Shoulder exoskeleton is a popular solution to work-related shoulder disorders and muscle fatigue. With a wide range of exoskeletons designed, a comprehensive report on how the use of shoulder exoskeletons changes shoulder biomechanics is still missing. In this project, the impact of exoskeletons on shoulder biomechanics was investigated with the musculoskeletal simulation OpenSim. This study proposed a "human-in-the-loop" optimization-based design tool for shoulder exoskeletons. This design tool incorporates the predicted biomechanical effects of a shoulder exoskeleton from musculoskeletal simulations into design considerations. This design tool was validated with a case study designing a shoulder exoskeleton based on a compliant beam and testing the design in the musculoskeletal simulation and experiments. The exoskeleton design tool is a coupling of finite element analysis and OpenSim. OpenSim calculates the deformation of the exoskeleton with human motion, and the finite element analysis calculates the force exerted from the exoskeleton upon deformation. Then OpenSim computes muscle activities under the external force from the exoskeleton. By merging muscle activities and the resultant glenohumeral joint reaction force to an objective function, the optimization-based design loop is closed by looking for the best objective value iteratively. Several exoskeletons were designed by the new design tool to assist different types of tasks. The design tool exhibited good ability in finding optimal solutions for a range of design choices and design requirements. Simulated tests of designed exoskeletons showed significant effects on reducing muscle activities and good robustness in resisting the influence of perturbed motions in arm-elevated tasks. An exoskeleton was selected to be tested with an experiment set up in the same way as the simulated test. Experiment results supported the performance of the exoskeleton predicted in the simulated test. This project established a method to comprehensively predict the effect of an exoskeleton on shoulder biomechanics and provided a more comprehensive understanding of biomechanical effects of shoulder exoskeletons. This facilitated the “human-in-the-loop” design process of shoulder exoskeletons which could greatly save money and time investments into prototyping, testing, and validation.

Flexure mechanisms are widely utilized in precision mechanisms, but their practical use is limited by three major factors, namely restricted range of motion, parasitic motion, and significant reduction in support stiffness when deflected. To address this limitation, in this research the potential of variable thickness flexures in minimizing the aforementioned issues is evaluated. Two novel parametrizations are utilized to optimize these variable thickness flexures, which are then compared to their commonly used constant thickness counterparts. Furthermore, initially curved flexures have been found to be promising in optimizing mechanisms with high performance in terms of parasitic motion and stiffness tuning. Three novel designs are proposed and optimized in this research for improved performance. As variable thickness showed promising results, these newly designed mechanisms are further optimized by incorporating variable thickness into the initially curved flexure mechanisms. The outcomes of this study demonstrate a significant enhancement in terms of support stiffness and range of motion without compromising other important factors.

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.

In conventional compressor technology, high pressure ratios are often achieved by multiple, successive compression stages. This is done to avoid high temperatures due to the adiabatic nature of most compression processes which deteriorates the working of oil lubrication. The aim of this work is to reduce a conventional four-stage system to only two stages as this may improve the size and expenses of the system. This goal combined with a long desired lifetime, makes that a compressor is developed that operates based on gas bearing technology. The design is focused on two main subjects. Firstly, the load capacity of the gas bearings is significantly lower than oil lubricated bearings due to the reduced viscosity. To avoid mechanical contact and wear of the components this has been thoroughly analysed using finite element methods. The oscillating nature of the loads in the system enhances the squeeze effect from the Reynolds equation. Secondly, the sealing function of gas bearings opposing internal leakage is evaluated carefully to obtain a desired efficiency. Based on these simulations, the mechanical design of the compressor is optimized to improve the manufacturing of the compressor components.

