Method and system for the quantitative detection of deformations and / or movements of an object

Abstract

The invention relates to methods for the quantitative detection of deformations and / or movements of an object (100) by means of a system (10) for electronic speckle pattern interferometry, the system (10) comprising a light source (20) for providing coherent light, an illumination and imaging optic (30), a camera unit (40) with a spatially resolved electronic image sensor (42), and an evaluation unit (50). The invention further relates to a corresponding system (10) configured for carrying out these methods.

Description

[0001] The invention relates to methods for the quantitative detection of deformations and / or movements of an object by means of an electronic speckle pattern interferometry system, the system comprising a light source for providing coherent light, illumination and imaging optics, a camera unit with a spatially resolved electronic image sensor, and an evaluation unit. The invention further relates to an electronic speckle pattern interferometry system for the quantitative detection of deformations and / or movements of an object, the system comprising a light source for providing coherent light, illumination and imaging optics, a camera unit with an electronic image sensor, and an evaluation unit.

[0002] In modern technical applications, there is often a requirement to detect even slight deformations and / or movements of objects and, in particular, to determine their magnitude. Slight deformations within the meaning of the invention can be as small as 10 to 100 nm. One area of ​​application is, for example, the monitoring of systems or the machines running within them during operation, where vibrations occurring on the external surfaces of the system can be measured. Irregularities in these vibrations, or the occurrence of a vibration in general or of specific frequencies, allow conclusions to be drawn about the condition of the machine. In this way, for example, damage to bearings in the system can be detected at an early stage.

[0003] Electronic speckle pattern interferometry is a known method in the prior art for quantitatively measuring the aforementioned small deformations and / or movements; see, for example, Yang, L., Xie, X., Zhu, L. et al., “Review of electronic speckle pattern interferometry (ESPI) for three-dimensional displacement measurement” in Chinese Journal of Mechanical Engineering (2024). In this method, a surface of the system under observation is illuminated with coherent light, and the reflected light is spatially resolved using an electronic camera, such as a CCD or CMOS image sensor. Superimposing this light with light from the same source, also focused on the image sensor, causes interference to form a speckle pattern. Analyzing temporal changes in the speckle pattern allows conclusions to be drawn about movements of the surface.The second light beam can either be reflected off the surface beforehand or directed directly onto the image sensor. The former allows for the detection of surface movements parallel to the image sensor, the latter for the detection of movements perpendicular to the image sensor.

[0004] As described above, electronic speckle pattern interferometry evaluates temporal changes in the recorded interference pattern. For this, the recorded intensities of two consecutive images must be compared for each pixel, for example, by calculating the difference. This represents a considerable time and computational effort, especially at higher resolutions, which leads to limitations regarding the achievable temporal and / or spatial resolution of the respective measurement.

[0005] Alternative devices for electronic speckle pattern interferometry can also employ event-based image sensors; see, for example, JP 2023-059422 A, WO 2023 / 126766 A1, Ge, Z. et al. “Event-based laser speckle correlation for micro motion estimation” in Optics Letters (2021), or Ge, Z. et al. “Dynamic laser speckle analysis using the event sensor.” in Applied optics, (2021).

[0006] The object of the present invention is to improve upon the prior art described above. In particular, the object of the present invention is to provide methods and a system that enable the quantitative detection of deformations and / or movements of an object with high temporal and spatial resolution.

[0007] The object of the invention is achieved by the independent claims. In particular, the object is achieved in a first aspect of the invention by a method according to independent claim 1, in a second aspect of the invention by a method according to independent claim 3, and in a third aspect of the invention by a system according to claim 11.

[0008] Further developments of the methods and system according to the invention are described in the dependent claims, the description, and the drawings. Features and advantages described with respect to the methods according to the first and second aspects of the invention also apply to the system according to the third aspect of the invention, and vice versa.

[0009] According to a first aspect of the invention, the problem is solved by a method for the quantitative detection of deformations and / or movements of an object by means of a system for electronic speckle pattern interferometry, the system comprising a light source for providing coherent light, an illumination and imaging optic, a camera unit with a spatially resolving electronic image sensor and an evaluation unit.

