Reluctance sensor for penetration depth control in friction stir welding

We propose a detailed design of a reluctance position sensor for determining the penetration of the welding tool in a friction stir welding machine. It functions by sensing the variations of the inductance of a coil due to the changes in the gap of the magnetic circuit created by the welding tool and the working bench. Intensive finite element simulations have been performed to decide the best configuration, including the geometry of the sensor, the winding of the coil and the properties of the magnetic materials. Static measurements in a functional prototype demonstrate the validity of the method and the design.