Domenico Prattichizzo

Image-Based Visual Servoing for Nonholonomic Mobile Robots Using Epipolar Geometry

We present an image-based visual servoing strategy for driving a nonholonomic mobile robot equipped with a pinhole camera toward a desired configuration. The proposed approach, which exploits the epipolar geometry defined by the current and desired camera views, does not need any knowledge of the 3-D scene geometry. The control scheme is divided into two steps. In the first, using an approximate input-output linearizing feedback, the epipoles are zeroed so as to align the robot with the goal. Feature points are then used in the second translational step to reach the desired configuration. Asymptotic convergence to the desired configuration is proven, both in the calibrated and partially calibrated case. Simulation and experimental results show the effectiveness of the proposed control scheme

Using Kinect for hand tracking and rendering in wearable haptics

Wearable haptic devices with poor position sensing are combined with the Kinect depth sensor by Microsoft. A heuristic hand tracker has been developed. It allows for the animation of the hand avatar in the virtual reality and the implementation of the force rendering algorithm: the position of the fingertips is measured by the hand tracker designed and optimized for Kinect, and the rendering algorithm computes the contact forces for wearable haptic display. Preliminary experiments with qualitative results show the effectiveness of the idea of combining Kinect and wearable haptics.

The automatic control telelab: a user-friendly interface for distance learning

In this paper, a remote laboratory of automatic control is presented. The main target of this laboratory is to allow students to easily interact with a set of physical processes through the Internet. The student will be able to run experiments, change control parameters, and analyze the results remotely. The automatic control telelab (ACT) allows the user to design his/her own controller by means of the MATLAB/Simulink environment, and to test it on the actual plant through a user-friendly interface. An additional feature of ACT is its architecture, allowing for an easy integration of new processes for control experiments. The ACT is reachable at http://www.dii.unisi.it//spl sim/control/act.

The automatic control telelab

A remote laboratory for automatic control is presented. The main aim of this laboratory is to allow students to easily interact with a set of physical processes through the Internet. The student can run experiments, change control parameters, and analyze the results remotely. The automatic control telelab (ACT) allows the user to choose a predefined controller or synthesize a new controller through the Matlab/Simulink environment, and to test it on actual plant through a user friendly interface. An additional feature of ACT is its architecture, allowing for an easy integration of processes for control experiments.

On the role of hand synergies in the optimal choice of grasping forces

Recent work on the analysis of natural and robotic hands has introduced the notion of postural synergies as a principled organization of their complexity, based on the physical characteristics of the hand itself. Such characteristics include the mechanical arrangements of joints and fingers, their couplings, and the low-level control reflexes, that determine the specific way the concept of “hand” is embodied in a human being or a robot. While the focus of work done so far with postural synergies has been on motion planning for grasp acquisition, in this paper we set out to investigate the role that different embodiments have on the choice of grasping forces, and on the ultimate quality of the grasp. Numerical results are presented showing quantitatively the role played by different synergies (from the most fundamental to those of higher-order) in making a number of different grasps possible. The effect of number and types of engaged synergies on the distribution of optimal grasp forces is considered. Moreover, robustness of results is investigated with respect to variation in uncertain parameters such as contact and joint stiffness.

Cutaneous Force Feedback as a Sensory Subtraction Technique in Haptics

A novel sensory substitution technique is presented. Kinesthetic and cutaneous force feedback are substituted by cutaneous feedback (CF) only, provided by two wearable devices able to apply forces to the index finger and the thumb, while holding a handle during a teleoperation task. The force pattern, fed back to the user while using the cutaneous devices, is similar, in terms of intensity and area of application, to the cutaneous force pattern applied to the finger pad while interacting with a haptic device providing both cutaneous and kinesthetic force feedback. The pattern generated using the cutaneous devices can be thought as a subtraction between the complete haptic feedback (HF) and the kinesthetic part of it. For this reason, we refer to this approach as sensory subtraction instead of sensory substitution. A needle insertion scenario is considered to validate the approach. The haptic device is connected to a virtual environment simulating a needle insertion task. Experiments show that the perception of inserting a needle using the cutaneous-only force feedback is nearly indistinguishable from the one felt by the user while using both cutaneous and kinesthetic feedback. As most of the sensory substitution approaches, the proposed sensory subtraction technique also has the advantage of not suffering from stability issues of teleoperation systems due, for instance, to communication delays. Moreover, experiments show that the sensory subtraction technique outperforms sensory substitution with more conventional visual feedback (VF).

Vision-Based Localization for Leader–Follower Formation Control

This paper deals with vision-based localization for leader-follower formation control. Each unicycle robot is equipped with a panoramic camera that only provides the view angle to the other robots. The localization problem is studied using a new observability condition valid for general nonlinear systems and based on the extended output Jacobian. This allows us to identify those robot motions that preserve the system observability and those that render it nonobservable. The state of the leader-follower system is estimated via the extended Kalman filter, and an input-state feedback control law is designed to stabilize the formation. Simulations and real-data experiments confirm the theoretical results and show the effectiveness of the proposed formation control.

Localization of autonomous underwater vehicles by floating acoustic buoys: a set-membership approach

This paper addresses localization of autonomous underwater vehicles (AUVs) from acoustic time-of-flight measurements received by a field of surface floating buoys. It is assumed that measurements are corrupted by unknown-but-bounded errors, with known bounds. The localization problem is tackled in a set-membership framework and an algorithm is presented, which produces as output the set of admissible AUV positions in a three-dimensional (3-D) space. The algorithm is tailored for a shallow water situation (water depth less than 500 m), and accounts for realistic variations of the sound speed profile in sea water. The approach is validated by simulations in which uncertainty models have been obtained from field data at sea. Localization performance of the algorithm are shown comparable with those previously reported in the literature by other approaches who assume knowledge of the statistics of measurement uncertainties. Moreover, guaranteed uncertainty regions associated to nominal position estimates are provided. The proposed algorithms can be used as a viable alternative to more traditional approaches in realistic at-sea conditions.

Towards Wearability in Fingertip Haptics: A 3-DoF Wearable Device for Cutaneous Force Feedback

Wearability will significantly increase the use of haptics in everyday life, as has already happened for audio and video technologies. The literature on wearable haptics is mainly focused on vibrotactile stimulation, and only recently, wearable devices conveying richer stimuli, like force vectors, have been proposed. This paper introduces design guidelines for wearable haptics and presents a novel 3-DoF wearable haptic interface able to apply force vectors directly to the fingertip. It consists of two platforms: a static one, placed on the back of the finger, and a mobile one, responsible for applying forces at the finger pad. The structure of the device resembles that of parallel robots, where the fingertip is placed in between the static and the moving platforms. This work presents the design of the wearable display, along with the quasi-static modeling of the relationship between the applied forces and the platforms orientation and displacement. The device can exert up to 1.5 N, with a maximum platform inclination of 30 degree. To validate the device and verify its effectiveness, a curvature discrimination experiment was carried out: employing the wearable device together with a popular haptic interface improved the performance with respect of employing the haptic interface alone.

Vision-based Localization of Leader-Follower Formations

This paper focuses on the localization problem for a mobile camera network. In particular, we consider the case of leader-follower formations of nonholonomic mobile vehicles equipped with vision sensors which provide only the bearing to the other robots. We prove a sufficient condition for observability and show that recursive estimation enables a leader-follower formation if the leader is not trapped in an unobservable configuration. We employ an Extended Kalman Filter for the estimation of each follower position and orientation with respect to the leader and we adopt a feedback linearizing control strategy to achieve a desired formation. Simulation results in a noisy environment are provided.