Power operated back rest

Claim 1

An adjustable body rest assembly comprising: a base adapted to be placed on and be supported by an upwardly facing surface of a bed or other support structure with said base in generally horizontally extending condition; a back rest hinged to said base for pivotal movement about a first essentially horizontal axis through different inclined positions and forming a variable acute dihedral angle with said base; an extensible screw and nut mechanism located above said base and within said dihedral angle and including a screw part and a threaded interengaged nut part one of which is actuable along a second axis relative to the other to lengthen said mechanism in response to relative rotation of the parts about said second axis; said two parts exerting force in generally opposite directions against said base and said back rest at locations offset from said first axis to swing said back rest between said different inclined positions; a rotary motor located above said base and within said dihedral angle and connected to said screw and nut mechanism and operable to drive one of said screw and nut parts rotatively relative to the other in a relation actuating said back rest between said different inclined positions; a first pivotal connection attaching both said motor and said screw and nut mechanism at one end of the latter to said base for upward and downward swinging movement of both the motor and the screw and nut mechanism in unison within essentially a vertical plane disposed essentially transversely of said first axis and during actuation of said back rest about said first axis; and a second pivotal connection at the other end of said extensible screw and nut mechanism through which force is transmitted from said mechanism to the back rest to actuate it.