Image forming device

Abstract

To provide an image forming device capable of correcting a digital value from an A-D conversion unit to obtain a desired digital value.SOLUTION: A printer 1 comprises a first A-D conversion unit 92, a second A-D conversion unit 100, and a main control circuit 71. The main control circuit 71 computes a correction value using a result of analog-to-digital conversion of an input signal performed by the second A-D conversion unit 100 and corrects a sensor value using the correction value.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with an AD conversion unit. [Background technology]

[0002] The AD conversion unit is a circuit that performs analog-to-digital conversion of an input signal with an N-bit resolution with a reference voltage as the maximum value. For example, if the AD conversion unit has a 10-bit resolution, the digital value corresponding to the reference voltage is 1023, and the input signal is converted into a digital value between 0 and 1023. Patent Document 1 describes a technology relating to an AD conversion device that finds that the reference voltage may affect the accuracy of analog-to-digital conversion, and detects the reference voltage using a reference voltage detection unit and corrects the AD conversion result according to the detected reference voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-42082 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is an image forming apparatus that has a sensor that outputs an analog signal obtained by dividing an input voltage according to the detection result, and converts the analog signal output from the sensor into a digital value by an AD conversion unit, and performs control using the digital value. In the image forming apparatus, when the voltage input to the sensor and the reference voltage of the AD conversion unit are different from each other, there is a problem that a difference between the voltage actually input to the sensor and the voltage that is the design reference occurs, resulting in a difference between the actually measured digital value and the desired digital value.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide an image forming apparatus capable of acquiring a desired digital value by correcting the digital value from an AD conversion section. [Means for solving the problem]

[0006] In order to solve the above problems, the image forming apparatus disclosed in this embodiment includes an AD conversion unit, a sensor that receives a first voltage and detects a physical quantity of the image forming apparatus and outputs a sensor signal that is an analog signal obtained by dividing the first voltage by the physical quantity, a first AD conversion unit that receives a second voltage different from the first voltage and the sensor signal, performs analog-to-digital conversion on the sensor signal using the input second voltage as a reference voltage, and outputs a sensor value that is the result of the analog-to-digital conversion, a second AD conversion unit that receives the first voltage and an input signal that is the second voltage or the sensor signal, and performs analog-to-digital conversion on the input signal using the input first voltage as a reference voltage, and a control unit. The control unit calculates a correction value using the result of the analog-to-digital conversion performed by the second AD conversion unit on the input signal, and corrects the sensor value using the correction value.

[0007] When the first AD conversion unit performs analog-to-digital conversion on the sensor signal, the conversion is performed using a second voltage different from the first voltage used by the sensor as a reference voltage. Therefore, due to the influence of deviation of the first voltage that generates the sensor signal from the design reference voltage, a deviation may occur between the sensor value resulting from the analog-to-digital conversion performed by the first AD conversion unit and the true value. Therefore, in the image forming apparatus configured as described above, the control unit uses a second AD conversion unit that performs analog-to-digital conversion using the first voltage as a reference voltage to calculate a correction value for correcting the deviation of the sensor value caused by the first AD conversion unit. The control unit corrects the sensor value of the first AD conversion unit with the correction value, thereby correcting the deviation of the sensor value of the first AD conversion unit and obtaining a desired digital value.

[0008] The image forming apparatus includes a process unit that forms a developer image on a sheet, a heating rotor, and a pressure rotor that forms a nip between the heating rotor and the pressure rotor, and a fixing unit that fixes the image formed on the sheet to the sheet, and the sensor is a thermistor that measures the temperature of the heating rotor. In the above configuration, the sensor value obtained by analog-to-digital conversion of the sensor signal from the thermistor is corrected to obtain the desired temperature of the heating rotor of the fixing unit.

[0009] The input signal is a signal that is a second voltage, and the control unit calculates the correction value based on an actual measurement value that is a result of the second AD conversion unit performing analog-to-digital conversion on the second voltage using the first voltage as a reference voltage, and a theoretical value that is a result of the second voltage performing analog-to-digital conversion using a voltage value that is a reference voltage for design. In the above configuration, the control unit can calculate the correction value based on the actual measurement value when the second AD conversion unit performs analog-to-digital conversion on the input signal that is the second voltage, and the theoretical value that is a result of the second voltage performing analog-to-digital conversion using a voltage value that is a reference voltage for design.

[0010] The control unit calculates the correction value by dividing the theoretical value by the actual measurement value. In the above configuration, the correction value can be calculated as a value indicating the ratio of the theoretical value to the actual measurement value, so that the sensor value can be corrected by multiplying the sensor value by the correction value, and an increase in the load on the control unit when performing the correction can be suppressed.

[0011] The control unit is composed of a main control circuit and a sub-control circuit, the sub-control circuit has a second AD conversion unit and calculates a correction value using an actual measurement value from the second AD conversion unit, and the main control circuit has a first AD conversion unit and obtains the correction value from the sub-control circuit and corrects the sensor value from the first AD conversion unit using the correction value. In the above configuration, by having the sub-control circuit calculate the correction value, it is possible to suppress an increase in the processing load of the main control circuit.

[0012] The device includes a process unit that forms a developer image on a sheet, and a high-voltage power supply board that applies a high-voltage voltage to the process unit according to a control signal and outputs a feedback signal corresponding to the applied high-voltage voltage by dividing a first voltage, and the sub-control circuit further performs analog-to-digital conversion of the feedback signal using the first voltage as a reference voltage using a second AD conversion unit, and outputs a control signal to the high-voltage power supply board according to the result. In the above configuration, the second AD conversion unit of the sub-control circuit not only calculates a correction value, but also performs analog-to-digital conversion of the feedback signal output by the high-voltage power supply board. As a result, the sub-control circuit can control the high-voltage power supply board by outputting a control signal to the high-voltage power supply board according to the result of the analog-to-digital conversion.

[0013] The main control circuit transmits a correction value acquisition command, which is an instruction to acquire a correction value, to the sub-control circuit before transmitting an instruction to start applying a high-voltage voltage from the high-voltage power supply board to the process unit, and the sub-control circuit calculates the correction value upon receiving the correction value acquisition command, and causes the high-voltage power supply board to start applying the high-voltage voltage to the process unit upon receiving an instruction to start applying the high-voltage voltage. In the above configuration, the sub-control circuit calculates the correction value prior to the generation of voltage by the high-voltage power supply board, thereby preventing the processing load of the sub-control circuit from becoming too high.

[0014] The printer includes a heating rotator, a pressure rotator that forms a nip between the heating rotator and the pressure rotator, and a fixing device that fixes an image formed on a sheet to the sheet, the sensor is a thermistor for measuring the temperature of the heating rotator, and the main control circuit acquires the temperature of the heating rotator using the temperature indicated by the sensor value corrected by the correction value before sending an instruction to the sub-control circuit to start applying a high voltage voltage, and heats the heating rotator until the estimated temperature of the heating rotator reaches a predetermined temperature. In the above configuration, the desired temperature of the heating rotator can be acquired in the heater control that controls the temperature of the heating rotator, which is performed prior to the start of application of the high voltage voltage.

[0015] The main control circuit transmits a correction value acquisition command to the sub-control circuit before the temperature of the heating rotor reaches a predetermined temperature, corrects the acquired sensor value using the correction value acquired from the sub-control circuit based on the transmission of the correction value acquisition command, and acquires the temperature of the heating rotor using the corrected sensor value. With the above configuration, it is possible to acquire the desired temperature of the heating rotor.

[0016] The main control circuit transmits a correction value acquisition command to the sub-control circuit until the temperature of the heating rotor reaches a predetermined temperature, corrects the sensor value every time a correction value acquired from the sub-control circuit based on the transmission of the correction value acquisition command is acquired, and acquires the temperature of the heating rotor using the corrected sensor value. In the above configuration, a new correction value is acquired every time the temperature of the heating rotor is acquired, and the sensor value is corrected, thereby making it possible to acquire the desired temperature of the heating rotor.

