Force transducer

Abstract

To provide a force transducer in which the influence of an error in a sticking position of a strain gauge is reduced.SOLUTION: A force transducer 1 is provided with a force point 4, a support unit 5, a strain-causing unit 2k, a Wheatstone bridge circuit, and a strain-sensitive resistor G, thereby receiving, detecting, and converting forces from a plurality of directions into electrical signals. The force point 4 introduces the respective forces, the support 5 receives and supports the respective forces, the strain-causing unit 2k is provided between the force point 4 and the support 5 and is elastically deformed by the respective forces, and the Wheatstone bridge circuit includes a strain-sensitive resistor G. The strain-sensitive resistor G detects at least one of forces in two orthogonal directions and is attached to the strain-causing unit 2k with maximum sensitivity in a direction in which the detection of a strain generated in the strain-causing unit by a force in a direction orthogonal to the respective forces in the two directions is canceled.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a force transducer that detects force and converts it into an electrical signal. [Background technology]

[0002] 2. Description of the Related Art Conventionally, force transducers are known that detect forces applied from a plurality of directions separately for each direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-071189 Summary of the Invention [Problem to be solved by the invention]

[0004] A known method for detecting forces in the orthogonal x and y directions involves detecting shear strain generated in a strain-generating part and detecting forces in each of the x and y directions. To detect shear strain, a strain gauge with its maximum sensitivity direction is typically attached to the strain-generating part at a 45-degree angle to the shear direction. In a force transducer that detects the orthogonal x and y directions, if the maximum sensitivity directions of all of the multiple strain gauges can be precisely aligned and attached, the effect of a force applied in the z direction, orthogonal to the x and y directions, can be canceled out even if a force relatively greater than that in the x and y directions is applied. However, it is practically difficult to precisely align and attach all of the multiple strain gauges. The inventors discovered a problem: if a force relatively greater than that in the x and y directions is applied to a force transducer that detects the orthogonal x and y directions in the z direction, the force in the z direction will affect the strain gauges used to detect the x and y directions.

[0005] In view of the above problems, an object of the present invention is to provide a force transducer that reduces the influence of errors in the position where the strain gauge is attached. [Means for solving the problem]

[0006] In order to achieve the above object, a force transducer according to one aspect of the present invention comprises: A force transducer comprising a force point portion, a support portion, a strain-generating portion, a Wheatstone bridge circuit, and a strain-sensitive resistor, which receives and detects forces from a plurality of directions and converts them into electrical signals, The force point introduces each force, The support part receives and supports each force, The strain-generating portion is provided between the force point portion and the support portion and is elastically deformed by each force, The Wheatstone bridge circuit is configured to include a strain-sensitive resistor, The strain-sensitive resistor detects at least one of a force in a first direction and a force in a second direction perpendicular to the force in the first direction, and is attached to the strain-sensitive portion with maximum sensitivity in a direction that cancels out the detection of strain caused in the strain-sensitive portion by a force in a third direction perpendicular to each of the force in the first direction and the force in the second direction.

[0007] Furthermore, the direction of maximum sensitivity of the strain sensitive resistor is determined from the Poisson's ratio of the strain generating portion. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view showing an external appearance of a force transducer according to an embodiment of the present invention and an adapter adapted to an object to be measured. [Figure 2] FIG. 1 is a perspective view of a force transducer according to an embodiment of the present invention. [Figure 3] FIG. 1 is an exploded view of a force transducer according to an embodiment of the present invention. [Figure 4] FIG. 1 is a perspective view of a force transducer according to an embodiment of the present invention. [Figure 5] 1 is a diagram of a force transducer according to an embodiment of the present invention; [Figure 6] 1 is a cross-sectional view of a force transducer according to an embodiment of the present invention. [Figure 7] 1 is a diagram of a strain gauge of a force transducer according to an embodiment of the present invention; [Figure 8]1 is a circuit diagram including a Wheatstone bridge circuit including strain sensitive resistors of a force transducer according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0009] A force transducer according to an embodiment of the present invention will be described in detail below with reference to the drawings. Figure 1 is a perspective view of a force transducer 1 and an adapter 6 according to an embodiment of the present invention. Figure 2 is a perspective view of the force transducer 1 according to an embodiment of the present invention.

