An enhanced force bounding approach for stable haptic interaction by including friction

The goal of this paper is to develop haptic-visual interaction training system for aircraft fuel supply simulation. Operators can use this system to simulate refueling aircraft in virtual environment with tactile and visual feedback. The simulator is built based on haptic device Omega 3DOF. Hardware and software are discussed to meet the requirement of training simulation. Experiment results show that the system can provide stable simulation of aircraft refueling operation. For aviation engineers, fuel supply is an operation to use fuel supply system to refuel aircrafts. The structures of refueling system and aircraft fuel tank are complex. Moreover, the evaporated fuel may pollute the environment and cause explosion in the refueling process. Therefore, the aviation engineers should strictly obey the operating rules and expertly grasp the skill to refuel aircraft. They should take sufficient time for a long practice in aircraft refueling. Now, the cultivation of aviation engineers' refueling operation includes watching demo to learn the operating rule and actual operation with the guiding of teachers. After watching the correct refueling operation and learning the operating rule, operators may finish the refueling operation with the instruction of the professional. However, they need to practice enough times to grasp this skill, and the instruction of teacher is necessary in the whole training process. This training needs a long period to cultivate an eligible operator and the cost is high. Therefore, a haptic interaction system realistically mimicking refueling environment would significantly contribute to the improvement of refueling operation training. The aircraft refueling training system is a haptic interaction system with the capacity of haptic-visual display. Operators can use it to simulate aircraft refueling operation in a virtual environment and can sense haptic-visual feedback that is similar to that of the same operation in physical world. The operators can learn the operating rules and grasp the operating skill based on virtual operation. It will help to reduce the time and the cost of actual operation for refueling operation training.

Haptic interaction in slow virtual environments (VEs) can become unstable due to the phase lag introduced in the control loop by the slow update rate of the VE. Increasing the physical damping and/or limiting the contact stiffness rendered to users can mitigate the destabilizing effect of the low VE update rate. However, large physical damping and compliant virtual contacts decrease the sense of presence in VEs, especially during interaction with rigid virtual objects. To increase the maximum virtual contact stiffness that can be rendered to users without increasing the interface damping, this paper proposes a control strategy based on multirate wave communications between a haptic interface and a VE updated at a slow and fixed rate. The multirate wave communications are shown to be guaranteed passive only if the decrease of the wave sampling rate at the connection between the haptic interface and the VE does not cause aliasing. Therefore, an antialiasing low-pass filter is placed before the wave rate drop in the communications. The passivity condition is verified analytically and numerically for multirate haptic interaction in VEs with various contact stiffnesses and update rates. The transparency of haptic interaction in slow VEs to which users connect via passive multirate wave communications is investigated analytically in the frequency domain. Experiments validate that passive multirate wave communications can render stiffer contact in slow VEs than conventional direct coupling, and illustrate the destabilizing effect of the aliasing caused by the sampling rate drop in the communications.

In recent years, there has been a growing interest in developing force feedback interfaces that allow people to access information presented in 3D virtual reality environments (VEs). One of the major application fields is medicine. Several cases exist where standard medical treatment cannot be applied to patients for several reasons, such as distance from hospital, lack of specialized doctor, and lack of medical equipment. The use of haptic‐enabled virtual environments provides an alternative solution in a variety of such cases, thus enabling assessment and treatment of patients. Furthermore, haptic‐enabled virtual environments provide a nonhazardous means of treatment for several disorders like phobia treatment, where the patient has to be exposed to the phobia object. Training of disabled people, like the visually impaired, is another important application of haptic‐enabled VEs. This chapter presents an extended description of haptic virtual environments and the major methodologies and techniques used in medical applications. Further, it demonstrates indicatively a number of applications in order to illustrate the applicability of VEs in several areas of medical treatment and training.

This paper presents a control method using an adjusting output-limiter for stable haptic rendering in a virtual environment. In a simulation of force-reflecting interaction with deformable objects in a virtual environment, a quick computation of the accurate impedance of deformable objects is rare. This is particularly true when physics-based models, such as tensor-mass models or mass-spring models, are used. The problem is aggravated if the simulation involves changes in the geometry and/or impedance of the deformation model, such as cutting or suturing. The proposed control method guarantees stable haptic interactions with deformable objects of unknown and/or varying impedance. The method is based on the time-domain passivity theorem and the two-port network model. The controller adjusts the maximum permissible force to guarantee the passivity of the haptic system at every sampling instant. The controller notes only the magnitude of the reflective force, and does not depend on properties of the employed force model. This allows the proposed control method applicable to haptic systems involving deformable objects with unknown, nonlinear, and/or time-varying impedance. Designs of the controllers are presented for impedance-type and admittance-type haptic systems. The method is also extended for multiple degrees-of-freedom.

