Sensing steering axis inclination and camber with an accelerometer

Abstract

Methods and devices for measuring and calculating wheel alignment angles. Light weight and mechanically robust accelerometers in measurement heads are attached to a vehicle's wheels during an alignment procedure. The output of the accelerometers may be compensated for effects of temperature or thermal hysteresis by memory lookup or a temperature based feedback control loop.

What is claimed is:  
     
         1 . A method for measuring a wheel alignment angle, the method comprising: 
 attaching to a wheel a measurement head including an accelerometer; and    measuring, with the accelerometer, a wheel angle with respect to gravity.    
     
     
         2 . The method of  claim 1 , wherein the accelerometer comprises a micro-electromechanical systems (MEMS) device.  
     
     
         3 . The method of  claim 1 , wherein the accelerometer includes a solid proof mass.  
     
     
         4 . The method of  claim 1 , wherein the accelerometer measures internal changes in heat transfer caused by acceleration.  
     
     
         5 . The method of  claim 1 , further comprising: 
 calculating, by a computing device, at least one wheel alignment parameter based on the measured angle.    
     
     
         6 . The method of  claim 5 , wherein the wheel alignment parameter includes at least one of toe, camber, and steering axis inclination.  
     
     
         7 . A method for measuring a wheel alignment angle, the method comprising: 
 attaching to a wheel a measurement head including an accelerometer;    operatively connecting a thermal sensor to the accelerometer;    measuring, with the accelerometer, an uncompensated wheel angle;    measuring, with the thermal sensor, a temperature to which the accelerometer is subjected; and    calculating a compensated wheel angle as a function of the uncompensated wheel angle and the measured temperature.    
     
     
         8 . The method of  claim 7 , wherein the accelerometer comprises a micro-electromechanical systems (MEMS) device.  
     
     
         9 . The method of  claim 7 , wherein the accelerometer includes a solid proof mass.  
     
     
         10 . The method of  claim 7 , wherein the accelerometer measures internal changes in heat transfer caused by acceleration.  
     
     
         11 . A measurement head for a wheel alignment system, the measurement head comprising: 
 an accelerometer configured to measure an uncompensated wheel angle with respect to gravity;    a thermal sensor configured to measure a temperature to which the accelerometer is subjected; and    a compensator operatively coupled to the accelerometer and the thermal sensor and configured to calculate a compensated wheel angle as a function of the uncompensated wheel angle and the measured temperature.    
     
     
         12 . The measurement head of  claim 11 , further comprising: 
 a memory component operatively coupled to the compensator and configured to store at least one of a plurality of angles and corresponding temperatures and an adjustment function.    
     
     
         13 . The measurement head of  claim 11 , wherein the accelerometer comprises a thermal accelerometer and the compensator is further configured to compensate for sensitivity and for zero gravity offset of the thermal accelerometer.  
     
     
         14 . The measurement head of  claim 11 , wherein the compensator implements a feedback control loop to compensate for at least one of thermal sensitivity and zero gravity offset.  
     
     
         15 . The measurement head of  claim 11 , wherein the compensator implements an approximation using at least two temperature points for calculating zero gravity offset.  
     
     
         16 . A wheel alignment system comprising: 
 a measurement head including an accelerometer configured to calculate a wheel angle with respect to gravity; and    a computing device operatively coupled to the measurement head and configured to receive the wheel angle and to compute a wheel alignment parameter based on the wheel angle.    
     
     
         17 . The wheel alignment system of  claim 16 , wherein the wheel alignment parameter includes at least one of toe, camber, and steering axis inclination.  
     
     
         18 . The wheel alignment system of  claim 16 , wherein the accelerometer comprises a micro-electromechanical systems (MEMS) device.  
     
     
         19 . The wheel alignment system of  claim 16 , wherein the accelerometer includes a solid proof mass.  
     
     
         20 . The wheel alignment system of  claim 16 , wherein the accelerometer measures internal changes in heat transfer caused by acceleration.