Image forming apparatus

Abstract

To provide an image forming apparatus that does not require provision of a power source dedicated to input reference voltage to a comparator, and reduces cost compared to before.SOLUTION: A printer 1 can set a standby state that is a non-power saving mode, and a sleep state that is a power saving mode in which power consumption is reduced compared to the non-power saving mode, and comprises: a first comparator 221 that compares a first sensor voltage with a first reference voltage, and when the first sensor voltage exceeds the first reference voltage, outputs a first output signal; and an ENG 3.3 V power supply in which output of voltage is turned on when the printer 1 is in the standby state, and output of voltage is turned off when the printer 1 is in the sleep state. The first sensor voltage and the first reference voltage are both generated on the basis of the voltage output from the same ENG 3.3 V power supply.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus equipped with a comparator. [Background technology]

[0002] Conventionally, as an image forming apparatus for printing an image on a sheet as a printing object, an image forming apparatus has been known which heats the sheet onto which a toner image has been transferred to fix the image and then print. In addition, the sheet is generally heated by a fixing device heated by an energized heater, but an image forming apparatus has been proposed which has an overheat detection circuit made up of a comparator to prevent the temperature of the fixing device from overheating.

[0003] For example, Japanese Patent Application Laid-Open No. 2023-86031 discloses a configuration in which a reference voltage is input to one input terminal of a comparator and a voltage corresponding to the temperature of the fixing device is input to the other input terminal, and if the voltage corresponding to the temperature of the fixing device exceeds the reference voltage, a signal is sent to a control circuit to turn off the heater. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-86031 A (paragraphs 0130-0161, Figure 12) Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, a dedicated power supply is provided for inputting a reference voltage to one input terminal of the comparator, which results in an increase in costs.

[0006] The present invention has been made to solve the above-mentioned problems in the conventional art, and aims to provide an image forming apparatus that does not require a dedicated power supply for inputting a reference voltage to a comparator, thereby reducing costs compared to conventional apparatuses. [Means for solving the problem]

[0007] In order to achieve the above object, the image forming apparatus of the present application is an image forming apparatus that forms an image on a sheet and can be set to a first mode and a second mode that consumes less power than the first mode, and is characterized in that it comprises: a first sensor that detects a first physical quantity of the image forming apparatus and outputs a first sensor voltage corresponding to the detected first physical quantity; a first sensor input terminal to which the first sensor voltage is input; and a first reference voltage input terminal to which a first reference voltage is input, a first comparator that compares the first sensor voltage with the first reference voltage and outputs a first output signal when the first sensor voltage exceeds the first reference voltage; and a first power supply that is one of the power supplies provided in the image forming apparatus and is controlled so that voltage output is turned on when the image forming apparatus is in the first mode and turned off when the image forming apparatus is in the second mode, and the first sensor voltage and the first reference voltage are generated based on the voltage output from the first power supply. [Effects of the Invention]

[0008] The image forming apparatus according to the present application having the above configuration includes a first power supply that turns on voltage output in the first mode and turns off voltage output in the second mode, and generates a first sensor voltage and a reference voltage based on the voltage output by the first power supply, i.e., by generating the first sensor voltage and the reference voltage from the same power supply, it is not necessary to provide a separate power supply dedicated to inputting the reference voltage to the input terminal of the comparator, which results in cost reduction compared to conventional methods. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating the configuration of a printer according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating the printer with the rear cover open. [Figure 3] FIG. 2 is a diagram illustrating a state in which the fixing device is removed from the printer. [Figure 4] FIG. 2 is a front view of the internal structure of the fixing device. [Figure 5] FIG. 2 is a rear view of the internal structure of the fixing device. [Figure 6] 10A and 10B are diagrams illustrating a pressure contact / separation mechanism. [Figure 7] FIG. 2 is a diagram showing the electrical configuration of the printer. [Figure 8] 3 is a diagram showing the electrical configuration of a relay board included in the fixing device according to the first embodiment. FIG. [Figure 9] FIG. 3 is a diagram showing the electrical configuration of a hard limiter circuit provided on the main board according to the first embodiment. [Figure 10] 4 is a flowchart of a temperature abnormality detection process according to the first embodiment. [Figure 11] FIG. 10 is a diagram showing the electrical configuration of a hard limiter circuit provided on a main board according to a second embodiment. [Figure 12] FIG. 10 is a diagram showing the electrical configuration of a hard limiter circuit provided on a main board according to a third embodiment. [Figure 13] FIG. 10 is a diagram showing the electrical configuration of a hard limiter circuit provided on a main board according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, first to fourth embodiments in which the image forming apparatus according to the present invention is embodied as a printer will be described with reference to the drawings.

[0011] First Embodiment First, the overall configuration of the printer 1 according to the first embodiment will be described. Fig. 1 shows a schematic configuration of the printer 1 according to the first embodiment. In the following description, the front-rear and up-down directions are as shown on the paper.

[0012] [Overall printer configuration]

[0013] The printer 1 according to the first embodiment is an electrophotographic color laser printer that prints a desired image on a sheet S. However, the printer 1 may also be a monochrome laser printer. The printer 1 comprises a main body housing 2, a conveying section 3, a process section (image forming section) 4, and a fixing device (fixing unit) 9 that is detachable from the main body housing 2.

[0014] The main body housing 2 has a front cover 11, a rear cover 12, a supply tray 13, a discharge tray 22, a first transport path 25, a second transport path 26, and a third transport path 27. The front cover 11 is a cover that opens and closes a front opening 2A provided at the front of the main body housing 2, and is attached to the front surface of the main body housing 2 in an openable and closable manner. The rear cover 12 is a cover that opens and closes a rear opening 2B provided at the rear of the main body housing 2, and is attached to the rear surface of the main body housing 2 in an openable and closable manner. The supply tray 13 is detachably attached to the bottom of the main body housing 2. Sheets S are placed on the supply tray 13. The sheets S are standard-sized sheets such as A4 size. The sheets S are paper media such as plain paper or cardboard, but are not limited to these, and may also be transparencies. The discharge tray 22 is provided at the top of the main body housing 2, and sheets S on which images have been formed are placed on the discharge tray 22.

[0015] Furthermore, a multipurpose tray (manual feed tray) 14 is formed in a part of the front cover 11, and by tilting the multipurpose tray 14 toward the front, it is possible to manually insert a sheet S from the multipurpose tray 14. The printer 1 is capable of selectively printing not only on sheets S supplied from the supply tray 13, but also on sheets S inserted from the multipurpose tray 14.

[0016] The conveying section 3 has a pickup roller 33, a separation roller 34, a registration roller 35, a first conveying roller 36, a second conveying roller 37, a first switchback roller 38, a second switchback roller 39, a plurality of third conveying rollers 40, a flapper 30, and a main motor 201A (see FIG. 7). A part of the second conveying path 26 is formed by the rear cover 12 in the closed state.

[0017] The pickup roller 33 picks up the sheets S in the supply tray 13 that have been pushed upward by the sheet pressing plate 32, and transports them toward the first transport path 25. The separation roller 34 separates the sheets S picked up by the pickup roller 33 one by one.

[0018] The registration rollers 35 are disposed upstream of the process unit 4 on the first transport path 25. The registration rollers 35 align the direction of the leading edge of the sheet S, and then transport the sheet S toward the process unit 4. The transport direction in which the registration rollers 35 transport the sheet is from the front to the rear.

[0019] When the conveying unit 3 conveys the sheet S outside the main body housing 2, if the rear cover 12 is closed, the sheet S conveyed from the process unit 4 is conveyed by the first conveying roller 36 and guided to the first conveying path 25 by the flapper 30 (30A). Thereafter, the conveying unit 3 conveys the sheet S guided to the first conveying path 25 by the second conveying roller 37 and the first switchback roller 38 and discharges the sheet S onto the discharge tray 22.

[0020] Furthermore, when the conveying unit 3 conveys the sheet S out of the main body housing 2 and the rear cover 12 is open, the sheet S conveyed from the process unit 4 is conveyed by the first conveying roller 36, guided rearward by the flapper 30 (30B) that has swung to the position shown by the imaginary line, and discharged through the rear opening 2B onto the open rear cover 12. The printer 1 is capable of forming an image on the sheet S even when the rear cover 12 is open, and the rear cover 12 is a cover that, when open, allows the sheet S on which an image has been formed to be discharged from the rear opening 2B.

[0021] Furthermore, when the conveying unit 3 conveys the sheet S conveyed from the process unit 4 again, the conveying unit 3 conveys the sheet S conveyed from the process unit 4 by the first conveying roller 36 and guides the sheet S to the first conveying path 25 or the second conveying path 26 by the flapper 30. When the conveying unit 3 guides the sheet S to the first conveying path 25, the conveying unit 3 conveys the sheet S in the first conveying path 25 to the third conveying path 27 by the second conveying roller 37 and the first switchback roller 38. When the conveying unit 3 guides the sheet S to the second conveying path 26, the conveying unit 3 conveys the sheet S in the second conveying path 26 to the third conveying path 27 by the second switchback roller 39.

[0022] The sheet S conveyed to the third conveying path 27 is supplied again to the processing unit 4 by the third conveying roller 40, the registration roller 35, etc. After that, an image is formed on the sheet S in the processing unit 4, and then the sheet S is discharged onto the discharge tray 22 by the conveying unit 3.

[0023] The conveying unit 3 also includes a separation pad 42 and a pickup feed roller 43 for separating and conveying the sheets S manually inserted from the multipurpose tray 14. The separation pad 42 and the pickup feed roller 43 separate the sheets S inserted from the multipurpose tray 14 one by one and convey them toward the process unit 4. The subsequent flow is the same as when the sheets are conveyed from the supply tray 13 described above.

[0024] On the other hand, the process unit 4 has a function of forming an image (toner image) on the sheet S and transferring the toner image onto the sheet S. The process unit 4 includes an exposure unit 5, a drum unit 6, four developing cartridges 7Y, 7M, 7C, and 7K, and a transfer unit 8.

[0025] The exposure unit 5 is disposed in the upper part of the main body housing 2, and includes a light source, a polygon mirror, a lens, a reflecting mirror, etc. (not shown). The exposure unit 5 exposes the surface of the photosensitive drum 61 by emitting a light beam indicated by a dashed dotted line onto the surface of the photosensitive drum 61.

[0026] The drum unit 6 is disposed between the supply tray 13 and the exposure unit 5 inside the main body housing 2, and includes four photosensitive drums 61, four chargers 62, a pinch roller 64, and a support frame 65 that supports the photosensitive drums 61 and other components. The drum unit 6 is detachable from the main body housing 2 through the front opening 2A when the front cover 11 is open. The pinch roller 64 faces the registration roller 35. The pinch roller 64 rotates following the rotation of the registration roller 35, and transports the sheet S together with the registration roller 35.

[0027] The developer cartridges 7Y, 7M, 7C, and 7K correspond to four colors: yellow (Y), magenta (M), cyan (C), and black (K), respectively, and are detachably mounted in the drum unit 6 in that order from the front to the rear of the printer 1. Each of the developer cartridges 7Y, 7M, 7C, and 7K includes a developer roller 71, a supply roller 72, and a toner storage section 73. Although the developer cartridges 7Y, 7M, 7C, and 7K differ in toner color, they are otherwise configured the same, and therefore, hereinafter, any one of them may be referred to as the developer cartridge 7.

