SUBSEA ELECTRIC ACTUATORSAND LATCHES FOR THEM
Introduction
The technical development described in this application for a patent principally
concerns electric actuators which are primarily intended for use in subsea
installations such as process control systems.
Such actuators are used t o control various devices, and particularly but not
exclusively t o open and close valves which themselves control the flow of fluids
such as fluid hydrocarbons.
Summary of the state of the art
EP-0984133 discloses an actuation module in which a motor drives a rotatable
socket which rotates and thereby advances and retracts a drive screw. The motor
is provided with a self-contained secondary power source.
WO2002/039203 and US2006/0048602 disclose an actuator in which a drive
shaft is connected t o a rotating sleeve connected t o a fixed ball nut which
displaces axially a rotating spindle coupled to an actuating stem by a spindle
head.
NO2000/02528 and US6595487 disclose an actuator in which either of two
motors with respective storage batteries can drive by way of a reduction
gearbox an axially fixed nut which drives a valve spindle.
WO2007/027097 discloses an actuator wherein the spindle of a motor directly
drives a nut which is connected t o a valve spindle by an auxiliary frame which
can be used t o retract the valve spindle when the nut is decoupled from the
valve spindle.
Background
Two important requirements of an electric actuator intended for use in a subsea
installation are to minimise the power required for operation and to allow the
actuator to be put into a predetermined state (typically one which closes a
respective valve) on the occurrence of partial or complete failure of the electrical
supply to a motor which drives the actuator. These two requirements may well
be in conflict. More particularly, it is currently considered desirable t o provide a
return spring which is disposed to act t o return the actuator to a datum state. A
drive system which has to work against the force of the return spring consumes
power unnecessarily and it is one object of the electric actuator to include the
safety feature of a return (or 'fail-safe') spring and to allow normal working of
the motor or motors for the actuator free from the action of the return spring.
Summary of the claimed inventions
In one aspect of the technical development a subsea electric actuator comprises
an electric motor, a telescopic drive connection from the motor t o a drive unit
which can be moved to and fro and converts rotary motion of the connection to
linear motion of an operating member, a return spring operable on the drive unit
to urge the operating member towards a datum state and a latch, which is
operative when set to maintain the drive unit in a predetermined position so as
t o decouple the action of the return spring on the operating member, whereby
the stem can be advanced and retracted relative t o the drive unit free from the
action of the return spring, and is operative on release to allow the return spring
to operate on the drive unit t o return the operating member t o the datum state.
Whether a return spring is employed or not, it is desirable to provide a
construction which allows working of the actuator by a motor or either one of
two motors or possibly any one of more than two motors in a manner which
allows the movement of the actuator, for example either by a spring or by ROV
intervention, t o a datum state without decoupling of the drive system.
In another aspect of the technical development therefore a subsea electric
actuator comprises an electric motor, a telescopic drive connection between the
motor and a drive unit which can move to and fro and includes a drive nut which
couples rotary motion of the drive connection to a screw which is disposed for
axial movement without rotation and is connected to an operating member.
As will be apparent from further explanation herein, practical embodiments of
the electric actuator include a latch which is operative to decouple the action of
a return spring on the actuator and is operative on the absence of electrical
supply to the latch t o release the action of the return spring. Various
embodiments of such latches are described herein. However, at least some of
the latches have a utility independent of the specific purpose of latching a return
spring.
The technical development further provides various latches for maintaining a
unit (such as a drive unit as aforesaid) in a predetermined position so as to
prevent movement of that unit away from that position in a given direction but
to allow such movement on release of the latch. These latches are defined in
respective independent claims.
There follows a description by way of example of a specific embodiment of an
electric actuator as well as embodiments of latches which may be used in such
an actuator or otherwise.
Introduction to the Drawings
Figure 1 is a schematic drawing of an electric actuator and associated
components.
Figure 2 is a schematic drawing of a system comprising an electrical supply and
control system and the actuator shown in Figure 1.
Figure 3 is a drawing which illustrates one embodiment of an electromagnetic
latch with adjacent parts of an actuator.
Figures 4 and 5 illustrate the latch shown in Figure 3 in a different phase of
operation.
Figure 6 is a schematic drawing which illustrates another embodiment of an
electromagnetic latch with adjacent parts of an actuator.
Figures 7 and 8 illustrate the latch shown in Figure 6 in various phases of
operation.
Figure 9 is another illustration of the latch shown in Figure 6.
Figure 10 is a schematic drawing which illustrates another embodiment of an
electromagnetic latch with adjacent parts of an actuator.
