Unmanned aerial system for overhead drilling on elevated structure

Abstract

An unmanned aerial system (UAS) for overhead drilling on an elevated structure is provided, preferably for, but not limited to, performing resistography for wooden structure inspection of an elevated wooden structure. The UAS includes: a body frame; a first gripper mechanism arranged at a first portion of the body frame; a second gripper mechanism arranged at a second portion of the body frame; a drill bit arranged at a third portion of the body frame and is operable for overhead drilling, the third portion located in between the first and second portions of the body frame; and one or more thrust units affixed to the body frame for generating thrust to support a flight of the UAS. In particular, the first and second gripper mechanisms each includes a pair of perching arm members and a depressible protruding engagement member coupled to the pair of perching arm members via a mechanical linkage, the mechanical linkage is configured to adjust the pair of perching arm members between an open state and a gripping state when the depressible protruding engagement member is adjusted between an extended state and a depressed state, and the depressible protruding engagement member is configured to depress from the extended state to the depressed state when the depressible protruding engagement member is depressed against a surface of the elevated structure via an applied upward force towards the elevated structure from the thrust generated by the one or more thrust units for adjusting the pair of perching arm members to the gripping state for overhead perching of the UAS onto the elevated structure.

Description

UNMANNED AERIAL SYSTEM FOR OVERHEAD DRILLING ON ELEVATEDSTRUCTURECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore Patent Application No. 10202401024Y, filed on 8 April 2024, the content of which being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] The present invention generally relates to an unmanned aerial system (UAS) for overhead drilling on an elevated structure (e.g., natural or built / man-made structure), preferably for, but not limited to, performing resistography for wooden structure inspection of an elevated wooden structure.BACKGROUND

[0003] There are various tasks or applications where drilling may be required to be performed on an elevated structure at elevated heights. A particular or preferred application (although not limited to such a particular application) is resistography application, namely, to perform resistography for wooden structure inspection of an elevated wooden structure.

[0004] For example, in the pursuit of a collective effort to sustain the global forest, more trees are planted internationally, aiming to grow the forest area by 3%. Urban forests are increasingly recognized for their potential to yield psychological and societal advantages. Nevertheless, with the proliferation of urban forest initiatives, there arises a critical need to safeguard the well-being of the flora, particularly in the context of mature and sizable trees. To address this concern, resistography emerges as a conventional yet non-destructive methodology employed for the assessment of internal structural conditions and the overall integrity of arboreal specimens, as well as timber and wooden constructions. The procedure entails the insertion or drilling of a slender needle or probe into the material of interest, with subsequent measurement of the encountered resistance. In addition to the preservation efforts aimed at trees, numerous ancient heritage buildings in Asian nations, often constructed using timber as a primary material, are undergoing conservation endeavors. Within this context, resistography has found utility in the examination of the wooden components of these historic structures. Its role encompasses the identification and characterization of decay types and their specificlocations within the timber elements. Although this method is non-destructive for the subject, ascertaining the condition of the structures often requires the resistograph to be manually used at an elevated height, putting the human operator or worker at risk of falls. Hence, safety measures such as scaffolds, harnesses, and / or mobile elevated work platforms (MEWPs) have to be set in place prior to operations. Accordingly, such traditional practices for performing drilling at elevated heights do not only present safety hazards for human operators but are also inefficient with respect to time and costs.

[0005] A need therefore exists to provide an UAS for overhead drilling on an elevated structure (e.g., natural or built / man-made structure) that seeks to overcome, or at least ameliorate, one or more deficiencies in conventional drilling systems or practices for overhead drilling, and more particularly, that improves human safety and efficiency with respect to time and costs, such as for performing resistography for wooden structure inspection of an elevated wooden structure. It is against this background that the present invention has been developed.SUMMARY

[0006] According to a first aspect of the present invention, there is provided an unmanned aerial system (UAS) for overhead drilling on an elevated structure, the UAS comprising: a body frame; a first gripper mechanism arranged at a first portion of the body frame; a second gripper mechanism arranged at a second portion of the body frame; a drill bit arranged at a third portion of the body frame and is operable for overhead drilling, the third portion located in between the first and second portions of the body frame; and one or more thrust units affixed to the body frame for generating thrust to support a flight of the UAS, wherein the first and second gripper mechanisms each comprises a pair of perching arm members and a depressible protruding engagement member coupled to the pair of perching arm members via a mechanical linkage, the mechanical linkage is configured to adjust the pair of perching arm members between an open state and a gripping state when the depressible protruding engagement member is adjusted between an extended state and a depressed state, and the depressible protruding engagement member is configured to depress from the extended state to the depressed state when the depressible protruding engagement member is depressed against a surface of the elevated structure via an applied upward force towards the elevated structurefrom the thrust generated by the one or more thrust units for adjusting the pair of perching arm members to the gripping state for overhead perching of the UAS onto the elevated structure.

[0007] According to a second aspect of the present invention, there is provided a method of forming the UAS according to the above-mentioned first aspect of the present invention.BRIEF DESCRIPTION OF THE DRAWINGS100081 Embodiments of the present invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:FIG. 1 depicts a UAS for overhead drilling on an elevated structure, according to various embodiments of the present invention;FIG. 2 depicts a schematic diagram of a method of forming the UAS for overhead drilling on an elevated structure, according to various embodiments of the present invention;FIG. 3 illustrates an example UAS for overhead drilling on an elevated wooden structure, according to various example embodiments of the present invention;FIG. 4 depicts schematic drawings of a side view of the UAS according to various example embodiments of the present invention for illustrating a gripper mechanism process for different operational states or phases for an example elevated wooden beam structure;FIG. 5A depicts a schematic drawing of a side view of the UAS according to various example embodiments of the present invention at an open state;FIGs. 5B and 5C depict schematic drawings of a side view of a section (enclosed by a dashed box in FIG. 4) of the UAS according to various example embodiments of the present invention at the gripping state for two example elevated wooden structures;FIG. 6 depicts superimposed illustration of free body diagram and gripper mechanism with springs members, according to various example embodiments of the present invention;FIG. 7A depicts a multi-modal tether system according to various example embodiments of the present invention;FIG. 7B depicts a schematic drawing of a structure of the multi-modal tether system (flexible shaft cable), according to various example embodiments of the present invention;FIG. 8 depicts top and side views of a free body diagram of drill bit;FIG. 9 depicts a table (Table I) of drill resistance variables in mock-up experiments;FIGs. 10A to 10D illustrate variance in the perching arm characteristics for optimized design, according to various example embodiments of the present invention;FIG. 11 depicts an efficiency plot for mechanical power transmission for various tethered drill configurations;FIG. 12 illustrates grasping on various diameter beams and a plot showing gripper force characterization conducted to test the physical limitations of the gripping mechanism, according to various example embodiments of the present invention;FIG. 13 depicts a schematic drawing of an onboard drill assembly, according to various example embodiments of the present invention;FIGs. 14A to 14D show timelapse images of the UAS in operation for overhead drilling on a beam structure, according to various example embodiments of the present invention;FIGs. 15A to 15D show timelapse images of the UAS in operation for overhead drilling on a flat surface, according to various example embodiments of the present invention; andFIG. 16 depicts a plot showing drilling resistance (%) against the duration of drill (seconds) on ceiling and beam surfaces during drill operation, according to various example embodiments of the present invention.DETAILED DESCRIPTION

[0009] Various embodiments of the present invention provide an unmanned aerial system (UAS) for overhead drilling on an elevated structure (e.g., natural or built / man-made structure), preferably for, but not limited to, performing resistography for wooden structure inspection of an elevated wooden structure.

