Opinions/Comments on Linear Slide With Ecentric Lift Point 1

[CPosner]

I am designing a lifting mechanism for a large glass panel approximately 3500lbs 8ft tall x 17ft wide. Two large columns will support the two linear rail slides mounted to each side of the glass. Two Carriages per side. Lifting the panel vertically.

The question is, I would ideally like to use one ball screw jack on one side of the frame to lift the glass. The screw has the capacity to for the weight, but the loading point is obviously not on center/centroid of any axes due to tight packaging requirements. I am wondering if there will be any significant moment created by the loading point and cause a binding in the linear slides. I have spec'd the track size and screw via calculations and the applications engineers with the manufacturers. I am also discussing possible options with them as well.

Thanks!

 

[CPosner]

Pardon my spelling error **Eccentric

Thanks

 

[GregLocock]

Assuming your top slide is at the top, and the other is at the bottom, you will see a lateral force of about 3.5 tons on the lower slide, just before it jams. Then it will jam good and solid and your name will be mud.

If this is a one-off unit then lift it from both sides. If you are building a hundred of them then it may be worth investigating the mechanics in detail, to ecomise of the number of ball screws, but I note that the only roughly similar systems I can think of (vehicle hoists, fork lifts) use a screw in each 'leg' or drive the load from the centre.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dvd]

Roger that. I have seen it happen also. I vote for using 2 jacks.

 

[CPosner]

I always thought in the back of my head that I would end up with two screw jacks. This just makes it more interesting with packaging and installation. There are some tight space requirements and installing this massive glass panel will not be easy. Granted there is a trade off...I think I will lose some strength in the ball nut mounts with the two screw option so the glass can be assemble in a reasonable manner. I will see if it is ok to post a picture. Thanks!


More suggestions are welcome!

 

[CPosner]

Also, going with the two screw option..I need a simple way to keep the ball nuts synchronized. Speed sync is not a problem obviously. One motor with a timed/cogged drive system..But the nuts need to be in the same position..Is all of this taken care of in the initial setup? Can the nuts come out of alignment? I think there is minimal lash in the screws, but lash in the worm gear drive box that controls the screw. I'll find out from the applications engineers also..

Thanks

 

[prohammy]

Just some words of caution.

Running two leadscrew systems together is difficult. There will be a lot of set-up to ensure that they travel together. Make sure you leave enough adjustability, such that whoever is assembling the systema cen ensure that the axes of travel are as parallel to each other over the full travel as possible. A very good idea, after the systems have been set up to their running position is to have independant set-up blocks (can be as simple as a block with slots) that can be added to the mechanism that 'record' the X-Y (and Z if required) positions of the slides so that they can be dis-assembled at some future date and put back to their original position.

Re the nut, make sure that the leadscrew nuts are anti-backlash, and bronze is generally the preferred material (depending on the application this may be nylon)

Hope this helps

Kevin Hammond

Mechanical Design Engineer
Derbyshire, UK

 

[prohammy]

CPosner,

Just another thing that came to me last night....

When it comes to choosing the slide itself, because you have (as far as I can see) two pretty stringent design requirements (1. The material you are lifting is glass and 2. the load is high) I would recommend you use GUIDED slides. There are many on the market, but you will need to concentrate on two main specification criteria. Be very careful that the slide system is repeatable (wrt to travel) and that it can take the moment that the glass plate (+ whatever metal you add). From this point of view, it is the guiding that will be of utmost importance. Look at guides that have bearings/cam followers running on machined surfaces. Some companies that Ihave used before and found very good are

Thomson Slides (www.danahermotion.com)[Personally, the best option]
Origa (

http://www.hoerbigeroriga.com)

Good luck.


Kevin Hammond

Mechanical Design Engineer
Derbyshire, UK

 

[GizmoGeek]

Have you concidered connecting lifting the panel with two cables routed to a single side. The ball screw can then be located wherever convinent to pull the panel up. Let gravity (occasionally a constant) pull it back down.