[0017] The main control circuit has a plurality of first AD conversion units corresponding to each of the plurality of sensors, and corrects the sensor values ​​from the plurality of first AD conversion units using the correction value obtained from the sub-control circuit. In the above configuration, even when the image forming apparatus has a plurality of sensors, it is possible to obtain a desired value for each sensor.

[0018] The image forming apparatus includes a process unit that forms a developer image on a sheet, a heating rotor, and a pressure rotor that forms a nip between the heating rotor and the pressure rotor, and a fixing device that fixes the image formed on the sheet to the sheet, and the sensors are a thermistor for measuring the temperature of the heating rotor, a first light receiving sensor that is disposed opposite the belt on whose surface a patch made of toner is formed and receives specularly reflected light from the belt, and a second light receiving sensor that is disposed opposite the belt on whose surface a patch made of toner is formed and receives diffusely reflected light from the belt. With the above configuration, the image forming apparatus can obtain the desired temperature of the heating rotor, the amount of specularly reflected light from the belt, and the amount of diffusely reflected light.

[0019] The input signal is a sensor signal, and the control unit calculates the correction value based on an actual value that is a result of the second AD conversion unit performing analog-to-digital conversion on the sensor signal using the first voltage as a reference voltage and a theoretical value that is a result of the first AD conversion unit performing analog-to-digital conversion on the sensor signal using the second voltage as a reference voltage. In the above configuration, the correction value can be calculated using the sensor values ​​from the two AD conversion units.

[0020] The control unit is composed of a main control circuit and a sub-control circuit, the sub-control circuit has a second AD conversion unit and calculates a correction value using the second AD conversion unit, and the main control circuit has a first AD conversion unit and obtains the correction value from the sub-control circuit and corrects the sensor value from the first AD conversion unit using the correction value. In the above configuration, by having the sub-control circuit calculate the correction value, it is possible to suppress an increase in the processing load of the main control circuit.

[0021] The image forming apparatus includes a process unit that forms a developer image on a sheet, a heating rotor, and a pressure rotor that forms a nip between the heating rotor and the pressure rotor, and a fixing unit that fixes the image formed on the sheet to the sheet, and the multiple sensors are a thermistor for measuring the temperature of the heating rotor, a sensor that is arranged opposite the belt on which a patch made of toner is formed and receives specular reflected light from the belt, and a sensor that is arranged opposite the belt on which a patch made of toner is formed and receives diffuse reflected light from the belt, and the main control circuit has multiple first AD conversion units corresponding to each of the multiple sensors, and corrects the sensor values ​​from the multiple first AD conversion units using a correction value obtained from the sub control circuit. In the above configuration, the desired temperature of the heating rotor, the amount of light received from the specular reflection from the belt, and the amount of light received from the diffuse reflection can be obtained in the image forming apparatus. Effect of the Invention

[0022] According to the present invention, it is possible to provide an image forming apparatus capable of acquiring a desired digital value by correcting the digital value from the AD conversion unit. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a cross-sectional view of a laser printer. [Diagram 2] FIG. 2 is an electrical configuration diagram of the laser printer. [Diagram 3] FIG. 2 is a diagram illustrating a detailed electrical configuration of the laser printer. [Figure 4] FIG. 4 is a diagram illustrating electrical connections of a concentration sensor. [Diagram 5] 4 is a flowchart illustrating a process executed by a main control circuit. [Figure 6] 6 is a flowchart illustrating a process executed by a sub-control circuit. [Figure 7] FIG. 2 is a diagram illustrating analog-to-digital conversion. [Figure 8] 10 is a flowchart illustrating a process executed by a main control circuit according to a second embodiment. [Figure 9] FIG. 10 is a diagram illustrating the electrical configuration of a laser printer according to a third embodiment. [Figure 10] 6 is a flowchart illustrating a process executed by a sub-control circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] A color laser printer, which is an embodiment of an image forming apparatus, will be described below with reference to FIG. 1. FIG. 1 shows a cross-sectional view of the schematic configuration of a color laser printer (hereinafter, printer) 1 according to this embodiment. Printer 1 is a so-called tandem type laser printer that uses four color toners. In the following description, the description will be based on the direction as seen by a user using printer 1, as shown in FIG. 1. That is, the right side in FIG. 1 will be referred to as the "front", the left side as the "rear", the top side as the "top", the bottom side as the "bottom", the near side as the "left" and the far side as the "right".

[0025] As shown in FIG. 1, the printer 1 includes a main body housing 2, a paper feed unit 10, a process unit 20, and a fixing unit 60. The main body housing 2 houses the paper feed unit 10, the process unit 20, and the fixing unit 60. An ejection tray 5 onto which the sheet S is ejected is formed on the top surface of the main body housing 2. The front surface of the main body housing 2 includes an opening 2b and a front cover 2a for opening and closing the opening 2b. The front cover 2a rotates about a rotation shaft 2c to change between a position for closing the opening 2b and a position for opening the opening 2b.

[0026] The paper feed section 10 includes a paper feed tray 11 in which sheets S are stored, a pickup roller 12, a separation pad 13, a pressure plate 14, and various rollers. The sheets S are, for example, standard sheets such as A4 size. The sheets S are not limited to paper media such as plain paper and thick paper, but may be other recording media such as OHP film. The paper feed tray 11 is detachably attached to the lower part of the main body housing 2. The pressure plate 14 is provided in the paper feed tray 11. A displacement mechanism (not shown) is provided below the pressure plate 14. The displacement mechanism displaces the pressure plate 14 to an inclined state so that the front side is higher prior to image formation. As a result, the sheets S stored in the paper feed tray 11 are brought toward the pickup roller 12 by the pressure plate 14, separated one by one by the pickup roller 12 and the separation pad 13, and transported to the process section 20 by various rollers.

[0027] The process unit 20 is provided in the approximate center of the inside of the main body housing 2, and includes developing cartridges 30C, 30M, 30Y, and 30K corresponding to the respective colors, an exposure unit 35, a driving roller 51, a driven roller 52, a conveyor belt 53, and a plurality of (four in this embodiment) transfer rollers 54. The developing cartridges 30C, 30M, 30Y, and 30K contain cyan, magenta, yellow, and black toners, respectively. The four developing cartridges 30C to 30K are provided in the order of developing cartridges 30K, 30C, 30M, and 30Y from the front to the rear of the printer 1. The developing cartridges 30C to 30K can be removed and replaced by opening the front cover 2a and taking them out through the opening 2b of the main body housing 2.

[0028] The developing cartridge 30K includes a photosensitive drum 31, a charger 32, and a toner cartridge 33. The other developing cartridges 30C, 30M, and 30Y have different toner colors, but are otherwise configured the same as the developing cartridge 30K. Therefore, the following will only describe the developing cartridge 30K, and will not describe the other developing cartridges 30C, 30M, and 30Y.

[0029] The charger 32 is, for example, a Scorotron type charger including a charging wire 32a and a grid portion 32b. Prior to forming an electrostatic latent image on the surface of the photoconductor drum 31 during image formation, the charger 32 uniformly charges the surface of the photoconductor drum 31 in a positive manner. The device for charging the photoconductor drum 31 is not limited to a Scorotron type charger, but may be another device such as a roller-type charging roller. Furthermore, the polarity for charging the photoconductor drum 31 is not limited to a positive charge, but may be a negative charge.

