JP2018105803A - Humidity handling controller and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect humidity over a wide range with high accuracy while suppressing costs and make it possible to control a control object on the basis of high-accuracy humidity.SOLUTION: Provided is a humidity handling controller 8, where a resistance variable circuit 61 is electrically connected in series to a humidity sensor 60 of electric resistance type, forming, together with the humidity sensor 60, a voltage-dividing circuit 62 to which a given DC voltage is applied, with the electric resistance switched stepwise in accordance with the type of inputted control signals Sc1, Sc2. A control unit 7 outputs the control signals Sc1, Sc2 to the resistance variable circuit 61, and further determines whether or not a humidity detection level that is the level of the output voltage V1 of the voltage-dividing circuit 62 is in a permissive state. The control unit 7 changes the type of control signals Sc1, Sc2 when the humidity detection level is not in the permissive state. The control unit 7 controls a control object in accordance with the humidity detection level when the humidity detection level is in the permissive state.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a humidity control device and an image forming apparatus.

  In general, an electrophotographic image forming apparatus includes a temperature sensor and a humidity sensor that detect the temperature and humidity of an installed environment, and controls a control target according to the detected temperature and the detected humidity. For example, the control objects include a charging voltage, a developing voltage, a transfer voltage, and heater power in the fixing device.

  In other words, the image forming apparatus includes a humidity control circuit including a humidity detection circuit including the humidity sensor and a control unit that controls a control target according to a humidity detection result by the humidity detection circuit.

  In the humidity control device, the humidity sensor is often an electrical resistance type sensor whose electrical resistance changes according to humidity. For example, it is conceivable that an RC circuit including an electrical resistance humidity sensor is adopted as the humidity detection circuit. The RC circuit includes the electric resistance humidity sensor and a capacitor connected in series, and an oscillation signal is input to the RC circuit.

  Generally, in the humidity detection circuit including the electrical resistance humidity sensor, the humidity detection range and the humidity detection resolution are in a trade-off relationship. Therefore, in order to ensure a sufficient humidity detection range and humidity detection resolution, the humidity control device may include a plurality of types of humidity detection circuits corresponding to a plurality of humidity ranges. In this case, a plurality of the electric resistance humidity sensors are required.

  Further, in order to sufficiently secure a humidity detection range and a humidity detection resolution, the humidity detection circuit includes one electrical resistance humidity sensor, a plurality of capacitors having different capacitances, and a circuit selection unit. (For example, refer to Patent Document 1).

  The circuit selector selectively electrically connects one of the plurality of capacitors to the electric resistance humidity sensor. Thereby, one of the RC circuits of a plurality of systems is selectively enabled. When the time until the effective output voltage of the RC circuit reaches a predetermined level is longer than a predetermined time, the time is used for humidity detection.

JP 2013-50317 A

  By the way, a general capacitor has a large variation in capacity (for example, about plus or minus 20%). In addition, a capacitor having a high capacity is expensive. Therefore, in the humidity detection circuit based on the RC circuit, it is difficult to detect a wide range of humidity with high accuracy while suppressing cost.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a humidity control device capable of detecting a wide range of humidity with high accuracy and controlling a controlled object based on the humidity with high accuracy, and an image forming apparatus including the same. It is in.

  A humidity control device according to one aspect of the present invention includes a humidity detection circuit and a control unit. The humidity detection circuit is a circuit including an electric resistance type humidity sensor. The said control part controls a control object according to the level of the output voltage of the said humidity detection circuit. The humidity detection circuit further includes a resistance variable circuit. The variable resistance circuit is electrically connected in series with the humidity sensor, forms a voltage dividing circuit to which a constant DC voltage is applied together with the humidity sensor, and is electrically connected according to the type of control signal input. Resistance switches in multiple stages. The variable resistance circuit includes a plurality of resistance elements and at least one control switch capable of changing an electrical connection state of the plurality of resistance elements to the humidity sensor in accordance with a type of the control signal. The control unit outputs the control signal to the resistance variable circuit, and whether or not the humidity detection level, which is the level of the output voltage of the voltage dividing circuit, is within a predetermined allowable range. An allowance determination process for determining The control unit changes the type of the control signal output to the resistance variable circuit when it is determined that the humidity detection level is not in the allowable state. The control unit controls the control target according to the humidity detection level when it is determined that the humidity detection level is in the allowable state.

