Latching system and method for VTOL vehicles

Abstract

A system for latching an unmanned aerial vehicle (UAV) includes a first UAV for performing a mission, the first UAV configured with a latchable structure; a second UAV connected to a latching mechanism for assisting the first UAV in performing the mission; and a controller for dispatching the second UAV toward the first UAV to assist the first UAV in performing the mission and for commanding the latching mechanism to latch the latchable structure of the first UAV in mid-air. A UAV landing method includes dispatching the second UAV toward the first UAV with a cable extending from the latching mechanism movably connected to a landing platform; latching mechanism latches to the latchable structure of the first UAV; and landing the first UAV on the landing platform by reducing a length of the cable from the latching mechanism to the landing platform.

Description

[Technical field]

[0001] The present invention relates to the field of air vehicles, and more particularly to a latching system and method for a VTOL vehicle. [Background technology]

[0002] Air vehicles, such as unmanned aerial vehicles (UAVs) that undergo vertical take-off and landing (VTOL) maneuvers, whether rotary-wing or fixed-wing vehicles, often have difficulty landing precisely in a desired small area due to weather disturbances, such as the presence of high winds or precipitation, which can adversely affect control of the aircraft. These difficulties are exacerbated when it is desired to land on a moving platform, such as that of a truck or ship.

[0003] Some attempts have been made to mitigate the effects of weather disturbances during landing maneuvers by latching the aircraft to a landing platform and pulling the latched aircraft to the landing platform. However, dedicated and expensive equipment is required to perform such a latching operation. Other disadvantages of this approach relate to the difficulty of targeting the latching means deployed on the landing platform to an object tied or otherwise fixed to the aircraft, and to the difficulty of connecting this object to the latching means. When the landing platform undergoes three-dimensional movements (e.g., a shipboard platform), such a latching operation is almost impossible to perform and also creates a safety problem for the aircraft if the cables tied to the aircraft object get tangled with the ground station's fixtures.

[0004] It is an object of the present invention to provide an improved system and method for ensuring precise landing of a VTOL vehicle.

[0005] Another object of the present invention is to provide a system and method for ensuring reliable latching of a VTOL vehicle prior to landing, even when the landing platform is in motion.

[0006] It is another object of the present invention to provide a system and method for ensuring a safe landing of a VTOL vehicle.

[0007] Other objects and advantages of the present invention will become apparent as the description proceeds. Summary of the Invention

[0008] A system for latching an unmanned aerial vehicle (UAV) includes a first UAV adapted to conduct a mission, the first UAV configured with a latchable structure; a second UAV adapted to assist the first UAV in conducting the mission, the second UAV non-removably connected to a latching mechanism; and a controller operable to dispatch the second UAV towards the first UAV to assist the first UAV in conducting the mission and to command latching of the latching mechanism to the latchable structure of the first UAV in mid-air.

[0009] The second UAV is significantly smaller than the first UAV and allows for efficient latching operation without a battery, e.g., when a cable movably connected to a ground station extends to the second UAV and powers the second UAV.

[0010] Preferably, the latchable structure preferably extends downwardly from a lower surface of the first UAV such that at least one bar of the latchable structure is spaced downwardly from the lower surface, and the latching mechanism is configured with an element that yields and changes its shape when contacted by the latchable structure to initiate a latching operation therewith. The controller is operable to command movement of the first UAV to cause forcible contact between the at least one bar of the latchable structure and the yielding element of the latching mechanism when the first UAV is less than a predetermined distance away from the ground station.

[0011] In one embodiment, the latching mechanism includes a hook provided with a spring-loaded, inwardly pivoting latch and a post extending downwardly from the hook to a hub of the second UAV.

[0012] In one aspect, the latching mechanism of the second UAV is a multi-link connector that is maintained in an upwardly curved arrangement prior to latching and is configured to encompass at least one downwardly spaced bar of the latchable structure when latched.

[0013] In one aspect, the latching mechanism is adapted to assist the first UAV in landing on a landing platform, whereby the cable is wound onto a spool mounted to the landing platform, and a winch operably connected to the spool is operable to activate following the latching operation to reduce the length of the cable from the spool to the latching mechanism during the landing maneuver.

[0014] In one embodiment, the cable further includes a hose through which injectable fuel can flow into the first UAV following the latching action.

