Hi Mick,
kool.

Nice to know they back their gear, of course it would be nicer that it didn't blow in the first place,
but replacing it without question comes a close second.

Craig

Totally agree.
Going back to the spindle debate. What do you think about using 2 X 1.5kw motors on the spindle? Instead of a 3kw 3 phase.
Cheers

Hi,
why?

First: two 1.5kW servo drives which have the same power factor as one 3kW drive will draw the same current.

Second: if the motors were running in torque or velocity mode then its probable you could get them to share the load.
If running a closed position loop then they won't share the load, one servo will always be a few arc minutes ahead (or behind)
its partner and will therefore have to provide the lions share of the effort.

Third: is the price of two 1.5kW servos and drives cheaper than one 3kW servo and drive?. I think the price would favour one large
servo/drive. DO NOT LET THE MISSUS READ THIS OR YOU ARE SUNK!!!

Craig

Hi Craig

First: two 1.5kW servo drives which have the same power factor as one 3kW drive will draw the same current.

I'm not concerned about the power factor.

Second: if the motors were running in torque or velocity mode then its probable you could get them to share the load.
If running a closed position loop then they won't share the load, one servo will always be a few arc minutes ahead (or behind)
its partner and will therefore have to provide the lions share of the effort.

Can you expand on this?

Third: is the price of two 1.5kW servos and drives cheaper than one 3kW servo and drive?. I think the price would favour one large
servo/drive. DO NOT LET THE MISSUS READ THIS OR YOU ARE SUNK!!!



The price is very similar.

The thing that is bugging me is the phase converter. The company I bought it from are no longer selling these units. They still offer a repair service at the moment but not sure how long for. What I can sell the phase converter for would go a long way to paying for the spindle set up. Old ground but if I wanted to sell the lathe it would be more saleable as a single phase machine. No, I'm not thinking of selling it.

Just exploring and want to make sure I cant use single phase set up before ordering the 3 phase motor and drive.

Mick
 

Hi,
imagine for instance that one servo is mounted 1 degree rotated in its mount relative to its
partner.

When trying to share load when executing an indexed move (position), the leading servo will try to be at 90⁰
at moment t=nnn.nnn and likewise servo 2 will try to be at 90⁰ at the same time. However the leading
servo will actually be at 91⁰ at time t=nnn.nnn. The trailing servo will treat this as the load advancing
on its ideal commanded position and therefore try to retard the leading servo.

This was an artificial construction to illustrate the idea, but any two position servos will inevitably be slightly different
to each other, and if that error differs by more than the 'zero error window' they will fight each other.

In torque they should share equally. In velocity mode imagine one servo is programmed to be a fraction faster than the other.
Which servo powers the load and would not the slower servo be dragging the faster one? There again I have made a
worst case to illustrate the idea but two velocity servos are never going to be identical. What happens to load
sharing then?

I'm not concerned about the power factor.

Yet!!!

Craig

Hi Craig

Makes sense.

Cheers
Mick

Hi,
if you want 3kW single phase then go Allen Bradley 2098-DSD-030 and matching servo and
be prepared to pay extra for the line reactor/filters.

It is the biggest single phase servo drive I know of.

The only other alternative is to strip the DC link circuitry off a three phase 230V drive and make your own DC llink,
you will almost certainly need buck/boost PFC correction beyond 3 kW but in theory you could make it whatever
 size you want

Craig

Wouldn't be the way I would go (2 motors)  and not sure if your drives support it but if they do then slaving the second drive to the master may work.
Could be called Master/Slave, Electronic Gearing, Master/Follower etc.

Hi Hood,
master/slave works really well on a gantry say with two ballscrews but Mick is talking about
having two servos locked together on one shaft. I think thats a good way to generate a lot
of expensive smoke.

Craig

I am talking about it being done in the drives rather than Mach, one drive controlled from Mach, the second follows the first by using master/follower mode..
I once messed about with it and the AB drives and it worked well, was sync'ing a live tool to the spindle for cutting Hex etc, can't recall the name of it at the moment, so not the same thing as being proposed here.
As said though it is not a route I would choose, just inviting issues to rear their ugly head.


Edit, Polygon turning was the thing I was trying to remember the name of. Not relevant to this discussion other than I used Follower mode for it.