[ngr1]

Hello, I am considering some Renco encoders for servo motors I have yet to buy.

Can I assume, with respect to encoders, that the term resolution and CPR mean the same thing?

I am planning on directive drive configuration between the motors and ball screws. What would be an appropriate CPR rating for a 1:1 configuration.

The Renco encoders I am looking at have a resolution of 400.

Thanks... Norman

[Bubba]

Ngr1,
CPR and resolution of the table are inter-reactive. If we ass/u/me a ball screw with a .2 pitch, at 400 CPR, that is 1600 in quadrature divided into .2 is 0.000125" per step. If on the other hand, you use 1000 CPR for example you will have 4000 into .2 and gives 0.00005" resolution however at a sacrifice of speed if your system can't handle it.
Bottom line, will 400 CPR work, YES; Is it accurate enough for your purposes, only YOU can answer that one!

[ngr1]

Thanks Bubba!

I have a bench top mill (RF 25 Type) that I am planning to convert and I would like to follow the successful conversions found in this forum by using the same parts (i.e. ballscrews, encoders etc). Most people seem to be using 250 CPR with a belt drive (2:1) and 500 CPR w/ 1:1.

I do not understand you statement "CPR and resolution of the table are inter-reactive". The spec on the encoder state "Resolution of 400 pulses per revolution" what is the equivalent to in terms of a CPR rating?

Norman

[Al_The_Man]

Can I assume, with respect to encoders, that the term resolution and CPR mean the same thing?
The Renco encoders I am looking at have a resolution of 400.

Resolution and CPR or counts per rev. does not always mean the the same thing, but they are tied together.
It all depends on how your control allows you to use the encoder, a 400c/r incremental encoder supplies two square waves 90deg apart (hence quadrature) at 400 counts per rev.
Now some controllers will allow you to increase this resolution by the way it counts the pulses, the minumum would be of course to count the leading edge of one pulse only, this would be 400c/rev, if you count both leading edges then this raises the resolution by 2x, a third option is to count both leading and trailing edges of both square waves which give you 4x resolution of the encoder.
Some controller allow you to choose any option of the three.
Al.

[ESjaavik]

And your motor will not follow the commanded position to the last count of resolution. A servo drive must have some error because it it driven by the error. I suggest you choose as high number of counts/rev as your system can handle at the max speed you need. And the counter resolution should be much better than the positioning resolution you need.

So if you need 1/100mm resolution and design with 100 count/mm, you will not get what you want.