Numerical and experimental investigation of a semi-active vibration control system by means of vibration energy conversion

A vibration control concept based on vibration energy conversion and storage with respect to a serial-stiffness-switch system (4S) has previously been proposed. Here, we first present a rotational electromagnetic serial-stiffness-switch system as a novel practical vibration control system for experimental validation of the concept and, furthermore, an improved control strategy for higher vibration suppression performance is also proposed. The system consists of two spring-switch elements in series, where a parallel switch can block a spring. As an alternating mechanical switch, the experimental system uses two electromagnets with a shared armature. By connecting the armature to the rotating load or the base, the electromagnets decide which of the two spiral springs is blocked, while the other is active. A switching law based on the rotation velocity of the payload is used. Modelling and building of the experimental system were carried out. The corresponding experiment and simulation were executed and they matched well. These results prove that our serial-stiffness-switch system is capable of converting vibration energy and realizing vibration reduction under a forced harmonic disturbance. The effects of disturbance frequency, disturbance amplitude and sampling frequency on the system performance are shown as well. A position feedback control-based switching law is further put forward and experimentally verified to improve the repositioning accuracy of the disturbed system

Energy-Optimal Control of Underactuated Bipedal Locomotion Systems

The paper deals with modeling and design of energy-optimal motion of mechatronic system having less number of actuators than degrees of freedom. Such mechatronic system is termed underactuated. We consider an underactuated mechatronic system modeled a bipedal locomotion robot with 11 degrees of freedom. The system comprises nine links and is used to represent the bipeds planar dynamics in sagittal plane. The bodies are connected by friction-free hinge joints. Its assumed that the control inputs are torque actuators acting only at hip and knee joints. The ankle and the metatarsal joints of the feet are spanned with springs al-lowing discrete switching of their stiffness parameters in accordance to varying constraints imposed on the systems motion. The algorithm has been developed for synthesizing the energy-optimal anthropomorphic motion of the bipedal locomotion system with passively controlled feet and discrete switching of their joint stiffness parameters. Algorithm uses the smoothing cubic splines for approximation of variable functions, inverse dynamics approach, extern penalty functions method, and minimization of the nonsmooth objective function in orthogonal directions. The efficiency of the developed algorithm has been confirmed by simulation of human gait like motions for considered underactuated system. Applications of the results obtained can be found in robotics, bioengineering (prosthetics, orthotics), others

Energy-Optimal Control of Underactuated Bipedal Locomotion Systems

The paper deals with modeling and design of energy-optimal motion of mechatronic system having less number of actuators than degrees of freedom. Such mechatronic system is termed underactuated. We consider an underactuated mechatronic system modeled a bipedal locomotion robot with 11 degrees of freedom. The system comprises nine links and is used to represent the bipeds planar dynamics in sagittal plane. The bodies are connected by friction-free hinge joints. Its assumed that the control inputs are torque actuators acting only at hip and knee joints. The ankle and the metatarsal joints of the feet are spanned with springs al-lowing discrete switching of their stiffness parameters in accordance to varying constraints imposed on the systems motion. The algorithm has been developed for synthesizing the energy-optimal anthropomorphic motion of the bipedal locomotion system with passively controlled feet and discrete switching of their joint stiffness parameters. Algorithm uses the smoothing cubic splines for approximation of variable functions, inverse dynamics approach, extern penalty functions method, and minimization of the nonsmooth objective function in orthogonal directions. The efficiency of the developed algorithm has been confirmed by simulation of human gait like motions for considered underactuated system. Applications of the results obtained can be found in robotics, bioengineering (prosthetics, orthotics), others

Learning Compliant Stiffness by Impedance Control-Aware Task Segmentation and Multi-objective Bayesian Optimization with Priors

Rather than traditional position control, impedance control is preferred to ensure the safe operation of industrial robots programmed from demonstrations. However, variable stiffness learning studies have focused on task performance rather than safety (or compliance). Thus, this paper proposes a novel stiffness learning method to satisfy both task performance and compliance requirements. The proposed method optimizes the task and compliance objectives (T/C objectives) simultaneously via multi-objective Bayesian optimization. We define the stiffness search space by segmenting a demonstration into task phases, each with constant responsible stiffness. The segmentation is performed by identifying impedance control-aware switching linear dynamics (IC-SLD) from the demonstration. We also utilize the stiffness obtained by proposed IC-SLD as priors for efficient optimization. Experiments on simulated tasks and a real robot demonstrate that IC-SLD-based segmentation and the use of priors improve the optimization efficiency compared to existing baseline methods.Comment: Accepted to IROS202

