Sensor device and image forming apparatus

Abstract

To achieve a sensor device that, even when the power supply voltage of an AC signal becomes larger than the upper limit of an input voltage of a control unit, allows the control unit to calculate humidity based on the input voltage.SOLUTION: A sensor device (50) comprises: a humidity sensor (40); a first fixed resistance (56) that is connected in series with the humidity sensor (40) and forms a series circuit with the humidity sensor (40); a first control signal output unit (53) that outputs a first control signal (S1); a second control signal output unit (54) that outputs a second control signal (S2); a first reference voltage application circuit (51) that applies a first reference voltage (Vref1) and a ground voltage (Vgnd) to both ends of the series circuit; and a second reference voltage application circuit (52) that applies a second reference voltage (Vref2) and the ground voltage (Vgnd) to both ends of the series circuit.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a sensor device and an image forming apparatus.

Background Art

[0002] Patent Document 1 describes an image forming apparatus including sensors such as a temperature sensor and a humidity sensor. In the image forming apparatus of Patent Document 1, various information such as temperature and humidity detected by the sensors is used to control the image forming apparatus.

[0003] The humidity sensor often uses a resistance change type sensor. More specifically, the humidity sensor has a series circuit in which a resistance change type sensor and another resistance element are connected in series. An AC signal in which the power supply voltage and the ground voltage are switched with respect to time is input to the series circuit, whereby the power supply voltage is applied across the series circuit.

[0004] The power supply voltage of the AC signal is divided by the resistance change type sensor and another resistance element, and the voltage divided by the resistance change type sensor is input to the control unit of the image forming apparatus. The control unit calculates the humidity based on the input voltage and determines a transfer bias or the like according to the calculated humidity.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the conventional sensor device, the power supply voltage of the AC signal and the upper limit of the input voltage of the control unit were the same. However, when the power supply voltage of the AC signal becomes larger than the upper limit of the input voltage of the control unit, there is a problem that the control unit cannot calculate the humidity based on the input voltage.

[0007] An object of the present invention is to realize a sensor device and an image forming apparatus capable of calculating humidity based on an input voltage by a control unit even when a power supply voltage of an AC signal becomes larger than an upper limit of the input voltage of the control unit.

Means for Solving the Problems

[0008] In order to solve the above problems, a sensor device according to Aspect 1 of the present invention includes a resistance change type sensor, a first fixed resistor connected in series with the resistance change type sensor and forming a series circuit together with the resistance change type sensor, a control signal output unit that outputs a control signal in which a power supply voltage and a ground voltage are switched according to time, a reference voltage application circuit that applies a reference voltage smaller than the power supply voltage and the ground voltage, which are switched according to the switching between the power supply voltage and the ground voltage, to both ends of the series circuit, and a control unit that receives a divided voltage obtained by dividing the reference voltage by the series circuit and detects humidity based on the divided voltage.

[0009] According to Aspect 1 of the present invention, by newly providing a reference voltage application circuit, a reference voltage smaller than the power supply voltage of the control signal and a voltage in which the ground voltage alternates can be applied to both ends of a series circuit including a resistance change type sensor and a first fixed resistor. Therefore, even when the power supply voltage of the control signal is larger than the upper limit of the input voltage of the control unit, a voltage divided by the series circuit and equal to or lower than the upper limit of the input voltage of the control unit is input to the control unit, so that the control unit can calculate humidity based on the input voltage.

[0010] The sensor device according to Aspect 2 of the present invention is the sensor device according to Aspect 1, wherein the control unit calculates humidity based on a voltage obtained by analog-digital converting the divided voltage, and the reference voltage is equal to or lower than a maximum value of voltages that can be input to the control unit when the control unit performs analog-digital conversion of the divided voltage.

[0011] According to aspect 2 of the present invention, the maximum value of the divided voltage obtained by dividing the reference voltage by the series circuit is the reference voltage. According to the above configuration, it is possible to match the reference voltage with the maximum value of the voltage that can be input when the control unit performs analog-digital conversion.

[0012] The sensor device according to aspect 3 of the present invention is, in the above aspect 1 or 2, wherein the reference voltage application circuit has a switching element that switches between on and off in response to the switching between the power supply voltage and the ground voltage of the control signal, and the reference voltage and the ground voltage are switched and applied to both ends of the series circuit in response to the switching between on and off of the switching element.

[0013] According to aspect 3 of the present invention, the switching element switches between on and off in response to the switching between the power supply voltage and the ground voltage of the control signal. Then, the reference voltage and the ground voltage are switched in response to the switching between on and off of the switching element and applied to both ends of the series circuit. Therefore, according to the above configuration, the reference voltage and the ground voltage are switched in response to the switching between the power supply voltage and the ground voltage of the control signal and applied to both ends of the series circuit.

[0014] The sensor device according to aspect 4 of the present invention is, in the above aspect 3, wherein the switching element is connected between a power supply that outputs the reference voltage and a resistor connected to the ground, and the sensor device further includes a storage unit that stores in advance a ratio between the reference voltage and a corrected reference voltage corrected by the voltage drop by the switching element from the reference voltage, and the control unit corrects the divided voltage input to the control unit using the ratio stored in the storage unit.

[0015] According to Aspect 4 of the present invention, by previously storing in the storage unit the ratio between the corrected reference voltage in which the voltage drop by the switching element is corrected and the reference voltage, the control unit can correct the divided voltage using the ratio stored in the storage unit. Therefore, the control unit can accurately calculate the humidity without being affected by the voltage drop by the switching element.

[0016] The image forming apparatus according to Aspect 5 of the present invention is an image forming apparatus having the sensor device according to Aspect 4 above, and includes an image forming unit, a high voltage power supply board that outputs a high voltage power supply to be output to the image forming unit, the high voltage power supply board having the resistance change type sensor, a main board having the control unit, the first fixed resistor, the reference voltage application circuit, and the control signal output unit, and controlling image formation of the image forming unit and output of the high voltage power supply of the high voltage power supply board using the control unit. The high voltage power supply board and the main board are electrically connected such that the resistance change type sensor and the first fixed resistor are connected in series, and the divided voltage is input to the control unit.

