A method is developed and validated to reconstruct the full-length longitudinal residual-stress field in railway rails from measurements on a short, partially relaxed specimen. The approach represents the stress on the rail cross-section using a set of admissible (self-equilibrated) basis functions, generated from out-of-plane bending mode shapes of a thin-plate model of the cross-section. Stress relaxation due to specimen extraction is simulated for each basis function, enabling the measured relaxed field to be decomposed and mapped back to the corresponding initial field. Numerical tests and contour-method measurements on a used rail show that the method can recover the main features of the pre-extraction stress state and capture the dominant large-scale relaxation behavior, while remaining reasonably robust to smaller-scale measurement artefacts. The framework is intended to make residual-stress assessment more practical when only short specimens can be extracted, and it is expected to transfer to other continuously processed components. ... Read more

Until recently, multi-stable mechanical metamaterials have been primarily used in passive energy absorption systems. However, the ability to actively program these structures has gained significant interest, expanding their functionality to enable on-demand adaptive deformation. While existing active programming methods effectively induce global state transitions, localized actuation remains largely unexplored. This study introduces a novel approach to actively programming multi-stable metamaterials via local thermal stiffness modulation at boundary conditions. Using a polymer bi-material design with distinct glass transition temperatures between the beam and boundary supports, the system can transition from a bi-stable to a mono-stable state, enabling controlled snap-back behaviour after deformation. An analytical model is developed to characterize the snap-through behaviour of the unit cell, providing insight into the geometric interactions and sensitivities associated with various design parameters. Experimental implementation, using multiple additive manufacturing techniques, revealed key limitations and design considerations. In particular, the importance of constraining the second buckling mode and careful material selection emerged as fundamental design requirements for ensuring functionality. This work contributes to the growing field of actively programmable mechanical metamaterials, with implications for compact motion systems in future work. ... Read more

This thesis presents the design and control of the TActile Soft Quadruped (TASQ), a pneumatically actuated soft robot equipped with integrated tactile sensing for adaptive locomotion. Two core contributions are introduced. First, a novel tactile suction cup sensor is developed, capable of simultaneously providing foot contact information and generating suction-based adhesion. The sensor combines embedded magnets and magnetometers to estimate ground reaction forces via a learned calibration model, enabling lightweight, compliant, and robust tactile feedback essential for closed-loop control in soft robotics. Second, a learning-based control framework is proposed that integrates behavior cloning with domain-randomized reinforcement learning to achieve adaptive and robust locomotion. The approach first imitates a reference gait to initialize a stable walking policy and then refines it in simulation using the Soft Actor–Critic algorithm. The learned policy exploits proprioceptive and tactile feedback to enable goal-directed, stable motion and transfers effectively from simulation to real hardware. Experimental validation demonstrates that the learned closed-loop controller outperforms open-loop control on the physical robot, improving forward speed by 41\% on flat terrain and by 91\% on a $2.5^{\circ}$ incline. Ablation studies further confirm the importance of tactile and inertial feedback for stability and performance. Overall, this work establishes a unified sensing and learning framework for a soft legged robot, paving the way toward adaptive, environment-aware locomotion without reliance on vision. ... Read more

Inspecting large-scale infrastructure on-site often poses significant risks to operators and incurs high insurance costs. Despite the implementation of various safety measures to prevent accidents, the increasing need to monitor difficult-to-access areas has led to the development of aerial robots capable of interacting with their environment. This paper presents a novel approach to aerial manipulation, featuring a compact passively actuated manipulator designed specifically for the placement and retrieval of magnetic sensors. The proposed design incorporates two-stage (placed and retrieved) static balancing, a simplistic passively actuated Pick&Place mechanism, and a modular structure for payload variations. Experimental results demonstrate the high reliability achieved in both placement and retrieval tasks on vertical surfaces showcasing the robustness and potential of this compact, custom aerial design. ... 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

Meta-materials provide many possibilities with their specially tailored properties on the macro level caused by their micro level structure in the form of unit cells. These unit cells often take the form of Compliant Mechanisms (CM), which have been widely researched. CM are often made neutrally stable to improve their energy efficiency, making it plausible that meta-materials can be made neutrally stable as well. This research aims to create such a neutrally stable meta-material using constant force (zero-stiffness) unit cells. This was achieved by optimizing the geometry of coiled spatially curved shell structures such that their buckling mode under compression facilitated a constant force region under compression. Simulations of the optimized structures within a meta-material lattice are compared to experimental tests performed on 2 different prototypes of such a meta-material. The experimental results show that the force-displacement curves indeed have a constant force trend line under compression. However, the magnitude of the trend line for one experiment is significantly lower than expected in the simulations. Despite this magnitude difference, the shapes of the experimental force-displacement curves are similar to the curves of the simulations. Small regions of neutral stability are observed for the deformed unit cells of the meta-material, but sawtooth-like behaviour of the force-displacement curves around the trend line caused these regions to be small and unstable. ... Read more

