Minimally Invasive Torque Sensor for Tendon-Driven Robotic Hands

The purpose of this paper is to present preliminary results on the use of a torque sensor based on a Bragg grating for torque control applications of tendon-driven mechanisms. Owing to the minimally invasive nature of optical fibres, one of the most promising applications can be the integration of the sensor into anthropomorphic robotic hands for accurate impedance or compliance control. In fact, the sensing element of the proposed torque sensor can be easily bonded directly to the tendon following its natural routing with a significantly reduced invasiveness with respect to conventional sensors. These are usually based on strain gauges, which are cumbersome and require additional mechanical components and interfaces in order to provide the necessary measurement, while the Bragg sensor is embedded into the optical fibre whose typical diameter is about 125 pm which allows its integration into the tendon itself. The experimental results presented here have been obtained on a simple test-bench realized by using off-the-shelf and cheap components conceived to demonstrate the potentiality of the sensor and its effectiveness in an actual compliance control scheme.