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Basis of ED program control
If ED automatic control system acts according to previously set program, then such control is called program.
Program can be set by various methods, which essentially improve in process of ED developing:
- in the form of previously manufactured patterns and models (in copying machines);
- in the form of servo ED supplies in process of complex units manufacturing;
- in the form of numerical programs with the help of which numerical data of drawing is directly entered into computer at providing of unit automatic manufacturing (systems of numerical program control - NPC).
Equipment with NPC has high technical and economic indices, especially at manufacturing of complex by configuration products in small-scale or individual productions.
There exist two groups of NPC systems relatively to technological conditions of operation:
- positioning systems (of position control), here it is necessary to provide s position of product relatively to equipment in certain discrete moments of time, with this character of displacement trajectory from one position to another has no importance (drilling machine, hole-piercing presses and so on);
- systems of contour (continuous) control, here continuous motion control of manufactured unit relatively to equipment is necessary (milling machines for manufacturing of punches and press-forms, gas-cutting machines and so on).
With the developing of digital control fringes between named methods are smoothing. In first turn it is connected with using of multi-operational machines, manufacturing centers, where so-called universal NPC systems are used, that allow to use positioning as well as contour control.
In these NPC systems not only geometrical information but the great number of technological and additional commands (substituting of equipment, speed changing, cleaning of cuttings) are programmed, that allow completely automate the cycle of unit manufacturing on machine.
Entering of the program is realized on carriers of various type (punched strips, punched cards, magnetic strips, magnetic disks (flexible or rigid), CD-Rom and so on).
The method of program set depends on type of carrier and types of feedback givers. For magnetic carriers program is set in the form of command impulses.
For digital program control of small machines of medium accuracy discrete ED based on step motors are widely used. In this case even opened systems can be used (without feedbacks), because SM together with electronic commutator directly converts the specified sequence of control impulses into correspondent mechanical discrete displacement (at forced commutation of control windings as well as at autocommutation) .
NPC systems not always can programmatically provide the necessary regime of manufacturing, especially due to influence of various casual factors. But in machines with NPC of main drive and supply drive the principle of adaptive control can be used, i.e. choice of optimal manufacturing regime, support it with providing if it is necessary correspondent correction is realized automatically.
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