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FIELD OF THE INVENTION 
     The present invention relates to tools adapted to recover objects lodged within a well bore. More particularly, the present invention relates to a jarring apparatus that delivers controlled percussive impact to a lodged object. In a different aspect, the present invention relates to an apparatus that provides a telemetry link to the lodged object during the jarring sequence. 
     GENERAL BACKGROUND OF THE INVENTION 
     During the course of drilling, completing, testing or working over a well for producing hydrocarbons, objects may become stuck within a well bore through which the hydrocarbons are recovered. Objects that can become lodged or otherwise immobile relative to a well bore can include drilling equipment, tool strings, bottomhole assemblies or other items typically conveyed into a well bore environment. In order to loosen and recover these objects, jars have been developed that have the effect of providing a jarring impact to the object. 
     Conventional jarring tools usually use either a mechanical or hydraulic system to loosen and dislodge a stuck object. Conventional hydraulic jars have a piston disposed in a cylinder that is filled with hydraulic oil. The piston, or jar rod, is accelerated by hydraulic fluid through a stroke. At the completion of the stroke, an impact force is delivered to the jar housing. One disadvantage of hydraulic jars involves the difficulties associated with maintaining a hydraulic fluid system in a downhole environment. These systems typically use pumps, reservoirs, fluid conduits, seals that can be expensive to incorporate into downhole tooling and can require frequent maintenance. 
     Mechanical jars, like hydraulic jars, typically use a piston-cylinder arrangement. The piston, however, is driven or propelled by a device such as a Bellville washer stack or other mechanical biasing mechanism. Often, the spring is compressed by pulling up on a work string until a desired spring force is reached. This spring force is then used to accelerate a piston that strikes the jar housing. Some jarring tools utilize means to reset the piston to deliver a second impact if needed. Conventional mechanical jars, however, do not satisfactorily control the delivery of the impact force nor provide a reliable arrangement to reset the jar tool. 
     Further, conventional jar tools are usually interposed in a string, such as a wireline or work string, that incorporates a telemetry system for communicating with one or more tools attached to the string. It is often desirable to maintain communication with these tools even when the jarring tool is activated. Conventional tool strings often use a telemetry cable that has one or more coiled portions that expand to provide added length to accommodate the extension of the jarring tool. Such devices, however, have not provided a reliable telemetry connection with the downhole tools. 
     The present invention addresses these and other disadvantages of conventional jarring tools. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for providing a percussive or jarring force to an object having at least a portion thereof lodged in a well bore. In a preferred embodiment, the apparatus includes anvil, a hammer, and a button member. The anvil includes a sleeve and is connected to the object with a mandrel. The hammer includes an axial bore that can receive a portion of the anvil sleeve and a transverse bore in which the button member is disposed. The button member has a first position wherein the anvil sleeve cannot enter the hammer axial bore and a second position wherein the button allows the anvil sleeve to enter the hammer axial bore. The button member is actuated by a trigger that moves the button member from the first position to the second position. A spring member provided on the hammer urges the button member from the second position to the first position. Preferably, a housing encloses at least a portion of the hammer and the anvil. The housing has a first section, a second section, and a frangible member connecting the first and second sections. The frangible member is preferably a shear screw that disintegrating upon encountering a pre-determined force. Upon disintegration, the first section can move axially away from the second section. The preferred apparatus also includes a telemetry link for exchanging electrical signals with the object. In a preferred arrangement, the telemetry link includes at least one inner tube telescopically disposed within at least one outer tube. At least a portion of the inner tube and outer tube are formed of a conductive material. The inner tube is drawn out of the outer tube when the housing first section moves axially away from the housing second section. 
