Estimating load inertia

aand74

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Join Date
Dec 2005
Location
Deinze
Posts
131
I am doing a revamp of a machine with motion control.
I have no data of the inertia of the load on a certain motor, but I should want to know it for my engineering.
In the old drives I can capture analog output that indicates the setpoint speed, and an analog output for the current. I am not sure if I can set it at the torque generating current or if it is only possible to read the total current.
I should be able to scale the two signals so I have signals in rpm and ampere.
I also know the reduction ratios of the gearbox.
What could now be a procedure to get a value for the inertia of the load?
The old motor is a servomotor.
 
Apply a step speed demand and measure the time it takes to get from 20% to 80% of the speed ensuring that the torque during the accel is constant. Repeat from that speed and measure the time from 80% to 20%. Average the two values to eliminate friction and then calculate the inertia from T=I.Alpha
 
If you know the weight you can do a calculation. What kind of load is it? IE a rotating roll, moving on a track, etc?

Also keep in mind that the inertia reflected through a gearbox is scaled by the gear ratio squared.
 

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