Showing papers in "IEEE Transactions on Haptics in 2011"

The Role of Haptics in Medical Training Simulators: A Survey of the State of the Art

Abstract: This review paper discusses the role of haptics within virtual medical training applications, particularly, where it can be used to aid a practitioner to learn and practice a task. The review summarizes aspects to be considered in the deployment of haptics technologies in medical training. First, both force/torque and tactile feedback hardware solutions that are currently produced commercially and in academia are reviewed, followed by the available haptics-related software and then an in-depth analysis of medical training simulations that include haptic feedback. The review is summarized with scrutiny of emerging technologies and discusses future directions in the field.

Tool Contact Acceleration Feedback for Telerobotic Surgery

Abstract: Minimally invasive telerobotic surgical systems enable surgeons to perform complicated procedures without large incisions. Unfortunately, these systems typically do not provide the surgeon with sensory feedback aside from stereoscopic vision. We have, thus, developed VerroTouch, a sensing and actuating device that can be added to Intuitive Surgical's existing da Vinci S Surgical System to provide auditory and vibrotactile feedback of tool contact accelerations. These cues let the surgeon feel and hear contact with rough textures as well as the making and breaking of contact with objects and other tools. To evaluate the merits of this approach, we had 11 surgeons use an augmented da Vinci S to perform three in vitro manipulation tasks under four different feedback conditions: with no acceleration feedback, with audio feedback, with haptic feedback, and with both audio and haptic. Subjects expressed a significant preference for the inclusion of tool contact acceleration feedback, although they disagreed over which sensory modality was best. Other survey responses and qualitative written comments indicate that the feedback may have improved the subject's concentration and situational awareness by strengthening the connection between the surgeon and the surgical instruments. Analysis of quantitative task metrics shows that the feedback neither improves nor impedes the performance of the chosen tasks.

Tactile and Haptic Illusions

Abstract: This paper surveys the research literature on robust tactile and haptic illusions. The illusions are organized into two categories. The first category relates to objects and their properties, and is further differentiated in terms of haptic processing of material versus geometric object properties. The second category relates to haptic space, and is further differentiated in terms of the observer's own body versus external space. The illusions are initially described and where possible addressed in terms of their functional properties and/or underlying neural processes. The significance of these illusions for the design of tactile and haptic displays is also discussed. We conclude by briefly considering a number of important general themes that have emerged in the materials surveyed.

Integrating Haptics with Augmented Reality in a Femoral Palpation and Needle Insertion Training Simulation

Abstract: This paper presents a virtual environment for training femoral palpation and needle insertion, the opening steps of many interventional radiology procedures. A novel augmented reality simulation called PalpSim has been developed that allows the trainees to feel a virtual patient using their own hands. The palpation step requires both force and tactile feedback. For the palpation haptics effect, two off-the-shelf force feedback devices have been linked together to provide a hybrid device that gives five degrees of force feedback. This is combined with a custom built hydraulic interface to provide a pulse like tactile effect. The needle interface is based on a modified PHANTOM Omni end effector that allows a real interventional radiology needle to be mounted and used during simulation. While using the virtual environment, the haptics hardware is masked from view using chroma-key techniques. The trainee sees a computer generated patient and needle, and interacts using their own hands. This simulation provides a high level of face validity and is one of the first medical simulation devices to integrate haptics with augmented reality.

Five-Fingered Haptic Interface Robot: HIRO III

Abstract: This paper presents the design and characteristics of a five-fingered haptic interface robot named HIRO III. The aim of the development of HIRO III is to provide a high-precision three-directional force at the five human fingertips. HIRO III consists of a 15-degrees-of-freedom (DOF) haptic hand, a 6-DOF interface arm, and a control system. The haptic interface, which consists of a robot arm and hand, can be used in a large workspace and can provide multipoint contact between the user and a virtual environment. However, the following problems peculiar to a multi-DOF robot have arisen: a large amount of friction, a backlash, and the presence of many wires for many motors and sensors. To solve these problems, a new mechanism and a wire-saving control system have been designed and developed. Furthermore, several experiments have been carried out to investigate the performance of HIRO III. These results show the high-precision force display and great potential of HIRO III.

