JPH058977B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field The present invention relates to a physical quantity-to-electrical quantity converter, and more specifically, to a converter for transmitting physical quantities such as load, pressure, displacement, acceleration, etc. to a strain-generating part via an introduction part. The present invention relates to a strain gauge-type physical quantity-to-electrical quantity converter which deforms the strain generating part and obtains an electric signal corresponding to the physical quantity using a strain gauge attached to the strain generating part.

(b) Prior Art Various types of strain gauge type physical quantity-to-electrical quantity converters have been proposed and put into practical use, such as load transducers, pressure transducers, displacement transducers, and acceleration transducers.

Regarding load transducers, the main types currently in practical use include diaphragm type, cylindrical type, washer type, single beam type, and cross beam type (also known as cross beam type). be.

Figures 2A and 2B are a plan view showing the main part configuration of a conventional diaphragm type load converter, and
- An X-ray sectional view, and FIG. C is a bending stress distribution diagram of the conventional example.

In the figure, a transducer main body 1 includes an elastic, thick-walled cylindrical outer shell 2, and a small-diameter, thick-walled cylindrical load seat 3 that introduces the load to be measured at the center of the outer shell 2. A strain-generating portion 4 made of a thin diaphragm is connected between the outer periphery of the load seat 3 and the inner periphery of the outer shell portion 2 with their respective surfaces perpendicular to each other. In this load converter, four strain gauges SG are installed on the strain generating part 4 at a part near the outer periphery of the load seat 3 and a part near the inner periphery of the outer shell part 2, respectively.
Each sheet is attached by adhesive or other means with a sensitive direction determined so that the bending strain (stress) of the strain-generating portion 4 can be detected.

However, this type of conventional load transducer has the following drawbacks.

That is, first of all, if a low capacity diaphragm type load transducer is to be manufactured, the wall thickness of the strain generating portion 4 must be made extremely thin. However, it is very difficult to reduce the wall thickness by cutting, and there is a limit to how thin it can be (currently the limit is about 0.2 mm), and in that case, the cost becomes extremely high. On the other hand, since there is a constraint that the wall thickness cannot be reduced below a certain level, in order to make the wall thickness up to a certain level and achieve a lower capacity, the inner diameter of the outer shell 2 should be increased and the thinner part (diaphragm) It is possible to reduce the bending rigidity, but if this is done, the following problem arises.

That is, as the outer diameter of the strain-generating portion 4 increases, the outer diameter of the transducer body 1 inevitably increases, making it virtually impossible to manufacture a small-sized load transducer, and at the same time reducing the bending rigidity. As it is made smaller, a decrease in response frequency is unavoidable. This causes a problem that dynamic loads cannot be measured. In addition, there are structural limits to thin wall processing, so in the end,
There is a problem that a small and low capacity load transducer cannot be manufactured in reality.

Second, as shown in the stress distribution diagram in Figure 2C,
The stress distribution change in the diametrical direction of the strain-generating portion 4 is rapid, and a strain gauge cannot be attached to the position where the maximum stress occurs, so the strain detection efficiency is poor and the stress change decreases rapidly. The average detection sensitivity of the strain gauge as a whole decreases. That is, it has the drawback of low strain detection efficiency and low strain detection sensitivity.

Thirdly, as described above, it is necessary to output a required strain detection output even if the strain detection efficiency is low, so that a very large stress is substantially generated in the strain-generating portion (diaphragm) 4. As a result, the fatigue life is shortened, in other words, the durability is deteriorated, the overload tolerance range is narrowed, and the load-strain characteristics are also deteriorated, which makes it impossible to obtain a highly accurate load transducer. be.

3A and 3B are a plan view and a sectional view taken along the line Y-Y of FIG. 3A of a conventional so-called cross-beam type load converter, and FIG. FIG.

As is clear from the figure, this cross beam type load converter has a diaphragm part (corresponding to the strain generating part 4) of the diaphragm type load converter mentioned above.
Hollow out in 4 fan shapes at equal angles.
It is formed by forming a cross beam,
5 is the converter body, 6 is the outer shell, 7 is the load seat, 8 ₁
~8 ₄ is a cross beam as a strain generating part, and SG is a strain gauge. Therefore, compared to the diaphragm type load transducer, this cross-beam type load transducer has the advantage that the strain-generating part can be made somewhat thicker, and the stress distribution in the diametrical direction is as shown in Fig. 3C. As can be seen from the stress distribution diagram shown in , the stress distribution is almost the same as that of the diaphragm type load transducer, so the strain detection efficiency and sensitivity of the diaphragm type load transducer are low and the durability is low. It has drawbacks such as a narrow overload tolerance range and poor load-strain characteristics.

