Hydraulic Human Power Extender

An experimental Six-Degree-of-Freedom Hydraulic Extender designed and built at U.C. Berkeley for loading and unloading aircraft. The payload of this power extender is 500 lbf, and its gripper jaws open up to 30 inches. Two sets of piezoelectric force sensors (one set between the human and the machine, and one set between the machine and the load) measure forces for arbitrary force augmentation and force reflection in the machine. Three microcomputers, communicating over parallel I/O boards, control the six axes of this extender. This human power extender is like virtual reality machines that can simulate forces on the worker’s arms and trunk, forces which are different from and usually much less than the forces needed to maneuver a load. In its simplest behavior, when a worker uses the proposed assist device to move a load, the extender transfers to her/his arms, as natural feedback, a scaled-down value of the load’s actual weight. For example, for every 100 pounds of load, the wearer supports 5 pounds while the extender supports 36 pounds. The wearer still “feels” the load’s weight, but what he/she feels is less than what he/she would feel without the extender.

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