Fatigue test on optical fiber angle sensors based on polymeric materials for flexion–extension applications

Polymer Optical Fiber (POF) and Cyclic Transparent Optical Polymer (CYTOP) based sensors present some advantages related to their light weight, flexibility, and reduced dimensionality for applications in assistive robotics compared to conventional sensors that are rigid and heavy. To ensure adequate functionality, usability, and controllability of the systems over time, the measurements made by the sensors must be maintained in optimal ranges of functionality. Considering that for most robotic assistance applications an adequate range of motion of the limbs is at approximately 80°, this study presents a fatigue test performed on three Polymeric Optical Fiber sensors for angle measurement in this range. The tests were performed on a bending system that generates variations at a frequency of 2 Hz recording the voltage variation. For fatigue measurement each sensor was instrumented into the system and set to perform a total of 40,000 cycles, repeating the tests two times per sensor. The results show that the CYTOP optical fiber-based sensor did not break during the trial; however, it is determined that this type of fiber is more sensitive to light variations in the environment. On the other hand, the other two sensors reached a time of approximately 70 min for a total of 8,360 cycles to rupture. These results have potential usability in characterizing systems incorporating angle sensors to estimate proper system performance.