Multiple Axis' off of a single servo Amplifer?

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20 Mar 2021 02:51 #202928 by deerefanatic
Hello,

I'm beginning to do research on my Wotan Horizontal Boring mill retrofit (build thread here: forum.linuxcnc.org/30-cnc-machines/41951...-1-linuxcnc-retrofit ) and had a question about a unique situation..

The boring mill was retrofit back in the 90's to a Dynapath control. The mill has X/Y/Z axis using Allen Bradley 1388 servo amps and Brushed DC Servos. The mill also has a W axis (the spindle quill) and a B axis rotary table. But instead of having separate servo amps, they wired the machine to have a single servo amp, an then contactors to switch the power between the motors and also switch the tach generators coming into the amp. The Dynapath was wired in with a single W/B axis Enable output on it's plc, and then separate W and B enable outputs that would select which axis would be driven.

My guess is that the reason this was done is that quill movements are typically positional type movements or used for drilling/tapping cycles, thus there would never be a need for simultaneous movement on these two axis'

The real question, is this possible for LinuxCNC to control? there are Linear scales on the machine, so I think they kept track of the positioning of these two axis by referencing those.

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20 Mar 2021 13:19 #202973 by scotth
On a Devlieg we always used individual drives. For a true XYZWB configuration.
Geometrically the problem was always bar droop. You are looking at the cost of one drive and far fewer problems.

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20 Mar 2021 18:35 #203004 by andypugh

deerefanatic wrote: The real question, is this possible for LinuxCNC to control?


Yes. In fact it helps that one of the axes is a rotary, as LinuxCNC has built-in handling of brakes for rotary axes (I keep meaning to remove the limitation to rotary axes).
If you configure the changeover to be operated by the B axis "brake" (even if it isn't a brake...) so that W is active when B is stopped then it should all be automatic.

Look for "locking_indexer" on this page: linuxcnc.org/docs/2.8/html/config/ini-config.html

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22 Mar 2021 17:20 #203264 by deerefanatic
Well, that is great news, as that will save me some significant money vs buying another servo drive.. Even these Old AB servos on eBay are still kinda spendy.

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