Actuator gripping force estimation device and actuator gripping force estimation method

Abstract

This actuator holding force estimation method estimates, as a holding force, a force acting in a direction orthogonal to a tube axis when the fluid pressure actuator is bent and not bent, the fluid pressure actuator having a tube-shaped main body part that is curved while being shortened in the tube axis direction as a result of an increase in the internal pressure inside the tube on one side of the tube circumference, the force acting in the direction orthogonal to the tube axis when the fluid pressure actuator is not bent. The base end side of a cylinder shaft of the fluid pressure actuator is fixed to a base body, the tip end of the cylinder shaft moves relative to the base body, and L is the length from one end to the other end of the side surface where the contraction of the main body portion is the largest, P is the internal pressure in the cylinder, F is the holding force, and L is the length from the other end to the other end of the side surface where the contraction of the main body portion is the largest. The holding force is estimated from an equation F = [omega] 1P (L-Lmin) + [omega] 2, where [omega] 1 and [omega] 2 are parameters set on the basis of the basic characteristics of the fluid pressure actuator, and Lmin is a constant on the basis of the geometric characteristics of the fluid pressure actuator.

Description

Technical Field

[0001] The present invention relates to an actuator holding force estimation device and an actuator holding force estimation method for a fluid pressure actuator. Background Art

[0002] Conventionally, a McKibben-type fluid pressure actuator is known as a fluid pressure actuator having a rubber tube and a sleeve (a sleeve formed by weaving high-tensile fibers) covering the outer surface of the rubber tube. Such a McKibben-type fluid pressure actuator can change the axial length of the rubber tube and the sleeve.

[0003] In addition, a technology has been proposed in which a restraining member is partially provided in the circumferential direction from one end side to the other end side of the rubber tube in the axial direction, thereby shortening the side of the fluid pressure actuator where the restraining member is not provided and performing bending deformation (see Japanese Patent Publication No. 2021-88999). Summary of the invention

[0004] Problem that the invention aims to solve

[0005] Japanese Patent Application Laid-Open No. 2021-88999 proposes combining a plurality of fluid pressure actuators to form a finger that holds an object by bending and deforming the finger. In this case, it is necessary to find the force used by the fluid pressure actuator to hold the object.

[0006] The present disclosure has been made in view of the above-mentioned circumstances, and an object of the present disclosure is to provide an actuator holding force estimation device and an actuator holding force estimation method that can easily estimate a force of a fluid pressure actuator that acts in a direction perpendicular to a cylinder axis.

[0007] Solutions for solving problems

[0008] In order to achieve the above-mentioned purpose, the actuator holding force inference device of the first technical scheme infers the force of the fluid pressure actuator that acts in a direction orthogonal to the cylinder axis when not bent due to bending as the holding force. The above-mentioned fluid pressure actuator has a cylindrical main body part that is shortened and bent in the cylinder axis direction due to the increase in the internal pressure in the cylinder. The base end side of the cylinder axis of the above-mentioned fluid pressure actuator is fixed to the base, and the top end moves relative to the base. The actuator holding force inference device comprises: a pressure sensor, which obtains the cylinder pressure of the main body; a length acquisition unit, which obtains the length from one end to the other end of the side of the main body with the largest shortening amount; and a holding force inference unit, which sets the length obtained by the length acquisition unit as L, the internal pressure in the cylinder obtained by the pressure sensor as P, the holding force as F, the parameters set based on the basic characteristics of the fluid pressure actuator as ω1 and ω2, and the constant based on the geometric characteristics of the fluid pressure actuator as Lmin When F=ω1P(LL min )+ω2 to infer the holding force.

[0009] In the actuator holding force estimation device of the first technical solution, the holding force of the fluid pressure actuator is estimated using the above formula. Thus, the holding force can be easily estimated using the internal pressure in the cylinder and the length from one end to the other end of the side of the body that contracts the most.

[0010] In the actuator holding force inference device of the second technical solution, the length acquisition part comprises: a wire member, one end of which is installed on the base, and the middle part is arranged on the curved side of the main body in a manner following the bending deformation; a wire holding member, which holds the wire member in a position along the main body; and a measuring part, which applies tension to the wire member and measures the length change of the wire member.