[0010] As discussed in the background, traditional practices for performing drilling at elevated heights do not only present safety hazards for human operators but are also inefficient with respect to time and costs. In this regard, various embodiments of the present invention provide an UAS for overhead drilling on an elevated structure that seeks to overcome, or at least ameliorate, one or more deficiencies in conventional drilling systems or practices for overhead drilling, and more particularly, that improves human safety and efficiency with respect to time and costs, such as for performing resistography for wooden structure inspection of an elevated wooden structure. The UAS may also be referred to as an unmanned aerial vehicle (UAV), an aerial robot, a rotorcraft or a drone, such as a multirotor drone.

[0011] FIG. 1 depicts an UAS 100 for overhead drilling on an elevated structure, according to various embodiments of the present invention The UAS 100 comprises: a body frame 1 10; a first gripper mechanism (or a first gripper system) 120-1 arranged at a first portion (e.g., at a first side or edge portion) of the body frame 1 10; a second gripper mechanism (or a secondgripper system) 120-2 arranged at a second portion (e.g., at a second side or edge portion) of the body frame 110 (e.g., the first and second portions may be at opposite sides of the body frame 110); a drill bit 130 arranged at a third portion (e g., at a middle or central portion) of the body frame 110 and is operable for overhead drilling; and one or more thrust units 140 (e.g., four thrust units shown in FIG. 1 as an example) affixed to the body frame 1 10 for generating thrust to support a flight of the UAS 100. The third portion is located in between the first and second portions of the body frame 110. In particular, the first and second gripper mechanisms 120-1, 120-2 each comprises a pair of perching arm members 122-1, 122-2 and a depressible protruding engagement (or trigger) member 124-1, 124-2 coupled to the pair of perching arm members 122-1, 122-2 via a mechanical linkage 126-1, 126-2. The mechanical linkage 126-1, 126-2 is configured to adjust the pair of perching arm members 122-1, 122-2 between an open state and a gripping state when the depressible protruding engagement member 124-1 , 124-2 is adjusted between an extended state and a depressed state. In particular, the depressible protruding engagement member 124-1, 124-2 is configured to depress from the extended state to the depressed state when the depressible protruding engagement member 124-1, 124-2 is depressed (or engaged) against a surface of the elevated structure via an applied upward force towards the elevated structure from the thrust generated by the one or more thrust units 140 for adjusting the pair of perching arm members 122-1, 122-2 to the gripping state for overhead perching of the UAS 100 onto the elevated structure.

[0012] It will be appreciated by a person skilled in the art that the present invention is not limited to any particular type of UAS, and any type of UAS may be employed as desired or as appropriate, as long as the UAS is operable to navigate or fly to the elevated structure for overhead drilling on the elevated structure and comprises the body frame 110, the first gripper mechanism 120-1; the second gripper mechanism 120-2; the drill bit 130; and the one or more thrust units 140 described herein according to various embodiments of the present invention. Therefore, it will be appreciated by a person skilled in the art that the present invention is not limited to the specific type and configuration of the UAS shown in FIG. 1, which is merely an example illustration. In addition, operations and flight controls of an UAS is well known in the art and thus need not be described herein for clarity and conciseness.

[0013] In various embodiments, for each of the first and second gripper mechanisms 120- 1, 120-2, the mechanical linkage 126-1, 126-2 thereof is configured to adjust the pair of perching arm members 122-1, 122-2 to the gripping state by adjusting the pair of perching arm members 122-1 , 122-2 to press against the elevated structure.

[0014] In various embodiments, for each of the first and second gripper mechanisms 120- 1, 120-2, the mechanical linkage 126-1, 126-2 thereof comprises a first pivot joint and a second pivot joint respectively coupled to a first perching arm member and a second perching arm member of the pair of perching arm members 122-1, 122-2. In this regard, the mechanical linkage 126-1 , 126-2 thereof is configured to adjust the pair of perching arm members 122-1, 122-2 to the gripping state via the first and second pivot joints to respectively adjust the first and second perching arm members 122-1, 122-2 to press against the elevated structure.

[0015] In various embodiments, for each of the first and second gripper mechanisms 120- 1, 120-2, each perching arm member of the pair of perching arm members 122-1, 122-2 thereof has a prismatic structure.

[0016] In various embodiments, the prismatic structure comprises an outer shell and a plurality of cross beams extending between opposing sides of the outer shell and spaced apart along the outer shell. In this regard, the plurality of cross beams is compressible (e.g., flexible) to provide impact absorption.

[0017] In various embodiments, a side of the prismatic structure arranged for pressing against the elevated structure at the gripping state is curved.

[0018] In various embodiments, the above-mentioned each perching arm member 122-1, 122-2 is configured to be flexible for conforming to a shape of the surface of the elevated structure when pressed against the elevated structure at the gripping state.

[0019] In various embodiments, the above-mentioned each perching arm member 122-1, 122-2 is made of a material (e.g., thermoplastic material, such as PLA (polylactic acid) thermoplastic material) that is flexible for conforming to the shape of the surface of the elevated structure when pressed against the elevated structure at the gripping state.

[0020] In various embodiments, the drill bit 130 is adjustable (or movable) between a base state and an elevated state. In this regard, the elevated state is configured for penetrating the drill bit into the elevated structure.

[0021] In various embodiments, for each of the first and second gripper mechanisms 120- 1, 120-2, the depressible protruding engagement member 124-1, 124-2 thereof is coupled to a first spring member such that the depressible protruding engagement member 124-1, 124-2 is depressible from the extended state to the depressed state when the depressible protruding engagement member 124-1 , 124-2 is depressed (or engaged) against the surface of the elevated structure via the applied upward force being sufficient to overcome a spring force of the first spring member. Furthermore, the depressible protruding engagement member 124-1 , 124-2 isrestorable from the depressed state to the extended state in the absence of the above-mentioned applied upward force sufficient to overcome the spring force of the first spring member.

[0022] In various embodiments, the drill bit 130 is adjustable (relative to the first and second gripper mechanisms 120-1 , 120-2) between the base state and the elevated state by one or more second spring members such that the drill bit 130 is adjustable (or movable) (relative to the first and second gripper mechanisms 120-1, 120-2) from the base state to the elevated state when the applied upward force is sufficient to further overcome a spring force of the one or more second spring members. Furthermore, the drill bit 130 is restorable from the elevated state to the base state in the absence of the above-mentioned applied upward force sufficient to further overcome the spring force of the one or more second spring members.

