JP7308108B2 - image forming device - Google Patents

Description

An embodiment of the present invention relates to an image forming apparatus.

An image forming apparatus forms an image on a sheet using developer such as toner. The image forming apparatus fixes an image formed on the sheet to the sheet by heating with a fixing device. Some fixing devices use a planar heater and an endless belt (fixing belt). In such a fixing device, grease is placed between the heater and the fixing belt to prevent the drive torque of the fixing device from increasing. However, when the deterioration of the grease between the heater and the fixing belt progresses, the driving torque of the fixing device may increase.

Japanese Patent No. 5511252

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of suppressing an increase in driving torque of a fixing device.

An image forming apparatus according to an embodiment has a fixing device, an acquisition section, and a control section. A fixing device has a heating element, a fixing belt, a rotating body, and a lubricant. A heating element generates heat. The fixing belt is a strip-shaped thin film that slides on the surface of the heating element while its inner peripheral surface is in contact with the heating element. The rotating body can be pressed against the outer peripheral surface of the fixing belt and can rotate. A lubricant is in contact with the inner peripheral surface. The acquisition unit acquires a physical quantity that changes according to the magnitude of the torque of the rotating body. The control unit causes the rotator to perform a predetermined operation to create a gap between the heating element and the fixing belt based on the physical quantity acquired during image formation by the fixing device when not during image formation.

1 is an external view showing an example of the overall configuration of an image forming apparatus according to an embodiment; FIG. 1 is a block diagram showing a configuration example of an image forming apparatus according to an embodiment; FIG. FIG. 2 is a cross-sectional view showing a configuration example of a fixing device according to the embodiment; 4A and 4B are diagrams showing an example of the state of the lubricant according to the embodiment; FIG. FIG. 4 is a diagram showing an example of contact positions according to the embodiment; FIG. 4 is a diagram showing an example of positions in an envelope mode according to the embodiment; FIG. 5 is a diagram showing an example of positions in a separation mode according to the embodiment; FIG. 5 is a diagram showing an example of change in current value of the motor according to the embodiment; 4 is a flowchart showing an operation example of the image forming apparatus according to the embodiment;

An image forming apparatus according to embodiments will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is an external view showing an example of the overall configuration of an image forming apparatus 100 according to an embodiment. The image forming apparatus 100 is, for example, a multifunction machine. The image forming apparatus 100 includes a display 110 , a control panel 120 , a printer 130 , a sheet storage section 140 and an image reading section 200 .

The image forming apparatus 100 forms an image on a sheet using developer such as toner. The sheet is, for example, paper or label paper. The sheet may be any material on which the image forming apparatus 100 can form an image.

The display 110 is an image display device such as a liquid crystal display or an organic EL (Electro Luminescence) display. Display 110 displays various information about image forming apparatus 100 .

Control panel 120 has a plurality of buttons. Control panel 120 accepts user operations. Control panel 120 outputs a signal corresponding to an operation performed by a user to the control unit of image forming apparatus 100 . Note that the display 110 and the control panel 120 may be configured as an integrated touch panel.

The printer 130 is a device that forms an image on a sheet using developer and fixes the formed image to the sheet. The printer 130 forms an image on a sheet based on the image information generated by the image reading section 200 or the image information received via the communication path.

The printer 130 forms an image by, for example, the following processing. The image forming section of the printer 130 forms an electrostatic latent image on the photosensitive drum based on image information. The image forming section of the printer 130 forms a visible image by applying developer to the electrostatic latent image. A specific example of the developer is toner. A transfer section of the printer 130 transfers the visible image onto the sheet. A fixing unit of the printer 130 fixes the visible image on the sheet by applying heat and pressure to the sheet. The sheet on which an image is formed may be a sheet accommodated in the sheet accommodating portion 140 or may be a manually inserted sheet.

The sheet storage unit 140 stores sheets used for image formation in the printer 130 .

The image reading unit 200 reads image information to be read as brightness and darkness of light. The image reading unit 200 records the read image information. The recorded image information may be transmitted to another information processing apparatus via a network. The recorded image information may be image-formed on a sheet by the printer 130 .

FIG. 2 is a block diagram showing a configuration example of the image forming apparatus 100 according to the embodiment. The image forming apparatus 100 includes a display 110 , a control panel 120 , a printer 130 , a sheet storage section 140 , a storage section 150 and a processing device 160 . The printer 130 has a control circuit 131 and a fixing device 132 .