People in healthcare, warehousing, and the agriculture sector all have one thing in common. They require labour which can be demanding on the human body, this could lead to problems in the long term. A way to alleviate these problems is to use a passive exoskeleton. While passive exoskeletons can have a variety of different use cases and types of support, this thesis will focus on a wearable passive back support. A company specialising in these passive wearable back supports is Laevo. They have their own version of such a mechanism using torsional springs which are attached to the upper torso and legs. This ensures that when bending the mechanism provides support. However when walking, these springs are also activated and make walking more difficult and require more energy. A way to solve this problem is to use a differential mechanism. Such a mechanism can be quite complex and bulky and comprised of a lot of parts. A solution could be found in the world of compliant mechanisms. The goal of this project is to create and analyse a compliant differential mechanism for use in passive exoskeleton design. As a basis for a design, the proposed mechanism by Maurice Valentijn was used. The two main challenges were the location of the rotational axis and a relatively low stiffness ratio between the bending and walking scenario. While this mechanism showed potential as a compliant differential mechanism, it did have some problems which needed to be overcome before the use in a passive exoskeleton would be feasible. The proposed design to solve these challenges consists of a thin-walled beam, with an H-shaped cross section, which has two curves forming a U-shape. By applying constraints on the sides the rotational axis of the mechanism could be changed to align with the rotational axis of the hip joint. This mechanism in combination with reintroduction of potential energy using springs to lower the stiffness of the mechanism when walking. This allowed for a design which could be used as a compliant differential mechanism in the use of exoskeleton design. To investigate the proposed design for a compliant differential mechanism, the mechanism first needs to be modelled and optimised to meet the requirements needed for the use in an exoskeleton. For the optimisation, a framework is proposed which integrates the use of a simulated Ansys model in combination with a Matlab optimisation problem. With this optimised model the behaviour of the mechanism can be analysed. The behaviour of the mechanism is investigated in the paper in Chapter 4. In this paper the simulated model is validated using an experimental setup. This paper is the main contribution of this thesis. Findings of the paper show that the stiffness of the mechanism can be significantly reduced by reintroducing potential energy into the system to compensate the stored potential elastic energy in the material during walking. This caused the mechanism to have different types of behaviour: positive stiffness, zero stiffness, and negative stiffness. These stiffnesses depend on the initial preload of the springs, more initial preload means more energy is stored in the springs and releases more energy for the same displacement. This changes the overall potential energy to have these three aforementioned stiffness states. Zero stiffness is the most interesting for exoskeleton design, this minimises the amount of work required while walking without having bistable behaviour in the mechanism. Finally, As a proof of concept for the mechanism a wearable exoskeleton prototype has been created to get a practical understanding of the mechanism and to find problems with the implementation of the mechanism for future works. The wearable exoskeleton prototype showed a lot of potential, the behaviour of the mechanism in the experimental setup was transferred to the prototype and low stiffness while walking was achieved without effecting the bending support.

Inspired by phenomena in the plant world, a meteoro-sensitive rotational actuator is developed. The design uses a hygro-active shell, whose water-based swelling is restricted at selective locations to form a helicoid structure. The influence of geometrical parameters on the performance is investigated using a numerical analysis of various geometries, by looking at resulting rotation and torque during this rotation. Prototypes are built of five key geometries in the design space, to validate the simulations and to investigate the real-life behaviour of the design. These prototypes are submerged in water to investigate their deformation, after which they are placed in a torsion machine to investigate the torque during rotation. The experiments result in similar rotations and torques as the simulations. The designed Hygromorphic Rotational Actuator is capable of passively rotating its own structure, thereby expanding the possibilities of engineers and designers when designing passive autonomous systems.

Patients with degenerative neuromuscular diseases experience decreasing muscle function, starting from a very young age. While a wheelchair can partially replace the lost use of the legs, many activities needed in daily life require the use of the arms. For these activities patients rely on the help of caregivers. Several devices designed to support the arms of patients with decreased muscle function exist: some use static balancing techniques to reduce the force required to lift the arm, some use actuators to supplement or replace muscle force and some use a combination of both. Most of these devices are bulky and conspicuous, and can be seen as stigmatizing by the patients for whom they are designed. In this project, the combination of pneumatic artificial muscles and compliant shell mechanisms was explored with the goal of designing compact, close-to-body arm supports that can support the arms of patients with little to no muscle function. The design of a single degree of freedom arm support is presented, which supports the weight of the lower arm using a combination of just two soft pneumatic artificial muscles and a compliant shell mechanism, designed using a shape optimization procedure based on isogeometric analysis. In the motion under consideration, the designed device reduces the torque required of the user’s biceps by 96%.

