JP2015026001A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to maintain temperature-conditioning controllability of a fixing roller, while saving electric power.SOLUTION: A printer 1 having a fixing unit 30 configured to allow a sheet to pass through a fixing nip for thermal fixation by means of a fixing roller 33 heated by a heater 34 includes: a thermoelectric transducer 134; a heat conductive member 131 thermally coupled thereto; a thermoelectric conversion unit moving mechanism 135 which moves at least a part of the heat conductive member 131 in a close/far direction with respect to the fixing roller 33, between a first position and a second position closer to the fixing roller 33 than the first position; and a control unit 6 which controls the heater 34 so that the temperature of the fixing roller 33 reaches a target temperature, and controls the thermoelectric conversion unit moving mechanism 135 so as to move the heat conductive member 131 to the second position when reducing the temperature of the fixing roller 33 in accordance with the control, and to retract it to the first position when increasing and maintaining the temperature.

Description

  The present invention relates to an image forming apparatus including a fixing device, and more particularly to power saving in the fixing device.

An image forming apparatus such as a printer is formed on a recording sheet by, for example, pressing a pressure roller against a fixing roller heated by a heater to form a fixing nip and passing the recording sheet through the fixing nip. And a fixing device for fixing an unfixed toner image.
In recent years, due to a demand for power saving, it has been considered to convert the waste heat of the fixing device into electric power by a thermoelectric conversion element and reuse it.

  For example, in the fixing device of Patent Document 1, a thermoelectric conversion element such as a Seebeck element is brought into direct contact with an inner peripheral surface or an outer peripheral surface of a cylindrical fixing roller in which a heater is inserted, or heat conductive Heat generated by the fixing roller is converted into electric power by being indirectly contacted through a high heat collecting member.

JP 2004-133340 A JP 2009-224684 A

However, in the case of Patent Document 1, since the heat is always taken from the fixing roller, there is a problem that the rate of temperature increase is reduced and the time required for warm-up is increased.
Also, since the conversion efficiency of thermoelectric conversion elements is not so high in the first place, converting a part of the fixing roller to electric power while heating the fixing roller is contrary to the purpose of power saving and is effective in exhaust heat. It's not a use.

  The present invention has been made in view of the above-described problems, and saves power by effectively using the exhaust heat of the fixing device without reducing the temperature increase rate of a heating rotator such as a fixing roller. An object of the present invention is to provide an image forming apparatus capable of achieving the above.

  In order to achieve the above object, an image forming apparatus according to the present invention forms a fixing nip by pressing an outer peripheral surface of a heating rotator heated by a heating unit with a pressure member, and an unfixed image is formed in the fixing nip. An image forming apparatus having a fixing unit that heats and fixes a sheet on which the sheet is formed, comprising: a thermoelectric conversion element; a heat conductive member thermally coupled to the thermoelectric conversion element; and the heat conductive member Moving means for moving at least a part of the first position and a second position closer to the heating rotator than the first position in a perspective direction with respect to the heating rotator. And a temperature control means for controlling the heating means so that the surface temperature of the heating rotator becomes a target temperature, and when the temperature of the heating rotator is to be lowered, To the position of the And a movement control means for controlling the movement means so as to retract the heat conducting member to the first position when the temperature is to be maintained and the target temperature is maintained. .

  The heat conducting member is supported so as to be swingable with respect to the fixing device main body in a state where a part of the heat conducting member protrudes from the housing of the fixing device. It is desirable that the conversion element is attached, and at least a part of the portion existing inside the casing is configured to move in a perspective direction with respect to the heating rotating body by a swinging operation.

The moving means can move a part of the heat conducting member to a third position in contact with the heating rotator, and the control means can complete the heat fixing operation of the sheet. It is desirable to control the moving means so that the heat conducting member moves to the third position when heating of the heating rotator is stopped.
In addition, an acquisition unit that acquires a type of an unfixed image to be fixed is provided, and the control unit sets the target temperature to a first temperature and a temperature higher than the first temperature according to the type of the unfixed image. The movement control means switches the heat conducting member when the temperature of the heating rotating body is lowered when the temperature is switched from the first temperature to the second temperature. It is desirable to move to the second position.

Here, the type of the unfixed image is a monochrome image or a color image, and the control unit sets the target temperature to the second temperature when the unfixed image is a monochrome image. At the same time, when the unfixed image is a color image, it is desirable to set the target temperature to the first temperature.
Alternatively, the type of the unfixed image is a text image and an image image, and the control unit sets the target temperature to the second temperature when the unfixed image is a text image. When the unfixed image is an image, the target temperature may be set to the first temperature.

And the said heat conductive member has a curved part which curves along the outer peripheral surface of the said heating rotary body, and it is comprised so that the said curved part may be closest to a heating rotary body in the said 2nd position. It is desirable to be characterized.
Moreover, it is desirable that the heat conducting member is composed of a heat pipe composed of a plurality of tubes filled with a refrigerant.

According to the above configuration, when the heating member is heated to increase the temperature of the heating rotator or to maintain the temperature of the heating rotator at a predetermined temperature, the heat conducting member is retracted to the first position. The heat is less likely to escape from the heating rotator to the heat conducting member, and waste of power during heating can be reduced.
On the other hand, when the temperature of the heating rotator is lowered without heating, the heat conducting member moves to the second position, and the heat of the heating rotator is easily transferred to the thermoelectric conversion element. It can be converted to a power saving.

1 is a schematic cross-sectional view illustrating a configuration of a printer as an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a partially cutaway perspective view illustrating a configuration of a fixing device provided in the printer. (A) And (b) is an operation | movement figure of the said fixing device. FIG. 2 is a functional block diagram illustrating a relationship between a control unit of the printer and functional units connected to the control unit. It is a flowchart which shows the content of the waste heat recovery control which the said control part implements. It is a flowchart which shows another form of the temperature control control of the fixing device which can apply the said waste heat recovery control. FIG. 10 is a diagram showing a change in temperature of the fixing roller when the exhaust heat recovery control is applied and when it is not applied in the another embodiment. In the other embodiment, it is a flowchart showing the contents of exhaust heat recovery control performed by the control unit.

