Trade-off analysis and design of a Hydraulic Energy Scavenger

In the last years there has been a growing interest in intelligent, autonomous devices for household applications. In the near future this technology will be part of our society; sensing and actuating will be integrated in the environment of our houses by means of energy scavengers and wireless microsystems. These systems will be capable of monitoring the environment, communicating with people and among each other, actuating and supplying themselves independently. This concept is now possible thanks to the low power consumption of electronic devices and accurate design of energy scavengers to harvest energy from the surrounding environment. In principle, an autonomous device comprises three main subsystems: an energy scavenger, an energy storage unit and an operational stage. The energy scavenger is capable of harvesting very small amounts of energy from the surroundings and converting it into electrical energy. This energy can be stored in a small storage unit like a small battery or capacitor, thus being available as a power supply. The operational stage can perform a variety of tasks depending on the application. Inside its application range, this kind of system presents several advantages with respect to regular devices using external energy supplies. They can be simpler to apply as no external connections are needed; they are environmentally friendly and might be economically advantageous in the long term. Furthermore, their autonomous nature permits the application in locations where the local energy grid is not present and allows them to be ‘hidden' in the environment, being independent from interaction with humans. In the present paper an energy-harvesting system used to supply a hydraulic control valve of a heating system for a typical residential application is studied. The system converts the kinetic energy from the water flow inside the pipes of the heating system to power the energy scavenger. The harvesting unit is composed of a hydraulic turbine that converts the kinetic energy of the water flow into rotational motion to drive a small electric generator. The design phases comprise a trade-off analysis to define the most suitable hydraulic turbine and electric generator for the energy scavenger, and an optimization of the components to satisfy the systems specification

Sensing and Rheological Capabilities of MR Elastomers

Magnetorheological elastomers (MREs) are smart materials where polarized particles are suspended in a non-magnetic solid or gel-like matrix. Two kinds of MREs, namely anisotropic and isotropic, are fabricated either under a magnetic field or without a field [1,2]. In anisotropic MREs, polarised particles are arranged in chains within a polymer media such as silicon rubber or natural rubber. The shear modulus of MRE can be controlled by the external magnetic field, which has led to many applications, such as tuned vibration absorbers, dampers and sensor

Feedforward and Modal Control for a Multi Degree of Freedom High Precision Machine

High precision industrial machines suffer the presence of vibrations due to several noise sources: ground vibration, acoustic noise, direct force disturbances. In the last years the need of higher processing quality and throughput result in a continuing demand for higher accuracy. Therefore vibration isolation systems became mandatory to satisfy these requests. In general, machine supports are designed for high stiffness to obtain a robust machine alignment with respect to its surroundings. However, in the presence of significant ground vibration levels the support stiffness is commonly sacrificed to reduce their transmission to the payload stage. Efforts to go towards these issues are recorded in several applications and the solutions are different for any particular situation, depending on the nature of the vibration sources, the amount of the disturbances and the machine environment. This chapter focuses on the evaluation of a vibration isolation device on the working cell of a micro-mechanical laser center, using active electromagnetic actuators. The machine is composed by two main parts: a frame support and a payload stage where the laser cutting is performed. The machine potential in terms of accuracy and precision is reduced by the presence of two main vibration sources: the ground and the stage itself. The active device should meet two main goals: the payload vibrations damping and the reduction of the transmissibility of ground disturbances. In this work the phases followed to design, realize and validate the device are illustrated with a particular attention to the mechatronics aspects of the project and to the control strategies. The chapter starts on the description of the common solutions and of the techniques described in literature. The requirements analysis and a trade-off phase on the available opportunities for vibration isolation are described. An analysis of the plant components is reported in the second section along with an exhaustive explanation of a) actuation subsystem consisting in four voice-coils, two per axis; b) sensing subsystem aimed to measure the absolute velocities of the frame support and of the stage are measured by means of eight geophone sensors. The considerations leading to the choice of this sensing system are reported along with the signal conditioning block. The active control is performed with a digital platform based on DSP and FPGA. The core of the chapter is the description of the modeling approach and of the control strategies design. The bond-graph approach is used to represent the system behavior, in particular the interactions between the mechanical and electrical subsystems are illustrated. The realized model includes the plant, the sensing, the control and the actuation blocks. The plant is considered as a classical two mass-spring-damper system resulting on a multi-input multi-output system (MIMO), considering disturbances from the stage and the ground and the actuators action between the two masses. Time and frequency domain computations are carried out from the model to evaluate vibration levels and displacements and to identify which parameters need to be carefully designed to satisfy the requirements. The control strategy is focused on the attenuation of the effects of microvibrations on the stage caused by different sources. The technique consists in a combination of two actions, the goal being the minimization of the ground vibrations transmission and the payload vibrations damping: • A single-axis decentralized action consisting in a modal controller used to compensate the high-pass band dynamic of the geophone sensors and to control the vibrations. • A feedforward action working on the disturbances coming from the payload and from the ground. This control is not generated in on-line, but computed in advance from the data of machine responses to the direct disturbances coming from the floor and the stage and resulting in vibrations on the payload and on the frame. The first action itself is aimed to perform active isolation and vibration that nevertheless could be not sufficient for severe specifications applications. The feedforward action is hence used to face this shortcoming by suppressing direct disturbance. The controller design phases along with its performance evaluation are described. The chapter concludes on the illustration of the results obtained with the proposed modeling and control strategy

