JPH0283424A - Piezoelectric type pressure distribution sensor - Google Patents

Abstract

PURPOSE:To accurately measure pressure by suppressing the effect of the temp. of an object to be measured received by a piezoelectric element by constituting a pressure plate of a plurality of heat insulating members for suppressing the transmission of heat between the object to be measured and the piezoelectric element, and the highly heat-conductive member held between a plurality of the heat insulating members to diffuse heat. CONSTITUTION:The pressure plate 14 placed on an earth electrode 32 is constituted of felt sheets 33, 34 having high heat insulating properties, the highly heat-conductive metal foil sheet 35 held between both felt sheets and the reinforcing plate-shaped members 36, 37 integrally adhered to the upper surface of the felt sheet 33 and the under surface of the felt sheet 34. When an object to be measured having temp. higher than that of a piezoelectric element 22 is placed on the pressure plate 14, since the felt sheets are low in heat conductivity, the heat transmitted to the metal foil sheet 35 from the object to be measured through the upper felt sheet 33 of the pressure plate 14 becomes slight and is diffused by the metal foil sheet 35. Heat transmission is prevented more effectively by the felt sheet 34 provided to the lower part of the pressure plate 14.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a piezoelectric pressure distribution sensor, and particularly to a piezoelectric pressure distribution sensor that detects contact pressure distribution using a plurality of piezoelectric elements arranged in a matrix. Regarding.

[Prior Art] As a conventional piezoelectric pressure distribution sensor, for example, Japanese Unexamined Patent Application Publication No. 62-297735 discloses a configuration in which piezoelectric elements are arranged in a matrix to detect contact pressure (i). There is.

With this configuration, the pressure applied to each piezoelectric element can be calculated by determining the potential difference δP1 between the electrodes provided at both the upper and lower ends of the piezoelectric element, and the pressure distribution can be determined based on this. It has become.

When implementing the conventional configuration specifically, for example, the eighth
It is conceivable to have a structure as shown in the figure. In FIG. 8, a substrate 1 has a wiring pattern 2 on its upper surface.

Piezoelectric cords 3 are placed on predetermined positions of the wiring pattern 2, respectively.
is placed.

The piezoelectric element 3 has a pair of electrodes at each of its upper and lower ends, and the lower electrode is fixed to a predetermined position of the wiring pattern 2 with a conductive adhesive.

A flexible pressure plate 4 made of polyurethane rubber sheet is arranged above the piezoelectric element 3. A wiring pattern 5 is formed on the lower surface of the pressure plate 4. An electrode formed at the upper end of the piezoelectric cable 3 is fixed to a predetermined position of the wiring pattern 5 with a conductive adhesive.

In the configuration shown in FIG. 8, when an object is placed on the pressure plate 4, pressure is applied to the piezoelectric elements 3 according to the pressure distribution on the object.

As a result, the piezoelectric cord 3 generates an electric charge based on the piezoelectric effect. By detecting the amount of charge using a pressure distribution detection device (not shown), it is possible to know the pressure distribution based on the object.

[Problems to be Solved by the Invention] The polyurethane rubber sheet used for the pressurization of the conventional piezoelectric pressure distribution sensor has good thermal conductivity, so
If an object with a temperature higher or lower than the temperature of the piezoelectric cord 3 is placed on the pressure plate 4, the temperature of the piezoelectric cord 3 will change due to the temperature difference between the object and the pressure plate. However, the amount of charge generated in the piezoelectric element 3 also depends on spontaneous polarization due to pyroelectricity, and this spontaneous polarization is a function of temperature change. Therefore, in the configuration shown in FIG. 8, if the temperature of the piezoelectric element 3 changes, the piezoelectric element 3
This results in the accumulation of unnecessary charges.

Therefore, with the configuration shown in FIG. 8, pressure measurement is easily affected by temperature changes, and accurate pressure distribution cannot be measured.

Therefore, an object of the present invention is to suppress the influence of the temperature of the object to be measured on the piezoelectric element, and to enable accurate pressure measurement.

[Means for Solving the Problem] A piezoelectric pressure distribution sensor according to the present invention includes a piezoelectric sensor element 1 having a plurality of piezoelectric elements arranged in a matrix for detecting pressure distribution, and a piezoelectric sensor element 1 having a plurality of piezoelectric elements for detecting pressure distribution arranged in a matrix. and a flexible pressure plate disposed above the piezoelectric element so as to be in pressure contact with the upper end. In the piezoelectric pressure distribution sensor according to the present invention, the pressure plate includes a plurality of heat insulating members for suppressing heat transfer between the object to be measured and the piezoelectric element;
and a highly thermally conductive member sandwiched between the plurality of heat insulating members for diffusing heat.

[Function] In the piezoelectric pressure distribution sensor according to the present invention, the object to be measured is placed on the pressure plate. In response to the pressing force from the object to be measured, charges are generated in each of the plurality of piezoelectric elements arranged in a matrix due to the piezoelectric effect. By detecting this amount of charge, the pressure distribution can be determined.

