Perfect static balance with normal springs

In biomechanical engineering, gravity balancers are often used in orthoses carrying the weight of paralyzed limbs. In these applications, simplicity is an insuperable demand. However, known gravity balancers do not combine simplicity with perfect balance. This paper describes several gravity equilibrators providing perfect static balance. As opposed to many known solutions, the proposed balancers incorporate normal off-the-shelf springs, rather than the zero-free-length springs (springs with a length equal to zero when not preloaded or loaded externally) usually employed. The conceptional synthesis is presented, dimensional design criteria are derived, and prototypes are shown. Based on the prototype's working principle, an ankle prosthesis, which stabilizes the patient, will be developed.