Exploratory Strategies in Haptic Softness Discrimination Are Tuned to Achieve High Levels of Task Performance

Abstract: Haptic perception essentially depends on the executed exploratory movements. It has been speculated that spontaneously executed movements are optimized for the computation of associated haptic properties. We investigated to what extent people strategically execute movements that are tuned for softness discrimination of objects with deformable surfaces. In Experiment 1, we investigated how movement parameters depend on expected stimulus compliance. In a discrimination task, we measured exploratory forces for less compliant (hard) stimuli and for more compliant (soft) stimuli. In Experiment 2, we investigated whether exploratory force also depends on the expected compliance difference between the two stimuli. The results indicate that participants apply higher forces when expecting harder objects as compared to softer objects, and they apply higher forces for smaller compliance differences than for larger ones. Experiment 3 examined how applied force influences differential sensitivity for softness as assessed by just noticeable differences (JNDs). For soft stimuli, JNDs did not depend on force. For hard stimuli, JNDs were “worse” (higher) if participants applied less force than they use naturally. We conclude that applying high force is a robust strategy to obtain high differential sensitivity, and that participants used this strategy if it was required for successful discrimination performance.

Physics-Based Haptic Simulation of Bone Machining

Abstract: We present a physics-based training simulator for bone machining. Based on experimental studies, the energy required to remove a unit volume of bone is a constant for every particular bone material. We use this physical principle to obtain the forces required to remove bone material with a milling tool rotating at high speed. The rotating blades of the tool are modeled as a set of small cutting elements. The force of interaction between a cutting element and bone is calculated from the energy required to remove a bone chip with an estimated thickness and known material stiffness. The total force acting on the cutter at a particular instant is obtained by integrating the differential forces over all cutting elements engaged. A voxel representation is used to represent the virtual bone and removed chips for calculating forces of machining. We use voxels that carry bone material properties to represent the volumetric haptic body and to apply underlying physical changes during machining. Experimental results of machining samples of a real bone confirm the force model. A real-time haptic implementation of the method in a dental training simulator is described.

Constraint-Based Haptic Rendering of Multirate Compliant Mechanisms

Abstract: The paper is dedicated to haptic rendering of complex physics-based environment in the context of surgical simulation. A new unified formalism for modeling the mechanical interactions between medical devices and anatomical structures and for computing accurately the haptic force feedback is presented. The approach deals with the mechanical interactions using appropriate force and/or motion transmission models named compliant mechanisms. These mechanisms are formulated as a constraint-based problem that is solved in two separate threads running at different frequencies. The first thread processes the whole simulation including the soft-tissue deformations, whereas the second one only deals with computer haptics. This method builds a bridge between the so-called virtual mechanisms (that were proposed for haptic rendering of rigid bodies) and intermediate representations (used for rendering of complex simulations). With this approach, it is possible to describe the specific behavior of various medical devices while relying on a unified method for solving the mechanical interactions between deformable objects and haptic rendering. The technique is demonstrated in interactive simulation of flexible needle insertion through soft anatomical structures with force feedback.

Design and Evaluation of Identifiable Key-Click Signals for Mobile Devices

Abstract: As touch based input becomes more popular in mobile devices, there is an increasing need for haptic feedback on key-less input surface. Four experiments were conducted to design and evaluate identifiable emulated key-click signals using a piezoelectric actuator. Experiments I and II assessed the information transmission capacity for the amplitude, frequency, and number of cycles of raised cosine waveforms used to drive the piezo actuators under fixed- and roving-background conditions, respectively. Experiment III estimated the total information transfer for all three parameters. The results were used to reduce the number of stimulus alternatives in the key-click signal set with the goal to achieve perfect identification performance. Experiment IV verified that up to 5 to 6 identifiable key-click signals could be achieved with the experimental setup. The present study outlines an information theoretic approach to conducting identification experiments to guide the design of and to evaluate a perfectly identifiable stimulus set. The methodology can be applied to other applications in need of perceptually identifiable stimulation patterns.

