JP7628852B2 - Fixing device and image forming apparatus - Google Patents

Description

This invention relates to a fixing device and an image forming apparatus, and in particular to a fixing device and an image forming apparatus that are equipped with a fixing rotor and a pressure rotor, and that thermally fix a toner image formed on a recording medium.

One example of a conventional fixing device is disclosed in Patent Document 1. The fixing device in Patent Document 1 includes a heating member (fixing rotor) whose base material is an endless metal sleeve, a radiant heat source provided inside the heating member, a support member (fixing pad) having a sliding surface that slides against the inner surface of the heating member, a pressure roller (pressure roller) that forms a nip between the sliding surface of the support member to apply pressure by sandwiching the heating member and the supporting member, and drives the heating member to rotate in a predetermined direction, and a backup member that is located on the opposite side of the sliding surface of the support member and receives the pressure force of the pressure roller applied to the support member.

Another example of a conventional fixing device is disclosed in Patent Document 2. The fixing device in Patent Document 2 includes a drive mechanism (contact pressure change mechanism) that moves the fixing roller toward and away from the fixing roller by driving a motor, a detection means for detecting the current value of the motor, an estimation unit for estimating the load torque of the motor based on the current value detected by the detection means, and a contact pressure control unit for controlling the contact pressure of the fixing roller based on the load torque estimated by the estimation unit.

JP 2007-233011 A JP 2019-164187 A

In the technology of Patent Document 1, the fixing rotor is rotated in response to the rotation of the pressure rotor. However, during warm-up to raise the temperature of the fixing rotor to a predetermined temperature, high frictional forces are generated between the fixing pad and the fixing rotor, which may cause the fixing rotor to slip against the pressure rotor or lock the drive source (motor) of the pressure rotor, resulting in the fixing rotor to malfunction. If the fixing rotor is heated in a malfunctioning state, a part of the fixing rotor will heat up suddenly and abnormally rise in temperature, causing damage to the fixing rotor, such as distortion or peeling.

On the other hand, according to the technology of Patent Document 2, by controlling the contact pressure between the fixing rotor and the pressure rotor based on the load torque of the motor that drives the contact pressure change mechanism, it is possible to adjust the contact pressure to a target contact pressure according to the paper type and paper thickness even if there is variation in the component precision and assembly precision of each part. However, the technology of Patent Document 2 does not take into consideration the malfunction of the fixing rotor during warm-up.

Therefore, the primary object of this invention is to provide a novel fixing device and image forming device.

Another object of the present invention is to provide a fixing device and an image forming device that can appropriately prevent malfunction of the fixing rotor during warm-up.

A first invention is a fixing device that thermally fixes a toner image formed on a recording medium, the fixing device including a fixing rotator, a heat source that heats the fixing rotator, a pressure rotator that contacts an outer circumferential surface of the fixing rotator to form a nip portion between the fixing rotator and the pressure rotator and drives the fixing rotator to rotate, a motor that drives the pressure rotator to rotate, a current value detection unit that detects a current value of the motor, a contact pressure change mechanism that can change the contact pressure of the pressure rotator against the fixing rotator, and a current value of the motor detected by the current value detection unit during warm-up to raise the temperature of the fixing rotator to a target temperature. The fixing device includes a contact pressure control unit that controls the contact pressure change mechanism so as not to exceed a preset upper limit value , and increases the contact pressure of the pressure roller against the fixing roller until it reaches a target contact pressure . The contact pressure control unit linearly increases the contact pressure of the pressure roller from a first contact pressure, temporarily stops changing the contact pressure of the pressure roller when the motor current value reaches an upper limit value, and increases the contact pressure of the pressure roller again when the motor current value drops to a threshold value, thereby increasing the contact pressure of the pressure roller to the target contact pressure within the range where the motor current value is between the upper limit value and the threshold value .

According to the first invention, the contact pressure of the pressure rotating body against the fixing rotating body is controlled according to the current value of the motor that rotates the pressure rotating body, so that poor rotation of the fixing rotating body during warm-up can be appropriately prevented.

A second aspect of the present invention is an image forming apparatus including the fixing device according to the first aspect of the present invention.

According to the second aspect of the invention, similarly to the first aspect of the invention, it is possible to appropriately prevent the fixing rotator from failing to rotate during warm-up.

This invention can effectively prevent the fixing rotor from failing to rotate during warm-up.

The above and other objects, features and advantages of the present invention will become more apparent from the detailed description of the embodiments given below with reference to the drawings.

1 is a schematic cross-sectional view showing an internal structure of an image forming apparatus according to a first embodiment of the present invention; FIG. 2 is a schematic cross-sectional view showing a fixing device. FIG. 2 is a plan view showing a pressure roller provided in the fixing device. FIG. 2 is a perspective view showing a pressure unit included in the fixing device. FIG. 2 is a schematic front view showing a pressurizing unit. FIG. 4 is a front view showing a separation and engagement cam provided in the pressure unit. FIG. 2 is a block diagram showing an example of an electrical configuration of the image forming apparatus. FIG. 8 is a diagram showing an example of a memory map of a RAM shown in FIG. 7 . FIG. 8 is a flowchart showing an example of a warm-up process executed by the CPU shown in FIG. 7 . FIG. 11 is a flowchart showing an example of a warm-up process executed by a CPU of an image forming apparatus according to a second embodiment of the present invention. FIG. 11 is a flowchart showing an example of a warm-up process executed by a CPU of an image forming apparatus according to a third embodiment of the present invention.

