Computer Numercal Control and its Components

A computer Numerical Control (CNC) machine is an NC machine with the added feature of an on-board computer. The on-board computer is often referred to as the Machine Control Unit or MCU. Control units for CNC machines are usually hard wired. This means that all machine functions are controlled by the physical electronic elements that are built into the controller. The on-board computer, on the other hand, is "Soft" wired. Thus the machine fuctions are encoded into the computer at the time of manufacture. They will not be erased when the machine is truned off. Computer memory that holds such information is known as ROM or read-only memory. The MCU has usually alphanumerical keyboard for direct or manual data input (MDI) for all part programs. Such programs are stored in RAM or Random Access Memory portion of the computer. They can be played back, edited and processed by the control. All programs residing in RAM, however, are lost when the CNC machine turned off. These programs can be saved on auxiliary storage device such as punched tape or magnetic disk. Newer MCU units have graphic screens that can display not only the CNC program but the cutter paths generated and any errors in the program.

CNC comprises on following main components;

Machine Control Unit

A small, powerful computer that controls and operates a CNC machine.It generates, stores, processes CNC programs. The machine control unit also contains the machine motion control in the form of an executive software program.

NC Machine

Responds the programmed signal from the machine control unit and manufactures the part.

Numerical Control definition (Concepts and Advantages)

Numerical control has been used in industry for more than 50 years. Simply put Numerical control is a method of automatic operating a manufacturing machine based on code of letters, neumbers and characteristics. A complete set of coded instruction for executing an operation is called a program. The program is translated into corresponding electrical signals for input to motors that run the machine. Numerical control machine can be program manually.

Traditionally, numerical control systems have been composed of the following components.

Tape Punch- Converts written instructions into a corresponding whole pattern. The hole is punched into a tape, which pass through this device. Much older units used a type writer device called flexowriter. Later devices included a microcomputer coupled with a tape punch unit.

Tape Reader- Read the whole pattern on the tape and converts the pattern to a corresponding electrical signal code.

Controller- Receives the electrical signals from the tape reader and subsequently causes the NC machine to respond.

NC Machine- Responded the programmed signals from the controller. Accordingly, the machine executes the required motions to manufacturing a part (Spindle rotation on/off or spindle movement along programmed axis direction etc.)


Advantages of NC system over manual methods of production

NC system offers some of the following advantages over manual methods of production

1. Better control of tool motion under optimum cutting conditions





2. Improved part quality and repeatability





3. Reduced time to manufacture parts





4. Reuced scrap





5. Better production planning and placement of machining operations in the hands of engineers
   

THE EVOLUTION OF NC

It was in 1947 when numerical control was born. It began when john C. Parsons of the parsons corporation Traverse city Michigan (a manufacturer of helicopter rotor blades) could not make his templates fast enough so he invented a way of coupling computer equipment with a jig borer. Mr. Parsons used punched cards to operate his digit Ron system.

1949 was the year of another "Urgent need". The US Air Material Command realized that parts for its planes and missiles were becoming more complex. Also as the design were constantly improved, changes in the drawing were frequently made. Thus in their search for methods of faster production, an air force study contract was awarded to the Parsons Corporation. The servo mechanisms laboratory of the Massachusetts Institute of Technology (MIT) was the subcontractor.

In 1951, MIT took over the complete job, and in 1952 the prototype of today's NC machine, a modified Cincinnati Hydrtel Milling Machine, was successfully demonstrated. The term numerical control was originated at MIT.