Control Techniques Epsilon EP-P, Reference Manual

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Epsilon EP-P Drive Reference Manual
189
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Revision A4 www.controltechniques.com
Figure 145: Inertia Setting (5)
2. Increase the response parameter
The Response is normally the final adjustment when tuning. For best performance the Response should be lower with a
higher inertia mismatch (>10:1) and higher with a lower inertia mismatch.
If your system has some torsional compliance, such as with a jaw type coupling with a rubber spider, or if there is a long drive
shaft, the Response should be decreased. The highest recommended Response with High Performance Gains enabled is 100
Hz.
Also, enabling the Low Pass Filter helps diminish the resonant frequency of torsionally compliant loads. In such cases, using
the Low Pass Filter usually allows for higher Response values. The optimum Low Pass Filter frequency is at the frequency of
the resonance.
Feedforwards can be enabled if the performance requirements are very demanding. However when using them, make sure
the Inertia Ratio and Friction values are an accurate representation of the load. Otherwise, the system performance will
actually be degraded or stability will suffer. Enabling the Feedforward makes the system less tolerant of inertia or friction
variations during operation.
6.6 Tuning Parameters
Inertia Ratio
Inertia Ratio specifies the load to motor inertia ratio and has a range of 0.0 to 50.0. A value of 1.0 specifies that load inertia
equals the motor inertia (1:1 load to motor inertia). The drives can control up to a 10:1 inertia mismatch with the default Inertia
Ratio value of 0.0. Inertial mismatches of over 50:1 are possible if response is reduced.
The Inertia Ratio value is used to set the internal gains in the velocity and position loops, including feedforward compensation
if enabled.
To calculate the Inertia Ratio value, divide the load inertia reflected to the motor by the motor inertia of the motor. Include the
motor brake as a load where applicable. The resulting value should be entered as the Inertia Ratio parameter.
Where:
IR = Inertia Ratio

RLI = Reflected Load Inertia (lb-in-sec
2
)

MI = Motor Inertia (lb-in- sec
2
)
If the exact inertia is unknown, a conservative approximate value should be used. If you enter an inertia value higher than the
actual inertia, the resultant motor response will tend to be more oscillatory.
If you enter an inertia value lower than the actual inertia, but is between 10 and 90 percent of the actual, the drive will tend to
be more sluggish than optimum but will usually operate satisfactorily. If the value you enter is less than 10 percent of the actual
inertia, the drive will have a low frequency oscillation at speed.
Friction
In the drive, this is a viscous friction parameter, characterized in terms of the rate of friction increase per 100 motor RPM. The
range is 0.00 to 100.00 in units of percent continuous torque of the specified motor/drive combination. The Friction value can
either be estimated or measured.
MRI
RLI
R I
