Double-acting flexible wall actuator

A double-acting actuator includes a first tubular body made of an elastic material, a first reinforcing braided structure surrounding the first tubular body, a second tubular body made of an elastic material surrounding the first reinforcing braided structure to form a space outwardly thereof, and a second reinforcing braided structure surrounding the second tubular body. The actuator further includes closure members for closing and joining ends of the first and second tubular bodies and reinforcing braided structures, and guiding device for permitting axial movements of the first and second tubular bodies but restraining lateral movements thereof. The first and second reinforcing braided structures are so constructed that initial braided angles thereof permit of the first braided structure elongating and permit of the second braided structure contracting when the pressurized fluid is supplied into the first and second tubular bodies.

BACKGROUND OF THE INVENTION 
This invention relates to an actuator of an air-bag type extensible and 
contractible in axial directions by supplying and exhausting a pressurized 
fluid. 
There has been known an actuator, for example, as shown in FIG. 1 as an 
air-bag type actuator capable of converting energy of a pressurized fluid 
into kinetic energy with high efficiency. 
This actuator 10 includes a tubular body 12, a reinforcing braided 
structure 14 externally arranged thereon, and closure members 16 closing 
both ends of the tubular body 12 and the reinforcing braided structure 14. 
When a pressurized fluid is supplied into an internal space 20 of the 
tubular body 12 through a connecting aperture 18 formed in at least one of 
the closure members 16, an enlargement of initial braided angles .theta. 
of the reinforcing braided structure 14 or a pantograph movement of the 
braided structure 14 causes an expansion of a diameter of the tubular body 
12 and a contraction of the body 12 in axial directions owing thereto or a 
contraction of a distance between both the closure members 16. Such an 
actuator has various advantages in that it is very light weight because of 
the construction above described and compliance as an actuator can be 
suitably changed by adjusting pressure of the pressurized fluid to be 
supplied. 
In general, the tubular body 12 is preferably made of a rubber or 
rubber-like elastic material or a material equivalent thereto in 
consideration of impermeability to pressurized fluids and sufficient 
flexibility. The reinforcing braided structure 14 is preferably made of 
organic or inorganic high tension fibers having braided structures whose 
braided angles vary from initial braided angles, for example, 10.degree. 
to 25.degree. to so-called "angle of repose" (54.degree.44') when the 
tubular body expands at a maximum diameter. 
With such an actuator, when the pressurized fluid is exhausted from the 
internal space 20, the actuator can return to its original shape with the 
aid of an elastic returning force of the tubular body 12. However, as the 
returning force is not sufficient, it is necessary to provide an elastic 
member such as a compression spring assisting in returning of the actuator 
to its original shape. 
However, as the elastic member such as a compression spring has an 
invariable spring constant and a constant outer diameter, it will 
encounter a difficulty when it is required to change the compliance of the 
actuator including the elastic member and its outer shape and size. In 
this case, it is again needed to design and manufacture a spring member 
whose spring constant and outer diameter and outer size need respective 
requirements. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved actuator which 
eliminates all the disadvantages of the prior art and is able to change 
the compliance of the actuator freely without requiring any elastic member 
such as a compression spring. 
In order to accomplish this object, a double-acting actuator according to 
the invention comprises a first tubular body made of an elastic material, 
a first reinforcing braided structure surrounding the first tubular body, 
a second tubular body made of an elastic material surrounding the first 
reinforcing braided structure to form a space outwardly thereof, a second 
reinforcing braided structure surrounding the second tubular body, closure 
members for closing and joining ends of the first and second tubular 
bodies and reinforcing braided structures, and guide means for permitting 
axial movements of the first and second tubular bodies but restraining 
lateral movements thereof, said first reinforcing braided structure having 
initial braided angles permitting elongation movements of the first 
tubular body in axial directions on being supplied with a pressurized 
fluid thereinto and said second reinforcing braided structure having 
initial braided angles permitting contracting movements of the second 
tubular body in axial directions on being supplied with the pressurized 
fluid thereinto, thereby enabling the actuator to do reciprocative 
movements by supplying and exhausting the pressurized fluid into and from 
the respective tubular bodies. 
The first tubular body and the first reinforcing braided structure are 
closed at both opening ends by means of the closure members. As initial 
braided angles of the braided structure are within 65.degree. to 
85.degree., when the pressurized fluid is supplied into the first tubular 
body, it slightly contracts radially inwardly, but extends radially 
inwardly. 
On the other hand, the second tubular body and the second reinforcing 
braided structure are closed at both opening ends by the closure members. 
As initial braided angles of the braided structure are within 10.degree. 
to 25.degree., when the pressurized fluid is supplied into the second 
tubular body, it expands radially outwardly, but contracts in the axial 
directions. 
