The company Intespring is currently developing a load-carrying exoskeleton for military personnel in order to reduce the impact of the ever increasing backpack load on their body: the Exobuddy. The current mechanical design gives rise to problems, i.e. the exoskeleton occupies a large space and applies torques on the legs of the user during operation, rendering it unsuitable for use in the field. This research is comprised of the redesign of the mechanical structure, where the functionality of the current exoskeleton is maintained, while eliminating the mentioned problems. The chosen solution, based on Storable Tubular Extendible Members (STEMs), is further developed and dimensioned according to a set of requirements. Finally a prototype is built to validate the design. It is shown that the proposed design is capable of carrying loads matching backpack loads of military personnel. Additionally, it is shown that the anisotropic material properties of Fibre Reinforced Composites can be exploited in such a way that a compact mechanism can be obtained.

The human machine-interface is more important than ever in the field of exoskeletons. Current design approaches lack a way of systematically designing the ergonomics of exoskeletons. Methods with a more pro active approach to ergonomics have to be developed. This thesis extends existing methods by which self aligning mechanisms are created with a systematic approach. A synthesis method is proposed by which all possibilities are synthesized. These possibilities are then excluded based on kinematic requirements on the system. The remaining possibilities are optimized based on ergonomic guidelines to obtain a set of solutions from which the designer can make well founded design choices. A force-deflection analysis was performed on the resulting solutions. This proposed method is applied to a planar passive exoskeleton for the shoulder. The method was successfully applied by using the total link length, reachable workspace, distance to the body and singularity avoidance as objectives for the optimization. Stiffness was added to the joints to obtain the required force-deflection behavior. The resulting objective values were verified by means of a prototype. The test results showed to be within reasonable bounds to verify the method for the planar case. The force-deflection analysis showed results that can be achieved by linear springs. This has to be verified by additional tests. The proposed method can be used as a tool in future exoskeleton design and can be extended with additional objective functions and constraints and can be extended to the three dimensional case.

Rotational electric actuators are the most popular choice for actuation in modern day automation. These actuators are commonly used in combination with a transmission system. In this paper, the development of a new rotational to linear transmission technology, called the ring screw, is described, and its real-world performance is evaluated experimentally. The ring screw consists of freely rotating rings that constrain a rod to a screwing motion. The line contact between those rings and the rod allows for perfect rolling, resulting in a highly efficient screw transmission. The theoretical performance of the ring screw for the metrics maximal velocity, maximal thrust force and mechanical efficiency are explored analytically. Based on these performance metrics, this paper presents a method to find the optimal design parameters when the desired properties are provided. A prototype was evaluated in a custom developed test rig. In these experiments the ring screw is proven to be able to operate at 15,000RPM and deliver 750N with an efficiency of 90%. The ring screw operates at more than double the speed possible with other screw transmissions such as a ball screw, with the same high efficiency.

Compliant shell mechanisms utilize spatially curved thin-walled structures to transfer or transmit force, motion or energy through elastic deformation. To design with spatial mechanisms designers need non-linear characterization methods. This work introduces a comprehensive non-linear characterization method and framework which is experimentally validated and applied on promising shell mechanisms, with the objective to enhance the design process of a compliant scoliosis brace.

Passive exoskeletons that support the weight of the surgeon’s arms could yield a significant ergonomic improvement in the Laparoscopic theatre. However, the cost and regulations associated with sterilization complicates adoption of such devices. In this work a compact passive arm support mechanism is designed that can be worn underneath the surgical gown to circumvent sterility requirements. The design utilizes shape optimized compliant shell mechanisms who’s geometry can remain substantially close to the body as well as achieve the nonlinear stiffness characteristic that is desired for balancing the arm’s weight. A shell design with the desired torque-rotation characteristic is designed using shape optimization and fabricated for validation testing. Measurements show the prototype balances 19% of an average adult’s arm weight within ±4 percentage points between 0 and 90 degrees of arm abduction and or flexion. A prototype of the mechanism remains within 34mm of the arm, nearly twice as compact as the state of the art.

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.

In the semiconductor industry, integrated circuits with nanometre scale structures are manufactured on silicon wafers. Particle contamination on the topside of the wafer can result in the defectivity of the entire die. In the ever-increasing efforts to create smaller structures onto a wafer particle contamination becomes more restrictive to prevent the defectivity of the die. In order to reduce the risk of particle contamination the wafer is placed in a vacuum environment. But further risks exist, during the grasping and positioning of the wafer new particles are generated and are able to transport to critical surfaces. This study investigates what guidelines need to be followed for the design of a kinematic coupling for use in a vacuum, whilst keeping particle generation as low as possible. The guidelines can be used to determine an optimal kinematic coupling design for any arbitrary object shape, size and mass. First of all, it is determined that abrasive wear, adhesive wear, contact stresses and outgassing are the predominant factors that have an effect on particle generation and influence the design of a kinematic coupling. The first guideline optimizes the constraint method of the kinematic coupling. Here, the guideline states that each constraint needs to be able to translate parallel to the surface of the object, doing so minimizes abrasive and adhesive wear. This can be achieved by suspending the contact points by using, for example, (folded) leaf springs. The second guideline encompasses the contact point shape and size. To equally distribute contact stresses, a spherical indenter shape should be chosen. Here, the radius of the indenter is chosen to be as small as possible to prevent adhesive wear. The third and last guideline optimizes the position of the contact points placed on the object. These positions influence the positioning repeatability, an algorithm is introduced that can calculate the optimal position for the contact points to maximize this repeatability. Also, the stability of the grasp is determined in terms of maximum allowable external disturbance forces.

