Abstract
To indicate a lighting means for a machine vision application where the resulting irradiance (P′) in an illuminated area (5) at a working distance (d) can be precisely adjusted, an optical covering (2) of the lighting means (1) is provided, which is configured such that a transmitted part (t2) of the incident light (L) passes through (1) the optical covering (2), and a reflected component (r2) of the incident light (L) is reflected in the optical covering (2), wherein a light sensor (3) is provided that detects the intensity (Ir2) of the reflected component (r2) in the optical covering (2). Furthermore, a method is indicated, according to which the intensity (Ir2) of the reflected component (r2) is detected and the radiant power (P) of the light source (1) is regulated on the basis of the intensity (Ir2) in order to adjust the irradiance (P′) of the transmitted component (t2).
Claims
1. A lighting means for illumination in a machine vision application, comprising: at least one light source (7) that emits light (L) with a radiant power (P), wherein an optical covering (2) is provided that is configured such that a transmitted component (t2) of the incident light (L) passes through (1) the optical covering (2) and a reflected component (r2) of the incident light (L) is reflected in the optical covering (2), and wherein a light sensor (3) is provided that detects the intensity (Ir2) of the reflected component (r2) in the optical covering (2).
2. The lighting means according to claim 1, wherein the light sensor (3) detects the intensity of the reflected component (r2) at an edge (2′) of the optical covering (2).
3. The lighting means according to claim 2, wherein a plurality of light sensors (3), preferably four, are provided, which detect the intensity (Ir2) of the reflected component (r2) at a plurality of locations, preferably four, on the edge (2′).
4. The lighting means according to claim 2, wherein the light sensor/light sensors (3) is/are located at the edge (2′) of the optical covering (2).
5. The lighting means according to claim 1, wherein an inner surface (A1) of the optical covering (2) that faces the lighting means (1) is non-reflective.
6. The lighting means according to claim 1, wherein total reflection occurs in the optical covering (2).
7. The lighting means according to claim 1, wherein the light sensor (3) is configured as a spectral sensor that detects the various spectral ranges of the reflected component (r2) in the optical covering (2).
8. The lighting means according to claim 1, wherein a temperature sensor (6) is installed in the vicinity of the light source (7), which serves to detect the ambient temperature (T) of the light source (7).
9. An arrangement with a lighting means according to claim 1 and with a control unit (4), wherein the control unit (4) is connected to the light sensor (3) and the light source (7) and is configured to regulate the radiant power (P) of the light source (7) by means of a control variable (I) based on the intensity (Ir2) of the reflected component (r2) in order to use the transmitted component (t2) to adjust an irradiance (P′) in an illuminated area (5).
10. The arrangement according to claim 9, wherein the control unit (4) is integrated into the lighting means (1).
11. An arrangement with a lighting means (1) according to claim 1, a temperature sensor (6) and a modeling unit (M), wherein the temperature sensor (6) is located in the vicinity of the light source and serves to detect the ambient temperature (T) of the light source (7) and is connected with the modeling unit (M), wherein the modeling unit (M) converts the ambient temperature (T) into the temperature of the light source (7) using a prescribed temperature model.
12. The arrangement according to claim 11, wherein the modeling unit (M) is integrated into the lighting means.
13. A use of the lighting means (1) according to claim 1 for the constant illumination of an illuminated area (5) in a machine vision application.
14. A method for illumination in a machine vision application, wherein light (L) with radiant power (P) is emitted by a light source (7), comprising: a transmitted component (t2) of the light (L) is transmitted through an optical covering (2) and a reflected component (r2) of the light is reflected in the optical covering (2), and in that an intensity (Ir2) of the reflected component (r2) is detected, and in that the radiant power (P) of the light source (1) is regulated on the basis of said intensity (Ir2) so that the transmitted component (t2) can be used to adjust an irradiance (P′) in an illuminated area (5).
15. The method according to claim 14, wherein the intensity (Ir2) of the reflected component (r2) is detected in a plurality of locations, preferably four, in the optical covering (2).
16. The method according to claim 14, wherein the irradiance (P′) at a working distance (d) is kept constant.
17. The method according to claim 14, wherein the ambient temperature (T) of the light source (7) is detected and is drawn upon by a prescribed temperature model to regulate radiant power (P).
18. The method according to claim 17, wherein a conclusion is drawn about the degree of contamination on the optical covering (2) based on the intensity (Ir2), radiant power (P) and temperature (T).
