JP2022146058A - Fixing device and image forming apparatus - Google Patents

Abstract

To provide a fixing device that can prevent a failure in rotation of a fixing rotating body.SOLUTION: A fixing device comprises: a contact pressure control unit CPU 100 that controls a contact pressure changing mechanism. During warm-up for increasing the temperature of a fixing rotating body (fixing belt) to a target temperature, the contact pressure control unit controls the contact pressure changing mechanism based on a current value of a motor (first motor) that rotates a pressure rotating body (pressure roller) to change the contact pressure of the pressure rotating body against the fixing rotating body.SELECTED DRAWING: Figure 9

Description

The present invention relates to a fixing device and an image forming apparatus, and more particularly to a fixing device and an image forming apparatus which have a fixing rotator and a pressure rotator and thermally fix a toner image formed on a recording medium.

An example of a conventional fixing device is disclosed in Japanese Unexamined Patent Application Publication No. 2002-200512. The fixing device of Patent Document 1 includes a heating member (fixing rotary member) having an endless metal sleeve as a base material, a radiant heat source provided inside the heating member, and a sliding member that slides against the inner surface of the heating member. A support member (fixing pad) having a surface and a sliding surface of the support member form a nip portion for sandwiching and applying pressure to the heating member. and a backup member located on the side opposite to the sliding surface of the support member and receiving the pressure of the pressure roller applied to the support member.

Another example of a conventional fixing device is disclosed in Japanese Unexamined Patent Application Publication No. 2002-200021. The fixing device disclosed in Japanese Patent Application Laid-Open No. 2002-200000 includes a drive mechanism (a contact pressure changing mechanism) that causes a fixing roller to contact and separate by driving a motor, a detecting means that detects a current value of the motor, and a current value detected by the detecting means. and an estimating unit for estimating the load torque of the motor, and a contact pressure control unit for controlling the contact pressure of the fixing roller based on the load torque estimated by the estimating unit.

Japanese Patent Application Laid-Open No. 2007-233011 JP 2019-164187 A

In the technique disclosed in Japanese Patent Application Laid-Open No. 2002-130000, the fixing rotator is driven to rotate in accordance with the rotation of the pressure rotator. A high frictional force is generated between them, and the fixing rotator may slip on the pressure rotator, or the drive source (motor) of the pressure rotator may be locked, resulting in rotation failure of the fixing rotator. there were. If the fixing rotator is heated in a state of improper rotation, a portion of the fixing rotator is rapidly heated to an abnormal temperature rise, and damage such as distortion or peeling occurs in the fixing rotator.

On the other hand, according to the technique of Patent Document 2, by controlling the contact pressure between the fixing rotator and the pressure rotator based on the load torque of the motor that drives the contact pressure changing mechanism, the component accuracy of each component is improved. And even if there is a variation in assembly accuracy, the contact pressure can be adjusted to the target contact pressure according to the paper type and paper thickness. However, the technique disclosed in Japanese Patent Application Laid-Open No. 2002-200002 does not consider the rotation failure of the fixing rotating body during warm-up.

SUMMARY OF THE INVENTION Therefore, a primary object of the present invention is to provide a novel fixing device and image forming apparatus.

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

A first invention is a fixing device for thermally fixing a toner image formed on a recording medium, comprising: a fixing rotary body; a heat source for heating the fixing rotary body; A pressurizing rotator that forms a nip portion between itself and the fixing rotator and causes the fixing rotator to rotate, a motor that drives the pressure rotator to rotate, a current value detector that detects the current value of the motor, and a fixing rotator. based on the current value of the motor detected by the current value detection unit during warm-up to raise the temperature of the fixing rotor to the target temperature. The fixing device includes a contact pressure control section that controls a contact pressure changing mechanism to change the contact pressure of the pressurizing rotator with respect to the fixing rotator.

According to the first invention, the contact pressure of the pressure rotator against the fixing rotator is controlled in accordance with the current value of the motor that drives the pressure rotator to rotate. Defects can be properly prevented.

A second aspect of the invention is a fixing device for thermally fixing a toner image formed on a recording medium, comprising: a fixing rotary member; a heat source for heating the fixing rotary member; A pressurizing rotator that forms a nip portion between itself and the fixing rotator and causes the fixing rotator to rotate, a motor that drives the pressure rotator to rotate, a temperature detection section that detects the temperature of the fixing rotator, and a fixing rotator. based on the temperature of the fixing rotator detected by the temperature detection unit during warm-up for raising the temperature of the fixing rotator to a target temperature. The fixing device includes a contact pressure control section that controls a contact pressure changing mechanism to change the contact pressure of the pressurizing rotator with respect to the fixing rotator.

According to the second invention, the contact pressure of the pressure rotating body against the fixing rotating body is controlled according to the temperature of the fixing rotating body, so that rotation failure of the fixing rotating body during warm-up can be appropriately prevented.