On the other hand, the pressure plate includes a plurality of heat insulating members for suppressing heat transfer between the fixed object and the piezoelectric element, and a highly thermally conductive member sandwiched between the heat insulating members. Therefore, even if the humidity of the object 11-1 is higher or lower than that of the pressurizing plate, the heat transfer is prevented by the heat insulating member, and a small amount of heat that has been transmitted through the heat insulating member is transferred to the high thermal conductive member. Because it is diffused, the piezoelectric element is less affected by the temperature of the object to be measured. Therefore, the piezoelectric pressure distribution sensor according to the present invention is less susceptible to the influence of the temperature of the object to be measured, making it possible to accurately measure pressure.

Embodiment of the Invention FIGS. 3 and 4 are schematic diagrams showing the overall configuration of an embodiment of the invention. In FIGS. 3 and 4, the piezoelectric pressure distribution sensor 10 has a rectangular flat plate-shaped base 11. The stand 11 is mainly made of Bakelite, and a group of sensor cords 12 arranged in a matrix are fixed on the stand 11.

Also, on the peripheral edge of the stand 11, there is a young protrusion ==1 that protrudes upward.
A frame 13 that can be used is attached. An F+J flexible pressure plate 14 is arranged in the opening of the frame 13. The pressure plate 14 has flexibility so as to be able to press the upper end surface of the sensor element group 12, and its peripheral portion is fixed to the frame 13 side. An input/output connector 15 is formed at each end of the pressure distribution sensor 10 in the longitudinal direction.

Each sensor element 21 constituting the sensor cable group 12 has a fifth
As shown in the figure, each has a piezoelectric element 22, a field effect transistor 23, and a capacitor 24. Further, along the arrangement of the sensor elements 21 arranged in a matrix, control lines C, C2, . . .
・CI and l are installed. Further, reading lines R, , R2 . . . R are arranged in each column direction. moreover,
A ground wire 26 connected to the ground 25 is arranged in the direction of each column.

FIG. 6 shows an equivalent circuit of one sensor cord 21. In FIG. 6, the gate electrode of field effect transistor 23 is connected to control line C. In FIG.

The other of the source or drain electrodes of the transistor 23 is connected to an electrode 28 formed on the upper end surface of the piezoelectric element 22.
It is connected to the. An electrode 29 formed on the lower end surface of the piezoelectric element 22 is connected to a ground wire 26. Further, a capacitor 24 is connected between an electrode 28 on the upper end surface of the piezoelectric element 22 and a ground wire 26. That is, this capacitor 24 is connected in parallel to the piezoelectric element 22. Note that as the piezoelectric element 22, an element made of a highly rigid piezoelectric material such as piezoelectric ceramics or piezoelectric single crystal is used.

Next, the specific structure of each sensor cord 21 portion will be explained.

As shown in FIG. 1, piezoelectric cords 22 are arranged on the stand 11 of the pressure distribution sensor 10 at predetermined intervals. A flat metal readout electrode 31 is arranged between the piezoelectric cord 22 and the stand 11. The readout electrode 31 and the electrode at the lower end of the piezoelectric cable 22 are hardened by an intervening conductive adhesive. At the upper end of the piezoelectric cord 22, a metal earth electrode 32 is arranged. The ground electrode 32 and the seven hypopoles at the upper end of the piezoelectric element 22 are fixed by an intervening conductive adhesive. The readout electrode 31 and the ground electrode 32 are
It is electrically connected to a wiring pattern on a board (not shown) provided on the stand 11.

A pressure plate 14 is placed on the ground electrode 32 . The pressure plate 14 is integrally bonded to a felt sheet 33 with high heat insulation properties, a highly thermally conductive metal foil sheet 35 sandwiched between both felt sheets, and the upper surface of the felt sheet 33 and the lower surface of the felt sheet 34. Plate member 3 for reinforcement
6.37. Felt sheet 34.3
5 is made of wool, for example, and the metal foil sheet 35 is made of, for example, aluminum foil.
6.37 is made of glass and epoxy resin, for example.

FIG. 2 shows the thermal conductivity characteristics of the above felt sheet and a conventionally used polyurethane rubber sheet. Figure 2 shows
A felt sheet and a polyurethane rubber sheet with a thickness of 2 mm were placed on a plate maintained at 60° C., and the surface temperature of each sheet was measured at predetermined intervals.

When an object to be measured whose temperature is higher than that of the piezoelectric element 22 is placed on the pressure plate 14, as shown in FIG. Only a small amount of heat is transferred from the object to be measured to the metal foil sheet 35. The slight amount of heat transferred to the metal foil sheet 35 is diffused by the metal foil sheet 35.

This prevents local temperature increases. Moreover,
Heat transfer is more effectively prevented by the felt sheet 34 provided under the pressure plate 14.

It goes without saying that the same effect as described above can be obtained even when the temperature of the object to be measured is lower than that of the piezoelectric element 22. That is, in this embodiment, heat transfer is significantly reduced by the heat insulating effect of the double felt sheets and the heat diffusion effect of the metal foil sandwiched between the felt sheets. Therefore, even when the temperature of the fixed object 71p1 placed on the pressure plate 14 is higher or lower than the temperature of the piezoelectric element 22, the temperature change of the piezoelectric element 22 is prevented. In addition. Since the pressure plate 14 is constructed as described above, it has flexibility.

