JP2001171344A - Catching detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of a large signal in the event of catching through a pyroelectric effect which is generated by the temperature change of a piezoelectric sensor provided along a window frame of an automobile caused by direct sunlight or a change in an outside air temperature. SOLUTION: This detection device has the piezoelectric sensor 6 made of a flexible piezoelectric material, disposed in at least one of an opening/closing part 5 and an opening part 4, and generating an output signal according to deformation; an amplification means 21 amplifying the output signal when the piezoelectric sensor 6 is deformed; a decision means 22 deciding the catching of an object between the opening part 4 and the opening/closing part 5 on the basis of the output signal of the amplification means 21; and a discharge means 20 for discharging electric charges generated by the piezoelectric sensor 6, provided between two electrodes of the piezoelectric sensor 6. Thereby, the charges caused by the pyroelectric effect are quickly lost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pinch detection device for detecting a pinch of an object between an opening and an opening / closing section for opening / closing the opening.

[0002]

2. Description of the Related Art A conventional pinch detection device is disclosed, for example, in Japanese Patent Application Laid-Open No. Hei 10-132669. As shown in FIG. 13, a piezo cable 1 made of a high-molecular piezoelectric material such as polyvinylidene fluoride is disposed along a window frame 2 of an automobile, and a window frame 2 and a window glass are formed based on an output signal of the piezo cable 1. 3 is to detect that an object is caught between the object No. 3 and the object No. 3.

[0003]

However, in the conventional pinch detection device, since the piezo cable 1 is disposed along the window frame 2 of the automobile, the influence of the change of the outside air temperature and the change of the temperature due to the direct sunlight can be reduced. When the temperature of the piezo cable 1 changes, a voltage is generated due to the pyroelectric effect, and there is a problem that normal pinch detection cannot be performed.

In general, a piezoelectric element has a pyroelectric effect in addition to the piezoelectric effect. The pyroelectric effect is a phenomenon in which electric charge is accumulated on the surface of a piezoelectric material when the temperature of the piezoelectric material changes.
Further, the piezoelectric material has a capacitance C (farad), and when a charge Q (coulomb) is accumulated, a voltage V (volt) corresponding to a quotient obtained by dividing the charge Q by the capacitance C is generated. Will be. When the temperature of the piezo cable changes due to changes in the outside air temperature, etc., the temperature change occurs over almost the entire area of the piezo cable. A higher voltage is output from the piezo cable than the charge generated when deformed. further,
The charge once accumulated due to temperature change is not easily disappeared because the total amount is large, and the state where the high voltage is maintained lasts for a long time,
It took a long time to return to a state where normal pinch detection can be performed.

[0005]

In order to solve the above-mentioned problems, a pinch detecting device according to the present invention is provided with discharging means for discharging electric charges accumulated in a piezoelectric sensor.

Accordingly, even if charges due to the pyroelectric effect are generated in the piezoelectric sensor under the influence of changes in the outside air temperature, the charges can be quickly eliminated by the discharging means, and a high voltage is applied to the output of the piezoelectric sensor. It can be prevented from being maintained for a long time.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to solve the above-mentioned problems, a first aspect of the present invention will be described.
The invention of the opening, an opening and closing unit for opening and closing this opening,
A piezoelectric sensor, which is provided at at least one of the opening / closing portion and the opening and is made of a flexible piezoelectric material that generates an output signal according to deformation, and amplifies the output signal when the piezoelectric sensor is deformed; Amplifying means; determining means for determining whether an object is pinched between the opening and the opening / closing section based on an output signal of the amplifying means; and discharging the electric charge generated by the piezoelectric sensor between the two electrodes of the piezoelectric sensor In this case, even if charge due to the pyroelectric effect is generated in the piezoelectric sensor under the influence of a change in the outside air temperature, the charge can be quickly eliminated by the discharge means.

[0008] The invention described in claim 2 is the first invention.
The discharge means in the invention described in (1) is a resistor connected in parallel between two electrodes of the piezoelectric sensor, and can discharge electric charges generated in the piezoelectric sensor due to a temperature change with a very simple configuration.

The invention described in claim 3 is the same as the invention in claim 2
The reciprocal of the time constant determined by the product of the resistance value of the discharging means and the capacitance value of the piezoelectric sensor according to the invention described in the above, is the basic value of the signal generated when an object is sandwiched between the opening and the opening / closing part. By selecting so as to be smaller than 10 times the angular frequency expression value of the frequency, the charge generated in the piezoelectric sensor due to a temperature change without greatly attenuating the signal amplitude of the fundamental frequency output from the piezoelectric sensor at the time of pinch detection. Can be quickly discharged.

