Wrap Spring Clutch Design? 1

[JMOwen]

Can anyone help me to determine the relationship between the slip torque of a wrap spring clutch and the pre assembly interfence of the spring internal diamter and the hub.

I'm trying to determine the sensitivity of the clutch slip torgue to manufacturing tolerances.

Cheers

Justin

 

[tbuelna]

JMOwen,

I used one as a torque limiter in a spacecraft mechanical actuator. I selected this type because it gave very consistent slip characteristics over a very wide temperature range. The interference fit limits were determined thru a development test. We controlled the fit to extremely close tolerance by honing the spring ID to match the pin at assembly. Fortunately, we were only building half a dozen units, so this approach was practical for us.

As for a more analytical method, I can only recommend taking a look at the formulas for helical compression springs. Helical compression spring coil diameters grow in a similar fashion under load.

Good luck,
Terry

 

[strokersix]

If you are looking for torque in the release direction I would try to use curved beam bending to determine interface pressure and assume a friction coefficient. I have not done this so it's just a guess as to what approach to take.

A more direct approach is to test it. Create samples with various interference and test.

If you are referring to slip in the driving direction, wrap spring clutches usually don't. They typically drive until the spring pulls apart or the internal member crushes.

 

[israelkk]

Mechanical analysis and design Arthur H. Burr 1982 page 100. Has all the data and formulations to design and calculate Wrap Spring Clutch. There is a newer 1995 version but the 1982 is better to my best judgement.

 

[JMOwen]

Thanks all,

Isrealkk, could you let me have the formula? The book's out of print and hard to find here in the UK, it's available from amazon etc but on a 2-4 week lead which is too late...

The clutch design is simply two bars pushed into the ends of helical spring. Torque requirement in 0.1 - 0.2Nm CW and locked CCW. Max diameter on the mechanism is 8mm, length ~ 30mm

Justin

 

[JMOwen]

Thanks Guys

Managed to source a paper from The Institute of Spring Technology, Sheffield UK with the calculations I need.

Justin

 

[Trukker]

JMOwen,

I am also looking for information on wrap spring clutch design. In my case the the spring is located on the inside of the driving and driven rings and engages in the unwinding mode. My need to to achieve consistency in time to engagement as the motion to be transmitted is very small and variations can nullify the motion.

Could ypu let me know which is the paper you sourced from the Institute of Spring Technology. This will cut down my time to identify what I need.

Thank you

JohnMLouis

 

[JMOwen]

John,

The information was difficult to find but there are two sources that I found useful.

The info from IST was the most relevent for my application.

It is a paper imaginatively titled 'The Spring Clutch' by C.F Wiebusch, New York, from the Journal of Applied Mechanics, September 1939. I have the paper in .pdf form.

Another source which is more to your application maybe:

http://www.ses.swin.edu.au/homes/browne/probabilisticdesign/coursenotes/notespdf/Simulation.pdf

Hope this helps!

 

[andyross33]

JMOwen,
I too am looking for info on designing wrap spring clutches. I haven't been able to source 'The Spring Clutch' paper from IST or the Journal of Applied Mechanics (I could only get papers back to 2000). Can you tell me how you went about getting it?
Thanks!

 

[andyross33]

Requested the 'Spring Clutch' article directly from IST yesterday and received it by email this morning (great, fast response!) They also offered consultant services for anyone needing spring design. I'm not affiliated with them, but from their efforts to get back to me as quickly as they did, I wouldn't hesitate to consider them as a consultant.