Direct force control of robots is challenging, particularly since the interaction with the environment can render the robot unstable. This paper presents the results of novel approaches for passivity-based stability for a particular direct force control method, namely explicit force control. A step-by-step procedure to passivate and stabilise the control loop is presented and it explains how Time Domain Passivity Approach, a passivity-based tool widely used in teleoperation and haptics has been extended and applied in explicit force control. The electrical circuit and network-port representations derived in the process allows the analytical evaluation of the system and can be applied in other control architectures as well. The stability methods are presented both qualitatively and quantitatively with simulations and hardware experiments. A discussion about the results obtained and the energy behavior is also provided. Results are promising and suggest that these methods can be used for stable and high-bandwidth force control of robotic manipulators.

Multiple robotic agents, autonomous or teleoperated, can be employed to synergise and cooperate to achieve a common objective more effectively. Tasks using robotic manipulators can be eased and improved in terms of reliability, adaptability and ergonomics via robot cooperation. In spite of visual and haptic feedback, cooperative telemanipulation of multiple robots by distant operators can still be challenging due to practical limitations in synchronisation and supervision. This paper presents a new control approach for haptic intention augmentation between two human operators handling objects via teleoperation in a cooperative manner. The force feedback to each operator is enhanced by information on the motion intention of the other operator observed by a force sensor at the input devices. Besides on-ground experiments, an experiment is presented that involves the cooperative teleoperation of an on-ground robot by a cosmonaut on the International Space Station and another distant operator on ground.

In this paper we present a passive and reliable explicit discrete integrator, which allows to preserve the energy and dynamic properties of a physical body rendered on a hardware-in-the-loop simulator. Starting from the standard Euler integrator, we identify the energy generation that results from the integration process. This energy makes the time discrete dynamics deviate from the ideal one, resulting in position drifts or stability issues. By exploiting the time domain passivity approach, the simulated dynamics is reshaped in order to preserve its physical energy properties. The proposed integration method allows precise simulation of virtual bodies on industrial robot facilities. The method has been validated in simulation and experimentally tested on the DLR OOS-SIM facility.

This paper proposes a passive and explicit integrator for simulating a rotational rigid-body dynamics rendered by a robot. Considering the Euler integration method, active energy terms are identified. These sources of energy are due to the external torque and the coupled dynamics which can lead to a non-physical behavior of the simulated dynamics. The proposed method dissipates this energy using a variable damper regulated by an energy observer. The new algorithm guarantees not only passivity but also a consistent energetic integration. The integration method is sustained by simulations and tested on a real-time hardware-in-the-loop simulator.

This paper presents a new robot controller for space telerobotics missions specially designed to meet the requirements of KONTUR-2, a German & Russian telerobotics mission that addressed scientific and technological questions for future planetary explorations. In KONTUR-2, Earth and ISS have been used as a test-bed to evaluate and demonstrate a new technology for real-time telemanipulation from space. During the August 2015' experiments campaign, a cosmonaut teleoperated a robot manipulator located in Germany, using a force-feedback joystick from the Russian segment of the International Space Station (ISS). The focus of the paper is on the design and performance of the bilateral controller between ISS joystick and Earth robot. The controller is based on a 4-Channels architecture in which stability is guaranteed through passivity and the Time Delay Power Network (TDPN) concept. We show how the proposed approach successfully fulfills mission requirements, specially those related to system operation through space links and internet channels, involving time delays and data losses of different nature.

This paper presents initial results of a set of experiments to compare time-delayed teleoperation performance of selected architectures based on two popular passivity based methods, namely, Wave Variables Transformation (WVT) and Time Domain Passivity Approach (TDPA). Five different architectures widely used and available in literature are selected: 2-channel and 3-channel for both WV and TDPA, and 4-channel based on TDPA. An empirical approach for measuring transparency is proposed, which presents three main qualities: 1) Controller independency 2) Frequency dependency of performance and 3) Removal of the human operator out of the loop. In order to achieve this, the human operator is replaced by a linear actuator equipped with a force sensor. Deterministic interactions between the simulated operator and the rest of the system can thus be easily implemented and registered. Therefore, this approach allows to isolate pure effects of any control method and perform a proper analysis in terms of selected attributes for a desired metrics. In this article, these are chosen to be effective impedance and position tracking error, both in the frequency domain. In addition to the quantitative results, a qualitative analysis is presented which underlines practical implications of each architecture and control method. The comparison sample presented contains five different delays, varying from 0 to 200 milliseconds, five different environmental impedances and 5 bilateral control architectures along with an analysis of the results obtained.