[0011] In the actuator holding force estimation device of the second technical solution, the middle portion of the wire member is arranged on the curved side of the main body of the fluid pressure actuator in a manner that follows the bending deformation. By applying tension to the wire member using the measuring unit and measuring the length change of the wire member, the length of the inner side of the bend of the fluid pressure actuator can be easily obtained even in the bent state.

[0012] The actuator holding force inference method of the third technical solution infers the force of the fluid pressure actuator that acts in a direction orthogonal to the cylinder axis when not bent due to bending as the holding force. The above-mentioned fluid pressure actuator has a cylindrical main body part that is shortened and bent in the cylinder axis direction due to the increase in internal pressure in the cylinder. The base end side of the cylinder axis of the above-mentioned fluid pressure actuator is fixed to the base, and the top end moves relative to the base, wherein the length from one end to the other end of the side surface where the shortening of the main body is the largest is set to L, the internal pressure in the cylinder is set to P, the holding force is set to F, the parameters set based on the basic characteristics of the fluid pressure actuator are set to ω1, ω2, and the constant based on the geometric characteristics of the fluid pressure actuator is set to L min When F=ω1P(LL min )+ω2 to infer the holding force.

[0013] In the actuator holding force estimation method of the third technical solution, the holding force of the fluid pressure actuator is estimated using the above formula. Thus, the holding force can be easily estimated using the internal pressure in the cylinder and the length from one end to the other end of the side of the body that contracts the most.

[0014] In the actuator holding force inference method of the fourth technical solution, a wire member whose one end side is installed on the base and whose middle part is arranged along one side of the bending of the main body and the direction of the cylinder axis is maintained in a position along the main body, tension is applied to the wire member, and the length change of the wire member is measured to obtain the length from one end to the other end of the side surface of the main body with the largest contraction.

[0015] In the actuator holding force inference method of the fourth technical solution, since the middle portion of the wire member is arranged on the bent side of the main body of the fluid pressure actuator in a manner that follows the bending deformation, the length of the inner side of the bend of the fluid pressure actuator can be easily obtained even in the bent state by measuring the length change of the wire member.

[0016] Effects of the Invention

[0017] According to the present disclosure, it is possible to easily estimate the force of the fluid pressure actuator that acts in a direction orthogonal to the cylinder axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a side view of a fluid pressure actuator which is a measurement target of the actuator gripping force estimation device according to the present embodiment.

[0019] Figure 2 It is a partially exploded perspective view of a fluid pressure actuator.

[0020] Figure 3 is a cross-sectional view of a fluid pressure actuator.

[0021] Figure 4 This is a diagram showing a state (non-bending state) in which a fluid pressure actuator is mounted on the actuator holding force estimation device.

[0022] Figure 5 This is a diagram showing a state (bent state) in which a fluid pressure actuator is mounted on the actuator holding force estimation device.

[0023] Fig. 6A This is a graph showing the estimated holding force and the measured holding force in time series as test results, and is a case where the length L1 is 0.074 m when the target pressure is 200 kPa.

[0024] Figure 6B This is a graph showing the estimated holding force and the measured holding force in time series as test results, and is a case where the length L1 is 0.072 m when the target pressure is 200 kPa. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments for realizing the technology of the present disclosure will be described in detail with reference to the drawings.

[0026] In addition, in all the drawings, the same reference numerals are given to components and processes having the same role and function, and repeated descriptions may be appropriately omitted. In addition, the present disclosure is not limited to the following embodiments, and can be implemented by appropriately adding changes within the scope of the purpose of the present disclosure.

[0027] <Structure of Fluid Pressure Actuator>

[0028] exist Figure 1 2 shows a fluid pressure actuator 20 that is a measurement target of the actuator gripping force estimation device 10 of the present disclosure. The fluid pressure actuator 20 includes an actuator body 22 and sealing members 30A and 30B.

[0029] Also like Figure 2 As shown, the actuator body 22 has a tube 24, a sleeve 26 and a restraining member 28. The tube 24 is a cylindrical shape that can be expanded and contracted by elastic deformation, and expands and contracts according to the pressure change of the internal fluid. The axial direction of the tube 24 is set to "axial S". The tube 24 can be made of elastic materials such as butyl rubber. As the fluid supplied to the tube 24, air can be used. In this case, the fluid pressure actuator 20 becomes an air actuator. In addition, when the fluid pressure actuator 20 is set to hydraulic drive, it is preferably set to at least one selected from the group consisting of NBR (nitrile rubber) with higher oil resistance, hydrogenated NBR, chloroprene rubber and epichlorohydrin rubber.