[0010] The invention described in claim 4 is the first invention.
The electric discharge means in the invention described in the above is discharged by discharging the electric charge generated in the piezoelectric sensor immediately before judging the presence or absence of entrapment, and by controlling not to discharge the electric charge generated in the piezoelectric sensor when judging the existence of the entrapment, The charge generated in the piezoelectric sensor due to the temperature change can be discharged without causing a loss in the signal amplitude output from the piezoelectric sensor at the time of detection.

[0011] The invention described in claim 5 is the same as in claim 4.
The discharge means in the invention described in (1) can be very easily controlled whether or not to discharge by constituting an electric circuit switching element such as a switch.

[0012] The invention according to claim 6 is the same as the invention according to claim 5.
Since the electric circuit switching element according to the invention described in (1) is closed at predetermined time intervals by a signal from the transmitter, a discharging operation can be performed periodically.

The invention according to claim 7 is the first invention.
The discharge means according to the invention described in (1) discharges the electric charge generated in the piezoelectric sensor immediately after the opening / closing section starts the closing operation, and controls the electric discharge generated in the piezoelectric sensor not to discharge in the other operation, thereby detecting the entrapment. The electric charge generated in the piezoelectric sensor due to the temperature change can be discharged without causing a loss in the signal amplitude output from the piezoelectric sensor.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is an external view of an entrapment detection apparatus according to an embodiment of the present invention, which is applied to a power window of an automobile. FIG. 2 (a), (b)
2A is a cross-sectional view taken along the line AA ′ in FIG. 1, and FIG. 2A illustrates a state where the object M is not sandwiched, and FIG. 2B illustrates a state where the object M is sandwiched.

First, from FIG. 1, reference numeral 4 denotes a window frame as an opening,
Reference numeral 5 denotes a window glass as an opening / closing unit. A piezoelectric sensor 6 is arranged on the periphery of the window frame 4. Reference numeral 7 denotes a circuit unit including an amplifying means for amplifying an output signal of the piezoelectric sensor 6 and a judging means for judging whether or not an object is caught between the window frame 4 and the window glass 5 based on the signal. It is arranged in the door body near the mirror mounting position.

Reference numeral 8 denotes a power window driving device;
Is control means for controlling the power window driving device 8. Here, the power window driving device 8 includes a motor 8a,
It comprises a wire 8b, a support 8c for the window glass 5 and a guide 8d. The wire 8b is moved by the motor 8a,
The window glass 5 is opened and closed by raising and lowering the support 8c connected to the guide b along the guide 8d. The power window driving device 8 is not limited to the above-described system using wires, but may be another system. The control means 9 may be integrated with the motor 8a.

As shown in FIGS. 2A and 2B, the piezoelectric sensor 6 is provided so as to be wrapped in an elastic body 17 having a supporting portion 10. The support portion 10 of the elastic body 17 is supported by the window frame 4 by being fitted into a slot 12 formed in the window frame 4. When the object M is sandwiched between the window frame 4 and the window glass 5 as shown in FIG. 2B, the elastic body 17 bendably deforms, and naturally, the piezoelectric sensor 6 inside also deforms. 1
3 is a weather strip. The elastic body 17 is the window glass 5
Are supported by the window frame 4 so as to be substantially parallel to the opening / closing direction. 2A and 2B, the left side of the window glass 5 is the vehicle interior, and the right side is the vehicle exterior.

FIGS. 3A and 3B are external views of the elastic body 17 enclosing the piezoelectric sensor 6. FIG. FIG. 3A shows the object M
3 (b) shows a state in which the object M is sandwiched, and FIG. 3 (b) is a view of the elastic body 17 in FIG. is there. FIG. 4 shows the structure of the piezoelectric sensor 6, in which a flexible core electrode 16 is provided at the center, and a piezoelectric layer is formed by mixing a rubber-elastic organic base material with a sintered powder of piezoelectric ceramic. 14, a flexible shield electrode 15 is wrapped therearound, and the outermost part is entirely wrapped with an outer skin 18, and has an appearance similar to a general shield wire. Lastly, the piezoelectric sensor 6 is configured by performing a polarization process, has excellent flexibility, and generates an output signal corresponding to deformation. As the rubber elastic body, for example, chlorinated polyethylene is used, and as the piezoelectric ceramic, for example, a sintered powder of lead zirconate titanate is used.

