JP2014126736A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image forming method for maintaining constant the amount of paper passing through a secondary transfer part to be wound around a secondary transfer roller.SOLUTION: Tension roller moving parts 45 (45a, 45b, and 45c) moves a tension roller 18 from a home position to a lower rear part in a traveling direction of an intermediate transfer belt 4 by a distance according to the hardness of paper 3 (3a, 3b,...) as indicated by an arrow f. In response to the movement of the tension roller 18, a secondary transfer roller 19 makes a downward shift with respect to a driven roller 6 to press the intermediate transfer belt 4 to the inside, so as to increase a range of a grip part D1 formed by the secondary transfer roller 19 and the intermediate transfer belt 4, and a range of a grip part D2 formed by the secondary transfer roller 19 and the driven roller 6 with the intermediate transfer belt 4 therebetween. Hard cardboard 3b is secondarily transferred with a toner image with the same winding amount to the secondary transfer roller 19 as in the case of soft plain paper 3a.

Description

  The present invention relates to an image forming apparatus and an image forming method that always maintain a constant amount of paper wound around a secondary transfer roller of paper passing through a secondary transfer portion.

  2. Description of the Related Art Conventionally, there is an image forming apparatus that prints a color image (hereinafter also referred to as “printing” or “image formation”) using an electrophotographic method using toner. In color printing using toner, the total of magenta (M), cyan (C), and yellow (Y) colors and black (K) dedicated to the black portion and characters of an image for one page of paper. Four color toner images are superimposed and transferred.

  A transfer medium such as a sheet as an image forming medium onto which four color toner images are transferred is fixed with a color image on the paper surface by applying heat and pressure in a fixing device.

  When the toner image is transferred to a transfer medium, the image is transferred directly from a photosensitive drum or the like as an image carrier to a transfer medium, or the image is temporarily transferred from the image carrier to an intermediate transfer body and then the primary transfer image. There is known an intermediate transfer type image forming apparatus that performs secondary transfer from an intermediate transfer member to a transfer medium.

  In such an intermediate transfer type image forming apparatus, for example, an intermediate transfer belt is used as an intermediate transfer member, and a primary transfer image on the intermediate transfer belt is secondarily transferred to a transfer medium in a secondary transfer portion and then transferred onto the transfer medium. I'm getting an image.

  Thus, in order to secondary transfer the toner image primarily transferred onto the intermediate transfer belt to the transfer medium, a secondary transfer voltage is applied to the transfer medium by, for example, a secondary transfer roller in the secondary transfer unit.

  At this time, if the secondary transfer voltage applied to the transfer medium is not a secondary transfer voltage suitable for the transfer medium, a good image cannot be formed on the transfer medium. Conventionally, it has been found that the quality of an image formed on a transfer medium is affected by the temperature and humidity inside the image forming apparatus.

  Therefore, as a method of determining the secondary transfer voltage for forming a good image, the temperature and humidity in the image forming apparatus is detected by a temperature and humidity detection device or the like, and the temperature and humidity information obtained by this detection is used. An image forming apparatus in which the secondary transfer voltage is made variable is disclosed. (For example, refer to Patent Document 1.)

JP 2000-147924 A

  However, in the secondary transfer voltage control method in the conventional image forming apparatus as in Patent Document 1, the secondary transfer voltage is varied based on the temperature and humidity information in the image forming apparatus as described above. The secondary transfer voltage cannot be adjusted in accordance with the change of the transfer medium whose thickness and strength change depending on the material.

  The setting element between the members which is important in the secondary transfer part is that the transfer medium enters the secondary transfer part, first presses against the intermediate transfer belt, and then sticks to the secondary transfer roller by the transfer bias voltage. After the image is transferred, the amount of winding around the secondary transfer roller until the image is peeled off from the secondary transfer roller while being sent out in the conveying direction is decisive.

  Since a normal or thin transfer medium (hereinafter also referred to as “paper”) is generally flexible, the amount of winding around the secondary transfer roller is relatively large. Normally, the secondary transfer conditions such as the secondary transfer voltage and the pressure contact force to the paper are set with this state as a standard.

  However, for example, there are papers that are thick and firm, such as postcards, and papers that are stiff even if not thick, such as OHP paper. If the waist is strong, the position where the paper is peeled off from the secondary transfer roller is shorter in terms of distance in the feeding direction than the case of paper with a weak waist. That is, the amount of winding around the secondary transfer roller is reduced.

