The measuring area of the ABSODIAM system.
The wire industry needs to be able to reliably measure the diameters
of its products. But until the ABSODIAM project, there was no instrument
that could measure diameters less than 200 micrometres accurately
enough to say that the measurements were absolute. Six partners
from industry, a university and a national metrology institute developed
a prototype system to meet this need, as well as a series of wire
reference materials that can be used to calibrate industrial machines.
The final version of the prototype will be on the market in spring
The smaller things are, the more difficult they are to measure. This is certainly true when it comes to wires. The thinner they are, the fewer instruments there are available to measure them. Thin wire diameters can be measured using several different technologies. Some of the most widely used include weighing, laser scanning, micrography and laserinterferometry.
"However, the different methods do not produce comparable data for diameters smaller than 0.2 mm. The lack of such reliable data causes many problems on the market between producers and users of wire and thread," says Dr Michael Kraft of the firm KJM Gesellschaft für optoelektronische Messtechnik. If there were suitably accurate measurement systems, wires that have a given diameter could be prepared and sent out to wire manufacturers, who could use these reference materials to calibrate industrial instruments. Worldwide, there were no absolute measurement systems or certified reference materials for measuring wire diameters of less than 200 micrometres.
Seeing the problems this caused the wire industry, Dr Kraft and researchers from three other industrial firms, a national metrology institute and a university decided to develop the systems and reference materials to rectify the situation. With funding support from the Standards, Measurements and Testing programme, they began the ABSODIAM (Absolute Diameter Measurement) project.
As their first task, the partners had to decide which measurement technology to use. "Diffraction analysis (DA) seemed to be the most promising. KJM had a system based on this technique on the market and this was the major starting point," says Dr Kraft, the project coordinator. DA has a suitable measurement range and can be used for threads as well as wires.
After deciding which technique to pursue, they worked on a laser module that can accurately measure wavelengths, a crucial part of the diffraction analysis system. In this theoretical work, they also refined the mathematical formula that gives wire diameter measurements from diffraction patterns and developed the equations required to analyse the uncertainty in the measurements. This allowed existing software to be refined and new modules were also created.
The results of the existing diffraction analysis instrument were verified by comparison with other instruments. This work showed that the system could already measure absolute values for diameters between 150 and 500 micrometres.
From there, the team combined all aspects of the earlier tasks to develop a prototype system. Mechanical and optical parts and the control system had to be designed and constructed. The ABSODIAM prototype measures the absolute diameters of wire, enamelled wire and plastic thread with diameters ranging from 10 micrometres to 0.2 mm, with an absolute accuracy of 50 hm and a repeatability accuracy of 10 hm. If the repeatability accuracy is small, it shows that the measurement can be repeated many times with little change in the results.
The prototype will be used for industrial exploitation and will be further developed within the framework of other projects, including a second SMT project that began in 1998. A calibrated version of the tool will be put on the market in the coming months. To improve the final version of this calibration system KJM, PTB and Monocrom are making the final adjustments. If necessary, KJM will register a new patent for the final enhanced system. Although still currently at a prototype stage, two of the partners, KJM and PTB already have plans to market the system to European calibration institutions in spring 1999. If all goes to plan, they will continue this for the next two years.
To start the commercial ball rolling and to raise the profile of the ABSODIAM system, partners have presented the project results at 12 conferences and at trade fairs as well as in a range of industrial journals. This is both in Europe and further afield. KJM also promotes it in one of their company brochures.
Point of reference
Along with the prototype, the project also produced special dies to make invar wires with diameters that are known precisely within 20 micrometres. These wires serve as transfer standards that wire producers can use to calibrate their own measurement tools or to calibrate the DA system. These wires are suitable for establishing a future European Standard for wire diameter measurement. To reach this goal, the project team is beginning the process to certify these reference materials.
"There is significant commercial potential for the project results and they will bring substantial benefits to the European wire industry by helping them improve quality control of wire production. Developing a globally unique absolute measurement system to produce calibrated reference materials will respond to a big demand from the wire producers and drawing die producers," continues Dr Kraft. "These companies are mainly SMEs. As a result, the competitiveness of SMEs in this sector will improve and some jobs will be secured."