A third aspect of the present invention is a fixing device for thermally fixing a toner image formed on a recording medium, comprising: a fixing rotary member; a heat source for heating the fixing rotary member; A pressurizing rotator that forms a nip portion between itself and the fixing rotator and causes the fixing rotator to rotate, a motor that drives the pressure rotator to rotate, a current value detector that detects the current value of the motor, and a fixing rotation A speed control unit is provided for controlling the motor based on the current value of the motor detected by the current value detection unit during warm-up to raise the temperature of the body to a target temperature, thereby changing the rotational speed of the pressurizing rotor. , the fixing device.

According to the third invention, since the rotation speed of the pressure rotator is controlled according to the current value of the motor that drives the pressure rotator, rotation failure of the fixing rotator during warm-up can be appropriately prevented. can.

A fourth aspect of the invention is a fixing device for thermally fixing a toner image formed on a recording medium, comprising: a fixing rotary member; a heat source for heating the fixing rotary member; A pressurizing rotator that forms a nip portion between itself and the fixing rotator and causes the fixing rotator to rotate, a motor that drives the pressure rotator to rotate, a temperature detection section that detects the temperature of the fixing rotator, and a fixing rotation member. a speed control unit for controlling a motor based on the temperature of the fixing rotator detected by the temperature detecting unit during warm-up to raise the temperature of the body to a target temperature, thereby changing the rotation speed of the pressure rotator; It is a fixing device.

According to the fourth invention, since the rotation speed of the pressure rotating body is controlled according to the temperature of the fixing rotating body, it is possible to appropriately prevent rotation failure of the fixing rotating body during warm-up.

A fifth invention is an image forming apparatus comprising the fixing device according to any one of the first to fourth inventions.

According to the fifth invention, similarly to any one of the first to fourth inventions, it is possible to appropriately prevent rotation failure of the fixing rotator during warm-up.

According to the present invention, it is possible to appropriately prevent rotation failure of the fixing rotator during warm-up.

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

1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus according to a first embodiment of the invention; FIG. 2 is a schematic cross-sectional view showing a fixing device; FIG. 3 is a plan view showing a pressure roller included in the fixing device; FIG. 3 is a perspective view showing a pressure unit included in the fixing device; FIG. It is a schematic front view showing a pressurizing unit. FIG. 4 is a front view showing a contact/separation cam included in the pressurizing unit; 2 is a block diagram showing an example of the 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. FIG. 8 is a flowchart showing an example of warm-up processing executed by the CPU shown in FIG. 7; FIG. 9 is a flowchart showing an example of warm-up processing executed by the CPU of the image forming apparatus according to the second embodiment of the present invention; FIG. 11 is a flowchart showing an example of warm-up processing executed by the CPU of the image forming apparatus according to the third embodiment of the present invention;

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

First, the basic configuration of the image forming apparatus 10 will be schematically described. In this specification, the surface facing the standing position of the user, that is, the surface on which the operation unit 106 (see FIG. 7) is provided is defined as the front surface (the front surface). direction). Further, the left-right direction (horizontal direction) of the image forming apparatus 10 and its constituent members is defined based on the state of viewing the image forming apparatus 10 from the user.

As shown in FIG. 1, in this first embodiment, the image forming apparatus 10 is a multifunction peripheral (MFP) having a copying function, a printer function, a scanner function, a facsimile function, and the like. The image forming apparatus 10 includes an apparatus body 12 having an image forming section 30 and the like, and an image reading device 14 arranged thereabove.

The image reading device 14 includes a document table 16 made of a transparent material. A document holding cover 18 is attached above the document table 16 via a hinge or the like so as to be freely opened and closed. The document holding cover 18 is provided with an ADF (automatic document feeder) 24 for automatically feeding the documents placed on the document placement tray 20 one by one to the image reading position 22 . Further, on the front side of the document table 16, an operation unit 106 is provided for receiving an input operation such as a print instruction by the user. The operation unit 106 is appropriately provided with a display such as a touch panel display and various operation buttons.

The image reader 14 also incorporates an image reader 26 including a light source, a plurality of mirrors, an imaging lens, a line sensor, and the like. The image reading unit 26 exposes the surface of the document with a light source, and guides the reflected light reflected from the surface of the document to the imaging lens with a plurality of mirrors. Then, the image forming lens forms an image of the reflected light on the light receiving element of the line sensor. The line sensor detects the luminance and chromaticity of the reflected light imaged on the light receiving element, and generates image data based on the image of the surface of the document. A CCD (Charge Coupled Device), CIS (Contact Image Sensor), or the like is used as the line sensor.

The apparatus main body 12 incorporates a control section 28 including a CPU 100, a RAM 102, an HDD 104 and the like (see FIG. 7), an image forming section 30, and the like. The control unit 28 (specifically, the CPU 100 ) transmits control signals to each part of the image forming apparatus 10 including the fixing device 46 in response to the user's input operation to the operation unit 106 , and the image forming apparatus 10 . Cause various actions to be performed.