[First embodiment]
1, an image forming apparatus 10 according to a first embodiment of the present invention is an apparatus for forming a multi-color or monochrome image on paper by electrophotography. As will be described in detail later, the image forming apparatus 10 includes a fixing device 46 that thermally fixes a toner image formed on paper (recording medium).

First, the basic configuration of the image forming device 10 will be briefly described. Note that in this specification, the surface facing the user's standing position, i.e., the surface on which the operation unit 106 (see FIG. 7) is provided, is defined as the front (front), and the front-to-rear direction (depth direction) of the image forming device 10 and its components are defined. In addition, the left-to-right direction (horizontal direction) of the image forming device 10 and its components are defined based on the state in which the image forming device 10 is viewed by the user.

As shown in FIG. 1, in this first embodiment, the image forming device 10 is a multifunction peripheral (MFP) having a copying function, a printer function, a scanner function, a facsimile function, etc. The image forming device 10 includes a device main body 12 equipped with an image forming unit 30, etc., and an image reading device 14 disposed above the device main body 12.

The image reading device 14 has a document placement platform 16 made of a transparent material. A document pressing cover 18 is attached above the document placement platform 16 via a hinge or the like so that it can be opened and closed freely. This document pressing cover 18 is provided with an ADF (automatic document feeder) 24 that automatically feeds documents placed on a document placement tray 20 one by one to an image reading position 22. In addition, on the front side of the document placement platform 16, an operation unit 106 is provided that accepts input operations such as printing instructions from the user. This operation unit 106 is appropriately provided with a display such as a touch panel display and various operation buttons, etc.

The image reading device 14 also has a built-in image reading unit 26 that includes a light source, multiple mirrors, an imaging lens, and a line sensor. The image reading unit 26 exposes the document surface to the light source, and guides the light reflected from the document surface to the imaging lens using multiple mirrors. The imaging lens then focuses the reflected light on the light receiving element of the line sensor. The line sensor detects the luminance and chromaticity of the reflected light focused on the light receiving element, and generates image data based on the image of the document surface. A CCD (Charge Coupled Device) or a CIS (Contact Image Sensor) is used as the line sensor.

The device main body 12 includes a control unit 28 including a CPU 100, a RAM 102, and a HDD 104 (see FIG. 7), and an image forming unit 30. The control unit 28 (specifically, the CPU 100) transmits control signals to each part of the image forming device 10, including the fixing device 46, in response to input operations by a user to the operation unit 106, causing the image forming device 10 to perform various operations.

The image forming section 30 includes an exposure unit 32, a developing device 34, a photoconductor drum 36, a cleaner unit 38, a charger 40, an intermediate transfer belt unit 42, a secondary transfer roller 44, and a fixing device 46, and forms an image on paper conveyed from a paper feed tray 48 or a manual paper feed tray 50, and discharges the paper with the image formed on it to a paper discharge tray 52. As image data for forming an image on the paper, image data read by the image reading section 26 or image data sent from an external computer is used.

The image data handled by the image forming device 10 corresponds to color images of four colors: black (K), cyan (C), magenta (M), and yellow (Y). For this reason, four of each of the developing device 34, photoconductor drum 36, cleaner unit 38, and charger 40 are provided to form four types of latent images corresponding to each color, and these constitute four image stations.

The photoconductor drum 36 is an image carrier in which a photosensitive layer is formed on the surface of a cylindrical conductive base body, and the charger 40 is a member that charges the surface of the photoconductor drum 36 to a predetermined potential. The exposure unit 32 is configured as a laser scanning unit (LSU) equipped with a laser emission section and a reflecting mirror, etc., and exposes the charged surface of the photoconductor drum 36 to light, thereby forming an electrostatic latent image on the surface of the photoconductor drum 36 according to the image data. The developer 34 visualizes the electrostatic latent image formed on the surface of the photoconductor drum 36 with four color (YMCK) toners. The cleaner unit 38 removes toner remaining on the surface of the photoconductor drum 36 after development and image transfer.

The intermediate transfer belt unit 42 includes an intermediate transfer belt 54, a driving roller 56, a driven roller 58, and four intermediate transfer rollers 60, and is disposed above the photosensitive drum 36. The intermediate transfer belt 54 is a flexible endless belt that is stretched by a plurality of rollers, such as the driving roller 56 and the driven roller 58, and is disposed so that its surface (outer circumferential surface) abuts against the surface of the photosensitive drum 36. The intermediate transfer belt 54 rotates (moves in a circular motion) in a predetermined direction in accordance with the rotational drive of the driving roller 56. The intermediate transfer rollers 60 are disposed at positions facing each of the photosensitive drums 36 across the intermediate transfer belt 54. During image formation, the intermediate transfer rollers 60 are used to transfer the toner images of each color formed on each photosensitive drum 36 to the intermediate transfer belt 54 in a sequentially overlapping manner, thereby forming a multi-color toner image on the intermediate transfer belt 54.

The secondary transfer roller 44 is disposed opposite the drive roller 56 with the intermediate transfer belt 54 in between. When paper passes through the secondary transfer nip between the secondary transfer roller 44 and the intermediate transfer belt 54, the toner image formed on the intermediate transfer belt 54 is transferred to the paper.