[0017] According to Aspect 5 of the present invention, an image forming apparatus having the same effect as the above sensor device can be realized.

[0018] The image forming apparatus according to Aspect 6 of the present invention is the image forming apparatus according to Aspect 5 above, in which, in the reference voltage application circuit, the switching element is connected between a power supply that outputs the reference voltage and a resistor connected to the ground, the switching element and the resistor constitute the series circuit in which the switching element and the resistor are connected in series, and the divided voltage obtained by dividing the reference voltage by the series circuit is the corrected reference voltage.

[0019] According to Aspect 6 of the present invention, an image forming apparatus having the same effect as the above sensor device can be realized.

[0020] In the image forming apparatus according to aspect 7 of the present invention, in the above aspect 6, in a state where the high-voltage power supply board is removed from the main board, the control unit obtains, as the correction reference voltage, the voltage of the input port of the control unit to which the divided voltage is input by the control signal output unit outputting the control signal, determines the ratio based on the obtained correction reference voltage and the reference voltage, and stores the determined ratio in the storage unit.

[0021] According to aspect 7 of the present invention, by obtaining the ratio in advance in a state where the high-voltage power supply board is removed from the main board and storing it in the storage unit, the divided voltage input to the input port of the control unit during the operation of the image forming apparatus can be corrected.

[0022] The image forming apparatus according to aspect 8 of the present invention, in any one of the above aspects 5 to 7, the control signal output unit includes a first control signal output unit that outputs a first control signal in which the ground voltage and the power supply voltage are switched according to time, and a second control signal output unit that outputs a second control signal in which the power supply voltage and the ground voltage are switched according to time and the phase is inverted with respect to the first control signal, and the reference voltage application circuit includes a first reference voltage application circuit that applies, to one end of the series circuit, a first reference voltage smaller than the power supply voltage and the ground voltage that are switched according to the switching between the power supply voltage and the ground voltage, and a second reference voltage application circuit that applies, to the other end of the series circuit, a second reference voltage smaller than the power supply voltage and the ground voltage that are switched according to the switching between the power supply voltage and the ground voltage.

[0023] According to aspect 8 of the present invention, the first reference voltage and the second reference voltage can be switched and applied to the series circuit by using the first control signal and the second control signal whose phases are inverted to the control unit.

[0024] In the image forming apparatus according to aspect 9 of the present invention, in the above aspect 8, the main board further includes a second fixed resistor connected in parallel to the resistance change type sensor, and the divided voltage divided by the second fixed resistor, the combined resistor formed by the resistance change type sensor, and the second fixed resistor is input to the input port of the control unit.

[0025] In the image forming apparatus according to aspect 10 of the present invention, in the above aspect 9, the control unit controls the output of the first control signal of the first control signal output unit and the output of the second control signal of the second control signal output unit, thereby adjusting the duty ratio of the switching between the first reference voltage and the second reference voltage applied to the series circuit.

Advantages of the Invention

[0026] According to one aspect of the present invention, it is possible to realize a sensor device and an image forming apparatus capable of calculating humidity based on an input voltage by a control unit even when the power supply voltage of an AC signal becomes larger than the upper limit of the input voltage of the control unit.

Brief Description of the Drawings

[0027]

Figure 1

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Mode for Carrying Out the Invention

[0028] 〔Embodiment 1〕 Hereinafter, an embodiment of the present invention will be described below with reference to the drawings. The image forming apparatus 10 according to Embodiment 1 is an apparatus that forms an image on a sheet.

[0029] <Overall Configuration of Image Forming Apparatus 10> FIG. 1 is a schematic cross-sectional view showing the internal configuration of the image forming apparatus 10. In the following description, the right side in FIG. 1 is taken as the front of the image forming apparatus 10. Further, the image forming apparatus 10 is an LED color printer that forms a color image with four-color (black K, yellow Y, magenta M, cyan C) colorants. Hereinafter, when distinguishing each component by color, K (black), Y (yellow), M (magenta), and C (cyan) meaning each color are attached to the end of the reference numeral of the component. Furthermore, the image forming apparatus 10 is not limited to an LED color printer, and may be, for example, a laser color printer, a facsimile apparatus, or a so-called multifunction device having a printer function and a reading function (scanner function).

[0030] The image forming apparatus 10 includes a main body casing 11, and a paper feed tray 21 on which sheets of paper 3 are stacked is provided at the bottom of the main body casing 11. Further, the front surface of the main body casing 11 serves as an access port for accessing an image forming unit 25 described later, and a front cover 15 is rotatably installed at the access port. Thereby, the access port can be closed or opened. Also, an open / close sensor 22 is arranged adjacent to the front cover 15. The open / close sensor 22 generates a detection signal corresponding to the opening and closing of the front cover 15 and supplies the detection signal to a high-voltage power supply board 30.

[0031] A paper feed roller 19 is provided above the front end of the paper feed tray 21, and as the paper feed roller 19 rotates, the uppermost sheet of paper 3 accumulated in the paper feed tray 21 is sent out to a registration roller 18. After performing skew correction and the like on the sheet of paper 3, the registration roller 18 conveys the sheet of paper 3 onto a belt unit 23 of the image forming unit 25.

[0032] The image forming unit 25 includes a belt unit 23, an exposure unit 27, a process cartridge 24, a developing roller 31, a photosensitive drum 32, a transfer roller 34, a fixing unit 35, a belt cleaning device 16, and the like.

[0033] At the time of image formation, the photosensitive drum 32 is rotationally driven, and accordingly, the surface of the photosensitive drum 32 is uniformly positively charged by a charger 33. Then, the positively charged portion is exposed by the high-speed scanning of light from an LED unit 37, and an electrostatic latent image corresponding to the image to be formed on the sheet of paper 3 is formed on the surface of the photosensitive drum 32.

