JP7547068B2 - Heating device, image forming device and electronic device - Google Patents

Description

The present invention relates to a heating device, an image forming device, and an electronic device, and in particular to a heating device and an image forming device that implements a method for detecting whether a control signal that controls the power supply to a heating element is being transmitted normally over a transmission line.

In a heating device that uses a ceramic heater as a heat source, when a recording paper (small size paper) with a paper passing width shorter than the length of the heating element is conveyed, it is known that the temperature in the heating area and non-paper passing area becomes higher than the paper passing area. Therefore, a configuration has been proposed that has multiple heating elements of different lengths and switches the heating element used to supply power depending on the width of the recording paper, thereby reducing the temperature rise in the non-paper passing area (see, for example, Patent Document 1). In such a configuration, the power supply to the heating elements is switched by a switching element such as a relay or triac, and the switching element is controlled based on a control signal output from the control unit.

JP 2001-100558 A

In conventional configurations, if a phenomenon occurs in which the control signal that controls the switch element is not transmitted properly along the transmission line from the control unit to the switch element, power is supplied to a heating element other than the heating element corresponding to the width of the recording paper. This causes the temperature of non-paper passing areas to rise, and there is a risk of damage to the heating element or the components surrounding the heating element. For this reason, there is a need to accurately detect whether the control signal that controls the switch element is being transmitted properly along the transmission line.

The present invention was made under these circumstances, and aims to accurately detect whether a control signal that controls a switch element is being transmitted normally through a transmission line.

In order to solve the above problems, the present invention has the following configuration.

(1) A heating device comprising at least one heating element, a switch element which supplies or cuts off power from an AC power source to the heating element, a drive means which drives the switch element in accordance with a control signal, and a control means which controls the switch element via the drive means by setting the control signal, the heating device further comprising: a detection means which outputs a signal corresponding to the control signal transmitted via a transmission line; a zero-cross detection means which outputs a signal corresponding to the AC voltage of the AC power source; and a switching means which switches between a first state in which a signal from the detection means is input to the control means and a second state in which a signal from the zero-cross detection means is input to the control means, the at least one heating element comprising a first heating element and a second heating element having a longitudinal length shorter than that of the first heating element; a third heating element having a length in the longitudinal direction shorter than that of the second heating element, wherein the switch elements include a first switch element that supplies or cuts off power to the first heating element, a second switch element that supplies or cuts off power to the second heating element or the third heating element , and a third switch element that switches between a state in which power supplied via the second switch element is supplied to the second heating element and a state in which power is supplied to the third heating element, and the drive means includes first drive means that drives the first switch element in accordance with a first control signal, second drive means that drives the second switch element in accordance with a second control signal, and third drive means that drives the third switch element in accordance with a third control signal .
(2) An image forming apparatus comprising: a forming means for forming a toner image on a recording material; and the heating device described in (1) for fixing an unfixed toner image formed on the recording material by the forming means.
(3) An electronic device comprising at least one load, a switch element which supplies or cuts off power from an AC power source to the load, a drive means which drives the switch element in accordance with a control signal, and a control means which controls the switch element via the drive means by setting the control signal, the electronic device further comprising: a detection means which outputs a signal corresponding to the control signal transmitted via a transmission line; a zero-cross detection means which outputs a signal corresponding to an AC voltage of the AC power source; and a switching means which switches between a first state in which a signal from the detection means is input to the control means and a second state in which a signal from the zero-cross detection means is input to the control means, the at least one load being a first load and a second load having a longitudinal length shorter than that of the first load. and a third load having a length in the longitudinal direction shorter than that of the second load, the switch elements including a first switch element supplying or cutting off power to the first load, a second switch element supplying or cutting off power to the second load or the third load , and a third switch element switching between a state in which power supplied via the second switch element is supplied to the second load and a state in which power is supplied to the third load, and the drive means includes first drive means for driving the first switch element in accordance with a first control signal, second drive means for driving the second switch element in accordance with a second control signal, and third drive means for driving the third switch element in accordance with a third control signal .

According to the present invention, it is possible to accurately detect whether a control signal that controls a switch element is being transmitted normally through a transmission line.

1 is a schematic cross-sectional view showing an image forming apparatus according to first and second embodiments; FIG. 1 shows a heater and a heater control circuit according to a first embodiment. FIG. 1 is a diagram showing a current path of a heater and a heater control circuit according to a first embodiment. A flowchart showing a process for detecting a transmission state of a control signal according to the first embodiment. FIG. 13 is a diagram showing a heater and a heater control circuit according to a second embodiment of the present invention; FIG. 13 is a diagram showing a drive circuit for an electromagnetic relay and a triac according to a second embodiment of the present invention;

Below, an embodiment of the present invention will be described with reference to the drawings. In the following examples, the passage of recording paper through the fixing nip is referred to as "paper being passed through." Additionally, an area where the heating element is generating heat and through which recording paper is not passed is referred to as a non-paper passing area (or non-paper passing section), and an area through which recording paper is passed is referred to as a paper passing area (or paper passing section). Additionally, the phenomenon in which the temperature of the non-paper passing area becomes higher than that of the paper passing area is referred to as non-paper passing section temperature rise.

[Overall configuration]
Fig. 1 is a configuration diagram showing an in-line type color image forming apparatus, which is an example of an image forming apparatus equipped with a fixing device that is a heating device of the first embodiment. The operation of the electrophotographic color image forming apparatus will be described with reference to Fig. 1. The first station is a station for forming a yellow (Y) toner image, 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.