The storage unit 150 is a non-volatile recording medium (non-temporary recording medium) such as flash memory. The storage unit 150 stores, for example, a drive program for the printer 130 . The storage unit 150 may have a volatile recording medium such as a DRAM (Dynamic Random Access Memory).

The processing device 160 includes an acquisition unit 161 and a control unit 162 . A part or all of the processing device 160 is implemented as software by a processor such as a CPU (Central Processing Unit) executing a program stored in the storage unit 150 . A part or all of the processing device 160 may be implemented using hardware such as an LSI (Large Scale Integration circuit).

Next, details of the fixing device 132 will be described.
FIG. 3 is a cross-sectional view showing a configuration example of the fixing device 132 of the embodiment. The fixing device 132 has a film unit 10 and a pressure roller 11 . The film unit 10 has a fixing belt 14 , a support member 15 , a stay 16 , a heater unit 17 , a heat transfer member 18 , a heater thermometer 19 , a film thermometer 20 and a thermostat 21 .

The pressure roller 11 and the film unit 10 form a nip 300 by contacting the pressure roller 11 with the film unit 10 . The pressure roller 11 and the fixing belt 14 sandwich and support the sheet at the nip 300 . A toner image is formed on the sheet.

The pressure roller 11 (rotating body) presses the sheet entering the nip 300 . The pressure roller 11 conveys the sheet by rotating. The pressure roller 11 has a metal core 12, an elastic layer 13, and a release layer (not shown).

The material of the cored bar 12 is metal such as stainless steel. The shape of the cored bar 12 is cylindrical. The cored bar 12 is rotatably supported at both axial ends of the cored bar 12 . The cored bar 12 is rotationally driven by a motor (not shown) such as a brushless motor. The cored bar 12 contacts a mechanism such as a cam member (not shown). The cam member (abutment mechanism) rotates to bring the metal core 12 closer to the film unit 10 . The cam member may rotate to bring the elastic layer 13 into contact with the fixing belt 14 . The cam member (spacing mechanism) separates the core metal 12 from the film unit 10 by further rotating.

The elastic layer 13 is made of an elastic material such as silicon rubber. The elastic layer 13 is formed with a constant thickness on the outer peripheral surface of the cored bar 12 . The release layer (not shown) is made of a resin material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer). A release layer is formed on the outer peripheral surface of the elastic layer 13 . The hardness of the outer peripheral surface of the pressure roller 11 is, for example, 40 to 70 degrees under a load of 9.8 N measured by an ASKER-C hardness tester. Thereby, the area of the nip 300 and the durability of the pressure roller 11 are ensured.

Control unit 162 controls the operation of each unit of image forming apparatus 100 . For example, the control section 162 issues an instruction to the control circuit 131 . The control circuit 131 controls the operation of the fixing device 132 based on the instructions. The pressure roller 11 can approach the film unit 10 by rotating the cam member under the control of the control section 162 . A nip 300 is formed when the control unit 162 brings the pressure roller 11 closer to the film unit 10 and presses it with an elastic body.

The pressure roller 11 can be separated from the film unit 10 by rotating the cam member according to control by the control section 162 . For example, when a sheet jam occurs in the fixing device 132 , the cam member separates the pressure roller 11 from the film unit 10 . When the pressure roller 11 is separated from the film unit 10, the user can remove the sheet from the fixing device 132. FIG. Plastic deformation of the fixing belt 14 is prevented by the cam member separating the pressure roller 11 from the film unit 10 when the rotation of the fixing belt 14 is stopped, such as during sleep.

The pressure roller 11 is driven by a motor to rotate under the control of the controller 162 . When the pressure roller 11 rotates with the nip 300 formed, the fixing belt 14 of the film unit 10 is driven to rotate. The pressure roller 11 conveys the sheet in the conveying direction by rotating on its axis while the sheet is placed in the nip 300 . The arrow "W" shown in FIG. 3 represents the sheet conveying direction.

The fixing belt 14 is a strip-shaped thin film formed in a cylindrical shape. The fixing belt 14 has a base layer, an elastic layer, and a release layer in order from the inner peripheral side. The base layer is formed in a tubular shape from a material such as nickel or polyimide. The base layer comprises a heat generating layer such as ceramic or metal. A fluorine-based or polyimide-based coating may be applied to the inner side of the base layer for the purpose of improving the slidability of the fixing belt 14 with respect to the heater unit. The elastic layer is laminated on the outer peripheral surface of the base layer. The elastic layer is made of an elastic material such as silicone rubber. The release layer is laminated on the outer peripheral surface of the elastic layer. The release layer is made of a material such as PFA resin.