The circuit unit 7 including the amplifying means and the judging means is directly connected to the end of the piezoelectric sensor 6 as shown in FIG. Therefore, a lead wire or a connector for connecting between the piezoelectric sensor 6 and the circuit unit 7 becomes unnecessary.

FIG. 5 is a block diagram of a circuit for receiving and processing an output signal of the piezoelectric sensor 6 of the pinch detection device according to the embodiment of the present invention. Reference numeral 20 denotes a discharging means, which is constituted by a resistor. One end is connected to the core electrode 16 of the piezoelectric sensor 6, and the other end is connected to the shield electrode 15 of the piezoelectric sensor 6. 2
Reference numeral 1 denotes an amplifying means, and a non-inverting input terminal 21a is connected to the piezoelectric sensor 6
, The inverting input terminal 21 b is connected to the piezoelectric sensor 6.
Are connected to the shield electrode 15. This amplification means 2
When there is no signal from the piezoelectric sensor 6 in the output 1, a DC voltage of 2.5 V is normally output. Broken line frame 22
Indicates a determination means. The contents of the judging means 22 include a comparator 23 and a reference voltage source 25. Amplifier 21
Is connected to the inverting input 23b of the comparator 23. The reference voltage source 25 is a non-inverting input 2 of the comparator 23.
3a. Here, the reference voltage source 25 is 3 volts. Therefore, there is no signal from the amplifying means 21 and 2.
When the voltage is around 5 volts, the output of the comparator 23 is at a high level. On the other hand, when the signal from the amplifying means 21 exceeds 3 volts, the output of the comparator 23 becomes low level.

FIG. 6A shows the output of the amplifying means 21 when the object M is sandwiched, and FIG. 6B shows the output of the judging means 22. When the object M is interposed, the piezoelectric sensor 6
The signal is deformed as shown in (b), and as a result, a signal having a waveform as shown in FIG. As shown in FIG. 6 (b), when the signal from the amplifying means 21 exceeds 3 volts, the output of the comparator 23 becomes low level.

Next, the operation will be described. FIG. 7 shows how the output voltage of the piezoelectric sensor 6 changes when the temperature of the piezoelectric sensor 6 slightly increases under the influence of a change in the outside air temperature. When the discharge resistor 20a is not provided, the generated voltage does not return to the original level even after a lapse of time as shown by the broken line in FIG. This is because the temperature change of the piezoelectric sensor 6 has occurred over almost the entirety, so that the total amount of charges generated by the pyroelectric effect is very large and it takes a lot of time to spontaneously disappear. However, when the resistor 20a, which is the discharging means 20, is attached, the charge generated by the pyroelectric effect is discharged by the resistor 20a as shown by the solid line in FIG. And return to the original reference level again. Here, the slope of the rise of the voltage without the resistor 20a shown by the broken line in FIG. 7 depends on the speed at which the temperature of the piezoelectric sensor 6 rises. The voltage at this time increases as the temperature change increases. Then, the smaller the value of the resistor 20a, the earlier the time to return to the original reference level after discharging. However, if the value of the resistor 20a is too small, the amplitude of a signal obtained when an object is sandwiched becomes small. FIG. 8 is an equivalent circuit diagram of a circuit for extracting a voltage generated in the piezoelectric sensor 6. Reference numeral 27 denotes a signal generated by the piezoelectric sensor 6 as a voltage source, and reference numeral 28 denotes a capacitance component of the piezoelectric sensor 6 as a capacitor. The voltage source 27, the capacitor 28, and the resistor 20a as the discharging means 20 are They are connected in series. As is apparent from FIG. 8, the signal from the voltage source 27 is applied to the resistor 20a through the capacitor. Therefore, the signal from the voltage source 27, that is, the signal from the piezoelectric sensor 6 is applied to the capacitor 28 and the resistor 20.
As a result, the lower frequency components pass through the high-pass filter composed of the resistor 20a, and are less likely to appear at both ends of the resistor 20a. FIG. 9 is a frequency characteristic diagram of a high-pass filter including the capacitor 28 and the resistor 20a, and shows how much a signal of each frequency output from the voltage source 27 is attenuated and appears on the resistor 20a. In FIG. 9, the horizontal axis represents frequency (Hz) and expressed on a logarithmic scale, and the vertical axis represents signal level and expressed on a logarithmic scale in decibels (dB). Further, f _c that is noted in the frequency axis is high-pass filter cutoff frequency comprised of a capacitor 28 resistor 20a, a frequency component higher than this frequency f _c appears in the resistance 20a without being too attenuated.
However, at frequencies lower than f _c, the attenuation as the frequency becomes lower hardly appear in greater becomes the resistance 20a,
If the frequency is reduced to 1/10, the amount of attenuation is 10 times (20 dB)
become. The cut-off frequency f _c by using the resistance value R (ohm) of the capacitance C (in farads) and the resistance 20a of the capacitor 28

