Endoscope steering section

A steering section for an endoscope or borescope employs a plurality of steering cables that pass through peripheral bores of axially aligned flat washers. Spacer beads are strung on the cables between the washers to define hinge points for the bending of the steering section. The spacer beads are tapered beads having a relatively wide base and relatively small, flat nose surface. A through-passage in the bead has a relatively narrow nose portion with a small clearance with respect to the steering cable, and a tapered or countersunk portion that expands basewards and prevents the spacer bead from binding the cable.

BACKGROUND OF THE INVENTION 
This invention relates to controllably bendable tube assemblies, and 
especially to a hollow steering section of a borescope or endoscope. 
An endoscope is generally characterized as an elongated flexible tube with 
a viewing head in its distal or forward end, and a control section at its 
proximal end for controlling or steering the distal end. In such an 
endoscope, a bendable tube steering section is provided at the distal end 
adjacent to the viewing head. One or two pairs of control cables extend 
through the bendable tube steering section and the remainder of the 
flexible tube, and these cables connect with a steering control in the 
control section. One or both pairs of these cables are displaced in order 
to bend the bendable tube steering section to facilitate the inspection of 
an object. 
An endoscope is typically inserted into the body cavity of a patient to 
investigate visually the tissues within the cavity. For example, an 
endoscope can be inserted into the colon or stomach, or into the lung of a 
patient. Because the esophagus, bronchii and the colon are narrow, 
tortuous passageways, the steering section must be bent rather precisely, 
and the bend should occur as close to the head as possible, in order to 
obtain the necessary penetration without damaging the patient's tissues. 
It is most desireable that the slack in the cable be kept to an absolute 
minimum, so that steering can be controlled precisely. 
A borescope is a similar device, but intended for visual inspection of a 
mechanical device, such as a jet engine or turbine, where it would be 
difficult or impossible to examine the device's internal elements. The 
borescope needs to be insertable into narrow tortuous passageways, and 
must observe similar steering and bending considerations. 
A number of types of steering mechanisms are known. For example, helically 
coiled strips are employed in endoscopes or borescopes as described in 
U.S. Pat. Nos. 3,610,231 and 3,739,770. Steering sections having 
thin-walled cylindrical segments or bands that are joined by means of pins 
or bifurcations or other similar articulations such that the segments are 
rockable on one another, are described in U.S. Pat. Nos. 3,583,393; 
3,669,098; 3,799,151; and 4,347,837. A previously-proposed endoscope that 
had a provision to control the degree of bending is described in U.S. Pat. 
No. 3,557,780. 
The steering mechanisms for these previously-proposed endoscopes are rather 
elaborate structures, with many parts that can fail and which are 
relatively expensive to produce. Further, in many cases it has been 
necessary to provide the cables with a significant amount of slack because 
the steering sections bend at discrete points, and not in a perfectly 
smooth curve. 
U.S. Patent Application Ser. No. 806,667, filed Dec. 9, 1985, now U.S. Pat. 
No. 4,700,693, granted Oct. 20, 1987, and having a common assignee 
herewith, addresses the above problem. The disclosure in that patent 
application is incorporated herein by reference. 
In the steering section of the endoscope or borescope described in 
Application Ser. No. 806,667, the steering section has, within its 
flexible sheath, a plurality of axially aligned washers, each having a 
central passage and a number of peripheral bores. Pairs of these 
peripheral bores are disposed generally diametrically opposite each other. 
The steering cables pass through the respective axially aligned peripheral 
bores of the washers, and spacing structure is disposed at the location of 
predetermined ones of these peripheral bores to define bending locations 
for the steering section, such that the displacement of certain pairs of 
the steering cables results in bending of the steering section in one 
plane or another. As disclosed in that patent application, the washers are 
flat washers, and the spacer structure includes pairs of hemispherical 
beads that are disposed in nose-to-nose fashion over the respective cables 
between successive washers. The beads have their spherical surfaces facing 
one another, and their flat surfaces facing outward against their 
associated washers. 
The upshot of this construction is that when the steering section is bent, 
the spherical surfaces of the hemispherical beads should roll over one 
another to achieve smooth bending without a significant amount of slack in 
the cable. 
Unfortunately, with this design, the hemispherical spacer beads tended to 
degrade in service over time. The basic reason for this is that the 
steering cable had to have a significantly smaller diameter than the 
diameter of the through-bore of the beads to achieve proper clearance for 
the cable. Because of the difference in diameters of the cable and the 
spacer bead through-bores, there is a tendency for the hemispherical 
spacer beads to shift off axis by the amount of the clearance. When the 
spacer beads rock over one another, the intersecting edges of the 
through-holes cut into one another in the radially displaced beads. This 
eventually works into a saddle and binds on the cable. 
