JP2013130443A - Force sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress variation in detection result of pressure even if the position of a piezoelectric substance is fluctuated, without providing a circuit for feedback control.SOLUTION: A force sensor 100 comprises a primary coil 2 and a piezoelectric substance 3 in which impedance is changed in accordance with pressure received from the outside. Furthermore, the force sensor 100 comprises a support member 20 which supports the piezoelectric substance 3 to a pedestal 1 and is formed from an elastic body which is deformed elastically by the pressure received in the piezoelectric substance 3. Moreover, the force sensor 100 comprises a pair of electrodes 4, 5 provided on both sides of the piezoelectric substance 3 and a secondary coil 6 connected to the pair of electrodes and electromagnetically coupled with the primary coil 2. The primary coil 2 is divided into a first coil piece 21 and a second coil piece 22 which are connected in series. The first coil piece 21 and the second coil piece 22 are disposed while being spaced apart from each other in a moving direction X of the piezoelectric substance 3 based on the elastic deformation of the support member 20. The secondary coil 6 is disposed between the first coil piece 21 and the second coil piece 22 with respect to the moving direction X.

Description

  The present invention relates to a force sensor that detects a pressing force acting on a piezoelectric body in a state where an AC voltage is applied to the piezoelectric body.

  In general, an end effector of an assembly robot, for example, a robot hand such as a parallel gripper or a multi-point support device, is provided with a force sensor in order to detect a gripping force of a workpiece. As conventional force sensors, strain gauges, capacitance types, etc. have been developed, but since all force sensors using these use deformation of members, it is possible to increase the sensitivity and range of measurement. To achieve this, a sufficient amount of deformation is required. For this reason, when the external dimensions are reduced, a sufficient amount of deformation cannot be obtained, so that the output signal amplitude is reduced, resulting in a situation in which the signal amplitude is lower than the external noise noise, and the accuracy is low. It was.

  Therefore, a force sensor using a piezoelectric body is known (see Patent Document 1). The piezoelectric body generates a voltage for an instantaneous force, but does not generate a voltage for a steady force. Therefore, based on the fact that an AC voltage is applied to the piezoelectric body to generate vibration in the piezoelectric body, and the impedance of the piezoelectric body changes due to the pressing force acting on the piezoelectric body from the outside, the voltage amplitude at both ends of the piezoelectric body at that time The force is detected by the amount of change. In Patent Document 1, a primary coil connected to an AC power source and a secondary coil connected to a pair of electrodes are electromagnetically coupled to supply power to the pair of electrodes in a non-contact manner.

  As a power supply structure for this type of force sensor, as shown in FIG. 7, electric wires 33, 34 routed from the outside to a pair of electrodes 31, 32 fixedly provided on the piezoelectric body 30 are soldered or conductive adhesive. In general, a connection structure is used.

  Further, although different from the invention of the force sensor, a method for compensating for power supply fluctuation due to fluctuation of coupling degree between coils has been proposed (see Patent Document 2). In this patent document 2, the output from the secondary coil is detected and feedback controlled.

JP 2008-275548 A JP 2009-189197 A

  However, in the structure in which the wires 33 and 34 routed from the outside are connected to the electrodes 31 and 32 to supply power to the force sensor as shown in FIG. The vibration characteristics of the piezoelectric body 30 will change depending on how it is routed. Therefore, it is difficult to detect the pressing force with high accuracy in the configuration in which the electric wires 33 and 34 are connected to the electrodes 31 and 32.

  In the conventional configuration, the secondary coil is provided separately from the piezoelectric body, but it is also conceivable to provide the secondary coil integrally with the piezoelectric body. When a piezoelectric body is directly provided on a rigid base, the vibration state of the piezoelectric body changes suddenly with a small pressing force, and the detection output is saturated immediately. A support member that is elastically deformed may be interposed between the piezoelectric body and the base on which the piezoelectric body is provided. When the support member is interposed in this way, the position of the piezoelectric body changes due to compressive deformation of the support member due to the pressing force, so the relative position between the primary coil and the secondary coil changes, and the degree of coupling between the coils changes. However, another problem that the output of the force sensor changes occurs.

