Haptic rendering of rigid contacts using impulsive and penalty forces

A new simulation approach is proposed to improve the stability and the perceived rigidity of contacts during haptic interaction with multirigid body virtual environments. The approach computes impulsive forces upon contact and penalty and friction forces during contact. The impulsive forces are derived using a new multiple collision resolution method that never increases the kinetic energy of the system. When new contacts arise, the impulsive forces generate large hand accelerations without requiring increased contact stiffness and damping. Virtual objects and linkages are regarded as points in the configuration space, and no distinction is made between them in the proposed approach.     

Haptic force control based on impedance/admittance control aided by visual feedback

This paper demonstrates a haptic device for interaction with a virtual environment. The force control is added by visual feedback that makes the system more responsive and accurate. There are two popular control methods widely used in haptic controller design. First, is impedance control when user motion input is measured, and then, the reaction force is fed back to the operator. The alternative method is admittance control, when forces exerted by user are measured and motion is fed back to the user. Both, impedance and admittance control are also basic ways for interacting with a virtual environment. In this paper, several experiments were performed to evaluate the suitability of force-impedance control for haptic interface development. The difference between conventional application of impedance control in robot motion control and its application in haptic interface development is investigated. Open loop impedance control methodology is implemented for static case and a general-purpose robot under open loop impedance control was developed as a haptic device, while a closed loop model based impedance control was used for haptic controller design in both static and dynamic case. The factors that could affect to the performance of a haptic interface are also investigated experimentally using parametric studies. Experimental results for 1 DOF rotational motion and 2 DOF planar translational motion systems are presented. The results show that the impedance control aided by visual feedback broaden the applicability of the haptic device and makes the system more responsive and accurate.

An augmented Lagrangian optimization method for contact analysis problems, 2: numerical evaluation

The ALM2 solution procedure is evaluated by solving two simple contact analysis problems for different friction conditions. These example problems are devised to have closed form solutions. This way there is no uncertainty about the target solution for evaluation of the proposed algorithm as well as existing algorithms. The numerical results with ALM2 are compared with the analytical solutions as well as with the penalty, Lagrange multiplier and existing augmented Lagrangian methods. All the algorithms are analysed for stick and slip friction conditions. The example problems are used to show clearly the dependence of the existing solution methods on the number of load steps and penalty values. It is concluded that convergence of incremental solution schemes employed in these methods does not guarantee accuracy of the contact solution even with the use of solution enhancement schemes such as automatic load stepping and contact load prediction. The example problems are also used to demonstrate solution independence of the proposed ALM2 procedure from penalty values, and from the number of load steps. The proposed formulation for calculation of frictional forces and the ALM solution algorithm have worked quite well for the example problems. However, the algorithm needs to be developed and evaluated for more complex contact analysis problems.     

Comparison of two slideline methods using ADINA

Two general methods of treating sliding interface problems were implemented in ADINA. The first method uses constraint equations and is based on the work of Taylor, Hughes et al. The second method is a penalty function method where finite stiffnesses are used to simulate the contact forces. This is similar to the method used by Hallquist in NIKE2D. These may be used as notension sliding interfaces, with or without friction, or as a non-sliding interface to interpolate between different mesh regions. We briefly review the theory behind these methods and describe the implementation in ADINA. Several application problems have been run, including metal forming problems. Based on this experience the methods are compared in terms of ease of use, accuracy, reliability, influence on bandwidth, and solution time. Neither method is ideal. The penalty method is generally more efficient but may be inaccurate, whereas the constraint equations are accurate but less efficient.     

Effects of vision and friction on haptic perception

OBJECTIVE: Two experiments were conducted to examine the effects of vision and masking friction on contact perception and compliance differentiation thresholds in a simulated tissue-probing task. BACKGROUND: In minimally invasive surgery, the surgeon receives limited haptic feedback because of the current design of the instrumentation and relies on visual feedback to judge the amount of force applied to the tissues. It is suggested that friction forces inherent in the instruments contribute to errors in surgeons' haptic perception. This paper investigated the psychophysics of contact detection and cross-modal sensory processing in the context of minimally invasive surgery. METHOD: A within-subjects repeated measures design was used, with friction, vision, tissue softness, and order of presentation as independent factors, and applied force, detection time, error, and confidence as dependent measures. Eight participants took part in each experiment, with data recorded by a custom force-sensing system. RESULTS: In both detection and differentiation tasks, higher thresholds, longer detection times, and more errors were observed when vision was not available. The effect was more pronounced when haptic feedback was masked by friction forces in the surgical device (p < .05). CONCLUSION: Visual and haptic feedback were equally important for tissue compliance differentiation. APPLICATION: A frictionless endoscopic instrument can be designed to restore critical haptic information to surgeons without having to create haptic feedback artificially.     

