TABLE OF CONTENTS

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PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x

ACKNOWLEDGEMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

CHAPTER 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.1. Accuracy and precision. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

CHAPTER 2 System Calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.1. Traction requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.2. Critical traction ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.2.1. Angle of wrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.2.2. Friction factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.3. Static balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.3.1. Multiple reeving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.4. Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332.4.1. Ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362.4.2. Asymmetric compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372.4.3. Symmetric compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422.4.4. Compensator pulley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432.4.5. Over compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

2.5. Dynamic traction ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462.5.1. The system model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492.5.2. Dynamic rope tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492.5.3. Suspension ropes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512.5.4. Travelling cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512.5.5. Compensation ropes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512.5.6. Car and counterweight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522.5.7. Pulleys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532.5.8. Frictional losses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

2.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592.6.1. Critical traction ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602.6.2. Static balance ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612.6.3. Dynamic traction ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

CHAPTER 3 Electromechanical Braking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653.2. Normal operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663.3. The effect of machine inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683.4. Basic requirements for electromechanical braking. . . . . . . . . . . . . . . . . . . . . . . 693.5. Stopping in the down direction with rated load . . . . . . . . . . . . . . . . . . . . . . . . . 71

3.5.1. 125% Rated load travelling down. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733.5.2. Partially operational brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

3.6. Empty car travelling upwards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

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3.7. Maximum traction ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793.8. Electromechanical braking rated load upwards/empty car downwards . . . . . . . 82

3.8.1. Fully loaded car travelling upwards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843.8.2. Empty car travelling downwards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 863.8.3. Simplified example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

3.9. Emergency braking and jerk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953.10. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

CHAPTER 4 The Elevator Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

4.1. Radial loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 984.2. Power and torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

4.2.1. The elevator motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1054.3. Energy and power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1084.4. Energy requirements of the mechanical handling operation . . . . . . . . . . . . . . 110

4.4.1. Efficiency of an elevator drive system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114.4.2. Kinetic energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1144.4.3. Power factor in solid state drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

4.5. Electrical requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164.5.1. Single elevator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174.5.2. Groups of elevators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

4.6. Power failure and emergency supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234.6.1. Power supply needs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234.6.2. Supply changeover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

CHAPTER 5 Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

5.1. The national safety code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1295.1.1. Prescribed design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1315.1.2. Prescribed performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

5.2. International agreement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1335.3. Risk assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

5.3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375.3.2. Risk analysis and assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1395.3.3. Documentation of risk assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

CHAPTER 6 Ropes and Roping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

6.1. Factor of safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1486.2. Basic construction of steel wire ropes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

6.2.1. Tensile strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1526.2.2. Common constructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

6.3. Elongation and elastic stretch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1536.3.1. Elongation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1536.3.2. Elastic stretch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1536.3.3. Rope terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

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6.4. Developments in rope materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1566.4.1. Reference to standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1566.4.2. Coated steel belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1576.4.3. Synthetic fibre ropes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1616.4.4. Service life and traction issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

6.5. Suspension system dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1636.5.1. The “slowly varying” system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1656.5.2. The dynamic model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

6.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174CHAPTER 7 Overspeed in the Down Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1777.1. Emergency arrest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

7.1.1. Rocking arm overspeed governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1797.1.2. Pivoted bob-weight overspeed governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

7.2. Instantaneous and progressive safety gears . . . . . . . . . . . . . . . . . . . . . . . . . . . 1807.2.1. Cam type instantaneous safety gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1817.2.2. Captive roller type safety gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1817.2.3. Progressive safety gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1827.2.4. Instantaneous safety gear with buffered effect . . . . . . . . . . . . . . . . . . . . . . . . . 1837.2.5. Safety gear operating mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

7.3. Criteria for arrest of overspeed in the down direction . . . . . . . . . . . . . . . . . . . 1847.4. The masses to be considered. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1867.5. Acceleration to overspeed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

7.5.1. Emergency stopping sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1907.5.2. Overspeed governor/safety gear combination . . . . . . . . . . . . . . . . . . . . . . . . . 1917.5.3. Overspeed governor operating time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1927.5.4. The effect of acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1947.5.5. Safety gear operating forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

