JP2022019106A - Force converter - Google Patents

Abstract

To provide a small force converter which is less affected by the position on which a force is applied.SOLUTION: The force converter includes: a force point 50 on which a force is applied; a supporting unit 3 for supporting in reception of the force; a columnar strain unit 4 elastically deformable between the force point 50 and the supporting unit 3; a strain sensitive resistor attached to the strain unit 4; and a Wheatstone bridge circuit including the strain sensitive resistor, and the force converter converts force into an electric signal. The strain sensitive resistor is attached while having the largest sensitivity in a direction in which the bending moment generated in the strain unit 4 by the force is cancelled out.SELECTED DRAWING: Figure 3

Description

The present invention relates to a force transducer that measures force and converts it into an electrical signal.

Conventionally, as an example of a force transducer, a three-component force converter that detects an applied force in a three-dimensional direction XYZ has been known.

Japanese Unexamined Patent Publication No. 2020-071189

In such a force transducer, for example, as shown in FIG. 10, when a force Fx is applied to the force point portion 51, the strain-causing portion 4 is distorted and is attached to the recess 4b of the thin-walled portion of the strain-causing portion 4. The plurality of resistance temperature detectors G1 to G4 provided have a configuration for detecting shear strain. That is, the maximum sensitivity direction of the resistance thermometer G1 is the p direction at an angle of +45 degrees with respect to the central axis AX of the strain-causing portion, and the maximum sensitivity direction of the resistance thermometer G2 is the central axis AX of the strain-causing portion. It is generally attached so as to be in the q direction at an angle of minus 45 degrees. However, depending on the shape of the measurement target or the like, the force point portion 51 may be changed to the force point portion 52 short in the z direction, and the force transducer 1 may be used. That is, the user of this force transducer 1 changes the distance between the force point portion and the support portion. At this time, the resistance thermometers G1 and G2 detect the shear strain generated in the strain-causing portion 4 by applying the force Fx, but at the same time, the components of the bending moment are simultaneously affected by the position shift of the resistance thermometer. It was happening to detect.

Therefore, the bending moment differs depending on the difference between the length from the resistance thermometers G1 and G2 to the force point portion 51 and the length from the resistance thermometers G1 and G2 to the force point portion 52, so that the detected force differs. There was a problem. As a method for solving this, for example, the invention of Patent Document 1 is disclosed.

However, in the invention of Patent Document 1, it is necessary to arrange strain-sensitive resistors side by side in the Z direction shown in FIG. 10 in the strain-causing portion, and it is necessary to secure the space, so that extremely miniaturization is required. There was a problem that it was difficult to apply it to a force converter.

In view of such problems, it is an object of the present invention to provide a compact force transducer in which the influence of the position where a force is applied is reduced.

The force transducer according to one aspect of the present invention is used to achieve the above object.
The force point part where force is applied and
A support part that receives and supports force,
A column-shaped strain-causing part that elastically deforms between the force point part and the support part,
The resistance temperature detector attached to the strain-causing part,
A Wheatstone bridge circuit that includes a resistance thermometer and a force transducer that converts force into an electrical signal.
The strain-sensitive resistor is attached with maximum sensitivity in the direction of canceling the distortion of the bending moment generated in the strain-causing portion by the force.

According to the present invention, it is possible to provide a compact force transducer in which the influence of the position where a force is applied is reduced by the maximum sensitivity direction and arrangement of the resistance thermometer that cancels the influence of the bending moment generated in the strain-causing portion.

It is a perspective view of the force transducer which concerns on embodiment of this invention. It is a perspective exploded view of the force transducer which concerns on embodiment of this invention. It is a figure of the strain | strain part and the force point part of the force converter which concerns on embodiment of this invention. It is a conceptual diagram of the deformation of the strain-causing portion of the force converter according to the embodiment of the present invention. It is a figure of the strain | strain part and the force point part of the force converter which concerns on embodiment of this invention. It is a figure of the strain | strain part and the force point part of the force converter which concerns on embodiment of this invention. It is a figure of the strain | strain part and the force point part of the force converter which concerns on embodiment of this invention. It is sectional drawing of the strain | strain part and the force point part of the force converter which concerns on embodiment of this invention. It is a circuit diagram which includes the Wheatstone bridge circuit which includes the resistance temperature detector of the force converter which concerns on embodiment of this invention. It is a figure of the strain raising part and the force point part of the conventional force converter.

