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Vibration actuators are widely used in handheld devices to provide vibrotactile feedback or silent notification to the users. In most cases, miniature DC motors with eccentric rotors or the so-called coin-type shaftless vibration motors are utilized. The common disadvantage of the single rotor designs is that the frequency and the intensity of the generated vibration cannot be adjusted separately. The construction composed of two independently driven coaxial eccentric rotors -which makes a strongly coupled nonlinear system -allows for the separate control of the frequency and amplitude by the adjustment of the angular speed and the total eccentricity. This paper presents a complete control design approach based on quasi-linear parameter varying (qLPV) modelling and linear matrix inequality (LMI)-based synthesis utilizing the tensor product (TP) model transformation to determine the convex polytopic representation of the parameter dependent nonlinear system. The design approach is demonstrated via a concrete numerical example using the parameters of a real dual-excenter prototype device. The control performance is validated through numerical simulations. This case study goes through a complete nonlinear control problem from the modelling phase to the implementation-ready controller, while drawing generalizable conclusions for qLPV modelling.

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DC motor drives are widely used in many devices in mechatronics and industry. Since the performance of these motors depends on their angular velocity, there are some interesting phenomena originating from the counter-action of the drive and the driven mechanical system. The present work proposes a four-degree-of-freedom mechanical model with two DC motor driven eccentric rotors. Only translational in-plane motion of the base is considered. Based on the stationary motions of the proposed system, the changed DC motor performance and the phenomenon of selfsynchronization have been showed analytically and by some simulation results.

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