[0023] In various embodiments, the UAS 100 further comprises a platform adjustable relative to the first and second gripper mechanisms 120-1, 120-2 between a base state and an elevated state by the one or more second spring members. In this regard, the drill bit 130 is supported by the platform such that the drill bit 130 is adjustable from the base state to the elevated state, via the platform, when the applied upward force is sufficient to further overcome the spring force of the one or more second spring members, and the drill bit 130 is restorable from the elevated state to the base state, via the platform, in the absence of the above-mentioned applied upward force sufficient to further overcome the spring force of the one or more second spring members.

[0024] In various embodiments, the one or more second spring members are configured within one or more leg members, respectively, of the UAS 100.

[0025] In various embodiments, the drilling system 100 further comprises a tether system comprising a flexible shaft comprising a first end portion coupled to a ground-based drill motor and a second end portion coupled to the drill bit 130. In particular, the drill motor is configured to transfer mechanical power to the drill bit 130 via the flexible shaft.

[0026] In various embodiments, the tether system further comprises an electrical cable for transmitting electrical power to the UAS 100.

[0027] In various embodiments, the second end portion of the flexible shaft is coupled to the drill bit via a planetary gearbox.

[0028] In various embodiments, the elevated structure is an elevated wooden structure. In this regard, the UAS 100 is configured to perform resistography for wooden structure inspection of the elevated wooden structure.

[0029] In various embodiments, the elevated wooden structure has a planar (or flat) surface, is a beam structure or is a branch (e.g., of a tree) which the UAS 100 is configured to overhead perch onto at the gripping state.

[0030] FIG. 2 depicts a schematic diagram of a method 200 of forming the UAS 100 for overhead drilling on an elevated structure according to various embodiments of the present invention. The method 200 comprises: providing or forming (at 202) a body frame 110; providing or forming (at 204) a first gripper mechanism (or a first gripper system) 120-1 arranged at a first portion (e.g., at a first side or edge portion) of the body frame 110; providing or forming (at 206) a second gripper mechanism (or a second gripper system) 120-2 arranged at a second portion (e.g., at a second side or edge portion) of the body frame 110 (e.g., the first and second portions may be at opposite sides of the body frame 110); providing (at 208) a drill bit 130 arranged at a third portion (e g., at a middle or central portion) of the body frame for overhead drilling; and providing (at 210) one or more thrust units 140 affixed to the body frame 110 for generating thrust to support a flight of the UAS 100. The third portion is located in between the first and second portions of the body frame 110. In particular, the first and second gripper mechanisms 120-1, 120-2 each comprises a pair of perching arm members 122-1, 122- 2 and a depressible protruding engagement member 124-1, 124-2 coupled to the pair of perching arm members 122-1, 122-2 via a mechanical linkage 126-1, 126-2. As described hereinbefore according to various embodiments, the mechanical linkage 126-1 , 126-2 is configured to adjust the pair of perching arm members 122-1, 122-2 between an open state and a gripping state when the depressible protruding engagement member 124-1, 124-2 is adjusted between an extended state and a depressed state. In particular, the depressible protruding engagement member 124-1, 124-2 is configured to depress from the extended state to the depressed state when the depressible protruding engagement member 124-1, 124-2 is depressed (or engaged) against a surface of the elevated structure via an applied upward force towards the elevated structure from the thrust generated by the one or more thrust units 140 for adjusting the pair of perching arm members 122-1, 122-2 to the gripping state for overhead perching of the UAS 100 onto the elevated structure.

[0031] The method 200 is for forming the UAS 100 as described hereinbefore with reference to FIG. 1, therefore, various steps or operations of the method 200 correspond to forming, providing or configuring various components, modules or portions of the UAS 100 as described herein according to various embodiments, and thus such corresponding steps or operations need not be described or repeated with respect to the method 200 for clarity andconciseness. In other words, various embodiments described herein in context of the UAS 100 are analogously valid for the method 200 of forming the UAS 100 having various components, modules, portions and configurations as described hereinbefore according to various embodiments, and vice versa. It will be appreciated by a person skilled in the art that FIG. 2 does not limit any particular order of operations / steps in which the method 200 can be performed to form the UAS 100. Furthermore, one or more operations / steps of the method 200 may be performed concurrently or integrally as desired or as appropriate without going beyond the scope of the present invention. For example, various components or parts of the UAS 100 may be 3D printed components or parts, such as but not limited to, the body frame 110 and / or the first and second gripper mechanisms 120-1, 120-2 including the pair of perching arm members 122-1, 122-2, along with various other components or parts of the UAS 100, and assembled to form the UAS 100 as described herein according to various embodiments of the present invention.

[0032] It will be appreciated by a person skilled in the art that the terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0033] Any reference to an element or a feature herein using a designation such as “first”, “second” and so forth does not limit the quantity or order of such elements or features, unless stated or the context requires otherwise For example, such designations may be used herein as a convenient way of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not necessarily mean that only two elements can be employed, or that the first element must precede the second element, unless stated or the context requires otherwise. In addition, a phrase referring to “at least one of’ a list of items refers to any single item therein or any combination of two or more items therein.

[0034] In order that the present invention may be readily understood and put into practical effect, various example embodiments of the present invention will be described hereinafter by way of examples only and not limitations. It will be appreciated by a person skilled in the art that the present invention may, however, be embodied in various different forms orconfigurations and should not be construed as limited to the example embodiments set forth hereinafter. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0035] Tn particular, for better understanding of the present invention and without limitation or loss of generality, various example embodiments of the present invention will now be described with respect to an UAS for overhead drilling on an elevated wooden structure (e.g., natural or built / man-made structure) for performing resistography for wooden structure inspection for clarity and conciseness. It will be understood by a person skilled in the art that the drilling system is not limited to resistography applications, and may be applied various tasks or applications as desired or as appropriate where overhead drilling is required to be performed on an elevated structure at elevated heights, without going beyond the scope of the present invention.

[0036] As discussed in the background, traditional practices for performing drilling at elevated heights do not only present safety hazards for human operators but are also inefficient with respect to time and costs. In recent years, the advancement of technologies has presented an array of opportunities for robotics to revolutionize traditional practices. In this regard, robotic solutions have the potential to tackle various problems, including improving productivity, optimizing resource management and minimizing workplace hazards. In particular, the field of aerial robotics, and more particularly unmanned aerial systems (UAS), has undergone significant advancements due to the increased accessibility, miniaturization, and affordability of electronics; transitioning from theoretical frameworks and research prototypes to commercially applicable products. Modern UAS are able to carry out more sophisticated and complex tasks on behalf of humans, especially for jobs at elevated heights. In this regard, to overcome, or at least ameliorate, one or more deficiencies in conventional drilling systems or practices in resistography for wooden structure inspection, various example embodiments of the present invention provide a UAS configured for elevated remote drilling on an elevated wooden structure, that improves human safety (e.g., human safety risk-free resistography) and efficiency with respect to time and costs (e g., improving productivity).