Energy Harvesting toward the Vibration Reduction of Turbomachinery Blades via Resonance Frequency Detuning

Piezoelectric-based energy harvesting devices provide an attractive approach to powering remote devices as ambient mechanical energy from vibrations is converted to electrical energy. These devices have numerous potential applications, including actuation, sensing, structural health monitoring, and vibration control -- the latter of which is of particular interest here. This work seeks to develop an understanding of energy harvesting behavior within the framework of a semi-active technique for reducing turbomachinery blade vibrations, namely resonance frequency detuning. In contrast with the bulk of energy harvesting research, this effort is not focused on maximizing the power output of the system, but rather providing the low power levels required by resonance frequency detuning. The demands of this technique dictate that harvesting conditions will be far from optimal, requiring that many common assumptions in conventional energy harvesting research be relaxed. Resonance frequency detuning has been proposed as a result of recent advances in turbomachinery blade design that have, while improving their overall efficiency, led to significantly reduced damping and thus large vibratory stresses. This technique uses piezoelectric materials to control the stiffness, and thus resonance frequency, of a blade as the excitation frequency sweeps through resonance. By detuning a structure*s resonance frequency from that of the excitation, the overall peak response can be reduced, delaying high cycle fatigue and extending the lifetime of a blade. Additional benefits include reduced weight, drag, and noise levels as reduced vibratory stresses allow for increasingly light blade construction. As resonance frequency detuning is most effective when the stiffness states are well separated, it is necessary to harvested at nominally open- and short-circuit states, corresponding to the largest separation in stiffness states. This presents a problem from a harvesting standpoint however, as open- and short-circuit correspond to zero charge displacement and zero voltage, respectively, and thus there is no energy flow. It is, then, desirable to operate as near these conditions as possible while still harvesting sufficient energy to provide the power for state-switching. In this research a metric is developed to study the relationship between harvested power and structural stiffness, and a key result is that appreciable energy can be harvested far from the usual optimal conditions in a typical energy harvesting approach. Indeed, sufficient energy is available to power the on-blade control while essentially maintaining the desired stiffness states for detuning. Furthermore, it is shown that the optimal switch in the control law for resonance frequency detuning may be triggered by a threshold harvested power, requiring minimal on-blade processing. This is an attractive idea for implementing a vibration control system on-blade, as size limitations encourage removing the need for additional sensing and signal processing hardware

Deterministic and stochastic responses of smart variable stiffness and damping systems and smart tuned mass dampers

Semi-active control algorithms are developed and examined for a variety of civil engineering applications subjected to a wide range of excitations. Except two control algorithms based on continuous variable structure control and Lyapunov control, the semi- active controllers developed in this study are based on real-time estimation of instantaneous (dominant) frequency and the evolutionary power spectral density by time-frequency analysis of either the excitation or the response of the structure. Time-frequency analyses are performed by either short-time Fourier transform or wavelet transform. The semi-active strategies are applied to three categories of structures: (1) smart single- and multi- degree-of-freedom (sSDOF/sMDOF) systems subjected to pulse-type and random ground excitations, (2) single/multiple smart tuned mass dampers (sTMD/sMTMD) subjected to random wind and ground excitations, and (3) smart tuned liquid column dampers (sTLCD) subjected to random wind and ground excitations. For sMDOF/sMDOF systems, nonlinear control algorithms developed to independently vary stiffness (continuous variable structure control) and damping (Lyapunov control) are examined against near-fault earthquakes and pulse type of excitations fitted to them. Another semi-active (time-frequency) controller is developed based on minimizing the instantaneous H2 norm of the response of the structure. Two time-frequency controllers (feedforward and feedback) are developed for single/multiple smart tuned mass dampers (sTMD/sMTMD) subjected to either force or base excitation. In the feedforward control, the smart tuned mass damper stiffness and damping are varied based on the instantaneous (dominant) frequency of the excitation, whereas in the feedback control the smart tuned mass damper stiffness is varied based on the instantaneous (dominant) frequency of the response. The developed algorithms are also extended to semi-active smart tuned liquid column dampers (sTLCD) subjected to either force or base excitation. The performance of the control algorithms are evaluated by studying the deterministic and stochastic responses of the examined semi-active structures. Stochastic responses are computed from Monte Carlo simulations of various target evolutionary spectra. It is shown that smart variable stiffness and variable damping systems and smart tuned mass/liquid column dampers lead to significant response reduction over a broad frequency range and under a wide set of excitations

New semi-active vibration control with Serial-Stiffness-Switch-System based on vibration energy harvesting

