Robotic Manipulation Under Stochastic Contact Constraints
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Solution Overview
Problem
Current robotic manipulation systems face challenges in robust control due to uncertainties in frictional interaction systems, leading to stochastic dynamics and infeasibility in optimization problems, particularly in contact modeling using linear complementarity problems (LCP).
Innovation Solution
A chance constrained optimization formulation is proposed using Mixed-Integer Quadratic Programming with Chance Constraints (MIQPCC) to address stochastic complementarity constraints, converting hard constraints into soft constraints and employing expected residual minimization-based penalties to optimize trajectories in stochastic discrete-time complementarity systems (SDLCS).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LCP-based contact models are used for trajectory optimization, then contact dynamics can be modeled, but stochastic complementarity constraints cause infeasibility in the optimization problem
Solution Approach 1:
The patent introduces a barrier function as an intermediary mathematical tool to handle the stochastic complementarity constraints. The barrier function transforms the infeasible stochastic complementarity constraints into a feasible optimization problem by penalizing constraint violations in a differentiable manner, allowing the use of standard optimization algorithms while maintaining the physical meaning of contact constraints.
Solution Approach 2:
The patent transforms the stochastic complementarity constraints by changing the parameter representation from direct complementarity conditions to expected value constraints with variance penalties. This parameter transformation converts the infeasible stochastic problem into a feasible deterministic equivalent that can be solved using standard optimization techniques while accounting for uncertainty.
2Reliability
If hard constraints are imposed on SDLCS for robust trajectory optimization, then solution feasibility is ensured, but the optimization problem becomes difficult to solve
Solution Approach 1:
The patent transforms the static hard constraints into dynamic soft constraints that adapt during optimization. By using expected residual minimization with penalty functions, the constraints become flexible during the optimization process, allowing the solver to navigate the feasible region more easily while still converging to solutions that satisfy the original hard constraints with high probability.
Solution Approach 2:
The patent applies beforehand cushioning by introducing penalty terms that anticipate constraint violations. The expected residual minimization approach pre-penalizes potential constraint breaches in the objective function, cushioning against infeasibility before it occurs and guiding the optimization toward feasible solutions without requiring complex constraint handling during the solving process.
3Ease of manufacture
If soft constraints with ERM-based penalty are used on SDLCS, then optimization can be performed, but the resulting trajectories are less robust
Solution Approach 1:
The patent incorporates feedback by using the expected residual information from the soft constraints to guide the optimization toward more robust solutions. The penalty terms provide feedback about constraint satisfaction levels, allowing the optimizer to adjust control inputs to maintain feasibility under uncertainty, thereby improving robustness while keeping the problem computationally tractable.
Solution Approach 2:
The patent substitutes the mechanical hard constraint enforcement with a statistical mechanics approach using expected value constraints and penalty functions. This substitution replaces the rigid feasibility enforcement with a probabilistic framework that achieves similar robustness goals while enabling the use of efficient gradient-based optimization methods.
Data Source
AI summary
A robotic system for manipulating an object with a robotic manipulator is provided. The robotic system is configured to collect a digital representation of a task for manipulating the object; solve a robust control problem to optimize a sequence of control forces to be applied by the robotic manipulator to change a state of the object, where an evolution of the state of the object is governed by a stochastic complementarity system modeling the task with a predefined probability. The robust control problem optimizes a cost function to generate the sequence of control forces performing the task subject to joint chance constraints including a first chance constraint on the state of the object being manipulated and a second chance constraint on stochastic complementarily constraints modeling manipulation of the object. The robotic system is further configured to control the manipulation of the object based on the sequence of control forces.


