JPS6247677A - Fixing device - Google Patents

Abstract

PURPOSE:To eliminate paper wrinkles and an image shift and to prevent transfer paper from being fed slantingly, and to improve copy quality by controlling the pressing force of a back-up roller to a fixing roller on the basis of a temperature difference detected between a fed paper surface and an unfed paper surface. CONSTITUTION:The rotating speed of a motor 13 is controlled by comparing a rotating speed detected by an encoder 18 with an angle f rotation detected by a potentiometer provided on a screw shaft 9 for moving a spring unit 7 and a temperature difference measured by sensors 24 and 25 provided at both ends of the back-up roller 3 with an initial temperature difference set in a CPU. Then, a pressure roller 6 which receives a force from the unit 7 generated by the rotating force of a motor 13 through a belt 14 energizes an arms 4 supporting a roller 3 rotatably and the fixing roller 1 is energized so as to press the roller 3. Consequently, the pressing force is controlled on the basis of the temperature difference.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a fixing device that heats and fixes an unfixed toner image electrostatically transferred onto a transfer paper onto the same paper.

(Prior Art) In recent years, image forming apparatuses such as electrophotographic copying machines
It is required that the transfer paper used can be of various sizes, from postcard or business card size to large AI size.

However, when a transfer paper of Al size or smaller is passed through the fixing device using a fixing roller of a heating constant Ng device that can be used up to A1 size transfer paper, for example, the paper passing surface and non-paper passing surface of the fixing roller are separated. There is a difference in surface temperature. In addition, while the heat from the paper passing surface of the fixing roller is absorbed by the transfer paper, the heat is not absorbed from the non-paper passing surface. Therefore, the thermal expansion ratio of the backup roller is different between the non-paper passing surface and the paper passing surface of the fixing roller, and the roller diameter on the non-paper passing surface is larger than the roller diameter on the paper passing surface. If A4 size transfer paper is passed through the fixing device in this state, problems such as paper wrinkles, skewed transfer of the transfer paper, image shift, and increased curling of the transfer paper on the non-passing surface are likely to occur. This tendency becomes more and more noticeable as image forming apparatuses become faster.

Conventionally, rounding is the first method to solve such problems.
The second means is to make the core metal of the fixing roller thicker in order to improve the thermal conductivity in the longitudinal direction of the fixing roller. A method that maintains a uniform temperature in the long axis direction of the fixing roller by disposing at least two or more heaters consisting of nine-rogen lamps, which are formed asymmetrically in the direction, on the fixing roller and controlling the amount of electricity supplied to the heaters. It's a friend of mine.

(Problems to be Solved by the Invention) However, in the first means described above, if the core metal of the fixing roller is made thicker, the time required to raise the temperature to the fixing temperature becomes long, and the operating efficiency becomes extremely poor. It contained problems.

On the other hand, in the second means, although it is effective as a means for making the surface temperature of the fixing roller uniform along the longitudinal direction, there is a difference in temperature between the paper passing surface portion and the non-paper passing surface portion of the fixing roller. If we compare the temperature differences between the respective surfaces of the backup roller, as shown in FIG. 7, the temperature change of the back-up roller is larger than the temperature change a of the fixing roller.

In the figure, C indicates the temperature distribution of the fixing roller during standby, L indicates the total length of the fixing roller, %L1 indicates the paper passing surface length b of A3 size transfer paper, and I4 indicates the paper passing surface section of human size transfer paper (bird size The lengths of the non-paper-passing surfaces are shown, respectively, and the state of temperature change after passing 250 sheets of transfer paper of 7ta and bmu bird size is shown.

As a result, even if only the surface temperature of the fixing roller is controlled to be uniform, the temperature difference between the paper passing surface L'x and the non-paper passing surface of the backup roller will cause the paper passing surface L' The outer diameter difference at part L/ is the 8th
As is clear from the figure, there is a significant difference, so the above-mentioned problem cannot be fundamentally solved.In particular, in the case of this backup roller, the core metal generally has a sufficient thickness (3 to 15 m). However, the rubber has a large thermal expansion, which increases the difference in outer diameter. Incidentally, FIG. 8 shows the difference in the outer diameter of the backup roller at room temperature and after passing 250 sheets of AI size transfer paper.