  When the amount of wrap around the secondary transfer roller is small, not only the time during which the secondary transfer voltage is applied is shortened, but also the range in the conveyance direction in which the sheet is pressed and sandwiched between the intermediate transfer belt and the secondary transfer roller is shortened. . That is, a good secondary transfer result cannot be obtained.

  In the technique of Patent Document 1, as described above, the thickness of the sheet, the strength of the waist, and the like change, in other words, the property of the sheet changes, and the secondary transfer voltage is adjusted according to the change in the property. As described above, it cannot be done.

  The present invention solves the above-described conventional problems, and an image forming apparatus and an image forming apparatus that always maintain a constant amount of paper wound around a secondary transfer roller regardless of the type of paper that passes through the secondary transfer unit. It aims to provide a method.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a backup roller, an intermediate transfer belt stretched over the backup roller, and a secondary transfer unit that is in pressure contact with the backup roller via the intermediate transfer belt. The intermediate transfer belt is disposed upstream of the secondary transfer roller in the running direction of the intermediate transfer belt, and the intermediate transfer belt is stretched by pressing the intermediate transfer belt from the inside. An angle formed by a tension roller that performs the intermediate transfer belt traveling direction of the intermediate transfer belt toward the secondary transfer portion and a transfer medium traveling direction of the transfer medium toward the secondary transfer portion is defined as the transfer medium. A tension roller moving unit that moves the tension roller so as to change according to the properties of the.

  In order to solve the above-described problems, an image forming method of the present invention includes a backup roller, an intermediate transfer belt stretched over the backup roller, and a secondary transfer unit that is in pressure contact with the backup roller via the intermediate transfer belt. In the vicinity of the secondary transfer portion having a secondary transfer roller, the intermediate transfer belt is pressed more than the secondary transfer roller to press the intermediate transfer belt from the inside to stretch the intermediate transfer belt. A step of disposing a tension roller upstream of the intermediate transfer belt traveling direction; the intermediate transfer belt traveling direction toward the secondary transfer portion of the intermediate transfer belt; and a transfer medium toward the secondary transfer portion of the transfer medium. A tension roller moving step of moving the tension roller so that the angle formed by the running direction changes according to the properties of the transfer medium; Image forming method, which comprises.

  The present invention can provide an image forming apparatus and an image forming method in which the amount of paper wound around the secondary transfer roller is always kept constant regardless of the type of paper passing through the secondary transfer portion.

1 is a schematic side cross-sectional view schematically showing an internal configuration of an image forming apparatus according to Embodiment 1. FIG. 1 is a circuit block diagram including a control device of an image forming apparatus according to Embodiment 1. FIG. In the image forming apparatus according to the first embodiment, (a) is a diagram illustrating a mode when plain paper is passed through the secondary transfer unit, (b) is an enlarged view of the secondary transfer unit at that time, and (c). FIG. 6 is a diagram for explaining a problem that occurs when a thick sheet is passed through the secondary transfer unit in the same manner as in (b). In the image forming apparatus according to the first embodiment, (a) is a diagram illustrating an aspect in which the tension roller is moved to maintain the amount of thick paper wound around the secondary transfer roller within a certain range similar to that of plain paper. (b) is an enlarged view of the secondary transfer portion at that time. In the image forming apparatus according to the first exemplary embodiment, (a), (b), and (c) are diagrams illustrating three examples of a configuration of a tension roller moving unit that moves the position of the tension roller.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic cross-sectional side view schematically showing the internal configuration of the image forming apparatus according to the first embodiment. The figure shows a tandem color image forming apparatus as an example.

  A color image forming apparatus 1 shown in FIG. 1 is a small color image forming apparatus having a size that can be placed on, for example, a desktop personal computer rack. A paper cassette 2 is detachably attached to the bottom of a main body base. I have. A large number of sheets 3 are placed and stored in the sheet cassette 2.

  An intermediate transfer belt 4 is arranged in a flat loop shape on the left and right sides of the figure at substantially the center inside the color image forming apparatus 1. The intermediate transfer belt 4 is looped around the driving roller 5 and the driven roller 6 and circulates in the counterclockwise direction indicated by the arrow A in the figure.

  In the upper circulation portion of the intermediate transfer belt 4, four photosensitive drums 7 (7c, 7m, 7y, 7k) are multi-staged from the upstream side to the downstream side in the image transport direction (from the right to the left in the figure). It is installed side by side.

