To create an X-ray Interferometry test bed a high precision adjustable slit mechanism is needed. Com pliant mechanisms are ideal solutions for such high precision mechanisms. This research presents the design, manufacturing, and testing of such a compliant mechanism. Furthermore, topology optimization is explored and evaluated as an alternative design method to find a novel mechanism that performs better than a traditionally synthesized counterpart. A traditionally designed mechanism was first designed and characterized using a 405 nm laser source and Fraunhofer diffraction analysis. Although optical verification was limited to a minimum slit width of 3 μm, experimental results demonstrate that the traditionally developed design has the potential to achieve dimensional requirements, with demonstrated step sizes of 0.2 μm. Simultaneously, a topology optimization model was developed, implementing penalized strain energy, parasitic displacement, and decoupling constraints, along with a robust formulation, to generate an alternative multi-degree-of-freedom mechanism. Although topology optimization proved a tool capable of producing an alternative compliant mechanism, there is still work to be done to fully mature this synthesis method. The research concludes that the developed mechanism meets the requirements set for the X-ray Interferometry test bed, whilst the topology optimization proves a viable alternative, albeit complex, method for future high-performance iterations. ... Read more

Through exploiting origami-inspired folding principles, flat sheet metal can be transformed into three-dimensional structures that combine lightweight design, geometric rigidity, and cost-effective manufacturing. Stiffness to the design is added through modifying the cross-section of a structure through folding instead of thickness variations. Plastic deformation and residual stresses are a result of folding metal. These folded so-called creaselines, influence the structure's stiffness and fatigue performance. The impact of these influences is yet unknown. Therefore, this study investigates two geometric parameters and their influence on the endurance limit of the sample. Through computational modelling and experimental testing, this study aims to establish design guidelines for this manufacturing approach. The computational model produces a numerical study demonstrating the impact of the two parameters, which is then validated through a straingauge experiment. Furthermore, two geometries are subjected to three million cyclical loads to identify the dominant failure mechanisms. The results demonstrate that the folded sheet metal flexures can sustain stress amplitudes exceeding the manufacturer-specified endurance limit. This indicates that folding does not reduce the fatigue performance. The failures mostly occur along the fillet, while the result of the influence of the creaseline distances remains limited and inconclusive. To conclude, the study demonstrates the possibilities of this alternative manufacturing approach for compliant mechanisms. Furthermore, the validated numerical analysis provides a foundation for future work aimed at establishing robust design rules for folded sheet metal flexures. ... Read more

This thesis presents a piezoelectric energy-harvesting push-button that applies stiffness compensation to reduce input work and improve mechanical-to-electrical efficiency. The design combines a compliant compressive force amplifier with two negative-stiffness flexure shuttles mounted in parallel at the input.

An analytical model and finite element (FE) simulation were developed to predict the performance of a machined and 3D-printed prototype. The results show good agreement in trends between the models and experiments. The force amplifier achieves an amplification factor of approximately 9 with an input stiffness of 29 N/mm, while adding the negative-stiffness mechanisms reduces the effective stiffness to about 21.5 N/mm. Under equal mechanical input, the harvested electrical energy doubles from roughly 0.11 mJ to 0.22 mJ, demonstrating the effectiveness of stiffness compensation.

These findings confirm that integrating negative stiffness can enhance the efficiency of piezoelectric energy harvesters. Although the prototype is not yet at normal button dimensions, the principle is scalable and shows potential for compact, self-powered devices such as switches and sensors. ... Read more

Mechanical vibrations can reduce the performance of precision systems, motivating the development of adaptable vibration isolation solutions. This thesis investigates a beam-node metamaterial, designed to exhibit quasi-zero-stiffness behavior through geometric nonlinearity. A simplified two-dimensional model consisting of horizontal, vertical, and diagonal slender beams is optimized using a genetic algorithm to address discrete design variables and nonlinear structural response. The optimized design is manufactured and experimentally evaluated through static compression and dynamic vibration tests. Numerical simulations are compared with experimental results to assess the predictive accuracy of the model. The results show that the simplified beam-node model captures the key static behavior of a single unit cell. While deviations occur for small metamaterials due to boundary effects and material-related phenomena. Furthermore, deviations in the dynamic behavior of small metamaterials are identified, and the source of this behavior is explained through additional testing. This study shows that a simple beam-node metamaterial combined with an efficient optimization strategy is a viable approach for vibration isolation solutions, laying the foundation for its experimental realization. ... Read more

