JPH05188821A - Cam device for releasing nip pressure for fixing device - Google Patents

Abstract

PURPOSE:To easily execute the releasing action of nip pressure by light force by using a cam member having a cam surface expressed by a multidimensional system in a heat roll system fixing device which fixes a large-sized paper. CONSTITUTION:In the heat roll system fixing device which is obtained by facing and arranging a heating roll and a pressure roll and which releases the nip pressure by depressing a roll supporting arm supporting the pressure roll by the cam member, the cam member 10 is arranged with respect to the roll supporting arm and the pressure roll is separated from the heating roll by rotating the cam member 10. On the cam member 10, a small-diameter arc-like part 13 and a large-diameter arc-like part 14 are provided and the cam surface expressed by a multidimensional curve is set by the part 14. A section where the radius of a cam is suddenly increased is set between an actuation starting point B and an intermediate point C and a part where the radius of the cam is gently changed is set at a part where a spring is largely elongated between the point C and an upper dead point E.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cam member for releasing a nip pressure between both rolls in a heat roll type fixing device, and more particularly to a fixing device for a large size sheet. When the nip pressure is released against the force of a strong spring, the driving torque for the cam member can be set substantially constant from the operation start point of the cam member to the top dead center. The present invention relates to a cam device for releasing the nip pressure of a fixing device.

[0002]

2. Description of the Related Art In an apparatus such as an electronic copying machine or a printer for forming a toner image on an image bearing member such as a photosensitive drum by using an electrophotographic system, the toner image formed on the photosensitive drum is printed on a paper sheet. After the transfer, the image is fixed through a fixing device to make a copy. As the fixing device, a general heat roll type device is used, and in the heat roll type fixing device, a mechanism for pressing a pressure roll against a heating roll containing a heating source is used. ing. Then, in order to set a nip pressure of a predetermined value between the two fixing rolls, a pressure roll is supported by a spring against a heating roll supported by the frame of the fixing device, and the pressure is applied by the spring. A means for pressing the roll is used.

As the fixing device, for example, Japanese Unexamined Patent Application Publication No. Hei 2
As shown in JP-A-282773, JP-A-64-44967, etc., a device in which a spring for setting the nip pressure and a cam member for releasing the nip pressure are combined is used. There is. The mechanism for turning on / off the nip pressure in the fixing device is configured as shown in FIG. 5. The fixing device 1 includes a heating roll 2 provided with a heating source and a heating source. The pressure roll 3 that does not have or has a heating source is arranged to face.

In the conventional example, the heating roll 3 is supported by the roll supporting arm 5, and one end of the roll supporting arm 5 is supported by the frame of the fixing device via the fulcrum 6 and the other end is supported. A spring 8 for tension setting is arranged between the support frame 9 and the support frame 9 so that the pressure roll 3 is pressed toward the heating roll 2. Further, a cam member 15 is arranged to release the nip pressure between the both rolls, and by driving the cam member through the cam shaft 17, the roll support arm 5 is moved through the fulcrum 6. Then, the pressure roller 3 is swung clockwise against the force of the spring 8 to separate the pressure roller 3 from the heating roller 2. Only when the fixing operation is performed in the fixing device, the pressing action of the cam member is released and the nip pressure is set by the spring 8.

[0005]

As shown in FIG. 5, when controlling the nip pressure using a cam member,
Generally, a cam member 15 as shown in FIG. 6 is used. In the cam member 15, between the bottom dead center A and the top dead center E, the cam surface 1 is shaped so that the radius of the cam gradually increases.
6 is formed. Then, the roll support arm pressed by the cam surface 16 is gradually swung greatly via the fulcrum while countering the force of the spring as the cam member rotates. When the cam member as shown in FIG. 6 is used, as shown in the graph of FIG. 7, it acts so that the radius of the cam gradually increases with respect to the rotation angle of the cam member. When the radius of the cam member is plotted on the vertical axis of the graph and the rotation angle of the cam member is plotted on the horizontal axis, the rotation radius changes substantially linearly from the point B of the cam member 15 to the point D. Become.

However, since the operation of pushing down the roll support arm is performed against the force of the spring by rotating the cam member, it is proportional to the length of extension of the spring. There is a problem that the torque for driving the cam member increases. When the cam member is used, as the rotation angle increases, as shown in the graph of FIG.
The torque value S increases in a quadratic curve. The increase in the rotation torque of the cam member means that, for example, in a fixing device provided in a relatively small electronic copying machine, the spring force is not so large that a motor or the like having a relatively weak driving force with respect to the cam member is used. Even if it is used, it can be dealt with easily.

