Build a Robot IV
Cameras have been mounted on robots for decades (going all the way back to the bulky one that gave SRI's Shakey its shake). Cameras are most commonly used on robots that are teleoperated, that is, operated by a human at a distance (either at the end of a tether of control cables or over a radio link). With the advent of the Internet and cheap digital Web cameras, robots can now send video signals through the Net so that humans can see what the robot sees, or even control the robot remotely.
Getting a robot vision system to analyze its video input (moving, real-time, unpredictable input) and make sense of it is still a daunting challenge. However, those in the field of biometrics are making inroads into this challenge. Human facial identification is becoming a more common technology, especially in security systems. Here, face size and proportional information, skin tone, and other factors can be used to match a face with a database of stored faces. Unfortunately, this only works if the person is staring directly into the camera lens.
Robot vision systems are getting better at detecting humans in a "scene," tracking moving objects, making out saturated colors, and roughly understanding three dimensional objects. They still struggle with telling men from women, interpreting objects if the camera is in motion, determining what materials objects are made of, and determining "gaze direction" (where the person is looking). Honda has made some advances with the latter problem. The current version of its Asimo humanoid can tell where a person is looking if the person both looks at and points to the target object.
Security robots and others designed to detect fire are outfitted with what are called infrared pyroelectric sensors. These sensors detect a combination of heat and movement. If they see some nasty, dancing flames in front of them (registering both movement and heat), the sensors are triggered (and the robot will usually call for human backup). These same sensors are used as motion detectors and will detect the heat and movement of a person within a certain range (see Figure 4.13).
The infamous Genghis, the six-legged robocritter built at MIT's AI Lab in the late '80s, used six pyroelectric sensors on its "head" so that it would follow humans around, attracted to their movement and body heat. Photo courtesy of Rodney Brooks and the MIT AI Lab.
Robots can be outfitted with "electric noses" that can sense a variety of toxic gases. Common on security or industrial robots, triggering this type of sensor usually means a call to a human who decides the nature of the threat. Robots might have become fairly sophisticated, but we're still not comfortable letting them handle a ruptured gas main on their own.
Other Types of Sensors
There are dozens more sensor types than what we've already covered. Here are just a few more and a word or two on each:
- Encoders-Optical or magnetic sensors that "read" the rotation of a robot's wheels to measure distance traveled.
- GPS receiver-A device that can access the Global Positioning Satellite (GPS) system, using the location of several orbiting satellites to pinpoint a robot's location on the ground (outdoor robots only).
- Strain gauges-For measuring the physical force exerted on an object. Used in touch sensors, gripper force feedback, and collision detection.
- Tilt sensors-Used to indicate the attitude of a robot. Sometimes used for balance, especially in walking robots. If the sensor detects that the robot is on a dangerous angle, and at risk of falling over, it will "ask" the robot's controller to back it away from the threatening terrain.
The Absolute Beginner's Guide to Building Robots by Gareth Branwyn, ISBN-10: 0-78972971-7 is available from InformIT. Permission to reprint granted by Pearson Publshing.