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From 507 mechanical movements, No. 63, we get the following diagram and description. pawl mechanism

  1. Jumping or intermittent rotary motion, used for meters and revolution-counters. The drop and attached pawl, carried by a spring at the left, are lifted by pins in the disk at the right. Pins escape first from pawl, which drops into next space of the star-wheel. When pin escapes from drop, spring throws down suddenly the drop, the pin on which strikes the pawl, which, by its action on star-wheel, rapidly gives it a portion of a revolution. This is repeated as each pin passes.

I redrew the figure with colors and labels to help the discussion here:

enter image description here

As far as I can tell, the author means this: the wheel $D$ with pins is rotating clockwise, coming into contact with the "drop", $B$ (blue) and the pawl $C$ (red). The drop also has a pin $a$ which can collide with the pawl. It's not clear whether the components $A$ (in green) are the "spring at the left" that he mentions. According to the description, a pin of $D$ escapes the pawl first, the pawl then drops into the next space of the star wheel; then the pin escapes the drop, which (due to the spring) is thrown down, and what I think is the pin $a$ strikes the pawl, which "by its action on star-wheel", causes a rapid rotation.

But how does the pawl work here? If the pawl and star-wheel are coplanar, does that mean the pins of $D$ cause both the star-wheel and the pawl to be deflected? How does a pin catch the pawl anyway? From the drawing it's not clear. Would the pawl allow rotation of the star-wheel in both directions? It seems close to being able to move against the star-wheel when the star-wheel moves counterclockwise (so the pawl goes up, not down). I doubt the drawing is accurate in terms of scale and how things fit, but even being loose with the interpretation I'm having a hard time understanding what he means.


UPDATE 1: I tried to partially animate the mechanism based on the comment from @jsotola, and maybe this will help clarify things. [Old Image, see Update 2] It's hard to animate this by hand because I'm not sure if the pivots are correct, e.g. does the BC assembly pivot on A as shown, and do they rotate relative to each other?


UPDATE 2.

I redrew the animated parts to be more idealized, and moved the driving wheel a bit closer. The result has some obvious issues, and I wonder how the pawl hitting the star wheel is supposed to make it rotate rapidly? Which direction is it expected to move?

enter image description here

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  • $\begingroup$ some observations: D spins clockwise ... E spins counter-clockwise ... C, E and pins on D are coplanar ... B and pins on D are coplanar ... BC assembly pivots around the left tip of A ... pin on D turns E, E pushes on C, which pushes on B ... then pin on D takes over and pushes on C or B ... eventually C clears the pin on D, and drops into the next spot on E ... then B clears the pin on D and B slams down on C $\endgroup$
    – jsotola
    Oct 6, 2022 at 2:20
  • $\begingroup$ @jsotola I tried to partially animate the mechanism based on your comment, but there are a few issues I'm having with when certain parts rotate to each other (for example there are obvious collisions in the animation). Think I'm on the right track or big changes needed? $\endgroup$ Oct 6, 2022 at 13:10
  • $\begingroup$ make D diameter larger or put it closed to E $\endgroup$
    – jsotola
    Oct 6, 2022 at 14:38
  • $\begingroup$ Redrew some things, still not sure what the intention is, should the star wheel always move ccw, and how would the pawl make that happen? $\endgroup$ Oct 6, 2022 at 16:21
  • $\begingroup$ since A is a spring, move the pivot point of the BC assembly closer to center of A ... try increasing diameter of D $\endgroup$
    – jsotola
    Oct 6, 2022 at 17:21

1 Answer 1

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Thanks to @JonathanRSwift I was able to finally understand how this mechanism works. As mentioned in his comment, the pegs do not interface with the star gear, and this, combined with the insights from @jsotola, allowed me to really understand what's going on. I think this animation is accurate for the desired operation, although it's not perfect. Key insights missing from the original description:

  • The pawl is free to rotate down, but the pin attached to the drop prevents it from rotating up
  • The spring is a pivot point for the pawl-drop assembly
  • The star-wheel does not interface with the pegs

I'm not sure I've understood what is meant by the spring yet, but this makes sense now.

enter image description here

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  • $\begingroup$ Yeah, this looks good - how I imagined it behaving anyway, and it matches the description of "intermittent rotary motion" on the star gear $\endgroup$ Oct 7, 2022 at 14:11
  • $\begingroup$ very nice ... +1 $\endgroup$
    – jsotola
    Oct 7, 2022 at 16:02
  • $\begingroup$ The spring is the green lever loading the assembly into contact with the star wheel. $\endgroup$
    – Solar Mike
    Oct 7, 2022 at 17:48

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