7.6. Performance of a progressive safety gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2017.6.1. The dynamic model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2027.6.2. Arrest in free descent (intact suspension) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2027.6.3. Safety gear set for arrest in free fall (failed suspension) . . . . . . . . . . . . . . . . . 210

CHAPTER 8 Emergency Arrest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2138.1. Overspeed in the up direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

8.1.1. Counterweight safety gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2158.1.2. Upward acting safety gear on the car . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2168.1.3. Rope brake and sheave brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217

8.2. Buffers and overtravel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2178.2.1. Energy accumulation buffers (spring type). . . . . . . . . . . . . . . . . . . . . . . . . . . . 2178.2.2. Energy accumulation buffers (non-linear type) . . . . . . . . . . . . . . . . . . . . . . . . 2208.2.3. Energy dissipation buffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2218.2.4. Buffer reaction forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2238.2.5. Emergency terminal slowdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

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8.3. Uncovenanted movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2278.4. Counterweight jump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

8.4.1. Spring anchorage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2308.4.2. Maximum rope tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2338.4.3. Lock down compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

CHAPTER 9 Interface to the Civil Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2449.1. Guides and guiding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

9.1.1. Nominal minimum plumb (NMP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2449.1.2. The vertical datum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

9.2. Strength of the guiding system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2499.2.1. The guide brackets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2519.2.2. Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2539.2.3. Flange bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2549.2.4. Buckling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2559.2.5. Composite stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2569.2.6. Guide rail deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

9.3. Forces acting on the guides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2579.3.1. Buckling force during safety gear operation . . . . . . . . . . . . . . . . . . . . . . . . . . 2589.3.2. Lateral forces on the guides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2599.3.3. Sill loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

9.4. Quality of ride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2629.4.1. Design issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2639.4.2. Transmission of vibration and noise to the building . . . . . . . . . . . . . . . . . . . . 2749.4.3. Measurement of ride quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

CHAPTER 10 Entrances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28010.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

10.1.1. Landing (hoistway) doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28010.1.2. Car doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28110.1.3. Entrance configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28110.1.4. Selection of door panel and entrance sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281

10.2. Entrance construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28310.2.1. Integrity of a closed entrance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

10.3. Tripping and trapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28710.4. Entrance operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28810.5. Malfunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28910.6. Fire resistance of the hoistway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290

10.6.1. Fire resistant entrances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29010.7. Fire testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

10.7.1. Design aspects of a fire resistant entrance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29410.8. Automatic power operated doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296

10.8.1. Closing force and kinetic energy of the closing doors . . . . . . . . . . . . . . . . . . . 296

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10.8.2. Control of the door motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30110.8.3. Operational interface with the elevator control . . . . . . . . . . . . . . . . . . . . . . . . 30210.8.4. Synchronisation of the door operation with car levelling . . . . . . . . . . . . . . . . 304

CHAPTER 11 The Machine Room Less (MRL) Traction Elevator . . . . . . . . . . . . . . . 30711.1. Underslung elevators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30711.2. The strength of the guiding system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30911.3. Basic outline of MRL elevators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310

11.3.1. Other equipment supported from the guide rails . . . . . . . . . . . . . . . . . . . . . . . 31311.3.2. MRL system employing coated steel belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31611.3.3. MRL with disc motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31811.3.4. MRL without counterweight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

11.4. Other implications of the MRL arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . 32311.4.1. Control equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32311.4.2. Accommodation and resetting of the overspeed governor . . . . . . . . . . . . . . . . 32411.4.3. Emergency operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32411.4.4. Safe working on MRL equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

CHAPTER 12 Hydraulic Elevators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32712.1. Civil engineering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

12.1.1. Location of machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32812.2. Loading on the building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32812.3. Space requirements in the hoistway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32912.4. Energy considerations and environmental issues . . . . . . . . . . . . . . . . . . . . . . . 32912.5. Hydraulic elevator with a balancing weight . . . . . . . . . . . . . . . . . . . . . . . . . . . 33112.6. Other environmental issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33212.7. Levelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33312.8. Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33312.9. Jack arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

12.9.1. Direct acting below . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33412.9.2. Direct acting at the side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33412.9.3. Indirect acting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33412.9.4. Twin jack arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335

12.10. Telescopic jacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33612.10.1. Chain synchronisation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33812.10.2. Hydraulic synchronisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

