An overview of Computerised Numeric Control (C.N.C.) and Programmable Logic Control (P.L.C.) in machine automation

Throughout the ages people have been working in research institutes and industries in machine automation so as to have less involvement of operator in machine operations. In the development of automation controllers the trend has been to move towards soft controllers so as to provide better control, more flexibility and more reliability with intelligent diagnostics of machine faults. So industries have gradually moved from conventional relay logic control to programmable logic control and then to computarised numeric control. Here we shall deal how a programmable logic controller works in automation and the control of a computarised numeric controller on P.L.C. and servo drives to provide automation with accuracy.We shall further deal with the working of self diagnostics of machine faults and the flexibility it provides. Introduction: Since there were problems related to large electrical panels with a number of electrical components and extensive wiring, people felt the need for software logic controllers. So they gave birth to Programmable Logic Controller (P.L.C) wherein the control logic is developed in ladder diagram,a software logic control, with a number of inputs taken from the environment and generating the outputs ,depending on the logic programmed, to the environment. This helped to control any machine sequence with small electrical panels, less number of electrical components and less wiring with more flexibility to change machine sequence and providing ease to reusability of the components. These fulfilled some of their needs but the desire to obtain software controlled automation with accuracy necessitated the development of Computer Numeric Control (C.N.C). Here the controller acts as a master over the P.L.C. and connected with encoders to provide positional feedback .In order to have better control for positioning, controlled speed and quick reversal of direction of slide movement, servo motors having less inertia, along with servo drives are interfaced with the C.N.C . The user based part program decoded by the C.N.C. provides the desired profile with the control being transferred to P.L.C. and drives as and when required. Special measuring devices as locators, gauges being interfaced with the C.N.C. through independent controllers provide more accuracy. Programmable Logic Controller[1]: The diagram below shows the functional units of