Quite an Unusual one

[EddyCurrent]

A question ?????
There is something i don't understand about boards and servos. Why all speak of the encoders to go in the BOB? Dont they go to the servo drive and the servo drive controls the closed loop? I read at Galil and KFLOP that the BOB closes the loop? Or am i mistaken?

I would always expect encoder feedback to go directly to the driver, you don't way any delay introduced, it should go directly to the summing junction that should also exist in the driver.
If feedback does go via the bob on any system, I would steer clear of it.

[Clive S]

I would always expect encoder feedback to go directly to the driver, you don't way any delay introduced, it should go directly to the summing junction that should also exist in the driver.
If feedback does go via the bob on any system, I would steer clear of it.

Or perhaps to the motion control board (driver) .. Clive

[EddyCurrent]

Or perhaps to the motion control board (driver) .. Clive

Clive, sorry I'm not sure what you mean ?
To clarify, by driver I meant motion control board. Feedback should go to that and not via the bob.

[Clive S]

Clive, sorry I'm not sure what you mean ?
To clarify, by driver I meant motion control board. Feedback should go to that and not via the bob.

You are 100% correct of course, I was just trying to differentiate between a simple BOB and a full blown motion controller (driver) type.

Sorry for any confusion. ..Clive

[EddyCurrent]

You are 100% correct of course, I was just trying to differentiate between a simple BOB and a full blown motion controller (driver) type.

Sorry for any confusion. ..Clive

I thought I'd had too many 'old speckled hens'

[Jonathan]

Clive, sorry I'm not sure what you mean ?
To clarify, by driver I meant motion control board. Feedback should go to that and not via the bob.

There's actually a lot of debate on this topic when using LinuxCNC. Since LinuxCNC is real-time, you can implement the PID controller within the computer (instead of the motor drive), and have the computer output speed instead of position (step/dir) signals. That can work well, especially if you use a PCI card. Some people consider that better as then the computer is always tracking the following error... but just saying that is really oversimplifying the situation so if interested, Google it.