The image forming section 30 includes an exposure unit 32, a developing device 34, a photosensitive drum 36, a cleaner unit 38, a charging device 40, an intermediate transfer belt unit 42, a secondary transfer roller 44, a fixing device 46, and the like. Alternatively, an image is formed on the paper conveyed from the manual paper feed tray 50 and the paper on which the image has been formed is discharged to the paper discharge tray 52 . As image data for forming an image on paper, image data read by the image reading unit 26, image data transmitted from an external computer, or the like is used.

The image data handled by the image forming apparatus 10 corresponds to four color images of black (K), cyan (C), magenta (M) and yellow (Y). For this reason, four developing devices 34, photosensitive drums 36, cleaner units 38, and charging devices 40 are provided so as to form four types of latent images corresponding to each color, thereby forming four image stations. Configured.

The photoreceptor drum 36 is an image carrier in which a photosensitive layer is formed on the surface of a conductive cylindrical substrate, and the charger 40 is a member that charges the surface of the photoreceptor drum 36 to a predetermined potential. be. The exposure unit 32 is configured as a laser scanning unit (LSU) having a laser emitting section, a reflecting mirror, and the like, and exposes the surface of the charged photoreceptor drum 36 to an electrostatic latent image corresponding to the image data. An image is formed on the surface of the photoreceptor drum 36 . The developing device 34 visualizes the electrostatic latent image formed on the surface of the photosensitive drum 36 with toner of four colors (YMCK). Also, the cleaner unit 38 removes toner remaining on the surface of the photosensitive drum 36 after development and image transfer.

The intermediate transfer belt unit 42 includes an intermediate transfer belt 54 , a drive roller 56 , a driven roller 58 , four intermediate transfer rollers 60 , etc., and is arranged above the photosensitive drum 36 . The intermediate transfer belt 54 is a flexible endless belt, stretched by a plurality of rollers such as a driving roller 56 and a driven roller 58, and its surface (outer peripheral surface) is aligned with the surface of the photosensitive drum 36. is arranged to abut on the The intermediate transfer belt 54 rotates (rotates) in a predetermined direction as the driving roller 56 rotates. The intermediate transfer rollers 60 are arranged at respective positions facing the respective photosensitive drums 36 with the intermediate transfer belt 54 interposed therebetween. At the time of image formation, the intermediate transfer roller 60 is used to sequentially transfer the toner images of the respective colors formed on the photoreceptor drums 36 onto the intermediate transfer belt 54 so as to transfer multicolor toner onto the intermediate transfer belt 54 . An image is formed.

The secondary transfer roller 44 is provided so as to face the driving roller 56 with the intermediate transfer belt 54 interposed therebetween. The toner image formed on the intermediate transfer belt 54 is transferred onto the sheet by passing the sheet through the secondary transfer nip portion between the secondary transfer roller 44 and the intermediate transfer belt 54 .

The fixing device 46 includes a fixing belt 62, a pressure roller 64, and the like, and is arranged above the secondary transfer roller 44 (on the downstream side in the paper transport direction). A fixing pad 76 and a heat source 82 (see FIG. 2) are provided inside the fixing belt 62, and the fixing belt 62 is heated by the heat source 82 to a predetermined fixing temperature (for example, 170.degree. C.). Further, the pressure roller 64 is provided so as to press the fixing belt 62 against the fixing pad 76 . As the paper passes through the fixing nip portion 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. The toner image is thermally fixed. A specific configuration of the fixing device 46 will be described later.

In the apparatus main body 12, there is provided a feed tray 48 or a manual feed tray 50 for sending the paper to the discharge tray 52 via the registration roller 68, the secondary transfer roller 44 and the fixing device 46. 1 paper transport path L1 is formed. Also, when performing double-sided printing on a sheet of paper, after single-sided printing has been completed and the sheet has passed through the fixing device 46, the sheet is transferred to the first sheet conveying path L1 on the upstream side of the secondary transfer roller 44 in the sheet conveying direction. A second paper transport path L2 for returning is formed. A plurality of transport rollers 66 are appropriately provided in the first paper transport path L1 and the second paper transport path L2 for providing auxiliary driving force to the paper.

Next, the mechanical configuration of the fixing device 46 will be described with reference to FIGS. 2 to 6. FIG. The fixing device 46 includes a fixing belt 62, which is an example of a fixing rotating member, and a pressure roller 64, which is an example of a pressing rotating member. , to fix the toner image on the paper.

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. Each member of the heater unit 70 and the pressure unit 72 is integrally held in a predetermined arrangement by a fixing frame (not shown).

