[ohsnapfit]

I built a 3 axis CNC around a Masso G3 controller and bought their closed loop stepper motors.
After getting frustrated by Masso's inability to use macros and their very limited probing routines, I decided to upgrade to an centroid Allin1 and sold the Masso. The Allin1 can accept linear glass scales, so there is an opportunity for an extra improvement.
My question: can I use the centroid with linear glass scales and connect to the closed loop steppers? It seems like there would be two error corrections and I'm unclear which one will win (race condition?), or how this will behave. Has anyone done this?

[joeavaerage]

Hi,
firstly....do you need glass scales? Are the closed loop steppers not good enough as is?. The whole point about closed loop steppers is that they will always drive to their commanded position.....
so in a sense you might describe them as being perfect. What a glass scale, also called 'load sensing' is measure the actual position of the load, which might accommodate any non-lineraity
in the drive train between the steppers and the load. Does your machine suffer from that sort of inaccuracy?

May I suggest have a look at Delta A2 servos, I'm not neccessarily suggesting you get them, they are expensive but they illustrate what a manufacturer can do.
Like any modern AC servo it has a high resolution encoder mounted on the servo shaft, and that angular position is very much required for the servo drive to control the servo. The A2 series
servo have a secondary encoder input to which you can connect a glass scale. The servo drive uses both encoders, the builtin rotary encoder to control the torque and velocity of the servo motor
but uses the secondary encoder to close the position loop.

Delta are far from the only manufacturer doing this, all the top tier servo manufacturers have models that include 'load sensing'.

What you are suggesting is that the controller close the position loop and command the steppers to a give position. That may be possible but not easy.
I presume you'd be OK programming and tuning a PID loop? If you don't know what that means then it also suggests that you are 'jumping in the deep end' and there is a high risk that despite
the time and money invested you will not get a result.

Despite the cost of 'load sensing' servos like the A2 series the probability of a 'very good to excellent' result is high.

I don't know about you, but the more time, money and effort I spend on something the more risk averse I become, I want some certainty that's its going to work, if there is
a distinct probability that it will not work......then I would not attempt it.

Craig