JP2007309954A - Rotary cam mechanism and image forming apparatus provided therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotary cam mechanism applicable even to the existing image forming apparatus, capable of reducing loads applied to a gear, an electromagnetic clutch or the like and shafts supporting them, in secondary transferring and further capable of securing a stable operation. <P>SOLUTION: The rotary cam mechanism in an image forming apparatus comprises: an image carrier; an intermediate transfer unit having a primary transfer roller of primarily transferring a toner image formed on the image carrier to a transfer belt; a secondary transfer roller of secondarily transferring the toner image primarily transferred to the transfer belt to a sheet material; and a driving roller arranged so as to be confronted with the secondary transfer roller with the transfer belt sandwiched. In both the end parts of either the driving roller or the secondary transfer roller, a pair of eccentric cams for making the surface of the transfer belt and the surface of the secondary transfer roller to be freely pressure-contacted/separated are arranged, and a pair of the eccentric cams are formed in such a manner that the pressure-contact/separation starting position and the maximum torque position are made different between either cam and the other cam. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rotary cam mechanism and an image forming apparatus including the rotary cam mechanism. The present invention relates to a cam mechanism and an image forming apparatus including the cam mechanism.

  2. Description of the Related Art Conventionally, image forming apparatuses such as printers, copiers, facsimiles, and the like use a transfer belt for secondary transfer of a toner image primarily transferred from an image carrier such as a photoreceptor to a transfer belt onto a sheet material such as copy paper. Some have a rotating cam mechanism with an eccentric cam for allowing the toner image transfer surface and the secondary transfer roller surface to be pressed against and separated from each other.

The eccentric cams, for example, are disposed in pairs at both ends of the driving roller disposed opposite to the secondary transfer roller across the transfer belt, and are disposed at both ends of the secondary transfer roller. A pair of so-called cam receivers are in pressure contact with each other.
Therefore, by rotating this eccentric cam, a rotating cam mechanism is constructed in which the surface of the secondary transfer roller is selectively displaced to the pressure contact position or the separation position with respect to the toner image transfer surface of the transfer belt.

By the way, in the conventional rotary cam mechanism, the pair of eccentric cams are formed in substantially the same shape, and therefore, the operation start position of the press contact / separation and the position where the rotational torque becomes maximum exist at substantially the same position. It becomes. Further, since the eccentric cam is eccentric as the name suggests, the rotational torque varies greatly according to the rotational angle.
For this reason, when the eccentric cam rotates, a great load is generated on the gear, the electromagnetic clutch, and the shaft that supports them, and there is a problem of causing slippage of the electromagnetic clutch and acceleration or damage of the gear teeth and shaft.

  As a measure against this, for example, in Patent Document 1, a pair of eccentric cam portions (main eccentric cam portions) is provided on a rotation shaft, and a driven portion (main slave) is brought into pressure contact with the eccentric cam portion by rotation of the rotation shaft. A rotating cam mechanism of the image forming apparatus that displaces the moving portion), a sub eccentric cam portion that is rotated by a rotating shaft and whose rotational torque is in reverse phase with respect to the main eccentric cam portion, There is disclosed a method of providing a balancer mechanism portion that cancels fluctuations in rotational torque based on a main eccentric cam portion by a sub driven portion that is in pressure contact with the eccentric cam portion.

However, in the rotating cam mechanism by such a method, it is necessary to additionally arrange a member as a balancer mechanism portion, and the configuration of the rotating cam mechanism itself is different from the conventional one. That is, in order to use this rotating cam mechanism, an image forming apparatus to which the rotating cam mechanism can be mounted must be prepared.
Further, since the rotating cam mechanism is increased in size, the image forming apparatus is inevitably increased in size, which does not meet the space saving demanded in recent years.

JP 2002-156844 A

  The present invention has been made in view of the above circumstances, and can be applied to currently used image forming apparatuses, and can reduce a load on a gear, an electromagnetic clutch, and the like and a shaft supporting them in secondary transfer. Another object of the present invention is to provide a rotating cam mechanism that can ensure a stable operation and an image forming apparatus including the rotating cam mechanism.