  Further, when feedback control is performed as in Patent Document 2, a complicated circuit for feedback control is required, resulting in a problem of high cost and large size.

  Accordingly, an object of the present invention is to provide a force sensor that can suppress fluctuations in the detection result of the pressing force even if the position of the piezoelectric body fluctuates without providing a circuit for feedback control. It is.

  The present invention includes a primary coil connected to an AC power source, a base on which the primary coil is fixed, a plate-like piezoelectric body whose impedance changes according to a pressing force received from the outside, and the base. A support member that is interposed between the piezoelectric body, supports the piezoelectric body with respect to the base, and is elastically deformed by the pressing force received by the piezoelectric body; and both surfaces of the piezoelectric body A pair of electrodes provided on the secondary coil, a secondary coil connected to the pair of electrodes and electromagnetically coupled to the primary coil, and a detection unit that detects a change in impedance of the piezoelectric body as the pressing force. One of the primary coil and the secondary coil is divided into a first coil piece and a second coil piece connected in series, and the first coil piece and the second coil piece are Based on elastic deformation of support member In the moving direction of the piezoelectric body, the other coils of the primary coil and the secondary coil are spaced apart from each other, the first coil piece and the second coil piece with respect to the moving direction. It is arrange | positioned between these, It is characterized by the above-mentioned.

  According to the present invention, power can be supplied to the pair of electrodes in a non-contact manner by electromagnetic coupling of the primary coil and the secondary coil, and there is no need to connect an external power supply line to the pair of electrodes. Variations in the detection result of the pressing force can be suppressed without being affected by the connection state or contact state of the electric wire. Furthermore, even when the position of the piezoelectric body changes and the positional relationship between the primary coil and the secondary coil changes, fluctuations in the detection result of the pressing force can be suppressed.

It is sectional drawing which shows schematic structure of the force sensor which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows a piezoelectric unit, (a) is a front view of a piezoelectric unit, (b) is sectional drawing of a piezoelectric unit, (c) is a bottom view of a piezoelectric unit. It is an electric circuit diagram which shows the circuit structure of a force sensor. It is an electric circuit diagram which shows the circuit structure of the modification of a force sensor, (a) is an electric circuit diagram which shows the circuit structure in which a detection part detects the voltage between the terminals of an impedance element, (b) is a detection part by a primary coil It is an electric circuit diagram which shows the circuit structure which detects the electric current which flows into. It is sectional drawing which shows schematic structure of the force sensor which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows schematic structure of the force sensor which concerns on 3rd Embodiment of this invention. It is sectional drawing which shows schematic structure of the conventional force sensor.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a cross-sectional view showing a schematic configuration of a force sensor according to the first embodiment of the present invention. As shown in FIG. 1, the force sensor 100 includes a base 1 that is a rigid body, a primary coil 2 fixed to the base 1, a plate-like piezoelectric body (also referred to as a piezoelectric vibrator) 3, and a piezoelectric body. 3 and a pair of electrodes 4 and 5 provided on both surfaces 3a and 3b. The force sensor 100 includes a secondary coil 6 that is connected to the pair of electrodes 4 and 5 and is disposed in non-contact with the primary coil 2 and electromagnetically coupled to the primary coil 2.

  Of the pair of electrodes 4, 5, one electrode (first electrode) 4 is fixedly provided on one plane 3 a of the piezoelectric body 3, and the other electrode (second electrode) 5 is formed of the piezoelectric body 3. It is fixed to the other plane 3b. In the first embodiment, the secondary coil 6 is fixedly provided across both surfaces 3a and 3b of the piezoelectric body 3. A piezoelectric unit 8 is constituted by the piezoelectric body 3 and the pair of electrodes 4, 5 and the secondary coil 6.

  The force sensor 100 is interposed between the base 1 and the piezoelectric body 3 (ie, the piezoelectric unit 8), supports the piezoelectric body 3 (ie, the piezoelectric unit 8) with respect to the base 1, and the piezoelectric body 3 is A support member 20 formed of an elastic body that is elastically deformed (compressed and deformed) by a pressing force F received is provided. The support member 20 is an elastic body such as rubber or sponge.