Haptic rendering has the potential to increase the quality of human-computer interaction with virtual environment by accommodating the sense of touch. In this paper, a 7 DOF arm type exoskeleton device is designed and implemented. Human user can haptically interact with virtual environment by using this light-weight device. The principles of measuring user's arm motions are presented, which include the dimensional mechanism. The motion of each joint of the proposed haptic device is nearly independent. The virtual contact force is also calculated in real time to meet the stringent requirement of real time haptic rendering. Experiments results show promising feasibility of the arm type exoskeleton device.

Adaptive nonlinear controllers have been proposed to improve the stability and transparency in haptic rendering. Through a separation of control and dynamic simulation, the proposed controllers can couple impedance-type haptic devices with impedance and admittance-type virtual environment simulators. The intervening dynamics of the interface, subject to stability constraints, can be replaced with an adjustable mass-damper tool within the proposed framework. Nonlinear dynamics for haptic device and parametric uncertainty in user's arm dynamics are considered in the design of controllers which require position, velocity and force measurements. The transparency and stability of the proposed haptic control systems are investigated using a Lyapunov analysis. The controllers are implemented on a two-axis impedance-type haptic device for interacting with impedance and admittance-type virtual environments. In the impedance-type environment, interaction with a virtual wall is modeled by a spring-damper coupler. This model along with an alternative constraint-based rigid wall model are employed in the admittance-type simulations. Although the two controllers behave similarly in free motion, the controller for admittance-type environments is capable of rendering markedly stiffer rigid contacts.

Maintaining a stable haptic interaction with virtual environments, especially with physically-based deformable objects, has long been an active area of research. We address this issue by presenting a comprehensive haptic system architecture and virtual reality simulation, where a physically-based modeling using the Finite Element Method (FEM) combined with an “elementary displacement” approach has been implemented. This approach ensures the stability of haptic interaction with deformable objects and considers interaction with multipoints contacts. The Future Haptic Science Encyclopedia (FHSE) we developed to verify our proposal and demonstrate the new haptic interface HIRO II. We also present an objective and subjective evaluation of FHSE simulation.

In this paper, we consider generalized delay-dependent stability conditions of Takagi-Sugeno fuzzy systems with discrete and distributed time-delays. For fuzzy systems with discrete time-delays, both delay-independent stability conditions and delay-dependent stability conditions have already been obtained. However, no stability condition for fuzzy systems with distributed time-delays has appeared in the literature. This is also true in case of the robust stability for uncertain fuzzy systems with distributed time-delays. With the aid of the stability theorems of linear systems with distributed time-delays, we employ a similar Lyapunov functional for the stability of fuzzy time-delay systems. Then we introduce many free matrices to such a Lyapunov functional, in order to obtain delay-dependent stability conditions. These techniques lead to generalized and less conservative stability conditions. In fact, delay-dependent stability conditions thus obtained are given in linear matrix inequalities(LMIs) and guarantee a wide stability region. We also consider the robust stability of fuzzy time-delay systems with uncertain parameters. Applying the same techniques made on the stability conditions, we obtain delay-dependent sufficient conditions for the robust stability of uncertain fuzzy systems with discrete and distributed time-delays. Moreover, we consider the state feedback stabilization. Based on stability and robust stability conditions, we obtain conditions for the state feedback controller to stabilize the fuzzy time-delay systems. Finally, we take some examples to illustrate our results.

This paper investigates Hey yaa, a haptic wearable interaction system that allows sensory-motor communication through vibration. The system allows users to call each other attention through haptic sensation, without using voice or vision. Hey yaa, thereby, meets the special needs of the hearing impaired and works as an assistive technological solution to call people when they usually wouldn't be able to do so. Hey yaa prototype consists of two waist belts. When a button is pressed in one, the other one vibrates, drawing the user's attention. We evaluated Hey yaa concept and prototype regarding usability, usefulness, usage learning, communication with interlocutor and appearance. As a result, test users confirmed its relevance and gave directions for further improvement.

