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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
     This disclosure relates to downhole tools in general, and, more specifically, to impact jars for freeing stuck tools. 
     BACKGROUND OF THE INVENTION 
     Drilling operations have become increasingly expensive as the need to drill in harsher environments, through more difficult materials, and deeper than ever before have become reality. Additionally, more testing and evaluation of completed and partially finished well bores has become a reality in order to make sure the well produces an acceptable return on investment. 
     In working with more complex and deeper well bores, a greater danger anises that work strings and tools will be stuck within the bore. In addition to the potential to damage equipment in trying to retrieve it, the operation of the well must generally stop while tools are fished from the bore. Moreover, with some fishing techniques, it is possible to damage the well bore itself. 
     What is needed is a device for addressing the above and related concerns. 
     SUMMARY OF THE INVENTION 
     The invention disclosed and claimed herein, in one aspect thereof comprises a jarring tool. The tool has a first lower sub end, a second upper sub end, and an extensible joint connecting the first and second sub ends. The joint comprises a first inner latch piece connected to the lower sub end, and second outer latch piece connected to the upper sub end, and a stationary restraining collar. The joint, in a latched position, has the outer latch piece latched to the inner latch piece and the inner and outer latch pieces restrained from unlatching by the restraining collar. The joint, under tensile force, unlatches into an unlatched position by the inner latch piece pulling the outer latch piece through the restraining collar into a position where the inner and outer latch pieces are free to separate. An impact force is generated from the tensile force when the joint unlatches and reaches a maximum extension. 
     The joint may relatch into a latched position by the inner latch piece pushing the outer latch piece back through the restraining collar into a position where the inner and outer latch pieces are free to relatch. The outer latch piece may comprises a collet device. The collet may have a plurality of fingers with nubs along distal ends that contact a lip on the inner latch piece when being moved into the latched or unlatch positions through the restraining collar. The collet may be biased toward the inner latch piece by a coil spring. 
     In some embodiments, the tool further comprises a lower shaft interconnecting the inner latch piece to the lower sub end, and a lower stop slidably receiving the lower shaft. The impact force at maximum extension results from contact between the lower shaft and the lower stop. 
     Some embodiments will also comprise an upper sub housing connected to the upper sub end, a lower sub housing, a center connector connecting the upper sub housing and the lower sub housing, an upper shaft slidably received through the center connector and connecting to the upper latch piece, and a plurality of springs biasing the upper shaft away from the center connector. The restraining collar may be attached in a fixed relationship to the lower sub housing. The plurality of springs may comprise a plurality of spring washers. A coil spring may abut the plurality of spring washers and a spring cage may partially surrounding the coil spring. A central passage may be defined through the extensible joint and through the upper and lower sub ends. An electrical conductor may be carried within the central passage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1D  taken together provide a side cutaway view of one embodiment of the jarring tool of the present disclosure. 
         FIGS. 2A-2E  taken together provide a side cutaway view of another embodiment of the jarring tool of the present disclosure. 
         FIG. 3  is a side cutaway view of the embodiments of  FIG. 2A-2E  showing the jarring tool in an extended position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 1A-1D , a side cutaway view of one embodiment of a downhole jarring tool according to aspects of the present disclosure is shown. These drawings are meant to be understood sequentially as adjoining segments of a jarring tool  100 .  FIG. 1A  illustrates the uppermost end of the tool  100 , which is to be followed by  FIG. 1B ,  FIG. 1C , and  FIG. 1D . In the present embodiment,  FIG. 1D  illustrates the bottom most portion of the jarring tool  100 . In the present embodiment, the jarring tool  100  includes an upper sub housing  102  having a distal end  104  attached to an upper sub end  106 . A proximal end  108  of the upper sub housing  102  interconnects with a center connector  110 . The center connector  110  joins the upper sub housing  102  with a lower sub housing  112 . A proximal end  114  of the lower housing  112  connects to the center connector  110 . 
     A distal end  116  of the lower housing  112  is connected to a lower stop  118 . In the present embodiment, the lower stop  118  provides for sliding engagement and limited passage of the lower shaft  120 . The lower shaft  120  may be interconnected to a lower sub end  122 . The range of motion of the lower shaft  120  relative to the lower housing  112  may be limited by both the lower sub end  122  and by an inner shoulder  124  of the lower stop  118 . The lower shaft  120  provides a shoulder  126 , which will be too wide to pass through the lower stop  118 . As will be described in greater detail below, when the jarring tool  100  is activated, the upper sub end  106  will extend away from the lower sub end  122  to the point where inner shoulder  124  of the lower stop  118  contacts the lower shaft shoulder  126 . 
