JP2009214277A - Equivalent sphere joint structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new equivalent sphere joint structure capable of attaining a wide movable range. <P>SOLUTION: The new equivalent sphere joint structure is formed by jointing four rotation joints of which five rigid body links that are a first bend part (14), a second bend part (18), an intermediate joint part (16), a first joint part (12), and a second joint part (20) have 1 freedom degree, is a joint structure that is equivalent to a sphere joint by applying a special posture avoiding means (22) that restricts a rotation movable range of the first bend part (14) to the intermediate joint part (16) between the first bend part (14) and the intermediate joint part (16) to an open loop spherical surface link mechanism having 4 degrees of freedom, and provides an extraordinarily wide movable range compared to the existing sphere joint and the like. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an equivalent spherical joint structure, and more particularly to an equivalent spherical joint structure having a wide movable range.

  Conventionally, various studies have been made on manipulator structures for industrial robots. Many of the existing manipulators have a serial type structure in which links and joints are connected in series, but in recent years, parallel type manipulators with higher rigidity and higher speed movement than serial type manipulators. Is attracting attention. Many of the parallel manipulators use a ball joint because of its structure, but until now, in many cases, a ball joint structure using a spherical bearing has been used. FIG. 10 shows a ball joint structure 40 using a spherical bearing that has been widely used in the past. In the ball joint structure 40 shown in FIG. 10, the link 42 has an end 44 formed in a convex spherical shape fitted to a bearing 46 formed in a concave spherical shape. It is configured to be movable in the direction. However, in the ball joint structure 40, since the link 42 interferes with the bearing, the movable range θ is only about 60 °, and the narrowness of the movable range of the ball joint is a variety of motions of the parallel manipulator. It became a bottleneck in pursuit of sex.

  In this regard, Japanese Patent Application Laid-Open No. 2002-276683 (Patent Document 1) discloses a universal joint structure characterized in that a joint material is bent at an angle of 90 ° or more. In the universal joint structure disclosed in Patent Document 1, the first member and the second member are rotatably connected to the first joint material and the second joint material, respectively, and the rotational resistance force about the axes of both joint materials is provided. By making the difference, interference between the joint materials is avoided as much as possible, and thus the members connected to the joint materials can be bent to the same extent in all directions. In this universal joint structure, since the first member can move with respect to the second member with three degrees of freedom, it can also be regarded as an equivalent spherical joint structure provided between the first member and the second member. However, the universal joint structure disclosed in Patent Document 1 cannot completely eliminate the possibility of interference between joint materials because of its structure, and in this respect, guarantees complete equivalence with a ball joint. It wasn't.

In the future, expansion of the movable range of the ball joint will be an important issue when considering further application development of industrial robots, including parallel manipulators, and the creation of a new equivalent spherical joint structure with a wider range of motion It was desired.
JP 2002-276683 A

  The present invention has been made in view of the above problems in the prior art, and an object of the present invention is to provide a novel equivalent spherical joint structure having a wide movable range.

  As a result of intensive studies on a novel equivalent spherical joint structure having a wide range of motion, the present inventor has conducted a four-degree-of-freedom open-loop spherical link in which five rigid links are connected by four rotary joints having one degree of freedom. By adding a mechanism that restricts the rotational movable range between predetermined links to the mechanism, a joint structure equivalent to a ball joint is realized, and the movable range is significantly higher than that of existing ball joints. It has been found that it has become wide and has led to the present invention.

  That is, according to the present invention, an equivalent spherical joint structure including a link mechanism in which five rigid links are connected by four rotary joints and a unique posture avoiding means (22), wherein the link mechanism is a rigid link. The first bent portion (14), the second bent portion (18), the intermediate connecting portion (16), the first connecting portion (12), and the second connecting portion (20). The first connecting portion (12) is connected to the first bent portion (14) by a first rotating joint (24), and the first bent portion (14) is connected to the first rotating joint (26) by the second rotating joint (26). The intermediate connection part (16) is connected to the second connection part (18) by a third rotary joint (28), and the second connection part (18) is connected to the second connection part (16). The first joint shaft (C) of the first rotary joint (24) is connected to the second connecting portion (20) by a four rotary joint (30). A second joint axis (B) of the rolling joint (26), a third joint axis (D) of the third rotary joint (28), and a fourth joint axis (A) of the fourth rotary joint (30); Intersect at one point, the second joint axis (B) and the third joint axis (D) are orthogonal, and the third joint axis (D) and the fourth joint axis (A) are orthogonal. The five rigid links are connected by the four rotary joints so that the first joint axis (C) and the second joint axis (B) intersect at an acute angle, and the singular posture avoiding means (22) The first joint axis (C) is such that the first joint axis (C) does not fall into a posture existing on a plane including both the second joint axis (B) and the third joint axis (D). An equivalent spherical joint structure, which is a means for applying a restoring force between the bent portion 14 and the intermediate connecting portion 16, is provided.

