Kent Davey

The analysis of fields and torques in spherical induction motors

The advent of robotics and automated manufacturing processes has brought about an urgent need for novel electromechanical transducers with unusual design and performance characteristics. Operating flexibility, ruggedness, size, force-to-weight ratio, and robust control capabilities are design attributes which place a heavy burden on conventional machines used for manipulation purposes. The spherical induction motor is an electromechanical drive which holds considerable promise in these application areas. A general analysis of both the fields and resultant forces generic to the spherical induction motor is presented. The analysis properly accounts for the diffusion of the magnetic field with changing frequency and motor speed. To aid in the prediction and conceptualization of the torque and commensurate motor losses, normalized plots of these parameters are given for various limiting values of skin depth ratio to conductor thickness. Results indicate that the device is capable of continuous speed control and efficient torque production.

Development of a novel intelligent robotic manipulator

This paper describes the design features of a new robotic manipulator incorporating a novel spherical motor capable of three degrees of motion in a single joint for purposes of dexterous actuation, a loadable device at the end of the wrist actuator as the end effector with tactile and proximity sensing capabilities, and appropriate conventional and intelligent planning and control algorithms to support the execution of a series of complex tasks in an uncertain or hostile environment. The spherical wrist actuator is developed through analytic studies and the design of position and torque control instrumentation. The end effector is a micromanipulator based on the principle of in-parallel mechanisms. Heuristics, manifested in fuzzy logic, are employed to incorporate artificial intelligence for decision making and control in the robotic manipulator. The intent is to provide an overview of the significant design and algorithmic features of the manipulator deferring a detailed treatment of the proposed approaches to forthcoming publications.

Prediction of magnetically induced electric fields in biological tissue

Noninvasive magnetic stimulation of neurons in the brain can be realized by high-intensity rapidly changing magnetic fields. Attention is focused on the calculation of the induced electric fields commensurate with rapidly changing magnetic fields in biological tissue. The problem is not a true eddy current problem in that the magnetic fields induced do not influence the source fields. Two techniques are introduced for numerically predicting the fields, each employing a different gauge for the potentials used to represent the electric field. The first method employs a current vector potential and is best suited to two-dimensional (2-D) models. The second represents the electric field as the sum of a vector plus the gradient of a scalar field; because the vector can be determined quickly using the Biot-Savart rule (which for circular coils degenerates to an efficient evaluation employing elliptic integrals), the numerical model is a scalar problem even in the most complicated three-dimensional geometry. These two models are solved for the case of a circular current carrying coil near a conducting body with sharp corners.<<ETX>>

Toward functional magnetic stimulation (FMS) theory and experiment

Examines the use of magnetic fields to functionally stimulate peripheral nerves. All electric fields are induced via a changing magnetic field whose flux is entirely confined within a closed magnetic circuit. Induced electric fields are simulated using a nonlinear boundary element solver. The induced fields are solved using duality theory. The accuracy of these predictions is verified by saline bath experiments. Next, the theory is applied to the stimulation of nerves using small, partially occluded ferrite and laminated vanadium permendur cores. Experiments demonstrate the successful stimulation of peripheral nerves in the African bullfrog with 11 mA, 153 mV excitations. These results offer a new vista of possibilities in the area of functional nerve stimulation. Unlike functional electric stimulation (FES), FMS does not involve any half cell reactions, and thus would not have the commensurate FES restrictions regarding balanced biphasic stimulation, strength duration balances, and oxidation issues, always exercising care that the electrodes remain in the reversible operating regime.<<ETX>>

Dynamic Load and Storage Integration

Modern technology combined with the desire to minimize the size and weight of a ships power system are leading to renewed interest in more electric or all-electric ships. An important characteristic of the emerging ship power system is an increasing level of load variability, with some future pulsed loads requiring peak power in excess of the available steady-state power. This inevitably leads to the need for some additional energy storage beyond that inherent in the fuel. With the current and evolving technology, it appears that storage will be in the form of batteries, rotating machines, and capacitors. All of these are in use on ships today and all have enjoyed significant technological improvements over the last decade. Moreover, all are expected to be further enhanced by todays materials research. A key benefit of storage is that, when it can be justified for a given load, it can have additional beneficial uses such as ride-through capability to restart a gas turbine if there is an unanticipated power loss; alternatively, storage can be used to stabilize the power grid when switching large loads. Knowing when to stage gas turbine utilization versus energy storage is a key subject in this article. The clear need for storage has raised the opportunity to design a comprehensive storage system, sometimes called an energy magazine, that can combine intermittent generation as well as any or all of the other storage technologies to provide a smaller, lighter and better performing system than would individual storage solutions for each potential application.