  An image forming apparatus according to another aspect of the present invention includes a rotating image carrier, a charging device, a developing device, a transfer device, a fixing device, and the humidity control device. The charging device includes a charging member that charges the surface of the image carrier and a charging voltage application unit that applies a charging voltage to the charging member. The developing device includes a developing roller that carries toner and rotates, and a developing voltage applying unit that applies a developing voltage to the developing roller, and the electrostatic latent image formed on the surface of the charged image carrier is converted into toner. Develop to image. The transfer device includes a transfer roller that rotates in contact with the image carrier and a transfer voltage application unit that applies a transfer voltage to the transfer roller, and the toner image formed on the surface of the image carrier is transferred to the sheet. Transfer to The fixing device includes a fixing roller, a heater that heats the fixing roller, and a heater power source that supplies heater power to the heater, and the toner image is fixed to the sheet by heating the toner image by the fixing roller. Let The humidity control device controls one or more of the charging voltage, the developing voltage, the transfer voltage, and the heater power.

  According to the present invention, it is possible to provide a humidity-compatible control device capable of detecting a wide range of humidity with high accuracy and controlling a control target based on high-precision humidity and an image forming apparatus including the same, while suppressing costs. Is possible.

FIG. 1 is a configuration diagram of an image forming apparatus including a control unit according to the first embodiment. FIG. 2 is a configuration diagram of the control unit according to the first embodiment. FIG. 3 is a configuration diagram of a control unit according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: It does not have the character which limits the technical scope of this invention.

First Embodiment: Configuration of Image Forming Apparatus 10
First, the configuration of the image forming apparatus 10 including the control unit 8 according to the first embodiment will be described with reference to FIG. The image forming apparatus 10 is an apparatus that forms an image on the sheet 9 by electrophotography. The sheet 9 is a sheet-like image forming medium such as paper or an OHP sheet.

  As shown in FIG. 1, the image forming apparatus 10 includes a sheet conveying unit 3, an image forming unit 4, a control unit 8, and the like. As will be described later, the control unit 8 includes a humidity detection circuit 6 including a humidity sensor 60 and a CPU (Central Processing Unit) 7 that controls a control target in accordance with the humidity detection result by the humidity detection circuit 6. The control unit 8 is an example of a humidity control device.

  The sheet conveying unit 3 includes a sheet sending unit 30 and a plurality of pairs of conveying rollers 31. The sheet sending unit 30 sends the sheet 9 placed on the sheet supply unit 101 to the sheet conveyance path 300 in the apparatus. The plurality of pairs of conveyance rollers 31 convey the sheet 9 along the sheet conveyance path 300. A pair of the plurality of pairs of conveying rollers 31 provided at the most downstream position of the sheet conveying path 300 discharges the sheet 9 from the sheet conveying path 300 to the discharge tray 102.

  The image forming unit 4 includes an optical scanning unit 40, a photoreceptor 41, a charging device 42, a developing device 43, a toner replenishing unit 44, a transfer device 45, a cleaning device 46, a fixing device 47, and the like.

  In the image forming unit 4, the drum-shaped photoconductor 41 rotates, and the charging device 42 uniformly charges the outer peripheral surface of the photoconductor 41. The optical scanning unit 40 writes an electrostatic latent image on the outer peripheral surface of the photoconductor 41 by scanning the outer peripheral surface of the charged photoconductor 41 with beam light. The photoreceptor 41 is an example of an image carrier on which an electrostatic latent image is formed on the surface.

  The charging device 42 includes a charging roller 421 that charges the surface of the photoconductor 41, and a charging voltage application circuit 422 that applies a charging voltage to the charging roller 421. The charging roller 421 rotates while being in contact with the surface of the photoconductor 41 in a state where the charging voltage is applied.

  The charging voltage application circuit 422 includes, for example, a constant voltage circuit and an AC voltage circuit, and generates the charging voltage in which the AC voltage is superimposed on the DC voltage. The charging roller 421 and the charging voltage application circuit 422 are examples of a charging member and a charging voltage application unit, respectively.

