Haptography: capturing the feel of real objects to enable authentic haptic rendering (invited paper)

Haptic interfaces are designed to allow humans to touch virtual objects as though they were real. Unfortunately, virtual surface models currently require extensive hand tuning and do not feel authentic, which limits the usefulness and applicability of such systems. The proposed approach of haptography seeks to address this deficiency by basing models on haptic data recorded from real interactions between a human and a target object. The studio haptographer uses a fully instrumented stylus to tap, press, and stroke an item in a controlled environment while a computer system records positions, orientations, velocities, accelerations, and forces. The point-and-touch haptographer carries a simply instrumented stylus around during daily life, using it to capture interesting haptic properties of items in the real world. Recorded data is distilled into a haptograph, the haptic impression of the object or surface patch, including properties such as local shape, stiffness, friction, and texture. Finally, the feel of the probed object is recreated via a haptic interface by accounting for the device\u27s natural dynamics and focusing on the feedback of high-frequency accelerations

Modeling Induced Master Motion in Force-Reflecting Teleoperation

Providing the user with high-fidelity force feedback has persistently challenged the field of telerobotics. Interaction forces measured at the remote site and displayed to the user cause unintended master device motion. This movement is interpreted as a command for the slave robot and can drive the closed-loop system unstable. This paper builds on a recently proposed approach for achieving stable, high-gain force reflection via cancellation of the master mechanism’s induced motion. Such a strategy hinges on obtaining a good model of the master’s response to force feedback. Herein, we present a thorough modeling approach based on successive isolation of system components, demonstrated on a one-degree-of-freedom testbed. A sixth-order mechanical model, including viscous and Coulomb friction as well as a new method for modeling hysteretic stiffness, describes the testbed’s high-frequency resonant modes. This modeling method’s ability to predict induced master motion should lead to significant improvements in force-reflecting teleoperation via the cancellation approac

Haptic Displayof Realistic Tool Contact via Dynamically Compensated Control of a Dedicated Actuator

High frequency contact accelerations convey important information that the vast majority of haptic interfaces cannot render. Building on prior work, we present an approach to haptic interface design that uses a dedicated linear voice coil actuator and a dynamic system model to allow the user to feel these signals. This approach was tested through use in a bilateral teleoperation experiment where a user explored three textured surfaces under three different acceleration control architectures: none, constant gain, and dynamic compensation. The controllers that use the dedicated actuator vastly outperform traditional position-position control at conveying realistic contact accelerations. Analysis of root mean square error, linear regression, and discrete Fourier transforms of the acceleration data also indicate a slight performance benefit for dynamic compensation over constant gain

Improving Telerobotic Touch Via High-Frequency Acceleration Matching

Humans rely on information-laden high-frequency accelerations in addition to quasi-static forces when interacting with objects via a handheld tool. Telerobotic systems have traditionally struggled to portray such contact transients due to closed-loop bandwidth and stability limitations, leaving remote objects feeling soft and undefined. This work seeks to maximize the user’s feel for the environment through the approach of acceleration matching; high-frequency fingertip accelerations are combined with standard low-frequency position feedback without requiring a secondary actuator on the master device. In this method, the natural dynamics of the master are identified offline using frequency-domain techniques, estimating the relationship between commanded motor current and handle acceleration while a user holds the device. During subsequent telerobotic interactions, a high-bandwidth sensor measures accelerations at the slave’s end effector, and the real-time controller re-creates these important signals at the master handle by inverting the identified model. The details of this approach are explored herein, and its ability to render hard and rough surfaces is demonstrated on a standard master-slave system. Combining high-frequency acceleration matching with position-error-based feedback of quasi-static forces creates a hybrid signal that closely corresponds to human sensing capabilities, instilling telerobotics with a more realistic sense of remote touch

HALO: Haptic Alerts for Low-hanging Obstacles in White Cane Navigation

White canes give the visually impaired the freedom to travel independently in unknown environments, but they cannot warn the user of overhead hazards such as tree branches. This paper presents the development and evaluation of a device that provides haptic cues to warn a visually impaired user of low-hanging obstacles during white cane navigation. The Haptic Alerts for Low-hanging Obstacles (HALO) system is a portable and affordable attachment to traditional white canes. By pairing distance data acquired from an ultrasonic range sensor with vibration feedback delivered by an eccentric mass motor, the device aims to alert users of low-hanging obstacles without interfering with the standard functionality of a white cane. We conducted a preliminary validation study wherein twelve blindfolded subjects navigated a custom obstacle course with and without vibration alerts from HALO. The results showed that this new device is intuitive and highly effective at enabling the user to safely navigate around low-hanging obstacles

