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.

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.

The precision and intricacy behind mechanical watches has long captivated horologists and is driven by centuries of innovations. Mechanical watch complications such as chronographs, can further increase mechanical complexity and present challenges due to the reliance on numerous rigid components requiring precise movements. These movements can result in wear, friction, and reliability issues building up over use. Compliant mechanisms offer a promising solution by utilising material flexibility to enable motion with minimal wear, backlash, and a reduced part count. These advantages however come with challenges, such as a more complex integrated design process, limited mobility, and fatigue considerations.

This thesis therefore presents the design, modelling and evaluation of a compliant bi-state switching mechanism designed for fabrication from a silicon wafer and integrated with the horizontal clutch and braking system sub-components of mechanical chronographs. The functional requirements of the chronograph sub-functions include reliable switching between the engaged and braking states, secure gear engagement with minimal misalignment during the engaged state, and precise timekeeping through minimal brake timing delay and slippage of the chronograph seconds hand during the braked state. The design is modelled and validated using both an analytical pseudo-rigid body model and a numerical finite element model. A scaled PETG-based proof-of-concept was then fabricated to verify the performance.

The PETG proof-of-concept demonstrator experimentally showed a robust switching success rate of 99.8\%, stops the seconds hand within 2.4 $ms$, and prevents slippage up to a 2.5g loading case meeting the functional requirement. The gear engagement functional requirement however was not fully meet with a success rate of 95\%. The underlying cause of this issue was identified and recommendations for redesign were provided. Additionally, the simulation model results indicate that the design offers a durable performance with von Mises stress levels within desired limits of under 300 $MPa$. Future works for this design include to develop a functional one-to-one silicon wafer prototype and integrate the mechanisms with additional chronograph sub-functions, such as the minute counter and reset mechanism.

This thesis provides two key contributions. First, it introduces a novel bi-state compliant switching mechanism based on a latch-lock design. This design hold potential applications in MEMS devices, mechanical logic designs, and robotics and is capable of scaling with minimal modifications or impact on performance. Second, as silicon wafer fabrication was desired, a practical methodology was developed to translate the silicon wafer requirements and expected behaviour from the experimental PETG results and scaled demonstrations.

Metamaterials are tessellated structures that introduce unique properties to motion system applications. The research on behaviour changes caused by this tessellation remains limited. This paper outlines the change in behaviour from a compliant unit cell to a metamaterial motion system, regarding linear stiffness, range of motion (RoM) and crosstalk. These properties are achieved through the analysis of series and parallel configurations, as well as scaling variations. The concept of an ideal shear cell is presented, describing desired motion system characteristics. Roberts mechanism approximates the ideal shear cell, bringing embodiment for finite element analysis and experimental validation. Results indicate that parallel configurations increase stiffness, while series arrangements reduce it, with RoM and crosstalk displaying opposing trends. Additionally, variations in flexure thickness introduce a trade-off between stiffness and range of motion. Different scaling strategies affect overall stiffness with minimal impact on RoM and crosstalk. While the main findings do not indicate inherent performance benefits to compliant mechanisms. This research contributes valuable insights into the design and performance of metamaterial-based motion systems, providing a foundational framework for future studies and applications.

In this master thesis, the development of an innovative gripper specifically designed for grasping the delicate peduncles of vine tomato trusses is presented. This research addresses a critical challenge in agricultural automation: efficiently and safely manipulating high-value crops without causing damage. The thesis begins with a comprehensive review of the current state of agricultural automation, particularly focusing on the post-harvest handling of vine tomatoes.
Building on identified limitations in existing robotic grippers and automated systems, a novel gripper design is proposed. This design uniquely approaches grasping the peduncle of vine tomato trusses. Traditionally, trusses have been grasped by the peduncle with standard pinching grippers for pick and place operations. The proposed gripper in this paper grasps the truss with a hook around the peduncle, often optimally at the centre of mass, increasing the success rate of grasping, stability, and avoiding damage to the truss. Furthermore, it has a higher tolerance for detection errors, allowing for inaccurate positioning of the robotic system. A hook-gripper can successfully grasp a wider range of tomato varieties than a pinch gripper.
The hook, consisting of two fingers, allows for more stable lifting of the truss and can handle peduncles in hard-to-grasp positions, such as in a crate filled with tomatoes. In addition to increased reach capabilities, the hook-gripper also enables manipulations like dragging and pushing.
The study involved an iterative design process, prototyping, and rigorous testing of the gripper. Key features include a hook mechanism for secure grasping, enhanced mobility for reaching into cramped spaces like packed crates, and a delicate touch to prevent bruising or damaging the fruit. The research also integrates the gripper with advanced detection systems for precise and effective operation within automated setups.
Results from extensive testing demonstrate that the newly designed gripper not only improves the success rate of grasping and manipulating vine tomato trusses but also significantly reduces the risk of damage compared to conventional pinch grippers. Individual trusses can be grasped with great success.
Testing for the different positions showed an increased range of grasping position that resulted in a successful grip. In practical experiments, the gripper performed well, lifting trusses with ease. Other test results show that the position of the peduncle is of great importance for the success rate. Test results indicated an 80% success rate in grasping trusses positioned near the edges of the crate. Replaying waypoint with "learning from demonstration" improves the grasping of the trusses compared to existing detection possibilities, and that emptying a crate is a challenging task.
The specialized hook-gripper offers insights into a practical solution for picking and placing vine tomatoes using the peduncle. This thesis contributes to the field of agricultural robotics and facilitates a step towards future innovations in the automation of high-value crop handling. The study delves into hook-gripper design and actuation, crucial for optimal performance in robotic manipulation systems.

This study proposes a novel design of monolithic compliant variable torsional stiffness (VTS) mechanism whose stiffness can be tuned continuously. This mechanism is then used to create a compliant variable stiffness (VS) ball joint. This compliant VS ball joint can be beneficial in various applications such as exoskeletons, prostheses, and bio-mimicking due to their high adaptability to environmental changes and the capability for multitasking.

Individuals suffering from neuromuscular conditions, such as Duchenne muscular dystrophy (DMD), experience a progressive weakening of muscles. During the progression, the affected patients require supporting devices like orthoses or exoskeletons to perform their daily activities. Although immense efforts are put into the development of exoskeletons, due to the challenge involved in balancing the weight on the hand, where the torque at the wrist changes with the position of the hand, there are limited wrist support devices available. Existing solutions either rely on rigid body mechanisms or active power sources, which come with drawbacks like bulkiness and discomfort. This research introduces an innovative approach to passively counterbalance hand weight using a simplified torque profile for a single degree of freedom in hand movement, namely flexion and extension. By employing parametric optimization, a compliant mechanism has been developed that can compensate for the weight of the hand against gravity. The resultant compliant mechanism design is compact, lightweight, and safe, rendering it an optimal choice for supporting the wrist’s degrees of freedom and for the application of the device. Through the experimental validation of the model, the results are interpreted as the mechanism’s usefulness in wrist flexion and extension support. In short, this study underscores the utility of employing compliant mechanisms in wrist support orthoses, particularly for individuals with neuromuscular conditions like DMD.