Tire uniformity testing
A method and apparatus for testing tires in a repeatable manner. Testing steps are performed in a manner that minimizes impact on the tire characteristics being measured. In one aspect, tire rotation reversal is performed at a zero crossing of a first harmonic of radial load variation exerted on a load carriage by the tire. In another aspect, load carriage retraction is performed so that the tire is unloaded when the tire stops rotating.
1. A method for testing a tire comprising the steps of:
mounting the tire on a rotatable spindle;
rotating the tire in a first rotation direction and measuring one or more tire parameters as a function of the tires rotational position;
determining a tire rotational position at which to reverse the rotation of the tire based on the measured parameters; and
reversing the rotation direction when the tire reaches the determined rotational position.
2. The method of claim 1 wherein the measured parameter comprises a radial force variation.
3. The method of claim 2 comprising the step of calculating a first harmonic of the radial force variation and wherein the step of reversing the tire rotation direction is performed based on the calculated first harmonic.
4. The method of claim 3 wherein the step of reversing the tire rotation direction is performed at a positive-going zero crossing of the first harmonic of radial force variation.
5. The method of claim 3 wherein the step of reversing the tire rotation direction is performed at a negative-going zero crossing of the first harmonic of radial force variation.
6. The method of claim 3 wherein the step of reversing the tire rotation direction is performed at a first encountered zero crossing of the first harmonic of radial force variation.
7. A method for testing a tire comprising the steps of:
mounting the tire on a rotatable spindle;
applying a load to a tire perimeter with a moveable load carriage by moving the load carriage into contact with the tire perimeter;
rotating the tire and measuring one or more tire parameters as a function of the tire's rotational position;
determining a desired tire stop position;
determining a retraction distance that will be traveled by the load carriage to unload the tire;
determining a retraction time required for the load carriage to move the retraction distance;
calculating an angle of rotation that will occur during the retraction time;
deducing a tire retraction position at which retraction must begin such that the load carriage will complete retraction at the desired tire stop position; and
beginning load carriage retraction at the tire retraction position.
8. An apparatus for testing a tire comprising:
a rotatable spindle for rotating a tire to be tested in a first direction;
a load carriage movable along a retraction axis perpendicular to the spindle for contacting the tire being tested, applying a load to the tire, and measuring tire parameters;
load cells mounted on the load carriage for measuring radial forces exerted on the load carriage by the tire; and
a controller for recording the measured tire parameters as a function of tire rotational position, calculating a first harmonic of radial force variation as a function of tire rotational position, and determining a tire rotational position at which to reverse the rotation direction based on the calculated first harmonic.
9. The apparatus of claim 8 wherein the controller causes tire rotation reversal to occur at a zero crossing of the first harmonic of radial force.
10. An apparatus for testing a tire comprising:
a rotatable spindle for rotating a tire to be tested in a first direction;
a load carriage movable along a retraction axis perpendicular to the spindle for contacting the tire being tested, applying a load to the tire, and measuring tire parameters;
load cells mounted on the load carriage for measuring radial forces exerted on the load carriage by the tire; and
a controller for recording the measured tire parameters as a function of tire rotational position, determining a desired tire stop position based on the measured parameters; determining a retraction distance that will be traveled by the load carriage to unload the tire; determining a retraction time required for the load carriage to move the retraction distance; calculating an angle of rotation that will occur during the retraction time; and deducing a tire retraction position at which retraction must begin such that the load carriage will complete retraction at the desired tire stop position; wherein the controller causes the load carriage to retract at the same time the tire rotation is stopped by beginning load carriage retraction at the tire retraction position.