  The developing device 43 includes a developing roller 431, a circulation conveyance unit 432, a development voltage application circuit 433, and the like. The circulation conveyance unit 432 circulates and conveys the developer 90 containing toner in the developing device 43.

  The developing roller 431 is rotatably supported so as to face the photoconductor 41 having the electrostatic latent image formed on the surface thereof. The development voltage application circuit 433 applies a development voltage to the development roller 431. The developing voltage is a bias voltage applied to the developing roller 431 with the photoconductor 41 as a reference.

  The development voltage application circuit 433 is a circuit that includes, for example, a constant voltage circuit and an AC voltage circuit, and generates the development voltage in which the AC voltage is superimposed on the DC voltage. The development voltage application circuit 433 is an example of a development voltage application unit.

  The transfer device 45 transfers the toner image formed on the surface of the photoconductor 41 to the sheet 9 moving on the sheet conveyance path 300. The transfer device 45 includes a transfer roller 451 that rotates with the sheet 9 interposed between the transfer member 45 and a transfer voltage application circuit 452 that applies a transfer voltage to the transfer roller 451.

  The transfer voltage application circuit 452 is a constant voltage circuit that generates a DC voltage having the same polarity as the charging polarity of the toner, for example. Further, like the development voltage application circuit 433, the transfer voltage application circuit 452 may be a circuit that generates the transfer voltage in which an AC voltage is superimposed on a DC voltage. The transfer voltage application circuit 452 is an example of a transfer voltage application unit.

  The fixing device 47 fixes the toner image on the sheet 9 by heating the toner image transferred to the sheet 9. The fixing device 47 includes a fixing roller 471, a pressure roller 472, a heater 473 that heats the fixing roller 471, a heater power supply 474, a fixing temperature sensor 475, and the like.

  The fixing roller 471 and the pressure roller 472 rotate with the sheet 9 on which the toner image is transferred interposed therebetween. The heater power supply 474 supplies power to the heater 473. The power supplied from the heater power supply 474 to the heater 473 is referred to as heater power.

  The fixing temperature sensor 475 is a temperature sensor such as a thermistor that detects the temperature of the fixing roller 471. The heater power supply 474 is, for example, an inverter power supply circuit that can adjust the heater power by PWM control.

  The heater power is adjusted by feedback control based on a comparison between the fixing temperature detected by the fixing temperature sensor 475 and the target temperature. Therefore, the heater power changes as the target temperature is changed.

  The cleaning device 46 removes the toner remaining on the surface of the photoreceptor 41 after passing through the transfer device 45. The toner replenishing unit 44 stores the toner for replenishment and replenishes the developing device 43 with the toner.

[Overview of control unit 8]
The control unit 8 includes a temperature detection circuit 5, a humidity detection circuit 6, a CPU 7, and the like. The temperature detection circuit 5 and the humidity detection circuit 6 detect the temperature and humidity of the environment where the temperature detection circuit 5 and the humidity detection circuit 6 are installed, respectively.

  The CPU 7 determines a control target such as the charging voltage, the developing voltage, the transfer voltage, or the heater power in the image forming apparatus 10 according to the environmental temperature and the environmental humidity detected by the temperature detection circuit 5 and the humidity detection circuit 6. Control. The CPU 7 is an example of a control unit that controls the control target according to the humidity detection result by the humidity detection circuit 6.

  The humidity sensor 60 included in the humidity detection circuit 6 is an electrical resistance type sensor whose electrical resistance changes according to humidity. Conventionally, it is known that an RC circuit including an electric resistance humidity sensor is employed as a circuit for detecting humidity. The RC circuit includes the electric resistance humidity sensor and a capacitor connected in series, and an oscillation signal is input to the RC circuit.

  By the way, in order to sufficiently secure a humidity detection range and a humidity detection resolution, a circuit for detecting humidity includes one electric resistance humidity sensor, a plurality of capacitors having different capacitances, and a circuit selection unit. It is possible to prepare The circuit selector selectively electrically connects one of the plurality of capacitors to the electric resistance humidity sensor.

