JP2011232554A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus effectively preventing condensation or freezing of a heat absorption section when a heat pump is started when the image forming apparatus carries out cooling of a recording medium heated by the fixing section with the heat absorption section of the heat pump and carries out heating of the fixing section by using the heat absorbed in the heat absorption section.SOLUTION: The heat pump 20 has a bypass flow channel 30e for circulating working fluid in a second heat absorption section 26 connected to a flow channel 30a for the working fluid between an expansion valve 37 and a first heat absorption section 8a and a flow channel 30b for the working fluid between the first heat absorption section 8a and a compressor 33 and has switching valves 29a, 29b arranged in a connecting section between the flow channels 30a, 30b and the bypass flow channel 30e. When a printing command is inputted, surface temperature T2 of an endless belt 21b in the first heat absorption section 8b is detected and when T2≤T0, a second circulating route is used. Then, switching valves 29a, 29b are activated at the point when paper passage is started and T2>T0 is satisfied and the switch is made from the second circulating route to a first circulating route.

Description

  The present invention relates to an image forming apparatus including a fixing device that heats and pressurizes a sheet carrying an unfixed toner image to melt the unfixed toner and fixes the unfixed toner on the sheet.

  In an electrophotographic image forming apparatus, a toner image formed on an image carrier is transferred onto a recording medium such as transfer paper, and then the recording medium is heated and pressed by a fixing device to thereby form toner on the recording medium. The image is fixed to make a permanent image.

  As a heating source of such a fixing device, a halogen heater, an infrared lamp, an electromagnetic induction coil, or the like is used. However, since all use Joule heat generated by an electric current, the current is converted into heat. There were also problems that efficiency was low and power consumption was large.

  In addition, since the heat applied to the recording medium in the fixing device is dissipated into the air, the internal temperature of the image forming apparatus increases. Furthermore, since the heat of the recording medium is dissipated wastefully, the energy use efficiency is low, which is disadvantageous in terms of energy saving.

  Therefore, a technique has been proposed in which the recording medium onto which the toner image has been transferred is efficiently heated and fixed, and the heat applied to the recording medium is used to raise the temperature of the fixing device. An image forming apparatus is disclosed in which a high temperature portion (heat radiating portion) of a heat conversion device having a heat pump function is used as a heating source of a fixing device, and a low temperature portion (heat absorption portion) of the heat conversion device is used as a cooling source of a recording medium after fixing. Yes.

  Patent Document 2 includes a heat storage member that contacts the heat absorption member of the heat pump, and a heat storage member moving device for changing a contact position of the heat storage member with respect to the heat absorption member, and includes the heat storage member and the heat absorption member at the start of heating. An image forming apparatus is disclosed in which the contact state of the heat storage member is changed according to the temperature of the contact position while being brought into contact.

JP 2005-258003 A JP 2009-31401 A

  However, in the method of Patent Document 1, dew condensation occurs due to overcooling of the heat absorbing portion immediately after the start of heating, and the recording medium after fixing is wetted. Moreover, the heat exchange efficiency in a heat absorption part falls by freezing, and heat absorption cannot be performed stably. On the other hand, although it is conceivable to gradually increase the operation of the heat pump so as not to cause condensation or freezing, there is a problem that the warm-up time becomes long. In addition to supplying heat from the heat conversion device, it is also described that power is supplied from the secondary battery to heat, but if the heat pump is driven immediately after the start of heating, condensation will also occur in the heat absorption part There was a risk.

  Further, in the method of Patent Document 2, since a heat storage member and a heat storage member moving device are separately provided, the device is increased in size and a complicated mechanism is required for operation control of the heat storage member. Furthermore, there is also a drawback that the heat pump does not contribute to the improvement of the heating efficiency of the fixing unit while heat is being transferred between the heat storage member and the heat absorbing unit.

  SUMMARY OF THE INVENTION In view of the above problems, an image forming apparatus that cools a recording medium heated by a fixing unit using a heat absorbing unit of a heat pump and heats the fixing unit using heat absorbed by the heat absorbing unit. An object of the present invention is to provide an image forming apparatus capable of effectively preventing dew condensation and freezing of the heat absorbing portion when the heat pump is activated.

  To achieve the above object, the present invention provides a fixing unit that heats and pressurizes a recording medium carrying an unfixed toner image, and a recording that is disposed downstream of the fixing unit in the recording medium conveyance direction and passes through the fixing unit. A fixing device including a first heat absorption unit that absorbs heat of the medium; and the fixing unit and the first heat absorption unit. The heat absorbed by the heat absorption unit is transferred to the fixing unit by circulating a working fluid. An image forming apparatus comprising: a heat pump that moves and dissipates heat; and a control unit that controls driving of the heat pump. The heat pump includes a second heat absorption unit disposed outside a conveyance path of the recording medium, and the second heat absorption unit. Or a switching valve that circulates the working fluid in any one of the first heat absorption parts, and a heat absorption part temperature sensor that detects the temperature of the first heat absorption part is provided, and the control means includes the heat pump The drive of Depending on the temperature of the first endothermic part detected by the endothermic temperature sensor at the start, either the first endothermic part or the second endothermic part is selected to circulate the working fluid and the second endothermic part When the section is selected, the working fluid circulation path is switched to the first heat absorbing section after the conveyance of the recording medium is started.