12.11. Operational and dimensional limitations on jacks . . . . . . . . . . . . . . . . . . . . . . 34112.11.1. Hydraulic pressure in the cylinder and system. . . . . . . . . . . . . . . . . . . . . . . . . 34212.11.2. Mechanical buckling load on the ram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34212.11.3. Engineering procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

12.12. Principles of hydraulic control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34712.12.1. Upward motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34812.12.2. Downward motion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

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12.13. Protection against overspeed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35312.13.1. Upward overspeed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35312.13.2. Downward overspeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35412.13.3. Protection against free fall of an indirect acting installation . . . . . . . . . . . . . . 35912.13.4. Twin jack systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35912.13.5. Low pressure valve/slack rope switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35912.13.6. Anti-creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

12.14. Protection against overtravel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36112.14.1. Manual lowering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

CHAPTER 13 Hydraulic Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36513.1. The effect of viscosity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

13.1.1. Simplified fluid mechanics of a control orifice . . . . . . . . . . . . . . . . . . . . . . . . 36713.2. Pressure compensated system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370

13.2.1. Operation of a pressure compensated down valve . . . . . . . . . . . . . . . . . . . . . . 37013.2.2. Pressure compensated up-valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372

13.3. Flow monitored elevator systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37313.3.1. Open valve or closed valve system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37313.3.2. Dynamics of a flow monitored system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

13.4. Energy consumption of a valve controlled system. . . . . . . . . . . . . . . . . . . . . . 37513.5. Variable delivery control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37713.6. The ‘hydraulic counterweight’ system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380

13.6.1. Operation with rated load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38113.6.2. Operation with no load in the car . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38313.6.3. The hydraulic accumulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38513.6.4. Lowest point in the travel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38613.6.5. Highest point in the travel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38713.6.6. Initial charge pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38713.6.7. Accumulator pressure during elevator travel . . . . . . . . . . . . . . . . . . . . . . . . . . 38913.6.8. Energy considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391

CHAPTER 14 Control Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39714.1. Control system arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39714.2. The power system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40014.3. Control of the elevator motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400

14.3.1. Pattern generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40214.3.2. Pattern generation for short journeys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403

14.4. Control of the elevator motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40514.4.1. Speed control for an elevator drive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408

14.5. Control algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41014.5.1. Speed feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41014.5.2. Motor current feedback. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41214.5.3. Inspection operation and re-levelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412

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14.6. Safety systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41414.6.1. Failure modes and effects analysis (FMEA). . . . . . . . . . . . . . . . . . . . . . . . . . . 41714.6.2. Safety integrity level (SIL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419

14.7. Electromagnetic compatibility (EMC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42014.7.1. Generation of interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42114.7.2. Protection and containment of interference . . . . . . . . . . . . . . . . . . . . . . . . . . . 423

14.8. The automatic (“Auto”) control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42714.9. The supervisory system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428

14.9.1. Measures of performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42914.9.2. Service paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43014.9.3. The control strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434

CHAPTER 15 System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43715.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43715.2. Case study 1 – 800 kg, 20 m travel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

15.2.1. Rope selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43915.2.2. Critical traction ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44115.2.3. Emergency braking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44215.2.4. Traction in normal operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44615.2.5. Counterweight stalled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44615.2.6. Other deceleration conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44715.2.7. The traction motor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44915.2.8. Guide calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450

15.3. Case Study 2 – 1600 kg, 5 m/s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45215.3.1. Rope selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45315.3.2. Compensation system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45415.3.3. Critical traction ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45715.3.4. Emergency braking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45815.3.5. Traction in normal operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46315.3.6. Counterweight stalled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46315.3.7. Other deceleration conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46415.3.8. The traction motor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46615.3.9. Guide calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46615.3.10. Emergency terminal slowdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47115.3.11. Pre-opening of the doors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

CHAPTER 16 Firefighting and Evacuation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47416.1. Firefighting elevators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475

16.1.1. Firefighting operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47516.1.2. Construction of the hoistway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47716.1.3. Electrical supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48016.1.4. Equipment in the hoistway and pit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

16.2. Firefighting operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48316.3. Evacuation of persons with impaired mobility . . . . . . . . . . . . . . . . . . . . . . . . . 48416.4. General evacuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

