Strong electrical control of PMC and machine tools
Posted by jingwang
from the Agriculture category at
01 Nov 2022 10:07:15 am.
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To compile the PMC (PLC) control logic of the machine tool, it is first necessary to clarify the controlled (to be realized) machine tool action, and the timing of each detail of the action, that is, the step-by-step sub-steps (sub-actions) to achieve the action are sequenced out of the sequence table, and the necessary steps must also estimate its execution time, but also consider the interrelationship between the actions, the interlocking and unlocking conditions between the actions, and understand the electrical components that realize each subtle action and execute the PMC command. PMC logic is to use PMC instructions (language) to represent the execution of these subtle actions in order. For sequential logic programs, different system manufacturers provide different formats, commonly used: statement tables and ladder diagrams. FANUC's PMC logic program uses a ladder diagram format, which is characterized by intuitiveness, similar to the relay logic diagram of a machine tool, so it is very easy to understand.
Moreover, the PMC language uses many specialized instructions, called functional instructions. In this way, the logic diagram is compiled quite concisely.
There are about 50 functional instructions of FANUC PMC, but there are about 20 commonly used ones, such as: timers, counters, rotation instructions, decoders, etc. The following two figures show the function instruction format and the function instruction set (partial).
Ladder diagram
Execution of PMC
After the CNC is turned on, the CNC and PMC run at the same time. If the PMC receives the X signal of the machine tool operator to ask the CNC to implement a certain operation, such as starting the automatic machining program, the X signal is sent to G7.2 in the ladder diagram, and the CNC receives the instruction, knowing that it is to execute the automatic cycle start subprogram, that is, it is executed immediately. Output F0.5 during execution informs PMC that the CNC is running the machining program.
If the CNC finds that there are M, T and other instructions in the program segment when executing the processing program, that is, the instruction is decoded and sent to the PMC with F signal address, for example: M code, sent to F10~F13. After PMC processing (decoding, sequencing and interlocking), it is sent to the strong electric cabinet through a certain Y address, and the actuator (relay, etc.) performs the necessary control actions. If there is a feed axis movement instruction in the program section of the part processing program where the M command is located, after the controlled shaft has completed the required amount of movement, it is also necessary to determine whether the PMC has completed the action given (instruction) by the CNC, so it is required that the PMC must return a completion signal FIN when executing M, T and other instructions. When the CNC receives this signal, it can read the next segment and execute the next program segment.
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