Patent Application
20140064905
The present invention relates generally to electroadhesion and other electrostatic applications, and more particularly to the use of electroadhesion to retrieve or handle foreign objects.
Solutions for rendezvous, docking and other object handling applications in outer space can present a number of challenges. In fact, existing spacecraft tend to utilize a substantial portion of their total mass simply for rendezvous and docking systems. This “dead mass” cannot be used for other cargo, and usually represents a complicated system that usually gets expended after a single mission. Further, many rendezvous and docking procedures involve close-in maneuvers or even “precision crashes” between large, high-inertia, extremely expensive objects. Such procedures typically takes place with the contact distance between objects being so small (e.g., less than 10 m) that all objects are at risk during the maneuver. Concerns over such issues results in a tendency to shy away from mission architectures that require multiple rendezvous and docking operations.
In light of such concerns, the National Aeronautics and Space Administration (“NASA”) has recently solicited rendezvous and docking solutions for autonomously collecting a sample canister for a Mars Sample Return mission. In particular, the Small Business Innovation Research & Technology Transfer Program Solicitation No. SBIR S5.04—Rendezvous and Docking Technologies for Orbiting Sample Capture—implicates such issues with respect to controlling and retrieving a canister in space. One of the potential solutions that NASA has been studying involves scooping the canister up into a funnel, closing a lid over the funnel to keep the canister from bouncing out, and then feeding the canister through a tunnel into the reentry capsules. Other alternative autonomous rendezvous and docking schemes use robot arms and the like.
Unfortunately, approaches such as the foregoing funnel-lid or robot arm based solutions tend to be overly complex and thus costly to implement. Such approaches can require the use of “capture target” mechanisms on the target vehicle or object, and can also require very precise orbit and velocity matching before rendezvous can proceed. As such, vehicles or other objects (e.g., space debris) that have not been prepared with capture target mechanisms in advance typically cannot be manipulated by such systems. These approaches can also require the use of multiple complex and precise components, the failure of any of which can cause havoc with the overall rendezvous and docking process.
Although various rendezvous and docking systems have generally worked well in the past, there is always a desire for improvement. In particular, what is desired are rendezvous and docking systems and procedures that are simpler, safer and cheaper, while still enabling rendezvous and docking with targets that have not been specifically designed for being captured.
It is an advantage of the present invention to provide improved rendezvous and docking systems and techniques. Such systems and techniques can generally present a lowered overall risk, allow for larger velocity or position misalignment between objects, keep pre-contact maneuvers for both vehicles or objects far enough away to eliminate the probability of accidental collisions, offload enough of the work from the “target vehicle” side to allow capture of uncooperative targets, and minimize the amount of vehicle mass dedicated to rendezvous and docking. This can be accomplished at least in part through applying a different approach that involves the use of electroadhesion and a boom coupled to the electrostatic components.
In various embodiments of the present invention, an electroadhesive system can include an electrostatic adhesion pad and a boom coupled at a first boom location to the electrostatic adhesion pad. The electrostatic adhesion pad can be configured to adhere electrostatically and detachably to a surface of a separate foreign object, and as such can include one or more electrodes adapted to produce collectively an electrostatic force between the pad and the object that is suitable to maintain a current position of the pad relative to the object. The boom can be adapted to provide control for positioning of the electrostatic adhesion pad with respect to the foreign object, and also for movement of the pad and object combination when the pad and object are electrostatically adhered together.
In various detailed embodiments, further system components can include a sensing component adapted to sense when the electrostatic adhesion pad is electrostatically adhered to the foreign object, as well as a control mechanism adapted to control the boom. Such a control mechanism can be coupled to the boom at a second boom location remote from the first boom location. In addition, the inertia of the control mechanism can be greater than the inertia of the boom, such that the greater distance between control mechanism and foreign object by way of the boom is a distinct advantage.
In various further embodiments, the electrostatic adhesion pad can include a deformable surface adapted for interfacing with the object surface such that at least a portion of the deformable surface moves closer to the object surface when the pad is adhering to the object. In addition, the electrostatic adhesion pad can comprise a flat or flexible component, and/or can include a plurality of separately controllable fingers. Further, the electrostatic adhesion pad can also be configured to adhere electrostatically and detachably to a surface of a second separate foreign object while the pad is simultaneously adhered to the original separate foreign object.
In further detailed embodiments, the boom can be elongated, and the first boom location can be at a distal end of the boom. Also, the boom can be extendable, retractable or both. In various embodiments, the foreign object can be a loose object within a zero-gravity environment, and the electroadhesive system can be adapted to manipulate the foreign object at a significant distance from any other object within the zero-gravity environment. Furthermore, the electroadhesive system can be adapted to manipulate the physical location of the foreign object, the rotational velocity of the foreign object, or both.
In still further embodiments, methods of operating an electroadhesive device are provided. Such methods can involve physically controlling a foreign object, and can include the use of an electroadhesive device or system such as that set forth above. Various method steps can include, for example, contacting an electrostatic adhesion pad to a surface of a separate foreign object, where the electrostatic adhesion pad includes one or more electrodes, applying an electrostatic adhesion voltage difference at one or more of the electrodes, electrostatically adhering the electrostatic adhesion pad to the object surface using an electrostatic attraction force provided by the electrostatic adhesion voltage difference, and changing the physical location of the foreign object, the rotational velocity of the foreign object, or both by controlling a boom coupled to the electrostatic adhesion pad while the pad and object are electrostatically adhered together.
