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

Abstract

The present invention relates to a method for analyzing the interaction between a sample surface and a liquid, comprising the following steps: a) applying a droplet of the liquid to the sample surface; b) irradiating the droplet with a plurality of light sources, which are respectively arranged in a light source position around the droplet; c) detecting light reflections of the light sources from the droplet with a camera, and for each detected light reflection, determining a sensor position on the sensor of the camera; d) matching each individual light source position with each individual sensor position, so that there are pairs consisting of a sensor position and a corresponding light source position respectively; e) calculating the position and size information of the droplet from these pairs.

Description

Technical Field

[0001] The invention relates to a method and a device for analyzing the interaction between the surface of a sample and a liquid, droplets of the liquid being applied to the sample surface and measured. This method gives conclusions about the surface properties of the sample, since these properties determine the interaction with the applied liquid. Background Art

[0002] The data that is usually used in this case to characterize the surface properties is the so-called contact angle, which occurs in contact with a specific test liquid. In order to determine the contact angle, a method is known, for example, from the document DE 197 54 765 C1, in which a shadow image of a droplet is recorded from a lateral viewing direction. The contour of the droplet and the boundary surface with the sample can be identified in the shadow image, so that the contact angle can be directly obtained from the shadow image. However, the boundary surface and the droplet contour cannot always be clearly identified in the shadow image, which may lead to inaccuracies. In addition, automatic evaluation can only be achieved to a limited extent. Usually, an experienced operator is required to obtain reliable results.

[0003] In another known method, the contact angle of a droplet is calculated based on the known volume of the droplet and the diameter of the droplet detected from above by a camera. In order to accurately determine the diameter, the distance between the camera and the droplet must be known. In addition, greater errors occur in the case of large contact angles, because for large contact angles the diameter of the droplet changes only slightly with the contact angle.

[0004] Another method for determining the contact angle is known from document EP 2 093 557 B1, in which the droplet is likewise observed from above by means of a camera. Two light sources are arranged at a lateral distance from the optical axis of the camera, on which the droplet must lie. The camera captures an image of the light reflections of the light sources. The distances of the relevant image points from the optical axis or from one another are evaluated. If the distance to the sample surface is known, the radius of the droplet can be calculated from this distance information. However, the exact arrangement of the droplet or the sample surface relative to the measuring system must be known.

[0005] A method for determining the volume of an ink drop is known from JP 2007132929 A. The ink drop is metered into an ink receptacle by a metering unit, and the ink receptacle with the ink drop is subsequently conveyed to an observation unit.

[0006] A method for determining the volume of an ink drop is also known from document KR 2016 0117206 A.

[0007] Document DE 10 2017 007 301 A1 describes a method by which the contact angle of a water droplet on a fruit surface can be determined in order to distinguish fruit treated with surfactants and pesticides from untreated fruit. A design is mentioned here for determining the curvature and contact angle of a droplet by means of a reflection point. Summary of the invention

[0008] Starting from this, the object of the present invention is to provide a method for analyzing the interaction between a surface of a sample and a liquid and a corresponding device which can be used particularly flexibly and easily.

[0009] The object is achieved by a method for analyzing the interaction between the surface of a sample and a liquid. The method comprises the following steps:

[0010] a) applying a drop of liquid to the sample surface,

[0011] b) irradiating the droplet with a plurality of light sources, each of which is arranged in a light source position around the droplet,

[0012] c) detecting light reflections of the light source from the droplets with a camera, and for each detected light reflection, determining a sensor position on the sensor of the camera,

[0013] d) associating individual light source positions with individual sensor positions, so that there are pairs consisting of a sensor position and an associated light source position,

[0014] e) The position and size information of the droplet are calculated from these pairs.

