JPH0320844Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a heat fixing unit in a copying machine, and more specifically, it fixes copying paper by passing it between a pair of rollers, one of which is heated. This invention relates to a type of heat fixing unit.

In the field of copying machines, generally the surface of a photoreceptor drum is charged with a positive or negative charge by corona discharge, image exposure is performed, and then this is applied to a developing operation to form a toner image on the surface of the photoreceptor drum. Copying is performed by transferring a toner image onto copy paper and fixing the transferred toner image using heat, pressure, or the like.

However, when this transferred toner image formed on the copy paper is fixed by pressure, troubles such as so-called paper jams of the copy paper tend to occur, and the fixing performance is poor, so a fixing method using heat fixing is used. Widely used.

As a fixing method using heat fixing, a method is currently widely adopted in which copying paper having a heat-fusible toner image is passed between a pair of rollers, one of which is heated, for fixing. However, this method has disadvantages in that the two rollers are always under pressure, so the roller surfaces are easily damaged, and when rubber rollers are used as the rollers, they are likely to be deformed.

That is, the purpose of the present invention is that the two rollers are in contact only when the copying machine is operating to perform the heat fixing operation, and when the copying machine is stopped, the pressure is automatically released and the two rollers are not in contact with each other. The present invention provides a thermal fusing unit that is maintained in contact.

Another object of the present invention is to provide a heat fixing unit in which the contact and non-contact operations of two rollers are automatically performed by a simple mechanism using a spring coil made of a shape memory alloy.

According to the present invention, the roller pair includes a fixed roller whose position is fixed and a movable roller that can move up and down and which is arranged below the fixed roller, and a framework that accommodates the roller pair, and one of the rollers is a heating roller. In the heat fixing unit for a copying machine, the movable roller is supported by support arms extending at both ends of the roller shaft in a direction perpendicular to the shaft, and
one end of the support arm is rotatably supported by the frame;
The other end is supported by the frame so as to be able to move up and down via a spring coil made of a shape memory alloy that memorizes its expanded or contracted shape at a predetermined temperature. When the spring coil is sensed by the alloy and the spring coil is expanded or contracted, the movable roller rises through the support arm and comes into contact with the fixed roller, and in this state, the copy paper with the transferred toner image is placed between the rollers. The transferred toner image is thermally fixed, and when the copying machine stops operating, the shape memory alloy detects a drop in the ambient temperature inside the unit, and the spring coil returns to its original state, allowing it to move again. There is provided a heat fixing unit for a copying machine, characterized in that the rollers are lowered via a support arm and the rollers are brought into a non-contact state again.

In the present invention, a shape memory alloy is an alloy that exhibits so-called shape memory; for example, if a straight wire made of this alloy is bent at room temperature, it will instantly return to its original straight state when the flame of a lighter is brought close to it. However, when a coil whose shape has been memorized at high temperature is heated under tension, it exhibits the behavior of shrinking back to its original coil shape.

The behavior of such shape memory alloys has been reported in detail in, for example, the section on applications and problems of shape memory alloys in Kagaku Kogyo (April 1982 issue, pp. 59-66), but the so-called thermoelastic type This is a phenomenon that occurs when the low-temperature phase generated by martensitic transformation is deformed and then reversely transformed into the high-temperature phase by heating. Examples of such shape memory alloys include TiNi alloy called nitinol and betaloyd. CuZnAl alloy called Cu ₃ Al, CuAlNi, AuCd, Fe ₃ Pt, etc.
Various alloys such as InTl are known.

The present invention uses such a shape memory alloy to detect the temperature of the atmosphere in the heat fixing area, and uses the change in shape caused by this temperature change to move the lower roller of the heat fixing roller pair up and down. .

The present invention will be explained below based on specific examples shown in the accompanying drawings.

In FIGS. 1, 2-A, and 2-B showing preferred embodiments of the present invention, a thermal fixing unit generally designated by 1 includes a frame 2 and a pair of rollers 3 housed within the frame 2. , 4. The upper roller 3 has heating means (not shown) such as a heater inside.
It is a heating roller and is fixed to the machine frame 2. The lower roller 4 is movable up and down and serves as a so-called pressure roller. That is, the lower roller 4 is supported at both ends 5,5 of its shaft by support arms 6,6.

One end of this support arm is rotatably provided on the machine frame 2 with a pin 7 or the like, and the other end is connected to a spring coil 8 to allow vertical movement. The other end of the spring coil 8 is connected to a support rod 9 fixed to the upper part of the machine frame 2 by a screw or the like.

In addition, a guide plate 10 is provided on the copy paper introduction side between the rollers.
A feed plate 11 is provided on the discharge side.

That is, in this embodiment, when the operation of the copying machine is stopped, the spring coil 8 is in an extended state as shown in FIG. 2-A, and the heating roller 3 and the pressure roller 4 are in a non-contact state. When the copying machine operates, as shown in FIG. 2-B, the spring coil 8 is in a contracted state, and one end of the support arm 6 is raised, causing the pressure roller 4 to rise and come into contact with the heating roller 3. In this state, the copy paper having the transferred toner image is introduced between the rollers via the guide plate 10, and heat fixing is performed under pressure.

