Voluntary-Opening Prehensors with Adjustable Grip Force

A novel concept for adjusting grip force in voluntary-opening prehensors is introduced. The vector mechanism allows the user to rotate a stiff elastic band within the prehensor to change grip force substantially with very low energy input. Two prototype vector prehensors are described: one modeled after a split hooka, the other modeled after a TRS Grip IIIb. The performances of the prototypes are evaluated and compared with those of commercially available prehensors primarily through laboratory testing. The vector prehensors allow grip force to be adjusted quickly and easily among 13 settings ranging from ½ to 20 lbs. This added capability was achieved without adding significant weight or bulk to the device. Preliminary field tests demonstrated the practical feasibility of the device, but a clinical evaluation has not been performed.