(1) Embodiment Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.
(1-1) Configuration of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view for explaining the configuration of a printer that is an example of an image forming apparatus according to an embodiment of the present invention.

The printer 1 includes an image forming unit 10, a paper feeding unit 20, a fixing unit 30, a control unit 6, and a power supply unit 7.
The paper feeding unit 20 includes a paper feeding cassette 21, a feeding roller 22, a winding unit 23, a timing roller pair 24, and the like.
The paper feed cassette 21 accommodates recording sheets.

The feeding roller 22 contacts the uppermost recording sheet of the paper feed cassette 21 and feeds it to the recording sheet conveyance path.
In the winding section 23, the sheet feeding roller 23a and the winding roller 23b are in contact with each other to form a winding nip, and a torque limiter (not shown) is attached to the winding roller 23b, and the direction opposite to the conveyance direction with respect to the recording sheet. It is the structure which provides friction resistance to.

As a result, even if there is a recording sheet fed by the feeding roller 22, the recording sheet is no longer conveyed, and the recording sheet is rolled up and separated into one sheet.
The timing roller pair 24 feeds the recording sheet to the downstream side in the conveyance direction at a timing instructed by the control unit 6.
As shown in the figure, the image forming unit 10 includes image forming units 11Y, 11M, 11C, and 11K corresponding to the respective colors of Y (yellow), M (magenta), C (cyan), and K (black). The unit includes a primary transfer roller 14 facing the photosensitive drum 12 incorporated in these units, an intermediate transfer belt 13, a secondary transfer roller 15, and the like.

As shown in the figure, the image forming units 11Y, 11M, 11C, and 11K are arranged along the intermediate transfer belt 13 at predetermined intervals in this order.
For example, the image forming unit 11 </ b> K includes a photosensitive drum 12, and a charger 16, an exposure unit 17, a developing device 18, and a cleaner 19 arranged along the circumferential direction of the photosensitive drum 12.

The photosensitive drum 12 is rotationally driven by a driving source (not shown), and after the residual toner on the surface is removed by the cleaner 19, the photosensitive drum 12 is uniformly charged by the charger 16 and is emitted from the exposure unit 17. Is exposed and scanned, and an electrostatic latent image is formed on the surface of the photosensitive drum 12.
The electrostatic latent image formed on the photosensitive drum 12 is developed by the developing device 18, and thereby a black toner image is formed on the surface of the photosensitive drum 12.

The other image forming units 11Y, 11M, and 11C have the same configuration as the image forming unit 11K except for the color of the toner, and the Y, M, and C colors are provided on the photosensitive drums 12 of the image forming units 11Y, 11M, and 11C. The toner image is formed.
The image forming operations in the image forming units 11Y, 11M, 11C, and 11K are executed at different timings so that the toner images are transferred to the same position on the intermediate transfer belt 13, and the primary transfer roller 14 is transferred onto the intermediate transfer belt 13 in a multiple manner, and a color toner image is formed.

  In accordance with the movement of the color toner image formed on the intermediate transfer belt 13 to the secondary transfer position, the recording sheet is fed from the paper feed unit 20 via the timing roller pair 24, and the secondary transfer position is reached. The toner image on the intermediate transfer belt 13 is secondarily transferred onto the recording sheet by the electrostatic force generated by the voltage applied to the secondary transfer roller 15 at the transfer position, and then conveyed to the fixing unit 30.

The fixing unit 30 includes a fixing roller 33 having a built-in heater and a pressure roller 32 that presses the fixing roller 33, and a fixing nip is formed at a portion in contact with each other.
In the process in which the recording sheet passes through the fixing nip, the toner image transferred to the surface of the recording sheet is heated and pressed to be thermally fixed on the recording sheet, and then discharged through a pair of discharge rollers 31a. The paper is discharged to the tray 31b.

  The power supply unit 7 is connected to a commercial AC power supply, and supplies power to a heater 34 (described later) provided in the fixing unit 30 and a device such as a drive source (not shown) based on an instruction from the control unit 6. The electric power supplied from the thermoelectric conversion unit 35 (described later) provided in the fixing unit 30 is stored in the power storage unit 70 formed of a secondary battery, for example, as power to be supplied to the control unit 6 Use.

The electric power supplied from the thermoelectric conversion unit 35 is obtained by converting a part of the heat released from the fixing unit 30 into electric power.
The control unit 6 controls the image forming unit 10, the paper feeding unit 20, the fixing unit 30, and the like in a unified manner so that the image forming operation is smoothly performed.
As part of this, based on a temperature sensor 36 (see FIG. 3) disposed in proximity to the surface of the fixing roller 33 of the fixing unit 30, a known temperature control for maintaining the surface temperature of the fixing roller 33 at a target fixing temperature is performed. carry out.

Further, the control unit 6 swings the thermoelectric conversion unit 35 so that a heat conduction member 131 (described later) that greatly contributes to thermoelectric conversion is brought close to or away from the fixing roller 33, and is then moved from the fixing unit 30 to the outside. A process (hereinafter referred to as “exhaust heat recovery control”) for converting the recovered exhaust heat into electric power and recovering it is executed. Details will be described later.
(1-2) Configuration of Fixing Unit FIG. 2 is a partially cutaway perspective view showing the configuration of the fixing unit 30.

As shown in the figure, the fixing unit 30 includes a fixing roller 33, a pressure roller 32, a thermoelectric conversion unit 35, a thermoelectric conversion unit moving mechanism 135, a heater 34, and a casing 37 that accommodates these.
<Fixing roller>
The fixing roller 33 includes a cylindrical cored bar 33a such as aluminum and a cylindrical elastic body 33b that covers a portion excluding both ends thereof.

