Page 180 - Concise Encyclopedia of Robotics

Jointed Geometry
the physical location or orientation of the robot has changed within the
work environment.
JOINTED GEOMETRY
See ARTICULATED GEOMETRY.
JOINT-FORCE SENSING
Joint-force sensing keeps a robot joint from exerting too much force. A
feedback system is used. The sensor works by detecting the resistance the
robot arm encounters. As the applied force increases, so does the resist-
ance. The sensor is programmed to reduce or stop the joint if a set
amount of resistance is exceeded.
See also BACK PRESSURE SENSOR.
JOINT-INTERPOLATED MOTION
In a robot arm having more than one joint, the most efficient mode of
operation is known as joint-interpolated motion. In this scheme, the joints
move in such a way that the end effector reaches the required point at the
exact instant that each of the joints has completed its assigned motion.
In order for a multijointed robot arm to position the end effector at
a designated location, each joint must turn through a certain angle.
(For some joints this angle might be zero, representing no rotation.) The
designated location can be reached by any sequence of events such that each
joint rotates through its assigned angle; the same end point will result
whether or not the joints move at the same time. For example, each joint
can rotate through its assigned angle while all the others remain fixed,
but this is a time-consuming and inefficient process. The fastest and most
efficient results are obtained when all the joints begin rotating at a certain
instant in time t 0, and all of them stop rotating at a certain instant t 1,
which is (t 1 t 0) later than t 0.
Suppose a robot arm using articulated geometry has three joints that
rotate through angles X = 39 degrees, Y = 75 degrees, and Z = 51 degrees,
as shown in the illustration. Suppose the end effector is programmed to
reach its end point exactly 3 seconds after the joints begin to rotate. If the
joints rotate at the angular speeds shown (13, 15, and 17 degrees per sec-
ond, respectively), the end effector arrives at its designated stopping
point precisely when each joint has turned through its required angle.
This is an example of joint-interpolated motion.
See also ARTICULATED GEOMETRY and DEGREES OF ROTATION.

JOINT PARAMETERS
The joint parameters of a robot arm or end effector are the scalar values,
usually measured in linear displacement units and angular units, all of

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