JP2939921B2 - Acceleration transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration transducer,
More specifically, a weight is supported via a flexible portion on a driven portion that moves integrally with the measured object, and when the driven portion receives acceleration, the weight is moved relative to the driven portion. The present invention relates to an acceleration converter of a type in which a strain at the time of relative displacement is converted into an electric signal by a strain gauge to detect the acceleration.

[0002]

2. Description of the Related Art Acceleration transducers are widely used, for example, when measuring the impact strength of a structure or analyzing the acceleration waveform of vibration generated in the structure. As a conventional acceleration converter used in this way, for example, when the driven portion is subjected to acceleration, the weight is displaced relative to the driven portion to generate a strain, that is, the acceleration is sensed. An electric resistance type strain gauge (in the form of foil or wire) attached to the surface of a flexure element, the resistance value of which varies with strain
No. 52899) and a type to which a diffusion type semiconductor gauge is attached (Japanese Patent Application Laid-Open No. 59-158566).

[0003]

In such an acceleration converter, it is required that the output signal be sufficiently large with respect to noise even with a small acceleration, and that the response be good. As a measure for improving the sensitivity of the acceleration converter, there is a method of increasing the weight and increasing the beam displacement. However, this method has a drawback that the natural frequency is low and the response frequency range is narrow.

Further, if the spring constant of the strain generating portion is reduced,
Although the flexure of the strain-generating portion increases and the strain output increases, the natural frequency decreases and the response frequency range narrows as described above. In addition, in order to develop an ultra-small acceleration transducer, it is necessary to minimize the strain gauge. However, the current metal foil strain gauge method has certain limitations, and is small and has a high resistance value (resistivity). It is difficult to manufacture strain gauges.

On the other hand, there is another type using the above-mentioned diffusion type semiconductor in addition to the electric resistance type strain gauge. In this type, a strain generating body is formed on a crystalline silicon substrate, and the diffusion type semiconductor is formed on this substrate. By doing so, a strain receiving element is formed.

[0006] In the case of this diffusion type semiconductor gauge, although the gauge factor can be obtained much higher than that of the above-mentioned electric resistance type strain gauge, it has a large temperature coefficient of resistance and therefore requires a complicated temperature compensation circuit. Since the silicon substrate has a low elasticity limit and is brittle, great care must be taken at the time of assembling, and brittle fracture is easily caused by mechanical overload.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to make it possible to increase the strain output sensitivity while increasing the natural frequency, and to facilitate the assembly. Another object of the present invention is to provide an acceleration converter that can be used stably for a long period of time.

[0008]

According to the present invention, in order to achieve the above object, a weight is supported via a flexible part on a driven part which moves integrally with the object to be measured. In an acceleration converter of a type in which the weight is relatively displaced relative to the driven part when the driven part receives the acceleration, the strain is converted into an electric signal by a strain gauge and the acceleration is detected. By forming slits with a fixed depth from both sides of the opposing side peripheral surface in the middle part of the presenting beam, a rigid follower with a large rigidity at the base end and a weight with a rigid rigidity at the distal end The intermediate portion has a flexible portion having flexibility, and the driven portion and the weight are arranged so as to straddle a cantilever beam and a pair of slits formed in the intermediate portion of the cantilever beam. Thin and flexible jointed to the peripheral surfaces on both sides of the 1 pair and strain inducing plate, and at least one pair of strain gauges each adapted to detect impregnated with strain slit side surface portion of the strain inducing plate of the pair that,
And the tensile and compressive strain acting on the strain plate by the deformation of the cantilever with the acceleration acting on the weight portion, and the strain plate itself by the acceleration acting on the strain plate The present invention is characterized in that it is configured to be able to detect a bending strain caused by deformation by adding the pair of strain gauges.

[0009]

In the acceleration converter constructed as described above, the flexible portion formed in the intermediate portion of the cantilever beam functions as a beam hinge and receives acceleration from the object to be measured via the driven portion. At this time, bending strain is intensively generated in the flexible portion. But,
The pair of strain plates, which are joined to the peripheral portions on both sides of the driven portion and the weight portion so as to straddle a pair of opposed slits formed to provide the flexible portion, respectively, prevent bending of the beam. One strain plate receives a tensile force and the other strain plate receives a compressive force to generate tensile strain or compressive strain, respectively.

On the other hand, not only these tensile and compressive strains are generated on the strain generating plate, but also bending strains caused by the deformation of the strain generating plate itself by the acceleration acting on the strain generating plate are generated. I do.

