JPH10148653A - Device for detecting disconnection of piezoelectric film sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the disconnection and damage of a piezoelectric film sensor by comparing the DC output voltage of a DC conversion means with a reference voltage. SOLUTION: The high-frequency signal of an oscillator 2 transmitted through an FET amplifier 3 is detected by a detector 5, the detected high-frequency component becomes a DC voltage at an integrator 7, is outputted to a comparator 8, and is compared with a reference voltage. A DC voltage that is outputted from the integrator 7 becomes a constant voltage while the piezoelectric film sensor 1 is operating normally, so that the difference to the reference voltage of the comparator 8 also becomes constant. When the piezoelectric sensor 1 is disconnected or damaged, a high-frequency signal that passes through the piezoelectric film sensor 1 reaches zero or decreases, so that a DC voltage that is outputted from the integrator 7 also changes accordingly, a difference to the reference voltage of the comparator 8 is generated, and a light-emitting diode 9 for display is turned on to send an alarm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disconnection detecting device for a piezoelectric film sensor such as a piezo film or a Kyner film used for detecting contact with an object or pressing of an object.

[0002]

2. Description of the Related Art Piezo film and Kynar film and other piezoelectric film sensors have very small thicknesses, so they can be applied to touch sensors that are installed in small places where the mounting location is small and thin. It is widely used as a safety sensor for stopping a function when a person or an object comes into contact, or for issuing an alarm.

[0003]

A piezoelectric film sensor such as a piezo film or a Kynar film has an advantage that chattering can be completely eliminated by using an FET circuit for a signal amplifier circuit, but the sensor itself is a dielectric material. Therefore, even if a direct current is passed and the current is monitored, the disconnection of the sensor cannot be detected, and it cannot be known whether or not the sensor is operating normally. There was a problem.

An object of the present invention is to solve the above-mentioned problems. An object of the present invention is to supply a high-frequency current by utilizing a function of a piezoelectric film sensor as a capacitor, or to provide a capacitance as a capacitor. It is an object of the present invention to provide a disconnection detecting device for a piezoelectric film sensor which can detect whether or not the piezoelectric film sensor is operating normally by using the device as an oscillation element.

[0005]

According to a first aspect of the present invention, there is provided an apparatus for detecting disconnection of a piezoelectric film sensor, comprising: a high-frequency oscillator for supplying a high-frequency current to the piezoelectric film sensor; Amplifier for amplifying the high-frequency current sent thereto, DC conversion means for converting the output signal of the amplifier into a DC voltage, and disconnection of the piezoelectric film sensor by comparing the DC output voltage of the DC conversion means with a reference voltage. Alternatively, a comparator for detecting breakage is provided.

Preferably, the amplifier is an FET amplifier as described in claim 2, and the DC converter is constituted by a detector and an integrator as described in claim 3. It is desirable to do.

According to another aspect of the present invention, there is provided a piezoelectric film sensor disconnection detecting device, comprising: an oscillator incorporating a capacitance as a capacitor of the piezoelectric film sensor as an oscillation frequency determining element; A low-pass filter whose pass band is set so as to pass the oscillation output of the oscillator when the sensor is normal, and block the oscillation output when the piezoelectric film sensor is disconnected, and through the low-pass filter A frequency detection circuit for detecting and monitoring an oscillation output obtained when the piezoelectric film sensor is normal from the transmitted oscillation signal, and outputting a disconnection detection signal when the oscillation output is no longer obtained; The oscillation output of the oscillator sent via the sensor is converted into a DC voltage, and the converted DC voltage is used as a reference voltage. It is characterized in that a short-circuit detecting circuit for detecting a short circuit of the piezoelectric film sensor by compare.

It is preferable that the oscillator comprises a multivibrator oscillating circuit.

[0009]

FIG. 1 shows a first embodiment of a disconnection device for a piezoelectric film sensor according to the present invention. This first
The first embodiment shows an example in which a high-frequency current is supplied to a piezoelectric film sensor and the disconnection or breakage of the piezoelectric film sensor is detected by monitoring the high-frequency current.

In FIG. 1, reference numeral 1 denotes a piezoelectric film such as a piezo film or a Kynar film, and a high-frequency oscillator 2 is applied to a negative lead 1a, and an impedance is converted to a positive lead 1b to facilitate handling. An FET amplifier 3 for stabilizing the output is connected.

