JP2024115655A - Cam mechanism and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably reduce a problem where a step part of a cam is brought into contact with a movable body.

SOLUTION: A cam mechanism is provided with a cam 93 that is brought into contact with a secondary transfer sub unit 70 (movable body) to move the secondary transfer sub unit 70, and drive transmission mechanisms 94-97 that drive to rotate the cam 93 in normal and reverse directions. The cam 93 has a step part 93c formed on a cam face of the cam 93, and pins 79A, 79B (cam-side projections) are provided to project laterally on a side face 93m (93n) of the cam 93. The cam mechanism is provided with holding member-side projections 80A, 80B (restriction members) that are brought into contact with the pins 79A, 79B to restrict a rotation range of the cam 93 so that the secondary transfer sub unit 70 is not brought into contact with the step part 93c of the cam 93.

SELECTED DRAWING: Figure 10

COPYRIGHT: (C)2024,JPO&INPIT

Description

This invention relates to a cam mechanism that moves a movable body such as a secondary transfer unit or a pressure roller in a fixing device, and an image forming device equipped with the cam mechanism, such as a copier, printer, facsimile, or a combination machine of these.

2. Description of the Related Art Conventionally, there have been known image forming apparatuses such as copiers and printers that are provided with a cam mechanism for moving a movable body such as a pressure roller of a fixing device in a vertical direction (see, for example, Japanese Patent Application Laid-Open No. 2003-233636).
In many cases, the cams installed in such cam mechanisms have a step formed on the cam surface for the sake of function.

On the other hand, Patent Document 1 discloses a technology that provides a detection means for detecting the rotational position of the cam so that the stepped portion of the cam does not come into contact with the pressure roller, and limits the rotational range of the cam based on the detection results, with the aim of preventing the pressure roller (movable body) coming into contact with the stepped portion of the cam and causing a sudden displacement of the pressure roller.

The technology of Patent Document 1 is provided with a detection means for detecting the rotational position of the cam, and is therefore expected to have the effect of preventing the stepped portion of the cam from coming into contact with the movable body.
However, if the detection means fails, it is not possible to prevent the step portion of the cam from coming into contact with the movable body.

This invention was made to solve the above-mentioned problems, and aims to provide a cam mechanism and an image forming device that steadily reduces the problem of the stepped portion of the cam coming into contact with the movable body.

The cam mechanism in this invention comprises a cam for contacting a movable body to move the movable body, and a drive transmission mechanism for driving the cam to rotate in forward and reverse directions, the cam has a stepped portion formed on the cam surface, a cam side protrusion is provided on the side surface of the cam so as to protrude laterally, and a limiting member is provided that contacts the cam side protrusion to limit the rotation range of the cam so that the movable body does not contact the stepped portion.

The present invention provides a cam mechanism and an image forming device that reliably reduces the problem of the stepped portion of the cam coming into contact with the movable body.

1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; FIG. 2 is an enlarged configuration diagram showing a part of an image forming unit. FIG. 2 is a schematic diagram showing the vicinity of an intermediate transfer belt and a secondary transfer unit. FIG. 2 is a diagram illustrating a configuration of a secondary transfer unit. 1A is a diagram showing a state in which the secondary transfer subunit has rotated toward the intermediate transfer belt, and FIG. 1B is a diagram showing a state in which the secondary transfer subunit has rotated away from the intermediate transfer belt. FIG. 2 is a diagram showing the configuration of the secondary transfer unit and its vicinity. FIG. 4 is an enlarged view showing the vicinity of an end portion in the width direction of the secondary transfer unit. 11A and 11B are diagrams illustrating an operation in which a secondary transfer unit is pulled out from the main body of the image forming apparatus. 1A is a side view showing a state in which the secondary transfer unit is fitted onto the positioning pins of the intermediate transfer unit, and FIG. 1A is a diagram showing a state in which the cam has rotated in a pressure application direction (forward direction), and FIG. 1B is a diagram showing a state in which the cam has rotated in a pressure reduction direction (reverse direction). 13 is a diagram showing a state in which a cam serving as a comparative example is rotated in a pressure application direction (forward direction). FIG. 1A is a diagram showing the cam, driven pulley, and detected plate on one axial end side, and FIG. 1B is a diagram showing the cam, driven pulley, and detected plate on the other axial end side. 13A is a diagram showing a state in which the cam rotates in the pressure application direction (forward direction) as modified example 1, and FIG. 13B is a diagram showing a state in which the cam rotates in the pressure reduction direction (reverse direction). FIG. 11 is an enlarged view showing the vicinity of an end portion in the width direction of a secondary transfer unit according to a second modified example. FIG. 11 is a configuration diagram showing the vicinity of a secondary transfer unit according to a third modified example.

The following describes in detail the embodiments of the present invention with reference to the drawings. Note that in each drawing, the same or corresponding parts are given the same reference numerals, and their repeated explanations will be appropriately simplified or omitted.

First, the overall configuration and operation of an image forming apparatus 100 will be described with reference to FIGS.
FIG. 1 is a diagram showing the configuration of a printer as an image forming apparatus, and FIG. 2 is an enlarged view showing a part of the image forming section.
1, an intermediate transfer belt 8 serving as an intermediate transfer body is provided in the center of the image forming apparatus 100. In addition, imaging units 6Y, 6M, 6C, and 6K corresponding to the respective colors (yellow, magenta, cyan, and black) are provided in parallel so as to face the intermediate transfer belt 8.
Further, an operation display panel 150 (operation display unit) is provided on the upper portion of the image forming apparatus 100 for displaying information related to the printing operation (image forming operation) and for performing operations.

Referring to FIG. 2, the imaging unit 6Y corresponding to yellow is composed of the photoconductor drum 1Y as an image carrier, and a charging unit 4Y, a developing unit 5Y, a cleaning unit 2Y, a lubricant supply device 3, a discharging unit, etc., which are arranged around the photoconductor drum 1Y. Then, the image creation process (charging process, exposure process, development process, transfer process, cleaning process, discharging process) is performed on the photoconductor drum 1Y, and a yellow image is formed on the photoconductor drum 1Y as an image carrier.

The other three imaging units 6M, 6C, and 6K are configured in a similar manner to the imaging unit 6Y corresponding to yellow, except that they use different toner colors, and form images corresponding to their respective toner colors. Below, we will omit the explanation of the other three imaging units 6M, 6C, and 6K as appropriate, and only explain the imaging unit 6Y corresponding to yellow.

2, the photoconductor drum 1Y as an image carrier is rotated counterclockwise by a main motor, and the surface of the photoconductor drum 1Y is uniformly charged at the position of a charging section 4Y (charging step).
Thereafter, the surface of the photosensitive drum 1Y reaches a position irradiated with the laser light L emitted from the writing unit 7 (exposure section), and an electrostatic latent image corresponding to yellow is formed by exposure scanning in the width direction (the direction perpendicular to the paper surface in Figures 1 and 2, which is the main scanning direction) at this position (this is the exposure process).
The writing unit 7 includes a light source, a polygon motor, a group of mirrors, a group of lenses, a control board, an electrical component section, and the like, housed in a sealed case.

Thereafter, the surface of the photoconductor drum 1Y reaches a position facing the developing unit 5Y, where the electrostatic latent image is developed to form a yellow toner image (developing step).
Thereafter, the surface of the photoconductor drum 1Y reaches a position facing the intermediate transfer belt 8 and the primary transfer roller 9Y, and the toner image formed on the surface of the photoconductor drum 1Y at this position is primarily transferred onto the surface of the intermediate transfer belt 8 (the primary transfer process). At this time, a small amount of untransferred toner remains on the photoconductor drum 1Y.

Thereafter, the surface of the photoreceptor drum 1Y reaches a position facing the cleaning section 2Y, and the untransferred toner remaining on the photoreceptor drum 1Y at this position is collected into the cleaning section 2Y by the cleaning blade 2a (cleaning process).
Here, a lubricant supplying device 3 (photoconductor lubricant supplying device) consisting of a lubricant supplying roller 3a, a solid lubricant 3b, a compression spring 3c (biasing member), etc. is installed inside the cleaning section 2Y. The lubricant supplying roller 3a, which rotates clockwise in Fig. 2, scrapes off the lubricant little by little from the solid lubricant 3b, and the lubricant is supplied to the surface of the photoconductor drum 1Y by the lubricant supplying roller 3a.
Finally, the surface of the photosensitive drum 1Y reaches a position facing the charge removing section, where the residual potential on the photosensitive drum 1Y is removed.
Thus, a series of image forming processes carried out on the photosensitive drum 1Y is completed.

The above-mentioned image forming process is performed in the other image forming units 6M, 6C, and 6K in the same manner as in the yellow image forming unit 6Y. That is, a laser beam L based on image information is irradiated from a writing unit 7 disposed above the image forming units toward the photosensitive drums 1M, 1C, and 1K of the image forming units 6M, 6C, and 6K. In detail, the writing unit 7 emits laser beam L from a light source, and irradiates the laser beam L onto the photosensitive drums via a plurality of optical elements while scanning the photosensitive drums with a polygon mirror that is rotated. Note that the writing unit 7 may be one in which a plurality of LEDs are arranged in the width direction.
Thereafter, the toner images of each color formed on the photoconductor drums 1M, 1C, and 1K through the developing processes by the developing units 5M, 5C, and 5K are primarily transferred onto the intermediate transfer belt 8 in a superimposed manner. In this manner, a color image is formed on the intermediate transfer belt 8.

