (see FIG. 1) passes between the pressure roll 651 and the heating belt 652a in a state where the toner image is held on the heating belt 652a side. The toner image is fixed on the paper by being heated and pressed by the fixing device 65. The paper that has passed through the fixing device 65 is peeled from the heating belt 652a by the paper peeling member 653 and further travels on the conveyance path 291. The curler of the paper is corrected by the decurler 66 and further travels. Details of the decurler 66 will be described later.

  The sheet that has passed through the decurler 66 is guided by the guide member 71 and passes through the gate 72. The gate 72 is a member that switches whether the conveyed paper is discharged to one of the two paper discharge trays 21_1 and 21_2 by changing the angle.

  In FIG. 2, the gate 72 is directed to discharge the conveyed paper to the paper discharge tray 21 </ b> _ <b> 2, and the paper conveyed on the conveyance path 291 is guided to the gate 72 and proceeds on the conveyance path 292. Then, the paper passes through the discharge roll 67_2 and is discharged onto the discharge table 21_2. When the direction of the gate 72 is changed, the sheet conveyed on the conveyance path 291 is guided by the gate 72 and proceeds on the conveyance path 293, and further conveyed downstream by the conveyance roll 73 and discharged by the discharge roll 67_1. It is discharged onto 21_1.

  In the double-sided copy mode, a sheet on which an image is formed only on the first side of the sheet travels on the conveyance path 293 and is discharged halfway onto the sheet discharge table 21_1 by the discharge roll 67_1. Thereafter, the angle of the gate 72 is changed to the direction shown in FIG. 2, and the discharge roll 67_1 and the transport roll 73 rotate in reverse. Then, the sheet advances on the conveyance path 294 with the rear end so far as the head. After that, as described above, the rear end that is the head proceeds to the standby roll 28 (see FIG. 1), and proceeds along the same route as when the timing is adjusted by the standby roll 28 and an image is formed on the first surface. This time, an image is formed on the second surface and discharged onto the paper discharge tray 21_1 or the paper discharge tray 21_2.

  The copying machine 1 has an envelope mode in addition to the normal mode and the duplex copy mode. This envelope mode is a mode in which an image is formed on an envelope, that is, two sheets of paper connected at the periphery. Here, as shown in FIG. 2, the fixing device 65 has a structure in which a rubber pressure roll 651 is pressed against the receiving block 652 b via the heating belt 652 a, and a part thereof is pressed by the pressure roll 651. It becomes a curved conveyance path. For this reason, when the thickness of the sheet passing therethrough is taken into consideration, the length of the sheet conveyance path differs between the front surface and the back surface of the sheet.

  In the present embodiment, the conveyance path on the front side (heating belt 652a side) is long, and the conveyance path on the back side (pressure roll 651 side) is short. In this way, if the lengths of the conveyance paths are different between the front and back surfaces, wrinkles may occur when the envelope passes through them. In order to suppress the generation of wrinkles, it is effective to reduce the pressing force of the pressure roll 651 on the heating belt 652a side in the fixing device 65. This is because if the pressing force is strong, there is a difference in the transport amount of the two sheets forming the envelope, and the sheet is deformed in the nip portion where the pressure roll 651 is pressed against the heating belt 652a. This is because the paper is crushed and becomes wrinkled because the pressing force for crushing the paper is superior to the elastic force of the paper.

  On the other hand, when this pressing force is lowered, even if the paper is deformed in the nip portion, the elastic force of the paper is superior to the pressing force that crushes the paper, so that the paper is not crushed and the generation of wrinkles is suppressed. However, if this pressing force is lowered to a level that suppresses the generation of wrinkles, the envelope itself will cause the displacement of the two sheets on the front and back surfaces of the envelope due to the difference in the length of the transport path on the front and back surfaces by the elastic force of the envelope. There is a case where the image surface is rubbed in the fixing device and the image is distorted in order to correct the image.

