 This lecture will focus mainly as you see the little picture in the bottom. It's about how CD-ROM drive works, okay? So we pondered over this question like, you know, you have been using some CD-ROM or CD drives in the past. You might have, I'm not very sure nowadays, like, you know, people don't use them so much, but I'm sure you might have listened to some music on CDs, maybe a few years in the past maybe, okay? So one has to think about, like, what is there inside this drive and how the data is, is there stored on the surface of a CD and how that data is read, what kind of system, a mechanical system is needed to do that job, okay? So we'll start this with a very different kind of approach. We'll not, like, you know, do some theoretical kind of understanding first and then, like, you know, see, okay, what is there? We'll actually open up the CD-ROM drive and I'll show you the pictures of this as we go along and start kind of, you know, discussing some of the interesting aspects that you see there, okay? So now while thinking about CD-ROM drive, we need to think about these four elements that are there here, okay? So you can see these are the four elements that we are discussing, you know, microcontroller, actuator, then, like, you know, you have actual CD system and then you'll have feedback, some kind of a feedback from the system. You may have, like, you know, these so sensors, these are plant here and then there are sensors here, okay? So actuator, plant, sensors and controller, okay? These four elements will be indispensable for any of the mechatonic system, okay? Or you may have many subsystems that will be there as a part of a big mechatonic system, okay? So either way, like, you know, we need to look at all the subsystems we've broken up into these components, okay? And then, like, you know, there are other aspects of the design that will go along as we start opening up, that will come up, okay? So maybe let us start with the discussion here on the thing to question. First is, you know, how do you think it works? So you might have maybe looked at or like some Google date and saying, okay, oh, this CD-ROM has some optical way, the data is on the surface and there is some optical pickup which picks up the data from the surface. So let's get into the more details about it. So the goal here is to kind of develop the philosophy of design of mechanized systems, not particularly this particular system, but how do you think in terms of, like, you know, design for such a system, okay? So given problem, how do you kind of synthesize a solution? And then you'll see the need for this critical thinking in both the domains, okay, mechanical domain and electronic domain together to see, okay, how we come up with, like, you know, the requirements, how do you give the solution to the requirements of the application. And then other aspect is to kind of look at already existing elegant solutions to these problems which are already solved and understand some of the design principles which are optimized principles in some way, that how do we make use of that in our case, okay? And then finally learn about several aspects of the design which requires modification in mechanical domain to suit implementation. So this is like no integrated philosophy of thinking that we will try to learn through, okay? So let me get a point here, okay? Okay, so now let's move on with the problem at hand. Okay, think about what is the function of CDROM drive? As we have seen, said already, okay, it has to store a huge amount of data, okay? This data is stored in form of say some small pits and lands on the surface of CD. We don't worry about where this, how this data is written, okay? But it is written in some kind of form and when a user demands that, okay, I want to open some file or I want to listen to some music that is there in the CD, I should be able to get it, okay? So when the user demands that, you know, I want to open this particular file, you have to kind of do something to go to that part portion of the CD and pick up that data from there and give it to the user. That is a kind of a problem that we are looking at. So now let's look at a CD and how it looks under microscope, okay? So this, let's do that now, okay? So can you see that the CD has a surface which has this use of these different colors? Can you ponder over and see why these colors have to be seen here, okay? Think about this question, like, you know, why do you see the surface of CD has this kind of a different colors coming up, okay? So what is the physics of light that is going on there which gives you these different use of the colors? Now under microscope, we will come to that question when we discuss or you may answer that in the discussions, okay? So if you zoom in in this small part of the surface, you'll find a data, so you so many dots that kind of are seen here. It's not very clear, you may not very clearly see anything in microscope, but as you zoom in further, you may see these kind of tracks that are there on the surface of CD, okay? These tracks also are not so kind of a sharp, sharply visible because their dimensions are almost coming to the wavelength of the light, okay? So light wavelength, for example, in the visible range, you know, say for example this red light that we'll have is 630 nanometers kind of a range and these tracks will be like no 1.6 microns kind of a dimension or 0.5 micron each track kind of a dimension, then they'll not be visible clearly, okay? So to discern, you need the features to be much more sized than the wavelength of the light. These are more sized than the wavelength of light, but they're not much more than the wavelength of light, so