Object re-identification and tracking lay the foundation for various computer vision and robotics applications. In this study, we propose a method for personalizing a neural network to enhance and continuously adapt the re-identification of a specific target. Employing an unsupervised continual learning approach in conjunction with an intelligent image pool collection, we can effectively track the target and mitigate the issue of catastrophic forgetting, a challenge prevalent in this research domain. Our primary goal is to provide a robust person re-identification approach to extend the capabilities of recent tracking frameworks employed in robotics, which we have adopted as our baselines for evaluation. Our results demonstrate our approach’s efficacy in successfully re-identifying the target, even when the target drastically changes his clothing appearance and the baseline frameworks struggle. To optimally tune the framework parameters, we conducted an ablation study and substantiated our findings with saliency maps to elucidate the reasons behind the effectiveness of our approach.

The flexibility and adaptability of modular and re-configurable robots opens up new opportunities for on-demand robot morphology optimization for varying tasks. In particular, multi-arm robotic systems can expand the solution space for any given task. In this paper, we present a novel approach to exploit this feature for generating optimal fit-to-task robot structures with respect to a minimum-effort objective. By describing the task in terms of relative poses between the end-effector and the constraint frame, and making use of the relative Jacobian, the minimum effort optimization problem can be equally expressed for single-arm or multi-arm robots. We test our approach for a peg-in-hole and a contour-following task and compare the performance of the optimal solution obtained with that of a standard manipulator configuration.

This paper presents a reactive legged locomotion generation scheme that enables our quadruped robot CEN-TAURO to adapt to varying payloads while walking. The center-of-mass (CoM) trajectories are generated in real time in a model predictive control (MPC) fashion, trading off large stability margins against evenly stretched legs. Vertex-based zero-moment-point (ZMP) constraints are imposed to ensure quasi-static walking stability. A Kalman filter is then implemented to estimate the CoM states and the impact of external payloads which can vary online and affect/disturb the locomotion differently. The CoM estimation is used to update the MPC motion planner at every replanning instant so that the robot can react to unknown and time-varying payloads on the fly.We validate the proposed scheme through experimental trials where the robot walks on flat ground or steps on different surface levels while carrying heavy payloads. It is shown that the proposed reactive locomotion strategy enables the robot to carry 20 kg payloads, which is close to the maximum capacity of the robot arms.

Humans commonly exploit interaction with the environment constraints to assist the execution of the loco-manipulation tasks they perform. One particular example is the exploration of contacts during manipulation to relax the loading of those arm joints that are not directly involved in the generation of the manipulation motions and forces, e.g. establishing a contact with the elbow joint to reduce the effort of the upper arm while executing wrist level manipulation. In this paper, we shall explore the possibility of actively (a) utilizing the environment for a non-end-effector support contact towards reducing the joints efforts during manipulation tasks. This is achieved by our proposed control scheme with a three-level hierarchical compliance controller. The highest priority task is assigned to an impedance control that regulates the interaction at the contact control point on the arm in the normal direction of the support plane prior to contact, and is switched to an optimal contact force control for minimizing the joint effort after the contact is built. The second priority task is an impedance control at the same point in the tangential directions of the plane to stabilize the contact. In the end, an impedance behavior at the end-effector is designed to deal with the interaction forces required by the manipulation tasks. The efficacy of the proposed control scheme was corroborated by simulations and experiments, where significant joint effort reduction was observed.

Robotics teleoperation has been extensively studied and considered in the past in several task scenarios where direct human intervention is not possible due to the hazardous environments. In such applications, both communication degradation and reduced perception of the remote environment are practical issues that can challenge the human operator while controlling the robot and attempting to physically interact within the remote workspace. To address this challenge, we introduce a novel shared-autonomy Tele-Interaction control approach that blends the motion commands from the pilot (master side) with locally (slave side) executed autonomous motion and impedance modulators. This enables a remote robot to handle and autonomously avoid physical obstacles during manoeuvring, reduce interaction forces during contacts, and finally accommodate different payload conditions while at the same time operating with a “default” low impedance setting. We implemented and experimentally validated the proposed method both on simulation and on a real robot platform called CENTAURO. A series of tasks, such as maneuvering through the physical constraints of the remote environment in an autonomous manner, pushing and lifting heavy objects with autonomous impedance regulation and colliding with the rigid geometry of the remote environment were executed. The obtained results demonstrate the effectiveness of the shared-autonomy control principles that eventually aim to reduce the level of attention and stress of human pilot while manoeuvring the slave robot, and at the same time to enhance the robustness of the robot during physical interactions even if accidentally occurred.

