Field

The invention relates to a device which provides optical-thermal processes for the transmission of infrared radiation in the space between the laser thermography system, the surface to be measured and the surrounding environment to ensure the correct function of, for example, non-destructive inspection of the quality of spot welds, in particular of shiny metal sheets.

Prior art

Currently, laser thermography systems are used either as a laser technology for material processing, for example in welding or hardening with process control using a thermal camera, or as a measuring device for non-destructive testing of materials using active thermography.

The laser thermography system consists of a laser part and a thermographic part. The laser part provides non-contact heating of the material and typically consists of a laser source and an optomechanical system that shapes and positions the laser beam. The thermographic part provides non-contact sensing of the infrared radiation of the heated surface and typically consists of a thermal camera that senses the areal distribution of heat flux from the material surface being measured. The material or product to be measured is located within the working space defined by the optical characteristics of the laser and thermographic part, and at a distance from the laser thermographic system.

For practical use, especially in the context of serial industrial production, two basic variants of the overall arrangement of the laser thermography system and the material to be measured are used. Either the laser thermography system is stationary and the material or product to be measured is moved in the work area or the material (product) is stationary and the laser thermography system is moved. Movement is provided by an industrial robot, gantry or other type of manipulator.

These devices have several disadvantages resulting from the non-contact remote application of the laser and thermographic process on the measured material or product.

The use of a laser source brings the need to address safety measures to prevent damage to surrounding persons and equipment in the event of uncontrolled exposure to the laser beam, either directly or by reflection from the surface of the material. Safety precautions are usually taken by placing the laser system in an optically sealed box around the workplace. The disadvantages of such a solution are the increased footprint, the need to deal with opening/closing hatches for material handling into the work area and the associated time and financial costs.

Another disadvantage is due to non-contact remote sensing of infrared radiation, which is affected by the reflections of ambient radiation from the surface being measured. This is particularly important in cases of measuring metallic shiny surfaces of materials with low emissivity values, measuring relatively small temperature changes and high requirements for accuracy in determining temperature changes. If the effect of ambient radiation reflections is not addressed, it adversely affects the repeatability and accuracy of the measurement system and negatively affects the results of the quality control performed. Addressing the problem by technical and organisational measures to prevent unwanted ambient thermal reflections creates additional costs or reduces the time of use of the equipment. Solving the problem by installing sensors to measure the reflected ambient radiation and the corresponding evaluation algorithms imposes additional costs and does not solve the problem satisfactorily. of the invention

The essence of the invention is that the workspace cover of the laser thermography system comprises a casing which has at least one inlet aperture and at least one outlet aperture, and further which comprises a reference element having a surface finish with at least one high emissivity region and with at least one low emissivity region.

The casing consists of a rigid part and a flexible part, wherein the inner surface of the casing has a laser radiation absorption greater than 0.6 and an emissivity greater than 0.6. In the interior of the casing is an optical sensor which register enclosure of the casing.

The outlet is located in the work area and the reference element is located in the work area. The reference element may be movable and, in one position, visually covers the outlet opening. The surface finish of the reference element shall include at least one high emissivity region with an emissivity greater than 0,6 and at least one low emissivity region with an emissivity less than 0,4. A reference radiation source is located in the internal space of the casing.

The advantage of using the enclosure according to the invention is that it allows the laser beam to be applied to the material or product, measurements to be made with an infrared camera and calibration procedures to be carried out, and at the same time prevents unwanted reflections of thermal radiation from the surroundings and leakage of laser radiation into the surroundings.

Without the casing, the laser thermography system was exposed to reflections of thermal radiation from the surrounding environment and at the same time its laser radiation could freely escape into the surrounding environment.

