Real-Time Impulse-Based Simulation of Rigid Body Systems for Haptic Display

This paper studies a new sensorial approach to improving communication between partners during collaborative tasks taking place in abstract and non-visual virtual reality environments. The sensorial approach was investigated in the context of the search and identification of targets in a simplified 2D environment. It consists in finding a spatial configuration corresponding to a defined criterion such as a maximum, minimum, or defined score. During the collaborative search, users need to be aware of their results and also the results of their partners. In addition, they need to compare examined scores (e.g., docking score or physical value) with other results to make decisions. To support these features, an audio---haptic display was developed employing binaural audio with an intermodal stimuli synthesis design to improve the collaborative search. This rendering tool allows for simultaneous use of the audio and haptic channels which enables an efficient individual search and comparison of results. In addition, it improves the communication and activity coordination between the partners. An experiment was carried out to evaluate the contribution of the tool to improve the collaborative search of targets in a 2D non-visual environment. The results clearly show a significant improvement in performance and working efficiency with the audio---haptic display as compared to a traditional haptic-only condition. Moreover, we observed a reduction in the need for verbal communication during some steps of the search process. However, this approach introduces some communication conflicts during the steps presenting high-level interactions between partners which reduce the working efficiency of some groups.

Encountered-Type Haptic Displays (ETHDs) represent a field of haptic displays with the premise of not using any type of actuator directly in contact with the user skin, thus providing an alternative integration of haptic displays in virtual environments. In this paper, we present novel interaction techniques (ITs) dedicated to ETHDs. The techniques aim at addressing the issues commonly presented for these devices such as limited contact areas, lags and unexpected collisions with the user. First, our paper proposes a design framework based on several parameters defining the interactive process between user and ETHD (input, movement control, displacement and contact). Five techniques based on different ramifications of the design space framework were conceived, respectively named: Swipe, Drag, Clutch, Bubble and Follow. Then, a use-case scenario was designed to depict the usage of these techniques on the task of touching and coloring a wide, flat surface. Finally, a user study based on the coloring task was conducted to assess the performance and user experience for each IT. Results were in favor of Drag and Clutch techniques which are based on manual surface displacement, absolute position selection and intermittent contact interaction. Taken together our results and design methodology pave the way to the design of future ITs for ETHDs in virtual environments.

Impedance-type kinesthetic haptic displays aim to render arbitrary desired dynamics to a human operator using force feedback. To render realistic virtual environments, the difference between desired and rendered dynamics must be small. In this paper, we analyze the closed-loop dynamics of haptic displays for three common virtual environments: a spring, a damper, and a spring-damper, including the effects of time delay and low-pass filtering. Using a linear model, we identify important parameters for the rendered dynamics in terms of effective impedances, a conceptual tool that decomposes the displays closed-loop impedance into components with physical analogs. Our results establish bandwidth limits for rendering effective stiffness and damping. The effective stiffness bandwidth is limited by the virtual stiffness and device mass, and the effective damping bandwidth is limited by the cut-off frequency of the low-pass filter which filters the device velocity estimate. We show that a general system impedance can be characterized by a mass, damper, and spring optimally by the solution to a convex optimization problem, and we present a quantitative metric, the Average Distortion Error (ADE), to describe the fidelity of this model. Time delay has no significant effect on characterized stiffness, and reduces characterized damping by the product of virtual stiffness and total time delay. Reducing the low-pass filter cut-off frequency reduces the characterized damping. Experimental data gathered with a Phantom Premium 1.5 validates the theoretical analysis. We also conducted human user experiments to investigate the effects of time delay and low-pass filtering on perceived stiffness and damping. Similar to the characterized dynamics results, we observed no significant effect of time delay on perceived stiffness, and increasing time delay resulted in reduced perceived damping. Lower filter cut-off frequencies resulted in lower perceived damping. This work informs haptic display design by presenting how closed-loop behavior changes with key parameters.

