Robot arm mechanism

This application is a continuation application of International Patent Application No. PCT/JP2015/080037 filed on Oct. 23, 2015, which is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2014-217856, filed Oct. 24, 2014, the entire contents of which are incorporated herein by reference.

Embodiments described herein relate generally to a robot arm mechanism.

FIG. 14 shows a conventional vertically articulated arm mechanism. The vertically articulated arm mechanism requires three-degree-of-freedom (x, y, z) regarding a position and three-degree-of-freedom (φ, θ, ψ) regarding a posture, which are generally realized by rotational joints J 1 , J 2 and J 3 called root three axes and rotational joints J 4 , J 5 and J 6 called wrist three axes. For example, a revolute joint is applied to joints J 1 , J 4 and J 6 , and a bending joint is applied to joints J 2 , J 3 and J 5 .

This type of the articulated arm mechanism has countless postures called singular points in which a degree of freedom in a specific direction is lost despite being within a movable range. The singular point posture causes uncontrollable condition due to countless solutions (sets of joint angles satisfying a certain coordinate position) that exist for a coordinate transformation operation of Cartesian coordinates and sets of joint angles, and causes “out-of-control” because an infinite angular velocity is required for the joint and a movement of the joint becomes rapidly fast in the vicinity of the singular point. Thus, in current situation, the problem is handled by avoiding the singular point or sacrificing a hand movement speed. For example, as the singular point, there is a so-called wrist singular point at which axes of rotation RA 1 , RA 4 and RA 6 of the revolute joints J 1 , J 4 and J 6 are made coaxial by setting all the bending joints J 2 , J 3 and J 5 to zero degree as shown in FIG. 15A ; and in this situation, it is impossible to uniquely determine rotation angles of these revolute joints J 1 , J 4 and J 6 . This situation similarly occurs when at least two revolute joints are aligned in the same axis. As other singular point postures, known are a so-called shoulder singular point at which an intersection point of the axes of rotation RA 4 , RA 5 and RA 6 of the joints J 4 , J 5 and J 6 of the wrist three axes is located on the axis of rotation RA 1 of the revolute joint J 1 forming an arm base as shown in FIG. 15B , and a so-called elbow singular point at which an intersection point of the axes of rotation RA 4 , RA 5 and RA 6 of the joints J 4 , J 5 and J 6 of the wrist three axes is located on a plane including axes of rotation RA 2 and RA 3 of bending joints J 2 and J 3 of the root three axes as shown in FIG. 15C .

The object of the present invention is to provide a robot arm mechanism capable of structurally eliminating or reducing singular point postures within a movable range.

The robot arm mechanism according to the present embodiment has a plurality of joints. Of the joints, a first joint is a rotational joint that rotates on a first axis, a second joint is a rotational joint that rotates on a second axis, and a third joint is a linear motion joint that moves along a third axis. The second axis is perpendicular to the first axis and is a first distance away from the first axis. The third axis is perpendicular to the second axis and is a second distance away from the second axis.

FIG. 1 is an external perspective view of a robot arm mechanism according to the present embodiment;

FIG. 2 is a perspective view illustrating an internal structure of the robot arm mechanism in FIG. 1 ;

FIG. 3 is a view illustrating the internal structure of the robot arm mechanism in FIG. 1 viewed from a cross section direction;

FIG. 4 is a diagram illustrating the robot arm mechanism in FIG. 1 with symbolic representation;

FIGS. 5A and 5B are a diagram illustrating an example of offset distances L 1 and L 2 in FIG. 4 ;

FIGS. 6A and 6B are a diagram illustrating another example of the offset distances L 1 and L 2 in FIG. 4 ;

FIG. 7 is a diagram illustrating a case in which a specific posture is prevented from being a singular point posture by the present embodiment;

FIGS. 8A and 8B are a diagram illustrating an example of offset distances L 1 , L 2 and L 3 in FIG. 4 ;

FIGS. 9A and 9B are a diagram illustrating another example of the offset distances L 1 , L 2 and L 3 in FIGS. 8A and 8B ;

FIG. 10 is a diagram illustrating yet another example of the offset distances L 1 , L 2 and L 3 in FIGS. 8A and 8B ;

FIG. 11 is a diagram illustrating a structure by which the singular point is not generated according to the present embodiment;

FIG. 12 is a diagram illustrating a link length of the robot arm mechanism according to the present embodiment;

FIGS. 13A, 13B and 13C are a diagram illustrating a singular point posture eliminated by the present embodiment;

FIG. 14 is a diagram illustrating a conventional typical vertically articulated robot arm mechanism with symbolic representation; and

FIGS. 15A, 15B and 15C is a diagram illustrating a conventional typical singular point posture.

