This thesis explores the use of reset control to improve disturbance rejection in systems subjected to wideband noise. In the high-tech industry, there is a continuous push for improved performance, particularly in achieving fast and stable motion with nanometer-level precision. Linear controllers, though industry-standard, are constrained by limitations such as Bode's gain-phase relation. Reset control offers a promising alternative, but its behaviour under wideband disturbances remains unexplored. However, such excitation is common in the context of active vibration isolation. The wide-spectrum excitation may result in dominant slow or excessive resetting, depending on the system. In both cases, the behaviour of the reset element will be different than designed. Also, the traditional method of Describing Function (DF) will not sufficiently represent the reset element's behaviour under such conditions, as it is defined for single sinusoidal excitation. This thesis studies the Power Spectral Density (PSD) of the reset triggering signal of the reset element to understand the resetting behaviour. The method of Best Linear Approximation (BLA) is applied to enable the analysis of the reset element in frequency domain. Furthermore, a novel method is developed to shape the reset triggering signal, to achieve the desired behaviour of the reset element at the frequency of interest. Both simulations and experiments showed the feasibility of the method in achieving the desired behaviour of the reset element. Depending on the properties of the system, this will result in improvement of the disturbance rejection. ... Read more

Integrating compliant mechanisms into high-precision motion systems has facilitated the development of lightweight and frictionless designs. However, these systems often face challenges related to low-frequency parasitic resonance modes and limited structural damping, leading to compromised position accuracy and restricted control bandwidth. While notch filters are conventionally used to suppress these parasitic resonance peaks and enable higher control bandwidths, undesired effects persist in closed-loop disturbance rejection performance. To address this limitation, researchers have explored the concept of overactuation, employing a greater number of actuators than the number of rigid body modes to be controlled.
This approach allows for additional closed-loop feedback interconnections, offering
increased freedom to enhance performance. This research presents a novel overactuation based solution where: (1) the use of additional actuators enables the implementation of active damping control to improve closed-loop disturbance rejection performance and (2) the integration of multiple distributed piezoelectric bender actuator-sensor pairs in a collocated configuration enhances damping performance. A mathematical framework is formulated to demonstrate the benefits, and an experimental setup is constructed to validate the numerical findings and serve as a proof of concept. The proposed solution effectively suppresses the
parasitic resonance mode, enhances disturbance rejection on the end-effector, and enables higher control bandwidth in the positioning system. ... Read more

This research presents a novel data-based modal control method for actively dampening the flexible mode in a multi-input multi-output (MIMO) system. Traditional passive damping methods add significant mass to the system, making recent advances in sensor and actuator technology, such as lightweight piezoelectric materials, a more appealing solution. The key contribution of this research is a novel modal decoupling method for active damping that uses the MIMO frequency response function to circumvent the need for a parametric model. This method facilitates the design of a single-input, single-output (SISO) controller that actively dampens a flexible mode using all available sensors and actuators. This approach significantly reduces the complexity of the controller design and tuning effort compared to the conventional decentralized control architecture. Experimental validation is carried out on a cantilever beam, which shows near-perfect isolation of the mode of interest. The study's findings may offer critical insights for future mechatronics systems, enabling the creation of more efficient and powerful machines. ... Read more

Undesired vibrations are one of the most significant sources of error in any type of mechatronic system or component. The emerging field of elastic (locally resonant) metamaterials offers a viable solution to successfully suppress these by generating bandgaps in both resonant and non-resonant regions. In this thesis, metamaterials in a sensor-actuator configuration using piezoelectric transducers are employed to generate vibration attenuation regions in beam-like structures. The main contribution of this thesis consists in studying the practical issues involved in the experimental implementation of such metamaterial architectures, often overlooked in the literature. To this aim, parasitic dynamics such as time delay and RC roll-off characteristics of piezoelectric transducers are considered, and their influence on controller choice is evaluated. The research was conducted using full model simulations in SPACAR and an experimental setup. The RC roll-off characteristic of piezoelectric transducers was found to be significant in limiting the bandgap generation capabilities of the system in non-resonant regions. The reason for this was the added phase caused by the parasitic effect, which required a reduction in controller gain for stability and ultimately reduced the bandgap performance. This was not the case for resonant bandgaps, where the phase lead was compensated by the increase in gain at the resonance. This ultimately allowed for optimal resonant bandgaps to be generated and observed. Methods to compensate for such parasitic effects are proposed and suggestions on how to implement these to attain non-resonant bandgaps are made. ... Read more