Additional method steps can include increasing the surface area contact between the pad and the object surface by deforming a deformable surface on the electrostatic adhesion pad such that at least a portion of the deformable pad surface moves closer to the object surface after electrostatically adhering the electrostatic adhesion pad to the object surface, and also maintaining the electrostatic adhesion voltage difference while the deformable pad surface contacts the object surface of the substrate. Still further steps can include releasing the electrostatic adherence between the pad and the object by reducing or eliminating the electrostatic adhesion voltage difference, moving the electrostatic adhesion pad with respect to the foreign object while the electrostatic adhesion voltage is reduced or eliminated, and also reapplying an electrostatic adhesion voltage difference at one or more electrodes after the electrostatic adhesion pad has been moved to a different location of the foreign object.
In addition to, or alternatively to the foregoing, other method steps can also include sensing when the electrostatic adhesion pad is electrostatically adhered to the foreign object, and controlling the boom in response to sensing that the pad is electrostatically adhered to the foreign object. In addition, one or more of the recited steps can be performed with respect to one or more additional separate foreign objects. For example, the changing step can result in connecting the foreign object with a second separate foreign object.
Other apparatuses, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.
The included drawings are for illustrative purposes and serve only to provide examples of possible structures and arrangements for the disclosed inventive applications and systems for an electroadhesive sticky boom. These drawings in no way limit any changes in form and detail that may be made to the invention by one skilled in the art without departing from the spirit and scope of the invention.
Exemplary applications of apparatuses and methods according to the present invention are described in this section. These examples are being provided solely to add context and aid in the understanding of the invention. It will thus be apparent to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the present invention. Other applications are possible, such that the following examples should not be taken as limiting.
In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments of the present invention. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the invention, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the invention.
The present invention relates in various embodiments to systems and methods involving the improved manipulation of objects. In some embodiments, various electroadhesive “sticky” boom systems and techniques are adapted to capture or otherwise manipulate objects. Such capture or manipulation can occur in outer space or other vacuum and/or no gravity environments, among other possible applications. In general, the invention can include the integration of electrostatic adhesion devices in combination with a deployable boom. In various detailed embodiments, the invention can involve the rendezvous and/or docking of objects in outer space. In particular implementations, the disclosed embodiments can be responsive to NASA SBIR S5.04—Rendezvous and Docking Technologies for Orbiting Sample Capture—which solicited rendezvous and docking solutions for autonomously collecting a sample canister for a Mars Sample Return mission.
The combination of a rendezvous boom with an electrostatic adhesion pad has several advantages both for this particular problem and in the context of a much wider commercial applicability. Various advantages can include, for example:
While the various examples disclosed herein focus on particular aspects of specific electroadhesive applications, it will be understood that the various inventive principles and embodiments disclosed herein can be applied to other electrostatic applications and arrangements as well. For example, an electrolaminate application involving one or more electrostatically charged sheets can utilize the same types of general electrostatic principles for gripping and controlling foreign objects.
Furthermore, while the particular applications described herein are made with respect to spacecraft or other foreign objects in outer space, it will be readily appreciated that the combination electrostatic pad and boom combination can be used in a variety of other applications that are not necessarily in outer space, in vacuum or in zero gravity environments.
In providing various details for the contemplated embodiments, the following disclosure provides an initial discussion regarding electroadhesion, followed by a brief description of electrostatic properties seen within vacuum environments, and then various details regarding electroadhesive sticky booms and other electrostatic applications in similar contexts. A particular method of operating an electroadhesive sticky boom is then provided.
As the term is used herein, “electroadhesion” refers to the mechanical coupling of two objects using electrostatic forces. Electroadhesion as described herein uses electrical control of these electrostatic forces to permit temporary and detachable attachment between two objects. This electrostatic adhesion holds two surfaces of these objects together or increases the traction or friction between two surfaces due to electrostatic forces created by an applied electrical field. Although electrostatic clamping has traditionally been limited to holding two flat, smooth and generally conductive surfaces separated by a highly insulating material together, the present invention involves electroadhesion devices and techniques that do not limit the material properties, curvatures, size or surface roughness of the objects subject to electroadhesive forces and handling. Furthermore, while the various examples and discussions provided herein typically involve electrostatically adhering a robot or other device to a foreign substrate, it will also be understood that many other types of electrostatic applications may also generally be implicated for use with the disclosed invention. For example, two components of the same device may be electrostatically adhered to each other, such as in an electrolaminate or other type of arrangement.