Hereinafter, a robot arm mechanism according to the present embodiment is described with reference to the accompanying drawings. In the following description, the same reference numerals denote components having substantially identical functions and structures, and the repeated description thereof is made only when necessary.

FIG. 1 is an external perspective view of the robot arm mechanism according to the present embodiment. FIG. 2 and FIG. 3 are diagrams illustrating an internal structure of the robot arm mechanism in FIG. 1 . FIG. 4 is a diagram illustrating the robot arm mechanism in FIG. 1 with symbolic representation. The robot arm mechanism includes a substantially cylindrical base 1 and an arm section 2 connected to the base 1 . A hand end-effector 3 called an end effector is attached to a tip of the robot arm section 2 . In FIG. 1 , a hand section capable of holding an object is shown as the hand end-effector 3 . The hand end-effector 3 is not limited to the hand section, but may be another tool, a camera, or a display. At the tip of the robot arm section 2 , an adapter which can be replaced by any type of the hand end-effector 3 may be provided.

The robot arm section 2 includes a plurality (herein, six) of joints J 1 , J 2 , J 3 , J 4 , J 5 and J 6 . The plurality of the joints J 1 , J 2 , J 3 , J 4 , J 5 and J 6 are arranged in order from the base 1 . Generally, a first axis RA 1 , a second axis RA 2 and a third axis RA 3 are called root three axes, and a fourth axis RA 4 , a fifth axis RA 5 and a sixth axis RA 6 are called wrist three axes which change the posture of the hand section 3 . At least one of the joints J 1 , J 2 and J 3 constituting root three axes is a linear motion joint. Herein, the third joint J 3 is the linear motion joint, particularly a joint with a relatively long extension distance. The first joint J 1 is a revolute joint that rotates on the first axis of rotation RA 1 which is held, for example, perpendicularly to a base surface. The second joint J 2 is a bending joint that rotates on the second axis of rotation RA 2 perpendicular to the first axis of rotation RA 1 . The third joint J 3 linearly extends or contracts along the third axis (axis of movement) RA 3 perpendicular to the second axis of rotation RA 2 . The fourth joint J 4 is a revolute joint that rotates on the fourth axis of rotation RA 4 which matches the third axis of movement RA 3 . The fifth joint J 5 is a bending joint that rotates on the fifth axis of rotation RA 5 orthogonal to the fourth axis of rotation RA 4 . The sixth joint J 6 is a bending joint that rotates on the sixth axis of rotation RA 6 orthogonal to the fourth axis of rotation RA 4 and perpendicular to the fifth axis of rotation RA 5 .

The arm section 2 turns together with the hand section 3 in accordance with rotation of the first joint J 1 . The arm section 2 rotates on the second axis of rotation RA 2 of the second joint J 2 together with the hand section 3 in accordance with rotation of the second joint J 2 . An arm support body (first support body) 11 a forming the base 1 has a cylindrical hollow structure formed around the axis of rotation RA 1 of the first joint J 1 . The first joint J 1 is mounted on a fixed base (not shown). When the first joint J 1 rotates, the first support body 11 a axially rotates together with the turn of the arm section 2 . The first support body 11 a may be fixed on a ground plane. In this case, the arm section 2 turns independently of the first support body 11 a . A second support body 11 b is connected to an upper part of the first support body 11 a.