In the first station, the photosensitive drum 1a, which is an image carrier, is an OPC photosensitive drum. The photosensitive drum 1a is a metal cylinder on which multiple layers of functional organic materials, such as a carrier generation layer that is photosensitive to light and generates charges, and a charge transport layer that transports the generated charges, are laminated, and the outermost layer has low electrical conductivity and is almost insulated. A charging roller 2a, which is a charging means, is abutted against the photosensitive drum 1a, and as the photosensitive drum 1a rotates, it uniformly charges the surface of the photosensitive drum 1a while rotating in accordance with the rotation of the photosensitive drum 1a. A voltage in which a DC voltage or an AC voltage is superimposed is applied to the charging roller 2a, and the photosensitive drum 1a is charged by generating discharges in minute air gaps on the upstream and downstream sides of the rotation direction from the nip portion between the charging roller 2a and the surface of the photosensitive drum 1a. The cleaning unit 3a is a unit that cleans the toner remaining on the photosensitive drum 1a after transfer, which will be described later. The developing unit 8a, which is a developing means, is composed of a developing roller 4a, a non-magnetic one-component toner 5a, and a developer coating blade 7a. The photosensitive drum 1a, charging roller 2a, cleaning unit 3a, and developing unit 8a form an integrated process cartridge 9a that is detachable from the image forming device.

The exposure device 11a, which is an exposure means, is composed of a scanner unit or an LED (light-emitting diode) array that scans laser light using a polygon 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 is a voltage supply means to the charging roller 2a. The developing roller 4a is connected to a developing high voltage power supply 21a, which is a voltage supply means to the developing roller 4a. The primary transfer roller 10a is connected to a primary transfer high voltage power supply 22a, which is a voltage supply means to the primary transfer roller 10a. The above is the configuration of the first station, and the second, third, and fourth stations have the same configuration. For the other stations, parts having the same functions as the first station are given the same reference numerals, and the suffixes b, c, and d are added to the reference numerals for each station. In the following description, the suffixes a, b, c, and d are omitted except when a specific station is described.

The intermediate transfer belt 13 is supported by three rollers, the secondary transfer opposing roller 15, the tension roller 14, and the auxiliary roller 19, which serve as tension members. Only the tension roller 14 is applied with a spring 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), and the intermediate transfer belt 13 wound around its periphery rotates. The intermediate transfer belt 13 moves at approximately the same speed in the forward direction (for example, clockwise direction in FIG. 1) as the photosensitive drums 1a to 1d (for example, rotating counterclockwise in FIG. 1). In addition, the intermediate transfer belt 13 rotates in the direction of the arrow (clockwise direction), and the primary transfer roller 10 is disposed on the opposite side of the photosensitive drum 1 across the intermediate transfer belt 13, and rotates in response to the movement of the intermediate transfer belt 13. The position where the photosensitive drum 1 and the 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 of them will be omitted.

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 in the standby state, it starts the image forming operation. The photosensitive drum 1, the intermediate transfer belt 13, etc. start to rotate in the direction of the arrow at a predetermined process speed by the main motor (not shown). The photosensitive drum 1a is uniformly charged by the charging roller 2a to which a voltage is applied by the charging high-voltage power supply 20a, and then an electrostatic latent image according to the image information (also called image data) is formed by the scanning beam 12a irradiated from the exposure device 11a. The toner 5a in the developing unit 8a is negatively charged by the developer application blade 7a and applied to the developing roller 4a. A predetermined developing voltage is then supplied to the developing roller 4a from the 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 the first color (for example, 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 delaying the write start signal from the controller (not shown) 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 in order 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.

After that, the recording material, paper P, loaded in the cassette 16 is transported along the transport path Y in accordance with the formation of the toner image. Specifically, the paper P is fed (picked up) by a paper feed roller 17 that is driven to rotate by a paper feed solenoid (not shown). The fed paper P is transported to a registration roller (hereinafter referred to as a registration roller) 18 by the transport roller. The paper P then passes a paper width sensor 1112 that detects the length (hereinafter referred to as the width) in a direction perpendicular to the transport direction. Here, the paper width refers to the length of the paper P in a direction perpendicular to the transport direction. A registration sensor (hereinafter referred to as a registration sensor) 1113 is disposed downstream of the registration roller 18. The registration sensor 1113 detects the presence of the paper P when the leading edge of the paper P arrives, and detects the absence of the paper P when the trailing edge of the paper P passes by.

The paper P is conveyed by the registration roller 18 to the transfer nip portion, which is the contact portion between the intermediate transfer belt 13 and the secondary transfer roller 25, in synchronization with the toner image on the intermediate transfer belt 13. A voltage of the opposite polarity to that of the toner is applied to the secondary transfer roller 25 by the secondary transfer high voltage power source 26, and the four-color multi-toner image carried on the intermediate transfer belt 13 is transferred to the paper P (onto the recording material) all at once (hereinafter referred to as secondary transfer). The members (e.g., the photosensitive drum 1, etc.) that contributed to the formation of the unfixed toner image on the paper P function as a forming means. On the other hand, after the secondary transfer is completed, the toner remaining on the intermediate transfer belt 13 is cleaned by the cleaning unit 27. After the secondary transfer is completed, the paper P is conveyed to the fixing device 50, which is a fixing means, and after the toner image is fixed, it is discharged to the discharge tray 30 as an image formation (print, copy). Fixing device 50, which is a heating device, has film 51, which is a first rotating body, nip forming member 52, pressure roller 53, which is a second rotating body that forms a nip portion together with film 51, and heater 100. Heater 100 has multiple loads, specifically multiple heating elements, and is provided so as to be in contact with the inner surface of film 51. The nip portion is formed by the multiple heating elements and pressure roller 53 via film 51.

