GB2475938A

GB2475938A - Release mechanism

Info

Publication number: GB2475938A
Application number: GB201014936A
Authority: GB
Inventors: Miles Warwick Ashcroft; Andrew John Bowyer
Original assignee: MAGNA PARVA Ltd
Current assignee: MAGNA PARVA Ltd
Priority date: 2009-11-25
Filing date: 2010-09-08
Publication date: 2011-06-08
Anticipated expiration: 2030-09-08
Also published as: GB0920646D0; GB2475938B; GB201014936D0

Abstract

A deployable pin (6) is held by means of a pin latch (4, 8, 11). The deployable pin (6) is released by applying a suitable electric current to a piezo-electric ceramic element (7), the movement of which is amplified by a distance multiplier such as levers (2, 3) to release the pin latch. The deployable pin (6) is ejected by a spring (10) and ejector (5). The device may be reset by pushing the deployable pin (6) back into the mechanism, against the force generated by the spring (10), until it latches into position.

Description

Release Mechanism

Field of Invention

The present invention relates to mechanisms which act to restrain a load against an applied force, until commanded to release the aforementioned load. This invention has particular application in the aerospace fields, in retaining deployable structures and other such items, but may be used in any application whereby a reusable and/or releasable latching device is desired.

Prior Art

Releasable restraint mechanisms are described in the patent literature. Representative patents include U.S. Pat. Nos. US 5,771,742 A; US 5,129,753 A; US 6,269,748 B1; US 6,450,064 B1; US 5,191,252; and US 4,783,610.

In current practice, a range of methods have been employed in the prior art for the retention and controlled release upon command of a structure or mechanism. Such devices are used, for example, in aerospace for the purposes of restraining deployable sensor booms, solar panels, hatches and releasable stores such as missiles and sensor packages. Other applications are found in marine engineering, safety devices and automotive systems.

The methods in current use may take the form of a pyrotechnic device, which employs an explosive charge to cut a bolt or other structural element; such devices impart a large shock load on the structure to which they are attached, and present a risk of premature activation through spurious signals or thermal variations. Pyrotechnics also generate a quantity of debris, in gaseous and solid form, which is undesirable in many applications.

Other systems utilise thermal wire-cutters whereby a heated knife is in contact with a fusible element of the tie-down structure. The application of heat severs the tie-down, thus releasing the restrained structure. Thermal knives have inherent disadvantages due to the weak link' in the tie down, and the slow release action of the cutting process.

Resettable or reusable devices such as those used in the release of stores from moving aircraft often employ pneumatic or hydraulically-operated systems. In such systems, the working fluid is maintained at a suitably high pressure within a storage vessel, when the system is commanded to release, a valve is opened allowing the pressurised fluid to act upon a ram, piston or other form of actuator, thereby operating a latch mechanism. Such fluid-operated systems are disadvantageous in that they require frequent and skilled maintenance due to the high pressures involved in their operation. The non-operating lifetime of the sealing elements in these designs also prevents them from being stored in a state of readiness and they are not suitable for use in clean environments or in space due to leakage of the working fluid. Other resettable release devices may employ electromagnetic or so-called smart' materials. The use of electromagnets is objectionable due to the high current demands posed by such devices and the stray magnetic field generated upon release, which may interfere with the operation of other systems in close proximity to the release mechanism. Smart materials such as nitinol require that the release mechanism be kept at a given temperature such that the phase-change temperature of the material is not exceeded, which precludes their use in many aerospace and critical applications.

U.S. Pat. No. US 5,771,742 A discloses a mechanism which uses a wire comprising a shape memory alloy, which changes in shape upon the application of heat. The motion thus generated is used to disengage a ball latch from a groove cut into a moveable component. In this manner a bolt or pin is released when an electrical current is passed through the device. The mechanism may be reset by means of a tool, which returns the internal mechanisms to their starting positions, thus the prior art shows that a release mechanism may be resettable.

U.S. Pat. No. US 5,191,252 discloses a system whereby the change in size of a piezo-electric ceramic element subjected to an electric charge is multiplied by means of flexures and levers, such that useful work may be done. The dimensions of the lever arms and the piezo-electric element may be adjusted to achieve a wide variety of actuation forces and stroke lengths as required. The prior art therefore shows that piezo-electric ceramic materials may be utilised to actuate mechanisms with considerable force and a useful stroke length.

