Mesh convergence and manufacturability of topology optimized designs have previously mainly been assured using density or sensitivity based filtering techniques. The drawback of these techniques has been gray transition regions between solid and void parts, but this problem has recently been alleviated using various projection methods. In this paper we show that simple projection methods do not ensure local mesh-convergence and propose a modified robust topology optimization formulation based on erosion, intermediate and dilation projections that ensures both global and local mesh-convergence.

On projection methods, convergence and robust formulations in topology optimization

Giga-voxel-resolution computational morphogenesis is used to optimize the internal structure of a full-scale aeroplane wing, yielding light-weight designs with more similarities to animal bone structures than to current aeroplane wing designs. Computational morphogenesis is used to design the best possible shapes and material distributions for the desired structural properties, such as high strength at minimal weight. In plants and animals, morphogenesis occurs naturally through slow genetic evolution. In engineering, a much faster iterative approach for optimum material distribution has been adopted, called topology optimization. So far, it has been used to calculate only small or simple structures owing to limited resolution. Niels Aage et al. have developed a morphogenesis tool that can be run on a supercomputer and can calculate two orders of magnitude more voxels (the three-dimensional equivalents of pixels) than was previously attainable. This makes it possible to design structures with unprecedented detail, yielding new insights into optimal material distribution. The authors calculate an optimized full aircraft wing structure with remarkable structural detail at several length scales, which displays similarities to naturally occurring bone structures such as those seen in bird beaks. The new tool could inspire surprising design approaches for a range of structures, including wind turbine blades, tower masts and bridges. In the design of industrial products ranging from hearing aids to automobiles and aeroplanes, material is distributed so as to maximize the performance and minimize the cost. Historically, human intuition and insight have driven the evolution of mechanical design, recently assisted by computer-aided design approaches. The computer-aided approach known as topology optimization enables unrestricted design freedom and shows great promise with regard to weight savings, but its applicability has so far been limited to the design of single components or simple structures, owing to the resolution limits of current optimization methods1,2. Here we report a computational morphogenesis tool, implemented on a supercomputer, that produces designs with giga-voxel resolution—more than two orders of magnitude higher than previously reported. Such resolution provides insights into the optimal distribution of material within a structure that were hitherto unachievable owing to the challenges of scaling up existing modelling and optimization frameworks. As an example, we apply the tool to the design of the internal structure of a full-scale aeroplane wing. The optimized full-wing design has unprecedented structural detail at length scales ranging from tens of metres to millimetres and, intriguingly, shows remarkable similarity to naturally occurring bone structures in, for example, bird beaks. We estimate that our optimized design corresponds to a reduction in mass of 2–5 per cent compared to currently used aeroplane wing designs, which translates into a reduction in fuel consumption of about 40–200 tonnes per year per aeroplane. Our morphogenesis process is generally applicable, not only to mechanical design, but also to flow systems3, antennas4, nano-optics5 and micro-systems6,7.

/pdf/giga-voxel-computational-morphogenesis-for-structural-design-4fs8r63d2g.pdf

Giga-voxel computational morphogenesis for structural design

Design of compliant mechanisms using continuum topology optimization: A review

This paper presents a robotic system that is capable of both picking up and releasing microobjects with high accuracy, reliability, and speed. Due to force-scaling laws, large adhesion forces at the microscale make rapid, accurate release of microobjects a long-standing challenge in micromanipulation, thus representing a hurdle toward automated robotic pick-and-place of micrometer-sized objects. The system employs a novel microelectromechanical systems (MEMS) microgripper with a controllable plunging structure to impact a microobject that gains sufficient momentum to overcome adhesion forces. The performance was experimentally quantified through the manipulation of 7.5-10.9 ?m borosilicate glass spheres in an ambient environment. Experimental results demonstrate that the system, for the first time, achieves a 100% success rate in release (which is based on 700 trials) and a release accuracy of 0.45 ± 0.24 ?m. High-speed, automated microrobotic pick-and-place was realized by visually recognizing the microgripper and microspheres, by visually detecting the contact of the microgripper with the substrate, and by vision-based control. Example patterns were constructed through automated microrobotic pick-and-place of microspheres, achieving a speed of 6 s/sphere, which is an order of magnitude faster than the highest speed that has been reported in the literature.

/pdf/autonomous-robotic-pick-and-place-of-microobjects-sap76wez63.pdf

Autonomous Robotic Pick-and-Place of Microobjects

A new microgripper dedicated to micromanipulation and microassembly tasks is presented in this paper. Based on a new actuator, called thermo-piezoelectric actuator, the microgripper presents both a high range and a high positioning resolution. The principle of the microgripper is based on the combination of the thermal actuation (for the coarse positioning) and the piezoelectric actuation (for the fine positioning). In order to improve the performances of the microgripper, its actuators are modeled and a control law for both the position and the manipulation force is synthesized afterwards. A new control scheme adapted for the actuators of the hybrid thermo-piezoelectric microgripper is therefore proposed. To prove the interest of the developed microgripper and of the proposed control scheme, the control of a pick-and-release task using this microgripper is carried out. The experimental results confirm their efficiency and demonstrate that the new microgripper and the control law are well suited for micromanipulation and microassembly applications.

