CA1047887A - Actuator having ring-shaped cylinder tube - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
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.

Description

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 .. ~. ~ , . . . .

~047~7 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 ., , 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.

10478~7 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 "

, . . . . .

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 - - ,, .', , ' : ` ` ~ : ,~
.

~047~87 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 '' ':

11)47887 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 , . ' ' . . ........................ ,., ,, : . ~ . , : ~ -- . . : - - . '- . ': ' '. ' ~'' '' :

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 :

, :; ~-.. . . . .

~)47~87 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 - ` , : - .

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.

1~)47887 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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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A rotary actuator comprising a shaft, a completely ring-shaped 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, wherein, when said piston rod mounting stay and a middle partition wall are in a straight line with one another in a plane perpendicular to the shaft, the angle formed, between a straight line passing through the center of said output shaft and perpendicular to the middle partition and each of the two pistons, is within a range between 0° and 45°.

2. An actuator according to Claim 1, wherein arrangement of the piston rod mounting stay, the partition walls and the pistons is such that said angles formed by the pistons are as close to 0° as possible.

3. An actuator according to Claim 1, wherein the piston rod is in the form of a split annulus and passes through all the partitions.

4. An actuator according to Claim 1, 2 or 3, wherein the said shaft is a fixed shaft, the pressure of the pressure medium acting to rotate the cylinder tube.

5. An actuator according to Claim 1, wherein said cylinder tube is provided with a handle for manual operation.

6. An actuator according to Claim 1, wherein said piston passes also through the middle partition wall.

7. An actuator according to Claim 1, wherein said piston rod is provided with grooves for engagement with mounting plates for fixing the pistons, each pair of mounting plates engaging the grooves of the piston rod to hold a piston therebetween.