The increasing demand for virtual reality applications in several scientific disciplines feeds new research perspectives dealing with robotics, automation, and computer science. In this context, one of the topics is the design of advanced force-feedback devices allowing not only kinesthetic interaction with virtual objects but also locomotion and navigation inside virtual worlds. This has the main advantage to stimulate human vestibular apparatus, thus increasing the overall realism of simulation. Particularly, this paper deals with mobile haptic interfaces (MHIs), built by combining standard force-feedback devices with mobile platforms. We investigated which factors may affect the transparency of this kind of devices, identifying in mobile robot dynamics a possible cause of loss of transparency. Hence, in this paper, we present a method to analyze dynamic performance of an MHI and some basic guidelines to design controller in order to meet desired specifications. Experimental validation of the theoretical results is reported.

Despite a wealth of literature on discrimination thresholds for displacement, force magnitude, stiffness, and viscosity, there is currently a lack of data on our ability to discriminate force directions. Such data are needed in designing haptic rendering algorithms where force direction, as well as force magnitude, are used to encode information such as surface topography. Given that haptic information is typically presented in addition to visual information in a data perceptualization system, it is also important to investigate the extent to which the congruency of visual information affects force-direction discrimination. In this article, the authors report an experiment on the discrimination threshold of force directions under the three display conditions of haptics alone (H), haptics plus congruent vision (HVcong), and haptics plus incongruent vision (HVincong). Average force-direction discrimination thresholds were found to be 18.4°, 25.6°, and 31.9° for the HVcong, H and HVincong conditions, respectively. The results show that the congruency of visual information significantly affected haptic discrimination of force directions, and that the force-direction discrimination thresholds did not seem to depend on the reference force direction. The implications of the results for designing haptic virtual environments, especially when the numbers of sensors and actuators in a haptic display do not match, are discussed.

Rendering stiff virtual objects remains a core challenge in the field of haptics. A study of this problem is presented, which relates the maximum achievable object stiffness to the elements of the control loop. In particular, we examine how the sampling rate, quantization, computational delay, and amplifier dynamics interact with the inertia, natural viscous, and Coulomb damping of the haptic device. Nonlinear effects create distinct stability regions, and many common devices operate stably, yet in violation of passivity criteria. An energy-based approach provides theoretical insights, supported by simulations, experimental data, and a describing function analysis. The presented results subsume previously known stability conditions

Rendering a stiff virtual wall remains a core challenge in the field of haptics. A passivity study of this problem is presented, which relates the maximum achievable wall stiffness to the system discretization and sampling delays, to the quantization of the encoder, to the inertia of the haptic device, as well as to both the natural viscous and Coulomb damping present in the haptic device. The resulting stability criterion generalizes previously known results. Its analytic derivation is verified in both simulation and experiments on a one degree of freedom testbed.

This paper presents a series of kinematic and haptic analysis, which lead to the design of a particularly simple, yet useful multi-hand multi-finger haptic interface. We also discuss rendering issues, which must be addressed in utilizing it, including and extension of the proxy to more general contact.

Ultrasound technologies have been widely used in gynecology and obstetrics. Modern ultrasound systems allow the reconstruction of a 3D model of the subject being scanned. Even though visual interfaces have reached very high standards, the problem of representing a 3D image on a 2D computer screen still exists. Moreover, no physical interaction is possible with such model. The FeTouch system, developed at Siena University in the last two years, partially solves such issues by using stereo visual feedback and haptic devices. While the system can be used with any 3D model obtained from ultrasound scans, its current prime use is to allow mothers to interact with a model of the fetus they are carrying. The system, which is freely available on the project web page, has been tested on twelve cases which have been monitored by doctors at Siena Hospital.

