Exploring the Physical Limits of Axial Magnetic Bearings Featuring Extremely Large Vertical Levitation Distances

Bonetti, Reto; Bortis, Dominik; Beglinger, Lars; Kolar, Johann W.

doi:10.1109/tia.2021.3096170

Cited by 2 publications

(36 citation statements)

References 18 publications

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“…This section first introduces the ECS, tailored explicitly for the analyzed MLP. Next, the main properties of the RFS concept proposed in [12] are summarized in Section 3, and a detailed comparison of the two position-sensing technologies is finally performed starting from Section 4.…”

Section: Eddy Current Position Sensor For the Mlpsmentioning

confidence: 99%

“…The theoretical and practical implementation of an axially symmetric MLP potentially suitable for zero-power gravity compensation applications was analyzed in [11] and [12] with the aim of extending the vertical air gap (i.e., the levitation height h in Figure 1) between the stator and mover. Similar systems based on commercially available levitation modules have been sporadically analyzed in the literature regarding structural optimizations and closed-loop control [13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

“…This necessitates an effective method for obtaining the position of the MLP's mover, especially in scenarios demanding high versatility, such as, e.g., operation within stainless-steel (non-magnetic) process chambers where traditional optical position sensing is infeasible. Consequently, [12] introduces a novel position measurement methodology that relies on observing the reaction forces exerted on the stator by the mover's movements, called the reaction force-based position sensor (RFS). This approach is notably beneficial for facilitating the automated manufacture and manipulation of objects, enabling robot arms to seamlessly navigate through the air gap between the stator and the mover.…”

Section: Introductionmentioning

confidence: 99%

“…While the complexity and noise inherent in the force sensor may impact the precision of the RFS method, the technique's universal applicability and ability to accommodate conductive objects within the air gap stand out. The second advantage could also be achieved by Hall effect sensors, which are, however, not applicable to this MLP because the high magnetic field near the stator PM would saturate the measuring circuit output [12]. The considerable advantage of accommodating conductive materials in the air gap is not achievable with other types of position sensors, such as eddy current-based sensors (ECSs).…”

Section: Introductionmentioning

confidence: 99%

“…In Section 2, we introduce the geometry and display the operating principles of the ECS. A brief repetition of the operating principles of the RFS, which are extensively discussed in [12], is given in Section 3. The position sensor's dynamics modeling and verification is covered in Section 4.…”

Section: Introductionmentioning

confidence: 99%

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Comparative Analysis of Force and Eddy Current Position Sensing Approaches for a Magnetic Levitation Platform with an Exceptional Hovering Distance

Bonetti,

Mirić,

Kolar

2024

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This paper provides a comparative analysis between a force sensor and an eddy current sensor, focusing on their usability to determine the position of a circular levitating permanent magnet (PM) mover within an axially symmetric magnetic levitation platform (MLP) with an exceptionally large air gap. The sensors enable closed-loop control, which is essential for accurately and stably maintaining the mover’s radial position. For the considered MLP, a change in radial position in principle results in a tilting of the mover, i.e., a deviation from the parallel alignment relative to the stator. As both the radial position and the tilting angle affect the sensors’ (force and eddy current) output voltage, an observer must deduce the radial position from the output sensor’s voltage, requiring a comprehensive MLP dynamic model and calibration of the models for both sensing approaches. The paper discusses the advantages and weaknesses of each sensor concept, exploring operational principles and performance in levitation tests. The force sensor exhibits versatility, proving functional across various application scenarios, such as when the mover is sealed in a conductive, non-magnetic chamber. In contrast, due to its high-frequency operation, the eddy current sensor is more straightforward to characterize, simplifying its behavior relative to the mover’s slower dynamics. Measurements are conducted to validate the models, showing the eddy current sensor’s robustness against disturbances and imperfections in the MLPs and its immunity to cross-axis interference. Conclusively, in levitation experiments where the mover is vertically distanced at 104 mm from the stator, the eddy current sensor achieves a position tracking precision about ten times better and a signal-to-noise ratio (SNR) ten times higher compared to the off-the-shelf force sensor, confirming its better performance and reliability; however, it cannot be used in applications where conductive objects are present in the air gap. Furthermore, additional experiments are conducted on the MLP using the eddy current sensor to show the controller’s robustness and dynamic reference tracking capability, with and without a payload.

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Section: Eddy Current Position Sensor For the Mlpsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Comparative Analysis of Force and Eddy Current Position Sensing Approaches for a Magnetic Levitation Platform with an Exceptional Hovering Distance

Bonetti,

Mirić,

Kolar

2024

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Reaction Force-Based Position Sensing for Magnetic Levitation Platform with Exceptionally Large Hovering Distance

Bonetti,

Beglinger,

Mirić

et al. 2024

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This work introduces a novel sensing concept based on reaction forces for determining the position of the levitating magnet (mover) for magnetic levitation platforms (MLPs). Besides being effective in conventional magnetic bearings, the applied approach enables operation in systems where the mover is completely isolated from the actuating electromagnets (EMs) of the stator (e.g., located inside a sealed process chamber) while levitating at an extreme levitation height. To achieve active position control of the levitating mover by properly controlling the stator’s EM currents, it is necessary to employ a dynamic model of the complete MLP, including the reaction force sensor, and implement an observer that extracts the position from the force-dependent signals, given that the position is not directly tied to the measured forces. Furthermore, two possible controller implementations are discussed in detail: a basic PID controller and a more sophisticated state-space controller that can be chosen depending on the characteristics of the MLP and the accuracy of the employed sensing method. To show the effectiveness of the proposed position-sensing and control concept, a hardware demonstrator employing a 207 mm outer-diameter (characteristic dimension, CD) stator with permanent magnets, a set of electromagnets, and a commercial multi-axis force sensor is built, where a 0.36 kg mover is stably levitated at an extreme air gap of 104 mm.

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Exploring the Physical Limits of Axial Magnetic Bearings Featuring Extremely Large Vertical Levitation Distances

Cited by 2 publications

References 18 publications

Comparative Analysis of Force and Eddy Current Position Sensing Approaches for a Magnetic Levitation Platform with an Exceptional Hovering Distance

Comparative Analysis of Force and Eddy Current Position Sensing Approaches for a Magnetic Levitation Platform with an Exceptional Hovering Distance

Reaction Force-Based Position Sensing for Magnetic Levitation Platform with Exceptionally Large Hovering Distance

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