Using the principles of dimensionless ratios, the data from a Higgins-Leighton method at constant pressure may be easily and quickly usedto predict the pressure may be easily and quickly usedto predict the highest constant rate of injection of water that is possible without fracturing the reservoir rock at the possible without fracturing the reservoir rock at the wellbore,to predict quickly the performance to the ultimate life of a waterflood with a constant rate of injection,to predict the life of a waterflood using a high constant rate early in the flood when the pressure at the wellhead may be low and then, later, a pressure at the wellhead may be low and then, later, a reduced rate to avoid fracture, andto estimate, after the flooding is started, the time at which the kick (first increase in oil rate) will occur and the relative size of the kick. These are all useful in making an economic analysis of a potential waterflood. With the method presented we can quickly process the predictions using relative permeabilities that appreciably influence recovery of oil. The method includes the use of layers to determine the effect of vertical permeability variations. All of this information is useful in designing the constant-rate pumps used to inject water into reservoirs. With these features, we can use the predicted performance at a constant pressure to obtain the predicted performance history at a constant injection rate during the entire life of the flood. Also, we can quickly predict the performance of a flood at different constant rates performance of a flood at different constant rates during the life of the flood; that is, at a very high rate for the short initial period when the well may be operating under nearly vacuum conditions at the wellhead, then at decreasing sets of constant rates or even at continuously changing rates. The economics of a flood is affected by the size and cost of constant-rate pumps and the rate of return of the investment during the life of a flood. With the performance data vs the rate of injection, the performance data vs the rate of injection, the economic feasibility can be easily determined. The relationships among time, rates and volumes have been checked by computer runs. They were tested on the individual layers and on combinations of layers of different absolute permeability. The ratio relationship was found to reproduce exactly the produced volumes and other data. At the time of this produced volumes and other data. At the time of this writing, it has not been tested on combinations of layers of different relative permeability-saturation curves. But, in principle, it should hold for these combinations also. The highest constant injection rate that will require a pressure just less than would be expected to fracture the formation can be determined with a model computer run at constant pressure. When the mobility ratio is greater than one, the injection rate for the model will decrease, pass through a minimum, and then increase. This minimum injection rate is the maximum permissible constant injection rate. Any constant rate in excess of this would require a pressure that would probably fracture the formation at pressure that would probably fracture the formation at some time during the flood. This highest permissible pressure is used in the Higgins-Leighton prediction method. The printout of the results of the calculations using the Higgins-Leighton method at constant pressure or a plot of the results will show lowest injection rate. P. 1246

We tested whether humans can learn to sense and compensate for interaction forces in contact tasks. Many tasks, such as use of hand tools, involve significant interaction forces between hand and environment. One control strategy would be to use high hand impedance to reduce sensitivity to these forces. But an alternative would be to learn feedback compensation for the extrinsic dynamics and associated interaction forces, with the potential for lower control effort. We observed subjects as they learned control of a ball-and-beam system, a visuo-motor task where the goal was to quickly position a ball rolling atop a rotating beam, through manual rotation of the beam alone. We devised a ball-and-beam apparatus that could be operated in a real mode, where a physical ball was present; or in a virtual training mode, where the ball's dynamics were simulated in real time. The apparatus presented the same visual feedback in all cases, and optionally produced haptic feedback of the interaction forces associated with the ball's motion. Two healthy adult subject groups, vision-only and vision-haptics (each n= 10), both trained for 80 trials on the simulated system, and then were evaluated on the real system to test for skill transfer effects. If humans incorporate interaction forces in their learning, the vision-haptics group would be expected to exhibit a smoother transfer, as quantified by changes in completion time of a ball-positioning task. During training, both groups adapted well to the task, with reductions of 64%-70% in completion time. At skill transfer to the real system, the vision-only group had a significant 35% increase in completion time (p < 0.05). There was no significant change in the vision-haptics group, indicating that subjects had learned to compensate for interaction forces. These forces could potentially be incorporated in virtual environments to assist with motor training or rehabilitation.

Creating a compelling haptic sense of immersion in a virtual environment is a challenging task for the control engineer. A haptic display must render both low impedance free-space motion and high impedance rigid constraints while ensuring stable interaction. This paper outlines a control design approach for the most common haptic display implementation, the impedance display. Two-port absolute stability criteria are used to develop explicit design bounds for virtual coupling networks which guarantee system stability for a broad class of human operators and virtual environments. The technique is applied to the Excalibur three-axis force display. The resulting absolutely stable haptic interface is the centerpiece of a virtual building block simulation which emulates the behavior of LEGO/sup TM/ bricks in a virtual environment.

In wireless sensor networks, clustering is a very crucial problem. Basically clustering means grouping some specific objects based on their behavior and functionality. Clustering can be formulated for different optimization problems, such as nonsmooth, nonconvex problems. This paper is based on the review of the optimization algorithm that was proposed in the paper A Convergent Incremental Gradient Method With Constant Step Size by Blatt et al called Incremental Aggregate Gradient method. A novel algorithm called Incremental Clustered Aggregate Gradient Method was proposed in this paper to counter the shortcomings of the previous one. It has many similarities with the earlier method but it is more efficient for wireless sensor networks. The main aim of Incremental Gradient Method was to minimize the sum of continuously differentiable functions and also it required a single gradient evaluation per iteration and used a constant step size. For quadratic functions, a global linear rate of convergence was proved. It was claimed that it is more suitable for sensor networks. Although the experiments performed in this work confirm the convergence properties of it, it was found that it is not suitable for sensor networks. The proposed method addresses the flaws of the previous method as regards to sensor networks. When both algorithms operate with their respective optimal step sizes, they require approximately the same number of gradient evaluations for convergence.

