LiJiang Qin

Synchronous disturbance attenuation in magnetic bearing systems using adaptive compensating signals

New adaptive vibration control algorithms are developed for minimizing selected vibration performance measures by adjusting the amplitude and phase of a synchronous signal injected at the summing junction of the magnetic bearing feedback control loop. Two methods have been investigated. One is the application of the filtered-x adaptive filtering techniques to directly attenuate the magnitude of the rotor displacements or currents and this will be referred to as a direct method for synchronous disturbance attenuation. The other method minimize the magnitude of the magnetic bearing system error signal and will be referred to as an indirect method for synchronous disturbance attenuation. The developed algorithms have been experimentally tested and the results showing the effectiveness of the algorithms are reported.

Design and fabrication of a micro magnetic bearing

A micro magnetic bearing actuator has been designed using electromagnets. In this design, the rotor position is actively controlled in the radial directions and passively supported in the axial direction. A micro position sensor, along with a proportional plus derivative (PD) control system, constitutes the feedback network, which ensures that the rotor is actively suspended in the radial directions. The circular stator has four control coils which are sandwiched between two stator end plates. The diameter of the stator and rotor are 2.1 and 2.6 mm respectively, while the thickness is fixed at 250 µm. The air gap between the stator and rotor has been fixed at 10 µm. The stator and rotor plates were fabricated using Permalloy electroplating, while the control coils of the stator were hand-wound using conventional coil winding techniques. The bearing components were assembled using normal micro assembly techniques. The details of the fabrication and assembly techniques employed for the micro bearings are presented, along with the test results.

Smart magnetic structures for MEMS

Abstract By exploiting the special properties of magnetic materials, magnetic microelectromechanical system (MEMS) technology offers many challenging opportunities for useful device development in the future. This article discusses some of the magnetic materials used in MEMS devices and methods of fabricating them. Some key design issues are addressed, and applications of these technologies to electromagnetic devices developed at RMIT and to thermally controlled magnetic devices are examined.

A simplified approach for accurate estimation of transverse magnetic forces in micro-actuators having inclined pole faces

This paper proposes a fringing range method for accurately evaluating transverse magnetic forces in micro-actuators having inclined pole faces. In this method, the fringing flux in an air gap is assumed to be uniformally distributed in a range that is represented by a fringing coefficient, which is then adjusted systematically to ensure the magnetic forces are accurately determined under defined conditions of actuator physical symmetry. Although this approach can be generalized to other cases, this paper focuses on its application to the case of semi-infinite inclined pole faces. It is shown that the fringing range method can be used with good accuracy if the pole thickness is much larger than the air-gap length. This method was applied in designing a micro magnetic bearing actuator whose diameter is 2.6 mm.

Phase differential angular rate sensor: concept and analysis

This paper describes the structure and operation of a new differential phase angular rate sensor and analyses its response to input rotation. It employs a vibrating beam mass structure that is forced into an elliptical path when subject to rotation due to the Coriolis effect. Two sensing elements are strategically located to sense a combination of drive and Coriolis force on each to create a phase differential representative of the input rotation rate. A general model is developed describing the device operation. The main advantages of the phase detection scheme are shown, including removing the need to maintain constant drive amplitude, independence of sensing element gain factor and novel response shapes. A ratio of device parameters is defined and shown to determine the device response shape. This ratio can be varied to give a high sensitivity around zero input rate or a response shape not seen before, that can give maximum sensitivity around an offset from the zero-rate input. This may be exploited in an array configuration for a highly accurate device over a wide input range. A worked example shows how the developed equations can be used as design tools to achieve a desired response.

Modeling and control of a micro magnetic bearing

A prototype micro magnetic bearing actuator having an outside diameter of 2.6 mm has been fabricated at Royal Melbourne Institute of Technology and reported previously with an emphasis on fabrication issues. The discussion of this paper will focus on the design and control of the micro magnetic bearing with a particular emphasis on control system design and analysis. To this end, a simplified dynamic model for the micro actuator has been developed and used in determining controller parameters, leading to a successfully suspended non-rotating rotor in the micro magnetic bearing system.

Magnetic MEMS used in smart structures which exploit magnetic materials properties

Magnetic MEMS technology, by exploiting the special properties of magnetic materials, offers many challenging possibilities for useful device development in the future. In this paper we explore some of the magnetic materials used in MEMS devices, and methods of fabricating them. Some of the key design issues are briefly addressed and applications of this technology to electromagnetic devices developed at RMIT and to thermally controlled magnetic devices, which are of increasing interest, are examined.

Micro displacement sensing system and its application to micro magnetic bearings

In this paper we present a novel displacement sensing system where the sensing direction is in the plane of the planar sensor coils. Particular emphasis in this work is given to the design and micro fabrication of the sensor coils. It has been found that the position of the sensor coils is extremely important as the location of the sensor coils relative to the target significantly affects the sensitivity of the resultant sensing system. Extensive experiments have been carried out and show that best sensitivity is achieved when the sensor coil is located so that the overlap area between the rotor and the sensor coil turns changes most rapidly with the rotor displacement. Following the preliminary analysis and experiments, new optimized sensor coils have been designed and micro fabricated using UV lithography and electroplating, as detailed in the paper. Performance testing of the resultant sensing system has been carried out and is reported in the paper.

Design methodology for micromagnetic bearing systems

In this paper we describe a design methodology which has been successfully developed for the design of magnetic bearings. Its adaptation and application to the design of a micro magnetic bearing is presented. Particular design problems of micro magnetic bearing system are addressed, such as the selection of the bearing topologies, the magnetic modeling and design of the actuators, and the modeling and performance simulation of these bearing system. The design trade-offs are considered and it is shown that the design of actuators and their control systems need to be considered concurrently. As an example, design result for a micro magnetic bearing with a diameter of 2.1 mm are presented.