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CHAPTER 17 Modification and Modernisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48617.1. Risk assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48717.2. Standards for refurbishment and modification . . . . . . . . . . . . . . . . . . . . . . . . . 48817.3. Significant modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

17.3.1. Change to car side fixed mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49017.3.2. Change to rated load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49517.3.3. Change to rated speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49717.3.4. Change of travel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49817.3.5. Refuge space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49817.3.6. Apron/Guard plate and balustrade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49917.3.7. Pulleys in the hoistway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501

17.4. Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501APPENDIX 1 The Dynamics of Multiple Reeving. . . . . . . . . . . . . . . . . . . . . . . . . . . . 502A.1.1. Reeving factor 1:1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502A.1.2. Reeving factor 2:1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504A.1.3. Reeving factor ‘r’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506A.1.4. Acceleration of the reeving pulleys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510APPENDIX 2 The Intermediate Tension in a Double Wrap Application . . . . . . . . . . . 513

APPENDIX 3 Rope Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516A.3.1. Rope mass for safety gear operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516A.3.2. Rope stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518APPENDIX 4 The Dynamics of a Harmonic Operator. . . . . . . . . . . . . . . . . . . . . . . . . 521A.4.1. Door speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521A.4.2. The ‘Code Zone’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523A.4.2.1. Kinetic energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524A.4.3. Door closing force. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525APPENDIX 5 Pattern Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527A.5.1. Acceleration pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527A.5.2. Short journeys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533A.5.3. Very short journeys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534APPENDIX 6 Significant Hazards to be Addressed . . . . . . . . . . . . . . . . . . . . . . . . . . . 536A.6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536A.6.2. Accessibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536A.6.3. Vandalism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536A.6.4. Behaviour in the event of fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536A.6.5. Hoistway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536A.6.6. Machine and pulley rooms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536A.6.7. Landing doors and car doors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536

ix

A.6.8. Car, counterweight and balancing weight. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537A.6.9. Suspension, compensation, overspeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537A.6.10. Guide rails, buffers, final limit switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537A.6.11. Distances car/landing doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537A.6.12. Elevator machine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537A.6.13. Electric installation/appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538A.6.14. Protection against electric faults, etc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538A.6.15. Notices, markings, operating instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539

LIST OF SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549

CHAPTER 1 INTRODUCTION

12

With the advent of computer based systems for the calculation of system parameters and the selectionof appropriate equipment, the number of design staff who are fully conversant with the underlying prin-ciples and theory relating to the design of elevator systems is becoming smaller and smaller. Much hasbeen written regarding the specification of vertical transportation systems for buildings, and there areexcellent texts regarding the design and performance parameters of individual elevator components.However, the literature is somewhat lacking in the intermediate stage between the individual elevatorcomponents and the complete vertical transportation system.

Consequently, the objective of this text is to provide a commentary on how individual components ofan elevator are brought together to provide a system which will carry the required load at the requiredspeed over the necessary travel, and to examine how this process is moderated and supported by the re-quirements of safety codes.

The basic parameters of an elevator system are the rated load, the rated speed and the required travel.In the underlying philosophy of our approach in this text, we differentiate quite clearly between the con-cept of “Vertical Transportation” and “Elevator System Engineering”. We shall use the former termwhen we wish to refer to the complex and demanding process of determining the requirements of a par-ticular building in terms of the number, location, rated load and rated speed of the elevators (and, whereappropriate, escalators) together with the dimensions and location of their associated access routes andareas, in order to provide efficient movement of people and goods. This aspect of the technology hasbeen dealt with comprehensively by a number of authors [Strakosch (2010), Barney (2002), Peters(2002)] and so we do not propose to add to these texts. On the other hand, we shall use the term Eleva-tor System Engineering to define the systems engineering process which is of interest to us here, the as-semblage and interfacing of the various major components of the elevator system in order to provide asuitable hoisting system which will move people and goods within a building in accordance with therequirements of the vertical transportation specification.

We shall deal with component design only insofar as it is essential to the understanding of specificaspects of applications engineering. For detail of component design, the reader is referred to an appro-priate existing text (e.g. Janovsky, 2001).

