Illuminating Robotics and the Role of Optical Sensors in Continuum Robots

Early version continuum robot arm performing welding in an ultra-modern factory © Jack -stock.adobe.com

The field of continuum robotics is advancing rapidly, driven by innovations in kinematic structures, locomotion principles, and control strategies. A continuum robot is a flexible, continuously deformable robotic structure that mimics biological limbs, such as human-like flexible arms, octopus arms or elephant trunks, allowing smooth, continuous, and adaptive motion without rigid joints (1,2).

A new study published in Sensors by researchers from the Technical University of Košice in Slovakia and the University of Texas at Austin reviewed the latest sensing technologies, with a special emphasis on optical sensors that are transforming the field. Led by Peter Jan Sincak and his colleagues Erik Prada, Ľubica Miková, Roman Mykhailyshyn, Martin Varga, Tomas Merva, and Ivan Virgala, the review highlights how spectroscopic techniques and optical fibers are being used to enhance robotic sensing (1).

Continuum robots, with their flexible structures, require precise sensing mechanisms to track their shape and interactions with the environment. Among the various sensing approaches, optical-based sensors—particularly those utilizing spectroscopic principles—have emerged as the most reliable and versatile solutions. These sensors use light transmission, reflection, and interference to measure deformations and environmental interactions with high precision (1,2).

Optical Sensors: The Gold Standard in Continuum Robotics

The study identifies optical fiber sensors as the dominant technology in shape perception and environmental sensing. The most widely used approach is Fiber Bragg Grating (FBG) sensors, which employ periodic variations in the refractive index along an optical fiber. These variations create a specific wavelength reflection pattern that changes when the fiber is strained. By analyzing the shift in the reflected wavelength, researchers can precisely reconstruct the shape of the continuum robot in real time (1).

Spectroscopic techniques integrated into optical sensors allow for enhanced precision in measuring strain, temperature, and pressure variations along the robot’s flexible body. The advantages of optical sensing include resistance to electromagnetic interference, high sensitivity, and the ability to function in harsh environments where other sensors may fail (1).

Comparing Optical Sensors to Other Technologies

While electrical and magnetic sensors have their advantages, optical sensors stand out due to their accuracy and immunity to external disturbances. The study classifies sensing methods into three categories (1):

Optical-Based Sensors—These include FBG and interferometric sensors that leverage changes in light properties to track robotic movement. Optical sensors provide unparalleled precision and are increasingly used in medical and industrial robotic applications where fine control is essential.

Electrical-Based Sensors—These sensors rely on changes in electrical resistance or capacitance to measure deformation. While cost-effective, they are prone to signal interference and may not provide the same level of accuracy as optical solutions.

Magnetic-Based Sensors—Using permanent magnets or electromagnetic coils, these sensors track movement based on changes in magnetic fields. Although useful in miniaturized designs, they are susceptible to interference from surrounding metallic objects.

Spectroscopic Applications in Continuum Robotics

The integration of spectroscopic techniques within optical sensors is revolutionizing continuum robotics. Spectroscopy enables the precise measurement of strain and stress distributions along the robot's structure, providing crucial data for real-time shape reconstruction. Additionally, hyperspectral and multispectral imaging techniques can be incorporated to enhance environmental perception, allowing robots to detect chemical compositions or subtle material variations in their surroundings (1).

Future Directions and Challenges

Despite advantages, optical sensors still face challenges related to cost and integration complexity. The study highlights the need for further miniaturization and the development of more flexible, cost-effective optical fibers to enhance the feasibility of large-scale adoption. Combining optical sensing with AI-driven data analysis could further improve robotic adaptability and precision in dynamic environments (1,2).

As continuum robots continue to advance, optical sensors and spectroscopic applications will play an increasingly vital role in future robotic intelligence and autonomy. This review provides a crucial roadmap for researchers aiming to harness the power of light to drive the next generation of flexible robotic systems.

References

(1) Sincak, P. J.; Prada, E.; Miková, Ľ.; Mykhailyshyn, R.; Varga, M.; Merva, T.; Virgala, I. Sensing of Continuum Robots: A Review. Sensors 2024, 24 (4), 1311. DOI: 10.3390/s24041311

(2) van Veggel, S.; Wiertlewski, M.; Doubrovski, E. L.; Kooijman, A.; Mazzolai, B.; Scharff, R. B. Optoelectronically Innervated Suction Cup Inspired by the Octopus. Adv. Intell. Syst. 2025, 2400544. DOI: 10.1002/aisy.202400544