Amplitude control of constant speed vibratory equipment

Claim 1

IN APPARATUS FOR DOING WORK BY VIBRATION, IN COMBINATION, A MEMBER TO BE VIBRATED, AN ECCENTRIC WEIGHT ROTATABLY MOUNTED ON SAID MEMBER, DRIVE MEANS CONNECTED TO SAID WEIGHT FOR ROTATING SAID ECCENTRIC WEIGHT AT A CONSTANT SPEED TO APPLY A VIBRATORY FORCE AT SUBSTANTIALLY CONSTANT AMPLITUDE TO THE MEMBER, A SECOND MEMBER, RESILIENT MEANS CONNECTING SAID MEMBERS AND FORMING WITH THE MEMBERS A VIBRATORY SYSTEM HAVING A NATURAL FREQUENCY GENERALLY EQUAL TO SAID CONSTANT SPEED, SAID RESILIENT MEANS INCLUDING AT LEAST ONE EXPANSIBLE CHAMBER THE VOLUME OF WHICH VARIES WITH RELATIVE DISPLACEMENT OF THE MEMBERS AND WHICH APPLIES SUBSTANTIAL SPRING FORCE TO THE MEMBERS, FLUID IN THE CHAMBER AT LEAST SOME OF WHICH IS GASEOUS, A PORT IN THE CHAMBER, AND AN ADJUSTABLE RESTRICTION CONNECTED TO THE PORT AND ARRANGED TO RESTRICT THE FLOW OF FLUID TO AND FROM THE CHAMBER AS THE MEMBERS VIBRATE.