This contribution to the soft robotics toolkit aims at providing a first numerical software for modeling and control of soft-robot. This tool could be used by the community for design and control assistance of soft robots. The approach seeks to be generic and could be applied for various shape of soft robots and (for now) two types of actuators: cables (tendons) and pneumatics. The different steps followed to build a numerical model of a soft robots are described in a tutorial using an example of a soft gripper recently proposed in the community. Some additional examples are provided to show the other features of our software.
Current limitations and Future work
There are some limitations of our approach:
- We provide a virtual machine with the already installed software so the performance are far from optimal. We are working hard on providing a downloadable version of our software but currently, the different steps to install sofa and the needed plugins still require an expert.
- The deformable model used in the examples and tutorial is a non-linear geometric model under linear elasticity assumption (restricted to deformations in the linear part of the stress-strain curve of the material, ie. small deformations but large transformations). For more accurate model of the mechanical behavior of the deformable material ie. a mechanically accurate deformation law. Our current implementation doesn’t consider hyperelasticity yet (which is more computationally intensive). We currently work on adapting the fast hyper elastic formulations recently available in SOFA to our control method to overcome this limitation.
- Our approach can handle all types of geometry but one should limit the 3D mesh model within a range of around 2200 vertices and not use finely detailed models for computational burden concerns. We have some ongoing work about model reduction [Bosman et al. 2015] that will allow to combine better accuracy of the model and real-time computation and also the mix between deformable and rigid parts on the robot.
- Our SoftRobot plugin proposes the following actuators: tendon-driven and pneumatic actuators. We plan to add the hydraulic actuation by considering a combination of the pressure action (present in pneumatic actuators) and the simultaneous effect of the liquid’s weight. We also aim at modeling more complex types of actuation found in current soft robots such as: electroactive polymers and shape-memory alloys.
- Finally, while direct simulation of the robot (from forces to displacements) can handle contacts (as shown in the grasping part of this tutorial), the inclusion of interaction with the environment in the inverse simulation (from desired displacements to required forces) is still a work in progress with major challenges in the optimization problem.