[0015] The application of the droplets to the sample surface can be carried out in any manner and form, in particular using a suitable metering device. For example, the droplets can be formed suspended on a cannula and deposited on the sample surface by lowering the cannula until it is close to the sample surface. The cannula can then be withdrawn. It is also known to apply the droplets with a liquid jet, as described in the applicant's document EP 2 899 528 B1. The volume of the applied droplets is usually in the range of 0.1 μl to 20 μl, generally about 1 μl.

[0016] In a further method step, the droplet is illuminated by a plurality of light sources. Each light source is located at a defined light source position, i.e. the arrangement of the light sources relative to the camera is known. All light sources are arranged around the droplet, in particular such that the light from the light sources falls on the droplet. The distance from the light source to the droplet depends on the position of the droplet. The distances may be of equal size or may vary. The distances are typically in the range of 1 mm to 50 mm.

[0017] The light source can be implemented in different ways and forms, for example by means of a nearly point-shaped light source or by using a large-area light source in combination with a suitable shutter. It is also possible to use a large-area luminous screen with purposefully controlled individual pixels or groups of individual pixels. For the generation of light reflections, it is only important that each light source has a limited spatial extension and is surrounded by dark areas on all sides. The light sources must also be arranged at a spatial distance from each other so that they can be clearly distinguished from each other. Under these preconditions, a light reflection (Lichtreflex) is generated by reflection on the droplet surface, which is imaged on the sensor as an area with clearly illuminated boundaries, so that the sensor position can be determined for each light reflection to be included in the evaluation.

[0018] In another method step, a camera is used to detect the light reflection from the droplet of the light source. The camera has a sensor. The camera can be, for example, a CCD camera. The camera also has an optical element, with which the field of view detected by the camera is projected / imaged onto the sensor. The prerequisite for the formation of light reflection is that the droplet surface at least partially reflects the light incident by the light source. This is the case for most liquids, especially for test liquids that are usually used to describe sample characteristics. Transparent or opaque liquids, such as dyed liquids, can be selected as test liquids.

[0019] A sensor position can be determined for each detected light reflection. The sensor position consists, for example, of the two-dimensional coordinates of the image of the light reflection on the sensor surface. Depending on the geometry of the light source, its arrangement and its brightness distribution as well as the reflective properties and geometric properties of the droplet surface, the image of the light reflection on the sensor can be approximated as a point or can be stretched to a certain extent. If it extends over a plurality of image points of the sensor, the sensor position can be calculated from the brightness distribution as a basis for further evaluation, for example as the brightest image point or the center of gravity or the midpoint of the brightness distribution.

[0020] Therefore, after detecting the light reflection, a plurality of sensor positions are obtained, which respectively describe a detected light reflection. It is understood that further light reflections may occur, which are imaged on the sensor but are not taken into account in the evaluation. It is not necessary to determine the sensor position for these further light reflections.

[0021] At this point, in the next step, the individual light source positions are assigned to the individual sensor positions. By this assignment, pairs consisting of sensor positions and corresponding light source positions are generated. These are important for further evaluations, since these pairs allow conclusions to be drawn about the droplet surface, on which the light emitted by the relevant light source is reflected. The assignment of the light sources to the individual sensor positions can be realized in different ways and forms, a few examples of which are discussed below.

[0022] The method offers different possibilities with respect to the number of light sources and light reflections. In principle, at least two pairs of sensor positions and corresponding light source positions are required for the calculations performed in step e). However, if a larger number of pairs is used, for example at least three pairs, at least four pairs, at least five pairs or at least ten pairs, the accuracy can be increased. This can be achieved on the one hand by increasing the number of light sources, i.e., for example, by using more than two light sources, in particular three, four, five or more light sources. Another possibility is to use an additional camera. If, for example, two cameras are used to detect the light reflections of two light sources, a total of four pairs of sensor positions and corresponding light source positions can be used for further evaluation.

