shown schematically in Fig. 5. This arrangement makes
use of the change in phase angle, , (Fig. 4) caused
by changes in frequency ratio, to provide automatic
compensation through the resulting changes in physical
displacement of the coupling.3 The range of stability
is limited by the stiffness, or spring rate, of the
coupling.
If a fixed-value impressed force is applied, by means
of a rotating unbalance or linear inertia-force generator,
the equivalent coupling stiffness is zero; the impressed
force at constant speed will be constant at any
frequency ratio, and the range of stability will be very
narrow. This characteristic limits the constant-force
exciter drive to applications where damping is light,
and material loading fairly constant.
On the other hand, if the impressed force is applied
through a solid coupling, such as a wrist pin, the equivalent
coupling stiffness is infinite, and the range of