Active materials are a type of material that can respond to external stimuli and change their physical properties as a response. Neutrally stable compliant mechanisms are a class of compliant mechanisms that use the flexibility of their members to deform and maintain that deformed configuration without requiring external work. In order to make a compliant mechanism neutrally stable, pre-stress is required. In most cases, this pre-stress is applied when the neutrally stable compliant mechanisms are being made. Therefore, neutrally stable compliant mechanisms are always in a zero-stiffness state. In this research, a new Compliant Active Neutrally Stable joint (CANS-J) is developed in which this pre-stress can be turned on and off using active materials. This means that the joint can switch between a stiff state and a zero-stiffness state. This change in the stiffness is realized by a Flexinol SMA wire. A Flexinol wire can contract when it is heated. This active behavior of the Flexinol wire is used to turn on and off the pre-stress when required. Results show that the CANS-J shows behavior which is close to neutral stability in the active state with a significant range of motion. The CANS-J can for instance be used to transport a satellite with solar panels to its orbit around the world. During transportation the solar panels are folded for which the joints are required to be in a stiff state. In orbit, the solar panels are unfolded for which the joints are required to have zero stiffness.

Existing scoliosis braces preclude spinal movement for activities of daily living, which reduces the willingness to wear the brace and treatment success. This work develops a scoliosis brace that meets corrective requirements while retaining patient mobility. The primary compliance vector (PCV) captures the predominant kinematic degree of freedom of a mechanism. Its path describes large deformation mechanism behavior. This work presents a general framework that optimizes the PCV path of compliant shell mechanisms. It refines mechanism shape to satisfy kinematic requirements. This work designs a shell mechanism that circumferences the human torso, that allows for sagittal bending, and transmits corrective forces. The optimization framework refines this mechanism to align the PCV with the sagittal bending axis of the human spine.

In Chapter 1, the focus is on the classification of force generators, which is the family of mechanisms to which balancers belong to. The goal of this chapter is to introduce a bottom-up classification method to identify the complete solutions space of transmissions in force generators based on their transfer function. Using this method, spring-to-mass balancers with one non-auxiliary revolute joint will be classified to identify their working principles and find new design opportunities. In Chapter 2, the focus is on balancers applied in exoskeletons and robotic manipulators. The goal of this chapter is twofold. The first goal is to introduce the optimal balancer adjustment types for application in exoskeletons and robotic manipulators. The second goal is to compare their performance based on the balancing quality, energy involved in adjustment and dimensions through an analytical MATLAB model. The introduced adjustment types incorporate a commercial available spring with realistic properties and their performance is considered in their complete range of motion. The results of the complete thesis research are discussed in Chapter 3, and in Chapter 4, the main conclusions are highlighted. This thesis ends with additional information about the performed research, which can be found in Appendices A to H.

Normal linear springs have spring characteristics that are often too simplistic for complex applications. For instance in balancing applications, constant force or negative stiffness mechanisms are required. A tape loop, which consists of a two-fold tape spring, is a compliant shell mechanism which can act as a force generator with theoretically any force-displacement behavior by adjusting the tape spring’s cross-section. In this thesis, a synthesis method is developed to determine the required tape spring geometry for obtaining the desired force-displacement behavior. Fifteen force-displacement curves are defined which all describe a unique characteristic behavior. These fifteen force-displacement curves are used as input to synthesize fifteen tape spring geometries. The resulting geometries are simulated in a finite element model to validate the synthesis method. The geometry with a non-zero constant force characteristic, is optimized, produced and tested in an experiment. It is shown that a tape loop can generate all fifteen force-displacement curves by varying its cross-section and thereby can act as an all-purpose force generator. The production of tape loops however is challenging.

This thesis studies the possibility of energy increase in tape-spring assemblies through stacking, defined as the practice of placing tape-springs on top of each other in parallel. consists of five chapters. Chapter 2 consists of a paper that presents a theoretical approach to stacking of tape-springs, and studies the potential of energy storage using analytical functions of tape-spring strain energy and deformation behaviour. The goal of this simplified approach is to understand the potential of energy increase through stacking, and subsequent material considerations, without taking practical considerations in account yet. This creates context for the next chapter, in which a more specific configuration is further worked out. Chapter 3 consists of a paper with a simulation and experimental approach on energy increase in tape-springs, considering a specific configuration of boundary conditions, comparable to an arm support system. The goal of this paper is to verify the energy storage increase for a practical implementation of a stack of tape-springs. The strain energy distribution in the material and the resulting force-deflection behaviour is studied in a finite element shell model in MATLAB. The force-deflection behaviour of a stack of two tape-springs is experimentally validated, and compared to the force-deflection behaviour of the individual tape-springs. Chapter 4 contains the general discussion of the findings for both the theoretical, as well as for the simulation and experimental approach to the stacking of tape-springs. The main findings are highlighted in chapter 5. Some additional information on this thesis is added in the appendices.

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.

Kinematic couplings (KCs) are a subclass of couplings known for reaching unmatched precision, through relatively simplistic designs. The 3-vee-groove and Kelvin clamp are the archetype designs, and are still being further investigated for their potential. One of the limiting factors in the field of kinematic couplings is the lack of proper knowledge on how to assure stability of newly designed couplings. In this paper, the theoretical gap between the field of robotic grasping and the field of kinematic coupling is researched. It is shown that by making small alterations in the way of modelling the design problem, one can lend the performance measures that are used in the field robotic grasping for quantification of grasp performance, and apply these on the design process of kinematic couplings. This allows a designer to quantify and predict performance of newly designed couplings. The measures analysed in this paper are compared and scored in a table, where a tool is presented to help guide future coupling designers in the process.