The second support body 11 b has a hollow structure continuous to the first support body 11 a . One end of the second support body 11 b is attached to a rotating section of the first joint J 1 . The other end of the second support body 11 b is open, and a third support body 11 c is set rotatably on the axis of rotation RA 2 of the second joint J 2 . The third support body 11 c has a scaly hollow structure communicating with the first support body 11 a and the second support body 11 b . In accordance with the bending rotation of the second joint J 2 , a rear part of the third support body 11 c is accommodated in or sent out from the second support body 11 b . The rear part of the third joint J 3 which constitutes a linear motion joint of the arm section 2 is housed inside the continuous hollow structure of the first support body 11 a and the second support body 11 b by contraction thereof.

The first joint J 1 includes an annular fixed section and a rotating section and is fixed to a base at the fixed section. The first support body 11 a and the second support body 11 b are attached to the rotating section. When the first joint J 1 rotates, the first support body 11 a , the second support body 11 b and the third support body 11 c turn around the first axis of rotation RA 1 together with the arm section 2 and the hand section 3 .

The third support body 11 c is set rotatably, at the lower part of its rear end, on the axis of rotation RA 2 with respect to a lower side of an open end of the second support body 11 b . In this way, the second joint J 2 serving as the bending joint that rotates on the axis of rotation RA 2 , is formed. When the second joint J 2 rotates, the arm section 2 rotates vertically (in other words, undulates) on the axis of rotation RA 2 of the second joint J 2 together with the hand section 3 . The axis of rotation RA 2 of the second joint J 2 is perpendicular to the first axis of rotation RA 1 of the first joint J 1 serving as a revolute joint.

As described above, the third joint J 3 serving as a joint section constitutes a main constituent of the arm section 2 . The hand section 3 described above is provided at the tip of the arm section 2 . Rotation, bending and extension and contraction of the first to sixth joints J 1 -J 6 enable positioning two-fingered hand 16 of the hand section 3 at any position and posture. In particular, the linear extension and contraction distance of the third joint J 3 enables the hand section 3 to act on an object in a wide range from a position close to the base 1 to a position far from the base 1 .

The third joint J 3 is characterized by the linear extension and contraction distance realized by a linear extension and contraction arm mechanism constituting the third joint J 3 . The linear extension and contraction distance is achieved by the structure shown in FIG. 2 and FIG. 3 . The linear extension and contraction arm mechanism includes a first connection piece column 21 and a second connection piece column 20 . In an alignment pose where the arm section 2 is horizontally positioned, the first connection piece column 21 is located below the second connection piece column 20 , and the second connection piece column 20 is located on the top of the first connection piece column 21 .

The first connection piece column 21 includes a plurality of first connection pieces 23 having the same U-shaped cross section and connected in a column by pins at their back surface parts. The first connection piece column 21 is bendable in its back surface direction BD but, conversely, not bendable in its front surface direction FD due to the shape of the cross section of the first connection piece 23 and connection positions by the pins. The second connection piece column 20 has a substantially flat plate shape with a width substantially equivalent to that of the first connection piece 23 , and includes a plurality of second connection pieces 22 connected in a column by pins in a bendable state in both the back surface direction and the front surface direction. The first connection piece column 21 is joined to the second connection piece column 20 at the tip part by a joining piece 26 . The joining piece 26 has an integrated shape of the first connection piece 23 and the second connection piece 22 . When the second connection piece column 20 is sent out from the third support body 11 c together with the first connection piece column 21 starting with the joining piece 26 , the first connection piece column 21 and the second connection piece column 20 are jointed to each other. The first connection piece column 21 and the second connection piece column 20 are joined at their tip parts by the joining piece 26 , and are each held in a jointed state at their rear part by being firmly held inside the third support body 11 c and prevented from being pulled out. When the first connection piece column 21 and the second connection piece column 20 are held in the jointed state, the bending of the first connection piece column 21 and the second connection piece column 20 is restricted, whereby the first connection piece column 21 and the second connection piece column 20 constitute a columnar body having a certain stiffness. When the first connection piece column 21 and the second connection piece column 20 are separated from each other, the bending restriction is canceled, and the bendable state thereof is restored. The first connection piece column 21 and the second connection piece column 20 are joined in the vicinity of the opening of the third support body 11 c and are sent out. The first connection piece column 21 and the second connection piece column 20 are separated from each other in the third support body 11 c , and each become bendable. The first connection piece column 21 and the second connection piece column 20 are bent individually and accommodated in the first support body 11 a as separate bodies.

