To facilitate pulse Nd–YAG laser spot weld development, it is common practice to adjust the pulse energy, duration, and focus spot size. An accurate understanding of the effect of these parameters on melting, weld appearance, and heat input is thus required. Calorimetric measurements of the net heat input to 304 stainless steel workpieces for laser spot welds have been completed. A pulse Nd–YAG laser was used with varying pulse energies from 1 to 5·5 J, and pulse durations of 2·2 and 7·0 ms. Measurements showed the absorption for spot welds produced using the pulsed Nd–YAG laser to vary from 38 to 67% and to be relatively insensitive to beam intensity. Analysis of the continuous point source equation for conduction heat flow in solids was used to predict the weld size for the pulse energy and duration measured in the experiment. Calculations of the weld pool volume from the weld metallography were used to determine the melting for each spot weld. Comparisons of the measured weld size with the three-dimensional model predicted size indicated that the observed weld pools are larger than is expected from the measured workpiece energy. Analysis of the experimental data and the theoretical model has revealed a substantial increase in melting for short duration pulses versus long duration pulses of the same energy. The benefit of laser spot welding parameter optimisation is hence indicated.

This paper reviews issues related to the use of aeroelastic tailoring as a cost-effective, passive means to shape the power curve and reduce loads. Wind turbine blades bend and twist during operation, effectively altering the angle of attack, which in turn affects loads and energy production. It is possible to build a small amount of desirable twisting into the load response of a blade with proper asymmetric fiber lay up in the blade skin. The tailored twisting can create an aeroelastic effect that has payoff in either better power production or in vibration alleviation, or both. Several research efforts have addressed different parts of this issue. Research and development in the use of aeroelastic tailoring on helicopter rotors is reviewed. Potential energy gains as a function of twist coupling are reviewed. The effects of such coupling on rotor stability have been studied and are presented. Fatigue damage estimates due to turbulent inflow have been computed for rotors employing several different control schemes, with and without twist-coupled blades. Energy output and maximum loads are also computed and compared 4

Abstracl-An optimized path-planning approach is presented for flexible dynamic systems. Feedforward command profiles are determined for rest-tomst large angle maneuvers that keep vibrations to a minimum. The pelromance index included both minimum energy and minimum h e optimization problems. The feedfoward command profiles wem generated by solving a discrete-time optimal control problem via Discrete Dynamic Programming (DDP). A simple planar two-link flexible robot m was utilized to demonstrate the DDP path-planning scheme. Numerical simulation results included: 1) minimum eflort, 2) minimum ellort with bounds, 3) mini" time, and 4) minimum torque-rate or power, respectively. The DDP approach demonstrated an elkdive alternative for numerical optimization, to generate optimal feedlorward trajeclory profdles.

This book is the result of over ten (10) years of research and development in flexible robots and structures at Sandia National Laboratories. The authors decided to collect this wealth of knowledge into a set of viewgraphs in order to teach a graduate class in Flexible Robot Dynamics and Controls within the Mechanical Engineering Department at the University of New Mexico (UNM). These viewgraphs, encouragement from several students, and many late nights have produced a book that should provide an upper-level undergraduate and graduate textbook and a reference for experienced professionals.The content of this book spans several disciplines including structural dynamics, system identification, optimization, and linear, digital, and nonlinear control theory which are developed from several points of view including electrical, mechanical, and aerospace engineering as well as engineering mechanics. As a result, the authors believe that this book demonstrates the value of solid applied theory when developing hardware solutions to real world problems. The reader will find many real world applications in this book and will be shown the applicability of these techniques beyond flexible structures which, in turn, shows the value of multidisciplinary education and teaming.The authors have placed a strong emphasis on real world applications and handson hardware solutions. As a result, this book steps through a systematic procedure for applying theory to practice while leaving the rigorous theorem development to a rich collection of references. Also, the authors realize that most educational institutions do not have ready access to hardware platforms, so the authors have chosen an analytical example problem to be utilized throughout the book. By analytical, one means the example problem model is solvable in closed form and it has been verified against experimental results. The analytical example problem is the overhead gantry crane robot that supports a spherical pendulum payload. Gantry robots are found throughout the robot user community and provide a straight forward, real world application. v (belongs to), ~ (finite difference, or increment), iff (if and only if), II II (vector magnitude), I I (absolute value), and the end of proof symbol as D. All other special variables and symbols are defined and explained as needed.

Calorimetric measurements of the net heat input to the workpiece have been made to determine the effect of very high travel speeds on laser weld melting efficiency. Very high welding speeds are required in welding applications such as automotive where lasers are now applied extensively. Travel speeds as fast as 530 mm/s for continuous wave CO 2 laser welding on 304 stainless steel have been examined in this study. Melting efficiency indicates what fraction of the laser power absorbed is used to produce melting rather than undesirable base metal heating. It was found that melting efficiency initially increased then slowly decreased as fusion zone dimensions changed. Dimensionless parameter correlations for melting efficiency based on heat flow theory have been presented for both 2D and 3D heat flow geometries. The levels of melting efficiency observed are close to the maximum values that are predicted with these correlations. Determinations of the melting point isotherms and analysis of changes to the dimensionless parameters have been shown to predict the observed changes in melting efficiency. The results indicate that an enhanced melting efficiency is obtained in high speed laser welding when either the fusion zone aspect ratio or the joint geometry promote 2D heat flow.