Heating device and image forming apparatus

Abstract

To provide a device that, even when switching a heating element supplying power by using a contact switch, prevents radiation of electromagnetic noise due to arc discharge during the operation of a contact switch, and prevents the occurrence of shortening of its life due to contact wear.SOLUTION: A heating device comprises: a substrate 54a; a heating element 54b1; heating elements 54b2, 54b3; a first triac 56a for turning on / off the supply of power to the heating element 54b1; a triac 56b for turning on / off the supply of power to the heating element 54b2 or the heating element 54b3; and an electromagnetic relay 57c having a contact 57c1 connected to one ends of the heating element 54b2 and heating element 54b3, a contact 57c3 connected to the other end of the heating element 54b2, and a contact 57c2 connected to the other end of the heating element 54b3, connects the contact 57c1 and the contact 57c3 to each other when supplying power to the heating element 54b2, and connects the contact 57c1 and the contact 57c2 to each other when supplying power to the heating element 54b3.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a heating device and an image forming apparatus, and more particularly to a fixing heater used in an image forming apparatus and a control circuit for controlling the fixing heater. [Background technology]

[0002] In a heating device using a ceramic heater as a heat source, when recording paper (hereinafter referred to as small-size paper) having a width shorter than the length of the heating element is conveyed, the following phenomenon is known to occur: That is, a phenomenon in which the temperature in the heating area of ​​the heating element, which is also a non-paper-passing area, becomes higher than that in the paper-passing area (hereinafter referred to as non-paper-passing area heating). The heating area refers to the area where the heating element generates heat. The non-paper-passing area refers to the area of ​​the heating area that does not come into contact with small-size paper. The paper-passing area refers to the area of ​​the heating area that comes into contact with small-size paper. Non-paper-passing area heating is also called edge heating. If the temperature rise due to non-paper-passing area heating becomes too large, it may damage surrounding components, such as the components supporting the ceramic heater. Therefore, many heating devices and image forming apparatuses have been proposed that include multiple heating elements of different lengths and selectively use a heating element with a length corresponding to the width of the recording paper to reduce the temperature rise in the non-paper-passing area. For example, Patent Document 1 discloses that the electrodes of at least some of the heating elements that are provided on an insulating substrate and can be driven independently are made common, thereby making effective use of the substrate. It has also been proposed to make the number of electrodes provided on both ends of the substrate the same, thereby making it possible to commonize the connectors connected to the ends and to make the heat distribution in the longitudinal direction of the ceramic heater uniform. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-100558 Summary of the Invention [Problem to be solved by the invention]

[0004] The prior art describes a configuration in which a contact switch (an electromagnetic relay with a contact c configuration) switches between heating elements to which power is supplied. When an electromagnetic relay with a contact c configuration is operated in the prior art configuration, an arc discharge occurs between the relay contacts. Normally, when an electromagnetic relay is operated, power supply to the heating element is stopped (the triac is in a non-conducting state). In the prior art configuration, a potential difference exists between the contacts of the electromagnetic relay in this state, causing an arc current to flow through the capacitance components at both ends of the triac (such as stray capacitance of the wiring pattern and noise suppression components placed at both ends of the triac). Arc discharge between the contacts of an electromagnetic relay can radiate electromagnetic noise, causing EMI issues and potentially causing malfunctions in the circuits surrounding the electromagnetic relay. Furthermore, arc discharge between the contacts of an electromagnetic relay can cause contact wear, shortening the life of the electromagnetic relay and, ultimately, the life of the device.

[0005] The present invention was made under these circumstances, and aims to provide a device that does not emit electromagnetic noise due to arc discharge when the contact switch is operated, even when switching the heating element to which power is supplied using the contact switch, and does not suffer from reduced lifespan due to contact wear. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) A heating device comprising: a substrate; a first heating element; second and third heating elements whose longitudinal lengths in the substrate are shorter than that of the first heating element; a first triac for turning on / off the supply of power to the first heating element; a second triac for turning on / off the supply of power to the second heating element or the third heating element; and a contact switch having first contacts connected to one end sides of the second heating element and the third heating element, a second contact connected to the other end side of the second heating element, and a third contact connected to the other end side of the third heating element, which connects the first contact and the third contact when power is supplied to the second heating element, and connects the first contact and the second contact when power is supplied to the third heating element.

[0008] (2) An image forming apparatus comprising: an image forming means for forming an image on a recording material; and the heating device according to (1) above for heating the image formed on the recording material. [Effects of the Invention]

[0009] According to the present invention, even when a contact switch is used to switch the heating element to which power is supplied, a device can be provided in which electromagnetic noise due to arc discharge is not emitted when the contact switch is operated, and the lifespan is not reduced due to contact wear. [Brief explanation of the drawings]

[0010] [Figure 1] Overall configuration diagram of the image forming apparatus according to the first to fourth embodiments [Figure 2] Control block diagram of an image forming apparatus according to first to fourth embodiments [Figure 3] Schematic cross-sectional view of the fixing device of Examples 1 to 4 near the center in the longitudinal direction [Figure 4] FIG. 1 is a diagram showing a heater and a heater control circuit according to a first embodiment. [Figure 5] FIG. 1 is a diagram showing a current path of a heater and a heater control circuit according to a first embodiment. [Figure 6] FIG. 10 is a diagram showing a heater and a heater control circuit according to a second embodiment. [Figure 7]FIG. 10 is a diagram showing a current path of a heater and a heater control circuit according to a second embodiment. [Figure 8] FIG. 10 is a diagram showing a heater and a heater control circuit according to a third embodiment. [Figure 9] FIG. 10 is a diagram showing a current path of a heater and a heater control circuit according to a third embodiment. [Figure 10] FIG. 10 is a diagram showing a heater and a heater control circuit according to a fourth embodiment. [Figure 11] FIG. 10 is a diagram showing a current path of a heater and a heater control circuit according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described with reference to the drawings. [Example]

[0012] In the following example, when there are three heating elements and three power supply paths to be switched, a contact switch is used to switch one of the power supply paths. A configuration will be described in which, even when the power supply path is switched using a contact switch, electromagnetic noise caused by arc discharge is not emitted when the contact switch is operated, and there is no reduction in lifespan due to contact wear. In addition, in a heating device having three or more systems of heating elements, the number of electrodes (hereinafter referred to as the first to fourth contacts) provided at both ends of the substrate is made the same, thereby enabling the connectors connected to both ends of the substrate to be standardized and achieving uniform heat distribution in the longitudinal direction of the ceramic heater.

