This invention relates to an actuation means for sequential
control of a plurality of fluid supply valves. Prior art actuation means according
to the preamble of claim 1 are known for instance from
Sequential control of fluid supply valves may be required
in a number of situations. One is where compressed air or vacuum is supplied to
a number of inflatable cuffs, typically four, providing varying pressure on a wound.
Only one cuff changes state at any one time, and there is normally a predetermined
sequence of inflation and deflation of the cuffs. Each cuff is supplied from a manifold,
connected to compressed air or vacuum, under the control of its own fluid supply
valve, which remains open until the state of the cuff is to be changed. In this
situation, it is advantageous to provide operation of the valves in a simple and
inexpensive way, without requiring too much power, and with the actuation means
being as small as possible. Given these constraints, it is not feasible to provide
an individual actuator for each valve, as this will make the actuation means too
large, and relatively complex to control.
According to a first aspect of the present invention, an
actuation means for sequential control of a plurality of fluid supply valves for
controlling fluid flow between a fluid supply and a port comprises a reciprocable
linear actuator operative to control all the valves through a rotary drive means,
a transmission means and a cam means acting on the valves, the cam means being rotated
by the drive means which translates movement of the linear actuator into rotary
movement, and the transmission means being arranged between the drive means and
the cam means such that the cam means is rotated by the drive means for one direction
of movement of the linear actuator, but is not rotated for the other direction of
movement of the linear actuator.
Thus, actuation of the linear actuator in one direction
rotates the cam means to operate a first valve, which then remains operated when
the linear actuator moves in the other direction to return to its original position.
Another actuation rotates the cam means to return the first valve to its original
position and to operate another valve, and so on. A single actuator can therefore
operate all the valves, so that the actuation means can be kept small. The control
of the actuator is simple, as any valve can be operated by a given number of actuations
of the linear actuator. Further, because the valves remain operated when the actuator
returns, no power is required to keep the valves open.
Preferably, the linear actuator comprises a solenoid acting
on a non-rotatable member, against the action of a return spring. This keeps the
power requirement to a minimum, as a pulse of current is all that is required to
actuate the solenoid, which is then returned to its original position by the spring.
Alternatively, the linear actuator may comprise a fluid-pressure operated piston
acting on a non-rotatable member.
In either case the non-rotatable member has a helical engagement
with the drive means, which is free to rotate. The helical engagement is preferably
a screw thread. The drive means conveniently comprises a drive ring mounted externally
on the non-rotatable member.
The transmission means may comprise a frictional engagement
between the drive means and the cam means, which transmits rotary movement in one
direction but not the other. Alternatively, the transmission means may comprise
a toothed engagement such as ratchet teeth, which transmits rotary movement in one
direction but allows the teeth to ride over each other in the other direction. Conveniently,
movement is transmitted on the actuation stroke of the linear actuator rather than
the return stroke.
The cam means may be a cylindrical member having an actuating
cam for operating each valve. It may also have a neutral position, in which none
of the valves are actuated. The actuating cams preferably comprise radial projections
spaced round the cylindrical member.
Each fluid supply valve preferably comprises a spring-loaded
ball valve, which is normally closed to prevent fluid flow to or from the port,
and which is opened by movement of a pin operated by the cam.
According to a second aspect of the invention, we provide
a series of inflatable cuffs for providing pressure on a wound dressing, a supply
of fluid, valve means controlling inflation of the cuffs and an actuation means
in accordance with the first aspect of the invention.
According to a third aspect of the invention, we provide
a valve assembly for controlling fluid flow between a fluid supply and a plurality
of ports the assembly comprising a fluid supply valve for each port and an actuation
means in accordance with the first aspect of the invention for sequential control
of the valves to control fluid flow between the fluid supply and each port.
An embodiment of the actuation means is illustrated in
the accompanying drawings, in which:
- is a plan view of an actuation means; and
- is a longitudinal section along the line 2-2 of Figure 1.
The figures show a device for sequential control of a plurality
of fluid supply valves 1. Each valve 1 controls the supply of compressed air or
vacuum from a manifold 2 to a respective port 3. Each port 3 is connected to an
inflatable cuff (not shown) providing pressure on a wound dressing. The cuffs are
inflated or deflated sequentially, so that the state of no more than one cuff is
changing at any given time. The device has actuation means 4 controlling operation
of the valves 1, comprising a linear actuator 5, rotary drive means 6, drive transmission
means 7 and cam means 8 which operates the valves 1.
The device comprises a housing body 9 closed by an end
cap 10. The actuation means 4 is accommodated in a longitudinal bore 11, comprising
a stepped main bore 12 in the housing body 9 and a blind bore 13 in the end cap
10. The housing body 9 also has a set of stepped bores 14, perpendicular to and
opening into the main bore 12. Each bore 14 houses a valve 1, to be described in
more detail later.
