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1. Momentum based Whole-Body Optimal Planning for a Single-Spherical-Wheeled Balancing Mobile Manipulator

   Shu, R. ; Hollis, R. ( October 2021 , IEEE International Conference on Robotics and Automation)

   null (Ed.)

   In this paper, we present a planning and control framework for dynamic, whole-body motions for dynamically stable shape-accelerating mobile manipulators. This class of robots are inherently unstable and require careful coordination between the upper and lower body to maintain balance while performing manipulation tasks. Solutions to this problem either use a complex, full-body nonlinear dynamic model of the robot or a highly simplified model of the robot. Here we explore the use of centroidal dynamics which has recently become a popular approach for designing balancing controllers for humanoid robots. We describe a framework where we first solve a trajectory optimization problem offline. We define balancing for a ballbot in terms of the centroidal momentum instead of other approaches like ZMP or angular velocity that are more commonly used. The generated motion is tracked using a PD- PID cascading balancing controller for the body and torque controller for the arms. We demonstrate that this framework is capable of generating dynamic motion plans and control inputs with examples on the CMU ballbot, a single-spherical-wheeled balancing mobile manipulator. 

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2. Generation of Time-Varying Feedback-Based Wheel Lock Attack Policies with Minimal Knowledge of the Traction Dynamics

   Mohammadi, Alireza ; Malik, Hafiz ( August 2023 , Intelligent Computing. SAI 2023. Lecture Notes in Networks and Systems)

   There are a variety of ways, such as reflashing of targeted electronic control units (ECUs) to hijacking the control of a fleet of wheeled mobile robots, through which adversaries can execute attacks on the actuators of mobile robots and autonomous vehicles. Independent of the source of cyber-physical infiltration, assessing the physical capabilities of an adversary who has made it to the last stage and is directly controlling the cyber-physical system actuators is of crucial importance. This paper investigates the potentials of an adversary who can directly manipulate the traction dynamics of wheeled mobile robots and autonomous vehicles but has a very limited knowledge of the physical parameters of the traction dynamics. It is shown that the adversary can exploit a new class of closed-loop attack policies that can be executed against the traction dynamics leading to wheel lock conditions. In comparison with a previously proposed wheel lock closed-loop attack policy, the attack policy in this paper relies on less computations and knowledge of the traction dynamics. Furthermore, the proposed attack policy generates smooth actuator input signals and is thus harder to detect. Simulation results using various tire-ground interaction conditions demonstrate the effectiveness of the proposed wheel lock attack policy. 

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3. Insect-scale jumping robots enabled by a dynamic buckling cascade

   https://doi.org/10.1073/pnas.2210651120  

   Wang, Yuzhe ; Wang, Qiong ; Liu, Mingchao ; Qin, Yimeng ; Cheng, Liuyang ; Bolmin, Ophelia ; Alleyne, Marianne ; Wissa, Aimy ; Baughman, Ray H. ; Vella, Dominic ; et al ( January 2023 , Proceedings of the National Academy of Sciences)

   Millions of years of evolution have allowed animals to develop unusual locomotion capabilities. A striking example is the legless-jumping of click beetles and trap-jaw ants, which jump more than 10 times their body length. Their delicate musculoskeletal system amplifies their muscles’ power. It is challenging to engineer insect-scale jumpers that use onboard actuators for both elastic energy storage and power amplification. Typical jumpers require a combination of at least two actuator mechanisms for elastic energy storage and jump triggering, leading to complex designs having many parts. Here, we report the new concept of dynamic buckling cascading, in which a single unidirectional actuation stroke drives an elastic beam through a sequence of energy-storing buckling modes automatically followed by spontaneous impulsive snapping at a critical triggering threshold. Integrating this cascade in a robot enables jumping with unidirectional muscles and power amplification (JUMPA). These JUMPA systems use a single lightweight mechanism for energy storage and release with a mass of 1.6 g and 2 cm length and jump up to 0.9 m, 40 times their body length. They jump repeatedly by reengaging the latch and using coiled artificial muscles to restore elastic energy. The robots reach their performance limits guided by theoretical analysis of snap-through and momentum exchange during ground collision. These jumpers reach the energy densities typical of the best macroscale jumping robots, while also matching the rapid escape times of jumping insects, thus demonstrating the path toward future applications including proximity sensing, inspection, and search and rescue. 

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4. A New Extensible Continuum Manipulator Using Flexible Parallel Mechanism and Rigid Motion Transmission

   https://doi.org/10.1115/DETC2020-22173  

   Liu, Yujiong ; Ben-Tzvi, Pinhas ( August 2020 , Proceedings of the ASME 2020 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. Volume 10: 44th Mechanisms and Robotics Conference (MR))

   null (Ed.)

   An extensible continuum manipulator (ECM) has specific advantages over its non-extensible counterparts. For instance, in certain applications, such as minimally invasive surgery or tube inspection, the base motion might be limited or disallowed. The additional extensibility provides the robot with more dexterous manipulation and larger workspace. Existing continuum robot designs achieve extensibility mainly through artificial muscle/pneumatic, extensible backbone, concentric tube, and base extension etc. This paper proposes a new way to achieve this additional motion degree of freedom by taking advantage of the rigid coupling hybrid mechanism concept and a flexible parallel mechanism. More specifically, a rack and pinion set is used to transmit the motion of the i-th subsegment to drive the (i+1)-th subsegment. A six-chain flexible parallel mechanism is used to generate the desired spatial bending and one extension mobility for each subsegment. This way, the new manipulator is able to achieve tail-like spatial bending and worm-like extension at the same time. A proof-of-concept prototype was integrated to verify the mobility of the new mechanism. Corresponding kinematic analyses are conducted to estimate the workspace and the motion non-uniformity.

    

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5. A New Extensible Continuum Manipulator Using Flexible Parallel Mechanism and Rigid Motion Transmission

   https://doi.org/10.1115/1.4050097  

   Liu, Yujiong ; Ben-Tzvi, Pinhas ( June 2021 , Journal of Mechanisms and Robotics)

   null (Ed.)

   Abstract An extensible continuum manipulator (ECM) has specific advantages over its nonextensible counterparts. For instance, in certain applications, such as minimally invasive surgery or pipe inspection, the base motion might be limited or disallowed. The additional extensibility provides the robot with more dexterous manipulation and a larger workspace. Existing continuum robot designs achieve extensibility mainly through artificial muscle/pneumatic, extensible backbone, concentric tube, and base extension, etc. This article proposes a new way to achieve this additional motion degree-of-freedom by taking advantage of the rigid coupling hybrid mechanism concept and a flexible parallel mechanism. More specifically, a rack and pinion set is used to transmit the motion of the i-th subsegment to drive the (i+1)-th subsegment. A six-chain flexible parallel mechanism is used to generate the desired spatial bending and one extension mobility for each subsegment. This way, the new manipulator can achieve tail-like spatial bending and worm-like extension at the same time. Simplified kinematic analyses are conducted to estimate the workspace and the motion nonuniformity. A proof-of-concept prototype was integrated to verify the mechanism’s mobility and to evaluate the kinematic model accuracy. The results show that the proposed mechanism achieved the desired mobilities with a maximum extension ratio of 32.2% and a maximum bending angle of 80 deg. 

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