A PLC is used to control the sequence in an automatic drilling operation. A human operator loads and clamps a raw work part into a fixture on the drill press table and presses a start button to initiate the automatic cycle. The drill spindle turns on, feeds down into the part to a certain depth (the depth is determined by limit switch), and then retracts. The fixture then indexes to a second drilling position, and the drill feed-and-retract is repeated. After the second drilling operation, the spindle turns off, and the fixture moves back to the first position. The worker then unloads the finished part and loads another raw part.
(a) Specify the input/output variables for this system operation and define symbols for them (e.g., X1, X2, C1, Y1, etc.).
(b) Construct the ladder logic diagram for the system.
(c) Write the low level language statements for the system.