This question may be too general, so apologies in advance if that is the case. I'm looking for a (relatively simple) mechanical system that will cause the driven element to move fast under no-load conditions, until it encounters opposing torque, at which point the system will automatically "gear down" to decrease speed but increase torque. Is there a name for such a system, or generally accepted solutions?
To make this more concrete, think of something like a vise. It's driven by a screw, so normally it trades input speed for mechanical advantage. But what if you wanted the jaws to close quickly (high speed, low torque), then "shift gears" as soon as resistance is encountered, to a low-speed, high-torque arrangement? You don't know in advance how big or small the item you want to clamp is, so you can't shift based on absolute position.
Obviously something like a car's automatic transmission can do this, but I'm looking for a simpler mechanical solution. I've been toying around with ideas about swinging/sliding gear carriers to bring elements into and out of engagement, but if there's a specific term I should be looking for or examples of something like this, I'd appreciate being pointed in the right direction!