System, device, and method for detecting a robot interface rigidified during free flyer object capture

Abstract

Provided herein are a system and related method for use in a grapple fixture to detect stiffening of a robotic capture interface between the grapple fixture and a robotic arm. The system includes a movable component configured to couple to a mounting end of a grapple probe, a resistive component for resisting movement of the movable component until a threshold force is reached, the threshold force being correlated to a required preload force of the robotic interface, a detection component, and a trigger component, wherein movement of the movable component causes the trigger component to move and effect a change in state of the detection component, and the threshold force of the resistive component is configured to be overcome only when a defined preload of the robotic capture interface is reached.

Description

Technical Field

[0001] The following disclosure generally relates to robotic systems, and more particularly to systems, devices, and methods for detecting a rigidified robotic capture interface.

Background Art

[0002] Robotic components can be coupled to other robotic systems or components through a robotic interface. For example, the robotic end effector of a robotic arm or manipulator can be coupled to an object (“captured object”) or payload such that the object can be manipulated by the robotic arm. When the object is manipulated, the object can be decoupled from the robotic end effector. One use of such systems is in space applications. The reason is that the harsh external environment in space may require the use of robotic systems instead of human labor, and in space applications, the capture of free-flyer objects may be particularly necessary.

[0003] Such systems can additionally be implemented in non-space applications, such as underwater / subsea environments, when the object has buoyancy within the atmosphere or during free fall, or when a load that needs to be captured and controlled is suspended from a crane.

[0004] When the robot interface is successfully connected, it may be desirable to send a signal to the system. For example, it may be advantageous to determine the moment when the end effector is connected to an object so that the robotic arm can be instructed to move. Some current robotic systems include a system for detecting when the connection of such components is fully executed. For example, an electrical switch can be present within the end effector, which can be triggered when an object is connected. The circuit associated with such a switch can be monitored by the on-board computer equipment of the robotic arm or related platform.

[0005] It may also be advantageous to detect similarly on the object side when the object is successfully connected to the end effector. This may be particularly important in the case of free-flyer object capture. It may be possible to transmit the known interface status from the end effector part of the interface to the other side of the interface through a conductive or radio frequency-based electrical communication channel. However, such a method can be technically complex, prone to failure, or otherwise affect the functionality of the interface.

[0006] Additionally, it is preferable that the detection of free-flyer rigidification does not interfere with free-flyer soft capture. For example, some rigidification detection mechanisms can apply residual forces that are designed to be applied to the free-flyer object, which can deflect or reorient the free-flyer object in space and interfere with the free-flyer soft capture process itself. To avoid such capture problems, there is a need for a rigidification detection mechanism that applies a sufficiently small force to the free-flyer object prior to soft capture. Summary of the Invention Problems to be Solved by the Invention

[0007] Accordingly, there is a need for an improved system and method for detecting a rigidified robot interface during robotic capture of an object that overcomes at least some of the disadvantages of existing systems and methods.

Means for Solving the Problem

[0008] Disclosed herein is a system for use in a grapple fixture for detecting stiffening of a robotic capture interface between a grapple fixture and a robotic arm, according to one embodiment. The system is disposed within an internal compartment of a grapple fixture base and is a movable component movable in a first direction and an opposite second direction along a first axis, and is configured to couple to a mounting end of a grapple probe such that when assembled within the grapple fixture, a force applied to the grapple probe along the first axis is applied to the movable component. A movable component, a resistance component disposed within the internal compartment of the grapple fixture to resist movement of the movable component in a first direction along the first axis until a threshold force is reached, the threshold force being correlated to a defined preload force of the robotic interface, a detection component disposed within the internal compartment of the grapple fixture base to register a first state and a second state, the first state corresponding to a non-stiffened interface state and the second state corresponding to a stiffened interface state, and a trigger component configured to move with the movable component along the first axis, wherein movement of the movable component in the first direction causes the trigger component to move in the first direction and effect a state change of the detection component from the first state to the second state. The threshold force of the resistance component is configured to be overcome only when the defined preload of the robotic capture interface is reached.

[0009] According to some embodiments, the movable component is a grapple force transmission component.

[0010] According to some embodiments, the resistance component is a spring subsystem including at least one spring.

[0011] According to some embodiments, at least one spring is a wave spring.

[0012] According to some embodiments, at least one spring is two springs.

[0013] According to some embodiments, the trigger component is an arm that extends generally perpendicularly from the outer surface of the movable component.

[0014] According to some embodiments, the state change includes physical contact.

[0015] According to some embodiments, the detection component is a contact mechanism.

[0016] According to some embodiments, the trigger component includes three arms, the detection component includes three detection components, each detection component is configured to register a state based on an interaction with each of the three arms, the detection component implements a voting architecture for determining a voted output state based on the states registered by the three detection components, and the voted output state corresponds to the majority state condition of the three detection components.

[0017] According to some embodiments, the detection component includes three contact mechanisms.

[0018] According to some embodiments, the trigger component triggers through a non-contact mechanism.

[0019] According to some embodiments, the detection component is an optical sensor.

[0020] According to some embodiments, the detection component is a capacitance sensor.

[0021] Disclosed herein is a method for detecting, through a grapple fixture, a rigid state of a robotic capture interface between a robotic capture device and the grapple fixture, according to one embodiment. The method includes providing a grapple fixture including a probe, a movable component coupled to the probe, a resistive component coupled to the movable component, a detection component, and a trigger component; resisting, via the resistive component, movement of the movable component from a first position to a second position when a tensile force applied to the probe is less than a defined amount of force; triggering, by the trigger component, a first state change registered by the detection component when the movable component moves from the first position to the second position; communicating, from the detection component, a first state condition when the detection component registers the first state change; and returning, via the resistive component, the movable component from the second position to the first position when the tensile force applied to the probe drops below the defined amount of force.

[0022] According to some embodiments, the method further includes triggering, by the trigger component, a second state change registered by the detection component when the movable component moves from the second position to the first position; and communicating, from the detection component, a second state condition when the detection component registers the second state change.

[0023] According to some embodiments, the resistive component is configured to have a pre-determined amount of force overcome only when a required threshold force of the robotic capture interface is reached.

[0024] According to some embodiments, the resistive component is a spring subsystem including at least one spring.

[0025] According to some embodiments, at least one spring is a wave spring.

[0026] According to some embodiments, at least one spring is two springs.

[0027] According to some embodiments, the state change includes physical contact.

[0028] According to some embodiments, the detection component is a contact mechanism.

[0029] According to some embodiments, the detection component includes three contact mechanisms.

[0030] According to some embodiments, the detection component is configured to register a state change through a non-contact mechanism.

[0031] According to some embodiments, the detection component is an optical sensor.

[0032] According to some embodiments, the detection component is a capacitance sensor.

[0033] Described herein is a method of assembling a rigidification detection system for detecting a rigidified state of a robotic capture interface between a robotic capture device and a grapple fixture. The method includes providing a grapple fixture base, a probe, a movable component, a resistive component, and a detection component; coupling the movable component to the probe such that the movable component moves along the same axis as the probe moves along an axis, the movable component including a trigger component; disposing the resistive component between the movable component and an inner surface of the grapple fixture base such that the resistive component resists movement of the movable component along the axis until a predetermined threshold amount of pulling force is applied to the probe along the axis and returns the movable component to a first position when the pulling force applied to the probe drops below the predetermined threshold amount of force; and disposing the detection component within an inner compartment of the grapple fixture base, the detection component being positioned such that the detection component can be triggered by the trigger component and being configured to register a change in state and communicate the change in state as a signal when triggered.

[0034] Other aspects and features will become apparent to those skilled in the art upon review of the following description of some exemplary embodiments.

[0035] The drawings included herein are for purposes of illustrating various examples of the articles, methods, and apparatuses of this specification.

Brief Description of the Drawings

[0036]

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DETAILED DESCRIPTION OF THE INVENTION

[0037] Various devices or processes will be described below to provide examples of respective claimed embodiments. The embodiments described below do not limit any claimed embodiment, and any claimed embodiment may cover processes or devices different from those described below. A claimed embodiment is not limited to a device or process having all of the features of any one device or process described below, nor is it limited to features common to a plurality or all of the devices described below.

[0038] As used herein, the terms "free flying object", "free flyer object", or "free flyer" refer to an object that is not fixed in an inertial frame. That is, the object is free to move or accelerate in multiple degrees of freedom. Thus, forces resulting from contact with another object will tend to accelerate the free flyer in the opposite direction. A strong initial contact force during an attempt to capture a free flyer object will tend to "chip off" the object. This is why the robotic capture systems and devices of the present disclosure are configured to perform "soft capture" (low forces applied at relatively high speeds to prevent chipping off) and "hard capture" or "rigidification" (high forces at relatively low speeds after chipping off has already been prevented by soft capture). Generally, a free flyer object is not physically connected to the body part that "captures" it, which is the body part to which the robotic capture device is attached. The body part that "captures" has the ability to control itself in six degrees of freedom (DOF), but does not have relative six DOF control between the capturing body part and the free flyer. "Free flyer capture" is the act of obtaining control of the relative six DOF motion between the capturing body part and the free flyer. On Earth, two bodies that are not directly connected often have an indirect connection through gravity and friction, and through the ground between the objects, and thus are not unconstrained free flyers. The systems and methods of the present disclosure can be used to facilitate capture in other environments where chipping off of the captured object can occur during grappling attempts. Additional environments in which the systems and methods can find use include underwater / under-sea environments or within space / in flight, including when the object is buoyant in the atmosphere or in free fall. The systems and methods can be used in Earth-based environments, for example, when some, if not all, of the DOF are not controlled. One such example is a load suspended from a crane that needs to be captured and controlled.