     The lower shaft  120  connects to an inner latch piece  128 . The inner latch piece  128  interfits with an outer latch piece  130 . In the present embodiment, the outer latch piece  130  is a collet device. In order to secure adequate transmission of tensile forces between the inner latch piece  128  and the outer latch piece  130 , the inner latch piece  128  may have a lip  129  extending substantially around a proximal end of the latch piece  128 . Similarly, outer latch piece  130  may have a lip  131  on one or more of the collet fingers of the latch piece. Additionally, a release sleeve  132 , which restricts the diameter to which the outer latch  130  may open, may be placed in an appropriate fixed location within the lower sub housing  112 . 
     The upper latch piece  130  may be connected to an upper shaft  134 . In the present embodiment, there may be a number of interposing parts, such as a latch connector  136 , an outer latch connector  138 , and a bias spring  140 . The full function of the additional parts will be explained in greater detail below. However, from the present description, it can be appreciated that the latch connector  136  and outer latch connector  138  serve generally to interconnect the upper shaft  134  to the outer latch piece  130 . The outer latch connector  138  may slide in through the outer latch piece  130  and interfit into the latch connector  136 . The outer latch connector  138  allows a limited degree of sliding to occur with respect to the outer latch piece  130 . In the present embodiment, the bias spring  140  will keep the outer latch piece  130  generally extended away from the upper shaft  134  but will allow a limited degree of movement in the direction of the upper shaft  134 . 
     The upper shaft  134  may extend generally through the upper sub housing  102  and engage a washer stack  142  or other spring mechanism. The washers of the washer stack  142  may be spring washers, such as Belleville washers. In some embodiments, the entire region between a distal end  135  of the upper shaft  134  and the center connector  110  will be substantially filled with the washer stack  142 . However, in other embodiments, such as the one shown in  FIG. 1 , it may not be necessary or desirable to completely fill this region with spring washers. In such case, a slack spring  144  may be provided and may be separated from the washer stack  142  by a washer  146 . The washer  146  may be a flat washer that may or may not be attached to the upper shaft  134 . As will be described in greater detail below, the washer stack  142  will be subject to compressive forces between the distal end  135  of the upper shaft  134  and the center connector  110 . Because the slack spring  144  may have a much lower spring rate than the washer stack  142 , a spring cage  148  may be utilized to limit the amount of compression received by the slack spring  144 . 
     In some embodiments, the slack spring and/or washer stack  142  may bear directly against the center connector  110  when the device  100  is under tensile stress. However, in the present embodiment, the center connector  110  is provided with an adjustment sleeve  149  on the end connecting to the upper sub housing  102 . Thus, in the present embodiment, the spring cage  148  or the slack spring  144  will bear against the adjustment sleeve  149 . The adjustment sleeve  149  may be threaded or otherwise adjustably attached to the center connector  110 . A set screw  150  may be utilized to prevent the sleeve  149  from coming out of adjustment. In some embodiments, the relative location of the washer stack  142  and the slack spring  144  may be reversed. Additionally, the adjustment sleeve  149  may be located at the distal end  135  of the upper shaft  134 . 
     In operation, the jarring tool  100  may be used in a well bore or other downhole environment to free stuck tools or other equipment. The present exemplary embodiment is designed primarily for use with a slick line work string, but other embodiments are also contemplated as described below. 
     In one method of use, the jarring tool  100  will be included with the downhole work string, possibly near the bottom of the string. For example, the upper sub end  106  could connect to the uphole string while the lower sub end connects to a tool on location in the work string where a stickage is likely to result. In some respects, the tool  100  may be considered as a pair of sub ends  106 ,  122  having an extensible joint therebetween. 
     In the configuration shown in  FIGS. 1A-1D , the jarring tool  100  is shown in a closed or latched position. At the point the line or tool becomes stuck within a well bore, the tool may be activated by supplying sufficient tensile forces to the sub ends  106 ,  122 . As the sub ends  106 ,  122  are pulled apart, it will be appreciated that the lower shaft  120  will pull against the inner latch piece  128 . The inner latch piece  128  and/or the lip  129  coming in contact with the outer latch piece  130  and/or lip  131  will pull the distal end  135  of the upper shaft  134  against the washer stack and/or slack spring  134 . 
     The slack spring  144  may have a limited range of motion before the spring cage  148  will engage the washer  146  and/or the washer stack  142 . It will be appreciated that the washer stack  142  may have an extremely high spring rate such that many hundreds or thousands of pounds of force are required to effectively overcome the force of the springs. In the present embodiment, the outer latch  130  is limited in its ability to disconnect from the inner latch  129  by the fixed release sleeve  132 . However, when sufficient tensile strength has been applied to the tool  100 , so as to displace the inner latch  128  and the outer latch  130  sufficiently through the release sleeve  132 , the outer latch  130  will be free to slip free from the inner latch  128 . The energy stored in the work line will rapidly displace the tool  100  in the direction of the upper sub end  106 . However, the lower sub end  122 , being attached to the stuck tool or line, will remain in place. The lower shaft  120  will then slide axially through the lower stop  118  until the lower shaft shoulder  126  impacts the inner shoulder  124  of the stop  118  (see, e.g.,  FIG. 3 ). It is this impact resulting from the line tension on the work string suddenly being released that will create a sufficient upward impact on the lower sub end  122  to free the stuck tool, line, or other device. 
