JPH04346041A - Piezoelectric load sensor and applied device and circuit thereof - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric load sensor wherein the output can be decreased and an external capacitor can be omitted. CONSTITUTION:Of three piezoelectric elements 2A-2C, e.g. the polarizing directions of 2A, 2B and 2C are made to be the reverse directions to each other. The generated electric charges of the piezoelectric elements 2A and 2C are made to offset each other. Thus, an external capacitor can be omitted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric load sensor and a device and circuit using the same.

0002

[Prior Art] Conventionally, many of these types of sensors have been used with load cells or strain gauges attached, but load cells have problems in usability, and all of them require the use of bridge circuits. First, there is a problem that the measurement circuit is complicated and expensive. Furthermore, there is a problem in that strain gauges require skill to attach and that it is difficult to ensure long-term reliability. Therefore, a piezoelectric load sensor as shown in FIG. 11 has been proposed. In the same figure,
41 is a piezoelectric element, 42 is a parallel capacitor, 43 is a discharge resistor, and 44 is an amplifier having a charge-voltage conversion circuit (not shown). That is, when guiding the output from the piezoelectric element 41 to the amplifier 44, a capacitor 42 is used to reduce the piezoelectric element output. This is because if a voltage higher than the power supply voltage of the amplifier 44 is applied, the amplifier will be damaged, so a capacitor 42 is inserted in parallel to lower the voltage. A discharge resistor 42 is also provided, which is used to set the output to zero in a no-load state.
This is for discharging the residual charge of the piezoelectric element 41.

0003

[Problems to be Solved by the Invention] As described above, the conventional device not only requires an external capacitor to reduce the output, but also has a discharge circuit, so the output waveform of the amplifier 44 is As a result, a measuring device with a peak hold function is required, and it is mainly suitable only for measuring impact loads. Therefore, the main object of the present invention is to provide a piezoelectric load sensor and its application device and circuit that can be applied to general load measurement without the need for a capacitor or discharge resistor.

0004

[Means for Solving the Problems] In order to solve such problems, in the first invention, one of the three piezoelectric elements and the remaining two are laminated so that the polarization directions are opposite to each other. The piezoelectric element is characterized in that the piezoelectric element is connected so that the electric charges of the one piezoelectric element and one of the remaining two elements cancel each other out. Moreover, in the second invention, 3
The piezoelectric elements are stacked so that the polarization directions of one of the piezoelectric elements and the remaining two are opposite to each other, and the electric charges of the one piezoelectric element and one of the remaining two elements cancel each other out. In a piezoelectric load sensor that is connected to a container, is housed in a container, and applies a load via a spring and a pressure receiving piece, the pressure receiving piece has a stepped structure, and an electric charge is generated in a space between the pressure receiving piece and the spring. It features a built-in amplifier circuit that includes a voltage conversion circuit. In the third invention, one of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and one of the one piezoelectric element and the remaining two The present invention is characterized in that a reset switch for discharging the charge is provided to the piezoelectric load sensor connected so that the charges thereof cancel each other out, so that the load can be reset when the load is zero. Further, in the fourth invention, one of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and the one piezoelectric element and the remaining two are stacked so that the polarization directions are opposite to each other. A reset switch for discharging the charge and a detection means for detecting the output thereof are provided for the piezoelectric load sensor connected so that the charges thereof cancel each other, and the output of the piezoelectric load sensor becomes negative. The present invention is characterized in that the reset switch is operated to enable automatic reset. In the fifth invention, one of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and one of the one piezoelectric element and one of the remaining two A piezoelectric load sensor and a laminated piezoelectric element are housed in a container, and the laminated piezoelectric element is driven by applying a driving load and a voltage command to the laminated piezoelectric element. . Furthermore, in the sixth invention, one of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and the one piezoelectric element and the remaining two In a linear actuator circuit that is composed of a piezoelectric load sensor and a laminated piezoelectric element that are connected so that charges of either of them cancel each other out, the linear actuator circuit operates in response to a driving load and a voltage command. It is characterized in that a constant stroke is ensured by detecting the drive load and controlling the voltage corresponding to the drive load by adding it to the voltage command.

[0005]

[Operation] By devising the polarization direction and connection of each of the three piezoelectric elements, the output is reduced and an external capacitor is not required. In addition, it is possible to reset each load and sensor output when they are zero, thereby eliminating the influence of residual charge and enabling highly accurate measurement. Furthermore, by using the present invention together with another laminated piezoelectric element, a linear actuator with a simple structure is provided, and furthermore, by using this, a linear actuator circuit that can always ensure a constant stroke regardless of the load is provided.