  According to the present invention, in the image forming apparatus having the above-described configuration, a fixing unit temperature sensor that detects the temperature of the fixing unit is provided, and the control unit is configured to control the working fluid based on the detected temperature of the fixing unit temperature sensor. The circulation path is switched to the first heat absorption part.

  According to the present invention, in the image forming apparatus having the above-described configuration, the control unit switches a circulation path of the working fluid to the first heat absorption unit based on a temperature detected by the heat absorption unit temperature sensor.

  According to the present invention, in the image forming apparatus having the above configuration, the control unit selects the second heat absorbing unit when the temperature detected by the heat absorbing unit temperature sensor at the start of driving the heat pump is equal to or lower than the environmental temperature. The working fluid is circulated, and when the temperature detected by the heat absorption unit temperature sensor exceeds the environmental temperature, the first heat absorption unit is selected to circulate the working fluid.

  According to the present invention, in the image forming apparatus having the above configuration, a heating member for heating the fixing unit is provided, and the control unit controls the temperature of the fixing unit by using the heat pump and the heating member in combination. It is characterized by doing.

  According to the present invention, in the image forming apparatus configured as described above, the fixing unit and the first heat absorbing unit are inscribed in an endless belt that is rotatable at a substantially constant speed with respect to a conveyance speed of the recording medium, and inscribed in the endless belt. And a heat exchange member connected with a flow path for circulating the working fluid of the heat pump, and a nip portion for contacting the heat exchange member with a predetermined pressure via the endless belt to insert a recording medium. And a pressure roller.

  According to the present invention, in the image forming apparatus configured as described above, a circulation path through which the working fluid of the heat pump passes is formed inside the heat exchange member, and the working path flows in the circulation path. And a large number of ribs.

  According to the present invention, in the image forming apparatus configured as described above, the rib is formed so as to penetrate through the inside of the heat exchange member in a pressure contact direction of the pressure roller.

  In the image forming apparatus having the above-described configuration, the nip width of the heat absorption nip portion formed in the heat absorption portion is larger than the nip width of the fixing nip portion formed in the fixing portion.

  In the image forming apparatus having the above-described configuration, the nip width in the belt circumferential direction of the heat absorption nip portion is changed according to the type of the recording medium.

  According to the present invention, in the image forming apparatus configured as described above, the heating member that heats the endless belt is disposed between the endless belt and the heat exchange member and contacts the entire width direction of the endless belt. It is characterized by providing a heater.

  According to the present invention, in the image forming apparatus having the above-described configuration, the endless belt is a belt made of metal or having a metal thin film layer, and the endless belt is heated by electromagnetic induction as a heating member that heats the endless belt. An electromagnetic induction coil is provided.

  According to the first configuration of the present invention, when the temperature of the first heat absorption unit is equal to or lower than the predetermined temperature when the heat pump is started, the working fluid of the heat pump is circulated to the second heat absorption unit, so that the excess of the first heat absorption unit is achieved. Generation of condensation due to cooling can be effectively prevented. In addition, since the circulation path is switched from the second heat absorption unit to the first heat absorption unit after the conveyance of the recording medium is started, the heat of the first heat absorption unit can be efficiently recovered and used for heating the fixing unit. .

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the first endothermic path of the working fluid is routed based on the detected temperature of the fixing unit temperature sensor that detects the temperature of the fixing unit. By switching to the unit, it is possible to reliably determine whether or not the fixing unit has been heated to the fixing possible temperature, to reliably detect the start of conveyance of the recording medium, and to switch the circulation path to the first heat absorbing unit.

  Further, according to the third configuration of the present invention, in the image forming apparatus having the first configuration, the endothermic portion is switched by switching the working fluid circulation path to the first endothermic portion based on the temperature detected by the endothermic temperature sensor. Since the circulation path can be switched to the first heat absorption part when the part rises to a predetermined temperature, dew condensation due to overcooling of the first heat absorption part can be more reliably prevented.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, the first circulation path or the second circulation path is selected when the heat pump is activated. By setting the threshold value of the detected temperature of the first heat absorbing part as the environmental temperature, it is possible to effectively prevent the occurrence of condensation in the first heat absorbing part regardless of the use environment of the apparatus.

  According to the fifth configuration of the present invention, in the image forming apparatus having any one of the first to fourth configurations, the heating member for heating the fixing unit is provided, and the heat pump and the heating member are used in combination. By controlling the temperature of the fixing unit, it is possible to quickly raise the temperature of the fixing unit to a fixable temperature by energizing the heating member when the heat pump is started, thereby shortening the warm-up time of the apparatus. . Further, when using a recording medium having a large heat capacity such as cardboard, the temperature of the fixing unit can be stably controlled by using the heating member as an auxiliary heating unit.

  According to the sixth configuration of the present invention, in the image forming apparatus having any one of the first to fifth configurations, the fixing unit and the heat absorption unit can be rotated at substantially the same speed as the conveyance speed of the recording medium. An endless belt, a heat exchange member that is inscribed in the endless belt and that circulates the working fluid of the heat pump, and a heat exchange member that is in contact with the heat exchange member through the endless belt at a predetermined pressure for recording By adopting a configuration that includes a pressure roller that forms a nip that allows media to pass through, the heat capacity can be reduced compared to a configuration that uses a heating roller, so the warm-up time to reach the fixable temperature is further reduced. It becomes possible. In addition, by using the heat exchange member as a fixing member and also as a pressing member for the endless belt, the number of components is reduced, and leakage of the working fluid at the connecting portion between the heat exchange member and the flow path can be easily and reliably prevented. be able to.

