FxLMS Algorithm for Active Vibration Control of Structure By Using Inertial Damper with Displacement Constraint

Engine is the main source of vibration that generates unwanted noise and vibration of vehicle chassis. Especially, in submarine applications, radiation of noise signatures can be detected at some distance away from the submarine using a sonar array. Thus quiet operation is crucial for submarine’s survivability. This study addresses reduction of the force transmissibility originating from engines and transmitted to hull through engine mounts. An inertial damper, as an actuator of hybrid mount system, is addressed to reduce even further the level of vibration. Narrow band FxLMS algorithms are broadly used to cancel the vibration of engine mount because of its excellent performance of canceling narrow band noise. However, in real active dampers, the maximum displacement of damper mass is kinematically restricted. When the control input signal from the FxLMS algorithm exceeds this limitation, the damper mass will collide with the mechanical stops and results in many problems. Originated from these, a modified narrow band FxLMS algorithm based on the equalizer technique with the maximum allowable displacement of active damper mass is proposed in this study. Some simulation results showed that the propose algorithm is effective to suppress vibration of engine mount while ensuring given displacement constraint.

A Novel Bi-Stable Piezoelectric Energy Harvester Inspired by the Venus Flytrap

This paper studies the nonlinear dynamics and energy harvesting performance of a novel bi-stable piezoelectric energy harvester inspired by the rapid shape transition of the Venus flytrap leaves. The harvester is composed of a piezoelectric MFC transducer, a tip mass, and two sub-beams. The two sub-beams are akin to the bidirectionally curved Venus flytrap leaves that could rapidly snap-through from the open state to the closed state. To realize the bistability of the Venus flytrap leaves induced by the stored potential energy, an in-plane pre-displacement constraint is applied to the free ends of the sub-beams. The pre-displacement constraint leads to bending and twisting deformations and creates the potential energy in the harvester. The bio-inspired design is introduced in detail and a prototype is fabricated to validate the conceptual design. The nonlinear dynamics of the bio-inspired bi-stable piezoelectric energy harvester is investigated under base acceleration excitations. Results show that the sub-beams of the harvester experience more complicated local vibrations containing broadband high-frequency components as the snap-through motion happens. The energy harvesting performance of the harvester is evaluated at different excitation levels. The broadband energy harvesting is achieved at higher excitation levels and an average power output of 0.193 mW is attained under the excitation of 10 Hz and 4.0 g.

Fabrication, Experiment, and Simulation of a Flexible Microvalve-Integrated Microarm for Microgrippers Using Electrorheological Fluid

Because of the power density advantages of fluid power systems, many researchers have developed microactuators using homogeneous electrorheological (ER) fluids (ERFs) for applications to various micromachines. An ER valve, as a critical component of the ER actuator, can control ERF flow by the apparent viscosity increase resulting from the applied electric field without any mechanical moving parts. Hence, it is adequate for the miniaturization of a fluidic microactuator. However, it is not easy to integrate rigid ER valves into soft microrobots. To overcome these limitations, we developed a novel elastic ER microarm using flexible ER valves (FERVs) in this study. Each microarm consists of an FERV, a movable chamber, and a displacement constraint element, so that it bends with the inner pressure controlled by the FERV. We proposed and developed a micro-electromechanical system fabrication process for the FERV, movable chamber, and displacement constraint element. By utilizing the proposed method, we successfully fabricate a FERV-integrated microarm. The characteristics of the FERV were experimentally clarified. In addition, the bending motion of the FERV-integrated microarm was demonstrated by experiments and verified by finite-element method simulation. This ER microarm was shown to be feasible for an ER microgripper composed of multiple microarms.

The Effect of Displacement Constraints on the Failure of MEMS Tuning Fork Gyroscopes under Shock Impact

Displacement constraints such as stops are widely used in engineering to improve the shock resistance of microelectromechanical system (MEMS) tuning fork gyroscopes. However, in practical applications, it has been found that unexpected breakage can occur on MEMS tuning fork gyroscopes with stops. In this paper, the effects of two displacement constraints on the failure mode of MEMS tuning fork gyroscopes are studied. The MEMS tuning fork gyroscope is simplified to a two-degree-of-freedom (2DOF) model, then finite element analysis (FEA) is used to study the effects of displacement constraint on the gyroscope. The analysis proves that even if the displacement constraint of direct contact with the weak connecting beam is not established, the equivalent stiffness of the gyroscope can be enhanced by limiting the displacement of the movable mass, thereby improving the shock resistance of the gyroscope. However, under the shock of high-g level, displacement constraint with insufficient spacing will cause multiple collisions of the small-stiffness oscillating frame and lead to an increase in stress. The cause of failure and shock resistance of a MEMS tuning fork gyroscope are verified by the shock test. By comparing the results, we can get a conclusion that is consistent with the theoretical analysis.

Slip Line Theory Based Stability Analysis on the Influence of Deep Excavation on Adjacent Slope

The impact of deep excavation to the stability of adjacent slope is evaluated based on the slip line theory. Stress field of slope under various excavation conditions is simulated by finite element method, while slip line field is determined by non-associated flow rule. Factor of safety is obtained by integrating the skid-resistance and the shear stress on each slip line, and the slip line with minimum factor of safety corresponds to the critical slip surface. Two typical displacement constraint boundaries are considered. The results indicate that the critical slip surface moves towards to the slope surface and develops downwards. The factor of safety decreases with the excavation process. For flexible displacement constraint boundary, large deformation of supporting pile causes obvious variation of critical slip surface and factor of safety. In terms of the stiff displacement constraint boundary with internal supports, deep excavation only has limited effect on the slope stability.