Someone should publish a running list of lock types, with little sketches or photos. This would be an open database that anyone could later add to. It would not make that person money or much prestige but it would be incredibly useful for all of us in origami, for all sorts of reasons.
I am not a modularist, but merely gaze on the field from a respectful distance. Yet even for us single-sheeters locks are important, and it is clear that modulars is where the subject is explored most thoroughly and directly. It has to be.
I work on faces and much of the work tries to keep the sheet flat or nearly so, but sooner or later one wants to bend the sheet around and then the question is, how do you join the edges in back.
Three-dimensional animal origami, which is all the rage nowadays, and rightly so, obviously also faces the same problem. Invariably there is a seam line, under or in back of the model. This is a consequence, almost mathematical, of the fact that the paper starts out with edges; and when you work flat, edges, though probably different ones, stay present every step of the way. You come to the end and still have them. If you started out with a tube you might have less of this problem, and with a sphere possibly not at all (nature’s clearest origami is indeed spherical--there is a blastula: it gastrulates), though even with these the problem of locking flaps exists. Also, such rounded forms are harder to work with: we actually need those edges of the flat sheet pretty badly.
One has to admit, the sort of thinking that comes to the end of a process and asks ‘now what’, finding itself stuck with a problem it should have known all along it would encounter, is pretty defective. Though that’s the state a lot of us are still mired in. Komatsu in his owl, Diaz in his polyhedral/volume studies, and Joseph Wu in some of his 3D work have made efforts to carry us a little beyond this primitive condition.
In any case locks are interesting, I want to say “satisfying”, all by themselves, quite apart from any pragmatic function they may serve in hiding ugly seam lines and as a replacement for glue. There’s a distinct pleasure when a flap fits into a slot and ties a form nicely together; when all the messy sliding about gets brought under single control; when all degrees of freedom suddenly disappear. --And it is origami’s job to study what is satisfying.
So how about it, Miyuki? It would take you all of five minutes. (OK, five hours.)