JPH10260091A - Load sensor free from force point - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load sensor using strain gages, in which the strain gages can be simply attached to a leaf spring, and which is free from a force point so that the degrees of strain of the strain gages can be set to be uniform even though the force point having one and the same load and applied to a leaf spring is displaced. SOLUTION: A pair of strain gages 2, 3 are attached to the front surface or the front and rear surfaces of a leas spring 1, at laterally symmetric positions with respect to the center line S between two fulcrums for supporting the leas spring 1. Terminals (a or c), on one side, of the strain gages 2, 3 at the front surface or the front and rear surface of the leaf spring 1 are connected together, and terminals on the other side thereof are used as external terminals which are then are connected as resistance elements of resistors of a Wheatostone bridge circuit, at one side if the pair of strain gages are attached to the front surface of the leaf spring 1, but at adjacent sides if the pair of gages are attached to the front and rear surfaces of the leaf spring. With this arrangement, both strain gages can deliver a constant output even through a degree of strain is such that a force point of a load is exerted between the pair of strain gages on the outer surface of the leaf spring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load sensor capable of obtaining an electrical output from a load applied to a leaf spring having two fulcrums using a strain gauge.

[0002]

2. Description of the Related Art In a conventional load sensor, for example, in the case of a weighing sensor, a pair of strain gauges are mounted at symmetrical positions on the same surface of a leaf spring, and the output terminals of the pair of strain gauges are connected to a Wheatstone bridge circuit. The two sides are connected as resistance elements of two adjacent resistors, and the other two sides are fixed resistance elements to form a measurement circuit. The loading part has a ramen structure, and the center of the load is the two pieces described above. It has a complicated structure such that it is accurately applied to the center between the strain gauges, and if one of the pair of strain gauges expands, the other strain gauge contracts. The amount is detected and an electrical output is obtained.

[0003]

According to the above-mentioned prior art, the structure of the loading portion is complicated and required to be precise, and the electrical detection accuracy is good, but the cost is greatly restricted and the demand as a load sensor is required. Despite being an industrial field, its application is limited. In addition, since the structure and shape of the loading portion limited to individual applications are not versatile, the work of attaching the strain gauge is inevitably a manual operation, which also causes a cost increase. Then, if the power point of the load moves, the measured value may be affected by an error.
The structure in which the load sensor is mounted so as to cover the center of the strain gauges also requires precision, which is an obstacle in terms of application.

The present invention proposes to solve these problems. Conventionally, the present invention has a complicated structure in which the center of load is accurately applied to the center between a pair of strain gauges. It is an object of the present invention to provide a load point-free load sensor that can detect a constant amount of strain and obtain an electrical output even when a power point of the same load applied between the pair of strain gauges moves.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, the center line of a leaf spring having a symmetrical shape with respect to the center line of two fulcrums is provided on the same plane. A pair of strain gauges are attached symmetrically to each other, and one of the two output terminals provided on the pair of strain gauges is connected so as to be added to each other, and the other output terminal is added. In addition, the present invention is characterized in that the external output terminal is a load point-free load sensor that can obtain a constant output from the external output terminal even when the same load applied between the pair of strain gauges of the leaf spring moves.

[0006] The invention described in claim 2 is the invention according to claim 1.
In addition to the above, the external output terminals of a pair of strain gauges are connected as a resistance element of a resistor on one side of a Wheatstone bridge circuit consisting of resistors on four sides, and it is a force point free load sensor that can measure load. I have.

According to a third aspect of the present invention, a pair of strain gauges are symmetrically formed on a plane of a leaf spring symmetrical with respect to the center line of the two fulcrums. Attached at both symmetrical positions on the front surface and the back surface of the leaf spring, and connected so that one of the two output terminals of the front surface and the back surface provided on the pair of strain gauges on the front surface and the back surface are added to each other, The other output terminal is an added external output terminal, and the front and rear external output terminals are connected as resistance elements of two adjacent resistors in a Wheatstone bridge circuit having four resistors. A fixed point resistance element is used as a resistor on the two sides of the leaf spring, and even when the point of force of the same load applied between the pair of strain gauges on the surface of the leaf spring moves, a constant output is obtained from the external output terminals on the front and rear surfaces. Load sensor It is characterized in that.

[0008] The invention described in claim 4 is the first invention.
Wherein a piezoelectric element made of a ceramic and a quartz oscillator is used instead of the strain gauge, and the piezoelectric element is a force-point-free load sensor capable of obtaining an electrical output by an external force.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be specifically described below with reference to FIGS.

