Apparatus and methods for improving uniformity measurements

Abstract

Apparatus and methods for use in measuring the uniformity of a body such as a tire, wheel or the like wherein a waveform related to the uniformity of the body is digitally sampled to acquire a series of data samples, each of which is correlated with a respective physical location on the body. According to a first aspect of the invention, a non-repetitive error component of the waveform is corrected for by sampling the same location on the body at two different times and determining the difference between the corresponding data samples. A part of the total difference is allocated to each of the data samples in the series according to a predetermined methematical function which at least approximately describes the non-repetitive component of the waveform. The part of the difference allocated to each sample is then subtracted from it to obtain a corrected series of data sample. According to a second aspect of the invention, the maximum, minimum and/or peak-to-peak values of the waveform are more accurately determined by relating selected extreme data samples and one or more data samples adjacent thereto to a polynomial function of at least second order. The function is then evaluated at the location where its first derivative equals zero to determine a more accurate and repeatable approximation of a maximum, minimum or peak-to-peak value of the waveform. According to yet another aspect of the present invention the first and second aspects above are practiced in conjunction with one another.