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# Episode #8: What is the Lifespan of My Industrial Actuator?

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### The Motion Control Show

Today we're talking about specsmanship.  Specifically, we're looking at a load-ratings on mechanics by using the bearing life curves.  I'm Corey Foster of Valin Corporation.  Let's see what we have in store.

What is specmanship?  Why do we care?  Well, in case you haven’t noticed, the catalog specs are not always straight forward as they appear.  Let's look at a couple examples.

Something relatively simple: let's look at the normal load capacity.  We call this actuator “A”.  The load rating on this is 50 kilograms.  About 50 kilograms at earth gravity is 490 Newtons.  We'll call that actuator “A’s” normal load, 490 Newtons, and we'll pin that for comparison.  We'll go on to the next actuator.

Actuator “B”: it calls a dynamic load capacity of 3,065 Newtons.  That's significantly more than that 490N.  Well, these actuators, these stages, are actually about the same size.  They are comparable in precision.  They are two typical actuators that people might look at, that you might look at, in order to solve your application.  But, someone, if they're going just by this, they're going to say I'm going to go with the one that can handle 3,000 Newtons.  Why not if they're the same price, same precision level?  It must be a better actuator.  Well, let's look a little bit deeper.  First thing we can see here in the fine notes out of the datasheet, is that this travel life is based upon a 100,000 meters.  That is 100 kilometers.  Okay, good to know.  If we go down to 50,000 meters, we can actually multiply that load by 1.26.  Reading a little bit further, it has a maximum permissible load that should only be equal to half the dynamic characteristics.  Hmmm…not sure what that means, so, we'll pass on that.  Suitable load, with respect to the desired service life, loads up to about 20 percent of the characteristic dynamic values have proved acceptable.  All right, so, 3,065 times 20 percent is 613 Newtons.  All right, but the next fine note there says at the same time the following may not be exceeded: maximum permissible loads, permissible drive torque.  But, that maximum permissible, that puts us right back up here which is half of the dynamic characteristics.  Okay, half of 3000 is 1500.  That's still more than that 613 Newtons, so we'll go with the 613.  We'll call it actuator “B's” dynamic load is 613 Newtons and we'll pin that for a comparison.  The 613 is still more, but it's a far cry from that 3,000 we initially were looking at.

Okay, so let's go back to actuator “A” and see what that 490 Newtons means.  The datasheet for that one says that these forces include both the static components resulting from the payload weight and the dynamic components due to the acceleration and deceleration of the load.  It seems to be pretty comparable.  But, that Footnote 1 on actuator “A's” normal load indicated we should look at the bearing life curves.  So, here's the bearing life curve for that which is the red line.  The blue line is actually another family member compared to “A” but we're not looking for that one so we're looking at this red one.  Okay, notice there that the catalog values are rated at 2,540 kilometers of life.  That's 25 times what we were just looking at the ratings for 100 kilometers the other actuator.  If we look there, that's where the 490 Newtons is at 2500 kilometers of life.  Well, the other one told us to look at the 20% of that 3000 which gave us 613 which is there.  But that was really only at a hundred kilometers of life?  If we extrapolate actuator “B’s” curve, that means that this actuator “A” can really handle a lot more for only doing 100 kilometers of life.  Well, what if actuator “B” we want to go up to a thousand kilometers?  How do we figure out what that value is?  That catalog for actuator “B” has a bunch of equations we can look at.  We can go through and figure out what the forces are, figure out what the nominal life is and here's all the calculations.  But we don't really feel like going into that.  Sound like a lot.  So how do we untangle this?

That's what we at Valin Corporation do.  We specialize in figuring this stuff out for you.  We work with a number of different manufacturers.  We call the factory.  We do the calculations.  We can help you out.  Give us a call.  We're happy to help you out.  The primary point here is not just to look at two individual specifications and compare them because 50 kilograms is not necessarily the same 50 kilograms or, in that case, 490 Newtons.  This is certainly not the same definition as that 3,065.  Don't get caught up in specific numbers like that.

If you have any questions and are wanting to know more, reach out to us at (855) 737-4716, or fill out our online form.
##### A lesson for me is that I need to involve you earlier in the program.

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