FIG. 1 is a view in which a pair of strain gauges are mounted on the same plane of a leaf spring symmetrical with respect to the center line of two fulcrums described later and symmetrically with respect to the center line. Leaf springs for attaching a pair of strain gauges, 2 and 3 are strain gauges for detecting the strain of the leaf spring 1, a and b are output terminals of the strain gauge 2, c and d are output terminals of the strain gauge 3, The output terminals a and c are connected to each other, the output terminals b and d are external output terminals for connection to an external measuring unit, and S is a distance between the two fulcrums of the leaf spring 1 having two fulcrums described later. Is the center line between the strain gauges 2 and 3.

FIG. 2 shows the connection between the external output terminal b of the strain gauge 2 and the external output terminal d of the strain gauge 3 described in FIG. 1 as a resistance element of a resistor on one side of a Wheatstone bridge circuit. Even if a force point of the same load applied between the strain gauges 2 and 3 of the spring 1 moves, a mechanically minute change in compression applied to the strain gauges 2 and 3 is fixed as an electric signal. R1, R2, and R3 are fixed resistance elements connected as resistors on the other three sides of the Wheatstone bridge circuit, E is a bridge voltage power supply, and 6 is a Wheatstone bridge circuit. An amplifier for amplifying the detected output, and 7 is a measuring section output terminal for sending the output of the amplifier 6 to an external measuring section.

FIG. 3 shows that the strain gauge 2 and the strain gauge 2 attached to the leaf spring 1 described with reference to FIG. FIG. 4 is a view for explaining that the sum of bending moments applied to the mounting portions of the two strain gauges with the gauge 3 is constant. S1 and S2 are two fulcrums supporting the leaf spring 1, W is a load applied to the leaf spring 1, and L Is the distance between the fulcrum S1 and S2, L1 is the distance from the fulcrum S1 to the power point P, L2 is the distance from the fulcrum S2 to the power point P, P1 is the mounting part which is the center of the strain gauge 2, and P2 is the center of the strain gauge 3. X1 is a mounting part P1 of the strain gauge 2 from the fulcrum S1 and a mounting part P of the strain gauge 3 from the fulcrum S2.
X2 = L-X1.

In FIG. 1, the shape of the leaf spring 1 is rectangular, but can be changed depending on the application.
A material such as plastic can be used in addition to metal, and the strain gauge 2 and the strain gauge 3 mainly use a foil gauge. The strain gauge 2 and the strain gauge 3 are attached to the leaf spring 1 on a flat surface of the leaf spring 1 using an adhesive suitable for use conditions.

Next, the operation of the first embodiment will be described. First, in the first embodiment of FIG. 3, even if the position of the force point P where the load W applied to the leaf spring 1 presses changes, the bending moment applied to the mounting portions P1 and P2 of the strain gauge 2 and the strain gauge 3 is constant. Explain that.

The pair of strain gauges 2 and 3 on the leaf spring 1 are compressed when the load W is applied, and their bending moments are represented by minus (-). The bending moment of M1 and the mounting part P2
Is defined as M2, the bending moment M
1, M2 is given by the following equation.

[0016]

(Equation 1)

From FIG. 3, since the force point P of the load W and the mounting portions P1 and P2 of the strain gauges are equidistant from the fulcrums S1 and S2, L2 = L-L1, X2 = L-X1 and the bending moment M1, M2 is given by the following equation.

[0018]

(Equation 2)

Now, when the force point P of the load moves to the right by, for example, α and L1 becomes L1 + α, the bending moments M1, M2
Is represented by the following equation.

[0020]

(Equation 3)

Therefore,

[0022]

(Equation 4)

Thus, M1 + M2 becomes irrelevant even if the power point P moves by α. That is, since X1 is known, M1 + M2∝W, and the sum of the bending moments M1 and M2 is proportional to the applied load W even when the force point P of the load moves.

The bending moment according to the above description is proportional to the amount of strain of the member of the leaf spring, and since the strain gauge is used for measuring the amount of strain, the strains attached to the mounting portions P1 and P2 of the present invention are measured. Since the bending moments M1 and M2 applied to the strain gauges, that is, the load W applied to the leaf spring, can be measured by the gauge, in order to measure the load W, the strain amounts of the strain gauges of the mounting portions P1 and P2 are measured. You just have to measure it.