[0010] The force transducer 1 comprises a main body 2, a plate 3, and a support 5. The support 5 is fixed to a base 7, such as a fixed structural member, with bolts Ba, and covers and protects the main body 2 from the external environment. The main body 2 is partially covered by the support 5 and connected to the plate 3 by a connection 2g exposed to the outside. The plate 3 has, for example, a rectangular flat plate shape and is fixed to the connection 2g. Force points 4xa, 4xb, 4ya, 4yb, and 4z are arranged on the plate 3. The force point 4xa is arranged to receive a force Fx in the positive x-direction, the force point 4xb a force Fx in the negative x-direction, the force point 4ya a force Fy in the positive y-direction, the force point 4yb a force Fy in the negative y-direction, and the force point 4z a force Fz in the negative z-direction from the adapter 6. Here, if force Fx is defined as a force in a first direction, force Fy perpendicular to the force in the first direction is defined as a force in a second direction, and force Fz perpendicular to both the force in the first direction and the force in the second direction is defined as a force in a third direction.

[0011] Each force point part has a spherical tip and receives force through point contact at this spherical part. Each force point part has a press-fit or threaded part for insertion into plate 3. Each force point part is designed not to easily deform when subjected to the force of the object to be measured. Note that the force point parts and plate 3 are not limited to this shape and may be configured as an integrated member. The user of force transducer 1 can then configure a force transducer to suit the object to be measured by replacing the force point parts.

[0012] The cable gland 8 is attached to the side of the support part 5, and fixes a cable 9 for supplying power to the main body part 2 and transmitting electrical signals from the main body part 2, and keeps the wiring airtight.

[0013] The adapter 6 is attached to the object to be measured, contacts the force points 4xa, 4xb, 4ya, 4yb, and 4z with almost no gap, and introduces the force received from the object to the force transducer 1. The adapter 6 is, for example, cylindrical with a bottom, and its side is in contact with the object to be measured and press-fitted, but is not limited to this. Furthermore, if the direction of the force received by the adapter 6 changes in the opposite direction, a structure may be used in which pressure is applied to each force point from the adapter 6 side in advance to set the clearance to zero.

[0014] FIG. 3 is an exploded view of the force transducer 1 including the adapter 6 according to an embodiment of the present invention. FIG. 4 is a perspective view of the main components of the force transducer 1 according to an embodiment of the present invention. The main body 2 includes a connection portion 2g, a flange portion 2f, and a column portion 2a. The connection portion 2g has a shape that is highly rigid and does not easily deform. The connection portion 2g is connected to the plate 3 with a bolt Bb. The flange portion 2f also has a shape that is highly rigid and does not easily deform. The flange portion 2f is connected to the support portion 5 with a bolt Bc. Opposing recesses are provided in the column portion 2a, forming portions with lower rigidity than the connection portion 2g and the flange portion 2f. Therefore, a thin-walled strain-generating portion 2k is formed at the bottom of this recess, which elastically deforms when force is applied. In this embodiment, the column portion 2a has a rectangular parallelepiped shape, but this is not limited thereto and may also be cylindrical. In addition, the flange portion 2f is a round flange in this embodiment but may be a square flange. Meanwhile, the connection portion 2g is also square in this embodiment but may be round.

[0015] 5 is a diagram of the force transducer 1 according to an embodiment of the present invention, omitting the support portion 5 and mainly showing the main body portion 2 and the plate 3. Fig. 5(a) is a view as viewed from the arrow A in Fig. 4 (viewed in the positive x direction), and Fig. 5(b) is a view as viewed from the arrow B in Fig. 4 (viewed in the positive y direction).

[0016] In Figure 5(a), the directions of the force from the object to be measured are, for example, a force Fy in the positive y direction and a force Fz in the negative z direction. The flat portion 2b provided on the main body 2 is the bottom of a plane recessed in the positive x direction from the side of the column portion 2a, and strain-sensitive resistors Gya and Gyb are attached to this plane. The wiring patterns of the strain-sensitive resistors Gya and Gyb are symmetrical with respect to the axis AX. Each strain-sensitive resistor is a so-called strain gauge. The strain-sensitive resistor is formed by forming a metal foil with a folded fine-line pattern on a thin electrical insulator such as polyimide film, and providing electrodes for wiring connection.

[0017] The planar portions 2b and 2d are shown by dashed lines in Figure 5(b) as viewed from the y direction. Planar portion 2d is the bottom of a plane recessed in the minus x direction from the side of column portion 2a. Planar portions 2d and 2b are in the same position in the y and z directions. Therefore, strain-flexing portion 2k is thin-walled by planar portions 2d and 2b, and is elastically deformed by force Fy.