[0037] FIG. 3 illustrates an example UAS 300 for overhead drilling on an elevated wooden structure, according to various example embodiments of the present invention. FIG 3 also illustrates example applications of the UAS 300 being employed for overhead drilling on an overhanging tree branch and a wooden beam structure for wooden structure inspection,according to various example embodiments of the present invention, compared with conventional resistography practices.

[0038] To check the health of the wooden structures at an elevation, there are two forms of wood health inspection, namely, non-invasive with visual inspection and invasive with resistography There have been prior works on tree health diagnosis via visual inspection of tree cavities. Although this form of tree health inspection is effective, it is heavily reliant on the presence of tree cavities which are uncommon and size-dependent. A more effective form is resistography which requires the task of drilling (e.g., micro-drilling) into the wooden structure to check for the presence of cavities that are located within the material, such as due to internal decay. In this regard, to conduct resistography on an elevated or high structure, various example embodiments provide an UAS that is able to perch itself onto the elevated structure of interest and conduct overhead drilling operation thereon effectively.

[0039] Regarding perching mechanisms, unmanned aerial (UA) perching can be categorized into two distinct approaches, namely, top-down (conventional) or bottom-up (overhead) approaches. The top-down approach, inspired by avians and insects, involves emulating their ability to land and rest on a perch after a flight, allowing for the UAS to maintain a low-to-no motor thrust. Conversely, the bottom-up approach involves the UAS perching itself onto, for example, a ceiling structure, akin to the perching behavior observed in bats, to exploit the ceiling effect to maintain optimal motor thrust in the perched state. However, various example embodiments found that there is still a research gap in areas of the gripping mechanics of aerial robots that employ bottom-up approaches for enabling effective overhead drilling operation. In this regard, to enable the overhead drilling operation to be performed in an effective manner, and more particularly, for enhancing stability in overhead drilling, various example embodiments seek to provide a UAS having the ability to grasp onto overhead structures (e.g., beam structures orbranches) effectively for overhead drilling while maintaining an optimal thrust proportional to the feed (or normal) force. In various example embodiments, the perching mechanism (e.g., corresponding to the first and second gripper mechanisms 120- 1, 120-2 described hereinbefore according to various embodiments of the present invention) is designed to passively tighten its grasp with increased feed force, or upward thrust delivered by the motors of the UAS. As a result, the perching mechanism is able to prevent counter-torque reaction due to the spinning of the drill bit during the drilling operation, essentially improving the axial thrust forces and providing stabilization in overhead drilling.

[0040] Regarding the drilling operation, the UAS must be able to conduct remote drilling. During the drilling process, it is necessary to exert a feed force onto the rotating drill bit in order to penetrate into the material of the elevated structure. Depending on the method of perching, the feed force that acts on the onboard drill can either be applied by its own body weight (conventional top-down perching approach) or by applied thrust (bottom-up (or overhead) perching approach). While the feed force may be directly proportional to the cutting force of the drill, a larger cutting force would require a higher torque motor. This conventionally leads to a larger drill and hence, a larger UAS platform. In various example embodiments, the UAS 300 is configured for overhead drilling with an overhead perching mechanism, which has been found to achieve a range of feed force. In this regard, various example embodiments consider the UAS’s all-up weight (AUW) to reserve sufficient additional thrust to boost the feed force. In various example embodiments, to further enhance the drilling operation to be performed in an effective manner, the UAS 300 is configured to utilize a multimodal tether system 360 that incorporates a flexible shaft connected to an onboard drill bit 330. Accordingly, the drill bit 330 is powered by a ground-based, high-torque motor 380 via the multimodal tether system 360. The flexible shaft allows for the effective transmission of torque (mechanical power) along an irregular path. Flexible shafts have been extensively utilized in various applications (e.g., soft robotics manipulation and surgical applications) and are known in the art, and thus need not be described herein for clarity and conciseness. To maximize the efficiency of the UAS 300, the multimodal tether system 360 is configured to supply electrical power for powering the UAS 300 and transfer mechanical power (mechanical torque) for operating the drill bit 330.

[0041] Accordingly, various example embodiments provide a UAS 300 having integrated therein a drilling system capable of overhead perching for overhead drilling on an elevated wooden structure for resistography applications In this regard, various example embodiments address power transmission and feed force aspects for elevated drilling scenarios with an overhead gripper mechanism (e g., overhead prismatic gripper) that allows the UAS 300 to hang from the elevated wooden structure (e g., overhead wooden beams or branches). In particular, various example embodiments of the present invention design and develop an effective gripper mechanism 320 (e g., a prismatic gripper end-effector mechanism) for overhead perching and locomotion on an elevated structure (e g., capable of both flat surfaces and beam structures or branches)

[0042] The UAS 300 for overhead drilling on an elevated wooden structure for wood health inspection will now be described in further detail according to various example embodimentsof the present invention, as well as the modelling for the overhead gripper mechanism 320 and the development of the UAS optimized approach. Detailed insights into the mechanical versatility and capability of the gripper mechanism 320 designed specifically to be capable of accommodating drilling on both flat-surfaces (e.g., ceilings) and overhead beams or branches will be described according to various example embodiments of the present invention.

[0043] For illustration purpose, FIG. 4 depicts schematic drawings of a side view of the UAS 300 according to various example embodiments of the present invention at different operational states or phases for an example elevated wooden beam structure, namely, an approaching state (whereby the depressible protruding engagement (or trigger) members are at an extended state, the perching arms (or gripping arms) are at an open state and the drill bit is at a base state), a gripping state (whereby the depressible protruding engagement members are at a depressed state, the perching arms are at a gripping state and the drill bit is at the base state) and a drilling state (whereby the depressible protruding engagement members are at the depressed state, the perching arms are at the gripping state and the drill bit is at an elevated state).

[0044] FIG. 5A depicts a schematic drawing of a side view of the UAS 300 according to various example embodiments ofthe present invention at the open state. FIGs. 5B and 5C depict schematic drawings of a side view of a section (enclosed by a dashed box in FIG. 4) ofthe UAS 300 according to various example embodiments of the present invention at the gripping state for two example elevated wooden structures, namely, an example planar (or flat) wooden structure (FIG. 5B) and an example wooden beam (FIG. 5C).

