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Autonomous Excavation of Challenging Terrain using Oscillatory Primitives and Adaptive Impedance Control

Noah Franceschini, Pranay Thangeda, Melkior Ornik, Kris Hauser

Abstract

This paper addresses the challenge of autonomous excavation of challenging terrains, in particular those that are prone to jamming and inter-particle adhesion when tackled by a standard penetrate-drag-scoop motion pattern. Inspired by human excavation strategies, our approach incorporates oscillatory rotation elements -- including swivel, twist, and dive motions -- to break up compacted, tangled grains and reduce jamming. We also present an adaptive impedance control method, the Reactive Attractor Impedance Controller (RAIC), that adapts a motion trajectory to unexpected forces during loading in a manner that tracks a trajectory closely when loads are low, but avoids excessive loads when significant resistance is met. Our method is evaluated on four terrains using a robotic arm, demonstrating improved excavation performance across multiple metrics, including volume scooped, protective stop rate, and trajectory completion percentage.

Autonomous Excavation of Challenging Terrain using Oscillatory Primitives and Adaptive Impedance Control

Abstract

This paper addresses the challenge of autonomous excavation of challenging terrains, in particular those that are prone to jamming and inter-particle adhesion when tackled by a standard penetrate-drag-scoop motion pattern. Inspired by human excavation strategies, our approach incorporates oscillatory rotation elements -- including swivel, twist, and dive motions -- to break up compacted, tangled grains and reduce jamming. We also present an adaptive impedance control method, the Reactive Attractor Impedance Controller (RAIC), that adapts a motion trajectory to unexpected forces during loading in a manner that tracks a trajectory closely when loads are low, but avoids excessive loads when significant resistance is met. Our method is evaluated on four terrains using a robotic arm, demonstrating improved excavation performance across multiple metrics, including volume scooped, protective stop rate, and trajectory completion percentage.
Paper Structure (18 sections, 21 equations, 5 figures, 2 tables)

This paper contains 18 sections, 21 equations, 5 figures, 2 tables.

Table of Contents

  1. INTRODUCTION
  2. Related Work
  3. Excavation
  4. Excavator Trajectory Planning
  5. Excavation Control
  6. Methodology
  7. Parameterized Scooping Primitive
  8. Swivel Primitive
  9. Twist Primitive
  10. Dive Primitive
  11. Reactive Attractor Impedance Controller
  12. Experiments and Results
  13. Setup Overview
  14. Controller Parameter Tuning
  15. Effects of Primitive Parameters
  16. ...and 3 more sections

Figures (5)

  • Figure 1: Strobe-effect visualization of a robot excavating large-grained slate. Motion of the scoop is illustrated via tinting progressing from red to blue hue. Left: standard Penetrate-Drag-Scoop (PDS) motion with impedance control fails due to jamming forces triggering a protective stop (red X). Right: using our "swivel" primitive and Reactive Attractor Impedance Controller (RAIC), the robot breaks through jammed particles and excavates a large volume (outlined in white). Trajectory of the scoop is illustrated as an orange curve.
  • Figure 2: Illustration of the PDS trajectory.
  • Figure 3: Illustration of our proposed primitives. Bottom row shows side and t op-down views of oscillatory trajectories. Scoop tint indicates magnitude of roll (cyan - orange), yaw (blue - yellow), and pitch (green).
  • Figure 4: Parameter exploration showing how primitive parameter settings are related to excavated volume. Dive sweep = None is equivalent to the standard penetrate-drag-scoop trajectory.
  • Figure 5: Testing on hidden obstacles, showing movement via strobe-effect. Left: a rigid slope is embedded in gravel. Right: a large rock embedded in soil. Top row: a standard impedance controller is unable to comply to these obstacles when jamming is encountered, triggering a protective stop. Bottom row: the RAIC controller successfully adapts to these obstacles.