| When early machine tools were designed there was | | | | to be weighed against a healthy cost penalty. |
| an obvious emphasis on manual operation with the | | | | By the early 1970s, electronics had become more |
| slide positioning being controlled by human involvement. | | | | sophisticated so that complete minicomputers were |
| To achieve this level of control "men" used their | | | | being fitted to CNC machine tools; this meant that the |
| "sensors" - eyes and ears - whilst the central | | | | previous "hard-wired" options were now contained |
| processing unit - the brain together with servos (arms | | | | within the software package. As a result of these |
| and legs) - allowed them to control machine tools by | | | | software options, greater flexibility of programming |
| communication of all these interrelated functions using | | | | was possible utilising computer logic for specifying |
| the central nervous system. Until the advent of | | | | commands in absolute, incremental and polar |
| micro-electronics this method for machine control was | | | | coordinates, etc., making them infinitely more capable, |
| the best system of universal adaptability available, but it | | | | but at no real extra cost. Other bonuses directly |
| suffered from serious shortcomings: | | | | related to computer usage included the ability to be |
| A period of lengthy training was required for the | | | | programmed at a later date using different tape |
| craftsman, people can easily become distracted, a | | | | formats, as these are within the computer logic at its |
| persons performance is dependent upon their physical | | | | time of original manufacture. When one considers the |
| or mental condition, their efficiency is inversely | | | | CNC designed MCU, it can be readily appreciated that |
| proportional to time, their speed of operation is limited. | | | | the "soft-wired" controllers are significantly different |
| If these obvious disadvantages could be overcome | | | | from their older "hard-wired" cousins and have an |
| using the latest CNC machining technology, how should | | | | "executive program" allowing the controller to "think" as |
| it be developed? At the heart of computerised | | | | either a turning or machining centre. The company |
| machine tools is the machine control unit (MCU); this is | | | | building the CNC will load an "executive program" into it |
| the connection between the programmer and the | | | | and the machine tool company will modify it to suit their |
| machine tool. If a part program is written with/without | | | | requirements. In this manner the machine tool builder will |
| the use of computer assistance, it must be produced in | | | | use a portion of the memory for such features as: |
| a suitable medium for conversion by the MCU into | | | | interface logic, tool changer control and so on, to give |
| machine motions via electrical, or hydraulic | | | | the controller the ability to be used in a specific type of |
| servo-mechanisms. During the early 1950s the | | | | machine tool. |
| numerical control units tended to be bulky, whilst | | | | The latest CNC machine tools are incredibly |
| today's CNC machining utilises the latest | | | | sophisticated using a visual display of programming |
| microprocessor technology. The early NC systems | | | | parameters on the cathode ray tube (CRT), similar to |
| were "hard-wired" - meaning that functions such as | | | | a TV screen. However, the real difference lies in the |
| interpolation, tape format, positioning methods of | | | | fact that the screen is often a multi-function type and |
| slideways and others, were determined by the | | | | can display the full operational and parametric data |
| electronic elements built into the MCU. Purchasers of | | | | together with screen graphics. Together with the |
| early NC machinery had to specify whether they | | | | functions concerned with actually running the program, |
| wanted the equipment to function in an absolute, or | | | | other necessary functions that are also displayed |
| incremental format and so on, as this considerably | | | | include: diagnostic maintenance backup and |
| affected the cost of the MCU. The advantages gained | | | | trouble-shooting guidance together with many other |
| by having a large range of programming options had | | | | features that may be displayed on CRT. |