Plasma table

[m_c]

Could it be that due to tuning/resonance, the motors are ending up driving each other, with a resulting over voltage?
I'd try adding braking resistors. If you're desperate to get up and running, I have a selection waiting for my next retrofit, which you could borrow if there's a couple the right size.

 

[Hood]

Could it be that due to tuning/resonance, the motors are ending up driving each other, with a resulting over voltage?
I'd try adding braking resistors. If you're desperate to get up and running, I have a selection waiting for my next retrofit, which you could borrow if there's a couple the right size.

The tuning is the same as before so not sure why it would just start doing it. Granted there is less weight on that axis than before so I suppose it could be something to look at if I still have problems tomorrow.

The drives don't have shunt circuitry in them so active shunts are required, I have 3 spares here so I will try them tomorrow.

 

[henry Kadzielski]

^^^^ I feel your pain. It was working perfectly before the move, what has happened to cause this . This is the very frustrating part of doing these things. Then you think why did I touch this when it was working. Knowing full well that the changes are required for a better table

 

[Hood]

Could it be that due to tuning/resonance, the motors are ending up driving each other, with a resulting over voltage?
I'd try adding braking resistors. If you're desperate to get up and running, I have a selection waiting for my next retrofit, which you could borrow if there's a couple the right size.

You could be on to something regarding the tuning.
I tested this morning to make sure I still had the fault and after a while it showed up. I then removed the belt and the pinion from the port side and ran up and down at least 20 times and no problem. I have now un-slaved the port motor and again it is running fine.

With the gantry now being a good bit shorter than before I am thinking I may get away with running from one side so I will test it out and see. If it is ok then that is good as it gives me a spare servo drive and motor. If it is not then I can hook it back up and try tuning.

I wonder what the other tables wit an 1800mm or so span gantry have, do they have a slaved motor or are they just running a single motor? I will have to investigate.

 

[Hood]

Ok I have done some tests, if I push the gantry with the motor holding the other side I can move it about 1mm either way but as soon as I release the pressure it goes back to within +/- 0.10mm and as soon as I jog one way or the other it comes back to +/- 0.02mm so I think it should be fine. Homing and then doing a rapid onto the clock and it reads +/- 0.02mm, jogging off then doing short sharp back forth moves then rapid back to the clock and again +/- 0.02mm max, so far it looks like it will work well and it has given me an extra 250mm space at the opposite side now that I have removed the motor/pinion etc.

 

[Hood]

After the servo problem and getting around it by removing the slave motor, things have gone well today.

I got a single phase switched socket fitted for the compressor, also got the 3 phase one properly fitted.

I got the compressor and dryer connected up.

The PC had been bolted to the outside of the control cabinet but due to its position it would be right beside the door and exposed to rain blowing in. I decided to relocate it to inside the cabinet so it is now bolted to the door. Still have to tidy the wiring.

I got the arm for the plasma torch lead fitted.

Bolted the stool I had previously made for the Jasic to the wall, it keeps the Jasic out of harms way. I am waiting on P Clips so I can keep the cable from being caught in the gantry. I will also have to extend the control wires to the cabinet and get them fitted across the roof and also get a 3 phase socket run to the plasma. Oh, also need to extend the air hose.

Vid of the axes running to all extents to make sure the plasma cable can reach and the arm swivels as it should.

 

[henry Kadzielski]

^^ It does seem strange that you had a heavier gantry and all was working fine and a lighter one is causing drives to trip. I went from a reasonably heavy gantry (in comparison to others out there) to a much heavier and doubled my speed almost. I did have tripping on deceleration, now when I think about it when the speed was about 25m/min on the rapids. I set it about 20m/min as it was shaking the table with the inertia, also 20m/min is really fast enough. When I watch it doing it's rapids it does seem quite fast

 

[Hood]

I have my X and Y axes set at 20m/min, it was the same on the last table. Yesterday I tried reducing both accel and rapid speed but it didn't cure the issue.
I think @m_c may be correct in that it is the tuning as it wasn't tripping when decelerating, it was tripping with the axis in full flow, it also occasionally tripped when I was moving via MPG. As it seems to be working well with one side driven I will leave it that way and if through using I discover it is not accurate enough then I will put the motor back on and do some tuning.

 

[m_c]

Servo tuning is highly dependant on inertia. By running a lighter gantry, there is less mass, so the inertia load is reduced, which will make tuning more unstable.
There is also the added complexity that the gantry is narrower, which means it'll likely be stiffer, so there won't be the same flex between the motors.

Out of curiousity, are you running the servos in speed/torque mode, or step/dir?

 

[Brad93]

I wonder if my table has one motor or two.

 

[Hood]

Servo tuning is highly dependant on inertia. By running a lighter gantry, there is less mass, so the inertia load is reduced, which will make tuning more unstable.
There is also the added complexity that the gantry is narrower, which means it'll likely be stiffer, so there won't be the same flex between the motors.

Out of curiousity, are you running the servos in speed/torque mode, or step/dir?

Step/Dir on the plasma

 

[m_c]

Step/Dir on the plasma

I would have thought step/dir would be a bit more tolerant of this.
Did you match the rack teeth side to side? I wonder if the fact straight cut rack and pinion doesn't give perfect rotation to linear movement, is contributing to resonance at speed which the servos are then fighting each other against.

Regardless, it's only a plasma cutter, so single side drive should be fine.

 

[Hood]

I would have thought step/dir would be a bit more tolerant of this.
Did you match the rack teeth side to side? I wonder if the fact straight cut rack and pinion doesn't give perfect rotation to linear movement, is contributing to resonance at speed which the servos are then fighting each other against.

Regardless, it's only a plasma cutter, so single side drive should be fine.

It is bevel rack/pinion

 

[Hood]

That pic of the rack doesn't really show it is bevel, this one is better.

 

[Brad93]

That pic of the rack doesn't really show it is bevel, this one is better.

View attachment 263622

Bet that’s not cheap to buy

 

[Hood]

Bet that’s not cheap to buy

I would imagine it to be rather expensive, thankfully it cost me nothing

 

[henry Kadzielski]

I know what the straight gear was cost wise, so from memory here the helical was over double. It would be the only thing that I would change if I ever did another one. Much smoother action and quieter running as opposed to straight. Since I already had all the pinions, which were also already bored and half the rack to complete it was a no brainer, coupled to the fact that I was running out of funds. Any one who has built something like this will know that there are costs and hidden expenses that you aren't aware of at first. As you build you discover better and or improved ways and additional features that you wish to incorporate whilst building, so costs go up

 

[northwest]

It is bevel rack/pinion

Very reasonable.

 

[Hood]

Now that I have had to move the table over to the opposite side and also have it further into the container I am thinking it may be more awkward for me to load sheets myself.
Sitting at home with the cogs turning slowly I have come up with what I think may work.
It is made from 50mm x 3mm wall SHS Aluminium and will have 4 castors on it to wheel it into place.

Hopefully I will not need it but I might as well have something planned if I do.

Anyway a screen grab of what I have come up with, I may be able to simplify it a bit after some thought but it should work as is.

An animation showing how I envisage it working.

 

[RichardM]

Is it a loading table to fit at the end of the plasma and then roller the sheets into place on the plasma table?

Would it be better with a longer supported length tilting, just thinking of possible kick up when the sheets go over CoG