Integrated Optical Deformation Measurement with TIR Prism Rods

• Published in: Sensors (Basel, Switzerland) Vol. 23; no. 2; p. 943
• Main Author: Wolf, Alexander
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 13.01.2023; MDPI
• Subjects: Biomechanical Phenomena; Communication; condition monitoring; Deformation; integrated measurement; Interferometry; Laser beams; Lasers; Light; Load; Optical measurement; Position measurement; Principles; prism rods; Radiation; Rods; Sensitivity; Sensors; Strain gauges; torsion; integrated measurement; prism rods; optical measurement; torsion; deformation; condition monitoring; decency level of sensitivity; total internal reflection
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s23020943

In this paper, a novel optical measurement principle for deformation, especially torsion, is presented. A laser beam is guided via total internal reflection (TIR) in a prism rod. Every single reflection causes an increasing change in the beam path, which can be measured by its effect on the outcoupling position of the laser. With a diameter of the prism rod of 10 mm and a length of 120 mm, the system achieves torsion sensitivities between 350 µm/° and more than 7000 µm/°, depending on the actual torsion angle φ. A decency level of sensitivity is defined for comparison, which is exceeded by a factor of ~55 at φ=0. The presented principle of TIR prism rods can be adapted to measure different load cases. Using two laser beams, bending and torsion can be distinguished and combined load cases analyzed. The resulting system can be integrated into machine elements, such as screws, to perform condition monitoring on mechanically loaded components.