中英文翻譯數(shù)控技術(shù)-展示頁(yè)
2025-02-01 21:47本頁(yè)面
【正文】 devices．Manual input requires that the operator set the controls for each operation．It is a slow and tedious process and is seldom justified except in elementary machining applications or in special cases．In practically all cases，information is automatically supplied to the control unit and the machine tool by cards，punched tapes，or by magnetic tape．Eight—channel punched paper tape is the most monly used form of data input for conventional N／C systems．The coded instructions on the tape consist of sections of punched holes called blocks．Each block represents a machine function，a machining operation，or a bination of the two．The entire N／C program on a tape is made up of an accumulation of these successive data blocks．Programs resulting in long tapes all wound on reels like motionpicture film．Programs on relatively short tapes may be continuously repeated by joining the two ends of the tape to form a loop．Once installed，the tape is used again and again without further handling．In this case，the operator simply loads and unloads the parts．Punched tapes ale prepared on type writers with special tape—punching attachments or in tape punching units connected directly to aputer system．Tape production is rarely errorfree．Errors may be initially caused by the part programmer，in card punching or pilation，or as a result of physical damage to the tape during handling，etc．Several trial runs are often necessary to remove all errors and produce an acceptable working tape． While the data on the tape is fed automatically，the actual programming steps ale done manually．Before the coded tape may be prepared，the programmer，often working with a planner or a process engineer, must select the appropriate N／C machine tool，determine the kind of material to be machined，calculate the speeds and feeds，and decide upon the type of tooling needed. The dimensions on the part print are closely examined to determine a suitable zero reference point from which to start the program．A program manuscript is then written which gives coded numerical instructions describing the sequence of operations that the machine tool is required to follow to cut the part to the drawing specifications．The control unit receives and stores all coded data until a plete block of information has been accumulated．It then interprets the coded instruction and directs the machine tool through the required motions．The function of the control unit may be better understood by paring it to the action of a dial telephone，where，as each digit is dial
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