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. ... Read more

In the field of mechanical metamaterials, unconventional physical properties are realized by changing the geometric structure of a unit cell. A metamaterial is composed of numerous unit cells. Researchers have taken it a step further by making a reprogrammable unit cell. A reprogrammable metamaterial has additional elements or mechanisms in the unit cells that allow their properties to be modified. The state of the unit cell corresponds to a physical property. Switching this state requires an external stimulus. Each unit cell in the metamaterial requires an external stimulus to realise a distinctive state. To decrease the number of external stimuli for a tessellated structure, a unit cell is required that switches state depending on stored information. The focus of this thesis is to design a state switching mechanism for a single unit cell. Recently developed state dependent switching mechanisms consist of parallel distributed compliant beams connected in the centre. An off-centre actuation of a single beam requires less input force than a beam actuated in the centre. There is no model that can be used to develop a state switching mechanism with the ability to change the position of the connecting element. The connecting element must be flexible to allow for rotation. Therefore, in this thesis a Pseudo-Rigid-Body Model (PRBM) of a single input switching mechanism is developed that includes the off-centre connection to perform an analysis of the key parameters. The model consists of lumped beams to have a clear deformation path. The model is developed in MATLAB and validated with a finite element model (FEM). Additionally, a 3D printed prototype is made and experimentally validated to compare with the PRBM and FEM simulation. This model enables the ability to understand the effect of the flexible connecting segment and the decrease in force magnitude to actuate the system. The geometrical advantage can be tuned through preload and the ratio between the rigid beam segments. The developed model is a powerful tool that can be used to validate the functionality of any set of parameters of a coupled beam contact-based state switching mechanism. ... Read more

This paper presents a validation of a parametric compliance matrix of a circularly curved leaf flexure (CCLF), which has been obtained using the direct method. This is done for three case studies. In case study one, the compliance matrix of a single flexure is evaluated. The results are compared with the results from a finite element analysis over a range of geometrical parameters. This maps how the geometry of the flexure affects the accuracy of the compliance matrix. It is shown that an increase of both the sweep angle and the height of the flexure show a decrease in the accuracy. Additionally a test setup was built to measure the stiffness of a single flexure to validate the compliance matrix. Furthermore, in case study two and three, the compliance matrices of mechanisms containing multiple flexures in series and parallel are derived with the compliance matrix method, using adjoint transformation matrices. The results are validated by comparison with FEA and measurements from a test setup. A parallel combination of flexures show a decrease in error, when compared to a single flexure. ... Read more

Building a distributed fluidic actuation system is a challenge due to every actuator needs its own control valve. Due to this, an n by an array of actuators needs n 2 number of valves. A logic network of valves provides a solution by reducing the number of valves needed to operate such distributed fluidic actuation system. These compliant fluidic networks could have a broad application in different fields such as biomedical, microfluidics, or in soft robotics. An example in the biomedical field is for creating an actuated surface that is controlled by a fluidic logic that goes around a hollow organ. This sleeve could provide support to the organ by externally providing actuation. The main goal of the paper is to design a compliant valve that easily could be integrated into a large fluidic logic network, to demonstrate the network a demultiplexer is built. Compliant is defined as soft material (small E modules) with hyperplastic properties. To get a better understanding of what is already done in the field of distributed actuation systems a literature study is conducted. The thesis will provide information on the design steps of creating a valve and how to integrate them in a fluidic network that is a demultiplexer. The operating principle of this valve is that there are 2 channels on top of each other on a 90-degree angle, one channel will be inflated and will choke the other channel. Different valve designs based on this principle have been built and tested using different shapes and combinations of materials. Using FEM software the closing pressure is calculated. After that prototypes have been built and experiments are conducted. During experiments, the pressure drop has been measured in the channel that will be closed. The next step is to understand how these valves operate in a large network. A Simulink model of a demultiplexer has been built, it was shown that 2.4 seconds to inflate an array of 8 small bellow actuators with a stroke of 5 mm. After simulating a demultiplexer is created. Experimental results show that the best-performing valve completely closes a line with a pressure of 12 kPa with an operating pressure of 26 kPa. As a demonstrator of a large-scale network a demultiplexer is built, unfortunately, it did not perform due to manufacturing problems. To answer the main question of this paper a fully functioning logic network has not yet been achieved however, it could be said that this paper has laid a good foundation for further improvement of the creation of a scalable solution for an actuating surface. It also has to be noted that the valve designs that are discussed in this paper operate on an mm scale instead of an cm-scale which is commonly found in the literature. ... Read more

Duchenne Muscular Dystrophy (DMD) patients suffer from a severe form of progressive muscular weakness. Consequently, as the disease progresses these patients become more and more dependent on assistive devices for their daily activities. For instance lifting their arms against gravity already becomes challenging. So far, a considerable amount of effort has been put in the development of assistive devices. However, compensating the weight of the hand remains challenging as the required balancing torques are dependent on the position of the hand and the orientation of the forearm.

In this research a solution is proposed to passively compensate the weight of the hand by making use of a simplified torque profile (a constant torque). The effectiveness of this profile was assessed experimentally in a group of healthy subjects. For this the wrist muscle activity required to lift the hand against gravity was measured through surface electromyography, for several types of compensation. From this experiment the conclusion can be drawn that a constant torque profile performs similar to the theoretically ideal type of balancing, showing a similar reduction in the anti-gravity muscle activity.

