2 Attachment(s)
VFD Recommendations for Robotool retrofit
HI all, I am looking for some solid VFD recommendations for a retrofit I am planning out. I wouldn't mind learning a bit about whats important to have in a VFD as well. From what I have read it seems like a vector sensorless drive is desirable for low speed power requirements.
Something I am a little fuzzy on is the breaking aspects built into these drives. Most of the VFDs i have looked at seem to say they have some braking capability, some suggest a braking transistor might be required, but then some suggest it is not necessary in smaller HP ratings.
These are a couple of the drives I am looking at. The Hitachi WJ200 seems to come up a lot, so that could be an option. The spindle motor on my machine is an 8.6 amp, 3 phase, 1720 rpm motor.
https://www.wolfautomation.com/revie.../category/165/
https://www.precision-elec.com/shop/i51ae222b10011000s/
The RoboTool also has an airbrake hooked up to the spindle. Would it be advisable to use the VFD for braking and remove the airbrake? or use the airbrake and not use the VFD braking function?
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
WesM
HI all, I am looking for some solid VFD recommendations for a retrofit I am planning out. I wouldn't mind learning a bit about whats important to have in a VFD as well. From what I have read it seems like a vector sensorless drive is desirable for low speed power requirements.
Something I am a little fuzzy on is the breaking aspects built into these drives. Most of the VFDs i have looked at seem to say they have some braking capability, some suggest a braking transistor might be required, but then some suggest it is not necessary in smaller HP ratings.
These are a couple of the drives I am looking at. The Hitachi WJ200 seems to come up a lot, so that could be an option. The spindle motor on my machine is an 8.6 amp, 3 phase, 1720 rpm motor.
https://www.wolfautomation.com/revie.../category/165/
https://www.precision-elec.com/shop/i51ae222b10011000s/
The RoboTool also has an airbrake hooked up to the spindle. Would it be advisable to use the VFD for braking and remove the airbrake? or use the airbrake and not use the VFD braking function?
You can't use the air brake to stop the spindle, when using a VFD you will burn it up, but you will need your brake, to hold the spindle when you change the tools
The VFD if you want to stop fast, then you will need a Breaking Resistor, this has nothing to do with what size the VFD is or the motor Hp, you have a lot of spinning mass, in the head of these machines, so if you want to stop fast, then you will need a Braking Resistor, any general purpose VFD will do what you need
To help slow the spindle down you can use some DC Braking, this is a parameter you can set in the VFD
Re: VFD Recommendations for Robotool retrofit
The LG drive says it has a braking transistor built in, would that be functionally the same as the braking resistor?
https://www.wolfautomation.com/products/ac-drives/ac-drive-200-240v
EDIT: Found the answer to my own question, which is no they are not the same.
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
mactec54
You can't use the air brake to stop the spindle, when using a VFD you will burn it up, but you will need your brake, to hold the spindle when you change the tools
Hi mactec54,
Only asking for my own learning experience...
If you set the VFD parameter to coast to stop, will this still cause and ill effect to VFD ?
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
Dan911
Hi mactec54,
Only asking for my own learning experience...
If you set the VFD parameter to coast to stop, will this still cause and ill effect to VFD ?
Obviously Mactec will be the authority on this. But if im not mistaken damage will only be caused to the VFD if the voltage generated from the braking action exceeds the voltage rating of the drive. So coasting to a stop should not endanger the drive under normal circumstances.
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
WesM
Obviously Mactec will be the authority on this. But if im not mistaken damage will only be caused to the VFD if the voltage generated from the braking action exceeds the voltage rating of the drive. So coasting to a stop should not endanger the drive under normal circumstances.
Thanks WesM
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
Dan911
Hi mactec54,
Only asking for my own learning experience...
If you set the VFD parameter to coast to stop, will this still cause and ill effect to VFD ?
No it will not cause any problems, just takes a little longer to stop
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
WesM
No the built in braking resistor can only control around 50%, with a external Braking resistor you can get as much as 150% to 200%
Almost all VFD drive of any quality have a built in Breaking Resistor
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Re: VFD Recommendations for Robotool retrofit
Dan the Lenze manual I was just reading through gave a decent summery. I would advise looking through your specific VFD manual and see how they suggest managing the braking.