[0010] The inventive method according to the first aspect comprises the following continuously performed steps, wherein at least steps a), b1), c1) and d) are carried out simultaneously: a) Generating two illumination beams from coherent light through the light source and the illumination and imaging optics; b1) Illuminating the object with the two beams of light via the lighting and imaging optics; c1) Focusing the light scattered by the object from both illumination beams through the illumination and imaging optics onto the image sensor of the camera unit to create an interference image; d) Spatially resolved acquisition of interference patterns by the image sensor; and e) Evaluation of the spatially resolved interference images acquired in step d) by the evaluation unit for the quantitative detection of deformations and / or movements of the object.

[0011] The inventive method according to the first aspect of the invention is characterized in that an event-based image sensor is used as the image sensor in the camera unit and that in step d) only temporal changes in the intensity of the interference images are detected by this sensor, and in step e) these changes detected in step d) are used as the basis for the evaluation.

[0012] The method according to the first aspect of the invention is carried out using a suitable system for electronic speckle pattern interferometry. Preferably, a system according to the third aspect of the present invention can be used.

[0013] The system includes, in particular, a light source that provides coherent light for illuminating a surface of the object to be measured. The light source can preferably be a laser light source.

[0014] As part of the system, an illumination and imaging optic ensures both the desired and necessary illumination of the surface and the reliable guidance of light to the system's camera unit. Specifically, for the purposes of this invention, the term "illumination optic" encompasses all elements used to illuminate the object; in other words, a corresponding light beam passes through one or more components of the illumination optic and then strikes the object to be illuminated. The imaging optic, on the other hand, refers to those elements used to guide and / or shape the light to the camera unit. In other words, a corresponding light beam (originating from the object) passes through one or more components of the imaging optic and then strikes an image sensor of the camera unit.The illumination and imaging optics have the necessary optical components for this purpose, in particular, for example, lenses, mirrors, apertures, beam splitters, prisms, or similar.

[0015] It should be noted that when multiple light beams are present, different elements of the illumination and imaging optics can be used to guide and / or shape the respective light beams. In other words, individual elements of the illumination and imaging optics can be used to guide and / or shape only one of the multiple light beams. It is also possible, for example, to direct one of the light beams directly onto the image sensor of the camera unit, so that this light beam is guided and / or shaped only by elements of the imaging optics, and the illumination optics are not used for this light beam at all.

[0016] The system's camera unit contains the electronic image sensor as a key component. This image sensor is particularly spatially resolved to enable high-resolution measurement of the speckle pattern. In addition to illumination and imaging optics, the camera unit may also include its own optical elements for focusing, guiding, and / or cropping, specifically lenses, mirrors, prisms, apertures, or similar devices.

[0017] An evaluation unit, which is connected to the image sensor for data communication or at least connectable to it, forms a further component of the system used to carry out the method according to the invention. The evaluation unit usually includes a processing unit such as a processor and memory elements in order to be able to evaluate the acquired image data.

[0018] The method according to the first aspect of the invention enables quantitative detection of deformations and / or movements of an object, in particular movements parallel to the electronic image sensor of the camera unit of the system.

[0019] The essential aspect of the invention is that an event-based image sensor is used as the electronic image sensor of the camera unit. With conventional spatially resolved image sensors, such as CCD or CMOS image sensors, all pixels are read out simultaneously. In other words, a complete image exists for every point in time. To determine changes, particularly of intensity, with spatial resolution, all pixels of temporally successive images must be compared with each other, for example, by calculating the difference. This is very complex, especially with high spatial and / or temporal resolution, and therefore limits the achievable accuracy, particularly with regard to temporal resolution, and especially makes real-time evaluation difficult or impossible.

[0020] However, the speckle pattern interferometry method described below relies precisely on these intensity changes, which reflect changes in the interference patterns of the speckle patterns and thus of the surface.

[0021] In contrast to the CCD or CMOS image sensors described above, event-based image sensors read each pixel individually and only when the intensity measured by that pixel exceeds or falls below a certain threshold. In other words, compared to conventional image-based systems, the pixels in event-based image sensors operate independently. A pixel is only activated when it detects a change in intensity. This results in an asynchronous data stream that describes intensity changes with spatial and temporal resolution. Event-based image sensors often exhibit an intrinsic temporal resolution in the microsecond range, which corresponds to more than 10,000 images per second.At the same time, the spatial resolution of the detectable deformations or movements is determined by the evaluation of the interference images using the wavelength of the light used, which means that, for example, when using light in the visible range, spatial resolutions in the measurement direction of less than 1 µm can be easily achieved.

