Active vs. passive magnetic bearing 10/27/14

A bearing is an important machine part that has the role of constraining relative motion and of significantly reducing the friction between the active parts of the machine. This means that a bearing has the potential of providing a linear movement or a rotation movement where it is required, while ensuring that the moving parts are protected against wear and tear. A magnetic bearing is a type of bearing that uses magnetic levitation to offer support to the moving part of the machine without any type of physical contact. This ability makes magnetic bearings highly efficient and the most popular choice when it comes to industrial applications. The fact that this technology allows relative motion with extremely low friction has determined machine manufacturers and engineers to use this type of bearing to support high speeds, as they determine no mechanical wear. Choosing magnetic bearing is a natural thing to do taking into consideration all its advantages, the main decision manufacturers have to face is whether to choose an active or a passive magnetic bearing.

Considering the fact that friction has a negative impact on a rotating machine, magnetic bearing offers a great solution to a very old problem. The overall performance of a system with moving parts can be greatly improvised with the installation of a magnetic bearing, thus, almost all modern machines have been implemented with wither passive or active magnetic bearing. Integrating bearing in these systems can eliminate the mechanical loses completely. When it comes to choosing between passive and active magnetic bearing, there are certain things that are generally taken into account. The difference between passive and active bearing is simple to understand: while passive magnetic bearings have permanent magnets and do not need an input power to function, active magnetic bearings use electromagnets that require a power input and a system responsible with the control of the load.

However, passive magnetic bearing or PMB is limited by its diamagnetic material need. Besides the fact that materials to create a passive bearing are hard to find, designing the perfect bearing is also difficult. A deep understanding of the Earnshaw theorem will shed light on the design limitations that have given manufacturers reason to invest in active magnetic bearing or AMB. In fact, most magnetic bearings in use today are active, despite the dependency on an input power. The AMB systems are very efficient, fast and have a prolonged life. The most popular system is actually a combination of PMB and AMB, where the passive bearing take on the static load while the active bearing comes into action when the mechanical part levitated starts to deviate from its course. Non-contact, friction and wear-free bearing offers great benefits such as low maintenance needs and energy consumption, durability and reliability. The demand for bearing has increased tremendously in the past few years, so the need to increase performance and reduce energy needs has determined many engineers come up with improved magnetic bearing designs.