EP0199556A1

EP0199556A1 - Pneumatic actuator

Info

Publication number: EP0199556A1
Application number: EP86302905A
Authority: EP
Inventors: Martinus Gerardus Cornelis Van Gastel; Brian Charles Tregenna
Original assignee: Colt International Ltd
Current assignee: Troldtekt Ltd
Priority date: 1985-04-20
Filing date: 1986-04-18
Publication date: 1986-10-29
Also published as: GB2174758B; GB8609551D0; GB8510352D0; GB2174758A

Abstract

@ A pneumatic actuator unit comprises a pair of in line, single acting pistons and cylinders (9,18,7,21) for performing two control functions in squence. The cylinders (7, 21) have a common head (15) with a single compressed air inlet (30), which serves also as an air exhaust outlet (30) during the spring return strokes of the pistons (9,18) and which is in communication with one of the cylinders (7) on the headside of its piston (9). The piston (9), at the completion of its outstroke under the action of compressed air supplied through the inlet (30), to perform one control function, uncovers a port (32) in a tubular spiggot (8) slidable in a bore in the piston (9) and its piston rod (5) to supply compressed air through the head (15) into the other cylinder (21) to outstroke its piston (18) and perform the second control function. A non-return valve (23, 25, 26) in the head (15) communicates the cylinder (21) with the exhaust outlet (31) during the return stroke of its piston (18). Cushioning air is exhausted through the outlet (30) from the cylinder (7) over the last portion of the return stroke of the piston (9) between piston rings (10, 12) on the piston (9) and the head (15) respectively, via a restriction (37) and an annular clearance gap between a piston (9) inner portion (34) and a bore (14) of the head (15).

Description

The present invention relates to pneumatic actuators.
Pneumatic actuators are conveniently employed for performing controlled functions in sequence. One example is the selective or automatic closing of a hinged flap, and the subsequent engagement of a catch for holding the flap closed. Thus a first pneumatic actuator may be operated to close the flap and a second pneumatic operator then operated to engage the catch.
In a particular example, the flap may be movable to open and close the ventilation opening of a fire ventilator in which case it is desirable to locate the pneumatic actuators in a position which does not obstruct the ventilation opening. Furthermore, for aesthetic reasons, it may be desirable to locate the pneumatic actuators in a confined space, for example within a hollow frame member of the ventilator defining the ventilation opening so that the actuators are hidden from view.
The object of the present invention is to provide a pneumatic actuator unit for performing two controlled functions in a predetermined sequence, the unit being compact and having a single compressed airline connection.
According to the present invention such a unit comprises a pair of pneumatic pistons and cylinders of which the cylinders have a common head having a single compressed air inlet which serves also as an exhaust outlet in communication with one of the cylinders on one side of the piston therein, said piston in said one of said cylinders, after performing a predetermined movement in said one of said cylinders under the action of compressed air supplied through said inlet, uncovering a port for the supply of compressed air from said one of said cylinders on said one side of the piston therein to the other of said cylinders on one side of the piston therein for displacing the piston in said other of said cylinders, there being a non-return valve in said head for communicating said other of said cylinders on said one side of the piston therein with said exhaust outlet for exhausting air from said other of said cylinders on said one side of the piston therein.
A specific embodiment of the present invention will now be described by way of example and not by way of limitation with reference to the accompanying drawing which is a cross sectional elevation of an pneumatic actuator unit in accordance with the present invention.
With reference to the accompanying drawing, the actuator unit comprises a pair of in line cylinders 7 and 21 having respective outer end plugs 3 and 27 forming the cylinder outer.end walls and defining bores 4 in the cylinder outer end walls for the piston rods 5 and 20 of pistons 9 and 18 associated with the cylinders 7 and 21 respectively, the cylinders having a common head 15 disposed between them having a single compressed air inlet 30 which serves also as an exhaust outlet through which air under pressure may be supplied to or air exhausted from the unit under the control of a conventional two way valve (not shown).
A non-return valve 23, 25, 26 is housed in an enlarged end portion 23 of a bore 31 in the head 15 which communicates with the compressed air inlet and exhaust air outlet 30 and the cylinder 7 space on the inside of the piston 9 that is to say, the side adjacent the head 15.
The head carries a central tubular spiggot 8 which aligns with the common axis of the cylinders 7 and 21 and which slides in a bore in the piston 9 and its piston rod 5. The spiggot 8 has slot-like ports 32 at its outer end which admit compressed air from the cylinder 7 space on the inside of the piston 9 to the cylinder 21 space on the inside of the piston 18 via the hollow interior of the sriggot 8 when the piston 9 uncovers the ports 32 at the end of its outstroke.
The piston 9 has a reduced diameter inner portion 34 which enters a bore 14 of the head 15 which communicates in turn with the bore 31. A pair of piston ring seals 10 and 12 are carried respectively by the piston 9 and in the wall of the bore 14 of the head 15 to entrap between them cushioning air over a last portion of the instroke of the piston 9 the cushioning air exhausting through bores 36, 37 of the head, along the clearance between the portion 34 of the piston 9 and the wall of the bore 14 and the bore 31 to reach the exhaust outlet 30. A screw plug 13 adjusts the restriction in the bore 37.
The piston 9 has a frusto-conical outer end portion to enter a foreshortened return spring 6 which is mounted on, and centered by,a boss of the outer end plug 27, the return spring 6 being compressed between the plug 27 and the piston 9 proper on the full outstroke of the piston 9.
The piston 18 has a conventional return spring 19.
Air bleed holes 1 in the cylinder end plugs 3 and 27 allow the flow of air into and out of the outside cylinder spaces on stroking of the pistons.
Screw threaded mounting holes seen in the head 15 are used to mount the unit.. One such further mounting hole may be provided in the end plug 27 and is seen in the drawing.
The operation of the unit will now be described by way of further example and not by way of limitation with reference to the opening and closing of a fire ventilator flap and the movement of a catch to retain the flap in its closed position and thereafter to release the catch to allow the flap to be opened.
The unit is mounted within a side frame member of the ventilator defining the opening controlled by the flap, the flap being hinged for opening and closing movement along its lower edge and having a substantially vertical closed position.
Extension of the piston 9 and the piston rod 5 under the action of air under pressure supplied through the compressed air inlet 30 moves a slide block (not shovm) which pivots a flap stay hinged to the flap and to the slide block to move the flap from its open to its closed position. Towards the end of the outstroke of the piston 9 the piston uncovers the ports 32 and air under pressure is supplied to the inside of the piston 18 to extend the piston rod 20 thereby rotating the catch to lock the flap closed.
When the control valve supplying compressed air to the inlet 30 is adjusted to connect the inlet with atmosphere, the inlet 30 then serving as an exhaust outlet, air is exhausted from the inside of the piston 18 through the non-return valve 23, 25, 26 and the spring 19 returns the piston 18 through its instroke and the catch is rotated to release the flap. The piston 9 is accelerated by the spring 6 through an initial portion of its instroke to force the flap open and the resulting gravitational opening movement of the flap is finally arrested by the act on of the cushioning air bled through the re -iction at 37 to the exhaust outlet 30.
The two-position control valve supplying compressed air to the inlet 30 will be placed at a convenient remote location.
The ventilator just described may be as described in detail in GB-85 14571 or EP-A-85 304499.8 with reference to Fig. 22 of its specification, the piston rod 5 of the pneumatic unit described herein and forming the unit 175 in the specifications referred to being connected to operate the slider 172 and the piston rod 20 of the pneumatic unit described herein being connected to operate the latch hook 173 in the specifications referred to.