The fixing belt 14 is supported from inside the fixing belt 14 by a resin flange (not shown). Both ends of the fixing belt 14 are open. The fixing belt 14 follows the rotation of the pressure roller 11 . Note that the pressure roller 11 may be provided with a drive mechanism such as a motor via a gear.

In FIG. 3, a straight line "CL" connecting the center "pc" of the pressure roller 11 and the center hc of the film unit 10 is defined. The heater unit 17 heats the area of the nip 300 on the sheet. The heater unit 17 has a substrate 171 and a heating element set 172 . The x-direction center 18c of the substrate 171 is arranged in the +x direction with the straight line "CL" as a reference position. As a result, the substrate 171 extends in the +x direction of the nip 300 , so that the sheet that has passed through the nip 300 is easily separated from the film unit 10 .

The x-direction center 19c of the heating element set 172 is arranged on the straight line "CL". Heating element set 172 heats the sheet passing through nip 300 . Heating element set 172 is contained entirely within the area of nip 300 and is centrally located in nip 300 . As a result, the heat distribution in the nip 300 is uniform, so that the sheet passing through the nip 300 is evenly heated.

FIG. 4 is a diagram showing a state example of the lubricant 400 of the embodiment. At the start of use of the image forming apparatus 100, the lubricant 400 contains few impurities and the oil does not volatilize from the lubricant 400, so the motor can drive the pressure roller 11 with low torque. When the image forming apparatus 100 is used for a long period of time, the lubricant 400 deteriorates due to abrasion powder of the fixing belt 14 and volatilization of the oil of the lubricant 400 . When the lubricant 400 deteriorates, the pressure roller 11 cannot be driven with low torque. The pressure roller 11 must be able to be driven even with low torque until the fixing device 132 is replaced.

The heater unit 17 is arranged inside the fixing belt 14 . A lubricant 400 is applied to the inner peripheral surface of the fixing belt 14 and the heat generating element set 172 . Lubricant 400 is, for example, fluorine-based grease. The heater unit 17 contacts the inner peripheral surface of the fixing belt 14 via the lubricant 400 . When the heater unit 17 generates heat, the viscosity of the lubricant 400 decreases. The surface tension of lubricant 400 changes according to the viscosity of lubricant 400 . The lubricant 400 permeates into the gap between the heater unit 17 and the fixing belt 14 according to the surface tension of the lubricant 400 .

For the length of the straight line "CL" shown in FIG. 3, for example, three lengths are predetermined. That is, the pressure roller 11 has a predetermined contact position, an envelope mode position, and a separation mode position, for example. When the pressure roller 11 moves to the contact position, since the pressure roller 11 and the fixing belt 14 are in contact with each other at the nip 300, the pressure roller 11 applies a pressure of about 300 N to the fixing belt 14. be done. When the pressure roller 11 is moved to the envelope mode position, the fixing belt 14 is applied with a pressure of less than 300 N by the pressure roller 11 . When the pressure roller 11 is moved to the separation mode position, there is a gap between the pressure roller 11 and the fixing belt 14 , so pressure from the pressure roller 11 is not applied to the fixing belt 14 .

The lubricant 400 may stagnate at the position where the support member 15 and the fixing belt 14 contact each other. For example, lubricant 400 may become stagnant upstream of nip 300 . As the gap between the heater unit 17 and the fixing belt 14 widens appropriately, the lubricant 400 easily permeates into the gap between the heater unit 17 and the fixing belt 14 . That is, by adjusting the length of straight line "CL" shown in FIG. Thereby, the slidability between the heater unit 17 and the fixing belt 14 is ensured.

FIG. 5 is a diagram showing an example of contact positions according to the embodiment. The fixing device 132 includes a motor 22 , a fulcrum 23 , a cam member 24 , an arm 25 , a rotating shaft 26 , an elastic body 27 and bearings 28 . The motor 22 drives the fulcrum 23 of the cam member 24 under the control of the control section 162 . The fulcrum 23 rotates the cam member 24 according to the drive by the motor 22 .