A printing mode in which images are printed continuously on multiple sheets of paper P is hereinafter referred to as continuous printing or continuous job. In continuous printing, the space between the rear end of the paper P on which the preceding printing is performed (hereinafter referred to as the preceding paper) and the front end of the succeeding paper P on which the printing is performed following the preceding paper (hereinafter referred to as the succeeding paper) is referred to as the paper gap. The image forming device of the first embodiment is a center-based image forming device that performs printing operations by aligning the center positions of each member and the paper P in the direction perpendicular to the transport direction (longitudinal direction). Therefore, the center positions of each paper P are aligned whether the printing operation is performed on a paper P with a large length in the direction perpendicular to the transport direction or a paper P with a small length in the direction perpendicular to the transport direction. Note that the transport reference is the center reference, but other references such as the edge reference may be used.

[Heater and heater control circuit]
The heater and heater control circuit used in the heating device of the first embodiment are shown in Fig. 2. Fig. 2(a) shows the heater 100 of the first embodiment, a zero-cross detection circuit 128 which is a zero-cross detection means, and a detection circuit 126 which is a detection means for detecting the state of a control signal. Fig. 2(a) also shows a switching unit 127 which is a switching means for switching between a second state in which a signal from the zero-cross detection circuit 128 is output and a first state in which a signal from the detection circuit 126 is output to a control unit 125 which is a control means mounted on a control board 124. Fig. 2(b) shows a cross section of the heater 100 taken along line pp'.

The heater 100 has at least one heating element, for example, heating elements 101 to 103 formed mainly on a ceramic substrate 104. The heater 100 has a first contact 106a (hereinafter referred to as contact 106a), a third contact 106b (hereinafter referred to as contact 106b), a fourth contact 106c (hereinafter referred to as contact 106c), a second contact 106d (hereinafter referred to as contact 106d), and insulating glass 105. The first heating element 101 (hereinafter referred to as heating element 101), the second heating element 102 (hereinafter referred to as heating element 102), and the third heating element 103 (hereinafter referred to as heating element 103) are specific examples of loads of electronic devices. The heating elements 101 to 103 are resistors that generate heat when power is supplied from an AC power source 107, and the insulating glass 105 is provided to insulate the user from the heating elements, which have approximately the same potential as the AC power source 107. Heating element 101 is a heating element that is primarily used when fixing toner to paper P with the widest paper width among the papers P that can be transported to fixing device 50. Therefore, the longitudinal dimension of heating element 101 is set to be several mm longer than the LTR size paper width of 215.9 mm. Heating element 101 is also a heating element that is primarily used when fixing device 50 is started up (when fixing device 50 is brought up to a predetermined temperature from a cold state), and is designed to supply the power required when fixing device 50 is started up. Heating element 101 is connected to contacts 106a and 106d.

Heating element 102 corresponds to the width of B5 size paper, and the longitudinal dimension of heating element 102 is set to be several mm longer than the width of B5 size paper, 182 mm. Heating element 102 is connected to contacts 106b and 106d. Heating element 103 corresponds to the width of A5 size paper, and the longitudinal dimension of heating element 103 is set to be several mm longer than the width of A5 size paper, 148 mm. Heating element 103 is connected to contacts 106b and 106c. Heating element 102 and heating element 103 are assumed to be used when fixing device 50 is in a state where it is somewhat warmed up, and the rated power of heating element 102 and heating element 103 is set lower than the rated power of heating element 101. In other words, heating element 101 is positioned as the main heater, and heating element 102 and heating element 103 are positioned as sub-heaters. Therefore, the main heater (heating element 101) and the sub-heater (heating elements 102 and 103) are switched between use, mainly during startup and when the load changes.

The heater 100 also has three heating elements with different lengths in the paper width direction, which suppresses temperature rise in non-paper passing areas and aims to achieve high productivity even with LTR and paper less than A4 in width (hereinafter referred to as small size paper). Therefore, from this perspective as well, the performance of the heater 100 is maximized by frequently switching between the main heater (heating element 101) and the sub-heater (heating elements 102 and 103). Furthermore, the heating elements 101 to 103 are arranged in the short direction of the ceramic substrate 104 in the order of one heating element 101, one heating element 102, one heating element 103, and the other heating element 101.

The electromagnetic relay 113, which is a third switch element, has contacts 113a, 113b, and 113c. When contacts 113a and 113b are connected, the power supply path is switched to supply power to the heating element 102, which is also referred to as a state switched to the heating element 102. When contacts 113a and 113c are connected, the power supply path is switched to supply power to the heating element 103, which is also referred to as a state switched to the heating element 103. The switching operation of the connection state of the electromagnetic relay 113 is performed by a driving circuit A 130, which is a third driving means. The driving circuit A 130 is controlled by a control signal A, which is a third control signal transmitted from the control unit 125.

The triac 108, which is a first switching element, controls the power supply to the heating element 101 by being in a conductive or non-conductive state. The conductive or non-conductive state of the triac 108 is controlled by a driving circuit B 131, which is a first driving means. The driving circuit B 131 is controlled by a control signal B, which is a first control signal transmitted from the control unit 125. The triac 109, which is a second switching element, controls the power supply to the heating element 102 or the heating element 103 by being in a conductive or non-conductive state. The conductive or non-conductive state of the triac 109 is controlled by a driving circuit C 132, which is a second driving means. The driving circuit C 132 is controlled by a control signal C, which is a second control signal transmitted from the control unit 125.

