Re: Using linear encoders.

Pete:

Such machines do exist but they are very expensive and clearly out of
the hobby price range. What you are describing is a very complex
motion control system. The major problems to overcome are loop
stability and velocity control. Even with very fast scales most
designs still depend on shaft encoders or tachometers for velocity
control.

The two most popular software drivers, Mach2 and TurboCNC can not do
this. Unless one has a LOT of experience in motion control system
design (and a lot of money) this will not work. The hunting problem
you mention is the loop stability problem I am refering to and it's a
bear to solve. Stick with shaft encoders and save a lot of headaches.

Sorry for the bad news;

Ken

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Peter Reilley" <micrio@m...>
wrote:

> Can you use linear encoders in a servo system? This would be on a
> Bridgeport type machine with ball screws. I can see where any

backlash,

> no mater how small, would result in a continual hunting for position.
> However, I know that there is at least one commercial CNC conversion

system

> that uses the linear scales for feedback.
>
> Is this a reasonable thing to do or should I go with the rotary encodes
> mounted on the servo motors.
>
> Thanks,
> Pete.