JP2018169450A - Image forming apparatus - Google Patents

Abstract

To reduce a deterioration in image quality accompanying an impact at the entry of a medium, compared with a configuration where only the amount of biting of a transfer member into an image holding body is changed according to a transfer condition.SOLUTION: An image forming apparatus (U) comprises: a transfer member (T2b) that transfers an image held on an image holding body (B) to a medium (S), the transfer member (T2b) supported movably in a direction approaching or separating from the image holding body (B); pressing members (12) that press the transfer member (T2b) against the image holding body (B); a first adjustment device (6) that adjusts the amount of biting of the transfer member (T2b) into the image holding body (B) according to a transfer condition; and a second adjustment device (17) that increases or decreases a pressing force (f1) of the pressing members (12) in conjunction with the adjustment of the biting amount and with a tendency according to the increase or decrease of the biting amount.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  In the image forming apparatus, a technique described in Patent Document 1 below is conventionally known as a technique for suppressing an image defect caused by an impact when a medium enters a transfer region.

  In Japanese Patent Application Laid-Open No. 2015-102836 as Patent Document 1, a pressing force is applied to the intermediate transfer unit in a direction opposite to the pressing direction by the secondary transfer member in accordance with the timing at which the recording medium enters the secondary transfer unit. The structure which gives is described.

Japanese Patent Laying-Open No. 2015-102836 (“0044” to “0049”, FIGS. 2 and 3)

  It is a technical object of the present invention to reduce image quality deterioration due to an impact at the time of entering a medium, as compared with a configuration in which only the amount of biting of a transfer member into an image carrier is changed according to transfer conditions.

In order to solve the technical problem, an image forming apparatus according to claim 1 is provided.
An image carrier,
A transfer member for transferring an image held on the image carrier to a medium, the transfer member supported so as to be movable toward and away from the image carrier;
A pressing member that presses the transfer member toward the image carrier;
A first adjusting device that adjusts an amount of biting of the transfer member into the image holding member according to transfer conditions;
In conjunction with the adjustment of the amount of biting, a second adjustment device that increases or decreases the pressing force of the pressing member with a tendency according to the increase or decrease of the amount of biting,
It is provided with.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
A first support that supports the transfer member so as to be movable toward and away from the image carrier;
The first adjusting device having a first actuating member for actuating the first support;
It is provided with.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
A first support that supports the transfer member so as to be movable toward and away from the image carrier;
The pressing member configured by a spring that presses the first support;
A second support member that supports the pressing member and is supported so as to be movable toward and away from the image carrier, and the second support member that approaches and separates from the image carrier. A second actuating member that moves in the same direction as the moving direction of the first support, and
It is provided with.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect,
A first support that supports the transfer member so as to be movable toward and away from the image carrier;
The pressing member configured by a spring that presses the first support;
A second support member that supports the pressing member and is supported so as to be movable toward and away from the image carrier, and the second support member that approaches and separates from the image carrier. A second actuating member that moves in a direction to move, the second adjusting device,
With
The second support body is moved so that the first support body generated by the pressing member relaxes the increase and decrease of the force pushing the first adjusting device.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect,
The second actuating member set such that the amount of movement of the second support is greater than the amount of movement of the first support;
It is provided with.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects,
A drive source for driving the first adjustment device and driving the second adjustment device;
It is provided with.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects,
The second adjusting device for continuously changing the pressing force of the pressing member according to the change in the amount of biting;
It is provided with.

The invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 6,
The second adjusting device that changes the pressing force of the pressing member stepwise in accordance with the change in the amount of biting;
It is provided with.

According to the first aspect of the present invention, it is possible to reduce image quality deterioration due to impact at the time of entering the medium, compared to a configuration in which only the amount of biting of the transfer member into the image carrier is changed according to the transfer conditions. .
According to the second aspect of the present invention, the amount of biting of the transfer member can be adjusted by moving the first support with the first adjusting device.
According to the third aspect of the invention, the pressing force of the pressing member can be adjusted by moving the second support with the second adjusting member.
According to the fourth aspect of the present invention, the first support is compared with the case where the second support is not moved so as to reduce the increase or decrease in the force with which the first support presses the first adjusting device. The force with which the body pushes the first adjusting device can be reduced. Therefore, the rigidity of the component parts can be reduced, and the manufacturing cost can be reduced.

According to invention of Claim 5, pressing force can be changed according to the amount of biting.
According to the sixth aspect of the present invention, the drive source can be shared, and the manufacturing cost can be reduced as compared with the case where the drive source is provided separately.
According to the seventh aspect of the present invention, it is possible to increase the effect of suppressing the image quality deterioration caused by the impact, compared to the case where the change is made in stages.
According to the eighth aspect of the present invention, control can be facilitated as compared with the case of continuously changing.