  According to the first aspect of the present invention, an image bearing member, an intermediate transfer unit having a primary transfer roller for primarily transferring a toner image formed on the image bearing member to the transfer belt, and the image transferred on the transfer belt. A secondary transfer roller for secondary transfer of a toner image onto a sheet material, and a drive roller disposed opposite to the secondary transfer roller with the transfer belt interposed therebetween, the drive roller and the secondary transfer roller A rotating cam mechanism in an image forming apparatus in which a pair of eccentric cams for freely pressing and separating from the other roller is provided at both ends of any one of the rollers, wherein the pair of eccentric cams is Further, the present invention relates to a rotating cam mechanism in an image forming apparatus, wherein the press contact / separation start position and the maximum torque position are formed so as to be different between one cam and the other cam.

  According to a second aspect of the present invention, in the pair of eccentric cams, the press contact / separation end positions of the one cam and the other cam are substantially the same. The present invention relates to a cam mechanism.

  The invention according to claim 3 is characterized in that the pair of eccentric cams are arranged coaxially with a roller on which the eccentric cams are arranged. The present invention relates to a cam mechanism.

  According to a fourth aspect of the present invention, in any one of the driving roller and the secondary transfer roller, a rotating member that rotates in accordance with the operation of pressing and separating is provided, and the rotating operation of the rotating member is performed. The rotary cam mechanism in the image forming apparatus according to claim 1, further comprising a pressure contact / separation detection unit that detects the pressure contact / separation detection unit.

  According to a fifth aspect of the present invention, there is provided an image forming apparatus comprising the rotating cam mechanism according to any one of the first to fourth aspects.

  According to the first aspect of the present invention, the pair of eccentric cams are formed such that the press contact / separation start position and the maximum torque position are different between the one cam and the other cam, and thus an additional member is required. Therefore, it is possible to reduce the load on the gear, the electromagnetic clutch, and the like and the shaft supporting them in the secondary transfer.

  According to the second aspect of the present invention, the pair of eccentric cams have the press contact / separation end positions formed substantially the same by the one cam and the other cam, thereby making it possible to prevent a transfer failure of the toner image. Thus, reliable transfer to the sheet material is possible.

  According to the third aspect of the invention, the pair of eccentric cams are arranged coaxially with the roller on which the eccentric cam is arranged, so that more reliable transfer to the sheet material is possible.

  According to the fourth aspect of the present invention, either one of the driving roller and the secondary transfer roller is provided with a rotating member that rotates according to the operation of pressing and separating, and the rotating operation of the rotating member is performed. By providing the pressure contact / separation detection unit for detection, it is possible to prevent malfunction during transfer of the toner image.

  According to the fifth aspect of the invention, an image forming apparatus capable of reducing the load on the gear, the electromagnetic clutch, and the like and the shaft supporting them in the secondary transfer while securing the conventional space saving performance. .

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a rotating cam mechanism and an image forming apparatus including the rotating cam mechanism according to the invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view illustrating an example of an image forming apparatus.
The configuration of the image forming apparatus will be described below with reference to FIG.

  The image forming apparatus (1) shown in FIG. 1 is a so-called color printer, and includes a developing device (2) having a plurality (four in the illustrated example) of toner cartridges, and the toner of the developing device (2) as a toner image. An intermediate having an image carrier (3) to be carried (hereinafter referred to as a photoreceptor) and a primary transfer roller (42) for primarily transferring a toner image formed on the photoreceptor (3) to a transfer belt (41). A transfer unit (4) and a secondary transfer roller (5) for secondary transfer of the toner image primarily transferred to the transfer belt (41) onto the sheet material (P) are provided.

As shown in FIG. 1, in the image forming apparatus (1), the developing device (2) is rotatably arranged around the axis, and has four colors (for example, black, yellow, cyan, magenta). Toner cartridges 21, 22, 23, and 24, and toner transport rollers 211, 221, and 24 that transport toner from the toner cartridges 21, 22, 23, and 24 to the photoreceptor 3. 231 and 241).
By applying a bias to the toner conveying rollers (211, 221, 231, 241), a toner image is formed on the electrostatic latent image formed on the surface of the photoreceptor (3).
The electrostatic latent image on the surface of the photoconductor (3) is obtained by uniformly charging the surface of the photoconductor (3) to a predetermined charge with the charging device (31), and then exposing the photoconductor (3) according to the input image information (32). ) By exposing the surface of the photoreceptor (3) and removing the charge at the exposed portion.
The photosensitive member (3) can be rotated in the opposite direction to the developing device (2), that is, counterclockwise.