[0013] [Overall configuration] FIG. 1 is a structural diagram showing an in-line color image forming apparatus, which is an example of an image forming apparatus equipped with the fixing device of the first embodiment. The operation of the electrophotographic color image forming apparatus will be described using FIG. 1. The first station is a station for forming a yellow (Y) toner image, and the second station is a station for forming a magenta (M) toner image. The third station is a station for forming a cyan (C) toner image, and the fourth station is a station for forming a black (K) toner image.

[0014] In the first station, the photosensitive drum 1a, which serves as an image carrier, is an OPC photosensitive drum. The photosensitive drum 1a is a metal cylinder with multiple layers of functional organic materials, including a carrier generation layer that generates charge upon photosensitivity and a charge transport layer that transports the generated charge. The outermost layer has low electrical conductivity and is nearly insulating. A charging roller 2a, which serves as a charging means, contacts the photosensitive drum 1a and rotates as the photosensitive drum 1a rotates, uniformly charging the surface of the photosensitive drum 1a. A DC voltage or a superimposed AC voltage is applied to the charging roller 2a, and discharge occurs in the small air gaps upstream and downstream of the nip between the charging roller 2a and the surface of the photosensitive drum 1a in the direction of rotation, thereby charging the photosensitive drum 1a. A cleaning unit 3a cleans toner remaining on the photosensitive drum 1a after transfer, as described below. A developing unit 8a, which serves as a developing means, consists of a developing roller 4a, a non-magnetic single-component toner 5a, and a developer application blade 7a. The photosensitive drum 1a, the charging roller 2a, the cleaning unit 3a, and the developing unit 8a are integrated into a process cartridge 9a that is detachably mounted on the image forming apparatus.

[0015] The exposure device 11a, which serves as an exposure means, is composed of a scanner unit or an LED (light-emitting diode) array that scans laser light using a polygonal mirror, and irradiates the photosensitive drum 1a with a scanning beam 12a modulated based on an image signal. The charging roller 2a is connected to a charging high-voltage power supply 20a, which supplies voltage to the charging roller 2a. The developing roller 4a is connected to a developing high-voltage power supply 21a, which supplies voltage to the developing roller 4a. The primary transfer roller 10a is connected to a primary transfer high-voltage power supply 22a, which supplies voltage to the primary transfer roller 10a. The above describes the configuration of the first station, and the second, third, and fourth stations have similar configurations. Components of the other stations that have the same functions as those of the first station are designated by the same reference numerals, with the suffixes b, c, and d added to the reference numerals for each station. In the following description, the suffixes a, b, c, and d will be omitted except when describing a specific station.

[0016] The intermediate transfer belt 13 is supported by three rollers that serve as tensioning members: a secondary transfer opposing roller 15, a tension roller 14, and an auxiliary roller 19. Only the tension roller 14 is subjected to a spring force in the direction of tensioning the intermediate transfer belt 13, so that an appropriate tension is maintained on the intermediate transfer belt 13. The secondary transfer opposing roller 15 rotates by receiving rotational drive from a main motor (not shown), causing the intermediate transfer belt 13 wound around its periphery to rotate. The intermediate transfer belt 13 moves in the forward direction (e.g., clockwise in FIG. 1) relative to the photosensitive drums 1a-1d (e.g., counterclockwise in FIG. 1) at approximately the same speed. The intermediate transfer belt 13 also rotates in the direction indicated by the arrow (clockwise), and the primary transfer roller 10 is located on the opposite side of the intermediate transfer belt 13 from the photosensitive drum 1 and rotates in response to the movement of the intermediate transfer belt 13. The position where the photosensitive drum 1 and primary transfer roller 10 are in contact with each other across the intermediate transfer belt 13 is called the primary transfer position. The auxiliary roller 19, tension roller 14, and secondary transfer opposing roller 15 are electrically grounded. Note that the primary transfer rollers 10b to 10d of the second to fourth stations have the same configuration as the primary transfer roller 10a of the first station, so a description thereof will be omitted.

[0017] Next, the image forming operation of the image forming apparatus of the first embodiment will be described. When the image forming apparatus receives a print command while in standby mode, it starts the image forming operation. The photosensitive drum 1, intermediate transfer belt 13, etc. begin to rotate in the direction of the arrow at a predetermined process speed driven by a main motor (not shown). The photosensitive drum 1a is uniformly charged by a charging roller 2a to which a voltage is applied from a charging high-voltage power supply 20a. Then, an electrostatic latent image according to image information is formed by a scanning beam 12a irradiated from an exposure device 11a. The toner 5a in the developing unit 8a is negatively charged by a developer application blade 7a and applied to the developing roller 4a. A predetermined developing voltage is then supplied to the developing roller 4a from a developing high-voltage power supply 21a. When the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the developing roller 4a, the electrostatic latent image is visualized by the adhesion of negative toner, and a toner image of a first color (e.g., Y (yellow)) is formed on the photosensitive drum 1a. The stations (process cartridges 9b-9d) for the other colors M (magenta), C (cyan), and K (black) operate in the same way. Electrostatic latent images are formed on the photosensitive drums 1a-1d by exposure, while the write start signal from the controller (not shown) is delayed at a fixed timing according to the distance between the primary transfer positions of each color. A high DC voltage of opposite polarity to the toner is applied to each of the primary transfer rollers 10a-10d. Through the above process, the toner images are transferred sequentially to the intermediate transfer belt 13 (hereinafter referred to as primary transfer), and a multiple toner image is formed on the intermediate transfer belt 13.