[0023] In the last method step, the position and size information of the droplet are calculated from the pair. The position can be, for example, the center point of the droplet, and the size information can be, for example, the radius of the droplet. However, depending on the geometry of the droplet or the mathematical model underlying the geometry of the droplet, the size information can also be other dimensions describing the surface geometry of the droplet, such as ellipse semi-axes, diameters, volumes, heights or other dimensions describing the shape of the droplet, for example, derived from these dimensions.

[0024] The specific calculation steps to be performed to calculate the position and size information of the droplet mainly depend on the number of light sources used and the arrangement of the light sources and the mathematical model adopted for the droplet geometry. Several examples of possible calculation methods are described in detail below. The main common point of the calculation steps is that based on the pair, both the position of the droplet and the size information can be calculated. The basis is the establishment of a correspondence between the position of each individual light source and the position of each individual sensor involved in the previous method steps. That is, only based on the detected light reflection, both the arrangement of the droplet relative to the measurement system and the desired size information can be determined. This is an important advantage of the method, because unlike the methods known from the prior art, it is not necessary to accurately control the distance from the measurement system to the sample surface, nor is it necessary to accurately control the arrangement of the droplet relative to the measurement system, such as the optical axis of the camera. Therefore, especially considering the irregularly constructed sample surface, the method can be designed to be significantly more flexible. From the beginning, the error source caused by the wrong positioning of the droplet in the measurement method known from the prior art is excluded. Therefore, the requirements for applying the droplet are also less, and if necessary, it can also be applied by personnel with less specific expertise.

[0025] Another advantage of the method is that the evaluation can be performed essentially automatically. No manual execution or checking of individual evaluation steps is required. The method can therefore be designed to be particularly simple.

[0026] In one embodiment, the light source is formed by discrete light emitting devices. The light emitting devices may be light emitting diodes (LEDs), for example. Each light emitting device is fixed at a specific light source position. As already mentioned, the light source can be formed in principle in a variety of ways and forms, and it is also possible to use a large-area light screen in which individual subareas form the light source. In this case, the precise arrangement of the light sources is achieved by controlling the light screen. However, the use of discrete light emitting devices is particularly simple and can provide a light source with a high light intensity and a clearly demarcated brightness distribution.

[0027] In one design, a template is created based on the light source position, the template describing the expected sensor position of the light reflection, and the detected light reflection is compared with the template in step d). The light source position is known relative to the camera. In order to generate the template, an image corresponding to the camera image can be calculated, for example, assuming that a typical droplet is set at a typical position. This calculated image is a template describing the expected sensor position of the light reflection. If a camera image of a real droplet is detected later when implementing the method, it can be compared with the template in a template matching step to match the detected light reflection or the corresponding sensor position with the respective light source position. This processing method is very helpful in practice, because the camera image actually detected usually appears as a light reflection that is not or is not only from the surface of the droplet. This is the case especially when using samples with a mirror-reflecting surface or when using transparent liquids. When using transparent liquids on mirror-reflecting sample surfaces, particularly complex reflections occur. In this case, the light beam entering the droplet may be reflected on the boundary surface of the droplet, especially the boundary surface between the sample and the droplet, and multiple reflections may also occur. This will produce a camera image that shows a large number of light reflections even when a small number of light sources are used. At this time, the use of a template can make it easy to determine the correspondence between the light reflections actually originating from the droplet surface and the positions of the various light sources.

[0028] In one embodiment, steps b) and c) are repeated for individual light sources and / or different groups of individual light sources. This measure also makes it easier to determine the assignment of detected light reflections to the positions of the light sources, since only the light reflections of individual light sources or groups of individual light sources are detected at a specific time, rather than the light reflections from all light sources. In order to carry out steps b) and c) in sequence, the individual light sources can be activated or deactivated, in particular by switching them on and off.

[0029] In one embodiment, a single light source is included in at least two different groups of single light sources. By comparing camera images detected by two different groups of single light sources, it is relatively easy to determine which light reflections originate from the light sources included in the two different groups.

