Episode # 59: Electric Actuators for Applications in a Vacuum

Contact Valin today for more information at (855) 737-4716, or fill out our online form.

The Motion Control Show

Extreme environments often require custom actuators and motors for that matter.  Vacuum applications are one of those types of environments whether it is out in space or in a small chamber where all the gases are pumped out.  Those gases might be pumped out in order to get all of the impurities out or as well just to get all the particles, all the atoms, all the molecules of even the gases out so they don't interfere with all the really small stuff being used in them.  I am Corey Foster at Valin Corporation.  Let's see what we can learn.

The request I typically get for mechanics is “Are your actuators vacuum compatible or vacuum rated?”  And while that does work sometimes for actuators and sometimes it does work for motors, it does not necessarily work for every application.  You really have to treat every application as a custom application with custom actuator and custom motor requirements.  The reason being is that there are a lot of different considerations. 

There is the vacuum level.  I've worked with some really, really, really strong vacuums, at least with customers with the really strong vacuums because they are working on cutting edge technology on beam lines and things like that.  So, you have to look at the vacuum level.

Then you need to look at the gases being used.  What are they putting in there…maybe in place of the air?  Is it nitrogen or something else? 

You have to look at the bake-out temperature.  We do not necessarily do this, nor our manufacturers, but the customer may.  They bake-out the product which means to basically burn out all the last impurities in that product before putting it into the into the vacuum. 

You need to look at the ambient temperature of what the temperature is actually going to be at in the chamber or in that vacuum while the actuator is in there.  In outer space, it is going to be really cold, but in a vacuum chamber, because it is an enclosed environment, and there might be heat going into that environment, like the motor’s power and all that, you have to look at that temperature.

There are the acceptable lubricants.  The concern with vacuum is that if you put some plastics or lubricants into that environment, because there is no pressure in there, the lubricants or the gases of the plastics are going to out-gas.  They are going to go out and become gaseous and then that can fall down into the application, onto the surface, or onto the product that the customer is using in that chamber.  So the question is whether or not the customer can handle particular materials or not.  Often times they might specify a particular grease that is okay to use and maybe some plastics are okay and others are not.  But that is very application dependent.

Then there is the anodized aluminum.  Can it be removed as well for the same reason as the outgassing over their material?  Can it be acceptable in that application?  You see XY stages here on the right hand side.  You see that they have a lead screw or ball screw and there is no anodization on the aluminum on these stages.  And then there is probably special lubricant on these screws, and then the bearings probably have a particular lubricant, or no lubricant at all.  Maybe they are running dry.  Those are some of the different considerations we have to look at.

Last one is the component compositions.  What are the components, the bearings, the metal?  What are all those materials that are used in there?

The motors can sometimes be marketed that they are vacuum-rated and those motors do exist.  However, one of the things you need to remember about the motors is that the vacuum environments are usually hot in a vacuum chamber.  If you go back and look at my speed/torque curve episodes in the past, this reduces the power capability of the motors.  So, if you are running a motor at 20C and the motor overheats at 100C, you have this much room that the motor can heat up to go from 20C to 100C.  If it is hot in there and you are starting at 60C, you only have this much temperature rise in the motor left.  So you only have this much torque versus this much torque in a hotter application.  That becomes very important because then maybe you have to oversize the motor or you can only power the motor for so long.

Last thing to think about is sometimes a vacuum chamber application can be used with an actuator from the outside going through a specialty device like a bellows or inserter from outside the chamber.  In my experience, what I have learned with my customers, is that you have to size the stages appropriately because if you have an actuator going in through bellows into that chamber, that vacuum is pulling on the bellows which is putting a linear force on that actuator which means that actuator and that motor have to be sized in order to be able to counteract that force.  Something you may not be thinking about that because you are just thinking about the load that is on there, but actually the major part of the load is really that vacuum pulling down on it.  I have worked quite a bit with vacuum applications here in the Bay Area of California with the semiconductor industry and the linear accelerator centers, so I have quite a bit of experience in talking about these.  I hope this helps.

I am Corey Foster at Valin Corporation.  Reach out to us here at this information below.  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.