By enclosing the workspace of the laser thermography system optically and thermally with an enclosure according to the invention, its functional properties are significantly improved. Preventing the effect of the reflection of radiation from the surrounding environment improves the repeatability and accuracy of quantitative temperature measurement by the infrared camera. This is particularly relevant to processes where objects or persons that represent parasitic time-varying sources of thermal radiation are in the vicinity of the laser thermography system. Preventing the leakage of laser radiation into the surroundings enables the operation of the laser thermography system without the need to cover the entire workplace, thus significantly saving financial resources for the implementation of the workplace and simplifying material handling and possibly reducing the footprint, which brings further financial cost savings.

In the current state of the art, quality control of the laser thermography system was carried out using reference elements placed in the work area manually or semi-automatically during nonproductive times of the workstation operation.

By making the reference element an integral part of the cover according to the invention, all necessary calibration procedures can be automatically performed on it as part of quality assurance. These calibration procedures can be run without the involvement of a human operator, which reduces the cost of operating the laser thermography system, and at shorter time intervals, which contributes to fewer false indications caused by changes in the functional characteristics of the laser thermography system during operation. In addition, the placement of the reference element inside the cover prevents the negative effects of ambient radiation reflection and improves the repeatability and accuracy of calibration measurements.

Brief description of drawings

An exemplary embodiment of the invention is shown in the attached pictures, where Fig. 1 schematically shows an empty cover, which is the subject of the invention, Fig. 2 shows a laser thermographic system with a workspace cover, Fig. 3 shows the part around the entrance opening of the cover in a variant where the measuring system is inside the cover, Fig. 4 shows the part around the inlet opening of the cover in a variant where the measuring system is outside the cover Fig. 5 shows the part around the outlet opening of the cover with a fixed reference element from the side view, Fig. 6 shows the part around the outlet opening of the cover with a fixed with the reference element from a plan view, Fig. 7 shows the part around the outlet opening of the cover with the movable reference element from the side view, Fig. 8 shows the part around the outlet opening of the cover with the movable reference element from the top view, Fig. 9 shows the surface of the reference element with areas with high and low emissivity value, Fig. 10 shows the method of surface treatment of the reference element by deposition layer with a high emissivity value and Fig. 11 shows the method of surface treatment of the reference element by applying a layer with a low emissivity value.

Exemplary embodiment of the invention

An exemplary embodiment of the cover of the working space of the laser thermographic system according to the invention is shown in Fig. 1. The largest part of the cover is the casing 4, which separates the internal space 11 of the cover from the outer space 12. The cover includes at least one inlet opening 5 and at least one outlet opening 6. The casing 4 serves at the same time to attach other parts of the cover. The cover must not interfere with the laser space 14 and the thermographic space 15, and from the point of view of external dimensions, it should be as small as possible, especially at the outlet opening 6, so that it is possible to measure complex shape products with the finest details and to get inside the openings.

In the internal space 11 of the cover, a reference element 7 is advantageously located, which serves to implement several methods of calibrating the laser thermographic system, a sensor 8 of the optical closure of the cover, which serves to implement a safety control of the closure of the cover, and a source of reference radiation 18, which serves to implement the method measurement of the area distribution of the reflectivity of the surface 3 of the measured material 23. Further measuring systems can be placed in the internal space 11 of the cover, for example for measurement of the geometric characteristics of the surface 3 of the material 23.

In terms of optical-thermal properties, the internal surface 19 of the casing 4 has the function of absorbing laser and thermal radiation that falls on it. This is ensured by a suitable choice of material or surface treatment of the inner surface of the casing 4, preferably with an absorption and emissivity value greater than 0.6. This can be realized, for example, with thermoplastic by means of 3D printing or with stainless steel with a surface treatment of thermographic reference paint. The casing 4 may be maintained at a specific temperature by the addition of a heating or cooling system.

The schematic arrangement of the laser thermography system with the working space cover is shown in Figure 2. The laser head 1, which provides the shaping and positioning of the laser beam, is located in the internal space 11. A thermal imaging camera 2, which provides the measurement of infrared radiation, is also located in the internal space 11. The surface of the material to be measured 3 optically encloses the outlet 6. The laser heating action and the measurement of the thermal radiation of the surface 3 of the material to be measured 23 is carried out through the outlet 6.

