JP7700487B2 - Sensor device and image forming apparatus - Google Patents

Description

The present invention relates to a sensor device and an image forming device.

Patent document 1 describes an image forming device equipped with sensors such as a temperature sensor and a humidity sensor. The image forming device of Patent document 1 controls the image forming device using various information such as temperature and humidity detected by the sensors.

Humidity sensors often use resistance change sensors. More specifically, humidity sensors have a series circuit in which a resistance change sensor is connected in series with another resistive element. An AC signal that switches between a power supply voltage and a ground voltage over time is input to the series circuit, and a power supply voltage is applied to both ends of the series circuit.

The power supply voltage of the AC signal is divided by the resistance change sensor and other resistive elements, and the voltage divided by the resistance change sensor is input to the control unit of the image forming device. The control unit calculates the humidity based on the input voltage and determines the transfer bias and other parameters according to the calculated humidity.

JP 2013-096823 A

In conventional sensor devices, the power supply voltage of the AC signal and the upper limit of the input voltage of the control unit were the same. However, if the power supply voltage of the AC signal became higher than the upper limit of the input voltage of the control unit, there was a problem that the control unit could not calculate the humidity based on the input voltage.

The present invention aims to realize a sensor device and an image forming device that enable a control unit to calculate humidity based on the input voltage even when the power supply voltage of the AC signal becomes higher than the upper limit of the input voltage of the control unit.

In order to solve the above problems, the sensor device according to aspect 1 of the present invention includes a resistance change sensor, a first fixed resistor connected in series with the resistance change sensor and constituting a series circuit together with the resistance change sensor, a control signal output unit that outputs a control signal that switches between a power supply voltage and a ground voltage depending on time, a reference voltage application circuit that applies a reference voltage smaller than the power supply voltage and the ground voltage that switches depending on 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.

According to aspect 1 of the present invention, by providing a new reference voltage application circuit, a voltage that alternates between a reference voltage smaller than the power supply voltage of the control signal and the ground voltage can be applied to both ends of a series circuit consisting of a resistance change sensor and a first fixed resistor. Therefore, even if the power supply voltage of the control signal is higher than the upper limit of the input voltage of the control unit, the voltage that is divided by the series circuit and is 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 the humidity based on the input voltage.

In the sensor device according to aspect 2 of the present invention, in the above aspect 1, the control unit calculates the humidity based on the voltage obtained by analog-digital conversion of the divided voltage, and the reference voltage is equal to or less than the maximum voltage that can be input to the control unit when the control unit performs analog-digital conversion of the divided voltage.

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 becomes the reference voltage. With the above configuration, the reference voltage can be made to match the maximum voltage that can be input when the control unit performs analog-to-digital conversion.

The sensor device according to aspect 3 of the present invention is the same as that according to aspect 1 or 2 above, in which the reference voltage application circuit has a switching element that switches between on and off in response to the switching of the control signal between the power supply voltage and the ground voltage, and switches between the reference voltage and the ground voltage in response to the switching of the switching element between on and off, and applies the reference voltage and the ground voltage to both ends of the series circuit.

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. The reference voltage and the ground voltage switch between on and off in response to the switching between the power supply voltage and the ground voltage of the switching element, and are applied to both ends of the series circuit. Therefore, according to the above configuration, the reference voltage and the ground voltage switch between on and off in response to the switching between the power supply voltage and the ground voltage of the control signal, and are applied to both ends of the series circuit.

The sensor device according to aspect 4 of the present invention is the same as in aspect 3 above, except that the switching element is connected between a power source that outputs the reference voltage and a resistor connected to ground, and the sensor device further includes a memory unit that pre-stores a ratio between the reference voltage and a corrected reference voltage that is corrected from the reference voltage by the voltage drop caused by the switching element, and the control unit corrects the divided voltage input to the control unit using the ratio stored in the memory unit.

According to aspect 4 of the present invention, by storing in advance in the memory unit the ratio between the reference voltage and the corrected reference voltage in which the voltage drop due to the switching element has been corrected, the control unit can correct the divided voltage using the ratio stored in the memory unit. Therefore, the control unit can accurately calculate the humidity without being affected by the voltage drop due to the switching element.

