Systems, methods, and devices for robotic capture of free flyers or other unsupported objects - Patents.com

Abstract

Systems, methods, and devices are provided for robotic capture of objects. A system for robot-based capture of a free-flying object includes a grapple fixture for attachment to the free-flying object and an end effector for capturing the free-flying object by interfacing with the grapple fixture. The grapple fixture includes a base and a deflectable probe. The end effector includes a probe guide surface for deflecting and guiding a probe tip of the probe through an opening in the probe guide surface into a grappling position. The end effector includes a probe sensing element for sensing when the probe tip is in the grappling position and for triggering a capture mechanism. The capture mechanism grapples the probe tip and an actuator retracts the capture mechanism to a predetermined position to establish a load-bearing interface between the free-flying object and the end effector.

Description

[Technical field]

[0001] The following relates generally to robotic systems and devices, and more particularly to robotic devices for capturing free-flying or other unsupported objects. [Background technology]

[0002] The behavior of free flying objects presents various challenges for capture by robotic systems. Such systems are particularly desirable in environments where humans may not be able to operate or service machines, such as underwater or in outer space.

[0003] Conventional approaches may require precise engagement or initial contact of the grapple fixture and end effector to capture and handle the free-flying object. The free-flying object may be in a state of "free drift," in which the rate of change of position and orientation in any direction is non-zero. In some cases, a free-flyer in a "free drift" state may have a significant angular rotation rate and may then be considered to be "tumbling." Alternatively, the free-flying object may have its own attitude and / or reaction control system, may be able to autonomously change linear and angular rates, or may not act like a passive inertial mass.

[0004] The robotic capture system will use a set or sets of sensors to ascertain the relative position and orientation of the free flyer and its relative linear and angular drift rates, and then calculate the trajectory required for capture. Any inaccuracies in this system will result in misalignment between the end effector (robotic capture system) and the grapple fixture (mounted on the free flyer). Misalignment of the end effector and grapple fixture probes can prevent the robotic capture device from successfully engaging or making initial contact with the probe, thereby failing to capture the free flyer object and hindering the ability to steer or manipulate the free flyer object (or components thereon).

[0005] During a capture attempt, if there is contact between the end effector and the grapple fixture, where the misalignment is large enough that no successful physical connection is made (i.e., the contact occurs outside the "capture envelope" of the device), the free flyer will be pushed away rather than captured. The contact force will cause the free flyer drift rate to change due to this contact. In some cases, this may cause a freely drifting free flyer to drift at an increased rate that makes a subsequent recapture attempt impossible. Or, the rate control capabilities of an actively controlled free flyer may be overwhelmed by the imparted contact energy, and the free flyer cannot control its position and orientation. The contact force of an unsuccessful capture may cause irreparable damage to the free flyer due to the misalignment. It is therefore important that the end effector and grapple fixture system provide robust capture reliability with a sufficient "capture envelope" that exceeds the misalignment that may occur upon contact.

[0006] The movement of the object to be captured can present challenges in matching, soft capturing, and then rigidifying to establish a load-bearing interface between the captured object and the end effector, which may be applicable to free flight scenarios or other scenarios where the movement of the object to be captured is less predictable. Summary of the Invention [Problem to be solved by the invention]

[0007] Thus, a need exists for improved systems, methods, and devices for capturing and manipulating free-flying objects that overcome at least some of the shortcomings of existing systems and methods. [Means for solving the problem]

[0008] A system for robotic capture of a free-flying object is provided. The system includes a grapple fixture for attachment to the free-flying object and an end effector for interfacing with the grapple fixture to capture the free-flying object. The grapple fixture includes a base having a mounting surface for attachment to the free-flying object and a mating surface opposite the mounting surface for mating with the end effector, and a deflectable probe connected to the base via a deflectable joint to enable deflection of the deflectable probe. The deflectable probe includes a probe tip that enables grappling.The end effector includes an interface for connecting to a robotic arm ("robot arm interface") and allowing manipulation by the robotic arm or connection to a spacecraft with capability to allow direct capture; a probe guide surface for deflecting and guiding a probe tip of a deflectable probe toward and through an opening in the probe guide surface into a grappling position when the end effector is moved toward the grapple fixture and when the grapple fixture is within the capture envelope of the end effector; a capture mechanism (or "grapple") configured to grapple the probe tip when triggered by the presence of the probe tip (thus entering a state known as a "soft capture", where there is a non-separable connection that constrains some, but not all, degrees of freedom); and a capture mechanism triggered sensing element for sensing when the probe tip is in the grappling position and when the capture mechanism is triggered. and an actuator configured to retract the capture mechanism along a capture axis to a predetermined position where a mating surface of the base of the grapple fixture is preloaded against the probe guide surface to establish a load-bearing interface between the free-flyer object and the end effector (known as a "hard capture").

[0009] The deflectable joint may further include a buffer spring for buffering initial contact between the probe tip and the probe guide surface.

[0010] The deflectable joint can be a spring-centered spherical joint.

[0011] The system may further include a robotic arm and a robotic arm controller for controlling the robotic arm, the robotic arm controller configured to command the robotic arm to move the end effector towards the grapple fixture upon approach such that the relative velocity of the end effector and the free-flyer object is maintained within a predetermined velocity band known to promote successful soft capture.

[0012] The mating surface of the grapple fixture can include a first alignment component and the probe guide surface can include a second alignment component, the first and second alignment components configured to mate with one another to match a connection between the grapple fixture and the probe guide surface of the end effector.

[0013] The second alignment element can be a raised annulus and the first alignment element can be a recessed annulus.

[0014] The first alignment component can include a plurality of recesses in the mating surface and the second alignment component can include a plurality of protrusions, each one of the plurality of protrusions configured to mate with a respective one of the plurality of recesses.

[0015] Each of the multiple recesses can include a bottom surface and multiple angled or curved side alignment surfaces, and each of the multiple protrusions (e.g., "fins") can include a rounded surface profile that can urge the protrusion to slide over the bottom surface when it contacts one of the multiple side alignment surfaces, thus bringing the interface into a fully constrained alignment state in a "hard capture."

[0016] The capture mechanism can constrain the linear motion of the free-flyer object through the grappling of the probe tip, which constrains the center of the probe tip in x / y / z but allows motion of the grapple fixture (and thus the free-flyer) relative to the constrained point.

[0017] Angular and lateral offsets of the free-flyer object relative to the end effector can be removed by retracting the capture mechanism and mating the grapple fixture body with alignment surfaces on the end effector. In doing so, angular motion is constrained.

[0018] The capture mechanism can be configured to constrain linear motion in a soft capture, or to constrain all degrees of freedom ("DOFs") in a hard capture.

[0019] A robotic end effector is provided for capturing a free-flying object via a grapple fixture attached to the free-flying object. The end effector includes a robot arm interface for connecting to and enabling manipulation by the robot arm. The end effector also includes a probe guide surface for deflecting and guiding a probe tip of a deflectable probe of the grapple fixture toward and through an opening in the probe guide surface to a grappling position when the end effector is moved toward the grapple fixture and when the grapple fixture is within a capture envelope of the end effector. The end effector includes a probe sensing element for sensing when the probe tip is in the grappling position and for triggering a capture mechanism upon sensing that the probe tip is in the grappling position, and a capture mechanism configured to grapple the probe tip when triggered by the probe sensing element. The end effector further includes an actuator configured to retract the capture mechanism along the capture axis to a first predetermined position when the probe tip is grappled, where at the first predetermined position a mating surface of the base of the grapple fixture is preloaded against the probe guide surface to establish a load-bearing interface between the free-flyer object and the end effector.

[0020] The probe guide surface may be concave.

[0021] The end effector may further include a plurality of protrusions disposed on the probe guide surface for mating with complementary recesses on the mating surface of the grapple fixture during capture to align a connection between the grapple fixture and the probe guide surface of the end effector.

[0022] The probe guide surface may include a raised annulus for mating with a complementary recessed annulus on a mating surface of the grapple fixture.

[0023] Each one of the plurality of protrusions can include a rounded surface to encourage the fin to slide along the side alignment surface of each one of the complementary recesses and onto the bottom surface of the respective complementary recess. In some embodiments, the protrusion can slide along the side alignment surface and not contact the bottom surface of the respective complementary recess. Rather, the outer annulus surface of the end effector (raised annulus) and the outer annulus surface of the grapple fixture (recessed annulus) can contact and react to the load at the interface (to spread the interface preload in a more beneficial manner). This can include leaving a small amount of clearance at the protrusion and recess within the acceptable alignment variance.

[0024] The capture mechanism can include a spring-based compliant member, and the actuator can be configured to further retract the capture mechanism, compressing the compliant member and providing a preload to the interface between the grapple fixture and the end effector. Use of such a spring-based compliant member can provide a preload to the interface that is less sensitive to manufacturing tolerances, promotes mechanism repeatability, and reduces thermal distortion due to differences in expansion coefficients. In other embodiments, the compliant member can be omitted and the capture mechanism can still generate a preload. However, omission of the compliant member can increase the risk of losing the preload or risk of component failure if a more flexible element is not included in the preload path.

[0025] In one embodiment, the spring-based compliant member can be a Belleville spring stack.

[0026] The capture mechanism can include a pair of jaws connected to a probe sensing element and configured to move from an open position to a closed position to grapple the probe tip when the grapple probe tip triggers the capture mechanism to close. The capture mechanism can be configured to passively move to the closed state by deflection of a trigger linkage. The probe sensing element can sense the triggered capture mechanism. For example, a limit switch can be used to sense that the capture mechanism has been triggered by the presence of the probe tip.

[0027] The capture mechanism may include a concave insert component that forms a portion of the probe guide surface including the opening when the capture mechanism is positioned fully forward along the capture axis, and the concave insert component is retracted along with the capture mechanism during retraction.

[0028] Also provided is a method of robotic capture of a free-flying object. The method includes moving an end effector via a robotic arm towards a grapple fixture over the free-flying object such that the grapple fixture is within a capture envelope of the end effector. The method further includes contacting a deflectable probe of the grapple fixture with a probe guide surface of the end effector within the capture envelope, and continuing to move the end effector towards the free-flying object, thereby deflecting the deflectable probe with the probe guide surface towards an opening in the probe guide surface, and guiding the deflectable probe through the probe guide surface and through the opening to a grappling position. The method further includes sensing that the deflectable probe is in the grappling position and triggering a grappling mechanism, and upon sensing that the deflectable probe is in the grappling position, grappling the deflectable probe with the grappling mechanism to constrain linear motion of the free-flying object. The method further includes retracting the grappled deflectable probe along the capture axis to a predetermined position to remove angular and lateral offsets of the free-flyer object relative to the end effector and bring a base of the grapple fixture into contact with the probe guide surface, and rigidifying the interface between the grapple fixture and the end effector by retracting the grapple mechanism to a point where the grapple fixture is preloaded against alignment features on the probe guide surface.

[0029] Moving the end effector via the robotic arm towards the grapple fixture may further include detecting a machine vision target on the free-flyer object via the machine vision system, and tracking the machine vision target with the machine vision system as the robotic arm moves the end effector towards the grapple fixture.

[0030] The method may include cushioning initial contact between the deflectable probe and the probe guide surface via a cushioning spring in the deflectable probe.

[0031] Moving the end effector via the robotic arm towards a grapple fixture over the free-flying object can include maintaining, via the robotic arm controller, a relative approach speed / approach trajectory of the end effector and the free-flying object within a predetermined speed band known to promote successful soft capture of the grapple fixture.

