There a few neat mechanisms that allows only one way motion without the use of a pawl or ratchet. This is one of them:
What I'm looking for is a mechanism that can't be undone once it has gone from one position to another (without taking it apart; i.e., removing a pin) after it is rotated. This could be useful in certain applications, but my search turns up nothing like I remember.
I can think there might be a four or five-bar mechanism that has a critical point where the mechanism can't undone, but can't remember (or where to search for it)!
I do remember seeing one many years ago at one of my first engineering jobs, but can't recall the details other than "that was neat!" The mechanism I saw had I believe 3 to 4 moving parts.
There are some other mechanisms that don't use springs or latches; a search for this turned up something also nifty, but not quite what I was looking for:
Any thoughts on this?
No magnets, no springs; this was a strictly mechanical thing (nothing hidden; I could take it apart, and the mechanical lock was fascinating). The closest analogy I can think of is to those Sokoban games (and perhaps this is a way to think about it) where if you perform a certain order of operations, you lock up the puzzle.
This is one solution I came up with this morning, but I'm wondering if there is a list of them, a search term I'm missing, or other examples.
In this example, a plunger enters from the left; I'm not too sure of the geometry, but I think this is an example of how it could work. When the plunger brings the two locking elements behind it, it can't go back, because of a stop at the end of the plunger, prevents the linkage from reversing.
Even cooler - I believe the mechanism I saw had no linkages - just a series of Sokoban-like moves where the system went from one state to another, but couldn't be reversed without taking a part out of the 2D plane it was in.