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

Dynamics of Ultrasonic Motors

This thesis is treating theory, modeling, model analysis and experiments of traveling wave type ultrasonic motors. A framework to derive models for ultrasonic motors is given here, which is based on the continuum theory of electromechanical solids. This includes the modeling of the stator-rotor contact and the electromechanical behavior of piezoceramic stators. The principle of virtual power is stated for electromechanical systems, where the terms of virtual power due to normal and tangential contact stresses are expressed explicitly. Using this principle and a symbolic equation manipulation tool, a planar motor model based on BERNOULLI-EULER kinematics is derived. Subsequently, a scaling analysis is carried out. Then, a model analysis scheme is given, based on the derived motor model at steady-state. Contact boundary and transition conditions, continuity equations at the contact boundaries and contact search equations are stated. After that, a spatial discretization is carried out, using a GALERKIN discretization method with both, global and local Ansatz-functions. Compared to Finite-Element-Methods this reduces the number of degrees of freedom drastically, thus saving computer time. For the resulting algebraic equations, a contact algorithm is given. Using the computer code developed from this, numerical analyses are carried out. Particular resonance curves and speed-torque characteristics are computed and discussed. In the experimental part, the focus is on the resonance, the temperature and the steady-state motor operation behavior of a typical ultrasonic motor. Resonance curves of the electric admittances of stator and motor were measured and discussed as well as those of the velocity of surface points of both, stator and rotor. The resonance curves show a non-linear softening behavior. For sufficiently high stator vibration amplitudes this goes along with a jump phenomenon. It is found that material non-linearities in the piezoceramics may be the reason for this effect. Furthermore, the influence of the temperature rise due to the frictional contact mechanism is investigated. Speed-torque characteristics were measured and their dependence on various external parameters is investigated. At the same time, the time histories of different motor quantities like rotational speed, motor torque, electric current or velocity of surface points were recorded. Different effects in the motor behavior were observed, among them overhang speed-torque characteristics and hysteretic behavior. Finally, resistive and reactive power components as well as efficiencies along the speed-torque characteristics were computed

Enhancement of Shock Absorption Using Hybrid SMA-MRF Damper by Complementary Operation

A hybrid damper concept is presented here using a combination of a Magnetorheological (MR) Fluid (MRF) and Shape Memory Alloy (SMA)-based energy dissipation. A demonstration is performed utilizing the shear operating mode of the MRF and the one-way effect of the SMA. The damping performance of different MRF-SMA configurations is investigated and the corresponding energy consumption is evaluated. We demonstrate that the operation of MRF and SMA dampers complement each other, compensating for each other’s weaknesses. In particular, the slow response from the MR damper is compensated by passive SMA damping using the pseudoplastic effect of martensite reorientation, which can dissipate a significant amount of shock energy at the beginning of the shock occurrence. The MR damper compensates for the incapability of the SMA to dampen subsequent vibrations as long as the magnetic field is applied. The presented hybrid SMA-MR damper demonstrates superior performance compared to individual dampers, allowing for up to five-fold reduction in energy consumption of the MR damper alone and thereby opening up the possibility of reducing the construction volume of the MR damper

Identification of Active Magnetic Bearing Systems Utilizing a Modulating Function Technique

An application of modulating function (MF) technique to the direct closed-loop identification for the estimation of a continuous-time model of multi-input-multi-output magnetic bearing system from sampled data are presented in this paper. The plant description given as a differential matrix polynomial is transformed into a matrix of difference equations using the modulating function approach, which allows to avoid numerical problems by aproximating time derivatives. Additionally, the initial conditions can be neglected as a characteristic of the MF technique. The system parameter estimation represents a solution of a least-squares problem derived from the difference system model with experimental data from an industrial magentic bearing system

A Randomized Controlled Trial on Functional Relaxation as an Adjunct to Psychoeducation for Stress

This randomized controlled trial investigated whether adding the psychodynamically based body-oriented psychotherapy “Functional Relaxation” (FR) to psychoeducation (PE) is more effective than PE alone to reduce stress and stress-associated complaints. Eighty-one participants with elevated stress-levels, ≥50 points on the global scale of the Perceived Stress Questionnaire (PSQ), received either 10 sessions of manualized FR + PE (n = 42) or two sessions of manualized PE alone (n = 39) in a group setting. Six FR trainers took part in this study. Stress-level (PSQ) was the primary outcome and secondary outcomes were depression (PHQ-9) and somatization (PHQ-15). Multilevel models for discontinuous change revealed that FR + PE was more helpful to reduce stress-levels than PE from pre-treatment to post-treatment (t0 → t1) as well as from pre-treatment to 6-month follow-up (t0 → t2) (both p < 0.05) with effect sizes (d) being medium for PE (dt0 → t1 = 0.57; dt0 → t2 = 0.67) and large for FR + PE (dt0 → t1 = 1.57; dt0 → t2 = 1.39). Moreover, FR + PE affected depression and somatization more positively than did PE from t0 to t1 as well as from t0 to t2 (all p < 0.05). Effect sizes for depression were small to medium for PE (dt0 → t1 = 0.52; dt0 → t2 = 0.37) and large for FR + PE (dt0 → t1 = 1.04; dt0 → t2 = 0.95). Effect sizes for somatization were small for PE (dt0 → t1 = 0.18; dt0 → t2 = 0.19) and medium to large for FR + PE (dt0 → t1 = 0.73; dt0 → t2 = 0.93). In summary, the combination of FR and PE was more effective than PE alone. The results of the present trial provide first evidence of FR as a potent component of stress interventions. Adding FR to such interventions might better help prevent clinically relevant disorders such as depression or somatization

