In this paper, we propose a closed-loop force sensor based nested admittance/impedance control strategy to actively estimate and minimize the effects of geometric misalignment that naturally occur during assembly tasks with compliant robots. The method allows the robot to be used with a stiff impedance control setting, which is beneficial for free air motion performance, yet allows to adjust for large misalignment errors between parts that need be assembled. First, the stability bounds on the control parameters of this method are established through numerical simulation, after which they are compared with the experimentally determined parameters. Trial peg-in-hole insertion experiments are performed with a 6-DOF KUKA LWR-4+ robot under various degrees of rotational misalignment, where metal pegs are being inserted into metal holes under tight tolerances. The proposed method allows successful peg insertions even under large rotational misalignments of up to 20° (13 fold increase compared to 1.5° we achieved with traditional impedance control alone), without the need to adjust the position trajectories with complex models on the fly. Moreover, it provided a 5 fold reduction of the average forces exerted on the environment compared with using impedance control alone.

This paper introduces a new Learning from Demonstration (LfD)-based method that makes usage of robot effector forces and torques recorded during expert demonstrations, to generate force-based haptic guidance reference trajectories on-line, that are intended to be used during haptic shared control for additional operator `guidance'. Derived haptic guidance trajectories are superimposed to master-device inputs and feedback forces within a bilateral control experiment, to assist an operator by the guidance during peg-in-hole insertion. We show that 96 peg-in-hole expert demonstrations were sufficient to obtain a good model of the task, which was used on-line to generate haptic guidance trajectories in real-time with a 1kHz sampling rate.

On June 5that 21:10 CEST, the European Space Agency's Telerobotics and Haptics Laboratory conducted the first in history haptic handshake between space and Earth. This demonstration was part of the Haptics-2 experiment, which makes use of two haptic joysticks; one located in space on-board the International Space Station (ISS), and the other one on ground at ESA's laboratory in the Netherlands. Both systems can be connected through the TDRSS geosynchronous satellites via a real-time data link with sufficient performance to perform haptic teleoperation tests. This paper describes the mechatronic design of the haptic devices, the software and the system implementation required for the Haptics-2 experiment. It reports results of a real-time high-frequency characterization of the satellite data-link indicating a round-trip time delay of approximately 850 milliseconds and presents mechatronic performance data of the haptic joysticks. Moreover, the paper presents experimental results from the first haptic handshake conducted between space and ground with astronauts on-board the ISS.

The purpose of this paper is to analyze the effects of inaccuracies of haptic guidance systems during execution of constrained tasks. The Lawrence teleoperation framework is extended in this paper by addition of an impedance type, position based attractive haptic guidance and analyzed from a control system perspective. Specifically, we focus on systems where haptic guidance is used together with position or force based feedback from a slave robot to a master device. The forces due to the inaccuracy of the guidance partially counteract the feedback force, effectively masking this problematic inaccuracy from the operator. This effect is discussed by using the proposed framework and quantified. Theoretical results are supported with numerical simulation and experimentally verified on a real 6-DOF haptic teleoperation setup.

In a typical space teleoperation task, mismatches between the viewing direction of the operator and the direction of their required control input are often unavoidable. To execute these tasks, the operator is then required to perform mental rotations. Recent studies have shown that the task performance can thereby significantly decrease. In this paper, for the first time, the influence of mental rotations on task performance is studied if hap tic feedback is provided to the operator. A human factors experiment is conducted which analyses the influence of two different hap tic feedback control methods via various visual missmatch angles. The rotation is thereby set to the extreme cases of 0. and 180. to clearly analyze the effects. The first hap tic feedback method consists of direct, scaled force and torque feedback to the operator as measured by a force/torque sensor at the slave robot. The second method consists of hap tic shared control which provides artificially generated guidance forces to the operator. It is shown that mental rotations decrease teleoperation performance despite the addition of direct force feedback. In contrast, hap tic shared control provides lower increase in the operator mental workload and also less between-operator variability of errors made due to the mental rotations.

In this paper a new model-mediated teleoperation framework based on rate-control input is presented. The system facilitates force feedback teleoperation and is inherently robust to severe time delays yet still provides high level of rate/force tracking fidelity. Previously published methods on model-mediated teleoperation are here extended to accept rate commands and use the slave robot's programmed impedance as a contact model for force feedback generation. The system is designed to ensure decoupling of the control loops in case of environment changes, which also allows to cope with severe and possibly variable time delay in the communication channel. Stability and performance is analyzed and the system is shown to remain stable for finite delays. Tuning guidelines with design trade-offs are provided. The presented method is demonstrated on an experimental 1-DOF master/slave setup in a teleoperation scenario, showing stability and reference rate & force tracking performance over 2 seconds of round-trip communication delay in bilateral control.

