Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 221)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 221
Motor Control Chapter 4
Inertia Adaption Inertia adaption is used to compensate for lost motion, which occurs when a gear
box and/or a springy coupling is present. Lost Motion describes the condition in
which an input to a mechanism creates no corresponding displacement at the
output. This is most noticeable in systems with large inertia ratios using a gear-
box or flexible couplings. The term inertia adaption refers to how this function
adapts or changes the dynamic inertia seen by the speed regulator. Inertia
adaption can allow an increase in the speed regulator bandwidth, normally
limited by the mechanical transmission, by up to four times. This feature is only
available on PowerFlex 755 drives. P35 [Motor Ctrl Mode] must be set to vector
control and use a motor speed feedback device. Inertia adaption is not enabled by
default.
For example, a motor connected to a gearbox is shown.
This gearbox can be represented by a spring (K) and gear backlash (BL).
When the speed of the motor increases, there is a period of time (represented by
Δ x = backlash) before the teeth of the gearbox engage. After that time, there is
some twisting (like a spring) in the shaft after the teeth of the gearbox engage.
This lost motion causes mechanical instability and limits how high the speed
regulator bandwidth can be set without causing instability. Inertia adaption
detects the lost motion and a higher speed regulator bandwidth can be achieved
without instability.
Motor Gearbox Load
M1 M2
Motor
K
Load
M1 M2
BL
f
Δ x
Slope due to springy nature
(K) of shafts after gearbox
teeth engage.
Backlash (BL) before
gearbox teeth engage.