Modelling and Sensors for Magnetically-Levitated Disc Drives

The development of new industrial applications has diverted the focus of research towards compacter and faster rotatory drives. These requirements push the classical ball-bearings of electric motors to the limits in terms of operational lifetime and friction losses. Advances in sensor systems, electronics, and semiconductors have thus rendered contactless, magnetically-levitated drives as a compelling alternative for the miniaturization of drives and the striving towards high rotational speeds. The possibility of hermetically sealing the rotor and stator has also opened new industrial applications in which high purity and robust operation are required. In this thesis, the conception of a compact yet simple magnetically-levitated electric drive is approached, from its analytical basis to the constitution of sensor systems, until the fabrication of two operating prototypes. One of the prototypes is ultimately deployed as a functioning actuator at high rotatory speeds.

This thesis thus tackles the different subjects that epitomize the complexity of a magnetically-levitated drive. In this regard, literature research is initially performed to investigate which structures of electric motors have successfully integrated magnetic bearings. A focused analysis upon small magnetically-levitated drives shows that few small flat drives -deemed as ''disc drives''- have been tested with a mechanical load. The lack of documented electric motors at this scale and speed, working with a mechanical load, thus represents a novel, untasted research opportunity.

This work treats the electromagnetic principles that enable the magnetic levitation and spinning of drives. For better accuracy, the computational modelling of magnetically-levitated disc drives, along with an assessment of their passive, active, and power loss characteristics is proposed. A framework and a parametric analysis for the evaluation of these characteristics are provided. Followingly, an analysis of different contactless sensor possibilities is supplied. The composition of an adjustable, low-cost system for the estimation of rotor position is presented. This that can be easily integrated into existing magnetic levitation systems. The correct electromagnetic conception of the drives and its relevant sensor system, coupled to readily available electronics result in two working prototypes. One of these is deployed as an axial blower, which can turn at speeds of 10000 rpm, blow airflows of 40 liter/min, and attain differential pressures of 10 Pa. Finally, the lessons drawn from this manuscript are summarized, and future research work -that can improve the existing hardware, validate the electromagnetic design framework, or ameliorate alternative sensor systems- is proposed.