The mechanisms that move plants can serve as biological role models for engineers, designers and architects. This practice is slowly being implemented in various engineering fields, with architects often being pioneers. Various methodologies have been written about the subject, but often only from an architectural point of view. The classification presented in this paper provides a different perspective on the subject. It is structured like a toolbox, containing a clear classification of the technical working principles that plants use to generate motion. With the working principles abstracted, it is no longer necessary to dive deep into the inner workings of plants. The Scopus and Web of Science databases have been systematically searched for compliant plant movements. Plants mainly move by reallocating water, either actively via osmosis or passively via hygroscopic tissue. In compliant plant mechanisms, these basic movement initiators bring about deformations of plant parts. These movements are classified according to their goal: does the plant move quasi-static or dynamic? And does the plant only use a mechanism or does it rely on the gradual storage and fast release of elastic energy as well? Quasi-static movements are often only mechanical and reversible, while dynamic movements rely on energy storage and are often irreversible due to their failure-based release. A bilayer structure in one form or another is present in almost all mechanisms, proving its large adaptability to various circumstances. This adaptability is achieved by the various configurations of the two layers, including fibre-orientation and cellular set-up. Existing bio-inspired devices are classified according to the same system. This enables identification of plant mechanisms that are already suited for implementation and exposes plant movements that are not yet used in the human world. Additionally, a lot could be gained from copying mechanisms on a cellular level rather than on a macroscopic level. Most importantly, a change in mindset needs to happen in order to fully benefit the intricate mechanisms that the plant world has to offer.

Neuromuscular diseases often result in elevated passive joint impedance (PJI), impacting the daily lives of affected individuals. To be able to apply assistive devices that compensate for PJI, it is essential to identify the PJI correctly. This study aims to identify and model the PJI of the elbow joint, to improve the control of force-based controlled active-assistance exoskeleton devices by distinguishing the voluntary from the passive forces. We used an elbow device to measure the PJI in twelve healthy males with the shoulder abducted at a 90˚ angle. The study investigates both static and dynamic conditions, encompassing various contraction velocities (≤ 0.20 rad/s) and shoulder flexion positions (0˚ and ±45˚). The analysis estimates the hysteresis, equilibrium position, and elastic property. Subsequently, based on the average elbow PJI, we developed a regression model, with the statistical analysis revealing no significant differences between the conditions, except for the observed hysteresis under varying velocities. Based on the tested conditions, the findings indicate that a single low-velocity dynamic measurement can serve as the basis for deriving a general elbow PJI regression model.

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.

The bending stiffness of a structure is highly dependent on its shape, and this relation can be utilized to allow for a structure to morph into different shapes during deformation. This paper focuses on shape-morphing into multiple shapes (Multi Shape-Morphing), and presents a design method for a parametric structure consisting of beams, that is able to approximate a set of objective shapes during deformation by exploiting its geometry. Several designs are generated with this design method and experimental validation has been performed on several physical models verify the multi shape-morphing performance. A sensitivity analysis has been conducted on relevant design vari- ables of generated designs to identify their relative importance concerning the structure’s multi shape-morphing performance. To demonstrate the feasibility of the proposed design method for use with exoskeletons, a human-scaled prototype has been designed, and validated.

In the engineering industry, all structural parts have to be designed as efficient and lightweight as possible. Traditionally, the design process has been carried out through manual design iterations, which can be time-consuming and require significant engineering expertise. Over the last decades however, several computational design techniques like Topology Optimization and Generative Design have been developed to support engineers in the structural part design process. Even though these techniques can have a positive influence on the design process, they both also have their downsides. Topology Optimization only gives a single result that is often a local optimum, influenced by boundary conditions and numerical settings. Commercial Generative Design tools explore multiple design options in a single run using AI algorithms, but need cloud-based systems to carry out their demanding simulations which still take several hours per run. It is however expected that a combination of the two, a Topology Optimization based Generative Design approach in the form of an auxiliary tool, has potential to improve the early stages of the design process even more. With such a design approach, multiple design solutions are explored quickly to study the effect of boundary conditions or numerical settings. This can help designers by giving direction and insight in trade-offs between multiple objectives, early on in the design process when design decisions still have the highest impact. The goal for this research was therefore to research the effect of such a Topology Optimization based Generative Design approach on the design performance and experience. In order to do so, a robust and user-friendly TOP-GD tool was created. In this tool, multiple design solutions are explored quickly by implementing a batch-run setup that varies several chosen parameters, without needing to manually run several optimizations consecutively. Calculations are done with a simple TO script using coarse geometries, and without taking into account manufacturing methods yet. This asks for less demanding, detailed and complicated calculations than AI-based Generative Design tools currently offer, while at the same time moving from a single TO result to generating a range of candidate solutions. A lot of effort was put in the user-friendliness of the TOP-GD tool, enabling an easy workflow for the setup of design problems and a clear presentation of the results by means of a simple GUI. The use of the TOP-GD tool in the design process was evaluated in an experiment, where it was compared with a more simple TO tool and a basic manual design approach using just pen and paper. This was done by giving the participants of the experiments three simple design assignments, that they had to carry out using each of the design approaches one by one. Evaluation of the approaches was done by comparing the design performance, and assessing the design experience with a survey and using Eye-tracking techniques. The results of this experiment did not show enough evidence to conclude that the different design approaches had an effect on the design performance for the simple assignments executed during the experiment. However, the results of the survey show a clear positive impact of both the TO tools on the design experience, compared to manually designing. Furthermore, the TOP-GD tool has the largest positive impact on the design experience and its use in the design process is considered a big improvement, especially in quickly exploring new design directions and creating overview. This confirms the expectation that a Topology Optimization based Generative Design approach has a positive effect on the early stages of the design process. The differences found with Eye-tracking between the TO tools support this, although a more extensive experiment should be done to convincingly confirm this conclusion.