The electromagnetic relay 114, which is the fourth switch element, has contacts 114a and 114b. When contacts 114a and 114b are connected, power can be supplied from the AC power source 107 to the heater 100. The switching operation of the electromagnetic relay 114 between the connected state and the disconnected state is performed by a drive circuit D 133, which is the fourth drive means. The drive circuit D 133 is controlled by a control signal D, which is a seventh control signal, sent from the control unit 125.

(Zero cross detection circuit)
The zero-cross detection circuit 128 includes a current limiting resistor (hereinafter referred to as resistor) 115, a pull-up resistor (hereinafter referred to as resistor) 116, and a photocoupler 117. The anode terminal of the photodiode 117d of the photocoupler 117 is connected to the contact 106d and the electromagnetic relay 113 via the resistor 115, and the cathode terminal is connected to the bidirectional thyristors (hereinafter referred to as triacs) 108 and 109. The collector terminal of the phototransistor 117t of the photocoupler 117 is connected to a predetermined power supply voltage (not shown) via the resistor 116, and the emitter terminal is grounded. The connection point between the resistor 116 and the phototransistor 117t of the photocoupler 117 is connected to the control unit 125, and the detection result of the zero-cross detection circuit 128 is transmitted to the control unit 125 via this transmission line as a zero-cross signal.

The zero-cross detection circuit 128 detects the timing when the voltage phase of the AC power supply 107 becomes approximately zero degrees, and outputs a zero-cross signal to the control unit 125. The control unit 125 controls the timing of power supply to the heater 100 based on the input zero-cross signal. Here, we will explain the electromagnetic relay 114 with a contact a configuration, which is controlled by the drive circuit D 133 that operates with a control signal D. The electromagnetic relay 114 sets the power supply from the AC power supply 107 to the heater 100 in a connected state or a disconnected state (cut-off), and also sets the current supply to the zero-cross detection circuit 128 in a connected state or a disconnected state.

(Detection circuit)
The detection circuit 126 includes a transistor 119, a diode 120 which is a third diode, a diode 121 which is a first diode, and a diode 122 which is a second diode. The collector terminal of the transistor 119 is connected to a transmission line (hereinafter, referred to as a zero-cross signal line) which transmits the above-mentioned zero-cross signal, and the emitter terminal is grounded. The base terminal of the transistor 119 is connected to the cathode terminals of the diodes 120, 121, and 122. The anode terminal of the diode 120 is connected to the control unit 125, and a control signal A is transmitted from the control unit 125 via this transmission line. The anode terminal of the diode 121 is connected to the control unit 125, and a control signal B is transmitted from the control unit 125 via this transmission line. The anode terminal of the diode 122 is connected to the control unit 125, and a control signal C is transmitted from the control unit 125 via this transmission line.

Here, control signal A is output to diode 120 and also to drive circuit A 130, which switches the connection state of electromagnetic relay 113. Control signal B is output to diode 121 and also to drive circuit B 131, which controls triac 108. Control signal C is output to diode 122 and also to drive circuit C 132, which controls triac 109.

As described above, the detection circuit 126 is connected in parallel to the base terminal of the transistor 119 with the control signal A via the diode 120, the control signal B via the diode 121, and the control signal C via the diode 122. The diodes 120 to 122 are backflow prevention diodes that prevent current from flowing into the control unit 125. The collector terminal of the transistor 119 is also connected to the zero-cross signal line, and the logic of the zero-cross signal line is switched by the logic of the control signals A to C or the switching unit 127 described later. In this way, the zero-cross signal line serves both as a transmission line for the signal from the zero-cross detection circuit 128 and as a transmission line for the signal that is the detection result of the detection circuit 126. In the first embodiment, the three signals of the control signals A to C are input to the base terminal of the transistor 119, but if the control signal increases, a control signal can be added in parallel. The control unit 125 detects the detection result of the detection circuit 126 using the zero-cross signal line.

(Switching section)
The switching unit 127 has a transistor 123. The collector terminal of the transistor 123 is connected to the base terminal of the transistor 119 of the detection circuit 126, and the emitter terminal is grounded. The base terminal of the transistor 123 is connected to the control unit 125, and a control signal D is transmitted from the control unit 125 through this transmission line. Here, the control signal D is output to the transistor 123 and is also output to a drive circuit D 133 that switches the connection state of the electromagnetic relay 114. In other words, the control signal D is also used as a control signal that controls the drive circuit D 133 that operates the electromagnetic relay 114 of the a-contact. The switching unit 127 can switch between outputting a zero-cross signal to the zero-cross signal line or outputting the detection result of the detection circuit 126 based on the logic of the control signal D.

[Current Path]
(Power supply to heating element 101)
FIG. 3 shows three current paths to the heating elements 101 to 103 when the heater 100 and heater control circuit of the first embodiment are used. When power is supplied from the AC power source 107 to the heating elements 101 to 103, the electromagnetic relay 114 is in a state in which the contacts 114a and 114b are connected, i.e., in an ON state. The control unit 125 turns on the electromagnetic relay 114 via the drive circuit D 133 by setting the control signal D to, for example, a high level. FIG. 3(a) is a diagram showing a current path when power is supplied to the heating element 101. When power is supplied from the AC power source 107 to the heating element 101, the current flows through the route shown by the thick line in FIG. 3(a). The power supply from the AC power source 107 to the heating element 101 is controlled by the triac 108. The triac 108 is controlled by the drive circuit B 131 operating according to the control signal B. In addition, the electromagnetic relay 113 that switches the power supply path to the heating element 102 and the power supply path to the heating element 103 is in a state in which the contacts 113a and 113b are connected in FIG. 3(a), but it may also be in a state in which the contacts 113a and 113c are connected.

