A GMR based magnetic pretouch sensing system for a robot grasper

Pretouch sensors are capable to classify objects and estimate their position prior to touching and thus close the gap between vision and contact based sensing. This will be particularly useful for robotics applications, not just for manipulation of objects but also with respect to safety. As robots will more and more operate in “open environments” where there is little prior knowledge it will be important to gather as much information on the environment as possible. However, although there are many measurement principles that might be applied, only a few can cope with the requirements, e.g., limitations with respect to spatial dimensions, weight and power consumption. In this paper we investigate a measurement system for ferromagnetic materials, which are common in many industrial applications. Inspired by magnetic field tomography we use a permanent magnet and apply GMR sensors to measure the field deformation caused by ferromagnetic objects. Based on the measurement results we solve an inverse problem with respect to the object position. We present experimental results for a prototype implementation and provide a description of the calibration method.