(Purpose) This invention was devised in view of the current situation, and its purpose is to eliminate paper wrinkles and image distortion caused by the temperature difference between the paper passing surface and non-paper passing surface of the backup roller. It is an object of the present invention to provide a complete fixing device that can reliably prevent troubles such as misalignment or skewing of transfer paper and completely improve copying quality.

(Means for Solving the Problems) In order to achieve the above objects, the present invention includes a fixing roller whose heating is controlled to a temperature suitable for the fixing temperature, and both ends of which are brought into contact with the roller surface with a predetermined pressure. and a backup roller supported by a support device, the contact pressure on the fixing roller increases in the long axis direction in response to the surface temperature difference in the long axis direction of the four rollers. 0 (Embodiment) The present invention will be described in detail below based on the embodiment shown in the accompanying drawings.

FIG. 1 schematically shows the overall configuration of an embodiment of the present invention, in which 1 is a fixing roller, which is rotatably attached and supported on a stationary side plate (not shown), and which is attached to a tanabata (also not shown) fixing roller. It is rotatably driven and is provided with a heater 2 serving as a heat source inside.

The member shown as being in contact with the fixing roller 1 with the entire nip formed according to the broken line in the figure is a pick-up roller 3, and both ends of this roller 3 are rotatable by left and right arms 4. Supported.

Each of these arms 4 is rotatably supported at one end by a support s5 provided on a fixed side plate (not shown).
The notch-up roller 3 is pressed against the fixing roller 1 and separated from the fixing roller 1 by rotation of =9. When the roller 3 is pressed by the roller 1, the roller 3 rotates along with the roller 1 due to frictional force.

Reference numeral 6 denotes a pressure roller that pushes up the arm 4, and as shown in the figure, the pressure roller engages with the arm at the other end (the left end in the figure) opposite to the one end on the rotation center side of the arm 4, and is connected to the pressure roller from the coil spring unit described later. The arm 4 is configured to receive a force (elastic force) and apply a rotational force to the arm 4 in the direction of pressing the backup roll 3 against the fixing roll 1 (clockwise direction in the figure).

Reference numeral 7 designates a coil spring unit having a compression spring built therein, which applies the aforementioned elastic force to the pressure roller through the entire pressure shaft shown in FIG. Reference numeral 8 denotes a pressure rod that supports the pair of coil spring units 7.7, which are disposed corresponding to both ends of the axis of the backup roller 3, at both ends, and a bell nut is provided in the middle of the pressure rod to prevent rotation. It is firmly fixed. 9 screws into the pole nut and fc
The pole screw shaft 10 is a support member fixed to a fixed side plate (not shown), and supports the ball screw shaft 9 so as to be rotatable but not movable in the axial direction. The pole nut screwed onto the ball screw shaft 9, and therefore the pressurized coil spring unit 7 integrated therewith, is restricted from rotating around the ball screw shaft 9 with respect to the support member 10, as will be described later. As the ball screw 4119 rotates, it non-rotationally moves in the t-axis direction on the shaft 9. The same unit 7 has left and right arms 4.
They are placed on the left and right correspondingly.

A potentiometer 11 is arranged and fixed at one end of the ball screw shaft 9 to detect the rotation angle of the chisel screw @9. 12 is a ball screw! 1Nl 19 is assembled on the same end side, and 13 is a motor for driving the timing held 14, which is attached to the support member 0. 15 is a timing pulley fixed to the output shaft of the motor 13, and 16 is a timing pulley 15.
An electromagnetic brake 14 is arranged and fixed coaxially with the shaft 3, and a timing belt 14 is stretched between the timing pulley 12 and the timing pulley 150. 18 is motor 1
A rotary encoder fixed to a shaft in the opposite direction to the output shaft of No. 3 detects the rotation speed of the motor 13.

The drive device shown in FIGS. 1 and 2, which includes a pressure mechanism, a motor 13, etc., is configured to support the support member 10 so as to support and drive the left and right arms 4 that support both ends of the backup roller 3. One is placed at each end.

22.23f'', z, temperature detection sensors arranged at both ends of the fixing roller 1 at a required interval of PJr; 24.25 are arranged at both ends of the backup roller 3 at a required interval of 1 door; -fc temperature The temperature values detected by these sensors 22, 23, 24, 25 are input to an external temperature detection circuit.