[0024]

(Equation 1) When this is expressed by the angular frequency ωc,

[0025]

(Equation 2) And is the reciprocal of a time constant determined by the capacitance C of the capacitor 28 and the resistance value R of the resistor 20a.

The capacitance of the piezoelectric sensor 6 used in the present embodiment varies depending on the length.
000 pF. The fundamental frequency component of the signal output from the piezoelectric sensor when the pinch occurs is about 10 Hz, depending on the conditions at the time of the pinch. Therefore, 10
In order for a Hz signal to appear through a 2000pF capacitor to the resistor 20a without significant attenuation

[0027]

(Equation 3) Or

[0028]

(Equation 4) It is necessary to use a resistor having a resistance value larger than R _c represented by 2000pF to C of equation (3), substituting 10Hz to f _c R _c is about 8Emuomega. The time constant at this time is C
× R _c , which is approximately 16 milliseconds.
The charge generated due to the change of the temperature is discharged and about 37% of the initial
Indicates the time required to decrease to. The time required for the generated charge due to the change in the temperature of the piezoelectric sensor 6 to be completely negligible is considered to be 10 times or more the time constant, and in this case, it is about 160 times.
Milliseconds.

Here, the value of the resistor 20a is calculated with the target of the signal attenuation being approximately 0 dB. However, the amplification factor of the amplifying means 21 is increased, and the voltage values of the reference voltage sources 25 and 26 of the judging means 22 are amplified. By further approaching the twenty-one reference level of 2.5 volts, the signal attenuation is reduced by about one tenth (−2).
If it is up to 0 dB), it is considered that it can be complemented. Thus the cut-off frequency f _c is sufficiently complementary can signal level if up to 10 times the 100Hz of 10 Hz. The resistance value of the resistor 20a when the cutoff frequency is 100 Hz is
2000pF to C of equation (2) is about 800kΩ Substituting 100Hz to f _c. The time constant at this time is calculated by C × R _c , and is about 1.6 milliseconds. The time required for the temperature of the piezoelectric sensor 6 to change to a negligible amount of the generated electric charge is the same as described above. Is calculated to be about 16 milliseconds, which means that discharge can be performed even faster.

As described above, according to the embodiment of the present invention, the resistance value R of the discharging means 20 is changed to the capacitance value C of the piezoelectric sensor 6.
By selecting such that the reciprocal of the time constant determined by the product of is smaller than 10 times the angular frequency expression value of the fundamental frequency of the signal generated when an object is sandwiched between the opening and the opening / closing section, The charge generated by the temperature change can be discharged quickly without attenuating the signal component at the time of entrapment to the extent that it cannot be complemented, and even if the temperature of the piezoelectric sensor changes due to the change of the outside air temperature, the object will be interposed normally. It can be detected.

(Embodiment 2) In FIG. 10, the same parts as in FIG. 5 of Embodiment 1 will not be described. Reference numeral 30 denotes an opening / closing section of a relay serving as an electric circuit opening / closing element of the discharging means. Reference numeral 31 denotes an exciting coil of a relay for moving the opening / closing section 30 by magnetic force. Reference numeral 32 denotes a relay drive unit for stopping or supplying a current to the exciting coil 31. Reference numeral 33 denotes a transmitter that periodically sends a control signal to the relay driving unit 32 to close or open the relay opening / closing unit 30 to determine the discharge timing of the electric charge accumulated in the piezoelectric sensor 6.

