ranging sensors - sns courseware

Ranging Sensors

By

Mr. K Samba Siva Rao, AP/EIE

SNS COLLEGE OF TECHNOLOGY

(An Autonomous Institution)

Coimbatore-35

Robotics & Automation Unit 2 IV EIE K. Samba Siva Rao 7/24/2019 1

Recap of previous session


Proximity & Ranging Sensors

• Proximity sensors provide a binary output and indicate the presence of an object within a specified distance of travel.

• Range sensors are used to measure the distance between the object and the sensor.

• Generally, proximity and range sensors are located on the wrist or end – effector of the robot.


Types of proximity Sensors


Contact type Proximity Sensor


Ultrasonic Proximity Sensor


Acoustic Proximity Sensor


Eddy Current type Proximity Sensor • Can be used to detect non – magnetic but

conductive materials

• when a coil is supplied with an alternating current, an alternating magnetic field is produced

• If there is a metal object in close proximity to this alternating magnetic field, then eddy currents are induced in it

• The eddy currents themselves produce a magnetic field, which distort the magnetic field already existing. This change in flux density indicates the presence of an object

7/24/2019 Robotics & Automation Unit 2 IV EIE K. Samba Siva Rao 8

Basic Eddy Current type Proximity Sensor


Killed oscillator type Eddy Current Sensor


Advantages & Disadvantages

Advantages

• High flexibility

• High sensitivity to small displacements

• Smaller size

• Less expensive

Disadvantages

• Must be calibrated for the type of metal used for the target

• Size of sensor depends on effective linear measuring range (larger distances require larger probes)


Magnetic Proximity Sensors • It is made using a reed switch and permanent

magnet. (Reed Switch Working, Example)

• The permanent magnet can be either made a part of object being detected or can be part of the sensor device.

• In either case, the presence of object in the region of the sensor completes the magnetic circuit and activates the reed switch.

• The advantages of these sensors are: – Simple construction

– No external power supply is required.


C:/Users/kssrao/Desktop/Reed Switch Working.mp4

C:/Users/kssrao/Desktop/Reed Switch Example.mp4

Time for


Range Sensing Techniques

• The range sensing techniques are:

– Triangulation technique

– Structured lighting approach

– Time – of – flight range finder


Triangulation Technique


Structured lighting approach


Structured lighting approach

H:/Structured Light Field for 1 ms High-Speed Depth Estimation.mp4

Time-of- flight range finder • These methods involve the use of laser and ultrasonic

waves.

• The time it takes for an emitted pulse of light (laser) to return coaxially i.e. along the same path from a reflecting surface (object to be detected) is used to estimate the distance.

• The relation between distance and time of flight is given by:

𝑙 =𝐶 ∗ 𝑡𝑝𝑡

2

Where,

– l is the distance between light source and object

– C is the velocity of light

– tpt is the pulse transit time


Session Conclusion


ranging sensors - sns courseware

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