 So, let us start. So, today what I am going to talk about is actuators and sensors in mechatronics system. Yesterday you saw the overview of mechatronics system and like why, what is a mechatronics, what is special in mechatronics way of handling things and with the example of I think governor of the steam governor. So, let us continue that thread and like see little more details what are the different elements of mechatronics system and like will focus on mostly the sensors and actuator elements ok. So, this is the outline of my talk. First we will see various examples where in practical mechatronics system you see actuators and sensors ok. We will try to classify or like identify these actuators and sensors in mechatronics system and then we will talk about the sensor elements like various kinds of possibilities for sensors. So, when you are synthesizing mechatronics system like what all things you can use as a sensors for a particular application that is there in your mind then we will go for similar kind of exercise we will do for actuators and the there are like more futuristic kind of sensors and actuators that we will handle in the next lecture that is based on the MEMS ok. And then we will see what are the issues in selection of sensors and actuators and finally, how to interface sensors and actuators with microcontroller that or microprocessor that you have seen already in the yesterday's talk ok. So, these are the this is a schematic showing all the elements of mechatronics system and it consists of mainly actuators, sensors, controller on in the electronic domain and then mechanical system which is system which is being controlled ok. So, various kinds of applications can be developed by combining such single system or like multiple systems together like say for a like we will talk about those examples and then you will understand like you can have multiple such mechatronics systems integrated and then like you can have a more complex job that can be done. So, yesterday you saw governor example and how the actuation and actuator and decision, actuation and decision can be separated in the mechatronics framework ok. So, with that in mind like we will try to identify what are sensors, actuators, controller and plant in that kind of a system ok. So, sensor actuators are I mean it is self-actuated like it has energy it is taking energy from the process itself and then it is it is actuating its own way based on the ball inertia ok. The more they more the speed more the inertia and more is actuation force ok. Then sensors basically you are sensing speed which is changing the position of the throttle because of the governor principle. Then controller like this is a controller through mechanical way the linkage mechanism that the type of our selection of the ball inertia and ball weight ok. All those things are going to govern like the kind of a control law that is getting implemented inherently. I mean you do not have really control over that control law ok. You cannot change like tomorrow if you say like if I want to change, you have to physically change the system ok. But in the case of electronic processing like you can do that by changing the either electronics components or by changing your program which you have downloaded in your microprocessor ok. So, that is the basic advantage in having like that is the basic philosophy of mechatonic system like your decision making is separated from actuation ok. So, that is what is so special about mechatonic system and there that gives tremendous flexibility in terms of like application that can be covered with the same kind of a electronic framework or electronics hardware available ok. So, feedback in this case is speed ok. So, again you can see like this in terms of this kind of a framework of I mean the main see this is this is this diagram is going to be our focus for discussion ok. And this is the most fundamental way of like classifying mechatronics elements of mechatonic system. And like if you understand each of the elements then putting and integration of those elements then putting and synthesis of a putting together of a mechatonic system is very easy. So, another example is driving of a car ok. So, now in this case like your actuators are engine of the car your hands legs you are controlling the acceleration then you are steering by your hands. Sensors are basically your eyes and ears ok you sense something you see some person crossing the street and you immediately like brake. So, that all processing is going on in your head. So, your brain is basically a controller in this case ok. Then plant is car itself and then feedback is all position and speed of a car ok. So, there is this is not really I mean I mean you can see that this other example where human being is involved in the mechatronics I mean framework of the controller sensors actuators and actually plant ok. So, he is another example that illustrates different elements of mechatonic system and where the actuation and sensing is going on. Next is example of robot manipulator ok. Suppose you want to build a robot manipulator or there is a robot manipulator available or you see that now it is a mechatonic system ok. So, in that what are the actuators typically for robot like you can have motors in addition to transmission then hydraulic cylinders in case it is really a big huge robot which is handling very high payloads ok. So, for example, that Kawasaki robot which was in the first slide was basically on the basis of hydraulic cylinders ok. Then sensors you can have encoders, tachometers I mean encoders are basically for position sensing, tachometers are for speed sensing. So, like that you can integrate