This repository provides implementation and closed-loop simulation of various control strategies for planar HSA robots. Furthermore, it contains ROS2 nodes for planning and control of the planar HSA robots.

Abstract: 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.

This simulator is part of the publication An Experimental Study of Model-based Control for Planar Handed Shearing Auxetics Robots presented at the 18th International Symposium on Experimental Robotics. You can find the publication online in the Springer Proceedings on Advanced Robotics (SPAR): https://doi.org/10.1007/978-3-031-63596-0_14

Please use the following citation if you use our software in your (scientific) work:

@inproceedings{stolzle2023experimental,
  title={An experimental study of model-based control for planar handed shearing auxetics robots},
  author={St{\"o}lzle, Maximilian and Rus, Daniela and Della Santina, Cosimo},
  booktitle={International Symposium on Experimental Robotics},
  pages={153--167},
  year={2023},
  organization={Springer}
}

1. Please follow the JAX installation instructions on GitHub.
2. Then, you can install the requirements with pip install -r requirements.txt.
3. Finally, if you have locally cloned the jax-soft-robot-modelling repository, you can install it with pip install -e . from the root directory of the repository.

This repository also contains various ROS2 nodes for planning and control. As usual, clone this repository into your ROS2 workspace and build it with colon build. Furthermore, we rely on the ROS2 packages in the ros2-hsa repository for the communication with the hardware (both actuation and motion capture), inverse kinematics and visualization. You can launch the nodes with ros2 launch hsa_planar_control ./launch/hsa_planar_cl_control.py.

You can use the provided script examples/system_identification/epu_identify_system_params_statically to identify the nominal stiffness S_a_hat, the rest length elongation factor C_varepsilon, change of the axial stiffness C_S_a, and the bending parameters S_b_hat, S_sh_hat, S_b_sh, C_S_b, and C_S_sh using linear least-squares. Please modify the SYSTTEMID_STEP variable accordingly.

You might also be interested in the following repositories:

• The jax-soft-robot-modelling repository contains a JAX implementation of various soft robot models, which can be, for example, used to simulate the robot's forward dynamics.
• The jax-spcs-kinematics repository contains an implementation of the Selective Piecewise Constant Strain (SPCS) kinematics in JAX. Our paper shows that this kinematic model is suitable for representing the shape of HSA rods.
• The HSA-PyElastica repository contains a plugin for PyElastica for the simulation of HSA robots.