Real-Time Motion Planning of a Hydraulic Excavator using Trajectory Optimization and Model Predictive Control

TL;DR

This paper introduces a real-time, integrated motion planning framework for hydraulic excavators that combines global trajectory optimization with local receding horizon control, ensuring constraint satisfaction and disturbance handling during excavation tasks.

Contribution

It presents the first real-time motion planning framework for hydraulic excavators that guarantees constraint feasibility and disturbance robustness using trajectory optimization and model predictive control.

Findings

Global trajectories computed in about one second.

Local planner tracks trajectories at over 30 Hz.

Framework successfully handles hydraulic and soil interaction disturbances.

Abstract

Automation of excavation tasks requires real-time trajectory planning satisfying various constraints. To guarantee both constraint feasibility and real-time trajectory re-plannability, we present an integrated framework for real-time optimization-based trajectory planning of a hydraulic excavator. The proposed framework is composed of two main modules: a global planner and a real-time local planner. The global planner computes the entire global trajectory considering excavation volume and energy minimization while the local counterpart tracks the global trajectory in a receding horizon manner, satisfying dynamic feasibility, physical constraints, and disturbance-awareness. We validate the proposed planning algorithm in a simulation environment where two types of operations are conducted in the presence of emulated disturbance from hydraulic friction and soil-bucket interaction: shallow and deep excavation. The optimized global trajectories are obtained in an order of a second, which is tracked by the local planner at faster than 30 Hz. To the best of our knowledge, this work presents the first real-time motion planning framework that satisfies constraints of a hydraulic excavator, such as force/torque, power, cylinder displacement, and flow rate limits.