 So, good morning everybody I am Roushadh Mistry from Valgenist Reflectional Sholapur and for today's discussion I am going to talk about Rains Senses. Now the learning outcomes for this are you will be able to define Rains Sensing and explain types of Rains Senses specifically the non-contact types that is basically the scope of this particular session. Now if if you recall from the previous class we had discussed about different types of sensors such as displacement sensors, force sensors, flow sensors, temperature sensors. The scope obviously falls from the point of view of robotic applications. I will try to expand this particular scope for other applications as well and I have decided to go ahead with Rains Senses today. For the reason being is it is more interesting that something new that you could come across and it is now being very widely used in applications right from home automation to factory automation and even automobiles. So that is typically the scope that these sensors have today and for this particular session we will just have an overview take a look at some of the types the measurement techniques involved and we will be covering applications a bit later. So that this is basically the scope of it. Now how can you actually define range? Now conceptually speaking let us say range or sometimes it is called as distance is determining the length of a one-dimensional line joining two points in a 3D space. So here we are not interested in the coordinates XYZ coordinates only straight line distance between two points. Sometimes we do not really refer to a straight line distance it can be a geodesic distance as well. But the original definition remains like this that it is involved in determining the length of a one-dimensional line joining two points in a 3D space. Now typically we tend to refer to those measurements which involve sensor to object measurements. So this is what we typically look at reinsensing so you have a sensor at one end you have an object which is a bit far away and you are typically interested in finding what is the distance between that particular sensor and the object. So this is you can say the simplest definition that you can come up for reinsensing. Let me clarify different authors have slightly different definitions but the handbook typically tends to concur on this particular definition. So what are then reinsensors? It involves collection information about spatially distributed this is about range imaging and it involves collection of information about spatially distributed variables and basically involves several ranging measurements. So if I have to differentiate simple reinsensing and what is called as range imaging. So range imaging takes it to another level. So you are not just involved regarding how far the object is but you want more qualitative information sometimes with the intent of building some sort of a 3D model of it. So this is how range imaging works into picture or building a three-dimensional map. So that is you can say at reinsensing taken to another high level. An extension of ranging is also what is called as position tracking which involves keeping the range at keeping basically a tab of the range over a period of time. So the object obviously range has been identified and if it's a moving object it's of definitive interest to me what is the state of that object as it moves over the horizon. And this is very typically if you can say in military applications other applications where I want to keep a track of it. So that's why we say position tracking. Now here position added actually one more feature that you need to know exactly where it is located. So that is one extra addition what comes into picture. So the next part in this is how do we tend to differentiate range, distance, position and proximity. Because this is a sort of issue of classification and definition which is often confusing. And there are instances where authors have to use definitions which are a bit overlapping. So let me clarify a few things about this. Rain sensor when we typically refer to like in the previous slide we are interested in finding out the distance between the sensor and an object. So it's a basically a straight line distance, we are not interested in any other parameter. Whereas when we use the term position we are typically looking at from the point of view of three dimensional coordinates like for example position, global positioning system. So that is a precise information in terms of latitude, longitude and an added information also could be the altitude. So in position the reference is very critical. In case of ranging typically the reference point is the position of the sensor itself. Whereas in case of position the reference point is some global center or a global reference that you can use. For example in case of a machine it will be the center of the machine. If you are looking at GPS then it will probably be the meridians of latitude and longitude which is taken as the reference. And when you talk about proximity it's a very special case of distance sensing in which the threshold is fixed. So proximity is either you measure the closeness in a sort of a yes and no format either you are close or not. So we typically tend to say there are very specific class of distance sensors in which the threshold is predetermined. So that's the you can say the definitions and comparisons of these. So what is the importance of this? With mechatronics becoming more and more prevalent and it's touching every aspect of our life. Obviously that's true with range sensing as well. Using an automation applications range sensors have found applications since a very long time. This is actually used to judge distance of objects. Robots typically tend to have some sort of distance sensing though