Topometric system for measuring length changes in vacuum

Abstract

System (1) comprising at least a first vacuum chamber (2), a vacuum pump, viewing windows and apparatus connected to the first chamber via flanges, and a measurement object (4) arranged in the first vacuum chamber (2), characterized in that a topometric measuring device is provided with which a change in length due to temperature changes under vacuum conditions of the measurement object (4) arranged in the first vacuum chamber (2) can be measured, wherein the topometric measuring device consists of a projector (6) and at least one camera (5), and the projector (6) and the camera (5) are arranged on a common displaceable support (7) outside the vacuum chamber (2).

Description

[0001] The present invention relates to a system for measuring changes in length of a measuring object in a vacuum.

[0002] Measurement methods in general, and optical measurement methods in particular, are already well known in the art. For example, it is common practice to measure distances using an optical measurement method. A laser is typically used for this purpose. There are basically three possible variants of this type of laser measurement. A first alternative to distance measurement is time-of-flight measurement. In this method, a temporal light pulse is emitted. The so-called pulse time of flight is measured. In conjunction with the speed of light, the pulse time of flight can be used to determine the distance between the light source and the measurement object.

[0003] Another measurement alternative is phase shift measurement. The phase shift of the reflected light beam relative to the emitted beam depends on the distance traveled. The distance is determined using the measured phase shift.

[0004] Another method for distance measurement is laser triangulation. In this method, a laser beam is focused on a target and observed with a camera located in a sensor, a spatially resolving photodiode, or a CCD array. If the distance of the target from the sensor changes, the angle at which the light spot is observed also changes, and thus the position of its image on the photoreceptor. Using the triangular functions, the distance of the object from the laser source can be calculated.

[0005] Furthermore, general topometric measuring methods are known, which are used particularly in medicine, dentistry or pathology. Systems are also known in the automotive and aircraft industries. Here, the object to be measured is illuminated by a projector with a pattern of parallel stripes at constant distances. From the perspective of the projector, these projected stripes do not provide any information about the topography of the measuring object. A CCD camera is positioned at a defined distance from the projector and thus records the measuring object at an angle. From this perspective, the third dimension becomes recognizable. Given the known distance between the projector and the camera, the coordinates of the object point can be calculated using the laws of triangulation.

[0006] A general problem with such measurement methods is the dependence of light on refractive indices. For example, when measuring distances under atmospheric conditions, the refractive index depends on factors such as air pressure, temperature, and humidity. All of these factors can distort the measurement result, which is why these factors must be measured at all times to account for the changing refractive index when calculating the distance. In topometric systems, the most important influencing factors are lighting, surface texture, and temperature, with lighting having the greatest influence on the measurement result.

[0007] Furthermore, devices are known that can measure objects within closed temperature chambers in order to measure the effects of temperature on the object. The measuring device is usually located outside the temperature chamber to prevent exposure to the temperatures inside the chamber, as this could, for example, damage the sensors. For this reason, the temperature chambers are equipped with viewing windows through which, for example, a light beam can be directed onto the object.

[0008] However, this presents the problem that the light beam must pass through various media. This can lead to increased measurement inaccuracy, as the refractive index changes depending on the medium and temperature. In this common method, the light beam must pass through the air outside the temperature chamber, through the viewing window, and then through the air inside the temperature chamber. As the temperature inside the chamber changes, the refractive index of the air also changes. Furthermore, the different temperatures inside and outside the chamber can lead to changes in the material of the viewing window, which in turn changes the refractive index of the viewing window. Such deformation of glass, for example, due to different temperatures is very difficult to determine, which makes error correction in this type of arrangement complicated.

[0009] Furthermore, vacuum chambers are also generally known from the prior art, in which a specific negative pressure can be generated using a vacuum pump. Such a chamber must be completely sealed. When conducting measurements or experiments within such chambers, a problem can arise that, depending on the complexity of the measuring equipment, several access points through the chamber wall for cables, sensors, viewing windows, etc. must be sealed. This means that the more complex the system design, the more difficult it becomes to achieve complete sealing.

[0010] US 2004 / 0212795 A1 essentially shows the improvement of a measuring method for measuring deformations, but not for a change in temperature.

[0011] WO 1984 / 01998 A1 relates to a camera in which a length measurement of an object located therein is carried out, but not in the event of a temperature change or a temperature influence.