[0030] The sleeve 26 is formed into a cylindrical shape covering the outer circumference of the tube 24. The sleeve 26 is a stretchable structure formed by weaving fiber cords oriented in a predetermined direction, and the oriented cords intersect the axial direction S at a predetermined angle θ. By having such a shape, the sleeve 26 deforms like a change in the expansion and contraction of the tube 24, and follows the contraction and expansion while restricting the contraction and expansion.

[0031] Aromatic polyamide (aramid fiber) or polyethylene terephthalate (PET) fiber cords are preferably used as the cords constituting the sleeve 26. However, the fiber cords are not limited to such types, and other high-strength fiber cords such as PBO fiber (polyparaphenylene benzobisoxazole) may be used.

[0032] The restraining member 28 is provided between the tube 24 and the sleeve 26. The restraining member 28 is provided in a long plate shape, and its longitudinal direction is arranged along the axial direction of the tube 24, covers part of the outer circumference of the tube 24, and is arranged from one end of the tube 24 to the other end.

[0033] The restraining member 28 is formed of a material that does not expand or contract due to pressure, and can bend and deform in the direction in which the ends are close to each other. As the restraining member 28, a so-called leaf spring can be used. The size of the leaf spring is determined according to the size of the fluid pressure actuator 20, the required holding force, etc. In addition, the material of the leaf spring is not particularly limited, but typically, it can be a material such as stainless steel or other metal that is easy to bend and deform and has a strong compression resistance. In addition, it can also be formed by a thin plate of carbon fiber reinforced plastic (CFRP) or the like.

[0034] The sealing member 30A includes a sealing connector 32 , a locking ring 34 , and a caulking member 36 .

[0035] The sealing connector 32 has an integrally formed cover portion 32A and an insertion portion 32B. The cover portion 32A is formed into a hexagonal prism having a diameter larger than the outer diameter of the tube 24, and the insertion portion 32B is formed extending from the center of one end side of the cover portion 32A along the axial direction S. The insertion portion 32B is set in a so-called bamboo shoot shape and inserted into one end side of the tube 24 on the inner side of the sleeve 26. A mounting portion 33 is formed on the side of the cover portion 32A opposite to the insertion portion 32B. A mounting hole 33A is formed in the mounting portion 33 that passes through in a direction orthogonal to the axial direction S. As the sealing member 30A, metals such as stainless steel can be suitably used, but are not limited to such metals, and hard plastic materials can also be used.

[0036] like Figure 3 As shown, the sealed connector 32 has a flow path R. The flow path R is formed in the radial center of the insertion portion 32B and extends in the axial direction, and is connected to the connection hole H on the side of the cover portion 32A. An air supply hose 50 is connected to the connection hole H, and compressed air is supplied. The air supply hose 50 is provided with a servo valve 54 that controls the supply air pressure to a desired value.

[0037] The locking ring 34 is annular and is disposed outside the sleeve 26 so as to sandwich the sleeve 26 between the locking ring 34 and the insertion portion 32B, locking the sleeve 26 to the sealed connector 32. The sleeve 26 is folded back toward the outer periphery via the locking ring 34. The locking ring 34 can be made of metal, hard plastic, fiber, rubber, or other materials.

[0038] The caulking member 36 is arranged on the outer periphery of the actuator body 22 so as to cover the portion into which the insertion portion 32B is inserted, and caulks the actuator body 22 to the sealed connector 32. Thus, the actuator body 22 is fixed to the sealed connector 32. As the caulking member 36, a metal such as aluminum alloy, brass, and iron can be used.

[0039] The sealing member 30B has the same sealing connector 32, locking ring 34 and caulking member 36 as the sealing member 30A. However, the sealing connector 32 does not have a connection hole H and a flow path R, and its tip is R-shaped.

[0040] <Operation of Fluid Pressure Actuator>

[0041] like Figure 4 As shown, the fluid pressure actuator 20 is used in a manner in which the sealing member 30A at one end side is fixed and the sealing member 30B at the other end side is a free end.