[0030] In one design, in step e), multiple normal vectors are calculated for each pair, each of which describes a possible arrangement of the reflective surface area. The mirror reflection on the droplet surface is performed symmetrically with respect to the normal vector of the surface according to the principle of "the angle of incidence is equal to the angle of incidence". By tracking the corresponding line of sight of the camera, the direction of the incident light beam can be calculated from the sensor position. However, since the distance between the surface and the camera is not known, even if the position of the light source position corresponding to the light reflection is known, the exact arrangement of the mirror-like surface cannot be determined. However, multiple normal vectors can be given, each of which corresponds to a possible distance of the mirror-like surface and describes the mirror reflection of the light beam at this point. That is, for each pair, multiple normal vectors can be calculated, each of which describes a possible arrangement of the reflective surface area. If the calculation is performed for multiple pairs, the surface geometry can be determined based on multiple normal vectors set along each line of sight, and the surface geometry can be coordinated with all detected pairs. At this time, the size information of the droplet is obtained from the surface geometry.

[0031] In one design, in step e), the assumed droplet surface is varied during the optimization process and compared with the normal vector calculated for the pair. For example, for each assumed droplet surface, a normal vector on the droplet surface can be calculated at a point where it intersects the line of sight. At this point, in the optimization method, the deviation between the normal vector on the assumed droplet surface and the normal vector describing the reflection calculated by the pair is minimized. In this way, the actual droplet surface can be identified. This optimization process can provide very accurate results. If reasonable assumptions are made about the droplet surface, the optimization process converges very quickly. The assumptions can include parameters that determine the droplet position and the geometry of the droplet surface, for example, when assuming a sphere, the parameters include the midpoint of the droplet and the radius of the droplet. If, in particular, assumptions different from a sphere are made for the geometry of the droplet, in order to take into account the deformation of the droplet geometry due to gravity, more accurate results can be obtained in some cases. For example, it can be assumed that the droplet has an elliptical shape.

[0032] In one design, in step e), in order to calculate the position of the droplet, the intersection of the planes including a light source position and a line of sight of the camera is calculated, and the line of sight corresponds to the sensor position corresponding to the light source position. According to a pair, that is, according to a light source position and a corresponding sensor position, a plane including a line of sight of the camera and the light source position can be calculated. The plane is defined by a vector along the line of sight and a vector from the camera to the light source position. The plane also contains such a point on the surface of the droplet, at which the detected light reflection is formed by the reflection of the droplet surface. At this point, the normal vector of the droplet surface is also located in the calculated plane. In any case, when the droplet has a geometric shape that is approximately spherical, the midpoint of the droplet is located on the straight line described by the normal vector of the droplet surface and is also located within the calculated plane. Therefore, if multiple such planes can be calculated, the midpoint of the droplet, that is, the position of the midpoint, is obtained from the intersection of these planes. In this way, the position of the droplet can be determined particularly easily in some cases. No optimization calculations or assumptions about the droplet arrangement form are required.

[0033] In one embodiment, in a further calculation step, the contact angle of the drop is calculated based on the dimensions calculated in step e). If, for example, it is assumed that the drop is spherical and that the sample surface is flat in the region of the drop, the contact angle can be calculated based on the dimension information in the form of the drop center point and the drop radius. Depending on the assumptions made or the desired accuracy, other dimensions that are assumed to be known or detected by measurement technology can be taken into account in the calculation of the contact angle, in particular the volume of the drop or the distance between the sample surface and the measuring device, which volume can be predetermined by correspondingly precise metering when the drop is applied.

[0034] In one embodiment, in step c), further light reflections of the light source from the droplets are detected by means of a further camera, and for each further light reflection the sensor position on the sensor of the further camera is determined. As already mentioned, in this way a greater number of pairs of sensor positions and light source positions can be taken into account in the evaluation using a further camera or, if necessary, also two or more further cameras. This makes it possible to achieve a higher accuracy and / or a higher reliability of the evaluation. When the described calculation of the droplet position is carried out based on a plurality of planes, each of which includes a light source position and a line of sight, a particular advantage is obtained, because when using a plurality of cameras, planes with angular positions that differ greatly from each other can be taken into account in the evaluation.

