tailieunhanh - An Encyclopedia of the History of Technology part 45

An Encyclopedia of the History of Technology part 45. This one of a kind encyclopedia presents the entire field of technology from rudimentary agricultural tools to communication satellites in this first of its kind reference source. Following an introduction that discusses basic tools, devices, and mechanisms, the chapters are grouped into five parts that provide detailed information on materials, power and engineering, transportation, communication and calculation, and technology and society, revealing how different technologies have together evolved to produce enormous changes in the course of history | PART TWO POWER AND ENGINEERING CONTROL REVOLUTION AND ELECTRONIC METROLOGY Alan Turing s work on calculating machines enabled him to design the machine to decipher the German Enigma machine codes and he built an electric computer with memory in 1944. In 1948 John Parsons in the USA was transferring the ideas of punched-card control of accounting into the control of machine tools by demonstrating with a universal precision milling machine that all its movements and speed changes could be controlled by mathematical computation. A government contract for more development was given in 1949 to MIT Servo-Mechanisms Laboratory which produced the first numerically controlled NC machine tool in 1954. The system was based on a Cincinnati vertical spindle contour milling machine modified to servo control of table cross slide and spindle through hydraulic units gears and leadscrews giving a motion of for each electrical pulse received from the control unit. This was provided by a valve electronic unit and Flexowriter using eight-column paper tape to represent an eight-digit number on each line with holes as units and unpunched positions as zeros. Feedback the basis of automation was provided by synchronous motors geared to the slide motions which provided electrical signals to the control for comparison with the input signal to verify the slide position. This machine and the report on its practical possibilities was the beginning of NC machine development taken up by many companies. Giddings Lewis produced Numericord a contouring machine for aircraft frames which employed magnetic tape to control five axes of motion simultaneously. This system required a computer to interpolate the decimal calculations of points on the profile entered from paper tape which was then time co-ordinated and recorded on the magnetic tape to give contour control. Other systems were limited to point to point control of the tool position and employed simple electrical relays and .