U.S. Pat. No. US 5,282,729 A discloses a device which employs a threaded nut, which is divided into three segments, the segments being held in place by means of a wire wrapped around their periphery. A bolt or threaded rod is therefore held by means of the threaded nut, until such time as a release cable is pulled, removing the wire securing the segments. A spring-loaded cone forces the segments apart, releasing the threaded pin.

The system is not resettable without disassembly and requires a mechanical actuation force to be applied to the release cable.

U.S. Pat. No. US 6,450,064 Bi discloses a resettable release mechanism which employs a flywheel containing a number of roller elements. A cage retains the roller elements against locking features within the device by means of an over centre latch. To release the mechanism, a shape memory alloy wire is heated, which forces the latch into the unlocked position, allowing the roller elements to disengage and the mechanism to release.

U.S. Pat. No. US 3,722,944 discloses a mechanism for the restraint and release of aircraft stores which employs a sear latch with an over-centre locking mechanism. The mechanism is released by means of an electrically-actuated explosive gas-generator, which furnishes sufficient gas pressure to disengage the over-centre means and rotate the sear mechanism in order to release the store. The prior art disclosed shows that such means require that the explosive gas generator be replaced between each use of the release mechanism.

U.S. Pat. No. US 5,406,876 discloses a stores release mechanism whereby the store is held by means of a conical lug, which is releasably engaged with a plurality of locking fingers. The fingers are urged to disengage from the lug by means of an actuator, which may be hydraulic, pneumatic or electromagnetic in operation. The movement of the actuator is simultaneously communicated to the two latches by means of connecting rods and bell-cranks, such that they operate simultaneously.

Statement of the Invention

The invention provides a resettable mechanism for restraining and releasing a load as defined in claim 1. Preferred but non-essential features of the invention are defined in the dependent claims.

The invention provides a system whereby the aforementioned processes may be met without the requirement for a dedicated reset tool' and without the need for pyrotechnics, thermally-sensitive materials such as shape-memory alloys, or rotating mechanical parts.

The device is without corrosive or hazardous components, and may operate over a range of temperatures. The materials used in the construction of a mechanism according to the disclosures herein can be low outgassing and suitable for extreme environments. In particular, the invention relates to a novel arrangement which provides many simplifications over current state of the art methods which allow savings in the mass of aerospace structures and reduced demands on the power systems of these vehicles.

Furthermore, the resettable nature of the device allows its use in a great many applications where previously multiple devices would be required, and allows the device to be tested prior to its deployment. The maintenance demands of a mechanism built according to the invention will be lower than those posed by current state of the art mechanisms, as it does not incorporate working fluids and associated sealing elements, furthermore, there are no fundamental limits to the number of times which the mechanism may be operated.

According to one preferred formulation of the invention, a piezo-electric ceramic element is placed into contact with a distance multiplier comprising a series of levers formed from a high stiffness material such as tool steel or similar, which pivot on knife-edge fulcra and are held in mutual contact by means of a preload tension applied to the system. When a suitable electrical charge is applied to the piezo-electric ceramic element, it will expand by a predetermined amount, causing the levers to displace. The lengths of the aforesaid levers and the positions of the fulcra upon which they pivot are so arranged to generate sufficient motion to release a sliding member; the sliding member may thereupon be caused to move by means of the strain energy stored in a spring, thus releasing a pin latch which retains a deployable pin against the force of a further compressed spring. The pin latch may be formed by a pair of dowels manufactured from hard steel or some other such material, which engage in a groove or detent formed in the deployable pin, the pins being held in place by the sliding member.

In a further embodiment of the invention, the levers and casing are formed by a single piece of material, with hinge points being formed by local thinning of the material into flexures, and the use of a selective hardening process, which causes the pivot points to possess a lower stiffness than the arm sections. Such an arrangement possesses the advantage of being constructed from fewer components and therefore being less susceptible to jamming due to foreign body contamination.

In a further embodiment of the invention, the levers are arranged so as to pivot on pin hinges passing through the bodies of the respective levers and the casing of the device.

The advantage of this variation of the invention is that the device shall be more resistant to premature release caused by vibration and shock loads, or failure to release due to relative motion between levers, because the levers will be more rigidly constrained within the mechanism.

