Control Techniques Epsilon EP-P, Reference Manual

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Epsilon EP-P Drive Reference Manual
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www.controltechniques.com Revision: A4
If estimated, always use a conservative (less than or equal to actual) estimate. If the friction is completely unknown, a value of zero should be
used. A typical value used here would be less than one percent.
If the value entered is higher than the actual, system oscillation is likely. If the value entered is lower than the actual a more sluggish response
is likely but generally results in good operation.
Response
The Response adjusts the velocity and position loop bandwidths with a range of 1 to 500 Hz. In general, it affects how quickly the drive will
respond to commands, load disturbances and velocity corrections. The Response bandwidth is set to the Response value. It reflects both the
velocity command and the load disturbance correction bandwidth. Increasing the Response value will increase loop stiffness. The maximum
Response level recommended is approximately 100 Hz.
If the Inertia Ratio and Friction values are exactly correct, changing the Response will not affect the damping (percent of overshoot and
number of ringout cycles) to velocity command changes or load disturbance corrections but will affect their cycle frequency. The response level
generally should be decreased as the load to motor inertia ratio increases.
Feedforwards
Feedforward gains are essentially open loop gains that generate torque commands based on the commanded velocity, accel/decel and the
known load parameters (Inertia Ratio and Friction). Using the feedforwards reduces velocity error during steady state and reduces overshoot
during ramping. This is because the Feedforwards do not wait for error to build up to generate current commands.
Feedforwards should be disabled unless the absolute maximum performance is required from the system. Using them reduces the forgiveness
of the servo loop and can create instability if the actual inertia and/or friction of the machine varies greatly during operation or if the Inertia Ratio
or Friction parameters are not correct.
The internal feedforward velocity and acceleration gains are calculated by using the Inertia Ratio and Friction parameters. The feedforward
acceleration gain is calculated from the Inertia Ratio parameter and the feedforward velocity gain is calculated from the Friction parameter.
When Feedforwards are enabled, the accuracy of the Inertia Ratio and Friction parameters is very important. If the Inertia Ratio parameter is
larger than the actual inertia, the result would be a significant velocity overshoot during ramping. If the Inertia parameter is smaller than the
actual inertia, velocity error during ramping will be reduced but not eliminated. If the Friction parameter is greater than the actual friction, it may
result in velocity error or instability. If the Friction parameter is less than the actual friction, velocity error will be reduced, but not eliminated.
Low Pass Filter Group
The Low Pass Filter will reduce machine resonance due to mechanical coupling and other flexible drive/load components by filtering the
command generated by the velocity loop. A check box on the Tuning view enables a low pass filter applied to the output of the velocity
command before the torque compensator. The low pass filter frequency parameter defines the low pass filter cut-off frequency. Signals
exceeding this frequency will be filtered at a rate of 40 dB per decade. The default value is 600Hz.
6.7 Determining Tuning Parameter Values
For optimum performance you will need to enter the actual system parameters into the drive. This section discusses the methods which will
most accurately determine those parameters.
NOTE
If you have an application which exerts a constant unidirectional loading throughout the travel such as in a vertical axis, the inertia tests must
be performed in both directions to cancel out the unidirectional loading effect.
Initial Test Settings
When running the tests outlined in this section, the motor and drive must be operational so you will need to enter starting values.
If your application has less than a 10:1 inertia mismatch, the default parameter settings will be acceptable. If the inertial mismatch is greater
than 10:1, use the following table for initial parameter settings.
Determining Friction
This parameter represents friction that increases proportionally as motor velocity increases. The viscous friction of your system can be
determined by reading the percent of continuous torque required to operate the loaded motor at two different speeds.
Parameter Setting
Friction 0.00
Inertia Ratio 1/3 to 1/2 Actual
Response 500/Inertia Ratio
Feedforwards Enabled