Abstract:
In order to facilitate cutting of the abdominal skin of the carcass, the skin is stretched to a taut condition just prior to commencing a cut of the skin. In a preferred embodiment, such stretching is accomplished through the use of a cam-actuated flapper plate that engages the skin and draws it toward one leg of the carcass, maintaining it in such taut position throughout the cutting process. In an embodiment used for making an opening cut to the body cavity, the knife swings along a skewed path of travel relative to the line of symmetry between the backbone and keel bone of the carcass so as to produce an angled cut that avoids nicking the keel bone.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to high speed, automated poultry processing and, more particularly, to improvements in the way in which cuts are made in the abdominal skin of the carcass, such as during vent cutting and making the opening cut into the abdominal cavity.  
         BACKGROUND  
         [0002]    The abdominal skin of a poultry carcass, covering the abdominal cavity that contains the entrails, is loose and flaccid. This condition sometimes causes difficulties in making accurate cuts in the skin without damaging the entrails, such as when the vent plug is being removed or the opening cut to the abdominal cavity is being made. Further, with known opening cut machinery, it is sometimes possible to nick the keel bone as the knife moves through its cutting stroke, which degrades the acceptability of the product in the eyes of the consumer.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention contemplates stretching the abdominal skin tight before making the cut and then maintaining the skin in a taut condition as the cutting action is carried out. This greatly facilitates severance of the skin and helps reduce the risk of accidentally cutting into entrails located close to the abdominal skin, since the cutting stroke can be more restricted and better controlled. Further, the present invention contemplates making an angled opening cut in the skin from the vent hole adjacent the backbone generally toward the keel bone, but at an oblique angle so that the path of travel of the knife is off to one side of the keel bone.  
           [0004]    In a preferred embodiment of the invention, a stretcher is located in close proximity to one leg of the straddle bar that is straddled by the legs of the carcass. The stretcher comprises a plate-like, rigid flap that overlies the abdominal skin when the carcass is lifted up into its processing position. At the appropriate time, the flap is turned down into engagement with the skin and rotated through almost 90° of travel to pull the skin sideways toward one of the legs of the carcass. While the skin is thusly stretched taut, the cutter performs its cutting operation on the tight skin. Rotation of the stretcher between its standby and operated positions is effected by a stationary cam that engages a follower on the stretcher as the stretcher moves by.  
           [0005]    Making the opening cut angled rather than parallel to an axis of symmetry between the backbone and keel bone of the carcass is accomplished by skewing the swing path of the knife relative to the carcass. Instead of swinging the knife along the axis of symmetry in a path of travel that is generally perpendicular to the back of the carcass, the knife is mounted in such a way that its cutting stroke is oblique to such axis and off to one side of the keel bone. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a top plan view of a processing machine constructed in accordance with the principles of the present invention and capable of carrying out the inventive methods;  
         [0007]    [0007]FIG. 2 is a vertical cross sectional view through the machine taken substantially along line  2 - 2  of FIG. 1;  
         [0008]    [0008]FIG. 3 is a vertical cross sectional view through the machine taken substantially along line  3 - 3  of FIG. 1;  
         [0009]    [0009]FIG. 4 is an enlarged, fragmentary horizontal cross sectional view looking downwardly at the machine taken approximately mid-height thereof;  
         [0010]    [0010]FIG. 5 is a horizontal cross sectional view through the machine at a slightly higher level than FIG. 4 and illustrating one of the ring segments of the carousel and its relationship to the holding fixtures;  
         [0011]    [0011]FIG. 6 is an enlarged, fragmentary vertical cross sectional view through one of the straddle bars of a holding fixture illustrating also the abdominal skin stretcher and associated components, the stretcher being illustrated in its standby position;  
         [0012]    [0012]FIG. 7 is similar to FIG. 6 but shows the stretcher in its operated position;  
         [0013]    [0013]FIG. 8 is an enlarged, fragmentary, horizontal cross sectional view through the center of the machine taken substantially along line  8 - 8  of FIG. 3;  
         [0014]    [0014]FIG. 9 is a transverse cross sectional view through one of the fixtures just above the knife illustrating the skewed relationship of the knife to the guide rods of the fixture;  
         [0015]    [0015]FIG. 10 is a fragmentary vertical cross sectional view of the fixture taken substantially along line  10 - 10  of FIG. 9;  