Figures 11 and 12 illustrate the latch shown in Figure 10 in various phases of
operation.
Figure 13 is another illustration of the latch shown in Figure 10.
Figure 14 is a schematic drawing which illustrates another embodiment of an
electromagnetic latch with adjacent parts of an actuator.
Figures 15 and 16 illustrate the latch of Figure 14 in various phases of operation.
Figure 17 is drawing which illustrates various details of the latch in Figure 14.
Figure 18 is a drawing showing a preferred form of the latch of Figure 14.
Detailed Description
Figure 1 is a schematic drawing of an electric actuator 1 in accordance with the
inventive concepts envisaged herein.
The actuator is intended for operation by either one of dual redundant electrical
devices which each comprise a storage battery, an electric motor and associated
electrical components. In Figure 1 the two devices are disposed within
respective enclosures 2 and 2a disposed at one end of an enclosure 3 for the
actuator. The enclosure 3 is in this example integral with a valve bonnet 4.
Extending through the enclosure 3 and protruding from each end is an operating
member 5 which for convenience will be termed hereinafter as the valve stem,
since the actuator's primary use is in the operation of a valve.
This valve stem 5 is intended t o be moved to and fro axially t o operate the valve
(not shown) or other device. It is shaped at its right-hand end t o engage (for
example) a valve gate. Its left-hand end 6 may be engaged, employing a suitable
interface, by an ROV (remotely operating vehicle) whereby the ROV can operate
the valve by movement of the stem 5.
A first drive shaft 8 protrudes from the actuator enclosure 3 into the motor
enclosure 2 so as t o be driven by the respective motor. The drive shaft 8 is
supported by bearings in an end wall 7 of the enclosure 3 and an end wall 9 of
a gear train casing. Beyond the wall 9 the shaft 8 drives a gear train 10 (which
may comprise a pinion and a sun gear) for driving through a speed reduction a
roller nut 11 which is rotatable (and supported by bearings) within a casing 12
which can move axially within the actuator enclosure 3. The roller nut 11 has an
internal screw threading engaging a complementary roller screw threading 13
formed on or otherwise connected to the stem 5. The gear train 10, the nut 11
and the drive casing 12 constitute a moveable drive unit by which the rotary
movement of the drive shaft is converted to linear movement of the stem 5.
More complex gear trains (e.g. epicyclic) may be employed provided that the
gear train, the nut and the casing can move as a unit.
In like manner, the motor within enclosure 2a is coupled t o drive the roller nut
by way of a second, respective drive shaft 8a which is coupled to the drive unit in
the same manner as is the shaft 8. Thus either motor (or both) can drive the
stem 5.
Each of the drive shafts 8 and 8a is 'telescopic', i.e. it is axially extensible and
collapsible to accommodate, without loss of drive connection, movement of the
drive unit and the stem 5 relative to the motor t o and fro in the enclosure 3.
The shaft 8 may for example and as shown in other Figures comprise a splined
rod within an outer sleeve. In Figure 1 the telescopic nature of the shafts 8 and
8a is denoted schematically by the double headed arrows X
This embodiment includes a return, or 'fail-safe' spring 14 in order t o return the
actuator stem t o a datum position in the event of power failure. In this example
the spring 14 is disposed in the actuator enclosure 3 and bears against the
casing 12 for the gear train and the roller nut. The spring 14 in this example is
constituted by a stack of conical disc springs, but other forms of spring may be
employed.
In order to maintain the drive unit in a predetermined position against the force
of the return spring 14, and thereby t o decouple the action of the return spring
from the actuator stem the actuator includes an ESD (emergency shut down)
latch mechanism 15. This is shown purely diagrammatically in Figure 1. Various
embodiments of a suitable latch will be described later.
The stem 5 has end stops which limit the axial movement of the valve stem in
each axial direction. These stops are shown in later Figures.
Operation of the actuator
The basic operation of the actuator shown in Figure 1 is as follows. The roller nut
is driven by way of the gear train from the shaft 8 or the shaft 8a. The stem is
held (e.g. by means of splines) against rotation, and accordingly the nut 11 and
the drive unit advance against the force of the return spring 14. The drive unit
reaches a position in which it is latched by the latch mechanism 15 against
rearward movement. Reversing the direction of rotation of the nut 11 will now
drive the actuator stem forwards so as for example to open the valve. 5ince the
action of the return spring on the stem is effectively decoupled, and the drive
unit is held in position, the stem may be moved to and fro to close and open the
valve without expenditure of power against the spring 14.
