Control of Machines with FrictionIt is my ambition in writing this book to bring tribology to the study of control of machines with friction. Tribology, from the greek for study of rubbing, is the discipline that concerns itself with friction, wear and lubrication. Tribology spans a great range of disciplines, from surface physics to lubrication chemistry and engineering, and comprises investigators in diverse specialities. The English language tribology literature now grows at a rate of some 700 articles per year. But for all of this activity, in the three years that I have been concerned with the control of machines with friction, I have but once met a fellow controls engineer who was aware that the field existed, this including many who were concerned with friction. In this vein I must confess that, before undertaking these investigations, I too was unaware that an active discipline of friction existed. The experience stands out as a mark of the specialization of our time. Within tribology, experimental and theoretical understanding of friction in lubricated machines is well developed. The controls engineer's interest is in dynamics, which is not the central interest of the tribologist. The tribologist is more often concerned with wear, with respect to which there has been enormous progress - witness the many mechanisms which we buy today that are lubricated once only, and that at the factory. Though a secondary interest, frictional dynamics are note forgotten by tribology. |
Contents
Introduction | 1 |
Friction in Machines | 7 |
21 The Contemporary Model of Machine Friction | 11 |
a Domain of Many Choices | 21 |
23 Relaxation Oscillations | 24 |
24 Friction Modeling in the Controls Literature | 35 |
25 An Integrated Friction Model | 41 |
Experiment Design | 43 |
71 Dimensional Analysis | 98 |
72 Perturbation Analysis | 101 |
73 The Impact of Static Friction Rising as a Function of Dwell Time | 108 |
74 Integral Control | 116 |
Demonstrations of Friction Compensation | 125 |
82 OpenLoop Motion of Three Joints | 129 |
83 Friction Compensated Force Control | 134 |
Suggestions Toward Friction Modeling and Compensation | 141 |
Repeatability | 47 |
BreakAway Experiments | 55 |
52 Building the Compensation Table | 58 |
Friction as a Function of Velocity Negative Viscous Friction Revealed | 63 |
61 Analysis of Variance in the Motion Friction Data | 64 |
62 Friction at Low Velocities | 66 |
63 Friction During Compliant Motion | 68 |
64 The Dahl Effect | 78 |
65 The Stribeck Effect | 80 |
66 Temporal Effects in the Rise and Decay of Friction | 88 |
67 Variance in Friction as Process Noise | 91 |
Analysis of StickSlip | 95 |
91 Suggestions on Experimental Technique | 142 |
92 Suggestions on Control | 143 |
93 Conclusion | 144 |
Bibliography | 147 |
Small Studies | 157 |
A2 Joint 2 Motor Alone and Joint 2 Link Alone | 159 |
A3 Trials with Dither | 162 |
A4 Friction as a Function of Load | 164 |
A5 Creep | 166 |
A6 Effects that were not Observed | 167 |
| 169 | |
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Common terms and phrases
acceleration accelerometer analysis applied torque asperities Bell and Burdekin boundary lubrication break-away data break-away torque Compliant Motion contact force cycles per radian Dahl effect damping desired velocity dimensional analysis dimensionless dither dwell dynamics EP additives equation experimental force control force error friction forces friction model friction parameters Friction Torque frictional lag full fluid lubrication function of velocity Hertz Hess and Soom hydrodynamic lubrication integral control joint kinetic and viscous kinetic friction kinetic plus viscous kp/M limit cycle load low velocity machine magnitude measured mechanism motion friction motion of figure motor negative viscous friction Newton-meters Newtons non-linear observed Open-Loop Motion partial fluid lubrication phase plane PUMA PUMA arm Rabinowicz regime residual rising static friction Robotics sample shown in figure Soom 90 spatial frequency static friction static plus kinetic steady stick-slip cycle stiffness Stribeck effect Stribeck friction surface t₂ trials tribology unperturbed trajectory variance zero velocity
Popular passages
Page 151 - Friction at a Lubricated Line Contact Operating at Oscillating Sliding Velocities,
Page 155 - The Effect of Transmission Design on the Performance of Force-Controlled Manipulators," PhD Thesis, Mechanical Engineering Dept., Massachusetts Institute of Technology.
Page 155 - Stribeck, R. (1902). Die Wesentlichen Eigenschaften der Gleit- und Rollenlager — the key qualities of sliding and roller bearings.