JP7200508B2 - Image forming apparatus and control method - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming apparatus control method. In particular, the present invention relates to operation control of a fixing device.

2. Description of the Related Art Conventionally, image forming apparatuses such as copiers, printers, facsimile machines, or multifunction machines thereof are known. This image forming apparatus includes a fixing device that heats and melts a toner image formed on a recording material such as paper to fix the image on the recording material.

For example, Japanese Patent Application Laid-Open No. 2002-200000 discloses a method for controlling such a fixing device. Specifically, Japanese Patent Application Laid-Open No. 2002-200000 discloses a fixing device that aims to reduce the drive torque when the rotation of the fixing belt is started, and to suppress wear and deterioration of the fixing belt.

Specifically, the fixing device disclosed in Japanese Patent Application Laid-Open No. 2002-200001 is a belt fixing type device that includes a fixing belt that is wound between a fixing roller and a heating means. In the heating means for heating the fixing belt, the other end corresponding to the upstream side in the rotation direction of the fixing belt is angled by the angular displacement imparting means in a direction in which the other end corresponding to the upstream side in the rotation direction approaches the fixing roller so that the fixing belt is in a relaxed state when the rotation is started. displaced.

JP 2010-286743 A

In Patent Document 1, in order to reduce the drive torque (starting torque, starting torque) at the time of starting, the fixing device has to have a complicated structure. Therefore, the number of parts of the fixing device increases.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide an image forming apparatus and a control method capable of reducing the driving torque at the time of starting the fixing device with a simple configuration. It is in.

According to one aspect of the present disclosure, an image forming apparatus includes a fixing device that fixes an unfixed image on a recording material, and a control device that controls the operation of the fixing device. The fixing device includes an endless fixing belt, a heat source for heating the fixing belt, a first direction for conveying the recording material to the downstream side of the conveying path, and a second direction opposite to the first direction. It has a rotatable pressure roller and a nip forming member forming a nip area therebetween. The fixing belt is supported under tension by the nip forming member and the heat source, and rotates following the rotation of the pressure roller. It is bent on one side and the other side with respect to . The amount of deflection on one side is greater than the amount of deflection on the other side. When starting rotation of the pressure roller after stopping rotation of the pressure roller, the control device rotates the pressure roller in a direction in which the deflection amount in one of the first direction and the second direction decreases.

Preferably, one side is downstream of the transport path than the other side. The direction in which the amount of deflection on one side decreases is the second direction. Based on acceptance of a print job, the control device performs control to rotate the pressure roller in a first direction to fix an unfixed image, control to stop rotation of the pressure roller, and and control to rotate the pressure roller in the second direction in order to reduce the amount of deflection are executed in this order.

Preferably, the image forming apparatus further includes a temperature detection section that detects the temperature of the fixing belt. The control device rotates the pressure roller in a direction in which the deflection amount in one of the first direction and the second direction decreases, provided that the detected temperature is equal to or lower than a predetermined temperature. .

Preferably, one side is downstream of the transport path than the other side. The direction in which the amount of deflection on one side decreases is the second direction. When a print job is accepted, the control device rotates the pressure roller in a second direction to reduce the amount of deflection on one side, provided that the detected temperature is equal to or lower than a predetermined temperature. to start the control. The control device performs control to stop the rotation of the pressure roller after rotating the pressure roller in the second direction, and control to rotate the pressure roller in the first direction to fix the unfixed image. are executed in this order.

Preferably, when receiving a print job, the control device performs control to heat the fixing belt with the heat source on condition that the detected temperature is equal to or lower than a predetermined temperature. When the detected temperature exceeds a predetermined temperature, the control device stops the rotation of the pressure roller and moves the pressure roller in the first direction to fix the unfixed image. and control to rotate are executed in this order.

Preferably, the image forming apparatus further includes a torque detection section that detects driving torque of the pressure roller. When receiving a print job, the control device performs control to heat the fixing belt with a heat source on condition that the detected temperature is equal to or lower than a predetermined temperature. The control device controls the pressure roller on the condition that the drive torque when rotating the pressure roller in the second direction to reduce the amount of deflection on one side becomes equal to or less than a predetermined torque due to heating. Control to stop the rotation of the pressure roller and control to rotate the pressure roller in the first direction to fix the unfixed image are executed in this order.

Preferably, the fixing device is configured such that the amount of deflection on one side is within a predetermined range.

According to another aspect of the present disclosure, a control method is executed by an image forming apparatus that includes a fixing device that fixes an unfixed image on a recording material onto the recording material, and a control device that controls the operation of the fixing device. be. The fixing device includes a heat source for heating an endless fixing belt, a pressure roller rotatable in a first direction and a second direction opposite to the first direction, and a nip between the pressure roller. and a nip forming member defining a region. The fixing belt is supported under tension by the nip forming member and the heat source, and rotates following the rotation of the pressure roller. The control method comprises stopping rotation of the pressure roller in the first direction. When the rotation in the first direction is stopped, the fixing belt is flexed on one side and the other side with respect to the nip area, and the amount of flexure on one side is the amount of flexure on the other side. Larger than quantity. The control method further comprises restarting rotation of the pressure roller after stopping rotation of the pressure roller in the first direction, wherein the step of restarting rotation rotates the pressure roller in the second direction.

According to the above disclosure, it is possible to reduce the driving torque at the start of the fixing device with a simple configuration.

1 is a diagram illustrating an example of the configuration of an image forming apparatus; FIG. FIG. 2 is a diagram for explaining a specific configuration of a fixing device; FIG. 4 is a diagram for explaining control of a fixing device executed by a control device; FIG. FIG. 5 is a diagram for explaining main torque applied as a load when the fixing device starts to start. FIG. 10 is a diagram for explaining a C set of pressure rollers; FIG. 5 is a diagram for explaining changes in torque when the fixing device is started; FIG. 5 is a diagram for explaining changes in torque in a comparative example; It is a graph showing the data of this example and the data of a comparative example. 2 is a block diagram for explaining the hardware configuration of the image forming apparatus; FIG. It is a block diagram for explaining the functional configuration of the control device. 3 is a flowchart for explaining the flow of processing executed in the image forming apparatus; FIG. 4 is a diagram for explaining control of a fixing device executed by a control device; FIG. 3 is a flowchart for explaining the flow of processing executed in the image forming apparatus; FIG. FIG. 10 is a diagram for explaining a specific configuration of a fixing device used in another embodiment; FIG. 10 is a flowchart for explaining the flow of processing executed in an image forming apparatus having another fixing device; FIG. 10 is a diagram for explaining a specific configuration of a fixing device used in still another embodiment; FIG. 10 is a flowchart for explaining the flow of processing executed in an image forming apparatus having another fixing device; FIG. 5 is a diagram for explaining the bending of the fixing belt on the downstream side; FIG. 10 is a diagram for explaining a change in torque when starting the fixing device in a case where the amount of deflection on the downstream side is configured to be within a predetermined range; 2 is a diagram for explaining the configuration of a fixing device according to the embodiment; FIG.

An image processing apparatus according to an embodiment will be described below with reference to the drawings. In the embodiments described below, when referring to the number, amount, etc., the scope of the present disclosure is not necessarily limited to the number, amount, etc., unless otherwise specified. The same reference numbers are given to the same parts and equivalent parts, and redundant description may not be repeated.

In the drawings, there are portions that are not illustrated according to actual dimensional ratios, but are illustrated with changed ratios so as to clarify the structure in order to facilitate understanding of the structure. In addition, each embodiment and each modified example described below may be selectively combined as appropriate.

