A hydraulically or pneumatically actuated fluid-dynamic motor has an elongated elastomeric bladder, a braid disposed over the bladder, and a flexible but substantially incompressible spine disposed between the braid and the bladder. The muscle or motor is configured in a helix with the spine arranged on the inside of the helix. Application of fluid under pressure to the bladder causes one end of the helical motor to untwist or rotate relative to the other end. Upon deflation of the bladder, the spine causes the bladder to deflate and rotate the other end in the opposite direction. This fluid dynamic motor provides an azimuthal motion that can be employed for the steering section of an elongated flexible probe, such as a borescope or endoscope.

BACKGROUND OF THE INVENTION 
This invention relates to hydraulically or pneumatically actuated motors, 
and is more particularly directed to a torsional fluid-dynamic muscle 
which can be made of small diameter and incorporated into a steering or 
articulation section of a flexible elongated probe. The invention is also 
directed to improvements in borescopes and/or endoscopes which permit 
four-way steering of the distal end of an insertion tube without reliance 
on the conventional, but delicate and trouble-prone cable-type steering 
movement. Additionally, the torsional fluid-dynamic muscle or motor of 
this invention has other applications including rotary actuators and 
gauges, grabbers, and supports for remote tools. The invention can also be 
regarded as a pump for converting an angular or torsional force to a fluid 
pressure. 
Borescopes or similar flexible probes are generally configured as an 
elongated flexible insertion tube with a viewing head at its distal or 
forward end and a control housing for controlling or steering the distal 
or forward end. The typical borescope has a bendable tubular steering 
section or articulation section at the distal end adjacent the viewing 
head. The steering section comprises a series of alternating wobble 
washers and spacers, with control cables that extend through the wobble 
washers and then through the remainder of the flexible insertion tube. The 
steering cables connect with a steering control unit in the control 
section. Each such pair of cables is differentially displaced to bend the 
steering section. The viewing head can be remotely oriented to facilitate 
inspection of an object. Borescopes are often required to bend in narrow, 
tortuous passageways, so the diameter of the borescope is often quite 
limited, e.g. 6 mm. Also, the pathway to the object or target can be quite 
long, which then requires the insertion tube and the steering cables to be 
rather long, e.g. fifteen meters or more. 
A number of cable-actuated articulation or steering mechanisms are known, 
and typical ones are discussed in U.S. Pat. Nos. 3,610,231; 3,739,770; 
3,583,393; 3,669,098; 3,779,151; and 4,347,837. Another steering mechanism 
is described in U.S. Pat. No. 4,700,693. 
These cable-actuated articulation mechanisms require the cables to have a 
significant amount of slack or play because bends and coils in the 
insertion tube effectively shorten the cables and because the articulation 
section bends at discrete points rather than following a smooth arc. 
However, in many applications the articulation section must be bent rather 
precisely to penetrate the tortuous passages into the area to be inspected 
without damaging delicate engine parts. For these reasons, cable tension 
must be limited and cable slack must be minimized. However, where the 
insertion tube is long, extra cable slack is often included to accommodate 
the increased cable tightening due to the substantial coiling and bending 
of the insertion tube through which the steering cables pass. A proposed 
arrangement to permit steering cables to be kept short as possible is 
described in U.S. Pat. No. 4,794,912. That patent describes a "muscle," 
i.e. a linear traction motor, that addresses many of the problems found in 
these prior-art steering mechanisms. Specifically, fluid dynamic muscles 
mounted adjacent the distal end of the insertion tube are actuated by 
pneumatic or hydraulic pressure supplied through small flexible tubes 
within the borescope insertion tube. Short steering cables connect the 
respective muscles with the articulation mechanism. As fluid pressure is 
applied differentially to a pair of muscles, the cables move 
differentially and the articulation mechanism bends the steering section a 
desired amount. 
While this system avoids many of the above-mentioned problems, especially 
those associated with extremely long cables, there are remaining problems 
because of the reliance on an otherwise conventional cable steering 
mechanism. The steering section is rather complex and expensive, and does 
not follow a natural arc, as mentioned before. Further simplification, by 
replacing the cable drive steering mechanism, would be required to reduce 
or eliminate these residual drawbacks. 
A hydraulic or pneumatic bending neck is proposed in copending and 
commonly-assigned U.S. patent application Ser. No. 538,232, filed June 18, 
1990. In that arrangement, an articulation or steering mechanism is formed 
of an elongated fluid-controlled muscle that has a flexible spine arranged 
in the axial direction along one side and disposed in the interface 
between the bladder and the braid. The braid confines the bladder such 
that when the bladder is inflated, the bladder and braid expand laterally, 
but shorten axially. Because of the spine, the braid can shorten only on 
the side away from the spine, so the spine defines a bending plane for the 
bending neck. Preferably, the spine is arcuately biased in one direction 
so that when no pressure is applied the bending neck is bent in one 
direction in the bending plane. At full pressure the bending neck is bent 
in the opposite direction, and at an intermediate pressure, the bending 
neck is held straight. 
