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Перевод текста Computer, Abrasive machining
Описание работы:
Electronic digital computers have progressed through three generations.
The first
generation was composed of vacuum tube machines. They came in several modals and sizes. Their most notable features – aside from the revolution they affected in business, government, military and scientific methods – were the banks of vacuum tube they contained. These tubes generated and manipulated the electronic impulses with which the computers operated. But they also gave off a considerable amount of heat and burned occasionally. As a result, an integral part of most early computer installations was a large air conditioning system, plus the necessity of having a consumer engineer or maintenance man readily available at all times
The second generation – the so-called solid-state machines eliminated vacuum tubes in favour of transistors, resistors, diodes and similar semiconductor components. Most of the computers of this generation fall into this category. They require less power, throw off considerably less heat, take up less space and are far more reliable than their predecessors. In addition, most are faster, have greater memory capacity and are general easier to program than first-generation machines.
Third-generation computer are featuring smaller internal components, faster operating speeds, increased memory capacity and new concepts in data processing.
Most computers, it is important to note, are build as “general purpose” machines and can be adapted to almost any one of the jobs.
It is stored program that separates the electronic digital computer from all other types of counting devices. By storing instructions within the machine the computer can go about its work without manual intervention.
Abrasive machining
Work by Lemaster (1992) showed that acoustic emission (AE) was sensitive to contact area, condition of abrasive, grit size, radial and longitudinal faces of the workpiece. Lemaster and Domelfeld (1993) showed that AE signal increased with increasing feed speed but was relatively intensive to arbor speed. They also found that the greater the depth of cut the greater the material removal rate and the greater the acoustic emission signal. There was a special effect on the acoustic emission signal. Lemaster and Domelfeld (1993) also found that while the AE signal was sensitive to the wear of the abrasives it was relatively insensitive to whether the abrasive was cleaned. Work by Murase et.al (1995, 1997) also showed that the AE signal increased with an increase in grit number. This was probably due to the fact that 220 grit had more contact area then 100 grit abrasive which had fewer, larger grains. Murase et.al also showed that when sanding perpendicular to the wood grain the AE signal was greater than when sanding parallel to the grain. This was correlated to the stock removal rates which were greater when sanding perpendicular to the grain. Their work also showed that an increase in sanding pressure resulted in an increase in AE signal. Their work, however, showed a decrease in AE while the work by Lemaster (1992) and Lemaster and Domfeld (1993) showed an increase in AE. This could probably be explained due to the fact that the two research projects used different parameters to quantify the AE signal. The work by Lemaster use the root mean squared of the AE signal (AE) whereas the work by Murase used AE count rate. The AE count rate is a threshold dependent parameter. The work by Murase showed that the number of high amplitude peakes in the AE signal decreased while the work by Lemaster showed that the energy content of the AE signal increased with an increase sanding time. This is an important observation as the two AE parameters together can provide more precise information on the AE signal. In this case, the number of lower amplitude peaks of the AE signal must increase with increasing sanding time. Work by Matsumoto and Murase (1997) also showed that cleaning of the abrasives resulted in an increase stock removal rate but did not change the AE signal level. Примерный внешний вид работы:
Тип работы: Контрольная работа