[0015] The UAV landing method includes the steps of dispatching an escort UAV, which is irremovably connected to a latching mechanism, toward an initiating landing UAV, wherein a cable extending from the latching mechanism is movably connected to a landing platform; latching the latching mechanism to a latchable structure of the initiating landing UAV; and landing the initiating landing UAV on the landing platform by reducing the length of the cable from the latching mechanism to the landing platform. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of an embodiment of a UAV latching system. [Diagram 2] FIG. 2 is a front perspective view of a latching mechanism usable with the system of FIG. [Diagram 3] FIG. 3 is a top perspective view of an escort UAV equipped with the latching mechanism of FIG. 2. [Figure 4] 4 is a method for performing a landing operation by the escort UAV of FIG. 3. [Diagram 5] A method for performing aerial refueling. [Figure 6] A method for performing an airborne battery swap. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Landing an aerial vehicle on a moving platform by latched VTOL maneuvers is difficult due to the need to align and latch the moving platform with the unmanned aerial vehicle (UAV). When the landing platform moves in more than one direction in response to swell, roll, and pitch motions caused by changing wind or wave directions (e.g., a ship-based platform), the ability to land reliably is significantly limited. Often, the latching means deployed on the moving platform cannot be successfully targeted, and the UAV fails to land, for example colliding with a ship or even falling into the sea.

[0018] It has now been discovered that the effects of a moving landing platform can be mitigated or eliminated entirely by using an escort UAV that is configured to latch with the initiating landing UAV in mid-air. Instead of exposing the initiating landing UAV to the risk of not successfully latching with the moving platform, the initiating landing UAV will be securely latched with the escort UAV in mid-air and then attracted to the landing platform.

[0019] The use of escort UAVs has utility for other missions as well.

[0020] 1 illustrates a system 10 for latching a UAV prior to a landing maneuver onto a platform 1, according to one embodiment, the system 10 being capable of being autonomous. The latching system 10 includes an initiating UAV 5 and a smaller escort UAV 15 adapted to assist the initiating UAV 5 during the landing maneuver.

[0021] The escort UAV 15 is a small-sized aircraft, e.g., a quadcopter, driven by an electric motor, which is permanently tethered to the ground docking station 11 by a cable 16 and can have a maximum take-off weight (MTOW) of about 1.5 kg, while being able to withstand crosswinds of up to 30 knots. The estimated carrying weight of the escort UAV 15 can be up to 0.5 kg of the cable 16, which typically includes a fiber optic communication cable and a power cable adapted to transport data and control commands. The MTOW of the escort UAV 15 can be maintained at such a low weight by not having batteries on board, while its motors are powered through the power cable. A typical length of the cable 16 is up to 10 m. Due to being tethered to the docking station 11 by the cable 16 as opposed to an extendable arm, the airborne stability of the escort UAV 15 can be advantageously maintained.

[0022] The battery-less escort UAV15 is guided by an autopilot, which is equipped with a real-time kinematic (RTK) precise GPS-based navigation device, which allows it to have relative GPS (RGPS) capability, with an accuracy of 1 cm relative to the landing-initiating UAV5.

[0023] The central hub of the escort UAV 15 is non-removably connected to a latching mechanism 18. A cable 16 is shown extending from the latching mechanism 18 and has a first end movably connected to the docking station 11, for example by a spool 19 attached to the bottom surface of the landing platform 1 through an aperture 9 formed in the landing platform, or alternatively to its upper surface, around which the cable is wound. A winch W operably connected to the spool 19 controls the extension or retraction of the cable 16.

[0024] The landing initiation UAV 5 is configured with a sturdy downwardly extending latchable structure 7, which is shown to be U-shaped with two spaced apart bars 2 and 3 extending downwardly, optionally diagonally from a lower surface 8 of the UAV 5, and one or two interconnecting bars 4 extending from the ends of the bars 2 and 3 and connecting them to each other to form the illustrated U-shaped configuration, but which could equally take any other suitable latchable shape.