This article describes the architecture of the "Museum of Pure Form", a virtual reality system where the user can interact, through the senses of touch and sight, with digital models of 3D art forms and sculptures. Two different realizations of "Museum. of Pure Form" systems are currently being developed at PERCRO, Pisa, Italy. In one realization "The Museum of Pure Form" is conceived as a system placed inside several museums and art galleries around Europe and made available to people visiting such institutions. In the second realization the system will be placed and tested inside a CAVE environment. Considerations on technological aspects concerning the implementation of a virtual environment endowed with haptic feedback for cultural heritage applications are reported throughout the paper.

Many motion base simulators have been developed in the last thirty years for many different types of vehicles. In order to make a simulation more realistic, linear accelerations and angular rates are exerted on the pilot by moving the platform on which the mock-up vehicle is located. This has to be accomplished without driving the simulator out of its workspace. The software component that is in charge of this is commonly referred to as washout filter. Washout filters have been widely investigated in the past, mainly in the field of flight simulators. We present a washout filter designed for a motorcycle simulator. The solution is preliminary and follows, as a reference point, techniques previously adopted for large aircraft simulators. Differences between motorcycle and aircraft simulation are analyzed and a preliminary customized solution is proposed. The washout filter to be used to drive a motorcycle simulator currently being built at PERCRO, has been tested off-line showing good results and will soon be tested on real riders.

Many motion based simulators have been developed for many different types of vehicles. In order to make a simulation more realistic, linear accelerations and angular rates are exerted on the pilot by moving the platform on which the mock-up vehicle is located. This has to be accomplished without driving the simulator out of its work-space. The software component that is in charge of this is commonly referred to as the washout filter. Washout filters have been widely investigated in the past, mainly in the field of flight simulators. We present a washout filter designed for a motorcycle simulator. The solution is preliminary and follows, as a reference point, techniques previously adopted for large aircraft simulators. Differences between motorcycle and aircraft simulation are analyzed and a preliminary customized solution is proposed. The washout filter, which will be used to drive a motorcycle simulator, currently being built at PERCRO, has been tested off-line showing good results and will soon be tested on real riders.

Intention tremor severely compromises everyday life tasks in patients suffering with multiple sclerosis or Parkinson's disease. The paper reports the current achievements in the analysis of subjects' movements. The trajectories produced by patients affected by tremor are investigated. Indexing procedures for the evaluation of the tremor which is present in the trajectories are proposed. Such indexes should be sensitive to tremor while they are not to ordinary movements. The properties of the indexes have been verified both with analytical considerations and with numerical tests. An experimental setup has been realized for the analysis of tremor on patients affected by multiple sclerosis tremor. The data collected within this experiment have been compared with expected results. Furthermore the indexing procedure has been applied for the evaluation of a filtering system. The case of handwriting has been chosen as the reference task for the evaluation of achieved results. The results of clinical tests are presented. Finally the applicability of the index-based procedures to the control of filtering systems is discussed. The control architectures in the case of force-feedback less interfaces as well as haptic interfaces are presented and discussed.

The hand force feedback system is an anthropomorphic haptic interface for the replication of the forces arising during grasping and fine manipulation operations. It is composed of four independent finger dorsal exoskeletons which wrap up four fingers of the human hand (the little finger is excluded). Each finger possesses three electrically actuated DOF placed in correspondence with the human finger flexion axes and a passive DOF allowing finger abduction movements. Each exoskeleton finger has three points of attachment to the operator's finger (two for the thumb) at the middle of the phalanges. Mechanical fixtures guarantee that just a force perpendicular to the finger and in its sagittal plane is exchanged at each point of attachment. Such force component is sensed and it is actively controlled in feedback. The paper illustrates the design and testing of the controller for the thumb exoskeleton. First the mechanical system is analyzed and the features which influence the controller design, such as the presence of unidirectional tendon transmission, are modeled. Then haptic controllers, i.e. feedback controllers aiming at improving the performance of the device when used as a haptic interface for virtual environments or telemanipulation, are designed and tested experimentally. Finally the experimental results are discussed.