JP2016188807A - Humidity sensor driving circuit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent, when oscillation of a control signal is stopped, which is input to a circuit that generates an AC voltage supplied to a humidity sensor from a DC voltage, the DC voltage from being applied to the humidity sensor irrespective of the cause of the stoppage.SOLUTION: A feeder circuit 11 receives an input of a control signal Sct forming a pulse wave and a DC voltage Vdc, converts the DC voltage Vdc into an AC voltage synchronized with the control signal Sct, and supplies the AC voltage to a humidity sensor 80. A power feed stopping circuit 12 receives an input of the circuit signal Sct, and when oscillation of the control signal Sct is stopped, stops supply of power from the feeder circuit 11 to the humidity sensor 80.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a humidity sensor driving circuit and an image forming apparatus including the same.

  In general, it is known that an electrophotographic image forming apparatus includes a humidity sensor that detects humidity when supplied with an AC voltage. In the image forming apparatus, the detection result of the humidity sensor is used for controlling a transfer voltage. The transfer voltage is a voltage applied to a transfer unit that transfers a toner image from an image carrier to a sheet material.

  The image forming apparatus includes a circuit that converts a DC voltage into an AC voltage synchronized with a control signal that forms a pulse wave, and the circuit supplies the AC voltage to the humidity sensor. In this case, when the control signal is stopped, the DC voltage is applied to the humidity sensor, and the humidity sensor may be damaged.

  On the other hand, it is known that the image forming apparatus includes a circuit that shuts off the DC voltage power source from the humidity sensor in response to an input of a reset signal (see, for example, Patent Document 1). The reset signal is a signal that stops a control unit that outputs the control signal. In this case, even if the output of the control signal by the control unit is stopped due to the generation of the reset signal, the DC voltage is not applied to the humidity sensor.

JP 2007-263702 A

  By the way, the oscillation of the control signal may stop due to a cause other than the stop of the control unit, such as generation of a surge voltage due to static electricity or lightning, and malfunction of the control unit. Therefore, it is desirable to prevent the DC voltage from being applied to the humidity sensor when the oscillation of the control signal is stopped for various reasons including the stop of the control unit.

  An object of the present invention is to apply a DC voltage to a humidity sensor when oscillation of a control signal input to a circuit that generates an AC voltage supplied to the humidity sensor from a DC voltage is stopped regardless of the cause of the stop. An object of the present invention is to provide a humidity sensor driving circuit capable of preventing this and an image forming apparatus including the same.

  A humidity sensor drive circuit according to one aspect of the present invention includes a power supply circuit and a power supply stop circuit. The power supply circuit is a circuit that receives a control signal and a DC voltage that form a pulse wave, converts the DC voltage into an AC voltage synchronized with the control signal, and supplies the AC voltage to the humidity sensor. The power supply stop circuit stops power supply from the power supply circuit to the humidity sensor when the control signal is input and oscillation of the control signal stops.

  An image forming apparatus according to another aspect of the present invention includes the humidity sensor driving circuit according to one aspect of the present invention and a humidity sensor to which an AC voltage is supplied from the humidity sensor driving circuit.

  According to the present invention, when the oscillation of the control signal input to the circuit that generates the AC voltage supplied to the humidity sensor from the DC voltage stops, the DC voltage is applied to the humidity sensor regardless of the cause of the stop. It is possible to provide a humidity sensor driving circuit and an image forming apparatus including the humidity sensor driving circuit.

FIG. 1 is a block diagram of an image forming apparatus including a humidity sensor driving circuit according to the embodiment. FIG. 2 is a circuit diagram of a humidity sensor driving circuit according to the embodiment. FIG. 3 is a time chart of various signals during which the control signal is oscillating in the humidity sensor driving circuit according to the embodiment. FIG. 4 is a time chart of various signals when the oscillation of the control signal is stopped in the humidity sensor driving circuit according to the 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.

