How does the articulation system on a fiberscope work?

Question

A fiberscope is the snakelike, fiber-optic camera that doctors use during an endoscopy. The tips of these scopes can articulate: you can control the rate at which they bend in one or more directions.

For instance, the tip on one end of this fiberscope can bend in various directions and at various angles. You control this via the controller on the other end.

How is this done? I'm assuming it involves a sort of spring/flexible tube and some sort of cable system that controls the rate at which the spring/tube bends, but I can't imagine how this would work.

Edit: This image from this article refers to a (or possibly four) "tip bending control wire(s)".

(here's another one)

I guess the question is: what do these wires do? Do they bend the tip by contracting/expanding? Is there some sort of mechanical device in the "bendy" part that is controlled by these wires?

Answer 1

The principal is fairly simple.

As in the diagram there are 4 wires or cables around the circumference of the sleeve. They are constrained so that they can slide freely along its length but are otherwise fixed in the 12, 3, 6 and 9 o'clock positions. The ends of the wire are attached to the head end but free at the control end.

To bend the wire in one direction you pull one wire, this effectively shortens the length of wire inside the sleeve and so tends to want to form the inside of a radius.

You can also think about it by a reverse analogy. If you bend a flexible tube the inside of the bend gets shorter and the outside gets longer here you are just pulling on one side to create the bend. You can create abend in any direction by pulling adjacent wires different amounts.

You the 'joint' is created by having most of the sleeve incompressible along it's length (eg like a tightly coiled spring) except for where you want the joint (eg by opening up the coils of the spring).

This is broadly the way that the flexing of human fingers work. Most of the hand muscles are actually in the forearm and are connected to the fingers by long tendons.