Here, an intermediate transfer belt 8 serving as an intermediate transfer body is stretched and supported by a plurality of roller members 16 to 22 and 80, and is moved endlessly in the direction of the arrow in FIG. 3 by the rotational drive of one roller member (drive roller 16) by a motor.
The four primary transfer rollers 9Y, 9M, 9C, and 9K sandwich the intermediate transfer belt 8 between the photoconductor drums 1Y, 1M, 1C, and 1K, respectively, to form primary transfer nips. A transfer voltage (primary transfer bias) having a polarity opposite to that of the toner is applied to the primary transfer rollers 9Y, 9M, 9C, and 9K.
Then, the intermediate transfer belt 8 travels in the direction of the arrow and passes sequentially through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of each color on the photoconductor drums 1Y, 1M, 1C, and 1K are primarily transferred onto the surface of the intermediate transfer belt 8 in a superimposed manner (primary transfer process).

Then, the intermediate transfer belt 8, on which the toner images of each color are superimposed and primarily transferred, reaches a position facing the secondary transfer belt 71 as a secondary transfer member. At this position, the secondary transfer opposing roller 80 sandwiches the intermediate transfer belt 8 and the secondary transfer belt 71 between itself and the secondary transfer roller 72 to form a secondary transfer nip. The four-color toner image formed (primary transfer) on the intermediate transfer belt 8 is then secondarily transferred onto a sheet P, such as paper, that has been transported to the position of this secondary transfer nip (secondary transfer process). At this time, untransferred toner that has not been transferred to the sheet P remains on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 reaches the position of the intermediate transfer cleaning unit 10. At this position, the untransferred toner and other deposits adhering to the surface of the intermediate transfer belt 8 are removed.
Furthermore, the intermediate transfer belt 8 reaches the position of a lubricant supplying device 30 serving as an intermediate transfer lubricant supplying device. At this position, a lubricant is supplied onto the surface of the intermediate transfer belt 8.
Thus, a series of transfer processes carried out on the intermediate transfer belt 8 is completed.

Referring now to FIG. 1, the sheet P transported to the position of the secondary transfer nip is transported from a paper feed section 26 arranged below the device main body 100 via a paper feed roller 27, a pair of registration rollers 28, etc.
More specifically, a plurality of sheets P such as transfer paper are stored in a stack in the paper feed section 26. When the paper feed roller 27 is rotated counterclockwise in FIG. 1, the topmost sheet P is fed toward between the rollers of the pair of registration rollers 28 via the first transport path K1.

The sheet P transported to the registration roller pair 28 (timing roller pair) stops temporarily at the roller nip of the registration roller pair 28, which has stopped rotating. Then, in time with the color image on the intermediate transfer belt 8, the registration roller pair 28 is rotated and the sheet P is transported toward the secondary transfer nip. In this way, the desired color image is transferred onto the sheet P.

Thereafter, the sheet P onto which the color image has been transferred at the secondary transfer nip (transfer nip) is transported by the secondary transfer belt 71, and after being separated from the secondary transfer belt 71, is transported by the transport belt 61 (transport unit 60) to the fixing section 50. At this position, the color image transferred onto the surface is fixed onto the sheet P by heat and pressure from the fixing belt and pressure roller (fixing process). The transport unit 60 is composed of a plurality of rollers, the transport belt 61 stretched and supported by the plurality of rollers, a transport guide plate (not shown), and the like.
Thereafter, the sheet P passes through a second transport path K2 and is discharged to the outside of the apparatus by a pair of discharge rollers. The sheets P discharged to the outside of the apparatus by the pair of discharge rollers are sequentially stacked on a stack unit as output images.
In this manner, a series of image forming processes in the image forming apparatus is completed.

As shown in FIG. 1, the image forming apparatus 100 in this embodiment is provided with a double-sided conveying device 40 that conveys the sheet P toward the secondary transfer nip (transfer nip) in order to transfer the toner image on the intermediate transfer belt 8 to the back side of the sheet P after the toner image has been transferred to the front side at the secondary transfer nip.
Specifically, when a "duplex printing mode" is selected in which printing is performed on both sides (front and back) of the sheet P, the sheet P after the fixing process on the front side is not discharged as it is as when the above-mentioned "single-sided printing mode" is selected, but is guided to the third conveying path K3 in the duplex conveying device 40, and after its conveying direction is reversed, it is conveyed again toward the position of the secondary transfer nip (secondary transfer unit 69) via the fourth conveying path K4. Then, at the position of the secondary transfer nip, an image is formed (secondary transfer) on the back side of the sheet P by the image forming process (image forming operation) similar to that described above, and then the sheet undergoes a fixing process in the fixing unit 50 and is discharged from the image forming apparatus main body 100 via the second conveying path K2.

Next, the configuration and operation of the developing section 5Y (developing device) in the image forming section will be described in more detail with reference to FIG.
The developing unit 5Y is composed of a developing roller 51Y facing the photosensitive drum 1Y, a doctor blade 52Y facing the developing roller 51Y, two transport screws 55Y disposed in the developer container, and a concentration detection sensor 56Y for detecting the toner concentration in the developer. The developing roller 51Y is composed of a magnet fixed inside and a sleeve rotating around the magnet. The developer container contains a two-component developer G consisting of a carrier and a toner.

The developing section 5Y thus configured operates as follows.
The sleeve of the developing roller 51Y rotates in the direction of the arrow in Fig. 2. The developer G carried on the developing roller 51Y by the magnetic field formed by the magnet moves on the developing roller 51Y as the sleeve rotates. The developer G in the developing unit 5Y is adjusted so that the ratio of toner in the developer G (toner concentration) falls within a predetermined range. Specifically, when a toner concentration sensor installed in the developing unit 5Y detects a low toner concentration, new toner is replenished from the toner container 58 into the developing unit 5Y so that the toner concentration falls within the predetermined range.
Thereafter, the toner replenished from the toner container 58 into the developer storage section is circulated between the two separated developer storage sections (movement in the direction perpendicular to the plane of the paper in FIG. 2) while being mixed and stirred by the two transport screws 55Y together with the developer G. The toner in the developer G is attracted to the carrier due to frictional charging with the carrier, and is carried on the developing roller 51Y together with the carrier by the magnetic force formed on the developing roller 51Y.

The developer G carried on the developing roller 51Y is transported in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52Y. The developer G on the developing roller 51Y is adjusted to an appropriate amount at this position, and then transported to a position facing the photoconductor drum 1Y (the developing area). The toner is then attracted to the latent image formed on the photoconductor drum 1Y by the electric field formed in the developing area. The developer G remaining on the developing roller 51Y then reaches the top of the developer container as the sleeve rotates, and is separated from the developing roller 51Y at this position.
The toner container 58 is detachably (replaceably) installed in the developing unit 5Y (image forming apparatus 100). When the new toner contained therein becomes empty, the toner container 58 is removed from the developing unit 5Y (image forming apparatus 100) and replaced with a new toner.

Next, the intermediate transfer unit 15 in this embodiment will be described in detail with reference to FIG.
3, the intermediate transfer unit 15 is composed of an intermediate transfer belt 8 as an intermediate transfer body, four primary transfer rollers 9Y, 9M, 9C, and 9K, a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposed roller 20, a lubricant opposed roller 21, a backup roller 22, an intermediate transfer cleaning section 10, a lubricant supplying device 30 as an intermediate transfer lubricant supplying device, a secondary transfer opposed roller 80, and the like.

The intermediate transfer belt 8, which acts as an intermediate transfer body, contacts the four photosensitive drums 1Y, 1M, 1C, and 1K (image carriers) that respectively carry toner images of each color, forming a primary transfer nip. The intermediate transfer belt 8 is stretched and supported mainly by eight roller members (a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning counter roller 20, a lubricant counter roller 21, a backup roller 22, and a secondary transfer counter roller 80).

In this embodiment, the intermediate transfer belt 8 is made of a single layer or multiple layers of PVDF (vinyldiene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc., with a conductive material such as carbon black dispersed therein. The intermediate transfer belt 8 is adjusted so that the volume resistivity is in the range of 10 ⁶ to 10 ¹³ Ωcm, and the surface resistivity of the back side of the belt is in the range of 10 ⁷ to 10 ¹³ Ωcm. The thickness of the intermediate transfer belt 8 is set to be in the range of 20 to 200 μm. In this embodiment, the thickness of the intermediate transfer belt 8 is set to about 60 μm, and the volume resistivity is set to about 10 ⁹ Ωcm.
If necessary, a release layer can be coated on the surface of the intermediate transfer belt 8. In this case, the material used for the coating can be a fluororesin such as ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), or PVF (vinyl fluoride), but is not limited thereto.