[0030] The toner cartridge 33K includes a toner storage chamber 33a, an agitator 33e, a supply roller 33b, a developing roller 33f, and a layer thickness regulating blade 33d. The toner storage chamber 33a stores black toner. The agitator 33e agitates the toner stored in the toner storage chamber 33a. The supply roller 33b is provided in the toner storage chamber 33a and rotates by receiving a driving force from a process motor (FIG. 2) provided in the main body housing 2. The supply roller 33b supplies the toner supplied from the toner storage chamber 33a to the developing roller 33f. The photosensitive drum 31 rotates, for example, in a clockwise direction in FIG. 1. The developing roller 33f is provided diagonally behind and below the supply roller 33b and is in contact with the supply roller 33b. The developing roller 33f rotates by receiving a driving force from a process motor 83 (FIG. 3) provided in the main body housing 2, which will be described later. A positive voltage is applied to the roller shaft of the developing roller 33f. The toner supplied to the developing roller 33f is carried on the developing roller 33f as the developing roller 33f rotates. The layer thickness regulating blade 33d is provided so as to be in pressure contact with the developing roller 33f from above, and regulates the thickness of the toner adhering to the outer peripheral surface of the developing roller 33f to a constant value.

[0031] The exposure unit 35 is provided at the top inside the main body housing 2, and includes a laser light source, a polygon mirror, a lens, a reflecting mirror, etc. (not shown). A laser beam emitted from the laser light source is deflected by a polygon mirror, etc., and is emitted from the exposure unit 35. The exposure unit 35 exposes the surface of the photoconductor drum 31 by emitting a light beam shown by a dashed line in FIG. 1 to the surface of the photoconductor drum 31. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 31. The toner carried on the development roller 33f moves to the electrostatic latent image on the photoconductor drum 31 due to the potential difference between the development roller 33f and the electrostatic latent image formed on the photoconductor drum 31, and forms a toner image.

[0032] Each of the multiple transfer rollers 54 is disposed at a position facing each photoconductor drum 31 in the up-down direction, with a paper transport surface 53A, which is the outer peripheral surface of the transport belt 53, sandwiched therebetween, and is in contact with the transport belt 53 from the rear side of the paper transport surface 53A. A negative transfer voltage is applied to each of the multiple transfer rollers 54 in accordance with the transport timing of the sheet S, thereby transferring the toner image carried on the surface of the photoconductor drum 31 to the sheet S transported on the paper transport surface 53A. The transport belt 53 is, for example, an endless belt formed by shaping a belt in a loop, and is stretched between the drive roller 51 and the driven roller 52.

[0033] The fixing unit 60 is provided downstream of the process unit 20 in the conveying direction. The fixing unit 60 includes a heating roller 61, a pressure roller 62 that forms a nip between the heating roller 61 and the sheet S, a heater 63 (FIG. 2) that heats the heating roller 61, and a thermistor 64 (FIG. 2). The fixing unit 60 conveys the sheet S while gripping it between the heating roller 61 and the pressure roller 62, thereby thermally fixing the toner image transferred to the sheet S to the sheet S. The sheet S with the printed image is discharged to the discharge tray 5 by discharge rollers 65.

[0034] Next, the electrical configuration of the printer 1 will be described with reference to Figures 2 and 3. As shown in Figure 2, in addition to the above-mentioned configuration, the printer 1 is equipped with a main board 70, a low-voltage power supply board 80, a main motor 81, a high-voltage power supply board 82, a process motor 83, and a density sensor 40. The low-voltage power supply board 80 is equipped with an AC / DC circuit (not shown) and converts AC voltage supplied from an external commercial power source via a power cable into DC voltage, and outputs it to each device of the printer 1. The low-voltage power supply board 80 can also output AC voltage supplied from the commercial power source to the fixing unit 60.

[0035] The main board 70 is a board having a function of controlling the printer 1 in an integrated manner, and includes a main control circuit 71, a sub-control circuit 72, a DC / DC conversion circuit 73, motor drivers 74 and 75, a ROM 76, a RAM 77, and a non-volatile memory 78. The main control circuit 71 is a SoC (System On a Chip) and includes a CPU 93 (FIG. 3). Note that the main control circuit 71 is not limited to a SoC, and may be an ASIC (abbreviation for Application Specific Integrated Circuit).

[0036] The DC / DC conversion circuit 73 steps down the DC voltage supplied from the low-voltage power supply board 80 to generate a DC voltage of 3.3 V. The DC voltage of 3.3 V generated by the DC / DC conversion circuit 73 is supplied to the main control circuit 71, the sub-control circuit 72, and the various sensors 40, 64. As will be described later, the DC voltage of 3.3 V supplied to the sub-control circuit 72 and the various sensors 40, 64 is used as a first voltage Vref1, which is a reference voltage.

[0037] The main control circuit 71 is connected to a process motor 83 via a motor driver 75, and controls the driving of the process motor 83. The process motor 83 functions as a driving source for rotating, for example, the four developing rollers 33f and the four photosensitive drums 31. The main control circuit 71 is also connected to a main motor 81 via a motor driver 74, and controls the driving of the main motor 81. The main motor 81 functions as a driving source for rotating the heating roller 61 of the fixing device 60 and various rollers. The various rollers are, for example, the driving roller 51 and the pickup roller 12. The number and uses of the motors described above are merely examples. For example, the printer 1 may have separate motors for rotating the developing roller 33f and the photosensitive drum 31, and may have separate motors for rotating the driving roller 51 and the driven roller 52.

[0038] The ROM 76 stores various control programs and various setting information for controlling the printer 1. In the main control circuit 71, the CPU 93 executes the control programs read from the ROM 76 to execute processing according to signals input from various sensors, and stores the processing results in the RAM 77 and the non-volatile memory 78 while controlling each part of the printer 1. The RAM 77 is, for example, a DRAM, and is used as a working area for reading out various control programs and a storage area for temporarily storing image data based on a print job. The non-volatile memory 78 is, for example, an NVRAM, and is used for storing flag values ​​for determining the state of the printer 1. The storage medium for storing the control programs is not limited to the ROM 76, and may be an NVRAM, HDD, SSD, or the like. The storage medium for storing the control programs may be an external storage medium such as a USB memory.

[0039] 3, the main control circuit 71 has three first AD conversion units 90, 91, and 92, a CPU 93, a signal generation circuit 94, a light amount adjustment circuit 95, an LDO (Low Drop Out) 96, and voltage division circuits 97, 98, and 99. The 3.3V DC voltage generated by the DC / DC conversion circuit 73 is also input to the LDO 96 of the main control circuit 71. The LDO 96 is a linear regulator, and generates a second voltage Vref2, which is a DC voltage of 1.8V, by stepping down the 3.3V DC voltage. The second voltage Vref2 generated by the LDO 96 is a voltage that fluctuates less than the first voltage Vref1.

[0040] As shown in Fig. 3 and Fig. 4, the density sensor 40 has a specular reflection light receiving element 41, a diffuse reflection light receiving element 42, and a light emitting element 43. The light emitting element 43 is an element that irradiates infrared light onto the conveyor belt 53, and is, for example, an LED. The specular reflection light receiving element 41 is a sensor that measures the amount of infrared light (intensity) that is specularly reflected at the same angle as the angle of incidence of the infrared light irradiated from the light emitting element 43 onto the conveyor belt 53. The diffuse reflection light receiving element 42 is a sensor that measures the amount of diffuse reflection light that is reflected at an angle different from the angle of incidence of the infrared light irradiated from the light emitting element 43 onto the conveyor belt 53.

[0041] As shown in FIG. 4, the light-emitting element 43 is connected to the CPU 93 via a light amount adjustment circuit 95 of the main control circuit 71. The CPU 93 outputs a PWM signal for adjusting the light amount of the light-emitting element 43 to the light amount adjustment circuit 95. The light amount adjustment circuit 95 includes a smoothing circuit for smoothing the PWM signal from the CPU 93, and a transistor for passing a drive current corresponding to the smoothed current to the light-emitting element 43. The light-emitting element 93 irradiates the conveyor belt 53 with infrared light with a light amount corresponding to the duty ratio of the PWM signal. The main control circuit 71 does not include the light amount adjustment circuit 95, and the light amount adjustment circuit 95 may be disposed between the main control circuit 71 and the light-emitting element 43 of the density sensor 40.

