pVEJ: A modular passive viscoelastic joint for assistive wearable robots

In complex dynamical tasks human motor control notably exploits the possibility of regulating joints mechanical impedance, both for stability and for energetic optimization purposes. These biomechanical findings should translate in design requirements for wearable robotics joints, which are required to produce adaptable intrinsic viscoelastic behaviors. This paper describes the design of a purely mechanical, rotary, passive ViscoElastic Joint (pVEJ), functionally equivalent to a torsional spring connected in parallel to a rotary viscous damper. The device has a modular design, which allows to modify the stiffness characteristics by replacing cam profiles. Damping coefficient can be also regulated off-line, manually acting on a valve. Prototype performances are characterized using a custom-developed dynamometric test-bed. Results demonstrate the capability of the system to render both the desired stiffness and damping values, in a range of impedance and peak torque compatible to that of wearable robotics for gait assistance.