DE3009690C2 - Optical arrangement for measuring the mean gray value of a reflecting surface - Google Patents

Description

characterized by the following features:

d) there is a rieh over each sub-area (2) prism-shaped light guide body (3) with trapezoidal, plane-parallel base (7) and top surfaces that are perpendicular to the partial surface (2) (8), each with a prism side surface (9) that is not perpendicular to the parallel prism side surfaces (11,12), on the Partial surface (2) stands, the mutually parallel prime side surfaces (11, 12) to Avoiding regular reflections on the partial surface (2) with this one of 90 ° include different angle;

e) the base surfaces (7) and top surfaces (8) are mirrored on the inside;

f) the parallel side surfaces of the prism (11,12) are inside rait a light-absorbing Layer provided;

g) there is a light source in each case on the prismatic surface (10) opposite the partial surface (2) (4) and an optical receiver (5) arranged; .in

h) the light source (4) and the optical receiver (5) are each so opposite to the associated Partial area (2) shifted that an incident perpendicular for an imaginary reflection of rays of the Light source (4) lies on the measuring surface to the optical receiver (5) outside of the partial surface (2).

2. Optical arrangement after spoke!, Marked by the feature:

50

i) in order to avoid reflection within a safety angle ± <5, which depends on the unevenness of the reflecting measuring surface (1), there is also an incidence perpendicular rotated by the safety angle δ for an imaginary reflection of rays from the light source (4) on the measuring surface (1) ) to the optical receiver (5) outside the partial area (2).

3. An optical arrangement according to claim 1 or 2, characterized in that the light source (4) each perpendicular to at least about Deiri net edge portion of a narrow side of the associated Teilfläclhe (2) angeord · ¹

'4. Optical arrangement according to one of Claims to 3, characterized in that the Partial surface (2) in each case opposite prism side surface (10) is perpendicular to each other parallel opposite prism side surfaces (11,12).

5. Optical arrangement iiach one of the claims 1 to 4, characterized in that the light guide bodies (3) each have a matrix row with adjacent Base surfaces and top surfaces have a common light source (4).

6. Optical arrangement according to one of claims 1 to 5, characterized in that each a partition is located between the light source (4) and the associated optical receiver (5) which neither in the angle of incidence of the light source

(4) on the associated surface area (2) still in the receiving angle range of the optical receiver

(5) extends in from the associated partial area (2)

7. Optical arrangement according to claim 6, characterized in that the partition consists of two in at an angle to each other facing diaphragms (S).

8. Optical arrangement according to one of claims 1 to 7, characterized in that the optical axis of the optical receiver (5) is more inclined to the measuring surface (1) by the angle β than the parallel prism side surfaces (11, 12).

9. Optical arrangement according to one of claims 1 to 8, characterized in that the light guide body (3) are hollow.

10. Optical arrangement according to one of the claims 1 to 9, characterized in that the aspect ratio of the partial areas (2) is approximately between 7: 1 and 20: 1

The invention relates to an optical arrangement for measuring the mean gray value of a reflective Area with the characteristics:

a) a light source as an optical emitter is above the Measuring surface attached;

b) an optical receiver is mounted above the measuring surface in such a way that it receives only the radiation from the light source which is diffusely reflected nn the measuring surface;

c) the measuring area is in a matrix of several sub-areas in the form of narrow rectangles divided.

A device for measuring the average density distribution of a transparent original with the Features a) to c) are known from DE-OS 26 41 130. It becomes application-related The reason for this is that the original surface is subdivided into a matrix of sub-areas and the mean luminance factor as a measuring surface measured on each sub-area. The matrix of luminance factors determined in this way can then, for example can be used to automatically adjust the ink feed on printing machines.

According to the present invention, the mean gray values of a non-transparent original, z. B. a print template, can be determined by measuring an average luminance factor.

With such a measurement, matt and glossy colors with the same gray values must be the same be rated.

This means that regular reflections, i.e. h, reflections may not be taken into account. Exclusively reflected by diffuse surface scattering Rays are allowed to be used in the optical receiver

will. Both the low intensity of this radiation and the uniform illumination of the partial areas bring technical problems for the realization taking into account the prohibition of mirroring.

The present invention is based on the object of overcoming these problems, but in doing so to forego the use of focusing elements. A matrix of many individual optics would make the optical arrangement very expensive.

To solve this problem, with an optical arrangement of the type mentioned at the beginning proposed the following features according to the invention:

d) there is a prism-shaped one above each sub-area Light guide body with trapezoidal, plane-parallel, base and top surfaces that are perpendicular to the partial surface, each with a prism side surface, which is not at right angles to the parallel prism side surfaces on the partial surface stands, the mutually parallel prism side surfaces to avoid regular reflections on the surface with this an angle deviating from 90 °! lock in;

e) the base and top surface: are inside mirrored;

f) the parallel side surfaces of the prism are coated on the inside with a light-absorbing layer Mistake;

g) on the side face of the prism opposite the part face, there are each a light source and a optical receiver arranged;

h) the light source and the optical receiver are each in such a way opposite to the associated partial surface » moved that an incidence line for an imaginary reflection of rays of the light source at the Measuring surface to the optical receiver is outside of the sub-area

The prism-shaped light guide body are, in other words, in each case an open at the end faces, preferably hollow box with two plane-parallel rectangular ^f örmigen narrow sides and with two plane-parallel trapezoidal broadsides. The narrow sides are coated on the inside to absorb light, the broad sides are mirrored on the inside. Such a box serves to guide light radiation in parallel and can therefore also be referred to as an optical parallel point.