[0025] During the flight, the docking station 11 communicates with the landing initiation UAV 5 and thus knows its real-time location and its intention to land on the docking station. When the landing initiation UAV 5 is less than a predetermined distance away from the docking station 11 and the landing maneuver is initiated, the escort UAV 15 is dispatched towards the landing initiation UAV 5, which typically hovers at a certain altitude up to 10 m (e.g., 3 m) above the landing platform 1 as determined by the on-board GPS system. Control commands are sent from the docking station 11 to the autopilot of the escort UAV 15 via cable 16 during the dispatch operation, such that the escort UAV will approach the U-shaped latchable structure 7 from below to prevent collision, and then perform a latching operation, whereby the latching mechanism 18 is set into engagement with the structure 7. After the UAV 15 is tethered to the landing platform 1, it is pulled towards the platform to ensure a safe landing.

[0026] A controller 20 located near the landing platform 1 coordinates the operations of the landing initiation UAV 5 and the escort UAV 15. The controller 20 can also be mounted on board the escort UAV 15 and governs the controlled activation and deactivation of its various motors and components. Alternatively, the controller 20 can be stationary and mounted on the landing platform 1 or in a structure built on the landing platform or on a docking station and can be in wireless communication with the motors and components of the UAV 15.

[0027] To govern the operation of the initiating UAV 5, the controller 20 can be configured to wirelessly transmit a request for a handshake signal when the initiating UAV 5 is less than a predetermined distance away from the docking station 11. The docking station 11 tracks the real-time location of the initiating UAV 5 and updates the controller 20 with this information. Following the transmission of the handshake signal from the initiating UAV 5 to the controller 20, in response, the controller temporarily takes over the motors and components of the UAV 5 and then dispatches the escort UAV 15 towards the initiating UAV 5. The controller 20 commands a controlled displacement of one or both of the initiating UAV 5 and the escort UAV 15 until the latching mechanism 18 of the UAV 15 is set into an engaged relationship with the structure 7 of the UAV 5, after which the motors of the initiating UAV 5 are commanded to be inactivated.

[0028] It should be understood that the controller 20 may govern the operation of the landing-initiating UAV 5 in other manners as well.

[0029] 2 illustrates a latching mechanism 38 according to one embodiment. In this embodiment, the latching mechanism 38 is a hook 36 provided with a spring-loaded, inwardly pivoting latch 39, which may have a length of about 20 cm and may be oriented substantially vertically. The latch 39 is adapted to yield when contacted by a latchable structure and is urged to pivot inwardly about axis 32 into the interior 33 of the hook 36. When the bar of the latchable structure is sufficiently introduced into the hook interior 33 such that it is spaced between the latch 39 and the inner surface of the hook 36, the force applied to the latch is released and the latch is pivoted outwardly about axis 32, its angular displacement limited by the lip 31 until the latch returns to its original position.

[0030] The latch 39 may be configured with a schematic RGPS sensor 29, which is in data communication with the controller 20 (FIG. 1) and a counterpart RGPS sensor mounted on the landing-initiating UAV 5 (e.g., housed within one of the bars of the latchable structure 7) to detect the relative distance to the UAV 5.

[0031] It should be understood that any other suitable latching mechanism comprising an element that yields and changes its shape when contacted by a latchable structure may also be used.

[0032] For example, the latching mechanism can be embodied by a multi-link connector, extending from the second end of the cable and including a plurality of serially extending links (e.g., five links), the total length of which is 40 cm, each joint of the connector being interconnected with two adjacent links, although any other number of links is within the scope of the invention. The links are interconnected such that the connector is always maintained in an upwardly curved arrangement extending upward above the height of the escort UAV, providing the appearance of the connector floating in the air while the escort UAV flies towards the initiating landing UAV. The distal link can be provided with a first magnet and the cable adjacent link can be provided with a second magnet. Following forced contact between the latchable structure and the connector, the various links are urged to be angularly displaced until the first and second magnets are coupled together, causing the connector to include one or two interconnections of the latchable structure. An electromechanical lock can be actuated to lock the end link and the cable adjacent link together following the latching action.

[0033] 3 illustrates an exemplary escort UAV 45 equipped with a latching mechanism 38. A short pole 42, having a length of, for example, about 20 cm, extends from the hub 41 of the escort UAV 45 to the latching mechanism 38 located above the hub 41 to facilitate the latching operation without interference with its propellers 47. The cable 16 extends downward from the pole 42 (or from the hub 41) and is prevented from becoming entangled with any of the propellers 47 during the landing operation by a cylindrical shield 49 having a vertical longitudinal axis that surrounds each propeller.