An important feature of the present invention is the use of a shape memory alloy as the spring coil 8, which memorizes its contracted shape at a predetermined temperature. That is, when the copying machine operates, the temperature of the heating roller 3 rises, and the temperature of the heating roller 3 increases.
Since thermal fixing is performed at a temperature of 150 to 200° C., the atmospheric temperature within the thermal fixing unit 1 also rises. Therefore, when the ambient temperature exceeds the above temperature, the shape memory alloy forming the spring coil 8 undergoes a crystal transformation called reverse transformation, and assumes the contracted shape as described above, so that the tip of the support arm 6 rises and its As a result, the pressure roller 4 rises and comes into contact with the heating roller 3,
In this state, the copy paper bearing the toner image is introduced between the rolls and thermally fixed. As mentioned above, this temperature is appropriately determined in consideration of the atmospheric temperature within the unit during heat fixing, but it is usually preferably in the range of 40 to 50°C.

Furthermore, when the operation of the copying machine is stopped, the atmospheric temperature inside the unit drops and returns to room temperature, and the internal stress of the shape memory alloy becomes zero, so the pressure roller 4 returns to its original state due to its own weight. . Therefore, the pressure roller 4 descends to its original lower position, and the rollers are brought into a non-contact state.

In this embodiment, the distance l ₁ between the support part of the support arm 6 and the pressure roller shaft support point and the distance l ₂ between the support part and the connection point of the spring coil 8 are determined by the weight of the pressure roller 4 and the spring coil. It may be determined as appropriate, taking into consideration the maximum additional load (approximately 5 kg) of item 8.

Further, in the present invention, the shape memory alloy forming the spring coil 8 may be used by storing the elongated shape.

In this case, referring to FIGS. 3-A and 3-B, the free end of the support arm 6 is connected to a support rod 9 that is movable up and down. This support rod 9 can move up and down through a fixing plate 12 provided on the machine frame 1, and a spring coil 8 made of a shape memory alloy is provided above the fixing plate 12.

The spring coil 8 is fixed to the upper end of the support rod 9 and to the fixed plate 12.

That is, in this embodiment, the expanded shape is memorized in the shape memory alloy at the ambient temperature inside the unit during heat fixing, and therefore, when the moving body of the copying machine is stopped, the spring coil 8 contracts as shown in FIG. 3-A. In this state, the pressure roller 4 is located at the lower part, and is maintained in a non-contact state with the heating roller 3.

However, when operating the copying machine, as shown in Figure 3-B, as the temperature of the heat roller 3 rises, the ambient temperature inside the unit rises and the spring coil 8 becomes in an extended state, so that the support rod 9 rises. As a result, the pressure roller 4 rises via the support arm 6 and comes into contact with the heating roller 3, and in this state the copy paper having the toner image is fed between the rollers and thermal fixing is performed.

Furthermore, if the operation of the copying machine is stopped again, the atmospheric temperature inside the unit will drop, the pressure roller 4 will fall under its own weight, and the spring coil 8 will be in an expanded state, resulting in the state shown in Figure 3-A. be understood.

As detailed above, the present invention has the remarkable effect that the vertical movement of the pressure roller 4 is automatically performed in accordance with the operation of the copying machine due to the extremely simple structure of using a shape memory alloy as the spring. It has the following.

In addition, in this invention, the maximum additional load of the shape memory alloy used for the spring coil is generally about 5
Since the roller is relatively small at about Kg, it is desirable to use rubber rollers for both the heating roller 3 and the pressure roller 4 in order to achieve surface contact between them.

In the present invention, the lower pressure roller 4 is held via a spring coil made of a shape memory alloy, and the vertical movement of the pressure roller is performed using the thermal shape change of this spring coil. Therefore, when the pressure is released, the weight of the pressure roller 4 acts in the direction of releasing the pressure, so that the pressure is released extremely quickly.

In addition, since the pressure applied to the copy paper fed between the rollers is an elastic force caused by a spring coil, the roller gap follows the thickness of the copy paper.
A constant pressure is applied regardless of the thickness of the copy paper. Furthermore, even if the rollers are deformed, the copy paper can smoothly pass through the roller gap.

[Brief explanation of the drawing]

1 is a perspective view showing a preferred embodiment of the heat fixing unit of the present invention; FIG. 2-A is a side sectional view showing the heat fixing unit of FIG. 1 in a state when the copying machine is stopped;
FIG. 2-B is a side sectional view showing the state of the copying machine in the heat fixing unit of FIG. 1 when it is in operation, and FIG. 3-A is a side sectional view showing the state of the copying machine in the heat fixing unit according to another preferred embodiment of the present invention when the copying machine is stopped. Side sectional view showing the state at the time, No. 3-B
This figure is a side sectional view showing the state of the copying machine in FIG. 3-A during operation. Reference number 1 is the heat fixing unit, 2 is the machine frame, 3 is the heating roller, 4 is the pressure roller, 6 is the support arm,
Reference numeral 8 indicates a spring coil, and reference numeral 9 indicates a support rod.

Claims (1)

[Claims for Utility Model Registration] Consisting of a roller pair consisting of a fixed roller whose position is fixed and a movable roller disposed below the roller that can move up and down, and a framework that accommodates the roller pair, any one of the rollers is In a heat fixing unit in a copying machine that is a heating roller, the movable roller is supported by support arms extending at both ends of the roller shaft in a direction perpendicular to the shaft, and one end of the support arm is rotatably attached to the frame. The other end is supported by a frame so as to be movable up and down via a spring coil made of a shape memory alloy that memorizes its expanded or contracted shape at a predetermined temperature. The shape memory alloy detects this and the spring coil assumes an expanded or contracted shape, causing the movable roller to rise via the support arm and come into contact with the fixed roller, and in this state transfer the toner image between the rollers. When the copying machine stops operating, the shape memory alloy detects a drop in the atmospheric temperature within the unit, and
When the spring coil returns to its original state, the movable roller descends via the support arm,
A heat fixing unit in a copying machine characterized in that the rollers are again in a non-contact state.