The primary transfer rollers 9Y, 9M, 9C, and 9K are in contact with the corresponding photoconductor drums 1Y, 1M, 1C, and 1K, respectively, via the intermediate transfer belt 8. In more detail, the yellow transfer roller 9Y is in contact with the yellow photoconductor drum 1Y via the intermediate transfer belt 8, the magenta transfer roller 9M is in contact with the magenta photoconductor drum 1M via the intermediate transfer belt 8, the cyan transfer roller 9C is in contact with the cyan photoconductor drum 1C via the intermediate transfer belt 8, and the black transfer roller 9K is in contact with the black photoconductor drum 1K via the intermediate transfer belt 8.

The drive roller 16 is positioned downstream of the four photosensitive drums in the running direction of the intermediate transfer belt, and is disposed so as to abut against the inner peripheral surface of the intermediate transfer belt 8 with the intermediate transfer belt 8 wrapped around it at a winding angle of about 120 degrees. The drive roller 16 is driven to rotate in the clockwise direction in FIG. 3 by a motor Mt1 controlled by the control unit 90. This causes the intermediate transfer belt 8 to run in a predetermined running direction (clockwise in FIG. 3).

The driven roller 17 is positioned upstream of the four photosensitive drums in the running direction of the intermediate transfer belt 8, and is arranged to abut against the inner peripheral surface of the intermediate transfer belt 8 with the intermediate transfer belt 8 wrapped around it at a winding angle of about 180 degrees. The portion of the intermediate transfer belt 8 from the driven roller 17 to the drive roller 16 is set to be a nearly horizontal plane. The driven roller 17 rotates clockwise in FIG. 3 as the intermediate transfer belt 8 runs.

The tension roller 19 contacts the outer circumferential surface of the intermediate transfer belt 8. The pre-transfer roller 18, the cleaning opposed roller 20, the lubricant opposed roller 21, the backup roller 22, and the secondary transfer opposed roller 80 contact the inner circumferential surface of the intermediate transfer belt 8.
Between the secondary transfer opposing roller 80 and the lubricant opposing roller 21, an intermediate transfer cleaning unit 10 (cleaning blade) is provided so as to come into contact with the cleaning opposing roller 20 via the intermediate transfer belt 8.
A lubricant supplying device 30 (intermediate transfer lubricant supplying device) is installed between the cleaning facing roller 20 and the tension roller 19 so as to contact the lubricant facing roller 21 via the intermediate transfer belt 8. The lubricant supplying device 30 is composed of a lubricant supplying roller, a solid lubricant, a compression spring (urging member), and the like, similar to the lubricant supplying device 3 for the photosensitive drum. The lubricant supplying roller rotates counterclockwise in FIG. 3 to scrape off a small amount of lubricant from the solid lubricant, and the lubricant is supplied to the surface of the intermediate transfer belt 8 by the lubricant supplying roller.
All of the roller members 17 to 22 and 80 except for the driving roller 16 are rotated in the clockwise direction in FIG. 3 as the intermediate transfer belt 8 travels.

4, the secondary transfer opposing roller 80 is in contact with the secondary transfer roller 72 (secondary transfer unit 69) via the intermediate transfer belt 8 and the secondary transfer belt 71. The secondary transfer opposing roller 80 is formed by forming an elastic layer 83 (layer thickness is about 5 mm) made of NBR rubber having a volume resistance of about 10 ⁷ to 10 ⁸ Ω and a hardness (JIS-A hardness) of about 48 to 58 degrees on the outer circumferential surface of a cylindrical core metal made of stainless steel or the like.

In this embodiment, the secondary transfer opposing roller 80 is electrically connected to a power supply unit 111 (bias output means), and a secondary transfer bias of about -5 kV is applied from the power supply unit 111. The secondary transfer bias applied to the secondary transfer opposing roller 80 is for secondary transfer of the toner image primarily transferred onto the surface of the intermediate transfer belt 8 onto the sheet P conveyed to the secondary transfer nip, and is a secondary transfer bias (DC voltage) of the same polarity as the polarity of the toner (negative polarity in this embodiment). As a result, the toner carried on the toner carrying surface (outer peripheral surface) of the intermediate transfer belt 8 is electrostatically moved from the secondary transfer opposing roller 80 side toward the secondary transfer roller 72 (secondary transfer unit 69) side by the secondary transfer electric field.

Hereinafter, the secondary transfer unit 69 serving as a holding member will be described with reference to FIG.
With reference to FIG. 4, the secondary transfer unit 69 is disposed so as to face the intermediate transfer belt 8 (intermediate transfer unit 15).
The secondary transfer unit 69 as a holding member is composed of a secondary transfer subunit 70 as a movable body, a cam mechanism 92 (pressure subunit), an optical sensor 85, etc. The secondary transfer subunit 70 (movable body) is composed of a secondary transfer belt 71 as a secondary transfer member, a secondary transfer roller 72, a separation roller 73, a sensor facing roller 74, a first tension roller 75, a second tension roller 76, a third tension roller 77, a fourth tension roller 78, etc.

The secondary transfer belt 71 is an endless belt (belt member) stretched and supported by seven roller members (secondary transfer roller 72, separation roller 73, sensor facing roller 74, and first to fourth tension rollers 75 to 78), and is made of approximately the same material as the intermediate transfer belt 8. The secondary transfer belt 71 (belt member) abuts against the intermediate transfer belt 8 (intermediate transfer body) to form a secondary transfer nip as a transfer nip, and transports the sheet P sent out from the secondary transfer nip.

The secondary transfer roller 72 sandwiches the intermediate transfer belt 8 and the secondary transfer belt 71 between the secondary transfer roller 72 and the secondary transfer opposing roller 80 to form a secondary transfer nip. The secondary transfer roller 72 is formed (covered) with an elastic layer having a hardness (Asker C hardness) of about 40 to 50 degrees on a hollow core metal made of stainless steel, aluminum, or the like. The elastic layer of the secondary transfer roller 72 can be formed in a solid or foamed sponge shape by dispersing conductive filler such as carbon or by incorporating an ionic conductive material in a rubber material such as polyurethane, EPDM, or silicone. In this embodiment, the volume resistance of the elastic layer is set to about 10 ^6.5 to 10 ^7.5 Ω in order to suppress the concentration of the transfer current. In this embodiment, the secondary transfer roller 72 is grounded (earthed).
4 by a drive motor (not shown) controlled by the control unit 90, causing the secondary transfer belt 71 to rotate (run) in the counterclockwise direction in Fig. 3 and Fig. 4. In accordance with this, the multiple roller members 73 to 78 in contact with the inner circumferential surface (or outer circumferential surface) of the secondary transfer belt 71 are rotated by the rotation.

The separation roller 73 is disposed at a position downstream of the secondary transfer nip in the transport direction of the sheet P. The sheet P sent out from the secondary transfer nip is transported along the secondary transfer belt 71 traveling in the counterclockwise direction in FIG. 4, and then separated from the secondary transfer belt 71 at the position of the separation roller 73 (curvature separation) by the secondary transfer belt 71 having a curved surface formed along the outer periphery of the separation roller 73.
The sensor facing roller 74 is a roller member that faces the optical sensor 85 across the secondary transfer belt 71, and will be described in detail later.
In addition, in this embodiment, the secondary transfer belt 71 is configured to be tensioned and supported by seven roller members 72 to 78, and only the third tension roller 77 is configured to abut against the outer peripheral surface of the secondary transfer belt 71, but the number of roller members that tension and support the secondary transfer belt 71, and the number and positions of the roller members that abut against the outer peripheral surface of the belt are not limited to those in this embodiment.

Next, the characteristic configuration and operation of the secondary transfer unit 69 as a holding member will be described in more detail with reference to FIGS.
As described above, in this embodiment, the secondary transfer unit 69 as a holding member is made up of the secondary transfer subunit 70 as a movable body, the cam mechanism 92 (pressure subunit), the optical sensor 85, and the like.
As shown in Figure 4, the secondary transfer subunit 70 as a movable body is provided with a plurality of roller members (seven roller members: a secondary transfer roller 72, a separation roller 73, a sensor facing roller 74, and first to fourth tension rollers 75 to 78) and a secondary transfer belt 71 stretched across the plurality of roller members 72 to 78.
The secondary transfer belt 71 as a belt member is in pressure contact with the secondary transfer opposing roller 80 via the intermediate transfer belt 8 .

4 to 6, the secondary transfer subunit 70 functions as a movable body configured to be rotatable (swingable) around a rotation center 74a of one of the roller members 72 to 78 (the sensor facing roller 74).
As described above, among the multiple roller members 72 to 78, the secondary transfer roller 72, which is another roller member different from the sensor opposing roller 74 (one roller member), is pressed against the intermediate transfer belt 8 via the secondary transfer belt 71.

The cam mechanism 92 (pressure applying subunit) is configured to be able to adjust the contact pressure (nip pressure, secondary transfer nip pressure) of the secondary transfer belt 71 against the intermediate transfer belt 8 by moving (rotating) the secondary transfer subunit 70, which is a movable body, around a rotation center 74a (which is the rotation center of the sensor opposing roller 74).
6, the cam mechanism 92 is provided with a cam 93 that comes into contact with a contact portion (which protrudes downward in a curved shape in this embodiment) at the bottom of the unit side plate 70a of the secondary transfer subunit 70. In this embodiment, a motor 97 for driving the cam 93 to rotate is provided in the transport unit 60, not in the secondary transfer unit 69.
On the other hand, seven roller members 72 to 78 are rotatably supported via bearings on the unit side plate 70a, and a drive motor (not shown) that rotates and drives the secondary transfer roller 72 is also fixedly installed.
Then, by controlling the motor 97 by the control unit 90, the cam 93 is rotated to a target posture (posture in the direction of rotation) (the cam 93 is rotated by the target amount of rotation), and the contact pressure (nip pressure of the secondary transfer nip) of the secondary transfer belt 71 (secondary transfer roller 72) against the intermediate transfer belt 8 (secondary transfer opposing roller 80) is adjusted.

