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 divisional application of U.S. application Ser. No. 12/609,756, filed on Oct. 30, 2009 now U.S. Pat. No. 7,878,255, which is a continuation of U.S. patent application Ser. No. 11/678,067, filed Feb. 23, 2007 now abandoned, the entireties of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present invention relates to locking apparatus for downhole tools, and more particularly, to a pressure activated locking slot assembly. 
     Typically, when tools are run into the well bore, a mandrel is held in the run-in-hole position by interaction of a lug with a J-slot. To move the tool out of the run-in-hole position generally involves the application of torque and longitudinal force. Such an arrangement can be problematic in offshore or highly deviated sections of a well bore, where dragging forces on the tool string may create difficulty in estimating the proper torque to apply at the surface to obtain the desirable torque at the J-slot. A continuous J-slot wraps all the way around the mandrel and typically has two lugs, so that the direction of torque applied need not be reversed in order to actuate. Rather, the tool may simply be picked up and put back down to cycle. 
     A problem may arise when running such a tool into an offshore or highly deviated well bore. Dragging of the tool string on the well bore may cause the mandrel move relatively upwardly and rotate with respect to the drag block assembly sufficiently to result in premature actuation of the J-slot assembly. If such premature actuation occurs, subsequent downward load on the tool string may rupture the tool elements, or the tool elements may be damaged by dragging along the well bore. In addition, premature actuation may result in the tool string jamming in the well bore. 
     SUMMARY 
     The present invention relates to locking apparatus for downhole tools, and more particularly, to a pressure activated locking slot assembly. 
     In one embodiment of the present invention a locking slot assembly comprises: a slot; a lug configured to move within the slot; and a lock configured to prevent the lug from moving within the slot until a triggering event occurs; wherein the lock is further configured to allow the lug to move within the slot after the triggering event has occurred, so long as a predetermined condition is maintained. The triggering event may be the application of a predetermined pressure, and the predetermined condition may be a minimum pressure. 
     In another embodiment of the present invention a downhole tool assembly comprises: a sleeve having a slot; a lug rotator ring configured to move axially relative to the sleeve, the rotator ring having a lug configured to move within the slot; and a lock configured to prevent the lug from moving within the slot until a predetermined pressure is applied; and wherein the lock is further configured to allow the lug to move within the slot after the predetermined pressure has been applied, so long as a minimum pressure is maintained. 
     In yet another embodiment of the present invention a method of activating a downhole tool assembly comprises: providing a downhole tool assembly in a well bore; applying a predetermined pressure to the downhole tool assembly; and moving the downhole tool assembly upward; wherein the downhole tool assembly comprises a sleeve having a slot, a lug rotator ring configured to move axially relative to the sleeve, the rotator ring having a lug configured to move within the slot, and a lock configured to prevent the lug from moving within the slot until a predetermined pressure is applied. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side cross-sectional view showing one embodiment according to the present invention. 
         FIG. 1B  is a side cross-sectional view of the embodiment illustrated in  FIG. 1A , showing an unlocked position. 
         FIG. 2A  is a side cross-sectional view showing another embodiment according to the present invention. 
         FIG. 2B  is a side cross-sectional view of the embodiment illustrated in  FIG. 2A , showing an unlocked position. 
         FIG. 3A  is a side view showing one embodiment according to the present invention. 
         FIG. 3B  is a side view of the embodiment illustrated in  FIG. 3A , showing an unlocked position. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings and more particularly to  FIGS. 1A and 1B , the locking slot assembly of the present invention is shown and generally designated by the numeral  10 . locking slot assembly  10  is disposed adjacent to a lower end of a tool  12  (shown in  FIG. 2A ), which is of a kind known in the art, such as a valve, a packer, or any tool requiring different positions. Tool  12  may connect to a tool string (not shown) and the entire tool string may be positioned in a well bore. The well bore may be defined by a casing (not shown) and may be vertical, or the well bore may be deviated to any degree. 
     Locking slot assembly  10  is illustrated below the tool  12 . Tool  12  may include, or be attached to, an inner, actuating mandrel  14 , which may be connected to the tool string. Locking slot assembly may include the actuating mandrel  14 , attached at a lower end to bottom adapter  16 . Actuating mandrel  14  and at least a portion of bottom adapter  16  may be situated within a fluid chamber case  18  and/or a lock  20 . The fluid chamber case  18  and the lock  20  may be removably attached, fixedly attached, or even integrally formed with one another. Alternatively fluid chamber case  18  and lock  20  may be separate. 
