Device that prevents human body from being pinched by utilizing the change of electrostatic capacitance

Abstract

The present invention relates to a device for preventing a human body from being clamped by utilizing a sensor part for sensing a change in electrostatic capacitance, which can prevent a safety accident caused by a human body being clamped. The device comprises: a sensor part for sensing a change in electrostatic capacitance corresponding to a change in the interval between an external conductor and an internal conductor that is squeezed by a human body approaching a passive body; a signal processing part for comparing a sensing signal of the sensor part with a reference value and outputting a clamping occurrence signal indicating a phenomenon in which a human body is clamped by the passive body; a motor driving part for driving a motor in order to move the passive body; and a control part for controlling the motor driving part to stop the passive body or move it in the opposite direction upon receiving the clamping occurrence signal input from the signal processing part, thereby preventing a safety accident caused by a human body being clamped.

Description

Technical Field

[0001] The present invention relates to a device for preventing a human body from being clamped by utilizing a sensor part for sensing a change in electrostatic capacitance, which can prevent a safety accident caused by a human body being clamped. Background Art

[0002] The sliding door of a car can be opened or closed by the driver or the passenger with a single button, which is convenient. However, if the driver closes the door without checking the passenger in time, the body may be pinched by the sliding door, resulting in injury to the passenger.

[0003] In order to solve this problem, the prior art Korean Patent No. 10-0520356 (granted on October 4, 2005, Patent Document 1) discloses a technology that includes a laser light emitting unit for irradiating laser light and a laser light receiving unit for receiving the laser light irradiated from the laser light emitting unit, and the laser light receiving unit senses the state in which the object is clamped by the clamping unit of the sliding door of the shared vehicle. However, in the case of the above-mentioned Patent Document 1, since expensive equipment, namely, the laser light emitting unit and the laser light receiving unit are used, the economic burden of the user is increased, and if the vehicle is operated under adverse conditions such as a dirt road, there is a problem of malfunction of the laser light emitting unit and the laser light receiving unit due to vibration generated during the operation of the vehicle.

[0004] In addition, in Korean Patent No. 10-1566977 (granted on November 2, 2015, Patent Document 2), an optical sensor is used to sense an object between a sliding door and a vehicle body to prevent a safety accident in which a person or a corner of clothing is caught between the sliding door and the vehicle body. However, in Patent Document 2, there is a problem in safety because the optical sensor is contaminated by foreign matter or malfunctions due to flying dust or strong sunlight.

[0005] In another prior art, although a technology is disclosed that senses the rotation state of a motor and senses the clamping of an object and controls the motor to move a sliding door, the abnormal state of the motor can only be sensed when the door is clamped and a certain mechanical pressure is generated. Therefore, there is a problem of causing serious safety accidents to the elderly, the weak, or children who have slow reaction speed.

[0006] In another prior art, although a method of sensing an object using an electrostatic capacitance sensor is disclosed, the object cannot be accurately sensed when it is soaked by rain water, which may lead to erroneous operation. Summary of the invention

[0007] Technical issues

[0008] The object of the present invention is to provide a device for preventing a human body from being clamped by utilizing changes in electrostatic capacitance, wherein the device senses changes in electrostatic capacitance by utilizing a sensor portion squeezed by touch pressure applied by the human body, thereby preventing safety accidents caused by the human body being clamped.

[0009] Problem Solving Solutions

[0010] The device for preventing the human body from being clamped by utilizing the change of electrostatic capacitance according to the present invention which is intended to achieve the above-mentioned purpose is characterized in that it includes: a sensor part, which senses the change of electrostatic capacitance corresponding to the interval between the external conductor and the internal conductor electrically grounded on the passive body; a signal processing part, which compares the sensing signal of the above-mentioned sensor part with a reference value, and outputs a clamping occurrence signal indicating that the human body is clamped on the above-mentioned passive body; a motor driving part, which drives the motor in order to move the above-mentioned passive body; and a control part, which, upon receiving the input clamping occurrence signal from the above-mentioned signal processing part, controls the above-mentioned motor driving part to stop the above-mentioned passive body or move it in the opposite direction.

