Salvatore Pirozzi

Effects of hysteresis compensation in feedback control systems

Analyzes the performances of closed-loop control systems when real hysteretic actuators (e.g., Terfenol-D-based devices) are of concern. Shown is a simple but effective strategy, based on the simple idea of pseudo-compensator, for transducers hysteresis compensation. Such a strategy improves the control systems behavior, not only in terms of tracking error reduction but also in decreasing the control signal so as to avoid saturation and harmful stress to the actuator on the one hand and reducing hysteretic energy losses on the other. Experiments are performed on a magnetostrictive actuator used for a micropositioning task.

The DEXMART hand: Mechatronic design and experimental evaluation of synergy-based control for human-like grasping

This paper summarizes recent activities carried out for the development of an innovative anthropomorphic robotic hand called the DEXMART Hand. The main goal of this research is to face the problems that affect current robotic hands by introducing suitable design solutions aimed at achieving simplification and cost reduction while possibly enhancing robustness and performance. While certain aspects of the DEXMART Hand development have been presented in previous papers, this paper is the first to give a comprehensive description of the final hand version and its use to replicate human-like grasping. In this paper, particular emphasis is placed on the kinematics of the fingers and of the thumb, the wrist architecture, the dimensioning of the actuation system, and the final implementation of the position, force and tactile sensors. The paper focuses also on how these solutions have been integrated into the mechanical structure of this innovative robotic hand to enable precise force and displacement control of the whole system. Another important aspect is the lack of suitable control tools that severely limits the development of robotic hand applications. To address this issue, a new method for the observation of human hand behavior during interaction with common day-to-day objects by means of a 3D computer vision system is presented in this work together with a strategy for mapping human hand postures to the robotic hand. A simple control strategy based on postural synergies has been used to reduce the complexity of the grasp planning problem. As a preliminary evaluation of the DEXMART Hand’s capabilities, this approach has been adopted in this paper to simplify and speed up the transfer of human actions to the robotic hand, showing its effectiveness in reproducing human-like grasping.

Integrated Mechatronic Design for a New Generation of Robotic Hands

Abstract In this paper, an overall description of the design of a robotic hand is discussed, with particular attention to the required sensory subsystem, its integration within the mechanical structure of the hand and the required control architecture. Different solutions for the joint configuration and the structure of the tendon network adopted for the transmission system are present together with three types of sensors applied on the finger and on the actuators. The integrated design of the hand finger and the sensors is reported and the motivations leading to this particular implementation are thoroughly addressed, taking into account both the mechanical constraints and the control requirements.

Innovative Technologies for the Next Generation of Robotic Hands

With the aim of reproducing the grasping and manipulation capabilities of humans, many robotic devices have been developed all over the world in more than 50 years of research, starting from very simple grippers, normally used in industrial activities, to very complex anthropomorphic robotic hands. Unfortunately, the reduced functionality and/or reliability of the devices developed so far prevent, together with the cost, their usability in unstructured environments, and in particular in human everyday activities. The adoption of design solutions inherited from conventional mechanics and the lack of purposely developed sensors and actuators are among the main causes of the partial fail in achieving the final goal of reproducing human manipulation capabilities. Our research activity aims at developing innovative solutions concerning the mechanical design, the sensory equipment and the actuation system for the implementation of anthropomorphic robotic hands with improved reliability, functionality and reduced complexity and cost, considering also aspects related to safety during human–robot interaction, paving the way toward the next generation of robotic hands.

Feedback control systems for micropositioning tasks with hysteresis compensation

This paper proposes the analysis of a control loop system employing a Terfenol-D actuator driving a real mechanical load. The aim of the paper is to analyze the performances of such a system when a strategy of hysteresis compensation is employed. Such strategy has demonstrated its effectiveness in simpler feedback systems (with no mechanical load) by improving the tracking error, decreasing the control signal so as to avoid saturation and harmful stress to the actuator. As a consequence, the algorithm allows also to reduce energy losses in the actuator.

