【正文】 that general purpose puters were reduced in size coupled to the fact that their cost of production had fallen considerably. The multipie benefits of cheaper electorics with greater reliability have result in the CNC fitted to the machine tools today, with the power and sophistication progtessing considerably in the last few years, allowing an almost artificial intelligence(AI) to the latest systems. Over the years, the machine tools builders have produced a large diversity in the range of applications of CNC and just some of those development will be reviewed in Volume Ⅲ 。s positionafter retraction of the drill. Of course, the rapid motion of the sideways could be achieved by each axis in a sequential and independent manner, or simultaneously. If a separate control was utilisec for each axis, the former method of table travel was less essential to avoid any backlash in the system to obtain the required degree of positional accuracy and so it was necessary that the approach direction to the next point was always the same. The earliest examples of these cheaper pointtopoint machines usually did not use recalculating ball screws。s conclusion was that the metal cutting industry throughout the entire country could not copy with the demands of the American Air Force, let alone the rest of industry! As a direct result of the survey, the US Air Force contracted the Persons Corporation to see if they could develop a flexible, dynamic, manufacturing system which would maximize productivity. The Massachusetts Institute of Technology (MIT) was subcontracted into this research and development by the Parsons Corporation, during the period 19491951,and jointly they developed the first control system which could be adapted to a wide range of machine tools. The Cincinnati Machine Tool Company converted one of their standard 28 inch HydroTel milling machines or a threeaxis automatic milling made use of a servomechanism for the drive system on the axes. This machine made use of a servomechanism for the drive system on the axes, which controlled the table positioning, crossslide and spindle head. The machine cab be classified as the first truly three axis continuous path machine tool and it was able to generate a required shape, orcurve, by simultaneous slide way motions, if necessary. At about the same times as these American advances in machine tool control were taking Place, Alfred Herbert Limited in the United Kingdom had their first Mutinous path control system which became available in the next few years in both the USA and Europe, further development work occurred. These early numerical control developments were principally for the aerospace industry, where it was necessary to cut plex geometric shapes such as airframe ponents and turbine blades. In parallel with this development of sophisticated control systems for aerospace requirements, a pointtopoint controller was developed for more general machining applications. These less sophisticated pointtopoint machines were considerably cheaper than their more plex continuous path cousins and were used when only positional accuracy was necessary. As an example of pointtopoint motion on a machine tool for drilling operations, the typical movement might be fast traverse of the work piece under the drill39。s SmartCam system uses the following approach. First, the programmer makes a mental model of the part to be machined. This includes the kind of machining to be performedturning or milling. Then the part print is studied to develop a machining sequence, roughing and finishing cuts, drilling, tapping, and boring operations. What workholding device is to be used, a vise or fixture or clamps? After these considerations, puter input can be started. First es the creation of a JOBPLAN. This JOBPLAN consists of entries such as inch or metric units, machine type, part ID, type of workpiece material, setup notes, and a description of the required tools. This line of information describes the tool by number, type, and size and includes the appropriate cutting speed and feed rate. After all the selected tools are entered, the file is saved. The second programming step is the making of the part. This represents a graphic modeling of the projected machining operation. After selecting a tool from the prepared JOBPLAN, parameters for the cutting operation are entered. For a drill, once thecoordinate location of the hole and the depth are given, a circle appears on that spot. If the location is incorrect, the UNDO mand erases this entr y and allows you to give new values for this operation. When an end mill is being used, cutting movements (toolpath) are usually defined as lines and arcs. As a line is programmed, the toolpath is graphically displayed and errors can be corrected instantly. At any time during programming, the mand SHOWPATH will show the actual toolpath for each of the programmed tools. The tools will be displayed in the sequence in which they will be used during actual machining. If the sequence of a tool movement needs to be changed, a few keystrokes will to that. Sometimes in CAM the programming sequence is different from the actual machining order. An example would be the machining of a pocket in a part. With CAM, the finished pocket outline is programmed first, then this outline is used to define the roughing cuts to machine the pocket. The roughing cuts are puter generated from inputs such as depth and width of cut and how much material to leave for the finish cut. Different roughing patterns can be tried out to allow the programmer to select the most efllcient one for the actual machining cuts. Since each tool is represented by a different color, it is easy to observe the toolpath made by each one. A CAM system lets the programmer view the graphics model