FIG. 2 shows the first embodiment embodied in an electric circuit. In FIG. 2, the gauge resistances of the strain gauges 2 and 3 are R0 and R0 ′, and the changes in the gauge resistances are values of △ R0 and △ R0 ′. The gauge resistance of the gauge 3 becomes a value of R0− △ R0 and R0′− △ R0 ′, respectively, the gain of the amplifier 6 is A0, R1 = R2 = R3 = R, △
R0 + △ R0 ′ = △ R, R0 = R0 ′ = R / 2, distortion amount d
= △ R / R, the combined resistance of the strain gauge 2 and the strain gauge 3 is given by the following equation.

(R0- △ R0) + (R0'- △ R0 ')
= R−ΔR = R (1−ΔR / R) = R (1−d) Further, assuming that the output of the measuring section output terminal 7 at this time is Z, since the bridge voltage power supply is E, the output is Z can be represented by the following equation.

[0027]

(Equation 5)

Here, since the change in resistance that occurs when the strain gauge is subjected to strain is extremely small and d = ／ R / R << 2, the above equation can be expressed by the following equation.

[0029]

(Equation 6)

If K = (1/4) × E × A0 in the above equation, Z = K × d, and the output of the measuring section output terminal 7 is proportional to the amount of strain d. This is possible by electrically detecting a change in resistance that occurs when the strain gauge receives a strain.

Next, a second embodiment of the present invention will be described in detail with reference to FIGS.

FIG. 4 shows a pair of strain gauges on the back surface of the leaf spring 1 in addition to the strain gauges 2 and 3 attached to the surface of the leaf spring 1 shown in FIG. And a pair of strain gauges of a strain gauge 2 and a strain gauge 3 attached to the front surface of the leaf spring 1 and a pair of strain gauges attached to the back surface thereof are attached at symmetrical positions. Reference numerals 5 and 5 denote strain gauges for detecting the strain of the leaf spring 1. Although not shown, the output terminals of the strain gauges 4 and 5 are:
Since the output terminals a and b of the strain gauge 2 correspond to the strain gauge 4 and the output terminals c and d of the strain gauge 3 correspond to the strain gauge 5, a of the strain gauge 4 and c of the strain gauge 5 are equal to each other. Strain gauge 2
Similarly, the terminals of the strain gauge 4 and the strain gauge 5 are connected as external output terminals for connection to the outside.

FIG. 5 shows the Wheatstone bridge circuit of the first embodiment shown in FIG. 2 in which the resistance elements connected as bridge resistors on the four sides are exchanged, and the resistance of one side of two adjacent sides is changed. The output terminal b of the strain gauge 2 is connected to the output terminal d of the strain gauge 3 as a body, and the output terminal b of the strain gauge 4 is connected to the output terminal d of the strain gauge 5 as a resistor on the other side. A fixed resistance element is connected to the resistors on the two sides of the above, so that even when a force point of the same load applied between the strain gauges 2 and 3 on the surface of the leaf spring 1 moves, the strain gauge 2 and A constant output is obtained as an electric signal due to the mechanical small change in compression applied to the strain gauge 3 and the mechanical change in mechanical expansion applied to the strain gauge 4 and the strain gauge 5. Twice as much output as sometimes A diagram illustrating that the, R1, R
2 is a fixed resistance element connected as a resistor on the other two sides of the Wheatstone bridge circuit, E is a bridge voltage power supply, 6 is an amplifier for amplifying an output detected by the Wheatstone bridge circuit, and 7 is an external output of the amplifier 6. 2 shows a measuring unit output terminal to be sent to the measuring unit.

FIG. 6 shows a pair of strain gauges attached to the back surface of the leaf spring 1 in addition to the strain gauges 2 and 3 attached to the surface of the leaf spring 1 shown in FIG. The pair of strain gauges of the strain gauge 2 and the strain gauge 3 attached to the front surface of the leaf spring 1 and the pair of strain gauges attached to the back surface are attached at symmetrical positions. Even if the power point of the same load applied between the strain gauges 2 and 3 attached to the surface moves, the minus point applied to the mounting portion P1 of the strain gauge 2 and the mounting portion P2 of the strain gauge 3 is expressed. FIG. 4 is a diagram for explaining that the bending moment and the bending moment expressed by a plus applied to the mounting portion of the strain gauge 4 and the mounting portion of the strain gauge 5 are constant. P3 is the center of the strain gauge 4. The mounting part, P4, is the center of the strain gauge 5. Is an attachment portions.

