Shihao Cheng
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Research

Phase-Variable Control for Continuous Locomotion Transitions

A phase-variable controller for powered knee-ankle prostheses that produces smooth walk–stair transitions across all eight inter-leg cases, without relying on abrupt discrete mode switching. Plainly: the prosthesis doesn't just switch from ‘walking mode’ to ‘stair mode’ — it continuously changes its motion through the transition.

Award IROS 2023 Best Student Paper Award
IEEE TNSRE 2024 Phase-Variable Control Walk-Stair Transition Powered Prosthesis
Watch Video TNSRE 2024 Paper
Related: IROS 2023 Paper ->
Loop demo comparing discrete switching and continuous variable-transition control during stair transitions.
OST vs CVT comparison Stair ascent Stair descent Real-time kinematics
Problem & Contribution

Walk–stair transitions are brittle when a controller depends on one perfect switching moment; making them smooth and timing-robust is one of the strongest results of my Ph.D. work.

My Role

I developed and validated the phase-variable transition controller, including the CVT formulation, OST comparison, delay robustness analysis, and human-subject experiments.

Challenge

Powered-prosthesis controllers often switch abruptly between steady-state modes during activity transitions.

Contribution

Smooth walk–stair transition control demonstrated on a powered knee-ankle prosthesis across inter-leg cases.

Ph.D. research conducted in the LocoLab at the University of Michigan, advised by Prof. Robert D. Gregg.

Controller Comparison
CVT — Continuous Variable Transition (proposed)
  • Blends walking and stair behavior continuously via a phase variable
  • Robust to mistimed switching and sensing delay
  • Smooth across all inter-leg transition cases
OST — One-Shot Transition (baseline)
  • Switches modes at a single detected instant
  • Sensitive to when that switch fires
  • Abrupt behavior change at the transition
Evidence
2023 IROS Best Student Paper Award for continuous transition control
Award context for the continuous transition control work recognized at IROS 2023.
All 8 Inter-Leg Transition Cases
Coverage
Smoother Transitions
vs. Switching
IROS 2023 Best Student Paper
Award
Experimental evaluation of continuous inter-leg transitions (TNSRE 2024)
Experiment overview showing stair-transition photos, participant setup in parallel bars, and an overhead footprint map of the stair, ramp, and platform circuit. Adapted from Cheng et al., IEEE TNSRE 2024. © 2024 IEEE.

Technical Stack

Phase-Variable Control Continuous Transition Control Inter-Leg Transitions CVT vs OST Delay Robustness Human-Subject Validation
More Related Work
View all projects →
tmrb2022_concept Modeling Transitional Kinematics for Continuous Locomotion Control The hardest moment in locomotion is often the transition itself; this work models walk–stair transitions as first-class movement, not just the gap between steady-state activities. View Project → tnsre2026_gagraphic Control Continuous Impedance Control for Wearable Locomotion Smooth swing motion isn't enough — during stance the robot must also provide the right support, so this extends continuous transition control into impedance behavior during weight-bearing. View Project → ICF-based intent recognition concept Intent Interpretable Intent Recognition for Wearable Robots Intent recognition decides when a wearable robot changes behavior, so making it fast, interpretable, and adaptive keeps the whole control system trustworthy. View Project →
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