Anders Wallin wrote: >> I would like to fit a VFD to the spindle of my 3 axis mill. How should I >> set about controlling it? Apart from obvious speed control, I would >> like to achieve oriented stop (boring and tool changer) I am currently >> using an m5i20 and m7i33 under EMC 2.1.6. > > How you control the VFD will depend on what control options your > particular VFD has. Some older ones have a 0-10V analog input and one > digital input for start/stop and another for forward/reverse. > > I'll be interfacing EMC to a new VFD soon and I'm hoping to use its > pulse train input so I won't have to mess around with digital to analog > conversion. > > oriented stop will require an encoder on the spindle, and probably the > VFD has to work in some kind of position-mode. Doable with a modern VFD > but could be harder with an old one. > The encoder will give you rigid-tapping capability too! (and you can > follow how much rpm drops under load)
A spindle encoder (with index pulse) is definitely needed for oriented stop. Most VFDs have a speed command input, +/-10V or otherwise. When running normally, you send EMC's spindle speed command to the VFD (thru a DAC or equivalent). When doing a spindle orient, use a HAL mux2 block to disconnect the VFD from EMC and connect it to the output of a PID loop. The PID block takes the encoder position as feedback, and uses a constant value as its command. It sends speed commands to the VFD to make the encoder position match the commanded value. That's what we did for spindle orient on the Mazak at the CNC workshop, and you can view the HAL files as part of the "demo_mazak" sample configuration. The demo mazalk config has some additional HAL and ladder logic to handle gear changes (it has a two speed gearbox with neutral). The motor speed command is derived from the spindle speed command by running the command thru a pair of scale blocks. One block calculates the motor speed for low gear, the other for high gear, and a mux switches between the two. The mux also sets the motor speed command to 15 RPM during gear changes - the motor needs to be turning slowly to let the gears mesh. It is very unlikely that the demo mazak config is exactly appropriate for any other machine, but it is an example of what can be done. Regards, John Kasunich ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