In a yet further embodiment of the invention, the distance multiplier comprises a train of gears, manufactured from a material having suitable hardness properties and being mounted within the casing such that they may rotate in response to the movement of the piezoelectric element. This embodiment has an advantage in that the transfer of motion through the distance multiplier is by means of rolling contact, thereby reducing the friction within the mechanism.

In a further embodiment of the invention, the distance multiplier comprises a hydraulic circuit, with pistons configured to be operated on by the actuator, and to operate on the latch mechanism. This embodiment has the advantage that the actuator may be positioned remote from the latch.

In an alternative embodiment of the invention, the sliding member is retained by a pair of lever arrangements arranged on either side of the deployable pin and sliding member.

Each lever assembly could be actuated by mechanically separate, electrically connected, piezo-electric ceramic elements or by an appropriate mechanical couple from a single piezo-electric ceramic element. This embodiment has the advantage of decreasing the likelihood of premature release under shock loads, without increasing the thickness of the system, which may be of advantage in applications where the volume available is limited.

In a further, exemplary embodiment of the invention, the sliding member is in the form of an annular collar containing a plurality of balls in place of the pins. The collar is retained by a number of lever arrangements and the whole system is actuated either by a single annular piezo-electric ceramic element or by a number of smaller elements arranged about the periphery of the device. The advantage of this arrangement is that a greater cross sectional area of piezo-electric ceramic element may be accommodated, allowing much larger loads to be retained and released for a given actuator volume.

In a further embodiment of the invention, the mechanism is reconfigured to act as a pin puller. In this configuration, the springs powering the deployable pin and sliding member are reversed such that it is drawn into the body of the release mechanism when the device is activated.

Preferably, in order to prevent the ingress of water, dust or other such contaminants, and to prevent loose cabling or other obstructions from fouling the moving parts of the device, it shall be encased within a casing. The casing may be conductive, if the piezo-electric ceramic element is suitably protected from short circuit; this allows the casing to be used as a return for the actuation signal, thereby reducing the mass associated with wiring.

Preferably, the mechanism will incorporate a preloading means, which applies a force to one or more elements within the mechanism, in order to compensate for wear of components, to compensate for the manufacturing tolerances used when the components are made and to pre-stress any piezo-ceramic elements employed such that they do not become damaged due to excessive expansion. The preloading means may take the form of a simple screw adjustment, shims or may be provided by elastically deforming the casing of the mechanism during manufacture. The preloading means may also be adjustable remotely by means of an actuator, allowing for wear and other factors to be compensated for without the need to disassemble or replace the device.

In any of the embodiments herein, the required actuation signal depends on the dimensions of the piezo-electric ceramic element employed within the device. Such elements commonly will require about 90 to about 200 volts of direct current electricity and will draw a few milli-amperes of current. This signal may readily be generated by means of a Cockcroft-Walton multiplier or switching power supply of the type used to power electroluminescent display backlights, vacuum fluorescent displays and the like.

Other methods of generating the actuation signal will be readily apparent to those skilled in the art, the wide range of which allows the employment of this device in a wide variety of applications. Further variations in the design of a release mechanism according to the invention herein may make use of other forms of actuator or force generator instead of the piezo-electric ceramic element, such as but not limited to, pneumatic rams, hydraulic rams, electromagnetic solenoids, linear motors, or other such devices.

An advantage of the invention is that the spring powering the ejection of the deployable pin may be tailored to allow a range of actuation forces. This allows the pin to be merely released, or forcibly ejected from the mechanism casing. It is an advantage of this aspect of the invention that the shock loads transferred to the deployed object and to the parent object may be minimised in any particular application. Furthermore, the mechanism may include a means for altering the ejection spring tension, either manually or by means of an actuator, which allows the mechanism to provide a range of ejection forces without the need for disassembly or remanufacture.

A further variation of the invention employs the release mechanism to operate a further secondary latching or holding device, which may be a clamp, shear, brake or other such means as will be apparent to those skilled in the art, thereby allowing the mechanism to retain and release a greater load than would otherwise be possible.

A further advantage of the invention is that the general principles of operation and layout of its elements may be scaled to produce a wide range of devices, possessing various actuation force and retention force capabilities. Those skilled in the art will appreciate that the respective features may not necessarily scale linearly. An increase in piezo-electric ceramic element cross section will enable greater retention forces to be achieved while an increase in length of the piezo-electric ceramic element will result in a greater lever displacement to be achieved.

