91 accepted papers
In kinesthetic teaching, a robot is manually guided by a human operator to demonstrate a task. Most methods focus on replaying the recorded motion, but are agnostic to contact transitions, which can be critical when interacting with rigid environments. To overcome this limitation, we propose a frame
We propose a control framework that integrates model-based bipedal locomotion with residual reinforcement learning (RL) to achieve robust and adaptive walking in the presence of real-world uncertainties. Our approach leverages a model-based controller—comprising a Divergent Component of Motion (DCM)
We propose a control framework that integrates model-based bipedal locomotion with residual reinforcement learning (RL) to achieve robust and adaptive walking in the presence of real-world uncertainties. Our approach leverages a model-based controller—comprising a Divergent Component of Motion (DCM)…
The Time Domain Passivity Approach (TDPA) was developed to guarantee passivity while avoiding conservative constant controller parametrization. For this sake, the TDPA applies adaptive damping to dissipate excessive energy resulting from communication delay in bilateral teleoperation setups. Despite
A robot with kinematical redundancy with respect to a main task may perform additional tasks simultaneously with the main one. Often, it is desirable to prioritize the performance of some tasks over that of others. To create a strict priority between the different tasks, meaning the performance of h…
In on-orbit servicing missions using robotic manipulators, certain challenging scenarios require the use of combined control i.e. actuation of spacecraft and the manipulator, to meet mission requirements. The low frequency of the controller of the spacecraft compared to the manipulator can compromis
In on-orbit servicing missions using robotic manipulators, certain challenging scenarios require the use of combined control i.e. actuation of spacecraft and the manipulator, to meet mission requirements. The low frequency of the controller of the spacecraft compared to the manipulator can compromis…
Suspended multirotor platforms are fascinating systems that can be employed in construction applications to provide safe transportation of heavy loads. Such a system comprising a cable-suspended platform with attached load features seven degrees of freedom (DoF) motion for the whole system. In this …
This paper studies the experimental comparison of two different whole-body control formulations for humanoid robots: inverse dynamics whole-body control (ID-WBC) and passivity-based whole-body control (PB-WBC). The two controllers fundamentally differ from each other as the first is formulated in ta
In this work, we present a novel control approach based on partial feedback linearization (PFL) for the stabilization of a suspended aerial platform with an attached load. Such systems are envisioned for various applications in construction sites involving cranes, such as the holding and transportat
A robot with kinematical redundancy with respect to a main task may perform additional tasks simultaneously with the main one. Often, it is desirable to prioritize the performance of some tasks over that of others. To create a strict priority between the different tasks, meaning the performance of h
One of the essential aspects of humanoid robot running is determining the limb-swinging trajectories. During the flight phases, where the ground reaction forces are not available for regulation, the limb swinging trajectories are significant for the stability of the next stance phase. Due to the con
Variable Stiffness Actuators (VSAs) are promising for advanced robotic systems, offering benefits such as improved energy efficiency, impact safety, stiffness adaptability, mechanical robustness, and dynamic versatility. However, traditional designs often rely on complex mechanical assemblies to ach
Spring loaded inverted pendulum (SLIP) is a template dynamics used to model the steady-state running of humans and animals ranging from cockroaches to horses. This study extends the conventional 3D SLIP model with a foot and an active controller to also model transitioning from stationary to high-sp
Some impact tasks for robot manipulators, like stamping, demand that the end-effector does not slip off the target at the contact transition. We refer to this class of impacts as targeted non-slippage impacts and provide solutions to perform them. We present a model-based analysis and provide impact
In this work, we present a novel actuation strategy for a suspended aerial platform. By utilizing an underactuation approach, we demonstrate the successful oscillation damping of the proposed platform, modeled as a spherical double pendulum. A state estimator is designed in order to obtain the defle…
This article introduces a framework for complex human-robot collaboration tasks, such as the co-manufacturing of furniture. For these tasks, it is essential to encode tasks from human demonstration and reproduce these skills in a compliant and safe manner. Therefore, two key components are addressed…
The on-ground validation of orbital manipulators is a challenging task because the robot is designed for a gravity-free operational environment, but it is validated under the effect of gravity. As a consequence, joint torque limits can be easily reached in certain configurations when gravity is acti…
