On Wed, Feb 26, 2014 at 3:58 PM, Gene Heskett <[email protected]> wrote:
> > That is generally a no, unless the stepper is running in idle mode. > > The problem is the negative torque curve of the stepper vs its speeds, > meaning that if it slips a cog, it will be stopped as its in-capable of > resuming the speed it was moving at when it failed by re-accelerating to > that speed in a single step. All the feedback obtained from the encoder > can do is attempt to speed it up to catch up, and its not capable of that > while under the load that caused it to slip that cog in the first place. > > The best you can do with the encoders feedback is to use its error should > the motor slip, to exert the fastest possible e-stop and hopefully save the > part. If the part isn't damaged, then you'll need to rehome the machine > and re-start the operation, running at a slower rate by sliding the > feedrate knob to slower as that portion of the operation is being re- > approached, hoping it will get thru the hard cut the next time. > > That said, I think there have been some attempts to use it, and you will > find some discussion of it in the wiki. I have read it myself several > times without fully understanding how it was used to dynamically rehome the > slipped axis to get it back in step even after slowing the rest of the > machine so it might be able to catch up with the rest of the machine now > running slower. > > To me it seemed like a lot of expense and complexity for a limited CYA > gain. Far better off to slow the operation to within the steppers > abilities and/or raise the voltage on the drivers so the torque falloff is > not as pronounced. > > I was nicely amazed by the speeds I could get out of my lathe, whose motors > are running on around 37 volts, compared to the same motor and driver on my > mill but running at 28 volts. A finicky 30 ipm on the mill, vs a rock > solid 60 ipm on the lathe just by going up 9 volts. A side effect of the > higher voltage on that particular driver, a 2M542 from fleabay at around a > $50 bill a copy, is that this driver runs cooler at the higher voltage. > > But look it up on the wiki & make up your own mind. I'm just the resident > retired old fart. ;-) > > > > Cheers, Gene > Gene pretty much nailed it. If you're going to try an cob together something that tries to talk like a servo, walk like a servo, and maybe quack once in a while, you might just as well skip the cobbing and use a servo. Or not worry about it, and use the stepper within it's capabilities. Mark ------------------------------------------------------------------------------ Flow-based real-time traffic analytics software. Cisco certified tool. Monitor traffic, SLAs, QoS, Medianet, WAAS etc. with NetFlow Analyzer Customize your own dashboards, set traffic alerts and generate reports. Network behavioral analysis & security monitoring. All-in-one tool. http://pubads.g.doubleclick.net/gampad/clk?id=126839071&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