Perception and Action in Teleoperated Needle Insertion

Abstract: We studied the effect of delay on perception and action in contact with a force field that emulates elastic soft tissue with a rigid nonlinear boundary. Such a field is similar to forces exerted on a needle during teleoperated needle insertion. We found that delay causes motor underestimation of the stiffness of this nonlinear soft tissue, without perceptual change. These experimental results are supported by simulation of a simplified mechanical model of the arm and neural controller, and a model for perception of stiffness, which is based on regression in the force-position space. In addition, we show that changing the gain of the teleoperation channel cancels the motor effect of delay without adding perceptual distortion. We conclude that it is possible to achieve perceptual and motor transparency in virtual one-dimensional remote needle insertion task.

Haptic Simulator for Prostate Brachytherapy with Simulated Needle and Probe Interaction

Abstract: This paper presents a haptic simulator for prostate brachytherapy. Both needle insertion and the manipulation of the transrectal ultrasound (TRUS) probe are controlled via haptic devices. Tissue interaction forces that are computed by a deformable tissue model based on the finite element method (FEM) are rendered to the user by these devices. The needle insertion simulation employs 3D models of needle flexibility and asymmetric tip bevel. The needle-tissue simulation allows a trainee to practice needle insertion and targeting. The TRUS-tissue interaction simulation allows a trainee to practice the 3D intraoperative TRUS placement for registration with the preoperative volume study and to practice TRUS axial translation and rotation for imaging needles during insertions. Approaches to computational acceleration for realtime haptic performance are presented. Trade-offs between accuracy and speed are discussed. A graphics-card implementation of the numerically intensive mesh-adaptation operation is also presented. The simulator can be used for training, rehearsal, and treatment planning.

Improved Tactile Shear Feedback: Tactor Design and an Aperture-Based Restraint

Abstract: Tactile feedback could replace or augment visual and auditory communication in a range of important applications. This paper advances the field of tactile communication by presenting performance data on a variety of tactors and a finger restraint that is suitable for use in portable devices. Tactors, the contact elements between the device and the skin, and finger restraints were evaluated using a tangential skin displacement direction identification task. We tested tactors of three sizes and two different textures. Rough textured tactors improved communication accuracy compared to smooth tactors, but tactor size did not have a statistically significant effect. Aperture-based restraints of three sizes were evaluated on both the index finger and the thumb. The aperture-based restraint was effective when used on both the index finger and the thumb, with performances on par with our previously tested thimble-based restraint. Participants performed better with larger apertures than with smaller apertures, but there was no interaction between aperture size and finger size, meaning that the same aperture could be used with a range of finger sizes. Subjects' perceptual acuity varied with stimulus direction. We discuss the effects of contact force, finger size, and differences in perceptual acuity between the index finger and thumb.

The Role of Gesture Types and Spatial Feedback in Haptic Communication

Abstract: The sense of touch is a fundamental part of social interaction as even a short touch from another person can elicit emotional experiences. Previous studies on haptic communication indicate that the benefits of interpersonal touch exist even when touch is artificially mediated between people that are physically apart. In the current study an evaluation of three input gestures (i.e., moving, squeezing, and stroking) was conducted to identify preferred methods for creating haptic messages using a hand-held device. Furthermore, two output methods (i.e., one or four haptic actuators) were investigated in order to determine whether representing spatial properties of input gestures haptically provides additional benefit for communication. Participants created haptic messages in four example communication scenarios. The results of subjective ratings, postexperimental interviews, and observations showed that squeezing and stroking were the preferred ways to interact with the device. Squeezing was an unobtrusive and quick way to create haptic content. Stroking, on the other hand, enabled crafting of more detailed haptic messages. Spatial haptic output was appreciated especially when using the stroking method. These findings can help in designing haptic communication methods for hand-held devices.

