This document provides an overview of how liquid crystal displays (LCDs) work. It discusses how liquid crystals are neither fully solid nor liquid, but have properties of both. LCDs use liquid crystals and polarized filters to control the transmission of light and display images. The document covers the basic components of LCDs, including color filters to produce color displays, and how advances like active matrix displays improved image quality. It also provides a brief history of LCD development.

1. How LCDs Work
by Jeff Tyson › Introduction to How LCDs Work
› Liquid Crystals
› Building a Simple LCD
› Backlit vs. Reflective
› LCD Systems
› Color
› LCD Advances
› Lots More Information
› Shop or Compare Prices
You probably use items containing an LCD (liquid crystal display) every day. They are all
around us -- in laptop computers, digital clocks and watches, microwave ovens, CD players
and many other electronic devices. LCDs are common because they offer some real
advantages over other display technologies. They are thinner and lighter and draw much less
power than cathode ray tubes (CRTs), for example.
A simple LCD display from a calculator
But just what are these things called liquid crystals? The name "liquid crystal" sounds like a
contradiction. We think of a crystal as a solid material like quartz, usually as hard as rock,
and a liquid is obviously different. How could any material combine the two?
In this edition of HowStuffWorks, you'll find out how liquid crystals pull off this amazing trick,
and we will look at the underlying technology that makes LCDs work. You'll also learn how
the strange characteristics of liquid crystals have been used to create a new kind of shutter
and how grids of these tiny shutters open and close to make patterns that represent
numbers, words or images!
LCD History
Today, LCDs are everywhere we look, but they didn't sprout up overnight. It took a long
time to get from the discovery of liquid crystals to the multitude of LCD applications we
now enjoy. Liquid crystals were first discovered in 1888, by Austrian botanist Friedrich
Reinitzer. Reinitzer observed that when he melted a curious cholesterol-like substance
(cholesteryl benzoate), it first became a cloudy liquid and then cleared up as its
temperature rose. Upon cooling, the liquid turned blue before finally crystallizing. Eighty
years passed before RCA made the first experimental LCD in 1968. Since then, LCD
manufacturers have steadily developed ingenious variations and improvements on the
technology, taking the LCD to amazing levels of technical complexity. And there is every
indication that we will continue to enjoy new LCD developments in the future

2. Liquid Crystals
We learned in school that there are three common states of matter: solid, liquid or gaseous.
Solids act the way they do because their molecules always maintain their orientation and
stay in the same position with respect to one another. The molecules in liquids are just the
opposite: They can change their orientation and move anywhere in the liquid. But there are
some substances that can exist in an odd state that is sort of like a liquid and sort of like a
solid. When they are in this state, their molecules tend to maintain their orientation, like the
molecules in a solid, but also move around to different positions, like the molecules in a
liquid. This means that liquid crystals are neither a solid nor a liquid. That's how they ended
up with their seemingly contradictory name.
So, do liquid crystals act like solids or liquids or something else? It turns out that liquid
crystals are closer to a liquid state than a solid. It takes a fair amount of heat to change a
suitable substance from a solid into a liquid crystal, and it only takes a little more heat to turn
that same liquid crystal into a real liquid. This explains why liquid crystals are very sensitive
to temperature and why they are used to make thermometers and mood rings. It also
explains why a laptop computer display may act funny in cold weather or during a hot day at
the beach!
Just as there are many varieties of solids and liquids, there is also a variety of liquid crystal
substances. Depending on the temperature and particular nature of a substance, liquid
crystals can be in one of several distinct phases (see below). In this article, we will discuss
liquid crystals in the nematic phase, the liquid crystals that make LCDs possible.
One feature of liquid crystals is that they're affected by electric current. A particular sort of
nematic liquid crystal, called twisted nematics (TN), is naturally twisted. Applying an electric
current to these liquid crystals will untwist them to varying degrees, depending on the
current's voltage. LCDs use these liquid crystals because they react predictably to electric
current in such a way as to control light passage.
Liquid Crystal Types
Most liquid crystal molecules are rod-shaped and are broadly categorized as either
thermotropic or lyotropic.
Image courtesy Dr. Oleg Lavrentovich, Liquid Crystal Institute
Thermotropic liquid crystals will react to changes in temperature or, in some cases, pressure.
The reaction of lyotropic liquid crystals, which are used in the manufacture of soaps and
detergents, depends on the type of solvent they are mixed with. Thermotropic liquid crystals
are either isotropic or nematic. The key difference is that the molecules in isotropic liquid
crystal substances are random in their arrangement, while nematics have a definite order or
pattern.
The orientation of the molecules in the nematic phase is based on the director. The director
can be anything from a magnetic field to a surface that has microscopic grooves in it. In the
nematic phase, liquid crystals can be further classified by the way molecules orient themselves
in respect to one another. Smectic, the most common arrangement, creates layers of