that's why you can see them somewhat, but you cannot see them very, very clearly, okay? So now the question, okay? So what can you think of a system to read these data? So I want you to kind of pause here for a while and think about, okay? See, what can you think to kind of read this data from the surface of an actual CD? So given that, okay, you have this data which is written in these forms of like no small lines and pits, how do you kind of design a system which will read this data? So let's assume that, okay, if there is some kind of a read head which can read, you can shine a light on the surface of the CD and the light falls on the surface and it gets reflected from the surface of the sponge back and if it is falling on land, it will kind of reflect like a white light and then like, no, if it is falling in the pit, then it cannot reflect, okay? So that's one simple kind of a way one can think about that, okay? I'm shining a light very focused, tightly focused light on the surface of a track and then the track, if it has a, it has that land or data written in zero or one form, then if it is a land, it is light is getting reflected or not reflected from the surface will tell me whether the data is zero or one, okay? That's a simple kind of a head that can be possible. Now the question is you want to make sure that this head moves on the track all the time. How would you do that? These tracks, if you see, they are so close to each other, okay? So if you see that, they are so close to each other, as you can see here, okay? So such a closeness of the tracks, how do you kind of maintain that your focus spot remains on the surface of the, on the single track, okay? And it continues to remain there as you start reading the data they said a CD is spinning and spinning at some speed and like this track is getting faster. So this CD is spinning here and this track is passing under the head and you need to make sure that head is moved only like no such that it is kind of continues to remain on the track, okay? Oh, by the way, the data that is written here is in the form of a single spiral, okay? So the spiral starts from the small end of the CD and continues to, continues in a way to the larger radius. So small radius it starts and continues to the larger radius, okay? Like that a single spiral is there. So you need to kind of make sure that, okay, the head is continuously moved on the surface in the radial direction with the precision of like, no, say something like, can you guess what is the precision? If this is, say, the track between the track, the distance is about 1.5 microns, the precision that is needed will be what? At least some hundreds of nanometers or like, no, 100 or less, little less than 100 nanometers kind of a precision will be needed, okay? So 10 percent, also if you say like, no, 10 percent of 1.6 microns is 160 nanometers kind of a precision that will be needed there, okay? So we want to kind of create a system which can do this kind of a nanometric precision kind of a movement on the surface. How would we, how would we, what do you want? Like, no thoughts come to your mind based on your knowledge. So far we have done with like, no, some microcontroller programming and things like that. What kind of actuators can you think about for such a system to exist, okay? So let's, so you give a good thought to these before kind of proceeding from here, okay? So wherever these questions are known, I will not stop for the sake of memory of the lecture that we are recording here, but at every point of this, where this, you see this little icon here, okay? A person thinking, you know, you need to be doing that job, okay? And see what kind of things come to your mind when, see because it's very important that you raise these questions in your own mind to understand what is there and like, no, it will open up like, no, really, you know, interesting kind of dimension, okay? Because we start thinking in whatever, based on whatever knowledge that we have, and then we start putting things together, at least on the paper for such a, such a thing. And then like, no, we'll see, oh, you know, when actually you open up and see some stuff, it will have some different understanding that will happen. And that is what is important, because that will kind of correct some of the base you were thinking previously to, you know, what is the right direction to think. So that process is very important. I'm reiterating here, but please pause here. Don't go through unless you have thought about this question yourself. Okay. So the question I raised is not just this, but like, no, how do you kind of like, no, move the things on the surface of the city? Okay, that question also you should think about. Now let us open up the, the, yeah, these are the questions that actually I wanted to know you to think about and pause here. So maybe you can list on some of your ideas and like, you know, on the paper and start thinking about them and things like that. And we'll proceed for actually seeing what is there inside. Okay. So we'll actually take a CDROM drive, open it up and start looking inside and observing our keen observation. As I said earlier also, we is going to kind of like, teach us something. Okay. So let us start with the opening. Okay. So you have this CDROM drive, the brand new CDROM drive, and then you can locate like, you know, there are these four screws up here. Okay. This is screws you remove and then like, you know, you'll be able to open this top thing up. And in addition, you can see like, you know, you can observe that there are a lot of mechanical interlocking that is provided. Okay. To reduce the number of screws and anything like