Mysterious Screw

[Pat Fairbank]

Even cooler than lead screws, in my opinion, are ball screws. They perform the same function as lead screws, but instead of relying on surfaces sliding against each other, they have lots of ball bearings inside (and a mechanism for recirculating the balls between the bottom and top).

[jimbot]

So do ball screws do anything better than a lead screw? Or was it just another case of an engineer with to much time on his hands and to many resources? (Creepy Thoughts)

[MrForbes]

Ball screws have been used in automotive steering gears for the past 50 years or so....

[spazdemon548]

Ball Screws have less friction and maintain a lot higher linear tolerance than lead screws.

[MrForbes]

They can also handle a heavy load with marginal lubrication.

[Teched3]

Ball screws provide less friction in the mechanism, and you could find them at the end of older vehicles and truck steering columns before rack and pinion became the norm.

[joshsmithers]

As a warning: MULTIPLE leadscrews are a MUST for any build team if you have too many freshmen. Just tonight, in fact, we had a minor argument over who's turn it was to hold the "cool screw thing."

We've never used it, but it is notorious for being either the the most useful or useless thing in the KOP. Come to think of it, didn't 330 use it in 2007 inside their arm to activate their claw?

EDIT: Nevermind, that was pneumatically actuated.

[Akash Rastogi]

Hehe, I found one application that I think I need it for.

Need help with this. So for robotics, I'm creating a simple manufacturing workcell that autonomously places sheets of aluminum into a dye and then pneumatics come down to just bend the sheets. What I wanted to use the lead screw and a motor for is to have a custom made vice run on a bed (much like a vice would on a mill) to come forward and make sure the sheet is positioned correctly but I don't know how to set up the lead screw to do this. Also which motor should I use to have the sheet of metal positioned quickly using the vice and screw? Thanks, any help would be appreciated.

[DonRotolo]

Originally Posted by Akash Rastogi

I'm creating a simple manufacturing workcell that autonomously places sheets of aluminum into a dye and then pneumatics come down to just bend the sheets. What I wanted to use the lead screw and a motor for is to have a custom made vice run on a bed (much like a vice would on a mill) to come forward and make sure the sheet is positioned correctly but I don't know how to set up the lead screw to do this. Also which motor should I use to have the sheet of metal positioned quickly using the vice and screw?

First, Pneumatics are not a good choice for bending metal, you cannot get the power required. Hydraulics are the better choice. But, that's not your question.

To use the leadscrew as a positioning element, you first need to create the system that drives the leadscrew - for example a window lifter motor. Then, you need a system to know the exact* position of the nut on the screw. Using a PID loop, you drive the motor until it is in the desired location.

*Exact is relative. 0.001" is hard to do with a quadrifilar leadscrew, 1/8" should be possible.

For repeatable. low-load positioning, you should consider pneumatics. Use an adjustable end stop on your mechanism to set the exact spot to push the material to. That also actuates a switch, which makes the hydraulic press come down onto the die and do whatever you want. Then another thingus comes up and pulls the workpiece off while a new one is being put on.

[ks_mumupsi]

take a look at the 2016 robot when you get a chance... we will post more details when we get to competition.
you can also take a look at 2753's arm as we have a joint effort here.

That lead screw is an integral part of our design and it works amazingly well.

[EricH]

Originally Posted by joshsmithers

We've never used it, but it is notorious for being either the the most useful or useless thing in the KOP. Come to think of it, didn't 330 use it in 2007 inside their arm to activate their claw?

EDIT: Nevermind, that was pneumatically actuated.

330 hasn't used one on a competition robot since 2002. Then they used two small ones...and come to think of it I'm not even quite sure they were leadscrews. I do know they came out of a gearbox that we haven't gotten since then.

The leadscrew's only function other than wasting time is to turn rotational motion into linear motion. While it is theoretically possible to go the other way, reality wins and it's pretty hard to do so.

[MrForbes]

But you can have fun with the concepts of friction and angles by figuring out just how steep the thread angle has to be to keep it from backdriving.

The fancy coating, low friction plastic nut, and multiple threads make it so that the KOP lead screw can indeed be back driven, but normal nuts and bolts can't.

[Al Skierkiewicz]

Large versions of this little screw are used to adjust position on satellite dishes all over the world. I work with one dish that has a lead screw for elevation and it is connected to a 3/4 HP motor with an electric brake. The screw is about 4' long and at least 2" in diameter. Another dish that is much larger has two, one for azimuth and one for elevation. Both can be operated by a hand crank or electric drill attachment. The dish is 6 meters in diameter.

[hillale]

1625 has used leadscrews very successfully in the past. In 2006 it was used to actuate the hood on our turreted shooter and in 2008 it was used to bring our shooter from pick-up to shooting position.

[MrForbes]

Originally Posted by Al Skierkiewicz

Large versions of this little screw are used to adjust position on satellite dishes all over the world. I work with one dish that has a lead screw for elevation and it is connected to a 3/4 HP motor with an electric brake. The screw is about 4' long and at least 2" in diameter. Another dish that is much larger has two, one for azimuth and one for elevation. Both can be operated by a hand crank or electric drill attachment. The dish is 6 meters in diameter.

The dishes I worked on way back when used gear drive...10 meters with a pretty heavy equipment room attached to the az drive....

If you ever get the chance to peer into the workings of a 1957-59 Ford Retractable car, you can see several lead screws. An engineering marvel.