[0011] The device for preventing a human body from being clamped by utilizing changes in electrostatic capacitance according to the present invention is characterized in that the passive body is one of a side door, a trunk door, a window, a sunroof, an elevator door, and a subway door as an accessory installed on a car, and the sensor portion is formed in the form of a strip curved to correspond to the side shape of the passive body.

[0012] The device for preventing the human body from being clamped by utilizing the change of electrostatic capacitance according to the present invention is characterized in that the sensor part integrates the external conductor, the internal conductor and the support part, and the support part cooperates between the external conductor and the internal conductor to prevent the external conductor and the internal conductor from directly contacting each other, thereby realizing electrical insulation.

[0013] The device for preventing the human body from being clamped by utilizing the change of electrostatic capacitance according to the present invention is characterized in that protruding columns are vertically formed on both sides of the above-mentioned support part along the length direction, and a recessed installation groove is formed between the protruding columns opposite to each other, and the bottom surface of the internal conductor is in contact with the above-mentioned installation groove.

[0014] The device for preventing the human body from being clamped by utilizing the change of electrostatic capacitance according to the present invention is characterized in that a pair of first slits extending along the length direction are formed on the outer side of the two side columns of the above-mentioned support part, and a pair of first embedded protrusions extending along the length direction are formed on the inner side of the two side columns of the above-mentioned support part.

[0015] The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to the present invention is characterized in that a pair of second embedding protrusions are formed on the inner side of the external conductor, and the second embedding protrusions are matched with the first slit of the support portion.

[0016] The device for preventing the human body from being clamped by utilizing the change of electrostatic capacitance according to the present invention is characterized in that a pair of second slits extending along the length direction are formed on the outer sides of the two side columns of the above-mentioned internal conductor, and the first embedding protrusion of the support part cooperates with the above-mentioned second slits.

[0017] According to the device for preventing human body from being clamped by utilizing the change of electrostatic capacitance of the present invention, the first signal cable buried in the internal conductor is led out to the outside and connected to the signal processing unit, and the second signal cable buried in the external conductor is led out to the outside and connected to the signal processing unit.

[0018] The device for preventing a human body from being clamped by utilizing changes in electrostatic capacitance according to the present invention is characterized in that the external conductor is formed into a dome shape, one end of the external conductor and one end of the internal conductor are formed into a serrated shape, and an air layer is formed between the external conductor and the internal conductor.

[0019] The device for preventing human body from being pinched using electrostatic capacitance change according to the present invention is characterized in that the sensor portion is formed integrally with the external conductor, the internal conductor and the support portion by a triple injection molding machine.

[0020] The device for preventing human body from being clamped by utilizing the change of electrostatic capacitance according to the present invention is characterized in that the external conductor is made of a soft material that is squeezed by the touch pressure applied by the human body.

[0021] The device for preventing human body from being pinched using electrostatic capacitance change according to the present invention is characterized in that the external conductor and the internal conductor can be molded from a composite material of a thermoplastic elastomer and carbon nanotubes.

[0022] The device for preventing human body from being pinched by utilizing electrostatic capacitance change according to the present invention is characterized in that the mixing ratio of the carbon nanotubes blended into the thermoplastic elastomer is 20 to 60% by weight.

[0023] The device for preventing human body from being pinched using electrostatic capacitance change according to the present invention is characterized in that the support portion can be molded from a thermoplastic elastomer.

[0024] The device for preventing the human body from being clamped by utilizing the change of electrostatic capacitance according to the present invention is characterized in that the above-mentioned sensor part outputs the change of electrostatic capacitance and resistance according to the interval between the external conductor and the internal conductor, and the above-mentioned signal processing part includes a first comparator for comparing the sensed electrostatic capacitance of the above-mentioned sensor part with a preset first reference value and a second comparator for comparing the voltage divider corresponding to the resistance change of the above-mentioned sensor part with a preset second reference value. If the sensed electrostatic capacitance is greater than the first reference value, the above-mentioned first comparator outputs a clamping signal, and if the voltage divider corresponding to the sensed resistance is less than the second reference value, the above-mentioned second comparator outputs a clamping signal.

