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STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefore. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to excavation tools, as exemplified by a conventional rotor tiller; and more particularly to a remote excavation tool for robotically removing soil, where the tool has a relatively low mass that efficiently utilizes low power and high rotation to excavate, where the tool is fitted to a remotely controlled robotic platform. 
     2. Background 
     Robotic platforms nominally have a robotic arm that can be remotely controlled. The platform can include lights, transmitted video, GPS positioning, and movement of the robotic arm, which often includes a gripping device. Depending on the mission, the robotic platform can also include sensors; one or more propulsion means including continuous tracks, wheels, propellers, fixed wings, jets and rockets. Military robots can also have weapons including projectiles and may be fitted to carry items that are heavy and/or dangerous, such as unexploded ordnance. 
     Another example of a robotic platform is the MTRS platform (Man Transportable Robotic System). The robotic device can be used to dispense detonation chord. 
     Tilling implements use rotating tines to break up soil. Rotation is relatively slow, often approximately 250 rpm. The slow rotation is usually clockwise, thus enabling an operator to keep pace with the tiller, while not needing to have to pull the tiller forward. Even home garden tillers are purposely heavy so that tines generate enough force to penetrate and loosen the soil. Conventional tillers require a large power source to carry its mass. 
     The tine count on conventional tilling implements is relatively low so that the downward and forward force is focused. Slow rotating tines are often sharply curved so that that a greater volume of soil can be churned at a slow rate of rotation. Clockwise rotation tends to move the loosened soil backwards, and a rear plate is usually present to contain the backward movement of the tilled soil. 
     SUMMARY OF THE INVENTION 
     The invention is a tool for remotely excavating soil, where the tool has a low mass and utilizes a low amount of power. The tool may be attached to a robotic platform. An aspect of the invention includes one or more interfacing elements, which enable the low mass high speed rotation tool to be attached to a robotic arm extending from the robotic platform or gripped by a robotic claw on the robotic arm or elsewhere on the robotic platform. The excavation tool, may be remotely controlled through existing electronics on the robotic platform. 
     The tool includes an extension boom and a drive train assembly, where the drive train assembly transmits rotational power from a rotor shaft of a motor to a polygonal shaft. The polygonal shaft rotates tilling elements mounted on the polygonal shaft. The motor has a forward fastening element and it is mounted to the extension boom. Power from the motor is conveyed through the drive train assembly to achieve the desired torque and rpm. The drive train assembly includes a drive shaft and a system of belts and pulleys or a variable mechanical interface or an electrical controller, or a combination thereof. The motor has a rearward mount for attaching the tool to an interface element, where the interface element enables the tool to be connected directly or indirectly to the robotic platform. The motor is nominally powered by a remotely controlled robotic platform. 
     Another aspect of the invention is that the tilling elements include a plurality of tined disks, where each tined disk has a plurality of tines. Each tine has a leading edge and a peripheral edge that are hardened and tapered. A plurality of tines radiate from a plate with a center opening, therein forming the tined disk. A pair of tined disks, where the tines curve toward a common vertical plane, define a couple, where the couple are two fastened disks. The couple functions as a toothed blade. 
     The tined disks are rotated by the polygonal shaft. Viewed from the right side, the polygonal shaft rotates counterclockwise. Tines on the tined disks rotate so they tend to dig deeper, pushing into the soil; which is in contrast to a conventional tilling implement, where the tines are rotated clockwise so as to pull the tilling implement forward. When rotated counterclockwise, the tapered edges of the tines on the disks are leading. 
     Left and right lengths of the polygonal shaft are fitted with multiple couples of tined disks, and between them are rotating round brushes that are mounted on the polygonal shaft. The rotating round brushes push loosened soil forwards and sideways, and a diameter of a brush limits the depth of penetration of the tines. Excavation is more uniform, and less likely to overly strain either the right or the left length of the polygonal shaft. Generally, with the invention, soil is pushed forward, away from the excavation tool and the robotic platform. 