Haptic guidance systems support the operator in task execution using additional forces on the input device. Scaling of the guidance forces determines the control authority of the support system. As task complexity may vary, one level of the guidance scaling may be insufficient, and adaptation of the control authority may be helpful. The available literature mostly proposed to adapt the authority based on external cues (e.g. actual performance or safety) and the user had no direct way to modulate the desired level of support. In this paper we investigated a variable authority guidance scheme based on the user grip force. During a user study (with 8 subjects) we explored two opposite approaches to trade the control authority (i.e. increasing or decreasing guidance force magnitude with increased user grip). To simulate increased task difficulty and imperfections of the haptic guidance system, at random times either an unpredictable force disturbance was added or subjects were presented with incorrect guidance. While the performance differences between the fixed- and the variable-authority schemes were not significant, the “decreasing guidance with increased user grip” scheme allowed to substantially reduce the user control effort (steering force), especially when the guidance system was incorrect. The presented method essentially provides additional control over the guidance system without reducing the performance.

The CyberGrasp™ is a well known dataglove-exoskeleton device combination that allows to render haptic feedback to the human fingers. Its design, however, restricts its usability for teleoperation through a limited control bandwidth and position sensor resolution. Therefore the system is restricted to low achievable contact stiffness and feedback gain magnitudes in haptic rendering. Moreover, the system prohibits simple adaption of its controller implementation. In this paper, the ExHand Box is presented, a newly designed back-end to widen the CyberGraspTM's bandwidth restrictions and to open it up for fully customized controller implementations. The ExHand Box provides a new computer, interface electronics and motor controllers for the otherwise unmodified CyberGloveand CyberGraspTMhand systems. The loop frequency of the new system can be freely varied up to 2 kHz and custom controllers can be implemented through an automatic code generation interface. System performance identification experiments are presented that demonstrate improved behavior in hard contact situations over a range of sampling periods. Maximum contact stiffnesses of up to 50kN/m in a stable condition are demonstrated, which is significantly higher than what could be achieved with the non-customized original system version. Moreover, a bilateral control experiment is conducted to demonstrate the new system's usability for generic teleoperation research. In this experiment a raycasting algorithm is introduced for pre-contact detection in order to compensate for high delay and jitter communication links between master and slave as they appear in an Ethernet network. It is demonstrated that the contact stiffness can be maintained in the order of magnitude of the system performance identification with a demonstrated stiffness of 41kN/m in a stable condition.

For the purpose of ergonomic human-machine interaction and geometrical design of hand held haptic devices, a kinematic model that represents the functional anatomy of different human hands is desired. It is the goal of this paper to present a kinematic hand model that is based on human physiology and that is easily adaptable to represent various real human hand sizes. This is achieved by exploiting body proportions to derive finger segment lengths from the hand length. A partial hand model validation, involving index- and middle finger validation using a group of subjects, indicates that the use of body proportions offers a good estimate of finger length from a given hand length. Model estimated fingertip positions over a motion trajectory remain within reasonable limits when compared with experimental data for this subject group. The model is promising for usage in practical situations since only hand length, which is easy to measure or to obtain from literature, is required as an input. Phalange lengths, which are sparsely available from literature and difficult to measure, are generated by the model.

This paper introduces the mechatronic design and a first performance analysis of a new haptic exoskeleton, the X-Arm-2. The X-Arm-2 is a fully actuated force-reflecting human arm exoskeleton that is based on our previously proposed approach to ergonomic and human-centered exoskeleton design [1] [2]. The X-Arm-2 is a highly power-dense impedance-type haptic device that (1) can interact with natural human arm movement of varying operators without requiring adjustments and creating constraint forces, (2) provides crisp force-feedback through high actuator bandwidth, low residual friction and good joint torque sensor resolution, (3) has a low total mass of only 6.2 kg and (4) low inertia through a human-oriented mixed implementation of Bowden-cable relocated and directly-integrated DC actuators.

This paper introduces a study aimed to help quantify the benefits of limited-performance force-feedback user input devices for space telemanipulation with a dexterous robotic arm. A teleoperated robotic hand has been developed for the European Space Agency by the German Aerospace Center (DLR) for a lunar rover prototype. Studies carried out on this telerobotic system investigated several criteria critical to telemanipulation in space: (1) grasping task completion time, (2) grasping task difficulty, (3) grasp quality, and (4) difficulty level for the operator to assess the grasp quality. Several test subjects were allocated to remotely grasp regular and irregular shaped objects, under different combinations of visual- and force-feedback conditions. This work categorized the benefits of visual- and force-feedback in teleoperated grasping through several performance metrics. Furthermore, it has been shown that, with local joint-level impedance control, good grasping performance with rigid hard objects can be achieved, even with limited force-feedback information and low communication bandwidth. On the other hand, a performance ceiling was also found when grasping deformable objects, where the limited force-feedback setup cannot sufficiently reflect the object boundary to the teleoperator.

