Incremental measuring instrument

DETAILED DESCRIPTION The present invention is directed to an instrument of the type mentioned at the outset, in which the measuring signal corresponding to the brightness fluctuations of the image zone presents an amplitude and frequency sufficient for the further processing of the signal and in which the interference constituent of the measuring signal is low.
In the instrument of this invention, the stripes of the striped pattern of the disc are arranged in the form of involutes, which proceed from a base circle centered at the pivot point of the disc.
Furthermore, the projection of the one striped pattern on the other striped pattern is arranged such that the stripes of the striped pattern of the scale are oriented substantially perpendicular to a tangent passing from the image of these stripes at the disc onto the base circle of the involute stripes of the striped pattern of the disc.
Because the involute stripes of the striped pattern of the disc have the same center of curvature in the image zone the involute stripes can be brought into virtually complete alignment with stripes arranged parallel to one another on the striped pattern of the scale.
A striped pattern with a plurality of involute stripes can be arranged on the disk.
The frequency of the measuring signal is higher than the frequency of the disk by a factor equal to the number of involute stripes on the disk.
It is particularly advantageous to place the image zone in such a way that the length of the tangent between the base circle and the intersection of the striped patterns is large in the scale of the image in comparison to the length of the stripes of the striped patterns in the image.
By reason of the small relative change of radius of curvature between the involute stripes in the image zone, the curvature of these stripes is virtually the same and these stripes can be brought into very good alignment with the stripes of the scale.
The stripes of the scale can be formed either as adjacent, like-oriented, slightly curved stripes having a radius of curvature that corresponds to the mean radius of curvature of the involute stripes of the disk, or alternately, as straight, parallel stripes