     The apparatus utilizes high speed rpm rotation, on the order of about 1500 rpm+/−100 rpm, in contrast to conventional excavation equipment, which uses comparatively low speed rotation to excavate soil. Recall, that conventional excavation equipment rotates at about 250 rpm. 
     Both the desired cutting depth and feed rate may be adjusted robotically depending on the amount of soil removed and the cutting resistance. 
     The apparatus utilizes a “high cycle, low force” methodology. The low mass of the invented robotic apparatus enables control of an effective cutting depth. In contrast to a conventional a rotor tiller (such as on a garden tiller), where substantially the entire actual weight of the excavating tool is used to push down on the soil—making control of the cutting depth extremely difficult. In further contrast to conventional technology, the amount of force that the inventive tool applies against the ground is largely controlled by its angle relative to the ground and the speed of the robotic platform. Of course the angle that the tool is extending from the robot and the speed of the robot are remotely controllable. 
     An object of the invention is to mitigate vibration and maintain reaction-force symmetry. This objective is achieved based on the following exemplary structure. Assuming each side of the polygonal shaft is fitted with a set of four paired tined disks, where the tines are uniformly staggered and positioned, then the tines are offset about the same number of degrees on both sides of the tool. Also, the symmetry provides that only one left tine and one right tine will hit the ground, if the ground is substantially level. Staggering the tines increases the frequency of impact, and the symmetry nominally transmits a smoother force response. The center holes maintain an exact angle on the polygonal shaft 
     The transmitted cutting force onto the ground with simultaneous contact of two tines with the ground, means less tine area, and therefore a more focused pressure is applied, therein fracturing soil more effectively. The concentration of the force is augmented by the counter-rotation, which causes the remote excavator tool to dig down, once the surface is breached. A balance of depth, forward speed, angle and rate of rotation influence the feed rate of soil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing invention will become readily apparent by referring to the following detailed description and the appended drawings in which: 
         FIG. 1  is an elevated perspective right-side view of an exemplary embodiment of the invented remote excavation tool, wherein the tool is has an interface element that is fastened to the tool&#39;s rearward mount and can be clamped to a robotic arm on a robotic platform; 
         FIG. 2  is a side perspective left-side view of the embodiment shown in  FIG. 1 , wherein the interface element is clamped around a lower portion of the robotic arm; 
         FIG. 3  is a perspective view of another interface element illustrating a claw mounting device, wherein the claw mounting device can be attached to the rearward mount, which the claw on the robotic arm can then grasp to hold the remote excavation tool; 
         FIG. 4  is a perspective partial view of an illustrated robotic arm having a claw, wherein the claw is gripping the claw mounting device illustrated in  FIG. 3  (the tool is not shown); 
         FIG. 5   a  is a perspective view of a first tined disk having tapered leading edges and wherein the four tines curve inward; 
         FIG. 5   b  is a perspective view of a second tined second disk, wherein the tines are a mirror image of the first tined disk, so that when coupled with a first tined disk the tines curve toward the first disk and the tapered edges are similarly on the leading edges; 
         FIG. 6  is a perspective side view as seen from the right side of a full set of tined disks and brushes, wherein the full set of tined disks and brushes are loaded on the polygonal shaft of the embodiment shown in  FIG. 1 ; 
         FIG. 7   a - 7   c  is a plan view as seen from the right side of the tool, wherein the coupled disks are shown in  FIG. 7   a  and  FIG. 7   c , and the brush on the right is shown in  FIG. 7   b;    
         FIG. 8   a - 8   c  is a plan view as seen from the left side of the tool, wherein the coupled disks are shown in  FIG. 8   a  and  FIG. 8   c , and the brush on the left side is shown in  FIG. 8   b;    
