JP2004109169A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a fixing device in an electrophotographic forming apparatus where the fluctuation of paper carrying speed caused by disturbance such as temperature rise is restrained to be little. <P>SOLUTION: The fixing device is constituted of a fixing and heating roller, a pressure roller, a driving transmitting mechanism for inputting rotational driving force in the pressure roller, a driving motor, a sensor for detecting the circumferential speed of the fixing and heating roller (the sensor is a reflection type image sensor using an LED as a light emitting part) and a driving control unit (provided that the driving control unit performs constant-speed control so that output from the sensor for detecting the circumferential speed of the fixing and heating roller may be converged to target speed). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device in an electrophotographic image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer (for example, a laser printer), a facsimile machine, and a word processor which forms an image on a recording medium using an electrophotographic image forming method.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, a toner image transferred onto a recording medium at a transfer unit is nipped and conveyed by a pair of rotating rollers in pressure contact with each other, and heat is applied at the contact portion to apply toner to the recording medium (paper). ).
[0003]
To fix the toner on the recording medium, heat is applied to the toner until the toner has a desired viscosity, and this is mechanically pressed to generate a bonding force such as an intermolecular force between the toner and the cellulose fibers of the paper. This is the process of bonding and fixing.
[0004]
Here, for example, if the heat transmitted to the toner is insufficient, the toner will not sufficiently dissolve into the paper, resulting in a cold offset in which the toner is offset toward the fixing roller. Conversely, even if the toner is overheated, the cohesive force between the toners is reduced, resulting in a hot offset that is offset to the fixing roller. Even if such image defects do not occur, especially in full-color printers, uneven coloring of the toner causes uneven gloss, uneven hue and saturation, and a decrease in color development, and the uniform melting of the toner is particularly sensitive. is there.
[0005]
As a means for making the melting state of the toner uniform, a heat-resistant silicon rubber layer is provided on the surface of a metal base material such as aluminum of a fixing heating roller contacting the toner surface and a pressure roller contacting the back surface of the paper. The effect of the above is to make the pressure distribution uniform and to make the heat transfer uniform.
[0006]
In addition, the silicon rubber layer on the fixing and heating roller side has the function of diffusing the heat obtained by taking the base material from the heat source to make it uniform, and the function as a heat storage part to avoid the surface temperature drop during continuous paper passing. In addition, the silicon rubber layer on the pressure roller side has a heat insulating action between the fixing nip portion and the pressure roller shaft.
[0007]
As described above, when a roller having an elastic layer of silicon rubber or the like on its outer periphery is used for a fixing device, the roller diameter changes due to thermal expansion, and the paper conveyance speed changes.
[0008]
This change in transport speed can be a cause of image defects, paper wrinkles, and paper jams when paper is pushed in or when paper is pressed or fed when the transfer unit and fixing unit are close to each other due to continuous paper feeding. It becomes.
[0009]
As a method of detecting the paper conveyance speed in the conventional fixing device,
(1) A method of detecting the transport speed from the number of rotations of the transport rollers of the paper supply / discharge unit.
(2) The speed detecting roller is driven to rotate by contact with the fixing heating roller to detect the number of rotations of the roller shaft.
However, in the case of (1), since rotation cannot be detected during non-sheet passing, control of the first sheet passing cannot be performed and intermittent printing cannot be performed.
[0010]
In the case of (2), damage to the surface of the fixing roller directly appears as an image, so that contact of the roller with the fixing roller should be avoided. In addition, since both (1) and (2) are affected by the sliding of the rollers and the thermal expansion of the rollers themselves, it has been difficult to detect a variation in the transport speed of at most about ± 3%.
[0011]
[Problems to be solved by the invention]
The present invention realizes a fixing device in an electrophotographic forming apparatus in which a change in a sheet conveyance speed due to disturbance such as a temperature rise is small.
[0012]
[Means for Solving the Problems]
(Constitution)
A fixing device in an electrophotographic image forming apparatus having the following configuration.
[0013]
(1) A fixing heating roller. Here, the outer diameter portion of the fixing heating roller comes into contact with the surface of the recording medium sent from the transfer portion where the unfixed toner exists, and applies heat to fix the toner to the recording medium.