[0045] The UAS 300 comprises: a body frame 310 (e.g., the main aerial robot body); a first gripper mechanism (or a first gripper system) 320 arranged at a first portion (e.g., at a first side or edge portion) of the body frame 310; a second gripper mechanism (or a second gripper system) arranged at a second portion (e.g., at a second side or edge portion) of the body frame 310 (e.g., the first and second portions may be at opposite sides of the body frame 310) (the second gripper mechanism is not shown in FIGs. 4 and 5A to 5C since they are side views); and a drill bit 330 arranged at a third portion (e.g., at a middle or central portion) of the body frame 310 and is operable for overhead drilling. The third portion is located in between (e.g., middle) the first and second portions of the body frame 310. Although cannot be seen in FIGs. 4 and 5B to 5C since they are side views, but can be seen in FIG. 3, the UAS 300 further comprises thrust units 340 affixed to the body frame 410 for generating thrust to support a flight of the UAS 300 In particular, the first and second gripper mechanisms each comprises a pair ofperching arms 322 and a depressible protruding engagement (or trigger) member 324 coupled to the pair of perching arms 322 via a mechanical linkage 326. The mechanical linkage 326 is configured to adjust the pair of perching arms 322 between an open state and a gripping state (e.g., FIGs. 5B and 5C illustrate the gripping state) when the depressible protruding engagement member 324 is adjusted between an extended state (e.g., fully extended state) and a depressed state (e.g., fully depressed state) (FIGs. 5B and 5C illustrate the depressed state). In particular, the depressible protruding engagement member 324 is configured to depress from the extended state to the depressed state when the depressible protruding engagement member 324 is depressed (or engaged) against a surface of the elevated structure via an applied upward force towards the elevated structure from the thrust generated by the thrust units 340 for adjusting the pair of perching arms 322 to the gripping state for overhead perching of the UAS 300 onto the elevated structure, such as illustrated in FIGs. 4, 5A and 5B.

[0046] Accordingly, in various example embodiments, passive gripper mechanisms (the first and second gripper mechanisms) 320 are provided. As shown in FIGs. 5A to 5C, each gripper mechanism 320 comprises two perching arms 322 (e.g., each having a prismatic structure) mechanically coupled with a passive depressible protruding engagement member 324 (e.g., comprising a trigger pad). Two individually spring-loaded prismatic shafts 328 (e.g., configured or housed within the leg members 350 of the UAS 300) may be mechanically coupled with the gripper mechanism 320. A spring member 332 (“Spring 3”) within the gripper mechanism 320 coupled to the depressible protruding engagement member 324 is configured to have a lower spring constant compared with the spring members 334 (“Springs 1 and 2”) respectively coupled to the two individually spring-loaded prismatic shafts 328. Therefore, when the UAS 300 approaches the target structure or object, the trigger pad of the passive depressible protruding engagement member 324 engages the target structure first and compresses the spring member 332 (“Spring 3”). This compression causes the perching arms 322 to close and either grip (e.g., they engage a beam structure) or flatten (if they engage a flat surface) depending on the target structure. Subsequently, spring members 334 (“Springs 1 and 2”) compress further with an increase in upward thrust force. In addition, the gripping force of the gripper mechanism 320 is proportional to the thrust force; as the thrust force increases, the gripping force becomes stronger. In this manner, the perching arms 322 provide or enhance impact absorption and stability when the UAS 300 is in a perched state (e.g., the gripping or drilling state), as well as to enable the application of a range of drill feed forces. In this regard, various example embodiments optimize the drill force by studying the forces that act on theUAS 300. In the perched state, the UAS 300 experiences the ceiling effect, where the proximity to the ceiling results in an increase in upward thrust. Exploiting this effect, according to various example embodiments of the present invention, the induced upward thrust acts as a beneficial additional feed force for the UAS 300. Consequently, the perching arms 322 also serve the purpose of acting as supplementary cushions, mitigating the impact on the UAS 300 caused by the ceiling effect. As shown in FIG. 6, the drill feed force f drub forces that act in the positive z-axis direction (z+), may be given by: for beamsfor ceiling ’(Equation 1) where Ftis the thrust force, Fceis the ceiling effect, Fsis the spring force (based on ksshown in FIG. 6), and F0Sis the gripper spring force (based on kgsshown in FIG. 6).100471 Regarding ceiling drilling, as the UAS 300 approaches the ceiling, the ceiling effect becomes prominent. This phenomenon is beneficial for the UAS 300 as any additional z+force will aid in driving the total drill feed force, Fdri;;. For example, the ceiling effect force may be given by:(Equation 2) such that,(Equation 3) where p is the air density, A is the cross-sectional area of the propeller disc (7rrp2rop) such that rpropis the radius of the propellers, cr0 1are the dimensionless coefficients for non- axisymmetric flow and wake re-circulation respectively, v, is the input velocity to the z-th motor, and 8 is the propeller radius to ceiling ratio given by:(Equation 4) 100481 For any additional thrust force acting on the UAS body in the perched state (zero change in spring compression length Azs= 0):(Equation 5) where i is the respective motor on the UAS, k is an appropriately-dimensioned constant, m is the angular velocity of the motors and mg is the weight of the UAS.

[0049] The angular velocity can be obtained through the brushless motor electrical equation, given by:(Equation 6) where R is the electrical resistance of the motor’s winding and Keis the back EMF constant.

[0050] Once the perching anus 322 are loaded (Azs> 0), the spring force Fsis active.2 Fs= - S ksLzs,(Equation 7) Accordingly, in ceiling drilling mode, the UAS 300 (or more specifically, the protruding engagement members 324) engages with a planar surface of the ceiling that is larger than the length of each pair of perching arms 322. In this configuration, the pair of perching arms 322, assisted by the corresponding gripper spring 332, are pressed against the surface of the ceiling and are activated to establish contact. Upon activation, the perching arms 322 serve as a mechanical interface to provide anti-torque and anti-slip stabilization, thereby enabling the onboard drill bit 330 to penetrate the material of the ceiling effectively with additional thrust provided by the UAS 300 at the drilling state.

[0051] Regarding beam drilling (or branch drilling), the approach of beam drilling shares similarities with ceiling drilling, with the main difference being that the target surface in beam drilling is significantly narrower than the length of the active gripper, lgripper-Wbeam — lgripper(Equation 8)

[0052] The top section of each gripper mechanism 320 comprises the perching anus 322depressible protruding engagement member). When the UAS 300 perches against a beam, a downward force, Fflsis applied onto the gripper spring 332 which activates and passively depresses the depressible protruding engagement member 324, which in turn adjusts or closes the perching arms 322 to the gripping state for overhead perching of the UAS 300 onto thebeam, thereby grasping onto the beam. This grasping action, due to the application of a load, is analogous to a loaded torsional spring where the spring rate is governed by:(Equation 9) Accordingly, in the beam drilling mode, the UAS 300 targets a surface area that is smaller than the length of each pair of perching arms 322. In this scenario, the beam compresses the gripper spring 332 (or more specifically, the protruding engagement members 324) directly, causing the pair of perching arms 322 to close and wrap around the beam. This gripping action secures the UAS 300 to the beam, providing anti -torque and anti-slip stability during the drilling operation performed by the drill bit 330.

[0053] Accordingly, in various example embodiments, for each of the first and second gripper mechanisms 320, the mechanical linkage 326 thereof is configured to adjust the pair of perching arms 322 to the gripping state by adjusting the pair of perching arms 322 to press against the elevated structure. In various example embodiments, for each of the first and second gripper mechanisms 320, the mechanical linkage 326 thereof comprises a first pivot joint and a second pivot joint respectively coupled to a first perching arm and a second perching arm of the pair of perching anns 322. In this regard, the mechanical linkage 326 thereof is configured to adjust the pair of perching arms 322 to the gripping state via the first and second pivot joints to respectively adjust the first and second perching arms 322 to press against the elevated structure.