3. molecules. There are many variations of the smectic phase, such as smectic C, in which the
molecules in each layer tilt at an angle from the previous layer. Another common phase is
cholesteric, also known as chiral nematic. In this phase, the molecules twist slightly from one
layer to the next, resulting in a spiral formation.
Ferroelectric liquid crystals (FLCs) use liquid crystal substances that have chiral molecules
in a smectic C type of arrangement because the spiral nature of these molecules allows the
microsecond switching response time that make FLCs particularly suited to advanced displays.
Surface-stabilized ferroelectric liquid crystals (SSFLCs) apply controlled pressure through
the use of a glass plate, suppressing the spiral of the molecules to make the switching even
more rapid.
Building a Simple LCD
There's far more to building an LCD than simply creating a sheet of liquid crystals. The
combination of four facts makes LCDs possible:
• Light can be polarized. (See How Sunglasses Work for some fascinating information
on polarization!)
• Liquid crystals can transmit and change polarized light.
• The structure of liquid crystals can be changed by electric current.
• There are transparent substances that can conduct electricity.
An LCD is a device that uses these four facts in a surprising way!
To create an LCD, you take two pieces of polarized glass. A special polymer that creates
microscopic grooves in the surface is rubbed on the side of the glass that does not have the
polarizing film on it. The grooves must be in the same direction as the polarizing film. You
then add a coating of nematic liquid crystals to one of the filters. The grooves will cause
the first layer of molecules to align with the filter's orientation. Then add the second piece of
glass with the polarizing film at a right angle to the first piece. Each successive layer of TN
molecules will gradually twist until the uppermost layer is at a 90-degree angle to the bottom,
matching the polarized glass filters.
As light strikes the first filter, it is polarized. The molecules in each layer then guide the light
they receive to the next layer. As the light passes through the liquid crystal layers, the
molecules also change the light's plane of vibration to match their own angle. When the light
reaches the far side of the liquid crystal substance, it vibrates at the same angle as the final
layer of molecules. If the final layer is matched up with the second polarized glass filter, then
the light will pass through.

4. If we apply an electric charge to liquid crystal molecules, they untwist! When they straighten
out, they change the angle of the light passing through them so that it no longer matches the
angle of the top polarizing filter. Consequently, no light can pass through that area of the
LCD, which makes that area darker than the surrounding areas.
Building a simple LCD is easier than you think. Your start with the sandwich of glass and
liquid crystals described above and add two transparent electrodes to it. For example,
imagine that you want to create the simplest possible LCD with just a single rectangular
electrode on it. The layers would look like this:
The LCD needed to do this job is very basic. It has a mirror (A) in back, which makes it
reflective. Then, we add a piece of glass (B) with a polarizing film on the bottom side, and a
common electrode plane (C) made of indium-tin oxide on top. A common electrode plane
covers the entire area of the LCD. Above that is the layer of liquid crystal substance (D).
Next comes another piece of glass (E) with an electrode in the shape of the rectangle on the
bottom and, on top, another polarizing film (F), at a right angle to the first one.
The electrode is hooked up to a power source like a battery. When there is no current, light
entering through the front of the LCD will simply hit the mirror and bounce right back out. But
when the battery supplies current to the electrodes, the liquid crystals between the common-
plane electrode and the electrode shaped like a rectangle untwist and block the light in that
region from passing through. That makes the LCD show the rectangle as a black area.

5. Backlit vs. Reflective
Note that our simple LCD required an external light source. Liquid crystal materials emit no
light of their own. Small and inexpensive LCDs are often reflective, which means to display
anything they must reflect light from external light sources. Look at an LCD watch: The
numbers appear where small electrodes charge the liquid crystals and make the layers
untwist so that light is not transmitting through the polarized film.
Most computer displays are lit with built-in fluorescent tubes above, beside and sometimes
behind the LCD. A white diffusion panel behind the LCD redirects and scatters the light
evenly to ensure a uniform display. On its way through filters, liquid crystal layers and
electrode layers, a lot of this light is lost -- often more than half!
In our example, we had a common electrode plane and a single electrode bar that controlled
which liquid crystals responded to an electric charge. If you take the layer that contains the
single electrode and add a few more, you can begin to build more sophisticated displays.
LCD Systems
Common-plane-based LCDs are good for simple displays that need to show the same
information over and over again. Watches and microwave timers fall into this category.
Although the hexagonal bar shape illustrated previously is the most common form of
electrode arrangement in such devices, almost any shape is possible. Just take a look at
some inexpensive handheld games: Playing cards, aliens, fish and slot machines are just
some of the electrode shapes you'll see!
There are two main types of LCDs used in computers, passive matrix and active matrix.
Passive-matrix LCDs use a simple grid to supply the charge to a particular pixel on the
display. Creating the grid is quite a process! It starts with two glass layers called substrates.
One substrate is given columns and the other is given rows made from a transparent
conductive material. This is usually indium-tin oxide. The rows or columns are connected to

