 talk about like the normal low-speed control motion control stages typically like you know some kind of application so some small motion that you need in the lab kind of a level to add just some optics or some some kind of some like normal motion stages I would say microscope we are observing something and you need to move like no under microscope some things okay so it was kind of a motion stages like no you typically will have make use of a screw or rack and pinion kind of arrangements okay so wherever you feel like no there is a bad reliability possibility then like no you will go for the screw arrangement okay and rack and pinion are those other kind of drive arrangements can be prepared where there is a back drivability is not an issue okay so we don't want system to be back drivable then like no you use screw because screws typically even designed properly the screw helix angle for some certain helix angles that are designed on the screws it will not be back drivable otherwise I mean you see that your car jack for example okay so you raise like no that's you tighten the screw and the car is raised up now see if it it has been if the helix angle or that screw is not properly designed then you know more more even if you tighten it like after some time like no the system is going to kind of you know get practically one by the weight of the car itself and it will start rotating in a policy direction and you lose the you lose the purpose of the jack okay so screw jacks would be designed to have a non back drivability kind of arrangement so you you drive and like no the system stays there it is not getting back driven by the weight of the car itself okay that is a kind of a concept of back drivability here so now let's see how do we can take care of these alignment or rather misalignment with the screw axis with the with the guide axis okay so see some part of this we have seen while doing like no CD-ROM example we have seen the guide there one car one rod is complete guide another rod is not so like no completely kind of adding okay so that is taking care of some kind of a misalignment of the two rods guiding rods in the system now if you have a screw in addition okay so the screw axis will have some kind of a direction for the motion and then with respect to guide axis you need to make sure the screw axis is aligned and guide also needs to have like no two places it needs to be guided the system cannot be guided only on one side you know for the reasons that it is not fully constrained then okay so you need to have typically two guiding places for the for the motion for the linear motion to happen and along now along with that you have now the screw arrangement that is going to be there so how do you think like this system can be what kind of arrangement can be done to take care of this issue how this misalignment when you are driving with the screw is taken care of okay so think about think about that and we'll talk about that in a while now and and other issue that that one can think you see it's like no how to get like no low resolution or large range again here when you are using some kind of a screw kind of a drive to get low resolution I mean extremely like no your resolution I mean the resolution should be high in actually low resolution is not a correct word to use here is a high resolution means like you need a very tight motion tolerances here you want to kind of move maybe say 5 micron 10 micron okay and you need to have that over the large range you want to kind of like maintain that kind of a high resolution yeah how do you get get that when the screw drive means there typically when you see the screw car jack kind of a stuff those screws would it be helpful in here okay or any kind of screw you might have seen okay screw and a nut arrangement you imagine okay you have a nut and screw arrangement and like no you see how loosely the nut moves on the screw and if you just hold the screw tight and move the nut in the actual direction okay then you'll find that there is some kind of a play that will happen okay so you have a screw and a nut together and then you just move it and like no you'll see that there is a play that can happen there so under this scenario like no you you will again need some kind of a backlash prevention so this is like a backlash element right you move in one direction and it touches one side of the screw threads and in the other direction other side of the screw threads but now we do we we have this screw as a complete you know circular screw there and the nut also is a complete circular nut so how can we we think of the some of the ideas that we had with the CD-ROM screw okay in the CD-ROM screw you remember like we had these two stuffs which were kind of pressing against the screw now we have say single nut okay what we can do so you might guess that okay look you need to have some kind of a preload somewhere like you know some kind of a you know the loading of the of the screw nut against the screw and should happen somehow okay so if that is happening then like no I'll have this application going good okay and that's precisely he's done see if you if you just use stubs here stubs kind of a thing for the screw then this may have a load bearing capacity will be reduced okay with those small stubs like no may not be able to carry a very large load if you want to drive daily a good you know load when you move the screw typically so imagine like no in the in the again the car jack you cannot have stubs which are holding the screw there I know that's that kind of a weight of the car can be cannot be taken by just small some stubs which are up there in fact in there like no your screw will have many many more threads engaged at a time okay rather than only single thread engage at a time single or two engage at a time okay so we want this total circular kind of a engagement to happen but still we want to kind of do some kind of a you know preloading of the screw so how do we do that okay so let's see some actual motion and of the state systems this is one of the motion state systems from this company called Howlmark okay so if you open up this okay so this is a screw we can see this like a you have a micrometer screw gauge kind of a screw there and it is pushing this this stage okay on which you can mount whatever things that you want to move and as I tighten this screw like you know this this will push this stage but then like no this engagement here the the screw threads are in this piece okay and then the stage is just guided in the linear fashion here by some bearings up here and here there are two side guides here for the for the screw as we open up we'll see in these details but the screw is in here okay so screw is not attached to the stage okay so that is how like no one can say that okay the guides axis and the screw