The fixing device 46 includes a fixing belt 62 and a pressure roller 64, and is disposed above the secondary transfer roller 44 (downstream in the paper transport direction). A fixing pad 76 and a heat source 82 (see FIG. 2) are provided within the fixing belt 62, and the fixing belt 62 is heated by the heat source 82 to a predetermined fixing temperature (for example, 170°C). The pressure roller 64 is provided so as to press the fixing belt 62 between itself and the fixing pad 76. When the paper passes through the fixing nip N (see FIG. 2) between the pressure roller 64 and the fixing belt 62, the toner image transferred to the paper is melted, mixed, and pressed against the paper, and the toner image is thermally fixed to the paper. The specific configuration of the fixing device 46 will be described later.

In the device main body 12, a first paper transport path L1 is formed for sending paper from the paper feed tray 48 or manual paper feed tray 50 to the paper output tray 52 via the registration rollers 68, secondary transfer roller 44, and fixing device 46. In addition, when performing double-sided printing on the paper, a second paper transport path L2 is formed for returning the paper after single-sided printing is completed and the paper has passed through the fixing device 46 to the first paper transport path L1 upstream of the secondary transfer roller 44 in the paper transport direction. In the first paper transport path L1 and the second paper transport path L2, a plurality of transport rollers 66 are appropriately provided to provide auxiliary propulsion force to the paper.

Next, the mechanical configuration of the fixing device 46 will be described with reference to Figures 2 to 6. The fixing device 46 includes a fixing belt 62, which is an example of a fixing rotor, and a pressure roller 64, which is an example of a pressure rotor, and fixes a toner image to the paper by passing the paper through the fixing nip N formed between them.

Specifically, as shown in Figs. 2 and 3, the fixing device 46 includes a heater unit 70 having a fixing belt 62 and the like, and a pressure unit 72 having a pressure roller 64 and the like. The members of the heater unit 70 and the pressure unit 72 are integrally held in a predetermined arrangement by a fixing frame (not shown).

The heater unit 70 is provided with a fixing belt 62 that is formed in a generally cylindrical shape and extends in the front-rear direction (width direction of the paper). The fixing belt 62 is, for example, a belt-shaped base material formed of a synthetic resin such as polyimide or a metal such as nickel, with a release layer provided on the surface. Such a fixing belt 62 is provided so as to be rotatable around its axis, and has an inner diameter of, for example, 30 mm. Inside the fixing belt 62, a fixing pad 76, a support member 78, a reflector 80, a heat source 82, and the like are provided.

The fixing pad 76 is a fixed member fixedly provided so as to be in sliding contact with the inner peripheral surface of the fixing belt 62, and is formed in the shape of a long plate extending along the axial direction of the fixing belt 62. The fixing pad 76 has a sliding sheet 76a on its outer peripheral surface (at least the sliding surface with the fixing belt 62), and sliding oil is applied to this sliding sheet 76a to reduce friction with the fixing belt 62. The length of the fixing pad 76 is the same as the axial length (width) of the fixing belt 62.

The support member 78 is a member that supports the fixing pad 76 while pressing it against the inner peripheral surface of the fixing belt 62, and both ends of the support member 78 are fixed to the fixing frame. In this first embodiment, the support member 78 is formed with a generally L-shaped cross section, and has a long plate-shaped fixing portion 78a to which the fixing pad 76 is fixed, and a long plate-shaped standing portion 78b that stands from the widthwise end of the fixing portion 78a. In addition, a thin plate-shaped reflecting plate 80 is attached to the support member 78 so as to cover the surface on the heat source 82 side.

The heat source 82 is a member for heating the fixing belt 62, and is provided so as to extend along the axial direction of the fixing belt 62. A lamp heater such as a halogen lamp is used as the heat source 82. In this first embodiment, the heat source 82 includes a first lamp heater 82a that heats the axial center portion of the fixing belt 62, and a second lamp heater 82b that heats both axial ends of the fixing belt 62. The first lamp heater 82a and the second lamp heater 82b are used differently depending on the paper width.

The pressure unit 72 includes a pressure roller 64 that is disposed in a position facing the fixing pad 76 with the fixing belt 62 in between. The pressure roller 64 is disposed so as to extend parallel to the axial direction of the fixing belt 62, and forms a fixing nip portion N between the pressure roller 64 and the fixing pad 76 by pressing the fixing belt 62 against the fixing belt 62.

Specifically, as shown in FIG. 3, the pressure roller 64 includes a cylindrical roller portion 84. The roller portion 84 has a cylindrical core material made of a metal such as aluminum, an elastic layer made of an elastic material such as silicone rubber and covering the surface of the core material, and a release layer made of a material with a low friction coefficient such as a fluorine-based resin and covering the surface of the elastic layer. The axial length of the roller portion 84 is the same as the axial length of the fixing belt 62.

In addition, in this first embodiment, both ends of the roller portion 84 are provided with thin grip portions 86 made of a material with high friction resistance (i.e., good gripping power) such as silicone rubber. The grip portions 86 are positioned on the outer side (outside the paper width) in the width direction of the paper passing through the fixing nip portion N, and their thickness (protruding height from the release layer) is, for example, 200 μm. By providing such grip portions 86 on the roller portion 84, the rotational force of the pressure roller 64 can be appropriately transmitted to the fixing belt 62 even when the pressure roller 64 is in a low contact pressure state as described below.

