Episode # 64: Linear Motors in Vertical Applications

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The Motion Control Show

Electric actuators that have linear motors as their drive trains in them are great for high performance applications, especially when they are applied correctly.  However, there is one type of application where we really hesitate before we apply them in that situation, and that is vertical applications.  I am Corey Foster at Valin Corporation.  Reach out to us here at this information below.  We are always happy to help.  Let's see what we can learn.

First off, let us talk about what the problem is with linear motors in vertical applications.  You can refer to earlier episodes of The Motion Control Show to see what linear motors are and how they are different from ball screws and belts and pulleys.  But just a quick reminder here…

This is a big magnet here. It is actually a big series of magnets.  This carriage right here has a coil in it that slides up this slot here.  The magnets in this case, it is an ironless linear motor, it has a “U” and it has an “I” that goes right up through those magnets.  So, there is nothing touching there.  There is no mechanical advantage.  The whole load is actually supported by this bearing here.  Here is a different type of linear motor.  It is an iron core, in this case.  Again, the whole load is supported by these bearings.  It has a coil here, and it has magnets underneath this carriage.  If all that is supporting the load here is these bearings, this slides very easily back and forth when it is horizontal.  When its power is off, you can just run it up and down those bearings because there is nothing stopping it.  With a ball screw, you cannot do that.  You have to really push against it. 

So, what happens when we take this actuator and we put it vertically?  Well, it is going to fall like a rock.  One solution is using a counterbalance.  Here is a pneumatic one here.  Here is a magnetic one here.  Those are both different solutions to the same problem that when the power goes off it is going to stop it from dropping like a rock.  The pressure of this pneumatic one has to be adjusted a little bit in order for it to balance out properly.  I have actually worked on a linear motor in a vertical application that was maybe 6 feet of travel.  It had a big pneumatic actuator next to it holding it, but what was really interesting was that, if you turned off the power, you had to adjust the pneumatic pressure just right so that it did not actually push the actuator up when it was off nor did it let it drop.  We had to find that balance in between where the pressure was right for it to basically be zero load when the power was off.

Another approach to the solution is a rail brake.  Here is a linear guide that the load might be resting on, and this is a pneumatic brake that can clamp onto the rail and hold it in place.  It is basically a linear version of a brake that might go on the back of a servo motor or on the end of a ball screw.  There are a couple of variations on this.  There is one for round rails.  There are other ones out there on the market,  I am sure.  This is just something else to consider for linear motors in vertical applications.

I am Corey Foster at Valin Corporation.  Reach out to us using this information here.  I hope that helped.

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.