3-D printing. Fields of Study Computer Science; Digital Media

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1 3-D printing Fields of Study Computer Science; Digital Media Abstract Additive manufacturing (AM), or 3-D printing, comprises several automated processes for building threedimensional objects from layers of plastic, paper, glass, or metal. AM creates strong, light 3-D objects quickly and efficiently. Prinicipal Terms binder jetting: the use of a liquid binding agent to fuse layers of powder together. directed energy deposition: a process that deposits wire or powdered material onto an object and then melts it using a laser, electron beam, or plasma arc. material extrusion: a process in which heated filament is extruded through a nozzle and deposited in layers, usually around a removable support. material jetting: a process in which drops of liquid photopolymer are deposited through a printer head and heated to form a dry, stable solid. powder bed fusion: the use of a laser to heat layers of powdered material in a movable powder bed. sheet lamination: a process in which thin layered sheets of material are adhered or fused together and then extra material is removed with cutting implements or lasers. vat photopolymerization: a process in which a laser hardens layers of light-sensitive material in a vat. Additive Manufacturing 3-D printing, also called additive manufacturing (AM), builds three-dimensional objects by adding successive layers of material onto a platform. AM differs from traditional, or subtractive, manufacturing, also called machining. In machining, material is removed from a starting sample until the desired structure remains. Most AM processes use less raw material and are therefore less wasteful than machining. The first AM process was developed in the 1980s, using liquid resin hardened by ultraviolet (UV) light. By the 2000s, several different AM processes had been developed. Most of these processes use liquid, powder, or extrusion techniques. Combined with complex computer modeling and robotics, AM could launch a new era in manufacturing. Soon even complex mechanical objects could be created by AM. Software and Modeling 3-D printing begins with a computer-aided design (CAD) drawing or 3-D scan of an object. These drawings or scans are usually saved in a digital file format known as STL, originally short for stereolithography but since given other meanings, such as surface tessellation language. STL files tessellate the object that is, cover its surface in a repeated pattern of shapes. Though any shape can be used, STL files use a series of non-overlapping triangles to model the curves and angles of a 3-D object. Errors in the file may need repair. Slices of the STL file determine the number and thickness of the layers of material needed. Liquid 3-D Printing The earliest AM technique was stereolithography (SLA), patented in 1986 by Chuck Hull. SLA uses liquid resin or polymer hardened by UV light to create a 3-D object. A basic SLA printer consists of an elevator platform suspended in a tank filled with light-sensitive liquid polymer. A UV laser hardens a thin layer of resin. The platform is lowered, and the laser hardens the next layer, fusing it to the first. This process is repeated until the object is complete. The 1

2 3-D printing Principles of Computer Science FDM Process SLA Process Supports Liquifier head (moves in x and y direction) Extrusion nozzles Foam slab Recoater blade Scanning system Supports Laser Support material spool Build material spool Build platform (moves in z direction) Liquid Photopolymer Resin Platform SLS Process Scanning system CO 2 laser Temperature-controlled build chamber with nitrogen atmosphere Powder-leveling roller Powder bed on build piston Powder feed Excess powder takeup This presents a comparison of the three common 3-D printing processes: SLA (in which liquid polymer resin is solidified by a laser and support material is removed after completion), SLS (in which powder is fused by a CO 2 laser and unfused powder acts as support), and FDM (in which liquid modeling material is extruded through extrusion nozzles and solidifies quickly, and a build material and a support material can be used in tandem, with the support material being removed after completion). EBSCO illustration. 2

