Package: hsa-pyelastica
A plugin to PyElastica for the simulation of HSA robotsThis repository contains a plugin forPyElasticato simulate
robots based on Handed Shearing Auxetics (HSA).
Elastica makes use of the Discrete Cosserat Rod Model (DCM) to simulate the behaviour of slender rods.
We model the HSA rods as Cosserat rods, but perform several modifications to the DCM to account for the auxetic behaviour of HSAs.
Namely, we couple twist strains to an adjustment of the rest length of the rod.
This will let the rod extend when torsional torques are applied to it.
Additionally, the axial stiffness of the rod is modelled to be a linear function of the twist strain to account for a proportional
increase of the spring constant with increasing twist angles, as shown by Good et al.[1]in their characterization
of the mechanical properties of HSAs.
We refer to thepublicationfor more details.Currently, we are able to simulate the behaviour of closed HSAs
(i.e. the printed length is equal to the minimum length). Adaptations would be necessary to accommodate the simulation of
semi-closed and open HSAs. Specifically, this would include non-linear couplings between the twist strains
and the material properties such as the axial stiffness.At the moment, the plugin is only able to simulate the behaviour of a single-segment HSA robot.
This corresponds to a parallel arrangement of HSAs, where each HSA is connected to an electric actuator at its proximal end.
All HSA rods are attached at their distal end to a (circular) platform.
An extension to multi-segment HSA robots would require the implementation of different kinds of constraints,
joints, etc.CitationThis simulator is part of the publicationModelling Handed Shearing Auxetics:
Selective Piecewise Constant Strain Kinematics and Dynamic Simulationpresented at the6th IEEE-RAS International Conference on Soft Robotics (RoboSoft 2023).
You can find the publication online onIEEE Xplore.Please use the following citation if you use our method in your (scientific) work:@inproceedings{stolzle2023modelling,title={Modelling Handed Shearing Auxetics: Selective Piecewise Constant Strain Kinematics and Dynamic Simulation},author={St{\"o}lzle, Maximilian and Chin, Lillian and Truby, Ryan L. and Rus, Daniela and Della Santina, Cosimo},booktitle={2023 IEEE 6th International Conference on Soft Robotics (RoboSoft)},year={2023},organization={IEEE}}InstallationThe plugin can be installed from PyPI:pipinstallhsa-pyelasticaor locally from the source code:pipinstall.Please note that this plugin is currently compatible with the PyElastica version 0.3.x.
Any future changes in the private interface / API of PyElastica might break the plugin.UsageWe provide two simulators:HsaRodSimulatorand `HsaRobotSim`` to simulate individual HSA rods and assembled
HSA robots, respectively.HsaRodSimulatorTheHsaRodSimulatorcan be used to simulate the behaviour of individual HSAs.
First, we define the rod parameters:</code></pre><h2>Gettingstarted</h2><p>Weprovideseveralscriptsinthe<code>examples</code>foldertogetyoustartedwiththeplugin.</p><h3>VerificationofsimulatoragainstexperimentalresultsbyGoodetal.<ahref="#1">[1]</a></h3><p>Thecommand</p><prelang="bash"><code>pythonexamples/hsa_rod/verification_sim_against_good_et_al/hsa_rod_steady_state_characterisation.pysimulates the steady-state behaviour of individual HSA rods to identify several mechanical characteristics such as
holding torque, minimum energy length, spring constant, and blocked force.
We have tuned the parameters of the simulator to match the experimental results of Good et al.[1]as closely as
possible.
Finally, we compare the results of the simulation with the experimental results to verify the steady-state behaviour of the
simulator. This can be done by running the following command:pythonexamples/hsa_rod/verification_sim_against_good_et_al/plot_verification_sim_against_good_et_al.pySee alsoYou might also be interested in the following repositories:Thejax-spcs-kinematicsrepository contains an implementation
of the Selective Piecewise Constant Strain (SPCS) kinematics in JAX. We have shown in our paper that this kinematic
model is suitable for representing the shape of HSA rods.You can find code and datasets used for the verification of the SPCS model for HSA robots in thehsa-kinematic-modelrepository.References[1]Good, Ian, et al.
"Expanding the Design Space for Electrically-Driven Soft Robots Through Handed Shearing Auxetics."
2022 International Conference on Robotics and Automation (ICRA). IEEE, 2022.