On an adjustable-stiffness spring composed of two antagonistic pairs of nonlinear leaf springs working in post-buckling

We consider the prototype of adjustable-stiffness spring recently developed by some of the authors of this note, and published in Mechanism and Machine Theory, Vol. 46: pp. 1970–1979, 2011. The elastic device is an antagonistic setup consisting of two pairs of non-linear leaf springs working in bending, simultaneously and in opposition, and undergoing large displacements. In this work, the case of both pairs of leaf springs working in post-buckling conditions is studied. To this purpose, a mathematical model is proposed in order to predict the mechanical behavior of one leaf spring. Also, a prototype of one leaf spring is fabricated and tested, showing excellent agreement with the numerical results derived from our model. Finally, the force–displacement curves of the new spring are obtained and compared with the ones of the previous case.

► A new antagonistic setup is proposed as an adjustable-stiffness actuator. ► It is composed of two pairs of non-linear leaf springs working in post-buckling. ► A mathematical model is developed to predict the post-buckling of one leaf spring. ► A prototype of leaf spring has been fabricated and tested for different cases. ► Experimental results corroborate the results derived from the mathematical model.