数控专业外文翻译5-数控设计(编辑修改稿)

数控专业外文翻译5-数控设计(编辑修改稿)内容摘要：

／ 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 a puter 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． 宁夏大学机械工程学院 2020 届毕业设计 70 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 dialed，it is stored． When the entire number has been dialed， the equipment bees activated and the call is pleted． Silicon photo diodes， located in the tape reader head on the control unit， detect light as it passes through the holes in the moving tape． The light beams are converted to electrical energy， which is amplified to further strengthen the signal． The signals are then sent to registers in the control unit, where actuation signals are relayed to the machine tool drives． Some photoelectric devices are capable of reading at rates up to 1000 characters per second． High reading rates are necessary to maintain continuous machine— tool motion； otherwise dwell marks may be generated by the cutter on the part during contouring operations． The reading device must be capable of reading data blocks at a rate faster than the control system can process the data． A feedback device is a safeguard used on some N／ C installations to constantly pensate for errors between the manded position and the actual location of the moving slides of the machine tool． An N／ C machine equipped with this kind of a direct feedback checking device has what is known as a closedloop system． Positioning control is acplished by a sensor which， during the actual operation， records the position of the slides and relays this information back to the control unit． Signals thus received ale pared to input signals on the tape， and any discrepancy between them is automatically rectified． In an alternative system， called an open— loop system， the machine is positioned solely by stepping motor drives in response to mands by a controllers． There are three basic types of NC motions, as follows: Point。