that. Okay. As you start opening up, you'll find somewhere you need to move some some mechanical lock. I'll show some some picture of some of the locks to just kind of like, you know, slide that lock and let things you open up. Okay. So we'll proceed now. So this is what you once you open up the cover, this is what you'll see inside. Okay. Now, so we need to kind of now slowly observe things carefully and start making sense. Okay. So this electronics, we may not be able to make much sense because we cannot like, you know, we can just see the chips and like, you know, maybe take their data data sheets, I mean, take their numbers and look at the data sheets and like, then we can make make more sense of circuits. Okay. But mechanical things certainly will be able to do a lot of make a lot of sense of mechanical components. Okay. So let's observe them. So there is this one of the locks that, you know, you need to push this lock in the in the side in this direction that and then like, no, it will open up from this, it will release this PCB so that you can leave the PCB up. Okay. And then you'll find that there are these flat connectors that are used. Okay. See, there are a lot of things that you can observe. I have listed only a few of them. I mean, I'm living more for you to kind of explore and observe and think about and ask questions. Okay. That's what we should, we should, then it will be much more healthier kind of a process rather than I'm pointing all the time up to some kind of things in the observations. So this is like some kind of a PCB which is doing the control and reading the data from the surface of the CD storing it somewhere and communicating it to your PC. Then you'll find that these are kind of a flat cables that are used for connection. Okay. Now one can think about why this is kind of a flat cables are used. Okay. And not you know, normal wires. So think about that. And then like, no, you'll need to remove these cables to kind of get access, like better access to mechanical components. Okay. So that is done here. So there are a lot of like small, small aspects that will come. This is a tray of, this is a tray that is holding the CD. Okay. That tray needs to be coming out to come out, for that rate, there are some kind of interlocks that will be provided or clips that could be provided. And then you need to push something and then like, no, this tray can be pulled out. Those kind of things you need to do. See, it will be excellent if you can like, no, get some, some of these, these kind of systems like CD-ROM or hard disk drive, which is gone from your like, no neighborhood shop, which is repairing shop. Okay. Repair shop may like, no, some people may have this thing available. They may give you some from throw away price, or they may kind of just give you without any cost, okay, free of cost. Because anyway, it is gone, not working kind of a drive, then like, you just want to kind of explore it, people may be able to give you a spare it for you. Okay. We usually do in, in the normal classes, like, you know, in physical classes, we give you actually these, some of these kind of systems and let you explore them. Okay. So that opens up a lot of different kind of thinking and paradigm in our mind. In fact, everything we can talk about, say, for example, like, no, how do you see through for such a design of such a frame? Okay. That itself is a, is a very interesting topic to kind of deal with. How do you kind of think for such a design and like, no, it can be manufactured. What is the way this can be manufactured? Okay. So what kind of a dye system we can have so that you can manufacture such kind of components? Okay. I see because these are to be done in a, in a, in a masses. Okay. So, so then like, no, the, the price of such system comes down because like, no, they are fabricated in, in bulk. Okay. So for bulk fabrication or mass fabrication, you are mass manufacturing, you need to have a systems or thought processes which are different than like, no, one off system or two off system applications. Okay. So, there are a lot of things that can be talked about. But right now our focus is only on these on the mechatronics part of it. Okay. We will not get into too many details about manufacturing and, and materials and the, the, the, the gory details of, of even some, some small mechanical designs such as like, you know, this, this kind of a release clips and things like that. Okay. So our focus will just focus on the mechatronics aspect of things. So this is like, you know, one of the systems when we, when you open up, like you, you observe this, this kind of rubber or like a belt driven wheel and which is operating like, no, some, some system here with the gears and things to, to get it and then like, no, that exists gear, which will kind of get a tray out and tray in for the, for the CD, because the CD tray is, so you, I don't know whether, like, if you have operated, you'll remember that, okay, you push some button on the, on the, on the CD drive and then the tray pops out actually. Okay. So the CD tray pops out, you put a CD there and then like, no, it is taken inside and it is set in, in some way, okay, somewhere. Okay. So, so this is the mechanism which does the tray operation kind of a mechanism. So, so why this typically the belt drive is used here is, is to prevent the damage in cases, in case the tray is blocked, okay. If the tray is blocked and then you, you still start like, no, they're driving the motor. See, this is a motor up here. There is a motor below this, this small little wheel is driven by this motor and if something is locked and this wheel is not rotating, then the motor still keeps on rotating and