Auxetic metamaterials are engineered structures commonly characterised by their negative Poisson’s ratio, which indicates transverse expansion when the structure is stretched axially. However, Poisson’s ratio becomes increasingly difficult to apply and interpret for non-cubic unit cells with higher-order symmetry or complex geometries. This limitation contributes to the strong focus on cubic unit cells in current research, despite their limited robustness due to a restricted number of symmetry axes. This study proposes volumetric strain as an alternative and geometry-independent measure of auxeticity. The approach is demonstrated through a case study on non-cubic polygon-prism unit cells generated by in-plane copy rotation. The mechanical behaviour of 2-, 4-, 6-, and 8-fold configurations is analysed using an analytical rigid-body replacement model, finite element simulations, and experimental testing. A Hoberman ring is introduced as an intermediary mechanism to enable uniform multi-directional actuation using a one-dimensional tensile tester. The results show that volumetric strain provides a consistent and robust description of auxetic behaviour across all configurations and modelling approaches. In contrast, Poisson’s ratio exhibits strong sensitivity to small deviations near zero strain and leads to inconsistencies between analytical, numerical, and experimental results. The experimental force–displacement response confirms a linear scaling with the number of bases, while the volumetric strain remains independent of the initial polygonal shape of the unit cell. These findings demonstrate that volumetric strain is a reliable measure of auxeticity for non-cubic unit cells and offers clear advantages for the analysis and experimental validation of complex auxetic geometries. The proposed framework provides a foundation for extending auxetic metamaterial design towards more intricate structures, including spatially copy-rotated unit cells and honeycombs based on Archimedean solids.

This dissertation explores the development and evaluation of mechanical grippers with flexure-driven eversion mechanism fingers, designed to address the challenges of grasping objects in confined spaces—a common issue in the agri-food and food processing industry that hinders robotic automation. Conventional mechanical grippers face significant difficulties in dense environments, such as within piles or plants, as their grasping process relies on positioning fingers around the object performing inward-outward movements from its sides. This approach requires considerable clearance, often obstructed by neighboring obstacles. To overcome this challenge, this research introduces in Chapter 1 a novel grasping approach in which the gripper fingers move tangentially along the surface of the object, utilized as flexure-driven eversion mechanisms, to set or release the grasp while reducing environmental disturbances. This approach significantly reduces the required space, as well as unwanted displacements and forces in the surroundings, and leverages environmental interactions to aid finger navigation.

The main objective is to develop and evaluate flexure-driven eversion mechanism fingers for mechanical grippers, aimed at grasping food in confined spaces, as presented in Chapter 1. The finger design incorporates a curved flexure as the structural backbone, which navigates along the object’s surface—displacing adjacent obstacles if necessary—and securely holds it once enclosed. The flexure is combined with the principles of eversion mechanisms to reduce friction forces during operation by ensuring zero relative speed differences with the environment.

This thesis is divided into two parts. The first part, presented in Chapter 2, investigates the applicability of flexures within the proposed finger concept by analyzing their ability to navigate predictably through multiple obstacles when driven from the base. A case study was conducted, modeling the kinematics and kinetics of a straight base-driven flexure, which bends and moves through two consecutive circular obstacles when pushed forward, using a pseudo-rigid-body modeling (PRBM) approach. This analysis required an extension of existing PRBM techniques, enabling the analysis of flexures in event-based scenarios (e.g., abrupt load changes) and with multiple loads at unknown locations along their length. This was achieved by systematically switching and stitching PRBM-topologies while maintaining the system’s potential energy within reasonable bounds. Experimental validation confirmed the compatibility of base-driven flexures with the proposed finger concept, demonstrating their ability to navigate through obstacles in a predictable manner, with both trajectory and interaction forces modeled with high accuracy for design purposes.

In the second part of this thesis, two finger designs were developed and manufactured as prototype grippers, which were experimentally validated based on defined performance criteria. Chapter 3 presents a preliminary gripper design with three fingers, each implemented as a Dual-Belt Curved-Flexure Eversion Mechanism (DBCF-EM)—a single curved base-driven flexure, with its inner and outer contours covered by two everting (outwardly unrolling) belts guided through rollers. Chapter 4 presents an evolved gripper design featuring Sleeved Concentric-Flexure Eversion Mechanisms (SCF-EM) as fingers—a base-driven channeled backbone comprising two concentric curved flexures, fully enclosed along its circumference by a latex sleeve with engineered stretchability, which everts from the channel. The design is completed by a cable-pulley system that synchronizes both movements.