The use of passive viscoelastic damping and active piezoelectric damping in a hybrid side-by-side configuration is explored in this paper. The goal is to combine the strengths of both individual methods to achieve better damping performance when targeting a single eigenmode or multiple resonances. It is found that a hybrid configuration where a passive constrained layer element covers the strain peak of a mode, with a active element placed next to it performs better than a passive or active damping treatment of the same size. It is more robust and uses lower control gains than active vibration control, and changes the system dynamics less than passive methods. ... Read more

The most problematic eigenmode in machines involving flexure mechanisms is represented by flexural modes. However, it can be noticed that also out-of-plane modes, that occur in the space outside the nominal plane of movement of the mechanism, can be very important, especially in machines with several and coupled degrees of freedom, like 3D positioning stages. In this thesis a new design based on piezoelectric shunt damping is proposed in order to tackle out-of-plane modes of flexure mechanisms, without affecting the capability of attenuating the more common flexural modes. This new concept is validated both analytically and using the FEM software COMSOL and it is shown that attenuations of the order of 15 dB can be achieved. Furthermore, the possibility to add active control to the shunted piezoelectric materials, giving rise to a hybrid control strategy, is explored and it is shown that it results in further increase of the added damping. Finally, a completely new technique based on Eddy current dampers is discussed and shown to be inadequate for out-of-plane mode attenuation. ... Read more

Vibrations and disturbances are becoming more of a concern as lightweight, flexible structures in high-tech systems are pushed towards faster speeds and higher precision. Active Vibration Control (AVC) methods have been effectively used to attenuate vibrations and increase the bandwidth of these systems. With the miniaturisation of electronics, an increasing amount of sensor and actuator pairs can be used for AVC applications. Not only does this allow for higher active damping, it also grants more flexibility in terms of control. This trend has led to the study of robotic metamaterials and meta-structures: large-scale engineered materials build out of a repeating pattern of unit cells, where each unit cell contains a sensor, actuator and sometimes even a computing unit. The optimal control architecture to use for these systems is a difficult dilemma, since decentralised and centralised control schemes both have fundamental trade-offs in terms of performance and scalability. In this paper we study distributed control, a promising middle-ground solution that is hardly used in AVC applications. We show with the use of LQR that a distributed control architecture can achieve optimal performance in the low-frequency range for robotic materials with relative measurements. Additionally, the actuators use lower maximum control forces and a distributed control architecture remains scalable for implementation in large-scale systems. In this paper the robotic cantilever beam is studied as a specific example as it represent many typical high-tech applications. Furthermore, implications on periodic robotic meta-structures are made using LQR in the Spatial Fourier Domain.

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In this paper, the implementation of an active unit-cell metamaterial used for vibration control is discussed. The active unit-cell metamaterial is designed for implementation in a hexapod strut. As each of the unit-cells can be sensed and actuated, over-sensing and over-actuation are introduced in the system. This can be used to create vibration isolation behaviour. This is done using the interaction between the unit-cells.
Using the commercial FEM software COMSOL, the amount of unit-cells used in the strut is determined. By looking at the transmissibility of the system, the required controllers are also determined. The presented unit-cell design makes use of simple active damping controllers in order to improve control flexibility for different systems.
The system is validated using a realistic model made in the commercial software Simulink. The model includes sensor dynamics, sensor noise, and a realistic disturbance. By looking at the transmissibility and the disturbance response, the system is compared to an existing solution. Compared to the existing solution, the transmissibility is lowered by at minimum 13 dB in the frequency range of interest. The transmitted disturbance is lowered roughly 20 times with roughly 6.6 times bigger required control effort. ... Read more

The high-tech industry is constantly searching for methods to make more efficient, more accurate, and faster machines. One of the methods to improve the performance of these machines is active vibration control(AVC) which can help to achieve faster transient responses. One of the ways to achieve this is better controllability which means more actuators to control more modes. These actuators are mostly Piezo transducers in AVC and each group of actuators needs a high voltage amplifier. At some point, the number of amplifiers will be limited by factors such as volume or mass, so if the group of actuators can share an amplifier, that would be beneficial. This can be achieved with time-division multiplexing(TDM). This method in combination with AVC is researched in this thesis. The most important aspects are performance comparison to conventional systems without multiplexing. First, some simulations are done, to show that the TDM is a feasible solution, secondly, a setup is built to check performance and validate the simulations. ... Read more

To improve Active Vibration control methods like Independent Modal Space Control (IMSC), an estimate of the modal contribution of vibrational eigenmodes of compliant structures is required. In this work, three Recursive Bayesian input and state estimation algorithms previously introduced in civil engineering are evaluated for use on on high-tech compliant mechanisms to estimate modal contributions for use in Active Vibration Control. The difference in environment when applying these algorithms from civil engineering into high-tech compliant motion stages allows for a significantly different sensor configuration possibly improving estimation performance.