(c) Purpose The present invention has been made in view of the problems existing in the above-mentioned prior art, and its purpose is to enable ultra-low capacity, ultra-small size, and low cost, which were previously considered impossible. The object of the present invention is to provide a strain gauge type physical quantity-to-electrical quantity converter which has high physical quantity detection sensitivity and detection efficiency, good strain characteristics of a strain generating part, high precision, and durability.

(d) Structure The feature of the present invention is that physical quantities such as load, pressure, displacement, acceleration, etc. are transmitted to the strain-generating part through the introducing part to deform the strain-generating part, and the strain attached to the strain-generating part is In a strain gauge type physical quantity-to-electrical quantity converter that obtains an electrical signal corresponding to the physical quantity using a gauge, a circumferential groove with a narrow width and a constant depth is cut in the axial center of an elastic thick-walled hollow cylinder. By doing so, a thin cylindrical part is formed in the central part in the axial direction, and thick cylindrical parts are formed on both sides of this thin cylindrical part, and further extend from each outer end to each inner end of each thick cylindrical part. A transducer body in which a pair of thick circular arc plate parts are formed on each side of the thin cylindrical part by cutting slits of a constant width that are symmetrical about the center axis, and which are sandwiched between the slits on both sides. The thin-walled cylindrical portion of the region is a strain-generating portion, and the thick-walled circular arc plate portions on both sides at angular positions 90° shifted from the strain-generating portion around the central axis are used as introduction portions, and from this introduction portion
The thick circular arc plate portions on both sides at angular positions shifted by 180° are used as supporting portions, and strain gauges are attached to the inner circumferential side and/or outer circumferential side of the strain generating portion. By doing so, the above object of the present invention can be completely achieved.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

1A to 1F all relate to the present invention, of which figure A is a front view showing the overall configuration of an embodiment of the bending type load converter according to the present invention, and figure B is a A side view showing the configuration of the main body of the converter, which is the main part of the present invention.
Figure D is a stress distribution diagram of the strain-generating part in the same example, Figure E is a schematic sectional view equivalent to Figure C, and Figure F is the same strain-generating part as Figure D. It is a stress distribution diagram.

In FIGS. 1A and 1B, 10 is a transducer main body having a generally hollow cylindrical overall shape, and is formed in the following manner. In other words, a material that is suitable for the purpose of use is one of elastic materials such as nickel-chromium steel, nickel-chromium-molybdenum steel, beryllium-copper alloy, aluminum alloy, Amber (trade name), etc. to form a thick hollow cylinder. A circumferential groove 11 having a narrow width (for example, 4 mm width) and a constant depth (for example, 2 mm depth) is cut on the outer periphery of the central portion of this thick-walled hollow cylinder in the direction of the central axis OO using, for example, a lathe. As a result,
A thin cylindrical portion 12 is formed at the center in the axial direction, and both sides of this thin cylindrical portion 12, that is, FIG.
Thick-walled cylindrical portions are formed on both left and right sides.

Next, slits 13 of a constant width (in this example, a width of 4 mm) are made along the central axis O-O from each outer end to each inner end of each thick-walled cylindrical portion on both sides.
A and 13b are cut using a milling machine, for example. As a result, the thick cylindrical portion on each side has a slit 13.
a and 13b, and a pair of thick circular arc plate parts 1 are provided on both sides of the thin cylindrical part 12.
4a, 14b and 14c, 14d are formed. Note that it is desirable that the inner circumferential surface of the thin cylindrical portion 12 be smoothed using a reamer or the like.

In the converter main body 10 thus formed, the thin cylindrical portion 12 in the region sandwiched between the slits 13a and 13b on both sides is used as the strain-generating portion 15.

Also, from the strain-generating portion 15 around the central axis O,
The thick circular arc plate portions 14a and 14c on both sides at the angular position shifted by 90° serve as the load introducing portion 16, and the thick circular arc plate portions 14b and 14d at the angular position shifted by 180° from the load introducing portion 16 carry the load. It is considered as a support part 17. Although FIGS. 1A to 1C show an example in which the load introducing section 16 is placed at the top and the load bearing section 17 is placed at the bottom, it is not always necessary to use this position (arrangement). For example, when trying to detect a lateral (horizontal) load, from the state shown in Figure 1 A,
It will be placed in a 90° tilted position.

On the inner and outer sides of the strain generating section 15, there are a plurality of strain gauges SG whose sensing axis direction is set so as to detect bending strain of the strain generating section 15.
is attached by adhesion, vapor deposition, sputtering, welding, or other suitable means. A Wheatstone bridge (not shown) is formed using multiple strain gauges SG attached in this way (four in this example).
is formed.