[0042] The specular reflection light receiving element 41 is a phototransistor, the collector of which is supplied with a first voltage Vref1, and the emitter of which is grounded via a fixed resistor R11 and a variable resistor R12. As the amount of received light increases, the voltage drop due to the fixed resistor R11 and the variable resistor R12 increases, the potential of the emitter of the specular reflection light receiving element 41 rises, and the sensor signal Vspec corresponding to the amount of received light is output. The sensor signal Vspec is input to an analog input terminal 71a of the main control circuit 71. Similarly, the diffuse reflection light receiving element 42 is a phototransistor, the collector of which is supplied with a first voltage Vref1, and the emitter of which is grounded via a fixed resistor R13 and a variable resistor R14. As the amount of received light increases, the voltage drop due to the fixed resistor R13 and the variable resistor R14 increases, the potential of the emitter of the diffuse reflection light receiving element 42 rises, and the sensor signal Vdiff corresponding to the amount of received light is output. The sensor signal Vdiff is input to an analog input terminal 71b of the main control circuit.

[0043] The fixing unit 60 includes a thermistor 64 that detects the temperature of the heating roller 61. The thermistor 64 includes a resistive element R14 whose resistance value changes in response to temperature changes. One end of the thermistor 64 is supplied with a first voltage Vref1, and the other end is grounded via a fixed resistor R15. The thermistor 64 outputs a sensor signal Vthm according to the temperature by changing its resistance value in response to temperature changes. The sensor signal Vthm is a signal obtained by dividing the first voltage Vref1 by the resistive element R14 of the thermistor 64 and the fixed resistor R15. The sensor signal Vthm can be calculated using the following (Equation 1). Sensor signal Vthm=Vref1×R15 / (R14+R15) … (Equation 1) The sensor signal Vthm from the thermistor 64 is input to an analog input terminal 71 c of the main control circuit 71 .

[0044] The first AD conversion unit 90 is connected to the analog input terminal 71a of the main control circuit 71 through a voltage divider circuit 97. The voltage divider circuit 97 is configured by connecting two resistors R1 and R2 in series (FIG. 4), and divides the sensor signal Vspec from the specular reflection light receiving element 41 input through the analog input terminal 71a by a voltage division ratio (R2 / (R1+R2)) and inputs the divided signal to the first AD conversion unit 90. The voltage division ratio of the voltage divider circuit 97 is determined so that the sensor signal Vspec is equal to or less than the second voltage Vref2 (1.8V). The first AD conversion unit 90 outputs a sensor AD value (Vspec) by analog-to-digital conversion of a value corresponding to the sensor signal Vspec (i.e., a value divided by the voltage divider circuit 97) using the second voltage Vref2 supplied from the LDO 96 as a reference voltage. In this embodiment, the specular reflection light receiving element 41 and the voltage divider circuit 97 are an example of a first light receiving sensor.

[0045] The first AD conversion section 90 has a resolution of 10 bits (that is, 0 to 1023), and the theoretical value of the sensor AD value output from the first AD conversion section 90 can also be calculated using the following (Equation 2).

[0046] Sensor AD value = sensor signal / second voltage Vref2 × resolution … (Formula 2) In this embodiment, the second voltage Vref2 is 1.8 V and the resolution is 1023. For example, in the first AD conversion unit 90, if the value obtained by dividing the sensor signal Vspec by the voltage divider circuit 97 is 1.8 V, the sensor AD value (Vspec) becomes "1023." The same applies to the first AD conversion units 91 and 92 described later.

[0047] The first AD conversion unit 91 is connected to the analog input terminal 71b of the main control circuit 71 through a voltage divider circuit 98. The voltage divider circuit 98 is configured by connecting two resistors R3 and R4 in series, and divides the sensor signal Vdiff input through the analog input terminal 71b by a voltage division ratio (R4 / (R3+R4)) and inputs the divided signal to the first AD conversion unit 91. The voltage division ratio of the voltage divider circuit 98 is determined so that the sensor signal Vdiff is equal to or less than the second voltage Vref2 (1.8V). The first AD conversion unit 91 outputs a sensor AD value (Vdiff) by analog-to-digital conversion of a value corresponding to the sensor signal Vdiff from the diffuse reflection light receiving element 42 (i.e., a value divided by the voltage divider circuit 98) using the second voltage Vref2 supplied from the LDO 96 as a reference voltage. In this embodiment, the diffuse reflection light receiving element 42 and the voltage divider circuit 98 are an example of a second light receiving sensor.

[0048] Returning to FIG. 3, the first AD conversion unit 92 is connected to the analog input terminal 71c of the main control circuit 71 via a voltage divider circuit 99. The voltage divider circuit 99 is configured by connecting two resistors R5 and R6 in series, and divides the sensor signal Vthm from the thermistor 64 input via the analog input terminal 71c by a voltage division ratio (R6 / (R5+R6)) and inputs the divided signal to the first AD conversion unit 92. The voltage division ratio of the voltage divider circuit 99 is determined so that the sensor signal Vthm is equal to or less than the second voltage Vref2 (1.8V). The first AD conversion unit 92 outputs a sensor AD value (Vthm) by analog-to-digital conversion of a value corresponding to the sensor signal Vthm from the thermistor 64 (i.e., a value divided by the voltage divider circuit 99) using the second voltage Vref2 supplied from the LDO 96 as a reference voltage. In this embodiment, the thermistor 64 and the voltage divider circuit 99 are an example of a sensor.

[0049] The low-voltage power supply board 80 is also connected to the heater 63 via a relay (not shown). The low-voltage power supply board 80 is provided with a zero-cross detection circuit that detects the zero-cross timing of the AC power supplied to the heater 63, and when it detects the zero-cross timing of the AC power, it outputs a zero-cross signal, which is a pulse signal, to the main control circuit 71. The CPU 93 causes the signal generating circuit 94 to output an on / off signal for controlling the power supply time from the low-voltage power supply board 80 to the heater 63, in response to the sensor AD value (Vthm) from the thermistor 64 and the zero-cross signal from the low-voltage power supply board 80. This allows the main control circuit 71 to execute heater control for controlling the power supply to the heater 63 in response to the sensor AD value (Vthm).

[0050] The sub-control circuit 72 is communicably connected to the main control circuit 71. The sub-control circuit 72 is an MCU (Micro Controller Unit), and has a second AD conversion unit 100 in addition to a calculation unit (not shown).

[0051] A high-voltage power supply board 82 is connected to the sub-control circuit 72. The high-voltage power supply board 82 generates a charging voltage, a developing voltage, and a transfer voltage, which are high voltages supplied to the process unit 20. The high-voltage power supply board 82 includes a charging voltage application circuit that applies a charging voltage to each charger 32 of the developing cartridges 30C to 30K, a developing voltage application circuit that applies a developing voltage to each developing roller 33f of the developing cartridges 30C to 30K, and a transfer voltage application circuit that applies a transfer voltage to the transfer roller 54 corresponding to the developing cartridges 30C to 30K. The high-voltage power supply board 82 generates the charging voltage, the developing voltage, and the transfer voltage in response to a control signal from the sub-control circuit 72, which will be described later, and supplies them to the process unit 20. The high-voltage power supply board 82 also outputs an FB (feedback) signal of a voltage corresponding to the generation of the charging voltage, the developing voltage, and the transfer voltage by dividing the first voltage Vref1 supplied from the DC / DC conversion circuit 73.

[0052] In the printer 1 having the above configuration, at a known timing such as when the printer 1 is turned on, the main control circuit 71 performs density correction for correcting the amount of toner supplied from the developing cartridges 30C to 30K according to the gradation value of each color indicated by the image data. In the density correction, first, the main control circuit 71 causes the process unit 20 to print patch marks on the conveyor belt 53. Specifically, the process unit 20 prints patch marks on the conveyor belt 53 by printing each of black, cyan, magenta, and yellow toner at a predetermined gradation value. The main control circuit 71 rotates the conveyor belt 53 to move each patch mark to a position facing the density sensor 40, and performs a process of reading sensor AD values ​​obtained by analog-to-digital conversion of the sensor signals of the specular reflection light receiving element 41 and the diffuse reflection light receiving element 42 while adjusting the light amount of the light emitting element 43. Then, if the measurement result of the patch is normal, the main control circuit 71 calculates correction parameters and ends the density correction.