Specifically, as shown in Fig. 5A, when the secondary transfer subunit 70 is rotated counterclockwise around the rotation center 74a by the cam mechanism 92, the nip pressure of the secondary transfer nip increases. In contrast, as shown in Fig. 5B, when the secondary transfer subunit 70 is rotated clockwise around the rotation center 74a by the cam mechanism 92, the nip pressure of the secondary transfer nip decreases.
The state in which the nip pressure of the secondary transfer nip is small also includes a state in which the secondary transfer belt 71 is completely separated from the intermediate transfer belt 8 and the nip pressure becomes zero, as shown in FIG. 5B.

More specifically, in this embodiment, when the thickness (paper thickness) of the sheet P transported (passed) through the secondary transfer nip is thick, the cam mechanism 92 is controlled by the control unit 90 so that the nip pressure of the secondary transfer nip is smaller than when the thickness (paper thickness) of the sheet P is thin. This ensures good transportability of the sheet P through the secondary transfer nip regardless of the thickness of the sheet P.
Furthermore, when the type (paper type) of sheet P transported (passed) to the secondary transfer nip has low transferability, the cam mechanism 92 is controlled by the control unit 90 so that the nip pressure of the secondary transfer nip is greater than when the type (paper type) of sheet P has high transferability. This ensures good transferability at the secondary transfer nip regardless of the type of sheet P.
Furthermore, when the image area ratio (the ratio of the image area to the effective image area) of the toner image (image) secondarily transferred to the sheet P is low, the cam mechanism 92 is controlled by the control unit 90 so that the nip pressure of the secondary transfer nip is smaller than when the image area ratio is high. This ensures stable transferability in the secondary transfer nip regardless of the size of the image area ratio.
The control unit 90 can obtain information about the thickness and type of the sheet P based on information about the sheet P input by the user operating the operation display panel 150. The control unit 90 can obtain information about the image area ratio based on information written by the writing unit 7.

In addition, in this embodiment, as shown in FIG. 5B, the secondary transfer belt 71 is configured to be able to be completely separated from the intermediate transfer belt 8.
The control to achieve such a state is mainly performed when the printing operation (image forming process) is not performed in the image forming apparatus 100, such as when the main power is turned off or printing is stopped. By performing such control, it is possible to reduce problems such as elastic distortion caused by the intermediate transfer belt 8 and the secondary transfer belt 71 being constantly in pressure contact.

Now, referring to Figures 4 to 6, in this embodiment, the optical sensor 85 is fixed to the secondary transfer unit 69 so as to face the sensor opposing roller 74 (a roller member that serves as the center of rotation) via the secondary transfer belt 71, without being linked to the rotation of the secondary transfer sub-unit 70 by the cam mechanism 92.
More specifically, the optical sensor 85 is a reflective photosensor in which a light emitting element and a light receiving element are arranged to face the outer circumferential surface of the belt, and is fixed to the transport unit 60. In other words, the optical sensor 85 is not fixed to the secondary transfer subunit 70, but is fixed to the transport unit 60 so as not to be linked to the rotation of the secondary transfer subunit 70.
The cam mechanism 92 will be described in more detail later with reference to FIGS.

Here, in this embodiment, at a timing different from the timing of normal image formation, such as before the start of printing or between sheets, the image pattern (toner image for image adjustment) formed on the intermediate transfer belt 8 by the image forming process described above is secondarily transferred onto the secondary transfer belt 71, not onto the sheet P, and the image pattern (or background portion) is optically detected by the optical sensor 85. Then, based on the result of detection by the optical sensor 85 in this way, various conditions during the secondary transfer process (secondary transfer bias, nip pressure of the secondary transfer nip, number of rotations of the secondary transfer roller 72, etc.) and the writing timing of each color YMCK by the writing unit 7 onto the photosensitive drum are adjusted. This optimizes the transfer efficiency (image density) in the secondary transfer process and reduces the positional deviation of the secondary transfer image on the sheet P.
The position of the optical sensor 85 in the width direction (main scanning direction) is set so as to coincide with the position in the width direction (writing position in the main scanning direction) of the image pattern written by the writing unit 7 (so that the image pattern can be detected).

In this manner, in this embodiment, the optical sensor 85 is installed to face the roller member (sensor facing roller 74) whose rotation center 74a is the rotation center of the secondary transfer subunit 70, and the optical sensor 85 is fixed so that it does not move in conjunction with the rotation of the secondary transfer subunit 70. As a result, even if the secondary transfer belt 71 (secondary transfer subunit 70) is rotated, the detection accuracy of the optical sensor 85 that detects the surface of the secondary transfer belt 71 is less likely to vary, and the secondary transfer unit 69 is less likely to become large and expensive.

Although not shown, in this embodiment, a plurality of optical sensors 85 are provided at intervals along the axial direction of the rotation center 74a of the sensor facing roller 74 (the left-right direction in FIG. 7).
Therefore, when adjusting the various conditions during the secondary transfer process described above and the writing timing of the writing unit 7, the image pattern (or background portion) formed on the secondary transfer belt 71 can be detected across the width direction (axial direction) by the multiple optical sensors 85. Therefore, based on the results of detection by the multiple optical sensors 85, the various conditions during the secondary transfer process and the writing timing of the writing unit 7 can be adjusted across the width direction with uniform precision.

The characteristic configuration and operation of the image forming apparatus 100 in this embodiment will be described in detail below with reference to Figures 6 to 9, etc. The characteristic configuration and operation of the image forming apparatus 100 in this embodiment will be described in detail below with reference to Figures 6 to 9, etc.

As described above, the image forming apparatus 100 in this embodiment is provided with the intermediate transfer unit 15, the secondary transfer unit 69, and the transport unit 60 (see FIGS. 6, 8A, etc.).

The intermediate transfer unit 15 is provided with an intermediate transfer belt 8 (intermediate transfer body) onto which an image (toner image) formed on the surface of a photoconductor drum 1Y (image carrier) is primarily transferred.
The intermediate transfer unit 15 is held in the image forming apparatus main body 100. Specifically, as shown in Fig. 8, in this embodiment, the intermediate transfer unit 15 is positioned (fixed) to main body side plates 110 provided at both ends in the width direction of the image forming apparatus main body 100 by screw fastening or the like.

The secondary transfer unit 69 as a holding member is held by the intermediate transfer unit 15 and rotatably holds the secondary transfer subunit 70. The secondary transfer unit 69 is provided with a cam 93 that abuts against the secondary transfer subunit 70 so as to adjust the contact pressure of the secondary transfer belt 71 against the intermediate transfer belt 8. The secondary transfer unit 69 is detachably held by the intermediate transfer unit 15 held in the image forming apparatus main body 100.
The secondary transfer subunit 70 as a movable body is provided with a secondary transfer belt 71 (secondary transfer member) for secondary transfer of an image (toner image) on the surface of the intermediate transfer belt 8 onto a sheet P transported to the secondary transfer nip with the intermediate transfer belt 8 (intermediate transfer body).

The transport unit 60 is configured to be able to transport the sheet P in a predetermined transport direction (the direction perpendicular to the paper surface in Figures 8 (A) and 9 (A), and the up-and-down direction in Figure 9 (B)), and is provided with a transport belt 61 (see Figures 1 and 3).
Here, in this embodiment, as shown in FIG. 8, the transport unit 60 is configured to be able to be pulled out in the width direction (the direction perpendicular to the transport direction, that is, to the right in FIG. 8) relative to the image forming apparatus main body 100 while holding the secondary transfer unit 69 (which is detached from the intermediate transfer unit 15 held in the image forming apparatus main body 100).

Specifically, the transport unit 60 is held in the image forming apparatus main body 100 via a slider (not shown) so as to be movable in the left-right direction in Fig. 8. The transport unit 60 is configured so that it can be pulled out from the image forming apparatus main body 100 together with the secondary transfer unit 69 in the direction of the white arrow as shown in Fig. 8(A) to the outside of the image forming apparatus main body 100 together with the secondary transfer unit 69 as shown in Fig. 8(B).
In this specification, the state in which the transport unit 60 is "removable" from the image forming apparatus main body 100 is defined to include not only a state in which the transport unit 60 can be pulled out so that only a portion of the transport unit 60 is exposed outside the image forming apparatus main body 100, but also a state in which the transport unit 60 is completely detached from the image forming apparatus main body 100.

