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1. Design, Characterization and Control of a Whole-body Grasping and Perching (WHOPPEr) Drone

   https://doi.org/10.1109/IROS55552.2023.10341722  

   Tao, Weijia; Patnaik, Karishma; Chen, Fuchen; Kumar, Yogesh; Zhang, Wenlong (December 2023, 2023 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS))

   Flying robots can exploit perching abilities to position themselves on strategically-chosen locations and monitor the areas of interest from a critical vantage point. Moreover, they can significantly extend their battery life by turning off the propulsion systems when carrying out a surveillance mission. However, unknown disturbances arise from the physical interactions between the robot and the object, making it challenging to stabilize the robot during perching. In this paper, we present a Whole-body Grasping and Perching (WHOPPEr) Drone, which is capable of fast and robust perching by utilizing its entire body as the grasper in lieu of an add-on grasper. We first present the design concept, parameter selection and characterization of the novel whole-body grasping drone. Next, we analyze the grasping ability of the morphing chassis and present an aerodynamic analysis for the effect of motor thrust on the compliant arm. We finally demonstrate, via real-time experiments, the performance of WHOPPEr in autonomous perching and payload delivery tasks. 

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2. Investigation of Resistive Forces in Variable Recruitment Fluidic Artificial Muscle Bundles

   Kim, Jeong Yong; Mazzoleni, Nicholas; Bryant, Matthew (January 2020, Proceedings of the 38th IMAC, A Conference and Exposition on Structural Dynamics 2020)

   This paper experimentally investigates the mechanical behavior of inactive and low-pressure fluidic artificial muscle (FAM) actuators under applied axial load. In most cases, the active characteristics of an actuator are of interest because they provide valuable information about its force-strain relationship. However, a system of actuators requires attention to the interaction between individual units. One such configuration is a bundle of McKibben artificial muscle actuators arranged in parallel and used for load-adaptive variable recruitment. This bio-inspired actuator bundle sequentially increases the number of actuators activated depending on the load required, which is analogous to how motor units are recruited in a mammalian muscle tissue. While using the minimum number of actuators allows the bundle to operate efficiently, the resistive force of inactive elements acts against total bundle contraction due to their inherent stiffness. In addition, when the bundle transitions between recruitment levels, motor units for a given recruitment level may be gradually pressurized; these low-pressure motor units can also cause resistive forces. Experiments were conducted to characterize the complex interaction between the bladder and braided mesh that cause the resistive force and deflection of inactive and low-pressure elements. Based on observations made from experiments, the paper proposes the initial criteria for developing a model of the resistive forces of a McKibben actuator, both individually, and within the context of a variable recruitment bundle. 

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3. Analysis of Force Capacity in Magnetic Bearings and Bearingless Motors from the Perspective of Airgap Space Harmonic Fields

   Khamitov, Anvar; Severson, Eric L (July 2023, 18th International Symposium on Magnetic Bearings)

   This paper studies the force creation capabilities of active magnetic bearings (AMBs) and bearingless motors from the perspective of multiple airgap space harmonics/pole-pairs. This approach is analytic-based and is useful in explaining the underlying physics of the machine and conducting force capacity analysis for different numbers of phases/poles. The presented per unit (p.u.) model makes the force capacity results applicable to any motor dimensions and peak airgap field value. An explanation of the force capacity in bearingless motors is provided when only two harmonics are controlled (which is the typical approach in bearingless motor literature) and the relationship between torque, force, and magnetizing field values is identified. Using this relationship, optimal magnetizing field values for maximum torque-force capability are identified, which is useful to consider when designing a bearingless motor. This paper extends the force capacity analysis to bearingless motors with multiple (more than two) controllable space harmonics and proposes that force enhancement can be achieved through the control of the magnitudes and angles of these harmonics. Results show that potential force enhancement of over 40% in bearingless machines can be achieved when controlling four airgap harmonics as opposed to two harmonics. These results suggest that being able to control multiple harmonics can yield high performance designs. 

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4. Smart Coils for Mitigation of Motor Reflected Overvoltage Fed by SiC Drives

   https://doi.org/10.1109/APEC43580.2023.10131221  

   Fard, Majid T.; He, JiangBiao; Sadoughi, Milad; Mirafzal, Behrooz; Fateh, Fariba (March 2023, IEEE)

   High dv/dt from the emerging SiC variable-frequency drives can easily induce overvoltage across the motor stator winding terminals, especially for long-cable-connected and high-voltage motor-drive systems. Due to the fast switching speed and surge impedance mismatch between cables and motors, this overvoltage can be two times or even higher than the DC-bus voltage of the inverter, resulting in motor insulation degradation or irreversible breakdown. The most common solution to mitigate such overvoltage is to install a dv/dt or a sinewave filter at the output of the drive, which decreases the efficiency and power density of the system. Among different stator coils, the first one (close to the drive side) is the most susceptible to insulation breakdown since it experiences higher overvoltage than the others due to the nonlinear distribution of the reflected surge voltages. In this paper, an innovative high-efficiency ultracompact mitigation solution is introduced, which is a tiny auxiliary circuit embedded inside the motor stator (or at the motor terminal box), specifically across the first few coils of each phase (i.e., smart coils). The proposed smart coil circuit effectively mitigates the surge overvoltage, which can be scalable to any type of motor-drive systems, regardless of cable length and semiconductor rise time. The proposed solution can dramatically improve the reliability, efficiency, and power density of motor-drive systems. 

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5. Analysis and Design of Multi-Phase Combined Windings for Bearingless Machines

   https://doi.org/10.1109/ECCE47101.2021.9595992  

   Khamitov, Anvar; Severson, Eric L. (October 2021, 2021 IEEE Energy Conversion Congress and Exposition (ECCE))

   A multi-phase (MP) combined winding design procedure for bearingless machines is proposed and developed. Using this procedure, new bearingless motor windings can be designed and conventional motor designs with MP windings can be transformed into bearingless motors by simply modifying the phase currents. The resulting MP winding is excited by two current components – one responsible for torque creation and another for suspension force creation. By applying the appropriate Clarke transformation, independent control of force and torque can be achieved. Although there are numerous papers in the literature studying bearingless machines with MP windings and their advantages, this is the first paper to provide a formal design procedure that can be applied to any MP winding configuration. The proposed approach can be used to realize popular winding designs, including concentrated- and fractional-slot windings. The paper uses the Maxwell stress tensor to formulate the force/torque model for the MP combined winding and uses the results to derive design requirements for the MP combined winding. A sequence of winding design steps is proposed and used to design example MP combined windings. 

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