You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/511,185 filed on Jul. 29, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 12/424,853 filed on Apr. 16, 2009 and which is now U.S. Pat. No. 7,669,663 issued on Mar. 2, 2010. U.S. patent application Ser. No. 12/511,185 is also a continuation-in-part of U.S. patent application Ser. No. 12/391,358 filed on Feb. 24, 2009. Both of which are herein incorporated by reference for all that they disclose. 
    
    
     BACKGROUND 
     This invention relates to actuation mechanisms for tools in a downhole environment, such as reamers. Various efforts to provide reliable mechanical actuation of downhole tools are disclosed in the prior art. 
     U.S. Pat. No. 4,893,678 to Stokley et al. discloses a downhole tool suitable for multiple setting and unsetting operations in a well bore during a single trip. The downhole tool is suspended in the wellbore from a tubing string, and is activated by dropping a metal ball which plugs the passageway through the tubing string, such that tubing pressure may thereafter be increased to activate the downhole tool. A sleeve is axially movable within a control sub from a ball stop position to a ball release position, and has a cylindrical-shaped interior surface with a diameter only slightly greater than the ball. Collet fingers carried on the sleeve are radially movable from an inward position to an outward position to stop or release the ball as a function of the axial position of the sleeve. Fluid flow through the tubing string is thus effectively blocked when the sleeve is in the ball stop position because of the close tolerance between the sleeve and the ball, while the ball is freely released from the sleeve and through the downhole tool when the sleeve is moved to the ball release position. 
     U.S. Pat. No. 4,889,199 to Lee discloses a downhole drilling device utilizing a spring-loaded sleeve within the casing for controlling circulation of fluid material. A plastic, i.e., deformable ball is used to block a flow opening in the sleeve for positioning the sleeve and aligning flow ports. Subsequently, the ball is deformed and the drilling operation continues. In one form, an expandable packer may be operated to close off the annulus about the casing. 
     U.S. Pat. No. 7,416,029 to Telfer discloses a downhole tool which can perform a task in a well bore, such as circulating fluid radially from the tool. The function is selectively performed by virtue of a sleeve moving within a central bore of the tool. Movement of the sleeve is effected by dropping a ball through a ball seat on the sleeve. Movement of the sleeve is controlled by an index sleeve such that the tool can be cycled back to the first operating position by dropping identical balls through the sleeve. Embodiments are described wherein the balls are deformable, the seat is deformable and the seat provides a helical channel through which the ball passes. 
     U.S. Pat. No. 3,703,104 to Tamplen discloses a positioning apparatus for effecting movement of a first body with respect to a second body in response to movement of a third body characterized by a slot traversal member engaging a set of driving slots and a set of driven slots that are formed respectively in the first and second bodies. One of the sets of driven and driving slots comprises a closed pattern of slots; and the other comprises a single slot having at least two portions that have the same design and are movable so as to be coextensive with the slots of the closed pattern of slots. Also disclosed are tubular and planar constructions employing the driving and driven slots. 
     BRIEF SUMMARY 
     In one aspect of the present invention, a downhole tool comprises a fluid path defined by a bore formed within a tubular body of the tool, a reciprocating sleeve located within the bore, the sleeve comprising a segmented seat or a seat with a moveable portion. The seat also comprises a fluid by-pass. The at least one seat segment or moveable portion is positioned by an outer diameter of the sleeve to complete the seat, and a relief formed in a wall adjacent the outer diameter of the sleeve, wherein when the seat is occupied by an obstruction only a portion of the fluid path is obstructed and fluid impinging the obstruction causes the sleeve to move in the direction of flow until the at least one segment is relieved by the relief and releases the obstruction. The relief may be a diametrically increased inner diameter of the wall, slot, grove, recess, or combinations thereof. 
     The at least one seat segment or movable portion of the seat may comprise a sliding pin, a pivoting lever, a compliant portion, one or more fluid passageways, or combinations thereof. The at least one seat segment may comprise a biasing element such as a coil spring or torsion spring. 
     The obstruction may comprise a generally spherical ball. 
