Active Damping of Vibrations of a Cantilever Beam by Axial Force Control

In several fields, e.g. aerospace applications, robotics or the bladings of turbomachinery, the active damping of vibrations of slender beams which are subject to free bending vibrations becomes more and more important. In this contribution a slender cantilever beam loaded with a controlled force at its tip, which always points to the clamping point of the beam, is treated. The equations of motion are obtained using the Bernoulli-Euler beam theory and d’Alemberts principle. To introduce artificial damping to the lateral vibrations of the beam, the force at the tip of the beam has to be controlled in a proper way. Two different methods are compared. One concept is the closed-loop control of the force. In this case a nonlinear feedback control law is used, based on axial velocity feedback of the tip of the beam and a state-dependent amplification. By contrast, the concept of open-loop parametric control works without any feedback of the actual vibrations of the mechanical structure. This approach applies the force as harmonic function of time with constant amplitude and frequency. Numerical results are carried out to compare and to demonstrate the effectiveness of both methods.

Geometric Optimization of a Piezoelectric Power Harvesting Plate for Increased Bandwidth

The continual advances in wireless technology and low power electronics have allowed the deployment of small remote sensor networks. However, current portable and wireless devices must be designed to include electrochemical batteries as the power source. The use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement. Furthermore, the growth of battery technology has remained relatively stagnant over the past decade while the performance of computing systems has grown steadily, which leads to increased power usage from the electronics. In the case of wireless sensors that are to be placed in remote locations, the sensor must be easily accessible or of disposable nature to allow the device to function over extended periods of time. For this reason the primary question becomes how to provide power to each node. This issue has spawned the rapid growth of the energy harvesting field. Energy scavenging devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The concept of power harvesting works towards developing self-powered devices that do not require replaceable power supplies. However, when designing a vibration based energy harvesting system the maximum energy generation occurs when the resonant frequency of the system is tuned to the input. This poses certain issues for their practical application because structural systems rarely vibrate at a signal frequency. Therefore, this effort will investigate the optimal geometric design of two dimensional energy harvesting systems for maximized bandwidth. Topology and shape optimization will be used to identify the optimal geometry and experiments will be performed to characterize the energy harvesting improvement when subjected to random vibrations.

System Identification of the High Performance Drilling Process for Network-Based Control

A simple, fast, network-based experimental procedure for identifying the dynamics of the high-performance drilling (HPD) process is proposed and successfully applied. This identification technique utilizes a single-input (feed rate), single-output (resultant force) system with a dual step input function. The model contains the delays of both the network architecture (a PROFIBUS type network) and the dead time related with the plant dynamic itself. Classical identification techniques are used to obtain first order, second order, and third order models on the basis of the recorded input/output data. The developed models relate the dynamic behavior of resultant force versus commanded feed rate in HPD. Model validation is performed through error-based performance indices and correlation analyses. Experimental verification is performed using two different work piece materials. The models match perfectly with real-time force behavior in drilling operations and are easily integrated with many control strategies. Furthermore, these results demonstrate that the HPD process is somewhat non-linear with a remarkable difference in gain due to work piece material; however, the dynamic behavior does not change significantly.

A Sensitivity-Enhancing Control Approach for Structural Model Updating

Model updating plays an important role in structural design and dynamic analysis. The process of model updating aims to produce an improved mathematical model by correlating the initial model with the experimentally measured data. There are a variety of techniques available for model updating using dynamic and static measurements of the structure’s behavior. This paper focuses on the model updating methods using the measured natural frequencies of the structure. The practice of model updating using only the natural frequencies encounters two well-known limitations: deficiency of frequency measurement data, and low sensitivity of measured natural frequencies with respect to the physical parameters that need to be updated. To overcome these limitations, a novel model updating method is presented in this paper. First, closed-loop control is applied to the structure to enhance the sensitivity of natural frequencies to the updating parameters. Second, by including the natural frequencies based on a series of sensitivity-enhanced closed-loop systems, we can significantly enrich the frequency measurement data available for model updating. Using the natural frequencies of these sensitivity-enhanced closed-loop systems, an iterative process is utilized to update the physical parameters in the initial model. To demonstrate and verify the proposed method, case studies are carried out using a cantilevered beam structure. The natural frequencies of a series of sensitivity-enhanced closed-loop systems are utilized to update the mass and stiffness parameters in the initial FE model. Results show that the modeling errors in the mass and stiffness parameters can be accurately identified by using the proposed model updating method.

Active Roll Control of Heavy Single Unit Vehicles Employing MEMS Angular Rate Sensors

The present paper is concerned with the use of active roll control to improve the roll stability of heavy road-vehicles and the application of Micro-electro-mechanical System (MEMS) angular rate sensors in the feedback monitoring. For this purpose, mathematical models that represent the roll/yaw dynamics for a torsionally rigid Single Unit Vehicle (SUV) is presented. The state-space models that represent the vehicle dynamics are also developed for the purpose of performing numerical simulations. A linear Quadratic Gaussian (LQG) based controller, using Kalman estimator to estimate certain states, is employed to design a full-state active roll control system. A mathematical model that represents the dynamic behavior of a low-cost MEMS gyroscope is derived for the purpose of investigating the suitability of applying this class of angular rate sensor in the roll control of heavy vehicles. Some reliability issues related to MEMS sensors, such as noise and drift, are introduced and included in vehicle dynamic models.