[0034] Next, when the toner carried on the developing roller 31 and positively charged rotates and comes into contact with the photosensitive drum 32, it is supplied to the electrostatic latent image formed on the surface of the photosensitive drum 32. Thereby, the electrostatic latent image on the photosensitive drum 32 is visualized, and a toner image with toner adhering only to the exposed portions is carried on the surface of the photosensitive drum 32.

[0035] Thereafter, the toner image carried on the surface of each photoreceptor drum 32 is sequentially transferred onto the sheet 3 by the negative transfer voltage applied to the transfer roller 34 while the sheet 3 conveyed by the belt 36 passes through each transfer position between the photoreceptor drum 32 and the transfer roller 34. The sheet 3 onto which the toner image has been thus transferred is then conveyed to the fixing unit 35.

[0036] The fixing unit 35 includes a heating roller 29 having a heat source and a pressure roller 28 that presses the sheet 3 toward the heating roller 29 side, and thermally fixes the toner image transferred onto the sheet 3 onto the paper surface. Then, the sheet 3 thermally fixed by the fixing unit 35 is conveyed upward and is configured to be discharged onto a discharge tray provided on the upper surface wall 11A of the main body casing 11.

[0037] Also, inside the main body casing 11, a high-voltage power supply board 30, a low-voltage power supply board 12, and a control board 20 that controls the high-voltage power supply board 30 and the low-voltage power supply board 12 are provided. The control board 20 is an example of a main board.

[0038] A temperature sensor 41 that detects the temperature inside the main body casing 11 and a humidity sensor 40 that detects the humidity inside the main body casing 11 are arranged on the high-voltage power supply board 30. The humidity sensor 40 is a resistance change type sensor in which the resistance value between a pair of terminals of the sensor changes based on humidity. Here, as the humidity sensor 40 of the resistance variable type, preferably, a polymer-based (water-soluble) humidity sensor is used. This is because the polymer-based (water-soluble) humidity sensor is low-cost and has a wide humidity detection range, so it can suitably detect humidity even in a high-humidity environment. Further, in the humidity sensor of the resistance change type sensor, the humidity is measured using the resistance value of the polymer film. Since the polymer film has a relatively high relative permittivity, when the application direction of the voltage is fixed, polarization occurs in the polymer film and the resistance value cannot be accurately measured. That is, the humidity sensor 40 is an AC drive sensor that is used by applying an AC signal.

[0039] The temperature sensor 41 is a resistance change type sensor in which the resistance value between a pair of terminals of the sensor changes based on temperature.

[0040] <Functional configuration of the image forming apparatus 10> Next, with reference to FIG. 2, the functional configuration of the image forming apparatus 10 will be described. The image forming apparatus 10 further includes a control unit 42 and a high voltage power supply 49. As shown in FIG. 2, the control unit 42 mainly includes an ASIC (Application Specific Integrated Circuit) 43, an EEPROM (Electrically Erasable Programmable Read-Only Memory) 45 (registered trademark), a RAM (Random Access Memory) 47, a ROM (Read Only Memory) 46, and an analog-digital conversion unit 48. These are connected via a bus 2 so as to be able to transmit and receive data to and from the image forming unit 25 and the like. The ASIC 43 includes a CPU (Central Processing Unit) 44, and the CPU 44 and the ASIC 43 cooperate to perform various processes on the image forming unit 25. Programs and the like for the CPU 44 to control various operations are stored in the ROM 46. The RAM 47 is used as a storage area for temporarily recording data, signals, etc. used when the CPU 44 executes the above programs, or as a work area for data processing. Setting information to be retained even after the power is turned off is stored in the EEPROM 45. The analog-digital conversion unit 48 converts the analog information acquired by the control unit 42 into a digital signal. The control unit 42 is connected to the high voltage power supply 49, the humidity sensor 40, and the temperature sensor 41. A temperature detection voltage Vthm is input from the temperature sensor 41 to the control unit 42. And a humidity detection voltage Vout is input from the humidity sensor 40 to the control unit 42.

[0041] The high voltage power supply 49 is connected to the charger 33, the developing roller 31, and the transfer roller 34. The high voltage power supply 49 controls the charging voltage of the charger 33, the developing bias of the developing roller 31, and the transfer voltage of the transfer roller 34 based on commands from the control unit 42.

[0042] Based on the temperature detection voltage Vthm of the temperature sensor 41 and the humidity detection voltage Vout of the humidity sensor 40, the control unit 42 controls the value of the transfer voltage of the transfer roller 34.

[0043] <Schematic configuration of the sensor device 50> FIG. 3 shows a schematic configuration diagram of the sensor device 50. The control unit 42, the first reference voltage application circuit 51, the second reference voltage application circuit 52, and the first fixed resistor 56 arranged on the control board 20, and the humidity sensor 40 and the temperature sensor 41 arranged on the high-voltage power supply board 30 constitute the sensor device 50.

[0044] The control unit 42 includes a first control signal output unit 53, a second control signal output unit 54, a first analog-to-digital conversion unit 48A, a second analog-to-digital conversion unit 48B, and a storage unit 55. The first control signal output unit 53 and the second control signal output unit 54 are realized by the CPU 44 executing programs and the like stored in the ROM 46.

[0045] In FIG. 2, the first analog-to-digital conversion unit 48A and the second analog-to-digital conversion unit 48B in FIG. 3 are collectively referred to as the analog-to-digital conversion unit 48. Also, in FIG. 3, the EEPROM 45, the RAM 47, and the ROM 46 in FIG. 2 are collectively referred to as the storage unit 55.

[0046] The first control signal output unit 53 is an example of a control signal output unit, and the first reference voltage application circuit 51 is an example of a reference voltage application circuit. The second control signal output unit 54 is an example of a control signal output unit, and the second reference voltage application circuit 52 is an example of a reference voltage application circuit.

[0047] The control unit 42 is supplied with a power supply voltage Vcc and a reference voltage Vref. The first control signal output unit 53 generates a first control signal S1 using the power supply voltage Vcc. The first control signal output unit 53 outputs the first control signal S1 to the first reference voltage application circuit 51. Also, the second control signal output unit 54 generates a second control signal S2 using the power supply voltage Vcc. The second control signal output unit 54 outputs the second control signal S2 to the second reference voltage application circuit 52.