  Further, the force sensor 100 is provided facing a plane 3 a opposite to the plane 3 b facing the support member 20 of the piezoelectric body 3, and transmits the force F acting from the outside to the piezoelectric body 3 evenly. A member 19 is provided. In the first embodiment, the force transmission member 19 is composed of the same elastic body as the support member 20.

  The base 1 is, for example, a finger main body in a robot end effector, a robot main body of a robot arm, or a separate body from these main bodies and is a fixed body fixed to the main body.

  A recess 11 is formed in the base 1. In the recess 11, the support member 20, the piezoelectric unit 8, and the force transmission member 19 are sequentially stacked from the bottom surface 11 a of the recess 11 toward the opening end 11 b. The support member 20 is provided on the bottom surface 11 a of the recess 11 so as to be interposed between the bottom surface 11 a and the piezoelectric body 3.

  In FIG. 1, for convenience of explanation, the support member 20, the piezoelectric unit 8, and the force transmission member 19 are illustrated at intervals, but actually, the support member 20, the piezoelectric unit 8, and the force transmission member are illustrated. Nineteen adjacent ones are in contact with each other.

  A cover member 12 that accommodates and holds the force transmission member 19, the piezoelectric unit 8, and the support member 20 in the recess 11 is fixed to the surface of the base 1 so as to cover the recess 11, that is, to cover the force transmission member 19. Is provided. The cover member 12 restricts the force transmission member 19, the piezoelectric unit 8, and the support member 20 from dropping from the recess 11. The cover member 12 is made of an elastic body such as rubber or sponge, and can transmit the pressing force F to the force transmission member 19.

  2A and 2B are explanatory views showing the piezoelectric unit 8. FIG. 2A is a front view of the piezoelectric unit 8, FIG. 2B is a cross-sectional view of the piezoelectric unit 8, and FIG. 6 is a bottom view of the unit 8. FIG.

In the first embodiment, the secondary coil 6 includes a first coil pattern 41 formed on one plane 3 a of the piezoelectric body 3, and a second coil pattern 51 formed on the other plane 3 b of the piezoelectric body 3. The coil patterns 41 and 51 are connected by the wiring pattern 7.
Each of the first coil pattern 41 and the second coil pattern 42 is formed in a spiral shape on each of the flat surfaces 3a and 3b. The wiring pattern 7 is formed on the side surface of the piezoelectric body 3, specifically, a part of the outer surface 3 c. The first electrode 4 is formed on one plane 3 a of the piezoelectric body 3, and the second electrode 5 is formed on the other plane 3 b of the piezoelectric body 3.

  The electrodes 4 and 5, the coil patterns 41 and 51, and the wiring pattern 7 are integrally formed on the piezoelectric body 3 using a mask by, for example, screen printing, physical vapor deposition (PVD), chemical vapor deposition (CVD), or the like. Alternatively, after forming a conductive film on the piezoelectric body 3, etching may be performed using a mask to form the electrodes 4 and 5, the coil patterns 41 and 51, and the wiring pattern 7.

  As shown in FIGS. 2A and 2B, the first electrode 4 and the first coil pattern 41 are integrally formed on the same plane 3a. Therefore, it is not necessary to connect the first electrode 4 and the first coil pattern 41 with solder or a conductive adhesive. As shown in FIGS. 2B and 2C, the second electrode 5 and the second coil pattern 51 are integrally formed on the same plane 3b. Therefore, it is not necessary to connect the second electrode 5 and the second coil pattern 51 with solder or a conductive adhesive.

  The first electrode 4 and the second electrode 5 face each other across the piezoelectric body 3. One end 41 a of the first coil pattern 41 is connected to the wiring pattern 7, and the other end 41 b is connected to the first electrode 4. One end 51 a of the second coil pattern 51 is connected to the wiring pattern 7, and the other end 51 b is connected to the second electrode 5.