     During use, the preferred apparatus provides one or more jarring or percussive impacts to the object. An exemplary jarring sequence includes an activation phase, a loading phase, a release phase, and a reset phase. During the activation phase, an axial traction force is imposed on the tool housing to separate the two housing sections. In the loading phase, the first housing section moves axially away from the object and causes a piston to compress a biasing member. The button member, which is in the first position, prevents the hammer from sliding toward the anvil. A release phase is entered when a trigger provided on the housing first section moves the button member from the first position to the second position. Once the button member is in the second position, the biasing member accelerates the freed hammer axially against the anvil. The percussive impact of the hammer is transferred from the anvil to the object through a mandrel. If this action does not free the object, the apparatus is put into the reset phase. In this phase, the first housing section is permitted to slide axially towards the second section. This movement returns the hammer to its initial position and allows the button member to return to its first position. With the hammer and anvil interlocked by the button member, the jarring sequence can be again performed. 
     The axial length changes of the housing during the several phases of the jarring sequence are accommodated by the telescoping feature of the telemetry link. During separation of the housing sections, the inner tube of the telemetry link is extracted out of the outer tube. As the first housing section moves toward the second section, the inner tube slides into the outer tube. Thus, during all phases of the jarring sequence, a reliable telemetry communication path is maintained with the stuck object. 
     It should be understood that examples of the more important features of the invention have been summarized rather broadly in order that detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention can be obtained when the following detailed description of exemplary embodiments are considered in conjunction with the following drawings, in which: 
     FIG. 1 is an elevation view of a preferred embodiment of the present invention used in conjunction with a conventional tool string disposed in a well bore; 
     FIG. 2 is a schematic illustration of a preferred jarring tool; 
     FIG. 3 is cross-sectional side view of a section of the preferred jarring tool that includes an exemplary telemetry system, anvil and associated components; 
     FIG. 4 is cross-sectional side view of a section of the preferred jarring tool that includes an exemplary hammer, biasing member, mandrel assembly and associated components; 
     FIG. 5 is cross-sectional side view of a section of the preferred jarring tool that includes an exemplary biasing member, trigger housing, mandrel assembly and associated components; 
     FIG. 6 is cross-sectional side view of a section of the preferred jarring tool that includes an exemplary telemetry system, separator housing, bottom sub and associated components; 
     FIG. 7 illustrates a cross-sectional side view of a preferred button member in a first position; and 
     FIG. 8 illustrates a cross-sectional side view of a preferred button member in a second position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily drawn to scale and certain figures may be shown in exaggerated or generalized form in the interest of clarity and conciseness. 
     The present invention relates to devices and methods for providing a percussive or jarring force to an object lodged in a well bore. Such an object may be tooling or equipment used during any phase of hydrocarbon recovery, including drilling, completion and production. For simplicity, the present invention will be described in the context of a tool string that may include, for example, wireline tools, a bottom hole assembly, or completion equipment such as perforating guns. The present invention, thus, is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. 
     Referring initially to FIG. 1, there is shown a conventional tool string  10  disposed in a well bore  12  formed in a subterranean formation  14 . A surface structure  16  supports the tool string  10  in the well bore  12  with a work string or suspension line  18 . The tool string  10  can be a single tool or a package of tools that include known equipment and instrumentation adapted to perform functions such as detecting geophysical characteristics (e.g., porosity, gamma radiation, resistivity, etc.) and determining tool orientation. The tool string  10  can also include a telemetry system that communicates with surface equipment  20  via the telemetry wires (not shown) in the suspension line  18 . For convenience, the tool string  10  is shown as having an upper section  22  and a lower section  24 . During deployment of the wireline  10 , the tool string lower section  24  may become stuck in a well bore restriction or obstruction, the obstruction being generally denoted with numeral  13 . An exemplary jarring tool  100  made in accordance with the present invention provides a controlled and, if needed, repeated percussive or jarring force that dislodges the tool string lower section  24  from the obstruction  13  and thereby frees the tool string  10 . In a preferred arrangement, the jarring tool  100  is interposed between the upper section  22  and lower section  24  of the tool string  10 . 
