Actuator

Abstract

To provide an actuator exhibiting high output, high accuracy, and low contact rigidity.SOLUTION: An actuator 100 includes a movable element 122, an electromagnetic torque generating unit 106 which has n (n≥3) permanent magnets 116 and coils 114 and can rotate the movable element 122 with multiple degrees of freedom by imparting electromagnetic torque to the movable element 122, and a fluid pressure torque generating unit 108 which has n fluid pressure cylinders 124 and can rotate the movable element 122 with multiple degrees of freedom by imparting fluid pressure torque to the movable element 122.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to actuators. [Background technology]

[0002] Conventionally, devices such as robots and machine tools use multi-degree-of-freedom drive mechanisms using servo motors. Although the inclusion of a reducer allows for high torque and high-precision driving, the high contact stiffness makes it difficult to ensure safety in the event of unexpected contact with a person. In response to this, Non-Patent Document 1 proposes a structure that generates two degrees of freedom rotational motion by arranging three pneumatic (bellows) actuators at 120° intervals. With this structure, the contact stiffness is relatively low, making it possible to ensure safety in the event of unexpected contact with a person. In addition, because it relies on air pressure, high output can be achieved. [Prior art documents] [Patent documents]

[0003] [Non-Patent Document 1] M. Hofer et al., Design, fabrication, modeling and control of a fabric-based spherical robotic arm,Mechatronics, vol. 68, 102369, 2020 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the structure described in Non-Patent Document 1, it is difficult to compensate for the response delay and friction characteristics caused by the compressibility of air, and high accuracy cannot be achieved.Also, high accuracy cannot be achieved because the center of rotation of the mover is significantly shifted.

[0005] The present disclosure has been made in view of the above problems, and an exemplary objective of an embodiment thereof is to provide an actuator having high output, high precision, and low contact stiffness. [Means for solving the problem]

[0006] In order to solve the above problems, an actuator of one embodiment of the present invention comprises a mover, an electromagnetic torque generating unit including n (n≧3) permanent magnets and coils and capable of applying electromagnetic torque to the mover to rotate the mover with multiple degrees of freedom, and a fluid pressure torque generating unit including n fluid pressure cylinders and capable of applying fluid pressure torque to the mover to rotate the mover with multiple degrees of freedom.

[0007] Another aspect of the present invention is an actuator. The actuator includes a mover and a fluid pressure torque generating unit including n (n≧3) fluid pressure cylinders and capable of applying fluid pressure torque to the mover to rotate the mover with multiple degrees of freedom. The fluid pressure cylinders include a cylinder tube, a piston disposed within the cylinder tube, and two expansion and contraction members disposed within the cylinder tube to sandwich the piston and expand and contract in response to the pressure of a fluid supplied therein. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide an actuator that has high output, high accuracy, and low contact stiffness. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of an actuator according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of the electromagnetic torque generating portion of FIG. [Diagram 3] FIG. 2 is a perspective view of the fluid pressure torque generating section of FIG. 1. [Figure 4] FIG. 2 is a perspective view of the fluid pressure torque generating section of FIG. 1. [Diagram 5] 5(a) to (c) are diagrams for explaining the operating principle of the electromagnetic torque generating portion of FIG. [Figure 6] FIG. 4 is a vertical sectional view of the fluid pressure cylinder of FIG. 3. [Figure 7]7(a) to (c) explain the operating principle of the fluid pressure torque generating portion of FIG. [Figure 8] 8(a) and (b) are diagrams illustrating the electromagnetic torque characteristics of the electromagnetic torque generating portion of FIG. [Figure 9] 9(a) and (b) are diagrams for explaining the fluid pressure torque characteristics by the fluid pressure torque generating portion of FIG. [Figure 10] 10(a) and 10(b) are diagrams illustrating the combined torque characteristics of the electromagnetic torque and the fluid pressure torque. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 1 to 4. Actuator 100 according to the embodiment is an actuator that combines, in parallel, an electromagnetic actuator capable of generating rotation with multiple degrees of freedom and a fluid pressure actuator capable of generating rotation with multiple degrees of freedom. Actuator 100 can be used in various devices including robots and machine tools.

