Haptic Applications Research Articles

Perceived Hardness through Actual and Virtual Damped Natural Vibrations.

Humans perceive hardness of objects from damped natural vibrations by tapping their surfaces. We investigated the roles of six parameters characterizing the vibration in virtual and real environments. The effects of some parameters differed between the two environments. This finding provides valuable information to the developers of haptic applications.

Evaluation of Velocity Estimation Methods Based on Their Effect on Haptic Device Performance

This paper comparatively evaluates the effect of real-time velocity estimation methods on the passivity and fidelity of virtual walls implemented using haptic interfaces. Impedance width or $Z$ -width is a fundamental measure of performance in haptic devices. Limited accuracy of velocity estimates from position encoder data is an impediment in improving the $Z$ -width in haptic interfaces. We study the efficacy of Levant's differentiator as a velocity estimator to allow passive implementation of higher stiffness virtual walls as compared to some of the commonly used velocity estimators in the field of haptics. We first experimentally demonstrate feasibility of Levant's differentiator as a velocity estimator for haptics applications by comparing $Z$ -width performance achieved with Levant's differentiator and commonly used finite difference method (FDM) cascaded with a low-pass filter. A novel $Z$ -width plotting technique combining the passivity and fidelity of haptic rendering is proposed, and used to compare the haptic device performance obtained with Levant's differentiator, FDM+low-pass filter, first-order adaptive windowing (FOAW), and Kalman-filter-based velocity estimation methods. Simulations and experiments conducted on a custom single degree-of-freedom haptic device demonstrate that the stiffest virtual walls are rendered with velocity estimated using Levant's differentiator, and the highest wall rendering fidelity is achieved by FOAW-based velocity estimation scheme.

Implementation of a revolute-joint-based asymmetric Schönflies motion haptic device with redundant actuation

In this work, a revolute joint-based asymmetric Schönflies motion (SM) haptic device with 4-Degree-of-Freedom (DOF) force feedback capability is developed. The SM haptic device is composed of a redundantly actuated parallel sub-module which has translational 3-DOF output motion, a pantograph limb which takes the role of providing 1-DOF rotational output motion, and a revolute joint allowing the relative motion between them. All five DC motors without gearhead are placed on the ground by employing proper parallel transmission linkages for power transmission. The large singularity-free workspace and the improved kinematic characteristics are secured by redundantly actuating the 3-DOF sub-module. Thus, the SM haptic device has excellent features such as the unlimited 1-DOF rotational output motion, minimal friction, minimal inertia, and large dexterous workspace. Mobility analysis, kinematic modeling, singularity analysis, optimal design, and linear inertia modeling of the SM haptic device are conducted. Then a prototype with two operational modes such as gravity compensation and linear inertia compensation modes is implemented. Through friction measurements, motion tests for gravity and/or linear inertia compensation modes, and virtual wall experiments, it is confirmed that the prototype possesses minimal friction as well as good gravity and linear inertia compensation performances sufficient for the high-quality haptic device applications such as medical training, robot-assisted surgery, etc.

Low-cost ultra-stretchable strain sensors for monitoring human motion and bio-signals

The emerging need for interactive wearable devices has been a driving force for the development of flexible electronics. Due to their ability to conform to the complex nature of the human physique, stretchable strain sensors have been extensively used to measure bio-signals and monitor human motion. Here, a new fabrication method of a piezo-resistive strain sensor is introduced, and the ability of the sensor to measure the human heartbeat and track a wide range of human motion is demonstrated. The sensor is fabricated by infusing graphene nano-flakes into a rubber-like adhesive pad. The fabricated sensor is highly stretchable and can withstand strain up to 350%. Even after 10,000 cycles of stretching and relaxing a robust and stable electrical response is maintained. Furthermore, the gauge factor of the sensor ranges from 2 to upto 160; which in turn allows the sensor to monitor a great variety of human motions. Hence, three wearable devices are developed using the fabricated graphene-based strain sensor to measure human knee movement, finger movement and heartbeat through the radial artery. The sensor is also used in a robotic haptic application to control a robotic finger. These experiments demonstrate the applicability of the sensor for real-time monitoring, specifically in wearable human interactive devices.

Operator dynamics for stability condition in haptic and teleoperation system: A survey.