[0048] The first reference voltage application circuit 51 includes a first switching element 51S and a first reference resistor 51R. The first switching element 51S is a PNP transistor. The reference voltage Vref is supplied to the emitter terminal of the first switching element 51S. The base terminal of the first switching element 51S is connected to the first control signal output unit 53. The collector terminal of the first switching element 51S is connected to one terminal 51Ra of the first reference resistor 51R and the port P1. The other terminal 51Rb of the first reference resistor 51R is connected to the ground GND. Note that the first switching element 51S is not limited to a PNP transistor.

[0049] The first reference voltage application circuit 51 converts the first control signal S1 into a first reference signal Sref1 and outputs the first reference signal Sref1 to the port P1.

[0050] The second reference voltage application circuit 52 includes a second switching element 52S and a second reference resistor 52R. The second switching element 52S is a PNP transistor. A reference voltage Vref is supplied to the emitter terminal of the second switching element 52S. The base terminal of the second switching element 52S is connected to the second control signal output section 54. The collector terminal of the second switching element 52S is connected to one terminal 52Ra of the second reference resistor 52R and port P3. However, a first fixed resistor 56 is connected between the collector terminal of the second switching element 52S and port P3. The other terminal 52Rb of the second reference resistor 52R is connected to the ground GND. Note that the second switching element 52S is not limited to a PNP transistor.

[0051] The second reference voltage application circuit 52 converts the second control signal S2 into a second reference signal Sref2 and outputs the second reference signal Sref2 to port P3.

[0052] Here, in the first embodiment, the relationship between the resistance value Rref1 of the first reference resistor 51R and the resistance value Rref2 of the second reference resistor 52R is as shown in the following formula (1). Rref1≒Rref2···(1) Also, it is assumed that the first switching element 51S and the second switching element 52S have substantially the same characteristics. For this reason, the relationship between the voltage Vtr1 between the emitter and collector of the first switching element 51S and the voltage Vtr2 between the emitter and collector of the second switching element 52S is as shown in the following formula (2). Vtr1≒Vtr2···(2) The humidity sensor 40 has one terminal 40a connected to port P2 and the other terminal 40b connected to port P4.

[0053] When port P3 and port P4 are connected, the other terminal 40b of the humidity sensor 40 and one terminal 56a of the first fixed resistor 56 are connected in series. The serially connected humidity sensor 40 and first fixed resistor 56 form a series circuit. The other terminal 56b of the first fixed resistor 56 and one terminal 52Ra of the second reference resistor 52R of the second reference voltage application circuit 52 are connected. Also, the other terminal 40b of the humidity sensor 40 and the first analog-digital conversion unit 48A are connected via the input port Pin. A humidity detection voltage Vout, which is a divided voltage applied to the humidity sensor 40 and the first fixed resistor 56, is input to the first analog-digital conversion unit 48A. The first analog-digital conversion unit 48A performs analog-digital conversion of the humidity detection voltage Vout based on the reference voltage Vref.

[0054] When port P1 and port P2 are connected, one terminal 40a of the humidity sensor 40 is connected to the first reference voltage application circuit 51.

[0055] The temperature sensor 41 has one terminal 41a connected to port P6 and the other terminal 41b connected to the ground GND. When port P5 and port P6 are connected, a reference voltage Vref is applied to one terminal 41a of the temperature sensor 41 via a resistor. Also, the second analog-digital conversion unit 48B is connected to one terminal 41a of the temperature sensor 41. A temperature detection voltage Vthm of the temperature sensor 41 is input to the second analog-digital conversion unit 48B. The second analog-digital conversion unit 48B performs analog-digital conversion of the temperature detection voltage Vthm based on the reference voltage Vref.

[0056] A humidity correction table TB, which will be described later, is stored in the EEPROM 45 of the storage unit 55.

[0057] FIG. 4 is a time chart of each of the first control signal S1, the second control signal S2, the first reference signal Sref1, the second reference signal Sref2, and the potential difference Vhum applied across both terminals of the humidity sensor 40. The vertical axis of each time chart indicates level, and the horizontal axis indicates time. The times Δt1, Δt2, Δt3, Δt4, Δt5, and Δt6 are the same.

[0058] (First control signal S1) The level of the first control signal S1 is the power supply voltage Vcc at times Δt1, Δt3, and Δt5. On the other hand, the level of the first control signal S1 is the ground voltage Vgnd at times Δt2, Δt4, and Δt6. The first control signal S1 is a PWM (Pulse Width Modulation) signal whose level alternates between the power supply voltage Vcc and the ground voltage Vgnd every cycle. For example, the power supply voltage Vcc is 3.3V. The ground voltage Vgnd is 0V.

[0059] (Second control signal S2) The level of the second control signal S2 is the ground voltage Vgnd at times Δt1, Δt3, and Δt5. On the other hand, the level of the second control signal S2 is the power supply voltage Vcc at times Δt2, Δt4, and time Δ6. The second control signal S2 is a PWM signal whose level alternates between the ground voltage Vgnd and the power supply voltage Vcc every cycle. For example, the power supply voltage Vcc is 3.3V. The ground voltage Vgnd is 0V.

[0060] (Relationship between the first control signal S1 and the second control signal S2) As shown in FIG. 4, the first control signal S1 and the second control signal S2 are in antiphase with each other.

[0061] (First reference signal Sref1) When the level of the first control signal S1 is the power supply voltage Vcc, the first switching element 51S turns off. Therefore, the level of the first reference signal Sref1 becomes the ground voltage Vgnd.

[0062] On the one hand, when the level of the first control signal S1 is the ground voltage Vgnd, the first switching element 51S turns on. Therefore, the level of the first reference signal Sref1 becomes the first reference voltage Vref1. In this case, the first reference voltage Vref1 is represented by the following equation (3). Vref1 = Vref - Vtr1 ··· (3) (Second reference signal Sref2) When the level of the second control signal S2 is the power supply voltage Vcc, the second switching element 52S turns off. Therefore, the level of the second reference signal Sref2 becomes the ground voltage Vgnd.