[Configuration of Image Forming Apparatus 10]
First, a configuration of an image forming apparatus 10 including a humidity sensor driving circuit 1 according to the embodiment will be described with reference to FIG. The image forming apparatus 10 is an electrophotographic image forming apparatus.

  As shown in FIG. 1, an image forming apparatus 10 includes a sheet supply unit 2, a sheet conveying unit 3, an image forming unit 4, an optical scanning unit 5, a fixing unit 6, a humidity sensor 80, and a humidity sensor driving circuit in a casing 100. 1 and a control unit 8.

  The image forming apparatus 10 is, for example, a printer, a copier, a facsimile machine, or a multifunction machine. The multifunction machine has both the printer function and the copier function.

  The sheet supply unit 2 includes a sheet receiving unit 21 and a sheet sending unit 22. The sheet receiving portion 21 is configured to be able to stack a plurality of sheet materials 9 on top of each other. The sheet material 9 is a sheet-like image forming medium such as paper, coated paper, postcard, envelope, and OHP sheet.

  The sheet delivery unit 22 sends out the sheet material 9 from the sheet receiving unit 21 toward the conveyance path 30 by rotating in contact with the sheet material 9.

  The sheet conveyance unit 3 includes a registration roller 31, a conveyance roller 32, a discharge roller 33, and the like. The registration roller 31 and the conveyance roller 32 convey the sheet material 9 supplied from the sheet supply unit 2 toward the image forming unit 4. Further, the discharge roller 33 discharges the sheet material 9 after the image formation from the discharge port of the conveyance path 30 onto the discharge tray 101.

  The image forming unit 4 forms an image of a developer 90 such as a toner on the surface of the sheet material 9 moving on the conveyance path 30. The image forming unit 4 includes a drum-shaped photoreceptor 41, a charging unit 42, a developing unit 43, a transfer unit 45, a cleaning unit 47, and the like. The photoconductor 41 is an example of an image carrier.

  The photoconductor 41 rotates, and the charging unit 42 uniformly charges the surface of the photoconductor 41. Further, an electrostatic latent image is written on the surface of the photoreceptor 41 charged by the optical scanning unit 5 scanning the laser beam. Further, the developing unit 43 supplies the developer 90 to the photoreceptor 41 to develop the electrostatic latent image.

  The transfer unit 45 transfers the image on the surface of the photoreceptor 41 to the sheet material 9 that is moving along the conveyance path 30. The image forming apparatus 10 includes a transfer voltage application unit 450 that applies a transfer voltage to the transfer unit 45. The transfer voltage is a voltage at which the potential difference between the photosensitive member 41 and the transfer portion 45 with respect to the potential of the photosensitive member 41 is opposite to the charged polarity of the developer 90. Further, the cleaning unit 47 removes the developer 90 remaining on the surface of the photoreceptor 41.

  The fixing unit 6 includes a heating roller 61 and a pressure roller 62 that enclose a heater 610. The heating roller 61 and the pressure roller 62 feed the sheet material 9 on which an image is formed between them to a subsequent process. As a result, the fixing unit 6 fixes the image on the sheet material 9 on which the image, that is, the image of the developer 90 is formed, by heating.

  The humidity sensor 80 is a sensor that measures the humidity of the installation environment of the image forming apparatus 10. The humidity sensor 80 is supplied with an AC voltage from the humidity sensor drive circuit 1. In the following description, the voltage supplied to the humidity sensor 80 is referred to as a power supply voltage Vsup. The humidity sensor 80 detects the humidity of the surrounding air by supplying an AC voltage as the power supply voltage Vsup.

  The control unit 8 controls various devices included in the image forming apparatus 10. The control unit 8 includes a CPU (Central Processor Unit) 81, a storage unit 82, and the like. The CPU 81 is a processor that executes various arithmetic processes.