Standing-up is a task that humanoids need to be able to perform in order to be employed in real-world scenarios. This paper proposes a new robust strategy for a humanoid to stand up in challenging scenarios where no completely preplanned motion can accomplish the same task. This strategy exploits th
Hardware-in-the-loop simulation (HILS) allows a more realistic evaluation of control approaches than what is possible with pure software simulations, but without the actual complexity of the complete system. This is important for some complex systems such as orbital robots, where testing of the syst…
During operation, aerial manipulation systems are affected by various disturbances. Among them is a gravitational torque caused by the weight of the robotic arm. Common propeller-based actuation is ineffective against such disturbances because of possible overheating and high power consumption. To o…
Controlling the contact force on various surfaces is essential in many robotic applications such as in service tasks or industrial use cases. Mostly, classical impedance and hybrid motion-force control approaches are employed for these kinds of physical interaction scenarios. In this work, an extend
This study extends the whole-body control (WBC) formulation for bipedal humanoid robots that include closed (parallel) kinematic chains in their structure. Along with general formulation, we also stress the implementation of this formulation on Kangaroo, which is a highly dynamic humanoid robot deve…
In this paper, we propose a detumbling strategy that stabilizes the motion of a tumbling client satellite using an orbital servicing manipulator, which is the goal of the post-grasp phase. One of the critical aspects in this phase is ensuring that excessive contact forces are not generated at the gr…
Actuation failure and fault-tolerant control under the actuation failure scenario have drawn more attention in accordance with the recent increasing demand for reliable robot control applications such for long-term and remote operation. The emergence of control torque loss, i.e., the free-swinging f
This paper proposes a parameterization method to represent SO (3) over multiple turns. This method is called a memory-based parameterization, because the idea is to integrate the past trajectory of exponential coordinates. The parameterization is consistent in the sense that the true rotation matrix…
Adaptive control can significantly improve tracking performance of robot manipulators subject to modeling errors in dynamics. In this letter, we propose a new framework combining the composite adaptive controller using a natural adaptation law and an extension of the adaptive variance algorithm (AVA
With emerging capabilities, robots will advance gradually into human environments in the near future. Thereby, safety and robustness is currently tackled through intrinsically soft robotics or variable impedances, mainly stiffnesses. In tele-operation, for instance, the control stiffness can be adap
Gait generation frameworks for humanoid robots typically assume a constant centroidal angular momentum (CAM) throughout the walking cycle, which induces undesirable contact torques in the feet and results in performance degradation. In this work, we present a novel algorithm to learn the CAM online…
Embedding elastic elements into legged robots through mechanical design enables highly efficient oscillating patterns that resemble natural gaits. However, current trajectory planning techniques miss the opportunity of taking advantage of these natural motions. This work proposes a locomotion planni…
This work addresses the problem of global set-point control of elastic joint robots by combining elastic structure preserving (ESP) control with non-collocated integral action. Despite the popularity and extensive research on PID control for rigid joint robots, such schemes largely evaded adoption t
Since safe human-robot interaction is naturally linked to compliance in these robots, this requirement presents a challenge for the positioning accuracy. The class of variable-stiffness robots features intrinsically soft contact behavior where the physical stiffness can even be altered during operat
In this letter, a novel partitioned shared controller is proposed, which exploits a fully-actuated orbital robot to perform a primary end-effector task involving environmental interactions. This task is remotely performed using a bilateral teleoperation controller, while a secondary task is automati
Multi-agent control of a robot using multiple controllers is vital in domains like shared control and reliable control. The strategy of assigning a varying priority (authority) to each agent controller, and commanding the robot using an authority-weighted sum of the forces produced by all the agents…
In this letter, we propose a novel method for the on-ground simulation of a space robotic mission, while exploiting a robotic hardware-in-the-loop facility. The simulated dynamics replicated by the robots are defined with respect to a nominal motion. This approach enables simulating the motion of la
Adaptive control of robot manipulators based on the use of a sliding variable and the passivity property of the dynamic equations was originally designed and successfully applied to task tracking in joint space few decades ago. Surprisingly, no extension is available to date for the multi-task case
