Image forming device

Abstract

To reduce the size of a switch that opens and closes in conjunction with opening and closing of a cover to reduce manufacturing cost of an image forming apparatus.SOLUTION: An image forming apparatus comprises a plurality of heaters, a switch part, a first supply line, and a second supply line. The switch part opens and closes in conjunction with opening and closing of a cover. The first supply line connects one ends of the heaters and the switch part to each other. The second supply line connects the other ends of the heaters and the switch part to each other. The second supply line includes a branch part. The other ends of the heaters are connected with any one of branch lines being electric wires branched at the branch part. The switch part is arranged between the branch part and an AC power supply.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus including a heater for fixing a toner image. [Background technology]

[0002] An image forming apparatus that uses toner to perform printing is provided with a fixing device. Generally, the fixing device includes a heater for heating the toner image transferred onto paper. In addition, a mechanism may be provided that cuts off the power supply to the heater when an excessive temperature rise in a member heated by the heater is detected. Patent Document 1 describes an image forming apparatus that cuts off the power supply to the heater using multiple relays.

[0003] Specifically, Patent Document 1 describes an image forming apparatus that forms a toner image on a sheet and fixes the toner image formed on the sheet, the apparatus comprising: a heater that operates as a heat source and generates heat when an AC voltage is applied from an AC power source; power control means that controls the application of the AC voltage to the heater; a first relay and a second relay that are disposed between the AC power source and the heater and cut off current from the AC power source to the heater; detection means that detects whether or not an AC voltage is input after the first and second relays; and a detection means that outputs a drive signal to turn on one of the first and second relays before the AC voltage is applied to the heater when image formation starts and turns on the other relay. The image forming apparatus described in this publication performs a first relay abnormality detection operation to determine whether or not an AC voltage is input by the detection means when a drive signal to turn on the relay is not being output, and performs a second relay abnormality detection operation to determine whether or not an AC voltage is input by the detection means when a drive signal to turn on one of the first and second relays is not being output and a drive signal to turn on the other is being output after the application of the AC voltage to the heater is completed after the image formation is completed, and performs a process for the abnormality of the first and second relays when the input of the AC voltage is detected by at least one of the first and second relay abnormality detection operations. In a heat fixing device having two relays, the safety of the multiple relays is attempted to be confirmed without increasing the time until the start of a print operation (see Patent Document 1: Claim 1, paragraph

[0008] , etc.). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-042573 A Summary of the Invention [Problem to be solved by the invention]

[0005] There is an image forming apparatus in which part of the cover (housing) opens. The cover is opened when performing maintenance. A maintenance worker opens the cover to inspect and check the inside. For example, the worker can replace parts, remove jammed paper, or remove dirt.

[0006] Meanwhile, inside the image forming apparatus, there are parts to which a relatively high voltage is applied. For example, AC voltage from a commercial power source may be applied to a heater. When a worker puts his or her hand inside the image forming apparatus for maintenance, there is a risk that the worker may touch a part to which a relatively high voltage is applied. To prevent electric shock, a switch that is linked to the opening and closing of the cover may be provided. The switch is connected to an electric wire that supplies power to the part to which the voltage application should be cut off. For example, when the cover is opened, the switch also opens (turns OFF). As a result, when the cover is opened, the voltage application to the specific part is cut off. Even if the worker touches a part inside the image forming apparatus, he or she will not receive an electric shock.

[0007] Here, the more components (targets) to which voltage application is stopped when the cover is opened, the more power supply wires are connected to the switch. The more wires connected to the switch, the more poles (number of built-in switches) a switch needs to have. The more poles there are, the larger the switch becomes. A larger switch increases the manufacturing cost of the image forming apparatus. Another problem is that a larger switch reduces the degree of freedom in designing the image forming apparatus.

[0008] The technology described in Patent Document 1 is a technology that uses a relay to stop the application of AC voltage to the heater. The technology described in Patent Document 1 cannot solve the problem related to the switch that opens and closes in conjunction with the opening and closing of the cover.

[0009] The present invention has been made in consideration of the above-mentioned problems with the conventional technology, and aims to reduce the size of a switch that opens and closes in conjunction with the opening and closing of a cover, thereby reducing the manufacturing costs of an image forming apparatus and increasing the degree of freedom in design. [Means for solving the problem]

[0010] The image forming apparatus according to the present invention comprises a plurality of heaters, a switch unit, a first supply line, and a second supply line. The plurality of heaters heat a toner image. The switch unit is connected to an AC power source. The switch unit opens and closes in conjunction with opening and closing of a cover. The first supply line connects one end of each of the heaters to the switch unit. The second supply line connects the other end of each of the heaters to the switch unit. The second supply line comprises a branch unit. The other end of each of the heaters is connected to one of the branch lines, which are electric wires branched off at the branch unit. The switch unit is disposed between the branch unit and the AC power source. Effect of the Invention

[0011] According to the present invention, the switch that opens and closes in conjunction with the opening and closing of the cover can be made smaller than before. The smaller size reduces the manufacturing costs of the image forming apparatus. The smaller size reduces restrictions on component placement, allowing for greater freedom in mechanical design. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 illustrates an example of a printer according to an embodiment. [Diagram 2] FIG. 1 illustrates an example of a printer according to an embodiment. [Diagram 3] FIG. 2 is a diagram illustrating an example of a fixing device according to an embodiment. [Figure 4]FIG. 2 is a diagram illustrating an example of a fixing device according to an embodiment. [Diagram 5] FIG. 4 is a diagram showing an example of an arrangement of heaters in a fixing device according to an embodiment; [Figure 6] 5 is a diagram illustrating an example of power supply to a heater of the fixing device according to the embodiment. FIG. [Figure 7] 4A and 4B are diagrams illustrating an example of a first switch and a second switch according to the embodiment. [Figure 8] FIG. 1 is a diagram showing an example of an arrangement of a conventional interlock switch unit. [Figure 9] 11A and 11B are diagrams illustrating an example of a process of determination based on a zero-crossing detection signal according to the embodiment. [Figure 10] 13 is a diagram showing an example of power supply to a heater 6 of a fixing device 5 according to a modified example. FIG. [Figure 11] 13 is a diagram illustrating an example of a process of determination based on a first zero-cross detection signal and a second zero-cross detection signal according to a modified example. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment and a modified example of the present invention will be described with reference to Figs. 1 to 11. An image forming apparatus according to an embodiment will be described with reference to Figs. 1 to 9. An image forming apparatus according to a modified example will be described with reference to Figs. 10 and 11. In the following description, a printer will be taken as an example of an image forming apparatus according to the embodiment and the modified example. The elements of the configuration, arrangement, etc. described in this embodiment do not limit the scope of the invention and are merely illustrative examples.

[0014] (Printer 100) 1 and 2 are diagrams illustrating an example of a printer 100 according to an embodiment. As illustrated in FIGS. 1 and 2, the printer 100 includes a printing unit 40. The printing unit 40 includes a paper feed unit 4a, a first transport unit 4b, an image forming unit 4c, a fixing device 5, and a second transport unit 4d. The paper feed unit 4a is disposed at the bottom inside the printer 100. The paper feed unit 4a includes a plurality of paper feed cassettes 41 and a plurality of paper feed rollers 42. The paper feed cassette 41 stores a plurality of sheets of paper. During a print job, one of the paper feed rollers 42 rotates. As a result, paper is sent out from one of the paper feed cassettes 41.