  The storage unit 82 is a non-volatile storage unit in which a control program for causing the CPU 81 to execute various processes and other information are stored in advance. Furthermore, the storage unit 82 is also a storage unit in which various information can be read and written by the CPU 81.

  The control unit 8 comprehensively controls the image forming apparatus 10 by the CPU 81 executing various control programs stored in advance in the storage unit 82.

  For example, when the CPU 81 executes the transfer voltage control program Pr1 stored in the storage unit 82, the control unit 8 controls the transfer voltage output from the transfer voltage application unit 450. More specifically, the control unit 8 controls the transfer voltage according to the detection result of the humidity sensor 80.

  For example, when the humidity detected by the humidity sensor 80 is high, the control unit 8 reduces the transfer voltage so that the potential difference between the photoconductor 41 and the transfer unit 45 with respect to the potential of the photoconductor 41 becomes smaller. Adjust.

  The humidity sensor drive circuit 1 includes a circuit that supplies an AC voltage to the humidity sensor 80. As will be described later, the humidity sensor drive circuit 1 includes a circuit that converts the DC voltage Vdc into the AC voltage synchronized with the control signal Sct that forms a pulse wave, and the circuit supplies the AC voltage to the humidity sensor 80. (See FIG. 2).

  The control signal Sct is a signal output from the CPU 81 of the control unit 8. For example, it is conceivable that the control signal Sct is a pulse width modulation signal (PWM signal).

  When transmission of the control signal Sct is stopped, the DC voltage Vdc is applied to the humidity sensor 80, and the humidity sensor 80 may be damaged. For example, when the operation of the control unit 8 stops when the image forming apparatus 10 shifts to the power saving state, the oscillation of the control signal Sct stops.

  Incidentally, the oscillation of the control signal Sct may stop due to a cause other than the stop of the control unit 8 such as generation of a surge voltage due to static electricity or lightning and malfunction of the CPU 81 in the control unit 8. Therefore, it is desirable to prevent the DC voltage Vdc from being applied to the humidity sensor 80 when the oscillation of the control signal Sct is stopped for various reasons including the stop of the control unit 8.

  The humidity sensor drive circuit 1 provided in the image forming apparatus 10 causes the stop when the oscillation of the control signal Sct input to the circuit that generates the AC voltage supplied to the humidity sensor 80 from the DC voltage Vdc is stopped. Regardless, the application of the DC voltage Vdc to the humidity sensor 80 is prevented. The details will be described below.

[Humidity sensor drive circuit 1]
FIG. 2 is a circuit diagram of the humidity sensor driving circuit 1. The humidity sensor drive circuit 1 includes a power supply circuit 11, a power supply stop circuit 12, and a detection signal adjustment circuit 13.

  The power feeding circuit 11 is a known circuit that supplies the AC voltage to the humidity sensor 80. A control signal Sct and a DC voltage Vdc forming a pulse wave are input to the power feeding circuit 11.

  The power feeding circuit 11 converts the DC voltage Vdc into the AC voltage synchronized with the control signal Sct, and supplies the AC voltage to the humidity sensor 80. The DC voltage Vdc is supplied from the DC power supply 7. The power supply voltage Vsup is supplied to the humidity sensor 80 through a pair of power supply lines 14 that connect the power supply circuit 11 and the humidity sensor 80.

  FIG. 3 is a time chart of various signals during which the control signal Sct in the humidity sensor driving circuit 1 is oscillating. As shown in FIG. 3, the supply voltage Vsup when the control signal Sct is oscillating is an alternating current in which the DC voltage Vdc is alternately applied to the pair of input terminals of the humidity sensor 80 in the reverse direction in synchronization with the control signal Sct. Voltage.

  The detection signal adjustment circuit 13 is a circuit that converts the detection signal of the humidity sensor 80 while the control signal Sct is oscillating into a humidity detection signal Swet that can be input by the CPU 81 of the control unit 8. In the example illustrated in FIG. 2, the detection signal adjustment circuit 13 is an RC integration circuit including a resistance element and a capacitor.