Current service and installation activities for offshore wind turbines are carried out by jack-up vessels, which eliminate wave disturbances to a large extent. The use of these vessels imposes several disadvantages, including high operational costs and the limitation of operating in restricted water depths. An alternative is a crane mounted on a floating vessel (monohull), which is quicker in operation and multi-deployable. With these vessels, however, a motion compensator is needed to eliminate most of the hydrodynamic disturbances. The purpose of this graduation assignment is to develop a concept design for a passive motion compensator (PMC) to isolate the vessel motion from the payload. This goal is achieved by the implementation of a multi-objective optimization algorithm based on genetic programming (GP) that constructs a two-dimensional PMC based on the principle of quasi-zero stiffness. The GP employs a set of genetic operators to explore the design space in terms of topology and design variables, which effectively mimics Darwin’s Theory of Evolution. The better a mechanism performs, the higher the fitness, and thus the higher the chance this design appear in future generations. Each design is a composition of cylinders and nodes that are assembled into a mechanism. During the fitness evaluation, all mechanisms are examined by a nonlinear finite element method to extract the force-displacement relations. The arc-length control method is used due to the large displacements and rotations of the members in the mechanism, whereby both the nodal displacement vector and external load vector are varied to follow an equilibrium path in an incremental-iterative way. To provide sufficient support to the payload, the mechanism is prestressed, which is applied by using the arc-length procedure as well. Static and dynamic results show that the GP is suitable for constructing a high-level planar QZS mechanism for the intended application in various sea states. From multiple runs, it can be concluded that the optimizer generally produces designs with the same topology. Dynamic analyses in the time domain show that motions are effectively mitigated in the horizontal and vertical directions for the chosen designs. In addition, analysis in the frequency domain shows that the mechanisms effectively attenuate motions in the frequencies of interest.

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.

This paper presents a manufacturing method for a zero-stiffness compliant mechanism to be used as a flexible head support. The manufactured design consists of two curved, thin-walled U-beams made of high strength steel. The beams are prestressed in opposite directions to obtain zero torsional stiffness so that rotation of the head is allowed. The presented manufacturing method for the beams consists of three different steps; (1)Production of a straight U-beam using a saw mill, (2)Bending the U-beam with a bending tool based on press die forming, (3)Heat treatment to increase the strength of the profile. C75 high strength steel is used for the production of the beams. The straight U-beams with a wall thickness of 0.4 mm were produced within an accuracy of 0.03 mm. The formed U-beams in step 2 approximately follow the desired curve with a maximum lateral error of 1mm which is deemed sufficient for this application. Finally, the beams were strengthened using a standard quenching and tempering heat treatment which increased the yield strength with a factor of 4 up to 1650 MPa. A prototype was made which consists of a 3D printed lower and upper base, as well as two prestressed curved U-beams produced with the presented manufacturing method. The performance of the compliant mechanism design with the produced beams is analysed in terms of the moment-angle curve. Prestressing reduced the maximum moment between -60 and 60 degrees with a factor of about 60 to 0.015 Nm.