This paper introduces a performance oriented method for simulating stable free-floating satellite dynamics on a position controlled robot. Intrinsic latencies found in robot controllers, i.e. between input and output data, are known to produce stability issues and performance degradation. These issues are even more apparent during contact phases, where impact dynamics play a major role. The approach presented in this paper guarantees stability through passivity and preserves the performance through the use of an optimal damping. The energy produced by delays found in the closed loop system is monitored and dissipated when necessary. In order to implement the dynamics accurately, the damping process is formulated as an optimization problem. Thus, over-dissipation can be avoided and the system becomes less conservative. Performance and effectiveness of the method are shown in simulation and verified experimentally on a position controlled seven degrees of freedom Light Weight Robot equipped with a force-torque sensor at the end-effector.

On-orbit servicing involves a new class of space missions in which a servicer spacecraft is launched into the orbit of a target spacecraft, the client. The servicer navigates to the client with the intention of manipulating it, using a robotic arm. Within this framework, this work presents a new robotic experimental facility which was recently built at the DLR to support the development and experimental validation of such orbital servicing robots. The facility allows reproducing a close-proximity scenario under realistic three-dimensional orbital dynamics conditions. Its salient features are described here, to include a fully actuated macro-micro system with multiple sensing capabilities, and analyses on its performance including the amount of space environment volume that can be simulated.

Field robots used in unstructured and dynamic environments - and teleoperation have shifted into the focus of a variety of industrial branches in the past few years. The lack of space in the atomic industry, on oil platforms and in space applications demands additional adaptations to current robotic setups. In this paper a MMSS (Multi-Master-Single-Slave) haptic teleoperation system is proposed through which one operator using two master arms can manipulate objects in a cooperative way via one slave robot and a virtual gripping point. To ease the execution of a peg-in-hole task of big objects, a task allocation in the cartesian frame of the virtual gripping point is introduced additionally. The stability of this multilateral system with time delay is guaranteed by the Time Domain Passivity Approach. Therefore the system is divided into several modular subsystems which renders the system easily adaptable to other scenarios.

This paper describes a control strategy to achieve high fidelity dynamics simulation rendered on admittance controlled robotic facilities. It explores the reasons for an increasing energy found in the virtual dynamics of a free-floating satellite rendered on a six degree of freedom robot, which can lead the system to become unstable and proposes a method to cope with it. The proposed method identifies the sources of intrinsic instability provoked by time delays that are found in the computational loop of the rendered dynamics and counteracts their destabilizing effects using the passivity criteria. The performance of the system and the benefits of the method are shown in simulations and are verified experimentally.

Abstract-This article accompanies a video that presents a bimanual haptic device composed of two DLR/KUKA Light weight Robot (LWR) arms. The LWRs have similar dimensions to human arms, and can be operated in torque and position control mode at an update rate of 1kHz. The two robots are mounted behind the user, such that the intersecting workspace of the robots and the human arms becomes maximal. In order to enhance user interaction, various hand interfaces and additional tactile feedback devices can be used together with the robots. The presented system is equipped with a thorough safety architecture that assures safe operation for human and robot. Additionally, sophisticated control strategies improve performance and guarantee stability. The introduced haptic system is well suited for versatile applications in remote and virtual environments, especially for large unsealed movements.

In this paper, a decentralized platform for Simultaneous Localization and Mapping (SLAM) with multiple robots is developed. A novel occupancy grid map fusion algorithm is proposed. Map fusion is achieved through a multi-step process that includes image pre-processing, map learning, relative transformation extraction and then verification of the results. The proposed map learning method is a process based on the Self Organizing Map (SOM). In the learning phase, the obstacles of the map are learned by clustering the occupied cells of the map. The clusters represent the spatial form of the map and make further analyses of the map easier and faster. Also, clusters can be interpreted as features extracted from the occupancy grid map so the map fusion problem becomes a task of matching features. Results of the experiments from tests performed on a real environment with multiple robots prove the effectiveness of the proposed solution.

The Time Domain Passivity Control Approach (TDPA) is a powerful tool to guarantee passive interaction between a robot and its environment. Rather than establishing fixed control parameters to keep the system stable in any possible environment, the TDPA observes the energy flow due to the interaction and applies a dissipative term in the case the interaction becomes active. In a robot manipulator the rationale behind the Passivity Controller requires a criterion on how to distribute the energy to be dissipated among the multiple joints and must be adjusted according to the general control goal of the application. This paper presents a method for distributing the dissipation between decoupled subspaces of a redundant manipulator, prioritizing dissipation in the null-space. The method allows to preserve passivity while avoiding disturbance of the general control goal defined in the task-space. Thus the general control goal can, to some extent, be as well decoupled from passivity considerations and thus a less conservative controller can be achieved. The approach is sustained with a numerical simulation.

