Topology optimization of multi-component thermal-mechanical-optical coupled systems

Stijn Koppen (PhD candidate) and Max van der Kolk (PhD candidate), Floris van Kempen (PhD candidate), Jan de Vreugd and Matthijs Langelaar (supervisor)


Throughout the high tech engineering field, instrumentation and high-performance equipment rely on adjustable mounts for fine alignment of optical components. However, current manual or actuated adjustable mounts and mechanisms typically consist of many parts, are voluminous, lack crosstalk-free control of individual degrees of freedom, and are sensitive to mechanical and thermal disturbances. Radical technological innovation is needed to overcome these limitations without a severe penalty in terms of engineering costs. This project develops a design methodology that uses computational topology optimization methods in order to generate multi-degrees of freedom monolithic compliant mechanisms with fully decoupled kinematic adjustment modes. The latter is optimized for dynamic aspects as well as mechanical and thermal stability and can be readily manufactured by additive manufacturing.

Topology optimization of thermomechanically stable and dynamically stiff mirror mount. This is an example of a 2D topology optimized structure representing the back of a mirror. The back of the mirror and frame have a varying coefficient of thermal expansion, causing the structure the deform and the mirror to bend under a heat load. This topology is optimized such that the mirror remains flat under a uniform temperature change, while simultaneously remaining a high fundamental eigenfrequency.
The design evolution of the topology optimization of a thermomechanically stable and dynamically stiff mirror mount. Note that under a uniform temperature change, due to a difference in coefficient of thermal expansion between mirror and frame, the mirror deforms causing the optical performance te to degrade. As the design evolves one can observe the deformed topology is such that the mirror stays almost flat.
The design evolution of a thermal-mechanical-optical coupled multi-component topology optimization problem. An incoming beam (for example high-power laser) is reflected by two mirrors before focused on a sensor. Without any disturbances, the system has a minimum spot size of zero. Both mirrors are subjected to rigid body movements induced by deformations of the frame as well as thermal loads from the light source. The aim is to minimize the system spot size error while constrained by a maximum beam position error and total mass. Additional constraints are the maximum surface form error and minimum eigenfrequency of each component. The approach proved highly effective; an improvement of over 95% compared to the component-by-component optimization approach. Allowing the optimizer to distribute unavoidable errors over multiple components in the system enlarges the feasible domain and the potential for superior system designs. The coupled analysis allows the mirrors to compensate for each other’s errors, which is a design solution that would otherwise be inaccessible to the optimizer.