In addition, the portions of the thick circular arc plate portions 14a and 14c that are in approximately linear contact with the load introduction portion 16 are:
It is the load seat 18 that receives the load, and similarly the load bearing part 1 in the thick circular arc plate parts 14b and 14d.
7 is in substantially line contact with a load bearing seat 19 disposed on the stationary part.

Although not shown, the converter main body 10
The strain gauge SG is housed in a transducer case, and is generally provided with a sealing means to block the outside air, especially to prevent oxidation and a decrease in insulation resistance due to moisture absorption of the strain gauge SG. In addition, in the figure, the members marked with the symbol l are as follows:
This is the gauge lead connected to the gauge tab of strain gauge SG.

Next, the operation of the embodiment configured as described above will be explained.

A load seat 18 is attached to the load introduction part 16 of the converter main body 10.
When, for example, a compressive load is applied in the direction of the load axis N-N through Since the strain-generating portion 15 of the thin-walled cylindrical portion 12 is made thicker and has sufficiently high rigidity than the strain-generating portion 15, the strain-generating portion 15 of the thin-walled cylindrical portion 12 is elastically deformed without causing almost any strain (deformation). (curvature changes) and distortion occurs. As a result, a bending moment proportional to the applied load acts on the strain-generating portion 15 due to the compressive load, and bending stress is generated.

Here, when the load W is applied to the load introduction part 16 of the converter main body 10, the bending moment Mb that acts on the center part P of the strain-generating part 15 will be considered.

The outer diameter of the strain-generating portion 15 (thin-walled cylindrical portion 12) is D, the inner diameter is d, and the diameter of an imaginary circle passing through the center of the wall thickness t of the strain-generating portion 15 is Dc, as shown equivalently in FIG. 1E. Assuming that the converter main body 10 is a beam supported at both ends with a rectangular cross section of length Dc, thickness t, and width b, and a load W is applied to the center of the beam, the beam length Dc
is Dc=(D+d)/2, and the bending moment Mb at point P of the rectangular cross-section beam is Mb=W・Dc/8, so the bending moment Mb at the center P of the strain-generating part 15 is as follows. It is given by Eq.

Mb=W・(D+d)/2/8=W・(D+d)/16...(1) Therefore, the bending stress ∂b is given by the following equation (2).

∂b=3W(D+d)/4b・^t2 ...(2) The bending stress distribution in the circumferential direction in the strain-generating portion 15 of the above embodiment exhibits a very gentle curved shape as shown in FIG. 1D. ing. As you can see from this figure,
The difference between the maximum bending stress εbmax and the minimum εbmin is very small and can be ignored in terms of the detection range of the strain gauge. Therefore, unlike the previously mentioned diaphragm type and cross beam type transducers, there is no sharp change in stress within the detection range of the strain gauge SG, so there is no chance of localized high strain occurring in the strain gauge SG. Therefore, the detected strain level is high, and the average strain can be detected with high sensitivity. As mentioned above, in the stress distribution of the diaphragm type and cross beam type, very high stress occurs outside the strain detection range of the strain generating part, so when considering the mechanical strength of the transducer, it is difficult to When the stress in a region is reduced, the strain level in the strain detection range is naturally reduced. On the other hand, the maximum stress of the strain generating part 15 in the load converter of the above embodiment is:
Since it is located at the center of the strain detection range of the strain generating section 15, and the strain level in the strain detection range can be considered to be approximately constant, highly sensitive strain detection is possible, and the stress level in other parts of the strain generating section 15 is low. Since the load is low, it is possible to obtain a highly sensitive and accurate load transducer that is sufficiently durable even against repeated loads.

Next, a description will be given of how the present invention can reduce the size of the converter and realize a low capacity ratio.

That is, in the transducer according to the present invention, since it is only necessary to form the circumferential groove 11 and the slits 13a and 13b in the thick-walled hollow cylinder, the hollow cylinder can be made small and the thin-walled cylindrical part 12 forming the strain-generating part 15 can be made small. By shortening the axial length, a small and low capacity converter can be easily manufactured. In other words, when compared with the size of conventional diaphragm type or cross beam type load converters, the size can be reduced to the extent that it can be called ultra-compact.

Also, for a low load capacity ratio, the depth of cut during machining of the circumferential groove 11 may be increased to narrow the groove width b.

According to the above manufacturing procedure, it is possible to provide a small-sized, low-capacity load converter at low cost and easily.

Regarding the response frequency, in order to lower the capacitance of conventional diaphragm type and cross beam type as mentioned above, due to their structure, they have no choice but to reduce the bending rigidity. However, according to the present invention, a load transducer with a high response frequency and low capacity can be easily obtained.

