Performing logic operations using mechanical systems dates back to the advent of computation (Babbage 1889). With the recent interest in microscale manufacturing, there has been a resurgence of interest in mechanical computation (Roukes 2004). This feasibility study set out to demonstrate that functionally complete digital micromechanical logic gates could be designed and fabricated with additive manufacturing and could possibly be integrated into the microstructure of a material. These gates are of interest for their low power consumption and ability to operate in harsh environments. While there are several researchers looking at various aspects of mechanical logic gates, to date there has not been a solution that is functionally complete, operates at the microscale, and is capable of being printed directly into the microstructure of an architected material. Specifically, this project demonstrated the feasibility of creating logic gates using additive-manufacturing techniques by answering the following three questions:
The first computers were based on mechanical logic. In the mid-1800s, Charles Babbage and Ada Lovelace designed the first programmable, Turing-complete computer called the analytical engine, which was based on mechanical logic (Babbage 1889). While the computing industry quickly moved to electronic logic systems, mechanical logic still offers several advantages if it can be readily scaled down to the microscale. Mechanical logic circuits do not require an electrical power source, thus computers built from them have a negligible electromagnetic signature and are able to operate in extreme environments. In fact, NASA recently unveiled a mechanical computer-based rover concept for the exploration of Venus' harsh environment (Sauder 2017).
Recent advancements in additive manufacturing allow precise placement of materials in three dimensions. Lawrence Livermore National Laboratory's Center for Engineered Materials and Manufacturing recently demonstrated the ability to control the microarchitecture of materials with feature sizes down to 10 microns using a stereolithography technique. Two-photon stereolithography (2PS) techniques can create structures that are even smaller, with feature sizes down to hundreds of nanometers. With these techniques, it may be possible to design mechanical logic circuits into the microstructure of a material creating so-called material logic. Material logic would allow basic calculations to be performed by the material itself with no electrical power input; the material would be able to passively sense its environment over long time scales and provide concealed output. Without the need for electrical power, such a logic system could be deployed in high-radiation environments and be impervious to electromagnetic interference.
The logic systems designed during this project had several advantages over those found in the literature (Merkle et al. 2018, Ion et al. 2017, Raney et al. 2016, Sharma et al. 2009): The logic gates are functionally complete and any digital operation can be performed with them; they can operate continuously; there is no need for an external clock or reset operation; they are scale-independent; they operate the same on the nanoscale as on the macroscale; and both binary value representations are of equal energy, which allows the system to consume very little energy during operation.
The goal of this project was to develop a complete logic system with purely mechanical functionally that can be fabricated with existing microscale additive-manufacturing techniques. Logic signals would be propagated via physical displacement of input and output tabs. Specifically, we set out to answer the three questions listed above.
The first two questions were definitively answered in the affirmative. Though the third question was not definitively answered, it was demonstrated to be technically feasible through numerical modeling and the production of a key component of the logic system at the scale that would be necessary for integration into an architected material.
The logic gates we developed were designed using flexure linkages. Several initial flexure designs were considered, and with the assistance of a finite-element model (FEM), an optimized design was chosen for fabrication and testing. We fabricated the logic units using three techniques: fused deposition modeling (FDM), projection microstereolithography, and two-photon lithography. The logic gates printed with FDM were selected for mechanical testing, and their performance matched predictions from the finite-element model.
Mechanical logic circuits do not require electrical power to operate and can be made of many different types of materials. Though polymer gates were demonstrated in this project, the same designs could also be fabricated in metal or ceramic. These circuits are therefore hardened against radiation and can operate in extreme environments where semiconductor-based logic circuits would fail. Furthermore, these circuits could be fabricated directly into the microstructure of architected materials, which would enable these materials to process data in response to environmental stimuli. This research has direct application to the Laboratory's broad national security mission, and its mission area in stockpile stewardship and weapons of mass destruction threat reduction.
The results of this study have proven that mechanical logic gates can be designed and fabricated using existing additive-manufacturing techniques. While this project has demonstrated a functionally complete set of logic gates, it has not demonstrated true computation. To fully realize a mechanical computer, two additional issues need to be addressed: the integration of logic gates into functional circuits and the development of input/output interfaces to feed data into the mechanical computer and extract data out of it.
Babbage, C. 1889. "Babbage's Calculating Engines." Cambridge University Press. https://monoskop.org/images/4/40/Babbage_Charles_Calculating_Engines.pdf.
Ion, A., et al. 2017. "Digital Mechanical Metamaterials." in Proceedings of CHI 2017, May 2017, Denver, CO. doi: 10.1145/3025453.3025624.
Merkle, R. C., et al. 2018. "Mechanical Computing Systems Using Only Links and Rotary Joints." ASME Journal on Mechanisms and Robotics 10: 061006. doi: 10.1115/1.4041209.
Raney, J. R., et al. 2016. "Stable Propagation of Mechanical Signals in Soft Media Using Stored Elastic Energy." Proceedings of the National Academy of Sciences 113(35): 9722–27. doi: https://doi.org/10.1073/pnas.1604838113.
Roukes, M. L. 2004. "Mechanical Compution, Redux? [Nanoelectromechanical Systems]." In IEDM Technical Digest. IEEE International Electron Devices Meeting, 2004. 539–42. doi: 10.1109/IEDM.2004.1419213.
Sauder, J. 2017. "Automaton Rover For Extreme Environments." NASA Innovative Advanced Concepts (NIAC) Phase I: Final Report https://www.nasa.gov/sites/default/files/atoms/files/niac_2016_phasei_saunder_aree_tagged.pdf.
Sharma, A., et al. 2009. "Mechanical Logic Devices and Circuits." NaCoMM-09-Paper ID RCA18. 14th National Conference on Machines and Mechanisms (NaCoMM-09), NIT, Durgapur, India, December, 2009.
Song, A., et al. 2018. "Feasibility Study on Micro-Mechanical Logic Gates and Systems." 2018 ASPE Winter Topical Meeting in Precision Engineering for Micro and Nanotechnology. Livermore, CA, October 2018. LLNL-POST-744669.
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