Thomas Hulin

Evaluation of a vibrotactile feedback device for spatial guidance

In the present study, a vibrotactile feedback device for spatial guidance was evaluated in a tracking task paradigm. Participants (N = 18) had to translate and rotate virtual objects according to the vibrotactile vs. verbal cues without visual information. Both types of spatial guidance were evaluated using objective performance data (i.e. speed, accuracy) as well as subjective judgments. Results indicate that distinguishing spatial cues during the translational task was more difficult when being guided by vibrotactile feedback compared to verbal feedback. Nevertheless, individuals with vibrotactile guidance showed better performance at rotational tasks. Implications for the further design process and other areas of application are discussed.

Stability boundary for haptic rendering: Influence of human operator

Recent analysis on the stability boundary for haptic rendering assumed a stabilizing effect through a human operator holding a haptic device, without considering his/her dynamics directly. This paper derives stability boundaries of a linear model of a haptic system including those dynamics. It shows that all three elements of the human arm modeled as mass-spring-damper system contribute to stability. The haptic system itself is composed of a haptic device colliding with a virtual wall modeled as time-delayed discrete-time spring-damper system. Furthermore, the article proves that the recently found linear stability condition for haptic devices of Gil et al. still holds if a human is holding the haptic device. Finally, a relation to Colgatepsilas passivity condition defining a robustly stable region is given.

Stability Boundary for Haptic Rendering: Influence of Physical Damping

Physical damping is increasing the z-width of haptic simulations. This paper derives the normalized stability boundaries for physically damped one degree of freedom haptic devices colliding with a virtual wall represented as spring-damper system. These boundaries are independent of the haptic devices mass and the sampling time. Furthermore, the dependency of the maximum stable virtual stiffness is discussed. Moreover, this paper illustrates that the passive region which is defined by Colgates passivity condition is a subset inside the stable region for undelayed systems, but not for delayed systems

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.

Passivity and Stability Boundaries for Haptic Systems With Time Delay

This paper presents a passivity and a stability analysis of a one degree of freedom haptic device that is interacting with a virtual wall. These two analyses take into account the influence of a human operator and time delay. A peculiarity of the presented approach is the exact combination of discrete- and continuous-time elements, which reveals fundamental parameter dependencies for passivity and stability. These dependencies do not only differ in scale for passivity and stability, but consist in substantially different relations. By using realistic parameter ranges for human arms, this paper clearly illustrates that the maximum stable stiffness of virtual walls is far higher than admitted by passivity. Responsible for this great disparity is the limited stiffness of real human arms, as passivity covers a stiffness range that is orders of magnitudes larger than feasible. Finally, useful guidelines for designing stable haptic systems are concluded.

Stability Boundary for Haptic Rendering: Influence of Damping and Delay

The influence of viscous damping and delay on the stability of haptic systems is studied in this paper. The stability boundaries have been found by means of different approaches. Although the shape of these stability boundaries is quite complex, a new linear condition which summarizes the relation between virtual stiffness, viscous damping and delay is proposed. This condition is independent of the mass of the haptic device. The theoretical results are supported by simulations and experimental data using the DLR light-weight robot.

A benchmarking suite for 6-DOF real time collision response algorithms

We present a benchmarking suite for rigid object collision detection and collision response schemes. The proposed benchmarking suite can evaluate both the performance as well as the quality of the collision response. The former is achieved by densely sampling the configuration space of a large number of highly detailed objects; the latter is achieved by a novel methodology that comprises a number of models for certain collision scenarios. With these models, we compare the force and torque signals both in direction and magnitude. Our device-independent approach allows objective predictions for physically-based simulations as well as 6-DOF haptic rendering scenarios. In the results, we show a comprehensive example application of our benchmarks comparing two quite different algorithms utilizing our proposed benchmarking suite. This proves empirically that our methodology can become a standard evaluation framework.

Workspace comparisons of setup configurations for human-robot interaction

In virtual assembly verification or remote maintenance tasks, bimanual haptic interfaces play a crucial role in successful task completion. This paper proposes a method for objectively comparing how well a haptic interface covers the reachable workspace of human arms. Two system configurations are analyzed for a recently introduced haptic device that is based on two DLR-KUKA light weight robots: the standard configuration, where the device is opposite the human operator, and the ergonomic configuration, where the haptic device is mounted behind the human operator. The human operator directly controls the robotic arms using handles. The analysis is performed using a representation of the robot arm workspace. The merits of restricting the comparisons to the most significant regions of the human workspace are discussed. Using this method, a greater workspace correspondence for the ergonomic configuration was shown.

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.

Evaluation of visual and force feedback in virtual assembly verifications

This work presents an evaluation study of two different collision feedback modalities for virtual assembly verification: visual and force feedback. Forty-three subjects performed several assembly tasks (peg-in-hole, narrow passage) designed with two levels of difficulty. The used haptic rendering algorithm is based on voxel and point data-structures. Both objective - time and collision performance - and subjective measures have been recorded and analyzed. The comparison of the feedback modalities revealed a clear and highly significant superiority of force feedback in virtual assembly scenarios. The objective data shows that whereas the assembly time is similar in most cases for both conditions, force collision feedback yields significantly smaller collision forces, which indicate higher assembly precision. The subjective ratings of the participants define the force feedback condition as the most appropriate for determining clearances and correcting collision configurations, being the best suited modality to predict mountability.