Hydraulic and Electro-Hydraulic Control Systems

ISBN-13: 9781851665563 / Angielski / Twarda / 1991 / 268 str.

R. B. Walters

Opis

Force and motion control systems of varying degrees of sophistication have shaped the lives of all individuals living in industrialized countries all over the world, and together with communication technology are largely responsible for the high standard ofliving prevalent in many communities. The brains of the vast majority of current control systems are electronic, in the shape of computers, microprocessors or programmable logic controllers (PLC), the nerves are provided by sensors, mainly electromech anical transducers, and the muscle comprises the drive system, in most cases either electric, pneumatic or hydraulic. The factors governing the choice of the most suitable drive are the nature of the application, the performance specification, size, weight, environ mental and safety constraints, with higher power levels favouring hydraulic drives. Past experience, especially in the machine tool sector, has clearly shown that, in the face of competition from electric drives, it is difficult to make a convincing case for hydraulic drives at the bottom end of the power at fractional horsepower level. A further, and frequently range, specifically overriding factor in the choice of drive is the familiarity of the system designer with a particular discipline, which can inhibit the selection of the optimum and most cost-effective solution for a given application. One of the objectives of this book is to help the electrical engineer overcome his natural reluctance to apply any other than electric drives."

Spis treści

1 Introduction.- 2 Hydraulic Power Source.- 3 Working Pressures.- 4 Hydraulic Actuators.- 5 Control Elements.- 5.1 Pressure Controls.- 5.2 Flow Controls.- 6 Data Transmission Elements.- 7 The Control System.- 7.1 The Controller.- 7.2 The Closed Loop Option.- 8 Control Concepts.- 8.1 Definition of Terms.- 8.1.1 Stability.- 8.1.2 Transfer Function.- 8.1.3 Steady-State Gain.- 8.1.4 Loop Gain.- 8.1.5 Frequency Response.- 8.1.6 Stability Criteria.- 9 Principles of Flow Control for Valve-Operated Systems: Part 1.- 10 Principles of Flow Control for Valve-Operated Systems: Part 2.- 10.1 Effect of Quiescent Leakage on Linearity.- 11 Introduction to System Analysis.- 12 System Analysis of Electro-hydraulic Control System.- 13 Modular Optimized System Simulation.- 14 System Analysis in the Time Domain.- 15 Transient Response Characteristics.- 16 Further Case Studies.- 16.1 Third Order System with Flow Feedback.- 16.2 Fourth Order Hydrostatic Transmission.- 16.3 Fifth Order System.- 16.4 Seventh Order System with Flow Feedback.- 17 Non-symmetrical Systems.- 17.1 Oil Compliance.- 17.2 Cavitation Effects of Overrunning Loads.- 17.3 Worked Example.- 18 Response to Large Step Demand.- 19 Valve Operating Forces.- 19.1 Spool Valves.- 19.2 Flapper-Nozzle Valves.- 19.3 Poppet Valves.- 20 The Electronic Interface.- 21 System Enhancement.- 21.1 Input Shaping.- 21.1.1 Ramp-Step Demand.- 21.1.2 Negative Ramping.- 21.1.3 Superimposed Negative Impulse..- 21.2 Passive Networks.- 21.3 Adaptive Control.- 21.4 Multiple Feedback.- 21.5 Three-Term Controller.- 21.6 Performance Summary.- 22 Analysis of Pressure Control System.- 23 Efficiencies and Power Dissipation.- 24 Elastically Mounted Mass Systems.- 25 The Flow Feedback Option.- 26 Non-linearities.- 27 Steady-State System Analysis.- 27.1 Velocity Error.- 27.2 Hysteresis Error.- 27.3 Load Error.- 27.4 Conclusions.- 28 Applications.- 29 National and International Standards.