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FM-3 Programming Module Reference Manual

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 viscuous 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.

MRI

RLI

R I =

1 2 ... 169 170 171 172 173 174 175 176 177 178 179 ... 229 230

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