Present stroke rehabilitation devices for the arm are often difficult to use by the patient himself and cannot be used at home. A compliant shell mechanism could overcome the shortcomings of the current available devices. By the use of monolithic shell mechanisms a simple to use device can be designed, which can be made wearable. It would make it easier for stroke rehabilitation patients to do repetitive rehabilitation exercises at home. The focus lies on balancing the gravity during the lifting of the upper-arm. To achieve that a negative stiffness in the compliant shell mechanism is necessary. Negative stiffness arises when tape springs are bent and buckle for a short range of motion. Tape springs are thin-walled beams with a curved cross section. The short range of the negative stiffness limits the use for static balancing over a longer range of motion. In this project an analysis is presented on how the range of the negative stiffness can be increased by changing the geometry. The addition of longitudinal curvature to the tape spring results in a more gradual negative stiffness for a longer range of motion. It is shown why the addition of longitudinal curvature results in a more gradual and longer range of negative stiffness during the bending of shell.

The goal of this study is to develop a measurement setup that can accommodate the water-cooled modules present in the innovative e-beam lithography tool developed by Mapper Lithography and to perform flow verfication measurements on them. The overall objective is to verify the stage-stability requirements set for the Matrix-machine with regards to FIV by observing the induced cooling forces. This requires measuring in 6-DOF, over a wide frequency range (10-300 Hz) and at a very low noise level (e-11 N^2/Hz). Most challenging for this design is to be able to observe the FIV while in the presence of a variety of dominant environmental disturbances. The final design consists of a mass-optimized triple mass-spring-damper (MSD) system, weighting 828 kg. It uses six low-noise piezoelectric force transducers to observe the 6-DOF reaction-forces exerted by the modules. These modules under testing are supported by the piezos through custom designed stiff-flexible struts with a high axial/radial stiffness ratio. This improves measured signal and protects the piezos from damaging bending moments. This sensitive part of the measurement setup is isolated from floor vibrations by a double MSD Vibration Isolation (VI) platform (granite stones on airmounts). Acoustic shielding has been achieved by a custom designed enclosure that disconnects at the bottom granite stone. Flow vibrations in the supply tubing are discharged at various stages. Water flow is provided under constant pressure and flow rate by a hydrostatic pressure vessel. This prevents measuring distinct resonances from asynchronous motor characteristics inherent to a centrifugal pump. Verification measurements have been performed showing a noise floor characteristic at the level of the theoretically predicted effect of all disturbances combined (2.5 e-11 N^2/Hz). The main findings of this study are: - when aiming to measure very low-level dynamic reaction forces (0.35 microN-rms) in the presence of dominant disturbances that transmit through parasitic stiffnesses, quartz piezoelectric sensors proof to be a better solution when compared to (seismic) accelerometers. - flow vibrations induced in supply tubing can have a significant impact on the measured signal, if the stiffness train that connects the sensor with the measurement setup is relatively low. An effective method to minimize this disturbance is to discharge the bulk of the input to different stages of the vibration isolation platform, if present. - of all disturbances, environmental acoustics have shown to be most difficult to shield. The most effective means to reduce its effect is to fully enclose the sensitive part of the measurement setup and to rigidly connect this casing to a heavy mass with an attractive transfer path to the sensor e.g. the bottom stage of a two MSD VI platform. - when measuring direct forces using sensitive piezoelectric sensors that cannot withstand transverse loading / bending moments, stiff-flexible support struts with a high axial/radial stiffness ratio (roughly > 500) are found to be a solution. Concluding, the design process detailed in this thesis describes a method on how to effectively design a low-level reaction force measurement system, while in the presence of a variety of disturbances. In the report, generic design guidelines are listed that can serve as a reference to others when aiming to measure low-level FIV.