Further, although an image forming apparatus as a color printer will be described below, the image forming apparatus is not limited to a color printer. For example, the image forming apparatus may be a monochrome printer, a FAX, or a multi-function peripheral (MFP: Multi-Functional Peripheral) of monochrome printer, color printer and FAX.
[Embodiment 1]
<A. Overall configuration>
FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus 100. As shown in FIG.

Referring to FIG. 1, image forming apparatus 100 includes imaging units 1Y, 1M, 1C, and 1K, intermediate transfer belt 30 (transfer material), primary transfer roller 31, secondary transfer roller 33, and cassette 37. , a fixing device 40 , a cleaning blade 53 , and a control device 101 .

The image forming apparatus 100 includes a toner bottle 15Y that supplies yellow (Y) toner, a toner bottle 15M that supplies magenta (M) toner, a toner bottle 15C that supplies cyan (C) toner, and a black toner bottle. A toner bottle 15B for supplying (BK) toner can be attached. The imaging unit 1Y receives toner supplied from the toner bottle 15Y and forms a yellow (Y) toner image. The imaging unit 1M receives supply of toner from the toner bottle 15M and forms a magenta (M) toner image. The imaging unit 1C receives supply of toner from the toner bottle 15C and forms a cyan (C) toner image. The imaging unit 1K receives supply of toner from the toner bottle 15K and forms a black (BK) toner image. The imaging units 1Y, 1M, 1C, and 1K are arranged in order along the rotation direction of the intermediate transfer belt 30, respectively.

Imaging units 1Y, 1M, 1C, and 1K each include a photoreceptor 10, a charging roller 11, an exposure section 12, a developing device 13, and a cleaning blade 17. As shown in FIG. Imaging units 1Y, 1M, 1C, and 1K are detachable from the main body of image forming apparatus 100 .

The photoreceptor 10 is an image carrier that carries a toner image. As an example, the photoreceptor 10 is a photoreceptor drum having a photosensitive layer formed on its surface.

The charging roller 11 uniformly charges the surface of the photoreceptor 10 . The exposure unit 12 irradiates the photoreceptor 10 with a laser according to a control signal from the control device 101, and exposes the surface of the photoreceptor 10 according to a designated image pattern. Thereby, an electrostatic latent image corresponding to the input image is formed on the photoreceptor 10 .

The developing device 13 develops the electrostatic latent image using developer containing toner, carrier, and external additives. Developer is supplied from a toner bottle. Developing device 13 includes a developing roller 14 . The developing device 13 applies a developing bias to the developing roller 14 to cause toner to adhere to the surface of the developing roller 14 . The developing device 13 rotates the developing roller 14 to transfer the toner from the developing roller 14 to the photoreceptor 10 . As a result, a toner image corresponding to the electrostatic latent image is developed on the surface of the photoreceptor 10 .

The photoreceptor 10 and the intermediate transfer belt 30 are in contact with each other at the portion where the primary transfer roller 31 is provided. A predetermined transfer bias is applied to the contact portion, and the toner image developed on the photoreceptor 10 is transferred to the intermediate transfer belt 30 by the transfer bias. At this time, a yellow (Y) toner image, a magenta (M) toner image, a cyan (C), and a black (BK) toner image are sequentially superimposed and transferred onto the intermediate transfer belt 30 . Thereby, a color toner image is formed on the intermediate transfer belt 30 .

The cleaning blade 17 is pressed against the photoreceptor 10 and collects toner remaining on the surface of the photoreceptor 10 after transfer to the intermediate transfer belt 30 .

Cassette 37 is provided, for example, in the lower portion of image forming apparatus 100 . A sheet S (transfer medium) as a recording material is set in the cassette 37 . Sheets S are fed one by one from cassette 37 to secondary transfer roller 33 . The secondary transfer roller 33 transfers the toner image transferred to the intermediate transfer belt 30 onto the sheet S. As shown in FIG. By synchronizing the timing of feeding and transporting the paper S with the position of the toner image on the intermediate transfer belt 30, the toner image is transferred to the appropriate position on the paper S. FIG. After that, the paper S is sent to the fixing device 40 .

The fixing device 40 fixes an unfixed image on paper (recording material) onto the paper. Specifically, the fixing device 40 fuses the toner image on the paper S passing through the fixing device 40 to fix the toner image on the paper S. As shown in FIG. After that, the sheet S is discharged to the tray 48 . A specific configuration of the fixing device 40 will be described later.

The cleaning blade 53 is pressed against the intermediate transfer belt 30 and collects toner remaining on the intermediate transfer belt 30 after the toner image is transferred. The toner is transported by a transport screw (not shown) and collected in a waste toner container (not shown).

The control device 101 controls a motor for controlling rotation of the photoreceptor 10, a motor for controlling rotation of the primary transfer roller 31, and the like. The control device 101 also controls the operation of the fixing device 40 . The motor is driven by PWM (Pulse Width Modulation) control, for example.

<B. Configuration of main parts>
FIG. 2 is a diagram for explaining a specific configuration of the fixing device 40. As shown in FIG.

Referring to FIG. 2, fixing device 40 includes heating member 401, fixing belt 402, holding member 403, nip forming member 405, sliding sheet 406, curvature imparting member 407, and pressure roller 408. , a motor 409 . The nip forming member 405 has a connecting shaft 454 .

A heating member 401 is a heat source for warming the fixing belt 402 . Heating member 401 includes a halogen heater 451 and a housing 452 . A halogen heater 451 is installed in a housing 452 . The outer surface of the housing 452 is in contact with the fixing belt 402 . Heating member 401 transfers heat generated by halogen heater 451 to fixing belt 402 via housing 452 .

In this example, the halogen heater 451 is composed of two heaters with different heat generating regions. The housing 452 is a pipe made of aluminum or stainless steel and having a thickness of about 0.2 mm to 0.5 mm. The inner peripheral surface of the housing 452 is painted black in order to increase the absorption of light generated from the halogen heater 451 . In addition, the outer peripheral surface of the housing 452 is coated with fluorine to prevent contamination.

Note that in this example, even if the fixing belt 402 rotates, the heating member 401 does not rotate. However, the present invention is not limited to this, and the heating member 401 may be configured to rotate following rotation of the fixing belt 402 .

The fixing belt 402 is an endless belt. Fixing belt 402 is supported under tension by nip forming member 405 and heating member 401 , and rotates following the rotation of pressure roller 408 .

The fixing belt 402 has a base layer made of polyimide resin (PI) or nickel and having a thickness of about 50 μm to 100 μm, an elastic layer made of silicone rubber having a thickness of about 100 μm to 300 μm, and a thickness of about 10 μm to 50 μm. It consists of a fluorine-based release layer.

Specifically, the fixing belt 402 has an elastic layer on the base layer and a release layer on the elastic layer. The base layer contacts the outer peripheral surface of the housing 452 of the heating member 401 . The release layer contacts the surface of the pressure roller 408 and the paper S. As shown in FIG. More specifically, the release layer contacts the unfixed image G on the paper S. As shown in FIG.

The holding member 403 holds the nip forming member 405 . The holding member 403 is made of U-shaped sheet metal with a thickness of about 2 mm. The holding member 403 has a hole at a position corresponding to the connecting shaft 454 of the nip forming member 405 so as to fit with the connecting shaft 454 .

Nip forming member 405 forms a nip area with pressure roller 408 . The nip forming member 405 is made of resin such as LCP (Liquid Crystal Plastic). Also, the connecting shaft 454 of the nip forming member 405 protrudes to the side opposite to the nip region. The nip forming member 405 is wrapped around the sliding sheet 406 .