[0032] Also provided is a capture tool for performing robotic capture of a free-flying object having a grapple fixture mounted thereon. The capture tool includes a probe guide surface, a grapple, and a hard capture mechanism. The probe guide surface guides a probe of the grapple fixture to a soft capture position. The grapple grapples the probe of the grapple fixture when the probe is in the soft capture position and constrains linear motion of the probe tip. The hard capture mechanism constrains angular motion of the probe by retracting the grappled probe until the grapple fixture is preloaded against the probe guide surface to establish a load-bearing interface between the free-flying object and the capture tool.

[0033] Other aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of several exemplary embodiments.

[0034] The drawings included hereby are intended to illustrate various examples of the articles, methods, and apparatus herein. [Brief description of the drawings]

[0035] [Figure 1]1 is a flowchart of a method for robotic capture of an object, such as a free-flying object, according to one embodiment. [Diagram 2] FIG. 1 is a block diagram of a system for robotic capture of an object, according to one embodiment. [Figure 3A] 1 is a schematic diagram of a free flyer capture system including a servicing satellite and a free flyer object, showing the robotic arm of the free flyer capture system moving from a parking position to a position ready for capture, and the free flyer object moving from a first location to a second location, according to one embodiment. [Figure 3B] 3B is a schematic diagram of the free-flyer capture system of FIG. 3A showing capture of a free-flyer object by a robotic arm of a servicing satellite through a connection between an end effector and a grapple fixture on the free-flyer object, according to one embodiment. [Figure 3C] 3A and 3B showing a robotic arm moving a captured free-flyer object from a pre-berthing position to a berthing position, according to one embodiment. FIG. [Figure 4A] 3A-3C, further implementing a transfer of an orbital replacement unit (ORU) from a free-flyer object to a servicing satellite, including capture of the ORU by an end effector, in accordance with one embodiment; FIG. [Figure 4B] 4B is a schematic diagram of the free flyer capture system of FIG. 4A that provides transfer of the captured ORU from the free flyer object to a servicing satellite and power transfer to the ORU by the servicing satellite, according to one embodiment. [Figure 5A] FIG. 1 illustrates a front perspective view of an end effector for capturing a free-flyer object, according to one embodiment. [Figure 5B] FIG. 5B is a front view of the end effector of FIG. 5A. [Figure 5C] FIG. 5B is a side view of the end effector of FIG. 5A. [Figure 6A]FIG. 5C is a front perspective view of a grapple fixture for attachment to a free-flyer object and for capture by the end effector of FIGS. 5A-5C, according to one embodiment. [Figure 6B] FIG. 6B is a front view of the grapple fixture of FIG. 6A. [Figure 6C] FIG. 6B is a cross-sectional side view of the grapple fixture of FIG. 6A. [Figure 7A] FIG. 13 is a cross-sectional side view of an end effector during a first stage of a capture sequence, according to one embodiment. [Figure 7B] FIG. 7B is a cross-sectional side view of the end effector of FIG. 7A during a second stage of a capture sequence, according to one embodiment. [Figure 7C] FIG. 7B is a cross-sectional side view of the end effector of FIG. 7A during a third stage of the capture sequence (soft capture achieved), in accordance with one embodiment. [Figure 7D] FIG. 7B is a cross-sectional side view of the end effector of FIG. 7A during a fourth stage of a capture sequence, according to one embodiment. [Figure 7E] FIG. 7B is a cross-sectional side view of the end effector of FIG. 7A at a fifth stage of the capture sequence (all misalignments removed and the surface is seated), according to one embodiment. [Figure 7F] FIG. 7B is a cross-sectional side view of the end effector of FIG. 7A in a sixth stage of a capture sequence (rigidified), according to one embodiment. [Figure 8A] 6A-6C and the end effector of FIG. 7A-7F, showing the grapple fixture being misaligned as it approaches the receiving end of the end effector, according to one embodiment. [Figure 8B] 7A-7F are schematic cross-sectional side views of a capture sequence involving the grapple fixture of FIGS. 6A-6C and the end effector of FIGS. 7A-7F showing initial contact between a probe tip of a deflectable probe of the grapple fixture and a probe guide surface of the end effector, in accordance with one embodiment; [Figure 8C] 6A to 6C and the end effector of FIG. 7A to 7F, showing deflection of a deflectable probe by a probe guide surface towards an opening in the probe guide surface, according to one embodiment. [Figure 8D] 6A to 6C and the end effector of FIG. 7A to 7F, showing the probe tip of the deflectable probe entering the internal compartment of the end effector through an opening to a grapple position, according to one embodiment. [Figure 8E] 7A to 7F are schematic cross-sectional side views of a capture sequence involving the grapple fixture of FIGS. 6A to 6C and the end effector of FIGS. 7A to 7F , showing that the probe tip of the deflectable probe has triggered grappling of the probe tip by the capture mechanism of the end effector through contact with a probe sensing element, in accordance with one embodiment. [Figure 8F] 7A-7F are schematic cross-sectional side views of a capture sequence involving the grapple fixture of FIGS. 6A-6C and the end effector of FIGS. 7A-7F , showing an initial retraction of the capture mechanism and grappled deflectable probe toward a hard capture position along the capture axis, according to one embodiment. [Figure 8G] 7A-7F are schematic cross-sectional side views of a capture sequence involving the grapple fixture of FIGS. 6A-6C and the end effector of FIGS. 7A-7F showing the capture mechanism retracted to a hard capture position to rigidify the interface between the grapple fixture and the end effector, according to one embodiment. [Figure 8H] 6A-6C and the end effector of FIG. 7A-7F, showing the capture mechanism being driven forward along the capture axis to disengage the probe tip to allow release of the grapple fixture, according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Various apparatus or processes will be described below to provide examples of each claimed embodiment. The embodiments described below are not intended to limit any claimed embodiment, and any claimed embodiment may cover a process or apparatus different from that described below. The claimed embodiments are not limited to an apparatus or process having all of the features of any one apparatus or process described below, or to features common to some or all of the apparatus described below.

[0037] Additionally, although process steps, method steps, algorithms, or the like may be described (in this disclosure and / or in the claims) in a sequential order, such processes, methods, and algorithms may be configured to work in alternative orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. Steps of processes described herein may be performed in any order that is practical. Additionally, some steps may be performed simultaneously.

[0038] It will be readily apparent that when a single device or article is described herein, two or more devices / articles (whether they cooperate or not) can be used in place of the single device / article. Similarly, when two or more devices or articles are described herein (whether they cooperate or not), it will be readily apparent that a single device / article can be used in place of the two or more devices or articles.

[0039] The following relates generally to robotic systems and devices, and more particularly to robotic devices for capturing free-flying objects.

[0040] The terms "free flying object", "free flyer object", or "free flyer" as used herein 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. Strong initial contact forces during an attempt to capture a free flyer object will tend to "tip 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 tip-off) and "hard capture" or "rigidification" (high forces at relatively low speeds after tip-off has already been prevented by soft capture). Generally, a free flyer object is not physically connected to a "capturing" body, which is a body to which a robotic capture device is connected. The "capturing" body has the ability to control itself in six degrees of freedom (DOF), but does not have control of the relative 6 DOF between the capturing body and the free flyer. A free flyer in the relative sense, and a "free flyer capture" is the act of gaining control of the relative 6 DOF motion between a capturing body and a free flyer. On Earth, two bodies that are not directly connected often have indirect connections through gravity and friction, as well as through the ground between the bodies, and are thus not tethered free flyers. The systems and methods of the present disclosure can be used to facilitate capture in other environments where tip-off of the captured object may occur during a grapple attempt. Additional environments in which the systems and methods may find application include underwater / sea environments or in space / 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, where some, if not all, DOFs are not controlled. One such example is a load suspended from a crane that needs to be captured and controlled.

[0041] In general, the present disclosure provides systems, methods, and devices for robotic capture of an object, including capturing an object by grappling a grapple fixture attached to the object, and rigidifying an interface between the 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 to the object through the end effector. The object, referred to herein as a "capture object," can be an object that is not connected to any system to which the robotic arm used to manipulate the end effector is connected, making alignment generally more challenging. For example, the object can be a free-floating underwater object or a free-flying object (such as a free-flyer object, e.g., an active functioning satellite, a decommissioned or failed satellite, a used upper stage of a launch vehicle, or an orbital debris object). Thus, the end effectors of the present disclosure can be configured with a relatively large capture envelope to address the potential for misalignment during approach and capture.

[0042] The robotic capture system and device of the present disclosure can also be used to perform "pick and place" operations on objects, allowing the object to be grabbed and moved to another location at the end of a robotic manipulator system. The robotic capture system and device of the present disclosure can also be used to perform docking of free-flyer objects, where the free-flyer includes the end effector and the larger "more stationary" object includes the grapple fixture. In such cases, the servicer spacecraft can perform all the maneuvers without a robotic arm. As such, the free-flyer capture mechanism can reside on either the servicer or the client.

[0043] The robotic capture systems, methods, and devices of the present disclosure advantageously provide a less expensive method for free-flyer capture than existing methods, such as the "snare cable" based methods used on the shuttle and station arms. The systems, methods, and devices can be used for smaller and lighter free-flyers than existing snare cable methods, while also being scalable for use with larger and heavier free-flyer objects. For example, the embodiments described herein, including compliant probes, mousetrap capture mechanisms, and rigidified motors, among others, provide simple implementations that can capture free-flyer objects.

[0044] In an embodiment, the end effector is directed by the robot arm to approach the grapple fixture. The grapple fixture includes a probe having a tip that contacts a probe guide surface at a 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 in the grapple position is sensed by the end effector and a capturing mechanism is engaged to grapple the tip of the probe of the grapple fixture. The capturing mechanism is retracted, drawing the probe further into the end effector and bringing the base of the grapple fixture into mating contact with the probe guide surface. The capturing 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.

[0045] The multi-stage capture and rigidification described above can advantageously allow for easier and more successful initial capture of the object. The multi-stage approach advantageously allows for rotation of the object to achieve proper alignment for more complete capture.

[0046] 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 this disclosure, that function includes capturing a free-flying asset. As used herein, the term "end effector" includes devices that are permanently or inseparably attached to the end of a robotic arm and devices that have a separable interface with the end of the robotic arm. A separable interface can allow the end effector to be picked up, used, and put down (i.e., separated from the robotic arm). An instance of an end effector with a separable interface can also be referred to as a "tool" or an "end of arm tool." In such an instance, a robotic arm can have a first end effector attached to its end that has the functionality of a tool changer that allows the robotic arm to use multiple different tools, and a second end effector with a separable interface, where the second end effector can be engaged by the first end effector and function as a tool. In such cases, the first "tool changer" end effector and the second "tool" end effector are each considered to be end effectors. Thus, any reference herein to an "end effector" is intended to include all such devices as described in the foregoing unless otherwise specified.

[0047] 1, a method 100 of robot-based object capture, according to an embodiment, is now shown. The method 100 can be implemented using a robotics system including a machine vision system, a robot arm controller, a robot arm, and an end effector. In one embodiment, the method 100 can be used to capture free-flying objects in space-based applications, such as, for example, satellites.

[0048] At 102, a machine vision target mounted on an object to be captured (the "capture object") is detected by a machine vision system. The capture object may be a free-flying object. The machine vision system may then generate a signal that the capture object has been detected and communicate the signal to a robot arm controller.

[0049] In some cases, the capture object may also be referred to as a "target object." The object or vehicle that performs the capture via the end effector and to which the end effector is connected may be referred to as a "chaser." For example, in a space-based application, the chaser may be a spacecraft.

[0050] In variations in which the capture object is a free-flying object, the free-flying object may be, for example, a free-flying object that has only attitude control, a free-flying object that has thrusters that may be used for propulsion to also control its trajectory, or a free-flying object that has no attitude or reaction control.