Roughness Perception in Virtual Textures

Abstract: Haptic devices allow the production of virtual textured surfaces for psychophysical experiments. Some studies have shown inconsistencies between virtual and real textures with respect to their psychophysical functions for roughness, leading to speculation that virtual textures differ in some way from real ones. We have determined the psychophysical function for roughness using textures rendered with a high-fidelity magnetic levitation haptic device. A constraint surface algorithm was used to simulate the motion of a spherical probe over trapezoidal gratings and randomly dithered cones. The shape of the psychophysical functions for roughness is consistent between subjects but varies with changes in texture and probe geometry. For dithered cones, inverted “U”-shaped functions were found nearly identical, in maxima and curvature, to those in the literature for real textures with similar geometry.

Force, Torque, and Stiffness: Interactions in Perceptual Discrimination

Abstract: Three experiments investigated whether force and torque cues interact in haptic discrimination of force, torque, and stiffness, and if so, how. The statistical relation between force and torque was manipulated across four experimental conditions: either one type of cue varied while the other was constant, or both varied so as to be positively correlated, negatively correlated, or uncorrelated. Experiment 1 showed that the subjects' ability to discriminate force was improved by positively correlated torque but impaired with uncorrelated torque, as compared to the constant torque condition. Corresponding effects were found in Experiment 2 for the influence of force on torque discrimination. These findings indicate that force and torque are integrated in perception, rather than being processed as separate dimensions. A further experiment demonstrated facilitation of stiffness discrimination by correlated force and torque, whether the correlation was positive or negative. The findings suggest new means of augmenting haptic feedback to facilitate perception of the properties of soft objects.

Vibrotactile Stimuli Applied to Finger Pads as Biases for Perceived Inertial and Viscous Loads

Abstract: The perception of the mass and viscosity of an object is based on the dynamic forces applied to our hands when we jiggle or lift the object [1], [2], [3]. This force is commonly assumed to be sensed by kinetic receptors [4] in our muscles or tendons. When jiggling objects, we also experience the cutaneous deformation of our finger pads. In this study, we show that the dynamic vibration on the finger pad influences our perception of mass and viscosity. We experimentally confirm that the vibration on the finger pad, that synchronizes with the hand's accelerations or velocities, enhances the perceived changes in the mass or viscosity when the vibrotactile stimuli and the changes in the mass and viscosity are in the same perceptual direction. For example, when the increased mass and an acceleration-synchronized tactile stimulus-which is a positive bias for the mass-are simultaneously presented to the experiment participants, they respond that the perceived increase in the mass is enhanced. In contrast, when the tactile and proprioceptive stimuli are in perceptually opposite directions, the vibrotactile stimuli cancel the perceived changes in the mass and viscosity. In particular, the effect of the velocity-synchronized vibration on perception is stronger than the effect of the actual viscosity.

Haptics in medicine and clinical skill acquisition [special section intro.]

Abstract: This special section is about understanding the role of touch in medicine and clinical skill acquisition. three major areas of haptics in medicine and clinical skill acquisition are identified, and papers are presented on each of these topics in the special section: 1. Human haptic perception and motor performance as relevant to medical examinations and procedures. This includes characterization of the nature of haptic information, and how it is perceived, which is necessary to understand how medical professionals use haptics in medical examinations and interventions. 2. Haptic systems and the role of haptics in training and evaluating clinical skills. Haptic simulators address a growing need for effective training and evaluation of clinical skills. Such simulators can be applied in a wide variety of medical professions and disciplines, including surgery, interventional radiology, anaesthesiology, dentistry, veterinary medicine, and the allied health professions. These simulators rely on both technology development (devices, software, and systems) and an understanding of how humans use haptic feedback to perform established clinical skills or learn novel skills. 3. Using haptics to improve the performance of medical interventions. Current trends in interventional medicine remove direct contact between the patient and the clinician. Bilateral teleoperators and ?smart? instruments that use tactile sensing/display devices, sensory substitutions systems, and other methods to enhance haptic feedback to a clinician should improve the performance of interventions.

