1982-05-17
1984-10-02
Henry, Jon W.
350374, 350401, G02B 2760
Patent
active
044744307
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a leading mark, more precisely to an instrument for marking a definite direction for an observer.
Instruments utilizing light interference technique for indicating a plane are previously known a.o. through the Swedish patent specifications Nos. 7611513-8 and 354 354, which relate to an instrument utilizing moire technique for bringing about for an observer the indication of a certain horizontal or vertical plane.
The instrument according to said patents comprises three screens, each of which consists of opaque lines separated by transparent interstices. When viewing the instrument, indication is obtained that the observer is outside a certain plane defined by the instrument, in that an interference pattern, a so-called moire pattern arises which includes lines with a discontinuous angular deviation.
In the Swedish patent specification No. 354 354 an instrument is disclosed, at which two screen plates are provided angularly relative one another, and the division of the screens, i.e. the number of opaque lines per length unit perpendicular to the opaque lines, are selected so that an interference pattern arises which is to be read in respect of the symmetry of the pattern.
An accurate determination of the indicated plane by means of such a pattern is extremely difficult.
The instruments above referred to per se render a very high accuracy, but this type of indication does not meet certain requirements for leading marking.
One of these requirements is that upon viewing the instrument it must be clearly apparent therefrom, in a simple way, preferably by marking in the form of arrows, in which direction a deviation from the leading line prevails.
A further requirement is very uniform quality in respect of the active elements of the instruments and of their location, in order thereby to obtain identical interference patterns produced by different instruments for the same deviation from the leading line.
The present invention solves the aforesaid problems by a combination of the design of the screens and their attachment means. The screens according to the invention are formed so that the precision of the position in a first direction is less essential, and so that the necessary precision in respect of their position in a direction perpendicular to the first direction is obtained automatically by the attachment means.
The present invention relates to an instrument for marking leading lines, comprising a front screen and a behind screen, which include opaque lines separated by transparent interstices, in such a manner, that upon viewing the instrument an interference pattern, a so-called moire pattern, arises, said screens having different division, i.e. different distances between the opaque lines. The invention is characterized in that each of said screens comprises a plate, which centrally is bent to form an obtuse angle, that two such screen plates are positioned by attachment means so that the obtuse angles either face toward each other, in which case the front screen plate is provided with a screen division of greater density than the behind screen plate, or alternatively so that the obtuse angles face away from each other, in which case the front screen plate is provided with a screen division more sparse than the behind screen plate.
The invention is described in greater detail in the following, with reference to the accompanying drawings, in which
FIGS. 1 and 6 schematically show screen settings according to the invention,
FIG. 2 shows the instrument seen along its stated leading line,
FIG. 3 is a view where the right-hand side piece in FIG. 2 has been removed,
FIG. 4 shows the instrument observed to the left of its stated leading line,
FIG. 5 shows the instrument observed to the right of its stated leading line.
In FIG. 1 a screen setting according to the invention is shown schematically, where each screen 1,2 includes opaque lines 3 separated by transparent interstices 4. The screens 1,2 are arranged overlapping so that an observer viewing the screens from a direction indicated
REFERENCES:
patent: 3604813 (1971-09-01), Te Kronnie et al.
patent: 4166699 (1979-09-01), Bergkvist
patent: 4242000 (1980-12-01), Bergkvist
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