The results showed that both grippers operated as intended, following the object’s surface and navigating adjacent obstacles, and successfully validated the proposed grasping method, enabling form-closed grasps of densely packed objects. Practical tests involving integration into a robotic set-up tasked with emptying a crate of tomatoes, one at a time, demonstrated an exceptionally high grasp success rate, previously unobserved. While the gripper with DBCF-EM fingers occasionally encountered issues such as mis-grasps, object damage, and hygiene concerns due to its open structure, the gripper with SCF-EM fingers achieved a 100% success rate in picking and placing tomatoes without damaging them or the surroundings. Additionally, the SCF-EM fingers offered improved hygiene compliance, durability, and robustness due to the enclosed eversion sleeve creating a barrier and a reduction in the number of mechanical components. Technical tests of both designs measured relatively low disturbance forces and sufficient holding forces. Comparative studies showed that the integration of the eversion mechanism reduced friction forces by around 90%, reducing both damage and mis-grasps.

In general, these findings demonstrate the effectiveness of the proposed finger designs for grasping objects in confined spaces and their suitability to gently and securely handle fragile agri-food products while accommodating natural variations, although additional engineering, testing, and refinement are required to ensure industrial readiness. Ultimately, the most important outcome is that this dissertation introduces flexure-driven eversion mechanisms for the first time and convincingly demonstrates their exceptional potential for navigation in complex and confined environments. This breakthrough constitutes the central scientific contribution of this work, arising from the need for alternative gripper methods for grasping tasks in tight spaces. This contribution provides a solid foundation for further applications in domains such as medical devices, search-and-rescue robotics, and inspection systems for hard-to-reach environments.

This dissertation presents theory and methods to predict, measure, and steer the film height in soft elastohydrodynamic lubrication. It specifically focuses on the application of roll-to-plate nanoimprinting, addressing the challenges of current roller-based imprint systems to achieve uniform film heights on large-area, non-flat substrates. The research is structured in three parts, which directly correspond to the goals of film height prediction, film height measurement, and film height steering. In the first part, numerical models are developed and experimentally validated to describe the soft elastohydrodynamic lubrication in roll-to-plate nanoimprinting. The second part presents a refined analytical model and the experimental validation of the ratiometric fluorescence film height measurement method. Lastly, the third part proposes a novel concept to steer the film height in soft elastohydrodynamic lubrication, inspired by inverse lubrication theory. Overall, the developed theory and methods on film height prediction, measurement, and steering form a solid basis for future research and facilitate practical implementation to further improve the film height uniformity in soft elastohydrodynamic lubrication processes.

The research presented in this dissertation shows experimentally and numerically how magnetorheological fluids could be used as lubricant in hydrodynamic journal bearings to improve film thickness at low shaft speeds, and friction at high shaft speeds.

Trendelenburg gait is an abnormal gait pattern caused by failure of the hip abduction mechanism. Under the external adduction moment caused by the body weight, this results in excessive adduction characterized by a drop of the pelvis on the contralateral side. Existing assistive devices are inadequate for this condition. Therefore, this thesis aimed to develop a hip orthosis that uses a compliant mechanism to correct Trendelenburg gait. Compared to traditional mechanisms, compliant mechanisms offer several advantages in orthotic applications, including compactness, low mass, adaptability to misalignment, and adjustable levels of support. However, despite these benefits being recognized, research on practical implementation remains limited.

The design process distinguished between the attachment parts and the mechanism of the orthosis. For the attachment parts, the goal was to evaluate whether the established orthotic methods and materials are suitable for this application. A preliminary design confirmed their suitability. For the mechanism, the goal was to develop an innovative compliant solution by either advancing previous work or introducing a new concept. The latter showed more potential for flexion stiffness minimization, as well as a lightweight and compact design and was therefore selected for further development.