[0035] In one embodiment, the camera and the further camera have viewing directions that differ from each other by an angle of 10° or more. This angular difference can be, for example, 15° or more, 20° or more or also 30° or more. This arrangement of the two cameras can also improve the accuracy and / or reliability of the evaluation.

[0036] In one embodiment, the light sources have a regular arrangement around the droplet. In principle, the light sources can be arranged around the droplet in any manner and form. However, a regular arrangement may help to detect clearly recognizable light reflections. In particular, the correspondence between the positions of the light sources and the light reflections can be simplified by a regular arrangement, as described above, mainly by using a template.

[0037] In one design, the arrangement of the light sources covers a spatial angle in the range of π / 8sr to 2πsr, as viewed from the droplet. The maximum spatial angle of 2πsr given corresponds to a hemisphere. In principle, it is desirable to detect light reflections at points on the surface of a sphere that are as far apart as possible. The larger the spatial angle range covered by the arrangement of the light sources, the better this can be achieved. However, the theoretical optimum value of the range depends on the contact angle. At very small contact angles, the excessively large angular spacing between the individual light sources quickly leads to the fact that light reflections can no longer be detected from each light source. Experiments have shown that the described spatial angle range is particularly suitable for most applications.

[0038] In one design, the light source includes a first light source and a second light source, the first light source being smaller than the second light source and / or being arranged at a smaller distance from each other than the second light source. The distance between the light sources used to set the light sources is particularly related to the angular spacing when viewed from the droplet. The use of different light sources is helpful, in particular in combination with different contact angles. When the contact angle is small, the droplet has a larger radius of curvature. At this time, only a smaller area of ​​the light source can be projected onto the sensor of the camera by mirror reflection on the surface of the droplet. In this case, it is purposeful to evaluate the reflection of light originating from the first light source. When the contact angle is large, the droplet has a smaller radius of curvature, and a larger angular range around the droplet is projected onto the sensor of the camera by mirror reflection on the surface of the droplet. This makes the use of the second light source particularly purposeful. In general, the use of different light sources can make the method purposefully adapted to the corresponding measurement task.

[0039] The above object is also achieved by a device for analyzing the interaction between a sample surface and a liquid. The device has the following characteristics:

[0040] means for applying the droplet onto the sample surface at the application location,

[0041] a plurality of light sources, each of which is arranged at a light source position around the application position,

[0042] a camera with a sensor oriented toward the application location and configured to detect light reflections of a light source from the applied droplets, and

[0043] An electronic evaluation device, which is designed to:

[0044] (i.) for each detected light reflection, determine the sensor position on the camera sensor,

[0045] (ii.) assigning each light source position to each sensor position so that there are pairs consisting of a sensor position and a corresponding light source position, and

[0046] (iii.) Calculating the position and size information of the applied droplet based on the pair.

[0047] The device is particularly designed for carrying out the method according to the invention. The evaluation device is connected to the camera and, if appropriate, to the further camera or to a plurality of further cameras. In addition, the evaluation device can also be connected to light sources and is particularly designed for activating and deactivating or switching the light sources on and off individually and / or in groups. By designing in accordance with the corresponding method features, that is, in particular by designing the device features of the evaluation device accordingly, it is achieved that the device is adapted to the above-described embodiment of the method. For the features and advantages of the device, reference is made to the above-described description of the method, which applies accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing.

[0049] in:

[0050] Figure 1 Schematic diagram showing the equipment used to analyze the interaction between the sample surface and the liquid.

