15HP motor drive, vectorless at 300hz? 1

[fastline12]

We are still trying to decide an economical solution for a CNC machine spindle to get better torque regulation from it. Right now it runs a 7.5HP 4 pole motor with a 15HP Magnetek drive in V/Hz. When cutting material, it pulls down very bad and will stall easily because the drive has no clue other than the current to the motor but does nothing about it. We purchased an older but new Mitsubishi drive for it planning to run it in sensorless vector but then found out that drive is only good to about 150hz in sensorless. It has the encoder feedback card so we were going to do that but then found out it can't do that either....


Is sensorless or encoder feedback at 300hz a specialty application for drives? I am still trying to determine if we can mount an encoder direct to the motor but I do know there is already an encoder that is on the other side of the transmission used for rigid tapping. Why it is not direct on the spindle, I will never know. However, I would sure like to use the output of that encoder for the drive BUT there seems to be a question if that will be a problem for the drive or control? I can't see why a pulse train of 1s and 0s from the encoder could not be shared but maybe I am missing something. However, I DO know the encoder is NOT 1:1 with the motor shaft and not sure if that would be the main issue.


As well, I am trying to determine drive sizing for this application. I can tell you that typically machine tool spindles have a bigger drive to get better accel and decel which is what I am after as well. Faster in every way. I will have to install a thermal sensor on the motor though. Might be easiest to run that back to the drive.

 

[jraef]

The term "spindle motor" bundles a number of design criteria into a simplistic name, because it implies a high speed motor which presents a lot of challenges compared to a general purpose motor. Mechanical forces at high RPMs are very different, so material selection and manufacturing methods become much more critical. Lubrication, cooling, bearing design, tool holding capability of the shaft, all of that goes into it to make them very different.

As to the heat dissipation, although what you see on the outside appears plain, inside there is a highly engineered air flow design typically using channels and/or labyrinths.

"Will work for (the memory of) salami"