Each light guide has its own optical receiver and its own light source, according to According to an advantageous embodiment, the light guide bodies each have a matrix row with adjacent ones Base surfaces and top surfaces have a common light source, for example in the form of a fluorescent lamp or flash lamp.

An arrangement according to the invention forms a cost-saving solution to this problem. In comparison The optics to be focused are not only cheap to manufacture; they are also regarding the evaluable light intensity technically better than focusing optics. The mirror surfaces will the light source apparently lengthened depending on the reflectance of the mirror used, the The angle of reflection in planes perpendicular to the mirror surfaces cannot be changed. The degree of inclination these planes to the partial surfaces is retained in such reflections. A reflection on the face to the recipient is therefore not caused by it. Without the apparent elongation, the intensity would be the radiation of the falling on a Tdifurface Light source inversely proportional to the square of the distance between the light source and the surface area. With the apparent elongation of the light source decreases the exponent, and the proportional dependence reads

where / is the incident light intensity and r is the ίο distance of the light source from the surface area. χ has a value between 1 and 2 and is dependent on the quotient L / r with L as the apparent length of the light source.

The reduced dependence of the intensity on the

The distance between the light source and the sub-area also reduces the different assessment of the sub-area edges the narrow sides, which are caused by their different distances from the light source and from the optical Receiver is caused As a result, an arrangement according to the invention achieves a largely uniform one Evaluation of the measuring surface.

An advantageous embodiment of the arrangement according to the invention provides the following feature:

i) to avoid reflection within a safety angle ± δ, which depends on the unevenness of the reflecting measuring surface, there is also an incidence perpendicular rotated by the safety angle <5 for an imaginary reflection of rays from the light source on the measuring surface to the optical receiver outside the partial surface.

This means that it should be prevented with certainty that even with an uneven measuring surface, as is the case with Color fringes is the case, a reflection to the optical receiver takes place.

If the prohibition of the reflection on a partial surface the light source and the optical receiver as possible moved away from the space vertically above the partial surface and the inclined position of the light guide body is caused, then For the most uniform possible illumination of the partial area, it is advantageous if the light source in each case is arranged perpendicularly at least over the edge part of a narrow side of the associated partial area; the The light source should therefore, if possible, still be above the partial area in order to make up the difference in the distances to the To keep the narrow sides of the part surface small.

It is also advantageous if each of the sub-areas opposite prism side surface is perpendicular to the mutually opposite prism side surfaces parallel to each other. The trapezoidal shape of the bottom surfaces and top surfaces of the light guide body then only softens the side common to the partial areas from the rectangular shape.

According to a more advantageous embodiment * ■> L.! Is found between the light source and the associated optical receiver a partition that is neither in the angle of incidence of the light source on the associated partial area still in the iümpfangswinkelbcreich of the optical receiver extends from the associated surface area

This also avoids direct irradiation of the optical receiver by the light source. These Partition wall can also 7, We) at an angle facing one another. They delimit the area between the angle of incidence and the reception area.

In the figures of the drawing are two AusÜÜhrungsbeispiele an optical arrangement according to the invention

shown. It shows

F i g. 1 is an overall perspective view,

2 shows the side view of an individual light guide body,

3 shows the top view of a single light guide body and

4 again the side view of an individual light guide body with a different arrangement of the light source.

Dimensioning rules should be applied to FIGS. 2 and 4 which guarantee compliance with the underlying conditions.

In FIG. 1, a measuring surface 1 is divided into three rows with nine partial surfaces 2 each. The sub-areas 2 are rectangles with an aspect ratio of about 1: 7. Above the sub-areas 2 - in the drawing it is shown the other way round for the sake of clarity, ie hanging under the sub-areas 2 3 zn stand. Fr is a prism-shaped box with a trapezoidal cross-section and is open on the opposing, non-parallel prism rope surfaces 9, 10. The other non-parallel prism surface 10 is perpendicular to the closed prism side surfaces 7, 8, 11, 12. The mutually opposing, mutually parallel prism side surfaces 11, 12 are compared with the normal to the surface portion 2 by the so tilted angle a, that is, all light-guiding body 3 are at the same angle obliquely on the partial surfaces 2. Their base surfaces 7 and top surfaces 8 are perpendicular to the partial surfaces 2. The trapezoidal shape of the prism cross-section therefore only deviates from the J5 rectangular shape on one side. A rod-shaped light source 4 lies transversely above each row of light guide bodies 3, approximately in the middle of the open prism side surface 10, which lies opposite the sub-surface 2 located below. In the corner of this open prism side surface 10, which lies on the shorter closed prism side surface 11, an optical receiver 5 is arranged in each case.