The intermediate transfer unit (4) is arranged in parallel with the lower portion of the photoconductor (3) and performs primary transfer of a toner image formed on the surface of the photoconductor (3).
The intermediate transfer unit (4) includes a transfer belt (41) as an intermediate transfer body described above and a primary transfer for primary transfer of a toner image formed on the surface of the photoreceptor (3) to the transfer belt (41). It has a roller (42) and three rollers, that is, a drive roller (43), a tension roller (44), and a guide roller (45).

The transfer belt (41) is formed in an endless shape, and the toner image formed on the surface of the photoreceptor (3) is primarily transferred onto the surface of the transfer belt (41). The transfer belt (41) is suspended from the three rollers (the driving roller (43), the tension roller (44), and the guide roller (45)), and is configured to be rotated clockwise by the driving roller (43). Yes.
The transfer belt (41) is sandwiched between the photosensitive member (3) and the primary transfer roller (42) by a predetermined pressing force.

  The primary transfer roller (42) is disposed to face the photoconductor (3) in parallel with the transfer belt (41) interposed therebetween. The primary transfer roller (42) electrostatically transfers the toner image formed on the surface of the photoreceptor (3) onto the surface of the transfer belt (41) by applying a bias.

The secondary transfer roller (5) is for secondary transfer of the toner image primarily transferred to the transfer belt (41) to the sheet material (P) that is the printing material, and is a drive roller with the transfer belt (41) interposed therebetween. (43) is arranged to face each other in parallel.
The surface of the secondary transfer roller (5) is configured to be able to be pressed and separated from the surface of the transfer belt (41), that is, the primary transfer surface. In the pressed state, the driving roller is interposed via the transfer belt (41). A nip portion (hereinafter referred to as a secondary nip portion) is formed between (43) and the toner image is secondarily transferred to the sheet material (P).

Secondary transfer to the sheet material (P) is achieved by applying a bias to the secondary transfer roller (5), as in the case of the primary transfer.
After this secondary transfer, the toner remaining on the transfer belt (41) is removed by the cleaning device (6).
A specific configuration related to the pressure contact and separation of the secondary transfer roller (5) will be described later.

A plurality of sheets (for example, 200 to 300 sheets) are stored in the supply cassette (P1), and the sheet material (P) is fed one by one to the conveyance path (R) by the sheet feeding roller (P2). It is configured.
The sheet material (P) is conveyed toward the downstream side of the conveyance path (R), and the toner image is secondarily transferred at the secondary nip portion. Thereafter, the toner image is fixed by being heated and pressurized in a fixing device (7) provided further downstream, and is conveyed outside the image forming apparatus.

Based on the above configuration, the operation of the image forming apparatus (1) will be described.
When image information is input to the image forming apparatus (1), the surface of the photoreceptor (3) is uniformly charged to a predetermined potential by the charging device (31), and then the photoreceptor (3) is exposed by the exposure device (32). ) The surface is exposed according to the input image information, and the charge in the exposed portion is removed. Thereby, an electrostatic latent image is formed on the surface of the photoreceptor (3).

Next, one of the toner cartridges (21, 22, 23, 24) accommodated in the developing device (2), for example, a toner of a black toner cartridge (hereinafter referred to as toner B) is exposed to light via a conveyance roller. It adheres to the electrostatic latent image on the surface of the body (3).
Next, the toner B attached to the electrostatic latent image on the surface of the photoreceptor (3) is primarily transferred to the transfer belt (41) by the primary transfer roller (42).
Thereafter, the same process is repeated until the remaining toner is primarily transferred to the transfer belt (41). (Excluding the process of forming an electrostatic latent image on the surface of the photoreceptor (3))
At this time, the surface of the secondary transfer roller (5) and the surface of the transfer belt (41) are in a separated state.