The design of system components and of the overall elevator is closely controlled within the require-ments of safety standards and codes. Although there are variations between the codes specific to vari-ous territories around the world, there is increasing recognition that it is possible to define a number of“Essential Safety Requirements” (ESR’s) lying at the heart of every safety code. In the European con-text, these are defined by European Parliament and Council Directive 95/16/EC (the “Lifts Directive”).Subsequent to the work in Europe, the International Standards Organisation has published the first partof an important three part standard:

ISO 22559-1: Safety Requirements for Lifts (elevators) – Part 1 Global Essential Safety Require-ments (GESR’s)

This standard seeks to provide an international basis for elimination of barriers to trade similar to thebasis provided within Europe by the aforementioned Lifts Directive.

Within this text, we shall seek, as far as possible, to describe the process of elevator system engineeringin the context of these international norms, referring back to particular regional codes only where theseresult in an interesting or important variation in engineering practice. In these cases, we shall seek toexplore the practical differences which result from the regional variations.

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The study commences with an analysis of the fundamental design calculation for an elevator system,taking as its parameters:

• An estimate of the frictional characteristics of the traction system.• An estimate of the friction losses to be expected in the hoistway.• The rated load and speed. • An estimate of the masses/inertias of the various components in the hoistway. • The maximum accelerations to be expected under normal and emergency conditions.

The design calculation uses these parameters to calculate the nature and mass of compensation means(if any) required to avoid1 slippage between the ropes and the driving sheave under defined conditions.

In considering the system calculation, we shall introduce six important parameters of an elevator system:

• T1 and T2, the dynamic tensions in the suspension ropes on either side of the traction sheave, whereT1 is always taken as the greater and T2 the lesser tension.

• a, the angle of wrap of the suspension ropes on the traction sheave.

• f, the friction factor between the suspension ropes and the traction sheave. Note at this stage thatwhilst f depends, inter alia, on m, the coefficient of friction between the ropes and the sheave, the fric-tion factor f is different from the coefficient of friction m.

• The applied traction ratio

• The critical traction ratio efα

It is important not only to establish the characteristics of the system in terms of driving the load, but alsothe issues which arise during slowing and stopping, particularly where the system is brought to rest bythe electromechanical brake. Where the system is driven or slowed by the elevator motor, the torque em-ployed will be matched by the motor control to the current characteristics of the system (driving or over-hauling with rated load, an intermediate load or no load). Under electromechanical braking, the torqueis mechanically preset to bring safely to rest rated load travelling down. Consequently, if the electro-mechanical brake is applied at other states of load, the deceleration characteristics will be different.

Having established, via the system calculation, the overall mass and inertia of the elevator system, wecan then proceed to consider the total radial load on the driving sheave and diverter/secondary pulley,together with the power requirements for the system drive, taking account of the various efficiencies in-volved in the system. In considering power requirements we need to look at the transfer of energy be-tween the power source (i.e. the public mains supply) and the moving elements in the hoistway. We mustnote in particular that the transfer of energy is not exclusively from power source to the hoistway, butthat the power system must cater for the need to control a flow of energy coming from the hoistway, e.g.when a fully loaded elevator car is descending.

These first three chapters set out the basic engineering parameters of an elevator system. It is appro -priate now to turn our attention to the requirements of safety codes. As noted earlier, the main thrust of all the leading safety codes (EN81, A17/B44, AS1732, Building Standard Law of Japan,

1For safety reasons, the systems calculation also seeks to guarantee that under some circumstances slippage between ropes andtraction sheave must occur.

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Enforcement order Section 2, etc.) is the same, and we commence by considering why it is advantageousthat an elevator safety code should be adopted over and above general national requirements for healthand safety, and the protection afforded by product liability case law and legislation.

Once the desirability of a safety code has been established, we move on to consider how such a codemay be composed, and debate the relative merits of prescriptive codes as opposed to codes based on theestablishment of appropriate performance criteria and/or the assessment and avoidance of the risksassociated with the product. In this part of our study, we shall give attention to an ISO technical report:

ISO/TR 11071: Comparison of worldwide lift safety standards –

Part 1: Electric lifts (elevators)

Part 2: Hydraulic lifts (elevators)

in order to draw appropriate comparisons between the practice in various territories.