6. integrated circuits that control when a charge is sent down a particular column or row. The
liquid crystal material is sandwiched between the two glass substrates, and a polarizing film
is added to the outer side of each substrate. To turn on a pixel, the integrated circuit sends a
charge down the correct column of one substrate and a ground activated on the correct row
of the other. The row and column intersect at the designated pixel, and that delivers the
voltage to untwist the liquid crystals at that pixel.
The simplicity of the passive-matrix system is beautiful, but it has significant drawbacks,
notably slow response time and imprecise voltage control. Response time refers to the
LCD's ability to refresh the image displayed. The easiest way to observe slow response time
in a passive-matrix LCD is to move the mouse pointer quickly from one side of the screen to
the other. You will notice a series of "ghosts" following the pointer. Imprecise voltage control
hinders the passive matrix's ability to influence only one pixel at a time. When voltage is
applied to untwist one pixel, the pixels around it also partially untwist, which makes images
appear fuzzy and lacking in contrast.
Active-matrix LCDs depend on thin film transistors (TFT). Basically, TFTs are tiny
switching transistors and capacitors. They are arranged in a matrix on a glass substrate. To
address a particular pixel, the proper row is switched on, and then a charge is sent down the
correct column. Since all of the other rows that the column intersects are turned off, only the
capacitor at the designated pixel receives a charge. The capacitor is able to hold the charge
until the next refresh cycle. And if we carefully control the amount of voltage supplied to a
crystal, we can make it untwist only enough to allow some light through. By doing this in very
exact, very small increments, LCDs can create a gray scale. Most displays today offer 256
levels of brightness per pixel.

7. Color
An LCD that can show colors must have three subpixels with red, green and blue color
filters to create each color pixel.
Through the careful control and variation of the voltage applied, the intensity of each
subpixel can range over 256 shades. Combining the subpixels produces a possible palette
of 16.8 million colors (256 shades of red x 256 shades of green x 256 shades of blue), as
shown below. These color displays take an enormous number of transistors. For example, a
typical laptop computer supports resolutions up to 1,024x768. If we multiply 1,024 columns
by 768 rows by 3 subpixels, we get 2,359,296 transistors etched onto the glass! If there is a
problem with any of these transistors, it creates a "bad pixel" on the display. Most active
matrix displays have a few bad pixels scattered across the screen.
LCD Advances
LCD technology is constantly evolving. LCDs today employ several variations of liquid crystal
technology, including super twisted nematics (STN), dual scan twisted nematics (DSTN),
ferroelectric liquid crystal (FLC) and surface stabilized ferroelectric liquid crystal (SSFLC).
For an in-depth (and pretty technical) article that addresses all of technologies, see Liquid
Crystal Materials.
Display size is limited by the quality-control problems faced by manufacturers. Simply put, to
increase display size, manufacturers must add more pixels and transistors. As they increase
the number of pixels and transistors, they also increase the chance of including a bad
transistor in a display. Manufacturers of existing large LCDs often reject about 40 percent of
the panels that come off the assembly line. The level of rejection directly affects LCD price
since the sales of the good LCDs must cover the cost of manufacturing both the good and
bad ones. Only advances in manufacturing can lead to affordable displays in bigger sizes.
For more information on LCDs and related topics, check out the links on the next page.

8. How Plasma Displays Work
by Tom Harris › Introduction to How Plasma Displays
Work
› What is Plasma?
› Inside the Display
› Lots More Information
› Shop or Compare Prices
For the past 75 years, the vast majority of televisions have been built around the same
technology: the cathode ray tube (CRT). In a CRT television, a gun fires a beam of
Photo courtesy Sony
A plasma display from Sony
electrons (negatively-charged particles) inside a large glass tube. The electrons excite
phosphor atoms along the wide end of the tube (the screen), which causes the phosphor
atoms to light up. The television image is produced by lighting up different areas of the
phosphor coating with different colors at different intensities (see How Televisions Work for a
detailed explanation).
Cathode ray tubes produce crisp, vibrant images, but they do have a serious drawback: They
are bulky. In order to increase the screen width in a CRT set, you also have to increase the
length of the tube (to give the scanning electron gun room to reach all parts of the screen).
Consequently, any big-screen CRT television is going to weigh a ton and take up a sizable
chunk of a room.
Recently, a new alternative has