In situations of harsh impacts, damping injection directly on the link of an articulated soft robot is challenging and usually requires high actuator torques at the moment of impact. In this work, we discuss the underlying reasons and analyze the performance limitations arising in the implementation
This letter presents a compliant feedback controller of an arm-equipped spacecraft, which does not enforce requirements on the spacecraft position and attitude. The controller is applicable to the pre-contact, contact, and post-contact phases of a robotic operation. In contrast to conventional float
The regulation of the link positions of compliant robots, damping out undesired link oscillations while preserving the system's inherent elasticity is still a challenging task in practical applications. This task becomes even harder to be tackled in the case of compliant robots driven by agonistic-a
This letter presents a new push recovery algorithm for humanoid robots in balancing scenarios by exploiting the system's rotational dynamics. The proposed framework actively generates centroidal angular momentum (CAM) references based on the force magnitude and direction of the push to counteract th
In this paper, we present a highly efficient Divergent Component of Motion (DCM) reference trajectory generator capable of adapting online to large perturbations acting on the center-of-mass (push recovery) and on the swing foot (stumble recovery). For push recovery, we propose an analytic solution…
Ensuring stability in time-delayed teleoperation can be difficult in some cases where the feedback forces need to be modified as defined by the user, to increase transparency. In the present letter, we propose an approach to ensure stability of any feedback controller selected by the user by conside
Air density changes depending on the local atmosphere and affects the rotor thrust of flying robots. This effect has to be compensated by the flight controller in order to realize precise tracking of a desired trajectory. So far, the influence of the air density has been disregarded or only consider
In the present paper, we propose a novel system-driven adaptive shared control framework in which the autonomous system allocates the authority among the human operator and itself. Authority allocation is based on a metric derived from a Bayesian filter, which is being adapted online according to re…
In the present paper, we first adopt explicit force control from general robotics and embed it into teleoperation systems to enhance the transparency by reducing the effect of the perceived inertia to the human operator and simultaneously improve contact perception. To ensure stability of the propos…
Hierarchical impedance control has been recently shown to effectively allow trajectory tracking, while guaranteeing the order of priorities during the execution. Nevertheless, the choice of the tasks is required to be such that, after being properly decoupled, they are all feasible and lead to an in
In this paper, we propose three novel Hardware-in-the-loop simulation (HLS) methods for a fully-actuated orbital robot in the presence of external interactions using On-Ground Facility Manipulators (OGFM). In particular, a fixed-base and a vehicle-driven manipulator are considered in the analyses. T…
Lightweight robots are known to be intrinsically elastic in their joints. The established classical approaches to control such systems are mostly based on motor-side coordinates since the joints are comparatively stiff. However, that inevitably introduces errors in the coordinates that actually matt…
This work introduces the so-called Modular Passive Tracking Controller (MPTC), a generic passivity-based controller, which aims at independently fulfilling several subtask objectives. These are combined in a stack of tasks (SoT) that serves as a basis for the synthesis of an overall system controlle…
This paper presents a design of oscillation damping control for the cable-Suspended Aerial Manipulator (SAM). The SAM is modeled as a double pendulum, and it can generate a body wrench as a control action. The main challenge is the fact that there is only one onboard IMU sensor which does not provid…
The application of the position-position architecture for enabling position synchronization of two robotic agents has been proven effective in the fields of telemanipulation and rendezvous of autonomous vehicles. Nevertheless, the approaches presented to this date with the purpose of rendering the p
Instability due to delayed communication is one of the main challenges in the coupling of autonomous robots but also in teleoperation with applications reaching from space to tele-healthcare scenarios. The Time Domain Passivity Approach assures stability despite delay and has already been validated
Attaching a robotic manipulator to a flying base allows for significant improvements in the reachability and versatility of manipulation tasks. In order to explore such systems while taking advantage of human capabilities in terms of perception and cognition, bilateral teleoperation arises as a reas…
This letter addresses the coordinated control of the spacecraft's attitude and the end-effector pose of a manipulator-equipped space robot. A controller is proposed to simultaneously regulate the spacecraft's attitude, the global center-of-mass, and the end-effector pose. The control is based on a t