Next, the operation of the second embodiment will be described. First, in the second embodiment shown in FIG. 6, even if the position of the force point P for pressing the load W on the leaf spring 1 changes, the mounting portions P1 and P2 of the strain gauges 2 and 3, the strain gauges 4 and 5, That the sum of the bending moments applied to the mounting portions P3 and P4 is constant.

In the second embodiment shown in FIG.
The bending moment applied to the mounting portions P1 to P4 of the strain gauges 2 to 5 is such that the mounting portions P1 and P1 of the strain gauges 2 and 3 are changed even if the position of the force point P for pressing the load W on the leaf spring 1 changes. The bending moment of P2 is the first bending moment shown in FIG.
The bending moments of the attachment portions P3, P4 of the strain gauges 4 and 5 on the back surface of the leaf spring 1 are such that when the load W is applied, the strain gauges 4 and 5 are stretched. So each bending moment is
(1) to (1) to about the bending moments M1 and M2 described in the first embodiment only by being represented by plus (+).
The equation obtained by removing the minus (-) in the equation (7) becomes the bending moments M3 and M4 of the strain gauges 4 and 5 on the back surface of the leaf spring 1 in the second embodiment, and the leaf spring also in the second embodiment. Since the sum of the bending moments M1 and M2 and the bending moments M3 and M4 is proportional to the load W received by each of the pair of strain gauges on both surfaces of the leaf spring 1 even when the force point P of the load applied to the plate spring 1 moves. In order to measure W, the strain amount of a pair of strain gauges on both surfaces of the leaf spring may be measured.

FIG. 5 shows the second embodiment embodied by an electric circuit.

In FIG. 5, the combined resistance of the strain gauge 2 and the strain gauge 3 is R (1−1) as described in the first embodiment.
d), the combined resistance of the strain gauges 4 and 5 changes as the strain gauges are stretched as described above, so that the resistance increases. R (1 + d) of the opposite polarity to the combined resistance of R.3. Assuming that the output of the measuring section output terminal 7 at this time is Z ', the power supply for the bridge voltage is E. Therefore, the output Z' is expressed by the following equation in the same manner as the equation of the first embodiment shown in FIG. You.

[0039]

(Equation 7)

Therefore, comparing the expression (9) of the second embodiment with the expression (8) of the first embodiment, the expression (9) is as follows.
It is proved that the output is twice as large as the formula (8), and in the second embodiment, twice as much output is obtained.

In the above equation (9), K '= (1/2) × E
If XA0, then Z ′ = K ′ × d, and the output of the measurement unit output terminal 7 is proportional to the amount of strain d. Therefore, in the second embodiment, the measurement of the load W is also based on the fact that the strain gauge is distorted. This is made possible by electrically detecting a change in resistance that occurs in such a case.

In general, the resistance value of a metal material is such that it is given a force from the outside, increases when stretched, and decreases when compressed. The above-mentioned strain gauge uses the principle, and when used in a Wheatstone bridge circuit, the strain gauge connected to the leaf spring efficiently conducts electricity even when the resistance value changes little even when the strain is small. Can be replaced by a signal. In addition, if a piezoelectric element such as a ceramic or quartz oscillator is used instead of a strain gauge that measures the load, ceramics can be measured with a Wheatstone bridge circuit as described above with high sensitivity over a wide temperature range as a resistor obtained when a load is applied. Can be
In a crystal oscillator, an output when a load is applied can be obtained at a frequency, so that the load can be measured without requiring analog processing or an amplifier.

[0043]

As described above, according to the present invention, a pair of strain gauges are placed on the plane of a leaf spring having two fulcrums to a position symmetrical with respect to the center line of the two fulcrums only on the surface or on the surface. And the back side, two pairs are mounted at symmetrical positions, and one pair of strain gages on the front side and one pair of strain gages on the front and back sides are connected so as to be added to each other, and the other output terminal is connected to the other. The strain gauge outputs a constant amount of strain even if the same load applied between the pair of strain gauges moves, and the output is processed by a measuring unit provided outside. This is a force-point-free load sensor that can be measured in this way, so the load force point does not have to be at a fixed point, so the mounting structure of the load sensor is simplified,
It is possible to obtain a load sensor that can be reduced in size and weight in terms of economy and performance, and that is easy to make as a whole in terms of application.

