Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 1 Motor and Motion Control Systems 9
• In derivative control the signal that drives the motor is proportional
to the time derivative of the difference between the input command
and the measured actual output.
• In proportional-integral-derivative (PID) control the signal that
drives the motor equals the weighted sum of the difference, the time
integral of the difference, and the time derivative of the difference
between the input command and the measured actual output.
Open-Loop Motion Control Systems
A typical open-loop motion control system includes a stepper motor with
a programmable indexer or pulse generator and motor driver, as shown in
Figure 1-9. This system does not need feedback sensors because load
position and velocity are controlled by the predetermined number and
direction of input digital pulses sent to the motor driver from the controller.
Because load position is not continuously sampled by a feedback
sensor (as in a closed-loop servosystem), load positioning accuracy is
lower and position errors (commonly called step errors) accumulate over
time. For these reasons open-loop systems are most often specified in
applications where the load remains constant, load motion is simple, and
low positioning speed is acceptable.
Figure 1-9 Block diagram of
an open-loop motion control
system.
Kinds of Controlled Motion
There are five different kinds of motion control: point-to-point, sequencing,
speed, torque, and incremental.
• Inpoint-to-point motion control the load is moved between a
sequence of numerically defined positions where it is stopped before
it is moved to the next position. This is done at a constant speed, with
both velocity and distance monitored by the motion controller. Pointto-point
positioning can be performed in single-axis or multiaxis systems
with servomotors in closed loops or stepping motors in open