     At least one fluid chamber  22  may be situated between actuating mandrel  14  and lock  20 . Fluid chamber  22  may be sealed via one or more seals  24 , along with a rupture disk  26  situated in the lock  20 . Air at atmospheric pressure may initially fill the fluid chamber  22 . As the tool  12  is lowered into the well bore, hydrostatic pressure outside the tool  12  increases. Once the hydrostatic pressure reaches a predetermined value, the rupture disk  26  may rupture. After the rupture disk  26  has ruptured, the fluid outside the tool  12  will enter the tool  12  through a port  28  formed therein. The resulting increased pressure within the fluid chamber  22  will cause the fluid chamber  22  to expand (as shown in  FIG. 1B ). This expansion causes the longitudinal movement of the lock  20  with respect to the actuating mandrel  14 , thus “unlocking” the locking slot assembly  10 .  FIGS. 3A and 3B , which will be discussed below, further show the locked position and unlocked position respectively. 
     Referring now to  FIGS. 2A and 2B , shown therein is an alternate embodiment of the locking slot assembly  10 . This embodiment has no rupture disk  26 . Instead, one or more shear pins  30  to prevent the lock  20  from moving until adequate pressure is present. A spring  32  may be included to keep the locking slot assembly  10  in an unlocked position. While the spring  32  shown is a coil spring, the spring  32  may be any biasing member. Likewise, the shear pin  30  may be a screw, spring, or any other shearable member. Other than the use of a rupture disk  26  and/or a spring  32 , the embodiment of  FIGS. 2A and 2B  functions similarly to the embodiment of  FIGS. 1A and 1B . An increase in pressure causes the lock  20  to move longitudinally with respect to the actuating mandrel  14 , resulting in the unlocking of the locking slot assembly  10  (as shown in  FIG. 2B ). 
     Referring now to  FIGS. 3A and 3B , one or more lugs  34  may extend from a lug rotator ring  36  into a continuous slot  38  in a sleeve  40 , thus providing locking assembly  10 . As previously discussed, pressure may cause the lock  20  to become unlocked. In the locked position, a locking portion  42  of the lock  20  occupies space within the slot  38 , keeping the lugs  34  in a run-in-hole position, and preventing the lugs  34  from moving relative to the slot  38 . As the lock  20  moves downwardly because of increased pressure, the locking portion  42  moves out of the slot  38 , allowing the lugs  34  to move relative to the slot  38  if there is an upward or downward force acting on the sleeve  40 . 
     In the run-in-hole, locked position, the lock  20  is in an upward position, in which lugs  34  are engaged with locking portion  42  of the lock  20 . As the tool string is lowered into well bore, the locking slot assembly  10  will remain in the locked position shown in  FIGS. 1A ,  2 A, and  3 A, with the lock  20  preventing relative longitudinal movement of the lug rotator ring  36  with respect to the sleeve  40 . 
     Once pressure is applied and the locking slot assembly  10  is unlocked (as shown in  FIGS. 1B ,  2 B, and  3 B), the locking slot assembly  10  may be actuated, allowing the lug rotator ring  36  to move longitudinally with respect to the sleeve  40 . In other words, the tool  12  may be set by pushing downward on the tool string, which lowers lug  34 . While any type of slot  38  may be used, the embodiment shown uses a j-slot, and in particular, shows a continuous J-slot. Depending on the specific application and the type of slot, setting the tool may involve pushing downward on the tool string multiple times. Thus, when a continuous j-slot is used, the tool  12  may be set by up and down motion alone. This may prevent the operator from cycling through the slot and setting the tool  12  prematurely. 
     For retrieval, the tool string is simply pulled upwardly out of the well bore. This will cause the lug  34  to re-engage the slot  38 . Additionally, as the pressure outside the tool  12 , and thus, the pressure within the fluid chamber  22  is reduced, the lock  20  may move back into the locked position, preventing any subsequent relative movement of the lug rotator ring  36  with respect to the sleeve  40 . 
     While the application of pressure is disclosed above as one triggering event to allow the lug  34  to move within the slot  38 , other events may also occur to allow the lug  34  to move within the slot  38 . In this case, the lock  20  may be configured to allow the lug  34  to move within the slot after the triggering event has occurred, so long as a predetermined condition is maintained. For example, but not by way of limitation, the triggering event may be a timer reaching a predetermined value, and the predetermined condition may be that the timer has not yet reached a second predetermined value. 
     Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.

Summary:
A downhole tool assembly has a sleeve with a continuous j-slot, a lug rotator ring configured to move axially relative to the sleeve and having a lug configured to move within the continuous j-slot, and a rupture disk configured to prevent the lug from moving within the continuous j-slot during run-in. A method of activating the downhole tool assembly includes lowering the downhole tool assembly into a well bore on a tool string, rupturing the rupture disk, allowing the lug to move within the continuous j-slot, and setting the downhole tool assembly by lifting upward and pushing downward on the tool string.