外文翻译--磁轴承时代的来临
外文资料
Magnetic Bearings Come Of Age
Magnetic-bearings, which support shafts with magnetic levitation rather than mechanical contact, have been in industrial use for decades. Magnetic bearings offer a host of advantages to users, including high-speed capabilities and the ability to operate lubrication-free and in vacuum environments. They generate no friction, experience minimal wear, and operate contamination free with extremely low vibration. And the bearings can precisely control shaft position, measure external forces acting on the shaft, and even monitor a machine's operating condition. Recent technological developments, especially in digital processing and control, have made magnetic bearings a more-robust and cost-effective design solution than ever. Today's bearings are suitable for a wide range of applications, from semiconductorfabrication equipment to microturbines,from refrigeration compressors to vacuum pumps. MAGNETIC-BEARING BASICS:
Magnetic-bearing systems electromagnetically suspend shafts by applying electric current to a bearing's ferromagnetic materials. The systems have three main elements: bearing actuators, position sensors, and controller and control algorithms. Typical units consist of two magnetic radial bearings and one magnetic thrust bearing. They control the shaft along five axes: two axes for each radial bearing and a fifth axis along the shaft. Magnetic bearings have stationary and rotating components —the stator and rotor, respectively. The radial magnetic bearing stator resembles an electricmotor stator. The radial stator is formed by a buildup of laminations, each of which is shaped with poles. The laminations stack together, and coils of wire are wound around each pole. Controlled electric currents passing through the coils produce an attractive force on the ferromagnetic rotor and levitate it within an air gap. The gap usually measures about 0.5 mm but, in some applications, can be as large as 2 mm.The rotor fits over the shaft, which is in the air gap but need not be centered. This is useful in applications where it is valuable to compensate for wear, or if the shaft oscillates — such as in machine-tool grinding processes where the wheel wears over time. A magnetic thrust bearing provides axial control. The thrust-bearing rotor is a solid steel disk attached to the shaft and positioned at a preset distance from the stator on one or both sides. During operation, electromagnetic forces produced by the stator act on the rotor and control axial movement. Magnetic-bearing arrangements also include touchdown or auxiliary bearings. Their main function is to support the
shaft when the machine is idle and protect machine components in case of power outage or failure. The touchdown bearing's inner ring is smaller than the magnetic-bearing air gap to prevent potential damage if the shaft delevitates. CONTROL SYSTEMS:
The control system regulates bearing current and, thus, the force of the bearings. During operation, radial and axial position sensors feed data on shaft location and movement to the controller. It compares actual and desired shaft position, calculates the force required to maintain the shaft in the preset position and, if necessary, commands the amplifier to adjust the electric current to raise or lower the level of magnetic flux. The main parts of the control system are the digital signal-processing (DSP) electronics, a power supply, and amplifiers. Generally, the larger the machine, the larger the amplifiers. Controller size also depends on the dynamic load capacity required, which is typically greater in heavy machines. The shaft can be controlled through Single Input/Single Output (SISO) or Multiple Input/ Multiple Output (MIMO) algorithms for high-speed and more-demanding applications. The controller typically measures and processes position signals at 10-kHz frequency, enabling precise control of machinery rotating at speeds of 100,000 rpm and higher. A significant benefit of magnetic-bearing technology is that the controller functions as a built-in condition-monitoring system, providing extensive real-time information and making other monitoring devices unnecessary. Software, such as MBScope from SKF, provides detailed diagnostic information about machine health and helps schedule preventive maintenance more effectively. The software includes configuration tools for tuning input parameters and checking clearances prior to start-up. Its viewing tools include real-time monitoring of positions, currents, and forces; an alarm log that captures all system variables before and after an unusual event; and short or long-term trending. This lets users view information in various formats for bearing tuning and machine diagnostics. Adaptive vibration control (AVC) is another important tool. AVC computes the forces necessary to cancel out vibration in two ways. One is to let the shaft rotate around its geometric center and tightly control shaft displacement, eliminating runout caused by imbalance. This is useful in high-precision applications, such as machine tools. The other way is to rotate the shaft around its center of mass to reduce vibrations transferred to the housing or casing (to <0.01 m m). This is a valuable feature in turbomolecular pumps and other semiconductor-manufacturing equipment. AVC can increase machine reliability and the time between service
intervals. Its adaptive feature minimizes vibrations even with rotor fouling over time and, by canceling out process disturbances, can extend equipment's operating range. DESIGN CONSIDERATIONS:
The ultimate goal of magnetic-bearing design is reliable, noncontacting rotation over the machine's entire speed range. It is also essential to meet OEM and end-user cost targets without compromising performance. Reducing the size of digital-control systems means more cost-efficient solutions, and compact magnetic-bearing designs can lead to smaller, more-robust machines. When developing magnetic-bearing systems, main factors to consider are the speeds, loads, and operating environment. The mechanical strength of the shaft typically limits speed. Surface speeds of 3.5 X 10 6 DN (diameter in mm 3 rpm) are possible. Static capacity — the maximum force magnetic bearings generate to lift the shaft —is a function of variables such as amplifier current, surface area of the magnetic poles, number of coil windings, and air-gap dimensions. A good rule of thumb is 75 lb of force/sq in. of bearing. Dynamic capacity —the rate at which magnetic bearings change the applied force —is determined by a single variable, amplifier voltage. Consider, for example, a 150-N magnetic bearing connected to a 2-A/40-V control system. Switching to a larger, 200-N bearing with more coil turns, a larger magnetic pole area, and so on, will increase static capacity. If the controller remains the same, however, there will be no effect on dynamic capacity —the ability to handle shaft imbalances and other dynamic forces during operation. Conversely, retaining the 150-N magnetic bearing but switching to a 3-A/50-V control system will increase the unit's dynamic capacity but have no effect on static capacity.
