Bio-Inspired Musculoskeletal Antagonistic Joint

End-to-end actuator design, fabrication, and antagonistic joint integration for full motion range.

Outcome

I designed, built, and validated an antagonistic electrohydraulic muscle-clutch system that lets one muscle side contract while the opposite side can safely extend. This restores practical full-joint motion in musculoskeletal antagonistic joints. Compared with a matched HASEL-only baseline, the integrated system increased usable strain by about 58%.

Problem

Non-stretchable artificial muscles in antagonistic setups lose usable displacement because tendon slack blocks extension. In practice, this can significantly reduce functional joint range.

Mechanism overview: antagonistic non-stretchable muscles with electrostatic clutch for full-range motion

The goal of this project was to remove that bottleneck and enable both contraction and extension in one antagonistic architecture, while preserving fast actuation and controllable motion.

System

  • Actuation: non-stretchable HASEL muscle packs (8 pouches in series) characterized up to 16.3 N force or 18.0 mm displacement at 8 kV
  • Clutch layer: electrostatic clutch units integrated with elastic textile packaging (up to 5.5 N/cm^2 friction force density at 150 V)
  • Joint integration: antagonistic tendon-driven musculoskeletal joint using paired HASEL-clutch units
  • Control strategy: synchronized state-machine feed-forward control (clutch AC square-wave, HASEL ramp actuation)
  • Instrumentation: high-voltage amplifiers, magnetic encoder, NI DAQ, and MATLAB data-acquisition control pipeline

Contribution

  • Analytical modeling of antagonistic muscle-clutch mechanics for full-range operation
  • End-to-end actuator and clutch design, fabrication workflow development, and build execution
  • Joint-level integration, testbench setup, control implementation, and frequency-sweep experiments

Technical Stack

  • HASEL actuator design and force-displacement characterization
  • Electrostatic clutch design and stretchable packaging
  • Antagonistic tendon-joint integration
  • Feed-forward state-machine control for synchronized muscle-clutch actuation
  • High-voltage actuation, sensing, and DAQ-based experimental control
  • Hardware prototyping, benchmarking, and repeatability analysis

Key Results

  • Increased antagonistic joint range from +-52 deg (HASEL-only) to +-82 deg with HASEL-clutch integration under matched input conditions (~58% gain in usable strain)
  • Demonstrated smooth antagonistic switching and motion transitions up to 3.2 Hz
  • Reached approximately 160 deg bidirectional joint range during 2.5 Hz cyclic operation
  • Established an extensible architecture that can be transferred to other non-stretchable muscle technologies
  • Published at IEEE ICRA (2025)

Media

Video demo: stretchable antagonistic electrohydraulic joint behavior.

Impact and Future Direction

This project addresses a core bottleneck in bio-inspired robotics: recovering full antagonistic joint motion when muscles are non-stretchable. The mechanism-level solution is modular and can be reused beyond HASELs, including with other non-stretchable muscle technologies such as McKibben-type actuators. Based on the paper’s conclusions, the next steps are heavier-load validation, horizontal testing without gravity-assisted return, and clutch-elasticity tuning for resonance-aware higher-speed motion.

Skills

actuator design electrostatic clutch fabrication antagonistic joints feed-forward control high-voltage robotics experimental validation system integration