     Referring now to FIG. 2, there is a strictly schematic illustration of a jarring tool  100  attached at opposing ends to the tool string upper section  22  and lower section  24 . It will be apparent that FIG. 2 merely provides a convenient means to illustrate the interaction and general arrangement of the various exemplary features of the preferred jarring tool  100 . For convenience, the arrow labeled “U” denotes an uphole direction and the arrow labeled “D” denotes the downhole direction. The jarring tool  100  of the present invention may be adapted to provide a jarring force to the tool string  10  in either or both of the uphole (“U”) and downhole (“D”) directions. For simplicity, the embodiment of the jarring tool  100  described below is directed to dislodging a tool string  10  by providing a controlled jarring force in the “U” direction. A jarring tool  100  so adapted includes a housing  200 , a jarring assembly  300 , a mandrel assembly  400  and a telemetry link  500 . 
     The housing  200  of the jarring tool  100  provides a mechanical connection between the upper and lower sections  22 , 24  of the tool string  10  during normal operations. Referring now to FIGS.  2 , 3  and  6 , a preferred housing  200  includes a bottom sub  210 , a frangible member  212 , and an upper assembly  220 . The bottom sub  210  attaches to an adapter  600  associated with the tool string lower section  24  via known devices such as threaded connection. Likewise, the upper assembly  220  attaches to an adapter  602  associated with the tool string top portion  24  via known devices such a threaded connection. The bottom sub  210  and upper assembly  220  are connected to each other, however, with at least one frangible member  212 . Referring now to FIG. 6, the bottom sub  210  has a substantially rigid connection to the mandrel assembly  400 , the details of which will be discussed below. 
     Referring still to FIG. 6, the frangible member  212  allows the bottom sub  210  to separate from the upper assembly  220  when the adaptor  600 /tool string lower section  24  become stuck in the well bore  12  (FIG.  1 ). The frangible member  212  is preferably a device such as one or more shear screws that snap or otherwise disintegrate upon encountering a pre-determined load. This pre-determined load may be produced by pulling the upper assembly  220  in a generally “U” direction while the bottom sub  210 , and connected tool string lower section  24 , are stuck in the well bore  12  (FIG.  1 ). The arrangement used to connect the bottom sub  210  to the upper assembly  220  can also utilize a shear pin (not shown), a spring-biased detent ball, or chemical compounds or materials that disintegrate or release under known loading conditions. Alternatively, an electro-mechanical locking device (e.g., a solenoid), which can be energized by surface personnel, may be used. In any event, the present invention is not limited to any particular device or material for connecting the bottom sub  210  to the upper assembly  220 . It should be understood that the frangible member  212  may not be needed in certain arrangements where the tool may be operated without the necessity of separating the housing  200 . 
     Referring back to FIG. 2, the upper assembly  220  is a generally tubular structure having a central passage  221  that is adapted to enclose the jarring assembly  300 . Referring now to FIGS. 3-6, the upper assembly  220  is formed of a plurality of interconnected housings including a top sub  222  (FIG.  3 ), an anvil housing  224  (FIG.  3 ), a hammer housing  226  (FIG.  4 ), a trigger housing  228  (FIG.  4 ), a spring housing  230  (FIGS.  4 - 5 ), a first piston housing  232  (FIG.  5 ), a second piston housing  234  (FIGS.  5 - 6 ), and a separator housing  236  (FIG.  6 ). The construction of housings  222 - 236  are known in the art and utilize known features such as corrosion resistant metals, threaded pin-box connections and sealing members such as elastomeric “O”-rings. Accordingly, such general features will not be discussed in detail. It will be appreciated that the jarring tool  100  may be several feet in length. Accordingly, for ease of fabrication, handling, assembly, and maintenance, it is preferred that the upper assembly  220  be formed of a plurality of housings. Depending on the desired application, however, greater or fewer housings may be used. 
     The housings  222 - 236  include one or more features that cooperate with other components, e.g., the jarring assembly  300 , to perform one or more functions. For example, the separator housing  236  (FIG. 6) includes one or more bores  237  adapted to receive the frangible member  212 , and the trigger housing  228  (FIG. 4) includes an inwardly projecting trigger ledge  229 . Additionally, the anvil housing  224  (FIG. 4) has a pin end  225  having an inner diameter slightly smaller than the diameter of the passage  221 . For clarity, the functions these features are described in the discussion of the components with which they coact. 
