Optimal Magnetic Spring for Compliant Actuation—Validated Torque Density Benchmark

Mrak, Branimir; Lenaerts, Bert; Driesen, W.; Desmet, Wim

doi:10.3390/act8010018

Cited by 17 publications

(28 citation statements)

References 19 publications

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“…Each pair has two pole pairs. The spring design is described in more detail in [12]. The rocker inertia is connected to the load inertia with another, more flexible shaft, with a diameter d 2 = 15 mm and length l 2 = 380 mm.…”

Section: Experimental Validation 41 Experimental Setupmentioning

confidence: 99%

“…A magnetic spring is a fatigue-free alternative to a mechanical spring, allowing one to improve the energy efficiency of the drivetrain and to downsize the actuator. In order to design such a magnetic spring for a specific application, Mrak [12,13] developed a design methodology and validated this methodology using both virtual designs and one physical prototype. Although this research illustrates the potential benefit of using magnetic springs, it also highlights the complexity of their torque characteristic.…”

Section: Introductionmentioning

confidence: 99%

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Exploiting Cyclic Angle-Dependency in a Kalman Filter-Based Torque Estimation on a Mechatronic Drivetrain

et al. 2022

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Torsional vibrations play a critical role in the design and operation of a mechanical or mechatronic drivetrain due to their impact on lifetime, performance, and cost. A magnetic spring allows one to reduce these vibrations and improve the actuator performance yet introduces additional challenges on the identification. As a direct torque measurement is generally not favourable because of its intrusive nature, this paper proposes a nonintrusive approach to identify torsional load profiles. The approach combines a physics-based lumped parameter model of the torsional dynamics of the drivetrain with measurements coming from a motor encoder and two MEMS accelerometers in a combined state/input estimation, using an augmented extended Kalman filter (A-EKF). In order to allow a generic magnetic spring torque estimation, a random walk input model is used, where additionally the angle-dependent behaviour is exploited by constructing an angle-dependent estimate and variance map. Experimental validation leads to a significant reduction in bias in the load torque estimation for this approach, compared to conventional estimators. Moreover, this newly proposed approach significantly reduces the variance on the estimated states by exploiting the angle dependency. The proposed approach provides knowledge of the torsional vibrations in a nonintrusive way, without the need for an extensive magnetic spring torque identification. Further, the approach is applicable on any drivetrain with angle-dependent input torques.

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Section: Experimental Validation 41 Experimental Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Exploiting Cyclic Angle-Dependency in a Kalman Filter-Based Torque Estimation on a Mechatronic Drivetrain

et al. 2022

Self Cite

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“…It did not need mechanical stiffness-adjusting components; however, some of the weaknesses of dielectric elastomer transducer technology have not been addressed [ 30 ]. Mrak B et al designed a magnetic spring as a fatigue-free alternative to mechanical springs in compliant actuators [ 31 ]. These technologies have certain advantages over traditional commercial springs in some respects, but their reliability and cost need to be improved.…”

Section: Introductionmentioning

confidence: 99%

Design and Control of a Series–Parallel Elastic Actuator for a Weight-Bearing Exoskeleton Robot

Wang

Zheng

Zhao

et al. 2022

Sensors

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Weight-bearing exoskeletons are robots that need to carry loads and interact with humans frequently. Therefore, the actuators of these exoskeletons are supposed to be capable of outputting sufficient force with high compliance and little weight. A series–parallel elastic actuator (SPEA) is designed, in this work, to meet the demanding requirements of an exoskeleton robot called PALExo. A gas spring is installed in parallel with an electric cylinder to adjust the force output range of the actuator according to the needs of the exoskeleton. A series elastic module (SEM) is installed in series with the electric cylinder and gas spring to improve the compliance of the actuator, the stiffness of which is variable to adapt to the different stiffness requirements of the exoskeleton’s legs in the standing phase and swinging phase. A force controller combining dynamic compensation and a cascade control with an inner velocity loop and a disturbance observer is designed for the SPEA. The performance of the force controller is verified by experiments and the results demonstrate that the controller has good adaptability to the stiffness of the SEM.

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“…Magnetic springs are an alternative to mechanical springs in applications that require long lifetime with no fatigue failure. Recent efforts introduced them to the industrial and academic audiences as a promising technology for torque ripple reduction in highly dynamic motion systems [1,2]. Although the previously demonstrated torsional magnetic springs typically have sinusoidal torque characteristics, for reasons of cost efficiency, there are many motion systems in the industrial practice that could benefit from a deviation from it.…”

Section: Introductionmentioning

confidence: 99%

Methodology for Shape Optimization of Magnetic Designs: Magnetic Spring Characteristic Tailored to Application Needs

2022

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Topology and shape optimization are still rarely applied to problems in electromagnetic design due to the computational complexity and limited commercial tooling, even though components such as electrical motors, magnetic springs or magnetic bearings could benefit from it, either to improve performance (reducing torque ripple and losses through shaping harmonic content in back electromotive force) or reduce the use of rare-earth materials. Magnetic springs are a fatigue free alternative to mechanical springs, where shape optimization can be exploited to a great degree—allowing for advanced non-linear stiffness characteristic shaping. We present the optimization methodology relying on a combination of several approaches for characteristic shaping of magnetic springs through either a modular design approach based on: (i) Fourier order decomposition; (ii) breaking conventional design symmetry; or (iii) free shaping of magnets through deviation from a nominal design using problem formulations such as spline and polynomials for material boundary definitions. Each of the parametrizations is formulated into a multi-objective optimization problem with both performance and material cost, and solved using gradient free optimization techniques (direct search, genetic algorithm). The methodology is employed on several benchmark problems—both academic and application inspired magnetic spring torque characteristic requirements. The resulting designs fit well with the requirements, with a relatively low computational cost. As such, the methodology presented is a promising candidate for other design problems in 2D shape optimization in electrical motor research and development.

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Optimal Magnetic Spring for Compliant Actuation—Validated Torque Density Benchmark

Cited by 17 publications

References 19 publications

Exploiting Cyclic Angle-Dependency in a Kalman Filter-Based Torque Estimation on a Mechatronic Drivetrain

Exploiting Cyclic Angle-Dependency in a Kalman Filter-Based Torque Estimation on a Mechatronic Drivetrain

Design and Control of a Series–Parallel Elastic Actuator for a Weight-Bearing Exoskeleton Robot

Methodology for Shape Optimization of Magnetic Designs: Magnetic Spring Characteristic Tailored to Application Needs

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