The base surfaces 7 and top surfaces 8 of each light guide body 3 are mirrored on the inside. The one another Opposite prism side surfaces 11, 12 are provided on the inside with a light-absorbing layer.

In FIG. 2 shows a single light guide body 3 in a side view. This side view shows the trapezoidal cross-section with the corner points A, B, C, D. At A the trapezoid has the obtuse angle 90 ° + «, at B the acute angle 90 ° -ä. at C and D each have a right angle. A and B delimit the partial surface 2 over which the light guide body 3 is arranged. The angle of inclination of the light guide body 3 caused by the different angles at A and B is α. The short side of the parallel trapezoidal sides 11 has the length h, the long side 12 the length k - their distance from each other is called c , the distance AB is called b , & L is the length of the partial surface 2. About the middle of the rectangular bounded Trapezoidal side 10, the light source 4 is in cross-section At the edge of this trapezoidal side 10 at C, on the parallel short trapezoidal side 11. The optical receiver is 5. The outermost distance of the light source 4 from the short parallel trapezoidal side 11 is denoted by «/, the outermost Distance of the optical receiver 5 therefrom with g. The optical receiver 5 is inclined in its optical axis with respect to the short parallel trapezoidal side U by the angle β in the direction of point B, that is to say to the partial surface 2. Between the light source 4 and the optical receiver 5 there is an angular diaphragm 6, the tip of which extends into the light guide body and roughly delimits the angular range between the angle of incidence of the light source 4 on the partial surface 2 and the reception angle range of the optical receiver 5 from the partial surface 2. The entry point of the optical receiver 5 is designated in its optical axis with E , the corresponding point of the light source in its optical axis with F. The outermost point of the optical receiver 5 at the distance g from the short parallel trapezoidal side 11 is designated with G , the corresponding point of the light source 4 with the distance t / with H. The length of the connecting line EA is W, that of the connecting line EB is h ". The length of the connecting line FA is I ₂ ', that of the connecting line FB is //'.

In FIG. 2, the rays are included which, in the worst case, could cause a reflection on the partial surface 2. These are the connections HA at the angle <p2_S ^e g ^{er |} to the normal on the compound A and GA at an angle relative to the normal on φι A. Their bisector has respect to the normal on the angle A O = '/ 2 (φι + φ _2).

In order to avoid reflection on the partial surface, this angle must be ό> 0, provided that the partial surface 2 is completely flat. Under realistic conditions where the angle of reflection = angle of incidence ± ό. ie where a safety angle ί?, ί has to be observed due to uneven surface area 2, the angle ό of the bisector between G and H in relation to A must have at least this value. For the angle of inclination λ of the light guide body 3 and the length / 1, taking into account δ, c / and g, the following relationship applies:

tan (ff - δ) =

2 /,

(Fig. 2)

For the optimization of the uniformity of the evaluation over the entire sub-area 2, the factor k < 1 is given, which specifies the maximum permissible difference in the intensities from points A and B of sub-area 2. The optical arrangement must then be designed with the following relationships:

> k

/ ί = / (CS) ² + /! / Γ = ν ^ ΤΤΓ = V (C - d) ² +% H = I ₁ -τ b ■ sin a C. - b cos ir

⁼ Exponent of the distance dependency
of intensity J

ftrl * fo * ^Bf TrdfVn «

walls

The F i g. 3 shows the top view of a light guide body 3, as a rope view of the prism shape, rectangular in that the prism side surfaces are perpendicular to the bottom surface 7 and top surface 8.

In FIG. 4 with the trapezoid ABCD as a side view of a light guide body 3, the light source 4 and the optical receiver 5, it is clear how the fictitious reflection points /, K come to lie when mirroring on the measuring surface k / iJ outside the partial surface 2, the light source 4 is so far moved over the partial surface 2 that it is still perpendicular to the edge part at A

comes to stand. Da «is favorable for uniform illumination. A reflection would first take place at the point /. This means that the perpendicular would be on point /, which, however, is far from point A outside of sub-area 2. If one takes into account the safety angle <5 and a possible incidence perpendicular to this angle, then it would be at point K, at which the reflection would then take place.But since this point K is also outside the partial area 2, reflection is definitely avoided.

llicrzu 3 sheets of drawings

130225/471

i2ä ^^

Claims (1)

Patent claims: 1, Optical arrangement for measuring the mean gray value of a reflective surface with the Features: a) a light source as an optical radiator is attached above the measuring surface; b) an optical receiver is mounted over the measuring surface in such a way that it only touches the Measuring surface receives diffusely reflected radiation from the light source; c) the measuring area is in a matrix of several sub-areas in the form of narrow rectangles divided;