A random walk is a path that is comprised of random steps taken in random directions. Random walks present themselves in a variety of environments, and for this reason they have been a subject of relevance spanning disciplines ranging from economics to biology. A cycle in a random walk consists of the choice of a random direction, followed by a step forward, occurring for some duration. We investigated isotropic and non-isotropic random walks involving the following four cycle variations: 1. constant time, constant step size 2. constant time, varied step size 3. varied time, constant step size 4. varied time, varied step size. In biological terms, these cases of a random walks are of interest in modeling dispersal of organisms. In this study we have attempted to establish a mechanism to better study cases of non-normal diffusion in a population using a simplistic model.

This paper presents a real-time outside-in camera-based tracking system for wireless 3D pose tracking of a user’s head and hand in a virtual environment. The system uses four unsynchronised cameras as sensors and passive retroreflective markers arranged in rigid bodies as targets. In order to achieve high update rates and to cope with the unsynchronised data a single-constraint-at-a-time (SCAAT) Extended Kalman Filtering approach is used that recursively integrates measurements as soon as they are available one-at-a-time. Tests show that this approach is more robust to occlusions and provides less noisy pose estimates with a higher update rate than a conventional stereo triangulation approach.

The high force update rate is a key factor for achieving high performance of haptic rendering, which imposes a stringent real-time requirement upon the execution environment of the haptic system. To fulfil this requirement, haptic systems are often limited to simplified virtual environments (VEs) for reducing computational load. This paper presents a novel pipelined threading architecture, which uses several threads running consecutively for implementing haptic rendering algorithms. With the proposed method, the haptic forces updating rate is effectively increased, which leads to improved system performance and makes complex VE scenes possible in haptic rendering. Based on the 3-DOF Delta haptic device, experiments with a virtual wall haptic system are carried out and verify the proposed method.

Smooth haptic force feedback is an important task for multirate 6-DOF haptic rendering for both rigid and deformable objects. The update rate of the haptic force may be too low and changed during the simulation as the high computation time is required for complex physical simulation. Therefore, to implement a stable and smooth haptic rendering, we need a method to update the force in a higher regular rate during the physical simulation. We propose a prediction method using interpolation to calculate smooth haptic interaction force in a high update rate. The auto-regressive model is used to predict the force value based on the previous haptic force calculation. In addition, we introduce a spline function to interpolate force values for the haptic force output. We demonstrate that the proposed method can provide smooth and accurate haptic force feedback in a high update rate during a low frequency physical simulation of complex and deformable models. In the experiments, we show the feasibility of the proposed method and compare its accuracy and stability with the linear force prediction algorithm.

Chapter 7 - Wearable haptics

This research paper uses two-stage explicit fractional numerical schemes to solve fractional-order initial value problems of ODEs. The proposed methods exhibit structural symmetry in their formulation, contributing to enhanced numerical stability and balanced error behavior across computational steps. The schemes utilize constant and variable step sizes, allowing them to adapt efficiently to solve the considered fractional-order initial value problems. These schemes employ variable step-size control based on error estimation, aiming to minimize computational costs while maintaining good accuracy and stability. We discuss the linear stability of the proposed numerical schemes and observe that a higher-stability region is obtained when the fractional parameter value equals one. We also discuss consistency and convergence analysis of the proposed methods and observe that as the fractional parameter values rise from 0 to 1, the scheme’s convergence rate improves and achieves its maximum at 1. Several numerical test problems are used to demonstrate the efficiency of the proposed methods in solving fractional-order initial value problems with either constant or variable step sizes. The proposed numerical schemes’ results demonstrate better accuracy and convergence behavior than the existing methods used for comparison.

My work in the field of computer vision has focused on building high speed visual tracking systems to provide position feedback for the control of unstable tasks. In order to make a juggling robot or a robotic helicopter stable, three qualities are essential -- high update rate, low latency, and decent accuracy and resolution. We want to put multiple vision systems on small robotic devices with limited payloads. Therefore the system must be very small, light, and cheap. However, we allow marking of the environment so the sophistication of the vision task can be extremely low. These constraints guided the development of AVS (which, due to lack of a better name, stands for Anne's Vision System).

The problem of solving discrete-time Lyapunov equations (DTLEs) is investigated over multiagent network systems, where each agent has access to its local information and communicates with its neighbors. To obtain a solution to DTLE, a distributed algorithm with uncoordinated constant step sizes is proposed over time-varying topologies. The convergence properties and the range of constant step sizes of the proposed algorithm are analyzed. Moreover, a linear convergence rate is proved and the convergence performances over dynamic networks are verified by numerical simulations.