The high-end electric forklift stacker is controlled by PLC, and it works in a sequential scanning and continuous cycle. That is, when the forklift PLC is running, the CPU compiles a program that is stored in the user memory according to the control requirements of the user, and performs periodic cyclic scanning according to the instruction step number or address number. If there is no jump instruction, it will be executed sequentially from the first instruction. The user program until the program ends, and then returns to the first instruction to start the next round of scanning. In each scanning process, the sampling of the input signal and the refresh of the output state are also completed.
The scanning process of the electric forklift stacker can be divided into three stages: input sampling, program execution and output refresh, and carry out periodic cycles.
(1) Input sampling stage
In the input sampling stage, the forklift first reads the on-off state or input data of all the input terminals temporarily stored in the input latch in sequence by scanning, and stores it in the corresponding input state register, that is, refresh the input . Then close the input port and enter the program execution stage. During the program execution phase, even if the input state changes, the content of the input state register will not change. The changed input signal state can only be read during the input sampling phase of the next scan cycle.
(2) Program execution stage
In the program execution stage, the stacker scans and executes each instruction in the order in which the user program instructions are stored. The required execution elements can be read from the input status register and the current output status register. The result is then written into the output status register, so all the contents of the output status register change with the execution of the program.
(3) Output refresh stage
When all instructions are executed, the on-off state of the output status register is sent to the output latch in the output refresh stage, and output through a certain method (relay, transistor or thyristor) to drive the stacker to work, which is the actual PLC. output.
