Download Sensors

Sensors
Sensors
• Sensors changes a robot from dumb to
intelligent.
– The ability to adapt to particular surroundings is
one definition of intelligence.
Classes of Sensors
• Sensors for robots can be divided into three
classes:
– internal sensors,
– external sensors,
– interlocks
• Most sensors are some type of transducer.
– E.g. The ear converts sound energy into electrical
signals.
Internal Sensors
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Limit switches
Haptic perception
Governor
Lead screws
Shaft-encoder
Direct-readout encoders or absolute-readout
encoders
External Sensors
• Microswitch or pressure sensor
• Photoelectric device
Interlocks
• Interlocks are devices that do not allow an
operation to be performed until certain
conditions exists.
• Can be internal or external.
Sensor Areas for Robots
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Vision
Touch
Range and proximity detection
Navigation
Speech output
Speech input
Smell
Vision
• Present-day industrial robots use vision to
locate and orient parts.
Limits of Robot Vision
• The robot grasps a part or parts from the bin.
• The robot places the parts on a table that has
an artificial skin surface.
• The skin locates the orientation of the parts.
• The robot is instructed in how to grasp the
part with the part with proper orientation for
the rest of task.
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Touch
• Tactile sensing, the sense of
touch for robots, is needed
if a robot is to perform
delicate assembly
operations.
• When a robot touches
something, force is
reflected back through each
joint.
• In screwing nut and bolt,
touch is more imp then
vision.
Types of Touch Detection
• Single-point detection
• Simple edge detection
• A multiple-point shape detector
Range and Proximity Detectors
• Range Detector detects objects situated at
some distance from the robot.
– Non-contact devices
• Laser, radar, sonar, vision and infrared devices.
• A proximity detector detects objects in the
immediate vicinity of the robots.
– can be contact or non-contact devices.
• E.g. A magnetic detector
Speech Output
• Speech output is not handled by sensor.
• It allows the robot to communicate with us
through additional sensor of our hearing.
• Voice output is often used in conjunction with
voice input to confirm that the robot
understands a voice commands.
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Speech Output (Contd...)
• A robot using voice output may not even be
heard.
• Voice output is a valuable safety feature when
robots are used in offices or hospitals.
• The use of robots by disabled people is easier
if a robots has a voice.
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Speech Output (Contd...)
• Voice output is also useful in medical robots
for the disabled people who cannot speak.
• Voice output, voice synthesis or speech
synthesis for a robot can be accomplished by
three different methods.
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Speech Output (Contd...)
• The oldest method is to have a human record
the desired words, phrases, or sentences on
individual pieces of magnetic tape.
• A computer or robot then plays back the
appropriate piece of tape to produce the
desired message.
• Because this method plays back the real
human speech, the individual words sound
very natural.
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Speech Output (Contd...)
• The second method of voice output involves
having a human speak the words into a
microphone.
• A computer stores each word digitally, and
this digital information is then converted back
into analog speech one word at a time, as the
computer or robot speaks.
• This method tend to sound very much like a
human speaker.
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Speech Output (Contd...)
• The third method of voice output constructs
speech from stored phonemes for the English
language.
• This method tends to sound very mechanical.
• There is no emotion or inflection in the
speech.
• The frequency of the speech can be changed
as though it were being said by man, or
woman.
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Speech Output (Contd...)
• Adding an inflection or emotion content
circuit to the speech synthesizer would make
it much more acceptable to human..
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Speech Input
• Voice input commands is not practical in noisy
factory.
• Voice input has become highly desirable.
• The area of sensory input interpretation is one
that will benefit with the advances greatly in
artificial intelligence.
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Speech Input (Contd...)
• Robots can use speech input by the use of
microphone.
• This speech information can be converted into
digital forma nd stored in robot’s memory.
• Most speech recognition systems now in use
recognize a very small vocabulary.
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Smell
• Industrial robots of today do not have the sense
of smell.
• Sensors already exist that can detect nitrates and
explosives.
• Smoke detectors can react to the particles in the
air.
• Exhaust gas analyzers are available for checking
car exhaust emissions.
• The military has sniffers, for detecting
unauthorized people.
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Smell
• Domestic robots could use synthetic noses for
detecting natural gas leakage from a water
heater or owen or a freon leak from a
refrigerator or air conditioner.
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Noise Issues
• Real sensors are noisy
• Origins: natural phenomena + less-than-ideal
engineering
• Consequences: limited accuracy and
precision of measurements
• Filtering:
– software: averaging, signal processing algorithm
– hardware tricky: capacitor
Electrical Noise and Sensor
Information
• Generally robot works with a high level of
noise.
• This noise is created by the machinery around
the robot and by robot itself
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Electrical Noise and Sensor
Information (Contd...)
• The memory and control circuits in a robot’s
controller respond to a signal which is
millionth of a second.
• A burst of electrical noise lasts long enough to
change the controller’s memory and mislead
what is supposed to be doing.
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Electrical Noise and Sensor
Information (Contd...)
• What can we do to eliminate this electrical
noise?
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Electrical Noise and Sensor
Information (Contd...)
• The power supply of the motors should be
separate from power supply of controller and
sensor.
• The wiring for the motors should be separate
from and round separately from the wiring for
controller and sensor.
• We can use shielded cable or wires for all
wiring of the controller, signals and the
sensors.
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Electrical Noise and Sensor
Information (Contd...)
• If controller and manipulator are not contained
in the same area connecting wires must be run
between the two devices.
• The farther apart the two devices are
physically, the better antenna the wiring makes
for picking up electrical noise from the robot
and from surrounding machinery.
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Electrical Noise and Sensor
Information (Contd...)
• The noise problem will be greatest, if point to
point wiring is used.
• Point to point wiring uses individual wires
from one point on the circuit to the other point
on the circuit.
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Electrical Noise and Sensor
Information (Contd...)
• The noise is decreased by using twisted pairs
of wires, wires run on pairs from one point to
another in a circuit with one of the two wires
in each pair grounded.
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Electrical Noise and Sensor
Information (Contd...)
• The noise is lowest if shielded wires are used.
• Each wire have a grounded shield surrounding
the wire.
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Electrical Noise and Sensor
Information (Contd...)
• Signals transmitted at low level of voltages.
• The lower the voltage level the greater will be
the noise effect.
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Electrical Noise and Sensor
Information (Contd...)
• A signal can be send over a distance by using
differential signal.
• This uses differential drivers and receiver
circuits.
• The signal is sent over two wires.
• Voltage level is not what it sensed on either
wires, but the difference in the voltages
between the two wires.
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Electrical Noise and Sensor
Information (Contd...)
• This type of transmission also tends to cancel
the electrical noise, because such noise is
picked up equally in both wires.
• Another form of signal transmission that is
unaffected by electrical noise is fiber optics.
• The signals are light beams sent along an
optical fiber.
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Electrical Noise and Sensor
Information (Contd...)
• Noise in a signal can cause serious safety
problems, some type of signal error detection
should be used.
• This may mean adding extra information to a
signal to determine weather it has been
changed.
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Electrical Noise and Sensor
Information (Contd...)
• We can check the signal, by sending it more
than once.
• A human being reduces the probability of
information errors by sending information over
more than one path.
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Electrical Noise and Sensor
Information (Contd...)
• It is easier to obtain sensor information, than to
interpret it. Why?
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Electrical Noise and Sensor
Information (Contd...)
• Most sensor interpretation is currently done
through the software of an electronic
computer.
• The robot’s controller is not yet powerful
enough to do its own interpreting.
• Especially for vision system.
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