  The first coil pattern 41 and the second coil pattern 51 face each other across the piezoelectric body 3. That is, when one of the coil patterns 41 and 51 is projected onto the other, they overlap each other in plan view.

  In the first embodiment, the secondary coil 6 has a configuration in which the first coil pattern 41 and the second coil pattern 51 are connected in series. However, the present invention is not limited to this. The secondary coil 6 may be a coil pattern provided on only one of the two surfaces 3 a and 3 b of the piezoelectric body 3. Further, the case where the secondary coil 6 is formed integrally with the pair of electrodes 4 and 5 has been described, but the present invention is not limited to this, and is fixed to the piezoelectric body 3 so as to move integrally with the piezoelectric body 3. It only has to be. At that time, the secondary coil 6 may be electrically connected to the pair of electrodes 4 and 5.

  By supplying power from the primary coil 2 to the secondary coil 6 in a non-contact manner as shown in FIG. 1, an alternating voltage is applied to the pair of electrodes 4, 5, and the piezoelectric body 3 sandwiched between them has a pair of electrodes The electric field by 4 and 5 is applied, and thereby the piezoelectric body 3 is physically vibrated.

  In this state, when a pressing force F acts on the piezoelectric body 3 from the outside via the cover member 12 and the force transmission member 19, the pressing force F acts on the supporting member 20 via the piezoelectric body 3, and the supporting member 20 is compressed and deformed. To do. Thereby, the pressing force F from the force transmission member 19 acts on one surface 3 a of the piezoelectric body 3, and the pressing force F due to the reaction from the support member 20 acts on the other surface 3 b of the piezoelectric body 3. Thus, the pressing force F acts on the piezoelectric body 3 evenly from both surfaces 3a and 3b. The vibration state of the piezoelectric body 3 is changed by the pressing force F, and the impedance of the piezoelectric body 3 is changed according to the pressing force F.

  FIG. 3 is an electric circuit diagram showing a circuit configuration of the force sensor. As shown in FIG. 3, the force sensor 100 includes an impedance element 14 connected in series to the primary coil 2 and a detection unit 15 that detects a change in impedance of the piezoelectric body 3 as a pressing force F acting on the piezoelectric body 3. And. The detection unit 15 is a voltage detector that is connected between the terminals of the primary coil 2 and directly detects the voltage between the terminals of the primary coil 2 that changes according to the impedance of the piezoelectric body 3. That is, the detection unit 15 directly detects the voltage between the terminals of the primary coil 2 as a change in the impedance of the piezoelectric body 3. The impedance element 14 is a passive element such as a resistance element, a capacitor element, or an inductance element. Primary coil 2 is connected to AC power supply E via impedance element 14. The AC power source E is a constant voltage power source that outputs a constant AC voltage at a constant frequency. The primary coil 2 is driven by an AC signal supplied from an AC power source E.

  A high-frequency AC voltage from the AC power source E is applied to the series circuit composed of the impedance element 14 and the primary coil 2. An AC voltage is induced in the secondary coil 6 by the AC voltage applied to the primary coil 2. An electrical resonance circuit is formed by the secondary coil 6 and the piezoelectric body 3 sandwiched between the pair of electrodes 4, 5. An alternating voltage is applied to the pair of electrodes 4, 5, and the piezoelectric body 3 is alternately connected. An electric field is applied. Thereby, the piezoelectric body 3 vibrates.

  When the pressing force F acts on the piezoelectric body 3 and the vibration state changes, the impedance of the piezoelectric body 3 changes, and the resonance state of the electric resonance circuit changes according to this change, and the voltage on the secondary coil 6 side fluctuates. To do. Thereby, the voltage between the terminals of the primary coil 2 fluctuates. That is, signals are exchanged between the primary coil 2 and the secondary coil 6 by electromagnetic coupling.

  The detection unit 15 detects the inter-terminal voltage of the primary coil 2 that changes according to the impedance of the piezoelectric body 3 as the pressing force F. That is, the voltage (voltage amplitude) of the primary coil 2 detected by the detection unit 15 corresponds to the impedance of the piezoelectric body 3, and the detection unit 15 acts on the impedance of the piezoelectric body 3, that is, the piezoelectric body 3. A signal indicating the pressing force F is detected.