Currently, haptic systems ignore the varying impedance of the human hand with its countless configurations and thus cannot recreate the complex haptic interactions. The literature does not reveal a comprehensive survey on the methods proposed and this study is an attempt to bridge this gap. The paper includes an extensive review of human arm impedance modeling and control deployed to address inherent stability and transparency issues in haptic interaction and teleoperation systems. Detailed classification and comparative study of various contributions in human arm modeling are presented and summarized in tables and diagrams. The main challenges in modeling human arm impedance for haptic robotic applications are identified. The possible future research directions are outlined based on the gaps identified in the survey.

Toward Haptic Communications Over the 5G Tactile Internet

Touch is currently seen as the modality that will complement audition and vision as a third media stream over the Internet in a variety of future haptic applications which will allow full immersion and that will, in many ways, impact society. Nevertheless, the high requirements of these applications demand networks which allow ultra-reliable and low-latency communication for the challenging task of applying the required quality of service for maintaining the user’s quality of experience at optimum levels. In this survey, we enlist, discuss, and evaluate methodologies and technologies of the necessary infrastructure for haptic communication. Furthermore, we focus on how the fifth generation of mobile networks will allow haptic applications to take life, in combination with the haptic data communication protocols, bilateral teleoperation control schemes and haptic data processing needed. Finally, we state the lessons learned throughout the surveyed research material along with the future challenges and infer our conclusions.

Design of A Novel Passive Binary-Controlled Variable Stiffness Joint (BpVSJ) Towards Passive Haptic Interface Application

In this paper we present the design, development and experimental validation of a novel Binary-Controlled Variable Stiffness Joint (BpVSJ) towards haptic teleoperation and human interaction manipulators applications. The proposed actuator is a proof of concept of a passive revolute joint, where the working principle is based on the recruitment of series-parallel elastic elements. The novelty of the system lies in its design topology, including the capability to involve an (n) number of series-parallel elastic elements to achieve ( $2^{n}$ ) levels of stiffness, as compared to current approaches. Accordingly, the level of stiffness can be altered at any position without the need to revert to the initial equilibrium position. The BpVSJ has low energy consumption and short switching time, and is able to rotate freely at zero stiffness without limitations. Further smart features include scalability and relative compactness. This paper details the mathematical stiffness modeling of the proposed actuator mechanism, as well as the experimentally measured performance characteristics. The experimental results matched well with the physical-based modeling in terms of stiffness variation levels. Moreover, Psychophysical experiments were also conducted using (20) healthy subjects in order to evaluate the capability of the BpVSJ to display three different levels of stiffness that are cognitively realized by the users. The participants performed two tasks: a relative cognitive task and an absolute cognitive task. The results show that the BpVSJ is capable of rendering stiffness with high average relative accuracy (Relative Cognitive Task relative accuracy is 97.3%, and Absolute Cognitive Task relative accuracy is 83%).

Protruding organic surfaces triggered by in-plane electric fields

Coatings with a dynamic surface topography are of interest for applications in haptics, soft robotics, cell growth in biology, hydro- and air dynamics and tribology. Here we propose a design for creating oscillating surface topographies in thin liquid crystal polymer network coatings under an electric field. By applying an alternating electric field, the coating surface deforms, and pre-designed local corrugations appear. The continuous AC electric field further initiates oscillations superimposed on the formed topographies. This effect is based on microscopic free volume creation. By exciting the liquid crystal network at its resonance frequency, maximum free volume is generated and large surface topographies are formed. Molecular simulation is used to examine this behaviour in microscopic detail as a function of oscillation frequency. Surface topography formation is fast and reversible. Excess free volume is energetically unfavourable, thus the surface topographies disappear within seconds once the electric field is removed.

A Control-Oriented Framework for Direct Impulse-Based Rendering of Haptic Contacts

In many haptic applications, producing a sharp feeling of impact is crucial for high-fidelity force feedback rendering of virtual objects (VOs). Although suitable for rendering collision-rich haptic interactions, impulse-based methods are rarely used in a pure form. Instead, they are combined with penalty-based elements in different forms such as virtual couplings (VCs) and hybridization. In this paper, we first propose the direct impulse-based paradigm for rendering haptic contacts using a new sampled-data interpretation of the impact problem. Then, we cast this interpretation into a systematic framework entitled the generalized contact controller (GCC). This enables us to implement different contact rendering methods as controllers and to improve them by appropriating a wide array of analysis and design tools developed in the control field. We specifically show how to apply position and velocity corrections to the purely impulse-based contact controller for enhancing its energy and sustained contact characteristics, and how to add an anti-windup compensator (AWC) for meeting actuation limits. These propositions are validated via simulation and experiments, as well as via human perception studies. Results show the promising aspects of the proposed impulse-based methods for generating a sharper unfiltered feeling of rigid-body contacts even at low sampling rates.