The sliding sheet 406 is made of a glass cloth sheet or a PTFE (polytetrafluoroethylene) sheet covered with a fluororesin having excellent sliding properties. By sandwiching the sliding sheet 406 between the nip forming member 405 and the fixing belt 402 and rotating the fixing belt 402, resistance during sliding can be reduced. As a result, the fixing belt 402 can be stably rotated.

Further, the sliding sheet 406 has unevenness with a depth of about 50 μm to 200 μm on the surface that contacts the fixing belt 402 . As a result, the contact area with the fixing belt 402 can be reduced, so that the resistance during sliding can be reduced. Further, by applying grease as a lubricant between the fixing belt 402 and the sliding sheet 406, the resistance during sliding is reduced.

In order to fix the position of the sliding sheet 406 when the sliding sheet 406 is wound around the nip forming member 405 and fixed, the connecting shaft 454 between the upstream side and the downstream side of the sliding sheet 406 corresponds to the connecting shaft 454 . is perforated. The connecting shaft 454 passes through the through hole of the slide sheet 406 and the through hole of the holding member 403 . Further, in this state, the sliding sheet 406 is sandwiched between the nip forming member 405 and the holding member 403 by the pressing force of the pressure roller 408, and the position of the sliding sheet 406 is held. be.

The curvature imparting member 407 imparts curvature to the portion of the fixing belt 402 that has passed through the nip region. The curvature imparting member 407 is made of resin such as LCP, like the nip forming member 405 .

The pressure roller 408 is rotatable in the forward direction (direction of arrow Q in the drawing) for transporting the sheet S from the upstream side to the downstream side of the transport path, and in the reverse direction. When the pressure roller 408 rotates in the forward direction, the fixing belt 402 also rotates in the forward direction (direction of arrow R in the figure). In FIG. 2, since the sheet S is transported from bottom to top along the transport path as indicated by arrow 15, the upstream side is the lower position and the downstream side is the upper position.

The pressure roller 408 is made of silicone rubber with a diameter of about 20 mm to 40 mm. In addition, the surface of the silicon rubber is covered with a fluorine-based tube in order to improve releasability.

Motor 409 is a driving device for rotating pressure roller 408 in the forward direction (the direction of arrow Q) and the reverse direction. The motor 409 is connected to the rotating shaft of the pressure roller 408 via a gear (not shown).

A motor 409 rotates the pressure roller 408 forward and backward according to a command from the control device 101 . Specifically, the motor 409 can rotate forward and backward according to the input current generated by the control device 101 . As the motor 409 rotates forward and backward, the pressure roller 408 can also rotate forward (rotate in the forward direction) and reversely (rotate in the reverse direction).

<C. Contents of Control of Fixing Device 40>
FIG. 3 is a diagram for explaining control of the fixing device 40 executed by the control device 101. As shown in FIG.

Referring to FIG. 3, when a print job is received, control device 101 fixes an unfixed image on sheet S and conveys sheet S on which the image is fixed, as shown in state (A). The pressure roller 408 is rotated forward (in the direction of the arrow in the drawing) in order to convey the sheet to the downstream side of the path. In this case, the fixing belt 402 also rotates in the positive direction (the direction of the arrow in the figure) following the rotation of the pressure roller 408 . A print job is for forming a specified image on one or more sheets of paper.

When the fixing process ends (that is, the print job ends), the control device 101 stops (temporarily stops) the forward rotation of the pressure roller 408 as shown in state (B). This also stops the rotation of the fixing belt 402 . Note that this stop is typically a momentary stop to perform reverse rotation.

Immediately after that, the control device 101 starts the reverse rotation of the pressure roller 408 (in the direction of the arrow in the figure), as shown in state (C). When such reverse rotation is started, the fixing belt 402 also rotates reversely (in the direction of the arrow in the figure) following the rotation of the pressure roller 408 .

Control device 101 stops the reverse rotation of pressure roller 408 as shown in state (D) after a predetermined period of time has elapsed since the reverse rotation of pressure roller 408 was started (state (C)). This also stops the rotation of the fixing belt 402 .

The control device 101 waits for the next print job while the fixing device 40 is in the state (D) (standby state). In the state (D) in which the pressure roller stops rotating, the fixing belt 402 is flexed on the downstream side and the upstream side of the transport path of the sheet S with the nip area as a reference. Specifically, since the pressure roller 408 is rotated in the reverse direction immediately before the state (D), the amount of deflection of the fixing belt 402 on the upstream side (hereinafter also referred to as the amount of deflection on the downstream side) is larger than that of the fixing belt 402 . .

More specifically, when the forward rotation of pressure roller 408 is stopped (for example, momentary power failure state (B)), the amount of deflection on the upstream side of fixing belt 402 is smaller than the amount of deflection on the downstream side. From this state, by rotating the pressure roller 408 in the reverse direction and then stopping the pressure roller 408 (states (C) and (D)), the amount of deflection on the upstream side and the amount of deflection on the downstream side are large or small. Relationships can be reversed. The dashed line in state (D) represents the bent state of fixing belt 402 in state (C).

When receiving the next print job in the standby state, the control device 101 fixes the unfixed image on the sheet S onto the sheet and transports the sheet S with the fixed image to the conveying path, as shown in state (E). The pressure roller 408 can be rotated forward (in the direction of the arrow in the drawing) in order to transport the sheet downstream. In this case, the fixing belt 402 also rotates forward (in the direction of the arrow in the figure) following the rotation of the pressure roller 408 . That is, the fixing device 40 operates in the same manner as in state (A). Thereafter, a series of processes shown in states (B), (C), and (D) are executed in this order. The dashed line in state (E) represents the bent state of fixing belt 402 in state (D).

(Brief Summary)
(1) When the pressure roller 408 stops rotating (B), the fixing belt 402 is bent on one side and the other side with respect to the nip area. At this time, the amount of deflection on one side is greater than the amount of deflection on the other side. When the controller 101 starts rotating the pressure roller 408 as shown in state (C) after stopping the rotation of the pressure roller 408 (after state (B)), the control device 101 moves the paper S to the downstream side of the transport path. One of the first conveying direction (that is, the forward direction) and the second direction that is opposite to the first direction (that is, the reverse direction), the pressure roller is moved in a direction in which the amount of deflection on one side decreases. 408 is rotated.

(2) Specifically, as shown in state (B), the one side is located downstream of the other side in the conveying path. The direction in which the amount of deflection of the one side decreases is the second direction (reverse direction). Based on the reception of the print job, the control device 101 performs control (state (A)) to rotate the pressure roller 408 in the first direction (positive direction) to fix the unfixed image, Control to stop the rotation of the roller 408 (state (B)) and control to rotate the pressure roller 408 in the second direction (reverse direction) in order to reduce the deflection amount of the one side (downstream side). (State (C)) are executed in this order.

(3) In the state (D) in which the pressure roller 408 stops rotating, the fixing belt 402 is bent on one side and the other side with respect to the nip area. At this time, the amount of deflection on one side is greater than the amount of deflection on the other side. When the control device 101 starts rotating the pressure roller 408 as shown in state (E) after stopping the rotation of the pressure roller 408 (after state (D)), the control device 101 moves the paper S to the downstream side of the transport path. One of the first conveying direction (that is, the forward direction) and the second direction that is opposite to the first direction (that is, the reverse direction), the pressure roller is moved in a direction in which the amount of deflection on one side decreases. 408 is rotated.

<D. Load torque>
Next, the reason why the control shown in FIG. 3 is performed will be described by focusing on the torque.

FIG. 4 is a diagram for explaining the main torque applied as a load when starting the fixing device 40 is started.