[0012] J. Cordero et al.: Interferometry-based high-precision dilatometry for dimensional characterization of highly stable materials. Measurement Science and Technology, Vol. 20, No. 9 (2009) concerns an optical dilatometer for measuring the linear coefficient of thermal expansion. The measuring apparatus is located within a chamber, as is the object. Vacuum values are not specified.

[0013] G. Bianchini, et al.: Interferometric dilatometer for thermal expansion coefficient determination. Measurement Science and Technology, Vol. 20, No. 9 (2006) concerns a measuring device for length measurement based on temperature changes.

[0014] DE 10 2017 003 084 A1 shows a system with a vacuum chamber, a vacuum pump and a measuring object arranged therein.

[0015] The object of the invention is therefore to provide a system for measuring changes in length of a measuring object in a vacuum, which solves the problems mentioned above and provides a simple and reliable measuring system.

[0016] The object is achieved according to the invention by a system according to claim 1. Further advantageous embodiments are the subject of the subclaims.

[0017] According to the invention, a system is provided comprising at least a first chamber, in particular a vacuum chamber, a vacuum pump, viewing windows and apparatus connected to the first vacuum chamber via flanges, and a measurement object arranged in the first vacuum chamber. According to the invention, a topometric measuring device is provided for measuring a change in length due to temperature changes under vacuum conditions of a measurement object arranged in the first vacuum chamber. A topometric measuring device is advantageous because it is based on the recording of patterns of light and dark sections, on which refractive indices have only a very minor influence. Thus, the transition of light from air to glass and vacuum plays no or only a very minor role in the recording of the light and dark sections.

[0018] Further apparatuses connected to the at least first vacuum chamber may include temperature sensors, connection elements for a power supply or various means for transmitting data, which may, for example, transmit the values measured by the sensor to a computing unit arranged outside the chamber.

[0019] Furthermore, an elongated viewing window is preferably flanged to the vacuum chamber, which can be located on any side of the vacuum chamber to ensure measurement of the measuring object.

[0020] Alternatively, it is also conceivable to surround the measurement object with a temperature control sleeve. This would be particularly advantageous because it would allow the temperature to be transferred directly to the measurement object and allow expansion to be controlled in a specific direction. This would simplify the measurement of the measurement object's expansion.

[0021] In a preferred embodiment, an additional chamber is arranged within the first chamber. For example, the measurement object can be arranged in this additional chamber if at least part of the topometric measuring device is located within the chamber. This is advantageous because it prevents or at least reduces the temperature influence on the measuring device, since in this case, only the additional chamber is heated.

[0022] In a further advantageous embodiment, the topometric measuring device is a fringe projection system. This system can be used to perform a 3-dimensional scanning process, which allows objects to be represented in three dimensions without contact. The surface information acquired by the scanning process is recorded as point clouds in the universal ASCII format.

[0023] Stripe projection is an active triangulation method in which a projector projects a stripe pattern onto a measurement object. Depending on the shape of the object, this stripe pattern is deformed, and the deformed stripe pattern is recorded by at least one camera. This recording serves as the basis for determining the topography of the measurement object. In this way, even irregular lengths of the measurement object can be reliably recorded.

[0024] A structured light scanner with a coded light approach is a system capable of achieving depth resolutions and measurement accuracies of 0.05 mm. To achieve this accuracy, various measurement principles and algorithms, such as the triangulation method, the light section method, the coded light approach, and the phase-shift method, interact.

[0025] The topometric measuring device consists of a projector and at least one camera, the camera being a video camera. In an advantageous embodiment, at least two cameras can be arranged together with the projector. An arrangement with two cameras can advantageously increase the measurement accuracy.

[0026] The projector and the camera are arranged on a common movable support outside the vacuum chamber. Alternatively, at least the camera can be arranged stationary within the vacuum chamber. By arranging the system on a common movable support, the measuring field can be expanded while maintaining fixed triangulation angles, provided that the projector and the at least one camera are fixedly arranged on the support. Fixed triangulation angles can be advantageous because they allow an optimal angle for measurement to be permanently set. Alternatively or cumulatively, both the projector and the camera can be pivoted on the support. This is advantageous for better detection of edges or protrusions.

