International audience

This paper presents a new control framework for virtual humans (VHs) in a physics-based virtual environment. This framework combines multiobjective control with motion capture techniques. Each motion-tracking task is associated with a task wrench. Bounds are imposed on lower priority task wrenches to ensure the controller performance of higher priority tasks. An optimization problem is solved to compute optimal task wrenches that are based on wrench bounds. Finally, joint torques are computed using the optimal task wrenches. The novelty of our wrench-bound method is that it can handle inequality constraints on a higher priority task and maintain passivity as well. This control framework allows an operator to interact with the VH in real time, without the necessity of compromising the VH's balance. It also allows the VH to generate appropriate motions to handle interactions with the virtual environment, rather than to simply emulate captured motions. The effectiveness of our approach is demonstrated by a VH performing reaching and manipulation tasks.

This paper proposes a new framework of online hybrid control for virtual characters, which combines multi-objective control and motion capture techniques. At each time step, the motions of the operator are captured and sent to the character. These captured motions help the character understand what task the operator wants it to perform. Then, the character decides by itself how to execute proper actions while maintaining its balance, in a virtual environment which is different from the real world. Given a manipulation task, the desired virtual task wrench is computed thanks to a force control approach. The control system takes these task wrenches into consideration and solves a constrained quadratic problem for joint torques, which are then used to drive the virtual character. The whole control problem is solved online so that the virtual character can interact in real-time with the virtual environment as well as the operator. Examples using this control framework are presented as results from simulation.

This paper describes a 6 DOFs haptic cooperative platform dedicated to CAD objects simulation and virtual prototyping tasks. This system is based on several distributed physical engines linked together by a network subject to time delay. To deal with the destabilizing effect of time delay, a wave variable transformation is used. The wave variable formalism is adapted to the platform, therefore the behavior of each physical engine is similar. Several prototyping tasks have been tested on this system. A case is presented where two users are manipulating two distinct objects and interacting with each other.

In this paper we introduce a "spatialized haptic rendering" technique to enhance 6DOF haptic manipulation of virtual objects with impact position information using vibrations. This rendering technique uses our perceptive ability to determine the contact position by using the vibrations generated by the impact. In particular, the different vibrations generated by a beam are used to convey the impact position information. We present two experiments conducted to tune and evaluate our spatialized haptic rendering technique. The first experiment investigates the vibration parameters (amplitudes/frequencies) needed to enable an efficient discrimination of the force patterns used for spatialized haptic rendering. The second experiment is an evaluation of spatialized haptic rendering during 6DOF manipulation. Taken together, the results suggest that spatialized haptic rendering can be used to improve the haptic perception of impact position in complex 6DOF interactions.

In this paper, we propose to evaluate the benefits of event-based haptic rendering in virtual environments subject to high damping or low contact stiffness. In such context, the degraded perception of contact impairs the manipulation performance and the overall user's experience. Haptic rendering techniques known as event-based (or open-loop) rendering have been proposed to improve the realism of contacts in such contexts.

While realizing a task, human-beings are able to use grasping inside their environment in order to keep the most stable balance. Although such a behavior is quite natural for humans, it is very difficult to find the best formulation to adapt human motion to humanoid robots. This paper proposes a conceptually simple framework of human posture control based on optimization which takes into account grasp and friction and achieves robustness against external disturbances. A new stability criteria is also introduced. Contrary to most other approaches, our method deals not only with unilateral contacts with friction but also with bilateral grasps. This allows for arbitrarily pulling, pushing or twisting on a handhold. Additionally, and in contrast to classical methods based on ZMP, our method also accounts for contacts not being all in the same plane.

This paper decribes a general event-based approach to improve multimodal rendering of 6DOF (degree of freedom) contact between objects in interactive virtual object simulations. The contact events represent the different steps of two objects colliding with each other: (1) the state of free motion, (2) the impact event at the moment of collision (3) the friction state during the contact and (4) the detachment event at the end of the contact. The different events are used to improve the classical feedback by superimposing specific rendering techniques based on these events. First we propose a general method to generate these events based only on the objects' positions given by the simulation. Second, we describe a set of different types of multimodal feedback associated to the different events that we implemented in a complex virtual simulation dedicated to virtual assembly. For instance, we propose a visual rendering of impact, friction and detachment based on particle effects. We used the impact event to improve the 6DOF haptic rendering by superimposing a high frequency force pattern to the classical force feedback. We also implemented a realistic audio rendering using impact and friction sound on the corresponding events. All these first implementations can be easily extended with other event-based effects on various rigid body simulations thanks to our modular approach.