  In the present invention, the unique posture avoiding means (22) counteracts the relative rotational motion of the first bent portion (14) and the intermediate connecting portion (16) around the second joint axis (B). It can be a means to give the restoring force to do. In the present invention, the means for applying the restoring force is an urging means provided between the first bent portion (14) and the intermediate connecting portion (16), and the urging means includes: With respect to the first bent portion (14) and the intermediate connecting portion (16), the first joint axis (C) has both the second joint axis (B) and the third joint axis (D). The biasing means provided as an equilibrium state can be a state that does not exist on the plane that includes it, and the biasing means can be a torsion spring. Furthermore, in the present invention, the second bent portion (18) is a rigid link formed by bending in an L shape, and the intermediate connecting portion (16) is a rigid link formed in a straight line. The first bent portion (14) can be configured as a rigid link formed by bending with an obtuse angle.

  As described above, according to the present invention, a novel equivalent spherical joint structure having a much wider movable range than the conventional one is provided.

  Hereinafter, the present invention will be described with reference to embodiments shown in the drawings, but the present invention is not limited to the embodiments shown in the drawings.

  FIG. 1 is a perspective view showing an equivalent spherical joint structure 10 of the present embodiment. As shown in FIG. 1, the equivalent spherical joint structure 10 of the present embodiment includes a first connecting portion 12, a first bent portion 14, an intermediate connecting portion 16, a second bent portion 18, and a second connecting portion 20. One rigid link includes a link mechanism connected by four rotary joints. Specifically, the first connecting portion 12 and the first bent portion 14, the first bent portion 14 and the intermediate connecting portion 16, the intermediate connecting portion 16 and the second bent portion 18, and the second bent portion 18 and the second connected portion. The parts 20 are connected by rotary joints each having one degree of freedom. When the equivalent spherical joint structure 10 is used, the first connecting portion 12 and the second connecting portion 20 are connected to a rigid link X and a rigid link Y (not shown), respectively. Works equivalent to.

  In addition, the equivalent spherical joint structure 10 of the embodiment further includes a unique posture avoiding means. The unique posture avoiding means is means for avoiding that the equivalent ball joint structure 10 loses its equivalence with the ball joint, and in the embodiment shown in FIG. 22. The function / action of the unique posture avoiding means will be described in detail later. The physical configuration of the equivalent spherical joint structure 10 of the present embodiment has been outlined above. Next, the link mechanism of the equivalent spherical joint structure 10 of the present embodiment will be described below with reference to FIG. Hereinafter, in FIGS. 2 to 9, common elements are denoted by the same reference numerals, and description thereof is omitted as appropriate.

  FIG. 2 is a conceptual diagram for explaining the link mechanism of the equivalent spherical joint structure 10 of the present embodiment. In FIG. 2, the unique posture avoiding means 22 is omitted for convenience of explanation.

  As described above, the link mechanism of the equivalent spherical joint structure 10 of the present embodiment includes five rigid links (first connecting portion 12, first bent portion 14, intermediate connecting portion 16, second bent portion 18, second connected portion). The part 20) is configured as an open loop structure formed by connecting four rotary joints having one degree of freedom indicated by ★ in the drawing. The first connecting portion 12 and the first bent portion 14 are connected by a rotating joint 24, the first bent portion 14 and the intermediate connecting portion 16 are connected by a rotating joint 26, and the intermediate connecting portion 16 and the second bent portion 18 are connected. The second bent portion 18 and the second connecting portion 20 are connected by a rotating joint 30 and all the rigid links described above are constrained to one degree of freedom. Therefore, the link mechanism as a whole has 4 degrees of freedom (1 degree of freedom × 4). The ball joint constrains the motion between two objects coupled to it to three degrees of freedom. In view of this point, the equivalent ball joint structure 10 of the present embodiment has four degrees of freedom. It is configured redundantly for the degree of freedom. This redundancy is associated with the specific posture avoiding means described in detail later, so that the equivalent spherical joint structure 10 can be preferably equivalent to the spherical joint.