[0018] Thereafter, in synchronization with the formation of the toner image, paper P, which is a recording material loaded in cassette 16, is fed (picked up) by paper feed roller 17, which is driven to rotate by a paper feed solenoid (not shown). The fed paper P is transported by a transport roller to registration rollers (hereinafter referred to as registration rollers) 18. Synchronized with the toner image on intermediate transfer belt 13, paper P is transported by registration rollers 18 to a transfer nip, which is the contact point between intermediate transfer belt 13 and secondary transfer roller 25. A voltage of opposite polarity to that of the toner is applied to secondary transfer roller 25 by secondary transfer high-voltage power supply 26, and the four-color multi-layered toner image carried on intermediate transfer belt 13 is transferred simultaneously onto paper P (recording material) (hereinafter referred to as secondary transfer). Components (e.g., photosensitive drum 1, etc.) that contributed to the formation of the unfixed toner image on paper P function as image forming means. Meanwhile, after the secondary transfer is completed, a cleaning unit 27 cleans any remaining toner on intermediate transfer belt 13. After the secondary transfer is completed, the paper P is transported to the fixing device 50, which is a fixing means, where the toner image is fixed and the paper P is discharged to the discharge tray 30 as an image-formed product (print, copy). The fixing device 50 corresponds to the heating device of the present invention. The film 51, nip forming member 52, pressure roller 53, and heater 54 of the fixing device 50 will be described later.

[0019] [Block diagram of image forming device] 2 is a block diagram illustrating the operation of the image forming apparatus, and the printing operation of the image forming apparatus will be explained with reference to this diagram. The host computer PC 110 outputs print commands to a video controller 91 inside the image forming apparatus and transfers image data of the print image to the video controller 91.

[0020] The video controller 91 converts image data from the PC 110 into exposure data and transfers it to an exposure control device 93 in the engine controller 92. The exposure control device 93 is controlled by a CPU 94, and turns the exposure data on and off and controls the exposure device 11. When the CPU 94, which is the control means, receives a print command, it starts the image formation sequence.

[0021] The engine controller 92 is equipped with a CPU 94, a memory 95, and other components, and performs pre-programmed operations. The high-voltage power supply 96 is composed of the charging high-voltage power supply 20, the developing high-voltage power supply 21, the primary transfer high-voltage power supply 22, and the secondary transfer high-voltage power supply 26. The power control unit 97 is composed of a bidirectional thyristor (hereinafter referred to as a triac) 56 and a heating element switch 57 that switches the heating element to which power is supplied. The power control unit 97 selects the heating element that generates heat in the fixing device 50 and determines the amount of power to supply. The drive unit 98 is composed of a main motor 99, a fixing motor 100, and other components. The sensor 101 is composed of a fixing temperature sensor 59 that detects the temperature of the fixing device 50, a paper presence sensor 102 that has a flag and detects the presence or absence of paper P, and other components. The detection results of the sensor 101 are sent to the CPU 94. The CPU 94 obtains the detection results of the sensor 101 within the image forming apparatus and controls the exposure device 11, the high-voltage power supply 96, the power control unit 97, and the drive unit 98. As a result, the CPU 94 performs processes such as forming an electrostatic latent image, transferring the developed toner image, and fixing the toner image to the paper P, thereby controlling the image forming process in which the exposure data is printed as a toner image on the paper P. Note that the image forming apparatus to which the present invention is applied is not limited to the image forming apparatus with the configuration described in FIG. 1, but may be any image forming apparatus that is capable of printing on paper P of different widths and that includes a fixing device 50 having a heater 54, which will be described later.

[0022] [Fixing device] Next, the configuration of the fixing device 50 in the first embodiment will be described with reference to Fig. 3. Here, the longitudinal direction refers to the direction of the rotation axis of the pressure roller 53, which is approximately perpendicular to the transport direction of the paper P, which will be described later. The length of the paper P in the direction (longitudinal direction) approximately perpendicular to the transport direction is called the width. Fig. 3 is a cross-sectional schematic diagram of the fixing device 50.

[0023] 3, a sheet of paper P carrying an unfixed toner image Tn is heated while being transported from left to right in the figure in the fixing nip N, thereby fixing the toner image Tn to the sheet of paper P. The fixing device 50 in the first embodiment is composed of a cylindrical film 51, a nip forming member 52 that holds the film 51, a pressure roller 53 that forms the fixing nip N together with the film 51, and a heater 54 for heating the sheet of paper P.

[0024] The film 51, which is the first rotating body, is a fixing film that functions as a heating rotating body. In Example 1, for example, polyimide is used as the base layer. An elastic layer made of silicone rubber and a release layer made of PFA are used on the base layer. Grease is applied to the inner surface of the film 51 to reduce the frictional force generated between the film 51 and the nip forming member 52 and heater 54 due to the rotation of the film 51.

[0025] The nip forming member 52 guides the film 51 from the inside and forms a fixing nip N between the film 51 and the pressure roller 53 via the film 51. The nip forming member 52 is a rigid, heat-resistant, and heat-insulating member made of a liquid crystal polymer or the like. The film 51 is fitted onto the outside of the nip forming member 52. The pressure roller 53, which is the second rotating member, is a roller that functions as a pressure rotating member. The pressure roller 53 is composed of a core metal 53a, an elastic layer 53b, and a release layer 53c. The pressure roller 53 is rotatably supported at both ends and is driven to rotate by a fixing motor 100 (see FIG. 2). The film 51 is rotated by the rotation of the pressure roller 53. The heater 54, which is a heating member, is supported by the nip forming member 52 and is in contact with the inner surface of the film 51. A fixing temperature sensor 59 detects the temperature of the heater 54. The heater 54 will be described later.