  By the way, in this 1st Embodiment, as shown in FIG.1 and FIG.3, the primary coil 2 as one coil among the primary coil 2 and the secondary coil 6, and the 1st coil piece 21 connected in series, and It is divided into second coil pieces 22. As shown in FIG. 1, the first coil piece 21 and the second coil piece 22 are arranged at intervals in the moving direction X of the piezoelectric body 3 based on elastic deformation (compression deformation) of the support member 20. . In the first embodiment, the movement direction X is a direction perpendicular to the bottom surface 11 a of the recess 11 of the base 1.

  The secondary coil 6, which is the other of the primary coil 2 and the secondary coil 6, is disposed between the first coil piece 21 and the second coil piece 22 with respect to the movement direction X. That is, the piezoelectric body 3 to which the secondary coil 6 is fixed is disposed between the first coil piece 21 and the second coil piece 22 with respect to the movement direction X. The first coil piece 21 of the primary coil 2 is disposed on the opening end 11 b side of the recess 11, and the second coil piece 22 is disposed on the bottom surface 11 a side of the recess 11.

  In the first embodiment, the coil pieces 21 and 22 are directly fixed to the base 1, but may be fixed to the base 1 via a fixture or the like.

  Next, in FIG. 1, when an external force acts on the piezoelectric unit 8 composed of the piezoelectric body 3 sandwiched between the secondary coil 6 and the pair of electrodes 4, 5, and moves in the vertical direction of FIG. Will be described.

  The operation when the piezoelectric unit 8 moves downward with respect to the base 1 will be described. When the piezoelectric unit 8 moves downward, the distance between the first coil piece 21 of the primary coil 2 and the secondary coil 6 increases. As a result, the degree of coupling between the coils 21 and 6 decreases, and the secondary coil 6 is excited by a signal supplied from the AC power source E, which is a signal source, via the first coil piece 21 of the primary coil 2. Power is reduced. At the same time, the distance between the second coil piece 22 of the primary coil 2 and the secondary coil 6 is shortened. As a result, the degree of coupling between the coils 22 and 7 increases, and the secondary coil 6 is excited by a signal supplied from the AC power source E, which is a signal source, via the second coil piece 22 of the primary coil 2. Power rises. By such an operation, the power supplied to the pair of electrodes 4 and 5 by the signal from the AC power source E as a signal source is kept almost constant regardless of the influence of the movement of the piezoelectric body 3.

  Next, an operation when the piezoelectric unit 8 moves upward with respect to the base 1 will be described. When the piezoelectric unit 8 moves upward, the distance between the first coil piece 21 of the primary coil 2 and the secondary coil 6 is shortened. As a result, the degree of coupling between the coils 21 and 6 is increased and excited by the secondary coil 6 by a signal supplied from the AC power source E, which is a signal source, via the first coil piece 21 of the primary coil 2. Increased power. At the same time, the distance between the second coil piece 22 of the primary coil 2 and the secondary coil 6 becomes longer. As a result, the degree of coupling between the coils 22 and 6 decreases, and the secondary coil 6 is excited by a signal supplied from the AC power source E, which is a signal source, via the second coil piece 22 of the primary coil 2. The power decreases. By such an operation, the power supplied to the pair of electrodes 4 and 5 by the signal from the AC power source E as a signal source is kept almost constant regardless of the influence of the movement of the piezoelectric body 3.

  As described above, according to the first embodiment, power can be supplied to the pair of electrodes 4 and 5 in a non-contact manner by electromagnetic coupling of the primary coil 2 and the secondary coil 6. In addition, since it is not necessary to connect an external power supply line to the pair of electrodes 4 and 5, it is not affected by the connection state or contact state of the power supply line, and fluctuations in the detection result of the pressing force can be suppressed. Furthermore, even when the position of the piezoelectric body 3 changes and the positional relationship between the primary coil 2 and the secondary coil 6 changes, fluctuations in the detection result of the pressing force by the detection unit 15 can be suppressed. Therefore, it is not necessary to separately provide a compensation circuit for performing feedback control, the detection result by the detection unit 15 can be stabilized with a simple configuration, and the increase in cost can be suppressed. Since it can be omitted, the force sensor 100 can be downsized.