Performance improvement of haptic collision detection using subdivision surface and sphere clustering.

Haptics applications such as surgery simulations require collision detections that are more precise than others. An efficient collision detection method based on the clustering of bounding spheres was proposed in our prior study. This paper analyzes and compares the applied effects of the five most common subdivision surface methods on some 3D models for haptic collision detection. The five methods are Butterfly, Catmull-Clark, Mid-point, Loop, and LS3 (Least Squares Subdivision Surface). After performing a number of experiments, we have concluded that LS3 method is the most appropriate for haptic simulations. The more we applied surface subdivision, the more the collision detection results became precise. However, it is observed that the performance becomes better until a certain threshold and degrades afterward. In order to reduce the performance degradation, we adopted our prior work, which was the fast and precise collision detection method based on adaptive clustering. As a result, we obtained a notable improvement of the speed of collision detection.

Haptic Collision Detection on Disjoint Objects with Overlapping and Inclusive Bounding Volumes.

This paper presents a method to alleviate performance degradation issues of Haptic Collision Detection when the Bounding Volumes or Bounding Volume Hierarchies of multiple disjoint objects are overlapping or inclusive and force the Haptic Collision Detection methods into narrow phase collision detection with all involved objects. The proposed method aims to generate tighter, mutually exclusive Bounding Volumes at the pre-processing stage, and to quickly cull irrelevant nearby objects at the broad phase to ensure that the Haptic Collision Detection methods will not be overloaded with unnecessary narrow phase collision detection. The proposed method is based on a hybrid representation of Bounding Volume and Space Partitioning and is implemented as an algorithm that automatically generates these new Bounding Volumes for disjoint objects, with details and corner cases discussed. A series of experiments based on real-life Haptic Collision Detection applications has been conducted. The results are analyzed and compared with those from an existing Haptic Collision Detection algorithm. The outcome demonstrates the capability of the proposed method in maintaining a stable Haptic Collision Detection performance under various challenging situations.

Fuzzy-PID 알고리듬을 이용한 MR 브레이크의 토크 추종 제어

In the present work, torque tracking control performance of MR brake is evaluated through experimental test. After manufacturing the MR brake, which has been originally designed for haptic application, torque characteristics are investigated with respect to input currents. To achieve enhanced tracking control performance, a new Fuzzy-PID control algorithm is designed and implemented to the system. Torque tracking control performances are evaluated by adopting various desired torque trajectories with sinusoidal, square input signals and square input with multi-magnitudes. It is demonstrated that the proposed MR brake can successfully generate braking torques according to desired inputs by applying proper input current which can be determined based on the proposed control algorithm.

A cable-pulley transmission mechanism for surgical robot with backdrivable capability

Abstract Compact actuators, low friction and back-drivable transmissions are essential components in haptic and impedance type surgical robotic systems, since their performances affect overall volume, force feedback capability and power consumption. An innovative miniaturized, low friction, back-drivable reducing mechanism for haptic or surgical robot applications has been designed, developed and evaluated. A new differential mechanism having a cable comprises a sheave wheel supported by a yolk is also implemented. Low friction and back-drivable, compared to conventional non-back-drivable mechanisms based on gear coupling, is achieved by means of differential cable driven method. The system has been integrated with a permanent-magnet DC motor and a drum on which a tendon is wound, and then finally connected to the remote end joint. Several experiments to validate the feasibility of the reducing device were carried out.

Human Head Stiffness Rendering

Human head stiffness rendering is important in haptic interactive applications, because it defines a realistic physical interaction between human operator(s) and a human avatar created in a virtual environment. In this paper, we propose a hybrid method for rendering the appropriate stiffness property on a human head polygon mesh that combines popular haptic rendering approaches: study the sophisticated deformation behavior of a deformable object and then interpret and render this behavior as the resulting stiffness property on the individual’s head mesh. The stiffness property is estimated from a registered and shape-adapted skull template mesh as a reference and modeled from the deformation behavior of soft tissue in a finite-element method (FEM) framework. Our method consists of different procedures, including facial landmark detection, model registration using the iterative closest point technique, adaptive shape modification processed with a modified weighted free-form deformation, and FEM simulation. After the stiffness property is rendered on a head polygon mesh, we perform a user study by inviting participants to experience the haptic feedback rendered from our results. According to the participants’ feedback, the stiffness property of the head polygon mesh is properly rendered, because it satisfies their expectations.