9. What is Plasma?
If you've read How Televisions Work, then you understand the basic idea of a standard
television or monitor. Based on the information in a video signal, the television lights up
thousands of tiny dots (called pixels) with a high-energy beam of electrons. In most systems,
there are three pixel colors -- red, green and blue -- which are evenly distributed on the
screen. By combining these colors in different proportions, the television can produce the
entire color spectrum.
The basic idea of a plasma display is to illuminate tiny colored fluorescent lights to form an
image. Each pixel is made up of three fluorescent lights -- a red light, a green light and a
Tuning In
Most plasma displays aren't technically
televisions, because they don't have a
television tuner. The television tuner is the
device that takes a television signal (the
one coming from a cable wire, for example)
and interprets it to create a video image.
Like LCD monitors, plasma displays are just
monitors that display a standard video
signal. To watch television on a plasma
display, you have to hook it up to a
separate unit that has its own television
tuner, such as a VCR.
blue light. Just like a CRT television, the plasma display varies the intensities of the different
lights to produce a full range of colors.
The central element in a fluorescent light is a plasma, a gas made up of free-flowing ions
(electrically charged atoms) and electrons (negatively charged particles). Under normal
conditions, a gas is mainly made up of uncharged particles. That is, the individual gas atoms
include equal numbers of protons (positively charged particles in the atom's nucleus) and
electrons. The negatively charged electrons perfectly balance the positively charged protons,
so the atom has a net charge of zero.
If you introduce many free electrons into the gas by establishing an electrical voltage across
it, the situation changes very quickly. The free electrons collide with the atoms, knocking
loose other electrons. With a missing electron, an atom loses its balance. It has a net
positive charge, making it an ion.

10. In a plasma with an electrical current running through it, negatively charged particles are
rushing toward the positively charged area of the plasma, and positively charged particles
are rushing toward the negatively charged area.
In this mad rush, particles are constantly bumping into each other. These collisions excite the
gas atoms in the plasma, causing them to release photons of energy. (For details on this
process, see How Fluorescent Lamps Work.)
Xenon and neon atoms, the atoms used in plasma screens, release light photons when
they are excited. Mostly, these atoms release ultraviolet light photons, which are invisible to
the human eye. But ultraviolet photons can be used to excite visible light photons, as we'll
see in the next section.

11. Inside the Display
The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny
cells positioned between two plates of glass. Long electrodes are also sandwiched between
the glass plates, on both sides of the cells. The address electrodes sit behind the cells,
along the rear glass plate. The transparent display electrodes, which are surrounded by an
insulating dielectric material and covered by a magnesium oxide protective layer, are
mounted above the cell, along the front glass plate.
Both sets of electrodes extend across the entire screen. The display electrodes are arranged
in horizontal rows along the screen and the address electrodes are arranged in vertical
columns. As you can see in the diagram below, the vertical and horizontal electrodes form a
basic grid.

12. To ionize the gas in a particular cell, the plasma display's computer charges the electrodes
that intersect at that cell. It does this thousands of times in a small fraction of a second,
charging each cell in turn.
When the intersecting electrodes are charged (with a voltage difference between them), an
electric current flows through the gas in the cell. As we saw in the last section, the current
creates a rapid flow of charged particles, which stimulates the gas atoms to release
ultraviolet photons.
The released ultraviolet photons interact with phosphor material coated on the inside wall
of the cell. Phosphors are substances that give off light when they are exposed to other light.
When an ultraviolet photon hits a phosphor atom in the cell, one of the phosphor's electrons
jumps to a higher energy level and the atom heats up. When the electron falls back to its
normal level, it releases energy in the form of a visible light photon.

13. The phosphors in a plasma display give off colored light when they are excited. Every pixel
is made up of three separate subpixel cells, each with different colored phosphors. One
subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel
has a blue light phosphor. These colors blend together to create the overall color of the pixel.
By varying the pulses of current flowing through the different cells, the control system can
increase or decrease the intensity of each subpixel color to create hundreds of different
combinations of red, green and blue. In this way, the control system can produce colors
across the entire spectrum.
The main advantage of plasma display technology is that you can produce a very wide
screen using extremely thin materials. And because each pixel is lit individually, the image is
very bright and looks good from almost every angle. The image quality isn't quite up to the
standards of the best cathode ray tube sets, but it certainly meets most people's
expectations.
The biggest drawback of this technology has to be the price. With prices starting at $4,000
and going all the way up past $20,000, these sets aren't exactly flying off the shelves. But as
prices fall and technology advances, they may start to edge out the old CRT sets. In the near
future, setting up a new TV might be as easy as hanging a picture!
To learn more about plasma displays, as well as other television technologies, check out the
links on the next page.

