Dynamic modeling and analysis of a high speed precision drilling machine

This paper describes the modeling and dynamic analysis of a high speed precision circuit board drilling machine. The drilling machine has two banks of movable drill spindles supported between parallel granite beams on an air bearing suspension. Each drill spindle is programmed to move laterally between the beams under the position control of a servo-feedback system. The drill spindles must complete a nominal 3.048 mm (0.12 in.) lateral move and a vertical drilling sequence every 200 ms. while maintaining an absolute positioning accuracy within 0.01778 mm (0.0007 in.). In order to meet these demanding specifications the dynamic behavior of the complete drill spindle/air bearing/granite beam system must be well understood. A specialized finite element model (FEM) is used to examine the dynamic responses of the critical components of this machine. The FEM code is capable of analyzing a sprung two degrees of freedom system moving on an elastic beam in an arbitrary fashion. The discussion concentrates on the engineering modeling considerations and compromises which were necessary to analyze the drilling machine with this computer code. The modeling rationale and use of experimental data to form an effective computer model capable of analyzing the dynamic behavior of the drilling machine are emphasized. Typical results from the finite element model are presented to illustrate the obtainable level of accuracy, detail and the limitations for modeling a system of this nature.