         [0016]    [0016]FIG. 11 is a fragmentary vertical cross sectional view through a fixture illustrating the manner in which the back stop is operated by a cam track of the machine;  
         [0017]    [0017]FIG. 12 is a view of the fixture similar to FIG. 11 but illustrating how the degree of extension of the back stop is adjusted by raising or lowering the cam track that controls the lifting and clamping apparatus of the fixture;  
         [0018]    [0018]FIG. 13 is a flat pattern of the cams for the machine illustrating critical points in the processing operation;  
         [0019]    [0019]FIG. 14 is an enlarged, fragmentary cross sectional view through the lower cam track in FIG. 13 and taken substantially along line  14 - 14  of FIG. 13 to illustrate the manner in which a short section of the lower track is spring-loaded;  
         [0020]    FIGS.  15 - 20  illustrate the fixture at various points in a cycle of operation;  
         [0021]    [0021]FIG. 21 is a fragmentary vertical cross sectional view of a carcass mounted on one of the fixtures and illustrating the manner in which the carcass is oriented for processing; and  
         [0022]    [0022]FIG. 22 is a plan view from the tail end of a carcass illustrating the approximate path of travel taken by the opening knife as it makes an angled opening cut in the carcass. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    This invention is susceptible of embodiment in many different forms. While there is shown in the drawings and described in the specification certain preferred embodiments of the invention, it is to be understood that the present disclosure is only an exemplification of the principles of the present invention. There is no intent to limit the broad aspects of the present invention to the particular disclosed embodiments.  
         [0024]    The machine  10  includes a carousel  19  adapted for rotation in a counterclockwise direction viewing FIG. 1, driven by an overhead conveying line that brings successive poultry carcasses hanging by their hocks to the machine in the direction of the arrow  12  in FIG. 1. Broadly speaking, the carcasses enter machine  10  behind the guide rail  14  and are intercepted by corresponding holding fixtures  16  spaced about the periphery of the carousel  19 . Each fixture  16  receives a carcass, secures it into a properly located position, and maintains that control over the carcass as a processing operation is carried out thereon. Once the operation is complete and the fixture has rotated around to the far side of the machine, the fixture releases the carcass for conveyance by the overhead line to the next station in the processing facility. Although the particular machine  10  selected for purposes of illustration is an opener for making an opening cut into the abdominal cavity of the carcasses, it will be appreciated that certain principles of the present invention are not limited to that particular type of machine and may, in fact, be embodied in many different types of processing machines.  
         [0025]    The carousel  19  is generally in the shape of a truncated cone as illustrated in FIGS. 2 and 3. A stationary, central tubular shaft  18  provides the main means of support for carousel  19  and defines its upright axis of rotation. A stationary, open, supporting framework (not shown) for shaft  18  and carousel  19  is located around the outside of carousel  19  and stands upright on the floor of the processing plant. Such framework supports a horizontally extending top channel  17  (FIGS. 2 and 3) at the upper end of the machine that serves as a means of suspending shaft  18  from the framework. The uppermost end of shaft  18  projects upwardly through the floor of channel  17  and has a nut  21  that bears the load of shaft  18  on channel  17 . A hydraulic cylinder  23  (FIG. 2) fixed to channel  17  has its extendable ram  23   a  in load-bearing engagement with a member  25  of the framework to support channel  17 . Channel  17  may lift or lower shaft  18  relative to the framework by extending or retracting ram  23   a.    
         [0026]    A top circular disk  20  of carousel  19  is rotatably supported upon shaft  18 , while a larger diameter bottom plate  22  of the carousel rotates around shaft  18  adjacent the lower end of the machine. The top disk  20  and the bottom plate  22  are fixedly interconnected by multiple pairs of upwardly and inwardly inclined, circumferentially spaced guide rods  24  which in effect form a tapered sidewall of the carousel  19  and comprise part of the holding fixtures  16 . An upstanding driver  26  on the top disk  20  (FIG. 2) is operably coupled with a drive wheel or the like (not shown) that is driven by the overhead conveying line such that the carousel is rotated at the same speed as the conveying line. A set of four horizontal, end-to-end ring segments  28  (detailed in FIG. 5) are bolted to the guide rods  24  along the interior surfaces thereof to serve as a means for supporting various components of the machine as will be further described. Thus, ring segments  28  rotate with carousel  19  about shaft  18 .  