[0018] 5(b), the directions of the forces from the object to be measured are, for example, a force Fx in the positive x direction and a force Fz in the negative z direction. The flat portion 2c provided on the main body 2 is the bottom of a plane recessed in the positive y direction from the side of the column portion 2a, and strain-sensitive resistors Gxa and Gxb are affixed to this plane. The wiring patterns of the strain-sensitive resistors Gxa and Gxb are symmetrical with respect to the axis AX.

[0019] The planar portion 2c and the planar portion 2e are shown by the dashed line in Figure 5(a) as viewed from the x direction. As shown in Figure 5(a), the planar portion 2e is the bottom of a plane recessed in the minus y direction from the side surface of the column portion 2a. The planar portions 2c and 2e are in the same position in the y and z directions. Therefore, the strain-flexing portion 2k is thin-walled by the planar portions 2c and 2e and is elastically deformed by the force Fx.

[0020] In this embodiment, the strain-sensitive resistor is attached to the bottom surface of the recess, but this is not limited to this. Depending on the magnitude of the force to be detected and the shape of the main body 2, the strain-sensitive resistor may be attached to a flat surface arranged on the side surface of the pillar.

[0021] 6(a) and 6(b) are cross-sectional views of a force transducer according to an embodiment of the present invention. FIG. 6(a) is a cross-sectional view of FIG. 3 taken along a plane parallel to the yz plane and including the axis AX. FIG. 6(b) is a cross-sectional view of FIG. 3 taken along a plane parallel to the xz plane and including the axis AX. The main body 2 has a flange 2h between the column 2a and the connecting portion 2g. A groove is provided on the outer periphery of the flange 2h, into which an O-ring 10 is fitted. This O-ring 10 forms a closed space S between the main body 2 and the support portion 5. Therefore, a strain-sensitive resistor and the electrical and electronic circuit components described below can be placed in this space S, protecting them from external foreign matter, water droplets, and the like. A cable 9 is inserted into this space S, enabling power supply and signal extraction.

[0022] As shown in Fig. 6(a), strain-sensitive resistors Gxa and Gxb are attached to the flat portion 2c side of strain-sensitive portion 2k, and strain-sensitive resistors Gxc and Gxd are attached to the flat portion 2e side of strain-sensitive portion 2k. The strain-sensitive resistors Gxa and Gxc, and the strain-sensitive resistors Gxb and Gxd are attached so that their maximum sensitivity directions face the same direction. As shown in Fig. 6(b), strain-sensitive resistors Gya and Gyb are attached to the flat portion 2b side of strain-sensitive portion 2k, and strain-sensitive resistors Gyc and Gyd are attached to the flat portion 2d side of strain-sensitive portion 2k. The strain-sensitive resistors Gya and Gyc, and the strain-sensitive resistors Gyb and Gyd are attached so that their maximum sensitivity directions face the same direction. In this embodiment, strain-sensitive resistors Gxa, Gxb, Gxc, Gxd and strain-sensitive resistors Gya, Gyb, Gyc, Gyd are arranged to detect forces acting from the x and y directions, respectively. However, if it is necessary to detect only one type of force, and if there are dimensional constraints on the main body 2 in the z direction, it is also possible to arrange only strain-sensitive resistors that detect only the desired direction.

[0023] Here, the reason why the present invention can accurately detect the x-direction force Fx and the y-direction force Fy even when a larger force is applied to the force point 4z than to the force points 4xa, 4xb, 4ya, and 4yb will be explained using Figures 7(i) to 7(iv). Figure 7(i) conceptually illustrates the deformation of the strain-flexing part 2k. A virtual square area represented by a dashed-dotted line with points O, U, H, and J as its vertices represents the case when no force is applied. The solid lines exaggerate and schematically illustrate the deformation state due to the shear stress τ caused by the application of force. Specifically, point U, which faces point J, moves to point V due to the shear stress τ, and point R, which faces point O, moves to point R due to the shear stress τ. The tensile shear strain is maximized when the angle between the line segments JU and JH is 45 degrees, and the compressive shear strain is maximized when the angle between the line segments OH and JH is 45 degrees. Therefore, it is a well-known method to attach a strain-sensitive resistor to the strain-generating part 2k so that the direction of the line segment JU and the direction of the line segment OH are the maximum sensitivity.

