Note: Descriptions are shown in the official language in which they were submitted.
1047887 :
The present invention relates to a fluid pressure
rotary actuator for imparting rotary motion to an element.
With actuators for imparting rotary motion through a
given angle, the problem of the weight and bulk of the whole
arrangement or the problem of sealing against the acting fluid
becomes more troublesome as the output torque increases. This
is because if importance is attached to the sealing against high
acting fluid pressure a cylinder with a linearly reciprocable
piston must be utilized and the linear movement must be converted
into a rotating movement, while with so-called rotary actuator
type directly providing rotary movement, there is still a problem
of sealing against the acting fluid.
It is considered that a structure in which the cylinder
tube is bent into an annulus or toroid for directly producing
the rotating power will make the conversion from linear to rotary
motion unnecessary, and will solve at least the problem of sealing
against the fluid pressure medium. The prototype of such struc-
ture is shown for example in the Japanese Patent Publication No.
1960-1710. In this structure, only two working chambers can be
~0 provided. In a structure with only two chambers, only one of
the chambers is fLlled with fluid under high pressure, so that a
non equilibrium force is produced in obtaining the rotating force ~ -
and therefore the piston rod in the form of a segment of an
annulus requires high rigidity. Also, a force which is equal to
the total pressure applied to the piston by the high pressure
acting fluid is itself applied to the output shaft as a radial
load. This is a serious problem for an actuator required to be
wear-resistant and durable. Furthermore, an actuator of this kind
having an operating angle of 90 and only two acting chambers is
of complicated construction.
Now, if it were tried to arrange four working chambers
symmetrically with respect to the center of the output shaft
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arranged at the axis of the toroid, the operating angle of the
output shaft would be remarkably restricted, and it would be
impossible to obtain an angle of 90. Since for the purposes
of employment of actuators of this kind, for example automatic
operation of valves, cocks, etc., it is necessary to secure an
operating angle of at least 90, and consequently the actuator
in said Patent Publication is of limited use.
In providing a small-sized, light weight and highly
reliable actuator having a toroidal cylinder tube and an annular
piston rod for resolving the above mentioned problem, it is
desirable to make the following three improvements: Firstly the
non-equilibrium force should be reduced as far as possible;
secondly the piston rod itself should have a smaller diameter and
thirdly while securing an operating angle of at least 90 within a
limited space, the working chambers should be increased to four
in number to increase the output torque without excessively in-
creasing the non-equilibrium forces on the output shaft.
With a view to fulfilling the above objectives, the -;
present invention provides a rotary actuator comprising a shaft,
an arcuate piston rod centered on the shaft, a piston rod mounting
stay extending between the shaft and the piston rod, a cylinder
tube in the form of at least a segment of a toroid surrounding -
the piston rod, a plurality of partitions fixed within the cylinder
tube and at least two of which slidably guide the piston rod,
two pistons secured to the piston rod and slidable within the
cylinder tube, each piston being arranged in between a respective
pair of partitions to divide the space between said pair of
partitions into two variable volume working chambers, and means
for introducing pressure medium into the working chambers on the
opposite sides of each piston to cause relative rotation between
the shaft and the cylinder tube.
The invention will now be described further, by way of
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example, with reference to the accompanying drawings, in which:
Fig. 1 is a schematic diayram for explaining the
mechanical characteristics of the present invention, the cylinder
tube, the pistons, the piston rod, etc. shown schematically in
solid line;
Fig. 2 is a sectional view of an essential part of an
actuator having a ring-shaped cylinder tube of conventional type;
Fig. 3 is a sectional view of one embodiment of the
present invention taken along the line III - III of Fig. 4;
Fig. 4 is a sectional elevational view taken along the
line IV - IV of Fig. 3;
Fig. 5 is a partial sectional view which is similar to
the right half of Fig. 4, but taken adjacent a piston; and
Fig. 6 is the bottom view corresponding to the lower
side of Fig. 4.
The fundamental idea of the present invention will be
explained herebelow with reference to Fig. 1 of the accompanying
drawings:
In Fig. 1, for convenience, the piston rod, the pistons,
the partition walls, etc. are schematically shown by single lines.
A piston rod mounting stay 5 is arranged horizontally to the left
of the center 0, that is, on the X - X axis, while a central
partition wall 6 is arranged on the X-axis opposite to the stay 5.
The two piston faces 2, 2 and the two partition walls 6, 6 are
completely symmetrically arranged with respect to the X-axis.
