Control Techniques Epsilon EP-P, Reference Manual

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Epsilon EP-P Drive Reference Manual
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Revision A4 www.controltechniques.com
6 Tuning Procedures
The drive uses closed loop controllers to control the position and velocity of the attached motor. These position and velocity
controllers and the associated tuning parameters are in effect when the drive is in velocity or pulse mode and have no effect
when the drive is in Torque mode.
Many closed loop controllers require tuning using individual user-specified proportional, integral and derivative (PID) gains
which require skilled “tweaking” to optimize. The combination of these gains along with the drive gain, motor gain, and motor
inertia, define the system bandwidth. The overall system bandwidth is usually unknown at the end of the tweaking process.
The drive closes the control loops for the user using a state-space pole placement technique. Using this method, the drive’s
position control can be simply and accurately tuned. The overall system’s bandwidth can be defined by a single user-specified
value (Response).
The drive’s default settings are designed to work in applications with up to a 10:1 load to motor inertia mismatch. Most
applications can operate with this default setting.
Some applications may have performance requirements which are not attainable with the factory settings. For these
applications a set of measurable parameters can be specified which will set up the internal control functions to optimize the
drive performance. The parameters include Inertia Ratio, Friction, Response and Line Voltage. All the values needed for
optimization are “real world” values that can be determined by calculation or some method of dynamic measurement.
6.1 PID vs. State-Space
The power of the state-space control algorithm is that there is no guessing and no “fine tuning” as needed with user-specified
PID methods. PID methods work well in controlled situations but tend to be difficult to setup in applications where all the
effects of the system are not compensated for in the PID loop. The results are that the system response is compromised to
avoid instability.
The drive state-space control algorithm uses a number of internally calculated gains that represent the wide variety of effects
present in a servo system. This method gives a more accurate representation of the system and maximizes the performance
by minimizing the compromises.
You need only to setup the system and enter three parameters to describe the load and the application needs. Once the
entries are made the tuning is complete - no guessing and no “tweaking”. The drive uses these entries plus motor and
amplifier information to setup the internal digital gain values. These values are used in the control loops to accurately set up a
stable, repeatable and highly responsive system.
6.2 Motor Tuning and Motor Auto-Tuning
The unloaded motor parameters are set by the motor .ddf file or by using the motor Auto-tuning. This is a separate process
that is separate from this system tuning. The motor tuning should be set prior to tuning the system.
6.3 Tuning Procedure
Once the initial setup has been completed, you can run the system to determine if the level of tuning is adequate for the
application. A drive can be tuned basically to four levels.
• No Tuning
• Basic Level
• Intermediate Level
• Fully Optimized Level
Each level is slightly more involved than the previous one requiring you to enter more information. If your system needs
optimization, we recommend that you start with the Basic Level, then determine if further tuning is needed based on axis
performance.
The setup procedures explained here assume that you are using PowerTools Pro software.
6.4 Initial Settings
Set the drive tuning parameters as follows:
• Inertia Ratio = 0
• Friction = 0
• Response = 50
• Feedforwards = Disabled
6.5 Tuning Steps
If your Inertia Ratio is greater than 10 times the motor inertia go directly to the Intermediate Level tuning.
6.5.1 No Tuning
No tuning will be required in most applications where the load inertia is 10 times the motor inertia or less.
6.5.2 Basic Level
Adjust Response to obtain the best performance.