[0034] FIG. 4 illustrates an embodiment of a method for performing a landing operation by the escort UAV 45 of FIG.

[0035] After the docking station determines in step 52 that the landing-initiating UAV is separated from the docking station by less than a predetermined distance, the controller instructs the escort UAV to be dispatched toward the landing-initiating UAV with the assistance of the RPGPS sensor after lifting off from the landing platform in step 54. When the controller identifies a predetermined proximity (e.g., up to 10 m) between the landing-initiating UAV and the escort UAV in step 56, the landing-initiating UAV is instructed to accelerate until the latchable structure forcibly contacts the latch of the latching mechanism 38 shown in FIG. 3 (or the yielding element of any other suitable latching mechanism) to initiate a latching operation in step 58. The controller determines that a forcible contact has been made between the latchable structure and the latch of the latching mechanism by a touch sensor provided by the latchable structure and by the transmission of a corresponding signal between the landing-initiating UAV and the controller, and instructs the landing-initiating UAV to stop accelerating instead in step 62 upon completion of the latching operation.

[0036] In the next phase, the landing operation is initiated. While the initiating UAV and the escort UAV are latched together, the cable connecting the escort UAV to the landing platform is tensioned in step 64 when the initiating UAV is commanded to generate a certain lift while hovering, and at the same time the winch is activated. Since the cable remains tensioned, it is prevented from becoming entangled with the winch. A suitable rotation of the spool pulls the initiating UAV towards the landing platform with limited power by reducing the cable length between the spool and the latching mechanism in step 66.

[0037] When the cable length is sufficiently reduced, the initiating landing UAV approaches the landing platform, and then, in step 68, at least a portion of the initiating landing UAV passes through an aperture formed in the landing platform, which is configured to receive and support said portion. For example, the aperture has multiple areas, each of which is slightly larger than the contour of the corresponding rotor of the initiating landing UAV and the rotor of the latched escort UAV. Alternatively, the aperture can be a single cone-shaped aperture that surrounds all of the rotors. When a dedicated tool subsequently forcibly contacts the latch of the latching mechanism at the landing platform, and when the escort UAV is subsequently controllably moved laterally, for example, by special rigging or a movable floor surface, the latching mechanism is released from the latchable structure in step 70 in anticipation of a subsequent takeoff procedure.

[0038] In other embodiments, the escort UAV can assist the other UAV (hereafter the "main UAV") in carrying out other aerial missions after being latched together. The controller is operable to coordinate the operations of the main UAV and the escort UAV to ensure reliable performance of the respective missions described herein.

[0039] Although the following description is in terms of UAVs, it should be understood that the primary air vehicle can be any VTOL aircraft (e.g., multi-rotor, helicopters, fixed-wing aircraft with VTOL capabilities, etc.), whether unmanned or manned.

[0040] One additional mission enabled by the latching operation of the present invention is to assist the main UAV in air-to-air refueling, as illustrated in FIG. 5. Thus, while the main UAV is hovering in step 72, the escort UAV becomes latched with the main UAV in step 74 by the latchable structure 7 of FIG. 1 or by any other suitable latchable structure, such as adjacent to the main UAV area that needs to be interfaced to perform the air-to-air refueling operation thereafter. In this embodiment, the cable connected to the docking station is hollow and includes an inner hose that is generally fixedly attached to the outer cable layer, through which the fuel required by the main UAV can flow. A power cable for powering the escort UAV, as well as a fiber optic communication cable adapted to transfer data and control commands to the escort UAV, can be embedded in the outer cable layer while being appropriately isolated from the fuel flowing through the hose, for example, when the cable and / or hose are made of an electrical isolating material. Alternatively, the motor of the escort UAV can be powered by an on-board battery and controlled by remote wireless commands.

[0041] Following a latching action in which the latching mechanism surrounds the interconnect bar of the latching structure and the cable can be freely displaced along the length of the interconnect bar, an additional latching action is performed to center the cable and couple it with a fixed interface element provided by the main UAV. In this additional latching action, an arm in data communication with the controller redirects the terminal end of the cable towards the interface element, for example by an electromagnetic actuator or by mechanical engagement, and couples the terminal end with the interface element. The interface element can be a protruding element that protrudes from the body element of the main UAV and is equipped with a nozzle at its other invisible end that is in fluid communication with the fluid tank of the main UAV. When the female end of the hose is redirected by the arm to surround the protruding element, it becomes mechanically engaged with the protruding element, for example by a spring-loaded releasable arrangement. Alternatively, the terminal end of the hose can be provided with a nozzle and can be caused by the arm to be inserted into an interface cavity of the main UAV that is in fluid communication with the fluid tank.