[0028] The transfer unit 8 is disposed between the supply tray 13 and the drum unit 6 inside the main body housing 2, and includes a drive roller 81, a driven roller 82, a conveyor belt 83, and four transfer rollers 84. The conveyor belt 83 is stretched between the drive roller 81 and the driven roller 82, and its upper surface is in contact with the photosensitive drum 61. The four transfer rollers 84 are disposed inside the conveyor belt 83 so as to sandwich the conveyor belt 83 between themselves and the corresponding photosensitive drum 61.

[0029] When attached to the printer 1, the fixing device 9 is located behind the process unit 4 inside the main body housing 2. More specifically, the fixing device 9 is located between the closed rear cover 12 and the process unit 4. The fixing device 9 has a heating roller (heating rotator) 91 that heats the sheet S, and a pressure roller (pressure rotator) 92 that nips the sheet S between the heating roller 91 and the pressure roller 92. In the first embodiment, the heating roller 91 has a heater 93 therein that heats the heating roller 91. As will be described later, the fixing device 9 also has a pressure contact / separation mechanism that switches the heating roller 91 and the pressure roller 92 between a pressure contact state and a spaced state. The internal structure of the fixing device 9 will be described in detail later.

[0030] The process unit 4 uniformly charges the surface of the photosensitive drum 61 using the charger 62, and exposes the surface of the photosensitive drum 61 using the exposure unit 5, thereby forming an electrostatic latent image on the surface of the photosensitive drum 61. The process unit 4 also supplies toner from a toner storage unit 73 to a supply roller 72, which then supplies the toner to the developing roller 71. The toner supplied to the developing roller 71 is carried on the developing roller 71 as the developing roller 71 rotates.

[0031] The process unit 4 supplies the toner carried on the development roller 71 to the electrostatic latent image formed on the photosensitive drum 61, thereby forming a toner image on the surface of the photosensitive drum 61. Thereafter, the process unit 4 transfers the toner image on the photosensitive drum 61 to the sheet S by transporting the sheet S supplied from the supply tray 13 by the transport unit 3 between the photosensitive drum 61 and the transport belt 83. Thereafter, the process unit 4 transports the sheet S to the fixing device 9.

[0032] The fixing device 9 fixes the toner image transferred onto the sheet S to the sheet S by transporting the sheet S between the heating roller 91 and the pressure roller 92 (fixes the toner image formed on the sheet S) to form an image on the sheet S.

[0033] In addition, downstream of the fixing device 9 in the sheet conveying direction, there is also provided a discharge sensor SE4 that detects the passage of the sheet S that has passed between the heating roller 91 and the pressure roller 92, i.e., after the developer image has been fixed by the fixing device 9.

[0034] The printer 1 further includes a fixing fan 63 inside the main body housing 2. The fixing fan 63 is provided so as to exhaust air inside the main body housing 2 to the outside of the main body housing 2 when driven.

[0035] Meanwhile, the fixing device 9 is equipped with two fixing temperature sensors TH1 and TH2 for detecting the temperature of the fixing device 9 (more specifically, the heating roller 91). The fixing temperature sensors TH1 and TH2 are equipped with variable resistors whose resistance value changes depending on the detected temperature, and are capable of outputting a signal corresponding to the detected temperature. Here, fixing temperature sensors TH1 and TH2 are both arranged facing the heating roller 91 in a non-contact state, but each detects a different area; fixing temperature sensor TH2 detects the temperature of an area near the center of the heating roller 91, and fixing temperature sensor TH1 detects the temperature of an area near the edge of the heating roller 91.

[0036] The fixing device 9 can be attached to and detached from the main body housing 2 through a rear opening 2B of the main body housing 2, which is opened by opening the rear cover 12. FIG. 2 shows the state in which the rear cover 12 is open. As shown in FIG. 2, the fixing device 9 includes a fixing housing 120, a fixed handle 130, and a lever 140. The fixed handles 130 are provided on both the left and right ends of the fixing housing 120, and the levers 140 are attached to the fixed handles 130.

[0037] 3, when the user holds each lever 140 and pulls each fixed handle 130 backward, the fixing device 9 can be detached from the main body housing 2. At this time, the fixing connector 160 provided on the fixing device 9 also detaches from the main body connector 150 provided on the main body housing 2. In other words, the fixing connector 160 and the main body connector 150 are connected when the fixing device 9 is attached to the main body housing 2, and are detached when the fixing device 9 is removed from the main body housing 2.

[0038] Although not shown, the main body housing 2 also has a fixed / unfixed detection switch 15 (see FIG. 7) at a location in contact with the fixing device 9 for detecting whether the fixing device 9 is attached to the main body housing 2. The fixed / unfixed detection switch 15 is turned on when the fixing device 9 is attached to the main body housing 2, and is turned off when the fixing device 9 is removed from the main body housing 2.

[0039] [Configuration of fixing device] Next, among the various components of the printer 1 described above, the fixing device 9, which is detachably attached to the main body housing 2 of the printer 1 and fixes the toner image on the sheet S, will be described in more detail with reference to the drawings. Figures 4 and 5 are views showing the internal structure of the fixing device 9 from the front and rear, respectively, with the outer housing wall covering the outside removed. In the following description, the front-to-back and up-to-down directions are as shown on the paper.

[0040] The fixing device 9 includes a heating roller (heating rotor) 91 as an example of a heating member that heats the sheet S, a pressure roller (pressure rotor) 92 that nips the sheet S between the heating roller 91, side frames 94A, 94B, a connecting frame 94C, arms 95A, 95B, springs 96A, 96B, and cams 97A, 97B.

[0041] The heating roller 91 extends in the longitudinal direction and rotates around its rotation axis. The heating roller 91 rotates by receiving the driving force of a main motor 201A provided in the printer 1. The heating roller 91 is a metal tube, and is heated by a heater 93 disposed inside. The heater 93 is, for example, a halogen heater.

[0042] In the following description, the longitudinal direction of the heating roller 91 will be simply referred to as the longitudinal direction. The longitudinal direction also refers to the direction of the rotation axis of the heating roller 91. The sheet S is transported from the front to the rear of the fixing device 9 and passes through the fixing device 9. After passing through the fixing device 9, the sheet S is transported on a first transport path 25 toward above the fixing device 9, as shown in FIG. 1.

[0043] The pressure roller 92 rotates following the rotation of the heat roller 91, and nips the sheet S between itself and the heat roller 91. The pressure roller 92 is made of an elastic member such as rubber.

[0044] The side frames 94A and 94B are located at both ends in the longitudinal direction of the heating roller 91 and the pressure roller 92. The side frames 94A and 94B support the heating roller 91 so that it can rotate.

[0045] The connecting frame 94C is a metal plate that extends in the longitudinal direction and connects the side frame 94A on one side in the longitudinal direction to the side frame 94B on the other side in the longitudinal direction.

[0046] The cam 97A is located adjacent to the side frame 94A and is rotatably supported relative to the side frame 94A. Similarly, the cam 97B is located adjacent to the side frame 94B and is rotatably supported relative to the side frame 94B. The cams 97A and 97B are connected to each other by a camshaft 98.

[0047] The arms 95A, 95B, springs 96A, 96B, and cams 97A, 97B constitute a pressure contact / separation mechanism that can switch between a pressure contact state in which the heating roller 91 and the pressure roller 92 are pressed together (nipped) and a separated state in which the heating roller 91 and the pressure roller 92 are separated. The pressure change mechanism can switch between the pressure contact state and the separated state by moving at least one of the heating roller 91 and the pressure roller 92 relative to the other (for the pressure contact state, the nip pressure can also be adjusted). Particularly in the first embodiment, the pressure contact / separation mechanism switches between the pressure contact state and the separated state by moving the pressure roller 92 relative to the heating roller 91.

[0048] The pressure contact / separation mechanism will be described below with reference to Fig. 6. Note that the operations of arm 95A, spring 96A, and cam 97A in side frame 94A are the same as those of arm 95B, spring 96B, and cam 97B in side frame 94B, so the operations of arm 95A, spring 96A, and cam 97A in side frame 94A will be described below as an example.

[0049] 6, the arm 95A has one end 110, the other end 111, a first portion 112, and a second portion 113. The arm 95A has one end 110 supported by the side frame 94A via a shaft 114 so as to be rotatable about the arm axis X1. The other end 111 has a cam follower 115. The cam follower 115 is capable of coming into contact with the cam 97A.

[0050] The first portion 112 and the second portion 113 are located between the one end 110 and the other end 111. The first portion 112 rotatably supports the pressure roller 92. The second portion 113 is a portion to which a spring 96A is connected. One end of the spring 96A is hooked to the second portion 113, and the other end of the spring 96A is hooked to the side frame 94A. The spring 96A biases the pressure roller 92 toward the heating roller 91 via the arm 95A.

[0051] The cam 97A is rotatably supported by the side frame 94A on one side in the longitudinal direction via a camshaft 98, and is rotatable about the cam axis X2. As shown in FIG. 6, the cam 97A has a distorted semicircular shape, and as it rotates, it comes into contact with the cam follower 115, causing the arm 95A to rotate about the arm axis X1. As the arm 95A rotates, the pressure roller 92 moves relative to the heating roller 91, switching between a pressure-contact state and a spaced state. The cam 97A is rotatable counterclockwise as shown in FIG. 6.

[0052] Here, the upper diagram in Fig. 6 shows a pressed state in which the heating roller 91 and the pressure roller 92 are pressed together. The lower diagram in Fig. 6 shows a separated state in which the heating roller 91 and the pressure roller 92 are separated. The middle diagram in Fig. 6 shows a state in the middle of transitioning from the pressed state to the separated state.

[0053] 4 and 5, continuing the description of the fixing device 9, the fixing device 9 further includes a cam gear 121 and a fixing gear 122. The cam gear 121 is fixed to one end of the camshaft 98 in the longitudinal direction. The cam gear 121 is connected to the cams 97A and 97B via the camshaft 98 and transmits driving force to the cams 97A and 97B. The cam gear 121 has a plurality of gear teeth 121A and a flange 121B extending from near the base of the gear teeth 121A to one side in the longitudinal direction. The flange 121B has a notch 121C for detecting the phase of the cam 97A.

[0054] The fixing gear 122 also has a plurality of gear teeth. The fixing gear 122 is fixed to one end of the heating roller 91 in the longitudinal direction. The fixing gear 122 is provided coaxially with the heating roller 91 and rotates integrally with the heating roller 91 around the rotation axis. The fixing gear 122 transmits driving force to the heating roller 91.

[0055] Furthermore, the fixing device 9 includes fixing temperature sensors TH1 and TH2 that detect the temperature of the heating roller 91, a nip detection sensor SE3, a discharge sensor SE4, a fixing connector 160, and a relay board 161.

[0056] The fixing temperature sensor TH1 is a sensor that detects the temperature of the heating roller 91, particularly in the area near the end. As shown in Fig. 4, the fixing temperature sensor TH1 is fixed to the connecting frame 94C with screws or the like at a position spaced above the heating roller 91 at the longitudinal end (on the side of the side frame 94A). The fixing temperature sensor TH1 is, for example, a thermistor, and includes a variable resistor whose resistance value changes depending on the detected temperature, and is capable of outputting a signal corresponding to the detected temperature.

[0057] On the other hand, the fixing temperature sensor TH2 is a sensor that detects the temperature of the heating roller 91, particularly in the region near the center. As shown in Fig. 4, the fixing temperature sensor TH2 is fixed to the connecting frame 94C with screws or the like at a position spaced apart above the heating roller 91 in the center in the longitudinal direction. The fixing temperature sensor TH2 is, for example, a thermistor, and has a variable resistor whose resistance value changes depending on the detected temperature, and is able to output a signal corresponding to the detected temperature.

