Detection of the form deviation of rotor blades for wind turbines

Executive summary Measurement of rotor blades of the Enercon E-126 turbine using a tachymeter to determine the deviation from the CAD model.

1. Introduction

First a short presentation of my person: I am an international welding specialist and was employed by the company MAM in Magdeburg from 2008-2013. This company belongs to the ENERCON group and mainly produces assemblies for wind turbines and hydroelectric power plants. First of all I was hired for the qualitative assessment of welding seams. But soon there were increased quality requirements for the rotor blades made of steel. These were to be assessed by means of 3D measurement and measures to increase quality in production were to be introduced. A total station, the Sokkia Net1 and the associated software were purchased from GLM.After a 2-day briefing the measurement started! 2. Measurement task and its solution The first generation of rotor blades to be measured still consisted of eight individual sections, which were about 3m long. This made it easy to place and measure them on a turntable. Rotor blades of the new generation, on the other hand, are made of metal sheets with an individual length of over 11m. The new measuring conditions which arose from this had to be mastered. At this point I would like to give a small insight into the production of the rotor blades for the wind turbine E-126!

System E-126

Rotor blade with backboxes

2.1 Hot forming and cutting

The rotor blade for the E-126 turbine consists of 12 individual LP sheets which are rolled from a single piece of steel plate in different thicknesses. These are then heated to normal annealing temperature in the heating oven. They are then formed in a press. The forming boxes built for this purpose were measured by us and marked by means of iterative staking out in such a way that 3 tips each could later be inserted to determine the contour on the formed sheet. The final shape of the sheet metal is created by a robot on a plasma cutting machine using the measured tips.



2.2 Assembly

After the sheets have been ground and preblasted, they are joined together in a building slipway. The blade and separating flange are then aligned and pre-welded. The rotor blade is then welded and undergoes several non-destructive tests. The rotor blade is then stress-relief annealed and mechanically processed.

Building slipway, open

Building slipway, closed

2.3 Measurement

The actual measurement begins with the assembly.

To determine length, twist and parallelism, target marks are applied to the blade flange and separating flange. The position of the rotor blade is determined by measuring 3 target marks on the blade flange. A program is then started which automatically measures 40 reflectorless measuring points on the blade flange. Then 2 targets for the twist and 8 targets for parallelism are measured manually at the separating flange. In the 3D program:Rhinoceros the data is evaluated by means of the GLM Plug-In: 3-Dim PT and the rotor blade is released for further processing.

After completion of the raw part, the dimensions of the rotor blade are determined once again to make them available for the mechanical processing of the two flanges.

When all production steps including painting are finished, the final measurement starts.

The rotor blade is positioned on 2 roller units and rotated to its initial position.

Target marks are attached to the blade flange and the separating flange to determine the position in space. The first 2 sections are now scanned automatically, reflectorless.

Since not all sections can be scanned from one location, the current position is determined at the end of the 1st measurement with the help of 3 ball targets.

The rotor blade is now turned further. With the help of the ball target marks we determine its position again.

These steps are repeated until the entire rotor blade has been scanned.

Complete measurement

3. Evaluation

The data of the measurement are loaded into the CAD program Rhinoceros.

With the evaluation tool 3-Dim PT the measured point cloud is compared with the 3D model. With the help of arrows and dimensional figures, any deviations can be detected visually. These can then be exported to an Excel table if required.

Evaluation in Rhinoceros

4. Application of the measurement results

By intensive evaluation of the measurement results, corrections to the moulds and the welding sequence during production could be improved.

For example, the twisting of the two flanges in relation to each other was improved from 1 degree to less than 0.2 degrees, and this with a distance of 24200 mm and a 3D deformed component! The dimensional deviations of the entire component could be reduced to less than 5 mm from the nominal contour.

If you have similar tasks and projects, please contact me and we will find a solution. No matter whether in mechanical engineering, rail vehicle construction or the construction of wind energy plants. Please contact me.

Henry Dietrich


Gottfried-von-Herder-Straße 2

06388 Stadt Südliches Anhalt Ortsteil Edderitz

Tel.: +491712362682



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