A first motor 90 (see FIG. 7) is connected to one end (rear end) of the roller shaft 88 of the pressure roller 64 via a gear or gear train (not shown). The pressure roller 64 is driven to rotate by receiving a driving force from the first motor 90, and the fixing belt 62 is rotated in the opposite direction to the rotation direction of the pressure roller 64 as the pressure roller 64 is driven to rotate. That is, the pressure roller 64 abuts against the outer surface of the fixing belt 62 to form a fixing nip N between the pressure roller 64 and the fixing belt 62, and transmits a rotational driving force to the fixing belt 62 through the fixing nip N, thereby rotating the fixing belt 62. In addition, the first motor 90 is provided with a current sensor 92 (see FIG. 7) such as a current transformer that detects the current (motor current value) flowing through the first motor 90.

Returning to FIG. 2, the fixing device 46 includes a temperature sensor 94 such as a thermopile or thermistor that detects the surface temperature of the fixing belt 62. The temperature sensor 94 includes, for example, a first temperature sensor that detects the surface temperature of the axial center of the fixing belt 62, and a second temperature sensor that detects the surface temperature of the axial end of the fixing belt 62. In addition, a peeling plate 96 is provided downstream of the fixing nip portion N in the paper transport direction to prevent the paper from wrapping around the fixing belt 62.

The fixing device 46 also includes a contact pressure change mechanism 110 (separation mechanism) capable of changing the contact pressure of the pressure roller 64 against the fixing belt 62. In this first embodiment, the contact pressure change mechanism 110 is provided in the pressure unit 72, and the contact pressure (pressing force) of the pressure roller 64 against the fixing belt 62 is changed by moving the pressure roller 64 in the contact/separation direction relative to the fixing belt 62. The contact pressure change mechanism 110 is also capable of completely separating the pressure roller 64 from the fixing belt 62. An example of the contact pressure change mechanism 110 will be described below with reference to Figures 4 to 6. However, the specific configuration of the contact pressure change mechanism 110 is not limited to this.

4 and 5, the contact pressure change mechanism 110 is provided at both ends of the pressure unit 72 and includes a pair of pressure levers 112 extending in a direction perpendicular to the axial direction of the pressure roller 64. Each of the pressure levers 112 rotatably supports the roller shaft 88 of the pressure roller 64 at its center via a bearing 114. Each of the pressure levers 112 also has an engagement hole 118 at one end (lower end) that engages with a pivot shaft 116 provided in the fixing frame. The pivot shaft 116 is provided to extend parallel to the axial direction of the fixing belt 62, and the pressure lever 112 can rotate in a direction (left and right direction) in which it moves toward and away from the fixing belt 62 with the pivot shaft 116 as a fulcrum. The pressure roller 64 is displaced in a direction in which it moves toward and away from the fixing belt 62 in conjunction with the rotation of the pressure lever 112. Furthermore, each of the pressure levers 112 has a locking portion 120 at the other end (upper end) that locks one end of a tension coil spring (not shown), which is an example of a biasing member. The other end of the tension coil spring is locked to the fixing frame, and a predetermined biasing force acts on the pressure lever 112 (and thus the pressure roller 64) in the direction in which the pressure roller 64 presses against the fixing belt 62 (to the left).

The contact pressure change mechanism 110 also includes a cam shaft 122 that extends parallel to the axial direction of the fixing belt 62. Both ends of the cam shaft 122 are rotatably supported by the fixing frame. Also, at both ends of the cam shaft 122, a contact cam 124 is provided adjacent to the pressure lever 112, and the pressure lever 112 is provided with a contact portion 126 with the contact cam 124. Furthermore, a second motor 128 (see FIG. 7) is connected to one end (rear end) of the cam shaft 122 via a gear or gear train (not shown). The cam shaft 122 receives a driving force from the second motor 128 and is driven to rotate in the forward and reverse directions around its axis, and the contact cam 124 rotates together with the cam shaft 122.

As shown in FIG. 6, the separation cam 124 is shaped so that in region R1, the distance from the axial center of the camshaft 122 gradually increases from Ls to Le. Therefore, the separation cam 124 receives a rotational driving force from the second motor 128 and rotates in the forward and reverse directions at a rotational position where the contact position with the contact portion 126 is in region R1, thereby rotating the pressure lever 112 and changing the contact pressure (pressure) of the pressure roller 64 against the fixing belt 62. Note that when the separation cam 124 contacts the contact portion 126 at position E where the distance from the axial center of the camshaft 122 is the farthest (the state in FIG. 5), the pressure roller 64 is separated from the fixing belt 62.

In this fixing device 46, when forming an image, the fixing belt 62 maintains a predetermined fixing temperature, and the pressure roller 64 contacts the fixing belt 62 with a predetermined contact pressure (pressing force), so that the paper passes through the fixing nip N, fixing the toner image to the paper. Therefore, when the temperature of the fixing belt 62 is low, such as at the time of startup, a warm-up operation is performed to increase the temperature of the fixing belt 62 to a predetermined fixing temperature (target temperature) while rotating the fixing belt 62 before forming an image on the paper. At this time, when the temperature of the fixing belt 62 is low, the viscosity of the sliding oil of the fixing pad 76 increases, and a high frictional force is generated between the fixing belt 62 and the fixing pad 76. For this reason, there is a risk that the fixing belt 62 will slip against the pressure roller 64, or that a large load will be applied to the first motor 90 that drives the pressure roller 64, causing the first motor 90 to lock, resulting in a rotation failure of the fixing belt 62. Therefore, a technology is required that prevents the fixing belt 62 from slipping while suppressing the load on the first motor 90.