Geodesic Spline Interface for Haptic Curve Rendering

Abstract: Several haptic devices have been developed in recent years in order to reproduce the sensation of physical contact with virtual objects. Many of these devices are point-based, and some haptic interfaces behave like small surfaces that conform to a virtual shape. None of these allow a full-hand contact with the shape, and they are, in general, too small to render big surfaces. The simulation of tasks, such as the exploration of aesthetic surfaces made by industrial designers in order to check the quality of prototypes, require full-hand contact with the shape on a one-to-one scaled representation of the object. These explorations follow trajectories that can be approximated with planar or geodesic curves. In this paper, we describe the design and implementation of a linear haptic device that is able to render these trajectories. The device is part of a multimodal system including stereoscopic visualization that allows visual representation of the entire surface. Industrial designers use the system for checking the quality of shapes while exploiting their manual and visual skills. The system has been tested by industrial designers and the results are reported in this paper.

Feeling through Tactile Displays: A Study on the Effect of the Array Density and Size on the Discrimination of Tactile Patterns

Abstract: Tactile arrays are devices that can provide spatially distributed cutaneous signals delivering crucial information during virtual haptic exploration or remote manipulation procedures. Two of the key specifications of a tactile array are the tactor spacing and array size that are believed to directly affect the device performance. In most of the systems developed so far, these two parameters have been chosen by trial and error or by trying to match the tactor density to the spatial resolution in the human fingertip. The objective of this work is to study the effect of tactor spacing and array size on the tactile arrays performance by measuring human tactile discrimination ability. Psychophysical experiments were performed to obtain the differential threshold for discrimination of a ridge angle and the shape recognition performance while exploring edge-based patterns. The patterns were explored through different passive (nonactuated) tactile arrays of vertically moving pins and also directly with the finger. Results indicate that a tactile array of 1.8 mm tactor spacing and 1 cm2 array size transmits the pattern information with a good level of accuracy. This work shows that tactile devices with low complexity (small number of tactors) are still effective in conveying tactile cues. Moreover, this work provides performance measures that determinate the capabilities of tactile pin arrays to convey accurately tactile information.

What you can't feel won't hurt you: Evaluating haptic hardware using a haptic contrast sensitivity function

Abstract: In this paper, we extend the concept of the contrast sensitivity function - used to evaluate video projectors - to the evaluation of haptic devices. We propose using human observers to determine if vibrations rendered using a given haptic device are accompanied by artifacts detectable to humans. This determination produces a performance measure that carries particular relevance to applications involving texture rendering. For cases in which a device produces detectable artifacts, we have developed a protocol that localizes deficiencies in device design and/or hardware implementation. In this paper, we present results from human vibration detection experiments carried out using three commercial haptic devices and one high performance voice coil motor. We found that all three commercial devices produced perceptible artifacts when rendering vibrations near human detection thresholds. Our protocol allowed us to pinpoint the deficiencies, however, and we were able to show that minor modifications to the haptic hardware were sufficient to make these devices well suited for rendering vibrations, and by extension, the vibratory components of textures. We generalize our findings to provide quantitative design guidelines that ensure the ability of haptic devices to proficiently render the vibratory components of textures.