DIVERSE APPLICATIONS：
The unique design and wide-ranging capabilities of magnetic bearings offer solutions in a host of diverse applications. One example is semiconductorfabrication, particularly front-end operationsinvolving the production of silicone wafers. Magnetic bearings can improve yields in these operations, which are highly sensitive to contamination and vibration. For instance, magnetic bearings permit edge rotation of 300-mm wafers, allowing convenient access to both wafer sides. Because magnetic bearings have an air gap, they are ideal for certain biological and pharmaceutical applications. Blood cells or other liquids can pass through the air gap without damage. Refrigeration compressors are another important application. Magnetic bearings can run at the high speeds required by new-generation refrigerants and, unlike conventional oil-lubricated bearings, they pose minimal risk of contamination.
Magnetic bearings can also be hermetically sealed and are therefore attractive for processes handling corrosive fluids that would attack windings and laminations. WHERE MAGNETIC BEARINGS MAKE SENSE：
Magnetic bearings operate without contact. This results in many unique characteristics that are valuable in a wide range of equipment. Applications that require more than one of the following attributes are generally suitable for magnetic bearings.
Lubrication-free: Consider magnetic bearings when lubrication systems for other types of bearings are expensive, unreliable, or unsafe; the lubricant contains environmentally unfriendly components and disposal becomes an issue; or the lubricant is incompatible with or contaminates the fluid or process.
Reliability. The bearings offer superior reliability, comparable to that of electric motors, and it is reasonable to expect an operational life of 15 to 20 years. The control system has reliability typical of electronic components with conservative mean time between failures of 5 years.
Operation in vacuum. High vacuums are difficult environments for lubricants. Many systems in high to ultrahigh vacuums (to 10- 16 Torr) are sensitive to outgassing and contamination of volatile lubricants.
Low vibration: Magnetic bearings are suitable for applications sensitive to machine vibration. Typical casing vibration is 0.01 m m.
Force measurement: The controller can determine bearing load and force direction by measuring current and position within the bearings. This gives valuable information for machine designers when developing magnetic-bearing systems. Forces can be measured with accuracy generally better than 5%.
Shaft-position control: Because sensors monitor shaft location, the control system can reposition or oscillate the shaft while it is rotating. For example, the control system can compensate for wear and adjust the shaft axial position during operation to optimize the grinding-plate gaps and improve product quality in pulp refiners.
Precision: Tight control eliminates shaft runout caused by unbalance. This is accomplished with Adaptive Vibration Control. Shaft displacement at the running speed can be reduced to about 1 m m, important for precision grinding and machine-tool cutting operations.
Contamination: Processes sensitive to microcontaminants benefit from magnetic bearings with stainless-steel cans or barriers. With the advent of 300-mm
wafers and 0.25-mm device sizes, it has become critically important to eliminate microcontaminants in all aspects of wafer processing.
Submerged operation: Magnetic bearings can operate directly in the process fluid and eliminate the need for mechanical seals. This reduces emissions, machine cost, and operating maintenance costs.
Reduced energy consumption: Magnetic bearings reduce frictional losses, resulting in higher overall mechanical efficiency. And the lack of a lubrication system eliminates the cost of operating pumps, cooling fans, reservoir ventilation fans, and so on.
Condition monitoring: Magnetic bearings have built-in condition-monitoring capabilities. This eliminates the need for devices like accelerometers and vibration sensors, as well as monitoring equipment and interface software. In addition, magnetic-bearing control systems directly observe shaft and process-fluid behavior with no need to interpret rolling-element and race frequencies.