14. On the most basic level, human beings are made up of five major components:

15. • A body structure
Photo courtesy NASA
Like you, NASA's robonaut has a movable
body, brain, power system and sensor
system.
• A muscle system to move the body structure
• A sensory system that receives information about the body and the surrounding
environment
• A power source to activate the muscles and sensors
• A brain system that processes sensory information and tells the muscles what to do
Of course, we also have some intangible attributes, such as intelligence and morality, but on
the sheer physical level, the list above about covers it.
A robot is made up of the very same components. A typical robot has a movable physical
structure, a motor of some sort, a sensor system, a power supply and a computer "brain" that
controls all of these elements. Essentially, robots are man-made versions of animal life --
they are machines that replicate human and animal behavior.
In this edition of HowStuffWorks, we'll explore the basic concept of robotics and find out
how robots do what they do.
What is a Robot?
Joseph Engelberger, a pioneer in industrial robotics, once remarked "I can't define a robot,
but I know one when I see one." If you consider all the different machines people call robots,
you can see that it's nearly impossible to come up with a comprehensive definition.
Everybody has a different idea of what constitutes a robot.
You've probably heard of several of these famous robots:
• R2D2 and C-3PO: The intelligent, speaking robots with loads of personality in the
Star Wars movies
• Sony's AIBO: A robotic dog that learns through human interaction
• Honda's ASIMO: A robot that can walk on two legs like a person
• Industrial robots: Automated machines that work on assembly lines
• Data: The almost human android from Star Trek
• BattleBots: The remote control fighters on Comedy Central
• Bomb-defusing robots
• The Mars Pathfinder: NASA's exploration robot
• HAL: The ship's computer in Stanley Kubrick's 2001: A Space Odyssey

16. • Robomower: The lawn-mowing robot from Friendly Robotics
• The Robot in the television series "Lost in Space"
• MindStorms: LEGO's popular robotics kit
HowStuffWorks has several articles on other types of robots:
• How Robotic Surgery Will Work
• How Robonauts Will Work
• How Snakebots Will Work
• How Rumble Robots Work
• How Stinger Missiles Work
All of these things are considered robots, at least by some people. The broadest definition
around defines a robot as anything that a lot of people recognize as a robot. Most roboticists
(people who build robots) use a more precise definition. They specify that robots have a
reprogrammable brain (a computer) that moves a body.
By this definition, robots are distinct from other movable machines, such as cars, because of
their computer element. Many new cars do have an onboard computer, but it's only there to
make small adjustments. You control most elements in the car directly by way of various
mechanical devices. Robots are distinct from ordinary computers in their physical nature --
normal computers don't have a physical body attached to them.
In the next section, we'll look at the major elements found in most robots today.
Robot Basics
The vast majority of robots do have several qualities in common. First of all, almost all robots
have a movable body. Some only have motorized wheels, and others have dozens of
movable segments, typically made of metal or plastic. Like the bones in your body, the
individual segments are connected together with joints.

17. Robots spin wheels and pivot jointed segments with some
sort of actuator. Some robots use electric motors and
solenoids as actuators; some use a hydraulic system; and
some use a pneumatic system (a system driven by
compressed gases). Robots may use all these actuator
Photo courtesy NASA
types. A robotic hand, developed by NASA, is
made up of metal segments moved by tiny
motors. The hand is one of the most
difficult structures to replicate in robotics.
A robot needs a power source to drive these actuators. Most robots either have a battery or
they plug into the wall. Hydraulic robots also need a pump to pressurize the hydraulic fluid,
and pneumatic robots need an air compressor or compressed air tanks.
The actuators are all wired to an electrical circuit. The circuit powers electrical motors and
solenoids directly, and it activates the hydraulic system by manipulating electrical valves.
The valves determine the pressurized fluid's path through the machine. To move a hydraulic
leg, for example, the robot's controller would open the valve leading from the fluid pump to a
piston cylinder attached to that leg. The pressurized fluid would extend the piston, swiveling
the leg forward. Typically, in order to move their segments in two directions, robots use
pistons that can push both ways.
The robot's computer controls everything attached to the circuit. To move the robot, the
computer switches on all the necessary motors and valves. Most robots are
reprogrammable -- to change the robot's behavior, you simply write a new program to its
computer.
Not all robots have sensory systems, and few have the ability to see, hear, smell or taste.
The most common robotic sense is the sense of movement -- the robot's ability to monitor its
own motion. A standard design uses slotted wheels attached to the robot's joints. An LED on
one side of the wheel shines a beam of light through the slots to a light sensor on the other
side of the wheel. When the robot moves a particular joint, the slotted wheel turns. The slots
break the light beam as the wheel spins. The light sensor reads the pattern of the flashing
light and transmits the data to the computer. The computer can tell exactly how far the joint
has swiveled based on this pattern. This is the same basic system used in computer mice.
These are the basic nuts and bolts of robotics. Roboticists can combine these elements in an
infinite number of ways to create robots of unlimited complexity. In the next section, we'll look
at one of the most popular designs, the robotic arm.
The Robotic Arm
The term robot comes from the Czech word robota, generally translated as "forced labor."
This describes the majority of robots fairly well. Most robots in the world are designed for
heavy, repetitive manufacturing work. They handle tasks that are difficult, dangerous or
boring to human beings.

