KR20090091300A - Control system and method for negative attenuation compensation in magnetic levitation - Google Patents

Abstract

The magnet flotation control system 100 includes a sensor 106 configured to measure a gap between the electromagnet and the stage and generate a gap measurement signal. The gap filter 112 is configured to receive a gap measurement signal and provide a phase read signal that predicts and compensates for the delay between the gap measurement signal and the compensation operation. Prediction block 114 is configured to receive the phase read signal and provide a compensation operation in accordance with the phase read signal such that negative stiffness and negative attenuation are compensated in the control system.

Description

CONTROL SYSTEM AND METHOD FOR NEGATIVE DAMPING COMPENSATION IN MAGNETIC LEVITATION

The present invention relates to magnetic levitation, and more particularly, to a control system and method for compensating for negative attenuation.

Maglev relates to a system or device that uses a magnetic field to repel an object (s) to balance other forces, such as gravity, for example. Maglev can be used in transportation systems in which vehicles are injured and propel down the track. Other applications include semiconductor processing (eg, to float a wafer support platen), contactless bearings (eg, magnetically floating shafts), or medical equipment (eg, CT scanners). It may include.

Stiffness is the ability of a material to push back when it is pushed, for example a spring resists compression. This reaction determines the strength and ability of the material to dampen vibrations. This is a positive stiffness. Some materials or systems have "negative stiffness", i.e., such as springs that spontaneously spontaneously begin to compress, their structures cause more compression when pressure is applied but their stored energy is in the same direction. Twisted or bent in such a way.

In magnetic levitation, the gap between the magnetic core and the floating object is said to have inherently negative stiffness. Negative stiffness can be compensated in the magnetic levitation system by a calibration formula that can offset the negative stiffness effect. However, the delay introduced between the time this gap is measured and the time this gap is compensated for often results in negative attenuation. Negative attenuation cannot be explained in the same way as negative stiffness. Therefore, a need exists to compensate for negative attenuation in magnetically levitated systems.

According to the present invention, the magnetic levitation control system includes a sensor configured to measure a gap between the electronic magnet and the stage and generate a gap measurement signal. The gap filter is configured to receive a gap measurement signal and provide a phase read signal that predicts and accounts for the delay between the gap measurement signal and the compensation operation. The predictive block receives the phase read signal and provides a compensation operation in accordance with the phase read signal such that both negative stiffness and negative attenuation effects are compensated for in the control system.

The method of controlling the gap in a magnetic levitation system is to generate and maintain a gap between the stage and the electromagnetic magnet core according to the realized current, to generate a magnetic field to float the stage, and to measure the gap to output a gap measurement signal. Filtering the gap measurement signal to provide a phase read signal according to past measurements, to account for the delay between the gap measurement signal and the compensation operation, and to compensate for negative stiffness and negative attenuation in adjusting the gap. Generating a realized current in accordance with the phase read signal.

In an alternative embodiment, the gap measurement can be reconfigured to allow prediction of the gap measurement without the need for side-by-side sensors. The realized current is preferably generated in accordance with the phase read signal, and the current output calculated from the predictive block is amplified at the point where the calculated current is based on the phase read signal. The method may include reducing noise introduced by the filtering. The method may further include extrapolating the delay from the previous gap measurement such that the phase read signal is based on the extrapolated delay.

These and other objects, features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the invention, which should be read in conjunction with the accompanying drawings.

The disclosure of the present invention will be described in detail in the following description of preferred embodiments with reference to the following figures.

1 is a block / flow diagram showing a magnetic levitation system according to one embodiment.

2 is a block / flow diagram showing a magnetic levitation system in accordance with a more detailed embodiment.

FIG. 3 is a magnitude (dB) or phase angle (angle) vs. frequency graph showing reference signals and responses for different configurations of gap filters according to FIG. 2.

4 is a flow chart showing an exemplary method for controlling a gap in a magnetic levitation system.

The disclosure of the present invention describes a control system adapted for use in a magnetic levitation system, where the negative damping is referred to as a floating portion or device (hereinafter referred to as a mechanical plant) and a magnetic core (hereinafter referred to as plant core). Compensation by estimating the delay between the measurement and compensation for gap variations. In one particularly useful embodiment, the delay is expected by a gap filter, which provides a phase lead to eliminate the negative attenuation experienced in this system. Instead of or in addition to a gap filter, historical measurements or gap prediction criteria can be used to more accurately predict the actual gap to help eliminate negative attenuation. While the present invention will be described with respect to a specific magnetic levitation system, it should be understood, however, that the teachings of the present invention are much broader and applicable to any magnetic levitation system that may have negative attenuation as a result of the delay introduced into the feedback loop. . In addition, it should be understood that the circuitry of the illustrative example may be adapted to include additional components or that the components may be integrated on one or more integrated circuit chips. In addition, the depicted components can be implemented on software or on a standalone device or circuit. In a particularly useful embodiment, the components depicted in the figures can be implemented in various combinations of hardware and software, and can provide functionality that can be combined into a single component or a plurality of components.