Turning first to
Thus, the electrostatic adhesion voltage provides an overall electrostatic force, between the electroadhesive device 10 and inner material 16 beneath surface 12 of foreign object 14, which electrostatic force maintains the current position of the electroadhesive device relative to the surface of the foreign object. The overall electrostatic force may be sufficient to overcome the gravitational pull on the foreign object 14, such that the electroadhesive device 10 may be used to hold the foreign object aloft. In various embodiments, a plurality of electroadhesive devices may be placed against foreign object 14, such that additional electrostatic forces against the object can be provided. The combination of electrostatic forces may be sufficient to lift, move, pick and place, or otherwise handle the foreign object. Electroadhesive device 10 may also be attached to other structures and hold these additional structures aloft, or it may be used on sloped or slippery surfaces to increase normal friction forces
Removal of the electrostatic adhesion voltages from electrodes 18 ceases the electrostatic adhesion force between electroadhesive device 10 and the surface 12 of foreign object 14. Thus, when there is no electrostatic adhesion voltage between electrodes 18, electroadhesive device 10 can move more readily relative to surface 12. This condition allows the electroadhesive device 10 to move before and after an electrostatic adhesion voltage is applied. Well controlled electrical activation and de-activation enables fast adhesion and detachment, such as response times less than about 50 milliseconds, for example, while consuming relatively small amounts of power. Larger release times may also be valuable in many applications.
Electroadhesive device 10 includes electrodes 18 on an outside surface 11 of an insulating material 20. This embodiment is well suited for controlled attachment to insulating and weakly conductive inner materials 14 of various foreign objects 16. Other electroadhesive device 10 relationships between electrodes 18 and insulating materials 20 are also contemplated and suitable for use with a broader range of materials, including conductive materials. For example, a thin electrically insulating material (not shown) can be located on the surfaces of the electrodes where surface 12 is on a metallic object. As will be readily appreciated, a shorter distance between surfaces 11 and 12 results in a stronger electroadhesive force between the objects. Accordingly, a deformable surface 11 adapted to at least partially conform to the surface 12 of the foreign object 14 can be used.
As the term is used herein, an electrostatic adhesion voltage refers to a voltage that produces a suitable electrostatic force to couple electroadhesive device 10 to a foreign object 14. The minimum voltage needed for electroadhesive device 10 will vary with a number of factors, such as: the size of electroadhesive device 10, the material conductivity and spacing of electrodes 18, the insulating material 20, the foreign object material 16, the presence of any disturbances to electroadhesion such as dust, other particulates or moisture, the weight of any objects being supported by the electroadhesive force, compliance of the electroadhesive device, the dielectric and resistivity properties of the foreign object, and the relevant gaps between electrodes and foreign object surface. In one embodiment, the electrostatic adhesion voltage includes a differential voltage between the electrodes 18 that is between about 500 volts and about 15 kilovolts. Even lower voltages may be used in micro applications. In one embodiment, the differential voltage is between about 2 kilovolts and about 5 kilovolts. Voltage for one electrode can be zero. Alternating positive and negative charges may also be applied to adjacent electrodes 18. The voltage on a single electrode may be varied in time, and in particular may be alternated between positive and negative charge so as to not develop substantial long-term charging of the foreign object. The resultant clamping forces will vary with the specifics of a particular electroadhesive device 10, the material it adheres to, any particulate disturbances, surface roughness, and so forth. In general, electroadhesion as described herein provides a wide range of clamping pressures, generally defined as the attractive force applied by the electroadhesive device divided by the area thereof in contact with the foreign object
The actual electroadhesion forces and pressure will vary with design and a number of factors. In one embodiment, electroadhesive device 10 provides electroadhesive attraction pressures between about 0.7 kPa (about 0.1 psi) and about 70 kPa (about 10 psi), although other amounts and ranges are certainly possible. The amount of force needed for a particular application may be readily achieved by varying the area of the contacting surfaces, varying the applied voltage, and/or varying the distance between the electrodes and foreign object surface, although other relevant factors may also be manipulated as desired.
Although electroadhesive device 10 having electroadhesive gripping surface 11 of
Referring to
In some embodiments, an electroadhesive gripping surface can take the form of a flat panel or sheet having a plurality of electrodes thereon. In other embodiments, the gripping surface can take a fixed shape that is matched to the geometry of the foreign object most commonly lifted or handled. For example, a curved geometry can be used to match the geometry of a cylindrical paint can or soda can. The electrodes may be enhanced by various means, such as by being patterned on an adhesive device surface to improve electroadhesive performance, or by making them using soft or flexible materials to increase compliance and thus conformance to irregular surfaces on foreign objects.
Continuing with
Electrode set 42 is disposed on a top surface 23 of insulating layer 44, and includes an array of linear patterned electrodes 18. A common electrode 41 electrically couples electrodes 18 in set 42 and permits electrical communication with all the electrodes 18 in set 42 using a single input lead to common electrode 41. Electrode set 40 is disposed on a bottom surface 25 of insulating layer 44, and includes a second array of linear patterned electrodes 18 that is laterally displaced from electrodes 18 on the top surface. Bottom electrode set 40 may also include a common electrode (not shown). Electrodes can be patterned on opposite sides of an insulating layer 44 to increase the ability of the electroadhesive end effector 60 to withstand higher voltage differences without being limited by breakdown in the air gap between the electrodes, as will be readily appreciated.
