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

[autophile]

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:

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