Velocity jumps vs reflected inertia

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Ryan Carlyle

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Sep 8, 2019, 12:10:53 PM9/8/19
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Working on book content and something struck me as possibly worth doing some calculations. Background:
  • A common technique in servo drivetrain design is matching the load's reflected inertia (what's seen at the motor shaft through gearboxes etc) to the rotor inertia. This is done for feedback loop stability reasons, but does help match the motor, load, and drivetrain together. If the load's reflected inertia is too high, the motor struggles to control the load. If the ratio is too low, the motor or gearbox is oversized. 
  • The magnitude of drivetrain acceleration during velocity jumps (corner jerks) comes from how oversized the motor is for the load. If the motor is super oversized, it will produce a very sharp impulse torque to snap the drivetrain to the new velocity. If the motor is not oversized, it has to exert a lower torque over a longer period to accomplish the velocity jump.
So, what I'm wondering is if there's a simple / predictable / useful relationship between reflected inertia ratio and the peak velocity jump acceleration. It's possible that the reflected inertia ratio and the real peak corner acceleration of printer drivetrains could plot pretty tightly on some line or curve on a graph. That would be an EXTREMELY useful printer design tool. 

I'm parking the thought here in case somebody else wants to work on it and so I don't forget.
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