In order to avoid this problem, it was necessary to provide a relatively 
wide bearing surface at the facing noses of the beads to compensate for 
this lateral sliding of the spacers relative to one another. However, if 
the nose surface is wide enough to compensate for the entire clearance 
between the steering cable and the spacer bead through-bores, then as one 
spacer bead tilts with respect to another as the steering section is bent, 
the required length of the cable is increased. Since the actual cable 
length does not increase, the effect of this is to tighten the cable when 
the steering section is deflected, and thereby increase steering forces. 
Of course, a smaller bearing nose surface could be employed if there were a 
smaller diametrical clearance between the cable and spacer bead, but in 
that case the cable would bind against the spacer beads when the spacers 
tilted with respect to each other. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an endoscope 
bendable steering section which avoids the drawbacks of the prior art. 
It is a further object of this invention to provide a steering section 
which keeps the slack or play in the steering cables to a minimum, but 
which will not bind the steering cables when bent. 
It is a still further object of this invention to provide a bendable 
steering section with smooth, crisp, and precise bending action. 
As aforesaid, this invention resides in the steerable endoscope or 
borescope of the type having a viewing head and a cable-bendable steering 
section disposed proximally of the viewing head. The steering section has 
a flexible sheath, a plurality of washers, with each of the washers having 
a central passage and a plurality of peripheral bores therethrough, a 
plurality of steering cables passing through respective axially aligned 
ones of the peripheral bores of the washers, and pairs of spacer beads 
disposed in nose-to-nose fashion over the steering cables at the locations 
between certain ones of the washers. 
According to an aspect of this invention, the spacer beads are tapered 
beads and have a relatively wide base surface facing the associated one of 
the successive washers, and a relatively narrow flat nose surface facing 
against a like nose surface of the other of the pair of spacer beads. 
These beads each have an axially bore that is flared out towards the base 
surface, so that at the nose surface of the spacer bead, the axially bore 
has a small clearance over the steering cable, but a wide clearance at the 
base to prevent the spacer bead from binding on the steering cable. 
In the preferred embodiments, the steering cable has a diameter of between 
about 0.015 and 0.030 inches, and the axial bore, at the nose surface of 
the spacer bead, has a clearance, or difference in diameter from the 
cable, of only about 0.005 to 0.007 inches. 
The spacer beads can have a frustoconic outer wall, or can have a 
cylindrical wall towards the base and a spherical wall connecting the 
cylindrical wall to the nose surface. 
Preferably, the flared portion of the spacer bead bore is a conic axial 
bore which opens toward the base surface with an apex angle of about forty 
degrees, and the nose surface has a diameter of about one-half to 
three-quarters the diameter of the base surface of the spacer bead. 
The above and many other objects, features, and advantages of this 
invention will be more fully understood from the ensuing detailed 
description of a preferred embodiment, which should be considered in 
connection with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawing, and initially to FIG. 1 thereof, a generally 
cylindrical steering section 10 of one type of endoscope has its proximal 
end (to the left in the drawing) connected to an elongated flexible tube, 
and on its distal end (to the right in the drawing) is mounted a video or 
fiber optics type viewing head (not shown). The steering section 10 is 
formed of a stack of washers 12, a typical one of which is shown in plan 
in FIG. 2. With these washers 12 there are associated two pairs of 
steering cables 14, which are preferably twisted strand stainless steel 
cables. The tapered-side spacer beads 16 (shown in section in FIG. 3 and 
in perspective in FIG. 4) are disposed over the cables 14 in the alternate 
spaces between the washers 12, i.e. at alternate pairs of the steering 
cables, considered in progression from one washer to the next. The 
assembly is covered with a flexible sheath 18. 
The washers 12 as shown in FIG. 2 can favorably be composed of aluminum 
bronze or beryllium copper. The washers 12 are basically in the form of a 
circular ring 20 which has a generally cruciform central passage 22 
defined among four inwardly directed lobes 24 that are spaced at 90 degree 
intervals on the ring 20. Peripheral through-bores 26 penetrate these 
lobes 24, and the steering cables 14 pass through these bores 26. The 
stack of washers 12 has respective bores aligned in registry with one 
another. 
The spacer beads 16 each have an axial passage 30, a relatively wide base 
surface 32 that abuts a lobe 24 of the associated washers 12, a tapered 
sidewall 34, here a frustoconic surface, and a relatively narrow flat nose 
surface 36. The axial passage 30 has a cylindrical nose portion 38, which, 
as aforesaid, has a relatively small clearance over the associated 
steering cable 14, and a flared base portion 40 that expands baseward, 
here with an apex angle of forty degrees. 
Pairs of these washers 16 are disposed in alternate inter-washer spaces on 
each of the steering cables 14, i.e., at the top and bottom in the 
drawing, and in the remaining spaces over the other two cables 14, that 
is, the front and back (obscured) in the drawing. 
Each pair of these beads 16 has its nose surfaces 36 abutting one another. 
