Torsional actuator

Abstract

The present invention comprises a torsion actuator comprising a housing, a tube provided inside the housing, a first torsion member having one end fixed to the upper end of the housing and having a cylindrical Kresling structure, a second torsion member having one end connected to the first torsion member and having a cylindrical Kresling structure, and a rotatable jig connected to the other end of the second torsion member and formed to be rotatable, wherein the first torsion member and the second torsion member are configured such that the lower end of the second torsion member is rotatable by causing length deformation due to a difference in air pressure, thereby allowing the gripper of a robot arm to efficiently drive the gripping and twisting motions to effectively grasp an object.

Description

Technology Field

[0001] The present invention relates to a torsion actuator capable of controlling rotational and gripping movements of a gripper of a robot arm by providing a plurality of torsion members formed in a Kresling structure and compressing or extending the torsion members. Background Technology

[0002] Generally, torsional motion could achieve a very limited angle of rotation, and rather than independent torsional motion, it was combined with bending and linear motion.

[0003] Even in grippers of robot arms that utilize such twisting motions, forms in which the gripper simultaneously implements grasping and twisting motions are very rare and are generally achieved by using a combination of other mechanisms or actuation approaches. Furthermore, the problem is that integrating these complex elements into a single design inevitably increases the complexity of manufacturing and control.

[0004] In addition, when a robot arm performs bending movements to grasp an object, the length of the robot arm may be deformed, which presents a problem in that the robot arm's gripper is difficult to use in locations where the space for the robot arm to move is limited. Prior art literature

[0005] Korean Registered Patent No. 10-2222633 (Pneumatic gripper and gripper system using an origami pump) The problem to be solved

[0006] The present invention aims to provide a torsion actuator comprising a first torsion member and a second torsion member formed in a criss-crossing structure, so that a gripper of a robot arm can easily perform grasping and twisting movements.

[0007] In addition, the present invention aims to provide a torsion actuator configured such that when a first torsion member is extended or compressed, a second torsion member is compressed or extended, so that an actuator driving a robot arm, etc., can be used without length deformation and without limitations on the space where it is installed.

[0008] In addition, the present invention aims to provide a torsion actuator in which the polygonal unit of the first torsion member and the polygonal unit of the second torsion member are configured to be compressed or extended in different directions so as to enable the gripper to perform a grasping action while rotating.

[0010] The purposes of the embodiments of the present invention are not limited to those mentioned above, and other unmentioned purposes will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0011] According to one embodiment of the present invention, a torsion actuator may be provided, comprising a housing, a tube provided inside the housing, a first torsion member having one end fixed to the upper end of the housing and having a cylindrical Kresling structure, a second torsion member having one end coupled to the first torsion member and having a cylindrical Kresling structure, and a rotatable jig coupled to the other end of the second torsion member and formed to be rotatable, wherein the first torsion member and the second torsion member are configured such that a length deformation occurs due to a difference in air pressure, thereby allowing the lower end of the second torsion member to rotate.

[0013] In addition, according to one embodiment of the present invention, a torsion actuator may be provided such that when a length deformation occurs in the first torsion member or the second torsion member, the first torsion member and the second torsion member are formed to be folded or unfolded in different directions.

[0015] In addition, according to one embodiment of the present invention, a torsion actuator may be provided such that when one of the first torsion member or the second torsion member is compressed and undergoes length deformation, the other is elongated and undergoes length deformation.

[0017] In addition, according to one embodiment of the present invention, the first torsion member and the second torsion member may be provided with a torsion actuator having an air hole through which air is introduced from the outside or air is discharged from the inside.

[0019] In addition, according to one embodiment of the present invention, a torsion actuator may be provided such that when a length deformation occurs in the first torsion member or the second torsion member, the sum of the length of the first torsion member and the length of the second torsion member is maintained constant.

[0021] In addition, according to one embodiment of the present invention, a torsion actuator may be provided, comprising a connecting member provided between the first torsion member and the second torsion member to guard the first torsion member and the second torsion member.

[0023] In addition, according to one embodiment of the present invention, the tube may be provided with a torsion actuator in which the first torsion member and the second torsion member are accommodated inside.

