A NEW BIDIRECTIONAL INDUCTIVE FORCE SENSOR

This paper presents a new kind of inductive force sensor that gives th e amplitude and the direction of the force in a plane, and that is dif ferent from the lately developped technologies utilizing the magnetost rictive or magnetoresistive effect. It is constituted of a magnetic ci rcuit with airgaps that varie in length with the applied force. When a force is exerted, a bar is bent and one of the airgaps becomes wider, the reluctance of the corresponding magnetic circuit increases and th e inductance of the coil located on this circuit decreases; the other airgap becomes narrower. The bending of the bar is proportional to the applied force, so, the inductance variations are an image of this for ce. The use of two coils leads to a differential structure. The same c onstruction is done to measure the force in the orthogonal direction. This structure gives the two components of a force in a plane. The sen sor is studied first to optimize its geometry with regard to the dimen sional parameters. An optimum is found that gives the maximum airgap v ariations for a given force, and so the maximum signal variations. A m agnetic study is done with finite elements calculations. A prototype w as built to measure lift and drag of a rudder on a ship.