VFDs, v/hz, sensorless, full vector for machine tool
VFDs, v/hz, sensorless, full vector for machine tool
(OP)
Basically I have a machine that has an open loop or v/hz type spindle drive. Has been installed for many years but just not happy with the performance. The drive just cannot respond to all the varying loads and bogs easily.
I have decided to install a difference drive with a feedback circuit. For this application, around 1% or so of rpm variance would be tolerable but load can vary quickly and motor needs to respond quick to keep spindle at speed.
Would todays sensorless systems be a decent solution or do I need true vectoring with an encoder? Will true vector really shine well above? My target is to get bad fast accel/decel rates as well as reasonable torque response for cutting loads for a machine tool.
Due to the high costs and this old machine, I would prefer a used drive for this. Because I do not need tight rpm control, a simple tach would probably do for the sensor but would a true vector system work with this or do they all need a true encoder?
I have decided to install a difference drive with a feedback circuit. For this application, around 1% or so of rpm variance would be tolerable but load can vary quickly and motor needs to respond quick to keep spindle at speed.
Would todays sensorless systems be a decent solution or do I need true vectoring with an encoder? Will true vector really shine well above? My target is to get bad fast accel/decel rates as well as reasonable torque response for cutting loads for a machine tool.
Due to the high costs and this old machine, I would prefer a used drive for this. Because I do not need tight rpm control, a simple tach would probably do for the sensor but would a true vector system work with this or do they all need a true encoder?





RE: VFDs, v/hz, sensorless, full vector for machine tool
RE: VFDs, v/hz, sensorless, full vector for machine tool
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFDs, v/hz, sensorless, full vector for machine tool
RE: VFDs, v/hz, sensorless, full vector for machine tool
Curt Wilson
Delta Tau Data Systems
RE: VFDs, v/hz, sensorless, full vector for machine tool
I would select a drive that has SVC but allows for an inexpensive upgrade to Full Vector by simply adding the encoder feedback from the motor. Many if not most are now that way.
Re:used drives. I am not a fan of this, you seldom can tell how a VFD was used and how long it has been out of service. Often times a VFD is sold off because the machine it was used on was a failed application, and that may mean the drive was abused before they gave up.
But if you do it, be careful. If left sitting on a shelf for a year or more, the capacitors usually need to be "reformed" in order to avoid damaging them when first energized.
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RE: VFDs, v/hz, sensorless, full vector for machine tool
RE: VFDs, v/hz, sensorless, full vector for machine tool
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RE: VFDs, v/hz, sensorless, full vector for machine tool
I still am unable to quantify the actual difference in an application such as this. I am not too interested to spend an extra grand just to shave off .25s of spindle accel but might consider if we are talking 2 seconds.
I am also curious about decel rate. Does the encoder system work the same way to rapidly watch the decel rate to inject power at the right time and actually improve decel, or is this just a simple situation of adding resistor capacity to slow down faster?
It seems as though the actual at-speed load response time might be pretty close in which there might be little difference here but again, I am still trying to compare the two.
RE: VFDs, v/hz, sensorless, full vector for machine tool
RE: VFDs, v/hz, sensorless, full vector for machine tool
RE: VFDs, v/hz, sensorless, full vector for machine tool
I do not run a machine that low very often but with a large saw, I have run in the 50-100rpm range. I also have to think about tap reversal.
So, are there any other drives than the one I saw here (Optidrive) than has proven to provide really good response at low rpm?
RE: VFDs, v/hz, sensorless, full vector for machine tool
My list (in order of people I used to work for or with for lack of a more random plan)
Siemens
ABB
Teco
Bardac (US version of the Optidrive)
Schneider / Toshiba
Yaskawa
Allen Bradley
My preferences in terms of ease of use:
ABB
Yaskawa
Bardac
Teco
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RE: VFDs, v/hz, sensorless, full vector for machine tool
hi range is .8:1 over driven so max speed at motor is 202hz, and max spindle is 7500.
Low range is 3.36:1 so 202hz is 1800 max at the spindle.
That puts us at 100rpm at the motor for our lowest application at 30rpm at the spindle. That pulls us back to 18:1. What do you think?
I had a drive retailer end up calling ABB to talk with a specific engineer for machine tools and he was not sweating the ACS800 sensorless system for this. They advertise near full torque at 0 rpm on the drive though another engineer said 1hz. The response time to load condition was 2-3ms and I am not sure if this is in line with an encoder system.
I really wish I could find a comparison of drives to verify this level of performance but the linky above was testing the ACS350 and it was unable to do much at 0 rpm, even with an encoder but the optidrive pulled the load great. I would just like confirmation of this. It would certainly save some time and hassle if we can go sensorless but I respect JRaef's opinion here due to the vast experience in drives.
Again, if I can achieve 99% of the performance with sensorless, I will not chase vector, but if that gap grows to say 90&%, I probably would.
RE: VFDs, v/hz, sensorless, full vector for machine tool
The ACS350 is not going to give you zero speed performance but you didn't ask for that in your original posting. At 30rpm, ABB, Siemens, Mitsi, and Yaskawa will all give you good torque and speed regulation using sensorless vector control.
RE: VFDs, v/hz, sensorless, full vector for machine tool
It is kind of looking like sensorless might work. I also have to consider tapping performance where a tap will dive into a work piece and reverse. Breaking the tap free for reversal is my only concern. Right now, the machine really struggles with 1/2x13 taps.
RE: VFDs, v/hz, sensorless, full vector for machine tool
RE: VFDs, v/hz, sensorless, full vector for machine tool
I'm surprised Control Techniques didn't make your list. I haven't had any dealings with them since they were assimilated by Emerson but as an independent company they were right up there in terms of performance and reliability. The Unidrive is at least worth a look.
Their technical folks at Telford were good too, although I don't know if that survived being Emersonised either. I hope it did.
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If we learn from our mistakes I'm getting a great education!
RE: VFDs, v/hz, sensorless, full vector for machine tool
I know it is a dirty word in a lot of circles, but have you looked at DC motor/drive combo's? We used DC for years on belt feeders that run slow and require a lot of torque.
Joel Olson
RE: VFDs, v/hz, sensorless, full vector for machine tool
Nobody around me is selling or supporting the Control Techniques drives as far as I can tell. They used to have a local integrator (wholly owned), but they shut them down about 6 years ago. Nobody picked up the ball as far as I can tell.
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