axis is made free so this this screw axis screw is just touching up here okay so we can you can open up and see here okay this is a screw here the screw has no the the threads are in this piece okay and then this is a screw okay and the screw has this small kind of a you know piece that is coming out and touching and pushing this this up like no upper stage this is the upper stage and you can see these two little springs here the springs are like no tensioned and like no they they're attached to this bottom piece bottom piece is where like no here this assume this screw is assembled on the bottom piece here so when you tension these springs and attach it to the bottom piece like no the the there is a relative kind of a pull between this top and the bottom piece in this direction okay and this screw is is actually preventing that pull to happen okay so as I tighten the screw I'll I'll I'll push this more and more and like the pushing force is going to get increased because the springs are getting tensioned more and more okay and as I like no loosen the screw I mean push it then the spring is moving the stage okay the screw is just like no releasing the the position of of the the head screw head relatively okay so the screw is head position is moved relatively and then the the stage gets pushed by the springs will like no which are pretensioned here this is how like no you create this preload in the system and like no move the system such that the motion happens in both the directions so the push is active motion by the screw but pull is happening here because of the springs that is how the things happen so what are what are the problems for such an arrangement you can imagine and see that you know that okay if I have a force which is much more than the spring force okay at any point then in the in the appropriate direction in the direction say in this case like no against like no the like against losing the contact or in the direction of losing the contact between the screw and where it touches so the place where it touches is somewhere like no on this somewhere here okay so you see this little kind of a pin or some some something here this is very hard surface on which like no this this head will be touching so um so there's this if I apply a force in the in this direction then their touch will be lost okay I'm my by my force so there is no active thread engagement which will hold it firmly there okay that okay all these force is applied and it goes against some threads to and the threads will take a bit and like no not allow us to move as that kind of a thing will not happen so this will allow that motion to happen if that force is much higher depending upon application what where you want to use you need to think about carefully about the whether this is okay for your application or not and take a decision take a call about that uh what little things that you see here are basically the bearings there's one there are these two bearings on on on each side or maybe many more maybe on one on each side and then like no there is this uh guide which will have these bearings put there and there will be some kind of a small adjustment for these guide rods these are guide rods which are kind of like placed here in some cavity and those guide rods will have like no some kind of adjusting grub screws that are put inside this piece okay so those adjusting grub screws will kind of like no make sure that the both sides are aligned to each other okay so that there is no jam in the in the bearings so that that some kind of a skilled operation needs to be done initially to engage these two together and make sure that you know these bearings are guiding in such a way that for entire motion there is no jam that is happening and there is no play that is happening also that kind of a skilled operation needs to be done to begin with because now here we have we don't have full guide on one side and like you know half guide on the other side that arrangement could also have been made here possibility is there but here that has like you know the weight load bearing capacity will be lesser in that case load bearing capacity in such a kind of a guides is better typically but then like you know it comes at a cost of doing this additional adjustment of these both the side guides such that there is no jamming that will happen as you would kind of imagine otherwise if these are not like aligned properly you know then there is a possibility of jamming that will happen for the stage okay so so this is like you know typically the arrangement for the motion stages now we want to kind of see so as as you see here like you know as I move more and more okay the springs are getting stretched more and more then like you know the amount of force in the springs will increase as they stretch more and more so which is not really desirable right I mean that then that means like you know I'm I'm kind of restricted to a small range of motions with these kind of stages I cannot move a very large motion because my spring is going to apply a very large force at one end and you know relatively smaller force at the other end of the stage and that's how like the force will vary along the length of the stage so for that I'll need to do something okay so think of what arrangement can we do to get rid of this issue that okay large range even if I move whatever large range I want to move this problem will not bother me but I still have like you know some arrangement for you know the misalignment of the axis of the screw and guide axis okay the guide axis will be adjusted by these guides in some way so the guide axis will be defined by the guides and now in this case if you see the screw axis if it is even if it is the guide axis is like no tilted with respect to the screw axis it's not going to create a major issue okay because so because there is a relative kind of first sidewise motion that will happen at this contact point okay so contact point way is is so as a titan and like you know the guides supposed to go in the in one kind of tilted direction and then screw is going other direction but since there is no firm engagement of the screw there is only like no pushing contact there the push can be kind of move slightly on the surface of the of these you know things that is getting pushed okay so there is a relative sidewise motion that can be possible between the the surface that is getting pushed the stage that is getting pushed and the screw motion so that's how like you know this alignment misalignment problem is taken care of and then backlash problem is taken care of by the spring but what problem I invite by using this is like you know if I have to kind of if I want to go for larger range I'll the spring force will increase tremendously high and I'll need more kind of a effort to move against you know in the