Review of Soft Actuator Technologies for Human-Robot Interaction: Materials, Control Strategies, and Safety Considerations

Abstract

The emergence of collaborative robotics and human-robot interaction applications has exposed fundamental limitations of traditional rigid actuators, which pose inherent safety risks and lack the compliance necessary for safe, natural interaction with humans. Soft actuators, fabricated from compliant materials and exhibiting inherent flexibility, have emerged as a promising alternative technology that addresses these limitations while enabling novel robotic capabilities. This comprehensive review examines the state-of-the-art in soft actuator technologies specifically for human-robot interaction applications, analyzing materials, actuation principles, control strategies, and safety considerations. We systematically categorize soft actuators into four primary classes based on actuation mechanisms: pneumatic soft actuators including McKibben muscles and bending actuators, hydraulic systems, shape memory alloy-based actuators, and electroactive polymer actuators including dielectric elastomers and ionic polymer-metal composites. For each category, we evaluate key performance characteristics including force output, response time, energy efficiency, durability, and manufacturing complexity. The review addresses the unique control challenges posed by soft actuators, including highly nonlinear dynamics, hysteresis, time-varying parameters, and modeling uncertainties, examining control approaches ranging from model-based methods to learning-based adaptive strategies. Safety considerations are thoroughly analyzed, including intrinsic safety through compliance, force limitation mechanisms, failure mode analysis, and human factors in physical interaction. We examine integration challenges such as proprioceptive sensing for soft robots, compact valve systems for pneumatic actuation, and power supply considerations for portable applications. Application domains including rehabilitation robotics, assistive devices, wearable exoskeletons, and service robots are discussed with specific examples illustrating the advantages of soft actuation. Future research directions are identified, including multi-material fabrication techniques, self-sensing soft actuators, and bio-inspired designs. This review provides a comprehensive resource for researchers and engineers developing safe, compliant robotic systems for human interaction.