Controlling the contact levels of details for fast and precise haptic collision detection

For accurate and stable haptic rendering, collision detection for interactive haptic applications has to be done by filling in or covering target objects as tightly as possible with bounding volumes (spheres, axis-aligned bounding boxes, oriented bounding boxes, or polytopes). In this paper, we propose a method for creating bounding spheres with respect to the contact levels of details (CLOD), which can fit objects while maintaining the balance between high speed and precision of collision detection. Our method is composed mainly of two parts: bounding sphere formation and two-level collision detection. To specify further, bounding sphere formation can be divided into two steps: creating spheres and clustering spheres. Two-level collision detection has two stages as well: fast detection of spheres and precise detection in spheres. First, bounding spheres are created for initial fast probing to detect collisions of spheres. Once a collision is probed, a more precise detection is executed by examining the distance between a haptic pointer and each mesh inside the colliding boundaries. To achieve this refined level of detection, a special data structure of a bounding volume needs to be defined to include all mesh information in the sphere. After performing a number of experiments to examine the usefulness and performance of our method, we have concluded that our algorithm is fast and precise enough for haptic simulations. The high speed detection is achieved through the clustering of spheres, while detection precision is realized by voxel-based direct collision detection. Our method retains its originality through the CLOD by distance-based clustering.

Flexible Zinc-Tin Oxide Thin Film Transistors Operating at 1 kV for Integrated Switching of Dielectric Elastomer Actuators Arrays.

Flexible high-voltage thin-film transistors (HVTFTs) operating at more than 1 kV are integrated with compliant dielectric elastomer actuators (DEA) to create a flexible array of 16 independent actuators. To allow for high-voltage operation, the HVTFT implements a zinc-tin oxide channel, a thick dielectric stack, and an offset gate. At a source-drain bias of 1 kV, the HVTFT has a 20 µA on-current at a gate voltage bias of 30 V. Their electrical characteristics enable the switching of DEAs which require drive voltages of over 1 kV, making control of an array simpler in comparison to the use of external high-voltage switching. These HVTFTs are integrated in a flexible haptic display consisting of a 4 × 4 matrix of DEAs and HVTFTs. Using a single 1.4 kV supply, each DEA is independently switched by its associated HVTFT, requiring only a 30 V gate voltage for full DEA deflection. The 4 × 4 display operates well even when bent to a 5 mm radius of curvature. By enabling DEA switching at low voltages, flexible metal-oxide HVTFTs enable complex flexible systems with dozens to hundreds of independent DEAs for applications in haptics, Braille displays, and soft robotics.

A Multi-Finger Interface with MR Actuators for Haptic Applications.

Haptic devices with multi-finger input are highly desirable in providing realistic and natural feelings when interacting with the remote or virtual environment. Compared with the conventional actuators, MR (Magneto-rheological) actuators are preferable options in haptics because of larger passive torque and torque-volume ratios. Among the existing haptic MR actuators, most of them are still bulky and heavy. If they were smaller and lighter, they would become more suitable for haptics. In this paper, a small-scale yet powerful MR actuator was designed to build a multi-finger interface for the 6 DOF haptic device. The compact structure was achieved by adopting the multi-disc configuration. Based on this configuration, the MR actuator can generate the maximum torque of 480 N.mm with dimensions of only 36 mm diameter and 18 mm height. Performance evaluation showed that it can exhibit a relatively high dynamic range and good response characteristics when compared with some other haptic MR actuators. The multi-finger interface is equipped with three MR actuators and can provide up to 8 N passive force to the thumb, index and middle fingers, respectively. An application example was used to demonstrate the effectiveness and potential of this new MR actuator based interface.

Intermanual Apparent Tactile Motion and Its Extension to 3D Interactions.

