DETERMINATION OF A TUBE PRESSURE BY MEANS OF LASER INTERFEROMETRY AND APPARATUS HEREFOR

Abstract

The present invention relates to a method of observing a changing surface by means of laser interferometry, in particular by means of laser speckle interferometry, wherein the changing surface is preferably a surface of a tube and the method is used to determine the pressure in the tube. A further aspect of the invention relates to a corresponding apparatus.

Claims

1. A method of observing a changing surface by means of laser interferometry, in particular by means of laser speckle interferometry, wherein the changing surface is preferably a surface of a tube and the method is used to determine the pressure in the tube.

2. A method in accordance with claim 1, characterized in that the changing surface is arranged in a stationary manner relative to a laser light source and/or a laser receiver or sensor during a measurement process.

3. A method in accordance with claim 1, characterized in that the stretching of the changing surface is determined with reference to an interference pattern and/or a speckle pattern by means of laser interferometry and the pressure in the tube can be deduced therefrom.

4. A method in accordance with claim 3, characterized in that an analysis takes place, in particular taking account of an observed speckle pattern, by means of which observed changes of the surface due to a movement of the surface can be distinguished from observed changes of the surface due to a stretching of the surface.

5. A method in accordance with claim 1, characterized in that the change of the diameter of the tube is determined by means of laser interferometry by means of a laser-based distance measurement, in particular by a time of flight measurement or by laser triangulation interferometry, from which the pressure in the tube can be deduced.

6. A method in accordance with claim 1, characterized in that it is determined by means of an evaluation unit whether a measurement value of the pressure in the tube is within a tolerance range; and in that an alarm is triggered if the measurement value is not within the tolerance range.

7. A method in accordance with claim 1, characterized in that the tube is fixedly, but releasably, arranged in a fixture before the carrying out of the method.

8. An apparatus for determining a pressure in the interior of a tube by means of laser interferometry, in particular by means of laser speckle interferometry, comprising: a laser light source; an optical sensor for detecting the light transmitted by the laser light source; and an evaluation unit that is adapted to evaluate the optical signals detected by the optical sensor.

9. An apparatus in accordance with claim 8, furthermore comprising a guide in which a tube can be fixedly, but releasably, placed.

10. An apparatus in accordance with claim 9, characterized in that the guide is formed as a tube chicane that preferably has a U-shaped guide groove for receiving a tube.

11. An apparatus in accordance with claim 9, characterized in that the laser light source transmits laser light of at least two different colors.

12. An apparatus in accordance with claim 8, characterized in that the apparatus is arranged at a tube of an extracorporeal blood treatment machine to determine the pressure of the tube.

13. A system of an apparatus in accordance with claim 8 and of a tube, characterized in that the tube has a structure optimized for the measurement at least in a section at which the tube pressure is to be determined, is in particular thin-walled and/or produced from a material whose properties are relatively temperature independent and/or has a particularly rough surface structure for amplifying a speckle pattern or has a particularly smooth structure for improving the reflection properties.

14. An apparatus for extracorporeal blood treatment having at least one apparatus in accordance with claim 8.

Description

[0051] FIG. 1 an overview of different approaches in accordance with the invention for the contactless determination of the pressure in a tube;

[0052] FIG. 2 a fixture/guide in the form of a chicane for a tube; FIG. 2a) shows a cross-section of the chicane with an inserted tube and FIG. 2b) shows a plan view of the chicane with an inserted tube; and

[0053] FIG. 3 a flow diagram of a method in accordance with the invention.

[0054] As shown in FIG. 1, the method in accordance with the invention is based on a changing surface (preferably a surface of a tube of an extracorporeal blood treatment machine, but the invention is not restricted thereto) being observed to draw conclusions on changes in the pressure in the tube with reference to changes of the surface.

[0055] Three variants are conceivable to detect/observe the changes of the surface by means of a laser and are shown schematically in FIG. 1:

[0056] It is assumed in all variants that a tube 1 is received in a fixture/guide 2. The diameter of the tube changes due to changes of the pressure in the tube 1, as is illustrated by the line 3 (in the example of FIG. 1, the pressure in the tube 1 increases and the diameter thus increases; the surface of the tube expands).

[0057] As shown in FIG. 1a), the measurement of the tube diameter can take place by means of a time of flight measurement. In this respect, laser light 4 is transmitted pulse-wise by a laser 5 and the time or the time interval Δt is determined starting from a transmission of the laser light 4 until an optical detector receives a reflection of the light.

