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Intermittent linear motion from rotary motion, very low duty cycle?

Intermittent linear motion from rotary motion, very low duty cycle?

Intermittent linear motion from rotary motion, very low duty cycle?

(OP)
Hi all,

Before I start, this isn't for a production system, nor for a system intended for production, but it is a bespoke system. So if I have to machine a weird-looking part, that wouldn't be an obstacle.

Here is the application: I have a series of 1/8" horizontal shafts, stacked vertically one on top of another, separated center-to-center by 1/2". Starting with the bottom shaft, call it shaft 1, each shaft needs to be pushed in along its axis by 5/8". The shafts do not necessarily have a return mechanism, so once pushed in, they could remain pushed in unless pulled, or pushed from the opposite end.

The timing of the shaft movements is as follows:

CODE

Start: t=0
Push shaft 1 start: t=0
Push shaft 1 end: t=0+dt
Wait: t=0+dt to T
Push shaft 2 start: t=T
Push shaft 2 end: t=T+dt
Wait: t=T+dt to 2T
.
.
.
Push shaft n start: t=(n-1)T
Push shaft n end: t=(n-1)T+dt
Wait: t=(n-1)T+dt to nT

Where n can be as much as 10, dt is a period of time less than T/4, and T is some period left unspecified (but preferably on the order of 1/2 second).

So at the end of the time period nT, all the shafts will be pushed in.

Finally, the reverse operation has to be done, so shaft n is pulled (or pushed from the opposite end), then shaft n-1, and so on, with the same essential timing.

At first I had considered one cam per shaft, with all the cams being attached to a single vertical shaft. The problem is that if dt is, say, T/4, and n=10, then we would need a cam able to push a shaft 5/8" within a cam angle of 9 degrees (360 for 10 shafts = 36 degrees per shaft, one quarter of that is 9 degrees). This is what I meant by very low duty cycle: the period of activity for each shaft is 1/40 of a cycle.

If I wanted the angle of the cam surface relative to the shaft to be no greater than 45 degrees (which I guess is a reasonable assumption: I'm an electrical, not a mechanical), then the cam would need a radius of about 4 inches.

So to move shafts sequentially by 5/8", I would need a mechanism 8" across.

Is there a better way? I would ideally like to limit whatever mechanism it is to under 4" across. A secondary concern is limiting the number of moving parts per shaft.

Any ideas? Thanks for any insights or hints you can give. I may have made assumptions that are not true, because I'm not mechanical, so please feel free to point those out and correct me.

--Rob

 

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