Now, for simplicity, the following assumption is
introduced: The area center points of the piston faces 2 are at
points P, P' where a piston rod 3 is connected to the pistons.
To these points P and P' are applied forces of equal magnitude
represented by vectors PA and P'A', respectively, which have the
directions of the tangents at said points of the circle formed by
the piston rod.
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The vectors PA and P'A' are resolved into the X-axis
component and the vertical Y-axis component, and will be discussed
with respect to the vectors ~, sA, P's' and B'A'. Constructing
perpendiculars from the points s and B' to the vectors F~ and
P'A', respectively, there are obtained the feet of perpendiculars
C and C', respectively. The force of the vector P~ acting on
the point P of the piston 2 imparts a rotary motion to the output
shaft as a moment ~ . Discussion will be made with respect to
the vector PA resolved into vectors ~ and ~. The vectors P~
and ~ correspond to the vectors P~ and ~, respectively.
Now, parallel translation to the Y-axis of the vectors
PB and P'B' is made and consideration is made of the vectors DE
and D'E' with tails D and D', respectively, corresponding to the
feet of perpendiculars dropped from the points P and P' to the
Y-axis, respectively. ~ODP is similar to ~PCB, because ~DPO + -
/ BPC =~R, so that /POD =~BPC. Therefore, there is eStablished
the following relation:
OD: OP = PC: PB
OP PC = OD PB
Since PB = DE, the above relation is converted into the following:
OP PC = OD DE
This indicates the following fact: The moment represented by the
product of the vector P~, which is a part of the vector PA, and
the distance OP, that is, the rotation output, is replaced by
a rotation moment represented by the product of the vector DE(PB)
and the distance OD. This is also the case with the point P':
The output due to the vector P'CI is replaced by a rotation moment
represented by the product of the vector D ' E' and the distance -
, ~- . .
Now, the vector DE is compared with the vector D'EI: -
These two vectors are of equal magnitude, of opposite senses, and
at equal distances from the center O. Thus they constitute a
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rotating couple, and therefore are completely converted into
rotation output without any need of auxiliary acting force,
therefore without any frictional resistance.
Now, let us consider the vectors As and A's'. These
forces act on the points P and P', respectively, with the same
sense, so that they act somewhere in the actuator without making
equilibrium. For example, if the whole of the piston rod 3, the
stay 5 and the connecting part of these are rigid, then a force
corresponding to the vector AB plus the vector A'B' acts directly
on the output shaft as a radial load. This is indicated by the
vector T in Fig. 1. If the connecting part between the piston
rod 3 and the stay 5 is of relatively low rigidity, the load is
; applied at dispersed positions as indicated by vectors Sl, S2,
Sl' and S2'. These loads are necessary for the vectors CA and
C'A', which are parts of the vectors PA and ~, respectively,
to become rotation outputs, and there is produced frictional
resistance. Accordingly, it is desirable that the force corres- -
ponding to the vector PB is as large as possible, while the force
corresponding to the vector AB is as small as possible.
This situation is dominated by a factor of the angle
; ~ (~ DOP). For considering the effect of diminishing the frict-
ional force due to the arrangement of the two pistons symmetric-
ally with respect to the X-axis as shown, the magnitudes of the
~ectors PA and BA will be compared.
In the conventional system as shown in Fig. 2 all of the
forces acting on the pistons are non-equilibrium forces, so that
on the bearing part there acts a force corresponding to the vector
PA with the very same magnitude, as radial load. Accordingly,
in the system of Fig. 1, the frictional force is diminished at
the rate of: `
AB / PA = sin ~.
So far as the operational rotation angle of the system of Fig. 1
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is 90, the value of ~ is limited, that is, the value of ~ is
restricted within the range of:
0 < ~ < 45.
It is desirable for diminishing the non-equilibrium force that
~ is of a value which is as near to zero as possible within this
range.
One feature of the fundamental structure according to
the present invention is that the direction of the non-equilibrium
force is different from that of conventional structure. In the
example of conventional structure as shown in Fig. 2, only force
of direction which is perpendicular to the piston surface acts,
and the piston rod is required to have a enough rigidity to
transmit the whole of the force of this direction to the output
shaft substantially almost without producing any distortion.
According to the present invention, the non-equilibrium force
acts transversely of the piston 2 with the angle ~. Thus, the
arrangements are so made that the major part of the non-equilibrium
force is allotted to the piston 2 itself, while on the piston rod
3 there acts a very slight extra force other than the rotating
couple with itself producing the rotation output. This feature
is the reason why the piston rod 3 of the present invention is
formed into a perfect ring, and this contributes greatly to
- diminishing the diameter of the piston rod itself.