Two mechanism design variations were developed: one using a conventional leaf flexure and one using a leaf flexure incorporating warping constraints. As anticipated, warping constraints enabled further reduction of the flexion stiffness. The hip flexion moment required to achieve a 30° flexion angle was 7.9 Nm in the design using a conventional leaf flexure, and 0.55 Nm in the design using a leaf flexure incorporating warping constraints. This result indicates the potential of warping constraints for broader implementation in compliant mechanisms to improve the ratio between lateral and bending stiffness in leaf flexures at large deflections. The main tradeoff for this improvement was increased mass, from 0.36 kg to 0.98 kg. Both designs provided sufficient adduction stiffness to constrain adduction under the adduction moment applied by the body weight, and are therefore effective in correcting Trendelenburg gait.

The resulting overall orthosis design is a promising solution, providing the foundation for future research to validate its technical and clinical performance and development into a usable product.

Mechanical metamaterials (MMs) are artificial structures that derive unique mechanical properties from their geometry rather than composition. Traditional continuum models often fail to capture the full complexity of these architected materials, especially when micro-rotational effects are significant. This thesis presents an experimental validation of the decoupled micropolar elastic constants of a planar chiral mechanical metamaterial unit cell. A novel, assumption-free experimental framework is developed to isolate and measure all components of the decoupled micropolar elasticity (DME) tensor, without relying on symmetry constraints or reduced formulations. The method is applied to a specific unit cell geometry, yielding a complete elastic tensor that is compared against analytical models and symmetry-based predictions. Results show agreement along diagonal components but reveal discrepancies in off-diagonal coupling terms, suggesting physical couplings exist that are presently often assumed negligible. The findings highlight the importance of higher-order continuum theories in capturing the true mechanical response of MMs, especially for applications in compact motion systems. The approach offers a foundation for future extensions to three-dimensional geometries and supports the development of inverse design strategies using micropolar elasticity as a predictive tool.

Determining the ripeness of fruits is a major point of interest for the fruit industry, since this dictates harvest time, storage conditions and edibility. However, the current state of the art method, which is the penetrometer, performs destructive measurements on the fruits. Recently, ripeness-estimating grippers are being developed to overcome this destructiveness. However, the extra tactile sensors used to achieve this increase complexity, costs and susceptibility to wear. Therefore, in this paper, a gripper is designed that can determine the grasped object's stiffness without using additional force or pressure sensors, but instead estimates force from actuator calibration data, position sensor readings and the control signal. The gripper is designed to be affordable and simple to fabricate to facilitate potential commercial use in the end. To achieve this, a compliant linear guide is designed with on each of the two ends a gripper finger. The mechanism is printed as a single part on an FDM 3D-printer out of PETG, which facilitates the ease of fabrication. The chosen actuator is a solenoid actuator and a Time of Flight (ToF) distance sensor is chosen for position recording. To enable the device to measure object stiffness, calibration of the actuator and the mechanism's intrinsic stiffness is performed. To test the mechanism's performance, calibrated metal compressive springs with a known stiffness are used as test object for the gripper. The stiffness value that was estimated by the gripper is then compared to the known stiffness calibration value. The measured stiffness values differ by 1.0%-8.0% from the calibrated spring stiffness values, which on the low error value side compared to general stiffness estimation methods. This implicates that the gripper works satisfactory in terms of stiffness estimation accuracy. Therefore, it can be stated that the main objective of this project is achieved, while also keeping the device low-cost and simple to manufacture.

Designing suspension systems for military terrain vehicles presents challenges due to conflicting performance requirements and demanding operational environments. This work applies a Systems Engineering V-Model approach to the tolerance-based redesign of a military terrain vehicle suspension. The project is part of the development of a new vehicle platform based on an existing prototype. The project begins with a literature review that compares suspension architectures based on key performance criteria, such as ride quality, wheel travel, ground clearance, and reliability. Based on this literature review, stakeholder needs, and user requirements, a double wishbone suspension is selected as the most suitable architecture for the new vehicle platform. To verify design requirements, a tolerance analysis is conducted to evaluate the effect of manufacturing tolerances on suspension angles, specifically camber and caster. A Python-based Kinematic model is developed to determine the effect of tolerances on the location of the suspension hardpoints. DynaTune-XL is used to simulate the suspension angles during wheel travel. The analysis shows that tolerances can be relaxed without exceeding predefined limits. Based on these insights, a redesign of the lower wishbone is made, focusing on manufacturability. The resulting redesign features a simplified geometry with a new shock absorber interface, optimized for production through sand casting followed by finishing machining. Material and process selection is done using Ansys Granta Edupack. The redesigned wishbone is verified through structural analysis using Altair SimSolid. The project demonstrates how the V-Model, commonly applied in aerospace and software development, can also effectively guide the development of suspension systems in the automotive/defense sector. In this work, the V-Model ensured full traceability from stakeholder needs and user requirements to verification, which helped translate high-level requirements into specific, verifiable suspension requirements. The introduced tolerance analysis method provided quantifiable insight into how dimensional variation in components led to variation in suspension angles during wheel travel. This demonstrated that the tolerances of the outer ball joints of the wishbones could be relaxed without exceeding predefined limits. The resulting lower wishbone redesign lays the foundation for transitioning from prototype to series production.