(Power supply to heating element 102)
3B is a diagram showing a current path when power is supplied to the heating element 102. When power is supplied from the AC power source 107 to the heating element 102, the current flows along the route shown by the thick line in FIG. 3B. At this time, the electromagnetic relay 113 having a c-contact configuration has a contact 113a and a contact 113b connected, and is connected to the triac 109 side by controlling the triac 108 to maintain a non-conducting state. This allows the triac 109 to control the power supply from the AC power source 107 to the heating element 102. The electromagnetic relay 113 is controlled by a drive circuit A 130 that operates with a control signal A. The triac 109 is controlled by a drive circuit C 132 that operates with a control signal C. Here, since the contact impedance of the electromagnetic relay 113 having a c-contact configuration is sufficiently smaller than that of the heating element 103, almost no current flows through the heating element 103, and only the heating element 102 can be heated.

(Power supply to heating element 103)
3C is a diagram showing a current path when power is supplied to the heating element 103. When power is supplied from the AC power source 107 to the heating element 103, the current flows along the route shown by the thick line in FIG. 3C. At this time, the electromagnetic relay 113 having the c-contact configuration has the contact 113a and the contact 113c connected, that is, connected to the contact 106d side. This allows the triac 109 to control the power supply from the AC power source 107 to the heating element 103. The electromagnetic relay 113 is controlled by a drive circuit A 130 that operates with a control signal A. The triac 109 is controlled by a drive circuit C 132 that operates with a control signal C. Here, since the contact impedance of the electromagnetic relay 113 having the c-contact configuration is sufficiently smaller than that of the heating element 102, almost no current flows through the heating element 102, and only the heating element 103 can be heated.

[Operation of detection circuit and switching unit]
4 and Table 1, the specific operations of the detection circuit 126 and the switching unit 127 will be described. Fig. 4 shows a flowchart explaining the detection process for detecting the states of the control signals A to D, and Table 1 shows a truth table for the logic of the control signals A to D.

In Table 1, the first column shows the numbers (No. a to No. i) indicating the detection state, the second column shows the state of the transmission line of each control signal (normal, abnormal), and the third column shows the setting value of the control signal D (Low (low level), High (high level)). The fourth column shows the setting value of the control signal A (Low, High, any), the fifth column shows the setting value of the control signal B (Low, High, any), and the sixth column shows the setting value of the control signal C (Low, High, any). The seventh column shows the output of the zero cross signal line (Low, High, zero cross signal), and the eighth column shows the detectable content (for example, "control signal A is not Low"). For example, the control unit 125 sets the control signal D to a low level, and the output from the detection circuit 126 is input to the control unit 125 via the zero cross signal line. In this state, when the control signal A is set to a high level and the control signals B and C are set to a low level, the control unit 125 judges that the transmission line No. b is in a normal state if the output of the zero cross signal line is at a low level, and that the transmission line No. g is in an abnormal state if the output of the zero cross signal line is at a high level. In the abnormal state of No. g, the control unit 125 judges that the control signal A is actually at a low level, even though the control signal A is set to a high level. In this way, the control unit 125 judges whether or not the set value of each control signal matches the result (actual state) output from the detection circuit 126. In a state in which a signal from the detection circuit 126 is input, the control unit 125 judges that the state is normal if the signal input from the detection circuit 126 matches the set control signal. On the other hand, the control unit 125 judges that the state is abnormal if the signal input from the detection circuit 126 does not match the set control signal.

In FIG. 4, when the process for detecting whether the control signal is being normally transmitted on the transmission line is started, the control unit 125 executes the process from step (hereinafter, S) 201 onwards. In S201, the control unit 125 sets the control signal D to a low level (illustrated as Low, the same applies below). As a result, the control unit 125 turns off the transistor 123 of the switching unit 127 and opens (disconnects) the electromagnetic relay 114, thereby preventing the zero-cross signal from being output to the zero-cross signal line.

In S202, the control unit 125 sets the control signal A, the control signal B, and the control signal C to a low level. In S203, the control unit 125 judges whether the output of the detection circuit 126, i.e., the input from the zero-cross signal line, is at a high level (illustrated as High, the same below). Here, if the control signals A to D are transmitted normally, the transistor 119 is turned off. Therefore, the output of the zero-cross signal line is a power supply voltage (e.g., 3.3 V) not shown connected via the resistor 116, and is in a high level state (state No. a in Table 1). On the other hand, if a failure occurs such that any of the control signals A to C are at a high level and there is an abnormality in the transmission of the control signal, the transistor 119 is turned on and the zero-cross signal line is at a low level (state No. f in Table 1). If the control unit 125 judges in S203 that the zero-cross signal line is at a high level, the process proceeds to S205, and if the control unit 125 judges that the zero-cross signal line is at a low level, the process proceeds to S204. In S204, the control unit 125 determines that there is an abnormality in the transmission line, notifies the user by, for example, displaying a message to that effect on a display unit (not shown) of the image forming device, and ends the process.

In S205, the control unit 125 sets the control signal A to a high level, the control signal B to a low level, and the control signal C to a low level. In S206, the control unit 125 judges whether the output of the detection circuit 126, i.e., the input from the zero-cross signal line, has become low level. Here, if the transmission of the control signal A is normal, the transistor 119 turns on, and the zero-cross signal line becomes low level (state No. b in Table 1). On the other hand, if the zero-cross signal line is high level even though the control signal A is set to a high level, there is an abnormality in the transmission of the control signal A (state No. g in Table 1). In S206, if the control unit 125 judges that the zero-cross signal line is low level, the process proceeds to S207, and if the control unit 125 judges that the zero-cross signal line is high level, the process proceeds to S204.