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
WesM
Dan the Lenze manual I was just reading through gave a decent summery. I would advise looking through your specific VFD manual and see how they suggest managing the braking.
You have to understand that you can't use a VFD braking function on all AC motors, the motor will fail after a short while when using Dc injection for stopping on a standard AC motor, that is why they build inverter duty motors, a standard AC motor, can only use about 20% of what is available, the motor on your machine is Chinese made and I would rate that even lower than the 20% to be safe
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
mactec54
You have to understand that you can't use a VFD braking function on all AC motors, the motor will fail after a short while when using Dc injection for stopping on a standard AC motor, that is why they build inverter duty motors, a standard AC motor, can only use about 20% of what is available, the motor on your machine is Chinese made and I would rate that even lower than the 20% to be safe
Hey its Taiwanese! haha joking aside...
How would that apply to dynamic braking? If using an external braking resistor could I get it down to a lower RPM (maybe 300-400 RPM?) using dynamic braking and then kick in the DC injection braking? I wish there were some speed tests to compare different VFD braking techniques. I wont really care about stopping the motor in 1 second... but maybe 5-6 seconds?
Re: VFD Recommendations for Robotool retrofit
It would proabaly coast to stop in 5 or 6 seconds, I have mine set for 3 second stop.
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
WesM
Hey its Taiwanese! haha joking aside...
How would that apply to dynamic braking? If using an external braking resistor could I get it down to a lower RPM (maybe 300-400 RPM?) using dynamic braking and then kick in the DC injection braking? I wish there were some speed tests to compare different VFD braking techniques. I wont really care about stopping the motor in 1 second... but maybe 5-6 seconds?
Every application is different, in your case you have a lot of rotating mass, this takes a lot more time to slow down, than a motor and pulley or a direct drive motor, each system is completely different, and you setup a VFD to suit your motor quality and what you are wanting to do with it, a regular motor like what you have was not designed to be run with a VFD, but they will, and last for years, if not over stressed, by expecting more out of the motor than what it was made to do
Taiwanese !! do you think there is any difference in quality :)
You can get those times with normal Deceleration Parameter settings, no other help needed
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
mactec54
Taiwanese !! do you think there is any difference in quality :)
You can get those times with normal Deceleration Parameter settings, no other help needed
That should work then, I may play around with my VFD settings and see if I can shave a second or two off without stressing the motor, but thats not a priority.
Far as Taiwan goes, it depends on the industry in my experience. Some stuff that comes out of Taiwan can be top notch, other stuff not so much. This Robo has great iron and nice ground ballscrews. knee travel is the smoothest I have seen on a knee mill to date and the general quality of components seems to be pretty decent. I'm interested to see what kind of tolerances this machine can hold once I get it up and running.
Re: VFD Recommendations for Robotool retrofit
Quote:
Originally Posted by
WesM
That should work then, I may play around with my VFD settings and see if I can shave a second or two off without stressing the motor, but thats not a priority.
Far as Taiwan goes, it depends on the industry in my experience. Some stuff that comes out of Taiwan can be top notch, other stuff not so much. This Robo has great iron and nice ground ballscrews. knee travel is the smoothest I have seen on a knee mill to date and the general quality of components seems to be pretty decent. I'm interested to see what kind of tolerances this machine can hold once I get it up and running.
I agree Taiwan had a head start, but anything like this from China is just as good now in quality, for the same item, you just have to shop for the best components you can find, I have a Chinese made mill like your mill, 15 years old, and all the ways are ground, it has been a great manual mill, as far as machining accuracy goes, most mills like this don't do much better than .0005" I have one that will hold .0001"on machined parts, but this mill which is similar to yours, has the best of everything, to make this happen, so if your Ballscrews are a C5 Grade, which may not be, the best you will get over a 300mm travel is .0005" with everything else in perfect condition, the motors and encoders you have also will play a big part of what your machines part accuracy will be, this is your weak link, with what you have at present
