The first example of programming a material transport cart controlled by PLC

1、 Control requirements

There are 6 workbenches in a certain workshop, and the feeding truck travels back and forth between workbenches to feed. Each workbench is equipped with a position switch (SQ) and a breathing button (SB). The specific control requirements are as follows:

(1) The feeding truck should be able to stop at any of the six workstations at the position of the in place switch.

(2) Assuming the feeding vehicle is currently suspended at workstation m (SQ m is ON), workstation n will call (SQ n is ON). If:

（a） m>n ， Drive the feeding vehicle to the left until SQ n moves and stops in place. When the number of the stop position SQ of the feeding vehicle is greater than the number of the call button SB, the feeding vehicle runs to the left until it reaches the call position and stops.

（b） m<n ， Drive the feeding vehicle to the right until SQ n moves and stops in place. When the number of the stop position SQ of the feeding vehicle is smaller than the number of the call button SB, the feeding vehicle runs to the right to the call position and stops.

（c） m=n ， The feeding truck remains stationary in its original position. When the number of the stop position SQ of the feeding vehicle is the same as the number of the call button SB, the feeding vehicle does not move.

II Implementation of PLC hardware

1. I/O allocation table

2. External wiring of I/O

三、Implementation of PLC software

In the figure, the current position of the feeding vehicle is sent to data register D0, and the calling workstation number is sent to data register D1. Then, by comparing the data in D0 and D1, the direction of the feeding vehicle's operation and the target position it reaches are determined.