[0024] However, as shown in Figure 7(ii), the strain-flexible part 2k of this embodiment is also subjected to a relatively large force Fz, and this compressive stress causes the virtual area with its apex at point JHUO to deform into an area with its apex at point WMNO. Therefore, if the maximum sensitivity direction of a conventional strain-sensitive resistor is oriented in the direction of its maximum sensitivity, the strain component of the strain-flexible part 2k due to this force Fz will also be detected. If the maximum sensitivity directions of these multiple strain-sensitive resistors were precisely aligned and attached to the strain-flexible part 2k at a 45-degree angle, the component of force Fz could be canceled out, but this is difficult in practice.

[0025] Therefore, in this embodiment, the strain-sensitive resistor is positioned so that its maximum sensitivity direction is oriented at angle θ, where length L1 of imaginary line segment JP connecting points P and J on line segment MN, which is deformed by force Fz, is equal to length L2 of imaginary line segment JQ connecting points Q and J on line segment MN. In other words, if length L1 = length L2, the amount of strain in the strain-sensitive resistor is the same, so it is possible to avoid the influence of compressive strain due to force Fz. The angle θ can be calculated as follows:

[0026] The length z is the unknown length that determines the angle θ. The length a is the length of the line segment ON defined in the imaginary area before the force is applied. ν is the Poisson's ratio of the strain-causing part 2k, and k is the elongation rate.

[0027] The length L1 of the virtual line segment JP is expressed by the following equation.

number

[0028] On the other hand, the length L2 of the virtual line segment JQ is expressed by the following equation.

number

[0029] Next (L1) 2 =(L2) 2 Find z such that:

number

[0030] Organizing for z gives the following equation:

number

[0031] Since tanθ=z / a, θ can be expressed by the following equation.

number

[0032] Here, for example, the elongation rate k is very small, so if we set k to 0, it can be expressed by the following equation.

number

[0033] Therefore, if the Poisson's ratio of the strain-generating part 2k is ν=0.3, then θ=28.7 degrees. Note that the shear strain that the strain-sensitive resistor can detect at this time is τsin2θ on the Mohr circle, so approximately 78.5% of the actual shear strain is detected. Therefore, the control unit 13 can obtain the original force value by multiplying the detected value by the reciprocal of this.

[0034] In this embodiment, the force Fz acts in compression on the strain-generating part 2k, but it can also be a tensile load, in which case just replace (1+kν) with (1-kν) and (1-k) with (1+k) in equation 1. When the elongation rate k=0.1, strictly speaking the angle θ will differ depending on the direction of the force Fz, but because the sensitivity of the strain-sensitive resistor to the force Fz is very low, it can be said that correction based on the design angle of the strain-sensitive resistor alone is sufficient.

[0035] 8 is a circuit diagram of a Wheatstone bridge circuit including a strain-sensitive resistor of a force transducer according to an embodiment of the present invention. The force transducer 1 includes a power supply E, amplifiers 11a and 11b, A / D converters 12a and 12b, a control unit 13, and a display 14.

[0036] The power supply E supplies power to the strain sensitive resistors Gxa-Gxd and Gya-Gyd. The amplifier 11a amplifies the signals output from the coupling terminals Tx2 and Tx4 from the Wheatstone bridge circuit. The amplifier 11b amplifies the signals output from the coupling terminals Ty2 and Ty4 from the Wheatstone bridge. The A / D converters 12a and 12b convert analog signals into digital signals, and convert the analog signals amplified by the amplifiers 11a and 11b into digital signals, respectively. The control unit 13 includes a central processing unit (CPU), read only memory (ROM), random access memory (RAM), other storage devices, and input / output devices. The control unit 13 performs calculations based on the digital signals output from the A / D converters 12a and 12b, and displays the results on a display 14.

[0037] Next, the arrangement of each strain sensitive resistor in the Wheatstone bridge circuit will be explained. In the Wheatstone bridge circuit including the strain sensitive resistors Gxa to Gxd, the strain sensitive resistor Gxd and the strain sensitive resistor Gxa are on adjacent sides, and their coupling terminal Tx1 is connected to the power supply E. The strain sensitive resistor Gxb and the strain sensitive resistor Gxc are on adjacent sides, and their coupling terminal Tx3 is connected to the power supply E. Furthermore, the strain sensitive resistor Gxa and the strain sensitive resistor Gxc are on opposing sides, and the strain sensitive resistor Gxb and the strain sensitive resistor Gxd are on opposing sides. The coupling terminal Tx2 between the strain sensitive resistor Gxa and the strain sensitive resistor Gxb, and the coupling terminal Tx4 between the strain sensitive resistor Gxc and the strain sensitive resistor Gxd, form the outputs of the Wheatstone bridge circuit.