3 Principles of Computer Science 3-D printing object is then cleaned and cured by UV. This AM technique is also called vat photopolymerization because it takes place within a vat of liquid resin. Various types of SLA printing processes have been given alternate names, such as photofabrication and photo-solidification. Powder-Based 3-D Printing In the 1980s, engineers at the University of Texas created an alternate process that uses powdered solids instead of liquid. Selective layer sintering (SLS), or powder bed fusion, heats powdered glass, metal, ceramic, or plastic in a powder bed until the material is sintered. To sinter something is to cause its particles to fuse through heat or pressure without liquefying it. A laser is used to selectively sinter thin layers of the powder, with the unfused powder underneath giving structural support. The platform is lowered and the powder compacted as the laser passes over the object again. Extrusion Printing Material extrusion printing heats plastic or polymer filament and extrudes it through nozzles to deposit a layer of material on a platform. One example of this process is called fused deposition modeling (FDM). As the material cools, the platform is lowered and another layer is added atop the last layer. Creating extruded models often requires the use of a structural support to prevent the object from collapsing. Extrusion printing is the most affordable and commonly available 3-D printing process. Emerging and Alternative Methods Several other 3-D printing methods are also emerging. In material jetting, an inkjet printer head deposits liquefied plastic or other light-sensitive material onto a surface, which is then hardened with UV light. Another inkjet printing technique is binder jetting, which uses an inkjet printer head to deposit drops of glue-like liquid into a powdered medium. The liquid then soaks into and solidifies the medium. In directed energy deposition (DED), metal wire or powder is deposited in thin layers over a support before being melted with a laser or other heat source. Sheet lamination fuses together thin sheets of paper, metal, or plastic with adhesive. The resulting object is then cut with a laser or other cutting tool to refine the shape. This method is less costly but also less accurate than others. The Future of 3-D Printing While AM techniques have been in use since the 1980s, engineers believe that the technology has not yet reached its full potential. Its primary use has been in rapid prototyping, in which a 3-D printer is used to quickly create a 3-D model that can be used to guide production. In many cases, 3-D printing can create objects that are stronger, lighter, and more customizable than objects made through machining. Printed parts are already being used for planes, race cars, medical implants, and dental crowns, among other items. Because AM wastes far less material than subtractive manufacturing, it is of interest for conservation, waste management, and cost reduction. The technology could also democratize manufacturing, as small-scale 3-D printers allow individuals and small businesses to create products that traditionally require industrial manufacturing facilities. However, intellectual property disputes could also occur more often as AM use becomes more widespread. Micah L. Issitt Bibliography About Additive Manufacturing. Additive Manufacturing Research Group. Loughborough U, Web. 6 Jan Hutchinson, Lee. Home 3D Printers Take Us on a Maddening Journey into Another Dimension. Ars Technica. Condé Nast, 27 Aug Web. 6 Jan Knowledge Base: Technologies in 3D Printing. DesignTech. DesignTech Systems, n.d. Web. 6 Jan Matulka, Rebecca. How 3D Printers Work. Energy. gov. Dept. of Energy, 19 June Web. 6 Jan The Printed World. Economist. Economist Newspaper, 10 Feb Web. 6 Jan D Printing Processes: The Free Beginner s Guide. 3D Printing Industry. 3D Printing Industry, Web. 6 Jan

4 A Agile robotics Fields of Study Robotics Abstract Movement poses a challenge for robot design. Wheels are relatively easy to use but are severely limited in their ability to navigate rough terrain. Agile robotics seeks to mimic animals biomechanical design to achieve dexterity and expand robots usefulness in various environments. Prinicipal Terms anthropomorphic: resembling a human in shape or behavior; from the Greek words anthropos (human) and morphe (form). autonomous: able to operate independently, without external control. biomechanics: the study of how living things move and the laws governing their movement. dexterity: finesse; skill at performing delicate or precise tasks. dynamic balance: the ability to maintain balance while in motion. humanoid: resembling a human. Robots That Can Walk Developing robots that can match humans and other animals ability to navigate and manipulate their environment is a serious challenge for scientists and engineers. Wheels offer a relatively simple solution for many robot designs. However, they have severe limitations. A wheeled robot cannot navigate simple stairs, to say nothing of ladders, uneven terrain, or the aftermath of an earthquake. In such scenarios, legs are much more useful. Likewise, tools such as simple pincers are useful for gripping objects, but they do not approach the sophistication and adaptability of a human hand with opposable thumbs. The cross-disciplinary subfield devoted to creating robots that can match the dexterity of living things is known as agile robotics. Inspired by Biology Agile robotics often takes inspiration from nature. Biomechanics is particularly useful in this respect, combining physics, biology, and chemistry to describe how the structures that make up living things work. For example, biomechanics would describe a running human in terms of how the human body muscles, bones, circulation interacts with forces such as gravity and momentum. Analyzing the activities of living beings in these terms allows roboticists to attempt to recreate these processes. This, in turn, often reveals new insights into biomechanics. Evolution has been shaping life for millions of years through a process of high-stakes trial-and-error. Although evolution s goals are not necessarily those of scientists and engineers, they often align remarkably well. Boston Dynamics, a robotics company based in Cambridge, Massachusetts, has developed a prototype robot known as the Cheetah. This robot mimics the four-legged form of its namesake in an attempt to recreate its famous speed. The Cheetah has achieved a land speed of twenty-nine miles per hour slower than a real cheetah, but faster than any other legged robot to date. Boston Dynamics has another four-legged robot, the LS3, which looks like a sturdy mule and was designed to carry heavy supplies over rough terrain inaccessible to wheeled transport. (The LS3 was designed for military use, but the project was shelved in December 2015 because it was too noisy.) Researchers at the Massachusetts Institute of Technology (MIT) have built a soft robotic fish. There are robots in varying stages of development 4

