David L. Trumper

This paper describes and implements a semi analytical modelling approach for an interior permanent magnet bearinglesss slice motor. The method is developed to estimate the cogging torque, motor torque and suspension force as a first optimization step for the design. All these parameters are important for the bearingless motor performance. Major nonlinearities associated with an IPM motor that affect these parameters are considered in modelling using different methods. A reluctance based circuit model is used to obtain the rotor and stator flux individually. This model contains the basic geometry information and the saturation of rotor bridges. The effect of stator slots are included by redistributing the airgap flux. When both stator induced and rotor induced flux are obtained in the airgap, the net flux is used to calculate the cogging and motor torque using energy method and force using stress tensor. The results are shown and discussed in the paper and the model is able to estimate the behavior closely. Despite some magnitude offset, the model can predict cogging torque trends and airgap harmonics, making it a useful design optimization tool.

Rheology describes the flow of fluids from food and plastics, to coatings, adhesives, and 3D printing inks, and is commonly denoted by viscosity alone as a simplification. While viscometers adequately probe Newtonian (constant) viscosity, most fluids have complex viscosity, requiring tests over multiple shear rates, and transient measurements. As a result, rheometers are typically large, expensive, and require additional infrastructure (e.g., gas lines), rendering them inaccessible for regular use by many individuals, small organizations, and educators. Here, we introduce a low-cost (under USD$200 bill of materials) Open Source Rheometer (OSR), constructed entirely from thermoplastic 3D printed components and off-the-shelf electromechanical components. A sample fluid rests in a cup while a micro stepping motor rotates a tool inside the cup, applying strain-controlled shear flow. A loadcell measures reaction torque exerted on the cup, and viscosity is calculated. To establish the measurement range, the viscosity of four Newtonian samples of 0.1-10 Pa.s were measured with the OSR and compared to benchmark values from a laboratory rheometer, showing under 23% error. Building on this, flow curves of three complex fluids - a microgel (hand sanitizer), foam (Gillette), and biopolymer solution (1% Xanthan Gum) - were measured with a similar error range. Stress relaxation, a transient test, was demonstrated on the biopolymer solution to extract the nonlinear damping function. We finally include detailed exposition of measurement windows, sources of error, and future design suggestions. The OSR cost is ∼1/25th that of commercially available devices with comparable minimum torque (200 µN.m), and provides a fully open-source platform for further innovation in customized rheometry.

In bearingless slice motors, the passive axial and tilt stiffnesses acting on the rotor are important for constraining rotor motions. This paper presents a novel approach to increasing these stiffnesses by using axial castellation. In this approach, the stator and rotor surfaces facing the working airgap are formed with teeth (castellation) in the axial direction. This tooth structure enhances magnetic energy variation with respect to axial and tilt motions, and consequently raises the stiffness in these degrees of freedom. The paper also shows that a further increase in these stiffnesses can be achieved by including small radially magnetized inter-tooth permanent magnets located in the slots between the teeth. To support this new design, a reluctance-based circuit model is created to elucidate the mechanisms contributing to enhanced passive stiffness. Finite element simulations are then used for the detailed motor design, and to optimized the passive stiffness via parametric studies. A representative design has been constructed to allow experimental measurement of the axial and tilt stiffnesses. These experimental results demonstrate a significant improvement in the passive stiffness for bearingless motors with the castellation, and with the use of inter-tooth magnets. This paper also discusses alternate motor modifications to enhance the passive stiffnesses.

This paper presents analytical modeling and design of a high-acceleration, low-vibration slotless double-sided linear motor with an arbitrary Halbach array for lithography machines used in semiconductor manufacturing technology. Amperian current and magnetic charge models of permanent magnets are integrated into a hybrid approach to develop comprehensive analytical modeling. Unlike conventional methods that treat magnets as sources for Poisson's equations, the solution is reduced to Laplace's equations, with magnets being represented as boundary conditions. The magnetic fields and potentials within distinct regions, along with machine quantities such as shear stress, force-angle characteristics, torque profile, attraction force, misalignment force, and back-EMF, are derived, comprehensively analyzed, and compared to FEM results for accuracy validation. In addition, two models based on Poisson's equations in terms of scalar and vector potentials are derived, compared, and analyzed. Finally, design optimization and sensitivity analysis of a linear stage for lithography applications are discussed.