Range of Motion of Upper Limb Joint Angles During Two Tasks for Transradial Prosthetic Design

During wartime, the numbers of amputees will likely increase adding to the need for progress in upper limb prosthetic design. Improvement of prostheses often requires knowledge of how the body adapts. Added weight and fatigue are complaints of upper limb prostheses users. Current improvements in the design of a transradial prosthesis include advanced technology in control systems and electronics that improve its functions. However, these improvements often require excess mass distally along the prosthesis. A transradial prosthesis without a dynamic wrist component may cause awkward compensatory motion in the shoulder and elbow. This work analyzes the ranges of joint movement of shoulder and elbow during two tasks: drinking from a cup and lifting a box. The main purpose of this study was to determine if simulating a basic transradial prosthesis by limiting motion of the forearm and wrist using a brace, would cause significant changes in the compensatory motion of the shoulder and elbow during the tasks. The second purpose of the study was to determine if the location of added mass of 96 g (mass of an electrical wrist rotator) would affect shoulder and elbow angles during these same tasks. A group of able-bodied participants were asked to complete the tasks during the following conditions: (1) no intervention (2) while wearing a brace that restricted forearm and wrist motion of their dominant arm (right) (3) wearing the same brace with a 96 g mass added near the elbow, (4) with the same brace and a 96 g mass added near the wrist. Subject movements were captured using a motion capture system and ranges of movement of shoulder and elbow, as well as degree of asymmetry (DoA) during the box lift were calculated for each subject. Three trials were collected for each test condition and were averaged as a representative for each subject. Statistical analysis of the results concluded that during drinking elbow flexion was significantly different in case 1 from the other 3 levels. Statistical analysis of lifting found significant differences in the dominant (right) shoulder and elbow flexion between all 4 levels, while their relative degree of symmetry was found to be statistically different between level 1 and 3–4. The study concludes that bracing limits forearm and wrist affects shoulder and elbow flexion and their relative DoA. The position of a 96g mass did not cause any statistical differences in the movements observed or in their DoA. Further testing will examine the transradial amputee population as well as the effects of position of added mass on joint torques during common tasks.

Distributed Friction Damping of Traveling Wave Vibration in Rods

A ring damper can be affixed to a rotating base structure such as a gear, an automotive brake rotor, or a gas turbine’s labyrinth air seal. Depending on the frequency range, wavenumber, and level of preload, vibration of the base structure can be effectively and passively attenuated by friction that develops along the interface between it and the damper. The assembly is modeled as two rods that couple in longitudinal vibration through spatially-distributed hysteretic friction, with each rod having periodic boundary conditions in a manner analogous to an unwrapped ring and disk. As is representative of rotating machinery applications, the system is driven by a traveling wave disturbance, and for that form of excitation, the base structure’s and the damper’s responses are determined without the need for computationally-intensive simulation. The damper’s performance can be optimized with respect to normal preload, and its effectiveness is insensitive to variations in preload or the excitation’s magnitude when its natural frequency is substantially lower than the base structure’s in the absence of contact.

A Magnetorheological Actuation System: Part I — Testing

There is a demand for compact hybrid actuation systems which combines actuation and valving systems in a compact package. Such self-contained actuation systems have potential applications in the field of rotorcraft (as active pitch links) and automotive engineering (as active vibration control devices). Hybrid hydraulic actuation systems, based on frequency rectification of the high frequency motion of an active material, can be used to exploit the high bandwidth of smart material to design devices with high force and stroke. Magnetorheological (MR) fluids are active fluids whose viscosity can be changed through the application of a magnetic field. By using MR fluids as the hydraulic fluid in such hybrid devices, a valving system with no moving parts can be implemented. Such a system will be attractive in rotorcraft applications with large centrifugal force loading. Thus, MR fluids can be used to control the motion of an output cylinder. The MR fluid based valves can be configured in the form of a Wheatstone bridge to produce bi-directional motion in an output cylinder by alternately applying a magnetic field in the two arms of the bridge. In this study, the actuation is performed using a compact Terfenol-D stack driven actuator. The frequency rectification of the stack motion is done using reed valves. This actuator and valve configuration form a compact hydraulic system with fluidic valves. The advantages of such systems are that part count is low, absence of moving parts and the possibility of continuous controllability of the output cylinder. By applying varying magnetic fields in the arms of the bridge (by applying different currents to the coils), the differential pressure acting on the output cylinder can be controlled. The description of the experimental setup, the tests performed and the experimental results are presented in this paper.

On the Dynamic Characterization for Flywheel Touchdown Bearing System Design

NASA Glenn Research Center has been developing efficient flywheel batteries for a variety of space power applications, which provide the advantages of higher energy density, longer life span, and lower maintenance over electrochemical batteries as a next-generation energy storage device. As a component of enhancing the reliability of a flywheel module, the touchdown bearing system plays a crucial role in case of the malfunction or failure of magnetic bearings. In this paper, a design for touchdown support system has been proposed, a mathematical model for characterizing the dynamic behavior for the touchdown bearing system developed and then the numerical analysis using key design parameters followed. Transient simulations for the flywheel 1G delevitation onto the touchdown bearings suggest a design guide for the touchdown system, which maximizes the minimum air gap at the magnetic bearings and minimizes the dynamic loading as well as allows a safe flywheel rotor landing.

Energy Regenerative and Active Control of Automobile Suspension

A new energy regenerative and active control of automobile suspension is introduced. It is intended to improve vibration reduction capability using the regenerated energy. A PM type linear AC motor is used as an energy regenerative and active control suspension. This idea is applied to a quarter-car model and vibration control is performed. Energy regenerative and active control modes can not operate at the same time. A new control law is introduced to switch control modes and to follow the ideal force. The ideal force is calculated using the LQ control theory. The PWM switches are driven in proportion to the difference between the ideal control force and the actuator force using the modulation circuit. Experimental setup is made to confirm the proposed technique and the damping capability is tested.