[0025] In addition, according to one embodiment of the present invention, a torsion actuator may be provided comprising a gripper coupled to the lower end of the housing and connected to the other side of the rotary jig to repeatedly grip by the rotation of the rotary jig. Effects of the invention

[0026] In the present invention, a first torsion member and a second torsion member formed in a crisscross structure are included in a torsion actuator, and the first torsion member and the second torsion member are combined and provided, so that a gripper of a robot arm coupled to a housing can efficiently perform a gripping motion and a twisting motion.

[0027] In addition, in the present invention, when the first torsion member is extended or compressed, the second torsion member is configured to be compressed or extended, so that an actuator driving a robot arm, etc., can be driven without length deformation and can be used without limitations on the space where it is installed.

[0028] In addition, in the present invention, the polygonal unit of the first torsion member and the polygonal unit of the second torsion member are configured to be compressed or extended in different directions, thereby enabling the gripper to efficiently perform the operation of gripping an object while rotating. Brief explanation of the drawing

[0029] FIG. 1 is a drawing illustrating a torsion actuator according to one embodiment of the present invention. FIG. 2 is a drawing illustrating a torsion member formed in a cresling structure of a torsion actuator according to one embodiment of the present invention. FIG. 3 is a drawing illustrating the length deformation of the first torsion member and the second torsion member of a torsion actuator according to one embodiment of the present invention, in terms of compression or elongation. FIG. 4 is a drawing illustrating a gripper of a torsion actuator according to one embodiment of the present invention. Specific details for implementing the invention

[0030] The advantages and features of the embodiments of the present invention, and the methods for achieving them, will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments described below but may be implemented in various different forms. These embodiments are provided merely to ensure that the invention is complete and to fully inform those skilled in the art of the scope of the invention, and the invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0031] In describing the embodiments of the present invention, specific descriptions of known functions or configurations will be omitted if it is determined that such detailed descriptions could unnecessarily obscure the essence of the invention. Furthermore, the terms described below are defined in consideration of their functions in the embodiments of the present invention, and these definitions may vary depending on the intentions or practices of the user or operator. Therefore, such definitions should be based on the content throughout this specification.

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0034] FIG. 1 is a drawing illustrating a torsion actuator according to an embodiment of the present invention, FIG. 2 is a drawing explaining a torsion member formed in a cresling structure of a torsion actuator according to an embodiment of the present invention, FIG. 3 is a drawing illustrating a length deformation of compression or elongation of a first torsion member and a second torsion member of a torsion actuator according to an embodiment of the present invention, and FIG. 4 is a drawing explaining a gripper of a torsion actuator according to an embodiment of the present invention.

[0036] Referring to FIGS. 1 to 4, a torsion actuator (100) according to one embodiment of the present invention may include a housing (111), a tube (112), a first torsion member (113), a second torsion member (114), a connecting member (115), a rotary jig (116), a gripper (121), etc.

[0037] The housing (111) is the main body of the torsion actuator (100), is provided in a tubular shape, and may have a receiving space formed inside. A tube (112) is fixed in the receiving space, and a first torsion member (113), a second torsion member (114), etc. are formed inside the tube (112), and a gripper (121) may be attached to the lower part.

[0039] A tube (112) is provided inside a housing (111), and a first twist member (113), a second twist member (114), etc., can be accommodated inside. Here, the tube (112) may be formed from a material such as acrylic. The first twist member (113) and the second twist member (114) each have air pressure formed as negative pressure, and can repeatedly compress or extend while rotating due to the difference in air pressure. Here, during the process of the first twist member (113) and the second twist member (114) compressing or extending in the longitudinal direction, the direction of compression or extension may be twisted in a horizontal direction relative to the longitudinal direction. If the direction of compression or extension of the first twist member (113) and the second twist member (114) is twisted in this way, it is difficult to accurately adjust the rotation angle of the first twist member (113) and the second twist member (114).

[0040] A tube (112) according to one embodiment of the present invention may be formed such that its diameter corresponds to the diameters of the first twist member (113) and the second twist member (114). Accordingly, when the first twist member (113) and the second twist member (114) are inserted into the interior of the tube (112) and rotated to compress or extend, the direction of compression or extension may be limited by the tube (112) even if it is twisted in the horizontal direction, so that the first twist member (113) and the second twist member (114) can be compressed or extended in the longitudinal direction.

