Systems and methods for producing a pure vibration force from a synchronized dual array of eccentric rotating masses

A vibration device, comprising:

• a subframe;
• a first rotary motor attached to the subframe, the first rotary motor including:
• a first motor case;
• a first rotatable shaft coupled to the first motor case, the first rotatable shaft having a first axis of rotation therealong, and the first rotatable shaft having its center of mass is located on the first axis of rotation;
• a primary eccentric rotating member (ERMp1) attached to the first rotatable shaft, the ERMp1 having a first center of mass, a first radius between the first center of mass and the first axis of rotation, and a first eccentricity defined as the mass of the ERMp1 multiplied by the first radius;
• a secondary eccentric rotating member (ERMs1) attached to the first rotatable shaft, the ERMs1 having a second center of mass, a second radius between the second center of mass and the first axis of rotation, and a second eccentricity defined as the mass of the ERMs1 multiplied by the second radius;
• wherein:
• a normal projection of the first center of mass onto the first axis of rotation is at a first point Pp1;
• a normal projection of the second center of mass onto the first axis of rotation is at a second point Ps1;
• Pp1 and Ps1 are different points;
• and
• the first rotary motor has a net eccentricity>0;
• a second rotary motor attached to the subframe, said second rotary motor including:
• a second motor case;
• a second rotatable shaft coupled to the second motor case, the second rotatable shaft having a second axis of rotation therealong, the second axis of rotation being aligned with the first axis of rotation, the second rotatable shaft having its center of mass is located on the second axis of rotation;
• a primary eccentric rotating member (ERMp2) attached to the second rotatable shaft, the ERMp2 having a third center of mass, a third radius between the third center of mass and the second axis of rotation, and a third eccentricity defined as the mass of the ERMp2 multiplied by the third radius;
• a secondary eccentric rotating member (ERMs2) attached to the second rotatable shaft, the ERMs1 having a fourth center of mass, a fourth radius between the fourth center of mass and the second axis of rotation, and a fourth eccentricity defined as the mass of the ERMss1 multiplied by the fourth radius;
• wherein:
• a normal projection of the third center of mass onto the second axis of rotation is at a third point Pp2;
• a normal projection of the fourth center of mass onto the second axis of rotation is at a fourth point Ps2;
• Pp2 and Ps2 are different points;
• and
• the second rotary motor has a net eccentricity>0;
• and
• wherein:
• a first distance d1 is defined as the distance between Pp1 and Pp2;
• a second distance d2 is defined as the distance between Ps1 and Ps2;
• and
• the distance d1 is less than the distance d2.

A vibration device, comprising:

• a subframe;
• a first rotary motor including:
• a first motor case attached to the subframe;
• a first rotatable shaft coupled to the first motor case, the first rotatable shaft having a first axis of rotation therealong, the first rotatable shaft having its center of mass is located on the first axis of rotation;
• a primary eccentric rotating member (ERMp1) attached to the first rotatable shaft;
• a secondary eccentric rotating member (ERMs1) attached to the first rotatable shaft;
• a second rotary motor including:
• a second motor case attached to the subframe;
• a second rotatable shaft coupled to the second motor case, the second rotatable shaft having a second axis of rotation therealong, the second axis of rotation being aligned with the first axis of rotation, and the second rotatable shaft having its center of mass is located on the second axis of rotation;
• a primary eccentric rotating member (ERMp2) attached to the second rotatable shaft;
• a secondary eccentric rotating member (ERMs2) attached to the second rotatable shaft
• wherein design parameters of ERMs1 and ERMs2 are selected and ERMs1 and ERMs2 are arranged along the first rotatable shaft and second rotatable shaft, respectively, to produce a counter-torque onto the subframe that mitigates a parasitic torque produced by ERMp1 and ERMp2 onto the subframe, and also to produce a counter-force which reduces but does not cancel out combined forces of ERMp1 and ERMp2 onto the subframe of the vibration device.