[0058] Nip detection sensor SE3 is a sensor that detects the phase of cam 97A. More specifically, nip detection sensor SE3 is an optical sensor that has a light-emitting element that emits light and a light-receiving element that receives the light from the light-emitting element. When heating roller 91 and pressure roller 92 are in a pressed-contact state as shown in the upper diagram of FIG. 6, the light from the light-emitting element is blocked by a gear of the pressure-contact / separation mechanism (specifically, flange 121B of cam gear 121). On the other hand, when heating roller 91 and pressure roller 92 are in a separated state as shown in the lower diagram of FIG. 6, the light from the light-emitting element passes through notch 121C provided in flange 121B of cam gear 121, allowing the light-receiving element to receive the light without being blocked. As a result, as described below, the control unit of the printer 1 can determine that the pressure-contact / separation mechanism is in a separated state when the light-receiving unit receives light, and can determine that the pressure-contact / separation mechanism is in a pressed state when the light-receiving unit does not receive light.

[0059] However, by adjusting the position of notch 121C in flange 121B, it is also possible to reverse the relationship between the light-blocking state of nip detection sensor SE3 and the state of the pressure contact / separation mechanism. That is, in the pressure contact state where heating roller 91 and pressure roller 92 are pressed together as shown in the upper diagram of Fig. 6, light from the light-emitting unit can be received by passing through notch 121C, and in the separated state where heating roller 91 and pressure roller 92 are separated as shown in the lower diagram of Fig. 6, light from the light-emitting unit can be blocked. In this case, the control unit of printer 1 can determine that the pressure contact / separation mechanism is in the pressure contact state when the light-receiving unit receives light, and can determine that the pressure contact / separation mechanism is in the separated state when the light-receiving unit does not receive light.

[0060] The discharge sensor SE4 is a sensor that detects the sheet S that has passed between the heating roller 91 and the pressure roller 92, i.e., after the developer image has been fixed by the fixing device 9. The discharge sensor SE4 includes an actuator that can rotate around a rotation axis and a photosensor, and when the sheet S passes between the heating roller 91 and the pressure roller 92 and comes into contact with the rollers, causing the actuator to fall, the photosensor located near the rotation axis of the actuator detects that the actuator has fallen, i.e., that the sheet S has been discharged after the developer image has been fixed by the fixing device 9.

[0061] On the other hand, when the fixing device 9 is attached to the main body housing 2 of the printer 1, the fixing connector 160 can be connected to a main body connector 150 (see FIG. 3) provided on the main body housing 2. The fixing connector 160 is located outside the side frame 94B in the longitudinal direction.

[0062] The relay board 161 relays signals from the fixing temperature sensors TH1 and TH2, the nip detection sensor SE3, and the discharge sensor SE4 to the fixing connector 160. The relay board 161 has a plurality of connectors (terminals) 162 for connecting to the sensors, and the connectors 162 are connected to the sensors by cables. The relay board 161 also has a connector 162 for connecting to the fixing connector 160, and the connector 162 and the fixing connector 160 are also connected by cables.

[0063] The heater 93 provided in the heating roller 91 is also connected to the fixing connector 160 by a power cable. More specifically, the heater 93 is connected to the fixing connector 160 by a power cable via a thermostat (TM). The thermostat TM has a function of cutting off power when the temperature of the heating roller 91 exceeds the control range and becomes overheated.

[0064] When the fixing device 9 having the above configuration is attached to the main body housing 2 of the printer 1, the fixing connector 160 is connected to the main body connector 150. When the fixing connector 160 and the main body connector 150 are connected, temperature information detected by the fixing temperature sensors TH1 and TH2, the state of the pressure contact / separation mechanism detected by the nip detection sensor SE3, and sheet information detected by the discharge sensor SE4 can be transmitted to the control unit of the printer 1. When the fixing connector 160 and the main body connector 150 are connected, power can be supplied to the heater 93 from the power supply board of the main body housing 2. The power supply board is controlled by the control unit and supplies power to the heater 93 based on the temperature information detected by the fixing temperature sensors TH1 and TH2.

[0065] [Printer electrical configuration] Next, the electrical configuration of the printer 1 including the fixing device 9 will be described with reference to Fig. 7. Fig. 7 shows the electrical configuration of the printer 1 including the fixing device 9. Note that Fig. 7 mainly describes components necessary for explaining the first embodiment, and other components of the printer 1 are omitted.

[0066] As shown in Fig. 7, the main body housing 2 is provided with a main board (control board) 200, a main motor board 201, a high-voltage power supply board 202, and a low-voltage power supply board 203. The boards are connected to each other via harnesses. A main motor 201A is mounted on the main motor board 201. When the main motor 201A is driven, the heating roller 91 of the fixing device 9 and the rollers of the conveying section 3 rotate.

[0067] The high-voltage power supply board 202 supplies high voltages HV such as a development voltage and a charging voltage to the process unit 4. The high-voltage power supply board 202 has a high-voltage generation circuit 202C. The high-voltage generation circuit 202C generates a high voltage HV of, for example, about 1 kV based on a DC voltage, for example, DC 24 V, supplied from the low-voltage power supply board 203 via the main board 200, and supplies the high voltage HV to the process unit 4.

[0068] Furthermore, the main board 200 and the high-voltage power supply board 202 are connected via a first connection line CA1. An ASIC (control unit, an abbreviation for Application Specific Integrated Circuit) 210 mounted on the main board 200 controls the high-voltage power supply board 202, and therefore needs to send and receive control signals between the main board 200 and the high-voltage power supply board 202. The first connection line CA1 is for transmitting these control signals. Since there are multiple control signals, there are also multiple signal lines for transmitting these multiple control signals. Therefore, the first connection line CA1 is configured by a harness that bundles multiple signal lines.

[0069] The low-voltage power supply board 203 has an AC-DC conversion circuit 203C, which inputs an AC voltage supplied by a commercial power source, for example, AC 100 V, and converts this AC 100 V to a DC voltage, for example, DC 24 V, by the AC-DC conversion circuit 203C. The low-voltage power supply board 203 is connected to the main board 200 via a fourth connection line CA4, and outputs the generated DC 24 V to the main board 200.

[0070] The main board 200 has a DC-DC conversion circuit 211, which converts DC 24V from the low-voltage power supply board 203 to, for example, DC 3.3V by the DC-DC conversion circuit 211. This DC 3.3V is a voltage for driving various electronic components mounted on the main board 200. However, if there are electronic components that are driven by another DC voltage value, for example, DC 5V, multiple DC-DC conversion circuits may be provided to generate DC 5V or the like in addition to DC 3.3V.

[0071] The DC-DC conversion circuit 211 generates voltages of DC 3.3V and DC 1.8V to be input to the fixing device 9, in addition to the voltages for driving the various electronic components mounted on the main board 200. The DC 3.3V voltage is generated separately from the DC 3.3V voltage for driving the various electronic components mounted on the main board 200 and is hereinafter referred to as ENG3.3V. The ENG3.3V and DC1.8V voltages are supplied to the fixing device 9 via the main connector 150 along with the ground potential. The relay board 161 provided in the fixing device 9 uses these supplied voltages and the ground potential to operate the fixing temperature sensors TH1 and TH2, the nip detection sensor SE3, and the discharge sensor SE4 and outputs signals from each sensor to the ASIC 210. Specifically, the fixing temperature sensor TH1, the nip detection sensor SE3, and the discharge sensor SE4 operate at ENG3.3V, and the fixing temperature sensor TH2 operates at DC1.8V.

[0072] Meanwhile, among the various electronic components mounted on the main board 200, the hard limiter circuit 220 receives, in addition to DC 3.3V, voltages of ENG 3.3V and DC 1.8V generated to be supplied to the fixing device 9. The hard limiter circuit 220 is a circuit for transmitting a signal (heater hard limiter signal) to the ASIC 210 when the temperatures detected by the fixing temperature sensors TH1 and TH2 exceed a predetermined temperature (i.e., a circuit for detecting overheating), and uses the voltages ENG 3.3V and DC 1.8V as reference voltages for the comparators in addition to DC 3.3V. In the first embodiment, ENG 3.3V and DC 1.8V are used for the operation of the fixing temperature sensors TH1 and TH2 (i.e., as sensor voltages input to the comparators) and are also used as reference voltages for the comparators, eliminating the need for a separate power supply dedicated to inputting reference voltages to the input terminals of the comparators. Furthermore, since multiple types of power supplies are used as the power supplies used to drive the fixing temperature sensors TH1 and TH2 and as the power supplies to which the reference voltages of the comparators are input, even if the power supply line is cut or the DC-DC conversion circuit 211 is broken, that is, even if one of the voltages ENG 3.3V and DC 1.8V cannot be supplied, it is possible to detect an excessive temperature rise by at least one of the fixing temperature sensors. Note that the details of the operation of the hard limiter circuit 220 will be described later.

[0073] Furthermore, when the printer 1 is in the "standby state (first mode, non-power saving mode)" and does not receive an image formation execution command or data related to image formation, and a predetermined time has passed since it entered the "standby state," the power consumption state transitions from the "standby state" to the "sleep state (second mode, power saving mode)." The "sleep state" is a mode that consumes less power than the "standby state," and, for example, the display is turned off, the CPU clock is slowed down (clock down), and the supply of the above-mentioned ENG 3.3V is also stopped. However, DC 3.3V and DC 1.8V are continuously supplied. When an image formation execution command or data related to image formation is received in the "sleep state," the printer returns to the "standby state" and starts printing.

[0074] Furthermore, the low-voltage power supply board 203 is connected to the main body connector 150 via a third connection line CA3, and is connected to an inlet (plug, terminal) 204 via a fifth connection line CA5. The inlet 204 is for inputting an AC voltage (AC 100V) supplied from a commercial power source, and this AC voltage is also supplied to the fixing device 9 from the inlet 204 via the fifth connection line CA5, the low-voltage power supply board 203, the third connection line CA3, the main body connector 150, and the fixing connector 160. The voltage supplied to the fixing device 9 is also supplied to the heater 93 described above via a thermostat (TM).

[0075] The ASIC 210 mounted on the main board 200 has, for example, a CPU, memory, and input / output circuits (none of which are shown), and controls the entire printer 1, including the processing unit 4, by performing various arithmetic processing based on programs and data stored in the memory. The memory is an embedded memory, and may be configured by combining ROM, RAM, NVRAM, SSD, HDD, etc. It is used when various programs are executed.

[0076] In addition to the ASIC 210, the main board 200 is equipped with a motor drive circuit MD for driving the main motor 201A, an ON / OFF circuit 212 for switching whether or not to supply DC 24V to the high voltage generation circuit 202C of the high voltage power supply board 202, a detection circuit (DET) 213 for detecting whether the fixing presence / absence detection switch 15 for detecting whether or not the fixing device 9 is attached to the main body housing 2 is in the ON or OFF state, the above-mentioned hard limiter circuit 220, and the above-mentioned DC-DC conversion circuit 211.

[0077] The AC-DC conversion circuit 203C of the low-voltage power supply board 203 is connected to the DC-DC conversion circuit 211 via a power line PL. The power line PL connecting the AC-DC conversion circuit 203C and the DC-DC conversion circuit 211 is included in the fourth connection line CA4. The power line PL branches off at a branch point BP0 on the main board 200 before being input to the DC-DC conversion circuit 211, and extends therefrom, and is connected to the input side of the fixing presence / absence detection switch 15.