[0063] On the other hand, when the level of the second control signal S2 is the ground voltage Vgnd, the second switching element 52S turns on. Therefore, the level of the second reference signal Sref2 becomes the second reference voltage Vref2. In this case, the second reference voltage Vref2 is represented by the following equation (4). Vref2 = Vref - Vtr2 ··· (4) (Relationship between the first reference signal Sref1 and the second reference signal Sref2) As shown in FIG. 4, when the level of the first reference signal Sref1 is the ground voltage Vgnd, the level of the second reference signal Sref2 is the second reference voltage Vref2. Also, when the level of the first reference signal Sref1 is the first reference voltage Vref1, the level of the second reference signal Sref2 is the ground voltage Vgnd.

[0064] As described above, the first reference signal Sref1 is output to one terminal 40a of the humidity sensor 40, and the second reference signal Sref2 is output to the other terminal 56b of the first fixed resistor 56. Therefore, if one terminal 40a of the humidity sensor 40 is the ground voltage Vgnd, the other terminal 56b of the first fixed resistor 56 becomes the second reference voltage Vref2. Hereinafter, in this case, the potential difference Vhum applied across both terminals of the humidity sensor 40 is referred to as the potential difference V-hum.

[0065] On one hand, if one terminal 40a of the humidity sensor 40 is the first reference voltage Vref1, the other terminal 56b of the first fixed resistor 56 will be at the ground voltage Vgnd. Hereinafter, in this case, the potential difference Vhum applied across both terminals of the humidity sensor 40 is referred to as the potential difference V+hum.

[0066] At times Δt1, Δt3, and Δt5, the potential difference V-hum applied across both terminals of the humidity sensor 40 is represented by the following equation (5). V-hum = -Vref2 × Rhum / (Rhum + R1 + Rref1) ··· (5) Here, Rhum is the resistance value of the humidity sensor 40, and R1 is the resistance value of the first fixed resistor 56.

[0067] At times Δt2, Δt4, and Δt6, the potential difference V+hum applied across both terminals of the humidity sensor 40 is represented by the following equation (6). V+hum = Vref1 × Rhum / (Rhum + R1 + Rref2) ··· (6) In this way, the potential difference V-hum and the potential difference V+hum are alternately applied across both ends of the humidity sensor 40 so that polarization does not occur in the humidity sensor 40.

[0068] <Humidity acquisition method> The humidity detection voltage Vout is input to the first analog-digital conversion unit 48A. The humidity detection voltage Vout is represented by the following equation (7). Vout = Vref1 × (R1 + Rref2) / (Rhum + R1 + Rref2) ··· (7) The humidity detection voltage Vout decreases as the resistance value Rhum of the humidity sensor 40 increases, and converges to the first reference voltage Vref1 as the resistance value Rhum decreases.

[0069] The first analog-digital conversion unit 48A performs analog-digital conversion of the humidity detection voltage Vout with reference to the reference voltage Vref.

[0070] Here, it is ideal for the reference voltage Vref and the first reference voltage Vref1 to match. However, as shown in the above equation (3), since there is a voltage drop by the voltage Vtr1 between the emitter and collector of the first switching element 51S, the first reference voltage Vref1 does not match the reference voltage Vref. As a result, an error of the voltage Vtr1 between the emitter and collector of the first switching element 51S is superimposed on the digital signal obtained by analog-digital conversion by the first analog-digital conversion unit 48A.

[0071] Therefore, the control unit 42 corrects the humidity detection voltage Vout and calculates a corrected humidity detection voltage Vout' from the following equation (8). The corrected humidity detection voltage Vout' is an example of a corrected reference voltage. Vout' = Vout × B ··· (8) The ratio B is a constant. The ratio B is obtained from the following equation (9). B = Vref / Vref2 ··· (9) The following equation (10) is derived from the above equations (2), (3), and (4). Vref1 ≒ Vref2 ··· (10) The first reference voltage Vref1 and the second reference voltage Vref2 are substantially equal. Therefore, if the second reference voltage Vref2 can be detected, the first reference voltage Vref1 can be detected. In the first embodiment, the ratio B between the second reference voltage Vref2 and the reference voltage Vref is calculated, and the corrected humidity detection voltage Vout' is calculated using the ratio B.

[0072] <Ratio acquisition process> Therefore, in the first embodiment, the second reference voltage Vref2 is detected when the humidity sensor 40 is electrically disconnected from the ports P1 and P3 of the control board 20. The humidity detection voltage Vout input to the first analog-digital conversion unit 48A when the humidity sensor 40 is electrically separated is represented by the following equation (11). Vout = Vref2 ··· (11) When the humidity sensor 40 is electrically disconnected, no current flows through the first fixed resistor 56. Therefore, the humidity detection voltage Vout becomes the second reference voltage Vref2 applied to one terminal 52Ra of the second reference resistor 52R.

[0073] Fig. 5 shows a flowchart of the ratio acquisition process. Here, the control board 20 and the high-voltage power supply board 30 are disconnected, and the ports P1 and P2, port 3 and port 4, and port 5 and port 6 are all electrically separated.

[0074] Step S101: The first control signal output unit 53 outputs the first control signal S1, and the second control signal output unit 54 outputs the second control signal S2. When the first control signal S1 is the power supply voltage Vcc and the second control signal S2 is the ground voltage Vgnd (YES in step S101), the control unit 42 proceeds to step S102. Otherwise (NO in step S101), it proceeds to step S105.

[0075] Step S102: The humidity detection voltage Vout is input to the first analog-digital conversion unit 48A via the input port Pin. Since the humidity sensor 40 is electrically disconnected, no current flows through the first fixed resistor 56, and the humidity detection voltage Vout is equal to the second reference voltage Vref2. Therefore, the first analog-digital conversion unit 48A detects the second reference voltage Vref2. The control unit 42 holds the second reference voltage Vref2 as the humidity detection voltage Vout. Next, it proceeds to step S103.

[0076] Step S103: The control unit 42 obtains the ratio B from the above equation (9). Next, it proceeds to step S104.