[0011] The actuator 100 includes a mover 122, an electromagnetic torque generating unit 106 that generates torque due to electromagnetic force (hereinafter also referred to as "electromagnetic torque") in the mover 122, a fluid pressure torque generating unit 108 that generates torque due to fluid pressure (hereinafter also referred to as "fluid pressure torque") in the mover 122, and a rod 150.

[0012] In the following, the upper side in FIG. 1 will be described as "top" and the lower side as "bottom", or in other words, the side on which rod 150 is provided relative to movable element 122 will be described as "top" and the opposite side as "bottom", but these directional notations do not limit the usage position of actuator 100, and actuator 100 can be used in any position.

[0013] The mover 122 is a spherical member. The mover 122 is supported by a gimbal mechanism (not shown) so as to be rotatable around the center of the sphere. The mover 122 may be supported by a spherical bearing. In either case, the center of rotation of the mover 120 is constrained. A rod 150 is fixed to the mover 122 for outputting the rotational motion to the outside. An extension line of the rod 150 passes through the center of the spherical mover 122.

[0014] Next, the basic configuration of the electromagnetic torque generating portion 106 will be described with reference to FIGS.

[0015] The electromagnetic torque generating unit 106 includes three coils 114, three permanent magnets 116, and three yokes 118. That is, the electromagnetic torque generating unit 106 includes the same numbers of coils 114, permanent magnets 116, and yokes 118.

[0016] The three coils 114 are, for example, air-core coils. The three coils 114 are formed in a curved disk shape. For example, the outer periphery of the three coils 114 is fixed to a fixing member (not shown).

[0017] The three permanent magnets 116 are formed in the shape of elongated plates curved in an arc. The three yokes 118 are made of a magnetic material, preferably a soft magnetic material, and may be, for example, soft magnetic iron. The three yokes 118 are formed in the shape of elongated plates curved in an arc. Each of the three yokes 118 is fixed to the radial inside of the corresponding permanent magnet 116, for example, by adhesion.

[0018] In this embodiment, the three coils 114 and the three permanent magnets 116 are arranged at equal intervals in the circumferential direction, i.e., at intervals of 120°. However, they may also be arranged at non-equidistant intervals in the circumferential direction. Each of the three coils 114 is arranged so as to face the corresponding permanent magnet 116 in the radial direction. The three permanent magnets 116 are magnetized in parallel, and the magnetization directions of adjacent permanent magnets 116 are reversed.

[0019] The three permanent magnets 116 and the three yokes 118 are entirely housed in a recess 122a formed on the outer periphery of the mover 122, and are fixed to the mover 122 therein. The recess 122a has a shape corresponding to (i.e., a complementary shape with) the permanent magnets 116 and the yoke 118. Since the three permanent magnets 116 and the three yokes 118 are fixed to the mover 122, they can also be considered as a part of the mover 122.

[0020] Next, the operating principle of the electromagnetic torque generating unit 106 will be described with reference to FIG.

[0021] For ease of explanation, an XYZ Cartesian coordinate system is considered below, with the center of rotation of the mover 120 (not shown in FIG. 5) as the origin. The X-axis is an axis parallel to the direction in which the coils 114_2 and 114_3 face each other. The Y-axis is an axis perpendicular to the X-axis and passes through the center of the coil 114_1. The Z-axis is an axis perpendicular to the X-axis and the Y-axis.

[0022] Since the coil 114 is fixed, when electricity is applied to the coil 114, torque due to magnetic attraction force and Lorentz force is applied to the mover 122 via the permanent magnet 116 and the yoke 118, as shown in Fig. 5(a). In this embodiment, since three coils 114 are arranged at intervals of 120°, the mover 122 can be rotated with two degrees of freedom by combining the torques generated by applying electricity to them.

[0023] 5(b), a current in a certain direction is passed through the first coil 114_1, and a current of the same magnitude and in the opposite direction to that of the first coil 114_ is passed through the second coil 114_2 and the third coil 114_3. This causes the permanent magnet 116 and the yoke 118, and thus the mover 122, to rotate around the X-axis. When the direction of the current passed through the three coils 114 is reversed, the mover 122 rotates in the opposite direction around the X-axis.

[0024] 5(c), no current flows through the first coil 114_1, and currents of the same magnitude but opposite directions flow through the second coil 114_2 and the third coil 114_3. This causes the permanent magnet 116 and the yoke 118, and thus the mover 122, to rotate around the Y axis. When the direction of the current flowing through the second coil 114_2 and the third coil 114_3 is reversed, the mover 122 rotates in the opposite direction around the Y axis.

