User Manual

Selecting the Motor Control Modes
Advanced Digital Motor Controller User Manual 91
Closed Loop Speed Position Control
In this mode, the controller computes the position at which the motor must be at every
1ms. Then a position loop compares that expected position with the current position and
applies the necessary power level in order for the motor to reach that position. This mode
is especially effective for accurate control at very slow speeds. Details on this mode can
be found in Closed Loop Speed and Speed-Position Modes on page 133.
Position Counter
Trajectory
Speed
Command
PWM
Motor
Position Feedback
Expected
Position
-
PID
FIGURE 7-5: Closed Loop Speed Position mode
Closed Loop Position Relative Control
In this mode, illustrated in Figure 7-6, the axle of a geared down motor is typically cou-
pled to a position sensor that is used to compare the angular position of the axle versus
a desired position. The motor will move following a controlled acceleration up to a user
defined velocity and decelerate to smoothly reach the desired destination. This feature of
the controller makes it possible to build ultra-high torque “jumbo servos” that can be used
to drive steering columns, robotic arms, life-size models and other heavy loads. Details on
how to wire the position sensing potentiometers and operating in this mode can be found
in “Closed Loop Relative and Tracking Position Modes” on page 141.
Position Sensor
Gear box
Position Feedback
FIGURE 7-6. Motor with potentiometer assembly for position operation
Position Sensor
-1000 to +1000
Position Command
-1000 to +1000 Feedback
Trajectory
PWM
Motor
Expected
Position
-
PID
FIGURE 7-7. Closed Loop Position Relative mode