No abstract

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 µm 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]

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.

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 paper 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.

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.