There are sewing machines that work in other ways (in fact I own one) but in my experience this is the most common mechanism. Very nice animation!
The machines used for stitching very thick stuff, like 1/4 leather for saddles, typically also have a separate punch and may have a punch clearing pin.
Thought. A roller that would apply some mild adhesive to the bottom thread. (Or maybe use a hot-melt-glue impregnated bottom thread.)
That way the thread is fixed to the fabric, and if either thread gets severed over time by wear and tear, the adhesive holds it in place, preventing growth of joint failure.
Hot-melt glue would tend to do bad things when washed at high heat or ironed. However, in this case it would be of minimal utility anyway as the lockstitch which is illustrated does not unravel easily, and if one happens to find a broken thread later on then a tiny drop of super-glue may applied then without the deleterious side-effects.
It unravels relatively easily. 
Hot-melt adhesives are used for those iron-on patches, nonwoven reinforcements and other such things, so the washing and ironing is compatible. Small enough amount has to be used to not smear around, though. The thought possibly needs some refining, and maybe some experimentation…
The amount of force needed to pull out the stitches increases as the trailing ends get longer. With waxed natural-fiber thread binding natural materials this adds up quickly, but with slippery synthetics doesn’t help much at all. Mechanisms exist to puncture previous stitches or knot the threads instead of just chain-locking them, but they are either relatively finicky and failure-prone or mostly manual.
If you are hand-stitching leather that will be subject to serious stress, it’s not a bad idea to knot the threads every three or four stitches. Knotting every stitch is not worth the time involved. Be aware that if you do this too well you may cause the leather to rip instead of the stitching, which necessitates a more difficult repair. Anticipating failure modes is always good engineering! I generally use a stitching awl and knot strategically as suitable for the specific item’s intended purpose.
My sewing machine doesn’t turn the bobbin hook continuously. Instead, it turns first one way, then the other-- you might say it oscillates. I must say, this particular diagram is head and shoulders above something like this
I can see it now!
“Just what the hell do you think you’re doing with MY sewing machine!”
What about to put some adhesive in between the layers of leather? Kind of like riveting AND adhesive are used in joining plates of aircraft skin?
That would be a chain stitch, rather notorious for coming apart at the seams…
This is done sometimes - I have a pair of boots which are both sewn and glued at the seams. (Though in this case I believe it is to aid in water-proofing.)
There is such a thing, you can purchase fusible thread. I’ve never done it, but I believe most sewists double thread it through the needle then fuse. That said, my general experience with fusibles is to avoid them at all costs. I moved to sew-in interfacing (the reinforcement you mention) and never looked back.
Glue definitely has a place in my kit though! When sewing something that will be washed, I use plain old glue sticks liberally.
The difficulty with a machine that glues as it sews is that sewing generally involves removing a lot of stitches. I would say on an average garment I remove 1/3 of the stitches I sew, and on a gown or a suit I would remove as many or more than I leave in.
Chain stitching is still used in machines designed for specific applications-- blind hems, buttonholes, etc… I was referring to the gif itself, which lacks elegance.
This is really cool, I’d always wondered about just how they worked, but not enough to look into it.
Glue on any seam that’s going to touch my skin can die in a fire.
When I was a kid, I used to love opening sacks of stuff (like dog food, charcoal, rice, etc.) because they were closed with a chain stitch. You just had to find the end of the thread and give a pull, and the whole seam would unravel. But while there are some brands that still stitch their bags closed, it seems like most glue them shut these days.
Double-needle saddle stitch machine. The threads pass through each other repeatedly, as the needles puncture each other’s stitches. Pulling one thread increases its grip on the thread that passes through it, providing a truly locking stitch rather than a chained stitch.
An oscillating boat shuttle similar to the one in my sewing machine (mine’s actually double-ended like a canoe):
@Shaddack, it’s common to glue and then stitch, or to use basting tape. Basting tape is double-sided tape that comes in two varieties - there’s one kind that dissolves in hot water, and another kind that’s permanent. Because woven textiles flex very differently depending on how they are cut, you often don’t want a welded or glued junction because it would change the way the finished piece would behave - for example, if you wear pants made of thick square-woven cloth you’ll want a bias-cut crotch gusset let into them so that you can do heavy physical work or kick above your shoulder without crushing your own testicles, and that gusset will need to be held by stitches, not glue, in order to work properly.
So cool, despite my mother being a pretty prolific sewer of things and she was a costumer for a while too I never understood how the machine worked.
I wish I had learned to sew when she tried to teach me, but the machine terrified me and I never got the timing down for how fast to move the fabric and how hard I worked the pedal.
Not to mention the thought of sewing right through your fingernail.
I take it that you don’t have any wetsuits in your wardrobe?