Therefore, a strain gauge attached to the inner side or the opposing surface of the pair of strain generating plates, in other words, the strain gauge attached to the slit-side surface portion of the strain generating plate, increases or decreases the gap between the driven portion and the weight. Not only the tensile strain or the compressive strain caused but also the bending strain that the flexure plate itself is bent by receiving acceleration is detected, and the strain output can be greatly increased.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a side sectional view schematically showing the entire configuration of the acceleration converter according to the present invention, and FIG. 2 is a view showing the configuration of the acceleration converter in a state where a casing is removed in order to explain the operation of the embodiment. FIG. 3 is a cross-sectional view schematically showing a relationship between a flexible portion of a cantilever, a strain plate, and a strain gauge in the embodiment of FIG. 1, and FIG. 4 is a configuration of the embodiment of FIG. FIG.

FIG. 5 is a circuit diagram showing the configuration of a Wheatstone bridge circuit assembled with strain gauges attached to the strain generating plates of the embodiment shown in FIGS.
In FIG. 1, a casing 1 of the acceleration converter is formed in a quadrangular prism-shaped cylindrical body, and one surface side of the casing 1 (FIG. 1).
Is attached to the wall surface of the measured object 2 by fixing means (not shown) such as screwing.

The inner peripheral wall of the casing 1 has a cantilever 3
, That is, the base end of the driven portion 3a is firmly fixed by screwing, welding, or other fixing means, although not shown.

The method of forming the cantilever 3 is as follows. The slits 3b, 3 having a certain depth from opposing side peripheral surfaces (the upper surface and the lower surface in FIG. 1) are formed in the middle of the beam having a rectangular cross section.
By forming c, a flexible portion 3d having a predetermined thickness h is provided at the center in the thickness direction of the beam, and a weight portion 3e is provided on the tip side (free end side) of the flexible portion 3d. I have.

That is, only the flexible portion 3d is thin and flexible, and has a hinge function when acceleration is applied to the driven portion 3a, so that the driven portion 3a and the weight 3e are separated from each other. And the flexible portion 3d is sufficiently thicker than the flexible portion 3d, has high rigidity, and does not bend even when substantially subjected to acceleration. It is an element that determines the frequency and also an element that determines the acceleration detection sensitivity.

The driven portion 3 is set so as to straddle (bridge) a pair of slits 3b and 3c formed in the intermediate portion of the cantilever 3.
A spring material such as beryllium copper, phosphor bronze, or the like, is formed on the peripheral surfaces of both sides of the weight portion 3e and the weight portions 3e by firmly bonding, welding, screwing, or other means, respectively. Are joined. That is, the strain plates 4 and 5 are set so that their plate surfaces are parallel to the plate surface of the flexible portion 3d when no load is applied (when no acceleration is applied).

Slits 3b and 3 of strain plates 4 and 5
As shown by broken lines in FIG. 4, each of the two surface strain portions SG1 and SG2 is provided on each surface layer portion facing c, that is, each surface layer portion on the inner surface opposed to each other with the flexible portion 3d interposed therebetween. SG3, SG4 not shown in the figure are bonded, CV
It is attached by a vapor deposition means such as chemical vapor deposition such as D or physical vapor deposition such as sputtering.

The strain gauges SG1 to SG4 are shown in FIG.
As shown in FIG. 3A, the sensing axis is directed along the longitudinal direction of the cantilever 3 so that the two sensing pieces are arranged side by side and the sensing portions thereof face the slits 3b and 3c. It is attached so as to be located at the center. In the case of the present embodiment, when the strain gauges SG1 to SG4 are directly vapor-deposited or fused on the strain generating plates 4 and 5, in the case of the present embodiment, the strain generating plates 4 and 5
u alloy), suitable means, for example, SiO 2
₍₂₎ It is necessary to form an insulating film such as a film on the surfaces of the strain plates 4 and 5 in advance.

One end of a gauge lead is connected to each of the gauge tabs of the strain gauges SG1 to SG4, and the other end of the gauge lead is connected to a measuring device for measuring acceleration via a gauge terminal, a lead wire, or the like. Led,
Inside or near the acceleration transducer, the strain plate 4
As shown in FIG. 5, the strain gauges SG1 and SG2 attached on the upper side are opposite to each other, and the other strain gauges SG3 and SG4 attached on the strain generating plate 5 are on opposite sides adjacent thereto. Are connected to form a Wheatstone bridge circuit (hereinafter abbreviated as “bridge circuit”).