[0051] Generally, "capturing" refers to the process by which an end effector or capturing tool and grapple fixture (on a captured object) as described herein transitions from an ungrappled state to a grappled and rigidified state. This process can typically be used to bring a captured object, such as a free flyer, to the same speed as the captured object on which the end effector is disposed.

[0052] As described herein, the capture process includes both "soft capture" and "hard capture" processes. Hard capture can also be referred to as rigidification. Soft capture can be considered a process in which a non-separable connection that constrains some, but not all, degrees of freedom is established between the grapple fixture on the captured object and the end effector. Generally, this involves constraining the linear motion of the tip of the grapple probe of the grapple fixture. For example, the center of the probe tip can be constrained in x / y / z while allowing the grapple fixture (and captured object) to move relative to that constraint point. In hard capture, all degrees of freedom are constrained. This can include constraining angular motion, for example, by removing angular and lateral offsets. Hard capture can be achieved by retracting the grapple probe to a pre-determined position where the grapple fixture is preloaded against the end effector, establishing a load-bearing interface between the captured object and the end effector.

[0053] At 104, the robotic arm moves the end effector towards a grapple fixture over the capture object. The grapple fixture is used to enable grappling and capture of the capture object and can be a standardized interface. The robotic arm controller is configured to control the movement of the robotic arm at 104 such that as the end effector approaches the grapple fixture, the grapple fixture is within the capture envelope of the end effector.

[0054] The term "capture envelope" as used in this disclosure will now be explained. When a capture or docking device is positioned for use, it needs to be placed in a specific relative position to the grapple element or fixture of the capture object to ensure that the mechanism will successfully close around the grapple fixture when the soft capture operation is performed. While the capture operation is occurring, there are multiple influences that work against successful capture, including that the mechanism itself has specific geometric and dynamic positioning requirements, that the vision system has a specific amount of measurement uncertainty, and that the captured object is still potentially drifting relative to the platform of the capture system. Adding up all these influences (potential errors) creates positioning requirements in x, y, z, yaw, pitch, roll that the capture mechanism must be within to guarantee capture. This is referred to as the "capture envelope". The larger the capture envelope, the more objects can be captured for a given set of these influences (drift rate, targeting and positioning accuracy, system speed to keep up with a "tumbling" or "drifting" FF). Also, there may be a minimum "capture envelope" that is required based on influences in the system that work against capture. A larger envelope provides a margin in the ability to capture, making the free flyer capture sequence more reliable.

[0055] The machine vision system can continue to track the capture object via the machine vision target, communicate with the robot arm controller, keep pace with the capture object, and perform a final inward (towards the capture object) motion guided by the target to obtain the 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 capture object at a predetermined rate. This can include tracking the capture object, and when the capture object is drifting, the robot arm controller controls the arm to keep pace so that there is a constant vector between the end effector and the capture object. At an appropriate point, the robot arm controller can then add a delta command. The delta command represents a closing speed that will bring the receiving end of the end effector towards the grapple fixture of the capture object. The delta command can include closing within a certain speed range (e.g., a pre-determined band, as described below).

[0056] The robot arm controller can be configured to move the robot arm and the end effector at a predetermined rate toward the capture object such that the relative velocity of the end effector and the capture object is maintained within a predetermined band. The predetermined band represents a range of relative velocities known to promote or result in successful soft capture of the grapple fixture (e.g., through sliding along the probe guide surface and through the opening into the internal compartment, as described below). The predetermined relative velocity band can be determined based on various system characteristics (including characteristics of the robot system and the capture object). Such system characteristics can include, for example, characteristics of the deflectable probe of the grapple fixture, such as spring stiffness or friction characteristics of the probe and probe guide surface, etc. Maintaining the relative velocity of the capture object and the end effector during approach can be particularly important in free-flyer capture applications. This is because such a relative speed that is too fast or too slow can cause the probe of the grapple fixture to contact the probe guide surface, deflect, and fail to slide over the probe guide surface through the opening and into the internal compartment for grappling.

[0057] It is important that a useful capture device is tolerant with respect to the relative velocity between the capture system and the captured object. Many robotic capture system designs are driven by factors or principles such as, for example, reducing friction, minimizing spring stiffness, reducing tip-off forces, and increasing the speed of the soft capture action. The need to achieve rigidification sometimes violates these driving principles. For example, fins on the capture device (e.g., fins 532 in Figs. 5A, 5B) that ensure good constraint on roll after capture can create an obstacle to soft capture that is somewhat mitigated by the design to keep the capture envelope as large as possible and to reduce the relative rate requirements on the capture system. Means of achieving roll constraint in the rigidified state necessarily compromise the design's largest possible capture envelope, and making that envelope as large as possible adds margin to successful soft capture capacity. The device of the present disclosure addresses misalignment through flexible members in the capture system. Deflection of the flexible member (probe) to correct for misalignment occurs upon contact with the free flyer. It takes a small amount of energy (in the form of a force-displacement product) to deflect the flexible member into alignment. If the approach is too slow, the free-flyer object will be pushed away from the end-effector capture device before a "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 rotational mass inertia, trigger force) 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.

[0058] At 106, a deflectable probe of the grapple fixture contacts a probe guide surface on the receiving end of the end effector within the capture envelope.

[0059] At 108, the initial contact between the deflectable probe at 106 and the probe guide surface is cushioned by a cushioning spring in the deflectable probe. Such cushioning of the initial impact can prevent the probe from bouncing off the receiving end of the end effector. This can be particularly advantageous in applications where the captured object is a free-flying object.

[0060] At 110, the deflectable probe is deflected by the probe guide surface from a rest position (e.g., the probe perpendicular to the surface of the capture object on which the grapple fixture is mounted) with continued motion of the end effector towards the capture object, towards an opening in the probe guide surface located at or near the center of the probe guide surface. The probe guide surface can be concave to facilitate deflection of the deflectable probe towards the opening. The opening provides access by the deflectable probe to an internal compartment of the end effector in which the capture mechanism is disposed.

[0061] The deflectable probe includes a deflection element to allow the probe to deflect from a rest position in the direction of an applied force and to return to the rest position upon removal of the applied force. In the case of 110, the shape of the probe guide surface and the movement of the end effector towards the capture object apply a force to the deflectable probe that deflects the probe towards the opening in the probe guide surface. The deflectable element can include one or more spring components to facilitate deflection.

[0062] At 112, the probe guide surface guides the deflected probe through the opening and into a soft capture (or grapple) position within the internal compartment. Continued motion of the end effector toward the capture object and the profile of the probe guide surface causes continued deflection of the deflectable probe and sliding of the end of the deflectable probe across the probe guide surface toward and through the opening.

[0063] At 114, the presence of the deflectable probe in the soft capture position is sensed by the end effector, triggering a grapple mechanism ("grapple") of the end effector.

[0064] In one embodiment, sensing of the deflectable probe can be performed by positioning a sensing element or trigger that is contacted by the end of the deflectable probe as it enters the opening into the internal compartment of the end effector in line with the capture axis (the axis along which the deflectable probe is oriented into the internal compartment of the end effector). A force applied to the sensing element by the deflectable probe contact can then cause the sensing element to engage the grapple.

[0065] 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 the force tripping a microswitch, the force as measured by a suitably installed load cell / strain gauge, optical methods, capacitive methods, inductive methods, and electrical resistive methods. Force tripping of a microswitch can advantageously provide a simple and effective way of measuring state changes. Other sensing methods can generally be used if such methods make sense for a particular embodiment.

[0066] At 116, the deflectable probe is grappled by the grapple. Grappling of the deflectable probe constrains linear motion of the captured object relative to the end effector. In one embodiment, the grapple can include a pair of jaws configured to move from an open position to a closed position when triggered, thereby gripping the probe. In one embodiment, the end of the probe is spherical to enable grappling of the probe (and to facilitate sliding of the probe along the probe guide surface).

[0067] At 118, the grappled deflectable probe is retracted into the internal compartment of the end effector along the capture axis in a direction opposite the receiving end of the end effector to remove angular and lateral offset of the captured object relative to the end effector. Generally, in some embodiments, the roll misalignment must be maintained within a certain maximum 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 a potentiometer or the like. Retraction of the grappled probe moves the base of the grapple fixture, which is connected to the deflectable probe, further toward and into contact with the probe guide surface. The grapple fixture base and the probe guide surface can be complementarily shaped to promote sliding of the base along and / or mating of the base with the probe guide surface. The grapple fixture base and the probe guide surface may each include alignment features configured to interface with one another and promote alignment between the grapple fixture base and the probe guide surface as the probe is retracted and the end effector and the captured object are moved closer to one another.

[0068] At 120, the interface between the grapple fixture and the end effector is rigidified. Rigidification is accomplished 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 a contact annulus, as described herein. In other embodiments, the preload can be on a number of protrusions (or "fins"). In certain embodiments, the alignment features include a raised contact annulus and a number of fins, and the grapple fixture is preloaded against the raised contact annulus and is not preloaded against the alignment fins.

[0069] Rigidification of the interface allows full authority by the capture system to define the relative position and orientation of the captured object. This allows low uncertainty in, and control of, the relative position and rate between the two objects. This state is typically suitable for situations in which the robot servicer is then going to apply loads while the robot servicer is fixing, adjusting, or refueling the captured object, or while the robot servicer is propelling the captured object to a new trajectory or to a new attitude. In the soft captured state, the capture system has some authority over the captured object in certain DOFs, but not in others (hence it does not have the ability to generate forces or moments on the free-flyer object to steer it to any position and orientation). Once achieved, the hard captured 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 DOF and being the determining factor in where the free flyer is held allows for 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.

[0070] At 122, the rigidified capture object is manipulated (e.g., moved) by a robotic arm connected to the end effector. In one example, the capture object can be moved to a mooring location.

[0071] 2, a system 200 for robotic capture of an object is shown, according to an embodiment. System 200 can be used, for example, to capture a free flying object such as a satellite. System 200 can be used to implement method 100 of FIG.

[0072] The system 200 includes a capture object 202 and a robotic system 204 for capturing the capture object 202 and for manipulating the capture object 202 once captured.

[0073] 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 a machine vision system 208 of the robotic system 204 can detect and track the machine vision target 206.

[0074] The machine vision system 208 may include a camera for visualizing the machine vision target 206, a processor for generating and processing image data collected by the camera, memory for storing the image data, and a communication interface for communicating with other components of the robotic system 204 (e.g., communicating information about the detection and tracking of the machine vision target 206).

[0075] The robotic system 204 also includes a robotic arm controller 210 for controlling the movement of the robotic arm 212. The robotic 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 robotic arm 212. For example, the robotic 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 capture object 202) and generate arm movement commands based on the received machine vision data. The robotic arm controller 210 can then send arm movement commands to the robotic arm 212 to control the movement of the robotic arm 212.

[0076] In some cases, the robot arm controller 210 can be configured to determine the relative approach velocity and to maintain the relative approach velocity within a predetermined range to facilitate soft capture of the capture object 202.

[0077] The robotic system 200 also includes an end effector 214 connected to the robotic arm 212. The end effector 214 is configured to capture (grapple and rigidify) the capture object 202 via a grapple fixture 216 on the capture object 202. The end effector 214 can also be configured to pass any one or more of power, data, and torque to the capture object 202, once captured, through an interface present on the capture object 202.

[0078] The grapple fixture 216 can be attached to the capture object 202 at a location proximate to the machine vision target 206 such that the machine vision target 206 can be used to orient the end effector 214 towards the grapple fixture 216 for capture.