[0039] Generally, the present disclosure provides a system, method, and device for robotic capture of an object, including capturing the object by grappling a grapple fixture attached to the object and rigidifying an interface between an end effector and the grapple fixture to establish a load-bearing interface so that the object can be manipulated by a robotic system. This manipulation can include, for example, moving the object from one location to another or passing any one or more of power, data, or torque through the end effector to the object. The object referred to herein as the "captured object" or "payload" can be an object that is not connected to any system to which a robotic arm used to operate the end effector is connected, generally making alignment more challenging. For example, the object can be a freely floating underwater object or a free-flying object (a free flyer object, such as an active functioning satellite, a retired or malfunctioning satellite, a spent upper stage of a launch vehicle, or an orbital debris object, etc.). Thus, the end effector of the present disclosure can be configured to have a relatively large capture envelope to address the possibility of misalignment during approach and capture.

[0040] The robotic capture systems and devices of the present disclosure can also be used to perform "pick and place" operations on an object, enabling the object to be grasped and moved to another location at the end of a robotic manipulator system. Further, the robotic capture systems and devices of the present disclosure can also be used to perform docking of a free flyer object, where the free flyer includes the end effector and a larger "more stationary" object includes the grapple fixture. In such a case, the servicing spacecraft can perform all maneuvers without a robotic arm. As such, the free flyer capture mechanism can be present on either the servicing or the client.

[0041] In one embodiment, the end effector is directed by a robotic arm to approach a grapple fixture. The grapple fixture includes a probe having a tip that contacts a probe guide surface at the receiving end of the end effector. The tip is guided by the probe guide surface through an opening in the probe guide surface to a grappling position. The presence of the probe at the grappling position is sensed by the end effector, and a capture mechanism is engaged to grapple the tip of the probe of the grapple fixture. The capture mechanism is retracted to draw the probe further into the end effector and to matingly contact the base of the grapple fixture with the probe guide surface. The capture mechanism is retracted to a position where the interface between the grapple fixture and the end effector is rigidified, and a desired preload is generated. The captured and rigidified object can then be manipulated by the robotic system, such as by maneuvering the object via the robotic arm.

[0042] The foregoing multi-stage capture and rigidification can advantageously enable easier and more successful initial capture of an object. The multi-stage approach to capture advantageously allows rotation of the object during the capture process to achieve proper alignment for a more than sufficient capture. Additionally, in the multi-stage capture and rigidification operation, it is desirable to know when the interface is fully captured and rigidified. The systems and methods described herein are capable of providing such capabilities.

[0043] As used herein, the term "end effector" generally refers to a robotic device or element at the end of a robotic arm that performs a function. In the present disclosure, that function includes capturing a free-flying asset or a non-free-flying asset. The term "end effector" as used herein includes devices that are permanently or inseparably attached to the end of a robotic arm and devices having a separable interface with the end of the robotic arm. The separable interface can enable the end effector to be picked up, used, and placed down (i.e., separated from the robotic arm). An example of an end effector having a separable interface can also be referred to as a "tool" or an "end of arm tool". In such an example, the robotic arm can have a first end effector attached to its end that has a tool changer function that enables the robotic arm to use a plurality of different tools, and a second end effector having a separable interface, and the second end effector can be engaged by the first end effector and function as a tool. In such a case, the first "tool changer" end effector and the second "tool" end effector are each considered end effectors. Accordingly, any reference herein to an "end effector" is intended to include all devices as described in the foregoing, unless otherwise stated.

[0044] The systems and methods described herein further enable detecting a rigidified robotic capture interface between an end effector and a grapple fixture on a free flyer object through the grapple fixture of the free flyer object. The grapple fixture of the free flyer object is configured such that when the interface is fully coupled (e.g., realizing soft capture and rigidification / hard capture in a multi-stage capture process), the grapple fixture end of the interface can independently confirm that the interface is fully coupled without using an electrical communication system that communicates across the interface to improve system reliability.

[0045] In one embodiment, detecting the rigidified state of the robotic capture interface is accomplished using three switches (spaced 120° apart by any two switches sufficient to confirm full capture) with mechanical armatures that move when the grapple probes of the grapple fixture are rigidified by the end effector. This design enables a highly reliable confirmation of full capture. In some cases, this can include a voting architecture implemented as part of the design, where the states from multiple sensing components (e.g., three) are detected and communicated, and each communicated state is counted as a vote, and the votes are tallied according to one or more pre-determined rules to generate a voted or confirmed state. This solution includes multiple wave springs that are specifically tuned or selected such that the switches can only be changed with respect to their state when sufficient interface preload force is achieved.

[0046] Referring now to FIG. 1, a free flyer capture system 100 is shown herein that includes a platform 116 and a free flyer object 104 (e.g., a satellite, etc.) that implements a capture sequence according to one embodiment.

[0047] The platform 116 can be the surface of a satellite, a space station, or other spacecraft. The platform 116 includes a robotic arm 102 and an end effector 106, the end effector 106 has a receiving end 110, and is connected to the robotic arm 102 to implement the capture of the free-flyer object 104. The end effector 106 can be, for example, the end effector in FIG. 2, the end effector in FIG. 5, or the end effectors in FIGS. 9-10. The operation of the robotic arm 102 is controlled via a robotic arm controller 114.

[0048] The free-flyer object 104 includes a grapple fixture 108 mounted on the outer surface of the free-flyer object 104 to interface with the end effector 106. The grapple fixture can be, for example, the grapple fixture in FIG. 2 or the grapple fixtures in FIGS. 6-10.

[0049] An arm vision system (not depicted) can confirm the correct target tracking of the free-flyer object 104. This can include tracking a machine vision target on the free-flyer object 104. The machine vision target can be positioned near the grapple fixture 108.

[0050] Generally, in the operation of system 100, the robotic arm 102 can be maneuvered such that the end effector 106 is in a position for capturing the grapple fixture 108 of the free flyer object 104. Thereafter, the receiving end 110 of the end effector 106 can grapple the grapple fixture 108 to softly capture the free flyer object 104. Next, the interface can be rigidified such that the grapple fixture 108 is further pulled into the receiving end 110 until the free flyer object 104 is fixed and preloaded relative to the end effector 106. At this point, the free flyer object 104 can be safely and reliably manipulated by the robotic arm 102. A rigidification detection system within the grapple fixture 108 can detect the state of rigidification of the interface, which can then be communicated to other components of the grapple fixture 108 and / or components of the free flyer object 104.

[0051] Referring now to FIG. 2, a system 200 for robotic capture of an object, according to an embodiment, is shown herein. The system 200 can be used, for example, to capture a free flying object such as a satellite. In other embodiments, the system 200 can be used to capture a non-free flying object.

[0052] The system 200 includes a capture object 202 and a robotic system 204 for capturing the capture object 202 and, once captured, manipulating the capture object 202.

[0053] The capture object 202 includes a machine vision target 206 on the capture object 202. The machine vision target 206 is positioned on the capture object 202 such that the machine vision system 208 of the robotic system 204 can detect and track the machine vision target 206.

[0054] The machine vision system 208 can include a camera for visualizing the machine vision target 206, a processor for generating and processing the image data collected by the camera, a memory for storing the image data, and a communication interface for communicating with other components of the robot system 204 (e.g., communicating information about the detection and tracking of the machine vision target 206).

[0055] Also, the robot system 204 includes a robot arm controller 210 for controlling the movement of the robot arm 212. The robot arm controller 210 includes a processor for processing data, a memory for storing data, and a communication interface for communicating with the machine vision system 208 and the robot arm 212. For example, the robot arm controller 210 can receive data from the machine vision system 208 regarding the detection and tracking of the machine vision target 206 (and thus the captured object 202), and generate an arm movement command based on the received machine vision data. The robot arm controller 210 can then send the arm movement command to the robot arm 212 and control the movement of the robot arm 212.

[0056] In some cases, the robot arm controller 210 can be configured to determine a relative approach speed and to maintain the relative approach speed within a pre-determined range in order to facilitate the soft capture of the captured object 202.

[0057] The robot system 200 also includes an end effector 214 connected to the robot arm 212. The end effector 214 is configured to capture (grapple and rigidify) the captured object 202 via a grapple fixture 216 on the captured object 202. Also, the end effector 214 can be configured to pass any one or more of power, data, and torque to the captured object 202 through an interface present on the captured object 202 once it is captured.

[0058] The grapple fixture 216 can be attached to the captured object 202 in a location close to the machine vision target 206, and the machine vision target 206 can be used to direct the end effector 214 towards the grapple fixture 216 for capture.

[0059] The grapple fixture 216 includes a base 218 and a deflectable probe 220 connected to the base 218.

[0060] The base 218 is attached to the outer surface of the captured object 202. The deflectable probe 220 is connected to the base 218 and is generally perpendicular to the base 218 when the deflectable probe is in a rest state (i.e., not deflected).