Alternatively, electrodes may also be patterned on the same surface of the insulating layer, such as that which is shown in
Another distinguishing feature of electroadhesive devices described herein is the option to use deformable surfaces and materials in electroadhesive device 10 as shown in
Electrodes 18 may also be compliant. Compliance for insulating material 20 and electrodes 18 may be used in any of the electroadhesive device arrangements 10 described above. Compliance in electroadhesive device 10 permits an adhering surface 32 of device 10 to conform to surface 12 features of the object it attaches to.
Adhering surface 32 is defined as the surface of an electroadhesive device that contacts the substrate surface 12 being adhered to. The adhering surface 32 may or may not include electrodes. In one embodiment, adhering surface 32 includes a thin and compliant protective layer that is added to protect electrodes that would otherwise be exposed. In another embodiment, adhering surface 32 includes a material that avoids retaining debris stuck thereto (e.g., when electrostatic forces have been removed). Alternatively, adhering surface 32 may include a sticky or adhesive material to help adhesion to a wall surface or a high friction material to better prevent sliding for a given normal force.
Compliance in electroadhesive device 10 often improves adherence. When both electrodes 18 and insulating material 20 are able to deform, the adhering surface 32 may conform to the micro- and macro-contours of a rough surface 12, both initially and dynamically after initial charge has been applied. This dynamic compliance is described in further detail with respect to
The compliance permits electroadhesive device 10 to conform to the wall surface 12 both initially—and dynamically after electrical energy has been applied. This dynamic method of improving electroadhesion is shown in
At some time when the two are in contact as shown in
When the force of attraction overcomes the compliance in electroadhesive device 10, these compliant portions deform and portions of surface 32 move closer to surface 12. This deformation increases the contact area between electroadhesive device 10 and wall surface 12, increases electroadhesion clamping pressures, and provides for stronger electroadhesion between device 10 and wall 14.
This adaptive shaping may continue. As the device surface 32 and wall surface 12 get closer, the reducing distance therebetween in many locations further increases electroadhesion forces, which causes many portions of electroadhesive device 10 to further deform, thus bringing even more portions of device surface 32 even closer to wall surface 12. Again, this increases the contact area, increases clamping pressures, and provides for stronger electroadhesion between device 10 and wall 14. The electroadhesive device 10 reaches a steady state in conformity when compliance in the device prevents further deformation and device surface 32 stops deforming.
In some embodiments, electroadhesive device 10 includes porosity in one or more of electrodes 18, insulating material 20 and backing 24. Pockets of air may be trapped between surface 12 and surface 32; these air pockets may reduce adaptive shaping. Tiny holes or porous materials for insulator 20, backing 24, and/or electrodes 18 allows trapped air to escape during dynamic deformation. Thus, electroadhesive device 10 is well suited for use with rough surfaces, or surfaces with macroscopic curvature or complex shape. In one embodiment, surface 12 includes roughness greater than about 100 microns. In a specific embodiment, surface 12 includes roughness greater than about 3 millimeters.
An optional backing structure 24, such as shown in
With some electroadhesive devices 10, softer materials may warp and deform too much under mechanical load, leading to suboptimal clamping. To mitigate these effects, electroadhesive device 10 may include a graded set of layers or materials, where one material has a low stiffness or modulus for coupling to the wall surface and a second material, attached to a first passive layer, which has a thicker and/or stiffer material. Backing structure 24 may attach to the second material stiffer material. In a specific embodiment, electroadhesive device 10 included an acrylic elastomer of thickness approximately 50 microns as the softer layer and a thicker acrylic elastomer of thickness 1000 microns as the second support layer. Other thicknesses may be used.
The time it takes for the changes of
In some embodiments, electroadhesion as described herein permits fast clamping and unclamping times and may be considered almost instantaneous. In one embodiment, clamping or unclamping may be achieved in less than about 50 milliseconds. In a specific embodiment, clamping or unclamping may be achieved in less than about 10 milliseconds. The speed may be increased by several means. If the electrodes are configured with a narrower line width and closer spacing, then speed is increased using conductive or weakly conductive substrates because the time needed for charge to flow to establish the electroadhesive forces is reduced (basically the
“RC” time constant of the distributed resistance-capacitance circuit including both electroadhesive device and substrate is reduced). Using softer, lighter, more adaptable materials in device 10 will also increase speed. It is also possible to use higher voltage to establish a given level of electroadhesive forces more quickly, and one can also increase speed by overdriving the voltage temporarily to establish charge distributions and adaptations quickly. To increase unclamping speeds, a driving voltage that effectively reverses polarities of electrodes 18 at a constant rate may be employed. Such a voltage prevents charge from building up in substrate material 16 and thus allows faster unclamping. Alternatively, a moderately conductive material 20 can be used between the electrodes 18 to provide faster discharge times at the expense of some additional driving power required.