larger force of the spring and typically if I have a motor to drive this then the motor will have will see this differential load like okay depending upon the position of the stage I'll have a load that I need to apply because the friction will change at different points so these are the kind of typically drop back so nothing is free if you want to take care of the backlash you put some load preload then like know the load on the motor is going to increase more the preload like no better kind of a system you may get but that much more kind of a torque or friction torque that man has to overcome to drive my system okay now so these are the kind of like no issues that come up and like no this is a way things could be designed to get get them working so you can think like no how do you achieve larger kind of designs and if you have some kind of ideas thought then like no you can move on from from there okay you can pause again at this point and then let's move on so so this is like now an arrangement for the larger kind of a range positioning without having now these two big kind of springs there so you see this in this element again like no this is opened up stage what you observe here is this is not cage here this is not like a single single single nut I'll show you what is there inside in a minute but this is some kind of arrangement here so imagine that okay this had been only the nut okay there's no some kind of arrangement this is just like a nut here and then the top there are four screws which are like no attached to this stage that moves on the surface and then there are these guide rod here and guide rail here these are two guide rails here and here and they'll have some kind of you know limit switches that they have put here for like knowing the limits of the things so that you can turn off the motor so this is already motor mounted here this is motor driven stuff that is you can see here that is a flexible coupling and then all these arrangement is there so when it is assembled it looks like this when it is opened like you know the top stage is always these bearings are open then like no you you get this kind of a view okay and then there is a screws typically these screws are with very fine threads so the fine threads mean that they'll not be pack drivable and for a for a large motion of the rotation you'll get very small motion of the screw so that it will have a very high you know positioning accuracy can be possible okay so for one step of the motor you'll get a very tiny motion that is happening for the for the stage given that like you know we don't have a backlash issues and given that we don't have a misalignment issue so see this axis of this screw and the guide axis again there might be possibility that okay they may get small misalignment and then you'll see that the screw will get jammed in no time if there is no special arrangement that is done inside this so think about what can arrangement can be there inside these to take care of these two problems one is like a backlash another is like a your misalignment of the guide axis and the screw axis and if you open up further you'll get this everything now so you see this is a part here and then this is a part here opened up like inside that this is a nut okay so this is only the nut and then this is some kind of a cage around the nut okay so this cage has this typical construction like okay is a C kind of a cage and inside there is a there is a hole here and there is a hole on the other side and nut is slanted inside and now you can imagine so now you can imagine if this axis of the screw and axis of the guide has small misalignment or small tilt okay then this screw is going to move inside the cage but the cage is attached to the top thing which is guided so the cage is guided by these two side rails which is attached to this this piece here which is a stage motion stage which is guided by these two side guys so the axis of this is like you know this cage is moving along one axis and then this is moving along another axis and then there is a relative motion that is created between these two because this is just sliding inside this okay so this is the arrangement that is made to make sure that you know your misalignment of this axis is taken care of and then you see small little kind of a holes here okay these holes like you know if you see carefully I mean I mean they are not there here but you can imagine that these holes like no one can put springs there when you are put springs in these holes here there they are like no pressed against this top so I have to kind of really push this and put springs in pre compression to align the whole of the nut to the whole of the cage to kind of get the screw inside the nut okay so that will make sure that you know I have some kind of a pre-loading of the screw done okay so so nut with respect to screw is getting pre-loaded on the on the surface and whether the nut is here or here or here or here any position I put put this cage the spring load is not going to change right so this is how like no one takes care of like giving the solving the problem of misalignment also and having now we have removed those big springs that were causing less you know the the increase of the force okay so this is how like the things are done here okay so maybe it's a good point we can pause here and we have so these are more kind of pictures that you can see for this arrangement of the guide so so you can see that here 45 degree cuts made in the guides and then like the the small little boy bearings that are actually the cylindrical rollers which are put inside these to make sure that is added and then there are some kind of adjustment screws that are provided at the back here for the for the alignment of both the guides to be done okay so so so we can kind of pause here for the for the discussion and then like no we'll we'll discuss more in the in the other class but these are kind of a summer some salient features or summary of things that that are that we have learned today okay so for removing backlash you do some kind of arrangement for removing like maintaining the parallel axis motion with the with the misalignment problem is taken care of by some kind of arrangement so so one can do this kind of one like no designs thinking and effect like no the the design in such a way that you don't have to do a lot of treasury in control domain okay so these are like no all these kind of things are done to make sure like no you have no paints in like no motion actually having the motion and also you will have a little bit of ease in in driving the systems in the in the electronics domain and i would like to think i'd like you to think about okay now what is the cost that we are paying for putting the spring loading things in the on the electronics side okay so think about that