Therefore, in this first embodiment, during warm-up, the contact pressure change mechanism 110 (specifically, the second motor 128) is controlled based on the current value of the first motor 90, which is proportional to the rotation torque of the pressure roller 64, to change the contact pressure of the pressure roller 64 against the fixing belt 62, thereby preventing the fixing belt 62 from rotating poorly.

Specifically, at the start of warm-up, the contact pressure of the pressure roller 64 is set to a first contact pressure (e.g., 30 N) that is a low contact pressure that does not cause the fixing belt 62 to slip. Then, while monitoring the current value of the first motor 90, the contact pressure of the pressure roller 64 is gradually increased until it reaches the target contact pressure (e.g., 300 N) so that the current value does not exceed a preset upper limit (e.g., 1800 mA) within a range in which the first motor 90 can be driven appropriately. For example, when the current value of the first motor 90 falls below a preset threshold value (e.g., 1500 mA) that is lower than the upper limit, the contact pressure is increased by a predetermined value, and the contact pressure of the pressure roller 64 is increased in stages (e.g., in 3 to 5 stages) up to the target contact pressure. Alternatively, the contact pressure of the pressure roller 64 may be increased linearly from the first contact pressure, the change in the contact pressure may be stopped once the current value of the first motor 90 reaches the upper limit, and the contact pressure of the pressure roller 64 may be increased again when the current value of the first motor 90 falls to the threshold value, so that the contact pressure of the pressure roller 64 may be increased to the target contact pressure within the range where the current value of the first motor 90 falls between the upper limit and the threshold value. This control method is based on the knowledge confirmed by the inventors through verification experiments that the rotation torque of the pressure roller 64 decreases as the temperature of the fixing belt 62 increases, whereas the rotation torque of the pressure roller 64 increases as the contact pressure of the pressure roller 64 increases. A specific control method during warm-up will be described later using a flow chart.

Figure 7 is a block diagram showing an example of the electrical configuration of the image forming device 10. As shown in Figure 7, the image forming device 10 includes a CPU 100, to which a RAM 102, a HDD 104, an operation unit 106, an image reading device 14, an image forming unit 30, and the like are connected via a bus.

The CPU 100 performs overall control of the image forming apparatus 10 according to the programs stored in the HDD 104. The CPU 100 also executes the warm-up process of this first embodiment, and functions as a temperature detection unit, a current value detection unit, a contact pressure control unit, a rotation speed control unit, and the like. The RAM 102 is used as a working area and a buffer area for the CPU 100. The HDD 104 appropriately stores control programs and necessary data for the CPU 100 to control the operation of each part of the image forming apparatus 10. However, other non-volatile memories such as SSDs, flash memories, and EEPROMs may be used instead of or together with the HDD.

The operation unit 106 includes a display with a touch panel, operation buttons, etc. The display is a general-purpose monitor such as an LCD, and is connected to the CPU 100 via a display control circuit (not shown). The display control circuit includes a GPU, a VRAM, etc. Under the instruction of the CPU 100, the GPU uses image generation data stored in the RAM 102 to generate display image data in the VRAM for displaying various screens on the display, and outputs the generated display image data to the display. The touch panel detects touch operations within the effective touch range, and outputs touch coordinate data indicating the position of the touch operation to the CPU 100. The operation buttons are hardware keys, and include various keys or buttons such as a home button, a power saving key, and a power button.

The image reading device 14 and the image forming unit 30 are as described above, and the image forming unit 30 includes the fixing device 46 and the like. The fixing device 46 also includes the heat source 82, the temperature sensor 94, the first motor 90, the current sensor 92, and the second motor 128 and the like.

As described above, the heat source 82 is a heater for heating the fixing belt 62 from the inner surface side. The temperature sensor 94 is a sensor for detecting the surface temperature of the fixing belt 62, and outputs the detection result (a signal corresponding to the surface temperature of the fixing belt 62) to the CPU 100 based on an instruction from the CPU 100. The CPU 100 controls the heat source 82 based on the detection result by the temperature sensor 94 so that the surface temperature of the fixing belt 62 becomes the desired temperature.

The first motor 90 is a motor for rotating the pressure roller 64, and rotates the motor shaft based on a control signal from the CPU 100 so that the pressure roller 64 rotates at the desired rotation speed. The current sensor 92 is a sensor for detecting the motor current flowing through the first motor 90, and outputs the detection result (a signal corresponding to the motor current value) to the CPU 100 based on an instruction from the CPU 100. The second motor 128 is a motor for rotating the cam shaft 122, and rotates the motor shaft based on a control signal from the CPU 100 so that the separation cam 124 is at the desired rotation position. That is, the CPU 100 controls the rotation position (angle) of the motor shaft of the second motor 128 to control the rotation position of the separation cam 124 and control the contact pressure between the fixing belt 62 and the pressure roller 64. In addition, in this first embodiment, during warm-up, the CPU 100 controls the rotational position of the separation cam 124 based on the detection results of the current sensor 92 so that the contact pressure between the fixing belt 62 and the pressure roller 64 gradually approaches the target contact pressure from the first contact pressure.

Figure 8 is a diagram showing an example of a memory map 200 of RAM 102. As shown in Figure 8, RAM 102 includes a program memory area 202 and a data memory area 204. In the program memory area 202 of RAM 102, an operation detection program 202a, an image formation program 202b, a contact pressure control program 202c, etc. are stored.