  Each of the photosensitive drums 7 is surrounded by a peripheral surface (hereinafter, only a peripheral device around the photosensitive drum 7k is representatively shown), and a cleaner 8, a charging roller 9, optical writing A head 11, a developing roller 13 of the image forming unit 12, and a primary transfer roller 14 are disposed. The developing roller 13 is a magnet roller.

  The four optical writing heads 11 are supported by the image forming apparatus main body frame via a support member (not shown). Further, the intermediate transfer belt 4, the driving roller 5, the driven roller 6, the primary transfer roller 14 and the like constitute a belt unit together with tension rollers 17 and 18 described later.

  From the image forming unit 12 corresponding to the photoconductive drum 7c to the image forming unit 12 corresponding to the photoconductive drum 7k, in the toner container 16 of the developing kit 15 of each image forming unit 12, cyan (which is a subtractive primary color, cyan ( C), magenta (M) and yellow (Y) toners, and black (K) toner dedicated to printing of black portions of characters and images, respectively.

  The driven roller 6 disposed at the upstream end of the intermediate transfer belt 4 also serves as a secondary transfer backup roller. A secondary transfer roller 19 disposed so as to face the driven roller 6 as a backup roller via the intermediate transfer belt 4 is pressed against and rotated.

  A secondary transfer portion 20 is formed by the driven roller 6, the intermediate transfer belt 4, and the secondary transfer roller 19. The intermediate transfer belt 4 primarily transfers the toner image directly to the belt surface, and conveys the toner image to the secondary transfer unit to further transfer the toner image onto the paper 3.

  Further, the tension roller 17 is in pressure contact with the intermediate transfer belt 4 on the back surface of the downstream end portion of the upper running portion, and the tension roller 18 is in pressure contact with the right end side rear surface of the lower running portion in the drawing. As a result, the intermediate transfer belt 4 is always urged outward by the tension rollers 17 and 18 to maintain an appropriate tension. The tension roller 18 also has other functions, which will be described later.

  Further, a paper take-out roller 21, a feeding roller 22, and a separating roller 23 are disposed in the vicinity of the sheet feeding opening (right side in the drawing) of the sheet cassette 2. A standby roller pair 24 is arranged in the middle of the sheet conveyance path up to the point.

  A belt-type fixing device 25 is disposed on the downstream side (upward in the drawing) of the secondary transfer unit 20. On the further downstream side of the belt-type fixing device 25, a pair of unillustrated unloading rollers for unloading the fixed paper 3 from the belt-type fixing device 25, and a paper discharge on which the unloaded paper 3 is formed on the upper surface of the device. A pair of paper discharge rollers 27 for discharging the paper to the tray 26 is provided.

  FIG. 2 is a circuit block diagram including the control device of the color image forming apparatus 1 described above. As shown in FIG. 2, the circuit block has a CPU (central processing unit) 30 as a center, and an interface controller (I / F_CONT) 31 and a printer controller (PR_CONT) 32 are connected to the CPU 30 via a data bus. ing. A printer printing unit 33 is connected to the PR_CONT 32.

  Connected to the CPU 30 are a ROM (read only memory) 34, an EEPROM (electrically erasable programmable ROM) 35, an operation panel 36 of the main body operation unit, and a sensor unit 37 to which outputs from sensors arranged in the respective units are input. Has been. The ROM 34 stores a system program, and the CPU 30 performs processing by controlling each unit in accordance with the system program.

  That is, in each unit, first, the I / F_CONT 31 converts print data supplied from a host device such as a personal computer into bitmap data and develops it in the frame memory 38. In the frame memory 38, a storage area is set for each of black (K), magenta (M), cyan (C), and yellow (Y), and data of each color is developed in a corresponding area.

  The data developed in the frame memory 38 is output to PR_CONT 32 and is output from PR_CONT 32 to the printer printing unit 33.

  The printer printing unit 33 is an engine unit, and under the control of the PR_CONT 32, controls the drive output to the belt drive unit 39 that performs the vertical movement of the belt unit shown in FIG. To do.

  Further, the printer printing unit 33 includes a conveyance mechanism drive unit 41 that drives a conveyance mechanism that includes rotationally driven units such as a sheet take-out roller 21 to a discharge roller pair 27, the photosensitive drum 7, and a heating roller of the belt-type fixing device 25. Controls the drive output to

  Further, the printer printing unit 33 applies a voltage to a process load of an image forming unit having a driven unit such as the charging roller 9, the optical writing head 11, the primary transfer roller 14, and a rotational driving system including the secondary transfer roller 19. The output of the applied voltage output unit 42 is controlled.