[0025] Alternatively, the actuator 100 may include three H-bridge circuits provided corresponding to the three coils 114, and the magnitude and direction of the current flowing through the corresponding coils 114 may be adjusted by the three H-bridge circuits.

[0026] Next, the structure of the fluid pressure torque generating portion 108 will be described with reference to FIGS.

[0027] The fluid pressure torque generating unit 108 includes three fluid pressure cylinders 124. In the following, it is assumed that the working fluid of the fluid pressure cylinders 124 is air. In other words, it is assumed that the fluid pressure cylinders 124 are pneumatic cylinders. However, the technical ideas of the embodiments can also be applied to gas pressure cylinders in which the working fluid is a gas other than air, and liquid pressure cylinders in which the working fluid is a liquid, as long as there is no contradiction.

[0028] In this embodiment, the three fluid pressure cylinders 124 are disposed at equal intervals in the circumferential direction, i.e., at intervals of 120°. The three fluid pressure cylinders 124 are particularly disposed between the three coils 114. That is, the three fluid pressure cylinders 124 and the three coils 114 are disposed at equal intervals in the circumferential direction, for example, at intervals of 60°, in the following order: fluid pressure cylinder 124, coil 114, fluid pressure cylinder 124, coil 114, fluid pressure cylinder 124, coil 114. The three fluid pressure cylinders 124 are fixed to a fixing member (not shown).

[0029] Each of the three hydraulic cylinders 124 includes a cylinder tube 126, a piston 128, a shaft 129, a slider 131, and two telescopic members 130.

[0030] The cylinder tube 126 includes a cylindrical portion 132 extending in an arc shape, and fluid supply portions 134 provided at both ends of the cylindrical portion 132. The cross section perpendicular to the longitudinal direction of the cylindrical portion 132 has a circular shape. The piston 128 is a disk-shaped member. The piston 128 is housed in the cylindrical portion 132 such that two main surfaces 128a, 128b generally face the ends of the cylindrical portion 132.

[0031] The piston 128 is connected to the slider 131 via a shaft 129. The shaft 129 is passively rotatable relative to the slider 131. The slider 131 is movable on a rail 122b formed on the outer periphery of the mover 122 in the extension direction of the rail 122b. The rail 122b is formed in an annular shape at a portion of the mover 122 that corresponds to the equator. The equator refers to a great circle formed by the intersection of a plane perpendicular to the rod 150 and the outer periphery of the mover 120. On the other hand, the movement of the slider 131 is restricted in a direction perpendicular to the extension direction of the rail 122b. Therefore, when the slider 131 moves up and down in accordance with the up and down movement of the piston 128, the mover 122 rotates.

[0032] The two telescopic members 130 are housed in the cylinder tube 126 so as to sandwich the piston 128. The telescopic members 130 are bellows-shaped cylindrical members. The material of the telescopic members 130 is not particularly limited. The telescopic members 130 may be made of a metal material such as stainless steel or aluminum. A fluid (e.g., air) is supplied to the telescopic members 130 from a pressure controller (not shown) via a fluid supply unit 134. Alternatively, the fluid is sucked by the pressure controller via the fluid supply unit 134. This changes the pressure of the fluid in the telescopic members 130, and the telescopic members 130 expand and contract in response to the pressure. In other words, the telescopic members 130 expand and contract in response to the pressure of the fluid supplied inside.

[0033] Next, the operating principle of the fluid pressure torque generating unit 108 will be described with reference to FIG.

[0034] In the fluid pressure cylinder 124, when the pressure in the upper telescopic member 130a is made higher than the pressure in the lower telescopic member 130b, the upper telescopic member 130a extends (expands) and the lower telescopic member 130b contracts in the cylindrical portion 132, as shown in FIG. 7(a), causing the piston 128 and the movable member 122 to rotate counterclockwise in the figure. When the pressure in the lower telescopic member 130b is made higher than the pressure in the upper telescopic member 130a, the lower telescopic member 130b extends (expands) and the upper telescopic member 130a contracts in the cylindrical portion 132, causing the piston 128 and the movable member 122 to rotate clockwise in the figure. By using the telescopic member 130, leakage of fluid can be suppressed.