The oscillator 2 is connected to an inverter circuit 4 for inverting the phase of the high-frequency oscillation output of the oscillator 2 by 180 degrees, and the FET amplifier 3 includes a detector 5 and the F
An arithmetic circuit 6 that adds the high-frequency signal from the ET amplifier 3 and the high-frequency signal whose phase has been inverted by 180 degrees from the inverter circuit 4 is connected.

A comparator 8 is connected to the detector 5 via an integrator 7. Reference numeral 9 denotes a light-emitting diode that is turned on when the piezoelectric film sensor 1 is disconnected or damaged.

Next, the operation of the circuit will be described. A high-frequency signal is supplied from an oscillator 2 to a lead wire 1a on the negative side of the piezoelectric film sensor 1, and this high-frequency signal is combined with an output signal of the piezoelectric film sensor itself via the capacitance of the piezoelectric film sensor to generate a positive signal. Output to lead wire 1b.

This output signal is impedance-converted by the FET amplifier 3 and output to the detector 5 and the arithmetic circuit 6.
Since the high-frequency signal whose phase has been inverted by 180 degrees from the oscillator 2 via the inverter circuit 4 is input to the arithmetic circuit 6, the arithmetic circuit 6 adds the output from the FET amplifier 3 and the output from the inverter circuit 4. Output.

That is, since the high-frequency signal sent from the FET amplifier 3 and the high-frequency signal sent from the inverter circuit 4 have the same magnitude and opposite phases, these signals are added by the arithmetic circuit 6. It becomes zero, and only the piezoelectric signal generated by the piezoelectric film sensor itself is output from the arithmetic circuit 6. Therefore, when an external force is applied to the piezoelectric film sensor 1, a signal is output from the output terminal of the arithmetic circuit 6, and it is detected that an external pressure is applied to the piezoelectric film sensor 1.

On the other hand, the high-frequency signal of the oscillator 2 sent through the FET amplifier 3 is detected by the detector 5,
The detected high-frequency component becomes a DC voltage after a time constant determined by the integrator 7, is output to the comparator 8, and is compared with the reference voltage. Here, the DC voltage output from the integrator 7 is a constant voltage when the piezoelectric film sensor 1 is operating normally, so that the difference from the reference voltage of the comparator 8 is also constant.

When the piezoelectric film sensor 1 is disconnected or damaged, the high-frequency signal passing through the piezoelectric film sensor 1 is reduced to zero or reduced, so that the DC voltage output from the integrator 7 changes accordingly. The difference from the reference voltage of the comparator 8 is generated, and the light emitting diode 9 for display is turned on.

Note that a buzzer or the like may be sounded in place of turning on the light emitting diode 9, or when the sensor is applied to a sensor for stopping a function when a person or an object comes into contact, the function may be disabled. May be automatically stopped.

FIG. 2 shows a second embodiment of the disconnection device for a piezoelectric film sensor according to the present invention. The second embodiment is an example in which the capacitance of a piezoelectric film sensor is used as an oscillation element of an oscillator, and disconnection or breakage of the piezoelectric film sensor is detected from a change in the oscillation frequency of the oscillator. It is shown.

In FIG. 2, reference numeral 11 denotes a piezoelectric film sensor such as a piezo film or a Kynar film. The piezoelectric film sensor 11 includes an impedance conversion circuit 12 such as an FET amplifier, a multivibrator oscillation circuit 1 and the like.
3. The short detection circuit 14 is connected.

The multivibrator oscillating circuit 13 is an oscillating circuit in which the capacitance as a capacitor of the piezoelectric film sensor 11 is incorporated as an oscillating frequency determining element.
It is configured to oscillate at a predetermined oscillation frequency f _S determined by a time constant CR between the capacitance and the resistance inside the circuit. The oscillation frequency f _S, together are set to be the maximum frequency f _MAX high frequency f _S than that contained in the piezoelectric signal that is generated when the piezoelectric film sensor 11 is pressed by an external force, the piezoelectric film sensor 11 Is broken, the time constant CR becomes small and the oscillation frequency becomes f _S
Higher f _D becomes than, the piezoelectric film sensor 11
Is configured to stop oscillation when a short circuit occurs.

The low-pass filter 14 is a piezoelectric film cell.
Oscillation output f when the sensor 11 is normal _SLet through,
Oscillation output f when the piezoelectric film sensor 11 is disconnected_D
Is a filter whose passband is set to reject
is there. The frequency detection circuit 15 controls the low-pass filter 14
From the incoming oscillation signal
Oscillation output f obtained when the system sensor 11 is normal_SExtract
Out and monitor the oscillation output f_SIs no longer available
Is a circuit for outputting a disconnection detection signal.