[0038] Similarly, in a Wheatstone bridge circuit including strain sensitive resistors Gya-Gyd, strain sensitive resistor Gyd and strain sensitive resistor Gya are located on adjacent sides, and their coupling terminal Ty1 is connected to a power supply E. Strain sensitive resistor Gyb and strain sensitive resistor Gyc are located on adjacent sides, and their coupling terminal Ty3 is connected to a power supply E. Furthermore, strain sensitive resistor Gya and strain sensitive resistor Gyc are located on opposing sides, and strain sensitive resistor Gyb and strain sensitive resistor Gyd are located on opposing sides. The coupling terminal Ty2 between strain sensitive resistor Gya and strain sensitive resistor Gyb and the coupling terminal Ty4 between strain sensitive resistor Gyc and strain sensitive resistor Gyd become the outputs of the Wheatstone bridge circuit.

[0039] In this configuration, when a force Fx as shown in Figure 5(b) is applied to the force point 4xa, the strain-sensitive resistor Gxa becomes the tensile side under shear stress, and the strain-sensitive resistor Gxb becomes the compressive side under shear stress. On the other hand, the strain-sensitive resistor Gxc becomes the tensile side under shear stress, and the strain-sensitive resistor Gxd becomes the compressive side under shear stress.

[0040] The same is true for a Wheatstone bridge circuit including strain-sensitive resistors Gya-Gyd. That is, when a force Fy as shown in Fig. 5(a) is applied to the force point 4ya, the strain-sensitive resistor Gya becomes the tension side under shear stress. And the strain-sensitive resistor Gyb becomes the compression side under shear stress. On the other hand, the strain-sensitive resistor Gyc becomes the tension side under shear stress. And the strain-sensitive resistor Gyd becomes the compression side under shear stress.

[0041] In this embodiment, each Wheatstone bridge circuit is provided with four active strain-sensitive resistors, but it may be configured with two active strain-sensitive resistors. For example, in Fig. 8, only the strain-sensitive resistors Gxa and Gxb may be active strain-sensitive resistors, and the strain-sensitive resistors Gxc and Gxd on the other sides may be fixed resistors.

[0042] The present invention has been described above based on a preferred embodiment, but the present invention is not limited to the above-described embodiment and various modifications are possible without departing from the spirit of the present invention. [Industrial Applicability]

[0043] As an example of application of the present invention, it can be applied to a device for measuring force. [Explanation of symbols]

[0044] 1: Force transducer 2: Main body 2a:Column part 2b, 2c, 2d, 2e: Flat part 2f: Flange part 2g: Connection part 2h:Tsubabe 2k: Strain part 3: Plate 4 (4xa, 4xb, 4ya, 4yb, 4z): point of force 5: Support part 6: Adapter 7: Bass 8: Cable gland 9: Cable 10: O-ring 11a, 11b: Amplifier 12a, 12b: A / D converter 13: Control section 14:Display unit Fx: Force in the first direction (x direction) Fy: Force in the second direction (y direction) Fz: Force in the third direction (z direction) Gxa, Gxb, Gxc, Gxd: sensory resistance Gya, Gyb, Gyc, Gyd: sensory resistance

Claims

1. A force transducer comprising a force point portion, a support portion, a strain-generating portion, a Wheatstone bridge circuit, and a strain-sensitive resistor, which receives and detects forces from a plurality of directions and converts them into electrical signals, The force point portion introduces the forces, The support portion receives and supports each of the forces, the strain-flexing portion is provided between the force point portion and the support portion and elastically deforms due to the forces; the Wheatstone bridge circuit is configured to include the strain sensitive resistor, The strain-sensitive resistor is a force transducer that detects at least one of a force in a first direction and a force in a second direction perpendicular to the force in the first direction, and is attached to the strain-flexible portion with maximum sensitivity in a direction that cancels out detection of strain caused in the strain-flexible portion by a force in a third direction perpendicular to each of the force in the first direction and the force in the second direction.

2. 2. A force transducer according to claim 1, wherein the direction of maximum sensitivity of said strain-sensitive resistor is determined from the Poisson's ratio of said strain-generating portion.

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