As shown in FIG. 2 , a linear gear 22 a is formed on the inside of each of the second connection pieces 22 . The linear gears 22 a are connected to form a continuous linear gear when the second connection piece column 20 has a linear shape. As shown in FIG. 3 , the second connection piece 22 is sandwiched between a roller R 1 and a drive gear 24 a inside the third support body 11 c . The linear gear 22 a is engaged with the drive gear 24 a . The second connection piece column 20 is sent out from the third support body 11 c together with the first connection piece column 21 by forward rotation of the drive gear 24 a by a motor M 1 . At that time, the first connection piece column 21 and the second connection piece column 20 are sandwiched between a pair of an upper roller R 2 and a lower roller R 4 provided in the vicinity of the opening of the third support body 11 c , are pressed against each other, and are linearly sent out in a joined state along the third axis of movement RA 3 . The reverse rotation of the drive gear 24 a by a motor M 1 causes cancellation of the joined state of the second connection piece column 20 and the first connection piece column 21 and separation thereof in the third support body 11 c behind the upper roller R 2 and the lower roller R 4 . The separated second connection piece column 20 and first connection piece column 21 restore their bendable state, and are guided by guide rails provided inside the second support body 11 b and the third support body 11 c to be bent in a direction along the first axis of rotation RA 1 and housed inside the first support body 11 a.

The hand section 3 is provided at the tip of the arm section 2 as shown in FIG. 1 . The hand section 3 is moved to a given position by the first joint J 1 , the second joint J 2 and the third joint J 3 , and is positioned to take a given posture by the fourth joint J 4 , the fifth joint J 5 and the sixth joint J 6 . The hand section 3 has two fingers 16 a and 16 b configured to be opened and closed. The fourth joint J 4 is a revolute joint having the axis of rotation RA 4 which typically matches a center axis of the arm section 2 along the extension and retraction direction of the arm section 2 , that is, the axis of movement RA 3 of the third joint J 3 . When the fourth joint J 4 rotates, the hand section 3 rotates on the axis of rotation RA 4 from the fourth joint J 4 to the tip thereof.

The fifth joint J 5 is a bending joint having the axis of rotation RA 5 orthogonal to the axis of rotation RA 4 of the fourth joint J 4 . When the fifth joint rotates, the hand section 3 rotates up and down. The sixth joint J 6 is a revolute joint having the axis of rotation RA 6 orthogonal to the axis of rotation RA 4 of the fourth joint J 4 and perpendicular to the axis of rotation RA 5 of the fifth joint J 5 . When the sixth joint J 6 rotates, the hand 16 turns left and right.

FIG. 4 is a diagram illustrating the robot arm mechanism in FIG. 1 with symbolic representation. The robot arm mechanism realizes three-degree-of-freedom of position and three-degree-of-freedom of posture by the first joint J 1 , the second joint J 2 and the third joint J 3 which constitute the root three axes, and the fourth joint J 4 , the fifth joint J 5 and the sixth joint J 6 which constitute the wrist three axes. The first joint J 1 is arranged between the first support body 11 a and the second support body 11 b and is formed as a revolute joint that rotates on the axis of rotation RA 1 . The axis of rotation RA 1 is perpendicular to a base plane BP of the base on which the fixed section of the first joint J 1 is installed. Z axis is defined to be parallel to the axis of rotation RA 1 . For convenience of description, a rotational coordinate system (XYZ) that rotates together with the rotation of the first joint J 1 which rotates on the Z axis is defined.

