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This robotic hand is capable of performing the
delicate task of
picking up and holding an egg without breaking it. A tactile array sensor located
on the right half of its gripping
mechanism sends information to the robot's control computer about the pressure the robotic
hand exerts; given
this information, the control computer instructs
the robotic hand to loosen, tighten, or maintain the current gripping force. This
feedback loop repeats continuously,
enabling the robotic hand to stay in between the two extremes of dropping and crushing the egg.
Microsoft® Encarta® Encyclopedia 2000. © 1993-1999 Microsoft Corporation. All
In gas and steam turbines and internal-combustion
engines, where fuel furnishes the energy to the machine, the governor
regulates the flow of fuel. To control the speed of a hydraulic turbine generator,
a governor can alter the water flow by opening and closing gates and valves.
Another type of mechanical governor, used to regulate the speed of
aircraft engines, varies the pitch of the propeller blades attached
to the engine.
The most common type of mechanical governor
operates by means of the forces of inertia (the resistance to change or
motion) that arise from longitudinal or rotary motion. For example, when a spring-loaded
mechanical governor is rotated, the flyweights, or flyballs, are flung outward
by centrifugal force (see Centripetal Force). At a given speed, the
flyweights are in an equilibrium position and the spring is partially compressed. An
increase in speed causes the flyweights to rise as they pull farther out
from the axis of rotation. This causes a further compression of the spring. The
spring sets up a control force that may close a valve or in some other way
decrease the energy input to the machine. As a result, the speed
of the machine decreases, at which point the flyweights begin to fall.
Then, the spring becomes less compressed and valve is opened once again.
The piezoelectric effect occurs in several
crystalline substances, such as barium titanate and tourmaline.
The effect is explained by the displacement of ions in crystals that have a nonsymmetrical
unit cell, the simplest polyhedron that makes up the crystal structure (see Crystal).
When the crystal is compressed, the ions in each unit cell are displaced,
causing the electric polarization of the unit cell. Because of
the regularity of crystalline structure, these effects accumulate,
causing the appearance of an electric potential difference between certain
faces of the crystal. When an external electric field is applied to
the crystal, the ions in each unit cell are displaced by
electrostatic forces, resulting in the mechanical deformation of the whole
The Hall effect occurs when a conductor or
semiconductor carrying an electric current is placed in a
magnetic field. A voltage, called the Hall voltage, is created across the
conductor or semiconductor perpendicular to both the current and
the magnetic field. This voltage arises because the magnetic field distorts the flow of
electrons or other charge carriers that constitute the
current, pushing the charged particles to one side of the conductor.
voltage is proportional to the current and magnetic field and inversely
proportional to the number of electrons or other charged particles. For
instance, the Hall voltage across a metal is much smaller than across
a semiconductor carrying the same current in the same magnetic field because
the metal contains more charged particles than the semiconductor.
Resistors with adjustable resistance
are called rheostats or potentiometers. These types of resistors are used in appliances when the
current needs to be adjusted or when the resistance needs to be varied, as with lights that dim or adjustable
Pairs of machines known
as synchros, selsyns, or autosyns are used to transmit torque
or mechanical movement from one place to another by electrical means. They consist
of pairs of motors with stationary fields and armatures wound with three sets
of coils similar to those of a three-phase alternator. In use, the
armatures of selsyns are connected electrically in parallel to each other
but not to any external source. The field coils are connected in
parallel to an external AC source. When the armatures of both selsyns
are in the same position relative to the magnetic fields of their respective machines,
the currents induced in the armature coils will be equal and will cancel each other
out. When one of the armatures is moved, however, an imbalance is created that
will cause a current to be induced in the other armature. The
magnetic reaction to this current will move the second armature until it is
in the same relative position as the first. Selsyns are widely used for remote-control
and remote-indicating instruments where it is inconvenient or impossible to make a
"Electric Motors and Generators," Microsoft® Encarta®
Encyclopedia 2000. © 1993-1999 Microsoft
Corporation. All rights reserved.