[0042] The first torsion member (113) may be formed with a cylindrical Kresling structure, with one end portion fixed to the upper portion of the housing (111). The first torsion member (113) may be formed with a hollow interior in a cylindrical shape. Accordingly, air may be introduced into or out of the interior of the first torsion member (113).

[0043] A first torsion member (113) according to one embodiment of the present invention may be formed as a kresling structure. Here, the kresling structure may be formed as a series of interlocking polygonal units (e.g., triangles or hexagons) arranged in a manner that creates a three-dimensional shape having structural stability.

[0044] A first twisting member (113) according to one embodiment of the present invention may be formed into a three-dimensional cresling structure in which a plurality of triangular units are interlocked and arranged. First, a polyvinyl chloride sheet (PVC, thickness about 0.2 mm) may be cut into identical triangles using a paper cutter (e.g., Cameo 4, Silhouette). Next, these triangular units may be attached to a cresling tape (thickness about 0.05 mm, BLEX) at a 1.2 mm interval between two adjacent triangular units according to a cresling pattern. Then, a layer of the same Kapton tape may be attached once more on top to form a thin layer. The PVC portion will form a sandwich structure that forms the surface of the cresling unit, and the areas without PVC may form nodes by bonding with two layers of tape.

[0045] A cresling complex can be formed by folding the nodes of an origami unit of such a two-dimensional cresling pattern to create a three-dimensional structure, and then connecting the ends of the origami units to another origami unit.

[0046] The cresling unit and composite operate as an air pressure drive device, and for this purpose, the origami composite of the cresling pattern can be driven by sealing it with strong upper and lower polygonal plates produced through 3D printing (using reinforced tough resin, eSUN).

[0048] When air leaks out from inside the first twist member (113), the multiple interlocked triangular units are folded and compressed, so the length of the first twist member (113) may be shortened. On the other hand, when air flows into the inside of the first twist member (113), the multiple interlocked triangular units are unfolded and extended, so the length of the first twist member (113) may be lengthened.

[0049] Additionally, when the first twist member (113) is compressed or extended, the rotation direction of the first twist member (113) can be determined according to the direction in which a plurality of interlocking triangular units of the first twist member (113) are folded.

[0050] Referring to FIG. 2, when the folding direction of the triangular unit of the first twist member (113) is formed in a diagonal direction such as A, the first twist member (113) is compressed and the triangular unit is folded, and the first twist member (113) can rotate in a counterclockwise direction (CCW). Also, when the folding direction of the triangular unit of the first twist member (113) is formed in a diagonal direction such as B, the first twist member (113) is compressed and the triangular unit is folded, and the first twist member (113) can rotate in a clockwise direction (CW). Additionally, when the folding direction of the triangular unit of the first twist member (113) is horizontal, the first twist member (113) is compressed and the triangular unit is folded, and the first twist member (113) can be compressed in a vertical direction without rotation.

[0051] According to one embodiment of the present invention, a first torsion member (113) may have one end connected to a housing (111) and the other end connected to a second torsion member (114). When the first torsion member (113) rotates during a length deformation process of compression or extension, since one end of the first torsion member (113) is fixed to the housing (111), the one end of the first torsion member (113) may be fixed in a stationary state without rotating. On the other hand, the other end of the first torsion member (113) may be connected to one end of the second torsion member (114) or a connecting member (115), and the one end of the second torsion member (114) or the connecting member (115) is not fixed. Accordingly, when the first torsion member (113) rotates during the length deformation process of compression or extension, the other end of the first torsion member (113) may rotate clockwise or counterclockwise depending on the direction in which the triangular unit is folded.

[0052] In one embodiment of the present invention, the first torsion member (113) may have an air hole (not shown) formed therein so that air may be introduced into the interior of the first torsion member (113) or air may be discharged from the interior. In particular, the first torsion member (113) may undergo length deformation such as compression or elongation by forming negative air pressure inside the first torsion member (113) and allowing air to be discharged through the air hole.

[0053] Whether the first torsion member (113) is compressed or extended depends on the difference between the air pressure inside the first torsion member (113) and the air pressure inside the second torsion member (114). A detailed explanation regarding this will be provided later.

