Here at MISUMI we offer such a wide variety of coupling types.
So how will you know which type suits your application?
You'll find the answer to that question right now on
Engineer to Engineer.
Welcome to our new series, Engineer to Engineer.
I'm Matthew McMaster and today
our Senior Motion Systems Application Engineer
Chuck Leonard
will be demonstrating coupling selection for our linear guides and linear actuators.
You'll also be learning about a few different coupling types
as well as which types work best for your applications,
as Chuck shows you just how much flexibility various couplings will allow for
when torque is applied.
So let's go join Chuck.
Hello, my name is Chuck Leonard
I'm the Senior Motion Systems Application Engineer here at MISUMI
And today we're going to talk about coupling selection for our linear guides and linear actuators.
MISUMI offers a wide variety of different types of couplings
from a simple rigid type coupling similar to this
to our standard Oldham type coupling which has plastic spiders inside of it
And then we have a variety of universal joint type couplings
Some very large clamping type couplings
simple bellows couplings,
down to very small, simple little plastic couplings.
But primarily what we're looking at today and what we're going to discuss
is the type of coupling that we would use on a linear actuator.
Now primarily, what a linear actuator does
is it transfers rotary motion to linear motion.
So inside of this unit we've got a screw that's going to be moving back and forth.
What we're going to do is we would attach a motor to this end of the unit.
What we need now, is because we have a shaft on our motor
and we have shaft on our actuator,
we need to be able to have a coupling that's going to be able to fit
within our motor frame here.
So this is one of our first criteria.
And we also need to know what our shaft diameters are
for our actuator shaft
and what the shaft diameter is for our motor.
Now different types of actuators have different types of pilot openings.
This is our LX45.
It's one of our largest units
And you can stick up to a 32 to 40 millimeter diameter coupling inside of this.
But most of our couplings, the way they're rated,
we've got a variety of these,
a lot of people like to use this slit-type coupling on actuators.
It's got very high precision
and it also has very good repeatability
with a fair amount of torque.
Now one thing a coupling does is it allows you to have
just a little bit of misalignment
or angular difference
between the actual two motor shafts that you might have that are moving.
Now, this misalignment
this coupling can account for.
Now if you were to use something like a rigid coupling
which is primarily just a coupling
that is a piece of solid metal
and it's made to clamp down on your two shafts.
This type of coupling has no misalignment capabilities
but it's got the advantage that it's going to have very high repeatability
and it's also going to have very high torque transfer.
Where if you were to go with something like our oldham coupling
which has go a whole lot of flexibility in this
as far as angular misalignment
You can get 2 to 3, 4 degrees worth of misalignment with this coupling
But you're going to have a problem in here
that's it's got a lot of flexibility to
And then if you're looking for precision repeatability on your actuator,
as your motors reverse and go forward
you're going to end up with flexibility inside of the coupling.
And in the bellows, we have a similar issue here
we have a lot of flexibility in this thing
but the thing with a coupling like this is it's not going to transfer a lot of torque.
The bellows is very good in that
it does very good repeatability but it doesn't have a very good torque rating.
Now a couple of things we talk about now for very high torque.
This is what we call a disc-type coupling
And what this coupling has in it, you've got components here
that are actually mounted together with flat spring discs.
that are riveted between the coupling.
It allows for about a 1 to 2 degree misalignment
but it has very high torque transfer
and these discs are very, very good
for repeatability because they're not very flexible.
Now what I'm going to do is I'm going to hook it up,
this is a little jigging fixture that we've put together
and primarily what we can do with this thing
is I can take one of our couplings
and I can mount it
inside of this fixture
And we'll set it up here
Now all these couplings I have here use a clamping-type coupling
We also offer couplings with
set screw sets
or keyed couplings
The difference between these,
the set screw actually digs into the shaft
and it can make it a little difficult to remove.
Where a clamping type actually just clamps down around the shaft
so it doesn't mar the shaft up.
Another type of coupling a keyway type coupling
Now the advantage of a keyway is you physically have a piece of metal
that creates a key between the coupling and the shaft
And it also keeps it from turning.
About the only disadvantage of those
on the keyway is that you have to have the proper sized key
for the type of coupling that you're using.
Now what we're going to do is we've got a torque wrench here
Now if you'll notice, this needle is just about set on zero.
Now we've got a torque wrench that we've set up
It's got a small gauge on it
and we can record
the actual amount of force that I apply on this unit
and then we can take and actually measure
what we're going to see as
flexibility in this coupling.
So if I run this unit out
we're going to put about
20 Newton meters of force on this coupling.
This is way above the range that it would normally do
But you can see that we're actually flexing this coupling
at about 20 degrees
So this would be play that would be in your system
and this would not be desirable for a very high precision type of system
Now it does have some advantages if you're using this on a motor
and you were doing quick and short stops and starts on your motor
and you wanted to absorb some of the shock in that system
that's where and Oldham coupling would fall in.
Now I'm going to take this coupling off and we're going to replace it with a disc-type coupling.
Alright, I've mounted this second coupling on it
now this is our disc-type coupling, it's got the two discs
that are riveted to the outer clamping parts
of the shaft coupling
Now I'm going to reset my gauge here.
And I'm going to try to get
about the same amount of force
we're going to go up to about 20 Newton meters
Uh, I've got slippage.
Alright, I've remounted our coupling here
now we've got our slit-type coupling here
where it's got the disc plates in it.
It's about a 10 millimeter coupling
and I'm going to apply
about the same amount of force.
Now these couplings that I'm using are rated for about
1 to 25 Newton meters of force depending on the unit
I'm actually going to run this above its force rating
So we're going to run this one on up to about 20 Newton meters again
So as I apply the force to it
we're going to hit about 20 Newton meters here
And see, I'm not really moving that needle at all.
So we've got some pretty high-end torque
Now what this gives you here
and what this torque relates to with this type of system
if you have a lot of flexibility between your motor and your coupling and your shaft
you're going to get different positions
on this actuator as it moves.
And the whole design behind one of these actuators
is to have it very precise
so that as you put the number of pulses to
rotate this motor
the repeatability of this actuator repeats back to exactly the same place every single time.
and depending on the type of actuator that you get
we have repeatability as high as
3 microns on these actuators
Standard actuators will repeat to about 5 micron repeatability
But that repeatability is dependent upon you having the proper type of coupling tied to your motor
and that your motor shaft is properly tightened and not slipping.
Again, a lot of times when you go into the different types of couplings
and people look at these
and they say "Well, what type of coupling do you use?"
The Oldham type coupling is fairly standard for
single direction motor-type use
The bellows is very flexible
and very repeatable but it's not going to put out a lot of torque.
Our slit-type coupling
it's a very repeatable coupling
it can take a modest amount of torque
but will not allow for any misalignment whatsoever,
it will fracture the unit
We have our rigid-type coupling
The rigid-type coupling is an extremely good coupling
it's got a lot of capabilities as far torque transfer
but it has to have absolute alignment of both shafts
And then we get back into our
double disc and single disc type alignments
The double disc will give you more flexibility
a reasonable amount of flexibility with the shaft
but it gives you that high repeatability and high torque transfer
that you're looking for for rapid movement
and very high-end precision placement of your linear actuator.
Well, that does it for this episode of Engineer to Engineer.
If you'd like to check out our wide variety of couplings
go to misumiusa.com
and type "couplings" into the search box.
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