[0022] Since limiting the collected data solely to changes results in significantly less data being generated, and in particular eliminates the time-consuming and computationally intensive processing step of comparing all pixels, the use of event-based image sensors can achieve a particularly high temporal resolution in the quantitative detection of deformations and / or movements of the object, thereby enabling the provision of evaluation results in real time or at least in near real time.

[0023] The method used here is described below. In a first step a) of the method according to the first aspect of the invention, two illumination beams of coherent light are generated. Coherent light has the particular property of being monochromatic, i.e., having a single frequency or wavelength, and that, furthermore, the individual light waves have a fixed phase relationship. This is a prerequisite for the light of the two illumination beams to interfere with each other. Preferably, a laser source is used as the light source, since laser light already possesses these properties.

[0024] Either within the light source itself or downstream in the illumination and imaging optics, the coherent light generated in the light source is split into the two illumination beams used in the method according to the invention, for example by a suitable beam splitter. The illumination and imaging optics further ensure the guidance of the two illumination beams to their destination. For this purpose, the illumination and imaging optics comprise suitable optical components, such as mirrors, lenses, apertures, prisms, or the like.

[0025] In step b1) of the method according to the first aspect of the invention, the object to be measured, in particular a surface of this object, is illuminated with the two illumination beams. The two illumination beams are provided by the illumination and imaging optics in such a way that they illuminate the object at the same location. "At the same location" within the meaning of the invention means, in particular, that the respective illumination areas on the surface of the object, which are illuminated by each of the illumination beams, overlap, in particular by more than 50%, preferably by more than 75%, and most preferably by more than 95%. The two illumination beams can be aligned parallel to each other. Preferably, however, the two illumination beams are aligned at two different illumination angles with respect to the object to be measured or its surface.Different illumination angles within the meaning of the invention are particularly present when the two illumination beams are not aligned parallel to each other.

[0026] The light from both illumination beams striking the object in step b1) is scattered at its surface. At least a portion of this scattered light is focused onto the image sensor of the camera unit by the illumination and imaging optics in step c1). Since coherent light from both illumination beams strikes the surface in the overlap region described above, scattered light from a region of the surface illuminated by both beams is focused onto the image sensor, forming an interference pattern. Because the scattering process at the surface depends primarily on the orientation of the respective surface region relative to the two illumination beams, the corresponding interference pattern will change if the region moves, for example, due to vibration.

[0027] This interference pattern, which changes over time due to the deformations and / or movements of the object, is continuously and spatially resolved by the image sensor in step d) of the method according to the first aspect of the invention. Since the object is illuminated continuously, not just a single interference pattern is recorded, but rather these are captured in temporal sequence. Temporal sequential capture, as defined by the invention, means in particular that the event-based image sensor captures changes in the intensity of the interference pattern with spatial resolution. In other words, in step d) of the method according to the first aspect of the invention, the data on the time-changing interference patterns are captured and determined, with these changes reflecting the deformations and / or movements of the object being measured.Conversely, static scenes of parts of the surfaces, i.e., areas of the surfaces that are not subject to any temporal change of deformation or movement, do not lead to any temporal change of interference, which is reflected in a lack of recordings by the corresponding pixels of the event-based image sensor.

[0028] This enables, in step e) of the method according to the first aspect of the invention, an evaluation of the interference patterns acquired in step d), or of the changes in the interference patterns acquired therein. By using the event-based image sensor, spatially and temporally resolved information about changes in the intensity of the interference patterns is already available, without the need for the complex differentiation of complete image files known from the prior art. The size, shape, and temporal sequence of the changes in the interference patterns allow conclusions to be drawn about the temporal change of the surface of the object illuminated by both illumination beams.Including data on the geometric setup, such as illumination angles, distances, or similar, and on illumination parameters, such as the wavelength of the light used, the phase relationship of the individual illumination rays, or similar, can enable the relative and, in particular, the absolute magnitude of the deformations and / or movements of the object, i.e., a quantitative determination of the deformations and / or movements.

[0029] In summary, the result of this evaluation is the quantitative detection of deformations and / or movements of the object. As explained above, the use of event-based image sensors allows for particularly high temporal resolution in the quantitative detection of deformations and / or movements of the object, enabling the real-time provision of the evaluation results. The illumination by two light beams, as described above in step b1), allows for the detection of surface movements and / or deformations that are aligned parallel to the image sensor. It should be noted that steps a), b1), c1), and d) are performed simultaneously and continuously. Step e) can also be performed simultaneously, but alternatively or additionally, it can include saving the data acquired in step d) for later evaluation.