         FIG. 9  is an elevated perspective partial view of the invention illustrating a drive train assembly having a first and second belt-and-pulley drive trains, where in both drive trains a driven smaller pulley drives grooved belt which turns a larger pulley, wherein the first and second belt-and-pulley drive trains have a common driveshaft seated in the bearing housing, where an out-board end of the driveshaft has a larger diameter pulley than the inboard pulley in the extension boom, wherein the assembly terminates in a slower turning polygonal shaft projecting from the extension boom; 
         FIG. 10  is a diagrammatic view that illustrates how the tines are staggered; and 
         FIG. 11  (TABLE 1), which contains the performance data for the motor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is a remote excavation tool that enables soil to be excavated using a low power, low mass tool. An exemplary embodiment is illustrated in the following drawings. In  FIG. 1  and  FIG. 9 , the tool  10  includes a drive train assembly and an extension boom  20  where the extension boom has a bearing housing  70 , which supports a driveshaft  22  (see  FIG. 9 ). The driveshaft is common to a first and a second belt-and-pulley drive train  24   a , 24   b  as shown in  FIG. 9 . The belt-and-pulley drive trains  24   a , 24   b  work in combination to increase in torque and decrease in rpm of a polygonal shaft  26 . The polygonal shaft  26  turns the tilling elements  30 . The first drive train derives power from a rotor shaft  51  of a motor  50 . The first belt-and-pulley drive train  24   a  has a first smaller pitch diameter grooved pulley  63 , a first larger pitch diameter grooved pulley  64  on an out-board end  23  of the driveshaft  22 , and a first grooved belt  61  that is tensioned with a first idler roll  65 . The first belt  61  transmits rotational power from the rotor shaft  51  of the motor  50  to the driveshaft  22 . 
     The second belt-and-pulley drive train  24   b  is located within the extension boom  20 , and the drive train  24   b  has a second smaller pitch diameter grooved pulley  66  on an in-board end  25  of the driveshaft  22 , a second larger pitch diameter grooved pulley  67  on the polygonal shaft  26 , and a second belt  68  that is tensioned with a second idler roll  69 . The second belt  68  transmits rotational power from the second smaller diameter pulley  66  to the second larger diameter pulley  67  which drives the polygonal shaft  26 . Taken together, the two drive trains increase torque and decrease the rpm. A nominal rpm range from about 1400 to about 1600 rpm is obtained using the motor described later. 
     The illustrated polygonal shaft  26  is a square bar, and it rotates the tilling elements  30  mounted on the square bar. The motor in the illustrated exemplary embodiment includes a housing  51 . The extension boom  20  is substantially contiguous with the motor housing which provides a forward fastening element  52  whereby the motor is mounted to the extension boom  20 . In an example of the drive train assembly utilizing grooved belts (timing belts), the first belt-and-pulley drive train has a first smaller pulley with a pitch diameter of about 0.637 inches and 10 grooves, and a first larger pulley with a pitch diameter of about 1.4010 inches and 22 grooves, where the rpm is reduced by a factor of about 22/10, or 2.2. The second belt-and-pulley drive train has a second smaller pulley with a pitch diameter of about 0.637 inches and 10 grooves, and a second larger pulley with a pitch diameter of about 1.146 inches and 18 grooves, the rpm is reduced by a factor of about 18/10, or 1.8. Cumulatively, the combined reduction is 1.8*2.2=3.96. 
     The drive train assembly  60  may utilize other means, including a gear box, a variable mechanical interface (i.e., intersecting cones), an electrical controller, or a combination thereof. In the illustrated embodiment, a suitable motor is, in an exemplary embodiment, a product of MIDWEST MOTION PRODUCTS®, and the performance parameters are given in Table 1. The rated speed of the DC motor is about 5700 rpm. The desired rpm for the polygonal shaft is about 1500+/−100 rpm. Based on the calculated reducing of 3.96, then the rpm is about 1439 (5700/3.96=1439 rpm). The illustrated motor  50  has a fan  56  to cool the motor and to maintain a positive air pressure on the extension boom  20 . The motor and the fan also may be used as a dynamic braking device, by altering the electrical power coming from the robotic platform. 