The low-pass filter 16 removes the oscillating outputs f _S and f _D of the multivibrator oscillating circuit 13 wrapping around via the piezoelectric film sensor 11 and is generated when the piezoelectric film sensor 11 is pressed by an external force. F
_This filter allows only a piezoelectric signal having a frequency component equal to or lower than _MAX to pass. The monostable multivibrator circuit 17 is a circuit that outputs a touch detection signal having a constant pulse width when receiving a piezoelectric signal transmitted through the low-pass filter 16.

Although not shown, the short-circuit detection circuit 18 includes a circuit similar to the detection circuit 5, the integrator 7 and the comparator 8 shown in FIG. After converting the oscillation output of the obtained multivibrator oscillation circuit 13 into a DC voltage, the circuit detects the short-circuit of the piezoelectric film sensor 11 by comparing the converted DC voltage with a reference voltage, and outputs a short-circuit detection signal. is there.

The output circuit 19 is connected to the frequency detection circuit 1
5, monostable multivibrator circuit 17,
This is a circuit that outputs a desired control signal based on each detection signal from the short detection circuit 18.

Next, the operation of the circuit will be described. Piezoelectric
If the film sensor 11 is normal,
The oscillator circuit 13 has a predetermined oscillation frequency f_SAlways
Oscillating. Therefore, the oscillation output f _SIs a low pass
It passes through the filter 14 and is sent to the frequency detection circuit 15
If the piezoelectric film sensor 11 is normal, the frequency
The detection circuit 15 does not output a disconnection detection signal. Ma
The oscillation output f_SThrough the piezoelectric film sensor 11
Is also sent to the short detection circuit 18 so that
A short detection signal is also output from the detection circuit 18.
There is no.

Further, the oscillation output f _S is also sent to the impedance conversion circuit 12 where it is amplified, and the amplified oscillation output f _S is supplied to the low-pass filter 1
6 and is not sent to the monostable multivibrator circuit 17. Therefore, when the piezoelectric film sensor 11 is normal, only the piezoelectric signal having a frequency component equal to or lower than f _MAX can pass through the low-pass filter 16. As a result, the piezoelectric signal is sent to the monostable multivibrator circuit 17 only when the piezoelectric film sensor 11 is pressed, and the touch detection signal indicating that the piezoelectric film sensor 11 is pressed from the monostable multivibrator circuit 17. Is output.

On the other hand, the piezoelectric film sensor 11 was disconnected.
In this case, the CR time constant for determining the oscillation frequency is small.
Therefore, the oscillation frequency of the multivibrator oscillation circuit 13
Is f _STo f_DTo be higher. Therefore, the high frequency
Oscillation output f_DIs the value that passes through the low-pass filter 14.
Is blocked because it cannot be sent to the frequency detection detection circuit 15.
No longer. Therefore, the piezoelectric film sensor 11 is disconnected.
The oscillation output is not sent to the frequency detection circuit 15.
And the disconnection detection signal is output from the frequency detection circuit 15.
Is forced.

When the piezoelectric film sensor 11 is short-circuited, the capacitance C of the piezoelectric film sensor 11 that determines the oscillation frequency is lost, so that the multivibrator oscillation circuit 13 stops the oscillation. Therefore, the oscillation output is not sent to the short detection circuit 18 via the piezoelectric film sensor 11, so that the DC voltage obtained by the short detection circuit 18 becomes smaller than the reference voltage, and the short detection signal is output from the short detection circuit 18. You.

When receiving the touch detection signal from the monostable multivibrator circuit 17, the output circuit 19 generates an output for performing a predetermined control operation and sends it to a predetermined circuit. When a disconnection detection signal is received from the frequency detection circuit 15, a light-emitting diode or the like (not shown) for displaying a disconnection is turned on.
When a short-circuit detection signal is received from 8, a short-circuit display light-emitting diode (not shown) or the like is turned on to notify that an abnormality has occurred in the piezoelectric film sensor 11.

Also in the second embodiment, a buzzer or the like may be sounded instead of turning on the light emitting diode or the like, or a sensor for stopping the function when a person or an object comes into contact. In the case of applying the function, the function may be automatically stopped.