Vibrations deteriorate the performance of machines and instruments, especially when high precision and efficiency are required. Multiple approaches for vibration mitigation exist, mostly constituting separate bodies of research. This thesis establishes a connection between the active vibration control practice, advances in other control fields, and metamaterials research. To this end, three research gaps are addressed.

First, in Chapter 2, the design requirements of active vibration control are expressed in the frequency domain, using the loop-shaping approach commonly used in motion control. The use of the proposed approach is shown in the experimental evaluation of a vibration isolation system based on piezoelectric stack actuators.

Second, the loop-shaping approach is related to the design for bandgap in active metastructures. Chapter 3 adopts a modal analysis approach for finite metamaterial beams, relating the underlying control problem to the active damping of a single-degree-of-freedom system by assuming an infinite number of infinitesimally small transducer pairs distributed along a beam. This allows the application of design methods developed in the preceding chapter. The experiments demonstrate that controllers initially developed for damping resonance peaks can effectively induce bandgaps, even in structures featuring a small number of sparsely placed transducer pairs. Chapter 4 studies when the obtained models and approximations are accurate, highlighting the correlation between the minimal number of transducers required for model accuracy and the dominant vibration mode within the controller's targeted frequency range.

Third, the frequency-domain approach is applied for the design of fractional order and reset controllers for vibration mitigation to relax the limitations imposed using low-order linear controllers. In Chapter 5, a design for a fractional-order resonant element tailored for AVC, which preserves the characteristics of its integer-order counterpart but provides greater design freedom, is presented and evaluated in a simplified vibration isolation system. In Chapter 6, the same element is implemented within a unit cell of a granular metamaterial. For such a fractional-order metamaterial, both the dispersion characteristics of the infinite structure and the transmissibility of a finite chain are presented.

The use of nonlinear elements, like reset systems, poses additional challenges in vibration control. Since an exact frequency-domain representation of such elements does not exist, their behaviour is approximated using the describing functions. While this enables the loop-shaping design, the describing function approximation does not represent the system well in the presence of wide-band excitations and multiple resonance peaks in the plant. Chapter 7 explores how such conditions influence the reset elements and how to ensure that the use of reset is still beneficial. Additionally, assessing the stability of a reset system solely based on controller dynamics and experimentally measured plant frequency response is an open problem. To address this, the Negative Imaginary systems approach for stability analysis, originally developed for AVC of flexible systems with uncertain dynamics, is extended to reset systems in Chapter 8.

This dissertation focuses on the frequency response analysis and design of Linear Time- Invariant systems (LTI) reset feedback control systems for precision motion applications. In the precision motion industry, there is a growing demand for control systems that deliver higher positioning resolution, faster response, and enhanced stability. However, inherent limitations in linear controllers, such as the “waterbed effect” and the Bode phase gain trade-off, limit their performance, posing challenges in meeting these evolving requirements.

Reset feedback control has emerged as an effective solution to address the limitations of linear control systems in precision motion applications. The practical implementation of control strategies relies on reliable analysis methods. Among these, frequency response analysis stands out as an effective and widely utilized method across industries. However, existing frequency response analysis methods for both open-loop and closed-loop reset control systems face challenges, including accuracy limitations and restrictions to specific control system structures. The first category of contributions in this dissertation addresses these challenges by introducing frequency response analysis methods for open-loop and closed-loop Single-Input and Single-Output (SISO) LTI reset control systems within a generalized control system structure. Moreover, to further realize the potential of reset control, the second category of contributions focuses on proposing novel reset control designs to enhance system performance. The content is organized into nine chapters…

