CNC PLC Programming:
CNC PLC Controls TroubleshootingCNC PLC programming may be done within the CNC controller/CNC operator control panel or as in most cases there is a separate PLC for CNC machine. In the latter, maintenance would connect directly with the PLC and use that particular PLC vendor's software to access the CNC PLC programming.
This post and article referenced is about troubleshooting the CNC PLC control, and who can do what. Typically the CNC machine operator troubleshooting task is limited to responding to alarms on CNC control panel and visual inspections. Then if CNC operator can not resolve issue, maintenance is called and they will often use PLC ladder logic to speed more technical troubleshooting process as shown in the CNC PLC Control troubleshooting flowchart. The multi-meter is another supporting tool maintenance uses once the PLC ladder logic has quickly narrowed down the area of the system to test.
The PLC programming for CNC machine is commonly simple as the PLC typically only controls peripheral devices that support the CNC controller. Like this CNC PLC Control troubleshooting flowchart article example, the CNC door closed confirmation signal is detected by PLC and then communicated to CNC. The PLC may control and/or monitor other supporting device too like the coolant pump, the chip conveyor, indicator lights, air solenoid, etc. That article is a great example of use of PLC in CNC machines and sheds some additional light on difference between PLC and CNC machines.
There are exceptions to every rule, so in some more rare CNC designs, things can get more complicated than described above. Instead of the PLC communicating to the CNC (industrial computer), the PLC could be emulated by the CNC controller itself. (Just like a PAC does, as a PAC is an industrial computer emulating a PLC.) Also if the CNC is having motor drive issues it can get more complex. Some CNCs communicate axis speeds and feeds to PLC which then in turn sends data to motor drives, some CNCs send data directly to drives and only use PLC for peripheral device.
Increasing CNC operator maintenance level training is a growing trend to help reduce maintenance workload so maintenance can better keep up with the ever growing technological advances in the industry and to reduce downtime waiting on maintenance to arrive. That possibility is explored in article linked to above using the CNC PLC Control troubleshooting flowchart with door closed signal example, If PLC LEDs are made visible to CNC operator, and they receive basic PLC training, they can often narrow down problem even further saving maintenance time. (... without using a computer or multi-meter) Often figuring out on their own and not needing maintenance, thus reducing downtime.