Some devices act as both
sensor and transducer. A thermocouple has two junctions of wires of different
metals; these generate a small electric voltage that depends on the
temperature difference between the two junctions. A thermistor
is a special resistor, the resistance of which varies with temperature. A
variable resistor can convert mechanical movement into an electrical signal.
Specially designed capacitors are used to measure distance, and photocells
are used to detect light (see Photoelectric Cell).
The image-orthicon tube
and the vidicon tube were invented in the 1940s and were a vast improvement on
the iconoscope. They needed only about as much light to record a
scene as human eyes need to see. Instead of camera tubes,
most modern cameras now use light-sensitive integrated circuits (tiny,
electronic devices) called charge-coupled devices (CCDs).
A CCD used for recording
visual information is made of an array of photodiodes
(devices that conduct electricity when light strikes them) on top
of a semiconductor (a material that conducts electricity better than
electrical insulators but not as well as electrical conductors). When light
strikes a photodiode, an electric current proportional to the amount
of light is sent to a capacitor, which stores the charge. The semiconductor processes the
signal from the capacitor and sends it to a computer or other device
that can analyze the data about the light that hit the CCD.
The applied sensor system consists of two
grayscale CCD-cameras mounted on a pan-tilt-verge camera mount. The movements
of the camera mount and the image processing are controlled by the local coordination
the three-dimensional model only from discrete positions during a still stand
to avoid vibrations of the cameras. During the motion the sensor system is
used as an optical bumper
scanning the free
space in front of the vehicle for obstacles. The other possible behavior is
shown in this MPEG
where the optical bumper was switched off. A moving object occluded the
planned path and caused a collision. The vehicle moves back several centimeters
to inspect the unexpected obstacle.
The exploration system consists of
several processes communicating with each other via the
RPC-mechanism. This allows a free distribution of the processing power among
the available computers.
The whole system can be subdivided into three layers with different tasks:
- data acquisition and interpretation, hardware control
- planning and control of the system based on cartesian
- abstract topological planning, interaction with the user
The binocular stereo camera system shown
in this MPEG
not use any specialized hardware. The image processing and the
three-dimensional reconstruction is computed on a single Pentium-PC @ 133 MHz
running LinuxOS. The achieved cycle time of 0.6s is sufficient for this
application. An example of a 3D reconstruction is shown in the following MPEG
which we have implemented were designed in our lab and are known as the Fast Eye Gimbals (FEGs). The FEGs provide directional
positioning for our cameras using a similar
drive mechanism as the WAM. The two joints are cable driven and have ranges of
motion of +/- 90 degrees and +/- 45 degrees
in the base and upper joint axes respectively. These two FEGs are currently strategically mounted on ceiling rafters
with a wide baseline for higher position
accuracy using stereo vision methods. The independent nature of the FEGs allow us to position each one at different locations in
order to vary the baseline or orientation of
the coordinate frame as well as easily add additional cameras to provide
focusing on spherical balls of various sizes, we are now experimenting with
various objects of unknown dynamic
characteristics, such as sponge balls, long cylindrical cans, and paper airplanes. Our system uses low cost vision
processing hardware for simple information extraction.
Each camera signal is processed independently on vision boards designed by
other members of the MIT AI Laboratory (the
Tracking System). These vision boards provide us with the center of area, major axis,
number of pixels, and aspect ratio of the color
keyed image. The two Fast Eye Gimbals allow us to locate and track fast
randomly moving objects using
"Kalman-like" filtering methods assuming no fixed model for the behavior of the motion. Independent of the tracking
algorithms, we use least squares techniques
to fit polynomial curves to prior object location data to determine the future
path. With this knowledge in hand, we can
calculate a path for the WAM to match trajectories with the object to accomplish catching and smooth object/WAM
addition to the basic least squares techniques for path prediction, we study
experimentally nonlinear estimation
algorithms to give "long term" real-time prediction of the path of
moving objects, with the goal of robust
acquisition. The algorithms are based on stable on-line construction of approximation networks composed of state
space basis functions localized in both
space and spatial frequency. As a initial step, we have studied the network's
performance in predicting the path of light
objects thrown in air. Further application may include motion prediction of objects rolling, bouncing, or breaking up
on rough terrains.
successful results for the application of this network have been obtained in catching of sponge balls and even paper airplanes!