As the term is used herein, an electrostatic adhesion voltage refers to a voltage that produces a suitable electrostatic force to couple electroadhesive device 10 to a wall, substrate or other object. The minimum voltage needed for electroadhesive device 10 will vary with a number of factors, such as: the size of electroadhesive device 10, the material conductivity and spacing of electrodes 18, the insulating material 20, the wall or object material 16, the presence of any disturbances to electroadhesion such as dust, other particulates or moisture, the weight of any structures mechanically coupled to electroadhesive device 10, compliance of the electroadhesive device, the dielectric and resistivity properties of the substrate, and the relevant gaps between electrodes and substrate. In one embodiment, the electrostatic adhesion voltage includes a differential voltage between the electrodes 18 that is between about 500 volts and about 10 kilovolts. In a specific embodiment, the differential voltage is between about 2 kilovolts and about 5 kilovolts. Voltage for one electrode can be zero. Alternating positive and negative charges may also be applied to adjacent electrodes 18.
Various additional details and embodiments regarding electroadhesion, electrolaminates, electroactive polymers, wall-crawling robots, and applications thereof can be found at, for example, U.S. Pat. Nos. 6,586,859; 6,911,764; 6,376,971; 7,411,332; 7,551,419; 7,554,787; and 7,773,363; as well as International Patent Application No. PCT/US2011/029101; and also U.S. patent application Ser. No. 12/762,260, each of the foregoing of which is incorporated by reference herein.
Given that at least some of the contemplated embodiments involve use in outer space or a similar vacuum and/or zero gravity type environment, it may be worth considering the implications of such environments on electrostatic applications. In particular, a comprehensive validation of electroadhesion in such environments should consider testing in vacuum, electron bombardment, ultraviolet radiation, temperature extremes and/or plasma environments, among other potential considerations. Plasma in particular may pose some challenges to electroadhesion and other electrostatic applications, since plasma can be weakly conductive and thus potentially neutralize charges and/or require greater power consumption.
As a first step toward validating electrostatic applications in such environments of interest, testing was conducted under a high vacuum using electroadhesion clamps comprised of materials having properties that are already in use in outer space environments. Turning next to
As shown, the actual test apparatus consisted of a small electroadhesion pad (10 cm×10 cm active window) clamped to a substrate plate inside of a vacuum chamber. Clamping forces were measured by pulling on the pad through a vacuum rated mechanical bellow using a linear actuator located outside the vacuum chamber. Universal joints at the actuator end and the pad end were mounted to allow misalignment between the electroadhesion pad and the pulling linear actuator. A Mark-10 force gage (50 lb maximum force, or approximately 222 N) was mounted in-line with the linear actuator to measure pull force. The differences between the forces when no voltage was supplied to the EA clamp, and those when voltage was supplied to the clamp using an HV amplifier, were measured and tabulated.
The electroadhesion pads for this test were made out of a Delrin® frame attached to an Aluminum-coated Mylar, such as a polyethylene terephthalate (“PET”) sheet made by Tap Plastics. This sheet had a total thickness of 25 micrometers and an aluminum coating, which can be patterned by using a tape-based lift-off process. The electrode pattern used had three broad regions, which included a narrow central band connected to ground and two broader traces on either side. These broader traces were each powered using a Trek Model 510D high voltage amplifier, using a bipolar AC waveform (+/−2 kV, 1 Hz square wave) to prevent permanent charging of the Mylar insulator. The two broad traces were activated by waveforms which were 90 degrees out of phase, so as to prevent them from simultaneously going through the 0-point during polarity reversal of the waveform.
In order to prevent the electroadhesion pad from arcing or eroding the electrodes due to self-generated plasma, the back-side of the clamp was covered with a high temperature polyimide (Kapton®) tape (Digikey part # 47029). Forces were measured on an aluminum plate acting as a substrate. Forces were also measured by insulating the aluminum plate using polyimide film of various thicknesses, so as to simulate an insulated metal material.
Such a strong influence of trapped air gaps on clamping forces was further confirmed using Finite Element Modeling (“FEM”). The FEM was conducted using Matlab® scripting of the FE software COMSOL® in a Linux-based setup. A parametric simulation of eleven design parameters was conducted, including variables for electroadhesive pad insulation material thickness, substrate insulation thickness, conductivity of medium (to simulate plasma environments) and material properties (conductivities) for both substrate and spacer (insulator), among other factors.
Representative results from this modeling found that when the gap between the electroadhesive pad and substrate is zero (i.e., the pad is in intimate contact with the substrate), then the conductivity of the medium does not affect the clamping force. When there is a non-zero gap, however, then the conductivity does influence the clamping force, with greater conductivities reducing the clamping force. The exact nature of space plasma is much more complicated, and the gap between the pad and substrate is likely to be close to zero in some places, but non-zero in others.
Apart from the above drop with conductivity, having a small air gap in some places between the EA pad and substrate could be beneficial in some instances. For example, the gap can only exist in some places, since contact is necessary to achieve frictional load transfer between substrate and pad. In general, more resistive substrate materials will tend to exhibit less clamping force than more conductive substrate materials.
Again, various particular embodiments of the present disclosure are directed toward an electroadhesive “sticky” boom system that is adapted to capture or otherwise manipulate objects, such as in outer space or other vacuum and/or zero gravity environments, among other possible applications. In general, the disclosed embodiments can include the combination of electrostatic adhesion devices with a boom. Such a boom can be deployable in an extendable and/or retractable manner. As noted above, various embodiments can involve the rendezvous and/or docking of objects in outer space.