The operation detection program 202a is a program for detecting operations on each part of the image forming apparatus 10, including the operation unit 106. The image forming program 202b is a program for controlling components such as the photoconductor drum 36 to print a multi-color or monochrome image on paper. The contact pressure control program 202c is a program for controlling the second motor 128 of the contact pressure change mechanism 110 to control the contact pressure between the fixing belt 62 and the pressure roller 64. This contact pressure control program 202c includes a program for controlling the second motor 128 based on the detection result by the current sensor 92 during warm-up to change the contact pressure of the pressure roller 64 against the fixing belt 62.

Although not shown in the figure, the program memory area 202 also stores other programs for executing various functions by the CPU 100 as appropriate.

In addition, the data storage area 204 of the RAM 102 stores a setting value table 204a, cam position data 204b, current value data 204c, temperature data 204d, etc.

The setting value table 204a is a table that stores data such as setting values used to execute the contact pressure change operation in the fixing device 46, such as the target temperature of the fixing belt 62, the target rotation speed of the pressure roller 64, the target contact pressure of the pressure roller 64, and the threshold and upper limit of the current value of the first motor 90.

The cam position data 204b is data for identifying the cam position of the contact cam 124, and includes data indicating that the contact cam 124 is located at, for example, an initial position, a target position, an intermediate position, or a separation position. Here, the initial position is a cam position where the contact pressure of the pressure roller 64 becomes a first contact pressure (a low contact pressure that does not cause the fixing belt 62 to slip). The target position is a cam position where the contact pressure of the pressure roller 64 becomes a predetermined contact pressure (target contact pressure) according to the paper type. The intermediate position is a cam position at each stage where the contact pressure of the pressure roller 64 becomes any contact pressure between the first contact pressure and the target contact pressure (such as the second contact pressure and the third contact pressure). The separation position is a cam position where the pressure roller 64 is separated from the fixing belt 62.

The current value data 204c is a value measured by the current sensor 92, i.e., data on the motor current value flowing through the first motor 90. The temperature data 204d is a value measured by the temperature sensor 94, i.e., data on the surface temperature of the fixing belt 62.

Although not shown in the figure, the data memory area 204 is provided with timers (counters) or registers necessary for executing the control program, and stores other data necessary for executing the control program.

The above-described operation of the fixing device 46 (image forming device 10) is realized by the CPU 100 executing a control program read into the RAM 102. An example of the warm-up process (contact pressure change process) in the fixing device 46 will be described below with reference to the flow chart shown in FIG. 9.

As shown in FIG. 9, when the warm-up process starts, the CPU 100 checks the cam position of the separation and engagement cam 124 in step S1. Here, it checks that the separation and engagement cam 124 is in the initial position where the contact pressure of the pressure roller 64 is the first contact pressure (e.g., 30 N). If the separation and engagement cam 124 is not in the initial position, a control signal is sent to the second motor 128 to rotate the separation and engagement cam 124 to the initial position.

In the next step S3, the pressure roller 64 starts to rotate. Here, a control signal is sent to the first motor 90 to rotate the pressure roller 64 at a predetermined rotation speed (target rotation speed). The fixing belt 62 rotates in response to the rotation of the pressure roller 64. In the following step S5, heating of the fixing belt 62 starts. That is, a control signal is sent to the heat source 82 to cause the heat source 82 to generate heat. The temperature of the fixing belt 62 rises as the heat source 82 generates heat.

In the next step S7, it is determined whether the motor current value flowing through the first motor 90 is equal to or less than the threshold value. If the answer is "NO" in step S7, that is, if the motor current value of the first motor 90 exceeds the threshold value, the process proceeds to step S9. In step S9, the contact pressure of the pressure roller 64 is maintained, and the process returns to step S7. In other words, the contact pressure of the pressure roller 64 is maintained at the current level until the motor current value falls below the threshold value.

On the other hand, if step S7 is "YES", that is, if the motor current value of the first motor 90 is equal to or less than the threshold value, the process proceeds to step S11. In step S11, the contact pressure of the pressure roller 64 is increased. Here, a control signal is sent to the second motor 128 to rotate the contact/detach cam 124, and the contact pressure of the pressure roller 64 is increased stepwise by a predetermined value. For example, the contact pressure of the pressure roller 64 is increased from the first contact pressure to the second contact pressure (e.g., 100 N), from the second contact pressure to the third contact pressure (e.g., 200 N), or from the third contact pressure to the target contact pressure (e.g., 300 N).

In the next step S13, it is determined whether the contact pressure of the pressure roller 64 has reached the target contact pressure. If the result of step S13 is "NO", that is, if the contact pressure of the pressure roller 64 has not reached the target contact pressure, the process returns to step S7. On the other hand, if the result of step S13 is "YES", that is, if the contact pressure of the pressure roller 64 has reached the target contact pressure, the process proceeds to step S15. Note that in steps S7 to S13, rather than increasing the contact pressure of the pressure roller 64 in stages, the contact pressure of the pressure roller 64 can also be gradually increased to the target contact pressure within the range in which the current value of the first motor 90 falls between the upper limit value and the threshold value.

In the next step S15, it is determined whether the surface temperature of the fixing belt 74 has reached the target temperature. If the answer is "NO" in step S15, that is, if the fixing belt 74 has not reached the target temperature, the process waits until the fixing belt 74 reaches the target temperature. On the other hand, if the answer is "YES" in step S15, that is, if the fixing belt 74 has reached the target temperature, the warm-up process ends and the process moves to image formation process in which an image is formed on paper.

