Techniques are generally described for adjusting a magnetic field in a magnetic bearing by moving permanent magnets in real time. Some example devices or systems include a magnetic bearing comprising electro-actuators adapted to move permanent magnets relative to a rotor to balance the rotor. For instance, in one example, each electro-actuator includes electro-active material adapted to deform in response to being exposed to an electrical field. This deformity causes permanent magnets attached to a surface of each electro-actuator to move relative to a rotor to balance the rotor. In many examples, a measurement circuit may be coupled to each electro-actuator and adapted to measure a capacitance of each electro-actuator. The capacitance measurement may be used to determine an adjustment signal to adjust the magnetic field in real time.

BACKGROUND

Magnetic bearings support a rotor using magnetic levitation. In general, magnetic bearings utilize electromagnets to balance forces. In particular, the electromagnets adjust a magnetic field generated by the magnetic bearing to balance the rotor. That is, current applied to the electromagnets may be adjusted in real time in order to adjust the magnetic field to compensate for instabilities that build up in the rotor. Typically, sensors are used to detect the position of the rotor relative to the static electromagnets to determine the amount of current to apply to each electromagnet in order to adjust the magnetic field. Magnetic bearings may be preferred in some applications, since magnetic bearings are capable of operating at higher speed than conventional bearings. By operating in a nearly frictionless environment, magnetic bearings generally do not experience wear caused by friction.

SUMMARY

The present disclosure describes a magnetic bearing for balancing a rotor. Some example magnetic bearings may include a plurality of electro-actuators mounted on a support structure. Each of the plurality of electro-actuators may include a first electrode spaced apart from a second electrode and an electro-active material positioned between the first electrode and the second electrode. The electro-active material of each of the plurality of electro-actuators may be configured to deform in response to a voltage difference between the first electrode and the second electrode. A layer of ferromagnetic material may be secured to a surface of the first electrode of each respective electro-actuator. Each layer of ferromagnetic material may be configured to move relative to the rotor as the electro-active material deforms in response to the voltage difference and moving the layer of ferromagnetic material may cause a magnetic field in the magnetic bearing to be adjusted.

The present disclosure describes a system for affecting a magnetic field in a magnetic bearing. Some example systems include a magnetic bearing comprising a plurality of electro-actuators, each of the plurality of electro-actuators including a first electrode spaced apart from a second electrode and an electro-active material positioned therebetween. A respective layer of ferromagnetic material may be secured to a surface of each first electrode. The electro-active material of each electro-actuator may be configured to deform in response to a first voltage difference provided across each respective first electrode and second electrode thereby causing each corresponding layer of ferromagnetic material to move to a first position and affecting the magnetic field in the magnetic bearing. A measurement circuit may be coupled to the magnetic bearing. The measurement circuit may be configured to measure a capacitance of each of the plurality of electro-actuators. A microcontroller may be coupled to the magnetic bearing. The microcontroller may be configured to receive the measured capacitance for each of the plurality of electro-actuators and to generate an adjusted activation signal. A power source may be coupled to the magnetic bearing and the microcontroller. The power source may be configured to receive the adjusted activation signal and in response to receiving the adjusted activation signal, provide a second voltage difference across each respective first electrode and second electrode thereby causing each corresponding layer of ferromagnetic material to move to a second position and affecting the magnetic field in the magnetic bearing.

The present disclosure describes a method of balancing a rotor utilizing a magnetic bearing. Some example methods may include applying a respective first voltage across a respective one of a plurality of electro-actuator having a layer of ferromagnetic material secured to a surface thereof. The first voltage may be applied at a first level. In response to the first voltage, each electro-actuator may contract or expand thereby causing the correspondingly secured layer of ferromagnetic material to move relative to the rotor to affect a magnetic field in the magnetic bearing. The method may further includes measuring a capacitance of each of the plurality of electro-actuators and determining an adjusted level for each respective first voltage. The adjusted level may be a function of the measured capacitance of the corresponding electro-actuator. The method may further include applying a respective second voltage across a respective one of the plurality of electro-actuators. The second voltage may be at the adjusted level. In response to the second voltage, each electro-actuator may contract or expand thereby causing the correspondingly secured layer of ferromagnetic material to move relative to the motor to change a shape and/or strength of the magnetic field in the magnetic bearing.

DETAILED DESCRIPTION

The following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative examples described in the detailed description, drawings, and claims are not meant to be limiting. Other examples may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are implicitly contemplated herein.