[0030] Furthermore, the method can be characterized in that, in step b1), the object is illuminated by the two illumination beams at two different illumination angles, wherein the illumination angles span a common illumination plane and are mirror images of each other with respect to a normal to the surface of the object located in this illumination plane. In other words, the two illumination beams are oriented in opposite directions and illuminate the jointly illuminated area from different sides, but at the same illumination angle. Particularly good illumination can thus be achieved while simultaneously maximizing the difference in the scattered light of the two illumination beams.This is particularly evident in pronounced interference patterns, which can facilitate evaluation and / or increase the accuracy in quantitatively determining the deformations and / or movements of the object.

[0031] According to a second aspect of the invention, the problem is solved by a method for the quantitative detection of deformations and / or movements of an object by means of a system for electronic speckle pattern interferometry, the system comprising a light source for providing coherent light, an illumination and imaging optic, a camera unit with a spatially resolving electronic image sensor and an evaluation unit.

[0032] The inventive method according to the second aspect comprises the following continuously performed steps, wherein at least steps a), b2), c2) and d) are carried out simultaneously: a) Generating two illumination beams from coherent light through the light source and the illumination and imaging optics; b2) Illuminating the object by means of a first of the two illumination beams at an illumination angle via the illumination and imaging optics; c2) Focusing the light of the first illumination beam scattered by the object and widening and guiding the second illumination beam through the illumination and imaging optics onto the image sensor of the camera unit to create an interference image; d) Spatially resolved acquisition of interference patterns by the image sensor; and e) Evaluation of the spatially resolved interference images acquired in step d) by the evaluation unit for the quantitative detection of deformations and / or movements of the object.

[0033] The inventive method according to the second aspect of the invention is characterized in that an event-based image sensor is used as the image sensor in the camera unit and that in step d) only temporal changes in the intensity of the interference images are detected by this sensor, and in step e) these changes detected in step d) are used as the basis for the evaluation.

[0034] For the method according to the second aspect of the invention, the corresponding system for electronic speckle pattern interferometry is used, which is essentially also used in carrying out the method according to the first aspect of the invention. Reference is made to the corresponding description of this system above, and it is also used for the method according to the second aspect of the invention. Again, a system according to the third aspect of the present invention can preferably be used.

[0035] For the method according to the second aspect of the invention, it is also essential that an event-based image sensor is used as the electronic image sensor of the camera unit. In particular, the use of event-based image sensors also enables a particularly high temporal resolution for the quantitative detection of deformations and / or movements of the object in the method according to the second aspect of the invention, whereby, in particular, the real-time provision of the evaluation results is made possible.

[0036] The method according to the second aspect of the invention differs from the method according to the first aspect of the invention, in particular by steps b2) and c2), which are performed instead of steps b1) and c1). These differences relate specifically to the method of illuminating the surface of the object to be measured and the generation of the interference patterns. All features and advantages described for the further steps a), d), and e) of the method according to the first aspect of the invention can also be achieved by the identical steps a), d), and e) of the method according to the second aspect of the invention.

[0037] In contrast to step b1) of the method according to the first aspect of the invention, in step b2) of the method according to the second aspect of the invention, the object is illuminated with only a single illumination beam. Light scattered at the surface from this first illumination beam is focused onto the image sensor by the illumination and imaging optics in step c2), analogous to step c1). However, in step c2), the second illumination beam in the method according to the second aspect of the invention is not used to illuminate the object, but is also diffused by the illumination and imaging optics and directed onto the image sensor. In other words, the second illumination beam is used as a so-called reference beam.In particular, only elements of the imaging optics are used for this widening and guiding, which, moreover, such as an element for widening the second illumination beam, are not used for focusing the reflected light of the first illumination beam.

[0038] Since the light from the two illumination beams, and consequently also the light from the first illumination beam reflected from the object and the light from the reference beam, is coherent in the method according to the second aspect of the invention, interference patterns are also obtained in the image plane of the camera sensor. Because only the first illumination beam is scattered by the surface of the object and the second illumination beam acts as a reference beam, the method according to the second aspect of the invention can be used, in particular, to detect deformations and / or movements of the object that occur perpendicular to the image sensor.