19. The method according to claim 14, wherein an alarm is emitted if the maximum intensity (Ir2) of the reflected component (r2) is exceeded.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The present invention is explained below in greater detail on the basis of FIGS. 1 through 5, which portray advantageous embodiments of the invention in an exemplary, schematic and non-limiting way. The following is shown:
[0034] FIG. 1 shows an arrangement of a machine vision application,
[0035] FIG. 2 shows the claimed device,
[0036] FIG. 3 shows an optical covering with a reflectionless inner surface and total reflection in the covering,
[0037] FIG. 4 shows an optical covering with a reflective inner surface and no total reflection in the covering,
[0038] FIG. 5 shows a top view of a lighting means with four light sensors, four temperature sensors and a plurality of light sources.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0039] A typical arrangement of a machine vision application is represented in FIG. 1. A lighting means 1 with a light source 7 illuminates an illuminated area 5 in a work station 6, e.g. a machining or processing system. The illuminated area 5 of the lighting means 1 contains a component 9, which is illuminated by the lighting means 1 with light that has irradiance P′ and that is recorded by a camera 8, which covers the illuminated area 5 (or a part of it). The image recorded by the camera 8 is evaluated by an evaluating unit 10, and the information obtained therefrom is utilized to control or regulate the work station 6 and/or a processing unit 11 in the work station 6. Of course, the lighting means 1 can also be an integral component of the (smart) camera 8 and/or the evaluating unit 10. Since the design of a machine vision application is sufficiently well-known, the details of machine vision applications and systems will not be discussed here. The claimed method can aid in the constant illumination of the illuminated area 5.
[0040] The claimed lighting means 1 is described in more detail in FIG. 2. To protect the light source 7, the lighting means 1 is covered with a transparent, preferably flat, optical covering 2, e.g. consisting of a suitable glass or plastic. The optical covering 2 thus serves, for example, to protect the light source 7 from dirt or mechanical damage, but, because of the light transmitted through the optical covering 2, it can also perform optical tasks, such as implementing an optical filter or generating a diffuse transmitted light. The largest portion of the light L that is generated by the light source 7 with radiant power P emerges through the covering 2 as transmitted component t2 and has an irradiance P′ at a prescribed or known working distance d in an illuminated area 5. However, a portion of the light L emitted by the light source 7 is reflected in the covering 2 between the optical boundary surfaces of the covering 2. The intensity Ir2 of the reflected component r2 that is reflected in the optical covering 2 is detected by a light sensor 3. The intensity Ir2 is further supplied to the control unit 4, which then regulates the radiant power P of the light source 7 via a control variable I. The control variable I can represent an electric current or an electric output. The control unit 4, which can also be an integral component of the lighting means 1 and/or the camera 8, utilizes the control variable I, preferably a pulse-pause ratio of the control variable I, to regulate the radiant power P of the light source 7 of the lighting means 1, which is adjusted e.g. by a constant current source in order to set a desired, prescribed irradiance P′ at a defined working distance d. The control unit 4 as well as the memory units and processors it requires can be located separately from the lighting means 4 so that they do not require any space within the lighting means 4, or they can also be integrated into the lighting means 1.
[0041] Based on a known relationship between the radiant power P emitted by the light source 7 and the reflected component r2 or measured intensity Ir2 of the reflected component r2 (with a predetermined optical covering 2, predetermined light source 7 and geometry of the arrangement), it is possible to determine from the transmitted component t2 what the irradiance P′ in the illuminated area 5 currently is. Regulating the light source 7 can then aid in adjusting the irradiance P′ or keeping it constant at a working distance d, e.g. on the illuminated surface 5.
[0042] As FIG. 3 shows, the optical covering 2 has as its optical boundary surfaces an inner surface A1, which faces the light source 7, and an outer surface A2, which faces away from the light source 7 and thus faces toward the illuminated area 5. The light L emitted by the light source 7 insides onto the reflectionless inner surface A1 (on the side of the light source), is not reflected in this instance and, in FIG. 3, is conducted to the outer surface A2 as the first transmitted component t1, which corresponds to the incident light L. A reflected component r2 of the first transmitted component t1 (which corresponds here to the incident light L) is reflected on the outer surface A2 back to the inner surface A1. Since a total reflection of the reflected component r2 occurs in the optical covering 2 in FIG. 3, the reflected component r2 is reflected back and forth between the inner surface A1 and outer surface A2 without any further outcoupling and conducted to the edge 2′ of the optical covering 2. The intensity Ir2 of the reflected component r2 is detected by the light sensor 3, e.g. at an edge 2′ of the optical covering 2. Multiple light sensors 3 can also be provided, each of which detects the intensity Ir2 of the respective reflected component r2. In FIG. 3, the light sensor 3 is placed at the edge 2′ of the optical covering. Placing the light sensor 3 on the sides of the optical covering 2, for example, permits an optimal incoupling of the reflected component r2 into the sensor 3. Moreover, the light sensor 3 can be configured as a spectral sensor. Different spectral ranges of the reflected component r2 can thus be detected; in other words, it is possible to differentiate between wavelength and/or color, whereby the intensity of various spectral ranges can be measured separately. The reflected components r2 of light sources 7 which emit light L in different spectra (IR, R, G, B, . . . ) can therefore be distinguished, for example, in the evaluating unit. It is thereby ensured that the necessary sensitivity of the light sensor 3 is established for illumination in different spectral ranges. Particularly in the IR range, simple light sensors 3 that cannot differentiate among spectral ranges have only very low sensitivity or cannot detect these spectra at all. In addition, the radiant power P of the differently colored types of light sources 7 (LED types) can be compared in this way. Irregular behavior of the different types of light sources (e.g. type-dependent, disproportionately declining radiant power P under the same operating conditions) can be detected, and various countermeasures (e.g. increasing the control variable I, longer pauses between pulses of the control variable I to lower the temperature of the lighting means 1, etc.) can then be carried out in response.
