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1. ArUco based Reference Shaping for Real-time Precision Motion Control for Suspended Payloads

   Vexler, David; Stein, Adrian; Singh, Tarunraj (July 2024, IEEE Xplore)

   This work presents a real-time time-delay filtering approach for reference shaping of high precision motion control of vibratory systems. The motion of the system is initiated with a judicious (arbitrary) step command and the acquired motion data is used to estimate the modal parameters in realtime.The modal data is subsequently used to synthesize the subsequent step commands to mitigate the residual vibrations. The proposed control algorithm is tested on a gantry crane structure with a suspended payload. Our method estimates the system parameters based on computer vision while tracking an ArUco fiducial marker which is integral with the payload. Computational efficiency is ensured by using C++ to deploy the algorithm. The goal is to minimize the residual energy at the terminal displacement for rest-to-rest maneuvers of a suspended payload with unknown dynamics. An inertial measurement unit is used to track the pendular angular velocity at the end of the maneuver and is not used in the model identification process. 

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2. Control Design for an Aerial Manipulator for Pick-and-Place Tasks

   https://doi.org/10.2514/6.2019-1291  

   Sun, Donglei; Wan, Neng; Dai, Weichen; Zhang, Yu; Hovakimyan, Naira (January 2019, AIAA SciTech Forum)

   This paper presents a control architecture for an aerial manipulator operating in indoor environments. The objective is to provide a viable solution to the growing need for indoor assistive technology. The study tries to address the problem of payload pick-and-place with unknown mass. The control structure consists of i) a baseline pitch angle tracking controller that provides satisfactory performance for the quadrotor without a payload; ii) an adaptive augmentation that compensates for the disturbance in the rotational dynamics due to the unknown payload; iii) a horizontal position tracking controller that generates the pitch angle command; iv) a baseline vertical position tracking controller; and v) another adaptive augmentation controller that compensates for the disturbance in the vertical motion from the pick-and-place of the unknown payload. Since the robotic manipulator operates in the vertical plane of symmetry of the quadrotor, the control design is considered for the motion only in this plane. The controller is verified in a simulation environment. 

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3. On avoiding Moving Objects for indoor autonomous quadrotors

   https://doi.org/10.1109/COASE.2016.7743447  

   Shin, Donghyeok; Kim, Junwhan; Yu, Byunggu; Jeong, Dong H. (August 2016, 2016 IEEE International Conference on Automation Science and Engineering (CASE),)

   A mini quadrotor can be used in many applications, such as indoor airborne surveillance, payload delivery, and warehouse monitoring. In these applications, vision-based autonomous navigation is one of the most interesting research topics because precise navigation can be implemented based on vision analysis. However, pixel-based vision analysis approaches require a high-powered computer, which is inappropriate to be attached to a small indoor quadrotor. This paper proposes a method called the Motion-vector-based Moving Objects Detection. This method detects and avoids obstacles using stereo motion vectors instead of individual pixels, thereby substantially reducing the data processing requirement. Although this method can also be used in the avoidance of stationary obstacles by taking into account the ego-motion of the quadrotor, this paper primarily focuses on providing our empirical verification on the real-time avoidance of moving objects. 

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4. Development of a Humanoid Dual Arm System for a Single Spherical Wheeled Balancing Mobile Robot

   https://doi.org/10.1109/Humanoids43949.2019.9034999  

   Shu, Roberto; Hollis, Ralph (October 2019, International Conference on Humanoid Robots (Humanoids))

   This paper presents a new 14-DoF dual manipulation system for the CMU ballbot. The result is a new type of robot that combines smooth omnidirectional motion with the capability to interact with objects and the environment through manipulation. The system includes a pair of 7-DoF arms. Each arm weighs 12.9 kg, with a reach of 0.815 m, and a maximum payload of 10 kg at full extension. The ballbot's arms have a larger payload-to-weight ratio than commercial cobot arms with similar or greater payload. Design features include highly integrated sensor-actuator-control units in each joint, lightweight exoskeleton structure, and anthropomorphic kinematics. The integration of the arms with the CMU ballbot is demonstrated through heavy payload carrying and balancing experiments. 

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5. Searching for structural predictors of plasticity in dense active packings

   https://doi.org/10.1039/D1SM01675J  

   Giannini, Julia A.; Stanifer, Ethan M.; Manning, M. Lisa (February 2022, Soft Matter)

   In amorphous solids subject to shear or thermal excitation, so-called structural indicators have been developed that predict locations of future plasticity or particle rearrangements. An open question is whether similar tools can be used in dense active materials, but a challenge is that under most circumstances, active systems do not possess well-defined solid reference configurations. We develop a computational model for a dense active crowd attracted to a point of interest, which does permit a mechanically stable reference state in the limit of infinitely persistent motion. Previous work on a similar system suggested that the collective motion of crowds could be predicted by inverting a matrix of time-averaged two-particle correlation functions. Seeking a first-principles understanding of this result, we demonstrate that this active matter system maps directly onto a granular packing in the presence of an external potential, and extend an existing structural indicator based on linear response to predict plasticity in the presence of noisy dynamics. We find that the strong pressure gradient necessitated by the directed activity, as well as a self-generated free boundary, strongly impact the linear response of the system. In low-pressure regions the linear-response-based indicator is predictive, but it does not work well in the high-pressure interior of our active packings. Our findings motivate and inform future work that could better formulate structure-dynamics predictions in systems with strong pressure gradients. 

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