The shape of the arm 25 is, for example, substantially L-shaped. A rotating shaft 26 is provided at the bent portion of the arm 25 . Arm 25 supports a bearing 28 connected to the central “pc” axis of pressure roller 11 . A rotating shaft 26 rotatably supports the arm 25 . The elastic body 27 is a pressure spring, such as a compression coil spring. The elastic body 27 is arranged between the wall provided in the fixing device 132 and the arm 25 . The elastic body 27 is compressed by the arm 25 rotated clockwise and the wall provided in the fixing device 132 . The compressed elastic body 27 presses the arm 25 so that the arm 25 contacts the cam member 24 . The bearing 28 rotatably supports the pressure roller 11 at the center “pc” of the pressure roller 11 . In FIG. 5, the point of contact between the cam member 24 and the arm 25 is denoted as contact point "A" at the abutment position. In FIG. 5, the cam member 24 receives pressure from the arm 25 at contact point "A" in the abutment position according to the length of the compressed elastic body 27. In FIG. Since the distance between the fulcrum 23 and the contact point "A" of the contact position is longer than the predetermined distance, the film unit 10 and pressure roller 11 are in contact with each other.

FIG. 6 is a diagram showing an example of the envelope mode position (half-contact position) of the embodiment. In FIG. 6, the point of contact between the cam member 24 and the arm 25 is denoted as contact point "B" at the semi-contact position. In FIG. 6, cam member 24 receives pressure from arm 25 corresponding to the length of compressed elastic body 27 at contact point "B" in the semi-contact position. The distance between fulcrum 23 and contact point "B" in the semi-contact position is less than the distance between fulcrum 23 and contact point "A" in the contact position. Therefore, the arm 25 rotates counterclockwise in the figure about the rotation shaft 26 . The length of straight line “CL” shown in FIG. 6 is longer than the length of straight line “CL” shown in FIG. 5 depending on the rotation angle of arm 25 .

FIG. 7 is a diagram showing an example of positions in the separation mode (separation positions) of the embodiment. In FIG. 7, the point of contact between the cam member 24 and the arm 25 is denoted as contact point "C" at the separated position. In FIG. 7, the cam member 24 receives pressure from the arm 25 at contact point "C" in the spaced position, corresponding to the length of the compressed elastic body 27. In FIG. The distance between the fulcrum 23 and the contact point "C" in the spaced position is less than the distance between the fulcrum 23 and the contact point "B" in the semi-contact position. As a result, the arm 25 further rotates counterclockwise in the figure about the rotation shaft 26 . The length of straight line “CL” shown in FIG. 7 is longer than the length of straight line “CL” shown in FIG. 6 depending on the rotation angle of arm 25 . The film unit 10 and the pressure roller 11 are separated from each other because the distance between the fulcrum 23 and the contact point "C" at the separated position is less than a predetermined distance. Therefore, the heat of heater unit 17 is not transmitted to pressure roller 11 .

Returning to FIG. 3, the description of the configuration example of the fixing device 132 is continued. The heat transfer member 18 (heat equalizing member) is made of a metal material with high thermal conductivity such as copper. The outer shape of the heat transfer member 18 is the same as the outer shape of the substrate 171 of the heater unit 17 . The heat transfer member 18 is arranged in contact with the surface of the heater unit 17 in the -z direction. The surface in the −z direction is the surface opposite to the surface where the heater unit 17 contacts the fixing belt 14 .

The support member 15 (heater holder) is made of a resin material such as liquid crystal polymer. The support member 15 is arranged so as to cover both sides of the heater unit 17 in the -z direction and in the x direction. The support member 15 supports the heater unit 17 via the heat transfer member 18 . Both ends of the support member 15 in the x direction are chamfered. The support member 15 supports the inner circumferential surface of the fixing belt 14 at both ends of the heater unit 17 in the x direction.

When a sheet passing through the fixing device 132 is heated, a temperature distribution is generated in the heater unit 17 according to the size of the sheet. If the temperature of the heater unit 17 becomes high locally, the temperature of the heater unit 17 may exceed the heat-resistant temperature of the support member 15 made of a resin material. If the temperature of the heater unit 17 exceeds the heat-resistant temperature of the support member 15, the resin material forming the support member 15 will melt and be damaged. The heat transfer member 18 averages the temperature distribution of the heater unit 17 . Thereby, the heat resistance of the support member 15 is ensured.

