User guide

Xenus XTL User Guide Operational Theory
Copley Controls Corp. 9
2.5: Operating Modes
2.5.1: Modes and Control Loops
Nesting of Control Loops and Modes
Copley Controls amplifiers use up to three nested control loops - current, velocity, and position - to
control a motor in three associated operating modes.
Control Loops Illustration
In position mode, the amplifier uses all three loops. As shown below, the position loop drives the
nested velocity loop, which drives the nested current loop.
Target
Position
Position
Command
Actual CurrentDerived VelocityActual Position
Velocity
Command
Cur r ent
Command
Limited
Velocity
Limited
Current
PWM
Command
Trajectory
G
enerator
Position
L
oop
Velocity
L
imiter
Cur rent
L
imiter
Current
L
oop
Motor/
S
ensors
Limits
Velocity
L
oop
FILTER
FILTER
In velocity mode, the velocity loop drives the current loop. In current mode, the current loop is
driven directly by external or internal current commands.
Basic Attributes of All Control Loops
These loops (and servo control loops in general) share several common attributes:
Loop Attribute Description
Command input Every loop is given a value to which it will attempt to control. For example, the velocity loop
receives a velocity command that is the desired motor speed.
Limits Limits are set on each loop to protect the motor and/or mechanical system.
Feedback The nature of servo control loops is that they receive feedback from the device they are
controlling. For example, the position loop uses the actual motor position as feedback.
Gains These are constant values that are used in the mathematical equation of the servo loop. The
values of these gains can be adjusted during amplifier setup to improve the loop
performance. Adjusting these values is often referred to as tuning the loop.
Output The loop generates a control signal. This signal can be used as the command signal to another
control loop or the input to a power amplifier.