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Fast, simple, precise and extremely reliable

Post Time:Oct 24,2008Classify:Glass QuotationView:441

The demand for solar parabolic mirrors being put into operation to exploit solar energy is increasing around the world. To assure that the production process is economically efficient, the ever growing number of cycles requires that the mirrors undergo an automatic 3D in-line inspection. For this purpose, camera-based methods offer clear advantages over the laser gauging techniques with regard to speed, simplicity and accuracy.

The cost of energy is on the rise. What’s more, there is a growing concern about global warming caused by humans as a result of, among other things, the rise in CO2 emissions. The solar industry is benefiting from these developments, which is currently reaping the rewards of an almost unstoppable upward trend. Solar technology has the ability to make use of the sun’s radiation to generate energy.

Especially in areas with plenty of sunshine, an extremely popular method of exploiting solar energy is based on the use of solar parabolic mirrors. The technology focuses the direct sunlight onto receiver pipes filled with a fluid. By means of classic turbine technology, the thermal energy collected this way is converted into electric power. Around the world, the demand for these kinds of parabolic mirrors is growing. This is why there is an ever growing demand for production methods with increasingly shorter cycle times.

Solar parabolic mirrors are made up of four components, of which two of each of these are identical – the two outer and the two inner mirrors. These are assembled to the form of a parabola. The individual mirror segments are approx. 1700 mm in size. When assembled, they are pieced together to form long channels.

Manufacturing solar parabolic mirrors requires constant inspection. The process involves gauging manufacturing tolerances. Up until now, laser systems were frequently put to use to inspect these kinds of mirrors. However, for an automatic 3D in-line inspection, meaning an inspection of the ongoing production process integrated directly into the equipment, these kinds of systems are simply too slow.

Now, with FORMSCAN Solar, a system has become available that can satisfy the requirements for the production of solar parabolic mirrors without any restrictions. The system consists of standard components, which makes it possible to adjust to the relative production conditions flexibly and easily. The system measures any deviations in the mirror angle to the target value (focus deviation). This is the space through which an incident parallel sun ray passes by the focus point. This space may not be any larger than the radius of the pipe.

New benchmarks with regard to accuracy

Typically, a mirror is measured before the mirror layer is applied, i.e. as a sheet of glass. However, it is also possible to measure mirrored glass. The system is usually used as an in-line system in a mirror production process and in this application it sets new benchmarks with regard to accuracy. The cycle time for a complete mirror is only about 20 s. The camera-based inspection system is thus significantly quicker than any laser technology that runs at lower speeds and that can typically only achieve an inspection pattern of 50 mm.

Deflectometric inspection process

The inspection process is based on a deflectometric method, which is particularly suitable for inspecting inspect angles. Cameras are used to observe the reflected image of a reference sample. The measured variables are defined by using the distortion of the sample. Usually, a system is made up of four cameras and two illumination units. The sheets are not inspected in their installation position, but instead in their production position. This means they are positioned with the open side facing upwards, in a “bowl-like position” so to speak. Other than a means to illuminate the reference sample, the system does not require any other lighting equipment.

This method provides an extremely accurate measurement of the sheet. With a system that can be configured easily, it is possible for measurements to be performed quickly within the production cycle. No moving parts are attached to the measuring system itself. Accurate results are achieved by applying sophisticated algorithms, integrated in which is a huge amount of industry expertise.

Conclusion

The camera-based in-line inspection of solar parabolic mirrors is easier, faster and more accurate than any comparable laser gauging technology. The system´s extreme reliability assures top inspection quality every time. The user benefits from the excellent cost-benefit ratio. The data obtained during inspection can also be used for optimizing the production process.

Source: ISRA Vision AGAuthor: shangyi

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