[0025] Effects of the Invention

[0026] According to the present invention, the external conductor and the internal conductor are integrated into a thin strip form, so that they can be set to be bent corresponding to the shape of the object, thereby making the setting operation easy and simple, and can be applied to multiple fields such as sliding doors of automobiles, electric windows, sliding doors of lifts, etc.

[0027] According to the present invention, it is possible to sense the occurrence of clamping based on the change in electrostatic capacitance of a sensor portion composed of an external conductor and an internal conductor, and when an excessive external force is applied to the external conductor causing the external conductor and the internal conductor to fit together, it is possible to sense the occurrence of clamping based on the change in resistance of the sensor portion, thereby ensuring working stability in a variety of usage environments.

[0028] According to the present invention, the external conductor and the internal conductor are formed in a serrated shape to increase the relative surface area between the external conductor and the internal conductor, thereby being able to sensitively sense the electrostatic capacitance that changes in proportion to the interval between the external conductor and the internal conductor, thereby being able to improve sensor performance.

[0029] According to the present invention, the external conductor of the sensor part is sealed and the external conductor is grounded, thereby preventing malfunction caused by foreign matter such as rainwater and dust, thereby improving reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a perspective view showing the appearance of a sensor section according to an embodiment of the present invention.

[0031] Figure 2 is an exploded perspective view of a sensor unit according to an embodiment of the present invention.

[0032] Figure 3 AA is a cross-sectional view of the sensor portion according to the embodiment of the present invention.

[0033] Figure 4is a detailed circuit diagram of a sensor section and a signal processing section according to an embodiment of the present invention.

[0034] Figure 5 is a graph showing electrostatic capacitance varying with touch pressure applied to a sensor portion by a human body according to an embodiment of the present invention.

[0035] Figure 6 4 is a control block diagram of a device for preventing a human body from being clamped using a change in electrostatic capacitance according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present invention with reference to the accompanying drawings to illustrate the present invention. The same reference symbols shown in the various drawings represent the same components. In addition, in the process of describing the present invention, the specific description of the related known functions or structures will be omitted if it is judged that it is possible to make the gist of the present invention unnecessarily obscure.

[0037] In addition, when it is mentioned that a certain part “includes” a certain constituent element, it means that other constituent elements can be further included rather than excluding other constituent elements, unless otherwise specifically described to the contrary.

[0038] In order to deal with the situation where a human body is pinched due to user negligence when a sliding door installed in a car is driven by an electric motor, a device for preventing human body from being pinched by using a change in electrostatic capacitance according to an embodiment of the present invention has an anti-pinch function that utilizes a sensor part that senses the change in electrostatic capacitance to automatically stop the sliding door or drive it in the opposite direction, thereby ensuring the safety of the user.

[0039] This device for preventing a person from being clamped by utilizing a change in electrostatic capacitance can be applied to various technical fields in which an electric motor is used to drive a passive body. For example, in the case where an electric automatic opening and closing system is used as one of the user convenience functions, which can automatically open and close the side doors, trunk doors, windows, and sunroofs installed as accessories of the car, the safety device of the automatic sliding door according to the embodiment can be added. As another example, even in the case of an automatic opening and closing method such as an elevator door or a subway door of a building, the safety device of the automatic sliding door according to the embodiment can be added.

[0040] like Figure 1 and Figure 2 As shown, the human body pinching prevention device using electrostatic capacity change according to an embodiment of the present invention may include a sensor part 100 that senses a change in electrostatic capacity proportional to a touch pressure applied by a human body approaching an automatic sliding door.

[0041] Figure 1 is a perspective view showing the appearance of a sensor portion according to an embodiment of the present invention, Figure 2 is an exploded perspective view of a sensor unit according to an embodiment of the present invention.

[0042] The sensor unit 100 may be disposed on the side of the sliding door as a passive body moved forward or backward by the electric motor. The position of the sensor unit 100 is not particularly limited, and it may be disposed without restriction at a location exposed to the outside to be able to react to the touch pressure applied by an approaching human body.

[0043] like Figure 1 and Figure 2 As shown, the sensor part 100 may be formed to extend in the length direction. The sensor part 100 may be formed in a strip shape that is bent corresponding to the side shape of the sliding door. The sensor part 100 may include a support part 110 , an inner conductor 120 , and an outer conductor 130 .

