1. Field of the Invention
The present invention relates to medical instruments and, more particularly, to an endoscope having flexible tubes within a passive deflection section.
2. Prior Art
Endoscopes with passive and active deflection sections are known in the art. U.S. Pat. No. 4,580,551 shows an endoscope with an elongated flexible plastic tube comprising a continuous sequence of connected vertebra-like elements. U.S. Pat. No. 3,162,214 discloses a thin walled tube of elastic material internally supported throughout its length by a series of tubular rigid rings. In one prior art embodiment, control wires from a deflection control to a distal tip of the active deflection are provided with a wire sheath along the passive deflection section. The wire sheath comprises a coiled wire to form a flexible tube around each control wire. A problem exists with these coil wire sheaths in that the coil shape can expand during compression. This can result in a loss of deflection at the active deflection section of the endoscope. In another prior art embodiment, stainless steel tubes are used as the sheaths for the control wires. However, these are only used in applications which have a large bend radius. These tubes can kink very easily, have no resilience, and can fatigue and permanently deform thereby shortening the working life of the endoscope.