     The motor  50  has a rearward mount  54  for attaching the tool to an interface element  100 , or a variation of the interface element  110  as depicted in  FIG. 3  The interface element enables the tool to be connected directly or indirectly to a robotic platform, such as a Man Transportable Robotic System (MTRS) (see  FIG. 2 ). The motor, and hence the rotation of the tines, may be controlled remotely. Wires  80 , shown diagrammatically, enable the tool  10  to tap into the power (such as, BB2590 batteries) and communication capabilities of the robotic platform to which the tool is attached. Existing robotic platforms, for example a MTRS, have auxiliary connections, and control of the invented tool is enabled by activating an auxiliary switch (not shown). In an exemplary embodiment, the BB2590 batteries have about 207 Wh, a rugged case construction, a high energy density (144 Wh/kg), a wide operating temperature range, and are relatively light weight. 
     Communication with the robotic platform  1  enables remote control of the tool  10 . Capabilities include starting, stopping, and dynamic braking the tilling elements  30  on the tool  10 . Remote auxiliary control maybe largely independent of other robotic platform activities or in concert with them. For example, video feedback from the platform&#39;s camera  6 , provides an operator with a way to observe the excavation, and based on the video the operator can remotely adjust how the tool is being used. 
     The interface element  100  includes an adjustable extension assembly  102  with a pivotal lower collar  108 , and a pivoting strut assembly  104  with a pivotal upper collar  106 . The extension assembly  102  attaches to the rearward mount  54 . The collars  108 , 106  may be disassembled to be positioned, and tightened around the robot arm to secure the attachment. As shown in  FIG. 2  the robotic platform  1  has a jointed arm  2  with a forearm  2   f , an elbow joint  3   a , an arm joint  3   b , an upper-arm  2   u , and a claw  4 . The illustrated robotic platform has right and left track drives  5   r , 5   l . The robot is remotely controlled through a communication antenna  7 . A camera  6  provides video feedback. Electronics and energy sources (i.e., batteries) are protected by a body  9 . Auxiliary power and detonation chord may be pulled by the strain relief  7 . The tilling elements  30  rotate pushing excavated soil forward and to the side. The depth and angle that the excavation tool impinges the ground may be adjusted by changing the angle of the arm  2 , and in particular the upper-arm  2   u  at the arm joint  3   b.    
     A variation of the arm interface element  100  is shown in  FIG. 3  and  FIG. 4 . The interface element  110 , which is a variation, is a claw interface element  110 . The claw interface element  110  includes a pair of parallel elongate plates  112  with holes  114  for fastening to the rearward mount  54 . A rear  117  and upper mid-section  119  of the plates  112  are connected to a first crossed frame  118 . A spacer  115  separates and joins the first crossed frame  118  to a second crossed frame  116 . The thickness of the spacer  115  is selected such that jaws  4   r , 4   l  of the claw may grip the spacer  115 , leaving the first and second crossed frames  118 , 116  to span a gap  4   g  between the jaws of the claw. 
     Returning to  FIG. 1 , in the illustrated embodiment the tilling elements  30 , which include brushes  40   l , 40   r  and tined disks  32   l , 32   r  that are rotated by the polygonal shaft  26 . The tilling elements are so close together in this view that most of the polygonal shaft  26  is not visible. A better view is shown in  FIG. 9 . A flanged screw  28  attaches to a tapped end  27  of the polygonal shaft  26 , therein securing the tined disk  32   r . Tined disk  32   r  is coupled to an adjoined facing tined disk with screws  23 . 
     The tilling elements  30  on one side of the tool include a round brush  40  positioned between two coupled tined disks. 
