Influences of Elastic Supports on Moving Load Identification of Euler–Bernoulli Beams Using Angular Velocity

This work investigates the effect of elastic support stiffness on the accuracy of moving load identification of Euler–Bernoulli beams. It uses the angular velocity response in solving the ill-posed inverse vibration problem and Tikhonov regularization in the load identification process of two moving loads. The effects from moving loads’ traveling direction, measurement location arrangements, number of participant measurements, and damping ratios are considered in the studies under noisy disturbance conditions. Results show that the stiffness of the translational rotational springs at the boundaries can impact the accuracy of identified moving loads considerably. Angular velocities presented much better results than accelerations under low stiffness conditions when vertical elastic supports were used. However, acceleration showed better performance when a very soft translational spring was used at one end and a much stiffer translational spring at the other end, as well as when rotational springs with large stiffness were used with simply supported beam conditions. The combination of angular velocities and accelerations provided a balanced solution for a wide range of elastic supports with different stiffnesses.

Synthesis of Flexure Based Translational Springs

Translational springs are employed to generate desired force-displacement relationships. Conventional translational springs utilize elastic deformations of coiled spring strips to fulfill their functions. The one-dimensional motion of a conventional translational spring is produced by the three-dimensional deformation of its coiled spring strip, which is bending plus twisting of the coiled spring strip. Different from conventional translational springs, flexure based translational springs usually have simple planar monolithic structures, and are convenient to manufacture and maintain. The translation of a flexure based translational spring is from the two-dimensional elastic or recoverable deformations of its planar flexible members. The flexure based translational springs synthesized in this research are required to endure large input translations. Because of large deformation and geometric nonlinearity, flexure based translational springs face difficulties that include parasitic drift, spring stiffness deviation, and high stress in the deformed springs. The research of this paper is motivated by surmounting these difficulties. Flexure based translational springs with different arrangements are synthesized to eliminate parasitic drifts and have desired spring rates and reasonable maximum stress.

Design and Modeling of Semi Compliant Prosthetic Knee Joint

This paper presents the design phases and modeling of multi axial compliant prosthetic knee joint comprised of rigid and flexible members providing a better performance than traditional spring-loaded rigid multilink joints. Mechanism consists of monolithic compliant five bar incorporating large deflecting flexure hinges, two rigid body representing the upper and lower legs, translational spring and flexure joints simulating ankle motion. Dynamical modeling is studied by integrating pseudo rigid body modeling of small-length flexure hinge method and Lagrange equations under the assumption that link 2 (left base link) is fixed and link 3 is rotated quasi-statically at constant speed. Torsional stiffness of ankle springs is obtained by using MSC Adams simulations. Initial prototype is built by 3D printing the parts using polylactic acid (PLA) filament. Mechanism is potentially suitable for pediatric prosthetic knee systems due to its simple design, versatility and light weight.

Dynamics and Stability of a Flexible, Slender Cylinder Flexibly Restrained at One End and Free at the Other and Subjected to Axial Flow

In this paper, Lagrange’s equations along with the Ritz method are used to obtain the equation of motion for a flexible, slender cylinder subjected to axial flow. The cylinder is supported only by a translational and a rotational spring at the upstream end, and at the free end, it is terminated by a tapering end-piece. The equation of motion is solved numerically for a system in which the translational spring is infinitely stiff, thus acting as a pin, while the stiffness of the rotational spring is generally non-zero. The dynamics of such a system with the rotational spring of an average stiffness is described briefly. Moreover, the effects of the length of the cylinder and the shape of the end-piece on the critical flow velocities and the modal shapes of the unstable modes are investigated.

On nonlinear horizontal dynamics and vibrations control for high-speed elevators

In this work, the horizontal nonlinear response of a three-degree-of-freedom vertical transportation model excited by guide rail deformations is investigated. The equation of motion contains nonlinearities in the form of Duffing stiffness for the translational spring in tilting motion of the cabin. In order to improve the comfort for passengers a control strategy based on the State-dependent Ricatti Equation (SDRE) is proposed. Numerical simulations are performed to study the nonlinear behavior of the adopted mathematical model. In addition, we test the robustness of the SDRE control technique considering parametric errors and noise. The obtained results confirm that the proposed strategy can be effective in controlling the response of the system.

PREDICTING THE TRANSMISSIBILITY OF A GLOVE MATERIAL TO THE PALM USING A SIMPLE LUMPED PARAMETER MODEL OF THE HAND AND THE GLOVE

Assessing a glove for its ability to reduce vibration transmitted to the hand can be improved if the transmissibility of the glove to the hand can be predicted. This study proposes a simple lumped parameter model of the hand and the glove for predicting the transmissibility of a glove to the hand. The model of the hand consists of three main body segments: the palm, the fingers, and the palm tissues, connected via translational and rotational springs and dampers. The glove material was represented by translational spring and damper. The results showed that the glove transmissibility predicted using the model overestimated the glove transmissibility measured experimentally at frequencies greater than 62 Hz, implying that a simple three degree-of-freedom model of the hand and the glove may not be able to provide a reasonable prediction of glove transmissibility.

Mechanical Design and Evaluation of a Novel Knee-Ankle-Foot Robot for Rehabilitation

This paper presents the mechanical design and evaluation of a knee-ankle-foot robot, which is compact, modular, and portable for stroke patients to carry out overground gait training at outpatient and home settings. The robot is driven by a novel series elastic actuator (SEA) for safe human-robot interaction. The SEA employs one soft translational spring in series with a stiff torsion spring to achieve high intrinsic compliance and the capacity of providing peak force. The robotic joint mechanism and the selection of the actuator springs are optimized based on gait biomechanics to achieve portability and capability. The robot demonstrated stable and accuracy force control in experiments conducted on healthy subjects with overground walking. Major leg muscles of the subjects showed reduced level of activations (Electromyography, EMG) while maintaining normal gait patterns with robotic assistances, indicating the robot’s capability of providing effective gait assistance.

Harvesting Human Biomechanical Energy to Power Portable Electronics

It is known that human body contains rich chemical energy, part of which is converted to mechanical energy up to 200W, especially when human in walking, so human body is an ideal sustainable energy resource for portable electronic devices. The motion pattern of human movement in normal walking is studied, showing that the arm swinging, knee motion and hip motion can be approximated as sinusoidal functions with relatively large amplitude. In order to harvest such human motion, several methods are investigated, including pendulum, translational spring and torsion spring, which can also be mathematically formatted as second order differential equation with damped item. This paper also gives a typical device to harvest human motion: a novel energy harvester which directly converts human motion to electricity based on electromagnetic induction. Detail structures of the harvesting device are illustrated with mathematical analysis. Simulation studies are also made.