When all the toner images are primary-transferred, the secondary transfer roller (5) comes into pressure contact with the transfer belt (41), and the sheet material (P) passes through the conveyance path (R) at a predetermined timing. The toner image formed on the transfer belt (41) is secondarily transferred to the sheet material (P).
The sheet material (P) onto which the toner image has been secondarily transferred further proceeds downstream in the conveyance path (R), is fixed by the fixing device (7), is discharged to the outside of the image forming apparatus, and a series of operations is performed. Complete.
Note that the timing of this series of operations can be achieved by using a known detection sensor or registration switch and performing control by a control unit such as a microcomputer.

Next, the configuration of the pressure contact and separation between the transfer belt (41) (drive roller (43)) and the secondary transfer roller (5) will be described in detail.
FIG. 2 is a schematic perspective view showing the periphery of the cam mechanism in the image forming apparatus according to the present invention, and shows a state in which the transfer belt surface and the secondary transfer roller surface are in a pressure contact state.
FIG. 3 is a partially omitted side view of FIG.
FIG. 4 is a schematic perspective view showing the periphery of the cam mechanism in the image forming apparatus according to the present invention, and shows a state where the transfer belt surface and the secondary transfer roller surface are in a separated state.
FIG. 5 is a partially omitted side view of FIG.
FIG. 6 is a view showing the shape of an eccentric cam applied to the cam mechanism in the image forming apparatus according to the present invention.
FIG. 7 is a partially omitted plan view showing the periphery of the cam mechanism in the image forming apparatus according to the present invention.
Hereinafter, a description will be given with reference to FIGS.

The press contact and separation between the transfer belt (41) and the secondary transfer roller (5) are performed by a cam mechanism.
The cam mechanism is a pair of rollers provided on the drive shaft (431) of the drive roller (43) for rotating the transfer belt (41) and sandwiching both ends of the drive roller (43). A pair of rotating members (9, 9) that always contact the eccentric cams (81, 82) and the eccentric cams (81, 82) and support the secondary transfer roller (5) in a rotatable state. (Hereinafter referred to as a cam receiving portion).

The cam receiving portions (9, 9) are supported by a rotating shaft (91) provided at one end thereof (the left portion in FIGS. 3 and 5) and can rotate around the rotating shaft (91). Yes. Further, as shown in the figure, the upper portion of the central portion of the cam receiving portion (9, 9) is formed in an arc shape, and this arc-shaped portion is formed by an eccentric cam (not shown) by an urging force of an elastic body (not shown) such as a spring. 81, 82) are always in contact with each other, that is, pressed.
Further, the secondary transfer roller (5) supported by the cam receiving portions (9, 9) is substantially concentric with the center of the arc-shaped portion.

As a result, when the eccentric cam (81, 82) rotates, the cam receiver (9, 9) rotates around the rotation shaft (91) according to the shape of the eccentric cam (81, 82) (see FIG. (Clockwise in 3 and 5).
At this time, as shown in FIG. 3, the distance from the rotation center of the eccentric cam (81, 82) to the arc-shaped portion of the cam receiving portion (9, 9) is minimum (the thickness of the eccentric cam is minimum). In this embodiment, the surface of the secondary transfer roller (5) is in pressure contact with the surface of the transfer belt (41).
Thereafter, when the eccentric cam (81, 82) rotates from the state shown in FIG. 3, the distance from the rotation center of the eccentric cam (81, 82) to the arc-shaped portion of the cam receiving portion (9, 9) gradually increases. Thus, the surface of the secondary transfer roller (5) starts to be separated from the surface of the transfer belt (41). (FIG. 5 shows a state in which the separation is maximum)

As described above, when the cam receiving portions (9, 9) rotate in accordance with the rotation operation of the eccentric cams (81, 82), the secondary transfer roller (5) is relative to the transfer belt (41). Therefore, the operation of pressing and separating is performed.
With the above configuration, the press contact and separation by the cam mechanism is possible.

Next, a specific configuration of the eccentric cam (81, 82) will be described.
As described above, in the image forming apparatus using a plurality of colors, the primary transfer process for forming the toner image on the transfer belt (41) has to be performed a plurality of times. During this time, the secondary transfer roller (5) It must be separated from the transfer belt.
Accordingly, the eccentric cams (81, 82) are provided on the drive shaft (431), but are not fixed to the drive shaft (431) itself, and even if the drive shaft (431) simply rotates, It is configured to idle without rotating together.
The rotation operation of the drive shaft (431) is performed by drive means such as a motor (not shown).