Wearable devices capable of perturbing and measuring wrist orientation during daily activities are essential, as traditional measurement systems are often restricted to controlled environments and limit natural movement. A compact and lightweight 4-RUU parallel manipulator mounted on the wrist can generate ungrounded forces in three translational degrees of freedom, while keeping the hand and arm unobstructed. The inverse kinematics of this mechanism is analytically derived, enabling control with an open-loop feedforward system for the four servo motors for precise perturbations.A simulation of the concept parallel manipulator is used to optimize the main dimensions of the device for the intended application. A prototype is then constructed and evaluated, both for its ability to generate forces using a force sensor and for its ability to measure real-time orientation using an inertial and magnetic measurement unit with an implemented Madgwick filter. The force measurements showed that along every axis and combination of axes, a certain repeatable force generation profile can be distinguished, where a minimal peak of 5.0N is generated. The lack of end-effector acceleration, due to limiting servo performance, resulted in a loss of forces in the mechanism lie between 14–50 %. The orientation estimation is fast and accurate in real time with a maximum total angle error of 5°. ... Read more

This paper introduces a fully compliant spherical joint with an optimized stiffness profile specifically for balancing a pendulum. The design builds on previous work that has successfully created a fully compliant spherical joint using tetrahedron-shaped elements connected in series. To efficiently compute and optimize the balancing behaviour of these compliant joints, a novel algorithm is developed and presented. Using this algorithm, optimizations are conducted to obtain simulated pendulum balancers under five different conditions. The performances of these results are analysed to assess the potential and limitations of the algorithm and these spherical joints. Based on one of the optimized results, a prototype is fabricated and expermentally validated, achieving a moment reduction of 90.5%. The deformation calculated by the TetraFEM tool closely matches the prototype’s deformation with an accuracy of 89.6%, demonstrating its potential for application in the development of shoulder exoskeletons. ... Read more

In the semiconductor and photovoltaic industries, contactless positioning systems are increasingly employed to handle ultra-thin wafers, minimizing the risk of mechanical damage. A suitable and integrated sensor system would make this handling method more attractive in future applications. This Msc. thesis explores a novel concept in planar position measurement for flat, reflective objects using fiber optic sensors distributed across a measurement plane. This sensor configuration creates light profiles via transmitting fibers and utilizes the reflected light detected by receiving fibers to localize the object's position.
A Gaussian-distributed intensity pattern is first applied to the light profiles to validate this concept, establishing the theoretical relationship between brightness and planar positions. A prototype with a single set of fibers is then constructed to verify the proposed brightness model and determine the optimal, sparsest fiber spacing that maintains adequate resolution. In the next phase, algorithms are developed using simulated sensor arrays to calculate planar degrees of freedom based on the actual positions and brightness values from receiving fibers near the object's boundary. These algorithms are then implemented in a fabricated sensor array prototype, forming a complete distributed fiber optic sensor system.
The sensor's performance is evaluated using samples with varying center positions and orientations, resulting in an average error of less than 1 mm in the in-plane directions. In conclusion, the proposed sensor configuration limits planar position errors to sub-millimeter accuracy. The measurement range is significantly extended, and the sensor element no longer needs to be attached to the measured object. As a result, this system offers promising potential for contactless planar positioning of thin, fragile products with specular surfaces. ... Read more

An earlier study introduced a formula for determining the holding force of a toroidal hydrostat gripper when gripping an object of constant radius, considering a linear stress/strain relationship. However, beyond the holding force, understanding the grasping disturbance force exerted on the object due to the rolling behavior during grip adjustment is crucial to ensure the objects are not damaged or displaced, and are successfully picked up. This study aims to extend the existing model by incorporating the disturbance force for objects with variable radii and using a non-linear stress/strain relationship for the membrane material.
A parametric model was developed to estimate these forces as a function of its geometric and material properties. The model was validated through experimental testing and refined using a tuning parameter obtained via optimization algorithms to address parameter uncertainties.
The model approximated the holding forces well, with a maximum deviation of 15\% at the maximum swallow distance. It overestimated the peak disturbance forces by a factor of 2.5. But when normalized, the force curves showed good resemblance.
Surprisingly, the obtained tuning parameter reached a high value of $1.45$. as the parameter uncertainties are thought to be less than 20%. This overestimation could be the result of an additional vacuum force, as evidenced by a clear difference in holding force and gripper behavior is observed in pulling tests for objects with smooth and rough surfaces. ... Read more

