Interferometric Six Degree-of-Freedom Direct Fibre Optic Shape Sensing

• Applicant: Professor Dr. Thomas Kissinger
• Subject Area: Measurement Systems
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536023270

Direct fibre-optic shape sensing (DFOSS) is an emerging technology to measure the shape of a sensing cable and therefore infer the shape/deformation of the structure to which the cable is attached to. The capability to directly measure shape without an external observer is very interesting from a research perspective and can enable novel solutions in areas as diverse as aerospace, robotics or medicine. The fiber-segment interferometry (FSI) interrogation approach pioneered by the applicant has already shown superior resolution compared to competing interrogation approaches in many demanding applications. Also, the FSI concept promises improved shape accuracy due to its capability for theoretically exact strain integration over defined fiber segments and its immunity to strain gradients. However, up to date the FSI technology has not yet been extended to torsion sensing, which would be of crucial importance to many practical applications where cable torsion cannot be ruled out. Furthermore, the rigidity of typical sensing cables often prohibits the use of DFOSS in situations where flexible elongation of the sensor cable is required. Also, the direct measurement of the elongation would be required to achieve DFOSS with all 6 degrees-of-freedom (DoF). This has not yet been demonstrated in prior art but could benefit many potential applications, such as continuum and soft robotics. In this proposal fundamental research into new sensing cable structures will be conducted that aim to extend interferometric DFOSS to five DoF (including torsion) and six DoF (including torsion and elongation) for the first time. Extensive theoretical modelling will be required to gain an understanding of the necessary sensing cable configurations. This will be followed by a thorough static and dynamic characterization of the achievable resolution and accuracy performance of the fabricated sensing cables. This proposal will culminate in a dedicated demonstrator system for full 6-DoF DFOSS employed to showcase the capability to measure the position and orientation of a moving 6-DoF parallel-kinematic robot platform. In particular this proposal aims to achieve the following novel contributions to science: 1) The first demonstration of the combination of interferometric DFOSS and torsion sensing using a sensing cable structure with an helical fiber arrangement. 2) The first demonstration of full 6-DoF interferometric DFOSS using coiled sensing cables, where the coiled structure provides low axial stiffness to enable safe operation over extended expansion ranges and permits the measurement of the elongation itself. 3) The first demonstration of DFOSS employed as position and orientation encoder with six DoFs.

• DFG Programme: Research Grants