[0043] FIG. 4 shows a more general case, in which no total reflection occurs in the optical covering 2, and the inner surface A1 on the side of the light source 7 is not reflectionless. A first reflected component r1 of the incident light L is thus reflected back to the lighting means 2 on the inner surface A1 of the covering 2. This first reflected component r1 is influenced primarily by the angle of incidence of the light L, surface roughness of the inner surface A1 and the refractive index of the optical covering. If a first reflected component r1 is greater than zero, then the first transmitted component t1 of the light L that emerges through the inner surface A1 is less than the incident light L. If the incident light is not reflected on the inner surface A1, then the first transmitted component t1 corresponds to the incident light L, as is represented in FIG. 3.
[0044] The first transmitted component t1, in turn, insides onto the outer surface A2, wherein part of it is transmitted as transmitted component t2 and part of it is reflected back to the inner surface as reflected component r2. The transmitted component t2 subsequently aids in illuminating the illuminated area 5 and accordingly should be sufficiently powerful. The reflected component r2 continues to be reflected between the inner surface A1 and outer surface A2. If total reflection occurs, as in FIG. 3, then the reflected component r2 remains constant, apart from attenuation losses, and is conducted to the edge 2′ of the optical covering 2, where it exits and where the intensity is detected by a light sensor 3. If there is no total reflection within the optical covering 2, as is represented in FIG. 4, then with every reflection a part of the reflected component r2 is coupled out of the optical covering, which functions as a waveguide, and a further reflected component r2′, r2″, r2′″ that has been weakened is detected by the light sensor 3. Of course, this weakening must subsequently be taken into account during the calculation of radiant power P and the control variable I required for it. The aforementioned outcoupling also produces a further reflected component r1′, r1″, r1′″, which, like any emerging reflected component r1, is conducted to the light source 7. Moreover, a further transmitted component t2′, t2″ is brought about, which must be added to the transmitted component t2. Therefore, as long as total reflection does not occur, it is apparent that the calculation of radiant power P and the control variable I requires further reflection and transmission parameters to be provided, although said parameters can be assumed to be known or can be detected by measurement.
[0045] The reflected component r2, the transmitted component t2, the further reflected components r2′, r2″, r2′″ and the further first reflected components r1′, r1″, r1′″ as well as the further transmitted components t2′, t2″ are thus dependent upon the type and characteristics of the covering 2 used, in particular the refractive index and the angles of incidence and reflection. Furthermore, the type of light source 7 (e.g. LED, . . . ) in the lighting means 1 is critical, as is the radiant power P emitted by the light source 7. These parameters can be determined (empirically) in advance for any desired combinations of coverings 2 and light sources 7 and can be considered to be known.
[0046] Owing to external influences, especially temperature fluctuations, it is possible that fluctuations in radiant power P will still occur, which can be offset by detecting the ambient temperature T of the light source 7 by means of a temperature sensor 6, as is indicated in FIG. 2. In addition, a prescribed temperature model is utilized by a modeling unit M, which in this instance is integrated into the control unit 4, and it calculates the actual temperature of the lighting means 1 and corrects the radiant power P in accordance with the temperature. Moreover, a conclusion can be drawn about the contamination of the optical covering 2 based on the temperature and current radiant power P of the light source 7 and the intensity Ir2 of the reflected component r2 in the optical covering (2). The modeling unit M and/or the control unit 4 can be an integral component of the lighting means 1, as shown in FIG. 2, but they can also be located separately.
[0047] FIG. 5 shows a top view of a lighting means 1 with four light sensors 3, all of which are positioned in different sections of the edge 2′ of the optical covering 2. The lighting means 1 comprises a plurality of light sources 7, which share the optical covering 2. The temperature sensors 6 in this instance are advantageously positioned behind the light sources 7, i.e. on the side of the lighting means 1 facing away from the covering 2, in order to minimize the formation of shadows, but they nevertheless permit a precise measurement of the temperature.