The heater unit 70 includes a fixing belt 62 that is formed in a substantially cylindrical shape and extends in the front-rear direction (the width direction of the paper). As the fixing belt 62, for example, a band-shaped base material formed of a synthetic resin such as polyimide or a metal such as nickel and provided with a release layer on the surface thereof is used. Such a fixing belt 62 is provided rotatably around its axis, and its inner diameter is, for example, 30 mm. A fixing pad 76 , a support member 78 , a reflector 80 , a heat source 82 and the like are provided inside the fixing belt 62 .

The fixing pad 76 is a fixing member that is 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 contact sheet 76a on its outer peripheral surface (at least the sliding contact surface with the fixing belt 62). Sliding oil is applied. 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 circumferential 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 to have a substantially L-shaped cross section, and includes a long plate-shaped fixing portion 78a to which the fixing pad 76 is fixed, and a fixing portion 78a extending from the widthwise end of the fixing portion 78a. and a long plate-shaped standing portion 78b. A thin reflector 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 central portion of the fixing belt 62 in the axial direction, and a second lamp heater 82b that heats both ends of the fixing belt 62 in the axial direction. The first lamp heater 82a and the second lamp heater 82b are selectively used according to the paper width.

The pressure unit 72 includes a pressure roller 64 arranged at a position facing the fixing pad 76 with the fixing belt 62 interposed therebetween. The pressure roller 64 is provided so as to extend parallel to the axial direction of the fixing belt 62 , and presses the fixing belt 62 against the fixing pad 76 to form a fixing nip portion N between itself and the fixing belt 62 . do.

Specifically, as shown in FIG. 3 , the pressure roller 64 has a cylindrical roller portion 84 . The roller portion 84 is formed of a cylindrical core material made of metal such as aluminum and an elastic material such as silicone rubber, and is composed of an elastic layer covering the surface of the core material and a material having a low coefficient of friction such as fluorine-based resin. and a release layer 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 .

Further, in the first embodiment, both ends of the roller portion 84 are provided with thin grip portions 86 made of a material having a large frictional resistance (that is, having a gripping force) such as silicone rubber. The grip portion 86 is arranged at a position on the outside in the width direction of the paper passing through the fixing nip portion N (outside the width of the paper), and its thickness (protruding height from the release layer) is, for example, 200 μm. By providing such a grip portion 86 in the roller portion 84, even if the pressure roller 64 is in a low contact pressure state as described later, the rotational force of the pressure roller 64 can be appropriately transmitted to the fixing belt 62. can.

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 the driving force from the first motor 90 , and as the pressure roller 64 is driven to rotate, the fixing belt 62 is driven to rotate in the direction opposite to the rotation direction of the pressure roller 64 . do. That is, the pressure roller 64 abuts on the outer peripheral surface of the fixing belt 62 to form a fixing nip portion N between itself and the fixing belt 62 , and applies a rotational driving force to the fixing belt 62 via this fixing nip portion N. By transmitting, the fixing belt 62 is driven to rotate. Further, the first motor 90 is provided with a current sensor 92 (see FIG. 7) such as a current transformer for detecting the current (motor current value) flowing through the first motor 90 .

Returning to FIG. 2, the fixing device 46 has a temperature sensor 94 such as a thermopile or a thermistor that detects the surface temperature of the fixing belt 62 . Temperature sensor 94 includes, for example, a first temperature sensor that detects the surface temperature of the central portion of fixing belt 62 in the axial direction, and a second temperature sensor that detects the surface temperature of the ends of fixing belt 62 in the axial direction. A peeling plate 96 for preventing the paper from winding around the fixing belt 62 is provided on the downstream side of the fixing nip portion N in the paper conveying direction.

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

As shown in FIGS. 4 and 5, the contact pressure changing mechanism 110 includes a pair of pressure levers 112 provided at both ends of the pressure unit 72 and extending in a direction orthogonal to the axial direction of the pressure roller 64. Prepare. Each pressure lever 112 rotatably supports the roller shaft 88 of the pressure roller 64 via a bearing 114 at its central portion. Further, each pressure lever 112 has an engagement hole 118 at one end (lower end) that engages with a pivot shaft 116 provided on the fixing frame. Rotating support shaft 116 is provided so as to extend parallel to the axial direction of fixing belt 62 , and pressure lever 112 moves in a direction (horizontal direction) to separate and contact fixing belt 62 with rotation supporting shaft 116 as a fulcrum. It is rotatable. As the pressure lever 112 rotates, the pressure roller 64 is displaced in a direction away from and in contact with the fixing belt 62 . Furthermore, each pressure lever 112 has, at its other end (upper end), a locking portion 120 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 the pressure lever 112 (and thus the pressure roller 64) is provided in a direction (leftward direction) in which the pressure roller 64 is pressed against the fixing belt 62. A predetermined urging force acts on .