There is a number of territories where one or other of the leading codes (EN 81, A17/B44, etc) has beenadopted on a local basis. Whilst the conformity of an installation to the adopted code is normally estab-lished at the commissioning stage, there can be problems later on in establishing requirements which en-sure that the system is maintained to that standard through its service life. In the ‘native’ territory for thecode (e.g. member states of the European Union for EN 81, or individual states in the United States ofAmerica for A17/B44), such compliance is established through supplementary legislation, or throughthe general requirements for health and safety/product liability.

Whilst the core of the safety code embodies the requirements for safety in ‘normal operation’, i.e. themotion of the elevator car within the hoistway, and for users accessing the car (whether as a passengeror during maintenance operations), it is axiomatic that the safety code will need to deal with the main-tenance of safety of users during system failure, whether minor or catastrophic, and with the potentialfor misuse. Consequently, our discussion will move on to a discussion of the safety systems which devolve from the ESR’s for an elevator system.

Arising from the traction design, we must consider the suspension, and precautions for the avoidance ofsuspension failure, either as a consequence of overload or of wear or deterioration of the suspensionmembers. A further consideration at this point will be the propensity for the system to exhibit resonantvibration due to the (varying) natural frequency of the suspended mass system.

It is generally accepted that the precautions imposed by safety codes effectively eliminate the possibil-ity of suspension failure. Nevertheless public acceptability and engineering prudence dictate the provi-sion of systems to arrest uncovenanted motion of the car (in either direction) with or without an intactsuspension. Consequently, we must consider the systems provided for the arrest of free fall and of un-covenanted motion – the buffers located in the pit, the governor/safety gear combination, and, of course,the status and function of the electromechanical brake.

Discussion of the precautions against overspeed and free fall brings into question the guiding systemand its interface to the civil structure. We may define an elevator as:

“A permanently installed system, with traction, positive drive or hydraulic drive, serving defined land-ing levels and having a car designed for the carriage of persons or goods, suspended by ropes or chains,or supported by a hydraulic jack and moving on or between guide rails”.

INTRODUCTION

15

We shall consider only vertical motion, although, with some modification, many of the concepts discussedwill apply also to inclined elevators and to funicular systems.

The operation of the guiding system is fundamental to our definition. First and foremost, the guidingsystem defines the datum of the spatial relationship between the elevator and the building which itserves. In this context, the objective is to ensure that the elevator car (and counterweight where appropriate)follow, accurately, a defined path through the building with appropriate clearance from equipment associ-ated with the elevator operation (e.g. landing entrances).

Provided that the suspension centres are accurately located above (or below, for a hydraulic installation)the centre of mass of the car, forces acting on the guide rails will not be great. With an offset suspension orhydraulic piston, lateral forces come into play. Nevertheless, in normal operation these are still not great.

However, during safety gear operation in particular, the loadings due to the deceleration of the car, andits subsequent support after stopping, are transmitted to the foundation via the guide rails which, in con-sequence, are subjected to significant buckling forces.

In consequence of its function in maintaining the car in a pre-defined path, the guide rail system willimpose forces, particularly lateral forces, on the elevator car via the guide shoes. Although, as impliedabove, these forces will be relatively small in normal operation, the quality of the ride experienced bypassengers is directly related to the quality of the alignment and straightness of the guide rail system.

We shall discuss these issues, together with some of the measures and systems which may be applied tocompensate for imperfections in guide rail alignment.

Apart from a possible slight apprehension regarding the possibility of free fall, the normal passengerprobably does not give much thought to the motion control of an elevator, nor to the issues we have con-sidered so far. Indeed, thus far we have confined ourselves to those elements which are almost entirelythe province of the elevator engineer. However, the elevator entrance is a different matter. The normalpassenger is most frequently vulnerable to injury when entering or leaving the car, either from contactwith a moving door, or due to the potential tripping hazard between the car and landing thresholds. Fur-thermore, it is the elements which surround the entrance which are perhaps most vulnerable to misuseor interference. Consequently, we must devote some attention to the design and operation of the entrance,and to the co-ordination of the entrance operation with the motion control of the elevator. It is the land-ing entrance which gives access to the hoistway, and must prevent any such access except by qualified,competent and authorised individuals, e.g. maintenance mechanics, inspection bodies and, where necessary,emergency services.