Both ends of the cored bar 33a are rotatably supported by a pair of bearings (not shown).
The elastic body 33b is a cylindrical member having both heat resistance and elasticity, such as silicone rubber.
<Heater>
The heater 34 is, for example, a halogen heater or the like, and is inserted into the core metal 33 a of the fixing roller 33.

<Casing>
The casing 37 is for suppressing the heat of the fixing roller 33 heated by the heater 34 from leaking to the outside.
<Pressure roller>
The pressure roller 32 has a cylindrical cored bar 32a and an elastic body 32b.

Both ends of the cored bar 32a are rotatably supported by a pair of bearings (not shown), and one end is connected to a pressure roller drive source 160 (see FIG. 4).
The pressure roller 32 is rotationally driven by a pressure roller drive source 160. Further, the fixing roller 33 is driven to rotate along with the rotation.
The elastic body 32b is a cylindrical member made of a material having both heat resistance and elasticity, such as silicone rubber, and covers portions other than both ends of the cored bar 32a.

<Thermoelectric converter>
The thermoelectric conversion unit 35 includes a plurality of heat conduction members 131 arranged along the rotation axis direction (Y-axis direction) of the fixing roller 33, a holder 132 that holds these heat conduction members 131 in an aligned state, One heat sink 133 joined to the upper end 131b of the heat conducting member 131 and a plurality of thermoelectric conversion elements 134 provided along the longitudinal direction on the upper surface of the heat sink 133 are provided.

Each heat conducting member 131 is a heat pipe in which a part of a copper straight pipe is curved along the surface shape of the elastic body 33b of the fixing roller 33, and a refrigerant (not shown) such as R600a is enclosed therein. is there.
The holder 132 holds the plurality of heat conducting members 131 aligned in the Y-axis direction.

The heat sink 133 is a long member having excellent thermal conductivity, such as copper or aluminum, and its back surface is in thermal contact with the upper end portions 131b of the plurality of thermal conductive members 131. The heat transmitted from each heat conducting member 131 is stored in the heat sink 133.
A plurality of thermoelectric conversion elements 134 are fixed to the surface side of the heat sink 133 in close contact with each other.

The thermoelectric conversion element 134 is a Seebeck element, and generates an electromotive force (electromotive voltage) by giving a temperature difference between the front and back surfaces.
The plurality of thermoelectric conversion elements 134 are electrically connected in series, and a voltage obtained by integrating the output voltage of each thermoelectric conversion element 134 is output to the power supply unit 7.
The thermoelectric conversion part 35 is provided in the casing 37 in a state where the heat sink 133 and the thermoelectric conversion element 134 are located outside the casing 37 via support shafts 132a provided on both end surfaces of the holder 132 in the Y-axis direction. It is supported by a frame (not shown) (see FIGS. 3A and 3B).

<Thermoelectric converter swing mechanism>
The thermoelectric conversion unit moving mechanism 135 is a mechanism that swings the thermoelectric conversion unit 35 about the rotation shaft 132a of the holder 132, and is a thermoelectric that rotates the rod 135a, the cam 136, the biasing member 137, and the cam 136. It consists of the conversion part drive source 161 (refer FIG. 4).
A boss portion 135b is provided at the upper end portion of the rod 135a. The boss portion 135b is inserted into a pin 133a erected at the end portion on the front side in the longitudinal direction of the heat sink 133, and the lower end portion of the rod 135a is A cam follower 135d that abuts the circumferential surface of 136 is provided.

  The rod 135a is inserted into a through hole of a rod holding portion 31d provided on the side surface of the casing 37 and is held so as to be movable up and down. A flange portion 135c is formed at a position slightly above the cam follower 135d of the rod 135a, and an urging member 137 such as a compression spring is inserted between the rod holding portion 31d and the flange portion 135c. The rod 135a is urged downward, so that the cam follower 135d moves up and down following the rotation of the cam 136.

The cam 136 is pivotally supported by a cam holding portion 31e provided on the lower surface of the casing 37, and its drive shaft is connected to a thermoelectric conversion portion drive source 161 (see FIG. 4).
The thermoelectric conversion unit drive source 161 is a motor that can easily control the rotation angle, such as a stepping motor, and rotates the thermoelectric conversion unit 35 by a predetermined angle according to an instruction from the control unit 6, thereby rotating the thermoelectric conversion unit 35 to the rotation shaft 132 a of the holder 132. Swing around the center.

(1-3) Operation of Thermoelectric Conversion Unit Moving Mechanism FIGS. 3A and 3B are diagrams showing the operation of the thermoelectric conversion unit moving mechanism 135. In order to easily understand the inside, one of the front surfaces of the casing 37 is illustrated. The part is cut out.
Normally, the cam 136 is maintained at an angle that pushes the cam follower 135d upward as shown in FIG.

At this time, the curved portion 131a of the heat conducting member 131 of the thermoelectric conversion portion 35 is in a state farthest from the fixing roller 33, and a position where the heat conducting member 131 exists in this state is hereinafter referred to as a separated position.
The amount of radiant heat received by the curved portion 131a of the heat conducting member 131 from the fixing roller 33 is approximately inversely proportional to the square of both distances. Therefore, when the heat conducting member 131 is in the separated position shown in FIG. There is not much heat deprived from the roller 33.

On the other hand, by rotating the cam 136 by a predetermined angle and pushing up the cam follower 135d as shown in FIG. 3B, the heat conducting member 131 of the thermoelectric conversion section 35 moves from the separation position to the fixing roller 33. It moves to a position where the shortest distance from the surface is, for example, 2 mm to 5 mm (hereinafter referred to as “proximity position”).
As a result, the refrigerant accumulated in the curved portion 131a of the heat conducting member 131 is heated and vaporized, and heat is absorbed by the action of the latent heat at this time, and the vaporized refrigerant moves upward and is cooled and condensed. And release heat. And the condensed refrigerant | coolant repeats the operation | movement which flows into the curved part 131a by the effect | action of gravity.