In mass-produced precision machinery, achieving high accuracy while minimizing costs is essential. The Ball Screw and Linear Guide (BSLG) mechanism, provides a large translation at a low cost but faces challenges in accuracy, particularly in terms of repeatability and virtual play. This study addresses these challenges by integrating a flexure system designed to eliminate overconstraints in the BSLG mechanism to improve its accuracy. Additionally, we explore cost-effective manufacturing processes for producing the flexure system without compromising its performance. A model was developed to calculate the virtual play of a BSLG mechanism, which was validated through measurements on an X-stage BSLG mechanism. The integration of the flexure system resulted in a 55% reduction in virtual play (from 3961nm to 1790nm) and 52% reduction in unidirectional repeatability (from 909nm to 441nm). Importantly, alternative manufacturing processes, despite introducing stiffness variations, had a negligible impact on the overall performance, enabling cost reduction without sacrificing accuracy. This study demonstrates the effectiveness of using flexure systems to remove overconstraints and enhance precision. Given the widespread application of the BSLG mechanism, the flexure system designed in this article can improve machinery across a wide range of fields.

The analysis presented in this work confirms that optimizing the diameter ratio and wrap angle is crucial for tailoring the auxetic properties of HAYs. A higher diameter ratio enhances the auxetic effect, making the material more responsive to axial strain with sustained lateral expansion. Conversely, a lower wrap angle improves the initial auxetic response but limits the range of strain over which this response is maintained. These insights are critical for designing materials with desired mechanical properties, particularly in applications requiring specific auxetic behavior within a defined range of strain.

Model 3, introduced in this work, generally provides a reasonable approximation of the contact pressure behavior as a function of axial strain, especially at low strains. However, as strain increases, the limitations of Model 3 become apparent due to its simplified assumptions. The discrepancies observed between the theoretical models and simulation results suggest that further refinement or calibration might be needed to improve their accuracy, particularly in predicting the exact magnitude of contact pressure under different loading conditions.

Overall, this work contributes valuable insights into the design of auxetic materials, offering guidelines for optimizing HAYs' performance while minimizing adverse effects like engulfment. Future work should include experimental validation to fully bridge the gap between theory, simulation, and real-world application, ensuring that the theoretical advancements can be reliably applied in practice.

Each year in the Netherlands almost two thousand people are diagnosed with End Stage Kidney Disease, amounting to a total of 7 million people worldwide. With an insufficient amount of donors available, most of these patients are treated using haemodialysis where the blood is filtered with a dialysis machine. Prior to this treatment an arteriovenous fistula (AVF) or arteriovenous graft(AVG) is created to increase their blood flow sufficiently to speed up the filtration process. Another result of increasing the blood flow is the size increase of the vein, leading to easier access. Unfortunately, the continuous high flow rate is linked to various negative effects. To counter these negative effects a Dynamic Arteriovenous System (DAS) or dynamic AVF (dAVF) was developed that can regulate the flow on demand. This allows for the flow to be increased temporarily during dialysis and to return to nominal values outside of dialysis with the ultimate goal of increasing life expectancy. Earlier iterations of the dAVF encountered reliability issues due to the formation of fibrous tissue on critical locations of the implant hindering actuation on the anastomosis. For this project, a compliant implantable dAVF-Valve is developed that minimizes the influence of ingrowth and provides a more robust solution.

This research investigates a novel approach to vibration energy harvesting (VEH) using a statically balanced lever mechanism to compress piezoelectric stacks. Current state-of-the-art VEH methods struggle with scaling and harvesting energy efficiently, this proposed prototype addresses these limitations by utilizing the piezoelectric charge constant more efficiently. A prototype was developed and tested, showing a maximal stiffness reduction of 95% and demonstrating the principle's improvement in increasing power output by at most a factor of 116. A model is introduced to predict power output from the response and to estimate the generated power of an unbalanced mechanism. The scalability and improved performance highlight the potential of this approach for future VEH applications.

