In this article, a new learning-based time-varying impedance controller is proposed and tested to facilitate an autonomous physical human-robot interaction (pHRI). Novel adaptation laws are ...formulated for online adjustment of robot impedance based on human behavior. Two other sets of update rules are defined for intelligent coping with the robot's structured and unstructured uncertainties. These rules ensure stability via Lyapunov's theorem and provide uniform ultimate boundedness (UUB) of the closed-loop system's response, without a need for HRI force/torque measurement. Accordingly, the convergence of response signals, including errors in tracking, online impedance learning, robot parameter adaptation, and controller gain variation, is proven to operate in a bounded region (compact set) in the presence of robot and human uncertainties and bounded disturbances. The performance of the developed intelligent impedance-varying control strategy is investigated through comprehensive experimental studies in a repetitive following task with a moving target.
This letter proposes a hybrid control methodology to achieve full body collision avoidance in anthropomorphic robot manipulators. The proposal improves classical motion planning algorithms by ...introducing a Deep Reinforcement Learning (DRL) approach trained ad hoc for performing obstacle avoidance, while achieving a reaching task in the operative space. More specifically, a switching mechanism is enabled whenever a condition of proximity to the obstacles is met, thus conferring to the dual-mode architecture a self-configuring capability in order to cope with objects unexpectedly invading the workspace. The proposal has been finally tested relying on a realistic robot manipulator simulated in a V-REP environment.
Control Barrier Functions With Circulation Inequalities Goncalves, Vinicius Mariano; Krishnamurthy, Prashanth; Tzes, Anthony ...
IEEE transactions on control systems technology,
07/2024, Letnik:
32, Številka:
4
Journal Article
Recenzirano
Control barrier functions (CBFs) when paired with quadratic programming (QP) offer an increasingly popular framework for control considering critical safety constraints. However, being closely ...related to artificial potential fields, they suffer from the classical stable spurious equilibrium point problem, in which the controller can fail to drive the system to the goal. The main contribution of this article is showing that this problem can be mitigated by introducing a circulation inequality as a constraint, which forces the system to explicitly circulate obstacles under some conditions. This circulation is introduced in the configuration space and is simple to implement once we have the CBF-constraint, adding a negligible complexity to the resulting optimization problem. Theoretical guarantees are provided for this framework, indicating, under appropriate conditions, the feasibility of the resulting optimization problem, continuity of the control input, characterization of the equilibrium points, a weak form of Lyapunov stability, and uniqueness of the equilibrium points. The provided experimental studies showcase the overall properties and applicability in different scenarios.
Achieving fast and agile swimming still remains extremely challenging for a self-propelled robotic fish due to the constraint of actuator's propulsion capability. In this article, we report an ...untethered bioinspired robotic fish, which combines a high-frequency oscillation and a compliant passive mechanism to realize fast swimming, high pitch maneuvers, and even the leaping motion. For pursuing the explosive propulsion of the robotic fish, we propose an actuation system with a powerful output and a compact structure. A dynamic model is established and indicates that the compliant joint is able to modulate the power transmitted to a caudal fin to affect its velocity in the return stroke for generating more peak thrust. The design is validated with extensive experimental results. Namely, the robotic fish can surprisingly reach up to a speed of 3.8 body lengths per second (BL/s). Compared to the case with a rigid joint, dramatic improvements, involving a speed of 1.2 BL/s and a swimming distance of 141.2 m (70.6%), have been obtained, which reveal that besides the high-frequency oscillation, the compliant passive mechanism is also of great significance to perform high-speed swimming. Additionally, the robotic fish demonstrates its high pitch maneuvers by performing an agile front flip motion with a radius of 0.4 BL and an average angular velocity of 439<inline-formula><tex-math notation="LaTeX">^\circ</tex-math></inline-formula>/s. Most importantly, with a simple control strategy, our robotic fish can remarkably leap out of water completely. Results from this study provide significant insights into the innovative designs of next-generation robotic fishes, which require high speed and maneuverability.
One photothermal responsive and self-healing nanocomposite hydrogel serves as flowing valve by stimulating the bilayer and “hinge-type” hydrogel composites.
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•GO-based nanocomposite ...hydrogels with PNIPAM and PDMAA possess good mechanical property.•One bilayer-type photothermal responsive nanocomposite hydrogel serves as controllable valve.•The “hinge-type” hydrogel presents repeatable and obvious deformation under NIR irradiation.
