Texture gives real objects an important perceptual dimension that is largely missing from virtual haptic interactions due to limitations of standard modeling and rendering approaches. This paper presents a set of methods for creating a haptic texture model from tool-surface interaction data recorded by a human in a natural and unconstrained manner. The recorded high-frequency tool acceleration signal, which varies as a function of normal force and scanning speed, is segmented and modeled as a piecewise autoregressive (AR) model. Each AR model is labeled with the source segment's median force and speed values and stored in a Delaunay triangulation to create a model set for a given texture. We use these texture model sets to render synthetic vibration signals in real time as a user interacts with our TexturePad system, which includes a Wacom tablet and a stylus augmented with a Haptuator. We ran a human-subject study with two sets of ten participants to evaluate the realism of our virtual textures and the strengths and weaknesses of this approach. The results indicated that our virtual textures accurately capture and recreate the roughness of real textures, but other modeling and rendering approaches are required to completely match surface hardness and slipperiness.

Modeling and Rendering Realistic Textures from Unconstrained Tool-Surface Interactions

The tactual scanning of five naturalistic textures was recorded with an apparatus that is capable of measuring the tangential interaction force with a high degree of temporal and spatial resolution. The resulting signal showed that the transformation from the geometry of a surface to the force of traction and, hence, to the skin deformation experienced by a finger is a highly nonlinear process. Participants were asked to identify simulated textures reproduced by stimulating their fingers with rapid, imposed lateral skin displacements as a function of net position. They performed the identification task with a high degree of success, yet not perfectly. The fact that the experimental conditions eliminated many aspects of the interaction, including low-frequency finger deformation, distributed information, as well as normal skin movements, shows that the nervous system is able to rely on only two cues: amplitude and spectral information. The examination of the “spatial spectrograms” of the imposed lateral skin displacement revealed that texture could be represented spatially, despite being sensed through time and that these spectrograms were distinctively organized into what could be called “spatial formants.” This finding led us to speculate that the mechanical properties of the finger enables spatial information to be used for perceptual purposes in humans with no distributed sensing, which is a principle that could be applied to robots.

/pdf/the-spatial-spectrum-of-tangential-skin-displacement-can-2o8y0k1peu.pdf

The Spatial Spectrum of Tangential Skin Displacement Can Encode Tactual Texture

This paper introduces the Penn Haptic Texture Toolkit (HaTT), a publicly available repository of haptic texture models for use by the research community. HaTT includes 100 haptic texture and friction models, the recorded data from which the models were made, images of the textures, and the code and methods necessary to render these textures using an impedance-type haptic interface such as a SensAble Phantom Omni. This paper reviews our previously developed methods for modeling haptic virtual textures, describes our technique for modeling Coulomb friction between a tooltip and a surface, discusses the adaptation of our rendering methods for display using an impedance-type haptic device, and provides an overview of the information included in the toolkit. Each texture and friction model was based on a ten-second recording of the force, speed, and high-frequency acceleration experienced by a handheld tool moved by an experimenter against the surface in a natural manner. We modeled each texture's recorded acceleration signal as a piecewise autoregressive (AR) process and stored the individual AR models in a Delaunay triangulation as a function of the force and speed used when recording the data. To increase the adaptability and utility of HaTT, we developed a method for resampling the texture models so they can be rendered at a sampling rate other than the 10 kHz used when recording data. Measurements of the user's instantaneous normal force and tangential speed are used to synthesize texture vibrations in real time. These vibrations are transformed into a texture force vector that is added to the friction and normal force vectors for display to the user.

One hundred data-driven haptic texture models and open-source methods for rendering on 3D objects

Immersion, interaction, and imagination are three features of virtual reality (VR). Existing VR systems possess fairly realistic visual and auditory feedbacks, and however, are poor with haptic feedback, by means of which human can perceive the physical world via abundant haptic properties. Haptic display is an interface aiming to enable bilateral signal communications between human and computer, and thus to greatly enhance the immersion and interaction of VR systems. This paper surveys the paradigm shift of haptic display occurred in the past 30 years, which is classified into three stages, including desktop haptics, surface haptics, and wearable haptics. The driving forces, key technologies and typical applications in each stage are critically reviewed. Toward the future high-fidelity VR interaction, research challenges are highlighted concerning handheld haptic device, multimodal haptic device, and high fidelity haptic rendering. In the end, the importance of understanding human haptic perception for designing effective haptic devices is addressed.