Hereinafter, the force transducer according to the embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective external view of the force transducer 1 according to the embodiment of the present invention. FIG. 2 is a perspective exploded view of the force transducer 1 according to the embodiment of the present invention.

The force transducer 1 includes a housing 3, a strain generating portion 4, a mounting plate 6, and a force point portion 50. The housing 3 is fixed to a base 2 such as a fixed structural member with bolts 7 and covers the strain generating portion 4 to protect it from the external environment. The strain-causing portion 4 has a columnar shape and is located between the flange 4a and the flange 4f, which have high rigidity and are not easily deformed. It has recesses 4b to 4e. In the present embodiment, the shape of the strain-causing portion 4 between the flanges is a rectangular parallelepiped, but the shape is not limited to this, and may be a cylindrical shape. Further, the flange 4a may be a round flange in the present embodiment but may be a square flange, while the flange 4f may also be a square flange in the present embodiment but may be a round flange. In the present embodiment, the flange 4a, the strain generating portion 4, and the flange 4f are integrally configured, but the present invention is not limited to this. The flange 4a is a support portion that is fastened to the housing 3 fixed to the fixed structural member with bolts 8 and supports the strain generating portion 4 and the like together with the housing 3.

The mounting plate 6 has, for example, a square flat plate shape, and is fastened to the flange 4f with bolts 9. Power point portions 51 and 52 are attached to the central portion of the mounting plate 6.

The force point portions 51 and 52 have a partially spherical portion at one end of a cylindrical member. The force point portions 51 and 52 have a press-fitting portion or a screw portion to be fastened to the mounting plate 6 at the other end. The force point portions 51 and 52 receive a force by point contact at this spherical portion. The force point portions 51 and 52 are not easily deformed by the force of the measurement target. The force point portions 51 and 52 and the mounting plate 6 are not limited to this shape, and may be formed of an integral member. Further, the user of the force transducer 1 is not limited to the shape of the portion of the force point portions 51 and 52 having a spherical shape, and can select and use the optimum shape according to the object to be measured. The user of the force transducer 1 can configure the force transducer by integrating the force point portion and the mounting plate 6 or by exchanging the force point portion.

A strain-sensitive resistor is attached to the recesses 4b to 4e constituting the strain-causing portion 4. Therefore, the resistance temperature detector detects the components of the force received by the force point portion 50 in the x-direction and the y-direction as the strain amount. Therefore, the force converter 1 can convert the force applied to the force point portion 50 into an electric signal.

Further, in the present embodiment, the strain-sensitive resistor is attached to the bottom surface of the recess, but the present invention is not limited to this, and the strain-causing portion 4 has no recess depending on the magnitude of the detected force. It may be a deformation such as being arranged on the side surface of the pillar of 4.

FIG. 3 (i) is a schematic view of the strain-causing portion 4 and the force point portion 51 of the force converter according to the embodiment of the present invention as viewed in the negative direction of the y-axis of FIG. 2 (plan view of FIG. 2). FIG. 3 (ii) is a schematic view of the strain-causing portion 4 and the force point portion 52 of the force converter according to the embodiment of the present invention as viewed in the same negative direction of the y-axis. In FIGS. 3 (i) and 3 (ii), the strain-sensitive resistor Gxa and the resistance thermometer Gxb exaggerate their sizes. The notation method for exaggerating the resistance temperature detector is the same in FIGS. 5 to 7 and 10.

The difference between the configurations in FIGS. 3 (i) and 3 (ii) is the length of the force point portion 51 and the force point portion 52 in the z direction. Both the force point portion 51 and the force point portion 52 receive the force Fx in the negative direction on the x-axis. Since the strain-causing portion 4 is fixed to the base 2 via the housing 3 by the flange 4a, the strain-causing portion 4 has a bending moment Mx1 in FIG. 3 (i) and bending in FIG. 3 (ii). Moment Mx2 is generated.