  Further, the printer printing unit 33 always adjusts the amount of winding of the paper 3 around the secondary transfer roller 19 regardless of the thickness of the paper 3 passing through the secondary transfer unit for secondary transfer of the toner image and the strength of the waist. In order to keep it constant, the movement drive of the tension roller moving unit 43 that moves the position of the tension roller 18 is controlled.

  The black (K), magenta (M), cyan (C), and yellow (Y) data output from the PR_CONT 32 are respectively sent from the printer printing unit 33 to the corresponding optical writing heads 11 shown in FIG. To be supplied.

  The print data of each color supplied to the optical writing head 11 is written as an electrostatic latent image on the photosensitive drum 7, and the electrostatic latent image is developed into a toner image by the developing roller 13, and the developed toner is developed. The image is primarily transferred to the intermediate transfer belt 4.

  The primarily transferred toner image is conveyed to the secondary transfer unit 20 by the intermediate transfer belt 4 and is secondarily transferred to the sheet 3 taken out from the sheet cassette 2 and conveyed to the secondary transfer unit 20. At this time, there is no problem if the paper 3 is a normal relatively thin office paper (hereinafter referred to as plain paper).

  However, if the paper is thicker than plain paper, or is not as thick as paper but is as stiff as thick paper (hereinafter collectively referred to as thick paper), the corresponding secondary transfer voltage cannot be adjusted. Mentioned above.

  However, in this example, the secondary transfer voltage is not adjusted, but the amount of winding of the paper around the secondary transfer roller 19 is kept constant so that a constant amount of secondary transfer voltage can be supplied to the paper. To solve the above problem.

  FIG. 3A is a view showing a mode when the plain paper 3a is passed through the secondary transfer unit 20, and FIG. 3B is an enlarged view showing the secondary transfer unit 20 at that time. 3 (c) is a diagram for explaining a problem that occurs when the thick paper 3b is passed through the secondary transfer unit 20 in the same manner as in FIG. 3 (b).

  As shown in FIG. 3A, when the plain paper 3a is passed through the secondary transfer unit 20, the tension roller 18 is located almost directly below the driven roller 6 (secondary transfer backup roller). The intermediate transfer belt 4 between the tension roller 18 and the driven roller 6 is slightly inclined to the right, but is stretched in a substantially vertical state.

  The secondary transfer roller 19 that forms a secondary transfer portion 20 in pressure contact with the driven roller 6 via the intermediate transfer belt 4 is biased obliquely downward with respect to the driven roller 6 by a pressing biasing member 44. As a result, the secondary transfer roller 19 is shifted slightly downward with respect to the driven roller 6 and is in pressure contact with the intermediate transfer belt 4 before the intermediate transfer belt 4 is engaged with the driven roller 6.

  The downward shift amount of the secondary transfer roller 19 with respect to the driven roller 6 includes a horizontal straight line a passing through the center of the support shaft of the driven roller 6, the center of the support shaft of the driven roller 6, and the support of the secondary transfer roller 19. It can be represented by an angle α formed by an inclined straight line b connecting the center of the axis.

  Further, since the secondary transfer roller 19 is shifted downward as described above, the secondary transfer roller 19 is located below the horizontal line a passing through the center of the support shaft of the driven roller 6 and the intermediate transfer belt 4 is moved inside the belt. It is arranged in the form of pushing into.

  In other words, the paper grip portion formed by the secondary transfer roller 19 and the intermediate transfer belt 4 is inclined obliquely downward and downward with respect to the vertical conveyance path shown in FIG. As a result, the plain paper 3a carried into the secondary transfer unit 20 enters while forming a fixed winding amount around the secondary transfer roller 19 from a position slightly shifted to the left from the lower vertical conveyance path.

  Similarly, the sheet gripping portion formed by the secondary transfer roller 19 and the intermediate transfer belt 4 is inclined obliquely upward and to the upper right due to the downward shift of the secondary transfer roller 19. As a result, the plain paper 3a discharged from the secondary transfer unit 20 is discharged while forming a constant winding amount around the secondary transfer roller 19 in the direction indicated by the arrow c slightly shifted to the right from the upper vertical conveyance path. The

  In this way, as shown in FIG. 3B, the plain paper 3a enters the secondary transfer portion 20 while forming a constant pressure contact amount B1 from the bottom to the intermediate transfer belt 4 from the position Tb1 to the position Tb2. .