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, and includes an image forming unit, a high-voltage power supply board that outputs a high-voltage power supply to the image forming unit, the high-voltage power supply board having the resistance change sensor, and a main board that has the control unit, the first fixed resistor, the reference voltage application circuit, and the control signal output unit, and uses the control unit to control image formation of the image forming unit and the output of the high-voltage power supply of the high-voltage power supply board, the high-voltage power supply board and the main board are electrically connected so that the resistance change sensor and the first fixed resistor are connected in series, and the divided voltage is input to the control unit.

According to aspect 5 of the present invention, it is possible to realize an image forming device that has the same effect as the above-mentioned sensor device.

The image forming apparatus according to aspect 6 of the present invention is the same as in aspect 5 above, in which in the reference voltage application circuit, the switching element is connected between a power source that outputs the reference voltage and a resistor connected to ground, the switching element and the resistor form 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.

According to aspect 6 of the present invention, it is possible to realize an image forming device that has the same effect as the above-mentioned sensor device.

In the image forming apparatus according to aspect 7 of the present invention, in the above aspect 6, when the high-voltage power supply board is removed from the main board, the control unit acquires, 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 acquired correction reference voltage and the reference voltage, and stores the determined ratio in the memory unit.

According to aspect 7 of the present invention, by obtaining the ratio in advance with the high-voltage power supply board removed from the main board and storing it in the memory unit, it is possible to correct the divided voltage input to the input port of the control unit when the image forming device is operating.

The image forming apparatus according to aspect 8 of the present invention is characterized in that, in any one of aspects 5 to 7 above, the control signal output unit has a first control signal output unit that outputs a first control signal that switches between a ground voltage and a power supply voltage depending on time, and a second control signal output unit that outputs a second control signal that switches between a power supply voltage and a ground voltage depending on time and has an inverted phase with respect to the first control signal, and the reference voltage application circuit has a first reference voltage application circuit that applies a first reference voltage that switches in response to the switching between the power supply voltage and the ground voltage and that is smaller than the power supply voltage and the ground voltage to one end of the series circuit, and a second reference voltage application circuit that applies a second reference voltage that switches in response to the switching between the power supply voltage and the ground voltage and that is smaller than the power supply voltage and the ground voltage to the other end of the series circuit.

According to aspect 8 of the present invention, the control unit can switch between the first reference voltage and the second reference voltage and apply them to the series circuit using the first control signal and the second control signal that are inverted in phase.

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 sensor, and the divided voltage obtained by dividing the combined resistance of the second fixed resistor and the resistance change sensor and the second fixed resistor is input to an input port of the control unit.

In the image forming apparatus according to aspect 10 of the present invention, in the above aspect 9, the control unit adjusts the 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 from the first control signal output unit and the output of the second control signal from the second control signal output unit.

According to one aspect of the present invention, it is possible to realize a sensor device and an image forming device that enable the control unit to calculate humidity based on the input voltage even when the power supply voltage of the AC signal becomes higher than the upper limit of the input voltage of the control unit.

1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a functional configuration diagram of the image forming apparatus. FIG. 2 is a functional configuration diagram of the sensor device according to the first embodiment of the present invention. 5 is a time chart of first and second reference voltages and a voltage applied to a humidity sensor with respect to first and second control signals; 13 is a flowchart of a ratio acquisition process. 13 is a flowchart of a humidity acquisition process. 13 is an example of a humidity correction table based on temperature and humidity detection voltage. FIG. 11 is a schematic configuration diagram of a sensor device according to a second embodiment of the present invention. This is an ideal voltage waveform applied to a humidity sensor. 4 is an actual voltage waveform applied to a humidity sensor. 4 is a waveform of a voltage applied to a humidity sensor. 13 is a flowchart of a duty ratio and ratio acquisition process. 13 is a flowchart of a humidity acquisition process.

[Embodiment 1]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus 10 according to a first embodiment of the present invention is an apparatus for forming an image on a sheet.

<Overall Configuration of Image Forming Apparatus 10>
1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 10. In the following description, the right side in FIG. 1 is the front of the image forming apparatus 10. The image forming apparatus 10 is an LED color printer that forms color images with colorants of four colors (black K, yellow Y, magenta M, and cyan C). Hereinafter, when each component is to be distinguished by color, K (black), Y (yellow), M (magenta), or C (cyan) is added to the end of the reference numeral of the component, which indicates each color. 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 machine, or a so-called multifunction machine equipped with a printer function and a reading function (scanner function), etc.

