计算机科学基础知识全解

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Principles of Computer Science 《Principles of Computer Science》是一本涵盖计算机科学基础知识的书籍，旨在为读者提供一个坚实的起点和更深入的理解和欣赏这个复杂的主题。该书涵盖了计算机科学的相关领域，包括计算机工程、软件工程、生物技术、安全、机器人学、游戏和编程语言等。本书共包含117个条目，从3D打印到工作场所监控，按字母顺序排列，使读者易于找到感兴趣的主题。每个条目都包括： * 相关领域的研究，以说明计算机科学的各个分支之间的联系，包括计算机工程、软件工程、生物技术、安全、机器人学、游戏和编程语言等； * 对主题的简洁、具体的总结，以及该条目如何组织的说明； * 与讨论相关的主要术语，以便读者更好地理解所呈现的概念； * 通过模型、图表和图表等方式，阐明难以理解的概念，如广域网（WAN）、电子电路和量子计算等； * 对计算机科学领域中重要贡献者的照片； * 示例问题，以进一步展示所呈现的概念； * 相关条目的进一步阅读列表。通过阅读这本书，读者可以获得计算机科学的基础知识，并对这个领域有一个更深入的理解和欣赏。同时，该书还涵盖了计算机科学的相关领域，帮助读者更好地理解计算机科学的各个分支之间的联系。在计算机科学领域中，计算机工程是指设计、开发和测试计算机硬件和软件的过程。软件工程则是指设计、开发和测试软件的过程。生物技术是指使用生物学原理来开发新产品和服务的过程。安全是指保护计算机系统和数据免受未经授权的访问、使用、披露、破坏或修改的过程。机器人学是指研究和开发机器人的过程，机器人是指可以自动执行任务的机器。游戏是指使用计算机或其他电子设备进行娱乐的活动。编程语言是指使用特定的语法和语义来编写计算机程序的语言。本书的编辑Donald R. Franceschetti博士是美国Memphis大学的教授，他在计算机科学领域中有着丰富的经验和知识。本书的出版商是Salem Press和Grey House Publishing，他们都是知名的学术出版商。《Principles of Computer Science》是一本非常有价值的书籍，适合计算机科学专业的学生和从业者，以及任何对计算机科学感兴趣的人。

3-D PRINTING

FIELDS OF STUDY

Computer Science; Digital Media

ABSTRACT

Additive manufacturing (AM), or 3-D printing, com-

prises several automated processes for building three-

dimensional 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 ﬁla-

ment 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 suc-

cessive 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 com-

plex 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 draw-

ings or scans are usually saved in a digital ﬁle format

known as STL, originally short for “stereolithog-

raphy” but since given other meanings, such as “sur-

face 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

Principles of_Computer_A-B_001-048.indd 1 10/10/16 7:58 PM

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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 cre-

ated an alternate process that uses powdered solids

instead of liquid. Selective layer sintering (SLS), or

powder bed fusion, heats powdered glass, metal, ce-

ramic, or plastic in a powder bed until the material

is “sintered.” To sinter something is to cause its par-

ticles to fuse through heat or pressure without lique-

fying 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 struc-

tural support to prevent the object from collapsing.

Extrusion printing is the most affordable and com-

monly 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 ma-

terial 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 be-

fore 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 ac-

curate 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 customiz-

able 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 sub-

tractive manufacturing, it is of interest for conserva-

tion, 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 re-

quire 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,

2015. Web. 6 Jan. 2016.

Hutchinson, Lee. “Home 3D Printers Take Us on a

Maddening Journey into Another Dimension.” Ars

Technica. Condé Nast, 27 Aug. 2013. Web. 6 Jan.

2016.

“Knowledge Base: Technologies in 3D Printing.”

DesignTech. DesignTech Systems, n.d. Web. 6 Jan.

2016.

Matulka, Rebecca. “How 3D Printers Work.” Energy.

gov. Dept. of Energy, 19 June 2014. Web. 6 Jan.

2016.

“The Printed World.” Economist. Economist

Newspaper, 10 Feb. 2011. Web. 6 Jan. 2016.

“3D Printing Processes: The Free Beginner’s Guide.”

3D Printing Industry. 3D Printing Industry, 2015.

Web. 6 Jan. 2016.

Principles of_Computer_A-B_001-048.indd 3 10/10/16 7:58 PM

AGILE ROBOTICS

FIELDS OF STUDY

Robotics

ABSTRACT

Movement poses a challenge for robot design.

Wheels are relatively easy to use but are severely lim-

ited in their ability to navigate rough terrain. Agile

robotics seeks to mimic animals’ biomechanical de-

sign to achieve dexterity and expand robots’ useful-

ness 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 en-

vironment 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 adapt-

ability 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 run-

ning human in terms of how the human body—mus-

cles, bones, circulation—interacts with forces such

as gravity and momentum. Analyzing the activities of

living beings in these terms allows roboticists to at-

tempt 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 evo-

lution’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 pro-

totype 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 an-

other four-legged robot, the LS3, which looks like a

sturdy mule and was designed to carry heavy supplies

over rough terrain inaccessible to wheeled trans-

port. (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

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Agile robotics

that mimic snakes’ slithering motion or caterpil-

lars’ 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 an-

imals when it comes to physical challenges. Primates

are often much better climbers. Bears are much

stronger, cheetahs much faster. Why design anthro-

pomorphic 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-and-

blood astronaut, particularly for jobs that are too

dangerous or dull for humans. Its most remark-

able 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 them-

selves. A robot meant to integrate into human society

could get around much more easily if it shared a sim-

ilar body plan. Another reason to create humanoid

robots is psychological. Robots that appear more

human will be more accepted in health care, cus-

tomer service, or other jobs that traditionally require

human interaction.

Agile robots are designed to have dexterity, ﬂexibility, and a wider range of motions to allow for more re-

sponsiveness to their surroundings. By Manfred Werner - Tsui, CC-BY-SA-3.0 (http://creativecommons.org/

licenses/by-sa/3.0/), via Wikimedia Commons.

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