15-02-2016, 04:53 PM
Introduction
Industrialization has triggered rapid advances in technology all over the world has placed the need for machine tools to be controlled to very high levels of accuracy. Thus the concept of Computer Numerical Control arose which has revolutionized the machine tooling and made it possible to machine intricate jobs with high accuracy.
Machine tools are now controlled by CNC systems. The basic advantage of this over conventional machines is the flexibility being offered by the CNC system. This control system is a closed loop position control system where the position of the machine tool is controlled. The control system interfaced with the machine tool issues appropriate signals to various drives of the machine tool, which results in precise motion of these axes for accurate machining. The drives used are either DC or AC drives which provide better speed control features using electronic control with thyristor stacks.
The numerical data (set of commands) is fed into the control system through a suitable input medium (either alphanumeric keyboard of control system or floppy diskette). The data is stored in the data storage area and all the comparisons are computed in the computational area and distributed in respective servo drive axis. The servo drive gets activated and moves the axis slides and spindle. The position feedback transducer at each slide monitors the instantaneous position of the slide and gives the feedback to the control system where the instantaneous slide position is compared with the commanded position.
The CNC machine basically entails three main regions
• The control system
• The drives (driving elements) and
• The machine tool
In the dissection that follows a complete insight into these functions of the CNC system have been taken up with the interfacing of each to the other.