Light-driven hydrogel actuators show increasing advantages in flowing control, soft robot and microreactor. Herein, we proposed one photothermal responsive and self-healing nanocomposite hydrogel containing poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-dimethylacrylamide) (PDMAA) to serve as light-driven valves by stimulating the bilayer and “hinge-type” hydrogel composites. With graphene oxide (GO) and clay, the hydrogels possess good mechanical property and near-infrared (NIR)-driven self-healing behavior because of the non-covalent bonding between the polymer chains and clay. Such bilayer-type hydrogels present local folding with the guide of NIR laser and can realize solid/liquid transportation and controllable trigger of the reaction. We proposed the integration of inhomogeneous structure via NIR light healing to form “hinge-type” hydrogel, consisting of one bilayer hydrogel as the “hinge” section and two PDMAA hydrogels as the “blade” section. The “hinge-type” hydrogel presents repeatable and obvious deformation with irradiation. Thus, the photothermal responsive and self-healing hydrogel may have potential applications in soft actuator, microfluidic, and microreactor.
Accounting for wheel–terrain interaction is crucial for navigation and traction control of mobile robots in outdoor environments and rough terrains. Wheel slip is one of the surface hazards that ...needs to be detected to mitigate against the risk of losing the robot's controllability or mission failure occurring. The open problems in the Terramechanics field addressed are (1) the need for in situ wheel‐slippage estimation in harsh environments using low‐cost/power and easy to integrate sensors, and (2) removing the need for prior information of the soil, which is not always available. This paper presents a novel slip estimation method that utilizes only two proprioceptive sensors (IMU and wheel encoder) to estimate the wheel slip using deep learning methods. It is experimentally shown to be real‐world feasible in outdoor, uneven terrains without prior soil information assumptions. Comparison with previously used machine learning algorithms for continuous and discrete slip estimation problems show more than 9% and 14% improvement in estimation performance, respectively.
Combining aerial and continuum robots harnesses both their flexibility and manoeuvrability to potentially perform dangerous maintenance tasks. However, such systems require heavy payloads to interact ...with its environment. An aerial-ground tethered tendon-driven continuum robot is thus proposed to tackle the limitations of on-board payload aerial systems and the underactuation of multirotors. Due to the natural limitation on the tendons used in the implementation of aerial ground tethered continuum robots, we explore the use of hybrid polynomial and parallel routes to achieve desired workspace profiles, while providing intuition on choosing suitable tendon routes. In this work, we leverage on geometrically exact methods to derive the differential kinematics of the aerial continuum robot using actuation sensors particularly for polynomial tendon routes. We demonstrate that both position and orientation can be controlled using a single stage continuum robot with hybrid tendon routing. Finally, a simple manoeuvre is executed by the aerial continuum robot prototype to validate the proposed proof of concept.
Soft dielectric elastomer actuators (SDEAs) have manifested tremendous potentials in the field of soft robots. However, the tracking control of the SDEA still confronts enormous challenges because of ...its complicated nonlinear characteristics. In this paper, a nonlinear proportional-integral-derivative (NPID) controller is devised to fulfil the tracking control of the SDEA. A dynamic model of the SDEA is established, and then applied to construct a simulation system to coarsely tune the parameters of the NPID controller based on the iterative optimisation algorithm. Subsequently, according to the results of the coarse tuning, the parameters of the NPID controller are finely tuned in practical experiments. Finally, the NPID controller of the SDEA is proved to be effective via several tracking control experiments with different reference trajectories.
Properly designing a system to exhibit favorable natural dynamics can greatly simplify designing or learning the control policy. However, it is still unclear what constitutes favorable natural ...dynamics and how to quantify its effect. Most studies of simple walking and running models have focused on the basins of attraction of passive limit cycles and the notion of self-stability. We instead emphasize the importance of stepping beyond basins of attraction. In this paper, we show an approach based on viability theory to quantify robust sets in state-action space. These sets are valid for the family of all robust control policies, which allows us to quantify the robustness inherent to the natural dynamics before designing the control policy or specifying a control objective. We illustrate our formulation using spring-mass models, simple low-dimensional models of running systems. We then show an example application by optimizing robustness of a simulated planar monoped, using a gradient-free optimization scheme. Both case studies result in a nonlinear effective stiffness providing more robustness.
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