Here, the conventional force transducer will be described first. 10 (i) and 10 (ii) are conventional force transducers, in which the resistance temperature detectors G1 and G2 are attached side by side in the z direction to the bottom surface of the recess 4b provided near the flange 4a. .. Then, for example, the resistance thermometer G1 is arranged on the left side of the center of the recess 4b in the z direction so that the maximum sensitivity direction is the p direction of plus 45 degrees with respect to the central axis AX. On the other hand, the resistance thermometer G2 is arranged on the right side of the center of the recess 4b in the z direction so that the maximum sensitivity direction is minus 45 degrees in the q direction with respect to the central axis AX. The arrangement of the strain-sensitive resistors G1 and G2 is a normal method for detecting the strain generated in the strain-causing portion 4, and when the force point portion receives the force Fx, the strain-sensitive resistor G1 detects the compression strain due to the shear stress. , The strain-sensitive resistor G2 detects the tensile strain due to the shear stress, and the force converter 1 calculates and outputs the force Fx based on these.

If the user of the force transducer 1 changes the force point portion 51 shown in FIG. 10 (i) to the force point portion 52 shown in FIG. 10 (ii), a force Fx of the same magnitude is applied. , The forces detected by the force transducer 1 should be the same. However, in the conventional arrangement of the resistance thermometers G1 and G2, the phenomenon that the force transducer does not output the same force value has occurred. The inventor has found that this is because the strain resistance thermometers G1 and G2 detect the strain component due to the bending moments Mx1 and Mx2 generated in the strain-causing portion 4. Normally, the influence of this bending moment is eliminated by arranging the strain sensitive resistors G1 and G2 so as to be aligned with the neutral plane (line) parallel to the z direction. However, it is difficult to completely eliminate the influence of this bending moment due to the processing accuracy of the strain-sensitive portion, the sensitivity distribution of the resistance temperature detector, the positional deviation of the resistance temperature detector, and the like. Conventionally, in general, trial and error has been performed such as reattaching the resistance thermometer and removing a part of the strain-causing portion, but it has been difficult to deal with the force point portion at various distances.

In contrast to this conventional arrangement of the resistance thermometer, in the present invention, as shown in FIGS. 3 (i) and 3 (ii), the resistance thermometer Gxa is formed on the bottom surface of the recess 4b provided near the flange 4a. The resistance thermometer Gxb is arranged in series in the x direction, which is the direction of the force Fx to be detected. Then, the strain-sensitive resistor Gxa has the maximum sensitivity in the q direction and is attached to the strain-causing portion 4. On the other hand, the strain-sensitive resistor Gxb has the maximum sensitivity in the p direction and is attached to the strain-causing portion 4. The details of the angles in the p direction and the q direction will be described later.

Here, using FIGS. 4 (i) to 4 (vi), the reason why the same force can be detected when a force Fx of the same magnitude is applied to both the force point portion 51 and the force point portion 52 is used. explain. FIG. 4 (i) conceptually shows the deformation of the strain-causing portion 4. When no force is applied, the deformation state due to the shear stress τ generated by the application of force is exaggerated based on the virtual region of the square represented by the alternate long and short dash line having points O, U, H, and I at the corners. It is shown schematically. That is, the point U facing the point O is deformed like the point V by the shear stress τ. Since the tensile strain of shear is maximized when the angle formed by the line segment OU and the central axis AX is 45 degrees, the strain-sensitive resistor (G2, FIG. 10 (G2, FIG. 10) so that the direction of the line segment OU has the maximum sensitivity. It is a well-known method in the past that i)) is attached to the strain-causing portion 4.

However, on the other hand, as shown in FIG. 4 (ii), in the strain-causing portion 4 of the present embodiment, a bending moment is also generated, and the apex U is deformed like the apex W by the tensile stress T. Therefore, in the direction of the maximum sensitivity of the conventional resistance temperature detector, the strain component of the strain-causing portion 4 due to this bending moment is also detected.

Therefore, in the present embodiment, in FIGS. 4 (iii) and 4 (iv), the length L1 of the virtual line segment OQ connecting the points Q and the points O on the line segment JW deformed by the tension of the bending moment is used. The strain-sensitive resistor is arranged so that the maximum sensitivity direction of the strain-sensitive resistor faces at an angle θ where the length L2 of the virtual line segment OP connecting the point P and the point O on the line segment HU becomes equal. .. That is, if the length L1 = the length L2, the amount of strain of the resistance temperature detector is the same, so that it can be prevented from being affected by the tensile elongation due to this bending moment. The angle θ can be obtained as follows.