/pdf/development-and-force-position-control-of-a-new-hybrid-nkjlaojh8q.pdf

Development and Force/Position Control of a New Hybrid Thermo-Piezoelectric MicroGripper Dedicated to Micromanipulation Tasks

Nanorobotic handling of carbon nanotubes (CNTs) using microgrippers is one of the most promising approaches for the rapid characterization of the CNTs and also for the assembly of prototypic nanotube-based devices. In this paper, we present pick-and-place nanomanipulation of multi-walled CNTs in a rapid and a reproducible manner. We placed CNTs on copper TEM grids for structural analysis and on AFM probes for the assembly of AFM super-tips. We used electrothermally actuated polysilicon microgrippers designed using topology optimization in the experiments. The microgrippers are able to open as well as close. Topology optimization leads to a 10-100 times improvement of the gripping force compared to conventional designs of similar size. Furthermore, we improved our nanorobotic system to offer more degrees of freedom. TEM investigation of the CNTs shows that the multi-walled tubes are coated with an amorphous carbon layer, which is locally removed at the contact points with the microgripper. The assembled AFM super-tips are used for AFM measurements of microstructures with high aspect ratios.

http://iopscience.iop.org/article/10.1088/0957-4484/19/49/495503/pdf

Rapid prototyping of nanotube-based devices using topology-optimized microgrippers

Carbon nanotubes (CNTs) are one of the most promising materials for nanoelectronic applications. Before bringing CNTs into large-scale production, a reliable nanorobotic system for automated handling and characterization as well as prototyping of CNT-based components is essential. This paper presents the NanoLab setup, a nanorobotic system that combines specially developed key components such as electrothermal microgrippers and mobile microrobots inside a scanning electron microscope. The working principle and fabrication of mobile microrobots and electrothermal microgripper as well as their interaction and integration is described. Furthermore, the NanoLab is used to explore novel key strategies such as automated locating of CNTs for pick-and-place handling and methods for electrical characterization of CNTs. The results have been achieved within the framework of a European research project where the scientific knowledge will be transfered into an industrial system that will be commercially available for potential customers.

NanoLab: A nanorobotic system for automated pick-and-place handling and characterization of CNTs

Microgrippers that are able to manipulate nanoobjects reproducibly are key components in 3-D nanomanipulation systems. We present here a monolithic electrothermal microgripper prepared by silicon microfabrication, and demonstrate pick-and-place of an as-grown carbon nanotube from a 2-D array onto a transmission electron microscopy grid, as a first step toward a reliable and precise pick-and-place process for carbon nanotubes.

/pdf/multimodal-electrothermal-silicon-microgrippers-for-nanotube-1js36gbp5z.pdf

Multimodal Electrothermal Silicon Microgrippers for Nanotube Manipulation

Topology optimized electrothermal polysilicon microgrippers

The reason behind the majority of difficulties encountered in the integration of nanoscale objects with microelectromechanical systems can almost always be traced back to the lack of batch-compatible fabrication techniques at the nanoscale. On the one hand, self-assembly products do not allow a high level of control on their orientation and numbers, and hence, their attachment to a micro device is problematic. On the other hand, top-down approaches, such as e-beam lithography, are far from satisfying the needs of mass fabrication due to their expensive and serial working principle. To overcome the difficulties in micro–nano integration, a batch-compatible nanowire fabrication technique is presented, which is based on fabricating nanowires using simple lithographic techniques and relying on guided self-assembly. The technique is based on creating cracks with a predetermined number and orientation in a thin SiO2 coating on Si substrate, and then filling the cracks with an appropriate material of choice. After the SiO2 coating is removed, nanowires remain on the Si surface as a replica of the crack network. The technique, previously confined to electroless deposition, is now extended to include electroplating, enabling the fabrication of nanowires of various alloys. As an example, arrays of NiFe nanowires are introduced and their magnetic behaviour is verified.

https://iopscience.iop.org/article/10.1088/0957-4484/17/9/026/pdf

Ozlem Sardan

Papers

Rapid prototyping of nanotube-based devices using topology-optimized microgrippers

NanoLab: A nanorobotic system for automated pick-and-place handling and characterization of CNTs

Multimodal Electrothermal Silicon Microgrippers for Nanotube Manipulation

Topology optimized electrothermal polysilicon microgrippers

Self-assembly-based batch fabrication of nickel-iron nanowires by electroplating