As described above, according to this first embodiment, during warm-up, the contact pressure of the pressure roller 64 against the fixing belt 62 is controlled according to the current value of the first motor 90, so that the fixing belt 62 can be prevented from slipping and the first motor 90 can be prevented from locking, and rotation problems of the fixing belt 62 can be appropriately prevented. In other words, the fixing belt 62 can be stably driven to rotate. In addition, because the rotation torque of the pressure roller 64 can be suppressed, a low-output first motor 90 can be used.

[Second embodiment]
Next, an image forming apparatus 10 according to a second embodiment of the present invention will be described with reference to Fig. 10. This second embodiment differs from the first embodiment in that the contact pressure change mechanism 110 is controlled based on the temperature of the fixing belt 62 instead of the current value of the first motor 90. Since the other parts are similar, the same reference numbers are used for parts common to the first embodiment, and duplicated descriptions are omitted or simplified.

In this second embodiment, during warm-up, the contact pressure of the pressure roller 64 against the fixing belt 62 is changed by controlling the contact pressure change mechanism 110 based on the surface temperature of the fixing belt 62 detected by the temperature sensor 94. Specifically, at the start of warm-up, the contact pressure of the pressure roller 64 is set to a first contact pressure, which is a low contact pressure. Then, while monitoring the surface temperature of the fixing belt 62, the contact pressure of the pressure roller 64 is increased in stages (for example, in 3 to 5 stages) when the surface temperature of the fixing belt 62 reaches a preset intermediate temperature (such as the first temperature and the second temperature), so that the contact pressure of the pressure roller 64 is gradually increased until it reaches the target contact pressure. This control method is based on the knowledge confirmed by the inventors through a verification experiment that the higher the temperature of the fixing belt 62, the lower the rotation torque of the pressure roller 64.

An example of a warm-up process (contact pressure change process) in the fixing device 46 will be described below with reference to the flow diagram shown in FIG. 10. As shown in FIG. 10, when the warm-up process starts, the CPU 100 checks in step S21 that the cam position of the separation cam 124 is in the initial position where the contact pressure of the pressure roller 64 is the first contact pressure. In the next step S23, the pressure roller 64 starts to rotate, and is rotated at the target rotation speed. In the following step S25, heating of the fixing belt 62 starts.

In the next step S27, it is determined whether the surface temperature of the fixing belt 62 has reached a first temperature (for example, 70°C). If the result of step S27 is "NO", that is, if the surface temperature of the fixing belt 62 has not reached the first temperature, the process proceeds to step S29. In step S29, the contact pressure of the pressure roller 64 is maintained and the process returns to step S27. On the other hand, if the result of step S27 is "YES", that is, if the surface temperature of the fixing belt 62 has reached the first temperature, the process proceeds to step S31. In step S31, a control signal is sent to the second motor 128 to increase the contact pressure of the pressure roller 64 from the first contact pressure to the second contact pressure.

In the next step S33, it is determined whether the surface temperature of the fixing belt 62 has reached a second temperature (for example, 120°C). If the answer is "NO" in step S33, the process proceeds to step S35, where the contact pressure of the pressure roller 64 is maintained and the process returns to step S33. On the other hand, if the answer is "YES" in step S33, the process proceeds to step S37, where a control signal is sent to the second motor 128 to increase the contact pressure of the pressure roller 64 from the second contact pressure to the third contact pressure.

In the next step S39, it is determined whether the surface temperature of the fixing belt 62 has reached the target temperature (for example, 170°C). If the answer is "NO" in step S39, the process proceeds to step S41, where the contact pressure of the pressure roller 64 is maintained and the process returns to step S39. On the other hand, if the answer is "YES" in step S39, the process proceeds to step S43, where a control signal is sent to the second motor 128 to increase the contact pressure of the pressure roller 64 from the third contact pressure to the target contact pressure, and the warm-up process ends.

According to this second embodiment, the contact pressure of the pressure roller 64 against the fixing belt 62 is controlled according to the surface temperature of the fixing belt 62 during warm-up, so that, as in the first embodiment, it is possible to appropriately prevent the fixing belt 62 from having poor rotation. In addition, a low-output first motor 90 can be used.

[Third Example]
Next, a fixing device 46 according to a third embodiment of the present invention will be described with reference to Fig. 11. This third embodiment differs from the first embodiment in that the rotational speed of the pressure roller 64 is controlled based on the current value of the first motor 90 instead of the contact pressure changing mechanism 110. Since the other parts are similar, the same reference numbers are used for parts common to the first embodiment, and duplicated descriptions are omitted or simplified.

In this third embodiment, during warm-up, the first motor 90 is controlled based on the current value of the first motor 90 to change the rotation speed of the pressure roller 64. Specifically, at the start of warm-up, the rotation speed of the pressure roller 64 is set to a first speed that is lower than the predetermined rotation speed (target rotation speed) during image formation. Then, while monitoring the current value of the first motor 90, the rotation speed of the pressure roller 64 is gradually increased to the target rotation speed so that the current value does not exceed a preset upper limit value within a range in which the first motor 90 can be appropriately driven. This control method is based on the knowledge confirmed by the inventors through a verification experiment that the rotation torque of the pressure roller 64 decreases as the temperature of the fixing belt 62 increases, while the rotation torque of the pressure roller 64 increases as the rotation speed of the pressure roller 64 increases.