  However, a general capacitor has a large variation in capacity (for example, about plus or minus 20%). In addition, a capacitor having a high capacity is expensive. Therefore, in the humidity detection circuit based on the RC circuit, it is difficult to detect a wide range of humidity with high accuracy while suppressing cost.

  On the other hand, the control unit 8 can detect a wide range of humidity with high accuracy while controlling the cost, and can control the control object based on the humidity with high accuracy. Hereinafter, details of the control unit 8 will be described.

[Details of control unit 8]
As shown in FIG. 2, the control unit 8 includes a data storage unit 70 in addition to the temperature detection circuit 5, the humidity detection circuit 6, and the CPU 7.

  The temperature detection circuit 5 and the humidity detection circuit 6 are circuits including a plurality of semiconductor elements mounted on a control board and electrically connected by a wiring pattern. Further, it is conceivable that the CPU 7 and the data storage unit 70 are also mounted on the control board. In this case, the CPU 7 and the data storage unit 70 are each a plurality of semiconductor elements electrically connected by one semiconductor element or a wiring pattern.

  The temperature detection circuit 5 is a circuit including a temperature sensor 50 that detects the temperature of the environment in which the image forming apparatus 10 is installed. For example, it is conceivable that the temperature sensor 50 is a thermistor. In this case, the temperature detection circuit 5 includes a temperature sensor 50 and a resistance element (not shown) constituting a voltage detection circuit for temperature detection. Furthermore, the temperature detection circuit 5 amplifies the output voltage of the voltage dividing circuit for detecting the temperature, and outputs a signal of the amplified temperature detection voltage VL2.

  The humidity detection circuit 6 includes a resistance variable circuit 61 electrically connected in series with the humidity sensor 60, a constant voltage power supply 63 that outputs a constant DC reference voltage V0, and an amplifier 64. The humidity sensor 60 and the resistance variable circuit 61 form a voltage dividing circuit 62 to which a constant DC reference voltage V0 is applied.

  In the example shown in FIG. 2, the humidity sensor 60 is disposed on the ground side with respect to the resistance variable circuit 61. In other words, the variable resistance circuit 61 is disposed on the constant voltage power supply 63 side with respect to the humidity sensor 60.

  The resistance variable circuit 61 is a circuit in which the electrical resistance is switched in a plurality of stages in accordance with the types of input switch control signals Sc1 and Sc2. In the present embodiment, the CPU 7 can output three types of switch control signals Sc1 and Sc2 by changing the combination of the first switch control signal Sc1 and the second switch control signal Sc2, which are binary signals.

  The resistance variable circuit 61 has at least one control capable of changing the electrical connection state of the plurality of resistance elements 61a to 61c with respect to the humidity sensor 60 according to the types of the plurality of resistance elements 61a to 61c and the switch control signals Sc1 and Sc2. A switch 65.

  In the example shown in FIG. 2, the resistance variable circuit 61 includes three resistance elements 61 a to 61 c and two control switches 65 a and 65 b that are one less than the number of resistance elements 61 a to 61 c. The two control switches 65a and 65b are electrically connected to the remaining second resistance element 61b and the third resistance element 61c except for the first resistance element 61a having the smallest electrical resistance among the three resistance elements 61a to 61c. Are connected in parallel.

  If the first control switch 65a connected in parallel to the second resistance element 61b is in the cut-off state, the second resistance element 61b is in the valid state, and if the first control switch 65a is in the short-circuit state, the second resistance element 61b is Invalid state. The valid state is a state forming a part of the electric resistance of the voltage dividing circuit 62, and the invalid state is a state in which the effective state is electrically disconnected from the voltage dividing circuit 62.

  Similarly, if the second control switch 65b connected in parallel to the third resistance element 61c is in the cut-off state, the third resistance element 61c is in the effective state, and if the second control switch 65b is in the short-circuit state. The third resistance element 61c is in the invalid state.

  The resistance variable circuit 61 shown in FIG. 2 is a circuit in which the electrical resistance is switched in three stages according to the types of the switch control signals Sc1 and Sc2.