Legged-wheeled robots combine the advantages of efficient wheeled mobility with the adaptability to real-world terrains through the legged locomotion. Due to this hybrid mobility skill, they can excel in many application scenarios where other mobile platforms are not suitable for. However, their versatile mobility increases the number of constraints in their motion control where both the properties of legged and wheeled systems need to be considered. Relevant schemes for legged-wheeled platforms so far have been developed exploiting separate motion control of the wheeled and legged functionalities. This paper discusses the legged-wheeled motion kinematics without constraining the camber angles of the wheels, and it proposes a first-order inverse kinematics scheme that stabilizes the legged-wheeled system in the wheeled motion. Furthermore, the work adopts a floating base model that allows to easily incorporate the legged motion to the scheme. The developed controller is tested in simulation and experiments on a legged-wheeled centaur-like robot - CENTAURO.

This paper introduces the design of a novel under-actuated hand with highly integrated modular finger units, which can be easily reconfigured in terms of finger arrangement and number to account for the manipulation needs of different applications. Each finger module is powered by a single actuator through an under-actuated transmission and equipped with a sensory system for delicate and precise grasping, which includes absolute position measurements, contact pressure sensing at finger phalanxes and motor current readings. Finally, intrinsic elasticity integrated in the transmission system make the hand robust and adaptive to impacts when interacting with the objects and environment. This highly integrated hand (HERI II) was developed for the Centauro Robot to enable robust and resilient manipulation. A set of experiments demonstrating the hand's grasping performance were carried out and fully verified the design effectiveness of the proposed hand.

This work presents a method to increase the peak output speed of surface permanent magnet synchronous machine (SPMSM) motor drives with application in robotics using field weakening control. Contrary to most existing works, the strategy is stateless and operates using only a motor torque reference as input, making it suitable for robotics applications in which reference torque and speed are continuously and rapidly changing. Based on the system dynamics and constraints, we obtain four different operating modes. The strategy is extensively validated using three different experiments, which show an increase in peak velocity of up to 33%. The results demonstrate that the proposed strategy is effective in extending the dynamic performance and explosive motion capabilities of robots.

This paper presents orientation planning algorithms respecting the requirements of task space trajectory generation, particularly in robotics applications. The proposed algorithms fulfill the following conditions: (i) permitting to impose constraints at angular velocity and acceleration in addition to orientation at endpoints; (ii) rendering continuous acceleration profiles even when interpolating multiple orientations; and (iii) being computationally fast enough for realtime implementation. The generated spline trajectories are essentially a concatenation of polynomial in time curves parameterized by quaternion coefficients. To impose the unitariness condition critically required for quaternion representation of orientation, we develop an on-line update mechanism which successively reparameterizes the polynomials constructing the spline, towards suppressing distortions that the normalization operation might incur. Experiments on an anthropomorphic robot upper-body are carried out to demonstrate the efficacy and real-time compatibility of the proposed algorithms in comparison with a standard spherical interpolation method.

The understanding of human arm stiffness have brought several significant advances to robotics. For the most part, the end-point stiffness of human arm serves as an important role in guiding and shaping the Cartesian stiffness of robot arm in the execution of complicated interaction tasks because of the convenience of using the common space where both stiffnesses function. However, investigation of the joint stiffness of human arm, on the other hand, will provide a more comprehensive perspective on the human arm stiffness and enable other appealing robotic applications, for instance, whole-arm interaction with unstructured environment. As a fundamental research for these applications, the feasibility of an online joint stiffness transfer approach from human to anthropomorphic arms is discussed in this paper. This is realized by a proposed concept of physiological joint stiffness, which is shared by the human and anthropomorphic arms. The desired joint stiffness of robot arm is transformed from the estimated joint stiffness of human arm by requiring both arms to have the same apparent physiological joint stiffness. To make the calculated joint stiffness achievable in a robot controller, the stiffness matrix is subsequently optimized to be symmetric and positive definite. Proof-of-concept experiment is performed on a fully integrated robotic teleoperation setup to validate the efficacy of the proposed method.

