Joint Notation Scheme
A robot joint is a mechanism that permits relative movement between parts of a robot arm. The joints of a robot are designed to enable the robot to move its end-effector along a path from one position to another as desired.
The basic movements required for a desired motion of most industrial robots are:
1. Rotational movement: This enables the robot to place its arm in any direction on a horizontal plane.
2. Radial movement: This enables the robot to move its end-effector radially to reach distant points.
3. Vertical movement: This enables the robot to take its end-effector to different heights.
4. These degrees of freedom, independently or in combination with others, define the complete motion of the end-effectors.
These motions are accomplished by movements of individual joints of the robot arm. The joint movements are basically the same as relative motion of adjoining links. Depending on the nature of this relative motion, the joints are classified as prismatic or revolute.
Prismatic joints are also known as sliding as well as linear joints. They are called prismatic because the cross section of the joint is considered as a generalized prism. They permit links to move in a linear relationship.
Revolute joints permit only angular motion between links. Their variations include:
Rotational joint (R)
Twisting joint (T)
Revolving joint (V)
In a prismatic joint, also known as a sliding or linear joint (L), the links are generally parallel to one another. In some cases, adjoining links are perpendicular but one link slides at the end of the other link.
The joint motion is defined by sliding or translational movements of the links. The orientation of the links remains the same after the joint movement, but the lengths of the links are altered.
A rotational joint (R) is identified by its motion, rotation about an axis perpendicular to the adjoining links. Here, the lengths of adjoining links do not change but the relative position of the links with respect to one another changes as the rotation takes place.
A twisting joint (T) is also a rotational joint, where the rotation takes place about an axis that is parallel to both adjoining links.
A revolving joint (V) is another rotational joint, where the rotation takes place about an axis that is parallel to one of the adjoining links. Usually, the links are aligned perpendicular to one another at this kind of joint. The rotation involves revolution of one link about another.