Method and apparatus for measuring vehicle wheel roll radius

A method for measuring a plane angle value (Ψ) between a rack plane and a vehicle plane of a motor vehicle resting on an alignment rack, comprising the steps of:

• measuring a first roll radius value (R1) of a first wheel of the motor vehicle and a second roll radius value (R2) of a second wheel of the motor vehicle;
• measuring a horizontal displacement value (Wb) between a first center of the first wheel and a second center of the second wheel;
• determining the plane angle value according to the relationship ψ = Tan - 1 ⁡ ( R 2 - R 1 W b ) ;
• and
• modifying one or more values associated with an alignment of the motor vehicle based on the plane angle value.

A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, cause the one or more processors to measure a roll radius value (R) of a wheel having an optically scannable target attached thereto by performing the steps of:

• optically scanning the target when the wheel is in an initial position and creating and storing values representing the initial position;
• rolling the wheel from the initial position to a final position;
• optically scanning the target at the final position and creating and storing values representing the final position;
• measuring a distance traveled value (P) during the rolling of the wheel based on the position values;
• measuring an angle of rotation value() traversed during the rolling of the wheel based on the position values;
• creating and storing the roll radius value of the wheel according to the relationship R = 360 ⁢ ⁢ ( P ) 2 ⁢ πϑ .

A computer-readable medium carrying one or more sequences of instructions which, when executed by one or more processors, cause the one or more processors to measure a plane angle value (Ψ) between a rack plane and a vehicle plane of a motor vehicle resting on an alignment rack by performing the steps of:

• measuring a first roll radius value (R1) of a first wheel of the motor vehicle and a second roll radius value (R2) of a second wheel of the motor vehicle;
• measuring a horizontal displacement value (Wb) between a first center of the first wheel and a second center of the second wheel;
• determining the plane angle value (Ψ) according to the relationship ψ = Tan - 1 ⁡ ( R 2 - R 1 W b ) ;
• and
• modifying one or more values associated with an alignment of the motor vehicle based on the plane angle value.

An apparatus for measuring a plane angle value (Ψ) between a rack plane and a vehicle plane of a motor vehicle resting on an alignment rack, the motor vehicle having two or more wheels, each wheel having a target fixedly attached, comprising:

• a vision imaging apparatus that detects a first image of a first target fixedly attached to a first wheel and a second image of a second target fixedly attached to a second wheel;
• and
• a data processor that is programmed to (a) determine a first roll radius value (R1) of the first wheel and a second roll radius value (R2) of the second wheel, (b) measure a horizontal displacement value (Wb) between a first center of the first wheel and a second center of the second wheel based upon the first image and the second image, (c) determine the plane angle (Ψ) according to the relationship ψ = Tan - 1 ⁡ ( R 2 - R 1 W b ) ;
• and
• (d) modify one or more values associated with an alignment of the motor vehicle based on the plane angle value.

A method of measuring a roll radius value of a wheel, comprising the computer-implemented steps of:

• creating and storing values representing an initial position of the wheel;
• rolling the wheel from the initial position to a final position;
• creating and storing values representing the final position of the wheel;
• measuring a distance traveled value (P) during the rolling of the wheel by comparing the initial position values and the final position values;
• measuring an angle of rotation value() traversed during the rolling of the wheel by comparing the initial position values and the final position values;
• creating and storing the roll radius value (R) of the wheel according to the relationship R = 360 ⁢ ⁢ ( P ) 2 ⁢ πϑ .