  According to the seventh configuration of the present invention, in the image forming apparatus having the sixth configuration, a circulation path is provided in which a plurality of ribs through which the working fluid of the heat pump passes are provided inside the heat exchange member. As a result, the contact area between the heat exchange member and the working fluid can be increased to increase the heat exchange efficiency.

  According to the eighth configuration of the invention, in the image forming apparatus of the seventh configuration, the heat exchange is performed by forming the rib so as to penetrate the inside of the heat exchange member in the pressure contact direction of the pressure roller. It is possible to reduce the heat capacity by reducing the thickness of the heat exchange member while securing the strength required when the member is also used as a pressing member.

  According to the ninth configuration of the invention, in the image forming apparatus having any of the sixth to eighth configurations, the nip width of the heat absorption nip portion formed in the heat absorption portion is formed in the fixing portion. By making it larger than the nip width of the fixing nip portion, the heat absorption efficiency at the heat absorption portion is increased, so that the heat exchange efficiency of the heat pump can be improved.

  According to the tenth configuration of the present invention, in the image forming apparatus having the ninth configuration, by changing the nip width in the belt circumferential direction of the heat absorbing nip portion according to the type of the recording medium, The balance of the heat exchange efficiency in the heat absorption part can be appropriately adjusted according to the heat capacity of the recording medium.

  According to the eleventh configuration of the present invention, in the image forming apparatus having any one of the sixth to tenth configurations, the heating member that heats the endless belt is provided between the endless belt and the heat exchange member. By using the heater that is disposed in contact with the entire width direction of the endless belt, the configuration of the heating member that heats the endless belt can be simplified and miniaturized.

  According to the twelfth aspect of the present invention, in the image forming apparatus having any one of the sixth to tenth aspects, the endless belt is a metal or a belt having a metal thin film layer, and the endless belt is heated. By using an electromagnetic induction coil that heats the endless belt by electromagnetic induction as the heating member that performs heating, the temperature rise performance of the fixing unit can be enhanced and the warm-up time can be further shortened.

1 is a schematic diagram illustrating a configuration example of an image forming apparatus of the present invention. 1 is a schematic cross-sectional view showing a configuration of a fixing device and a heat pump mounted in an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an enlarged view of the fixing unit. Enlarged view of the endothermic part in FIG. TS diagram showing operation of heat pump The top view of the heat exchange member in FIG. 1 is a block diagram showing a control path of an image forming apparatus according to a first embodiment. 6 is a flowchart illustrating an example of heating control of the fixing device according to the first embodiment. Schematic sectional view showing a state where the heat pump is operated using the second circulation path Schematic sectional view showing a state in which the heat pump is operated using the first circulation path FIG. 6 is a schematic cross-sectional view illustrating a configuration of a fixing unit of a fixing device mounted on an image forming apparatus according to a second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view of an image forming apparatus of the present invention. In the printer 100, when a copying operation is performed, an electrostatic latent image based on document image data transmitted from a personal computer (not shown) is formed in an image forming unit P in the apparatus body, and development is performed. The apparatus 4 attaches toner to the electrostatic latent image to form a toner image. The toner is supplied to the developing device 4 from the toner container 5. In such a printer 100, an image forming process for the photosensitive drum 1 is executed while rotating the photosensitive drum 1 clockwise in FIG.

  The image forming unit P includes a charging unit 2, an exposure unit 3, a developing device 4, a transfer roller 6, a cleaning device 7, and a charge removal device (not shown) along the rotation direction (clockwise) of the photosensitive drum 1. Is arranged. The photosensitive drum 1 is formed, for example, by laminating a photosensitive layer on an aluminum drum, and the surface is charged by the charging unit 2. Then, an electrostatic latent image in which charging is attenuated is formed on the surface that has received the light beam from the exposure unit 3 described later. The above-mentioned photosensitive layer is not particularly limited. For example, amorphous silicon (a-Si) having excellent durability, or an organic photosensitive layer (high-resolution image can be obtained with little generation of ozone during charging). OPC) and the like are preferable.

  The charging unit 2 uniformly charges the surface of the photosensitive drum 1. For example, a corona discharge device that discharges by applying a high voltage using a thin wire or the like as an electrode is used as the charging unit 2. Instead of the corona discharge device, a contact-type charging device that applies a voltage while a charging member typified by a charging roller is in contact with the surface of the photosensitive member may be used. The exposure unit 3 irradiates the photosensitive drum 1 with a light beam (for example, a laser beam) based on the image data, and forms an electrostatic latent image on the surface of the photosensitive drum 1.

  The developing device 4 forms toner images by attaching toner to the electrostatic latent image on the photosensitive drum 1. Here, a single-component developer (hereinafter also simply referred to as toner) composed only of magnetic toner components is accommodated in the developing device 4. The transfer roller 6 transfers the toner image formed on the surface of the photosensitive drum 1 to the sheet conveyed through the sheet conveyance path 11 without disturbing the toner image. The cleaning device 7 includes a cleaning roller, a blade material, and the like that are in linear contact with the longitudinal direction of the photosensitive drum 1, and removes residual toner remaining on the surface of the photosensitive drum 1 after the toner image is transferred to the paper. To do.