         [0027]    In addition to the guide rods  24 , each holding fixture  16  includes a horizontally disposed, generally loop-shaped straddle bar  30  that is fixed to the corresponding pair of guide rods  24  and to the corresponding ring segment  28  by a mounting bar  32  that is integral with straddle bar  30  and by a bolt  34  at the inboard end of straddle bar  30 . The straddle bar  30  is straddled by the legs of the poultry carcass while the carcass remains suspended by its hocks from the overhead, moving conveyor line. A tail bar  36  spans the legs of the straddle bar  30  at a location spaced slightly outwardly from the mounting bar  32  to serve as a stop that abuts the tail end of the poultry carcass for locating purposes during operation.  
         [0028]    Each fixture  16  further includes lifting mechanism  40  for lifting the carcass up against the straddle bar  30  and tail bar  36  and securely holding the carcass in such location as the opening cut is made in the abdominal skin of the carcass. In the preferred embodiment, lifting mechanism  40  is similar to that disclosed and claimed in U.S. Pat. No. 5,569,072 assigned to the assignee of the present invention. Accordingly, the &#39;072 patent is hereby incorporated by reference into the present specification.  
         [0029]    Briefly, lifting mechanism  40  includes a block  42  of synthetic resinous material that is reciprocally mounted on the guide rods  24 . A pair of leg clamps  44  and  46  are mounted on block  42  for pivoting movement about respective pivots  48  and  50 . A stationary cam bar  52  is fixed to the rods  24  below block  42  and is engaged with the lower ends of leg clamps  44  and  46 . The lower ends of leg clamps  44  and  46  are so configured relative to cam bar  52  that as block  42  rises along guide rods  24 , the upper ends of leg clamps  44  and  46  are caused to swing inwardly about pivots  48  and  50  to clamp against the legs and opposite sides of the trunk of the carcass immediately below the hip joints. This clamping action, coupled with the upward movement of the block  42 , causes the carcass to be forced upwardly against the straddle bar  30  and the tail bar  36  and securely held in that position (see FIG. 21). When the block  42  is lowered on guide rods  24 , cam bar  52  causes leg clamps  44  and  46  to pivot in the opposite direction, releasing their grip on the legs and trunk of the carcass. Block  42  also carries a fixed neck yoke  54  for receiving and controlling the neck of the carcass.  
         [0030]    Up and down movement of the lifting block  42  along guide rods  24  is effected by a roller  56  on the rear of block  42  and by a cam track  58  that captively receives roller  56 . Cam track  58  is formed in the outer circumferential periphery of an annular, lower cam cone  60  that encircles the upright shaft  18  and is held against rotation thereby. Cone  60  is supported by a plurality of radial spokes  62  (FIGS. 2 and 3) that are bolted to cone  60  at their outer ends and are fixed to a central hub  64  at their inner ends. Hub  64  encircles the lower end of shaft  18  and is adjustably reciprocal up and down along the latter by virtue of bushings  66  and  68  at upper and lower ends of hub  64 . A clamp  70  at the lower end of hub  64  encircles the latter and supports a guide disk  72  provided with an outer circumferential surface upon which guide rollers  74  of bottom plate  22  ride for guidance during rotation of the carousel. A central opening  76  in bottom plate  22  is aligned with guide disk  72  so as to permit guide disk  72  to move up and down with hub  64  relative to bottom plate  22  during vertical adjustment of hub  64 .  