A Comparative Study of Haptic Stiffness Identification by Veterinarians and Students

Abstract: Palpation is an important clinical skill in both veterinary and medical health professions. The present study compares the ability of practicing veterinarians and veterinary students to identify the stiffness of virtual surfaces through palpation. An absolute identification paradigm was used where a force-feedback haptic device rendered virtual surfaces with five levels of stiffness within a “clinically relevant” range (0.2-0.5 N/mm). The mean information transfer was 0.97 bits (almost two perfectly identifiable stiffness levels) for 12 veterinarians and 0.58 bits (one correctly identified level) for 14 veterinary students. Although the difference between the two groups was significant (p <; 0.001), neither group was able to reliably identify more than two levels of stiffness, indicating that the success of veterinarians in clinical practice probably relies on additional properties such as size, shape, and texture. Analyses of force versus time and displacement versus time recordings suggest that the superior performance of the veterinarians may be partially attributable to motor strategy. Specifically, veterinarians used a greater mean maximum force (2.0 N) compared to students (1.6 N) (p <; 0.05). However, further studies are required to investigate motor strategy in more detail. The implications of our findings for veterinary education and quantitative skill assessment are discussed.

Collocation Accuracy of Visuo-Haptic System: Metrics and Calibration

Abstract: Human resolution of collocation error between haptic and stereoscopic displays influences the design of visuo-haptic rendering algorithms, yet it is not well characterized. In the present study, we propose quantified metrics to measure the visuo-haptic collocation error and a prototype based on half-silvered mirror is established to validate the metrics. After defining collocation error in terms of the spatial correspondence between a tool and a surface, a mathematical model is derived that relates collocation error to the visual and haptic rendering modules within the computational pipeline. A calibration method consisting of Perspective Calibration (PC) and Model Calibration (MC) is then proposed to compensate for manufacturing and assembly tolerances. Based on measurement values by a precise measurement apparatus, i.e., the FARO Arm, parameters for the PC and MC were determined. System performance is evaluated by measuring the collocation error between a real handle and its visual avatar. The average collocation error was 1.8 mm within the XwYwOw plane, and the error never exceeded 7 mm within an 80 mm × 80 mm × 80 mm workspace.

Figure/Ground Segmentation via a Haptic Glance: Attributing Initial Finger Contacts to Objects or Their Supporting Surfaces

Abstract: The current study addresses the well-known “figure/ground” problem in human perception, a fundamental topic that has received surprisingly little attention from touch scientists to date. Our approach is grounded in, and directly guided by, current knowledge concerning the nature of haptic processing. Given inherent figure/ground ambiguity in natural scenes and limited sensory inputs from first contact (a “haptic glance”), we consider first whether people are even capable of differentiating figure from ground (Experiments 1 and 2). Participants were required to estimate the strength of their subjective impression that they were feeling an object (i.e., figure) as opposed to just the supporting structure (i.e., ground). Second, we propose a tripartite factor classification scheme to further assess the influence of kinetic, geometric (Experiments 1 and 2), and material (Experiment 2) factors on haptic figure/ground segmentation, complemented by more open-ended subjective responses obtained at the end of the experiment. Collectively, the results indicate that under certain conditions it is possible to segment figure from ground via a single haptic glance with a reasonable degree of certainty, and that all three factor classes influence the estimated likelihood that brief, spatially distributed fingertip contacts represent contact with an object and/or its background supporting structure.

Effect of Grip Force and Training in Unstable Dynamics on Micromanipulation Accuracy

Abstract: This paper investigates whether haptic error amplification using unstable dynamics can be used to train accuracy in micromanipulation. A preliminary experiment first examines the possible confounds of visual magnification and grip force. Results show that micromanipulation precision is not affected by grip force in both naive and experienced subjects. On the other hand, precision is increased by visual magnification of up to 10×, but not further for larger magnifications. The main experiment required subjects to perform small-range point-to-point movements in 3D space in an unstable environment which amplified position errors to the straight line between start and end point. After having trained in this environment, subjects performing in the free conditions show an increase in success rate and a decrease in error and its standard deviation relative to the control subjects. This suggests that this technique can improve accuracy and reliability of movements during micromanipulation.