[0042] When compressed air flows into the connection hole H via the air supply hose 50, the pressure in the fluid pressure actuator 20 increases. As the internal pressure increases, the tube 24 elastically deforms and expands, and the sleeve 26 deforms in such a way that the angle θ becomes larger, and a force is applied in the direction of shortening the length L0 (the length when not shortened) of the actuator body 22. At this time, since the outer peripheral side wall of the actuator body 22 on which the restraining member 28 is arranged is restricted from shortening, the outer peripheral wall of the actuator body 22 on the side where the restraining member 28 is not arranged when viewed from the axial direction S (hereinafter referred to as the "bent inner wall 22A") is shortened. As a result, the restraining member 28 is flexed and deformed, as shown in FIG. Figure 5 As shown in FIG. 1 , the entire actuator body 22 is curved. The length from one end to the other end where the amount of shortening of the curved inner wall 22A is the largest is defined as L1.

[0043] As described above, the force acting on the sealing member 30B in the direction perpendicular to the axial direction S (hereinafter referred to as “axis-perpendicular direction X”) when the actuator body 22 is bent is referred to as the holding force F.

[0044] <Actuator holding force estimation device>

[0045] like Figure 4 As shown, the actuator gripping force estimation device 10 includes a base 12 , a wire winding unit 14 , a measuring unit 15 , a wire member 16 , a wire holding member 18 , a pressure sensor 52 , and a controller 40 .

[0046] The base 12 is a portion to which one end of the fluid pressure actuator 20 is fixed, and a sealing member 30A of the fluid pressure actuator 20 is fixed to its lower surface via a mounting portion 33. An air supply hose 50 is connected to a connection hole H of the sealing member 30A.

[0047] The pressure sensor 52 detects the pressure of the portion of the air supply hose 50 downstream of the servo valve 54, and outputs the detected pressure to the AD board 42 described later of the controller 40. The pressure sensor 52 detects the internal pressure of the actuator body 22.

[0048] The wire winding section 14 is provided on the support section 12C and is rotatable about the winding axis M. The wire winding section 14 acts a force to wind up the other end side of the wire member 16 so that the wire member 16 cannot be loosened. This force is set to be smaller than the restoring force of restoring from the bent state to the straight state by returning the pressure in the fluid pressure actuator 20 to the atmospheric pressure.

[0049] The other end of the wire member 16 is fixed to the position (the curved inner wall 22A side) on the outer periphery of the sealing member 30B opposite to the restraining member 28 by a fixing member 31C. One end of the wire member 16 is mounted on the wire winding portion 14. The wire member 16 is formed of a long wire material that can be wound, and a metallic cord, fiber, or other wire can be used. The wire member 16 is inserted into the wire holding member 18 from the other end to just before being wound on the wire winding portion 14.

[0050] The wire holding member 18 is configured to be tubular (tube-shaped) and is arranged at a position (on the side of the curved inner wall 22A) opposite to the restraining member 28 on the outer periphery of the sealing member 30B. The wire holding member 18 is configured to cover the length from one end to the other end of the actuator main body 22 in a non-compressed state (longer than the actuator main body 22). The wire holding member 18 is configured in a manner along the axial S direction. As the wire holding member 18, a flexible tube can be used. A locking portion 31A is formed at a position corresponding to the curved inner wall 22A side in the circumferential direction in the sealing member 30A. The locking portion 31A has a hole 31B that is open in the axial direction S and through which the wire holding member 18 can pass, and the wire member 16 passes through the hole 31B. The locking portion 31 is used to limit the movement of the wire holding member 18 relative to the sealing member 30A in the circumferential and radial directions. In addition, relative movement of the wire holding member 18 and the sealing member 30A is allowed in the axial direction S. Thus, the wire holding member 18 is arranged along the curved inner wall 22A of the actuator body 22 from one end to the other end, and follows the movement of the actuator body 22 .

[0051] The measuring unit 15 is formed of a rotary encoder that detects a signal according to the rotation of the wire winding unit 14 around the winding axis M, and sends the detection signal to a counter board 44 described later of the controller 40. The counter board 44 counts the signal sent from the measuring unit 15 to obtain the winding length LR of the wire member 16.

[0052] Here, the action of the fluid pressure actuator 20 and the length L1 of the curved inner wall 22A are explained. The length L1 of the curved inner wall 22A is the length L0 when the fluid pressure actuator 20 is in a non-bent state, and is shortened when the pressure in the fluid pressure actuator 20 rises. Due to this shortening, the wire member 16 arranged along the curved inner wall 22A is wound up by the wire winding portion 14 and cannot be relaxed. The other end side of the wire member 16 is fixed to the curved inner wall 22A side of the top end (sealing member 30B) of the fluid pressure actuator 20, and one end side of the wire member 16 is mounted on the wire winding portion 14. Therefore, the protruding length of the wire member 16 from the wire winding portion 14 can be measured based on the winding rotation of the wire member 16 by the wire winding portion 14.

