Method and system for steering a gantry crane

1. A method for steering a gantry crane having wheel assemblies, the method including the following steps:

initiating movement of the gantry crane; and

rotating the wheel assemblies wherein the front wheel assemblies rotate in a first rotational direction and the rear wheel assemblies rotate in a second rotational direction, the first rotational direction being opposite to the second rotational direction and

wherein a first side wheel assemblies rotate at a first rotational speed and a second side wheel assemblies rotate at a second rotational speed, such that the gantry crane moves from a linear path to an arcuate path with a turning radius decreasing to substantially zero for rotation about a central axis, and

wherein the angular position of the first side rear wheel assembly and of the second side front and rear wheel assemblies are calculated according to the angular position of the first side front wheel assembly.

2. The method of claim 1 , wherein the first rotational direction is clockwise and the second rotational direction is counter-clockwise.

3. The method of claim 2 , wherein the first rotational speed is less than the second rotational speed.

4. The method of claim 2 , wherein the first side front wheel assembly rotates 45°, the second side front wheel assembly rotates 135°, the first side rear wheel assembly rotates 45°, and the second side rear wheel assembly rotates 135° from respective initial positions of 0°.

5. The method of claim 1 , wherein the first rotational direction is counter-clockwise and the second rotational direction is clockwise.

6. The method of claim 5 wherein the first rotational speed is greater than the second rotational speed.

7. The method of claim 5 wherein the first side front wheel assembly rotates 135°, the second side front wheel assembly rotates 45°, the first side rear wheel assembly rotates 135°, and the second side rear wheel assembly rotates 45° from respective initial positions of 0°.

8. The method of claim 1 , wherein the angular position of the first side rear wheel assembly and of the second side front and rear wheel assemblies are calculated according to the angular position of the first side front wheel assembly, using the following formulas:

α1°= P 1/(| P 1|)*{90−[ tan −1 (( C+P 1*tan(90−β1))/[ P 1|)]}−90*(1−β1/(|β1|));

β2°+−β1°;

α2°=α1°,

wherein C is the width of the gantry crane, P1 is half of the distance between the rear wheel assemblies and the front wheel assemblies, P2 is the same value is P1, with the opposite sign; β1 is the angle of the first side front wheel assembly and α1, β2, and α1 are the corresponding angles of the first side rear wheel assembly and of the second side front and rear wheel assemblies.

9. A steering system for a gantry crane, the steering system comprising:

front wheel assemblies connected proximate a front portion of the gantry crane, the front wheel assemblies comprising a first side front wheel assembly and a second side front wheel assembly;

rear wheel assemblies connected proximate a rear portion of the gantry crane, the rear wheel assemblies comprising a first side rear wheel assembly and a second side rear wheel assembly;

a user interface for steering control of the gantry crane; and

a programmable controller for controlling the angular position of each wheel assembly to effect a concentric rotary steering mode selected through the user interface, and

wherein the angular position of the first side rear wheel assembly and of the second side front and rear wheel assemblies are calculated according to the angular position of the first side wheel assembly.

10. The steering system of claim 9 , further comprising a plurality of sensors for monitoring the angular position of the respective wheel assemblies.

11. The steering system of claim 9 , further comprising a drive engine coupled to the wheel assemblies to effect movement of the gantry crane.

12. The steering system of claim 9 , wherein the angular position of the first side rear wheel assembly and of the second side front and rear wheel assemblies are calculated according to the angular position of the first side front wheel assembly, using the following formulas:

α1°= P 1/(| P 1|)*{90−[ tan −1 (( C+P 1*tan(90−β1))/[ P 1|)]}−90*(1−β1/(|β1|));

β2°+−β1°;

α2°=α1°,

wherein C is the width of the gantry crane, P1 is half of the distance between the rear wheel assemblies and the front wheel assemblies, P2 is the same value as P1, with the opposite sign; β1 is the angle of the first side front wheel assembly and α1, β2, and α1 are the corresponding angles of the first side rear wheel assembly and of the second side front and rear wheel assemblies.