18. Robotic arms are an essential part of car manufacturing.
The most common manufacturing robot is the robotic arm. A typical robotic arm is made up
of seven metal segments, joined by six joints. The computer controls the robot by rotating
individual step motors connected to each joint (some larger arms use hydraulics or
pneumatics). Unlike ordinary motors, step motors move in exact increments (check out this
site to find out how). This allows the computer to move the arm very precisely, repeating
exactly the same movement over and over again. The robot uses motion sensors to make
sure it moves just the right amount.
An industrial robot with six joints closely resembles a human arm -- it has the equivalent of a
shoulder, an elbow and a wrist. Typically, the shoulder is mounted to a stationary base
structure rather than to a movable body. This type of robot has six degrees of freedom,
meaning it can pivot in six different ways. A human arm, by comparison, has seven degrees
of freedom.

19. Your arm's job is to move your hand from place to place. Similarly, the robotic arm's job is to
move an end effector from place to place. You can outfit robotic arms with all sorts of end
effectors, which are suited to a particular application. One common end effector is a
simplified version of the hand, which can grasp and carry different objects. Robotic hands
often have built-in pressure sensors that tell the computer how hard the robot is gripping a
particular object. This keeps the robot from dropping or breaking whatever it's carrying. Other
end effectors include blowtorches, drills and spray painters.
Industrial robots are designed to do exactly the same thing, in a controlled environment, over
and over again. For example, a robot might twist the caps onto peanut butter jars coming
down an assembly line. To teach a robot how to do its job, the programmer guides the arm
through the motions using a handheld controller. The robot stores the exact sequence of
movements in its memory, and does it again and again every time a new unit comes down
the assembly line.
Most industrial robots work in auto assembly lines, putting cars together. Robots can do a lot
of this work more efficiently than human beings because they are so precise. They always
drill in the exactly the same place, and they always tighten bolts with the same amount of
force, no matter how many hours they've been working. Manufacturing robots are also very
important in the computer industry. It takes an incredibly precise hand to put together a tiny
microchip.
Writing Robots
The Czech playwright Karel Capek originated the term robot in his 1920 play "R.U.R." In
the play, machine workers overthrow their human creators when a scientist gives them
emotions. Dozens of authors and filmmakers have revisited this scenario over the years.

20. Isaac Asimov took a more optimistic view in several novels and short stories. In his
works, robots are benign, helpful beings that adhere to a code of nonviolence against
humans -- the "Laws of Robotics."
Mobile Robots
Robotic arms are relatively easy to build and program because they only operate within a
confined area. Things get a bit trickier when you send a robot out into the world.
Photo courtesy NASA
NASA's FIDO Rover is designed for exploration on Mars.
The first obstacle is to give the robot a working locomotion system. If the robot will only need
to move over smooth ground, wheels or tracks are the best option. Wheels and tracks can
also work on rougher terrain if they are big enough. But robot designers often look to legs
instead, because they are more adaptable. Building legged robots also helps researchers
understand natural locomotion -- it's a useful exercise in biological research.
Typically, hydraulic or pneumatic pistons move robot legs back and forth. The pistons attach
to different leg segments just like muscles attach to different bones. It's a real trick getting all
these pistons to work together properly. As a baby, your brain had to figure out exactly the
right combination of muscle contractions to walk upright without falling over. Similarly, a
robot designer has to figure out the right combination of piston movements involved in
walking and program this information into the robot's computer. Many mobile robots have a
built-in balance system (a collection of gyroscopes, for example) that tells the computer
when it needs to correct its movements.

21. Photo courtesy NASA
NASA's Frogbot uses springs, linkages and motors to hop from place to place.
Bipedal locomotion (walking on two legs) is inherently unstable, which makes it very difficult
to implement in robots. To create more stable robot walkers, designers commonly look to the
animal world, specifically insects. Six-legged insects have exceptionally good balance, and
they adapt well to a wide variety of terrain.
Some mobile robots are controlled by remote -- a human tells them what to do and when to
do it. The remote control might communicate with the robot through an attached wire, or
using radio or infrared signals. Remote robots, often called puppet robots, are useful for
exploring dangerous or inaccessible environments, such as the deep sea or inside a
volcano. Some robots are only partially controlled by remote. For example, the operator
might direct the robot to go to a certain spot, but not steer it there -- the robot would find its
own way.
What is it Good For?
Mobile robots stand in for people in a number of ways. Some explore other planets or
inhospitable areas on Earth, collecting geological samples. Others seek out landmines in
former battlefields. The police sometimes use mobile robots to search for a bomb, or
even to apprehend a suspect.
Mobile robots also work in homes and businesses. Hospitals may use robots to transport
medications. Some museums use robots to patrol their galleries at night, monitoring air
quality and humidity levels. Several companies have developed robots that will vacuum
your house while you sleep.