The second joint J 2 is formed as a bending joint that rotates on the axis of rotation RA 2 . The axis of rotation RA 2 of the second joint J 2 is parallel to the X axis in the rotational coordinate system. The axis of rotation RA 2 of the second joint J 2 is perpendicular to the axis of rotation RA 1 of the first joint J 1 . Furthermore, the axis of rotation RA 2 of the second joint J 2 is away from the axis of rotation RA 1 of the first joint J 1 in the Y axis direction. In other words, the axis of rotation RA 2 of the second joint J 2 is away from the axis of rotation RA 1 of the first joint J 1 in a direction orthogonal to the axis of rotation RA 1 of the first joint J 1 and the axis of rotation RA 2 of the second joint J 2 . In that direction, the axis of rotation RA 2 of the second joint J 2 is a predetermined distance (offset distance) L 1 away from the axis of rotation RA 1 of the first joint J 1 . Thus, the second joint J 2 is arranged in a state in which the axis of rotation RA 2 thereof does not intersect with the axis of rotation RA 1 of the first joint J 1 (offset). The second support body 11 b and the first support body 11 a are configured in such a manner that the axis of rotation RA 2 of the second joint J 2 is offset with respect to the axis of rotation RA 1 of the first joint J 1 by an offset distance L 1 in the above-described direction. A virtual arm rod section (link part) for connecting the second joint J 2 to the first joint J 1 has a crank shape formed by combining two hook shaped bodies with tips bent into right angles. The virtual arm rod section is formed by the first support body 11 a and the second support body 11 b each of which includes a hollow structure.

Structurally arranging the second joint J 2 with respect to the first joint J 1 in such a manner that the axis of rotation RA 2 of the second joint J 2 is offset with respect to the axis of rotation RA 1 of the first joint J 1 as described above includes not only arranging a structural center of the second joint J 2 to be offset with respect to a structural center of the first joint J 1 in the Y axis direction by the offset distance L 1 , but also arranging the structural center of the second joint J 2 to be offset also in the X axis direction, that is, the axis of rotation RA 2 of the second joint J 2 , by a given distance.

The third joint J 3 is formed as a linear motion joint that moves along the axis of movement RA 3 . The axis of movement RA 3 of the third joint J 3 is perpendicular to the axis of rotation RA 2 of the second joint J 2 . In the alignment pose in which the rotation angle of the second joint J 2 is zero degree, in other words, the luffing angle of the arm section 2 is zero degree, and the arm section 2 is horizontal, the axis of movement RA 3 of the third joint J 3 is perpendicular to both the axis of rotation RA 1 of the first joint J 1 and the axis of rotation RA 2 of the second joint J 2 . In the rotational coordinate system, the axis of movement RA 3 of the third joint J 3 is parallel to the Y axis which is perpendicular to the X axis and the Z axis. Furthermore, the axis of movement RA 3 of the third joint J 3 is away from the axis of rotation RA 2 of the second joint J 2 in a direction orthogonal to the axis of rotation RA 2 and the axis of movement RA 3 . The distance (offset distance) between the axis of movement RA 3 of the third joint J 3 and the axis of rotation RA 2 of the second joint J 2 is L 2 . The axis of movement RA 3 does not intersect with the axis of rotation RA 2 (offset).

In this way, the axis of movement RA 3 of the third joint J 3 is provided perpendicular to the axis of rotation RA 2 of the second joint J 2 and an offset distance L 2 away from the axis of rotation RA 2 of the second joint J 2 , and the third joint J 3 is structurally arranged with respect to the second joint J 2 in such a manner that the axis of movement RA 3 of the third joint J 3 is positioned with respect to the axis of rotation RA 2 of the second joint J 2 in the above-described way. The virtual arm rod section (link part) that connects the third joint J 3 to the second joint J 2 has a hook-shaped body whose tip is vertically bent. The virtual arm rod section includes the second support body 11 b and the third support body 11 c.

Structurally arranging the third joint J 3 with respect to the second joint J 2 in such a manner that the axis of movement RA 3 of the third joint J 3 is offset with respect to the axis of rotation RA 2 of the second joint J 2 as described above includes not only arranging a center line (axis of movement RA 3 ) of the third joint J 3 to be offset with respect to the structural center of the second joint J 2 only by the offset distance L 2 , but also arranging the center line of the third joint J 3 to be offset also in the X axis direction, that is, the axis of rotation RA 2 of the second joint J 2 , by a given distance.