The contact pressure changing 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 a fixing frame. Further, on both ends of the cam shaft 122 , contact and separation cams 124 are provided at positions adjacent to the pressure lever 112 , and the pressure lever 112 is provided with a contact portion 126 with the contact and separation cam 124 . Further, a second motor 128 (see FIG. 7) is connected to one end (rear end) of the camshaft 122 via a gear or gear train (not shown). The cam shaft 122 receives a driving force from a second motor 128 and is driven to rotate about its axis in forward and reverse directions, and the contact/separation cam 124 rotates together with the cam shaft 122 .

As shown in FIG. 6, the contact/separation cam 124 has a shape in which the distance from the center of the cam shaft 122 gradually increases from Ls to Le in the region R1. Therefore, the contact/separation cam 124 receives the rotational driving force from the second motor 128, and rotates in the normal and reverse directions at the rotational position where the contact position with the contact portion 126 is the region R1, thereby applying pressure. The lever 112 can be rotated, and the contact pressure (pressing force) of the pressure roller 64 against the fixing belt 62 can be changed. Note that when the separation/contact cam 124 is in contact with the contact portion 126 at the position E where the distance from the center of the cam shaft 122 is the furthest (the state shown in FIG. 5), the pressure roller 64 is separated from the fixing belt 62. state.

In such a fixing device 46, during image formation, 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). By passing the paper through the nip portion N, the toner image is fixed on the paper. Therefore, when the temperature of the fixing belt 62 is low at the time of start-up or the like, a warm-up operation is performed to raise the temperature to a predetermined fixing temperature (target temperature) while rotating the fixing belt 62 before forming an image on paper. . At this time, when the temperature of the fixing belt 62 is low, the sliding oil of the fixing pad 76 has a high viscosity, and a high frictional force is generated between the fixing belt 62 and the fixing pad 76 . As a result, the fixing belt 62 slips on the pressure roller 64 , or the first motor 90 that drives the pressure roller 64 is subjected to a large load and the first motor 90 is locked. There was a risk of poor rotation. Therefore, a technique for preventing the fixing belt 62 from slipping while suppressing the load applied to the first motor 90 is required.

Therefore, in the first embodiment, during warm-up, the contact pressure changing mechanism 110 (specifically, the second motor 90) is adjusted based on the current value of the first motor 90, which is proportional to the rotational torque of the pressure roller 64. By controlling the motor 128) and changing the contact pressure of the pressure roller 64 against the fixing belt 62, rotation failure of the fixing belt 62 is prevented.

Specifically, at the start of warm-up, the contact pressure of pressure roller 64 is set to a first contact pressure (for example, 30 N) that is low enough to prevent fixing belt 62 from slipping. Then, while monitoring the current value of the first motor 90, the pressure roller 64 is controlled so that the current value does not exceed a preset upper limit value (for example, 1800 mA) within a range in which the first motor 90 can be driven appropriately. The contact pressure is gradually increased until reaching the target contact pressure (for example, 300N). For example, the contact pressure of the pressure roller 64 is increased by a predetermined value when the current value of the first motor 90 falls below a preset threshold value (for example, 1500 mA) lower than the upper limit value. It is preferable to raise the target contact pressure step by step (for example, in 3 to 5 steps). Alternatively, the contact pressure of the pressure roller 64 is linearly increased from the first contact pressure, and when the current value of the first motor 90 reaches the upper limit, the change of the contact pressure is temporarily stopped, and the first motor When the current value of 90 drops to the threshold value, the contact pressure of the pressure roller 64 is increased again. The contact pressure may be raised to the target contact pressure. In such a control method, as the temperature of the fixing belt 62 increases, the rotational torque of the pressure roller 64 decreases. This is based on the finding confirmed by the verification experiment by the inventors that the torque increases. A specific control method during warm-up will be described later using a flow chart.

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

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

The operation unit 106 includes a display with a touch panel, operation buttons, and the like. The display is a general-purpose monitor such as LCD, and is connected to CPU 100 via a display control circuit (not shown). The display control circuit includes GPU, VRAM, and the like. Under instructions from the CPU 100, the GPU uses the 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 a touch operation within the touch effective 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, power saving key and power button.

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

As described above, the heat source 82 is a heater for heating the fixing belt 62 from the inside. Temperature sensor 94 is a sensor for detecting the surface temperature of fixing belt 62 , and outputs a detection result (a signal corresponding to the surface temperature of fixing belt 62 ) to CPU 100 based on an instruction from CPU 100 . CPU 100 controls heat source 82 based on the result of detection by temperature sensor 94 so that the surface temperature of fixing belt 62 reaches a 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 reaches a desired rotational speed. Current sensor 92 is a sensor for detecting the motor current flowing through first motor 90 , and outputs a detection result (a signal corresponding to the motor current value) to CPU 100 based on an instruction from CPU 100 . The second motor 128 is a motor for rotating the cam shaft 122 , and rotates the motor shaft so that the contact/separation cam 124 is at a desired rotational position based on a control signal from the CPU 100 . That is, the CPU 100 controls the rotational position (angle) of the motor shaft of the second motor 128 to control the rotational position of the contact/separation cam 124, thereby increasing the contact pressure between the fixing belt 62 and the pressure roller 64. Control. In the first embodiment, the CPU 100 gradually increases the contact pressure between the fixing belt 62 and the pressure roller 64 from the first contact pressure to the target value based on the detection result of the current sensor 92 during warm-up. The rotational position of the contact/separation cam 124 is controlled so as to approach the contact pressure.