Diese Dissertation untersucht eine neuartige semi-aktive Schwingungsteuerung mit einem seriellen-Steifigkeit-Schalter-System (4S) basierend auf der Speicherung von Schwingungsenergie. Auf Basis der Schwingungsreduktionsanalyse für ein passives und ein semi-aktives Schaltsystem werden Probleme vorhandener Schwingungsteuerungssystemen aufgezeigt und durch das 4S Konzept gelöst. Um seine Leistungsfähigkeit zu untersuchen, wird zunächst 4S im offenen Regelkreis analysiert und die äquivalente Steifigkeit und Eigenfrequenz des Schaltsystems abgeleitet. Es folgt die Analyse für 4S im geschlossenen Regelkreis. Zur Schwingungsreduzierung wird ein Geschwindigkeits-Nulldurchgangs Schaltgesetz verwendet, das auf der Speicherung von Schwingungsenergie basiert. Dies wird unter einer harmonischen Störung numerisch validiert. Anschließend werden Grenzen der Energiespeicherung analysiert. Es folgt eine experimentelle Validierung dieser neuartigen Strategie zur Schwingungssteuerung vorgestellt und ein drehender Prüfstand entwickelt. Der Prüfstand verwendet zwei ringförmig angeordnete Elektromagnetplatten zusammen mit einer Ankerwelle als zwei mechanische Schalter, um die Verbindung oder Trennung von zwei Spiralfedern mit einem Lastträgheitsmoment zu erreichen. Die Speicherung von Schwingungsenergie und die Schwingungsreduktion werden auf diesem Versuchssystem getestet. Neben einer harmonischen Störung wird auch eine Anfangsgeschwindigkeit ungleich Null berücksichtigt. Um in diesem Fall die Schwingungsreduktion zu verbessern, wird ein neues Schaltgesetz vorgeschlagen. Mit Hilfe der Phasenebene wird das transiente und stationäre Ratterverhalten von 4S analysiert. Das Schaltgesetz ermöglicht eine schnelle Umwandlung der anfänglichen kinetischen Energie, die in beiden Federn zu gleichen Teilen gespeichert wird. Dies ist numerisch und experimentell validiert. Zusätzlich wird einer harmonischen Störung an dem neuen Schaltgesetz getestet, das ein besseres Positionierverhalten als das Geschwindigkeits-Nulldurchgangs Schaltgesetz aufweist. Schließlich wird 4S zur Schockisolierung eingesetzt. Die maximale Reduzierung des Überschwingens des Wegs beim Schock und die Reduktion der Restschwingungen nach dem Schock werden numerisch validiert. Darüber hinaus wird auch der Einfluss verschiedener Designparameter von 4S auf das Isolationsverhalten untersucht.This dissertation investigates a novel semi-active vibration control with Serial-Stiffness-Switch-System (4S) based on vibration energy harvesting. On the basis of the vibration reduction performance analysis for a passive and a semi-active switching system, the problem in the present vibration control systems is stated and 4S concept is consequently put forward. In order to examine its performance, 4S in open loop control is analyzed firstly and the equivalent stiffness and natural frequency of the switching system are derived. Following is the analysis for 4S in closed loop control. A velocity zero-crossing switching law based on vibration energy harvesting is used for vibration reduction. This is numerically validated under a harmonic disturbance. Afterwards, vibration energy harvesting limit is analyzed. An experimental validation on this novel vibration control strategy is then presented and a rotational test rig is developed. The test rig uses two ring-arranged electromagnet-plates together with an armature-shaft as two mechanical switches to achieve the connection or disconnection of two spiral springs to or from a primary plate. The vibration energy harvesting and vibration reduction performance of 4S are tested on this experimental system. Apart from a harmonic disturbance, a nonzero initial velocity vibration is also considered. To improve vibration reduction performance in this case, a new switching law is proposed. By means of phase plane, the transient and steady chattering response of 4S are analyzed. The switching law enables a fast transformation of initial vibration energy into potential energy equally stored in two springs. This is numerically and experimentally validated. Additionally, a harmonic disturbance is also exerted on the new switching law. The results show that 4S has a better positioning performance than that for the velocity zero-crossing switching law. Finally, 4S is further applied for shock isolation. The maximum displacement response reduction during shock and the residual vibration suppression after shock are numerically validated. Moreover, the effect of several design parameters of 4S on the shock isolation performance is investigated as well

Roadmap for optical tweezers

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects, ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in the life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nano-particle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration.journal articl

Roadmap for optical tweezers

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMOptical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects, ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in the life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nano-particle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space explorationEuropean Commission (Horizon 2020, Project No. 812780