Omron SYSMAC CJ Series, Operation Manual

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Mechanical system Section 1-10
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1-10 Mechanical system
1-10-1 Inertia ratio
The inertia ratio is a stability criterion. The higher the intertia of the load in
relation to the intertia of the motor, the lower the gains you can set in your
system before you reach oscillation, and the lower the performance you can
reach.
With a ratio of 1:30 for small Servo Drivers and a ratio of 1:5 for big Servo
Drivers you can reach the maximum dynamic of the motor-driver combination.
1-10-2 Rigidity
If a machine is more rigid and less elastic, you can set higher gains without
vibration, and you can reach higher dynamic and lower Following Error.
1-10-3 Resonant frequency
A mechanical system has at least one resonant frequency. If you excite your
mechanical system to the resonant frequency, it starts oscillating. For motion
systems, it is best to have mechanical systems with a very high resonant
frequency, that is, with low inertia and high rigidity.
The resonant frequency of the mechanical system is the limit for the gain
settings.