机械专业英语课件12.ppt

上一课回顾 单词复习： Diesel/ gasoline engines synchronous /asynchronous angular velocity strip slider-crank /cam pneumatic Lesson 12 Machine Tool Motor 机床电机 重点词汇： prime mover 原动机 magnetic pole/ magnetic field instantaneously Paragraph 1 Electric Motors are the prime mover for most machine tool functions. They are made in a variety of types to serve three general machine tool needs: spindle power, slide drives, and auxiliary power. Most of them use 3-phase AC power supplied at 380V. 电动机是大多数机床的原动机。 Paragraph 2: The Basic All electric motors use the principle that like magnetic poles repel and unlike poles attract. Current through a coil or permanent magnets creates magnetic fields . 所有电机都遵循磁极同极相斥，异极相吸的原理。电流通过线圈或永久磁铁时产生磁场。 Motors deliver torque by shifting the magnetic fields within the motor, so the rotor is constantly drawn around. Paragraph 3: Initially, all motors used direct current (DC). This current creates magnetic fields in the stator and rotor, then mechanically energizing and de-energizing stator coils cause a moving field that draws the rotor around. With alternating current (AC) motors, the current itself switches in polarity from positive to negative. Sending AC to the stator coils creates fields that draw rotor around. 交流电机中，电流会自动从正极变到负极。将交流电供给定子线圈就会产生磁场使转子旋转起来。 Paragraph 4: For most machine tool applications, versions of the AC asynchronous motor are used for spindle drives, while slide drives are generally synchronous. Paragraph 5 A Little History  The design problem through the years with machine tools and motors has been how to get high torque at a variety of speeds. Initially, mechanical transmissions consisting of gears, belts, and gear/belt combinations gave speed changing capability. Up to 36 speed ranges（速率范围） were common at one time. But all this extra hardware is costly and needs maintaince. In the last decade, as speed requirements have risen the inaccuracy caused by vibration, which was not a problem at l