The image forming device 10 has a main casing 11, and a paper feed tray 21 on which paper 3 is stacked is provided at the bottom of the main casing 11. The front of the main casing 11 is provided as an access opening for accessing the image forming unit 25 described below, and a front cover 15 is installed at the access opening so that it can be rotated. This allows the access opening to be closed or opened. An opening/closing sensor 22 is also disposed adjacent to the front cover 15. The opening/closing sensor 22 generates a detection signal in response to the opening or closing of the front cover 15, and supplies the detection signal to the high-voltage power supply board 30.

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 topmost sheet of paper 3 stacked in the paper feed tray 21 is sent to the registration roller 18. The registration roller 18 performs skew correction on the paper 3, and then transports the paper 3 onto the belt unit 23 of the image forming unit 25.

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

During image formation, the photoconductor drum 32 is rotated, and the surface of the photoconductor drum 32 is uniformly positively charged by the charger 33. The positively charged portion is then exposed to high-speed scanning of light from the LED unit 37, and an electrostatic latent image corresponding to the image to be formed on the paper 3 is formed on the surface of the photoconductor drum 32.

Next, as the developing roller 31 rotates, the positively charged toner carried on the developing roller 31 comes into contact with the photoconductor drum 32 and is supplied to the electrostatic latent image formed on the surface of the photoconductor drum 32. This makes the electrostatic latent image on the photoconductor drum 32 visible, and a toner image is carried on the surface of the photoconductor drum 32, with toner adhering only to the exposed areas.

The toner images carried on the surface of each photoconductor drum 32 are then transferred sequentially to the paper 3 by a negative transfer voltage applied to the transfer roller 34 as the paper 3, transported by the belt 36, passes through each transfer position between the photoconductor drum 32 and the transfer roller 34. The paper 3 to which the toner image has been transferred in this way is then transported to the fixing unit 35.

The fixing unit 35 is equipped with a heating roller 29 having a heat source and a pressure roller 28 that presses the paper 3 toward the heating roller 29, and thermally fixes the toner image transferred onto the paper 3 to the paper surface. The paper 3 that has been thermally fixed by the fixing unit 35 is then transported upward and is configured to be discharged onto a paper discharge tray provided on the top wall 11A of the main casing 11.

In addition, the main casing 11 includes 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. The control board 20 is an example of a main board.

The high-voltage power supply board 30 is provided with a temperature sensor 41 for detecting the temperature inside the main casing 11 and a humidity sensor 40 for detecting the humidity inside the main casing 11. 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 the humidity. Here, a polymer-based (water-soluble) humidity sensor is preferably used as the resistance variable humidity sensor 40. This is because polymer-based (water-soluble) humidity sensors are low cost and have a wide humidity detection range, so they can detect humidity appropriately even in high humidity environments. Furthermore, in the resistance change type humidity sensor, the humidity is measured using the resistance value of the polymer film. Since the polymer film has a relatively high dielectric constant, if the direction of voltage application is constant, polarization occurs in the polymer film, and the resistance value cannot be measured accurately. In other words, the humidity sensor 40 is an AC-driven sensor that is used by applying an AC signal.

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

<Functional configuration of image forming apparatus 10>
Next, the functional configuration of the image forming apparatus 10 will be described with reference to FIG. 2. 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 is mainly composed of 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, which are connected to the image forming unit 25 and the like via a bus 2 so as to be able to transmit and receive data. The ASIC 43 includes a CPU (Central Processing Unit) 44, and the CPU 44 and the ASIC 43 work together to perform various processes for the image forming unit 25. The ROM 46 stores programs and the like for the CPU 44 to control various operations. The RAM 47 is used as a storage area for temporarily recording data, signals, and the like used when the CPU 44 executes the above programs, or as a work area for data processing. The EEPROM 45 stores setting information that should be retained even after the power is turned off. The analog-digital conversion unit 48 converts analog information acquired by the control unit 42 into a digital signal. The control unit 42 is connected to a high-voltage power supply 49, a humidity sensor 40, and a temperature sensor 41. The control unit 42 receives a temperature detection voltage Vthm from the temperature sensor 41. The control unit 42 also receives a humidity detection voltage Vout from the humidity sensor 40.

