321 kinematic structure
Encyclopedia
321 kinematic structure is a design method for robot
ic arms (serial manipulator
s), invented by Donald L. Pieper and used in most commercially produced robotic arms. The inverse kinematics
of serial manipulators with six revolute joint
s, and with three consecutive joints intersecting, can be solved in closed form
, i.e. a set of equations can be written that give the joint positions required to place the end of the arm in a particular position and orientation. An arm design that does not follow these design rules typically requires an iterative algorithm to solve the inverse kinematics problem.
The 321 design is an example of a 6R wrist-partitioned manipulator: the three wrist joints intersect, the two shoulder and elbow joints are parallel, the first joint intersects the first shoulder joint orthogonally (at a right angle). Many other industrial robots, such as the PUMA
, have a kinematic structure that deviates a little bit from the 321 structure. The offsets move the singular positions of the robot away from places in the workspace where they are likely to cause problems.
Robot
A robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...
ic arms (serial manipulator
Serial manipulator
Serial manipulators are by far the most common industrial robots. Often they have an anthropomorphic mechanical arm structure, i.e. a serial chain of rigid links, connected by joints, forming a "shoulder", an "elbow", and a "wrist"....
s), invented by Donald L. Pieper and used in most commercially produced robotic arms. The inverse kinematics
Inverse kinematics
Inverse kinematics is a subdomain of kinematics, which is of particular interest in robotics and computer animation. In contrast to forward kinematics, which calculates the position of a body after a series of motions, inverse kinematics calculates the motions necessary to achieve a desired...
of serial manipulators with six revolute joint
Revolute joint
A revolute joint is a one degree of freedom kinematic pair used in mechanisms. Revolute joints provide single-axis rotation function used in many places such as door hinges, folding mechanisms, and other uni-axial rotation devices. -See also:* Cylindrical joint* Kinematics* Degrees of freedom *...
s, and with three consecutive joints intersecting, can be solved in closed form
Closed-form expression
In mathematics, an expression is said to be a closed-form expression if it can be expressed analytically in terms of a bounded number of certain "well-known" functions...
, i.e. a set of equations can be written that give the joint positions required to place the end of the arm in a particular position and orientation. An arm design that does not follow these design rules typically requires an iterative algorithm to solve the inverse kinematics problem.
The 321 design is an example of a 6R wrist-partitioned manipulator: the three wrist joints intersect, the two shoulder and elbow joints are parallel, the first joint intersects the first shoulder joint orthogonally (at a right angle). Many other industrial robots, such as the PUMA
Programmable Universal Machine for Assembly
The PUMA is an industrial robot arm developed by Victor Scheinman at pioneering robot company Unimation...
, have a kinematic structure that deviates a little bit from the 321 structure. The offsets move the singular positions of the robot away from places in the workspace where they are likely to cause problems.