MR Fluid Damper and Its Application to Force Sensorless Damping Control System

Vibration suppression is considered as a keyresearch field in civil engineering to ensure the safety and comfort of their occupants and users of mechanical structures. To reduce the system vibration, an effective vibration control with isolation is necessary. Vibration control techniques have classically been categorized into two areas, passive and active controls. For a long time, efforts were made to make the suspension system work optimally by optimizing its parameters, but due to the intrinsic limitations of a passive suspension system, improvements were effective only in a certain frequency range. Compared with passive suspensions, active suspensions can improve the performance of the suspension system over a wide range of frequencies. Semi-active suspensions were proposed in the early 1970s [1], and can be nearly as effective as active suspensions. When the control system fails, the semi-active suspension can still work under passive conditions. Compared with active and passive suspension systems, the semi-active suspension system combines the advantages of both active and passive suspensions because it provides better performance when compared with passive suspensions and is economical, safe and does not require either higher-power actuators or a large power supply as active suspensions do [2]

SMA-Based Muscle-Like Actuation in Biologically Inspired Robots: A State of the Art Review

New actuation technology in functional or "smart" materials has opened new horizons in robotics actuation systems. Materials such as piezo-electric fiber composites, electro-active polymers and shape memory alloys (SMA) are being investigated as promising alternatives to standard servomotor technology [52]. This paper focuses on the use of SMAs for building muscle-like actuators. SMAs are extremely cheap, easily available commercially and have the advantage of working at low voltages. The use of SMA provides a very interesting alternative to the mechanisms used by conventional actuators. SMAs allow to drastically reduce the size, weight and complexity of robotic systems. In fact, their large force-weight ratio, large life cycles, negligible volume, sensing capability and noise-free operation make possible the use of this technology for building a new class of actuation devices. Nonetheless, high power consumption and low bandwidth limit this technology for certain kind of applications. This presents a challenge that must be addressed from both materials and control perspectives in order to overcome these drawbacks. Here, the latter is tackled. It has been demonstrated that suitable control strategies and proper mechanical arrangements can dramatically improve on SMA performance, mostly in terms of actuation speed and limit cycles

Smart actuation for helicopter rotorblades

Successful rotorcrafts were only achieved when the differences between hovering flight conditions and a stable forward flight were understood. During hovering, the air speed on all helicopter blades is linearly distributed along each blade and is the same for each. However, during forward flight, the forward motion of the helicopter in the air creates an unbalance. The airspeed is increased for the blade passing in the advancing side of the helicopter, while it is reduced in the retreating side. Moreover, when each blade enters the retreating side of the helicopter, a reverse flow occurs around the profile where the blade speed is lower than the forward speed of the helicopter. The balance of a rotorcraft is solved by a cyclic pitch control, but trade-offs are made on the blade design to cope with the great variety of aerodynamic conditions. A smart blade that would adapt its characteristics to this large set of conditions would improve rotorcrafts energy efficiency while providing vibration and noise control.\ud Smart rotor blades systems are studied to adapt the aerodynamic characteristics of the blade during its revolution and to improve the overall performances. An increase in the lift over drag ratio on the retreating side has been studied to design a blade with better aerodynamic efficiency and better stall performances in the low-speed region. The maximum speed of a rotorcraft is limited by the angle of attack that the profile can sustain on the retreating side before stall. Therefore, increasing the maximum angle of attack that a profile geometry can sustain increases the rotorcraft flight envelope. Flow asymmetry and aerodynamic interaction between successive blades are also investigated to actively reduce vibrations and limit noise.\ud These improvements can be achieved by deploying flaps, by using flow control devices or by morphing the full shape of the profile at a specific places during the blade revolution. Each of the listed methods has advantages and disadvantages as well as various degrees of feasibility and integrability inside helicopter blades. They all modify the aerodynamic characteristics of the profile. Their leverage on the various aerodynamic effects depends on the control strategy chosen for actuation. Harmonic actuation is therefore studied for active noise and vibration control whereas stepped deployment is foreseen to modify the stall behaviour of the retreating side of the helicopter.\ud Helicopter blades are subjected to various force constraints such as the loads from the complex airflow and the centrifugal forces. Furthermore, any active system embedded inside a rotor blade needs to comply with the environmental constraints to which a helicopter will be subjected  during its life-span. Other concerns, like the power consumption and the data transfer for blade control, play an important role as well. Finally, such a system must have a life-time exceeding the life-time of a rotor blade and meet the same criteria in toughness, reliability and ease of maintenance.\ud Smart system is an interplay of aerodynamics, rotor-mechanics, material science and control, thus a multidisciplinary approach is essential. A large part of the work consists in building processes to integrate these domains for investigating, designing and testing smart components.\ud Piezoelectric actuators are a promising technology to bring adaptability to rotor blades. They can be used directly on the structure to actively modify its geometry, stiffness and aerodynamic behaviour or be integrated to mechanisms for the deployment of flaps. Their large specific work, toughness, reliability and small form factor make them suitable components for integration within a rotor blade. The main disadvantage of piezoelectric actuators is the small displacement and strain available. Amplification mechanisms must be optimised to produce sufficient displacement in morphing applications.\ud Smart actuation systems placed inside rotor blades have the potential to improve the efficiency and the performances of tomorrow's helicopters. Piezoelectric materials can address many of the challenges of integrating smart components inside helicopter blades. The key aspect remains the collaboration between various domains, skills and expertise to successfully implement these new technologies