8A and 8B, the operation of pulling out such a transport unit 60 (and secondary transfer unit 69) is performed by opening an opening/closing door 120 provided on the front side (the side (front) operated by the user) of the image forming apparatus 100 and gripping a handle (not shown) provided on the front side of the transport unit 60. When attaching (setting) the pulled-out transport unit 60 (and secondary transfer unit 69) to the image forming apparatus main body 100, the operation is performed in the reverse order to that of the operation when pulling out.
Such an operation is performed when removing a sheet P that has jammed (becomes jammed) at the position of the transport unit 60. In particular, in the embodiment, the secondary transfer unit 69 can be pulled out of the apparatus together with the transport unit 60, so that a sheet P that has jammed at the position of the secondary transfer nip can be easily removed.
In this embodiment, the writing unit 7 and the intermediate transfer unit 15 are not configured to be removable, but are fixed and installed in the image forming apparatus main body 100 by means of screws or the like.

Also, referring to Figure 8 (A), in this embodiment, when the transport unit 60 is attached to the image forming apparatus main body 100, the widthwise position of the secondary transfer unit 69 is not determined in the transport unit 60, but the widthwise position of the secondary transfer unit 69 relative to the intermediate transfer unit 15 is directly determined.
In detail, the contact surface (face plate 69a1) of the secondary transfer unit 69 abuts against a reference surface (reference plate 15a) formed on the intermediate transfer unit 15, thereby determining the widthwise position of the secondary transfer unit 69 relative to the intermediate transfer unit 15.

8A, when the transport unit 60 is attached to the image forming apparatus main body 100, the secondary transfer unit 69 is not held by the transport unit 60 but is in a floating state (non-held state) and can move to a certain extent in the width direction. In this embodiment, the image forming apparatus main body 100 is provided with a guide portion (not shown) that loosely holds the secondary transfer unit 69 in a floating state relative to the transport unit 60 attached to the image forming apparatus main body 100 so as to be movable in the width direction.
Furthermore, a face plate 69a1 serving as a contact surface is provided on the front surface (end surface on one end side) of a unit case 69a (see FIG. 9) of the secondary transfer unit 69 so as to be perpendicular to the width direction and the transport direction and to protrude towards the intermediate transfer unit 15. Then, with the face plate 69a1 (contact surface) of the secondary transfer unit 69 (unit case 69a) in contact with a reference plate 15a (reference surface) on one end side of the intermediate transfer unit 15, the position of the secondary transfer unit 69 (optical sensor 85) in the width direction relative to the intermediate transfer unit 15 is determined directly without going through other members.

In this embodiment, the widthwise position of the transport unit 60 relative to the image forming apparatus main body 100 (main body side plate 110) is determined with the reference surface (the side surface of the unit housing perpendicular to the widthwise direction and transport direction) of the other end side (left side in FIG. 8) of the transport unit 60 abutting against the main body side plate 110 of the image forming apparatus main body 100. At this time, the secondary transfer unit 69 is in a floating state in the transport unit 60 and its position is not determined, so there is no direct effect on the positioning of the secondary transfer unit 69 relative to the intermediate transfer unit 15.
Although not shown in the figure, when the transport unit 60 is set in the image forming device main body 100, the reference surface on one end side (the right side in Figure 8) of the transport unit 60 also abuts against the main body side panel of the image forming device main body 100, and the widthwise position of the transport unit 60 relative to the image forming device main body 100 (main body side panel) is determined.

Here, in the image forming apparatus 100 of this embodiment, when the transport unit 60 is attached to the image forming apparatus main body 100 (the state shown in Figure 8 (A)), a tension spring 65 is provided as a biasing member that biases the secondary transfer unit 69 in a direction in which the widthwise position of the secondary transfer unit 69 is determined relative to the intermediate transfer unit 15 (the direction in which the face plate 69a1 abuts against the reference plate 15a, which is the leftward direction in Figure 8 (A)).
More specifically, the tension spring 65 as a biasing member is connected to the transport unit 60 and the secondary transfer unit 69. That is, the tension spring 65 has a hook portion at one end (the right side in FIG. 8) connected to the secondary transfer unit 69, and a hook portion at the other end (the left side in FIG. 8) connected to the transport unit 60.
With this configuration, when the transport unit 60 is attached to the image forming apparatus main body 100, the secondary transfer unit 69, which is in a floating state (unheld state) in the transport unit 60, is urged by the tension spring 65 (urging member) to abut the face plate 69a1 against the reference plate 15a. Therefore, the secondary transfer unit 69 (optical sensor 85) is accurately positioned in the width direction relative to the intermediate transfer unit 15.

Also, referring to Figures 9 (and 8) etc., in this embodiment, when the transport unit 60 is attached to the image forming apparatus main body 100 (the state shown in Figure 8 (A)), in a state in which the position of the secondary transfer unit 69 in the width direction (main scanning direction) in the transport unit 60 is not determined, a positioning pin 15b is provided on the intermediate transfer unit 15 as a positioning member that determines the position of the secondary transfer unit 69 in the transport direction (sub-scanning direction) relative to the intermediate transfer unit 15.
Specifically, in this embodiment, two positioning pins 15b are installed on a reference plate 15a (reference surface) of the intermediate transfer unit 15 at positions spaced apart in the transport direction (sub-scanning direction) so as to stand up toward one end in the width direction. On the other hand, two positioning holes (not shown) are formed in a face plate 69a of the secondary transfer unit 69, into which the two positioning pins 15b of the intermediate transfer unit 15 are respectively fitted. Note that the other end in the width direction is configured similarly to the one end in the width direction, although the units to which the positioning pins and the positioning holes are installed are reversed.
The positioning pin 15b (positioning member) configured in this manner functions as a member that determines the position of the secondary transfer unit 69 in the transport direction (sub-scanning direction) relative to the intermediate transfer unit 15, and also functions as a member that keeps the secondary transfer unit 69 in a floating state (unheld state) in the transport unit 60. Therefore, as shown in Fig. 8B, when the transport unit 60 is pulled out in the direction of the white arrow, the secondary transfer unit 69 is released from engagement with the positioning pin 15b, falls by its own weight in the direction of the black arrow, and is held by the transport unit 60.
The configuration of the positioning member is not limited to that of this embodiment. For example, the relationship between the positioning pin 15b and the positioning hole in this embodiment can be reversed, a positioning hole can be formed in the intermediate transfer unit 15, and a positioning pin can be installed in the secondary transfer unit 69.

Also, referring to Figure 8, in this embodiment, when the transport unit 60, which is pulled out together with the secondary transfer unit 69 relative to the image forming device main body 100, is attached to the image forming device main body 100 (when changing from the state of Figure 8 (B) to the state of Figure 8 (A)), the position of the secondary transfer unit 69 relative to the intermediate transfer unit 15 is determined, and then the position of the transport unit 60 relative to the image forming device main body 100 is determined.
8B, in the process of pushing the transport unit 60 holding the secondary transfer unit 69 into the image forming apparatus main body 100 along a slider (not shown), first, the face plate 69a1 (contact surface) of the secondary transfer unit 69 comes into contact with the reference plate 15a (reference surface) of the intermediate transfer unit 15. At this time, the positioning pin 15b of the reference plate 15a fits into the positioning hole of the face plate 69a1, and the secondary transfer unit 69 is raised above the transport unit 60.
Then, with the secondary transfer unit 69 positioned, the transport unit 60 (which is not holding the secondary transfer unit 69) is pushed further into the image forming apparatus main body 100, and eventually, as shown in Figure 8 (A), the reference surface on the other end of the transport unit 60 abuts against the main body side panel 110, and the widthwise position of the transport unit 60 in the image forming apparatus main body 100 is determined.
To enable such an operation, the widthwise length from the reference surface on the other end side of the transport unit 60 to the face plate 69a1, the widthwise length from the main body side plate 110 to the reference plate 15a, etc. are set.
Furthermore, by configuring in this manner, it is possible to smoothly transition from a state in which the transport unit 60 holds the secondary transfer unit 69 when pulled out to a state in which the transport unit 60 does not hold the secondary transfer unit 69 when installed (or vice versa, from installation to pulling out).

Thus, in this embodiment, when the transport unit 60 is set in the image forming apparatus main body 100, the transport unit 60 is completely held in the image forming apparatus main body 100 and becomes part of the image forming apparatus main body 100.
Furthermore, when the transport unit 60 is set in the image forming apparatus main body 100, the secondary transfer unit 69 is held by the intermediate transfer unit 15. In other words, when the transport unit 60 is set in the image forming apparatus main body 100, the secondary transfer unit 69 as a holding member is held by the image forming apparatus main body 100 via the intermediate transfer unit 15.

Here, as shown in Figures 6 to 8, in this embodiment, the motor 97 is not held by either the intermediate transfer unit 15 or the secondary transfer unit 69, but is indirectly held by the image forming apparatus main body 100 so as to be able to rotate the cam 93.
More specifically, the motor 97 which is the driving source for the cam 93 of the cam mechanism 92 is fixedly installed on the transport unit 60. Therefore, the motor 97 is held by the image forming apparatus main body 100 via the transport unit 60 (which is in a state of being attached to the image forming apparatus main body 100).

In this manner, in the present embodiment, the motor 97 for driving the cam 93 installed in the secondary transfer unit 69 held in the intermediate transfer unit 15 is held not in the secondary transfer unit 69 or the intermediate transfer unit 15 but in the image forming apparatus main body 100 (the transport unit 60), and therefore the load applied to the intermediate transfer unit 15 can be made relatively small.
That is, compared to a case in which a relatively heavy motor 97 is supported by the secondary transfer unit 69 or the intermediate transfer unit 15, the load applied to the intermediate transfer unit 15 or the secondary transfer unit 69 can be reduced.
Therefore, problems such as deformation of the intermediate transfer unit 15 and the secondary transfer unit 69 due to excessive load are less likely to occur.

