Episode #15: Ballscrew Actuators vs Belt Pulleys vs Linear Motors

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The Motion Control Show

Back in Episode 6, I explained to you the different types of linear mechanics.  This included ballscrews, belt & pulleys, linear motors and even rack & pinion.  I get the question all the time: which linear mechanics do I use?  That could be a short conversation or a long one, depending upon the application. 

In just a moment, I’m going to give you a quick overview of a good, better, best approach between the first three of those.  First, I'm going to have Michael Reynaud give you some visual explanations of a couple differences of the HMR series

The HMR Series can come as a belt-driven actuator or a screw-driven actuator.  We know these are belts based on how the motor is mounted to the actuator itself.  If this actuator was a screw-driven actuator, the motor will be mounted in-line with the axis of motion.  It would be right off the end or it would have a wrap around in parallel with the axis of motion. 

In belt & pulley actuator applications, most of the time we have to utilize a gearbox.  This is to match the inertia that is reflected on the motor due to the low mechanical advantage that the belt actuator provides.  If these actuators were ballscrew-driven, we would not be able to back drive them, but since we are utilizing belts, I am able to move them around freely. 

You'll notice though, I cannot move the Z-axis.  This is due to the fact that when sizing this axis, we added a brake to our servo motor.  This is because this is a belt & pulley vertical application.  If there is any power failure, we want to make sure that the load that our customer is utilizing does not free fall with gravity.

Thank you, Michael.  So, you might remember these graphics back from Episode 6 of the ballscrews, pulleys and linear motors.  I promised you a quick good, better, best overview of the differences between them.  So here you go: the typical requirements are precision, speed, whether the application is vertical or not, and, of course, cost.  Those tend to be the biggest priorities.  When we're talking about applications, loading and moment loading and some other things, of course, but those are the ones we start with.

Now, notice here I have a good, better, or best applied to each of those priorities for each of those three linear actuators.  Also notice here that the belt & pulley say “good” for vertical, it's by no means the “better” or “best.”  Linear motors and belt & pulleys just aren't great for vertical applications because the power goes out, they tend to drop like rocks.  However, in this case the priority of the speed was much higher than it being a vertical application.  Michael just showed you that we put a brake on it and so we were able to do that.  Now a brake on a linear motor is difficult, possible, but difficult.  So, perhaps we put a counterbalance on there instead. 

Michael also mentioned the back driving of linear motors.  If he had done that back driving with the linear motor, they would be very easy to move.  The belt & pulley have some friction, so they were not too easy to move around.  The ballscrews, they're still back drivable, but very difficult.  Usually you can back drive by hand and, unless they're under a high load, you really have to push against them.  A user may or may not have been able to move it by hand, depending upon the pitch of the screws.

I'm Corey Foster of Valin Corporation.  I hope this helps. 

If you have any questions, need some help putting an application together, or making some decisions, reach out to us at (855) 737-4716, or fill out our online form.