[0051] Figure 2 Shows a template,

[0052] Figure 3 schematically and simplifiedly shows an image detected by a camera of the device, and

[0053] Figure 4 A schematic diagram of a further device for analyzing the interaction between a surface of a sample and a liquid is shown with a view from above. DETAILED DESCRIPTION

[0054] Figure 1The sample shown with hatching at the edge of the lower figure has a sample surface 10. On the sample surface is a droplet T of a transparent liquid. The droplet T is approximately spherical and rests on the sample surface 10 at a contact angle α. The droplet is applied to the sample surface 10 using a suitable metering device.

[0055] The device for measuring a droplet T has two light sources L1 and L2, which are each located at a light source position, which is also referred to below as L1 and L2. In addition, the device comprises a camera K and an evaluation device 12 connected to the camera. The camera K is located at a fixed predetermined position relative to the two light sources L1 and L2, which is also referred to below as K. The evaluation device 12 can in particular be a microcomputer integrated into the device or an external computer, which is coupled to other elements of the device that can be combined to form a measuring head. The camera K has an optical device 14 and a sensor 16, which has a sensor surface, onto which the field of view of the camera K is projected by means of the optical device 14.

[0056] The two light sources L1 and L2 are arranged such that they illuminate the surface of the droplet T. The light beam 18 emitted from the light source L1 hits a point P1 on the surface of the droplet T at which point the light beam is oriented with respect to the normal vector n P1 The reflection occurs mirror-symmetrically. The light originating from the light source L1 reflected at the point P1 is projected onto the point K1 of the sensor 16. That is, the camera K detects the reflection of the light from the light source L1 at the sensor position K1. In the same way, the camera K detects the reflection of the light from the light source L2 at the sensor position K2. The corresponding mirror reflection of the light beam 20 originating from the light source L2 takes place at the point P2 on the surface of the droplet T and is about the normal vector n P2 Reflect with mirror symmetry.

[0057] From a single light reflection and the corresponding sensor position, it is usually not possible to determine the corresponding reflection point on the droplet surface. If the camera line of sight 22 belonging to the sensor position K1 is tracked, then the light hitting the sensor 16 at the sensor position K1 along this line of sight 22 may originate not only from the point P1, but also from any other point located on the line of sight, for example from the point P1', if there is a normal vector n at this point S1' In this case, light from source L1 will follow ray 18' to point P1'.

[0058] This non-uniqueness can be eliminated, for example, by including pairs consisting of light source position and sensor position in the evaluation and calibrating using an assumed surface geometry. Figure 1The explanation is made with reference to the hypothetical surface of another droplet T' shown by dashed lines. However, the normal vector n describing the orientation of the surface of the droplet T' at the point P1' where the light beam 18' must be reflected is P1' The direction of the reflection is the same as the unit vector n describing the reflection S1' This deviation indicates that the light hitting the sensor position K1 cannot actually originate from the surface of the hypothetical droplet T'.

[0059] exist Figure 1 In FIG. 1 , a hypothetical situation in which the light source L2 is reflected at a point P2′ of a hypothetical droplet T′ is also shown, using corresponding reference numerals. For this hypothetical reflection at point P2′, the normal vector n of the surface of the droplet T′ at the intersection with the line of sight 24 is P2' It is also related to the unit vector n that describes the theoretically conceivable specular reflection S2' This shows that when using a sufficient number of individual sensor positions K1, K2, ..., K i and the corresponding light source positions L1, L2, ..., L i The pairs K1-L1, K2-L2, ..., K i -L i When , it can be calculated whether the assumed droplet geometry corresponds to the pair under consideration. In this way, the position and size information of the droplets can be calculated, for example, using optimization methods.

[0060] It is important for this method that the sensor position K1, K2 of the detected light reflection can be uniquely assigned to a single light source position L1, L2. To this end, Figure 2 and Figure 3 The establishment of a correspondence with the aid of a template is shown, which describes the sensor positions at which light reflections are expected. The template shows seven light reflections represented as solid circles, which are caused by seven light sources in a certain arrangement. If the light beams emitted from these light sources are reflected on a typical droplet, the light reflections shown in the template are obtained.