  The amplifier 64 amplifies the output voltage V1 of the voltage dividing circuit 62 and outputs a signal of the amplified humidity detection voltage VL1.

  The CPU 7 includes a RAM (Random Access Memory) 7a that primarily stores a program Pr0 to be executed and a signal interface 7b. The signal interface 7b converts an input analog signal into digital data, and converts output target digital data into an analog signal.

  The CPU 7 outputs switch control signals Sc1 and Sc2 to the control switch 65 through the signal interface 7b. Further, the CPU 7 inputs the humidity detection voltage VL1 and the temperature detection voltage VL2 through the signal interface 7b.

  In the following description, the level of the humidity detection voltage VL1 input by the CPU 7 through the signal interface 7b is referred to as a humidity detection level. Similarly, the level of the temperature detection voltage VL2 input by the CPU 7 through the signal interface 7b is referred to as a temperature detection level. The humidity detection level corresponds to the level of the output voltage V1 of the voltage dividing circuit 62.

  The data storage unit 70 is a computer-readable non-volatile storage unit. For example, the data storage unit 70 may be a ROM (Read Only Memory) or a flash memory. The data storage unit 70 stores in advance a program Pr0 executed by the CPU 7, previous data D0 (described later), correction table data D1, and the like.

  In the following description, a predetermined range within the range of the humidity detection level corresponding to the input range of the signal interface 7b is referred to as an allowable range. The input range is a voltage range from a minimum voltage to a maximum voltage that can be input by the signal interface 7b. The minimum value of the allowable range is greater than the minimum voltage level of the input range. The maximum value of the allowable range is smaller than the maximum voltage level of the input range.

  Here, it is assumed that the electric resistances of the first resistance element 61a, the second resistance element 61b, and the third resistance element 61c are R1, R2, and R3, respectively. In this case, the three-stage electric resistance of the variable resistance circuit 61 is R1, (R1 + R2), and (R1 + R2 + R3).

  At the stage where the variable resistance circuit 61 is designed, a plurality of humidity ranges are determined within the required humidity detection range. The number of the humidity ranges set here is the number of steps of the electric resistance of the resistance variable circuit 61.

  Hereinafter, a case where three of the first humidity range, the second humidity range, and the third humidity range are set in the humidity detection range will be considered. The first humidity range is the lowest humidity range within the humidity detection range. The second humidity range is a range of humidity one step higher than the first humidity range in the humidity detection range. The third humidity range is a range of humidity one step higher than the second humidity range in the humidity detection range.

  The electrical resistance (R1 + R2 + R3) is set so that the humidity detection voltage VL1 is within the allowable range when the actual humidity is within the first humidity range.

  The electrical resistance (R1 + R2) is set so that the humidity detection voltage VL1 is within the allowable range when the actual humidity is within the second humidity range.

  The electrical resistance R1 is set so that the humidity detection voltage VL1 is within the allowable range when the actual humidity is within the third humidity range.

  Furthermore, the two humidity ranges corresponding to the allowable range of the level of the humidity detection voltage VL1 corresponding to the two continuous electrical resistances of the variable resistance circuit 61 partially overlap.

  For example, it is assumed that the required humidity detection range is 5% to 98%. In this case, it is conceivable that the first humidity range is set to 5 to 40%, the second humidity range is set to 35 to 70%, and the third humidity range is set to 65 to 98%.

  In the above case, the first humidity range (5 to 40%) and the second humidity range corresponding to the permissible range corresponding to the two continuous electric resistances (R1 + R2 + R3) and (R1 + R2) of the resistance variable circuit 61 (35-70%) overlaps in the range of 35-40%.

  Similarly, the second humidity range (35 to 70%) and the third humidity range (65 to 65) corresponding to the permissible range corresponding to two consecutive electrical resistances (R1 + R2) and R1 of the resistance variable circuit 61. 98%) overlap in the range of 65-70%.

  When the humidity detection circuit 6 is employed, appropriate types of switch control signals Sc1 and Sc2 are output from the CPU 7 to the control switch 65 according to the situation, so that a wide range of humidity can be detected with high resolution.