FIG. 1 is an overall explanatory view of an image forming apparatus according to a first embodiment. FIG. 2 is an enlarged explanatory diagram of the visible image forming apparatus according to the first embodiment. FIG. 3 is an explanatory diagram of a mechanism for adjusting the amount of biting in the image forming apparatus according to the first embodiment. FIG. 4 is an explanatory diagram of the relationship between the secondary transfer load and the amount of biting in Example 1, and is a graph with the amount of biting on the horizontal axis and the load on the vertical axis. FIG. 5 is an explanatory diagram of the relationship between the amount of movement of the moving member and the amount of secondary transfer biting in Example 1, where the horizontal axis represents the amount of movement of the housing and the movable frame, and the vertical axis represents the secondary transfer biting amount. This is a graph taken. FIG. 6 is a block diagram illustrating the functions of the control unit of the image forming apparatus according to the first embodiment. FIG. 7 is an explanatory diagram of the relationship between the secondary transfer load and the amount of biting in the prior art, and is a graph with the biting amount on the horizontal axis and the load on the vertical axis.

Next, examples as specific examples of embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following examples.
In order to facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, the up-down direction is the Z-axis direction, and arrows X, -X, Y, -Y, The direction indicated by Z and -Z or the indicated side is defined as the front side, the rear side, the right side, the left side, the upper side, the lower side, or the front side, the rear side, the right side, the left side, the upper side, and the lower side, respectively.
In the figure, “•” in “○” means an arrow heading from the back of the page to the front, and “×” in “○” is the front of the page. It means an arrow pointing from the back to the back.
In the following description using the drawings, illustrations other than members necessary for the description are omitted as appropriate for easy understanding.

FIG. 1 is an overall explanatory view of an image forming apparatus according to a first embodiment.
FIG. 2 is an enlarged explanatory diagram of the visible image forming apparatus according to the first embodiment.
In FIG. 1, a copying machine U as an example of an image forming apparatus includes an operation unit UI, a scanner unit U1 as an example of an image reading device, a feeder unit U2 as an example of a medium supply device, and an image recording device as an example. It has an image unit U3 and a medium processing device U4.

(Description of operation unit UI)
The operation unit UI has an input button UIa used for starting copying or setting the number of copies. Further, the operation unit UI has a display unit UIb on which the content input by the input button UIa and the state of the copying machine U are displayed.

(Description of feeder unit U2)
In FIG. 1, the feeder unit U2 has a plurality of paper feed trays TR1, TR2, TR3, TR4 as an example of a medium container. The feeder unit U2 has a medium supply path SH1 for taking out the recording paper S as an example of the image recording medium accommodated in each of the paper feed trays TR1 to TR4 and transporting it to the image forming unit U3. doing.

(Description of image forming unit U3 and medium processing device U4)
In FIG. 1, the image forming unit U3 includes an image recording unit U3a that records an image on the recording sheet S conveyed from the feeder unit U2 based on a document image read by the scanner unit U1.
1 and 2, the drive circuit D of the latent image forming apparatus of the image forming unit U3 is configured to output each color Y at a preset timing based on the image information input from the scanner unit U1. To K latent image forming apparatuses ROSy, ROSm, ROSc, and ROSk. Below each of the latent image forming apparatuses ROSy to ROSk, photosensitive drums Py, Pm, Pc, and Pk, which are examples of image carriers, are arranged.

The surfaces of the rotating photosensitive drums Py, Pm, Pc, Pk are uniformly charged by charging rolls CRy, CRm, CRc, CRk as an example of a charger. The surfaces of the photosensitive drums Py to Pk whose surfaces are charged are statically exposed by laser beams Ly, Lm, Lc, and Lk as examples of latent image writing light output from the latent image forming devices ROSy, ROSm, ROSc, and ROSK. An electrostatic latent image is formed. The electrostatic latent images on the surfaces of the photosensitive drums Py, Pm, Pc, and Pk are toner images as examples of visible images of yellow Y, magenta M, cyan C, and black K by the developing devices Gy, Gm, Gc, and Gk. Developed.
In the developing devices Gy to Gk, the developer consumed by the development is supplied from toner cartridges Ky, Km, Kc, and Kk as an example of a developer container. The toner cartridges Ky, Km, Kc, Kk are detachably attached to the developer supply device U3b.

The toner images on the surfaces of the photosensitive drums Py, Pm, Pc, and Pk are transferred onto an intermediate transfer belt B as an example of an intermediate transfer member by primary transfer rolls T1y, T1m, T1c, and T1k as an example of a primary transfer unit. The primary transfer areas Q3y, Q3m, Q3c, and Q3k are sequentially superimposed and transferred, and a color toner image as an example of a multicolor visible image is formed on the intermediate transfer belt B. The color toner image formed on the intermediate transfer belt B as an example of the image holding member is conveyed to the secondary transfer region Q4.
In the case of only K-color image information, only the K-color photosensitive drum Pk and the developing device Gk are used, and only the K-color toner image is formed.
The photosensitive drums Py, Pm, Pc, and Pk after the primary transfer are made up of residual developer and paper dust adhered to the surface by a drum cleaner CLy, CLm, CLc, and CLk as an example of an image carrier cleaner. Residue is removed.

