(19)
(11) EP 0 386 598 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
12.09.1990 Bulletin 1990/37

(21) Application number: 90103845.5

(22) Date of filing: 28.02.1990
(51) International Patent Classification (IPC)5F15B 15/08
(84) Designated Contracting States:
CH DE ES FR GB LI NL SE

(30) Priority: 06.03.1989 IT 1966289

(71) Applicant: UNIVER S.p.A.
I-20128 Milano (IT)

(72) Inventor:
  • Migliori, Luciano
    I-20090 Segrate, Milano (IT)

(74) Representative: Petruzzelli, Antonio European Patent Attorney 
C.so Italia, No. 43
20122 Milano
20122 Milano (IT)


(56) References cited: : 
   
       


    (54) Fluid operated rotary actuator


    (57) A rotary actuator operated by a pressure fluid; the actuator comprises an annular chamber (11) in which a piston member (12) reciprocates, said piston member (12) being operatively connected to an external power-­transmission member (17) through an annular slit (21) provided with a flexible sealing strip (25). The power transmission member (17) is rotatably supported coaxially to the annular chamber (11) and is loosely connected to the piston member (12).




    Description


    [0001] This invention relates to a rotary actuator, operated by a pressure fluid, in particular compressed air, and concerns more exactly an actuating cylinder of circular shape that can provide a driving torque.

    [0002] From "Fluid Power Handbook & Directory", 1986/87, many rotary actuators are known. Most of these actuators comprise one or two linear cylinders having opposing pistons whose linear movement is converted into the rotary movement of an output shaft by means of a helical system, linking systems, racks, or drive chains operatively connected to the cylinder piston or pistons. These actuators are complex and bulky in design. In addition, they are appreciably limited in terms of angular speed and of output torque values. Furthermore, there are considerable frictional forces between the moving parts and in certain cases this reduces the actuator efficiency to as little as 30%.

    [0003] From the same publication use is also known of rotary actuators comprising a revolving rotor in a cylindrical chamber, comprising one or two fins oppositely disposed in respect to a central output shaft. A narrow seal must be provided both along the outside edges of the fins, which come into contact with the cylindrical wall of the chamber, and in correspondence with the central output shaft. This second type of actuator has very low rotational speed in order to avoid the rapid deterioration of the sealing arising from any excessive pressure or speed. Moreover, the power and torque transmitted are relatively modest, or can be increased only by increasing the bulk and size of the actuator. With most of these actuators, too, it is essential to prevent axial thrust of the load or decentralised thrust. Such thrust could give rise to excessive friction on moving parts and especially on the sealing.

    [0004] From EP-A-O 147 803 rodless pneumatic cylinders are also known. These comprise a linear chamber containing a reciprocating piston which is rigidly connected to an external power-transmission member through a longitudinal slit in the cylinder chamber, said slit being normally sealingly closed by a flexible strip inside the chamber. This type off cylinder can only provide linear movement and has never been recommended or considered suitable for use as a rotary actuator because of the difficulties in adapting its structure to a circular shape which was sufficiently leak-proof for the fluid and which could guarantee an output torque that did not negatively affect the drive piston. Indeed, with regard both to the position of the slit and matching seal and to the type of connection between piston and external power-­transmission member, specialists were drawn towards other, strictly traditional solutions.

    [0005] According to this invention it has instead been discovered that by appropriately shaping the cylinder chamber, by suitably positioning the lateral slit and its closing seal, or by suitably designing the mechanical connection between the internal piston and the external power-transmission member, it is possible to make use of the teachings of common linear cylinders to construct a completely new fluid operated rotary actuator quite unlike traditional rotary actuators.

    [0006] Accordingly, the object of this invention is to provide a fluid operated circular actuator in particular by compressed air, which applies the teachings of linear rodless cylinders, and by means of which it is possible to avoid the drawbacks of traditional circular actuators providing an actuator of comparatively reduced dimensions.

    [0007] Another object of this invention is to provide a rotary actuator, as defined, by means of which it is possible to appreciably reduce problems of wear even at high working speeds.

    [0008] A further object of this invention is to provide a rotary actuator, as described above, which, for the same size bulk can provide greater driving torque and power than that obtainable from known types of rotary actuators.

    [0009] These and other objects may be obtained with a rotary actuator design consistent with the main claim, the introductory part of which refers to traditionally known circular actuators.

    [0010] A number of embodiments of a rotary actuator according to the invention will be described in greater detail below with reference to the appended drawings in which:

    Fig. 1 is a transverse cross-section mainly through the diametrical plane 1-1 of figure 2;

    Fig. 2 is a section in a plane at right angles to the former, along the line 2-2 of figure 1;

    Figs. 3 and 4 are enlarged details in correspondence to the actuator member's piston;

    Fig. 5 is a view similar to that in figure 2 for a double-piston actuator.



    [0011] Reference will first be made to the drawings in figures 1 and 2 which show the general characteristics of the rotary actuator according to this invention.

