Development of an optical force sensor: a novel approach for monitoring physical interaction in robotic walkers
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Data
2026-02-20
Autores
Garcia Alvarez, Daniel Eduardo
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Universidade Federal do Espírito Santo
Resumo
This dissertation presents the design, development, and experimental validation of an optical sensor (OS) for monitoring interaction forces in smart walkers (SWs). The proposed sensing approach integrates light-sensitive photodiodes and addressable RGB light-emitting diodes embedded within a compliant encapsulation material, enabling force estimation by measuring changes in optical signals caused by surface deformations. Compared to conventional force-sensing technologies (i.e., strain gauges, piezoelectric sensors, and high resolution triaxial force cells) and optical Ąber-based alternatives (i.e., polymer optical Ąbers and Ąber Bragg gratings), the proposed OS reduces system complexity while ofering a cost-efective and easily manufacturable design, facilitating its integration into SWs. The Ąrst OS prototype validated the feasibility of the proposed approach, achieving an average force estimation error of 2.4%. Meanwhile, it identiĄed contact zones with an accuracy of 98%. These results demonstrate reliable performance in both force regression and contact localization, as well as the ability to capture the spatial distribution of applied forces. A second development stage focused on a redesigned OS geometry optimized for walker-handle integration, enabling force sensing across multiple interaction zones. An evaluation of the efects of encapsulation materials and illumination wavelengths on OS performance revealed that combination of EcoĆex encapsulation and red light provided the best results, achieving the lowest mean squared error (MSE) (Validation: 4.72 ± 0.31; Test: 4.96), mean absolute error (MAE) (Validation: 1.61 ± 0.04; Test: 1.79), and the highest coeicient of determination (R2) (Validation: 0.98 ± 0.01; Test: 0.97). The optimized conĄguration also demonstrated good generalization to unseen loads, with an average error of 5.56%. To assess repeatability, four new OS units implementing the optimized conĄguration were fabricated and independently calibrated. Among them, the fourth OS achieved the best results, with the lowest prediction errors (MSE validation: 3.11 ± 0.55; test: 3.33; MAE validation: 1.18 ± 0.10; test: 1.24) and the highest correlation values (R2 validation: 0.98 ± 0.02; test: 0.98). Validation against a commercial reference system conĄrmed estimation errors below 5.78% across all four OSs. Finally, the integration of the OSs into a SW and their evaluation during path-following trials with ten healthy participants demonstrated consistent force redistribution patterns across straight and turning maneuvers, highlighting the sensorŠs capability to capture meaningful interaction dynamics in real-world scenarios. Overall, this work demonstrates that waveguide-based OS combined with data-driven models constitutes a robust, scalable, low-complexity, and cost-efective solution for estimating interaction forces in SWs.
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Dispositivos robóticos assistivos , Andadores inteligentes , Sensor óptico de força , Rede neural feedforward