Referring to FIG. 4, when the fixing device 40 is started, the main torques applied as loads are (a) torque due to sliding in the nip area (hereinafter referred to as "torque Za") and (b) Torque due to the C set of the pressure roller 408 (hereinafter referred to as “torque Zb”), (c) torque due to creep correction at the position supporting the fixing belt 402 (hereinafter referred to as “torque Zc”), ( d) Torque due to sliding at a position supporting the fixing belt 402 other than the nip area.

In FIG. 4 , two types of creep correction torque generated in the nip region and creep correction torque generated in the region of the heating member 401 are described as the “torque due to creep correction” in (c) above. Further, as the "torque due to sliding at the position supporting the fixing belt 402 other than the nip area" in (d) above, the torque due to sliding in the heating member 401 (hereinafter also referred to as "torque Zd") is described. ing.

It should be noted that when the fixing device 40 is started, torques other than these torques Za, Zb, Zc, and Zd are also applied as loads. The following description will focus on the torques Za, Zb, Zc, and Zd, which have a large influence.

Although the details will be described later, the load torque decreases with the lapse of time. The reason for this is that the temperatures of the fixing belt 402, the pressure roller 408, and the lubricant increase due to the heating by the heating member 401, thereby reducing the hardness of the fixing belt 402 and the pressure roller 408 and increasing the viscosity of the lubricant. This is because it decreases.

FIG. 5 is a diagram for explaining the C set of the pressure roller 408. As shown in FIG.
Referring to FIG. 5, pressure roller 408 contacts nip forming member 405 (specifically, sliding sheet 406 wound around nip forming member 405) when stopped. In addition, the pressure roller 408 deforms its surface portion due to the contact pressure at this time, and a concave portion 481 is formed. Such a variant is called a C set. When the pressure roller 408 is rotated from this state, the concave portion 481 gradually becomes smaller as shown in the order of states (A), (B), and (C).

(d1. Torque change at startup of fixing device 40)
FIG. 6 is a diagram for explaining changes in torque when the fixing device 40 is started. Specifically, FIG. 6 is a graph for explaining changes in torque when the control device 101 receives the next print job. Specifically, FIG. 6 is a graph for explaining temporal changes in torque when the fixing device 40 is started from the state (D) of FIG.

Referring to FIG. 6, data L51 represents changes in torque Za due to sliding in the nip region. Data L52 represents changes in torque Zb due to C set of pressure roller 408 . Data L53 represents a change in torque Zc due to creep correction. Data L54 represents changes in the torque Zd due to the sliding of the heating member 401 . Data L50 represents changes in the total torque generated in the fixing device 40 . That is, the data L50 represents changes in the sum of the torques Za, Zb, Zc, Zd and the sum of other torques not shown in FIG.

(1) Torque Za due to sliding in the nip area
At time t1, motor 409 receives a command from control device 101 to rotate pressure roller 408 forward. At time t2, pressure roller 408 starts forward rotation. From time t1 to t2, the positive rotation of pressure roller 408 is suppressed by the static friction force.

Referring to data L51, a torque Za is generated due to sliding in the nip region between times t1 and t2. Also, between times t1 and t2, the torque Za increases with the lapse of time. At time t2, the pressure roller 408 starts rotating, so the torque Za decreases momentarily. After that, the torque Za gradually decreases over time.

(2) Torque Zb by C set of pressure roller 408
Referring to data L52, immediately after pressure roller 408 starts rotating at time t2, torque Zb momentarily increases due to concave portion 481 (see state (A) in FIG. 5) generated by the contact pressure. . Torque Zb gradually decreases until recess 481 passes through the nip region. When recess 481 passes through the nip region, torque Zb becomes substantially zero.

As shown in FIG. 5, the recess 481 gradually becomes smaller over time. When the depression 481 reaches the nip region due to the rotation of the pressure roller 408, the torque Zb momentarily increases again. However, since the concave portion 481 is smaller, the peak of the torque Zb is smaller than the previous peak of the torque Zb. Also, the torque Zb gradually decreases until the concave portion 481 passes through the nip region. When recess 481 passes through the nip region, torque Zb is substantially zero. Thereafter, the above changes are repeated. Note that the peak of torque Zb is synchronized with the rotation period of pressure roller 408 .

(3) Torque Zc due to creep correction
Referring to data L53, immediately after pressure roller 408 starts rotating at time t2, torque Zc due to creep correction momentarily increases. This is due to the torque due to creep correction occurring in the nip region. The torque due to creep correction produced in the nip region decreases over time.

At time t4, the magnitude relationship of the bending of the fixing belt 402 is reversed between the downstream side and the upstream side, and the upstream side is in a state of being stretched (strongly stretched without slack) (state (E) in FIG. 3). reference).

Therefore, at time t4, torque due to creep correction occurring in the area of heating member 401 is generated, and torque Zc increases momentarily. After that, the torque Zc gradually decreases over time.

(4) Torque Zd due to sliding on heating member 401
Immediately after the pressure roller 408 starts rotating at time t2, the amount of bending of the fixing belt 402 on the upstream side is larger than the amount of bending on the downstream side. Therefore, no sliding occurs in the heating member 401 . Therefore, as indicated by data L54, torque Zd is not generated immediately after time t2. For the same reason, no torque Zd is generated between times t1 and t2.

From time t3 (t2<t4<t4) to just before time t4, torque Zd changes immediately before fixing belt 402 starts rotating. During this period (more specifically, until the moment when the upstream side is stretched), the fixing belt 402 moves only in the nip region, so that the heating member 401 does not slide and rotate. Therefore, during this period, torque corresponding to the static friction appears as torque Zd. As the fixing belt 402 starts to rotate, the state in which the sliding rotation is suppressed by the static friction force is released, so the torque Zd decreases instantaneously immediately before time t4.

Further, from the moment when the upstream side becomes taut (time t4), the entire fixing belt 402 starts to slide and rotate. Therefore, even after time t4, the torque Zd is generated due to the sliding of the heating member 401 . After time t4, the torque Zd becomes a constant value. The reason for this is that since the heating member 401 is not coated with lubricant, the torque Zd does not decrease over time.

(d2. Torque change at start-up of comparative example)
As a comparative example, a configuration in which the pressure roller is not temporarily rotated in reverse as in this example will be described. Note that the hardware configuration of an image forming apparatus as a comparative example is the same as that of the image forming apparatus 100 of this example. In the comparative example, the control method of the fixing device is different from that in this example.

Specifically, torque change in a configuration in which the magnitude relationship of bending of the fixing belt is not reversed between the downstream side and the upstream side even after the fixing process is completed will be described. Specifically, torque change in a configuration in which the amount of bending of the fixing belt on the downstream side is always kept larger than the amount of bending on the upstream side will be described.

FIG. 7 is a diagram for explaining changes in torque in a comparative example.
Referring to FIG. 7, data L61 represents changes in torque Za due to sliding in the nip region. Data L62 represents changes in the torque Zb due to the C set of the pressure roller. Data L63 represents a change in torque Zc due to creep correction. Data L64 represents changes in torque Zd due to sliding on the heating member. Data L60 represents the change in the total torque generated in the configuration of the comparative example. That is, the data L60 represents changes in the sum of the torques Za', Zb', Zc', Zd' and the sum of other torques.

(1) Torque Za' due to sliding in the nip area
Referring to data L61, the temporal change in torque Za' due to sliding in the nip region is the same as the temporal change in torque Za due to sliding in the nip region in this example. That is, data L51 and data L61 are the same.

