Controlled Escape from Trapped Contact Modes in Magnetic Bearing Systems

磁悬浮轴承允许转子在可控悬浮下高速旋转。然而，故障条件要求存在辅助辅助轴承，以使转子能够悬浮并安全运行。这是一个要求很高的条件，包括高接触应力、温度和应变。因此，辅助轴承的寿命非常有限，通常被引用为在机器停机后能够承受少量的转子跌落(例如10次)。辅助轴承的寿命问题一直是制约磁轴承系统广泛应用的一个因素。与其他传统轴承相比，磁力轴承可能允许转子高速运行，这在功率输出、消除润滑系统、重量和节省成本方面具有显著优势。如果这样的系统能够在涉及运动诱导干扰的环境中安全运行，就可以获得一系列新的好处。这种环境的一个例子是在飞机结构内，它受到操纵、着陆和湍流诱导的扰动运动，这些扰动运动将对转子施加有效载荷。基本的问题是，高水平的这些干扰将导致转子与辅助轴承接触，即使是在完全功能的磁轴承上也是如此。拟议的研究将确定控制策略，将辅助轴承的接触损坏降至最低，从而延长安全运行的寿命。磁力轴承控制器将被配置为防止转子在卡住模式下粘在辅助轴承上。此外，辅助轴承将被驱动，以允许围绕其标称平衡位置进行小规模可控运动。这将使辅助轴承能够抓住转子并使其快速返回无接触操作，而不会出现通常的高破坏性接触应力和应变水平。由于压电致动器允许在足够的力水平和很大的激励频率范围内进行小范围的运动，因此被认为是一种致动手段。这项研究将包括非线性动力学分析、控制设计和将压电作动器与辅助轴承相结合的设计方法。为了验证设计，将调试转子/磁力/辅助轴承系统，并将其安装在多轴模拟台上。这可以复制六个自由度的运动扰动，包括在飞机结构中经历的那些。将实施一项严格的控制战略测试方案。

Magnetic bearings allow rotors to spin at high speed under controllable levitation. However, fault conditions require that secondary auxiliary bearings are present to enable a rotor to de-levitate and be run down safely. This is a demanding condition involving high contact stresses, temperatures and strains. As a consequence, the auxiliary bearings have a very limited life, which is often quoted in terms of being able to sustain a small number of rotor drops (e.g. 10) followed by machine shutdown. The auxiliary bearing life problem has been a limiting factor in the widespread application of magnetic bearing systems. Potentially, magnetic bearings allow rotors to run at high speed compared with other conventional bearings, which leads to significant advantages in terms of power output, elimination of lubrication systems, weight and cost savings. If such systems could operate safely in environments involving motion induced disturbances, a new range of benefits could be derived. An example of such an environment is within an aircraft structure, which is subjected to manoeuvring, landing and turbulence induced disturbance motions that would apply effective loads to the rotor. The basic problem is that high levels of these disturbances will cause the rotor to make contact with the auxiliary bearings, even with fully functional magnetic bearings. The proposed research will determine control strategies for minimising contact damage to auxiliary bearings, thereby extending the life for safe operation. The magnetic bearing control will be configured to prevent the rotor from sticking to the auxiliary bearing in a trapped mode. Additionally, the auxiliary bearings will be actuated to allow small scale controllable motion about their nominal equilibrium position. This will give the auxiliary bearings the ability to catch the rotor and return it quickly to contact free operation, without the usual high damaging levels of contact stress and strain. Piezoelectric actuators are proposed as the means of actuation as they allow the small scale motion at sufficient force levels and over a significant range of exciting frequencies. The research will involve non-linear dynamic analysis, control design and design methodology to integrate the piezoelectric actuators with the auxiliary bearings. To validate the designs, a rotor/magnetic/auxiliary bearing system will be commissioned and mounted on a multi-axis simulation table. This can reproduce motion disturbances in six degrees of freedom, including those experienced within an aircraft structure. A rigorous programme of testing the control strategies will be undertaken.