Philipp Kremer

On-orbit servicing

Space robots were the topic of this paper. While on earth, nobody would follow such advice; in space, there are few other options than to replace a malfunctioning spacecraft. There are no repair shops and gas stations in the Earth orbit. Because of the lack of so-called on-orbit servicing (OOS) opportunities, some malfunctioning spacecraft continue operational work with reduced or hardly any performance. The only general modification, which can currently be undertaken to an arbitrary spacecraft in orbit, is a software update. In this paper, exploration and manipulation capabilities of space robots were discussed. Teleprescence through a data relay satellite and teleoperation capabilities were mentioned and discussed.

The DLR bimanual haptic device with optimized workspace

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 1 kHz. 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 unscaled movements.

Lossy data reduction methods for haptic telepresence systems

Telepresence systems are often deployed in scenarios where communication bandwidth is limited. Consequently, data exchanged between operator and teleoperator has to be reduced. In case of haptic telepresence, data reduction has an influence on the stability of the overall system. This paper provides a step towards a systematic framework for communication data bandwidth reduction in haptic telepresence systems discussing stability for a class of lossy data reduction (LDR) algorithms. Simulation and experimental results validate the efficacy

Passive Haptic Data-Compression Methods With Perceptual Coding for Bilateral Presence Systems

In this paper, lossy compression methods for haptic (velocity and force) data as exchanged in telepresence or virtual reality systems are introduced. Based on the proposed interpolative and extrapolative compression strategies, arbitrary passive compression algorithms can be implemented. The derived algorithms do not affect the stability of the presence system. Two algorithms were implemented and experimentally evaluated. The results show that constant data rate savings of 89% still lead to a perceptually transparent presence system.

Time Domain Passivity Control for multi-degree of freedom haptic devices with time delay

This paper generalizes the Time Domain Passivity Control concept originally introduced by J.-H. Ryu et al. (2004) in order to work for multi-degree of freedom (DoF) haptic systems with time delay. Its energy computation (named passivity observer) factors in the phase shift caused by time delay, and is improved by an energy estimation. Moreover, the variable damping of the passivity controller is generalized such that weighting by the mass matrix of the haptic device is possible. This transformation takes into account the direction-dependent inertia of multi-DoF haptic devices. Furthermore, a stability boundary for this damping is introduced for one as well as for several DoF allowing for high energy dissipation. Additionally, it is briefly shown that one single multi-DoF Cartesian passivity controller is advantageous compared to independent single-DoF passivity controllers in each joint of the haptic device. Finally, the generalized Time Domain Passivity Controller is experimentally verified using the DLR light weight robot arm as haptic device.

Virtual reality support for teleoperation using online grasp planning

Classic telepresence approaches allow a human to interact with a remote or a virtual reality environment (VR) with force feedback. Coupling with a remote robot can be used to work in dangerous environments without the human being on-site. The coupling with a VR system can be used for training and verification of task sequences or robotic actions.training and verification of task sequences or robotic actions. We present an enhanced telepresence system that uses the advantages of VR to perform manipulation tasks in remote environments with multifingered hands.It provides the user with an intuitive interface that visualizes the knowledge of the robot about its environment; and the combination of VR, telepresence and shared autonomy facilitates object manipulation for the user.

The Influence of Telemanipulation-Systems on Fine Motor Performance

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.

Assistance for telepresence using online grasp planning

This paper presents a user study evaluating teleoperated grasping performance and perceived workload of the human operator in a shared autonomy setup when working with different assistance modes and hand kinematics. The hands of a humanoid robot are operated using two approaches: direct mapping of human finger motions (telemanipulation), and “open/close” commands in combination with online grasp planning (shared autonomy). Human finger movements are measured with a data glove in both approaches. Grasp planning for the shared autonomy mode is based on the online calculation of reachable independent contact regions. In this approach, two visual assistance modes were tested: one indicating graspability in a binary manner (possible vs. impossible) and another one showing the potential contact regions for the fingertips. To analyze the influence of the hand kinematics on grasping performance and workload, two hands with different thumb positions are compared. The study shows that shared autonomy significantly decreases the task completion time and increases the grasp robustness compared to the direct mapping approach. The effect is more evident for a hand with optimized kinematics. The results reveal that choosing the appropriate control and assistance mode has a significant influence in telepresence performance.

A platform for bimanual virtual assembly training with haptic feedback in large multi-object environments

We present a virtual reality platform which addresses and integrates some of the currently challenging research topics in the field of virtual assembly: realistic and practical scenarios with several complex geometries, bimanual six-DoF haptic interaction for hands and arms, and intuitive navigation in large workspaces. We put an especial focus on our collision computation framework, which is able to display stiff and stable forces in 1 kHz using a combination of penalty- and constraint-based haptic rendering methods. Interaction with multiple arbitrary geometries is supported in realtime simulations, as well as several interfaces, allowing for collaborative training experiences. Performance results for an exemplary car assembly sequence which show the readiness of the system are provided.

Passive event-based extrapolation for lossy haptic data compression in bilateral presence systems

A new lossy compression method is proposed for haptic (force, velocity) data as exchanged in bilateral telepresence systems. The method is based on the passive extrapolative compression strategy proposed in [1]. The innovation is that the extrapolations do not have a stiff horizon, but are triggered by considerable changes (events) in the target environment. This enables longer average extrapolation horizons and thus, higher compression. Experiments are conducted using two DLR Light Weight Robots. The results indicate that the method outperforms older implementations.