As a numerical control (NC) ( English Numerical Control ) refers to a device for the control of machines , reads the control commands, which are present as a code on a recording medium, and converts it into work or motion. The first generation of numerical controls that did not yet have an integrated mini or microcomputer is meant here. See also CNC and manual input control . By exchanging the data carriers, a numerically controlled machine can be adapted very quickly to another product, which is why it is mainly used in machine tools . Pure NCs in the above sense were built from 1949 until the advent of mini and microcomputers (until around 1979).
John T. Parsons and Frank L. Stulen are considered pioneers , who introduced the concept to the aircraft industry in the late 1940s. The development took place in close cooperation with the Massachusetts Institute of Technology .
NCs are programmed with punched tape codes based on the technical means available at the time.
Typical program line:
- N1020 G40 G01 G90 X20.000 Y30.000 F1000 S2000.
- Block number 1020: Travel without tool radius compensation with absolute dimensions (see G code ) on X20 Y30 with a feed rate of 1000 mm / min and a spindle speed of 2000 / min.
While the first NC programs only contained binary machine-specific commands that led to binary instructions (e.g. “do not use needle x if there is a hole” or “play the sound associated with the position of the hole”), later with the help of 8-bit NC instruction sets consisting of numbers and letters that are quite common, certain operations can also be carried out in the machine (interpolation of lines or circles , conversion of a distance into stepper motor cycles with acceleration and braking ramps, e.g. “drive a semicircle with radius r, center xy and speed v “). Towards the end of the NC era, it was possible to make certain technological parameters or corrections on the machine ( post processing , e.g. correction of the kerf width when laser cutting, nesting of cut parts).
The following address letters, later laid down in DIN standards, were common:
X ... Y ... Z ... (ABC, UVW), G, F, S, M.
- X, Y, Z = target position
- G = geometry instruction = work instruction such as straight line interpolation, radius compensation, etc.
- F = feed rate = axis feed
- S = spindle speed
- M = auxiliary and additional function for program and spindle control
Program creation and storage
The work programs with control commands were created externally on data carriers that were current at the time, such as punched strips , punched cards or magnetic tapes, and could only be executed unchanged on the machine. The work instructions could no longer be changed on the machine itself. Since there was no main memory in the modern sense, the data carrier had to go through again for each execution. For machines controlled by punched tape, a rewind command was usual at the end of the program.
Historical development of numerical control
|1794-1800||The first metal lathe was built.|
|1808||Joseph Marie Jacquard used punched sheet metal cards for the automatic control of weaving machines.|
|1863||Invention of the punched tape (paper as a data carrier) by Henri Fourneaux.|
|1946||John W. Mauchly and John Presper Eckert supplied the first electronic digital computer to the US Army.|
|1949-1952||First numerically controlled machine developed by John T. Parsons (USA) in collaboration with the Massachusetts Institute of Technology for the US Air Force .|
|1954||First industrially manufactured NC from Bendix Corporation (USA), built with approx. 300 tubes .|
|1959||Introduction of the NC in Europe (Hanover Fair)|
|1960||First NC with transistors .|
|1960||First NC path control with straight and circular interpolation (from AEG ) on a Waldrich roll calibration lathe at the German Machine Tool Exhibition in Hanover|
|1963||Machine tools specially developed for control by NCs appear on the market.|
|1968||First NC with integrated circuits .|
|1972||First CNC, minicomputer with a special interface for controlling the axes.|
|1978||First microprocessor CNC.|
With the appearance of the microprocessor CNC, the era of the hardwired NC comes to an end.
Today, numerical control is usually equipped with a computer . This means that programs can be created and corrected directly on the control and the operator can be fully informed via screens . This control type CNC (Computerized Numerical Control) is a special case of NC control. In the 1970s and 1980s, the designation CNC was used to differentiate it from the older NCs. However, since all numerical controls are now equipped with computers, the terms NC and CNC have become synonymous.
- Hans Bernhard Kief : NC manual '80 . NC Society, Michelstadt, 1980, .
- Josef Daxl: Fundamentals of numerically controlled machine tools (CNC), main volume. Verlag Jugend und Volk, Vienna 2004, ISBN 3-7002-1399-9 .
- Herwig Braun, Ulrich Fischer, Helmut Höll u. a .: Metal expertise. 53rd edition. Verlag Europa-Lehrmittel, Haan-Gruiten 1999, ISBN 3-8085-1153-2 .