[0055] The second torsion member (114) may be formed with one end portion connected to the first torsion member (113) and having a cylindrical clessling structure. The second torsion member (114) may be formed with a hollow interior in a cylindrical shape. Accordingly, air may be introduced into or out of the interior of the second torsion member (114).

[0056] A second torsion member (114) according to one embodiment of the present invention can be made of polylactic acid plastic (PLA) using a 3D printer (Guider II, Flashforge).

[0057] A second torsion member (114) according to one embodiment of the present invention may be formed with a cresling structure, similar to the first torsion member (113). The second torsion member (114) may be formed with a plurality of polygonal units (e.g., triangles or hexagons) in a cresling structure. A second torsion member (114) according to one embodiment of the present invention may be formed with a structure in which a plurality of triangle units are interlocked and arranged.

[0058] The first twist member (113) and the second twist member (114) may be formed such that the folding direction of each triangular unit is different. As described above, the direction of rotation may be determined according to the direction in which the triangular unit is folded during the compression or extension process of the first twist member (113) and the second twist member (114). The folding direction of each triangular unit may be formed so that the first twist member (113) and the second twist member (114) can rotate in opposite directions to each other.

[0059] Referring to FIG. 2, FIG. 2 (a) to (c) can illustrate a process in which the first torsion member (113) extends and the second torsion member (114) compresses. The triangular unit of the first torsion member (113) may be formed to be folded in direction B, and the triangular unit of the second torsion member (114) may be formed to be folded in direction A.

[0060] Referring to the process from (a) to (c) in FIG. 2, as the triangular unit of the first twist member (113) unfolds in direction B, the first twist member (113) can undergo length deformation by elongation. Here, one end of the first twist member (113) is fixed and thus in a stationary state, while the other end of the first twist member (113) can rotate counterclockwise. Additionally, as the triangular unit of the second twist member (114) folds in direction A, the second twist member (114) can undergo length deformation by compression. Here, one end of the second twist member (114) is coupled to the other end of the first twist member (113) and can rotate counterclockwise, and accordingly, the other end can also rotate counterclockwise.

[0061] Referring to the process from (c) to (a) in FIG. 2, as the triangular unit of the first twist member (113) is folded in direction B, the first twist member (113) can undergo a length deformation that is compressed. Here, one end of the first twist member (113) is fixed and thus in a stationary state (i.e., the two white spots at the bottom are fixed), and the other end of the first twist member (113) can rotate clockwise. Additionally, as the triangular unit of the second twist member (114) is unfolded in direction A, the second twist member (114) can undergo a length deformation that is extended. Here, one end of the second twist member (114) is coupled to the other end of the first twist member (113) and can rotate clockwise, and accordingly, the other end can also rotate clockwise (i.e., the two black spots at the top move).

[0062] Additionally, referring to FIG. 2, one end of the first twist member (113) is fixed to the housing (111), and the other end of the second twist member (114) is connected to the rotary jig (116). Accordingly, the sum (Lt) of the length (L1) of the first twist member being deformed and the length (L2) of the second twist member (114) being deformed can be constant. That is, the first twist member (113) and the second twist member (114) can be maintained such that when the first twist member (113) is compressed, the second twist member (114) is extended, and when the first twist member (113) is extended, the second twist member (114) is compressed.

[0063] As described above, the first torsion member (113) and the second torsion member (114) can rotate clockwise or counterclockwise when compressed or extended, as the direction in which each triangular unit is folded is formed diagonally. Additionally, the first torsion member (113) and the second torsion member (114) can be formed differently as the direction in which each triangular unit is folded is formed differently, so that when one member undergoes a length deformation due to compression, the other member undergoes a length deformation due to extension. Furthermore, the length of deformation of the first torsion member (113) and the second torsion member (114) can be maintained as the sum (Lt) of their respective lengths (L1, L2). Here, the sum of the lengths (Lt) can be formed to be greater than the sum of the heights of the first torsion member (113) and the second torsion member (114) when fully contracted, and smaller than the sum of the heights of the first torsion member (113) and the second torsion member (114) when fully expanded.

[0064] In one embodiment of the present invention, a second torsion member (114) may have an air hole (not shown) formed therein so that air may flow into the interior of the second torsion member (114) or air may flow out from the interior. In particular, the second torsion member (114) may undergo length deformation such as compression or elongation by forming negative air pressure inside the second torsion member (114) and allowing air to flow out through the air hole.

