Computer numerical control: Difference between revisions

Content deleted Content added
No edit summary
No edit summary
Line 1:
'''Numerical control''' or '''numerically controlled''' ('''NC''') [[machine tool]]s are machines that are automatically operated based on commands that are fed into them. NC machines were first developed soon after [[World War II]] and made it possible for objectslarge quantities of the desired component to be very precisely and efficiently [[machining|machined]] in exactly the same way in a repeated fashion. These early machines were often fed instructions punched onto [[paper tape]] or [[punch card]]s. In the [[1960s]], NC machines largely gave way to [[CNC]], or [[computer]] numerical control, machines.
 
[[de:Numerische Steuerung]]
[[ja:NC加工]]
 
Numerical control (NC) is the precursor of computer numerical control (CNC)., which Computer numerical control iscontrols the automation controller forof machine tools and the cuttinginherent tool processprocesses offor which they stockare removaldesigned. The CNC machine tool is the [[servo]] [[actuator]] of the CAD/CAM (Computer Assisted Design/Computer Assisted Manufacturing) process both literally and figuratively.
CNC inherits from NC its essential character of by-the-numbers interpolation of transition points in the work envelope of a motion platform based on the separation of programming from operations. The program - usually an ASCII text file in which, in its simplest form, a line of text specifies the rectangular coordinate of a point in the work envelope of the machine determined by the stroke limits of the servo axes - is prepared from a blueprint or CAD file and transferred to the memory of the CNC via floppy drive, serial data interface or a network connection. Once in the CNC memory and selected for execution, pressing a key called NC Start or Cycle Start on the machine operator panel causes the CNC to execute the program.
 
==Historical notes==
Line 14:
In the M.I.T. scheme, a contour of constantly changing curvature (that is, a spline) is represented as a poly-line with the intersections between line segments being points on the curve and these points were listed in sequential order in the part program (like a child connecting the dots of a workbook to display a figure). The shorter the line segments the more closely the poly-line approximated the original curve. Thus, M.I.T. retained separation of programming from operations while redefining the servo control as interpolation rather than discrete positioning. M.I.T. demonstrated the first ever NC machine tool to a select group from the military, the aerospace industry, the machine tool industry and the technical media in September, 1952.
 
At the time when M.I.T. was developing numerical control, engineers at General Motors were putting position transducers on the lead screws of a conventional engine [[lathe]] and recording the motion of the axes as the machinist put the machine through its paces to make a workpiece. The machine was also fitted with a servo system that took data from the recording to reproduce the same sequence of motion to produce a second, third and more parts. This technique is called record/playback and it is reminicent of a musician making music on a piano that has been modified to record his keystrokes on a paper chart to be read by a player piano to reproduce the music. The popular novel, "The Player Piano", is inspired by this machine. The author [[Kurt Vonnegut]] was exposed to the machine when he worked as a publicist for General Electric. Record/playback is different from numerical control in that the program is produced by the machinist in the process of making the first part.
 
The Air Force wanted numerical control and not record feedback because the latter put the machinist in charge of program production. This was the same machinist who was a union member; thus union strikes could result in delays in military production. Also, numerical control demonstrated the ability to produce parts that were not possible by conventional, manual means. The Air Force used its deep pockets to get its way and while American manufacturing may have been better served with the simpler Parson concept or with record/playback, today this is a mute issue.