The length z is an unknown length that determines the angle θ. The length a is the length of the defined virtual area before the force is applied. ν is the Poisson's ratio of the strain-causing portion 4, and k is the elongation rate in the vertical direction (here, the x-axis direction) in the figure.

The length L1 of the virtual line segment OQ is expressed by the following equation.

On the other hand, the length L2 of the virtual line segment OP is expressed by the following equation.

Next, z such that (L1) ² = (L2) ² is obtained.

The following formula can be obtained by arranging z.

Since tan θ = z / a, θ is expressed by the following equation.

Here, for example, since the elongation rate k is very small, if k → 0, it is expressed by the following equation.

Therefore, if the Poisson's ratio ν = 0.3 of the strain-causing portion 4, then θ = 28.7 degrees. Since the shear strain that can be detected by the resistance thermometer at this time is τsin2θ in the Mohr's circle, about 78.5% of the actual shear strain is detected, so the control unit 13 inputs this reciprocal to the detected value. The original force value may be obtained by multiplying and calculating.

4 (v) and 4 (vi) show an example of the arrangement of the resistance temperature detectors Gxa and Gxb corresponding to FIGS. 4 (iii) and 4 (iv), respectively. The resistance temperature detectors Gxa and Gxb may be independent or may be patterned with an integral base material.

FIG. 5 (i) is a schematic view of the strain-causing portion 4 and the force point portion 51 of the force transducer according to the embodiment of the present invention, in the opposite direction of the schematic diagram of FIG. 3 (i), that is, in the positive direction of the y-axis. It is a figure seen in. FIG. 5 (ii) is a schematic diagram of the strain-causing portion 4 and the force point portion 52 of the force transducer according to the embodiment of the present invention, in the opposite direction of the schematic diagram of FIG. 3 (ii), that is, in the positive direction of the y-axis. It is a figure seen in. That is, FIGS. 5 (i) and 5 (ii) show the back sides of FIGS. 3 (i) and 3 (ii), respectively. Therefore, the p direction and the q direction are represented in FIGS. 5 (i) and 5 (ii) in the opposite directions of FIGS. 3 (i) and 3 (ii). The resistance thermometer Gxc and the resistance thermometer Gxd are arranged in series in the x-direction on the bottom surface of the recess 4c provided near the flange 4a. The recess 4c is provided back to back with the recess 4b.

The strain-sensitive resistor Gxc has maximum sensitivity in the q direction and is attached to the strain-causing portion 4. On the other hand, the strain-sensitive resistor Gxd has the maximum sensitivity in the p direction and is attached to the strain-causing portion 4.

The reason why the same force can be detected when a force Fx of the same magnitude is applied to both the force point portion 51 and the force point portion 52 has been described with reference to FIGS. 4 (i) to 4 (vi). It's a street.

FIG. 6 (i) is a schematic view of the strain-causing portion 4 and the force point portion 51 of the force converter according to the embodiment of the present invention as viewed in the positive direction of the x-axis of FIG. 2, FIG. 6 (ii). Is a schematic view of the strain generating portion 4 and the force point portion 52 of the force converter according to the embodiment of the present invention as viewed in the positive direction of the same x-axis. In FIGS. 6 (i) and 6 (ii), the force point portion 51 and the force point portion 52 both receive the force Fy in the positive direction on the y-axis. Since the strain-causing portion 4 is fixed to the base 2 via the housing 3 by the flange 4a, the strain-causing portion 4 has a bending moment My1 in FIG. 6 (i) and bending in FIG. 6 (ii). Moment My2 is generated.

As shown in FIGS. 6 (i) and 6 (ii), the resistance thermometer Gya and the resistance thermometer Gyb are arranged side by side in the y direction on the bottom surface of the recess 4d provided near the flange 4f. The strain-sensitive resistor Gya has maximum sensitivity in the r direction and is attached to the strain-causing portion 4. On the other hand, the strain-sensitive resistor Gyb has the maximum sensitivity in the s direction and is attached to the strain-causing portion 4.