    [0012] The actuator comprises a mainly circular body, indicated in its entirety by reference number 10, formed from two half-casings or shells 10a and 10b which together define an annular chamber 11 of circular cross-section or toroidal shape, inside which a piston 12 reciprocates, the external contours of said piston forming a fit with the toroidal contour of the actuator's chamber 11. Reference number 13 indicates a partition member inside the chamber 11 provided with appropriate peripheral seals 14. The partition member 13 is positioned in correspondence to passages 15 and 16 for the inlet and outlet of a pressure fluid, for example compressed air.

    [0013] The piston 12 is connected in the manner later described to an external power-transmission member 17 shown in figure 1 in the form of a cup-shaped element which covers the body 10 on one side and is connected to a hollow output shaft 18 from which rotary movement is derived. The shaft 18 is rotatably supported coaxially to the annular chamber 11 by means of suitable bearings or bushes 19 and 20 acting both in an axial as well as a radial sense. As shown in figure 1, the hub 26 has a conical end 26′ which extends into a conical seating in the half-casing 10b.

    [0014] The two half-casings 10a and 10b form a perfect join which is leak proof on the inside of the chamber 1 while, on the other hand, they provide a circular slit 21 along the most outward peripheral edges 21′ and 21˝ of the two half-casings through which a bracket or fork member 22 protrudes to connect the piston 12 with the external power-transmission member 17. The latter is fastened to the shaft 18 by, for example, a lock nut 23 and a screw 24 or in another effective manner.

    [0015] Inside the chamber 11 and along the entire circular slit 21 there is a sealing element 25 in the form of an annular flexible tape which is positioned against a cylindrical sealing surface inside a recess along the peripheral edges 21′ and 21˝ of the two half-casings 10a and 10b and is coaxial with the annular chamber so that the pressure of the fluid inside the chamber 11 sealingly forces the annular strip 25 against the edges of the slit 21.

    [0016] In particular, each of the actuator's half-casings 10a and 10b has an annular race concentrically arranged to the shaft 18, which delimits one side of the internal chamber 11 of the actuator; at the same time the half-­shell 10a has a hollow central hub 26 to support the hollow shaft 18 as well as an annular rib 27 on which may be fastened and adjusted, in the right position, at least one stopping or shock-absorbing element 28 which can be adjusted to the required angular position by sliding it along the rib 27 and clamping it, for example, by means of a pair of threaded dowels 29. The power-transmission element 17, in turn, has a projecting part 30 that strikes against the stopping or shock-absorbing element 28. In this way the amplitude of the angular oscillations of the power-­transmission member 17 - and therefore the piston stroke - can be controlled and adjusted, so preventing the latter from colliding against the partition wall 13 of the angular chamber 11.

    [0017] In the case of a single-piston actuator, the piston's stroke may be adjusted to within a broad angular range whose maximum value may be equal or over 280°, said maximum angle depending on the thickness of the partition wall 13 and the piston length 12. The piston 12, on its radially outer side facing the annular sealing, has a longitudinal internally slot 12a which, through the reciprocating movement of the piston allows the sealing strip 25 to be drawn away from the slit 21 in correspondence with the connecting bracket or fork 22 between the piston 12 and the external power-transmission member 17. Finally reference number 31 indicates the two lip-type annular gaskets at each end of the piston 12 which form a seal against the internal walls of the annular chamber 11.

    [0018] As previously stated, one of the characteristics of the rotary actuator according to this invention is the annular or toroidal shape of the chamber in which the piston slides as well as the external peripheral positioning, in a plane at right angles to the output shaft 18, of the slit 21 which is open to the passage of the connecting element 22 between the piston 12 and the external power-transmission member 17. In addition to allowing the sealing strip 25 to be appropriately located, this position of the slit 21 on the radially outer circumference of the annular chamber 11 also provides the maximum lever arm of the obtainable torque, given equal actuator outside dimensions, which therefore allow maximum torque values in excess of those of a traditional actuator, given equal power and outside dimensions. It is clear, however, that given the same power - leaving, that is, the cross-section of the annular chamber 11 basically unchanged - different torque values may be obtained through modifications to the annular chamber's diameter without in any way altering the design and operating principles. The actuator, for example, could be made with an annular chamber having a greater, or at least different average diameter from that shown - the term average diameter being understood here as the diameter of the circular central axis of the annular chamber.

    [0019] Figures 3 and 4 of the drawings show another characteristic of the rotary actuator according to the invention by virtue of which it is possible to eliminate all negative effects of thrust and movement discharged onto the piston and 12 and the external power-transmission member 17. This is attained by providing a loose connection - meaning that it can accomodate minor displacement in both senses of rotation between the piston 12 and the power-­transmission member 17 caused by clearances in correspondence to the connecting bracket. In the case shown the loose connection between the piston 12 and the member 17 is obtained by providing the latter with a rectangular opening 32 into which the folded or compressed end 22′ of the bracket or fork member 22 penetrates. The folded end 22′ of the connecting bracket is also surrounded, at least on two sides, by antifrictional pads 33 which reduce friction along the opposing edges 21′ and 21˝ of the slit 21. Accordingly, given that the folded portion 22′ of the bracket 22 is subject to possible oscillations and minor displacement, the stress acting on the external power-transmission member 17 can in no way affect the piston 12 and the sealing components. In this way the operating life of the actuator is greatly prolonged and performance is improved allowing fast drives and high torque values. At the same time the actuator dimensions are held to a minimum.

