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Case Study: Troubleshooting Problems | Solution heat treatment system
How to do basic automation control troubleshooting.
(This article is not about how to heat treat steel.)
Induction Hardening System
- Induction Hardening System Example:
A typical Raydyne ScanMaster induction hardening (heating) control system simultaneously controls scan speeds, rotation speeds, heat levels, heat times, quench times, quench temperature and time delays.
^^ Tap to Zoom ^^
This is a case study of troubleshooting problems and solution for a heat treatment induction hardening machine control. Some may consider it an advanced heat treat troubleshooting problem as it is on the automation control side of Raydyne induction heat treatment system. But as far as automation control troubleshooting problems goes, it is a simple and common example that the layman to machine automation control troubleshooting, can learn a lot from. Common to Robotics troubleshooting, mechatronics, servo encoder troubleshooting too. Hope it helps those just starting out.
Reported problem - heat treatment system:
I am in the IT department and need some help troubleshooting the Allen Bradley PLC in our Radyne induction heat treating machine.
The problem is - the rotating plate shaped platform has gone well below the level it usually does, I found the back plain of PLC is an old 32 bit system. How do I connect with it, solve the problem? Our go to PLC person no longer works here. Any insight or guidance would be humbly appreciated! (I'll email you pictures of the back plain, plate and control panel.)
The pictured sent was of a computer backplane, not a PLC backplane. Hey, he was an IT person and you go with what you know. But I have to mention that so you understand my reason for such details below on the basics of troubleshooting and PLC basics. My desire was to give Henry enough basic knowledge so he could make a sound decision on which way he wanted to go about finding a solution for his heat treatment system. Well. on to my initial reply ...
The picture you sent us of backplane you where looking at, was not a PLC, but a supporting computer. (Above is a where we mocked up the picture of the heat treatment control panel you sent, to show you where the PLC is, and what type it is. The odds are, your problem is not in the computer you were looking down into at the backplane.
The probability of failure/change are as follows …
- Sensor failure or adjustment like encoder or limit switch (physical/mechanical problem) 90% to 99% chance
- Someone accessed menu on HMI screen on front of panel and changed offset 1-10% chance
- Computer you have been looking at 2% (3-20% if extreme heat in panel, but symptoms do not match that type failure)
- Servo Driver (device below PLC in panel) 1% (2-10% if extreme heat in panel, but symptoms do not match that type failure)
- PLC (See picture above) 1% (Within PLC, sensor input i/o most likely, symptoms do not match micro-processor itself failure)
Heat treatment System Troubleshooting Solutions
- Get RSLogix 500 PLC training and Use PLC to troubleshoot. (See picture above to identify which component in panel is actual PLC that controls process.)
- Get local person trained in RSLogix 500 to troubleshoot. (I'll get Clifford of omega star to reach out to you, he lives in texas. he is a control automation designer that we trained and runs his the automation control engineering company.)
- call the phone number i gave you and have machine manufacturer schedule an on-site service call.
if we trained you, what you would need for plc troubleshooting is ...
- laptop with rslogix 500 and rslinx software on it. (xp would be more reliable and cheaper)
- an allen bradley (ab) 1747-uic or old pic box cable to connect laptop to rj485 port on front of ab 1747-l40 slc 500
- Discriptored backup copy of ladder logic program that is same as one in PLC. (not impossible to troubleshoot without discriptored copy of program, but extremely difficult for even the seasoned PLC expert.)
PLC Troubleshooting procedure:
Power up laptop, connect to PLC RJ485 port, go online with PLC, save a backup copy of current PLC program in machine. (Saving current copy is very important to do before you start poking around in the program.) Then search ladder logic for plate home position sensor and encoder input data. Study related ladder logic, to see why it is not going to normal position. Because that process may lead you to find PLC controller is going to position set in program and set value is coming from HMI. You would need machine manual from radyne aftermarket support packages to see how to navigate their hmi screens they designed and what setting is for position offset. if you find position is set at factory setting (not been changed) and see sensor input coming into ladder logic , you may suspect sensor adjustment or encoder failure, (servo slippage if positioning is not consistent).
also note: if computer, servo driver, hmi or plc itself failed due to high heat environment, they typically have catastrophic failure and nothing would be working. yet another indicator they are most likely not your problem. you are just using the plc controller to troubleshoot what is the actual problem.
after considering the information above, henry opted for the option to have clifford of omega star controls & technologies to go onsite to troubleshoot and investigate. the next day clifford generated a detailed report with component list, brand, model, schematics, pictures and recommended solutions to problems found. (summary, mechanical/physical problem) for those reading this heat treatment system troubleshooting case study, i am sharing below just some of the highlights from report , so readers may pick up a few things along the way...
initial troubleshooting of the heat treatment machine system hmi and controller revealed the software is sending and receiving inputs and outputs as expected.
utilized the hmi to “slow jog” the rotating up and the controller would fault immediately with “abort, error limit” message. attempted to perform the “homing” function and the controller faulted immediately with the same message. in either case the faults were cleared with the hmi controller reset button.
attempted to “slow jog” with lower limit switch actuated and the “homing” with home switch actuated with the same results. the controller would fault immediately with “abort, error limit”. however, there were no faults on the hardware.
generated faults on the hardware by removing the connections for the encoder.
note: without the plc software, unable to connect to the plc and gain any insight and would require reverse engineering.
further investigation into the hardware, found no blown fuses or any loose connections.
attempted to power the servo motor disconnected from the screw-lift for the rotation plate. during the removal found the amphenol connector for the brake release signal had been damaged. the motor side connector had been physically broken and the solder had been broken leaving the internal wiring as an open circuit. the broken solder may have been making intermittent contact for the brake would engage and disengage.
The broken connector and wire could be the initial problem for causing the brake to fail would allow the plate to continue to drop until a physical stop is reached which is beyond the predetermined lower limit switch.
As far as the controller failing to turn on the servo motor to lift the rotation plate, this could be one of two situations.
1. The encoder is not functioning properly. i.e. the controller is sending the signal for the servo motor to rotate and is not receiving the expected encoder pulses and would abort the attempt to protect the drive.
2. The brake on the servo motor is failing to release at the appropriate time causing the servo motor not to turn.
It has been my experience, the encoder failing to send a proper pulse count will cause most similar system faults. Replacing the servo motor (including the internal brake and encoder) is my recommendation. Although, it is possible to replace the encoder and/or repair the brake.
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