The part of the cover around the inlet opening 5 can be implemented in various ways, as shown in fig. 3 and fig. 4. The laser head 1 and the infrared camera 2 can be entirely located in the internal space 11 of the casing 4, as shown in fig. 3. In such a case, a wiring 17 consisting of a power supply, a control or measurement signal line and an optical fiber for conducting laser radiation from the source to the laser head 1 passes through the inlet 5. The laser head 1 and the infrared camera 2 may also be located entirely outside the internal space 11 of the casing 4, as shown in figure 4. In such a case, the casing typically has two inlet openings 5. One inlet opening 5 optically encloses the lens 16 of the laser head 1, and the other inlet opening 5 optically encloses the lens 16 of the infrared camera 2. Other arrangements are possible in which the laser head 1 and the infrared camera 2 are partly located in the internal space 11 of the housing and partly in the outer space 12. The casing 4 may be associated with a mounting 22 of the measuring system on a moving robot or gantry or on a stationary structure, depending on whether the measuring system or the material to be measured is positioned.

The part of the cover around the outlet 6 can be realized in the manner shown from the side view in Fig. 5 and from the top view in Fig. 6. The measured surface 3 of the measured material 23 optically closes the outlet 6 of the cover. Therefore, the casing 4 in this part of the cover consists of a fixed part 9 and a flexible part 10. The flexible part 10 is in direct contact with the surface of the measured material 3 and ensures optical tightness. The implementation can be done in different ways, for example using a brush or a bellows. The outlet opening 6 is placed in such a position that the surface 3 of the measured material 23 is in the workspace 13 of the laser thermographic system. This workspace 13 is formed by the intersection of the laser space 14 and the thermographic space 15. The laser space 14 is the space in which the laser beam from the laser head 1 can move. The thermographic space 15 is the space from which the measured radiation falls on the detector of the infrared camera 2. The definition of the laser space 14 or the thermographic space 15 can be done by hardware, for example by choosing optomechanical elements such as the lens, aperture, detector, mirrors, aperture, or by software by further reducing it.

In addition, the cover is usually constructed so that the surface 3 of the measured material 23 and the reference element 7 are placed at the so-called focusing distance from the laser head 1 and the infrared camera 2. The focusing distance for the infrared camera 2 represents the distance at which the image is focused. For a laser, this means the distance at which the laser beam has the smallest diameter. In certain cases, when it is convenient to heat the surface 3 of the measured material 23 with a larger diameter of the laser beam, the laser head can be placed at a different distance. Focusing distance then means the distance at which the laser beam has the desired diameter. In other words, it is the distance at which the surface 3 of the measured material 23 should be placed, so that the process of laser heating and measurement of the surface distribution of the radiated heat flux takes place according to the requirements.

The reference element 7 can be placed in the internal space 11 of the cover firmly in connection with the casing 4. In this case, the reference element 7 has such a shape and position that it is possible for part of the surface 3 of the measured material 23 and part of the surface of the reference element 7 to be at the same time affected with a laser beam from the laser head 1 and measure their temperature with an infrared camera 2. The reference element 7 can therefore, for example, have the shape of an annulus, where through the inner opening of the annulus, laser heating and non-contact measurement of the surface 3 of the measured material 23 takes place. The reference element 7 can also have, for example, a rectangular shape and can be placed on one side of the outlet opening 6 so that it partially covers this outlet opening 6. Laser heating and noncontact measurement of the surface 3 of the measured material 23 takes place on the other uncovered side of the outlet opening 6.

An example of the implementation of the invention with a movable reference element 7 is schematically shown from a side view in Fig. 7 and from a top view in Fig. 8. The reference element has two working positions. In the first position, it is located outside the workspace 13 and thus enables the action of the laser thermographic system on the surface 3 of the measured material 23. In the second position, it is located inside the workspace 13. It is therefore possible to heat its surface with a laser beam from the laser head 1 and measure its temperature with a infrared camera 2.