FIG. 2 shows details of the pressurizing mechanism. A compression coil spring 62 is housed in the cylindrical frame 61 of the coil spring unit 7 after being compressed by a predetermined compression forging process. One end of this spring 62 is in contact with a flange 64 of the coil spring unit 7, and the other end is in contact with a flange 71 of the pressure shaft 20 that supports the pressure roller 6 on the upper part.

Note that the lower part of the pressure M20 is fitted and supported in a slidable relationship in the axial direction to the lower flange 64 of the spring unit 7, while the lower part of the pressure flange 71 provided at the upper part of the pressure blade shaft 20 is Until the backup roller 3 comes into contact with the fixing roller 1, it is housed in contact with the flange surface 63 of the coil spring unit 7. 2
Reference numeral 1 is a pin that slides in contact with the side surface of the support member 10, and serves to prevent rotation of the pressure rod 8, which supports the coil spring unit 7 at both ends, when it moves in the axial direction of the ball screw @9. do. 211 of these bottles 1 per 8 pressure rods
Provide one or more. Note that the support member 10 is fixed to a side plate (not shown).

Next, the operation will be explained. Assuming that the electromagnetic brake 16 is released by the control circuit described later that controls the rotational drive of each motor 130, and the motors 13t begin to rotate approximately at the same time,
The rotational driving force of the motor 130 is transmitted to the ball screw shaft 9 via the timing pulley 15, the timing belt 14, and the timing pulley 12, and rotates the ball screw 11119 in a predetermined direction. 19 moves linearly along the Dahl screw shaft 9 in the direction of arrow A. Therefore, the Zeel nut 19 is fixed to the nine pressure rod 8, and the companion coil spring units 7 provided at both ends of this pressure rod 8 are also fixed.
It moves in the A direction together with 9. With this movement, the pressure roller 6 supported by the unit 7 pushes up one end of the arm 4, and the backup roller 3 supported by the arm 4 pushes up one end of the arm 4.
moves upward to come into contact with the fixing roller 1.

On the other hand, the input shaft of the nine potentiometer 11 fixed to one end of the Zeel screw shaft 9 rotates during the above operation.

Note that the potentiometer used here is preferably a multi-rotation type potentiometer whose input shaft rotates several times and can accurately detect the north rotation angle.

What is the output signal of each potentiometer? - Since the position of the nut 19 on the dial screw shaft 9 has a certain correlation, the rotation angle of each arm 4, that is, whether the backup roller 3 is in a position where it is in contact with the fixing roller 1 or is separated from it and is The position of the separation distance can be accurately known from the output of the potentiometer 11.

From the above, inputting the output signal of the rotary encoder 18 fixed to the shaft of each motor 13 to the control circuit,
In addition, by simultaneously inputting the output signal from the potentiometer 11 to the control circuit, the rotation speed of each motor 13 can be adjusted so that the optimum motor rotation speed can be obtained depending on the position of the backup roller 3 and the state of crimping or release operation. It becomes possible to control the

Figure 3 shows a control circuit that controls the pressure adjustment of the backup roller 3 configured as described above to the fixing roller l. Based on the content, the fixing roller 1 is heated by the heater 2. The minimum size of the transfer paper (size that can be copied) is input as an initial setting value in the ROM 30, and a temperature detection sensor 24.
25 and the initial pressure contact amount at both left and right ends of the roller 3 are input as initial values. In this state, when the number of copies, copy mode F, etc. are selected and the copy start button 31 is turned on, the backup roller 3 comes into pressure contact with the fixing roller 1.

This is because the computer CPU inputs a motor drive signal to the motor driver 33 that drives and controls the left and right motors 13 via the output interface 32 based on the initial pressure contact amount of the roller 3 input to the ROM, and this input signal In response to this, the motors 13 are driven, and the pressure roller 6 pushes up the left and right arms 4, and the roller 3 comes into pressure contact with the fixing roller 1. In this case, since the amount of rotation of each motor 13 is checked and controlled by each potentiometer 11, the amount of pressure applied by the backup roller 3 does not exceed the initial value.

On the other hand, the temperature detected by nine temperature detection sensors 24 and 25 disposed at both left and right ends of the backup roller 3,
After the detection signal is amplified by the amplifiers 34 and 34~Φ
The converter 35 converts the width to the input interface 36
The actual temperature difference X is calculated by the computer CPU, and then the initial setting f[! It is compared with Xo.