Thereby, the heat of the fixing roller 33 is transmitted from the curved portion 131a of the heat conducting member 131 to the upper end portion 131b, and then transmitted to the heat sink 133, where the heat equalization in the Y-axis direction is achieved, and further, It is transmitted to the thermoelectric conversion elements 134, and an electromotive force is generated in each thermoelectric conversion element 134.
Further, when the cam 136 is further rotated, the cam 136 moves to a position where the heat conducting member 131 and the surface of the fixing roller 33 come into contact (hereinafter referred to as “contact position”).

In this case, the movement of heat from the fixing roller 33 to the heat conducting member 131 adds not only radiation but also heat conduction, so that the movement of heat is further promoted and the electromotive force generated in the thermoelectric conversion element 134 also increases. .
Here, since the heat conducting member 131 has a curved portion 131a that is curved along the surface shape of the fixing roller 33, the heat conducting member 131 and the heat conducting member 131 can be compared with a case where such a curved portion 131a is not provided. The area and the contact area of the portion facing the surface of the fixing roller 33 can be increased, and accordingly, the heat of the fixing roller 33 can be transmitted to the heat conducting member 131 more efficiently.

Note that natural convection occurs in the casing 37 when the fixing roller 33 is heated.
More specifically, the air heated by the fixing roller 33 rises and hits the ceiling of the casing, and the air cooled there descends along the side surface of the casing, reaches the bottom surface of the casing, and reaches the fixing surface. The air is sucked up again by the rising airflow of the air heated by the roller 33.

As shown in FIG. 3A, when the heat conducting member 131 is in the separated position, the curved portion 131a is at a position lower than the fixing roller 33 and the ambient temperature is relatively low. The movement of heat to the heat conducting member 131 due to convection is also suppressed.
(1-4) Configuration of Control Unit FIG. 4 is a diagram illustrating a relationship between the configuration of the control unit 6 in the printer 1 and main components that are controlled by the control unit 6.

The control unit 6 includes a CPU 61, a communication interface (I / F) unit 62, a ROM 63, a RAM 64, a nonvolatile memory 65, and the like as main components.
The communication I / F unit 62 is an interface for connecting to a LAN such as a LAN card or a LAN board.
A ROM (Read Only Memory) 63 stores a program for executing control related to execution of printing and exhaust heat recovery control.

A RAM (Random Access Memory) 64 is a volatile memory and serves as a work area when the CPU 61 executes a program.
The nonvolatile memory 65 is an EEPROM (registered trademark) or the like, and serves as a data storage area of the CPU 61.
A CPU (Central Processing Unit) 61 reads out and executes a control program stored in the ROM 63, thereby executing the above-described printing operation.

  As part of this printing operation, the CPU 61 controls the power supply to the pressure roller drive source 160, which is the drive source of the pressure roller 32, and drives to rotate and stop the pressure roller 32 as necessary. In addition to executing the control, a known temperature control such as turning on / off the heater 34 to maintain the surface temperature of the fixing roller 33 at a target temperature based on a signal output from the temperature sensor 36 of the fixing unit 30. To implement.

Further, the CPU 61 executes exhaust heat recovery control for converting the exhaust heat of the fixing roller 33 into electric power and recovering it at a timing that does not interfere with the temperature control.
(1-4-1) Exhaust Heat Recovery Control FIG. 5 is a flowchart showing an execution procedure in the exhaust heat recovery control, and is executed in parallel with the surface temperature control (temperature control) of the fixing roller 33.

In the present embodiment, the temperature control is selectively executed in the following three modes according to the execution state of the print job from the viewpoint of power saving.
That is, the surface of the fixing roller 33 is maintained at 170 ° C., which is the optimum temperature for heat fixing, so that the fixing can be performed immediately, and the fixing roller 33 for a while after the print job is completed. The surface temperature of the heater 34 is maintained at a temperature slightly lower than 170 ° C. (for example, 145 ° C.), for example. Transition to the “power mode” and the “sleep mode” in which the power supply to the heater 34 is completely stopped and the power consumption is significantly reduced.

  For example, if the print job is not accepted even after a predetermined time T1 has elapsed since the previous print job was executed in the standby mode, the mode is shifted to the low power mode, and the print job is accepted even after the predetermined time T2 has elapsed. If there is no such information, or if the user inputs a power save instruction from the operation panel, the sleep mode is entered. The initial values of T1 and T2 are, for example, 5 minutes and 30 minutes, respectively, and the administrator of the device can log in and change arbitrarily.

When a print job is received during execution of the low power mode or sleep mode, control is performed so that warm-up is immediately started and the standby mode is restored.
The controller 6 executes exhaust heat recovery control as shown in FIG. 5 in parallel with the above temperature control.
This exhaust heat recovery control is started, for example, when the printer 1 is turned on.

  First, as an initial setting, the heat conducting member 131 is disposed at a separated position (FIG. 3A) (step S101). Then, it is determined whether or not the temperature control of the fixing roller 33 shifts to the above-described sleep mode (step S102). When the control does not shift to the sleep mode (step S102: NO), next, low It is determined whether or not to shift to the power mode (step S103).

If the mode does not shift to the low power mode (step S103: NO), the process returns to step S102, and the determination of whether to shift to the sleep mode is repeated.
When shifting to the low power mode (step S103: YES), the heat conducting member 131 is moved to the close position as shown in FIG. 3B (step S104).
That is, during the transition from the standby mode to the low power mode, it is only necessary to wait for the temperature of the fixing roller 33 to drop to the target temperature in the low power mode, and thus the heat conducting member 131 is moved to the close position in this way. At this time, since the fixing roller 33 and the curved portion 131a of the heat conducting member 131 are very close, the movement of heat from the fixing roller 33 to the heat conducting member 131 is promoted.

