A Deformation Sensor based upon Light Attenuation in a Silicone Waveguide: Construction and Characterisation

Abstract

The measurement of the displacement of soft robotic devices and configurations of actuators is essential for the implementation of force and position control. Conventional deformation sensors, such as capacitive and resistive, are unable to acheive the large extensions required to accurately measure these configurations. Recent advances in flexible optical deformation sensors over the last four years have provided sensor technologies that can measure the large extensions that are experienced in soft actuators. However, the majority of existing optical sensors suffer from performance issues relating to unknown losses in optical power and the lack of immunity to external light sources. To address these issues, a simple optical sensor, constructed using a silicone elastomer, has been tested. By measuring the ratio of two wavelengths of light with different attenuation coefficients, the effects of wavelength dependent optical losses and external light interference can be addressed. A clear silicone sensor was characterised using a RGB LED over 500 extension cycles up to 100 % extension, giving a repeatable output and low and linear hysteresis over all 500 cycles. The effect of different optical dyes was investigated, showing that different dyes can controllably attenuate specific wavelengths and thus affect the sensitivity of the measurements. This investigation demonstrates that a ratioed wavelength flexible optical deformation sensor is capable of repeatable measuring large deformations, suitable for use in a range of applications.