[0015] The first transport section 4b transports the paper sent from the paper feed section 4a to the image forming section 4c. The first transport section 4b includes a plurality of first transport roller pairs 43. During a print job, each of the first transport roller pairs 43 rotates. As a result, the paper is transported. The paper is transported along the transport guide of the first transport section 4b.

[0016] The image forming unit 4c includes a photoconductor drum 44, a charging device 45, an exposure device 46, a developing device 47, a transfer roller 48, and a cleaning device 49. The photoconductor drum 44 is supported so as to be rotatable. During printing, the photoconductor drum 44 rotates at a predetermined speed. The charging device 45 charges the surface of the photoconductor drum 44 at a constant potential. The exposure device 46 irradiates the charged photoconductor drum 44 with an optical signal (laser light, shown by a two-dot chain line) based on the image data of the image to be printed. As a result, an electrostatic latent image is formed on the circumferential surface of the photoconductor drum 44. The developing device 47 causes toner to fly and develops the electrostatic latent image on the photoconductor drum 44 with the toner. The transfer roller 48 comes into contact with the photoconductor drum 44. Paper passes through a nip (transfer nip) between the transfer roller 48 and the photoconductor drum 44. During a print job, a predetermined transfer voltage is applied to the transfer roller 48. As a result, the toner image is transferred onto the paper. The cleaning device 49 cleans the photoconductor drum 44 after the transfer.

[0017] The fixing device 5 applies heat and pressure to the paper onto which the toner image has been transferred. This fixes the toner image to the paper. The fixing device 5 then sends the paper to the second transport section 4d. The second transport section 4d includes a plurality of second transport roller pairs 410. During a print job, each of the second transport roller pairs 410 rotates. As a result, the second transport section 4d transports the paper that has passed through the fixing device 5 toward the discharge tray.

[0018] As shown in FIG. 2, the printer 100 includes a control unit 1, a storage unit 2, and an operation panel 3. The control unit 1 controls the operation of the printer 100. For example, the control unit 1 is a circuit board. The control unit 1 includes a control circuit 10, an image processing circuit 11, and a communication circuit unit 12. For example, the control circuit 10 is a CPU. The control circuit 10 performs calculations and processing based on the programs and data stored in the storage unit 2. The control circuit 10 controls the operation of each unit of the printer 100. For example, during a print job, the control unit 1 controls the operation of the paper feed unit 4a, the first conveying unit 4b, the image forming unit 4c, the fixing device 5, and the second conveying unit 4d.

[0019] For example, the image processing circuit 11 is an ASIC. An ASIC is an integrated circuit designed for image processing. The communication circuit unit 12 receives print data. Based on the data contained in the received print data (data described in a page description language), the image processing circuit 11 generates image data (raster data). According to the print settings (setting data) in the computer 200, the image processing circuit 11 performs image processing on the raster data and generates image data for print output. The control unit 1 causes the exposure device 46 to expose the photoconductor drum 44 based on the image data for print output.

[0020] The communication circuit unit 12 includes a connector, a communication processing circuit (communication IC), and a communication memory. The communication circuit unit 12 communicates with the computer 200. The communication memory stores communication software. Based on the communication software, the communication processing circuit performs communication processing. For example, the computer 200 is a PC or a server. The communication circuit unit 12 receives print data sent from the computer 200.

[0021] The printer 100 includes a ROM and a RAM as the memory unit 2. The printer 100 may also include a storage as the memory unit 2. For example, the storage is either an HDD or an SSD, or both.

[0022] The printer 100 includes an operation panel 3. For example, the operation panel 3 includes a display panel 31, a touch panel 32, and hard keys 33. The control unit 1 causes messages, setting screens, and software keys to be displayed on the display panel 31. Furthermore, based on the output of the touch panel 32, the control unit 1 recognizes which software key has been operated. Based on an output signal from the hard keys 33, the control unit 1 recognizes which hard keys 33 have been operated. The operation panel 3 accepts settings.

[0023] (Fixing device 5) An example of the fixing device 5 according to the embodiment will be described with reference to Figures 3 and 4. Figures 3 and 4 are diagrams showing an example of the fixing device 5 according to the embodiment. Figure 3 is a diagram showing an example of the fixing device 5 as seen from a direction perpendicular to the paper transport direction. Figure 4 is a diagram showing an example of the external appearance of the fixing device 5 with the fixing belt 50 removed.

[0024] As shown in Figures 3 and 4, the fixing device 5 includes a fixing belt 50, a pressure roller 51, a heater 6, and a belt end holding member 52. In the following description, the axial direction (main scanning direction) of the rotation of the fixing belt 50 and the pressure roller 51 is referred to as the Y-axis direction. The direction perpendicular to the Y-axis direction and parallel to the paper transport direction is referred to as the Z-axis direction. The direction perpendicular to the Z-axis direction and the Y-axis direction is referred to as the X-axis direction. The X-axis direction is the direction in which the transported paper is sandwiched.

[0025] The heater 6 heats the fixing belt 50. The heated fixing belt 50 heats the paper on which the toner image is transferred. The fixing belt 50 is endless. The fixing belt 50 is cylindrical and flexible. For example, the fixing belt 50 rotates about a first rotation axis L1. The fixing belt 50 extends in the Y-axis direction. A belt end holding member 52 is provided at each end of the fixing belt 50 (see FIG. 4). The two belt end holding members 52 hold the fixing belt 50 so that the position of the fixing belt 50 does not shift even when the fixing belt 50 rotates. The pressure roller 51 extends along the Y-axis direction. The pressure roller 51 includes a cylindrical rotation shaft 51a, an elastic layer 51b, and a release layer 51c. The rotation shaft 51a rotates about a second rotation axis L2 parallel to the Y-axis direction.

[0026] The fixing device 5 includes a heater 6, a heater holding member 53, and a reinforcing member 54. The heater 6 extends in the Y-axis direction. The heater 6 has a shape of a long and thin plate. For example, the heater 6 is a planar heater. The heater 6 includes multiple layers. For example, the heater 6 includes at least a glass layer, a heat generating layer, and a substrate layer. The heat generating layer is provided between the glass layer and the substrate layer. For example, the heat generating layer is a layer of heat generating paint. The heat generating paint generates heat when electricity is applied. For example, the material of the substrate layer is ceramic. For example, the surface of the glass layer contacts the fixing belt 50.

[0027] The heater holding member 53 holds the heater 6. For example, the heater holding member 53 is made of a heat-resistant resin. The heater holding member 53 extends in the Y-axis direction. The heater holding member 53 has a bottom wall surface 53a and a pair of side wall surfaces 53b. The bottom wall surface 53a faces the heater 6 and contacts the surface of the heater 6 opposite to the surface that contacts the fixing belt 50. In order to measure the temperature of the heater 6, a plurality of temperature sensors are provided in the fixing device 5. For example, a first temperature sensor 63a and a second temperature sensor 63b are provided (see FIG. 6). The heater holding member 53 has a plurality of openings into which the respective temperature sensors are fitted. Each temperature sensor is fitted into one of the openings and contacts the heater 6.

