Rigid lift mechanism

T Chap

I need to lift something 10” travel. For a simple illustration think of a coffee table that becomes a dining room table. The base can be up to 20”x20” and 16” tall. The weight is a few hundred TBD. I was thinking to use my typical Prop based main boards and brushless motors that I apply to various motion needs. In this case it’s a challenge.

I’ve built CNCs with linear rails and carriages. When carriages are spread out and you can have 2 per slide you can get a very rigid system. In this case I can fit 2 carriages back to back barely, not spread out at all With 4 rails vertically oriented in the base, at full height I’m not confident this will be super rigid.

I have used ball screws and nuts. In this case I have some ideas for 4- 3/4” ball screws in each corner doing the lifting. But again due to only having less than 16” height in a base to mount it all, I question if it will be stable. Meaning I don’t want to be able to push on this thing and have it move back and forth 1/4”.

I looked at various linear actuators and even if using 4, one in each corner I question the stability when fully extended. Also if using 4 separate linear motors will they be fairly synced.

What other options exists for a very robust lift that would not allow any bending or movement if pushed on? Meaning a tank.

AwesomeCronk

Might try a scissor lift.

Yanomani

Except the roller wheels, are you talking about something like this one?

papacad.com/wp-content/uploads/2017/07/Screw-scissor-table-CAD-project-2.jpg

My main concerns are about each pivoting joint being able to introduce some degrees of freedom, due to the small (and necessary) mounting gaps, which can admit unacceptable oscillations of the whole assembly.

T Chap

Those are interesting devices. I'm concerned that with a small space it can only be so rigid. Still looking at those. I've been working on something similar, a parallelagram set of hinged arms. This is likely the idea.

Phil Pilgrim (PhiPi)

You can add side-to-side rigidity by enclosing your ball screws within two sliding (i.e. telescoping) cylinders. This also has the advantage of hiding the mechanism.

-Phil

Yanomani

You are showing only one of the side views of the mechanism you are proposing.

From it, can I understand that you agree to tolerate the lateral movement that would happen, during the up/down lifting process?

And about hinges, are you thinking in using some kind of zig-zag, double pivot-axes piano hinges, up to the limit of your 20" space?

T Chap

The hinge arms I drew would be 1” thick aluminum arms with bearings. You see one set in section/side view. I’d likely have 4 sets spread over 30”. I can stabilize these sets of arms with plates attached to them.

Yanomani

Tapered bearings could be adjusted by means of suruounding spacer washers and setting nuts, provided you use threaded shaft ends. This would help keeping the unwanted gaps as small as possible.

T Chap

Here is the ball screw concept. The idea is a motor with timing belt will be added to drive the ball screws. There is a horizontal plate attached to all 4 ball nut flanges. There are 2 vertical side wall plates from that plate to the table. The top of the ball screws are secured via bearings to a side wall of a box. I think this might be pretty solid. I will work up the linear slide/rail concept as well.

erco

Firgelli's linear actuators aren't cheap but readily available and they come in a wide variety of sizes, throws and weight ratings.

https://www.firgelliauto.com/collections/linear-actuators

https://www.firgelliauto.com/collections/linear-actuators/products/feedback-rod-actuator

As for synchronizing, some of these have a built-in feedback pot, and IIRC some others operate like a servo, they travel to a specified position and stop.

Yanomani

You'll find many helpful tips related to ball and nut screws by googleing under the following search terms:

"linearmotiontips" AND "ball screw"

Hope they can help a bit

Henrique

Tubular

There are stable telescoping box kits ready to go, eg SKF

https://skfmotiontechnologies.com/en/se/products/telescopic-pillars/tlt

frank freedman

This a view of the base of a rad room table. There are four columns with a fairly heavy base plate and bearing supports at four corners. The lift mechanism is a shaft and gear driven by a worm gear motor. I think this table is rated for 400+ pounds. Position is monitored by a pot and gear assembly.

frank freedman

Yet another view. The base is fairly heavy and meant to be bolted to the floor. But it is rock steady,

kwinn

A rectangular (or round) tube sliding inside another tube with the ball screws mounted in the inside tube corners would make for a rigid structure. Using a cogged belt and single motor to drive all four ball screws would satisfy the need for synchronization and simplify the mechanics.

Phil Pilgrim (PhiPi)

kwinn wrote:

A rectangular (or round) tube sliding inside another tube with the ball screws mounted in the inside tube corners would make for a rigid structure.

You're right. That's what I said above.

-Phil

Mickster

IF shop_air_is_available AND table_load_is_constant THEN

Big a$$ pneumatic cylinder(s)?

Have pressure regulated so that the air pressure acts as a counter-balance and use a small motor to drive up/down.

Just to offer something different