  The exposure unit 3 emits a laser beam (light beam) on the photosensitive drum 1 based on image data input in advance from a personal computer or the like, so that an electrostatic latent image based on the image data is applied to the surface of the photosensitive drum 1. Form. Thereafter, the developing device 4 attaches toner to the electrostatic latent image to form a toner image.

  A sheet is conveyed from the sheet storage unit 10 through the sheet conveyance path 11 and the registration roller pair 13 at a predetermined timing toward the image forming unit P on which the toner image is formed as described above. The toner image on the surface of the photosensitive drum 1 is transferred onto the sheet by the transfer roller 6. Then, the sheet on which the toner image is transferred is separated from the photosensitive drum 1, conveyed to the fixing device 8, and heated and pressed to fix the toner image on the sheet.

  The fixing device 8 includes a fixing unit 8a that heats and pressurizes the sheet on which the toner image is transferred, and a heat absorption unit 8b that is disposed on the downstream side of the fixing unit 8a in the sheet conveyance direction. The heat absorption unit 8b absorbs heat released from the sheet heated by the fixing unit 8a to cool the sheet, and absorbs the absorbed heat to the fixing unit 8a via the compressor 33 (see FIG. 2) of the heat pump 20. Supply. The paper that has passed through the fixing device 8 passes through the discharge roller pair 14 and is discharged to the paper discharge unit 15.

  FIG. 2 is a schematic cross-sectional view illustrating the configuration of the fixing device and the heat pump mounted in the image forming apparatus according to the first embodiment of the present invention. FIGS. 3 and 4 are enlarged views of the fixing unit and the heat absorbing unit in FIG. FIG. As shown in FIGS. 2 and 3, the fixing unit 8a includes an endless belt 21a that rotates clockwise in the drawing, and a pressure that contacts the endless belt 21a with a predetermined pressure to form a fixing nip N1. The configuration includes a roller 23a, a heat exchange member 25a inscribed in the endless belt 21a, and a fixing section thermistor 60a that detects the surface temperature of the endless belt 21a. Flow paths 30c and 30d for circulating the working fluid (refrigerant) of the heat pump 20 are connected to the heat exchange member 25a. The heat exchange member 25a also serves as a pressing member for forming the fixing nip portion N1.

  As shown in FIGS. 2 and 4, the heat absorbing portion 8b has substantially the same configuration as the fixing portion 8a shown in FIG. 3, and an endless belt 21b that rotates clockwise in the drawing and a predetermined end on the endless belt 21b. A pressure roller 23b that forms a heat absorption nip portion N2 by contacting with pressure, a heat exchange member 25b that is inscribed in the endless belt 21b, and a heat absorption portion thermistor 60b that detects the surface temperature of the endless belt 21b are included. Flow paths 30a and 30b for circulating the working fluid of the heat pump 20 are connected to the heat exchange member 25b. The heat exchange member 25b also serves as a pressing member for forming the endothermic nip portion N2.

  The heat pump 20 imparts heat absorbed by the heat absorbing portion (evaporator) 8b to the fixing portion (condenser) 8a to increase heating efficiency. FIG. 5 is a TS diagram (a graph showing the relationship between temperature change and entropy change) showing the operation of the heat pump 20. The configuration and operation of the heat pump 20 will be described with reference to FIGS. 2 and 5. As shown in FIG. 2, the heat pump 20 includes an evaporator 8b, a compressor 33, a condenser 8a, and an expansion valve 37, and is a heat pump of a vapor compression refrigeration cycle that uses a refrigerant as a working fluid.

  The amount of heat Q2 absorbed by the heat absorbing unit 8b is supplied to the working fluid via the heat exchange member 25b. The evaporator (heat absorption part) 8b evaporates this working fluid to dry saturated steam A, and sends it to the compressor 33 via the flow path 30b. The compressor 33 compresses the working fluid (dry saturated steam A) evaporated by the evaporator 8b to a pressure equal to or higher than the saturated steam pressure with respect to a desired temperature in the condenser (fixing unit) 8a to form superheated saturated steam B. It sends to the condenser 8a via the path 30c. The superheated saturated steam B sent to the condenser 8a supplies (releases) the heat quantity Q1 to the endless belt 21a through the heat exchange member 25a. As a result, the working fluid is cooled and liquefied to become a saturated liquid C. This saturated liquid C is sent to the expansion valve 37 via the flow path 30d, isenthalpy-expanded by the expansion valve 37 to become wet steam D, and sent to the evaporator 8b via the flow path 30a, and the above-described thermal cycle is performed. repeat.

  By using this heat pump 20, heat absorbed from the sheet S is absorbed by the heat absorbing portion 8b, and heat is supplied to the fixing portion 8a having a temperature higher than that of the heat absorbing portion 8b, which is used for heating the endless belt 21a. Can do. Thereby, heating electric power can be reduced compared with the case where the endless belt 21a is heated using the heating means (halogen heater etc.) heated with electric power.

  The heat pump 20 used in the present invention connects the bypass flow path 30e to the flow path 30b that circulates the working fluid between the first heat absorbing portion 8b and the compressor 33, and the flow path 30b and the bypass flow path 30e The switching valve 29a is arranged at the connecting portion. Further, the bypass flow passage 30e is connected to a second heat absorbing portion 26 formed of a material having high thermal conductivity such as an aluminum alloy or a copper alloy. The bypass flow path 30e that has passed through the second heat absorption part 26 is connected to the flow path 30a that circulates the working fluid between the first heat absorption part 8b and the expansion valve 37, and the connection between the flow path 30a and the bypass flow path 30e. A switching valve 29b is arranged in the section.

