CNC Servo Control Machines: The Secret Behind High Level Industrial Machining
CNC servo control machines are machine tools operated by programmed commands that are encoded onto a storage medium, which these days is most frequently a computer. The machines evolved from old-school NC machines, originally manufactured in the 1940s and 50s on the basis of existing technology, which use handwheels or levers for control. The new ‘Numerically Controlled’ (NC) machines were fitted with motors that moved the system’s controls to follow a path indicated by ticker tape. With the dawning of the information technology revolution, these primordial servo motors would soon be augmented, with the input going fully electronic. Soon, the use of computers as the storage medium for NC machines became standard, with all obsolete NC machines being replaced by Computer Numerical Controlled machines, or CNCs.
Along with other new age devices, such as 3D printing machinery, modern CNC systems are capable of automating the manufacture of most products using CAD and CAM programs. In the case of 3D printers, CAD programs often require an input no more sophisticated than a 3D rendering of the product required to produce a flawless rendition in metal or plastic, ‘growing’ the product by laying down layer upon layer of adhesive dust. CNC servo control machines, on the other hand, often use numerous tools – saws, drills, stamps - and as such are packaged into ‘cells’ which provide a controlled environment in which machines can trace out complex, coordinated motion pathways. This process generally produces products that match CAD specifications more closely than any manual human rendering could do.
Generally given credit for the birth of the CNC servo control cutting machine is John Parsons, a salesman and machinist who saw the potential for using metal stringers (instead of wood) in helicopter propellers, then still a very young technology, at Sikorsky Aircraft in 1942. The technology to accurately cut the curves required in metal without extensive craftsmanship did not yet exist, however, a gap that led Parsons to conceive of creating an automated machine able to cut metal using a French curve, the tool long used by artists to provide the curvatures they required in sketching and painting.
However, producing a tool capable of cutting metal to such a curve as a far more difficult problem than it might first appear. The leap of genius that Parsons’ head engineer had was to use punch cards to direct the motion of the cutting machine. These could allow straight cutting between two points or coordinates the cards provided the machine, coordinates which had to be fed into the machine for each cut, an approach referred to as the ‘by the numbers’ method. Initially, the distance between these points required some manual sanding down to create the required curve after manufacture. What Parsons saw was that with enough points specified, little manual reworking would be needed. His additional insight was that having people feed cards into the machine slowed down the production process, and that having the machine input board directly affixed to the card reader would allow the machine to cut perfect shapes, every time.
With the help of MIT (who later tried, unsuccessfully, to steal Parson’s idea and take the patent for themselves), by the 1950s Parsons had patented a machine capable of doing just this, and the first true CNC servo control came into existence. Over the decades, the original design, which called for many units the size of refrigerators to be affixed to the central cutting unit, would be refined, to the point that a simple microchip board was all that was required to operate an entire CNC servo control package.