[0061] Figure 3 An image detected by a camera K is schematically shown, in which the outline of a droplet T is shown for illustration purposes. In some cases, the outline is not recognizable at all or is only recognizable weakly in the real camera image. In addition, this camera image shows a total of 11 light reflections, of which 7 are shown as solid circles. These seven light reflections originate from the reflections of the 7 light sources that serve as the template basis on the droplet T. The arrangement of these light sources is similar to Figure 2 The arrangement of the template in the image can be compared with the template. Figure 3The light reflections shown as solid circles in the figure are assigned to the positions of the individual light sources. Figure 3 The camera image of shows four further light reflections displayed as open circles. These light reflections originate from other light sources that should not be taken into account in the evaluation or are formed by disruptive multiple reflections, for example, inside the droplet or on the sample surface. These light reflections have no counterparts in the template and are therefore not included in the evaluation. Figure 3 The camera image and Figure 2 These light reflections can be simply identified as interference signals by comparing them with the template.

[0062] Figure 4 A further device for characterizing a sample surface is shown schematically from above, which has two cameras K and K'. Only one light source L1 is shown in this figure. Also shown is a droplet T with a midpoint M. Figure 4 In the illustration of , the line of sight is directed approximately from above to the sample surface (not shown), so that the droplet T appears as a full circle. For camera K, the unit vector d from camera K to light source L1 is shown. KL1 , and also shows the unit vector d KP1 , which corresponds to the line of sight from the camera to the reflection point P1 on the surface of the droplet T. These two unit vectors d KL1 and d KP1 Define a plane that includes the line of sight of camera K and light source L1. In addition, the normal vector n of the surface of droplet T at point P1 P1 and the midpoint M lies in this plane. The same applies to the unit vector d K'L1 and d K'P2 The two planes defined by the invention define a line which contains the midpoint M. When at least one further light source or also a further camera is used, three planes are obtained in this way which intersect at the midpoint M of the drop. Calculation of these planes therefore yields conclusions about the position of the drop T.

[0063] Reference numerals list

[0064] 10 Sample surface

[0065] 12 Evaluation Device

[0066] 14 Optical Devices

[0067] 16 Sensors

[0068] 18 L1 beam

[0069] 20 L2 beam

[0070] 22 Sight K1

[0071] 24 Sight K2

[0072] K Camera

[0073] K' Another Camera

[0074] K1 Sensor position for light reflection from L1

[0075] K2 Sensor location for light reflection of L2

[0076] L1 Light Source

[0077] L2 Light Source

[0078] P1, P2 Points on the surface of droplet T

[0079] T Droplet

[0080] T' Hypothetical droplet

[0081] P1', P2' are points on the surface of the hypothetical droplet T'

[0082] M Center point

[0083] α, α' contact angle

Claims

1. A method for determining size information of a droplet to analyze the interaction between a sample surface and a liquid, comprising the following steps: a) applying a drop of liquid to the sample surface, b) irradiating the droplet with a plurality of light sources, each of which is arranged in a light source position around the droplet, c) detecting light reflections of the light source from the droplets with a camera, and for each detected light reflection, determining a sensor position on the sensor of the camera, d) associating individual light source positions with individual sensor positions, so that there are pairs consisting of a sensor position and an associated light source position, e) calculating the size information of the droplet from the pair, wherein: For the pair, a plurality of normal vectors are calculated respectively along the relevant line of sight of the camera, which describe possible arrangements of the reflecting surface areas, and during the optimization a hypothetical droplet surface is varied and compared with the normal vectors calculated for the pair.

2. The method according to claim 1, characterized in that In step e), the position of the droplet is additionally calculated from the pair.