[0035] For example, the inside of the lower telescopic member 130b of the first fluid pressure cylinder 124_1 is pressurized to a pressure higher than atmospheric pressure, and the inside of the upper telescopic member 130a is set to atmospheric pressure, while the insides of the upper telescopic members 130a of the second fluid pressure cylinder 124_2 and the third fluid pressure cylinder 124_3 are pressurized to the same pressure but higher than atmospheric pressure, and the inside of the lower telescopic member 130b is set to atmospheric pressure. As a result, as shown in Fig. 7(b), an upward torque is generated in the piston 128 of the first fluid pressure cylinder 124_1, and a downward torque is generated in the pistons 128 of the second fluid pressure cylinder 124_2 and the third fluid pressure cylinder 124_3, and as a result, the mover 122 rotates around the X-axis.

[0036] Conversely, when the interior of the upper expandable member 130a of the first fluid pressure cylinder 124_1 is pressurized to a pressure higher than atmospheric pressure and the interior of the lower expandable member 130b is set to atmospheric pressure, and the interiors of the lower expandable members 130b of the second fluid pressure cylinder 124_2 and the third fluid pressure cylinder 124_3 are pressurized to the same pressure but higher than atmospheric pressure and the interior of the upper expandable member 130a is set to atmospheric pressure, the movable element 122 rotates in the opposite direction around the X-axis.

[0037] Also, for example, the first fluid pressure cylinder 124_1 sets both of the insides of the two telescopic members 130 to atmospheric pressure, the second fluid pressure cylinder 124_2 pressurizes the lower telescopic member 130b to a pressure higher than atmospheric pressure, sets the upper telescopic member 130a to atmospheric pressure, and the third fluid pressure cylinder 124_3 pressurizes the upper telescopic member 130a to a pressure higher than atmospheric pressure, sets the lower telescopic member 130b to atmospheric pressure. As a result, as shown in Fig. 7(c), an upward torque is generated in the piston 128 of the second fluid pressure cylinder 124_2, and a downward torque is generated in the piston 128 of the third fluid pressure cylinder 124_3, and as a result, the mover 122 rotates around the X-axis.

[0038] Conversely, (within both of the two expandable members 130 of the first fluid pressure cylinder 124_1 being at atmospheric pressure), when the upper expandable member 130a of the second fluid pressure cylinder 124_2 is pressurized to a pressure higher than atmospheric pressure and the lower expandable member 130b is at atmospheric pressure, and when the lower expandable member 130b of the third fluid pressure cylinder 124_3 is pressurized to a pressure higher than atmospheric pressure and the upper expandable member 130b is at atmospheric pressure, the movable element 122 rotates in the opposite direction around the Y axis.

[0039] As described above, when the mover 122 rotates, the sliders 131 of the three fluid pressure cylinders 124 move on the rails 122b of the mover 122 relative to the mover 122. Conversely, the sliders 131 run on the rails 122b, allowing the mover 122 to rotate. Since the shaft 129 is passively rotatable with respect to the slider 131, even if the slider 131 moves relative to the mover 122, the piston 128 can maintain a position in which the main surfaces 128a, 128b generally face the end of the cylindrical portion 132.

[0040] The electromagnetic torque by the electromagnetic torque generating unit 106 and the fluid pressure torque by the fluid pressure torque generating unit 108 described above can be generated independently. Therefore, by adjusting the current flowing through the three coils 114 of the electromagnetic torque generating unit 106 and the voltage supplied to the expansion and contraction members 130 of the three fluid pressure cylinders of the fluid pressure torque generating unit 108, a composite torque of the electromagnetic torque by the electromagnetic torque generating unit 106 and the fluid pressure torque by the fluid pressure torque generating unit 108 can be applied to the mover 122.