[0079] The grapple fixture 216 includes a base 218 and a deflectable probe 220 connected to the base 218 .

[0080] The base 218 is attached to an exterior surface of the capture object 202. The deflectable probe 220 is connected to the base 218 such that the deflectable probe is generally perpendicular to the base 218 when in a rest state (i.e., undeflected).

[0081] 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.

[0082] 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 promote 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 a required preload of the end effector grapple fixture interface.

[0083] In some embodiments, the preload can be on only a subset of the alignment features 226, 228 (or only a subset of the alignment features can be used to react to loads at the interface). For example, in certain embodiments, the alignment features 228 can include a raised contact annulus and multiple alignment fins along with a complementary alignment feature 226 on the grapple fixture, and only the annulus is used to react to loads at the interface (preload only on the contact annulus, not on the fins, "annulus reaction"). In embodiments where the alignment features include a contact annulus, the outer annulus surface of the end effector (raised annulus) and the outer annulus surface of the grapple fixture (recessed annulus) can come into contact and react to loads at the interface, which can advantageously spread the interface preload in a more beneficial manner.

[0084] In another embodiment, the annulus may not be present and alignment fins can be used to react to loads at the interface ("fin reaction").

[0085] 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 the two are brought together.

[0086] The alignment features 226, 228 can also be configured to allow for 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 in applications where the capture object 202 has a tumble rate, such as in the case of a free-flying object.

[0087] The alignment features 226, 228 can be configured to cause self-alignment of the interface as a result of rotational misalignment (eg, a 5 degree offset).

[0088] The deflectable probe 220 of the grapple fixture 216 includes a probe 230 that includes a shaft that terminates in a grapple end 232. The grapple end 232 may have a diameter that is greater than the diameter of the shaft. The grapple end 232 may include a spherical tip. In the case where the grapple end is rounded or spherical, the grapple end 232 may be referred to as a "grapple ball."

[0089] The deflectable probe 220 also includes a biasing element 234 to allow deflection of the probe 230 in the direction of the applied force. The biasing element 234 is also configured to return the probe 230 to a resting state (undeflected, no applied force) when the applied force is removed. The amount of applied force required to deflect the biasing element 234 can vary depending on the material used. In one embodiment, the biasing element includes one or more springs. In one embodiment, the biasing element 234 includes a spring-centered spherical joint.

[0090] In one embodiment, the probe 220 is configured to allow 3DOF rotation and lateral / off-axial deflection.

[0091] 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 may be attached or mounted directly to the base 218.

[0092] Generally, as the robotic arm 212 moves the end effector 214 towards the grapple fixture 216 of the capture object 202 , the grapple end 232 of the deflectable probe 220 contacts the probe guide surface 224 of the end effector 214 .

[0093] The probe guide surface 224 is curved to encourage deflection of the deflectable probe 220 towards the opening 236 when it contacts the grapple end 232. The opening 236 may be located at or near the center of the probe guide surface 224. In cases where the probe guide surface 224 is concave, the opening 236 may be located at an apex of the concave probe guide surface 224.

[0094] The probe guide surface 224 is constructed from a material suitable to allow the grapple end 232 of the deflectable probe 220 to slide along the probe guide surface 224. For example, a material can be selected to have an appropriate frictional force interaction between the probe guide surface 224 and the grapple end 232. Similarly, the grapple end 232 is constructed from a material suitable to allow the grapple end 232 to slide along the probe guide surface 224 with a desired or acceptable level of friction.

[0095] Generally, movement of the end effector 214 toward the grapple fixture 216, 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 and into the internal compartment 238 of the end effector 214 for grappling.

[0096] The internal compartment 238 houses a probe sensing element 240 , a grapple 242 , a linear displacement mechanism 244 , and a rigidification mechanism 246 .

[0097] 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 grasp the grapple end 232. The grapple 242 may also be referred to as a capture mechanism or a soft capture mechanism.

[0098] The probe sensing element 240 is positioned near the opening 236 such that when triggered by the grapple end 232 (e.g., by being depressed or otherwise contacted by the grapple end 232), the grapple 242 can grasp the grapple end 232. For example, in one embodiment, the grapple 232 can include a pair of jaws that remain open until triggered to close by the probe sensing element 240. The probe sensing element 240 is positioned such that the grapple end 232 moves into and occupies the space between the open jaws (a "grapple position" or "soft capture position") such that the grapple end 232 triggers the probe sensing element 240 (e.g., by physical contact therewith). The jaws can then be closed to grapple the grapple end 232.

[0099] The grapple 242 can be configured to constrain three degrees of freedom (linear movement) of the grapple fixture 216 when grappling the grapple end 232 of the probe 230.

[0100] Generally, the grapple 242 is configured to provide a soft capture of the grapple probe 230. In some embodiments, the grapple 242 is configured to passively move to the closed state by deflection of a trigger linkage. The deflection can be provided through physical contact with the probe tip 232. A sensor can be used to sense when the grapple 242 is triggered. In one embodiment, the sensor is a limit switch.

[0101] The linear displacement mechanism 244 is configured to translate the grapple 242 along the capture axis of the end effector 214. Once the grapple 242 grasps 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 away from the receiving end of the end effector 214. Retraction of the grapple 242 draws the deflectable probe 220 further into the internal 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 mentioned, in some embodiments, only a subset of the alignment features 226 may be in contact.

[0102] In one embodiment, the linear displacement mechanism 244 includes two ball screws, a ball nut 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 placed beside the rest of the mechanism on each side, making the balanced load shorter. This design can be particularly advantageous in robotic arm operations where a longer package is not preferred (e.g., using a single ball screw instead of two ball screws). Nevertheless, in other embodiments, a single ball screw can be used.

[0103] The linear displacement mechanism 244 is configured to retract the grapple 242 to a hard capture position. When the grappled deflectable probe 220 is retracted, the angular and lateral offsets of the capture object 202 are removed.

[0104] Hard capture (rigidification) of the grapple fixture 216 is achieved when the probe 220 is retracted to a point where the grapple fixture 216 is preloaded against the probe guide surface 224. This may include contacting and mating of alignment features 226, 228.

[0105] Among other things, 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 (e.g., a Belleville spring stack) that is compressed to a preload position (corresponding to compression of the compressible element) via retraction of the probe 220 by the linear displacement mechanism 244.

[0106] In certain embodiments, the compressible element can be a spring-based compliant member. Use of such a spring-based compliant member can provide a preload to the interface that is insensitive to manufacturing tolerances, promotes mechanism repeatability, and reduces thermal distortion due to differences in expansion coefficients. In other embodiments, the compressible or compliant member can be omitted and the capture mechanism can still generate a preload. However, omission of the compliant member can increase the risk of losing the preload or of component failure if a more flexible element is not included in the preload path.

[0107] The compressible elements provide a known stiffness-deflection relationship. The use of compressible elements (e.g., Belleville stacks) allows the load variation to be kept under control. Once in the hard-captured or rigidified position, there are several influences that can cause the load to change. These influences include temperature, where the coefficient of thermal expansion (CTE) of the structure is different than the mechanism, and therefore a change in temperature causes a change in the position of the mechanism relative to the structure. This is particularly relevant when used in environments where temperatures can vary dramatically (e.g., from -40°C to +100°C), such as in space. Influences that also cause the load to change once hard-captured include, for example, variation in the length of the grapple probe from fixture to fixture, and position variation / precision within the capture tool. The compressible elements are of lower stiffness compliance that allows the hard-captured load to be passively controlled without constant monitoring.

[0108] The capture mechanism can include a state change detection element to detect when soft capture and retraction of the grapple fixture is achieved and when rigidification should be initiated using a preload generator component. In one embodiment, the state change detection element includes a potentiometer configured to detect when the grapple end 232 reaches a "seated" position. The state change detection element is connected to and triggers the preload generator element. In one embodiment, when the soft capture indicator is tripped and the state change detection element differs from the soft capture indicator, the mechanism moves immediately 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 (predetermined) preload is achieved. A power off brake can be used to avoid continuous loss of power while holding onto a free-flyer object (payload) when power to the drive motor is cut. Typically, the system is calibrated (e.g., on the ground in space applications) to go to a specific location as the "hard capture position," which is a position that can only be obtained (while holding the grapple fixture) by compressing the preload generator element (e.g., a spring stack). In embodiments using a spring stack, a midpoint (or approximately a midpoint) in the stroke of the stack can be used so that changing influences (e.g., such as those described above) do not move the rigidification load outside of the range. The range is based on the external loads that will be reacted to once rigidified (i.e., no interface separation) and the strength of the components in the system.

[0109] Once rigidified, the end effector 214 can send a signal that the capture object 202 has been rigidified to the robot arm controller 210. The robot arm controller 210 can then operate the robot arm 212 by generating and sending arm movement commands to move the rigidified capture object 202 to a desired location.

[0110] The linear displacement mechanism 244 can also be used to release the grapple fixture 216 by driving the grapple 242 (or a component thereof) forward along the capture axis to drive the grapple 242 to an open position, allowing release of the grapple end 232 and thus the grapple fixture 216.

[0111] 3A-3C, there is shown a free flyer capture system 300 including a servicing satellite 302 and a free flyer object 304, such as a satellite, that performs a capture sequence, according to an embodiment. System 300 is an exemplary application of system 200 of FIG. 2 and method 100 of FIG. 1.

[0112] Servicing satellite 302 includes a robotic arm 306 attached to servicing satellite 302 and an end effector 308 connected to robotic arm 306 for effecting capture of free-flyer object 304. End effector 308 can be, for example, the end effector of Figure 2, the end effector of Figures 5A-5C, or the end effector of Figures 7A-7F. Servicing satellite 302 also includes a servicing mechanism 310 for berthing and servicing free-flyer object 304.

[0113] The free-flyer object 304 includes a grapple fixture 312 mounted on an exterior surface of the free-flyer object 304 for interfacing with the end effector 308, an anchoring component 314 for anchoring the free-flyer object 304 through an interface with the servicing mechanism 310, and an orbital replacement unit (ORU) 316 for transfer from the free-flyer object 304 to the servicing satellite 302 via the end effector 308. The grapple fixture can be, for example, the grapple fixture of Figure 2 or the grapple fixture of Figures 6A-6C.

[0114] In general, an ORU 316 is a replaceable unit, i.e., something that needs to be replaced or moved. Examples of ORUs 316 include batteries, pumps, tanks, control moment gyroscopes, current switching units, containers and logistics carriers, robotic components (for replacement), radiators, plasma dischargers, antennas, power conditioners, and fluid couplers.

[0115] FIG. 3A illustrates the robotic arm 306 moving 318 from a parked position 320 to a "ready for free flyer capture" position 322. Both spacecraft 302 and 304 maintain their attitude. A free flyer object 304 is shown moving 305 from outside the capture box or ready to capture volume into the capture box. When the vision system sees the target, the system will initiate a free flyer capture sequence. In general, the vision system can be configured to determine if the free flyer object 304 is within the capture box and is used by the robotic arm 306 to visually guide the robotic arm 306 so that the relative position and rate of the arm 306 to the free flyer object 304 establishes the free flyer 304 within the capture box.

[0116] The arm vision system of the servicing satellite 302 verifies correct target tracking of the free-flying object 304. This may include tracking a machine vision target on the free-flying object 304. The machine vision target may be positioned near the grapple fixture 312.

[0117] Attitude control is disabled on both spacecraft 302, 304. In some scenarios, the client spacecraft can be put into "velocity mode" where the reaction wheels run at a constant speed. This adds gyro stiffness to the system and can improve the soft capture probability without forcing the client attitude control system (ACS) against the grapple. In general, the system can be configured to avoid conditions where spacecraft control bandwidth may be against robotic capture.