(2) Torque Zb' by C set of pressure roller 408
Referring to data L62, the temporal change in torque Zb' due to C set of the pressure roller is the same as the temporal change in torque Zb due to C set of the pressure roller in this example. That is, data L52 and data L62 are the same.

(3) Torque Zc' due to creep correction
Referring to data L63, immediately after the pressure roller starts rotating at time t2, torque Zc due to creep correction momentarily increases. This is due to the creep-correction torque occurring in the nip area and the creep-correction torque occurring in the area of the heating element. Torque Zc decreases over time.

As described above, in the comparative example, torque due to creep correction occurring in the area of the heating member is generated at time t2, so the data L53 and data L63 are different.

(4) Torque Zd' caused by sliding on the heating member
Referring to data L64, in the comparative example, the amount of deflection of the fixing belt on the downstream side is greater than the amount of deflection on the upstream side. Immediately after time t1), torque Zd' occurs. Torque Zd' gradually increases until pressure roller 408 begins to rotate at time t2. At time t2, the torque Zd' decreases instantaneously and then remains constant.

Thus, in the comparative example, the torque Zd' is generated even before the pressure roller starts rotating, and the constant torque Zd' is generated immediately after the pressure roller starts rotating. Therefore, data L54 and data L64 are different.

From time t1 to just before time t2, changes in torque Zd' immediately before the fixing belt starts rotating are shown. During this time, torque corresponding to the static friction appears as torque Zd'. As the fixing belt starts to rotate, the state in which the sliding rotation is suppressed by the static friction force is released, so the torque Zd decreases momentarily at time t2.

Further, from time t2, the entire fixing belt starts to slide and rotate. Therefore, even after time t2, the torque Zd' is generated due to the sliding of the heating member. After time t2, the torque Zd' becomes a constant value. This is because the heating member is not lubricated, so the torque Zd' does not decrease over time.

(d3. Advantages of this example)
Advantages of this example will be described below in comparison with comparative examples.

In this example, the timing at which the heating member 401 starts to slide and the timing at which the creep correction starts are delayed by the amount of time until the degree of bending of the fixing belt 402 is reversed.

Specifically, referring to FIGS. 6 and 7, in this example, the timing at which torque Zd is generated due to the sliding of heating member 401 can be delayed from the timing at which torque Zd' is generated in the comparative example. . Further, in this example, as described above, the timing at which the creep correction torque generated in the region of the heating member 401 in the creep correction torque Zc is generated can be delayed compared to the comparative example.

FIG. 8 is a graph showing data L50 of this example and data L60 of a comparative example.
Referring to FIG. 8, data L50 is represented by a solid line, and data L60 is represented by a broken line. From time t1 to t2, the total torque indicated by data L50 is smaller than the total torque indicated by data L60 by the torque Zd' due to the sliding of the heating member. At times t2 to t3' (where t3<t3'<t4), the total torque indicated by data L50 is greater than the total torque indicated by data L60 by the amount of torque due to creep correction occurring in the region of the heating member. become smaller.

As can be seen from this, by performing the control described based on FIG. 3, the torque (load torque, driving torque) required to drive the fixing device 40 is reduced more than in the comparative example at least during times t1 to t3′. becomes possible. That is, it is possible to reduce the drive torque when the fixing device 40 is started.

Furthermore, the reduction in driving torque leads to the extension of the life of the fixing device 40 . Further, the operation described with reference to FIG. 3 only controls the rotation directions of the pressure roller 408 and the fixing belt 402 that rotates following the pressure roller 408 . Therefore, the only change in hardware is to increase the number of microcomputer ports and wiring in the control device 101 .

<E. Block Diagram>
FIG. 9 is a block diagram for explaining the hardware configuration of the image forming apparatus 100. As shown in FIG.

Referring to FIG. 9 , image forming apparatus 100 includes at least control device 101 , operation panel 102 , and fixing device 40 .

Operation panel 102 includes a touch screen 120 . The touch screen 120 is composed of a display 122 and a touch panel 121 superimposed on the display 122 .

The control device 101 includes a CPU (Central Processing Unit) 131 that executes programs, a ROM (Read Only Memory) 132 that stores data in a nonvolatile manner, a RAM (Random Access Memory) 133 that stores data in a volatile manner, It has a flash memory 134 and a communication IF 135 . The control device 101 can communicate with the operation panel 102 via the communication IF 135 .

Flash memory 134 is a non-volatile semiconductor memory. The flash memory 134 stores an operating system and various programs executed by the CPU 131, various contents and data. The flash memory 134 volatilely stores various data such as data generated by the image forming apparatus 100 and data obtained from an external device of the image forming apparatus 100 .

FIG. 10 is a block diagram for explaining the functional configuration of the control device 101. As shown in FIG.
Referring to FIG. 10 , control device 101 has a fixing device control section 150 for controlling the operation of fixing device 40 . The fixing device control section 150 has a pressure roller control section 151 and a heater control section 152 .

The pressure roller controller 151 controls the operation of the pressure roller 408 . Specifically, the pressure roller control unit 151 controls the rotation of the motor 409 to rotate the pressure roller 408 forward or backward. The processing described with reference to FIG. 3 is executed by the pressure roller control unit 151 .

The heater control unit 152 controls on and off of the halogen heater 451 . In one aspect, heater control unit 152 controls on and off of halogen heater 451 in order to maintain the temperature of fixing belt 402 at a predetermined value.

<F. Control structure>
FIG. 11 is a flowchart for explaining the flow of processing executed in image forming apparatus 100. As shown in FIG.

Referring to FIG. 11, when control device 101 receives a print job in step S1 (YES in step S1), in step S2, motor 409 is driven to correct pressure roller 408 in order to perform fixing processing. rotate. Note that the control device 101 receives a print job from an information processing device (not shown) or the operation panel 102 communicatively connected to the image forming apparatus 100 via a network. If the control device 101 has not received a print job (NO in step S1), it waits for a print job.

After step S2, in step S3, the control device 101 determines whether or not the fixing process has ended. For example, the control device 101 determines whether or not the fixing process is completed by determining whether or not all the sheets S required for the print job have passed through the fixing device 40 .

When control device 101 determines that the fixing process has ended (YES in step S3), in step S4, pressure roller 408 stops rotating. When control device 101 determines that the fixing process has not ended (NO in step S3), it continues the process of rotating pressure roller 408 forward.

In step S5, the control device 101 rotates the pressure roller 408 in the reverse direction. The control device 101 stores in advance the time to rotate the pressure roller 408 in the reverse direction. The control device 101 may use the number of rotations of the reverse rotation or the rotation angle of the reverse rotation instead of the time. That is, the control device 101 only needs to store the amount of rotation for reversing the bending as a rotation time or a rotation angle. In step S6, when the time has elapsed, the control device 101 stops the reverse rotation of the pressure roller 408, and advances the process to step S1 again.

Note that the processing of step S2 corresponds to state (A) in FIG. The processing of step S4 corresponds to state (B) in FIG. The processing of step S5 corresponds to state (C) in FIG.
[Embodiment 2]
In the present embodiment, a configuration in which the timing of rotating pressure roller 408 in reverse is different from that in the first embodiment will be described.

<A. Contents of Control of Fixing Device 40>
FIG. 12 is a diagram for explaining control of the fixing device 40 executed by the control device 101. As shown in FIG.

Referring to FIG. 12, when a print job is received, control device 101 fixes an unfixed image on sheet S and conveys sheet S on which the image is fixed, as shown in state (A). The pressure roller 408 is rotated forward (in the direction of the arrow in the drawing) in order to convey the sheet to the downstream side of the path. In this case, the fixing belt 402 also rotates forward (in the direction of the arrow in the figure) following the rotation of the pressure roller 408 .

