Showing papers by "Nancy M. Amato published in 2018"

SLAP: Simultaneous Localization and Planning Under Uncertainty via Dynamic Replanning in Belief Space

Abstract: Simultaneous localization and planning (SLAP) is a crucial ability for an autonomous robot operating under uncertainty. In its most general form, SLAP induces a continuous partially observable Markov decision process (POMDP), which needs to be repeatedly solved online. This paper addresses this problem and proposes a dynamic replanning scheme in belief space. The underlying POMDP, which is continuous in state, action, and observation space, is approximated offline via sampling-based methods, but operates in a replanning loop online to admit local improvements to the coarse offline policy. This construct enables the proposed method to combat changing environments and large localization errors, even when the change alters the homotopy class of the optimal trajectory. It further outperforms the state-of-the-art Feedback-based Information RoadMap (FIRM) method by eliminating unnecessary stabilization steps. Applying belief space planning to physical systems brings with it a plethora of challenges. A key focus of this paper is to implement the proposed planner on a physical robot and show the SLAP solution performance under uncertainty, in changing environments and in the presence of large disturbances, such as a kidnapped robot situation.

A General Region-Based Framework for Collaborative Planning

Abstract: Sampling-based planning is a common method for solving motion planning problems. However, this paradigm falters in difficult scenarios, such as narrow passages. In contrast, humans can frequently identify these challenges and can sometimes propose an approximate solution. A recent method called Region Steering takes advantage of this intuition by allowing a user to define regions in the workspace to weight the search space for probabilistic roadmap planners. In this work, we extend Region Steering into a generalized Region-Based framework that is suitable for any sampling-based planning approach. We explore three variants of our framework for graph-based, tree-based, and hybrid planning methods. We evaluate these variants in simulations as a proof of concept. Our results demonstrate the benefits of our framework in reducing overall planning time.

Sampling-based motion planning with reachable volumes for high-degree-of-freedom manipulators:

Abstract: Motion planning for constrained systems is a version of the motion planning problem in which the motion of a robot is limited by constraints. For example, one can require that a humanoid robot such as a PR2 remain upright by constraining its torso to be above its base or require that an object such as a bucket of water remain upright by constraining the vertices of the object to be parallel to the robot’s base. Grasping can be modeled by requiring that the end effectors of the robot be located at specified handle positions. Constraints might require that the robot remain in contact with a surface, or that certain joints of the robot remain in contact with each other (e.g., closed chains). Such problems are particularly difficult because the constraints form a manifold in C-space, and planning must be restricted to this manifold. High-degree-of-freedom motion planning and motion planning for constrained systems has applications in parallel robotics, grasping and manipulation, computational biology and mole...

A General and Flexible Search Framework for Disassembly Planning

Abstract: We present a new general framework for disassembly sequence planning. This framework is versatile allowing different types of search schemes (exhaustive vs. preemptive), various part separation techniques, and the ability to group parts, or not, into subassemblies to improve the solution efficiency and parallelism. This enables a truly hierarchical approach to disassembly sequence planning. We demonstrate two different search strategies using this framework that can either yield a single solution quickly or provide a spectrum of solutions from which an optimal may be selected. We also develop a method for subassembly identification based on collision information. Our results show improved performance over an iterative motion planning based method for finding a single solution and greater functionality through hierarchical planning and optimal solution search.

Topological Nearest-Neighbor Filtering for Sampling-Based Planners

Abstract: Nearest-neighbor finding is a major bottleneck for sampling-based motion planning algorithms The cost of finding nearest neighbors grows with the size of the roadmap, leading to significant slowdowns for problems which require many configurations to find a solution Prior work has investigated relieving this pressure with quicker computational techniques, such as kd-trees or locality-sensitive hashing In this work, we investigate an alternative direction for expediting this process based on workspace connectivity We present an algorithm called Topological Nearest-Neighbor Filtering, which employs a workspace decomposition to select a topologically relevant set of candidate neighbor configurations as a pre-processing step for a nearest-neighbor algorithm We investigate the application of this filter to several varieties of RRT and demonstrate that the filter improves both nearest-neighbor time and overall planning performance

Affordance Wayfields for Task and Motion Planning

Abstract: Affordances provide a natural means for a robot to describe its agency as actions it can perform on objects. Further, affordances can enable robots to reason complicated, multi-step tasks that involve proper use of a diversity of objects. This paper proposes the concept of affordance wayfields for representing manipulation affordances as objective functions in configuration space. Affordance wayfields quantify how well a path, or sequence of motions, will accomplish an afforded action on an object. Paths that enact affordances can be located by performing a randomized form of gradient descent over affordance wayfields. Incorporating obstacles, or other constraints into wayfields allows our method to adaptively generate valid motions for executing afforded actions. We demonstrate that affordance wayfields can enable robots, such as the Michigan Progress Fetch mobile manipulator, to solve complex real-world tasks such as assembling a table, or loading and unloading objects from a storage chest.

Fast Collision Detection for Motion Planning Using Shape Primitive Skeletons

Abstract: In many robotics applications, the environment (robots and obstacles) often have very complex geometries. These result in expensive primitive computations such as collision detection which in turn, affect the overall performance of these applications. Approximating the geometry is a common approach to optimize computation. Unlike other applications of geometric approximation where it is applied to one space (usually obstacle space), we approximate both obstacle and free workspace with a set of geometric shape primitives that are completely contained within the space and represent its topology (skeleton). We use these “shape primitive skeletons” to improve collision detection performance in motion planning algorithms. Our results show that the use of shape primitive skeletons improves the performance of standard collision detection methods in motion planning problems by 20–70% in our 2D and 3D test environments regardless of motion planning strategy. We also show how the same shape primitive skeletons can be used with robots of different sizes to improve the performance of collision detection operation.

Nested Parallelism with Algorithmic Skeletons

Abstract: Nested parallelism is a natural way to express programs for hierarchical systems. It enables a compositional programming approach that can then be mapped onto the system hierarchy. In this paper, we present nested algorithm composition in the STAPL Skeleton Library (SSL) which uses a nested dataflow model as its internal representation. We show how a high level program specification using SSL allows for asynchronous computation and improved locality. We study both the specification and performance of the stapl implementation of Kripke, a mini-app developed by Lawrence Livermore National Laboratory. Kripke has multiple levels of parallelism and a number of data layouts, making it an excellent test bed to exercise the effectiveness of a nested parallel programming approach. Performance results are provided for six different nesting orders of the benchmark demonstrating the flexibility and performance of nested algorithmic skeleton composition in stapl.