[0042] It should be understood that the arm assisted latching action alone may be performed without the need for a latching action in combination with a U-shaped latchable structure.

[0043] The arm, which may be configured with multiple interconnected links, a telescoping body, and / or a pivotally connected end effector, may be movably connected to the main UAV casing and may be equipped with suitable sensors, such as touch sensors, RGPS sensors, and image processing sensors, that are in data communication with the controller and adapted to appropriately locate the distal end of the hose in step 76, whereupon the arm comes into engagement with or in force transmitting relationship with the distal end in step 78, redirects it into the interface cavity in step 80, and the controller then commands the injection of fuel through the hose, nozzle, and fuel tank in step 82. Alternatively, the arm may be movably connected to the escort UAV casing or hub.

[0044] Another mission enabled by the latching operation of the present invention is to assist the main UAV to perform air recharging. In this embodiment, conductors electrically connected to a charger mounted on a docking station are embedded in the cable. An electrical connection can be made with the main UAV battery when the terminal end of the hose is coupled with the interface element in step 80, and the charger is then selectively operated in step 84 until the main UAV battery is sufficiently charged. A power cable for powering the escort UAV and a fiber optic communication cable adapted to transfer data and control commands to the escort UAV can be embedded in the outer cable layer or otherwise separated from the conductors connected to the charger.

[0045] Another mission enabled by the latching operation of the present invention is to assist the main UAV in an airborne battery exchange, as illustrated in FIG. 6. The escort UAV is dispatched when the payload of the escort UAV includes a freshly charged battery, and a sensor on the main UAV, configured to dynamically detect the remaining charge in the main UAV battery while the main UAV is hovering in step 72, updates the controller that the charge level has dropped below a predetermined threshold in step 86. This step is of course also applicable to airborne recharge missions. Following the latching operation in step 88, the previously described arm in data communication with the controller is adapted to remove the depleted battery from the main UAV in step 90 and position it on the platform of the escort UAV in step 92. The arm then transfers the freshly charged battery from the payload of the escort UAV to a socket on the main UAV where it is electrically coupled in step 94. The arm then transfers the depleted battery from the platform to the escort UAV's payload and then couples the depleted battery in step 96. The battery can be configured with suitable components with which the movable arm is in force transmitting relationship to facilitate the transfer operation.

[0046] A similar arrangement can be used when it is desired to transfer a payload from a ground docking station to an airborne main UAV.

[0047] By performing an airborne latching operation, valuable time and resources can be advantageously saved in that it avoids the need for the main UAV to land at a docking station to perform any of the missions described above.

[0048] While several embodiments of the present invention have been illustrated and described, it will be apparent that the present invention can be implemented with many modifications, variations and adaptations without going beyond the scope of the claims, and can be implemented with the use of numerous equivalents or alternative solutions that are within the scope of those skilled in the art. [Explanation of symbols]

[0049] 1. Platform 2 Bar 3. Bar 4 Interconnect Bars 5. UAV starting landing 7 Latchable Structures 8 Lower surface 9 Aperture 10. System 11 Ground Docking Station 15 Escort UAV 16 Cable 18 Latching mechanism 19 Spool 20 Controller 29 RGPS Sensor 31 Lip 32 axis 33 Inside 36 Hook 38 Latching mechanism 39 Latch 41 Hub 42 Paul 45 Escort UAV 47 Propeller 49 Cylindrical Shield