Design of Body-Grounded Tactile Actuators for Playback of Human Physical Contact

We present four wearable tactile actuators capable of recreating physical sensations commonly experienced in human interactions, including tapping on, dragging across, squeezing, and twisting an individual’s wrist. In seeking to create tactile signals that feel natural and are easy to understand, we developed movement control interfaces to play back each of these forms of actual human physical contact. Through iterative design, prototyping, programming, and testing, each of these servo-motor-based mechanisms produces a signal that is gradable in magnitude, can be played in a variety of temporal patterns, is localizable to a small area of skin, and, for three of the four actuators, has an associated direction. Additionally, we have tried to design toward many of the characteristics that have made high frequency vibration the most common form of wearable tactile feedback, including low cost, light weight, comfort, and small size. Bolstered by largely positive comments from naive users during an informal testing session, we plan to continue improving these devices for future use in tactile motion guidance

Shaping Event-Based Haptic Transients Via an Improved Understanding of Real Contact Dynamics

Haptic interactions with stiff virtual surfaces feel more realistic when a short-duration transient is added to the spring force at contact. But how should this event-based transient be shaped? To answer this question, we present a targeted user study on virtual surface realism that demonstrates the importance of scaling transients correctly and hints at the complexity of this dynamic relationship. We then present a detailed examination of the dynamics of tapping on a rigid surface with a hand-held probe; theoretical modeling is combined with empirical data to determine the influence of impact velocity, impact acceleration, and user grip force on the resulting transient surface force. The derived mathematical relationships provide a formula for generating open-loop, event-based force transients upon impact with a virtual surface. By incorporating an understanding of the dynamics of real interactions into the re-creation of virtual contact, these findings promise to improve the performance and realism of a wide range of haptic simulations

The AirWand: Design and Characterization of a Large-Workspace Haptic Device

Almost all commercially available haptic interfaces share a common pitfall, a small shoebox-sized workspace; these devices typically rely on rigid-link manipulator design concepts. In this paper we outline our design for a new kinesthetic haptic system that drastically increases the usable haptic workspace. We present a proof-of-concept prototype, along with our analysis of its capabilities. Our design uses optical tracking to sense the position of the device, and air jet actuation to generate forces. By combining these two technologies, we are able to detach our device from the ground, thus sidestepping many problems that have plagued traditional haptic devices including workspace size, friction, and inertia. We show that optical tracking and air jet actuation successfully enable kinesthetic haptic interaction with virtual environments. Given an appropriately large volume high-pressure air source, and a reasonably high speed tracking system, this design paradigm has many desirable qualities when compared to traditional haptic design schemes

Real-Time Graphic and Haptic Simulation of Deformable Tissue Puncture

A myriad of surgical tasks rely on puncturing tissue membranes (Fig. 1) and cutting through tissue mass. Properly training a practitioner for such tasks requires a simulator that can display both the graphical changes and the haptic forces of these deformations, punctures, and cutting actions. This paper documents our work to create a simulator that can model these effects in real time. Generating graphic and haptic output necessitates the use of a predictive model to track the tissue’s physical state. Many finite element methods (FEM) exist for computing tissue deformation ([1],[4]). These methods often obtain accurate results, but they can be computationally intensive for complex models. Real-time tasks using this approach are often limited in their complexity and workspace domain due to the large computational overhead of FEM. The computer graphics community has developed a large range of methods for modeling deformable media [5], often trading complete physical accuracy for computational speedup. Casson and Laugier [3] outline a mass-spring mesh model based on these principles, but they do not explore its usage with haptic interaction. Gerovich et al. [2] detail a set of haptic interaction rules (Fig. 2) for one dimensional simulation of multi-layer deformable tissue, but they do not provide strategies for integrating this model with realistic graphic feedback

Event-Based Haptics and Acceleration Matching: Portraying and Assessing the Realism of Contact

Contact in a typical haptic environment resembles the experience of tapping on soft foam, rather than on a hard object. Event-based, high-frequency transient forces must be superimposed with traditional proportional feedback to provide realistic haptic cues at impact. We have developed a new method for matching the accelerations experienced during real contact, inverting a dynamic model of the device to compute appropriate force feedback transients. We evaluated this haptic rendering paradigm by conducting a study in which users blindly rated the realism of tapping on a variety of virtually rendered surfaces as well as on three real objects. Event-based feedback significantly increased the realism of the virtual surfaces, and the acceleration matching strategy was rated similarly to a sample of real wood on a foam substrate. This work provides a new avenue for achieving realism of contact in haptic interactions