Sonar is a device that is used to
detect objects through sound waves. There are two main types of sonar:
Active and Passive. Sonar technology enters a signal into the water in
a narrow beam which has the speed of about 1500 m/s. If there is an
object in the beam, its sends sound energy back to the sonar dish. Then
the distance is calculated by range = sound speed x travel time / 2. In
active sonar a pulse signal is sent to a transducer which changes the
electrical signal into a sound signal. After that it is put out into
the water and it detects returning echos. A receiver amplifies the soft echos
and measures the range of each object. Passive Sonar is used mostly to
detect submaries and surface ships. Passive Sonar does not reveal any sound
so it is primarly used in submarines. The weak point is that it can not
detect the range. The aproximate range can be calculated by measuring
the curvature of the received sound wave. Passive sonar relys on
detecting noise that is generated by motors and hull vibrations.
Building environment maps from
sensory data is an important aspect of mobile robot navigation, particularly
for those applications in which robots must
function in unstructured environments. Ultrasonic range sensors are, superficially, an attractive sensor modality to use in
building such maps, due mainly to their low cost, high speed and simple output. Unfortunately, these sensors have a
number of properties that make map building a non-trivial process. In particular, standard sensors have very poor
angular resolution and can generate misleading range values in specular environments. The first of these problems
can be largely overcome by combining range measurements from multiple viewpoints. Elfes  and Moravec 
describe an approach in which range measurements from multiple viewpoints are combined in a two-dimensional
`occupancy grid'. Each cell in the grid is assigned a value indicating the probability that the cell is occupied.
Unfortunately, the occupancy grid approach does not work well in specular environments. Specular reflection may occur
whenever an ultrasonic pulse encounters a smooth extended surface. In such cases the pulse may not be
reflected back to the ultrasonic sensor; in effect, the surface may appear to be invisible. In ordinary office
environments which contain smooth walls and glass doors specular reflection is common. In this research, we have improved
on earlier grid-based approaches by introducing the concept of a `response grid'. The intent of the response
grid framework is to produce an approach which has the advantages of the occupancy grid framework, but also
performs well in specular environments.
The response grid framework attempts to
model the behaviour of ultrasonic range sensors in a more physically realistic fashion. The basic notion that the response
grid encapsulates is that a cell may generate a response (ie appears to be occupied) when viewed in one direction,
but will not generate a response when viewed from another. For example, a smooth planar surface will only generate
a response when the angle of incidence between the surface normal an the beam emitted by the sensor is
close to zero. At larger angles of incidence the surface will generate no response. In the original occupancy map
framework, this would present a contradiction, since this approach assumes that an occupied cell should generate
responses in every direction. A full description of the response grid framework can be found in  and
Our edge detection algorithm consists of
searching in 20 small windows. The windows are opened along the predicted edge
positions which were given by dynamical model. In each window we find a most
likely edge and finally linear-fit these data to get the whole stripes.
Develop a navigation system for the robot to recognize and walk along the
Analyzed the geometric relation of the system, developed
the algorithm to estimate robot's distance and angle position.
edge detection algorithm for image information processing.
the motion control strategy. The robot can walk stably along the hallway from
arbitrary position in tens of seconds.
walks at it mechanical speed 0.5m/s in the corridor.
sensor for a mechanical hand gives better feedback of the gripping force and
more-sensitive indication of when the hand
contacts an object. Optical fibers bring light into cells on the gripping surface. Light is reflected from a flexible
covering into other fibers leading to detectors.
Distortion due to tactile pressure changes the amount of reflected light. The
new device is superior to previous sensors.
