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.

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.

Compliant mechanisms and decoupled parallel mechanisms are topics of high interest. The combination has been manifested for lower-mobility mechanisms, yet not attempted for higher degrees of freedom. The scarcity is countered by designing a decoupled compliant spherical parallel mechanism (DCSPM), having three independent rotational degrees of freedom. Reasoning, that the spherical parallel mechanism has been studied extensively and is used for various applications, however not benefiting from the advantages that compliant- and decoupled mechanisms offer.
Extensive background knowledge is provided, which explains the common principles, applications, state- of-the-art and benefits of the decoupled compliant parallel mechanisms and forms the foundation for the design towards a decoupled compliant spherical parallel mechanism. Literature has revealed the type synthesis and optimization methods used for generating these intricate mechanisms and different methods are summarized for synthesizing compliant mechanisms. Besides, various grading criteria are introduced, such as parasitic error, range of motion and manufacturability. All possible kinematic architectures, which are able to produce a decoupled motion with three independent rotational degrees of freedom, are synthesized by using Screw Theory. This entails the number, sort, orientation and placement of joints present in each leg of the parallel mechanism. Moreover, strict decoupling criteria must be satisfied, resulting in the enumeration of several kinematic structures. Upon comparison and grading, a final structure (3-3R) is chosen, which via the use of rigid-body replacement techniques, is extended to a compliant variant of the mechanism.
An inevitable drawback of compliant mechanisms is their inability to produce continuous motion. As a result, parasitic errors are present during actuation. Because the final mechanism consists of revolute joints only, a remote center of motion mechanism based on curved flexures is developed, which is optimised to have minimal parasitic error. The latter is achieved by implementing a sequential quadratic optimisation algorithm in conjunction with surrogate models of the proposed compliant RCM mechanism. The latter results in design variables which have been optimised for minimal parasitic error, while adhering to the yield stress, minimum rotation and manufacturability constraints. The final RCM mechanism, containing flexures which are laser cut from 0.2 mm spring steel, is experimentally validated to have an axis drift of ±13.3 μm in x- direction and ±47.1 μm in y-direction for a rotation up to 18.3 deg. Upon comparison with existing compliant RCM mechanisms and several compliant revolute joints, the proposed compliant RCM mechanism shows satisfactory behaviour and complies with the conducted nonlinear FEA in Ansys.
During the experimental validation of the parasitic error present in the proposed RCM mechanism, existing measuring techniques showed several imperfections. As a result, a novel quantitative assessment method is proposed for identifying the parasitic error for planar rotary mechanisms, which aims to find the remote center-of-motion with the least amount of drift for various angles of rotation. By means of an arbitrary example, the latter is verified and the proposed method is compared with existing methods. Moreover, via a nonlinear finite element analysis on an existing compliant revolute joint, the applications, benefits, ease of use and results of the proposed method are exhibited.
The final DCSPM, 3-3R mechanism, is built up gradually; as one revolute joint, which is the proposed RCM mechanism based on curved flexures, is extended to a 2R, 2-2R, 3R and 3-3R mechanism. All individual sub parts have been experimentally investigated and exhaustive nonlinear FEA is carried out. Two versions of the final 3-3R mechanism are developed, one of which is assembled with spring steel flexures and a monotonically printed PLA variant.

There is a constant drive to make the next generation machines in the semiconductor industry more precise and faster. For this machines with a high repeatability, good dynamics and long lifetime are needed. Compliant mechanisms are suitable candidates to be used in this kind of machines because they can be manufactured monolithically, don’t wear out over time and do not suffer from backlash which makes them ideal for precision mechanisms. However, in these machines parasitic motions and cross-axis couplings are present. These unwanted motions reduce the precision and increases the control complexity respectively.

Strategies presented in literature to compensate for unwanted motions are summarized in the first part of this report. These strategies are evaluated and by combining two promising strategies a new compensation strategy is proposed. The second part of this report focusses on this new strategy. Using this new strategy a constant stiffness linear joint, a near zero parasitic motion translational guide with well constraint uncontrollable masses and a decoupled 2-DoF mechanism are synthesized. All these case studies needed to have a large range of motion because many effective strategies for small range of motion mechanisms are available in literature.