Modular robotics holds immense potential for space exploration, where reliability, repairability, and reusability are critical for cost-effective missions. Coordination between heterogeneous units is paramount for precision tasks -- whether in manipulation, legged locomotion, or multi-robot interaction. Such modular systems introduce challenges far exceeding those in monolithic robot architectures. This study presents a robust method for synchronizing the trajectories of multiple heterogeneous actuators, adapting dynamically to system variations with minimal system knowledge. This design makes it inherently robot-agnostic, thus highly suited for modularity. To ensure smooth trajectory adherence, the multidimensional state is constrained within a hypersphere representing the allowable deviation. The distance metric can be adapted hence, depending on the task and system under control, deformation of the constraint region is possible. This approach is compatible with a wide range of robotic platforms and serves as a core interface for Motion-Stack, our new open-source universal framework for limb coordination (available at https://github.com/2lian/Motion-Stack ). The method is validated by synchronizing the end-effectors of six highly heterogeneous robotic limbs, evaluating both trajectory adherence and recovery from significant external disturbances.

While it is expected to build robotic limbs with multiple degrees of freedom (DoF) inspired by nature, a single DoF design remains fundamental, providing benefits that include, but are not limited to, simplicity, robustness, cost-effectiveness, and efficiency. Mechanisms, especially those with multiple links and revolute joints connected in closed loops, play an enabling factor in introducing motion diversity for 1-DoF systems, which are usually constrained by self-collision during a full-cycle range of motion. This study presents a novel computational approach to designing one-degree-of-freedom (1-DoF) overconstrained robotic limbs for a desired spatial trajectory, while achieving energy-efficient, self-collision-free motion in full-cycle rotations. Firstly, we present the geometric optimization problem of linkage-based robotic limbs in a generalized formulation for self-collision-free design. Next, we formulate the spatial trajectory generation problem with the overconstrained linkages by optimizing the similarity and dynamic-related metrics. We further optimize the geometric shape of the overconstrained linkage to ensure smooth and collision-free motion driven by a single actuator. We validated our proposed method through various experiments, including personalized automata and bio-inspired hexapod robots. The resulting hexapod robot, featuring overconstrained robotic limbs, demonstrated outstanding energy efficiency during forward walking.

Supernumerary Robotic Limbs (SRLs) can enhance human capability within close proximity. However, as a wearable device, the generated moment from its operation acts on the human body as an external torque. When the moments increase, more muscle units are activated for balancing, and it can result in reduced muscular null space. Therefore, this paper suggests a concept of a motion planning layer that reduces the generated moment for enhanced Human-Robot Interaction. It modifies given trajectories with desirable angular acceleration and position deviation limits. Its performance to reduce the moment is demonstrated through the simulation, which uses simplified human and robotic system models.

A Robot Simulation Environment for Virtual Reality Enhanced Underwater Manipulation and Seabed Intervention T asks* Sumey El-M uft u 1 and Berke G ur 2 Abstract -- This paper presents the (MARUN) 2 underwater robotic simulator . The simulator architecture enables seamless integration with the ROS-based mission software and web-based user interface of URSULA, a squid inspired biomimetic robot designed for dexterous underwater manipulation and seabed intervention tasks. Utilizing Unity as the simulation environment enables the integration of virtual reality and haptic feedback capabilities for a more immersive and realistic experience for improved operator dexterity and experience. The utility of the simulator and improved dexterity provided by the VR module is validated through user experiments. I. INTRODUCTION Advancements in underwater robotic manipulation have paved the way for remote teleoperation and intervention in challenging aquatic environments. Several well-publicized recent developments have emphasized the increasing importance of dexterous underwater manipulation and intervention capabilities, in particular, for vehicles operating close to the seabed. In line with these developments, novel underwater robots specifically designed for such tasks have emerged over the recent years [1]-[3], including project URSULA.

Supernumerary robotic limbs (SRLs) are robotic structures integrated closely with the user's body, which augment human physical capabilities and necessitate seamless, naturalistic human-machine interaction. For effective assistance in physical tasks, enabling SRLs to hand over objects to humans is crucial. Yet, designing heuristic-based policies for robots is time-consuming, difficult to generalize across tasks, and results in less human-like motion. When trained with proper datasets, generative models are powerful alternatives for creating naturalistic handover motions. We introduce 3HANDS, a novel dataset of object handover interactions between a participant performing a daily activity and another participant enacting a hip-mounted SRL in a naturalistic manner. 3HANDS captures the unique characteristics of SRL interactions: operating in intimate personal space with asymmetric object origins, implicit motion synchronization, and the user's engagement in a primary task during the handover. To demonstrate the effectiveness of our dataset, we present three models: one that generates naturalistic handover trajectories, another that determines the appropriate handover endpoints, and a third that predicts the moment to initiate a handover. In a user study (N=10), we compare the handover interaction performed with our method compared to a baseline. The findings show that our method was perceived as significantly more natural, less physically demanding, and more comfortable.