  In FIG. 2, the joint axes of the rotary joints 24, 26, 28, and 30 are indicated by lines A to D. In FIG. 2, for convenience of explanation, the joint axis B and the joint axis D are shown as bent lines. However, when the rigid links are connected as shown in FIG. It should be understood that axis D is a straight line. In the equivalent spherical joint structure 10, the first connecting portion 12 is rotatable 360 ° about the joint axis C of the rotary joint 24 with respect to the first bent portion 14, and the intermediate connecting portion 16 is The second bending portion 18 is rotatable about the joint axis D of the rotary joint 28 with respect to the second bending portion 18. 360 A can be rotated about A as a rotation axis. On the other hand, the first bent portion 14 is configured to be rotatable with respect to the intermediate connecting portion 16 about the joint axis B of the rotary joint 26 as a rotation axis. However, unlike the above-described rigid link element, the first bent portion 14 Due to the action of a unique posture avoiding means (not shown) provided between the intermediate connecting portion 16 and the intermediate connecting portion 16, the rotational motion is subjected to certain restrictions. This point will be described in detail later.

  Further, in the equivalent spherical joint structure 10 of the present embodiment, as shown in FIG. 2, the joint axis A of the rotary joint 30, the joint axis B of the rotary joint 26, the joint axis C of the rotary joint 24, and the rotation The joint axis D of the joint 28 is configured to intersect at one point indicated by “S”. When the second connecting portion 20 is fixed, the first connecting portion 12 can move in all directions with the point S at which all of the joint axes A to D meet as the rotation center. That is, this point S corresponds to the center of rotation in the ball joint, and in this specification, the point S where all of the joint axes A to D intersect is designated as the “virtual center of rotation” of the equivalent spherical joint structure 10. And used below.

  Next, with reference to FIG. 3, each rigid link element in the link mechanism of the equivalent spherical joint structure 10 of the present embodiment will be described in more detail. 3A and 3B are diagrams for explaining each rigid link of the equivalent spherical joint structure 10, FIG. 3A is a side view of the second bent portion 18, and FIG. 3B is an upper surface of the intermediate connecting portion 16. FIG. 3C shows a side view of the first bent portion 14. As shown in FIG. 3A, the second bent portion 18 is a rigid body formed by bending in an L shape, and is connected to the rotary joint 28 and the rotary joint 30 indicated by ★ in the figure, At this time, the joint axis D of the rotary joint 28 and the joint axis A of the rotary joint 30 are configured to be orthogonal with the virtual rotation center S as an intersection. In the present embodiment, the shape and dimensions of the second bent portion 18 are determined so that the space d is defined by the L-shaped bent structure and the intermediate connecting portion 16. Here, the space d is the end of the first bent portion 14 to which the first connecting portion 12 is not connected when the first connecting portion 12 moves closer to the second connecting portion 20. Is a space that allows the second bent portion 18 to pass through without interfering with the second bent portion 18.

  Further, as shown in FIG. 3 (b), the intermediate connecting portion 16 is a rigid body formed in a straight line, and is connected to the rotary joint 28 and the rotary joint 26 indicated by ★ in the figure, The joint axis D of the rotary joint 28 and the joint axis B of the rotary joint 26 are configured to be orthogonal with the virtual rotation center S as an intersection. On the other hand, as shown in FIG. 3C, the first bent portion 14 is a rigid body formed by bending with an obtuse angle θ2, and is connected to the rotary joint 24 and the rotary joint 26 indicated by ★ in the drawing. In this case, the joint axis C of the rotary joint 24 and the joint axis B of the rotary joint 26 are not orthogonal to each other, and intersect with each other with an acute angle θ1 with the virtual rotation center S as an intersection.

  The equivalent spherical joint structure 10 of the present embodiment is provided with the above-described link mechanism, thereby realizing a remarkably large movable range as compared with a conventional spherical joint structure or a universal joint structure. FIG. 4 shows in time series how the equivalent spherical joint structure 10 of this embodiment moves. In FIG. 4, the change in the posture of the equivalent spherical joint structure 10 when the first connecting portion 12 is moved in all directions in a state where the second connecting portion 20 is fixed to the ground surface is fixed with a line of sight number 1. It was shown in time series in the order of .about.9. By referring to FIG. 4, it will be understood that the equivalent spherical joint structure 10 of the present embodiment realizes a movable range close to 300 ° in all directions with respect to the virtual rotation center.