Next, the operation will be described. FIG. 11 shows a periodic clock signal output from the transmitter 33. When the relay drive unit 32 is at the high level,
A current is supplied to 1 to close the opening / closing section 30. The period T is 1 second in this embodiment, and the pulse width is 10 milliseconds. Therefore, when the open / close portion of the relay is closed for 10 milliseconds every second, all the electric charges generated in the previous one second are discharged.
At this time, the charge is discharged instantaneously because the discharge resistance is extremely small. For this reason, the determination unit 22 only has to observe the output signal of the amplifier 21 during about one second when the output clock of the transmitter 33 changes from the high level to the low level and then changes to the high level.

As described above, according to the embodiment of the present invention, the switching unit 30 of the relay, which is an electric circuit switching element, is connected to the transmitter 33.
It is closed at regular time intervals by the clock signal, so that the discharging operation can be performed periodically and the charge generated by the temperature change does not continue to accumulate forever, and the discharging means is in the open state when judging the presence or absence of entrapment. For this reason, the pinch signal can be received without signal attenuation.

(Embodiment 3) In FIG. 12, the same parts as those in FIG. 5 of Embodiment 1 and FIG. 10 of Embodiment 2 will not be described. Reference numeral 34 denotes a discharge control unit, which sends a signal to the relay drive unit 32 while adjusting the timing to the control signal output by the power window control means 9 shown in FIG.

Next, the operation will be described. The power window control means 9 has a signal line 9a for outputting a high-level signal when the window glass 5 is closed, and outputs a high-level signal on the signal line 9b when the window glass 5 is opened. When detecting the change of the signal line 9a from the low level to the high level, the discharge control unit 34 outputs a high-level signal to the relay drive unit 32 for about 10 milliseconds to close the relay opening / closing unit 30 to close the piezoelectric unit. The electric charge accumulated in the sensor 6 is discharged.

As described above, the determination unit 22 ignores the output signal of the amplifying unit 21 only for 10 milliseconds immediately after the output signal of the control unit 9a changes from the low level to the high level. A state that is likely to occur,
Immediately after the window glass 5 starts closing, the electric charge accumulated due to the temperature change of the piezoelectric sensor 6 has already disappeared by the discharge, and it is possible to correctly determine the presence or absence of the pinch.

[0037]

As described above, according to the first aspect of the present invention, the provision of the discharging means for discharging the electric charge generated by the piezoelectric sensor provides the piezoelectric sensor with the influence of the change of the outside air temperature. It is possible to realize an excellent entrapment detection device capable of quickly eliminating charges by the discharging means even if charges are generated due to the pyroelectric effect.

According to the second aspect of the present invention, the electric charge generated in the piezoelectric sensor due to the temperature change can be discharged with a very simple configuration in which a resistor is simply connected between the electrodes of the piezoelectric sensor.

According to the third aspect of the present invention, the reciprocal of the time constant determined by the product of the resistance value of the discharging means and the capacitance value of the piezoelectric sensor is an object between the opening and the opening / closing section. The signal amplitude of the fundamental frequency output from the piezoelectric sensor at the time of pinch detection is greatly attenuated by selecting so that it is smaller than 10 times the angular frequency expression value of the fundamental frequency of the signal generated when the pinch is pinched. In addition, electric charges generated in the piezoelectric sensor due to a temperature change can be quickly discharged.

According to the fourth aspect of the present invention, the electric charge generated in the piezoelectric sensor is discharged immediately before judging the presence or absence of the electric discharge means, and the electric charge generated in the piezoelectric sensor when judging the existence of the electric charge is judged. Is controlled so as not to be discharged, the electric charge generated in the piezoelectric sensor due to the temperature change can be discharged without giving any loss to the signal amplitude output from the piezoelectric sensor at the time of pinch detection.

Further, according to the fifth aspect of the present invention, the control of whether or not to discharge can be performed very easily by configuring the discharging means with an electric circuit switching element such as a switch.

According to the sixth aspect of the present invention, the electric circuit switching element is closed at regular intervals by the signal of the transmitter, so that the charge generated by the temperature change does not continue to be accumulated forever. Further, when judging the presence or absence of the jamming, since the discharging means is in the open state, the jamming signal can be received without signal attenuation.

According to the present invention, the electric charge generated in the piezoelectric sensor is discharged immediately after the opening / closing section of the discharging means starts the closing operation, and the electric charge generated in the piezoelectric sensor in other operations. By controlling so as not to discharge, it is possible to discharge the electric charge generated in the piezoelectric sensor due to temperature change without causing loss in the signal amplitude output from the piezoelectric sensor at the time of pinch detection and receive the pinch signal without signal attenuation. Can be.

