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Honda's ASIMO robot.  See more pictures of robots.

Photo courtesy Honda Motor Co., Ltd.

Introduction to How ASIMO Works

Want a robot to cook your dinner, do your homework, clean your house, or get your groceries? Robots already do a lot of the jobs that we humans don't want to do, can't do, or simply can't do as well as our robotic counterparts. In factories around the world, disembodied robot arms assemble cars, delicately place candies into their boxes, and do all sorts of tedious jobs. There are even a handful of robots on the market whose sole job is to vacuum the floor or mow your lawn.

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Many of us grew up watching robots on TV and in the movies: There was Rosie, the Jetsons' robot housekeeper; Data, the android crewmember on "Star Trek: The Next Generation"; and of course, C3PO from "Star Wars." The robots being created today aren't quite in the realm of Data or C3PO, but there have been some amazing advances in their technology. Honda engineers have been busy creating the ASIMO robot for more than 20 years. In this article, we'll find out what makes ASIMO the most advanced humanoid robot to date.

The Honda Motor Company developed ASIMO, which stands for Advanced Step in Innovative Mobility, and is the most advanced humanoid robot in the world. According to the ASIMO Web site, ASIMO is the first humanoid robot in the world that can walk independently and climb stairs.

In addition to ASIMO's ability to walk like we do, it can also understand preprogrammed gestures and spoken commands, recognize voices and faces and interface with IC Communication cards. ASIMO has arms and hands so it can do things like turn on light switches, open doors, carry objects, and push carts.

Rather than building a robot that would be another toy, Honda wanted to create a robot that would be a helper for people -- a robot to help around the house, help the elderly, or help someone confined to a wheelchair or bed. ASIMO is 4 feet 3 inches (1.3 meters) high, which is just the right height to look eye to eye with someone seated in a chair. This allows ASIMO to do the jobs it was created to do without being too big and menacing. Often referred to as looking like a "kid wearing a spacesuit," ASIMO's friendly appearance and nonthreatening size work well for the purposes Honda had in mind when creating it.

ASIMO is just 4 feet 3 inches tall

Photo courtesy Honda Motor Co., Ltd.

ASIMO could also do jobs that are too dangerous for humans to do, like going into hazardous areas, disarming bombs, or fighting fires.

ASIMO's physiology is developed to mimic human physiology.

Photo courtesyHonda Motor Co., Ltd.

ASIMO's Motion: Walk Like a Human

Honda researchers began by studying the legs of insects, mammals, and the motion of a mountain climber with prosthetic legs to better understand the physiology and all of the things that take place when we walk -- particularly in the joints. For example, the fact that we shift our weight using our bodies and especially our arms in order to balance was very important in getting ASIMO's walking mechanism right. The fact that we have toes that help with our balance was also taken into consideration: ASIMO actually has soft projections on its feet that play a similar role to the one our toes play when we walk. This soft material also absorbs impact on the joints, just as our soft tissues do when we walk.

ASIMO has hip, knee, and foot joints. Robots have joints that researchers refer to as "degrees of freedom." A single degree of freedom allows movement either right and left or up and down. ASIMO has 34 degrees of freedom spread over different points of its body in order to allow it to move freely. There are three degrees of freedom in ASIMO's neck, seven on each arm and six on each leg. The number of degrees of freedom necessary for ASIMO's legs was decided by measuring human joint movement while walking on flat ground, climbing stairs and running.

ASIMO also has a speed sensor and a gyroscope sensor mounted on its body. They perform the tasks of:

  • sensing the position of ASIMO's body and the speed at which it is moving
  • relaying adjustments for balance to the central computer

These sensors work similarly to our inner ears in the way they maintain balance and orientation.

ASIMO also has floor surface sensors in its feet and six ultrasonic sensors in its midsection. These sensors enhance ASIMO's ability to interact with its environment by detecting objects around ASIMO and comparing gathered information with maps of the area stored in ASIMO's memory.

To accomplish the job our muscles and skin do in sensing muscle power, pressure and joint angles, ASIMO has both joint-angle sensors and a six-axis force sensor.

