Re: Clutch Mechanism

On 19 May, 01:21, "Dave" <dave.garn...@xxxxxxxxxxxxxxxx> wrote:
Brad Smallridge wrote:
Hi All,

I'm looking for a expertise in distributed power,
that is, a multiple cable pulling system working
off of one main motor or engine, that works with
clutches or other mechanical means.

Any ideas? People?

Brad Smallridge
AiVision

IBM typewriters (and probably others) used to use spring clutches.

Take a continuously revolving shaft, wrap a spring round the shaft. Connect
one end to something to be driven.

Now, if you move the other end of the spring in the opposite direction, the
spring tightens on the drive shaft and is driven round. Kind of difficult to
describe, but a very simple idea.

This way, a small solenoid can control quite a lot of power. These gadgets
are also pretty quick, inertia is low.

Drive is only one direction of course, but there are plenty of solutions to
that ...

YMMV

Dave

I never new anything like that was used in typewriters ! Sounds like
a very interesting mechanism.

I have had a similar idea in mind for years based on the principle of
the capstan - the rotating, indented shafts that are used on ships to
hall them in to a harbor wall. Anyway the capstan is a device which
amplifies the force pulling on a rope. It means that you could use a
bunch of small servo or stepper motors to control much larger pulling
forces. The key to doing it successfully would probably be accurate
measurement of the large forces and incorporation of these
measurements in a feedback control loop. My guess is the big
disadvantage would be wear and tear on the cables involved. It is
also difficult to effect correct tensioning of the low force side. If
the tension is not well controlled then 'sticking' can make the system
unstable and difficult to control. I have always thought that
materials science should come to the rescue and give us good materials
for the capstans and cables that would reduce these problems. Maybe by
using springs IBM has done just that.

The advantages of a multiple capstan system are -
-one big motor can make all of its force available on any single
cable .
-the motor's power can be shared between multiple cables
simultaneously.
-much lighter than using lots of big motors if all cables are not in
operation simultaneously.
-output is linear instead of rotary, very handy in robotics.

There is also the double-capstan which can pull in both directions.

If your Google-fu is strong you can find the maths of capstans and a
few control projects on the web.

.

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