The piezoelectric pressure distribution sensor 10 described above is incorporated into a pressure detection device 50 as shown in FIG. 7, for example. In FIG. 7, the control line CI* of the piezoelectric pressure distribution sensor 10
c21 . . . CI, l are connected to the control line switching circuit 51. In addition, the reading lines R,, R2゜...Ro are
It is connected to the read line switching circuit 52.

The read line switching circuit 52 is connected to an integrating circuit 53, and the integrating circuit 53 is connected to a peak hold circuit 54. The peak hold circuit 54 is connected to a data processing device 56 via an A/D converter 55. Furthermore, the seventh
The illustrated detection device 50 includes a matrix control circuit 57. The matrix control circuit 57 includes the control line switching circuit 51
In addition to controlling the read line switching circuit 52, a reset signal is sent to the peak hold circuit 54 at a predetermined timing, and an element switching information signal is sent to the data processing device 56. Further, the data processing device W56 is
The control signal for controlling the A/D converter 55 is
The signal is sent to a D converter 55.

Next, the operation of the piezoelectric pressure distribution sensor incorporated in the pressure distribution detection device 50 shown in FIG. 7 will be explained.

A piezoelectric pressure distribution sensor 10 detects a constant object such as a person's foot.
When placed on the pressure plate 14 of the object, charge is accumulated in each sensor element 21 according to the distribution of the pressure force based on the object. The pressure plate 14 is a felt sheet 33, 34 with high heat insulation properties.
and a highly thermally conductive metal foil sheet 35 sandwiched between both felt sheets, so even if a hot or cold object is placed on the piezoelectric cord 22, no pyroelectric effect will occur.

Therefore, the piezoelectric element 22 is influenced only by the pressure based on the constant object, and accumulates a charge corresponding to the pressure.

Next, the matrix control circuit 57 first turns on the transistor 23 connected to the control line C7 through the control line switching circuit 51. At this time, other control line C
2, C, . . . Cm are in a non-conducting state. As a result, the information on the sensor element 21 in the row corresponding to the control line C1 is
Reading lines R, , R2° . . . become readable through Ro.

In this state, first, only the reading line R3 is connected to the integrating circuit 53 through the reading line switching circuit 52. At this time,
Since the remaining reading lines R2, R, . . . Rn are in an open circuit state, the information in the corresponding sensor element 21 is retained.

When the read line R7 is connected to the integrating circuit 53, the charges accumulated in the corresponding piezoelectric element 22 are discharged to the integrating circuit 53 side. If this electric charge is integrated over time in the integrating circuit 53, the amount of electric charge accumulated by pressurizing the corresponding sensor element 21 can be measured.

The output of the integrating circuit 53 is sent to the peak hold circuit 54 in the subsequent stage.
．． Data processing device 561 through A/D converter 55
;Input.

Thereafter, the reading lines R2, R, . As a result, in the same way as described above, the information of each sensor element 21 arranged in the row corresponding to the control line C2 is read from the reading lines R,, R2,...Rn, and the information is stored in the data processing device 56. . Based on this accumulated data, it is possible to know the pressure force /i of the unknown object that is in contact with the piezoelectric pressure distribution sensor 10 without being affected by the force.

[Effects of the Invention] As described above, according to the present invention, the pressure plate is inserted between the plurality of heat insulating members for suppressing heat transfer between the object to be measured and the piezoelectric element. Since it is equipped with a highly thermally conductive member for diffusing heat, even when a high temperature or low temperature M1 constant object is set to JP1 constant, the influence due to the lH degree difference on the piezoelectric element is suppressed. Since it becomes possible to suppress errors caused by the pyroelectric effect, it becomes possible to determine an accurate pressure distribution i'1llll.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a piezoelectric pressure distribution sensor according to an embodiment of the present invention. Diagram T52 is a diagram showing the thermal conductivity characteristics of the felt sheet and the polyurethane rubber sheet. FIG. 3 is a partially cutaway front view showing the overall configuration of an embodiment of the present invention. FIG. 4 is a partially cutaway side view showing the overall configuration of an embodiment of the present invention. FIG. 5 is a schematic perspective view showing the arrangement of the sensor cord group. FIG. 6 is an equivalent circuit diagram of the sensor element. FIG. 7 is a block diagram of a pressure force (Ii detection device) to which a pressure distribution sensor according to an embodiment of the present invention is applied. FIG. 8 is a vertical cross-sectional view of a conventional piezoelectric pressure distribution sensor. , 12 is a sensor element group, 14 is a pressure plate, 22
33 and 34 are felt sheets, and 35 is a metal foil sheet. Figure 3 84 Figure 2 First O seconds

Claims (1)

[Scope of Claims] A piezoelectric sensor element group having a plurality of piezoelectric elements arranged in a matrix for detecting pressure distribution; and a flexible pressure plate arranged, the pressure plate being sandwiched between a plurality of heat insulating members for suppressing heat transfer between the object to be measured and the piezoelectric element, and the plurality of heat insulating members. and a highly thermally conductive member for dissipating heat.