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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
MI = Motor Inertia (lb-in- sec
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.
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 effect of Response is greatly influenced
by the status of the High Performance Gains.
With High Performance Gains disabled, the actual command bandwidth of the drive system will be equal to the Response
value. In this case the load disturbance correction bandwidth is very low (approximately 0.1 Hz). Increasing the Response
value will reduce the drive's response time to velocity command changes but will not affect the response to load or speed
disturbances.
When High Performance Gains are enabled, the Response bandwidth is set to the Response value. In this case, it reflects both
the velocity command and the load disturbance correction bandwidth. Increasing the Response when the High Performance
Gains are enabled will increase loop stiffness. With High Performance gains enabled, the maximum Response level
recommended is approximately 100 Hz.
If the Inertia Ratio and Friction values are exactly correct and the High Performance Gains are enabled, 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 or if High Performance Gains are enabled.
RLI
=
I
R
MRI
2
)
2
)
Tuning Procedures
231
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