[0026] [Heater and heater control circuit] FIG. 4 shows a heater and a power control unit 97, which is a heater control circuit, used in the heating device of Example 1. FIG. 4(a) shows the heater 54 and the power control unit 97 used in Example 1, and FIG. 4(b) shows a p-p' cross section of the heater 54. The heater 54 is composed of heating elements 54b1-54b3, contacts 54d1-54d4, and a protective glass layer 54e, such as insulating glass, mounted on a substrate 54a made mainly of ceramic or the like. The heating elements 54b1-54b3 are resistors that generate heat when supplied with power from an AC power source 55, such as a commercial AC power source. The contacts 54d1 and 54d2 are provided at one end of the substrate 54a in the longitudinal direction, and the contacts 54d3 and 54d4 are provided at the other end of the substrate 54a in the longitudinal direction. In this way, the number of contacts (electrodes) provided at both ends of the substrate 54a is the same, for example, two each. The protective glass layer 54e is provided to insulate the user from the heating elements 54b1 to 54b3, which are at approximately the same potential as the AC power supply 55.

[0027] The first heating element, heating element 54b1, is a heating element that is primarily used when fixing toner to paper P having the widest width among the paper sheets P that can be transported in the heating device. Here, the width refers to a direction substantially perpendicular to the transport direction of the paper P and is also the longitudinal direction of the heater 54. Therefore, the longitudinal length (dimension) of heating element 54b1 is set to be several millimeters longer than the width of a letter-size sheet, 215.9 mm. As shown in FIG. 4, two heating elements 54b1 are arranged on either side of substrate 54a, upstream and downstream in the transport direction of paper P (the vertical direction in FIG. 4(a)), sandwiching heating elements 54b2 and 54b3. In the longitudinal direction of substrate 54a, heating elements 54b2 and 54b3 are arranged within the area of ​​heating element 54b1. Heating element 54b1 is also the heating element that is primarily used when the heating device is started (i.e., when the temperature of the heating device is raised from a cold state (a state where the temperature is approximately the same as room temperature) to a predetermined temperature). For this reason, heating element 54b1 is designed to be able to supply the power required when the heating device is started. Heating element 54b1 is connected to contact 54d1, which is the first contact, and contact 54d4, which is the fourth contact.

[0028] The second heating element, 54b2, corresponds to the width of the B5 size, and its longitudinal length is set to be several millimeters longer than the 182 mm width of the B5 size. The heating element 54b2 is connected to the second contacts, 54d2 and 54d4. The third heating element, 54b3, corresponds to the width of the A5 size, and its longitudinal length is set to be several millimeters longer than the 148 mm width of the A5 size. The heating element 54b3 is connected to the contact 54d2 and the third contact, 54d3.

[0029] Heating elements 54b2 and 54b3 are designed to be used when the heating device is already warmed up to a certain extent, and the rated power of heating elements 54b2 and 54b3 is set lower than the rated power of heating element 54b1. In other words, heating element 54b1 is positioned as the main heater, and heating elements 54b2 and 54b3 are positioned as sub-heaters. Therefore, the main heater (heating element 54b1) and sub-heaters (heating elements 54b2 and 54b3) are switched between for use, mainly during startup or load fluctuations. In addition, heater 54 is equipped with three systems of heating elements 54b1 to 54b3, each with a different length in the width direction of paper P. This aims to suppress temperature rise in non-paper passing areas and achieve high productivity even when printing paper P with a width smaller than letter size or A4 size (hereinafter referred to as small size paper). Therefore, from this point of view as well, the performance of the heater 54 is exhibited by frequently switching between the main heater (heat generating element 54b1) and the sub-heaters (heat generating elements 54b2, 54b3).

[0030] Contact 54d1 is connected to a first pole of AC power supply 55 via bidirectional thyristor (hereinafter referred to as triac) 56a, which is a first switching means. Contact 54d2 is connected to a first pole of AC power supply 55 via triac 56b, which is a second switching means. Contact 54d3 is connected to a first pole of AC power supply 55 via triac 56c, which is a third switching means. Contact 54d4 is connected to a second pole of AC power supply 55 without going through a triac or the like. Contacts 54d2 and 54d4 are connected via electromagnetic relay 57a, which is a first switching means and has an a-contact configuration. Electromagnetic relay 57a switches the electrical path (power supply path) between contacts 54d2 and 54d4 between a connected state (hereinafter also referred to as a short-circuit state) or an open state. Electromagnetic relay 57a is not limited to an a-contact electromagnetic relay, and may be a contact switch such as an electromagnetic relay with a b-contact configuration or an electromagnetic relay with a c-contact configuration. Furthermore, the electromagnetic relay 57a may be a non-contact switch such as a solid state relay (SSR), a photoMOS relay, or a triac.

[0031] [Power supply route] FIG. 5 shows three current paths (electrical paths and power supply paths) to the heating elements 54b1 to 54b3 when the heater 54 and power control unit 97 of the first embodiment are used.

[0032] (Power supply to heating element 54b1) When power is supplied from AC power supply 55 to heating element 54b1, the current flows along the route indicated by the bold line in FIG. 5(a). The temperature of heater 54 is detected by a temperature detection element (not shown), such as a thermistor, and triac 56a operates based on temperature information and instructions from a microcomputer (not shown), thereby controlling heating element 54b1 to a predetermined temperature. Power supply to heating element 54b1 does not depend on triacs 56b and 56c and electromagnetic relay 57a with an a-contact configuration. In other words, when power is supplied to heating element 54b1, electromagnetic relay 57a may be in either an open state or a short-circuit state. Note that, in FIG. 5(a), electromagnetic relay 57a is shown in an open state as an example.

[0033] (Power supply to heating element 54b2) When power is supplied from AC power supply 55 to heating element 54b2, the current flows along the route shown by the thick line in Figure 5(b). When power is supplied to heating element 54b2, the contact of electromagnetic relay 57a with a contact configuration is set to an open state. Because the contact impedance of electromagnetic relay 57a with a contact configuration in the open state is sufficiently greater than that of heating element 54b2, almost no current flows through electromagnetic relay 57a with a contact configuration, allowing only heating element 54b2 to be heated. The power supplied to heating element 54b2 is controlled by triac 56b.

