On Wed, 2007-07-25 at 14:38 -0400, John Kasunich wrote: > RogerN wrote: > > For the 850 RPM gear range, I need 2-3 second decel, for the 2800 RPM, I > > need around 8 second decel. I could use a drive input to select between > > motor 1 and motor 2 and have different decel times for the motors. > > > > Thanks > > Roger Neal > > Are you sure you really need to close the speed loop? Or would it be > sufficient to simply send the appropriate command to the VFD? > "Appropriate" means that it has been corrected for the gear ratio for > whatever gear you are in at the moment.
When I first read this, I thought you would need feedback to do CSS (Constant Surface Speed), but I guess that is not true. You would only need feedback in situations where the commanded speed and the actual speed could be far enough apart to be considered out of tolerance, or if you needed to position the spindle for milling operations. I wonder if a VFD could be used for positioning? I am guessing that if the spindle speed varies more than a handful of percent from the commanded speed, the motor will stall. I would be interested in hearing anyone's experience with this. > If you can mount a switch to your machine that is actuated in one gear > (ideal), or if you are willing to click a GUI button to tell the system > what gear you are in, its not that difficult in HAL to generate two > speed commands, one for each gear, and route the appropriate one to the > DAC and then to the VFD. I am planning on using the Hardinge HNC codes M03 - Low Clutch and Motor Forward, M04 - Low Clutch and Motor Reverse and M43 - Low Clutch and Motor Forward, M44 - Low Clutch and Motor Reverse. Although, for the short term (probably forever) I will use one of the M62-5 or M100-199 codes. I am happier keeping it simple and commanding the (motor) speed and gear, and then, taking the active gear ratio into consideration in the programming. > That's what we do for the Mazak at the CNC workshop, but we went one > step farther there - we have classicladder logic that actually does the > gear change sequence. The Mazak has hydraulics to shift the gears, and > prox switches to tell what position the shifter is in. The HAL/Ladder > config we have automatically slows the motor to 15 RPM, then shifts to > neutral, shifts into the new gear, and accels to the final speed. > > Regards, > > John Kasunich ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