Photo courtesy Honda Motor Co., Ltd.

Unless you know a lot about robotics, you may not fully grasp the incredible milestone it is that ASIMO walks as we do. The most significant part of ASIMO's walk is the turning capabilities. Rather than having to stop and shuffle, stop and shuffle, and stop and shuffle into a new direction, ASIMO leans and smoothly turns just like a human. ASIMO can also self-adjust its steps in case it stumbles, is pushed, or otherwise encounters something that alters normal walking.

In order to accomplish this, ASIMO's engineers had to find a way to work with the inertial forces created when walking. For example, the earth's gravity creates a force, as does the speed at which you walk. Those two forces are called the "total inertial force." There is also the force created when your foot connects with the ground, called the "ground reaction force." These forces have to balance out, and posture has to work to make it happen. This is called the "zero moment point" (ZMP).

To control ASIMO's posture, engineers worked on three areas of control:

  • Floor reaction control means that the soles of the feet absorb floor unevenness while still maintaining a firm stance.
  • Target ZMP control means that when ASIMO can't stand firmly and its body begins to fall forward, it maintains position by moving its upper body in the direction opposite the impending fall. At the same time, it speeds up its walking to quickly counterbalance the fall.
  • Foot-planting location control kicks in when the target ZMP control has been activated. It adjusts the length of the step to regain the right relationship between the position and speed of the body and the length of the step.

ASIMO's Motion: Smooth Moves

ASIMO can sense falling movements and react to them quickly; but ASIMO's engineers wanted more. They wanted the robot to have a smooth gait as well as do something that other robots can't do -- turn without stopping.

When we walk around corners, we shift our center of gravity into the turn. ASIMO uses a technology called "predictive movement control," also called Honda's Intelligent Real-Time Flexible Walking Technology or I-Walk, to accomplish that same thing. ASIMO predicts how much it should shift its center of gravity to the inside of the turn and how long that shift should be maintained. Because this technology works in real time, ASIMO can do this without stopping between steps, which other robots must do.

Essentially, with every step ASIMO takes, it has to determine its inertia and then predict how its weight needs to be shifted for the next step in order to walk and turn smoothly. It adjusts any of the following factors in order to maintain the right position:

  • the length of its steps
  • its body position
  • its speed
  • the direction in which it is stepping

While reproducing a human-like walk is an amazing achievement, ASIMO can now run at speeds up to 3.7 miles per hour (6 kilometers per hour). In order to qualify as a true running robot, ASIMO must have both feet off the ground for an instant in each step. ASIMO manages to be airborne for .08 seconds with each step while running.

Honda engineers encountered an entirely new set of challenges while trying to give ASIMO the ability to run. They gave ASIMO’s torso a degree of freedom to aid in bending and twisting so that the robot could adjust its posture while airborne. Without this ability, ASIMO would lose control while airborne, possibly spinning in the air or tripping when landing.

In order to make turns smoothly while running, the engineers enhanced ASIMO's ability to tilt its center of gravity inside turns to maintain balance and counteract centrifugal force. ASIMO could even anticipate turns and begin to lean into them before starting the turn, much like you would if you were skiing or skating.

In the next section, we’ll look at how ASIMO is able to recognize images and sense its environment.

Photo courtesy Honda Motor Co., Ltd.

ASIMO's Senses

In robotics, vision is a captured image that is interpreted based on programmed templates. In a manufacturing environment, where robotic arms build cars or robots inspect the microscopic connections on semiconductor chips, you're dealing with a controlled environment. The lighting is always the same, the angle is always the same, and there is a limited number of things to look at and understand. In the real (and unstructured) world, however, the number of things to look at and understand increases greatly.

A humanoid robot that must navigate through homes, buildings, or outdoors while performing jobs must be able to make sense of the many objects it "sees." Shadows, odd angles and movement must be understandable. For example, to walk on its own into an unknown area, a robot would have to detect and recognize objects in real time, selecting features such as color, shape and edges to compare to a database of objects or environments it knows about. There can be thousands of objects in the robot's "memory."

