Synthesis of a torsional spring mechanism with mechanically adjustable stiffness using wrapping cams

Most adjustable springs that have appeared in the literature are based on the antagonistic actuation of two quadratic springs. When two quadratic springs are coupled antagonistically, the resulting system attains a linear spring behavior enabling the adjustment of the stiffness mechanically. However, a non-linear spring with perfect quadratic behavior is difficult to realize. In this study, the synthesis of a non-linear spring using mechanisms is investigated where the problem is reduced to a function generation problem. A wrapping cam mechanism is proposed as an effective mechanism to be used in non-linear spring synthesis. An analytical solution is developed to calculate the necessary cam profile. Later, the design of the wrapping cam mechanism specific to quadratic springs is investigated. A torsional spring with mechanically adjustable stiffness utilizing a wrapping cam mechanism has been designed, manufactured and experimentally tested. Strong linear behavior is observed and the experimental stiffness values are found to be in good agreement with the analytical solution.