  Here, the mechanism by which the equivalent spherical joint structure 10 of the present embodiment functions substantially equivalently to the spherical joint will be described. FIG. 5 shows a model link mechanism R for explaining the mechanism of the present invention. In a ball joint, the motion between two objects coupled to it is constrained to three degrees of freedom. From this point, the model link mechanism R has three joint axes (J1 to J3) as shown in FIG. 5A, and the three joint axes are configured to intersect at one point. Since the movement between the object to which the joint material T1 is coupled and the object to be coupled to the joint material T2 is restricted to three degrees of freedom, it is expected to function in the same manner as a ball joint. However, in the case of the model link mechanism R, as shown in FIG. 5 (b), in the posture in which the three joint axes (J1 to J3) exist on the same plane indicated by the broken line, the joint material T1 is connected to the object. It is impossible to rotate in the direction indicated by the arrow in the figure. That is, in this posture, the model link mechanism R loses equivalence with the ball joint.

  Regarding the above-described points, also in the present embodiment, a posture in which the three joint axes exist on the same plane occurs. FIG. 6 shows three postures that the equivalent spherical joint structure 10 of the present embodiment can take in the course of its movement. In the posture shown in FIG. 6A, the joint axes A, C, and D are all on the plane P indicated by the broken line, but the joint axis B does not exist on the plane P. In a state where is fixed, the first connecting part 12 can move in all directions with respect to the virtual rotation center. Similarly, in the posture shown in FIG. 6B, the joint axes A, B, and D are all on the plane P, but the joint axis C is not on the plane P. In the fixed state, the first connecting portion 12 can move in all directions with respect to the virtual rotation center, and even in the posture shown in FIG. 6C, the joint axes A, B, and D are all in the plane P. Although it exists above, the joint axis C does not exist on the plane P, and therefore the first connecting portion 12 can move in all directions with respect to the virtual rotation center in a state where the second connecting portion 20 is fixed. As described above, in the equivalent spherical joint structure 10 of the present embodiment, even if the three joint axes are on the same plane, as long as the remaining one joint axis does not exist on the plane P, It will be understood that equivalence with the ball joint is maintained. However, also in this embodiment, when all the joint axes A to D exist on the same plane, the equivalent spherical joint structure 10 may lose the equivalence with the spherical joint. This point will be described below with reference to FIG.

  FIG. 7 shows three other postures that the equivalent spherical joint structure 10 of the present embodiment can take in the course of its movement. In the posture shown in FIG. 7A, since all of the joint axes A to D are on the plane P indicated by the broken line, the first connecting portion 12 is virtually rotated in a state where the second connecting portion 20 is fixed. The rotational movement in the direction indicated by the arrow on the plane P with respect to the center is locked, and as a result, the equivalence with the ball joint is lost. Similarly, in the postures shown in FIGS. 7B and 7C, all of the joint axes A to D are present on the plane P indicated by the broken line, and therefore the first connection in the state where the second connection part 20 is fixed. The part 12 is locked to the rotational movement in the direction indicated by the arrow on the plane P with respect to the virtual rotation center, and as a result, the equivalence with the ball joint is lost. In the present specification, the posture of the link mechanism in which all of the joint axes A to D described above exist on the same plane is defined as “singular posture” and used hereinafter.

  As described above, in the link mechanism of the equivalent spherical joint structure 10 of the present embodiment, the joint axes existing on the same plane in the course of movement are three or less of the joint axes A to D. While maintaining such a posture, the equivalence with the ball joint is not lost, but when it falls into a posture where all of the joint axes A to D exist on the same plane, the moment It will be appreciated that equivalence with the ball joint may be lost.

  However, in practice, the equivalent spherical joint structure 10 of the present embodiment is prevented from falling into a specific posture by the action of the specific posture avoiding means, so that equivalence with the ball joint is always ensured. This point will be described in detail below with reference to FIGS.

  FIG. 8 is a view for explaining the unique posture avoiding means in the equivalent spherical joint structure 10 of the present embodiment. In FIG. 8, only the first bent portion 14 and the intermediate connecting portion 16 are extracted from the rigid link elements of the equivalent spherical joint structure 10 for convenience of explanation. FIG. 8A is a view of the equivalent spherical joint structure 10 as seen from the side surface direction of the first bent portion 14. In the present embodiment, the first bent portion 14 is provided with a shaft-like protrusion 32, and the shaft-like protrusion 32 is inserted into the opening 16 a formed in the intermediate connecting portion 16, whereby the joint shaft A rotating joint with B is realized. Here, a torsion spring 22 as a specific posture avoiding means is inserted into the shaft-like protrusion 32, one end 22 a of the torsion spring 22 is fixed to the intermediate connecting portion 16, and the other end 22 b is the tip of the shaft-like protrusion 32. It is fixed in the vicinity. The first bent portion 14 is connected to a first connecting portion 12 (not shown) via a rotary joint having a joint axis C.