In the first embodiment, the photosensitive drum Pk, the charging roll CRk, and the drum cleaner CLk are integrated as a K-color photosensitive unit UK as an example of an image holding unit. Similarly, for the other colors Y, M, and C, the photosensitive drum units PY, Pm, and Pc, charging rolls CRy, CRm, and CRc, and drum cleaners CLy, CLm, and CLc are used to form the photosensitive units UY, UM, and UC. It is configured.
A K-color visible image forming device UK + Gk is configured by the K-color photosensitive unit UK and the developing device Gk having a developing roll R0k as an example of a developer holding member. Similarly, Y, M, and C color photoreceptor units UY, UM, and UC and developing devices Gy, Gm, and Gc having developing rolls R0y, R0m, and R0c, respectively, are visible in Y, M, and C colors. Image forming apparatuses UY + Gy, UM + Gm, and UC + Gc are configured.

  A belt module BM as an example of an intermediate transfer device is disposed below the photosensitive drums Py to Pk. The belt module BM includes the intermediate transfer belt B, a driving roll Rd as an example of a driving member for the intermediate transfer member, a tension roll Rt as an example of a tension applying member, a walking roll Rw as an example of a meandering prevention member, and a driven member. A plurality of idler rolls Rf as an example, a backup roll T2a as an example of a counter member, and the primary transfer rolls T1y, T1m, T1c, T1k. The intermediate transfer belt B is supported so as to be rotatable in the direction of the arrow Ya.

A secondary transfer unit Ut is disposed below the backup roll T2a. The secondary transfer unit Ut has a secondary transfer roll T2b as an example of a secondary transfer member. A secondary transfer region Q4 is formed by a region where the secondary transfer roll T2b contacts the intermediate transfer belt B. Further, a backup roll as an example of a facing member is opposed to the secondary transfer roll T2b with the intermediate transfer belt B interposed therebetween. A contact roll T2c as an example of a power supply member is in contact with the backup roll T2a. A secondary transfer voltage having the same polarity as the toner charging polarity is applied to the contact roll T2c.
The backup roll T2a, the secondary transfer roll T2b, and the contact roll T2c constitute a secondary transfer device T2.

A medium transport path SH2 is disposed below the belt module BM. The recording sheet S fed from the medium supply path SH1 of the feeder unit U2 is conveyed to a registration roll Rr as an example of a conveyance timing adjustment member by a conveyance roll Ra as an example of a medium conveyance member. The registration roll Rr conveys the recording paper S downstream in accordance with the timing when the toner image formed on the intermediate transfer belt B is conveyed to the secondary transfer region Q4. The recording sheet S fed by the registration roll Rr is guided by the registration-side sheet guide SGr and the sheet guide SG1 before transfer, and is conveyed to the secondary transfer area Q4.
The toner image on the intermediate transfer belt B is transferred to the recording paper S by the secondary transfer unit T2 when passing through the secondary transfer region Q4. In the case of a color toner image, the toner images primarily transferred and superimposed on the surface of the intermediate transfer belt B are secondarily transferred onto the recording paper S all at once.
The primary transfer rolls T1y to T1k, the secondary transfer unit T2, and the intermediate transfer belt B constitute a transfer device T1y to T1k + T2 + B of Example 1.

  The intermediate transfer belt B after the secondary transfer is cleaned by a belt cleaner CLB as an example of an intermediate transfer member cleaner disposed downstream of the secondary transfer region Q4. The belt cleaner CLB removes residues such as developer and paper powder remaining without being transferred from the intermediate transfer belt B in the secondary transfer region Q4.

The recording sheet S on which the toner image has been transferred is guided by a sheet guide SG2 after transfer, and is sent to a medium conveying belt BH as an example of a conveying member. The medium conveyance belt BH conveys the recording paper S to the fixing device F.
The fixing device F includes a heating roll Fh as an example of a heating member and a pressure roll Fp as an example of a pressure member. The recording sheet S is conveyed to a fixing area Q5, which is an area where the heating roll Fh and the pressure roll Fp are in contact with each other. The toner image on the recording paper S is fixed by being heated and pressurized by the fixing device F when passing through the fixing region Q5.
The visible image forming devices UY + Gy to UK + Gk, the transfer devices T1y to T1k + T2 + B, and the fixing device F constitute the image recording unit U3a of Example 1.