     In some cases, it may be that a single jarring impact will not be sufficient to remove the stuck tool or line. It is also possible that once the tool or line has been freed, it will become stuck again. For this reason, the jarring tool  100  is resettable such that repeated impact jars may be provided in the wellbore. When a compressive force is applied to the tool after it is unlatched, the inner latch piece  128  will encounter the outer latch piece  130  within the release sleeve  132 . However, as described, the release sleeve  132  does not provide sufficient clearance for the inner latch  128  and the outer latch  130  to reconnect. Therefore, in order to reset or relatch the tool  100 , the outer latch piece  130  must be sufficiently displaced through the release sleeve  132  to allow sufficient clearance to relatch to the inner latch piece  128 . 
     In the present embodiment, the outer latch piece  130  may be slidably attached to the outer latch connector  138 . The bias spring  140  will normally keep the outer latch piece  130  within the release sleeve  132 . However, when the bias spring forces overcome the outer latch piece  130  may displace toward the proximal end  114  of the lower sub housing  112  a sufficient amount to clear the release sleeve  132  and thereby relatch with the inner latch piece  128 . At this point, the tool has been reset and may be activated to produce jarring forces again by reapplication of a tensile force. It will be appreciated that the spring rate of the bias spring  140  may be much lower than the spring rate of the washer stack  142 . In this way, the amount of force necessary to reset or relatch the tool  100  will be very small in comparison to the amount of force required to activate the tool  100  by unlatching. 
     Referring now to  FIGS. 2A-2E , another embodiment of the jarring tool of the present disclosure is shown. As with  FIG. 1 ,  FIGS. 2A-2E  comprise a segmented illustration of the entire length of the tool  200 . In the present disclosure, like numbered parts are similar from one drawing to the next, and thus it will be appreciated that the tool  200  bears many similarities to the tool  100 . However, the present embodiment  200  illustrates an e-line version of the jarring tool of the present disclosure 
     It can be seen that connected to the upper sub end  106  is a conductor housing  204 . The conductor housing  204  may be another sub section that forms a part of the work string. An upper electrical connector  202  may cap off the upper housing  204  and provide for electrical connections to a conductor  206  that runs the length of the tool  200 . The conductor  206  could be a single line or could be a braided or multiplexed line carrying a plurality of signals through the tool  200 . A plug  208  may be provided according to the type of conductor being utilized. As can be seen with reference to  FIGS. 2A-2E , a central passage  210  is provided through the entirety of the tool  200 . A lower electrical connector  216 , with a plug  212  for the conductor  206 , is provided for attachment to work line or tools that are below the jarring tool  200 . 
     The jarring tool  200  operates in a manner that is similar to the operation of the jarring tool  100  described previously. However, since there may be locations within the passageway  210  that the conductor  206  could be pinched or otherwise damaged, protective sheathing may be provided as needed. In the present embodiment, a stainless steel shaft  214  is provided to prevent the conductor  206  from being damaged by the inner latch  128  and/or the outer latch  130 . It will be appreciated that the length of the conductor  206  may need to change with the length of the tool  200  as the tool is examined for jarring or impacting. In the present embodiment, it can be seen that the conductor  206  may be coiled or otherwise stored within the conductor housing  204  such that the conductor is allowed to expand and contract with the tool  200 . 
     It will be appreciated that various embodiments of the tools of the present disclosure can be utilized with a wide variety of drilling and downhole technology. Non-limiting examples include drill pipe, e-line, and slick line strings. The sub ends  106 ,  122  may be chosen according to the work string. Similarly, the overall size of the tools  100 ,  200  may be chosen based on well bore size and other requirements. Both the jarring force and the tension required to activate the tools may be adjusted and fine tuned based upon the number and type of spring washers in the stack  142  and the adjustment of the adjusting sleeve  149 . 
     Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.

Summary:
A tool having a first lower sub end, a second upper sub end, and an extensible joint connecting the first and second sub ends. The joint has a first inner latch piece connected to the lower sub end, and a second outer latch piece connected to the upper sub end, and a stationary restraining collar. The joint, in a latched position, has the outer latch piece latched to the inner latch piece and the inner and outer latch pieces restrained from unlatching by the restraining collar. The joint, under tensile force, unlatches into an unlatched position by the inner latch piece pulling the outer latch piece through the restraining collar into a position where the inner and outer latch pieces are free to separate. An impact force is generated from the tensile force when the joint unlatches and reaches a maximum extension.