If however the latch mechanism is released, the spring 14 acts to force the return
of the drive unit and the valve stem. The roller nut 11 may be prevented from
rotating by de-energized electromechanical brakes 25, 25a (Figure 2) on each
motor. The dimensions of the enclosure and the stem need selection such that
the rearward movement of the drive unit caused by the spring is sufficient to
cause the stem to close the valve.
It will be noted that owing t o the provision of the telescopic drive shafts the
operation of the spring 14 does not require any decoupling of the drive
connection between the motors 2, 2a and the stem 5.
Each of the motors may receive power by way of a respective 'wet-mate'
connector 16, 16a.
The supply and instrumentation system
Figure 2 illustrates schematically the arrangements for the supply and control of
electrical power t o the modules 2 and 2a and t o the latch 15.
With reference t o Figure 2, the 'A' module 2 receives at a terminal 20 electrical
power from (for example) a respective line in a subsea umbilical or marine
electrical cable. This terminal is connected by way of a charger 21 t o a battery
pack 22 that supplies power t o a motor controller 23 which controls a first
motor 24 (which has a powered brake 25). The drive shaft 8 of the motor 24 is
coupled, as described with reference t o Figure 1, t o the gearbox (i.e. the gear
train 10) connected as previously described t o a valve 26. A fail-safe mechanism
(i.e. spring 14) is shown schematically between the gearbox 10 and the valve 26
and the ESD latch 15 is shown schematically as controlling the fail-safe
mechanism. The latch 15 can receive power from the Ά module 2. The'A'
module 2 can receive and can send data by way of and (for example) Ethernet
connection t o a 'CANbus' 1/0 card 27.
The 'B' module 2a is organised in a similar manner, corresponding parts being
denoted by the suffix 'a'. Figure 2 also indicates various instrumentation devices
by the quantities or signals they provide or control, particularly a charge status
and temperature of each battery, open and close commands t o the controllers,
temperature of the motor, the motor currents, the valve's position, the valve's
status, the status of the fail-safe mechanism, the status of the ESD latch, the
status of the gear box and the torque produced in the gearbox. The
instrumentation is, of course, essential t o operation of a practical actuator, but
its particular organisation is not essential t o the construction of the actuator and
the latches and will not therefore be described further.
Introduction to the Latches
Each of the latches described in the following is intended t o be capable of use as
the ESD latch 15 in the context of the actuator shown in Figure 1. They all have
the common features that they require a continuous electrical power supply to
maintain a latched state, in which the latch acts t o decouple the action of the
fail-safe mechanism on the electrical actuator, and t o allow the reassertion of
the action of the fail-safe mechanism when the supply fails either completely or
sufficiently t o release the latch. However, as indicated previously, each actuator
is of novel construction and has utility in other contexts.
The Star Disc Latch
Figure 3 is a schematic drawing of a latch which may be used in an actuator
according t o Figure 1.
The purpose of the latch in that context is t o maintain the return spring 14 of
Figure 1 in a tensed state but t o decouple the action of the return spring on the
actuator stem 5 so that for example the actuator can open and close the valve
without having to work against the force of the spring. The latch may be released
either by a failure in its power supply or by a command which deenergises the
latch. The latch may also be employed in other actuators or more generally to
maintain a moveable part in a predetermined position while in a latched state
but t o allow movement of the part from that position when in an unlatched
state.
ln this embodiment the latch is disposed within the enclosure 3 of the actuator.
An end plate 31 of the drive unit previously described defines with the enclosure
3 a chamber 32 for the return spring 14 (not shown in this Figure).
The telescopic drive shaft 8, driven by a motor (as previously described) extends
axially of the enclosure and into the drive unit which includes the roller nut 11
and the roller screw previously described. The roller nut 11 is disposed within a
sleeve which extends axially from the endplate 31 of the drive unit.
The drive unit includes an inner sleeve 34. The stem 5 extends through this
sleeve and through the left-hand endplate 7 of the enclosure 3. The end plate
7 has an axially extending socket 36 into which the stem 5 extends. The stem
further extends through an end wall 37 of the socket 36. The stem is splined
between two shoulders 38 and 39 which constitute end stops. The spline 40
engages the interior of the socket 36 so that the stem 5 (together with the
integral roller screw) can move axially but does not rotate. The outer end stop 38
can abut the end 37 of the socket 36 to limit the movement of the stem 5 and
the roller screw in the retracting direction, whereas the inner end stop 39 can
engage the end of the sleeve 34.
