Optimizing Positioning Accuracy On Laser Cutting Gantry Machine

Customer's Problem

A manufacturer of laser cutting machines would like to use rack & pinions to drive a five meter long gantry axis that will be driven on both sides. They would like to optimize the gantry axis for precise positioning over the entire travel and minimize the error across each side of the gantry.

They do not want to have to use servo compensation for eliminating the error, so they want to rely on standard mechanical components from ATLANTA to provide precise positioning.

ATLANTA's Solution

The customer ordered ten standard ATLANTA helical module 2.0 hardened & ground racks with matrix codes on them, which contain each rack's accuracy information. The matrix codes on the racks were scanned with the ATLANTA Service smartphone website and the following rack pitch error (GTf) values were found:

- Rack #1: -0.018 mm
- Rack #2: -0.010 mm
- Rack #3: -0.003 mm
- Rack #4: +0.003 mm
- Rack #5: +0.017 mm
- Rack #6: -0.016 mm
- Rack #7: +0.010 mm
- Rack #8: +0.011 mm
- Rack #9: -0.010 mm
- Rack #10: +0.004 mm

If the racks were assembled in the above order, with the first five racks being mounted on the left side of the gantry and the last five racks being mounted to the right side of the gantry, the total cumulative error for the gantry would be as follows:

- Left Side of Gantry: 0.031 mm (0.000 mm to -0.031 mm)
- Right Side of Gantry: 0.021 mm (+0.005 to -0.016 mm)
- Maximum Error From Left Side To Right Side Of Gantry: 0.036 mm (+0.005 mm Left Side, -0.031 mm Right Side)

Optimizing The Rack Mounting

In order to optimize the accuracy of both sides of the gantry, the gantry tool on the ATLANTA Service smartphone website was used. This gantry tool can determine the optimal mounting order of the racks for each side of the gantry, based on each rack's pitch error value. This results in the following optimized mounting order for each side of the gantry:

Left Side:

- Rack #1: -0.018 mm
- Rack #5: +0.017 mm
- Rack #2: -0.010 mm
- Rack #7: +0.010 mm
- Rack #3: -0.003 mm

Right Side:

- Rack #6: -0.016 mm
- Rack #8: +0.011 mm
- Rack #9: -0.010 mm
- Rack #10: +0.004 mm
- Rack #4: +0.003 mm

With this optimization of the rack mounting, the total cumulative error for the gantry was found to be:

- Left Side of Gantry: 0.018 mm (0.000 mm to -0.018 mm)
- Right Side of Gantry: 0.016 mm (0.000 to -0.016 mm)
- Maximum Error From Left Side To Right Side Of Gantry: 0.010 mm (-0.001 mm Left Side, -0.011 mm Right Side)

The total cumulative error on the left side of the gantry drops from 0.031 mm to 0.018 mm (a 42% improvement) and for the right side of the gantry drops from 0.021 mm to 0.016 mm (a 24% improvement) . The maximum error from the left side to right side of gantry drops from 0.036 mm to 0.010 mm (a 72% improvement).

Using the gantry mapping tool on the ATLANTA Service smartphone website with the matrix coded racks significantly improved the positioning accuracy of the gantry along its entire travel and minimized the positioning error from one side of the gantry to the other.

This accuracy optimization is especially helpful for long travel lengths where the rack pitch errors can add up. Using the gantry mapping tool is a quick and efficient way to make major improvements in machine precision and performance using standard off the shelf ATLANTA rack and pinion products.