  The second heat absorption part 26 has a large number of ribs 27 formed therein, and the working fluid circulating in the bypass flow path 30 e passes through a large number of gaps formed by the ribs 27. With this configuration, since the contact area between the second heat absorbing unit 26 and the working fluid is increased, heat exchange is efficiently performed between the second heat absorbing unit 26 and the working fluid. In addition, a large number of heat absorption fins 28 are formed on the surface of the second heat absorption portion 26 in order to increase the heat absorption efficiency from the outside air. Furthermore, a heat absorption effect may be enhanced by using a fan (not shown).

  The endless belts 21a and 21b have a plurality of layers including a base layer provided on the innermost side (heat exchange members 25a and 25b side) and a release layer provided on the outermost side (pressure rollers 23a and 23b side). It is an endless belt formed by lamination.

  As the base layer, a metal layer obtained by plating or rolling a metal such as nickel, or a synthetic resin layer such as a polyimide film is used. The release layer is made of a fluorine resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), and is formed by applying a paint or covering the tube. The release layer has a thickness of about 10 to 50 μm for a PFA tube and about 10 to 30 μm for a fluororesin paint.

  Further, a silicon rubber layer having a thickness of about 100 to 1000 μm may be provided as an elastic member layer between the base layer and the release layer. According to this configuration, the elastic member wraps the unfixed toner image on the paper and can be fixed softly. As a result, the image quality can be improved, and a high-performance fixing device can be obtained.

  By using the endless belt 21a having the above-described configuration, it is possible to reduce the heat capacity as compared with the configuration using the heating roller. As a result, high heating efficiency can be obtained, and the warm-up time until the surface of the endless belt 21a reaches a fixable temperature can be further shortened.

  In addition, a heat storage layer is provided between the base layer and the release layer of the endless belt 21a so that the heat obtained from the heat exchange member 25a is not released, and the surface temperature of the endless belt 21a is kept uniform. You can also. As a result, higher heating efficiency can be obtained, and the warm-up time can be shortened and the power consumption can be reduced.

  The heat storage layer is composed of silicon rubber having a high thermal conductivity, such as silica, alumina, magnesium oxide powder or the like, and a metal having a high thermal conductivity, such as aluminum, copper, nickel, etc. These are formed by covering or plating a tube-shaped product. The heat storage layer may be made of an elastic material such as silicon rubber. However, when it is made of metal, if the wall thickness is made too thick, the belt hardness increases, and the nip amount necessary to melt the toner is obtained. It will not be possible. Therefore, the thickness of the heat storage layer is 10 to 1000 μm, desirably 50 to 500 μm.

  Further, flange members (not shown) for holding the endless belts 21a, 21b in a certain shape (here, cylindrical) are fitted to both ends of the endless belts 21a, 21b in the width direction. The flange member is fixed in the fixing device 8, and the endless belts 21a and 21b slide along the outer peripheral surface of the flange member.

  Further, a fixing portion thermistor 60a and a heat absorbing portion thermistor 60b (see FIGS. 3 and 4) are provided so as to be in contact with the surfaces of the endless belts 21a and 21b. The fixing section thermistor 60a and the heat absorbing section thermistor 60b detect the temperature of the endless belts 21a and 21b, and control the fixing temperature by controlling ON / OFF of the heat pump 20, and also operate the switching valves 29a and 29b. Then, the circulation path of the working fluid circulating in the heat pump 20 is switched. Details of the control procedure will be described later.

  The pressure rollers 23a and 23b are provided with an elastic layer made of sponge silicon rubber or the like on the outside of a metal shaft made of stainless steel or the like. The pressure rollers 23a and 23b are brought into contact with the heat exchange members 25a and 25b through the endless belts 21a and 21b with a predetermined pressure, thereby forming a fixing nip portion N1 and a heat absorption nip portion N2 through which the paper S is inserted. . The pressure rollers 23a and 23b are rotationally driven by a drive motor and a drive gear (both not shown) so that the peripheral speed thereof is substantially the same as the paper transport speed. In the fixing nip portion N1 and the heat absorption nip portion N2, the endless belts 21a and 21b that are in contact with the pressure rollers 23a and 23b are driven by the pressure rollers 23a and 23b, respectively, and rotate at substantially the same speed as the sheet conveyance speed. To do.

  The heat exchange members 25a and 25b are preferably formed of a material having high thermal conductivity such as an aluminum alloy or a copper alloy. Thereby, the heat conductivity of the heat exchange members 25a and 25b is improved, and the heat of the working fluid is efficiently transmitted to the endless belt 21a, so that the warm-up time of the fixing device 8 can be shortened. In addition, a large number of ribs 27 are formed in the heat exchange members 25a and 25b in the pressure contact direction (in this case, the vertical direction) of the pressure rollers 23a and 23b.

  FIG. 6 is a plan view of the heat exchange member 25a. As shown in FIG. 6, flow paths 30 c and 30 d are connected to both ends of the heat exchange member 25 a, and the working fluid circulating in the flow paths 30 c and 30 d passes through a large number of gaps formed by the ribs 27. To do. With this configuration, the contact area between the heat exchange member 25a and the working fluid is increased, so that heat is efficiently exchanged between the heat exchange member 25a and the working fluid.

