Method and device for analyzing the interaction between a surface of a sample and a liquid

Abstract

A method for analyzing an interaction between a sample surface and a drop of liquid comprises applying the drop of liquid to the sample surface and illuminating the drop of liquid using at least two light sources. The at least two light sources are each arranged at a light source position surrounding the drop of liquid. Light reflected from the drop of liquid detecting and a sensor position on a sensor of a camera is determined for each detected light reflection. Light source positions are assigned to individual light source positions. A position of the drop of liquid is calculated relative to the sensor and an item of size information of the drop of liquid is determined. The position and the item of size information are calculated from the pairs of one sensor position and one associated light source position.

Claims

1. A method for analyzing an interaction between a sample surface and a drop of liquid, the method comprising: (a) applying the drop of liquid to the sample surface; (b) illuminating the drop of liquid using at least two light sources, wherein each of the at least two light sources is arranged at a light source position surrounding the drop of liquid; (c) detecting light reflecting from the drop of liquid; (d) determining a sensor position on a sensor of a camera for each detected light reflection; (e) assigning individual light source positions to individual sensor positions, such that at least four pairs each of one sensor position and one associated light source position are provided; and (f) calculating a position of the drop of liquid relative to the sensor and an item of size information of the drop of liquid, wherein the position and the item of size information are calculated from the at least four pairs of one sensor position and one associated light source position.

2. The method according to claim 1, wherein the at least two light sources are formed by discrete lamps.

3. The method according to claim 1, wherein the light sources comprise first light sources and second light sources, and wherein the first light sources arc smaller than the second light sources.

4. The method according to claim 1, wherein the light sources comprise first light sources and second light sources, and wherein the first light sources are positioned at a shorter distance from one another than the second light sources.

5. The method according to claim 1, wherein the detecting light reflections and the determining the sensor position are repeated for individual light sources and for different groups of individual light sources.

6. The method according to claim 5, wherein the individual light source is contained in at least two of the different groups of individual light sources.

7. The method according to claim 1, wherein additional light reflections from the drop of liquid are detected using an additional camera, and wherein a sensor position on a sensor of the additional camera is determined for each additional light reflection.

8. The method according to claim 7, wherein the camera and the additional camera include viewing directions that differ from one another by an angle of at least 10°.

9. The method according to claim 1, wherein the light sources are uniformly positioned around the drop of liquid.

10. The method according to claim 9, wherein the positions of the light sources when viewed from the drop of liquid cover a solid angle in range of π/8 sr to 2 π sr.

11. A method for analyzing an interaction between a sample surface and a drop of liquid, the method comprising: (a) applying the drop of liquid to the sample surface; (b) illuminating the drop of liquid using at least two light sources, wherein each of the at least two light sources is arranged at a light source position surrounding the drop of liquid; (c) detecting light reflecting from the drop of liquid; (d) determining a sensor position on a sensor of a camera for each detected light reflection; (e) assigning individual light source positions to individual sensor positions, such that pairs each of one sensor position and one associated light source position are provided; (f) calculating a position of the drop of liquid relative to the sensor and an item of size information of the drop of liquid, wherein the position and the item of size information are calculated from the pairs of one sensor position and one associated light source position; and (g) creating a template showing expected sensor positions of the light reflections based on the light source positions, wherein the detected light reflections are compared with the template prior to the calculating a position of the drop of liquid relative to the sensor and an item of size information of the drop.

12. A method for analyzing an interaction between a sample surface and a drop of liquid, the method comprising: (a) applying the drop of liquid to the sample surface; (b) illuminating the drop of liquid using at least two light sources, wherein each of the at least two light sources is arranged at a light source position surrounding the drop of liquid; (c) detecting light reflecting from the drop of liquid; (d) determining a sensor position on a sensor of a camera for each detected light reflection; (e) assigning individual light source positions to individual sensor positions, such that pairs each of one sensor position and one associated light source position are provided; and (f) calculating a position of the drop of liquid relative to the sensor and an item of size information of the drop of liquid, wherein the position and the item of size information are calculated from the pairs of one sensor position and one associated light source position, wherein the calculating the position of the drop of liquid relative to the sensor and an item of size information of the drop of liquid comprises calculating a plurality of normal vectors describing possible arrangements of a reflecting surface region for each of the pairs.

