Lecture II on the application of the hottest elect

Lecture on the application of electronic control technology (II)

3& Nbsp application example of electronic control technology

(1)   automatic round-trip control circuit of machine tool workbench

this is a simple control system, which mainly depends on the travel switch. The function of the travel switch is the same as that of the button switch, and it is also used to turn on and off the control circuit. The difference is that the action of the contact is not completed by fingers, but by the collision of some moving parts of the production machinery to make the contact act and disconnect some control circuits to meet certain control requirements. The symbols of the travel switch in the electrical schematic diagram are shown in Figure 3-26

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the automatic round-trip control circuit of the workbench controlled by the travel switch is shown in the figure. From the schematic diagram of the automatic round-trip of the workbench at the bottom of the figure, it can be seen that four travel switches are installed on the machine bed. Among them, SQ1 and SQ2 travel switches are used to realize the automatic round-trip of the workbench, SQ3 and sq4 travel switches are used for terminal protection at both ends. A block iron is installed on the edge of the workbench, block iron 1 can only collide with SQ1 and SQ3, and block iron 2 can only collide with SQ2 and sq4. Block iron After touching the travel switch, the workbench can stop and reverse, which makes the workbench move back and forth

the action principle of the control circuit is as follows: when the power switch QS is closed, press the start button SB1, the coil of contactor KM1 is energized, and the motor starts in forward rotation. When the workbench moves to a certain position, the stop iron 1 collides with the travel switch SQ1 to disconnect the normally closed contact sq1-1, the coil of contactor KM1 is powered off and released, and the motor is powered off and stopped. At the same time, the normally open contact sq1-2 of the travel switch SQ1 is closed, which energizes the contactor km2, and then the motor reverses, dragging the workbench to the right. At the same time, the travel switch SQ1 is restored to prepare for the next forward rotation. Since the normally open auxiliary point of contactor km2 here has been closed and self-locking, the motor continues to drive the workbench to the right. When the workbench moves to a certain position to the right, the stop iron 2 collides with the travel switch SQ2 to disconnect the normally closed contact sq2-1, the coil of contactor km2 is powered off and released, and the motor is powered off and stopped. At the same time, the normally open contact sq2-2 of travel switch SQ2 on the rotating cylinder of the plotter is closed, so that the coil of contactor km2 is energized again, and the motor starts to rotate forward again. This cycle enables the workbench to automatically return and return within the predetermined stroke

in the automatic round-trip movement of the workbench, if SQ1 or SQ2 fails, the workbench will move beyond the limit position to the limit position, resulting in accidents, which is obviously not allowed. For this reason, in the working closed-loop control; The load range is 100 kn to 2000 kn, and the limit position of the movement of the machine also determines that SQ3 and sq4 are installed in the front of the structure of the electronic universal tensile machine. When the workbench crosses the limited position, the stop iron will collide with SQ3 or sq4, automatically cut off the control circuit and force the motor to stop, so as to keep the workbench in the limit position and avoid accidents. The worktables and power head slides of common gantry planers and equal rail grinders use this control line to realize the automatic round-trip circulation of the worktable

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