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Machining Time Considerably Reduced by Fuzzy Control System
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Problem Statement
One of the leading machine tool manufacturers Soraluce S.Coop. wanted to boost its competitive capacity on the basis on new control functions, reducing the machining time up to 25%. |
Improvement Approach
Working with a commercial open CNC, a fuzzy control system has been designed, implemented and embedded that can provide an additional optimization function for cutting speed. |
Benefits
The embedded controller works using only internal CNC signals without any synchronization problems. The machining time can be reduced up to 25% and the total estimated savings are about 78%. |
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Contact information
GAMHE Research Group- CSIC
Instituto de Automatica Industrial (CSIC), N-III, km. 22,800. La Poveda. 28500, Madrid. Spain.
Phone +34 918711900 ,
Fax
+34 91 8717050
e-mail
rhaber@iai.csic.es
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Figure illustrates the machine tool, the part before and after roughing operation and the real-time. |
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Today’s manufacturing industry is characterized by an increase in the demand for just-in-time production and global manufacturing. One of the main activities the manufacturing industry has to deal with is machining, a process that includes operations that range from rough milling to finishing. There are a number of angles from which to view the optimization of the machining process, angles where minimum production cost, maximum productivity and maximum profit are significant factors.
There are also various different ways of implementing machining process optimization. The implementation on which we will focus here attains optimal goals via automatic control of the machining process.
In the incessant pursuit of better performance, newer approaches have been also tested such as Model Reference Adaptive Control (MRAC) and Robust Control based on the Quantitative Feedback Theory (QFT).
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The results of these tests, however, have not lived up to expectations, because all these approaches have the indispensable design requisite of an accurate (traditional) process model. Indeed, the complexity and uncertainty of processes like the machining process are what make what is known as intelligent systems technology a feasible option to classic formal description.
Fuzzy Logic (FL) is one such intelligent technique, and it has proven useful in control and industrial engineering as a highly practical optimizing tool. GAMHE’s technological albeit still theoretical work in this field was transferred to a machine-tool manufacturing company, which planned to include the new control functions as optional equipment in future catalogues, with the help of a CNC provider.
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The integration of any control system in the CNC is a complex task that requires the use of various software utilities, technologies and development tools. Three classical technologies were used: a software-developing tool (C++, Visual Basic), an open- and real-time CNC and communications technology.
First the fuzzy controller was programmed in C/C++ and compiled, and as a result a dynamic link library (DLL) was generated. Other tools were used as well. A Sun Workstation, the UNIX operating system and C++ were used to program the NCK. A PC, the WINDOWS 9X operating system and Visual Basic were used for programming the MMC. Inter-module communications between the MMC and the NCK was established through DDE. Finally, and for the sake of simplicity, the user interface was programmed in Visual Basic.The application was developed on the basis of a Siemens Sinumerik 840D CNC. The process of integrating the software application into the NCK involved a series of steps.
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An experimental control internal data-acquisition system was developed and used to record the control internal spindle-drive signal. The system enables a selected drive signal to be recorded and provides stored data on the hard drive of the SINUMERIK 840D user interface PC (MMC). Internal data-acquisition software was developed to obtain control information.
Tests were carried out in the SL400 SORALUCE machining center, which was equipped with a SIEMENS open-CNC Sinumerik 840D. The SL400 model SORAMILL milling machine has a traveling column and a fixed table configuration. It has high-precision slideways that allow all three axes to reach a speed of up to 15 m/min. The machine has high-rigidity, high-precision features, and the workpiece has no influence whatsoever on the moving part.
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The embedded fuzzy control system will have an immediate application in milling machines and machining centers. The methodology and algorithm can be applied in any cutting process in which cutting force is essential for productivity, such as turning and drilling.
In spite of the fact that the software was developed for one kind of open CNC, the architecture ensures flexibility and allows the integration of a variety of control strategies in order to embrace the largest possible number of applications.
Furthermore, the solution is highly competitive, since it uses the CNC’s own resources and requires no additional equipment such as sensors, acquisition and signal-processing cards or other external devices.
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On the basis of the economic study provided by SORALUCE S. Coop., this system would boost machine-tool suppliers’ competitive capacity considerably.
The economic benefits for machine-tool manufacturers would come basically from the increase in sales resulting from the availability of an easily installable, configurable, programmable solution that will lead to an increase in minimum machine price and an immediate pay-off of the manufacturer’s investment.
Machine-tool users can enhance their machine-tool use ratio, machining-operation safety (due the automatic selection of cutting speeds) and the useful life of their cutting tools (due to a reduction of improper cutting conditions).
SORALUCE S. Coop has run a major study to evaluate the savings provided by installing this system. An approximate calculation of 78% in savings was made.
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