constant torque spring - damping question
constant torque spring - damping question
(OP)
Hi all,
I have a constant torque spring that rotates the drive wheel of a Geneva mechanism. I am facing the following problem. I would like a very slow rotation of the drive wheel whenever the drive wheel is not driving the Geneva wheel of the Geneva mechanism (which is 270 degrees of a rotation). However, when the pin of the drive wheel rotates the Geneva wheel by 90 degrees, I need a lot of torque because there is a load connected to the Geneva wheel. Therefore, I need to use a high torque constant torque spring (7.50 in-lbs.).
I think that a rotational damper can help me slow down the rotation of the drive wheel (it is a timing mechanism, and the rotational velocity should be ~1 rpm), but when getting to the point of rotating the Geneva wheel, I would need the damping to be gone (because there, I need full torque).
Does anyone have a suggestion for a rotary damper that is capable of doing this? Or are there other ideas/designs that can solve the same problem in your opinion?
Thanks in advance!
I have a constant torque spring that rotates the drive wheel of a Geneva mechanism. I am facing the following problem. I would like a very slow rotation of the drive wheel whenever the drive wheel is not driving the Geneva wheel of the Geneva mechanism (which is 270 degrees of a rotation). However, when the pin of the drive wheel rotates the Geneva wheel by 90 degrees, I need a lot of torque because there is a load connected to the Geneva wheel. Therefore, I need to use a high torque constant torque spring (7.50 in-lbs.).
I think that a rotational damper can help me slow down the rotation of the drive wheel (it is a timing mechanism, and the rotational velocity should be ~1 rpm), but when getting to the point of rotating the Geneva wheel, I would need the damping to be gone (because there, I need full torque).
Does anyone have a suggestion for a rotary damper that is capable of doing this? Or are there other ideas/designs that can solve the same problem in your opinion?
Thanks in advance!





RE: constant torque spring - damping question
We need more information. How many revolutions before rewinding the spring? Speed accuracy required? (It won't be very constant using this method)
je suis charlie
RE: constant torque spring - damping question
RE: constant torque spring - damping question
For the 270 degrees where you need a retarding load rub against a braking surface.
RE: constant torque spring - damping question
The benefit of a flywheel is to store energy from the spring when not needed and release it when needed. The damper only consumes energy meaning you need a bigger spring.
Perhaps a clockwork mechanism would be better all round.
je suis charlie
RE: constant torque spring - damping question
je suis charlie
RE: constant torque spring - damping question
Why not skip all the Geneva gear and mechanical damping and use a servo motor to directly drive the load or use a gear box? Then you can get all the precision you need need. You can program any motion profile and change gains for different torque requirements during the motion. Modern motion controllers have the ability to execute cam profiles. Electronic damping is much more efficient than viscous or friction damping.
Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
RE: constant torque spring - damping question
RE: constant torque spring - damping question
The challenge here is to have a small (can't be much larger than 1 inch diameter and 1 inch tall) rotary damper, that costs very little (single digit dollars). I'm exploring some options now, if you have any suggestions, please let me know. I guess using a non-ideal cheap damper is one option and attach a gear box that gives me the speed I need, but that seems to take up quite a lot of space.
About the non-round friction wheel, interesting, but I'm not familiar with it. Do you have some more info on that (web page, youtube movie,..) Thanks!
RE: constant torque spring - damping question
I still have a problem with using friction to control the speed of a disc which has a constant torque (spring) applied. Friction will apply a constant retarding torque regardless of disc speed ie it provides a torque control not a speed control.
A mechanism like this Link includes everything you need - including (probably) an aerodynamic speed limiter.
EDIT In fact it looks like the vanes on the aero speed limiter might act like centrifugal bobweights and increase in profile as speed increases.
je suis charlie