Modal decoupling for MIMO self-oscillating systems - application to resonant force sensor control

In this paper we present a new method to control instantaneously MIMO oscillating systems. The algorithm and its hardware configuration are implemented on a multidimensional resonant force sensor. The robotic applications of this sensor require real-time resonant frequency measures. Inspired by the technique used in single quartz crystal oscillator, the method is extended to the MIMO case and is presented as an alternative solution to control multiple resonances of a force sensor. Three frequencies of one single active plate, on which several piezoelectric patches are bonded, are simultaneously excited. The method uses spatial modal decoupling technique implemented with analogue electronics thanks to a smart arrangement of the piezoelectric patches. This allows the full MIMO system to be transformed into three independent SISO subsystems. Then, for each of them, a controller is tuned to reinforce self-oscillation of the force sensor system to several resonant working points in a closed-loop configuration. Finally, experimental verification shows that the method can be successfully used for the control of a new type of resonant force sensors.