Haptic display is the process of applying forces to a human "observer" giving the sensation of touching and interacting with real physical objects. Touch is unique among the senses because it allows simultaneous exploration and manipulation of an environment. A haptic display system has three main components. The first is the haptic interface, or display device, generally some type of electro-mechanical system able to exert controllable forces on the user with one or more degrees of freedom. The second is the object model-a mathematical representation of the object containing its shape and other properties related to the way it feels. The third component, the haptic rendering algorithm, joins the first two components to compute, in real time, the model-based forces to give the user the sensation of touching the simulated objects. This paper focuses on a new haptic rendering algorithm for generating convincing interaction forces for objects modeled as rigid polyhedra. We create a virtual model of the haptic interface, called the god-object, which conforms to the virtual environment. The haptic interface can then be servo-ed to this virtual model. This algorithm is extensible to other functional descriptions and lays the groundwork for displaying not only shape information, but surface properties such as friction and compliance.

A constraint-based god-object method for haptic display

The use of virtual-reality technology in the areas of rehabilitation and therapy continues to grow, with encouraging results being reported for applications that address human physical, cognitive, and psychological functioning. This article presents a SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis for the field of VR rehabilitation and therapy. The SWOT analysis is a commonly employed framework in the business world for analyzing the factors that influence a company's competitive position in the marketplace with an eye to the future. However, the SWOT framework can also be usefully applied outside of the pure business domain. A quick check on the Internet will turn up SWOT analyses for urban-renewal projects, career planning, website design, youth sports programs, and evaluation of academic research centers, and it becomes obvious that it can be usefully applied to assess and guide any organized human endeavor designed to accomplish a mission. It is hoped that this structured examination of the factors relevant to the current and future status of VR rehabilitation will provide a good overview of the key issues and concerns that are relevant for understanding and advancing this vital application area.

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A SWOT analysis of the field of virtual reality rehabilitation and therapy

This paper addresses fundamental stability and performance issues associated with haptic interaction. It generalizes and extends the concept of a virtual coupling network, an artificial link between the haptic display and a virtual world, to include both the impedance and admittance models of haptic interaction. A benchmark example exposes an important duality between these two cases. Linear circuit theory is used to develop necessary and sufficient conditions for the stability of a haptic simulation, assuming the human operator and virtual environment are passive. These equations lead to an explicit design procedure for virtual coupling networks which give maximum performance while guaranteeing stability. By decoupling the haptic display control problem from the design of virtual environments, the use of a virtual coupling network frees the developer of haptic-enabled virtual reality models from issues of mechanical stability.

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Stable haptic interaction with virtual environments

Force feedback coupled with visual display allows people to interact intuitiv ely with complex virtual environments. For this synergy of haptics and graphics to flourish, however, haptic systems must be capable of modeling environments with the same richness, complexity and interactivity that can be found in existing graphic systems. To help meet this challenge, we have developed a haptic rendering system that allows for the efficient tactile display of graphical information. The system uses a common high-level framework to model contact constraints, surface shading, friction and tex ture. The multilevel control system also helps ensure that the haptic device will remain stable even as the limits of the renderer’s capabilities are reached.

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The haptic display of complex graphical environments

Enhanced telepresence and telesurgery systems automatically update coordinate transformations so as to retain alignment between movement of an input device and movement of an end effector as displayed adjacent the input device. A processor maps a controller workspace with an end effector workspace, and effects movement of the end effector in response to the movement of the input device. This allows the use of kinematically dissimilar master and slave linkages. Gripping an input member near a gimbal point and appropriate input member to end effector mapping points enhance the operator's control. Dexterity is enhanced by accurately tracking orientational and/or angles of movement, even if linear movement distances of the end effector do not correspond to those of the input device.

Camera referenced control in a minimally invasive surgical apparatus

1. Abstract This paper describes the PHANToM haptic interface - a device which measures a user’s finger tip position and exerts a precisely controlled force vector on the finger tip. The device has enabled users to interact with and feel a wide variety of virtual objects and will be used for control of remote manipulators. This paper discusses the design rationale, novel kinematics and mechanics of the PHANToM. A brief description of the programming of basic shape elements and contact interactions is also given.

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Thomas H. Massie

Papers

The PHANToM Haptic Interface: A Device for Probing Virtual Objects