  The first electrode 4 and the first coil pattern 41 are integrally formed on one plane 3 a of the piezoelectric body 3, and the second electrode 5 and the second coil pattern 51 are integrally formed on the other plane of the piezoelectric body 3. Since the film is formed on 3b, the variation in mass is smaller than when solder or conductive adhesive is used. Moreover, since the detection unit 15 detects the voltage generated in the primary coil 2 as the pressing force F, it is not necessary to connect a detection wire to the pair of electrodes 4 and 5. Therefore, it is possible to suppress fluctuations in the vibration characteristics of the piezoelectric body 3, the detection result by the detection unit 15 is stable, and the pressing force F can be detected with high accuracy.

  Further, since the piezoelectric body 3 (that is, the piezoelectric unit 8) is sandwiched between the support member 20 and the force transmission member 19 which are elastic bodies, the pressing force F acts on the piezoelectric body 3 from both surfaces 3a and 3b evenly. Accordingly, variation in the vibration state at each position of the piezoelectric body 3 is reduced, and as a result, the detection accuracy of the pressing force F is improved.

  As shown in FIG. 4A, the detection unit 15 that is a voltage detector is connected between the terminals of the impedance element 14, and detects the voltage between the terminals of the impedance element 14 to detect the primary coil 2. You may make it detect the voltage between terminals indirectly. Since the AC voltage output from the AC power source E is constant and is divided by the impedance element 14 and the primary coil 2, the voltage between the terminals of the impedance element 14 is caused by the fluctuation of the voltage between the terminals of the primary coil 2. Fluctuate accordingly. In any case, the voltage (voltage amplitude) detected by the detection unit 15 corresponds to the impedance of the piezoelectric body 3, and the detection unit 15 detects the impedance of the piezoelectric body 3, that is, the pressing force acting on the piezoelectric body 3. A signal indicating F is detected.

  Further, the detection unit 15 may be a current sensor that detects a current flowing through the primary coil 2 as shown in FIG. Since the current flowing through the primary coil 2 changes according to the impedance of the piezoelectric body 3 as well as the voltage, the detection unit 15 acts on the piezoelectric body 3 by detecting the current flowing through the primary coil 2. The pressing force F is detected. That is, the detection unit 15 only needs to detect at least one of the voltage and current of the primary coil 2, and it is not necessary to connect an electric wire to the pair of electrodes 4 and 5, thereby improving detection accuracy.

[Second Embodiment]
Next, a force sensor according to a second embodiment of the present invention will be described. FIG. 5 is a cross-sectional view showing a schematic configuration of a force sensor according to the second embodiment of the present invention. Note that in the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 5, the pair of coil pieces 21, 22 of the primary coil 2 of the force sensor 100 </ b> A of the second embodiment are arranged at positions facing the secondary coil 6 so as to sandwich the secondary coil 6. Has been. In the second embodiment, the first coil piece 21 faces the one surface 3 a of the piezoelectric body 3 and faces the first coil pattern 41 of the secondary coil 6, and the second coil piece 22 is formed of the piezoelectric body 3. The second coil pattern 51 of the secondary coil 6 is directly opposed to the other surface 3a.

  The piezoelectric body 3 moves in the moving direction X perpendicular to the bottom surface 11 a of the recess 11 of the base 1 by elastic deformation (compression deformation) of the support member 20, but each coil piece 21, 22 has coil patterns 41, 51 and Relative. Therefore, even if the position of the piezoelectric body 3 fluctuates, the facing state of the coil pieces 21 and 22 and the secondary coil 6 is maintained. Thereby, the electromagnetic coupling degree of the primary coil 2 and the secondary coil 6 becomes high, and the detection sensitivity of the pressing force F improves.