[Brief description of the drawings]

FIG. 1 is an external view of a pinch detection device according to a first embodiment of the present invention.

FIG. 2A is a cross-sectional view of a state in which an object in a window frame to which the piezoelectric sensor is attached is not sandwiched; FIG. 2B is a cross-sectional view of a state in which an object in a window frame to which the piezoelectric sensor is attached is sandwiched;

FIG. 3A is an external view of an elastic body containing the piezoelectric sensor. FIG. 3B is an external view of an elastic body containing the piezoelectric sensor sandwiched therebetween.

FIG. 4 is a structural diagram of the piezoelectric sensor.

FIG. 5 is a configuration diagram of a signal processing circuit of the piezoelectric sensor.

FIG. 6A is an output signal waveform diagram of the amplifying unit. FIG. 6B is an output diagram of the amplifying unit.

FIG. 7 is a signal waveform diagram of the piezoelectric sensor.

FIG. 8 is an equivalent circuit diagram of the high-pass filter.

FIG. 9 is a frequency characteristic diagram of the high-pass filter.

FIG. 10 is a configuration diagram of a signal processing circuit of a piezoelectric sensor according to a second embodiment of the present invention.

FIG. 11 is a signal waveform diagram of the transmitter.

FIG. 12 is a configuration diagram of a signal processing circuit of a piezoelectric sensor according to a third embodiment of the present invention.

FIG. 13 is an external view of a conventional pinch detection device.

[Explanation of symbols]

 Reference Signs List 4 window frame (opening part) 5 window glass (opening / closing part) 6 piezoelectric sensor 10 support part 12 slot 13 weather strip 14 piezoelectric layer 15 shield electrode 16 core electrode 17 elastic body 18 skin 20 discharge means 21 amplifying means 22 Judging means 23 Comparator 25 Reference voltage source 27 Voltage source 28 Capacitor 30 Relay opening / closing unit 31 Relay excitation coil 32 Relay drive unit 33 Transmitter 34 Discharge control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01H 35/00 H01H 35/00 Q (72) Inventor Koji Yoshino 1006 Kazuma Kazuma, Kadoma City, Osaka Matsushita Electric Industrial Incorporated (72) Inventor Biao Nagai 1006 Kadoma, Kadoma, Osaka Pref.Matsushita Electric Industrial Co., Ltd. (72) Inventor Yu Fukuda 1006 Odaka, Kadoma, Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. (72) Inventor Masahiko Ito 1006 Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor: Yuko Fujii 1006 Kadoma, Kazuma, Kadoma, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. GA08 GB06 KA13 KA15 KA16 3D127 AA02 AA07 BB01 CB05 CC05 DF04 DF35 FF14 FF17 5G006 AA07 LG02 5G055 DB01 DD06 DD29 DD34 DG02

Claims (7)

[Claims] An opening, an opening / closing unit for opening and closing the opening, and a flexible piezoelectric material disposed at at least one of the opening / closing unit and the opening to generate an output signal according to deformation. A piezoelectric sensor comprising: amplifying means for amplifying an output signal when the piezoelectric sensor is deformed; and a judging means for judging whether an object is pinched between the opening and the opening / closing part based on an output signal of the amplifying means. And a discharge detecting device for discharging electric charges generated by the piezoelectric sensor between two electrodes of the piezoelectric sensor. 2. The pinch detecting device according to claim 1, wherein the discharging means is a resistor connected in parallel between the two electrodes of the piezoelectric sensor. 3. The resistance value of the discharging means has a reciprocal of a time constant determined by a product of a capacitance value of the piezoelectric sensor and a signal generated when an object is sandwiched between the opening and the opening / closing section. 3. The pinch detection device according to claim 2, wherein the pinch detection device is selected to be smaller than ten times the angular frequency expression value of the fundamental frequency. 4. The pinch detection according to claim 1, wherein the discharging means discharges the electric charge generated in the piezoelectric sensor immediately before judging the presence or absence of the jamming, and does not discharge the electric charge generated in the piezoelectric sensor when judging the existence of the jamming. apparatus. 5. The pinch detection device according to claim 4, wherein the discharging means comprises an electric circuit switching element such as a switch. 6. The pinch detecting device according to claim 5, further comprising a transmitter for generating an electric signal for closing the electric circuit switching element at a constant cycle. 7. The pinch detection device according to claim 1, wherein the discharging means discharges the electric charge generated in the piezoelectric sensor immediately after the opening / closing section starts the closing operation.