[0061] The base 218 includes a mating surface 222 that is configured to interface and mate with a probe guide surface 224 of the end effector 214 during capture. The mating surface 222 includes one or more alignment features 226. The alignment features 226 are configured to interface with complementary alignment features 228 on the probe guide surface 224. The alignment features 226 are configured to drive the alignment of the grapple fixture 216 and the probe guide surface 224 through contact with the alignment features 228. The alignment features 226, 228 can be used to generate the necessary preload for the end effector grapple fixture interface. In some embodiments, the preload can be applied to only a subset of the alignment features 226, 228 (or only a subset of the alignment features can be used to respond to the load at the interface). For example, in certain embodiments, the alignment feature 228 can include a raised contact annulus and a plurality of alignment fins along with complementary alignment features 226 on the grapple fixture, and only the annulus is used to respond to the load at the interface (preload in only the contact annulus, not in the fins, "annulus reaction"). In another embodiment, the annulus may not be present, and the alignment fins can be used to respond to the load at the interface ("fin reaction"). The alignment features 226, 228 can be used to provide rotational and shear alignment of the grapple fixture 216 and the end effector 214 when brought together. Also, the alignment features 226, 228 can be configured to allow some level of offset (e.g., lateral offset, rotational offset) between the grapple fixture 216 and the end effector 214 during capture.This can be particularly advantageous, for example, in the case of a fly-by object, in applications where the captured object 202 has a tumble rate. The alignment features 226, 228 can be configured to cause self-alignment of the interface as a result of rotational misalignment (e.g., a 5-degree offset).

[0062] The deflectable probe 220 of the grapple fixture 216 includes a probe 230 that includes a shaft terminating at a grapple end 232. The grapple end 232 can have a diameter larger than the diameter of the shaft. The grapple end 232 can include a spherical tip. In cases where the grapple end is rounded or spherical, the grapple end 232 can be referred to as a "grapple ball".

[0063] Also, the deflectable probe 220 includes a deflection element 234 to enable deflection of the probe 230 in the direction of an applied force. Further, the deflection element 234 is configured to return the probe 230 to a stationary state (non-deflected state, no applied force) when the applied force is removed. The amount of applied force required to deflect the deflection element 234 can vary depending on the material used. In one embodiment, the deflection element includes one or more springs.

[0064] The deflection element 234 is connected to the probe 230 and the base 218 to facilitate deflection relative to the base 218. Also, in some cases, the probe 230 can be directly attached or mounted to the base 218.

[0065] The deflectable probe 220 further includes a base rigidification detection system 248. The base rigidification detection system 248 is configured to detect a rigidified state of a robotic capture interface between the grapple fixture 216 and the end effector 214 at an interface grapple fixture end. The base rigidification detection system 248 is capable of generating a signal to communicate the signal to a secondary subsystem on the captured object 202 (not shown) such that the state of the robotic capture interface (i.e., rigidified, not rigidified) can be communicated to the secondary subsystem. The secondary subsystem can be configured to change a state or perform an action or operation based on the received signal (e.g., release a captured or attached payload).

[0066] Generally, when the robotic arm 212 moves the end effector 214 toward the grapple fixture 216 of the captured object 202, the grapple end 232 of the deflectable probe 220 contacts the probe guide surface 224 of the end effector 214.

[0067] The probe guide surface 224 is curved to urge deflection of the deflectable probe 220 toward the opening 236 when contacting the grapple end 232. The opening 236 can be positioned at or near the center of the probe guide surface 224. In the case where the probe guide surface 224 is concave, the opening 236 can be positioned at the apex of the concave probe guide surface 224.

[0068] The probe guide surface 224 is composed of a material suitable for allowing the grapple end 232 of the deflectable probe 220 to slide along the probe guide surface 224. For example, the material can be selected to have an appropriate frictional interaction between the probe guide surface 224 and the grapple end 232. Similarly, the grapple end 232 is composed of a material suitable for allowing the grapple end 232 to slide along the probe guide surface 224 with a desired or acceptable level of friction.

[0069] Generally, the movement of the end effector 214 towards the grapple fixture 216, the deflection of the deflectable probe 220, and the shape and surface composition of the probe guide surface 224 and the grapple end 232 act together to guide the grapple end 232 through the opening 236 into the internal compartment 238 of the end effector 214 for grappling.

[0070] The internal compartment 238 houses the probe sensing element 240, the grapple 242, the linear displacement mechanism 244, and the rigidification mechanism 246.

[0071] The probe sensing element 240 is configured to sense the presence of the grapple end 232 of the probe 230 and trigger the grapple 242 to grip the grapple end 232.

[0072] The probe sensing element 240 is positioned near the opening 236 and enables the grapple 242 to grip the grapple end 232 when triggered by the grapple end 232 (such as by being pushed down or otherwise contacted by the grapple end 232, for example). For instance, in one embodiment, the grapple 232 can include a pair of jaws that are in an open state until triggered to close by the probe sensing element 240. The probe sensing element 240 is positioned such that the grapple end 232 enters and occupies the space between the open jaws (the "grapple position" or "soft capture position") in order for the grapple end 232 to trigger the probe sensing element 240 (such as by physical contact therewith). The jaws can then be closed to grapple the grapple end 232.

[0073] The grapple 242 can be configured to constrain the three degrees of freedom (linear motion) of the grapple fixture 216 when grappling the grapple end 232 of the probe 230.

[0074] The linear displacement mechanism 244 is configured to translate the grapple 242 along the capture axis of the end effector 214. When the grapple 242 grips the grapple end 232 of the deflectable probe 220, the linear displacement mechanism 244 retracts the grapple 242 (and the grappled probe 230) in a direction opposite to the receiving end of the end effector 214. The retraction of the grapple 242 further draws the deflectable probe 220 into the inner compartment 238, which brings the mating surface 222 and alignment features 226 of the grapple fixture base 218 closer to and into contact with the probe guide surface 224. As previously described, in some embodiments, only a subset of the alignment features 226 can come into contact.

[0075] In one embodiment, the linear displacement mechanism 244 includes two ball screws, ball nuts attached to each ball screw, and a motor for driving the rotation of the ball screws. The ball nuts are attached to the grapple 242, and when the ball screws rotate, the grapple 242 is translated via the ball nuts. By using two ball screws, the ball screws can be installed on each side next to the rest of the mechanism, and the balanced load shortens the tool. This design can be particularly advantageous in robotic arm operations where a longer package (such as using a single ball screw instead of two ball screws) is not preferred. Nevertheless, in other embodiments, a single ball screw can be used.

[0076] The linear displacement mechanism 244 is configured to retract the grapple 242 to the hard capture position. When the grappled deflectable probe 220 is retracted, the angular and lateral offsets of the captured object 202 are removed. The hard capture (rigidification) of the grapple fixture 216 is achieved when the probe 220 is retracted to the point where the grapple fixture 216 is preloaded against the probe guide surface 224 of the end effector 214. This can include the contact and mating of the alignment features 226, 228. In particular, the internal compartment 238 includes a rigidification mechanism 246 for rigidifying the interface between the grapple fixture 216 and the end effector 214. In one embodiment, the rigidification mechanism 246 includes a compressible element (such as a Belleville spring stack), and the compressible element is compressed to the preload position (corresponding to the compression of the compressible element) via the retraction of the probe 220 by the linear displacement mechanism 244. The compressible element can be a spring-based compliant member.

[0077] The compressible element provides a known stiffness bias relationship. The use of a compressible element (e.g., a Belleville stack) allows the load variation to be maintained in a controlled state. There are several effects that can cause the load to change when it reaches a hard capture or rigidified position. These effects include temperature, where the coefficient of thermal expansion (CTE) of the structure is different from that of the mechanism, and thus a change in temperature causes a change in the position of the mechanism relative to the structure. This is particularly relevant when used in an environment where the temperature can change dramatically (e.g., from -40°C to +100°C), such as in outer space. Also, the effects that cause the load to change once it is hard captured include, for example, variations in the length of the grapple probe for each fixture, and position variations / accuracy within the capture tool. The compressible element has a lower stiffness compliance that allows the hard capture load to be passively controlled without constant monitoring.

[0078] The capture mechanism can include a state change detection element for detecting when soft capture and retraction of the grapple fixture are achieved and when rigidification should be initiated using the preload generator component. In one embodiment, the state change detection element includes a potentiometer configured to detect when the grapple tip 232 reaches a "seated" position. The state change detection element is connected to the preload generator element and triggers the preload generator element. In one embodiment, when the soft capture indicator is tripped, the mechanism immediately moves to rigidify (hard capture) so that the interfaces cannot drift out of alignment before they come together. The preload generator element can then be compressed until the desired (pre-determined) preload is achieved. The power-off brake can be used to avoid continuously losing power while holding the payload on the flywheel object when power to the drive motor is cut. Generally, the system is calibrated to go to a specific position as the "hard capture position" (e.g., on the ground in a space application), which is a position that can be obtained only by compressing the preload generator element (e.g., spring stack) while holding the grapple fixture. In embodiments using a spring stack, an intermediate point (or approximate intermediate point) in the stack stroke can be used so that varying effects (such as those described above) do not move the rigidification load outside the range. That range is based on the external load that will be reacted once rigidified (i.e., no separation of the interfaces) and the strength of the components in the system.

[0079] Once rigidified, the end effector 214 can send a signal to the robot arm controller 210 indicating that the captured object 202 is rigidified. The robot arm controller 210 can then operate the robot arm 212 by generating and sending an arm movement command to move the rigidified captured object 202 to a desired location.

[0080] Also, the linear displacement mechanism 244 can be used to release the grapple fixture 216 by driving the grapple 242 (or its components) forward along the capture axis to drive the grapple 242 to the open position, enabling the release of the grapple end 232 and, in turn, the grapple fixture 216.

[0081] Referring now to FIG. 3, a system block diagram 300 is shown herein that details the sub-components of the base rigidification detection system 248 as referred to in FIG. 2 according to one embodiment.

[0082] The base rigidification detection system 248 includes a movable component 250, a resistive component 252, a trigger component 256, and a detection component 254.

