Basque machine tools, maximum accuracy even with large machines
The development of technologies and methods that will enable the geometrical accuracy, positioning and dynamics of machines and robots to be improved is experiencing a boom in the machine-tool sector and will be increasingly necessary to compete on the global market. CIC marGUNE, the Co-operative Research Centre into High-performance Manufacturing, is coordinating the MEDCON line of research that seeks to improve the accuracy of machine tools and enable manufacturers to optimise the design of their products and thus help to make Basque manufacturers more competitive. Today, the manufacture of large parts is a driving force in the machine-tool industry. This demand is posing a challenge for machine-tool manufacturers to come up with competitive designs on an increasingly bigger scale, while maintaining the accuracy level of smaller machines. However, the builders lack suitable tools to assess the positioning accuracy of large machines in a practical way. “The most suitable measuring technology for this task, known as multilateration, is similar to GPS,” explained Eneko Gómez-Acedo, coordinator of the MEDCON line of research at IK4-Tekniker. “It involves using a laser interferometer with a monitoring capability, high resolution and low measuring uncertainty. The idea involves combining the linear measurements from various positions taken sequentially by the interferometer. Afterwards, a mathematical calculation is made of the position and orientation of the tip of the tool following a diagram similar to that used in satnav.” When work is done using large machine tools, some of the limitations of this technology become apparent. Experiments conducted have shown that the main obstacle to achieve the theoretical accuracy limit of multilateration is instability in the environmental conditions like changing temperature gradients and the thermal behaviour associated with the machine. To overcome these difficulties, IK4-Tekniker has developed an innovative methodology by means of which it is possible to obtain a series of measurements by combining the data that have been obtained using a laser interferometer; this provides the positions of the tool together with the tilt measurements obtained using two electronic levels of accuracy used to measure the orientation of the tip of the tool. That way there is a dual benefit. “As it is a faster measurement, the machine undergoes fewer thermal deviations and, what is more, the measuring is more cost-effective. At the same time, by means of the complementary use of the levels of accuracy, not only is the measuring time reduced, but a valuable indicator of the machine’s stability during the time that has elapsed is also obtained,” stressed Gómez-Acedo. This methodology is supported by IK4-Tekniker’s in-house software, which, besides carrying out the mathematical calculations of the measurement, recommends the best positions, calculated by means of simulation, in which the equipment will need to be placed in order to obtain the lowest number of measurement uncertainties. The MEDCON line of research has made it possible to overcome the limitation existing in the use of the traditional techniques to verify machine tools, which do not allow the positioning errors throughout the batch of work to be known in an efficient way. What is more, the potential of the methodology developed by IK4-Tekniker will enable machine-tool manufacturers to optimise the design of their machines, and the users of the machines to carry out regular recalibrations to maximise the quality of their products.
Pays
Spain