In S207, the control unit 125 sets the control signal A to a low level, the control signal B to a high level, and the control signal C to a low level. In S208, the control unit 125 judges whether the output of the detection circuit 126, i.e., the input from the zero-cross signal line, has become low level. Here, if the transmission of the control signal B is normal, the transistor 119 turns on, and the zero-cross signal line becomes low level (state No. c in Table 1). On the other hand, if the zero-cross signal line is high level even though the control signal B is set to a high level, there is an abnormality in the transmission of the control signal B (state No. h in Table 1). In S208, if the control unit 125 judges that the zero-cross signal line is low level, the process proceeds to S209, and if the control unit 125 judges that the zero-cross signal line is high level, the process proceeds to S204.

In S209, the control unit 125 sets the control signal A to a low level, the control signal B to a low level, and the control signal C to a high level. In S210, the control unit 125 determines whether the output of the detection circuit 126, i.e., the input from the zero-cross signal line, has become low level. Here, if the transmission of the control signal C is normal, the transistor 119 turns on, and the zero-cross signal line becomes low level (state of No. d in Table 1). On the other hand, if the zero-cross signal line is high level even though the control signal C is set to a high level, there is an abnormality in the transmission of the control signal C (state of No. i in Table 1). If the control unit 125 determines in S210 that the zero-cross signal line is low level, the process proceeds to S211, and if the control unit 125 determines that the zero-cross signal line is high level, the process proceeds to S204.

In S211, the control unit 125 sets the control signal D to a high level. As a result, the control unit 125 turns on the transistor 123 of the switching unit 127, thereby setting the base terminal of the transistor 119 of the detection circuit 126 to a low level and turning off the transistor 119. Furthermore, since the control signal D is set to a high level, the electromagnetic relay 114 is short-circuited (connected), and current is supplied from the AC power source 107 to the zero-cross detection circuit 128. In this state, in S212, the control unit 125 determines whether a zero-cross signal is output to the zero-cross signal line. Here, if the transmission of the control signal D is normal, a zero-cross signal is output to the zero-cross signal line (state of No. e in Table 1). Note that, as shown in No. e in Table 1, the levels of the control signals A to C are arbitrary, but in the flowchart of FIG. 4, the control signal A and control signal B are low level and the control signal C is high level by the processing of S209. On the other hand, if no zero-cross signal is output to the zero-cross signal line, this indicates a malfunction, such as an abnormality in the transmission of the control signal D or an abnormality in the zero-cross detection circuit 128. If the control unit 125 determines in S212 that a zero-cross signal is output to the zero-cross signal line, the process proceeds to S213, and if the control unit 125 determines that a zero-cross signal is not output to the zero-cross signal line, the process proceeds to S204. In S213, the control unit 125 determines that the transmission lines for the control signals A to D are normal, and ends the process by, for example, starting control of the power supply to the heating elements 101 to 103.

By performing the above-described checking operation, it is possible to check whether the control signal that controls the power supply to the heating element is being transmitted normally through the transmission line. This makes it possible to prevent power being supplied to the heating element incorrectly due to an abnormality in the signal transmission, and to prevent damage to the heating element and the components surrounding the heating element. In addition, by using a switching unit to switch between outputting a zero-cross signal to the zero-cross signal line or outputting the results of the detection circuit, it is possible to check whether the control signal is being transmitted normally through the transmission line without increasing the number of signal lines.

As described above, according to the first embodiment, it is possible to accurately detect whether or not the control signal that controls the switch element is being transmitted normally through the transmission line.

Figure 5 shows the heater 100 used in the second embodiment, the zero-cross detection circuit 128, the detection circuit 126 that detects the state of the control signal, and the switching unit 127 that switches whether to output the zero-cross detection result or the detection result of the detection circuit 126 to the control unit 125. Note that the same parts as in the first embodiment are given the same reference numerals and their explanations are omitted.

[Input to detection circuit 126]
In the second embodiment, in order to check whether the control signal is normally transmitted through the transmission line at a location closer to the heating element, the following configuration is adopted. That is, signals output from the drive circuit A 130 driven by the control signal A, the drive circuit B 131 driven by the control signal B, and the drive circuit C 132 driven by the control signal C are input to the detection circuit 126. Specifically, when the drive circuit A 130 receives the control signal A from the control unit 125, it outputs the control signal A', which is the sixth control signal, to the detection circuit 126. When the drive circuit B 131 receives the control signal B from the control unit 125, it outputs the control signal B', which is the fourth control signal, to the detection circuit 126. When the drive circuit C 132 receives the control signal C from the control unit 125, it outputs the control signal C', which is the fifth control signal, to the detection circuit 126.

The switching unit 127 has the same configuration as in the first embodiment. The transistor 123 is turned on/off by a control signal D input to the base terminal of the transistor 123, thereby switching between outputting a zero-cross signal to the zero-cross signal line or outputting the detection result of the detection circuit 126. The control signal D is also used as a control signal for controlling the electromagnetic relay 114.