[0053] Furthermore, when the main control circuit 71 receives an execution command for the printing process, it executes the printing process for forming an image on the sheet S. FIG. 5 is a flowchart for explaining the process executed by the main control circuit 71 when the printer 1 receives a print execution command via a communication IF (not shown). When the main control circuit 71 receives an execution command for the printing process in step 10 (hereinafter, step is also referred to as S), it starts a preparatory operation by processing S11 to S16 described later before driving the process unit 20. The preparatory operation is an operation related to preparation for the printing process, a correction process, etc. If printing is performed immediately in a state in which the fixing unit 60 is not warmed up, the deterioration of the heating roller 61 and the pressure roller 62 may progress. For this reason, as the preparatory operation, a process for warming the fixing unit 60 to a predetermined fixing temperature is executed. Note that the contents of the preparatory operation are not limited to those described above. For example, the main control circuit 71 may execute a process for driving the agitator 33e of the developing cartridges 30C to 30K and agitating the toner as the preparatory operation. Alternatively, the main control circuit 71 may execute, as preparatory operations, a process for rotating the main motor 81 and the process motor 83 up to a predetermined rotation speed, a process for checking for failures, a test process for image formation, and the like.

[0054] In S11, the main control circuit 71 turns on the heater 63 in the fixing unit 60 to start raising the temperature of the heating roller 61. The main control circuit 71 outputs an on / off signal to the low-voltage power supply board 80, which controls the power supply time of the heater 63, in response to a zero-cross signal output from the low-voltage power supply board 80. The low-voltage power supply board 80 adjusts the power supply time of the heater 63 in response to the value of the on / off signal.

[0055] In S12, the main control circuit 71 reads from the memory the sensor AD value (Vthm) output from the first AD conversion unit 92. As described above, the sensor AD value (Vthm) is a value obtained by analog-to-digital conversion by the first AD conversion unit 92 of the sensor signal Vthm obtained by measuring the temperature of the heating roller 61 with the thermistor 64.

[0056] In S13, the main control circuit 71 transmits a correction value acquisition command to the sub-control circuit 72 to acquire a correction value for correcting the sensor AD value (Vthm) acquired in S12. When a deviation occurs between the first voltage Vref1 (3.3 V±Δ) used in each sensor 40, 64 and the design reference voltage (3.3 V), the deviation of the reference voltage may cause a deviation between the sensor AD value output by the first AD conversion units 90 to 92 and the desired sensor AD value. The DC / DC conversion circuit 73 that generates the first voltage Vref1 receives a supply of a DC voltage from the low-voltage power supply board 80, so that the DC voltage may fluctuate depending on the load of other circuits connected to the low-voltage power supply board 80, and the first voltage Vref1 generated by the DC / DC conversion circuit 73 may fluctuate.

[0057] Here, if the reference voltage used in each sensor 40, 64 is the same as the reference voltage used in the first AD conversion units 90-92, the deviation of the reference voltage is offset on the first AD conversion units 90-92 side, and the deviation between the sensor AD value and the desired sensor AD value is not noticeable. However, the first AD conversion units 90-92 use the second voltage Vref2 (1.8V) as a reference voltage, whereas the thermistor 64 and the concentration sensor 40 use the first voltage Vref1 (3.3V±Δ) as a reference voltage, and thus the reference voltages are different. Therefore, in this embodiment, the main control circuit 71 causes the sub-control circuit 72 to calculate a correction value for correcting the sensor AD value from the first AD conversion units 90-92, and corrects the sensor AD value by the calculated correction value.

[0058] 6 is a flowchart explaining the process executed when the sub-control circuit 72 receives the command in S13 from the main control circuit 71. When the sub-control circuit 72 receives the correction value acquisition command from the main control circuit 71 in S20 (S20: YES), the sub-control circuit 72 proceeds to S21 and acquires the sensor AD value (Vref2) from the second AD conversion unit 100. The sensor AD value (Vref2) is a value obtained by the second AD conversion unit 100 performing analog-to-digital conversion on the second voltage Vref2 supplied from the LDO 96 using the first voltage Vref1 as a reference voltage.

[0059] In S22, the sub-control circuit 72 acquires the theoretical AD value (Vref2). The theoretical AD value (Vref2) is a value obtained when the second AD conversion unit 100 performs analog-to-digital conversion on an input value of 1.8V using the first voltage Vref1 (i.e., 3.3V) assumed to be unchanged as a reference voltage. The input value of 1.8V is the voltage value of the second voltage Vref2 supplied from the LDO 96. In this embodiment, the sub-control circuit 72 calculates the theoretical AD value (Vref2) using the following (Equation 3).

[0060] Theoretical AD value (Vref2) = 1.8 / 3.3 × 1023 … (Equation 3)

[0061] In S23, the sub-control circuit 72 calculates a correction value by dividing the theoretical AD value (Vref2) acquired in S22 by the sensor AD value (Vref2) acquired in S21. Specifically, the sub-control circuit 72 calculates the correction value by the following (Equation 4).

[0062] Correction value = theoretical AD value (Vref2) / sensor AD value (Vref2) … (Equation 4)

[0063] The correction value calculated by the above (Equation 4) indicates the ratio of the sensor AD value (i.e., the theoretical AD value) when the first voltage Vref1 does not fluctuate to the sensor AD value (i.e., the actual measurement value) when the first voltage Vref1 fluctuates. As shown in FIG. 7, if the first voltage Vref1 is a design value (3.3V), the sensor signal is analog-digitally converted to the sensor AD value so that 3.3V becomes the maximum resolution value "1023". On the other hand, if there is a deviation in the first voltage Vref1, the sensor signal is analog-digitally converted to the sensor AD value so that "3.3±ΔV" becomes the maximum resolution value "1023". Therefore, the actual measurement value has a difference in the voltage of the sensor signal per unit resolution compared to the theoretical AD value. Therefore, in this embodiment, the correction value is calculated according to the value obtained by dividing the theoretical AD value by the actual measurement value of the sensor AD value. The sub-control circuit 72 outputs the calculated correction value to the main control circuit 71 in S24.

[0064] 5, in S14, the main control circuit 71 corrects the sensor AD value (Vthm) with the acquired correction value, and acquires the corrected sensor AD value (Vthm). Specifically, the main control circuit 71 acquires the corrected sensor AD value (Vthm) using the following (Equation 5).

[0065] Corrected sensor AD value (Vthm) = sensor AD value (Vthm) × correction value … (Formula 5)

[0066] In S15, the main control circuit 71 performs heater control using the corrected sensor AD value (Vthm). Specifically, the main control circuit 71 compares the temperature indicated by the corrected sensor AD value (Vthm) with the fixing temperature, which is the target temperature, and if the temperature indicated by the corrected sensor AD value (Vthm) is lower than the fixing temperature, adjusts the on / off signal from the signal generating circuit 94 so as to increase the temperature of the heater 63, and outputs the on / off signal according to the timing of receiving the zero cross signal. On the other hand, if the temperature indicated by the corrected sensor AD value (Vthm) is equal to or higher than the fixing temperature, the main control circuit 71 adjusts the on / off signal from the signal generating circuit 94 so as to decrease the temperature of the heater 63 or maintain the current temperature, and outputs the on / off signal according to the timing of receiving the zero cross signal. In this embodiment, a table indicating the correspondence between the corrected sensor AD value (Vthm) and the temperature of the heating roller 61 is stored in the memory. The main control circuit 71 can determine the current temperature of the heating roller 61 by referring to the table.