  Subsequently, the plain paper 3a is sandwiched between the intermediate transfer belt 4 and the secondary transfer roller 19 to form a constant winding amount B2 around the secondary transfer roller 19 from the position Tb2 to the position Tb3. Discharged.

  In this discharge, the secondary transfer roller 19 rotates in the direction away from the plain paper 3a, so that the plain paper 3a is peeled from the secondary transfer roller 19 at a position Tb3 which is the end of the winding amount B2. Is done.

  In FIG. 3B, the traveling direction of the plain paper 3a at the end Tb3 of the winding amount B2 where the plain paper 3a is peeled from the secondary transfer roller 19, and a horizontal straight line a passing through the center of the support shaft of the driven roller 6 are shown. Is an angle β.

  On the other hand, as shown in FIG. 3 (c), when the thick paper 3b is passed through the secondary transfer unit 20 in the same manner as described above, the thick paper 3b is stronger than the plain paper 3a. The amount C1 of contact with the intermediate transfer belt 4 when entering the portion 20 and the amount C2 of wrapping around the secondary transfer roller 19 until exiting from the secondary transfer portion 20 are smaller than those of the plain paper 3a. Become.

  Further, as shown in FIG. 3C, the traveling direction of the thick paper 3b at the end position Tc3 of the winding amount C2 from which the thick paper 3b is peeled from the secondary transfer roller 19 and the center of the support shaft of the driven roller 6 are passed. The angle γ formed by the horizontal straight line a increases. That is, in FIGS. 3B and 3C, B1> C1, B2> C2, and β <γ.

  As described above, in the case of the thick paper 3b, the application time of the secondary transfer voltage applied to the thick paper 3b is shorter than that in the case of the plain paper 3a as shown by B1> C1 and B2> C2. The transfer of the image becomes insufficient, resulting in a problem that the image quality of the formed image is deteriorated.

  In this example, in order to eliminate such a problem caused by the properties of the paper, when the paper passed through the secondary transfer unit 20 is the thick paper 3b, the CPU 30 of the control device shown in FIG. The moving unit 43 is controlled to move the tension roller 18 backward in the lower traveling direction of the intermediate transfer belt 4 by a distance corresponding to the material of the thick paper 3b.

  FIG. 4A is a diagram showing a mode in which the position of the tension roller 18 is moved to maintain the amount of wrapping of the thick paper 3b around the secondary transfer roller 19 within a certain range similar to the case of the plain paper 3a. FIG. 4B is an enlarged view of the secondary transfer unit 20 at that time.

  As shown in FIG. 4 (a), the tension roller 18 travels in the lower traveling portion of the intermediate transfer belt 4 as shown by an arrow f, rather than the position of the plain paper 3a shown in FIG. 3 (a). The position is moved backward in the direction.

  Thereby, the intermediate transfer belt 4 between the tension roller 18 and the driven roller 6 is greatly inclined obliquely in the lower left direction. In response to this inclination, the secondary transfer roller 19 is largely shifted obliquely downward relative to the driven roller 6 by the pressing and urging member 44 as indicated by an arrow g.

  Due to this shift, a straight line b ′ connecting the center of the support shaft of the driven roller 6 and the center of the support shaft of the secondary transfer roller 19 in the case of the thick paper 3b shown in FIG. 4A is shown in FIG. In the case of plain paper 3 a, an opening of an angle δ is formed with respect to a straight line b connecting the center of the support shaft of the driven roller 6 and the center of the support shaft of the secondary transfer roller 19.

  In this way, the secondary transfer roller 19 is largely shifted obliquely downward with respect to the driven roller 6, and the secondary transfer roller 19 moves the intermediate transfer belt 4 between the tension roller 18 and the driven roller 6 to the driven roller 6. It is pressed inside the belt so as to be wound around. Thereby, the range of the gripping portion between the secondary transfer roller 19 and the intermediate transfer belt 4 is formed so as to expand in the transport direction.

  When the thick paper 3b passes through the secondary transfer portion 20, as shown in FIG. 4B, the thick paper 3b forms a constant pressure amount D1 on the intermediate transfer belt 4 from the bottom to the position Td1 to the position Td2. However, it is sandwiched between the secondary transfer roller 19 and the intermediate transfer belt 4 and enters the secondary transfer unit 20.

