<snip> > Arturo has finally realized that the so-called reversing > relay lashup he > has on the C41 is worthless because it cannot be controlled > independently, > instead dropping out a few milliseconds after the PWM stops. > That will > destroy motor controllers and may damage the PM field magnets > when the > controller suddenly sees a motor it thought was turning 7 > grand in reverse, > suddenly being put in the fwd mode with no time to brake it, > and the analog > from the PWM has not decayed to zero yet. > > I think your 106 also does this as I put a dropout delay in > the .hal file > for my mill, and that did not stop the controller from > thumping the motor > pretty hard when I issue an M5 to stop the tool from about 250 rpm in > reverse, which I use, along with a G38.2 command to find the edge of > something. The slowly turning bit makes a good contact (I > have a .2 uf cap > across the probe so it "stores" the momentary contact without > touching the > work hard enough to mark it) > > So the next run of C41's he makes will do the reverse as long > as commanded > from its input. > > FWIW, that is not a problem with the 106 when running it from > the hand > switches, then it works correctly, but then my dynamic > braking there is > resistive. <snip>
I have a somewhat different viewpoint on how the interface is intended to work. The job of the interface is to supply control information to the motor driver representing the desired operation of the CNC program. It is the motor driver's job to assure that the drive electronics does what is reasonable for the motor that it runs. Using the direction command requests from the interface to directly control relays that switch the high current armature leads of a DC motor is not workable for a general purpose interface. The most common type of control interface for VFDs and high power DC motor drivers is one that accepts one switch that closes when forward run is desired and one switch that closes when reverse run is desired. This interface must open both switches to indicate stopping the motor. The alternative Run and Direction (European style) interface could accommodate holding the direction signal while stopping the motor, but that still ignores the issue of how long the control interface must be stopped before it is safe to request running in the opposite direction. VFDs and DC motor drivers with internal reversing circuits take care of the requirements to safely reverse the motor in response to their command inputs without expecting the command generator to follow any special rules. A special interface that accommodates reversing DC motors by controlling a relay that reverses the armature leads could be done, but it is not trivial due to the stored energy and the need to brake the motor. The market share of DC motor drives relative to those powered by VFD driven induction motors is small and we have not addressed it directly. Steve Stallings ------------------------------------------------------------------------------ Try New Relic Now & We'll Send You this Cool Shirt New Relic is the only SaaS-based application performance monitoring service that delivers powerful full stack analytics. Optimize and monitor your browser, app, & servers with just a few lines of code. Try New Relic and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
