We do alot of mechanical testing on specimens with a wide range of
stiffness. We're using a MTS sevohydraulic system with old analog
controllers which are very dependable but are old technology. With the
older technology, it is very difficult to hit and maintain end levels due to
specimen stiffness. We know can preset the servo gain by performing
preliminary tests but this is not always possible because of the
availibility and variability of each specimen. We can crank up the servo
gain at the beginning of the each test but that creates a problem because
the stiffness of the specimen could be changing too and the servo loop
control could cause the testing system to become unstable ("ringing").
Does anyone have a solution for this problem using our existing equipment???
Also, does anyone have any experience for solving this problem using the
digital controllers with "calculated variable control"???
Many thanks for any input.


Jerry W.Alexander
Research Associate
Institute of Orthopedic Research & Education
6565 Fannin
Mail Station F115
Houston, Texas 77030
Pager (713)764-1879
Fax (713)797-6658
e-mail: jerrya@bcm.tmc.edu

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