[0006]

[Embodiment] Fig. 1 is a sectional view showing an embodiment of this invention, Fig. 2
is a top view thereof. In these figures, 1 is a piezoelectric load sensor, 2A to 2C are piezoelectric elements, 3A, 3B
is a non-power generation material, 4 is a laminated electrode, 5 is an insulating resin, 6 is a metal foil, 7 is a conductive adhesive, 8 is a sealing resin, 9 is a solder part, 10,
10A to 10D are lead wires, 11 is a chamfered portion, and 12 is an electrode connection surface. That is, the piezoelectric load sensor 1 according to the present invention includes three piezoelectric elements 2A to 2C.
are sandwiched between non-power generation materials 3A and 3B, each of which is joined by a conductive laminated electrode 4. The end faces of the electrode layers are alternately grooved and filled with insulating resin 5.
Lead wires 10A to 10D are connected to the opposite side via metal foil 6, conductive adhesive 7, and solder portion 9. Here, the piezoelectric elements 2A to 2C are polarized to each other, and here, for example, as shown by arrows X, Y, and Z, the piezoelectric elements 2B and 2
Although the direction of polarization of C is made to be opposite, the present invention is not limited to this, and it is sufficient to make the remaining two piezoelectric elements opposite to one piezoelectric element. Further, when the thicknesses of the piezoelectric elements 2A to 2C are respectively t1 to t3, the dimensions are determined so that t1=t3 and t1≦t2. This is because if the lead wires are connected so that the charges generated by the piezoelectric elements 2A and 2C in FIG. 1 cancel each other out, the equivalent circuit becomes as shown in FIG. 3, and the output of the piezoelectric element 2B becomes dominant. This is to reduce the generated voltage by increasing the thickness t2 (the generated voltage is inversely proportional to the thickness). In other words, since the piezoelectric element can be regarded as a type of capacitor, by devising the direction of polarization and connection of these elements, the output can be reduced and the capacitor becomes unnecessary.

FIG. 4 shows an example of an applied circuit, and FIG. 5 shows the characteristics of a piezoelectric load sensor. Figure 5 shows the results when the load is increased and decreased three times without resetting the residual charge of the piezoelectric load sensor.As the number of uses increases, negative charges accumulate and the output gradually shifts to the negative side. It is shown that. Therefore, as shown in FIG. 4, an output detector (for example, a comparator) 13 is provided to detect the output of the piezoelectric load sensor, and when it is detected that the output has become negative, the reset switch 14 is closed. Make sure to reset the charge. Furthermore, since it is inconvenient that there is an output when the load on the piezoelectric load sensor is zero, the reset switch 14 is closed to enable reset at this time as well.

FIG. 6 is a sectional view showing an embodiment in which a piezoelectric load sensor is built into a case like a conventional load cell. In the figure, 16 is a pressure receiving piece having a spherical surface 17, 18 is a cover, 19 is a lid, 20 is a spring, 21 is a screw, 22 is a lead wire, and 1 is a piezoelectric load sensor. This is done by pressing the piezoelectric load sensor 1 with a spring 20 so that a compressive force is always generated, and transferring the electric charge generated when the piezoelectric load sensor 1 is compressed by an external force acting on the pressure receiving piece 16 to the outside. The load can be measured by converting it into voltage using a connected amplifier with a charge-voltage conversion circuit. FIG. 7 shows a modification of FIG. 6, in which a stepped portion 26 is formed on the pressure receiving piece 16 to create a space between it and the cover 18, and an IC chip serving as an amplifier including a charge-voltage conversion circuit is formed in this space. 24 is built-in. Note that 23 is a printed board, 25 is a sealing resin, 27 is a lead wire, and the other parts are the same as those in FIG. By doing so, there is no need to provide an amplifier including a charge-voltage conversion circuit externally, and miniaturization can be achieved.

FIG. 8 shows an example of a linear actuator. This is because a laminated piezoelectric element 32 is housed in the case 30 in addition to the piezoelectric load sensor 1, and displacement occurs when a voltage is applied to the laminated piezoelectric element 32 via the lead wire 33. The piezoelectric load sensor 1 detects the electric charge generated in response to the displacement, and is used when detecting displacement and performing position control. The reference numeral 28 indicates a movable piece to which a load is applied, 29 a guide, 31 a preload spring, and 34 a lead wire. In other words, in the past, when measuring displacement by housing the laminated piezoelectric element 32 in a case, the structure was complicated because a circuit or device for measurement was provided outside, but in this invention, the piezoelectric By using a load sensor, displacement can be easily measured with a simple structure.

FIG. 9 shows one of the linear actuator application circuits.
Give an example. In the figure, 35 is a controller, 36 is a DC power supply, 37 is a reversible chopper circuit, 38 is an amplifier, 3
9 indicates a charge-voltage conversion circuit. This is the DC power supply 36
The controller 35 controls the output voltage of the reversible chopper circuit 37 supplied with voltage from the controller 35 to obtain displacement according to the voltage command. At this time, if there is no load acting through the movable piece 28, the displacement as per the voltage command will be obtained, but if there is a load, the displacement as per the voltage command will not be obtained. Therefore, by detecting the charge of the piezoelectric load sensor 1 via the charge-voltage conversion circuit 39, and then adding an amount of voltage according to the load to the voltage command via the amplifier 38, the displacement (stroke) is always constant. It is designed to ensure that