In this embodiment, in order to adjust the nip pressure (the amount of rotation of the cam 93) by the cam mechanism 92 with high accuracy, a hybrid type stepping motor is used as the motor 97.
As shown in FIG. 7, a transmission type photosensor 106 (and a detection plate 105) is provided as a detection means for detecting the amount of rotation of the cam 93. The detection plate 105 is installed coaxially with the support shaft (rotation shaft) of the cam 93. The detection plate 105 has a light transmitting portion (or a light shielding portion) formed so that the position in the rotation direction coincides with the contact position (the position of the outer circumferential surface that contacts the unit side plate 70a) of the cam 93 corresponding to the nip pressure (secondary transfer nip pressure) adjusted in at least two stages. The light transmitting portion (or the light shielding portion) of the detection plate 105 is optically detected by the transmission type photosensor 106 that is installed non-rotatingly so as to sandwich the detection plate 105, so that the amount of rotation of the cam 93 is accurately grasped by the control unit 90. Based on the detection result, the control unit 90 controls the rotation drive of the motor 97 (hybrid type stepping motor).
This allows the cam mechanism 92 to adjust the nip pressure (secondary transfer nip pressure) with high precision.

Furthermore, image forming apparatus 100 in this embodiment is configured such that the drive of motor 97 is transmitted to cam 93 via drive transmission mechanisms 94 to 96. With reference to Figure 7 etc., the drive transmission mechanism is configured with a drive pulley 96 that is rotationally driven by motor 97, a driven pulley 94 that rotates together with cam 93, and a timing belt 95 that is wound (tensioned) around drive pulley 96 and driven pulley 94.
Therefore, the motor 97 and a part of the drive transmission mechanisms 94 to 96 (the drive pulley 96 ) are held by the image forming apparatus main body 100 via the transport unit 60 .

In this manner, in this embodiment, the drive force of the motor 97 installed in the transport unit 60 is transmitted to the cam 93 installed in the secondary transfer unit 69 via the timing belt 95 .
Therefore, as shown in Fig. 8A, when the transport unit 60 and the secondary transfer unit 69 are set in the image forming apparatus main body 100, the timing belt 95 is stretched with a predetermined tension between the drive pulley 96 located on the motor shaft of the motor 97 and the driven pulley 94 located on the same axis as the cam 93 (a state in which drive transmission is possible). On the other hand, as shown in Fig. 8B, when the transport unit 60 is pulled out from the image forming apparatus main body 100, the secondary transfer unit 69 that has moved (dropped) in the direction of the black arrow is placed on the transport unit 60 as described above, so that the axial distance between the drive pulley 96 located on the motor shaft of the motor 97 and the driven pulley 94 located on the same axis as the cam 93 becomes shorter, and the tension of the timing belt 95 becomes loose.
In other words, by using the timing belt 95 as the drive transmission mechanism, even if the motor 97 is installed in the transport unit 60 and the cam 93 is installed in the secondary transfer unit 69, it is possible for the secondary transfer unit 69 to move up and down relative to the transport unit 60 in conjunction with the attachment and detachment operations of the transport unit 60, as previously described using Figures 8 (A) and (B).
In addition, it is preferable to provide a guide portion for maintaining the position of timing belt 95 so that the loosened timing belt 95 does not fall off when in the state of Figure 8 (B) (so that timing belt 95 is stretched around pulleys 94, 96 when changing from the state of Figure 8 (B) to the state of Figure 8 (A)).

In this embodiment, a timing belt 95 is used as a drive transmission mechanism that transmits the drive of the motor 97 installed in the transport unit 60 to the cam 93 installed in the secondary transfer unit 69. However, it is also possible to use a drive transmission mechanism that does not use a timing belt (for example, a drive transmission mechanism composed only of a gear train). In that case, however, it becomes difficult to enable the secondary transfer unit 69 to move up and down relative to the transport unit 60 when the transport unit 60 is attached or detached, as described above.

Here, as shown in Figure 8 (A) etc., in this embodiment, the cams 93 are installed at both ends of the axial direction (the direction perpendicular to the transport direction of the sheet P, the left-right direction in Figure 8, and the width direction) of the secondary transfer unit 69.
Two drive transmission mechanisms (motors 97) are provided to rotate the two cams 93, respectively.
That is, in the image forming apparatus 100, cam mechanisms 92 to 97 for adjusting the nip pressure are provided at both ends in the width direction.
With this configuration, the secondary transfer subunit 70 can be pressurized and adjusted in a well-balanced manner by the cam mechanism 92, and the nip pressure (secondary transfer nip pressure) can be adjusted in a well-balanced manner across the width.

The cam mechanism 92, which is a feature of this embodiment, will be described in detail below with reference to FIG. 10 (as well as FIGS. 7 and 12).
As previously explained using Figures 6, 7, etc., the cam mechanism 92 in this embodiment is provided with a cam 93 for contacting the secondary transfer subunit 70 as a movable body to move the secondary transfer subunit 70 (moving it up and down), and drive transmission mechanisms 94-97 (drive mechanisms) for rotating the cam 93 in forward and reverse directions (clockwise and counterclockwise in Figure 10) around the support shaft 91.

The cam 93 is rotatably held by the secondary transfer unit 69 serving as a holding member.
More specifically, a support shaft 91 that rotatably supports a cam 93 is held (fixed) in a non-rotatable manner by the secondary transfer unit 69 as a holding member. With reference to Figures 7, 8A, etc., the support shaft 91 is provided as a bridge between both side plates of the secondary transfer unit 69. The cams 93 (and the driven pulley and detected plate 105) are rotatably provided on both axial ends of the support shaft 91.

7 and 12, the drive transmission mechanism includes a driven pulley 94, a timing belt 95, a drive pulley 96, a motor 97, and the like.
The driven pulley 94 is rotatably mounted on the support shaft 91 together with the cam 93 and the detected plate 105 so as to face an opposite side surface 93n (side surface) opposite to a side surface 93m (a side surface from which pins 79A and 79B, described later, stand) of the cam 93. Specifically, the support shaft 91 is inserted into a central hole 93x (actually formed at an eccentric position) of the cam 93, a central hole 94x of the driven pulley 94, and a central hole 105x of the detected plate 105. The cam 93, the driven pulley 94, and the detected plate 105 are rotatably mounted on the support shaft 91 in the order from the end side toward the center so as to be in close contact with each other. The cam 93 has a fitting hole 93w (a hole that passes through both side surfaces 93m, 93n) into which the protrusion 94a of the driven pulley 94 fits, and the driven pulley 94 has a fitting hole 94w into which the protrusion 105a of the detected plate 105 fits.
A timing belt 95 is wound around a driven pulley 94 and a driving pulley 96. A motor 97 drives and rotates the driving pulley 96, which is attached to a motor shaft. The motor 97 is a hybrid stepping motor that can rotate in both forward and reverse directions.
With this configuration, when the motor 97 is driven under the control of the control unit 90 , the cam 93 , the driven pulley 94 and the detected plate 105 rotate integrally about the support shaft 91 .

Specifically, when the motor 97 is driven in the forward direction, the cam 93, the driven pulley 94, and the detected plate 105 rotate integrally around the support shaft 91 in the forward direction (the direction of the arrow in Figure 8 (A) (clockwise)), causing the secondary transfer subunit 70 as a movable body to move upward (rotation in the direction of the arrow in Figure 5 (A)).
In contrast, when the motor 97 is driven in the reverse direction, the cam 93, the driven pulley 94, and the detected plate 105 rotate together around the support shaft 91 in the reverse direction (the direction of the arrow in Figure 8 (B) (counterclockwise)), and the secondary transfer subunit 70 as a movable body moves downward (rotation in the direction of the arrow in Figure 5 (B)).

Here, referring to Figure 10 etc., in this embodiment, the cam 93 has a step portion 93c formed on its cam surface (this is the peripheral surface that can actually abut against the secondary transfer subunit 70 if the rotation range is not limited).
In this specification, the "step portion" of a cam is defined as the step portion between the top dead point of the cam (the position on the cam surface where the distance (radius) from the cam center is the longest) and the bottom dead point (the position on the cam surface where the distance (radius) from the cam center is the shortest).
A step portion with a large step is required when, for example, it is desired to set as large as possible the distance (rotation angle) from the bottom dead center to the top dead center when the cam rotates in a specified direction, or when it is desired to set as large as possible the difference between the radius from the cam center to the bottom dead center and the radius to the top dead center.

Specifically, as shown in FIG. 10, in this embodiment, the cam surface of the cam 93 is formed so that the distance (radius) from the cam center (support shaft 91) gradually increases in the counterclockwise direction (reverse direction) from the bottom dead center 93b (start point) to the top dead center 93a (end point). The cam surface of the cam 93 is formed with a step portion 93c in which the distance (radius) from the cam center (support shaft 91) changes suddenly in the counterclockwise direction (reverse direction) from the top dead center 93a to the bottom dead center 93b. The step portion 93c in this embodiment is not a substantially straight line connecting the top dead center 93a to the bottom dead center 93b, but is curved toward the cam center so that the top dead center 93a protrudes in a substantially claw-like shape. This allows an operator in a manufacturing factory or the like to install the cam 93 in the cam mechanism 92 in the correct posture (position in the rotation direction) while visually checking the position of the top dead center 93a of the cam 93.