Now, a detailed description of the present invention -
will be made herebelow with reference to Figs. 3 to 7 which show
a practical embodiment.
Fig. 3 is a sectional view of the arrangement of two
pistons 2, a piston rod 3 and partition walls 6. Around a centra-
lly positioned output shaft 4 there is arranged a toroidal cylinder
tube 1, of which the cavity is divided by three partition walls 6,
fixed thereto. The middle partition wall 6 is positioned on the
central transverse line of the figure. At an angle of 180 with
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respect to this middle partition wall 6 and similarly on the
central transverse line there is arranged a piston rod mounting
stay 5, which is fixed by a key 7 to the output shaft 4 and can
swing by the angle 90 between the two partition walls 6, 6
positioned above and below it. The end portions of the piston
rod 3 opposite and straddling the stay 5 have a spacing wide
enough to accept the piston 2 and the partition wall 6. The
piston rod 3 passes through the two pistons 2, 2 and the three
partition walls 6, 6, 6 and then is fixed to the stay 5 through
a piston rod mounting member 8. Two mounting pins 9, 9 fix the
piston rod 3 to the mounting member 8. The two pistons 2, 2 are
each fixed to the piston rod 3 through a respective pair of
mounting plates 10, 10. The piston rod 3 is provided at the
positions accepting the mounting plates 10 with grooves engaging
the mounting plates 10. The pistons 2 are fixed to the rod 3
using the mounting plates 10 to engage the rod 3 with each of
the pistons 2 positioned between corresponding two mounting plates
10, 10. The partition walls 6, are fixed to the shown positions
with bolts 15 shown in broken lines.
In the illustrated embodiment the cylinder tube con-
sists of two parts which are assembled by a number of bolts 16,
16, ...... to keep them air-tight. The sealing at the pistons
2 is assured by O-rings 11 of small diameter and o-rings 13 of
large diameter, while the sealing of the partition walls 6 is
similarly assured by O-rings 12 of small diameter and o-rings 14
of large diameter. The small-diameter O-rings 11 of the pistons
2 and the large diameter O-rings 14 of the partition walls 6
have no sliding-con~act at the air-tight surfaces, so that for
them are employed O-rings of rubber material of excellent resil-
ience. On the other hand, for the large-diameter O-rings 13 of
the pistons 2 and the small-diameter O-rings 12 of the partition
walls 6 there are employed O-rings of fluorine resin material of
, . ' ' . . ........................ ,., ,, : . ~ . , : ~ -- . . : - - . '- . ': ' '. ' ~'' ''
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1(~47W7
excellent friction-wear characteristic.
Figs. 4 and 5 show the vertically positioned members
and structure of the mechanism shown in Fig. 3. The cylinder
tube 1 is provided at the central part thereof with bearing parts
22, 22 positioned above and below, supporting the output shaft 4
and provided with bushings 21. The upper and lower end portions
of the output shaft 4 are formed into square sections for conn-
ection with driven shafts. As shown in Fig. 4, at the upper and
outer portion of the cylinder tube 1 there are provided a plurality
of mounting screw holes 17, 17 for mounting the entire actuator.
On the lower side of the cylinder tube 1 there are provided fluid
inlet and outlets 18 on the both sides of the parkition wall 6
for letting fluid in and out of the working chambers within the
tube 1. To the lower end portion of the output shaft 4 is fixed
; a tongue 19 for fine adjustment of the angle of swing (acting
rotation angle) of the output shaft 4. A flange 20 surrounds
the range of swing of the tongue 19, as shown in detail in Fig. 6.
As shown in Figs. 3 and 4, the piston rod mounting
member 8 engages the groove of the stay 5 and is further fixed to
; 20 the stay 5 by means of bolts 23. As shown in Fig. 5, which showsa section in the neighborhood of the piston 2, the mounting plates
are provided with parallel sided recesses 24 which engage the
grooves of the piston rod 3.
Fig. 6 shows the lower side of the system shown in ~ -
; Fig. 4. The fluid inlet and outlets 18 are provided at four
positions which are near the partition walls 6, 6, 6 of the four
operating chambers. The flange 20 surrounding the tongue 19 is
bent at the end portions thereof toward the center of the output
shaft 4. These bent portions are provided with threaded holes
25, 25 into which are screwed slotted fixing screws 26, 26 which ~
abut the tongue 19 fixed to the output shaft 4 at the end of the ~`
range of the rotary movement of the tongue 19 so as to limit the
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operating angle of the output shaft 4. The positions of the
screws 26 once set are maintained by lock nuts 27.
