This paper presents a novel design for a Variable Stiffness 3 DoF actuated
wrist to improve task adaptability and safety during interactions with people
and objects. The proposed design employs a hybrid serial-parallel configuration
to achieve a 3 DoF wrist joint which can actively and continuously vary its
overall stiffness thanks to the redundant elastic actuation system, using only
four motors. Its stiffness control principle is similar to human muscular
impedance regulation, with the shape of the stiffness ellipsoid mostly
depending on posture, while the elastic cocontraction modulates its overall
size. The employed mechanical configuration achieves a compact and lightweight
device that, thanks to its anthropomorphous characteristics, could be suitable
for prostheses and humanoid robots.
After introducing the design concept of the device, this work provides
methods to estimate the posture of the wrist by using joint angle measurements
and to modulate its stiffness. Thereafter, this paper describes the first
physical implementation of the presented design, detailing the mechanical
prototype and electronic hardware, the control architecture, and the associated
firmware. The reported experimental results show the potential of the proposed
device while highlighting some limitations. To conclude, we show the motion and
stiffness behavior of the device with some qualitative experiments.Comment: 13 pages + appendix (2 pages), 19 figures, submitted to IJR