The three algorithms, namely, the Augmented Kalman Filter (AKF), Dual Kalman Filter (DKF) and Gilijns de Moor Filter (GDF) are implemented in simulation and on an experimental compliant motion stage setup. The modal contributions of the guidance flexures are estimated through a noisy acceleration measurement at the stage and strain measurement at the flexure base.

For validation, the filters are evaluated on overall fit quality and system acceleration dependency through the quality of estimation of the flexure tip location. The DKF is shown worst performance with lowest fit scores overall and high acceleration dependency while the AKF and GDF perform comparably well. The GDF is shown to transmit less noise into the estimate however, and thus performed overall best. ... Read more

The demand for faster production times and higher precisions in the industrial automation is ever-increasing. Resonance modes caused by flexural elements in these machines are limiting the maximum bandwidth. Because of this, high-precision motion systems in industrial machines are limited in the maximum operating speed and precision. To improve the performance of these machines, an active vibration control (AVC) system is needed. In present scientific literature, all AVC systems consist of an under-actuated or perfect-actuated setup. However, the damping performance of these systems could be increased by implementing an over-actuated setup. In an over-actuated setup, multiple actuators are used to control one resonance mode. In this way, control inputs for suppressing modes are provided at more efficient locations, which increases the amount of damping. In this thesis, an over-actuation and over-sensing strategy for active damping is proposed. In this new method, a large number of piezoelectric sensors and actuators are used to control the first four vibration modes of a cantilever beam. The damping performance is evaluated in an experimental setup. Finally, the performance of the new topology of sensors and actuators is compared to the state-of-the-art active damping method that uses a perfect-actuation strategy. The improvement of the new method compared to the state-of-the-art method is shown both in time and frequency domain. ... Read more

The pursuit of faster and more precise mechatronic systems necessitates the use of inventive mechanical designs and advanced control schemes. In recent years, flexible elements have seen increased use as they enable the development of high-precision motion systems in a wide variety of applications ranging from semiconductor fabrication to precision surgery. Although these flexures provide ample benefits for systems that require lightweight elements and predictable behavior, structural vibrations can restrict their effectiveness in achieving precise positioning. This motivates the need for vibration suppression in motion systems, particularly those with flexible components. To that end, smart structures with embedded transducers and a suitable control algorithm can be used to actively damp the underlying structure’s resonance modes, although time-varying parameters and uncertainties from various sources can degrade the performance of the vibration controller. In this thesis, an adaptive control scheme is developed to maintain the desired damping performance regardless of system variations. The method employs adaptive notch filters in a cascade arrangement to track multiple modal frequencies of a smart flexible structure, then tunes a positive position feedback controller for multimodal damping with a straightforward adjustment rule. The adaptation is shown to be fast, accurate, and efficient, with clear advantages in suppressing the vibrations of time-varying and uncertain systems. The method also provides key features absent from other adaptive damping implementations, including the ability to effectively estimate modal frequencies using brief transient signals typical of damped structures, as well as signals buried in noise. Finally, the adaptive scheme is validated experimentally with a flexible beam, showcasing its strong potential for practical applications. ... Read more

As the age of digitization evolves rapidly, there is an ever-increasing demand for improving precision and decreasing production times for industrial automation in general, and semiconductor manufacturing in particular. As these complex machines incorporate flexure-based elements to overcome friction and backlash, structural vibrations pose a new challenge. Hence, the need for controlling and quickly damping these vibrations are paramount. In this thesis, a novel reset-based bandpass filter that employs velocity feedback to achieve finite-time vibration suppression for damped systems is introduced. The development of this filter stems from an energy based mechanistic approach, providing a clear understanding of the underlying mechanism for the improved transient response, which also motivates the use of reset. Systematic tuning rules based on describing functions are also developed to enable design in the frequency-domain, thereby increasing its relevance for industries. Finally, the effectiveness of the Resetting Velocity Feedback framework for improved transient damping is demonstrated experimentally on a single degree-of-freedom flexure stage. The results are compared to a linear bandpass filter and validates the advantages of reset control for achieving better transient damping compared to linear control. ... Read more