[0028] The reinforcing member 54 maintains the position and posture of the heater holding member 53. The cross section of the reinforcing member 54 seen from the Y-axis direction is inverted U-shaped. The reinforcing member 54 extends in the Y-axis direction. The reinforcing member 54 contacts the heater holding member 53 and fixes the heater holding member 53. The heater 6, the heater holding member 53, each temperature sensor, and the reinforcing member 54 are inserted inside the tube of the fixing belt 50. Part of the surfaces of the heater 6 and the heater holding member 53 contact the inner circumferential surface of the fixing belt 50. The surface of the heater holding member 53 that contacts the inner circumferential surface of the fixing belt 50 is called the contact surface 53c. The heater 6 and the contact surface 53c tension the fixing belt 50. The fixing belt 50 is tensioned in a cylindrical shape (non-circular). The area where the fixing belt 50 and the pressure roller 51 contact each other is the fixing nip area F. In FIG. 3, The rectangle with one end omitted, located between the fixing belt 50 and the pressure roller 51, represents paper. The black rectangle on the upper surface of the rectangle representing the paper represents toner. Fig. 3 shows an example of a state in which the fixing belt 50 and the pressure roller 51 nip the paper.

[0029] The heater 6 receives pressure from the pressure roller 51 via the fixing belt 50. The heater 6 also receives pressure from the reinforcing member 54 via the heater holding member 53. The position of the heater 6 is fixed. A fixing motor (not shown) is provided to rotate the pressure roller 51. The pressure roller 51 is driven to rotate by the fixing motor. When the pressure roller 51 rotates, the fixing belt 50 is driven and rotates.

[0030] (Heater 6) Next, an example of the heater 6 provided in the fixing device 5 according to the embodiment will be described with reference to Fig. 5. Fig. 5 is a diagram showing an example of the arrangement of the heater 6 in the fixing device 5 according to the embodiment.

[0031] The fixing device 5 includes a heater 6. The heater 6 heats the fixing nip area F in the Y-axis direction (the longitudinal direction of the fixing belt 50, the direction perpendicular to the paper transport direction, the main scanning direction). In the printer 100, the heater 6 is divided into multiple parts. In this explanation, an example will be described in which the fixing device 5 includes two heaters 6, a first heater 61 and a second heater 62. Note that the number of heaters 6 included in the fixing device 5 may be three or more.

[0032] The first heater 61 and the second heater 62 are arranged (aligned) in a straight line along the Y axis direction. The first heater 61 heats the center portion in the Y axis direction of the fixing belt 50 and the fixing nip area F. The second heater 62 heats both end portions in the Y axis direction of the fixing belt 50 and the fixing nip area F.

[0033] FIG. 5 is a diagram showing an example of the arrangement of the first heater 61 and the second heater 62 in the fixing device 5. The largest rectangle in FIG. 5 indicates the fixing nip area F. The first heater 61 is provided at a position where it heats the center of the fixing nip area F in the Y-axis direction. The second heater 62 heats the end of the fixing nip area F in the Y-axis direction. The heating width W1 of the first heater 61 in the Y-axis direction is, for example, the same as the short side of an A4 sheet of paper, or is wider than the A4 sheet by a predetermined margin width. For example, the margin width is several mm to several cm. When printing using paper whose width in the Y-axis direction (main scanning direction) is equal to or smaller than the short side of an A4 sheet of paper, the control unit 1 operates only the first heater 61. This makes it possible to prevent the temperature at both ends of the fixing belt 50 from rising too much. The heating width W2 in the Y-axis direction when both the first heater 61 and the second heater 62 are used is wider than the heating width W1. The heating width W2 is equal to or larger than the short side of an A3 sheet of paper.

[0034] When printing using paper whose width in the Y-axis direction exceeds the short side of A4 paper (for example, A3 paper), the control unit 1 operates the first heater 61 and the second heater 62. As shown in Fig. 5, the second heater 62 is positionally divided into two. Specifically, the second heater 62 is divided into a first divided heater 62a and a second divided heater 62b. However, the first divided heater 62a and the second divided heater 62b are electrically connected in series.

[0035] (Power supply to heater 6) Next, an example of power supply and control to the heater 6 according to the embodiment will be described with reference to Figs. 6 to 8. Fig. 6 is a diagram showing an example of power supply to the heater 6 of the fixing device 5 according to the embodiment. Fig. 7 is a diagram showing an example of a first switch 81 and a second switch 82 according to the embodiment. Fig. 8 is a diagram showing an example of the arrangement of a conventional interlock switch unit 301.

[0036] First, the printer 100 includes a power supply unit 7. For example, the power supply unit 7 is a board (power supply board) including multiple power circuits. The power supply unit 7 is connected to an AC power source AC. For example, the AC power source AC is a commercial power source. The power supply unit 7 is connected to a power distribution outlet for the commercial power source via a power cord. The power supply unit 7 is connected to the non-grounded pole L (live) and grounded pole N (neutral) of the AC power source AC. The printer 100 also includes a switch unit 8. For example, the switch unit 8 includes two switches. Hereinafter, the respective switches are referred to as a first switch 81 and a second switch 82. In other words, the switch unit 8 is a unit with two poles. The number of poles refers to the number of circuits or wires that can be opened or closed with one operation.

[0037] As shown in FIG. 1, the printer 100 has a cover 101. The cover 101 can be opened and closed. FIG. 1 shows the cover 101 in a closed state. In FIG. 1, the arrow on the cover 101 indicates an example of the direction in which the cover can be opened. By opening the cover 101, the inside of the printer 100 can be exposed, making it possible to perform maintenance. For example, an operator (user) can visually check the internal state of the printer 100. Furthermore, by opening the cover 101, it is possible to remove jammed paper or replace parts.

[0038] The switch unit 8 is connected to an alternating current power source AC. The switch unit 8 (first switch 81 and second switch 82) opens and closes in conjunction with the opening and closing of the cover 101. The first switch 81 and the second switch 82 open when the cover 101 of the printer 100 is opened, and close when the cover 101 is closed.

[0039] 7 shows an example of a first switch 81 and a second switch 82. The first switch 81 and the second switch 82 are so-called interlock switches. The first switch 81 includes a first contact 81a, a second contact 81b, a movable plate 81c, an elastic body 81d, and an actuator 81e. The second switch 82 includes a first contact 82a, a second contact 82b, a movable plate 82c, an elastic body 82d, and an actuator 82e. The first switch 81 and the second switch 82 may have the same configuration.

[0040] The first switch 81 and the second switch 82 are connected to an AC power source AC. Specifically, a first contact 81a of the first switch 81 is connected to either the non-grounded side pole L or the grounded side pole N of the AC power source AC. A first contact 82a of the second switch 82 is connected to the other of the non-grounded side pole L or the grounded side pole N of the AC power source AC. An AC voltage is applied to each of the first contacts.

[0041] The printer 100 is equipped with a first supply line 91 and a second supply line 92. The first supply line 91 and the second supply line 92 are electric wires. As shown in Fig. 6, the first supply line 91 connects the second contact 81b to one end of each heater 6 (the first heater 61 and the second heater 62). For example, terminals are provided at one end of the first heater 61 and one end of the first divided heater 62a. The first supply line 91 connects these terminals at one end to the second contact 81b.