[0032]

As described above, according to the first aspect of the present invention, the oscillation output of the high-frequency oscillator transmitted through the piezoelectric film sensor is amplified by the amplifier, and the amplified high-frequency output is converted to the direct current. After converting to a DC voltage by the conversion means, the comparator is compared with a reference voltage to detect disconnection or breakage of the piezoelectric film sensor, thereby affecting the piezoelectric signal output from the piezoelectric film sensor. Therefore, disconnection of the wiring system of the piezoelectric film sensor and breakage of the piezoelectric film sensor itself can be reliably detected. For this reason, a piezoelectric film sensor excellent in safety can be provided.

According to the second aspect of the present invention,
According to the first aspect of the present invention, since the amplifier is constituted by the FET amplifier, impedance matching can be achieved, and more stable operation can be performed.

According to the third aspect of the present invention,
In the first or second aspect of the present invention, since the DC conversion means is constituted by the detector and the integrator, the high-frequency component is output to the comparator as a DC voltage after a time constant determined by the integrator. In addition, a detection signal is not output due to unexpected pulsation of a high frequency component or the like, and more stable operation can be realized.

According to the fourth aspect of the present invention,
The capacitance as a capacitor of the piezoelectric film sensor is incorporated as an oscillation frequency determining element of the oscillator, and by monitoring the frequency change of the oscillation output of the oscillator, breakage of the piezoelectric film sensor such as disconnection or short circuit is detected. Therefore, disconnection of the wiring system of the piezoelectric film sensor and damage to the piezoelectric film sensor itself can be reliably detected without affecting the piezoelectric signal output from the piezoelectric film sensor. For this reason, a piezoelectric film sensor excellent in safety can be provided.

Further, according to the fifth aspect of the present invention, in the fourth aspect of the present invention, since the oscillator is constituted by a multivibrator oscillation circuit, the capacitance and the capacitance can be reduced without using an expensive and large-volume inductance. The oscillator can be constituted only by the resistor. For this reason, the circuit of the disconnection detecting device can be simplified and downsized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1 Piezoelectric film sensor 2 High frequency oscillator 3 FET amplifier 4 Inverter circuit 5 Detector 6 Arithmetic circuit 7 Integrator 8 Comparator 9 Light emitting diode 11 Piezoelectric film sensor 12 FET amplifier 13 Multivibrator circuit 14 Low pass filter 15 Frequency detection Circuit 16 Low-pass filter 17 Monostable multivibrator circuit 18 Short-circuit detection circuit 19 Output circuit

Claims (5)

[Claims] 1. A disconnection detecting device for a piezoelectric film sensor such as a piezo film or a Kynar film, comprising: a high-frequency oscillator for supplying a high-frequency current to the piezoelectric film sensor; and a high-frequency current transmitted through the piezoelectric film sensor. An amplifier for amplifying the piezoelectric film sensor; a DC converter for converting an output signal of the amplifier into a DC voltage; and a comparator for detecting disconnection or breakage of the piezoelectric film sensor by comparing the DC output voltage of the DC converter with a reference voltage. And a disconnection detecting device for a piezoelectric film sensor. 2. The disconnection detecting device for a piezoelectric film sensor according to claim 1, wherein said amplifier is an FET amplifier. 3. The disconnection detecting device for a piezoelectric film sensor according to claim 1, wherein said DC converter comprises a detector and an integrator. 4. A disconnection detecting device for a piezoelectric film sensor such as a piezo film or a Kynar film, comprising: an oscillator incorporating capacitance as a capacitor of the piezoelectric film sensor as an oscillation frequency determining element; A low-pass filter whose pass band is set so as to pass the oscillation output of the oscillator in a normal case and block the oscillation output when the piezoelectric film sensor is disconnected, and is sent through the low-pass filter. A frequency detection circuit for detecting and monitoring an oscillation output obtained when the piezoelectric film sensor is normal from the incoming oscillation signal, and outputting a disconnection detection signal when the oscillation output is no longer obtained; The oscillating output of the oscillator transmitted through the converter is converted into a DC voltage, and the converted DC voltage is used as a reference voltage. Disconnection detection apparatus for a piezoelectric film sensor, characterized in that a short-circuit detecting circuit for detecting a short circuit of the piezoelectric film sensor by comparing the. 5. The disconnection detecting device for a piezoelectric film sensor according to claim 5, wherein said oscillator comprises a multivibrator oscillation circuit.