  Subsequently, the thick paper 3b is sandwiched between the intermediate transfer belt 4 and the secondary transfer roller 19, and is discharged from the secondary transfer portion 20 while forming a constant winding amount D2 from the position Td2 to the position Td3, and ends the winding amount D2. Is peeled off from the secondary transfer roller 19 at a position Td3.

  Since the thick paper 3b is relatively stiff, the wrinkle around the secondary transfer roller 19 is smaller than that of the plain paper 3a. However, as described above, the gripping portion between the secondary transfer roller 19 and the intermediate transfer belt 4 is small. The range is formed to extend in the transport direction.

  Therefore, even if the winding wrinkles are small, the winding amount D2 of the thick paper 3b around the secondary transfer roller 19 is substantially equal to the winding amount B2 of the plain paper 3a. That is, B2≈C2. Further, the angle δ at which the secondary transfer roller 19 shifts is substantially equal to the difference between the angle β and the angle γ. That is, β≈η.

  Therefore, the application time of the secondary transfer voltage applied to the thick paper 3b in this example is the same as that for the plain paper 3a, and the toner image is sufficiently transferred to the thick paper 3b, and the image quality of the formed image is increased. There will be no problem of lowering.

  FIGS. 5A, 5B, and 5C are diagrams showing three examples of the configuration of the tension roller moving unit 45 (45a, 45b, 45c) that moves the position of the tension roller 18 described above. The tension roller moving portion 45a shown in FIG. 5 (a) is composed of an eccentric cam 46.

  The eccentric cam 46 has a narrow fan shape, and is supported by a support shaft 47 in the vicinity of the root of the fan shape. The entire periphery of the fan-shaped edge is sequentially slidably contacted with the support shaft 48 of the tension roller 18. Rotating intermittently in the direction indicated by arrow h.

  The state shown in FIG. 5A is a state in which the edge cam surface 49-1 farthest from the support shaft 47 of the eccentric cam 46 is in sliding contact with the support shaft 48 of the tension roller 18 and the eccentric cam 46 is stopped. There is shown a state when the tension roller 18 is at the home position.

  When the eccentric cam 46 is intermittently rotated in the direction indicated by the arrow h by a drive unit (not shown), the sliding contact portion between the peripheral surface of the eccentric cam 46 and the support shaft 48 of the tension roller 18 is, for example, The edge peripheral surface sliding contact portions 49-1, 49-2, 49-3, 49-4 of the eccentric cam 46 move and change.

  When the edge peripheral surface 49-4 of the eccentric cam 46 and the support shaft 48 of the tension roller 18 are engaged, the tension roller 18 moves to the farthest rear in the traveling direction of the lower traveling portion of the intermediate transfer belt 4. For example, it is in the state shown in FIG.

  According to the tension roller moving unit 45a including the eccentric cam 46 of the present example, the eccentric cam 46 is rotated according to the type of paper, and the tension roller 18 is moved forward in the traveling direction of the lower traveling unit of the intermediate transfer belt 4. The position can be moved steplessly between the part (home position) and the last part (for example, the position shown in FIG. 4A).

  Further, the tension roller moving portion 45b shown in FIG. The rotating member 51 holds the support shaft 48 of the tension roller 18 at one end (diagonal right lower end portion in the figure), and the other end (diagonal left upper end portion in the figure) is pivotally supported by the hinge 52.

  The state shown in FIG. 5B is a state where the rotating member 51 is rotated to the rightmost and stopped, and shows a state when the tension roller 18 is at the home position.

  When driven by a drive unit (not shown) and the rotation member 51 rotates in the clockwise direction indicated by the arrow i with the hinge 52 as a fulcrum, the tension roller 18 that supports the support shaft 48 at one end of the rotation member 51. Moves to the left, for example, as shown in FIG.

  According to the tension roller moving unit 45b including the rotating member 51 of the present example, the rotating member 51 is rotated left and right according to the type of paper, and the tension roller 18 is moved to the lower traveling unit of the intermediate transfer belt 4. The position can be moved steplessly between the frontmost part (home position) and the last part (for example, the position shown in FIG. 4A) in the traveling direction.

  Further, the tension roller moving part 45 c shown in FIG. 5C is composed of a plate-like moving member 53. In the vicinity of the right end portion of the plate-like moving member 53, an arc-shaped long hole 54 is formed. The arc-shaped long hole 54 is formed from the upper end portion 54a to the lower end portion 54b by drawing an arc from the lower running portion of the intermediate transfer belt 4 in the running direction.