[0041] The electromagnetic torque characteristics of the electromagnetic torque generating unit 106 will be described with reference to FIG. 8. The inventors have determined the electromagnetic torque of the electromagnetic torque generating unit 106 by magnetic field analysis using a three-dimensional finite element method. The mesh model used in the analysis had 2,098,569 elements and 362,443 nodes. In this analysis, the torque was determined when the mover 122 was rotated around the X-axis from -25 degrees to 25 degrees in 5 degree increments. The torque was calculated similarly around the Y-axis. Note that when the maximum current density was 20 A / mm 2 As shown below, the maximum current was 2.51A, and N42SH was used as the material of the permanent magnet 116. SUY-1 was used as the material of the yoke 118. The number of turns of the coil 114 was 800. The outer diameter of the mover 122 was Φ80 mm, and the thickness and width of the permanent magnet 116 were 6.5 mm and 11 mm, respectively. In Figs. 8(a) and (b), the horizontal axis represents the rotation angle of the mover 122, and the vertical axis represents the torque. As shown in Fig. 8(a), the torque around the X-axis was approximately 1 Nm at maximum and approximately 0.76 Nm on average. As shown in Fig. 8(b), the torque around the Y-axis was approximately 0.85 Nm at maximum and approximately 0.61 Nm on average. Since the current patterns of the coil 114 were different, the maximum torques around the X-axis and the Y-axis were different. In any case, it can be seen from FIGS. 8(a) and 8(b) that by adjusting the magnitude of the current flowing through the three coils 114, it is possible to generate a constant torque in various directions.

[0042] With reference to FIG. 9, the fluid pressure torque characteristics of the fluid pressure torque generating unit 108 will be described. The inventors have calculated the fluid pressure torque characteristics around the X-axis and the Y-axis by numerical calculation. In detail, the fluid pressure torque when one of the two expandable members 130 of the fluid pressure cylinder 124 is pressurized to a pressure higher than atmospheric pressure and the other expandable member 130 is at atmospheric pressure was calculated from the product of the pressure receiving area of ​​the piston 128 and the pressure difference in the two expandable members 130. In FIG. 9(a) and (b), the horizontal axis is pressure and the vertical axis is torque. As shown in FIG. 9(a), the maximum fluid pressure torque around the X-axis was 5.9 Nm, and the maximum fluid pressure torque around the Y-axis was 5.1 Nm. The fluid pressure torque is constant regardless of the rotation angle, i.e., the attitude of the mover 122. It can be seen from FIG. 9(a) and (b) that it is possible to generate constant torque in various directions by adjusting the magnitude of the pressure of the three fluid pressure cylinders 124.

[0043] The torque characteristics of the composite of the electromagnetic torque and the fluid pressure torque will be described with reference to Fig. 10. The inventors calculated the composite torque by adding together the electromagnetic torque calculated by magnetic field analysis and the fluid pressure torque calculated by numerical calculation. In Figs. 10(a) and (b), the horizontal axis represents the rotation angle of the mover 122, and the vertical axis represents the torque. As shown in Fig. 10(a), the torque around the X-axis was maximum 6.9 Nm and average 6.7 Nm, and the torque around the Y-axis was maximum 6.0 Nm and average 5.8 Nm.

[0044] As described above, according to this embodiment, the actuator 100 applies electromagnetic torque and fluid pressure torque to the mover 120 to rotate the mover 120. Therefore, even in the event of unexpected contact, flexibility due to the compressibility of the fluid comes into play, and contact stiffness can be reduced by backdriving. Also, high output can be achieved by fluid pressure. Furthermore, the high responsiveness of the electromagnetic torque allows compensation control of friction characteristics and response delays caused by the compressibility of the fluid, contributing to high accuracy.

[0045] Furthermore, according to this embodiment, the center of rotation of the mover 122 is constrained by a gimbal mechanism or the like. This prevents the center of rotation of the mover 120 from shifting, thereby achieving more accurate movement of the mover 120.

[0046] The present disclosure has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each processing step, and that such modifications are also within the scope of the present disclosure.

[0047] (Variation 1) Unlike the embodiment, the arrangement of the coil 114 and the permanent magnet 116 may be reversed. That is, the coil 114 may be fixed to the mover 122, and the permanent magnet 116 may be fixed to a fixed member (not shown).

[0048] (Variation 2) Unlike the embodiment and the above-mentioned modified examples, the actuator 100 may have an electromagnetic torque generating unit 106 that includes n coils 114 (n≧4), n permanent magnets 116, and n yokes 118, and the fluid pressure torque generating unit 108 that includes n fluid pressure cylinders 124.