If the actual measured temperature difference X is compared to the initial setting [Xo, X≦, and The computer CPU maintains instructions.

After that, to finish copying, the computer CPU reversely rotates the motor 13 to release the pressure contact between the fixing roller 1 and the backup roller 3, and the backup roller 3 is placed in a standby state. will be reset to On the other hand, if the copying does not finish, the fourth
As shown in the figure, temperature detection by the temperature detection sensors 24 and 25 is performed in the same manner as described above.

In addition, if the actual measured temperature difference If the size of the transfer sheet is larger than that of the previous copy, the motor 13 that controls the amount of pressure on the higher temperature side of the pack-up roller 3 receives instructions from the computer CPU to reduce the nip on the higher temperature side of the pack-up roller 3. The drive is controlled by the In this case, the drive amount of the motor 13 is rotationally controlled based on an amount corresponding to a predetermined temperature difference.

When the copying process is completed in this manner, the size of the transfer sheet that was just copied is stored in the computer CPU in preparation for the fifth copying, as shown in FIG. After that, a decision is made to finish copying, and if copying is to be finished, both motors 13 are rotated in the opposite direction to release the pressure contact between the fixing roller 1 and the backup roller 3, and the backup roller 3 is reset to a standby state. On the other hand, if copying is not completed, temperature detection is performed using the above procedure.

Note that if the transfer paper size is the same as the previous transfer paper size or smaller, the above-mentioned troubles such as paper wrinkles will not occur, so there is no need to change the pressure contact lid of the backup roller 3.

FIG. 5 shows a second embodiment of the invention,
Left and right arms 4 that support both ends of the backup roller 3 in the field
is supported by a cam 26, and by controlling the rotation of this cam 26, the amount of pressure applied by the pack-up 7° roller 3 is adjusted.

Further, FIG. 6 shows a third embodiment of the present invention, in which left and right arms 4 that pivotally support both ends of the backup port 3 are supported by a wedge-shaped adjustment member 27. By moving the member 27 forward and backward, the inclined end portion 4a of the arm 4 that comes into sliding contact with the inclined surface 27a of the member 27 is adjusted up and down, thereby adjusting the press-contact cover of the backup roller 3.

(Effects of the Invention) As explained above, the present invention detects the temperature in the longitudinal direction of the backup roller, and changes the amount of pressure in the longitudinal direction of the backup roller based on the temperature difference near both ends. With this structure, it is possible to reliably prevent troubles such as paper wrinkles, image shift, and skew of the transfer paper from occurring, and it is possible to always obtain stable and high-quality constant N image errors.

[Brief explanation of the drawing]

FIG. 1 is a side view schematically showing the entire structure of a constant N device according to a first embodiment of the present invention, FIG. 2 is a side view partially cut away showing the structure of an arm support device, and FIG. A block diagram showing a control circuit that variably controls the pressure contact lid of the backup roller,
FIG. 4 is a 7 μm chart showing the operating state of the fixing device, FIG. 5 is a side view schematically showing the entire structure of the fixing device according to the second embodiment of the present invention, and FIG. 6 is the third embodiment of the fixing device according to the present invention. A side view schematically showing the entire configuration of the fixing device according to the embodiment, FIG. 7 is a graph showing the axial distribution of the fixing roller and the backup roller, and FIG. 8 is the outer diameter of the backup roller in the axial direction. It is a graph diagram showing a changing state. l... Fixing roller 2 2... Heater 3... Backup roller 6... Pressure roller 7... Coil spring unit 9... Dale Nezu shaft 11... Potentiometer 13... Motor 24, 25...Temperature detection sensor...Backup roller paper passing surface Lz...
- Non-paper passing surface of backup roller Patent applicant: Canon Co., Ltd. Figure 5 Figure 6

Claims (1)

[Claims] A fixing roller that is heated and controlled to a temperature suitable for the fixing temperature,
A fixing device comprising a backup roller whose both ends are supported by a support device so as to be in contact with the fixing roller surface with a predetermined pressure, wherein the backup roller has a surface temperature difference in the longitudinal direction of the roller. Correspondingly, the fixing device is characterized in that the fixing roller is supported by the support device under pressure control such that the contact pressure on the fixing roller is different at both ends in the longitudinal direction.