Safety-critical Autonomous Inspection of Distillation Columns using Quadrupedal Robots Equipped with Roller Arms

TL;DR

Problem: autonomous inspection in confined, multi-layer distillation-column trays requires strict safety guarantees in real industrial settings. Approach: a safety-critical autonomy stack for a quadruped with a roller arm combines a reduced-order planning model, two Control Barrier Functions (CBFs) for manway and edge, QP-based safety planning, footstep replanning, full-body inverse-dynamics control, intermediate motions via MIQP, and a perception loop, all governed by a state machine. Contributions: design and validation of the safety-critical framework, bridging intermediate motions, perception integration, and empirical validation in industry-grade trays. Significance: enables autonomous, safe inspection with minimal human intervention in hazardous industrial environments, bridging perception, planning, and control in tight spaces.

Abstract

This paper proposes a comprehensive framework designed for the autonomous inspection of complex environments, with a specific focus on multi-tiered settings such as distillation column trays. Leveraging quadruped robots equipped with roller arms, and through the use of onboard perception, we integrate essential motion components including: locomotion, safe and dynamic transitions between trays, and intermediate motions that bridge a variety of motion primitives. Given the slippery and confined nature of column trays, it is critical to ensure safety of the robot during inspection, therefore we employ a safety filter and footstep re-planning based upon control barrier function representations of the environment. Our framework integrates all system components into a state machine encoding the developed safety-critical planning and control elements to guarantee safety-critical autonomy, enabling autonomous and safe navigation and inspection of distillation columns. Experimental validation in an environment, consisting of industrial-grade chemical distillation trays, highlights the effectiveness of our multi-layered architecture.

Figures (8)

• Figure 1: Robotic system and industry-grade column tray: Our robotic system consists of a quadruped robot, roller arm, perception package, and tether system, as shown in the left figure.
• Figure 2: Overall structure of the proposed framework: The proposed framework consists of a locomotion stack, transition stack, and state machine for autonomy. In addition, the perception part provides the manway vertices to ensure the safety in the planning parts.
• Figure 3: Two CBFs for safety-critical planning in the tray: $h_1$ and $h_2$ are the CBFs to avoid the manway and the edge of the tray, respectively.
• Figure 4: Experimental result generating Pre-motion for downwawrd transition: By strategically planning intermediate motions prior to initiating the downward transition, the sequence of contact points ensures smooth joint configuration adjustments for the transition. CoM is maintained within the support polygon throughout these intermediate motions.
• Figure 5: Experimental result generating Post-motion for downward transition: (a) final configuration post downward transition, (b) front legs realigned to adjust the support polygon, (c) arm slightly folded to detach from the upper layer, (d) arm length adjustment, (e) arm fully folded in preparation for subsequent locomotion, (f) configuration for next locomotion.

Theorems & Definitions (1)

• Definition 1