This paper describes the structure and operation of a new differential phase angular rate sensor and analyses it's 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.
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.
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.
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.
Microengineering has evolved in the last decade as a subject of its own with the current research encompassing every possible area of devices from electromagnetic to optical and bio-micro electromechanical systems (MEMS). The primary advantage of the micro system technology is its small size, potential to produce high volume and low cost devices. However, the major impediments in the successful realization of many micro devices in practice are the reliability, packaging and integration with the existing microelectronics technology. Microengineering of actuators has recently grown tremendously due to its possible applicability to a wide range of devices of practical importance and the availability of a choice of materials. Selection of materials has been one of the important aspects of the design and fabrication of many micro system and actuators. This paper discusses the issues related to the selection of materials and subsequently their effect on the performance of the actuator. These will be discussed taking micro magnetic actuators and bearings, in particular, as examples. Fabrication and processing strategies and performance evaluation methods adopted will be described. Current status of the technology and projected futuristic applications in this area will be reviewed.
A micro magnetic bearing actuator, with an outside diameter of 2.6 mm, is being fabricated at RMIT. The rotor of the bearing actuator is structured to operate with active control in the radial directions while being supported passively in the axial direction. This paper addresses the design problem for micro magnetic bearing actuators. The key issue in the design is the evaluation of magnetic forces. By applying the 'fringing range method' developed by the authors, a magnetic circuit model is developed for this actuator, which is used for calculating the flux densities at key locations and the magnetic forces on the rotor. Expressions for magnetic forces have been developed previously and a design procedure is proposed in this paper. It is found by using these expressions and the proposed procedure, that we can easily investigate the influence of design parameters on actuator performance. Design results for the micro magnetic bearing are given in detail.
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.