Path generation mechanisms are those mechanisms that produce a predetermined path. Such mechanisms are prevalent in daily life, and many devices depend on path generation mechanisms or are derived from path generation mechanisms. One might think of examples such as vehicle suspension, film advance mechanisms or sewing machines. These are generally made with rigid body mechanics, such as linkages. However these rigid body mechanisms suffer from effects such as friction, play and wear. These problems are well known to be solved using compliant mechanisms. But, some path generation such as that necessary for a film advance mechanism can currently not be made using a fully compliant system. This is because full-cycle motion is necessary to produce the path that is generated by such mechanisms, and compliant mechanisms fundamentally are not able of producing full-cycle motion.
This thesis presents the synthesis of a compliant mechanism that is able to translate reversible reciprocating motion to a history dependent path that describes an area. This process is detailed in three separate texts. The first text is set up as a paper, and outlines the generated academic contribution. The second text is the design report, herein the full design and modelling process is described. The third text is the literature review in which the gap in research is detailed. ... Read more

Dynamic balancing can offer significant benefits to applications where moving parts are present. It aims to reduce the reaction forces and moments due to inertia of the parts, thereby reducing vibrations. Dynamic balancing receives significant academic interest for planar and spatial applications, but limited attention for spherical mechanisms. This leads to the following goal of this thesis: Present novel force balanced spherical mechanisms design using inherent balancing planar pantograph theory for use in micro precision applications.

To achieve this goal, the thesis has been divided into three sub goals. First is defining the qualitative benefit of dynamic balancing for applications requiring micro-precision. This qualitative analysis looked into six different 'high speed precise' applications with motion and determined a potentially significant benefit exists for applications such as (space) telescopes, space manipulation, additive manufacturing, motions stages and beam steering. Engines and drives require new balancing methods to achieve significant benefit. However, the analysis also showed that many different aspects other then inertia also influence precision, thereby potentially reducing the gained benefit in precision. This is due to the addition of extra components or mass in most common dynamic balancing methods.

The second goal presents five new shaking force balanced spherical mechanisms using inherent balancing theory. Here the planar knowledge of inherently balanced shapes such as the pantograph as well as the use of projections are used to design three novel types of balanced spherical pantographs, namely the spherical pantograph, double spherical pantograph and the double S shaped mechanism with surrounding 4R four-bar linkage. Also, two additional variations of the spherical pantograph and the double spherical pantograph are presented, which leads to a total of five new designs. Each design has its required constraints and available design freedom described. Also, the balance conditions for the double spherical pantograph are presented.

The last goal shows ten novel force balanced remote center mechanisms, using the three types of inherently balanced spherical pantographs. These remote center mechanisms are either using a swivel joint or are a combination of spherical pantographs to form a parallel manipulator. This allows all end effectors to show spherical movement, around a fixed Center of Rotation. The pros and cons as well as feasible variations and constraints are also discussed.
To show the use case of a force balanced remote center mechanism, a realistic design has been made for a beam steering application, where a mirror can perform a tip/tilt movement around a shared center of rotation. The mechanism uses three scaled shifted double spherical pantographs as legs to form a parallel manipulator, with a mirrored surfaced attached to the end effector and positioned in the center of rotation. ... Read more

Neutrally stable metamaterials can maintain differ- ent shapes without any energy input, making it a key innovation in the quest for more energy-efficient technologies. Despite this intriguing property, the research in this area is scarce. This study proposes a method for achieving neutral stability in metama- terials. This method is validated with a novel unit cell design that utilizing two identical beam elements that are mirrored. Each element displays a constant force characteristic. By pre- tensioning these elements, we align their constant force regions, thereby inducing a state of neutral stability. Through finite element method (FEM) simulations and geometrical optimisation, the beam of this design is optimised to achieve the optimal constant force response. A prototype is made and a test setup is constructed to validate the accuracy of the simulations and the feasibility of the method for achieving neutral stability. Results indicate that while perfect neutral stability was not fully achieved, this method can be applied on other constant force mechanisms to create neutrally stable metamaterials. ... Read more

Drones are increasingly used nowadays, primarily for visual inspection tasks facilitated by onboard cameras. The field of aerial manipulation tries to expand the capabilities of drones by attaching a manipulator, enabling physical interaction. Unfortunately, the usability of aerial manipulators is hindered by disturbances resulting from the movements of the manipulator. These disturbances, including reaction forces and a shifting centre of mass, not only affect manipulation accuracy but also pose safety risks by potentially destabilizing the drone. In this thesis, a design is presented that addresses this challenge by leveraging the theory of dynamic balance.
A new design approach of making a manipulator fly, instead of the common approach of mounting a manipulator arm to a drone was used. This new approach avoids interference with the drone's components, allowing to focus on the design of the manipulator arm. Furthermore, it made it possible to create a manipulator which can manipulate above, to the side and underneath itself. This makes the presented manipulator arm more versatile than common aerial manipulators whose workspace is mostly located only above or below the drone. The kinematics, workspace and balance conditions of the manipulator arm are presented. Furthermore, the design's workspace is optimised while the mass of the manipulator is minimized in a bilevel optimisation. Finally, the design is validated both by simulation and measurements performed with the built prototype.
The design presented is the first inherently fully dynamically balanced manipulator with omnidirectional workspace which can be used for aerial manipulation.
... Read more