  On the downstream side of the fixing device F, a switching gate GT1 as an example of a switching member is provided. The switching gate GT1 selectively switches the recording sheet S that has passed through the fixing region Q5 to either the discharge path SH3 or the reversing path SH4 on the medium processing apparatus U4 side. The recording sheet S conveyed to the discharge path SH3 is conveyed to the sheet conveyance path SH5 of the medium processing device U4. A curl correction member U4a, which is an example of a warp correction member, is disposed in the paper transport path SH5. The curl correction member U4a corrects the warp, that is, the so-called curl of the recording sheet S that has been carried in. The recording sheet S with the curl corrected is discharged by a discharge roll Rh as an example of a medium discharge member onto a discharge tray TH1 as an example of a medium discharge unit with the image fixing surface of the sheet facing upward.

The recording sheet S conveyed to the reversing path SH4 side of the image forming unit U3 by the switching gate GT1 is conveyed to the reversing path SH4 of the image forming unit U3 through the second gate GT2 as an example of a switching member.
At this time, when the image fixing surface of the recording paper S is discharged downward, the transport direction of the recording paper S is reversed after the rear end of the recording paper S in the transport direction passes through the second gate GT2. Here, the second gate GT2 of the first embodiment is configured by a thin-film elastic member. Therefore, the second gate GT2 once passes the recording sheet S conveyed to the reversing path SH4 as it is, and when the recording sheet S that has passed is reversed, so-called switched back, is guided to the conveying paths SH3 and SH5. To do. Then, the recording sheet S that has been switched back passes through the curl correction member U4a and is discharged to the discharge tray TH1 with the image fixing surface facing downward.

A circulation path SH6 is connected to the inversion path SH4 of the image forming section U3, and a third gate GT3 as an example of a switching member is disposed at the connection section. Further, the downstream end of the inversion path SH4 is connected to the inversion path SH7 of the medium processing apparatus U4.
The recording sheet S conveyed to the reversing path SH4 through the switching gate GT1 is conveyed to the reversing path SH7 side of the medium processing apparatus U4 by the third gate GT3. Similar to the second gate GT2, the third gate GT3 of the first embodiment is formed of a thin-film elastic member. Accordingly, the third gate GT3 guides the recording sheet S conveyed through the reversing path SH4 once to the circulation path SH6 when the recording sheet S that has passed through is switched back.

The recording sheet S conveyed to the circulation path SH6 is retransmitted to the secondary transfer area Q4 through the medium conveyance path SH2, and printing on the second side is performed.
A sheet transport path SH is constituted by the elements indicated by the symbols SH1 to SH7. Further, the sheet conveying device SU according to the first embodiment is configured by the elements indicated by the symbols SH, Ra, Rr, Rh, SGr, SG1, SG2, BH, and GT1 to GT3.

(Explanation of bite amount adjustment mechanism)
FIG. 3 is an explanatory diagram of a mechanism for adjusting the amount of biting in the image forming apparatus according to the first embodiment.
In FIG. 3, the secondary transfer roll T2b of Example 1 is rotatably supported by a housing 1 as an example of a first support at both ends in the front-rear direction. The housing 1 is supported so that the secondary transfer roll T2b can move in a direction in which the secondary transfer roll T2b approaches and separates from the backup roll T2a. In the first embodiment, the configuration in which the housing 1 is movable in the direction of approaching and separating from the backup roll T2a is illustrated, but the secondary transfer roll T2b is backed up by rotating around the rotation axis. It is also possible to adopt a configuration capable of moving in a direction approaching and separating from the roll T2a.
An abutting portion 2 as an example of a contacted portion is formed on the upper left portion of the housing 1.

  Above the butting portion 2, a constant displacement nip adjusting mechanism 6 as an example of a first adjusting device is disposed. The constant displacement nip adjusting mechanism 6 has an arm 7 as an example of a connecting member. The arm 7 is supported so as to be movable toward and away from the abutting portion 2. The lower end of the arm 7 is in contact with the butting portion 2. Above the arm 7, a first eccentric cam 8 as an example of a first actuating member is disposed in contact. The first eccentric cam 8 is supported so as to be rotatable about the rotation shaft 8a. A gear (not shown) is supported on the rotation shaft 8 a of the first eccentric cam 8. The gear meshes with an output gear 9a supported on an output shaft of a motor 9 as an example of a drive source. Therefore, as the motor 9 rotates, the first eccentric cam 8 rotates, and the arm 7 can move in a direction in which the abutting portion 2 is pushed or in a direction in which the arm 7 tends to move away from the abutting portion 2.

A movable frame 11 as an example of a second support is disposed below the housing 1. The movable frame 11 is supported so as to be movable toward and away from the housing 1, that is, toward and away from the backup roll T2a.
A spring 12 as an example of a pressing member is supported between the movable frame 11 and the housing 1.
An arm 13 that extends upward is formed at the front end of the movable frame 11. A pair of upper and lower cam followers 14 are formed at the upper end of the arm portion 13 as an example of a non-actuating portion.

