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: 
BACKGROUND 
     Field of the Invention 
     The present invention relates to power tongs for making up threaded connections between adjacent pipe sections. More specifically, the present invention relates to an improved latch mechanism for securing a power tong door in the closed position. 
     Background of the Related Art 
     Conventional power tongs include a bay having a lateral access. The bay is closed using a power tong door that is hinged to the power tong body at a proximal end of the door and latchable to the power tong body at a position across the lateral access to the bay at a distal end of the door. This configuration enables the door to engage the power tong body in a manner that opposes spreading of the power tong body during operation. 
     Many power tong doors are manually secured in the latched position and manually opened to laterally receive or surrender a tubular joint. Some power tong doors are automatically closed across the lateral access, automatically latched in the closed position and automatically unlatched and opened after the power tong is used to make up or break out a threaded connection between two adjacent tubular joints. 
     BRIEF SUMMARY 
     One embodiment of the present invention provides a power tong body with a door and an improved latch mechanism for securing the door of the power tong in the closed position across an interior bay of the power tong body, the power tong comprising a body having the interior bay for receiving an end of a pipe segment, a lateral access opening providing lateral access to the interior bay, a latch post disposed on the body adjacent to a lateral access to the interior bay, a door having a proximal end pivotally coupled to the body and a distal end having at least one static latch member with a well in a static latch member to receive and engage the latch post on the power tong body upon closure of the door across the lateral access opening, the distal end of the door further including at least one pivoting latch member pivotally coupled to the door adjacent to the at least one static latch member, the pivoting latch member having a proximal end and a distal end with a keeper to receive and engage the latch post on the body, the pivoting latch member being pivotally positionable relative to the door between an engaged position, to engage the keeper at the distal end of the at least one pivotal latch member with the latch post to secure the door in a closed position across the lateral opening, and a retracted position to disengage the distal end of the pivotal latch member and the keeper from the latch post to release the door from the closed position, the power tong further including a door cylinder coupled to the body with an extendable rod extendably received in the door cylinder, the extendable rod having a distal end pivotally coupled to the door, the extendable rod being extendable from the door cylinder to move the door from an open position to a closed position to close the lateral access to the interior bay of the body and the extendable rod being retractable into the door cylinder to move the door from the closed position to the opened position removed from the lateral access opening to the interior bay of the body, and the power tong further including a latch cylinder having a proximal end pivotally coupled to the door and a rod extendable from the latch cylinder with a distal end of the extendable rod coupled to a proximal end of the at least one pivotal latch member, the latch cylinder being extendable to pivot the at least one pivotal latch member to the retracted position and retractable within the latch cylinder to pivot the at least one pivotal latch member to the engaged position wherein the latch post is received into the keeper of the pivotal latch member, wherein the at least one pivotal latch member, in the engaged position, secures the door in the closed position to close the bay of the power tong body by application of a force against the latch post of the body in opposition to a force imparted to the latch post by the at least one static latch member. 
     In a related embodiment of the power tong of the present invention, the door cylinder and the latch cylinder are each one of hydraulic cylinders and pneumatic cylinders. These types of cylinders can be generically referred to as fluid cylinders. 
     In a preferred embodiment of the power tong of the present invention, the at least one static latch member comprises two static latch members having a gap therebetween to engage the latch post at two spaced-apart positions, and the at least one pivotal latch member comprises one single pivotal latch member, wherein the one pivotal latch member engages the latch post at a position on the latch post that is aligned with the gap between the two static latch members and intermediate two positions on the latch post engaged by the two static latch members. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a plan view of a power tong body having a door equipped with an embodiment of an improved power tong door latch of the present invention in the open and unlatched position. 
         FIG. 2  is the plan view of  FIG. 1  after the door is pivoted from the open and unlatched position to the closed and unlatched position. 
         FIG. 3  is a plan view of the power tong body and door of  FIG. 2  after the latch member is stroked by actuation of the latch cylinder into the engaged position to secure the door in the closed and latched position. 
         FIG. 4  is a perspective view of the power tong body, the door and the improved latch mechanism of the door in a position between the open position illustrated in  FIG. 1  and the closed position illustrated in  FIGS. 2 and 3 . 
         FIG. 5  is the perspective view of the power tong body, the door and the improved latch mechanism of the door of  FIG. 4  after the door is pivoted about the pivot member to the closed position and before the improved latch mechanism is used to secure the door in the closed and locked position. 
         FIG. 6  is the perspective view of the power tong body, the door and the improved latch mechanism of the door of  FIG. 5  after the improved latch mechanism is used to secure the door in the closed and locked position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a plan view of a power tong body  10  having a door  12  equipped with an embodiment of an improved power tong door latch of the present invention in the open and unlatched position. The door  12  is pivotally coupled to the power tong  10  at pivot member  14  to enable the door  12  to pivot between the open position (shown in  FIG. 1 ) to the closed position (shown in  FIG. 2 ). The door  12  is movable between the open and closed positions using a door cylinder  24  having a first end  27  pivotally coupled to the power tong body  10  at a first door cylinder pivot pin  29  and a second end  31  pivotally coupled to the door  12  at a second door cylinder pivot pin  28 . The door cylinder  24  may be a hydraulic cylinder or a pneumatic cylinder. The door cylinder  24  may be stroked from the retracted mode shown in  FIG. 1  to the extended mode illustrated in  FIG. 2  by providing pressurized fluid to the door cylinder  24  to extend the rod  26  from the door cylinder  24  and to impart a moment that pivots the door  12  about the pivot member  14  to the closed position shown in  FIG. 2 . In one optional embodiment, the door cylinder  24  may include a spring to bias the extendable rod to restore the door cylinder  24  to the retracted position when the door  12  is unlatched and the fluid pressure falls below a predetermined pressure. 