[0083] The base rigidification detection system 248 includes a plurality of components that can cooperate to enable the system 200 to detect whether the rigidification of the robotic capture interface between the end effector 214 and the grapple fixture 216 has been successfully achieved at the end of the grapple fixture 216 of the interface.

[0084] The base rigidification detection system 248 is capable of generating a mechanical or electrical signal in the grapple fixture 216, which can be communicated to the grapple fixture 216 or other components of the captured object 202 and / or can be read or processed by the grapple fixture 216 or other components of the captured object 202. For example, an electrical signal can be generated, which can activate another component or can be detected by an on-board computer system, a microcontroller, or other electronic devices.

[0085] The movable component 250 includes a physical component connected to the probe 230 and is adapted such that linear translational movement of the probe 230 along one or more axes can be transmitted to the movable component 250. For example, when the probe 230 is moved in a particular direction, the movable component 250 can also move proportionally along the same axis. In a particular example, when the probe 230 is gripped and pulled by the end effector 214, the movable component 250 can form the same applied force through its connection to the probe 230. The movable component 250 can be restricted with respect to movement in a single direction and / or along a linear axis, and the range of motion of the movable component 250 can be limited.

[0086] The trigger component 256 includes a physical component coupled to the movable component, which is capable of moving in proportion to the movable component 250 when the movable component 250 is moved. In some examples, the trigger component 256 can be integrated with the movable component 250 such that the trigger component 256 and the movable component 250 form a single integrated part. For example, the trigger component 256 can include an arm extending from the movable component 250. For example, the arm can extend from the movable component 250 at an angle generally perpendicular to the longitudinal axis of the probe 230 when the probe 230 is in a stationary state (e.g., not deflected).

[0087] The resistance component 252 includes a component positioned between the grapple fixture base 218 and the movable component 250. The resistance component 252 is coupled to both the grapple fixture base 218 and the movable component 250, or is otherwise positioned between the grapple fixture base 218 and the movable component 250 such that a resistance force is applied to any movement of the movable component 250. For example, the resistance component 252 can include a mechanical spring or a plurality of mechanical springs that apply a resistance force to the movement of the movable component 250 along a particular linear axis. The resistance force of the resistance component 252 can be adjusted or selected such that the level or amount of the resistance force applied to the movable component 250 is known or is consistent with other aspects of the system 200. In some examples, the resistance component 252 can include at least one wave spring. In a particular embodiment, the resistance component 252 can include two wave springs. Wave springs can be particularly advantageous. This is because they can be of a smaller volume and mass than other equivalent springs or mechanical resistance components having a given specification. Such characteristics can be particularly advantageous in space applications. This is because the reduced mass and volume can result in reduced launch costs and system capabilities.

[0088] The detection component 254 includes components that can change or generate a signal in response to rigidification. The detection component 254 can be disposed within the base 218 of the grapple fixture 216. The detection component 254 can be configured to register a first state and a second state. The detection component 254 can register a state change, such as a change from the first state to the second state or vice versa, based on some physical interaction with the trigger component 256. For example, in some embodiments, the trigger component 256 can activate and / or operate the detection component 254 when the trigger component 256 moves. In one example, the movement of the trigger component 256 from a first position to a second position can cause the detection component 254 to register a similar state change from the first state to the second state and vice versa. For example, the trigger component 256 can physically contact the detection component 254 at the first position (registering the first state) and no longer physically contact the detection component 254 at the second position (registering the second state). Generally, the detection component 254 communicates by generating different signals in each of the first and second states, which in some cases can simply be no signal / signal present. In some examples, the detection component 254 can include multiple detection components to improve reliability.

[0089] In some examples, the detection component 254 can include a contact mechanism detection component such as, for example, a switch or a strain gauge.

[0090] In some examples, the switch can be a small snap-action switch. A small snap-action switch can refer to an electrical switch that is actuated by a very small physical force, such as through the use of a tipping-point mechanism. The tipping-point mechanism can be referred to as an "over-center" mechanism. In some examples, the small snap-action switch can be a switch of the Micro Switch (trademark) brand, etc.

[0091] In some examples, the detection component 254 can include a non-contact mechanism detection component, such as an optical sensor, a capacitive sensor, a laser-based sensor, or a proximity sensor. In some examples, the detection component 254 can include a plurality of the components described above, or a combination of the components described above.

[0092] In some examples, instead of discrete and / or binary state changes, the detection component 254 can be configured such that the detection component 254 can detect a continuous state. In such examples, the detection component 254 can be a strain gauge, a potentiometer, or other component that can register a continuous state. In such examples, a position on the continuous spectrum of the state can be selected as the state change point, and a state greater than or less than this state change point can be considered the first state or the second state, respectively, or vice versa.

[0093] In one example, the probe 230 can be moved along a linear axis. Through a physical connection between the probe 230 and the movable component 250, the movable component 250 will be moved along this same axis in proportion to the movement of the probe 230. The movable component 250 can have a restraining force applied to it by the resistance component 252, such that a specific elevated amount of force must be applied to move the probe 230 and thus the movable component 250. The resistance component 252 is configured such that when a force is applied to the probe 230 by the grapple 242 during the rigidification process, a sufficient amount of force is applied to the probe 230 and the movable component 250 moves a sufficient distance (e.g., from a first position to a second position) to activate the switch of the detection component 254. In some examples, the trigger component 256 can move in conjunction with the movable component 250 to activate the switch. When this switch is activated, the circuit can be opened or closed, which can be detected by the associated computer system or microcontroller. In other examples, the switch can generate a pulse or signal that can similarly be detected by the associated computer system or microcontroller.

[0094] The base rigidification detection system 248 eliminates any force applied to the captured object 202 until soft capture is complete and minimizes interference with the free flyer capture process. The rigidification detection process of the present disclosure depends on a change in state driven by a change in the position of the components of the associated base rigidification detection system 248. The position of the components of the associated base rigidification detection system 248 can change without applying force to the captured object 202 until soft capture is complete. The base rigidification detection system 248 can change its state only when all degrees of freedom are constrained between the free flyer and the grapple fixture and a predetermined amount of preload is achieved at the interface without adversely affecting the soft capture force (e.g., chip-off of the free flyer). Such a configuration makes the base rigidification detection system 248 particularly well-suited for free flyer object capture because the impact on the free flyer object capture process is minimized.

[0095] Referring now to FIGS. 4A and 4B, a robotic-based object capture method 300 according to one embodiment is shown herein. Method 300 can be implemented using a robotic system that includes a machine vision system, a robot arm controller, a robot arm, and an end effector, such as system 200 of FIG. 2, for example. In one embodiment, method 300 can be used to capture a free flyer object in a space-based application, such as a satellite, for example.

[0096] At 302, a machine vision target mounted on the object to be captured (the "captured object") is detected by the machine vision system. The captured object can be a free flyer object. The machine vision system can then generate a signal indicating that the captured object has been detected and communicate that signal to the robot arm controller.

[0097] In some cases, the captured object can also be referred to as the "target object". An object or vehicle that performs the capture via an end effector, and the object or vehicle to which the end effector is connected can be referred to as the "chaser". For example, in space-based applications, the chaser can be a spacecraft.

[0098] In 304, the robotic arm moves the end effector towards the grapple fixture on the captured object. The grapple fixture is used to enable the grappling ring of the captured object and the capture and can be a standardized interface. The robotic arm controller is configured to control the movement of the robotic arm in 304 such that when the end effector approaches the grapple fixture, the grapple fixture enters the capture envelope of the end effector.

[0099] The term "capture envelope", as used in this disclosure, will now be described. When a capture or docking device is positioned for use, the device is positioned at a specific relative position with respect to the grapple element or fixture of the object to be captured in order to ensure that the mechanism will successfully close around the grapple fixture when the soft capture operation is performed. During the capture operation, there are a number of effects that work against a successful capture, including the fact that the mechanism itself has specific geometric and dynamic positioning requirements, the vision system has a certain amount of measurement uncertainty, and the object to be captured is potentially still drifting with respect to the platform of the capture system. Summing all of these effects (potential errors) creates the positioning requirements in x, y, z, yaw, pitch, and roll that the capture mechanism must be within in order to guarantee capture. This is referred to as the "capture envelope". The larger the capture envelope, the more objects can be captured with respect to a given set of these effects (drift rate, targeting and positioning accuracy, system speed to keep up with "tumbling" or "drifting" FFs). It is also possible that there is a minimum "capture envelope" required based on the effects within the system that work against capture. A larger envelope gives a margin of capture ability and makes the free flyer capture sequence more reliable.

[0100] The machine vision system continues to track the captured object via the machine vision target, communicates with the robot arm controller, keeps pace with the captured object, performs a final inward (towards the captured object) movement guided by the target, and can obtain a grapple fixture (e.g., the probe tip of the grapple fixture) within the capture envelope. For example, the robot arm controller can control the robot arm to approach the captured object at a predetermined rate. This can include tracking the captured object, and when the captured object is drifting, the robot arm controller controls the arm to keep pace so that a constant vector exists between the end effector and the captured object. At an appropriate point, the robot arm controller can then add a delta command. The delta command represents the closing speed that directs the receiving end of the end effector towards the grapple fixture of the captured object. The delta command can include closing within a specific speed range (e.g., a pre-determined band as described below).