the belts start slipping, okay. So, this arrangement is, is useful. See, if, if imagine if they insert this belt drive, okay, with a flexible kind of a belt, if you use a simple gear mechanism here, then what will happen is like, no, the, the, something is get stuck or you have holdings at the tray manually and then no motor is trying to push it, okay. The motor is not moving, okay. Then what, what happens is whenever motor is not moving, you are holding like the motor shaft and the still power is given to the motor. Can you imagine what, what's going to happen? Okay. Think about like, no, you are giving a power to the motor, okay, but we are holding the motor shaft, what is not allowed to rotate. Then like, you know, you are actually pushing in a good amount of current into the motor windings, they'll start hitting up and if the motor is not designed to like, you know, get that kind of a heat, I mean, you cannot sustain this heat for a long time. I mean, it will short, for short durations, the motor can sustain such kind of a heating, the temperatures don't go so high. But if you keep on doing that for like longer duration, then like, no, slowly the motor will start, the motor coils will start giving the heating so much that the enamel or like the insulation on the coil burns and you'll see that the motor may not function afterwards, okay. So motor will get burned, okay. If you don't, you know, take care of this blocking kind of an issue that, you know, when the output is blocked, motor is still allowed to rotate, but with the the belt will slip on the motor surface, okay, motor shaft. So this mechanism gets you the tray out. So we'll let's observe this mechanism a little more closely here, okay, with this video demonstration up here. So you can see here, like, this is the mechanism that moves. So now, like, no motor is removed from here, you can see that there is no, no motor here, the belt is removed, the belt is lying up here. But like, as this rotates, like, you know, there is some, some gear might also have been removed from the system. So the, no, no, this gear is still intact. So if this gear, you see this gear rotates, this when this gear rotates, like, no, this, this will move slide here. And the sliding will do some interesting thing here. If you see this sliding is pushing this small, like, no black tray up, okay, and then there is something that happens because this, this up and down motion that is needed is to kind of unload the CD from the, from the CD spinner, spinning motor, okay. So when it is, if you see when it is pushed on this side, the CD is loaded and like, no, in some other way, the CD will get, in the other direction, the CD will get unloaded, okay. So that is, that is the system for that. Now let's observe some, some more details about where the, the crux of the problem, okay, where exactly the CD is placed and how the, the CD optical pickup assembly actually, like, reads from the surface of a CD. Okay. So if you, if you see this after removing the, the couple of, you know, PCBs from the surface, you will have this clear view of the, the mechanism here. So what you observe here is, is these two rods here, you see this one rod and this other rod, okay. And so this was the mechanism up here for CD tray to be popped out and all the motors and the gears, let me know they have been removed. Now, and this is a motor which will drive the CD, okay. If you see a upside down view here, the CD is, is, is, is kept upside down, okay, here on the other side of the, of the motor, okay. We are looking from the back, back end, so to say, okay. CD will be put from the back side to kind of feed. And then this is a head which, or optical pickup assembly which moves on these two rods here, side wise. So the CD, imagine the CD has this as a axis, center of this motor as axis of rotation. And then like, no, the CD is rotating like this in a big CD is there to rotate in the, in the, on this axis. And then the head is moving radially inward and outward when the CD is rotating, okay. That is a kind of a two degree of freedom motion that is required for reading, you know, X, Y kind of a position, X, Y place tracks, lands and pits on the, on the CD tracks, okay. So you need to have X, Y positioning system for that. One axis of rotation is CD, rotation axis. And then other degree of freedom is radial motion on the, on the surface. So, so it's not like you have fixed CD and you move the head around it, no. It's a CD is rotating and just move the head radially inward and outward. So you can have multiple ways of picking up the position data, I mean, pick up the data from the surface of the CD. But I mean, this is the most, I mean, the way that is designed, like, no, the CD can be spun and you can have the radial motion possible for the head. Now let's observe, like, no, little things, little more, more details. You can see that here there is a, some kind of a screw mechanism. And then there is some motor here. There's four terminals that you see for this car. The other things that you, you may have here is think about now, like, these, these motors are for what purpose and how things are going to work in, in this case. So let's, let's, let's move on to next. There is other kind of a version of same CD, CD drive. But this is not the same company. It's a different company. It has different kind of an optical pickup head, you can see here. Now some of the components are here are removed. They don't kind of take it as it is, you know, you can see only these are, these are magnets here and the coils and other kind of stuff here from here is removed. Okay, I'll show you, like, more detail what is removed from here. And then, also that this