many different kinds of sensors in a robot for like giving a feedback to the controller ok. Then controller can be analog or digital. So, when you say analog it is all done in the on the electronics circuit ok. So, you have seen microcontrollers yesterday, but whatever job the microcontroller is doing say have you heard about PD control, PID control, PD control yeah you are aware about that. So, those kind of controllers you can also implement in electronic circuits ok directly you do not need really microcontroller to program PID and all ok. So, there are these two distinct classes analog and digital for controllers ok. So, there are pros and cons of each of these things like that is not a subject of today, but your controller can be analog or digital domain. And mostly here we will be talking about digital controllers for their basic advantages ok. The plant is robot and then feedback is speed of the joint or position of the joint, then you may have some gripper at the end. So, end effector forces that you can sense ok. So, there are there can be many different kinds of things which can be feedback and then accordingly some action can be taken ok. So, this is a Kawasaki manipulator that I was talking about and it has you can see this is a hydraulic cylinder in the in the robot and that is giving it like a lot of power to actuate at the industrial level ok. This is another example that you all are using CD-ROM drives ok. So, have you ever looked at like how exactly CD-ROM works ok. So, if you go to this howstuffworks.com website you will find the entire illustration of how CD-ROM works. Basically on the CD surface there are these tracks which are separated 1.6 microns apart ok. Then there are pits and lands on the surface of the CD on these pits and lands the data is encoded ok. Where there is a pit I mean there is some data there there is a land some data there. Like that the entire thing is written on the CD surface in the form of a single spiral ok. If you open up this spiral and like lay down it will be kilometers long ok. So, that is how like the entire data would be stored. Now if you see carefully like and think about the requirement here is that like your CD head should be on the track all the time. And that is to be obtained on the track with the accuracy of at least 0.6 microns. I mean this 1.6 microns is a distance. So, you need to have very accurately positioned CD head on the track. Then only that data will be picked up. Now how it is done ok. That is a very very sophisticated technology ok. They have something called voice coil linear actuators ok. So, they are based on like a coil placed in the magnetic field ok. And it is supported by a hinge like a cantilever type of beams ok. So, there is no friction involved anywhere ok. So, that is how the highest level of accuracy can be obtained. We will come to this point later on also when we discuss like about selection of actuators. I mean we will touch upon some of these points. Like if you want very high precision high accuracy, then how do you go about what actuators you will select for your application ok. So, there are in this particular application there are many kind of systems. Your CD while rotating can have like some small ups and downs ok. So, this data will be like at different locations from the lens ok. So, when the CD goes down, your lens also should go down. So, that is done automatically by focusing servo system ok in CD ROM drive ok. And why I mean this is this I am talking about with the accuracy of like with few microns. You have a feel for what is what is say for example, 100 microns. Can you give any example what is of 100 micron size? Yeah hair thickness exactly very good. So, your hair thickness is roughly in the 80 to 100 micron kind of a range. So, one tenth or one half of that I mean one tenth of that would be the accuracy of this servo system. Like within 10 micron like it will position itself. I mean it is much better I have it is just a exaggerated figure, but it will be much better than that ok. So, you need to have that kind of a precision and accuracy and you know like this you all use CD ROM drive. So, such a sophisticated mechatronics technology is available at your door steps in few thousand rupees ok. So, how like I mean you can see how much thought has gone into this business of CD ROM reading and writing ok. Because of that like people have like are constant I mean they are constantly increasing number of things like number of or size of data that you can write on a single CD ok that is increasing. So, that is basically achieved by decrease in this distance 1.6 microns. And when that distance decreases like your I mean whatever specifications on your mechatronics system are they become more stringent ok. So, this is a picture of like CD ROM drive which is taken in our lab. So, you can see the CD head over here this is a CD head ok. And then there is see the. So, there is a fine positioning system and gross positioning system ok. So, CD will actually be sitting I mean on the reverse side of this motor ok. So, this is a spindle motor on the reverse side of which the CD will be sitting and this head will be traversing across its radius ok. Radially it will be moving on the surface of CD. So, that is a gross positioning system ok. There is a gross positioning system and in the head itself there is a fine positioning system as shown say for example, here ok. So, this gross positioning is achieved by this kind of a say for example, ball screw or a rack and pinion kind of a mechanism ok. And so, that motor again has like a mechatronics system itself like ok. So, this gross positioning system is one mechatronics system. Then the fine