Brief Description of Drawings

Exemplary embodiments of the invention will now be described in greater detail with reference to the drawings; Fig. 1 Is a view of the exemplary embodiment of the device according to the invention, in the locked configuration.

Fig. 2 Is a view of the exemplary embodiment of the device according to the invention when the piezo-electric ceramic element is activated.

Fig. 3 Is a view of the exemplary embodiment of the device according to the invention, showing the detent pin fully unlocked.

Fig. 4 Is a view of the exemplary embodiment of the device according to the invention, in the released configuration.

Fig. 5 Is a view of the exemplary embodiment of the device according to the invention, in the resetting configuration.

Fig. 6 Is an exploded view of the device according to the exemplary embodiment of the invention.

Specific Description

Fig. 1 shows a mechanism for the retention and controlled release of a deployable pin (6), such that a structure or mechanism may be retained and released upon application of a voltage, represented here as a battery (23) and switch (24), to a piezo-electric ceramic element (7). The mechanism is easily resettable by disconnecting the voltage source (23), (24), and reinserting the deployable pin (6).

The casing (1) contains a pair of levers (2), (3), which are configured so as to multiply the length change of a piezo-electric ceramic element (7) and pivot on knife edge fulcra (15) and (16). In the locked position, the deployable pin (6) is located in a hole formed in the casing (1), by means of a pair of pins (8) that engage in a detent (20) formed in the shaft of the deployable pin (6). The pins (8) are located in channels in the casing (1), and retained in the detent by the locking collar plate (4). A pair of release springs (4) are located in holes (21) in the locking collar plate (4) and are compressed against a shoulder of the casing (1). The locking collar plate (4)is held against the force of the release springs (11) by the end (17) of the secondary lever (3), which engages the end face of the locking collar plate (4) due to the force provided by a bias spring (12) that is located in a pocket (22) in the lever (3) and compressed against a wall of the casing (1).

The whole system is preloaded by means of an adjustment screw (13) threaded into a hole in the casing (1) which is locked in place with a locking nut (14). The end of the adjustment screw (13) bears against the piezo-electric ceramic element (7), via a force distributing pad (9).

In order to release the deployable pin (6), a sufficient voltage (23), (24) is applied to the piezo-electric ceramic element (7) such that it expands sufficiently to cause the primary lever (2) to force the secondary lever (3) to disengage from the locking collar plate (4) against the force of the spring (12). At this point, the release springs (11) will force the locking collar plate (4) into the release position as is shown in Fig. 2. In this position the pins (8) no longer lock the deployable pin (6) in place, and the deployable pin is forced from the body (1) by the ejector (5) using the energy stored in the ejector spring (10). As soon as the secondary lever (3)is disengaged from the locking collar plate (4), the voltage (23), (24) applied to the piezo-electric ceramic element may be removed, as the remainder of the release and ejection process is powered by energy stored in the release springs (11) and the ejector spring (10).

Fig. 3 shows the locking collar plate (4) in the fully released position, whereby the pins (8) are completely disengaged from the detent (20) in the deployable pin (6). And the ejector (5) is free to force the deployable pin (6) from the casing (1).

Fig. 4 shows the device in the fully deployed configuration, whereby the deployable pin (6) is completely removed from the casing (1), and both the locking collar plate (4) and ejector (5) are in their deployed positions. The pins (8) are retained within the casing by the end of the ejector (5), the geometry of the channels within the casing (1) and the walls of the casing (1) itself.

Fig. 5 shows the device during the reset operation. The deployable pin (6) is inserted into the casing (1) and pushes the ejector (5) against the force of the ejector spring (10), until the face (19) engages with protrusions (18) on the locking collar plate (4). As the deployable pin (6) is inserted further into the casing (1), the locking collar plate (4) moves such that the pins (8) are driven into the detent (20) in the deployable pin (6), and are locked into place by the locking collar plate (4), which in turn is retained by the secondary lever (3) that is forced into the locked position by the spring (12).

The above description of the preferred embodiment has been given by way of an example.

From the disclosures given, those skilled in the art will understand the invention and its advantages, and will also find apparent changes and modifications to the structures and processes disclosed. It is sought therefore to cover all such changes that lie within the scope of the invention, as defined in the appended claims and equivalents thereof.