Identification method of sensor directions and sensitivities in multi-axis accelerometer

With conventional accelerometer examination, e.g. ISO standard, mainly adopts linear motion based on an assumption that each actual sensor direction corresponds to the package direction. However, actual sensor directions do not agree with the package directions in fact. In addition, conventional methods have major problems as follows. 1) About sensor output, it is almost impossible to separate the effects of sensor inclination and sensitivity. 2) Measuring actual sensor direction is very difficult because the offset voltage changes continuously. 3) With linear motion, the reference of the input acceleration includes large calculation error because 2nd order differential is required. 4) Even if allowing sensor inclination error, 3 times measurements are necessary to know all sensitivities of a 3-axis accelerometer. This study proposes a novel examination method with an exciter mechanism using parallel linkage. The exciter rotates a target accelerometer in a uniform circular motion keeping the accelerometer posture constant against the external coordinate system. With balanced structure, the exciter inputs stable sine wave acceleration for each sensor. The advantages of this method are as follows. 1) It is possible to separate the effects of sensor inclination and sensitivity from the phase and the amplitude of the sine wave output. 2) It is possible to measure the actual sensor direction because the offset change can be removed by referring stable cyclic input acceleration. 3) Calculated input acceleration is reliable because it requires only 1st order differential. 4) Only 2 times measurements are enough to examine 3 actual sensor directions and 3 sensitivities for 3-axis accelerometer. With commercially available MEMS 3-axis accelerometer, the sensor directions and sensitivities are measured individually by a prototype exciter. The results showed good agreement in two different experimental conditions. Between the two conditions, the maximum difference of the sensor directions and the sensitivities are less than 0.8% and 1.6% respectively.