This paper presents the development and analysis of a quadruped robot prototype designed to achieve statically stable rear leg standing. Existing quadruped robots such as Mini Cheetah and Go2 are versatile, but rely on dynamic movement to remain stable. We present a robot prototype that can transition from quadrupedal to an upright stance while remaining statically stable throughout using a tail. This Tail-assisted Transition Robot (further: TT-Bot) utilizes electric actuators and combines aluminum and 3D printed nylon components to form a lightweight yet robust structure. It aims for a functional approach through strategic motor placement and a belt-pulley system for knee joint actuation. Kinematic analyses guide the control strategies implemented to manage the transition. Initial results from simulations and physical tests indicate that TT-bot can effectively maintain an upright stance under controlled conditions. Stability tests indicate successful static stability across slopes from −10◦ to 5 ◦ . A payload test showed that it was able to transition with a payload of 3 kg. Challenges during transition remain with steeper inclines and higher payloads.

This study focuses on enhancing the performance and reliability of piezoelectric bistable vibration energy harvesters. The research systematically classifies and evaluates different design strategies, aiming to maximize power density through strategic stress manipulation. Five designs are selected for optimization using a finite element model and are evaluated based on a proposed performance metric. The study introduces a method for effectively placing piezoelectric material to enhance power density. Experimental validation shows significant performance improvements, with the best design demonstrating a 71% increase in performance over conventional designs. The findings underscore the importance of addressing performance and durability in developing practical energy harvesters.

In this study, a promising design for a compact, ultra-linear Compliant Torsion Reinforced Sarrus mechanism (CORS), capable of achieving ultra-linear motion is presented. The CORS prototype, made entirely of aluminum, is produced monolithically using electric discharge machining (EDM). The design incorporates four torsion-reinforced folded leaf springs, effectively reducing parasitic motion and enhancing support stiffness. To meet the specified requirements, a design optimization process is undertaken, carefully considering constraints to attain an optimal CORS configuration. Integration of the CORS with a voice coil actuator for driving force and confocal chromatic sensors for detecting parasitic motion is carried out. Experimental results demonstrate and validate the performance of the CORS.

This thesis presents the state-of-the art gripping literature and the implementation and extension of an existing Pseudo-Rigid Body Modelling (PRBM) method for modelling initially-curved compliant grippers out of which a circular object is extracted. From the existing literature, challenges are found in the design and evaluation of concepts of initially-curved compliant grippers, mainly involving the relevant design parameters, such as the thickness and enclosing angle of the finger.

The main goal of this thesis is therefore to present and validate the pull-out force modelling for these fingers within defined load conditions to provide comprehensive insights into the relation between important design parameters, such as the enclosing angle and thickness of the finger.

This goal is accomplished by extending an existing 3R PRB-model for initially-curved beams with a fifth link that represents the object and analysing the kinematics and kinetics to determine the relation for the pull-out force of a gripper finger with defined dimensions and a known load case.

This model is validated by designing and building an experimental test setup in which the reaction forces of a initially-curved testpiece of PLA and stainless steel material are measured. Errors for the kinetics between 12 and 32 percent were determined, consisting primarily of systematic errors.

The validated model is used for a parametric study, where relations between relevant design parameters, such as the enclosing angle and thickness of an initially-curved compliant gripper finger, are determined and visualized in a design chart that are be applied in the design of an initially-curved enclosing gripper prototype.

In mechanical systems, energy efficiency is often reduced by unwanted forces like friction and backlash, which significantly impact performance and, over time, lead to increased wear and maintenance costs. Implementing compliant joints can address these issues, simplifying assembly and improving performance. However, compliant mechanisms introduce higher internal loads due to elastic deformation in the flexures, limiting the range of motion and affecting overall efficiency. One way to solve this is using the principle of static balancing, which ensures that a point of interest remains in equilibrium, meaning that no added forces or moments are needed to keep it at rest at certain positions. This can be done by compensating the internal potential energy, which has been implemented in literature for 1 Degree of Freedom configurations. The goal of this paper was to expand the known method into designing a multi-degree of freedom without the use of external springs. The method was based on applying a preload to the compliant joints in the mechanism and optimize in such a way to create a constant potential energy curve. The model was validated using finite element analysis, prototyping and physical testing. It can be concluded that for the first time, a two degree of freedom statically balanced mechanism has been designed. It has a peak force reduction of $95\%$ and a moment reduction of $80\%$, while having a range of motion worth $50\%$ of the size of the mechanism. The mechanism can be used in vibration isolators or as fundamental inspiration for new applications where preloading could lead to lower exerted loads and thus improve efficiency.