[0049] For example, the mover 120, the electromagnetic torque generating unit 106, and the fluid pressure torque generating unit 108 may be arranged with n-fold rotational symmetry, which makes it relatively easy to calculate the current to be passed through the coil 114 and the pressure to be supplied to the fluid pressure cylinder 124 in order to control the mover 120 to a desired attitude.

[0050] For example, n-1 coils 114, permanent magnets 116, yokes 118 and fluid pressure cylinders 124 may be arranged with n-1 rotational symmetry in the circumferential direction, and the remaining coil 114, permanent magnet 116, yoke 118 and fluid pressure cylinder 124 may be arranged at an angle to the circumferential direction, thereby realizing three degrees of freedom of rotation of the mover 122.

[0051] (Variation 3) Unlike the embodiment and the modified examples described above, actuator 100 may include only fluid pressure torque generating unit 108 as a torque generating unit that applies torque to mover 122 to rotate mover 122 with multiple degrees of freedom. In other words, actuator 100 does not need to include electromagnetic torque generating unit 106.

[0052] (Each embodiment of the present disclosure) An actuator according to an embodiment of the present disclosure includes a mover, an electromagnetic torque generating unit including n (n≧3) permanent magnets and coils and capable of applying electromagnetic torque to the mover to rotate the mover with multiple degrees of freedom, and a fluid pressure torque generating unit including n fluid pressure cylinders and capable of applying fluid pressure torque to the mover to rotate the mover with multiple degrees of freedom. In this case, an actuator with high output, high accuracy, and low contact stiffness can be realized.

[0053] In one embodiment, the mover is a spherical member with a constrained center of rotation. In this case, the center of rotation of the mover does not shift, so that more accurate movement of the mover can be achieved.

[0054] In one embodiment, the fluid pressure cylinder includes a cylinder tube, a piston disposed within the cylinder tube, and two expandable members disposed within the cylinder tube so as to sandwich the piston, the expandable and contractable members expanding and contracting in response to the pressure of fluid supplied therein.

[0055] In one embodiment, the mover, the electromagnetic torque generator, and the fluid pressure torque generator may be arranged with n-fold rotational symmetry, which makes it relatively easy to perform calculations for controlling the mover to a desired attitude.

[0056] An actuator of another embodiment of the present disclosure comprises a mover, and a fluid pressure torque generating unit that includes n (n≧3) fluid pressure cylinders and is capable of applying fluid pressure torque to the mover to rotate the mover with multiple degrees of freedom, wherein the fluid pressure cylinders include a cylinder tube, a piston disposed within the cylinder tube, and two expansion and contraction members that are disposed within the cylinder tube to sandwich the piston and expand and contract in response to the pressure of a fluid supplied therein. [Explanation of symbols]

[0057] 100 actuator, 106 electromagnetic torque generating unit, 108 fluid pressure torque generating unit, 114 coil, 116 permanent magnet, 122 mover, 124 fluid pressure cylinder, 126 cylinder tube, 128 piston, 130 expandable member.

Claims

1. A movable element, an electromagnetic torque generating unit including n (n≧3) permanent magnets and coils, and capable of applying an electromagnetic torque to the mover to rotate the mover with multiple degrees of freedom; a fluid pressure torque generating unit including n fluid pressure cylinders and capable of applying a fluid pressure torque to the mover to rotate the mover with multiple degrees of freedom; An actuator comprising:

2. 2. The actuator according to claim 1, wherein the movable element is a spherical member whose center of rotation is constrained.

3. The fluid pressure cylinder includes: A cylinder tube; a piston disposed within the cylinder tube; two expansion and contraction members that are disposed in the cylinder tube so as to sandwich the piston therebetween and expand and contract in response to the pressure of a fluid supplied thereto; The actuator of claim 1 , comprising:

4. 2. The actuator according to claim 1, wherein the mover, the electromagnetic torque generating portion, and the fluid pressure torque generating portion are arranged with n-fold rotational symmetry.

5. A movable element, a fluid pressure torque generating unit including n (n≧3) fluid pressure cylinders and capable of applying a fluid pressure torque to the mover to rotate the mover with multiple degrees of freedom; Equipped with The fluid pressure cylinder includes: A cylinder tube; a piston disposed within the cylinder tube; two expansion and contraction members that are disposed in the cylinder tube so as to sandwich the piston therebetween and expand and contract in response to the pressure of a fluid supplied thereto; An actuator including:

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