[0054] In various example embodiments, the drill bit 330 is adjustable (or movable) (relative to the first and second gripper mechanisms 320) between a base state and an elevated state. In this regard, the elevated state is configured for penetrating the drill bit into the elevated structure.

[0055] In various example embodiments, for each of the first and second gripper mechanisms 320, the depressible protruding engagement member 324 thereof is coupled to a first spring member 332 (corresponding to kgsshown in FIG. 6) such that the depressible protruding engagement member 324 is depressible from the extended state to the depressed state when the depressible protruding engagement member 324 is depressed (or engaged) against the surface of the elevated structure via the applied upward force being sufficient to overcome a spring force of the first spring member 332 Furthermore, the depressible protrudingengagement member 324 is restorable from the depressed state to the extended state in the absence of the above-mentioned applied upward force sufficient to overcome the spring force of the first spring member 332.

[0056] In various example embodiments, the drill bit 330 is adjustable (relative to the first and second gripper mechanisms 320) between the base state and the elevated state by one or more second spring members 334 (corresponding to ksshown in FIG. 6) such that the drill bit 330 is adjustable (or movable) (relative to the first and second gripper mechanisms 320) from the base state to the elevated state when the applied upward force is sufficient to further overcome a spring force of the one or more second spring members 334. Furthermore, the drill bit 330 is restorable from the elevated state to the base state in the absence of the above- mentioned applied upward force sufficient to further overcome the spring force of the one or more second spring members 334.

[0057] In various example embodiments, the UAS 300 further comprises a platform 370 adjustable relative to the first and second gripper mechanisms 320 between a base state and an elevated state by the one or more second spring members 334. In this regard, the drill bit 330 is supported by the platform 370 (moves with the platform 370) such that the drill bit 330 is adjustable from the base state to the elevated state, via the platform 370, when the applied upward force is sufficient to further overcome the spring force of the one or more second spring members 334. In addition, the drill bit 330 is restorable from the elevated state to the base state, via the platform 370, in the absence of the above-mentioned applied upward force sufficient to further overcome the spring force of the one or more second spring members 334 In various embodiments, the one or more second spring members 334 are configured or housed within one or more leg members 350, respectively, of the UAS 300.

[0058] In various example embodiments, the UAS 300 utilizes or comprises a multi-modal tether system 360 that facilitates the integration of a flexible drill shaft (or flexible shaft cable) as illustrated in FIG. 7A. This obviates the need for the UAS 300 to bear the weight of a drill motor. Consequently, the drill motor 380 can be positioned on the ground, thereby rendering the UAS drill motor agnostic A proportional relationship exists between the operational torque and radius; as the radius decreases, the shaft’s capability to withstand torque diminishes. Unlike the conventional resistograph, in situations involving more pronounced bends, the internal wires experience heightened contact forces, leading to escalated levels of friction, heat generated, and mechanical strain. Nevertheless, in various example embodiments, to facilitatethe optimal efficiency in the transmission of mechanical power, the minimal bending radiusrshaft, for such a drill shaft may be defined by:(Equation 10) where xshaftrepresents the forward distance of the flexible shaft 360, from the drill motor 380, carried by the UAS 300; yShaft is the vertical distance between the drill motor 380 and UAS 300.

[0059] Various example embodiments note that a flexible shaft may encounter friction- related problems due to its dual structure involving an outer tube and an inner shaft. Firstly, the inner wall of the outer tube may wear away easily when the inner shaft rotates at high speed. Secondly, there is a greater loss of torque as friction increases due to heightened contact between the inner shaft and the outer tube, and this problem can worsen when the cable is coiled. In this regard, according to various example embodiments of the present invention as illustrated in FIG. 7B, the flexible shaft cable 360 is configured to include tension springs 704, which function as a protective sleeve between the outer tube 702 and the inner shaft 706 to address the above-mentioned potential problems. These tension springs 704 effectively mitigate wear on the inner wall of the outer tube 702 and the formation of sharp bends when the flexible shaft cable 360 is coiled. In addition, lubricant may be applied between the inner shaft 706 and the tension springs 704 to reduce friction significantly. To keep the flexible shaft cable 360 as light as possible, a thin polyolefin outer tubing may be utilized to encase the flexible shaft cable 360.

[0060] Regarding drill resistance, the kinematic forces that act on the drill bit 330 can be depicted by a free-body diagram (FBD) as illustrated in FIG. 8. The conventional equation for drill resistance can be described by the summation of two components: one arising from material deformation and the other stemming from frictional interactions between the drill bit 330 and the material:(Equation 11)

[0061] To emulate a conventional resistograph, it is necessary to show that the drill resistance measurement (DRM) can be achieved. The DRM measures the force required to drill a hole at constant rotation (RPM) and lateral feed rate (mm / min). To validate the feed force forthe drill gearbox, it is quintessential to quantify the amount of depth of cut per revolution dc, which may be given by:(@ input Parin')(Equation 12) where / ? is the feed rate, mm / min, and RPM is the revolution per minute of the drill bit. With Equation 12, the area of cut is:Ac— wdc(Equation 13) where w is the width of the drill bit. The localized compressive stress beneath the wear-flat in the direction of drill a is given by the maximum pressure Pa over the ratio of the depth below the surface, z to contact radius a, as follows:(Equation 14c) E2and v2are the young’s modulus and poisson’s ratio for the high carbon steel drill bit and the wood material respectively. The ratio of the normal and tangential components C is the back rake angle of the cutter shown in FIG. 8, such that:£ = tan(0)(Equation 15) where 6 is the back rake angle of the cutter. Fc, Fnc, Ftcare the cutting force, normal cutting force and tangential cutting force, respectively.

[0062] Referencing Equations 11-15, for the case of drill bits commonly used in conservation (drill bits with just two cutters), the radius-independent drilling resistance, is defined by:W t, £RRd drriiiltlWs J = —r= 2RPM + 2o-A(Equation 16)where the E is the internal specific energy of the drilled material when considering the energy required to remove a certain volume of material during the drilling process, o is the local compressive stress beneath the wear-flat and A represents the length of the wear-flat.

[0063] FIG. 9 depicts a table (Table I) of drill resistance variables. In particular, Table I provides a complete set of key variables for the drill bit used and a range of operational perimeters based on optimal flexible shaft transmission efficiency for computing drill resistance in resistography, which are used for realistic mock-up experiments.|0064| In various example embodiments, the resistography drilling is performed by the UAS 300, while measurement data processing for resistography may be performed by a ground- based computer. For example, during drilling operation, drill-related parameters, such as penetration depth and rotational speed, along with thrust data from the flight controller of the UAS 300, may be transmitted (e.g., based on wired or wireless communication, e.g., via a communication cable within the tether system 360) to the ground-based computer. This measurement data may then be used to generate and plot the resistograph profile for assessing a health of the wooden structure in a manner known to a person skilled in the art and thus need not be described herein for clarity and conciseness.