positioning system ok. So, you can see that these two arrows they indicate that this lens is capable of moving in these two directions ok. So, that is a very fine positioning that is happening using galvanos scanning ok that I was mentioning about like the lens has some coils which are suspended in a permanent magnet which is attached to this lead ok and those kind of allow the fine positioning to happen ok. Then you can see here this two arrows they indicate like focusing of a lens on the CD surface ok and there is a like lot of optics that go into the fabrication of this mechatronics system ok. Say for example, this focusing and feedback for the fine positioning in the lateral direction I mean it is totally based on optical effects like diffraction and lens focusing and astigmatism. So, there are lot of things people have used. I mean we do not have a lot of time to talk about all those things in this, but you can appreciate that this has very fine optics, electronics and mechatronics that has gone into this system ok for achieving this kind of a very nice application. Another example like in your day to day life is the hard disk that you use ok. So, that is again a different kind of a technology that is being used ok. So, now question here is now how to achieve these different objectives mentioned in these and many other such applications ok and is there any formal way of doing that and that is why like you are here I mean you want we will be seeing in this course like the formal way of like doing mechatronics ok. It requires like you all are from various different backgrounds, but you all can appreciate that ok like mechatronics like is a subject where all different backgrounds like I mean you need some knowledge of many different backgrounds ok. So, say for example, you need some some electronics fundamentals, you need some microprocessor fundamentals to really like construct your own mechatronic system no matter like which branch you are coming from, but like you need all these things to really put together a mechatronic system and use it. So, there are different ways of doing that. So, some of them you will learn in this course. So, first step is proper choice of these elements which are sensors, actuators, controller and your plant ok. So, let us now look at the sensors, sensor elements in mechatronic system ok. What all different kinds of sensors you might have already seen some of these in your basic instrumentation course or measurement course in your studies or many wherever you are in your workplace also many of you have come across some of these sensors or the other ok. We will just see what are different classifications of these sensors and then like just brush up like principles of each of these sensors ok. Let us then start with the first class based on output signal whether it is analog or digital like the sensor can be classified on based on that ok. Can you give any examples of analog sensors? Thermocouple. Thermocouple yeah very good. Any other thing you would have come across strain gauges exactly. Potentiometers. Potentiometers yeah they are also analog. Tachometer. Tachometer yes very good pressure sensors yeah they are based on again strain gauge principle usually ok. Then capacitive like displacement sensors LVDTs they are all they fall into this category. Then digital sensors encoders yeah then limit switches ok. So, so all those things they they fall into digital domain ok. Now ok we will we will talk about that in more detail but analog versus digital do you see advantages disadvantages you need to think about ok. What are the advantages that analog sensors offer or what are the disadvantages ok. So, major point I will tell you right now is analog sensors are all susceptible to noise ok. So, they will pick up a lot of electromagnetic and that kind of a noise ok. Ground loops that can be picked up by analog sensors very easily. So, you while you are putting together analog system I mean analog sensor in your system like you need to be that is a there is a alarm that that should be raised in your mind how I am going to do take care of noise ok. That should be raised immediately in your mind when you are doing analog processing ok. So, that is one thing and then in the in the case of digital that is not a great concern because like digital are either 0 or 1 and 0 typically is defined as voltage from 0 to 2.5 volts and 1 from like 3 to whatever 5 volts. So, as long as your voltages are within that range you are you are either is classifying it as 0 or 1. So, there is no problem ok that is why like digital sensors are not I mean they are immune to noise ok. But it is very difficult to get digital sensor sensing in from an electromechanical element that you are using like say for example, strain gauge I mean getting a digital sensor out of I mean digital output out of such a thing would be difficult ok. So, encoder is a very special class I mean we will talk about that ok. Then one can classify these sensors based on the principle of operation ok. You can have all these various different principles based on which your sensor can be working. Resistive, capacitive, inductive, optical you can have optical sensors where you can use fiber optics or like just LED and I mean I mean photodiode or like more complicated kind of a sensor with a photodiode array and the is complicated optics as used in the CD-ROM dry ok. So, there are various possibilities in optical sensing way. Then magnetic sensor which is Hall effect is one of the principles based on based on which magnetic sensors are working. Then piezoelectric transducers which you make use of as the name suggests piezoelectric effect and ultrasonic