[0101] The robot arm controller can be configured to move the robot arm and end effector at a predetermined rate towards the captured object such that the relative velocity of the end effector and the captured object is maintained within a pre-determined band. The pre-determined band represents a range of relative velocities known to promote or result in a successful soft capture of the grapple fixture (e.g., through a slide along a probe guide surface and into an internal compartment through an opening). The pre-determined relative velocity band can be determined based on various system characteristics, including characteristics of the robot system and the captured object. Such system characteristics can include, for example, characteristics of the deflectable probes of the grapple fixture, such as the spring stiffness or friction characteristics of the probes and the probe guide surface. Maintaining the relative velocity of the captured object and the end effector during approach can be particularly important in free flyer capture applications. This is because such relative velocities that are too fast or too slow can cause the probes of the grapple fixture to contact the probe guide surface, deflect, and fail to slide over the probe guide surface and through an opening into the internal compartment for grappling.

[0102] It is important that a useful capture device be tolerant with respect to the relative velocity between the capture system and the captured object. Many of the robotic capture system designs are driven by factors or principles such as reducing friction, minimizing spring stiffness, reducing chip-off force, and increasing the speed of the soft capture action. The need to achieve rigidification sometimes violates these driving principles. For example, fins on a capture device that guarantee good restraint against roll after capture (e.g., fin 532 of FIG. 5) can create an obstacle to soft capture that is somewhat mitigated by a design to keep the capture envelope as large as possible and to reduce the relative rate requirements for the capture system. The means to achieve roll restraint in a rigidified state will necessarily compromise the largest possible capture envelope of the design, and making that envelope as large as possible adds a margin to the successful soft capture capacity. The devices of the present disclosure address misalignment through flexible members within the capture system. The deflection of a flexible member (probe) to correct misalignment occurs upon contact with the free flyer object. Deflecting the flexible member to an aligned state requires a small amount of energy (in the form of the product of force and displacement). If the approach is too slow, the free flyer object will be pushed away from the end effector capture device before “soft capture” can be achieved. The minimum rate at which capture can still be achieved is based on the inertia of the free flyer (mass and moment of inertia of the rotational mass) and the trigger force of the soft capture mechanism itself. Thus, the capture system is configured to achieve a minimum relative rate between the capture tool (chaser side) and the grapple fixture (free flyer side) for effective capture.

[0103] In 306, the deflectable probe of the grapple fixture contacts the probe guide surface on the receiving end of the end effector within the capture envelope.

[0104] At 308, the initial contact between the deflectable probe and the probe guide surface at 306 is cushioned by a buffer spring within the deflectable probe. Cushioning such an initial shock can prevent the probe from bouncing back from the receiving end of the end effector. This can be particularly advantageous in applications where the captured object is a free flyer object.

[0105] At 310, the deflectable probe is deflected by the probe guide surface from a rest position (e.g., a probe perpendicular to the surface of the captured object on which the grapple fixture is mounted) toward an opening in the probe guide surface positioned at or near the center of the probe guide surface by the continuous movement of the end effector toward the captured object. The probe guide surface can be concave to urge the deflection of the deflectable probe in the direction of the opening. The opening provides entry of the deflectable probe into an internal compartment of the end effector in which the capture mechanism is disposed.

[0106] The deflectable probe includes a deflection element to enable the probe to deflect from the rest position in the direction of the applied force and return to the rest position when the applied force is removed. In the case of 110, the shape of the probe guide surface and the movement of the end effector toward the captured object apply a force to the deflectable probe that deflects the probe in the direction of the opening in the probe guide surface. The deflectable element can include one or more spring components to facilitate the deflection.

[0107] At 312, the probe guide surface guides the deflected probe through the opening to the soft capture position (or grapple position) within the internal compartment. The continuous movement of the end effector towards the captured object and the profile of the probe guide surface cause the continuous deflection of the deflectable probe and the end of the deflectable probe to slide across the probe guide surface towards and through the opening.

[0108] At 314, the presence of the deflectable probe at the soft capture position is sensed by the end effector, triggering the grapple mechanism (the "grapple") of the end effector.

[0109] In one embodiment, sensing of the deflectable probe can be performed by positioning a sensing element or trigger contacted by the end of the deflectable probe when the deflectable probe enters the opening and into the internal compartment of the end effector, in alignment with the capture axis (the axis along which the deflectable probe is oriented within the internal compartment of the end effector). The force applied to the sensing element by contact with the deflectable probe can then cause the sensing element to engage the grapple.

[0110] Any suitable method for sensing the presence of the probe can be used, and the type of sensing is not particularly limited. For example, in a variant, sensing the presence of the probe can be achieved via any one or more of a force that trips a switch, a force as measured by a suitably placed load cell / strain gauge, an optical method, a capacitive method, an inductive method, and an electrical resistivity method. Force tripping of a switch can advantageously provide a simple and effective way to measure a change in state. Other sensing methods can generally be used in other embodiments.

[0111] At 316, the deflectable probe is grappled by a grappler. The grappling of the deflectable probe constrains the linear movement of the captured object relative to the end effector. In some embodiments, the grappler can include a pair of jaws that move from an open position to a closed position when triggered, thereby configured to grip the probe. In some embodiments, the end of the probe is spherical to allow grappling of the probe (and to drive the slide of the probe along the probe guide surface).

[0112] At 318, the grappled deflectable probe is retracted into the internal compartment of the end effector in a direction opposite to the receiving end of the end effector along the capture axis, removing the angular and lateral offsets of the captured object relative to the end effector. Generally, in some embodiments, roll misalignment must be maintained within a certain maximum value between soft capture and rigidification. If the roll misalignment continues to grow beyond the maximum allowable misalignment after soft capture, rigidification may not be able to occur. The grappled probe can be retracted to a pre-determined position. The pre-determined position can be detected by, for example, a potentiometer. The retraction of the grappled probe further brings the base of the grappler fixture, which is connected to the deflectable probe, into contact with the probe guide surface facing the probe guide surface. The base of the grappler fixture and the probe guide surface can be complementarily shaped to drive the slide of the base along the probe guide surface and / or the fitting between the base and the probe guide surface. The grappler fixture base and the probe guide surface can each include alignment features that interface with each other and are configured to drive the alignment between the grappler fixture base and the probe guide surface as the probe is retracted and the end effector and the captured object are moved closer to each other.

[0113] At 320, the interface between the grapple fixture and the end effector is rigidified. The rigidification is achieved by retracting the grapple to a point where the grapple fixture is preloaded against one or more alignment features on the probe guide surface of the end effector. For example, in some embodiments, the preload can be on the contact annulus as described herein. In other embodiments, the preload can be on a plurality of protrusions (or "fins"). In certain embodiments, the alignment features include a raised contact annulus and a plurality of fins, and the grapple fixture is preloaded against the raised contact annulus and not against the alignment fins.

[0114] Rigidification of the interface enables full authority by the capture system to define the relative position and orientation of the captured object. This enables low uncertainty in the relative position and rate between two objects, and control of the relative position and rate between two objects. This state is typically suitable for situations where the robotic service is about to apply a load while the captured object is being fixed, adjusted, or refueled, or while the robotic service is propelling the captured object to a new trajectory or new attitude. In the soft capture state, the capture system has some authority over the captured object in certain DOFs, but not in other DOFs (thus, it does not have the ability to generate forces or moments on the free-flyer object to maneuver it to any position and orientation). Once achieved, the hard capture or rigidified state provides the ability to generate forces and moments in all directions on the captured object (e.g., to hold a handle attached to the object). Having 6-DOFs and being a determining factor at the location where the free-flyer is held enables handling of the object and alignment of the object with other connection features or other servicing features, such as a robotic servicing system or a refueling system.

[0115] In 322, the rigidified state of the robotic capture interface is detected through the rigidification detection system in the grapple fixture, as described herein. The state of the robotic capture interface can be communicated to other components of the system through the grapple fixture.

[0116] In 324, the rigidified captured object is manipulated (e.g., moved) by a robotic arm connected to the end effector. In one example, the captured object can be moved to a docking position.

[0117] Referring now to FIG. 5, a front perspective view 500a of an end effector 510 for capturing a free flyer object, according to one embodiment, is shown herein. The end effector 510 can be the end effector 106 of FIG. 1 or the end effector 214 of FIG. 2.

[0118] The end effector 510 can be used, for example, to capture a free flyer object such as a client spacecraft, which has a grapple fixture attached thereto, such as the grapple fixture 216 of FIG. 2. Generally, the end effector 510 is configured to capture a free flyer object by capturing and rigidifying the grapple fixture of the free flyer object.

[0119] The end effector 510 includes a receiving end 512 and a robot arm interface end 514. The receiving end 512 is configured to interface with and capture a grapple fixture attached to a captured free flyer object. The robot arm interface end 514 is configured to connect the end effector 510 to a robot arm for operation of the end effector 510 via the robot arm. Thus, the robot arm interface end 514 can include various mechanical or electrical connections to facilitate operation and movement of the end effector 510 via the robot arm.

[0120] In some cases, the end effector 510 can include components that enable the end effector 510 to be engaged by another end effector. For example, the end effector 510 can include a grapple fixture attached thereto for capturing the end effector 510 by a second end effector. Also, the end effector 510 can include one or more interfaces for passing power, data, or torque from the second end effector to the end effector 510.

[0121] The end effector 510 includes an outer housing 516. The outer housing 516 of the end effector is generally cylindrical in shape. In other embodiments, the outer housing 516 can have any other suitable shape. The outer housing 516 can include any number of pieces or components. The outer housing 516 surrounds an internal compartment (not shown), and various components for the operation of the end effector, including various components for the capture and rigidification of the free flyer grapple fixture, are disposed within the internal compartment.

[0122] Also, the end effector 510 includes a stowage / launch interface component 518 (not seen in FIG. 5). The stowage / launch interface component 518 can include a docking port for placing the end effector 510 down at a known location (e.g., on a spacecraft). The known location can have access to power or an umbilical connection to a heater through the stowage / launch interface component 518.