In general, an electrostatic adhesion pad or electroadhesion pad (“EA pad”) can be placed at the end of an extensible and/or retractable boom to enable easier rendezvous and docking, as well as capture of uncooperative satellites or other objects in outer space. The EA pad is preferably able to “stick” (i.e., electrostatically adhere) to many or all spacecraft or foreign object surfaces without requiring any sort of target mechanism on the vehicle or object being captured. In addition, the boom provides the benefit of a low-inertia connection at a distance between the controlling device and captured object. Such a “connection at a distance” serves to increase rendezvous and docking safety while also simplifying the various problems that arise as the objects near each other just before docking. That is, such a sticky boom system allows the general “last several meters” problem of a rendezvous or docking procedure to be solved non-propulsively. This can be done by using precision electric motors to guide the device to the target at a distance that is remote to the motors and controlling item, which significantly reduces the risk of an accidental collision between the controlling device and foreign object being captured.
Turning next to
In various detailed embodiments, the EA pad can be configured to be inherently capable of providing contact and proximity detection. As will be readily appreciated, the capacitance between electrodes will change in a detectable manner as a foreign surface approaches, such that provisions can be made to detect whether a surface is in or near contact. Such provisions can be by way of one or more capacitive contact sensors that detect when surface contact is made or an electrostatic clamp is present, or by measuring the leakage current that is inherent to such a clamp.
Such a feature can be important for various rendezvous or docking tasks, and can be used to provide feedback as to the existence and strength of a clamp to an operator or other overall controlling device. In the event that multiple EA pads are used, then multiple sensors can be used to provide varying states of on or off clamping.
In various embodiments, the EA pad or pads can take many possible forms. Such an EA pad could be a flat or flexible pad that is coupled to the boom using some form of compliant mechanism. Alternatively, the EA pad or pads could be combined with a more traditional electromechanical end effector. The EA pad could also use multiple petals or fingers, which may have artificial muscles on one or more sides to allow them to curl, uncurl or otherwise actuate. Further, the EA pad could comprise a multi-faceted ball-like object having multiple flat or curved pads on multiple sides. Such an arrangement can allow more freedom to maneuver the boom into final contact with the target surface in some embodiments.
Another advantage of the disclosed electroadhesive sticky boom is that a more ready and easy connection between two objects is enabled, even where the two objects have a modest relative velocity error between them. This can be accomplished by first making contact with the EA pad at the end of the boom, and then extending or retracting the boom at an appropriate rate that provides a steady, gradual deceleration (or acceleration as may be appropriate) until the two object velocity vectors have matched.
Continuing in the same general manner, the sticky boom can be used reduce spin gradually on an undesirably tumbling target, even one of substantial size. This can be accomplished by “grabbing” the object with the EA pad activated at a point on the object that is away from the spin axis. Some amount of deceleration can then be subjected at that point (i.e., providing a counter-torque on the body) as the object spins or rotates into the direction of the boom. The EA pad can then be turned off, the pad released, and the boom pulled back to reposition the pad. Any number of propulsive maneuvers on the boom, controlling device or host spacecraft can also be performed to null out relative motion, if needed or helpful. The entire process can then be repeated as many times as desired after the EA pad is relocated and adhered to the surface until the target object has had its spin reduced or eliminated.
In various embodiments, the boom can be any of a number of multiple forms. For example, the boom can have both significant tensile and compressive strengths, such as that which might be found for a stiff rod or object. Such booms can enable reaches of up to 20 to 50 meters in various embodiments. Greater distances are also achievable for some applications. Alternatively, a tensile-only boom can take the form of a cable or cord, which can enable very long reaches of greater than 1 km. Such tensile-only booms can have very low stowed volume and mass per unit length. As yet another alternative, a combination tensile/compressive and tensile-only boom can be used, with different portions of the boom having different properties.
Such a combination of tensile only and tensile/compressive booms mentioned can take several forms including, for example, a tether with a short STEM-style shape-memory alloy boom section attached at the EA pad end of the tether. The tether reel can be designed so that once the tether portion reels in far enough, then the STEM-part of the boom can enter the spooling mechanism and start providing compressive strength to the assembly. As another embodiment, a tether with a system at the end that includes its own tensile/compressive sticky-boom device can be used. As yet another embodiment, a tether that feeds out through the middle of a tensile/compressive boom section can be used, such that once the tether is retracted far enough, the EA pad contacts the end of the tensile/compressive boom system, and then the tensile/compressive boom and the tether are reeled in at the same rate.
In the event that a combination tether and tensile/compressive system mentioned is long enough, such a system can enable the contact operations to be performed with the target spacecraft or object outside of a “keep-out” volume for a space station or other host or controlling device. Such a distance can be on the order of 500 meters to one km, or more. By doing this, a spacecraft in a lower orbit, that never actually intersects with the station orbit (and is thus safe) can be grabbed, velocity matched, and then pulled-in to the station without ever having to do independent flight maneuvers that ever bring it within even several hundred meters of the station. Such an arrangement can make it much easier to bring small spacecraft to a given location, like ISS or a propellant depot.