This paper presents a novel use of sensor sytem for human gait recognition evolution to be employed in virtual environments exploration. The system allows free human motion inside a virtual environment employing human gait recognition. Experimental sessions have been organized in order to acquire acceleration data related to walking and running of several subjects. We present an algorithm that recognizes a person gait in real-time. The recognized motion can be used to enhance the presence of the user in the virtual environment. A simple scenario has been developed to assess the system functionality. The experiments carried out show that our system is suitable to classify human motion, count steps and, moreover, can be used both in virtual and augmented reality (VR) environments for an improved interaction.

In this paper, we propose the use of a nonlinear disturbance-observer for estimation of contact forces during haptic interactions. Most commonly used impedance-type haptic interfaces employ open-loop force control under the assumption of pseudostatic interactions. Advanced force control in such interfaces can increase simulation fidelity through improvement of the transparency of the device. However, closed-loop force feedback is limited both due to the bandwidth limitations of force sensing and the associated cost of force sensors required for its implementation. Using a disturbance-observer, we estimate contact forces at the tool tip, then use these estimates for closed-loop control of the haptic interface. Simulation and experimental results, utilizing a custom single degree-of-freedom haptic interface, are presented to demonstrate the efficacy of the proposed disturbance-observer (DO)-based control approach. This approach circumvents the traditional drawbacks of force sensing while exhibiting the advantages of closed-loop force control in haptic devices. Results show that the proposed disturbance-observer can reliably estimate contact forces at the human-robot interface. The DO-based control approach is experimentally shown to improve haptic interface fidelity over a purely open-loop display while maintaining stable and vibration-free interactions between the human user and virtual environment.

The emergence of low cost hap tic devices and the evolution of technologies for developing virtual reality environments for web have motivated the development of tools that allow the use of hap tic systems together with applications and web browsers. The availability of web hap tic systems results on the possibility of multisensory experiences for internet users. This paper analyzes technologies for integrating hap tic and web systems, exposing the features of each tool in order to find the best strategy to incorporate virtual touch in Museu3l by using the hap tic technology, so that it becomes one of the first virtual museums that makes hap tic interaction with a work of art in a web visit possible.

Efforts exist to combine a brain-machine interface (BMI) into a 3D virtual environment (VE) for visual tasks. User interaction via haptic stimuli within the VE is still unexplored for developing the BMI however, due to little understanding of cognitive processes related to such haptic interaction. Hence, we investigated a feasibility of estimating cognitive processes related to haptic interaction. Involved in the investigation, human participants undertook a task via different haptic stimuli (e.g., force and vibration) within a 3D VE. Their brain activities evoked by the stimuli were acquired as electroencephalography signals. Patterns of event-related potential and power spectral density were extracted from the signals, indicating activation in certain brain areas. The estimation of connectivity among these areas used directed transfer function, emphasizing on the middle of the $\beta$ band (14 30)

We show a novel encountered‐type haptic system, H‐Wall, to enable haptic feedback using a manipulator of seven degrees of freedom suitable for simulating indoor virtual reality environments, which are characterized and confined by a set of vertical walls and revolving doors. At runtime, our system tracks hand motion using a red–green–blue depth sensor and locates its configuration. Then, the robotic manipulator plans a trajectory for the end effector, attached to a rectangular rigid board, to make contact with the hand to deliver a sense of touch as long as the perceived hand contact force is substantial. The force feedback is generated in a passive sense for static walls that the rigid board, corresponding to a vertical wall, holds its position as long as the perceived hand contact force is substantial. For a revolving door, the force feedback is generated in an active sense based on impedance control. In order to address the issue of limited workspace, we also propose a new reachability map, calledper‐plane reachability map, that is optimized to answer whether passive haptic feedback can be generated by a manipulator when the user touches a vertical wall at a given orientation. We successfully demonstrate our system to provide an illusion to the user in a virtual environment with touch sensation to the surrounding environment.

This paper presents a Proportional Derivative (PD) controller with gain-scheduling depending on the distance for haptic interfaces and virtual environments subject to communication delays. It is well known that the presence of delays deteriorates the overall system performance. More precisely, depending on the proposed architecture as, for example, bilateral position-position coupling, time-delays introduce a feeling of viscosity in free motion and reduce the sense of stiffness in the case of hard contacts. Even in the presence of time-delays, the controller gains can be tuned in order to guarantee the desired behavior and performances for one case (free or restricted motion) with the price of the completely loss of the other case performances and behavior. To overcome this drawback, a gain-scheduling controller is designed, able to guarantee the desired behavior and performances for free and restricted motion. The experimental results obtained on a three-degree of freedom real-time experimental platform enforce the theoretical developments.