MTS Series 215 Rotary Actuator - Manual (Page 40)

Series 215 Rotary Actuator Product Manual 40
Definition of Useful Mathematical Terms
Operation
mounted in a force train using a 215 Rotary Actuator, the shaft expansion would
exert a resultant force of 6,000 lbs. on the actuator bearings.
To confine the resultant force to an acceptable maximum requires the addition of
diaphragm flexures to the force train. Multiplying the stiffness of the diaphragm
flexure by the amount of specimen expansion will give the thrust load imposed
on the actuator bearings.
Use the following formula to calculate the maximum thrust load applied to the
actuator bearings when using diaphragm flexures:
Flexure Stiffness (Flexure’s Maximum Thrust Deflection) = Maximum Thrust
Load
Side loads Side loads, which are normally induced by specimen misalignment or base plate
or T-slot table compliance, may be active at the same time thrust loads are active.
If the specimen is soft, such as a length of rubber hose, side loads on the actuator
are relatively small. This is because the specimen bends easily and exerts little
resistance to the deflection caused by base plate twisting. However, if the
specimen is stiffer (steel for example), the increased resistance of the specimen to
bending exerts substantial side loads on the actuator bearings and torque cell due
to the restraining characteristics of the test setup. As in the test setup for thrust
loads, diaphragm flexures can be used to reduce the side loads to a practical limit.
Note The service life of the actuator is normally reduced by significant thrust
and side loads. For this reason, the use of flexure diaphragms and a rigid
base plate is recommended even when the actuator’s thrust and side
load ratings are sufficient for the test situation.
Definition of Useful Mathematical Terms
The following terms are listed in alphabetical order and defined in both U.S.
Customary and SI Metric units of measure.
Mathematical Terms (part 1 of 3)
T ERM D EFINITION T ERM D EFINITION
a Distance from actuator's center line to
center of reaction base plate’s solid
height (mm) (in.). k2 Lateral stiffness of a solid cylindrical
specimen (kN/mm) (lbf/in.)
12 ET IL2 3
β 0.333 - 0.21 (d/b) k F1 Angular horizontal stiffness of actuator and
reaction bracket flexures (N·m/rad) (lbf·in./
rad).
M F1 / θ F1
b Width of reaction base plate (mm) (in.). k F2 Lateral stiffness of diaphragm flexures (lbf-
in./rad).
=M F2 / θ
F2
d Thickness of reaction base plate (mm)
(in.). Measurement of solid metal only.
Do not include T-slot depth. L 1 Length of base plate or T-slot table subjected
to twisting (mm) (in.).