  In the present embodiment, the pressing force of the pressure roll 651 is lowered to such an extent that no wrinkles are generated, and image blurring is prevented by devising the decurler 66 on the downstream side of the fixing device 65 in the paper transport direction.

  Hereinafter, details of the decurler 66 will be described.

  FIG. 3 is a schematic diagram showing the structure of the decurler.

  As shown in FIG. 1, the decurler 66 is disposed downstream of the fixing device 65 in the paper conveyance direction. The decurler 66 has two rotary shafts 661 and 662 arranged in parallel to each other, and three rolls 661a, 661b, 661c; 662a, 662b, 662c is supported. In this embodiment, these rolls 661a, 661b, 661c; 662a, 662b, 662c are all rolls having the same diameter. The sheet coming out of the fixing device 65 passes between these two rotating shafts 661 and 662, and further advances downstream while being sandwiched between the rolls 661a, 661b and 661c; 662a, 662b and 662c. Here, when the sheet that has passed through the fixing device 65 passes between the two rotation shafts 661 and 662, the surface of the fixing device 65 that is in contact with the heating belt 652a faces the rotation shaft 661 side, and is fixed. The back surface of the container 65 that is in contact with the pressure roll 651 passes in a posture facing the rotating shaft 662 side. These two rotary shafts 661 and 662 are rotationally driven by separate motors 81 and 82, respectively. These motors 81 and 82 rotate at respective rotational speeds corresponding to the respective controls to the respective motors 81 and 82 by the main control unit 40 shown in FIG. Of the three rolls 661a, 661b, and 661c supported by the rotary shaft 661, the central roll 661b shown by hatching in FIG. 3 is fixed to the rotary shaft 661, and the rotary shaft 661 rotates. Rotate together. Of the three rolls 661a, 661b, and 661c supported by the rotary shaft 661, the rolls 661a and 661c on both sides except the central roll 661b can freely rotate relative to the rotary shaft 661. It is a roll. In the present embodiment, these rolls 661a, 661b, 661c are all metal hard rolls in terms of material.

  On the other hand, with respect to the three rolls 662a, 662b, 662c supported by the other rotating shaft 662, two of the three rolls 662a, 662b, 662c on the both sides hatched in FIG. 662a and 662c are fixed to the rotating shaft 662. Accordingly, the two rolls 662a and 662c on both sides rotate together with the rotation of the rotation shaft 662. Of the three rolls supported by the rotary shaft 662, one central roll 662 b is a roll that can freely rotate relative to the rotary shaft 662.

  In the present embodiment, the three rolls 662a, 662b, 662c supported by the rotating shaft 662 are rubber rolls in terms of material, and the three metal rolls 661a, 661b facing each other. , 661c. Therefore, when the three pairs of rolls 661a, 661b, 661c; 662a, 662b, 662c facing each other are in contact with each other, the rubber rolls 662a, 662b, 662c follow the peripheral surface shape of the metal rolls 661a, 661b, 661c. Deform. In the present embodiment, the sheet that has passed through the fixing device 65 is curled so that the surface (the surface in contact with the heating belt 652a (see FIG. 2)) is inward. Therefore, in the decurler 66 shown in FIG. 3, curls are corrected by using 662a, 662b, 662c, which are in contact with the back surface of the paper (the surface in contact with the pressure roll 651 (see FIG. 2)), as rubber rolls. doing.

  Further, as described above, the two rotating shafts 661 and 662 are driven to rotate by separate motors 81 and 82, respectively. For this reason, these two rotating shafts 661 and 662 can be rotated at mutually different rotational speeds. In the example showing this embodiment, the six rolls 661a, 661b, 661c; 662a, 662b, 662c are all rolls having the same diameter. Therefore, when the two rotary shafts 661 and 662 are rotated at different rotational speeds, the roll 661b fixed to one rotary shaft 661 and the rolls 662a and 662c fixed to the other rotary shaft 662 are different from each other. It will rotate at the peripheral speed. Here, of the six rolls 661a, 661b, 661c; 662a, 662b, 662c supported by the rotary shafts 661, 662, a pair of rolls 661a, 662a; 661b, 662b; The drive roll and the other is a driven roll combination. Therefore, the two rotary shafts 661 and 662 can rotate without any problem at different rotational speeds while the pair of rolls 661a and 662a; 661b and 662b; 661c and 662c are in contact with each other.