transducers. These are basically various principles, fundamental principles ok. Now you can have a sensor which is using this principle, but it is sensing not just resistance it is sensing something else which changes the resistance ok. So, that can be like a combination of. So, these principles various principles can be combined with the mechanical fabrication and then like you can have say for example, pressure sensor which is like strain gauge based ok. So, basically pressure diaphragm when it deflects like whatever strain is generated is sensed. So, it has like it is basically sensing pressure, but it is based on a principle of strain gauge ok. So, or it can also be this diaphragm can be on the other side having a simple plate and capacitance between these two diaphragm and this plate reference plate is changing that is kind of capacitive pressure sensor ok. So, you can have combinations of these. So, we will not go into that area where you can have combination, but this fundamental principles are something that you should be very much acquainted with ok. So, that now like you can imagine and think on your own ok what can be a good sensor for my intended application ok. What can be good principle that I can use for my intended application and using that principle you can construct your own kind of a sensor or think of anything which is available in the market ok, but it is important that you know you are aware about this fundamentals fundamental principles. So, let us see resistive sensors which are basically strain gauge type they are they can be potentiometer also. So, basically it is a principle of change in resistance by whatever phenomena like say for example, you are you want to turning some shaft it is changing the potentiometer resistance ok. So, that is a basic idea here and if you see the way the strain gauges are used ok. Potentiometers are very easy to integrate and you are all aware about the way it works. Its strain gauges usually are used in the Vstone bridge configuration that also you might have studied a lot and like the strain gauges ok. I should tell you this that when you are looking for strain gauges in the market you should be looking for strain gauges which are based on the semiconductor devices ok. So, typically the gauge factor is what is what matters for a strain gauge which that is a I mean sensitivity indication ok. If you have higher gauge factor it is always better ok. For a given strain you will have higher voltage output the Vstone bridge kind of arrangement ok. And this is a formula that is between the strain and output voltage where the gauge factor plays a role and why silicon strain gauges because they have higher gauge factor ok. That is why you should you should be using I mean you should be looking for silicon based strain gauges ok when you are looking for strain gauge kind of a sensing application ok. Then it has this noise issues as because this is a analog domain sensor. So, you need to handle those also. We have many applications in our laboratories where we are using the strain gauge based sensors for very high end application like one of the applications we will be talk about in this lecture about slosh measurement ok. So, you can have like single axis strain gauges or multiple axis and there are various possible possibilities in this strain gauge with the same principle ok. So, applications are basically force measurement, torque measurement, pressure measurement and those kinds of means ok. Then capacitive sensors ok. The basic principle here is that you have this capacitance formula which is this is a dielectric constant ok and then area and the gap ok. These are the basic factors which are affecting capacitance ok. This formula is for parallel plate capacitance, but then like you can have various configurations like you can have cylindrical configuration also and then the formula will change. There will be some end effect terms that are coming into picture in the cylindrical capacitance. So, whatever like the basic principle is because of the change in either area or gap ok, you will have the capacitance change ok and that you will use for sensing whatever phenomena you want to ok. So, these are used in many different applications like one of them is displacement measurement. You can have capacitance sensors for measuring displacement especially in we will will talk about this in the next lecture also. The comb drives which are based on the principle of electrostatic actuation. So, those like comb drives when used as a capacitive sensors ok. You can use them for the displacement sensing for a micro size application ok. So, we will I will show you in more detail when I talk about MEMS ok in the next class. Then this these are also used like say this cylindrical configuration is used for liquid level measurement ok as liquid moves up and down ok. That is a that is a principle where like you are changing not area or the D, but you are changing the dielectric constant ok. So, as you have like liquid level change like the dielectric constant, I mean it is not really dielectric constant, but then the gap in some gap dielectric constant is changing ok. So, partly it is air and partly it is liquid. So, the part where it is liquid that is changing ok. So, that way you can measure liquid level ok. This is a next type of a sensor which is displacement transducer again. This is based on the principle of inductive coupling between primary and secondary coils and a magnetic core which is coupling them is actually moving as you change whatever application changes the displacement. And the advantage of this sensor is that it is a linear ok. See so, linearity is one of the basic requirements for