[Drive circuit configuration]
6A is a circuit diagram showing the configuration of the drive circuit A 130, and FIG. 6B is a circuit diagram showing the configuration of the drive circuit B 131. The configuration of the drive circuit C 132 is the same as that of the drive circuit B 131. The drive circuit A 130 has a diode 306, a transistor 307, and a resistor 308. The control signal A output from the control unit 125 is input to the base terminal of the transistor 307 via the resistor 308. The collector terminal of the transistor 307 is connected to the anode terminal of the diode 306, and the emitter terminal is grounded. The cathode terminal of the diode 306 is connected to a power supply voltage (not shown). The electromagnetic coil 113l of the electromagnetic relay 113 is connected in parallel to both ends of the diode 306. The control signal A' is a signal at the collector terminal of the transistor 307.

The drive circuit B 131 has a resistor 301, a phototriac coupler 302, a transistor 303, and a resistor 304. The control signal B output from the control unit 125 is input to the base terminal of the transistor 303 via the resistor 304. The collector terminal of the transistor 307 is connected to the cathode terminal of the photodiode 302d of the phototriac coupler 302, and the emitter terminal is grounded. The anode terminal of the photodiode 302d of the phototriac coupler 302 is connected to a power supply voltage (not shown) via the resistor 301. The phototriac 302t of the phototriac coupler 302 is connected in parallel to the triac 108. The control signal B' is a signal at the collector terminal of the transistor 303. The control signal C' is a signal at the collector terminal of the transistor (not shown) of the drive circuit C 132.

[Operation of the driving circuit]
In the drive circuit A 130, a control signal A is input to the base terminal of a transistor 307 via a resistor 308. The transistor 307 is controlled to be turned on/off by the control signal A. When the transistor 307 is turned on, a current flows through the electromagnetic coil 113l of the electromagnetic relay 113, and the electromagnetic relay 113 is in a state in which the contacts 113a and 113c are connected (a state in which power is supplied to the heating element 103). The diode 306 is a regenerative diode that regenerates electromagnetic energy generated when the transistor 307 is turned off. The drive circuit A 130 outputs a low-level control signal A' when the control signal A is at a high level.

In the drive circuit B 131, a control signal B is input to the base terminal of the transistor 303 via a resistor 304. The transistor 303 is controlled to be turned on/off by the control signal B. When the transistor 303 is turned on, a current flows through the photodiode 302d of the phototriac coupler 302, and a signal is transmitted to the phototriac 302t. This causes the triac 108 to be conductive. Note that the drive circuit C 132 also operates in a similar manner to cause the triac 109 to be conductive. The drive circuit B 131 outputs a low-level control signal B' when the control signal B is at a high level. The drive circuit C 132 outputs a low-level control signal C' when the control signal C is at a high level.

Table 2 is a truth table showing the output results of the zero cross signal line for each control signal.
In Table 2, the first column shows numbers (No. j to No. r) indicating the detection state. Columns 2 to 6 of Table 2 are similar to columns 2 to 6 of Table 1, and therefore explanations are omitted. Column 7 shows control signal A' (Low, High, any), column 8 shows control signal B' (Low, High, any), and column 9 shows control signal C' (Low, High, any). Columns 10 and 11 of Table 2 are similar to columns 7 and 8 of Table 1, and therefore explanations are omitted.

In the second embodiment, the control unit 125 judges signal transmission using control signals A'-C' taken from the collector terminals of transistors used in the drive circuits A-C controlled by the control signals A-C. The logic of the control signals A'-C' is the inverted value of the logic of the control signals A-C, so the set values of the control signals A-C are different from those in the first embodiment. For this reason, in the second embodiment, in the process of setting the control signals A-C in FIG. 4 described in the first embodiment, the values of the control signals A-C and the control signal D are set in the order of states No. j-No. n as shown in Table 2. This allows the control unit 125 to judge whether the signal is being transmitted normally through the transmission line. States No. o-No. r are the truth table when the transmission line is abnormal.

In the second embodiment, it is possible to check whether the control signal is normally transmitted to the transmission line closest to the heating element, and therefore it is possible to reliably prevent power being supplied to the wrong heating element. In addition, by setting the control signal D, it is possible to switch between outputting a zero-cross signal to the zero-cross signal line as in the first embodiment, or outputting the result of the detection circuit 126, and therefore it is possible to prevent an increase in costs due to an increase in the number of signal lines.

As described above, according to the second embodiment, it is possible to accurately detect whether or not the control signal that controls the switch element is being transmitted normally through the transmission line.

In the above-described embodiment, the switching unit is configured to switch whether the signal from the zero-cross detection circuit or the detection circuit is to be output to the control unit as a control signal for controlling a switch element that supplies power to a heater in a fixing device of an image forming apparatus. However, the device to which the zero-cross detection circuit, detection circuit, and switching unit are applied is not limited to an image forming apparatus. For example, the above-described detection circuit and switching unit can be applied to any electronic device that has a zero-cross detection circuit and to which a signal is sent from a control unit to control a switch element that supplies power to a load.