FIG. 8 is a diagram showing an example of the memory map 200 of the RAM 102. As shown in FIG. As shown in FIG. 8, RAM 102 includes program storage area 202 and data storage area 204 . The program storage area 202 of the RAM 102 stores an operation detection program 202a, an image forming program 202b, a contact pressure control program 202c, and the like.

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

Although not shown, the program storage area 202 also stores other programs for the CPU 100 to execute various functions as needed.

The data storage area 204 of the RAM 102 stores a set value table 204a, cam position data 204b, current value data 204c, temperature data 204d, and the like.

The set value table 204a contains set values used for executing the contact pressure changing 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 target pressure of the pressure roller 64. , and the threshold value and upper limit value of the current value of the first motor 90 are stored.

The cam position data 204b is data for identifying the cam position of the contact/separation cam 124, and includes, for example, data indicating that the contact/separation cam 124 is positioned at an initial position, a target position, an intermediate position, a separated position, and the like. . Here, the initial position is a cam position at which the contact pressure of the pressure roller 64 becomes the first contact pressure (low contact pressure at which the fixing belt 62 does not slip). The target position is a cam position at which the contact pressure of the pressure roller 64 becomes a predetermined contact pressure (target contact pressure) corresponding to the type of paper. Furthermore, the intermediate position means that the contact pressure of the pressure roller 64 is any contact pressure (second contact pressure, third contact pressure, etc.) between the first contact pressure and the target contact pressure. is the cam position at each stage. The separated position is a cam position where the pressure roller 64 is separated from the fixing belt 62 .

The current value data 204c is the value measured by the current sensor 92, that is, the data of the motor current value flowing through the first motor 90. FIG. The temperature data 204 d is data of the surface temperature of the fixing belt 62 , which is measured by the temperature sensor 94 .

Although illustration is omitted, the data storage area 204 is provided with a timer (counter) or a register necessary for executing the control program, and stores other data necessary for executing the control program.

The operation of the fixing device 46 (image forming apparatus 10 ) as described above is realized by executing the control program read out to the RAM 102 by the CPU 100 . An example of warm-up processing (contact pressure change processing) in the fixing device 46 will be described below with reference to the flowchart shown in FIG.

As shown in FIG. 9, when the warm-up process is started, the CPU 100 confirms the cam position of the contact/separation cam 124 in step S1. Here, it is confirmed that the contact/separation cam 124 is at the initial position where the contact pressure of the pressure roller 64 is the first contact pressure (for example, 30N). When the contact/separation cam 124 is not at the initial position, a control signal is sent to the second motor 128 to rotate the contact/separation cam 124 to the initial position.

In the next step S3, the pressure roller 64 starts rotating. Here, a control signal is sent to the first motor 90 to rotate the pressure roller 64 at a predetermined rotational speed (target rotational speed). The fixing belt 62 rotates following the rotation of the pressure roller 64 . In the subsequent step S5, heating of the fixing belt 62 is started. 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 subsequent step S7, it is determined whether the motor current value flowing through the first motor 90 is equal to or less than a threshold value. If "NO" in step S7, that is, if the motor current value of the first motor 90 exceeds the threshold, 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. That is, the current contact pressure of the pressure roller 64 is maintained until the motor current value becomes equal to or less than the threshold value.

On the other hand, if "YES" in step S7, that is, if the motor current value of the first motor 90 is equal to or less than the threshold, 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/separation 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 (eg 100N), or from the second contact pressure to the third contact pressure (eg 200N), The third contact pressure is increased to a target contact pressure (eg, 300N).

In the subsequent step S13, it is determined whether or not the contact pressure of the pressure roller 64 has reached the target contact pressure. If "NO" in step S13, 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 "YES" in step S13, that is, if the contact pressure of the pressure roller 64 reaches the target contact pressure, the process proceeds to step S15. In steps S7 to S13, instead of stepwise increasing the contact pressure of the pressure roller 64, the current value of the first motor 90 is within a range between the upper limit value and the threshold value. can be gradually increased to the target contact pressure.

In subsequent step S15, it is determined whether or not the surface temperature of the fixing belt 74 has reached the target temperature. If "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 "YES" in step S15, that is, if the fixing belt 74 has reached the target temperature, the warm-up process ends and the image forming process for forming an image on paper is started.

