Originally Posted by
cameraguy
A closed loop system is good for servos (required, actually), but not so good with steppers. A Taig-sized machine is best suited to steppers. I would avoid attempting to set up a closed loop system on one. The only commercial closed-loop system for them that I know of is godawful and completely pointless.
As for manual DRO's, the Chinese slides use a bizarre coding system that is simple, but entirely their own. I do recall the someone made a simple converter that plugged into them and output standard quadrature, however. Sure a search will turn it up.
The simple answer here is that one has to manage the physical backlash properly and keep things as 'tight' as you can. The latency in getting a position from a Chinese scale means that it is no use for controlling the actual position, only confirming a position once movement has ceased. Even the quadrature scale inputs into Mach3 can only be used to confirm position and produces an error if a final position is not reached.
'Closed loop' will only work by directly driving the motor and controlling the MOTOR position and since the Taig backlash is after the motor, even switching to servo's will not do anything for that. Putting the feedback sensor on the bed rather than the motor shaft will just create an unstable mess on this type of closed loop controller.
Mach3's backlash compensation works reasonably well as long as the backlash is being managed well by regular maintenance.
As for CNC versions of the Taig mill ... Buy the CNC ready basic mill and three stepper motor mounts, and then the only 'conversion' work is to add your own stepper motors and drivers. The cost of scales would go some way to buying the CNC kit instead?
Lester Caine - G8HFL
http://medw.co.uk - Home of electronics for the Model Engineer