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881

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 04, 2010, 12:48:17 PM »

Thanks Nosmo. Still can't see what would be the difference between a commutating encoder designed for an 8 pole motor and a one designed for a 6 pole motor, for instance?

Daniel

882

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 04, 2010, 11:28:32 AM »

Ah yes, forgot about the turbo speed   Just have to keep an eye out on eBay and check the specs if anything comes up.

Hood

Yep... guess that is what I'll have to do. The speed seems to be the biggest problem.

Daniel

883

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 04, 2010, 11:19:30 AM »

Here are some good resources I've found on feedback devices:

1. This one explains about Sin/Cos encoders operation:

http://www.sensorsmag.com/sensors/position-presence-proximity/understanding-integrated-hall-effect-rotary-encoders-1254?page_id=1

Apparently this type of encoders is not optical but they rather use hall sensors. As can be seen the resulting Sin/Cos signals have 90 degrees phase shift and their magnitude is not dependant on the shaft angle. This is why a servo drive that can use Sin/Cos encoder, can't use a resolver instead.

2. A very good document explaining resolvers operation:

http://www.admotec.com/TT02.pdf

3. Another one on resolvers:

http://www.amci.com/tutorials/tutorials-what-is-resolver.asp

4. This one covers several feedback devices and has some good information about resolvers:

http://www.motor-solutions.com/datasheets/servo_motor_feedback_devices.pdf

5. Another one on various feedback devices:

http://www.allegromicro.com/en/Products/Design/compumot/a39a44.pdf



So looks like I'll have to replace the resolver with an encoder if I want to use the motor with the Ultra 5000 drive.

Daniel

884

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 04, 2010, 08:52:21 AM »

Ah... I see. Saw, they also have encoders with differential outputs already. But the speed seems to be the problem with these. Also, most of their encoders don't have an Index channel.

Daniel

885

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 04, 2010, 07:58:59 AM »

Ha.. ha.. This is the exact same paper you once showed me I don't know, still think the number of poles should make no difference.

Yes, as I've mentioned in the previous post the Ultra 5000 does support self sensing as per the manual, so using a US digital encoder sounds like a good  solution. But what do you mean by a line driver?

Daniel

886

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 04, 2010, 07:01:54 AM »

Never looked deeply into it but I would assume that it is the spacing of the three signals that would let your drive know the commutation startup. So if it was two pole the signals would be 180 out, 3 pole 120 out, 4 pole  90.

I am afraid this is not correct as there are always 3 signals and they are equally spread along the 360 degrees of one revolution, meaning there would always be a 120 degrees phase shift between them. Also, brushless motors are essentially 3-phase motors so the control signal is always 3 phase 120 degrees apart and the commutation signal must match. You can also see this in the Ultra manuals where they specify the signals' phasing - nothing mentioned about the motor poles number. As I see it, the number of poles only dictates the control signal frequency to achieve a given speed and the commutation essentially follows that frequency.

Still dont think the resolver will work or I would imagine AB would mention it, then again only  one way to find out

Yep... will do some reading on Sin/Cos encoders and try to understand their operation. Hopefully the Sin/Cos signal of these encoders and those of a resolver are the same and AB say their Ultra drives don't support resolvers merely because their drives don't have an AC excitation signal required for resolvers. In this case an external signal might be used I assume.

As far as I am aware BLDC and AC servo motors are one in the same but it is the drives that are different in the way they do the commutation. The Ultra drives are AC.

Hood

Yes, I also thought the Ultra drives were AC, but if I understand what Nosmo says, then since they are using hall feedback they are BLDC?? 

Daniel

887

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 04, 2010, 03:50:40 AM »

Thanks for the info Nosmo. Does it make the AB drives BLDC commutation?? They do expect hall signals (the Ultra series).

Daniel

888

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 04, 2010, 03:44:37 AM »

Not sure I understand your question, these seem to be normal incremental encoders and as such you need the commutation channels on them to match your motors pole pairs. Or are you meaning something else?

That's what I had thought - you put a commutating encoder on a motor and its 3 hall signals have to match the motor poles. I hadn't realized that the NUMBER of poles had any affect - still same three hall signals from the encoder. But from that link it seems that an encoder is specific to a motor with the NUMBER of poles it was designed for. Am I missing something here? Are the signals from an encoder on a 4 pole motor different from those of an encoder on a 6 pole motor?

Found some info on encoders saying 30,000rpm but not sure if they are any use or not as have not really read it yet. http://www.moog.com/literature/MCG/opticalencoders.pdf

Yes, these look good. They are not commutating though.

Oh and if this is for a spindle you may not even need commutation signals, well not sure about the Ultra 5000's but the 3000's can do an auto sense for commutation startup which on a spindle I dont think would be an issue.
Hood

Ah... Hadn't noticed this detail in the manual before. This is perfect! The motor IS meant for a spindle indeed. Thanks for pointing me to this. So I wonder now what if I fed the Sin/Cos channels from the resolver to the the Ultra5000 while the resolver Ref is being excited by a DC voltage.. Does it make any sense? In second thought, seems it wouldn't work at low speeds because the resolver wouldn't be able to induce the Sin/Cos when the magnetic field changes slowly. But with a high frequency excitation I think the drive "will be confused"... Can you tell me how does the Sin/Cos encoder work? Is it the same phasing like normal, square wave signal, encoder?

Daniel

889

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 03, 2010, 04:50:46 PM »

I was referring to these:

http://www.quantumdev.com/products/optical_encoders/qd145.html

See that they differentiate the models by the number of poles. Max speed for these is only 8,000RPM though

Daniel

890

General Mach Discussion / Re: Allen Bradley Ultra5000 Sin/Cos Encoder? Resolver?

« on: May 03, 2010, 04:35:24 PM »

So it makes things even more complicated

Any idea about the possible relationship between the motor poles number and encoder commutation? As far as I know you simply put the number of poles in the drive and it makes the calculations of the waves based on it. Have no clue what does it have to do with the encoder itself?

Daniel