Low inertia counterbalance mechanism

摘要

A low inertia counterbalance mechanism for eliminating the effects of gravity on an upper body mass of a person secured in an input assembly of a trunk extension/flexion test, rehabilitation and exercise machine is disclosed. The mechanism disclosed does not add any appreciable inertia to the input assembly. A cam rotating on the same axis of rotation and mechanically connected to the input assembly comes in contact with a cable when the input assembly rotates downwardly. The cable at its bottom end is attached to a lever arm. The lever arm rotates upwardly when the cam comes in contact with the cable, and a constant force gas spring pivotally attached at its bottom end to an intermediate point on the lever arm is compressed when the lever arm pivots upwardly. This negates the increasing effects of gravity felt by the upper body mass of the person secured in the input assembly as the input assembly rotates downwardly. The top end of the spring is pivotally attached to a frame of the machine. The attachment point of the bottom end of the gas spring to the lever arm can be changed so as to passively carry the upper body mass of the person upwardly without the person exerting any upward rotational force. The point in the range of motion where the cam comes in contact with the cable is also adjustable.