We recently had to troubleshoot a problem with a customer’s assembly line. For no apparent reason every night one section of the line would shut down and have to be restarted. Even worse it occasionally started running without using the start switch.
This particular line has a very simple setup: a start/stop switch for the conveyor belt (which has 5 motors for the different belt sections of the line) and an emergency stop setup so the line can be stopped at any point along the entire conveyor belt line. There are no sensors or any other types of controls along the line.
At first we tried to replace the start/stop switches of which there were only 4. It was possible one had a bad contact. No luck. We also had a spare relay so we swapped it with the existing relay which plays a part in starting and stopping the line when the buttons are pushed. No luck again.
In the end it turned out to be loose terminal screws in the main control cabinet of the conveyor belt line. This system has been operational for more than 3 years but had never had any electrical maintenance performed on it. As part of yearly maintenance which includes things like cleaning dust off moving parts, lubrication, etc., it is also important to tighten things up. This includes terminal screws where wires are tied into. Electrical connections heat up causing the copper wires to expand and contract constantly which will loosen the connections over time. In this case it turned out to be the gremlin which was causing the mysterious stops and starts of the line.
Moral of the story, pay now or pay later. Yes money was saved not doing the maintenance (not that they were trying save the money it was more due to just not knowing the importance of such things) but they still had to pay to fix the problem. Not to mention the downtime and interruptions caused when the line stopped unexpectedly.