[0027] Locating the camera inside the vacuum chamber is advantageous because it reduces the influence of external light sources and any reflections on the viewing window or the vacuum chamber. This also results in more accurate measurement results.

[0028] Furthermore, it is particularly preferred that the measurement object be arranged within a temperature chamber. Such an arrangement is advantageous because it allows for more direct heating of the measurement object and prevents the influence of temperature on the measuring apparatus. The temperature chamber has an opening on the side facing the measuring device, so that the measurement object can be measured using the topometric measuring device.

[0029] In a preferred embodiment, temperatures in the temperature chamber can be set in a range from -300 °C to 800 °C, preferably from -180 °C to 300 °C.

[0030] In a further preferred embodiment, the measurement object is arranged so that it can be displaced relative to the measuring device. Such an arrangement is advantageous because the measuring device can remain stationary and, for example, the projector does not need to be pivoted. Thus, the triangulation angle does not change, which in turn can contribute to a more precise measurement, since the angle between the projector and the camera affects the measurement accuracy.

[0031] Further advantages, objects, and features of the present invention will be explained in the following description of the accompanying figures. Similar components may have the same reference numerals in the various embodiments. In the figures: Fig. 1 is a schematic view of a preferred embodiment of the system; Fig. 2 is a schematic view of another preferred embodiment of the system;

[0032] Fig. 1 shows a schematic view of a preferred embodiment of the system 1. In this view, the measurement object 4 is arranged on a pedestal 3 within a vacuum chamber 2. A preferably elongated viewing window 8 is flanged onto the top of the vacuum chamber 2. This elongated viewing window 8 is preferably the only viewing window in order to avoid unwanted exposure of the measurement object 4 from external sources. Furthermore, it is conceivable to arrange the viewing window 8 on any side of the vacuum chamber 2. The reference numeral 7 denotes a support to which the camera 5 and the projector 6 are attached. The projector 6 is pivotally mounted on the support 7 via a pivot axis 9, and the camera via a pivot axis 10. The support can also be designed to be displaceable relative to the measurement object. The triangulation angles are designated α, β, and γ here.

[0033] Fig.Figure 2 shows a schematic view of another preferred embodiment of the system 1. In this embodiment, at least the camera 5 is arranged within the vacuum chamber 2. However, it is necessary to arrange the measurement object 4 within a further chamber 11, which is also designed as a temperature chamber to protect the camera 5 from temperature influences. The camera 5 is arranged stationary within the vacuum chamber. Only the projector 6 is pivotally mounted via a pivot axis 9 to ensure that the entire measurement object 4 can be illuminated.

[0034] All features disclosed in the application documents are claimed as essential to the invention, provided that they are new, individually or in combination, compared to the prior art. List of reference symbols 1 system 2 vacuum chamber 3 podium 4 Measuring object 5 Camera 6 Projector 7 carriers 8 viewing windows 9 Projector swivel axis 10 Pan axis camera 11 Temperature chamber α,β,γ triangulation angles

Claims

[1] System (1) comprising at least a first vacuum chamber (2), a vacuum pump, viewing windows and apparatus connected to the first chamber via flanges, and a measurement object (4) arranged in the first vacuum chamber (2), characterized by that a topometric measuring device is provided with which a change in length due to temperature changes under vacuum conditions of the measuring object (4) arranged in the first vacuum chamber (2) can be measured, wherein the topometric measuring device consists of a projector (6) and at least one camera (5) and the projector (6) and the camera (5) are arranged on a common displaceable support (7) outside the vacuum chamber (2). [2] System (1), wherein the measuring object (4) is arranged displaceably relative to the measuring device, according to claim 1, characterized by that a further chamber (11) is arranged within the first vacuum chamber (2). [3] System (1) according to claim 1, characterized bythat the topometric measuring device is a fringe projection system. [4] System (1) according to one of claims 2 or 3, characterized by that the measuring object (4) is arranged within the further chamber designed as a temperature chamber (11). [5] System (1) according to claim 4, characterized by that temperatures in the temperature chamber (11) can be set in a range from -300 °C to 800 °C, preferably from -180 °C to 300 °C. [6] System (1) according to one of the preceding claims, characterized by that the measuring object (4) is arranged so as to be displaceable relative to the measuring device.

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