4th axis acting up?

[jake2465]

Yes, I could simply purchase a new set of pulleys that would give a 2:1 ratio, so the total ratio from motor to table is 180:1. I got those from Automation Direct. I imagine they have got to have a couple pulleys with the same belt type that can give that ratio.

Is it possible to see a high load on a servo during g a rapid even though it is not actually coupled to anything? I have not tried this yet, but I am wondering what kind of load I would see if I just disconnected the belt and called out some "a" moves.

[cncsnw]

Yes and no.

With Parameter 57 == 0 (so you are not using actual analog feedback from the drives), the "load meters" are actually just showing you the output of the PID algorithm. In velocity mode, that is simply the control's velocity request. It doesn't tell you anything about how much current the drive is putting out, or how much torque the motor is applying.

However, if the drive is unable to keep up with the expected move, for any reason, it will fall behind. If it falls behind, the PID loop is going to tell it to go faster, in order to catch up. If it does not catch up, the PID request will continue to increase, until it reaches maximum. This is readily apparent as a red bar on the load meter.

For what it's worth, actual analog monitoring (via Oak header pins 27 and 28, and Machine Parameter 57) does not appear to be available with the Estun drives.

[jake2465]

Ok, so it sounds like I am basically just seeing the difference between the actual position and the desired position for the PID. That's an interesting way to have it configured. So, it is entirely possible for the 4th axis servo to start lagging behind from lack of torque. Now the question is if I can beat the odds by giving the servo a 180:1 reduction to make up for the low torque, but require twice the rotation to get to the same end point. I guess there is only one way to find out.

[jake2465]

I put the order in for the change in pulleys. If anything, I am curious to see if the performance goes up.

[Sportbikeryder]

Perhaps you can just try it with half the feed rate programmed in Fusion 360? If it is just a servo overload, do you have a means of limiting feedrate to say 50% on your control? Try it and see if it solves the problem. If it doesn't, then changing the ratio likely will not solve it either.

[cncsnw]

I disagree. The torque required generally does not go up linearly with speed.

Cutting the speed in half (without changing the drive ratio) will not make nearly as much additional torque available as changing the drive ratio will make.

It is, of course, possible to limit feedrate by simply turning the feedrate override to 50%, or by changing the Max Rate value on the Machine Configuration -> Jog Parameters table. You could use either method to find out what the maximum speed is where you can rotate indefinitely without getting red load bars or a position error stall.

Jake2465 wrote:

so it sounds like I am basically just seeing the difference between the actual position and the desired position for the PID.

Not exactly. That would be just the 'P' part of PID. You also have an integral gain (the 'I' part), which contributes an extra amount that increases the longer the actual position trails behind. Optionally you could also have a derivative gain, which would have a positive contribution if the actual position were falling farther behind, and a negative contribution if the position were catching up to the target.

In addition, you have the kV1 value, which is a feed-forward term that attempts to predict how much of an output request to the servo drive will be required to perform a given move. It is kV1 which should be doing most of the work, and which accounts for the bulk of the "load meter" value during normal operation.

It does appear that you have never hand-tuned either your PID gains or your kV1 values. While performance can be tolerably good with factory-default values, you could probably get a little tighter position control using values tuned to your particular servos and machine.

[jake2465]

Perhaps you can just try it with half the feed rate programmed in Fusion 360? If it is just a servo overload, do you have a means of limiting feedrate to say 50% on your control? Try it and see if it solves the problem. If it doesn't, then changing the ratio likely will not solve it either.

The trouble is that the feed rate was already down to 12ipm. It was really odd that the machine was allowed to produce skewed pockets. That I have never seen before except on stepper motor systems that have no feedback. I am wondering if the F number for "g93" is just the desired time to produce a movement, but the control will make sure that the mill gets to it's target before moving on to the next move, or whether g93 is the primary value and the control goes on to the next move regardless if the machine reached it's target or not... I don't think it is the latter of the two because if that was the case, then the superiority of running servos over steppers to make sure the machine knows where it's at so accurate cuts can be performed would in effect be eliminated.

I plan to go and get some more round bar today and post videos of this thing making cuts at various speeds. Perhaps the results will help give a better picture of whats going on.

[jake2465]

It does appear that you have never hand-tuned either your PID gains or your kV1 values.

That is correct. I believe the technician that worked on my install did tuning work VIA serial port connection from his laptop to the Estun drives. I don't believe a whole lot was done on the control side in terms of tuning. That was the first system he had retrofitted using Estun drives that was an Oak Board. It's entirely possible that the control may have poor tuning parameters.

The "Centroid CNC Technical Support" YouTube channel put out this video for tuning DC drives:

https://www.youtube.com/watch?v=lDPyc7aYscU&t=316s

I am not sure if I can use those techniques to double check my tune with those Estun drives though. Of course, Estun uses those AC drives but I am not sure if that makes any difference when performing a PID tune.

[Sportbikeryder]

Perhaps you can just try it with half the feed rate programmed in Fusion 360? If it is just a servo overload, do you have a means of limiting feedrate to say 50% on your control? Try it and see if it solves the problem. If it doesn't, then changing the ratio likely will not solve it either.

The trouble is that the feed rate was already down to 12ipm. It was really odd that the machine was allowed to produce skewed pockets. That I have never seen before except on stepper motor systems that have no feedback. I am wondering if the F number for "g93" is just the desired time to produce a movement, but the control will make sure that the mill gets to it's target before moving on to the next move, or whether g93 is the primary value and the control goes on to the next move regardless if the machine reached it's target or not... I don't think it is the latter of the two because if that was the case, then the superiority of running servos over steppers to make sure the machine knows where it's at so accurate cuts can be performed would in effect be eliminated.

I plan to go and get some more round bar today and post videos of this thing making cuts at various speeds. Perhaps the results will help give a better picture of whats going on.

Hmmm. Looked like 25ipm in the video. How did the cut turn out in the other video running a pocket at 3ipm?

Either way, I'd try running a part at significantly lower feedrate. If that somehow doesn't reduce the torque required, so be it, but it will tell you if the control is lagging behind or if the f9999 values are causing an issue. Even with no ramped acceleration and applying full power to the servo for direction changes, Accelerating from zero to half or 1/3 of the speed you are currently commanding will result in lower loads on the drive components.
If the machine wont cut accurate geometry at 5ipm, it certainly wont do so at 25ipm.

25ipm for such a small tool in steel with the machine you are using seems to be a bit on the high side.

[jake2465]

Ok, i set it to "precision mill".