Reference is now made to figures in which like numerals represent the same or similar components, but first with reference to FIG. 1, a high-level diagram shows a magnetic levitation system 10 according to one exemplary embodiment. . The electronic magnet core 26 includes a winding, or coil 24, which receives a calibration current that allows to adjust the magnetic field generated by the core 26. This correction current from the amplifier 22 serves as feedback to adjust the gap 14 between the core 26 and the stage 12. The gap 14 is measured by the position sensor 16.

Stage 12, which magnetically floats using an electromagnetic core (E-core) 26, exhibits inherent negative stiffness. A calibration scheme can be used to counter negative stiffness effects, which can include the introduction of predefined calibration delays. This may include providing a calibration constant or parameter in the governing formula representing the force F and the current I as a function of the effective gap z. More complex ways, including rotation and gap imperfections, can also be used to compensate for this negative stiffness. If the negative stiffness counteracts the delay between position measurement and the use of this position to create a force, there will be a negative attenuation.

For small disturbances in the gap, the attenuation is equal to the stiffness multiplied by the delay between the position measurement of the gap 14 and the use of this position for compensation. Since this stiffness is negative, the attenuation is also negative, as shown in the following equation.

(즉,

)는 갭에서 순간 변화이고,

는 강성이고,

는 음의 감소에 대한 감쇠 계수이다. 이 감쇠는 절대치이고 또한 보상된 강성에 의존하는 것이 아니고 자기 부상의 명목상 강성에 의존함을 주의하자. Where F _t is the nominal force on the floating object at time _t , F _{t -1} is the nominal force at time t-1, F is the instantaneous force, and Δt is between the measurement and compensation Delay, z is the instant gap,

(In other words,

) Is a momentary change in the gap,

Is stiffness,

Is the attenuation coefficient for the negative decrease. Note that this attenuation is absolute and not dependent on the compensated stiffness, but on the nominal stiffness of the magnetic levitation.

The simplified calibration formula shows that the stiffness is inherently negative:

Where Ci is the calibration constant and I is the coil current. Stiffness will be negative as the derivative of the force function. Since the stiffness is negative in Equation 1, the attenuation is also negative. According to the principles of the present invention, the embodiments described below will provide such negative attenuation compensation. Compensation module 18 is included to provide compensation for negative stiffness as well as negative attenuation. After the gap measurement signal from the position sensor 16 is compensated, this compensated signal is used by the controller 20 to determine the output coil current. This coil current may be amplified by the amplifier 22 prior to being used to energize the coil 24.

With reference to FIG. 2, the magnetic levitation system 100 is illustratively illustrated to illustrate concepts in accordance with the principles of the present invention. Only the details of the individual block components that make up the system architecture known to those skilled in the art will be described in sufficient detail for the understanding of the present invention. Part or all of system 100 may be implemented on a central motion computer (eg, a personal computer) or distributed on a standalone controller. System 100 includes a magnet core or plant core 102. Plant core 102 may include an E-core or other magnetic device that responds to feedback currents, for example, they have a winding (not shown) near them. The winding receives current I _Realized , which includes an amplified and compensated signal as described in more detail below. The plant core 102 exerts a magnetic force F _Real on the mechanical plant device (s) (stage) 104. The mechanical plant 104 may include a platform, such as a vehicle, a platen for semiconductor processing, a rotating shaft, or the like. Gap _Real is maintained between plant core 102 and plant machine part 104. Plant core 102 and plant mechanical portion 104 include an inner loop 120 of system 100 that models the mechanical / physical aspects of system 100. This inner loop 120 may comprise actual physical components or may comprise digitally modeled components. Gap _Real may experience variations, rotations, or other deflections as a result of operating conditions. These variations are determined and corrected or compensated for according to the outer loop 130.

Outer loop 130 includes at least one sensor 106. Sensor 106 can include optical sensors, inductive sensors, mechanical sensors, or any other device or software to predict gap distances and variations in gaps over time. The sensor 106 can be any device measurement location (eg, inductive sensor). The sensor 106 outputs the measured gap (Gap _Measured ). This gap measurement can be an analog or digital signal. If the signal is analog, this signal is preferably converted into a digital signal by the analog-to-digital converter 108. The gap reconstruction module 110 does not require the sensor 106 to be placed side by side with the gap of the E-core 102. Gap reconstruction 110 is optional when the gap measurement is located side by side with the actual gap. If the sensor 106 is not positioned alongside the gap of the E-core 102, the gap reconstruction 110 _{calculates a} gap _calculated to account for the difference in position.