3. A method for determining the position of a droplet to analyze the interaction between a sample surface and a liquid, comprising the following steps: a) applying a drop of liquid to the sample surface, b) irradiating the droplet with a plurality of light sources, each of which is arranged in a light source position around the droplet, c) detecting light reflections of the light source from the droplets with a camera, and for each detected light reflection, determining a sensor position on the sensor of the camera, d) associating individual light source positions with individual sensor positions, so that there are pairs consisting of one sensor position and one associated light source position, respectively, and e) calculating the position of the droplet from the pair, wherein The intersection points of the planes respectively including a light source position and a line of sight of the camera corresponding to the sensor position corresponding to the light source position are calculated.

4. The method according to claim 3, characterized in that In step e), size information about the droplets is additionally calculated from the pairs.

5. The method according to any one of claims 1 to 4, characterized in that The light source is formed by discrete light emitting devices.

6. The method according to any one of claims 1 to 4, characterized in that From the light source positions a template is created, which describes the sensor positions where light reflections are expected, and in step d) the detected light reflections are compared with the template.

7. The method according to any one of claims 1 to 4, characterized in that Steps b) and c) are repeated for individual light sources and / or different groups of individual light sources.

8. The method according to claim 7, characterized in that At least two of the different groups of individual light sources contain one individual light source.

9. The method according to claim 1, 2 or 4, characterized in that: Based on the size information calculated in step e), the contact angle of the droplet is calculated in a further calculation step.

10. The method according to any one of claims 1 to 4, characterized in that In step c), further light reflections of the light source from the droplets are detected by a further camera, and a sensor position on the sensor of the further camera is determined for each further light reflection.

11. The method according to claim 10, characterized in that The camera and the further camera have viewing directions that differ by an angle of 10° or more relative to each other.

12. The method according to any one of claims 1 to 4, characterized in that The light sources are arranged in a regular pattern around the droplet.

13. The method according to claim 12, characterized in that The arrangement of the light sources covers a solid angle in the range from π / 8 sr to 2π sr, viewed from the droplet.

14. The method according to any one of claims 1 to 4, characterized in that The light source includes a first light source and a second light source, the first light source being smaller than the second light source and / or the first light source being arranged at a smaller distance from each other than the second light source.

15. A device for determining size information of a droplet to analyze the interaction between a sample surface and a liquid, the device having the following: means for applying a drop of the liquid onto the sample surface at an application location, a plurality of light sources, each of which is arranged at a light source position around the application position, a camera with a sensor oriented toward the application location and configured to detect light reflections of a light source from the applied droplets, and An electronic evaluation device, which is designed to: (i.) for each detected light reflection, determining the sensor position on the camera's sensor, (ii.) associating each individual light source position with each individual sensor position so that there are pairs consisting of a sensor position and a corresponding light source position, and (iii.) calculating size information of the applied droplet from the pair, wherein, For the pair, a plurality of normal vectors are calculated respectively along the relevant line of sight of the camera, which describe possible arrangements of the reflecting surface areas, and during the optimization a hypothetical droplet surface is varied and compared with the normal vectors calculated for the pair.

16. The device according to claim 15, characterized in that The electronic evaluation device is designed to additionally calculate the position of the drop from the pair.

17. Apparatus for determining the position of a droplet to analyse the interaction between a sample surface and a liquid, the apparatus comprising: means for applying a drop of the liquid onto the sample surface at an application location, a plurality of light sources, each of which is arranged at a light source position around the application position, a camera with a sensor oriented toward the application location and configured to detect light reflections of a light source from the applied droplets, and An electronic evaluation device, which is designed to: (i.) for each detected light reflection, determining the sensor position on the camera's sensor, (ii.) associating each individual light source position with each individual sensor position so that there are pairs consisting of a sensor position and a corresponding light source position, and (iii.) calculating the position of the applied droplet from the pair, wherein, The intersection points of the planes respectively including a light source position and a line of sight of the camera corresponding to the sensor position corresponding to the light source position are calculated.

18. The device according to claim 17, characterized in that The electronic evaluation device is designed to additionally calculate size information about the droplets from the pair.

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