In addition to its function of regulating personnel access to the hoistway, more than any other part ofthe elevator installation, the landing entrance is a component of the building structure. The hoistway pro-vides a shaft through the building which can contribute to the spread of fire or smoke, and it is the land-ing entrances at each floor which must provide an appropriate physical barrier to any such spread viathe hoistway.

Penetration of the elevator market by hydraulic power systems led manufacturers of traction systems toinvestigate means whereby the need for a separate machine room adjacent to the hoistway could beeliminated, hence the advent of the machine-room-less lift (MRL). We shall look at the innovationswhich have led to the successful introduction of MRL technology, and show how, although the inclu-sion of the elevator machine within the hoistway has led to a very different appearance and significant

INTRODUCTION

16

savings in space required for the installation, the basic technology of the traction elevator remains thesame, with the same safety rules and requirements, and, to all intents and purposes, the same equipment.

It will also be instructive to mention, briefly, the concept of the “counterweightless” traction elevatorand how this achieves a traction drive without the need for a counterweight.

Thus far, there has been an implicit assumption of traction elevator technology. However, no treatise onelevator engineering would be complete without a discussion of hydraulic power systems. Of course,many of the elements of the elevator system (entrances, buffers, safety gear etc.) will be common bothto traction and hydraulic elevators, albeit a hydraulic system may be able to dispense with the safetygear and/or the overspeed governor, depending upon configuration.

The hydraulic power system for an elevator installation differs from many other types of hydraulic sys-tems in that it is usually a high flow system with relatively low pressure, as opposed to many otherapplications of hydraulic power which depend upon the transmission of relatively high pressures, but withlimited movement of the hydraulic fluid. Further, in terms of elevator performance, it is the volumetricflow rate of the hydraulic fluid which is critical, not the pressure. We shall lay out the basic principlesof the hydraulic system and discuss how the inherent problems of high flow rates have been addressedthrough flow compensation.

It is a normal drawback to the application of hydraulic systems in elevators that in comparison with tractiondrive, the hydraulic power system requires significantly more power, and does not, as a rule regenerateany energy back to the mains supply. This has been addressed in the so-called ‘hydraulic counterweight’system. Whilst, at the date of writing, this system is a relatively recent innovation, nevertheless it willbe instructive to make some study of its principles.

Perhaps the fastest changing aspect of elevator technology is to be found in the control system, whetherit be the supervisory system or the motor control system. In either case, the advent of microprocessortechnology has, over the past 30 years, changed control system concepts almost beyond recognition. Thefast microprocessors now available, together with current fast power switching devices, powerful, rareearth magnet systems, solid state lamps and innovative sensors allow the economic provision of controltechniques which were inconceivable 25 years ago. Given that this part of the technology is fast changing,a detailed study of current implementations, particularly in the area of motor control, would be quicklyoutdated. Consequently, we shall attempt to outline the underlying principles which are relevant, usingcurrent implementations simply as examples of the application of these principles.

We shall show how the advent of electronic motor control has led, inevitably, to the incorporation ofelectronic and programmable systems into safety related applications, and will discuss the implicationsfor design and maintenance of elevator controls. Further, the signals within high speed microprocessorsinevitably operate at very low power levels, making them potentially vulnerable to external influences.On the other hand, the high speed switching techniques now employed, particularly in the power controlcircuit for the elevator motor, mean that an elevator control becomes a potential transmitter of electro-magnetic interference, either radiated or mains borne. Consequently, the achievement of electromagneticcompatibility (EMC), both within the system, and in conjunction with neighbouring systems becomesan important issue.

Having discussed the major components and design calculations associated with an elevator system andtheir relationships one with another, it will be useful to bring these together into a consideration of theoverall design process for an elevator system. Of course, organisations which undertake the designand/or manufacture of elevator systems will have in place appropriate, documented design procedureswhich ensure that the major issues discussed here are accounted for, but ensure that other relevant issues,

INTRODUCTION

17

particularly those associated with the manufacturing and installation processes and their logistics are alsocatered for. In a text such as this we can provide no more than a ‘broad brush’ overview of the process,drawing attention to the interaction between the various parts of the system and how these force thedesign to follow an iterative model as design constraints in one part of the system force re-considerationof other system components, e.g. as the compensation requirements are established through the systemcalculation, the loadings on the elevator machine will change, with the possible consequence of forcingan upgrade of the machine itself, which, in turn, may change the traction parameters, with consequencesin turn for the compensation scheme.