[0042] The second supply line 92 connects the second contact 81b to the other end of each heater 6 (the first heater 61 and the second heater 62). For example, a terminal is provided at the other end of the first heater 61. A terminal is also provided at the other end of the second split heater 62b. The other end of the first split heater 62a and one end of the second split heater 62b are connected by a separate electric wire. The second supply line 92 connects these other end terminals to the second contact 82b.

[0043] When closed, the first switch 81 connects the AC power source AC to the first supply line 91. When closed, the second switch 82 connects the AC power source AC to the second supply line 92. When each switch is closed, a current can flow to the first heater 61 and the second heater 62. The condition for current flow is that both the first switch 81 and the second switch 82 are closed.

[0044] The first switch 81 will be described. The movable plate 81c is a conductor. When the movable plate 81c is in contact with the first contact 81a and the second contact 81b, the switch is in a conductive state (closed state, ON state). The position of the movable plate 81c is changed by an elastic body 81d (spring) and an actuator 81e. The actuator 81e is in contact with the movable plate 81c. The elastic body 81d biases the actuator 81e in a direction in which the movable plate 81c moves away from each contact. When the force pressing the movable plate 81c is removed and the movable plate 81c moves away from the first contact 81a and the second contact 81b, the first switch 81 is in a non-conductive state (open state, OFF state).

[0045] The second switch 82 will be described. The movable plate 82c is a conductor. When the movable plate 82c is in contact with the first contact 82a and the second contact 82b, the switch is in a conductive state (closed state, ON state). The position of the movable plate 82c is changed by an elastic body 82d (spring) and an actuator 82e. The actuator 82e is in contact with the movable plate 82c. The elastic body 82d biases the actuator 82e in a direction in which the movable plate 82c moves away from each contact. When the force pressing the movable plate 82c is removed and the movable plate 82c moves away from the first contact 82a and the second contact 82b, the second switch 82 is in a non-conductive state (open state, OFF state).

[0046] The cover 101 is provided with a protrusion 102. The first switch 81 is provided with a hole 81f into which the protrusion 102 is inserted. The second switch 82 is provided with a hole 82f into which the protrusion 102 is inserted. When the cover 101 is closed, the protrusion 102 contacts the movable plate 81c and the movable plate 82c. When the cover 101 is closed, the protrusion 102 presses both the movable plate 81c and the movable plate 82c, and both the actuator 81e and the actuator 82e. The protrusion 102 moves each movable plate and each actuator so that the movable plate 81c contacts each contact. Note that a protrusion 102 for the first switch 81 and a protrusion 102 for the second switch 82 may be provided. Also, one protrusion 102 may act on both the movable plate of the first switch 81 and the movable plate of the second switch 82.

[0047] In conjunction with the cover 101 being closed, the first switch 81 and the second switch 82 are switched to a closed state (conductive state, ON state). On the other hand, when the cover 101 is opened, the protrusion 102 is no longer pressed against each movable plate. The protrusion 102 is no longer in contact with each movable plate. As a result, due to the bias of the elastic body 81d and the elastic body 82d, the actuator 81e moves the movable plate 81c in the direction in which the contacts move apart, and the actuator 82e moves the movable plate 82c in the direction in which the contacts move apart. In conjunction with the cover 101 being opened, the first switch 81 and the second switch 82 are switched to an open state (non-conductive state, OFF state).

[0048] Here, the second supply line 92 has a branch portion 93 (branching point). Hereinafter, the second supply line 92 branched at the branch portion 93 and connected to the other end of each heater 6 will be referred to as a branch line 94. The other end of each heater 6 is connected to one of the branch lines 94. Specifically, one branch line 94 is connected to the other end of the first heater 61. In addition, another branch line 94 is connected to the other end of the second split heater 62b (of the second heater 62).

[0049] FIG. 6 shows an example in which there are two branch lines 94. When the number of heaters 6 is three, the number of branch lines 94 is also three. The number of branch lines 94 provided is the same as the number of heaters 6. The switch unit 8 is disposed between the branch unit 93 and the AC power source AC. This allows the switch unit 8 to have only two poles, regardless of the number of heaters 6 and branch lines 94. Furthermore, when the switch unit 8 (first switch 81 and second switch 82) is turned OFF, the first supply line 91 and the second supply line 92 can be opened simultaneously.

[0050] In this description, an example is described in which the first split heater 62a and the second split heater 62b are connected in series. However, one end of the first split heater 62a and one end of the second split heater 62b may each be connected to the second contact 81b of the first switch 81. In this case, one branch line 94 is connected to the other end of the first heater 61. In addition, another branch line 94 is connected to the other end of the first split heater 62a. Yet another branch line 94 is connected to the other end of the second split heater 62b. There are a total of three branch lines 94. In other words, the first split heater 62a and the second split heater 62b may be treated as separate heaters 6.

[0051] The power supply device 7 also includes a zero-cross detection circuit 70. The zero-cross detection circuit 70 is connected to the first supply line 91 and the second supply line 92. That is, the voltage of the first supply line 91 and the voltage of the second supply line 92 are input to the zero-cross detection circuit 70. The zero-cross detection circuit 70 is a circuit that detects a periodic change in the AC voltage. The zero-cross detection circuit 70 generates a zero-cross detection signal S0. For example, the zero-cross detection circuit 70 generates a signal that is either a low level or a high level while the absolute value of the input AC voltage is equal to or less than a threshold, and is either a low level or a high level while the absolute value of the input AC voltage exceeds the threshold, as the zero-cross detection signal S0. For example, the zero-cross detection circuit 70 is a circuit that generates a signal that switches between a high level and a low level in accordance with a half cycle of the AC voltage as the zero-cross detection signal S0. The zero-cross detection circuit 70 may be a circuit using a photocoupler or a circuit using a comparator, and is not particularly limited.

[0052] A current control element 95 is provided on each of the branch lines 94. In order to apply an AC voltage to the heater 6, the current control element 95 is an element that passes a current in both directions. The current control element 95 is an element that can control a current in both directions. For example, the current control element 95 is a triac. The printer 100 also includes a fixing control unit 9 (corresponding to a determination circuit unit). The fixing control unit 9 is a board that includes a control circuit such as a microcomputer. The fixing control unit 9 is connected to a control terminal of the current control element 95. The fixing control unit 9 controls the conduction and non-conduction of the current control element 95. For example, during a print job, the fixing control unit 9 passes a current to the heater 6 to be used out of the first heater 61 and the second heater 62. The fixing control unit 9 can pass a current only to the first heater 61, or can pass a current to both the first heater 61 and the second heater 62.

[0053] As shown in FIG. 6, the fixing control unit 9 may receive an output value of a first temperature sensor 63a and an output value of a second temperature sensor 63b provided in the fixing device 5. For example, the first temperature sensor 63a measures the temperature at the center or approximately the center of the fixing belt 50 in the Y-axis direction. The second temperature sensor 63b measures the temperature at one side or the other side of the fixing belt 50 in the Y-axis direction. Based on the output of the first temperature sensor 63a, the fixing control unit 9 can recognize the temperature of the center part of the fixing belt 50 in the Y-axis direction (heating area of ​​the first heater 61). Also, based on the output of the second temperature sensor 63b, the fixing control unit 9 can recognize the temperature of the end part of the fixing belt 50 in the Y-axis direction (heating area of ​​the second heater 62).