  FIG. 8B is a view of the equivalent spherical joint structure 10 as viewed from the front direction of the intermediate connecting portion 16. As described above, since the first bent portion 14 and the intermediate connecting portion 16 are connected by the rotary joint having the joint axis B, the movement of the first connecting portion 12 (not shown) connected to the first bent portion 14 is performed. Accordingly, the first bent portion 14 and the intermediate connecting portion 16 can take various positional relationships. If the first bent portion 14 is rotated by 90 ° around the joint axis B in the direction indicated by the solid arrow Q, the joint axis C of the first bent portion 14 becomes the joint axis of the intermediate connecting portion 16. A state exists on a plane including both D and the joint axis B. When the intermediate coupling portion 16 rotates around the joint axis D while maintaining the state where the joint axes B to D exist on the same plane, the joint axis A and the joint axes B to D (not shown) exist on the same plane. A unique posture is caused.

  However, in the present embodiment, a torsion spring 22 is provided between the first bent portion 14 and the intermediate connecting portion 16, and the torsion spring 22 is in the state shown by the solid line in FIG. Since the state shown in FIG. 8A is attached in an equilibrium state, when the bent portion 14 rotates around the joint axis B in the direction indicated by the solid line arrow Q, the broken line 14 responds to the rotational motion and is broken. The restoring force of the torsion spring 22 instantaneously acts on the intermediate connecting portion 16 in the direction indicated by the arrow R, and accordingly, the intermediate connecting portion 16 rotates in the direction indicated by the broken arrow R with the joint axis B as the rotation axis. To do. In other words, the torsion spring 22 functions as a means for generating a restoring force that opposes the relative rotational movement of the first bent portion 14 and the intermediate coupling portion 16 around the joint axis B. Due to the action, a moderate repulsive force is always generated from a state in which the joint axis C included in the first bent portion 14 exists on a plane including both the joint axis D and the joint axis B included in the intermediate connecting portion 16. A unique posture in which the joint axes A to D exist on the same plane is avoided.

  The unique posture avoiding means in the present invention may be any means that can generate a restoring force that opposes the relative rotational movement of the first bent portion 14 and the intermediate connecting portion 16 around the joint axis B. The present invention is not limited to the torsion spring 22 described above, and can be appropriately designed using an elastic body such as rubber or a spring. However, in order to ensure equivalence with the ball joint, the above repulsive force is not excessive. It is more preferable to configure as described above.

  A mechanism for avoiding a specific posture in the equivalent spherical joint structure 10 of the present embodiment will be described more specifically with reference to FIG. The postures of the equivalent spherical joint structure 10 shown on the left side of the paper in FIGS. 9A to 9C correspond to the postures shown in FIGS. 7A to 7C, respectively. Everything is in a singular posture. In the equivalent spherical joint structure 10 of the present embodiment, when the first connecting portion 12 is moved in all directions with respect to the virtual rotation center with the second connecting portion 20 fixed, the first bent portion 14 and the intermediate connecting portion 16 are used. Since the restoring force of the singular posture avoiding means 22 always acts on the first bent portion 14 and the intermediate connecting portion 16 according to the relative angle of FIG. Although it does not fall into the state of the peculiar posture shown on the left side of the paper, for the convenience of explanation, it is assumed that the posture is very close to the state of the peculiar posture shown on the left side of the paper of FIGS. Think of a situation that has fallen into. According to the present embodiment, even when such a situation occurs, the intermediate connecting portion 16 and the second bent portion 18 are respectively connected to the joint axis B and the joint axis A by the restoring force of the torsion spring acting instantaneously. As a result, the singular posture is completely avoided, and as a result, the postures shown on the right side of the paper in FIGS. 9A to 9C, that is, the joint axes A to D are present on the same plane. The posture is restored so that there are 3 or less joint axes.