  Further, since the rib 27 is formed in the pressure contact direction of the pressure roller 23a, the strength of the heat exchange member 25a is also improved. The heat capacity can be reduced by reducing the thickness of 25a.

  Furthermore, by adopting a belt fixing system in which only the endless belt 21a rotates, the heat exchange member 25a can be used as a fixed member. Thereby, the leakage of the working fluid at the connecting portion between the heat exchange member 25a and the flow paths 30c and 30d can be easily and reliably prevented. Although the configuration of the heat exchange member 25a disposed in the fixing unit 8a has been described here, the configuration of the heat exchange member 25b disposed in the heat absorption unit 8b is exactly the same.

  Next, the control path of the image forming apparatus of the present invention will be described. FIG. 7 is a block diagram illustrating an example of a control path used in the image forming apparatus according to the first embodiment. It should be noted that since various control of each part of the apparatus is performed when the printer 100 is used, the control path of the entire printer 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a read / write storage unit, A plurality of (two in this case) I's for transmitting a control signal to each device in the temporary storage unit 94, the counter 95, and the printer 100 for storing image data and the like and receiving an input signal from the operation unit 50. / F (interface) 96 is provided at least. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores a control program for the printer 100, data necessary for control, and the like that are not changed during use of the printer 100. The RAM 93 stores necessary data generated during the control of the printer 100, data temporarily required for the control of the printer 100, and the like. The counter 95 adds up the number of printed sheets and counts it.

  The control unit 90 transmits a control signal from the CPU 91 to the respective units and devices in the printer 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. Examples of each part and device controlled by the control unit 90 include the image forming unit P, the fixing device 8, the heat pump 20, the image input unit 40, the power supply unit 41, and the operation unit 50.

  The image input unit 40 is a receiving unit that receives image data transmitted from the personal computer or the like to the printer 100. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The power supply unit 41 supplies predetermined power to each part of the apparatus including the heat pump 20 by an output signal from the control unit 90.

  The operation unit 50 is provided with a liquid crystal display unit, LEDs indicating various states, and the like, and displays the state of the printer 100 and displays the image forming status and the number of copies to be printed. Various settings of the printer 100 are performed from a printer driver of a personal computer.

  In addition, the operation unit 50 is provided with a stop / clear button used when image formation is stopped, a reset button used when various settings of the printer 100 are set to a default state, and the like.

  FIG. 8 is a flowchart illustrating an example of drive control of the fixing device in the image forming apparatus according to the first embodiment. The heating procedure of the fixing device in the image forming apparatus according to the first embodiment will be described along the steps of FIG. 8 with reference to FIGS.

  When a print command is input from the personal computer or the like to the control unit 90 (step S1), the CPU 91 detects the surface temperature T2 of the endless belt 21b of the first heat absorbing unit 8b by the heat absorbing unit thermistor 60b, and the detected surface temperature T2 is detected. Is judged whether or not the outside air temperature T0 or less (step S2). When the surface temperature T2 is equal to or lower than T0, a control signal is transmitted from the CPU 91 to the switching valves 29a and 29b, and as shown by hatching in FIG. 9, the second heat absorbing section 26 and the compressor 33 are passed through the bypass flow path 30e. And a path (hereinafter referred to as a second circulation path) through which the working fluid circulates between the expansion valve 37 and the expansion valve 37 (step S3).

  On the other hand, when the surface temperature T2 is equal to or lower than T0, as shown by hatching in FIG. 10, the working fluid flows between the first heat absorbing portion 8b, the compressor 33, and the expansion valve 37 via the flow paths 30a and 30b. A circulation path (hereinafter referred to as a first circulation path) is used (step S4).

  Next, a control signal is transmitted from the CPU 91 to the power supply unit 41 to supply power to the heat pump 20 (step S5). Then, the surface temperature T1 of the endless belt 21a is detected by the fixing unit thermistor 60a of the fixing unit 8a, and when the predetermined fixing possible temperature Ts is reached, paper passing (printing) is started (step S6).

  Thereafter, it is confirmed whether the first circulation path or the second circulation path is used (step S7). If the second circulation path is used, it is determined whether or not the surface temperature T2 exceeds T0. (Step S8), when T2> T0, the switching valves 29a and 29b are operated to switch to the first circulation path (Step S9). When the first circulation path is used, the sheet passing is continued without operating the switching valves 29a and 29b.

  Then, it is determined whether or not the paper has been passed (step S10). If the paper has been passed, the power supply to the heat pump 20 is turned off (step S11), and the process is finished. If the paper continues, the process returns to step S7, and the same control is performed thereafter (steps S7 to S10).

  According to the above control, when the surface temperature of the endless belt 21b of the first heat absorbing unit 8b is equal to or lower than the outside air temperature when the heat pump 20 is started, the working fluid of the heat pump 20 circulates through the second heat absorbing unit 26. Since two circulation paths are used, heat is not taken away from the first heat absorbing portion 8b. As a result, it is possible to prevent overcooling of the first heat absorbing portion 8b during warm-up, and to effectively suppress the occurrence of condensation in the first heat absorbing portion 8b.

