Background

In the field of soft robotics, the problem of shape (strains) estimation is complicated because of its long-range stress waves propagating  in between elastic elements. All six modes of deformations (normal/binormal bending and shear, twist and stretch) can be simultaneously engaged. As a consequence, localized loads are transferred to the entire soft structure in a nonlinear fashion, leading to complex dynamics and global morphological reconfigurations. Therefore, this project aims at developing and demonstrating methods and algorithms to estimate the (continuum) strain functions along the center line of a slender flexible body in 3D space.

Research description

We have an ongoing project together with roboticists to estimate and control the posture of a soft actuator.  The soft robot is called the BR2. 

Modeling.  The dynamics of a single octopus arm are modeled using the Cosserat theory of elastic rods.  In contrast to typical rigid link models of classical robotics, Cosserat rod models capture, through linear and angular momentum balances, the (one-dimensional) continuum and distributed nature of elastic slender bodies deforming in space. These models account for all modes of deformation – bend, twist, stretch, shear – induced by external and internal forces and couples.

Estimation.  The estimation problem is to recover the internal strains including shears, curvatures, extension and twist. In a path-breaking paper, our group provided the first such demonstration of the energy shaping based reconstruction methodology to solve this estimation problem (see videos below).  The real robot arm and its reconstruction is overlap on top of each other.

This project provides two main features. First, it establishes a physics informed framework that reconstructs normal and binormal bending, shear, twist, and stretch strain functions along any generic slender structure. Secondly, the results demonstrate the accuracy and robustness of the reconstructions with limited and noisy data. These demonstrations further underscore the practical research capability of integrated platform, for the characterization in laboratory settings of robotic prototypes or biological systems, as well as for the development of validated simulations and control strategies.

Presentations

Slides from the International Conference on Robotics and Automation, Philadelphia, PA, U.S., May 13-27, 2022

Publications

Kim, S. H., Chang, H. S., Shih, C. H., Uppalapati, N. K., Halder, U., Krishnan, G., ... & Gazzola, M. (2022, May). A Physics-informed, vision-based mehtod to reconstuct all deformation modes in slender bodies. In 2022 International Conference on Robotics and Automation (ICRA) (pp. 4810-4817). IEEE.

Acknowledgements

Financial support from the ONR MURI N00014-19-1-2373, NSF/USDA #2019-67021-28989, and NSF EFRI C3 SoRo #1830881 is gratefully acknowledged.