The eccentric cams (81 82) start rotating when the toner image is secondarily transferred to the sheet material (P).
This is because when a detection sensor (not shown) detects that the primary transfer to the transfer belt (41) is completed, an electromagnetic clutch (hereinafter, not shown) is applied to the drive shaft (431) of the drive roller (43). The secondary transfer clutch transmits the rotation of the drive shaft (431) to the separation / connection coupling (8a) shown in FIGS. 3 and 5, and is connected to the timing belt. This is done by applying a rotational force to the eccentric cams (81, 82) via (8b) and the gear (8c).
Thereby, in the secondary transfer stage, the eccentric cams (81 82) rotate in response to the rotation of the drive shaft (431).

  Here, as shown in FIG. 6, the contour of the eccentric cam (81, 82) is formed by pressure contact including the point (A) at which the distance from the cam rotation center (O) (hereinafter referred to as the displacement distance) is minimized. A region (R1), a separation start region (R2) in which the displacement distance increases abruptly, a separation formation region (R3) including a point (B) in which the displacement distance increases gradually and becomes the maximum displacement distance, It is formed from the press-contact start region (R4) in which the displacement distance decreases rapidly.

Most of the eccentric cam (81) and the eccentric cam (82) are formed in the same shape, but are formed so that the press-separation start position and the maximum torque position are different from each other.
That is, in FIG. 6, from the separation start region (R2) indicated by the hatched portion to the initial portion of the separation formation region (R3) and from the final portion of the separation formation region (R3) indicated by the dotted line portion ( The shape up to R4) is different. (In FIG. 6, the outer contour and the dotted portion of the hatched portion represent contour portions having different shapes of the eccentric cam (82)).
In this case, needless to say, in the eccentric cams (81, 82), the displacement distance of the part having the different shape is not made larger than the point (B) that is the maximum displacement distance.

By forming as described above, the separation start position (81a), the maximum torque position (82b) and the pressure contact start position (81c) of the eccentric cam (81) are separated from the separation start position (82a) of the eccentric cam (82), This is different from the maximum torque position (82b) and the pressing start position (82c).
That is, in FIG. 6, the separation start position (82a), the maximum torque position (82b) and the pressure contact start position (82c) of the eccentric cam (82) are the separation start position (81a) and the maximum torque of the eccentric cam (81). The cam receiving portions (9, 9) are in contact with each other before the position (82b) and the press contact start position (81c).
As a result, it is possible to prevent rattling of gears, electromagnetic clutches, timing belts, and the like in secondary transfer without requiring any additional member, and it is possible to reduce peak torque during pressure contact and separation, It is possible to reduce the load applied to the shaft that supports the gear, electromagnetic clutch, timing belt, and the like.
The order of contact with the cam receiving portions (9, 9) is not particularly limited. For example, the eccentric cam (81) comes first for the press contact separation start position, and the eccentric cam for the maximum torque position. You may comprise so that (82) may contact | abut first.

In the eccentric cams (81, 82), it is preferable that the press contact / separation end positions, that is, the points (A) and (B) are formed substantially the same.
This makes it possible to make the pressure contact force between the surface of the transfer belt (41) and the surface of the secondary transfer roller (5) substantially equal at the time of pressure contact separation in the secondary transfer, particularly at the time of pressure contact. As a result, it is possible to prevent transfer failure of the toner image, and it is possible to perform reliable transfer to the sheet material (P).
Further, as described above, the eccentric cams (81, 82) are arranged coaxially with the drive shaft (431) of the drive roller (43), so that the pressure contact force can be made more uniform. More reliable transfer to the sheet material is possible.

Further, the eccentric cams (81, 82) have a displacement distance so that even if the point (A) and the point (B) are slightly shifted between one cam and the other cam due to the timing of the clutch, etc. It is preferable to provide the maximum and minimum portions for a predetermined angle (for example, about 30 °).
Note that the shape of the eccentric cam (81, 82) is not limited to that described above, and, for example, a general elliptical cam can also be suitably used. In this case, it is needless to say that the eccentric cams (81, 82) are formed so that the pressure contact / separation start position and the maximum torque position are different, and the pressure contact / separation end positions are substantially equal.

