On 03/12/2016 10:12 PM, Gene Heskett wrote: > Greetings everybody; > > Given that I note the vfd's seem to have an adjustable accelleration > control, and that my couple of hours playing with it from its own front > panel, I am led at ask the question of just how fast can one of these > things be reversed from say 1000 rpm at the motor spindle? > > I ask because my present setup, using the OEM PM DC motor which is all > gear drive to the spindle, one of Jons pwm servo amplifiers and a 125 > volt dc supply, reversals at the turn around depth of this cycle of a > peck tapping operation, with the spindle doing 300 rpms, is a very small > fraction of a second, far less than 30 degrees of rotation. Based on > its reversal performance at 2500 rpms being a slim second, I am > concerned that the vfd may not be able to reverse so quickly, and will > impact my use of G33.1 because of the turnaround over shoots. On my > lathe, with its fragile drive train and a 5" chuck, this overshoot is > between 2 and 3 turns at 250 running rpms. Usable, but if I don't stop > it soon enough, the tap may bottom out and break. > > A strong VFD that doesn't have to current limit during the reversal, can reverse quite quickly. Our shop at work has 480, and their Bridgeports reverse so quickly you can't even hear it. (That's "plug reversing" off the mains, not a VFD.) I had to slow DOWN the reversal on my Bridgeport to make sure my Z axis could follow the reversal. I generally rigid tap with the spindle belt set on the high speed groove, so that the motor is running at about 20 Hz. It reverses much better in that case, as the motor's rotational inertia is dominant. In the case of a lathe, the chuck may be dominant, so this trick may not give as much advantage. I think I get the reversal done in about one rev, maybe less, I haven't really checked. (One could figure it out easily with Halscope looking at the spindle encoder.)
The VFD needs to have a braking resistor to do this reversing properly. Jon ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785111&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
