Apparatus for generating a reciprocating rotary motion

A chest compression device comprising:

• an apparatus for generating a rotary reciprocating motion, comprising:
• an input shaft having a rotation axis;
• a drive motor for providing unidirectional rotation of the input shaft about the rotation axis;
• an output shaft for delivering reciprocating rotary motion about the rotation axis, wherein the output shaft is for coupling to a load which limits the rotation of the output shaft thereby to prevent unidirectional rotation of the output shaft;
• a first magnetic or ferromagnetic ring disposed about the rotation axis, rotationally fixed to the input shaft;
• and
• a second magnetic or ferromagnetic ring disposed about the rotation axis, rotationally fixed to the output shaft,
• wherein the first and second rings are disposed one within the other around the rotation axis and wherein at least one of the first and second rings comprises an annular sequence of permanent magnetic elements;
• and
• a chest cpression belt for positioning around the chest of a subject, connected at opposite ends to the output shaft.

A method of generating a rotary reciprocating motion, comprising:

• driving an input shaft with unidirectional rotation about a rotation axis, thereby rotating a first magnetic or ferromagnetic ring, disposed about the rotation axis;
• inducing rotation of a second magnetic or ferromagnetic ring, disposed about the rotation axis, by magnetic coupling to the first ring, wherein at least one of the first and second rings comprises an annular sequence of permanent magnetic elements;
• delivering reciprocating rotary motion about the rotation axis of an output shaft coupled to rotation of the second ring;
• and
• providing a chest compression belt for positioning around a chest of a subject, connected at opposite ends to the output shaft.