  The CPU 7 loads the program Pr0 stored in advance in the data storage unit 70 into the RAM 7a. The CPU 7 executes a program Pr0 developed in the RAM 7a, thereby executing an allowance determination process and switch control described later while referring to data input through the signal interface 7b.

[Acceptance judgment processing]
When activated, the CPU 7 outputs the switch control signals Sc1 and Sc to the control switch 65 of the resistance variable circuit 61, and executes the tolerance determination process.

  In the present embodiment, the CPU 7 causes the data storage unit 70 to store the previous data D0 indicating the types of the switch control signals Sc1 and Sc2 being output before stopping or pausing the operation. The CPU 7 outputs the switch control signals Sc1 and Sc2 of the type corresponding to the previous data D0 stored in the data storage unit 70 to the resistance variable circuit 61 when the CPU 7 starts from the stop state or the hibernation state, and then performs the above-described allowable process. Execute the judgment process. The sleep state is a state in which the CPU 7 has shifted to the power saving mode, for example.

  The tolerance determination process is a process for determining whether or not the humidity detection level is in an allowable state within the allowable range. Further, the CPU 7 executes the switch control according to the determination result by the allowance determination process.

[Switch control]
When it is determined that the humidity detection level is not in the allowable state, the CPU 7 changes the types of switch control signals Sc1 and Sc2 output to the control switch 65 of the resistance variable circuit 61.

  Specifically, when it is determined that the humidity detection level is below the allowable range in the allowable determination process, the CPU 7 switches the switch control signal that decreases the electrical resistance of the resistance variable circuit 61 by one step from the current level. Sc1 and Sc2 are output. When it is determined that the humidity detection level exceeds the allowable range, the CPU 7 outputs switch control signals Sc1 and Sc2 that increase the electrical resistance of the resistance variable circuit 61 by one step from the current level.

  The CPU 7 repeats the allowance determination process and the switch control until it is determined that the humidity detection level is in the allowable state.

  However, when it is determined that the humidity detection level is below the allowable range under the condition where the electric resistance of the resistance variable circuit 61 is the smallest, the CPU 7 ends the switch control and the switch control signal at that time. The outputs of Sc1 and Sc2 are maintained. Similarly, when it is determined that the humidity detection level exceeds the allowable range under the situation where the electric resistance of the resistance variable circuit 61 is the largest, the CPU 7 ends the switch control and switches at that time. The outputs of the signals Sc1 and Sc2 are maintained.

  Then, when it is determined that the humidity detection level is in the allowable state in the allowable determination process, the CPU 7 controls the control target according to the humidity detection level. Even when it is determined that the humidity detection level is not in the allowable state, when the switch control is completed, the CPU 7 controls the control target according to the humidity detection level.

[Control based on humidity detection level]
For example, the control target based on the humidity detection level may be one or more of the charging voltage, the development voltage, the transfer voltage, and the heater power.

  In general, the photoconductor 41 is less likely to be charged when the humidity is higher than when the humidity is low. Therefore, when the humidity detection level is lower than a predetermined standard range, it is conceivable that the CPU 7 corrects the charging voltage in a direction of decreasing from the standard voltage according to the humidity detection level. Similarly, when the humidity detection level is lower than the standard range, it is conceivable that the CPU 7 corrects the charging voltage in a direction to increase from the standard voltage according to the humidity detection level.

  Further, the density of the toner image on the surface of the photoconductor 41 tends to be higher when the humidity of the photoconductor 41 is higher than when the humidity is low. Therefore, when the humidity detection level is lower than a predetermined standard range, it is conceivable that the CPU 7 corrects the development voltage from the standard voltage in accordance with the humidity detection level. Similarly, when the humidity detection level is lower than the standard range, it is conceivable that the CPU 7 corrects the developing voltage in a direction to increase from the standard voltage according to the humidity detection level.

  In addition, when the humidity is higher than when the humidity is low, the toner image on the photoconductor 41 is not transferred to the sheet 9 and the transfer defect remaining on the photoconductor 41 is likely to occur. Therefore, when the humidity detection level is higher than a predetermined standard range, it is conceivable that the CPU 7 corrects the transfer voltage from the standard voltage in accordance with the humidity detection level.

