Well I spent the last two summers as an intern at SpaceX working on several things, but one was that mechanism that the Canadian arm attaches to. I can't talk much about the specifics, but one of things I did was program the micro-controllers that interface with the motors that open the hatch door (and some other stuff) that contains the hook for the robotic arm to grab. I wish I could write more and even make a blog post, but I'm simply not allowed to do so.