These beads 16 serve as pivots to define hinge lines for bending the 
steering section 10. 
The cables 14 pass through the bores 26 and the bead through-passages 30, 
and slide relative to the beads 16 and the washers 12. The cables 14 are 
anchored to a point in the viewing head, and their displacement causes 
flexion of the steering section to bend the same in an arch, generally as 
indicated in FIG. 1, the general manner of which is well known. 
The relatively small nose surfaces 36 of the facing spacer beads 16 rock 
with respect to one another to form generally smooth bending points, while 
the flat base surfaces 32 of the beads 16 seat against the lobes 24 of the 
washers 12. Because there is a very small clearance as between the nose 
portion 38 of the axial passage 30 and the associated cable 14, there is 
very small lateral play as between facing spacer beads 16. Consequently, 
the flat nose surfaces 36 of the beads 16 remain in engagement with one 
another despite their small size. Also, because the base portion 40 of the 
axial passage is countersunk or flared, the axial passage 30 will not bind 
against the associated cable 14, even during extreme bending of the 
section 10. 
In this first embodiment, the endoscope is in the form of a gastroscope, 
having a nominal diameter of 9.5 millimeters. The diameter of the cables 
14 is substantially 0.018 inches, and the diameter of the narrow nose 
portion 38 of the through-passage 30 is substantially 0.023 inches, to 
0.025 inches. This provides a clearance of only about 0.005 to 0.007 
inches. 
The spacer beads 16 have a thickness dimension of about 0.021 inches, a 
width, at the nose portion, of 0.038 inches, and a width or diameter at 
the base portion of 0.050 inches. In this embodiment, the cylindrical nose 
portion 38 of the axial passage 30 has a length of about 0.006 inches. 
By way of contrast, in corresponding spacers employed with respect to the 
endoscopes described in application Ser. No. 806,667, where the steering 
cables had a diameter of about 0.018 inches, the spacer bead had a through 
passage of 0.033 inches, which gave a clearance of about 0.015 inches. 
A second embodiment of this invention is shown in FIGS. 5-8. In this second 
embodiment, elements that correspond to similar elements in the first 
embodiment are identified with corresponding reference numbers that are 
raised by 40. 
Here, the endoscope is a large channel biopsy colonoscope, and its steering 
section 50 includes a stack of washers 52 (also shown in FIG. 6), two 
pairs of steering cables 54, associated pairs of spacer beads 56, and a 
flexible sheath 58. 
As in the first embodiment, the washers 52 are formed of a ring 60 with a 
generally cruciform inner passageway 62 defined among four lobes 64 spaced 
at 90 degree intervals. A through-bore 66, through which an associated one 
of the steering cables 54 passes, is centered in each of the lobes 64. 
The spacer beads 56, shown in section in FIG. 7 and in perspective view in 
FIG. 8, each have a central axial passage 70, a relatively wide flat base 
surface 72, a cylindrical side surface 73, rising part way from the base 
surface 72 in the thickness direction of the bead 56, and a spherical 
surface 74 which extends from the cylindrical surface 73 to a relatively 
narrow, flat nose surface 76 of the bead 56. As in the first embodiment, 
the axial passageway 70 has a small-clearance cylindrical nose portion 78 
and a flared or countersunk base portion 80 which opens outward towards 
the base of the bead 56. The beads 56 are disposed in pairs in 
nose-to-nose configuration, with the nose surfaces 76 bearing upon one 
another, and the base surfaces 72 disposed against the corresponding lobes 
64 of the associated washers 52. 
In this embodiment, the steering cables 54 have a cable diameter of about 
0.027 inches, and the nose portion 78 of the axial passage 70 has a 
diameter of about 0.032 to about 0.034 inches. This provides a clearance 
of about 0.005 to 0.007 inches. By contrast, in previous spacer bead 
arrangements employing an 0.027 inch diameter steering cable, the spacer 
bead had a passage of 0.042 to 0.044 inches, which provided a clearance of 
0.015 inches. 
As further shown in this embodiment, the spacer beads 56 have a thickness 
dimension of about 0.038 inches, the base surface has the diameter of 
about 0.080 inches, and the nose surface 76 has a diameter of about 0.047 
inches. The neck portion 78 of the axial passage 70 has a thickness of 
about 0.0125 inches, and the countersunk or flared portion has an apex 
angle of about forty degrees. Also, the spherical surface 74 has a radius 
of curvature of 0.0465 inches centered at the geometrical center of the 
base surface 72. 
The beads 16 and 56 of these embodiments can be formed of a suitable metal, 
such as beryllium copper, aluminum bronze or any other metal exhibiting 
similar hardness or wear resistance. 
While the above description relates to specific preferred embodiments of 
this invention, it is clear that many modifications and variations thereof 
would be apparent to those of skill in the art without departing from the 
scope and spirit of this invention, as defined in the appended claims.