  Further, the toner image is less likely to be fixed on the sheet 9 when the humidity is higher than when the humidity is low. Therefore, when the humidity detection level is higher than a predetermined standard range, it is conceivable that the CPU 7 corrects the target value of the fixing temperature in a direction higher than the standard value according to the humidity detection level. Similarly, when the humidity detection level is lower than the standard range, it is conceivable that the CPU 7 corrects the fixing temperature target value to be lower than the target value in accordance with the humidity detection level.

  The correction control of the fixing temperature target value means that the heater power is indirectly corrected by correcting the fixing temperature target value. That is, when the humidity detection level is higher than the standard range by correction control of the fixing temperature target value, the heater power is corrected to increase, and when the humidity detection level is lower than the standard range. The heater power is corrected so as to decrease.

  In addition, a plurality of correction table data D1 corresponding to a plurality of electrical resistances of the variable resistance circuit 61 may be stored in the data storage unit 70 in advance. Each of the correction table data D1 is data representing a correspondence relationship between the humidity detection level and the correction value of the control target.

  In the correction control of the control target based on the humidity detection level, the CPU 7 selects one correction table data D1 corresponding to the electric resistance of the resistance variable circuit 61 at the time when the correction control is performed. Further, the CPU 7 specifies the correction value corresponding to the humidity detection level from the correction table data D1, and corrects the control target using the specified correction value.

  As described above, the CPU 7 outputs appropriate types of switch control signals Sc1 and Sc2 to the control switch 65 depending on the situation. Therefore, if the control unit 8 is employed, a wide range of humidity can be detected with high resolution.

  Further, the control unit 8 does not require a plurality of humidity sensors 60 and does not require a highly accurate capacitor. Therefore, the control unit 8 can be realized at a relatively low cost.

  In general, there are many cases where the humidity when the CPU 7 stops or pauses and the humidity when the CPU 7 starts up next are approximate. On the other hand, the CPU 7 determines the type of the switch control signals Sc1 and Sc2 at the time of activation based on the previous data D0. In this case, there is a high possibility that the CPU 7 can output the switch control signals Sc1 and Sc2 of a type corresponding to the surrounding humidity condition at the time of startup. As a result, the control based on the humidity detection level can be started quickly. This effect becomes more prominent as the number of electrical resistance switching steps in the resistance variable circuit 61 increases.

[Second Embodiment: Control Unit 8A]
Next, a control unit 8A according to the second embodiment will be described with reference to FIG. In FIG. 3, the same components as those shown in FIG. 2 are given the same reference numerals.

  The control unit 8 </ b> A is an example of a humidity control device, like the control unit 8. Hereinafter, differences from the control unit 8 in the control unit 8A will be described. The control unit 8A has a configuration in which the resistance variable circuit 61 in the control unit 8 is replaced with a resistance variable circuit 61A.

  The resistance variable circuit 61A includes a plurality of resistance elements 61a to 61c electrically connected in parallel and a plurality of control switches 65 electrically connected in series to the plurality of resistance elements 61a to 61c. . In the example shown in FIG. 3, the resistance variable circuit 61A includes three resistance elements 61a to 61c and three control switches 65a to 65c. That is, the resistance variable circuit 61A includes the same number of control switches 65a to 65c as the number of resistance elements 61a to 61c.

  In the present embodiment, the CPU 7 outputs switch control signals Sc1, Sc2, and Sc3 that selectively set only one of the plurality of control switches 65 to the short-circuit state. Thereby, only one of the plurality of resistance elements 61a to 61c is in the valid state, and the remaining two are in the invalid state.

  In the example shown in FIG. 3, the resistance variable circuit 61 is a circuit in which the electrical resistance is switched in three stages of R1, R2, and R3 according to the types of the switch control signals Sc1, Sc2, and Sc3.

  The electrical resistance R3 is set so that the humidity detection voltage VL1 falls within the allowable range when the actual humidity is within the first humidity range.

  The electric resistance R2 is set so that the humidity detection voltage VL1 is within the allowable range when the actual humidity is within the second humidity range.

  The electric resistance R3 is set so that the humidity detection voltage VL1 is within the allowable range when the actual humidity is within the third humidity range.