Between the pair of upper and lower cam followers 14, a second eccentric cam 16 as an example of a second operating member is disposed. The second eccentric cam 16 is supported so as to be rotatable about the rotation shaft 16a. A gear (not shown) is supported on the rotation shaft 16 a of the second eccentric cam 16, and this gear meshes with the output gear 9 a of the motor 9. Therefore, as the motor 9 rotates, the second eccentric cam 16 rotates together with the first eccentric cam 8, and the movable frame 11 moves in the vertical direction via the cam follower 14. When the movable frame 11 moves, the spring 12 is compressed or extended, and the pressing force f1 that the spring 12 presses the housing 1 changes.
A pressing load adjusting mechanism 17 as an example of the second adjusting device according to the first embodiment is configured by the members denoted by the reference numerals 11 to 16.

  In FIG. 3, the constant displacement nip adjusting mechanism 6 according to the first embodiment moves the secondary transfer roll T2b closer to and away from the backup roll T2a. Therefore, the distance between the rotation center of the secondary transfer roll T2b and the rotation center of the backup roll T2a changes (displaces), and the amount of biting is the amount by which the designed surface of the secondary transfer roll T2b bites into the surface of the backup roll T2a. Changes. The amount of elastic deformation of the secondary transfer roll T2b and backup roll T2a changes according to the amount of biting, and the contact load acting on the secondary transfer region Q4, the so-called nip load f3, changes. The pressing load adjusting mechanism 17 moves the movable frame 11 up and down to change the pressing force f <b> 1 that the spring 12 presses the housing 1. Therefore, a difference force between the pressing force f1 and the nip load f3 becomes a preload f2 that is a force by which the butting portion 2 presses the arm 7. As can be seen from FIG. 3, the pressing force f1 corresponds to the sum of the preload f2 and the nip load f3.

FIG. 4 is an explanatory diagram of the relationship between the secondary transfer load and the amount of biting in Example 1, and is a graph with the amount of biting on the horizontal axis and the load on the vertical axis.
FIG. 5 is an explanatory diagram of the relationship between the amount of movement of the moving member and the amount of secondary transfer biting in Example 1, where the horizontal axis represents the amount of movement of the housing and the movable frame, and the vertical axis represents the secondary transfer biting amount. This is a graph taken.
3 to 5, in the first embodiment, as the amount of biting increases with the rotation of the motor 9, as shown in FIG. 4, the cam 8 , 16 surface shapes, so-called profiles are set. Accordingly, the shapes 8 and 16 of the surfaces of the cams 8 and 16 are set so that the increase and decrease of the preload f2 is alleviated. In particular, the first embodiment is configured such that the preload f2 is constant, i.e., there is almost no increase or decrease in the preload f2.

  When the movement amount of the housing 1 and the movable frame 11 at the cams 8 and 16 is the same, the pressing load f1 does not change and is constant, so that the loads f1, f2, and f3 as shown in FIG. 4 are realized. Therefore, when the housing 1 and the movable frame 11 are controlled so as to approach the backup roll T2a, the moving amount of the movable frame 11 needs to be larger than the moving amount of the housing 1. As an example, in FIG. 5, when the secondary transfer biting amount is 1 mm, the housing 1 is moved 1 mm, while the movable frame 11 is moved 5 mm. The same applies when the housing 1 and the movable frame 11 are separated from the backup roll T2a. As an example, each of the cams 8 and 16 has a disc shape, and the eccentric amount of the second eccentric cam 16 is greater than the eccentric amount of the first eccentric cam 8 (the deviation between the center of the circle of the disc 8 and the rotation shaft 8a). This can be realized by increasing.

(Description of the control part of Example 1)
FIG. 6 is a block diagram illustrating the functions of the control unit of the image forming apparatus according to the first embodiment.
In FIG. 6, the control unit C of the copying machine U has an input / output interface I / O for inputting / outputting signals from / to the outside. In addition, the control unit C includes a ROM (read only memory) in which a program for performing necessary processing, information, and the like are stored. In addition, the control unit C includes a random access memory (RAM) for temporarily storing necessary data. The control unit C includes a central processing unit (CPU) that performs processing according to a program stored in a ROM or the like. Therefore, the control part C of Example 1 is comprised by the small information processing apparatus, what is called a microcomputer. Therefore, the control part C can implement | achieve various functions by running the program memorize | stored in ROM etc.

(Signal output element connected to control unit C)
The control unit C receives an output signal from a signal output element such as an operation unit UI.
The operation unit UI includes an input button UIa for inputting a copy start key, a numeric keypad, an arrow, and the like as an example of an input member.

(Controlled element connected to control unit C)
The control unit C is connected to the drive circuit D1 of the main drive source, the drive circuit D2 of the adjustment motor, the power supply circuit E, and other control elements (not shown). The controller C outputs these control signals to the circuits D1, D2, E, and the like.
D1: Main Drive Source Drive Circuit The main drive source drive circuit D1 rotationally drives the photoreceptors Py to Pk, the intermediate transfer belt B, and the like via a main motor M1 as an example of a main drive source.
D2: Adjustment Motor Drive Circuit The adjustment motor drive circuit D2 drives the motor 9 to rotate the eccentric cams 8 and 16, thereby adjusting the positions of the secondary transfer roll T2b and the movable frame 11.

