Preventing Jamming: How to Re-Engage a Planet Gear with a Gapped Ring Gear

[Michael_Michael_Motorcycle]

See this illustration of the gear set up I have.

I want to create a design where there is a gap in the teeth of the ring gear. This allows the planet gear to free-spin during part of the ring gear's rotation and then re-engage during the rest of the rotation.

The challenge I'm facing is figuring out how to design this assembly so that when the planet gear re-engages with the ring gear, it does so smoothly, without catching or jamming. Does anyone have suggestions or know of a way to achieve this?

Any advice on the design considerations or mechanisms that could help would be greatly appreciated!

 

[mfgenggear]

Op
Please advise the objective of your design.
Generally this is not common practice.
How ever there might be a different design that achieves you goal.
For example a face clutch teeth that in engages but but disengaged after high rpm. Having space between teeth is normally done for splines.
Tha act as a driver.
From my experience disengaging is done with a clutch to allow gears to engage and dis ingage.

 

[Michael_Michael_Motorcycle]

Thanks for your response.

The spur gear is driving a screwdriver-like component. I want to design the gear mechanism such that the user can only ever rotate the screwdriver a prescribed number of turns, no matter what. After each screwdriver torquing cycle, the torque must be released (hence the gap in the ring gear). The screw driver torqueing cycle must be repeated a few times.

There are certainly other ways to achieve this, but I figured having a gap in the gear teeth as shown might be the simplest, if it's achievable.

 

[Compositepro]

Jamming during engagement occurs when the flats at the tips of the gear teeth hit each other. This can be greatly minimized by grinding levels on the tips. This only works for lightly loaded gears. Of course your design also is only suitable for light loads.

 

[Michael_Michael_Motorcycle]

Oh yeah, that makes sense. Something like this?

This is definitely a low-load application, so that might work!

 

[Compositepro]

Yes.

 

[mfgenggear]

Op
It might but will eventually fail

 

[mfgenggear]

Op

Reverse engineer a common drill clutch

 

[Michael_Michael_Motorcycle]

Correct me if I'm wrong, but a power drill clutch limits torque whereas I am trying to limit number of rotations.

 

[mfgenggear]

Op
Once the max torque is reached it disengaged.
Ok I mis under stood.
I belive then your answer is not mechanical but
Electrical. Maybe be a limiter zwitch after so many rpm it disengaged.
Please advise the rpm. And torque. I may have
Been incorrect in my state prior to this.
A bendix on a starter for automobiles.
Where it ingages with a external ring gear. When energized. When electricity is stoped it dis ingages. The profile teeth are beveled on the profile of the pinion.
Please excuse my typing. I have cheap phone.

 

[mfgenggear]

The rate of rpm to the number of seconds , power can be switched on and off.

 

[3DDave]

We are all missing out on what is supposed to happen. What part is driven, what part drives the screw, what happens if the user doesn't stop, how is the "count" reset?

Any time a gear comes out of engagement there is a period where slight contact can be maintained damaging the gear teeth.

Counting mechanisms typically have a spring return and out-of-plane mechanism that moves to engage and disengage a clutch; the gear teeth don't leave engagement.

 

[Michael_Michael_Motorcycle]

Thanks for the reply, Dave.

"What part is driven" - The planet gear is driven and the ring gear is manually turned by the user.
"What part drives the screw" - the planet gear
"What happens if the user doesn't stop" - The screw driver will exceed its torque rating and break
"how is the "count" reset?" The idea was that the planet gear would build up torque until it comes out of contact with the ring gear, and then the screw driver torsion would be released, "resetting" it to zero torque.

 

[3DDave]

I meant, what happens to the mechanism; apparently the user can continue turning until it re-engages.

Is it 5 turns or too much torque? I don't know of a way to get exactly the right torque at exactly the right number of turns.

However, if there was simply a stop then the user would have to turn the entire device to continue turning the sun gear.

Otherwise what prevents the user from continuing to turn and re-engage on the other side of the gap?

 

[Michael_Michael_Motorcycle]

"I meant, what happens to the mechanism; apparently the user can continue turning until it re-engages."
I see. Yes, the gears will re-engage. It is necessary to perform the torqueing cycle a minimum of three times (this is to ensure the screw the screwdriver is attached to is fully bottomed out in its thread). So the mechanism would allow infinite repetitions of turning the planet gear at the prescribed number of rotations.

"Is it 5 turns or too much torque? I don't know of a way to get exactly the right torque at exactly the right number of turns."
Based on experiment, the planet gear must turn about 2 rotations to deliver the correct amount of torque. As long as the mechanism resets to 0, this cycle can be repeated infinitely without overloading the system.

"Otherwise what prevents the user from continuing to turn and re-engage on the other side of the gap?"
As mentioned above this is actually desirable.

 

[3DDave]

There are instrumented electric screwdrivers for this sort of work.

See

https://www.mountztorque.com/ECT50554-Transducerized-Electric-Screwdriver

for an example. $6k or so for the screwdriver and another $6.2k for the box that operates it.

https://www.mountztorque.com/ECTD-5000U-Controller-110V

These are used where screw installation is critical and provide proof when integrated into a suitable production line management system.

 

[Michael_Michael_Motorcycle]

Ah yes, I supposed I should have provided the important detail that this is for a disposable medical device, so an expensive electronic solution is not viable.

 

[3DDave]

Ahh, the intersection of very precise and very inexpensive. Which rarely happens.

Why does there have to be a reset if torque is enough and the user can just keep turning it?

 

[Michael_Michael_Motorcycle]

The screwdriver is connected to a screw that is threaded into a hole. It is required that the screwdriver rotate exactly two full turns once the screw is fully seated in its threads. However, the screw will not be fully seated at the start of the torqueing process, and it is impossible to determine how deep the screw is in the hole at the time of tightening.

To ensure the required two rotations are applied after the screw is fully seated, the solution is to rotate the screwdriver for two turns repeatedly, resetting the torque between each cycle. This approach guarantees that the necessary two rotations are achieved once the screw is bottomed out in its threads.

I hope this answers your question.

 

[Michael_Michael_Motorcycle]

Of importance is also that the screw driver shaft is inherently torque-limiting as it is slightly flexible. So if the screw is very tight and cannot tighten anymore, rotating the screw driver two turns cannot break the screw driver as that is within the allowable torsion limit. That is why the torqueing process can be repeated an arbitrary number of times.