7, 10, 12, etc., the cam 93 in this embodiment is provided on its side surfaces 93m, 93n (see FIG. 12) with pins 79A, 79B as cam side protrusions that protrude laterally.
The secondary transfer unit 69 as a holding member is provided with holding member side protrusions 88A, 88B as limiting members. The holding member side protrusions 88A, 88B contact the pins 79A, 79B as cam side protrusions and function as limiting members that limit the rotation range of the cam 93 so that the secondary transfer subunit 70 (unit side plate 70a) as a movable body does not contact the step portion 93c of the cam 93. For more details, referring to FIG. 7, the secondary transfer unit 69 (holding member) is formed with a surface portion 69m that faces a side surface 93m of the cam 93 (the side surface from which the pins 79A, 79B protrude). The holding member side protrusions 88A, 88B (limiting members) are formed so as to protrude from the surface portion 69m toward the side surface 93m of the cam 93. Specifically, as the holding member side protrusions 88A, 88B, for example, screws that are screwed into a female threaded portion formed on the surface portion 69m so that the screw head protrudes towards the cam 93 side can be used.

In other words, in this embodiment, the cam 93 is not configured so that its entire circumference (all rotational range of one revolution) can come into contact with the secondary transfer sub-unit 70 (unit side plate 70a), but is configured so that only the rotational range excluding the step portion 93c can come into contact with the secondary transfer sub-unit 70 (unit side plate 70a) by allowing the holding member side protrusions 88A, 88B to interfere with the pins 79A, 79B.

Specifically, as shown in FIG. 10, in this embodiment, a first pin 79A serving as a first cam side protrusion and a second pin 79B serving as a second cam side protrusion are provided as the cam side protrusion.
The first pin 79A (first cam side protrusion) is configured to be able to come into contact with the first holding member side protrusion 80A as a first limiting member when the cam 93 rotates in the forward direction (the direction of the arrow in FIG. 10A, which is the direction that pushes up the secondary transfer subunit 70) as shown in FIG. 10A. The contact position between this first pin 79A and the first holding member side protrusion 80A is set so that the cam 93 does not rotate too far in the forward direction and exceed the position of the top dead center 93a, causing the step portion 93c to come into contact with the secondary transfer subunit 70 (unit side plate 70a). This prevents the secondary transfer subunit 70 (unit side plate 70a) from coming into contact with the step portion 93c and being suddenly displaced.
In contrast, the second pin 79B (second cam side protrusion) is configured to be able to come into contact with the second holding member side protrusion 80B (installed at a different position from the first holding member side protrusion 80A) as a second limiting member when the cam 93 rotates in the reverse direction (the direction of the arrow in FIG. 10B, which is the direction in which the secondary transfer subunit 70 is lowered) as shown in FIG. 10B. The contact position between the second pin 79B and the second holding member side protrusion 80B is set so that the cam 93 does not rotate too far in the reverse direction and the step portion 93c does not come into contact with the secondary transfer subunit 70 (unit side plate 70a) beyond the position of the bottom dead center 93b. Therefore, a problem in which the secondary transfer subunit 70 (unit side plate 70a) comes into contact with the step portion 93c and is suddenly displaced is prevented.

In this manner, in the cam mechanism 92 in this embodiment, the rotation range of the cam 93 is limited by mechanical contact between the pins 79A, 70B (cam side protrusions) and the holding member side protrusions 80A, 80B (restriction members). Therefore, it is possible to mechanically and stably reduce the problem that the stepped portion 93c of the cam 93 abuts against the secondary transfer subunit 70 (unit side plate 70a).
More specifically, in this embodiment, the detection plate 105 that rotates together with the cam 93 on the support shaft 91 is detected by the transmission type photosensor 106 to grasp the attitude (rotational position) of the cam 93, and the rotation range of the cam 93 can be electrically controlled so that the step portion 93c of the cam 93 does not come into contact with the secondary transfer subunit 70 (unit side plate 70a). However, if the transmission type photosensor 106 breaks down, such control cannot be performed, and a problem occurs in which the step portion 93c of the cam 193 (which does not have a cam side protrusion) shown as a comparative example in Figures 11 (A) and (B) comes into contact with the secondary transfer subunit 70. In such a case, when the secondary transfer subunit 70 comes into contact with the step portion 93c, the secondary transfer subunit 70 is suddenly displaced and receives an impact force (see Figure 8 (B)). Such an impact force may damage the secondary transfer subunit 70 or may upset the adjustment accuracy of components that have been delicately adjusted in a manufacturing factory.
In contrast, in the present embodiment, the rotation range of the cam 93 is mechanically limited so that the stepped portion 93c of the cam 93 does not come into contact with the secondary transfer subunit 70, making such a problem less likely to occur.

In this embodiment, at least two cams 93 (cam mechanism 92) and holding member side protrusions 80A, 80B (regulating members) are provided at positions spaced apart in the axial direction.
Specifically, in this embodiment, as described above with reference to Fig. 8A etc., a cam mechanism 92 is provided at each of both axial ends (two cam mechanisms 92 are provided). Then, holding member side protrusions 80A, 80B (regulating members) are provided at both axial ends in correspondence with the cams 93 of the cam mechanisms 92 at both axial ends.
In this embodiment, the cam mechanism 92 and the holding member side protrusions 80A, 80B (regulating members) are disposed symmetrically in the axial direction.

12, in this embodiment, the pins 79A, 79B as the cam side protrusions are separate parts from the cam 93, and can also be installed on the opposite side surface 93n of the cam 93 opposite the side surface 93m.
More specifically, the cam 93 is formed with a through hole 93z penetrating between the side surface 93m and the opposite side surface 93n. The pins 79A and 79B (cam side protrusions) are configured to be able to fit into the through hole 93z. Specifically, the base sides of the two pins 79A and 79B are press-fitted into the two through holes 93z so that the tip sides protrude so as to be able to come into contact with the corresponding holding member side protrusions 80A and 80B, respectively.
With this configuration, the cams 93 installed at both ends in the axial direction can be used symmetrically as common parts simply by changing the side surfaces 79m, 79n on which the pins 79A, 79B are installed. In addition, the driven pulley 94 and the detected plate 105 installed at both ends in the axial direction can also be used symmetrically by flipping them left and right as shown in FIG.
Therefore, the number of parts in the cam mechanism 92 is reduced.

<Modification 1>
As shown in Figure 13, in variant example 1, as a regulating member installed on surface 69m of secondary transfer unit 69 (holding member), rather than using two holding member side protrusions 80A, 80B as in Figure 10, a single holding member side protrusion 80 is used.
That is, the first pin 79A (first cam side protrusion) is configured to be able to come into contact with one end of the holding member side protrusion 80 (restriction member) when the cam 93 rotates in the forward direction as shown in Fig. 13(A), and the second pin 79B (second cam side protrusion) is configured to be able to come into contact with the other end of the same holding member side protrusion 80 (restriction member) when the cam 93 rotates in the reverse direction as shown in Fig. 13(B).
Even in this configuration, it is possible to stably reduce the problem that the stepped portion 93c of the cam 93 comes into contact with the secondary transfer subunit 70 (movable body).

<Modification 2>
As shown in FIG. 14, the cam mechanism 92 (image forming apparatus 100) in variant example 2 has a drive transmission mechanism for transmitting the drive of a motor 97 held in the transport unit 60 (image forming apparatus main body 100) to a cam 93 held in the secondary transfer unit 69, which has a configuration different from that shown in FIG.
The image forming apparatus 100 in the modified example 2 is configured in the same manner as that described using Figures 1 to 8, 10, etc., except for the difference in the configuration of the drive transmission mechanism, and a secondary transfer unit 69 is held by the intermediate transfer unit 15.
As shown in FIG. 14, the drive transmission mechanism in the second variant is composed of a drive gear 99 mounted on the motor shaft of a motor 97, a driven gear 98 meshing with the drive gear 99, a drive pulley 96 (a drive pulley that is driven to rotate by the motor 97 via a gear train 98, 99) mounted coaxially with the driven gear 98, a driven pulley 94 that rotates together with the cam 93, and a timing belt 95 stretched between the drive pulley 96 and the driven pulley 94.
In this case, a part of the drive transmission mechanisms 94 to 97 , 98 , and 99 (the motor 97 , the drive gear 99 , the driven gear 98 , and the drive pulley 96 ) is held by the image forming apparatus main body 100 via the transport unit 60 .
Even in this configuration, it is possible to stably reduce the problem that the stepped portion 93c of the cam 93 comes into contact with the secondary transfer subunit 70 (movable body).
The "drive transmission mechanism" is not limited to the one shown in FIG. 7 or FIG. 14, and other types may be used.

