high helix ball screw with backdrive powered by a torsion spring? 3

[andrew0wills]

Hello
I would like to know if this is fundamentally possable.I am a industrail designer so could do with some engineering help please.
I have a good product idea that requires a ball screw device powered by a torsion spring to act in a simular way to a low powered gas strut.
the screw is required to have a linner range of 150mm (the spring will provide power for 4-5 revolutions.
over this range the screw will be required to support a load of 8kg (up and on the back drive) the load will be lifted and pushed down by hand the screw will only be required to support the load in the same place when you let go. the lead/ballscrew can be 260mm long and up to 40mm dia.
is this possable?

 

[desertfox]

Hi andrew0wills

Can you give us more details about your screw, I have never seen a conventional torsion spring do more than about 120 degrees during operation and its torque capablity decreases as it unwinds, however a large spring like a constant force spring or spiral spring might be able to do it.
A sketch of your device would help.

desertfox

 

[handleman]

It is possable to back-drive a linner ball screw mechanism. Is this intended to be an industrail type application? Because a backdrivable ball screw or simular linner-to-rotational motion mechanism will be rather expensive. If you want the screw/spring to support the load in the same place when you let go you will need to design a constant-torque torsion spring and your load will have to be constant.

-handleman, CSWP (The new, easy test)

 

[andrew0wills]

Thank you for responding I will do a drawing as soon as I can (might take a few day intill i have time ) the torsion spring can/would be 270mm long and 40mm in dia so I belive would power several turns(I have seen this type used to balance over head garage doors through a cable and cone drive arrangment) alternativly a power spring could be used and give a more constant force. yes as always the componates would have to be inexpensive. although the end product would/could be sold in volume so tooling money would be available(not sure if it would help) I guess my ? is could this 8kg support through the 150mm range assuming constant force be acheive with a set of low cost drive tooled parts. other factors such as backlash and general precsion are not so important in relative terms.
thanks again

 

[desertfox]

hi andrewwills

Yes I have a torsion spring on my garage doors but to my knowledge it doesn't revolve through complete turns.
At this stage, I must say I don't know about the constant force spring whether one could make one for your application or not, I'll need to look into my books,what I will say is that it might not be cheap to make such a spring like anything else it depends on quantity.
I'll look further into when you post your drawing.

desertfox

 

[bvanhiel]

desertfox,

Take a closer look at your garage door. If it's the torsion spring style then it turns through many revolutions.

andrew0wills,

Torsion springs are not constant torque. The more you twist them the more they resist. That means that your load is unlikely to stay where you put it. You might counterbalance this by varying the pitch on your screw, but that would make your sprew a pretty expensive part. If you want to continue down this path, you could look at power springs, but they won't have the same packaging as a torsion spring.

 

[macthenife]

A torsion spring can rotate through many revolutions eg.
the main spring of a mechanical watch.

Try Redditch or Birmingham for springs.

To compensate for "unwinding torsion fall" tapered rollers and fusee chain connected the spring output to the movement
on early watches.
They where called "turnip watches"in Coventry where these
time pieces where made.