机械工程专业英语第11课.pptVIP

TECHNICAL ENGLISH MECHANICAL ENGINEERING YAN NU 11 Computer Numerical Control Centerpiece：The central or most important feature. And please have a centerpiece for every table.? Ball screw 滚珠丝杠副 11 Computer Numerical Control 11 Computer Numerical Control The drive system is comprised of screws and motors that will finally turn the part program into motion. The first component of the typical drive system is a high-precision lead screw called a ball screw. 11 Computer Numerical Control Drive motors are the second specialized component in the drive system. The turning of the motor will turn the ball screw to directly cause the machining table to move. Several types of electric motors are used on CNC control systems, and hydraulic motors are also occasionally used. 11 Computer Numerical Control The simplest type of electric motor used in CNC positioning systems is the stepper motor (sometimes called a stepping motor). A stepper motor rotates a fixed number of degrees when it receives an electrical pulse and then stops until another pulse is received. 11 Computer Numerical Control Alternating current (AC) servomotors are currently the standard choice for industrial CNC machine tools. 11 Computer Numerical Control The function of a feedback system is to provide the control with information about the status of the motion control system, which is described in Figure 1. 11 Computer Numerical Control There are two main types of control systems: open-loop and closed-loop. An open-loop system does not have any device to determine if the instructions were carried out. For example, in an open-loop system, the control could give instructions to turn the motor 10 revolutions. Gear Manufacturing Methods Gear planing uses a reciprocating rack, stroking in the direction of the helix on a gear with a gradual generation of form as the rack effectively rolls round the gear blank. The rack is relieved out of contact for the return stroke as in normal sh