Displacement Sensing of an Active String Actuator Using a Step-Index Multimode Optical Fiber Sensor

Area of Science:

• Robotics and Mechanical Engineering
• Biomedical Engineering
• Materials Science

Background:

• McKibben artificial muscles are compact pneumatic actuators (1.8 mm outer diameter).
• Accumulating these muscles creates an "active string actuator" with high contractile displacement.
• Accurate length estimation is crucial for controlling active string actuators, but traditional sensors are unsuitable due to size and rigidity.

Purpose of the Study:

• To propose and validate a novel, simple sensing method for estimating the length of active string actuators.
• To overcome the limitations of bulky and rigid sensors in measuring the displacement of thin artificial muscles.

Main Methods:

• Integrated a step-index multimode optical fiber with the active string actuator.
• Utilized a light emitter and receiver to monitor light propagation through the optical fiber.
• Correlated changes in light transmission with the actuator's length during operation.

Main Results:

• Demonstrated a clear correlation between the optical fiber sensor's output and the actuator's length.
• The proposed sensing system showed that light propagation changes predictably with actuator displacement.
• Fundamental experiments confirmed the feasibility of the optical fiber sensing approach.

Conclusions:

• The developed optical fiber sensing system is a viable method for estimating the displacement of active string actuators.
• This simple, non-rigid sensor overcomes the limitations of conventional sensors for thin artificial muscles.
• The findings pave the way for improved control of McKibben artificial muscle-based actuators.