Compliant mechanisms, particularly helicoidal shell joints, present intriguing possibilities in mechanical design with applications in medical devices, robotics, automotive, and aerospace engineering. This research focuses on the synthesis of nonlinear torque-angle profiles using a compliant helicoidal shell mechanism such as gravity-balancing profiles. This study required a thorough exploration of the mechanism’s diverse design variations through Finite Element Modeling (FEM) and more specifically, Isogeometric Analysis (IGA). Subsequently, a targeted optimization process is utilized, incorporating both global geometric parameter adjustments and localized modifications by using splines. The prominent challenge addressed is the synthesis of gravity balancing torque-angle profile, achieved by tailoring the output profile of a compliant shell mechanism through optimization. Considering the inherent sine function output of a pendulum during gravitational equilibrium, an algorithm is developed to optimize the mechanism’s behavior to align with a sine function, hence enabling gravity balancing. Additionally, experimental validation was undertaken through manufacturing prototypes and conducting measurements to provide a crucial link between simulations and real-world behavior. The results of this research, encompassing optimized geometry and experimental data, are presented, and comprehensively discussed. This research contributes a numerical methodology that utilizes isogeometric analysis and optimization algorithm within the framework of finite element analysis for achieving nonlinear torque-angle profiles in complaint helicoidal shell mechanisms, such as gravity balancing profiles, offering valuable insights for possible applications in various engineering domains. ... Read more

Auxetic metamaterials offer various novel abilities, one of the abilities is to deform into a dome-shape under out-of-plane deformation. Contrary to a material with a positive Poisson's ratio, which deforms into a saddle-shape. A dome-shape is named synclastic deformation and a saddle-shape is named anticlastic deformation. Under out-of-plane deformation, the magnitude and sign of the Poisson's ratio influence the curvature of the material, and hence the final shape. Starting from a flat plane, manipulation of the Poisson's ratio can create various unusual shapes, such as an egg or a wave-shape. A desired shape might require a uniform Poisson's ratio or a varying Poisson's ratio distribution. Most of the current estimations on the relation between an auxetic material and the deformation shape are performed experimentally. This paper presents an analytical approach which shows the influence of a varying Poisson's ratio on the out-of-plane deformation of a material under pure bending conditions. Four Poisson's ratio distributions are applied which follow the formulas: S-curve, parabolic and cosine in one and two directions. The same model is build in the FEM software COMSOL which serves as the reference model. Comparison of the COMSOL model shows a Mean Absolute Percentage Error between 0.30% and 11.93% for the analytical model. Remarkably, the accuracy of the analytical model is high if a Poisson's ratio distribution varies in one direction, resulting in a Mean Absolute Percentage Error lower than one percent point. A limitation of the analytical model is that the Mean Absolute Percentage Error increases to 0.69% till 11.93% when the Poisson's ratio varies in two directions. The presented analytical approach provides a first step in determining a varying Poisson's ratio distribution that can deform into any desired shape. The resulting shapes are synclastic and combinations of synclastic and anticlastic. ... Read more

This work aims to achieve a softening moment-angle response by utilizing compliant parts. The approach uses the principle of contact release, which involves initially prestressed torsional bars arranged in series, separated by rigid bodies. By stepwise activation of the torsional bars, a softening behavior is achieved. Mechanical stops are employed to maintain the initial prestress.
A Pseudo Rigid Body Model (PRBM) is developed to calculate the moment-angle behavior of the complete prototype. The optimization of the PRBM is performed using a cost function based on the least square error. The optimization parameters are the stiffness of the torsional bars and their initial prestress. Additionally, a Finite Element Analysis (FEA) is conducted to analyze the behavior of an individual I-profile torsional bar. Experimental validation of both the PRBM and the FEA models is carried out using a prototype. The prototype is constructed based on the results obtained from the PRBM optimization to follow the desired graph closely. The results from both FEA and PRBM align closely with the predicted curves, confirming the effectiveness of the proposed approach. ... Read more

