DD201500B1 - METHOD FOR DETERMINING THE POSITION OF AN OPTICALLY ACTIVE STRUCTURE - Google Patents

Description

Field of application of the invention

The invention relates to a method for determining the photomethnic center of an optically active structure along a straight line by means of a known photoreceptor array by arithmetic evaluation of the signals of the structure obtained after projection onto the array. The method can be used both for interpolation in length measurements with measures as well as in the location of edges and spatially extended objects serve

Characteristic of the known technical solutions

There are methods for measuring the length by means of photoreceiver arrays (DE-OS 2543645), whose accuracy is limited by the grid size of the arrays An increase in accuracy by optical magnification (DE-OS 2543645) or by parallel evaluation offset from each other arranged arrays usual (CH -PS 571211) As a result, a higher resolution is possible only by considerably higher technical effort (ζ Β multiple arrays or elaborate optics)

Furthermore, a method is known which allows an increase in resolution by amplitude evaluation of the receiver signals (EP-A 29748). This is an interpolation method which is subject to considerable systematic errors and does not include a uniform definition of the structural position. However, this is more accurate for the application Measurement method important to ensure the comparability of the measurements

Object of the invention

The object of the invention is then to carry out an interpolation within the division of the photoreceptor array in such a way that the photometric center is determined here as the location of the optically active structure. In this way, an exact definition of the position of optically effective structures on photoreceiver arrays should be possible

Explanation of the essence of the invention

The invention has for its object to determine the position of the photometric center of an optically active structure (eg line and edge images) with higher accuracy than by the width of a photo receiver of the array or its equivalent, to determine the grid width of the array is not a resolution limiting Influence on the orientation The task is solved in such a way that the optically active structure is imaged on the photoreceptor array and that from the array or a device which scans the illuminance distribution in a coordinate direction so that the resulting signals that one Corresponding arrays, read signal is evaluated by calculation The position of the fotometnschen center of the structure is at a known illumination power distribution at stroke marks or unknown illumination intensity distribution at edges in the image arbitrarily accurate over with the help of readable from the photoreceiver array amplitude distribution By calculating the integrals required for the photometaneous position determination by summation of individual amplitudes of the receiver arrays. In the case of unknown illuminance distribution of line marks, the position of the photometric center of the latter also becomes from the amplitude distribution according to an approximation method

The nature of the structure will be explained by means of examples of graduations and edges for different illuminance distributions of the structures. The function of the method requires that the image of the optically active structure cover several receivers of the array. This can be done by appropriate magnification and / or targeted blurred imaging be achieved

Rectangular illumination distribution at graduation lines

In this case, under the condition that the receiving width is equal to the pattern width, the location of the photometric center can be exactly determined in fractions of the receiving width (FIG. 1 / FIG. 2).

^{V1 + xbH} = ^A m - ^{xbH + A} m ₊ 1

m + i _x =

^A m + i + Λπ ^A m-

Here, χ is the storage of the photometric center of the receiving edge in fractions of the receiver width b Sinusoidal illumination intensity distribution at graduation marks

The basis is always the signals A _{1 which can be} read out of the receiver array. If the form f (z) of the illuminance distribution is known, the position of the photometary center can be exactly determined from A _1. It results from the definition of the photometric center (see also FIG. 3).

A, = A _r

Ѵл _{і +} °; f (z) dz = £ A _{1 +} (y *> ^b f (z) dz i = O ^X -xb m + 1 ^X O

Furf (z) = cos ² z let xz B be calculated exactly from the following transcendental equation

ε a - T ¹ a = ^{xvir +} Ь ^{sin 2xv} ^

i = m ^x i = 1 ^A i ^Z

where νπ = b

Unknown illuminating distribution at dividing lines

The approximate determination of χ is possible in the following manner: The signals of the individual receivers correspond to the receiver width multiplied by the corresponding illumination intensity averaged over the receiver. The illumination intensity distribution is thus approximately represented by the step-shaped function according to FIG. 4 у be the fraction of a receiver width, The number of the receiver at which the photometsch center of the step function lies exactly within the receiver m is m

0 <у <1

For symmetrical illuminance distributions, this is the receiver with maximum A, and the definition of the photometric center again results

A ₁ = A _n The step function is thus according to FIG. 4

i = m + l

^A i ⁺ V ^A m = (^ y) A _n ⁺ * ^A i

у can be determined from the following equation

ηm-1

v 'Д ^ "Д

у = i = mi = l

^2A m

Any lighting distribution at edges

For finding a photometric edge location, analogous relationships apply. Assuming that the edge location is given by A | = A _r (Figure 5) defines, ζ Β

m-1 O η (1-x) b (1-x) b 5

£ A _{i +} | f (2) dz = £ A - J f (ζ) dz +; f (g) dz

i = 1 -xb m + 1 O O

In turn, m is the number of the recipient for whom:

0 <x <1 you get forx:

η η

^A i -

^{m + 1}

XI

¹ Ä

Hereinafter, the filing χ can be determined exactly for each f (z) without the function profile having to be known exactly.

embodiment

Hereinafter, a device for carrying out the method according to the invention will be described in more detail on an exemplary embodiment. The location of a bright tick mark within a range given by a CCD array should be determined. In the exemplary embodiment (FIG. 6), a reflective line mark 1 is illuminated by means of an incident light illumination system (not shown) and imaged onto the CCD array 3 via the objective 2. The amplitude distribution read from the array is processed in a computer. By the formula apparatus shown above, the photometric center of the bar mark can be determined.

Claims (6)

Invention claim. A method of determining the photometric center of an optically active structure by means of a receiver array or means which scans the illuminance distribution in a coordinate such that the resulting signals correspond to that of an array, characterized in that the photometric center of the structure is of the readable amplitude distribution with a higher accuracy than a receiving width or its equivalent is determined by the required for fotometnschen location determination integrals are determined by summation of individual amplitudes of the receiver array 2 method according to item 1, characterized in that the position of the fotometnschen center of stroke marks known illuminance distribution from the difference of the sums of the individual amplitudes left and right of the fotometnschen center is calculated by the solution of the integral of the illumination intensity distribution in the region of the central receiver element is taken into account 3. Method according to item 1, characterized in that the position of the photometric center of an edge of unknown illumination intensity distribution is calculated from the sum of the amplitudes of the individual receivers covered by the edge transition 4 Method according to item 1, characterized in that, irrespective of the illumination intensity distribution, the photometric center of a line mark is calculated to a good approximation from the readable amplitude distribution by replacing the solution of the integral of the illumination intensity distribution in the region of the central receiver element by an approximation and the difference of Sum of the individual amplitudes is calculated left and right of the photometsch center 5. The method according to item 1, 2 or 4, characterized in that to achieve the coverage of multiple receivers, a broadening of the pattern image by appropriate magnification 6. The method according to item 1, 2 or 4, characterized in that a broadening of the structure image is carried out by targeted fuzzy mapping For this 2 pages drawings