101, 102, 103 Heating elements 108, 109 Triac 113 Electromagnetic relay 125 Control unit 126 Detection circuit 127 Switching unit 128 Zero cross detection circuit 130, 131, 132 Drive circuits A, B, C

Claims (16)

At least one heating element;
A switch element that supplies or cuts off power from an AC power source to the heating element;
A driving means for driving the switch element in accordance with a control signal;
a control means for controlling the switch element via the driving means by setting the control signal;
A heating device comprising:
a detection means for outputting a signal corresponding to the control signal transmitted via a transmission line;
a zero-cross detection means for outputting a signal corresponding to the AC voltage of the AC power supply;
a switching means for switching between a first state in which a signal from the detection means is input to the control means and a second state in which a signal from the zero-cross detection means is input to the control means;
Equipped with
the at least one heating element includes a first heating element, a second heating element having a length in the longitudinal direction shorter than that of the first heating element, and a third heating element having a length in the longitudinal direction shorter than that of the second heating element;
the switch elements include a first switch element which supplies or cuts off power to the first heating element, a second switch element which supplies or cuts off power to the second heating element or the third heating element , and a third switch element which switches between a state in which the power supplied via the second switch element is supplied to the second heating element and a state in which the power is supplied to the third heating element;
a first control signal for driving the first switch element, a second control signal for driving the second switch element, and a third control signal for driving the third switch element . The heating device according to claim 1, characterized in that the control means determines the state of the control signal transmitted through the transmission line based on the signal input in the first state and the signal input in the second state. The heating device according to claim 2, characterized in that, in the first state, the control means determines that the device is normal if the signal input from the detection means matches the set control signal, and determines that the device is abnormal if the signal input from the detection means does not match the set control signal. The detection means includes:
a first diode having an anode terminal to which the first control signal is input;
a second diode having an anode terminal to which the second control signal is input;
a third diode, the third control signal being input to an anode terminal thereof;
the first diode, the second diode, and the third diode are connected in parallel;
a transistor having a base terminal connected to the cathode terminal of the first diode, the second diode and the third diode, an emitter terminal grounded, and a collector terminal connected to the control means;
The heating device according to any one of claims 1 to 3, characterized in that when the switching means switches to the first state, signals corresponding to the first control signal, the second control signal, and the third control signal are output to the control means. the first driving means outputs a fourth control signal corresponding to the first control signal to the detection means;
the second driving means outputs a fifth control signal corresponding to the second control signal to the detection means;
the third driving means outputs a sixth control signal corresponding to the third control signal to the detection means;
The detection means includes:
a first diode having an anode terminal to which the fourth control signal is input;
a second diode having an anode terminal to which the fifth control signal is input;
a third diode, the sixth control signal being input to an anode terminal thereof;
the first diode, the second diode, and the third diode are connected in parallel;
a transistor having a base terminal connected to the cathode terminal of the first diode, the second diode and the third diode, an emitter terminal grounded, and a collector terminal connected to the control means;
The heating device according to any one of claims 1 to 3, characterized in that when the switching means switches to the first state, signals corresponding to the fourth control signal, the fifth control signal, and the sixth control signal are output to the control means. 6. The heating device according to claim 1 , wherein the control means switches the state to the second state by the switching means when power is supplied to the heating element. a fourth switch element that connects or disconnects the power supply from the AC power source;
a fourth driving means for driving the fourth switch element in accordance with a seventh control signal;
Equipped with
7. The heating device according to claim 1 , wherein the control means sets the seventh control signal to control the switching means. a substrate on which the first heating element, the second heating element, and the third heating element are disposed;
Two of the first heating elements;
Equipped with
one of the first heating elements is disposed at one end in a short side direction of the substrate, and the other of the first heating elements is disposed at the other end in the short side direction;
8. The heating device according to claim 1, wherein the first heating element, the second heating element, the third heating element , and the other first heating element are arranged in this order in the short side direction. a first contact to which one end of the one first heating element and one end of the other first heating element are electrically connected;
a second contact to which the other end of the one first heating element, the other first heating element, and the other end of the second heating element are electrically connected;
a third contact to which one end of the second heating element and one end of the third heating element are electrically connected;
a fourth contact to which the other end of the third heating element is electrically connected; and
The heating device according to claim 8 , further comprising: a first rotating body heated by the plurality of heating elements;
a second rotating body that forms a nip portion together with the first rotating body;
The heating device according to any one of claims 1 to 9, further comprising: The heating device according to claim 10 , wherein the first rotating body is a film. the plurality of heating elements are provided so as to be in contact with an inner surface of the film,
12. The heating device according to claim 11 , wherein the nip portion is formed by the plurality of heating elements and the second rotating body via the film. a forming means for forming a toner image on a recording material;
a heating device according to claim 1 , which fixes an unfixed toner image formed on the recording material by the forming unit;
An image forming apparatus comprising: At least one load;
A switch element that supplies or cuts off power from an AC power source to the load;
A driving means for driving the switch element in accordance with a control signal;
a control means for controlling the switch element via the driving means by setting the control signal;
An electronic device comprising:
a detection means for outputting a signal corresponding to the control signal transmitted via a transmission line;
a zero-cross detection means for outputting a signal corresponding to the AC voltage of the AC power supply;
a switching means for switching between a first state in which a signal from the detection means is input to the control means and a second state in which a signal from the zero-cross detection means is input to the control means;
Equipped with
the at least one load includes a first load, a second load having a longitudinal length shorter than the first load, and a third load having a longitudinal length shorter than the second load;
the switch elements include a first switch element that supplies or cuts off power to the first load, a second switch element that supplies or cuts off power to the second load or the third load , and a third switch element that switches between a state in which the power supplied via the second switch element is supplied to the second load and a state in which the power is supplied to the third load,
the driving means includes first driving means for driving the first switch element in accordance with a first control signal, second driving means for driving the second switch element in accordance with a second control signal, and third driving means for driving the third switch element in accordance with a third control signal . 15. The electronic device according to claim 14, wherein the control means determines a state of the control signal transmitted through the transmission line based on a signal input in the first state and a signal input in the second state. 16. The electronic device according to claim 15, wherein the control means determines that the electronic device is normal when the signal input from the detection means matches a set control signal in the first state, and determines that the electronic device is abnormal when the signal input from the detection means does not match the set control signal.