A growing energy demand has sparked interest into harvesting energy from the human body. Often, a rotational proof mass is used to harness energy for a wearable from kinetic motion of its user. The addition of a spring has the potential to significantly increase efficiency for these low-power rotational energy harvesters. In this research a system characterisation is performed from which a dimensionless ratio is formulated to determine optimal spring stiffness for maximisation of average power output as a function of harvester design parameters and excitation inputs. Creating a system that is optimized for the entirety of its operational range rather than for one specific excitation input. Implementation is investigated in the field of horology, where rotational energy harvesters are widely implemented. To increase harvesting efficiency of existing rotational energy harvesters without requiring significant design alterations a compliant design is proposed, prototyped and tested. ... Read more

Compliant mechanisms are a popular alternative to conventional mechanisms because of their advantages on mass reduction, friction, backlash and lubrication. However, the major drawback in the use of compliant mechanisms is the stiffness is the desired direction of motion. The advantages of conventional and compliant mechanisms can be combined if the stiffness can be reduced or ideally removed, resulting in a zero-stiffness compliant mechanism. In current designs of zero-stiffness mechanisms, a preload is applied in the stiffest (compression) direction of a flexible beam. This working principle is based on Euler buckling. In this work, compliant mechanisms with zero-stiffness behaviour are obtained using lateral torsional buckling as their working principle. For this purpose, two compliant joints are modelled in a FEA, a translational and a rotational joint. The results of the FEA are verified by experiments. Also, a sensitivity analysis is performed on the cross-sectional dimensions of the flexible beams to optimize the range of zero-stiffness. Both types of joints showed zero-stiffness behaviour for the optimal preload and a good agreement is found between simulations and experiments. From the sensitivity analysis is found that a rectangular cross-section results in the largest range of zero-stiffness. ... Read more

The use of origami-based mechanisms in the engineering field is growing as their advantages are better understood. Origami-based mechanisms have the advantage of being lightweight, compact, and their ability to transform from a flat sheet into complex three-dimensional structures makes them a source of inspiration to meet design challenges. A fold in paper is realized by a localized reduction in thickness, which reduces stiffness. Since most materials do not exhibit this property when folded, other techniques are used to facilitate this stiffness reduction. These include sandwiching a thinner material between rigid facets, or by thinning to create a groove joint (notch joint). The drawbacks of these techniques are that the first technique requires assembly, and the second technique requires complex material removal. Another technique has been proposed to reduce stiffness with simpler manufacturing methods, namely lamina emergent joints. These joints require cutting through the material, which can be done using well-established sheet manufacturing methods, such as laser cutting or stamping. However, the removal of material involves a trade-off between range of motion and stiffness in directions other than the desired bending motion. Initial research indicates that the groove joint is able to maintain the highest stiffness and range of motion, thus outperforming the lamina emergent joint. Therefore, the objective of this paper is to design an improved lamina emergent joint that approaches the performance of the groove joint. This is achieved by quantifying and evaluating the stiffness performance and range of motion of existing lamina emergent joints and then combining them on strong features. Improved designs are proposed that made an approach toward the groove joint and the best design was selected for optimization. The results showed that the selected design was not able to outperform the groove joint on both stiffness and range of motion. However, it was able to achieve similar in-plane shear stiffness and higher torsion stiffness than a groove joint with a lower thickness ratio. However, this also allowed more range of motion for the groove joint. So figuring out this trade-off between stiffness and range of motion is challenging and essential to design suitable joints in the future. ... Read more

The exploration of compliant mechanisms, especially those providing linear motion, has become a central focus in recent engineering research. These mechanisms, characterized by their monolithic bodies and reduced component interactions, present an attractive alternative to traditional rigid mechanisms, having reduced friction, decreased energy losses, and cost efficiencies. Despite these advantages, designing and analyzing compliant mechanisms remain difficult tasks, with particular challenges arising when aiming for large-range linear motion with high support stiffness and minimal parasitic displacement. This study presents a unique design: the combination of a flexure-based linear guide with the features of a bistable compliant switch mechanism. Because a combination of these mechanisms has not been looked into while still offering a long stroke, high support stiffness and minimal parasitic motion. Through Finite Element Analysis (FEA) and subsequent iterations, an optimized model was conceived, prioritizing stiffness and minimizing undesired motions. This optimized design was turned into a 3D printed prototype. The experiments with the prototype confirmed the results of our computational insights, showcasing the parasitic motion of the prototype to be within 1mm, and its minimum stiffness at least being 10kN/m while still having a stroke of 70mm. A case study has been set up, of which the proof of concept works and is validated. ... Read more