[0039] In summary, the execution of the method according to the second aspect of the invention also results in the quantitative detection of deformations and / or movements of the object. Again, the use of event-based image sensors enables particularly high temporal resolution in the quantitative detection of deformations and / or movements of the object, and in particular allows for the provision of evaluation results in real time. By using the two illumination beams separately (first illumination beam) for illuminating the object and as a reference beam (second illumination beam), as described above in steps b2) and c2), movements and / or deformations of the surface that are oriented perpendicular to the image sensor can be detected. In the method according to the second aspect of the invention, steps a), b2), c2), and d) can also be carried out simultaneously and continuously.Step e) can also be carried out simultaneously, but alternatively or additionally it can also include saving the data determined in step d) for later evaluation.

[0040] The methods according to the invention can be further developed by alternately performing steps b1) and c1) or steps b2) and c2) in addition to steps a), d), and e). In other words, the method according to the first aspect of the invention and the method according to the second aspect of the invention are carried out alternately, with both methods observing the same area of ​​the surface of the object to be measured. Due to the associated change in the use of the two illumination beams—either both illumination beams to illuminate the surface or one illumination beam for illumination and the second as a reference beam—movements and / or deformations parallel to the image sensor as well as perpendicular to it can be quantitatively detected alternately, as described above. The application possibilities of the present methods according to the invention can thus be expanded.

[0041] Furthermore, in the methods according to the invention, it is provided that the light source generates coherent light with an illumination frequency, wherein the illumination frequency is selected from two or more frequency values ​​and the selection of the illumination frequency changes at least once during the execution of the method.

[0042] In a further development of the methods according to the invention, it can also be provided that the changing of the illumination frequency of the coherent light from a first frequency value to a second frequency value is carried out continuously. "Continuous" within the meaning of the invention also includes changing the illumination frequency from a first to a second frequency value in small steps, in particular in at least 50 or more steps, preferably 1000 or more steps, wherein the step size is more preferably the same in each case. During the continuous change of the illumination frequency from the first frequency value to the second frequency value, the steps of the methods according to the invention can be carried out continuously, so that a plurality of measurements at different frequency values ​​are available as a result.The advantages already described above for two measurements at two frequency values ​​can not only be made possible in the same way, but can even be further increased by measuring at a large number of different frequency values.

[0043] The methods according to the invention can also be characterized in that, in step a), the two illumination beams are generated with a phase difference, wherein the phase difference is selected from two or more difference values ​​and the selection of the phase difference changes at least once during the execution of the method. Changing the difference value of the phase difference of the coherent light between the two illumination beams also automatically changes the resulting interference pattern, even if the deformation and / or movement of the object to be measured does not change or at least does not change significantly between the two measurements with the different difference values. Accuracy in determining the actual quantitative magnitude of the movement and / or deformation can thus also be increased in this way, and in particular, a systematic error in the determination can be reduced.

[0044] The methods according to the invention can also be further developed with regard to changing the difference value of the phase difference by continuously performing the change from a first difference value to a second difference value. "Continuous" in the sense of the invention analogously also includes changing the phase difference from a first to a second difference value in small steps, in particular in at least 50 or more steps, preferably 1000 or more steps, wherein the step size is more preferably the same in each case. During the continuous change of the phase difference from the first difference value to the second difference value, the steps of the methods according to the invention can be carried out continuously, so that a multitude of measurements at different difference values ​​are available as a result.The advantages already described above for two measurements with two difference values ​​can not only be made possible in the same way, but can even be further increased by measuring with a large number of different difference values.

[0045] The methods according to the invention can also be characterized in that the object is moved in a controlled manner during the execution of the method, whereby the movement of the object is taken into account when evaluating the interference pattern in step e). In other words, a movement is intentionally performed with the object, which is then detected in step e) and subsequently subtracted to determine any remaining deformation and / or movement of the object. By detecting, and in particular quantitatively detecting, the known, intentionally performed movement, it can be ensured that the evaluation is carried out correctly. This approach can also be referred to as a "lock-in method".

[0046] According to a further development of the methods according to the invention, it can also be provided that the controlled movement of the object is an oscillating movement, preferably corresponding to a sinusoidal oscillation. Oscillating movements, especially sinusoidal oscillations, are movements performed periodically around a zero position. Due to their periodic repetition, these movements can be detected particularly easily and reliably. The lock-in method described above can thus be simplified, and its accuracy and reliability can be further increased.

