JPH0249449B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure detection device using a piezoelectric element.

Conventional pressure detection devices generally have a mechanical configuration, but recently it has been considered to electrically detect pressure using piezoelectric elements.
However, currently considered pressure detection devices using piezoelectric elements have a problem in that they can only detect pressure up to the strain limit of the piezoelectric element.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a pressure detection device capable of detecting pressures that exceed the strain limit of piezoelectric elements.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the circuit configuration when incorporated into an electronic wristwatch. In FIG. 1, reference numeral 1 denotes an oscillator that generates a reference signal for timekeeping, and its oscillation output is sent to a frequency divider circuit 2, where the frequency is divided into a signal having a period of, for example, one second. The one-second signal outputted from the frequency dividing circuit 2 is sent to the timer circuit 3 and is timed. The timekeeping circuit 3 performs timekeeping processing such as "hour" and "minute" based on the input one-second signal, and outputs the timekeeping data to the display section 6 via the AND circuit 4 and the OR circuit 5. On the other hand, reference numeral 7 denotes a piezoelectric element, and DC power is supplied from a battery 8 between both electrodes of the piezoelectric element through a switching N-channel MOS transistor (hereinafter referred to as MOS transistor) 9 and a diode 10 in series. In this case, the direction of the voltage polarity of the DC power source 8 is set so as to correct the distortion of the piezoelectric element 7 caused by pressure. Thus, the piezoelectric output of the piezoelectric element 7 is sent to a voltage detection section, for example, an A/D (analog/digital) converter 11. The output of this A/D converter 11 is input to the pressure conversion addition circuit 12, and also to the comparison circuit 13 and the zero detection circuit 1.
4. The comparison circuit 13 stores the strain limit voltage Va of the piezoelectric element 7 in advance, and the A/D
Compared to the voltage V detected by the converter 11, Va
<V, a “1” signal is output. The “1” signal output from this comparison circuit 13 is R-
The signal is input to the set terminal S of the S-type flip-flop 15, and is also input to the three-input AND circuit 18 via the timer circuit 16 and the inverter 17, which have a delay time longer than the operating time of the A/D converter 11. Further, the output of the zero detection circuit 14 is input to this AND circuit 18 via a one-shot circuit 19, and the Q of the flip-flop 15 is inputted to the AND circuit 18.
The side output is input. This flip-flop 15
The Q-side output of is input to the gate of the MOS transistor 9 and also to the pressure conversion adder circuit 12
is input to. This pressure conversion and addition circuit 12 converts the output voltage value of the A/D converter 11 directly into a pressure value and outputs it when the signal from the flip-flop 15 is "0".
When the signal from 5 is “1”, the A/D converter 11
The distortion limit voltage Va of the piezoelectric element 7 stored in advance is added to the output of , and the addition result is converted into a pressure value and output. The output of this pressure conversion and addition circuit 12 is sent to the display section 6 via an AND circuit 20 and an OR circuit 5. Further, the symbol S is a display changeover switch, and its operation causes a trigger flip-flop (hereinafter simply referred to as a flip-flop) 2.
1 operates in reverse. The output of the flip-flop 21 is input to the AND circuit 20 as a gate signal, and is also input to the AND circuit 4 via the inverter 22 as a gate signal.

In the above configuration, the flip-flop 21 is reset by operating the switch 7, that is, the Q
When the output is set to "0", the output of the inverter 22 becomes "1" and the gate of the AND circuit 4 is opened. Therefore, the clock data outputted from the clock circuit 3 is sent to the display section 6 via the AND circuit 4 and the OR circuit 5, and is digitally displayed as shown in FIG. 2a. Incidentally, No. 2a shows a display example at 10:58 am.

To switch from the watch mode to the pressure detection mode, the flip-flop 21 is reversed by operating the switch S. As a result, the Q output of the flip-flop 21 becomes "1" and the gate of the AND circuit 20 is opened. At this time, inverter 2
2 becomes "0", the gate of the AND circuit 4 is closed, and the transfer of clock data from the clock circuit 3 to the display section 6 is prohibited. When the gate of the AND circuit 20 opens as described above, the pressure data output from the pressure conversion and addition circuit 12 is sent to the display section 6 via the AND circuit 20 and the OR circuit 5 and displayed. For example, if the strain limit pressure is 5
When using the piezoelectric element 7 at atmospheric pressure, if a pressure of 1 atmosphere is applied to the piezoelectric element 7, a voltage corresponding to 1 atmosphere is taken out from the piezoelectric element 7 and input to the A/D converter 11. At this time, the flip-flop 15 is in the reset state and its Q output is "0", keeping the MOS transistor 9 in the off state. Therefore, at this point, the DC power supply 8 is cut off from the piezoelectric element 7. Therefore, the A/D converter 11 is
The analog voltage applied from the piezoelectric element 7 is converted into a digital voltage V and outputted to the pressure conversion and addition circuit 12, the comparison circuit 13, and the zero detection circuit 14. The comparison circuit 13 compares the voltage V applied from the A/D converter 11 with the distortion limit voltage Va of the piezoelectric element 7 stored inside. This strain limit voltage Va is for 5 atm. Therefore, when a pressure of 1 atm is applied to the piezoelectric element 7 as described above,
The state is Va>V. Therefore, the output of the comparison circuit 13 is in the "0" state, and the flip-flop 15 is held in the reset state. In a state where the flip-flop 15 is reset in this way, the pressure conversion and addition circuit 12 converts the output voltage V of the A/D converter 11 directly into a pressure value, and sends it to the display section 6 via the AND circuit 20 and the OR circuit 5. Output to. As a result, the display section 6 displays, for example, "1.0:P" indicating 1 atm, as shown in FIG. 2b.