Any delay in the outer loop 130 (eg, the calculation loop) relative to the inner loop 120 (which is the actual plant) causes negative attenuation. Gap filter 112 may be used to generate the phase read signal 113 to compensate for the gap delay. In one application, the stage 104 is steered or otherwise undergoes a change in direction, force or acceleration. Currently, gap prediction is needed from gap reconstruction 110 for gap filter 112. Gap filter 112 causes the Gap _Calculated signal to account for the delay between the measured gap (Gap _Measured ) and the I _Realized signal. The gap filter 112 may be a simple lead filter, a higher order filter (for better accuracy) or future gap prediction based on several past measurements. Gap filter 112 may be implemented in a manner to compensate for all delays encountered within the system.

The phase adjusted output from the gap filter 112 is input to the prediction block 114, which outputs an output current I _Calcuated and a gap (phase read signal (A) as a function of the force F applied to the stage 104. 113)) to provide the desired resilience. Since there is a gap filter 112, the delay is compensated to cause a more accurate current prediction. This reduces or eliminates negative attenuation. Depending on this implementation, I _Calulated may be digital and may be converted into an analog signal (voltage or current) by digital-to-analog converter 116. Amplifier 118 may be used to amplify or otherwise modify I _Calculated to provide I _Realized to core 102 in inner loop 120.

The random gap filter 112 that generates the phase lead is most likely to amplify the noise. However, this can be eliminated by the analog filter of the amplifier 118 using known methods. This result is that the phase lead is obtained and the attenuation is compensated for, while the negative effect is not seen in the gain. System 100 may be used in many other applications such as, for example, vehicle systems, semiconductor processing devices, contactless bearing systems, medical imaging devices, and the like.

Referring to FIG. 3, the effects of various implementations of the gap filter can be seen in the Bode diagram. The baseline plot 202 shows the magnitude and phase of the delay input into the prediction block without the gap filter. Plots 204, 206 and 208 show the magnitude and phase of the delay input into the predictive block with different configurations of gap filters, and gradually show compensation for phase delay. More compensation requires higher gain of the gap filter. Also in this case, the remaining negative stiffness 211 can be seen on the left side of the plot, where the lines are horizontal. The size is relatively the same for all plots.

Referring to FIG. 4, a method of controlling a gap in a magnetic levitation system is described by way of example. At block 302 a magnetic field is generated to float the stage and maintain a gap between the stage and the magnetic core in accordance with the realized current. This magnetic core includes a coil winding that is energized by a realized current to make adjustments to the gap. At block 304, the gap is measured by one or more sensors to output a gap measurement signal. At block 306, the gap measurement can be selectively reconfigured if it is necessary to allow calibration for the gap measurement between the measuring and filtering steps. This may be the result of signal conversion or other delay or change to the gap measurement signal before the gap measurement signal is filtered by the gap filter.

At block 308, the gap measurement signal is filtered by a gap filter to provide a phase read signal with delay, for example using a past measurement / history. This filter is designed to account for the delay between the gap measurement signal and the compensation operation. This compensation operation is preferably performed by a predictive block that calculates the output current so that the winding current adjusts / maintains this gap. At block 310, the amount of delay (eg, phase shift) is extrapolated from the previous gap measurement such that the phase lead signal is based on the extrapolated delay. This may be implemented using a lookup table or other memory storage device to determine or extrapolate an operation based on past history. Block 310 is optional.

At block 312, the calibration current or calculated current (or voltage) is generated by the predictive block in accordance with the phase read signal to compensate for negative stiffness and negative attenuation in adjusting the gap (current is represented by voltage). Can be). At block 314, a calibration current is generated in accordance with the phase read signal, which may include amplifying the calculated current output from the predictive block, wherein the calculated current is based on the phase read signal. At block 316, an amplifier may be used to reduce the noise introduced by amplifying and filtering the calculated (corrected) current output. The current realized in step 318 is output from the amplifier.

When interpreting the appended claims, the following should be understood:

a) The term "comprising" does not exclude the presence of elements or acts other than those listed in a given claim.

b) A singular component does not exclude the presence of a plurality of components.

c) Any reference sign in a claim does not limit the scope of the claim.

d) Several "means" may be represented by the same item or structure or function implemented in hardware or software.

e) No specific sequence of actions is intended to be required unless specifically indicated.