     A separated couple of tined disks  32 , 32 ′ is illustrated in  FIGS. 5   a  and  5   b . The tines illustrated in  5   b  are the mirror image of the tines in  5   a . The tapered edges  35 , 35 ′ and tapered ends  34 , 34 ′ are hardened and sharpened cutting edges, and the edges provide an effective tilling surface of the soil. The non-tapered edges  37 , 37 ′ provide strength. As illustrated, disk  32  has four tines  39   a , 39   b , 39   c , 39   d  and disk  32 ′ has four tines  39   a ′, 39   b ′, 39   c ′, 39   d ′. The tines radiate from a plate  38 , 38 ′ that has a polygonal center opening  36 , 36 ′, where the polygon is a square, having dimensions that enable a snug fit on the polygonal shaft, which is also square. All of the tines on a single disk are similar in shape and each individual tine is orthogonal to an adjacent tine. The tines on a single tined disk are separated by about 90 degrees. The tines curve at a distal point  39 ,  39 ′. More medially, the tines widen and have an elongate opening  31 , 31 ′ that enables shearing and lateral movement of soil during excavation. The plate  38 , 38 ′ has four holes  33 , 33 ′ for joining opposing disks. 
     The tined disks are mounted in pairs, and the angle of the mount is diagrammatically illustrated in  FIG. 10 . In an exemplary embodiment, assume a first square center opening  36  on a first tined disk has an angular position of 0°. A second square center opening on a second tined disk has an angular position that is angled 45° from the first disk. The disks in this figure are labelled with the degrees that they must be angled to have square center openings that are aligned. Combined first and second disks are inner disks (0°+45°). In order to align the second square center opening with the first square center opening, so that both disks can be positioned on the square bar, the tines on the second disk are rotated 45° degrees. The first and second disks have aligned square center openings, and the tines of the second disk bisect the tines on the first disk. A third square center opening in a third disk is rotated about 22.5° from the first disk, and a fourth square center opening on a fourth tined disk has an angular position that is about 45° from the third square center opening on the third disks (total of 67.5° from first disk). Combined third and fourth disks are outer couples)(22.5°+67.5°. Positioned on the square bar, the tines on the third disk and fourth disks will bisect the tines on the first and second disk. The combined effect is that the sixteen tines (0°+45°+22.5°+67.5°) on a right length of the polygonal shaft are separated by 22.5°. From inspection, the reader may see that only one tine on one side would be in orthogonal contact with the soil, assuming the ground is a horizontal plane. In the invention, both the right and left lengths of the shaft are loaded with sets of staggered disks, where the left and right inner disks are an inner couple having an angular position of 0° combined with a 45° disk. In the case of the outer fourth disk, it has an angular position that is 45° (66.7° from the first disk) from the third square center opening on the third disk, where the third square center opening in the third disk has already been rotated 22.5° from the first disk. The tines on the left side are positioned and aligned with the tines on the right side. 
       FIGS. 7   a , 7   b , 7   c  and  FIGS. 8   a , 8   b , 8   c  illustrate the confluence of the relative angle between disks as previously illustrated in  FIG. 10 , the brushes and the influence of the shape on the symmetry of the tined disks. In  FIG. 7   a , as seen looking down the polygonal shaft from the right side, right inner couple includes disks  30   r   1  and  30   r   2 . The vertices  36   v  of the open center square  36  are substantially aligned with the rear most tines of the first disk  30   r   1 . Rotation is counterclockwise so the leading edge  35  of the tines on the first disk is on the counterclockwise edges. The tines on the first disk are curved toward the viewer. The second disk is paired with the first disk  30   r   2 , and it faces the first disk  30   r   1 . The leading edges  35 ′ of the tines on the second disk  30   r   2  are also on the counterclockwise edges wherein the tines of the second disk are a mirror image of the tines on the first disk. The square center opening  36  on the second disk is rotated 45° from the first disk, so the tines on the second disk are aligned with the sides  36   s , instead of the vertices  36   v . In short, portions of the second disk are a mirror image; and the relative angle of the open center square has changed. 
