Modeling, Parameter Estimation and Compensation of Quasistatic Errors in Multi-Axis CNC Machining Centers
Kiridena, Vijitha Senaka
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https://hdl.handle.net/2142/72236
Description
Title
Modeling, Parameter Estimation and Compensation of Quasistatic Errors in Multi-Axis CNC Machining Centers
Author(s)
Kiridena, Vijitha Senaka
Issue Date
1993
Doctoral Committee Chair(s)
Ferreira, Placid M.
Department of Study
Mechancial Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Industrial
Engineering, Mechanical
Abstract
Dimensional accuracy is often the single most critical criterion that can be used to evaluate the quality of machined parts. Increasing demand for highly accurate and inexpensive mechanical parts has created a critical need for developing economical and efficient processes for their production.
Experimental evidence indicates that nearly seventy percent of the errors attributable to the machine tool are quasistatic errors. Attempting to control the quasistatic effects by improving rigidity of the machine tool and maintaining a constant thermal state during operation increases the initial, operational and maintenance costs. The overall objective of this thesis is to develop a methodology to increase the attainable accuracy of "production-class" multi-axis CNC machining centers by compensating quasistatic effects.
The objective of this thesis is achieved through several steps. First, a general quasistatic error model for three-axis CNC machining centers is developed using rigid body kinematics. This model compiles the effects of inaccuracies in the geometry and motion of machine members on its volumetric accuracy in its work space. For the general quasistatic error model to be used in a practical compensation scheme, its parameters need to be updated quickly and accommodated easily within the machine's work cycle. This is made possible by developing a method to identify few strategically located measurement points in the work space sufficient for robustly estimating the model parameters. Then efficient, and accurate computational strategies are developed for three-axis machining centers to introduce compensations using estimated quasistatic errors which produces the anticipated higher degree of accuracy. The modeling, estimation and compensation techniques together form a comprehensive methodology to track and compensate quasistatic errors for three axis machining centers.
As the first step towards extending this new methodology to five axis machining centers, positional error models are developed to investigate the effects of the positioning errors of the joints on the position and orientation of the cutting tool. Also a mathematical basis of a suitable experimental procedure is investigated in this thesis to measure the error characteristics of the rotary joints in five axis machine tools.
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