As described above, according to the first embodiment, since 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 during warm-up, the fixing belt 62 slips. Also, the first motor 90 can be prevented from being locked, and the rotation failure of the fixing belt 62 can be appropriately prevented. That is, the fixing belt 62 can be stably driven to rotate. Further, since the rotational torque of the pressure roller 64 can be suppressed, the first motor 90 with low output can be used.

[Second embodiment]
Next, referring to FIG. 10, an image forming apparatus 10 according to a second embodiment of the invention will be described. The second embodiment differs from the above-described first embodiment in that the contact pressure changing 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 the same, the parts common to the above-described first embodiment are denoted by the same reference numerals, and overlapping descriptions are omitted or simplified.

In the second embodiment, during warm-up, the contact pressure changing mechanism 110 is controlled based on the surface temperature of the fixing belt 62 detected by the temperature sensor 94 to adjust the contact pressure of the pressure roller 64 against the fixing belt 62 . to change Specifically, at the start of warm-up, the contact pressure of the pressure roller 64 is set to the 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 stepwise (for example, 3 to 5 steps), the contact pressure of the pressure roller 64 is gradually increased until reaching the target contact pressure. Such a control method is based on the knowledge confirmed by the inventors through verification experiments that the rotational torque of the pressure roller 64 decreases as the temperature of the fixing belt 62 increases.

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

In subsequent step S27, it is determined whether the surface temperature of fixing belt 62 has reached a first temperature (for example, 70° C.). If "NO" in step S27, 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, while maintaining the contact pressure of the pressure roller 64, the process returns to step S27. On the other hand, if "YES" in step S27, 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 subsequent step S33, it is determined whether the surface temperature of fixing belt 62 has reached a second temperature (for example, 120° C.). If "NO" in step S33, the process proceeds to step S35, and returns to step S33 while maintaining the contact pressure of the pressure roller 64. FIG. On the other hand, if "YES" in step S33, the process proceeds to step S37, and a control signal is transmitted 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 subsequent step S39, it is determined whether or not the surface temperature of fixing belt 62 has reached a target temperature (for example, 170.degree. C.). If "NO" in step S39, the process proceeds to step S41, and returns to step S39 while maintaining the contact pressure of the pressure roller 64. FIG. On the other hand, if "YES" in step S39, the process advances to step S43 to transmit a control signal 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. , terminates this warm-up process.

According to the 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. It is possible to appropriately prevent the occurrence of poor rotation in the Also, a low-output first motor 90 can be used.

[Third embodiment]
Next, referring to FIG. 11, a fixing device 46, which is a third embodiment of the invention, will be described. The third embodiment differs from the above-described first embodiment in that the rotation 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 the same, the parts common to the above-described first embodiment are denoted by the same reference numerals, and overlapping descriptions are omitted or simplified.

In this third embodiment, the rotation speed of the pressure roller 64 is changed by controlling the first motor 90 based on the current value of the first motor 90 during warm-up. 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 a predetermined rotation speed (target rotation speed) during image formation. Then, while monitoring the current value of the first motor 90, the target rotation speed of the pressure roller 64 is set so that the current value does not exceed a preset upper limit within a range in which the first motor 90 can be properly driven. Gradually increase the rotation speed. In such a control method, the rotational torque of the pressure roller 64 decreases as the temperature of the fixing belt 62 increases, whereas the rotational torque of the pressure roller 64 decreases as the rotational speed of the pressure roller 64 increases. This is based on the finding confirmed by the verification experiment by the inventors that .

An example of warm-up processing (rotational speed change processing) in the fixing device 46 will be described below with reference to the flowchart shown in FIG. As shown in FIG. 11, when the warm-up process is started, the CPU 100 confirms the cam position of the contact/separation cam 124 in step S51. Here, it is confirmed that the contact/separation cam 124 is at 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 rotating. Here, a control signal is sent to the first motor 90 to rotate the pressure roller 64 at a first rotation speed (for example, 50 mm/s) lower than the target rotation speed. In the subsequent step S55, heating of the fixing belt 62 is started.

In subsequent step S57, it is determined whether or not the motor current value flowing through the first motor 90 is equal to or less than a threshold value. If "NO" in step S57, the process proceeds to step S59, the contact pressure of the pressure roller 64 is maintained, and the process returns to step S57. On the other hand, if "YES" in step S57, the process proceeds to step S61. In step S61, the rotational speed of the pressure roller 64 is increased. Here, a control signal for the first motor 90 is transmitted to stepwise increase the rotation speed of the pressure roller 64 by a predetermined value. For example, the rotational speed of pressure roller 64 can be increased from a first rotational speed to a second rotational speed (eg, 100 mm/s), increased from the second rotational speed to a third rotational speed (eg, 180 mm/s), or 2 The rotation speed is increased to the target rotation speed (for example, 280 mm/s).