[0067] Here, the main control circuit 71 determines that the temperature indicated by the corrected sensor AD value (Vthm) is lower than the fixing temperature (S16: NO), and returns to S12. In S12, the main control circuit 71 reads out the sensor AD value (Vthm), and executes the processes of S13 to S16 again using the read out sensor AD value (Vthm).

[0068] On the other hand, if the temperature indicated by the corrected sensor AD value (Vthm) is equal to or higher than the fixing temperature (S16: YES), the main control circuit 71 proceeds to S17 and transmits a high-voltage power supply start command to the sub-control circuit 72. That is, since the temperature of the heating roller 61 of the fixing unit 60 has risen to the fixing temperature, the preparatory operation is ended, and the high-voltage power supply board 82 is started up to form an image on the sheet S.

[0069] When the sub-control circuit 72 receives a high-voltage power supply start command from the main control circuit 71 (S25 in FIG. 6: YES), the sub-control circuit 72 proceeds to S26 and acquires a sensor AD value (Vfb) obtained by AD converting the FB signal by the second AD conversion unit 100. That is, the sensor AD value (Vfb) acquired in S26 differs from the sensor AD value (Vref2) acquired in S21 in that the sensor AD value (Vfb) is a value obtained by analog-to-digital conversion by the second AD conversion unit 100 of the FB signal generated by dividing the first voltage Vref1 using the first voltage Vref1 as a reference voltage.

[0070] In S27, the sub-control circuit 72 controls the driving of the high-voltage power supply board 82 by transmitting a control signal generated using the acquired sensor AD value (Vfb) to the high-voltage power supply board 82. In response to the control signal from the sub-control circuit 72, the high-voltage power supply board 82 generates a charging voltage and charges the charger 32. The charging of the charger 32 charges the photosensitive drum 31. In response to the control signal from the sub-control circuit 72, the high-voltage power supply board 82 generates a developing voltage and applies it to the developing roller 33f. In response to the control signal from the sub-control circuit 72, the high-voltage power supply board 82 generates a transfer voltage and applies the transfer voltage to the transfer roller 54.

[0071] If the end condition of the printing process is not met (S28: NO), the sub-control circuit 72 returns to S26 and repeats obtaining the sensor AD value (Vfb) and controlling the high-voltage power supply board 82 using the control signal in S27. If the end condition of the printing process is met (S28: YES), the sub-control circuit 72 ends the process of FIG.

[0072] Returning to Fig. 5, the main control circuit 71 executes the print process in S18. The main control circuit 71 rotates each roller, controls the exposure unit 35 based on the image data included in the print job, and forms an electrostatic latent image on the positively charged photoconductor drum 31, thereby forming an image on the sheet S. The sheet S on which the image has been formed is transported to the fixing unit 60. The fixing unit 60 thermally fixes the image formed on the sheet S by the nip between the heating roller 61 and the pressure roller 62.

[0073] The present embodiment described above can provide the following advantages. In the printer 1, the sub-control circuit 72 uses the second AD conversion unit 100, which performs analog-to-digital conversion using the first voltage Vref1 as a reference voltage, to calculate a correction value for correcting the deviation of the sensor AD value caused by the first AD conversion unit 92. The main control circuit 71 corrects the sensor AD value of the first AD conversion unit 92, thereby making it possible to correct the deviation of the sensor AD value of the first AD conversion unit 92.

[0074] The sensor whose sensor AD value is corrected by the main control circuit 71 is the thermistor 64 for measuring the temperature of the heating roller 61. This allows the temperature of the heating roller 61 of the fixing device 60 to be measured with high accuracy, and the image formed on the sheet S can be thermally fixed satisfactorily.

[0075] The sub-control circuit 72 calculates the correction value based on an actual measurement value obtained by the second AD conversion unit 100 performing analog-to-digital conversion on the second voltage Vref2 using the first voltage Vref1 as a reference voltage, and a theoretical value obtained by performing analog-to-digital conversion on a voltage (1.8 V) indicating the second voltage Vref2 using a design reference voltage value (3.3 V) as a reference voltage. This allows the second AD conversion unit 100 of the sub-control circuit 72 to calculate the correction value based on the actual measurement value obtained by analog-to-digital conversion of the input signal that is the second voltage Vref2, and the theoretical value obtained by analog-to-digital conversion of the second voltage Vref2 using the design reference voltage value as a reference voltage.

[0076] The sub-control circuit 72 calculates the correction value by dividing the theoretical AD value by the actual measurement value. This allows the correction value to be used as a multiplication value for the sensor AD value, so that the main control circuit 71 can correct the sensor AD value by a simple calculation.

[0077] The sub-control circuit 72 calculates a correction value using the actual measurement value from the second AD conversion unit 100, and the main control circuit 71 acquires the correction value from the sub-control circuit 72 and corrects the sensor AD value from the first AD conversion unit 92 using the correction value. In this way, by having the correction value calculated by the sub-control circuit 72, it is possible to suppress an increase in the processing load of the main control circuit 71 in the preparatory operation.

[0078] The sub-control circuit 72 performs analog-to-digital conversion of the FB signal using the second AD conversion unit 100 with the first voltage Vref1 as a reference voltage, and outputs a control signal according to the result to the high-voltage power supply board 82. In this way, the sub-control circuit 72 not only calculates the correction value, but also performs analog-to-digital conversion of the FB signal output by the high-voltage power supply board 82. As a result, the sub-control circuit 72 can control the high-voltage power supply board 82 by outputting a control signal to the high-voltage power supply board 82 according to the result of the analog-to-digital conversion.

[0079] The main control circuit 71 transmits a correction value acquisition command, which is an instruction to acquire a correction value, to the sub-control circuit 72 before transmitting an instruction to start application of a high-voltage voltage from the high-voltage power supply board 82 to the process unit 20, and the sub-control circuit 72 calculates a correction value upon receiving the correction value acquisition command, and causes the high-voltage power supply board 82 to start applying a high-voltage voltage to the process unit 20 upon receiving an instruction to start applying the high-voltage voltage. This allows the sub-control circuit 72 to calculate the correction value before the high-voltage power supply board 82 generates a voltage, thereby suppressing an increase in the processing load of the sub-control circuit 72.

[0080] Before transmitting an instruction to start applying a high voltage to the sub-control circuit 72, the main control circuit 71 obtains the temperature of the heating roller 61 using the temperature indicated by the sensor AD value (Vthm) corrected by the correction value, and heats the heating roller 61 until the estimated temperature of the heating roller 61 reaches a predetermined temperature. This makes it possible to accurately heat the heating roller 61 in the preparatory operation performed prior to the start of application of a high voltage to the process unit 20.

[0081] Before the temperature of the heating roller 61 reaches a predetermined temperature, the main control circuit 71 transmits a correction value acquisition command to the sub-control circuit 72, and acquires the temperature of the heating roller 61 using the sensor AD value (Vthm) corrected using the correction value acquired from the sub-control circuit 72 based on the transmission of the correction value acquisition command. This makes it possible to accurately increase the temperature of the heating roller 61 in the preparatory operation performed prior to the start of application of a high voltage to the process unit 20.

[0082] (Modification of the first embodiment) In the first embodiment described above, the sensor AD value (Vthm) output from the thermistor 64 is corrected by the correction value. Instead of this, when the main control circuit 71 executes the concentration correction, the sensor AD value (Vspec) and the sensor AD value (Vdiff) output from the concentration sensor 40 may be corrected by the correction value. In this case, when the main control circuit 71 executes the concentration correction in the preparation operation, the main control circuit 71 acquires the correction value from the sub-control circuit 72 in a process similar to S13 in FIG. 5. Then, the main control circuit 71 corrects the sensor AD value (Vspec) from the first AD conversion unit 90 and the sensor AD value (Vdiff) from the first AD conversion unit 91 using the acquired correction value in a process similar to S14. Then, the main control circuit 71 calculates the correction parameters using the corrected sensor AD value (Vspec) and the sensor AD value (Vdiff).