[0078] The output side of the fixed-fixing detection switch 15 is connected to the input side of the ON / OFF circuit 212 via the power line PL, and branches off at a first branch point BP1 on the power line PL located between the output side of the fixed-fixing detection switch 15 and the input side of the ON / OFF circuit 212 to be connected to the input side of the motor drive circuit MD. Furthermore, the output side of the fixed-fixing detection switch 15 branches off at a second branch point BP2 downstream of the first branch point BP1 on the power line PL located between the output side of the fixed-fixing detection switch 15 and the input side of the ON / OFF circuit 212 to be connected to the input side of the detection circuit 213.

[0079] The output side of the motor drive circuit MD is connected to the main motor 201A. The motor drive circuit MD is supplied with a voltage applied to a first branch point BP1 on the power line PL. Since the output voltage from the fixed-image detection switch 15 is applied to the first branch point BP1, when the fixed-image detection switch 15 is in the ON state, DC 24 V is applied, and when the fixed-image detection switch 15 is in the OFF state, 0 V is applied.

[0080] The motor drive circuit MD also receives a signal EN from the output port of the ASIC 210. The signal EN is a signal for enabling or disabling the motor drive circuit MD. For example, when the value of the signal EN is H, the motor drive circuit MD is enabled, and when the value of the signal EN is L, the motor drive circuit MD is disabled. However, even if the signal EN is H, the motor drive circuit MD does not operate unless DC 24V is applied to the motor drive circuit MD. In other words, when DC 24V is applied to the motor drive circuit MD and a signal EN of H is input, the motor drive circuit MD starts operating. When DC 24V is applied to the motor drive circuit MD and a signal EN of L is input, the motor drive circuit MD stops operating. Therefore, when 0V is applied to the motor drive circuit MD, the motor drive circuit MD stops operating regardless of the value of the signal EN. Note that a well-known method may be used as the method by which the motor drive circuit MD controls the main motor 201A, and therefore a description thereof will be omitted.

[0081] The output side of the ON / OFF circuit 212 is connected to the power supply voltage input side of the high-voltage generation circuit 202C of the high-voltage power supply board 202. A control signal is also input to the high-voltage generation circuit 202C from an output port (not shown) of the ASIC 210. The high-voltage generation circuit 202C has, for example, a boost circuit including a transformer and a transformer drive circuit, and as described above, boosts the input DC 24V based on the input control signal and supplies the generated high voltage HV, specifically, the charging voltage, the developing voltage, and the transfer voltage, to the process unit 4.

[0082] ASIC 210 outputs an HVEN signal to ON / OFF circuit 212. The HVEN signal is a signal for controlling ON / OFF circuit 212, and takes on either an ON (=H) or OFF (=L) value. When DC 24V is input from fixing presence / absence detection switch 15, ON / OFF circuit 212 switches whether or not to input DC 24V to high voltage generation circuit 202C according to the value of the HVEN signal output from ASIC 210.

[0083] The output side of the detection circuit 213 is connected to an input port (not shown) of the ASIC 210. When the detection signal from the detection circuit 213 is L, the ASIC 210 determines that the fixing presence / absence detection switch 15 is in the ON state, and when the detection signal from the detection circuit 213 is H, the ASIC 210 determines that the fixing presence / absence detection switch 15 is in the OFF state.

[0084] Additionally, the input port of the ASIC 210 is connected to the output side of a rear cover open / close detection switch 16 that detects the opening and closing of the rear cover 12. The rear cover open / close detection switch 16 is provided near the rear cover 12 and outputs a rear cover open / close signal that indicates a value according to the opening and closing of the rear cover 12. The ASIC 210 can determine whether the rear cover 12 is open or closed by checking the value of this rear cover open / close signal.

[0085] The main board 200 is connected to the high-voltage power supply board 202 via a connector 200A on the main board 200 side, a first connection line CA1, and a connector 202A on the high-voltage power supply board 202 side. The high-voltage power supply board 202 is connected to the main connector 150 via a connector 202B on the high-voltage power supply board 202 side and a second connection line CA2.

[0086] As described above, the main body housing 2 includes the inlet 204, and the AC voltage supplied from the inlet 204 is input to the low-voltage power supply board 203 via the connector 203A on the low-voltage power supply board 203 side. The low-voltage power supply board 203 is connected to the main body connector 150 via the connector 203B on the low-voltage power supply board 203 side and the third connection line CA3.

[0087] Furthermore, when the fixing device 9 is attached to the main body housing 2 of the printer 1, the main body connector 150 is connected to the fixing connector 160. The fixing connector 160 is connected to the relay board 161 provided in the fixing device 9 via the connector 161A on the relay board 161 side. As described above, the fixing device 9 is equipped with the heater 93. An AC voltage, for example, AC 100 V input from the inlet 204 is supplied to the heater 93 via the low-voltage power supply board 203 (including the relay 203D), the third connection line CA3, the main body connector 150, and the fixing connector 160.

[0088] The heater 93 is heated by the AC 100 V supplied in this manner. When AC 100 V is supplied to the heater 93, the ASIC 210 controls the heating temperature of the heater 93 by controlling the on / off timing of the AC 100 V supplied to the heater 93.

[0089] The low-voltage power supply board 203 is also provided with a relay 203D that turns on / off the AC 100V input. The ASIC 210 outputs a relay on / off signal from an output port (not shown) to the low-voltage power supply board 203 to control the on / off of the relay 203D. The on / off control of the relay 203D is performed particularly when an excessive temperature rise in the fixing device 9 is detected by a hard limiter circuit 220 (described later). To control this heating temperature, fixing temperature sensors TH1 and TH2 are provided as described above. The fixing temperature sensors TH1 and TH2 are composed of two sensors as shown in FIG. 4. The fixing temperature sensors TH1 and TH2 are respectively positioned so as to be able to detect the temperatures of the end and center of the heating roller 91, which is long in the left-right direction.

[0090] Here, the fixing temperature sensor TH1, which detects the temperature of the end of the heat roller 91, receives ENG 3.3V from the relay board 161 and operates at this ENG 3.3V. Meanwhile, the fixing temperature sensor TH2, which detects the temperature of the center of the heat roller 91, receives DC 1.8V and operates at this DC 1.8V. The reason why the fixing temperature sensors TH1 and TH2 have different operating voltages is to enable temperature detection by at least one of the fixing temperature sensors even if the power line is disconnected or the DC-DC conversion circuit 211 is broken, as described above. Furthermore, when the printer 1 enters the sleep mode, the supply of ENG 3.3V is stopped, but the supply of DC 1.8V is maintained, as described above. This allows some fixing temperature sensors TH2 to operate even when the printer enters the sleep mode.

[0091] Then, in order for the ASIC 210 of the main board 200 to control the heating temperature of the heater 93, signals THM1 and THM2 related to the temperatures detected by the fixing temperature sensors TH1 and TH2, respectively, i.e., signals THM1 and THM2 detected within the fixing device 9, are transmitted from the fixing device 9 to the main board 200. More specifically, the signals THM1 and THM2 are transmitted to the main board 200 via the relay board 161, the fixing connector 160, the main body connector 150, the second connection line CA2, the high-voltage power supply board 202, and the first connection line CA1. The ASIC 210 of the main board 200 controls the on / off timing of the AC 100V supplied to the heater 93 based on the signals THM1 and THM2 from the fixing temperature sensors TH1 and TH2. Meanwhile, signals THM1 and THM2 from the fixing temperature sensors TH1 and TH2 are also input to a hard limiter circuit 220, and when the temperatures detected by the fixing temperature sensors TH1 and TH2 exceed a predetermined temperature, the hard limiter circuit 220 transmits a signal (heater hard limiter signal) detecting this to the ASIC 210. In addition to the detection signals from the fixing temperature sensors TH1 and TH2, the fixing device 9 also transmits detection signals from the nip detection sensor SE3 and the discharge sensor SE4 to the main board 200.

[0092] [Electrical configuration of relay board] Next, the electrical configuration of the printer 1 described above, particularly the electrical configuration of the relay board 161 provided in the fixing device 9, will be described in more detail using Figure 8. Figure 8 shows only the relay board 161 provided in the fixing device 9 and the related electrical configuration of the printer 1.

[0093] First, referring to FIG. 8, the fixing temperature sensor TH1 (a sensor that detects the temperature of an area on one end side of the heating roller 91; see FIG. 4) provided in the fixing device 9 will be described. The fixing temperature sensor TH1 has a variable resistor R2 whose resistance value changes depending on the detected temperature. One end of the variable resistor R2 of the fixing temperature sensor TH1 is connected to a power supply ENG3.3V provided on the relay board 161, and the other end is connected to a terminal of the fixing connector 160 via a signal line. The relay board 161 relays a signal from the fixing temperature sensor TH1 to the main board 200 via an output terminal 251. Meanwhile, on the main board 200 side, one end of the resistor R1, which has a predetermined resistance value, is connected to a terminal of the ASIC 210 that is connected to the output terminal 251 and to which the signal from the fixing temperature sensor TH1 is input. The other end of the resistor R1 is connected to the ground GND of the main board 200 (which is set to 0 V, for example, but may be a reference potential other than 0 V; the same applies below). One end of the resistor R1 is also connected to the hard limiter circuit 220, and the ASIC 210 is also equipped with an AD conversion circuit unit 210A. As a result, for the fixing temperature sensor TH1, an analog voltage obtained by dividing 3.3V using the variable resistor R2 and resistor R1 is input to the AD conversion circuit unit 210A and hard limiter circuit 220 of the ASIC 210. More specifically, for the fixing temperature sensor TH1, an analog voltage obtained by dividing 3.3V using the variable resistor R2 and resistor R1 is input to the AD conversion circuit unit 210A and hard limiter circuit 220 of the ASIC 210. The ASIC 210 then identifies the temperature detected by the fixing temperature sensor TH1 using the digital value converted by the AD conversion circuit unit 210A. The hard limiter circuit 220 also performs overheating detection for the fixing temperature sensor TH1. The AD conversion circuit section 210A and the hard limiter circuit 220 are input with an analog voltage (signal) of the following equation (1). Vin = ENG3.3V × R1 / (variable R2 + R1) (1) As described above, the variable resistor R2 varies with the change in the detected temperature, and the analog voltage Vin changes.

[0094] Next, referring to FIG. 8, the fixing temperature sensor TH2 (a sensor that detects the temperature of a region near the center of the heating roller 91; see FIG. 4) of the fixing device 9 will be described. The fixing temperature sensor TH2 has a variable resistor R2 whose resistance value changes depending on the detected temperature. One end of the variable resistor R2 of the fixing temperature sensor TH2 is connected to a DC 1.8V power supply provided on the relay board 161, and the other end is connected to a terminal of the fixing connector 160 via a signal line. The relay board 161 relays a signal from the fixing temperature sensor TH2 to the main board 200 via an output terminal 252. On the main board 200 side, one end of a resistor R1 having a predetermined resistance value is connected to a terminal of the ASIC 210 that is connected to the output terminal 252 and receives the signal from the fixing temperature sensor TH2, and the other end of the resistor R1 is connected to the ground GND of the main board 200. One end of the resistor R1 is also connected to the hard limiter circuit 220, and the ASIC 210 includes an AD conversion circuit unit 210B. As a result, for the fixing temperature sensor TH2, an analog voltage obtained by dividing 1.8V by the variable resistor R2 and resistor R1 is input to the AD conversion circuit unit 210B and hard limiter circuit 220 of the ASIC 210. More specifically, for the fixing temperature sensor TH2, an analog voltage obtained by dividing 1.8V by the variable resistor R2 and resistor R1 is input to the AD conversion circuit unit 210B and hard limiter circuit 220 of the ASIC 210. Then, the ASIC 210 identifies the temperature detected by the fixing temperature sensor TH2 based on the digital value converted by the AD conversion circuit unit 210B. In addition, the hard limiter circuit 220 performs overheating detection for the fixing temperature sensor TH2. The AD conversion circuit section 210B and the hard limiter circuit 220 receive an analog voltage of the following equation (2): Vin = DC1.8V × R1 / (variable R2 + R1) (2) As described above, the variable resistor R2 varies with the change in the detected temperature, and the analog voltage Vin changes.