In this paper it is shown how variation of the kinematic structure of an arm exoskeleton and variation of its fixation pressure on the human limb influences subjectively perceived task performance, such as comfort and the individual indices of the NASA TLX rating scale. It is shown by experimental results that the attachment pressure has a dominant effect on perceived comfort, mental load, physical demand and effort experienced by subjects and is optimal within a range of 10 30 mmHg. Furthermore, it is shown that the inclusion of passive compensatory joints inside an exoelectrons structure can reduce mental demand during a tracking task. When the outcome of this paper is interpreted in combination with a set of objective performance results that were presented earlier , the subjective performance metrics underline the fact that passive compensatory joints paired with an attachment pressure of 20 mmHg increase ergonomics and provide optimal conditions for task performance and comfort.

It is the goal of this paper to introduce an analytical model that allows predicting and interpreting the characteristics of constraint forces generated by misaligned joint axes between human operators and wearable robots during physical human-robot interaction (pHRI). The pHRI model is based on geometric parameters that describe the combined human-robot system. It is applied in this paper to measured constraint forces from a pHRI experiment. The model is validated with the experimental data. The geometrical model parameters are identified from force and position measurements by non-linear parameter optimization. The attachment stiffness and the actual offsets between the exoskeleton and the human joints are estimated. For the tested subject, the stiffness reaches 222 N/m and constraint forces are shown to be in the order of plusmn 10 N. It is shown in this paper how an ergonomically designed wearable robot with passive compensation joints can reduce such interaction forces.

This paper presents the development of SAM, the Sensoric Arm Master, a 7-DOF portable exoskeleton with integrated actuation and sensors. Local joint control is implemented to improve performances of the device. Some experiments have been conducted with the system to show the functionality of the exoskeleton device linked to a virtual reality.

It is the goal of this paper to present performance differences between a Direct Drive master actuator (DD) and a Bowden Cable relocated master actuator (BCD) in a typical force-feedback tele-manipulation experiment with a virtual slave. The BCD actuator is a candidate actuator for implementation in a wearable exoskeleton, in order to reduce mass and inertia on each joint of the movable structure. The BCD performance matches the one of the DD in terms of torque and position tracking in a 4 channel control. The maximum rendered contact stiffness is suitable for implementation in the ESA human arm exoskeleton, with a maximum of about 36 Nm/rad. When, instead of the DD, a relocated BCD actuator is implemented in an exoskeletons movable structure, the mechanical output power-density can be increased by more than 5 fold up to 31 mNm/cm3, with comparable performance. The specific power is then increased by more than 6 fold, to 13 Nm/kg. The Bowden Cable transmission wrapping angle alters the free movement friction only marginally by about 50 mNm only. The tracking performances are hardly affected and the contact stiffness increases with increasing wrapping angle. Transmission wrapping angles of up to 270 Deg. are tested.

This paper describes a novel ground development facility that is currently being built at the European Space Agency. The facility can be used to develop and test new man-machine interfaces for tele-control of dexterous space manipulators. Furthermore, the facility allows comparing performance of existing input devices, such as conventional joysticks, with novel devices, such as exoskeletons. The Ground Test-bed allows conducting tele-manipulation experiments with a real robot and to measure performance metrics during remote operations. The experimental comparisons planned to be undertaken with the test-bed are outlined.

This paper introduces a novel type of actuator that is investigated by ESA for force-reflection to a wearable exoskeleton. The actuator consists of a DC motor that is relocated from the joint by means of Bowden cable transmissions. The actuator shall support the development of truly ergonomic and compact wearable man-machine interfaces. Important Bowden cable transmission characteristics are discussed, which dictate a specific hardware design for such an actuator. A first prototype is shown, which was used to analyze these basic characteristics of the transmissions and to proof the overall actuation concept. A second, improved prototype is introduced, which is currently used to investigate the achievable performance as a master actuator in a master-slave control with force-feedback. Initial experimental results are presented, which show good actuator performance in a 4 channel control scheme with a slave joint. The actuator features low movement resistance in free motion and can reflect high torques during hard contact situations. High contact stability can be achieved. The actuator seems therefore well suited to be implemented into the ESA exoskeleton for space-robotic telemanipulation.