Creo mecanism ratchet

[ArnaudGOELZER]

Hello,

I'd like to analyse a geared wheel stoped by a ratchet using creo mecanism.

Ratchet and geared wheel

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Which contact should be used to simulate the ratchet on geared wheel ?
Please see my video attached
the video uses a cam follower to illustrate the case but I would like the ratchet to lock the gear wheel clockwise and the gear wheel to be able to rotate counter-clockwise.

is it possible to remove the ratchet part and simply prevent the gear wheel from rotating in one direction?

I'am using Creo 7.0.5.0

Regards

Arnaud

[SweetPeasHub]

I think a cam could work, but by the animation it appears that your mechanism relative tolerance needs to be much tighter to prevent jumping teeth. You will also want to include liftoff and friction for the Cam and have a reasonable coefficient of restitution. The mechanism tolerance is in File-Model Properties-Mechanism-relative tolerance. I would try 1E-6 rather than default 0.001. If you add lift-off of course you would need a spring on the pawl to keep it in contact with the gear (or turn on gravity to hold it in place but that is a more difficult situation)

There should also be a way to create a torque motor that responds to a negative torque on the gear to hold it in place from backward movement. You might want to look up in the community "mechanism PID control" This of course is only holding it in theory based on some servo motor system, To me it seems better to have an actual physical way like the cam model and pawl system you have already.

Also, in my opinion the CAM contact is the most robust contact method in Creo so I use it unless I absolutely have to use something else.

[ChrisKaswer]

Arnaud,

The best way to handle your situation is with cams...BUT, you will need to take care in the way you apply them for your clockwise rotation. You will need to create separate cam pairs for both sides of your teeth. This is because a cam pair can only have one contact point. One approach I can think of is to split your small radiused pawl tip into 2 sections. One will be the radius portion that contacts the "arresting" side of the tooth, and the other will contact the "free-spinning" side of each tooth. This will allow you to define the toothed gear contact side using the same single curve or set of surfaces (as long as they are continuous segments tangent to each other) for both cam-pairs. As "SPH" mentions, you'll need to define "lift-off" cams as well. As long as either cam cannot have two points in contact at the same time, you'll be all set.

Hope this helps!

[SweetPeasHub]

Good catch @ChrisKaswer about two points of contact! I would probably have just made the radius at the bottom/root of the tooth slightly larger than the pawl tip radius. @ArnaudGOELZER Please let us know how this goes as I think many times people might need to do something similar.

[ChrisKaswer]

@SweetPeasHub - good call on the radius too...another way to handle it if you can make the mating geometry limit itself to 1-point contact. This way you need to only make 1 cam-pair!