[0034] (Power supply to heating element 54b3) When power is supplied from AC power supply 55 to heating element 54b3, the current flows along the route shown by the bold line in Figure 5(c). When power is supplied to heating element 54b3, the contacts of electromagnetic relay 57a with an a-contact configuration are shorted, so that almost all of the current flows to heating element 54b3. Because the contact impedance of electromagnetic relay 57a with an a-contact configuration in the shorted state is sufficiently smaller than that of heating element 54b2, almost no current flows to heating element 54b2, allowing only heating element 54b3 to be heated. The power supplied to heating element 54b3 is controlled by triac 56c.

[0035] [Switching power supply paths] To switch between the power supply path to heating element 54b1 (FIG. 5(a)) and the power supply path to heating element 54b2 (FIG. 5(b)), the contacts of electromagnetic relay 57a with a contact a configuration are opened in advance. Switching between the power supply path (FIG. 5(a)) and the power supply path to heating element 54b2 (FIG. 5(b)) can be independently controlled only by the contactless switches of triac 56a and triac 56b. Because state transitions can be achieved solely by the operation of the contactless switches (=triac), it is possible to transition frequently between the power supply path (FIG. 5(a)) and the power supply path (FIG. 5(b)), or to use both the power supply path (FIG. 5(a)) and the power supply path (FIG. 5(b)).

[0036] The same applies to the power supply path to heating element 54b1 (FIG. 5(a)) and the power supply path to heating element 54b3 (FIG. 5(c)). The contacts of electromagnetic relay 57a, which has an a-contact configuration, are shorted in advance, and the paths are switched by controlling triacs 56a and 56b. Because state transitions are possible simply by the operation of the contactless switch (=triac), it is possible to transition frequently between the power supply path (FIG. 5(a)) and the power supply path (FIG. 5(c)), or to use both the power supply path (FIG. 5(a)) and the power supply path (FIG. 5(c)).

[0037] On the other hand, when switching between the power supply path for heating element 54b2 (FIG. 5(b)) and the power supply path for heating element 54b3 (FIG. 5(c)), the state of electromagnetic relay 57a with a contact a must be switched. Here, both ends of electromagnetic relay 57a with a contact a are connected to both ends of heating element 54b2. As a result, when triac 56b is non-conductive, both ends of electromagnetic relay 57a with a contact a are at the same potential regardless of whether relay 57a with a contact a is in an open or shorted state. Therefore, no arc discharge occurs between the contacts of electromagnetic relay 57a with a contact a when relay 57a with a contact a is operating (electromagnetic relay 57a is operated when triac 56b is non-conductive). Therefore, no electromagnetic noise is emitted, and contact wear (i.e., shortened life) due to arc discharge does not occur. This allows for a high degree of freedom in switching between the power supply paths (FIG. 5(b)) and (FIG. 5(c)), although they are mutually exclusive.

[0038] The use of the heater 54 and power control unit 97 of the first embodiment not only eliminates electromagnetic noise radiation and contact wear during electromagnetic relay operation, but also provides the following advantages. First, the number of electrodes (contacts) provided at both ends of the substrate 54a can be the same, which allows connectors connected to both ends of the substrate 54a to be standardized and heat distribution in the longitudinal direction of the ceramic heater to be uniform. Second, two of the three state transitions can be controlled by controlling only the contactless switch. This minimizes the state transitions affected by waiting for the contact switch to operate (waiting for the contact to stabilize due to relay contact bounce) and maximizes the performance of the heater 54, thereby improving productivity for small-size paper. For ease of explanation, noise filters and energy-saving functions such as isolating the noise filter from the AC power supply 55 for energy conservation are not shown, but adding circuits necessary for these actual functions does not change the effects of the present invention.

[0039] In this way, in a configuration in which a contact switch is used to switch the power supply path, it is possible to eliminate the electromagnetic noise radiation from the contact switch and the shortened lifespan due to contact wear. As described above, according to the first embodiment, even when a contact switch is used to switch the heating element to which power is supplied, it is possible to provide a device in which electromagnetic noise is not radiated due to arc discharge when the contact switch is operated and the shortened lifespan due to contact wear does not occur. [Example]

[0040] [Heater and power control unit] The heater 54 and power control unit 97 used in the heating device of Example 2 are shown in Figure 6. The heater 54 used in Example 2 is the same as that in Example 1, so a description thereof will be omitted. The power control unit 97 of Example 2 uses a single triac 56b that serves both as the triac 56b and the triac 56c of Figure 4, and instead has an electromagnetic relay 57b with a contact c, which serves as second switching means. This Example is characterized in that the electromagnetic relay 57b with a contact c plays the role of selecting which heating element the triac 56b is connected to and also plays the role of the electromagnetic relay 57b with a contact a of Figure 4.

[0041] Specifically, electromagnetic relay 57c, which serves as the second switching means and has a contact point c, has contact 57c1 connected to contact point 54d2, contact 57c2 connected to triac 56b and contact point 54d3, and contact 57c3 connected to AC power supply 55 and contact point 54d4. When contact point 57c1 and contact point 57c2 are connected, electromagnetic relay 57c supplies power to heating element 54b2. When contact point 57c1 and contact point 57c3 are connected, electromagnetic relay 57c supplies power to heating element 54b3. When contact point 57c1 and contact point 57c3 are connected, electromagnetic relay 57c also functions as the first switching means.

[0042] [Current supply path] 7 shows three current supply paths to heating elements 54b1 to 54b3 when heater 54 and power control unit 97 of the second embodiment are used. When power is supplied from AC power supply 55 to heating element 54b1, current flows along the route shown by the thick line in FIG. 7(a). Power supply from AC power supply 55 to heating element 54b1 is controlled by triac 56a. When power is supplied to heating element 54b1, electromagnetic relay 57c may be in a state where contacts 57c1 and 57c2 are connected, or where contacts 57c1 and 57c3 are connected.