The average worldwide internet traffic demand in 2022 is projected to be over 1200 Terabits per second. A fifth of this data would be transmitted using mobile networks. One of the technologies used for this is radio frequency (RF) telecommunication, but this technology is reaching its limits. Despite ongoing development, typical data rates are still in the order of Gigabits per second per link. TNO is working on a telecommunication link (called TOmCAT) that can reach data transfer rates of a Terabit per second. The high data rate is achieved using a very promising alternative to RF telecommunication: optical telecommunication, which is also known as laser communication. In order to reach the intended data rates, the data needs to be spread over multiple optical frequencies. These signals need to be combined into one transmitted beam using a free-space optical bulk multiplexer. The laser beams that are transmitted by their collimators need to be aligned with respect to each other in order to reach the satellite as one beam. The footprint available for the required alignment mechanisms is very limited. Furthermore, the system needs to achieve a good thermal and mechanical stability in order to meet the strict specifications. The aim of this thesis is two-fold: to show the need for achieving state-of-the-art alignment specifications with strict footprint constraints, and to defend the steps taken to achieve these requirements. The research spans the entire design process of the alignment assembly: from higher/system level trade-offs and calculations, to the derivation of the design specifications, to the conceptual and detailed design, and concluding with the manufacturing and testing of the first prototype.

Many mechanical applications involve the use of springs with specifically designed load-displacement characteristics. This paper presents a new mechanical concept, that uses prestressed nonlinear plate springs that can be designed for various load-displacement characteristics for the end effector of parallelogram linkages. An intuitive method is proposed to design the global geometry of the nonlinear plate springs within the given set of boundary conditions from the parallelogram. The results from this method enhance understanding in the design of nonlinear springs and can be used as initial condition for structural shape optimization methods. Three distinct spring characteristics are found using this method to show its applicability. The springs are modelled by a finite element model and validated with a protoype.

The mechanism presented in this paper generates a partially negative stiffness characteristic, which is suitable for the balancing of a pendulum in a gravity field. The mechanism uses deformation in the axial direction of the base joint to store potential energy. The proposed design is located next to the base joint of the pendulum in an area rarely used by other balancing mechanisms. Utilising this space makes it an attractive alternative when space in the plane of motion is restricted. The mechanism consists of two linear springs and a non-linear transmission that form a compact system which can be manufactured out of tubes. The balancing curve that is generated by the mechanism has a theoretical maximum error of < 0:05% between ±22:5° around the horizontal position. The difference between the test results and the theory ranged from 0.4 % and 1.7 %. This gravity balancing mechanism is interesting when the mechanism should be located beside the base joint and or when low hysteresis and low error are required.

2D flexure elements fulfil a pivotal role in the field of precision positioning systems as they do not suffer from backlash, friction or play and exhibit highly repeatable behaviour. However, planar building blocks are characterized by a limited design space as the majority of the flexure elements are flat and straight. In this thesis, it is proposed to investigate another type of flexure element that features spatial (3D) properties. More specifically, it considers the use of helical flexure geometries in motion stages. Insight into the linear kinematic behaviour of various helical surfaces with varying curvature is provided with the usage of parametric optimization, screw theory, unified stiffness method and a performance metric. The newly acquired insights served as a prerequisite for selecting a suitable topology capable of guiding a stage. For demonstration purposes, a motion stage prototype was fabricated consisting of three helical flexure elements. Additionally, an eigenfrequency analysis was performed and experimentally validated with a model vibration test. This has led to the successful realization of a helical based compliant motion stage.

For steel flexures, complex geometries are required to reach high support stiffness and limit axis drift over large ranges of motion. These complex flexures are expensive and difficult to manufacture. This paper presents a method of designing short, polymer wire flexures with high support stiffness and modelling their axis drift using a novel method, the arc method. The arc method is validated against finite element methods (FEM) and physical tests, showing at least a factor 10 lower error than existing pseudo-rigid-body models (PRBM) at 70 degrees deflection while maintaining a simple modelling approach. The use of polymers increases support stiffness of wire flexures by a factor 7800 with respect steel at 70 degrees deflection, even though the material stiffness is substantially lower. This is due to the large allowed strain of polymers increasing the possible diameter by a factor 110.

Trendelenburg gait is an abnormal gait that occurs when hip abduction muscles are weakened. These weakened muscles cannot deliver enough force to prevent the pelvis from drooping when standing on one leg. This results in an abnormal gait where the upper body sways from left to right to keep the center of gravity above the standing foot. Besides standing out from other people when walking, this causes problems at the hip joint, knees, and ankles. This thesis presents a conceptual design of a compliant hip orthosis to prevent Trendelenburg gait. The design has a high adduction over flexion-extension stiffness ratio, meaning that the upper body is supported while walking is still possible. Also, the design exerts minimal shear forces on the human body, increasing comfort, and does not protrude from the body, making it aesthetically more appealing.