[0065] Air is introduced into the interior of the first torsion member (113) and the second torsion member (114), and depending on the amount introduced, the compression or extension of the first torsion member (113) and the second torsion member (114) may be determined. In this case, positive air pressure may be formed inside the first torsion member (113) and the second torsion member (114).

[0066] In this manner, the first torsion member (113) and the second torsion member (114) increase in volume due to the inflow of air. As the volume of the first torsion member (113) and the second torsion member (114) increases, they can rotate in a clockwise or counterclockwise direction. However, in this case, the magnitude of the rotation angle is not formed significantly, and there is an inconvenience in that it is difficult to control the length deformation caused by compression or elongation due to the force of the air inside both members pushing out at the connection part of the first torsion member (113) and the second torsion member (114).

[0068] According to one embodiment of the present invention, the first torsion member (113) and the second torsion member (114) may be compressed or extended depending on the difference in internal air pressure (i.e., the difference in negative pressure) of each member. That is, the deformation shape may be determined according to the difference in negative pressure formed in the first torsion member (113) and the second torsion member (114). For example, if a negative pressure of -20 KPa is formed inside the first torsion member (113) and a negative pressure of -10 KPa is formed inside the second torsion member (114), the first torsion member (113) may be compressed and the second torsion member (114) may be extended (see FIG. 2 (a)). Additionally, when a negative pressure of -10KPa is formed inside the first torsion member (113) and a negative pressure of -20KPa is formed inside the second torsion member (114), the first torsion member (113) may be extended and the second torsion member (114) may be compressed (see Fig. 2 (c)). Also, when a negative pressure of -10KPa is formed inside the first torsion member (113) and a negative pressure of -10KPa is formed inside the second torsion member (114), no deformation of length occurs in the first torsion member (113) and the second torsion member (114) (see Fig. 2 (c)).

[0069] Additionally, the length to which each member is deformed may vary depending on the magnitude of the difference between the internal air pressure of the first torsion member (113) and the internal air pressure of the second torsion member (114). That is, if the magnitude of the difference between the internal air pressure of the first torsion member (113) and the internal air pressure of the second torsion member (114) increases, one member may be further compressed to form a shorter length, and the other member may be further extended to form a longer length (of course, the sum (Lt) of the length of the first torsion member (113) and the length of the second torsion member (114) is maintained constant).

[0071] A connecting member (115) is provided between the first twisting member (113) and the second twisting member (114) to guard the first twisting member (113) and the second twisting member (114).

[0072] According to one embodiment of the present invention, the first torsion member (113) and the second torsion member (114) are joined at their ends, and the first torsion member (113) and the second torsion member (114) can rotate in a clockwise or counterclockwise direction. Accordingly, the connection portion between the first torsion member (113) and the second torsion member (114) may be vulnerable to external forces. Additionally, since rotation occurs between the first torsion member (113) and the second torsion member (114), horizontal movement due to torsion may occur.

[0073] The connecting member (115) is positioned inside the tube (112) between the inner wall of the tube (112) and the first twist member (113) and the second twist member (114), thereby restricting the horizontal movement of the first twist member (113) and the second twist member (114) so ​​that deformation occurs in the longitudinal direction without the first twist member (113) and the second twist member (114) moving in the horizontal direction during the compression or extension process.

[0075] A rotary jig (116) may be coupled to the other end of the second twist member (114) and configured to be rotatable. The rotary jig (116) is fixed horizontally to the housing (111). The inner part of the rotary jig (116) is coupled to the other end of the second twist member (114) and can rotate with the longitudinal direction as an axis. Subsequently, when the second twist member (114) rotates, the rotary jig (116) can also rotate according to the rotation direction of the second twist member (114).

[0076] Additionally, since the rotary jig (116) is fixed in a horizontal direction inside the housing (111), the first twisting member (113) and the second twisting member (114), with the inner upper end of the housing (111) and the rotary jig (116) as their ends, may have a constant total length (Lt).

[0077] FIG. 3 is a drawing illustrating a torsion actuator (100) in which a gripper (121) is coupled to a rotary jig (116). FIG. 3 (a) illustrates a state in which the first torsion member (113) is maximally extended and the second torsion member (114) is maximally compressed.