Further, such a combination boom could also be in the form of a micro-tug capable of separating from the tether section. Such an arrangement could also include multiple EA pad sections or connections, for added flexibility in maneuvers and handling of difficult foreign objects, the boom, and the overall system. Under such a multiple EA arrangement, the separate micro-tug could then independently maneuver to a target, capture it using its own sticky-booms, and then haul it back to the tether, reattach to the tether, and the whole system gets reeled back in.
In these examples and various other embodiments, a given spacecraft or controlling device can use multiple sticky-booms, potentially of different configurations, to enable initial capture, velocity matching, pulling the spacecraft or other foreign object in, aligning the foreign object appropriately, and then performing a final berthing option. In addition, various gravity gradient effects can result in some long tether-like booms desirably operating along a line pointing between the station center of gravity and the center of the orbiting body.
In still further application examples, a tether based system can be fired out similar to a grappling hook. The tether boom can then be spooled out at a rate to avoid decelerating the EA pad at the end. Various rendezvous and docking techniques provided herein can be analogous to boat docking in some cases, where mooring lines are tossed from the boat to the pier and used to slowly pull the vessel in, with compressive fenders used to slow the boat down on initial contact. Such embodiments can also be analogous to mid-air refueling, where a low-inertia connection between the two vehicles is advantageously made.
In general, the use of electroadhesion for these applications is attractive in its flexibility, since EA pads can typically be used on a wide range of spacecraft surfaces. This enables the capture of a wide range of spacecraft and other items without the need to engineer custom hardware for each mission. The EA pad also enables a decrease in complexity by gripping spacecraft surfaces with no moving parts, while also providing an inherent ability for non-mechanical proximity and contact detection. Advantages of such systems are numerous, in terms of increased safety, lower propellant usage, lower impact and simpler systems and sensors.
For example, providing connection at a distance via a low-inertia EA pad/boom combination reduces the odds of accidental spacecraft collisions significantly compared to existing rendezvous and docking concepts. Depending on the length of the boom, it may even be feasible in some cases to capture a spacecraft that is in a close but non-intersecting orbit. Also by eliminating the need for close in propulsive maneuvering, spacecraft damage from RCS plume impingement becomes less of an issue. Furthermore, by allowing the last several tens of meters to be closed electromechanically, and due to the large tolerance for relative misalignments, velocity and angular rate mismatches, the amount of propellant needed for spacecraft capture is significantly lower than for existing rendezvous and docking approaches.
In addition, the use of a long boom or tether allows spacecraft momentum mismatches to be equalized over a much longer stroke, greatly reducing the shock loads and microgravity disturbances caused by a docking event, and significantly reducing the required shock absorption weight for a rendezvous and docking system. Still further, the disclosed sticky boom systems enable much simpler rendezvous and docking control due to the wide range of motion of the boom system, the higher tolerance for relative velocity and rotation mismatches, and the ability to steer the boom without the complexities of propulsive orbital dynamics. These systems also require less precise knowledge of relative orbital elements for the two vehicles, enabling the use of cheaper more robust sensors.
Moving next to
As shown, controlling craft 180 can include a number of components, including an electroadhesive sticky boom having an EA pad 110, a boom 135 and a boom deployment component 145. Such a sticky boom can be adapted to capture and control various items in space, such as debris or small item 101. Further features on controlling craft 180 can include, for example, a main body 184, one or more solar collectors 186 and a communications component 188, among others.
Continuing with
One issue that can arise with the use of an electroadhesive sticky boom such as that which is provided above concerns the ability of the EA pad to adhere or “stick” to the target object initially. In practice, it has been observed that such an initial adherence or sticking can be affected by various factors relating to the dynamic interaction between the EA pad and target object. For example, an initial physical contact between the EA pad and target object can result in a collision “bounce” that then separates these items and causes them to drift away from each other before an effective level of electroadhesion can be applied. Since the distance between objects is a critical factor in generating electroadhesive forces, the specific timing of applying charge to the electrodes prior to the bounced objects drifting apart can be important. Alternatively, or in addition, providing systems and techniques that prolong the length of time that the objects are in contact or extremely close proximity can be useful.
With respect to the timing of applying electroadhesive force, one or more sensors can be used to provide feedback as to when the objects are in actual contact or in critical proximity to each other. Such capacitive sensors or the like can help to determine an optimal time window for applying charges to the electrodes for an electroadhesive clamp in various embodiments. In some instances though, a very brief and/or imperfect type of bouncing contact between objects can result in a preference for additional features or techniques to facilitate a good adherence. For example, in some instances where only an edge or corner of an EA pad contacts the target object before a bouncing away occurs, then even a well timed application of electrostatic force may be insufficient.
As such, the use of features such as stiffenable joints or components, electroadhesive skins, or both can be helpful in providing a mode of initial physical contact or interaction that then facilitates a better adhesion when the EA pad is actuated. Such stiffenable joints or other components can involve, for example, an electrostatic clutch, joint brakes and/or locking structures that allow one or more portions of the EA pad and/or boom to transition from a soft or flexible state to a rigid state once a preferred location and/or orientation of the stiffenable item is realized. For example, where an EA pad is being manipulated about a jointed coupling to the end of a boom, such a jointed coupling can preferably be actuated to become stiff or rigid once an optimized orientation of the EA pad with respect to the target object is achieved. As another example, a segmented boom can have stiffenable joints that can then “freeze” a given end segment or other segments in a particular orientation when such an orientation is helpful.
