I am looking for a rotary encoder.

Hollow shaft, 180 mm internal diameter.
4000 pulse per revolution
4500 rpm electrical and mechanical speed.
1v~p/p incremental
Less than 6 arc/second error rate.

This is for a high speed rotary positioning application.

The signal can not have harmonics as it will be interpolated with a 2048 multiplier.

Anyone have any recommendations?

 

Your numbers don't make sense:

4500rpm -> 75 rev/sec

4000 line encoder @ 75 rev/sec -> 300,000 lines per second. (OK... so it is a sine-wave encoder. Instead of lines you have cycles. The output from the encoder is 300KHz.)

Now you're going to interpolate that with a 2048 multipler. (Most sine-wave interpolators I know of allow for multipliers of 8 or possibly 16.) The result, assuming your 2048 multiplier, is 614.4 million lines/sec at full speed!

I have never seen a position input circuit that could accept signals of this frequency.

Good luck!

> Anyone have any recommendations? <

Yes, check the requirements again.

Mark

 

Heidenhain?

 

Yes, you may get asked resolution with even smaller diameter from Heidenhain. Thus ERN 400 has 58 mm diameter or ERN 100 has 87 mm diameter only. Pay attention that 4000 PPR isn't standard resolution but you have 5000 PPR for the above encoders.
You may looking for RSF enocders also.

BTW Mark above doesn't pay attention that interpolator is external (for encoder) circuit.

 

I have checked with heidenhain and they have a few close fits but nothing that is perfect. The closest thing is the ERM-280.

Siemens 840D CNC has a position input frequency limit of 350Khz.

The machine I am developing is an inverted lathe/mill with a 30kw main spindle and 15kw sub spindle. The motor and spindle are integral frameless permanent magnet motor design.

The spindle shaft is about 180mm diameter at the area that the encoder will be mounted.

The object of the machine will be to be able to turn the part and to be able to mill/drill by positioning the main spindle.

As you can infer from the numbers I am looking for I am looking for very high positioning accuracy on the main spindle.

 

Actually - our ACC-51 series interpolators can take up to an 8 MHz SIN cycle, which translates into 32.768 GHz velocity in cts. For a 1000 line sinusoidal rotary encoder this leads to a maximum of 8000 RPS, or 480,000 RPM.

Davis Gentry
Senior Applications Engineer
Delta Tau Data Systems

 

Then try Renishaw, Sony, or Gurley.

 

Yes the Siemens 840D with 611 drives allows a feed back frequency of 350 khz with an internal interpolator of either 512 multiplication or 2048
multiplication depending on what hardware you buy we are buying the high performance module.

360*60*60=1296000 seconds per rotation

Siemens 840d registers with the encoder I am looking for (4000*2048)/2 = 4096000 positioning pulses per revolution

1296000/4096000 = 0.31640625 arc/seconds measuring system input.

Using a position pulse train of 10 times required position accuracy is optimal for this application. In this case I can go to the lower count of the heidenhain ERM with 2048 pulses as I really am only looking for 6 arc/seconds of accuracy but I was just hoping I could do better.

If no one has any recommendations it looks like that is what I will do. I just wanted to see if any one knew of any other encoder that could get me closer.

 

I think you'll probably have to get something made custom. Talk to BEI and Encoder Products.

 

Heidenhain and stegman make nice encoders. We've used a Stegman stainless steel ring encoder that can be had at various large diameters. You have to provide mounting for the ring and the encoder read head, but its kind of nice because the encoder ring can actually be made to be part of your load that you are controlling. So you don't have to worry as much about runout of your coupling system like you do on shaft encoders.

~Ken

 

all i can say about encoders is it is important to mount any encoder well as any wobble in either shaft type or socket /ring mounted encoders wont preform well over the long term rotational speed is a key factor as the bearings which the encoder run on will throw the lubricant all through the optical elements of the encoder making it record irregular and control will be impaired as long givity is always a concern duty cycle might be considered as constant running encoders will suffer from heavy work load and heat either ambient or internal when you write the coda that will read the encoder resolution number of pulses per revolution eg 500ppr 1000ppr 5000ppr each will be of course set by the equipment that it will control there are as many mechanical property's as well as electrical when choosing an appreciate encoder good luck with the project.

 

These concerns are valid, but in any design situation you have to weigh all of the concerns and pick the right tool for the job. If you are talking high accuracy situations shaft encoders do lots of strange things, like presenting a sinusoidal coupling error which is repeatable but not accurate. Also, if you have high torque, a relatively large inerrtial load, and a long motor shaft you get torsional error due to the inertia of the load twisting the shaft. The ring encoders we have used we designed a guard system in addition to the bearings having a seal on them, so there is no way you can disturb them unless you hose it down, which will not happen in this application.

~Ken

 

Have you tried a Renishaw system?
Have used them in the past and are very good indeed.