JP2012057999A - Strain sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain sensor capable of preventing the natural frequency of an oscillator in an unloaded condition from being varied even when excess pressing force is applied to a pressing member and having improved measurement accuracy.SOLUTION: The strain sensor applies voltage to a drive part 27 in a first oscillator 25 and a second oscillator 26 to oscillate the first oscillator 25 and the second oscillator 26 and detects the variation of natural frequencies of the first oscillator 25 and the second oscillator 26 due to loads as an output signal from a detection part 28 to measure stress to be applied to a both ends supported beam 22 through a stress transmission member 34.

Description

  The present invention particularly relates to a strain sensor that detects strain generated by applying a load.

  This type of conventional strain sensor has a configuration as shown in FIG.

  FIG. 7 is a top view of a conventional strain sensor.

  In FIG. 7, reference numeral 1 denotes a first vibrator, and the first vibrator 1 is configured to face a pair of tuning forks 2. Reference numeral 3 denotes a second vibrator, and the second vibrator 3 is configured to face a pair of tuning forks 4. Reference numeral 5 denotes a stress transmission member, and the stress transmission member 5 connects between the first vibrator 1 and the second vibrator 3, and the second vibrator 3 to the first vibrator 1. Stress is transmitted toward Reference numeral 6 denotes a support member, and this support member 6 is connected to one end of the first vibrator 1. Reference numeral 7 denotes a pressing member, which is connected to one end of the second vibrator 3.

  Next, the operation of the conventional strain sensor configured as described above will be described.

  When a pressing force in the Y-axis direction acts on the pressing member 7, a compressive force is applied to the first vibrator 1 and the second vibrator 3. Then, the natural frequency fa of the first vibrator 1 and the second vibrator 3 decreases. Therefore, the pressing force applied to the pressing member 7 can be detected by measuring the natural frequency fa of the first vibrator 1 and the second vibrator 3.

  As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.

JP 2009-80069 A

  However, in the above-described conventional configuration, since the pressing force from the pressing member 7 directly acts on the second vibrator 3 and the first vibrator 1, the excessive pressing force is applied to the first vibrator 1. When applied to the second vibrator 3, residual stress is generated in the first vibrator 1 and the second vibrator 3, thereby causing the first vibrator 1 and the second vibrator in the no-load state. Since the natural frequency of the vibrator 3 fluctuates, the pressing force cannot be measured with high accuracy.

  The present invention solves the above-described conventional problem, and even if an excessive pressing force is applied to the pressing member, the natural frequency of the vibrator in the no-load state does not fluctuate and the measurement accuracy is improved. An object of the present invention is to provide a strain sensor.

  In order to achieve the above object, the present invention has the following configuration.

  The invention according to claim 1 of the present invention includes a both-end support beam provided with a vibrator having a drive unit and a detection unit, a cylindrical stress transmission member having one end connected to both ends of the both-end support beam, A pressing member connected to the other end of the stress transmission member, and applying a voltage to the driving unit in the vibrator to drive the vibrator to vibrate, and to detect fluctuations in the natural frequency of the vibrator due to the load By detecting this as an output signal, the stress acting on the both-end beam is measured via the stress transmission member. According to this configuration, the stress acting on the both-end support beam via the stress transmission member Since the pressing force from the pressing member does not directly act on the vibrator, and no residual stress is generated in the vibrator, the natural frequency of the vibrator in the no-load state is reduced. As a result, it will not fluctuate And it has a effect that the pressing force can be accurately measured.

  The invention according to claim 2 of the present invention is such that, in particular, the drive unit and the detection unit have a laminated structure of a lower electrode, a piezoelectric layer, and an upper electrode. According to this configuration, the drive unit and the detection unit are Since the lower electrode, the piezoelectric layer, and the upper electrode are stacked, the drive unit and the detection unit can be formed in a small space.

  According to the third aspect of the present invention, the pressing member is provided with the flange portion so as to protrude outward, and the support member for supporting the lower side of the flange portion is provided. The pressing member is provided with the flange so as to protrude outward, and the support member for supporting the lower side of the flange is provided, so that the supporting member absorbs the pressing force applied to the pressing member via the flange. As a result, since the pressing force from the pressing member does not directly act on the vibrator, the natural frequency of the vibrator in the no-load state does not fluctuate, and the pressing force can be accurately measured. It is what has.

  A strain sensor according to the present invention includes a both-end support beam provided with a vibrator having a drive unit and a detection unit, a cylindrical stress transmission member having one end connected to both ends of the both-end support beam, A pressing member connected to the other end, and applying a voltage to the drive unit of the vibrator to drive the vibrator to vibrate, and detecting fluctuations in the natural frequency of the vibrator due to a load as an output signal from the detection unit By doing so, the stress acting on the both-end beam is measured via the stress transmission member. According to this configuration, the stress acting on the both-end beam is measured via the stress transmission member. Therefore, the pressing force from the pressing member does not directly act on the vibrator, and no residual stress is generated in the vibrator, so that the natural frequency of the vibrator in the no-load state does not fluctuate. As a result, the pressing force is precisely adjusted. Those having an effect that it is possible to provide a strain sensor which can be measured.