[0047] Furthermore, the methods according to the invention can be configured such that in step b1) the illumination angles change at least once during the execution of the method, and / or that in step b2) the illumination angle changes at least once during the execution of the method. The sensitivity of the measurement of the deformation and / or movement of the object can be dependent on the illumination angle at which the respective illumination beam strikes the surface of the object. This dependency can be at least partially determined by changing the illumination angles at least once. This allows the dependency to be taken into account during the evaluation in step e). The sensitivity and / or accuracy of the results when carrying out the methods according to the invention can thus be increased.

[0048] According to a third aspect of the invention, the problem is solved by a system for electronic speckle pattern interferometry for the quantitative detection of deformations and / or movements of an object, the system comprising a light source for providing coherent light, illumination and imaging optics, a camera unit with an electronic image sensor, and an evaluation unit. The system according to the third aspect of the invention is characterized in that the camera unit comprises an event-based image sensor, and that the system is configured to carry out the method according to one of the preceding claims.

[0049] The system according to the third aspect of the invention is a system configured to perform a method according to the first aspect of the invention and / or according to the second aspect of the invention. In particular, the system according to the third aspect of the invention comprises a camera unit with an event-based image sensor. All features and advantages described above with reference to one of the methods according to the first and / or second aspect of the invention are therefore also transferable to, and can be enabled by, the system according to the third aspect of the invention.

[0050] In the following, embodiments of the methods or systems according to the invention are described by way of example with reference to schematic figures. These show in detail... Fig. 1 A system according to the invention when carrying out a method according to the invention in accordance with the first aspect of the invention, and Fig. 2 A system according to the invention when carrying out a method according to the invention in accordance with the second aspect of the invention.

[0051] In the Fig. 1, Fig. Figure 2 shows a system 10 according to the invention, which is used to carry out the method according to the first aspect of the invention ( Fig. 1) or according to the second aspect of the invention ( Fig. 2) is designed. The system 10 comprises, in particular, a light source 20, an illumination and imaging optic 30, a camera unit 40 with the event-based image sensor 42 essential for the present invention, and an evaluation unit 50, which is designed at least for evaluating the data recorded by the image sensor 42 and is connected to the camera unit 40 for this purpose. Additionally, but in Fig. 1, Fig. 2 not explicitly shown, it may also be intended that the evaluation unit 50 also takes over the regulation and / or control of the entire system 10.

[0052] Both methods according to the invention have in common that two illumination beams 22 of coherent light are generated by the light source 20, in which Fig. 1, Fig. 2, designated “A” and “B” respectively, and that light from these two illumination beams 22 is guided through the illumination and imaging optics 30 onto the event-based image sensor 42 in order to interfere there to form an interference image. In both Fig. 1, Fig. For the sake of clarity, two light sources 20 are shown, but these are to be interpreted as part of a single light source 20.

[0053] The two methods according to the invention differ in that in the method according to the first aspect ( Fig. 1) Both illumination beams 22 (A, B) are used to illuminate the surface 110 of the object 100, and scattered light 200 (A, B) from both illumination beams 22 (A, B) is focused, in particular by the imaging optics 30, onto the image sensor 42 of the camera unit 40. In the method according to the second aspect ( Fig. 2) In contrast, the object 100 is illuminated only by one illumination beam 22 (A), and its diffused light 200 (A) is focused by the imaging optics 30 onto the image sensor 42 of the camera unit 40. The light of the second illumination beam 22 (B), however, is spread out by elements of the imaging optics 30 and directed over a surface onto the image sensor 42 of the camera unit 40.

[0054] The event-based image sensor 42 directly and exclusively captures spatially resolved changes in the interference patterns described in the previous paragraph and assigns them a timestamp. This data is evaluated in the evaluation unit 50. As a result, even the smallest deformations and / or movements of a surface 110 of an object 100 to be measured can be quantitatively detected with high temporal resolution and, in particular, in real time or at least near real time.

[0055] The two methods carried out by the respective system 10 according to the invention differ in particular in the actual use of the two illumination beams 22 (A, B). As already described, in both cases both illumination beams 22 (A, B) are formed by coherent light from the light source 20. Preferably, the light source 20 can be a laser light source.

[0056] According to the first aspect of the invention ( Fig. 1) Both illumination beams 22 (A, B) are used to illuminate an area of ​​the surface 110 of the object 100 at a preferably different illumination angle 24 (A, B). Diffuse light 200 (A, B) from both illumination beams 22 (A, B) is focused onto the image sensor 42 by the illumination and imaging optics 30.