Despite the growing focus on the design of compliant mechanisms for robotics actuators that manifest several advantages in terms of robustness and interaction-related characteristics, the incorporation of elasticity in the actuation drive renders under-damped vibration modes and reduces the bandwidth of the system. The addition of damping principles into compliant systems can address such impediments to accuracy and stability, and enhance the passivity characteristics of the controlled compliant actuator. However, passive damping mechanisms integrated into compliant systems to exhibit user-defined passive dissipation profiles have not been realized. This paper proposes a non-linear stiffness compliant module, and introduces a novel non-linear damper which complements the elastic element. The cam-follower mechanism was employed for rendering the user-defined non-linear behaviour. While the passive compliance of the module is replicated using a curved leaf spring, the passive damping is generated by rolling/sliding motion of a rigid cylinder on an elastomer. The design of the module is described, the theoretical modelling is presented, and experimental results validating the functionality of the proposed design in dissipating under-damped oscillations are demonstrated.

Developing a high physical performance robotic manipulation platform with considerable power density, strength and resilience is not a trivial task and frequently leads to heavy and bulky systems unable to meet the application requirements, i.e. such robots should have human body size compatibility to work in infrastructures designed for humans. In this work we present a new high performance human size and weight compatible bi-manual manipulation platform that demonstrates notable physical strength and power capabilities. To attain this performance, design features including custom high performance elastic drives and robust light weight structure principles were considered resulting in large payload to robot mass ratio that is greater than 1.5 for short time heavy payloads. The design principles and mechanics of the upper body bi-manual robot are presented providing details on the solutions adopted for the various mechatronics components. The performance of the system actuation and the strength capacity of the overall platform is verified through the execution of heavy payload motion and impact experiments.

The paper proposes a method to assess the feasible torque bandwidth for electrically driven torque controllable actuators over its entire torque amplitude range. The method solely relies on the knowledge of hardware parameters and thereby determines the physically feasible torque control bandwidth at a given torque amplitude, independent of a controller. The method yields torque-frequency diagrams that are suitable to benchmark torque controllers, formulate actuator design specifications and compare as well as select actuators for a specific torque control application. The paper exemplifies the method on a WALK-MAN leg actuator with locked actuator output and the more practical case of a varying load inertia.

Despite the important role of simulation in the development and control of robotics systems, the majority of open source simulation tools has however paid no attention to the progress and paradigm change on the robot design in the past 15 years with the consideration of soft actuation technologies as a mean to power new robotic systems. More specifically, the integration of series elastic actuators (SEAs) into robots modifies significantly the dynamics characteristics of the system while the incorporation of the passive compliance into the actuators is not applied in conventional simulators. This paper introduces a scheme for the implementation of the SEA dynamics on a Gazebo-ROS framework exploited for the simulation of a new centaur-like robot. This approach is based on designing a custom control plugin embodying the passive compliance dynamics so that the controller associated with each joint receives both collocated and non-collocated feedback. A simulation comparison with Matlab validating the performance of the designed control plugin is demonstrated. In the end, a whole-body simulation of the centaur robot driven/controlled by the proposed plugin is presented.

As a major inspiration of biologically inspired systems, multi-legged robots have been developed due to their superior stability feature resulting from their large support polygon. The leg design of a majority of such robots is motivated by the skeleton of vertebrates such as dogs, or that of invertebrates such as spiders. Despite a wide variety of multi-pedal robots on the basis of the two aforesaid leg designs, a thorough comparison of the two underlying design principles remains to be done. This work addresses this problem and presents a comparative study for the two mammal-like and spider-like designs by looking at the joint torque profile, the responsive motion of the legs, and the thrust force applied by the robot. To this end, a set of performance indexes are defined based on the gravity compensation torque, the dynamic manipulability polytope and the force polytope, and evaluated in various leg configurations of the two designs.

The development of variable impedance actuators (VIAs) has highlighted the need for proper control of passive impedance to attain suitable interaction performance. Until recently the regulation of the intrinsic impedance in VIAs is achieved in an open-loop model-based manner, mainly due to the lack of physical sensors capable of measuring impedance components such as stiffness and damping. Hence, the estimation of variable stiffness and damping has been explored, with the target to provide monitoring and feedback for potential closed loop control schemes. However, the use of the output of these estimators in the feedback control of variable impedance actuators has never been implemented/demonstrated in practice. This work contributes to the field with the development and experimental evaluation of a novel damping feedback control for a class of variable impedance compliant actuators able to realize a variable physical damping principle. The scheme is based on non-model-based damping estimation feedback to compensate model uncertainties in the action of an inner controller that uses a model-based friction estimator. Experimental results demonstrate the ability of the proposed scheme to replicate with good fidelity constant and time-varying damping levels.

