Louis B. Rosenberg

Virtual fixtures: Perceptual tools for telerobotic manipulation

In order to enhance operator performance and understanding within remote environments, most research and development of telepresence systems has been directed towards improving the fidelity of the link between operator and environment. Although higher fidelity interfaces are important to the advancement of a telepresence system, the beneficial effects of corrupting the link between operator and remote environment by introducing abstract perceptual information into the interface called virtual fixtures are described.<<ETX>>

Perceptual decomposition of virtual haptic surfaces

The analysis and construction of virtual haptic surfaces are considered from a perceptual point of view rather than from the dynamics and controls approach of prior work. The authors developed a perceptual decomposition of surface contact sensation by examining three qualities associated with the different stages of interaction with a haptic wall simulation. These qualities are the crispness of initial contact, the hardness of surface rigidity, and the cleanness of final release from the virtual walls surface. These qualities, plus an overall rating of wall quality, were employed consistently by seven subjects to evaluate a set of six simple haptic wall simulations. Three of the wall models consisted of single linear springs; the remainder, single viscous dampers. Highest rankings of subjective hardness were associated with the spring models; damper models received the highest crispness rankings. Subjects favored the simple spring models as having, overall, the more wall-like perceptual character.<<ETX>>

Virtual fixtures as tools to enhance operator performance in telepresence environments

This paper introduces the notion of virtual fixtures for use in telepresence systems and presents an empirical study which demonstrates that such virtual fixtures can greatly enhance operator performance within remote environments. Just as tools and fixtures in the real world can enhance human performance by guiding manual operations, providing localizing references, and reducing the mental processing required to perform a task, virtual fixtures are computer generated percepts overlaid on top of the reflection of a remote workspace which can provide similar benefits. Like a ruler guiding a pencil in a real manipulation task, a virtual fixture overlaid on top of a remote workspace can act to reduce the mental processing required to perform a task, limit the workload of certain sensory modalities, and most of all allow precision and performance to exceed natural human abilities. Because such perceptual overlays are virtual constructions they can be diverse in modality, abstract in form, and custom tailored to individual task or user needs. This study investigates the potential of virtual fixtures by implementing simple combinations of haptic and auditory sensations as perceptual overlays during a standardized telemanipulation task.

Virtual haptic overlays enhance performance in telepresence tasks

An empirical study was performed in which human subjects were asked to execute a peg- insertion task through a telepresence link with force-feedback. Subjects controlled a remote manipulator through natural hand motions by using an anthropomorphic upper body exoskeleton. The force-reflecting exoskeleton could present haptic sensations in six degrees of freedom. Subjects viewed the remote site through a high fidelity stereo vision system. Subjects performed the peg-insertion task under three different conditions: (1) in-person (direct manipulation), (2) through the telepresence link (telemanipulation), and (3) through the telepresence link while using abstract virtual haptic overlays known as `virtual fixtures (telemanipulation with virtual fixturing). Five different haptic overlays were tested which included virtual surfaces, virtual damping fields, virtual snap-to-planes, and virtual snap-to- lines. Results of subject testing confirmed that human performance was significantly degraded when comparing telepresence manipulation to direct in-person manipulation. Results also confirmed that by introducing abstract haptic overlays into telepresence link, operator performance could be restored closer to natural in-person capacity. The use of 3D haptic overlays were found to as much as double manual performance in the standard peg-insertion task.

The effect of interocular distance upon operator performance using stereoscopic displays to perform virtual depth tasks

When presenting virtual images to a user performing a simple task requiring depth perception, the use of stereoscopic projections results in a ten-fold reduction in mean alignment error as compared to the use of monocular projections. Although average physiological interocular distance is 6.3 cm, it is found that any interocular distance of greater than 3 cm used in the stereo projection model is adequate to provide a user with maximal performance in the depth perception task. No statistically significant increase in performance can be correlated to increasing interocular distances greater than 3 cm. Since it is often beneficial to reduce retinal disparity between the left and right images to increase the presentable depth range, reduce image fusion problems, and reduce operator fatigue, these results suggests that smaller than physiological interocular distances should be considered when implementing a stereoscopic vision system for virtual environments and telepresence systems.<<ETX>>