The fourth joint J 4 is formed as a revolute joint that rotates on the axis of rotation RA 4 . The axis of rotation RA 4 of the fourth joint J 4 substantially matches the axis of movement RA 3 of the third joint J 3 . The fifth joint J 5 is formed as a bending joint that rotates on the axis of rotation RA 5 . The axis of rotation RA 5 of the fifth joint J 5 is substantially orthogonal to the axis of movement RA 3 of the third joint J 3 and the axis of rotation RA 4 of the fourth joint J 4 . The sixth joint J 6 is formed as a revolute joint that rotates on the axis of rotation RA 6 . The axis of rotation RA 6 of the sixth joint J 6 is substantially orthogonal to the axis of rotation RA 4 of the fourth joint J 4 and the axis of rotation RA 5 of the fifth joint J 5 . The sixth joint J 6 is provided to turn the hand section 3 serving as a hand end-effector and may be installed as a bending joint of which axis of rotation RA 6 is substantially orthogonal to the axis of rotation RA 4 of the fourth joint J 4 and the axis of rotation RA 5 of the fifth joint J 5 .

As shown in FIGS. 5A, 5B , the offset distance L 1 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 is different from the offset distance L 2 of the axis of movement RA 3 of the third joint J 3 with respect to the axis of rotation RA 2 of the second joint J 2 . As shown in FIG. 5A , the offset distance L 1 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 is set to be longer than the offset distance L 2 of the axis of movement RA 3 of the third joint J 3 with respect to the axis of rotation RA 2 of the second joint J 2 . As shown in FIG. 5B , the offset distance L 1 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 is set to be shorter than the offset distance L 2 of the axis of movement RA 3 of the third joint J 3 with respect to the axis of rotation RA 2 of the second joint J 2 .

As shown in FIG. 6A , the offset distance L 1 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 may be maintained at a predetermined value, and the offset distance L 2 of the axis of movement RA 3 of the third joint J 3 with respect to the axis of rotation RA 2 of the second joint J 2 may be set to zero. In other words, the axis of movement RA 3 of the third joint J 3 may be orthogonal to the axis of rotation RA 2 of the second joint J 2 by offsetting the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 and not offsetting the axis of movement RA 3 of the third joint J 3 with respect to the axis of rotation RA 2 of the second joint J 2 . As shown in FIG. 6B , the offset distance L 2 of the axis of movement RA 3 of the third joint J 3 with respect to the axis of rotation RA 2 of the second joint J 2 may be maintained at a predetermined value, and the offset distance L 1 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 may be set to zero. In other words, the axis of movement RA 2 of the second joint J 2 may be orthogonal to the axis of rotation RA 1 of the first joint J 1 by offsetting the axis of movement RA 3 of the third joint J 3 with respect to the axis of rotation RA 2 of the second joint J 2 and not offsetting the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 .

In the present embodiment, at least one bending joint of the plurality of joints J 1 -J 6 , specifically, root three axes is replaced with a linear motion joint, as shown in FIGS. 5A, 5B , the axis of rotation RA 2 of the second joint J 2 is separated from the axis of rotation RA 1 of the first joint J 1 only by offset distance L 1 , and the axis of movement RA 3 of the third joint J 3 is separated from the axis of rotation RA 2 of the second joint J 2 only by offset distance L 2 different from offset distance L 1 . In the present embodiment, as shown in FIGS. 6 a , 6 B, either one of offset distance L 1 and offset distance L 2 is set to zero, and the axis of rotation RA 2 is separated from the axis of rotation RA 1 or the axis of movement RA 3 is separated from the axis of rotation RA 2 . Thereby as shown in FIGS. 5A,5B and FIGS. 6A, 6B , even if bending joints J 2 and J 5 are rotated to maximally extend the arm section 2 , as the arrangement in which the axis of rotation RA 1 of a revolute joint J 1 is deviated from the axis of rotation RA 4 of the other revolute joint J 4 by a difference between offset distance L 1 and offset distance L 2 is realized. As shown in FIGS. 13A and 13B , it is possible to structurally eliminate the singular point posture without aligning the axis of rotation RA 1 of the revolute joint J 1 and the axis of rotation RA 4 of the revolute joint J 4 in a straight line.

Furthermore, the posture in which the axes of rotation RA 2 and RA 5 of bending joints J 2 and J 5 are aligned in the straight line in a vertical direction as shown in FIG. 7 may appear to be a singular point posture; however, in the present embodiment, as the alignment can be avoided by the extension and contraction of the third joint J 3 by setting the third joint J 3 as a linear motion joint, it should be easy to understand that the above posture is not a singular point posture, and a singular point posture can be effectively structurally eliminated.