Fig. 9 schematically shows the implementation of the reference element 7. The surface of the reference element 7 is modified from the point of view of optical-thermal properties to include a high emissivity region 20 with a high emissivity value and a low-emissivity region 21 with a low emissivity value. These are placed in such a way as to enable surface and local heating by the laser beam from the laser head 1, and at the same time, with a different emissivity value, they create sufficient contrast for measuring the surface temperature distribution with the infrared camera 2. A possible realization of the treatment of the surface of the reference element 7 to create a high emissivity region 20 with a high emissivity value and a low emissivity region 21 with a low emissivity value is schematically shown in Fig. 10 and Fig. 11. In the case where a base material with a surface with a low emissivity value, as shown in Fig. 10, can be adapted for example by applying a reference thermographic paint with an emissivity higher than 0.9 or by laser surface treatment with heat treatment or micromachining technology. In such a case, the low emissivity regions 21 with a low emissivity value form either the original unmodified surface or a surface modified and cleaned. In the case shown in Fig. 11, when a base material with a surface with a high emissivity value is used, it is possible to create low emissivity regions 21 with a low emissivity value by applying a material with a low emissivity, for example a shiny metal. Reference element 7, can be made as composed of several separate parts. For example, one part with a high emissivity value and another part with a low emissivity value.

The laser thermography system workspace cover according to the invention is a permanent part of the laser thermography system workplace, so it is mounted when the system is installed and used throughout its operation.

During production, when materials or products are being measured, the cover fulfills the function of enclosing the work space against the leakage of laser radiation into the surroundings and the penetration of thermal radiation from the outside environment. After the outlet opening 6 is covered by the surface 3 of the measured material 23, the sensor 8 checks the optical closure of the cover. Subsequently, the laser and thermographic process takes place. After its completion, the position of the laser thermographic system or the measured material or product is changed to a new working position.

In the remaining non-productive time, checks are repeatedly started at certain intervals, which use the reference element 7 in the position in the workspace 13. During these checks, the laser beam from the laser head 1 heats the surface of the reference element 7 and the infrared camera 2 measures the temperature of the surface of the reference element 7.

By setting the time course of the power of the laser source and the spatial positioning of the laser beam along the surface of the reference element 7, together with the measurement of the time course of the area distribution of the surface temperature of the reference element 7, the position of the laser head 1 and the correct function of the positioning of the laser beam, the position of the infrared camera 2 and the correct function of the focus, the power intensity of the laser source and the calibration settings of the infrared camera 2 for quantitative temperature measurement can be checked.

The reference radiation source 18 together with the infrared camera 2 is used in cases where it is necessary to measure the area distribution of the optical-thermal properties of the surface 3 of the material 23 to be measured. This may occur at non-productive times as part of determining reflectance or emissivity values for the purpose of quantitatively evaluating the temperatures measured by the infrared camera 2. Alternatively, it may occur as part of productive times when the determination of the area distribution of the reflectance of the surface 3 of the measured material 23 is part of the inspection of the measured material or product, for example to specify the position of the spot welds to be tested, and precedes the laser thermography process. The reference radiation source 18 irradiates the surface 3 of the material 23, while the infrared camera 2 measures the area distribution of the reflected radiation.

Industrial applicability

The invention can be used in particular for industrial workplaces, where non-destructive quality control of materials or products, for example spot welds, is carried out in serial production by means of active thermography using a laser thermography system.

The invention can also be used for industrial workplaces where laser technology for material processing, i.e. welding, heat treatment, machining, or welding, is used in serial production, and the technological process is thermodiagnosed by a thermal camera. List of reference marks

1 - laser head

2 - infrared camera

3 - surface

4 - casing

5 - inlet

6 - outlet

7 - reference element

8 - sensor

9 - fixed part

10 - flexible part

11 - internal space

12 - outer space

13 - workspace

14 - laser space

15 - thermographic space

16 - lens

17 - wiring

18 - reference source

19 - internal surface

20 - high emisivity region

21 - low emisivity region

22 - mounting

23 - material to be measured