Based on these findings, a mechanism has been developed capable of providing an adjustable constant force, by making use of a combination of positive and negative stiffness springs, for implementation in a wrist support for DMD patients.
... Read more

The Netherlands has a severe shortage of care workers. The shortage is expected to increase in the coming years. Care-robots could provide a solution, by taking work out of the hands of the care workers. The potential utility of the care-robot is dependent on the functionality of the gripper. The goal of this study was to design and develop a new gripper for a care-robot, applicable in a care environment. Furthermore, the functional performance of the gripper was to be assessed and evaluated. The new gripper needed to outperform the previous gripper of the robot, named the RPG, in terms of functionality. A new gripper was designed in this study, named the 4FH. The 4FH has four fingers, resembling a human thumb, index, middle and ring finger. Sideways rotation of the thumb allows for two grasping modes, namely a pinch mode and a power grip mode. The 4FH has three DOFs in total. A glove is fitted around the gripper for hygiene. An improvement was made to the 4FH by modifying the shape of the thumb. The improved version is named the 4FH-i. A set of three assessments was drawn up for measuring functional performance of a gripper for a care-robot. The set consists of the the EIT, modified SHAP and modified AHAP. The SHAP and AHAP were modified in this study to make them representative for applications of a care-robot. Both the 4FH and 4FH-i outperformed the RPG on the modified SHAP and on the modified AHAP. All grippers passed the EIT. The results showed a significant increase in grasp stability, comparing the 4FH and 4FH-i to the RPG. The higher scores on the assessments indicated that the 4FH and 4FH-i have improved functional performance compared to the RPG. ... Read more

Vibration energy harvesting has proven to be a durable source of energy for a wide variety of applications, however not all of the positions these applications are placed at are suitable for conventional vibration energy harvesting. For some of these applications a frequency up-converted energy harvester could increase the power harvested. These systems are analysed in this thesis project, by first gaining insight in previously performed. After which a new method is designed and modelled. The design was then fabricated and a proof of concept was tested, of which the results are presented in this thesis project report.

... Read more

Compliant joints have significant advantages compared to rigid-body hinges due to a monolithic design and the absence of friction, which prevents effects like wear, backlash and stick-slip behaviour. However, the loading capability is often limited and the support stiffness generally decreases during rotation, caused by the use of solid leaf flexures. Previously, a new design principle called closed form pressure balancing was introduced, which uses an incompressible fluid as the main compliant element in the joint. Although it showed great potential in terms of stiffness performance, theoretically not much is known about this design principle. This thesis analyses the fundamental working principle of closed form pressure balancing and introduces a design model to analyse the characteristic behaviour and to provide a practical design tool. This design model has been validated with a finite element method model, which shows a quantitative agreement. Additionally, a solution for the limited shear stiffness characteristic for pressure balanced joints is proposed. The potential of this solution is shown with the use of a case study on the design of compliant piston-slipper mechanisms, for which a prototype has been designed, built and tested. ... Read more

The detachment of a product from a suction cup gripper is a challenge that emerged in recent years in the high-speed case packing of packaged food. In this industry suction cups are used to temporarily attach a product to a case packing robot. The detachment of products from the suction cup gripper threatens throughput. In, some cases, the industry notes robots to operate at only 40 picks per minute. This is 30 % of their maximum throughput.
This study aims to gain a better understanding of the dynamic grasping strength
of suction cups. This was done by reviewing the state-of-the-art from industry and state-of-the-practice from literature. It was found that suction cups are the best overall gripper class, and that actuation time poses the main limiting factor for other grippers to perform well in this industry.
Secondly, a six-axis force moment sensor that passes airflow for gripper actuation and without limiting the pull-out load measurement performance was designed, fabricated, and validated. With the current sensor technology, the vacuum hose must be placed over the sensor, leading to the generation of parasitic loads. Passing the airflow through the senor structure is essential to eliminate loads otherwise induced by the stiff vacuum hose. The sensor was designed using strain gauges and a Maltese cross sensor structure. Finite Element Modeling and optimization using sequential quadratic programming was used to determine the dimensions of the sensor. The sensor validation showed a maximum measurement error of 8% in the z direction.
Lastly, with the validated sensor, the dynamic grasping strength of compliant and stiff suction cups was measured using motion paths and products that are typically seen in the packaged food industry. For both the stiff and compliant suction cups, the moment around the axis perpendicular to the plane of motion showed to be a leading factor in detachment of a product from a suction cup gripper. The failure of stiff suction cups is explained by impulse loading, this results in peaks in the load in the force in horizontal direction and the moment perpendicular to the plane of motion. For the compliant suction cups, the detachment was found to be caused by accelerating downwards while the product was not in the center of the gripper. These results have led to the recommendation of two gripper designs. The first, is a suction cup-underactuated hybrid gripper. The second design intently provides rotation freedom to reduce the moment loading on the suction cup. The second design
requires input-shaping to reduce the vibrations at the end of the motion cycle.
... Read more