  The power supply stop circuit 12 is a circuit that stops power supply from the power supply circuit 11 to the humidity sensor 80 when the control signal Sct is input and the oscillation of the control signal Sct stops. The power supply stop circuit 12 includes an oscillation stop detection circuit 121 and a pair of short-circuit switch circuits 122.

  The oscillation stop detection circuit 121 is a circuit that receives the control signal Sct and outputs the switch signal Ssw. The oscillation stop detection circuit 121 outputs a negative switch signal Ssw when the control signal Sct is oscillating, and outputs an active switch signal Ssw when the control signal Sct stops oscillating.

  In the example illustrated in FIG. 2, the oscillation stop detection circuit 121 includes a preprocessing circuit 123 and a voltage detector 124. The voltage detector 124 is an integrated circuit called a reset IC or the like.

  This is a circuit that receives the control signal Sct and outputs the intermediate signal Smd. The intermediate signal Smd is a signal whose level deviates from a predetermined allowable level range in synchronization with the rise or fall of the control signal Sct.

  In FIG. 2, the preprocessing circuit 123 includes an inverting circuit 125 and a differentiating circuit 126. The inverting circuit 125 is a circuit that receives the control signal Sct and outputs an inverted signal Srev obtained by inverting the High and Low states of the control signal Sct.

  The differentiation circuit 126 is a circuit that receives the inverted signal and outputs the differentiated signal of the inverted signal Srev as the intermediate signal Smd. In the example shown in FIG. 2, the differentiating circuit 126 is an RC differentiating circuit.

  Note that the inverting circuit 125 realized by a transistor is interposed between the control signal Sct line and the differentiating circuit 126, so that the differentiating circuit 126 affects the control signal Sct input to the power feeding circuit 11. It also plays a role to prevent.

  As shown in FIG. 3, the intermediate signal Smd output from the preprocessing circuit 123 shown in FIG. 2 is a signal whose level falls below a predetermined allowable lower limit level Lmin in synchronization with the fall of the control signal Sct. In the example shown in FIG. 3, the allowable level range is a range from the allowable lower limit level Lmin to the upper limit level that the intermediate signal Smd can take.

  Note that the differentiation circuit 126 actually detects both the falling and rising edges of the inverted signal Srev and tries to change the intermediate signal Smd suddenly at both the falling and rising timings of the inverted signal Srev. However, at the rising edge of the inverted signal Srev, the level of the intermediate signal Smd is saturated at a possible upper limit level.

  The voltage detector 124 is a circuit that receives the intermediate signal Smd and outputs the switch signal Ssw. The voltage detector 124 switches the state (active or negative) of the switch signal Ssw to be output depending on whether or not the intermediate signal Smd is out of a predetermined allowable level range.

  In the example shown in FIG. 3, the switch signal Ssw is an active high signal and a negative low signal.

  More specifically, the voltage detector 124 determines that the state in which the intermediate signal Smd is maintained within the allowable level range from the time when the level of the intermediate signal Smd is out of the allowable level range for a predetermined maintenance time t1. The negative switch signal Ssw is output until it continues, and the active switch signal Ssw is output in other cases. The maintenance time t1 is longer than the oscillation period t0 of the control signal Sct.

  Therefore, if the control signal Sct oscillates at a cycle shorter than the sustain time t1, the voltage detector 124 continues to output the negative switch signal Ssw (see FIG. 3).

  In FIG. 3, the switch when the level of the intermediate signal Smd falls below the allowable lower limit level Lmin and then returns to the allowable level range, and the state of maintaining the allowable level range continues for the maintenance time t1 or longer. The change of the signal Ssw is indicated by a virtual line (two-dot chain line).

