This report documents how active structural control was used to significantly enhance the metal removal rate of a milling machine. An active structural control system integrates actuators, sensors, a control law and a processor into a structure for the purpose of improving the dynamic characteristics of the structure. Sensors measure motion, and the control law, implemented in the processor, relates this motion to actuator forces. Closed-loop dynamics can be enhanced by proper control law design. Actuators and sensors were imbedded within a milling machine for the purpose of modifying dynamics in such a way that mechanical energy, produced during cutting, was absorbed. This limited the on-set of instabilities and allowed for greater depths of cut. Up to an order of magnitude improvement in metal removal rate was achieved using this system. Although demonstrations were very successful, the development of an industrial prototype awaits improvements in the technology. In particular, simpler system designs that assure controllability and observability and control algorithms that allow for adaptability need to be developed.

This report documents how active structural control was used to significantly enhance the metal removal rate of a milling machine. An active structural control system integrates actuators, sensors, a control law and a processor into a structure for the purpose of improving the dynamic characteristics of the structure. Sensors measure motion, and the control law, implemented in the processor, relates this motion to actuator forces. Closed-loop dynamics can be enhanced by proper control law design. Actuators and sensors were imbedded within a milling machine for the purpose of modifying dynamics in such a way that mechanical energy, produced during cutting, was absorbed. This limited the on-set of instabilities and allowed for greater depths of cut. Up to an order of magnitude improvement in metal removal rate was achieved using this system. Although demonstrations were very successful, the development of an industrial prototype awaits improvements in the technology. In particular, simpler system designs that assure controllability and observability and control algorithms that allow for adaptability need to be developed.

The problem of understanding and modeling the complicated physics underlying the action and response of the interfaces in typical structures under dynamic loading conditions has occupied researchers for many decades. This handbook presents an integrated approach to the goal of dynamic modeling of typical jointed structures, beginning with a mathematical assessment of experimental or simulation data, development of constitutive models to account for load histories to deformation, establishment of kinematic models coupling to the continuum models, and application of finite element analysis leading to dynamic structural simulation. In addition, formulations are discussed to mitigate the very short simulation time steps that appear to be required in numerical simulation for problems such as this. This handbook satisfies the commitment to DOE that Sandia will develop the technical content and write a Joints Handbook. The content will include: (1) Methods for characterizing the nonlinear stiffness and energy dissipation for typical joints used in mechanical systems and components. (2) The methodology will include practical guidance on experiments, and reduced order models that can be used to characterize joint behavior. (3) Examples for typical bolted and screw joints will be provided. 3 AcknowledgmentThe authors thank the many managers and members of technical staff who have worked on this challenging problem at various times since its inception. For all of them, this involved a tremendous amount of hard work and for our management team it involved taking a substantial risk. To put significant resources year-after-year into a problem that had so successfully resisted the best efforts of the scientific community can be a gutsy decision on the part of manager. The authors believe that we have justified our managers' faith in us.Among the managers who should be recognized are

This paper details the analysis of vibration monitoring for end-point control in oxide CMP processes. Two piezoelectric accelerometers were integrated onto the backside of a stainless steel polishing head of an IPEC 472 polisher. One sensor was placed perpendicular to the carrier plate (vertical) and the other parallel to the plate (horizontal). Wafers patterned with metal and coated with oxide material were polished at different speeds and pressures. Our results show that it is possible to sense a change in the vibration signal over time during planarization of oxide material on patterned wafers. The horizontal accelerometer showed more sensitivity to change in vibration amplitude compared to the vertical accelerometer for a given polish condition. At low carrier and platen rotation rates, the change in vibration signal over time at fixed frequencies decreased approximately Yz -1 order of magnitude (over the 2 to 10 psi polish pressure ranges). At high rotation speeds, the vibration signal remained essentially constant indicating that other factors dominated the vibration signal. These results show that while it is possible to sense changes in acceleration during polishing, more robust hardware and signal processing algorithms are required to ensure its use over a wide range of process conditions.

Ingersoll's Octahedral Hexapod -a milling machine for the future -is described. The specific target applications and the performance goals for an enhanced version of the machine are illustrated. The approach to achieving the goals by incorporation of advanced composites and active chatter and vibration control using smart materials is discussed. The machine characterization performed on an existing machine, the FE models developed and the plans to use the characterization and the validated models in designing an enhanced machine are described.

IThe use of active feedback compensation to mitigate cutting instabilities in an advanced milling machine is discussed in this paper. A linear structural model delineating dynamics significant to the onset of cutting instabilities was combined with a nonlinear cutting model to form a dynamic depiction of an existing milling machine. The model was validated with experimental data. Modifications made to an existing machine model were used to predict alterations in dynamics due to the integration of active feedback compensation. From simulations, subcomponent requirements were evaluated and cutting enhancements were predicted. Active compensation was shown to enable more than double the metal removal rate over conventional milling machines.Keywords: milling, controls, chatter INTRODUCTIONMaximum metal removal rate is a quantitative measure of the productive capacity of a machine tool. This measure, which is machine as well as tool dependent, is limited by the onset of machining in~tabilities',~,~,~. Machining instabilities are minimized by enhancing the stability of structural vibratory modes significant to cutting dynamics.Active methods can be used to enhance the stability of pertinent structural vibratory modes for a variety of machining configurations. Although active methods are relatively immature5, potential performance enhancements resulting from active implementation overshadow performance enhancements resulting from current passive innovations.Active methods can be categorized into activelpassive, process control, and feedback compensation methods. Activelpassive methods actively tune or mimic stabilizing passive absorber^^^^^^. Process control methods alter or modulate operating parameters (spindle speed, feed rate, etc.) to locate, or oscillate between, predetermined stability domains9i10, and feedback compensation methods actively modify machine dynamics such that domains of stability are enlarged".'2713.Presented within this paper is the design of an active feedback compensator which will actively modify machine dynamics such that domains of stability are enlarged. This design process entails; 1) development and validation of a model, 2) modification of the model for active compensation, and 3) performance evaluation.In section 2, modeling and validation is discussed. In section 3, the modeling of dynamics essential for active compensation is discussed. And in section 4, performance earnings are presented. MODEL DEVELOPMENTA machine model is a set of mathematical relationships relating dynamic response parameters (displacement of tool tip center, force on tool, etc ...) to a set of process parameters (spindle speed, number of teeth on tool, etc ...). The goal of modeling is to create mathematical relationships which are sufficiently accurate for the purpose of prediction. Model accuracy is quantified by comparison with experimental data. The model discussed in this section is shown to compare well with experimental data.The machine model is the unification of a cutting model and a structural ...

This report summarizes experimental and test results from a two year LDRD project entitled Real Time Error Correction Using Electromagnetic Bearing Spindles. This project was designed to explore various control schemes for levitating magnetic bearings with the goal of obtaining high precision location of the spindle and exceptionally high rotational speeds. As part of this work, several adaptive control schemes were devised, analyzed, and implemented on an experimental magnetic bearing system. Measured results, which indicated precision positional control of the spindle was possible, agreed reasonably well with simulations. Testing also indicated that the magnetic bearing systems were capable of very high rotational speeds but were still not immune to traditional structural dynamic limitations caused by spindle flexibility effects.There were three separate papers written on various advanced schemes for levitating the bearing.

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