The present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without departing from the spirit thereof.

For example, in the above embodiment, a load converter is used as an example of a physical quantity-to-electrical quantity converter, but the load introducing section 16 of the converter main body 10 is connected to a physical quantity sensing means such as a diaphragm or a bellows. If configured to transmit force corresponding to a physical quantity, it becomes possible to manufacture highly accurate pressure transducers, earth pressure gauges, and other physical quantity transducers. Furthermore, by attaching mounting attachments to the load introducing section 16 and the load bearing section 17 described above, a strain gauge can be manufactured, and further,
By attaching a weight to the load introduction part 16, an acceleration converter can be manufactured.

In addition, in the embodiment, the strain gauge SG is
Although an example has been described in which it is attached to both the outer circumferential surface and the inner circumferential surface of the strain generating part 15, it may be attached only to the inner surface side or only to the outer surface side of the strain generating part 15.

(e) Effects As detailed above, according to the present invention, a circumferential groove is cut in the axial center of an elastic thick-walled hollow cylinder, and a circumferential groove is formed from each outer end to each inner end of the thick-walled hollow cylinder. Since the converter body can be formed by simply cutting the slit, it is extremely easy to manufacture, resulting in low cost and high processing precision.In addition, the hollow cylinder can be made small and its strain-generating part can be formed. By shortening the axial length of the thin-walled cylindrical part or increasing the depth of the circumferential groove, it is possible to easily produce an ultra-compact and ultra-low capacity transducer, and also without reducing bending rigidity. Since it is possible to lower the capacitance, it is possible to easily obtain a converter with a high response frequency and a low capacitance.

Further, according to the present invention, the bending stress distribution in the circumferential direction in the strain-generating portion exhibits a very gentle curved shape, in other words, the difference between the maximum value and the minimum value of bending stress is very small, and the strain There are no sudden changes in stress within the detection range of the gauge, and the average strain can be detected with high sensitivity.There is no localized high strain in the strain gauge, so it has sufficient durability against repeated loads. A highly sensitive and highly accurate strain gauge type physical quantity-to-electrical quantity converter can be provided.

[Brief explanation of drawings]

1A to 1F all relate to the present invention, of which figure A is a front view showing the overall configuration of an embodiment of the bending type load converter according to the present invention, and figure B is a A side view showing the configuration of the main body of the converter, which is the main part of the present invention.
Figure D is a stress distribution diagram of the strain-generating part in the same example, Figure E is a schematic cross-sectional view equivalently representing Figure C, and figure F is the same as Figure D, of the strain-generating part. Stress distribution diagrams, Figures 2A and 2B are a plan view showing the main part configuration of a conventional diaphragm type load converter, and a sectional view taken along the line X-X of Figure 2A, and Figure 2C is a bending stress diagram of the conventional example. Distribution diagram, Figures 3A and 3B are a plan view showing the main structure of a conventional cross-beam type load converter, a sectional view taken along the line Y-Y in Figure A, and Figure 3C is a strain-induced strain diagram in the conventional example. FIG. 10...Converter main body, 11... Circulating groove, 12...
...Thin cylindrical portion, 13a, 13b...Slit, 1
4a to 14d... thick circular arc plate part, 15... strain generating part, 16... load introducing part, 17... load bearing part,
18...Load seat, 19...Load bearing seat, SG...
strain gauge.

Claims (1)

[Claims] 1. Physical quantities such as load, pressure, displacement, acceleration, etc. are transmitted to the strain-generating part through the introduction part to cause the strain-generating part to deform, and the strain gauge attached to the strain-generating part corresponds to the physical quantity. In a strain gauge-type physical quantity-to-electrical quantity converter that obtains an electric signal, a narrow circumferential groove with a constant depth is cut in the axial center of an elastic thick-walled hollow cylinder. A thin-walled cylindrical portion is formed at the cylindrical portion, and thick-walled cylindrical portions are formed on both sides of the thin-walled cylindrical portion, and slits having a constant width symmetrical to the central axis are formed from each outer end to each inner end of each of the thick-walled cylindrical portions. Of the converter main body, in which a pair of thick circular arc plate portions are formed on each side of the thin cylindrical portion by cutting, the thin cylindrical portion in the region sandwiched between the slits on both sides is strained. 90° from the strain-generating part about the central axis
The thick circular arc plate parts on both sides at the angular position shifted from the introduction part are used as the introduction part, and the thick circular arc plate parts on both sides at the angular position deviated from the introduction part by 180 degrees are used as the support part. A strain gauge-type physical quantity-to-electrical quantity converter characterized in that a strain gauge is attached to the circumferential side and/or the outer circumferential side.