Dynamics of Ultrasonic Motors

This thesis is treating theory, modeling, model analysis and experiments of traveling wave type ultrasonic motors. A framework to derive models for ultrasonic motors is given here, which is based on the continuum theory of electromechanical solids. This includes the modeling of the stator-rotor contact and the electromechanical behavior of piezoceramic stators. The principle of virtual power is stated for electromechanical systems, where the terms of virtual power due to normal and tangential contact stresses are expressed explicitly. Using this principle and a symbolic equation manipulation tool, a planar motor model based on BERNOULLI-EULER kinematics is derived. Subsequently, a scaling analysis is carried out. Then, a model analysis scheme is given, based on the derived motor model at steady-state. Contact boundary and transition conditions, continuity equations at the contact boundaries and contact search equations are stated. After that, a spatial discretization is carried out, using a GALERKIN discretization method with both, global and local Ansatz-functions. Compared to Finite-Element-Methods this reduces the number of degrees of freedom drastically, thus saving computer time. For the resulting algebraic equations, a contact algorithm is given. Using the computer code developed from this, numerical analyses are carried out. Particular resonance curves and speed-torque characteristics are computed and discussed. In the experimental part, the focus is on the resonance, the temperature and the steady-state motor operation behavior of a typical ultrasonic motor. Resonance curves of the electric admittances of stator and motor were measured and discussed as well as those of the velocity of surface points of both, stator and rotor. The resonance curves show a non-linear softening behavior. For sufficiently high stator vibration amplitudes this goes along with a jump phenomenon. It is found that material non-linearities in the piezoceramics may be the reason for this effect. Furthermore, the influence of the temperature rise due to the frictional contact mechanism is investigated. Speed-torque characteristics were measured and their dependence on various external parameters is investigated. At the same time, the time histories of different motor quantities like rotational speed, motor torque, electric current or velocity of surface points were recorded. Different effects in the motor behavior were observed, among them overhang speed-torque characteristics and hysteretic behavior. Finally, resistive and reactive power components as well as efficiencies along the speed-torque characteristics were computed

Dynamics of ultrasonic motors

This thesis is treating theory, modeling, model analysis and experiments of traveling wave type ultrasonic motors. A framework to derive models for ultrasonic motors is given here, which is based on the continuum theory of electromechanical solids. This includes the modeling of the stator-rotor contact and the electromechanical behavior of piezoceramic stators. The principle of virtual power is stated for electromechanical systems, where the terms of virtual power due to normal and tangential contact stresses are expressed explicitly. Using this principle and a symbolic equation manipulation tool, a planar motor model based on BERNOULLI-EULER kinematics is derived. Subsequently, a scaling analysis is carried out. Then, a model analysis scheme is given, based on the derived motor model at steady-state. Contact boundary and transition conditions, continuity equations at the contact boundaries and contact search equations are stated. After that, a spatial discretization is carried out, using a GALERKIN discretization method with both, global and local Ansatz-functions. Compared to Finite-Element-Methods this reduces the number of degrees of freedom drastically, thus saving computer time. For the resulting algebraic equations, a contact algorithm is given. Using the computer code developed from this, numerical analyses are carried out. Particular resonance curves and speed-torque characteristics are computed and discussed. In the experimental part, the focus is on the resonance, the temperature and the steady-state motor operation behavior of a typical ultrasonic motor. Resonance curves of the electric admittances of stator and motor were measured and discussed as well as those of the velocity of surface points of both, stator and rotor. The resonance curves show a non-linear softening behavior. For sufficiently high stator vibration amplitudes this goes along with a jump phenomenon. It is found that material non-linearities in the piezoceramics may be the reason for this effect. Furthermore, the influence of the temperature rise due to the frictional contact mechanism is investigated. Speed-torque characteristics were measured and their dependence on various external parameters is investigated. At the same time, the time histories of different motor quantities like rotational speed, motor torque, electric current or velocity of surface points were recorded. Different effects in the motor behavior were observed, among them overhang speed-torque characteristics and hysteretic behavior. Finally, resistive and reactive power components as well as efficiencies along the speed-torque characteristics were computed

Ground vehicle guidance along collision-free trajectories using elastic bands

Latest developments in automotive sensor technology promise an unbroken innovation thrust for driver assistance systems. Accordingly, future vehicles might be able to navigate autonomously. For autonomous vehicles collision avoidance systems (CAS) are essential. Key elements of CAS are automatic path planning, path following and model based estimation of the driving conditions of a CAS-equipped car. For this purpose, a path planning technique using modified elastic bands is presented. Furthermore, a possible overall CAS-structure including path following control and driving condition estimation is discussed. Finally, simulation results for an evasion maneuver are given

Design of Contactlessly Powered and Piezoelectrically Actuated Tools for Non-Resonant Vibration Assisted Milling

This contribution presents a novel design approach for vibration assisted machining (VAM). A lot of research has already been done regarding the influence of superimposed vibrations during a milling process, but there is almost no information about how to design a VAM tool where the tool is actually rotating. The proposed system consists of a piezoelectric actuator for vibration excitation, an inductive contactless energy transfer system and an electronic circuit for powering the actuated tool. The main benefit of transferring the required power without mechanical contact is that the maximum spindle speed is no longer restricted by friction of slip rings. A detailed model is shown that enables for preliminary estimation of the system’s response to different excitation signals. Experimental data are provided to validate the model. Finally, some parts are shown that have been manufactured using the contactlessly actuated milling tool