FIG. 7 (i) is a schematic view of the strain-causing portion 4 and the force point portion 51 of the force converter according to the embodiment of the present invention as viewed in the negative direction of the x-axis of FIG. 2, FIG. 7 (ii). Is a schematic view of the strain generating portion 4 and the force point portion 52 of the force converter according to the embodiment of the present invention as viewed in the same negative direction of the x-axis. That is, FIGS. 7 (i) and 7 (ii) show the back sides of FIGS. 6 (i) and 6 (ii), respectively. Therefore, the r direction and the s direction are represented in FIGS. 7 (i) and 7 (ii) in the opposite directions of FIGS. 6 (i) and 6 (ii). The strain-sensitive resistor Gyc and the resistance thermometer Gyd are arranged in series in the y-direction on the bottom surface of the recess 4e provided near the flange 4f. The recess 4e is provided back to back with the recess 4d.

The strain-sensitive resistor Gyc has maximum sensitivity in the r direction and is attached to the strain-causing portion 4. On the other hand, the strain-sensitive resistor Gyd has the maximum sensitivity in the s direction and is attached to the strain-causing portion 4.

Of course, the reason why the same force can be detected in both the force point portion 51 and the force point portion 52 when a force Fx of the same magnitude is applied is as described in FIGS. 4 (i) to 4 (vi). Is.

FIG. 8 (i) is a cross-sectional view of the force transducer according to the embodiment of the present invention. FIG. 8 (i) is a diagram in which the force transducer 1 is cut in the yz plane passing through the central axis AX in FIG. FIG. 8 (ii) is a cross-sectional view of the force transducer according to the embodiment of the present invention. FIG. 8 (ii) is a diagram in which the force transducer 1 is cut in the xz plane passing through the central axis AX in FIG.

A flange 4g is provided between the strain generating portion 4 and the flange 4f, and an O-ring 10 is fitted in the flange 4g. The O-ring 10 maintains the airtightness between the strain-causing portion 4 and the housing 3, and protects the strain-sensitive resistors Gxa to Gxd and Gya to Gyd from the external environment. Further, the housing 3 is provided with a hole 3a, and for example, a sealed connector for drawing out wiring from the resistance thermometers Gxa to Gxd and Gya to Gyd to the outside is arranged in the hole 3a.

The recesses 4b and the recesses 4c provided in the strain raising portion 4 near the flange 4a are back-to-back, the strain-sensitive resistors Gxa and Gxb are on the bottom surface of the recesses 4b, and the resistance thermometers Gxc and Gxd are on the bottom surface of the recesses 4c. However, each is attached. The recesses 4d and the recesses 4e provided in the strain-causing portion 4 near the flange 4f are back-to-back, the strain-sensitive resistors Gya and Gyb are on the bottom surface of the recesses 4d, and the strain-sensitive resistors Gyc and Gyd are on the bottom surface of the recesses 4e. However, each is attached.

FIG. 9 is a circuit diagram having a Wheatstone bridge circuit including a resistance temperature detector of the force transducer according to the embodiment of the present invention. The Wheatstone bridge circuit includes a power supply E, amplifiers 11a and 11b, A / D converters 12a and 12b, a control unit 13, and a display 14.

The power supply E supplies power to the resistance thermometers Gxa to Gxd and Gya to 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 are converters that convert analog signals into digital signals, and convert the analog signals amplified by the amplifier 11a and the amplifier 11b into digital signals, respectively. The control unit 13 includes a central processing unit CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and other storage devices and input / output devices. The control unit 13 calculates based on the digital signals output from the A / D converters 12a and 12b, and displays the result on the display 14.

Next, the arrangement of each resistance temperature detector in the Wheatstone bridge circuit will be described. In the Wheatstone bridge circuit including the resistance thermometers Gxa to Gxd, the resistance thermometer Gxd and the resistance thermometer Gxa are adjacent to each other, and the coupling terminal Tx1 thereof is connected to the power supply E. The resistance thermometer Gxb and the resistance thermometer Gxc are on adjacent sides, and the coupling terminal Tx3 is connected to the power supply E. Further, the resistance thermometer Gxa and the resistance thermometer Gxc are on opposite sides of each other, and the resistance thermometer Gxb and the resistance thermometer Gxd are on opposite sides. Then, the coupling terminal Tx2 between the resistance thermometer Gxa and the resistance thermometer Gxb and the coupling terminal Tx4 between the resistance thermometer Gxc and the resistance thermometer Gxd are the outputs of the Wheatstone bridge circuit.