Haptic Recognition of Emotions in Raised-Line Drawings by Congenitally Blind and Sighted Adults

Abstract: 15 sighted and 15 congenitally blind adults were to classify raised-line pictures of emotional faces through haptics. Whereas accuracy did not vary significantly between the two groups, the blind adults were faster at the task. These results suggest that raised-line pictures of emotional faces are intelligible to blind adults.

Characterization of the Haptic Shape-Weight Illusion with 3D Objects

Abstract: The present study shows an effect of 3D shape on perceived weight of objects. This effect could be explained partly by the size-weight and the shape-size illusions, suggesting that the perceived size is not the only factor responsible for the shape-weight illusion.

Perception and Haptic Rendering of Friction Moments

Abstract: This paper considers moments due to friction forces on the human fingertip. A computational technique called the friction moment arc method is presented. The method computes the static and/or dynamic friction moment independent of a friction force calculation. In addition, a new finger holder to display friction moment is presented. This device incorporates a small brushless motor and disk, and connects the human's finger to an interface finger of the five-fingered haptic interface robot HIRO II. Subjects' perception of friction moment while wearing the finger holder, as well as perceptions during object manipulation in a virtual reality environment, were evaluated experimentally.

Multiple Factors Underlying Haptic Perception of Length and Orientation

Abstract: Information about the shape and spatial orientation of an object can be gathered during exploratory hand and arm movements, and then must be synthesized into a unified percept. During the robotically guided exploration of virtual polygons or triangles, the perception of the lengths of two adjoining segments is not always geometrically consistent with the perception of the internal angles between these segments. The present study further characterized this established inconsistency, and also found that subjects' internal angle judgments were influenced by the spatial orientations of the segments, especially the segment that was explored last in the sequence. Internal angle judgments were also biased by the subjects' own active forces, applied in the direction perpendicular to the programmed handle motion. For the last segment, but not for the earlier segments, subjects produced more outward force when they reported larger angles and more inward force when they reported smaller angles. Thus, the haptic synthesis of object shape is influenced by multiple geometric, spatial, and self-produced factors.

Modeling and Compensation of the Internal Friction Torque of a Travelling Wave Ultrasonic Motor

Abstract: This paper deals with the control and experimentation of a one-degree-of-freedom haptic stick, actuated by a travelling wave ultrasonic motor. This type of actuator has many interesting properties such as low-speed operation capabilities and a high torque-to-weight ratio, making it appropriate for haptic applications. However, the motor used in this application displays nonlinear behavior due to the necessary contact between its rotor and stator. Moreover, due to its energy conversion process, the torque applied to the end-effector is not a straightforward function of the supply current or voltage. This is why a force-feedback control strategy is presented, which includes an online parameter estimator. Experimental runs are then presented to examine the fidelity of the interface.

Exploration of Tactile Contact in a Haptic Display: Effects of Contact Velocity and Transient Vibrations

Abstract: Experiments were conducted using a novel tactile contact rendering device to explore important factors of the tactile contact event. The effects of contact velocity and event-based transient vibrations were explored. Our research was motivated by a need to better understand the perception of the tactile contact event and to develop a means of rendering stiff surfaces with a nonspecialized haptic device. A passive tactile display, suitable for mounting on a Phantom robot, was developed and is capable of rendering the tactile sensation of contact on a fingertip over a range of velocities commonly experienced during everyday manipulation and tactile exploration. Experiments were conducted with this device to explore how tactile contact dynamics affect the perceived stiffness of a virtual surface. It was found that contact velocity does not have a significant effect on perceived stiffness. These results can be explained by prior research that defines perceived hardness (akin to stiffness) in terms of rate-hardness. However, in agreement with prior literature with stylus-based studies, the addition of transient vibrations to the contact event can, in some cases, increase the perceived stiffness.