It is evident that changes in frequency ratio caused
by variances in material loading, plus any variance in
the damping factor, will affect magnification, and consequently
amplitude, unless:
(a) the frequency of the impressed force is adjusted
to maintain a constant ratio, or
(b) the magnitude of the impressed force is adjusted
to compensate for the change in magnification.
Automatic frequency compensation is theoretically
possible, but neither practical nor desirable; it would
lead, in the usual case of increasing frequency ratio,
to progressive reductions in forcing frequency with
accompanying reductions in conveying rate, compounding
to a full stall as the frequency ratio moves
above resonance.
The most practical way to maintain amplitude stability
at constant frequency, over a limited range of
variance in frequency ratio and damping factor, is with
the fixed-displacement crank, or eccentric, acting
through an elastic coupling of significant stiffness, as