This type of arrangement is capable of two-directional steering, i.e., 
bending that is confined to a single bending plane. It would be desirable 
to have four-way steering with fluid-dynamic bending, but as aforesaid, 
the bending neck is difficult to adapt for deflection in orthogonal 
directions. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of this invention to provide a simple, reliable steering 
mechanism which can be employed on an elongated flexible probe of small 
diameter. 
It is another object of this invention to eliminate cables, wobble washers, 
and other complex mechanical actuation devices from the steering section 
for a probe. 
According to an aspect of this invention a helical biased torsional fluid 
dynamic muscle or motor is constructed which is suited to provide a 
rotational or torsional direction of steering to a bending section of a 
borescope or similar probe. The fluid dynamic muscle has an elongated 
tubular elastomeric bladder in the form of a helix, a tubular braid 
disposed over the bladder in the helix, and a resiliently flexible but 
substantially incompressible helical spine that is situated between the 
bladder and the braid on the inner side of the helix. The bladder is 
sealed at its ends and the braid is attached at one end to an anchor 
member and at the other end to a swivel member. A pressure inlet through 
one end of the bladder permits fluid communication between a controlled 
fluid pressure source and the interior of the bladder. When pressure is 
applied, the fluid expands the bladder laterally, i.e., radially. 
The braid constrains the bladder so that as it expands laterally, it 
shortens in its lengthwise, i.e. helical, direction. The spine restrains 
helical motion on the inside of the helix, so the braid shortens on the 
outside of the helix. This serves to rotate the swivel member in one 
direction by an angle that depends on the amount of pressure applied to 
the muscle. When the pressure is relieved, the spine acts on the bladder 
and braid so that fluid is expelled from the bladder. This lengthens the 
bladder on the outside of the helix, and causes the muscle to rotate the 
swivel member in the opposite direction. The spine can be in the form of a 
helical leaf or ribbon. The swivel member can serve as a connector or 
mount on which a fluid dynamic bending neck is affixed. 
A signal and/or optical conduit can pass axially through the system from a 
video or optical viewing head at the distal tip. The conduit can be 
contained in a tubular core that passe from the swivel, proximally within 
the helix and out through a passage in the anchor member. 
The above and other objects, features, and advantages of this invention 
will be more fully appreciated from the ensuing description of a preferred 
embodiment which is to be read in conjunction with the accompanying 
Drawing:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the Drawing, and initially to FIG. 1, a flexible video 
probe 10 has an elongated flexible insertion tube 11, of which only a 
distal portion is shown, an azimuthal steering section 12 situated at the 
distal end of the insertion tube, and a bending section 13 situated at the 
distal end of the azimuthal steering section 12. At the distal end of the 
bending section 13 there is a video head 14. A conduit 15 that contains 
signal and control conductors and a fiber optic bundle for illumination 
extends axially within the insertion tube 11 and through the sections 12 
and 13 to connect the video head 14 with a video processor unit 16. 
The bending section 13 is capable of two-way bending in a bending plane 
that is up to 60 to 90 degrees either side of a straight orientation. 
In this arrangement, as shown, the bending neck 13 is arranged as generally 
as described in the copending patent application Ser. No. 539,232 having a 
common assignee. There is a proximal connector 17 that is screwed onto a 
threaded swivel member 18 at the distal end of the azimuthal steering 
section 12. A distal end piece 19 at the distal end of the bending section 
13 mounts the video viewing head 14. A passage 20 extends axially through 
the proximal connector 17 and a passage 21 extends through the distal end 
piece 19; these passages 20, 21 carry the conduit 15. In the bending 
section 13, an elongated elastomeric bladder 22 is coupled to the 
connector 17 and end piece 19, and a flexible but incompressible spine 23 
is situated on one side of the bladder and extends between the connector 
17 and the end piece 19. A braid 24 that is formed of right hand and left 
hand helically wound filaments is disposed over the bladder 22 and spine 
23 and is mechanically connected to the connector 17 and the end piece 19. 
The bending section 13 operates in a manner that is generally described in 
copending patent application Ser. No. 539,232. 
