The number of cars is increasing, and the traditional traffic light control mode uses timing control. Since the traffic flow is changing at any time, when there is no car passing at this time, the relative car has to wait until the green light in this direction ends to display a red light. Through, the strain performance in time and space is poor, which not only wastes time, but also causes the traffic jam in the opposite direction. The smooth flow of urban traffic is an important indicator to consider the level of urban economic development. Solving the problem of highway traffic light control is an important link to ensure safe, orderly and fast operation of traffic. Traffic lights are the most effective and common way of traffic guidance. In order to overcome the phenomenon that the car-free traffic at the green road of the vehicle-less intersection or the green traffic time of the multi-vehicle intersection is short and the traffic is jammed, the CPU 224 in the S7-200PLC series controls the traffic lights at the intersection.
1. Hardware design of PLC control system 1.1, control requirementsThe traffic light control is realized by PLC. The control requirements are as follows: red, green and yellow lights are arranged in the east and west directions of the intersection, and they are turned on according to a certain sequence. Use the start switch to control the start of the traffic light system, press the stop switch, and the system stops working.
(1) In the north-south direction, the red light is on for 55s in the north-south direction, the green light is on the east and west for 50s, and then the yellow light is on for 3s.
(2) In the east-west direction, the green light is on for 30s and then flashes for 2s, then the yellow light is on for 3s. The red light in the east-west direction is 35s.
(3) The flashing frequency of the green light is on for 0.5s and off for 0.5s.
(4) System cycle work. The specific control requirements are shown in Table 1.
Table 1 Traffic Light Control Requirements
This system uses the CPU 224 of the S7-200PLC series. This type of PLC has 14 input points and 10 output points. According to the control requirements, the I/O allocation table of the traffic light PLC control system is shown in Table 2. The system has two input points, the system start button and the stop button. The start button causes the system to start running normally, and the system is stopped with a stop button during maintenance. The six outputs are traffic lights in the north-south direction and the east-west direction.
Table 2 I/0 allocation table
Lights of the same color in the same direction work at the same time. In order to ensure the synchronization of the traffic lights of the same color in the same direction, parallel output can also save the output points. The north and south direction and the east and west direction 12 lights are combined into 6 outputs. Figure 1 is the wiring diagram of the principle of the traffic signal PLC control system.
Figure 1 PLC control traffic light principle wiring diagram
2, PLC control system software design 2.1, timing diagramThe traffic lights are different in the north-south direction from the east-west direction. In a period of 90s, the north-south direction: the red light is on for 55s, the green light is on for 30s and then on for 2s, then the yellow light is on for 3s. East-West direction: green light is on for 50s and flashes for 2s. After yellow light is on for 3s, red light is on for 35s. Figure 2 shows the running time diagram of traffic lights. The flashing frequency of the green light is on for 0.5s and off for 0.5s.
Figure 2 Traffic light operation timing chart
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