Structural Optimisation of a Force-torque Sensor through Its Input-output Relationship

This paper presents an advanced method to optimise the compliant structure of force-torque sensors at the design stage. To this end, some researchers used finite element analysis on the whole compliant structure or some of its components, while others proposed performance indices based on mechanism theory. This work proposes a new approach, which relies on a symbolic formulation of the wrench-displacement relationship, and by which we minimise the condition number of this linear input-output relationship. Our method is centered on the application requirements, thus, it takes into account constraints such as the measurement range, the maximum allowed compliance or maximum physical dimensions of the structure. Thus, the input-output relationship allows to match applied forces with sensor displacements to achieve a prescribed sensitivity. The resulting performance index can be expressed symbolically, which eases the synthesis task. The optimisation procedure, design, fabrication and experiments of a three-axis force sensor architecture are also presented to illustrate the theory.