[0054] The zero-cross detection signal S0 may also be input to the fixing control unit 9. The fixing control unit 9 may control the timing of conduction of the current control element 95 based on the input zero-cross detection signal S0 and the recognized temperature. In other words, the fixing control unit 9 may adjust the magnitude of the power supplied to each heater 6. For example, during a print job, the fixing control unit 9 may perform phase control. When performing phase control, the fixing control unit 9 may advance the phase of conducting the current control element 95 of the first heater 61 in the half wave of the AC voltage as the temperature recognized based on the output of the first temperature sensor 63a becomes lower. The fixing control unit 9 may advance the phase of conducting the current control element 95 of the second heater 62 in the half wave of the AC voltage as the temperature recognized based on the output of the second temperature sensor 63b becomes lower.

[0055] During a print job, the fixing control unit 9 may perform half-wave control. When performing half-wave control, the fixing control unit 9 may increase the number of half-waves for which the current control element 95 of the first heater 61 is conductive among a predetermined number of half-waves as the temperature recognized based on the output of the first temperature sensor 63a is lower. The fixing control unit 9 may increase the number of half-waves for which the current control element 95 of the second heater 62 is conductive among a predetermined number of half-waves as the temperature recognized based on the output of the second temperature sensor 63b is lower.

[0056] Here, an example of a switch unit 301 provided in a conventional image forming apparatus will be described. FIG. 8 shows an example of a power supply system of an image forming apparatus provided with a conventional switch unit 301. First, in the printer 100, the voltage of an AC power source 302 (commercial power source) is applied to a heater 303 and a fixing belt in contact with the heater 303. When opening the cover to remove jammed paper, an operator may touch the heater 303 or the fixing belt. The commercial power source has a relatively high voltage. In the case of AC 100V, the maximum voltage is about 140V. It is necessary to prevent the operator from getting an electric shock. Therefore, a switch unit 301 that opens and closes in conjunction with the opening and closing of the cover may be provided.

[0057] Conventionally, the power supply board 305 and the heater 303 are electrically connected using a wire (power supply wire 304) for supplying electricity to the heater 303. When a plurality of heaters 303 are provided, one of the power supply wires 304 is connected to one end of each heater 303. A separate power supply wire 304 is connected to the other end of each heater 303. Therefore, the number of power supply wires 304 is the number of heaters 303 + 1. Conventionally, a switch unit 301 is provided between the power supply board 305 and the fixing unit 306. The conventional switch unit 301 includes an interlock switch 307 for each power supply wire 304. This makes it possible to prevent electric shock even if a part of the interlock switch 307 breaks down. In other words, the number of poles of the switch unit 301 is the same as the number of power supply wires 304 connecting the power supply board 305 and the fixing unit 306.

[0058] FIG. 8 shows an example in which the fixing unit 306 is provided with two heaters 303. As shown in FIG. 8, when two heaters 303 are provided, the number of poles of the conventional switch unit 301 is three. That is, the switch unit 301 includes three interlock switches 307. When three heaters 303 are provided, the number of poles of the switch unit 301 is four. The larger the number of interlock switches 307 built in, the larger the switch unit 301 becomes. When the switch unit 301 becomes larger, the required pressing force also becomes larger. The pressing force here refers to the force required to press the cover to switch all the interlock switches 307 from OFF to ON. When the required pressing force is large, there is a tendency for the cover to be easily pressed in poorly (poor contact). When poor contact occurs, electricity cannot be applied to the heater 303, or electricity is unstable.

[0059] On the other hand, the switch unit 8 is disposed between the branch unit 93 and the AC power source AC. When the first switch 81 and the second switch 82 are opened, it is possible to make non-conductive all of the electric wires connecting the AC power source AC to one end of the first heater 61 and one end of the second heater 62, and the electric wires connecting the AC power source AC to the other end of the first heater 61 and the other end of the second heater 62. Even if the number of heaters 6 increases, the number of poles of the switch unit 8 is only two. The unit including the interlock switch does not become large.

[0060] As shown in Fig. 6, the power supply device 7 may include a power conversion circuit 7p. For example, the power conversion circuit 7p converts an AC voltage to generate a DC voltage. For example, the power conversion circuit 7p generates a DC voltage for driving a motor. For example, the power conversion circuit 7p is a switching power supply circuit including a transformer. The power supply device 7 may include a plurality of power conversion circuits 7p.

[0061] (Determination based on zero-cross detection signal S0) Next, an example of a process of determination based on the zero cross detection signal S0 according to the embodiment will be described with reference to Fig. 9. Fig. 9 is a diagram showing an example of a process of determination based on the zero cross detection signal S0 according to the embodiment.

[0062] The start of Fig. 9 is the time when the process of determination based on the zero-cross detection signal S0 begins. The time when the process begins is determined in advance. For example, it may be the time when the printer 100 is started by turning on the power (starting connection to the AC power source AC). It may also be the time when a predetermined time has passed since the previous process of determination based on the zero-cross detection signal S0 was performed. The predetermined time may be one second or less, one second, several seconds, or longer than 10 seconds.

[0063] In the following, an example will be described in which the determination circuit unit that performs the determination process is the fixing control unit 9. Note that the determination circuit unit does not have to be the fixing control unit 9. For example, the determination circuit unit may be the control circuit 10 (CPU) of the control unit 1, or a control circuit on another board.

[0064] The fixing control unit 9 monitors the zero-cross detection signal S0 for a certain period of time (step #11). The certain period of time is at least longer than a half cycle of the AC voltage. For example, the certain period of time may be a half cycle of the AC voltage, or may be one cycle or more. When the AC voltage is 50 Hz, the certain period of time may be longer than 1 / 100 seconds or longer than 1 / 50 seconds. The certain period of time may be several cycles of the AC voltage. Specifically, the fixing control unit 9 monitors whether the zero-cross detection signal S0 has changed between a high level and a low level during the certain period of time. The fixing control unit 9 may count the number of times the level of the zero-cross detection signal S0 has changed. When the zero-cross detection circuit 70 detects a periodic change in the AC voltage, the level of the zero-cross detection signal S0 changes periodically.

[0065] The fixing control unit 9 determines whether the zero-cross detection circuit 70 detects a periodic change in the AC voltage (step #12). Specifically, when the level of the zero-cross detection signal S0 changes during monitoring, the fixing control unit 9 may determine that the zero-cross detection circuit 70 detects a periodic change in the AC voltage. When the level does not change at all during monitoring, the fixing control unit 9 may determine that the zero-cross detection circuit 70 does not detect a periodic change in the AC voltage.

[0066] When the zero-cross detection circuit 70 determines that the periodic change in the AC voltage is detected (Yes in step #12), the fixing control unit 9 determines that the cover 101 and the switch unit 8 (the first switch 81 and the second switch 82) are closed (step #13→END). When the zero-cross detection circuit 70 determines that the periodic change in the AC voltage is not detected (No in step #12), the fixing control unit 9 determines that the cover 101 and the switch unit 8 are open (step #14).