     The reciprocating sleeve may be biased in an axial direction opposite the direction of fluid flow by a biasing element such as a compression spring. The relief may comprise a diametrically widened space inside the tubular body of the tool. A tapered portion may be disposed intermediate the diametrically widened space and an inside diameter of the downhole tool. The relief may comprise a plurality of recesses in the tubular body of the tool. 
     The reciprocating sleeve may comprise a flange sealed to the bore of the tubular body. The reciprocating sleeve may comprise one or more fluid passages in communication with the fluid path before the obstruction and in communication with a volume partially defined by the bore of the tool and a posterior surface of the flange. The reciprocating sleeve may be lubricated by a fluid isolated from the fluid in the fluid path. 
     One or more pins may position the reciprocating sleeve at an initial position relative to the tubular body of the tool, and the pins shear upon actuation by a first obstruction. The downhole tool may actuate a reamer, winged reamer, probe, radially or axially extendable sensor, a generator, drill bit jack element, vibrator, jar, steering tool, mechanical or electrical switch, acoustic source, electric source, nuclear source, central tap, perforating gun, valve, telemetry device, or combinations thereof. 
     In another aspect of the present invention, a downhole tool comprises a fluid path defined by a bore formed within a tubular body of the tool, a reciprocating sleeve located within the bore, the sleeve comprising a segmented seat with a fluid by-pass; at least one seat segment is positioned by an outer diameter of the sleeve to complete the seat, and a relief formed in a wall adjacent the outer diameter of the sleeve, wherein when the seat is occupied by an obstruction only a portion of the fluid path is obstructed and a minority of the flow is arrested, but a pressure differential caused by the obstruction causes the sleeve to move in the direction of flow until the at least one segment is relieved by the relief and releases the obstruction. 
     In another aspect of the present invention, a downhole tool comprises a fluid path defined by a bore formed within a tubular body of the tool, a reciprocating sleeve and a guided sleeve located within the bore, the sleeves substantially coaxial with one another, the guided sleeve comprises at least one guide recess, the reciprocating sleeve comprises at least one guide protrusion engaged in the guide recess; wherein a reciprocating movement of the reciprocating sleeve causes the guide protrusion and guide recess to disengage and upon reengagement the geometry of the guide recess repositions the guided sleeve. 
     The reciprocating sleeve may comprise an extension intermediate the sleeve and the at least one guide protrusion. The at least one guide recess may be disposed on an outer diameter of the guided sleeve. The reciprocating sleeve may be disposed substantially exterior to the guided sleeve, and the at least one guide recess may comprise partially helical geometry. The at least one guide protrusion may be disposed on an inside diameter of the reciprocating sleeve. 
     The guided sleeve may comprise fluid ports in communication with the fluid path in the tubular body of the tool. The fluid ports may be in selectable communication with fluid passages in the tool body. The guided sleeve may comprise first and second indexed positions corresponding to fluid passages and ports in communication, and fluid passages and ports separated. The guided sleeve may comprise a plurality of indexed positions alternating between fluid passages and ports in communication and fluid passages and ports separated. The guided sleeve may be rotatable more than one full revolution. A function of the downhole tool may be activated at the first indexed position. The downhole tool may comprise a reamer. 
     The reciprocating sleeve and the guided sleeve may be lubricated by a fluid flowing in the fluid path. In other embodiments, the reciprocating sleeve and guided sleeve may be lubricated by a fluid separated from the fluid flowing in the fluid path. 
     Rolling bearings such as balls or rollers may be disposed on an outer diameter of the guided sleeve intermediate the outer diameter and the bore of the tubular body. 
     The reciprocating sleeve may be biased in a direction opposite the direction of a flow of fluid in the fluid path. The reciprocating sleeve may be actuated by an obstruction. 
     In some embodiments, the obstruction may comprise a hollow sleeve with a spherical ball releaseably engaged in the hollow sleeve, wherein the hollow sleeve substantially blocks the fluid ports from communication with the fluid path in the tubular body of the tool. 