any kind of a sensor ok. Why it is there have you ever thought about? No look I will repeat the question why you need like the sensor to be linear as in this case like the straight line variation between the displacement and output voltage that you are getting out of the sensor. Interpolation is easy ok, what else? So, yeah so, that is a 0 point and but basically I mean what if I have this non-linear behavior ok. I mean that I still have null point I still have positive and negative side, but I have like a parabolic behavior for example, instead of linear. Exactly. So, you get a high voltage than higher than you expect ok. And if you see this will complicate your control ok. Your PID gains which are tuned for a particular like rate or like a slope of this line ok. See in the non-linear sensor this slope is not going to remain constant I mean this slope is going to change ok. So, say for example, I will show you one of the non-linearities ok. Instead of straight line you can have this kind of a variation ok. So, here the slope is not constant the slope here is this slope here is this ok. So, because of these like you are PID gains which we are we have tuned for one of the slopes ok. They may not be valid for the next slope it may take the system into unstable zone ok. Because of which like you need it is important I mean as long as possible like you need a linear sensor ok. Yeah curve exactly, exactly that is another difficulty. Yeah yeah yeah that is that is perfectly all right. So, to avoid these like you need to be thinking to use ok. When you go to the sensor specifications again this point will be striking you ok. What sensor to be selected I mean in the say if you go for like any data sheet about any of the sensors you will see that linearity specification is given that linearity is within 2 percent 3 percent ok. So, those specifications according to your applications like you need to select proper specifications so that like your sensor is linear ok. And see in some cases if you if you compromise like ok on linearity you will be able to save some cost ok. So, those kinds of things then like you may need to think about ok. If I can compensate for this linearity by as you were saying by using some kind of a interpolation, but my computation load increases. So, I need to have a microprocessor which is which is working at that speed which which can compute in whatever selected sampling time for the system like all the computations are completed and then it gives me output of the sensor ok. So, these are the pros and cons ok. You know like the general guideline is like go for linear sensor, but you should not have that fixed concept that ok. If the sensor is not linear I am not going to use that it is not it is not that ok. You need to balance it against like what what constraints you are working with and whether your cost permits not permits like all those kinds of things you need. So, that is where the whole integration or concept of mechatronics is coming into picture. See if a person is having the separately this knowledge of different fields, how to integrate it together and think about where I can change so that I can get some advantage here ok. I can save some cost here ok. Like that that kind of a thinking will develop once you have you know what is this integration ok. We will talk about this with some examples also and you will understand ok. Then there are these optical sensors the basic principle is using light source and light detection ok. So, you can have light source and photo detectors placed opposite to each other and then some slits are there in the disk which is rotating and it is cutting that light ok. That is a kind of one one kind of a way in which the encoder can be possible. Then you can use more complex phenomena like this merfinches to get see these are basically two different grating lines or like slits you can say or array of slits which are at an angle to each other ok. So, when this these slits move across ok these merfinches they will move in the direction perpendicular ok. So, this these fringes that you are seeing here they will start moving in this direction ok. As like you this these two two arrays of slits they move across in the perpendicular direction ok. So, your your slits are really moving in this direction, but these moir fringes they are moving in the in this direction. So, this this is basically enhancing the sensitivity of your sensor ok. For a very small displacement of these two slit arrays ok you will get a higher displacement on these moir fringes ok which will depend upon the angle at which you are setting this angle between this and this array of the slits ok. So, like that there are in optics like you can use lot of different variations and you can construct lot of different kinds of sensors ok. The other effect for example is a diffraction effect that one can use to create that is used in the the diffraction grating is used in CD-ROM drive to basically create three beams out of a single beam ok. And two beams side beams are used for tracking I mean fine tracking and then like central beam is used for reading the data. Like that you can have various different configurations optical configurations possible then you can use fiber optics for sensing sensing ok. This is one of the examples where like this is a very high precision encoder. You can see that the disc of 36 mm diameter has 81000 grating patterns like this small small patterns on the surface ok. Then this pitch is about 2.8 microns ok. This is a sensor that I used in my PLD problem ok for sensing very high precision sensing of a output of a harmonic drive ok. So, in addition to these see there are two sensing I