E: Power Supply Circuit The power supply circuit E includes a development power supply circuit Ea, a charging power supply circuit Eb, a transfer power supply circuit Ec, a fixing power supply circuit Ed, and the like.
Ea: Power supply circuit for development The power supply circuit Ea for development applies a development voltage to the development rolls of the development devices Gy to Gk.
Eb: Charging power supply circuit The charging power supply circuit Eb applies a charging voltage for charging the surfaces of the photoreceptors Py to Pk to the charging rolls CRy to CRk, respectively.

Ec: Power supply circuit for transfer The power supply circuit Ec for transfer applies a transfer voltage to the primary transfer rolls T1y to T1k and the backup roll T2a.
Ed: Power supply circuit for fixing The power supply circuit for fixing Ed supplies power to the heater of the heating roll Fh of the fixing device F.

(Function of control unit C)
The control unit C has a function of executing a process according to an input signal from the signal output element and outputting a control signal to each control element. That is, the control unit C has the following functions.
C1: Image Forming Control Unit The image forming control unit C1 drives each member of the scanner unit U1 and the image forming unit U3 in response to input to the operation unit UI or input of image information from an external personal computer or the like. In addition, the application timing of each voltage is controlled to execute a job which is an image forming operation.

C2: Drive Source Control Unit The drive source control unit C2 controls the drive of the main motor M1 via the main drive source drive circuit D1, and controls the driving of the photoreceptors Py to Pk and the like.
C3: Power Supply Circuit Control Unit The power supply circuit control unit C3 controls the power supply circuits Ea to Ed to control the voltage applied to each member and the power supplied to each member.

C4: Paper Type Information Acquisition Unit The paper type information acquisition unit C4 as an example of a transfer condition acquisition unit acquires a paper type that is the type of the recording paper S used at the time of a job as an example of a transfer condition. The paper type information acquisition unit C4 according to the first exemplary embodiment performs a job based on the paper type information registered in advance in each of the paper feed trays TR1 to TR4 and the paper feed trays TR1 to TR4 used in the job. Get information on the paper type used. In the first embodiment, the basis weight related to the thickness of the recording paper S is acquired as the paper type information.

C5: Operation amount setting means The operation amount setting means C5 sets the operation amount of the motor 9 based on the paper type. According to the thickness of the recording paper S, the working amount setting means C5 of the first embodiment is the biting amount, that is, the distance between the rotation center of the secondary transfer roll T2b and the rotation center of the backup roll T2a, the pressing load, That is, the load with which the spring 12 presses the secondary transfer roll T2b is set in advance. Specifically, as the thickness of the recording paper S increases, the amount of biting is reduced and the pressing load is reduced. Accordingly, the thicker the recording paper S is, the more the secondary transfer roll T2b moves away from the backup roll T2a, and the movable frame 11 moves in the direction away from the backup roll T2a. Therefore, in the operation amount setting means C5 of the first embodiment, the amount of biting according to the basis weight of the recording paper S and the amount of rotation of the motor 9 serving as a pressing load are set.

C6: Motor Control Unit The motor control unit C6 as an example of the drive source control unit controls the motor 9 via the adjustment motor drive circuit D2. The motor control unit C6 according to the first embodiment controls the motor 9 according to the rotation amount of the motor 9 set by the operation amount setting unit C5.

(Operation of Example 1)
In the copying machine U according to the first embodiment having the above-described configuration, when a job is started, the motor 9 is driven according to the basis weight of the recording paper S to be used. Accordingly, the constant displacement nip adjusting mechanism 6 is operated to set the biting amount according to the basis weight of the recording paper S, and the pressing load adjusting mechanism 17 is also operated to press according to the basis weight of the recording paper S. The load f1 is set.
When the front end of the recording paper S enters the secondary transfer area Q4, the recording paper S hits. At this time, an impact force acts on the intermediate transfer belt B. When an impact force is applied to the intermediate transfer belt B, the intermediate transfer belt B is displaced, the conveyance speed of the intermediate transfer belt B is instantaneously changed, and primary transfer is performed in the primary transfer regions Q3y to Q3k when an impact occurs. In this case, a band-like or band-like image defect called impulse banding occurs in the primary transfer image. The impact force at the time of paper entry increases according to the thickness of the recording paper S and the pressing load f1. For the purpose of improving the number of types of paper that can be used, that is, so-called paper versatility, impulse banding is particularly useful when printing on thick paper in an image forming apparatus in which the pressing load f1 is large and the amount of biting is widely adjusted. Likely to happen.