22. Autonomous Mobility
Autonomous robots can act on their own, independent of any controller. The basic idea is
to program the robot to respond a certain way to outside stimuli. The very simple bump-and-
go robot is a good illustration of how this works.
This sort of robot has a bumper sensor to detect obstacles. When you turn the robot on, it
zips along in a straight line. When it finally hits an obstacle, the impact pushes in its bumper
sensor. The robot's programming tells it to back up, turn to the right and move forward again,
in response to every bump. In this way, the robot changes direction any time it encounters
an obstacle.
Photo courtesy NASA
The Urbie is an autonomous robot designed for various urban operations, including
military reconnaissance
and rescue operations.
Advanced robots use more elaborate versions of this same idea. Roboticists create new
programs and sensor systems to make robots smarter and more perceptive. Today, robots
can effectively navigate a variety of environments.
Simpler mobile robots use infrared or ultrasound sensors to see obstacles. These sensors
work the same way as animal echolocation: The robot sends out a sound signal or a beam of
infrared light and detects the signal's reflection. The robot locates the distance to obstacles
based on how long it takes the signal to bounce back.
More advanced robots use stereo vision to see the world around them. Two cameras give
these robots depth perception, and image-recognition software gives them the ability to
locate and classify various objects. Robots might also use microphones and smell sensors to
analyze the world around them.
Some autonomous robots can only work in a familiar, constrained environment. Lawn-
mowing robots, for example, depend on buried border markers to define the limits of their
yard. An office-cleaning robot might need a map of the building in order to maneuver from
point to point.

23. More advanced robots can analyze and adapt to unfamiliar environments, even to areas
with rough terrain. These robots may associate certain terrain patterns with certain actions. A
rover robot, for example, might construct a map of the land in front of it based on its visual
sensors. If the map shows a very bumpy terrain pattern, the robot knows to travel another
way. This sort of system is very useful for exploratory robots that operate on other planets
(check out this page to learn more).
An alternative robot design takes a less structured approach -- randomness. When this type
of robot gets stuck, it moves its appendages every which way until something works. Force
sensors work very closely with the actuators, instead of the computer directing everything
based on a program. This is something like an ant trying to get over an obstacle -- it doesn't
seem to make a decision when it needs to get over an obstacle, it just keeps trying things
until it gets over it.
Homebrew Robots
In the last couple of sections, we looked at the most prominent fields in the world of robots --
industry robotics and research robotics. Professionals in these fields have made most of the
major advancements in robotics over the years, but they aren't the only ones making robots.
For decades, a small but passionate band of hobbyists has been creating robots in garages
and basements all over the world.
Homebrew robotics is a rapidly expanding subculture with a sizable Web presence. Amateur
roboticists cobble together their creations using commercial robot kits, mail order
components, toys and even old VCRs.
Homebrew robots are as varied as professional robots. Some weekend roboticists tinker with
elaborate walking machines, some design their own service bots and others create
competitive robots. The most familiar competitive robots are remote control fighters like you
might see on "BattleBots." These machines aren't considered "true robots" because they
don't have reprogrammable computer brains. They're basically souped-up remote control
cars.
More advanced competitive robots are controlled by computer. Soccer robots, for example,
play miniaturized soccer with no human input at all. A standard soccer bot team includes
several individual robots that communicate with a central computer. The computer "sees" the
entire soccer field with a video camera and picks out its own team members, the opponent's
members, the ball and the goal based on their color. The computer processes this
information at every second and decides how to direct its own team.
Check out the official RoboCup Web site for more information on Soccer robots, and this
page for information on other robot competitions. This page will give you more information on
building your own robots.
Adaptable and Universal
The personal computer revolution has been marked by extraordinary adaptability.
Standardized hardware and programming languages let computer engineers and amateur
programmers mold computers to their own particular purposes. Computer components are
sort of like art supplies -- they have an infinite number of uses.