A compression spring 41 is disposed within a hollow hammer 42 of which the
end remote from the end plate 35 has an aperture which fits over and is guided
by the sleeve 34. The hammer 42 has at its end nearer the end plate 7 a flange
43 which can abut an electromagnet 44 comprising a grooved ring of magnetic
material, the ring including a coil (not shown) which normally is continuously
energised so that the hammer 42 is held in position near the end plate 7 against
the force of the spring 41. As will become apparent from further description
herein, cessation or sufficient reduction of the energisation of the electromagnet
will release the hammer 42 and will cause release of the latch .
The drive unit includes in its outer cylindrical part circumferentially spaced
shoes 45 which are capable of radially inward movement. Each shoe has on its
outside a set of serrations which can engage grooves 46 in the inside of the
enclosure 3 as shown by the contact surface 47.
The drive unit is advanced against the force of the return spring by means of the
motor which drives the shaft 8 to rotate the roller nut t o produce axial
movement of the drive unit when the outer end stop 38 abuts the end of the
socket 36. When the shape-lock shoes 45 reach the grooves 46, they can engage
the grooves and thereby be prevented from rearward movement.
Within the drive unit is an inner member in the form of a ring 48, which extends
axially outside the stem 5 and is mounted on the sleeve 34. This ring member 48
supports at its periphery a lever coupling which engages the shoes 45. In this
example the coupling comprises two axially spaced sets of circumferentially
spaced levers 49 which extend from bearing slots in the outside of the ring to the
inside of the shoes. These levers have rounded ends which are received in partcircular
grooves 50 on the outside of the ring 48 and the insides of the shoes 45.
Multiple reload springs (of which only one spring 51 is shown) extend between
an inwardly directed rim 52 of the ring 48 and a wall of the drive unit. These
springs hold the ring 48 in a position wherein the connecting levers 49 hold the
shoes 45 in engagement with the grooves 46.
When the electromagnet 44 is de-energised the hammer's spring 41 propels the
hammer 42 towards the ring 48. When the hammer impacts on the ring 48, as
shown in Figure 4, it causes the levers 49 t o 'snap' through their dead-centre
positions t o withdraw the shoes 45 from the annular grooves 46. Since the shoes
45 are released, the fail-safe spring 14 can (as shown in Figure 5) displace the
drive unit and thereby the valve stem 5 until the valve is closed, the roller nut
being prevented from rotation by the electromechanical brakes on each motor.
The drive shaft 8 (and the drive shaft 8a) will axially contract to accommodate
the displacement while maintaining continuity of the respective drive train.
Re-energising the electromagnet 44 will retain the hammer 42 in its energised
'ready' state. The advancement of the gear train and the associated components
will eventually cause the shoes 45 to re-engage the grooves 46 to maintain the
assembly in a latched state.
Roller Lock Latch
Figures 6 to 9 illustrate the construction and manner of operation of a latch
which may be used in, and is illustrated in, the context of an actuator as
described with reference t o Figure 1. The latch operates to maintain the drive
unit comprising the gear train 10 and its casing 12 in position against the force
of the spring and allows the roller nut (previously described) to advance and
retract the valve stem 5 without expending energy in counteracting the force of
the spring.
In the construction shown in Figure 6, the inner rod 8' of the telescopic drive
shaft 8 extends through the gear train casing 12. It drives the gear train 10 as
described with reference to Figure 1 so as to rotate via a speed reduction the
roller nut 11 which advances and retracts the roller screw 13 which is connected
to the valve stem. The fail-safe spring 14 bears against the gear train casing 12.
The actuator is put in the state shown in Figure 6 by rotation of the shaft 8 while
a shoulder (not shown) on the left-hand end of the stem 5 engages an end stop
to prevent leftwards movement of the stem, whereby the gear train casing 12
advances against the force of the spring 14.
Extending leftwards (in the sense shown in the drawing) from the gear train
casing is a sleeve 61. On this sleeve is mounted an annular electromagnet 62. An
armature 63 for the electromagnet is connected by a tension spring 64 to a wall
of the gear train housing, so that if the energisation of the electromagnet 62 is
sufficiently reduced, the armature 63 will move rapidly to the right in the axial
direction of the stem 5.
The armature 63 has a pivot for a radial lever 65 which is pivotally connected to
an axially extending lever 66 which is pivoted about an axis coincident with a
roller 67 mounted in the casing 12. A roller 68 is carried on the axial lever 66.
The rollers 67 and 68 are in rolling contact. The lever 66 is shown straight in
Figures 7 and 8 but as shown in Figure 9 the roller 68 is offset from a line
connecting the pivot axes of the carrier lever 66.
