Novel tubular linear actuator with integrated magnetic bearing

Abstract

Linear actuators (LAs) are used for applications that require repetitive linear motion, such as linear pumps and compressors, servo drives in industrial automation, and pick-and-place robots in the pharmaceutical and semiconductor industry. These LAs usually have mechanical ball or slide bearings, which require frequent maintenance due to signs of wear limiting the LAs' usage in high-purity and high-precision processes of the latter applications. Therefore, this paper analyzes a novel LA with integrated magnetic bearings (MBs). It shows how the basic structure of the tubular LA is derived from a conventional rotary actuator. Afterwards, it explains the winding structures for the generation of the drive and bearing forces in detail, focusing on the impact of the linear motion on the bearing winding. Furthermore, two types of windings for the self-bearing LA, separated and combined, are analyzed and compared. It is shown that a combined winding structure leads to higher efficiency and a more simple drive system and has no disadvantages with respect to the control. Finally, measurement results verify the proper operation of a self-bearing tubular LA prototype with a combined winding structure.