FIGURE 1. Here are some of the sensors currently
offered by IFI. From left to right, these sensors include: the
VEX bumper switch, limit switch, ultrasonic ranger, and
optical encoder. Missing from this figure are the VEX IR
ranger, quadrature optical encoder, potentiometer, xyz
accelerometer, and a line following sensor.
Notice that they are all color-coded red to match the
Inventor’s Guide sensor subsystem.
www.servomagazine.com/index.php?/magazine/article/august2011_Ramirez
currently available, as well as other sensors that play
an important part in robotics.
Hearing
The human ear is an incredibly sensitive
instrument capable of hearing a broad range of sounds, and at
a frequency between 20 Hz and 20 kHz. Bats, on the other
hand, can hear up to 100 kHz and use this ability to fly in total
darkness using sonar.
Using transducers and microphones, a robot can pick up
sounds that exceed a bat’s ultrasonic hearing range but
unfortunately cannot understand what is being said, unless
voice recognition software (such as Dragon Systems) is used or
the robot has hardware that allows it to recognize words and
phrases, so it can carry out a set of commands.
One of the VEX sensors used to “hear” is the VEX
ultrasonic ranger which simulates a bat’s sonar by emitting
short 40 kHz chirps and receives the echoes in order to
compute the distance to objects anywhere from three
centimeters to three meters. One setup that can be used for
hearing is to connect a microphone (MIC) to one of the VEX
microcontroller’s analog-to-digital ports (ADC) with a preamp
and amplifier. Sounds and vocal commands can be processed
by a microcontroller or digital signal processor (DSP). Using a
microphone connected to the amplifier increases the signals so
that the 10-bit ADC can digitize the sounds into digital values
that range between 0 and 1023. Digital filtering may be
employed to convert the sounds and to compress the data.
Voice recognition involves analyzing the data using algorithms
to determine English words or commands. These commands
can be used to control your robot or prop using simple vocal
instructions such as “START,” “STOP,” “LEFT,” “RIGHT,” etc.
Sight
Sensors that let a robot “see” include the light sensor and
the IR Ranger sensor. The light sensor can detect if it is light or
dark in a room or outdoors. The Ranger uses IR ranging
techniques to determine the distance between the sensor and
an object nearby. The VEX wireless video camera provides the
human operator visual feedback, but does not directly help a
robot to see unless the information can be digitized using a
video digitizer. Image processing, image recognition, feature
extraction, edge detection, filters, FFT, etc., are the ways video
information can be used for various robotic applications.
Security systems automatically detect and track intruders. Pick-and-place robots are used in manufacturing to recognize the
shapes of parts, visually inspect circuit boards, and determine
the quality of components.
Feel
Our nervous system (and nerves) are located all over our
body, allowing us to feel ambient temperatures and humidity.
We feel pain if we bump into obstacles or if we accidently
touch very hot objects. This sense helps us to prevent injuring
ourselves. Robots can use pressure transducers and flexible
resistors (and even limit switches) to feel the surface of walls
and other objects, or cat whiskers made from piano wire
mounted on a sensitive limit switch can be utilized. Vibration
sensors, piezoelectric sensors, and accelerometers can detect
glass breakage, or can sense if someone is trying to break into
a vehicle. Seismographs can “feel” earthquakes and measure
their strength on the Richter scale.
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