Design and evaluation of a magnetic planetary gearbox for compact harsh environments

This paper presents the design, analysis, and realization of a magnetic planetary gearbox used in a compact harsh environment typical of oil well logging tools. Such tools are subjected to temperatures in excess of 175°C as well as severe shock and vibration. The tools are typically oil filled, and include fine pitched oil filters to prevent clogging of the fluid communication lines. Mechanical gear box wear is a significant contributor to the blocking of the fluid filters, a proposed solution is the introduction of the permanent magnet gear box (PMGB) to replace conventional mechanical gearboxes used in such applications. The noncontact nature of the PMGB, coupled with its ability to utilize stack length to increase reduction ratios and account for limitations in tool diameter, as well as the availability of rare earth permanent magnet material that can withstand high temperatures, promote the PMGB as a viable solution. The main contribution of this paper is that it provides the required equations needed for an initial design which can then be optimized using finite element analysis. The paper also investigates the effect of rotor eccentricity on the PMGB performance.