  Since the recording sheet S having a normal thickness is sufficiently thin with respect to the secondary transfer region Q4, the roll pair T2a and T2b are slightly deformed and easily enter the gap between the roll pair T2a and T2b. On the other hand, in the case of thick paper, it is difficult to catch up with the deformation of the roll pair T2a and T2b, and it is necessary to widen the roll axis itself, and it is difficult to enter the gap between the roll pair T2a and T2b. Accordingly, after the thick paper enters the secondary transfer region Q4, it is necessary to greatly separate the rolls T2a and T2b. Here, only the nip load f3 acts on the secondary transfer region Q4, but the pressing load f1 acts between the axes of the roll pairs T2a and T2b. Therefore, in order to spread the space between the shafts and pass the thick paper, a force (component force of the rotational force of the roll) that resists the pressing load f1 is required. Therefore, when the pressing load f1 is large, the impact at the time of entering the thick paper is likely to be larger than when the pressing load f1 is small, and impulse banding is likely to occur.

FIG. 7 is an explanatory diagram of the relationship between the secondary transfer load and the amount of biting in the prior art, and is a graph with the biting amount on the horizontal axis and the load on the vertical axis.
The conventional image forming apparatus is not provided with a configuration corresponding to the pressing load adjusting mechanism 17 of the first embodiment, and has a configuration in which the secondary transfer unit is pressed by a spring having a preset elastic force 01. . Therefore, as shown in FIG. 7, the elastic force 01 by the spring was constant. Then, as shown in FIG. 7, in order to increase the adjustment width of the biting amount and increase the adjustment width of the nip load 02, that is, the width of the horizontal axis of the graph of FIG. (The value on the vertical axis) needs to be increased. In such a configuration, impulse banding is particularly likely to occur when printing on thick paper.

In contrast, in the copying machine U according to the first embodiment, when the constant displacement nip adjusting mechanism 6 is operated to adjust the amount of biting, the pressing load adjusting mechanism 17 is operated in conjunction with the pressing load f1. Is done. When cardboard is used, the pressing load f1 is also reduced as shown in FIG. Therefore, the occurrence of impulse banding is suppressed as compared with the conventional configuration.
Note that, as in the technique described in Japanese Patent Application Laid-Open No. H10-228867, the technique of reducing the amount of biting in the secondary transfer area when the sheet enters and increasing the amount of biting after entering has a limit in the response of the amount of biting control. . Therefore, there is a problem that the transfer efficiency at the front end of the sheet is lowered and a density difference occurs, that is, there is a problem of transfer failure. On the other hand, in the first embodiment, the control is not performed according to the entry of the paper. Therefore, in the first embodiment, it is possible to suppress the occurrence of transfer failure while suppressing the occurrence of impulse banding as compared with the conventional technique.

In FIG. 7, in the conventional configuration, when the amount of biting is adjusted in this state, the nip load 02 acting on the secondary transfer region changes according to the amount of biting. Accordingly, the preload 03 acting on the arm and the abutting portion increases when the amount of biting is small, and increases when the amount of biting increases. Therefore, in the conventional configuration, it is necessary to ensure the rigidity of the arm and the abutting portion so as to cope with the case where the preload 03 is the largest. Therefore, it is necessary to make the arm and the abutting portion have a high rigidity, and there is a problem that the manufacturing cost increases.
On the other hand, in the first embodiment, as shown in FIG. 4, it is possible to significantly reduce the preload f2 as compared with the prior art while ensuring a wide adjustment range of the amount of biting. Therefore, the rigidity of the arm 7 and the butting portion 2 can be lowered. Therefore, compared with the prior art, it is possible to reduce the manufacturing cost while ensuring the versatility of the sheet by ensuring the adjustment range of the biting amount.
Furthermore, in the first embodiment, the constant displacement nip adjusting mechanism 6 and the pressing load adjusting mechanism 17 are driven by a common motor 9. Therefore, the manufacturing cost can be reduced as compared with a configuration in which a motor is separately provided.

(Example of change)
As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the said Example, A various change is performed within the range of the summary of this invention described in the claim. It is possible. Modification examples (H01) to (H08) of the present invention are exemplified below.
(H01) In the above embodiment, the copying machine U was exemplified as an example of the image forming apparatus. However, the present invention is not limited to this. For example, the copying machine U is configured by a printer, a FAX, or a multifunction machine having a plurality or all of these functions. It is also possible to do.

(H02) In the above embodiment, the copying machine U has exemplified the configuration in which four color developers are used. However, the present invention is not limited to this. For example, a single color image forming apparatus, five or more colors, or three colors or less. The present invention can also be applied to a multicolor image forming apparatus.
(H03) In the above embodiment, the configuration in which the common motor 9 is used by the constant displacement nip adjusting mechanism 6 and the pressing load adjusting mechanism 17 is exemplified, but the present invention is not limited to this. It is also possible to provide a motor separately. Further, the drive source is not limited to a motor, and a known operating member such as a solenoid or a manipulator can be used.