The calculation of transient eddy-current fields using null-field integral techniques

The transient eddy-current problem is characteristically computationally intensive. The motivation for this research was to realize an efficient accurate solution technique involving small matrices via an eigenvalue approach. Such a technique is indeed realized and tested using the null-field integral technique. Using smart (i.e., efficient, global) basis functions to represent unknowns in terms of a minimum number of unknowns, homogeneous eigenvectors and eigenvalues are first determined. The general excitatory response is then represented in terms of these eigenvalues and eigenvectors. Excellent results are obtained for the Argonne FELIX cylinder experiments using a 4 × 4 matrix. Extension to the three-dimensional problem (short cylinder) is set-up in terms of an 8 × 8 matrix.

A Manto Carlo Technique for Solving Eddy Current Problems

With the recent progress in the parallel processing technology, there comes the need to reinvestigate various techniques employed in computational electromagnetics. The Monte Carlo technique discussed is one alternative that has the attractive feature of requiring very little set up time. Because no grid or volume discretization is involved, a smaller demand on storage capacity is required. The approach proposed in based on the random walk idea of a particle saying about in a medium, and registering information upon contact with a boundary. The standard Helmholtz type equation encountered in eddy current problem in solved by lotting one particle become multiple particles in its walk through the problem. Application to a simple 2-D eddy current problem is presented. The results indicate that on a data parallel system such as Maspar MP-1, the Monte Carlo method become competitive as a total solution approach for problems involving more than 400 unknowns.

Transient eddy current analysis for generalized structures using surface impedances and the fast Fourier transform

Surface impedances have primarily been utilized in eddy current problems, where the skin depth is small compared to the conductor thickness being modeled. Their use is extended to arbitrary-thickness conductors. In addition, the authors investigated modeling different shapes as combinations of slabs. In particular, a cylinder was emulated as a polygon of slabs to verify the versatility of the technique. The application to sinusoidal steady-state problems is straightforward. Of greater interest is the extension to the transient problem. A solution was sought via the fast Fourier transform. With the surface impedance method, the calculation of each frequency solution is fast; the overhead required in setting up the problem, albeit the integral or finite-element matrix is geometry-dependent only, and need be performed but once. The calculation of the transient response of a cylinder placed in an exponentially decaying field is computed and compared to analytic results. Some discussion is given on the benefits of breaking up the excitation field into parts that start and end at the same level. >

The AMT maglev test sled-EML weapons technology transition to transportation

Technology spinoffs from prior electromagnetic launcher work enhance a magnetic levitation transportation system test bed being developed by American Maglev Technology of Florida. This project uses a series wound linear DC motor and brushes to simplify the magnetic levitation propulsion system. It takes advantage of previous related work in electromagnetic launcher technology to achieve success with this innovative design. Technology and knowledge gained from developments for homopolar generators and proposed rail gun are control are key to successful performance. This contribution supports a cost effective design that is competitive with alternative concepts. Brushes transfer power from the guideway (rail) to the vehicle (armature) in a novel design that activates the guideway only under the vehicle, reducing power losses and guideway construction costs. The vehicle carries no power for propulsion and levitation, and acts only as a conduit for the power through the high speed brushes. Brush selection and performance is based on previous EML homopolar generator research. A counterpulse circuit, first introduced in an early EML conference, is used to suppress arcing on the trailing brush and to transfer inductive energy to the next propulsion coil. Isolated static lift and preliminary propulsion tests have been completed, and integrated propulsion and lift tests are scheduled in early 1996.

3D transient eddy current fields using the u‐v integral‐eigenvalue formulation

The three‐dimensional eddy current transient field problem is formulated using the u‐v method. This method breaks the vector Helmholtz equation into two scalar Helmholtz equations. Null field integral equations and the appropriate boundary conditions are used to set up an identification matrix which is independent of null field point locations. Embedded in the identification matrix are the unknown eigenvalues of the problem representing its impulse response in time. These eigenvalues are found by equating the determinant of the identification matrix to zero. When the initial transient forcing function is Fourier decomposed into its spatial harmonics, each Fourier component can be associated with a unique eigenvalue by this technique. The true transient solution comes through a convolution of the impulse response, so obtained with the particular external field decay governing the problem at hand. The technique is applied to the FELIX (fusion electromagnetic induction experiments) medium cylinder experiment...