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.

The control unit 42 controls the value of the transfer voltage of the transfer roller 34 based on the temperature detection voltage Vthm of the temperature sensor 41 and the humidity detection voltage Vout of the humidity sensor 40.

<General configuration of sensor device 50>
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.

The control unit 42 includes a first control signal output unit 53, a second control signal output unit 54, a first analog-digital conversion unit 48A, a second analog-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 a program stored in the ROM 46.

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

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.

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. 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.

The first reference voltage application circuit 51 has a first switching element 51S and a first reference resistor 51R. The first switching element 51S is a PNP transistor. A 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 ground GND. Note that the first switching element 51S is not limited to a PNP transistor.

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.

The second reference voltage application circuit 52 has 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 unit 54. The collector terminal of the second switching element 52S is connected to one terminal 52Ra of the second reference resistor 52R and the port P3. However, a first fixed resistor 56 is connected between the collector terminal of the second switching element 52S and the port P3. The other terminal 52Rb of the second reference resistor 52R is connected to ground GND. Note that the second switching element 52S is not limited to a PNP transistor.

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.

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 expressed by the following formula (1).
Rref1 ≒ Rref2 (1)
The first switching element 51S and the second switching element 52S have approximately the same characteristics. Therefore, the relationship between the emitter-collector voltage Vtr1 of the first switching element 51S and the emitter-collector voltage Vtr2 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 the port P2 and the other terminal 40b connected to the port P4.

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

By connecting ports P1 and P2, one terminal 40a of the humidity sensor 40 is connected to the first reference voltage application circuit 51.

The temperature sensor 41 has one terminal 41a connected to port P6 and the other terminal 41b connected to ground GND. By connecting ports P5 and P6, a reference voltage Vref is applied to one terminal 41a of the temperature sensor 41 via a resistor. In addition, the second analog-digital conversion unit 48B is connected to one terminal 41a of the temperature sensor 41. The 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.

The humidity correction table TB described below is stored in the EEPROM 45 of the memory unit 55.

Figure 4 is a time chart 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 to both terminals of the humidity sensor 40. The vertical axis of each time chart indicates level, and the horizontal axis indicates time. Time Δt1, time Δt2, time Δt3, time Δt4, time Δt5, and time Δt6 are the same.

(First control signal S1)
The level of the first control signal S1 is the power supply voltage Vcc at time Δt1, time Δt3, and time Δt5. Meanwhile, the level of the first control signal S1 is the ground voltage Vgnd at time Δt2, time Δt4, and time 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 period. For example, the power supply voltage Vcc is 3.3V. The ground voltage Vgnd is 0V.

(Second control signal S2)
The level of the second control signal S2 is the ground voltage Vgnd at times Δt1, Δt3, and Δt5. Meanwhile, the level of the second control signal S2 is the power supply voltage Vcc at times Δt2, Δt4, and 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 period. For example, the power supply voltage Vcc is 3.3V. The ground voltage Vgnd is 0V.

(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 inverted in phase with each other.

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

On the other hand, when the level of the first control signal S1 is the ground voltage Vgnd, the first switching element 51S is turned 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 expressed by the following formula (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 is turned off, and the level of the second reference signal Sref2 becomes the ground voltage Vgnd.

On the other hand, when the level of the second control signal S2 is the ground voltage Vgnd, the second switching element 52S is turned 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 expressed by the following formula (4).
Vref2=Vref-Vtr2...(4)
(Relationship between First Reference Signal Sref1 and Second Reference Signal Sref2)
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, and 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.

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, the potential difference Vhum applied between both terminals of the humidity sensor 40 in this case will be referred to as the potential difference V-hum.

On the other 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 is the ground voltage Vgnd. Hereinafter, the potential difference Vhum applied between both terminals of the humidity sensor 40 in this case will be referred to as the potential difference V+hum.

At times Δt1, Δt3, and Δt5, the potential difference V-hum applied between both terminals of the humidity sensor 40 is expressed 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.

