Engineering Tools for Variable Stiffness Vibration Suppression and Isolation

With the advent of smart materials, the concept of semi-active control or dynamic control of stiffness and/or damping for vibration control of structures has become practical and has seen limited use. Semi-active control has advantages over active and passive control methods, since it provides almost as much capability as active control while requiring much less power. Its main disadvantage is its inherent nonlinearity, greatly complicating engineering design. The purpose of this research is to extend semi-active control vibration isolation tools and methods considering space launch and on-orbit systems

Aeronautical Engineering. A continuing bibliography with indexes, supplement 136, June 1981

This bibliography lists 424 reports, articles, and other documents introduced into the NASA scientific and technical information system in May 1981

Power transmission systems: from traditional to magnetic gearboxes

L'abstract è presente nell'allegato / the abstract is in the attachmen

Hybrid force and position control in robotic surface processing

PhD ThesisThis programme of research was supported by NEI Parsons Ltd. who sought a robotic means of polishing mechanical components. A study of the problems associated with robot controlled surface processing is presented. From this evolved an approach consistent with the formalisation of the demands of workpiece manipulation which included the adoption of the Hybrid robot control scheme capable of simultaneous force and position control. A unique 3 axis planar experimental manipulator was designed which utilized combined parallel and serial drives. A force sensing wrist was used to measure contact force. A variant of the Hybrid control 'scheme was successfully implemented on a twin computer control system. A number of manipulator control programs are presented. The force control aspect is shown both experimentally and analytically to present control problems and the research has concentrated on this aspect. A general analysis of the dynamics of force control is given which shows force response to be dependent on a number' of important parameters including force sensor, environment and manipulator dynamics. The need for a robust or adaptable force controller is discussed. A series of force controlled manipulator experiments is described and the results discussed in the context of general analyses and specific single degree of freedom simulations. Improvements to manipulator force control are suggested and some were implemented. These are discussed together with their immediate application to the improvement of robot controlled surface processing. This work also lays important foundations for long term related research. In particular the new techniques for actively controlled assembly and force control under 'fast' operation.Science and Engineering Research Council NEI Parsons Ltd

Energy harvesting from body motion using rotational micro-generation

Autonomous system applications are typically limited by the power supply operational lifetime when battery replacement is difficult or costly. A trade-off between battery size and battery life is usually calculated to determine the device capability and lifespan. As a result, energy harvesting research has gained importance as society searches for alternative energy sources for power generation. For instance, energy harvesting has been a proven alternative for powering solar-based calculators and self-winding wristwatches. Thus, the use of energy harvesting technology can make it possible to assist or replace batteries for portable, wearable, or surgically-implantable autonomous systems. Applications such as cardiac pacemakers or electrical stimulation applications can benefit from this approach since the number of surgeries for battery replacement can be reduced or eliminated. Research on energy scavenging from body motion has been investigated to evaluate the feasibility of powering wearable or implantable systems. Energy from walking has been previously extracted using generators placed on shoes, backpacks, and knee braces while producing power levels ranging from milliwatts to watts. The research presented in this paper examines the available power from walking and running at several body locations. The ankle, knee, hip, chest, wrist, elbow, upper arm, side of the head, and back of the head were the chosen target localizations. Joints were preferred since they experience the most drastic acceleration changes. For this, a motor-driven treadmill test was performed on 11 healthy individuals at several walking (1-4 mph) and running (2-5 mph) speeds. The treadmill test provided the acceleration magnitudes from the listed body locations. Power can be estimated from the treadmill evaluation since it is proportional to the acceleration and frequency of occurrence. Available power output from walking was determined to be greater than 1mW/cm³ for most body locations while being over 10mW/cm³ at the foot and ankle locations. Available power from running was found to be almost 10 times higher than that from walking. Most energy harvester topologies use linear generator approaches that are well suited to fixed-frequency vibrations with sub-millimeter amplitude oscillations. In contrast, body motion is characterized with a wide frequency spectrum and larger amplitudes. A generator prototype based on self-winding wristwatches is deemed to be appropriate for harvesting body motion since it is not limited to operate at fixed-frequencies or restricted displacements. Electromagnetic generation is typically favored because of its slightly higher power output per unit volume. Then, a nonharmonic oscillating rotational energy scavenger prototype is proposed to harness body motion. The electromagnetic generator follows the approach from small wind turbine designs that overcome the lack of a gearbox by using a larger number of coil and magnets arrangements. The device presented here is composed of a rotor with multiple-pole permanent magnets having an eccentric weight and a stator composed of stacked planar coils. The rotor oscillations induce a voltage on the planar coil due to the eccentric mass unbalance produced by body motion. A meso-scale prototype device was then built and evaluated for energy generation. The meso-scale casing and rotor were constructed on PMMA with the help of a CNC mill machine. Commercially available discrete magnets were encased in a 25mm rotor. Commercial copper-coated polyimide film was employed to manufacture the planar coils using MEMS fabrication processes. Jewel bearings were used to finalize the arrangement. The prototypes were also tested at the listed body locations. A meso-scale generator with a 2-layer coil was capable to extract up to 234 µW of power at the ankle while walking at 3mph with a 2cm³ prototype for a power density of 117 µW/cm³. This dissertation presents the analysis of available power from walking and running at different speeds and the development of an unobtrusive miniature energy harvesting generator for body motion. Power generation indicates the possibility of powering devices by extracting energy from body motion

