Mechanism with a linear actuator

[Neekman99]

Designing a machine. For it to work properly there would need to be a mechanism that connects the linear actuator to the stand that would allow for the actuator to move horizontally relatively freely with applied forces at the bottom, when there is simultaneously a downward applied force by the actuator of 300N and an external upward applied force of 350N. Is there a mechanism that makes this possible? or would the actuator always be subject to large frictional forces that make it hard to move horizontally? Thanks

 

[berkeman]

Can you upload a sketch? It's hard to picture what you are describing. Use the Upload button in the lower right of the Edit window to attach a PDF or JPEG file to a post here at the PF. Thanks.

 

[Neekman99]

Can you upload a sketch? It's hard to picture what you are describing. Use the Upload button in the lower right of the Edit window to attach a PDF or JPEG file to a post here at the PF. Thanks.

Yes sorry, was attempting to figure out how to upload the image after I posted it :D Have added it now.

 

[berkeman]

Great, thanks. That helps a lot.

So just a hinge or ball joint won't work for attaching the actuator to the stand? Do you need to assist the angular motion of the actuator at the hinge?

 

[Neekman99]

Great, thanks. That helps a lot.

So just a hinge or ball joint won't work for attaching the actuator to the stand? Do you need to assist the angular motion of the actuator at the hinge?

The actuator needs to remain parallel to the right side of the stand, so would use something like a standard prismatic joint but with the net upward force the friction would mean there is a large resistance to the horizontal motion. Do you know of any way to reduce this resistance for this joint or a different mechanism that would be able to do this? Thanks a lot for the help mate.

 

[berkeman]

So you want the vertical linear actuator to be able to resist horizontal forces down at the bottom of it, without having binding issues, right? To make it stronger horizontally, you could use an I-beam shape for the vertical part of the actuator to make it stronger in the horizontal direction. alternately, extend the actuator horizontally into a plate or structure, and use two linear actuators along the left and right edges of the plate/structure to drive it up and down. Can the actuator mechanism extend above the horizontal stand piece at the top as the actuator retracts?

 

[Neekman99]

So you want the vertical linear actuator to be able to resist horizontal forces down at the bottom of it, without having binding issues, right?

In the ideal model of it, the actuator would move left and right under the horizontal forces acting at the bottom of it without any horizontal resistance (I want it to move horizontally as it would if there was no stand i.e. was floating in mid-air). As this isn't possible, I'm trying to get as close to this model as I can

alternately, extend the actuator horizontally into a plate or structure, and use two linear actuators along the left and right edges of the plate/structure to drive it up and down.

Can't quite wrap my head around this idea

Can the actuator mechanism extend above the horizontal stand piece at the top as the actuator retracts?

In the original design the rod of the actuator (the lower part of it) just retracts into the housing (the upper segment of it). Would it be beneficial if it could extend above the stand?

 

[berkeman]

In the ideal model of it, the actuator would move left and right under the horizontal forces acting at the bottom of it without any horizontal resistance (I want it to move horizontally as it would if there was no stand i.e. was floating in mid-air).

I think I'm starting to understand. You want the horizontal forces at the bottom point to move the vertical linear actuator left and right with as little resistance and deformation as possible, right?

I think one way to do this would be to use two coordinated linear actuators that form a "V" shape, joining at the bottom and with their top ends separate by some distance. Use hinges at their tops to allow their angles to vary from maximum when retracted to minimum when fully extended. The top part of the "V" would be a crossbar that is on a horizontal roller track attached to the top horizontal part of your stand to allow the whole thing to move left and right due to the horizontal forces applied at the bottom joining joint of the "V".

There are other ways to do this, but you need to introduce some triangles or horizontal structure to give you strength horizontally to keep the actuator structure strong under the influence of the horizontal forces and torques, IMO. Hope that helps.

 

[jrmichler]

Linear actuators are not designed to handle any sideways forces. Typical linear actuators have loose tolerances in the sideways direction. They wobble. If you want to move a linear actuator sideways, the actuator should be inside some sort of telescoping structure that is designed to handle sideways forces. The linear actuator assembly is then supported at the moving end by a linear bearing (search the term).

The metal stamping industry solves a similar problem by using die sets. The stamping press is designed for large forces in one direction, but has loose tolerances in the perpendicular direction. They install a die set between the stamping press and the stamping die to transmit the press force, while holding tight tolerances in the perpendicular direction. Here is a randomly chosen die set catalog: https://www.supdie.com/resources/master-catalog/

 

[Baluncore]

What will it be used for, is it a press?
Normally in a press, a linear actuator or hydraulic jack will be held so it must remain vertical.
That is critically important as any sideways deflection will tend to accelerate and launch the work piece or job sideways.

You could have a bed made from a plate resting on bearing balls that will allow the work piece to move sideways and so remain under the press. There are x-y rail systems that could be used to allow horizontal freedom.

I would use at least two columns / legs, not just one, so eccentric leg extension does not result in misalignment of the actuator.

You would find better stability if you mounted the linear actuator by the bottom of it's outer tube rather than at the highest point. That would also reduce the the required support column length and flexibility.

 

[Tom.G]

The top of the actuator could ride on a trolley. Think of the wheel trucks on railroad cars. That approach is used in Gantry Cranes and Boom Cranes.
A Google search finds over 7 000 000 entries: https://www.google.com/search?q=gantry+crane
There is also a slide show at: http://www100.abb.com/Drives_DE/dcs...1/data/downloads/crane drive basics r0101.pdf

Since you also have an upward force, you would need additional wheels below the boom (horizontal section of your sketch).

Cheers,
Tom

 

[Neekman99]

I think one way to do this would be to use two coordinated linear actuators that form a "V" shape, joining at the bottom and with their top ends separate by some distance. Use hinges at their tops to allow their angles to vary from maximum when retracted to minimum when fully extended. The top part of the "V" would be a crossbar that is on a horizontal roller track attached to the top horizontal part of your stand to allow the whole thing to move left and right due to the horizontal forces applied at the bottom joining joint of the "V"

Ok thank you, I will definitely be testing this design!

the actuator should be inside some sort of telescoping structure that is designed to handle sideways force

Interesting, could I ask for more info on how this would work? Would it work as actuators inside other actuators? If so, could these actuators be designed to provide different forces? (with the smaller actuators providing smaller increments for accuracy and the larger one producing a bigger force so that larger forces can be achieved)

You could have a bed made from a plate resting on bearing balls that will allow the work piece to move sideways and so remain under the press. There are x-y rail systems that could be used to allow horizontal freedom.

Researched this, very helpful, thanks!

You would find better stability if you mounted the linear actuator by the bottom of it's outer tube rather than at the highest point. That would also reduce the the required support column length and flexibility.

Very true :D

There are x-y rail systems that could be used to allow horizontal freedo

The top of the actuator could ride on a trolley. Think of the wheel trucks on railroad cars. That approach is used in Gantry Cranes and Boom Cranes.
A Google search finds over 7 000 000 entries: https://www.google.com/search?q=gantry+crane
There is also a slide show at: http://www100.abb.com/Drives_DE/dcs...1/data/downloads/crane drive basics r0101.pdf

Since you also have an upward force, you would need additional wheels below the boom (horizontal section of your sketch).

Thanks for the advice mate!