On Mon, 2010-12-06 at 16:13 -0600, Igor Chudov wrote: ... snip > 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? > > i
My guess is that VFD's were used almost exclusively for manufacturing processes where the VFD was stand alone or on a PLC and the speed schedules were pretty simple. I think using VFD's for CNC spindle control is a fairly new thing. The newest VFD's are more complex. I have my VFD's setup so they will stop from full speed in around a second, so I have never felt the need to change it. I suppose the VFD could be set to stop in a very short time, then have a halcomponent or two keep the motion within limits you set based on the inputs you chose. But it's much easier to say than do (cheaper too). I seem to recall, one of my VFD's has a feature to control motor heating based on motor size and load, so there may be features on some VFD's that would affect braking, but not be obvious. If you have a mechanical brake, you could set the VFD to coast, but I seem to recall a thread were the brake and the VFD could conflict in some situations. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