     Referring back to FIG. 2, the jarring assembly  300 , when activated, delivers a jarring force to the tool string lower section  24  via the mandrel assembly  400 . Preferably, the jarring assembly  300  is disposed within the central passage  221  and includes a piston head  310 , a biasing member  320 , a hammer  330 , a button member  340 , and an anvil  350 . As will become apparent, the jarring assembly  300 , during the jarring sequence, produces a spring force in the biasing member  320  that is used to propel the hammer  330  against the anvil  350 . 
     Referring now to FIGS. 4 and 5, the piston head  310  is adapted to compress the biasing member  320  against the hammer  330 . The piston head  310  is preferably formed integral with the first piston housing  232 . The piston head  310  includes a transverse planar surface  312  that abuts the biasing member  320  and a passage  314  for receiving the mandrel assembly  400 . Thus, the piston  310  can slide axially along the outer surface of the mandrel assembly  400 . 
     The biasing member  320  provides a pre-determined amount of propelling force to the hammer  330 . The biasing member  320  is interposed between the piston head  310  and the hammer  330 . As will be explained below, the hammer  330  is held stationary during a portion of the jarring sequence. Axial movement of the piston head  310  compresses the biasing member  320  against the stationary hammer  330  and thereby generates the propelling force. The biasing member  320  includes at least one coil spring, but preferably two or more coil springs, that surround the mandrel assembly  400 . It will be understood that the magnitude of the spring force will depend on factors such as the size and number of the springs and the axial distance (i.e., the stroke) the springs are compressed. By changing the number of the springs, or selecting springs having a particular spring constant, the biasing member  320  may be customized to provide a selected amount of jarring force for a particular tool string. Other biasing mechanisms, such as Bellville springs or compressible fluids such as gas, may also prove effective in certain applications. 
     Referring now to FIGS. 3 and 4, the hammer  330 , when accelerated by the propelling force provided by the biasing member  320 , delivers a high-energy percussive or jarring force to the anvil  350 . Application of this jarring force displaces the anvil  350  in the generally “U” direction. The hammer  330  is elongated cylindrical member that is adapted to reciprocate along a pre-determined stroke within the central passage  221  of the housing upper assembly  220 . The hammer  330  includes an axial bore  332 , a transverse bore  334 , and a head  336 . The axial bore  332  permits the hammer  330  and the anvil  350  to engage in a piston-cylinder-type fashion that is described below. The head  336  has an outer diameter slightly larger than the pin end  225  of the anvil housing  224  and includes a passage  337  that is formed to receive and guide the anvil  350  into the axial bore  332 . The interfering relationship caused by the different diameters of the pin end  225  and the hammer head  336  allows the anvil housing  224  to urge the hammer  330  in the “D” direction, when needed. The transverse bore  334  is shaped complementary to and receives the button member  340 . Preferably, the hammer  330  is formed of a relatively durable material, such as stainless steel, and is massive enough, when accelerated, to deliver a percussive force for displacing the anvil  350 . 
     Referring now to FIG. 4, the button member  340  provides selective and controlled delivery of the jarring force produced by the jarring assembly  300 . The button member  340 , which is disposed within the hammer transverse bore  334 , has a first position and a second position. In the first position, as shown in FIG. 4, the button member  340 , during normal operations, does not play an active roll in maintaining a particular relationship between the hammer  330  and the anvil  350 . Referring now to FIG. 7, the button member  340  is still shown in the first position. The hammer  330 , however, has been displaced in the “U” direction by the biasing member  320  (FIG. 4) such that the anvil  350  has entered the hammer head passage  337  and abuts the button member  340 . In this instance, the button member  340  prevents the hammer  330  from further axial travel toward the anvil  350 . Referring now to FIG. 8, the button member  340  is shown in the second position wherein the hammer  330  is allowed to slide along a portion of the anvil  350 . 
