Tat Joo Teo

Electromagnetic Actuator Design Analysis Using a Two-Stage Optimization Method With Coarse–Fine Model Output Space Mapping

Electromagnetic actuators are energy conversion devices that suffer from inefficiencies. The conversion losses generate internal heat, which is undesirable, as it leads to thermal loading on the device. Temperature rise should be limited to enhance the reliability, minimize thermal disturbance, and improve the output performance of the device. This paper presents the application of an optimization method to determine the geometric configuration of a flexure-based linear electromagnetic actuator that maximizes output force per unit of heat generated. A two-stage optimization method is used to search for a global solution, followed by a feasible solution locally using a branch and bound method. The finite element magnetic (fine) model is replaced by an analytical (coarse) model during optimization using an output space mapping technique. An 80% reduction in computation time is achieved by the application of such an approximation technique. The measured output from the new prototype based on the optimal design shows a 45% increase in air gap magnetic flux density, a 40% increase in output force, and a 26% reduction in heat generation when compared with the initial design before application of the optimization method.

Analysis and design of a 3-DOF flexure-based zero-torsion parallel manipulator for nano-alignment applications

A flexure-based parallel manipulator (FPM) is a closed-loop compliant mechanism in which the moving platform is connected to the base through a number of flexural legs. Utilizing parallel-kinematics configurations and flexure joints, the FPMs can achieve extremely high motion resolution and accuracy. In this work, we focus on the analysis and design of a 3-DOF (θx -θy -Z) zero-torsion FPM for nano-alignment applications. Among various possible zero-torsion parallel-kinematics configurations, it is identified that the 3-legged Prismatic-Prismatic-Spherical (3PPS) is a suitable candidate. Based on the concept of instantaneous rotation, the critical kinematic design issues, such as displacement and workspace analyses, are addressed. With these analysis algorithms, the major kinematic parameters are readily determined to meet the task requirements. To achieve a large workspace, beam-based flexure joints are employed in the FPM design. As the beam-based Universal (U) flexure joints are able to accommodate the required passive prismatic and spherical motions, each flexure PPS leg can be replaced by a simple flexure PU leg. A research prototype of the 3-DOF 3PU FPM has been developed, which achieves position and orientation resolutions of 20 nm and 0.05 arcsecond throughout a workspace of 5° × 5° × 5 mm, respectively.

Toward Comprehensive Modeling and Large-Angle Tracking Control of a Limited-Angle Torque Actuator With Cylindrical Halbach

The single-phase limited-angle torque (LAT) motor with cylindrical Halbach magnetic array provides a smaller form factor, lighter moving mass, and higher force throughput within ±60° angle range, compared with the three-phase permanent magnet synchronous motor. Due to the imperfect flux distribution within the air-gap of the Halbach array, as well as the inherent angular dependent characteristics, it is mainly used for point-to-point motion applications in prior literature. In this paper, we would like to deal with above issues, so that it can be extensively used for large-angle tracking applications. First, we derive the ideal model of this LAT actuator. Next, we propose to identify its nominal model parameters by the relay feedback with sufficiently small oscillations near the neutral position. Later, a robust output feedback control with high-gain observer is proposed to handle both model uncertainty and angular-dependent nonlinear current-torque relationship, so that the precision tracking of a defined smooth trajectory is achieved with only position sensing. The real-time experiment on a prototype validates the practical appeal of proposed methods.

Modeling of a Two Degrees-of-Freedom Moving Magnet Linear Motor for Magnetically Levitated Positioners

This paper presents a novel analytical model that accurately predicts the current-force characteristic of a 2 degrees-of-freedom moving magnet linear motor (MMLM), where its translator is formed by a Halbach permanent magnet (PM) array. Unlike existing theoretical models, the uniqueness of this proposed model is based on a derived magnetic field model that accounts for the magnetic flux leakage at the edges of the Halbach PM array. Hence, it can be used to model an MMLM that employs a low-order Halbach PM array effectively. To implement the proposed model in high sampling rate control system, a model-based approximation approach is proposed to simplify the model. The simplified model minimizes the computation complexity while guarantees the accuracy of the current-force prediction. MMLM prototype with two separate translators, i.e., one with a single magnetic pole Halbach PM array and the other with six magnetic poles Halbach PM array, were developed to evaluate the accuracy of the proposed models.

Design and Modeling of a Six-Degree-of-Freedom Magnetically Levitated Positioner Using Square Coils and 1-D Halbach Arrays

This paper presents a novel design of six-degree-of-freedom (6-DOF) magnetically levitated (maglev) positioner, where its translator and stator are implemented by four groups of 1-D Halbach permanent-magnet (PM) arrays and a set of square coils, respectively. By controlling the eight-phase square coil array underneath the Halbach PM arrays, the translator can achieve 6-DOF motion. The merits of the proposed design are mainly threefold. First, this design is potential to deliver unlimited-stroke planar motion with high power efficiency if additional coil switching system is equipped. Second, multiple translators are allowed to operate simultaneously above the same square coil stator. Third, the proposed maglev system is less complex in regard to the commutation law and the phase number of coils. Furthermore, in this paper, an analytical modeling approach is established to accurately predict the Lorentz force generated by the square coil with the 1-D Halbach PM array by considering the corner region, and the proposed modeling approach can be extended easily to apply on other coil designs such as the circular coil, etc. The proposed force model is evaluated experimentally, and the results show that the approach is accurate in both single- and multiple-coil cases. Finally, a prototype of the proposed maglev positioner is fabricated to demonstrate its 6-DOF motion ability. Experimental results show that the root-mean-square error of the implemented maglev prototype is around 50 nm in planar motion, and its velocity can achieve up to 100 mm/s.