[0078] Additionally, FIG. 3(e) illustrates a state in which the first torsion member (113) is maximally compressed and the second torsion member (114) is maximally extended. Also, FIG. 3(b) to (d) illustrate a state in which the first torsion member (113) is compressed and the second torsion member (114) is extended. In this process, the first torsion member (113) and the second torsion member (114) can rotate clockwise. Additionally, the air pressure inside the first torsion member (113) can be compressed as it relatively increases, and the air pressure inside the second torsion member (114) can be extended as it relatively decreases.

[0079] On the other hand, the process from (e) to (a) in Fig. 3 is the opposite of the process described above, and the first torsion member (113) and the second torsion member (114) can rotate counterclockwise.

[0080] Through the above process, the rotary jig (116) can rotate, and the gripper (121) coupled to the rotary jig (116) can repeatedly perform gripping or releasing operations as the mutually opposing parts move closer or further apart.

[0081] FIG. 4 illustrates the angles at which the first torsion member (113) and the second torsion member (114) rotate while being compressed or extended. FIG. 4(a) illustrates a state of rotation at 0 degrees, FIG. 4(b) at 90 degrees, FIG. 4(c) at 180 degrees, FIG. 4(d) at 270 degrees, and FIG. 4(e) at 300 degrees. From FIG. 4(a) to FIG. 4(e), the first torsion member (113) is compressed and the second torsion member (114) is extended, causing rotation in a clockwise direction. If the angle of the position of the gripper (121) in FIG. 4(a) is 0 degrees, the angle of the position of the gripper (121) in FIG. 4(e) can be an angle of rotation of approximately 300 degrees.

[0082] In this way, the torsion actuator (100) according to one embodiment of the present invention can improve the gripping force of the gripper (121) as the gripper (121) twists at a certain angle while gripping an object, and the torsion actuator (100) can generate twisting through its internal configuration, so there is no external change, and thus the torsion actuator (100) can be used for various purposes and places.

[0084] Although various embodiments of the present invention have been presented and described in the above description, the present invention is not necessarily limited thereto, and those skilled in the art will readily understand that various substitutions, modifications, and changes are possible within the scope of the technical concept of the present invention. Explanation of the symbols

[0086] 100 : Torsion actuator 111 : Housing 112 : Tube 113 : First torsion member 114: Second torsion member 115: Connecting member 116 : Rotary jig 121 : Gripper

Claims

Claim 1 The apparatus comprises a housing having a tubular shape and an internal receiving space, a tube provided inside the housing, a first torsion member having one end fixed to the upper end of the housing and having a cylindrical Kresling structure, a second torsion member having one end connected to the first torsion member and having a cylindrical Kresling structure, a rotary jig connected to the other end of the second torsion member and formed to be rotatable, and a gripper connected to the lower end of the housing and connected to the other end of the rotary jig, which repeats gripping and releasing operations as mutually opposing parts move closer or further apart due to the rotation of the rotary jig, wherein the tube accommodates the first torsion member and the second torsion member inside, and the tube limits the direction in which the first torsion member and the second torsion member are compressed or extended, and the first torsion member and the second torsion member are, in response to an air pressure difference A torsion actuator, wherein a length deformation occurs by such a way, so that the lower end of the second torsion member is rotatably provided, and when a length deformation occurs in the first torsion member or the second torsion member, the first torsion member and the second torsion member are formed to be folded or unfolded in different directions, and when one of the first torsion member or the second torsion member is compressed and a length deformation occurs, the other is formed to be extended and a length deformation occurs, and when a length deformation occurs in the first torsion member or the second torsion member, the sum of the length of the first torsion member and the length of the second torsion member is maintained constant, and the sum of the lengths is formed to be greater than the sum of the heights of the first torsion member and the second torsion member in a contracted state and less than the sum of the heights of the first torsion member and the second torsion member in an expanded state. Claim 2 delete Claim 3 delete Claim 4 In claim 1, the first torsion member and the second torsion member are a torsion actuator having an air hole through which air is introduced from the outside or air is discharged from the inside. Claim 5 delete Claim 6 A torsion actuator according to claim 1, comprising a connecting member provided between the first torsion member and the second torsion member to guard the first torsion member and the second torsion member. Claim 7 delete Claim 8 delete

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