DE2714324C2 - Photoelectric reflected-light distance measuring device - Google Patents

Description

du = as the optically effective grating constant of the scale grid, which passes through _{with the optically effective gating constant d R of the reference grating}

dg = d / u (.l + v) linked ^f t, and in which the recipients perpendicular to the V ^ nier strip direction each have a mutual distance unequal

η ~ with η = 1,2,3, ..., according to patent

2653545, characterized in that the reference grating (11) is a phase grating is whose diffraction characteristic taking into account the distortion factor ν at least approximately coincides with that of the scale grid (12).

2. Photoelectric Aufllcht-Wegmeßeinrichtung according to claim 1, characterized in that the phase deviation between the individual structural elements of the reference grating corresponds to an optical path difference of about a quarter wavelength of the effective illuminating light and the physically formed grating constant of the reference grating is _{equal to the optically effective grating constant d K.}

The invention relates to a photoelectric transducer device according to patent 26 53 545, as it emerges from the preamble of claim 1.

The ones presented in connection with the main patent Exemplary embodiments each show amplitude grids as reference and scale grids. It is immediately recognizable that with a bridge / gap ratio 1: 1 the opaque bars of the reference grid suppress 50% of the illuminating light from the start.

As far as the webs do not completely cover this amount of light absorb, there may also be disturbing reflections. The same percentage of light losses arise when the light reflected on the scale grating emerges from the measuring system.

The present invention therefore has the object based on another embodiment of the main patent 26 53 545 anchored Aufllicht-Wegmeßeinrichtung indicate, the more luminous and largely free from disturbing reflexes.

With a photoelectric incident light measuring device of the type mentioned at the outset, this object is achieved according to the invention in that the reference grid is a phase grating whose diffraction characteristic at least takes into account the distortion factor ν corresponds approximately to that of the scale grid. The use of phase gratings in photoelectric Distance measuring devices which, however, do not have a distance between the reference and scale grids according to the main patent, is known per se (z. B. DE-OS 23 62 731).

The phase shift between the individual structural elements of the reference grating can correspond to an optical path difference of about a quarter wavelength of the effective illuminating light if the physically formed grating constant of the reference grating is equal to the optically effective grating constant (Iκ according to the main application.

An exemplary embodiment of an optical displacement measuring device according to the invention is given below with reference to described by figures. In detail shows

Fig. La the intensity distribution in the main diffraction orders with an amplitude grating,

F i g. 1 b the intensity distribution in the main diffraction orders with a phase grating with A / 4 phase deviation,

Flg. 2 a reflected light path measuring device in which the Reference grating is a phase grating with A / 4 phase deviation.

The FI g. 1 a and 1 b show the light intensities in comparison in the main diffraction orders for a transmitted-light amplitude grating and a transmitted-light phase grating. Apart from the inevitable reflection losses on air / gas surfaces, the Phase grating almost all of the incoming light passes through the grating. Each phase grating with from A / 2 (A = wavelength of the effective illuminating light) deviating phase deviation between the individual Structural elements also have light components in the 0th order of diffraction. If the phase deviation is about A / 4, then it can be seen that the light intensities In the +1. and the -1. Diffraction order together correspond to the light intensity In the 0th order of diffraction. The phase grating therefore behaves over a certain phase excursion range with regard to it Diffraction characteristics as well as an amplitude smoother same lattice constant with the advantage of almost doubled light intensity.

When explaining the functional principle of the exemplary embodiments according to the main application was made of a geometrically-optically generated silhouette assumed that arises in the interaction of the reference and the scale grid. Of course the resulting stripe pattern could also be less clearly visualized in terms of wave-optics due to interference explain between diffracted beams. Such a declaration would also be immediate for a Structure with a phase grating can be used as a reference grating, since this cannot be clearly explained "Shadow" throws. However, since it was stated above,

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that, under certain conditions, the phase grating is diffractive like an amplitude grating behaves and it is confirmed experimentally that the phase grating performs the same function as the amplitude reference grating, The same representation catfish is used here as in the main application.

In FIG. 2, the reference grating 11 is a phase grating with a preferably λ / 4 phase deviation between the individual structural elements. The measuring system is illuminated by an extended light source 10, for example. The light components reflected on the webs of the scale grating 12 produce the vernier stripe pattern after interaction with the scale grating 11 in the plane 13. In this case, it is' tung, assume in an analogous Betrach-I that the grooves of the phase grating ψ the permeable areas of lattice Amplitudeng and the webs of the opaque areas ύ an amplitude grating, respectively. This geome- '?. The result of the trisch-optical model concept is in V <agreement with the experiment.

v- In the plane 13 then produces a composed of bright and dark stripes j vernier Streifenmusler ■ '■' at a distance y / 5 between the light and ^dark: Ien strips. Preferably at a distance y / 4 are in the

Plane 13 photoelectric receiver 14, 15, 16, 17 reasonable, rules, which are charged at a relative displacement between ■ \ reference and scale grating with periodically alternating, mutually phase-shifted light fluxes. The evaluation of the resulting electrical signals takes place in a known manner. W.

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Claims (1)

Patent claims: 1. Photoelectric incident-light path measuring device with a light source, a reflective scale grid, a reference grid that can be displaced in relation to this and a transparent reference grid with a smoothing constant that differs from the scale grid, an air gap between the two grids, with at least two photoelectric receivers spaced apart in the direction of the path to be measured, which over the scale grid scan the reference grating and, measured in the direction of light, are arranged at least approximately at a distance χ from the grating with the larger optically effective grating constant, for which the following applies: χ = -with
ν a = optically effective air gap between reference and scale grid, ν = - - - = distortion factor y = distance between the vernier strips generated by both grids and with 15th