FIG. 10 is an explanatory diagram for explaining the operation, in which (a) shows voltage vs. displacement, (b) shows displacement vs. load, and (c) shows load vs. correction voltage. (d) shows the relationship between load and voltage. In other words, the same figure (a)
From the relationship in the same figure, it can be seen that as the applied voltage increases, the displacement increases.From the relationship in the same figure (b), it can be seen that the displacement decreases as the load increases, and from the relationship in the same figure (d), it can be seen that the displacement increases as the applied voltage increases. It can be seen that if the value increases, the applied voltage must be increased. Therefore, the correction voltage to obtain a constant displacement is small when the load is low, as shown as correction voltage 1 in the same figure (c), and correction voltage 2 is small when the load is high.
It becomes larger as shown in . Note that since the voltage vs. displacement characteristic has hysteresis, it will be used here only when increasing the stroke, that is, only the solid line part in Figure (A) will be used, and the broken line part will not be used. Also, in this case, it is necessary to discharge the residual charge with zero load before use.
linear) output characteristics can be obtained.

0012

According to the present invention, by devising the polarization direction and connection of each of the three piezoelectric elements, it is possible to reduce the output and eliminate the need for an external capacitor. In addition, since it is reset when the load or sensor output is zero, the influence of residual electric charge can be removed.
Highly accurate measurement becomes possible. In addition, by using it with another laminated piezoelectric element, a linear actuator with a simple configuration can be obtained, and by incorporating this into a circuit, it is possible to control the stroke to be constant regardless of the load. Benefits can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the invention.

FIG. 2 is a top view of FIG. 1;

FIG. 3 is an equivalent circuit diagram of FIG. 1;

FIG. 4 is a circuit diagram showing an application example of FIG. 1;

FIG. 5 is a characteristic diagram showing the relationship between compressive load and generated charge of a piezoelectric load sensor.

FIG. 6 is a sectional view showing an embodiment in which a piezoelectric load sensor according to the present invention is built into a case.

7 is a sectional view showing a modification of FIG. 6. FIG.

FIG. 8 is a sectional view showing an example of a linear actuator.

FIG. 9 is a block diagram showing an example of application of a linear actuator.

FIG. 10 is an explanatory diagram for explaining the operation of FIG. 9;

FIG. 11 is an explanatory diagram for explaining a conventional example of a piezoelectric load sensor.

[Explanation of symbols]

1 Piezoelectric load sensor 4 Laminated electrode 5 Insulating resin 6 Metal foil 7 Conductive adhesive 8 Sealing resin 9 Solder part 2A piezoelectric element 2B Piezoelectric element 2C piezoelectric element 3A Non-power generation material 3B Non-power generation material 10 Lead wire 11 Chamfered part 12 Electrode connection surface 13 Output detector 14 Reset switch 15 Amplifier 16 Pressure receiving piece 17 Spherical surface 18 Cover 19 Lid 20 Spring 21 Screw 22 Lead wire 23 Printed board 24 IC chip 25 Sealing resin 26 Stepped part 27 Lead wire 28 Movable piece 29 Guide 30 cases 31 Preload spring 32 Laminated piezoelectric element 33 Lead wire 34 Lead wire 35 Controller 36 DC power supply 37 Reversible chopper 38 Amplifier 39 Charge-voltage conversion circuit

Claims (6)

[Claims] 1. One of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and the one piezoelectric element and any of the remaining two A piezoelectric load sensor characterized by connections so that electric charges cancel each other out. 2. One of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and the one piezoelectric element and any of the remaining two In a piezoelectric load sensor that is connected so that electric charges cancel each other out, is housed in a container, and is applied with a load via a spring and a pressure receiving piece, the pressure receiving piece has a stepped structure, and the pressure receiving piece and the spring are connected together. A piezoelectric load sensor characterized by having an amplifier circuit including a charge-voltage conversion circuit built-in in a space. 3. One of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and the one piezoelectric element and any of the remaining two A reset circuit for a piezoelectric load sensor, characterized in that a reset switch for discharging the charge is provided for the piezoelectric load sensor connected so that the charges cancel each other out, so that the reset switch can be reset when the load is zero. 4. One of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and the one piezoelectric element and any of the remaining two A reset switch for discharging the charge and a detection means for detecting the output of the piezoelectric load sensor connected so that the charges cancel each other out are provided, and when the output of the piezoelectric load sensor becomes negative, the reset is performed. A reset circuit for a piezoelectric load sensor, characterized in that automatic reset is possible by operating a switch. 5. One of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and the one piezoelectric element and any of the remaining two A piezoelectric load sensor and a laminated piezoelectric element are housed in a container, and the piezoelectric load sensor and the laminated piezoelectric element are connected so that electric charges cancel each other out.
A linear actuator characterized in that the laminated piezoelectric element is driven by applying a drive load and a voltage command. 6. One of the three piezoelectric elements and the remaining two are stacked so that the polarization directions are opposite to each other, and the one piezoelectric element and any of the remaining two In a linear actuator circuit that is composed of a piezoelectric load sensor and a laminated piezoelectric element that are connected so that electric charges cancel each other out, and that operates in response to a driving load and a voltage command, the piezoelectric load sensor controls the driving load. A linear actuator circuit characterized in that a constant stroke is ensured by detecting and controlling a voltage corresponding to the detected voltage by adding it to the voltage command.