ASIMO's vision system consists of two basic video cameras for eyes, located in its head. ASIMO uses stereoscopic vision and a proprietary vision algorithm that lets it see, recognize, and avoid running into objects even if their orientation and lighting are not the same as those in its memory database. These cameras can detect multiple objects, determine distance, perceive motion, recognize programmed faces and even interpret hand motions. For example, when you hold your hand up to ASIMO in a "stop" position, ASIMO stops. The facial recognition feature allows ASIMO to greet "familiar" people.

ASIMO can recognize objects in motion by interpreting the images captured by the cameras in its head. It can assess a moving object’s distance and direction, which allows ASIMO to follow a person, stop its own progress to allow a moving object to cross its path, or greet you as you approach.

The cameras also relay what ASIMO sees to ASIMO's controller. That way, if you're controlling ASIMO from a PC, you can see what ASIMO sees.

In addition to the cameras in its head, ASIMO has several sensors that help it maneuver through environments and interact with objects and people. Floor surface sensors allow ASIMO to detect objects and changes in the floor. Ultrasonic sensors help orient ASIMO by detecting surrounding objects. The sensors help ASIMO resolve discrepancies between the internal map of the area preprogrammed in its memory and the actual environment.

ASIMO even has a sense of touch, in a way. The force sensors in ASIMO's wrists allow ASIMO to judge how much force to use when picking up a tray, handing you a file or shaking your hand. ASIMO can integrate information gathered by its cameras and force sensors to move in sync with a person while holding hands. When pushing a cart, ASIMO's force sensors help the robot to adjust the amount of force needed to push the cart (for example, ASIMO can push a cart with more force if the sensors detect an incline).

Another way ASIMO can sense the environment is through the use of IC Communication cards. IC cards use infrared signals to receive and transmit information. If you hold an IC card with your information encoded on it, ASIMO can detect your presence even if you aren’t within the line of sight of its cameras. These cards enhance ASIMO’s ability to interact with others. For example, if you were to visit Honda’s office and receive an IC card as a visitor pass, ASIMO could greet you and direct you to the right room after electronically reading the information encoded on your card.

Robot Competitions

Can you read my mind?

Honda Research Institute and ATR Computational Neuroscience Laboratories partnered in 2006 to develop a means of controlling ASIMO through thought. Scientists and engineers used an MRI Machine to record a subject’s brain patterns when making a series of hand gestures (a closed fist and the “V” peace sign). The recording was then transmitted to a robotic hand, which decoded the information and duplicated the subject’s gestures. Because the MRI system was non-invasive, there was no need for any surgical procedures.

Honda hopes that this is the first step in developing a system that will allow paralyzed people to control devices such as ASIMO by simply thinking about it. Much more research must be done to allow users to execute complex tasks and to develop a smaller, lightweight device to record brain patterns.

Curious About Servos?

Check out the Northwestern University Mechatronics Design Laboratory's Introduction to Servo Motors.

Controlling and Powering ASIMO

ASIMO is not an autonomous robot. It can't enter a room and make decisions on its own about how to navigate. ASIMO either has to be programmed to do a specific job in a specific area that has markers that it understands, or it has to be manually controlled by a human.

ASIMO can be controlled by four methods:

  • Wireless controller (sort of like a joystick)
  • Gestures
  • Voice commands

Using 802.11 wireless technology and a laptop or desktop computer, you can control ASIMO as well as see what ASIMO sees via its camera eyes. ASIMO can also use its PC connection to access the Internet and retrieve information for you, such as weather reports and news.

The wireless joystick controller operates ASIMO's movements the same way you would operate a remote-control car. You can make ASIMO go forward, backward, sideways, diagonally, turn in place, walk around a corner or run in circles. Making ASIMO move by remote control may not seem that advanced, but ASIMO does have the ability to self-adjust its steps. If you have it walk forward, and it encounters a slope or some sort of obstacle, ASIMO automatically adjusts its steps to accommodate the terrain.

