This is the machine, a 9 meters long double sided edge banding for chip boards
I was called to repair an IMA Combima double sided machine. The customer reported that the machine does not start because the reference cycle of the width adjustment does not finish and the machine reaches the max-width limit switch. The problem was obvious - The machine does not recognize the reference signal and therefore it travels to the limit switch.
Checking the reference position sensor
So i had first to check the reference position sensor. Since the problem appears at the width adjustment of the machine, the sensor had to be somewhere near the linear guides where the machine moves:
The linear guides are on the right side of the movable side of the machine
Underneath the sensor is visible
A ran some tests to see if the sensor is dead or the problem is the wiring or the PLC input. First i checked the PLC input - i simply removed the sensor from the PLC and then i fed 24V directly to the input. The input worked normally and the software recognized this input, so the PLC works. Then i measured the wires with an ohm-meter and i found them in good condition. Obviously, the sensor was dead. So i removed it and took it on my workbench for a quick surgery...
This is the sensor.
A German-type connector is used to interface it
It has 5 mechanical precision limit switches and one inductive sensor
The sensor part number is: Balluff BNS-819
One of the 5 mechanical limit switches is used for the maximum travel limit. The inductive sensor is used for the width adjustment reference. As expected, the inductive sensor causes the problem. Replacing the complete sensor was out of the question because it costs more than 500 Euro!!!
8 screws had to be removed to open the housing
one fore screw for the grounding
The inductive sensor has 3 wires. I wrote down which wire color goes to which sensor's connector
This is the inductive sensor
On the left side there is a tiny screw that has to be removed
The sensor has the inductive part which is a cylindrical 6.5mm sensor, and a rectangular part with the terminals