Realistic haptic rendering of interacting deformable objects in virtual environments

A new computer haptics algorithm to be used in general interactive manipulations of deformable virtual objects is presented. In multimodal interactive simulations, haptic feedback computation often comes from contact forces. Subsequently, the fidelity of haptic rendering depends significantly on contact space modeling. Contact and friction laws between deformable models are often simplified in up to date methods. They do not allow a "realistic" rendering of the subtleties of contact space physical phenomena (such as slip and stick effects due to friction or mechanical coupling between contacts). In this paper, we use Signorini's contact law and Coulomb's friction law as a computer haptics basis. Real-time performance is made possible thanks to a linearization of the behavior in the contact space, formulated as the so-called Delassus operator, and iteratively solved by a Gauss-Seidel type algorithm. Dynamic deformation uses corotational global formulation to obtain the Delassus operator in which the mass and stiffness ratio are dissociated from the simulation time step. This last point is crucial to keep stable haptic feedback. This global approach has been packaged, implemented, and tested. Stable and realistic 6D haptic feedback is demonstrated through a clipping task experiment.     

Sensation-preserving haptic rendering

Most human-computer interactive systems focus primarily on the graphical rendering of visual information and, to a lesser extent, on the display of auditory information. Haptic interfaces have the potential to increase the quality of human-computer interaction by accommodating the sense of touch. They provide an attractive augmentation to visual display and enhance the level of understanding of complex data sets. A haptic rendering system generates contact or restoring forces to prevent penetration into the virtual objects and create a sense of touch. The system computes contact forces by first detecting if a collision or penetration has occurred. Then, the system determines the (projected) contact points on the model surface. Finally, it computes restoring forces based on the amount of penetration. Researchers have recently investigated the problem of rendering the contact forces and torques between 3D virtual objects. This problem is known as six-degrees-of-freedom (6-DOF) haptic rendering, as the computed output includes both 3-DOF forces and 3-DOF torques. This article presents an overview of our work in this area. We suggest different approximation methods based on the principle of preserving the dominant perceptual factors in haptic exploration.     

Networked multiplayer cooperative interaction using decoupled motion control method in a shared virtual environment with haptic,visual and movement feedback

This paper focuses on multiplayer cooperative interaction in a shared haptic environment based on a local area network. Decoupled motion control, which allows one user to manipulate a haptic interface to control only one‐dimensional movement of an avatar, is presented as a new type haptic‐based cooperation among multiple users. Users respectively move an avatar along one coordinate axis so that the motion of the avatar is the synthesis of movements along all axes. It is different from previous haptic cooperation where all users can apply forces on an avatar along any direction to move it, the motion of which completely depends on the resultant force. A novel concept of movement feedback is put forward where one user can sense other users’ hand motions through his or her own haptic interface. The concept can also be explained wherein one person who is required to move a virtual object along only one axis can also feel the motions of the virtual object along other axes. Movement feedback, which is a feeling of motion, differs from force feedback, such as gravity, collision force and resistance. A spring‐damper force model is proposed for the computation of motion feedback to implement movement transmission among users through haptic devices. Experimental results validate that movement feedback is beneficial for performance enhancement of such kind of haptic‐based cooperation, and the effect of movement feedback in performance improvement is also evaluated by all subjects.Copyright © 2012 John Wiley & Sons, Ltd.     

A fast and stable penalty method for rigid body simulation

Two methods have been used extensively to model resting contact for rigid body simulation. The first approach, the penalty method, applies virtual springs to surfaces in contact to minimize interpenetration. This method, as typically implemented, results in oscillatory behavior and considerable penetration. The second approach, based on formulating resting contact as a linear complementarity problem, determines the resting contact forces analytically to prevent interpenetration. The analytical method exhibits expected-case polynomial complexity in the number of contact points, and may fail to find a solution in polynomial time when friction is modeled. We present a fast penalty method that minimizes oscillatory behavior and leads to little penetration during resting contact; our method compares favorably to the analytical method with regard to these two measures, while exhibiting much faster performance both asymptotically and empirically.     