[0057] This method of illumination leads, in particular, to changes in the interference pattern due to deformations and movements of the surface 110 parallel to the image sensor 42. In other words, the method according to the first aspect of the invention ( Fig. 1) is particularly sensitive to these deformations and movements of the surface 110 parallel to the image sensor 42.

[0058] As in Fig. As can be seen in Figure 1, the two illumination angles 24 (A, B), at which the illumination rays 22 (A, B) strike the surface 110, are arranged in a common illumination plane spanned by the illumination rays 22 (A, B), and are also mirror images of each other. This simplifies the evaluation of the data from the image sensor 42 by the evaluation unit 50.

[0059] According to the second aspect of the invention ( Fig. 2) In contrast, only one of the illumination beams 22(A) is used to illuminate the area of ​​the surface 110 of the object 100 at an illumination angle 24(A), and scattered light 200(A) of this illumination beam 22(A) is then focused by the illumination and imaging optics 30 onto the image sensor 42. The other illumination beam 22(B) is widened, in particular by elements of the imaging optics 30, and directed directly over a surface onto the image sensor 42 of the camera unit 40. With this method of illumination, in which one of the illumination beams 22(B) is used as a constant reference beam, deformations and movements of the surface 110 perpendicular to the image sensor 42, in particular, lead to a change in the interference pattern. In other words, the method according to the second aspect of the invention ( Fig. 1) is particularly sensitive to these deformations and movements of the surface 110 perpendicular to the image sensor 42.

[0060] It can be particularly advantageous that the system 10 according to the invention is designed such that it allows for a distinction between the Fig. 1 and Fig. to switch between the two lighting modes shown. In other words, with such a system 10, both methods according to the invention can be carried out alternately, thereby enabling quantitative detection of deformations and / or movements of the object 100 both parallel to the image sensor 42 and perpendicular to it.

[0061] In principle, the sensitivity of the detection with respect to a direction of the respective deformation or movement of object 100 is also influenced by the illumination angle 24 used. By changing the illumination angle 24, the corresponding sensitivity can therefore be influenced, both in the Fig. 1 shown illumination of the surface 110 of object 100 with two illumination beams 24 (A, B), as well as in the Fig. 2 lighting shown with only one lighting beam 24 (A).

[0062] As explained above, the light source 20 generates coherent light, from which the two illumination beams 22 (A, B) are formed. Coherent light is characterized by the fact that the two formed illumination beams 22 have an illumination frequency with a common, fixed frequency value and a phase difference with a defined, fixed difference value. By a controlled change of the illumination frequency from a first to a second frequency value, as provided for in the invention and taken into account by the evaluation unit 50 during evaluation, and optionally also a change of the phase difference from a first to a second difference value, the accuracy of detecting deformations and / or movements can be further increased.In particular, systematic errors in detection can be determined and thus avoided by such changes to the illumination frequency alone or to both the illumination frequency and the phase difference.

[0063] Preferably, the changes in lighting frequency or phase difference described in the previous paragraph can be made continuously.

[0064] Another way to improve the accuracy of the results when performing the test in Fig. 1, Fig.The method shown in two examples, which increases the detection of deformations and / or movements of object 100, consists of moving object 100 itself in a controlled manner, preferably in an oscillating motion such as a sinusoidal oscillation. The evaluation unit 50 also detects this additional movement of object 100, thus fundamentally verifying the detection of deformations and / or movements of the object using the methods according to the invention. Subtracting the controlled movement from the acquired data then reveals any remaining deformations and / or movements of object 100. In this way, systematic errors in the respective measurement can also be detected and corrected or taken into account. Reference sign 10 System 20 light sources 22 Lighting beam 24 lighting angles 30 Lighting and imaging optics 32 lens 40 camera units 42 event-based image sensor 50 evaluation units 100 objects 110 surface area 200 scattered light