[0118] 3B illustrates the robot arm 306 moving 326 from a ready-to-capture position to a capture position (non-deterministic location). The robot arm 306 begins the capture sequence (soft capture to rigidification).

[0119] In doing so, the robotic arm 306 causes the end effector 308 to approach the grapple fixture 312 of the free-flying object 304 and perform a capture (grapple and rigidify) of the free-flying object 304 via the grapple fixture 312. The capture sequence can be performed as described herein (e.g., FIGS. 7, 8).

[0120] The relative motion / velocity of the servicing satellite 302 and the free-flyer object 304 is forced to "zero."

[0121] FIG. 3C illustrates the robotic arm 306 moving the captured free-flyer object 304 from the capture position (in FIG. 3B) to a pre-berthing position, and then further moving 328 the robotic arm 306 to the berthing position. The purpose of this movement is to orient the berthing component 314 of the free-flyer object 304 to the servicing mechanism 310. The servicing mechanism 310 (docking connection) can perform other connectivity tasks that the capture system may not perform. The robotic arm 306 is limped in the berthing position, and the servicing mechanism 310 captures and berthe free-flyer object 304 through the berthing component 314. The "limped" reduces the load on the joints of the robotic arm 306 to approximately zero, so that the arm load does not oppose the berthing alignment.

[0122] Once parked, the robotic arm 306 releases the grapple fixture 312 and returns to a parking position (parking position 320 shown in FIG. 3A, not shown in FIG. 3C), allowing the robotic arm 306 to perform other tasks while the servicing mechanism 310 holds the free-flyer object 304.

[0123] 4A-4B, the free flyer capture system 300 of FIGS. 3A-3C is now shown performing an ORU transfer sequence after capture and berthing of a free flyer object 304 by a servicing satellite 302, according to an embodiment. While FIGS. 4A-4B show that the ORU transfer sequence is performed by the same robotic arm (arm 306) as for the capture sequence of FIGS. 3A-3C, it should be understood that the robotic arm may be the same manipulator or may be a separate manipulator depending on the embodiment (e.g., depending on the mission architecture in a space-based application). Similarly, the end effector 308 used in the ORU transfer sequence may be the same end effector as that of the capture sequence or may be a different end effector (which may or may not be specially configured for the task). For example, in one embodiment, the end effector 308 used in the capture sequence can be a free-flyer capture device tool that the arm 306 uses and puts away, and the end effector 308 used in the ORU transfer sequence can be an end-of-arm tool changer configured for ORU pick-and-place. In another embodiment, the free-flyer capture tool can be configured to also perform ORU pick-and-place.

[0124] 4A illustrates the robotic arm 306 moving 330 from a parking position 332 to a high hovering position (not shown) and then to a soft capture position 334. Moving to the soft capture position 334 results in a non-rigid capture of the ORU 316. The arm end effector 308 then rigidifies its grip on the ORU 316. The free-flyer object 304 can be commanded to remove power from the ORU 316. The arm end effector 308 releases the ORU latch, releasing the ORU 316, and the robotic arm 306 moves to a high hovering position above the free-flyer object 304 (not shown).

[0125] 4B illustrates movement 336 of the robotic arm 306 from the capture position 334 to a high hovering position (not shown) above the servicing satellite 302, and then to an ORU insertion position 338. In doing so, the robotic arm 306 moves the ORU 316 from the free flyer object 304 to an ORU insertion location 340 on the servicing satellite 302. When at the ORU insertion location 340, the end effector 308 is commanded to engage the ORU latch (which was released in FIG. 4A when releasing the ORU 316 from the free flyer object 304) to connect the ORU 316 to the servicing satellite 302 at the ORU insertion location 340.

[0126] In some cases, at this stage, the servicing satellite 302 may apply power to the ORU 316. Certain embodiments may include separate connectors for power and / or data transfer. In some cases, power may be provided to the ORU 316 via the end effector 308 (e.g., via a separate electrical connection device on the end effector 308 to make the electrical connection). The ORU 316 may require power to survive while being transferred from one interface to another. A data connection to the ORU 316 allows the health and operational status of the ORU 316 to be monitored. In some cases, the robotic arm 306 may pick up the ORU 316 and may use the ORU 316 to image or robotically interact with something. The ORU 316 typically requires power and data connections to be used in this manner, which may be enabled through a connection between the servicing satellite 302 and the ORU 316.

[0127] The robotic arm 306 can then command the end effector 308 to release the ORU 316, and the robotic arm 306 moves to a parking position (such as shown at parking position 332 in FIG. 4A).

[0128] 5A-5C, there are shown a front perspective view 500a, a front view 500b, and a side view 500c, respectively, of an end effector 510 for capturing a free-flyer object, according to an embodiment.

[0129] The end effector 510 can be used to capture a free-flying object, such as a client spacecraft, that has a grapple fixture attached to it. In general, the end effector 510 is configured to capture the free-flying object by capturing and rigidifying the grapple fixture of the free-flying object.

[0130] 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 free-flyer object being captured. The robot arm interface end 514 is configured to connect the end effector 510 to a robot arm for manipulation of the end effector 510 via the robot arm. As such, the robot arm interface end 514 can include various mechanical or electrical connections to facilitate manipulation and movement of the end effector 510 via the robot arm.

[0131] In some cases, the end effector 510 may include components that allow the end effector 510 to be engaged by another end effector. For example, the end effector 510 may include a grapple fixture attached to it for capturing the end effector 510 by a second end effector. The end effector 510 may also include one or more interfaces for passing power, data, or torque from a second end effector to the end effector 510.

[0132] 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 encloses an internal compartment (not shown) in which are disposed various components for operation of the end effector, including various components for capturing and rigidifying a free-flyer grapple fixture.

[0133] The end effector 510 also includes a stowage / launch interface component 518 (shown only in FIG. 5B, its location is shown in FIGS. 5A, 5C). The stowage / launch interface component 518 can include a docking port for placing the end effector 510 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.

[0134] The end effector 510 includes a front end component 520 that is attached to an outer housing 516 at a receiving end 512 for interfacing with a grapple fixture of a free-flying object.

[0135] The front end component 520 includes a raised annulus 522 that extends around the periphery of the front end component 520 to contact a complementary annulus (e.g., 618 as shown in FIGS. 6A-6C) 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 an even distribution of clamp loads and equal load carrying capacity independent of applied pitch / yaw loads. In some embodiments, the raised annulus 522 may be absent.

[0136] The front end component 520 also 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 in the capture mechanism. The opening 528 is positioned generally in the center of the probe guide surface 526 (e.g., at an 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 controlling the end effector 510 can be configured to cause the end effector 510 to approach the grapple fixture of the free-flyer object (e.g., without the probe bouncing off the surface 526 due to such parameters) with parameters (e.g., relative velocity, relative angle) known to facilitate successful guiding of the probe through the probe guide surface 526 and into the opening 528. Management of such parameters by the control system of the end effector 510 can be particularly important in free-flying object capture applications, where it is more prevalent that a misaligned grapple fixture can cause the free-flying object to bounce off the end effector 510.

[0137] The characteristics of the probe guide surface 526, such as the surface material and angle, can be selected to achieve a desired interaction with the probe of the grapple fixture. For example, the characteristics can be selected to achieve a desired level of friction or to more efficiently guide the contacting probe towards and into the opening 528.

[0138] Probe guide surface 526 includes a concave insert 530. Concave insert 530 is movable along a capture axis (e.g., capture axis 726 in FIG. 7A below) as part of a capture mechanism within an internal compartment of end effector 510. For example, concave insert 530 can be the forward-most component of the capture mechanism (proximal to receiving end 512). In FIGS. 5A and 5B, concave insert 530 is in a fully forward position and will retract along the capture axis toward arm interface end 514 during a capture sequence.

[0139] The concave insert 530 can be constructed from the same material and have the same surface characteristics as the rest of the probe guide surface 526. The concave insert 530 can simply be a continuation of the probe guide surface 526 that is attached to the section of the device that retracts to move from soft capture to hard capture (rigidification). In other embodiments, the probe guide surface 526 can be a single piece (i.e., where 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 as it retracts inward to align the interface. As such, an embodiment that uses the concave insert 530 can advantageously avoid such interference.

[0140] The front end component 520 also includes three protrusions or "fins" 532a, 532b, 532c (collectively referred to as fins 532 and generically referred to as fins 532) that are attached to the probe guide surface 526.

[0141] The fins 532 act as alignment features that help align the receiving end of the end effector 512 with the grapple fixture of the free-flying object. The fins 532 are configured to mate with complementary alignment features (pockets 620 shown in FIGS. 6A-6C). For example, when capturing the grapple probe of the free-flying object, there may be some level of offset present due to the free-flying object having a tumble rate. The capture mechanism that captures and retracts the probe of the grapple fixture may provide coupling, but may be translationally misaligned by a predetermined amount (e.g., a few inches). The fins 532 allow the grapple fixture and front end component 520 to align together even when the free-flying object is rotationally misaligned by a predetermined amount. In such cases, the fins 532 are designed to slide down the rounded edges of the respective pockets (triangular cutouts) of the grapple fixture base and sit inside the pockets. In doing so, the fins 532 (along with the pockets of the grapple fixture) provide the two rotational and shear alignment when the grapple fixture and front end component 520 are brought together. Thus, the fins 532 provide a mechanism for correcting rotational misalignment and for implementing self-alignment. In certain embodiments, the fins (and pockets) are configured to align up to 5 degrees of rotational offset. In some embodiments, such as when the front end component 520 does not include a raised annulus 522, the interface can be grounded on the fins 532. In such embodiments, 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 cases, a minimum of two fins 532 can be used on the front end component 520 for rotational alignment about the central axis.

[0142] The fins 532 have rounded surfaces that allow the fins 532 to travel down the rounded edges of a complementary pocket. The fins 532 can be dry lubricated. The lubrication can be selected based on suitability for the operating environment. The fins 532 can also have one or more rounded surfaces or angled corners to help guide or deflect the ball of the grapple probe toward the opening 528 when the probe contacts the fin 532.

[0143] An embodiment of the leading end component 520 that includes a raised annulus 522 for grounding the interface can provide certain advantages (e.g., over an embodiment that grounds the interface on the fins 532). Contact at three points (such as in the case of grounding on three fins 532) means that in a particular direction, the stance at which bending loads are reacted is very small (from the centerline to a line between two fins), whereas the annulus 522 always maximizes the stance at which loads are reacted, regardless of direction.

[0144] 6A to 6C, there are shown respectively a front perspective view 600a, a front view 600b, and a side cross-sectional view 600c of a grapple fixture 610 for attachment to a free-flyer object (or other object to be captured) and for capture by and mating with the end effector 510 of FIGS. 5A to 5C, according to an embodiment.

[0145] The grapple fixture 610 includes a base 612 .

[0146] The base 612 includes a mounting surface 614 for mounting the grapple fixture 610 to an exterior surface of a free-flyer object (or other object, as the case may be).

[0147] The base 612 also includes a mating surface 616 opposite the mounting surface 614 for mating or coupling with a probe guide surface 526 of the end effector 510. The mating surface 616 is convex in shape. The curvature of the mating surface 616 can be configured to match or substantially match the curvature of the probe guide surface 526 of the end effector 510, such that the two surfaces are complementary in shape.

[0148] 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 a raised annulus 522 of the end effector 510 upon capture.