[0095] As described above, the fixing temperature sensors TH1 and TH2 are provided with the resistor R1 on the main board 200 side and connected to the ground GND, so the analog voltage Vin has a potential based on the ground GND of the main board 200, not the relay board 161. This prevents ground deviation when analog-to-digital conversion is performed in the AD conversion circuit units 210A and 210B, making it possible to detect temperatures more accurately.

[0096] The power supply voltages of ENG 3.3V and DC 1.8V provided in the relay board 161 are generated in the DC-DC conversion circuit 211 of the main board 200 and supplied to the fixing device 9 via the main body connector 150 together with the ground potential (see FIG. 8).

[0097] [Electrical configuration of hard limiter circuit] Next, the electrical configuration of the printer 1 described above will be described in more detail, particularly the electrical configuration of the hard limiter circuit 220 provided on the main board 200, using Figure 9. Figure 9 shows only the electrical configuration of the printer 1 related to the hard limiter circuit 220 provided on the main board 200.

[0098] 9, the hard limiter circuit 220 includes a first comparator 221 corresponding to the fixing temperature sensor TH1 and a second comparator 222 corresponding to the fixing temperature sensor TH2. The first comparator 221 has an inverting input terminal (-) (first sensor input terminal) to which an analog voltage Vin (hereinafter referred to as the first sensor voltage) expressed by equation (1) is input from the fixing temperature sensor TH1, and a non-inverting input terminal (+) (first reference voltage input terminal) to which a reference voltage (hereinafter referred to as the first reference voltage) is input. The first comparator 221 compares the first sensor voltage Vin input from the inverting input terminal (-) with the first reference voltage input from the non-inverting input terminal (+). If the first sensor voltage Vin exceeds the first reference voltage, the first comparator 221 sends an L signal (first output signal) to the ASIC 210 as a heater hard limiter signal. On the other hand, if the first sensor voltage Vin is equal to or lower than the first reference voltage, an H signal is sent as a heater hard limiter signal to the ASIC 210. When an L signal is input from the hard limiter circuit 220, the ASIC 210 turns off the relay 203D (see FIG. 7) of the low-voltage power supply board 203 to cut off the input of AC voltage to the heater 93.

[0099] 9, the reference voltage generation circuit 223 has a first resistor Ra having one end connected to a power supply of ENG 3.3V (first power supply), a second resistor Re having one end connected to a power supply of DC 3.3V (third power supply), and a third resistor Rg having one end connected to the ground GND. The other end of the first resistor Ra, the other end of the second resistor Re, and the other end of the third resistor Rg are connected at a connection point, and a voltage applied to the connection point is input to the non-inverting input terminal (+) as the first reference voltage. The first reference voltage Vd input to the non-inverting input terminal (+) has a voltage value expressed by the following equation (3). Vd=Rg×(Ra×DC3.3V+Re×ENG3.3V) / (Ra×Re+Re×Rg+Rg×Ra)...(3)

[0100] Here, as mentioned above, the power supply ENG3.3V used to generate the first reference voltage is also used as the operating voltage for the fixing temperature sensor TH1 (Figure 8). In other words, in the first embodiment, the first sensor voltage Vin and the first reference voltage Vd are generated based on the voltage output from the same power supply ENG3.3V.

[0101] Furthermore, when the printer 1 is in a "sleep state (second mode, power saving mode)," the supply of ENG3.3V is stopped. Specifically, as shown in Figure 9, a signal EN is input to the DC-DC conversion circuit 211 from the output port of the ASIC 210, and when the printer 1 is in a standby state (including when printing is being performed), the value of the signal EN becomes H (on) to output ENG3.3V, and when the printer 1 is in a sleep state, the value of the signal EN becomes L (off), instructing the printer not to output ENG3.3V.

[0102] Therefore, if the first reference voltage Vd were input only from the ENG3.3V power supply, when the printer 1 transitioned to the sleep state, the first reference voltage input to the non-inverting input terminal (+) and the first sensor voltage Vin input to the inverting input terminal (-) would both be 0V, causing the non-output logic to become undefined and resulting in an erroneous determination (for example, an L signal being sent as the heater hard limiter signal even when the temperature of the heating roller 91 is sufficiently low). However, in the first embodiment, the non-inverting input terminal (+) to which the first reference voltage is input is connected to not only the ENG3.3V power supply but also the DC3.3V power supply that is supplied even when the printer 1 transitioned to the sleep state. Therefore, even when the printer 1 is in the sleep state, at least the voltage (third voltage) from the DC3.3V power supply is input to the non-inverting input terminal (+), so the first reference voltage does not become 0V and the output logic is determined, thereby making it possible to prevent such an erroneous determination.

[0103] Furthermore, when comparing the above equations (1) and (3), if ENG3.3V fluctuates, the first sensor voltage Vin and the first reference voltage Vd fluctuate in the same direction (same increase / decrease direction), making it possible to cancel out the fluctuations. On the other hand, fluctuations in DC3.3V have no effect on the first sensor voltage Vin, but only on the first reference voltage Vd. However, if Re>Ra, the effect of ENG3.3V on the first reference voltage Vd will be greater. Therefore, if the resistance Re is made sufficiently larger than the resistance Ra, it will be possible to suppress detection errors caused by using multiple power supplies.

[0104] On the other hand, the second comparator 222 has an inverting input terminal (-) (second sensor input terminal) to which an analog voltage Vin (hereinafter referred to as the second sensor voltage) expressed by equation (2) is input from the fixing temperature sensor TH2 described above, and a non-inverting input terminal (+) (second reference voltage input terminal) to which a reference voltage (hereinafter referred to as the second reference voltage) is input. The second comparator 222 compares the second sensor voltage Vin input from the inverting input terminal (-) with the second reference voltage input from the non-inverting input terminal (+). If the second sensor voltage Vin exceeds the second reference voltage, the second comparator 222 transmits an L signal (second output signal) as a heater hard limiter signal to the ASIC 210. On the other hand, if the second sensor voltage Vin is equal to or lower than the second reference voltage, the second comparator 222 transmits an H signal as a heater hard limiter signal to the ASIC 210. When an L signal is input from the hard limiter circuit 220, the ASIC 210 turns off the relay 203D (see FIG. 7) of the low-voltage power supply board 203, thereby cutting off the input of AC voltage to the heater 93. Therefore, when at least one of the conditions of receiving an L signal from the first comparator 221 or receiving an L signal from the second comparator 222 is satisfied, the ASIC 210 instructs the relay 203D to be disconnected.

[0105] Furthermore, the reference voltage input to the non-inverting input terminal (+) of the second comparator 222 is connected to a DC 1.8V power supply (second power supply) as shown in Fig. 9. Then, a voltage obtained by dividing 1.8V by resistors R3 and R4 is input to the non-inverting input terminal (+) as the second reference voltage. The second reference voltage Vd input to the non-inverting input terminal (+) has a voltage value expressed by the following equation (4). Vd=DC1.8V×R3 / (R3+R4) (4)

[0106] Here, as mentioned above, the DC 1.8V power supply used to generate the second reference voltage is also used as the operating voltage for the fixing temperature sensor TH2 (Figure 8). In other words, in the first embodiment, the second sensor voltage Vin and the second reference voltage are generated based on the voltage output from the same DC 1.8V power supply.

[0107] Furthermore, when comparing the above equations (2) and (4), if DC 1.8V fluctuates, the second sensor voltage Vin and the second reference voltage Vd fluctuate in the same direction (increase or decrease in the same direction), so the fluctuations can be canceled out.

[0108] [Control processing by the control unit] Next, among the various control processes executed by the ASIC 210 of the printer 1 having the above configuration, the process of detecting an abnormal temperature of the fixing device 9 will be described with reference to Fig. 10. Fig. 10 is a flowchart illustrating the main process executed after the printer 1 is powered on, particularly the process related to detecting an abnormal temperature of the fixing device 9. Note that each process shown in the flowchart in Fig. 10 below is stored in a memory provided in the printer 1 and is executed by the ASIC 210 (controller).

[0109] First, in step (hereinafter abbreviated as S) 1, the ASIC 210 starts the printing process in accordance with a print command. The print command is transmitted, for example, via a network interface provided in the printer 1 from a PC or the like connected by wire or wirelessly along with image data to be printed. Alternatively, the printing process can be started by receiving an image formation execution command at a user interface provided in the printer 1. When printing starts, as shown in FIG. 6, the cams 97A and 97B in the fixing device 9 rotate, moving the pressure roller 92 relative to the heating roller 91 to switch from a separated state to a pressed state. In addition to driving the process unit 4 and the main motor 201A, the ASIC 210 also controls the on / off timing of the 100V AC power supplied to the heater 93 based on signals THM1 and THM2 from the fixing temperature sensors TH1 and TH2.

[0110] Next, in S2, the ASIC 210 determines whether or not it has received an L signal from at least one of the first comparator 221 and the second comparator 222 of the hard limiter circuit 220. As described above, the first comparator 221 compares the first sensor voltage input from its inverting input terminal (-) with the first reference voltage input from its non-inverting input terminal (+). If the first sensor voltage exceeds the first reference voltage, i.e., if the temperature detected by the fixing temperature sensor TH1 is higher than the reference value, it sends an L signal to the ASIC 210 as a heater hard limiter signal. Similarly, the second comparator 222 compares the second sensor voltage input from its inverting input terminal (-) with the second reference voltage input from its non-inverting input terminal (+). If the second sensor voltage exceeds the second reference voltage, i.e., if the temperature detected by the fixing temperature sensor TH2 is higher than the reference value, it sends an L signal to the ASIC 210 as a heater hard limiter signal.

[0111] Then, if an H signal instead of an L signal is received from either the first comparator 221 or the second comparator 222 of the hard limiter circuit 220, that is, if it is determined that no temperature abnormality has occurred in the fixing device 9 (S2: NO), the process proceeds to S3.

[0112] Thereafter, in S3, the ASIC 210 determines whether the printing process according to the print command has been completed.

[0113] If it is determined that the printing process according to the print command has been completed (S3: YES), the program ends. On the other hand, if it is determined that the printing process according to the print command has not been completed (S3: NO), the program returns to S2 and continues to detect abnormal temperatures in the fixing device 9.

[0114] On the other hand, if an L signal is received from at least one of the first comparator 221 and the second comparator 222 of the hard limiter circuit 220, that is, if it is determined that a temperature abnormality has occurred in the fixing device 9 (S3: YES), the low-voltage power supply board 203 is instructed to disconnect the relay 203D to prevent any further temperature rise in the fixing device 9 (S4). This cuts off the input of AC voltage to the heater 93. The printing process is also forcibly terminated (S5), and a warning is issued to the effect that the printing process has been forcibly terminated.