[0044] The support portion 110 and the inner conductor 120 are integrated into the outer conductor 130 .

[0045] The support part 110 is fitted between the external conductor 130 and the internal conductor 120 to prevent direct contact between the external conductor 130 and the internal conductor 120. In addition, the support part 110 is made of an electrically insulating material, for example, thermoplastic elastomer (TPE) can be supplied to an injection molding machine for molding.

[0046] The outer conductor 130 is the outer skin of the sensor unit 100 exposed to the outside, and has a dome-shaped appearance with a hollow interior, and can be made of a soft material that can be squeezed by the touch pressure applied by the human body. A tunnel-shaped accommodation space 134 is formed inside the outer conductor 130, and the support unit 110 and the inner conductor 120 are accommodated in the accommodation space 134.

[0047] The external conductor 130 and the internal conductor 120 may be formed by supplying a composite material of thermoplastic elastomer (TPE) and conductive carbon nanotubes (CNT) to an injection molding machine. Here, carbon nanotubes (CNT) are blended into thermoplastic elastomer (TPE) at 20 to 60 weight %.

[0048] The support portion 110, the internal conductor 120 and the external conductor 130 can be integrally molded using a triple injection molding machine, and thermoplastic elastomer (TPE) is used as a common raw material. Therefore, the interface bonding strength of the internal conductor 120 and the external conductor 130 joined by the support portion 110 is excellent and the durability is improved.

[0049] like Figure 2As shown, with respect to the support portion 110 , protruding columns are vertically formed on both sides along the length direction, and a recessed mounting groove 112 is formed between the protruding columns facing each other.

[0050] The bottom surface and two side surfaces of the support portion 110 are in contact with the inner surface of the outer conductor 130 , and the bottom surface of the inner conductor 120 is in contact with the mounting groove 112 on the upper surface of the support portion 110 .

[0051] A pair of first slits 113 extending along the length direction are formed on the outer sides of the two side pillars of the support portion 110 , and a pair of first fitting protrusions 111 extending along the length direction are formed on the inner sides of the two side pillars.

[0052] A pair of second embedding protrusions 132 are formed inside the external conductor 130 , and the second embedding protrusions 132 are matched with the first slits 113 of the support portion 110 received in the receiving space 134 .

[0053] A pair of second slits 123 extending along the length direction are formed outside the two side columns of the inner conductor 120. The first insertion protrusion 111 of the support portion 110 is matched with the second slit 123 of the inner conductor 120 located in the installation groove 112.

[0054] The first signal cable 122 buried in the internal conductor 120 is led out to the outside and connected to a signal processing unit 200 described below, and the second signal cable 133 buried in the external conductor 130 is led out to the outside and connected to the signal processing unit 200 .

[0055] like Figure 3 As shown, the bottom surface of the external conductor 130 cooperates with the fixing portion 101 of the object, and the fixing portion 101 is specifically implemented as a conductor so that the external conductor 130 can be electrically grounded. Figure 3 AA is a cross-sectional view of the sensor unit according to the embodiment of the present invention. In addition, both side ends of the external conductor 130 may be sealed to ensure airtightness.

[0056] In an embodiment, the fixing portion 101 may be a part of a frame body of a car, but is not limited thereto. For example, the external conductor 130 may be electrically connected to a conductive object at a location where the external conductor 130 is installed to ground the object.

[0057] The accommodation space 134 of the outer conductor 130 has an empty space which is not filled by the support portion 110 and the inner conductor 120. Figure 3 As shown, an air layer 140 is formed between the inner upper portion of the outer conductor 130 and the inner conductor 120 .

[0058] The first tip 121 of the inner conductor 120 and the second tip 131 of the outer conductor 130 are arranged to face each other with a certain distance d therebetween via the air layer 140. In a normal state with the certain distance d therebetween, the electrostatic capacitance of the outer conductor 130 and the inner conductor 120 can be set to a reference value.