[0123] The end effector 510 includes a front end component 520 attached to the outer housing 516 at a receiving end 512 for interfacing with the grapple fixture of the free flyer object.

[0124] The front-end component 520 includes a raised annulus 522 that extends around the perimeter of the front-end component 520 to contact a complementary annulus (such as 618 as shown in FIG. 6) on the base of the grapple fixture. The raised annulus 522 includes a piece of material that is raised in profile relative to the outer annulus 524 of the front-end component 520. The raised annulus 522 provides a uniform distribution of clamping force and an equal load-bearing capacity independent of the applied pitch / yaw load. In some embodiments, the raised annulus 522 may not be present.

[0125] Also, the front-end component 520 includes a probe guide surface 526. The probe guide surface 526 is concave and includes an opening 528 for receiving a probe of the grapple fixture to position the probe within the capture mechanism. The opening 528 is positioned generally at the center of the probe guide surface 526 (e.g., at the apex of the concave surface). The probe guide surface 526 is configured to passively guide a probe of the grapple fixture into the opening 528 when the probe contacts the probe guide surface 526. A system that controls the end effector 510 can be configured with parameters (such as relative velocity, relative angle) known to promote successfully guiding a probe into the opening 528 via the probe guide surface 526 such that the end effector 510 approaches the grapple fixture of the free flyer object (e.g., without the probe bouncing off the surface 526 due to such parameters). Management of such parameters by the control system of the end effector 510 can be particularly important in free flyer object capture applications where it is more widely recognized that a misaligned grapple fixture can cause the free flyer object to bounce off the end effector 510.

[0126] The features of the probe guide surface 526, such as the surface material and angle, can be selected to achieve the desired interaction with the probe of the grapple fixture. For example, the features can be selected to achieve a desired level of friction or to more efficiently guide the contacting probe toward and into the opening 528.

[0127] The probe guide surface 526 includes a concave insert 530. The concave insert 530 is movable along the capture axis as part of a capture mechanism within an internal compartment of the end effector 510. For example, the concave insert 530 can be the most forward (proximal to the receiving end 512) component of the capture mechanism. In FIG. 5, the concave insert 530 is in its fully forward position and will move rearward along the capture axis toward the arm interface end 514 during the capture sequence.

[0128] The concave insert 530 can be composed of the same material as the remainder of the probe guide surface 526 and can have the same surface characteristics. The concave insert 530 can simply be a continuation of the probe guide surface 526 that is attached to a section of the device that moves rearward (rigidifies) to transition from soft capture to hard capture. In other embodiments, the probe guide surface 526 can be a single piece (i.e., here the surface is continuous rather than an outer surface plus an insert). However, using a single piece for the probe guide surface 526 instead of the concave insert 530 can result in interference with the grapple probe when the grapple probe is retracted inward to align the interface. Thus, embodiments using the concave insert 530 can advantageously avoid such interference.

[0129] In addition, the front-end component 520 includes three protrusions or "fins" 532a, 532b, 532c (collectively referred to as fins 532 and generically as fins 532) mounted on the probe guide surface 526.

[0130] The fin 532 acts as an alignment feature that helps to align the receiving end of the end effector 512 with the grapple fixture of the free flyer object. The fin 532 is configured to mate with complementary alignment features (the pockets 620 shown in FIG. 6). For example, when capturing the grapple probe of the free flyer object, there may be some level of offset present due to the free flyer object having a tumble rate. The capture mechanism that captures and retracts the probe of the grapple fixture can provide a coupling, but may be misaligned in the translational direction by a predetermined amount (e.g., a few inches). The fin 532 enables the grapple fixture and the front end component 520 to align and come together even when the free flyer object is misaligned in the rotational direction by a predetermined amount. In such a case, the fin 532 is designed to slide down the rounded edges of each pocket (triangular cutout) of the grapple fixture base and seat inside the pocket. In doing so, the fin 532 (along with the pockets of the grapple fixture) provides those two rotational and shear alignments when bringing the grapple fixture and the front end component 520 together. Thus, the fin 532 provides a mechanism for correcting rotational misalignment and for performing self-alignment. In one embodiment, the fin (and the pocket) is configured to align a rotational offset of up to 5 degrees. In some embodiments, for example, when the front end component 520 does not include the raised annulus 522, the interface can be grounded on the fin 532. In such an embodiment, three fins 532 are used for determinism. In embodiments where the interface is grounded on the raised annulus 522, the number of fins 532 can vary. In such a case, at least two fins 532 can be used on the front end component 520 for rotational alignment about the central axis.

[0131] The fin 532 has a rounded surface, which allows the fin 532 to travel down along the rounded edge of the complementary pocket. The fin 532 can be dry lubricated. The lubrication can be selected based on the compatibility with the operating environment. Also, the fin 532 can have one or more rounded surfaces or angled corners to propel the ball of the grapple probe towards the opening 528 when the probe contacts the fin 532.

[0132] An embodiment of the front-end component 520 including the raised annulus 522 for grounding the interface can provide certain advantages (such as over embodiments that ground the interface on the fin 532). Contacting at three points (such as the case of grounding on three fins 532) results in a very small stance in a particular direction where the bending load is reacted (from the centerline to the line between two fins), while the annulus 522 means that, regardless of the direction, it always maximizes the stance for reacting to the load.

[0133] Referring now to FIG. 6, a front perspective view 600a of a grapple fixture 610 for mounting a free flyer object (or other object to be captured) according to an embodiment, and for capturing by the end effector 510 of FIG. 5 and mating with the end effector 510 of FIG. 5, is shown here.

[0134] The grapple fixture 610 includes a base 612.

[0135] The base 612 includes a mounting surface 614 for mounting the grapple fixture 610 to the outer surface of a free flyer object (or, in some cases, other object).

[0136] Further, the base 612 includes a mating surface 616 that faces the mounting surface 614 for mating or connecting with the probe guide surface 526 of the end effector 510. The mating surface 616 is convex in shape. The curve of the mating surface 616 can be configured to match or substantially match the curve of the probe guide surface 526 of the end effector 510, such that the two surfaces are complementary in shape.

[0137] The mating surface 616 of the base 612 includes a flat annular portion 618 that extends around the periphery of the mating surface 616 for contacting and mating with the raised annulus 522 of the end effector 510 during capture.

[0138] Further, the mating surface 616 includes recesses (or pockets or cutouts) 620a, 620b, 620c (collectively referred to as recesses 620 and generically referred to as recesses 620) for promoting alignment between the grapple fixture 610 and the front end component 520 of the end effector 510. In particular, the recesses 620 are positioned on the mating surface 616 and are configured to receive the respective fins 532 on the end effector 510. The recesses 620 are triangular. In other embodiments, the recesses 620 can be of any other suitable shape. The triangular recesses or openings can advantageously reduce the likelihood that the fins 532 will contact the grapple fixture 610 prior to soft capture. The edges of the recesses 620 provide a guide toward the bottom of the fin alignment "V" shape feature. This is provided by the triangular cutouts. The recesses 620 have a flat or non-flat bottom surface and a curved or rounded side surface. The curved side surface promotes the sliding of the fins 532 toward the bottom surface and to the desired position. In some embodiments, the fins 532 do not reach the bottom surface and do not contact the bottom surface (e.g., in an annular reaction embodiment where the annulus is used to react to the load at the interface and the fins 532 are not), rather, a clearance (e.g., a small one) is left between the fins 532 and the bottom surface within an acceptable alignment variance.

[0139] In some embodiments, each recess 620 can include therein a fastener (not shown) that passes from the bottom surface of the recess 620 to the mounting surface 614. The fastener is used to attach the base 612 of the grapple fixture 610 to a free flyer object. The fastener can be embedded so as not to be obstructive, such that the fastener does not interact with the fins 532. In certain embodiments, the grapple fixture 610 can include insulation (thermal and electrical) under the fastener and also between the grapple fixture base 618 and the object (e.g., a spacecraft) to which the grapple fixture 610 is attached.

[0140] Also, the grapple fixture 610 includes a deflectable probe 624 mounted to the base 612. The deflectable probe 624 includes a shaft 626, a spherical (or ball) shaped end 628 connected to a first end of the shaft 626, and a mounting end 630 connected to a second end of the shaft 626. In variations, the probe end 628 can have a different shape.

[0141] The deflectable probe 624 is connected to a deflection element to enable the deflectable probe to deflect in the direction of an applied force from a rest position and to return to the rest position when the force is removed (the probe 624 is shown in the rest position in FIG. 6). The rest position can be substantially perpendicular to the base 612. The deflection element includes one or more springs to enable deflection. In some embodiments, the deflection element used to make the probe 624 deflectable can be any suitable mechanical spring in a compressed state, a pneumatic component (e.g., in marine applications), an actively tensioned component, a null spring, or a flexible shaft (over the shaft 626).

[0142] The deflectable probe 624 is additionally connected to a grapple fixture 610 (e.g., to a base rigidification detection system in a base rigidification detection system 248 (not depicted in FIG. 6)) such that rigidification can be detected from within the grapple fixture 610 (i.e., on the captured object side of the robotic capture interface).

[0143] Also, the deflectable probe 624 can include a coaxial spring (not shown). The coaxial spring is used for electrostatic shock conduction. The coaxial spring electrically connects the probe 624 to the base 612 of the grapple fixture 610. The coaxial spring permanently electrically connects the probe 624 to the base 612 of the grapple fixture 610. When the probe tip 628 contacts the conical interface (surface 526 in FIG. 5) on the end effector during capture, the coaxial spring then electrically connects the service ground to the free flyer ground through a dissipative resistor. This allows charge to flow, but with a significantly reduced current, so as to limit damage. This approach is used when the dry lubrication in the "knuckle - joint" of the probe 624 might be insulating. The coaxial spring can enable the capture system to be used in geosynchronous orbit and other high orbits having environmental conditions that lead to electrostatic charging of objects. For example, when two objects having different charge levels come into contact, a large electrostatic discharge event can occur, which can endanger avionics and power systems on either object (e.g., on the capture system side or the free flyer side).

