【正文】 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.。 deceleration than the best choice to improve the resolution of machine tools and systems converted to the driveshaft on the reduction of inertia。 were driven to another, that is, on both sides of the initiative the wheels with a motor drive. Small, medium and larger overhead crane with brake, and motor reducer bination into one of the triple play drive, the weight of the ordinary from the overhead crane for easy installation and adjustment, often drive the use of universal axis. Crane normally used only four active and driven wheels, if a great weight, increase mon approach to reduce wheel round pressure. When more than four wheels, must adopt a balanced hinged frame device so that the crane load evenly distributed in the wheels. Bridge metal structure from the main shum and shumposed of the main beam is divided into singleand doublegirder bridge having two categories. Singlebeam bridge from the main beam and a single on both sides of the span at the end of shum, dualbeam bridge by the two main shum and shumponent. Liang Liang Gang and the end of the linkbeam ends with wheels, for supporting an elevated bridge in the running. A main beam welding on track for the lifting trolley running. Having the structure of the main beam type is more a typical box structure, the four truss structure and fasting truss structure. Box structure can be divided into twotrack box girder, partial doubletrack boxbeam, singlebiasrail box and several main shum. Dualtrack box girder is the extensive use of a basic form, the main beam from the upper and lower flange on both sides of the plate and vertical web position, layout rail car in the center of the flange plates online, and its simple structure , manufacturing convenient, suitable for mass production, but larger forces. Partial tracks boxgirder and partial doubletrack boxsection of the main beam are from the upper and lower ranges flange plates and thick web of the main ponents, rail car in the main web layout above, the short Xiangbenna omit the stiffening plate, which tracks boxside main beam from a wide flange box instead of the main shum two main shum, respect smaller, but more plex manufacturing. 4 trusstype structure from four plane truss structure into a closed space, in the general level of the surface Truss shops follow plate, light weight, rigidity, but pared with other structures, and its dimensions, creating more plex, fatigue lower intensity, has been less productive. Partial fasting truss structure similar to the main tracks boxgirder from the four ponents of a closed steel structure, in addition to the main web for the Solid shaped beam, the other three plate in accordance with the design requirements cut into many windows, forming a noramps Fasting Truss, in the lower level of the surface occupied by taking truss plate, cranes and the operation of electrical equipment installed in the bridge house, lighter forces, the overall stiffness, and that in China is a more widely used type. General overhead crane used mainly driven power, the general is in the driver indoor manipulation, but also remote control. From the weight of up to 500 tons, up to 60 m span. Simple beam bridge crane known as shum cranes, and the structure and position of ordinary bridge crane similar to a weight, span and speed are smaller. Bridge is the main shum or other steel Ibeam and plate steel girder section posed of simple, handpull or electric hoist acpanied by gourd simple as lifting trolley car, the car us