is a motor here, on which the CD will sit. So you have seen that CD has this small little hole in the center. Okay, that hole will match with this step up here. So that the CD is located, like, no, radially, really well. So the center of the CD and center of this rotation of the motor is, is matched by using that kind of a small step there. And the CD sits on the surface and then, like, no, the head looks this optical pickup head lens is facing now the surface of the CD. Okay. Now, some of these observations, okay, so now you need to again ponder over these, these things. Let's go back. Okay, what are, what are the different components that you find there in the drive and what are they for? Okay, think about that. You may observe some things which, which is more than what I'm like, no, making you observe in couple of slides to come or in the previous slides also. But you need to think about different kind of components, why, why they're there in why they're that way only. Okay, so that kind of a discussions or that kind of a thinking process will be very, very useful for, you know, further incorporating those kind of concepts into your own kind of a design. Then what, what components in the CD can you see are responsible for achieving this kind of a very fine motion? Okay, so this, this is very important to kind of see that you what you saw there had some kind of a screw and like no some motor kind of a drive. Can that give you really this kind of a fine positioning is what you need to ponder over? Okay, if not, then what else is there to do the, to move? Then why do you need these components for, for, for achieving fine positioning? Okay, so some, some things you see is for fine positioning, something is there. And then you need to think, okay, why these, how they are kind of helping us to do the job? Okay, so this slowly we'll start exploring these questions as, as we start doing more and more keen observations. Okay, so, so see, these are kind of a mechanical interlock for the PCB as, you know, to avoid number of screws that are put in the, in the system. So you, you can see that, you know, the, this, some, some small holes are provided and some, like a pins are coming out of those holes, those plastic pins are kind of locating this PCB with respect to the motor or like, you know, those, those kind of locations with respect to this holder of the, or the tray, so that they don't move from place and they'll like, you know, get, when you assemble, disassemble, they'll go in exactly same place. So these locations of various components is, is an important consideration. Okay, from the mechanical design perspective. So we'll see this, how do we locate things with respect to each other so that they are in the right place when you assemble and disassemble later. We'll have a class, I mean, we'll have discussions in some of the future classes about that. Then you have this optical pickup system. So, so it's a gross motion for their system. You can see that there is a, this is now like, no, it's zoomed in view of that little screw that you're seeing. So this is a screw up here. And it has a motor on one end. This motor has these four terminals here. So, see, normally, we can identify based on this terminals here, like, no, what kind of motor it will be. Okay, if you have more than two terminals, it's not going to be a servo motor. Okay, servo motor will typically have two terminals plus and minus coming out. But this, this seems to have like, no more number of terminals. So this is, this is like a staple motor here. Okay, another way, like, no, you will start moving the screw and you'll observe that, okay, this moves in the steps. Okay, you can kind of feel that steps. Okay, that is another way to identify, okay, this is a staple motor really. Then there are these two snugs, okay, which are, which are moving on the screw. Why there are two? Think about that. Okay, how are they helping, like, no, why there are two things that are required here? And why not more than two? Okay, or why not less than two? Okay, why not only one? Okay, then what is this spring for? The spring is actually pushing this on this, like, no, two, two steps. Okay, so, and if you carefully observe this area, so one step will be, like, no, touching this side and other stuff is touching this side of the screw. So you see that for a, for a thread that is there on the, on the screw thread that is there on the shaft, one side is touched by one step and other side is touched by other stuff. Here what you observe is some small little rubber bush here and hole inside. So this, this goes on to something and this on the rubber bush, this, this entire thing is resting. They are like, like that rubber bushes, you'll see four of them at four different points or like, you know, at four corners of this assembly. And they help in, like, no, doing the shock absorption absorption. Okay, so mechanical vibrations that are coming from the mechanical vibrations are some shocks that are coming from ambient and they are prevented to go into the, into the, this high precision positioning system. And you can see this rod, which is guide rod for the, for the head to move. So we move further here and then, like, now observe some more things. Okay, so if you see now this is, like, how do you operate this? This is screw moves. I mean, like, you know, this, now we are doing a reverse kind of a drive here. We are, we are actually driving the, the stuff and then like the motor moves, actually. Okay, so this is how typically, like, you know, you have this drive system working. And you see, there is the other kind of a corner is a small little rubber bush, which is used for shock absorption. Okay.