ASIMO can recognize and react to several gestures and body postures, allowing users to command ASIMO nonverbally. You can point to a particular spot you want ASIMO to walk towards, for example, and it will follow your lead. If you wave to ASIMO, it will respond with a wave of its own. It can even recognize when you want to shake its hand.

ASIMO can understand and execute simple, preprogrammed verbal commands. The number of commands that can be programmed into its memory is practically unlimited. You can also have your voice registered in its programming, making it easier for ASIMO to recognize you.

In addition to the voice commands for controlling ASIMO's movements, there are also spoken commands to which ASIMO can respond verbally. This is the feature that has made it possible for ASIMO to work as a receptionist, greeting visitors and answering questions.

Like most other technologies in the robotics field, ASIMO is powered by servo motors. These are small but powerful motors with a rotating shaft that moves limbs or surfaces to a specific angle as directed by a controller. Once the motor has turned to the appropriate angle, it shuts off until it is instructed to turn again. For example, a servo may control the angle of a robot's arm joint, keeping it at the right angle until it needs to move, and then controlling that move. Servos use a position-sensing device (also called a digital decoder) to ensure that the shaft of the motor is in the right position. They usually use power proportional to the mechanical load they are carrying. A lightly loaded servo, for example, doesn't use much energy.

ASIMO has 34 servo motors in its body that move its torso, arms, hands, legs, feet, ankles and other moving parts. ASIMO manages a series of servo motors to control each kind of movement.

ASIMO is powered by a rechargeable, 51.8 volt lithium ion (Li-ION) battery that lasts for one hour on a single charge. The battery is stored in ASIMO's backpack and weighs about 13 pounds. ASIMO's battery takes three hours to fully charge, so a second (and third) battery is crucial if you needed ASIMO to operate for very long. Users can charge the battery onboard ASIMO through a power connection or remove the backpack to charge separately.

ASIMO's Life Story

Honda began development of its humanoid helper robot in 1986. Honda engineers knew the robot had to be able to easily navigate around a house or building, and that meant the walking technology had to be perfect. Therefore, their first attempts were basically boxes with legs. Once the walking mechanism was mostly developed, arms, hands and finally a head were added.

The ASIMO Timeline

  • 1986 - Static walking The first robot Honda built was called EO. EO walked very slowly, taking sometimes 20 seconds to complete a single step. This was because EO did what was called "static walking." In static walking, after the robot begins moving one foot forward, it has to wait until it has its weight balanced on that foot before it begins to move the other foot forward. Humans don't walk that way, so the research continued.
  • 1987 - Dynamic walking By now engineers had developed a method for "dynamic walking," which is much more human-like. With this walking technology, the robot (now called prototype E1, soon followed by E2 and E3 as research progressed) leaned into the next step, shifting its weight and moving the other foot forward to catch itself so that rather than falling forward, it walked forward.
  • 1991 - Walking like a pro In prototypes E4, E5 and E6, Honda's engineers perfected the walking mechanism to the point where the robot could easily walk on an incline, up stairs and on uneven terrain. Because truly walking as a human actually requires the use of the body, arms and head, engineers had to move on to the next step and add the rest of the body.
  • 1993 - A more human-looking robot With a body, arms, hands and a head, the next generation of prototypes (P1, P2 and P3) looked more like a "humanoid." P1, however, was a looming 6 feet 2 inches (188 cm) tall and weighed 386 pounds (175 kg). P2 was scaled down slightly in height, but weighed an even heavier 463 pounds (210 kg) -- not something you want stepping on your toes in the kitchen. However, it could walk very well on uneven surfaces, inclines, and could even grasp objects and push carts. P2 could even maintain its balance when pushed. Finally, P3 was built at a more comfortable (and less frightening) 5 feet 2 inches (157 cm) tall. Weighing 287 pounds (130 kg), P3 could walk faster and more smoothly than its predecessors.
  • 1997 - ASIMO Even more improvements were made to the walking system, allowing ASIMO to walk gracefully and easily in almost any environment. Sophisticated hip joints allowed ASIMO to turn smoothly -- something other robots have to stop and shuffle in order to do. In thinking about how ASIMO was to be used, the engineers made the decision to further reduce ASIMO's size to 4 feet (122 cm) so that not only would it not be intimidating to people who were seated (or standing, for that matter), it would actually be at eye level. This height also made it possible for ASIMO to work at table height or at a computer, reach light switches and turn door knobs. ASIMO's very strong but lightweight magnesium-alloy body, covered in plastic "skin," weighed in at only 115 pounds (52 kg). Technology called "predicted movement control" allowed ASIMO to predict its next movement automatically and shift its weight to make a turn. ASIMO's stride could also be adjusted in real time to make it walk faster or slower. P2 and P3 had to use programmed walking patterns.
  • 2005 - Better, Faster, Stronger Engineers further refined ASIMO's motion system, boosting its walking speed from 2.5 to 2.7 kilometers per hour and giving ASIMO the ability to run at speeds up to 6 kilometers per hour. Honda increased ASIMO's height to 4 feet 3 inches (130 centimeters), and the robot put on a little weight, tipping the scales at 119 pounds. The engineers switched ASIMO's power supply to a lithium battery that doubles the amount of time it can operate before recharging. They also implemented the IC Communication card technology that helps ASIMO interact with people. New sensors allowed ASIMO to move in sync with people while holding hands.

