Episode # 58: Electric Actuators with Custom Stroke Lengths

Are you looking for an electric actuator that has a very specific stroke length?  Or maybe it is the overall length that you care about.  Many variables, depending upon what your factors are for your application, what your technology is, maybe what manufacturer you want to use or don't want to use, or how many of these you plan on using, are going to factor in to what the potential solutions are.  We are going to discuss this.  I am Corey Foster at Valin Corporation.  Reach out to us at TheMotionControlShow.com.  Follow this hashtag (#MotionControlShow).  Here is our phone number, 855-737-4716, and email address.  We are always happy to help.  Let's see what we can learn.

Several episodes back (Episode 6: “Types of Linear Mechanics”), I talked about the different main types of linear actuators: belt and pulley, screw driven, and linear motor.  There are others, but these tend to be the most often used.  

Let's talk about the belt and pulley first.  Belt and pulley can vary widely in its stroke-length capabilities.  I personally have used and specified ones up to 30 feet, I think.  It was really long.  Each time we had to move it, we would tear it down into sections and then move them over to another room.  But they are relatively simple, and they can come in sections.  You can get the sections and you can butt them together, so they don't necessarily have to be shipped always at 30-feet travel-lengths.  Sometimes they do, sometimes they don't.  It depends upon the design.  Some of them can be ordered and specified in one-millimeter increments, so it makes it easy. You don't have to ask for a custom actuator.  Some of them you can specify as a custom stroke-length.  Other ones the manufacturer may not want to do that, because if you're only wanting one or five, perhaps they're shipping overseas or their manufacturing is such that they just don't want to do it in small quantities.  That's a business decision that they oftentimes make.  So, it really comes down to the design of the actuator itself and the business model of the particular manufacturer you might be looking at. 

Looking at screw driven, there are different form factors of screw-driven actuators.  The electric cylinders, like this one, tend to be a little more customizable.  This one here again is also specified in one-millimeter increments, so this one is pretty easy to specify at different custom lengths.  But, other ones, like the generation before this particular family, wasn't very easy to do in custom lengths.  So, again, some are easier than others.  This one just happens to be changing the screw length and the tube length here and, of course, then the housing and the bearings as well.  

Ball screw and lead screw stages tend to be a bit more difficult in order to customize.  This one was built in a way that it is a little bit easier, however there are plenty of ball screw stages that are not easy to get custom lengths.  The ball screws have to be machined on the ends. They have to be cut to length. Now that seems simple, and it is simple from a design standpoint, but it may not fit into the business model of that manufacturer in order to do that on the fly.  They may cut a whole bunch to length at a given time, so cutting one to a different length is just maybe not easy for them.  This one right here is definitely not as easy to customize as this larger one here probably just because the manufacturer chose not to go down that path.  They don't want to make it easy to customize this one perhaps.  Or maybe there are some technical reasons just because it's already a short length and so all these screws are pre-manufactured.  (The bearings on this one actually are all pre-made to certain lengths so they can’t just be cut to length.)

Linear Motors are definitely different than screw driven actuators because they are already designed in a modular fashion.  You have the magnets.  In this case, I am showing ironless linear motor magnets, but you have these magnets and they are built modularly.  So rather than putting down each little magnet, they are built in strips.  Maybe it is 5 inches.  Maybe it is 3 inches or maybe there's a 2-inch version.  Then they put those sections together in order to get the travel length desired.  So a customized one is going to be some combination of the segments that are available.  Then there are the linear guides or the bearings and then the cable and the housing.  Those are usually pretty easy to then customize.  However sometimes there are ones like this one here on the right where there is only one length of the magnet track available.  This one happens to be a smaller linear motor, so there isn’t a lot of reason to build custom travel lengths.  They certainly could from a technical standpoint, if the business case requires it, but they're not going to typically do it for just one or two units whereas the one on the left is much easier to do in low quantities because the modular design.  Linear motors, if you are building just from the motor itself and you are putting together the bearings and everything else, all the bits and pieces by themselves from scratch, you can build up pretty much whatever length you want, as long as you don't have to divide up those magnet tracks because you can't build them super short because you have to have the right number of North/South alternating poles.  So that is something to consider when you are wanting to use linear motors.

I have asked our Bruce Ng to give us some of his insights as to why you, the customer, would want to customize the stroke length on actuators.  Bruce, welcome!  Why would customers want to customize the stroke length on their actuators? 

Bruce Ng:  There are a couple different reasons why somebody might.  I will mention two of the more common ones.  One we typically see in the aerospace industry, where pretty much every ounce matters, we have done customs where we shave off pretty much every possible ounce we could think of.  One of the big factors there is the stroke length.  So, we get it to the closest millimeter.  Then another application could be where there is actually a set footprint and they just want to fit the actuator in that footprint.  So, based off of what space they have available, we will actually go in and fit the custom stroke length to make sure it fits within their specifications there.  And we can do customs off of that as well.

Corey Foster:  Gotcha.  So, what is the longest actuator that you have ever worked with? 

Bruce:  The longest one I have ever worked with is probably around 3 meters, but I know that there have been ones that have been done that are longer.

Corey:  Do you remember what technology was used? 

Bruce:  That one was a belt-driven actuator.  It is a little tougher to get ball screws that are very long.  So, yeah, that one was a belt.

Corey:  Gotcha.  And how about the shortest?  What was the shortest actuator you have ever worked with?

Bruce:  The shortest actuator...I know we can do down to a millimeter, but I have never actually seen somebody that needed just a millimeter of stroke.  So, I would say the shortest we have done is probably somewhere around 1/2 inch to an inch. 

Corey:  And what was that technology? 

Bruce:  That was a linear motor. 

Corey:  Oh!  Wow!  OK.  Must have been a tiny little one. 

There you have it.  I am Corey Foster at Valin Corporation.  That was Bruce Ng.  We are happy to help.  You can reach out to us here.  It definitely helps to know what your application is.  We cannot tell you whether the custom stroke length can be built for your application because we don't know which mechanics, which manufacturer, which technology to use and what your requirements are.  So, we have to talk about each application, come up with the desired mechanics and suggested place to start and see if we can make it fit.  Then see if we can customize from there.  Feel free to reach out to us.  We are always happy to help.

If you have any questions or are just looking for some help, we're happy to discuss your application with you.  Reach out to us at (855) 737-4716 or fill out our online form.