Although not shown, an external resistor for adjusting the initial imbalance of the bridge circuit and for compensating for the temperature is added to the bridge circuit. Next, the operation of the acceleration converter configured as described above will be described. The acceleration converter is such that its casing 1 is
And it is firmly fixed by screws or other means.

In this state, when the inertial force F acts on the cantilever 3 as shown in FIG. 2, for example, due to vibration or impact of the object 2 to be measured, the weight 3e is displaced relative to the casing 1. Then, while flexing the flexible portion 3d, the pair of upper and lower strain plates 4 and 5 are flexed as shown in FIG.

At this time, the upper strain plate 4 is provided with the slit 3b.
As shown in FIG. 2, when the opening end (upper end) is deformed so that the opening end (upper end) is opened, it is subjected to a pulling force and acceleration is applied to the strain generating plate 4 itself, as shown in FIG. Side), on the anti-slit side (outer side or upper side) of the strain plate 4,
A compressive strain is generated, and a tensile strain is generated on the slit 3b side.

The lower strain plate 5 is compressed by receiving a compressive force to deform so that the opening end of the slit 3c is closed, and acceleration is applied to the strain plate 5 itself, as shown in FIG. As shown in FIG. 5, since the flexure plate 5 bends to the side opposite to the slit 3c (the outer surface side or the lower surface side), a compressive strain is generated on the slit 3c side of the strain generating plate 5, and the side opposite to the slit 3c (the outer surface). Side or the lower surface side), tensile strain occurs.

Therefore, the two strain gauges SG1 and SG2 attached to the surface layer on the slit 3b side of the strain plate 4 are:
The cantilever 3 is deformed by the acceleration acting on the weight 3e as shown in FIG. 2, and the tensile strain caused by the expansion of the opening end (upper end) of the slit 3b and the strain acting on the strain generating plate 4 by the acceleration acting on the strain generating plate 4. 4 itself detects a tensile strain due to bending that bulges downward, and greatly increases its resistance value.

On the other hand, the two strain gauges SG3 and SG4 attached to the surface layer on the side of the slit 3c of the strain plate 5 are configured such that the cantilever 3 is moved by the acceleration acting on the weight 3e as shown in FIG. Compressive strain due to deformation and narrowing of the opening end (lower end) of the slit 3c, and compressive strain due to bending of the flexure plate 5 itself swelling downward due to acceleration acting on the flexure plate 5 are detected, Its resistance is greatly reduced.

The explanation of the operation described above is based on the case 1
When acceleration is applied in the upward direction, on the contrary, when acceleration is applied in the downward direction, the weight portion 3e is relatively displaced upward by the inertia force using the flexible portion 3d as a hinge. Therefore, the resistance values of the strain gauges SG1 and SG2 attached to the surface of the strain generating plate 4 on the side of the slit 3b are greatly reduced, contrary to the above, and attached to the surface of the strain generating plate 5 on the side of the slit 3c. It is easily understood that the measured resistance values of the strain gauges SG3 and SG4 greatly increase.

In contrast to the above embodiment, when a strain gauge is attached to the upper strain plate 4 on the side opposite to the slit 3b (upper side), the cantilever 3 is moved as shown in FIG. If it is deformed, a tensile force acts on the strain generating plate 4 due to the separation of the surface layer between the driven portion 3a and the weight portion 3e, and a tensile strain is generated. As a result, the surface layer on the opposite side of the slit generates a compressive strain, and the two cancel each other out, resulting in the strain gauge detecting only a small tensile strain. This is not practically desirable because it is greatly reduced and the S / N ratio is deteriorated.

Similarly, when a strain gauge is attached to the lower strain generating plate 5 on the opposite side (lower surface side) to the slit 3c, unlike the above embodiment, the cantilever 3 shown in FIG. If such deformation occurs, a compression force acts on the strain-generating plate 5 due to the closeness of the surface layer between the driven portion 3a and the weight portion 3e, and a compressive strain is generated. The surface layer on the opposite side of the slit generates tensile strain due to its own deformation due to acceleration, so the two cancel each other out, resulting in the strain gauge detecting only a small compressive strain. Therefore, the strain output is greatly reduced, and the S / N ratio is deteriorated.

According to the embodiment described above, the first
In addition, not only can a larger strain output be obtained than when a strain gauge is attached to the surface of the flexible portion 3d,
The flexible thin strain plates 4 and 5 are slit 3b and 3
Since the bridge is configured to straddle c, the cantilever 3
Can be effectively reinforced, and a relatively small, robust and highly sensitive acceleration transducer can be provided.