[0065] In various example embodiments, for each of the first and second gripper mechanisms 320, each perching arm of the pair of perching arms 322 thereof has a prismatic structure. In various example embodiments, the prismatic structure comprises an outer shell and a plurality of cross beams extending between opposing sides of the outer shell and spaced apart along the outer shell. In this regard, the plurality of cross beams is compressible (e.g., flexible) to provide impact absorption. In various example embodiments, each perching arm 322 is configured to be flexible for conforming to a shape of the surface of the elevated structure when pressed against the elevated structure at the gripping state. In various example embodiments, the above-mentioned each perching arm 322 is made of a material (e.g., thermoplastic material, such as PLA (polylactic acid) thermoplastic material) that is flexible for conforming to the shape of the surface of the elevated structure when pressed against the elevated structure at the gripping state. Accordingly, for example, the perching arms 322 may also be referred to as fin ray grippers.

[0066] In various example embodiments, each perching arm 322 comprises an outer shell and hinged cross beams. For example, each perching arm 322 may be entirely 3D printed, such as using PLA to the material’s ability to remain flexible while having some levels of rigidity to maintain structural integrity. In various example embodiments, to obtain the desiredfunctionality, the outer shell and cross beams may be kept at a minimal thickness of 0.5mm and 0.8mm respectively. By way of an illustrative example only and without limitation, the perching arm 322 may have a fixed base width W = 32.5mm, height H = 10mm, and length L = 103mm to keep the design compact while accommodating the dimensions of intended gripping objects. Furthermore, the outward-facing side of the outer shell may adopt the curvature of a minor arc (curved shell), such as to better conform to flat surfaces. Accordingly, in various example embodiments, a side of the prismatic structure arranged for pressing against the elevated structure at the gripping state is curved.

[0067] In various example embodiments, to maximize the contact with the target surfaces as illustrated in FIGs 10A to 10D, the perching arm design is optimized. In various example embodiments, three parameters with variables, arc angle [ Z AOB = 5, 7.5, 10]°, spacing between cross beams [S = 11, 16.5, 22] mm, and incline angle of cross beam [a = -10, -5, 0, 5, 10]° may be selected for optimization in sequence, such as using Solidworks Simulation. In a simulation performed, the perching arm 322 underwent isolated evaluation and FIGs. 10A to 10D illustrate the maximum displacement of the perching arm 322 when interacting with flat surfaces and gripping objects.

[0068] The optimization starts with arc angle ZAOB, which is defined by two stationary points A and B, and a variable origin O. Through observation when ZAOB is < 5° the gripper exhibits the same behaviour as V-shaped grippers. It cannot conform to a flat surface due to the inward bending of the tip pushing the body away from the flat surface. By prioritizing the displacement during the gripping of objects, an arc angle of 7.5° was adopted. Subsequently, as the spacing decreases, the number of cross beams increases, and the displacement is reduced for both scenarios. Hence, a spacing of 22 mm was adopted. Lastly, five inclined angles ranging from negative 10° to positive 10° were evaluated. As the incline angle transitions from negative to positive, the displacement of the gripper reduces while gripping the object, whereas the opposite trend is observed when exerting force against a flat surface. Therefore, to achieve a balanced design and performance, the median angle of 0° may be adopted according to various example embodiments of the present invention.

[0069] Various experiments conducted will now be discussed.

[0070] In relation to mechanical power transmission efficiency, to ensure that the tethered drill configuration is operating as efficiently as an onboard drill, a series of drill motor configurations for the flexible shaft were conducted on the RPM transmission: Straightened- unelevated (control), Coiled-unelevated, and Straightened-Elevated (ideal). The efficiency plotis illustrated in FIG. 11. From this plot, the respective efficiency of the three configurations is compared to the input drill motor’ s RPM. For the ideal case, the Straightened-Elevated obtained about 95.72% efficiency as long as the bend-radius in Equation 10 is met while the Straightened and Coiled are at 98.49% and 83.41% respectively.

[0071] Two bench-top experiments were conducted to evaluate the physical performance and limitations of the gripper mechanism 320, as illustrated in FIG. 12, namely, the grasping of beams with various diameters, and a plot characterizing the gripper's force response. As can be seen from FIG. 12, the gripper demonstrated its ability to confonn effectively to beams of different diameters when subjected to an applied force of 800 grams on the trigger pad (i.e., the above-mentioned protruding engagement member) 324. This force was delivered using calibrated weights to simulate the loading conditions experienced during in-flight perching by the UAS in drilling operations The plot in FIG. 12 presents the relationship between the gripping force and the applied input force. Four different input forces were applied to the gripper’s trigger pad 324 using weights, and the corresponding gripping forces were measured using load cells. The results indicate that the gripper mechanism 320 achieves an approximate efficiency of 40% in converting input force into gripping force. Furthermore, a force of approximately 450 grams is required to fully compress the mechanism under no-load conditions. These results validate the gripper’s effectiveness in delivering stable engagement with the target surface, contributing to enhanced stability during drilling tasks.

[0072] FIG. 13 depicts a schematic drawing of an onboard drill assembly 1300 comprising a drill bit 330, a drill chuck 1302, bearing 1304 and a planetary gear box 1306, according to various example embodiments of the present invention. As described hereinbefore, the onboard drill assembly 1300 is mechanically powered by a high-torque motor 380 located on the ground. The ground motor may operate at a high RPM, transmitting torque through the flexible shaft cable 360 and is coupled to the planetary gear box 1306 of the onboard drill assembly 1300. The planetary gear box 1306 helps to reduce the RPM and amplifies the torque output required for driving the drill bit 330. Inside the gearbox, the sun gear may be connected to the flexible shaft 360, which subsequently drives the drill bit 330 (e.g., 2cm long) via the output from the carrier. For example, the RPM is then reduced by the four planet gears with a ratio of 4: 1, ensuring that the drill operates within a range of 2000 to 3000 RPM, similar to that of a resistograph To minimize vibration and ensure straight rotation of the drill bit, a bearing is fitted on the carrier. By way of an illustrative example only and without limitation, the gearbox may have a dimension of 46mm x 30mm and may be 3D printed using Onyx material tomaintain a lightweight design. In this manner, for example, the onboard drill assembly 1300 may only way a total of 65 grams.

[0073] In relation to in-flight drilling, realistic mock-up drilling experiments of the respective beam and ceiling structures for real-world applications are conducted. The mock-up comprises a 10mm wooden structure for overhead-perch drilling. The UAS 300 is flown manually to perch onto the target surface when the gripper mechanism 320 presses on the outline of the target surface. Once it is perched, additional thrust is provided to allow the drill bit 330 to cut into the material as shown in FIGs. 14A-14D (for overhead drilling of a beam structure) and FIGs. 15A-15D (for overhead drilling of a ceiling structure). From FIG. 16, the resistance drops once the drill bit 330 penetrates across the material thickness, simulating the presence of a cavity within the material. The gripper mechanism 320 also provides anti-torque capabilities and allows the UAS 300 to concentrate the drill bit 330 into the material of the beam.

