Sensorless model-based tension control for a cable-driven exosuit

Area of Science:

• Robotics
• Biomechanics
• Rehabilitation Engineering

Background:

• Cable-driven exosuits offer potential for motor disability support.
• Current designs often incorporate costly and complex force sensors for tension measurement.

Purpose of the Study:

• To present a novel design and control strategy for an upper limb cable-driven exosuit that eliminates the need for force sensors.
• To evaluate the feasibility and effectiveness of a sensorless exosuit in terms of assistive torque control, movement quality, and muscular effort.

Main Methods:

• Developed a mechanically transparent exosuit design.
• Utilized data-driven friction identification for a model-based tension controller.
• Evaluated the system with 17 healthy participants performing arm movements, collecting kinematic, electromyography, and subjective data.

Main Results:

• Achieved root mean square error of 0.71 Nm (18%) in tracking desired assistive torque at 50% gravity support.
• Demonstrated significant reductions in electromyography signals for anterior deltoid (30%), trapezius (38%), and pectoralis major (38%) during arm raising.
• Observed increased posterior deltoid activity (32%) during lowering, with no significant change in position tracking but decreased movement smoothness.

Conclusions:

• The removal of force sensors is feasible and effective for cable-driven exosuits.
• The sensorless approach simplifies exosuit design and reduces cost, paving the way for more accessible assistive devices.
• Further improvements in exosuit ergonomics are needed to mitigate user discomfort.