Therefore, by suitably adjusting the supply and exhaust of the pressurized 
fluid into and from the first and second tubular bodies, their extending 
and contracting forces are increased or reduced, thereby causing requisite 
movements of the actuator. 
Moreover, the guide means arranged in the tubular body permit the 
respective tubular bodies to move in parallel with their axes, but 
restrains lateral movements of the tubular bodies, thereby constantly 
enabling moving directions of the actuator to be coincident with requisite 
directions.

DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS 
FIG. 2 illustrates in section an actuator 30 as one embodiment of the 
invention. The actuator 30 includes a first tubular body 32 made of a 
rubber or a rubber-like elastic material, and a first reinforcing braided 
structure 34 provided on an outer circumference of the first tubular body 
32. The first reinforcing braided structure is reinforced by cords which 
are organic or inorganic high tension fibers, for example, twisted or 
nontwisted filament bundles of aromatic polyamide fibers or very fine 
metal wires. Openings at both ends of the tubular body and the reinforcing 
braided structure are closed by closure members 36. Both the ends of the 
tubular body 32 and the braided structure 34 are clamped outwardly by 
first clamp sleeves 38 to prevent the tubular body 32 and the braided 
structure 34 from being dislodged from the closure members 36. 
A second tubular body 40 made of a material equivalent to that of the first 
tubular body 32 is arranged so as to surround the first reinforcing 
braided structure 34 form a space radially outwardly of the first 
reinforcing braided structure 34. Second reinforcing braided structure 42 
is arranged on an outer circumference of the second tubular body 40. 
Openings at both ends of the tubular body and the reinforcing braided 
structure are closed by closure members 36. Both the ends of the tubular 
body and the reinforcing braided structure are clamped outwardly by the 
second clamp sleeves 44 to prevent the second tubular body 40 and the 
second braided structure 42 from being dislodged from the closure members 
36. 
Each of the closure members 36 closing both the openings at the ends of the 
first and second tubular bodies and braided structures is constructed by 
two coaxial circular column members integrally connected whose outer 
diameters are substantially equal to inner diameters of the first and 
second tubular bodies 32 and 40 in this embodiment. However, it is not 
limited to this configuration. For example, the closure member 36 may be 
formed by separable members. In order to make easy mounting the actuator, 
the closure member 36 is preferably formed at end with internal threads 54 
in its axial direction. 
Moreover, each of the closure members 36 is formed with a connecting 
aperture 50 communicating with an inner space 46 in the first tubular body 
32 or a connecting aperture 52 communicating with an inner space 48 in the 
second tubular body 40. These connecting apertures serve to supply and 
exhaust a pressurized fluid into and from the inner spaces in these 
tubular bodies. Further, each of the closure members is formed at an 
opening of the connecting aperture 50 or 52 with internal threads to 
facilitate connecting with a piping (not shown) for supply and exhaust of 
the pressurized fluid. 
In the first tubular body 32 is provided guide means 56 which permits 
relative movements of the closure members 36 along axial directions of the 
tubular body, but restrains the closure members in lateral directions. 
In this embodiment, the guide means 56 comprises a cylindrical member 56a 
extending in the axial direction of the tubular body 32, whose one end is 
fixed to one of the closure members 36, and a bar member slidably fitted 
in the cylindrical member 56a, whose one end is fixed to the other closure 
member 36. However, the guide means may be constructed by a bar member 
having a groove extending in the axial direction and a member having at a 
free end a projection adapted to engage in the groove of the bar member. 
Initial braided angles .theta..sub.1 and .theta..sub.2 of the first and 
second reinforcing braided structures 34 and 42 should be noticed in this 
case. 
As shown in FIG. 3, the initial braided angle .theta..sub.1 of the first 
reinforcing braided structure 34 is so determined that when the 
pressurized fluid is supplied into the first tubular body 32, the tubular 
body 32 is permitted to elongate in the axial directions and when at a 
maximum elongation, the braided angle becomes a so-called "angle of 
repose" (54.degree.44'). The initial braided angle is preferably selected 
within a range of 65.degree. to 85.degree.. 
On the other hand, the initial braided angle .theta..sub.2 of the second 
reinforcing braided structure 42 is so determined that when the 
pressurized fluid is supplied into the second tubular body 42, the tubular 
body 42 is permitted to contract in the axial directions and when at a 
maximum contraction (minimum length), the braided angle becomes a 
so-called "angle of repose" (54.degree.44'). The initial braided angle is 
preferably selected within a range of 10.degree. to 25.degree.. 
When the initial braided angles of the first and second reinforcing braided 
structures 34 and 42 are selected as above described, the first and second 
tubular bodies and braided structures are moved in the following manner. 
Namely, when the pressurized fluid is supplied, the first tubular body 32 
and reinforcing braided structure 34 closed at the ends by the closure 
members 36 slightly contract radially inwardly, but axially elongate, 
while the second tubular body 40 and reinforcing braided structure 42 
closed at the ends by the closure members 36 expand radially outwardly, 
but axially contract. 