Haptic display for virtual reality: progress and challenges

During tool-mediated interactions with objects, we experience force and fingerpad skin stretch resulting from shear forces caused by friction between the fingerpad skin and the stylus. When probing an object, for the same penetration distance, a stiffer object causes a larger load force and, thus, greater fingerpad skin stretch. We hypothesized that rendering additional artificial skin stretch together with force will increase perceived stiffness. We created a Skin Stretch Stylus that renders skin stretch through tactor displacement, attached it to a force-feedback device, and performed a study to characterize the effect of tactor displacement-induced skin stretch on stiffness perception. Results showed that adding artificial skin stretch causes additive augmentation of perceived stiffness across a range of surface stiffness, and the addition is a linear function of tactor displacement gain. However, intersubject variability in the estimated slope coefficient was large. We propose a model that explains the additive effect and suggests potential sources for the intersubject variability. We conclude that augmenting force feedback with skin stretch can increase users' perception of stiffness, but the effect is user-specific. Such augmentation may be useful in virtual environment and teleoperation scenarios when force feedback gains must be kept low to prevent feedback-induced instabilities, or when force feedback is limited due to actuator force limits.

Augmentation Of Stiffness Perception With a 1-Degree-of-Freedom Skin Stretch Device

In this paper we present a method to record the surface texture of real life objects like metal files, sandpaper etc. These textures can subsequently be played back on virtual surfaces. Our method has the advantage that it can record textures using commonly available haptic hardware. We use the 3DOF SensAble PHANToM to record the textures. The algorithm involves creating recordings of the frequency content of a real surface, by exploring it with a haptic device. We estimate the frequency spectra at two different velocities, and subsequently interpolate between them on a virtual surface. The extent of correlation between real and simulated spectra was estimated and a near exact spectral match was obtained. The simulated texture was played back using the same haptic device. The algorithm to record and playback textures is simple and can be easily implemented for planar surfaces with uniform textures

Recordable Haptic textures

In this paper, we study five aspects of design for wheeled inverted pendulum (WIP) platforms with the aim of understanding the effect of design choices on the balancing performance. First, we demonstrate analytically and experimentally the effect of soft visco-elastic tires on a WIP showing that the use of soft tires enhances balancing performance. Next, we study the effect of pitch rate and wheel velocity filters on WIP performance and make suggestions for design of filters. We then describe a self-tuning limit cycle compensation algorithm and experimentally verify its operation. Subsequently, we present an analytical simulation to study the effects of torque and velocity control of WIP motors and describe the tradeoffs between the control methodologies in various application scenarios. Finally, to understand if motor gearing can be an efficient alternative to bigger and more expensive direct drive motors, we analyze the effect of motor gearing on WIP dynamics. Our aim is to describe electromechanical design tradeoffs appropriately, so a WIP can be designed and constructed with minimal iterative experimentation.

/pdf/design-for-control-of-wheeled-inverted-pendulum-platforms-1wv4d26k4r.pdf

Design for Control of Wheeled Inverted Pendulum Platforms

This paper describes an algorithm for generation of forces from two dimensional bitmapped digital images, the forces allow the user to feel the contours of the image with sufficient realism using haptic devices. The algorithm can also be used to generate textures for virtual surfaces in a simple and efficient manner. The paper describes the design of the mask to be used to achieve the above two objectives and discusses the factors affecting the performance of the algorithm. Although the main focus of this paper pertains to haptic interaction with static images, the algorithm developed could also be used to haptically interact with videos.

Tangible Images: Runtime Generation of Haptic Textures From Images

Physically dissipative damping can increase the range of passive stiffness that can be rendered by a haptic device. Unlike simulated damping it does not introduce noise into the haptic control system. A DC motor can generate such damping if it's terminals are shorted. We employ a configuration of the H-bridge which can cause this damping to impart stability to our haptic device. This results in an increase in passive wall stiffness of about 33.3% at a sampling rate of 100Hz and 16.6% at 1kHz over the performance of an undamped DC motor. We have also attempted to implement the system on the hybrid haptic control system [1], it was seen that a perceivable change in the performance of this system was not observed by the use of DC motor damping.

DC Motor Damping: A Strategy to Increase Passive Stiffness of Haptic Devices

Instability in conventional haptic rendering destroys the perception of rigid objects in virtual environments. Inherent limitations in the conventional haptic loop restrict the maximum stiffness th...

/pdf/rendering-stiffer-walls-a-hybrid-haptic-system-using-56i2dbt2ji.pdf

Hari Vasudevan

Papers

Recordable Haptic textures

Design for Control of Wheeled Inverted Pendulum Platforms

Tangible Images: Runtime Generation of Haptic Textures From Images

DC Motor Damping: A Strategy to Increase Passive Stiffness of Haptic Devices

Rendering stiffer walls : a hybrid haptic system using continuous and discrete time feedback