1 is an exploded perspective view of a strain sensor according to an embodiment of the present invention. Side sectional view of the strain sensor Top view of the strain sensor Plan view of the functional part of the bilateral beam of the strain sensor Side sectional view showing a state in which the strain sensor operates. The figure which shows the state from which the natural frequency of the 1st vibrator and the 2nd vibrator in the same strain sensor changes. Top view of a conventional strain sensor

  Hereinafter, a strain sensor according to an embodiment of the present invention will be described with reference to the drawings.

  1 is an exploded perspective view of a strain sensor according to an embodiment of the present invention, FIG. 2 is a side sectional view of the strain sensor, FIG. 3 is a top sectional view of the strain sensor, and FIG. It is a top view of the functional part in.

  1 to 4, reference numeral 21 denotes a strain detection element, and the strain detection element 21 includes a both-end support beam 22 and a ring-shaped connection portion 23 that connects both ends of the both-end support beam 22. In addition, a functional unit 24 is provided on the upper surface of the both-end supported beam 22 in the strain detection element 21. The functional unit 24 is provided so as to be orthogonal to the first vibrator 25 and the first vibrator 25. The second vibrator 26 is provided. Each of the first vibrator 25 and the second vibrator 26 in the strain detecting element 21 has a lower electrode (not shown) made of Pt and a piezoelectric layer (not shown) made of PZT on both ends. ) And an upper electrode (not shown) made of Au, a pair of drive units 27 is provided. In addition, a lower electrode (not shown) made of Pt, a piezoelectric layer (not shown) made of PZT, and an upper electrode (not shown) made of Au are laminated between the pair of driving units 27. A configured detection unit 28 is provided. The drive unit 27 and the detection unit 28 are each configured by laminating a lower electrode (not shown) made of Pt, a piezoelectric layer (not shown) made of PZT, and an upper electrode (not shown) made of Au. Yes.

  Since the drive unit 27 and the detection unit 28 have a laminated structure of a lower electrode (not shown), a piezoelectric layer (not shown), and an upper electrode (not shown), the drive unit 27 and the detection unit can be formed in a small space. 28 can be formed.

  Reference numeral 29 denotes a drive electrode, and the drive electrode 29 is electrically connected to an upper electrode (not shown) of the drive unit 27 in the first vibrator 25 and the second vibrator 26 through the wiring pattern 30. ing. Reference numeral 31 denotes a GND exposed electrode. The GND exposed electrode 31 includes a lower electrode (not shown) of the driving unit 27 and a lower electrode (not shown) of the detecting unit 28 in the first vibrator 25 and the second vibrator 26. (Not shown), and is provided over the entire functional unit 24. The above-described GND exposed electrode 31 is formed by cutting out a part of the insulating layer 32 provided over the entire functional unit 24. Reference numeral 33 denotes a detection electrode, and the detection electrode 33 is electrically connected to an upper electrode (not shown) of the detection unit 28 in the first vibrator 25 and the second vibrator 26. Reference numeral 34 denotes a cylindrical stress transmission member made of, for example, SUS430, and the stress transmission member 34 has a lower end fixed to the connection portion 23 of the strain detection element 21 and both ends of the both-end support beam 22. Reference numeral 35 denotes a pressing member made of, for example, SUS430. The pressing member 35 includes a circular thin plate-shaped flange portion 36 provided so as to protrude outward, and a columnar-shaped pressing portion 37. The lower surface is fixed to the upper end of the stress transmission member 34. Reference numeral 38 denotes a support member made of, for example, SUS430. The support member 38 has a cylindrical support portion 39 to which the lower surface outer end and the upper surface of the flange portion 36 are fixed, and a plate-like shape provided with the support portion 39 on the upper surface. A mounting portion 40 is provided, and a pair of mounting holes 41 are provided at the outer end of the mounting portion 40.

  Next, the assembly method of the strain sensor according to the first embodiment of the present invention configured as described above will be described.

  First, a lower electrode (not shown) made of Pt, a PZT thin film (not shown), and an upper electrode (not shown) made of Au are sequentially formed on the upper surface of an SOI substrate (not shown).

  Next, the upper electrode (not shown) is etched to form the drive unit 27, the detection unit 28, the wiring pattern 30, the drive electrode 29, and the detection electrode 33 on the upper surface of the functional unit 24.

  Next, the PZT thin film (not shown) is etched to expose a part of the lower electrode (not shown) to form the functional unit 24.

  Next, a semi-circular member is punched from the disc-shaped strain detecting element 21 to form a both-end supported beam 22 at the center of the strain detecting element 21, and then a functional unit 24 is attached to the both supported beams 22.