However, as the closure members 36 closing both the ends of the first and 
second tubular bodies and braided structures are commonly used, 
respectively, a distance between both the closure members or a stroke of 
the actuator can be freely changed by suitably adjusting the pressure to 
be applied into the inner spaces of the first and second tubular bodies. 
Moreover, when the pressurized fluid is applied into the tubular bodies, 
the first tubular body 32 positioned inwardly contracts radially inwardly, 
whereas the second tubular body 40 positioned outwardly expands radially 
outwardly. Therefore, the respective movements including movements of the 
reinforcing braided structures associated therewith do not interfere with 
each other. 
Moreover, when such an actuator is used, in an initial setting condition 
the tubular body 32 is previously elongated by applying an initial setting 
pressure in the inner space of the first tubular body 32 positioned 
inwardly. Therefore, respective natural lengths of the second tubular body 
40 and the reinforcing braided structure 42 are determined so as to be 
substantially equal to an effective length of the first tubular body 
elongated owing to the application of the initial setting pressure. 
Therefore, the second tubular body 40 and the second reinforcing braided 
structure 42 include slacks or sags at midways before applying the 
pressurized fluid into the inner space 48 thereof. 
The operation of the actuator will be explained hereinafter. It is assumed 
that the inner spaces of the tubular bodies 32 and 40 are communicated 
through the connecting apertures 50 and 52 connected with suitable 
operating pressure source including known valves for controlling the 
supply and exhaust of the pressurized fluid, for example, supply and 
exhaust pipings connected to an air compressor. 
When the initial setting pressure is applied into the inner space 46 of the 
first tubular body through a supply and exhaust piping (not shown) 
connected to the connecting aperture 50, the first tubular body elongates 
in the axial directions as decreasing the initial braided angle 
.theta..sub.1 of the first reinforcing braided structure 34, while the 
second tubular body 40 and braided structure 42 elongates in the axial 
directions. 
At this moment, the pressurized fluid is supplied into the inner space 48 
of the second tubular body 40 through a supply and exhaust piping (not 
shown) connected to the connecting aperture 52, as increasing the initial 
braided angle .theta..sub.2 of the second reinforcing braided structure 
42, the second tubular body 40 expands radially outwardly to cause 
contracting forces in the tubular body 40 against the elongating forces of 
the first tubular body 32 so that the contracting force in the second 
tubular body 40 and the elongating force of the first tubular body 32 are 
balanced. This condition is shown in FIG. 4. 
When the pressurized fluid is further supplied into the inner space 48 in 
the second tubular body, the contracting force of the second tubular body 
40 overcomes the elongating force of the first tubular body 32 so that the 
distance between the closure members 36 is shortened. 
In this case, the pressurized fluid is exhausted from the inner space 46 of 
the first tubular body 32 to reduce its elongating force in conjunction 
with the supply and exhaust of the pressurized fluid into and from the 
inner space 48 of the second tubular body 40. In this manner, the 
contracting force of the second tubular body can be converted into a 
kinetic energy with high efficiency, and at the same time the 
responsibility of the actuator can be improved. 
On the other hand, when it is desired to return the actuator 30 to its 
initially set condition, it can be accomplished by exhausting the 
pressurized fluid from the inner space 48 in the second tubular body to 
reduce its contracting force. In this case, of course, the pressurized 
fluid may be supplied into the first tubular body 32, while the 
pressurized fluid may be exhausted from the second tubular body 40 for the 
same purpose. Moreover, if the pressure of the fluid to be supplied into 
the first and second tubular bodies is set relatively high, the compliance 
as the actuator can be set at a high value. On the other hand, if the 
pressure of the fluid to be supplied into the first and second tubular 
bodies is set relatively low, the compliance of the actuator can be set at 
a low value. 
In either case, moreover, the guide means 56 provided in the first tubular 
body 32 restrains lateral movement of the first and second tubular bodies 
elongating upon being supplied with the pressurized fluid, so that the 
relative movement of the closure members 36 in the radial directions can 
be ensured. 
The invention is not limited to these embodiments. The guide means may be 
provided with detecting means for detecting the relative movement between 
the closure members, for example, differential transformer. The pressure 
of the fluid to be supplied into the respective tubular bodies may be 
controlled in response to signals from such a detecting means. Moreover, 
anchoring means may be provided for regulating the relative movements of 
the closure members. Various modifications and changes can be made within 
the scope of the invention. 
As can be seen from the above explanation, the invention can provide a 
double-acting actuator of the air-bag type which is very light weight and 
is able to elongate and contract in axial directions and whose compliance 
can be suitably changed by the controlling supply and exhaust of the 
pressurized fluid into and from the respective tubular bodies. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details can be made therein without departing from the spirit and scope of 
the invention.