Hengstler has introduced a range of encoders for sophisticated pitch control applications on wind turbines. Wind energy turbines are not only exposed to fluctuating wind conditions, but have to use these forces as efficiently as possible. Therefore, dynamic pitch control is essential to boost the efficiency of this renewable energy technology by adjusting the rotor blade to the required angle.
At low wind speeds, blades are directed more towards the wind and turned away again as the wind force increases, to ensure that the wind turbine continues to operate safely even at high wind speeds. Just as for many applications involving rotational movements, there are different approaches enabling the use of encoders – starting from simple solutions with only one incremental encoder right through to a combination of two redundant absolute encoders.
The gear motor positions the rotor blade while an additional brake ensures that the required position is maintained safely even in the event of a power failure. Since the encoder is mounted directly onto the drive, it has to return reliable positioning values within the temperature range from -40 to 100°C. The optical gear based multi-turn Acuro AC58 encoders from Hengstler have proven to be a most suitable solution in this regard.
The position is determined by means of an optical rear illumination method. The mechanical multi-turn gear is also scanned optically so that it is not necessary to test the magnetic effects which may be caused by the drive brakes, in particular. Such scanning is not susceptible to magnetic interference and therefore suitable for direct mounting on all motors that are provided with brakes. In addition, the encoder offers high resolution and is able to indicate both absolute and incremental signals, which can be used as reference values and/or for speed adjustments. As a result, no additional resolvers or tachometers are necessary.
Another alternative is to mount the encoder directly on the slewing ring of the rotor blade. In this case, it is coupled by means of a cog wheel mounted on the encoder shaft. Since the mechanical stresses on the sensor are significantly higher than in the case of motor installation, this application places totally different demands on the encoder. To reduce the encoder bearing load, bearing modules have often been used in the past. This installation variant calls for a specifically robust encoder such as Acuro AR62. Featuring a compact design and extremely sturdy ball bearings, it is suitable for very high axial and radial loads. With a maximum admissible load of 300 N (both axial and radial), it not only surpasses most of the common load module types, but also offer 10 times the load capacity of commercially available encoders.
Similar to AR58, AR62 is an electronic multi-turn encoder that also exhibits wear free pulse wire technology. Magnetic single turn and multi-turn scanning ensure high shock and vibration resistance. It is also resistant to environmental influences such as humidity and wide temperature ranges. Offering protection class IP69K this encoder type is suitable for complete outdoor installation.
Finally the encoder can also be mounted onto a limit switch box. On-site installation is facilitated by a complete, pre-adjusted component assembly. In this approach the mechanical requirements are not as high as compared to the direct installation on the rotor blade. Meeting all the demands for high precision and sturdiness the Acuro AR58 magnetic absolute encoder is a cost-efficient solution due to its mechanical design.
Both in the single and multi-turn variants, these encoders need only a single magnet. The multi-turn encoder uses pulse wire technology, which means that it operates completely wear free without battery and gear.
The energy required for position detection is produced from the rotational movement alone, a significant advantage of this technology.
For more information contact Gerry Bryant, Countapulse Controls, +27 (0)11 615 7556, bryant@countapulse.co.za, www.countapulse.co.za
| Tel: | +27 11 615 7556/7/8 |
| Email: | clive@countapulse.co.za |
| www: | www.countapulse.co.za |
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