[0067] When it is determined that the cover 101 and the switch unit 8 are open, the fixing control unit 9 may cause the notification unit to notify that the cover 101 is open (step #15 → END). The notification unit can detect that the cover 101 is open and can notify that there is no abnormality. For example, the notification unit is the display panel 31. The display panel 31 displays a message. For example, upon receiving a notification from the fixing control unit 9, the control unit 1 causes the display panel 31 to display a message notifying that the cover 101 is open. The control unit 1 may continue to display the message notifying that the cover 101 is open on the display panel 31 until the fixing control unit 9 determines that the cover 101 is closed.

[0068] The control unit 1 communicates with the fixing control unit 9. The control unit 1 receives a notification of the determination result from the fixing control unit 9. When the cover 101 and the switch unit 8 are open, the control unit 1 does not operate the motor that rotates the rotating body (roller) of the printing unit 40. After the cover 101 and the switch unit 8 are closed, the control unit 1 restarts the motor that rotates the rotating body (roller) of the printing unit 40. For example, when printing stops due to a paper jam, the paper is removed, the cover 101 is closed, and printing is resumed.

[0069] The image forming apparatus (printer 100) according to the embodiment includes multiple heaters 6 (first heater 61 and second heater 62), a switch unit 8, a first supply line 91, and a second supply line 92. The multiple heaters 6 heat a toner image. The switch unit 8 is connected to an AC power source AC. The switch unit 8 opens and closes in conjunction with the opening and closing of a cover 101. The first supply line 91 connects one end of each heater 6 to the switch unit 8. The second supply line 92 connects the other end of each heater 6 to the switch unit 8. The second supply line 92 includes a branch unit 93. The other end of each heater 6 is connected to one of branch lines 94, which are electric wires branched at the branch unit 93. The switch unit 8 is disposed between the branch unit 93 and the AC power source AC.

[0070] As a result, by simply opening the cover 101, all the terminals of the heaters 6 can be disconnected from the AC power source AC. Conventionally, when there are multiple heaters 6, a large switch is required because of the large number of poles (the number of built-in interlock switches). The length of the contact gap (the minimum distance between the contacts that must be secured) when the cover 101 is open may be determined by a standard. In many cases, the larger the number of poles, the larger the switch. In the image forming apparatus of the embodiment, the switch unit 8 is provided on the AC power source AC side rather than the branch unit 93. That is, the non-branched portion of the second supply line 92 is connected to the switch unit 8. Therefore, the switch unit 8 may be a mechanism that switches between conductive and non-conductive states of two electric wires. This allows the switch unit 8, which opens and closes in conjunction with the opening and closing of the cover 101, to be made smaller. Compared to the case where a large switch is used, the manufacturing cost of the image forming apparatus can be reduced. In addition, since the switch unit 8 can be small, there are fewer restrictions on the arrangement of parts of the image forming apparatus. This allows the degree of freedom in the design of the mechanism of the image forming apparatus to be increased. In addition, a large switch requires a large pressing force to switch from OFF to ON. If the required pressing force is large, pressing failure is likely to occur. However, since the switch portion 8 can be made smaller, the pressing force required to switch ON / OFF is also small. Therefore, pressing failure is less likely to occur.

[0071] The switch unit 8 includes a first switch 81 and a second switch 82. The first switch 81 is connected to either the non-grounded side pole L or the grounded side pole N of the AC power source AC. When the cover 101 is opened, the first switch 81 opens and does not connect the AC power source AC to the first supply line 91. When the cover 101 is closed, the first switch 81 closes and connects the AC power source AC to the first supply line 91. The second switch 82 is connected to the other of the non-grounded side pole L or the grounded side pole N of the AC power source AC. When the cover 101 is opened, the second switch 82 opens and does not connect the AC power source AC to the second supply line 92. When the cover 101 is closed, the second switch 82 closes and connects the AC power source AC to the second supply line 92. The connection between the first supply line 91 and the AC power source AC and the connection between the second supply line 92 and the AC power source AC can be interrupted. When the cover 101 is opened, the voltage application to each heater 6 can be stopped reliably.

[0072] The image forming apparatus according to the embodiment includes a zero-cross detection circuit 70, a determination circuit unit (a fixing control unit 9), and a notification unit (a display panel 31). The zero-cross detection circuit 70 is provided between the switch unit 8 and the heater 6. The zero-cross detection circuit 70 is connected to a first supply line 91 and a second supply line 92. The zero-cross detection circuit 70 generates a zero-cross detection signal S0 according to the AC voltage supplied from the AC power source AC. The determination circuit unit receives the zero-cross detection signal S0. The notification unit notifies a message. When the zero-cross detection circuit 70 does not detect a periodic change in the AC voltage, the notification unit notifies that the cover 101 is open. This allows the zero-cross detection circuit 70 to determine whether the cover 101 and the switch unit 8 are open. To detect whether the cover 101 is open, it is not necessary to provide a mechanical switch that comes into contact with the cover 101. Compared to the case where a mechanical switch is provided, the manufacturing cost of the image forming apparatus can be reduced.

[0073] Each branch line 94 is provided with a current control element 95 that controls bidirectional current based on the zero-cross detection signal S0. This makes it possible to precisely control the power supplied to the heater 6 during printing based on the zero-cross signal S0 (phase control, half-wave control). The zero-cross detection circuit 70 can be used to control the timing of power supply to the heater 6. The zero-cross detection circuit 70 can be used for a variety of purposes.

[0074] (Modification) Next, a modified example of the printer 100 according to the embodiment will be described with reference to Fig. 10 and Fig. 11. Fig. 10 is a diagram showing an example of power supply to the heater 6 of the fixing device 5 according to the modified example. Fig. 11 is a diagram showing an example of a process of determination based on the first zero-cross detection signal S1 and the second zero-cross detection signal S2 according to the modified example.

[0075] The printer 100A according to the modified example differs from the printer 100 according to the embodiment in that another zero-cross detection circuit is added. In other respects, the configuration of the printer 100 according to the embodiment and the printer 100A according to the modified example are the same. In the explanation of the modified example, the same components as those in the printer 100 according to the embodiment are given the same reference numerals as in the embodiment. Furthermore, the explanation of the same points will be used as an example, and detailed explanations will be omitted.

[0076] The printer 100A according to the modified example includes a first zero-cross detection circuit 71 and a second zero-cross detection circuit 72. The first zero-cross detection circuit 71 may be the same circuit as the zero-cross detection circuit 70 mounted on the printer 100 according to the embodiment. The first zero-cross detection circuit 71 is provided between the switch unit 8 and the heater 6, and is connected to a first supply line 91 and a second supply line 92, and generates a first zero-cross detection signal S1 according to the AC voltage supplied from the AC power source AC. The second zero-cross detection circuit 72 is provided between the switch unit 8 and the AC power source AC. The second zero-cross detection circuit 72 is connected to the non-grounded pole L and the grounded pole N of the AC power source AC. The second zero-cross detection circuit 72 generates a second zero-cross detection signal S2 based on the AC voltage.