Virtual prototyping of mechanical systems with tool mediated haptic feedback

Haptic feedback usually involves two types of stimulation forces: forces that address the touch sense and forces that address the kinesthetic perception. Touch forces have a low intensity and a complex structure since they reflect contact phenomena where friction plays an important role. Therefore, they are quite difficult to simulate. Virtual prototyping with haptic feedback should ideally involve both types of forces, but the integration of the touch feeling makes the simulator very complex. In this paper, we present a novel concept for virtual prototyping in which the touch interaction is separated from the kinesthetic force feedback. This is possible using a prototype that has a real part undertaking the touch interaction and a virtual part that simulate feedback for the kinesthetic forces. In this way, a full haptic interaction with the virtual prototype is established by means of a device that provides a realistic simulation of the product. In order to illustrate the concept, several experiments have been carried out for the case of specific subsystems of a car, which are particularly involved in the driver–car interaction: steering system, clutch pedal and the gearshift. A user test is described in the last part as well as the conclusions of the research.     

Design and analysis of an fMRI compatible haptic robot

Magnetic resonance (MR) compatible haptic devices have certain specific structural and operational properties, which are due to the magnetic field, and haptic requirements. Through the development of a haptic mechanism, which is compatible with a magnetic resonance environment, certain problems were solved, which are common to all robotic devices operating in an MR tunnel. This paper deals with the manipulability problem of a novel 3 DOF MR compatible haptic mechanism, considering limited space and its visualisation. An appropriate 3D visualisation method has been developed for analysing the manipulability characteristics of a haptic mechanism within an MR environment. Choosing a suitable driving system is one of the crucial design attributes for quality force transmission in haptic interfaces. This paper introduces certain adaptations, which have been done to enable the MR compatibility of a cable drive driven by an electric motor. It also presents the theoretical modelling of a cable drive for a 3 DOF MR compatible haptic mechanism, focusing on the hysteretic behaviour of polymeric cables.     

A Precomputed Approach for Real-Time Haptic Interaction with Fluids

The key to enhancing perception of the virtual world is improving mechanisms for interacting with that world. Through providing a sense of touch, haptic rendering is one such mechanism. Many methods efficiently display force between rigid objects, but to achieve a truly realistic virtual environment, haptic interaction with fluids is also essential. In the field of computational fluid dynamics, researchers have developed methods to numerically estimate the resistance due to fluids by solving complex partial differential equations, called the Navier-Stokes equations. However, their estimation techniques, although numerically accurate, are prohibitively time-consuming. This becomes a serious problem for haptic rendering, which requires a high frame rate. To address this issue, we developed a method for rapidly estimating and displaying forces acting on a rigid virtual object due to water. In this article, we provide an overview of our method together with its implementation and two applications: a lure-fishing simulator and a virtual canoe simulator     

Haptic Seat Interfaces for Driver Information and Warning Systems

The implementation of haptic interfaces in vehicles has important safety and flexibility implications for lessening visual and auditory overload during driving. The present study aims to design and evaluate haptic interfaces with vehicle seats. Three experiments were conducted by testing a haptic seat in a simulator with a total of 20 participants. The first experiment measured reaction time, subjective satisfaction, and subject workloads of the haptic, visual, and auditory displays for the four signals primarily used by vehicle navigation systems. The second experiment measured reaction time, subjective satisfaction, and subjective workloads of the haptic, auditory, and multimodal (haptic + auditory) displays for the ringing signal used by in-vehicle Bluetooth hands-free systems. The third experiment measured drivers' subjective awareness, urgency, usefulness, and disturbance levels at various vibration intensities and positions for a haptic warning signal used by a driver drowsiness warning system. The results indicated that haptic seat interfaces performed better than visual and auditory interfaces, but the unfamiliarity of the haptic interface caused a lower subjective satisfaction for some criteria. Generally, participants showed high subjective satisfaction levels and low subjective workloads toward haptic seat interfaces. This study provided guidance for implementing haptic seat interfaces and identified the possible benefits of their use. It is expected that haptic seats implemented in vehicles will improve safety and the interaction between driver and vehicle.     

Transient simulation of friction-induced vibrations using an elastic multibody approach

In this paper, by the use of elastic multibody dynamics and a master–slave contact approach with penalty formulation, computationally efficient time integrations of a brake system are performed for constant and time-dependent input parameters. As a result, the amplitudes of the friction-induced vibrations and the contact forces at the disc–pad interfaces are predicted. Besides, system outputs are viewed in phase diagrams, and the creation of a stable limit cycle for a low friction coefficient is identified. In this way, conclusions on the stability of the system are drawn, and statements based on frequency-domain analyses are complemented. Finally, a distinct need for a new criterion that quantifies the squeal propensity of such systems in the time domain is identified.