学习啦【英语散文】 韦彦时间：2016-09-14 16:57:24我要投稿
The computer calls the part program instructions from bulk storage and sends them to the individual machines as the need arises.
It also receives data back from the machines.
This two-way information flow occurs in real time, which means that each machine’s requests for instructions must be satisfied almost instantaneously.
Similarly, the computer must always be ready to receive information from the machines and to respond accordingly.
The remarkable feature of the DNC system is that the computer is servicing a large number of separate machine tools all in real time. Depending on the number of machines and the computational requirements that are imposed on the computer, it is sometimes necessary to make use of satellite computers, as shown in Fig.2.4.
These satellites are smaller computers, and they serve to take some of the burden off the larger central computer.
卫星计算机是更小的计算机 可以分担中央计算任务 减轻其负担。
Each satellite controls several machines.
Groups of part program instructions are received from the central computer and stored in buffers.
They are then dispensed to the individual machines as required Feedback data from the machines are also stored in the satellite’s buffer before being collected at the central computer.
Computer numerical control
Since the introduction of DNC, there have been dramatic advances in computer technology.
The physical size and cost of a digital computer have been significantly reduced at the sametime that its computational capabilities have been substantially increased.
In numerical control, the result of these advances has been that the large hard-wired MCU ofconventional NC have been replaced by control units based on the digital computer. Initially,minicomputers were utilized in the early 1970s.
As further miniaturization occurred in computers, minicomputers were replaced by today'smicrocomputers.
Computer numerical control is an NC system using dedicated microcomputer as the machinecontrol unit.
Because a digital computer is used in both CNC and DNC, it is appropriate to distinguishbetween the two types of system. There are three principal differences:
由于数字电脑用于CNC 和DNC 中,只近似区分两种类型。有三个区分原则?
DNC computers distribute instructional data to, and collect data from, a large number ofmachines. CNC computers control only one machine, or a small number of machines.
DNC 电脑接受和发送指令数据都是来自许多机器,CNC 电脑控制只是一个机器或多个机器。
DNC computers occupy a location that is typically remote from the machines under theircontrol. CNC computers are located very near their machine tools.
DNC 电脑占有一个位置通过控制来实现机器的旋转。CNC 电脑要非常靠近车床。
DNC software is developed not only to control individual pieces of production equipment, butalso to serve as part of a management information system in the manufacturing sector of thefirm.
CNC software is developed to augment the capabilities of a particular machine tool.
The general configuration of a computer numerical control system is pictured in Fig.2.5.
As illustrated in the diagram, the controller has a tape reader for initial entry of a partprogram.
In this regard, the outward appearance of a CNC system is similar to that of a conventionalNC machine.
However, the way in which the program is used in CNC is different.
With a conventional NC system, the punched tape is cycled through the tape reader for eachworkpart in the batch. The MCU reads in a block of instructions on the tape, executing thatblock before proceeding to the next block.
In CNC, the entire program is entered once and stored in computer memory.
The machining cycle for each part is controlled by the program contained in memory ratherthan from the tape itself.
Control algorithms contained in the computer convert the part program instructions intoactions of the machine tool (or other processing equipment).
Certain functions are carried out by hard-wired components in the MCU.
For example, circular interpolation calculations are often performed by hardwired circuitsrather than by stored program. Also, a hardware interface is required to make the connectionswith the machine tool servo systems.