I would not use the word range sensing over here in their grippers in order to estimate locations, avoid collision and so on and so forth. AGBs use it extensively for navigation and stuff. And modern day robot navigation this is basically referred to field robotics is exclusively based on an array of range sensors which include visual range sensing and even ultrasonic range sensing leaders and others. And the most common and we can say the oldest application of range sensing was collision detection. So that's you can say range sensors in a nutshell for you. So let me recall this range sensors are typically used to measure the distance of an object from a reference point. And if you if you tend to classify them we can say actually the most common way of classifying is either it's active or passive or if it's contact or non-contact. Now frankly it's been calling some a range sensor contact type in my opinion is a bit of a misnomer because if you're actually in contact something it might as well call it as a displacement sensor. So most range sensors typically are non-contact type and they are used to estimate a distance of an object at a considerable distance from what the sensor would be. And therefore the technologies typically used are light, ultrasonic waves, microwaves and computer vision. So these are the most commonly used techniques and this is where I would like to differentiate let's say displacement and proximity sensing from brain sensing because this is definitely over a wider range wider distance. Then before we proceed see where you have come across these terms. What do you think you can do with this sensor? Now we have some of these sensors with the RAM but I'm pretty sure even in other subjects you have come across this so just try to ponder over it and then we will see what exactly is the background of these particular sensors. Now let's continue from where we left off. Like I said most range sensors definitely will be non-contact type and there are different measuring techniques that you will use in order to estimate this range. Measure of the range typically of the object from the reference which usually the reference is the sensor itself is without direct physical contact and ranging techniques are one is triangulation. The other is by measurement of time of flight. The third would be by measurement of phase shift and the fourth obviously by measurement of intensity of the signal which bounces off the target. There are other techniques which are used as well we are typically visual techniques you have stereo triangulation and you have binocular vision but we have not taken that for discussion at this moment. These are complicated vision techniques which you typically study as a part of vision system not a part of these general group of range sensors. So here we can basically classify non-contact range sensors as active or passive. This is the most classic textbook classification you can have. When we say active or passive in active the source of energy is in the sensor itself in the sense that the sensor actually bounces some sort of a controlled energy from the target receives this energy and then tries to interpret obviously the range. In case of passive range sensing what it tries to do is it typically has very sophisticated receivers and these will try to detect any kind of energy emanation from the objects and then try to estimate its range. So this is how you can basically classify active or passive. Now if you recall this sonars are both active and passive so they can actually bounce a sound wave from the target or they can listen to the noise which the target is creating in order to estimate the range. So on the basis of this the most widely used sensing systems are one is radar everybody is aware of it that is radio detection and ranging. The next is LIDAR that is light detection and ranging and obviously sonar that is sound detection and ranging which finds extensive applications in see in naval applications especially for detection of other surface vessels and also submarines. The radar typically uses time of phase or phase shift or phase modulation in order to estimate range. Sonar uses basically mainly time of flight and LIDAR also is typically based on either time of flight but mainly uses phase shift for measurement as well. So let me recall that LIDAR actually uses phase shift in order to estimate the range. LIDAR has now become popular basically because of autonomous vehicles and it is very high resolution very high accuracy and in this case measurement of phase is more appropriate than measurement measuring the time of flight. Then what are the typical issues that you come across on contact range sensing is it depends mainly on the target cross section. So the range is not just based on the sensor configuration specification also depends upon the target cross section also depends upon target reflectivity and on the power of the emitted energy. So how strong is the rating of that particular search? It also depends upon the directivity of reflection which is what the oldest generation you can say stealth aircraft did. They had a very the directivity was such that the reflected waves never went to the main radar source so that is how they evaded the radar. So ranging difficulty difference upon like I said target cross section reflectivity power of the emitted energy and directivity of the reflection. So what I definitely recommend for you is you read the mechatronics handbook by Bishop, the introduction to mechatronics by Bolton and mechatronics system designed by Shetty and Holt. So we have a dedicated chapter for sensors on this and it covers a wide range wide range of rain sensors. Thank you and we will continue with more discussions on rain sensors and other sensors in in the next session.