[0149] The mating surface 616 also includes recesses (or pockets or cutouts) 620a, 620b, 620c (collectively 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. Among other things, 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 any other suitable shape. A triangular shaped recess or opening can advantageously reduce the likelihood that the fins 532 will come into contact with 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" shaped feature. This is provided by the triangular cutout. The recess 620 has a flat or non-flat bottom surface and curved or rounded side surfaces. The curved side surfaces encourage the sliding of the fin 532 to the bottom surface and to the desired position. In some embodiments, the fin 532 does not go all the way to the bottom surface or contact the bottom surface (e.g., in the case of annulus reaction embodiments where the annulus is used to react to loads at the interface and the fin 532 is not), rather, a clearance is left between the fin 532 and the bottom surface within the allowable alignment variance. The clearance can be slight.

[0150] Each recess 620 includes a fastener 622 (fasteners 622a, 622b, 622c) therein that passes from a bottom surface of the recess 620 to the mounting surface 614. The fasteners 622 are used to attach the base 612 of the grapple fixture 610 to the free-flyer object. The fasteners 622 can be recessed out of the way so that the fasteners 622 do not interact with the fins 532. In an embodiment, the grapple fixture 610 can include insulation (thermal and electrical) below the fasteners 622 and also between the grapple fixture base 618 and the object (e.g., a spacecraft) to which the grapple fixture 610 is attached.

[0151] The grapple fixture 610 also includes a deflectable probe 624 that is 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.

[0152] The deflectable probe 624 is connected to a biasing element to allow the deflectable probe to deflect from a rest position in the direction of an applied force and to return to the rest position when the force is removed (the probe 624 is shown in a rest position in FIGS. 6A-6C). The rest position can be substantially perpendicular to the base 612. The biasing element includes one or more springs to allow the deflection. In the embodiment of FIG. 6C, the biasing element includes a biasing spring 634 that returns the probe to a center or rest position when deflected. In other embodiments, the biasing element used to allow the probe 624 to deflect can be any suitable mechanical spring in compression, a pneumatic component (e.g., in marine applications), an actively tensioned component, a null spring, or a flexible shaft (over shaft 626).

[0153] The deflectable probe 624 also includes a coaxial spring 632. The coaxial spring 632 is used for electrostatic shock conduction. The coaxial spring 632 electrically connects the probe 624 to the base 612 of the grapple fixture 610. The coaxial spring 632 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. 5A) on the end effector during capture, the coaxial spring 632 then electrically connects the servicer ground to the free flyer ground through a dissipative resistor. This allows charge to flow, but with greatly reduced current, to limit damage. This approach is used when the dry lubrication in the "knuckle-joint" of the probe 624 may be insulating. The coaxial spring 632 may enable the capture system to be used in geosynchronous and other high orbits that have environmental conditions that lead to electrostatic charging of objects. For example, when two objects with different charge levels come into contact, a large electrostatic discharge event can occur that could compromise avionics and power systems on either object (e.g., on the capture system side or the free flyer side).

[0154] The coaxial spring 632 connects to the deflectable probe 624 at a mounting end 630. The grapple fixture 610 further includes a spring mounting component 636. The spring mounting component 636 may include one or more pieces. The coaxial spring 632 and the deflection spring 634 are attached to the spring mounting component 636, which is mounted to the base 612 via a mounting surface 614. The spring mounting component 636 may function as a spring retainer.

[0155] 7A-7F, a free-flyer capture end effector 700 is now shown at various stages of operation while performing soft and hard capture of a free-flyer object, according to an embodiment. The end effector 700 is shown in a cross-sectional side view. In FIGs. 7A-7F, the free-flyer object, including the grapple fixture mounted thereon, is not shown, but is understood to be present during the operation sequence (where appropriate).

[0156] 7A shows the end effector 700 in a fully forward position 702a, in which the end effector 700 is in a non-functional, stationary state (e.g., in orbit).

[0157] Various components of the end effector 700 are labeled in Figure 7A. In subsequent Figures 7B-7F, to reduce clutter, only certain components that perform functions at particular stages depicted in each figure may be labeled. It should be understood that such unlabeled components may still perform functions and may be referenced by their respective reference numbers.

[0158] The end effector 700 includes an outer housing 704 that encloses an internal compartment 706 in which are disposed various components for effecting capture (soft and hard capture) of a grapple fixture.

[0159] The end effector 700 also includes an arm interface component 708 and a launch / storage interface 710 mounted to respective exterior surfaces of the outer housing 704. The arm interface component 708 is mounted at an arm interface end 712 of the end effector 700. The arm interface component 708 is an interface to a robotic arm and may provide a tool changer interface. The launch / storage interface 710 is a device that allows for storage of the end effector when not in use.

[0160] The end effector 700 includes a receiving end 714 opposite the arm interface end 712 for receiving and interfacing with a grapple fixture of a free-flying object.

[0161] Positioned at the receiving end 714 of the end effector 700 is a probe guide surface 716. The probe guide surface 716 can be attached to the outer housing 704 at the receiving end 714. The probe guide surface 716 includes an opening 718 therein for receiving a probe of the grapple fixture. The probe guide surface 716 is designed and configured to guide the probe of the grapple fixture towards and into the opening 718 upon contact with the probe guide surface. Such contact and guiding of the probe can occur upon movement of the end effector 700, and particularly its receiving end 714, towards the grapple fixture of the free-flyer object for capture. The probe guide surface 716 is generally concave in shape. The shape or profile of the probe guide surface 716 can be configured such that it is complementary to and mates with the base of the grapple fixture.

[0162] The end effector 700 further includes three fins 720 attached to the probe guide surface 716. Only two fins 720 are visible in FIG. 7A. In variations, the number and location of the fins 720 on the probe guide surface 716 can vary. The fins 720 are configured to mate with complementary components on the base of the grapple fixture.

[0163] The end effector 700 includes a capture mechanism 722 (shown by a dashed line) disposed within the internal compartment 706 for capturing and rigidifying a grapple fixture. In the embodiment shown in FIGS. 7A to 7F, the capture mechanism 722 is a mousetrap mechanism. The capture mechanism 722 is mounted on first and second ball screws 724 (only one ball screw is visible in FIG. 7A). The capture mechanism 722 is movable (linearly displaceable) along a capture axis 726 via the ball screws 724. For example, the capture mechanism 722 is retractable (i.e., movable along the capture axis away from the receiving end 714) when performing capture, and movable in the opposite direction along the capture axis toward the receiving end 714 when releasing or preparing to capture the grapple fixture. Capture mechanism 722 is connected to ball screw 724 via a ball nut 725 , such that movement of ball nut 725 relative to ball screw 724 causes displacement of capture mechanism 722 along capture axis 726 .

[0164] The capture mechanism 722 includes a front end component 728 that includes a concave probe guide surface and a central opening (opening 718). Generally, the probe guide surface of the front end component 728 is configured to contact the probe of the grapple fixture and passively guide the probe toward and into the opening. The front end component 728 forms part of the probe guide surface 716 when the capture mechanism 722 is fully forward along the capture axis 726. Generally, the front end component 728 includes a conical insert that is part of the structure of the retracting capture mechanism 722. The mousetrap mechanism of the capture mechanism 722 is positioned near the conical surface of the front end component 728. The front end component 728 moves with the mousetrap mechanism. In other embodiments, the front end component 728 can be part of the probe guide surface 716 as one piece and not retract with the capture mechanism 722. Retracting the front end component 728 with the capturing mechanism 722 can advantageously avoid interference with the grapple shaft during retraction and alignment, which may occur in embodiments in which the front end component 728 does not retract with the capturing mechanism 722.

[0165] In one embodiment, the capture mechanism includes one or more detent plungers for maintaining the capture mechanism in place during soft capture and configured to maintain the capture mechanism in place during release such that the jaws open before a release condition is indicated.

[0166] The capture mechanism 722 includes a plunger 730 disposed along a capture axis 726. The plunger 730 includes a probe contact end 732. The plunger 730 is movable (linearly displaceable) in both directions along the capture axis. Generally, when the probe of the grapple fixture contacts the probe contact end 732 (the end effector and the grapple fixture move towards each other), the plunger 730 is displaced along the capture axis 726 towards the arm interface end 712. The shape of the probe contact end 732 can be shaped to ensure that the gripper 738 surrounds the probe end (e.g., probe end 628) of the grapple fixture.

[0167] The capture mechanism 722 further includes linkage arms 734a, 734b, gripper sliders 736a, 736b, and grippers 738a, 738b. The linkage arms 734a, 734b are attached at a first end to the plunger 730 and at a second end to the gripper sliders 736a, 736b, respectively. The gripper sliders 736a, 736b are configured to contact the grippers 738a, 738b, respectively. In particular, the gripper sliders 736a, 736b can move along the surfaces of the grippers 738a, 738b to move the grippers 738a, 738b between an open position and a closed position. The grippers 738a, 738b are configured to grip or grapple the probe of the grapple fixture when in the closed position and not contact the probe when in the open position (e.g., to facilitate entry of the probe into a soft capture position where the probe can be gripped and release of the probe). The grippers 738 are held open by a spring prior to soft capture to allow the probe to enter the soft capture mechanism (mousetrap). In general, the opening 718, the probe contact end 732 of the plunger 730, and the space between the first and second grippers 738a, 738b define the soft capture position 740 of the probe. In this sense, the probe guide surface 716 is configured to passively guide (with the relative motion of the end effector and the free-flyer object) the probe of the grapple fixture through the opening 718 to the soft capture position 740.

[0168] The capture mechanism 722 also includes a grapple housing 742. The grapple housing 742 encloses the various components of the capture mechanism 722 involved in grappling the probe. The front end component 728 is attached to the grapple housing 742 of the capture mechanism 722.

[0169] The capture mechanism 722 also includes a compressible element 744 for generating a predetermined preload to achieve a hard capture of the grapple fixture. In the end effector 700 of Figures 7A-7F, the compressible element 744 is a Belleville spring stack. The compressible element 744 is compressible along the capture axis 726 to generate the required preload.

[0170] The end effector 700 also includes first and second potentiometers 746, 748. The first and second potentiometers 746, 748 are linear potentiometers configured to measure the overall position of the capture mechanism 722. The potentiometers 746, 748 are used to sense when a particular state in the capture process is achieved and trigger a subsequent action.

[0171] A first potentiometer 746 is connected to the plunger 730 to measure a position of the plunger 730. Among other things, the potentiometer 746 can include a shaft disposed within the body and connected to the plunger 730 such that as the plunger moves along the capture axis 726, the shaft also moves along the capture axis 722 and relative to the body.

[0172] A second potentiometer 748 is connected to the grapple housing 742 to measure the position of the capturing mechanism 722 (via the position of the grapple housing 742). Among other things, the potentiometer 748 can include a shaft disposed within the body and connected to the grapple housing 742 such that when the capturing mechanism 722 (including the grapple housing 742) is moved along the capture axis 726, the shaft likewise moves along the capture axis 726 and relative to the body.

[0173] The end effector 700 includes two limit switches 750 (only one is visible in FIG. 7A ) disposed within the internal compartment 706. The two limit switches 750 provide reliability and redundancy. In other embodiments, a single limit switch 750 may be used. The limit switch 750 is configured to indicate in an immediate, deterministic, and binary manner that a soft capture has occurred. Upon such indication by the limit switch 750, retraction to hard capture / rigidification may occur immediately.

[0174] End effector 700 also includes a brake 752 disposed within interior compartment 706. Brake 752 holds the mechanism in a rigidified, preloaded state such that the motor drive at the end of the arm can be powered off and the capture interface remains preloaded so that it can react to a load.

