Transcript Sensors - IIT Kanpur

Rotary Encoder
Wikipedia- Definition

A rotary encoder, also called
a shaft encoder, is an electromechanical device that converts
the angular position or motion of
a shaft or axle to an analog or
digital code.
Types of Rotary encoders
Absolute
Incremental
Mechanical
Mechanical
Optical
Optical
Magnetic
Absolute Type Rotary Encoder
The absolute type of rotary encoder giver the absolute position of the shaft.
For example –
If the shaft has an absolute angle of 54(degrees) and it is 3 bit encoder.
3 bit encoder means it has 2^(3) divisions, therefore it will give value that
the angle is more then 45 and less then 90.
How to use this encoderJust calculate the angle difference and counts of full rotation.
This encoder will can be used in devices which has slow rotation speed and
high accuracy.
Encodings on rotary encoder- Binary
Standard Binary Encoding
Sector
Contact 1
Contact 2
Contact 3
Angle
1
off
off
off
0° to 45°
2
off
off
on
45° to 90°
3
off
on
off
90° to 135°
4
off
on
on
135° to 180°
5
on
off
off
180° to 225°
6
on
off
on
225° to 270°
7
on
on
off
270° to 315°
8
on
on
on
315° to 360°
Gray encodings
Gray Coding
Sector
Contact 1
Contact 2
Contact 3
Angle
1
off
off
off
0° to 45°
2
off
off
on
45° to 90°
3
off
on
on
90° to 135°
4
off
on
off
135° to 180°
5
on
on
off
180° to 225°
6
on
on
on
225° to 270°
7
on
off
on
270° to 315°
8
on
off
off
315° to 360°
Incremental Type Encoders

An incremental rotary encoder provides cyclical outputs (only) when the
encoder is rotated.

They employ two outputs called A & B which are called quadrature outputs as
they are 90 degrees out of phase.

There can be an optional third output: reference, which happens once every
turn.
Gray coding for
counter-clockwise rotation
Gray coding for
clockwise rotation
Phase
A
Phase
B
A
B
1
0
0
1
1
0
2
0
1
2
1
1
3
1
1
3
0
1
4
1
0
4
0
0
Two square waves in quadrature
(clockwise rotation).
Incremental Rotary encoder
How to find the Speed of rotation ?
AnsEach encoder has some fixed
number of slots per revolution.
Each slots generate one pulse.
If we count the number of
pulses and time taken by the
fixed number of pulses , we can
calculate the speed of rotation
of the shaft.
Applications

For odometery of mobile robot.

For precise measuring of the rotation of any shaft/rotation .

Linear encoder are also available which can be used for the linear distance
moved
Magnetic encoder

Strips of magnetized material are
placed on the rotating disc and
are sensed by a Hall-Effect sensor
or Magneto resistive sensor. Hall
effect sensors are also used to
sense gear-teeth directly, without
the need for a separate encoder
disc.
Optical Flow Sensor
An optical flow sensor is a vision sensor capable of measuring optical flow or
visual motion and outputting a measurement based on optical flow.
Applications

Optical mouse

Can act as vision for mobile robots.

Unmanned Ariel Vehicle (UAV’s)
ADNS 3080 Optical Flow sensor
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ADNS-3080 optical sensor.
High speed motion detection.
Up to 6400 fps update rate.
30x30 pixel resolution.
Includes an 8mm lens which
can be replaced, depending on
the use requirements
Light color sensor
Features of Color sensor

Four channel integrated light to digital converter
(Red, Green, Blue and Clear).

10 bit per channel resolution

Independent gain selection for each channel
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Wide sensitivity: 0.1k - 100k lux
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Two wire serial communication

Built in oscillator/selectable external clock
Reflective color sensing
By definition of reflective sensing, the
color sensor detects light reflected from a
surface or an object. The sensor module is
designed in such a way that both the
light source and the color sensor are
placed closed to the target
surface/object. Light coming from the
LED is bounced off a surface/object and
measured by the sensor.
White Calibration
Before the color sensor can be used for
reflective sensing, a one-time white
calibration is needed to be done to set the
sensor gain to the optimum setting. The
white calibration is important to ensure
minimal variation between different sensor
unit and different LED unit. A white surface
is illuminated by LED and detected by
sensor with recommended working distance
and the microcontroller/tester will perform
the calibration.
Laser Range Finder
Working

A laser rangefinder is a device which uses a laser beam to determine
the distance to an object. The most common form of laser rangefinder
operates on the time of flight principle by sending a laser pulse in a narrow
beam towards the object and measuring the time taken by the pulse to be
reflected off the target and returned to the sender
Parallax laser range finder
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Compact module with integrated CMOS camera and laser system

Optimal measurement range of 6–48 inches (15–122 cm) with an accuracy
error <5%, average 3%
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Maximum object detection distance of ~8 feet (2.4 meters)
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Range finding sample rate of 1Hz
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Single row, 4-pin, 0.1” header for easy connection to a host system
Proximity Sensor
• Easy to use digital obstacle
detecting sensor
• Easy calibration and very
accurate