[Third Embodiment]
Next, a force sensor according to a third embodiment of the present invention will be described. FIG. 6 is a cross-sectional view showing a schematic configuration of a force sensor according to the third embodiment of the present invention. Note that, in the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in FIG. 6, the force sensor 100B includes a primary coil 2A fixed to the base 1 and a secondary coil 6A connected to the pair of electrodes 4 and 5 and electromagnetically coupled to the primary coil 2A in a non-contact manner. And.

  In the third embodiment, of the primary coil 2A and the secondary coil 6A, the secondary coil 6A is divided into a first coil piece 61 and a second coil piece 62 that are connected in series. The first coil piece 61 is a spiral first coil pattern formed on one plane 3 a of the piezoelectric body 3, and the second coil piece 62 is formed on the other plane 3 b of the piezoelectric body 3. It is a spiral second coil pattern.

  The first coil piece 61 and the first electrode 4 are integrally formed on one plane 3a, and the second coil piece 62 and the second electrode 5 are integrally formed on the other plane 3b. Therefore, it is not necessary to use solder, conductive adhesive or the like to electrically connect them.

  The first coil piece 61 and the second coil piece 62 are connected in series by a wiring pattern 63 formed integrally with the coil pieces 61 and 62 on the side surface of the piezoelectric body 3, in the third embodiment, on the outer side surface 3 c. Connected. A piezoelectric unit 8A is constituted by the piezoelectric body 3, the pair of electrodes 4, 5 and the secondary coil 6A.

  The first coil piece 61 of the secondary coil 6A is fixed to the one plane 3a, and the second coil piece 62 is fixed to the other plane 3b. Therefore, the pair of coil pieces 61 and 62 are arranged at intervals in the moving direction X of the piezoelectric body 3 based on the elastic deformation of the support member 20. Specifically, the pair of coil pieces 61 and 62 are arranged at a distance from each other by the thickness of the piezoelectric body 3.

  The primary coil 2A, which is the other of the primary coil 2A and the secondary coil 6A, is disposed on the base 1 so as to be disposed at a position facing the side surface of the piezoelectric body 3, that is, the outer surface 3c in the third embodiment. It is fixed. As a result, the primary coil 2 </ b> A is disposed between the first coil piece 61 and the second coil piece 62 with respect to the movement direction X.

  The operation of the force sensor 100B of the third embodiment will be described. An electrical resonance circuit is formed by the secondary coil 6 </ b> A and the piezoelectric body 3 sandwiched between the pair of electrodes 4 and 5. In order to supply power to the resonance circuit, the primary coil 2A is disposed between the pair of coil pieces 61 and 62 of the secondary coil 6A, and the primary coil 2A is received by a signal supplied from an AC power supply (not shown). Driven. As a result, signals are exchanged between the primary coil 2A and the secondary coil 6A by electromagnetic coupling.

  Next, an operation when an external force acts on the piezoelectric body 3 and the piezoelectric unit 8A moves downward in FIG. 6 will be described. External force is evenly applied to both surfaces 3a and 3b of the piezoelectric body 3 via the force transmission member 19 and the support member 20 disposed on both surfaces 3a and 3b.

  When the piezoelectric unit 8A moves downward, the distance between the primary coil 2A and the second coil piece 62 of the secondary coil 6A increases. As a result, the degree of coupling between the coils 2A and 62 is lowered, and excited by the second coil piece 62 of the secondary coil 6A by a signal supplied from an AC power source (not shown) via the primary coil 2A. Power is reduced. At the same time, the distance between the primary coil 2A and the first coil piece 61 of the secondary coil 6A is shortened. As a result, the degree of coupling between the coils 2A and 61 is increased, and the electric power excited in the first coil piece 61 is increased by a signal supplied from the AC power source, which is a signal source, via the primary coil 2A.

  With such an operation, the power supplied to the pair of electrodes 4 and 5 by the signal driven from the AC power source as the signal source is kept substantially constant regardless of the influence of the movement of the piezoelectric unit 8A.

