Controlled Escape from Trapped Contact Modes in Magnetic Bearing Systems

磁轴承允许转子在可控的悬浮下高速旋转。然而，故障条件要求二级辅助轴承的存在，使转子去悬浮和运行安全。这是一个涉及高接触应力、温度和应变的苛刻条件。因此，辅助轴承的寿命非常有限，这通常是在能够维持少量转子下降（例如10）之后机器停机方面引用的。辅助轴承寿命问题一直是制约磁轴承系统广泛应用的一个制约因素。与其他传统轴承相比，磁性轴承可能允许转子高速运行，这在功率输出、消除润滑系统、重量和成本节约方面具有显着优势。如果这样的系统能够在涉及运动引起的干扰的环境中安全运行，则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中，它受到操纵，着陆和湍流引起的扰动运动，这些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接触辅助轴承，即使与功能齐全的磁轴承。提出的研究将确定控制策略，以尽量减少对辅助轴承的接触损伤，从而延长安全运行的寿命。磁轴承控制将被配置为防止转子在困住模式下粘在辅助轴承上。此外，辅助轴承将被驱动，以允许其标称平衡位置的小规模可控运动。这将使辅助轴承能够抓住转子并迅速返回到无接触操作，而不会产生通常的高损伤水平的接触应力和应变。压电致动器可以在足够的力水平和显著的激励频率范围内进行小尺度运动，因此提出了压电致动器作为驱动手段。研究将涉及非线性动力学分析、控制设计和设计方法，以整合压电致动器与辅助轴承。为了验证设计，转子/磁/辅助轴承系统将被委托并安装在多轴仿真台上。这可以重现六个自由度的运动扰动，包括在飞机结构中经历的运动扰动。将执行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.