     Referring now to FIG. 4, a preferred button member  340  includes a collar  342 , a spring member  343 , and fasteners  344 . The spring member  343  retains the collar  342  within the transverse bore  332  and provides a biasing force that urges the collar  342  from the second position to the first position show in FIG.  4 . The spring member  343  is fixed at one end to the hammer  330  with fasteners  334  and attached at the other end to the collar  342  using known means such as fasteners or a weld. 
     Referring now to FIGS. 4 and 7, the collar  342  is a dowel-like structure having an arcuate portion  345 , a shoulder portion  346 , and a passage  347 . When the button member  340  is in the first position, the arcuate portion  345  protrudes out of the transverse bore  334  and the shoulder portion  346  partially blocks the hammer axial bore  332 . As shown in FIG. 7, the radial offset between collar passage  347  and the hammer axial bore  332  provides a mechanical interference that prevents the anvil  350  from entering the axial bore  332  of the hammer  330 . Referring now to FIG. 8, when the button member  340  is in the second position, the collar passage  347  radially aligns with the axial bore  332 , thereby allowing the anvil  350  to enter the axial bore  332  via the collar passage  347 . Referring briefly to FIG. 7, the trigger ledge  229  is positioned to impinge the arcuate portion  345  of the collar  342  when the trigger housing  228  moves in the “U” direction relative to the hammer  330 . As can be appreciated, the arcuate portion  345  acts as a ramp that facilitates smooth contact between the trigger ledge  229  and the collar  342 . The interfering contact between the ledge  229  and the collar  342  forces the collar  342  to be depressed into the transverse bore  334 , thereby moving the collar  342  from the first position to the second position. 
     Referring now to FIGS. 3 and 4, the anvil  350  transfers the jarring force delivered by the hammer  330  to the tool string lower section  24  via the mandrel assembly  400 . The anvil  350  includes a base  352 , a reduced-diameter sleeve portion  354 , and a passage  356 . The base  352  is preferably configured to withstand repeated impact of the hammer head  336 . The sleeve portion  354  extends axially from the base  352  and provides a support surface on which the hammer  330  slides. The anvil passage  356  includes an internally threaded portion  357  for engaging the mandrel assembly  400 . The anvil passage  356  is further adapted to receive the telemetry link  500 . The sleeve portion  354  is shaped to enter the collar passage  347  and the axial bore  332  when these two openings are aligned. 
     Referring now to FIGS. 4-6, the mandrel assembly  400  provides a generally rigid structure that transmits the jarring force produced by the jarring assembly  300  to the tool string lower section  24 . The mandrel assembly  400  includes a spring mandrel  410  (FIG.  4 ), an intermediate piece  420  (FIG.  5 ), and a lower mandrel  430  (FIG.  6 ). The spring mandrel  410 , the intermediate piece  420  and the lower mandrel  430  are serially interconnected using known mechanical interfaces such as threaded connections. The spring mandrel  410  includes an externally threaded end  412  that mates with the enlarged diameter portion  357  of the anvil  350 . Similarly, the lower mandrel  430  includes a threaded portion  432  that engages complementary threads  434  formed on the bottom sub  210 . As noted earlier, the bottom sub  210  is rigidly connected to the tool string lower section  24  via the adapter  600 . Thus, it can be seen that a substantially rigid connection is made between the anvil  350  and the tool string lower section  24 . 
     The mandrel assembly  400  also includes a passage  402  through which the telemetry link  500  extends from the wireline upper section  22  to the lower section  24  (FIG.  2 ). Like the housing upper assembly  220 , the construction of the mandrel assembly  400  is known in the art and utilizes known features such as threaded pin-box connections and sealing members such as elastomeric “O”-rings. Accordingly, such features will not be discussed in detail. As noted earlier, the jarring tool  100  may be several feet in length. Accordingly, for ease of fabrication, handling, assembly, and maintenance, the mandrel assembly  400  is formed of the plurality of mandrels  410 , 420 , and  430 . Depending on the desired application, however, greater or fewer mandrels may be used. 