Multisensory platform for surgical simulation

Advanced display technologies have made the virtual exploration of relatively complex models feasible in many applications. Unfortunately, only a few human interfaces allow natural interaction with the environment. Moreover in surgical applications, such realistic interaction requires real time rendering of volumetric data-placing an overwhelming performance burden on the system. We report on a collaboration of a unique interdisciplinary group developing a virtual reality system that provides intuitive interaction with complex volume data by employing real time realistic volume rendering and convincing force feedback (haptic) sensations. We describe our rendering methods and the haptic devices in detail and demonstrate the utilization of this system in the real world application of Endoscopic Sinus Surgery (ESS) simulation.

Design of a virtual rigid surface: haptic/audio registration

Few design parameters have been developed for the display of wrtual percepts, This is particularly true for complex virtual constructs that include haptlc information displayed through a force reflecting interface. This study looks at a fundamental virtual percept for haptic display, the representation of a virtual rigid surface, and empirical y derives a design parameter for the registration of the haptic and audio perceptual content. Results of subject testing have revealed that a delay as high as 100ms can exist between the presentation of haptic and audio sensations in display of a virtual rigid surface before users notice any perceptual distortion. INTRODUCTION While the state of the art in visual and auditory information display for virtual environment systems has been advancing by leaps and bounds in recent years, the representation of virtual force information is still in its early infancy. What is probably the most frequently distorted sensory percept attempted by virtual force reflection systems is the representation of a virtual rigid surface. Although most of the tactual interactions we encounter in our dady lives involve contact with rigid surfaces, most force reflecting systems are unable to realistically reproduce such a percept. Virtual rigid surface contacts are often described as “mushy”, “sticky”, or “bouncy” by even the most forgiving users. Jex (1991), in reporting on informal “rules of thumb” derived from experience with high-performance force reflecting aircraft simulators, suggested that the ability to Permlsslon to copy without fee all or part of this material IS granted prov!ded that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the mle of the pubhcation and its date appear, and notice is given that copying IS by permission of the Association for Computing Machinery. To GOPY otherwisu, w t~ wpubl, sh, require. a fee andlor specific permission. CH194 Companmn-4/94 Boston, Massachusetts USA e 1994 ACM 0-89791 -651 -4/94 /0257 ...

Haptic interface for laptop computers and other portable devices

3.50 produce a convincing rigid wall is a primary requirement of any general purpose haptic interface. Of course the display of a convincing wrtual percept M not limited to the physical modalities. Audio and visual cues associated with a haptic display play a major role in the realistlc presentation of a virtual percept. Because of the basic importance of the realistic display of rigid surfaces for even the mcwt primitive force reflecting virtual environments, this study critically examines the rigid surface percept and addresses one small issue associated with incorporation of audio reformation to tlhe virtual percept: haptic/audio registration. The question to be answered by this study is as follows; how accurately must an audio signal Ibe registered (temporally) to the haptic representation of a virtual rigid surface. In other words, how long of a delay can exist between the haptic representation of a virtual rigid surface (i.e. the feel) and the auditory representation of contacting a virtual rigid surface (i.e. the sound) before an error is registration is perceived by the user. If accurate registration of auditory and haptic percepts is not a requirement of realistic virtual models, the hardware and computation requirements for the display of such virtulal percepts are significantly reduced. Thus it is valuable to ascertain what percephd requirements exist for audio/haptic registration in the presentation of a virtual rigid surface. In psychophysical terms, this experiment is intended to reveal the Just-Noticeable Registration Error (JNRE) between audio and haptic stimuli presented in a virtual rigid surface ~rcept. HARDWARE A two degree of freedom, force reflecting joystick was used to display a haptic model of a virtual rigid surface to twenty subjects. Each axis of the joystick is powered by disk armature permanent magnet motors and is equipped with optical encoders to sense position, tachometers for velocity, as well as accelerometers and an interface force transducer. The motors can produce continuous forces up to a maximum of 20N with zero cogging and negligible force