  Further, when the fixing unit 8a is heated up to a fixing possible temperature and the sheet passing is started and the surface temperature of the endless belt 21b becomes higher than the outside air temperature, the switching valve 29a, 29b causes the first through the second circulation path. Switch to the circulation path. As a result, the amount of heat of the sheet S collected in the first heat absorbing unit 8b can be fed back to the fixing unit 8a and used for heating the fixing unit 8a. Furthermore, when the endless belt 21b has been warmed in advance by the immediately preceding printing operation, the heat of the first heat absorbing portion 8b can be recovered by using the first circulation path from the time when the heat pump 20 is started.

  During the use of the second circulation path, heat is taken from the second heat absorption part 26, and the second heat absorption part 26 is supercooled. For this reason, condensation may occur on the surface of the second heat absorbing portion 26 during warm-up, but the second heat absorbing portion 26 is disposed outside the paper transport path, and the transported paper S may get wet due to condensation. There is no.

  Here, it is difficult to completely recover the amount of heat applied to the paper S in the fixing unit 8a by the first heat absorbing unit 8b, and a part of the heat remains in the paper S, or the paper transport path 11 and the heating unit 8b. The process proceeds to the pressure roller 23b and the like. In order to improve the heating efficiency of the fixing unit 8a by collecting as much heat as possible by the first heat absorption unit 8b, the length of the heat absorption nip N2 in the circumferential direction of the endless belt 21b is set to the circumferential direction of the endless belt 21a. It is preferable that the heat absorption efficiency at the heat absorbing portion 8b be as high as possible by making it larger than the fixing nip portion N1.

  Further, since the heat capacity of the paper changes depending on the thickness and type of the paper, the length of the heat absorption nip portion N2 in the circumferential direction of the endless belt 21b set for each paper type is stored in the ROM 92 (or RAM 93) in advance. It is preferable to select an optimal length according to the type of paper to be used. The length of the heat absorption nip N2 can be adjusted by the pressure contact force of the pressure roller 23b and the rubber hardness.

  Note that the control in FIG. 8 is an example, and the present invention is not limited to this. For example, in the control of FIG. 8, the switching from the second circulation path to the first circulation path is performed when the surface temperature T2 exceeds T0. However, the fixing unit 8a rises to a fixable temperature, and paper feeding is started. The timing and the timing at which the temperature of the first heat absorbing unit 8b rises are considered to be almost simultaneous. Therefore, when the sheet passing is started or when the surface temperature of the endless belt 21a of the fixing unit 8a rises to a predetermined fixable temperature, the circulation path is switched from the second circulation path to the first circulation path. Also good.

  FIG. 11 is a schematic cross-sectional view illustrating a configuration of a fixing unit of a fixing device mounted on an image forming apparatus according to a second embodiment of the present invention. The fixing unit 8a of this embodiment includes a heater 70 disposed between the endless belt 21a and the heat exchange member 25a. The other parts of the fixing unit 8a are the same as those of the fixing unit 8a of the first embodiment shown in FIG. 3, and the configurations of the first heat absorption unit 8b, the heat pump 20, the second heat absorption unit 26, and the like are also shown in FIG. The description is omitted because it is the same as the first embodiment shown.

  The heater 70 extends between the heat exchange member 25a and the endless belt 21a over almost the entire region in the longitudinal direction (the paper surface direction in the figure). As the heater 70, a planar heater such as a ceramic heater that efficiently radiates infrared rays, a halogen heater, or the like is used. Note that other heating means other than the heater 70 may be used. For example, there is a method in which an electromagnetic induction coil for heating an endless belt 21a made of metal such as stainless steel or nickel by an electromagnetic induction method is disposed around the endless belt.

  For example, by energizing the heater 70 when the heat pump 20 is started, the fixing unit 8a can be quickly heated to a fixable temperature, and the warm-up time of the printer 100 can be shortened. Further, when passing a sheet having a large heat capacity such as a thick sheet, the amount of heat released from the fixing unit 8a increases, and the temperature of the fixing unit 8a rapidly decreases. Therefore, the temperature control becomes unstable only with the heat pump 20. In such a case, the heater 70 may be used as auxiliary heating means even after the start of paper feeding.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the one-stage compression heat pump 20 shown in FIG. 2 is used, but a two-stage compression system in which two compressors are provided, or a two-stage compression system in which two compressors and two expansion valves are provided. A compression two-stage expansion heat pump can also be used.

  The fixing device of the present invention is not limited to the monochrome printer as shown in FIG. 1, and various image formations using an electrophotographic process such as a digital multifunction peripheral, a tandem color copying machine, a color printer, or a facsimile. Applicable to equipment.

  The temperature of the fixing unit 8a of the monochrome printer 100 shown in FIG. 1 provided with the fixing device 8 and the heat pump 20 shown in FIG. Was set to 10 mm, the nip width of the endothermic nip portion N2 was set to 15 mm, and the sheet feeding speed was set to 200 mm / sec. Under this condition, when the heat pump is started, the second circulation path is used, and when the surface temperature of the endless belt 21b exceeds the outside air temperature, the second circulation path is switched to the first circulation path (the present invention). The occurrence of condensation on the surface of the endless belt 21b was compared with the case where only the first circulation path was used from the start of the heat pump (comparative example).

