Tricky setup of VFD on machine tool spindle. Mits A500
Tricky setup of VFD on machine tool spindle. Mits A500
(OP)
Due to a drive failure today, we are installing a replacement A500 VFD. We planned to review this application more before attempting but hand is being forced due to down time.
The installation is very straight forward but this machine orients the spindle for a tool change by commanding a low rpm (approx 40rpm)while pushing a shot pin at a collar with a slot in it to lock the spindle in place. The way it was designed, when the pin falls in, there is an immediate signal to the drive to halt operation. However, the previous drive was a V/Hz drive with no knowledge of rpm. The new drive will be operated in sensorless vector mode and the concern is if the drive can out power this locking mechanism and damage it if signal to stop is not received very promtly.
Obviously there is too much being left out here to really say but I am more or less asking if other machines are doing something similar successfully with a sensorless system? Or even encoder feeback system. maybe the sensorless system in the A500 is slow enough to react to the stop? The motor would be spinning fast enough to develop full torque at these speeds.
The installation is very straight forward but this machine orients the spindle for a tool change by commanding a low rpm (approx 40rpm)while pushing a shot pin at a collar with a slot in it to lock the spindle in place. The way it was designed, when the pin falls in, there is an immediate signal to the drive to halt operation. However, the previous drive was a V/Hz drive with no knowledge of rpm. The new drive will be operated in sensorless vector mode and the concern is if the drive can out power this locking mechanism and damage it if signal to stop is not received very promtly.
Obviously there is too much being left out here to really say but I am more or less asking if other machines are doing something similar successfully with a sensorless system? Or even encoder feeback system. maybe the sensorless system in the A500 is slow enough to react to the stop? The motor would be spinning fast enough to develop full torque at these speeds.





RE: Tricky setup of VFD on machine tool spindle. Mits A500
Or would that be too hard to teach an old dog new tricks as it were?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Tricky setup of VFD on machine tool spindle. Mits A500
RE: Tricky setup of VFD on machine tool spindle. Mits A500
Lione - torque limiting is something we really need that this point but again does not look like we are going to have any type of extra signal to the drive at tool change from the control. The old v/hz drive would not have power at these speeds anyway so it was a non issue. I will double check though.
RE: Tricky setup of VFD on machine tool spindle. Mits A500
In addition, you should also be able to program a torque trip, meaning what could be desctibed as an "electronic shear pin" where if it sees an immediate increate in torque, as in the locking pin dropping in and locking the shaft, it will immediately shut down. I could do this for you on several other brands of drives (Rockwell comes to mind, but that's because they sign my paycheck...), but I would be highly surprised if the Mitsi is incapable of this. You need a good Mitsubishi drives expert.
Or a different brand of drive...
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RE: Tricky setup of VFD on machine tool spindle. Mits A500
RE: Tricky setup of VFD on machine tool spindle. Mits A500
RE: Tricky setup of VFD on machine tool spindle. Mits A500
Jraef, my concern with a torque limit is how the drive would otherwise perform in acceleration? IE, if we programmed a "less than 40" rpm reduced torque, every time the spindle accelerates, it would push from 0-? rpm. Would this affect acceleration or am I misunderstanding how the torque limits work?
RE: Tricky setup of VFD on machine tool spindle. Mits A500
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RE: Tricky setup of VFD on machine tool spindle. Mits A500
There is a section that will allow limits during accel, constant, and decel but I am inclined to think that if I only use the constant speed limiting, we really don't know when the shop pin would fall in and might be during spindle accel which could prove problematic.
So would it be reasonable to consider the drive would look directing at the commanded speed to validate the torque limit? IE, if limit is set to 40rpm and below and I command 50rpm, it would drive right through the limits to get to 50rpm?
Again, I realize not a Mits expert but I tend to think most drives would respond similar.
RE: Tricky setup of VFD on machine tool spindle. Mits A500
Keith Cress
kcress - http://www.flaminsystems.com
RE: Tricky setup of VFD on machine tool spindle. Mits A500
There must be some kind of signal to control the alignment pin. Why can't that signal be used to kick-in a reduced torque mode.
RE: Tricky setup of VFD on machine tool spindle. Mits A500
I would prefer not to create problems when tapping. As it is now, a 1/2x13 tap struggles when coming out of material due to the very low torque.
RE: Tricky setup of VFD on machine tool spindle. Mits A500
But, assuming we go for broke, signal to the drive to halt (or coast stop) is given only with the delay imposed by the switch which I will assume is deadly fast being a limit switch. So let's assume 10-20ms, Could the drive really even react in that amount of time to a stalled spindle? Speaking generally of course.