However, it is necessary to set the nip pressure of 100 kgf to 300 kgf in an electronic copying machine for copying a drawing or the like using a large size sheet such as A0 size. In such a large-sized fixing device, pressing the pressure roller by the cam member against the spring that applies the strong nip pressure makes the rotational torque for the cam member a very large value. Will be required. Then, in order to drive the cam member, it is necessary to dispose a driving motor, a shaft member of the cam member, and the like, and other mechanism attached thereto,
Since the support frame and the like are also formed to have a large strength, the influence on the manufacturing cost of the device is very large.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-described problem of the conventional nip pressure releasing mechanism, in which the rotational torque does not suddenly increase with respect to the cam member for turning on / off the nip pressure. An object of the present invention is to provide a cam member having such a cam surface, and further to provide a device that can reduce the force applied to the cam member and other drive members by using the cam member. It is an object.

[0009]

The present invention provides two means.
The two rolls are arranged to face each other, and the roll supporting arm for supporting the pressure roll is provided with the function of pressing the pressure roll so as to have a predetermined nip pressure with respect to the heating roll provided with the heating source. On the other hand, the present invention relates to a fixing device configured to perform a setting operation and a releasing operation of a nip pressure by using a driving means including a cam member and a spring. In the drive mechanism of the pressure roll of the present invention, the cam member is configured by a cam surface having a curve represented by a multidimensional formula, and the cam member is driven in a state of releasing the nip pressure between both rolls. It is configured so that the torque does not increase.

As described above, even when the cam member is pressed at all positions, the pressure roll can be pushed down in a condition that requires substantially the same rotational torque. The driving force of the motor required for driving can be reduced. Further, in the cam member of the present invention, since the load applied to the cam surface can be reduced, it is possible to reduce partial wear of the cam member and the counterpart member, and improve the durability of the drive member. It will be possible. If the nip pressure between the two rolls of the heat roll type fixing device is set to a very large value, the rotational torque that drives the cam shaft against the strong spring force. Since it can be set to be small, the driving device can be made small.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A nip pressure releasing cam device of a fixing device according to the present invention will be described with reference to the illustrated example. The example shown in FIG. 1 is similar to the case of the conventional example shown in FIG.
The fixing device 1 is arranged such that a heating roll 2 having a heating source inside and a pressure roll 3 having no heating source face each other. In the fixing device 1, the pressure roll 3 is supported by the roll supporting arm 5, and one end of the roll supporting arm 5 is supported by the frame of the fixing device via the fulcrum 6.
A spring 8 is arranged at the other end. Then, the force of the spring 8 causes the roll support arm 5 to swing counterclockwise via the fulcrum 6 to press the pressure roll 3 toward the heating roll 2 to perform the fixing operation. ..

A cam member 10 is arranged to release the nip pressure between the rolls 2 and 3.
By rotating the cam member via the cam shaft 12, the roll support arm 5 is swung clockwise through the fulcrum 6 against the pulling force of the spring 8. Then, the pressure roll 3 is separated from the heating roll 2 to release the nip pressure. That is, in the fixing device, only when the fixing operation is performed, the cam member is rotated by 1/2 turn to release the downward pressing action of the cam member on the roll support arm 5 and restore the nip pressure. Make it work.

In the fixing device 1, a cam member 10 having a structure as shown in FIG. 2 is arranged in order to swing the roll supporting arm 5. The cam member 10 is
It is configured by combining a small-diameter arc-shaped portion 13 and a large-diameter arc-shaped portion 14, and the small-diameter arc-shaped portion 1
The cam shaft 12 is arranged at a position corresponding to 3. In the cam member 10, the top of the small-diameter arcuate portion 13 is the bottom dead center A, and the top of the large-diameter arcuate portion 14 is the top dead center E.
The area between the connecting portion B of the two arcs and the bottom dead center A is set as the non-operating range. The area between the operation starting point B and the top dead center E is set as a range for performing the pressurizing action, and in the large diameter portion 14, as shown in FIG. Between C and C, the portion where the radius of the cam increases rapidly is set. Further, on the cam surface 11, between the points C and D, a portion where the radius of the cam changes gently is set, and between the points D and E, an area where the radius of the cam hardly changes is set. It is set.

