Development and characterization of a dynamic smart structure providing multi-axis force sensing for robotic applications

When considering force-controlled robots, one key-point to sense the arm-environment interaction is the availability of cheap but sufficiently precise multi-axis force sensors. Even if resonant sensors can overcome some well-known limitations such as noise and drift issues, designing multi-axial resonant force sensor is still non-intuitive due to dynamical nature and multiple modes interaction. This paper presents the development of an integrated three-component force sensing resonant structure, which may be used to simultaneously estimate, all the three components of the force applied on it, for the first time. The sensor principle relies on one single pre-stress composite plate where actuation and measurement are achieved with piezoelectric transducers. Feedback control based on Phase-Locked Loop is used to measure resonances, then estimate the applied forces. Multiple smart design strategies, such as modal superposition, spatial modal filtering using optimal transducers placement and intelligent signal conditioning, limit the electronic treatment and reduce the controller complexity. Experimental comparisons with other calibrated force sensors have shown that the applied force can be efficiently estimated with accuracy, demonstrating the interest of our approach to design integrated and inexpensive multi-axis force sensor solution for robotic applications.