[0014]
(2) A heating source for supplying heat to the fixing heating roller.
[0015]
(3) Pressure roller. Here, the pressure roller axis is parallel to the fixing and heating roller axis, is pressed by a predetermined force against the fixing and heating roller, and sandwiches the recording medium in the contact area between the two rollers to convey the recording medium.
[0016]
(4) A drive transmission mechanism for inputting a rotational driving force to the pressure roller. Here, the fixing heating roller follows the pressure roller because it is in direct pressure contact with the pressure roller or via the recording medium.
[0017]
(5) Drive motor.
[0018]
(6) A sensor for detecting the peripheral speed of the fixing heating roller. This sensor is a reflection type image sensor using an LED as a light emitting unit.
[0019]
(7) Drive control unit.
[0020]
Here, the drive control unit performs constant speed control such that the output of the fixing heating roller peripheral speed sensor converges to a target speed.
[0021]
(Description)
The configuration according to the present invention will be briefly described with reference to FIG.
[0022]
In the fixing device of this configuration, a pair of the fixing heating roller (100) and the pressure roller (102) is used. The axes of this roller pair are always parallel, and the pressure roller axis (102b) is urged by a means such as a spring in a direction to decrease its distance with respect to the fixing heating roller axis (100a) fixed in the space. ing. Therefore, the outer circumferences of the fixing heating roller (100) and the pressing roller (102) are in pressure contact with each other at the fixing nip (101).
The pressure roller (102) is driven and input from a roller drive gear (124) fixed on the pressure roller shaft (102b). The driving force is transmitted from the motor pinion (114) to the roller drive gear (124) via two two-stage idler gears (120, 122), and the speed is reduced in three steps from the motor shaft to the pressure roller shaft. .
[0023]
The motor (110) is a DC motor with a pulse generator (112).
[0024]
The speed sensor (130) is a reflection type image sensor using an LED as a light emitting unit, and detects a tangential speed around the outer periphery of the fixing heating roller (100).
[0025]
Here, as shown in FIG. 1B, the closed loop control is configured so that the detected speed Eo (152) converges within a certain error with respect to the transport speed target value Ei (150). The motor unit (162) performs shaft rotation speed feedback compensation in order to adapt particularly to disturbances such as load fluctuations.
[0026]
As described above, according to the fixing device of the configuration of the present invention, the driving and control of the fixing unit are performed independently of the main body, and the non-contact image sensor is used for the speed detection, so that the sheet conveyance speed can be stabilized with high accuracy. It is possible to make.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example)
(Main body of electrophotographic image forming apparatus using fixing device according to the present invention)
First, an electrophotographic image forming apparatus configured according to the present embodiment will be described with reference to FIG. FIG. 2 is a cross-sectional view showing a state in which a process cartridge B is mounted on an electrophotographic image forming apparatus main body A in this embodiment.
[0028]
The process cartridge B in the image forming apparatus main body A has a drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum 7. The photosensitive drum 7 is charged by a charging unit, and then a laser beam is irradiated from the optical unit 1 to form a latent image on the photosensitive drum 7 according to image information. This latent image is developed by the developing means of the process cartridge B, and becomes a visible image, that is, a toner image.
[0029]
On the other hand, in synchronization with the formation of the toner image, the recording medium 12 set in the sheet cassette is transported to the transfer position by the pickup roller 13, the transport roller pair 2, and the registration roller pair 3. A transfer roller 4 as a transfer unit is disposed at the transfer position, and transfers a toner image on the photosensitive drum 7 to a recording medium by applying a voltage.
[0030]
The recording medium to which the toner image has been transferred is conveyed to the fixing unit 11. The fixing unit 11 applies heat and pressure to the passing recording medium to fix the transferred toner image on the recording medium.
[0031]
The recording medium is conveyed by a pair of discharge rollers (8) and discharged to a discharge tray.
[0032]
(Fixing machine configuration)
FIG. 3 shows the configuration of the fixing device in this embodiment.