Lateral torsional buckling (LTB) of I-beams is an established buckling phenomenon in civil and structural engineering known for causing structural failures. However when a buckling instability is present the structure contains a form of negative stiffness. Due to the observed tendency of I-beams subject to LTB to twist about their longitudinal axis it is suspected that such I-beams contain a form of negative rotational stiffness about their longitudinal axis. Rather than considering LTB as a failure mode for structures, this work aims to investigate the potential of cantilever I-beams subject to LTB having a reduced rotational stiffness about their longitudinal axis with minimal lateral deflection on demand by subjecting the beam to LTB. By minimising the lateral deflection the longitudinal twisting behaviour approaches the behaviour of a compliant rotational joint. The occurrence of negative rotational stiffness in the buckled state is verified and a parameter study is executed to evaluate the stiffness reduction and co-occurring lateral deflection by means of 1-dimensional finite element modelling. Finally an optimisation is performed to obtain a beam with minimal lateral deflection and a significant reduction in longitudinal rotational stiffness. The simulated behaviour is experimentally validated. The simulation and experiment showed that rotational stiffness can be significantly reduced through LTB. Additionally the experiment verified the significant reduction of lateral deflection for the optimised beam. Overall this work forms an initial step towards the use of reduced rotational stiffness of beams by exploiting lateral torsional buckling.

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.

Curved crease origami (CCO) is a newer, interesting field in origami mechanisms. The surfaces on CCO can be bent to initiate folding, thus allowing for the use of planar bending actuation. In this work, the use of more or less of the available actuation surface of CCO is explored. This is done by heating a bilayer material made of paper and polypropylene tape to bend the origami surfaces. The use of more or less of this active material is explored, through measuring the folding displacement of the bilayer CCO metamaterial as a result of heating. Furthermore, the stiffness for folding up the varying origami patterns was measured. Additionally both experiments were modelled in an isogeometric analysis. The work shows that using more of the available surface on CCO for actuation, has a positive effect on the folding displacement. For straight crease origami, this effect is shown to occur when applying the active material in the fold lines. For CCO, the positive effect on the folding displacement is found when applying more active material between the fold lines.

Elastic neutral stability involves elastic deformation without stiffness or loads. It is a remarkable appearance, since the deformation of materials is normally associated with an increase of potential energy and a resulting opposing reaction force or moment. Neutrally stable mechanisms can be used to overcome unnecessary actuation which makes them an interesting topic for the aerospace industry, space exploration and the development of wearable assistive devices. This last group benefits from the use of spatially-curved thin-walled elastic structures, called compliant shell mechanisms. A literature review aims to give an overview of occurrences of elastic neutral stability and aims to find methods for creating neutrally stable compliant shell mechanisms. Single element mechanisms are herein further emphasized and a division between the application of pre-stress and the application of geometrical boundary conditions is proposed. So far, all neutrally stable (shell) mechanisms require either of the two conditions to be imposed. A new type of compliant shell structure, featuring a neutrally stable deformation mode without requiring one of the aforementioned conditions, is presented. The structure is composed of two initially flat compliant facets that are connected via a curved crease. It can be reconfigured into a second zero-energy state without apparent effort via propagation of a transition region. Both the structure’s local width and the local crease curvature turn out to be effective parameters for tuning the behavior regarding stability during transition. This structure shows potential for combining geometric simplicity with complex and highly tune-able behavior. However, its discontinuity obstructs physical realization. Therefore, a monolithic variant of this structure is investigated. The transition of a double-curved distributed compliant shell towards its second equilibrium configuration forms the basis of this investigation. A varying material thickness profile, described by an ideal set of design parameters, is obtained using an optimization procedure. Numerical analysis of the resulting optimized shell structure predicts a significant region of near-constant energy and associated near-zero loads within this unique deformation mode. Prototypes are manufactured using a 3D-printing process and demonstrate the validity of the modelled results by featuring a continuous equilibrium within a significant range of motion. These results lay the foundation for compliant beam elements with an internal statically balanced bending degree of freedom. Finally, a different deformation mode, involving crease actuation of the same type of structure, is examined. Curved creases are characterized by the coupled facet deformation upon actuation. The forces exerted by the facets can be used to oppose the effects of crease stiffness during actuation to achieve an overall stiffness decrease. An analytical approach, based on a combination of a pseudo-rigid-body model (PRBM) and plate theory, predicts the potential for constant-force actuation around its second stable, or ‘inverted’ state. The accuracy of the model is validated by numerical simulations. However, due to prototype inaccuracies, the experimental results do not feature the desired constant force behavior. Nevertheless, a stiffness decrease, or ‘softening’ is experienced, verifying the concept and marking a first step towards statically balanced curved creases.