  The pair of short-circuit switch circuits 122 is a circuit that receives a switch signal Ssw and switches whether the pair of power supply lines 14 is short-circuited to the conductive portion 15 having a predetermined potential according to the state of the switch signal Ssw. In the present embodiment, the conductive portion 15 is a reference potential portion, that is, a housing ground portion. For example, it is conceivable that the conductive portion 15 is a metal frame that forms part of the housing 100.

  The pair of short-circuit switch circuits 122 electrically disconnects between the pair of power supply lines 14 and the conductive portion 15 when the input switch signal Ssw is negative. Further, the pair of short-circuit switch circuits 122 short-circuit each of the pair of power supply lines 14 to the conductive portion 15 when the input switch signal Ssw is active. When each of the pair of power supply lines 14 is short-circuited with the conductive portion 15, the potential difference between the pair of power supply lines 14 becomes 0, and power supply to the humidity sensor 80 is stopped.

  As shown in FIG. 4, when the oscillation of the control signal Sct stops, the oscillation of the inverted signal Srev also stops. When the oscillation of the inverted signal Srev stops, a state in which the differentiating circuit 126 detects the falling edge of the inverted signal Srev does not occur, and the intermediate signal Smd maintains a level within the allowable level range.

  Therefore, when the maintenance time t1 has elapsed since the intermediate signal Smd finally returned to the allowable level range, the voltage detector 124 outputs the active switch signal Ssw and maintains the active state. As a result, each of the pair of feed lines 14 is short-circuited with the conductive portion 15 by the action of the pair of short-circuit switch circuits 122.

  When each of the pair of power supply lines 14 is short-circuited with the conductive portion 15, the potential difference between the pair of power supply lines 14, that is, the power supply voltage Vsup becomes 0, and power supply to the humidity sensor 80 is stopped.

  According to the present embodiment, when the presence or absence of oscillation of the control signal Sct itself is detected and the oscillation of the control signal Sct input to the power supply circuit 11 is stopped, the DC voltage is applied to the humidity sensor 80 regardless of the cause of the stop. It is possible to prevent Vdc from being applied. As a result, it is possible to prevent the humidity sensor 80 from being damaged due to the application of the DC voltage Vdc.

  In addition, by adopting the short-circuit switch circuit 122 that switches between connection and disconnection between the pair of power supply lines 14 and the conductive portion 15 according to the presence or absence of oscillation of the control signal Sct, a simple power supply stop circuit 12 can be configured. it can.

  Further, by employing the preprocessing circuit 123 including the inverting circuit 125 and the differentiating circuit 126, a simple oscillation stop detection circuit 121 can be configured using the voltage detector 124 which is a very general element.

  In the present embodiment, an intermediate signal Smd that temporarily changes suddenly in synchronization with the rise or fall of the control signal Sct is generated by the preprocessing circuit 123, and the intermediate signal Smd is input to the voltage detector 124. In this case, the maintenance time t1 is set to a time close to the oscillation period t0 of the control signal Sct, so that the stop of the oscillation of the control signal Sct can be detected at an early stage.

[Application example]
In the embodiment described above, the preprocessing circuit 123 may be a circuit that outputs the intermediate signal Smd that deviates from the allowable level range in synchronization with the falling edge of the control signal Sct. Similarly, the preprocessing circuit 123 may be a circuit that outputs an intermediate signal Smd that is out of the allowable level range in synchronization with the rising edge of the inverted signal Srev.

  It is also conceivable that the intermediate signal Smd is a signal that temporarily exceeds the upper limit level of the allowable level range in synchronization with the rise or fall of the control signal Sct. In this case, it is conceivable that an inverting circuit is provided between the preprocessing circuit 123 and the voltage detector 124. Alternatively, a pair of short-circuit switch circuits 122 that connect the pair of power supply lines 14 and the conductive portion 15 in accordance with the input of the negative switch signal Ssw may be considered.