The roller 68 can, when the lever 65 is substantially disposed in the axial
direction, enter an annular recess 70 on the inside of the actuator enclosure 3.
In this state of the mechanism, the force of the spring 14 is transmitted to the
enclosure 3, provided that the line of action of force from the roller 67 to the
roller 68 has an outward component.
Figure 7 illustrates the actuator and latch when the electromagnet 62 has been
de-energised. The levers 65 and 66 have rotated so as to allow the roller 68 to
roll out of the annular recess 70. Then the gear train casing 12 is free to move
and the fail-safe spring 14 is released to move the gear train housing 12 and the
associated components leftwards.
Figure 8 shows the mechanism when the spring 14 has moved the drive unit
until the sleeve 61 abuts the end plate 36 of the enclosure 3.
In a practical embodiment, there are several mechanisms as described, each with
respective rollers 67 and 68, spaced around the enclosure 3. This is illustrated in
Figure 9, which indicates several of the rollers 68.
PSC Latch
Figure 10 illustrates in context another embodiment of a latch which is primarily
intended for use in an actuator as described with reference to Figure 1 but may
have other uses.
The inner rod 8' of the telescopic drive shaft 8 extends into the gear train casing
12. It drives the gear train 10 and thereby the roller nut 11 which engages the
roller screw 13 on the stem 5 as previously described. The fail-safe spring 14
bears against the gear train casing 12.
Figure 10 is schematic and for simplicity shows only one latch mechanism. As is
indicated in Figure 13, there are preferably multiple parallel mechanisms spaced
around the central axis of the actuator.
The end plate 7 of the actuator enclosure 3 carries an annular frame 101 in
which is movable, in the axial direction, an annular plate 102. Reset pistons 103
(only one being shown in Figure 10) extend rearwardly of the plate 102. The
pistons are spaced around the plate. Each piston carries a reset spring 104 (see
Figure 13).
Each mechanism comprises a 'radial' lever 105 which is pivoted to the plate 102
and in the position shown in Figure 10 extends radially outwardly. To the distal
end of the radial lever 105 is pivoted a respective pivot arm 106 which is also
pivoted to a respective attachment arm 107 extending obliquely forwards of the
frame 101.
The end of the pivot arm 106 defines a shoulder 108 in which is located the distal
end of a respective 'snap' rod 109 extending to a pivot 110 on the gear train
casing.
The plate 102 is held against the force of the reset springs by means of an
electromagnet 111 disposed on the end plate 7.
As is shown in Figure 13, each reset spring 104 is disposed between the head 112
of the respective piston 103 and a datum surface within the frame 101. The plate
102 is urged away from the endplate 7 by the reset springs and will therefore
move to the right in the drawing when the electromagnet 111 is de-energised.
The mechanism reaches the condition shown in Figure 10 when the gear train
housing has been driven sufficiently far for the end of the snap rod 109 to locate
in the shoulder 108. At that point the force of the return spring 14 is supported
by the rod 109 and thereby via the arm 107 on the frame 101.
The latch can be released by cessation of the power supply t o the electromagnet
111. Thereupon the plate 102 is rapidly drawn away by the reset springs 104.
This action rotates each radial lever 105 and thereby the pivot arms 106 t o
displace the distal ends of the snap rods 109 from the shoulders 108 as shown in
Figure 11.
The fail-safe spring 14 is now released and forces the gear train casing and the
stem 5 rearwards, collapsing the latch mechanisms t o the state shown in Figure
12. In this state each rod 109 is disposed alongside the respective arm 106 and
the plate 102 has been pushed into proximity with the electromagnet 111
because the gear train casing has engaged the heads of the pistons 103.
Figure 13 also shows in more detail that the end of each pivot arm 106 has an
arcuate end 113 around a boss 114 formed on the respective attachment arm
107.
Pure Roller Latch
Figure 14 illustrates the relevant parts of the actuator and a roller latch which
can maintain the gear train casing 12 in position against the force of the fail-safe
spring 14 and allow the gear train 10 to transmit drive to the roller nut 11 and
thence t o the roller screw 13 and the stem 5 as previously described. The drive
may be transmitted through either of the telescopic drive shafts 8 and 8a.
On the end plate 7 of the actuator enclosure 3 remote from the fail-safe spring
14 is an annular electromagnet 141. While the electromagnet is sufficiently
energised it holds an annular hammer 142 against the force of a compression
spring 143 disposed between the end plate 7 and a rim of the hammer 142.