  As a result, in the present invention in which the circulation path is switched, no condensation occurs on the surface of the endless belt 21b, and the sheet that has passed through the endothermic nip portion N2 does not get wet. In contrast, in the comparative example in which the switching of the circulation path was not performed, dew condensation occurred on the surface of the endless belt 21b immediately after the heat pump 20 was started, and water droplets adhered to the paper that passed through the heat absorption nip portion N2. Further, when the operation of the heat pump was continued as it was, the heat exchange member 25b was frozen, and the heat exchange performance in the heat absorbing portion 8b was significantly lowered.

  The present invention is applicable to an image forming apparatus that heats a fixing device using a heat radiating portion of a heat conversion device having a heat pump function and cools a recording medium heated using a heat absorption portion of the heat conversion device, A first heat absorption unit that cools the recording medium as a heat absorption unit of the heat pump and a second heat absorption unit arranged outside the conveyance path of the recording medium are provided, and the temperature of the first heat absorption unit is detected when the heat pump is activated. Depending on the result, either the first heat absorbing part or the second heat absorbing part is selected as the working fluid circulation path of the heat pump to circulate the working fluid, and when the second heat absorbing part is selected, the conveyance of the recording medium is started. After that, the circulation path of the working fluid is switched to the first heat absorption part.

  Accordingly, it is possible to provide an image forming apparatus that can prevent overcooling of the first heat absorption unit when the heat pump is started and can prevent the occurrence of condensation in the first heat absorption unit at a low cost.

8 Fixing device 8a Fixing part (condenser)
8b 1st heat absorption part (evaporator)
20 heat pump 21a, 21b endless belt 23a, 23b pressure roller 25a, 25b heat exchange member 26 second heat absorption part 27 rib 29a, 29b switching valve 30a-30d flow path 30e bypass flow path 33 compressor 37 expansion valve 41 power supply 60a Fixing section thermistor (fixing section temperature sensor)
60b Endothermic Thermistor (Endothermic Temperature Sensor)
70 Heater (heating member)
90 Control unit (control means)
100 Printer N1 Fixing nip N2 Heat absorption nip

Claims (12)

A fixing unit that heats and pressurizes a recording medium carrying an unfixed toner image, and a first heat absorbing unit that is disposed downstream of the fixing unit in the recording medium conveyance direction and absorbs heat of the recording medium that has passed through the fixing unit. A fixing device comprising:
A heat pump that includes the fixing unit and the first heat absorbing unit, and moves and dissipates the heat absorbed by the first heat absorbing unit to the fixing unit by circulation of a working fluid;
Control means for controlling the drive of the heat pump;
In an image forming apparatus comprising:
The heat pump includes: a second heat absorption unit disposed outside a recording medium conveyance path; and a switching valve that circulates a working fluid in either the second heat absorption unit or the first heat absorption unit. An endothermic temperature sensor for detecting the temperature of one endothermic unit is provided,
The control means selects either the first heat absorption part or the second heat absorption part according to the temperature of the first heat absorption part detected by the heat absorption part temperature sensor at the start of driving of the heat pump. The image forming apparatus is characterized in that when the second heat absorbing portion is selected, the circulation path of the working fluid is switched to the first heat absorbing portion after the conveyance of the recording medium is started.   A fixing unit temperature sensor for detecting a temperature of the fixing unit is provided, and the control unit switches a circulation path of the working fluid to the first heat absorption unit based on a temperature detected by the fixing unit temperature sensor. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the control unit switches a circulation path of the working fluid to the first heat absorption unit based on a temperature detected by the heat absorption unit temperature sensor.   The control means selects the second heat absorption part to circulate the working fluid when the detection temperature of the heat absorption part temperature sensor at the start of driving of the heat pump is equal to or lower than the environmental temperature, and detects the heat absorption part temperature sensor. 4. The image forming apparatus according to claim 1, wherein when the temperature exceeds an environmental temperature, the first heat absorption unit is selected to circulate the working fluid. 5.   5. A heating member for heating the fixing unit is provided, and the control unit controls the temperature of the fixing unit by using the heat pump and the heating member in combination. The image forming apparatus according to any one of the above.   The fixing unit and the first heat absorbing unit are connected to an endless belt that can be rotated at a substantially constant speed with respect to the conveyance speed of the recording medium, and a flow path that is inscribed in the endless belt and circulates the working fluid of the heat pump. And a pressure roller that forms a nip portion through which a recording medium is inserted by contacting the heat exchange member with a predetermined pressure via the endless belt. The image forming apparatus according to claim 5.   A circulation path through which the working fluid of the heat pump passes is formed inside the heat exchange member, and a plurality of ribs are provided in the circulation path along the flow direction of the working fluid. The image forming apparatus according to claim 6.   The image forming apparatus according to claim 7, wherein the rib is formed so as to penetrate the inside of the heat exchange member in a pressure contact direction of the pressure roller.   The nip width in the belt circumferential direction of the endothermic nip portion formed in the heat absorbing portion is larger than the nip width in the belt circumferential direction of the fixing nip portion formed in the fixing portion. The image forming apparatus according to claim 8.   The image forming apparatus according to claim 9, wherein a nip width in the belt circumferential direction of the endothermic nip portion is changed according to a type of the recording medium.   The heating member that heats the endless belt is provided with a heater that is disposed between the endless belt and the heat exchange member and that contacts the entire width direction of the endless belt. The image forming apparatus according to claim 10.   The endless belt is a belt made of metal or having a metal thin film layer, and an electromagnetic induction coil for heating the endless belt by electromagnetic induction is provided as a heating member for heating the endless belt. The image forming apparatus according to claim 6.

Images