The stay 16 is made of a steel plate material or the like. A cross section of the stay 16 perpendicular to the y direction is formed in a U shape. The stay 16 is mounted in the -z direction of the support member 15 so that the support member 15 closes the U-shaped opening. The stay 16 extends in the y-direction. Both ends of the stay 16 in the y direction are fixed to the housing of the image forming apparatus 100 . The film unit 10 is thereby supported by the image forming apparatus 100 . The stay 16 improves the bending rigidity of the film unit 10 . Flanges (not shown) for restricting the movement of the fixing belt 14 in the y direction are attached near both ends of the stay 16 in the y direction.

The heater thermometer 19 is arranged in the −z direction of the heater unit 17 with the heat transfer member 18 interposed therebetween. For example, heater thermometer 19 is a thermistor. The heater thermometer 19 is attached to and supported by the -z direction surface of the support member 15 . The temperature sensing element of the heater thermometer 19 contacts the heat transfer member 18 through a hole penetrating the support member 15 in the z direction. A heater thermometer 19 measures the temperature of the heater unit 17 via the heat transfer member 18 .

The film thermometer 20 is arranged inside the fixing belt 14 and in the +x direction of the heater unit 17 . A film thermometer 20 contacts the inner peripheral surface of the fixing belt 14 to measure the temperature of the fixing belt 14 .

Thermostat 21 is arranged similarly to heater thermometer 19 . Thermostat 21 is incorporated into the electrical circuit. The thermostat 21 cuts off the energization of the heating element set 172 when the temperature of the heater unit 17 detected via the heat transfer member 18 exceeds a predetermined temperature.

Next, the details of the processing device 160 shown in FIG. 2 will be described.
Acquisition unit 161 acquires a physical quantity that changes according to the magnitude of the torque of pressure roller 11 . For example, the obtaining unit 161 obtains a current value of a motor (not shown) that drives the core bar 12 of the pressure roller 11 . A mechanism (not shown) for detecting the current value of the motor is arranged, for example, within a predetermined distance from the metal core 12 .

If the rated current value of the motor is, for example, 2A and a margin of, for example, 25% is ensured for the rated current value, the threshold value of the current value of the motor is determined to be 1.5A. The threshold information is stored in the storage unit 150, for example. The control unit 162 acquires threshold information from the storage unit 150 during image formation by the fixing device 132 . The time of image formation by the fixing device 132 is, for example, the execution of a print job.

The control unit 162 determines whether or not the current value of the motor that drives the cored bar 12 is equal to or greater than the threshold. If it is determined that the current value of the motor is equal to or greater than the threshold value and image formation by the fixing device 132 is not underway, the control unit 162 shifts the operation mode of the fixing device 132 to the lubricant circulation mode.

Examples of when the fixing device 132 is not forming an image include, for example, immediately after execution of a print job, before execution of a print job, during warming up of the fixing device 132, immediately after warming up of the fixing device 132, processing for maintaining image quality (toner density check processing), or alignment processing of a predetermined mechanism of the fixing device 132 is being executed.

The lubricant circulation mode is an operation mode in which the length of straight line "CL" shown in FIG. That is, the lubricant circulation mode is an operation mode in which the controller 162 changes the gap between the heater unit 17 and the fixing belt 14 while the rotation of the fixing belt 14 and the pressure roller 11 is stopped. In the lubricant circulation mode, controller 162 reduces the pressure applied from pressure roller 11 to heater unit 17 . In the lubricant circulation mode, controller 162 increases the distance between heater unit 17 and the central axis of pressure roller 11 .

The controller 162 may change the distance of the gap between the heater unit 17 and the fixing belt 14 multiple times in the lubricant circulation mode. Fresh lubricant 400 stagnant upstream of nip 300 penetrates the open gap between heater unit 17 and fuser belt 14 in the lubricant circulation mode. This restores the performance of lubricant 400 in nip 300 . When the control unit 162 causes the pressure roller 11 to perform the operation of changing the distance of the gap one or more times and then causes the pressure roller 11 to re-execute the operation of changing the distance of the gap when the predetermined condition is satisfied. , the operation of changing the distance of the gap may be executed multiple times. The predetermined condition is the condition that the number of sheets to be printed is equal to or less than the predetermined number, and the condition that the elapsed time is within the predetermined time. When the torque of the pressure roller 11 immediately increases (when the physical quantity increases) after the pressure roller 11 or the like operates in the lubricant circulation mode, the operation in the lubricant circulation mode is insufficient. there is a possibility. For this reason, if the torque of the pressure roller 11 immediately increases after the pressure roller 11 or the like operates in the lubricant circulation mode, the control unit 162 causes the pressure roller 11 to change the gap distance. may be run multiple times.

