On Mon, 6 Dec 2010 16:13:15 -0600, you wrote: >I have used many VFDs, but in all of them the stopping time is >programmed in terms of seconds. > >This does not translate well into operating machine tools with >multiple speeds. On such tools, slowly rotating spindle can be stopped >quickly and more time is needed to stop a fast rotating spindle. If >frequency is decreased too rapidly, the VFD would fault out on >overvoltage on the DC bus. > >Why don't they have VFDs with adaptive stopping cycle, so that they >reduce the frequency to maintain high bus voltage (to be dumped into >the brake resistor), adaptively, as opposed to mindlessly doing it on >a predetermined linear scale?
Have a look at Telemechanique Altivar Series. Linear acceleration or deceleration ramp times are from .1 to 999.9 seconds. They also have S, U or custom ramp and multiple ramp switching. If you set the decel ramp to a very short time, they can automatically adapt the ramp function to prevent faulting. They use DC injection braking on the above functions, not Braking resistors. Braking resistors don't lend themselves well to fancy behaviour and are more suited to stopping high inertia fixed speed machines in a given time. Steve Blackmore -- ------------------------------------------------------------------------------ What happens now with your Lotus Notes apps - do you make another costly upgrade, or settle for being marooned without product support? Time to move off Lotus Notes and onto the cloud with Force.com, apps are easier to build, use, and manage than apps on traditional platforms. Sign up for the Lotus Notes Migration Kit to learn more. http://p.sf.net/sfu/salesforce-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