[0115] As described above in detail, the printer 1 according to the first embodiment can be set to a standby state (a non-power-saving mode (first mode)) or a sleep state (a power-saving mode (second mode)) that consumes less power than the non-power-saving mode. It also includes a fixing temperature sensor TH1 that detects the temperature of the heating roller 91 as a first physical quantity and outputs a first sensor voltage corresponding to the detected temperature, a first comparator 221 having an inverting input terminal (-) to which the first sensor voltage is input and a non-inverting input terminal (+) to which a first reference voltage is input, that compares the first sensor voltage with the first reference voltage and outputs a first output signal if the first sensor voltage exceeds the first reference voltage, and a power supply ENG3.3V that outputs the first voltage when the printer 1 is in standby mode but does not output the first voltage when the printer 1 is in sleep mode. Because both the first sensor voltage and the first reference voltage are generated based on the voltage output from the same power supply ENG3.3V, there is no need for a separate power supply dedicated to inputting the reference voltage to the input terminal of the comparator. This results in reduced costs compared to conventional systems. The fixing device also includes a fixing temperature sensor TH2 that detects the temperature of the heating roller 91 in an area different from the first physical quantity as a second physical quantity and outputs a second sensor voltage corresponding to the detected temperature, an inverting input terminal (-) to which the second sensor voltage is input, and a non-inverting input terminal (+) to which a second reference voltage is input, a second comparator 222 that compares the second sensor voltage with the second reference voltage and outputs a second output signal if the second sensor voltage exceeds the second reference voltage, a DC 1.8V power supply that outputs the second reference voltage, and an ASIC 210 that receives the first output signal and the second output signal.Therefore, by comparing the second physical quantity with the reference voltage in the comparator in addition to the first physical quantity, it is possible to detect whether the reference quantity has been exceeded. The fixing device 9 also includes a process unit 4 that forms a developer image on the sheet S, and a fixing device 9 that fixes the developer image formed on the sheet S by the process unit 4. The fixing device 9 further includes a heating roller 91 that heats the sheet S, a pressure roller 92 that nips the sheet S between the heating roller 91, an inlet 204 to which AC voltage is input from a commercial power source, and a heater 93 connected to the inlet 204 via a relay 203D. The fixing temperature sensor TH1 is a temperature sensor for detecting the temperature of a first area of ​​the heating roller 91, and the fixing temperature sensor TH2 is a temperature sensor for detecting the temperature of a second area of ​​the heating roller 91 that is different from the first area. The ASIC 210 disconnects the relay 203D when at least one of the conditions of receiving a first output signal from the first comparator or a second output signal from the second comparator is met, so that it is possible to detect from the output signal from the comparator that the temperature in any area of ​​the heating roller has exceeded a reference amount, and further it is possible to cut off power to the heater. The first comparator 221 is also provided with a power supply that outputs DC 3.3V, and when the printer 1 is in standby mode, at least ENG 3.3V is input to the non-inverting input terminal (+), and when the printer 1 is in sleep mode, at least DC 3.3V is input to the non-inverting input terminal (+). Therefore, even if the printer 1 goes into sleep mode and the supply of voltage from the ENG 3.3V power supply stops, the first reference voltage does not become 0V and the output logic is determined, making it possible to prevent erroneous judgment by the first comparator. The first comparator 221 further includes a reference voltage generation circuit 223 that generates a first reference voltage to be input to the non-inverting input terminal (+). The reference voltage generation circuit 223 includes a first resistor Ra connected to a power supply of ENG 3.3V, a second resistor Re connected to a power supply of DC 3.3V, and a third resistor Rg connected to ground GND. The other ends of the first resistor Ra, the second resistor Re, and the third resistor Rg are connected at a junction, and a voltage applied to the junction is input to the non-inverting input terminal (+) as the first reference voltage. Therefore, if the ENG 3.3V fluctuates, the first sensor voltage and the first reference voltage fluctuate in the same direction, thereby canceling out the fluctuations. Meanwhile, fluctuations in DC 3.3V have no effect on the first sensor voltage, but only on the first reference voltage. However, if the second resistor Re is made sufficiently larger than the first resistor Ra, it is possible to reduce detection errors caused by using multiple power supplies. In addition, ENG3.3V, which is the drive voltage for the fixing temperature sensor TH1 and is also used as the first reference voltage for the first comparator 221, is also the drive voltage for the nip detection sensor SE3, which detects whether the fixing device 9 is in a pressed state or a separated state, so costs can be reduced by reducing the number of power supplies relative to the number of sensors and comparators. In addition, ENG3.3V, which is the driving voltage for the fixing temperature sensor TH1 and is also used as the first reference voltage for the first comparator 221, is also the driving voltage for the discharge sensor SE4, which detects that the sheet has been discharged after the developer image has been fixed by the fixing device 9, so costs can be reduced by reducing the number of power supplies relative to the number of sensors and comparators.

[0116] Second Embodiment Next, a printer according to a second embodiment will be described with reference to Fig. 11. In the following description, the same reference numerals as those in the configuration of the printer 1 according to the first embodiment shown in Figs. 1 to 10 indicate the same or equivalent parts as those in the configuration of the printer 1 according to the first embodiment.

[0117] The schematic configuration of the printer according to the second embodiment is almost the same as that of the printer 1 according to the first embodiment. In addition, the various control processes are also almost the same as those of the printer 1 according to the first embodiment. However, the printer 1 according to the first embodiment is different from the printer 1 according to the first embodiment in particular with respect to the electrical configuration relating to the hard limiter circuit 220 shown in FIG.

[0118] The electrical configuration of the hard limiter circuit 220 according to the second embodiment will be described in more detail below with reference to Fig. 11. Fig. 11 shows only the hard limiter circuit 220 provided on the main board 200 and the associated electrical configuration of the printer 1.

[0119] 11, the hard limiter circuit 220 according to the second embodiment differs from that of the first embodiment in the configuration of the reference voltage generation circuit 223 that generates the first reference voltage to be input to the non-inverting input terminal (+) of the first comparator 221 corresponding to the fixing temperature sensor TH1 in particular. On the other hand, the configuration of the second comparator 222 is basically the same as that of the first embodiment.

[0120] 11, the reference voltage generating circuit 223 according to the second embodiment has a first resistor Ra, one end of which is connected to a 3.3V power supply (first power supply) ENG, and a second resistor Rg, one end of which is connected to a ground GND. The other end of the first resistor Ra and the other end of the second resistor Rg are connected at a connection point, and a voltage applied to the connection point is input to the non-inverting input terminal (+) as a first reference voltage. Meanwhile, the ASIC 210 has an output terminal (port) 253 and a 3.3V DC power supply (third power supply), and the connection state between the output terminal 253 and the 3.3V DC power supply can be switched.

[0121] Specifically, when printer 1 is in a "standby state (non-power saving mode)", ASIC 210 controls the connection state between output terminal 253 and the DC 3.3V power supply to be open (disconnected), and when printer 1 is in a "sleep state (power saving mode)", ASIC 210 controls the connection state between output terminal 253 and the DC 3.3V power supply to be closed (connected).

[0122] Here, just like in the first embodiment, in the second embodiment, the supply of ENG3.3V is stopped when the printer 1 is in a "sleep state (power saving mode)." Specifically, as shown in Fig. 11, a signal EN is input to the DC-DC conversion circuit 211 from the output port of the ASIC 210, and when the printer 1 is in a standby state (including when printing is being performed), the value of the signal EN becomes H (on) and ENG3.3V is output, and when the printer 1 is in a sleep state, the value of the signal EN becomes L (off), instructing the printer not to output ENG3.3V.

[0123] Therefore, if the first reference voltage Vd were input only from the ENG3.3V power supply, when the printer 1 transitioned to the sleep state, the first reference voltage input to the non-inverting input terminal (+) and the first sensor voltage Vin input to the inverting input terminal (-) would both be 0V, causing the non-output logic to become undefined and resulting in an erroneous determination (for example, an L signal being sent as the heater hard limiter signal even though the temperature of the heating roller 91 is sufficiently low). However, in the second embodiment, the non-inverting input terminal (+) to which the first reference voltage is input is connected to the output port of the ASIC 210 in addition to the ENG3.3V power supply, and DC 3.3V (third voltage) is supplied from the output port of the ASIC 210 when the printer 1 transitioned to the sleep state. Therefore, even when the printer 1 is in the sleep state, at least a voltage from the ASIC 210 is input to the non-inverting input terminal (+), so that the first reference voltage does not become 0V and the output logic is determined, thereby making it possible to prevent such an erroneous determination.

[0124] When the printer 1 is in the "standby state (non-power saving mode)", the first reference voltage Vd input to the non-inverting input terminal (+) is a voltage value expressed by the following equation (5). Vd=Rg×(ENG3.3V) / (Ra+Rg)···(5) On the other hand, when the printer 1 is in the "sleep state (power saving mode)", the first reference voltage Vd input to the non-inverting input terminal (+) is a voltage value expressed by the following equation (6). Vd=DC3.3V (6)

[0125] On the other hand, the second comparator 222 is similar to that in the first embodiment, and the reference voltage input to the non-inverting input terminal (+) of the second comparator 222 is connected to a DC 1.8V power supply (second power supply) as shown in Fig. 11. Then, a voltage obtained by dividing 1.8V by resistors R3 and R4 is input to the non-inverting input terminal (+) as the second reference voltage. The second reference voltage Vd input to the non-inverting input terminal (+) has a voltage value expressed by the above formula (4).

[0126] As described above in detail, the printer 1 according to the second embodiment includes a reference voltage generation circuit 223 that generates a first reference voltage to be input to the non-inverting input terminal (+) of the first comparator 221, and the reference voltage generation circuit 223 has a first resistor Ra having one end connected to a power supply of ENG 3.3V and a second resistor Rg having one end connected to a ground GND, the other end of the first resistor Ra and the other end of the second resistor Rg are connected at a connection point, and a voltage applied to the connection point is input to the non-inverting input terminal (+) as the first reference voltage, and the ASIC 210 has an output terminal (port) 253 and a power supply of DC 3.3V, and Depending on the switching of the connection state with the power supply, a voltage of DC 3.3V can be input from the DC 3.3V power supply via output terminal 253 to the connection point of reference voltage generation circuit 223, and when printer 1 is in standby mode, output terminal 253 is disconnected from the DC 3.3V power supply, and when printer 1 is in sleep mode, output terminal 253 is connected to the DC 3.3V power supply. Therefore, even if printer 1 goes into sleep mode and the supply of voltage from the ENG 3.3V power supply stops, the voltage supplied from ASIC 210 prevents the first reference voltage from becoming 0V and determines the output logic, preventing erroneous judgment by the first comparator.

[0127] Third Embodiment Next, a printer according to a third embodiment will be described with reference to Fig. 12. In the following description, the same reference numerals as those in the configuration of the printer 1 according to the first embodiment shown in Figs. 1 to 10 indicate the same or equivalent parts as those in the configuration of the printer 1 according to the first embodiment.

[0128] The schematic configuration of the printer according to the third embodiment is almost the same as that of the printer 1 according to the first embodiment. In addition, the various control processes are also almost the same as those of the printer 1 according to the first embodiment. However, the printer 1 according to the first embodiment is different from the printer 1 according to the first embodiment in particular with respect to the electrical configuration relating to the hard limiter circuit 220 shown in FIG.

[0129] The electrical configuration of the hard limiter circuit 220 according to the third embodiment will be described in more detail below with reference to Fig. 12. Fig. 12 particularly illustrates only the hard limiter circuit 220 provided on the main board 200 and the associated electrical configuration of the printer 1.

[0130] 12, the hard limiter circuit 220 according to the third embodiment differs from that of the first embodiment in the configuration of the reference voltage generation circuit 223 that generates the first reference voltage to be input to the non-inverting input terminal (+) of the first comparator 221 corresponding to the fixing temperature sensor TH1 in particular. On the other hand, the configuration of the second comparator 222 is basically the same as that of the first embodiment.

