  Parallel robots based on Handed Shearing Auxetics (HSAs) can implement
complex motions using standard electric motors while maintaining the complete
softness of the structure, thanks to specifically designed architected
metamaterials. However, their control is especially challenging due to varying
and coupled stiffness, shearing, non-affine terms in the actuation model, and
underactuation. In this paper, we present a model-based control strategy for
planar HSA robots enabling regulation in task space. We formulate equations of
motion, show that they admit a collocated form, and design a P-satI-D feedback
controller with compensation for elastic and gravitational forces. We
experimentally identify and verify the proposed control strategy in closed
loop.