When a foil gauge is used as the strain gauge, the foil gauge is thin, so that the foil gauge can be easily attached with an adhesive, and the cost can be reduced in various applications.

As a specific detection circuit, an external output terminal to which a pair of strain gauges attached to only the front surface of the leaf spring or both surfaces of the front and rear surfaces is added is connected to one side or adjacent side of the Wheatstone bridge circuit. Since the two matching sides are connected as resistive elements, the output can be efficiently extracted by amplifying the output with an amplifier. Further, a remarkable effect that the amplifier when the pair of strain gauges are attached to the front surface and the back surface of the leaf spring can obtain twice the sensitivity as compared to when the pair of strain gauges are only the surface of the leaf spring. It has.

[Brief description of the drawings]

FIG. 1A is a plan view and FIG. 1B is a side view of a first embodiment in which a strain gauge is attached to a plane of a leaf spring.

FIG. 2 is an electric circuit diagram of the first embodiment.

FIG. 3 is a physical principle diagram of the first embodiment.

4A and 4B are a plan view and a side view, respectively, of a second embodiment in which strain gauges are attached to the front and back surfaces of a leaf spring.

FIG. 5 is an electrical circuit diagram of a second embodiment.

FIG. 6 is a physical principle diagram of the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Leaf spring 2,3,4,5 ... Strain gauge 6 ... Amplifier 7 ... Measurement part output terminal E ... Bridge voltage power supply R1, R2, R3 ... Fixed resistance element S ... Center between two fulcrums supporting the leaf spring Lines a, b, c, d: output terminals of strain gauges W: load S1, S2: fulcrum supporting plate spring P: force point of load P1, P2: mounting portion P3 serving as the center of strain gauge 2 and strain gauge 3 P4: a mounting portion serving as a center between the strain gauges 4 and 5 L: a distance between two fulcrums supporting the leaf spring L1: a distance from a fulcrum S1 of the leaf spring to a force point P of load L2: from a fulcrum S2 of the leaf spring Distance X1 to the force point P of the load. Strain gauge 2 and strain gauge 4 from the fulcrum S1 of the leaf spring.
X2 from the fulcrum S2 to the center of the strain gauge 3 and the strain gauge 5 X2... From the fulcrum S1 of the leaf spring to the strain gauge 3 and the strain gauge 5
Distance to mounting part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mamoru Yamaguchi 249-1, Moriya-ko, Moriya-cho, Kitasoma-gun, Ibaraki Prefecture Inside the Moriya Plant of Meisei Electric Co., Ltd. (72) Katsumi Ikuuma 2500 Shinkai, Iwata-shi, Shizuoka Yamaha Machine Co., Ltd.

Claims (4)

[Claims] A load sensor for detecting a load applied to a leaf spring having two fulcrums by a strain gauge.
A pair of strain gauges are mounted symmetrically with respect to the center line on the same plane of a leaf spring having a shape symmetrical with respect to the center line of the two fulcrums. One output terminal of the two output terminals is applied to each other, and the other output terminal is an added external output terminal, so that even when a force point of the same load applied between the pair of strain gauges of the leaf spring moves, the output terminal does not move. A force-point-free load sensor characterized by obtaining a constant output from an external output terminal. 2. An external output terminal of a pair of strain gauges is connected as a resistive element of one side of a Wheatstone bridge circuit having four sides of a resistor, and the other three sides of the strain gauge are fixed resistors. The force-point-free load sensor according to claim 1, wherein: 3. A load sensor for detecting a load applied to a leaf spring having two fulcrums using a strain gauge.
On a plane of a leaf spring having a shape symmetrical with respect to the center line of the two fulcrums, a pair of strain gauges are attached symmetrically with respect to the center line at both symmetric positions on the front and back surfaces of the leaf spring,
One output terminal of the two output terminals of the front surface and the back surface provided on the pair of strain gauges of the front surface and the back surface is added to each other, and the other output terminal is an added external output terminal, The front and back external output terminals are connected as resistance elements of two adjacent resistors in a Wheatstone bridge circuit having four sides of a resistor, and the other two sides of the resistor are fixed resistor elements, and the leaf spring A force point-free load sensor characterized in that a constant output is obtained from external output terminals on the front and rear surfaces even when a force point of the same load applied between a pair of strain gauges on the front surface moves. 4. The force-point-free load sensor according to claim 1, wherein a piezoelectric element made of ceramic and a quartz oscillator is used instead of the strain gauge.