[0074] As an example configuration, the body frame (or UAS frame) 310 may be designed to resemble a cage that surrounds the onboard components (e g., distance sensor, RPM sensor, flight controller, thrust units and so on) and may be custom-made with carbon fibre. Two passive prismatic gripper mechanisms 320 are mounted at the front and rear of the UAS 300. These gripper mechanisms 320 help balance the UAS 300 and distribute the load evenly during perching manoeuvres. The onboard drill assembly may be positioned at the centre of the UAS 300 for ease of aiming and to allow the multi-modal tether cable 360 to drop down from the center of the UAS 300. The onboard electrical components may be distributed evenly across the body frame 310 based on their weight to configure the UAS’ s centre of gravity at the center of the UAS 300. The thrust units 340 may each comprise a propeller and a motor configured to rotate or drive the propeller. In this regard, the motor and the propeller may be mounted in a push configuration for better efficiency.

[0075] Accordingly, the UAS 300 for remote elevated wood structure cavity inspection has been provided according to various example embodiments, such as based on a caged-design quadcopter UAS equipped with a prismatic gripper mechanism for overhead drilling. In this regard, the UAS 300 is advantageously able to perch onto the target surface, align the drill bit to the surface, and detect possible cavities within a wooden structure through drilling resistance.

[0076] While embodiments of the invention have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope ofthe invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

CLAIMS1. An unmanned aerial system for overhead drilling on an elevated structure, the unmanned aerial system comprising: a body frame; a first gripper mechanism arranged at a first portion of the body frame; a second gripper mechanism arranged at a second portion of the body frame; a drill bit arranged at a third portion of the body frame and is operable for overhead drilling, the third portion located in between the first and second portions of the body frame; and one or more thrust units affixed to the body frame for generating thrust to support a flight of the unmanned aerial system, wherein the first and second gripper mechanisms each comprises a pair of perching arm members and a depressible protruding engagement member coupled to the pair of perching arm members via a mechanical linkage, the mechanical linkage is configured to adjust the pair of perching arm members between an open state and a gripping state when the depressible protruding engagement member is adjusted between an extended state and a depressed state, and the depressible protruding engagement member is configured to depress from the extended state to the depressed state when the depressible protruding engagement member is depressed against a surface of the elevated structure via an applied upward force towards the elevated structure from the thrust generated by the one or more thrust units for adjusting the pair of perching arm members to the gripping state for overhead perching of the unmanned aerial system onto the elevated structure.

2. The unmanned aerial system according to claim 1, wherein for each of the first and second gripper mechanisms, the mechanical linkage thereof is configured to adjust the pair of perching arm members to the gripping state by adjusting the pair of perching arm members to press against the elevated structure.

3. The unmanned aerial system according to claim 2, wherein for each of the first and second gripper mechanisms, the mechanical linkage thereof comprises a first pivot joint and a second pivot joint respectively coupled to a first perching arm member and a second perching arm member of the pair of perching arm members, and the mechanical linkage thereof isconfigured to adjust the pair of perching arm members to the gripping state via the first and second pivot joints to respectively adjust the first and second perching arm members to press against the elevated structure.

4. The unmanned aerial system according to any one of claims 1 to 3, wherein for each of the first and second gripper mechanisms, each perching arm member of the pair of perching arm members thereof has a prismatic structure.

5. The unmanned aerial system according to claim 4, wherein the prismatic structure comprises an outer shell and a plurality of cross beams extending between opposing sides of the outer shell and spaced apart along the outer shell, and the plurality of cross beams is compressible to provide impact absorption.

6. The unmanned aerial system according to claim 4 or 5, wherein a side of the prismatic structure arranged for pressing against the elevated structure at the gripping state is curved.

7. The unmanned aerial system according to any one of claims 4 to 6, wherein said each perching arm member is configured to be flexible for conforming to a shape of the surface of the elevated structure when pressed against the elevated structure at the gripping state.

8. The unmanned aerial system according to claim 7, wherein said each perching arm member is made of a material that is flexible for conforming to the shape of the surface of the elevated structure when pressed against the elevated structure at the gripping state.

9. The unmanned aerial system according to claim 8, wherein the drill bit is adjustable between a base state and an elevated state, the elevated state being configured for penetrating the drill bit into the elevated structure.

10. The unmanned aerial system according to claim 9, wherein for each of the first and second gripper mechanisms, the depressible protruding engagement member thereof is coupled to a first spring member such that the depressible protruding engagement member is depressible from the extended state to the depressed state when the depressible protruding engagement member is depressed against the surface of theelevated structure via the applied upward force being sufficient to overcome a spring force of the first spring member, and the depressible protruding engagement member is restorable from the depressed state to the extended state in the absence of said applied upward force sufficient to overcome the spring force of the first spring member.

11. The unmanned aerial system according to claim 10, wherein the drill bit is adjustable between the base state and the elevated state by one or more second spring members such that the drill bit is adjustable from the base state to the elevated state when the applied upward force is sufficient to further overcome a spring force of the one or more second spring members, and the drill bit is restorable from the elevated state to the base state in the absence of said applied upward force sufficient to further overcome the spring force of the one or more second spring members.

12. The unmanned aerial system according to claim 11, further comprising a platform adjustable relative to the first and second gripper mechanisms between a base state and an elevated state by the one or more second spring members, wherein the drill bit is supported by the platform such that the drill bit is adjustable from the base state to the elevated state, via the platform, when the applied upward force is sufficient to further overcome the spring force of the one or more second spring members, and the drill bit is restorable from the elevated state to the base state, via the platform, in the absence of said applied upward force sufficient to further overcome the spring force of the one or more second spring members.

13. The unmanned aerial system according to claim 11 or 12, wherein the one or more second spring members are configured within one or more leg members, respectively, of the unmanned aerial system.

14. The unmanned aerial system according to any one of claims 1 to 13, further comprising a tether system comprising a flexible shaft comprising a first end portion coupled to a ground- based drill motor and a second end portion coupled to the drill bit, wherein the drill motor is configured to transfer mechanical power to the drill bit via the flexible shaft.

15. The unmanned aerial system according to claim 14, wherein the tether system further comprises an electrical cable for transmitting electrical power to the unmanned aerial system.

16. The unmanned aerial system according to claim 14 or 15, wherein the second end portion of the flexible shaft is coupled to the drill bit via a planetary gearbox.

17. The unmanned aerial system according to any one of claims 1 to 16, wherein the elevated structure is an elevated wooden structure, and the unmanned aerial system is configured to perform resistography for wooden structure inspection of the elevated wooden structure.

18. The unmanned aerial system according to claim 17, wherein the elevated wooden structure has a planar surface, is a beam structure or is a branch which the unmanned aerial system is configured to overhead perch onto at the gripping state.

19. A method of forming the unmanned aerial system according to any one of claims 1 to 18.

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