Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: Pythagoras on March 21, 2011, 09:34:21 PM

Title: Slave axis concerns
Post by: Pythagoras on March 21, 2011, 09:34:21 PM
I am about to install 2 ball screws on each side of an  axis.
Personally I would like to have just one drive turning both screws via a timing belt but this isnt practical.
I have two servo motors with different reduction setups.
Is it possible to use different setups for each side in a slaved setup?
If one servo stops for any reason, I can foresee massive damage. Is there a way of automatically making the machine stop if one drive does stop?
Regards Benny
Title: Re: Slave axis concerns
Post by: Hood on March 22, 2011, 03:25:23 AM
as far as I know when you slave an axis the same steps that the master is sent are sent to the slave so your slave has to be the same as the master. Your drives may have electronic gearing which could be set so they match, but if they are lower end servo drives then I would think, if they have electronic gearing, it will likely just be fixed values or possibly whole numbers that you can use for the gearing.
Regards the second question, if any of my servos trip then all the others will be halted and Mach will be informed of that fact, how you do that will depend on your drives. Mine are industrial drives with configurable I/O so its easy as I can set up outputs as fault signals and have them in a chain with the enables and also have them in a chain to tell Mach.

Title: Re: Slave axis concerns
Post by: Pythagoras on March 22, 2011, 04:22:04 AM
Thanks for your input Robin, at first I thought like you, that the same steps were sent for each axis (clone pulses), but what makes me wonder otherwise is that each motor can be set independantly for steps per mm. This makes me wonder for example, if one servo takes 1000 steps per mm and the other takes 2000 steps per mm then mach is sending indpendant pulses for each servo to travel for the set distance. But Im just not sure.

The drives I am using are gecko 340 I now see they do have a in/out error reset terminal. From my recent reading it seems like it will send a trip signal to mach, but what I cant determine is how many missed steps need to happen before the servo trips mach. In other words how much does the gantry warp before mach trips. It doesnt make me feel comfortable, easecially since the servos are geared down 40:1 and have massive torque.

This is a project I am doing with a friend. He insists on dual slaved drives, while I am fighting hard for a belt across the two screw and just on motor.

I am looking for evidence to support my case :)
I'm saying that mechanical interlock rules over electrical interlock.
Title: Re: Slave axis concerns
Post by: Hood on March 22, 2011, 04:31:37 AM
Easy enough for you to test whether slaved is same steps or not, I think you will probably find it is but just slaving an axis and having vastly different steps per in the motor tuning then commanding a move will tell you for sure. Dont even need a big move, one rev would tell you all you need to know.

Geckos used to be a fixed count error (128 i seem to recall) but now I believe they have a few settable values. Whether your drive is a new type or not I dont know as I have never really looked into Geckos much as they are too small for my applications.

No experience with gantries so I will leave the bickering in Oz  ;D