【文章內(nèi)容簡介】 a number of problems with NC at this point in its development. A major problem wad the fragility of the punched paper tape medium. It was mon for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each programmed instructions had to be return through the reader. If it was necessary to produce 100 copies of a given part,it was also necessary to run the paper tape through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use. This led to the development of a special magic plastic tape. Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magic dots. The plastic tape was much stronger than the paper taps, which solved the problem of frequent tearing and breakage. However, it still left two other problems. The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instructions, it necessary to interrupt machining operations and make a new tape. It was also still necessary to run the tape through the reader as many times as there were parts to be produced. Fortunately, puter technology became a reality and soon solved the problem of NC associated with punched paper and plastic tape. The development of a concept known as direct numerical control(DNC)solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control machine tools are tied, via a data transmission link, to a host puter. Programs for operating the machine tools are stored in the host puter and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend o a host puter. When the lost puter goes down, the machine tools also experience downtime. This problem led to the development of puter numerical control. The development of the microprocessor allowed for the development of programmable logic controllers(PNC)and microputer. These two technologies allowed for the development of puter numerical control(CNC). With CNC, each machine tool has a PLC or a microputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. It also allows programs to be developed offline and download at the individual machine tool. CNC solved the problems associated with downtime of the host puter, but it introduced another known as data management. The same program might be loaded on ten different being solved by local area works that connect microputer for better data management. CNC machine tool feed motion systems CNC machine tool feed motion systems, especially to the outline of the control of movement into the system, must be addressed to the movement into the position and velocity at the same time the realization of two aspects of automatic control, as pared with the general machine tools, require more feed system high positioning accuracy and good dynamic response. A typical closedloop control of CNC machine tool feed system, usually by paring the location of amplification unit, drive unit, mechanical transmission ponents, such as feedback and testing of several parts. Here as mechanical geardriven source refers to the movement of the rotary table into a linear motion of the entire mechanical transmission chain, including the deceleration device, turning the lead screw nut bee mobile and viceoriented ponents and so on. To ensure that the CNC machine tool feed drive system, precision, sensitivity and stability, the design of the mechanical parts of the general requirement is to eliminate the gap, reducing friction, reducing the movement of inertia to improve the transmission accuracy and stiffness. In addition, the feeding system load changes in the larger, demanding response characteristics, so for the stiffness, inertia matching the requirements are very high. Linear Roller Guides In order to meet these requirements, the use of CNC machine tools in general lowfriction transmission vice, such as antifriction sliding rail, rail rolling and hydrostatic guideways, ball screws, etc.。 transmission ponents to ensure accuracy, the use of prerational, the form of a reasonable support to enhance the stiffness of transmission。 deceleration than the best choice to improve the resolution of machine tools and systems converted to the driveshaft on the reduction of inertia。 as far as possible the elimination of drive space and reduce deadzone inverse error and improve displacement precision. Linear Roller Guides outstanding advantage is seamless, and can impose prepression. By the rail body, the slider, ball, cage, end caps and so on. Also known as linear rolling guide unit. Use a fixed guide body without moving parts, the slider fixed on the moving parts. When the slider moves along the rail body, ball and slider in the guide of the arc between the straight and through the rolling bed cover of Rolling Road, from the work load to nonwork load, and then rolling back work load, constant circulation, so as to guide and move the slider between the rolling into a ball. Bridge Crane Bridge crane is having an elevated track running in a bridgetype crane, also known as the crane. Bridge Crane in the laying of the bridge on both sides along the elevated track on the vertical run, lifting trolley along the bridge laying on the track in the horizontal ope