  Next, a cylindrical stress transmission member 34 and a thin disc-shaped flange 36 are formed on the pressing member 35 by, for example, deep drawing such as header processing.

  Next, the connection portion 23 in the strain detection element 21 is fixed to the lower surface of the stress transmission member 34 in the pressing member 35.

  Next, after pressing the plate-like support member 38 to form a pair of mounting holes 41, the support portion 39 is formed on the support member 38 by deep drawing.

  Finally, the outer peripheral side lower surface of the flange portion 36 of the pressing member 35 is fixed to the upper surface of the support portion 39 of the support member 38.

  Next, the operation of the strain sensor according to the embodiment of the present invention constructed and assembled as described above will be described.

  First, after inserting a bolt (not shown) into the mounting hole 41 in the support member 38, a nut (not shown) is screwed into the bolt (not shown), whereby the strain sensor is detected (not shown). )).

  And while applying the alternating voltage of the frequency substantially the same as the natural frequency fa of the 1st vibrator 25 to the drive part 27 in the 1st vibrator 25, to the drive part 27 in the 2nd vibrator 26, An alternating voltage having substantially the same frequency as the natural frequency fb of the second vibrator 26 is applied. Then, the first vibrator 25 vibrates at a natural frequency fa, while the second vibrator 26 vibrates at a natural frequency fb. In this state, when the output signal from the detection unit 28 in the first vibrator 25 is processed, the frequency fa is detected. Similarly, the frequency fb is detected from the detection unit 28 in the second vibrator 26. The Then, as shown in FIG. 5, when a pressing force is applied to the pressing portion 37 of the pressing member 35 from above, the joint portion between the flange portion 36 of the pressing member 35 and the supporting portion 39 of the supporting member 38 becomes a contact point, The flange portion 36 is bent, and a tensile force is applied to the both-end support beam 22 in the strain detection element 21. Then, as shown in FIG. 6, the natural frequency fa of the first vibrator 25 in the functional unit 24 decreases, while the natural frequency fb of the second vibrator 26 increases. Therefore, by processing the output signals from the detection units 28 of both the first vibrator 25 and the second vibrator 26, the pressing force applied to the pressing portion 37 of the pressing member 35 is detected as the amount of change in frequency. Is something that can be done.

  Similarly, when a tensile force is applied upward to the pressing portion 37 of the pressing member 35, the joint portion between the flange portion 36 of the pressing member 35 and the support portion 39 of the support member 38 becomes a contact point, and the flange portion 36 is bent. Thus, a tensile force is applied to the both-supported beam 22 in the strain detection element 21. Then, the natural frequency fa of the first vibrator 25 in the functional unit 24 increases, while the natural frequency fb of the second vibrator 26 decreases. Accordingly, by processing the output signals from the detection units 28 of both the first vibrator 25 and the second vibrator 26, the tensile force applied to the pressing portion 37 of the pressing member 35 is detected as the amount of change in frequency. Is something that can be done.

  Here, considering the case where an excessive tensile force is applied to the pressing member 35, in the strain sensor according to the embodiment of the present invention, the stress acting on the both-supported beam 22 is measured via the stress transmission member 34. Therefore, the pressing force from the pressing member 35 does not directly act on the first vibrator 25 and the second vibrator 26, thereby causing the first vibrator 25 and the second vibrator 26 to act. Since no residual stress is generated, the natural frequencies of the first vibrator 25 and the second vibrator 26 in the no-load state do not fluctuate, and as a result, the pressing force can be measured with high accuracy. Is.

  The strain sensor according to the present invention provides a strain sensor with improved reliability in which the natural frequency of the vibrator in an unloaded state does not fluctuate even when an excessive pressing force is applied to the pressing member. The present invention can be applied to applications that detect the weight of a seat such as an automobile.

DESCRIPTION OF SYMBOLS 22 Both-end support beam 25 1st vibrator | oscillator 26 2nd vibrator | oscillator 27 Drive part 28 Detection part 34 Stress transmission member 35 Pressing member 36 Grow part 38 Support member

Claims (3)

A holding beam provided with a vibrator having a drive unit and a detecting unit, a cylindrical stress transmission member having one end connected to both ends of the holding beam, and a pressure connected to the other end of the stress transmission member A stress transmission member by applying a voltage to the drive unit of the vibrator to drive the vibrator to vibrate, and detecting a fluctuation in the natural frequency of the vibrator due to a load as an output signal from the detection unit. A strain sensor that measures the stress acting on the both-ends beam via The strain sensor according to claim 1, wherein the drive unit and the detection unit have a laminated structure of a lower electrode, a piezoelectric layer, and an upper electrode. The strain sensor according to claim 1, wherein the pressing member is provided with a flange so as to protrude outward and a support member for supporting the lower side of the flange.

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