Although preferred embodiments have been described with respect to control systems and methods for negative attenuation compensation in magnetic levitation (these embodiments are by way of example and not intended to be limiting), modifications and variations are known to those skilled in the art in view of the above teachings. It is noted that this can be done by. Therefore, it should be understood that changes may be made within the scope and spirit of the embodiments disclosed herein as outlined by the appended claims. Thus, while details and specificities required by the patent law have been described, what is claimed and protected by the patent certificate is set forth in the appended claims.

The present invention is applicable to magnetic levitation and more particularly to control systems and methods that compensate for negative attenuation.

The method generates and maintains a magnetic field to float the stage and maintains a gap between the stage and the electron magnet core in accordance with the realized current, measures the gap to output a gap measurement signal, gap measurement signal and compensation Filtering the gap measurement signal to provide a phase read signal in accordance with past measurements to account for delays between operations, and implementing the phase read signal to compensate for negative stiffness and negative attenuation in adjusting the gap. Generating a current.

Claims (20)

As the magnetic levitation control system 100, A sensor 106 configured to measure a gap between the electronic magnet and the stage and generate a gap measurement signal; A gap filter (112) configured to receive the gap measurement signal and provide a phase lead signal (113) that predicts and accounts for the delay between the gap measurement signal and a compensation operation; And A prediction block 114 configured to receive the phase read signal and provide the compensation operation in accordance with the phase read signal such that negative stiffness and negative attenuation effects in the control system are compensated for Including, magnetic levitation control system. The method of claim 1, And a gap reconstruction module (110) configured to provide calibration between the measurement time and the filter time of the gap filter. The method of claim 1, The compensating operation includes an output signal (I _Calculated ) modified according to the phase read signal. The method of claim 3, wherein And an amplifier (118) configured to receive the output signal. The method of claim 4, wherein The amplifier (18) reduces the noise introduced by the gap filter (112). The method of claim 1, The gap filter (112) extrapolates the delay from a previous gap measurement delay such that the phase read signal is based on the extrapolated delay. As the magnetic levitation system 100, An electromagnetic magnet core 102 configured to generate a magnetic field to float the stage 104 and to maintain a gap between the stage and the electron magnet core in accordance with the realized current; A sensor (106) configured to measure the gap and generate a gap measurement signal; A gap filter (112) configured to receive the gap measurement signal and adjust the gap measurement signal to provide a phase read signal (113) in accordance with past measurements to account for the delay between the gap measurement signal and a compensation operation; And A prediction block 114 configured to receive the phase read signal and output a calculated current I _{Calculated that} is amplified to provide the realized current so that negative stiffness and negative attenuation are compensated in the control system. Including, magnetic levitation system. The method of claim 7, wherein And a gap reconstruction module (110) configured to provide calibration between the measurement time and the filter time of the gap filter. The method of claim 7, wherein Maglev system, wherein the calculated current I _Calculated is modified in accordance with the phase lead signal 113. The method of claim 7, wherein The amplifier 118 reduces the noise introduced by the gap filter 112. The method of claim 7, wherein A gap filter (112) extrapolates the delay from a previous gap measurement delay such that the phase read signal is based on the extrapolated delay. The method of claim 7, wherein Magnetic levitation system, wherein an electromagnetic magnet core (102) and stage (104) are used in a vehicle system. The method of claim 7, wherein The magnetic levitation system of which the electromagnetic magnet core 102 and the stage 104 are used in a semiconductor processing device. The method of claim 7, wherein Magnetically levitated system, wherein an electromagnetic magnet core (102) and a stage (104) are used in a contactless bearing system. The method of claim 7, wherein The magnetic levitation system, wherein the electronic magnet core 102 and the stage 104 are used in a medical imaging system. As a method of controlling the gap in a magnetic levitation system, Generating a magnetic field to float the stage and maintaining a gap between the stage and the electron magnet core in accordance with the realized current; Measuring (304) the gap to output a gap measurement signal; Filtering (308) the gap measurement signal to provide a phase read signal in accordance with past measurements to account for the delay between the gap measurement signal and the compensation operation; And Generating 312 a realized current in accordance with the phase read signal to compensate for negative stiffness and negative attenuation in the gap adjustment A method for controlling a gap in a magnetic levitation system comprising a. The method of claim 16, Reconstructing the gap measurement to allow prediction of the gap measurement without requiring sensors side by side. The method of claim 16, Generating the realized current in accordance with the phase read signal, step 302, includes amplifying the calculated current output from the predictive block, wherein the calculated current is based on the phase read signal. How to. The method of claim 18, Reducing the noise introduced by the filtering step (316). The method of claim 16, Extrapolating (310) a delay from a previous gap measurement such that the phase read signal is based on an extrapolated delay.

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