Abstract
An ultrasonic orientation sensor using the phase difference has been developed. The sensing system measures the orientation angles of a surface normal of an object by phase differences of reflected echoes. The measuring algorithm of the sensor is obtained from the mirror property of reflection from an infinite plate. However, the sound reflection from the actual objects with finite and curved surfaces is influenced by diffracted waves. They cause the significant error on measured orientations.
This paper discusses the errors caused by surface conditions on bases of the theory of sound reflection. The phase difference of two received echoes from the arbitrary shaped surfaces is analyzed using numerical solution of the Fresnel-Kirchhoff's diffraction formula. Using the calculation, the errors of measured orientation are evaluated for small rectangular plates and cylindrically or sinusoidally curved surfaces. The calculated results are compared with the experimental results and a good agreement between both results is obtained.
The spatial properties of the sensing system are also discussed. The orientation measurement along an undulated surface shows the characteristics as low-pass spatial filter. The analysis clarifies the limitation of the orientation measurement of curved surfaces and the ability of reducing the influence of small undulations on a surface.