The latch in this embodiment preferably has a multiplicity of sets of latching
rollers (shown in Figure 18), the sets being spaced apart around a sleeve 144
which extends axially of the gear train housing towards the end plate 7 and
covers part of the roller screw 13.
Two of the sets of rollers are shown in Figure 14, but for convenience only one
will be described in detail.
With reference to Figures 14 and 17, pivoted to the gear train housing is a
bracket 145 which extends inwardly towards the stem 5. At its end the bracket is
engaged by a compression spring 146 which urges the bracket away from the
axis of the stem 5. The bracket also forms the striker plate for the hammer 142
when that is released. The bracket 148 can rotate in a slot in a support 147
which has a curved roller surface 148 in rolling contact with a roller 149 mounted
for rotation on the bracket 145. The roller 149 is in rolling contact with a roller
150 carried on an arm 15 1 pivotally mounted within a seat 152 fixed in the side
wall 153 of the actuator enclosure 3. The seat has a rim on which the roller 149
makes rolling contact. The seat limits the movement of the arm 151, in
particular by means of a shallow cup 155 which can receive the roller 150.
The bracket includes a latch guide 156, which can extend between the two
halves of the roller 150 t o engage the end of the arm 151 so that under the
influence of the spring 146 the rotation of the bracket away from the axis causes
the rollers 149 and 150 t o be in a slightly over-centre position, whereby the force
of the spring 14 is transmitted through the support 147 and the rollers 149 and
150 to be sustained by the seat 152 and therefore by the enclosure 3.
On deenergisation of the electromagnet 141, the hammer 142 is released and is
driven by the spring 143 t o strike the bracket 145. On impact the bracket rotates
in a sense towards the axis of the stem 5. The roller 149 rolls around the roller
150 though a dead-centre position and the latch is released (Figure 15), freeing
the fail-safe spring 14 t o displace the drive unit and the stem 5. The mechanism
can be driven back to the state shown in Figure 16, wherein the hammer 142 has
been moved back t o the electromagnet 141 while the hammer's spring 143 is recompressed.
Re-energisation of the electromagnet will retain the hammer in its
'charged' state. A command to one or other of the drive motors enables the gear
train and roller screw assembly t o recharge the fail-safe spring and to cause the
actuator t o reach the state shown in Figure 14. An advantage of this
embodiment is that the latching and release actions are pure rolling actions,
reducing friction or the risk of damage.
As is shown in Figure 18, there are multiple sets of brackets 145, rollers 149, 150
and seats 152 spaced circumferentially about a central axis through the stem 5.
CLAIMS
1. A subsea electric actuator comprising an electric motor, a telescopic drive
connection (8) from the motor to a drive unit (10, 11, 12) which can be moved to
and fro and converts rotary motion of the connection t o linear motion of an
operating member (5), a return spring (14) operable on the drive unit to urge the
operating member towards a datum state and a latch (15), which is operative
when set t o maintain the drive unit in a predetermined position so as to
decouple the action of the return spring, whereby the operating member can be
advanced and retracted relative to the drive unit free from the action of the
return spring, and is operative on release to allow the return spring to operate
on the drive unit to return the operating member t o the datum state.
2. An actuator according to claim 1 in which the drive unit includes
reduction gearing (10).
3. An actuator according to claim 1 or 2 in which the drive unit comprises a
drive nut (11) on a roller screw (13) connected to the operating member (5).
4. An actuator according to claim 3 and further comprising means for
preventing rotation of the roller screw (13) and operating member (5).
5. An actuator according to any of claims 1 to 4, in which the actuator
includes two electric motors coupled for energisation by respective electrical
energy stores, each motor having a telescopic drive connection (8, 8a) to the
drive unit (10, 11, 12), which is configured for driving by either of the motors.
6. An actuator according to any of claims 1 to 5 in which the latch (15) is an
electromagnetic latch which is arranged to be in a set state when energised and
to release when de-energised.
7. An actuator according t o any of claims 1 to 6 in which the latch (15) is
adapted to be put into a set state latching the return spring on movement of the
drive unit t o the predetermined position against the force of the return spring
(14).
8. A subsea electric actuator comprising an electric motor, a telescopic drive
connection (8) between the motor and a drive unit (10, 11, 12) which can move
to and fro and couples rotary motion of the drive connection to a drive nut (11)
on a screw (13) which is disposed for axial movement without rotation and is
connected t o an operating member (5).
9. An actuator according t o claim 8, in which the actuator includes two
electric motors coupled for energisation by respective electrical energy stores,
each motor having a telescopic drive connection (8, 8a) to the drive unit, which is
configured for driving by either of the motors.
10. A subsea electric actuator according to claim 8 or 9 and further
comprising means including a latch (15) for maintaining the drive unit in a
predetermined position wherein the drive unit can drive the screw (13) forwards
and backwards.
11. An actuator according to any of claims 1 t o 5 or claim 10 in which the
latch comprises:
at least one locking shoe (45) positioned for engagement with a surface
(46) which inhibits movement of the shoe, said locking shoe (45) being inwardly
displaceable from said surface and mounted within said drive unit;
a member (48) mounted within the said drive unit;
a lever coupling (49) between the member and the shoe;
a spring-loaded hammer (42) which is operative by means of a driving
spring to strike the member (48) whereby t o pivot the lever coupling to allow
disengagement of the shoe from the said surface; and
an electromagnet (44) for holding the hammer against the spring loading
of the hammer.
12. An actuator according to claim 11 in which there is a plurality of shoes
(45) spaced apart around the member (48).
13. An actuator according to claim 12 in which the lever coupling comprises
at least one set of levers (49) connected between the member (48) and the
shoes.
14. An actuator according to claim 13 in which there are two sets of axially
spaced levers between the member (48) and the shoes (45).
15. An actuator according to any of claims 1 to 5 or claim 10, in which the
latch comprises:
an electromagnet (62) disposed on said drive unit;
an armature (63) which is held by the electromagnet while the
electromagnet is sufficiently energised;
a spring (64) for causing movement of the armature away from the
electromagnet on deenergisation of the electromagnet; and
a linkage (65-68) including a roller (68) which locates in a datum recess
(70) to support the drive unit against the action of the return spring, said linkage
being arranged to withdraw the roller from the recess in response to movement
of the armature away from the electromagnet.
16. An actuator according to claim 15 in which the roller (68) is in
engagement with a second roller (67) mounted on the drive unit.
17. An actuator according to claim 16 in which the linkage comprises a lever
(65) pivoted to the armature (63) and a carrier (66) which carries the firstmentioned
roller (68) and extends between the lever (65) and a pivot on the
drive unit.
18. An actuator according to any of claims 1 to 5 or claim 10, in which the
latch comprises:
a rod (109) pivoted to said drive unit and extending therefrom in the
direction away from the predetermined position;
a fixed support (101, 107);
a linkage (105, 106) which includes an arm (106) which is pivoted to the
support and includes a shoulder (108) for the reception of a distal end of the rod
(109), whereby movement of the drive unit towards said support is prevented;
a movable operating member (102) which is connected to the linkage and
movable by an operating spring (104) to collapse the linkage to free the said
distal end of the rod (109) from the shoulder (108) and thereby t o allow the
movement of the said drive unit; and
an electromagnet (111) for holding the actuating member (102) in a
position against the action of the operating spring and preventing collapse of the
linkage.
19. An actuator according to claim 18 in which the linkage comprises a lever
(105) pivoted to the operating member (102) and the said arm (106).
20. An actuator according to claim 19 in which the said rod (109) extends
alongside the arm (106) when the drive unit moves towards the said support.
21. An actuator according to any of claims 1 to 5 or claim 10, in which the
latch comprises:
a bracket (145) pivoted to the drive unit, the bracket carrying a first roller
(149);
an arm (151) pivoted to a fixed member and carrying a second roller
(150) for engagement with the first roller;
means for biasing said bracket to an angular position wherein a force of
said return spring on said drive unit is transmitted to said fixed member when
said drive unit is in the predetermined position; and
a hammer (142) which is disposed to be held against the force of an
operating spring by an electromagnet (141) and is moveable by said operating
spring on de-energisation of the electromagnet to strike said bracket to rotate
said bracket, the rotation of said bracket (145) causing relative rolling
movement of said rollers (149, 150) and disengagement thereof.
22. An actuator according to claim 21 in which the hammer (142) is disposed
such that it can be recaptured by the electromagnet in response t o movement of
the said drive unit towards the datum state.
23. An actuator according to claim 21 or 22 in which and including means for
limiting the movement of the arm (151) in a sense opposite the direction of the
said rotation.
24. An actuator according to any of claims 21 to 23 in which there is a
multiplicity of sets of said rollers (149, 150) spaced apart around the operating
member (5).
25. A latch for maintaining a unit (12) in a predetermined position so as to
prevent movement of that unit (12) away from that piston but to allow such
movement on release of the latch, comprising:
at least one locking shoe (45) positioned for engagement with a surface
(46) which inhibits movement of the shoe, said locking shoe (45) being inwardly
displaceable from said surface and mounted to the said unit (12);
a member (48) mounted for movement within said unit (12);
a lever coupling (49) between the member and the shoe;
a spring-loaded hammer (42) which is operative by means of a driving
spring to strike the member (48) whereby to pivot the lever coupling to allow
disengagement of the shoe from the said surface; and
an electromagnet (44) for holding the hammer against the spring loading
of the hammer.
26. A latch according to claim 25 in which there is a plurality of shoes (45)
spaced apart around the member (48).
27. A latch according to claim 26 in which the lever coupling comprises at
least one set of levers connected between the member (48) and the shoes.
28. A latch according to claim 27 in which there are two sets of axially spaced
levers between the member (48) and the shoes (45).
29. A latch according to any of claims 25 to 28 in which a return spring (14) is
disposed to move the unit (12) away from the said position when the latch is
released.
30. A latch for maintaining a unit (12) in a predetermined position within an
enclosure so as to prevent movement of that unit away from that position but t o
allow such movement on release of the latch, comprising:
an electromagnet (62) disposed on said unit (12);
an armature (63) which is held by the electromagnet while the
electromagnet is sufficiently energised;
a spring (64) for causing movement of the armature away from the
electromagnet on deenergisation of the electromagnet; and
a linkage (65-68) including a roller (68) which locates in a datum recess
(70) to support the unit (12) against the action of the return spring, said linkage
being arranged to withdraw the roller from the recess in response t o movement
of the armature away from the electromagnet.
2012/123694 -24-
31. A latch according to claim 30 in which the roller (68) is in engagement
with a second roller (67) mounted on the unit .
32. A latch according to claim 31 in which the linkage comprises a lever (65)
pivoted to the armature (63) and a carrier (69) which carries the first-mentioned
roller (68) and extends between the lever (65) and a pivot on the unit (12).
33. A latch according to any of claims 30 to 32 in which a return spring (14) is
disposed t o move the unit (12) away from the said position when the latch is
released.
34. A latch for maintaining a moveable unit (12) against movement in a
particular direction away from a predetermined position, comprising:
a rod (109) pivoted to the unit (12) and extending therefrom in the said
direction;
a fixed support (101, 107);
a linkage (105, 106) which includes an arm (106) which is pivoted t o the
support and includes a shoulder (108) for the reception of a distal end of the rod
(109), whereby movement of the unit (12) towards said support is prevented;
a movable operating member (102) which is connected t o the linkage and
movable by an operating spring (104) to collapse the linkage to free the said
distal end of the rod (109) from the shoulder (108) and thereby to allow the
movement of the unit (12); and
an electromagnet (111) for holding the actuating member (102) in a
position against the action of the operating spring and preventing collapse of the
linkage.
35. A latch according to claim 34 in which the linkage comprises a lever (105)
pivoted t o the operating member (102) and the said arm (106).
36. A latch according to claim 33 in which the said rod extends alongside the
arm (106) when the drive unit moves towards the said support.
37. A latch according to any of claims 34 to 36 in which a return spring (14) is
disposed to move the unit (12) away from the said position when the latch is
released.
38. A latch for maintaining a moveable unit (12) against movement in a
particular direction away from a predetermined position , comprising:
a bracket (145) pivoted to the unit (12), the bracket carrying a first roller
(149) ;
an arm (151) pivoted to a fixed position and carrying a second roller
(150) for engagement with the first roller;
means for biasing the bracket to an angular position wherein a force on
the said unit (12) in the said direction is transmitted to the fixed member when
the unit (12) is in the predetermined position; and
a hammer (142) which is disposed to be held against the force of an
operating spring (143) by an electromagnet (141) and is moveable by the
operating spring on de-energisation of the electromagnet to strike the bracket
to rotate the bracket, this rotation causing relative rolling movement rotation of
the roller (149, 150) and disengagement thereof.
39. A latch according to claim 38 in which the hammer (142) is disposed
such that it can be recaptured by the electromagnet (141) in response to
movement of the said member (12) in the said direction.
40. A latch according to claim 38 or 39 in which and including means for
limiting the movement of the arm (151) in a sense opposite the direction of the
said rotation.
41. A latch according t o any of claims 38 to 40 in which there is a multiplicity
of circumferentially spaced sets of rollers (149, 150).
42. A latch according to any of claims 38 to 41 in which a return spring (14) is
disposed to move the unit (12) away from the said position when the latch is
released.