     The guided sleeve may comprise pins that initially position the guided sleeve with respect to tubular body of the tool, wherein the pins shear upon actuation of the guided sleeve by a first obstruction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an embodiment of a drillstring. 
         FIG. 2  is a cross-sectional view of an embodiment of a downhole tool. 
         FIG. 3   a  is a cross-sectional view of another embodiment of a downhole tool. 
         FIG. 3   b  is a cross-sectional view of another embodiment of a downhole tool. 
         FIG. 4   a  is a perspective view of an embodiment of a guided sleeve and a reciprocating sleeve. 
         FIG. 4   b  is a perspective view of an embodiment of a guided sleeve and a reciprocating sleeve. 
         FIG. 4   c  is a perspective view of an embodiment of a guided sleeve and a reciprocating sleeve. 
         FIG. 4   d  is a perspective view of an embodiment of a guided sleeve and a reciprocating sleeve. 
         FIG. 5  is a cross-sectional view of another embodiment of a downhole tool. 
         FIG. 6  is a cross-sectional view of another embodiment of a downhole tool. 
         FIG. 7  is a cross-sectional view of another embodiment of a downhole tool. 
         FIG. 8  is a cross-sectional view of another embodiment of a downhole tool. 
         FIG. 9  is an exploded view of another embodiment of a guided sleeve. 
         FIG. 10  is a perspective view of another embodiment of a guided sleeve. 
         FIG. 11  is a cross-sectional view of another embodiment of a downhole tool. 
         FIG. 12   a  is a perspective view of an embodiment of a dart. 
         FIG. 12   b  is a perspective view of another embodiment of a downhole tool. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the figures,  FIG. 1  discloses an embodiment of a drilling operation. A drill string  100  is suspended by a derrick  101  and comprises a drill bit  104  and a downhole tool  103 . In this embodiment, downhole tool  103  comprises a reamer for enlarging a bore  106  in a formation  105 . It is desirable to selectively activate and deactivate the downhole tool  103  while the drill string  100  is in operation. 
       FIG. 2  discloses an embodiment of a downhole tool  200  with a first end  201  and a second end  202 . First end  201  connects to a portion of drill string that extends to the surface of a borehole, and second end  202  may connect to a bottom whole assembly or drill bit, measuring or logging while drilling system, or other downhole devices or drill string segments. Downhole tool  200  comprises a reamer  203 , a fluid path  204  through a tool body  205 , a reciprocating sleeve  206 , a guided sleeve  207 , and a droppable obstruction  208 . Droppable obstruction  208  may be dropped from the surface during the drilling operation when activating or deactivating the downhole tool  200  is desired. 
     In the prior art, many ball drop tool actuation systems substantially block the flow of drilling fluid, thereby generating sufficient pressure in the drilling fluid to force the drop ball or obstruction through the actuation mechanism. Drilling fluid may provide cooling and lubrication for the drilling machinery, as well as chip removal from the bit face, bore sealing, and data transmission. Therefore, a tool actuation system that allows drilling fluid to continue to flow while activating or deactivating the tool is desirable. 
       FIG. 3   a  discloses an embodiment of a downhole tool  300  comprising a reciprocating sleeve  206 A and a guided sleeve  207 A. An obstruction  208 A enters the reciprocating sleeve  206 A along direction  301 . The obstruction  208 A contacts a seat segment  302  and is retained against a wall  303  of the reciprocating sleeve  206 A and the seat segment  302 . The wall  303  may include protrusions to retain the obstruction  208 A away from the wall  303  and allow drilling fluid to flow. Drilling fluid flows in direction  301  and impinges on obstruction  208 A, creating a pressure differential. Drilling fluid is substantially free to flow around the obstruction  208 A, and a flow of the drilling fluid in the drilling assembly continues. The pressure differential forces the obstruction  208 A together with the reciprocating sleeve  206 A in direction  301  against the force of a biasing element  305 . In this embodiment, the biasing element  305  comprises a compression type coil spring. The biasing element  305  may also comprise a plurality of coil springs, Bellville springs, or other spring elements. 