The use of novel mechanical devices for enhancing the performance of railway vehicles

Following successful implementation of inerters for passive mechanical control in racing cars, this research studies potential innovative solutions for railway vehicle suspensions by bringing the inerter concept to the design of mechatronic systems. The inerter is a kinetic energy storage device which reacts to relative accelerations; together with springs and dampers, it can implement a range of mechanical networks distinguished by their frequency characteristics. This thesis investigates advantages of inerter-based novel devices to simplify the design of active solutions. Most of the research work is devoted to the enhancement of vertical ride quality; integrated active-plus-novel-passive solutions are proposed for the secondary suspensions. These are defined by different active control strategies and passive configurations including inerters. By optimisation of the suspension parameters, a synergy between passive and active configurations is demonstrated for a range of ride quality conditions. The evidence of cooperative work is found in the reduction of the required active forces and suspension travelling. This reveals a potential for reducing the actuator size. Benefits on power requirements and actuator dynamic compensation were also identified. One of the strategies features a nonlinear control law proposed here to compensate for 'sky-hook' damping effects on suspension deflection; this, together with inerter-based devices attains up to 50% in active force reduction for a setting providing 30% of ride quality enhancement. The study is developed from both, an analytical and an engineering perspective. Validation of the results with a more sophisticated model is performed. The lateral stability problem was briefly considered towards the end of the investigation. A potential use of inerter-based devices to replace the static yaw stiffness by dynamic characteristics was identified. This leads to a synergy with 'absolute stiffness', an active stability solution for controlling the wheelset 'hunting' problem, for reducing the creep forces developed during curve negotiation

Applied Measurement Systems

Measurement is a multidisciplinary experimental science. Measurement systems synergistically blend science, engineering and statistical methods to provide fundamental data for research, design and development, control of processes and operations, and facilitate safe and economic performance of systems. In recent years, measuring techniques have expanded rapidly and gained maturity, through extensive research activities and hardware advancements. With individual chapters authored by eminent professionals in their respective topics, Applied Measurement Systems attempts to provide a comprehensive presentation and in-depth guidance on some of the key applied and advanced topics in measurements for scientists, engineers and educators

Mathematical and Numerical Aspects of Dynamical System Analysis

From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”

Advanced Mobile Robotics: Volume 3

Mobile robotics is a challenging field with great potential. It covers disciplines including electrical engineering, mechanical engineering, computer science, cognitive science, and social science. It is essential to the design of automated robots, in combination with artificial intelligence, vision, and sensor technologies. Mobile robots are widely used for surveillance, guidance, transportation and entertainment tasks, as well as medical applications. This Special Issue intends to concentrate on recent developments concerning mobile robots and the research surrounding them to enhance studies on the fundamental problems observed in the robots. Various multidisciplinary approaches and integrative contributions including navigation, learning and adaptation, networked system, biologically inspired robots and cognitive methods are welcome contributions to this Special Issue, both from a research and an application perspective

