A Bending Angle Sensor Based on Magnetic Coupling Suitable for Soft Robotic Finger

Sensing the angle of bending of a soft robotic finger is valuable in many applications but it is a non-trivial task. In this paper, a simple but effective sensing approach based on variable mutual inductance is presented to sense the bending angle. Existing inductive bend sensors use concentric coil based designs and they are not easy to manufacture and integrate into the finger. The planar coil based bend sensor, proposed in this work, is integrated inside the soft robotic finger. The sensor comprises of two flexible printed circuit boards based spiral coils that are magnetically coupled. Three such units are proposed to use in a finger. Each set of planar coils is arranged in such a manner that they give a measure of the curvature of the finger. It can give localized bending of the corresponding parts of the structure which is useful if the bending is not uniform. The measurement circuit required for the sensor is very simple. A prototype sensor built and tested showed a repeatable input-output characteristic with a repeatability error of 0.6%. The proposed sensor does not use the grasping area, is easy to integrate and less expensive. The output of the sensor is immune to moisture, dust and oil.