  Here, as described above, the copying machine 1 in this embodiment has an envelope mode. In the envelope mode, the back surface of the envelope (which is in contact with the pressure roll 651) that has passed through the fixing device 65 is driven by the rotational drive of the two motors 81 and 82 in response to an instruction from the main controller 40 (see FIG. 1). The rotating shaft 662 on the side facing the rotating surface rotates at a higher speed than the rotating shaft 661 on the side facing the envelope surface (the surface in contact with the heating belt 652a). If it carries out like this, when an envelope passes this decurler 66, the back surface side of an envelope with a short conveyance path will be pulled. In this way, the difference in the conveyance amount of the paper on the front and back of the envelope is eliminated, and the occurrence of image rubbing is suppressed by eliminating the paper misalignment in the nip portion.

  Further, the decurler 66 has a driving roll, that is, a fixed position of the rolls 661b and 662a and 662c fixed to one of the rotating shafts 661 and 662, and is symmetrical with respect to the virtual target line E drawn at the center thereof. Yes. Therefore, the envelope passing through the decurler 66 is transported with equal force left and right on the front and back surfaces, and the envelope paper is prevented from tilting to the left or right.

  Here, consideration is given to the length of the conveyance path on the front side and the back side of the sheet when the conveyance path of the sheet is curved in a complicated manner.

  FIG. 4 is a diagram illustrating an example of a curved conveyance path.

In the example shown in FIG. 4, a conveyance path having a radius Ro ₁ is formed on the front surface side of the sheet passing through the angle θo ₁ from the upstream side to the downstream side of the conveyance path, and then the back surface. A conveyance path over an angle θu _{1 with} a radius Ru ₁ connected to an arc on the side is connected, and a conveyance path over an angle θo _{2 with} a radius Ro ₂ connected to an arc on the surface side. At this time, if a sheet of thickness d passes through this transport path, the length Lo of the transport path on the front side of the sheet is

And
The length Lu of the conveyance path on the back side of the paper is

It becomes. Therefore, the difference Δ between the lengths of the conveyance paths on the front and back sides of the paper is

It becomes. Generalizing equations (1) to (3),

It becomes. That is, the length of the conveyance path on the front side and the back side of the paper is determined by the total size of the front side and the back side of the angle forming the arc shape.

  Returning to the description of the copier and decurler of this embodiment.

  In the copying machine 1, the two rotating shafts 661 and 662 rotate at the same speed except in the envelope mode. Further, as described above, in the envelope mode, the pressing force of the pressure roll 651 of the fixing device 65 toward the heating belt 652a is such that fixing failure and other problems do not occur in order to suppress generation of wrinkles on the envelope. It is weakened by. On the other hand, in modes other than the envelope mode, it is not necessary to consider the occurrence of wrinkles unlike envelopes and the like, so the pressing force of the pressure roll 651 toward the heating belt 652a is increased, and the margin for fixing is increased. Yes.

  In the present embodiment, the six rolls 661a, 661b, 661c; 662a, 662b, 662c are all rolls having the same diameter, and therefore the explanation is based on the rotational speed of the rotary shaft. However, in the envelope mode, the back side of the envelope is pulled not by the rotational speed of the rotary shaft but by the circumferential speed difference between the rolls 661b; 662a and 662c fixed to the rotary shaft. Therefore, when the diameters of the rolls 661a, 661b, 661c; 662a, 662b, 662c supported by the two rotating shafts 661, 662 are different from each other, the respective rotating shafts 661 by the motors 81, 82 according to the difference in the diameters. , 662 is adjusted.