     Referring now to FIG. 2, the telemetry link  500  enables the exchange of data between the wireline upper housing  22  and lower section  24 . During deployment of the tool string  10 , data transmitted between the surface equipment  20  (FIG. 1) and the tool string  10  can electrically traverse the jarring assembly  300  via the telemetry link  500 . Advantageously, this function is maintained during the jarring sequence for freeing the wireline  10  from a downhole obstruction  13  (FIG.  1 ). Referring now to FIGS. 3 and 6, a preferred telemetry link  500  includes first and second electrical sockets  502 ,  504  and a telescoping assembly  506 . The electrical sockets  502 ,  504  provide an electrical interface between the telescoping assembly  506  and the tool string upper and lower sections  22 , 24 , respectively. Such sockets are known in the art and will not be described in detail. The telescoping assembly  506  is formed at least partially of conductive material adapted to transmit electrical signals and includes at least two members that are electrically coupled through one or more mating surfaces. In a preferred embodiment, the telescoping assembly  506  has an insulation sleeve  507  and at least one inner tube  508  that is concentrically positioned within at least one outer tube  510 . Preferably, at least a portion of the inner tube  508  is housed within the outer tube  510  during normal operations. A portion of the outer surface of the inner tube inner tube  508  is always in contact with a portion of the inner surface of the outer tube  510 . These two mating surfaces electrically couple the inner tube  508  to the outer tube  510 . The insulation sleeve  507  provides a mechanical and electrical barrier between the telescoping assembly  506  and the jarring tool  100 . 
     As can be appreciated, the telescoping assembly can have a relatively fixed first axial length and a variable second axial length. During normal operations, the telescoping assembly has a relatively compact length, the first axial length, because a relatively long portion of the inner tube  508  is disposed within the outer tube  510 . When needed, a portion of the inner tube  508  slides out of the outer tube  512 , thereby increasing the length of the telescoping assembly  506 . The telescoping assembly  506  adjusts or expands to accommodate the maximum axial travel of the upper assembly  220  relative to the bottom sub  210  or some intermediate variable length. Because the inner tube  508  and outer tube  512  maintain at least some mating surface, electrical signals can still travel between the wireline tubing upper and lower sections  22 , 24  via the telescoping assembly  506 . 
     The telemetry link  500  is amenable to numerous embodiments. For example, although the sockets  502 , 504  are shown, other electrical connections such as plugs, pin-type connectors, or soldered wires may be used. Indeed, the sockets  502 , 504  may be dispensed with entirely if, for example, the telescoping assembly  506  is electrically integrated into the tool string  10 . Furthermore, the members making up the telescoping assembly  506  may be strips, plates, wires, cables, or other elongated structures instead of tubing. The members need only be electrically coupled through mating surfaces that slide relative to each other. Additionally, the telescoping assembly  506  can use three or more members arranged in a telescoping relationship. 
     In the discussion below regarding the operation of the jarring tool, familiarity is presumed with the above discussed exemplary features of the exemplary preferred jarring tool. Accordingly, the numerals associated with these features are omitted for brevity. Furthermore, the described sequences and phases of operation are merely exemplary of certain embodiments of the present invention. One skilled in the art will understand that other embodiments may used different sequences and phases. 
     During use, the tool string and jarring tool are deployed into a well bore using a suspension line. If the lower portion of the tool string becomes stuck or otherwise immobile in the well bore, then the jarring tool has an initial condition wherein (a) the button member is in the first position, and (b) the anvil is immobile due to its connection to the tool string lower section via the mandrel assembly. The jarring sequence commences with an optional activation phase wherein the suspension line is drawn upwards to produce an axial traction force on the jarring tool housing. Because the housing bottom sub is fixed to the stuck tool string lower section, the frangible member connecting the bottom sub to the separator housing of the housing encounters a shearing force. Once this shearing force reaches a pre-determined value, the frangible member disintegrates and releases the separator housing and housing upper assembly from the bottom sub. This phase is optional because the jarring tool may be configured to be operated without necessarily having the housing separate. 
