Aerotech UNIDEX 600 Series, Руководство пользователя

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AerTune U600 User’s Guide
5-14
Aerotech, Inc.
Version 1.4
5.4.2.6. # Points to Collect in AutoTune
The # Points to Collect parameter determines how many data points that the AutoTune
program collects. The Gain calculations will be more accurate with more data points
collected. The number of points indirectly adjusts the length of time that the sinusoidal
input is entered into the system. 7500 points result in a system excitation of 7.5 seconds in
length (the data is sampled at 1 msec). The default number of points will work well in
almost all cases, and there is a point of diminishing returns if too many points are
collected. Two exceptions are where the Starting Frequency is very low, or, where
AutoTune Convergence errors have been previously displayed. In these cases, more
points may assist the AutoTuning algorithm to come to a correct set of servo loop gains.
5.4.3. Tuning Parameters
The following fields are available on the AutoTune screen.
5.4.3.1. Velocity Bandwidth
The Velocity Bandwidth parameter is used to set the desired closed-loop bandwidth of the
Velocity Loop. The default value is a good starting point in most cases. For systems that
require very fast movement or are very lightly damped, the bandwidth setting will most
likely need to be increased. On very large systems (i.e., a large gantry system) or systems
that do not require fast moves, the bandwidth may need to be reduced for optimum
performance.
The Position Loop Bandwidth is automatically determined based on the desired Velocity
Bandwidth setting and will be chosen to be approximately 20% of the velocity loop
bandwidth. It has been found that this Position Loop Bandwidth will give very good
performance in almost all cases. If needed, the user can manually raise or lower the
PGAIN after AutoTuning has been completed to adjust the Position Loop bandwidth.
Look at bandwidth from the response time point-of-view. A good approximation for the
rise time (10% to 90% of the move) of a system given a certain Position Loop bandwidth
(w
pos
) is t
rise
(sec) =1.8 / w
pos
. This presumes that the axis parameters such as ACCEL,
DECEL, etc. are properly set, so as not to unnecessarily slow down the speed of motion.
5.4.3.2. Damping
The Damping factor parameter determines the damping of the system. This damping
factor is sometimes referred to as Zeta (x) in control literature. A damping factor of 0 will
result in a system with no damping, large overshoot, and very oscillatory behavior. A
damping factor of 1 will result in smooth system response with very little, if any,
overshoot. Damping factors >1 can also be used and will result in an over-damped system
which will have no overshoot, but will also have a slower response.
Axes with larger inertia, such as an X axis with a Y and a vertically mounted Z axis, will
have more optimal gains calculated by the algorithm if the damping factor is much higher
(3.4 or greater), assuming the motor/drive can produce the required torque. Most likely,
you will need to sacrifice damping and reduce the damping factor to 0.4.
Typically, the value of useful damping factors will be between 0.5 and 1.0. As the
damping factor is reduced towards 0, the system step response will be quicker at the
expense of larger overshoot and longer settling times. As the damping factor is increased