Information provided by sensory systems is inherently ambiguous as to its source in the physical world. To arrive at a coherent representation, perception deploys heuristic rules and multimodal input, which potentially produce errors such as illusions. The current work uses these effects to create apparent tactile motion and illusory depth motion using sparse vibrotactile stimulation across the hands. Experiment 1 showed the effects of vibrotactile duration and temporal separation between the hands on the quality of perceived illusory linear motion. Experiment 2 indicated a compressed linear relation between the visual and tactile speeds, and established a linear function relating visual size to perceived tactile intensity at three durations. Experiment 3 introduced an "M-filter" algorithm that varies tactile stimulus amplitude by a parabolic function based on visual looming and receding. It demonstrated that the M-filters, accompanied by visual depth cues, can induce tactile motion in depth. Experiment 4 showed the M-filter algorithm is necessary to create tactile perception in depth, as opposed to apparent tactile motion. The current research has value for a basic understanding of haptic perception, as well as haptic applications that digitally generate perceptual representations of the distal world on small-sized devices in the space between the hands.

Non-smooth dynamics for an efficient simulation of the grand piano action

Models with impact or dry friction, yielding discontinuous velocities or accelerations, have motivated research for appropriate numerical methods in the community of non-smooth dynamics. In this work, we apply such methods on the grand piano action. This multibody system has two properties of interest in terms of modelling and simulation: it is extremely sensitive to small misadjustements, and its functioning strongly relies on dry friction and stick-slip transitions—known to be crucial for the touch of the pianist. Using numerical methods of non-smooth contact dynamics, the non-smooth character of dry friction was conserved, in contrast to classical approaches based on regularization which additionally impose the somewhat arbitrary choice of a regularizing parameter. The use of such numerical method resulted in computations about a few hundred times faster than those reported in recent literature. For the first time, the presented predictions of the piano action's simulations are forces (in particular, the reaction force of the key on the pianist's finger), instead of displacements which filter out most of the dynamical subtleties of the mechanism. The comparisons between measured and simulated forces in response to a given motion are successful, which constitutes an excellent validation of the model, from the dynamical and the haptic points of view. Altogether, numerical methods for non-smooth contact dynamics applied to a non-smooth model of the piano action proved to be both accurate and efficient, opening doors to industrial and haptic applications of sensitive multibody systems for which dry friction is essential. Simulation-based videos Simulations of a keystroke: Your browser does not support the video tag. Comparisons between simulations and experiments: Your browser does not support the video tag. Experimental and educational videos High-speed captures of the piano key mechanism (Left: piano keystroke. Right: forte keystroke.) [A. Thorin and X. Boutillon, LMS@Ecole polytechnique / CEA LIST] Your browser does not support the video tag. Your browser does not support the video tag. Explanations on how the mechanism works [A. Thorin based on O. Remez's drawing ] Your browser does not support the video tag. Tracking of the kinematics using J. Diener's implementation of KLT tracking algorithms: Your browser does not support the video tag.

Modeling and test of a kinaesthetic actuator based on MR fluid for haptic applications.

Haptic display units have been widely used for conveying button sensations to users, primarily employing vibrotactile actuators. However, the human feeling for pressing buttons mainly relies on kinaesthetic sensations (rather than vibrotactile sensations), and little studies exist on small-scale kinaesthetic haptic units. Thus, the primary goals of this paper are to design a miniature kinaesthetic actuator based on Magneto-Rheological (MR) fluid that can convey various button-clicking sensations and to experimentally evaluate its haptic performance. The design focuses of the proposed actuator were to produce sufficiently large actuation forces (resistive forces) for human users in a given size constraint and to offer a wide range of actuation forces for conveying vivid haptic sensations to users. To this end, this study first performed a series of parametric studies using mathematical force models for multiple operating modes of MR fluid in conjunction with finite element electromagnetism analysis. After selecting design parameters based on parametric studies, a prototype actuator was constructed, and its performance was evaluated using a dynamic mechanical analyzer. It measured the actuator's resistive force with a varying stroke (pressed depth) up to 1 mm and a varying input current from 0 A to 200 mA. The results show that the proposed actuator creates a wide range of resistive forces from around 2 N (off-state) to over 9.5 N at 200 mA. In order to assess the prototype's performance in the terms of the haptic application prospective, a maximum force rate was calculated to determine just noticeable difference in force changes for the 1 mm stoke of the actuator. The results show that the force rate is sufficient to mimic various levels of button sensations, indicating that the proposed kinaesthetic actuator can offer a wide range of resistive force changes that can be conveyed to human operators.