WHY MACHINES THAT BEND ARE BETTER? (COMPLIANT MACHINES)

 

What do satellite thruster, plastic tool and micro mechanical switch have in common?  well they all contain components that bend so-called compliant mechanisms . But it's always been considered to be bad to have flexibility in your machines well we've tried to take that thing that everybody hates that is trying to avoid and say how can we use flexibility to our advantage? how can we use that to do cool stuff ? so let's start with something basic probably the easiest compliant mechanism was this thing what it is is a compliant mechanism that is a gripper made of plastic so you can put something in there and it will get actually a really high force.

So compliant mechanisms have a number of advantages over traditional mechanisms but I thought in order to have a clever pithy way to remember all of these advantages so I came up with the eighth piece of compliant mechanisms and the first of those is part count compliant mechanisms have reduced part count because they have these bendy parts instead of having things like hinges and bearings and separate springs. This gripper is just a single piece of plastic but achieves a similar result to the much more complicated vice grips. But how much does it amplify the force? So you will be amazed to hear that it is about thirty to one so I could get for one pound force and get thirty pounds out so that's pretty good and it is super cheap and really inexpensive. so we can manufacture this by injection molding and this would cost cents and the other thing is because of its shape you could extrude it and then just chop them off so the simple design allows different production processes to be used which lowers the price these switches.

But how long can these last?

 After putting it in fatigue testing machine it have been able to go over a million cycles without failure.

where we got there all right now lets have a quiz.

okay if we gonna push on elephant's rump this direction and hold it and that little orange dot right there is that dot when I push on it is it gonna go left right up or down?

so that when you push on that it actually just rotates in space it doesn't move at all.  This mechanism is used in wind tunnels where you want to have say a model  that's attached  but you move it and all you want to do is is control its  angle and move it around in a wind tunnel don't displace it but devices like this demonstrate the compliant mechanisms are capable of producing very precise motion which I personally found pretty counterintuitive because these objects are made up of flexible parts but maybe that shouldn't be surprising because compliant mechanisms don't suffer from backlash. So backlash occurs when you have a hinge which is basically just a pin in a hole and it's moving in one direction and now if at some point the motion reverses it doesn't happen instantaneously because there's some give in the hinge this also causes wear and requires lubricant and that is why compliant mechanisms have better performance than their traditional counterparts.

This actually believe it or not compliant mechanism based machines are also used at the microscopic level. where we're building compliant making the on chips we had to be able to make these compliant mechanisms out of silicon which is as brittle as glass and if you're trying to make something like this out of glass, it's crazy hard but that also means once we figured out the design we could make it in material even like PLA which is also you know not the ideal compliant mechanism material. 

so just using the same process is used to make computer chips so another advantage of compliant mechanisms is that they can be made with significantly smaller proportions because they take advantage of production processes like photo lithography .

Compliant mechanisms are much more portable meaning lightweight which makes them perfect for space applications.

 

This is something NASA made,  a hinge that could replace bearings for deploying solar panels. This is 3d printed titanium but what's freaky about it is there's a piece of titanium that can bend plus minus 90 degrees  i.e 180 degree deflection that is solid titanium that is one piece of titanium that is 3d printed there's no alloy nothing to make it flexible.

Compliance mechanism is also used by NASA for thruster application.

where they put a thruster right there (refer the video) and now with two motor inputs they can direct that thruster in any direction that titanium device moves that you notice that's just all bending and and there's no pinch points for the fuel lines or electrical lines coming in here. This single piece of titanium allows you to use one thruster in place of two.

 

This is the safing and arming device for nuclear weapons. Its purpose is to ensure that no random vibrations say from an earthquake inadvertently disable safeties in arm the nuclear weapon now. One of the requirements was that this device be made as small as possible they could using true methods even using things like what the Swiss watch manufacturers were using with compliant mechanisms. They produced a device out of hardened stainless steel where some components were the size of a human hair.

This is high-speed video here the device is operating at 72 Hertz meaning the little hole makes two complete revolutions each second the way it's meant to work is an arming laser shines on the rotor wheel and when the proper input is given to the system the wheel rotates a notch if all the proper inputs are given then the hole lines up with the laser beam and crazy things happen from there so it is essential that this devices performance is perfectly predictable even if it sits unused for decades.

Compliant mechanisms have lots of advantages over traditional devices.

summarization in the 8 P's of compliant mechanisms:

 1. Part count (reduced by having flexible parts instead of springs, hinges)

 2. Productions processes (many, new, different enabled by compliant designs)

 3. Price (reduced by fewer parts and different production processes)

 4. Precise Motion (no backlash, less wear, friction)

 5. Performance (no outgassing, doesn't require lubricant)

 6. Proportions (reduced through different production processes)

 7. Portability (lightweight due to simpler, reduced part count designs)

 8. Predictability (devices are reliable over a long period of time)

Published by-

1) AAYUSH SURAWAR

2) SAMARTH TAKBHATE

3) DEVASHISH TAMBADE

4) UMESH WANARE

5) CHINTAN VORA