The control unit 162 may reduce the pressure applied from the pressure roller 11 to the heater unit 17 multiple times in the lubricant circulation mode. When the control unit 162 causes the pressure roller 11 to perform the operation of changing the pressure one or more times and then causes the pressure roller 11 to re-execute the operation of changing the pressure when the predetermined condition is satisfied, the control unit 162 changes the pressure. You may make the operation|movement to perform multiple times. The controller 162 may lengthen the distance between the heater unit 17 and the central axis of the pressure roller 11 multiple times in the lubricant circulation mode. After having the pressure roller 11 perform the operation of changing the distance between the heater unit 17 and the central axis of the pressure roller 11 one or more times, the control unit 162 performs the operation of changing the distance when a predetermined condition is satisfied. When the pressure roller 11 is caused to re-execute, the operation of changing the distance may be executed multiple times.

FIG. 8 is a diagram showing an example of changes in the current value of the motor according to the embodiment. The torque limit value of the rated load of the motor that drives the core bar 12 that rotates the pressure roller 11 is, for example, 100 mN·m. There is a correlation between the driving force of the motor that drives the pressure roller 11 and the amount of current input to the motor. The control unit 162 maintains the specified number of rotations of the pressure roller 11 and the fixing belt 14 by increasing the amount of current input to the motor according to the load torque of the pressure roller 11 .

At time t1 in FIG. 8, the control unit 162 determines that the current value of the motor is equal to or greater than the threshold. If it is determined that the current value of the motor is equal to or greater than the threshold value and the fixing device 132 is not forming an image, the control unit 162 shifts the operation mode of the fixing device 132 to the lubricant circulation mode. The lubricant 400 permeates the open gap between the heater unit 17 and the fixing belt 14 in the lubricant circulation mode. This restores the performance of lubricant 400 in nip 300 . Since the drive torque of the pressure roller 11 is temporarily lowered, the low torque state of the pressure roller 11 is maintained for a predetermined time.

The controller 162 can extend the life of the fixing device 132 by repeatedly changing the distance between the heater unit 17 and the fixing belt 14 in the lubricant circulation mode. At time t2 in FIG. 8, the control unit 162 determines again that the current value of the motor is equal to or greater than the threshold. If it is determined that the current value of the motor is equal to or greater than the threshold value and image formation by the fixing device 132 is not underway, the control unit 162 shifts the operation mode of the fixing device 132 to the lubricant circulation mode.

Note that the fixing device 132 may be replaced as a unit when toner images are formed on a predetermined number of sheets, for example, about 200,000 to 600,000 sheets.

Next, an operation example of the image forming apparatus 100 will be described.
FIG. 9 is a flowchart showing an operation example of the image forming apparatus 100 according to the embodiment. Acquisition unit 161 determines whether fixing device 132 is forming an image. That is, the acquisition unit 161 determines whether or not image formation is being performed by the fixing device 132 (ACT 101).

If it is during image formation (ACT101: YES), the acquisition unit 161 acquires a physical quantity that changes according to the magnitude of the torque of the pressure roller 11 (ACT102). Acquisition unit 161 returns the processing to ACT 101 .

If it is not during image formation (ACT101: NO), the control unit 162 determines whether or not the acquisition unit 161 has already acquired the physical quantity (ACT103). If the acquisition unit 161 has not acquired the physical quantity (ACT 103 : NO), the acquisition unit 161 returns the process to ACT 101 . If the acquisition unit 161 has acquired the physical quantity (ACT 103: YES), the control unit 162 determines whether the physical quantity is equal to or greater than the threshold (ACT 104).

If the physical quantity is less than the threshold (ACT104: NO), the controller 162 returns the process to ACT101. If the physical quantity is equal to or greater than the threshold (ACT 104: YES), the controller 162 causes the pressure roller 11 to perform a predetermined operation to create a gap between the heating element set 172 and the fixing belt 14 (ACT 103). . The control unit 162 returns the processing to ACT101.