  As described above, according to the second embodiment, power can be supplied to the pair of electrodes 4 and 5 in a non-contact manner by electromagnetic coupling of the primary coil 2A and the secondary coil 6A. In addition, since it is not necessary to connect an external power supply line to the pair of electrodes 4 and 5, it is not affected by the connection state or contact state of the power supply line, and fluctuations in the detection result of the pressing force can be suppressed. Furthermore, even when the position of the piezoelectric body 3 changes and the positional relationship between the primary coil 2A and the secondary coil 6A changes, fluctuations in the detection result of the pressing force by the detection unit can be suppressed. Therefore, it is not necessary to provide a compensation circuit for performing feedback control, the detection result by the detection unit can be stabilized with a simple configuration, the increase in cost can be suppressed, and the compensation circuit can be omitted. Therefore, the force sensor 100B can be downsized.

  In addition, the first electrode 4 and the first coil piece 61 of the secondary coil 6A are integrally formed on one plane 3a of the piezoelectric body 3, and the second electrode 5 and the second coil piece 62 of the secondary coil 6A Are integrally formed on the other flat surface 3 b of the piezoelectric body 3. A wiring pattern 7 that connects the first coil piece 61 and the second coil piece 62 is formed integrally with the coil pieces 61 and 62. With this configuration, the variation in mass is smaller than when solder or a conductive adhesive is used. Moreover, since the detection unit detects the voltage generated in the primary coil 2 </ b> A as the pressing force F, it is not necessary to connect a detection electric wire to the pair of electrodes 4 and 5. Therefore, it is possible to suppress fluctuations in the vibration characteristics of the piezoelectric body 3, the detection result by the detection unit is stable, and the pressing force F can be detected with high accuracy.

  In addition, since the piezoelectric body 3 (that is, the piezoelectric unit 8A) is sandwiched between the support member 20 and the force transmission member 19 which are elastic bodies, the pressing force F acts on the piezoelectric body 3 from both sides 3a and 3b evenly. Accordingly, variation in the vibration state at each position of the piezoelectric body 3 is reduced, and as a result, the detection accuracy of the pressing force F is improved.

  The present invention is not limited to the embodiments described above, and many modifications can be made by those having ordinary knowledge in the art within the technical idea of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Base, 2 ... Primary coil, 3 ... Piezoelectric body, 4 ... 1st electrode, 5 ... 2nd electrode, 6 ... Secondary coil, 15 ... Detection part, 20 ... Support member, 21 ... 1st coil piece 22 ... 2nd coil piece, 100 ... Force sensor

Claims (5)

A primary coil connected to an AC power source;
A base on which the primary coil is fixed;
A plate-like piezoelectric body whose impedance changes according to the pressing force received from the outside;
A support member formed between an elastic body that is interposed between the base and the piezoelectric body, supports the piezoelectric body with respect to the base, and is elastically deformed by the pressing force received by the piezoelectric body;
A pair of electrodes provided on both sides of the piezoelectric body;
A secondary coil connected to the pair of electrodes and electromagnetically coupled to the primary coil;
A detection unit that detects a change in impedance of the piezoelectric body as the pressing force;
One of the primary coil and the secondary coil is divided into a first coil piece and a second coil piece connected in series,
The first coil piece and the second coil piece are arranged at intervals in the moving direction of the piezoelectric body based on elastic deformation of the support member,
The other coil of the primary coil and the secondary coil is disposed between the first coil piece and the second coil piece with respect to the moving direction.
A force sensor characterized by that. The one coil is the primary coil;
The piezoelectric body is disposed between the first coil piece and the second coil piece with respect to the moving direction.
The force sensor according to claim 1. The one coil is the secondary coil;
The first coil piece is provided on one plane of the piezoelectric body, and the second coil piece is provided on the other plane of the piezoelectric body,
The primary coil is disposed at a position facing the side surface of the piezoelectric body.
The force sensor according to claim 1. The first coil piece is a spiral first coil pattern formed on one plane of the piezoelectric body,
The second coil piece is a spiral second coil pattern formed on the other plane of the piezoelectric body.
The force sensor according to claim 3. The detection unit detects at least one of the voltage and current of the primary coil that changes according to the impedance of the piezoelectric body as the pressing force.
The force sensor according to any one of claims 1 to 4, wherein:

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