Can I use Steppers with linear/glass encoders?

[lukesdaddy]

Hello,
I want to convert my Bridgeport mill and use Mach2 software and maybe the Gecko drives. I am a hobbiest so I don't have an unlimited budget. I was lucky enough to have an understanding wife to spend the money for the mill. I don't want to push my luck... I have not found cheap servos yet so I thought I would use steppers instead. But, I want closed loop and I want to use the existing quadrature glass scales used for the DRO. I know Mach2 will accept the quadrature inputs but can I use these inputs, in combination, with the steppers? I know that Mach2 handles servos with encoders.

Hope I conveyed my question. Thanks.

Lukesdaddy

[ger21]

Mach2 won't do closed loop. Even with servos. Anything that will will cost you several thousand dollars.

[lukesdaddy]

Thanks, Now you have really confused me..... Why does Mach2 have encoder inputs for the servo and servo/stepper tuning? I know Mach2 displays the actual position on the screen. Are you telling me this is for reference only? If not why have an encoder input to Mach2? My thought was to use the glass scales that are measuring the position of the table instead of measuring shaft position of the servo/stepper. That way, I don't have to worry as much about backlash. Or at least that is the theory. I did not want to replace my screws to mimimize the backlash. Again, I am trying to go as cheap as possible.

Thanks again.

[ger21]

Originally Posted by lukesdaddy Why does Mach2 have encoder inputs for the servo and servo/stepper tuning?

The encoder inputs have nothing to do with motor tuning. I looked through the manual, but there is very little info. But Art has stated that it's unlikely that Mach2 will ever be closed loop. I think it's due to the limitations in speed imposed by Windows.

Like I said before, closed loop is usually several thousand dollars. Mach2 is $150. It can't do everything.

[ger21]

Originally Posted by lukesdaddy I know that Mach2 handles servos with encoders.

The servo encoders are connected to the drives, usually Gecko or Rutex. Mach2 never sees the encoder signals. It doesn't know if it's driving steppers or servos.

[ESjaavik]

Originally Posted by ger21 Like I said before, closed loop is usually several thousand dollars. Mach2 is $150. It can't do everything.

EMC is $0. It can do closed loop too. Much more difficult to set up than Mach2 though. There is no proper user manual, just scattered info, some of it outdated. But there is a helpful mailing list.

Whether it is wise to use the linear encoders for feedback is another matter though. The coupling from motor to table and thus linear encoder must be very rigid, or the loop will be impossible to tune. That means preloaded ballnuts, angle contact bearings, if any gear it must be backlash free, and the mounts must not flex to any measureable amount. When the encoder sits on the end of the motor shaft, it is rigid.

[Al_The_Man]

Backlash Instability on a system using linear encoders etc is eliminated in sophisticated systems using a improved dual loop system, this entails an encoder on the motor as well as a scale or encoder on the final load.
The Galil site has some excellent training video's, one on this very subject if someone wishes to see an in-depth explanation. They have improved their download site now so the video's are in a couple of formats.
By the way, how easy is it to implement a Motion control Card into EMC and has anyone done it.
Al

[ger21]

Originally Posted by Al_The_Man By the way, how easy is it to implement a Motion control Card into EMC and has anyone done it. Al

http://pico-systems.com/motion.html

[Al_The_Man]

Gerry, That system looks like it still uses the parallel port method, I was thinking more along the lines of Galil, Acroloop or Delta-Tau dedicated cards.
Al

[ger21]

It uses the parallel port, but I believe it is closed loop in hardware using this
http://pico-systems.com/univpwm.html

I'm not sure if those other cards will work with EMC. I could be wrong, though.