[0033]
In FIG. 1, a sheet having an unfixed toner image on its upper surface is carried in through an inlet opening (302) along a conveying surface (301), and is discharged out of the machine through an outlet (303) through a fixing process.
[0034]
The fixing heating roller (100) is formed by spray-coating a heat-resistant silicon rubber layer of about 1 mm on the outer periphery of an aluminum pipe having a thickness of 1 mm as a base material, and then coating a PFA layer of about 50 μm on the outermost layer. The diameter is 30 mm. The fixing heating roller (100) has flanges at both ends thereof supported by a fixing frame (300) via bearings. An 800 W near-infrared halogen heater is provided on the shaft core as a fixing heat source.
[0035]
The pressure roller (102) is formed by casting a 5 mm heat-resistant silicon rubber layer on the outer periphery of a stainless steel shaft having an outer diameter of 20 mm, and maintains the outer diameter accuracy by outer diameter grinding. The pressure roller (102) is supported at both ends thereof on a pressure frame (310) via bearings. Further, the pressure frame (310) is supported swingably about a pivot shaft (312) provided on the fixing frame. The axes of the roller pair of the fixing heating roller (100) and the pressure roller (102) are always parallel, and the pressure roller axis (102b) is at a distance from the fixing heating roller axis (100a) fixed in the space. Is urged by means of a pressure spring (314) in the direction of decreasing the pressure.
[0036]
Therefore, the outer circumferences of the fixing heating roller (100) and the pressing roller (102) are in pressure contact with each other at the fixing nip (101). In this embodiment, in consideration of the area and the surface pressure distribution of the fixing nip formed by the deformation of the pair of rollers, the pressing force at this fixing nip is adjusted so that the nip average surface thickness becomes p = 3 kgf / cm ² . Set.
[0037]
Here, when the pressure roller (102) is driven from the outside, the fixing roller (100) receives a tangential force at the outer peripheral portion, and is accordingly driven.
[0038]
A speed sensor (130) is provided at the longitudinal center of the fixing roller of the fixing upper cover (305). The speed sensor (130) is a reflection type image sensor using an LED as a light emitting unit, and illuminates the outer peripheral portion of the fixing heating roller (100) by using a lens unit (130a) with a red LED (130c) as a light source. Then, this is imaged on the image sensor section in the chip (130b) through another part of the lens unit (130a). The tangential speed of the fixing roller is detected from the moving distance and time of the obtained pattern.
[0039]
Here, since the image sensor used in this example had a resolution sufficient to detect minute irregularities on the surface of the fixing heat roller, no marking for detection was particularly provided on the surface of the fixing heat roller, When using a sensor with a low resolution, or when increasing the distance between the sensor and the fixing roller to avoid heating the sensor, print a speed detection mark on the surface of the silicon rubber layer of the roller. A method such as coating PFA thereon can be used.
[0040]
(Fusing unit drive mechanism)
As shown in FIG. 1A, the pressure roller (102) is driven and input from a roller drive gear (124) fixed on a pressure roller shaft (102b). The driving force is transmitted from the motor pinion (114) to the roller drive gear (124) via two two-stage idler gears (120, 122), and the speed is reduced in three steps from the motor shaft to the pressure roller shaft. .
[0041]
The motor (110) is a DC motor with a pulse generator (112).
[0042]
FIG. 4 shows the arrangement of the gear train. Here, since the axis of the second idler gear (122) is on the swing shaft (312) of the pressure roller frame, the pressure roller frame is moved by the swing shaft (312) under the influence of the thickness of the paper passing through the nip portion. The center-to-center distance between the second idler gear (122) and the pressure roller gear (124) is constant even if it swings to the center.
[0043]
(Fixing unit constant speed control block)
FIG. 1B shows a speed control block of the fixing device according to the present embodiment.
[0044]
Here, the closed loop control is configured so that the detected speed Eo (152) converges within a certain error with respect to the target transport speed value Ei (150). The detection of Eo uses the output of the speed sensor (130).
[0045]
The motor unit (162) detects the rotation speed N by a pulse generator (112) attached to the motor shaft, and performs shaft rotation speed feedback compensation. This is to adapt to disturbances such as load fluctuations.