At times Δt2, Δt4, and Δt6, the potential difference V+hum applied between both terminals of the humidity sensor 40 is expressed by the following equation (6).
V+hum=Vref1×Rhum/(Rhum+R1+Rref2)...(6)
In this manner, the potential difference V−hum and the potential difference V+hum are alternately applied across the humidity sensor 40 so that the humidity sensor 40 is not polarized.

<Humidity acquisition method>
The humidity detection voltage Vout is input to the first analog-digital conversion unit 48A. The humidity detection voltage Vout is expressed 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.

The first analog-to-digital conversion unit 48A performs analog-to-digital conversion of the humidity detection voltage Vout by referring to the reference voltage Vref.

Ideally, the reference voltage Vref and the first reference voltage Vref1 should be the same, but as shown in the above formula (3), the voltage drops by the emitter-collector voltage Vtr1 of the first switching element 51S, so the first reference voltage Vref1 does not match the reference voltage Vref. As a result, an error of the emitter-collector voltage Vtr1 of the first switching element 51S is superimposed on the digital signal converted from analog to digital by the first analog-digital conversion unit 48A.

Therefore, the control unit 42 corrects the humidity detection voltage Vout to calculate a corrected humidity detection voltage Vout' using the following formula (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 and can be calculated using the following formula (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, a ratio B between the second reference voltage Vref2 and the standard voltage Vref is calculated, and the corrected humidity detection voltage Vout' is calculated using the ratio B.

<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-to-digital conversion unit 48A when the humidity sensor 40 is electrically disconnected is expressed 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.

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

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. If 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), the control unit 42 proceeds to step S105.

Step S102: The humidity detection voltage Vout is input to the first analog-digital conversion unit 48A via the input port Pin. Because 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, proceed to step S103.

Step S103: The control unit 42 obtains the ratio B from the above formula (9). Next, the process proceeds to step S104.

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

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

<Humidity acquisition process>
6 is a flow chart of the humidity acquisition process. When the image forming apparatus 10 starts an image forming operation, the control unit 42 starts the humidity acquisition process.

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, proceed to step S202.

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 control unit 42 proceeds to step S208.

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

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

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 obtained in step S203. Next, the process proceeds to step S206.

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

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

Here, FIG. 7 shows an example of a portion of the humidity correction table TB. The first analog-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, if the temperature is 12°C, the humidity detection voltage Vout is 0.215V, and the ratio B is 0.8, the corrected humidity detection voltage Vout' is 0.215 (V) x 0.8 = 0.172 (V). As shown by the arrow in the humidity correction table TB, the digital signal shifts from 11 to 8, and the humidity value is determined to be 31% in the column below the temperature of 12°C on the horizontal axis.

Step S208: The control unit 42 determines whether to acquire the temperature or humidity. If the image forming device 10 has not yet acquired the humidity, or if the image forming device 10 continues to form images, it is necessary to monitor the humidity, and the humidity may be acquired again. If the temperature or humidity is to be acquired (YES in step S208), the process returns to step S202. Otherwise (NO in step S208), the flow ends.

Effects of First Embodiment
According to the first embodiment, even if the power supply voltage Vcc and the reference voltage Vref of the first analog-digital conversion section 48A differ, the humidity detection voltage Vout of the humidity sensor 40 can be detected.

Furthermore, 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. This makes it possible to obtain an accurate humidity.

[Embodiment 2]
Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the first embodiment, and the description thereof will not be repeated.

Figure 8 is a schematic diagram of a sensor device 50A according to a second embodiment of the present invention. The sensor device 50A differs from the sensor device 50 according to the first embodiment in that it further includes a second fixed resistor 57.

As shown in FIG. 8, the second fixed resistor 57 is connected in parallel to 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 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. In addition, the other terminal 57b of the second fixed resistor 57 is connected to port P3 and one terminal 56a of the first fixed resistor 56. The second fixed resistor 57 is arranged on the control board 20.

9 shows an ideal time chart of the potential difference Vhum applied to the humidity sensor 40 according to the first embodiment. The potential difference V-hum shown in the above formula (5) and the potential difference V+hum shown in the above formula (6) are alternately applied to the humidity sensor 40. In the first embodiment, the potential difference Vhum applied to the humidity sensor 40 is set as shown in the following formula (12).
|V-hum|=|V+hum|...(12)
Here, |V-hum| indicates the absolute value of the potential difference V-hum, and |V+hum| indicates the absolute value of the potential difference V+hum.