13. The method according to claim 12, wherein an assumed drop surface is varied and compared with the normal vectors calculated for the pairs in an optimization process.

14. The method according to claim 13, wherein calculating the position of the drop of liquid comprises calculating points of intersection for planes that each comprise a light source position and a sight beam of the camera that corresponds to the sensor position associated with the light source position.

15. The method according to claim 13, wherein a contact angle of the drop of liquid is calculated using the calculated position of the drop of liquid and the item of size information.

16. A device for analyzing an interaction between a sample surface and a drop of liquid, the device comprising: an apparatus configured to apply the drop of liquid at an application site on the sample surface; a plurality of light sources each arranged at a light source position surrounding the application site and configured to illuminate the drop of liquid; a camera comprising a sensor and oriented toward the application site, wherein the camera is configured to detect light reflecting from the drop of liquid; and an electronic evaluation apparatus configured to, determine a sensor position on the sensor of the camera for each detected light reflection, assign individual light source positions to individual sensor positions, wherein at least four pairs each of one sensor position and one associated light source position are provided, and calculate a position of the drop of liquid relative to the sensor and an item of size information of the drop of liquid, wherein the position and the item of size information are calculated from the at least four pairs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be explained in greater detail based on the exemplary embodiments shown in the figures, in which:

(2) FIG. 1 illustrates a schematic representation of an embodiment of a device for analyzing an interaction between a surface of a sample and a liquid;

(3) FIG. 2 illustrates an embodiment of a template;

(4) FIG. 3 illustrates a schematic representation of an example of an image captured by a camera of the device; and

(5) FIG. 4 illustrates a top view of a schematic representation of another embodiment of a device for analyzing the interaction between a surface of a sample and a liquid.

DETAILED DESCRIPTION OF THE INVENTION

(6) A sample with a sample surface 10 is shown shaded in on the bottom edge of FIG. 1. A drop T of a transparent liquid is located on the sample surface. The drop T is approximately spherical and rests on the sample surface 10 so as to form a contact angle α. Said drop was applied to the sample surface 10 using a suitable dosing device.

(7) The device by means of which the drop T is measured comprises two light sources L.sub.1 and L.sub.2, which are each located at a light source position, which are also referred to as L.sub.1 and L.sub.2 in the following. Furthermore, the device comprises a camera K and an evaluation apparatus 12 connected to the camera. The camera K is located at a rigidly defined position, also referred to as K in the following, relative to the two light sources L1 and L2. The evaluation apparatus 12 may in particular be a microcomputer integrated in the device or an external computer that is coupled to the remaining elements of the device, which may be grouped together as a measuring head. The camera K comprises a lens 14 and a sensor 16, which comprises a sensor surface onto which a field of view of the camera K is imaged by means of the lens 14.

(8) The two light sources L1 and L2 are arranged such that they illuminate a surface of the drop T. A light beam 18 emanating from the light source L1 strikes a point P1 on the surface of the drop T, where it is reflected in a mirror-symmetrical manner with respect to a normal vector nP1. The light coming from the light source L1 and reflected at the point P1 is imaged onto the point K1 of the sensor 16. The camera K therefore detects a light reflection of the light source L1 at the sensor position K1. Similarly, the camera K detects a light reflection of the light source L2 at the sensor position K2. The reflection of the associated light beam 20 coming from the light source L2 takes place at the point P2 on the surface of the drop T, in a mirror-symmetrical manner with respect to the normal vector nP2.

(9) The associated reflection point on the drop surface generally cannot be determined from a single light reflection and the associated sensor position. Following the camera sight beam 22 associated with the sensor position K.sub.1, the light striking the sensor 16 along this sight beam 22 at the sensor position K.sub.1 could come not only from the point P.sub.1, but equally from any other point on the sight beam, for example from the point P.sub.1′ if there were a specularly reflective surface described by the normal vector n.sub.S1′ present at this point. In this case, the light emanating from the light source L.sub.1 would arrive at the point P.sub.1′ along a beam 18′.