As a result, heat moves in the order of the fixing roller 33, the curved portion 131a of the heat conducting member 131, the heat sink 133, and the thermoelectric conversion element 134, and the electromotive voltage of each thermoelectric conversion element 134 increases. Can be used effectively.
The fact that the heat transfer to the curved portion 131a is promoted by bringing the heat conducting member 131 close to the fixing roller 33 leads to lowering the temperature of the fixing roller 33, but just the target of the fixing roller 33. Since the timing is to lower the temperature from the current level, there is no problem with temperature control.

If it is necessary to return from the low power mode to the standby mode by accepting a print job or the like during the temperature drop to the target temperature in the low power mode (step S105: YES), the process returns to step S101 to The conductive member 131 is returned to the separated position.
This is because the warm-up of the fixing roller 33 is started in the temperature adjustment control to return to the standby mode, so that the heat is not lost.

Even when the standby mode is not restored (step S105: NO), even when the temperature falls to the target temperature in the low power mode (step S106: YES), the process returns to step S101 and the heat conducting member 131 is set to the separated position. Return.
Also in this case, it is necessary to heat intermittently in order to maintain the target temperature in the low power mode, so that the heat at this time is not taken away.

If the temperature has not dropped to the target temperature in the low power mode (step S106: NO), the target temperature of the fixing roller 33 is being lowered from the current level, and the heat conducting member 131 is brought close to the target temperature. Since it may be in the state moved to the position, the process returns to step S105, and the determination of whether or not it is necessary to return from the low power mode to the standby mode is repeated.
On the other hand, if it is determined in step S102 that it is time to shift to the sleep mode (step S102: YES), the power supply to the pressure roller driving source 160 is stopped and the fixing roller 32 is driven. The rotation is stopped (step S107), the thermoelectric converter drive source 161 is driven, and the curved portion 131a of the heat conducting member 131 is moved to a position (contact position) where it contacts the fixing roller 33 (step S108).

As a result, heat transfer is further added to the heat transfer from the fixing roller 33 to the heat conducting member 131 mainly by radiation so far, so that the heat transfer is further promoted and the thermoelectric power is correspondingly increased. The amount of power that can be recovered by the converter 35 can also be increased.
Note that the rotation of the fixing roller 33 is stopped in step S107 in order to prevent the surface of the fixing roller 33 from being worn or wrinkled by the contact of the heat conducting member 131. When the contact surface of the curved portion 131a of the member 131 with the fixing roller 33 is subjected to a low friction process and / or when the contact pressure is very small, the fixing roller 33 is not necessarily stopped. Alternatively, it may be rotated at the same speed or slower than that at the time of image formation. In this case, heat transfer from the fixing roller 33 to the heat conducting member 131 is further promoted.

Thereafter, when it becomes necessary to return from the sleep mode to the standby mode (step S109: YES), the process returns to step S101 to move the heat conducting member 131 to the separated position. At this time, warm-up is performed while rotating the pressure roller and the fixing roller in separately controlled temperature control.
On the other hand, if it is not necessary to return to the standby mode (step S109: NO), it is determined whether or not the temperature of the fixing roller 33 has reached room temperature (step S110), and if it has reached room temperature (step S110). : YES), returning to step S101, the heat conducting member 131 is moved to the separated position.

In this case, there is no longer any recovery of the exhaust heat from the fixing roller 33, so it is meaningless even if the heat conducting member 131 is in the close position, and it is to wait at the initial position in preparation for the next warm-up start. .
If the temperature of the fixing roller 33 has not reached room temperature (step S110: NO), the determination process in step S109 is repeated.

The exhaust heat recovery control ends when the printer 1 is turned off.
As described above, in the present embodiment, when the fixing roller 33 needs to be heated in order to raise the fixing roller 33 to a specific target temperature and to maintain the fixing roller 33 at a specific target temperature. Then, the heat conducting member 131 is retracted to the separated position so that the amount of heat is not lost as much as possible, and the fixing roller 33 does not need to be heated. Heat is converted to electric power.

The power generated as described above is stored in the power storage unit 70 of the power supply unit 7 and used as power for the control unit 6 and the like, which contributes to energy saving as a whole.
(1-5) Application of exhaust heat recovery control to other temperature control controls In the above, even if a page to be printed in color and a page to be printed in monochrome are mixed in one print job, the fixing roller 33 When the surface temperature is uniformly maintained at 170 ° C., the recording sheet on which an unfixed toner image is formed is passed through the fixing nip, and the toner image is discharged along with the known temperature control for heat fixing. Although the example which implements heat recovery control was explained, application of exhaust heat recovery control in this embodiment is not restricted to such well-known temperature control, for example, temperature control as shown below You may apply.

As a result of intensive studies by the inventors, when fixing a monochrome toner image (hereinafter referred to as “monochrome image”), even if the fixing temperature is lowered to about 150 ° C., for example, the fixing quality of the monochrome image is obtained. Turned out to be acceptable.
On the other hand, since a color toner image requires a high level of image quality, the fixing temperature is preferably set to 170 ° C.

In other words, when heat-fixing a monochrome image, the temperature of the fixing roller 33 is not uniformly set to 170 ° C. as in the past, but if the temperature is set to be as low as possible in the fixing temperature range, 170 ° C. The amount of power supplied to the heater 34 is reduced by the amount of temperature lower than 0 ° C., and power saving can be achieved.
In such temperature control (hereinafter referred to as “power-saving temperature control”), there are more opportunities to lower the fixing target temperature than in the known temperature control, and therefore, the exhaust heat recovery control is not performed. If applied to electric power temperature control, the opportunity to perform thermoelectric conversion increases, and more exhaust heat recovery can be expected.