This paper presents a radial position sensor for the bearingless slice motors with magnet free rotor. The sensor operates on the principle of eddy currents by interacting with a conductive target attached to the rotor. The conductive target varies the flux linkage and hence induced EMF in the sensor coils which is used to obtain the position measurements. The sensor is capable of measuring the radial degrees of freedom by accessing the rotor bottom surface only. The bottom surface has higher sensitivity for axial and tilt measurement and a lower sensitivity for radial measurement. The radial sensitivity depends on the axial gap between the rotor and target. The variation in airgap varies the flux linkages in the measurement coils and couples the tilt and axial motion to the radial measurement. The coupling of radial measurement to the tilt is overcome by sensor and target design [6]. The axial coupling is solved by adding another coil in the sensor to measure axial gap between sensor and target and the axial measurement is used to actively decouple the radial measurement. The construction and operation of the sensor is explained and the axial decoupling is verified using the simulation and experimental results.

High inductance actuators are found in many mechatronics systems and inverter requires higher voltage DC bus to drive these actuators with variable frequency and current magnitudes. Since the load is dominantly reactive, only a small current is required from the DC source to feed the active power of the load. In some applications, these actuators require AC and/or DC currents for the operation. In this paper, a control algorithm is proposed for a cascaded multilevel inverter with only one DC source to drive high inductance loads with AC and/or DC currents. It also offers the advantages of the multilevel inverter like multilevel voltage and low voltage rating switches. Multiple inverters can be added in series without DC source to get the desired voltage rating, but continuous active power rating is defined by the one inverter with DC source. The control system is developed to achieve the commanded AC and/or DC load current, to regulate the DC bus voltage of the inverter without DC source and manage the power sharing between the inverters during steady and transient operations. The experimental results are obtained to verify the inverter performance under various operational scenarios.

This paper describes a novel bearingless split tooth flux reversal motor with integrated centrifugal blood pump. This motor has a magnet-free rotor, and is capable of operating at up to 3000 rpm with up to 100 mNm torque. The motor also has 50 N radial force capability for centering the rotor. The motor rotor is 50 mm diameter, housed in a 170mm wide stator. The motor has a novel magnetic configuration wherein the force generation is independent of the rotor angle. This allows simple radial force generation using stator-fixed currents. The motor torque is generated using commutated two-phase currents. Finite element simulations are used to optimize the design in order to achieve sufficient radial force and motor torque, while minimizing cogging torque. The design also achieves an axial passive magnetic stiffness of 5.4 N/mm, which is the constraint on axial motions of the rotor. This paper includes mechanical design and fabrication details, as well as experimental closed loop levitation and speed control performance. With an integrated impeller, the rotor and the centrifugal pump are tested by pumping fluid in a closed circuit to obtain experimental pressure-flow curves with impeller-limited performance.

This article describes a position sensor with six degrees of freedom (DoF) measurement capability. This sensor is designed for the position sensing of the rotor in a bearingless slice motor to enable active control. The sensor is designed to fit entirely under the rotor and operates by accessing the rotor bottom surface only, enabling packaging of the pump on the top of the rotor. The sensor has two parts; both operate using eddy currents. One of these parts measures the two radial DoF of the rotor. The other part measures the axial, angular rotation and tip/tilt DoF. The sensor utilizes a conductive target fixed to the underside of the rotor. Motion of this target varies the magnetic fields, which can then be measured by the sensor as variation in either induced voltage or inductance value. The design and fabrication of the sensor along with the signal processing methods are presented in detail. The radial position measurements are the most critical for active levitation due to the small working gaps in these DoF, hence a resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt;1.2\ \mu \rm {m}$</tex-math></inline-formula> and bandwidth of 1 kHz is achieved. This article also describes the closed-loop behavior of a bearingless motor using this sensor.

