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Ultra-precise positioning of workpieces due to hovering guidance system

Ultra-precise positioning of workpieces due to hovering guidance system

Planar ultrasonic levitation magnetic guidance – levitation by ultrasound and stabilisation by means of magnets

In microelectronics, optics, aerospace and medical, sub-micron tolerances and surface finishes are required for the manufacture of parts and components. Ultra-precision machining is therefore essential. However, especially in micro machining, machine tools are based on scaled variations of conventional macro manufacturing concepts. The transferability and scalability of these concepts, especially in guidance systems, are affected by interference effects such as friction and stick-slip. The DFG project "Media-free and contactless multi-coordinate positioning system using ultrasonic levitation and magnetic guidance" is investigating a friction-free guidance system for the precise guidance and movement of workpieces and tools.

Several established methods are used to enable accurate positioning despite these challenges. These include fluidostatic, magnetic and ultrasonic guidance. However, these approaches require a constructive handle - as in the case of magnetic or ultrasonic guidance - or a dedicated supply of a medium to enable accurate guidance. The installation space of the machine is increased in the case of a handle, and the ability to downscale for precision applications is significantly limited. If fluid is supplied, the additional engineering required to supply or remove and prepare the fluid makes the design technically complex. In addition, the possible stiffnesses are limited.

Within the framework of the DFG research project, the concept of a planar ultrasonic levitation magnetic guidance (ULM guidance) is being investigated. The ULM guidance has already been successfully built for a uniaxial guidance system in a previous project. The results are to be implemented into a planar guidance system and the guide performance is to be improved by means of new actuators.

With the ULM guidance, the ultrasonic actuators are operated in vibration resonance, producing an air cushion caused by the static pressure component of the ultrasonic field. Consequently, the carriage of the guidance system is lifted by compressive forces, allowing it to float. To stabilize the system through tensile forces, magnetic actuators are integrated due to the unidirectionality of the ultrasonic actuators. This hybrid actuation system allows control of three degrees of freedom - roll, pitch and lift - as well as stiffness in the lift direction. Distance sensors are used to monitor these degrees of freedom and the air gap.

The planar ULM guidance offers the possibility of contactless and media-free guidance of workpieces and tools. In comparison with other guidance systems, such as combined magnetic-air guidance, this system has increased stiffness. By using a closed control loop, the system can be positioned within the micrometre range. This allows for compensation of both static and dynamic disturbances, such as those caused by thermal expansion or structural vibrations. The hybrid bearing structure employed is notable for possessing a relatively low compliance of less than 50 µm/kN, which is highly relevant for precision manufacturing applications.



For further information, please contact Derin Tasyürek, Institute of Production Engineering and Machine Tools (IFW) at Leibniz Universität Hannover, by phone +49 511 762 4607 or by e-mail at