Furthermore, in the present embodiment, as shown in FIGS. 8A and 8B , when the offset distance L 1 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 is set to be longer than the offset distance L 2 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 , the fifth joint J 5 and the sixth joint J 6 are arranged in such a manner that a distance L 3 between the axis of rotation RA 5 of the fifth joint J 5 and the axis of rotation RA 6 of the sixth joint J 6 is different from a difference (L 1 −L 2 ) between offset distance L 1 and offset distance L 2 . As shown in FIG. 8A , the distance L 3 between the axis of rotation RA 5 of the fifth joint J 5 and the axis of rotation RA 6 of the sixth joint J 6 is set to be shorter than the difference (L 1 −L 2 ) between offset distance L 1 and offset distance L 2 , or as shown in FIG. 8B , the distance L 3 between the axis of rotation RA 5 of the fifth joint J 5 and the axis of rotation RA 6 of the sixth joint J 6 is set to be longer than the difference (L 1 −L 2 ) between offset distance L 1 and offset distance L 2 .

Similarly, as shown in FIGS. 9A, 9B , when the offset distance L 1 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 is set to be shorter than the offset distance L 2 of the axis of rotation RA 2 of the second joint J 2 with respect to the axis of rotation RA 1 of the first joint J 1 , the fifth joint J 5 and the sixth joint J 6 are arranged in such a manner that the distance L 3 between the axis of rotation RA 5 of the fifth joint J 5 and the axis of rotation RA 6 of the sixth joint J 6 is different from a difference (L 2 −L 1 ) between offset distance L 1 and offset distance L 2 . As shown in FIG. 9A , the distance L 3 between the axis of rotation RA 5 of the fifth joint J 5 and the axis of rotation RA 6 of the sixth joint J 6 is set to be shorter than the difference (L 2 −L 1 ) between offset distance L 1 and offset distance L 2 , or as shown in FIG. 9B , the distance L 3 between the axis of rotation RA 5 of the fifth joint J 5 and the axis of rotation RA 6 of the sixth joint J 6 is set to be longer than the difference (L 2 −L 1 ) between offset distance L 1 and offset distance L 2 .

When the distance L 3 between the axis of rotation RA 5 and the axis of rotation RA 6 is substantially equal to the difference between the offset distance L 1 and the offset distance L 2 , as shown in FIG. 13A , in a case in which bending joint J 2 is rotated by 90 degrees, and bending joint J 5 is rotated by 90 degrees in a reverse direction from the alignment pose, or as shown in FIG. 13B , bending joint J 2 is rotated by 90 degrees, and bending joint J 5 is rotated by 90 degrees in the same direction from the alignment pose, a singular point posture in which the axis of rotation RA 1 of revolute joint J 1 and the axis of rotation RA 6 of revolute joint J 6 are aligned in the straight line is generated. However, as shown in FIGS. 8A, 8B and FIGS. 9A, 9B , by arranging the fifth joint J 5 and the sixth joint J 6 in such a manner that the distance L 3 between the axis of rotation RA 5 and the axis of rotation RA 6 is different from the difference between offset distance L 1 and offset distance L 2 , as shown in FIG. 8A and FIG. 9A , the axis of rotation RA 1 of revolute joint J 1 and the axis of rotation RA 6 of revolute joint J 6 can be offset only by a distance obtained by subtracting the distance L 3 between the axis of rotation RA 5 and the axis of rotation RA 6 from the difference between offset distance L 1 and offset distance L 2 , and it is possible to structurally eliminate the singular point posture in which the axis of rotation RA 1 of revolute joint J 1 and the axis of rotation RA 6 of revolute joint J 6 are aligned in a straight line. Similarly, as shown in FIG. 8B and FIG. 9B , the axis of rotation RA 1 of revolute joint J 1 and the axis of rotation RA 6 of revolute joint J 6 can be offset only by a distance obtained by subtracting the difference between offset distance L 1 and offset distance L 2 from the distance L 3 between the axis of rotation RA 5 and the axis of rotation RA 6 , and it is possible to structurally eliminate the singular point posture in which the axis of rotation RA 1 of revolute joint J 1 and the axis of rotation RA 6 of revolute joint J 6 are aligned in a straight line.