  When the control unit 8A is employed, the same effect as that obtained when the control unit 8 is employed can be obtained. However, the control unit 8A needs one more control switch 65 than the control unit 8.

3: Sheet conveying unit 4: Image forming unit 5: Temperature detection circuit 6: Humidity detection circuit 7: CPU
7a: RAM
7b: Signal interface 8, 8A: Control unit 9: Sheet 10: Image forming apparatus 30: Sheet sending unit 31: Conveying roller pair 40: Optical scanning unit 41: Photoconductor (image carrier)
42: charging device 43: developing device 44: toner replenishing unit 45: transfer device 46: cleaning device 47: fixing device 50: temperature sensor 60: humidity sensor 61, 61A: resistance variable circuit 61a: first resistance element 61b: second Resistance element 61c: Third resistance element 62: Voltage dividing circuit 63: Constant voltage power supply 64: Amplifier 65: Control switch 70: Data storage unit 90: Developer 101: Sheet replenishment unit 102: Discharge tray 300: Sheet conveyance path 421: Charging roller 422: Charging voltage application circuit 431: Development roller 432: Circulation conveyance unit 433: Development voltage application circuit 451: Transfer roller 452: Transfer voltage application circuit 471: Fixing roller 472: Pressure roller 473: Heater 474: Heater power supply 475 : Fixing temperature sensor D0: Previous data D1: Correction table data Pr0: Program Sc: Switch control signal V0: DC reference voltage V1: Output voltage VL1: Humidity detection voltage VL2: Temperature detection voltage

Claims (4)

A humidity detection circuit including an electric resistance type humidity sensor;
A control unit for controlling humidity according to a level of an output voltage of the humidity detection circuit, and a humidity control device comprising:
The humidity detection circuit is
The voltage sensor is connected in series with the humidity sensor and forms a voltage dividing circuit to which a constant DC voltage is applied together with the humidity sensor, and the electric resistance is switched in a plurality of stages according to the type of control signal inputted. Further including a resistance variable circuit,
The variable resistance circuit includes a plurality of resistance elements and at least one control switch capable of changing an electrical connection state of the plurality of resistance elements to the humidity sensor in accordance with a type of the control signal.
The control unit outputs the control signal to the resistance variable circuit, and whether or not the humidity detection level, which is the level of the output voltage of the voltage dividing circuit, is within a predetermined allowable range. If the humidity detection level is determined not to be in the allowable state, the type of the control signal output to the resistance variable circuit is changed, and the humidity detection level is set to the allowable state. When it determines with it being, it is a humidity corresponding | compatible control apparatus which controls the said control object according to the said humidity detection level. A non-volatile storage unit;
The control unit stores the previous data representing the type of the control signal being output in the storage unit before stopping or pausing the operation, and corresponds to the previous data stored in the storage unit when activated. The humidity control apparatus according to claim 1, wherein the tolerance determination process is executed after outputting the type of control signal to the resistance variable circuit.   The two humidity ranges corresponding to the allowable range of the humidity detection level corresponding to the two stages of the electrical resistance of the variable resistance circuit are partially overlapped with each other. Humidity control device. A rotating image carrier;
A charging device having a charging member for charging the surface of the image carrier and a charging voltage applying unit for applying a charging voltage to the charging member;
Development that develops an electrostatic latent image formed on the surface of the charged image carrier into a toner image, having a developing roller that carries toner and rotates, and a developing voltage application unit that applies a developing voltage to the developing roller Equipment,
A transfer roller that rotates with a sheet sandwiched between the image carrier and a transfer voltage application unit that applies a transfer voltage to the transfer roller, and the toner image formed on the surface of the image carrier is transferred to the sheet A transfer device for transferring to,
A fixing roller, a heater that heats the fixing roller, and a heater power source that supplies heater power to the heater, and a fixing device that fixes the toner image to the sheet by heating the toner image by the fixing roller;
A humidity control device according to any one of claims 1 to 3,
The humidity control apparatus is an image forming apparatus that controls one or more of the charging voltage, the developing voltage, the transfer voltage, and the heater power.

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