The 2022 NASA BIG Idea Challenge invited teams to develop novel extreme lunar terrain mobility technologies in support of the Artemis program, setting only the constraint to not propose a wheeled robot. This paper proposes a platform for field-reconfigurable walking robots that can be tailored to multiple missions and even repaired in the field. Design exploration started with listing potential missions for walking robots, and took inspiration from animals to conceptualize four different locomotion strategies and associated novel robot forms. We then synthesized all ideas into our field-reconfigurable robot platform architecture, the Walking Oligomeric Robotic Mobility System (WORMS). The elements of WORMS include identical articulating Worm robots, simple Accessories, such as shoes and chassis or pallets, as well as more sophisticated Species Modules (such as the ‘Mapper’). With a variety of elements in hand, different animal-like robots can be rapidly assembled and dispatched to support many different mission profiles. Specialization of function is accomplished using a variety of modular Accessories and Species Modules, such as different shoes, an anchoring drill, or a winch-and-cable. Each known robot configuration requires only the needed hardware elements plus software, meaning that new robots can be transmitted to the Moon. The system is designed for ease of assembly, operations and maintenance by non-specialists. In our WORMS-1 proof of concept which is presented here, six Worms with large Apollo-like shoes serve as legs to traverse high-porosity and steeply inclined terrain in order to set up a charging and radio relay station for other rovers inside permanently shadowed regions. Different robot configurations, working alone or in swarms, could traverse other terrain types and perform different missions. WORMS is enabled by three key technologies: (1) the Worm robot itself; (2) the universal interface block (UIB) which is a common mating adapter for all mechanical, electrical and data connections between Worms, Accessories and Species Modules and (3) the ability to safely share electrical power between Worms. In the paper, we present the architecture, trade studies, test results and path-to-flight considerations to evolve the as-built proof of concept WORMS-1 from its current Technology Readiness Level (TRL) 4 into a future TRL 6 design. We also describe the methods and lessons learned from our step-by-step architecting process, which included brainstorming, concept generation and concept fusion into a versatile platform design. We propose that WORMS is a resilient, easily maintainable, low-cost, evolvable, flexible, future-proof and modular architecture for the rapid field assembly of robots to support extreme terrain access and lunar infrastructure development. WORMS can therefore support many of the needs of NASA and its commercial and industrial partners throughout the Artemis program and on to Mars and beyond.

A magnetic positioner is provided which is capable of providing long travel in two dimension and short travel in the remaining four dimensions. The positioner has a movable stage and a stator oriented adjacent and substantially parallel to this stage. At least three sets of first magnetic elements, which for preferred embodiments are winding sets capable of generating forces in two directions, are on the portion of the stator adjacent to the stage at any given time, and at least two second magnetic elements, which are magnet arrays for the preferred embodiment, are on the stage adjacent to the stator. At least one of the second magnetic elements overlaps multiple first magnetic elements for all positions of the stage relative to the stator, with one magnet overlapping multiple windings for one preferred embodiment of the invention and two magnets on the stage overlapping multiple windings on the stator for a second embodiment. The windings form a linear motor providing forces in both a corresponding long travel dimension and in a dimension perpendicular to both long travel dimensions.

A precision positioning system is provided which provides long travel in two of the linear dimensions, while using non-contact bearings for both a first subassembly which provides long travel in one of the linear dimension and a second subassembly which provides long travel in the second linear dimension. The first or upper subassembly is preferably a magnetic subassembly which, in addition to providing long travel, also compensates or positions in three rotary dimensions and in the third linear dimension. The second subassembly is preferably either an air bearing or magnetic subassembly and is normally used only to provide long travel. Angled surfaces may be provided for magnetic bearings and capacitive or other gap sensing probes may be mounted to the stage and ground flush with the bearing actuators to provide more precise gap measurements.

Electromagnet arrays which can provide selected field patterns in either two or three dimensions, and in particular, which can provide single-sided field patterns in two or three dimensions. These features are achieved by providing arrays which have current densities that vary in the windings both parallel to the array and in the direction of array thickness.