24. Most robots to date have been more like kitchen appliances. Roboticists build them from the
ground up for a fairly specific purpose. They don't adapt well to radically new applications.
This situation may be changing. A new company called Evolution Robotics is pioneering the
world of adaptable robotics hardware and software. The company hopes to carve out a niche
for itself with easy-to-use "robot developer kits."
The kits come with an open software platform tailored to a range of common robotic
functions. For example, roboticists can easily give their creations the ability to follow a target,
listen to voice commands and maneuver around obstacles. None of these capabilities are
revolutionary from a technology standpoint, but it's unusual that you would find them in one
simple package.
The kits also come with common robotics hardware that connects easily with the software.
The standard kit comes with infrared sensors, motors, a microphone and a video camera.
Roboticists put all these pieces together with a souped-up erector set -- a collection of
aluminum body pieces and sturdy wheels.
These kits aren't your run-of-the-mill construction sets, of course. At upwards of $1,000,
they're not cheap toys. But they are a big step toward a new sort of robotics. In the near
future, creating a new robot to clean your house or take care of your pets while you're away
might be as simple as writing a BASIC program to balance your checkbook.
The Future: AI
AI in the Movies
• The Matrix
• AI
• Blade Runner
• 2001: A Space Odyssey
• Demon Seed
• Bicentennial Man
• Westworld
• The Terminator
• Short Circuit
Artificial intelligence (AI) is arguably the most exciting field in robotics. It's certainly the
most controversial: Everybody agrees that a robot can work in an assembly line, but there's
no consensus on whether a robot can ever be intelligent.
Like the term "robot" itself, artificial intelligence is hard to define. Ultimate AI would be a
recreation of the human thought process -- a man-made machine with our intellectual
abilities. This would include the ability to learn just about anything, the ability to reason, the
ability to use language and the ability to formulate original ideas. Roboticists are nowhere
near achieving this level of artificial intelligence, but they have had made a lot of progress
with more limited AI. Today's AI machines can replicate some specific elements of
intellectual ability.
Computers can already solve problems in limited realms. The basic idea of AI problem-
solving is very simple, though its execution is complicated. First, the AI robot or computer

25. gathers facts about a situation through sensors or human input. The computer compares this
information to stored data and decides what the information signifies. The computer runs
through various possible actions and predicts which action will be most successful based on
the collected information. Of course, the computer can only solve problems it's programmed
to solve -- it doesn't have any generalized analytical ability. Chess computers are one
example of this sort of machine.
Some modern robots also have the ability to learn in a limited capacity. Learning robots
recognize if a certain action (moving its legs in a certain way, for instance) achieved a
desired result (navigating an obstacle). The robot stores this information and attempts the
successful action the next time it encounters the same situation. Again, modern computers
can only do this in very limited situations. They can't absorb any sort of information like a
human can. Some robots can learn by mimicking human actions. In Japan, roboticists have
taught a robot to dance by demonstrating the moves themselves.
Some robots can interact socially. Kismet, a robot at M.I.T's Artificial Intelligence Lab,
recognizes human body language and voice inflection and responds appropriately. Kismet's
creators are interested in how humans and babies interact, based only on tone of speech
and visual cue. This low-level interaction could be the foundation of a human-like learning
system.
Kismet and other humanoid robots at the M.I.T. AI Lab operate using an unconventional
control structure. Instead of directing every action using a central computer, the robots
control lower-level actions with lower-level computers. The program's director, Rodney
Brooks, believes this is a more accurate model of human intelligence. We do most things
automatically; we don't decide to do them at the highest level of consciousness.
The real challenge of AI is to understand how natural intelligence works. Developing AI isn't
like building an artificial heart -- scientists don't have a simple, concrete model to work from.
We do know that the brain contains billions and billions of neurons, and that we think and
learn by establishing electrical connections between different neurons. But we don't know
exactly how all of these connections add up to higher reasoning, or even low-level
operations. The complex circuitry seems incomprehensible.
Because of this, AI research is largely theoretical. Scientists hypothesize on how and why we
learn and think, and they experiment with their ideas using robots. Brooks and his team
focus on humanoid robots because they feel that being able to experience the world like a
human is essential to developing human-like intelligence. It also makes it easier for people to
interact with the robots, which potentially makes it easier for the robot to learn.
Just as physical robotic design is a handy tool for understanding animal and human
anatomy, AI research is useful for understanding how natural intelligence works. For some
roboticists, this insight is the ultimate goal of designing robots. Others envision a world where
we live side by side with intelligent machines and use a variety of lesser robots for manual
labor, health care and communication. A number of robotics experts predict that robotic
evolution will ultimately turn us into cyborgs -- humans integrated with machines.
Conceivably, people in the future could load their minds into a sturdy robot and live for
thousands of years!
In any case, robots will certainly play a larger role in our daily lives in the future. In the
coming decades, robots will gradually move out of the industrial and scientific worlds and
into daily life, in the same way that computers spread to the home in the 1980s.

26. The best way to understand robots is to look at specific designs. The links on the next page
will show you a variety of robot projects around the world