PLC Training Courses

Industrial Training - The Best for Less

PLC Training

CNC Maintenance | PLC Troubleshooting Flowchart

Machine operator to maintenance technician.

 

PLC Troubleshooting Flowchart
Fig1. - CNC PLC Troubleshooting Flowchart

Click twice on fig 1 to zoom in on CNC operator level to maintenance PLC troubleshooting flowchart.

 

This CNC PLC troubleshooting flowchart example is based on the scenario the CNC machine wont start due to safety door not closed indicator on the CNC operator control panel. From machine operator level CNC troubleshooting to maintenance technician PLC troubleshooting, this CNC - PLC troubleshooting flowchart will help to understand the process.

 

CNC Operator:

 

Some CNC operators perform initial maintenance technician troubleshooting steps above, but the majority pretty much conform to the above flowchart. The CNC operator are typically limited to the limited control access a CNC controller provides in the CNC operator control panel, where as maintenance has access to the full control, performing PLC troubleshooting.

 

  • Visual Inspection (Is the CNC door closed?)
    • No?
      • Close Door, Try Again.
    • Yes?
      • Close up visual inspection of CNC door safety sensor.
      • Sensor needed tightened or adjusted?
        • Yes?
          • Close Door, Try Again.
        • No?
          • Call Maintenance
 

Maintenance Technician:

 

The maintenance technician job description (or field service technician) is to troubleshoot at a more complex level to determine faults with wiring, devices and communication issues between even more complex control devices (CNC PLC). The maintenance technician who has had proper PLC training, uses the PLC (Programmable Logic Controller) to make troubleshooting about 80% quicker and easier, and is referred to as "PLC Troubleshooting". Within the basics steps shown in above PLC troubleshooting flowchart, there are additional steps, but we simplified the flowchart for illustration purposes.

 

  • Is "Door Closed" sensor signal getting in to PLC? (PLC LED or Ladder Logic)
    • Yes?
      • [2] Is "Door Closed" signal getting to CNC from PLC?
        • No?
          • Check "Door Closed" bit in Message or Output card wire sent from PLC to CNC. If "No", trace back in PLC program and/or wiring accordingly.
        • Yes?
          • Seek CNC vendor support. There may be an additional input or M-code required for CNC operator control panel to indicate "Door Closed"
    • No?
      • Check voltage at PLC input screw.
        • Yes?
          • Is "Door Closed" Signal getting from PLC to CNC?
            • No?
              • Check "Door Closed" Bit in Message or output card wire sent to CNC
            • Yes?
              • Call CNC vendor
        • No?
          • Check voltage at CNC door sensor output
            • Yes?
              • Check wiring between CNC door sensor and PLC
            • No?
              • Check voltage at input to CNC door sensor
                • No?
                  • Check power source to CNC door sensor
                • Yes?
                  • Replace CNC door sensor

 

PLC Troubleshooting:

 

Most "CNC Maintenance" and even "CNC Troubleshooting" courses or sections in CNC manuals actually do not even include PLC Troubleshooting. But as you can see from the CNC PLC troubleshooting flowchart example above, the PLC is an integral part of CNC control. The CNC controller works with the PLC controller to complete the full process.

 

While PLC training has always been a critical part of maintenance technician job description, as machine operator jobs evolve to be more technical and to include some maintenance, PLC troubleshooting on a low level can greatly reduce downtime. Using troubleshooting flow charts like the one on this page, you can customize it to include more of the minor stages of PLC troubleshooting for the machine operator to perform. In that approach they will need the PLC Technician Training Software Bundle to build their technical knowledge level and sharpen their troubleshooting skills.

 

For example a CNC  operator or for that mater any machine operator could perform the troubleshooting steps that only require looking at PLC input and output LEDs on the face of the PLC. (not hooking up computer to PLC to monitor PLC program as that gets into the maintenance technician level and they need proper PLC training for that.) Also many sensors like the CNC door sensor in this example often have an LED on them to indicate if they are triggered or not. So a CNC operator would not need to know how to use a multi-meter for a quick low level check of sensor.

 

For the maintenance technician, though rare, the PLC troubleshooting can get, well ... complicated. Especially when it is a PLC CNC communication issue. Questions arise about system design, for example is the CNC controller sending feeds and speed to the PLC, which in turn sends them to Servo drives? The complicity is increased even more, if a PAC motion control is being used instead of a PLC? Or with a particular CNC, the PAC is built into CNC controller, sending feeds and speed directly to Servo drives and using RIO for door closed signal, etc.

plc cnc controller

Raise the maintenance skills level of your machine operators and CNC operators with the Autonomous Maintenance Training Program (Phase II).

 

About the Author: Don Fitchett founded the activity based costing system called "True Downtime Cost" (TDC), authored books and speaks at conventions on the topic and is president of BIN. Don has been in the industrial training sector for over two decades, setting up training programs around the world, and still conducts PLC training seminars and onsite PLC training workshops to this day.

 

Copyright 2016 BIN95.com (You may link to this article only)