5 Principles of Computer Science Agile robotics Agile robots are designed to have dexterity, flexibility, and a wider range of motions to allow for more responsiveness to their surroundings. By Manfred Werner - Tsui, CC-BY-SA-3.0 ( licenses/by-sa/3.0/), via Wikimedia Commons. that mimic snakes slithering motion or caterpillars soft-bodied flexibility, to better access cramped spaces. In nature, such designs help creatures succeed in their niches. Cheetahs are effective hunters because of their extreme speed. Caterpillars flexibility and strength allow them to climb through a complex world of leaves and branches. Those same traits could be incredibly useful in a disaster situation. A small, autonomous robot that moved like a caterpillar could maneuver through rubble to locate survivors without the need for a human to steer it. Humanoid Robots in a Human World Humans do not always compare favorably to other animals when it comes to physical challenges. Primates are often much better climbers. Bears are much stronger, cheetahs much faster. Why design anthropomorphic robots if the human body is, in physical terms, relatively unimpressive? NASA has developed two different robots, Robonauts 1 and 2, that look much like a person in a space suit. This is no accident. The Robonaut is designed to fulfill the same roles as a flesh-andblood astronaut, particularly for jobs that are too dangerous or dull for humans. Its most remarkable feature is its hands. They are close enough in design and ability to human hands that it can use tools designed for human hands without special modifications. Consider the weakness of wheels in dealing with stairs. Stairs are a very common feature in the houses and communities that humans have built for themselves. A robot meant to integrate into human society could get around much more easily if it shared a similar body plan. Another reason to create humanoid robots is psychological. Robots that appear more human will be more accepted in health care, customer service, or other jobs that traditionally require human interaction. 5 Principles of_computer_a-b_ indd 5 10/10/16 7:58 PM

6 ALGOL Principles of Computer Science Perhaps the hardest part of designing robots that can copy humans ability to walk on two legs is achieving dynamic balance. To walk on two legs, one must adjust one s balance in real time in response to each step taken. For four-legged robots, this is less of an issue. However, a two-legged robot needs sophisticated sensors and processing power to detect and respond quickly to its own shifting mass. Without this, bipedal robots tend to walk slowly and awkwardly, if they can remain upright at all. The Future of Agile Robotics As scientists and engineers work out the major challenges of agile robotics, the array of tasks that can be given to robots will increase markedly. Instead of being limited to tires, treads, or tracks, robots will navigate their environments with the coordination and agility of living beings. They will prove invaluable not just in daily human environments but also in more specialized situations, such as cramped-space disaster relief or expeditions into rugged terrain. Kenrick Vezina, MS Bibliography Bibby, Joe. Robonaut: Home. Robonaut. NASA, 31 May Web. 21 Jan Gibbs, Samuel. Google s Massive Humanoid Robot Can Now Walk and Move without Wires. Guardian. Guardian News and Media, 21 Jan Web. 21 Jan Murphy, Michael P., and Metin Sitti. Waalbot: Agile Climbing with Synthetic Fibrillar Dry Adhesives IEEE International Conference on Robotics and Automation. Piscataway: IEEE, IEEE Xplore. Web. 21 Jan Sabbatini, Renato M. E. Imitation of Life: A History of the First Robots. Brain & Mind 9 (1999): n. pag. Web. 21 Jan Schwartz, John. In the Lab: Robots That Slink and Squirm. New York Times. New York Times, 27 Mar Web. 21 Jan Wieber, Pierre-Brice, Russ Tedrake, and Scott Kuindersma. Modeling and Control of Legged Robots. Handbook of Robotics. Ed. Bruno Siciliano and Oussama Khatib. 2nd ed. N.p.: Springer, n.d. (forthcoming). Scott Kuindersma Harvard University. Web. 6 Jan ALGOL Fields of Study Programming Languages Abstract The ALGOL programming language was developed in 1958 as a program for the display of algorithms. It was elegant and included several design features that have since become staple features of advanced programming languages. ALGOL programs and procedures employ a head-body format, and procedures can be nested within other procedures. ALGOL was the first programming language to make use of start-end delimiters for processes within procedures, a feature now common in advanced object-oriented programming languages. The language allowed recursion and iterative procedures, dynamic array structures, and userdefined data types. Despite its elegance and advanced features, however, ALGOL never became widely used and is now one of the oldest and least used of programming languages. Prinicipal Terms algorithm: a set of step-by-step instructions for performing computations. character: a unit of information that represents a single letter, number, punctuation mark, blank space, or other symbol used in written language. function: instructions read by a computer s processor to execute specific events or operations. object-oriented programming: a type of programming in which the source code is organized into objects, which are elements with a unique identity that have a defined set of attributes and behaviors. 6