Industrial brushless servomotors / Peter Moreton.

Format:

Book

Author/Creator:

Moreton, Peter, Dr.

Language:

English

Subjects (All):

Electric motors, Brushless.

Servomechanisms.

Physical Description:

xviii, 186 pages : illustrations ; 24 cm

Place of Publication:

Oxford ; Boston : Newnes, 2000.

Summary:

-- Written by respected expert in the field -- Peter Moreton has both high level academic and industrial experience-- Indispensible guide to a rapidly growing new area of technology-- Concise and accessible with a minimum of maths

Industrial use of the brushless servomotor, for instance in robotics, is increasing rapidly, because of their low maintenance needs and capabilities at high transient speeds. They offer flexibility and high performance, and advances in power electronics and microelectronics means they are now more affordable. This handbook gives the user of brushless servomotors a comprehensive guide to their use, including a description of all main features of the brushless motor drive system.

Chapter 1 introduces the conventional brushed dc motor is described so key principles are clear as far as they are relevant to the brushless machine. Chapter 2 examines the construction and operation of the brushless industrial servomotor. The rest of the book offers a practical guide to these machines in use, covering the principles of brushless commutation, use within a control system, and a guide to selection of the appropriate servomotor for a particular application.

Throughout mathematics is kept to a minimum and practical guidance is given based on real-life experience. Peter Moreton is a Research Fellow at the University of Bristol, having spent time in industry and universities worldwide.

Contents:

List of units xv

Chapter 1 Brushed DC motors 1

1.2 Operational principles 2

Motor construction 2

Torque production 2

Magnetic flux [Phi] 3

Magnetic flux density B 4

The force on a conductor 4

Torque 4

The torque constant 7

Motor speed 7

Voltage generation 8

The voltage constant 9

K[subscript T] and K[subscript E] 9

Back emf and the terminal speed of the unloaded motor 9

1.3 The loaded motor at steady state 10

Steady-state characteristics 10

1.4 Motor rating 14

Power losses 15

The i[superscript 2]R winding loss 16

Friction, windage and iron losses 16

Torque loss and power loss at constant speed 16

Continuous operation 17

Intermittent operation 18

The form factor 19

Motor temperature 19

Thermal resistance and thermal time constant 20

Winding temperature ripple 21

Servomotor ratings 23

1.5 The brushed servomotor 23

Chapter 2 The brushless machine 28

2.2 Structure and operation 29

Stator construction 30

The permanent magnet rotor 31

Motor operation 31

Flux cutting and flux linkage 33

Torque 34

Back emf 36

2.3 The three-winding brushless motor 37

The squarewave motor 37

Torque production per phase 38

Magnitudes of back emf and torque per phase 39

Wye (Y) and delta ([Delta]) connections 41

Three-phase torque and back emf 43

Practical emf and torque waveforms 45

The sinewave motor 45

Sinusoidal AC input current 45

Sinusoidal flux density in the air gap 45

Sinusoidal winding distribution 45

Back emf 46

Torque 48

Three-phase torque and emf 50

K[subscript T] and K[subscript E] 51

Torques and ratings 52

The effective resistance 53

2.4 Permanent magnets and fields 54

Magnetic fields 54

Magnetomotive force mmf 54

Magnetic field intensity H 55

Permeability [mu] 55

The hysteresis B-H loops 56

The intrinsic curve 58

Permeability of the hard magnet 59

Armature reaction 59

Overload currents 60

Permanent magnet materials 61

Samarium cobalt (Sm-Co) 61

Neodymium iron boron (Nd-Fe-B) 61

Temperature effects 61

2.5 Characteristics 62

Specifications 64

Trapezoidal 64

Sinusoidal 65

Cogging torque 66

Emergency brakes 66

Chapter 3 Brushless commutation 69

3.2 Sensors 71

Hall effect (pole position) 71

Brushless AC tacho (shaft speed) 72

DC tachos 72

The resolver (pole position, shaft speed and position) 72

Digital encoders 73

Incremental encoders 73

Absolute encoders 75

3.3 Power electronics 75

The thyristor 76

Gate turn-off thyristor 77

The power mosfet 77

The power BJT 79

The IGBT 79

Power electronic inverters 80

Single phase 80

Full-bridge three-phase circuit 83

Control of current magnitude 83

PWM 83

Current regulation 84

3.4 Three-phase commutation 84

Operation of the full-bridge three-phase inverter 85

Commutation of the squarewave motor 86

Current magnitude 86

Measurement of pole position 87

Measurement of shaft speed 87

Measurement of shaft position 91

Commutation of the sinewave motor 91

Measurement of rotor angle 92

3.5 The motor-sensor combination 92

Trapezoidal motor

Hall-effect sensor 93

tacho and incremental encoder 94

Sinusoidal motor

resolver or absolute encoder 95

Chapter 4 Motor and load dynamics 97

4.2 Motor control 98

Closed loops 98

Speed regulation 100

Servo control 100

4.3 Motor equations 101

Constant speeds 101

Speed variations 102

The electrical equation 104

The dynamic equation 104

Electrical and mechanical time constants 105

The electromechanical equation 108

Frequency response 109

The s-plane 110

The Laplace transformation 111

The poles of the frequency response 113

Transfer functions 113

4.4 Variation of load inertia 115

Overshoot 116

System control 118

4.5 Optimization 119

Load velocity profiles 120

Stator i[superscript 2]R loss 121

The inertia match for the geared drive 124

The inertial load 124

Effect of load torque on the optimum gear ratio 127

Limitations to minimization of the i[superscript 2]R loss 129

The belt and pulley drive 130

The ball screw and lead screw drives 133

4.6 Torsional resonance 137

Effect of compliance at a fixed load inertia 138

Resonant frequency predictions and tests 140

Damping 141

Effect of load inertia 143

Predictions and tests 144

Compliance and inertia in practice 145

Chapter 5 Motor rating and selection 146

5.2 Motor heating 147

Soac curves 148

Speed-sensitive loss 149

Heatsinks and blowers 150

5.3 Steady-state rating 151

Torques 152

5.4 Intermittent torque 153

Motor temperature 153

Motor tests 157

Thermal models 159

5.5 Incremental motion 159

Motor selection for the rotating load 160

Stator heating energy 160

Selection criterion 161

Rating coefficient 162

Motor selection for the translating load 168

The belt and pulley drive 169

The ball screw drive 171

5.6 Precautions 175.

Notes:

Includes bibliographical references and index.

ISBN:

0750639318

OCLC:

44090737