(H04) In the above-described embodiment, as illustrated in FIG. 4, the configuration in which the loads f <b> 1 to f <b> 3 are continuously changed with respect to the amount of biting is illustrated, but the present invention is not limited to this. For example, the biting amount is 0 to 0.5 mm, the load is constant, the load is increased by 0.5 to 1 mm, and the load is further increased by 1 to 1.5 mm. Is possible.
(H05) In the above embodiment, as shown in FIG. 4, the configuration for controlling the preload f2 to be substantially the same is illustrated, but the present invention is not limited to this. For example, the preload f2 can be configured to gradually increase or decrease gradually as the amount of biting increases.

(H06) In the above-described embodiment, the constant displacement nip adjusting mechanism 6 has the configuration including the arm 7 and the first eccentric cam 8, but is not limited thereto. The first eccentric cam 8 may be in direct contact with the housing 1. In addition, the arm 7 can be constituted by two or more link mechanisms. Further, the place is not limited to the upper side of the secondary transfer region Q4, and can be set to any position that can be set, such as the lower side. Similarly to the constant displacement nip adjusting mechanism 6, the pressing load adjusting mechanism 17 can change the shape and position of the movable frame 11, the arm portion 13, the cam follower 14, the number of springs 12, and the like to arbitrary positions. Therefore, in the configuration of the embodiment, the moving amount of the movable frame 11 is larger than the moving amount of the housing 1, but the relationship of the moving amount is reversed depending on the configuration of the housing and the movable frame. There may be cases.

(H07) In the above embodiment, the thickness of the paper is exemplified as an example of the transfer condition, but the present invention is not limited to this. For example, the amount of biting is changed according to transfer conditions that affect transfer in the secondary transfer region Q4, such as changes in resistance value due to deterioration with time of the humidity, the backup roll T2a, and the secondary transfer roll T2b, and image density. It is possible.
(H08) In the above-described embodiment, the configuration in which the intermediate transfer belt B is provided as an example of the image carrier and the amount of biting in the secondary transfer region Q4 is adjusted is illustrated, but the present invention is not limited to this. For example, an image holding member of any form such as a configuration in which the photosensitive member Py to Pk is directly transferred to the recording sheet S, a configuration using a photosensitive belt as an example of an image holding member, a configuration using an intermediate transfer drum, etc. The present invention can be applied to a configuration that adjusts the amount of biting at the time of final transfer onto a recording sheet.

1 ... 1st support body,
6 ... 1st adjustment apparatus,
7: Connecting member,
8: First actuating member,
9 ... Driving source,
11 ... second support,
12 ... pressing member,
16 ... second actuating member,
17 ... second adjusting device,
B: Image carrier,
f1 ... pressing force,
S ... medium
T2b: transfer member,
U: Image forming apparatus.

Claims (8)

An image carrier,
A transfer member for transferring an image held on the image carrier to a medium, the transfer member supported so as to be movable toward and away from the image carrier;
A pressing member that presses the transfer member toward the image carrier;
A first adjusting device that adjusts an amount of biting of the transfer member into the image holding member according to transfer conditions;
In conjunction with the adjustment of the amount of biting, a second adjustment device that increases or decreases the pressing force of the pressing member with a tendency according to the increase or decrease of the amount of biting,
An image forming apparatus comprising: A first support that supports the transfer member so as to be movable toward and away from the image carrier;
The first adjusting device having a first actuating member for actuating the first support;
The image forming apparatus according to claim 1, further comprising: A first support that supports the transfer member so as to be movable toward and away from the image carrier;
The pressing member configured by a spring that presses the first support;
A second support member that supports the pressing member and is supported so as to be movable toward and away from the image carrier, and the second support member that approaches and separates from the image carrier. A second actuating member that moves in the same direction as the moving direction of the first support, and
The image forming apparatus according to claim 1, further comprising: A first support that supports the transfer member so as to be movable toward and away from the image carrier;
The pressing member configured by a spring that presses the first support;
A second support member that supports the pressing member and is supported so as to be movable toward and away from the image carrier, and the second support member that approaches and separates from the image carrier. A second actuating member that moves in a direction to move, the second adjusting device,
With
The said 2nd support body is moved so that the increase / decrease in the force which the said 1st support body which generate | occur | produces with the said pressing member pushes the said 1st adjustment apparatus may be relieve | moderated. Image forming apparatus. The second actuating member set such that the amount of movement of the second support is greater than the amount of movement of the first support;
The image forming apparatus according to claim 3, further comprising: A drive source for driving the first adjustment device and driving the second adjustment device;
The image forming apparatus according to claim 1, further comprising: The second adjusting device for continuously changing the pressing force of the pressing member according to the change in the amount of biting;
The image forming apparatus according to claim 1, further comprising: The second adjusting device that changes the pressing force of the pressing member stepwise in accordance with the change in the amount of biting;
The image forming apparatus according to claim 1, further comprising:

Images