This disclosure is drawn, inter alia, to methods, systems, devices, and/or apparatus generally related to adjusting a magnetic field in a magnetic bearing by moving permanent magnets in real time. Some example devices or systems include a magnetic bearing comprising electro-actuators adapted to move permanent magnets relative to a rotor to balance the rotor. For instance, in one example, each electro-actuator includes electro-active material adapted to deform in response to being exposed to an electrical field. This deformity causes permanent magnets attached to a surface of each electro-actuator to move relative to a rotor to balance the rotor. In many examples, a measurement circuit may be coupled to each electro-actuator and adapted to measure a capacitance of each electro-actuator. The capacitance measurement may be used to determine an adjustment signal to adjust the magnetic field in real time.

FIG. 1is a schematic illustration of some magnetic bearings100that are arranged in accordance with at least some examples of the present disclosure. The example magnetic bearing100includes a support structure102with a plurality of electro-actuators104formed thereon. Each electro-actuator104includes a top electrode106and a bottom electrode108and an electro-active material110positioned therebetween. A layer of ferromagnetic material112may be disposed on top of the top electrode106. Each of the plurality of electro-actuators104may be positioned to surround a rotor114.

Although the electro-actuators104may be fixed to the support structure102, a portion of the electro-actuators104may be configured to deform in response to experiencing a magnetic field, and thus move the layer of ferromagnetic material112relative to the rotor114. For instance, a power source may be coupled to each electro-actuator104to apply a voltage across the top electrode106and the bottom electrode108causing the top electrode106to be attracted to or repelled from the bottom electrode108. In response to this attraction, the electro-active material110may deform. That is, the attraction force between the top electrode106and the bottom electrode108causes the top electrode106to move in a direction (e.g., a radial-direction) along an axis (e.g., a radial-axis extending from a center of the rotor114) toward the bottom electrode108, thereby causing the electro-active material110to deform by contracting along the axis. This deformity causes the layer of ferromagnetic material112on the top electrode106to move farther away from the rotor114. As the voltage bias applied to the top electrode is reduced to an adjusted activation level, the top electrode106move farther away from the bottom electrode108thereby causing the electro-active material110to expand in the direction (e.g., the radial-direction) along the axis (e.g., the radial-axis). This deformity causes the layer of ferromagnetic material112to move closer to the rotor114. As each layer of the ferromagnetic material112on each electro-actuator104moves towards or away from the rotor114, the magnetic field in the magnetic bearing100may be adjusted.

The top electrode may be comprised of a material that is stretchable. In some examples, the top electrode may be comprised of a layer of thin gold, conductive organic polymers, carbon nanotube composite materials, or a combination thereof. In some examples the layer of thin gold is about 10 nanometers to 30 nanometers. In one example, the layer of thin gold is about 20 nanometers.

In some examples, the layer of ferromagnetic material112may include high anisotropy permanent magnets, such as Samarium Cobalt (SmCo) and Neodymium Iron Boran (NdFeB). The layer of ferromagnetic material112may be secured to a surface of the top electrode106, such as by an adhesive or by any other securing mechanism. In some examples, the layer of ferromagnetic material112may be secured to a surface of the top electrode106by a flexible adhesive, such as flexible adhesives typically used to join materials with different thermal expansion coefficients. For instance, in one example the adhesive is a polyurethane adhesives or a U1urethane adhesive. In some examples, the layer of ferromagnetic material112may be secured to the top electrode so that the top electrode may stretch without causing the layer of ferromagnetic material to stretch. In some examples, the layer of ferromagnetic material112may be assembled on top of the top electrode using standard pick-and-place techniques. In other examples, the layer of ferromagnetic material112may be formed by bonding or laminating a thin magnetic film to the top electrodes106and subsequently using scribing.

The structural support may be any material capable of supporting forces that may be exerted by the magnetic field in the bearing. In some examples the structural support may comprise a plastic, a composite, a metal, or any combination thereof. In one example, the structural support may comprise stainless steel.

The electro-active material110may be any material adapted to deform in response to an applied magnetic field. In some examples, the electro-active material110may achieve stretching or compression of less than about 1% and over about 300%. Some example electro-active material may include piezoelectric ceramics or polymers, magnetorheological polymers, and electro-active polymers. The preference of one material over another may depend on the application of the magnetic bearing and other factors, such as cost, reliability, and displacement and voltage requirements. In some examples, the electro-active material110may be pre-strained.