When the fixing process ends (that is, the print job ends), the control device 101 stops forward rotation of the pressure roller 408 as shown in state (B). This also stops the rotation of the fixing belt 402 . The control device 101 waits for the next print job while the fixing device 40 is in state (B) (standby state).

When the control device 101 accepts the next print job in the standby state, as shown in state (C), the pressure roller 408 starts to rotate in the reverse direction (in the direction of the arrow in the figure). When such reverse rotation is started, the fixing belt 402 also rotates reversely (in the direction of the arrow in the figure) following the rotation of the pressure roller 408 .

Control device 101 stops the reverse rotation of pressure roller 408 (temporarily stops the reverse rotation of pressure roller 408 as shown in state (D)) after a predetermined period of time has elapsed since the reverse rotation of pressure roller 408 was started (state (C)). Stop. This also stops the rotation of the fixing belt 402 . Note that this stop is typically a momentary stop for executing forward rotation.

In the state (D) in which the pressure roller 408 stops rotating, the fixing belt 402 is bent on the downstream side and the upstream side of the transport path of the sheet S with the nip area as a reference. Specifically, since the pressure roller 408 is rotated in the reverse direction immediately before the state (D), the amount of deflection on the upstream side is larger than the amount of deflection on the downstream side.

More specifically, when pressure roller 408 stops rotating forward (for example, state (B)), the amount of bending of fixing belt 402 on the upstream side is smaller than the amount of bending on the downstream side. From this state, by rotating the pressure roller 408 in the reverse direction and then stopping the pressure roller 408 (states (C) and (D)), the amount of deflection on the upstream side and the amount of deflection on the downstream side are large or small. Relationships can be reversed. The dashed line in state (D) represents the bent state of fixing belt 402 in state (C).

Immediately after the state (D), as shown in the state (E), in order to fix the unfixed image on the sheet S on the sheet S and to convey the sheet S on which the image is fixed to the downstream side of the conveying path, The pressure roller 408 is rotated forward (in the direction of the arrow in the figure). In this case, the fixing belt 402 also rotates forward (in the direction of the arrow in the figure) following the rotation of the pressure roller 408 . That is, the fixing device 40 operates in the same manner as in state (A). Thereafter, the processing shown in state (B) is executed. The dashed line in state (E) represents the bent state of fixing belt 402 in state (D).

(Brief Summary)
(1) When the pressure roller 408 stops rotating (B), the fixing belt 402 is bent on one side and the other side with respect to the nip area. At this time, the amount of deflection on one side is greater than the amount of deflection on the other side. When the controller 101 starts rotating the pressure roller 408 as shown in state (C) after stopping the rotation of the pressure roller 408 (after state (B)), the control device 101 moves the paper S to the downstream side of the transport path. The pressure roller 408 is rotated in a direction in which one of the first conveying direction (positive direction) and the second conveying direction (reverse direction) opposite to the first direction decreases the amount of deflection. .

(2) Specifically, as shown in state (B), the one side is located downstream of the other side in the conveying path. The direction in which the amount of bending of the one side decreases is the second direction (reverse direction). The control device 101 performs control (state (A)) to rotate the pressure roller 408 in the first direction (positive direction) to fix an unfixed image, and control (state (A)) to stop the rotation of the pressure roller 408 . (B)) are performed in this order, and then, based on acceptance of the print job, the second direction (reverse direction) is applied to reduce the deflection amount of the one side (downstream side). Control to rotate the pressure roller 408 (state (C)) is executed.

(3) In the state (D) in which the pressure roller 408 stops rotating, the fixing belt 402 is bent on one side and the other side with respect to the nip area. At this time, the amount of deflection on one side is greater than the amount of deflection on the other side. When the control device 101 starts rotating the pressure roller 408 as shown in state (E) after stopping the rotation of the pressure roller 408 (after state (D)), the control device 101 moves the paper S to the downstream side of the transport path. One of the first conveying direction (that is, the forward direction) and the second direction that is opposite to the first direction (that is, the reverse direction), the pressure roller is moved in a direction in which the amount of deflection on one side decreases. 408 is rotated.

(advantage)
Also in the present embodiment, as in the first embodiment, it is possible to reduce the driving torque when the fixing device 40 is started. In addition, the reduction in drive torque leads to the extension of the life of the fixing device 40 . Further, hardware changes only require an increase in the number of microcomputer ports and wiring in the control device 101 .

<B. Control structure>
FIG. 13 is a flowchart for explaining the flow of processing executed in image forming apparatus 100. As shown in FIG.

Referring to FIG. 13, when control device 101 receives a print job in step S11 (YES in step S11), in step S12, motor 409 is driven to rotate pressure roller 408 in the reverse direction. If the control device 101 has not received a print job (NO in step S11), it waits for a print job.

The control device 101 temporarily stops the rotation of the pressure roller 408 in step S13. Immediately after that, in step S14, control device 101 rotates pressure roller 408 forward in order to perform the fixing process.

After step S14, in step S15, the control device 101 determines whether or not the fixing process has ended. When control device 101 determines that the fixing process has ended (YES in step S15), in step S16, pressure roller 408 stops rotating. When control device 101 determines that the fixing process has not ended (NO in step S15), it continues the process of rotating pressure roller 408 forward. After step S16, the control device 101 advances the process to step S11.

It should be noted that the process of step S12 corresponds to state (C) in FIG. The processing of step S13 corresponds to state (D) in FIG. The processing of step S14 corresponds to state (E) in FIG.
[Embodiment 3]
In this embodiment, a modification of the second embodiment will be described. Specifically, in the present embodiment, processing for reducing the first copy time (FCOT) compared to the second embodiment will be described.

<A. Configuration of main parts>
FIG. 14 is a diagram for explaining a specific configuration of the fixing device 40A used in this embodiment.

Referring to FIG. 14, fixing device 40A includes heating member 401, fixing belt 402, holding member 403, nip forming member 405, sliding sheet 406, curvature imparting member 407, and pressure roller 408. , a motor 409 and a temperature detector 412 . The fixing device 40</b>A differs from the fixing device 40 in that it includes a temperature detection section 412 .

The temperature detection unit 412 is installed in a lower gap inside the fixing device 40A. Temperature detector 412 is typically a non-contact thermistor. A temperature detection unit 412 detects the surface temperature of the fixing belt 402 . A detection result by the temperature detection unit 412 is sent to the control device 101 .

<B. Control structure>
FIG. 15 is a flowchart for explaining the flow of processing executed in image forming apparatus 100 having fixing device 40A.

The difference from the flowchart (FIG. 13) described in the second embodiment will be described with reference to FIG. FIG. 15 differs from FIG. 13 in having steps S101, S102, and S103. Therefore, steps S101, S102, and S103 will be described below.

After step S<b>11 , in step S<b>101 , the control device 101 determines whether or not the temperature of the fixing belt 402 is equal to or lower than the threshold based on the detection result of the temperature detection unit 412 . If the control device 101 determines that it is equal to or less than the threshold value (YES in step S101), it turns on the halogen heater 451 in step S102. After step S102, the control device 101 advances the process to step S12. When determining that the threshold is exceeded (NO in step S101), the control device 101 advances the process to step S14.

After step S<b>12 , the control device 101 again determines whether or not the temperature of the fixing belt 402 is equal to or lower than the threshold based on the result of detection by the temperature detection unit 412 . When determining that the threshold is exceeded (NO in step S103), the control device 101 advances the process to step S13. If the control device 101 determines that it is equal to or less than the threshold (YES in step S103), the reverse rotation operation of the fixing belt 402 is continued.