FIG. 6 is a flowchart showing an example of such power saving temperature control.
Further, FIG. 7 shows the temporal change of the surface temperature of the fixing roller 33 when the power saving temperature control is performed without performing the exhaust heat recovery control, and the exhaust heat recovery control is performed along with the power saving temperature control. FIG. 6 is a diagram showing a change with time in the surface temperature of the fixing roller 33 in the case where the horizontal axis indicates a time axis.

The uppermost stage 71 in FIG. 7 includes a time for executing warm-up, a time for heat-fixing a monochrome image, a time for heat-fixing a color toner image (hereinafter referred to as “color image”), and sleep. The time spent in mode is shown.
Further, the middle stage 72 shows a change with time of the separation distance (shortest distance) between the heat conducting member 131 and the fixing roller 33 when the exhaust heat recovery control is executed along with the execution of the power saving temperature control. Has been.

  In the lower stage 73, when a monochrome image and a color image are heat-fixed, an allowable range of fixing temperature (hereinafter referred to as “allowable temperature range”) 171 that can ensure the fixing quality without any problem is omitted. A broken line 172 indicating a temporal change in the surface temperature of the fixing roller 33 only by the electric power temperature control, and a temporal change in the surface temperature of the fixing roller 33 when the exhaust heat recovery control is performed along with the electric power saving temperature control. A solid line 173 is shown.

This power-saving temperature control is executed by the control unit 6 when a print job is received.
First, when the CPU 61 receives a print job from an external personal computer or the like via the communication I / F unit 62 (step S201: YES), the image of each page is referred to by referring to the header part in the print job data. After determining whether it is color or monochrome (step S202), it is determined whether the current temperature control is in the standby mode (step S203).

Note that the fixing temperature, which is a control target in the standby mode, is set to a temperature TsL ° C. (150 ° C. in this example) at the time of monochrome image fixing as an initial value.
If it is not currently in the standby mode (step S203: NO), a warm-up for raising the fixing roller 33 to the fixing temperature TsL ° C. is performed, and the first page after the start of the warm-up is a fixing target. Sets the value of the flag W indicating “1” to “1” otherwise (see step S204, time t0 to time t1 in FIG. 7).

The value of the flag W may be stored in the nonvolatile memory 65.
In addition, even if a color image and a monochrome image are mixed in one page, if a color image is included in one page, it is considered that a color image is formed on the entire page. And Thereby, it is possible to prevent the fixing quality of the color image portion from being deteriorated.

If it is determined in step S203 that the current standby mode is set (step S203: YES), step S204 is skipped.
Then, the CPU 61 determines whether or not there is a color image on any of the first and second pages waiting for fixing (step S205), and there is a color image on any of the pages. (Step S205: YES), and when the first page is a monochrome image (Step S206: YES), immediately before fixing the color image of the second page, the surface temperature of the fixing roller is just the target temperature TsH ° C. Then, temperature control is started from the present time (step S207).

In addition, the value of temperature TsH in this Embodiment is set to 170 degreeC, for example.
Here, in step S207, “just before fixing the color image of the second page, temperature control is started from the present time so that the surface temperature of the fixing roller becomes just the target temperature TsH ° C.”, that is, 1 The fixing of the monochrome image of the page means that the fixing roller 33 is set to TsH ° C. immediately before the fixing of the color image of the second page is performed in a state where the temperature is changed. (See time t2 to time t3 in FIG. 7).

  The reason why such control is unavoidable is that, in the power-saving temperature control, when a plurality of recording sheets are thermally fixed, once fixing is started, a fixed time interval is set according to the system speed. However, the heating capability of the heater 34 is not sufficient so that the fixing temperature can be quickly switched between sheets, and a certain amount of time is required to raise the temperature of the fixing roller 33.

For example, in order to save power, it takes time Ta (about 1) to raise the temperature from TsL ° C., which is considered to be a more desirable fixing temperature, to TsH ° C., which is a fixing temperature suitable for a color image, when fixing a monochrome image. .. time for fixing 8 pages) (see FIG. 7).
That is, immediately after passing the leading edge of the monochrome image of the first page through the fixing nip, the temperature of the fixing roller 33 starts from 150 ° C., so that the leading edge of the color image of the second page passes through the fixing nip. At this time, the temperature of the fixing roller 33 reaches only 165 ° C.

Therefore, in order not to reduce the productivity, it is necessary to start the temperature increase from time t1 slightly before the leading edge of the monochrome image of the first page passes through the fixing nip (see FIG. 7).
Therefore, immediately after the start of the temperature adjustment to the target temperature TsH ° C. in step S207, the first page (monochrome image) at the present time is fixed (step S208).
The fixing temperature gradually rises until the recording sheet on which the page is printed is completed (between time t2 and time t3 in FIG. 7). However, in the case of a monochrome image as described above, the fixing image quality is required so much. The temperature change is within the allowable range.

Thereafter, it is determined whether or not all pages have been fixed and the print job is completed (step S209). If not completed (step S209: NO), if the value of the flag W is “1”. After rewriting this value to “0” (step S210), the process returns to step S205 to execute the process.
In the determination in step S206, if the first page to be fixed is a color image (step S206: NO) and the value of the flag W is “1” (step S211: YES), the first page is to be fixed. The first page is the first page after the end of warm-up executed with TsL.degree. C. as the target temperature, so the process waits until the fixing temperature reaches TsH.degree.

On the other hand, if the value of the flag W is “0” (step S211: NO), it is in the middle of continuously fixed pages, so step S212 is skipped and the processing from step S208 is executed.
This is because when the immediately preceding page is a color image, the fixing temperature has already reached TsH ° C., and when the immediately preceding page is a monochrome image, before the fixing, the target temperature TsH ° C. is reached. This is because the temperature control is started and the temperature has already been reached (see time t4 in FIG. 7).