High risk of a collision between rotor blades and the obstacles in a complex environment imposes restrictions on the aerial manipulators. To solve this issue, a novel system cable-Suspended Aerial Manipulator (SAM) is presented in this paper. Instead of attaching a robotic manipulator directly to an…
Humanoid robots typically display locomotion patterns that include walking with flat foot-ground contact, and knees slightly bent. However, analysis of human gait indicate that several physiological mechanisms like stretched knees, heel-strike and toe push-off increase the step length and energetic…
In this letter we design a novel control strategy for a space manipulator operating on a controlled base. The proposed controllers resolve the tracking of the end-effector and the regulation of the base. In particular, we focus on the effects due to the different sampling rates of the manipulator an
In recent years, the application of continuum mechanisms increased as they provide high dexterity, consume a low amount of space, and handle unforeseen collisions with ease. Typically, a deformation model of the continuum is applied to compute task space poses from actuator variables. However, simpl
Interactions between robots and their environment give rise to external wrenches acting on the robot structure. The estimation of the resulting torques in the joints is fundamental in human-robot interaction to detect/identify collisions and perform suitable reaction strategies. Other applications m…
Balancing is a critical feature for a robot interacting with an unstructured environment. The balancing control should account for unknown perturbation forces that might destabilize the robot when performing the intended tasks. In the case of humanoid robots this challenge is higher due to the inher
In this contribution the problem of vibration control is studied on the basis of a fundamental oscillatory system consisting of a mass spring system and an additional mass. The proposed control strategy couples the orbits of the two masses such that both masses stop, while simultaneously stabilizing…
The humanoid robot David is equipped with a novel robotic neck based on an elastic continuum mechanism (ECM). To realize a model-based motion control, the six dimensional stiffness characteristics needs to be known. This letter presents an approach to experimentally identify the stiffness characteri
Stability is not trivial in aerial manipulation tasks because of the dynamical coupling between the aerial vehicle and the manipulator. This is especially true when the manipulator becomes heavy, so that its dynamics can be significant. In this letter, a stabilizing controller for the regulation of
In this paper we address the problem of controlling a robotic system mounted on an actuated floating base for space applications. In particular, we investigate the stability issues due to the low rate of the base control unit. We propose a passivity-based stabilizing controller based on the time dom…
This letter presents an in-depth analysis of the convex properties of center-of-mass (CoM) trajectories for legged robot locomotion based on the concept of Divergent Component of Motion (DCM). In particular, we show that the union of all possible trajectories forms a bounded convex set under appropr
We present a new approach for Cartesian impedance control of compliantly actuated robots with possibly nonlinear spring characteristics. It reveals a remarkable stiffness and damping range in the experimental evaluation. The most interesting contribution, is the way the desired closed-loop dynamics…
Robotic teleoperation is a key technology for a wide variety of fields. Teleoperating a humanoid in particular is essential as it allows the user to act remotely on an interface designed especially for humans, e.g., in a space station, or operating tools and machinery in disaster scenarios. This pap…
This paper presents a passive compliance control for aerial manipulators to achieve stable environmental interactions. The main challenge is the absence of actuation along body-planar directions of the aerial vehicle which might be required during the interaction to preserve passivity. The controlle…
Reliable and robust balancing controllers are key elements of whole-body control frameworks for humanoid robots. Passivity-based balancing controllers have been proposed and tested successfully in various scenarios involving different types of ground surfaces. This letter extends the passivity consi
This paper proposes an integration of multi-body and actuator control for multi-contact balancing for robots with highly elastic joints. Inspired by the structure preserving control concept for series-elastic fixed-base robots, the presented approach aims to minimize the control effort by keeping th…
The Operational Space Formulation (OSF) from the 1980s is probably the most frequently applied task-space controller in robotics. In multipriority control of redundant robots via the OSF, a feedback linearization is performed on the first hierarchy level while lower-priority tasks are executed in th
This paper presents methods that facilitate the implementation of dynamic walking on torque-controlled robots in real world experiments. The work uses the Divergent Component of Motion (DCM) for walking trajectory generation and control. The DCM controller is embedded into a whole-body controller (W…
