Miniaturized optical-based force sensors for tendon-driven robots

In this paper, an innovative sensor based on optoelectronic components and compliant frames for the measurement of the tendon tension is presented. With respect to conventional solutions for force sensing, like strain-gauge or Bragg-grating based force sensors, this sensor presents several advantages, mainly in terms of compactness, simplicity of the implementation and conditioning electronics. The proposed sensor exploits the properties of optoelectronic components with a narrow angle of view to measure the very small deformation of a compliant frame caused by the tendon tension. The sensor can be placed at the tendon ends as such as in any position along the tendon. The paper reports the basic working principle and a simplified procedure for the design of the sensor frame together with the results of an experimental testbench where a couple of the proposed sensors are use for the feedback control of a tendon-driven robotic joint.