Virtual Model Control (VMC) is an approach to design a controller for force-controlled robots in complex uncertain environments. While this method was primarily investigated for legged robot locomotion in the past, it can be more generally applicable to other types of robotic systems. This paper investigates the VMC framework for reaching tasks in a force-controlled robotic arm. We propose six different approaches to designing virtual models in order to achieve reaching tasks in environments with obstacles and uncertainties. A force-controlled 8 degree-of-freedom humanoid robot was used to validate the proposed approach in the real world. We conducted three experiments to test the performance of VMC controllers in terms of predictability, sensitivity to external force, and adaptability against known and unknown obstacles. Experimental analyses show that, even though the proposed approach needs to sacrifice accuracy and trajectory optimality, it enables us to design complex reaching motions under uncertainties, in an intuitive and extendable manner.
Figures & tables
Fig. 1 : (a)-(f) Virtual mechanisms designed for satisfying different planning goals.
Fig. 2 : Experimental platform: Sciurus17 robot.
Fig. 3 : Control architecture.
Fig. 4 : Simple reaching with different stiffness . Black line: k=15 . Blue line : k=45 . Red dot : starting position. Green dot : goal. Top: trajectory of the end effector on the x-y plane. Bottom: time-evolution of the reach error.
Fig. 5 : Moving-reference reaching with different speeds . Black line: 0.1 m/s. Blue line : 0.5 m/s. Red dot : starting position. Green dot : goal. Top: trajectory of the end effector on the x-y plane. Bottom: time-evolution of reference and actual distances from the target.
Fig. 6 : Obstacle and multi-obstacle avoidance with known obstacles . Black line: robot trajectory. Blue area : cylindrical obstacles. Red dot : starting position. Green dots : ending positions. Green line : reference trajectory, 0.1 m/s. The arrows show the virtual mechanism forces. Blue arrow : force generated by obstacle avoidance virtual model. Green arrow : force generated by moving-reference reaching virtual model.
Fig. 7 : Simple reaching under undetected human interaction . The end effector is blocked by a person at x=40 cm. Black line: ( 2 ), k=15 . Blue line : ( 2 ), k=45 . Red line : inverse kinematics. Green dot : goal for VMC. Red dot : goal for inverse kinematics (which is different from VMC due to its inability to reach further using torso). Top: trajectory of the end effector on the x-y plane. Bottom: time-evolution of the reach error.
Fig. 8 : Force exerted by end effector during obstruction . Black: ( 2 ), k=15 . Blue : ( 2 ), k=45 . Red : inverse kinematics.
Fig. 9 : Moving-reference reaching under undetected obstacle . Top snapshots: 0 s - contact established, 1.5 s - sliding, 3.5 s - obstacle cleared, 4 s - goal reached. Bottom figure: perturbed end effector trajectory. Black - trajectory, red dot - starting position, green dot - goal, blue - acrylic plate.
The exploration of confined, occluded, and partially known spaces poses significant challenges in robotic manipulation. The overall pose of the robotic arm must be carefully controlled to respect tight geometric constraints while avoiding newly discovered obstacles. We address this problem by proposing an active exploration approach for redundant robotic arms with an eye-in-hand camera configuration. Our approach navigates and acquires information in real-time based on a novel scoring method that directly selects a target voxel from the unexplored space using the robot's current state and expected information gain. To move the robot safely toward the target voxel, we utilize Virtual Model Control, which guarantees compliance and enables whole-body reactive obstacle avoidance without the need for path replanning. Simulated and real-robot experiments in both confined and open environments demonstrate the effectiveness of our approach, achieving over 90% mapping coverage across all tested environments in under 120 seconds without colliding with obstacles.
Alessio Canzolino, Omar Faris, Alessandro De Blasi +1
Department of Electrical, Electronic, and Information Engineering “Guglielmo Marconi”, University of Bologna, Italy · Department of Engineering, University of Cambridge, UK.
Bimanual mobile manipulation requires a seamless integration between high-level semantic reasoning and safe, compliant physical interaction - a challenge that end-to-end models approach opaquely and classical controllers lack the context to address. This paper presents GenerativeMPC, a hierarchical cyber-physical framework that explicitly bridges semantic scene understanding with physical control parameters for bimanual mobile manipulators. The system utilizes a Vision-Language Model with Retrieval-Augmented Generation (VLM-RAG) to translate visual and linguistic context into grounded control constraints, specifically outputting dynamic velocity limits and safety margins for a Whole-Body Model Predictive Controller (MPC). Simultaneously, the VLM-RAG module modulates virtual stiffness and damping gains for a unified impedance-admittance controller, enabling context-aware compliance during human-robot interaction. Our framework leverages an experience-driven vector database to ensure consistent parameter grounding without retraining. Experimental results in MuJoCo, IsaacSim, and on a physical bimanual platform confirm a 60% speed reduction near humans and safe, socially-aware navigation and manipulation through semantic-to-physical parameter grounding. This work advances the field of human-centric cybernetics by grounding large-scale cognitive models into predictable, high-frequency physical control loops.
Marcelino Julio Fernando, Miguel Altamirano Cabrera, Jeffrin Sam +3
Intelligent Space Robotics Laboratory, Skolkovo Institute of Science and Technology, Moscow, Russia
In robot-assisted laparoscopic minimally invasive surgery (MIS), accurate enforcement of the remote center of motion (RCM) constraint is critical for safe and stable automatic field-of-view (FoV) adjustment. Although control-based RCM strategies are widely adopted due to their flexibility and cost-effectiveness, systematic comparison of different RCM formulations and image-based visual servoing (IBVS) frameworks remains challenging due to the lack of a unified and reproducible benchmark. This paper presents an open-source simulation framework integrating three representative RCM modeling approaches and six IBVS-based control architectures within a unified velocity-level formulation, enabling controlled and consistent evaluation. Through structured case studies, the framework reveals key structural sensitivities arising from modeling and controller interactions, including the impact of tangent-plane definition, constraint dimensionality, open- versus closed-loop enforcement, and robustness near kinematic singularities. All resources are released and demostrations are provided in the supplementary video, providing a reproducible foundation for RCM-constrained visual servoing research.
Jing Zhang, Mengtang Li
School of Intelligent Systems Engineering, Shenzhen Campus of Sun Yat-sen University, Shenzhen, China