[0043] When power is supplied from AC power supply 55 to heating element 54b2, current flows along the route shown by the thick line in Figure 7(b). At this time, electromagnetic relay 57c with contact c configuration has contacts 57c1 and 57c2 connected to be connected to triac 56b and contact 54d4, and triac 56b controls the power supply from AC power supply 55 to heating element 54b2. Because the contact impedance of electromagnetic relay 57c with contact c configuration is sufficiently smaller than that of heating element 54b3, almost no current flows through heating element 54b3, and only heating element 54b2 can be heated.

[0044] When power is supplied from AC power supply 55 to heating element 54b3, current flows along the route shown by the thick line in Figure 7(c). At this time, electromagnetic relay 57c with contact c configuration has contacts 57c1 and 57c3 connected to be connected to contact 54d3, and triac 56b controls the power supply from AC power supply 55 to heating element 54b3. Because the contact impedance of electromagnetic relay 57c with contact c configuration is sufficiently smaller than that of heating element 54b2, almost no current flows through heating element 54b2, and only heating element 54b3 can be heated.

[0045] Electromagnetic relay 57c with contact c configuration has a first function of short-circuiting (FIG. 7(b)) and opening (FIG. 7(c)) heat generating element 54b2 by short-circuiting (FIG. 7(b)) and opening (FIG. 7(c)) contacts 54d2 and 54d4. Electromagnetic relay 57c with contact c configuration also has a second function of short-circuiting (FIG. 7(c)) and opening (FIG. 7(b)) heat generating element 54b3. That is, electromagnetic relay 57c with contact c configuration is characterized by having both the first and second functions.

[0046] Here, contacts 57c1 and 57c2 of electromagnetic relay 57c with a contact c configuration are connected to both ends of heating element 54b3. As a result, when triac 56b is non-conductive, contacts 57c1 and 57c2 are at the same potential regardless of whether they are in an open or shorted state. Furthermore, contacts 57c1 and 57c3 of electromagnetic relay 57c with a contact c configuration are connected to both ends of heating element 54b2. As a result, when triac 56b is non-conductive, contacts 57c1 and 57c3 are at the same potential regardless of whether they are in an open or shorted state. In other words, when triac 56b is non-conductive, contacts 57c1, 57c2, and 57c3 are all at the same potential. As a result, no arc discharge occurs between any of the contacts of electromagnetic relay 57c with a contact c configuration when electromagnetic relay 57c with a contact c configuration is operating (electromagnetic relay 57c is operated when triac 56b is non-conductive). Therefore, when the electromagnetic relay 57c having the c-contact configuration is in operation, no electromagnetic noise is emitted, and contact wear (reduced life) due to arc discharge does not occur.

[0047] The configuration of the second embodiment is equivalent to using only the electromagnetic relay 57c with a contact point configuration to perform the functions of the electromagnetic relay 57a with an a-contact configuration and the triac 56c shown in Fig. 4 of the first embodiment. Therefore, by selecting the configuration of the second embodiment, it is possible to further reduce the number of circuit components while ensuring the same functions as those of the first embodiment.

[0048] In the configuration of Example 1, if an abnormal state occurs in which triac 56b is in a conductive state and the contacts of electromagnetic relay 57a, which has an a-contact configuration, are short-circuited, the output terminal of AC power supply 55 will be short-circuited. In this case, there is a risk that the current fuse (not shown) will melt, which could result in damage to the device. In contrast, in the configuration of Example 2, the output terminal of AC power supply 55 will not be short-circuited, and this can be said to be a more reliable configuration.

[0049] In this way, in a configuration in which a contact switch is used to switch the power supply path, it is possible to eliminate the electromagnetic noise radiation from the contact switch and the shortened lifespan due to contact wear. In addition, it is possible to provide a device that is less expensive, more space-saving, and more reliable than Example 1. As described above, Example 2 can provide a device that does not radiate electromagnetic noise due to arc discharge when the contact switch is operated, and does not experience shortened lifespan due to contact wear, even when a contact switch is used to switch the heating element to which power is supplied. [Example]

[0050] [Heater and power control unit] FIG. 8 shows the heater 54 and power control unit 97 used in the heating device of Example 3. The heating elements 54b1 and 54b3 of the heater 54 are the same as those of Examples 1 to 3. The longitudinal length of the second heating element 54b4 is the difference between the lengths of the heating elements 54b2 and 54b3 of the heater 54 of Examples 1 to 3. Two heating elements 54b4 are arranged on either side of the heating element 54b3 in a direction perpendicular to the longitudinal direction. That is, the sum of the longitudinal lengths of the heating elements 54b4 and 54b3 is set to be the same as the longitudinal length of the heating element 54b2 of the heater 54. As will be described later, the heating elements 54b3 and 54b4 may be used as a single heating element. For this reason, the resistance values ​​per unit length in the longitudinal direction of the heating elements 54b3 and 54b4 must be set to be equal.

[0051] [Current supply path] 9 shows three current paths to the heating element when using the heater 54 and power control unit 97 of the third embodiment. When power is supplied from the AC power supply 55 to the heating element 54b1, the current flows along the route shown by the bold line in FIG. 9(a). The power supply from the AC power supply 55 to the heating element 54b1 is controlled by a triac 56a. When power is supplied to the heating element 54b1, the electromagnetic relay 57a may be in an open state or a short-circuit state.

