Perla Maiolino

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.

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.

On the development of a tactile sensor for fabric manipulation and classification for industrial applications

In this paper a novel multi-modal tactile sensor is presented, featuring a matrix of capacitive pressure sensors, a microphone for acoustic measurements and proximity and ambient light sensor. The sensor is fully embedded and can be easily integrated at mechanical and electrical levels with industrial grippers. Tactile sensing design has been put on the same level of additional requirements, usually overlooked in tactile sensor research, such as the mechanical interface, cable harness and robustness against continuous and repetitive operations, just to name but a few. The performances of the different sensing modalities have been assessed in a test rig for tactile sensors. Experiments have been performed in order to show the capabilities of the sensor for implementing tactile based industrial gripper control and tactile based fabric classification.

A toolbox for supporting the design of large-scale capacitive tactile systems

In the process of covering a generic robot with artificial skin, it is necessary to use design tools allowing designers to specify and validate tactile requirements for the scenario at hand. In particular, given a set of well-defined functional requirements (e.g., minimum spatial sensitivity or minimum force to detect), there are two needs to be fulfilled: (i) to check the artificial skin capability to meet these requirements and criteria; (ii) to drive the customization process to find a reasoned trade-off between different (and possibly conflicting) design parameters, such as dielectric thickness or taxel diameter. The main contribution of this article is the description of a robot skin design toolbox based on Finite Element Analysis, able to provide the designer with insights in the behaviour of large scale tactile systems.

Large Scale Capacitive Skin for Robots

In order to allow robots to share our space and chores, tactile sensing is crucial. Indeed it allows safe interaction of robots with people and objects, because it provides the most direct feedback to control contact forces both in voluntary and involuntary interactions. Furthermore, it allows improving performance in tasks that require controlled physical interactions in uncontrolled environments where the location and the characteristics of contact cannot be predicted or modeled in advance and more complex forms of interactions are required. Therefore, a tactile sensor system capable of measuring contact forces over large areas is needed. Tactile sensing in robotics has been widely investigated in the past 30 years and many examples of engineering solutions to tactile sensing have been presented in the literature [1]. Research in this field has focused largely on transduction principles and transduction technologies [2]; however, various technical issues have limited the transition from a single tactile element (or a small matrix prototype) to a large scale integrated solution: it is easy to understand that a sensitive robot skin cannot be achieved by simply aggregating a large number of single sensors. In fact, the concept of robot skin entails a number of system level problems that simply do not appear when focusing on small tactile sensors or small area arrays:

A sensorized glove for experiments in cloth manipulation

In this paper, the description of a sensorized glove that has been developed to perform experiments in robot-based manipulation of clothes and objects is reported. The glove embeds a capacitive tactile sensing technology that has been designed in the past few years. The glove is used to provide an estimate of the expected tactile feedback related to involved forces and contact areas during common manipulation tasks. This information will be used in order to design a robot gripper for cloth manipulation.