[0077] Step S104: The control unit 42 stores the ratio B obtained in step S103 in the EEPROM 45 of the storage unit 55. Next, it proceeds to step S105.

[0078] Step S105: The control unit 42 determines whether to acquire the ratio B. If the ratio B is to be acquired (YES in step S105), the process returns to step S101. Otherwise (NO in step S105), the flow ends.

[0079] <Humidity acquisition process> FIG. 6 shows a flowchart of the humidity acquisition process. When the image forming apparatus 10 starts the image forming operation, the control unit 42 starts the humidity acquisition process.

[0080] Step S201: The first control signal output unit 53 starts outputting the first control signal S1 to the first reference voltage application circuit 51. The second control signal output unit 54 starts outputting the second control signal S2 to the second reference voltage application circuit 52. Next, the process proceeds to step S202.

[0081] Step S202: If the first control signal S1 is the ground voltage Vgnd and the second control signal S2 is the power supply voltage Vcc (YES in step S202), the control unit 42 proceeds to step S203. Otherwise (NO in step S202), the process proceeds to step S208.

[0082] Step S203: The control unit 42 acquires the humidity detection voltage Vout. Next, the process proceeds to step S204.

[0083] Step S204: The control unit 42 acquires the temperature detection voltage Vthm. Next, the process proceeds to step S205.

[0084] Step S205: The control unit 42 reads out the ratio B from the EEPROM 45, and calculates the corrected humidity detection voltage Vout' from the above formula (8) using the ratio B and the humidity detection voltage Vout acquired in step S203. Next, the process proceeds to step S206.

[0085] Step S206: The control unit 42 acquires the temperature from the temperature detection voltage Vthm. Next, the process proceeds to step S207.

[0086] Step S207: The control unit 42 obtains the humidity by referring to the humidity correction table TB. Next, it proceeds to step S208.

[0087] Here, a part of an example of the humidity correction table TB is shown in FIG. 7. The first analog-to-digital conversion unit 48A converts the humidity detection voltage Vout into an 8-bit digital value. The humidity is determined based on the temperature obtained by the temperature sensor 41 and the digital value of the humidity detection voltage Vout. For example, when the temperature is 12°C, the humidity detection voltage Vout is 0.215 V, and the ratio B is 0.8, the corrected humidity detection voltage Vout' is 0.215 (V) × 0.8 = 0.172 (V). As indicated by the arrow in the humidity correction table TB, the digital signal is shifted from 11 to 8, and it is determined that 31% in the lower column of the temperature of 12°C on the horizontal axis is the humidity value.

[0088] Step S208: The control unit 42 determines whether to obtain the temperature or the humidity. This is because when the image forming apparatus 10 has not yet obtained the humidity or when the image formation of the image forming apparatus 10 continues, it is necessary to monitor the humidity and the humidity may be obtained again. If the temperature or the humidity is to be obtained (YES in step S208), the process returns to step S202. Otherwise (NO in step S208), the flow ends.

[0089] <Effect of Embodiment 1> According to the first embodiment, even if the power supply voltage Vcc and the reference voltage Vref of the first analog-to-digital conversion unit 48A are different, the humidity detection voltage Vout of the humidity sensor 40 can be detected.

[0090] Also, according to the first embodiment, the second reference voltage Vref2 is detected to calculate the ratio B, and the corrected humidity detection voltage Vout' is calculated from the ratio B. Thereby, accurate humidity can be obtained.

[0091] 〔Embodiment 2〕 Other embodiments of the present invention will be described below. For the sake of convenience of explanation, members having the same functions as those described in Embodiment 1 are denoted by the same reference numerals, and their explanations will not be repeated.

[0092] FIG. 8 is a schematic configuration diagram of a sensor device 50A according to Embodiment 2 of the present invention. The difference between the sensor device 50A and the sensor device 50 of Embodiment 1 is that the sensor device 50A further includes a second fixed resistor 57.

[0093] As shown in FIG. 8, a second fixed resistor 57 is connected in parallel with the humidity sensor 40. More specifically, one terminal 57a of the second fixed resistor 57 is connected to the collector terminal of the first switching element 51S and the port P1. The other terminal 57b of the second fixed resistor 57 is connected to the first analog-to-digital conversion unit 48A via the input port Pin. Further, the other terminal 57b of the second fixed resistor 57 is connected to the port P3 and one terminal 56a of the first fixed resistor 56. The second fixed resistor 57 is disposed on the control board 20.

[0094] FIG. 9 shows an ideal time chart of the potential difference Vhum applied to the humidity sensor 40 according to Embodiment 1. The potential difference V-hum shown in the above equation (5) and the potential difference V+hum shown in the above equation (6) are alternately applied to the humidity sensor 40. In Embodiment 1, as shown in the following equation (12), the potential difference Vhum applied to the humidity sensor 40 is set. |V-hum| = |V+hum| ··· (12) Here, |V-hum| represents the absolute value of the potential difference V-hum, and |V+hum| represents the absolute value of the potential difference V+hum.

[0095] In Embodiment 1, the potential difference V-hum and the potential difference V+hum are alternately applied to the humidity sensor 40 at equal intervals of time, thereby reducing the polarization of the humidity sensor 40.

[0096] FIG. 10 shows the actual time chart of the potential difference Vhum applied to the humidity sensor 40 according to Embodiment 1. In Embodiment 1, as shown in the above equations (1) and (10), it was premised that the resistance value Rref1 of the first reference resistor 51R and the resistance value Rref2 of the second reference resistor 52R were substantially equal, and the first reference voltage Vref1 and the second reference voltage Vref2 were substantially equal. However, in reality, the resistance value Rref1 and the resistance value Rref2 may be different, or the first reference voltage Vref1 and the second reference voltage Vref2 may be different. In this case, unlike the above equation (11), |V-hum| and |V+hum| are different.