[0144] The coaxial spring is connected to the deflectable probe 624 at the mounting end 630. The grapple fixture 610 can further include a spring mounting component. The spring mounting component can include one or more pieces. The coaxial spring and the deflecting spring are attached to the spring mounting component, and the spring mounting component is attached to the base 612 via the mounting surface 614. The spring mounting component can function as a spring retainer.

[0145] Referring now to FIGS. 7 through 10, a system 700 for robotic capture, including a grapple fixture 718 and an end effector 722, according to one embodiment, is shown herein. The above description with reference to FIGS. 1 through 6 is applicable to the system 700 of FIGS. 7 through 10. The grapple fixture 718 and the end effector 722 respectively correspond to the grapple fixture 610 and the end effector 510.

[0146] FIGS. 7A and 7B show a cross-sectional view of the grapple fixture 718 alone in the non-rigidized state 701-1. The grapple fixture 718 further includes a probe 702, a movable component 710, a resistive component 714, a detection element 716, a resistive housing 730, and a resistive guide 732. The probe 702 further includes a probe end 704, a probe mounting end 708, and a probe shaft 706.

[0147] The resistive housing 730 houses a spring that allows the probe 702 to deflect during the mating of the grapple fixture 718 and the end effector 722. Any lateral or angular misalignment of the grapple fixture 718 with respect to the end effector 722 causes the probe 702 to deflect, creating a resultant force that axially pushes the resistive housing 730. The spring within the resistive housing 730 biases the probe 702 towards the neutral position, such that the probe 702 returns to the neutral position when no external force is applied to the probe 702. The resistive housing 730 additionally returns to the neutral position when the misalignment between the grapple fixture 718 and the end effector 722 is corrected, removing the external force applied to the probe 702.

[0148] The resistive guide 732 houses a portion of the resistive component 714 and guides the movable component 710 axially along during the mating and rigidification operations.

[0149] The movable component 710 according to one embodiment includes a generally cylindrical sleeve coupled to the probe 702. The movable component 710 can be coupled to the probe 702 via an axially compressible spring contained within the resistive housing 730. The force that compresses the axially spring causes the surface of the probe mounting end 708 to contact the adjacent concave surface of the movable component 710. As previously explained, a preload force exists between the resistive housing 730 and the probe 702 and is capable of biasing the probe 702 to the neutral position, at which time the probe 702 is generally coaxial with the first axis 724. The two contact surfaces of the probe mounting end 708 and the resistive housing 730 can be treated (e.g., dry lubricated) to minimize friction during probe deflection. In some examples, the interface surface or contact surface of the movable component 710 can also be treated (e.g., dry lubricated) to minimize friction during movement.

[0150] The movable component 710 is disposed within an internal compartment of a base 726 of the grapple fixture 718. The movable component 710 is generally movable along a first axis 724 within the base 726 of the grapple fixture 718. The first axis 724 is generally coaxial with the probe 702 when the probe 702 is in a neutral position or otherwise non-deflected position. The movable component 710 can be manufactured from metal, polymer, ceramic, or any other suitable material.

[0151] In the embodiments of FIGS. 7A and 7B, the movable component 710 can be referred to as a grapple force transmission component. The grapple force transmission component is configured to receive a force from a grapple mechanism of an end effector through a probe (e.g., probe 702) and transmit this received force to a trigger component (e.g., arm 712) such that a state change can be effected at a detection component (e.g., detection component 716).

[0152] Connected to the movable component 710 are three arms 712 (only one is visible in FIG. 7). In other embodiments, the number of arms can vary depending on the number of detection components (as described herein). In some examples, each arm 712 can be referred to as a trigger component. Each arm 712 extends generally away from the movable component in a direction perpendicular to the first axis 724. Each arm 712 is disposed within an internal cavity of the base 726 of the grapple fixture 702. When the movable component 710 moves along the first axis 724, each arm 712 will move in the same direction along parallel axes. In the embodiments of FIGS. 7 - 10, each arm 712 is integrated with the movable component 710, however, in other embodiments, each arm 712 can be a separate component fastened to the movable component 710.

[0153] The arm 712 can be separated from the base 726 by a distance 728-1 in the non-rigid state 701-1. When the system transitions from the non-rigid state 701-1 to the rigid state 701-2, the distance 728-1 can be decreased as the arm 712 moves with the movable component 710 in the direction of the probe 702.

[0154] The resistance component 714 is positioned between the movable component 710 and the grapple fixture base 726. The resistance component 714 can be connected to both the movable component 710 and the grapple fixture base 726, and the resistance component 714 is adapted to apply a resistance force against any movement of the movable component 710. In the examples of FIGS. 7-10, the resistance component 714 includes four wave springs.

[0155] Additionally, the resistance component 714 is positioned between the movable component 710 and the resistance guide 732. The detection component 716 includes a switch 722. When the arm 712 contacts the switch 722, the state of the switch is changed from a first state to a second state, and vice versa. In the embodiments of FIGS. 7-10, the grapple fixture 718 includes three detection components 716, and the three detection components 716 are generally positioned 120° apart from each other around the cylindrical movable component 710. In other examples, other types or numbers of detection components can be used in other configurations or arrangements in the grapple fixture 718.

[0156] Figures 8A and 8B show a cross-sectional view of the grapple fixture 718 alone in the rigidified state 701-2. As seen in Figures 8A and 8B, in the rigidified state 701-2, the distance 728-2 is smaller than the distance 728-1 in the non-rigidified state 701-1. The movable component 710 is being pushed upward along the axis 724 through the movement of the probe 702 in the same direction along the same axis 724. This upward movement is imparted to the arm 712, moving the arm upward along an axis parallel to the axis 724, such that the arm is lifted from the detection component 716 and the switch 722 is configured to register a second (rigidified) state. In some examples, when the system 700 includes three detection components 716, a plurality of logic gates (e.g., AND gates, OR gates, etc.) can be packaged together and a single output or signal of the system 700 can be read to indicate the majority state (i.e., voting architecture) of the three detection components. For example, when two of the three detection components 716 register a first state, the single output can register the first state. When all three of the three detection components 716 register a second state, the single output can register the second state.

[0157] Figures 9 and 10 show cross-sectional views of the grapple fixture 718 and end effector 722 that perform the capture and rigidification operations, as explained by method 300 of FIGS. 4A and 4B. When the grapple fixture 718 and end effector 722 are brought together so that they can be coupled, the grapple of the end effector 722 can grapple the probe 702 of the grapple fixture (after the interface is placed in the pre-capture position 701-1, as shown in FIG. 9). Once grappled, the grapple linearly retracts into the end effector 722, applying a force to the probe 702 and enabling the probe 702, and thus the grapple fixture 718, to retract into the opening of the end effector 722, as shown in FIG. 9. A first amount of force is applied to the grapple fixture 718 to enable the probe 702 to retract into the end effector 722. When the base of the grapple fixture contacts the probe guide surface, a second amount of force can then be applied to achieve an interface preload, at which point the grapple fixture 718 is held in force against the end effector 722 (and the interface is rigidified).

[0158] This second force can be greater than the first force. The resistance component 714 is configured such that a sufficient amount of resistance is applied to any movement of the movable component 710, at which time only a force greater than the first amount of force is applied to the probe 702 to achieve the preload and the movable component 710 is able to move a sufficient distance to create a state change in the detection component 716. This configuration can be achieved by adjusting the overall mechanical spring constant of the resistance component 714. This amount of force can be less than the second amount of force in some examples.

[0159] For example, in one embodiment, the first amount of force can be 180 N. 180 N can be continuously applied to the probe 702 along the axis 724 such that the probe 702 can be pulled into the end effector 722 by the grapple of the end effector 722. When the surfaces of the end effector 722 and the grapple fixture 718 reach contact, the force applied to the probe 702 by the end effector can be increased. For example, the force can be continuously increased at a constant rate from 180 N to a final force of 500 N. This final force of 500 N can be the second amount of force as referred to above. In some examples, this second amount of force (500 N) can be referred to as a preload force. The reason is that this can be the amount of force between the surface of the end effector 722 and the surface of the grapple fixture 718.

[0160] The resistance component 714 can be configured such that a sufficient amount of resistance is applied to any movement of the movable component 710, and only a force greater than 300 N (e.g., a threshold force) (or, in some examples, equal to 300 N) can effect a change in the state of each detection component 718 from the first non-rigidized state 701-1 to the rigidized state 701-2. This state change force of 300 N can be lower than the final expected preload force of 500 N. This force of 300 N may not reflect the truly maximally rigidized state, but selecting a state change force lower than the final 500 N preload force can advantageously reduce spurious tripping of the detection components when other loads are applied to the probe 702 through the end effector 722. For example, a high-mass component can impart additional force to the probe when being manipulated by a robotic arm connected to the end effector 722 (e.g., a sudden stop of the moving robotic arm). If the interface can withstand such loads (e.g., the interface remains mated and not separated), it is not desirable for such forces to change the detection state of the interface. Thus, this force buffer can provide higher rigidization detection system performance.