[0058] A conclusion can be drawn on the distance of the surface from the laser 5 from the time of flight and the speed of light. Since the laser 5 is fixedly installed, any changes to the time of flight are due to changes of the distance between the surface of the tube 1 and the laser 5 and thus to changes of the pressure in the tube 1.

[0059] FIG. 1b) illustrates the laser interferometry. The term interferometry here comprises interferometry using triangulation, i.e. laser light is irradiated at one location and runs on two different paths until it is merged at a second location. The light of the two different paths interferes. The one path is direct, i.e. a straight line from the laser 5 to a detector/sensor. The second path typically runs over a reflection, e.g. at a surface of the tube 1. The light from the laser 5 is e.g. reflected on the tube wall of the tube 1. Small differences of the path length Δφ can be observed as an interference pattern. The interference pattern changes accordingly by a stretching of the surface due to a pressure change in the tube.

[0060] FIG. 1c) illustrates the laser speckle interferometry. The basis for the interference of the laser light comprises the surface of the tube 1 having a certain structuring/roughness. Constructive or destructive interference takes place in dependence on the expansion of recesses/valleys on the tube surface. A spot pattern of light, the speckle pattern, thereby results. This characteristic pattern changes with a change of the surface of the tube such as with an expansion of the tube due to a pressure change.

[0061] The speckle pattern is detected by means of a speckle detector 6 and is preferably analyzed by means of an evaluation unit. The evaluation of the speckle pattern requires an image detection that goes beyond a light sensor. A 1 D sensor strip is preferably provided, but it can also be a 2D sensor field (or a multidimensional sensor field) or a camera. An image evaluation detects the speckle pattern and its change and thus determines the pressure in the tube.

[0062] FIG. 2 shows a fixture/guide 7 in the form of a chicane for a tube 1. FIG. 2a) shows a cross-section of the chicane 7 with an inserted tube 1. The chicane 7 surrounds the tube 1 on three or, sectionally, also on four sides and has a reception opening 8 by means of which the tube 1 can be inserted into a groove 9.

[0063] As shown in FIG. 2a), the laser 5 and the speckle detector/sensor 6 are integral components of the chicane 7 or are fixedly installed therein. As shown in FIG. 2a), the laser 5 and the speckle detector/sensor 6 are preferably embedded in a holding section 10 that holds the tube 1 in the groove 9 and secures it against an unwanted dropping out.

[0064] FIG. 2b) shows a plan view of the chicane 7 with an inserted tube 1. The holding section 10 can be recognized particularly well in this representation. The chicane 7 surrounds the tube 1 at four sides at the holding section 10.

[0065] The chicane 7 additionally has a U-shaped design that enables a particularly reliable fixing of the tube 1 in the groove 9.

[0066] The chicane 7 is preferably produced in one piece from plastic. A multi-piece design from another material is, however, likewise conceivable.

[0067] As shown in FIG. 3, a method in accordance with the invention of observing a changing surface by means of laser interferometry, in particular by means of laser speckle interferometry, can comprise the following steps: [0068] Step 1 (S1): Observing a first speckle/interference pattern on the observed surface; [0069] Step 2 (S2): Recognizing and marking regions and/or landmarks/reference points in the first speckle/interference pattern; [0070] Step 3 (S3): Tracking the marked regions and/or landmarks/reference points in order thus to detect changes of the speckle/interference pattern and therefore of the changing surface. The relative position with respect to one another and/or the absolute position of the marked regions and/or landmarks/reference points can be taken into account. On a pressure change in the tube, for example, the marked regions can move away from one another or can likewise be linearly displaced on a displacement of the tube. Light/dark transitions can furthermore be detected or tracked in the first speckle/interference pattern; [0071] Step 4 (S4): Associating the detected changes in the speckle/interference pattern with a change of the pressure in the tube, for example with an expansion of the tube. If a plurality of pressures are to be measured in the tube, a calibration step is preferably carried out between the measurements; [0072] Step 5 (S5): Correcting or taking account of the properties of the tube such as the elasticity, the diameter, the reflectivity, the surface roughness, etc. Step 5 can take place as part of the association of the changes in the speckle/interference pattern with a change of the pressure in the tube from Step 4. The correction can comprise a plausibility check.