We introduce two essential building blocks with binary stiffness for mechanical digital machines. The large scale fully compliant mechanisms have rectilinear and rotational kinematics and use a new V-shaped negative stiffness structure to create two extreme states of stiffness by static balancing. The use of a mechanical bistable switch allows us to toggle between near-zero-stiffness and high-stiffness states, effectively turning off and on stiffness. A stiffness reduction of 98.8% and 99.9% is achieved for linear and rotary motion over a range of 13.3% (20mm) and 0.4rad (23∘) respectively. Stiffness states can be reversibly changed by toggling the mechanical switch, or irreversibly by actuating the main stage. These binary stiffness mechanisms could set the stage for a new type of mechanical logic, adaptive and programmable metamaterials and other types of digital mechanical devices. Practical mechanical digital machines and materials require miniaturized and easily micro-manufactured components. We have therefore carefully considered scalability by integrating all required structures into a planar and monolithic architecture. This allows miniaturization and fabrication with conventional surface-micro-machining and additive manufacturing such as photolithography, two-photon lithography and fused deposition modeling.

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This thesis presents energy invariant mechanisms that can be scaled to micro size. They are also called statically balanced, because all static forces are balanced against each other. They enable effortless suspension of weight, and flexible devices without stiffness, seemingly defeating gravity and elasticity. In large scale applications such as movable bridges and ship lifts gravitational forces dominate elastic forces and counterweight balancing is the only practical approach. At small length scales, roles reverse: gravity becomes insignificant and elastic forces dominate. While other conservative forces such as magnetics or electrostatics also become relevant, focus will be placed on elastic forces. Static balancing is investigated at various scales, working our way down as we progress through the chapters. This investigation starts with a method for the analysis and synthesis of energy invariance in rigid body mechanisms, which are often used to aid the more difficult design of compliant mechanisms. It allows symbolic derivation of balancing conditions for serial kinematic chains with any number of links and zerofree-length springs. Virtual transmissions are introduced to temporarily constrain the chain to single degree of freedom and ease solving. Examples are provided in 2D and 3D. Static balancing is commonly used in civil engineering, robotics and large scale compliant mechanisms, where preloading is relatively easily applied by hand or preloading assembly. However, preloading becomes difficult at small scales and is identified as the primary reason the state of the art is not down-scalable. It is addressed by the design of various monolithic and planar architectures. The fully compliant mechanisms with linear and rotary motion incorporate a bistable mechanism that sustains the required preload in a reversible way. In one case, opposing constant force and torque achieves stiffness reduction by 98.5%and 90.5%respectively with increased relative range of motion (from 3.3% to 6.6 %) and reduced complexity compared to the state of the art. In the second case a new V-shape plate spring is used that minimizes and maximizes stiffness when preloaded and when not preloaded respectively. An unprecedented stiffness reduction of 99.9%and 98.5%is achieved under large deformations in fusedmodel deposition prototypes made out of polylactic acid. In all four cases switching between soft and hard modes can be done reversibly by toggling the bistable switch directly. Alternatively, the soft mode can be entered by actuating the shuttle over a force threshold. In addition, preloading is addressed by making it part of the manufacturing process by exploiting residual stress from thin film deposition. A stiffness reduction by a factor 9 to 46 is achieved over a range of 380 &m by thermal oxidation of silicon. The stiffness reduction is achieved in a passive way, allows for parallelized manufacturing, is space efficient and is scalable, since surface effects become more dominant at smaller scales. Miniature statically balanced mechanismswill be an enabling technology for low frequency sensors, mechanical energy harvesting, mechanical watch oscillators, mechanical logic and computing, microrobotics, compliant transmission mechanisms, and make small scale compliant mechanisms more energy efficient.@en

Stiffness in compliant mechanisms can be dramatically altered and even eliminated entirely by using static balancing. This requires elastic energy to be inserted before operation, which is most often done with an additional device or preloading assembly. Adding such devices contrasts starkly with primary motivations for using compliant mechanisms, such as part count reduction, increased precision, and miniaturization. However, statically balanced compliant mechanisms with a fully monolithic architecture are scarce. In this article, we introduce two novel statically balanced compliant mechanisms with linear and rotary kinematics that do not require preloading assembly, enabling miniaturization. Static balance is achieved by the principle of opposing constant force and extended to a rotational device by using opposing constant torque mechanisms for the first time. A constant force mechanism based on existing work is used and inspired a novel constant torque mechanism. A single-piece device is obtained by monolithically integrating a bistable switch for preloading, which allows static balance to be turned on and off. The linear device reduces stiffness by 98.5% over 10 mm, has significantly reduced device complexity and has doubled relative range of motion from 3.3% to 6.6% compared to the state of the art. The rotary device reduces stiffness by 90.5% over 0.35 rad.

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Residual stress from thermal oxidation can cause plastic deformation in silicon microelectromechanical systems (MEMS). This paper presents a novel method to distinguish elastic and plastic strain in silicon beams, by removing the oxide layer to show the plastic strain. A lever mechanism is used as a mechanical amplifier. The plasticity model by Alexander and Haassen (AH) is used in a numerical model to predict the elastic and plastic strain. Experiments in epitaxially grown silicon show significantly less plastic strain than predicted by the model. We conclude that the AH model is not valid for epitaxially grown silicon with very little initial dislocations. Since epitaxially grown silicon generally has less dislocations compared to floating zone silicon we recommend using the former when plastic deformation is to be avoided.

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Stiffness in compliant micro mechanisms can negatively affect performance. Current methods for stiffness reduction in micro electro mechanical systems (MEMS) consume power, have a large footprint or are relatively complex to manufacture. In this paper stiffness is reduced by static balancing. A building block commonly used for stiffness reduction in large scale compliant mechanisms is made compatible with MEMS. Preloading required to create negative stiffness is obtained from residual film stress by thermal oxidation of silicon. Instead of buckling a plate spring by moving its end points, a SiO 2 film 1900 nm to 2500 nm thick will stretch micro-beams 24 μ m wide, while the end points are fixed. To show efficacy of our method, the building block is coupled with a simple linear stage. However, the building block can readily be combined with other compliant micro mechanisms to reduce their stiffness. Statically balanced MEMS will enable novel designs in low-frequency sensor technology, low-frequency energy harvesting and pave the way to autonomous micro-robotics. We show a stiffness reduction of a factor 9 to 46. The balancing effect remained after SiO 2 removal, due to plastic deformation of the beams. [2019-0023]. @en

Robots would perform better when their mechanical structure is specifically designed for their designated task, for instance by adding spring mechanisms. However, designing such mechanisms, which match the dynamics of the robot with the task, is hard and time consuming. To assist designers, a platform that automatically designs dynamical mechanisms is needed. This letter introduces a novel string-based representation for mechanisms, including evolutionary operators, that allows an evolutionary algorithm to automatically design dynamical mechanisms for a designated task. The mechanism representation allows simultaneous optimization of topology and parameters. Simulation experiments investigate various algorithms to obtain best optimization performance. We show the efficacy of the representation, operators, and evolutionary algorithm by designing mechanisms that track straight lines and ellipses by virtue of both their kinematic and dynamic properties.@en

The presented research demonstrates the synthesis of two-dimensional kinematic mechanisms using feature-based reinforcement learning. As a running example the classic challenge of designing a straight-line mechanism is adopted: a mechanism capable of tracing a straight line as part of its trajectory. This paper presents a basic framework, consisting of elements such as mechanism representations, kinematic simulations and learning algorithms, as well as some of the resulting mechanisms and a comparison to prior art. Series of successful mechanisms have been synthesized for path generation of a straight line and figure-eight.

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