  A support shaft 48 of the tension roller 18 is slidably fitted into the arc-shaped long hole 54. The plate-like moving member 53 is not shown in the figure. It is arranged on both sides of the tension roller 18.

  The state shown in FIG. 5C is a state in which the plate-like moving member 53 moves to the lowest position and stops, and both ends of the support shaft 48 of the tension roller 18 are arc-shaped of the plate-like moving member 53. The position is fixed at the upper end portion 54 a of the long hole 54. This position indicates the position when the tension roller 18 is at the home position.

  When driven by a drive unit (not shown) and the plate-like moving member 53 moves upward as indicated by an arrow j, the support shaft 48, that is, the tension roller 18 is moved along the arc-shaped long hole 54. The lower traveling portion moves rearward in the traveling direction, and at the lower end portion 54b, for example, the state shown in FIG.

  According to the tension roller moving portion 45c formed of the plate-like moving member 53 of this example, the plate-like moving member 53 is moved up and down according to the type of paper, and the tension roller 18 is moved to the lower running portion of the intermediate transfer belt 4. The position can be moved steplessly between the frontmost part (home position) and the last part (for example, the position shown in FIG. 4A) in the traveling direction.

Although several embodiments of the present invention have been described, the present invention is included in the invention described in the claims and the equivalents thereof. Hereinafter, the invention described in the scope of claims of the present application will be appended.
[Appendix 1]

A backup roller,
An intermediate transfer belt stretched over the backup roller;
A secondary transfer roller that forms a secondary transfer portion in pressure contact with the backup roller via the intermediate transfer belt;
A tension roller that is disposed upstream of the secondary transfer roller in the intermediate transfer belt running direction of the intermediate transfer belt, and presses the intermediate transfer belt from the inside to tension the intermediate transfer belt;
The angle formed by the intermediate transfer belt traveling direction of the intermediate transfer belt toward the secondary transfer portion and the transfer medium traveling direction of the transfer medium toward the secondary transfer portion is determined according to the properties of the transfer medium. A tension roller moving unit that moves the tension roller to change,
An image forming apparatus comprising:
[Appendix 2]

2. The image forming apparatus according to claim 1, wherein the tension roller moving unit moves the tension roller according to a difference in thickness of the transfer medium or strength of the waist.
[Appendix 3]

When the transfer medium is thicker than usual, or when it is stiffer than usual, the tension roller moving unit moves the intermediate transfer belt according to the thickness or the strength of the waist and the transfer medium running. 3. The image forming apparatus according to appendix 1 or 2, wherein the tension roller is moved so that an angle formed by the direction becomes larger.
[Appendix 4]

When the transfer medium has a normal thickness or a normal waist strength, the tension roller moving unit reduces an angle formed by the intermediate transfer belt running direction and the transfer medium running direction. The image forming apparatus according to any one of appendices 1 to 3, wherein the tension roller is moved.
[Appendix 5]

The image forming apparatus according to any one of appendices 1 to 4, wherein the tension roller moving unit includes an eccentric cam that slides in contact with a support shaft of the tension roller and rotates.
[Appendix 6]

The tension roller moving unit is configured by a rotating member that holds a support shaft of the tension roller at one end, is pivotally supported by a hinge at the other end, and rotates around the hinge. The image forming apparatus according to any one of 1 to 4.
[Appendix 7]

The tension roller moving section is configured by a plate-shaped moving member that slidably fits and holds a support shaft of the tension roller in an arc-shaped elongated hole. Image forming apparatus.
[Appendix 8]

A backup roller,
An intermediate transfer belt stretched over the backup roller;
A secondary transfer roller that forms a secondary transfer portion in pressure contact with the backup roller via the intermediate transfer belt;
In the vicinity of the secondary transfer portion having
A step of disposing a tension roller on the upstream side of the intermediate transfer belt in the intermediate transfer belt traveling direction from the secondary transfer roller to press the intermediate transfer belt from the inside to stretch the intermediate transfer belt;
The angle formed by the intermediate transfer belt traveling direction of the intermediate transfer belt toward the secondary transfer portion and the transfer medium traveling direction of the transfer medium toward the secondary transfer portion is determined according to the properties of the transfer medium. A tension roller moving step of moving the tension roller to change;
An image forming method comprising:

  The present invention can be used in an image forming apparatus and an image forming method that always maintain a constant amount of paper wound around a secondary transfer roller of paper passing through a secondary transfer portion.