In subsequent step S63, it is determined whether or not the rotational speed of the pressure roller 64 has reached the target rotational speed. If "NO" in step S63, that is, if the rotational speed of the pressure roller 64 has not reached the target rotational speed, the process returns to step S57. On the other hand, if "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. In steps S57 to S63, instead of stepwise increasing the contact pressure of the pressure roller 64, the current value of the first motor 90 is within a range between the upper limit value and the threshold value. can be gradually increased to the target rotation speed.

In subsequent step S65, it is determined whether or not the surface temperature of the fixing belt 74 has reached the target temperature. If "NO" in step S65, wait until the fixing belt 74 reaches the target temperature, and if "YES" in step S65, this warm-up process ends.

According to the 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. Therefore, as in the first embodiment, the rotation failure of the fixing belt 62 does not occur. can be prevented from occurring. Also, a low-output first motor 90 can be used.

It should be noted that each of the technical features described in each of the above-described embodiments or modifications can be combined with each other. For example, the rotation speed of pressure roller 64 can be changed by controlling first motor 90 based on the surface temperature of fixing belt 62 detected by temperature sensor 94 . Further, for example, based on the current value of the first motor 90 , both the contact pressure of the pressure roller 64 against the fixing belt 62 and the rotation speed of the pressure roller 64 are controlled, or based on the surface temperature of the fixing belt 62 . It is also possible to control both the contact pressure of the pressure roller 64 against the fixing belt 62 and the rotation speed of the pressure roller 64 .

Further, in each of the above-described embodiments, the image forming apparatus 10 is illustrated as a multifunction machine combining a copier, a facsimile machine, a printer, etc., but the image forming apparatus 10 may be any one of a copier, a facsimile machine, a printer, or the like, or A multi-function machine combining at least two of these may be used.

Moreover, the specific numerical values, materials, and the like given above are merely examples, and can be appropriately changed according to requirements such as product specifications.

DESCRIPTION OF SYMBOLS 10... Image forming apparatus 30... Image forming part 46... Fixing device 62... Fixing belt (fixing rotator)
64 pressure roller (pressure rotating body)
82 ... heat source 90 ... first motor (motor for pressure roller)
92 ... current sensor 94 ... temperature sensor 100 ... CPU
REFERENCE SIGNS LIST 110: contact pressure changing mechanism 124: contact/separation cam 128: second motor (motor for contact/separation cam)

Claims (5)

A fixing device for thermally fixing a toner image formed on a recording medium,
fixing rotating body,
a heat source for heating the fixing rotating body;
a pressurizing rotator that abuts on the outer peripheral surface of the fixing rotator to form a nip portion with the fixing rotator and causes the fixing rotator to be driven to rotate;
a motor that rotates the pressurizing rotor;
a current value detection unit that detects a current value of the motor;
a contact pressure changing mechanism capable of changing the contact pressure of the pressurizing rotator against the fixing rotator; A fixing device, comprising: a contact pressure control section that controls the contact pressure changing mechanism based on the current value of the motor to change the contact pressure of the pressure rotating body against the fixing rotating body. A fixing device for thermally fixing a toner image formed on a recording medium,
fixing rotating body,
a heat source for heating the fixing rotating body;
a pressurizing rotator that abuts on the outer peripheral surface of the fixing rotator to form a nip portion with the fixing rotator and causes the fixing rotator to be driven to rotate;
a motor that rotates the pressurizing rotor;
a temperature detection unit that detects the temperature of the fixing rotating body;
a contact pressure changing mechanism capable of changing the contact pressure of the pressurizing rotator against the fixing rotator; A fixing device, comprising: a contact pressure control section that controls the contact pressure changing mechanism based on the temperature of the fixing rotator to change the contact pressure of the pressurizing rotator against the fixing rotator. A fixing device for thermally fixing a toner image formed on a recording medium,
fixing rotating body,
a heat source for heating the fixing rotating body;
a pressurizing rotator that abuts on the outer peripheral surface of the fixing rotator to form a nip portion with the fixing rotator and causes the fixing rotator to be driven to rotate;
a motor that rotates the pressurizing rotor;
a current value detection unit for detecting the current value of the motor; and during warm-up for raising the temperature of the fixing rotating body to a target temperature, the motor is operated based on the current value of the motor detected by the current value detection unit. A fixing device comprising a speed control section that controls and changes the rotational speed of the pressure rotating body. A fixing device for thermally fixing a toner image formed on a recording medium,
fixing rotating body,
a heat source for heating the fixing rotating body;
a pressurizing rotator that abuts on the outer peripheral surface of the fixing rotator to form a nip portion with the fixing rotator and causes the fixing rotator to be driven to rotate;
a motor that rotates the pressurizing rotor;
a temperature detecting section for detecting the temperature of the fixing rotating body; and during warm-up for raising the temperature of the fixing rotating body to a target temperature, the motor is operated based on the temperature of the fixing rotating body detected by the temperature detecting section. A fixing device comprising a speed control section that controls and changes the rotational speed of the pressure rotating body. An image forming apparatus comprising the fixing device according to claim 1 .

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