While the animals' Fin-to-Limb evolution has been well-researched in biology, such morphological transformation remains under-adopted in the modern design of advanced robotic limbs. This paper investigates a novel class of overconstrained locomotion from a design and learning perspective inspired by evolutionary morphology, aiming to integrate the concept of `intelligent design under constraints' - hereafter referred to as constraint-driven design intelligence - in developing modern robotic limbs with superior energy efficiency. We propose a 3D-printable design of robotic limbs parametrically reconfigurable as a classical planar 4-bar linkage, an overconstrained Bennett linkage, and a spherical 4-bar linkage. These limbs adopt a co-axial actuation, identical to the modern legged robot platforms, with the added capability of upgrading into a wheel-legged system. Then, we implemented a large-scale, multi-terrain deep reinforcement learning framework to train these reconfigurable limbs for a comparative analysis of overconstrained locomotion in energy efficiency. Results show that the overconstrained limbs exhibit more efficient locomotion than planar limbs during forward and sideways walking over different terrains, including floors, slopes, and stairs, with or without random noises, by saving at least 22% mechanical energy in completing the traverse task, with the spherical limbs being the least efficient. It also achieves the highest average speed of 0.85 meters per second on flat terrain, which is 20% faster than the planar limbs. This study paves the path for an exciting direction for future research in overconstrained robotics leveraging evolutionary morphology and reconfigurable mechanism intelligence when combined with state-of-the-art methods in deep reinforcement learning.

Supernumerary robotic limbs (SRLs) gained increasing interest in the last years for their applicability as healthcare and assistive technologies. These devices can either support or augment human sensorimotor capabilities, allowing users to complete tasks that are more complex than those feasible for their natural limbs. However, for a successful coordination between natural and artificial limbs, intuitiveness of interaction and perception of autonomy are key enabling features, especially for people suffering from motor disorders and impairments. The development of suitable human-robot interfaces is thus fundamental to foster the adoption of SRLs. With this work, we describe how to control an extra degree of freedom by taking advantage of what we defined the Intrinsic Kinematic Null Space, i.e. the redundancy of the human kinematic chain involved in the ongoing task. Obtained results demonstrated that the proposed control strategy is effective for performing complex tasks with a supernumerary robotic finger, and that practice improves users' control ability.

This paper studies the design, modeling, and control of a novel quadruped, featuring overconstrained robotic limbs employing the Bennett linkage for motion and power transmission. The modular limb design allows the robot to morph into reptile- or mammal-inspired forms. In contrast to the prevailing focus on planar limbs, this research delves into the classical overconstrained linkages, which have strong theoretical foundations in advanced kinematics but limited engineering applications. The study showcases the morphological superiority of overconstrained robotic limbs that can transform into planar or spherical limbs, exemplifying the Bennett linkage. By conducting kinematic and dynamic modeling, we apply model predictive control to simulate a range of locomotion tasks, revealing that overconstrained limbs outperform planar designs in omni-directional tasks like forward trotting, lateral trotting, and turning on the spot when considering foothold distances. These findings highlight the biological distinctions in limb design between reptiles and mammals and represent the first documented instance of overconstrained robotic limbs outperforming planar designs in dynamic locomotion.

Recently, a team of researchers at University of Minnesota (UMN) built a robotic hand that can be controlled by the user's thoughts, via a brain chip. This may sound like a cool prop from some sci-fi flick, but, in reality, mind-controllable robotic limbs are becoming a life-changing technology for people with amputations, including injured soldiers. Most current generation robotic body parts are equipped with sensors that recognize tiny movements in the remaining shoulder, chest, leg, or hand muscles. If a user needs to move their prosthetic part, he or she has to first trigger some muscular or bodily movement. Learning and adjusting to such artificial body parts requires training, time, and patience -- moreover, a physically weak individual may find it difficult to use them.

The man sat still in the chair, staring intently at a piece of cake on the table in front of him. Flanking him were two giant robotic arms, each larger than his entire upper body. One held a knife, the other a fork. Move right hand forward to start," ordered a robotic voice. The man concentrated on moving his partially-paralyzed right arm forward. His wrist barely twitched, but the robotic right hand smoothly sailed forward, positioning the tip of the fork near the cake. Another slight movement of his left hand sent the knife forward. Several commands later, the man happily opened his mouth and devoured the bite-sized treat, cut to personal preference with help from his robotic avatars. It had been roughly 30 years since he was able to feed himself. Most of us don't think twice about using our two arms simultaneously--eating with a knife and fork, opening a bottle, hugging a loved one, lounging on the couch operating a video game controller. Coordination comes naturally to our brains.