When the pressure applied to the piezoelectric element 7 rises to the strain limit and the relationship between the output voltage V of the A/D converter 11 and the strain limit voltage Va becomes Va<V, a "1" signal is output from the comparison circuit 13. It is output and flip-flop 15 is set. As a result, the Q output of flip-flop 15 becomes "1",
Turn on MOS transistor 9. As a result,
A DC power source 8 is applied to the piezoelectric element 7 via a MOS transistor 9 and a diode 10 . The DC power supply 8 is for applying a strain limit voltage Va to the piezoelectric element 7, and applies a voltage in a direction to eliminate the strain when the piezoelectric element strain limit pressure is applied.
Therefore, when a strain limit pressure is applied to the piezoelectric element 7, the MOS transistor 9 is turned on, thereby eliminating the strain, and the input voltage from the piezoelectric element 7 to the A/D converter 11 becomes "0". . on the other hand,
The pressure conversion addition circuit 12 includes a flip-flop 15.
When a "1" signal is given from , the internally stored distortion limit voltage Va is added to the output of the A/D converter 11, and the addition result is converted into a pressure value. Therefore, when the output of the A/D converter 11 is "0", conversion processing is performed for the distortion limit voltage Va, and as a result, the display section 6 shows "5.0:P", that is, 5
Atmospheric pressure is displayed. Then, if a pressure of 7.5 atmospheres is applied to the piezoelectric element 7,
The piezoelectric element 7 outputs a voltage corresponding to the correction by the DC power supply 8 , that is, 2.5 atm after subtracting 5 atm, and inputs it to the A/D converter 11 . Then, this A/D converter 11 outputs
The voltage V for 2.5 atm is the pressure conversion addition circuit 1.
2, it is added to the strain limit voltage Va, and the addition result is converted into a pressure value. Therefore, from the pressure conversion addition circuit 12, 2.5 atm and 5 atm are added.
A signal of 7.5 atmospheres is output, and "7.5:P" is displayed on the display section 6 as shown in FIG. 2c.

Therefore, the pressure applied to the piezoelectric element 7 is
Assuming that the strain limit pressure drops from 7.5 atm to below the strain limit pressure, for example 4 atm, the zero detection circuit 14 operates when the output of the A/D converter 11 drops to "0".
Outputs a detection signal. In response to this detection signal, a one shot pulse is output from the one shot circuit 19 and inputted to the AND circuit 18. On the other hand, when the pressure increases, the comparator circuit 13 connects the flip-flop 15.
When set, the comparison output becomes "0" as the output of the A/D converter 11 decreases. Therefore, the "0" output of the comparator circuit 13 is delayed for a certain period of time by the timer circuit 16, and then inverted to a "1" signal by the inverter 17, and the Q of the flip-flop 1 is
It is input to the AND circuit 15 along with the output. Therefore, as described above, when the one shot pulse is output from the one shot circuit 19, it is inputted to the reset terminal R of the flip-flop 15 via the AND circuit 18. This resets the flip-flop 15 and turns off the MOS transistor 9. By turning off this transistor 9, the DC power supply 8 is cut off from the piezoelectric element 7, and the state returns to the initial state. Therefore, the piezoelectric element 7 outputs a voltage corresponding to the 4 atmospheres applied at that time.
The signal is sent to the display section 6 via the A/D converter 11, the pressure conversion addition circuit 12, etc., and is displayed. In this way, even if a pressure exceeding the strain limit pressure is applied to the piezoelectric element 7, the pressure can be detected.

Further, in the pressure detection mode, by operating the switch S, the flip-flop 21 is reversed, the AND circuit 20 is turned off, and the AND circuit 4 is turned on, returning to the above-described clock mode.