  If it is determined in step S205 that there is no color image on any of the first and second pages that are currently waiting for fixing, that is, both pages are monochrome images (step S205). : NO) The target temperature of the fixing temperature of the first page is set to TsL ° C. and the temperature control is continued (step S213), and the page of the first monochrome image is fixed as it is (step S208).

  Since the second page is also a monochrome image following the first page, it is necessary to raise the temperature early from the stage of fixing the monochrome image of the first page, as when the second page was a color image. This is because the fixing roller 33 has already reached the fixing temperature TsL ° C. due to the warm-up in step S204. Further, when the page of the color image was fixed last time, the temperature of the fixing roller 33 sufficiently exceeds TsL ° C.

In step S205, when the number of remaining pages is one, the second page is not actually present, but the control determines that the second page of the monochrome image exists.
When the above process is repeated for each page and the print job is completed (step S209: YES), the power saving temperature control is finished for the print job, and the process is started when the next new print job is received. Executed.

FIG. 8 is a flowchart showing the contents of the exhaust heat recovery control when the power saving temperature control is executed, and is almost the same as the flowchart of the exhaust heat recovery control in FIG.
The difference from the exhaust heat recovery control shown in FIG. 5 is that steps S301 to S303 are added.
That is, if it is determined in step S103 that the mode does not shift to the low power mode (step S103: NO), it is next determined whether or not the target temperature of the fixing roller 33 is changed from TsH ° C. to TsL ° C. (Step S301). In the flowchart of FIG. 6, after fixing the page of the color image in step S208, this corresponds to the case where the target temperature is lowered to TsL ° C. to print the monochrome image in step S213.

  When the target temperature of the fixing roller 33 is changed from TsH ° C. to TsL ° C. (step S301: YES), the heat conduction member 131 is moved to a close position (step S302) and power conversion by the thermoelectric conversion element 134 is performed. When the temperature of the fixing roller 33 is lowered to TsL ° C. (step S303: YES), the heat conducting member 131 is moved to the separated position so as not to take away the heat necessary to maintain the temperature. (Step S101).

In FIG. 7, from the time t5 when the fixing of the color image is completed to the time t7 when the temperature of the fixing roller 33 reaches TsL ° C., the heat conducting member 131 is moved to the close position as shown in the middle stage 72. The heat of the fixing roller 33 is absorbed to perform thermoelectric conversion.
As a result, compared to the case where the exhaust heat recovery control is not performed, the temperature drop of the fixing roller 33 is accelerated, and at time t6 when the fixing of the monochrome image is started, the temperature is almost close to the temperature TsL ° C.

That is, according to this control, in addition to the improvement in heat conversion efficiency, it leads to an improvement in responsiveness in which the temperature is quickly lowered to the target fixing temperature.
In FIG. 7, the temperature control is shifted to the sleep mode at time t9. At this time, the heat conducting member 131 is in contact with the fixing roller 33 (step S108 in FIG. 8), so that the exhaust heat is recovered. As a result, it can be seen that the temperature lowering speed of the fixing roller 33 is increased.

<Modification>
The present invention is not limited to the above-described embodiment, and the following modifications can be implemented.
(1) In the above embodiment, the heat conducting member 131 is a heat pipe obtained by curving a part of the copper tube along the surface shape of the elastic body 33b of the fixing roller 33. The shape is not limited to a simple shape. In some cases, a simple metal plate may be used.

In order to cause the heat conducting member 131 to efficiently absorb the radiant heat from the fixing roller 33, the surface of the heat conducting member 131, particularly the curved portion 131a, may be painted with a color that easily absorbs the radiant heat.
(2) In the above embodiment, the curved portion 131a of the heat conducting member 131 is moved closer to or away from the fixing roller 33 by swinging the thermoelectric conversion portion 35. However, the present invention is not limited to this.

For example, a pair of rails are provided on opposing inner wall surfaces of the casing 37, and the holder 132 of the thermoelectric conversion unit 35 is slidably held in the perspective direction of the fixing roller 33 by the pair of rails, and the thermoelectric conversion unit moving mechanism The arrangement of 135 may be reviewed so that the moving direction of the rod 135a coincides with the sliding direction of the holder 132.
In short, it is sufficient that the heat conducting member 131 of the thermoelectric conversion unit 35 is configured to be movable in the perspective direction of the fixing roller 33.

(3) In the power-saving temperature control according to the above embodiment, it is determined whether there is a color image on any of the first and second pages that are waiting for fixing at the present time. Although the target temperature of the fixing roller 33 is reviewed, the present invention is not limited to this.
For example, the heating capacity of the heater 34 is lower than that of the above embodiment, and the temperature is raised from TsL ° C. to TsH ° C., which is a fixing temperature suitable for a color image. For example, when it takes time to fix 2.5 pages, it is determined whether or not there is a color image on any of the first to third pages waiting for fixing, and a color image of 3 pages ahead. In preparation for fixing, it is necessary to review the target temperature of the fixing roller 33 from the time of fixing the first page.

Thus, how many pages ahead the image type should be determined depends on the heating capacity of the heater 34.
Of course, when the print job is received, the image types of all pages may be known.
(4) In the power-saving temperature control according to the above embodiment, the target fixing temperature is switched depending on the type of monochrome or color, but the present invention is not limited to this.

  For example, when a character toner image (hereinafter referred to as “text image”) is compared with a toner image other than characters such as a photograph or a picture (hereinafter referred to as “image image”), the text image is fixed. As in the case of fixing a monochrome image, even if the fixing temperature varies within a predetermined range (170 ° C. to 150 ° C. in the embodiment), the fixing unevenness is not noticeable and the fixing quality is acceptable. The inventors found out after intensive studies.

For this reason, in the power-saving temperature control, when fixing a page with only a text image, it is handled in the same way as when fixing a monochrome image, and when fixing a page including an image image. In the same manner as in the case of fixing a color image, the power supplied to the heater 34 can be reduced and the power can be saved.
Of course, in this case as well, by performing the exhaust heat recovery control according to the above embodiment together, the heat radiated to the outside without contributing to fixing can be converted into electric power. Electricity becomes possible.