    [0020] As stated above, for equal power values it is possible to vary the torque by varying the dimensions of the actuator's chamber - for example, by varying the chamber's average diameter - without making any change to its transverse section. However, in figure 5 it is possible to vary both the torque and the power without altering the actuator's external dimensions. For this purpose use has been made in Figure 5 of two diametrically opposed pistons 12, fully identical to piston 12 in the example in Figure 1, similarly connected to the external power-transmission member 17. Use has also been made in the case of Figure 5 of two partition walls 13 spaced apart by an angle of 180°, so obtaining two semi-circular chambers 11a and 11b which, by means of internal passages are simultaneously charged and emptied, through inlet and outlet openings 15 and 16 for the pressure fluid. In all other respects the actuator in Figure 5 is similar to that in the preceding figures. Accordingly, similar or identical reference numbers have been used to identify the same or corresponding parts.


    Claims

    1. A fluid operated rotary actuator comprising a body (10) defining a chamber (11) including inlet and outlet openings (15, 16) for the fluid, as well as at least one reciprocating piston (12) in the chamber (11) operatively linked to an outer power-transmission member (17) through a slit (21) extending longitudinally to the chamber (11) and provided with sealing means in the form of a flexible sealing strip (25) positioned against the edges of said slit (21), characterised by the fact that said chamber (11) has an annular shape and comprises at least one partition wall member (13), the said piston (12) fitting with the annular shape of the chamber (11) and being loosely connected, through the circular slit peripherally arranged to the chamber (11), to a rotatable external power-transmission member (17) coaxially supported to the annular chamber (11).
     
    2. A rotary actuator as claimed in claim 1, characterised by the fact that the piston (12) is connected to the power-transmission member (17) through a bracket member (22) extending outwards through the slit (21) said bracket member (22) protruding into a seating in a wall portion of the power-transmission member (17).
     
    3. A rotary actuator as claimed in claim 1, characterised by the fact that said peripheral slit (21) is located in correspondence with the maximum external diameter of the annular chamber (11), and is provided with fluid-sealing means in the form of an annular strip of flexible material fitting against the internal edges of said slit (21).
     
    4. An actuator as claimed in claim 3, characterised by the fact that said flexible strip (25) is positioned to form a seal along a cylindrical surface coaxial to the actuator's chamber (11), and by the fact that the piston (12) has, on its side facing the slit, a longitudinal slot into which said annular sealing strip slide.
     
    5. A rotary actuator as claimed in claim 1, characterised by te fact that the power-transmission member (17) is connected to a power shaft (18) coaxial disposed to the annular chamber (11) of the actuator.
     
    6. A rotary actuator as claimed in claim 5, characterised by the fact that said shaft (18) is in the form of a hollow shaft.
     
    7. A rotary actuator as claimed in claim 1, characterised by the fact that said power-transmission member (17) is in the form of a cup-shaped member surrounding and covering on one side the body (10) of the actuator.
     
    8. A rotary actuator as claimed in claim 1, characterised by the fact that the actuator's body (10) has an outer annular rib (27) radially extending from said body, and at least one stop or shock-­absorbing element (28) adjustably fastened to said rib (27), and by the fact that the power-transmission member (17) has a projecting portion (30) striking said stop or shock-absorbing element (28).
     
    9. A rotary actuator as claimed in claim 1, characterised by the fact that said body (10) comprises first and second opposing half-casings (10a, 10b) in which each half-casing has an annular race defining one side of the actuators' chamber (11), at least one of the half-casings (10a, 10b) having a central hub (26) for supporting the power shaft (18) of the power-transmission member (17).
     
    10. A rotary actuator as claimed in claim 1, characterised by the fact that a bracket member (22) fixed to the piston (12) is provided to operatively connect the piston (12) to the power-transmission member (17), said bracket member (22) having a folded part extending through the peripheral slit (21) and loosely protruding into a seating (32) of a wall portion of the power-transmission member (17), said bracket member (22) additionally comprising antifriction pads sliding against the edges of the annular slit (21) of said chamber (11).
     
    11. A rotary actuator as claimed in any of the previous claims, characterised by the fact that it comprises a first and at least a second operating piston (12) diametrically opposed and operatively connected, to the external power-transmission member (17), there being also provided at least a first and second partition walls (13) dividing the chamber (11) into separate arch shaped chamber portions (11a, 11b), said chamber portions (11a, 11b) having inlet and outlet openings for the fluid.
     
    12. A rotary actuator as claimed in claim 1, characterised by the fact that said sealing strip (25) fits into an annular seating inside the chamber (11) and along said peripheral slit (21).
     
    13. A rotary actuator as claimed in claim 9, characterised by the fact that one end (26′) of said hub (26) in one of said half-casing (10a) extends into a seating in the other half-casing (10b).
     
    14. A rotary actuator as claimed in claim 13, characterised by the fact that said end (26′) of said hub (26) and said seating comprise conical mating surfaces.
     




    Drawing













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