In one example, the electro-active material may comprise piezoelectric ceramics, such as piezoelectric transducer (PZT). For instance, although conventional piezoelectric ceramics provide maximum stretching or compression in a range of approximately 0.1% to 0.2%, this displacement would be sufficient to allow an adjustments to be made to a magnetic field. Alternatively, a new generation of piezoelectric ceramics are being developed that may allow strains over 1% to provide larger adjustments to a magnetic field as is described in Fu, Huaxiang et al.,Polarization Rotation Mechanism for Ultrahigh Electromechanical Response in Single-crystal Piezoelectrics, Nature 403, 1999, 281-283, incorporated herein by reference to the extent it is consistent with this disclosure and for all purposes.

In another example, the electro-active material may comprise piezoelectric. Conventional piezoelectric polymers, such as Polyvinylidene Fluoride (PVDF) and other copolymers, may posses maximum stretching or compression of approximately less than about 1%. Modern piezoelectric polymers may be modified by defects induced by irradiation or an inclusion of bulky functional groups in the polymer chain, and can achieve stretching or compression over 5% in response to about an electric field of 100 volts per micrometer.

In yet another example, the electro-active material110may comprise electro-active polymers, such as dielectric elastomers. In one example the electro-active material110comprises a film material, such as silicone. Film material may achieve stretching or compression greater than about 30% and in cases where the film material has been pre-strained, stretching or compression greater than about 100% may be achieved. As a result, tens of microns of displacement may be achieved with less than 1 kilovolts of electric charge applied across the electrodes. In addition, film material may respond to applied fields in less than 1 millisecond.

Under Earnsha's theorem, a static field is theoretically not possible to maintain stability of a rotor in a magnetic bearing. Therefore, a magnetic field generated by a magnetic bearing may be adjusted in real time to keep the rotor stabilized. In general, the magnetic field may be adjusted by adjusting the distance between the magnets and the rotor. After each adjustment, a measurement may be made to detect the distance between the magnets and the rotor, thus detecting the forces being applied from the magnetic field. Based on the detected forces, adjustments may be made to balance the rotor.

As will be explained below, not only may each electro-actuator104function as an actuator, each electro-actuator104may also be utilized as a sensor to sense forces being applied within the magnetic bearing100. The sensed forces may be used to determine an adjusted level of voltage to be applied to each respective electro-actuator104. That is, based on the force each electro-actuator104experiences, the activation level applied to each electro-actuators104may be adjusted to adjust the magnetic field accordingly.

Each electro-actuator104may act as a sensor to sense forces, where the sensed forces can be determined by measuring a capacitance. In particular, each electro-actuator104includes an electro-active material110sandwiched between a top and bottom electrode106and108, and thus forms a capacitor between the plates formed by the electrodes. A measurement circuit (not shown) may be coupled to each of the electro-actuators104to measure capacitance. The measurement circuit may be external or integral with the magnetic bearing100. The measured capacitance may be utilized to calculate forces being applied to each of the electro-actuators104. In some examples, before measuring the capacitance of the electro-actuators104, the power source may be decoupled from each of the electro-actuators104to achieve steady state. Due to the magnetic field imposed on each electro-actuator104, the top electrode106may be attracted to or repelled from the bottom electrode108causing a deformity in the electro-active material110. That is, the electro-active material110may be contracted or stretched along a radial direction towards a center of the rotor. The measurement circuit may be utilized to measure the capacitance of each electro-actuator104. From the measured capacitance of each electro-actuator104, the distance between the top and bottom electrodes106and108of each electro-actuator104may be calculated to determine the displacement of the electro-active material110. Using known material properties of the electro-active material110and the displacement of the electro-active material110, a force applied to each of the electro-actuators may be calculated. Each force applied to each electro-actuator104may be analyzed in connection with the geometry of the magnetic bearing100to determine an adjusted magnetic field or an adjusted activation voltage level to be applied to the electro-actors104.

FIG. 2is a block diagram illustrating some example systems200for adjusting a magnetic field in a magnetic bearing, arranged according to at least some examples of the present disclosure. The example system includes a magnetic bearing210, such as the example magnetic bearing100described inFIG. 1, a measurement circuit220, a microcontroller230, a power source240, and a power amplifier250. In some examples, the microcontroller230includes a memory or may be coupled to an external memory. The magnetic bearing210may be coupled to the measurement circuit220, which may be coupled to the microcontroller230. The microcontroller230may be coupled to the power source240and the power amplifier250, which may be coupled to the magnetic bearing210, or in some examples, the power source240may be coupled directly to the magnetic bearing210. The power source240may be configured to selectively provide a bias voltage or current to each of the electro-actuators.