  Here, as described above, the link mechanism of the equivalent spherical joint structure 10 of the present embodiment has redundancy for one degree of freedom. What should be noted here is that the link mechanism itself has redundancy, but the four joint axes are configured to intersect at one point of the virtual rotation center. 12 is a point equivalent to a state restrained by a ball joint. In other words, the degree of freedom of movement of the first connecting portion 12 relative to the second connecting portion 20 is 3, and the redundancy for one degree of freedom of the above-described link mechanism is that of the second connecting portion 20 and the first connecting portion 12. The movement in between only appears as a movement for one degree of freedom in which the first bent portion 14, the intermediate connecting portion 16, and the second bent portion 18, which are three separated rigid link elements, are interlocked. In the present embodiment, this motion for one degree of freedom separated from the motion between the second connecting portion 20 and the first connecting portion 12 is utilized as a motion for avoiding a specific posture. Since the link mechanism according to the present invention is preferably avoided by the mechanism described above, the equivalence with the ball joint is preferably realized.

  As described above, according to the present invention, a novel equivalent spherical joint structure having a wide movable range is provided. With the equivalent spherical joint structure of the present invention, it has become possible to move in a parallel type manipulator that has been difficult to realize due to restrictions on the movable range of the ball joint, and such a parallel type manipulator can be applied to various industrial robots. Is expected to be.

The perspective view which shows the equivalent spherical joint structure of this embodiment. The conceptual diagram for demonstrating the link mechanism of the equivalent spherical joint structure of this embodiment. The figure which shows the rigid body link of the equivalent spherical joint structure of this embodiment. The figure which shows the aspect which the equivalent spherical joint structure of this embodiment moves in time series. The figure which shows the model link mechanism for demonstrating the mechanism of this invention. The figure which shows three attitude | positions which the equivalent spherical joint structure of this embodiment can take in the process of the exercise | movement. The figure which shows three specific attitude | positions in the equivalent spherical joint structure of this embodiment. The figure which shows the specific posture avoidance means in the equivalent spherical joint structure of this embodiment. The figure which shows the aspect by which a peculiar attitude | position is avoided in the equivalent spherical joint structure of this embodiment. The figure which shows the ball joint structure using the conventional spherical bearing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Equivalent spherical joint structure, 12 ... 1st connection part, 14 ... 1st bending part, 16 ... Intermediate | middle connection part, 18 ... 2nd bending part, 20 ... 2nd connection part, 22 ... Torsion spring, 24 ... Rotary joint , 26 ... rotary joint, 28 ... rotary joint, 30 ... rotary joint, 32 ... axial projection, 40 ... ball joint structure, 42 ... link, 44 ... end, 46 ... bearing

Claims (5)

An equivalent spherical joint structure including a link mechanism in which five rigid links are connected by four rotary joints and a unique posture avoiding means,
The link mechanism is configured to include a first bent portion, a second bent portion, an intermediate connecting portion, a first connecting portion, and a second connecting portion as a rigid link,
The first connecting portion is connected to the first bent portion by a first rotating joint, the first bent portion is connected to the intermediate connecting portion by a second rotating joint, and the intermediate connecting portion is connected to the third rotating portion. Connected to the second bent portion by a joint, and the second bent portion is connected to the second connected portion by a fourth rotating joint;
The first joint axis of the first rotary joint, the second joint axis of the second rotary joint, the third joint axis of the third rotary joint, and the fourth joint axis of the fourth rotary joint at one point. Crossing, the second joint axis and the third joint axis are orthogonal, the third joint axis and the fourth joint axis are orthogonal, and the first joint axis and the second joint axis are The five rigid links are connected by the four rotary joints so as to intersect at an acute angle,
The singular posture avoiding means includes the first bent portion and the intermediate coupling so that the first joint axis does not fall into a posture existing on a plane including both the second joint axis and the third joint axis. An equivalent spherical joint structure that is a means for applying a restoring force between the portions 16.   The equivalent posture according to claim 1, wherein the singular posture avoiding unit is a unit that applies a restoring force that opposes a relative rotational movement of the first bent portion and the intermediate coupling portion around the second joint axis. Ball joint structure.   The means for applying the restoring force is urging means provided between the first bent portion and the intermediate connecting portion, and the urging means is applied to the first bent portion and the intermediate connecting portion. 3. The equivalent spherical joint structure according to claim 1, wherein the first joint axis is provided as an equilibrium state in a state where the first joint axis does not exist on a plane including both the second joint axis and the third joint axis.   The equivalent spherical joint structure according to claim 1, wherein the biasing means is a torsion spring.   The second bent portion is a rigid link formed by bending in an L shape, the intermediate connecting portion is a rigid link formed in a straight shape, and the first bent portion is bent at an obtuse angle. The equivalent spherical joint structure according to any one of claims 1 to 4, wherein the equivalent spherical joint structure is a rigid body link formed as described above.

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