A Conformable Force/Tactile Skin for Physical Human–Robot Interaction

In this letter, a new sensorized flexible skin has been used to enhance safety and intuitiveness of physical human-robot interaction (HRI) in applications where both intentional and unintentional contacts may occur. The new technological contribution with respect to other skin sensors consists of the capability of measuring both the position of the contact point and the three components of the applied force with high repeatability and accuracy. To show how this innovative technology enables the exploitation of control laws for intuitive HRI, two standard control strategies have been implemented to perform both manual guidance with multiple contact points and safe reaction in case of unintentional collision detection, at the same time. In both cases, an admittance control scheme with a second order kinematic control is adopted. A multipriority redundancy resolution strategy is implemented in the case of manual guidance. The experimental verification of the sensor capabilities is made using a patch of the skin installed on a link of a KUKA LWR4 robot.

Miniaturized optical-based force sensors for tendon-driven robots

In this paper, an innovative sensor based on optoelectronic components and compliant frames for the measurement of the tendon tension is presented. With respect to conventional solutions for force sensing, like strain-gauge or Bragg-grating based force sensors, this sensor presents several advantages, mainly in terms of compactness, simplicity of the implementation and conditioning electronics. The proposed sensor exploits the properties of optoelectronic components with a narrow angle of view to measure the very small deformation of a compliant frame caused by the tendon tension. The sensor can be placed at the tendon ends as such as in any position along the tendon. The paper reports the basic working principle and a simplified procedure for the design of the sensor frame together with the results of an experimental testbench where a couple of the proposed sensors are use for the feedback control of a tendon-driven robotic joint.

Gray-Box Identification of Continuous-Time Models of Flexible Structures

A noniterative algorithm is proposed to identify the continuous-time state space model of lightly damped flexible structures. This paper is motivated by the need for accurate dynamic models to be used in design of active vibration control systems for, e.g., large space structures and aeronautical structures. A gray-box approach is adopted to preserve the physical meaning of the model parameters and to naturally impose physical constraints to the model, e.g., passivity and reciprocity. The procedure consists of two stages both in the frequency domain; first, a subspace method is applied to estimate the dynamic matrix, then, the input and output matrices are identified by solving a weighted least square problem, both in the colocated and noncolocated case. A numerical case study is carried out to illustrate the features of the algorithm and experimental results are presented by reporting and validating the identified model of a stiffened aeronautical panel in a broad frequency range. The experimental case study serves also for carrying out a comparison between the proposed identification procedure and some of the already existing algorithms.

Modal analysis of a cantilever beam by use of Brillouin based distributed dynamic strain measurements

In this work we report an experimental modal analysis of a cantilever beam, carried out by use of a Brillouin optical time-domain analysis (BOTDA) setup operated at a fixed pump–probe frequency shift. The employed technique permitted us to carry out distributed strain measurements along the vibrating beam at a maximum acquisition rate of 108 Hz. The mode shapes of the first three bending modes (1.7, 10.8, 21.6 Hz) were measured for the structure under test. The good agreement between the experimental and numerical results based on a finite-element method (FEM) analysis demonstrates that Brillouin based distributed sensors are well suited to perform the modal analysis of a vibrating structure. This type of analysis may be useful for applications in structural health monitoring where changes in mode shapes are used as indicators of the damage to the structure.

Limit cycles in control systems employing smart actuators with hysteresis

This paper presents theoretical and experimental results concerning a feedback control system employing a Terfenol-D-based smart actuator. Such magnetostrictive devices exhibit significant hysteresis, which, under some conditions, can generate self-sustained periodic oscillations in the control loop. The paper proposes a general procedure to find these conditions and to compute this periodic solution by exploiting some classical results about describing function analysis and the well-known Preisach operator theory. The theoretical findings are supported by a rigorous mathematical analysis resorting to fixed-point theorems.