Motion question

[PRW]

I have one shaft inside a tube. The tube is mounted in bearings.

I need a linkage that when moved by a linear actuator, will turn the inside shaft 25°. Then once the inside shaft has turned 25°, the outside shaft will also turn in conjunction until they have both turned another 20° then stop.

When the linear actuator retracts, both shafts must turn 45° in the opposite direction, then the outside shaft will stop and the inside shaft will continue turning another 25°.

Has anyone seen this type of setup, or can you point me in the right direction?

Thanks,

Paul

 

[Sparweb]

If I read your definition of the problem right, the two shafts end the cycle 20 degrees back from the point where they both started. But at the same position relative to each other.

STF

 

[PRW]

I seem to understand what you said, but let me further the definition of my problem:

Let's say there were arms hanging down from both the shaft and the tube. When in the starting position, the arm on the shaft would be 25° to the right of the arm on the tube.

At the end of the actuator travel, the arms would be in line with each other. I hope that makes sense.

Paul

 

[PRW]

Here is an image that might help.
print screen windows 7

 

[GregLocock]

Looks to me like a sloppy spring loaded joint would do it. Now you can add the rest of your requirements.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Jboggs]

Sounds to me like you need a barrel type cam to convert consistent linear motion into varying rotary motion. The tube and the shaft both rotate about the same axis, right? And the linear actuator operates on that same axis? Mount a barrel type cam on the linear actuator. For reference check out "

http://www.eesp.co/html/Downloads/PDF/A2-5.pdf".

The difference here is that your cam followers would be external to the cam and there would be two cam paths machined into the barrel.

 

[PRW]

Hi Jboogs,

Yes the shaft and tube are concentric, but the actuator is horizontal in relation to the picture and to the right of the blue arm.

 

[Jboggs]

Good luck. I don't know any way to get two independent rotary motions from one linear motion without using some kind of cam and follower arrangement.

 

[Dougt115]

If the Red arm in your drawing was spring loaded in a counter clockwise direction and had a slot in it of 25 degrees. Then the blue are would have a pin to match the slot. The red arm would not be connected to the actuator but does rotate about the actuator axis.

The blue arm would start as you have draw at an angle of 25 degrees from the red arm. When the blue arm is inline with the red the pin would reach the end of the slot and engage the red arm. Both arms would then track together, stop together and reverse directions. When the two arms become straight up and down the spring will stop the red arm and the blue arm will continue.


So basically a slot and a counter spring could work depending on the particulars of you application.

 

[PRW]

Doug,

That sound like an easy solution. I'll mock one up and give it a try.

THANKS for your help!

Paul

 

[PRW]

Doug,

I answered too quickly. If you look at the image and the order in which the levers must move, you will see that the blue lever first moves 25°( 1st pic), once together, (2nd pic). Next they both move together 45° (3rd pic). Next they both move together again in the opposite direction 45°. Finally, the blue lever continues moving another 25°.

Using the slot you mentioned together with a stop for the red part for the fourth step, so it can't move too far will be the answer.

Do you agree?

Paul

 

[Dougt115]

It sounds like it will work.

Every design has its own unique challenges. I would expect you will have to tailor the concept to meet your application.

Good luck, I would be interested in hearing how it works out.