Photo courtesy

ASIMO's Peers

In addition to ASIMO, there are some other pretty sophisticated humanoid robots out there that appear to do a lot of the same things. Most of them are built on a much smaller scale and are intended more for entertainment than service. Right now, ASIMO's greatest competition in terms of technology seem to be:

There are also several different robots used in hospitals around the world that navigate hallways and take elevators to deliver patient records, x-rays, medicines and other things all over the hospital. They travel on wheels and are programmed with the hospital layout or they identify and follow markers and bar codes placed on the walls.

Robots have been in use in many areas since the 1960s. With computer processors getting increasingly more powerful and technology in robotics expanding into new areas, it won't be long before we do have a "Rosie" to cook our meals and clean our houses.

For more information on ASIMO and other robots, as well as the technological advances that make humanoid robots possible, check out the links on the next page.

Lots More Information

Related HowStuffWorks ArticlesMore Great LinksSources
  • ASIMO http://asimo.honda.com
  • "ASIMO in Prague." Robotika.cz, August 26, 2003. http://robotika.cz/articles/asimo/en
  • ASIMO Technical Manual: Honda Motor Company http://asimo.honda.com/downloads/pdf/asimo-technical-information.pdf
  • D'Aluisio, Faith and Peter Menzel. "Evolution of a New Species: Robo Sapiens." MIT Press, 2000.
  • "Hospital porters go robotic." Engadget, June 24, 2004. http://robots.engadget.com
  • Kageyma, Yuri. "Honda devises way for brain signals to control robot." USA Today, May 24, 2006 http://www.usatoday.com/tech/news/robotics/ 2006-05-24-robot-brain_x.htm
  • MIT Artificial Intelligence Laboratory http://www.ai.mit.edu
  • NASA: Robotics Education Project http://robotics.nasa.gov
  • "The New Age of Service Robots: From Fighting Fires to Serving Beer." Knowledge at Wharton, The Wharton School, University of Pennsylvania, November 20, 2002.
  • Patent # 6016962: IC Communication Cards. United States Patent and Trademark Office. http://www.uspto.gov
  • Robot Hall of Fame http://www.robothalloffame.org
  • Robotics Online http://www.roboticsonline.com
  • Schulte, Bret. "ASIMO: Honda's New Compact Comes in Peace: It's Not Man's Best Friend, But It's No Terminator Either." Washington Post, August 3, 2002.
  • The Tech Museum of Innovation http://www.thetech.org/robotics
  • TrueForce: History Timeline of Robotics http://trueforce.com/Articles/Robot_History.htm
  • "Understanding Computers: Robotics." Time-Life Books, 1986.