On 08/06/2013 08:17 AM, Stephen Dubovsky wrote: > On Tue, Aug 6, 2013 at 9:41 AM, dave <dengv...@charter.net> wrote: > >> Too early in the morning and still on first cup of coffee but: if you are >> within the 1/4 >> step (null) then increased feedback of some kind won't fix it. >> > > It does fix it. The feedback will cause the control loop to shift the > commanded position away so that you ARE on the upslope of the torque > curve. Its fundamentally how servos work. You need to develop > Q(quadrature) current(flux) to get torque. The D(direct) current doesn't > do any work. Technically, once you have feedback in a stepper system you > can fully servo it and not require any 'holding current' if the application > doesn't currently demand it. The fixed current most stepper drivers use is > only because they don't know where they are in the DQ frame. So they > provide a ton of D and shaft error shifts the angle to produce some Q.
With much study, a fair amount of work and money, one 'could' get a stepper to act like a servo (except for the rapid torque fall-off at higher speeds, and resonance zones within the operating RPM range). But why bother when a real servo acts just like a servo? In my opinion, steppers fill a need for lower cost, and simplicity. If one needs to add complexity or cost to a stepper to get it to work, just use a servo. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/ ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite! It's a free troubleshooting tool designed for production. Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