Claims

1. A pneumatic actuator unit comprising a pair of pneumatic pistons and cylinders of which the cylinders have a common head having a single compressed air inlet which serves also as an exhaust outlet in communication with one of the cylinders on one side of the piston therein, said piston in said one of said cylinders, after performing a predetermined movement in said one of said cylinders under the action of compressed air supplied through said inlet, uncovering a port for the supply of compressed air from said one of said cylinders on said one side of the piston therein to the other of said cylinders on one side of the piston therein for displacing the piston in said other of said cylinders, there being a non-return valve in said head for communicating said other of said cylinders on said one side of the piston therein with said exhaust outlet for exhausting air from said other of said cylinders on said one side of the piston therein.

2. A pneumatic unit as claimed in claim 1 in which said pneumatic pistons and cylinders are in line.

3. A pneumatic unit as claimed in claim 2 in which the head carries a tubular spiggot which aligns with the common axis of the cylinders and which slides in a bore in said piston in said one of said . cylinders, said port being formed at the outer end of said spiggot and opening into the hollow interior of the spiggot to communicate said one of said cylinders on said one side of the piston therein with the other of said cylinders on said one side of the piston therein.

4. A pneumatic unit as claimed in claim 2 in which said port is formed as an open-ended slot in the wall of the spiggot.

5. A pneumatic unit as claimed in any preceding claim in which said piston in said one of said cylinders has a reduced diameter inner portion to enter a bore of the head over a terminal portion of its instroke thereby to entrap cushioning air at the inner end of said one of said cylinders, the cushioning air exhausting through exhaust bores of the head and said exhaust outlet.

6. A pneumatic unit as claimed in claim 5 in which said exhaust bores of said head include the bore which receives the reduced diameter inner portion of said piston in said one of said cylinders, the cushioning air exhausting along the clearance between the reduced diameter inner portion of the piston and that bore.

7. A pneumatic unit as claimed in claim 5 or 6 in which said exhaust _Dores include an adjustable restriction.

8. A ventilator comprising a frame, a flap hinged to the frame along its lower edge and movable to open and close a ventilation opening defined by the frame, the flap having a substantially vertical closed position closing said opening, a releasable catch engageable with the flap to retain the flap in its closed position and a pneumatic unit as claimed in any preceding claim carried by the frame and operable by compressed air supplied to said single compressed air inlet to close the flap and then engage said catch.

9. A ventilator as claimed in claim 8 in which said pneumatic unit is a unit as claimed in claim 5 and said piston in said one of said cylinders has a foreshortened return spring, housed in the outer end of said one of said cylinders, and operable to move the flap from its closed position towards its open position during its initial opening movement, the flap being moved to its fully open position by gravitational action and being arrested in its final opening movement by the action of cushioning air exhausted through said exhaust outlet.

10. A ventilator as claimed in claim 8 or 9 including a two position control valve for supplying compressed air to said inlet and for connecting said inlet with atmosphere respectively.