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Design of a ball screw drive wear compensation using shape memory alloy actuators

: Junker, Tom; Bucht, Andre; Navarro Y De Sosa, Iñaki; Pagel, Kenny; Drossel, Welf-Guntram

Vin, Leo J. de ; Karlstad University:
Mechatronics 2014, 14th Mechatronics Forum International Conference : Karlstad, Sweden, June 16-18, 2014
Karlstad, 2014
ISBN: 978-91-7063-564-9
International Conference "Mechatronics Forum" <14, 2014, Karlstad>
Fraunhofer IWU ()
ball screw drive; shape memory alloy; actuator; machine tool; self sufficient

Today's economic demands in manufacturing drive the requirements for high precision and productivity rates in machine tools design. One of the most common used machine tool drives for linear motion is the ball screw drive (BSD), which converts rotational motion of the servo motor to linear motion of the machine tool structural component. The advantages of modern BSD are high rigidity and low friction, and therefore a high efficiency compared to alternative systems like rack and pinion systems. However, to achieve the required accuracy it is necessary to preload the ball screw drive to prevent backlash. Backlash is caused by the clearance between the contacts of the ball bearings and the threads of the nut and screw. Clearance, however, is needed to prevent unnecessary friction during operation of the BSD. Different preload levels, on one hand, determine the rigidity and thus the maximum load a drive can carry and, on the other hand, the amount of heat to be dissipated due to friction which also leads to wear of the components.
Due to their high specific workloads and relatively small spatial requirements, shape memory alloys (SMA) possess an outstanding potential to serve as miniaturized positioning devices in adaptronic and mechatronic applications. In comparison to other actuators such as hydraulics, electric motors or piezoelectric actuators, SMA based-actuators have the highest mechanical work output per volume. Nevertheless, most of the known SMA drives are used in the application area of small and lightweight actuators such as flaps and locks in the automotive industry, medical technology and life science.
In this paper we present an approach to retrieve a preload loss which causes a loss to positioning accuracy in BSD due to wear over lifetime. The main purposes are reduced maintenance, longer service life and improved workpiece quality by regenerating previous preload conditions which leads to higher gainings for manufacturers. For this purpose, a novel SMA actuator driven module for BSD has been designed. The device was developed to be implemented in standard drives without major changes in component design. It is installed between flanged nut and counter nut and replaces a spacer usually used to define a specific preload. It was required to scale the actuator module over a wide range of screw diameters respectively nut diameters. Besides mechanical properties, thermal boundary conditions during operation of BSD must be taken into consideration. A prototype has been manufactured and tested to evaluate the current design and first results will be introduced.