Andre Schiele

Bowden Cable Actuator for Force-Feedback Exoskeletons

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

Ergonomics of exoskeletons: Objective performance metrics

In this paper it is shown how variation of the kinematic structure of an exoskeleton and variation of its fixation strength on the human limb influences objective task performance metrics, such as interface load, tracking error and voluntary range of motion in a signal tracking experiment.

SAM : A 7-DOF portable arm exoskeleton with local joint control

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.

Toward understanding the effects of visual- and force-feedback on robotic hand grasping performance for space teleoperation

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.

Influence of attachment pressure and kinematic configuration on pHRI with wearable robots

The goal of this paper is to show the influence of exoskeleton attachment, such as the pressure on the fixation cuffs and alignment of the robot joint to the human joint, on subjective and objective performance metrics i.e. comfort, mental load, interface forces, tracking error and available workspace during a typical physical human-robot interaction pHRI experiment. A mathematical model of a single degree of freedom interaction between humans and a wearable robot is presented and used to explain the causes and characteristics of interface forces between the two. The pHRI model parameters real joint offsets, attachment stiffness are estimated from experimental interface force measurements acquired during tests with 14 subjects. Insights gained by the model allow optimisation of the exoskeleton kinematics. This paper shows that offsets of more than ±10 cm exist between human and robot axes of rotation, even if a well-designed exoskeleton is aligned properly before motion. Such offsets can create interface loads of up to 200 N and 1.5 Nm in the absence of actuation. The optimal attachment pressure is determined to be 20 mmHg and the attachment stiffness is about 300 N/m. Inclusion of passive compensation joints in the exoskeleton is shown to lower the interaction forces significantly, which enables a more ergonomic pHRI.

A new generation of ergonomic exoskeletons - The high-performance X-Arm-2 for space robotics telepresence

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.

Performance difference of Bowden Cable relocated and non-relocated master actuators in virtual environment applications

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.

Time Domain Passivity Controller for 4-Channel Time-Delay Bilateral Teleoperation

This paper presents an extension of the time-domain passivity control approach to a four-channel bilateral controller under the effects of time delays. Time-domain passivity control has been used successfully to stabilize teleoperation systems with position-force and position-position controllers; however, the performance with such control architectures is sub-optimal both with and without time delays. This work extends the network representation of the time-domain passivity controller to the four-channel architecture, which provides perfect transparency to the user without time delay. The proposed architecture is based on modelling the controllers as dependent voltage sources and using only series passivity controllers. The obtained results are shown on a one degree-of-freedom setup and illustrate the stabilization behaviour of the proposed controller when time delay is present in the communication channel.

Ergonomics of exoskeletons: Subjective performance metrics

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.

Towards Intuitive Control of Space Robots: A Ground Development Facility with Exoskeleton

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 testbed 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