[0083] In the embodiment described above, the sensor AD values ​​from the multiple first AD conversion units 90-92 are corrected using the correction value acquired from the sub-control circuit 72. As a result, even in a configuration in which the printer 1 is equipped with multiple sensors, it is possible to correct each sensor AD value and control the printer 1.

[0084] Second embodiment In the second embodiment, the configuration different from the first embodiment will be mainly described. In the second embodiment, the same parts as in the first embodiment are given the same reference numerals, and the description thereof will not be repeated. In this embodiment, the main control circuit 71 is different from the first embodiment in the configuration in which the main control circuit 71 acquires the correction value from the sub-control circuit 72 multiple times during the preparation operation.

[0085] 8 is a flowchart for explaining the process executed by the main control circuit 71 in the second embodiment. When the main control circuit 71 receives a command to execute a print process in S10 (S10: YES), the main control circuit 71 starts increasing the temperature of the heating roller 61 by turning on the heater 63 in the fixing device 60 in S11.

[0086] In S30, the main control circuit 71 acquires the correction value by transmitting a correction value acquisition command to the sub-control circuit 72, similar to S13 already described. The process for the sub-control circuit 72 to calculate the correction value has already been described with reference to FIG.

[0087] In S12, the main control circuit 71 reads from the memory the sensor AD value (Vthm) output from the first AD conversion unit 92. As described above, the sensor AD value (Vthm) is a digital value corresponding to a sensor signal that measures the temperature of the heating roller 61 by the thermistor 64. In S14, the main control circuit 71 corrects the sensor AD value (Vthm) with the correction value output from the sub-control circuit 72, and acquires the corrected sensor AD value (Vthm).

[0088] In S15, the main control circuit 71 performs heater control using the corrected sensor AD value (Vthm). The heater control performed in S15 has already been described. If the temperature indicated by the corrected sensor AD value (Vthm) is lower than the fixing temperature (S16: NO), the main control circuit 71 returns to S30 and reacquires the correction value from the sub-control circuit 72. That is, in this embodiment, until the temperature indicated by the corrected sensor AD value (Vthm) reaches the fixing temperature, the main control circuit 71 requests the sub-control circuit 72 for a correction value, and the calculation of the correction value by the sub-control circuit 72 is repeated. In S12, the main control circuit 71 reads out the sensor AD value (Vthm), and in S14, corrects the read sensor AD value (Vthm) using the newly acquired correction value. Then, as already described, the main control circuit 71 executes the processes of S15 and S16 again.

[0089] When the temperature indicated by the corrected sensor AD value (Vthm) becomes equal to or higher than the fixing temperature (S16: YES), the main control circuit 71 proceeds to S17 and transmits a high voltage power supply start command to the sub-control circuit 72. That is, since the temperature of the heating roller 61 of the fixing unit 60 has risen to the fixing temperature, the preparatory operation is ended and a printing process for forming an image on the sheet S is started. The process by the sub-control circuit 72 to start up the high voltage power supply board 82 has already been described with reference to FIG. 6. The main control circuit 71 executes the printing process in S18.

[0090] In the embodiment described above, the main control circuit 71 can accurately acquire the temperature of the heating roller 61 by correcting the sensor AD value (Vthm) using a newly calculated correction value each time the main control circuit 71 acquires the temperature of the heating roller 61.

[0091] Third embodiment In the third embodiment, the configuration different from the first embodiment will be mainly described. In the third embodiment, the same parts as in the first embodiment are given the same reference numerals, and the description thereof will not be repeated. In this embodiment, the sub-control circuit 72 is different from the first embodiment in the configuration for calculating the correction value using the sensor AD value from the second AD conversion unit 100 and the sensor AD value from the first AD conversion unit 92.

[0092] 9 is an electrical configuration diagram of the printer 1 according to the second embodiment. In this embodiment, the output from the thermistor 64 is input to the input terminal of the first AD conversion unit 92 as well as to the input terminal of the second AD conversion unit 100 of the sub-control circuit 72. On the other hand, the LDO 96 of the main control circuit 71 is not connected to the input terminal of the second AD conversion unit 100.

[0093] 10 is a flowchart explaining a process executed when the sub-control circuit 72 receives a command from the main control circuit 71 in this embodiment. When the sub-control circuit 72 receives a correction value acquisition command from the main control circuit 71 in S20 (S20: YES), the sub-control circuit 72 proceeds to S40 and acquires a sensor AD value (Vthm)' from the second AD conversion unit 100. The sensor AD value (Vthm)' is a value obtained by analog-to-digital conversion of the sensor signal Vthm from the thermistor 64 by the second AD conversion unit 100 using the first voltage Vref1 as a reference voltage. In other words, the sensor AD value (Vthm)' is a value obtained by analog-to-digital conversion of an actual measurement value by the second AD conversion unit 100.

[0094] In this embodiment, Vthm is a signal obtained by dividing Vref1 by the resistance element R24 of the thermistor 64 and the fixed resistor R25, and is expressed by the following formula (6). Sensor signal Vthm=Vref1×R25 / (R24+R25) … (Equation 6) The sensor AD value (Vthm)' from the second AD conversion section 100 is a value obtained by using the following (Equation 7). Sensor AD value (Vthm)' = R25 / (R24+R25)×1023 … (Formula 7)

[0095] In S41, the sub-control circuit 72 acquires the sensor AD value (Vthm') from the first AD conversion unit 92. The sensor AD value (Vthm) is a value obtained by analog-to-digital conversion of the sensor signal Vthm from the thermistor 64 by the first AD conversion unit 91 using the second voltage Vref2 as a reference voltage.

[0096] Here, the sensor AD value (Vthm)" from the first AD conversion unit 92 is a value obtained by using the following (Equation 8). Sensor AD value (Vthm) = Vref1 x R25 / (R24+R25) x R6 / (R5+R6) / Vref2×1023 … (Formula 8) Here, "R6 / (R5+R6)" is the voltage division ratio of the voltage divider circuit 99, and in this embodiment, the value is determined so as to satisfy the relationship of the following (Equation 9). R6 / (R5+R6)=1.8 / 3.3 … (Formula 9)

[0097] By substituting 1.8 V for the second voltage Vref2 and substituting the above (Equation 9) into the above (Equation 8), the following (Equation 10) is derived. Sensor AD value (Vthm) = Vref1 x R25 / (R24+R25) / 3.3 x 1023 … (Equation 10)

[0098] In S42, the sub-control circuit 72 can calculate a correction value in the same manner as in the first embodiment, by using the sensor AD value (Vthm)′ acquired in S40 and the sensor AD value (Vthm)″ acquired in S41 according to the following (Equation 11). Correction value = Sensor AD value (Vthm) / Sensor AD value (Vthm) = Vref1(=3.3V±Δ) / 3.3V … (Formula 11)

[0099] In S24, the sub-control circuit 72 outputs the calculated correction value to the main control circuit 71. As already described, in S14 of FIG. 5, the main control circuit 71 corrects the sensor AD value (Vthm) using the acquired correction value, and acquires the corrected sensor AD value (Vthm). In S15, the main control circuit 71 performs heater control using the corrected sensor AD value (Vthm). Specifically, the main control circuit 71 compares the temperature indicated by the corrected sensor AD value (Vthm) with the fixing temperature, which is the target temperature, and adjusts the on / off signal from the signal generating circuit 94 so as to raise the temperature of the heating roller 61 if the temperature indicated by the corrected sensor AD value (Vthm) is lower than the fixing temperature.

[0100] In the present embodiment described above, the sub-control circuit 72 calculates the correction value based on the actual measurement value, which is the result of the second AD conversion unit 100 performing analog-to-digital conversion on the sensor signal using the first voltage Vref1 as the reference voltage, and the sensor AD value, which is the result of the first AD conversion unit 92 performing analog-to-digital conversion on the sensor signal using the second voltage as the reference voltage. This makes it possible to calculate the correction value using the sensor AD values ​​from the two AD conversion units.