     The round brush  40   r  is shown in  FIG. 7   b . The brush  40   r  has a square center axial opening  46  to affix the brush to the polygonal shaft. However, the symmetry of the round brush and the particular angularity is not relevant. The illustrated round wire brush has a plurality of radial stiff wire bundles  42 . As indicated in the figure the brush rotates in the same direction as the tined disks. 
     Disks  30   r   3  and  30   r   4  are illustrated in  FIG. 7   c . These disks are a right outer couple. The angle of the open center square  36  is the same as shown in  FIGS. 7   a  and  7   b . The square center opening  36  is now angled 22.5° from the position of the first disk  30   r   1 . When the third disk is loaded on the square polygonal shaft, the disk has to be turned back 22.5° to slide the third disk on the polygonal shaft. The net effect is that the tines on the third disk  30   r   3  are now 22.5° counter-clockwise to the tines on the first disk  30   r   1 . The fourth disk  30   r   4  faces the third disk  30   r   3 , and the tines are the same as the second disk  30   r   2 , that is a mirror image to the third disk  30   r   3 . In the fourth disk  30   r   4  the square center opening  36  is now angled 67.5° from the position of the first disk  30   r   1 , which is 45° more than the third disk. The fourth disk  30   r   4  is turned back 67.5° to slide the fourth disk on the polygonal shaft. The angle of the square center opening  36  is constant over  FIGS. 7   a ,  7   b  and  7   c , but the relative position of the tines has changed. Taken together, the four tines on the first disk are bisected by the four tines on the second disk, so that each tine is 45° apart. The third and fourth disks bisect the angle of separation down to 22.5°. 
       FIGS. 8   a , 8   b  and  8   c  are the same as  FIGS. 7   a , 7   b  and  7   c , except that it is a view of disk elements on the left side of the tool. Disks  30 L 1  and  30 L 2  are the left inner couple disks  30 L 3  and  30 L 4  are the left outer couple. There is a tine on the left side that has the same angle and position as a tine on the right side. This assembly mitigates vibration and has reaction-force symmetry. 
     The invented tines in the illustrated embodiment are hardened, fabricated out of, in an exemplary embodiment, D2 Tool Steel, heat treated to a hardness of 60-63 on the Rockwell C scale. The hardness of this steel provides a balance of toughness and hardness. Heat treatment imparts hardness at the surface of the tines to mitigate deformation and wear. The tine thickness-to-length ratio is about 0.1:1 (for example 3/16 in thick to 2 in length). Conventional tiller tines have a thickness-to-length ratio of about 0.03:1. The invented thicker tines have increased stiffness, therein maintaining an effective geometry though an excavation cut. 
       FIG. 6  illustrates all the tine elements illustrated in  FIGS. 7   a - c  and  FIGS. 8   a - c . The pairs of tined disks are joined with screws  23  and tightened onto the polygonal shaft with an axial screw  28 . 
     The rotating round brushes function to push the loosened soil forwards and sideways, and they limit the depth of penetration of the tined disks. Excavation is uniform, and less likely to asymmetrically deform the tines or the polygonal shaft. Generally, with the invention, soil is pushed forward and to the side of the excavation tool and the robotic platform. 
     Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.

Summary:
The remote excavator tool fastens to a robotic arm on a remotely controlled robotic platform that includes a track drive. The tool uses high speed tilling elements rotating at about 1500 rpm to dig, efficiently, a trench using a small amount of power. The tilling elements are hardened steel, rotating counterclockwise to a conventional tiller. The tilling elements are symmetrically mounted on a polygonal shaft, and include right and left multiple couples of paired facing disks with staggered curved tines, where the tines are thick and have tapered hardened edges. Round brushes are interspaced between couples. The loosen soil is pushed forward and to the sides to help protect the robotic platform and maintain control of the tool especially as the rate of the excavation partially depends on the characteristics of the material being excavated.