Steady-state, as opposed to transient, harmonic vibration
can be generated by applying a periodic force
to a spring-mass system. If the frequency of the impressed
force is at, or near, the natural frequency of
the spring-mass system, the vibration can be maintained
with a very small input force. This is the principle
employed in the design of the natural-frequency
vibrating conveyor.
The spring-mass system in the vibrating conveyor,
in its simplest form, comprises the conveyor trough
and associated "live" structure, springs made of some
elastic material such as steel, rubber, or fiber-reinforced
plastic laminates, a means for applying a small periodic
impressed force, and a fixed base against which the
spring force reacts. This system is shown schematically
in Fig. 1.
The impressed force may be applied by a fixed-displacement
eccentric crank, usually but not necessarily
connected to the trough structure through a resilient
coupling, or by a rotating unbalance or linear inertia
force that applies a constant periodic force component
along the line of action at the desired frequency. 1