Integrated Servo-Mechanical Design of a Fine Stage for a Coarse/Fine Dual-Stage Positioning System

Traditionally, the coarse and fine mechanical stages within a dual-stage positioning system are designed separately without consideration about their control performance in dual-stage integration. In this paper, a flexure-based Lorentz motor fine stage is designed concurrently with a simple PID controller to perform the dual-stage positioning, based on the existing coarse stage. The design of fine stage is carried out using a proposed integrated servo-mechanical design approach, where various specifications are considered and formulated as constraints in an optimization problem. Through the approach, both the plant modal parameters and controller parameters of fine stage are concurrently solved. It demonstrates that through suitable mechanical plant design, the fine stage can fulfill various control specifications by only using a simple PID controller, e.g., to compensate sensitivity peak, maintain stability, etc. Meanwhile, the proposed design approach also ensures certain open-loop positioning performance and the decoupling property of coarse/fine stages. The prototype of designed fine stage is fabricated, and experimental investigation indicates that the sensitivity peak is effectively reduced from 14.5 dB of coarse stage to 7.1 dB in the dual-stage system, and the fine stage is able to achieve submicrometer accuracy. The maximal tracking error is also reduced significantly from about 20 μm via the coarse stage to less than 2 μm through dual-stage positioning.

Finite element analysis of PMMA pattern formation during hot embossing process

Hot embossing process for thermoplastic polymers is one of the manufacturing technologies for microfluidics and optical components. It combines both micro-scale resolution and high throughput. This is a thermal process where a rigid stamp is pressed onto a polymer substrate so that micro-sized features or patterns can be replicated. PolyMethyl-MethAcrylate (PMMA) is one of the important engineering materials for this process; however, its nonlinear relationship between temperature and elastic-plastic behaviour, until now, has not been very well understood. This paper explores the development and use of finite element simulations to study how PMMA substrate would behave during hot embossing. This is achieved by converting stress-strain-temperature experimental data points into a mathematical form, matrix representation, without losing any salient behaviours of the PMMA material. The simulation results showed the flow behaviour of PMMA inside the mould during hot embossing process. This may assist future improvement of manufacturing quality and production throughput. Hot embossing experiments were also conducted and the results obtained were compared with the simulated ones. Although there was discrepancy between the two results, the current work laid path for future development and improvement.

Principle and Modeling of a Novel Moving Coil Linear-Rotary Electromagnetic Actuator

This paper presents a novel electromagnetic actuator that adopts an air-core coil mover to deliver decoupled linear and rotary motions. It uses light-weight moving coil to achieve high speed and dynamic response, and single-phase Lorentz-force driving scheme to realize direct and noncommutation actuation. To overcome the low thrust force of such driving scheme, unique magnetic circuits are used to enhance the thrust force and torque of the proposed actuator. Closed-form analytical solutions for modeling the magnetic field within the coil operating regions of these unique magnetic circuits are presented together with the complete thermal analyses. A prototype was developed and it delivers 10 mm stroke and 90° angular displacement. Using commercially available drivers, it achieved a high throughput of 8000 units/h with 20 μm, and 0.66° tracking accuracy.

Millimeters-Stroke Nanopositioning Actuator With High Positioning and Thermal Stability

This paper presented the design and modeling of a novel nanopositioning actuator that delivers millimeters stroke with high positioning and thermal stability. This actuator comprises a unique electromagnetic driving module (EDM) articulated from a segmented dual-magnet (DM) configuration, and flexurebased supporting bearings realized via a flexible membrane concept. In this paper, the fundamental insights on how to design and model the proposed segmented DM configuration are presented in detail. The remainder of this paper focuses on the thermal modeling of the unique EDM and the stiffness modeling of the unconventional flexure-based bearings. Subsequently, all theoretical models are evaluated through experimental investigations conducted via a developed prototype. The prototype also achieved an average positioning stability of ±10 nm with a thermal stability of ±0.1°C throughout a traveling range of 2 mm (±1 mm). Such actuator is useful for applications where direct feedback on the end effector is impossible.

A hybrid topological and structural optimization method to design a 3-DOF planar motion compliant mechanism

This paper proposes a novel design methodology to synthesize flexure-based parallel manipulators (FPM) for high precision micro/nano-scale manipulation. Unlike traditional synthesis methods, the proposed method uses a structural optimization algorithm that is independent of human intuition, to synthesize compliant joints with optimal stiffness characteristics. This algorithm is able to evolve the topology and shape of the compliant joints. Based on finite element analysis, the synthesized compliant joints are able to achieve better stiffness characteristics than the traditional compliant joints. This allows the synthesized joints to achieve a large deflection range while maintaining their capabilities to resist external wrenches in the non-actuating directions. A planar motion FPM with a workspace of 4 mm2 × 2° is formed by assembling the optimal compliant joints. The actuating compliance of the joints and FPM are validated by experiments and their deviation between the experimental results and the simulation prediction are within 10% and 18% respectively.