A new computer haptics algorithm to be used in general interactive manipulations of deformable virtual objects is presented. In multimodal interactive simulations, haptic feedback computation often comes from contact forces. Subsequently, the fidelity of haptic rendering depends significantly on contact space modeling. Contact and friction laws between deformable models are often simplified in up to date methods. They do not allow a "realistic" rendering of the subtleties of contact space physical phenomena (such as slip and stick effects due to friction or mechanical coupling between contacts). In this paper, we use Signorini's contact law and Coulomb's friction law as a computer haptics basis. Real-time performance is made possible thanks to a linearization of the behavior in the contact space, formulated as the so-called Delassus operator, and iteratively solved by a Gauss-Seidel type algorithm. Dynamic deformation uses corotational global formulation to obtain the Delassus operator in which the mass and stiffness ratio are dissociated from the simulation time step. This last point is crucial to keep stable haptic feedback. This global approach has been packaged, implemented, and tested. Stable and realistic 6D haptic feedback is demonstrated through a clipping task experiment.

This paper describes a set of visual cues of contact designed to improve the interactive manipulation of virtual objects in industrial assembly/maintenance simulations. These visual cues display information of proximity, contact and effort between virtual objects when the user manipulates a part inside a digital mock-up. The set of visual cues encloses the apparition of glyphs (arrow, disk, or sphere) when the manipulated object is close or in contact with another part of the virtual environment. Light sources can also be added at the level of contact points. A filtering technique is proposed to decrease the number of glyphs displayed at the same time. Various effects--such as change in color, change in size, and deformation of shape- can be applied to the glyphs as a function of proximity with other objects or amplitude of the contact forces. A preliminary evaluation was conducted to gather the subjective preference of a group of participants during the simulation of an automotive assembly operation. The collected questionnaires showed that participants globally appreciated our visual cues of contact. The changes in color appeared to be preferred concerning the display of distances and proximity information. Size changes and deformation effects appeared to be preferred in terms of perception of contact forces between the parts. Last, light sources were selected to focus the attention of the user on the contact areas.

In the present paper, we introduce a new control architecture aimed at driving virtual humans in interaction with virtual environments, by motion capture. It brings decoupling of functionalities, and also of stability thanks to passivity. We show projections can break passivity, and thus must be used carefully. Our control scheme enables task space and internal control, contact, and joint limits management. Thanks to passivity, it can be easily extended. Besides, we introduce a new tool as for manikin's control, which makes it able to build passive projections, so as to guide the virtual manikin when sharp movements are needed.

In this paper we consider deformable objects in haptic simulations. The physical simulation that drives haptic perception requires a good dynamic behavior. The inputs of the deformable model come from the treatment of the collision. We propose to focus on the contact restitution between deformable objects to guarantee "physical and perceptual realisms" of the haptic feedback. Signorini, in 1933, proposed a physical model of contact for deformable objects interacting with rigid static bodies (Signorini, S, 1933). This paper shows that the Signorini's model extents to contacts between two deformable objects using Gauss-Seidel resolution of complementarity problems. An interactive resolution of the overall formulation is presented and experienced on deformable objects using the finite linear-elements method.

The paper describes the HOMERE system: a multimodal system dedicated to visually impaired people to explore and navigate inside virtual environments. The system addresses three main applications: preparation for the visit of an existing site, training for the use of a blind cane, and ludic exploration of virtual worlds. The HOMERE system provides the user with different sensations when navigating inside a virtual world: a force feedback corresponding to the manipulation of a virtual blind cane, a thermal feedback corresponding to the simulation of a virtual sun, and an auditory feedback in spatialized conditions corresponding to the ambient atmosphere and specific events in the simulation. A visual feedback of the scene is also provided to enable sighted people to follow the navigation of the main user. HOMERE has been tested by several visually impaired people who were all confident about the potential of this prototype.

Using an industrial manipulator as a slave arm in a force-feedback teleoperation system requires to us deal with its poor backdrivability. Improving transparency of such a system, using a wrist force/torque sensor, is known as an effective and robust method. Another solution could be to use a base force/torque sensor. The paper focuses on the feasibility of such an approach in a force-feedback teleoperation context. It is then compared to a wrist force/torque sensor approach.

Tuning a telemanipulation system is still a real challenge. The task model is often unknown, the system must remain stable for a wide range of tasks, configurations, for different modes which share in a different way all the system degrees of freedom. Thinking of numerous controllers which come up with all these different situations is quite unrealistic. In fact, a compromise between the number of control parameters and the system performances has to be found. Here, we propose a method for the design of a decoupling controller allowing different tunings along teleoperated DOF and locally controlled ones.

It is shown that in hybrid position/force control as well as in multi-robot cooperation and teleoperation, the desired behavior of the system can be defined in terms of a massless mechanism whose joints act as ideal position or force sources. Based on this remark, a simple and robust controller is proposed. Experiments validate the approach.

In a teleoperation system, assistance can be given to the operator by constraining the telerobot position to remain within a restricted subspace of its workspace. A new approach to motion constraint is presented in this paper. The control law is established simulating a virtual ideal mechanism acting as a jig, and connected to the master and slave arms via springs and dampers. Using this approach, it is possible to impose any (sufficiently smooth) motion constraint to the system, including non-linear constraints (complex surfaces) involving coupling between translations and rotations. Physical equivalence ensures that the controller is passive. Experimental results obtained with a 6-DOF teleoperation system are given. Other applications of the virtual mechanism concept include hybrid position-force control and haptic interfaces.