Abstract
Mechanical efficiencies are calculated for a human doing work in a standing and stooping cycle while on a movable platform. An unsteady force is generated which does useful work in oscillating the platform on its suspension system. Such a vertical pumping motion has been proposed for a man-powered ornithopter. The theorem of virtual work provides the efficiency expression. Analog simulation reveals that square wave force exitation is more efficient than sinusoidal or triangular. Design curves show some unexpected requirements for matching man and machine, and very poor efficiency if care is not taken. Losses are due to gravity and human inability to store energy in unloading portions of the cycle. A spring-dashpot suspension allows efficiencies of up to 88% in cases involving sinusoidal exitation. If the spring force is set to zero, one obtains a maximum of 64% efficiency for harmonic exitation. Some improvement can be made by adding toe straps to the human and/or by forcing the cage in a square wave. The novel feature, making this work differ from ordinary vibration work, is the switching logic needed to distinguish loading and unloading portions of the cycle.
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