mean two sources or like single source of light is split into two and then it is used for sensing on either side ok. They are these two sensors are placed 90 degree out of phase with each other ok. And because of that there is additional advantage in sensing ok. And that also can be used for like sensing the direction in which you are going ok. If one is leading one signal is leading the other then you are going in one direction and reverse way in the other direction ok. So, that way you can sense otherwise it is very difficult or it is not possible to sense the direction when you have encoder kind of a setting ok. The next is this magnetic sensors which are basically using principle of Hall effect ok. So, the principle is very simple. You have magnetic flux in one direction and the current is going in another perpendicular direction in this say whatever sensing typically it is a silicon based or semiconductor based element. And then the Hall voltage will be generated across these two phases ok in other perpendicular direction. Basically this this current carrying coil placed in the magnetic field you know that there is a force that is getting applied on the on the current carrying coil ok. So, now there is there is nothing to move here ok electrons they get shifted on one side of this element ok which generates the Hall voltage across these two phases ok. So, current is going in this direction magnetic flux is in this direction there is a force applied on the electrons ok charge placed in the magnetic field it is a basic electromagnetics. And those those electrons will get shifted towards this end and then there will be a Hall voltage generated ok. So, that is the principle of this Hall effect sensor ok. And the the main advantage here is that semiconductor elements can be used in these sensors which makes these sensors really tiny ok. You can have very small Hall effect sensors placed at various places I mean. You know the CD ROM example that I was talking about it is using three Hall effect sensors for its sensing the motor position. I mean magnetic field for motor position it senses by using Hall effect sensors. And based on that magnetic field it will there is a complicated electrons that is processed and then like it controls basically the speed of rotation of this motor ok. So, another example we have here is this Hall sensor I mean these these ok. These Hall effect sensor chips are available directly in the market ok. And they are available along with their processing electronics ok. So, you can think of using them in the whatever specification you can see in the data sheet and see if it is suitable for your application ok. So, so most of the sensors ok unless you have very specialized requirement ok they will be available in the market you should be looking for them rather than like thinking of building your own ok. So, mostly whatever you think about would be available in the market. So, that is very important point otherwise you will waste lot of your time in just constructing this which is not really required. So, these Hall effect sensors are like these small chips they will be available in the market ok. You can just read the specifications if they match I mean you can just directly start using or like if they do not match you look for some other vendor I mean if not then like you have to develop basically. So, say for example, this liquid level sensor ok. In our application we whatever the liquid level sensors available in the market I mean this capacitive base I talked about like you have liquid that is a liquid in the tank ok and it is basically sloshing I will show you this video is there with us and then you want to measure the liquid level at this position and say for example, you put this kind of a capacitive sensor or parallel plate capacitive sensors here. I mean that is a most simple I am talking about usually they have cylindrical with the tube and concentric tube inside ok. So, if you place this what the problem is like the as a liquid level changes if it is changing very slowly you can detect that. But if it is changing fast I mean there is a water which is wiping the plates of this capacitor that causes some error in the reading and you cannot see that fast changing capacitance. So, here like here is that application that I was talking about that you need to like now develop a sensor for this kind of application. So, this development is going on we are trying various kinds of different ways like say for example, connecting this tube like say inserting some tube in the liquid and connecting that tube from here say for example, to a MEMS based pressure sensor ok. So, we are trying out different ways in which we can really sense the liquid level rather than like only slowly varying or we want to dynamically measure this liquid level ok. So, one of the applications. So, then we come to piezoelectric sensors the piezoelectric principle like you all are quite well aware that is generation of charge on application of force the important point here to note is like the charge will be produced only when there is a dynamic changing force ok. And once you press it there is some charge produce it will have some leakage somewhere I mean it has its own capacitance and then like it will basically get discharged ok. So, if you keep it for long time you cannot expect that charge to remain there for forever ok. So, it will or if you have external circuit connected it will get discharged to the external circuit. So, important point in the piezoelectric sensors is like all the dynamic changes it should be dynamically changing to get you really the sensor output ok. And they are really high frequency very fast sensors ok.