<Modification 3>
As shown in FIG. 15, in the cam mechanism 92 (image forming apparatus 100) in the modified example 3, the motor 97 is not held by either the intermediate transfer unit 15 or the secondary transfer unit 69, but is held directly by the image forming apparatus main body 100 so as to be able to rotate the cam 93.
That is, the motor 97 in the third modification is not indirectly held by the image forming apparatus main body 100 via the transport unit 60 as in the one shown in Fig. 6, but is directly held by the image forming apparatus main body 100. The image forming apparatus 100 in the third modification is configured similarly to that described using Figs. 1 to 8, 10, etc., except that the motor 97 is directly held by the image forming apparatus main body 100, and the secondary transfer unit 69 is held by the intermediate transfer unit 15.
15, the image forming apparatus main body 100 is provided with main body stays 115 that are bridged to main body side plates 110 (see FIG. 8A) that are installed at both ends in the width direction. The motor 97 is held (fixed) by the main body stays 115 of the image forming apparatus main body 100.
In this embodiment, the cam 93 of the cam mechanism 92 is configured so as not to directly contact the unit side plate 70a of the secondary transfer subunit 70, but to contact a roller 70a1 that is rotatably supported on the unit side plate 70a.
Even in this configuration, it is possible to stably reduce the problem that the stepped portion 93c of the cam 93 comes into contact with the secondary transfer subunit 70 (movable body).

As described above, the cam mechanism 92 (image forming apparatus 100) in this embodiment includes a cam 93 for contacting the secondary transfer subunit 70 (movable body) to move the secondary transfer subunit 70, and drive transmission mechanisms 94 to 97 for driving the cam 93 to rotate in forward and reverse directions. The cam 93 has a step portion 93c formed on the cam surface of the cam 93, and is provided such that the pins 79A and 79B (cam side protrusions) protrude laterally from the side surface 93m (93n) of the cam 93. The holding member side protrusions 80A and 80B (limiting members) are provided to contact the pins 79A and 79B and limit the rotation range of the cam 93 so that the secondary transfer subunit 70 does not contact the step portion 93c of the cam 93.
This makes it possible to stably reduce the problem of the stepped portion 93c of the cam 93 coming into contact with the secondary transfer subunit 70 (movable body).

In this embodiment, the present invention is applied to a cam mechanism 92 in which the secondary transfer subunit 70 is the movable body and the secondary transfer unit 69 is the holding member, but the cam mechanism to which the present invention is applied is not limited to this, and the present invention can naturally be applied to a cam mechanism in which a member other than the secondary transfer subunit 70 is the movable body, or a member other than the secondary transfer unit 69 is the holding member.
In addition, in this embodiment, the present invention is applied to an image forming apparatus 100 in which a secondary transfer unit 69 using a secondary transfer belt 71 as a secondary transfer member is installed, but the image forming apparatus to which the present invention is applied is not limited to this, and the present invention can also be applied, for example, to an image forming apparatus in which a secondary transfer unit using a secondary transfer roller as a secondary transfer member is installed.
Furthermore, in this embodiment, the present invention is applied to an image forming apparatus 100 in which an intermediate transfer unit 15 using an intermediate transfer belt 8 as an intermediate transfer body is installed, however, the image forming apparatus to which the present invention is applied is not limited to this, and for example, the present invention can also be applied to an image forming apparatus in which an intermediate transfer unit using an intermediate transfer drum as an intermediate transfer body is installed.
In the present embodiment, the present invention is applied to the image forming apparatus 100 that forms color images. However, the present invention can also be applied to an image forming apparatus that forms only monochrome images.
In addition, in this embodiment, the intermediate transfer unit 15 is configured to be directly held by the image forming apparatus main body 100, but the intermediate transfer unit 15 can also be configured to be indirectly held by the image forming apparatus main body 100 via another member (e.g., a slider, etc.).
Even in such cases, the same effects as those of this embodiment can be obtained.

It is clear that the present invention is not limited to this embodiment, and that within the scope of the technical concept of the present invention, this embodiment may be modified as appropriate in ways other than those suggested in this embodiment. Furthermore, the number, position, shape, etc. of the components are not limited to this embodiment, and may be any number, position, shape, etc. that is suitable for implementing the present invention.

1Y, 1M, 1C, 1K photoconductor drums (image carriers),
8 intermediate transfer belt (intermediate transfer body),
15 intermediate transfer unit,
60 Transport unit,
69 Secondary transfer unit (holding member),
69m face,
70 Secondary transcription subunit (mobile body),
70a: unit side plate,
71 secondary transfer belt (secondary transfer member),
72 secondary transfer roller (roller member),
74a rotation center (rotation center axis),
79A first pin (cam side protrusion, first cam side protrusion),
79B second pin (cam side protrusion, second cam side protrusion),
88, 88A, 88B: Holding member side protrusion (restricting member),
91 Support shaft,
92 cam mechanism,
93 Cam,
93a top dead center, 93b bottom dead center, 93c step portion,
93m side, 93n opposite side,
93z through hole,
94 driven pulley (drive transmission mechanism),
95 Timing belt (drive transmission mechanism),
96 Drive pulley (drive transmission mechanism),
97 Motor (drive transmission mechanism),
100 Image forming apparatus (image forming apparatus body).

In addition, the aspects of the present invention can also be combinations of Supplementary Notes 1 to 9 as follows.
(Appendix 1)
A cam for contacting the movable body to move the movable body;
a drive transmission mechanism that rotates the cam in forward and reverse directions;
Equipped with
The cam has a step portion formed on a cam surface of the cam, and a cam side protrusion is provided on a side surface of the cam so as to protrude laterally,
A cam mechanism comprising: a limiting member that contacts the cam protrusion and limits a rotation range of the cam so that the movable body does not contact the stepped portion.
(Appendix 2)
A holding member that rotatably holds the cam is provided,
2. The cam mechanism according to claim 1, wherein the limiting member is provided on the holding member.
(Appendix 3)
the holding member has a surface portion facing the side surface of the cam,
The cam mechanism according to claim 2, wherein the limiting member is a retaining member side protrusion formed on the surface portion so as to protrude toward the side surface.
(Appendix 4)
The cam mechanism according to any one of claims 1 to 3, wherein the cam side protrusion is a separate part from the cam and can be installed on the opposite side surface of the cam opposite the side surface.
(Appendix 5)
The cam has a through hole formed therein, the through hole passing between the side surface and the opposite side surface,
The cam mechanism according to claim 4, wherein the cam side protrusion is a pin that can be fitted into the through hole.
(Appendix 6)
The cam side protrusion is
a first cam side protrusion that comes into contact with the limiting member when the cam rotates in the forward direction;
a second cam side protrusion that contacts the limiting member or a second limiting member that is installed at a position different from that of the limiting member when the cam rotates in the reverse direction;
6. The cam mechanism according to claim 1, further comprising:
(Appendix 7)
a support member for supporting a support shaft that rotatably supports the cam;
The drive transmission mechanism includes:
A driven pulley is provided on the support shaft so as to be rotatable together with the cam and to face the opposite side surface of the side surface;
a timing belt wound around the driven pulley and the driving pulley;
A motor that rotates the drive pulley;
7. The cam mechanism according to claim 1, further comprising:
(Appendix 8)
The cam mechanism according to any one of claims 1 to 7, characterized in that at least two of the cams and the regulating members are provided at positions spaced apart in the axial direction.
(Appendix 9)
An image forming apparatus comprising the cam mechanism according to any one of claims 1 to 8.

JP 2019-159142 A

Claims (9)

A cam for contacting the movable body to move the movable body;
a drive transmission mechanism that rotates the cam in forward and reverse directions;
Equipped with
The cam has a step portion formed on a cam surface of the cam, and a cam side protrusion is provided on a side surface of the cam so as to protrude laterally,
A cam mechanism comprising: a limiting member that contacts the cam protrusion and limits a rotation range of the cam so that the movable body does not contact the stepped portion. A holding member that rotatably holds the cam is provided,
2. The cam mechanism according to claim 1, wherein the restricting member is provided on the holding member. the holding member has a surface portion facing the side surface of the cam,
3. The cam mechanism according to claim 2, wherein the restricting member is a holding member-side protrusion formed on the surface portion so as to protrude toward the side surface. The cam mechanism according to claim 1 or 2, characterized in that the cam-side protrusion is a separate part from the cam and can be installed on the opposite side of the cam to the side opposite the side of the cam. The cam has a through hole formed therein, the through hole passing between the side surface and the opposite side surface,
5. The cam mechanism according to claim 4, wherein the cam side projection is a pin that can be fitted into the through hole. The cam side protrusion is
a first cam side protrusion that comes into contact with the limiting member when the cam rotates in the forward direction;
a second cam side protrusion that contacts the limiting member or a second limiting member that is installed at a position different from that of the limiting member when the cam rotates in the reverse direction;
3. The cam mechanism according to claim 1, further comprising: a support member for supporting a support shaft that rotatably supports the cam;
The drive transmission mechanism includes:
A driven pulley is provided on the support shaft so as to be rotatable together with the cam and to face the opposite side surface of the side surface;
a timing belt wound around the driven pulley and the driving pulley;
A motor that rotates the drive pulley;
3. The cam mechanism according to claim 1, further comprising: The cam mechanism according to claim 1 or 2, characterized in that at least two of the cams and the regulating members are provided at positions spaced apart in the axial direction. An image forming device comprising the cam mechanism according to claim 1 or 2.

Images