As described above, the image forming apparatus 100 according to the first embodiment has the fixing device 132 , the acquisition section 161 and the control section 162 . Fixing device 132 has heater unit 17 , fixing belt 14 , pressure roller 11 , and lubricant 400 . The heater unit 17 emits heat. The fixing belt 14 is a strip-shaped thin film that slides on the surface of the heater unit 17 while contacting the heater unit 17 with the inner peripheral surface of the fixing belt 14 . The pressure roller 11 can press against the outer peripheral surface of the fixing belt 14 and is rotatable. The lubricant 400 is in contact with the inner peripheral surface of the fixing belt 14 . Acquisition unit 161 acquires a physical quantity that changes according to the magnitude of the torque of pressure roller 11 . The physical quantity is, for example, the amount of electric current. The acquisition unit 161 may acquire the measured torque information or temperature information of the pressure roller 11 . The controller 162 performs a predetermined operation to create a gap between the heater unit 17 and the fixing belt 14 based on the physical quantity acquired during image formation by the fixing device 132 when the pressure roller is not during image formation. 11 to execute.

Accordingly, the image forming apparatus 100 of the first embodiment can prevent the drive torque of the fixing device 132 from increasing.

In the image forming apparatus 100, the lubricant circulation mode is not executed simply because the predetermined time has passed, and the lubricant circulation mode is executed according to the torque of the pressure roller 11. is unnecessary, and an increase in the number of times consumables such as the pressure roller 11 and the fixing belt 14 are driven to rotate can be suppressed. Since the running distance of the fixing belt 14 is difficult to increase, the image forming apparatus 100 can drive the pressure roller 11 with a stable low torque until the prescribed unit replacement time for the fixing device 132 comes. . The image forming apparatus 100 can reduce lost time when a print job cannot be executed.

Note that the pressure roller 11 may be marked. The rotational speed of the marks provided on the pressure roller 11 may be measured using, for example, an image sensor. The obtaining unit 161 may derive the torque of the pressure roller 11 based on the relationship between the rotational speed of the mark provided on the pressure roller 11 and the current value of the motor. The control unit 162 may determine whether or not the torque of the pressure roller 11 is greater than or equal to the threshold. If it is determined that the torque of the pressure roller 11 is equal to or greater than the threshold value and the fixing device 132 is not forming an image, the control unit 162 may shift the operation mode of the fixing device 132 to the lubricant circulation mode.

(Second embodiment)
The second embodiment differs from the first embodiment in that the controller 162 rotates the pressure roller 11 and the fixing belt 14 in the lubricant circulation mode. In the second embodiment, differences from the first embodiment will be explained.

In the lubricant circulation mode, when the load torque of the pressure roller 11 is equal to or greater than a predetermined torque value, the controller 162 rotates the pressure roller 11 and the fixing belt 14 to reduce the gap between the heater unit 17 and the fixing belt 14. You can change the distance of Lubricant 400 located in nip 300 is heated by heater unit 17 . Therefore, the deterioration of the lubricant 400 positioned at the nip 300 progresses faster than the lubricant 400 positioned away from the nip 300 . The controller 162 changes the gap between the heater unit 17 and the fixing belt 14 and rotates the fixing belt 14 to move the lubricant 400 with a low degree of deterioration to a position closer to the nip 300 . In this manner, the controller 162 evenly degrades the lubricant 400 adhering to the inner peripheral surface of the fixing belt 14 . Thereby, the control unit 162 can keep the driving torque of the fixing device 132 low. In addition, in the lubricant circulation mode, the control unit 162 may reverse the rotation direction of the pressure roller 11 . This allows the controller 162 to deform the lubricant 400 .

As described above, the controller 162 of the second embodiment rotates the pressure roller 11 in the lubricant circulation mode. Conveyance by the fixing belt 14 increases the amount of the lubricant 400 supplied to the nip 300, so that the pressure roller 11 can be driven with a low driving torque. For example, even if the amount of lubricant 400 positioned at the nip 300 has decreased, the amount of lubricant 400 positioned at the nip 300 can be increased by rotating the fixing belt 14 . When the current value of the motor exceeds the threshold according to the drive torque, the fixing belt 14 may increase the amount of the lubricant 400 placed in the nip 300 by rotating.

(Third embodiment)
The third embodiment differs from the first embodiment in that the lubricant 400 is heated according to the control by the controller 162 in the lubricant circulation mode. 3rd Embodiment demonstrates difference with 1st Embodiment.

