1、Motors and Numerical Control Motors change electrical energy into mechanical energy . This is simply the mechanical forces between magnets .when two magnets (or electromagnets)approach each other ,one will be either pulled toward or pushed away from the other . 1.CONSTRUCTION Each type of motor is built to do its own special job .All of them have two main parts .One part is called the stator .The stator is stationary ;it does not move .The other part ,the rotor ,is mounted on bearings so it can
2、rotate .The rotor shaft sticks out beyond the housing .For a motor ,the rotor shaft is coupled to a mechanical load . 2.MOTORS The power input to a motor is electrical .Voltage is applied to a motors terminals resulting in a current .The power output of a motor is mechanical .This power is transmitted by the rotor shaft as a torque .This torque tends to rotate a load , such as a fan or pump . As a motor drives a load , mechanical power is drawn from the motor .The motor ,in turn ,draws electrica
3、l power from the source at the same rate 3.NUMERICAL CONTROL The major disadvantage of machine tool automation thus far described lies in the economics of the process .It is expensive to tool a installations for automatic production .Therefore ,unless the part is to be made in very large numbers ,the cost becomes prohibitive .Great need exists for a method that permits rapid automatic production ,economical in job-lot amounts .The answer has been found in the numerical control of machine tools .
4、 Computer Numerical Control .Numerical control (NC) is a form of programmable automation in which the processing equipment is controlled by means of numbers ,letters ,and other symbols .The numbers ,letters ,and symbols are coded in an appropriate format to define a program of instructions for a particular workpiece or job .When the job changes ,the program of the particular workpiece changes .The capability to change the program is what makes NC suitable for low-volume and medium-volume product
5、ion ,and it is much easier to write new programs than to make major alterations to the processing equipment . There is a wide area of performance duplication between numerical control and automatics .Numerical control , however ,offers more flexibility ,lower tooling cost ,quicker changes ,and less machine down-time . In machining contours ,numerical control can mathematically translate the defined curve into a finished product ,saving time and eliminating templates .This can in turn improve acc
6、uracy .Another advantage appears to be great saving of machine time ,the equivalent og increasing productive capacity with no increase in facilities . Numerical control (N/C) is a form of programmable automation in which the processing equipment is controlled by means of numbers , letters ,and other symbols .The numbers ,letters ,and symbols are coded in an qppropriate format to define a program of instructions for a particular workpart or job .When the job changes ,the program of instructions i
7、s changed .The capability to change the program is what makes N/Csuitable for low-and medium-volume production .It is much easier to write programs than to make major alterations of the processing equipment . There are two basic types of numerically controlled machine tools :point-to-point and continuous-path (also called contouring).Point-to-point machines use unsynchronized motors ,whit the result that the position of the machining head can be assured only upon completion of a movement ,or whi
8、le only one motor is running . The N/C system consists of the following components :data input ,the tape reader with the control unit ,feedback devices ,and the metal-cutting machine toll or other type of N/C equipment . Data input ,also called “man-to-control link” ,may be provided to the machine tool manually ,or entirely by automatic means .Manual methods when used as the sole source of input data are restricted to a relatibely small number of inputs .Examples of manually operated devices are
9、 kryboard dials ,pushbuttons ,switches ,or thumbwheel selectors .These are located on a console near the machine .Dials are analog devices usually connected to a synchro-type resolver or potentiometer .In most cases ,pushbuttons ,switches ,and other similar types of selectors are digital input devices .Manual input requires that the operator set the controls for each operation .It is a slow and tedious process and is seldom justified except in elementary machining applications or in special cases . In practically all cases , information is automatically supplied to the control unit and the machine too by cards ,punched tapes ,or by magnetic tape .Eight-channel punched paper tape is the most commonly used form of data input for conventional N/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 combination of the two .The
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