Feedback on Improving Precision in XYZ Gantry Dispensing Machine

[routercnc]

OK so it is a sort of pick and place machine with no real loads at the end effector (dispenser end)? And the positioning errors there when you just jog it about with no load on the effector?

I would say the machine you have build should hold a much tighter position from a mechanical point of view. Yes with a single drive at the centre of the gantry and what looks like 2 unsupported rails either side with a fair span between them it will rack if you push the uprights in opposite directions, as you have discovered. So back to needing to know a bit more about the issue and how it occurs.

Motors calibration
Have you calibrated the stepper motors? You need to tell the software how many steps should be sent per mm of travel - this can be calculated based on the microsteps on the driver (are you microstepping?), the steps per degree on the stepper motor itself (what motors are they?), the pitch of the ballscrew (where used), and any ratios on the drive pulleys. Or just iterate the value via trial and error for now if that is a bit much to work out for now.

Software
What software are you running for the controller? Is it ethernet, USB or parallel port ?

Drivers
What is the driver specification and what voltage are you using?

Stalling
What speeds are you running at and might you be missing steps? Run it very slow to make sure this is not the issue. It will get to the commanded position but just take longer (for testing).

Backlash
If you manually push the effector part back and forth, side to side etc. do you feel backlash anywhere across any parts of the machine? This must be pretty close to zero, or at least way less than the accuracy you are aiming for.


Quick tests . . .
If you suspect or want to rule out machine flex then temporarily:
1. clamp the base down to securely using G-clamps or similar to a very sturdy table (create shear panel on the base and stop it moving)
2. clamp a stout piece of wood (or spare extrusion if you have it) diagonally across the gantry side legs to reduce flex sideways [red bracing]
3. stopping the racking is not easy without modifications so maybe put a DTI up to each gantry leg and ensure they are both moving the same amount