The actuator according to the present invention of the
above mentioned structure operates in substantially the same
manner as other actuators. It will be readily understood that
into every other ones, namely the opposed pairs, of the four
operating chambers is alternately introduced high pressure fluid
through the fluid inlet-outlets 18 so that the output shaft 4
makes swinging movement to provide the desired acting rotation
angle.
The piston rod 3 is almost completely ring-shaped and
passes through all of the three partition walls 6, 6, 6, so that
the effective working area of the four chambers are equal to
each other. As explained with respect to Fig. 1, through appro-
priate arrangement of the two pistons 2, 2 there is obtained a
smooth rotating movement of good efficiency while power loss due -
to friction is kept low. The frictional force due to the non-
equilibrium force acts in large part on the piston 2 so that very
small non-equilibrium force is left on the piston rod 3. Thus
it can be considered that almost only the rotating couple acts
on the rod 3. Accordingly, the substantially complete annulus
of the piston rod 3 is advantageous for enabling the diameter
of the piston rod 3 to be smaller and increasing the effective
sectional area of the working chambers.
In the illustrated embodiment, the partition walls 6
are fixed only to the outer wall portion of the cylinder tube 1
by means of bolts lS. On these partition walls 6 act in addition
to shearing forces, bending moments with bending centers at the
outer end portions fixed by the bolts 15. Now, the land portions
of both end portions holding the large-diameter o-ring 14 have a
thickneæs constituting the whole of the partition wall. The land
portions are in close contact with the inner wall surface of the
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1~4788~
cylinder tube 1, so that excessive deformation due to a bending
moment is prevented by the wedging action at the land portions
in the tube walls. Accordingly, the main design consideration
relating to the fixing of the partition walls 6 by means of bolts
15 is the shearing forces.
The mounting plates 10 for fixing the pistons 2 to the
piston rod 3 hold the piston 2 between them and are securely
fixed by means of four bolts 28. This increases the mechanical
rigidity of the piston itself. Through such structure, the two
mounting plates 10, 10 fix the pistons 2 to the rod 3 in such
a manner that they do not affect the angle ~.
As mentioned in the explanation of Fig. 1, it is
advantageous for diminishing frictional force and improving
reliability that the two pistons 2, 2 are arranged as nearly on
a straight line as possible. The design factors limiting this
condition are the thicknessess of the stay 5, the partition wall 6
; and the piston 2. Practically, in the limit condition, the angle
9 is:
~ = [ 1 (thickness of the stay + thickness of one piston)
+ (thickness of one partition wall)]
In the illustrated example, the angle ~ is approximately 26.
Since sin 26`-, 0.438 and tan 26 -Ø488, the relative ratios of
; aforementioned PA, PB and AB are:
AB / PA = 0.438, AB / PB = 0.488.
Now, a comparison will be made between the actuator of
the example of the present invention and the conventional actuator
of Fig. 2: Assuming the frictional condition of the both actuators
to be the same, the actuator of the present invention causes the
frictional force to be diminished by as much as 54%, and further
gives excellent result with respect to reliability. In the
illustrated example, air is utilized as the pressure medium.
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This embodiment of the present invention confirms that, so long
as the fluid pressure is within an appropriate range, actuators
having toroidal cylinder tubes of this kind, which have been
hardly used before, can be put into practical use with sufficient
reliability.
While the present invention has been described with
reference to a single illustrated example, the technical scope of
the present invention is not restricted to the illustrated example:
The configuration of the radial section of the toroidal cylinder
tube 1 need not necessarily be circular, but may be oval, ellipt-
ical, rectangular, triangular, etc. The piston rod mounting stay
may be so formed as to surround the cylinder tube 1 and fix the
rod from the outer periphery side of the tube. The partition walls
positioned at both ends may be so formed as to close both end ;~
openings of the cylinder tube from outside. Also, the partition
walls may be fitted in annular grooves formed in the cylinder
tube. The cylinder tube may be integrally formed by means of
die casting, etc. For rationalizing the connecting part between
the piston and the rod, this part may be integrally formed by
means of die casting, etc. The illustrated output shaft may be
made a fixed shaft and the ring-shaped cylinder tube may be arr-
anged to be rotated. In this case, the cylinder tube may be
provided with a knob or a handle. This will facilitate manual ~ -
operation ln an emergency.
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