Differentiable Robotic Manipulation of Deformable Rope-like Objects Using Compliant Position-based Dynamics

Abstract

Robot manipulation of rope-like objects is an interesting problem that has some critical applications, such as autonomous robotic suturing. Solving for and controlling rope is difficult due to the complexity of rope physics and the challenge of building fast and accurate models of deformable materials. While more data-driven approaches have become more popular for finding controllers that learn to do a single task, there is still a strong motivation for a modelbased method that could be used to solve a large variety of optimization problems. Towards this end, we introduced compliant, position-based dynamics (XPBD) to model rope-like objects. Using geometric constraints, the model can represent the coupling of shear/stretch and bend/twist effects. Of crucial importance is that our formulation is differentiable, which can solve parameter estimation problems and improve the matching of rope physics to real-life scenarios (i.e., the realto-sim problem). For the generality of rope-like objects, two different solvers are proposed to handle the inextensible and extensible effects of varied material stiffness for the rope. We demonstrate our framework's robustness and accuracy on realto-sim experimental setups using the Baxter robot and the da Vinci research kit (DVRK) [1]. Our work leads to a new path for robotic manipulation of the deformable rope-like object taking advantage of the ready-to-use gradients.

State‐of‐the‐art improvements and applications of position based dynamics

“…Moreover, XPBD has been used to achieve differential parameter identification and shape control of linear objects by adding extra geometrical constraints for realto-sim robotic manipulation. 22 Figure 2: The comparison between the simulation results of a hippopotamus model with PD after 1, 10, and 20 iterations, and Newton's physical method. It could be seen that after 10 iterations, the simulation results are visually similar.…”

“…Deul et al 36 Introduce joint and contact constraints into PBD to simulate rigid bodies. For XPBD, although initial research studies focus on decoupling the dependence problem, some researchers have late proved its genericity to be applied in various scenarios, like rigid body 20 , muscle 21,73 , and rod simulation 22 . Compared with PBD, more realistic and controllable results obtained with XPBD have inspired further investigations.…”