Extravehicular activities (EVAs) are a hazardous and expensive procedural method to operate in outer space. A possible support or alternative for manned missions in terms of on-orbit servicing are telemanipulation-systems. Whether or not such systems can actually achieve the efficiency of suited astronauts remains a central issue in telemanipulation research. Both scenarios, extravehicular activities as well as telemanipulation-systems, are restricted by different environmental factors, especially in terms of tasks that require fine motor skills. For suited astronauts, different factors, such as restricted mobility and reduced tactile feedback through the gloves, as well as a restricted field of view, impair fine motor skills. On the other hand, time delay, limited degrees of freedom and restricted haptic and visual feedback are amongst the factors, which may cause impairment of performance during the work with telemanipulation-systems. In order to compare the efficiency of both scenarios, a testbed equipped with typical mounting tasks was developed. An experimental study showed that the testbed is a valid measure of fine motor skills. In two follow-up studies, the influence of some factors debilitating fine motor performance in telemanipulation-systems and simulated extra-vehicular activities was analysed and compared.

Telepresence-systems have the potential to take on an important role in on-orbit servicing scenarios. In comparison to manned missions, these systems offer a safer way to operate in outer space. One of the main goals of telepresence research is to learn whether immersive telepresence systems can achieve the efficiency of astronauts in typical mounting tasks, considering that astronauts' mobility is restricted by a range of factors including microgravity and space suits. In order to determine whether a telepresence system is more efficient in performing tasks compared to suited astronauts, an experimental study comparing both scenarios was accomplished.

The Time Domain Passivity Control Approach is gathering interest in the robotics field. Simplicity and flexibility and the fact that system design emerges from ideal cases make it a powerful stability tool for teleoperation systems. Communication time delay is an inherent attribute of nearly every realistic teleoperation system. Unless the communication channel guarantees transmission delays of less than the system sampling time, the delay must be considered in the design in order to guarantee stability and satisfy a desired degree of performance. In previous work it has been shown how passivity can be considered in the time domain and how control rules are derived from it in order to dissipate the energy produced by the delayed communication. However, a weakness of these approaches is the impossibility of observing the exact amount of energy stored in the communication channel due to its delayed nature. A passive estimation is therefore needed which outcomes in an over-dissipation and in turn impacts on transparency. In constrained communications over-dissipation may become apparent in the form of a non-neglectful position drift between master and slave. This paper tackles the over-dissipative behavior of the Passivity Controller by resembling the energetic behavior of an ideal communication, i.e. where no delay is present and the transmission is lossless. Thus, the communication channel is not just controlled to be passive, as has been the case up to now, but also lossless. Energy can be dissipated to prevent activity, but activity can be also produced to prevent dissipative behaviors. The approach is sustained with experimental results.

This video presents a telepresence system which enables a human operator to explore a remote environment by means of a multimodal man machine interface and rollin' JUSTIN as teleoperator. The man machine interface allows for bimanual, dexterous manipulation and, through two different operating modi of the man machine interface, wide area movement as well. A bimanual assembly task, consisting of grasping a connector, opening and closing it again, is shown in this video.

The time domain passivity framework is attracting interest as a method for granting stability in both telerobotics and haptic contexts; this paper employs this approach in order to introduce a novel concept, the Bilateral Energy Transfer for haptic telepresence. Loosely speaking, the Bilateral Energy Transfer is the straightforward transfer of energy between the two opposite sides of a teleoperation network, the master and slave robots. In an ideal telepresence scenario master and slave robots behave as rigid connected masses [1], and their power exchange is lossless; conversely, realistic scenarios include sources of energy leaks, i.e. elements that modify the power flows in the network. Moreover, if energy leaks have an active nature, they become source of instability for the system. This work isolates two sources of instability normally present in a teleoperation system, i.e. the delayed communication channel and robot velocity estimation based on digital position acquisition. These energy leaks are counterbalanced by two independent controllers, whose design is based on energetic consideration, and whose employment allows to achieve the Bilateral Energy Transfer. The presented arguments are sustained by simulations and experiments.

This paper presents a new control strategy based on the time domain passivity control approach which copes with the active nature of delayed communication channels. Describing the system by means of network elements, the energy of the communication channel can be computed in real time and subsequently dissipated, thus providing stable operation. This is done bilaterally, since the system energy may flow from master to slave and from slave to master. The approach is accompanied with some experiments which validate the method.

This paper analyses the time domain passivity control approach in the time-delayed telepresence context, and proposes a method which provides stable operation. The passivity controller for the two-port network which is created by the bilateral control and communication elements in (J. H. Ryu, et al., May 2002) is shown to be not valid if a time delay is introduced in the communication channel. Classical stability analysis for the delayed system is presented and used as argument and benchmark for the proposed solution. Simulations and experimental results are discussed and compared with classical stability analysis