[0101] (Other embodiments) The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified in various forms without departing from the spirit of the invention. For example, the following modifications are also possible. The printer 1 is only an example of a configuration in which the control unit includes the main control circuit 71 and the sub control circuit 72, and the control unit may include only the main control circuit 71. In this case, the main control circuit 71 includes the second AD conversion unit 100, and the correction value is calculated by the processes of S21 to S23 in FIG.

[0102] The printer 1 is not limited to a color printer, and may be a monochrome printer in which the process unit 20 is provided with only black toner.

[0103] The printer 1 has been described as an example of an image forming apparatus, but this is merely an example, and the image forming apparatus may be a multifunction peripheral. [Explanation of symbols]

[0104] 1... printer (image forming apparatus), 20... process unit, 40... density sensor, 71... main control circuit, 72... sub-control circuit, 60... fixing unit, 64... thermistor, 90, 91, 92... first AD conversion unit, 100... second AD conversion unit

Claims

1. An image forming apparatus including an AD conversion unit, a sensor that receives a first voltage and detects a physical quantity of the image forming apparatus, the sensor outputting a sensor signal that is an analog signal obtained by dividing the first voltage by the physical quantity; a first AD conversion unit that receives a second voltage different from the first voltage and the sensor signal, performs analog-to-digital conversion on the sensor signal using the second voltage as a reference voltage, and outputs a sensor value that is a result of the analog-to-digital conversion; a second AD conversion unit to which the first voltage and an input signal which is the second voltage or the sensor signal are input, and which performs analog-to-digital conversion on the input signal using the first voltage as a reference voltage; A control unit, The control unit is The second AD conversion unit calculates a correction value using a result of performing analog-to-digital conversion on the input signal; The image forming apparatus further comprises: a sensor unit configured to detect a detected value of the detected sensor value;

2. a process unit for forming a developer image on a sheet; a fixing device including a heating rotor and a pressure rotor that forms a nip between the heating rotor and the pressure rotor, and that fixes the image formed on the sheet to the sheet; Equipped with 2. The image forming apparatus according to claim 1, wherein the sensor is a thermistor for measuring the temperature of the heating rotor.

3. the input signal is a signal that is the second voltage; The control unit is 2. The image forming apparatus according to claim 1, wherein the second AD conversion unit calculates the correction value based on an actual value which is a result of performing analog-to-digital conversion on the second voltage using the first voltage as a reference voltage, and a theoretical value which is a result of performing analog-to-digital conversion on the second voltage using a design reference voltage as a reference voltage.

4. The control unit is 4. The image forming apparatus according to claim 3, wherein the correction value is calculated by dividing the theoretical value by the actual measurement value.

5. The control unit is composed of a main control circuit and a sub-control circuit, The sub-control circuit includes: The second AD conversion unit is provided, and the correction value is calculated using the actual measurement value from the second AD conversion unit; The main control circuit includes:

4. The image forming apparatus according to claim 3, further comprising the first AD conversion section, the correction value being acquired from the sub-control circuit, and the sensor value from the first AD conversion section being corrected using the correction value.

6. a process unit for forming a developer image on a sheet; a high-voltage power supply substrate that applies a high-voltage voltage to the process unit, the high-voltage power supply substrate applying the high-voltage voltage in accordance with a control signal and outputting a feedback signal corresponding to the applied high-voltage voltage by dividing the first voltage; Equipped with The sub-control circuit includes:

6. The image forming apparatus according to claim 5, further comprising: a second AD converter that performs analog-to-digital conversion of the feedback signal using the first voltage as a reference voltage; and outputs the control signal to the high-voltage power supply board in accordance with the result of the conversion.

7. The main control circuit includes: transmits a correction value acquisition command to the sub-control circuit before transmitting an instruction to start applying the high voltage from the high voltage power supply board to the process unit, the correction value being an instruction to acquire the correction value; The sub-control circuit Calculating the correction value upon receiving the correction value acquisition command; 7. The image forming apparatus according to claim 6, wherein the high-voltage power supply board is caused to start applying the high-voltage voltage to the process unit upon receipt of an instruction to start applying the high-voltage voltage.

8. a fixing device including a heating rotor and a pressure rotor that forms a nip between the heating rotor and the pressure rotor, and that fixes the image formed on the sheet to the sheet; Equipped with The sensor is a thermistor for measuring the temperature of the heating rotor, The main control circuit includes:

8. The image forming apparatus according to claim 7, wherein before transmitting an instruction to the sub-control circuit to start applying the high voltage, the temperature of the heating rotor is obtained using the temperature indicated by the sensor value corrected by the correction value, and the heating rotor is heated until the estimated temperature of the heating rotor reaches a predetermined temperature.

9. The main control circuit includes: before the temperature of the heating rotatable body reaches the predetermined temperature, the correction value acquisition command is transmitted to the sub-control circuit; 9. The image forming apparatus according to claim 8, further comprising: a correction value acquired from the sub-control circuit based on transmission of the correction value acquisition command, the correction value being used to correct the acquired sensor value; and the temperature of the heating rotor is acquired using the corrected sensor value.

10. The main control circuit includes: sending the correction value acquisition command to the sub-control circuit until the temperature of the heating rotatable body reaches the predetermined temperature; 9. The image forming apparatus according to claim 8, wherein the sensor value is corrected each time the correction value obtained from the sub-control circuit based on the transmission of the correction value acquisition command is obtained, and the temperature of the heating rotor is obtained using the corrected sensor value.

11. The sensor includes a plurality of sensors. The main control circuit includes: a plurality of the first AD conversion units corresponding to the plurality of sensors, 6. The image forming apparatus according to claim 5, wherein the sensor values ​​from the first AD conversion units are corrected using the correction value acquired from the sub-control circuit.

12. a process unit for forming a developer image on a sheet; a fixing device including a heating rotor and a pressure rotor that forms a nip between the heating rotor and the pressure rotor, and that fixes the image formed on the sheet to the sheet; Equipped with The plurality of sensors include a thermistor for measuring the temperature of the heating rotor; a first light receiving sensor disposed opposite the belt on whose surface a patch made of toner is formed, the first light receiving sensor receiving specularly reflected light from the belt; 12. The image forming apparatus according to claim 11, further comprising a second light receiving sensor disposed opposite the belt on whose surface a patch made of toner is formed, for receiving light diffusely reflected from the belt.

13. the input signal is the sensor signal; The control unit is 2. The image forming apparatus according to claim 1, wherein the correction value is calculated based on an actual value that is a result of the second AD conversion unit performing analog-to-digital conversion on the sensor signal using the first voltage as a reference voltage, and a theoretical value that is a result of the first AD conversion unit performing analog-to-digital conversion on the sensor signal using the second voltage as a reference voltage.

14. The control unit is composed of a main control circuit and a sub-control circuit, The sub-control circuit includes: The second AD conversion unit is provided, and the correction value is calculated using the second AD conversion unit; The main control circuit includes:

14. The image forming apparatus according to claim 13, further comprising the first AD conversion unit, the correction value being acquired from the sub-control circuit, and the sensor value from the first AD conversion unit being corrected using the correction value.

15. a process unit for forming a developer image on a sheet; a fixing device including a heating rotor and a pressure rotor that forms a nip between the heating rotor and the pressure rotor, and that fixes the image formed on the sheet to the sheet; Equipped with The plurality of sensors include a thermistor for measuring the temperature of the heating rotor; a sensor disposed opposite the belt on whose surface a patch made of toner is formed, the sensor receiving specularly reflected light from the belt; a sensor disposed opposite the belt on whose surface a patch made of toner is formed, the sensor receiving diffuse reflected light from the belt; The main control circuit includes: a plurality of the first AD conversion units corresponding to the plurality of sensors, 15. The image forming apparatus according to claim 14, wherein the sensor values ​​from the first AD conversion units are corrected using the correction value acquired from the sub-control circuit.

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