[0046]
As the disturbance D (154), speed fluctuation due to thermal expansion of the fixing roller and the pressure roller is mainly taken into consideration. However, since the sampling frequency of the speed sensor (130) is sufficiently high at 1.5 KHz, the impact of the nip rush, It was possible to follow the speed fluctuation due to the paper thickness.
[0047]
Conversely, if the only purpose is to reduce the speed fluctuation due to thermal expansion, the specifications of the speed sensor may be simplified and a cheaper sensor may be used.
[0048]
In the present embodiment, the above constant speed control is realized by software control by a DSP, but a PID circuit using an analog device may be used as a simpler method.
[0049]
Further, in the present embodiment, when the detected speed is lower than the target speed value by a certain value or more, a function of outputting an alarm signal by determining that a roller slip has been added. By configuring the logic to turn off the driving power and heater power by the output of this roller slip signal, it is possible to prevent accidents such as abnormal temperature rise of the roller when the roller stops, ignition due to stagnant paper in the nip, and roller seizure. it can.
[0050]
【The invention's effect】
According to the fixing device configuration of the electrophotographic image forming apparatus in the present invention,
A simple configuration has been realized in which the driving of the fixing unit is controlled at a constant speed independently of the main body. As a result, the degree of freedom in the layout of the main body configuration has been improved, for example, the distance between the transfer unit and the fixing unit has been reduced.
[0051]
The use of a non-contact image sensor for speed detection has made it possible to stabilize the paper transport speed with high accuracy.
[0052]
Further, by detecting the roller slip, it is possible to prevent an abnormal rise in the temperature of the roller when the roller is stopped, a fire due to a paper stagnation in the nip portion, and a burn-in of the roller.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a fixing device driving configuration and a constant speed control block diagram according to the present invention.
FIG. 2 is a cross-sectional view of the electrophotographic image forming apparatus according to the embodiment of the present invention.
FIG. 3 is a central sectional view of the fixing device according to the present invention.
FIG. 4 is a drive unit configuration diagram of a fixing device according to the present invention.
FIG. 5 is an external view of a fixing device according to the present invention.
[Explanation of symbols]
11 Fixing Unit 100 Fixing Heating Roller 102 Pressure Roller 130 Speed Sensor 110 Drive Motor 112 Pulse Generator 300 Fixing Frame 310 Pressing Frame 314 Pressing Spring 150 Speed Target Value 152 Speed Output Value 162: Drive motor block

Claims (3)

A fixing device in an electrophotographic image forming apparatus having the following configuration.
(1) A fixing heating roller. Here, the outer diameter portion of the fixing heating roller comes into contact with the surface of the recording medium sent from the transfer portion where the unfixed toner exists, and applies heat to fix the toner to the recording medium.
(2) A heating source for supplying heat to the fixing heating roller.
(3) Pressure roller. Here, the pressure roller axis is parallel to the fixing and heating roller axis, is pressed by a predetermined force against the fixing and heating roller, and sandwiches and conveys the recording medium in the contact area between the two rollers.
(4) A drive transmission mechanism for inputting a rotational driving force to the pressure roller. Here, the fixing heating roller follows the pressure roller because it is in direct pressure contact with the pressure roller or via the recording medium.
(5) Drive motor.
(6) A sensor for detecting the peripheral speed of the fixing heating roller. This sensor is a reflection type image sensor using an LED as a light emitting unit.
(7) Drive control unit.
Here, the drive control unit performs constant speed control such that the output of the fixing heating roller peripheral speed sensor converges to a target speed. 2. The electrophotographic image forming apparatus according to claim 1, wherein the drive motor is a DC motor having a pulse generator for detecting a rotation speed of an output shaft, and performs feedback compensation of the output rotation speed using the detected value. Fixing device in the device. The fixing heating roller peripheral speed obtained from the detection value of the pulse generator is compared with the peripheral speed obtained from the fixing heating roller peripheral speed sensor, and when the latter value becomes lower than a certain width, a roller slip signal is output. The fixing device according to claim 1, wherein the fixing device is a fixing device.

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