3 and 5, the tip of the cam receiving portion (9, 9) (the end opposite to the position where the rotation shaft (91) is provided) is used to rotate the eccentric cam (81, 82). Accordingly, it rotates in the substantially vertical direction.
Here, when the tip portion is below, that is, in the separated position, both ends of the thin portion of the tip portion are sandwiched (see FIG. 7), and the press-contact / separation detecting portion (10) is disposed. The press contact / separation detection unit (10) may use a known sensor.
As a result, it is possible to reliably detect the state in which the transfer belt (41) and the secondary transfer roller (5) are separated from each other, and the sheet material (P) is detected by a registration switch or the like using this detection signal. By controlling the conveyance of the toner image, it is possible to prevent malfunction during the secondary transfer of the toner image.

In the present specification, the configuration in which the eccentric cam is provided on the drive roller side has been described. However, it is naturally possible to provide the eccentric cam on the secondary transfer roller side, and other parts that require pressure contact and separation (for example, It is also possible to apply to a photoconductor and a transfer belt.
Although a color printer has been described as an example, it is needless to say that the present invention is not limited to this and can be applied to devices having a similar configuration such as a facsimile and a copying machine.

  The present invention can be suitably used as a toner image transfer mechanism in an image forming apparatus such as a printer, a copying machine, or a facsimile.

It is a schematic sectional drawing which shows an example of an image forming apparatus. FIG. 2 is a schematic perspective view showing the periphery of a cam mechanism in the image forming apparatus according to the present invention, and shows a state in which a transfer belt surface and a secondary transfer roller surface are in a pressure contact state. FIG. 3 is a partially omitted side view in FIG. 2. FIG. 2 is a schematic perspective view showing the periphery of a cam mechanism in the image forming apparatus according to the present invention, and shows a state where the transfer belt surface and the secondary transfer roller surface are in a separated state. FIG. 3 is a partially omitted side view in FIG. 2. It is a figure which shows the shape of the eccentric cam applied to the cam mechanism in the image forming apparatus which concerns on this invention. FIG. 3 is a partially omitted plan view showing the periphery of a cam mechanism in the image forming apparatus according to the present invention.

Explanation of symbols

3 Photoconductor (image carrier)
4 Intermediate transfer unit 41 Transfer belt 42 Primary transfer roller 5 Secondary transfer roller P Sheet material 81, 82 A pair of eccentric cams 9 Cam receiving portions (rotating members)
10 Pressure separation detection part

Claims (5)

An image carrier;
An intermediate transfer unit having a primary transfer roller for primarily transferring a toner image formed on the image carrier to a transfer belt;
A secondary transfer roller for secondary transfer of the toner image primarily transferred to the transfer belt to a sheet material;
A drive roller disposed opposite to the secondary transfer roller across the transfer belt,
A pair of eccentric cams for allowing the toner image transfer surface of the transfer belt and the surface of the secondary transfer roller to be pressed and separated from each other are arranged at both ends of either the driving roller or the secondary transfer roller. A rotating cam mechanism in an image forming apparatus provided,
The rotary cam mechanism in an image forming apparatus, wherein the pair of eccentric cams are formed such that a press contact / separation start position and a maximum torque position are different between one cam and the other cam.   2. The rotary cam mechanism in an image forming apparatus according to claim 1, wherein the pair of eccentric cams are formed so that the press contact / separation end positions are substantially the same in one cam and the other cam.   3. The rotating cam mechanism in an image forming apparatus according to claim 1, wherein the pair of eccentric cams are disposed coaxially with a roller on which the eccentric cam is disposed. In either one of the drive roller and the secondary transfer roller, a rotating member that rotates according to the pressure contact / separation operation is provided,
The rotary cam mechanism in the image forming apparatus according to claim 1, further comprising a press contact / separation detection unit that detects a rotation operation of the rotation member. An image forming apparatus comprising the rotating cam mechanism according to claim 1.

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