A synchronized subharmonic controller for a dual coil electromagnetic vibrator, which derives both power and timing from a single phase AC line, having a trigger circuit which operates the coils at one-third the power line frequency. A timing circuit is optically coupled to alternately fire a pair of oppositely-directed SCR's with each SCR connecting one of the coils across the AC line. The optical coupling reduces feedback from the coil circuitry to the timing circuit. A pair of capacitors supply additional power to operate the coils and to reduce the peak values of current supplied by the power line.
Mechanical resonance of the vibratory feeder is maintained by minimizing a phase angle difference between substantially sinusoidal drive voltage and current wave forms. The mass flow rate of material being fed is controlled by controlling the electrical power applied to the vibratory feeder compared with a desired electrical power computed from a desired flow rate. The preferred embodiment includes synthesized drive wave forms which are variable in frequency and amplitude in order to maintain the vibratory feeder in mechanical resonance at the desired flow rate. Resonant operation and accurate material flow are accomplished without use of electromechanical vibration sensors and control is accomplished using the magnitude and phase relationships between the applied voltage and current drive wave forms.
An orbital vibrator apparatus has a base mounted on vibration isolation mounts. An armature plate is resiliently mounted to the base by three flexural spring elements. An armature of magnetically attracted material is mounted to the armature plate. A first electromagnet and a second electromagnet are mounted on the base at right angles to one another and in a spaced apart relationship to the armature. A source of single-phase alternating current is connected to the first electromagnet and the second electromagnet by way of a control circuit. The control circuit includes a variable voltage transformer for controlling the voltage of the electric current and a phase shifting circuit. The phase shifting circuit shifts the phase of the alternating current by approximately ninety degrees. The first electromagnet is driven directly from the output of the voltage transformer and the second electromagnet is driven from the output of the phase shifting circuit. The motion that results from the two electromagnets acting on the armature ninety degrees out of phase from each other will be approximately circular. Optionally, the control circuit may also include a mode selector switch for selectively operating the vibration generator in a circular orbital vibratory mode, an elliptical vibratory mode and a reciprocating vibratory mode.