Another feature that can be used to achieve a better initial adherable contact interaction between EA pads and target objects can involve the use of “electroadhesive skins ” Such electroadhesive skins can be in the form of, for example, thin and flexible electroadhesive sheets that readily deform when contacting another object. Rather than experiencing a relatively hard bounce and drift apart when an EA pad contacts a foreign object then, such an EA pad in the form of an EA skin could more readily crumple, graze or otherwise deform in a manner that maintains contact with the foreign object. Such components can thus be used to crumple up against and/or graze gently along the surface of a foreign object in space, so as to maximize the amount of surface area between objects that is actually in contact or near contact. When used in combination, one or more stiffenable joints or components can then be used to freeze or lock the EA pad and/or boom in place once an EA skin has deformed or grazed along the foreign object into an orientation that is good for facilitating electroadhesion.
It will be readily appreciated that numerous other applications involving the various concepts relating to electroadhesion can also be used in similar outer space environments and applications. For example, the scope of spacecraft missions in general and CubeSat-based missions in particular could be dramatically increased by using electroadhesion capabilities to dock two or more CubeSat modules, or to reconfigure two or three unit satellites after deployment from a P-POD (Poly Picosat Orbital Deployer). Mechanical docking systems are complex to design and pose a significant technical risk to a mission, whereas electroadhesive applications provide simpler yet reliable alternatives where designed properly.
In keeping with the CubeSat paradigm, an electroadhesive based docking system is simple to design, inexpensive, and rugged, consisting of a few short wires, electrostatic pads, and a small power supply. Such a docking subsystem could have a far reaching impact on CubeSat mission utility. The ability to reconfigure multi-unit satellites could enhance antenna aperture, simplify repeated separation and reconnection of tethered pairs, and could enable a variety of experiments. A simple docking capability would be an enabling technology for multiple cooperative small spacecraft operations, including the use of small auxiliary spacecraft to inspect, maintain, or defend large, high-value satellites. Such a system would allow an auxiliary craft to wait in ready mode docked on its host, then deploy when needed and re-dock after performing its mission. Other possibilities include constellations of CubeSats that occasionally dock to enable a special function or to share resources.
Although a wide variety of applications involving providing manipulating objects using electroadhesion can be imagined, one basic method is provided here as an example. Turning lastly to
Beginning with a start step 300, an electroadhesion pad is contacted to a surface of a foreign vehicle or object at process step 302. An electrostatic adhesion voltage is then applied at process step 304, after which the foreign vehicle or object is adhered to the electroadhesion pad at process step 306. At a following process step 308, the system can then optionally sense whether or not the EA pad is actually adhered to the foreign vehicle or object.
If no actual adherence has been made, then the process reverts to step 302 and repeats until an actual adherence is made. When an adherence is made, then the process continues to step 312, where a deformable surface of then deformed to increase the surface area contact between the EA pad and the foreign object. Such a deformable surface can be the contact surface of the EA pad, for example. At a subsequent process the 314, the adhesion voltage is maintained while the deformable surface contacts the foreign object. As will be readily appreciated, a direct contact between the foreign surface and foreign object is not always necessary, since a thin insulator or other protective layer can be between the surfaces in some cases.
The method then continues to process step 316, where the physical location and/or rotational velocity of the foreign object is then changed by way of the boom and EA pad arrangement while adherence is maintained. After this is done, the electrostatic adhesion voltage is then reduced or eliminated at process step 318, after which an inquiry is made at decision step 320 as to whether the handling of the vehicle or other foreign object is finished. If not, then the method continues to process step 322, whereupon the electroadhesion pad is moved relative to the foreign object to a new location at its surface. The method then reverts to step 302 and repeats for all steps at the new location of contact for the EA pad.
In the event that object handling is finished at 320, however, then the method proceeds to finish at and end step 324. Further steps not depicted can include, for example, coupling the boom to the electroadhesive pad, or manipulating a plurality of electroadhesive pads rather than just one. Other steps can include providing feedback from one or more sensors to a controller to result in adjusted movements of the boom, for example, and any or all of the steps may be repeated any number of times, as may be desired.
Although the foregoing invention has been described in detail by way of illustration and example for purposes of clarity and understanding, it will be recognized that the above described invention may be embodied in numerous other specific variations and embodiments without departing from the spirit or essential characteristics of the invention. Various changes and modifications may be practiced, and it is understood that the invention is not to be limited by the foregoing details, but rather is to be defined by the scope of the claims.
This application claims priority to U.S. Provisional Patent Application No. 61/431,363, filed Jan. 10, 2010, and entitled “AN ELECTROADHESIVE STICKY BOOM SYSTEM FOR CAPTURING OBJECTS IN SPACE,” which is incorporated by reference herein in its entirety and for all purposes.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US12/20810 | 1/10/2012 | WO | 00 | 11/14/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61431363 | Jan 2011 | US |
