Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

8 Chapter 1 Motor and Motion Control Systems
Figure 1-8 Servomotors are
accelerated to constant velocity
and decelerated along a trapezoidal
profile to assure efficient
operation.
vomotor, the motion controller must command the motor amplifier to
ramp up motor velocity gradually until it reaches the desired speed and
then ramp it down gradually until it stops after the task is complete. This
keeps motor acceleration and deceleration within limits.
The trapezoidal profile, shown in Figure 1-8, is widely used because it
accelerates motor velocity along a positive linear “up-ramp” until the
desired constant velocity is reached. When the motor is shut down from
the constant velocity setting, the profile decelerates velocity along a negative
“down ramp” until the motor stops. Amplifier current and output
voltage reach maximum values during acceleration, then step down to
lower values during constant velocity and switch to negative values during
deceleration.
Closed-Loop Control Techniques
The simplest form of feedback is proportional control, but there are also
derivative and integral control techniques, which compensate for certain
steady-state errors that cannot be eliminated from proportional control.
All three of these techniques can be combined to form proportionalintegral-derivative
(PID) control.
• In proportional control the signal that drives the motor or actuator is
directly proportional to the linear difference between the input command
for the desired output and the measured actual output.
• In integral control the signal driving the motor equals the time integral
of the difference between the input command and the measured
actual output.