     The obstruction  208 A may comprise a metal material such as steel or other another iron alloy, zinc or brass alloys, or other metals. The obstruction may be substantially spherical, may be elongated or dart shaped, or may have other appropriate geometry. 
     The reciprocating sleeve  206 A comprises a cylindrical extension  306  and guide protrusions  307 . The guide protrusions  307  engage in partially helical guide recesses  308  disposed in the guided sleeve  207 A. As the reciprocating sleeve  206 A moves in direction  301 , the guide protrusions  307  slide in the partially helical guide recesses  308 , rotating the guided sleeve  207 A. The guided sleeve  207 A comprises a flange  313  that bears against a retaining ring  314 , preventing axial motion, but allowing rotation of the guided sleeve  207 A. The guided sleeve  207 A may have rolling bearings, such as needle or ball bearings, disposed intermediate, or between, guided sleeve  207 A and a body of the downhole tool  300 . In some embodiments, the bushings may be disposed intermediate the guided sleeve  207  and a body of the downhole tool  300 . The bushings may comprise brass, bronze, Babbitt metal, or wear resistant materials such as polycrystalline diamond. 
     Shear pins  315  may locate the reciprocating sleeve  206 A with respect to the body of the downhole tool  300 . 
     In  FIG. 3   b , the reciprocating sleeve  206 A is forced in direction  301  in response to the pressure differential generated by drilling fluid flowing in direction  301  against obstruction  208 A. The shear pins  315  fail under the load, allowing the reciprocating sleeve  206 A to move in direction  301  such that a roller  304  reaches a relief  310 . The seat segment  302  is thus able to slide away from the obstruction  208 A, allowing the obstruction  208 A to pass through the reciprocating sleeve  206 A, relieving the pressure differential. The seat segment  302  may comprise an element such as a coil spring or Bellville spring that biases the seat segment  302  to slide away from obstruction  208 A when the roller  304  reaches the relief  310 . After the obstruction  208 A passes through the reciprocating sleeve  206 A, the reciprocating sleeve biasing element  305  forces the reciprocating sleeve  206 A back in a direction opposite direction  301 . The guide protrusions  307  slide in the guide recesses  308  to further rotate the guided sleeve  207 A, and ports  311  in the guided sleeve  207 A align with fluid passages  312  enabling actuation of a downhole tool  300 . 
     Each successive obstruction that passes through the reciprocating sleeve  206 A alternates the guided sleeve  207 A between positions in which the fluid ports  311  are in communication with the fluid passages  312  in the body of the downhole tool  300  and positions in which the fluid ports  311  and the fluid passages  312  are separated. 
     The guided sleeve  207 A and the reciprocating sleeve  206 A may be lubricated against the body of the downhole tool  300  by a fluid separated from the fluid that flows through a fluid path of the downhole tool  300 , or may be lubricated by the drilling fluid flowing in the fluid path. The drilling fluid may pass through a self-cleaning filter before entering the guided sleeve  207 A or the reciprocating sleeves  208 A to reduce the solids content of the drilling fluid and prevent the guided sleeves  207 A, reciprocating sleeves  208 A and other mechanisms from packing with particulate material. 
     Referring now to  FIG. 4   a , an embodiment of a guided sleeve  401  and a reciprocating sleeve  402  is disclosed. Guide protrusions  407  engage guide recesses  408  disposed on an outside diameter  405  of the guided sleeve  401 . In  FIG. 4   b , the reciprocating sleeve  402  moves in direction  410 , and the guide protrusions  407  contact helical portions  403  of the guide recesses  408 . As the guide protrusion  407  travels in direction  410  and bears against a lower helical portion  403 , the guided sleeve  401  is forced to rotate. In  FIG. 4   c , the reciprocating sleeve  402  reaches a lowest position in direction  410  with respect to the guided sleeve  401 . In  FIG. 4   d , the reciprocating sleeve  402  moves in direction  411 , and the guide protrusions  407  bear against upper helical portions  412  of the guide recesses causing the guided sleeve  401  to rotate to a position in which ports  413  may align with fluid passages and activate a tool. 