[0077] The first zero-cross detection circuit 71 generates a first zero-cross detection signal S1 that is either a low level or a high level while the absolute value of the input AC voltage is equal to or less than a threshold, and is either a low level or a high level while the absolute value of the input AC voltage exceeds the threshold. For example, the first zero-cross detection signal S1 is a signal whose level changes in accordance with a half cycle of the AC voltage. When detecting a periodic change in the AC voltage, the first zero-cross detection circuit 71 outputs a signal that changes periodically.

[0078] The second zero-cross detection circuit 72 generates a second zero-cross detection signal S2 that is either a low level or a high level while the absolute value of the input AC voltage is equal to or less than a threshold, and is either a low level or a high level while the absolute value of the input AC voltage exceeds the threshold. For example, the second zero-cross detection signal S2 is a signal whose level changes in accordance with a half cycle of the AC voltage. When detecting a periodic change in the AC voltage, the second zero-cross detection circuit 72 outputs a signal that changes periodically. The first zero-cross detection circuit 71 and the second zero-cross detection circuit 72 may be circuits using a photocoupler or circuits using a comparator, and are not particularly limited. The first zero-cross detection circuit 71 and the second zero-cross detection circuit 72 may be circuits having the same circuit configuration or may be circuits having different circuit configurations.

[0079] Next, an example of the process of determination based on the first zero cross detection signal S1 and the second zero cross detection signal S2 in the printer 100A according to the modified example will be described with reference to FIG. 11. The start of FIG. 11 is the time point at which the process of determination according to the modified example begins. The time point at which this process begins is determined in advance. For example, it may be the time point at which the printer 100A is started up by turning on the power (starting connection to the AC power source AC). It may also be the time point at which a predetermined time has passed since the previous process of determination based on the zero cross detection signal S0 was performed. The predetermined time point may be one second or less, one second, several seconds, or longer than 10 seconds.

[0080] In the following, an example will be described in which the judgment circuit unit that performs the judgment process according to the modified example is the fixing control unit 9. Note that the judgment circuit unit does not have to be the fixing control unit 9. For example, the judgment circuit unit may be the control circuit 10 (CPU) of the control unit 1, or a control circuit on another board.

[0081] The fixing control unit 9 monitors the first zero-cross detection signal S1 and the second zero-cross detection signal S2 for a certain period of time (step #21). The certain period of time is at least longer than a half cycle of the AC voltage. For example, the certain period of time may be a half cycle of the AC voltage, or may be one cycle or more. When the AC voltage is 60 Hz, the certain period of time may be longer than 1 / 120 seconds or longer than 1 / 60 seconds. The certain period of time may be several cycles of the AC voltage. When each zero-cross detection circuit detects a periodic change in the AC voltage, the level of each zero-cross detection signal changes periodically. Specifically, the fixing control unit 9 monitors whether the level of the first zero-cross detection signal S1 has changed between a high level and a low level during the certain period of time. The fixing control unit 9 may count the number of times the level of the first zero-cross detection signal S1 has changed. The fixing control unit 9 also monitors whether the level of the second zero-cross detection signal S2 has changed between a high level and a low level during the certain period of time. The fixing control unit 9 may count the number of times the level of the second zero-crossing detection signal S2 changes.

[0082] Then, the fixing control unit 9 determines whether the first zero-cross detection circuit 71 detects a periodic change in the AC voltage (step #22). Specifically, when the level of the first zero-cross detection signal S1 changes during monitoring, the fixing control unit 9 may determine that the first zero-cross detection circuit 71 detects a periodic change in the AC voltage. When the level does not change at all during monitoring, the fixing control unit 9 may determine that the first zero-cross detection circuit 71 does not detect a periodic change in the AC voltage.

[0083] When it is determined that the first zero-cross detection circuit 71 has detected a periodic change in the AC voltage (Yes in step #22), the fixing control unit 9 determines whether or not the second zero-cross detection circuit 72 has detected a periodic change in the AC voltage (step #23). Specifically, when the level of the second zero-cross detection signal S2 changes during monitoring, the fixing control unit 9 may determine that the second zero-cross detection circuit 72 has detected a periodic change in the AC voltage. When the level has not changed at all during monitoring, the fixing control unit 9 may determine that the second zero-cross detection circuit 72 has not detected a periodic change in the AC voltage.

[0084] When it is determined that the second zero-cross detection circuit 72 also detects a periodic change in the AC voltage (Yes in step #23), the fixing control unit 9 determines that the cover 101 and the switch unit 8 are closed (step #24 → end). On the other hand, when it is determined that the second zero-cross detection circuit 72 does not detect a periodic change in the AC voltage (No in step #23), there is a discrepancy in the detection contents of each zero-cross detection circuit. A malfunction of the second zero-cross detection circuit 72 is considered. Therefore, the fixing control unit 9 determines that the second zero-cross detection circuit 72 is malfunctioning (step #25). In this case, it is necessary to notify the user of the malfunction. Therefore, the fixing control unit 9 causes the notification unit to notify the malfunction of the second zero-cross detection circuit 72 (step #26 → end). For example, the notification unit is the display panel 31. For example, upon receiving a notification from the fixing control unit 9, the control unit 1 causes the display panel 31 to display a message notifying the malfunction of the second zero-cross detection circuit 72.

[0085] On the other hand, when it is determined that the first zero-cross detection circuit 71 has not detected a periodic change in the AC voltage (No in step #22), the fixing control unit 9 determines whether the second zero-cross detection circuit 72 has detected a periodic change in the AC voltage (step #27). Step #27 is the same process as step #23.

[0086] When it is determined that the second zero-cross detection circuit 72 also detects a periodic change in the AC voltage (Yes in step #27), AC power is supplied to the switch unit 8, and the power is cut off by the switch unit 8. That is, the cover 101 is open, and the switch unit 8 is open. The fixing control unit 9 then determines that the cover 101 and the switch unit 8 (the first switch 81 and the second switch 82) are open (step #28). When it is determined that the cover 101 and the switch unit 8 are open, the fixing control unit 9 may cause the notification unit to notify that the cover 101 is open (step #29→END). It is possible to detect that the cover 101 is open, and to notify that there is no abnormality. For example, the notification unit is the display panel 31. The display panel 31 displays a message. For example, upon receiving a notification from the fixing control unit 9, the control unit 1 causes the display panel 31 to display a message notifying that the cover 101 is open.

[0087] When it is determined that the second zero-cross detection circuit 72 has not detected a periodic change in the AC voltage (No in step #27), the fixing control unit 9 is operating, but both detection circuits are unable to detect the AC voltage at all. Some kind of malfunction may have occurred. For example, both the first zero-cross detection circuit 71 and the second zero-cross detection circuit 72 may have malfunctioned. There may also be a problem with one of the electric wires. Also, opening and closing of the cover 101 cannot be clearly detected. Therefore, the fixing control unit 9 determines that a malfunction has occurred (step #210). In this case, it is necessary to notify the user of the malfunction. Therefore, the fixing control unit 9 causes the notification unit to notify the malfunction occurrence (step #211 -> end). Upon receiving the notification from the fixing control unit 9, the control unit 1 causes the display panel 31 to display a message notifying the user of the malfunction occurrence.