  In the present embodiment, the length of the conveyance path of the front side paper and the back side paper of the envelope passing through the fixing unit 65 is short on the back side (the side on which the pressure roll 651 contacts). Depending on the situation, the transport path may be shorter on the back side. In this case, in the envelope mode, the rotation speed of the roll of the decurler 66 in contact with the paper on the front side of the envelope is made faster than the rotation speed of the roll in contact with the paper on the back side.

  Further, in the present embodiment, the decurler 66 has been described as having the configuration shown in FIG. 3, but the drive device of the present invention does not have to be a decurler and is supported by two rotating shafts and their rotating shafts. It may be a drive device having a roll and independent of the decurler.

  Further, although the copying machine 1 shown in FIG. 1 has been described here, the image forming apparatus of the present invention is not limited to the copying machine, and the present invention can be applied to other forms of image forming apparatuses such as printers and facsimiles. The same can be applied.

DESCRIPTION OF SYMBOLS 1 Copier 1A Document reading part 1B Image formation part 50Y, 50M, 50C, 50K Image formation unit 61 Intermediate transfer belt 65 Fixing device 66 Decurler 71 Guide member 72 Gate 81, 82 Motor 651 Pressure roll 652 Heater 652a Receiving block 652c Heating coil 653 Paper peeling member 661, 662 Rotating shaft 661a, 661b, 661c; 662a, 662b, 662c Roll

Claims (5)

Conveying the recording medium on the downstream side in the conveying direction of the recording medium from a fixing device that fixes the toner image on the recording medium by heating and pressurizing the recording medium on which the toner image is formed and conveyed First and second rotating shafts arranged in parallel to each other at positions sandwiching the path and driven to rotate;
First and sends the first and second axis of rotation, the recording medium that has passed through it respectively fixed by fixing unit to position avoiding overlap each other in the direction in which the rotary shaft extends further downstream A second drive roll;
Of the first and second drive rolls, one of the drive rolls in contact with the first surface of the recording medium having a relatively long conveying path in the fixing device when the thickness of the recording medium is taken into consideration The circumferential speed of the other drive roll in contact with the second surface, which is relatively shorter than the circumferential speed of the fixing device, is relatively high. And a drive unit that rotationally drives the two rotation shafts.   A receiving unit configured to receive a mode switching signal, wherein the driving unit has the first and second rotating shafts so that the first and second driving rolls have different circumferential speeds in the first mode; And the first and second rotary shafts are driven to rotate so that the first and second drive rolls have the same peripheral surface speed in the second mode. The drive device according to claim 1. The recording medium is supported on each of the first and second rotating shafts so as to be relatively rotatable, and the recording medium is sandwiched between one of the first and second driving rolls and further downstream. The drive device according to claim 1, further comprising a driven roll for feeding. There are a plurality of at least one of the first and second drive rolls, and the first and second drive rolls extend from the first and second rotary shafts. The driving device according to claim 1, wherein the driving device is fixed at a symmetrical position with respect to the direction. A toner image forming unit for forming a toner image on a recording medium being conveyed;
  A fixing device that fixes the toner image on the recording medium by heating and pressurizing the recording medium on which the toner image is formed and conveyed; and
First and second rotating shafts that are arranged in parallel to each other at a position sandwiching the conveyance path of the recording medium on the downstream side in the recording medium conveyance direction from the fixing device and are driven to rotate;
The first and second rotary shafts are fixed at positions where they do not overlap each other in the direction in which the rotary shaft extends, and the recording media that have passed through the fixing device are sent further downstream. A driving roll;
Of the first and second drive rolls, one of the drive rolls in contact with the first surface of the recording medium having a relatively long conveying path in the fixing device when the thickness of the recording medium is taken into consideration The circumferential speed of the other drive roll in contact with the second surface, which is relatively shorter than the circumferential speed of the fixing device, is relatively high. An image forming apparatus comprising: a drive unit that rotationally drives the two rotation shafts.

Images