Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

10 Chapter 1 Motor and Motion Control Systems
loops. X-Y tables and milling machines position their loads by multiaxis
point-to-point control.
• Sequencing control is the control of such functions as opening and
closing valves in a preset sequence or starting and stopping a conveyor
belt at specified stations in a specific order.
• Speed control is the control of the velocity of the motor or actuator in
a system.
• Torque control is the control of motor or actuator current so that
torque remains constant despite load changes.
• Incremental motion control is the simultaneous control of two or
more variables such as load location, motor speed, or torque.
Motion Interpolation
When a load under control must follow a specific path to get from its
starting point to its stopping point, the movements of the axes must be
coordinated or interpolated. There are three kinds of interpolation: linear,
circular, and contouring.
Linear interpolation is the ability of a motion control system having
two or more axes to move the load from one point to another in a straight
line. The motion controller must determine the speed of each axis so that
it can coordinate their movements. True linear interpolation requires that
the motion controller modify axis acceleration, but some controllers
approximate true linear interpolation with programmed acceleration profiles.
The path can lie in one plane or be three dimensional.
Circular interpolation is the ability of a motion control system having
two or more axes to move the load around a circular trajectory. It
requires that the motion controller modify load acceleration while it is in
transit. Again the circle can lie in one plane or be three dimensional.
Contouring is the path followed by the load, tool, or end- effector
under the coordinated control of two or more axes. It requires that the
motion controller change the speeds on different axes so that their trajectories
pass through a set of predefined points. Load speed is determined
along the trajectory, and it can be constant except during starting and
stopping.
Computer-Aided Emulation
Several important types of programmed computer-aided motion control
can emulate mechanical motion and eliminate the need for actual gears