For a combined movement in several degrees of freedom, individual axes in machine tools have previously been connected in a serial arrangement. Due to the serial structure, the subordinate axis carries the axis arranged on it: This increases the space requirement and limits the achievable dynamics and precision. "To counteract these disadvantages, we have developed a new type of multi-coordinate direct drive," explains IFW employee Henning Buhl. The novelty of the drive is that it can move in linear and rotational axis directions with just one machine component (rotor) without serial kinematics. A hydrostatic bearing and clamping unit was specially designed for this purpose to ensure the load-bearing capacity of the rotor bearing even during highly productive machining.
The suitability of the multi-coordinate direct drive for machining processes has been successfully demonstrated at the institute. Buhl: "Our milling tests confirm that various geometries can be milled in full and half cuts with process stability.". No displacement of the axis position by the machining forces was detected, even at penetration depths of 5 mm. Milling was possible with stable axis control and axis position. The drive can be seen in action as a video under the following link (https://www.youtube.com/watch?v=7m4gLaebbMY).
With the combined drive, traverse paths along the Y linear axis of ± 100 mm and along the B rotation axis of ± 120 ° were achieved. These are similar to the travel paths of a conventional turning/milling centre. A maximum torque of 1,471.6 Nm and a feed force of 4,893.7 N were also achieved. In addition to its suitability for milling, the multi-coordinate drive has a high level of positioning accuracy, enabling reliable positioning in the single-digit µm range. Compared to conventional kinematics, the combined drive enables up to 16 % more compact installation space. Additional advantages are the 82 % lower moving mass in the Y-axis direction and the increased rigidity in the clamped axis state compared to serial kinematics.
Contact:
For further information, please contact Henning Buhl, Institute of Production Engineering and Machine Tools at Leibniz Universität Hannover, on +49 511 762 5210 r by e-mail (buhl@ifw.uni-hannover.de).