[0052] When power is supplied from AC power supply 55 to heating elements 54b3 and 54b4, the current flows along the route shown by the bold line in Figure 9(b). At this time, the contacts of electromagnetic relay 57a, which has a contact a configuration, are set to an open state, and current flows in series through heating elements 54b3 and 54b4. Hereinafter, the series-connected heating elements 54b3 and 54b4 may also be referred to as a series heating element. As a result, heating elements 54b3 and 54b4 both generate heat, and can provide heat in the longitudinal direction of heater 54 in the same range as heating element 54b2 in Examples 1 to 3. For example, they can be considered as a single heating element corresponding to the width of B5-sized paper. Power supply from AC power supply 55 to heating elements 54b3 and 54b4 in series is controlled by triac 56b. Since the contact impedance of the electromagnetic relay 57a in the open contact configuration is sufficiently greater than that of the heating element 54b4, almost no current flows through the electromagnetic relay 57a in the contact configuration, and only the heating elements 54b3 and 54b4 can be heated.

[0053] When power is supplied from AC power supply 55 to heating element 54b3, current flows along the route shown by the bold line in Figure 9(c). At this time, the contacts of electromagnetic relay 57a with a contact configuration are set to a short-circuited state, and triac 56b controls the power supply from AC power supply 55 to heating element 54b3. Because the contact impedance of electromagnetic relay 57a with a contact configuration in the short-circuited state is sufficiently smaller than that of heating element 54b4, almost no current flows through heating element 54b4, allowing only heating element 54b3 to be heated. Here, both ends of electromagnetic relay 57a with a contact configuration are connected to both ends of heating element 54b4. Therefore, as in Example 1, no electromagnetic noise is emitted when electromagnetic relay 57a with a contact configuration operates, and contact wear (i.e., shortened life) due to arc discharge does not occur. The configuration of Example 3 has the advantage that the power control unit 97 can be made inexpensive and small because the electromagnetic relay 57a can be an electromagnetic relay with an a-contact configuration, which is cheaper and smaller than the electromagnetic relay 57c with a c-contact configuration used in Example 2.

[0054] The heater 54 of Example 3 needs to be designed so that there is no difference in heat distribution (discontinuity in heat distribution) at the two boundaries between the heating elements 54b3 and 54b4 in the longitudinal direction. In practice, it is desirable to devise a method such as tapering the heating elements 54b3 and 54b4 at the two boundaries.

[0055] It should also be noted that there are constraints on the resistance values ​​of heating elements 54b3 and 54b4. Let the resistance value of heating element 54b3 be R103, and the resistance value of heating element 54b4 be R114. The resistance value Rs of the series resistors R103 and R114 has the relationship Rs = R103 + R114, so Rs must be greater than R103. However, the series heating element (resistance value Rs) that heats a wider sheet of paper P than heating element 54b3 requires more power than heating element 54b3. Therefore, Rs must have a lower resistance value than R103. Therefore, the resistance value Rs of the series heating element is determined first, and then the resistance value R103 of heating element 54b3 is set to a value lower than Rs. In other words, the resistance value R103 of heating element 54b3 must be set to a resistance value lower than the resistance calculated from the required power, which inevitably results in the heating element 54b3 being set to an exceeding specification. When using the configuration of the third embodiment, it is necessary to take this into consideration and establish a sufficient protection system for the heating element 54b3.

[0056] In this way, in a configuration in which a contact switch is used to switch the power supply path, it is possible to eliminate electromagnetic noise radiation from the contact switch and shortened lifespan due to contact wear. In addition, the power control unit 97 can be made cheaper and smaller than in Example 2. As described above, according to Example 3, even when a contact switch is used to switch the heating element to which power is supplied, it is possible to provide a device in which electromagnetic noise is not radiated due to arc discharge when the contact switch is operated and shortened lifespan does not occur due to contact wear. [Example]

[0057] [Heater and power supply] FIG. 10 shows the heater 54 and power supply unit used in the heating device of Example 4. The longitudinal length of the heating element 54b5, which is the second heating element formed on the heater 54, is the same as that of the heating element 54b3 of the heater 54 used in Examples 1 to 4. However, the difference is that the contacts to which the heating element 54b5 is connected are contacts 54d2 and 54d4. The longitudinal length and shape (separated into two) of the heating element 54b6, which is the third heating element, are also the same as those of the heating element 54b4 of the heater 54 used in Example 3, but the difference is that the contacts to which it is connected are contacts 54d2 and 54d3. The electromagnetic relay 57d, which is the third switching means, is an electromagnetic relay with an a-contact configuration, with one end connected to contact 54d3 and the other end connected to the second pole of the AC power supply 55 and contact 54d4.

[0058] [Current supply path] 11 shows three current paths to the heating element when using the heater 54 and power control unit 97 of the fourth embodiment. When power is supplied from the AC power supply 55 to the heating element 54b1, the current flows along the route shown by the thick line in FIG. 11(a). The power supply from the AC power supply 55 to the heating element 54b1 is controlled by the triac 56a. When power is supplied to the heating element 54b1, the electromagnetic relay 57d may be in either an open state or a short-circuit state.

[0059] When power is supplied from AC power supply 55 to heating elements 54b5 and 54b6, the current flows along the route shown by the bold line in Figure 11(b). At this time, the contacts of electromagnetic relay 57d, which has an a-contact configuration, are set to a short-circuit state, and current flows in parallel through heating elements 54b5 and 54b6. Hereinafter, the parallel-connected heating elements 54b5 and 54b6 may also be referred to as parallel heating elements. As a result, heating elements 54b5 and 54b6 both generate heat, and in the longitudinal direction of heater 54, they can be considered as a single heating element corresponding to the width of, for example, B5-size paper. Power supply from AC power supply 55 to the parallel heating elements, heating elements 54b5 and 54b6, is controlled by triac 56b.

