This paper presents a new control strategy for a spherical motion platform capable of three DOFs translational and three DOFs unlimited rotational motion undergoing time delay problems. The control is based on a state prediction and preview method to make a state correctly track a time-varying desired trajectory despite input time delay and disturbance. The spherical motion platform can suffer from a delay effect since it needs a wireless data link to control a cockpit sphere without any mechanical linkage. The delay decreases operation efficiency and further causes control instability. The proposed prediction-based preview control (PPC) offers that a state vector under input time delay is predicted using a disturbance predictor attenuating the disturbance effect. In addition, a predictor-based previewed reference with the state prediction is applied to the controller to achieve desired tracking control. In numerical simulations, it is shown that the proposed controller stabilizes the state to the desired trajectory under delay and disturbance, whereas most existing controllers only show delayed tracking. Finally, the proposed controller is applied to the motion platform, and the result shows excellent performance minimizing the effect of time delay and disturbance.

It is presented in this paper an active magnetic levitation system used for the nanogram detection in biomedical domain. The design, simulation and levitation experiment are presented in detail. The device is composed of three parts: planar coil electro magnetic (EM) as lower stator, permanent magnetic (PM) as rotor and capacitance plate as lower stator. The levitation force versus displacement is analyzed by Ansys software and the air damping coefficient is also calculated. A dynamic model of levitation control is build to select control parameter and explain the experimental measurement. The stiffness versus frequency is analyzed. Experimental results of initial levitation, square wave response and sine wave sweep frequency response are presented and discussed. Preliminary measurements indicate that the response time for initial levitation is 0.2s, and the control current is 0.17A when the levitation height is 1mm. The quick-response performance is in agreement with the dynamic simulation by Matlab/Simulink. From sweep frequency experiment, it can be seen that when the levitation height is 1mm, the resonant frequency is 27.34Hz. The relationship between minimum detectable mass and frequency has been got. At last, the prospective MEMS design is proposed, which is applicable for the cancer cell weight detection.

Abstract: This paper presents the design concept, models, and open-loop control of a particular form of a variable-reluctance spherical motor (VRSM), referred here as a spherical wheel motor (SWM). Unlike existing spherical motors where design focuses have been on controlling the three degrees of freedom (DOF) angular displacements, the SWM offers a means to control the orientation of a continuously rotating shaft in an open-loop (OL) fashion. We provide a formula for deriving different switching sequences (full step and fractional step) for a specified current magnitude and pole configurations. The concept feasibility of an OL controlled SWM has been experimentally demonstrated on a prototype that has 8 rotor permanent-magnet (PM) pole-pairs and 10 stator electromagnet (EM) pole-pairs.