The microcontroller230may be configured to provide an activation signal to the power source240to cause the power source240to provide a voltage difference across each of the electro-actuators in the magnetic bearing210. Similarly, the power amplifier250may include a plurality of power amplifiers each coupled to a respective electro-actuator in the magnetic bearing210. In these embodiments, each electro-actuator in the magnetic bearing210may be individually addressed and thus receive an individually determined activation level. In particular, the microcontroller230may be configured to couple each individually addressed activation level to a respective power amplifier. Each power amplifier may be configured to couple the amplified voltage difference to a respective electro-actuator in the magnetic bearing210. By coupling an adjusted voltage or current to each respective electro-actuator, the shape and/or strength of a magnetic field in the magnetic bearing210may be altered.

As is described above, each electro-actuator includes a capacitor formed by the top and bottom electrodes with the electro-active material provided therebetween. The measurement circuit220may be configured to measure a capacitance associated with each capacitor (i.e., the effective capacitance between the top and bottom electrodes) in each electro-actuator. In some examples, the measurement circuit220includes a plurality of measurement circuits each coupled to a respective electro-actuator in the magnetic bearing210. Each capacitance measurement may be utilized to determine the position of each electro-actuator. In some examples, before measuring the capacitance of each electro-actuator, a deactivation signal may be provided by the microcontroller230to the power source240causing the power source to be decoupled from the electro-actuators104and allowing the electro-actuators104to achieve steady state.

The microcontroller230may be configured to provide a measurement signal to the measurement circuit220. In response to the measurement signal, the measurement circuit220may be configured to measure the capacitance of each electro-actuator. The measured capacitance may then be provided from the measurement circuit220to the microcontroller230. Using the measured capacitance and known geometry and material properties of each electro-actuator, the microcontroller230may be configured to calculate the distance between the top and bottom electrodes using the following equation:

A=area of one of the top or bottom electrodes;

d=distance; and

The distance between the two electrodes on a particular electro-actuator may be used to determine the force being applied to the respective electro-actuator. Assuming the electroactive material behaves linearly, the distance between the top and bottom electrodes may be used to calculate a force being applied to the electro-active material using the following equations:

E=modulus of elasticity of the electro-active material;

F=the force exerted by the electro-active material when stretched or compressed;

A=area of the electro-active material prior to being stretched or compressed;

d1=distance between top and bottom electrodes prior to being stretched or compressed; and

Δd=change distance between the top and bottom electrodes.

In another example, a look-up table (LUT) or algorithm may be utilized to determine the force being applied to the electro-active material. For instance, in one example a LUT may be used when the electro-active material behaves nonlinearly. The LUT may correlate measured capacitance with force. That is, from the measured capacitance of an electro-actuator, the LUT may be accessed to determine the estimated force being applied to the electro-actuator. AlthoughFIG. 2shows that the LUT and memory may be stored in the microprocessor, it is to be understood the LUT and memory may be stored in a separate device.

From the distribution of forces being applied to each electro-actuator and the geometry of the magnetic bearing, a correction may applied to each activation signal to adjusted an amount of power being applied to each electro-actuator to stabilize the rotor. For instance, in an ideal state, the rotor exerts symmetric forces on each of the electro-actuators. Thus, the microprocessor may be configured to compare actuators on opposite sides and adjust the activation level accordingly. Once the amount of power applied to each electro-actuator has been adjusted, the power may be removed and the forces recalculated as described above. Thus, the example system200may continue the cycle of applying power, removing power and measuring capacitance, and using the measured capacitance to adjust the amount of power to be applied.

In some examples, the distance between the top and bottom electrodes may be determined based on a change in distance, rather than calculating the distance from the material properties of the capacitor. In these examples, a capacitor measurement is made of each electro-actuator while the magnetic bearing is in a relaxed state (i.e. no power supplied to the magnetic bearing). The area of one of the electrodes and the dielectric constant of each electro-actuator are assumed to remain constant. Thus, the change in capacitance may be used to calculate a change in distance using the following:

d1=distance between top and bottom electrodes in the relaxed state;

C2=measured capacitance at time seeking measurement; and

d2=distance between the top and bottom electrodes at time seeking measurement

As is described above, d2may be used to calculate forces being applied to the respective electro-actuator.