[0131] 12, the reference voltage generating circuit 223 according to the third embodiment includes a first resistor Ra having one end connected to a 3.3V power supply (first power supply) of ENG and a second resistor Rg having one end connected to a ground GND. The other end of the first resistor Ra and the other end of the second resistor Rg are connected at a connection point, and the voltage applied to the connection point is input to the non-inverting input terminal (+) as the first reference voltage. Meanwhile, the main board 200 also includes a switching circuit 224 that switches whether or not a voltage from a 3.3V DC power supply (third power supply) provided in the main board 200 is applied to the connection point.

[0132] Here, the switching circuit 224 includes a PNP transistor, the base of which is connected to the output terminal (port) 254 of the ASIC 210, the emitter of which is connected to the DC 3.3V power supply provided on the main board 200, and the collector of which is connected to the above-mentioned connection point of the hard limiter circuit 220. The PNP transistor is switched on and off by an H signal or L signal from the ASIC 210, and is configured to switch whether or not the voltage from the DC 3.3V power supply is applied to the above-mentioned connection point of the hard limiter circuit 220.

[0133] Here, as in the first embodiment, in the third embodiment, the supply of ENG3.3V is stopped when the printer 1 is in a "sleep state (power saving mode)." Specifically, as shown in Fig. 12, a signal EN is input to the DC-DC conversion circuit 211 from the output port of the ASIC 210, and when the printer 1 is in a standby state (including when printing is being performed), the value of the signal EN becomes H (on) to output ENG3.3V, and when the printer 1 is in a sleep state, the value of the signal EN becomes L (off), instructing the printer not to output ENG3.3V.

[0134] Therefore, if the first reference voltage Vd were input only from the ENG3.3V power supply, when the printer 1 transitioned to the sleep mode, the first reference voltage input to the non-inverting input terminal (+) and the first sensor voltage Vin input to the inverting input terminal (-) would both be 0V, causing the non-output logic to become undefined and resulting in an erroneous determination (for example, an L signal being sent as the heater hard limiter signal even though the temperature of the heating roller 91 is sufficiently low). However, in the third embodiment, the non-inverting input terminal (+) to which the first reference voltage is input is connected to the switching circuit 224 in addition to the ENG3.3V power supply, and DC 3.3V (third voltage) is supplied from the switching circuit 224 when the printer 1 transitioned to the sleep mode. Therefore, even when the printer 1 is in the sleep mode, at least the voltage from the switching circuit 224 is input to the non-inverting input terminal (+), so that the first reference voltage does not become 0V and the output logic is determined, thereby preventing such an erroneous determination.

[0135] Specifically, when the printer 1 is in standby mode, the ASIC 210 outputs an H signal to the switching circuit 224. The H signal from the ASIC 210 causes an H signal (3.3 V) to be input to the base of the PNP transistor, so no current flows from the emitter to the base of the PNP transistor (because the emitter potential and the base potential are the same). In other words, when the printer 1 is in standby mode, the PNP transistor cuts off the DC 3.3 V power supply from the hard limiter circuit 220. On the other hand, when the printer 1 is in standby mode, the value of the signal EN sent from the ASIC 210 to the DC-DC conversion circuit 211 is H (ON), so a voltage is output from the ENG 3.3 V power supply provided in the reference voltage generation circuit 223 to the non-inverting input terminal (+). As described above, when the printer 1 is in standby mode, the ASIC 210 instructs the switching circuit 224 not to input the voltage from the DC 3.3V power supply connected to the emitter of the PNP transistor to the non-inverting input terminal (+), while instructing the switching circuit 224 to output a voltage from the ENG 3.3V power supply provided in the reference voltage generating circuit 223 to the non-inverting input terminal (+). When the printer 1 is in the "standby state (non-power saving mode)", the first reference voltage Vd input to the non-inverting input terminal (+) is a voltage value expressed by the following equation (7). Vd=Rg×(ENG3.3V) / (Ra+Rg)···(7)

[0136] Meanwhile, when the printer 1 is in sleep mode, the ASIC 210 outputs an L signal to the switching circuit 224. The L signal from the ASIC 210 causes an L signal (0 V) to be input to the base of the PNP transistor, causing current to flow from the emitter to the base of the PNP transistor (because the emitter potential is 3.3 V and the base potential is 0 V, which is lower). This causes current to flow from the emitter to the collector of the PNP transistor; in other words, when the printer 1 is in sleep mode, the PNP transistor connects the DC 3.3 V power supply to the hard limiter circuit 220. Meanwhile, when the printer 1 is in sleep mode, the value of the signal EN sent from the ASIC 210 to the DC-DC conversion circuit 211 becomes L (off), and therefore no voltage is output from the ENG 3.3 V power supply provided in the reference voltage generation circuit 223 to the non-inverting input terminal (+). As described above, when the printer 1 is in sleep mode, the ASIC 210 instructs the switching circuit 224 to input the voltage from the DC 3.3V power supply connected to the emitter of the PNP transistor to the non-inverting input terminal (+), while instructing the reference voltage generating circuit 223 not to output voltage from the ENG 3.3V power supply to the non-inverting input terminal (+). When the printer 1 is in the "sleep state (power saving mode)", the first reference voltage Vd input to the non-inverting input terminal (+) is a voltage value expressed by the following equation (8). Vd=DC3.3V (8)

[0137] On the other hand, the second comparator 222 is similar to that in the first embodiment, and the reference voltage input to the non-inverting input terminal (+) of the second comparator 222 is connected to a DC 1.8V power supply (second power supply) as shown in Fig. 12. Then, a voltage obtained by dividing 1.8V by resistors R3 and R4 is input to the non-inverting input terminal (+) as the second reference voltage. The second reference voltage Vd input to the non-inverting input terminal (+) has a voltage value expressed by the above formula (4).

[0138] As described in detail above, the printer 1 according to the third embodiment includes a reference voltage generation circuit 223 that generates a first reference voltage to be input to the non-inverting input terminal (+) of the first comparator 221. The reference voltage generation circuit 223 has a first resistor Ra having one end connected to the ENG 3.3V power supply and a second resistor Rg having one end connected to the ground GND. The other end of the first resistor Ra and the other end of the second resistor Rg are connected at a connection point, and the voltage applied to the connection point is input to the non-inverting input terminal (+) as the first reference voltage. The printer 1 also includes a switching circuit 224 that switches whether or not DC 3.3V is applied to the connection point, and an ASIC 210 that controls the switching circuit 224. When printer 1 is in standby mode, ASIC 210 instructs switching circuit 224 not to input DC 3.3V, but to output voltage from the ENG 3.3V power supply, and when printer 1 is in sleep mode, ASIC 210 instructs switching circuit 224 to input DC 3.3V, but not to output voltage from the ENG 3.3V power supply. Therefore, even if printer 1 goes into sleep mode and the supply of voltage from the ENG 3.3V power supply stops, the voltage supplied from ASIC 210 will prevent the first reference voltage from becoming 0V and will determine the output logic, preventing erroneous judgment by the first comparator.

[0139] Fourth Embodiment Next, a printer according to a fourth embodiment will be described with reference to Fig. 13. In the following description, the same reference numerals as those in the configuration of the printer 1 according to the first embodiment shown in Figs. 1 to 10 indicate the same or equivalent parts as those in the configuration of the printer 1 according to the first embodiment.

[0140] The schematic configuration of the printer according to the fourth embodiment is almost the same as that of the printer 1 according to the first embodiment. In addition, the various control processes are also almost the same as those of the printer 1 according to the first embodiment. However, the printer 1 according to the first embodiment is different from the printer 1 according to the first embodiment in particular with respect to the electrical configuration relating to the hard limiter circuit 220 shown in FIG.

[0141] The electrical configuration of the hard limiter circuit 220 according to the fourth embodiment will be described in more detail below with reference to Fig. 13. Fig. 13 particularly illustrates only the hard limiter circuit 220 provided on the main board 200 and the associated electrical configuration of the printer 1.

[0142] 13, the hard limiter circuit 220 according to the fourth embodiment differs from that of the first embodiment in the configuration of the reference voltage generation circuit 223 that generates the first reference voltage to be input to the non-inverting input terminal (+) of the first comparator 221 corresponding to the fixing temperature sensor TH1 in particular. On the other hand, the configuration of the second comparator 222 is basically the same as that of the first embodiment.

[0143] 13, the reference voltage generating circuit 223 according to the fourth embodiment includes a first resistor Ra having one end connected to an ENG 3.3V power supply (first power supply) and a second resistor Rg having one end connected to a ground GND. The other end of the first resistor Ra and the other end of the second resistor Rg are connected at a connection point, and the voltage applied to the connection point is input to the non-inverting input terminal (+) as the first reference voltage. Meanwhile, the main board 200 also includes a switching circuit 224 that switches whether or not to apply a voltage from a DC 3.3V power supply (third power supply) provided in the main board 200 to the connection point, depending on whether or not an ENG 3.3V output is present.

[0144] Here, the switching circuit 224 includes a PNP transistor, the base of which is connected to the ENG 3.3V power supply, the emitter is connected to the DC 3.3V power supply provided on the main board 200, and the collector is connected to the above-mentioned connection point of the hard limiter circuit 220. The PNP transistor is switched on and off in conjunction with the presence or absence of output from the ENG 3.3V power supply, and is configured to switch whether or not the voltage from the DC 3.3V power supply is applied to the above-mentioned connection point of the hard limiter circuit 220.

[0145] Here, as in the first embodiment, in the fourth embodiment, the supply of ENG3.3V is stopped when the printer 1 is in a "sleep state (power saving mode)." Specifically, as shown in Fig. 13, a signal EN is input to the DC-DC conversion circuit 211 from the output port of the ASIC 210, and when the printer 1 is in a standby state (including when printing is being performed), the value of the signal EN becomes H (on) and ENG3.3V is output, and when the printer 1 is in a sleep state, the value of the signal EN becomes L (off), instructing the printer not to output ENG3.3V.

[0146] Therefore, if the first reference voltage Vd were input only from the ENG3.3V power supply, when the printer 1 transitioned to the sleep mode, the first reference voltage input to the non-inverting input terminal (+) and the first sensor voltage Vin input to the inverting input terminal (-) would both be 0V, causing the non-output logic to become undefined and resulting in an erroneous determination (for example, an L signal being sent as the heater hard limiter signal even when the temperature of the heating roller 91 is sufficiently low). However, in the fourth embodiment, the non-inverting input terminal (+) to which the first reference voltage is input is connected to the switching circuit 224 in addition to the ENG3.3V power supply, and DC 3.3V (third voltage) is supplied from the switching circuit 224 when the printer 1 transitioned to the sleep mode. Therefore, even when the printer 1 is in the sleep mode, at least the voltage from the switching circuit 224 is input to the non-inverting input terminal (+), so that the first reference voltage does not become 0V and the output logic is determined, thereby preventing such an erroneous determination.