Claims

[1] Method for quantitatively detecting deformations and / or movements of an object (100) by means of an electronic speckle pattern interferometry system (10), the system (10) comprising a light source (20) for providing coherent light, an illumination and imaging optic (30), a camera unit (40) with a spatially resolving electronic image sensor (42) and an evaluation unit (50), comprising the following continuously performed steps, wherein at least steps a), b1), c1) and d) are performed simultaneously: a) Generating two illumination beams (22) from coherent light through the light source (20) and the illumination and imaging optics (30); b1) Illuminating the object (100) by the two illumination beams (22) via the illumination and imaging optics (30); c1) Focusing of light (200) scattered at the object (100) of both illumination beams (22) through the illumination and imaging optics (30) onto the image sensor (42) of the camera unit (40) to create an interference image; d) Spatially resolved acquisition of interference patterns by the image sensor (42); and e) Evaluation of the spatially resolved interference patterns acquired in step d) by the evaluation unit (50) for the quantitative detection of deformations and / or movements of the object (100), characterized by , that in the camera unit (40) an event-based image sensor (42) is used as the image sensor (42) and in step d) only temporal changes in the intensity of the interference images are detected by this sensor, and in step e) these changes recorded in step d) are used as the basis for the evaluation, where the light source (20) produces coherent light with an illumination frequency, wherein the illumination frequency is selected from two or more frequency values ​​and the choice of illumination frequency changes at least once during the execution of the procedure. [2] Method according to claim 1, characterized by , that in step b1) the object (100) is illuminated by the two illumination rays (22) at two different illumination angles (24), wherein the illumination angles (24) span a common illumination plane and are mirror-aligned with respect to a normal to the surface (110) of the object (100) arranged in this illumination plane. [3] Method for quantitatively detecting deformations and / or movements of an object (100) by means of an electronic speckle pattern interferometry system (10), the system (10) comprising a light source (20) for providing coherent light, an illumination and imaging optic (30), a camera unit (40) with a spatially resolving electronic image sensor (42) and an evaluation unit (50), comprising the following continuously performed steps, wherein at least steps a), b2), c2) and d) are performed simultaneously: a) Generating two illumination beams (22) from coherent light through the light source (20) and the illumination and imaging optics (30); b2) Illuminating the object (100) by one of the two illumination beams (22) at an illumination angle (24) via the illumination and imaging optics (30); c2) Focusing of light (200) of the first illumination beam (22) scattered at the object (100) and widening and guiding the second illumination beam (22) through the illumination and imaging optics (30) onto the image sensor (42) of the camera unit (40) to generate an interference image; d) Spatially resolved acquisition of interference patterns by the image sensor (42); and e) Evaluation of the spatially resolved interference patterns acquired in step d) by the evaluation unit (50) for the quantitative detection of deformations and / or movements of the object (100), wherein an event-based image sensor (42) is used as the image sensor (42) in the camera unit (40) and in step d) only temporal changes in the intensity of the interference images are detected by this sensor, and in step e) these changes detected in step d) are used as the basis for the evaluation, characterized by , that the light source (20) generates coherent light with an illumination frequency, wherein the illumination frequency is selected from two or more frequency values ​​and the choice of illumination frequency changes at least once during the execution of the procedure. [4] Method according to one of claims 1 or 2 and according to claim 3, characterized by , that in addition to steps a), d) and e), steps b1) and c1) or steps b2) and c2) are performed alternately. [5] Method according to any of the foregoing claims, characterized by , that the changing of the illumination frequency of the coherent light from a first frequency value to a second frequency value is carried out continuously. [6] Method according to any of the foregoing claims, characterized by, that in step a) the two illumination beams (22) are generated with a phase difference, wherein the phase difference is chosen from two or more difference values ​​and the choice of phase difference changes at least once during the execution of the procedure. [7] Method according to claim 6, characterized by , that the change in the phase difference from a first difference value to a second difference value is carried out continuously. [8] Method according to any of the foregoing claims, characterized by , that during the execution of the procedure the object (100) is moved in a controlled manner, whereby the movement of the object (100) is taken into account in the evaluation of the interference pattern in step e). [9] Method according to claim 8, characterized by , that the controlled movement of the object (100) is an oscillating movement, wherein preferably the controlled movement of the object (100) corresponds to a sinusoidal oscillation. [10] Method according to any of the preceding claims, characterized by , that in step b1) the illumination angles (24) change at least once during the execution of the procedure, and / or that in step b2) the illumination angle (24) changes at least once during the execution of the procedure. [11] System (10) for electronic speckle pattern interferometry for quantitative detection of deformations and / or movements of an object (100), the system (10) comprising a light source (20) for providing coherent light, an illumination and imaging optic (30), a camera unit (40) with an electronic image sensor (42) and an evaluation unit (50), characterized by that the camera unit (40) has an event-based image sensor (42) as an image sensor (42), and that the system (10) is configured to perform the method according to one of the preceding claims.

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