     Upon the shearing member snapping, jarring tool enters a loading phase wherein the housing upper assembly moves axially away (i.e., direction “U”) from the tool string lower section. During this phase, the axial movement of the piston housing causes the piston head to engage one end of the biasing member. The hammer, which is positioned on the other end of the biasing member, is held stationary. As explained earlier, the button member is in the first position and thus prevents the hammer from sliding toward the anvil. Thus, the spring is compressed against the temporarily immobile hammer by the piston head. The axial movement of the housing upper assembly and piston housing thereby creates a compression force within the biasing member using the piston head. The axial movement of the housing also causes the ledge of the trigger housing to move towards the arcuate portion of the collar. 
     A release phase is entered upon the trigger ledge moving into interfering engagement with the arcuate portion of the collar. The axial movement of the trigger housing ledge in the “U” direction pushes the collar into the transverse bore of the hammer. It will be appreciated that, at this time, the piston head has compressed the biasing member a pre-determined amount. As the button moves from the first position to the second position, the passage of the collar and axial bore align with the sleeve portion of the anvil. Once aligned, the hammer is free to slide along the sleeve portion. The compressed biasing member, at this time, accelerates the hammer axially. In a projectile-type fashion, hammer travels along the sleeve portion and percussively strikes the base of the anvil. The anvil and connected mandrel assembly/tool string lower section are thereby urged in the generally “U” direction. This action in many instances will free the tool string lower section and allow the tool string to be retrieved from the well bore. 
     In certain instances, one or more hammer strikes may be needed to free the tool string. In these instances, the jarring tool is put into a reload phase. This phase is initiated by relieving the traction force on the tool string. The reduction of traction force permits the upper assembly to slide axially towards the lower assembly (i.e., direction “D”). During this movement, the pin end of the anvil housing contacts the hammer head and urges the hammer axially in direction “D”. At the same time, the ledge of the trigger housing moves out of contact with the arcuate portion of the collar. Once the sleeve of the anvil exits the hammer axial bore and the collar passage, the spring member returns the collar from the second position to the first position. With the hammer and anvil interlocked by the button member, the jarring sequence can be again performed. 
     It will be appreciated that during the several phases of the jarring sequence, the axial length of the housing increases and decreases. The telemetry link accommodates the housing length change by a telescoping action. That is, after the bottom sub and housing upper assembly separate and as the housing upper assembly moves the “U” direction, the inner tube of the telemetry link is extracted out of the outer tube. Conversely, when the housing upper assembly moves toward the bottom sub, the inner tube slides into the outer tube. Thus, during all phases of the jarring sequence, a reliable telemetry communication path is maintained with the tool string lower section. 
     It should be understood that the terms such as “upper”/“lower” and “uphole”/“downhole” are intended only to clarify the relative orientation of any described feature or component. As is known, well bore may have highly deviated or even horizontal portions. Such well bore environments do not affect the functionality of the present invention. Furthermore, the above-described embodiments of the present invention provide a percussive or jarring force in a generally uphole direction. It would apparent to one skilled in the art, however, that the present invention may be arranged to provide a percussive or jarring force in a generally downhole direction. 
     Although illustrative embodiments of the invention have been shown and described, a wide range of modification, changes and substitution is contemplated in the foregoing disclosure. In some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Summary:
A jarring tool uses a button member to control the jarring sequence used to free an object lodged in a well bore. A preferred tool includes an anvil having a sleeve portion adapted to enter a bore of a hammer. The button member allows selective entry of the anvil sleeve into the hammer bore. A preferred telemetry link includes two or more at least partially conductive members in a telescopic relationship for exchanging electrical signals with the object. The members extend and retract to accommodate length changes of the jarring tool. An exemplary jarring sequence includes a loading phase, a release phase, and a reset phase. In the loading phase, the button member prevents hammer movement toward the anvil. During the release phase, the button member allows the hammer to be propelled against the anvil. In the reset phase, the hammer and button returns to their initial positions.