Next, a specific example of a wristwatch constructed using the circuit shown in FIG. 1 will be described with reference to FIGS. 3 and 4. Figure 3 is a front view, Figure 4 is a of Figure 3.
- This is an enlarged view of the main part of the cross section as seen from line a. In FIGS. 3 and 4, reference numeral 31 denotes a case, and the transparent piezoelectric element 7 is provided on the upper opening surface of the case 31 with a packing 32 interposed therebetween. This transparent piezoelectric element 7 is used in place of a surface protection member such as glass. Voltage detection electrodes 33a and 33 are provided at the center of the upper and lower surfaces of the piezoelectric element 7.
b is provided. Furthermore, voltage application electrodes 34a and 34b are provided on the entire upper and lower surfaces of the piezoelectric element 7, except for voltage detection electrodes 33a and 33b.
Connectors 36a and 36b are provided on both lower sides of the piezoelectric element 7 and between it and the upper housing 35. The connectors 36a and 36b have a structure in which conductive rubber is integrally formed on both ends with insulating rubber interposed between them, and the upper housing 35
is attached to the top of the The above connectors 36a, 36
b indicates voltage detection electrodes 33a, 33b provided on the piezoelectric element 7, and voltage application electrodes 34a, 34b.
Connected to the lead-out terminal of In this case, voltage detection electrodes 33a, 33b, voltage application electrodes 34a, 34b
Insulating layers 38a and 38b are interposed at the locations where the lead-out terminals overlap each other. A lower housing 39 is provided below the upper housing 35 . A circuit board 40 is interposed between the housings 35 and 39, and an LSI 4 having the circuit configuration shown in FIG.
1 is installed. A reflective diffuser plate 42 is arranged above the LSI 41 so as to face the lower surface of the piezoelectric element 7 . Further, the circuit board 40 includes interconnectors 43a,
It is connected to connectors 36a and 36b via 43b. Further, a battery 44 is installed inside the lower housing 39, and the LSI is connected via the circuit board 40.
Apply operating voltage to 41. This LSI boosts the voltage supplied from the battery 44 to obtain the DC power supply 8 in FIG. As described above, an electronic wristwatch having a pressure detection function can be constructed.

In addition, in the above embodiment, the voltage detection electrodes 33a, 3
3b is provided at the center of the piezoelectric element 7, but it goes without saying that it may be provided at a location other than the center. Further, the method of drawing out the terminals from the piezoelectric element 7 is not limited to the above embodiment. Furthermore, although the piezoelectric element 7 is provided so as to serve as a protective member such as glass, it may also be attached to the back cover, or may be attached to the lower surface of glass as a protective member.

Further, in the above embodiment, the atmospheric pressure is displayed, but the water depth may be displayed.

Further, in the above embodiment, one DC power supply 8 was used to apply the strain limit voltage to the piezoelectric element 7, but by providing a plurality of power supplies, the applied voltage is doubled each time the pressure limit is reached. If the number is increased by three times..., pressure detection over an even wider range can be performed.

Further, in the above embodiment, the case where the invention is implemented in a wristwatch is shown, but it may be applied to a single water pressure gauge or a barometer.

As described above, according to the present invention, when the piezoelectric element for detecting pressure is at its strain limit, a voltage is applied in the direction to correct the strain, so that it is possible to reliably detect the strain exceeding the piezoelectric element's strain limit. A pressure sensing device can be provided.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention; FIG. 1 is a circuit configuration diagram, FIGS. 2 a to c are diagrams showing examples of time and pressure display, and FIG. 3 is a front view when implemented in a wristwatch. FIG. 4 is an enlarged view of a main part taken along the line a-a in FIG. 3. FIG. 7... Piezoelectric element, 8... DC power supply, 9... MOS transistor for switching, 11... A/D
Converter, 12... Pressure conversion addition circuit, 13...
... Comparison circuit, 14 ... Zero detection circuit, 31 ... Case, 32 ... Packing, 33a, 33b ... Voltage detection electrode, 34a, 34b ... Voltage detection electrode,
35... Upper housing, 36a, 36b... Connector, 38a, 38b... Insulating layer, 39... Lower housing, 40... Circuit board, 41...
LSI, 42...Reflection diffuser plate, 43a, 43b...
Interconnector, 44...battery.

Claims (1)

[Claims] 1 A piezoelectric element that generates a voltage in response to applied pressure, a voltage detection means that detects the value of the voltage generated by the piezoelectric element, and a voltage detection means that detects the voltage detected by the voltage detection means when it exceeds a set voltage value. a voltage comparison circuit that detects a state; a voltage application means that is driven by a detection signal output from the voltage comparison circuit and applies a voltage to the piezoelectric element so as to restore the distortion of the piezoelectric element; A pressure detection device comprising: correction means for correcting the voltage detected by the voltage detection means when a voltage is applied to the piezoelectric element by the pressure detection means.