The use of typical position controllers for robots working around humans can involve some risks when unintended physical human-robot interactions occur. In order to benefit from a proper tracking performance during normal operations, and a smooth and damped recovery from position errors due to contacts with external objects/agents, Proxy-based Sliding Mode Control was proposed. While the efficacy of this controller in fully actuated manipulators was discussed, the employment of this controller in underactuated systems has not been studied so far. This paper introduces a control scheme to implement this controller in a class of underactuated systems. Specifically, the control of flexible joint manipulators possessing passive elastic elements in series with motors is studied. The formulation of Proxy-based Sliding Mode Control is adopted according to the stability requirements of this type of dynamic systems, and a torque controller required for the regulation of the the output torque of actuation units is designed using the Feedback Linearization and the Linear Quadratic optimal control approach. The performance of the proposed scheme is demonstrated in dynamic simulation of an anthropomorphic compliant arm.

Recently-developed variable damping mechanisms have been exploited as a complement to compliant actuators. While accurate knowledge and control of generated damping is essential for achieving the desired performance, no physical sensor measuring the damping exists. This work introduces a novel non-model-based approach for the estimation of time-variant damping for variable impedance actuation systems. The approach is based only on torque and position/velocity measurements; without the knowledge of system's inputs, to ensure the estimation of both intentional and unintentional changes. Hence, a recursive least square estimator, modified for achieving a proper convergence for the estimation of time-variant parameters, is exploited. Experiments on a variable physical damping actuator are also presented to validate the performance of proposed approach.

This work focuses on the modeling and control of robotic manipulators powered by compliant actuation systems equipped with clutches for providing friction torque on demand. A novel control scheme is proposed for modulating the clutch friction torque in this particular class of compliant actuators to make the robot operate in “Rigid mode” when it does not interact with the environment to achieve high accuracy, bandwidth and controllability; meanwhile ensuring that the robot maximum static force is constrained to a maximum threshold permitting flexible reactions in potentially risky scenarios. The robot autonomously switches to “Compliant mode” (clutches off) when it interacts with external agents to exploit the advantages of compliance during contacts. Experimental results are presented to show the effectiveness of proposed approach in improving the robot performance (tracking accuracy) while still guaranteeing an interaction-friendly behavior when contact occurs.

On a new demand of safe human-robot interaction for robotic applications, the Compact Compliant Actuator, named CompActTM, is recently developed with physical compliance and active variable damping. In this mechanism, a desired physical damping behavior is realized by generating a friction force which is actively controlled by piezoelectric actuators (PEAs). However, nonlinearities such as hysteresis and creep effect make difficult to precisely control the generated piezoelectric force. This paper focuses on a development of precise force tracking controller for PEAs. A time delay estimation (TDE) using a force feedback is newly proposed to compensate a hysteretic behavior of the PEA and external uncertainties without a mathematical model. Thanks to the force-based TDE, the proposed control is accurate, computationally efficient and easily implementable on the real PEA system. The proposed control scheme is experimentally verified on the CompActTM. Root-mean-square values of the steady-state error for step commands are kept as less than error ratio of 0.13 % and the closed-loop system bandwidth for sinusoidal commands of 20 N stroke is confirmed as about 11 Hz under 100 N payload. In addition, the stability of the proposed control is proved to be bounded-input-bounded-output (BIBO) stable.

The CompAct™ actuator features a clutch mechanism placed in parallel with its passive series elastic transmission element and can therefore benefit from the advantages of both series elastic actuators (SEA) and rigid actuators. The actuator is capable of effectively managing the storage and release of the potential energy of the compliant element by the appropriate control of the clutch subsystem. Controlling the timing of the energy storage/release in the elastic element is exploited for improving motion control in this research. This paper analyses how this class of actuation systems can be used to maximize the link velocity of the joint. The dynamic model of the joint is derived and an optimal control strategy is proposed to identify optimal input reference profiles for the actuator (motor position/velocity and clutch activation timing) which permit the link velocity maximization. The effect of compliance of the joint on the performance of the system is studied and the optimal stiffness is analyzed.

This paper proposes a control strategy for a compliant actuator, the CompAct™ actuator, which is equipped with semi active friction dampers in its transmission system. Both the transmission flexibility and the nonlinearity of the friction based damping torque makes the control of this actuator not a trivial task. This paper studies model of the presented actuator and the control problem of accurate link position tracking based on sliding mode approach that considers the friction torque as an uncertainty. Stability analysis and simulations highlight the effectiveness of the proposed controller in compensating for the deflections and unknown friction torque of the actuator. The performance of the controller is also validated by experiment results that demonstrate the tracking performance of the CompAct™ actuator achieved by the presented control strategy.