In the image forming apparatus 100 including the fixing device 40A, when it is determined in step S101 that the temperature of the fixing belt 402 exceeds the threshold value, the reverse rotation of the pressure roller (step S12) and the reverse rotation stop operation ( Step S13) is not performed. In other words, the operations in states (C) and (D) shown in FIG. 12 are not performed. Specifically, when the control device 101 receives a print job in the state (B) of FIG. 12, it immediately rotates the pressure roller 408 forward.

On the other hand, if it is determined in step S101 that the temperature of fixing belt 402 is equal to or less than the threshold value, control device 101 warms fixing belt 402 while rotating in the reverse direction.

<C. Summary and Benefits >
(c1. summary)
(1) Image forming apparatus 100 further includes temperature detection unit 412 that detects the temperature of fixing belt 402 . On the condition that the detected temperature is equal to or lower than a threshold (predetermined temperature), the control device 101 controls the above-described first direction (that is, the forward direction) and the above-described second direction (that is, the reverse direction). The pressure roller 408 is rotated in the direction in which the amount of deflection of one of the above-mentioned sides decreases.

(2) When the control device 101 receives a print job, on condition that the detected temperature is equal to or lower than the threshold, the control device 101 rotates in the second direction (reverse direction) to reduce the deflection amount of the one side. , the control for starting the rotation of the pressure roller 408 is executed. Further, the control device 101 rotates the pressure roller 408 in the second direction (reverse direction), and then controls the rotation of the pressure roller 408 to stop, and controls the rotation of the pressure roller 408 to fix the unfixed image. (positive direction) and control to rotate pressure roller 408 in this order.

(3) When the control device 101 receives a print job, it controls the heating member 401 to heat the fixing belt 402 on condition that the detected temperature is equal to or less than the threshold. On the condition that the detected temperature exceeds the threshold, the control device 101 controls to stop the rotation of the pressure roller 408 and to apply pressure in the first direction (positive direction) to fix the unfixed image. and control to rotate the pressure roller 408 are executed in this order.

(c2. Advantage)
When the temperature of the surface of the fixing belt 402 exceeds the threshold, the belt stiffness and grease viscosity of the fixing belt 402 are lower than when the temperature is equal to or lower than the threshold. That is, when the temperature of the surface of the fixing belt 402 exceeds the threshold, the starting torque is smaller than when the temperature is below the threshold. Therefore, by omitting the reverse rotation shown in step S12, the FCOT can be reduced compared to the configuration of the second embodiment.

Note that when the surface temperature of the fixing belt 402 is equal to or lower than the threshold, the belt stiffness and grease viscosity of the fixing belt 402 are higher than when the temperature exceeds the threshold. In this case, the pressure roller 408 is reversely rotated and the heating of the fixing belt 402 is started. Thereby, the same effects as those of the second embodiment can be obtained.

Further, as shown in step S103, the temperature detection unit 412 monitors the temperature of the surface of the fixing belt 402, and when the temperature of the surface of the fixing belt 402 is below the threshold value, the pressure roller 408 is rotated forward. As a result, regardless of the surface temperature of fixing belt 402 immediately before start-up (for example, 0° C. or normal temperature), normal rotation can always be resumed in the shortest heating time. As a result, it is possible to suppress the lengthening of FCOT.
[Embodiment 4]
In this embodiment, a modification of the third embodiment will be described. Specifically, in the present embodiment, a configuration will be described in which the rotation of pressure roller 408 can be switched from the reverse rotation to the forward rotation at more accurate timing than in the third embodiment.

<A. Configuration of main parts>
FIG. 16 is a diagram for explaining a specific configuration of the fixing device 40B used in this embodiment.

Referring to FIG. 16, fixing device 40B includes heating member 401, fixing belt 402, holding member 403, nip forming member 405, sliding sheet 406, curvature imparting member 407, and pressure roller 408. , a motor 409 , a temperature detector 412 , and a torque detector 413 . Fixing device 40B differs from fixing device 40A of the third embodiment in that it includes torque detection section 413 .

The torque detection unit 413 detects the current value flowing through the motor 409 and calculates (estimates) the torque based on the detection result. Torque detection unit 413 sends the detection result to control device 101 . The torque detector 413 may be separate from the motor 409 or may be built in the motor 409 .

<B. Control structure>
FIG. 17 is a flowchart for explaining the flow of processing executed in image forming apparatus 100 having fixing device 40B.

Referring to FIG. 17, control device 101 executes step S104 instead of step S103 (see FIG. 15). 17 is the same as that of FIG. 15 for other processes.

In step S104, the control device 101 determines whether or not the drive torque calculated by the torque detection section 413 is equal to or less than the threshold. If the drive torque is equal to or less than the threshold (YES in step S104), control device 101 advances the process to step S13. If the driving torque exceeds the threshold (NO in step S104), control device 101 continues to rotate pressure roller 408 in the reverse direction.

<C. Summary and Benefits >
(c1. summary)
The image forming apparatus 100 includes a torque detection unit 413 that detects driving torque of the pressure roller 408 .

When receiving a print job, the control device 101 performs control to heat the fixing belt 402 by the heating member 401 on condition that the detected temperature is equal to or lower than the threshold. Further, the control device 101 determines that the drive torque when the pressure roller 408 is rotated in the second direction (reverse direction) in order to reduce the deflection amount of the one side is a predetermined torque by heating. Under the following conditions, the control to stop the rotation of the pressure roller 408 and the control to rotate the pressure roller 408 in the first direction (positive direction) in order to fix the unfixed image, Execute in this order.

(c2. Advantage)
The timing of switching to normal rotation after the reverse rotation of the pressure roller 408 is determined not by the surface temperature of the fixing belt 402 but by the drive torque detected by the torque detection unit 413 . As described above, in the present embodiment, since the determination is made directly by the torque, it is possible to switch to forward rotation at a more accurate timing than in the case of the third embodiment.
[Embodiment 5]
This embodiment is a modification of the first embodiment. In the first embodiment, as shown in state (C) of FIG. 3, when the reverse rotation of the pressure roller 408 is started, the amount of deflection on the downstream side becomes equal to the amount of deflection on the upstream side after a predetermined time has elapsed. . After that, as shown in state (D) in FIG. 3, the amount of deflection on the downstream side becomes smaller than the amount of deflection on the upstream side. Specifically, at time t4 in FIG. 6, the amount of deflection on the downstream side becomes the same as the amount of deflection on the upstream side.

FIG. 18 is a diagram for explaining the bending of the fixing belt 402 on the downstream side. In this embodiment, in the state (B) of FIG. 3, as shown in FIG. 18, the fixing device 40 is configured so that the amount of bending of the fixing belt 402 on the downstream side is within a predetermined range. . The "predetermined range" is a range in which the timing at which the amount of deflection on the downstream side becomes the same as the amount of deflection on the upstream side does not overlap with the timing at which the torque Zb is applied by the C set of the pressure roller 408. be.

19A and 19B are diagrams for explaining changes in torque when the fixing device 40 is started when the bending amount on the downstream side is configured to be within a predetermined range.

Referring to FIG. 19, data L51' represents changes in torque Za due to sliding in the nip region. Data L<b>52 ′ represents changes in torque Zb due to C set of pressure roller 408 . Data L53' represents a change in torque Zc due to creep correction. Data L54' represents changes in torque Zd due to sliding of the heating member 401. FIG. Data L50' represents changes in the total torque.

