Soft force sensor made of magnetic powder blended with silicone rubber

All Hall Effect-based soft force sensors developed so far employ a piece of solid Neodymium magnet, which is literally a rigid component. In addition, quick saturation of these kinds of sensors limits their measurable force range. This is even more critical when there is a need to use a soft sensing element with the least possible thickness. The proposed study develops a new soft Hall based sensor addressing these concerns by replacing the neodymium magnet with the magnetic powder blended with silicone rubber. In addition to eliminating extra components and providing a totally soft structure, this solution allows the user to fabricate and utilize the sensor in lower thicknesses due to weaker magnetic field of the powder. The sensor is designed and tested within a range of magnetic powder density, sensor dimension, and silicone hardness to achieve an optimum design in terms of sensitivity and output span. To better understand the sensor performance, a finite element modeling is carried out. Among all designed sensors, a specific prototype is selected and calibrated as our case of study. It is shown that the sensor can measure forces in the range of 0-20 N with the sensitivity of 2.85 mV/N for linear fitting and maximum hysteresis error of 12% of output span. The sensor was successfully implanted in the body of a cylindrical soft pneumatic actuator to measure the axial extending force. The results of the experiment confirmed that the developed sensor has the potential to be used in soft robotic applications. (C) 2019 Elsevier B.V. All rights reserved.