A conventional ‘general purpose’ elevator installation is provided simply to fulfil, in part or as a whole,the day by day vertical transportation needs of a particular building. As buildings become larger, andparticularly taller, the provision of means for evacuation and for the support of firefighting and emer-gency services becomes an issue. The idea of ‘fire control’ was established in the middle of the 20thCentury. However, this did not envisage the use of an elevator or elevators in supporting emergencyservices in a building which was itself on fire. That concept has evolved in more recent years into the‘firefighting elevator’ and the ‘evacuation elevator’. These require that the design of the elevator sys-tem and its surroundings are integrated more closely with the building design, and takes account of useby firefighters in particular, allowing for their special equipment and for their escape from the elevatorcar if required. Equally important, the elevator control must be able to co-ordinate with the emergencyand evacuation procedures for the building.

Finally, although the design life of buildings has reduced in the latter part of the 20th Century, never-theless, a building is a long-lived asset, and it may be desirable that it be modernised several times dur-ing its working life. Part of that modernisation will be the modernisation of the elevator systems withinthe building, since building owners will wish to take advantage of innovations and developments in ele-vator technology. Turning to code requirements, the expectations of the travelling public are likely tobecome more demanding as time goes by. As an example, the ±100 mm levelling accuracy of a singlespeed a.c. elevator 40 years ago is unlikely to be acceptable today. As time goes by, and elevator design-ers find ever more effective ways to preserve the comfort and safety of passengers and other users, codesand standards will evolve to reflect these developments. When an elevator is modernised, it becomesimportant to reflect, as far as possible, current code requirements in the modernised installation, and thisis a problem in itself, which is worthy of discussion.

In conclusion, this text seeks to lay out as much as possible of the range of issues to be encountered inthe design of a working elevator system. However, as with any engineering enterprise, elevator systemdesign is an inevitable series of compromises. Individual design companies will have their own criteriafor the design of their particular elevator systems, and in-house calculations and design norms will reflectthese. In the course of this text, we will give a number of examples and calculation methods. These areprovided solely for the purposes of illustration of underlying principles and are not offered as a completedesign solution, nor is it intended to advocate the particular design methodology. The reader must bearin mind that the text is simply a guide, and does not constitute a design, installation, maintenance orservice manual for an elevator system.

1.1. Accuracy and precision

Before proceeding to consider the basic calculations, we need to be very clear that however preciselywe may calculate the parameters of the installation, the outcomes of these calculations are an engineer-ing estimate, with limited accuracy.

As an instance, in calculating the critical traction ratio, we take a value for the coefficient of friction. Estab-lished practice indicates that the coefficient of friction between a cast iron or steel sheave and a steel

INTRODUCTION

18

wire suspension rope is of the order of 0.08–0.1, and that calculations based on this value can providea safe result. There have been techniques for increasing the coefficient of friction with steel wire ropesby means of groove ‘liners’ made from synthetic materials (Janovsky, 2001). In the case of other materials,e.g. aramid ropes with a synthetic resin traction sheave, values in the order of 0.2 have been reported(Koshak et al., 2003). However, in addition to the particular materials used for rope and groove, the actualcoefficient of friction achieved in practice will depend upon the site conditions, e.g. the state of wear ofthe sheave grooves, the relationship between the actual (rather than nominal) rope diameter and thegroove dimensions, the amount of rope lubricant present etc..

Further, in the initial calculation of an applied traction ratio, there will be estimated figures for the massof the car and other equipment in the hoistway.

It is a matter for the applications engineer to decide on the accuracy of these estimates, and to place suchtolerances as may be appropriate on the outcomes of any design calculation.

What is certain is that a calculation which provides a high degree of precision in its outcome, i.e. a largenumber of significant figures, does not necessarily reflect a high degree of accuracy – the prediction oflikely performance in practice may not be comparable with the number of significant figures in the out-come of the calculation. Consequently, unless otherwise stated, throughout this text, where arithmeticalcalculations are undertaken, calculations will progress to an accuracy considered appropriate to the context,taking account of the reliability of the input data. The degree of precision chosen will exceed the accuracyof the result in most cases, but will ensure that the outcome falls within an adequate confidence limit forthe engineering design.