Active Vibration Control For Chatter Suppression

Jon Pratt
Department of Engineering Science and Mechanics 
Virginia Polytechnic Institute and State University 
Blacksburg, Virginia   24061-02 

Sponsored by the Dept. of Engineering Mechanics

Date:  Friday, January 31, 1997
Time:  3:30 p.m.
Place:  306 Bancroft Hall
 

Boring bars for single-point turning on a lathe are particularly susceptible to chatter and have been the subject of numerous studies.  A variety of control solutions have been proposed, the most promising being an active vibration absorber or AVA.  AVA designs for boring bars are typically uniaxial, employing reaction mass actuators located within the boring bar, much the same as their passive counterparts.  I will point out some of the shortcomings of such designs and propose a new biaxial approach that uses Terfenol-D actuators to apply control forces directly to the bar in the horizontal and vertical directions.  In this new approach, the absorber effect is achieved by using tuned electronic circuits that are coupled to the bar through grounded actuators.  By locating the actuators near the base of the boring bar, I exploit their high-force/low displacement character and eliminate the need for strain amplification that is inherent in thereaction mass approach.  This design also allows for static compensation, an option that may be desirable in precision machining applications where tolerances to nanometers are not uncommon.  Because the system is essentially a tool holder equipped with high force actuators, it may also be designed to accommodate any type of tool, making it far more flexible.  Finally, the actuator system can easily apply control forces in two directions, a feature that I will show has great importance for robustness. 

I will begin with a video taped demonstration of my "smart" boring bar.  Then, I will give a detailed description of its primary components, configuration, and control methodology.  The boring process can possess a jump-type instability, as was reported by Hooke and Tobias for the case of turning on a lathe, and by Hanna and Tobias for the case of face milling.  An example of this behavior that occurred during single mode vibration control of the boring process will be shown in the video.  I will demonstrate that by applying control in the second axis one can effectively suppress this behavior.  I will conclude by suggesting how the control can be digitally implemented and made self-tuning.