[0175] 7B, the end effector 700 is now shown in an armed (soft capture ready) state 702b. In the armed state 702b, the grippers 738a, 738b are open and the linkage arms 734a, 734b are in an over-center position. "Over-center position" refers to the use of an over-center spring mechanism. An over-center spring mechanism can be used to mechanically hold a pivot structure in a selected rest position relative to a pivot point. An over-center spring mechanism can include a tension spring attached at one end to a fixed structure and at the other end to the pivot structure.

[0176] 7B allows the plunger 730 loom to move when the ball 628 of the grapple probe 624 contacts the front of the plunger 730 upon capture approach. The linkages 734a, 734b snap into closed jaws when the plunger 730 moves enough to return the spring linkages 734a, 734b past top dead center. The various components of the capture mechanism 722 can be dry lubricated using a lubricant appropriate for the operating environment.

[0177] 7C, the end effector 700 is now shown in a tripped (or soft-captured) state 702c.

[0178] In the tripped position 702c, the probe of the grapple fixture (not shown) is received through an opening 718 in the probe guide surface 716 into the soft capture position 740. Notably, as the probe enters the soft capture position 740, the end of the grapple fixture probe contacts the probe contact end 732 of the plunger 730, displacing the plunger 730 along the capture axis 726 toward the arm interface end 712, which corresponds to the grapple fixture (not shown) and soft capture being initiated.

[0179] When the probe of the grapple fixture enters the soft capture position 740 and contacts the probe contact end 732 of the plunger 730 and applies a force to the probe contact end 732 in the direction 754, the plunger is displaced in the direction 754 along the capture axis 726.

[0180] Displacement of plunger 730 in direction 754 causes displacement of linkage arms 734a, 734b from the position shown in Figure 7B to the position shown in Figure 7C. Displacement of linkage arms 734a, 734b causes gripper sliders 736a, 736b, which previously held grippers 738a, 738b in an open position, to slide along grippers 738a, 738b, causing the grippers to move to a closed position, thereby gripping the probe.

[0181] When the plunger 730 is displaced in the direction 754, the shaft of the first potentiometer 746 is also displaced in the direction 754. Telemetry of 746 can assist in determining a soft capture condition or an abnormal condition.

[0182] At this stage, the end of the grapple fixture probe that entered the capturing mechanism (eg, its spherical end) is grappled or grasped by the capturing mechanism (via grippers 738a, 738b).

[0183] For example, contact of the probe end with plunger 730 can cause a spring attached to linkage arm 734 to close the mousetrap, and if pushed far enough, closes gripper 738 around the ball tip of the probe.

[0184] 7D, the end effector 700 is now shown in an initiated retraction state 702d. Retraction is initiated in response to the limit switch 750 indicating that the capture device 722 has changed from a jaw open state to a jaw closed state. This occurs when the probe ball 628 enters the capture mechanism 722 and causes the capture mechanism 722 to snap over (i.e., like a mousetrap).

[0185] In position 702d, a ball screw actuator (not shown) rotates ball screw 724, causing ball nut 725 to translate in direction 754. Ball nut 725 is attached to plunger 730 through a slot 756 in plunger 730. In the case of FIG. 7D, ball nut 725 has moved in direction 754 from a first end of slot 756 proximal to receiving end 714 to a second end of slot 756 proximal to arm interface end 712. When in the position shown in FIG. 7D, if ball nut 725 is further translated in direction 754 via rotation of ball screw 724, it will cause plunger 730 to translate in direction 754, thus retracting capture mechanism 722.

[0186] 7E, the end effector 700 is now shown in a grapple fixture seated state 702e. In the grapple fixture seated position 700e, the capture mechanism 722 (which grapples or grasps the probe of the grapple fixture) has been fully retracted in direction 754 along the capture axis 726 to a seated position 758. Retraction of the capture mechanism 722 is achieved via further rotation of the ball screw 724 (as in FIG. 7D), which causes the ball nut 725 to translate the capture mechanism 722 (via its connection to the plunger 730 through slot 756) in direction 754 to the seated position 758.

[0187] As the capture mechanism 722 is translated in direction 754, the shaft of a second potentiometer 748, which is connected to the capture mechanism 722 via a connection to the grapple housing 742, is similarly translated (within the body of the potentiometer 748), which causes a state change in the potentiometer 748. The state change in the potentiometer 748 (to a tripped state) is detected, indicating that a soft capture of the grapple fixture has occurred and that it is time to rigidify the grapple fixture. The potentiometer 748 itself does not detect the state change after soft capture. The potentiometer 748 does not move during soft capture.

[0188] 7F, the end effector 700 is now shown in a hard captured or rigidified state 702f. In the hard captured state 702f, the grapple fixture is rigidified to the end effector 700. Specifically, the base of the grapple fixture is rigidified to the receiving end of the end effector 700.

[0189] To rigidify the interface between the grapple fixture and the end effector 700, the Belleville stack 744 is compressed to achieve a desired load. Compression of the Belleville stack 744 is achieved via movement of the ball nut 725 in the direction 754. The load corresponds to how far the grapple fixture should be retracted to achieve the desired load. More specifically, the load increase begins after the grapple fixture is seated, and the load corresponds to how far the ball screw is driven. The load can be pre-determined. For example, in the case of a space-based application, the load can be determined on the ground.

[0190] In particular, the bar 760 of the plunger 730, which is disposed in the plunger slot 756 between the ball nuts 725, presses against the spring stack 744. When the capture mechanism 722 cannot move axially due to the length of the grapple probe 624, the continued movement of the ball nut 725 then compresses the spring stack 744. This compression of the spring stack 744 preloads on the annular interface between the probe guide surface 716 of the end effector 700 and the grapple fixture 610. Thus, the bar 760, moving in the slot 756, moves with the ball nuts 725 and compresses the spring stack 744, where the capture mechanism 722 is fully retracted.

[0191] In alternative embodiments, other spring elements can be used in place of the Belleville stack 744. However, disc springs, or Belleville springs, can be particularly advantageous because they are a compact way of generating large loads in a small volume with relatively little deflection.

[0192] Once the grapple fixture is rigidified, the brakes 752 can be depowered and dropped closed, holding the free-flying object in a loaded position. Power to the drive motors (used to drive the movement of the capture mechanism 722) can be cut so as not to continuously lose power while holding onto a rigidified payload. This can be advantageous in situations where the end effector 700 may be holding a free-flying object (e.g., a client spacecraft) for an extended period of time (e.g., hours).

[0193] 8A-8H, a system 800 for robotic capture of a free-flying object at various stages of capture is now shown, according to an embodiment. The system 800 includes the end effector 700 of FIGS. 7A-7F and the grapple fixture 610 of FIGS. 6A-6C. The end effector 700 is attached to the end of a robotic arm, and the grapple fixture 610 is attached to an exterior surface of the free-flying object. For simplicity, the robotic arm and the free-flying object have been omitted.

[0194] 8A, an end effector 700 is now shown approaching a grapple fixture 610 as part of a capture approach. The grapple fixture 610 is misaligned. The grapple ball 628 of the deflectable probe is both laterally and angularly offset from the center (opening) of the front end component. In an embodiment, the end effector 700 can be configured to capture a grapple ball 628 that is laterally offset by up to 30 mm from the center 718 of the probe guide surface 716, angularly offset by up to 5 degrees around the ball 628, and offset by 5 degrees with respect to roll.

[0195] The capture mechanism 722 of the end effector 700 is in a ready state for actuation (such as 702b in FIG. 7B).

[0196] 8B, there is now shown initial contact between the deflectable probe 624 and the probe guide surface 716. The grapple ball 628 of the deflectable probe 624 contacts the probe guide surface 716, and the shaft centering spring 634 of the grapple fixture 610 cushions the initial impact of the deflectable probe 624. The probe guide surface 716 begins to passively guide the grapple ball 628 towards the opening 718 and the capture mechanism 722.

[0197] 8C, there is shown a deflection 802 of the deflectable probe 624 about the deflectable joint before the grapple ball 628 enters the opening 718 into the soft capture location 740. The deflectable probe 624 is deflecting as the end effector 700 continues to move towards the free-flyer object. The deflection 802 allows the grapple ball 628 (spherical tip) of the deflectable probe 624 to reach the soft capture location 740 without requiring movement of the free-flyer object itself (although the free-flyer is unconstrained and can (and will) move freely).

[0198] 8D, the deflectable probe 624 is now shown entering the capture mechanism 722 of the end effector 700. The deflectable probe 624 reaches the soft capture position 740 via deflection 802 without requiring a change in the orientation of the base 612 of the grapple fixture 610 (and thus, without requiring a change in the orientation of the free-flyer object to which the base 612 is attached). This can be seen by the constant orientation of the base 612 throughout Figures 8A-8D.

[0199] As can be seen, the grippers 738a, 738b of the capturing mechanism 722 are in an open position, allowing the grapple ball 628 to enter a soft capturing position 740 between the grippers 738.

[0200] 8E, there is shown the initiation of soft capture of the grapple fixture 610 by grappling the grapple ball 628. The grapple ball 628 of the deflectable probe 624 triggers the capture mechanism 722 by contacting the probe contact end 732 and displacing the plunger 730 along the capture axis 726 to achieve soft capture. Displacement of the plunger 730 in the direction 754 causes the gripper 738 to move from an open position to a closed position (as illustrated in FIG. 7C), thereby grappling the grapple ball 628 of the deflectable probe 624.

[0201] The soft capture of the grapple fixture 610 constrains three degrees of freedom (linear motion) of the grapple fixture 610. Three degrees of freedom (angular motion) of the grapple fixture 610 remain free. The soft capture grapples the grapple ball 628 such that the grapple ball 628 is held in translation but unrestrained in rotation.

[0202] 8F, the capture mechanism 722 of the end effector 700 is now shown beginning to retract towards the hard capture position.

[0203] As can be seen, retraction of the capture mechanism 722 grappling the deflectable probe 624 brings the base 612, and in particular the mating surface 616, of the grapple fixture 610 towards the probe guide surface 716 of the end effector 700 for mating.

[0204] Translation of capture mechanism 722 in direction 754 is achieved by translation of ball nuts 725 (which are connected to capture mechanism 722 ) in direction 754 via rotation of ball screw 724 .

[0205] During retraction, the angular and lateral offset of the free-flyer object relative to the end effector 700 is removed. The angular and lateral offset is removed by bringing together the conical features of the probe guide surface 716 of the end effector 700 and the mating surface 616 of the grapple fixture 610 along with the fins 532 and v-groove 620, which force the two sides of the interface into alignment as the gap between them closes.

[0206] 8G, hard capture (rigidification of the interface) of the grapple fixture 610 by the end effector 700 is now shown.

[0207] Hard capture of the grapple fixture 610 is achieved when the capture mechanism 722 is retracted to a point (reflected by a hard capture position 758) where the grapple fixture 610 is preloaded against alignment features on the front (probe guide surface 716) of the end effector 700. This involves mating alignment features present on the mating surface 616 of the base 612 of the grapple fixture 610 with alignment features (e.g., pins and recesses, annulus) present on the probe guide surface 716 of the end effector 700. The end effector 700 knows when the capture mechanism 722 has reached the hard capture position 758 via a load sensor disposed behind the spring stack 744. The load sensor determines the position that provides the target preload. An indication from the load sensor when the target position is reached is generated and used to stop the retraction. The accumulated drive shaft turns from the home position can be used to determine the proper position in calibrating the end effector 700.

[0208] Hard capture also involves compressing the Belleville stack 744, as in FIG. 7F.

[0209] Once the interface between the grapple fixture 610 and the end effector 700 is rigidified through a hard capture, a free-flyer object can be manipulated by the end effector 700 and a robotic arm attached to the end effector 700.

