Industrial Brushless Servomotors--Introduction

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The industrial brushless servomotor has developed through a remarkable combination of mechanical, electrical, power electronic and microelectronic technologies, and both the operation and application of the motor rely on many interdependent factors. I have tried to cover the fundamentals of the subject in a logical manner, taking a step-by-step approach, describing first the construction of the brushless machine itself and how it works, second, how the current is supplied, third, how the motor behaves when it is loaded and finally how it is rated and selected for a particular duty. The guide covers the important motor and load characteristics which affect the design of the control system, but does not include a detailed treatment of control techniques which are well described elsewhere.

The first section is devoted to a brief review of the brushed, permanent magnet motor. This allows the early introduction to the guide of some basic groundwork using what is perhaps a more familiar machine, and also allows a clearer comparison to be made with the brushless type later on. Throughout I have been aware of the needs of engineers and students with no previous knowledge of how brushed or brushless motors work, and so both forms are explained from first principles.

Theoretical analysis is developed in relation to practical examples, and rules of thumb are suggested wherever possible.

Any equations for motor rating and selection are simple enough for numerical results to be found using a calculator or spreadsheet. My hope is that this publication will be of some help to those who are already using brushless motors in servomechanisms, as well as to those who are studying the electrical and mechanical properties which are involved.

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