As described above, by configuring the cam surface 11 of the cam member 10 to have a multidimensional curve, as shown in the graph of FIG. 3, with respect to the rotation angle of the cam member shown on the horizontal axis. The change in the radius of gyration R of the cam member shown on the vertical axis does not change at all in the small-diameter portion from point A to point B, and the radius of the cam changes greatly from point B to point C. Is set. When the cam member 10 having the shape shown in FIG. 2 is driven, as shown in the graph of FIG. 4, the torque value S shown on the vertical axis is relative to the rotation angle taken on the horizontal axis. , The initial value from point B to point C rapidly increases, but the absolute value of the torque does not increase in the subsequent rotation of the cam member, but rather decreases from point D to point E. It becomes a state.

As shown in the graphs of FIG. 3 and FIG. 4, when the radius of the cam and the value of the torque sharply increase in the initial stage of rotation of the cam member, as shown in FIG. In the fixing device, the spring 8 supporting the pressure roll 3 is stretched, and in the initial stage of its operation, the spring can be stretched with a relatively light force. On the other hand, if the spring is stretched to a certain length and an attempt is made to further stretch it, it is necessary to apply a very large force. Therefore, in the cam member of the present invention, the radius of the cam surface is rapidly increased at the portion where the spring can be extended with a relatively light force, so that the spring can be extended greatly. On the other hand, in the part that requires a large force to extend the spring,
Set the radius of the cam to change gently so that the action of extending the spring can be easily performed.

Therefore, as shown in FIG.
Since the height of the peak portion of the torque value S can be set lower than that in the case of the graph of FIG. 8, the cam shaft is driven to release the nip pressure between both rolls of the fixing device. The power to do can be reduced. Then, in order to make a copy using a large size paper, an electronic copying machine using a large-sized heat roll type fixing device uses a strong spring to set the nip pressure. Such a device can be easily dealt with by using a relatively small drive mechanism having a weak force.

In the cam member of the present invention, when the shape of the cam surface is formed by a multi-dimensional curve, the changing state of the radius of the cam is arbitrarily set according to the nip pressure set by the spring. can do. For example, the degree of changing the radius of the cam in the portion from the point B to the point C can be appropriately set according to the characteristics of the spring provided in the fixing device and the like. Further, in the present invention, the cam member can be arranged at an arbitrary position with respect to the mechanism for supporting the pressure roll, and in addition to the fixing device having the mechanism as shown in FIG. Of the heat roll type fixing devices that have been generally used in the past, the present invention can be applied to any device in which the pressure roll is supported by the roll supporting arm.

[0018]

As described above, the cam member of the present invention has the following features.
The cam surface is formed with a multi-dimensional curve, and the roll support arm can be driven according to the state in which the spring is stretched, so it is easy to separate the pressure roll from the heating roll in the fixing device. Can be done. In addition, even when pressed at all positions on the cam surface,
Since the pressure roller can be pushed down by requiring the rotating torque of substantially the same value, the driving force of the motor required to drive the cam member can be reduced. Since the load applied to the cam surface can be reduced, the partial wear of the cam member and the counterpart member can be reduced, the durability of the drive member can be improved, and the drive device can be made compact. can do.

[Brief description of drawings]

FIG. 1 is a side view showing a configuration of a fixing device of the present invention.

FIG. 2 is a plan view showing a configuration of a cam member of the present invention.

FIG. 3 is a graph showing changes in the radius of the cam of the cam member shown in FIG.

FIG. 4 is a graph showing a relationship between a rotation angle of a cam member and a torque value.

FIG. 5 is a side view showing the configuration of a conventional fixing device.

FIG. 6 is a plan view showing a configuration of a conventional cam member.

7 is a graph showing changes in the radius of the cam of the cam member shown in FIG.

FIG. 8 is a graph showing a relationship between a rotation angle of a cam member and a torque value.

[Explanation of symbols]

1 fixing device, 2 heating rolls, 3 pressure rolls, 5 roll support arms, 8 springs,
10 cam member, 11 cam surface, 12 cam shaft, A bottom dead center, B operation start point, E top dead center.

Claims (1)

[Claims] 1. The two rolls are arranged so as to face each other, and the pressure roll is pressed against a heating roll provided with a heating source so that the pressure roll has a predetermined nip pressure. In a fixing device configured to perform a setting operation and a releasing operation of a nip pressure by using a driving unit including a cam member and a spring for a supporting roll supporting arm, the cam member is represented by a multidimensional expression. For releasing the nip pressure of the fixing device, the cam surface is formed with a curved line to prevent the torque for driving the cam member from increasing while releasing the nip pressure between both rolls. Cam device.