[0097] If the potential differences V-hum and V+hum are alternately applied to both terminals of the humidity sensor 40 at equal intervals of time while |V-hum| and |V+hum| are different, a difference will occur between the power when the potential difference V-hum is applied to the humidity sensor 40 and the power when the potential difference V+hum is applied. As a result, polarization will occur in the humidity sensor 40. As a result, the control unit 42 will not be able to accurately detect the humidity. In FIG. 10, the power when the potential difference V-hum is applied to the humidity sensor 40 is represented by the area of the portion marked with the symbol X. On the other hand, the power when the potential difference V+hum is applied to the humidity sensor 40 is represented by the area of the portion marked with the symbol Y. As shown in FIG. 10, the area of the portion marked with the symbol X and the area of the portion marked with the symbol Y are different.

[0098] Therefore, in Embodiment 2, when the absolute value |V-hum| of the potential difference V-hum applied to the humidity sensor 40 and the absolute value |V+hum| of the potential difference V+hum are different, the duty ratio D1 of the first control signal S1 and the duty ratio D2 of the second control signal S2 are adjusted to make the respective powers equal when the potential differences V-hum and V+hum are alternately applied to the humidity sensor 40.

[0099] FIG. 11 shows a time chart of the potential difference Vhum applied to the humidity sensor 40 according to Embodiment 2. Time Δt1A, time Δt3A, and time Δt5A are the same. Also, time Δt2A and time Δt4A are the same. In FIG. 11, the power when applying the potential difference V-hum to the humidity sensor 40 is represented by the area at the location marked with symbol X'. On the other hand, the power when applying the potential difference V+hum to the humidity sensor 40 is represented by the area at the location marked with symbol Y'. As shown in FIG. 11, the area at the location marked with symbol X' and the area at the location marked with symbol Y' are equal. Hereinafter, a specific description will be given.

[0100] In Embodiment 2, the potential difference V-hum applied to the humidity sensor 40 can be expressed by the following equation (13). V-hum = -Vref2 × Rhum' / (Rhum' + R1 + Rref1) ··· (13) Also, the potential difference V+hum applied to the humidity sensor 40 can be expressed by the following equation (14). V+hum = Vref1 × Rhum' / (Rhum' + R1 + Rref2) ··· (14) Here, Rhum' is the resistance value of the combined resistance of the resistance value Rhum of the humidity sensor 40 and the resistance value R2 of the second fixed resistor 57. The resistance value Rhum' is expressed by the following equation (15). Rhum' = Rhum × R2 / (Rhum + R2) ··· (15) When the absolute values of the potential difference V-hum and the potential difference V+hum applied to the humidity sensor 40 are different, the duty ratio D1 of the first control signal S1 and the duty ratio D2 of the second control signal S2 are adjusted according to the following equation (16). |V-hum| × Δt1A = |V+hum| × Δt2A ··· (16) Specifically, the duty ratio D1 of the first control signal is obtained by the following equation (17). D1 = Vref2 / (Vref1 + Vref2) ··· (17) Also, the duty ratio D2 of the second control signal is obtained by the following equation (18). D2 = Vref1 / (Vref1 + Vref2) ··· (18) Note that Vref1 and Vref2 can be obtained from equations (3) and (4) described in Embodiment 1, respectively.

[0101] <Duty Ratio and Ratio Acquisition Process> FIG. 12 shows a flowchart of the duty ratio and ratio acquisition process according to Embodiment 2. Here, the control board 20 and the high-voltage power supply board 30 are separated, and Port P1 and Port P2, Port 3 and Port 4, and Port 5 and Port 6 are all electrically separated.

[0102] Step S301: When the first control signal S1 is the power supply voltage Vcc and the second control signal S2 is the ground voltage Vgnd (YES in Step S301), the control unit 42 proceeds to Step S302. Otherwise (NO in Step S301), it returns to Step S301.

[0103] Step S302: The control unit 42 detects the humidity detection voltage Vout and holds it as the second reference voltage Vref2. Next, it proceeds to Step S303.

[0104] When the first control signal S1 is the power supply voltage Vcc and the second control signal S2 is the ground voltage Vgnd, the humidity detection voltage Vout is represented by the following equation (19). Vout = Vref2×(R2 + Rref1) / (R2 + R1 + Rref1) ··· (19) Since no current flows through the first fixed resistor 56 and the second fixed resistor 57, the humidity detection voltage Vout is represented by the following equation (20). Vout ≒ Vref2 ··· (20) Therefore, the second reference voltage Vref2 can be detected by detecting the humidity detection voltage Vout.

[0105] Step S303: When the first control signal S1 is the ground voltage Vgnd and the second control signal S2 is the power supply voltage Vcc (YES in Step S303), the control unit 42 proceeds to Step S304. Otherwise (NO in Step S303), it returns to Step S303.

[0106] Step S304: The control unit 42 detects the humidity detection voltage Vout and holds it as the first reference voltage Vref1. Next, it proceeds to step S305.

[0107] When the first control signal S1 is the power supply voltage Vcc and the second control signal S2 is the ground voltage Vgnd, the humidity detection voltage Vout is represented by the following equation (21). Vout = Vref1 × (R2 + Rref2) / (R2 + R1 + Rref2) ··· (21) Since no current flows through the first fixed resistor 56 and the second fixed resistor 57, the humidity detection voltage Vout is represented by the following equation (22). Vout ≒ Vref1 ··· (22) Therefore, by detecting the humidity detection voltage Vout, the first reference voltage Vref1 can be detected.

[0108] Step S305: The control unit 42 obtains the duty ratio D1 of the first control signal S1 from the above equation (17). Next, it proceeds to step S306.

[0109] Step S306: The control unit 42 obtains the duty ratio D2 of the second control signal S2 from the above equation (18). Next, it proceeds to step S307.

[0110] Step S307: The control unit 42 obtains the ratio B' from the following equation (23). Next, it proceeds to step S308. B' = Vref1 / Vref ··· (23) Step S308: The control unit 42 stores the duty ratio D1 obtained in step S305, the duty ratio D2 obtained in step S306, and the ratio B' obtained in step S307 in the EEPROM 45 of the storage unit 55. Next, it proceeds to step S309.