[0210] 8H, the release of the captured grapple fixture 610 is now shown.

[0211] To release the grapple fixture 610, the drive is driven forward (in direction 804) far enough to reset the linkages 734a, 734b of the capture mechanism 722 and drive the grippers 738a, 738b to the open position. In this embodiment, the PCT drive is a tool drive on the arm that implements the motion in the PCT through a torque shaft interface in the robot arm interface. Doing so releases the grip on the grapple ball 628 of the deflectable probe 624. Initiation of the release can depend on the system architecture. The release can be initiated via a sensor outside the end effector 700. The release can resemble the end effector 700 moving from the configuration shown in FIG. 7c to the configuration shown in FIG. 7B.

[0212] Although the above description provides examples of one or more devices, methods, or systems, it will be recognized that other devices, methods, or systems are possible within the scope of the claims, as interpreted by one of ordinary skill in the art. [Explanation of symbols]

[0213] 200 Systems 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 220 Deflectable Probe 222 Mating Surface 224 Probe Guide Surface 226 Alignment Features 228 Alignment Features 230 Probe 232 Grapple End 234 Deflection element 236 Opening 238 Internal Compartment 240 Probe Sensing Element 242 Grapple 244 Linear Displacement Mechanism 246 Rigid Mechanism 300 Free Flyer Capture System 302 Servicing Satellite 304 Free Flyer Objects 305 Move 306 Robot Arm 308 End Effector 310 Servicing Mechanism 312 Grapple Fixture 314 Berthing Components 316 Orbital Replacement Unit (ORU) 318 Move 320 Parking Position 322 "Free Flyer Capture Ready" Position 326 Move 328 Move 330 Move 332 Parking position 334 Soft Capture Position 336 Move 338 ORU insertion position 340 ORU insertion location 500a: Front perspective view of end effector 510 500b Front view of end effector 510 500c Side view of end effector 510 510 End Effector 512 Receiving end 514 Robot arm interface end 516 Outer Housing 518 Storage / launch interface components 520 Front end component 522 Raised Annulus 524 Outer Annulus 526 Probe Guide Surface 528 Opening 530 Concave insert 532 Finn 532a Fin 532b Fin 532c Fin 600a Front perspective view of grapple fixture 610 600b Grapple Fixture 610 Front View 600c Grapple Fixture 610 Side Cross-Sectional View 610 Grapple Fixture 612 Base 614 Mounting surface 616 Mating Surface 618 Flat annular section 620 Recess 620a Recess 620b Recess 620c Recess 622 Fasteners 622a Fasteners 622b Fasteners 622c Fasteners 624 Deflectable Probe 626 Shaft 628 Probe end, probe ball, grapple ball 630 Attachment end 632 Coaxial Spring 634 Deflection Spring 636 Spring-Mounted Components 700 Free Flyer Capture End Effector 702a Full forward position 702b Ready for operation (soft capture ready) 702c Tripped (or soft-captured) condition 702d Starting to retreat 702e Grapple Fixture Seated 702f Hard-captured or rigidified 704 Outer Housing 706 Internal Compartment 708 Arm Interface Components 710 Launch / Retract Interface 712 Arm Interface End 714 Receiving end 716 Probe Guide Surface 718 Opening 720 Fin 722 Capture Mechanism 724 Ball Screw 725 Ball Nut 726 Capture Axis 728 Front end component 730 Plunger 732 Probe Contact End 734a Linkage arm 734b Linkage arm 736a Grip Slider 736b Gripper Slider 738a Gripper 738b Gripper 740 Soft Capture Position 742 Grapple Housing 744 Compressible Elements 746 First Potentiometer 748 Second Potentiometer 750 Limit Switch 752 Brake 754 directions 756 Slots 758 Seating Position 760 Bar 800 Systems 802 Deflection 804 direction

Claims

1. 1. A system for robotic capture of a free-flying object, comprising: a grapple fixture for attachment to the free-flying object; and an end effector for interfacing with the grapple fixture to capture the free-flying object; The grapple fixture comprises: a base having a mounting surface for mounting to the free-flyer object and a mating surface opposite the mounting surface for mating with the end effector; a deflectable probe connected to the base via a deflectable joint to enable deflection of the deflectable probe, the deflectable probe including a probe tip for grappling; Including, The end effector includes: an interface for connecting to and enabling operation by a robotic arm or a spacecraft equipped with direct capture capability; a probe guide surface for deflecting and guiding the probe tip of the deflectable probe toward and through an opening in the probe guide surface into a grappling position when the end effector is moved toward the grapple fixture and when the grapple fixture is within a capture envelope of the end effector; a probe sensing element for sensing when the probe tip is in the grappling position and for triggering a capture mechanism upon sensing that the probe tip is in the grappling position; a capture mechanism configured to grapple the probe tip when triggered by the presence of the probe tip, where grappling the probe tip creates a non-separable connection that constrains some, but not all, degrees of freedom (a "soft capture"); and a capture mechanism trigger sensing element for sensing when the probe tip is in the grappling position and for triggering the capture mechanism; an actuator configured to retract the capture mechanism along a capture axis to a predetermined position, where the mating surface of the base of the grapple fixture is preloaded against the probe guide surface to establish a load-bearing interface between the free-flyer object and the end effector (a "hard capture"); Including, the system.

2. The system of claim 1 , wherein the deflectable joint further comprises a buffer spring for buffering initial contact between the probe tip and the probe guide surface.

3. 2. The system of claim 1, further comprising: the robotic arm; and a robotic arm controller for controlling the robotic arm, the robotic arm controller configured to command the robotic arm to move the end effector towards the grapple fixture upon approach such that a relative velocity of the end effector and the free-flyer object is maintained within a predetermined velocity band known to promote successful soft capture.

4. 2. The system of claim 1, wherein the mating surface of the grapple fixture includes a first alignment component and the probe guide surface includes a second alignment component, the first and second alignment components configured to mate with one another to align a connection between the grapple fixture and the probe guide surface of the end effector.

5. 5. The system of claim 4, wherein the second alignment component is a raised annulus and the first alignment component is a recessed annulus.

6. 5. The system of claim 4, wherein the first alignment component includes a plurality of recesses in the mating surface and the second alignment component includes a plurality of protrusions, each one of the plurality of protrusions configured to mate with a respective one of the plurality of recesses.

7. 7. The system of claim 6, wherein each of the plurality of recesses includes a bottom surface and a plurality of angled or curved side alignment surfaces, and each of the plurality of protrusions includes a rounded surface profile, and when the protrusion contacts one of the plurality of side alignment surfaces, it urges the fin to slide further into the recess, thereby bringing the interface into a fully constrained alignment state in a hard capture.

8. The system of claim 1 , wherein the capture mechanism constrains linear motion of the free-flyer object via grappling of the probe tip.

9. 2. The system of claim 1, wherein angular and lateral offsets of the free-flyer object relative to the end effector are removed by retracting the capture mechanism and by engaging the base of the grapple fixture with the probe guide surface on the end effector.

10. 1. A robot end effector for capturing a free-flying object via a grapple fixture attached to the free-flying object, comprising: a robot arm interface for connecting to a robot arm and enabling manipulation by the robot arm; a probe guide surface for deflecting and guiding a probe tip of a deflectable probe of the grapple fixture toward and through an opening in the probe guide surface into a grappling position when the end effector is moved toward the grapple fixture and when the grapple fixture is within a capture envelope of the end effector; a probe sensing element for sensing when the probe tip is in the grappling position and for triggering a capture mechanism upon sensing that the probe tip is in the grappling position; a capture mechanism configured to grapple the probe tip when triggered by the probe sensing element; an actuator configured to retract the capture mechanism along a capture axis when the probe tip is grappled, where in the first predetermined position a mating surface of a base of the grapple fixture is preloaded against the probe guide surface to establish a load-bearing interface between the free-flyer object and the end effector; a robot end effector.

11. The end effector of claim 10 , wherein the probe guide surface is concave.

12. 12. The end effector of claim 11, further comprising a plurality of protrusions disposed on the probe guide surface for mating with complementary recesses on the mating surface of the grapple fixture during capture to align a connection between the grapple fixture and the probe guide surface of the end effector.

13. 13. The end effector of claim 12, wherein each one of the plurality of protrusions includes a rounded surface to urge the protrusion to slide along a side alignment surface of a respective one of the complementary recesses and further into the respective complementary recesses.

14. The end effector of claim 11 , wherein the probe guide surface includes a raised annulus for mating with a complementary recessed annulus on the mating surface of the grapple fixture.

15. 11. The end effector of claim 10, wherein the capturing mechanism includes a spring-based compliant member, and the actuator is configured to further retract the capturing mechanism, compressing the spring-based compliant member and providing a preload to the interface between the grapple fixture and the end effector.

16. 11. The end effector of claim 10, wherein the capturing mechanism includes a pair of jaws connected to the probe sensing element and configured to move from an open position to a closed position to grapple the probe tip when the grapple probe tip triggers the capturing mechanism to close.

17. 12. The end effector of claim 11, wherein the capture mechanism includes a concave insert component that forms a portion of the probe guide surface including the opening when the capture mechanism is positioned fully forward along the capture axis, and the concave insert component is retracted with the capture mechanism during retraction.

18. 1. A method for robotic capture of a free-flyer object, comprising: moving the end effector via a robotic arm towards the grapple fixture above the free-flyer object such that the grapple fixture is within a capture envelope of the end effector; contacting a deflectable probe of the grapple fixture with a probe guide surface of the end effector within the capture envelope; continuing to move the end effector toward the free-flyer object to deflect the deflectable probe with the probe guide surface toward an opening in the probe guide surface; guiding the deflectable probe through the opening via the probe guide surface into a grappling position; sensing when the deflectable probe is in the grappling position and triggering a grappling mechanism; upon sensing that the deflectable probe is in the grappling position, grappling the deflectable probe with the grappling mechanism to constrain linear motion of the free-flyer object; retracting the grappled deflectable probe along a capture axis to a predetermined position to remove angular and lateral offsets of the free-flyer object relative to the end effector and bring a base of the grapple fixture into contact with the probe guide surface; rigidifying the interface between the grapple fixture and the end effector by retracting the grapple mechanism to a point where the grapple fixture is preloaded against alignment features on the probe guide surface; A method comprising:

19. 20. The method of claim 18, wherein moving the end effector via the robotic arm towards the grapple fixture further comprises: detecting a machine vision target on the free-flyer object via a machine vision system; and tracking the machine vision target with the machine vision system as the robotic arm moves the end effector towards the grapple fixture.

20. 20. The method of claim 18, further comprising: cushioning initial contact between the deflectable probe and the probe guide surface via a cushioning spring in the deflectable probe.

21. 20. The method of claim 18, wherein moving the end effector via the robotic arm towards the grapple fixture over the free-flyer object includes maintaining, via a robotic arm controller, a relative approach speed / approach trajectory of the end effector and free-flyer object within a pre-determined speed band known to promote successful soft capture of the grapple fixture.

22. The system of claim 1 , wherein the deflectable joint is a spring-centered spherical joint.

23. 1. A capture tool for performing robotic capture of a free-flying object, the capture tool having a grapple fixture mounted on the free-flying object, a probe guide surface for guiding a probe of the grapple fixture to a soft capture position; a grapple for grappling the probe of the grapple fixture when the probe is in the soft capture position, the grapple constraining linear motion of a probe tip; a hard capture mechanism for constraining angular motion of the grappled probe by retracting the grapple fixture until the grapple fixture is preloaded against the probe guide surface to establish a load-bearing interface between the free-flyer object and the capture tool; Including, capture tools.

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