[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.
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.