Fig. 38.15 shows the schematic form of robot with jointed- spherical co-ordinated system which is frequently used in many applications. It will be noted that this configuration consists of a base or trunk, an upper arm and a forearm which move in a vertical plane through the trunk. Further, an elbow joint is located between the forearm and upper arm and a shoulder joint is located between the upper arm and the trunk.
Rotary motion in the horizontal plane is also provided at the shoulder joint. The work envelope approximates a portion of a sphere. This configuration can operate in a large working volume for its size giving greater reach and thus greater application flexibility. It is also possible for the forearm to reach down into or onto objects as easily as if the robot were mounted overhead.
The links comprise the major axes and offer desired ‘degrees or freedom’ of the robot. As many as three additional degrees of freedom are provided at the extremity of the robot arm, the unit commonly called the ‘wrist’. Wrist axes include ‘roll’ (rotation in a plane perpendicular to the plane of the arm), ‘pitch’ (rotation in a vertical plane through the arm), and ‘yaw’ (rotation in a horizontal plane through the arm).
ADVERTISEMENTS:
Additional motions are possible by mounting the robot on a two-axis table or on a track on the floor or overhead. Many of the robots available are ‘modular’ in design and the user may select as few as two or as many as seven or eight degrees of freedom, depending upon his needs.