[0059] If the soft external conductor 130 is squeezed due to the touch pressure applied by the human body and temporarily deforms, the interval between the first prong 121 and the second prong 131 relative to each other will become narrower. Since the interval between the first prong 121 and the second prong 131 is narrowed or widened by the touch pressure, the change of the electrostatic capacitance can be induced corresponding to the change of the interval. In an embodiment, the first prong 121 of the internal conductor 120 and the second prong 131 of the external conductor 130 are formed in a sawtooth shape. Since the relative first prong 121 and the second prong 131 are formed in a sawtooth shape, the relative surface area becomes larger when they are close to each other, so that the change of the electrostatic capacitance can be sensitively sensed.

[0060] When the external conductor 130 is squeezed by a human body approaching the sliding door, the second tip 131 of the external conductor 130 approaches the first tip 121 of the internal conductor 120, and the interval d changes with the displacement of the external conductor 130. By sensing the change in electrostatic capacitance corresponding to the interval d, it is possible to identify the phenomenon of the human body being pinched.

[0061] Figure 4 is a detailed circuit diagram of a sensor unit and a signal processing unit according to an embodiment of the present invention, Figure 5 is a graph showing electrostatic capacitance varying with touch pressure applied to a sensor portion by a human body according to an embodiment of the present invention.

[0062] like Figure 4 As shown, the sensor unit 100 can be described by an equivalent circuit composed of an electrostatic capacitor Cs and a resistor Rs. The interval d between the first tip 121 of the inner conductor 120 and the second tip 131 of the outer conductor 130 changes with the displacement of the outer conductor 130, and a sensing signal based on the electrostatic capacitor Cs and the resistor Rs corresponding to the change in the interval d is applied to the signal processing unit 200.

[0063] The electrostatic capacitance C of the sensor unit 100 can be expressed by the following equation 1.

[0064] (Mathematical formula 1)

[0065] C=εS / d

[0066] Wherein, d is the distance between the first tip of the inner conductor and the second tip of the outer conductor, S is the relative surface area between the first tip of the inner conductor and the second tip of the outer conductor, and ε is the dielectric constant.

[0067] refer to Figure 5 If the external conductor 130 is squeezed by the touch pressure applied by the human body and the interval d becomes narrower, the electrostatic capacitance C of the sensor unit 100 becomes larger than the first reference value Cth. If the electrostatic capacitance C becomes larger than the first reference value Cth, it can be considered that the pinching phenomenon (the left area of ​​point K) occurs.

[0068] On the other hand, if the touch pressure applied by the human body is released, the applied pressure is released, and thus the external conductor 130 returns to its original shape, so that the interval d becomes wider, and the electrostatic capacitance C of the sensor unit 100 becomes smaller than the first reference value Cth and converges to the initial value Co. If the electrostatic capacitance C becomes smaller than the first reference value Cth and converges to the initial value Co, it can be considered that it is a safe state (Safe) where the pinching phenomenon (Pinch) does not occur (the right area of ​​point K).

[0069] like Figure 4 As shown, the signal processing unit 200 compares the sensing signal of the sensor unit 100 with a reference value, and applies a pinching occurrence signal to the control unit 210 described below when the sliding door is pinched.

[0070] The signal processing unit 200 may include a first comparator 201 , a second comparator 202 , and an OR gate 203 .

[0071] The first comparator 201 compares the capacitance Cs sensed by the sensor unit 100 with a preset first reference value Cth. When the capacitance Cs is greater than the first reference value Cth, that is, when clamping occurs, a clamping occurrence signal is applied to an OR gate 203 .

[0072] On the other hand, if the pressure applied to the external conductor 130 is too great and the second prong 131 of the external conductor 130 and the first prong 121 of the internal conductor 120 are attached to each other, the capacitor property is lost. As a result, the clamping phenomenon of the human body corresponding to the change in electrostatic capacitance cannot be recognized.

[0073] In view of this, the second comparator 202 of the signal processing unit 200 described below is provided to sense a change in the resistance Rs between the two conductors 130 and 120 , thereby being able to recognize the occurrence of clamping.

[0074] The second comparator 202 converts the divided voltage Vs obtained by the resistance change sensed by the sensor unit 100 into A v is compared with the preset second reference value Vth. A If v is smaller than a preset second reference value Vth, it is recognized as a clamping phenomenon and a clamping occurrence signal is applied to an OR gate 203 .