Claims

1. 1. A system for latching an unmanned aerial vehicle (UAV), comprising: a) a first UAV adapted to perform a mission, the first UAV being configured with a latchable structure comprising two spaced apart bars 2 and 3 and one or two interconnecting bars 4, the latchable structure comprising two spaced apart bars extending downward from a lower surface of the first UAV and at least one interconnecting bar connected to each other between the ends of the two spaced apart bars; b) a second UAV adapted to assist the first UAV in performing the mission when latched together with the first UAV, the second UAV being non-removably connected to a latching mechanism including a hook provided with a spring-loaded inwardly pivoting latch and a post extending downwardly from the hook to a hub of the second UAV, the latchable structure being configured to yield when contacted by at least one interconnect bar of the latchable structure to initiate a latching operation therewith; c) a cable movably connected to a ground station, the cable extending to the second UAV and including a fiber optic communication cable section and a power cable section adapted to power the second UAV and transfer data and control commands thereto; d) a controller operable to dispatch the second UAV upward from the first UAV towards the ground station upon sending a control command via the cable, and to command the latching of the latching mechanism connected to the second UAV in mid-air with the latchable structure of the first UAV while the second UAV is below the first UAV or horizontally spaced apart from the first UAV during the latching operation; Including, Following the latching action, the hook of the latching mechanism is configured to surround the at least one interconnect bar of the latching mechanism and is freely displaceable along a length of the at least one interconnect bar. system.

2. The system of claim 1 , wherein the second UAV is significantly smaller than the first UAV and is powered without a battery.

3. The system of claim 2 , wherein the latching mechanism is adapted to assist the first UAV in landing on a landing platform.

4. 4. The system of claim 3, wherein the cable is wound around a spool mounted on the landing platform, and a winch operably connected to the spool is operable to activate following a latching operation to reduce the length of the cable from the spool to the second UAV during a landing maneuver.

5. 2. The system of claim 1, wherein the controller is operable to command movement of the first UAV to cause forced contact between the at least one interconnect bar of the latchable structure and the yield latch of the latching mechanism when the first UAV is less than a predetermined distance away from the ground station.

6. 1. A method for landing a UAV, comprising: a) providing a first UAV comprising a latchable structure comprising two spaced apart bars 2 and 3 and one or two interconnecting bars 4, the latchable structure comprising two spaced apart bars extending downwardly from a lower surface of the first UAV and at least one interconnecting bar connected to each other between ends of the two spaced apart bars; b) providing a second UAV non-removably connected to a latching mechanism including a hook provided with a spring-loaded inwardly pivoting latch and a post extending downwardly from the hook to a hub of the second UAV, the latchable structure being configured to yield when contacted by at least one interconnect bar of the latchable structure to initiate a latching operation therewith, a cable extending from a lower surface of the second UAV and powering the second UAV being movably connected to a ground station; c) dispatching the second UAV upward from the ground station toward the first UAV while transmitting a command signal over the cable when the first UAV is determined to be less than a predetermined distance from the ground station by a controller in data communication with the first UAV, the second UAV, and a winch mounted on the landing platform and operably connected to a spool around which the cable is wound; d) commanding, by the controller, a controlled displacement of one or both of the first UAV and the second UAV to initiate a latching operation between the first UAV and the second UAV until the latch of the latch mechanism contacts at least one interconnect bar of the latchable structure in mid-air and the hook encircles the at least one interconnect bar while the second UAV is below the first UAV or horizontally spaced apart from the first UAV; e) landing the first UAV on the landing platform by commanding operation of the winch by the controller to reduce a length of cable from the second UAV to a landing platform; A method for landing a UAV, comprising:

7. The method of claim 6, wherein the step of commanding a controlled displacement of one or both of the first UAV and the second UAV is performed by commanding the first UAV to accelerate until the at least one interconnecting bar forcibly contacts a latch of the latching mechanism, the latch yielding in response to the forcible contact and urging the hook to encircle the at least one interconnecting bar.

8. The method described in claim 7, wherein the controller temporarily takes over motors and components of the first UAV until the at least one interconnect bar is forced into contact with a latch of the latching mechanism.

9. The method described in claim 8, wherein the controller determines that forced contact has been made between the at least one interconnect bar and the latch using a touch sensor provided on the latchable structure which sends a corresponding signal to the controller when forcibly contacted.

10. The method of claim 7, further comprising the step of instructing the first UAV by the controller to stop accelerating when the latching operation is completed.

11. The method of claim 6, wherein all steps are performed independently.

12. The method of claim 6, further comprising the step of causing the latch mechanism to decouple from a latchable structure on the landing platform in anticipation of a subsequent takeoff procedure by applying a force to a specialized tool that initiates additional forcible contact with the latch, whereby the shape of the hook is changed in response to the additional forcible contact until the hook surrounds at least one interconnecting bar.

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