       FIG. 1  also illustrates a latch post  30  on the power tong body  10 . The door  12  includes a well  19  in a static latch member  20  that receives the latch post  30  with the door  12  moved to the closed position.  FIG. 1  illustrates a interior bay  11  of the power tong body  10  into which a tubular joint, such as a casing joint, is introduced prior to closure of the door  12  and operation of the latch to secure the door  12  in the closed position.  FIG. 1  also shows a pivoting latch member  22  that is pivotable between a retracted position, illustrated in  FIG. 1 , and an engaged position illustrated in  FIG. 3 . The pivoting latch member  22  is pivotable about a latch member pivot pin  23  using a latch cylinder  16 . The latch cylinder  16  is illustrated in  FIG. 1  in the extended mode, with the second end  25  spaced apart from the latch cylinder  16  by the extendable rod  17 . The latch cylinder  16  includes a first end  15  that is pivotably coupled to the door  12  at a latch cylinder pivot pin  13 , an extendable rod  17  connected to a second end  25  that is pivotably coupled to the latch member  22  at pivotal coupling  18 . The latch member  22  can be stroked using the latch cylinder  16  from the retracted position (of  FIG. 1 ), in which the keeper  21  on the latch member  22  is retracted away from the well  19  of the static latch member  20  of the door  12 , to the engaged position (of  FIG. 3 ), in which the keeper  21  is pivoted to an engaged position with the latch post  30 . 
       FIG. 2  is the plan view of  FIG. 1  after the door is pivoted from the open position and unlatched position to the closed and unlatched position.  FIG. 2  illustrates the door cylinder  24  that is actuated to extend the rod  26  to the extended position to pivot the door  12  about the pivot member  14  (see  FIG. 1 ) to the closed position. It will be noticed that the latch mechanism has not been activated in  FIG. 2  and the door  12  is not in the latched position. It will be further understood that the latch cylinder  16  illustrated in  FIG. 2  has not been actuated, and the extendable rod  17  remains in the extended mode to dispose the latch member  22  in the retracted position out of engagement with the latch post  30 . The latch post  30  is affixed to the power tong body  10  and is shown in  FIG. 2  as having been received within the well  19  adjacent to the static latch members  20 . 
       FIG. 3  is a plan view of the power tong body  10  and door  12  of  FIG. 2  after the latch member  22  is stroked by actuation of the latch cylinder  16  into the engaged position to secure the door  12  in the closed and latched position.  FIG. 3  illustrates the use of the improved door latch mechanism to secure the door  12  in the closed and latched position. The latch cylinder  16  is actuated to retract the extendable rod  17  to the retracted configuration and to thereby pivot the latch member  22  from the retracted position shown in  FIG. 2  to the engaged position shown position shown in  FIG. 3 . In the engaged position, it can be seen that the keeper  21  of the latch member  22  is engaged with the latch post  30 . It will be further noted that the keeper  21  of the latch member  22  engages the latch post  30  in opposition to the static latch members  20  on the door  12 . This opposing relationship stabilizes the door  12  in the securely closed position. Maintaining fluid pressure on the latch cylinder  16  to bias the latch cylinder  16  and the latch member  22  coupled thereto to the latched position shown in  FIG. 3  will maintain the latch post  30  in a position trapped intermediate the keeper  21  of the latch member  22 , on a first side, and the static latch member  20  of the door  12  on the second and opposite side of the latch post  30 . 
       FIG. 4  is a perspective view of the power tong body  10 , the door  12  and the improved latch mechanism of the door  12  in between the open position illustrated in  FIG. 1  and the closed position illustrated in  FIGS. 2 and 3 . It will be noted that the door cylinder  16  remains in the extended mode with the extendable rod  17  in an extended position to distance the second end  25  from the door cylinder  16  and to position the keeper  21  in the retracted position to allow the latch post  30  to be received into the well  19  of the static latch member  20  of the door  12 . 
       FIG. 5  is the perspective view of the power tong  10 , the door  12  and the improved latch mechanism of the door of  FIG. 4  after the door  12  is pivoted about the pivot member  14  to the closed position and before the improved latch mechanism is used to secure the door  12  in the closed and locked position. 
       FIG. 6  is the perspective view of the power tong  10 , the door  12  and the improved latch mechanism of the door of  FIG. 5  after the improved latch mechanism is used to secure the door  12  in the closed and locked position. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components and/or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention. 
     The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Summary:
A latch mechanism for securing a pivoting door of a power tong in a closed position across a lateral opening to an interior bay of the power tong includes a door cylinder coupled at a proximal end to the body and having an extendable rod to pivot the door between a closed position, across the lateral opening, and an open position providing lateral access to the interior bay, the power tong further includes a latch cylinder coupled at a proximal end to the door and having an extendable rod to pivot a latch member to pivot between an engaged position, to engage a latch post on the body, and a retracted position to disengage the latch post of the body.