  (5) In the above embodiment, the configuration in which the fixing roller is heated using a heater such as a halogen lamp has been described as an example. However, the present invention is not limited to this. For example, the inner side of an endless belt having electric resistance is used. A roller (hereinafter referred to as “pressing roller”) is loosely inserted, and a pressing nip is pressed with a pressure roller through the belt to form a fixing nip, and a potential difference is given to both ends of the belt in the rotation axis direction. Therefore, the exhaust heat recovery control described in the above embodiment may be applied to a so-called resistance heating type fixing device that generates heat by flowing current.

  A printer that forms a fixing nip by inserting a pressure roller into an endless metal belt and pressing the pressure roller with the pressure roller through the belt. The exhaust heat recovery control described in the above embodiment may be applied to a heater that employs a so-called induction heating type heater that generates an alternating magnetic field and performs induction heating.

As described above, the heating target in the fixing device may include a belt in addition to the roller. In short, any heating rotating body that is heated while rotating may be used.
In addition, since various configurations can be considered for heating the heating rotator as described above, any configuration may be used as long as the heating rotator can be heated.

(6) In the embodiment and the modification (5), a pressure roller is used to form the fixing nip. However, instead of the pressure roller, the surface has a low friction material or the like. It is good also as a structure which press-contacts the pressure pad etc. which were covered with the fixing roller which concerns on the said embodiment, or the belt described in a modification (5).
In short, any configuration may be used as long as it is a pressure member that can press the fixing roller or the belt to form the fixing nip.

(7) Moreover, in the said modification (5), although the press roller was used, you may replace the said press roller with the press pad by which the surface was covered with the low friction material.
In addition, the said press pad hold | maintains the long press member which has the elasticity arrange | positioned along the rotating shaft direction of a pressure roller with the holding member which has rigidity, for example.
The surface of the pressing member on the side receiving the pressing force is preferably subjected to a low friction surface treatment or covered with a flexible low friction film.

(8) In the above embodiment, the example in which the image forming apparatus according to the present invention is applied to a tandem color printer has been described. However, the present invention is not limited to this, and may be applied to a monochrome printer. In general, the present invention can be applied to an image forming apparatus including a fixing device.
The above embodiment and the contents of the above embodiment may be combined as much as possible.

  The present invention can be widely applied to an image forming apparatus including a fixing device that thermally fixes a sheet on which an unfixed image is formed.

DESCRIPTION OF SYMBOLS 1 Printer 6 Control part 7 Power supply unit 10 Image formation part 30 Fixing part 32 Pressure roller 33 Fixing roller 34 Heater 35 Thermoelectric conversion part 36 Temperature sensor 37 Casing 61 CPU
131 Thermal Conductive Member 131a Curved Part 131b Upper End Part 132 Holder 133 Heat Sink 132a Rotating Shaft 133a Protruding Part 134 Thermoelectric Conversion Element 135 Thermoelectric Conversion Part Moving Mechanism 135a Shaft 135b Boss Part 135c Abutting Part 135d Cam Follower 136 Cam 137 Energizing Member 160 Pressure roller drive source 161 Thermoelectric converter drive source

Claims (8)

A fixing device that forms a fixing nip by pressing the outer peripheral surface of a heating rotator heated by a heating means with a pressure member, and passes a sheet on which an unfixed image is formed into the fixing nip to thermally fix the fixing device. An image forming apparatus having
A thermoelectric conversion element;
A heat conducting member thermally coupled to the thermoelectric conversion element;
At least a part of the heat conducting member in a perspective direction with respect to the heating rotator, between a first position and a second position closer to the heating rotator than the first position. Moving means for moving;
Temperature control means for controlling the heating means so that the surface temperature of the heating rotator becomes a target temperature;
When trying to lower the temperature of the heating rotator, moving the heat conducting member to the second position to increase the temperature of the heating rotator and maintaining the target temperature The image forming apparatus further comprises: a movement control unit that controls the moving unit to retract the heat conducting member to the first position. A part of the heat conducting member is supported so as to be able to swing with respect to the fixing device main body in a state of protruding from the housing of the fixing device to the outside, and the thermoelectric conversion element is provided in the portion protruding to the outside Is attached, and at least a part of the portion existing inside the housing is configured to move in a perspective direction with respect to the heating rotating body by a swinging operation.
The image forming apparatus according to claim 1. The moving means can move a part of the heat conducting member to a third position in contact with the heating rotator,
The control means controls the moving means so that the heat conducting member moves to the third position when heating of the heating rotator is stopped after completion of the heat fixing operation of the sheet. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An acquisition means for acquiring a type of an unfixed image to be fixed;
The control means selectively switches the target temperature between a first temperature and a second temperature lower than the first temperature according to the type of the unfixed image,
The said movement control means moves the said heat-conduction member to a 2nd position at the time of the temperature fall of the said heating rotary body when switching from the said 1st temperature to a 2nd temperature. The image forming apparatus according to claim 3. The type of the unfixed image is a monochrome image or a color image,
The control means includes
When the unfixed image is a monochrome image, the target temperature is set to the second temperature, and when the unfixed image is a color image, the target temperature is set to the first temperature. The image forming apparatus according to claim 4. The type of the unfixed image is a text image and an image image,
The control means includes
When the unfixed image is a text image, the target temperature is set to the second temperature, and when the unfixed image is an image image, the target temperature is set to the first temperature. The image forming apparatus according to claim 4. The heat conducting member has a curved portion that curves along an outer peripheral surface of the heating rotator, and is configured such that the curved portion is closest to the heating rotator at the second position. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The image forming apparatus according to claim 1, wherein the heat conducting member includes a heat pipe including a plurality of tubes in which a refrigerant is sealed.

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