自由表面による慣性航法-IV : 特有問題(1)

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In the latter half of the previous paper III, the author has reported a theoretical study of several characteristic problems concerning the FS (Free Surface) mechanizations of inertial navigation. This report IV continues the same sort of investigations and treats: 1. Two methods of realizing the free surface without using the accelerometers. One method is to slave the platform surface to the free surface of liquid in a container using non-contact distance sensors and servo-motors. The other simply make use of one or two spirit levelings with the aid of servo-motors. 2. Relations between the errors δβ_j, of the angle measuring sensors and those of the calculated specific force components a_x^n (east-west component) and a_Y^n (north-south component). Here β_j is the direction cosine of the angle a_j between the j-th reference axis and the platform axis Z_p. It was found that the type IN mechanization has a singularity at λ=0, λ is the lattitude, owing to the coincidence of the earth axis Z_E and the north-south axis Y_n, on the equator. This singularity can be removed if the mode of operation is changed from IN to NS or I (1) in the neighborhood of this lattitude. 3. A probabilistic law for obtaining a reasonable value of a_X^n when the calculated value of this component is very small or even imaginary, i.e., when |(a_x^_r|≅0. The reasonable value turns out to be (a_x^n)_r=0. This rule is to apply to the types NS, I (1) and IN mechanizations where the east-west component is calculated by the formula a_X^n=sgn(a_X^n)√<(a_Z^p)^2-(a_Y^n)^2-(a_Z^n)^2>. Here sgn(a_x^n) means the sign of a_X^n, a_Z^p is the negative of the total specific force, and a_Z^n is the vertical component of the specific force vector a. In conjunction with this, the term "insensitive zone of a_X^n around zero" is introduced, which is to be considered a common defect of the types NS, I (1) and IN mechanizations. It is of course desirable to reduce the width of this zone as small as possible, and an appropriate and sensible means for attaining this objective is to use high performance angle measuring devices for α_j thus reducing the errors in β_j. However, concerning the type IN mechanization, this defect can be overcome rather easily by a modification of the mechanization. This revised version which may be called the type IN (R) mechanization has no insensitive zone and does not require the sign monitoring of a_X^n.
社団法人日本航海学会の論文
1986-03-25

著者

成田正
防衛庁技術研究本部第1研究所

自由表面による慣性航法-IV : 特有問題(1)

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