Air gap: Some applications simply benefit from noncontact operation. For example, in biotech applications, heart pumps or mixers benefit by not damaging cells with contacting surfaces. In textiles, fibers can pass through the gap. Air gaps can be up to 2 mm.
High speed: Speed is limited by the mechanical strength of the shaft. Surface speeds on radial bearings are as high as 3.5 3 10 6 DN (diameter (mm) 3 rpm). This attribute becomes more valuable as lubrication becomes more difficult.
Phase control: Today's DSPs do more than just controlling the magnetic bearing, performing functions that can easily reduce the cost of a system by more than the cost of the magnetic bearing. One example is phase control. This feature synchronizes shaft rotation with external timing signals. Synchronization positions the shaft (phase) to within 0.05 of its reference mark while rotating at speeds to 36,000 rpm. Phase control is used in applications such as neutron choppers.
中文译文
磁轴承时代的来临
磁悬浮轴承不是靠机械触点而是利用磁悬浮的支撑轴，它已经在工业中使用了几十年。磁悬浮轴承给使用者带来了包括高速运转，无润滑和真空环境运作的能力等诸多方便和好处。磁悬浮的机械磨损小，能耗低，无油污染并且可以精确控制轴的位置，以及精确测量外部干扰力，从而可以监控机器的运转状况。随着近年来数字处理和控制技术的发展，磁轴承也相继成为一种比以前更加强健和划算的设计解决方案。今天的磁轴承从半导体到微涡轮机，从制冷压缩机到真空泵等方面得到了更加广泛的应用。
磁悬浮轴承基础知识:
磁轴承系统是通过电励磁使轴悬浮。该系统有三个主要元素：轴承制动器，位置传感器和控制器。机械系统包括两个磁径向轴承和一个磁推力轴承。他们从六个自由度来控制轴承。磁悬浮轴承有固定部分和旋转部分。——定子，转子。径向定子是由叠片堆积形成的，叠片堆积在一起形成极点。每一个极点上都绕有线圈。控制电流通过线圈，同时产生电励磁，电励磁对铁磁转子产生吸引力，并使其在气隙内悬浮。空气间隙通常约为0.5毫米，在某些应用里可以是大于两毫米。转子叠片装在气隙里的轴上。这在一些要弥补磨损的实例中得到了很大的应用，或如果轴摆动。例如在机床磨削过程中磨轮的磨损会随着时间增加而增多。磁推力轴承是提供轴向控制。推力轴承转子是固体铜磁盘，从定子一侧或两侧连接到轴，并定位在一个预定的距离。在操作时，有定子产生的电磁力作用在转子上并控制轴向运动。磁轴承配置还包括辅助轴承，其主要功能是当支撑轴处于空载时和在电流中断或失败的情况下保护机件。着陆轴承外圈内径小于磁轴承空气间隙主要是为了防止对轴承潜在损害。
控制系统：
控制系统是控制磁轴承的电流，从而控制轴承的电磁力。在操作期间，径向和轴向位置传感器把轴位置和动态数据传给控制器它比较实际和理想的轴的位置，计算使轴保持在预设位置处的力，如果有必要，控制器将控制电流的大小来改变电励磁磁通量。电子信号处理，电源和放大器是控制系统的三个主要部分。一般情况下，机器越大放大器就越大。控制器的大小取决于动态负载能力的需求，这在重机应用中尤为明显。可通过适应于高速和更苛刻的应用程序，如单输入/单输出或者多输入/输出算法控制轴。控制器通常一10千赫的频率来测量和处理位置信号。使旋转速度精确的控制在100000rpm或者更快的速度。磁悬浮技术的一个重要优点是控制器作为内置的监测系统提供广泛的实时信息，并使其不需要其他监控设备。像来自SKF的MBScope软件可以提供有关机器健康的详细诊断信