[0075] The OR gate 203 receives the clamping occurrence signal of the first comparator 201 and the clamping occurrence signal of the second comparator 202 and outputs the received clamping occurrence signal to the control unit 210 .

[0076] like Figure 6 As shown, if the control unit 210 receives a clamping signal applied from the OR gate 203 of the signal processing unit 200, the driving motor will be stopped or driven in the opposite direction in order to control the motor driving unit 220 to move the sliding door, thereby preventing safety accidents caused by the human body being clamped. Figure 6 4 is a control block diagram of a device for preventing a human body from being clamped using a change in electrostatic capacitance according to an embodiment of the present invention.

[0077] In addition, the control unit 210 outputs a warning sound through the warning sound output unit 230 so that an external user can confirm that the pinching occurs.

[0078] The above description of the present invention is intended to be illustrative, and a person skilled in the art will appreciate that the present invention can be easily modified into other specific forms without changing the technical concept or essential features of the present invention.

Claims

1. A device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance, characterized in that: include: a sensor portion that senses a change in electrostatic capacitance corresponding to a gap between an outer conductor electrically grounded to the passive body and an inner conductor; a signal processing unit that compares the sensing signal of the sensor unit with a reference value and outputs a clamping occurrence signal indicating that a human body is clamped in the passive body; A motor driving unit that drives a motor to move the passive body; and a control unit which controls the motor drive unit to stop the passive body or move it in the opposite direction upon receiving the clamping occurrence signal input from the signal processing unit, Both ends of the outer conductor are sealed to ensure airtightness, and one end of the outer conductor and one end of the inner conductor are formed into a sawtooth shape so that the relative surface area between the outer conductor and the inner conductor becomes larger. The sensor unit integrates the external conductor, the internal conductor and the support unit. The support portion is matched between the external conductor and the internal conductor to prevent the external conductor and the internal conductor from directly contacting each other, thereby achieving electrical insulation. Protruding columns are vertically formed on both sides along the length direction, and a recessed mounting groove is formed between the protruding columns facing each other. The bottom surface of the internal conductor contacts the mounting groove, a pair of first slits extending along the length direction are formed on the outer side of the two side columns of the support portion, and a pair of first embedding protrusions extending along the length direction are formed on the inner side of the two side columns of the support portion. A pair of second embedding protrusions are formed on the inner side of the outer conductor, and the second embedding protrusions are engaged with the first slits of the support portion.

2. The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to claim 1, characterized in that: The passive body is a side door, a trunk door, a car window, a sunroof, an elevator door, or a subway door installed as an accessory of a car. The sensor portion is formed in a strip shape that is bent to correspond to the side shape of the passive body.

3. The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to claim 1, characterized in that: A pair of second slits extending along the length direction are formed on the outer sides of the two side pillars of the internal conductor. The first embedding protrusion of the support portion cooperates with the second slit.

4. The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to claim 1, characterized in that: The first signal cable buried in the internal conductor is led out to the outside and connected to the signal processing unit, and the second signal cable buried in the external conductor is led out to the outside and connected to the signal processing unit.

5. The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to claim 1, characterized in that: The sensor portion is formed by integrally molding the external conductor, the internal conductor, and the support portion using a triple injection molding machine.

6. The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to claim 1, characterized in that: The external conductor is made of a soft material that is squeezed by the touch pressure applied by the human body.

7. The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to claim 1, characterized in that: The external conductor and the internal conductor can be formed from a composite material of a thermoplastic elastomer and carbon nanotubes.

8. The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to claim 1, characterized in that: The support portion may be formed of a thermoplastic elastomer.

9. The device for preventing a human body from being clamped by utilizing a change in electrostatic capacitance according to claim 1, characterized in that: The sensor unit outputs changes in capacitance and resistance according to the distance between the external conductor and the internal conductor. The signal processing unit includes a first comparator for comparing the electrostatic capacitance sensed by the sensor unit with a preset first reference value, and a second comparator for comparing a divided voltage corresponding to a resistance change of the sensor unit with a preset second reference value. If the electrostatic capacitance sensed is greater than the first reference value, the first comparator outputs a clamping occurrence signal. If the divided voltage corresponding to the sensed resistance is smaller than the second reference value, the second comparator outputs a clamping occurrence signal.

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