DEFINITION OF NUMERICAL CONTROL
Numerical Control technology as known today, emerged in the mid 20th century. It can be traced to the year of 1952, the U.S. Air Force, Massachusetts Institute of Technology in Cambridge, MA, USA, and the name of John Parsons (1913-2007), who is closely associated with the invention of numerical control. It was not applied in production manufacturing until the early 1960’s. The real boom came in the form of CNC, around the year of 1972, and a decade later with the introduction of affordable micro computers.
History and development of this fascinating technology has been well documented in many publications.
In manufacturing field, and particularly in the area of metal working, Numerical Control technology has caused something of a revolution. Even in the days before computers became standard fixtures in every company and many homes, machine tools equipped with Numerical Control system found their special place in many machine shops. The relatively recent evolution of micro electronics and the never ceasing computer development, including its impact on Numerical Control, has brought enormously significant changes to manufacturing sector in general and metalworking industry in particular.
In various publications and articles, many descriptions have been used during the years, to define what Numerical Control actually is. It would be pointless to try to find yet another definition, just for the purpose of this handbook. Many of these definitions share the same idea, same basic concept, just use different wording.
The majority of all the known definitions can be summed up into a relatively simple statement:
Numerical Control can be defined as an operation of machine tools by means of specifically coded instructions to the machine control system
The ‘specifically coded instructions’ are combinations of the letters of alphabet, digits and selected symbols, for example, a decimal point, the percent sign, or the parenthesis symbols. All instructions are written in a logical order and in predetermined form. The collection of all instructions necessary to machine a single part or operation is called an NC Program, CNC Program, or a Part Program. Such a
program can be stored for future use and used repeatedly to achieve identical machining results at any time.
NC and CNC Technology
In strict adherence to terminology, there is a difference in the meaning of abbreviations NC and CNC. The NC stands for the older and original Numerical Control technology, whereby the abbreviation CNC stands for the newer Computerized Numerical Control technology – a modern successor to its older relative. However, in everyday practice, CNC is the preferred abbreviation. To clarify the proper usage of each term, look at the major differences between NC and CNC systems.
Both systems perform the same tasks, namely manipulation of data for the sole purpose of machining a part. In both cases, the control system internal design contains all logical instructions that process the input data. At this point the similarity ends.
The NC system (as opposed to the CNC system) uses a fixed logical functions, those that are built-in and permanently wired within the control unit. These functions cannot be changed by the part programmer or the machine operator. Because of the fixed wiring of control logic, NC control system is synonymous with the term ‘hardwired’. The system can interpret a part program, but it does not allow any changes to the program at the control (using the control features). All required program changes must be made away from the control, typically in an office environment. Also, NC system typically requires the compulsory use of punched tapes for input of the program information.
The modern CNC system (but not the old NC system), uses an internal micro processor (i.e., a computer). This computer contains memory registers storing a variety of routines that are capable of manipulating logical functions. That means the part programmer or machine operator can change any program at the control unit (at the machine), with instantaneous results. This flexibility is the greatest advantage of CNC systems and probably the key element that contributed to such a wide use of the technology in modern manufacturing. Typically, CNC programs and the logical functions are stored on special computer chips, as software instructions, rather than used by the hardware connections, such as wires, that control the logical functions. In contrast to the NC system, the CNC system is synonymous with the term ‘softwired’.
When describing a particular subject that relates to numerical control technology, it is customary to use either the term NC or CNC. Keep in mind that NC can also mean CNC in everyday talk, but CNC can never refer to the older technology. The letter ‘C’stands for Computerized, and it is not applicable to the hardwired system. All control systems
manufactured today are of the CNC design. Abbreviations such as C&C or C’n’C are not correct and reflect poorly on anybody that uses them.