The Challenge of Manufacturing Between Macro and Micro
Classic ways of folding paper into dynamic shapes—origami, pop-up books—inspire methods to engineer millimeter-scale machines.
Making It Work
The origin of the pop-up book MEMS process is rooted in the assembly of microrobots such as the Micromechanical Flying Insect, a robotic microflyer inspired by house flies, which was designed by Ron Fearing’s group at the University of California, Berkeley. Its goal was to be at most 25 millimeters in diameter and to hover under its own power. From the early stages of the robotic-insect project in the early to mid-2000s, it was clear that neither MEMS nor macro-scale manufacturing methods were well suited for the mechanisms, structures, and actuators required to achieve flight with a robot the scale of a housefly. Laminated or folded beams were chosen for structural members, and articulation was achieved with compliant flexures. But again, all the folding was done by hand. There was a more subtle disadvantage to this process as well—difficulty in assembly and poor repeatability caused robot developers to be conservative in their designs.
The pop-up book MEMS process partly fulfills legendary physicist Richard Feynman’s prophesy, made in his 1959 lecture “Plenty of Room at the Bottom,” regarding little robots building even smaller robots. For example, after the Micromechanical Flying Insect, we began the RoboBees project, for which we have been able to construct monolithic robots in one or two assembly steps (depending on the complexity of the design) where the scaffold acts as the tiny hands that piece together the parts of the robot. This example takes advantage of many of the benefits of pop-up manufacturing: Complex structures and articulated mechanisms are created with minimal dexterous manipulation of the constituent components; electroactive materials are included directly in the layup, resulting in the “flight muscles” for the robot; and the laminate consists of a variety of materials.
Recently the scope of devices created using the pop-up book MEMS process has been dramatically expanded. Examples include flying and terrestrial insect-like robots that could quickly survey disaster areas or perform environmental monitoring, as well as surgical devices, new meso-scale actuators, bio-inspired sensors, and a host of polyhedra and parallel mechanisms that would be difficult or impossible to build by other means.
These advances in meso-scale manufacturing have opened the door to countless applications in consumer electronics, biomedical devices, on-demand tooling, and research and education. But there are still many barriers to widespread use. Infrastructure costs and design expertise still make many of the methods discussed here a challenge for novice users.
Clues to the solution to more universal access to meso-scale manufacturing come from the history of integrated circuits. Early in their development in the 1980s, the U.S. National Science Foundation and Department of Defense funded a service called MOSIS (Metal Oxide Semiconductor Implementation Service) that acted as a gateway to multiple integrated circuit foundries. Small amounts of wafer real estate on well-defined integrated circuit fabrication processes were made available to any researcher. Thus researchers could generate prototypes with minimal expense (compared to the cost of a full run, or investing in the infrastructure themselves) and with highly refined process standards, the details of which could simply be abstracted away by their design tools.
As the MOSIS service evolved, so did the design tools that automated common features and generally made it easier for novice users to generate new designs and intellectual property. Beyond the obvious benefits the service provided in terms of access to fabrication, MOSIS also generated a vibrant community of users that in turn pushed the limits of the processes, developed and disseminated new designs and design rules, and generally built up an intellectual foundation that pushed the proliferation of electronic devices that are now integral in our daily lives.
A similar trajectory could equally aid developers of multiscale, multimaterial, monolithic electromechanical devices. Given the relatively low infrastructure costs for processes such as pop-up book MEMS, and with the motivation to establish standardized process lines, there is a huge opportunity to establish a MOSIS-like system that will make the process accessible. But the foundry and processes alone would not be enough. Design rules and automation tools, such as computer-aided design software, must be published simultaneously.
One of the more intriguing consequences of a cheap, flexible monolithic manufacturing system is that it could inspire a rich user community, appealing to the fast-growing “maker” movement. Like the electronics hobbyists who started tinkering with integrated circuits starting in the 1970s, today’s makers may prove vital for building up design libraries and for finding novel applications of pop-up assembly. In a few decades, perhaps people will be manufacturing their own small robots as easily as they now print their digital photos.
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