Second, not only do the strain plates 4 and 5 function as reinforcing plates, but also the strain gauges SG1 to SG4 are attached to the front side, that is, when the strain gauges SG1 to SG4 are attached to the opposite sides of the slits 3b and 3c. Since the tensile strain and the compressive strain corresponding to the bending strain caused by the deformation of the strain generating plates 4 and 5 by the acceleration acting on the strain plates 4 and 5 are added and detected, the same gauge sensitivity (gauge rate) is obtained. in the case of,
If a higher sensitivity is obtained and the weight of the weight 3e is adjusted, an acceleration converter that can obtain a high resonance frequency (natural frequency) even with the same sensitivity can be provided.

Third, since a high strain sensitivity can be obtained as described above without using a semiconductor gauge as a strain gauge, temperature compensation is easier than that of a semiconductor gauge, and it is not brittle like a semiconductor gauge, so that cracks may occur. In addition, when the semiconductor gauge is generally thick, it is easy to assemble and the initial set value is not easily shifted. Even when acceleration is applied to the strain-generating plate to which the semiconductor gauge is attached, the strain-generating plate does not show a bulging deformation as shown in FIG. 2, and therefore, the strain sensitivity cannot be improved. By using a strain gauge or a strain gauge formed by sputtering or evaporation,
It is possible to provide an acceleration converter that can achieve the first effect.

It should be noted that the present invention is not limited to the embodiment described above and shown in the drawings, and various modifications can be made without departing from the scope of the invention. For example, in the above-described embodiment, the strain gauge is attached to the strain-generating plate. However, the case where the gauge element pattern coating is directly attached to the strain-generating plate by vapor deposition or the like is also included in the applicable range of the present invention.

The number of strain gauges is not limited to two when one strain gauge is attached, and one or three or more strain gauges may be used. Further, the strain plates 4 and 5 may be formed integrally with the cantilever 3 without being formed separately.

[0035]

As apparent from the above detailed description, it is relatively small, has a high strain sensitivity without lowering the natural frequency, has a strong toughness against shocks and vibrations, It is possible to provide an acceleration converter that can easily perform temperature compensation and maintain stability for a long time.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a configuration of an embodiment of an acceleration converter according to the present invention.

FIG. 2 is a side sectional view for explaining the operation of the embodiment shown in FIG. 1;

FIG. 3 is a sectional view taken along line XX of FIG. 1 showing a relationship among a flexible portion, a strain plate, and a strain gauge of the embodiment shown in FIG.

FIG. 4 is a perspective view of the embodiment shown in FIG.

FIG. 5 shows 4 applied to the acceleration transducer according to the present invention.
FIG. 3 is a circuit diagram showing a configuration of a Wheatstone bridge circuit assembled by a single strain gauge.

[Description of Signs] 1 casing 2 object to be measured 3 cantilever 3a driven portion 3b, 3c slit 3d flexible portion 3e weight portion 4, 5 strain-generating plate

Claims (3)

(57) [Claims] A weight is supported via a flexible part on a driven part that moves integrally with the object to be measured, and when the driven part receives an acceleration, the weight is moved relative to the driven part. An acceleration transducer that converts the strain at the time of relative displacement into an electric signal by a strain gauge and detects the acceleration is provided. By forming a slit of each,
A cantilever beam having a rigidly driven portion at the base end, a rigid weight portion at the distal end, and a flexible portion having flexibility at an intermediate portion; A pair of thin and flexible strain plates which are respectively joined to the peripheral portions of the driven portion and the weight portion so as to straddle a pair of slits formed in an intermediate portion of the beam; And at least one pair of strain gauges respectively attached to the slit-side surface portions of the pair of strain-generating plates so that strain can be detected, wherein the cantilever beam is accelerated by the weight acting on the weight portion. The tensile / compressive strain acting on the strain-generating plate by being deformed, and the bending strain caused by the deformation of the strain-generating plate itself by the acceleration acting on the strain-generating plate, are added to the pair of strain gauges. Acceleration conversion characterized by being configured to be detectable . 2. The acceleration transducer according to claim 1, wherein two strain gauges are attached to each strain plate in parallel. 3. The acceleration converter according to claim 1, wherein the strain plate is made of a Cu alloy such as beryllium copper or phosphor bronze so as to have flexibility.