Application Of Iterative Learning Control In Piston Numerical Control Machining

Piston is the one of the core part of the engine. The cross section of the piston is usually noncircular, which can't be machined by the conventional lathe but can be realized by the special servo tool. However the tolerance of the machined part is often large if the cross section is very complicated.A modified control strategy to improve the machining precision of complicated cross section is put forward in this dissertation based on the existing noncircular cylindrical piston numerical-control equipment. Iterative learning control, an important branch of intelligent control area, which has the learning ability for iterative problems or the analogy ones, is used to improve tracking precision for an iterative signal, as the process of the piston noncircular turning has the property of analogy iteration. As a result, the machining precision of the piston can be improved. The main contents are as follows:Firstly, the basic noncircular section piston process principle was introduced, and the character of typical piston section data is analyzed. At the same time, the basic control method for the existing servo tool-post is also present. Secondly, aim at the limited frequency band of the servo tool-post and its low precision, an improved control strategy of iterative learning control with its realization flow is put forward. Thirdly, the basic iterative learning control principle is introduced, and the anticipatory iterative learning control and learning feed-back and feed-forward control are presented in detail. The MATLAB program numerical simulation shows the feasibility for the iterative learning control scheme to be used for the machining of piston. Fourthly, the process data is modified by the off-line learning feed-back and feed-forward control. Applying iterative learning control to complex section piston numerical control machining, maximum error could be decreased from 0.0248mm to 0.0086mm in the case of 800rmp. This result show that the machining precision was efficiently improved after the process data was modified by iterative learning control strategy.Briefly, the research in the paper will help the precision improvement of complicated noncircular section piston machining.