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Robot Concepts
Breaking Continuous-Path Operation
The “basic” method of moving the robot (see page 82) causes program execution to be
suspended until the current robot motion reaches its destination location and <strong>com</strong>es to a
stop. This is called breaking continuous path. This method is useful when the robot must
be stopped while some operation is performed (for example, closing the gripper or
applying a dot of adhesive).
Joint-Interpolated Motion vs. Straight-Line Motion
The path a motion device takes when moving from one location to another can be either a
joint-interpolated motion or a straight-line motion. A joint-interpolated motion moves
each joint at a constant speed (except during the acceleration/deceleration phases-see
“Speed, Acceleration, and Deceleration” on page 137). With a rotationally-jointed robot,
the robot tool tip typically moves along a curved path during a joint-interpolated motion.
Although such motions can be performed at maximum speed, the nature of the path can
be undesirable.
Straight-line motions ensure that the robot tool tip traces a straight line. That is useful for
cutting a straight line, or laying a bead of sealant, or any other situation where a totally
predictable path is desired.
NOTE: For X, XY, XYZ, or XYZT devices, straight-line motion and
joint-interpolated motion result in identical paths, because the
(positioning) joints all move in straight lines themselves.
When bit N240:3/9 or <strong>Adept</strong>_Motion_Qualifier.9 is OFF, the robot uses joint-interpolated
motion; when that bit is ON, the robot uses straight-line motion.
Performance Considerations
Things that may impact performance in most applications include robot mounting, cell
layout, part handling, and programming approaches.
Robot Mounting Considerations
The mounting surface should be smooth, flat and rigid. Vibration and flexing will affect
performance. It is re<strong>com</strong>mended that a minimum 25mm (1 inch) steel plate with a rigid
tube frame be used. When positioning a robot in the workcell, take advantage of moving
multiple joints for faster motions. On a SCARA robot, the “Z” and “theta” axes are the
slowest, and motion of these joints should be minimized whenever possible. This can be
ac<strong>com</strong>plished by positioning the robot, and setting conveyor heights and pick and place
locations, to minimize Z-axis motion.
Cell Layout Considerations
Regarding cell layout and jointed arms, the same point-to-point distance can result in
different cycle times. Moving multiple joints <strong>com</strong>bines the joint speeds for faster motion.
If the same distance is traversed using motion of a single joint, the motion of that joint will
be longer, and therefore will take more time.
140 <strong>Adept</strong> <strong>Cobra</strong> <strong>PLC600</strong>/PLC800 Robot User’s <strong>Guide</strong>, Rev B