       FIG. 5  discloses another embodiment of a downhole tool  500 . In this embodiment, a reciprocating sleeve  501  disposed within a tool body  511  comprises a plurality of pivoting levers  502  comprising a distal end  504  and a proximal end  505 . The plurality of pivoting levers  502  retain an obstruction  508 . Fluid flows in direction  503  and impinges obstruction  508 , creating a pressure differential, thus causing the reciprocating sleeve  501  to move in direction  503  allowing the distal ends  504  of the plurality of pivoting levers  502  to enter a relieved portion  506 . The pivoting levers  502  rotate, moving the proximate ends  505  apart thereby allowing the obstruction  508  to pass through the reciprocating sleeve  501 . The pivoting levers  502  may be biased with torsion springs or coil springs. 
     The relieved portion  506  may comprise a diametrically widened space  507  with a tapered segment  510  intermediate, or between, the widened space  507  and an internal diameter  509  of the tool body  511 . The relieved portion  506  may comprise polycrystalline diamond, hard facing, or other hard, abrasion resistant materials. Such wear resistant materials may also be applied to the distal ends  504  and the proximal ends  505  of the plurality of pivoting levers  502  to reduce wear and increase reliability. 
     The reciprocating sleeve  501  includes ports  512  in communication with the fluid flow upstream from the obstruction  508  and a volume  513  partially defined by a flange  514  of the reciprocating sleeve  501  and the tool body  511 . The ports  512  may slow the movement of the reciprocating sleeve  501 , and allow more time for a pressure build up, so pressure sensors may more easily sense the effects of actuating the tool. 
       FIG. 6  discloses a reciprocating sleeve  601  comprising one or more sliding pins  602  and one or more pivoting levers  603 . A droppable obstruction  608  is retained by the pivoting levers  603  and the sliding pins  602 . Fluid flows in direction  604  and impinges on the droppable obstruction  608  creating a pressure differential, causing the reciprocating sleeve  601  to move in direction  604 . The sliding pins  602  are relieved by a relief  605  in a bore of the downhole tool  600 , and the pins  602  and the levers  603  move to allow the droppable obstruction  608  to pass through the reciprocating sleeve  601 . A biasing element  606  returns the reciprocating sleeve  601  to an initial position after the droppable obstruction  608  passes though. In this embodiment, the reciprocating sleeve  601  comprises a first flange  607  and a second flange  609 . The first flange  607  and the second flange  609  positively locate the reciprocating sleeve  601  in the downhole tool  600 , and may retain a lubricating fluid within space  610 . 
       FIG. 7  discloses another embodiment of a downhole tool  700 . In this embodiment, the downhole tool  700  comprises a reciprocating sleeve  701  with a seat comprising a plurality of seat segments  702 . The seat segments  702  comprise fluid passageways  703 , allowing the flow of drilling fluid to continue while an obstruction occupies the seat. 
       FIG. 8  discloses a downhole tool  800  comprising a reciprocating sleeve  801  and a guided sleeve  802 . The reciprocating sleeve  801  comprises a biasing element  803  and a plurality of sliding pins  804  that retain a droppable obstruction  805 . A fluid path  806  is disposed inside the downhole tool  800 . An indexing sleeve  807 , an actuation sleeve  808 , and a positioning sleeve  809  are disposed intermediate, or between, the reciprocating sleeve  801  and the guided sleeve  802 . The guided sleeve  802  comprises fluid ports  810  in selectable communication with fluid passages  811 . A downhole tool such as a reamer may be activated when the fluid ports  810  are in communication with the fluid passages  811  and deactivated when the fluid ports  810  are separated from the fluid passages  811 . 
       FIG. 9  discloses a guided sleeve  901 , an indexing sleeve  902 , a positioning sleeve  903 , and an actuation sleeve  904 . The indexing sleeve  902  comprises first guide recesses  907  and second guide recesses  908 , and the positioning sleeve  903  comprises guide protrusions  909  and a serrated crown  912 . The guided sleeve  901  comprises fluid ports  910 . 
