Giorgio Cannata

Methods and Technologies for the Implementation of Large-Scale Robot Tactile Sensors

Even though the sense of touch is crucial for humans, most humanoid robots lack tactile sensing. While a large number of sensing technologies exist, it is not trivial to incorporate them into a robot. We have developed a compliant “skin” for humanoids that integrates a distributed pressure sensor based on capacitive technology. The skin is modular and can be deployed on nonflat surfaces. Each module scans locally a limited number of tactile-sensing elements and sends the data through a serial bus. This is a critical advantage as it reduces the number of wires. The resulting system is compact and has been successfully integrated into three different humanoid robots. We have performed tests that show that the sensor has favorable characteristics and implemented algorithms to compensate the hysteresis and drift of the sensor. Experiments with the humanoid robot iCub prove that the sensors can be used to grasp unmodeled, fragile objects.

An embedded artificial skin for humanoid robots

A novel artificial skin for covering the whole body of a humanoid robot is presented. It provides pressure measurements and shape information about the contact surfaces between the robot and the environment. The system is based on a mesh of sensors interconnected in order to form a networked structure. Each sensor has 12 capacitive taxels, has a triangular shape and is supported by a flexible substrate in order to conform to smooth curved surfaces. Three communications ports placed along the sides of each sensor sides allow communications with adjacent sensors. The tactile measurements are sent to embed microcontroller boards using serial bus communication links. The system can adaptively reduce its spatial resolution, improving the response time. This feature is very useful for detecting the first contact very rapidly, at a lower spatial resolution, and then increase the spatial resolution in the region of contact for accurate reconstruction of the contact pressure distribution.

A Flexible and Robust Large Scale Capacitive Tactile System for Robots

Capacitive technology allows building sensors that are small, compact and have high sensitivity. For this reason it has been widely adopted in robotics. In a previous work we presented a compliant skin system based on capacitive technology consisting of triangular modules interconnected to form a system of sensors that can be deployed on non-flat surfaces. This solution has been successfully adopted to cover various humanoid robots. The main limitation of this and all the approaches based on capacitive technology is that they require to embed a deformable dielectric layer (usually made using an elastomer) covered by a conductive layer. This complicates the production process considerably, introduces hysteresis and limits the durability of the sensors due to ageing and mechanical stress. In this paper we describe a novel solution in which the dielectric is made using a thin layer of 3D fabric which is glued to conductive and protective layers using techniques adopted in the clothing industry. As such, the sensor is easier to produce and has better mechanical properties. Furthermore, the sensor proposed in this paper embeds transducers for thermal compensation of the pressure measurements. We report experimental analysis that demonstrates that the sensor has good properties in terms of sensitivity and resolution. Remarkably we show that the sensor has very low hysteresis and effectively allows compensating drifts due to temperature variations.

The design and development of the DIST-Hand dextrous gripper

Presents the first prototype of the DIST-Hand dextrous gripper. DIST-Hand is a 4-fingered tendon driven device with 16 degrees of freedom, designed for experiments in the area of grasping control, and tele-manipulation. The current version of the gripper is lightweight and can be easily installed on the various existing robots. The paper outlines the kinematic and structural characteristics of the hand. Furthermore, some general methodological issues addressed during the design phase are discussed.

An embedded tactile and force sensor for robotic manipulation and grasping

A new fully embedded tactile/force sensor system is presented. The sensor has been designed to be installed on a dextrous robot gripper (MAC-HAND). The tactile sensor consists of a matrix of 64 electrodes, etched on a flexible PCB covered by a conductive rubber layer. The force sensor is an off-the-shelf integrated three components micro-joystick. The analog and digital electronics is fully embedded with the sensor that is a self-standing module mounted on each finger phalange

Stability and robustness analysis of a two layered hierarchical architecture for the closed loop control of robots in the operational space

A two layered hierarchical architecture is considered as the fundamental scheme for the closed loop control of robots in operational space. By considering different kinds of information transfer from the outer to the inner controllers, it is shown that the architecture can take into account a wide class of control schemes, then the analysis of their stability and robustness properties can be performed in a unified framework. Then on this basis some general results concerning such properties are given.

Skin spatial calibration using force/torque measurements

This paper deals with the problem of estimating the position of tactile elements (i.e. taxels) that are mounted on a robot body part. This problem arises with the adoption of tactile systems with a large number of sensors, and it is particularly critical in those cases in which the system is made of flexible material that is deployed on a curved surface. In this scenario the location of each taxel is partially unknown and difficult to determine manually. Placing the device is in fact an inaccurate procedure that is affected by displacements in both position and orientation. Our approach is based on the idea that it is possible to automatically infer the position of the taxels by measuring the interaction forces exchanged between the sensorized part and the environment. The location of the contact is estimated through force/torque (F/T) measures gathered by a sensor mounted on the kinematic chain of the robot. Our method requires few hypotheses and can be effectively implemented on a real platform, as demonstrated by the experiments with the iCub humanoid robot.

A Minimalist Algorithm for Multirobot Continuous Coverage

This paper describes an algorithm, which has been specifically designed to solve the problem of multirobot-controlled frequency coverage (MRCFC), in which a team of robots are requested to repeatedly visit a set of predefined locations of the environment according to a specified frequency distribution. The algorithm has low requirements in terms of computational power, does not require inter-robot communication, and can even be implemented on memoryless robots. Moreover, it has proven to be statistically complete as well as easily implementable on real, marketable robot swarms for real-world applications.

Models for the Design of Bioinspired Robot Eyes

Active vision has the goal of improving visual perception; therefore, the investigation of ocular motion strategies must play an important role in the design of humanoid robot eyes. Listings law is a basic principle, which characterizes various ocular movements in humans, including saccades and smooth pursuit, and its neural or mechanical origin has been debated for a long time. Recent anatomical advances suggest that motions compatible with Listings law could be mainly caused by the mechanical structure of the eye plant. In this paper, we present a bioinspired model of the eye plant, and we formally prove that according to the model, the implementation of Listings law can be actually explained on the base of the geometry of the eye and of its actuation system. The proposed model is characterized by a limited number of geometric parameters, which can be easily used to set the guidelines for the design of humanoid, and possibly tendon-driven, robot eyes. Simulative and experimental tests performed on a robot prototype are eventually presented to perform a quantitative evaluation of the performance of the model, also in comparison with physiological data measured in humans and primates and reported in the literature.

Towards automated self-calibration of robot skin

This paper deals with the problem of calibrating a large number of tactile elements (i.e., taxels) organized in a skin sensor system after fixing them to a robot body part. This problem has not received much attention in literature because of the lack of large-scale skin sensor systems. The proposed approach is based on a controlled compliance motion with respect to external objects whose pose is known, which allows a robot to determine the location of its own taxels. The major contribution of this work is the formulation of the skin calibration problem as a maximum-likelihood mapping problem in a 6D space, where both the position and the orientation of each taxel are recovered. An effective calibration process is envisaged that, given a compliance control law that assures prolonged contact maintainance between a given body part and an external object, returns a maximum-likelihood estimate of detected taxel poses. Simulations validate the approach.