The linear actuator 5 of the actuator means 4 comprises
a solenoid-operated plunger 15. The plunger 15 is cylindrical, but has a square
end 16 received in the bore 13 in the end cap 10, so that it is non-rotatable. The
plunger 15 has a blind bore 17 opening away from the end cap 10, in which is fixed
the armature 18 of the solenoid 19. The solenoid coil 20 is provided outside the
housing body 9. The plunger 15 is biased towards the end cap 10 by a spring 21 acting
between the plunger and a shoulder 22 at the opposite end of the housing body 9.
Externally, the cylindrical part of the plunger 15 has a helical screw-thread formation,
which co-operates with a complementary internal screw-thread on the drive means
The drive means 6 comprises a stepped ring 23 accommodated
in a larger diameter portion of the bore 12. Linear movement of the plunger 15 in
either direction rotates the drive ring 23 correspondingly, by a given angular amount,
determined by the amount of the linear movement provided, and the helix angle of
the screw-thread formation.
The drive ring 23 co-operates with the cam means 8 for
operating the valves 1. The cam means 8 comprises a stepped cylindrical barrel 24
located round the spring 21. The barrel 24 has a radial cam projection 25 for operating
each valve 1. Only one projection 25 is shown, as the others are spaced round the
barrel 24 at appropriate axial locations to operate the valves.
The barrel 24 has an enlarged end 26 co-operating with
the drive ring 23 through the drive transmission means 7, which is not shown in
detail. The drive transmission means 7 comprises a toothed arrangement provided
on complementary radial surfaces of the drive ring 23 and the end 26, and arranged
so that rotary drive is transmitted from the drive ring 23 to the cam barrel 24
in one direction of rotation, but not the other. The drive transmission means therefore
operates like a one-way clutch, and may be a ratchet-type toothed arrangement, with
the teeth engaging to provide drive for one direction of rotation, but sliding over
each other in the other direction of rotation. A clearance 27 is provided between
the drive ring 23 and the end cap 10 to allow the teeth to separate. The drive ring
23 therefore has a limited amount of linear movement as well as rotary movement.
Thus, each actuation of the linear actuator 5 rotates the
cam barrel 24 by the predetermined amount. The cam projections 25 will be arranged
so that the cam barrel 24 has four positions in which only one valve 1 is operated,
and a neutral position in which none of the valves 1 is operated. The angular rotation
of the cam barrel 24 for each actuation is therefore 72°.
Each cam projection 25 acts on a valve actuation pin 28
working in a respective bore 14, to operate the corresponding valve 1.
Each valve 1 comprises a ball valve member 30 co-operating
with a seat 31 formed at an inclined part of the bore 14. A spring 32 acts on the
ball valve member 30 to bias it closed. The valve is opened by the actuation pin
28 lifting the ball 30 off the seat 31. When a valve 1 is open it allows fluid flow
between the manifold 2 and the port 3. The manifold 2 may be connected, through
a control valve (not shown), to a source of compressed air, a vacuum source, or
to atmosphere. This allows inflation or deflation of the cuff controlled by the
Thus, for operation, we assume that the cam barrel is in
its neutral position, with no valves open. The manifold 2 is connected appropriately
to the source of compressed air, vacuum or atmosphere. Current is supplied to the
solenoid coil 20 as a short pulse. Operation of the solenoid pulls the armature
18 and the plunger 15 outwardly, which in turn pulls the drive ring 23 into engagement
with the cam barrel 24. Movement of the plunger 15 also rotates the drive ring 23
and the cam barrel 24 by the given angular amount, as the drive is transmitted to
the cam barrel 24 in this direction of movement. Rotation of the cam barrel 24 brings
a cam projection 25 into engagement with an actuator pin 28 to open a valve 1 to
allow fluid flow to or from the cuff via the port 3.
When the current ceases, the spring 21 returns the plunger
15 and the drive ring 23 to their original position. The clearance 27 ensures that
the transmission means 7 disengages, so that the cam barrel 24 does not move. The
actuated valve 1 therefore remains open until the next actuation of the solenoid,
when that valve will close and another will open (unless the neutral position is
required). The device will therefore operate to provide the required pressure at
the ports 3, and is very simple in construction and operation, as it is only necessary
to provide short pulses of current to the solenoid. Actuation of any given valve
1 can be ensured by an appropriate number of current pulses to the solenoid.
It will be appreciated that the linear actuator 5 could
be operated by a piston rather than the solenoid. Similarly, it will be appreciated
that the drive transmission means 7 could be modified, and may simply rely on friction
rather than a toothed engagement. For example, a friction drive may be in the form
of self-releasing tapers on the complementary radial surfaces of the ring 23 and
It would also be possible for the rotation of the cam barrel
24 to occur on the return stroke of the linear actuator 5 rather than the actuation
The device can readily be modified to accommodate more
or fewer valves. The valves may also be of a different type.
Furthermore, it will be appreciated that the actuator/solenoid
may be located either wholly or partially inside or parallel to the cam barrel to
reduce the overall length of the actuator means if desired.