     In  FIG. 10 , the guided sleeve  901 , the indexing sleeve  902 , the positioning sleeve  903 , and the actuation sleeve  904  are shown assembled. In use, the actuation sleeve  904  abuts a reciprocating sleeve  905 , and the guided sleeve  901  abuts the positioning sleeve  903 . When the reciprocating sleeve  905  moves in direction  906 , the actuation sleeve  904  and the positioning sleeve  903  are kept in mechanical contact with the reciprocating sleeve  905  by a biasing spring  911 . The indexing sleeve  902  remains stationary and the guide protrusion  909  leaves the first guide recess  907 . The positioning sleeve  903  is rotated by contact between angled tabs  913  on the actuation sleeve  904  and the serrated crown  912 . The guide protrusion  909  enters the second guide recess  908  as the reciprocating sleeve  905  returns to an original position. The first guide recesses  907  correspond to a first position of the positioning sleeve  903 , and the second guide recesses  908  correspond to a second position of the positioning sleeve  903 . The guided sleeve  901  remains in an axial position defined by the position of the positioning sleeve  903  until the reciprocating sleeve  905  undergoes a subsequent reciprocation and the guide protrusions  909  return to the first guide recess  907 . Fluid ports  910  may be in communication with fluid passages in a tool body when the positioning sleeve  903  and the guided sleeve  901  are in the first position, and fluid ports  910  may be separated from fluid passages when the positioning sleeve  903  and the guided sleeve  901  are in the second position. 
       FIG. 11  discloses another embodiment of a downhole tool  1100  comprising a reciprocating sleeve  206 B with a segmented seat  1101 . An obstruction  208 B is retained by the segmented seat  1101 , and a pressure differential in the drilling fluid caused by the obstruction  208 B forces the obstruction  208 B and the reciprocating sleeve  206 B in direction  301 . As the reciprocating sleeve  206 B moves in direction  301 B, the segmented seat  1101  reaches a diametric relief  1103 , and compliant segments  1102  allow the segmented seat  1101  to expand, thereby allowing the obstruction  208 B to pass through the segmented seat  1101  and relieving the pressure differential. Drilling fluid may pass through slots  1151  formed between the compliant segments  1102 . The total slot area is large enough to allow sufficient amounts of drilling fluid to pass through to maintain the drilling fluid functions downstream while allowing enough of a pressure build-up to move the reciprocating sleeve  206 B forward. 
     In some embodiments, pressure relief ports  1150  that relieve a portion of the pressure build-up may be incorporated within an affected area. The pressure relief ports  1150  are optimized to slow the pressure build-up so sensors may have more time to sense the pressure increase. 
       FIG. 12   a  discloses an embodiment of a dart  1200 . The dart  1200  comprises a hollow sleeve  1201  with a diametrically enlarged end  1202  opposite a smaller end  1203  having a reduced diameter. An obstruction  1204  is releaseably engaged in the smaller end  1203 . 
     In  FIG. 12   b , the dart  1200  is lodged in a downhole tool  100 C. The diametrically enlarged end  1202  abuts a shoulder  1205  in the downhole tool  100 C, and the hollow sleeve  1201  blocks fluid ports  1206 . Drilling fluid flowing in direction  301 C creates a pressure differential and forces obstruction  1204  through the smaller end  1203  of hollow sleeve  1201 . 
     It may be desirable to completely inactivate the downhole tool  100 C, and by blocking the ports  1206  with the hollow sleeve  1201 , the downhole tool  100 C will not activate but will allow fluid flow to continue through the central bore of the downhole tool  100 C and the drilling operation may continue. 
     Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.

Summary:
A downhole tool actuation system has a fluid path defined by a bore formed within a tubular body of a tool. A reciprocating sleeve is located within the bore and the sleeve has a segmented seat with a fluid by-pass. At least one seat segment is positioned by an outer diameter of the sleeve to complete the seat, and a relief is formed in a wall adjacent the outer diameter of the sleeve. When the seat is occupied by an obstruction, only a portion of the fluid path is obstructed and fluid impinging the obstruction causes the sleeve to move in the direction of flow until the at least one segment is relieved by the relief thereby releasing the obstruction.