The timing (time t7) at which the magnitude relationship of the deflection amounts is reversed is later than the timing (time t4) in the case of the first embodiment. For this reason, the timing at which the torque Zd is generated by the sliding of the heating member 401 and the timing at which the torque Zb is applied by the C set of the pressure roller 408 do not overlap. More specifically, at time t6 after time t5 when the torque Zb by the C set of the pressure roller 408 becomes zero, the torque Zd due to the sliding of the heating member 401 is generated.

In this manner, the load torque at startup can be reduced more than the configuration of the first embodiment. Specifically, between time t2 and time t7 (between the start of rotation of pressure roller 408 and the time immediately before the magnitude relationship of the amount of deflection reverses), the load torque can be reduced more than in the configuration of the first embodiment. becomes.

Note that the configuration according to the present embodiment may be applied to the second embodiment.
[Embodiment 6]
FIG. 20 is a diagram for explaining the configuration of the fixing device 40D according to this embodiment.

Referring to FIG. 20, fixing device 40D includes heating member 401, fixing belt 402, temperature detecting portion 412, tension roller 414, fixing roller 415, pressure roller 408, and motor 409.

The fixing device 40D uses a fixing roller as a nip forming member. Fixing belt 402 is stretched by three-point support by fixing roller 415 , heating member 401 , and tension roller 414 .

The fixing roller 415 is composed of an elastic layer made of silicon rubber having a thickness of about 20 mm to 40 mm in diameter and a fluorine-based release layer formed on the elastic layer. A release layer is provided on the elastic layer.

Both ends of the tension roller 414 are rotatably supported. The tension roller 414 applies tension to the fixing belt 402 and assists the sliding of the fixing belt 402 . Tension roller 414 is arranged at a position such that the bending of fixing belt 402 on the downstream side is within the range shown in the fifth embodiment (within a predetermined range).

In this embodiment, temperature detection unit 412 detects the temperature of fixing belt 402 stretched between heating member 401 and tension roller 414 . With such a configuration, the temperature of only the fixing belt 402 that is not in contact with the heating member 401 can be detected. Therefore, the control device 101 can perform more accurate temperature control.

According to such a fixing device 40D, it is possible to reduce the drive torque when starting the fixing device 40, as in the first embodiment. In addition, the reduction in drive torque leads to the extension of the life of the fixing device 40 . Further, hardware changes only require an increase in the number of microcomputer ports and wiring in the control device 101 .

Further, since the bending amount of the fixing belt 402 on the downstream side is set within a predetermined range, the effect described in the fifth embodiment can be obtained also in this embodiment.

<Modification>
In Embodiments 1 to 6 above, the heating member 401 has been described as an example that does not rotate, but the heating member 401 is not limited to this. Heating member 401 may be a roller (heating roller) rotatable following fixing belt 402 .

It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

1C, 1K, 1M, 1Y Imaging unit 10 Photoreceptor 11 Charging roller 12 Exposure part 13 Developing device 14 Developing roller 15B, 15C, 15K, 15M, 15Y Toner bottle 17, 53 Cleaning blade 30 Intermediate Transfer Belt 31 Primary Transfer Roller 102 Operation Panel 33 Secondary Transfer Roller 37 Cassette 40, 40A, 40B, 40D Fixing Device 48 Tray 100 Image Forming Device 101 Control Device 120 Touch Screen 121 Touch Panel 122 display, 134 flash memory, 135 communication IF, 150 fixing device control unit, 151 pressure roller control unit, 152 heater control unit, 401 heating member, 402 fixing belt, 403 holding member, 405 nip forming member, 406 sliding sheet , 407 curvature imparting member, 408 pressure roller, 409 motor, 412 temperature detector, 413 torque detector, 414 tension roller, 415 fixing roller, 451 halogen heater, 452 housing, 454 connecting shaft, 481 concave portion, G unfixed Image, P paper.

Claims (6)

An image forming apparatus comprising: a fixing device for fixing an unfixed image on a recording material; and a control device for controlling the operation of the fixing device,
The fixing device
an endless fixing belt;
a heat source for heating the fixing belt;
a pressure roller rotatable in a first direction for conveying the recording material to the downstream side of the conveying path and in a second direction opposite to the first direction;
a nip forming member that forms a nip region with the pressure roller;
The fixing belt is
is supported under tension by the nip forming member and the heat source, and rotates following the rotation of the pressure roller;
When the pressure roller stops rotating, it is bent on one side and the other side with respect to the nip area,
the amount of deflection on the one side is greater than the amount of deflection on the other side;
When starting the rotation of the pressure roller after the rotation of the pressure roller is stopped, the control device moves the pressure roller in the direction in which the amount of deflection in one of the first direction and the second direction decreases. Rotate the pressure roller,
The image forming apparatus further includes a temperature detection unit that detects the temperature of the fixing belt,
On the condition that the detected temperature is equal to or lower than a predetermined temperature, the control device moves the deflection in the direction in which the amount of deflection in one of the first direction and the second direction decreases. An image forming apparatus that rotates a pressure roller. the one side is downstream of the conveying path relative to the other side;
The direction in which the amount of deflection of the one side decreases is the second direction,
The control device is
When a print job is accepted, on condition that the detected temperature is equal to or lower than a predetermined temperature, rotating the pressure roller in the second direction to reduce the amount of deflection of the one side. Execute the control to start the
control to stop the rotation of the pressure roller after rotating the pressure roller in the second direction; and rotate the pressure roller in the first direction to fix the unfixed image. 2. The image forming apparatus according to claim 1 , wherein the control is executed in this order. The control device is
when the print job is received, on condition that the detected temperature is equal to or lower than a predetermined temperature, performing control to heat the fixing belt by the heat source;
control to stop rotation of the pressure roller on condition that the detected temperature exceeds a predetermined temperature; and control the pressure roller in the first direction to fix the unfixed image. 3. The image forming apparatus according to claim 2 , wherein the control to rotate the . The image forming apparatus further includes a torque detection unit that detects driving torque of the pressure roller,
The control device is
when the print job is received, on condition that the detected temperature is equal to or lower than a predetermined temperature, performing control to heat the fixing belt by the heat source;
provided that the drive torque when the pressure roller is rotated in the second direction to reduce the amount of deflection of the one side is equal to or less than a predetermined torque due to the heating; 3. The image according to claim 2 , wherein control to stop rotation of the pressure roller and control to rotate the pressure roller in the first direction to fix the unfixed image are executed in this order. forming device. 5. The image forming apparatus according to any one of claims 1 to 4 , wherein said fixing device is configured such that the amount of bending of said one side is within a predetermined range. A control method for an image forming apparatus comprising: a fixing device for fixing an unfixed image on a recording material; and a control device for controlling operation of the fixing device, comprising:
The fixing device includes a heat source for heating an endless fixing belt, a pressure roller rotatable in a first direction and a second direction opposite to the first direction, and the pressure roller. a nip forming member forming a nip region therebetween;
the fixing belt is supported under tension by the nip forming member and the heat source, and rotates following the rotation of the pressure roller;
The control method includes a step of stopping rotation of the pressure roller, and in a state where the rotation is stopped, the fixing belt is bent on one side and the other side with respect to the nip area. and the amount of deflection on the one side is greater than the amount of deflection on the other side,
The control method is
a step of restarting rotation of the pressure roller after stopping rotation of the pressure roller;
and detecting the temperature of the fixing belt;
In the step of restarting the rotation of the pressure roller, on the condition that the detected temperature is equal to or lower than a predetermined temperature, the bending of the one side of the first direction and the second direction is performed. A control method, wherein the pressure roller is rotated in a direction of decreasing volume.

Images