[0147] Specifically, when the printer 1 is in standby mode, the switching circuit 224 inputs ENG3.3V to the base of the PNP transistor, so no current flows from the emitter to the base of the PNP transistor (because the emitter potential and the base potential are the same). That is, when the printer 1 is in standby mode, the PNP transistor disconnects the DC 3.3V power supply from the hard limiter circuit 220. Meanwhile, when the printer 1 is in standby mode, the value of the signal EN sent from the ASIC 210 to the DC-DC conversion circuit 211 is H (ON), so a voltage is output from the ENG3.3V power supply included in the reference voltage generation circuit 223 to the non-inverting input terminal (+). As described above, when the printer 1 is in standby mode, the output of ENG3.3V controls the printer 1 so that the voltage from the DC 3.3V power supply connected to the emitter of the PNP transistor is not input to the non-inverting input terminal (+). When the printer 1 is in the "standby state (non-power saving mode)", the first reference voltage Vd input to the non-inverting input terminal (+) is a voltage value expressed by the following equation (9). Vd=Rg×(ENG3.3V) / (Ra+Rg) (9)

[0148] Meanwhile, when the printer 1 is in sleep mode, 0V is input to the base of the PNP transistor, causing current to flow from the emitter to the base of the PNP transistor (because the emitter potential is 3.3V and the base potential is 0V, which is lower). This causes current to flow from the emitter to the collector of the PNP transistor; that is, when the printer 1 is in sleep mode, the PNP transistor connects the DC 3.3V power supply to the hard limiter circuit 220. Meanwhile, when the printer 1 is in sleep mode, the value of the signal EN sent from the ASIC 210 to the DC-DC conversion circuit 211 becomes L (OFF), preventing the ENG3.3V power supply included in the reference voltage generation circuit 223 from outputting voltage to the non-inverting input terminal (+). As described above, when the printer 1 is in sleep mode, ENG3.3V is not output, causing control so that the voltage from the DC 3.3V power supply connected to the emitter of the PNP transistor is input to the non-inverting input terminal (+). When the printer 1 is in the "sleep state (power saving mode)", the first reference voltage Vd input to the non-inverting input terminal (+) is a voltage value expressed by the following equation (10). Vd=DC3.3V (10)

[0149] On the other hand, the second comparator 222 is similar to that in the first embodiment, and the reference voltage input to the non-inverting input terminal (+) of the second comparator 222 is connected to a DC 1.8V power supply (second power supply) as shown in Fig. 13. Then, a voltage obtained by dividing 1.8V by resistors R3 and R4 is input to the non-inverting input terminal (+) as the second reference voltage. The second reference voltage Vd input to the non-inverting input terminal (+) has a voltage value expressed by the above formula (4).

[0150] As described above in detail, the printer 1 according to the fourth embodiment includes a reference voltage generation circuit 223 that generates a first reference voltage to be input to the non-inverting input terminal (+) of the first comparator 221, and the reference voltage generation circuit 223 has a first resistor Ra having one end connected to the power supply of ENG3.3V and a second resistor Rg having one end connected to the ground section GND, and further includes a switching circuit 224 that can switch whether or not to apply DC 3.3V to a connection point depending on whether or not the output of ENG3.3V is present, and the switching circuit 224 When printer 1 is in standby mode, ENG3.3V is output, thereby controlling so that DC3.3V is not input to the connection point, and when printer 1 is in sleep mode, ENG3.3V is not output, thereby controlling so that DC3.3V is input to the connection point. Therefore, even if printer 1 goes into sleep mode and the supply of voltage from the power supply of ENG3.3V stops, the first reference voltage will not become 0V due to the voltage supplied from switching circuit 224, and the output logic will be determined, making it possible to prevent erroneous judgment by the first comparator.

[0151] The present invention is not limited to the above-described embodiment, and it goes without saying that various improvements and modifications are possible within the scope of the present invention. For example, in the above embodiment, the physical quantity compared with the reference voltage by the hard limiter circuit 220 is the temperature detected by the fixing temperature sensors TH1 and TH2 for detecting the temperature of the heating roller 91, but it may also be a physical quantity detected by a sensor other than the fixing temperature sensors TH1 and TH2.

[0152] Furthermore, in the above embodiment, the first comparator 221 corresponds to the fixing temperature sensor TH1, and the second comparator 222 corresponds to the fixing temperature sensor TH2, but it is also possible to reverse this and make the first comparator 221 correspond to the fixing temperature sensor TH2, and the second comparator 222 correspond to the fixing temperature sensor TH1.

[0153] Furthermore, in the above embodiment, the first reference voltage input to the non-inverting input terminal (+) of the first comparator 221 is generated by a reference voltage generation circuit 223 including a power supply (first power supply) of ENG3.3V, but the first reference voltage may be generated by the reference voltage generation circuit 223 or may be generated directly from the power supply (first power supply) of ENG3.3V.

[0154] Furthermore, in the above embodiment, the fixing device 9 is removable from the main body casing 2 of the printer 1, but the printer 1 may also be one in which the fixing device 9 is fixed.

[0155] Furthermore, in the above embodiment, the printer 1 has been described as an example of an image forming apparatus, but it may also be, for example, a copy machine, a facsimile machine, or a multifunction machine having a printer function and a scanner function. [Explanation of symbols]

[0156] 1... printer (image forming apparatus), 2... main body housing, 9... fixing device, 91... heating roller, 92... pressure roller, 150... main body connector, 160... fixing connector, 161... relay board, 200... main board (control board), 210... ASIC (control unit), 220... hard limiter circuit, 221... first comparator, 222... second comparator, 223... reference voltage generation circuit, 224... switching circuit, TH1, TH2... fixing temperature sensor, SE3... nip detection sensor, SE4... discharge sensor, S... sheet

Claims

1. An image forming apparatus that forms an image on a sheet and that can be set to a first mode and a second mode that consumes less power than the first mode, a first sensor that detects a first physical quantity of the image forming apparatus and outputs a first sensor voltage corresponding to the detected first physical quantity; a first comparator having a first sensor input terminal to which the first sensor voltage is input and a first reference voltage input terminal to which a first reference voltage is input, the first comparator comparing the first sensor voltage with the first reference voltage and outputting a first output signal when the first sensor voltage exceeds the first reference voltage; a first power supply, which is one of the power supplies included in the image forming apparatus, and which is controlled so that voltage output is turned on when the image forming apparatus is in the first mode and is turned off when the image forming apparatus is in the second mode; The image forming apparatus according to claim 1, wherein the first sensor voltage and the first reference voltage are generated based on a voltage output from the first power supply.

2. The voltage output by the first power supply when in the first mode is a first voltage, a second sensor that detects a second physical quantity of the image forming apparatus and outputs a second sensor voltage corresponding to the detected second physical quantity; a second comparator including a second sensor input terminal to which the second sensor voltage is input and a second reference voltage input terminal to which a second reference voltage is input, the second comparator comparing the second sensor voltage with the second reference voltage and outputting a second output signal when the second sensor voltage exceeds the second reference voltage; a second power supply that is one of the power supplies included in the image forming apparatus and outputs the second reference voltage; 2. The image forming apparatus according to claim 1, further comprising: a control unit that receives the first output signal and the second output signal.

3. an image forming unit that forms a developer image on the sheet; a fixing device that fixes the developer image formed on the sheet by the image forming unit, The fixing device further comprises: a heating rotor that heats the sheet; a pressure rotating body that nips a sheet between itself and the heating rotating body; a terminal to which AC voltage is input from a commercial power source; a heater connected to the terminal via a relay, the first sensor is a temperature sensor for detecting a temperature of a first region of the heating rotator, the second sensor is a temperature sensor for detecting a temperature of a second region different from the first region of the heating rotator, 3. The image forming apparatus according to claim 2, wherein the control unit instructs the relay to be disconnected when at least one of the following conditions is satisfied: receiving the first output signal from the first comparator; or receiving the second output signal from the second comparator.

4. The voltage output by the first power supply when in the first mode is a first voltage, a third power supply that is one of the power supplies included in the image forming apparatus and outputs a third voltage; The first comparator When the image forming apparatus is in the first mode, at least the first voltage is input to the first reference voltage input terminal, 2. The image forming apparatus according to claim 1, wherein when the image forming apparatus is in the second mode, at least the third voltage is input to the first reference voltage input terminal.

5. a reference voltage generating circuit that generates the first reference voltage to be input to the first reference voltage input terminal; The reference voltage generating circuit a first resistor having one end connected to the first power supply, a second resistor having one end connected to the third power supply, and a third resistor having one end connected to a ground portion; 5. An image forming apparatus according to claim 4, wherein the other end of the first resistor, the other end of the second resistor, and the other end of the third resistor are connected at a connection point, and a voltage applied to the connection point is input to the first reference voltage input terminal as the first reference voltage.

6. a reference voltage generating circuit that generates the first reference voltage to be input to the first reference voltage input terminal; and a control unit; The reference voltage generating circuit a first resistor having one end connected to the first power supply and a second resistor having one end connected to a ground; the other end of the first resistor and the other end of the second resistor are connected at a connection point, and a voltage applied to the connection point is input to the first reference voltage input terminal as the first reference voltage; The control unit an output terminal and the third power supply, and the third voltage can be input from the third power supply to the connection point of the reference voltage generating circuit via the output terminal in response to switching of a connection state between the output terminal and the third power supply; 5. The image forming apparatus according to claim 4, wherein when the image forming apparatus is in the first mode, the output terminal is disconnected from the third power source, and when the image forming apparatus is in the second mode, the output terminal is connected to the third power source.

7. a reference voltage generating circuit that generates the first reference voltage to be input to the first reference voltage input terminal; The reference voltage generating circuit a first resistor having one end connected to the first power supply and a second resistor having one end connected to a ground; the other end of the first resistor and the other end of the second resistor are connected at a connection point, and a voltage applied to the connection point is input to the first reference voltage input terminal as the first reference voltage; a switching circuit that switches whether or not the third voltage is applied to the connection point, and a control unit that controls the switching circuit; The control unit when the image forming apparatus is in the first mode, instructing the switching circuit not to input the third voltage, while instructing the first power source to output the first voltage; 5. The image forming apparatus according to claim 4, wherein when the image forming apparatus is in the second mode, the switching circuit is instructed to input the third voltage, while the first power source is instructed not to output the first voltage.

8. a reference voltage generating circuit that generates the first reference voltage to be input to the first reference voltage input terminal; The reference voltage generating circuit a first resistor having one end connected to the first power supply and a second resistor having one end connected to a ground; the other end of the first resistor and the other end of the second resistor are connected at a connection point, and a voltage applied to the connection point is input to the first reference voltage input terminal as the first reference voltage; a switching circuit capable of switching whether or not the third voltage is applied to the connection point depending on whether or not the first voltage is output, The switching circuit When the image forming apparatus is in the first mode, the first voltage is output, thereby controlling so that the third voltage is not input to the connection point; 5. The image forming apparatus according to claim 4, wherein when the image forming apparatus is in the second mode, the first voltage is not output, and the third voltage is input to the connection point.

9. The voltage output by the first power supply when in the first mode is a first voltage, an image forming unit for forming a developer image on the sheet; a fixing device that fixes the developer image formed on the sheet by the image forming unit, The fixing device further comprises: a heating rotor that heats the sheet; a pressure rotating body that nips a sheet between itself and the heating rotating body; a pressure contact / separation mechanism that can switch between a pressure contact state in which the heating rotator and the pressure rotator are in pressure contact with each other and a separation state in which the heating rotator and the pressure rotator are separated from each other; a nip detection sensor capable of detecting whether the pressing state or the separation state is in the nip detection sensor; the first sensor is a temperature sensor for detecting the temperature of the heating rotor, 2. The image forming apparatus according to claim 1, wherein the first voltage is also a drive voltage for the nip detection sensor.

10. The voltage output by the first power supply when in the first mode is a first voltage, an image forming unit for forming a developer image on the sheet; a fixing device that fixes the developer image formed on the sheet by the image forming unit; a discharge sensor that detects that the sheet has been discharged after the developer image has been fixed by the fixing device, the fixing device further includes a heating rotor that heats the sheet, the first sensor is a temperature sensor for detecting the temperature of the heating rotor, 2. The image forming apparatus according to claim 1, wherein the first voltage is also a drive voltage for the discharge sensor.

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