[0053] Since the wire member 16 passes through the wire holding member 18 and is arranged along the curved inner wall 22A of the actuator body 22, the change amount of the wire member 16, that is, the winding length LR, is substantially the same as the shortened length of the actuator body 22. Therefore, the length L1 of the curved inner wall 22A is the length obtained by subtracting the winding length LR of the wire member 16 from the length L0 when the actuator body 22 is in the non-bent state. By subtracting the length LR from the length L0, the length L1 of the curved inner wall 22A can be calculated.

[0054] The controller 40 includes a CPU, a ROM, a RAM, a storage unit, etc. (not shown) and has a computer function. The controller 40 is also provided with a counter board 44 , an AD board 42 , and a DA board 46 .

[0055] The counter board 44 is connected to the measuring unit 15, and receives a signal from the measuring unit 15. The counter board 44 counts the input signal to obtain the winding length LR of the wire member 16, and transmits information on the length LR to the storage unit.

[0056] The AD board 42 is connected to the pressure sensor 52, and the pressure signal detected by the pressure sensor 52 is input. The AD board 42 digitally converts the input pressure signal into pressure data and sends it to the storage unit. The pressure data is used for calculating the holding force F described later. In addition, the pressure data can also be fed back to the servo valve 54 via the DA board 46 to adjust the opening of the servo valve 54.

[0057] The storage unit of the controller 40 stores various data such as the length L0 , a gripping force estimation model described later, the input length LR, and pressure data.

[0058] <Holding force estimation model>

[0059] The holding force estimation model is a model for estimating the holding force F of the fluid pressure actuator 20. The length from one end to the other end of the side surface of the main body of the actuator main body 22 where the contraction is the largest, that is, the length of the curved inner side wall 22A is set to L1 (m), the internal pressure of the actuator main body 22 is set to P (Pa), the holding force is set to F (N), the parameters set based on the basic characteristics of the fluid pressure actuator 20 are set to ω1 (m) and ω2 (N), and the constant based on the geometric characteristics of the fluid pressure actuator 20 associated with the length L0 (m) is set to L min (m), and the gripping force F (N) is calculated using the following formula (1).

[0060] F=ω1P(L1-L min )+ω2 (1)

[0061] The parameters ω1 and ω2 are determined based on the measured values ​​obtained by measuring the basic characteristics of the fluid pressure actuator 20. For example, the pressure of the fluid pressure actuator 20 is controlled, and the length L1 and the gripping force F are measured at a plurality of different pressures. Figure 4 The gripping force sensor 60 shown in the figure is used to measure the gripping force F. The gripping force sensor 60 is provided with a force receiving portion 62 and a movable leg portion 64, and the actual gripping force F is measured by pressing the force receiving portion 62 with the top end of the fluid pressure actuator 20. Then, by converting P(LL min ) is used as the explanatory variable to determine ω1 and ω2 by the least squares method.

[0062] In the controller 40, the length L1 is obtained by subtracting the input length LR from the pre-stored length L0, and the length L1 and the input pressure data P are substituted into the formula (1) to calculate the gripping force F. The calculated gripping force F is outputted according to the requirement. The output may be displayed on the display unit or may be an output for feedback for subsequent processing.

[0063] In the actuator holding force estimation device 10 of the present embodiment, the wire member 16 is arranged to follow the bending deformation of the curved inner wall 22A of the actuator body 22 of the fluid pressure actuator 20 by using the wire holding member 18. Therefore, by measuring the change amount of the wire member 16, that is, the length LR, the length of the curved inner side of the fluid pressure actuator 20 can be easily measured even in the bent state.

[0064] Furthermore, the gripping force F can be easily estimated using the equation (1) having only two variables, the length L1 and the pressure data P.

[0065] In the present embodiment, the length L1 is obtained from the amount of change in the wire member 16 , but the length L1 may be obtained by other methods. For example, a sensor that can measure the bending length may be used.