An example of the warm-up process (rotation speed change process) in the fixing device 46 will be described below with reference to the flow diagram shown in FIG. 11. As shown in FIG. 11, when the warm-up process starts, the CPU 100 checks the cam position of the separation cam 124 in step S51. Here, it is confirmed that the separation cam 124 is in the target position where the contact pressure of the pressure roller 64 becomes the target contact pressure. In the next step S53, the pressure roller 64 starts to rotate. Here, a control signal is sent to the first motor 90 to rotate the pressure roller 64 at a first rotation speed (e.g., 50 mm/s) that is slower than the target rotation speed. In the following step S55, heating of the fixing belt 62 starts.

In the next step S57, it is determined whether the motor current value flowing through the first motor 90 is equal to or less than a threshold value. If the answer is "NO" in step S57, the process proceeds to step S59, where the contact pressure of the pressure roller 64 is maintained, and the process returns to step S57. On the other hand, if the answer is "YES" in step S57, the process proceeds to step S61. In step S61, the rotation speed of the pressure roller 64 is increased. Here, a control signal is sent to the first motor 90, and the rotation speed of the pressure roller 64 is increased stepwise by a predetermined value. For example, the rotation speed of the pressure roller 64 is increased from the first rotation speed to a second rotation speed (e.g., 100 mm/s), from the second rotation speed to a third rotation speed (e.g., 180 mm/s), or from the second rotation speed to a target rotation speed (e.g., 280 mm/s).

In the next step S63, it is determined whether the rotation speed of the pressure roller 64 has reached the target rotation speed. If the answer is "NO" in step S63, that is, if the rotation speed of the pressure roller 64 has not reached the target rotation speed, the process returns to step S57. On the other hand, if the answer is "YES" in step S63, that is, if the rotation speed of the pressure roller 64 has reached the target rotation speed, the process proceeds to step S65. Note that in steps S57 to S63, instead of increasing the contact pressure of the pressure roller 64 in stages, the rotation speed of the pressure roller 64 can be gradually increased to the target rotation speed within the range where the current value of the first motor 90 falls between the upper limit value and the threshold value.

In the next step S65, it is determined whether the surface temperature of the fixing belt 74 has reached the target temperature. If the answer is "NO" in step S65, the process waits until the fixing belt 74 reaches the target temperature, and if the answer is "YES" in step S65, the warm-up process ends.

According to this third embodiment, during warm-up, the rotation speed of the pressure roller 64 is controlled according to the current value of the first motor 90, so that, as in the first embodiment, it is possible to prevent the fixing belt 62 from having poor rotation. In addition, a first motor 90 with low output can be used.

The technical features described in each of the above-mentioned embodiments or modifications can be combined with each other. For example, the first motor 90 can be controlled to change the rotation speed of the pressure roller 64 based on the surface temperature of the fixing belt 62 detected by the temperature sensor 94. For example, both the contact pressure of the pressure roller 64 against the fixing belt 62 and the rotation speed of the pressure roller 64 can be controlled based on the current value of the first motor 90, or both the contact pressure of the pressure roller 64 against the fixing belt 62 and the rotation speed of the pressure roller 64 can be controlled based on the surface temperature of the fixing belt 62.

In addition, in each of the above-described embodiments, the image forming device 10 is exemplified as a multifunction device that combines a copier, a facsimile, a printer, etc., but the image forming device 10 may be any one of a copier, a facsimile, a printer, etc., or a multifunction device that combines at least two of these.

Furthermore, the specific values and materials listed above are merely examples and can be changed as necessary depending on the product specifications, etc.

10: Image forming apparatus 30: Image forming section 46: Fixing device 62: Fixing belt (fixing rotor)
64 ... Pressure roller (pressure rotating body)
82 ... heat source 90 ... first motor (motor for pressure roller)
92 ... current sensor 94 ... temperature sensor 100 ... CPU
110: Contact pressure change mechanism 124: Contact/separation cam 128: Second motor (motor for contact/separation cam)

Claims (2)

A fixing device for thermally fixing a toner image formed on a recording medium, comprising:
Fixing rotor,
A heat source for heating the fixing rotor;
a pressure rotating body that comes into contact with an outer circumferential surface of the fixing rotating body to form a nip portion between the pressure rotating body and the fixing rotating body, and that rotates the fixing rotating body in a driven manner;
A motor that rotates the pressurizing rotor;
a current value detection unit that detects a current value of the motor;
a contact pressure change mechanism capable of changing the contact pressure of the pressure roller relative to the fixing roller; and a contact pressure control unit that controls the contact pressure change mechanism so that the current value of the motor detected by the current value detection unit does not exceed a preset upper limit value during a warm-up period in which the temperature of the fixing roller is increased to a target temperature, thereby increasing the contact pressure of the pressure roller relative to the fixing roller until the contact pressure reaches the target contact pressure ,
the contact pressure control unit linearly increases the contact pressure of the pressure rotating body from a first contact pressure, temporarily stops changing the contact pressure of the pressure rotating body when the current value of the motor reaches the upper limit value, and increases the contact pressure of the pressure rotating body again when the current value of the motor decreases to a threshold value, thereby increasing the contact pressure of the pressure rotating body to the target contact pressure within a range where the current value of the motor is between the upper limit value and the threshold value . An image forming apparatus comprising the fixing device according to claim 1 .

Images