On the vibration control of semi-active friction dampers with piecewise defined contact geometries

Suppressing unwanted vibrations has been a major challenge for more than a century. Semi-active dampers offer a compromise between the high energy costs of active solutions and their increased flexibility. A nonlinear system that utilizes dry friction and piecewise defined contact geometries is used as the basis for a semi-active damper. Furthermore, a slow frequency-based control that does not solely rely on dissipation is considered and compared to the conventional Skyhook Control. Simulations show that the strategy is an effective approach for vibration reduction

Passing through resonance of the unbalanced rotor with self-balancing device

The slow dynamics of unbalanced rotors with a passive self-balancing system are investigated considering the interaction of the mechanical system with a limited power engine. The slow dynamics equations are obtained using the averaging technique for partially strongly damped systems. Stationary system configurations, different types of nonstationary solutions while passing through resonance, and areas of stability and attraction are investigated

Asymptotic analysis of self-excited and forced vibrations of a self-regulating pressure control valve

Pressure vibrations in hydraulic systems are a widespread problem and can be caused by external excitation or self-exciting mechanisms. Although vibrations cannot be completely avoided in most cases, at least their frequencies must be known in order to prevent resonant excitation of adjacent components. While external excitation frequencies are known in most cases, the estimation of self-excited vibration amplitudes and frequencies is often difficult. Usually, numerical studies have to be executed in order to elaborate parameter influences, which is computationally expensive. The same holds true for the prediction of forced oscillation amplitudes. This contribution proposes asymptotic approximations of forced and self-excited oscillations in a simple hydraulic circuit consisting of a pump, an ideal consumer and a pressure control valve. Two excitation mechanisms of practical interest, namely pump pulsations (forced vibrations) and valve instability (self-excited vibrations), are analyzed. The system dynamics are described by a singularly perturbed third-order differential equation. By separating slow and fast variables in the system without external excitation, a first-order approximation of the slow manifold is computed. The flow on the slow manifold is approximated by an averaging procedure, whose piecewise defined zero-order solution maps the valve’s switching property. A modification of the procedure allows for the asymptotic approximation of the system’s forced response to an external excitation. The approximate solutions are validated within a realistic parameter range by comparison with numerical solutions of the full system equations

Noah Fidlin Senior Art Portfolio

An art, photography and design magazine that combines analog and digital media.https://digitalcommons.snc.edu/artportfolios/1044/thumbnail.jp

Energy-optimized bipedal running of a simple humanoid robot

A method to optimize energy efficiency for bipedal running robots is presented. A running model of a simple bipedal robot consisting of five rigid bodies connected by actuated revolute joints is introduced. The actuators’ torques are generated by a trajectory tracking controller to produce periodic running gaits. The controller’s reference trajectories are parameterized by Bézier polynomials. A numerical optimization is used to employ reference trajectories with optimal energy efficiency for average velocities in the range of 1.5 to 5.5 m/s

Friction Reduction in a Revolute Joint by the Use of Axial High-Frequency Excitation

While downscaling gains importance in many technical components, accuracy must increase as well. This is a challenge especially for dry bearings with small tolerances. To suppress friction induced phenomena like stick-slip-motions or break-away-effects, superposed oscillations can be used to specifically influence the friction characteristic. In this context, the present contribution deals with a friction revolute joint with axial high-frequency excitation to reduce friction torque. There is a special focus on the heat generation and its interaction with the system dynamics

Oscillations in a system of two coupled self‐regulating spool valves with switching properties

In hydraulic systems, valves can be considered as fundamental components. They serve as control elements to regulate hydraulic power transmission. In order to minimize control effort, self‐regulating spool valves enjoy great popularity. However, their disadvantage is a possible loss of stability, caused by the coupling between hydraulic and mechanical degrees of freedom via pressure feedback areas. So far, the self‐excited oscillations, evoked from the operating point\u27s loss of stability, have mostly been investigated using minimal models of individual valves. In real world applications, for example in automotive transmissions, typically several valves are employed which are coupled by hydraulic pipes. Here, it is expected, that dynamical phenomena occur, which cannot be portrayed by simple models of individual valves. Within this contribution, the oscillatory behaviour of a system employing two coupled self‐regulating valves is discussed. The resulting non‐stationary solutions are characterized by using Floquet theory and computing Lyapunov‐Exponents

On the Dynamic Balancing of a Planetary Moving Rotor using a Passive Pendulum-type Device

AbstractThe possibility of using self-balancing devices to reduce the vibration amplitudes in planetary moving rotors is investigated analytically using the averaging method for a partially strongly damped system. Self-balancing was shown to be effective for a planetary moving rotor in the overcritical speed domain. However, the centrifugal forces caused small vibrations of the pendulum balancers, which increased with the increase of the velocity of the planetary motion. The analytic results match the numeric simulations very well as long as the velocity of the planetary motion is sufficiently small. To avoid high amplitudes while passing through resonance, a special design of the switchable pendulums that are controlled by centrifugal force is suggested. This design utilizes the only stable stationary orientation of the pendulums in the undercritical domain to position them in an appropriate way before coming into resonance. The results obtained provide new possibilities for the design of self-balancing devices for high precision applications