[0066] <Evaluation experiment of the gripping force estimation model>

[0067] The holding force inference model is evaluated by measuring test data. Compressed air is supplied to the fluid pressure actuator 20 with a sine wave having an amplitude of 200 kPa and an average of 200 kPa as the internal pressure target, and the pressure data P, length L1, and actual holding force FR are measured. The pressure data P and length L1 of the test data obtained in this evaluation experiment are input into the holding force inference model to calculate the holding force F, and compared with the holding force FR actually obtained by measurement. In this evaluation test, the top end of the fluid pressure actuator 20 is in contact with the force-bearing part 62 when the internal pressure is 200 kPa, and measurements are taken for two conditions where the length L1 is 0.074 m and 0.072 m.

[0068] The relationship between the length L1 of the fluid pressure actuator 20 and the bending angle is:

[0069] L1=-3.2×10-4θ+0.085 (6)

[0070] The bending angle θ corresponding to L=0.074m is about 34 degrees, and when L=0.072m is about 40 degrees.

[0071] FIG6 shows the results of the estimated holding force FG and the measured holding force F. In the graph, the dotted line is the measured value (holding force FR), and the solid line is the holding force F obtained by the formula of the holding force estimation model. The external force on the top of the fluid pressure actuator 20 is always assumed to be in the direction of the reaction force. In this test, when the estimated holding force F is less than 0N (zero Newton), the threshold processing is performed to make the holding force F 0N (zero Newton). Compared with the peak value of the measured holding force FR of about 15N, the error of the estimated holding force FG is about 1N at most, and the estimation accuracy near the peak value is particularly improved.

[0072] The disclosure of Japanese Patent Application No. 2022-140033 filed on September 2, 2022 is incorporated herein by reference in its entirety.

[0073] All documents, invention patent applications, and technical specifications described in this specification are incorporated into this specification by reference to the same extent as if each document, invention patent application, and technical specification were specifically and separately described.

Claims

1. An actuator holding force estimation device, which estimates the force of a fluid pressure actuator that acts in a direction perpendicular to the cylinder axis when it is not bent as a holding force, wherein the fluid pressure actuator has a cylindrical main body portion whose side of the cylinder wall is shortened and bent in the cylinder axis direction due to the increase in internal pressure in the cylinder, and the base end side of the cylinder axis of the fluid pressure actuator is fixed to a base, and the top end moves relative to the base, wherein The actuator holding force estimation device comprises: A pressure sensor for acquiring the internal pressure of the main body; a length obtaining unit for obtaining the length from one end to the other end of the side of the main body having the largest shortening amount; as well as The holding force estimation unit sets the length obtained by the length acquisition unit to L, the internal pressure in the cylinder obtained by the pressure sensor to P, the holding force to F, the parameters set based on the basic characteristics of the fluid pressure actuator to ω1 and ω2, and the constant based on the geometric characteristics of the fluid pressure actuator to L. min When F=ω1P(LL min )+ω2 to infer the holding force.

2. The actuator holding force estimation device according to claim 1, wherein: The length acquisition part includes: a wire member, one end of which is installed on the base, and the middle part is arranged on the curved side of the main body in a manner following the bending deformation; a wire holding member, which holds the wire member at a position along the main body; and a measuring part, which applies tension to the wire member and measures the length change of the wire member.

3. A method for inferring the holding force of an actuator, wherein the force of a fluid pressure actuator acting in a direction perpendicular to the cylinder axis when not bent due to bending is inferred as the holding force, wherein the fluid pressure actuator has a cylindrical main body portion whose one side of the cylinder circumference is shortened and bent in the cylinder axis direction due to the increase in internal pressure in the cylinder, and the base end side of the cylinder axis of the fluid pressure actuator is fixed to a base, and the top end moves relative to the base, wherein The length from one end to the other end of the side of the main body with the largest contraction is set to L, the internal pressure in the cylinder is set to P, the holding force is set to F, the parameters set based on the basic characteristics of the fluid pressure actuator are set to ω1 and ω2, and the constant based on the geometric characteristics of the fluid pressure actuator is set to L min When F=ω1P(LL min )+ω2 to infer the holding force.

4. The actuator holding force estimation method according to claim 3, wherein: The wire member is held at a position along the main body, one end of which is attached to the base and the middle portion of which is arranged along one side of the curve of the main body and the direction of the cylinder axis. A tension is applied to the wire member, and a change in length of the wire member is measured to obtain a length from one end to the other end of the side surface of the main body portion where the contraction is greatest.

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