息并且可以更加有效地定期监测。该软件包括调整输入参数和在启动前检测空袭配置装置，其工具包括对位置，电流和力的实时监控器。记录在发生不正常情况前后的所有系统产量以及短期或长期趋势分析的警报日志。这使用户可以以不同的形式来查看轴承的信息以及机器诊断程序。自适应振动控制是另一个重要的工具。AVC利用两种方法来计算消除振动是的力，一种是严格控制轴的位移让轴围绕其几何中心旋转，从而消除不平衡引起的跳动，其在像机床这样的高精度程序中很有用。另一种方式是使轴围绕质量中心旋转以减少移到外壳上的振动，这是分子泵和半导体制造设备一个有价值的特点，AVC可以增加可靠性和服务间隔之间的时间。其自适应的功能是即使转子污垢积聚越来越厉害也能最大限度的减小振动来消除过程干扰，扩展设备的工作范围。
设计考虑事项：
磁悬浮轴承设计的最终目标是让机器在整个速度范围内可靠无接触运转。在不影响性能的情况下满足OEM和终端用户的成本目标也是非常重要的。减少控制系统的大小可以实现更合算的解决方案，紧密的磁性轴承的设计可以使机器变得更小更强大。发展磁悬浮轴承系统时，要考虑的主要因素是速度，荷载和操作环境。机械强度的轴通常限制速度。3.5 X 10 的表面速度6 DN (mm 3 rpm 的直径) 是可能的。静态能力——磁悬浮轴承产生的最大力量，它是一个函数变量。如放大器电流表面面积磁极，线圈绕组和气隙尺寸。动态能力——磁悬浮轴承改变外加力的速率，由放大器电压这一单一变量决定。例如，考虑将连接在2A.40V 的150N的磁悬浮轴承控制系统，转换到更大线圈砸数的200N或更大磁极范围等等，如果控制器不变则静态能力将会增大，但不会影响动态能力——在操作过程中处理轴的失衡状态和其他动态力量的能力。相反，保持150N的磁性轴承但切换到3A，50V，系统将增加该轴的动态能力，但对静态能力没有影响。
不同的应用程序：
磁悬浮轴承独特的设计和广泛应用的能力为不同应用程序提供了解决方案。其中一个例子是半导体制造，尤其是前端的生产包括有机硅生产。磁悬浮轴承可以提高生产产量，这些对振动和污染高度敏感。例如，磁性轴承允许 300 毫米晶片的旋转，允许方便地访问到双方晶圆片边缘。因为磁悬浮轴承有气隙，所以他们是某些生物制药应用的理想选择。血液细胞或其它液体可以安然无恙的通过空气隙。制冷压缩机是另一个重要的应用。磁悬浮轴承可以以新一代制冷剂所需的的高速度运行，与常规油润滑轴承不同的是，它们构成污染风险降至最低。磁悬浮轴承也可以密封，因此对处理会腐蚀线圈与叠片的流体很有吸引力。
磁悬浮轴承原理：
磁悬浮轴承的运作无接触。这会带来许多独特的特性，这些特性在很多的设备中很有价值。适合磁悬浮轴承的应用程序通常需要多个以下属性: 无润滑：考虑磁悬浮轴承当其他类型的轴承润滑系统是昂贵、不可靠的或不安全的；润滑剂包含不环保的成分和支配成为一个问题；或润滑剂与流体不兼容或可以造成污染。
可靠性：轴承提供优异的可靠性的电动马达，合理期望寿命15至20年。控制系统具有典型的保守平均 5 年故障时间与电子元器件的可靠性。
真空操作：高真空对润滑剂是种挑战。许多系统在高到超高真空系统(10- 16 托尔) 对排气和挥发性润滑剂污染很敏感。
测力：控制器可以通过测量电流和轴承内的位置确定轴承负荷和力方向。这给开发磁悬浮轴承系统的设计师提供了有价值的信息。可以测量的力的精度一般优于5%。
轴位置控制：因为传感器监测轴的位置，控制系统可以重新定位或摆动轴转动。例如，控制系统可以弥补磨损和调整轴向位置以优化间隙和提高纸浆炼油厂的产品质量。
精密：严格控制消除了不平衡所致的轴径向跳动。这是有自适应振动控制来完成的。轴位移在运行速度可以减至约 1 m m，对精密磨削加工和机床切割操作很重要。
污染：对微污染物敏感的操作可以从有不锈钢罐或障碍的磁悬浮轴承中受益。在晶元加工的所有方面，伴随着300毫米晶片和0.25毫米设备尺寸的出现，这些工序对减少微污染物来说已经变得尤为重要。
淹没操作：磁轴承可在工序中直接操作流体而不需用机械密封，这将减少排放，降低机器成本以及运营维护成本。
降低能耗：磁轴承可减少摩擦损耗，进而提高整体机械效率。而且摩擦损耗的减少可以部分省却润滑系统，进一步节省对于水泵、冷却风扇以及水库通风风扇等的操作费用。
状态监测。磁力轴承具有内置的状态监测能力，这消除了对一些设备的需求，比如加速表和振动传感器，以及监测设备和接口软件。此外，磁轴承控制系统直接观察轴和过程流体而无需解释转动体与运行频率。
气隙：某些应用程序受益于非接触式操作。例如，在生物技术应用中，心脏泵或搅拌机在不破坏细胞的接触面情况下可以受益。在纺织业，纤维可以通过差距。气隙可以到 2 毫米。
高速：轴的机械强度可以限制速度。径向轴承的表面速度高达 3.5 3 10 6 DN （直径(mm) 3 rpm）。随着润滑变得更加困难，此属性将变得更有价值。