[0161] In the example of FIGS. 7-10, the resistance component 714 includes an upper half and a lower half. The force applied to the probe 702 must first be high enough to overcome the resistance of the lower half of the resistance component 714, and then subsequently, the force must be high enough to compress the upper half of the resistance component 714. When the upper half of the resistance component 714 is compressed, the state change can be registered by the detection component 716.

[0162] Referring now to FIG. 11, a flowchart is shown here that illustrates a method 800 for detecting, through a grapple fixture, a rigidified state of a robotic capture interface between a robotic capture device and a grapple fixture, according to one embodiment. Method 800 can be implemented by a grapple fixture rigidification detection system, such as the systems of FIGS. 7-10 and the base rigidification system of FIGS. 2-3. Method 800 includes 802, 804, 806, 808, 810, 812, and 814. The method steps can be performed in any order in some embodiments.

[0163] At 802, method 800 includes providing a grapple fixture that includes a probe, a movable component coupled to the probe, a resistive component coupled to the movable component, a detection component, and a trigger component.

[0164] At 804, method 800 includes resisting movement of the movable component from a first position to a second position via the resistive component when a pulling force applied to the probe is less than a pre-determined amount of force.

[0165] At 806, method 800 includes triggering, by the trigger component, a first state change registered by the detection component when the movable component moves from the first position to the second position. Movement from the first position to the second position occurs when the pre-determined amount of force is reached.

[0166] At 808, method 800 includes communicating a first state condition from the detection component when the detection component registers the first state change.

[0167] At 810, method 800 includes returning the movable component from the second position to the first position via the resistive component when the pulling force applied to the probe drops below the pre-determined amount of force.

[0168] At 812, method 800 includes triggering, by a trigger component, a second state change registered by a detection component as a movable component moves from a second position to a first position.

[0169] At 814, method 800 includes communicating, from the detection component, a second state condition as the detection component registers the second state change.

[0170] Referring now to FIG. 12, a flowchart illustrating a method 900 of manufacturing or assembling a grapple fixture rigidized detection system, according to one embodiment, is shown herein. The grapple fixture rigidized detection system can be the system of FIGS. 7 - 10 or the base rigidized system of FIGS. 2 - 3. Method 900 includes 902, 904, 906, and 908. The method steps can be performed in any order in some embodiments.

[0171] At 902, method 900 includes providing a grapple fixture base, a probe, a movable component, a resistive component, and a detection component.

[0172] At 904, method 900 includes coupling the movable component, which includes a trigger component, to the probe such that the movable component moves along the same axis as the probe moves along the axis.

[0173] At 906, method 900 includes disposing a resistive component between the movable component and an inner surface of the grapple fixture base such that the resistive component resists movement of the movable component along the axis until a pre - determined threshold amount of tensile force is applied to the probe along the axis, and such that the resistive component returns the movable component to a first position when the tensile force applied to the probe drops below the pre - determined threshold amount of force.

[0174] In 908, method 900 includes disposing a detection component within a grapple fixture-based internal compartment, where the detection component is positioned such that the detection component can be triggered by a trigger component, and the detection component is configured to register a state change and communicate the state change as a signal when triggered.

[0175] The above description provides examples of one or more devices, methods, or systems, but it will be recognized that other devices, methods, or systems may be within the scope of the claims as interpreted by those skilled in the art.

Description of Reference Numerals

[0176] 100 Freeflyer Capture System 102 Robot Arm 104 Freeflyer Object 108 Grapple Fixture 110 Receiving End 114 Robot Arm Controller 116 Platform 200 System 202 Captured Object 204 Robot System 206 Machine Vision Target 208 Machine Vision System 210 Robot Arm Controller 212 Robot Arm 214 End Effector 216 Grapple Fixture 218 Grapple Fixture Base, Base 220 Deflectable Probe 222 Fitting Surface 224 Probe Guide Surface 226 Alignment Feature 228 Alignment Feature 230 Probe 232 Grapple End 234 Biasing element 236 Opening 238 Internal compartment 240 Probe sensing element 242 Grapple 244 Linear displacement mechanism 246 Rigidification mechanism 248 Base rigidification detection system 250 Movable component 252 Resistance component 254 Detection component 256 Trigger component 300 System block diagram, method 500a Front perspective view of end effector 510 510 End effector 512 Receiving end 514 Robot arm interface end 516 Outer housing 518 Storage / launch interface component 520 Front end component 522 Raised annulus 524 Outer annulus 526 Probe guide surface 528 Opening 530 Concave insert 532 Fin 532a Fin 532b Fin 532c Fin 600a Front perspective view of grapple fixture 610 610 Grapple fixture 612 Base 614 Mounting surface 616 Fitting surface 618 Flat annular portion 620 Recess 620a Recess 620b Recess 620c Recess 624 Deflectable probe 626 Shaft 628 Probe tip, probe ball, grapple ball 630 Mounting end 700 System 701-1 Non-rigid state 701-2 Rigidified state 702 Probe 704 Probe tip 708 Probe mounting end 706 Probe shaft 710 Movable component 712 Arm 714 Resistance component 716 Detection element 718 Grapple fixture 722 End effector 724 First axis 726 Grapple fixture base, base 728-1 Distance 728-2 Distance 730 Resistance housing 732 Resistance guide

Claims

Claim 1 A system for use in a grapple fixture for detecting stiffening of a robotic capture interface between the grapple fixture and a robotic arm, comprising: A movable component disposed within an internal compartment of the grapple fixture base and movable in a first direction and an opposite second direction along a first axis, the movable component being configured to couple to a mounting end of a grapple probe, such that when assembled within the grapple fixture, a force applied to the grapple probe along the first axis is applied to the movable component; A resistance component disposed within the internal compartment of the grapple fixture base for resisting movement of the movable component in the first direction along the first axis until a threshold force of the resistance component is reached, the threshold force being correlated to a defined preload force of the robotic capture interface; A detection component disposed within the internal compartment of the grapple fixture base for registering a first state and a second state, the first state corresponding to a non-stiffened interface state and the second state corresponding to a stiffened interface state; A trigger component configured to move with the movable component along the first axis, movement of the movable component in the first direction causing the trigger component to move in the first direction and effect a state change of the detection component from the first state to the second state; wherein: The threshold force of the resistance component is configured to be overcome only when the defined preload of the robotic capture interface is reached. Claim 2 The system of claim 1, wherein the movable component is a grapple force transfer component. Claim 3 The system of claim 1, wherein the resistance component is a spring subsystem including at least one spring. Claim 4 The system according to claim 3, wherein the at least one spring is two springs positioned around the movable component.

5. The system according to claim 1, wherein the trigger component is an arm extending generally perpendicularly from an outer surface of the movable component.

6. The system according to claim 1, wherein the state change is triggered by physical contact between two components.

7. The system according to claim 6, wherein the detection component is a contact mechanism, and the state change is registered when the physical contact between the two components occurs.

8. The trigger component includes three arms, the detection component includes three detection components, and each detection component is configured to register a state based on interaction with each of the three arms, the detection component implements a voting architecture for determining a voted output state based on the states registered by the three detection components, the voted output state corresponds to a majority state condition of the three detection components, according to the system of claim 5.

9. The system according to claim 1, wherein the trigger component triggers through a non-contact mechanism, and the state change is registered without physical contact between components.

10. The system according to claim 9, wherein the detection component is an optical sensor.

11. The system according to claim 9, wherein the detection component is a capacitance sensor.

12. A method of detecting a rigidified state of a robot capture interface between a robot capture device and a grapple fixture through the grapple fixture, comprising: providing a grapple fixture including a probe, a movable component connected to the probe, a resistance component connected to the movable component, a detection component, and a trigger component; resisting movement of the movable component from a first position to a second position through the resistance component when a pulling force applied to the probe is less than a defined amount of force; triggering, by the trigger component, a first state change registered by the detection component when the movable component moves from the first position to the second position; When the detection component registers the first state change, communicating a first state condition from the detection component; When the tensile force applied to the probe drops below the defined amount of force, returning the movable component from the second position to the first position via the resistance component A method comprising. **Claim 13** The method is When the movable component moves from the second position to the first position, triggering, by the trigger component, a second state change registered by the detection component; When the detection component registers the second state change, communicating a second state condition from the detection component The method according to claim 12, further comprising. **Claim 14** The method according to claim 13, wherein the resistance component is configured such that a predetermined amount of force is overcome only when a required threshold force of the robot capture interface is reached. **Claim 15** The method according to claim 12, wherein the resistance component is a spring subsystem including at least one spring. **Claim 16** The method according to claim 12, wherein the state change includes physical contact between two components. **Claim 17** The method according to claim 12, wherein the detection component is configured to register a state change through a non-contact mechanism. **Claim 18** The method according to claim 17, wherein the detection component is an optical sensor. **Claim 19** The method according to claim 17, wherein the detection component is a capacitance sensor. **Claim 20** A method of assembling a rigidification detection system for detecting a rigidified state of a robot capture interface between a robot capture device and a grapple fixture, Providing a grapple fixture base, a probe, a movable component, a resistance component, and a detection component; Connecting the movable component to the probe such that the movable component moves along the same axis when the probe moves along the axis, the movable component including a trigger component; Until a pulling force of a pre-determined threshold amount is applied to the probe along the axis, the resistive component resists the movement of the movable component along the axis, and when the pulling force applied to the probe drops below the pre-determined threshold amount of force, the movable component is returned to the first position, the step of disposing the resistive component between the movable component and the inner surface of the grapple fixture base; The step of disposing the detection component in the inner compartment of the grapple fixture base, the detection component being positioned such that the detection component is triggerable by the trigger component, the detection component being configured to register a state change and communicate the state change as a signal when triggered; A method comprising.

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