(10) This ambiguity can be solved, for example, by incorporating several pairs of light source positions and sensor positions into the evaluation and comparing these with assumed surface geometries. This is illustrated in FIG. 1 using an assumed surface of another drop T′, which is shown as a dashed line. However, the direction of the normal vector nP1′, which describes the orientation of the surface of said drop T′ at the point P1′ at which the light beam 18′ would have been reflected, deviates significantly from the direction of the unit vector nS1′ describing the reflection. This deviation shows that the light striking the sensor position K1 cannot actually come from the surface of the assumed drop T′.

(11) FIG. 1 also shows the hypothetical situation of a reflection of the light source L2 at the point P2′ on the assumed drop T′ using corresponding reference signs. In the case of an assumed reflection at this point P2′, too, the normal vector nP2′ on the surface of the drop T′ at the point of intersection with the sight beam 24 deviates significantly from the unit vector nS2′ describing the theoretically conceivable reflection. This shows that, when a sufficient number of pairs K1-L1, K2-L2, . . . , K1-Li of individual sensor positions K1, K2, . . . , Ki and associated light source positions L1, L2, . . . , Li are used, it is possible to calculate whether or not an assumed drop geometry is consistent with the observed pairs. In this way, the position and an item of size information of the drop can be calculated for example in an optimization method.

(12) It is important for the method that the sensor positions K1, K2 of the detected light reflections can be clearly assigned to the individual light source positions L1, L2. In this regard, FIGS. 2 and 3 illustrate assignment with the aid of a template, which indicates the expected sensor positions of the light reflections. The template shows seven light reflections that are represented as filled-in circles and that are produced by seven light sources in a specific arrangement. The light reflections shown in the template are based on the assumption that the light beams emanating from these light sources are reflected on a typical drop.

(13) FIG. 3 schematically shows an image captured by a camera K, in which the outline of the drop T is shown for illustrative purposes. In the real camera image, this outline is either hard to make out or, under certain circumstances, entirely indiscernible. The camera image also shows a total of eleven light reflections, of which seven are shown as filled-in circles. These come from the reflection on the drop T of the seven light sources on which the template is based. Their arrangement resembles that of the template in FIG. 2, and therefore, by means of comparison with the template, the light reflections detected by the camera and shown as filled-in circles in FIG. 3 can be assigned to the individual light source positions. The camera image in FIG. 3 also shows four other light reflections represented as circles that have not been filled in. These come either from other light sources that are not intended to be included in the evaluation or arise as a result of interfering multiple reflections, for example within the drop or on the surface of the sample. They have no equivalent in the template, and therefore they can simply be identified as interfering signals by comparing the camera image from FIG. 3 with the template from FIG. 2.

(14) FIG. 4 is a schematic view from above of another device for characterizing a surface of a sample and comprising two cameras K and K′. Only one light source L.sub.1 is shown in this figure. A drop T having a center M is also shown. In the representation in FIG. 4, the sample surface (not shown) is viewed approximately from above, and therefore the drop T appears as a full circle. A unit vector d.sub.KL1 from the camera K to the light source L.sub.1 is shown for the camera K, as is a unit vector d.sub.KP1 that corresponds to the sight beam from the camera to a reflection point P.sub.1 on the surface of the drop T. The two unit vectors d.sub.KL1 and d.sub.KP1 span a plane that comprises the sight beam of the camera K as well as the light source L.sub.1. The normal vector n.sub.nP1 on the surface of the drop T at the point P.sub.1 as well as the center M also lie in this plane. The same applies to the plane spanned by the unit vectors d.sub.K′L1 and d.sub.K′P2, meaning that a line containing the center M can be determined from the intersection of the two planes. When at least one other light source or another camera is used, three planes that intersect in the center M of the drop are obtained. The calculation of the planes therefore provides information about the position of the drop T.

LIST OF REFERENCE SIGNS

(15) 10 Sample surface 12 Evaluation apparatus 14 Lens 16 Sensor 18 Light beam from L.sub.1 20 Light beam from L.sub.2 22 Sight beam K.sub.1 24 Sight beam K.sub.2 K Camera K′ Additional camera K.sub.1 Sensor position of the light reflection from L.sub.1 K.sub.2 Sensor position of the light reflection from L.sub.2 L.sub.1 Light source L.sub.2 Light source P.sub.1, P.sub.2 Points on the surface of the drop T T Drop T′ Assumed drop P.sub.1′, P.sub.2′ Points on the surface of the assumed drop T′ M Center α, α′ Contact angle