Troubleshooting a Morbidelli Tolerance Error

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When the controller reports a tolerance error, the cause is probably mechanical. Pros get the details and probe the mystery. July 1, 2005

I have a Morbidelli Author 504 built in 1995. I am getting error 032 X axis: tolerance error. The book says causes - the n axis (X,Y,Z,E or A) indicated has a tolerance error which is too high, that is to say, the distance between the axis final and current positions is greater than the limit programmed for longer than the envisaged time of 200msec. Solutions: check whether there is an important mechanical cause. Modify the dynamic parameters of the axis to increase the axis torque on approach.

I phoned the tech support and they told me that the error is too much drag on the motor for the spindle head. We get the error when we are trying to drill a bank for holes. The more holes we drill the more often we get the error. Can anyone offer any help?

Forum Responses
(CNC Forum)
From contributor D:
First, let me say that I am not a Morbidelli expert. The error that you describe however sounds like a common error in closed loop servo systems. The systems that I deal with call this a lag error or following error. This simply means that the servo position as reported by the encoder did not come within a preset distance from command position within a preset time.

As your tech stated, the most common reason for this problem is mechanical drag. This can come from linear bearing problems, ballscrew problems, or anything else that may cause resistance. If your Morbidelli uses a rack to drive the X axis, I would look there first for damage or debris build up. If the X axis is a screw drive, turn the power off and check and see of the screw (or nut) turns freely. Next check the linear rails and bearings. Have you been finding little ball bearings rolling around on the floor lately? If so, one of your LM bearings may have destroyed itself. In general, a PTP axis should move very freely by hand with the power off. If it does not, you have a mechanical problem.

You can also get this error without an underlying mechanical cause. Encoder problems, failing conductors, failing drive amplifiers, and control problems can all cause this type of error. Check encoder and servo connections and give the power and feedback cables a thorough inspection. If you cannot find anything wrong after these inspections and tests, it may be time to call in the tech.

From the original questioner:
The only problem that I see with it being the screw drive or bearings is that there are 2 routers and one cutter on the unit and they use the same X,Y and Z servo drives, and they work fine. We have not found any bearings or extra parts. It does take a bit of effort to move the x axis with the power off, but it does not feel any harder than it has been before.

I am also wondering if anyone has purchased the spindle assembly and how much they are worth.

To the original questioner: Drilling a large number of holes usually involves more acceleration and deceleration than routing. This could cause problems, especially with a marginal amplifier, that might not show up while routing. The shock of acc/dec may also open connections or conductors that would be OK during more gentle movements.

Another very simple thing to check is whether or not the drills are out of the stock when X movement is commanded. I would think that this would just snap off the bits, but it could possibly give you a lag error. Finally, if the boring head is seriously out of plumb, it will tend to lead the tool carrier out of position. Again, you would think that it would just snap the bits, but you never know.

From original questioner:
I checked the servo packs for errors and they did not have any. I ran a few tests and the power is cut from the controller to the servo packs and that is what the second error is from. I checked the wires and connections and they all seem to be ok.

We talked to the tech today and he still thinks that the problem is that there is to much resistance in the motor for the spindles. His suggestion is to pull of the grease nipples and blow clean compressed air in there to see if there is a blockage. I do not know if this is a good idea or not - I tend to think that it's not. It does sound better than the owners idea of taking some diesel and oil and pump it through the spindle head and clean all the old grease and then add new grease.

The other thing that I am going to try to do is to change the resistance on the motor for the spindle head to see if that makes a difference.

To the original questioner: You mentioned a second error. What are the two errors that you are getting? Is the boring head tripping an overload and dropping out the servos? If so, I have completely misunderstood the problem.

As for the drill bank, if it is tightening up you probably have a bigger problem than clogged grease lines. I have added oil to the grease in a boring block to make it run cooler, but you have to be careful. The oil in the grease has to be the same type as the oil you add. Putting a mineral oil with a synthetic can make a real mess.

Before messing with the drill bank, I would check the motor (bearings and windings) the power that leads to the motor, and the contactor that runs the motor. Loss of a phase or a high resistance set of contacts on one leg can trip the overload.

From contributor J:
My guess is the problem lies in the Z axis, as it is works entensively while drilling. On many morbidelli's the guide rails for the z-axis run through the boring head, thus the "motor for the the drill head is causing the problem". Try slowing down your drill feed rate to test if the trip happens less frequently (V value). Also, in the axis parameters there is a value you can set for the following error. Increasing this may buy you time to plan downtime to fix the machine, (also try slowing down rapid feed rate override).

From contributor T:
We have an old morbi 503 and 2 morbi 600's. We had what sounds like the exact same problem you are having on our 503. The tech's even thought the same thing at first, mechanical drag from somewhere - (lead screw, bearings, drill head ect.).

When we were trying to line bore with all the 5 mm bits, the drill head would turn on and then the machine would just stop. The tech finally figured out that it was just a tolerance issue. Feed back from the encoder was showing that the machine did not get to where it was supposed to and stopped. We often got no error at all.

Turns out it was just a tolerance setting that we adjusted in the parameters. The factory setting was something like 2 100ths of a millimeter. I bumped it up to 4 and haven't had a problem so far. (None of our customers have complained about a 0.04 millimeters intolerance either.) I can't remember exactly which parameter to change, I will look on the machine tomorrow.

This may sound crazy, but right when the drills turn on and the the machine stops, hit the side of the machine head with your hand, and it will probably go again. Just a little shake to get it that last 1/100th mm of so. These old machines need a little beating every now and again.