Nonlinear modeling for adaptive suppression of axial drilling vibration

© The Society for Experimental Mechanics, Inc. 2014. Vibrations developed during drilling present challenges in an array of industries including mechanical, medical, structural, and oil extraction. Velocity weakening, intracranial vibrations, large amplitude standing pressure waves in material cavities, and failure of drill strings are prominent issues among these fields. Stick-slip (torsional) and bit-bounce (axial) vibrations have been found to be particularly problematic in precision drilling jobs such as machining to tight tolerances, dismantling vibration-sensitive devices, and surgical work. Current technologies to detect and suppress systematic vibrations have several shortcomings including malfunctioning, complete failure, complexity, and high power consumption. This paper proposes a method to suppress vibrations of drilling material surfaces using adaptive positive position feedback (APPF) control for efficient tunable damping. An experiment-based parametric study has been conducted to determine the relationship of force, rotational velocity, and acceleration on both drill vibrations and drilling material surface vibrations. Results of a parametric study and Rational Polynomial Fraction method are used to estimate fundamental behaviors of the drilling system to create a refined numerical model for simulating the drilling process. An APPF controller together with the model provided a method to evaluate new actuator designs for vibration suppression and has shown a 69.8 % reduction of displacement vibrations

The Doctor Will See You Shortly: The Ethical Significance of Time for the Patient-Physician Relationship

Many physicians and health care leaders express concern about the amount of time available for clinical practice. While debates rage on about how much time is truly available, the perception that time is inadequate is now pervasive. This perception has ethical significance, because it may cause clinicians to forego activities and behaviors that promote important aspects of the patient-physician relationship, to shortcut shared decision making, and to fall short of obligations to act as patient advocates. Furthermore, perceived time constraints can hinder the just distribution of physician time. Although creating more time in the clinical encounter would certainly address these ethical concerns, specific strategies—many of which do not take significantly more time—can effectively change the perception that time is inadequate. These approaches are critical for clinicians and health systems to maintain their ethical commitments and simultaneously deal with the realities of time