  It is also conceivable that the control unit 8 controls devices other than the transfer voltage application unit 450 according to the detection result of the humidity sensor 80. For example, the control unit 8 may control a heater power supply unit that supplies power to the heater 610 of the fixing unit 6 according to the detection result of the humidity sensor 80. In this case, it is conceivable that the control unit 8 adjusts the target temperature of the temperature feedback control in the heater power supply unit according to the detection result of the humidity sensor 80.

  It should be noted that the humidity sensor driving circuit and the image forming apparatus according to the present invention can be freely combined within the scope of the invention described in each claim, or the embodiments and application examples described above. It is also possible to configure by appropriately modifying or omitting a part.

1: Humidity sensor drive circuit 2: Sheet supply unit 3: Sheet conveying unit 4: Image forming unit 5: Optical scanning unit 6: Fixing unit 7: DC power supply 8: Control unit 9: Sheet material 10: Image forming apparatus 11: Power feeding Circuit 12: Power supply stop circuit 13: Detection signal adjustment circuit 14: Power supply line 15: Conductive part (grounding part)
21: Sheet receiving unit 22: Sheet sending unit 30: Conveying path 31: Registration roller 32: Conveying roller 33: Discharging roller 41: Photoconductor (image carrier)
42: charging unit 43: developing unit 45: transfer unit 47: cleaning unit 61: heating roller 62: pressure roller 80: humidity sensor 81: CPU
82: Storage unit 90: Developer 100: Housing 101: Discharge tray 121: Oscillation stop detection circuit 122: Short circuit switch circuit 123: Pre-processing circuit 124: Voltage detector 125: Inversion circuit 126: Differentiation circuit 450: Application of transfer voltage Unit 610: Heater Pr1: Transfer voltage control program Sct: Control signal Smd: Intermediate signal Srev: Inverted signal Ssw: Switch signal Swet: Humidity detection signal Vdc: DC voltage Vsup: Feed voltage t0: Oscillation cycle t1: Maintenance time

Claims (5)

A power supply circuit that receives a control signal and a DC voltage that form a pulse wave, converts the DC voltage into an AC voltage synchronized with the control signal, and supplies the AC voltage to the humidity sensor;
A humidity sensor drive circuit comprising: a power supply stop circuit that stops power supply from the power supply circuit to the humidity sensor when the control signal is input and oscillation of the control signal stops. The power supply stop circuit is
An oscillation stop detection circuit that receives the control signal, outputs a negative switch signal when the control signal is oscillating, and outputs the switch signal that is active when the oscillation of the control signal is stopped;
When the switch signal is input and the switch signal is negative, a pair of power supply lines connecting the power supply circuit and the humidity sensor are electrically disconnected from a predetermined conductive portion, and the switch The humidity sensor drive circuit according to claim 1, further comprising: a pair of short-circuit switch circuits that short-circuit each of the pair of power supply lines to the conductive portion when a signal is active. The oscillation stop detection circuit is
A preprocessing circuit that receives the control signal and outputs an intermediate signal whose level is out of a predetermined allowable level range in synchronization with the rising or falling edge of the control signal;
A predetermined time in which the state in which the intermediate signal is maintained within the allowable level range from the time when the intermediate signal is input and the level of the intermediate signal is out of the allowable level range is longer than the oscillation period of the control signal. The humidity sensor drive circuit according to claim 2, further comprising: a voltage detector that outputs the negative switch signal until it continues, and outputs the active switch signal in other cases. The pre-processing circuit is
An inverting circuit that receives the control signal and outputs an inverted signal obtained by inverting the control signal;
The humidity sensor drive circuit according to claim 3, further comprising: a differentiation circuit that receives the inverted signal and outputs a differential signal of the inverted signal as the intermediate signal. The humidity sensor drive circuit according to any one of claims 1 to 4,
A humidity sensor to which an AC voltage is supplied from the humidity sensor drive circuit;
An image forming apparatus comprising: a control unit that controls an apparatus according to a detection result of the humidity sensor.

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