MEMS Inertial Sensor to Measure the Gravity Gradient Torque in Orbit

Since the dawn of the Space Age, over six thousand satellites have been launched into Earth orbit. The function of determining the orientation of a satellite in orbit, so that it can point its antennas and instruments in the required direction is known as attitude determination. Depending on the nature of the mission, this important function is typically performed by means of optical instruments that determine the orientation of the satellite with respect to known bodies such as the Earth, the sun, and bright stars. Conventional Earth sensors use cameras and telescopes to locate the position of the Earth's horizon and hence to calculate the orientation of the satellite. In the event that a satellite starts to tumble, existing Earth sensors that use optical sensing are severely limited in their ability to reacquire the attitude due to the limited field of view of the instruments. Also, due to this limited field of view, multiple Earth sensor units need to be placed on all faces of the satellite to ensure 4π steradian coverage. Because of the optical sensing principle of existing Earth sensors, constraints are imposed on the positioning of solar panels and antennas so that they do not block the field of view of optical sensors. This thesis describes a novel inertial sensor that uses the Earth's gravity gradient as a reference for attitude determination on-board a satellite in low Earth orbit. Using the gravity gradient for attitude determination makes it possible to realise a single, compact Earth sensor instrument which can be positioned flexibly within the satellite. Due to its 4π steradian field of view, such an instrument can offer added capability as a backup sensor, or act as the main Earth sensor. By using Micro-Electro-Mechanical System (MEMS) technology for the inertial sensor, a target mass of 1 kg and target volume of 1 dm3 can be realised for the entire gravity gradient Earth sensor system. The gravitational force decreases as the square of the distance from the center of the Earth. An elongated object in orbit around the Earth will have slightly different values of gravity acting over the different points in its volume. This gives rise to a small torque, the Gravity Gradient Torque (GGT), on the object. A compact micromachined inertial sensor was designed with an elongated proof mass and compliant spring to measure the GGT, so that the orientation of the proof mass with respect to the normal from the Earth's surface can be determined. Such a sensor on-board a satellite can act as an Earth sensor, and provide information about the satellite attitude with respect to the normal to the Earth's surface. An inertial sensor to measure GGT, which with readout electronics fits within a 1 dm3 volume, has to measure a torque of magnitude 10-15 N.m. Currently, no inertial sensor is capable of such a fine measurement. In addition to the required performance in microgravity, the inertial sensor must be robust enough to be tested on Earth with no special handling, and must survive the vibration and shock of a launch, to be used in space. The readout scheme to measure the displacement due to GGT must also be simple and robust. The designs of two generations of a novel inertial sensor to measure the GGT are presented in the thesis. To be able to measure the GGT with the required accuracy a sensor is designed that has a proof mass 5 cm long, suspended by springs which have widths less than ten microns. The sensor resonant frequency of the inertial sensor is on the order of 1 Hz. A new fabrication process is developed for the sensor, which incorporates hard stops to limit the motion of the proof mass along all the axes, thus making it robust enough for testing without any special precautions. The sensor survives low magnitude vibration tests. A digital electronic readout based on capacitive sensing of the displacement due to GGT, is developed based on commercially available ICs, and allows easy interfacing of the inertial sensor output to a PC or microcontroller. To test the sensor on Earth, a dedicated test setup is developed to replicate the nm-scale motion of the proof mass expected in orbit. The electronic readout is capable of measuring the sub-nm displacements due to GGT. The 2nd generation sensor design with capacitive displacement sensing is the first demonstration of an inertial sensor capable of measuring the GGT in low Earth orbit, and an important step towards realization of a 1 kg, 1 dm3 Earth sensor that uses the gravity gradient of the Earth for attitude determination