FIG. 3is a flow chart illustrating an example method300of balancing a rotor utilizing a magnetic bearing that is arranged in accordance with at least some of the examples of the present disclosure. The method300may include one or more functions, operations, or actions as illustrated by blocks310-330. The example method300may begin at block310. In block310a respective electrical parameter may be applied (e.g. such as by power source, microcontroller, power amplifier) to a respective one of a plurality of electro-actuators. Block310may be followed by block320. In block320, a capacitance of each of the plurality of electro-actuators may be measured (e.g. such as by the measurement circuit220). Block320may be followed by block330. In block330, an adjusted level for each electrical parameter may be determined (e.g. such as by the micrcontroller). Block330may be followed by block340. In block340, the respective electrical parameter at the adjusted level may be applied (e.g. such as by power source, microcontroller, power amplifier) to a respective one of the plurality of electro-actuators. The method may continue back to block320and repeat blocks320-340to continuously measure capacitance and adjust the level of the electrical parameter being applied to each of the plurality of electro-actuators.

The various blocks described herein for method300may be performed sequentially, in parallel, or in a different order than those described herein. It should also be appreciated that in some implementations one or more of the illustrated blocks may be eliminated, combined or separated into additional blocks. The described and illustrated method300may also include various additional blocks not shown. For instance, the tested resonator and the control resonator may be measured at the same time.

FIG. 4is a block diagram illustrating an example computing device900that may be arranged for determining an adjusted level to apply to a respective one of the plurality of electro-actuator in accordance with the present disclosure. The computing device900may be substituted for the microcontroller230inFIG. 2. In a very basic configuration901, computing device900typically includes one or more processors910and system memory920. A memory bus930may be used for communicating between the processor910and the system memory920.

Depending on the desired configuration, processor910may be of any type including but not limited to a microprocessor (μP), a microcontroller (μC), a digital signal processor (DSP), or any combination thereof. Processor910may include one more levels of caching, such as a level one cache911and a level two cache912, a processor core913, and registers914. An example processor core913may include an arithmetic logic unit (ALU), a floating point unit (FPU), a digital signal processing core (DSP Core), or any combination thereof. An example memory controller915may also be used with the processor910, or in some implementations the memory controller915may be an internal part of the processor910.

Depending on the desired configuration, the system memory920may be of any type including but not limited to volatile memory (such as RAM), non-volatile memory (such as ROM, flash memory, etc.) or any combination thereof. System memory920may include an operating system921, one or more applications922, and program data924. Application922may include an algorithm923configured to determine respective adjusted levels of an electrical parameter to be provided to a respective one of the plurality of electro-actuators. The application may be configured to receive the measured capacitance for each electro-actuator and determine the adjusted level based on the measured capacitance. The application may be further configured to generate adjusted activation signals to be provided to the power source inFIG. 2. Program Data924may include a LUT925as described above in reference toFIG. 2. The LUT may be used to determine the force being applied to the electro-active material by comparing the measured capacitance to a known force that correlates with the measured capacitance. In some embodiments, application922may be arranged to operate with program data924on an operating system921in accordance with one or more the techniques, methods, and/or processes described herein. This described basic configuration is illustrated inFIG. 9by those components within dashed line901.

Computing device900may have additional features or functionality, and additional interfaces to facilitate communications between the basic configuration901and any required devices and interfaces. For example, a bus/interface controller940may be used to facilitate communications between the basic configuration901and one or more data storage devices950via a storage interface bus941. The data storage devices950may be removable storage devices951, non-removable storage devices952, or a combination thereof. Examples of removable storage and non-removable storage devices include magnetic disk devices such as flexible disk drives and hard-disk drives (HDD), optical disk drives such as compact disk (CD) drives or digital versatile disk (DVD) drives, solid state drives (SSD), and tape drives to name a few. Example computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data.

Computing device900may also include an interface bus942for facilitating communication from various interface devices (e.g., output interfaces, peripheral interfaces, and communication interfaces) to the basic configuration901via the bus/interface controller940. Example output devices960include a graphics processing unit961and an audio processing unit962, which may be configured to communicate to various external devices such as a display or speakers via one or more A/V ports963. Example peripheral interfaces970include a serial interface controller971or a parallel interface controller972, which may be configured to communicate with external devices such as input devices (e.g., keyboard, mouse, pen, voice input device, touch input device, etc.) or other peripheral devices (e.g., printer, scanner, etc.) via one or more I/O ports973. An example communication device980includes a network controller981, which may be arranged to facilitate communications with one or more other computing devices990over a network communication link via one or more communication ports982.

While various aspects and examples have been disclosed herein, other aspects and examples will be apparent to those skilled in the art. The various aspects and examples disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.