[0060] When power is supplied from AC power supply 55 to heating element 54b5, current flows along the route indicated by the bold line in Figure 11(c). At this time, the contacts of electromagnetic relay 57d with an a-contact configuration are set to an open state, and triac 56b controls the power supply from AC power supply 55 to heating element 54b5. Because the contact impedance of electromagnetic relay 57d with an a-contact configuration in the open state is sufficiently greater than that of heating element 54b5, almost no current flows through heating element 54b6, allowing only heating element 54b5 to be heated. Here, both ends of electromagnetic relay 57d with an a-contact configuration are connected to both ends of the series-connected heating elements, heating elements 54b5 and 54b6. Therefore, as in Example 1, no electromagnetic noise is emitted when electromagnetic relay 57a with an a-contact configuration is operating, and contact wear (i.e., shortened life) due to arc discharge does not occur.

[0061] As with the third embodiment, the configuration of the fourth embodiment also imposes constraints on the resistance values ​​of the heating elements 54b5 and 54b6. The resistance value of the heating element 54b5 is R116, and the resistance value of the heating element 54b6 is R117. The resistance value Rp of the parallel heating elements 54b5 and 54b6 is expressed as 1 / Rp = (1 / R116) + (1 / R117). If the resistance value R116 of the heating element 54b5 is set to 110 Ω and the resistance value Rp of the parallel heating elements is set to 90 Ω, the resistance value R117 of the heating element 54b6 must be 495 Ω. The heating element 54b6 must be made of a resistive material with a higher resistivity than the heating element 54b5 (specifically, approximately twice as high). Thus, the heaters 54 used in the third and fourth embodiments have different constraints on the setting of the resistance values ​​of the heating elements. Therefore, it is desirable to select a method that meets the design conditions.

[0062] In this way, in a configuration in which a contact switch is used to switch the power supply path, it is possible to eliminate the electromagnetic noise radiation from the contact switch and the shortened lifespan due to contact wear. As described above, according to the fourth embodiment, even when a contact switch is used to switch the heating element to which power is supplied, it is possible to provide a device in which electromagnetic noise is not radiated due to arc discharge when the contact switch is operated and the shortened lifespan due to contact wear does not occur. [Explanation of symbols]

[0063] 54a board 54b1~54b3 Heating element 54d1~54d4 contacts 56a, 56b Bidirectional thyristor 57c Electromagnetic Relay

Claims

1. A substrate; a first heating element; second and third heating elements each having a length in the longitudinal direction of the substrate shorter than that of the first heating element; a first triac for turning on / off the supply of power to the first heating element; a second triac for turning on / off the supply of power to the second heating element or the third heating element; a contact switch having a first contact connected to one end side of the second heating element and the third heating element, a second contact connected to the other end side of the second heating element, and a third contact connected to the other end side of the third heating element, which connects the first contact and the third contact when supplying power to the second heating element, and connects the first contact and the second contact when supplying power to the third heating element; A heating device comprising:

2. 2. The heating device according to claim 1, wherein when the first triac is on, power is supplied to the first heating element regardless of the state of the contact switch.

3. 3. The heating device according to claim 2, wherein the first contact and the third contact are connected by the contact switch, and the second triac is turned on, thereby supplying power to the second heating element.

4. 4. The heating device according to claim 3, wherein the first contact and the second contact are connected by the contact switch, and the second triac is turned on, thereby supplying power to the third heating element.

5. The heater is a first electrode to which one end of the first heating element is connected; a second electrode to which one end of the second heating element and one end of the third heating element are connected; a third electrode to which the other end of the third heating element is connected; a fourth electrode to which the other end of the first heating element and the other end of the second heating element are connected, the first electrode and the second electrode are disposed closer to one end of the substrate in a longitudinal direction than the first heating element, the second heating element, and the third heating element; 2. The heating device according to claim 1, wherein the third electrode and the fourth electrode are arranged closer to the other end of the substrate in the longitudinal direction than the first heating element, the second heating element, and the third heating element.

6. The heating device described in claim 1, characterized in that two of the first heating elements are arranged on both sides of the substrate in a short direction perpendicular to the longitudinal direction, and one of the second heating element and one of the third heating element are arranged inside the two first heating elements in the short direction.

7. 7. The heating device according to claim 6, wherein the second heating element and the third heating element are arranged within a region of the first heating element in the longitudinal direction.

8. 8. The heating device according to claim 7, characterized in that in the short side direction, the heating elements are arranged on the substrate in the following order: one of the two first heating elements, the second heating element, the third heating element, and the other of the two first heating elements; one of the two first heating elements and the second heating element are arranged at one end side of the substrate in the short side direction; and the third heating element and the other of the two first heating elements are arranged at the other end side of the substrate in the short side direction.

9. a first rotating body in which a heater including the substrate, the first heating element, the second heating element, and the third heating element is disposed in an internal space; a second rotating body that forms a nip portion together with the first rotating body; The heating device according to claim 1 , further comprising:

10. 10. The heating device according to claim 9, wherein the first rotating body is a cylindrical film.

11. the film is sandwiched between the heater and the second rotating body, 11. The heating device according to claim 10, wherein the image on the recording material is heated through the film at the nip portion formed between the film and the second rotating body.

12. an image forming means for forming an image on a recording material; a heating device according to claim 1 for heating an image formed on a recording material; An image forming apparatus comprising:

13. 2. The heating device according to claim 1, wherein the first contact and the second contact are connected to both ends of the second heating element, and the first contact and the third contact are connected to both ends of the third heating element, so that when the second triac is non-conductive, the first contact, the second contact, and the third contact are at the same potential.

14. the first triac has one end connected to the first heating element and the other end connected to a first pole of an AC power supply; 2. The heating device according to claim 1, wherein one end of the second triac is connected to the second heating element and the third heating element, and the other end is connected to the first pole of the AC power supply.

15. one end of the first heating element is connected to a first pole of an AC power supply via the first triac; one end side of the second heating element and the third heating element is connected to the first pole of the AC power supply via the second triac; the other end of the third heating element is connected to the first pole of the AC power supply; the other end sides of the first heating element and the second heating element are connected to a second pole of the AC power supply without passing through the first and second triacs; 2. The heating device according to claim 1, wherein one end of each of the second and third heating elements is connected to the other end of the first heating element via the contact switch.

Images