Furthermore, under a specific condition exemplified in FIG. 10 , a structure in which the distance L 3 between the axis of rotation RA 5 of bending joint J 5 and the axis of rotation RA 6 of bending joint J 6 is equal to the difference (L 1 −L 2 ) between offset distance L 1 and offset distance L 2 may be adopted. Of course, there is a structural rotation limit on the luffing angle (rotation angle) θ1 of bending joint J 2 . The luffing angle (rotation angle) θ1 of bending joint J 2 is an angle expressed by defining the angle of the time when the arm section 2 is in a horizontal posture, that is, the axis of movement RA 3 of the linear motion joint J 3 is horizontal, as zero degree, and defining angles above zero degree as plus angles and angles below zero degree as minus angles. The rotation angle θ2 of bending joint J 5 is an angle expressed by defining the angle of the time when an axis between centers (link axis) LA 56 between bending joint J 5 and revolute joint J 6 matches the axis of movement RA 3 of the linear motion joint J 3 as zero degree and defining angles above zero degree as plus angles and angles below zero degree as minus angles. In FIG. 10 , the maximum luffing angle (maximum rotation angle) is expressed as θ1 max. There is also a structural rotation limit on the rotation angle θ2 of bending joint J 5 , and the maximum rotation angle thereof is expressed as θ2 max. In a posture in which revolute joint J 4 is a reference angle, in other words, the axis of rotation RA 5 of bending joint J 5 is parallel to the axis of rotation RA 2 of bending joint J 2 , under the condition where even the maximum rotation angle θ1 max of bending joint J 2 and the maximum rotation angle θ2 max of bending joint J 5 cannot make the link axis LA 56 of bending joint J 5 and revolute joint J 6 horizontal, the axis of rotation RA 6 of revolute joint J 6 never becomes parallel to the axis of rotation RA 1 of revolute joint J 1 , and the posture cannot be the singular point posture. Typically, the maximum rotation angle θ1 max of bending joint J 2 is less than 90 degrees, and the maximum rotation angle θ2 max of bending joint J 5 is less than (90°+(90°−θ1 max)). Under this condition, in the robot arm mechanism according to the present embodiment, the distance L 3 between the axis of rotation RA 5 of bending joint J 5 and the axis of rotation RA 6 of revolute joint J 6 may be equal to the difference (L 1 −L 2 ) between offset distance L 1 and offset distance L 2 .

As shown in FIG. 13C , when bending joint J 2 is rotated to an angle other than 90 degrees and bending joint J 5 is further rotated so that the axis of rotation RA 6 of revolute joint J 6 becomes vertical from the alignment pose, the singular point posture in which the axis of rotation RA 1 of revolute joint J 1 and the axis of rotation RA 6 of revolute joint J 6 are aligned in a straight line can occur.

In the present embodiment, as shown in FIG. 11 , in order to prevent the singular point posture from occurring in structure, a combination of link lengths (distances between joint centers) d 0 -d 5 is adjusted so that the axis of rotation RA 6 of revolute joint J 6 stops in the front of the axis of rotation RA 1 of revolute joint J 1 in a state in which bending joint J 2 is rotated to the maximum luffing angle θmax (in this case, over 90°) of the structure. As shown in FIG. 12 , d 0 is the link length between the first joint J 1 and the second joint J 2 , d 1 is the link length between the first joint J 1 and the second joint J 2 , d 2 is the link length between the second joint J 2 and the third joint J 3 , d 3 +Δd (Δd is the maximum extension distance of the linear motion joint J 3 ) is the link length between the second joint J 2 and the fourth joint J 4 , d 4 is the link length between the fourth joint J 4 and the fifth joint J 5 , and d 5 is the link length between the fifth joint J 5 and the sixth joint J 6 .

According to the present embodiment, it is possible to eliminate or reduce occurrence of various singular point postures within the movable range by measures taken regarding the structure.

While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.