The temperature of the lubricant 400 is low when the environmental temperature inside the image forming apparatus 100 is extremely lower than normal temperature, or when the number of sheets (the number of copies) formed with toner images is small. When the temperature of the lubricant 400 is low, the lubricity of the lubricant 400 is low because the viscosity of the lubricant 400 is high. In the lubricant circulation mode, when the environmental temperature in image forming apparatus 100 is equal to or lower than a predetermined temperature, controller 162 causes heater unit 17 to heat fixing belt 14 while reducing the gap between heater unit 17 and fixing belt 14 . You can change the distance. As a result, the temperature of the lubricant 400 increases, so the viscosity of the lubricant 400 decreases and the lubricity of the lubricant 400 increases.

Since the fixing belt 14 and the pressure roller 11 are not rotating, the heater unit 17 heats the fixing belt 14 at a temperature that does not damage the fixing belt 14 and the pressure roller 11 . If the rated power of the heater unit 17 is, for example, 1000 W, the power that generates a temperature that does not damage the fixing belt 14 and the pressure roller 11 is, for example, about 300 W.

As described above, the controller 162 of the third embodiment causes the heater unit 17 to generate heat in the lubricant circulation mode when the environmental temperature is equal to or lower than the predetermined temperature. As a result, the image forming apparatus 100 of the third embodiment can further improve the slidability (lubricity of the lubricant 400) between the heater unit 17 and the fixing belt 14 compared to the first embodiment. is.

The first, second and third embodiments may be combined. For example, the image forming apparatus 100 determines that the temperature or load torque conditions have become severe when the interval between the execution time of the previous lubricant circulation mode and the current execution time of the lubricant circulation mode is within a predetermined time. . The image forming apparatus 100 may determine that the temperature or load torque conditions have become severe when the number of printed sheets reaches or exceeds a certain number. When it is determined that the temperature or load torque conditions have become severe, the image forming apparatus 100 rotates the pressure roller 11 and the fixing belt 14 in accordance with the control by the control unit 162 in the lubricant circulation mode. It may be executed with priority over the operation of the embodiment.

If the increase in the load torque of pressure roller 11 is caused by oxidation of lubricant 400 , control unit 162 may perform control to add a substance that neutralizes oxidation to lubricant 400 . In this case, the controller 162 does not have to change the distance between the heater unit 17 and the fixing belt 14 .

According to at least one embodiment described above, it is possible to prevent the driving torque of the fixing device from increasing.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 10... Film unit 11... Pressure roller 12... Core metal 13... Elastic layer 14... Fixing belt 15... Support member 16... Stay 17... Heater unit 18... Heat transfer member 19... Heater temperature Meter 20 Film thermometer 21 Thermostat 22 Motor 23 Fulcrum 24 Cam member 25 Arm 26 Rotating shaft 27 Elastic body 28 Bearing 100 Image forming apparatus 110 Display 120 Control panel 130 Printer 131 Control circuit 132 Fixing device 140 Sheet storage unit 150 Storage unit 160 Processing device 161 Acquisition unit 162 Control unit 171 Substrate 172 Heating element set 200 Image reading unit 300 Nip 400 Lubricant

Claims (4)

A heat generating element that emits heat, a fixing belt that is a strip-shaped thin film that slides on the surface of the heat generating element while being in contact with the heat generating element on the inner peripheral surface, and can be pressed against the outer peripheral surface of the fixing belt and rotatable. and a lubricant in contact with the inner peripheral surface;
an acquisition unit that acquires a physical quantity that changes according to the magnitude of the torque of the rotating body;
Control for causing the rotator to perform a predetermined operation to create a gap between the heating element and the fixing belt based on the physical quantity acquired during image formation by the fixing device when not during image formation. and
If a predetermined condition is satisfied after causing the predetermined operation to be performed and the predetermined operation is to be re-executed, the control unit performs the predetermined operation on the rotating body a plurality of times. image forming apparatus. 2. The image forming apparatus according to claim 1, wherein said predetermined operation is an operation of reducing pressure applied from said rotating body to said heating element. 2. The image forming apparatus according to claim 1, wherein said predetermined operation is an operation for increasing the distance between said heating element and the central axis of said rotating body. the physical quantity is a current value of a motor that drives the rotating body;
The image forming apparatus according to any one of claims 1 to 3, wherein the controller causes the predetermined operation to be performed when the current value is equal to or greater than a predetermined value.

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