In the first embodiment, the potential difference V-hum and the potential difference V+hum are alternately applied to the humidity sensor 40 at equal time intervals, thereby reducing the polarization of the humidity sensor 40.

Figure 10 shows an actual time chart of the potential difference Vhum applied to the humidity sensor 40 according to the first embodiment. In the first embodiment, as shown in the above formulas (1) and (10), it is assumed that the resistance value Rref1 of the first reference resistor 51R and the resistance value Rref2 of the second reference resistor 52R are approximately equal, and that the first reference voltage Vref1 and the second reference voltage Vref2 are approximately equal. However, in reality, the resistance value Rref1 and the resistance value Rref2 may differ, or the first reference voltage Vref1 and the second reference voltage Vref2 may differ. In this case, unlike the above formula (11), |V-hum| and |V+hum| are different.

If the potential difference V-hum and the potential difference V+hum are applied alternately at equal intervals to both terminals of the humidity sensor 40 while |V-hum| and |V+hum| are different, a difference occurs between the power when applying the potential difference V-hum to the humidity sensor 40 and the power when applying the potential difference V+hum to the humidity sensor 40, resulting in polarization of the humidity sensor 40. As a result, the control unit 42 cannot accurately detect the humidity. In FIG. 10, the power when applying the potential difference V-hum 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 applying the potential difference V+hum 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 is different from the area of the portion marked with the symbol Y.

Therefore, in the second embodiment, when the absolute value |V-hum| of the potential difference V-hum applied to the humidity sensor 40 differs from the absolute value |V+hum| of the potential difference V+hum, the duty ratio D1 of the first control signal S1 and the duty ratio D2 of the second control signal S2 are adjusted to equalize the power when the potential difference V-hum and the potential difference V+hum are alternately applied to the humidity sensor 40.

Figure 11 shows a time chart of the potential difference Vhum applied to the humidity sensor 40 according to the second embodiment. The times Δt1A, Δt3A, and Δt5A are the same. Furthermore, the times Δt2A and Δt4A are the same. In Figure 11, the power when applying the potential difference V-hum to the humidity sensor 40 is represented by the area of the location marked with the symbol X'. Meanwhile, the power when applying the potential difference V+hum to the humidity sensor 40 is represented by the area of the location marked with the symbol Y'. As shown in Figure 11, the area of the location marked with the symbol X' is equal to the area of the location marked with the symbol Y'. A detailed explanation will be given below.

In the second embodiment, 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)
Further, 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 formula (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 calculated by the following equation (17).
D1=Vref2/(Vref1+Vref2)...(17)
Moreover, the duty ratio D2 of the second control signal is calculated by the following equation (18).
D2=Vref1/(Vref1+Vref2)...(18)
It should be noted that Vref1 and Vref2 can be calculated from the formulas (3) and (4) described in the first embodiment, respectively.

<Duty ratio and ratio acquisition process>
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 ports P1 and P2, ports 3 and 4, and ports 5 and 6 are all electrically isolated.

Step S301: If 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), the control unit 42 returns to step S301.

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

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 expressed 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 expressed by the following equation (20).
Vout ≒ Vref2 (20)
Therefore, by detecting the humidity detection voltage Vout, the second reference voltage Vref2 can be detected.

Step S303: 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 S303), the control unit 42 proceeds to step S304. Otherwise (NO in step S303), the control unit 42 returns to step S303.

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

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 expressed 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 expressed by the following equation (22).
Vout≒Vref1 (22)
Therefore, by detecting the humidity detection voltage Vout, the first reference voltage Vref1 can be detected.

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

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

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

Step S309: If the control unit 42 determines to reacquire the duty ratio D1 of the first control signal S1, the duty ratio D2 of the second control signal S2, or the ratio B' (YES in step S309), the control unit 42 returns to step S301. Otherwise (NO in step S309), the flow ends.

<Humidity acquisition process>
13 is a flowchart of the humidity acquisition process according to the second embodiment. Only steps different from the first embodiment will be described below.

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, proceed to step S402.

Steps S402 to S408 correspond to steps S202 to S208 in embodiment 1, so they are omitted here.

