Identification of permanent sensor bolts using Cognex DataMan 100

The power in the wind

Identification of permanent sensor bolts using Cognex DataMan 100 July 2010.

Cognex Corporation: Larger and larger wind power turbines are bringing the forces of nature under control. The main structures, the powerful tower and rotors, are supported by parts that play a less obvious, but no less important role: bolts. As simple as it may look, precision tightening of bolts is an art form of its own. Intellifast GmbH is now ensuring perfect support in any weather using ultrasound permanent sensors and Data Matrix codes.

At first glance, all bolts look the same. But, when measured by ultrasound, each bolt reveals its individual inner life and a characteristic surface. It may only be in the µ range, but no two bolts are exactly the same in shape or length. Scattered friction values in the thread and under the head make it a real challenge to tighten bolts with precision. As a result, tightening factors of 1.8 to 2.0 (twice the maximum force actually required for pre-tension) are generally used for torque-controlled assembly for safety precautions.

Pre-tension instead of torque
Bolts can be tightened much more precisely if the target variable pre-tension is used as a reference variable instead of torque. Compared to the "force times lever arm“ of torque, which only takes into account the force required to adequately pre-tension a bolt regardless of friction values. Ultrasound measures the pre-tension of the bolt as it is being tightened. People have been working with ultrasound technology for decades to enable this real target variable to be applied accurately, however, there has always remained a potential source of measured value errors with this method: the transmission medium. Intellifast GmbH from Speyer developed permanent sensors for bolts to eliminate this type of error.

Connecting elements can thus be bolted together at the exact assembly pre-tension required with an accuracy of +/- 3%. The result: lighter-weight, smaller, and cheaper bolts and connecting elements, such as flanges, can be used.

Bolted to a specification
To be absolutely certain that the bolts have the optimum dimensions, Intellifast GmbH relies on the “digifast®” track-and-trace solution. This process uses lasers to apply an individual Data Matrix code to bolt heads or ends to indicate their ultrasound measurement.

At the assembly location, the DataMan® 100 ID reader from Cognex® recognises the individual bolt by reading the Data Matrix code. In the next step, the bolt’s data is passed to the Intellifast LP 3000B measuring device that assigns the hydraulic tool with the exact pre-tension required for assembly. The process is fully automatic. The simple control and rapid check by the permanent sensor system optimises the bolting process. Once in the bolted state, the Intellifast LP 3000B measuring system can also measure the bolt to make sure the pre-tension is correct as a doublecheck.

Incorporating DataMan 100 within digifast® gave the manufacturer the smallest and highest-performing industrial ID reading device in the world. The DataMan 100 guarantees reliable reading of the most complex codes. Highly compact, the ID reader integrates lighting, camera, processor and interfaces in a sturdy housing, enabling it to detect the Data Matrix codes of the bolts under even the most difficult conditions.

About Cognex
Cognex Corporation designs, develops, manufactures and markets machine vision sensors and systems, or devices that can "see." Cognex vision sensors and systems are used in factories around the world where they guide, inspect, gauge, identify and assure the quality of a wide range of items during the manufacturing process. Cognex is the world's leader in the machine vision industry, having shipped more than 500,000 machine vision systems, representing over $2.5 billion in cumulative revenue, since the company's founding in 1981. Headquartered in Natick, Massachusetts, USA, Cognex has regional offices and distributors located throughout North America, Japan, Europe, Asia and Latin America. For details, visit Cognex on-line at http://www.cognex.com.