Future planetary rovers will gain the ability to manipulate their environment in addition to the maneuverability of current systems. For dedicated contact interaction, Cartesian impedance control is a well-established approach from numerous terrestrial applications. In this paper we will present a w…
This paper presents a new method for planning and controlling dynamic multi-contact motions for humanoid robots. Our motion planner takes a sequence of multi-contact stances and generates closed-form reference trajectories for the robot center of mass (CoM) position, velocity, and acceleration, base…
In this paper, a tracking control approach for robot assisted landing of UAV rotorcraft, such as multicopters and helicopters, is presented. The aim is to safely land these type of flying vehicles under side wind conditions and on moving surfaces using a robot manipulator arm mounted on the ground.…
This paper presents that the joint torque control capability can be enhanced by adding physical damper to a series elastic actuator (SEA). Joint torque tracking of standard SEA has known limitations that the torque dynamics has an relative order of two, and, as a consequence, the torque controller o…
Series-elastic and viscoelastic robots can provide performance gains in applications with high dynamics. Harnessing these, requires an understanding of the dynamics of the system, which can be gained using optimization-based methods. The result are motions which make optimal use of the intrinsic beh…
Ensuring safety is a primary goal in physical human-robot interaction. In various collision experiments it was found that the robot's effective mass, velocity, and geometry are the key parameters which influence the human injury severity during an impact. Recently, a velocity controller was proposed…
Introducing humanoid robots in areas where space is limited, for example in search-and-rescue scenarios or industrial manufacturing, represents a huge challenge, especially when the environment is cluttered and unknown. The robot should be capable of utilizing multiple contact points distributed acr…
Modern robotic systems with a large number of actuated degrees of freedom can be utilized to perform several tasks at the same time while following a given order of priority. The most frequently used method is to apply null space projections to realize such a strict hierarchy, where lower priority t
The concept of hybrid zero dynamics is a promising approach for designing exponentially stabilizing controllers for dynamic walking with some degrees of underactuation. By this approach a feedback controller is designed such that a stable periodic orbit, within an invariant submanifold for the hybri…
This paper presents a novel multi-step closed-form walking trajectory generator based on the concept of Divergent Component of Motion (DCM) that guarantees smoothness of all resulting reference trajectories. Further, we introduce an analytical method for footstep adjustment to recover from strong di…
Admittance control is a well-established and popular control strategy in modern robotics. However, the standard admittance controller has several limitations. First, the passivity can be guaranteed by finding a set of control parameters that makes the admittance function positive real. However, this…
This paper presents a control method to implement trajectory tracking and disturbance rejection characteristics for the link-side dynamics of compliantly actuated robots with nonlinear spring characteristics. This is achieved by introducing new motor coordinates reflecting the damping and feedforwar
Legged humanoid robots need to be able to perform a variety of tasks including interaction with the environment while maintaining the balance. The external wrenches, which arise from the physical interaction, must be taken into account in order to achieve robust and compliant balancing. This work pr
In this letter, we consider the problem of generating periodic solutions for fully actuated robots with unknown disturbances, which can be modeled using a regressor matrix. We extend our previous work on limit cycle control based on energy function regulation for the case when disturbance torques ar
A manipulator with kinematic redundancy w.r.t. a main task enables to perform an additional, subordinate task in its null space. The classical hierarchy-based approach is to apply dynamically consistent null space projections such that this lower-priority task does not disturb the main task. The maj
This paper presents an adaptive and compliant approach-to-grasp strategy for multi-finger robotic hands, to improve the performance of autonomous grasping when encountering object position uncertainties. With the proposed approach-to-grasp strategy, the first robot finger to experience unexpected im…
This paper introduces a Biologically Inspired Dead-beat (BID) controller for bipedal running in 3D. The controller runs in real-time, is extremely robust against perturbations and allows for versatile running patterns. It is based on the encoding of leg forces and CoM trajectories during stance as p…
Biped walking control based on simplified models relies much on online feedback stabilizers to compensate the zero-moment point (ZMP) error which partially comes from the model inconsistency of pattern generation. Inspired by the fact that human improves the performance by practicing a task for mult…