Similarly, in the Wheatstone bridge circuit including the resistance thermometers Gya to Gyd, the resistance thermometer Gyd and the resistance thermometer Gya are on adjacent sides, and the coupling terminal Ty1 thereof is connected to the power supply E. The resistance thermometer Gyb and the resistance thermometer Gyc are adjacent to each other, and the coupling terminal Ty3 is connected to the power supply E. Further, the resistance thermometer Gya and the resistance thermometer Gyc are on opposite sides of each other, and the resistance thermometer Gyb and the resistance thermometer Gyd are on opposite sides. Then, the coupling terminal Ty2 between the resistance thermometer Gya and the resistance thermometer Gyb and the coupling terminal Ty4 between the resistance thermometer Gyc and the resistance thermometer Gyd are the outputs of the Wheatstone bridge circuit.

With this configuration, when the force Fx as shown in FIGS. 3 (i), 3 (ii), 5 (i), and 5 (ii) is applied to the force points 51 and 52, the resistance temperature detector Gxa shears. In stress, it is on the tension side. The resistance temperature detector Gxb is on the compression side under shear stress. On the other hand, the resistance thermometer Gxc is on the tensile side under shear stress. The resistance temperature detector Gxd is on the compression side under shear stress.

The same applies to the Wheatstone bridge circuit including the resistance thermometers Gya to Gyd. That is, when the force Fy as shown in FIGS. 6 (i), 6 (ii), 7 (i), and 7 (ii) is applied to the force points 51 and 52, the resistance thermometer Gya is tensioned by shear stress. Be on the side. The resistance temperature detector Gyb is on the compression side under shear stress. On the other hand, the resistance thermometer Gyc is on the tensile side under shear stress. The resistance thermometer Gyd is on the compression side under shear stress.

In the present embodiment, each Wheatstone bridge circuit is provided with four active resistance temperature detectors, but two active resistance temperature detectors may be provided. For example, in FIG. 9, only the resistance thermometer Gxa and the resistance thermometer Gxb are active resistance thermometers, and the resistance thermometers Gxc and the resistance thermometer Gxd on the other side are fixed resistance thermometers. May be. This is because in the present invention, the influence of the bending moment is canceled at each side of the Wheatstone bridge circuit.

Although the present invention has been described above based on the preferred embodiment, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist thereof.

As an example of utilization of the present invention, it can be applied to a device for measuring force such as a force meter.

1: Force transducer 2: Base 3: Housing (support)
3a: Hole 4: Distortion part 4a: Flange 4b, 4c, 4d, 4e: Recess 4f: Flange 4g: Flange 6: Mounting plate 7: Bolt 8: Bolt 9: Bolt 10: O-ring 11a, 11b: Amplifier 12a, 12b: A / D converter 13: Control unit 14: Display 50, 51, 52: Power point unit Gxa, Gxb, Gxc, Gxd: Resistance thermometer Gya, Gyb, Gyc, Gyd: Resistance temperature detector

Claims (3)

The force point part where force is applied and
A support part that receives and supports the force and
A column-shaped strain-causing portion that elastically deforms between the force point portion and the support portion,
The resistance thermometer attached to the strain-causing portion and
A force transducer comprising a Wheatstone bridge circuit including the resistance thermometer and converting the force into an electrical signal.
The resistance thermometer is a force transducer that is attached with maximum sensitivity in a direction that cancels the distortion of the bending moment generated in the strain-causing portion by the force. The force transducer according to claim 1, wherein the direction of the maximum sensitivity of the strain-sensitive resistor is determined from the Poisson's ratio of the strain-causing portion. The force transducer according to claim 1 or 2, wherein the resistance thermometers are arranged in series in the direction of the force to be detected and attached to the strain-causing portion.

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