[0088] The image forming apparatus according to the modified example includes a first zero-cross detection circuit 71, a second zero-cross detection circuit 72, and a notification unit. The first zero-cross detection circuit 71 is provided between the switch unit 8 and the heater 6. The first zero-cross detection circuit 71 is connected to a first supply line 91 and a second supply line 92. The first zero-cross detection circuit 71 generates a first zero-cross detection signal S1 according to the AC voltage supplied from the AC power source AC. The second zero-cross detection circuit 72 is provided between the switch unit 8 and the AC power source AC. The second zero-cross detection circuit 72 is connected to the non-grounded side pole L and the grounded side pole N of the AC power source AC. The second zero-cross detection circuit 72 generates a second zero-cross detection signal S2 according to the AC voltage. The notification unit notifies a message. When the first zero-cross detection circuit 71 does not detect a periodic change in the AC voltage and the second zero-cross detection circuit 72 detects a periodic change in the AC voltage, the notification unit notifies that the cover 101 is open. As a result, based on the first zero-cross detection signal S1 and the second zero-cross detection signal S2, it is recognized that the cover 101 and the switch unit 8 are open. It can be notified that the cover 101 and the switch unit 8 are open.

[0089] The image forming apparatus according to the modified example includes a determination circuit unit (fixing control unit 9) to which the first zero-cross detection signal S1 and the second zero-cross detection signal S2 are input. When the first zero-cross detection circuit 71 detects a periodic change in the AC voltage and the second zero-cross detection circuit 72 detects a periodic change in the AC voltage, the determination circuit unit determines that the cover 101 is closed. In this way, when the AC power source AC is regarded as the front side (upstream side), the zero-cross detection circuits 70 can be provided in both the front and rear stages of the switch unit 8. Based on the first zero-cross detection signal S1 and the second zero-cross detection signal S2, it can be recognized that the cover 101 and the switch unit 8 are closed.

[0090] When the first zero cross detection circuit 71 detects a periodic change in the AC voltage and the second zero cross detection circuit 72 does not detect a periodic change in the AC voltage, the notification unit according to the modified example notifies that the second zero cross detection circuit 72 has a malfunction. This makes it possible to detect a malfunction of the second zero cross detection circuit 72 based on the first zero cross detection signal S1 and the second zero cross detection signal S2. It is possible to notify that the second zero cross detection circuit 72 has a malfunction.

[0091] When the first zero-cross detection circuit 71 does not detect a periodic change in the AC voltage and the second zero-cross detection circuit 72 does not detect a periodic change in the AC voltage, the notification unit according to the modified example notifies that a fault has occurred. This makes it possible to detect the occurrence of a fault based on the first zero-cross detection signal S1 and the second zero-cross detection signal S2. It is possible to notify the occurrence of a fault.

[0092] The image forming apparatus according to the modified example includes a first zero-cross detection circuit 71 that is connected to a first supply line 91 and a second supply line 92 and generates a first zero-cross detection signal S1 according to the AC voltage supplied from an AC power source AC. Each of the branch lines 94 is provided with a current control element 95 that controls bidirectional current based on the first zero-cross detection signal S1. This makes it possible to precisely control the power supplied to the heater 6 during printing based on the zero-cross signal (phase control, half-wave control). The zero-cross detection circuit can be used to control the timing of power supply to the heater 6 during printing. The zero-cross detection circuit can be used for a variety of purposes.

[0093] The above describes the embodiment and modified examples of the present invention. The scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention. For example, in the above description, an example was described in which the notification unit is the display panel 31. However, either the display panel 31 or the communication circuit unit 12, or both, may be the notification unit. When issuing a notification, the communication circuit unit 12 transmits a message to any computer 200 with which it can communicate. [Industrial Applicability]

[0094] The present invention can be used in an image forming apparatus including a fixing device. [Explanation of symbols]

[0095] 100 Printer (image forming device) 101 Cover 31 Display panel (notification section) 6 Heater 61 1st heater (heater) 62 2nd heater (heater) 70 Zero-cross detection circuit 71 First zero-cross detection circuit 72 Second zero cross detection circuit 8 Switch section 81 1st switch 82 2nd switch 9 Fixing control section (judgment circuit section) 91 First supply line 92 Second supply line 93 Branch section 94 Branch line 95 Current control element AC power supply S0 Zero cross detection signal S1 1st zero cross detection signal S2 2nd zero cross detection signal L Non-grounded side pole N Grounded side pole

Claims

1. a plurality of heaters for heating the toner image; A switch section that is connected to an AC power source and opens and closes in conjunction with the opening and closing of the cover; a first supply line connecting one end of each of the heaters to the switch unit; a second supply line connecting the other end of each of the heaters to the switch unit; a first zero-cross detection circuit that is provided between the switch unit and the heater, that is connected to the first supply line and the second supply line, and that generates a first zero-cross detection signal in response to an AC voltage supplied from the AC power supply; a second zero-cross detection circuit that is provided between the switch unit and the AC power supply, that is connected to a non-grounded side electrode and a grounded side electrode of the AC power supply, and that generates a second zero-cross detection signal according to the AC voltage; a notification unit for notifying a message; Equipped with the second supply line includes a branch portion; The other end of each of the heaters is connected to one of the branch wires which are electric wires branched at the branch portion, the switch unit is disposed between the branch unit and the AC power supply, When the first zero-cross detection circuit does not detect a periodic change in the AC voltage and the second zero-cross detection circuit detects a periodic change in the AC voltage, The notification unit notifies the user that the cover is open.

2. the switch unit includes a first switch and a second switch, The first switch is The AC power supply is connected to either the non-grounded terminal or the grounded terminal of the AC power supply, When the cover is opened, the AC power source and the first supply line are not connected to each other. When the cover is closed, the cover is closed to connect the AC power source and the first supply line; The second switch is connected to the other of the non-grounded side terminal and the grounded side terminal of the AC power supply, When the cover is opened, the AC power source and the second supply line are not connected to each other.

2. The image forming apparatus according to claim 1, wherein the switch is closed when the cover is closed, and connects the AC power source and the second supply line.

3. a determination circuit unit to which the first zero-cross detection signal and the second zero-cross detection signal are input, When the first zero-cross detection circuit detects a periodic change in the AC voltage and the second zero-cross detection circuit detects a periodic change in the AC voltage, 3. The image forming apparatus according to claim 1, wherein the determination circuit determines that the cover is closed.

4. When the first zero-cross detection circuit detects a periodic change in the AC voltage and the second zero-cross detection circuit does not detect a periodic change in the AC voltage, The image forming apparatus according to claim 1 , wherein the notification unit notifies that the second zero-cross detection circuit has a malfunction.

5. When the first zero-cross detection circuit does not detect a periodic change in the AC voltage and the second zero-cross detection circuit does not detect a periodic change in the AC voltage, The image forming apparatus according to claim 1 , wherein the notification unit notifies the user that a failure has occurred.

6. a zero-cross detection circuit connected to the first supply line and the second supply line and generating a zero-cross detection signal corresponding to an AC voltage supplied from the AC power supply; 6. The image forming apparatus according to claim 1, wherein each of the branch lines is provided with a current control element that controls a current in both directions based on the zero-cross detection signal.

Images