DESCRIPTION OF SYMBOLS 1 Color image forming apparatus 2 Paper cassette 3 Paper 4 Intermediate transfer belt 5 Drive roller 6 Driven roller (backup roller)
7 (7c, 7m, 7y, 7k) Photosensitive drum 8 Cleaner 9 Charging roller 11 (11c, 11m, 11y, 11k) Optical writing head 12 Image forming unit 13 Developing roller 14 Primary transfer roller 15 Developing kit 16 Toner container 17 , 18 Tension roller 19 Secondary transfer roller 20 Secondary transfer section 21 Paper take-out roller 22 Feed roller 23 Rolling roller 24 Standby roller pair 25 Belt type fixing device 26 Paper discharge tray 27 Paper discharge roller pair 30 CPU (central processing unit)
31 Interface controller (I / F_CONT)
32 Printer controller (PR_CONT)
33 Printer section 34 ROM (read only memory)
35 EEPROM (electrically erasable programmable ROM)
36 Operation Panel 37 Sensor Unit 38 Frame Memory 39 Belt Drive Unit 41 Conveying Mechanism Drive Unit 42 Applied Voltage Output Unit 43 Tension Roller Moving Unit 44 Pushing and Bent Member 45 (45a, 45b, 45c) Tension Roller Moving Unit 46 Eccentric Cam 47 Support Shaft 48 Support shaft 49-1, 49-2, 49-3, 49-4 Edge peripheral surface sliding contact portion 51 Rotating member 52 Hinge 53 Plate-shaped moving member 54 Arc-shaped long hole 54a Upper end portion 54b Lower end portion

Claims (8)

A backup roller,
An intermediate transfer belt stretched over the backup roller;
A secondary transfer roller that forms a secondary transfer portion in pressure contact with the backup roller via the intermediate transfer belt;
A tension roller that is disposed upstream of the secondary transfer roller in the intermediate transfer belt running direction of the intermediate transfer belt, and presses the intermediate transfer belt from the inside to tension the intermediate transfer belt;
The angle formed by the intermediate transfer belt traveling direction of the intermediate transfer belt toward the secondary transfer portion and the transfer medium traveling direction of the transfer medium toward the secondary transfer portion is determined according to the properties of the transfer medium. A tension roller moving unit that moves the tension roller to change,
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the tension roller moving unit moves the tension roller according to a difference in thickness of the transfer medium or strength of the waist.   When the transfer medium is thicker than usual, or when it is stiffer than usual, the tension roller moving unit moves the intermediate transfer belt according to the thickness or the strength of the waist and the transfer medium running. The image forming apparatus according to claim 1, wherein the tension roller is moved so that an angle formed by a direction becomes larger.   When the transfer medium has a normal thickness or a normal waist strength, the tension roller moving unit reduces an angle formed by the intermediate transfer belt running direction and the transfer medium running direction. The image forming apparatus according to claim 1, wherein the tension roller is moved.   5. The image forming apparatus according to claim 1, wherein the tension roller moving unit includes an eccentric cam that rotates while slidingly contacting a support shaft of the tension roller. 6.   The tension roller moving part is configured by a rotating member that holds a support shaft of the tension roller at one end, is pivotally supported by a hinge at the other end, and rotates around the hinge. Item 5. The image forming apparatus according to any one of Items 1 to 4.   5. The tension roller moving part is configured by a plate-shaped moving member that slidably fits and holds a support shaft of the tension roller in an arc-shaped elongated hole. The image forming apparatus described. A backup roller,
An intermediate transfer belt stretched over the backup roller;
A secondary transfer roller that forms a secondary transfer portion in pressure contact with the backup roller via the intermediate transfer belt;
In the vicinity of the secondary transfer portion having
A step of disposing a tension roller on the upstream side of the intermediate transfer belt in the intermediate transfer belt traveling direction from the secondary transfer roller to press the intermediate transfer belt from the inside to stretch the intermediate transfer belt;
The angle formed by the intermediate transfer belt traveling direction of the intermediate transfer belt toward the secondary transfer portion and the transfer medium traveling direction of the transfer medium toward the secondary transfer portion is determined according to the properties of the transfer medium. A tension roller moving step of moving the tension roller to change;
An image forming method comprising: