GB2572735A

GB2572735A - Failsafe industrial actuator

Info

Publication number: GB2572735A
Application number: GB1800466.3A
Authority: GB
Inventors: Welzien Jan; Spittler Harald
Original assignee: Schischek Produktion Technischer Gerate GmbH; SCHISCHEK PRODUKTION TECHNISCHER GERAETE GmbH
Current assignee: Schischek Produktion Technischer Gerate GmbH; SCHISCHEK PRODUKTION TECHNISCHER GERAETE GmbH
Priority date: 2018-01-11
Filing date: 2018-01-11
Publication date: 2019-10-16
Anticipated expiration: 2038-01-11
Also published as: TWI779148B; CN213598526U; GB2572735B; DE212019000163U1; WO2019137839A1; GB201800466D0; TW201930773A

Abstract

An industrial actuator 10 comprising a first and second parallel drive train 12, 14 having respective first and second coaxial outputs 13, 15. A clutch assembly 17, 18 selectively connects drive from an input 16 to move one of the drive trains. A latching mechanism 20 selectively maintains an energy store 19 coupled to the first output in an energised state. A rotary ratchet coupling between the first and second output is configured such that the clutch assembly connects the drive to the first drive train and drives the first output in a forward direction energising the energy store; the clutch assembly connects the drive to the second drive train to drive the second output, such that the output may move a drive shaft coupled to the second output from a first, failsafe, position to a second position. Releasing the latching mechanism releases the energy from the energy store, causing the first output to be driven in a reverse direction, and the ratchet coupling provides a rotary engagement between the first and second output in the reverse direction such that the drive shaft is urged towards a failsafe position.

Description

FIELD OF INVENTION

The present invention relates to a failsafe industrial actuator. Particularly, but not exclusively, the actuator may be for use with industrial controls, such as valves and dampers. The failsafe industrial actuator is particularly, but not exclusively, a failsafe flow control actuator.

BACKGROUND OF INVENTION

Industrial actuators are used in a variety of different industries, including oil & gas, water and waste water, power, marine, mining, food, pharmaceutical and chemical industries, and in a variety of different locations, such as in buildings, tunnels and so on. Failsafe industrial actuators may be used in any application where it is desirable to control a flow of liquid, gases or powders and provide an emergency shut-down functionality.

Failsafe industrial actuators may also be utilised in HVAC (Heating, Ventilation and Air Conditioning) applications such as with industrial controls, such as valves and dampers which help to control the temperature and ventilation in such locations. In such applications a failsafe mechanism may be desirable for maintaining safety in an emergency such as a fire, particularly for example in tunnels such as Road or Rail tunnel and mining. For example, some actuators can be used to regulate the airflow in road tunnels to help ensure that the circulating air does not comprise a build-up of vehicle exhaust gases.

Dampers, for example, are typically spaced along a tunnel for ventilation (for example in rail tunnels to act in conjunction with the piston effect of the train travelling along the tunnel) and are essential for maintaining safety in tunnels in the case of an emergency, such as a fire.

When open, they can help to ventilate/extract the smoke produced by a fire to allow safer passage through the tunnel, and when closed, they can provide a barrier which can help to regulate/isolate the fire.

Typically the actuator controlling the damper is connected to a fire detector. When heat or smoke is detected, the actuator is automatically triggered to move the damper into the appropriate, failsafe, position. For some dampers, the failsafe position may be in a closed position, whereas the failsafe position for other dampers may be in the open position.

Failsafe actuators may generally utilise an energy store such as a spring which can bias the actuator to the failsafe position. During normal operation the drive of the actuator may have to act against this energy store and this will affect the sizing and torque requirements of the actuator.

Embodiments of the present invention seek to provide an improved failsafe actuator which may provides increased safety in, for example, tunnel environments and/or which may provide increased design freedom to optimise the sizing and torque requirements of the actuator dependent upon the required failsafe actuation.

SUMMARY OF INVENTION

According to the first aspect of the present invention there is provided a failsafe industrial actuator, comprising:

a first drive train comprising a first output;

a second drive train comprising a second output, the first and second drive trains being arranged in parallel to each other with the first and second output gears being co-axial;

a drive configured to move the first and/or second drive trains;

at least one clutch assembly arranged to selectively connect the drive to the first and/or second drive trains;

an energy store, the energy store being coupled to the first output;

a latching mechanism, arranged to selectively maintain the energy store in an energised state;

a drive shaft for connecting the actuator to the input of an industrial control and to enable positioning thereof by the actuator, the drive shaft being coupled to the second output; and a rotary ratchet coupling between the first output and second output; wherein the rotary ratchet coupling is configured such that:

a first clutch assembly connects the drive to the first drive train and drives the first output in a forward direction to energise the energy store, the energy store being latched in the energised state by the latching mechanism;

a second clutch assembly connects the drive to the second drive train to drive the second output, such that the output may effect corresponding movement of the drive shaft from a first, failsafe, position to at least a second position; and releasing the latching mechanism releases the energy from the energy store, causing the first output to be driven in a reverse direction, and wherein the rotary ratchet coupling provides a rotary engagement between the first output and second output in the reverse direction such that the second output is driven by the first output in the reverse direction to urge the drive shaft towards a failsafe position.

The failsafe industrial actuator may be a failsafe industrial flow control actuator. In the context of the present invention, the term industrial includes, but is not limited to, the tunnelling industry and the HVAC industry (heating, ventilation and air conditioning).

The first and second drive trains may comprise a series of gears which may rotate in a forward and/or a backwards direction, depending on the direction of the motor. The motor may drive the gears of the first drive train in a forward direction to energise the energy store. Once the energy store is full, that is the energy store is energised, it is latched in said energised position. The motor may also drive, simultaneously or subsequently, the gears of the second drive train in a forward and/or reverse direction (depending on the direction of the motor) to effect corresponding movement of the drive shaft (and also the industrial control) from the first, failsafe, position to at least the second position.

With the energy store in the energised state the first drive chain may be held stationary whilst the clutch connects the drive to only the second drive chain. As such the second output may slip relative to the first drive output during normal operation. However, during fail-safe operation the rotary ratchet coupling causes the first output to engage the second output such that both outputs are driven to the failsafe position. It will be appreciated that if the second output is in a partially open/closed position the first output may initially travel to the corresponding position before the rotary ratchet coupling causes engagement with the second output.

Advantageously, the latching mechanism releases the energy from the energy store, causing the first output and consequently the second output to be driven by the energy store in a reverse direction, such that the industrial control is rapidly moved to the failsafe position. As the energy store is a local power source the failsafe may operate in the event of a loss of power to the actuator (i.e. power to the drive is not required). Further the speed of the failsafe return may be configured by the selection of the energy store and is independent of the speed of the drive.

The energisation of the energy store via the first drive chain may occur during an initial stage of operation, for example immediately after the actuator is activated. The second drive chain may then be used as the primary position control for the actuator (for example it may be moved backwards and forwards as required by a controller to position the drive shaft). The first drive chain may remain in its fully open position until failsafe activation is required.

In a first embodiment, the rotary ratchet coupling may be configured such that:

in a first configuration the clutch assembly connects the drive to the first drive train and drives the first output in a forward direction to energise the energy store and in which the rotary ratchet coupling allows the first output to slip relative to the second output;

in a second configuration the energy store is latched in the energised state by the latching mechanism and the clutch assembly connects the drive to the second drive train to drive the second output such that the output may effect corresponding movement of the drive shaft from a first, failsafe, position to at least a second position, and wherein the rotary ratchet coupling allows the second output to slip relative to the first output; and in a third, failsafe, configuration the latching mechanism is released such that energy is released from the energy store and drives the first output in a reverse direction, and wherein the rotary ratchet coupling provides a rotary engagement between the first output and second output in the reverse direction such that the second output is driven by the first output in the reverse direction to urge the drive shaft towards a failsafe position.

Advantageously the first embodiment enables the drive to act upon the energy store and the drive shaft in different stages of operation. Such an arrangement can be advantageous in reducing the maximum torque output required from the drive (since in neither the first nor the second configuration is the drive acting through both drive chains simultaneously).

In a second embodiment, the rotary ratchet coupling may be configured such that:

in a first configuration the clutch assembly connects the drive to the first drive train and the second drive train, and simultaneously drives the first output in a forward direction to energise the energy store, and drives the second output to effect corresponding movement of the drive shaft from a first, failsafe, position to at least a second position;

in a second configuration the energy store is latched in the energised state by the latching mechanism; and in a third, failsafe, configuration the latching mechanism is released such that energy is released from the energy store and drives the first output in a reverse direction, and wherein the rotary ratchet coupling provides a rotary engagement between the first output and second output in the reverse direction such that the second output is driven by the first output in the reverse direction to urge the drive shaft towards a failsafe position.

In contrast to the first embodiment, the second embodiment may require a higher maximum torque output from the drive (since the maximum torque must be double the torque needed to move the drive shaft so as to overcome the energy store). However having the design flexibility to use such a configuration is useful since in some applications there may be fewer constraints on the available torque and it may be preferable to minimise the delay before the actuator can drive the drive shaft. Advantageously, a single actuator may be configured to operate in accordance with either embodiment without any substantial structural alterations.

In a third embodiment, the rotary ratchet coupling may be configured such that:

in a first configuration the clutch assembly connects the drive to the second drive train and drives the second output in a forward direction to effect corresponding movement of the drive shaft from a first, failsafe, position to at least a second position, and wherein the rotary ratchet coupling provides a rotary engagement between the first output and second output in the forward direction such that the first output is driven by the second output in the forward direction to energise the energy store;

In the second and third embodiments, the first and second outputs are simultaneously driven in the forward direction. In the second embodiment, the clutch assembly connects the drive to the first drive train and the second drive train, whereas in the third embodiment, the clutch assembly connects the drive only to the second drive train.

In said first, second, and third embodiments described above, in the first configuration the first output may be rotated between a first failsafe position and a second position in which the energy store is fully loaded. Said movement may correspond to a predetermined partial rotation of the first output. Furthermore, in the second configuration the first output may be held in a position rotated forward relative to its initial position.

In said second configuration, the rotary ratchet coupling may allow the second output to freely slip relative to the first output between a first position corresponding to the first failsafe position and a final position in which the second output has rotated by an amount corresponding to the second position of the first output. The final position will generally be the fully open or fully closed position for the drive shaft. Preferably, the rotary ratchet coupling provides a predetermined angular range of slip of the second output relative to the first output when the first output is in the latched position.

The rotary ratchet coupling may engage the second output when the first output is driven in the reverse direction. Preferably, the rotary ratchet coupling provides a rotary engagement between the first output and the second output such that the first output cannot return to the failsafe position without return of the second output to the first position.

The rotary ratchet coupling may comprise first and second radial bearing faces associated with the first and second output respectively. The rotary ratchet coupling may comprise first and second radial bearing faces defined on the first and second output respectively. Slip between the first and second output may open an angular clearance between the first and second radial bearing faces. Preferably, the radial faces drivingly engage when radially adjacent.

In exemplary embodiments, the energy store may be a spring. Preferably, the spring is a torsion spring or a leaf spring. The energy store may comprise a damper. The damper may reduce the force exerted on the energy store, for example a spring. Advantageously, this may help to prevent wear and tear on the spring accumulating over time due to the forces exerted on the spring, which may eventually cause the spring to break.

The drive means may be a motor. The latching mechanism may be a magnetic spring lock.

The industrial control may be one of a valve and a damper, such as an air damper. The failsafe industrial actuator is preferably for use in industrial flow control operations, for example HVAC. It is envisioned that the failsafe industrial actuator will have use in a variety of industries where such flow control operations are necessary, particularly in the tunnelling industry.

The failsafe industrial actuator may further comprise a manual override to move the drive shaft into the first, failsafe, position. The manual override may be a hand wheel.

The failsafe industrial actuator may also be retrofitted to the input of an existing industrial control.

Whilst the invention has been described above, it extends to any inventive combination set out above, or in the following description or drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be performed in various ways, and an embodiment thereof will now be described by way of example only, reference being made to the accompanying drawings, in which:

Figs, la and lb show a top view and a side view of the failsafe industrial actuator in accordance with the present invention;

Fig. 2 shows an exploded view of a failsafe industrial actuator in accordance with the present invention;

Fig. 3 shows a cross-sectional view through the assembled Fig. 2 failsafe industrial actuator;

Fig. 4 shows a perspective view of the Fig. 3 failsafe industrial actuator in a first configuration;

Figs. 5a - 5c show a perspective view of the Fig. 3 failsafe industrial actuator in a second configuration;

Fig. 6 shows a perspective view of the Fig. 3 failsafe industrial actuator in a third configuration;

Fig. 7 shows a perspective view of an embodiment of the failsafe industrial actuator in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figs, la, lb and 7 show a failsafe industrial actuator 10 comprising a first drive train 12 having a first output 13, and a second drive train 14 having a second output 15. The first and second drive trains 12, 14 are parallel to each other, and the first and second outputs 13, 15 are coaxial. The first and second outputs 13, 15 also have a rotary ratchet coupling (which will be explained in further detail below).

Figs. 2 and 3 show the first and second outputs 13, 15 in more detail. Fig. 2 shows an exploded view of the output assembly. The output assembly comprises the first and second output gears 13, 15, a spring shaft 21, tabs 22 and 24, a collar 23, and a drive shaft 25. The output gears 13, 15 are each non-rotatably connected to their respective shaft 21, 25 by a splined connection, for example provided by the tabs 22, 24. The first and second outputs 13, 15 are gears comprising teeth extending partially around the circumference of each gear.

The spring shaft 21 comprises a recess 26 which a lower portion of tab 22 slots into. The first output 13 also comprises a recess 27 which an upper portion of tab 22 slots into. The tab 22 therefore couples the first output 13 to the spring shaft 21. Similarly, the drive shaft 25 comprises a recess (not shown) which a lower portion of tab 24 slots into, and the second output 15 comprises a recess 28 which an upper portion of tab 24 slots into. The tab 24 therefore couples the second output 15 to the drive shaft 25. In use, the drive shaft 25 connects the actuator 10 to the input of an industrial control (not shown) such as a valve or a damper for use in the tunnelling and/or HVAC industries, and enables positioning thereof by the actuator 10.

The collar 23 slots into the opening of first output 13, while the flange portion of the collar 23 sits between the first and second outputs 13, 15. The flange portion provides a bearing surface to allow the first and second outputs 13, 15 to slip smoothly relative to each other. The assembled output assembly is shown in Fig. 3.

The rotary ratchet coupling between the first and second outputs 13, 15 comprises first and second radial bearing faces 29, 30 defined on the first and second output respectively. The first radial bearing face 29 is formed by a step in a flange 29a which is axially located on the first output 13. The step is formed at the interface between segments of the flange 29a which have a first external diameter and a segment having a reduced external diameter. The second radial bearing face 30 is formed by the end face of an outwardly extending tab 30a. When the actuator is assembled the tab 30a extends over the portion of the flange 29a which has a reduced external diameter. The relative circumferential length of the reduced diameter portion of the flange 29a and the tab 30a defines the degree of relative rotational slip which is possible between the outputs 13 and 15. The first and second radial bearing faces 29, 30 are arranged such that the faces radially oppose one another, and drivingly engage when they are radially adjacent. In use, any slip between the first and second outputs 13, 15 opens and closes an angular clearance 31 (see Figs. 4-6) between the first and second radial bearing faces 29, 30.

As shown in Figs, la, lb, and 7, the actuator 10 also comprises a drive in the form of a motor 16 coupled to the first and second drive trains 12, 14, and two clutch assemblies 17, 18. The motor 16 is configured to move the first and/or second drive trains 12, 14. The first clutch assembly 17 is associated with the first drive train 12, and the second clutch assembly is associated with the second drive train 14. The clutch assemblies 17, 18 are arranged to selectively connect the motor 16 to the first and/or second drive trains 12, 14.

An energy store in the form of a housing comprising a torsion spring 19, is coupled to the first output 13. A latching mechanism in the form of a magnetic spring lock 20 is located adjacent to the first output 13, and is arranged to selectively maintain the spring 19 in an energised state in use.

Figs. 4-6 show the failsafe industrial actuator 10 in use. The actuator 10 operates in two stages: firstly energising the torsion spring 19 and latching it in an energised state whilst the industrial control is operated, and secondly actuating the spring 19 (releasing the stored energy) to return the actuator 10 to a failsafe position.

Initially the motor 16 activates, which turns a shaft (not shown) extending through the first and second clutch assemblies 17, 18 and the first and second drive trains 12, 14. Whilst both clutches 17, 18 are in a de-energised state, the motor turns the shaft but no movement is transferred to the first or second drive trains 12,14. At this stage, both outputs 13, 15 are in a first, failsafe, position.

In a first configuration shown in Fig. 4, the first clutch assembly 17 is energised, and thus couples the motor 16 to the first drive train 12. The motor 16 then drives the first drive train 12, which in turn drives (rotates) the first output 13 in a forward direction from the failsafe position, to a second position. As the first output 13 rotates in the forward direction, the spring shaft 21 (coupled to the first output 13 and the torsion spring 19) also rotates and energises (winds up) the torsion spring 19. Whilst the first output 13 is driven towards the second position, the second output 15 remains in the first, failsafe, position. The rotary ratchet coupling allows the first output 13 to slip relative to the second output 15. Such relative movement creates an angular clearance 31 between the first and second radial bearing faces 29, 30.

The motor 16 drives the first output 12 until it reaches the second position, at which point the torsion spring 19 is fully energised. Said movement may correspond to a predetermined partial rotation of the first output 13. The magnetic spring lock 20 is then activated to latch/hold the first output 13 in the second position, and thus latch the torsion spring 19 in the energised state.

Figs. 5a - c show a second configuration. The first clutch assembly 17 is de-energised, thus decoupling the motor 16 from the first drive train 12, but the torsion spring 19 continues to be latched in the energised state.

The second clutch assembly 18 is then energised, thus coupling the motor 16 to the second drive train 14. The motor 16 then drives the second drive train 14, which in turn drives (rotates) the second output 15 in a forward direction and also a backwards direction if required (by reversing the direction of the motor), between the failsafe position, and at least a second position.

As the second output 15 is driven in the forward and backward direction, the industrial control (not shown), which is coupled to the second output 15 via drive shaft 25, is moved between an open and a closed position. The forward direction may correspond to the opening of the industrial control, and the backwards direction may correspond to the closing of the industrial control, or vice versa. The failsafe position of the industrial control may be a closed position, but there may be situations where the failsafe position of the industrial control is an open position.

Figs. 5a - c show the second output 15 rotating in a forward direction from the failsafe position, to a second, final, position (Fig. 5c) via some intermediate positions (Figs. 5a and 5b). The rotary ratchet coupling allows the second output 15 to freely slip relative to the first output 13. The second output 15 slips relative to the first output 13 until it reaches the second, final, position in which the second output 15 has rotated by an amount corresponding to the second position of the first output 13. Such relative movement in the forward direction reduces the angular clearance 31 between the first and second radial bearing faces 29, 30, until the faces 29,30 are adjacent to each other (Fig. 5c). Thus, the rotary ratchet coupling provides a predetermined angular range of slip of the second output 15 relative to the first output 13 when the first output 13 is in the latched position.

The second output 15 may now remain in the second position, thus keeping the industrial control (such as a valve or damper) in the open or closed position. If it is required to move the industrial control to the other of the open and closed position (the failsafe position), the direction of the motor is reversed, thus driving the drive train and the second output 15 in the reverse/backwards direction. The industrial control can be moved several times between the open and closed positions if required, by reversing the direction of the motor.

In an emergency situation, for example a loss of power or a fire, it may be required to quickly shut (or indeed open) the industrial control to prevent (or allow) fluid flow through the control. In a third configuration, shown in Fig. 6, the magnetic spring lock 20 is released, thus allowing the torsion spring 19 to de-energise (unwind). As the torsion spring 19 de-energises, it causes the first output 13 to rotate in a reverse direction from the second position, back to the first, failsafe, position.

The rotary ratchet coupling engages the second output 15 when the first output 13 is driven in the reverse direction. As the first output 13 rotates backwards (in a reverse direction), the rotary ratchet coupling between the first and second outputs 13, 15 provides a rotary engagement between the first and second radial bearing faces 29, 30, such that both the first output 13 and the second output 15 rotate together in the reverse direction towards the first, failsafe, position. The rotary ratchet coupling provides a rotary engagement between the first output 13 and the second output 15 such that the first output 13 cannot return to the failsafe position without return of the second output 15 to the first position. That is, the second output 15 is driven by the first output 13 in the reverse direction to urge the drive shaft 25 (and industrial control) towards the failsafe position.

In the event that the second output 15 needs to be moved manually into the failsafe position, thus moving the industrial control into the failsafe position, the actuator 10 further comprises a manual override in the form of a hand wheel 40, shown in Fig. lb. Advantageously, the manual override may provide a back-up in case the actuator does not automatically move the industrial control into the failsafe position.

Although the invention has been described above with reference to an exemplary embodiment, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

For example, in an alternative embodiment, the first and second clutch assemblies are energised at the same time. This causes the first output to move in a forward direction between the failsafe position and a second position to energise the torsion spring, and at the same time the second output moves in a forward direction between the failsafe position and at least a second position, which moves the industrial control coupled to the second output via the drive shaft into the open or closed position. The first output is then latched in the second position by a latching mechanism, and the second output is free to move in a forwards and backwards direction to open/close the industrial control as required, in the same way as described above. The actuator also works in exactly the same way as described above in emergency situations where it is required to quickly shut (or indeed open) the industrial control.

This embodiment may require a drive/motor with a torque rating sufficient to drive the two drive trains simultaneously.

In further alternative embodiments, only the second clutch assembly is energised. This causes the second output to move in a forward direction between the failsafe position and a second position to move the industrial control coupled to the second output via the drive shaft into the open or closed position. As the second output rotates in the forward direction, the second radial bearing face on the second output engages with the first radial bearing face on the first output, and drives the first output in a forward direction to energise the torsion spring. The first output is then latched in the second position by a latching mechanism, and the second output is free to move in a forwards and backwards direction to open/close the industrial control as required, in the same way as described above. The actuator also works in exactly the same way as described above in emergency situations where it is required to quickly shut (or indeed open) the industrial control.

It may be appreciated that as embodiments of the invention may be used in different configurations a single base actuator design may be utilised in a variety of applications or operational modes. The structural design of the actuator may not require any alteration to operate in different configurations and may simply require a simple software/control update or reconfiguration. For example the configuration may be selected depending upon the torque requirements and operation speed. Thus, embodiments of the invention provide an actuator with great flexibility and provide a range of design choices to the commissioning designer.

Furthermore, in some embodiments, the actuator can be retrofitted to the input of an existing industrial control, such as an existing valve or damper already in use. The existing actuator can be removed and replaced with the present actuator described herein to operate the industrial control.

Claims

1. A failsafe industrial actuator, comprising:

a first drive train comprising a first output;

a second drive train comprising a second output, the first and second drive trains being arranged in parallel to each other with the first and second output gears being coaxial;

a drive configured to move the first and/or second drive trains;

an energy store, the energy store being coupled to the first output;

the clutch assembly connects the drive to the first drive train and drives the first output in a forward direction to energise the energy store, the energy store being latched in the energised state by the latching mechanism;

the clutch assembly connects the drive to the second drive train to drive the second output, such that the output may effect corresponding movement of the drive shaft from a first, failsafe, position to at least a second position; and releasing the latching mechanism releases the energy from the energy store, causing the first output to be driven in a reverse direction, and wherein the rotary ratchet coupling provides a rotary engagement between the first output and second output in the reverse direction such that the second output is driven by the first output in the reverse direction to urge the drive shaft towards a failsafe position.

2. A failsafe industrial actuator as claimed in claim 1, wherein the rotary ratchet coupling is configured such that:

3. A failsafe industrial actuator as claimed in claim 1, wherein the rotary ratchet coupling is configured such that:

4. A failsafe industrial actuator as claimed in claim 1, wherein the rotary ratchet coupling is configured such that:

5. A failsafe industrial actuator as claimed in any one of claim 2 to claim 4, wherein in said first configuration the first output is rotated between a first failsafe position and a second position in which the energy store is fully loaded, said movement corresponding to a predetermined partial rotation of the first output.

6. A failsafe industrial actuator as claimed in any one of claim 2 to claim 5, wherein in the second configuration the first output is held in a position rotated forward relative to its initial position.

7. A failsafe industrial actuator as claimed in any one of claim 2 to claim 6, wherein in said second configuration, the rotary ratchet coupling allows the second output to freely slip relative to the first output between a first position corresponding to the first failsafe position and a final position in which the second output has rotated by an amount corresponding to the second position of the first output.

8. A failsafe industrial actuator as claimed in any preceding claim, wherein the rotary ratchet coupling provides a predetermined angular range of slip of the second output relative to the first output when the first output is in the latched position.

9. A failsafe industrial actuator as claimed in any preceding claim, wherein the rotary ratchet coupling engages the second output when the first output is driven in the reverse direction.

10. A failsafe industrial actuator as claimed in any preceding claim, wherein the rotary ratchet coupling provides a rotary engagement between the first output and the second output such that the first output cannot return to the failsafe position without return of the second output to the first position.

11. A failsafe industrial actuator as claimed in any preceding claim, wherein the rotary ratchet coupling comprises first and second radial bearing faces associated with the first and second output respectively, and wherein slip between the first and second output opens an angular clearance between the faces.

12. A failsafe industrial actuator as claimed in claim 11, wherein the radial faces drivingly engage when radially adjacent.

13. A failsafe industrial actuator as claimed in any preceding claim, wherein the energy store is a spring.

14. A failsafe industrial actuator as claimed in claim 13, wherein the spring is a torsion spring or a leaf spring.

15. A failsafe industrial actuator as claimed in any preceding claim, wherein the drive means is a motor.

16. A failsafe industrial actuator as claimed in any preceding claim, wherein the latching mechanism is a magnetic spring lock.

17. A failsafe industrial actuator as claimed in any preceding claim, wherein the industrial control is one of a valve and a damper.

18. A failsafe industrial actuator as claimed in any preceding claim, for use in industrial flow control operations.

19. A failsafe industrial actuator as claimed in any preceding claim, wherein actuator further comprises a manual override to move the drive shaft manually into the first, failsafe, position.

20. A failsafe industrial actuator as claimed in any preceding claim, wherein the manual override is a hand wheel.

21. A failsafe industrial actuator as claimed in any preceding claim, wherein the actuator is retrofitted to the input of an existing industrial control.