The azimuthal steering section 12 has a helical biased muscle or motor 25 
that is driven to rotate in the azimuthal direction by controlled fluid 
pressure (either pneumatic or hydraulic). This muscle 25 is formed of a 
helical elongated elastomeric bladder that is covered with a generally 
helical braid 20. A helical spine 28, which is formed of a ribbon of a 
flexible, but generally incompressible material such as a suitable spring 
metal alloy, is situated between the bladder 26 and the braid 27, but on 
the inside of the helix. The construction of the braid 27 and bladder 26 
can be generally as shown in FIG. 2. The helix should have a suitable 
number of turns, and, although only about four turns are shown in FIG. 1, 
the helically biased muscle 25 could be configured of twelve or more 
turns. 
A proximal connector 29 fits into the distal end of the insertion tube 11, 
while a distal end bushing 30 holds the swivel member 18 to permit 
rotation thereof. A sheath or skin 31 of a suitable material covers the 
azimuthal steering section 12 and extends between the connector 29 and the 
bushing 30. A tubular core 32 extends proximally from a protuberance 33 on 
the swivel member 18 and passes within the helix of the muscle 25 and 
through a central passage 34 in the proximal connector 29 and then 
continues axially within the insertion tube 11. A controllable pressure 
source 35 supplies pressurized fluid through the tubular core 32 to the 
interior of the bladder 22 of the bending section 13. The degree of 
arcuate bending of the section 13 depends on the pressure that is applied 
from this source 35. 
As shown in FIG. 3, the proximal connector 29 has a first annular region 36 
in which there is cut a slot 37 to receive a proximal end of the helical 
muscle 25. Favorably, the elongated braid 27 and bladder 26 are folded 
over at the end and inserted into the slot 37. Then the slot is potted in 
epoxy or other potting compound. The region 36 provides a surface from 
which the first turn of the helix starts. A second annular region 38 
receives the proximal end of the flexible sheath 31. A proximal-side 
protuberance 39 fits into the distal end of the insertion tube 11. 
An axial fluid passage 40 is bored through the connector 29 into the slot 
37 in which the end of the helical muscle 25 is affixed. An opening is 
bored through this hole into the potting and the proximal end of the 
muscle 25 to provide fluid communication with the interior of the bladder 
26. As shown in FIG. 1, a fluid conduit 41 extends proximally from the 
fluid passage 40 and extends within the insertion tube 11 to a 
controllable pressure source 42. The pressure source 42 provides pneumatic 
or hydraulic pressure at a selected level to control a degree of rotation 
of the swivel 18 and thus the bending plane of the bending section 13. 
This degree of rotation should be arranged to be 180.degree. or greater. 
The spine 28 is on the inside of the spiral in the helical muscle 25. When 
pressure is applied from the source 42 to inflate the bladder 26, the 
bladder expands radially, i.e., laterally. The filaments of the braid 27 
constrain this expansion so that the braid 27 will tend to shorten i.e. in 
the direction of the helix. The spine 28 prevents the inside of the muscle 
from contracting, so that the outside of the helix shortens 
differentially. Inflation tends to unwind the helical spine which, in this 
case, rotates the swivel 18 and the attached bending neck 13 in the 
direction of arrow A. When pressure is relieved from the bladder 26, the 
muscle 25 relaxes and elongates helically on the outside, thereby allowing 
the spine to rewind, which rotates the swivel 18 and the bending neck 13 
in the direction of arrow B. Preferably, the bending neck 13 should be 
capable of rotating 90.degree. or more on either side of the zero 
position. This zero position occurs at a pressure approximately halfway 
between zero gauge pressure and the maximum allowable gauge pressure. 
The arrangement as shown and described here can be configured for either 
pneumatic or hydraulic operation. In the case of a pneumatic device, a 
portable unit can be constructed which is controlled by a small cylinder 
of compressed gas. 
Also in this embodiment, the helical torsional motor 25 is wound as a 
right-hand helix, but in other embodiments, the motor could be configured 
as a left-hand helix. The left hand configuration would produce rotation 
in the direction of arrow B during inflation and rotation in the direction 
of arrow A when pressure is relieved. Moreover, in some applications, a 
pair of oppositely wound helices could be employed, and differentially 
controlled for precise azimuthal steering. Also, in alternative 
embodiments, the spine can be outside the braid, and bonded to it at the 
ends and one or more intermediate points. 
A rotational seal can be employed between the swivel 18 and the bushing 30. 
This permits the insertion tube 11 to serve as a conduit for air between 
the controlled pressure source 42 and the azimuthal steering section 12. 
In that case, the fluid conduit 41 could be eliminated or could terminate 
a short distance proximally of the connector 29. 
While this invention has been described in detail with reference to one 
preferred embodiment, it should be understood that the invention is not 
limited to that precise embodiment. Rather, many modifications and 
variations will present themselves to those of skill in the art without 
departing from the scope and spirit of this invention, as defined in the 
appended claims.