[0111] Step S309: When the control unit 42 determines to acquire the duty ratio D1 of the first control signal S1, the duty ratio D2 of the second control signal S2, or the ratio B' again (YES in step S309), it returns to step S301. Otherwise (NO in step S309), the flow ends.

[0112] <Humidity acquisition process> FIG. 13 shows a flowchart of the humidity acquisition process according to Embodiment 2. Hereinafter, only the steps different from those of Embodiment 1 will be described.

[0113] Step S401: The control unit 42 outputs the first control signal S1 and the second control signal S2 with the duty ratio D1 of the first control signal S1 and the duty ratio D2 of the second control signal S2 read from the storage unit 55. Next, it proceeds to step S402.

[0114] Steps S402 to S408 correspond to steps S202 to S208 of Embodiment 1, so they are omitted here.

[0115] <Effects of Embodiment 2> According to the present Embodiment 2, when the absolute values of the voltages V-hum and V+hum applied between both terminals of the humidity sensor 40 are different, the duty ratio D1 of the first control signal S1 and the duty ratio D2 of the second control signal S2 are adjusted according to the first reference voltage Vref1 and the second reference voltage Vref2. Then, the power when the voltage V-hum is applied to the humidity sensor 40 is made equal to the power when the voltage V+hum is applied. As a result, the polarization of the humidity sensor 40 is reduced, so that accurate humidity can be acquired.

[0116] 〔Supplementary Notes〕 The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Explanation of Reference Numerals

[0117] 10 Image forming apparatus 20 Control board 30 High-voltage power supply board 40 Humidity sensor 41 Temperature sensor 42 Control unit 48A First analog-digital conversion unit 48B Second analog-digital conversion unit 50 Sensor device 51 First reference voltage application circuit 51S First switching element 51R First reference resistor 52 Second reference voltage application circuit 52S Second switching element 52R Second reference resistor 53 First control signal output section 54 Second control signal output section 56 First fixed resistor 57 Second fixed resistor Pin Input port

Claims

1. A resistance change type sensor, a first fixed resistor connected in series with the resistance change type sensor and constituting a series circuit together with the resistance change type sensor, a control signal output unit that outputs a control signal in which the power supply voltage and the ground voltage are switched according to time, a reference voltage application circuit that applies, to both ends of the series circuit, a reference voltage smaller than the power supply voltage and the ground voltage that are switched according to the switching between the power supply voltage and the ground voltage, a control unit that inputs a divided voltage obtained by dividing the reference voltage by the series circuit and detects humidity based on the divided voltage, comprising: the control unit calculates humidity based on a voltage obtained by analog-digital converting the divided voltage, the sensor device is characterized in that the reference voltage is equal to or lower than the maximum value of the voltage that can be input to the control unit when the control unit performs analog-digital conversion of the divided voltage.

2. The reference voltage application circuit, has a switching element that switches between on and off according to the switching between the power supply voltage and the ground voltage of the control signal, The sensor device according to claim 1, wherein the reference voltage and the ground voltage are switched according to the switching between on and off of the switching element and applied to both ends of the series circuit.

3. The switching element is connected between a power supply that outputs the reference voltage and a resistor connected to the ground, the sensor device further includes a storage unit that stores in advance a ratio between the reference voltage and a corrected reference voltage corrected by a voltage drop amount due to the switching element from the reference voltage, The sensor device according to claim 2, wherein the control unit corrects the divided voltage input to the control unit using the ratio stored in the storage unit.

4. An image forming apparatus having the sensor device according to claim 3, an image forming unit, a high-voltage power supply board that outputs a high-voltage power supply to be output to the image forming unit, the high-voltage power supply board having the resistance change type sensor, a main board having the control unit, the first fixed resistor, the reference voltage application circuit, and the control signal output unit, and controlling image formation of the image forming unit and output of the high-voltage power supply of the high-voltage power supply board using the control unit, comprising: The high-voltage power supply board and the main board are electrically connected such that the resistance-variable sensor and the first fixed resistor are connected in series. An image forming apparatus, characterized in that the divided voltage is input to the control unit. **Claim 5** In the reference voltage application circuit, the switching element is connected between a power supply that outputs the reference voltage and a resistor connected to the ground, the switching element and the resistor constitute the series circuit in which the switching element and the resistor are connected in series, The image forming apparatus according to claim 4, characterized in that the divided voltage obtained by dividing the reference voltage by the series circuit is the corrected reference voltage. **Claim 6** In a state where the high-voltage power supply board is removed from the main board, the control unit obtains, as the corrected reference voltage, the voltage of the input port of the control unit to which the divided voltage is input by the control signal output unit outputting the control signal, determines the ratio based on the obtained corrected reference voltage and the reference voltage, The image forming apparatus according to claim 5, characterized in that the determined ratio is stored in the storage unit. **Claim 7** The control signal output unit is a first control signal output unit that outputs a first control signal in which the ground voltage and the power supply voltage are switched according to time, is a second control signal output unit that outputs a second control signal in which the power supply voltage and the ground voltage are switched according to time and the phase is inverted with respect to the first control signal, and has The reference voltage application circuit is a first reference voltage application circuit that applies, to one end of the series circuit, a first reference voltage smaller than the power supply voltage and the ground voltage that are switched according to the switching between the power supply voltage and the ground voltage, is a second reference voltage application circuit that applies, to the other end of the series circuit, a second reference voltage smaller than the power supply voltage and the ground voltage that are switched according to the switching between the power supply voltage and the ground voltage, The image forming apparatus according to any one of claims 4 to 6, characterized by having. **Claim 8** The main board further has a second fixed resistor connected in parallel to the resistance-variable sensor. The image forming apparatus according to claim 7, wherein the divided voltage divided by the second fixed resistor, the combined resistor formed by the resistance variable sensor, and the second fixed resistor is input to the input port of the control unit.

9. The control unit adjusts a duty ratio of switching between the first reference voltage and the second reference voltage applied to the series circuit by controlling the output of the first control signal of the first control signal output unit and the output of the second control signal of the second control signal output unit. The image forming apparatus according to claim 8.

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