<Effects of the Second Embodiment>
According to the second embodiment, 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. This reduces the polarization of the humidity sensor 40, making it possible to obtain an accurate humidity reading.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of 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.

REFERENCE SIGNS LIST 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 unit 54 Second control signal output unit 56 First fixed resistor 57 Second fixed resistor Pin Input port

Claims (9)

A resistance change sensor;
a first fixed resistor connected in series with the resistance change type sensor to form a series circuit together with the resistance change type sensor;
a control signal output unit that outputs a control signal that switches between a power supply voltage and a ground voltage according to time;
a reference voltage application circuit that applies a reference voltage smaller than the power supply voltage and the ground voltage, the reference voltage being switched in response to switching between the power supply voltage and the ground voltage, to both ends of the series circuit;
a control unit to which a divided voltage obtained by dividing the reference voltage by the series circuit is input and which detects humidity based on the divided voltage;
Equipped with
The control unit calculates humidity based on a voltage obtained by analog-to-digital conversion of the divided voltage,
The sensor device according to claim 1, wherein the reference voltage is equal to or less than a maximum value of a voltage that can be input to the control unit when the control unit performs analog-to-digital conversion of the divided voltage . The reference voltage application circuit includes:
a switching element that switches between on and off in response to switching of the control signal between a power supply voltage and a ground voltage;
2. The sensor device according to claim 1 , wherein the reference voltage and the ground voltage are switched and applied to both ends of the series circuit in response to the switching on and off of the switching element. the switching element is connected between a power supply that outputs the reference voltage and a resistor connected to ground,
The sensor device further includes a storage unit configured to store in advance a ratio between the reference voltage and a corrected reference voltage obtained by correcting the reference voltage by an amount of a voltage drop caused by the switching element,
3. 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. An image forming apparatus having the sensor device according to claim 3 ,
An image forming unit;
a high-voltage power supply substrate that outputs a high-voltage power supply to the image forming unit and has the resistance change type sensor;
a main board including the control unit, the first fixed resistor, the reference voltage application circuit, and the control signal output unit, and using the control unit to control image formation of the image forming unit and an output of a high voltage power supply of the high voltage power supply board;
Equipped with
the high-voltage power supply substrate and the main substrate are electrically connected so that the resistance change type sensor and the first fixed resistor are connected in series;
The image forming apparatus is characterized in that the divided voltage is input to the control unit. 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 ground,
the switching element and the resistor constitute the series circuit in which the switching element and the resistor are connected in series;
5. The image forming apparatus according to claim 4 , wherein the divided voltage obtained by dividing the reference voltage by the series circuit is the corrected reference voltage. In a state in which the high voltage power supply board is detached from the main board,
The control unit is
acquiring, as the correction reference voltage, a voltage of an input port of the control unit to which the divided voltage is input as a result of the control signal output unit outputting the control signal;
determining the ratio based on the acquired corrected reference voltage and the reference voltage;
6. The image forming apparatus according to claim 5 , wherein the determined ratio is stored in the storage unit. The control signal output unit is
a first control signal output unit that outputs a first control signal that switches between a ground voltage and a power supply voltage according to time;
a second control signal output section that outputs a second control signal that switches between a power supply voltage and a ground voltage according to time and has an inverted phase with respect to the first control signal;
having
The reference voltage application circuit includes:
a first reference voltage application circuit that applies a first reference voltage, which is switched in response to switching between the power supply voltage and the ground voltage and is smaller than the power supply voltage, and the ground voltage to one end of the series circuit;
a second reference voltage application circuit that applies a second reference voltage, which is switched in response to switching between the power supply voltage and the ground voltage and is smaller than the power supply voltage, and the ground voltage to the other end of the series circuit;
7. The image forming apparatus according to claim 4 , further comprising: the main board further includes a second fixed resistor connected in parallel to the resistance change type sensor,
8. The image forming apparatus according to claim 7 , wherein the divided voltage obtained by dividing a combined resistance of the second fixed resistor and the resistance change type sensor and the second fixed resistor is input to an input port of the control unit. The image forming apparatus according to claim 8, characterized in that the control unit adjusts the 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 from the first control signal output section and the output of the second control signal from the second control signal output section.

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