For example, television or other direct-viewing systems are not sensitive to contact pressure, and the contact
area is often hidden from view. Electrical sensors
are subject to electrical noise, especially at the low signal levels
associated with low contact pressure.
Optical sensors have been used to detect proximity or contact but not contact pressure. The new optical sensor is illustrated in the
figure. The sensing surface of the hand is divided
into cells by opaque partitions. An optical fiber brings light into each cell
from a lamp, light-emitting diode, or other
source. Another fiber carries light from the cell to a detector; for example, a photodiode or phototransistor. The cells are
covered by an elastic material with a reflective
interior surface. The rest of the cell is coated with a nonreflective
material. As shown in the figure, pressure
against a cell cover causes a distortion, which changes the internal reflection of light. The change is sensed by
the detector, and the output signal informs the operator of contact. The greater the pressure and distortion, the
greater is the change in light reflection.
Thus, grip pressure can be sensed using analog circuitry. If only a touch indication is desired, a threshold detector can be
included in the electronics. In an automatic manipulator, the detector signal could control the manipulator movements.
The cells can be arranged such that those
in each row share one light source, while those in each column share one detector. This reduces the number of sources and
detectors and facilitates scanning. For example,
a 10-by-10 matrix would have 100 sensing points while requiring only 10
sources and 10 detectors. The array can be
scanned by sequentially pulsing sources and detectors.
A sensor system measuring the surface
pattern of objects by using a spatial filtering tactile sensor. The sensor has
a band-pass spatial filtering function and changes its center of spatial
frequency with the tactile motion. The idea of this method is based on the
nervous system in human finger.
It is said that cutaneous receptors exist by 50 pieces per 1 mm2 at the tip
of a human finger and nervous units are distributed 1 unit per 1 mm2 . As the result,
(1) the cutaneous receptors construct a spatial filter and signals from them
are summed within the nervous unit. (2) In the touch motion performed by a
man, the delay of the signal transmission through nervous unit and touch motion
velocity changes the spatial filtering characteristic to make the spatial resolution
This sensor system is characterized by (1) robust measurement system for non-uniform
contact state and (2) adaptable for a wide spatial frequency range in the
surface pattern of objects. And high spatial resolution can be realized.
The horizontal arm of the CMM carries an
analog touch sensor (red) and a video camera (black) to inspect mechanical
parts. The camera "finds" the part and its features on the table so
high accuracy inspection can be done using the touch sensor
Photoelectric Cell, also phototube,
electron tube in which the electrons initiating an electric current originate by
photoelectric emission. In its simplest form the phototube is composed of a
cathode, coated with a photosensitive material, and an anode. Light falling upon the
the liberation of electrons, which are then attracted to the positively charged
anode, resulting in a flow of current proportional to the intensity of the
irradiation. Phototubes may be highly evacuated or may be filled with an inert
gas at low pressure to achieve greater sensitivity. In a modification called
the multiplier phototube, or the photomultiplier, a series of metal plates
are so shaped and arranged that the photoelectric emission is amplified
by secondary electron emission. The multiplier phototube is capable of detecting
radiation of extremely low intensity; hence, it is an essential tool for those working
in the area of nuclear research.
photoelectric cell, popularly known as the electric eye, is employed in operating burglar
alarms, traffic-light controls, and door openers. A phototube and a beam
of light (which may be infrared or invisible to the eye) form an essential
part of such an electric circuit. The light produced by a bulb at one end
of the circuit falls on the phototube located some distance away.
Interrupting the beam of light breaks the circuit. This in turn causes a relay to
close, which energizes the burglar-alarm, or other, circuit. Various types
of phototubes are used in sound recording, television, and the scintillation counter
(see Particle Detectors). They are also used in exposure
meters (see Photography: Lenses: Light
to mail couriers used in large corporations, Line Tracker follows a designed course. By using a
infrared emitter and light-sensor
circuitry, it demonstrates how robots "see" a pathway. Make a pathway with a black felt marker
or black tape and watch how infrared
sensors enable the robot's motors to
make course corrections.