         [0031]    Hub  64  is raised or lowered along shaft  18  by a long link  78  housed within shaft  18 . Link  78  carries a cross bolt  80  at its lower end that passes through vertical slots  82  and  84  in opposite sidewalls of shaft  18  and is fixed to hub  64 . The upper end of link  78  is secured to a bell crank  86  that pivots about a horizontal pivot  88  on channel  17 . Bell crank  86  is actuated by a pair of back to back air cylinders  92  and  94  extending between the outer end of bell crank  86  and a remote end of channel  17 . In the preferred embodiment, bell crank  86  has four adjusted positions about pivot  88  corresponding to conditions where cylinders  92  and  94  are both fully retracted, both fully extended, cylinder  92  is retracted while cylinder  94  is extended, and cylinder  94  is retracted while cylinder  92  is extended. A lower stabilizer denoted generally by the numeral  96  is secured to shaft  18  above spokes  62  and has depending forks  98  that straddle a pair of the spokes  92  so as to help in holding cam cone  60  against rotation on shaft  18  during operation.  
         [0032]    The block  42  of each lifting mechanism  40  is generally adapted to receive the back of the carcass on the fixture. The outer front face of block  42  is flat in the area of the pelvic bone structure of the carcass. In addition, however, the block  42  is provided with an adjustable back stop  100  in the nature of a stainless steel pin or plug that is received within a bore  102  in block  42  (FIGS. 11 and 12). Back stop  100  is shiftable within the bore  102  of block  42  along a line of action that is perpendicular to guide rods  24  and the path of up and down travel of block  42 . An enlarged head  104  at the outer end of back stop  100  limits the retraction of back stop  100  to a position in which head  104  is essentially flush with the outer face of block  42 . At the other extreme, a retaining ring  106  on the inner end of back stop  100  limits the amount of extension of back stop  100 , i.e., the distance which head  104  projects outwardly beyond the surface of block  42 .  
         [0033]    The back stop  100  is operated by a relatively short, generally arcuate cam segment  108  (see also FIG. 4) secured to the upper extremity of cam cone  60  by bolts  110 . Cam segment  108  has an outboard, vertical cam surface  112  that is disposed to engage the innermost end of back stop  100  to project it from block  42 . A beveled lead-in portion  112   a  of cam surface  112  causes progressive extension of back stop  100  from block  42 , while a constant radius central portion  112   b  of surface  112  maintains the projected position of back stop  100 . An oppositely beveled portion  112   c  of surface  112  at the exit end thereof permits the back stop  100  to be retracted by the body of the bird after it passes cam segment  108 .  
         [0034]    [0034]FIGS. 11 and 12 illustrate that when cam cone  60  is adjusted vertically to change the upper and lower limits of travel of the block  42 , such vertical adjustment also has the effect of adjusting the throw, or amount of extension, of the back stop  100  from block  42 . This is due to the fact that cam surface  112  of cam segment  108  is vertical, while the path of travel of block  42  is inclined. Consequently, as cam cone  60  and cam segment  108  are adjusted upwardly, cam surface  112  becomes disposed closer to the back side of block  42  than before, thus functioning to push back stop  100  further outwardly than prior to such adjustment. Similarly, when cam cone  60  and cam segment  108  are adjusted downwardly, the vertical cam surface  112  becomes spaced further away from the back side of block  42  to correspondingly push back stop  100  a shorter distance outwardly beyond the front face of block  42  during each actuation.  
         [0035]    It will be seen, therefore, that the distance back stop  100  projects outwardly from block  42  is a function of the extent to which the path of travel of the block  42  is displaced upwardly or downwardly along the inclined guide rods  24 . If the upper end of such path of travel is adjusted upwardly to account for smaller birds that are shorter in length, for example, the back stop  100  will correspondingly be projected further outwardly than before. Because smaller birds also have thinner backs it is necessary to position those carcasses further outwardly along the straddle bar  30  than larger carcasses in order to properly locate the vent hole for processing. On the other hand, if the upper limit of travel of the block  42  is adjusted downwardly along guide rods  24  by lowering guide cone  60  so as to accommodate larger carcasses, the back stop  100  will not be projected as far outwardly by cam segment  108  as it would prior to such adjustment. This allows the vent hole of the carcass to remain properly positioned.  
         [0036]    In one preferred embodiment of the invention, the angle of inclination of the guide rods  24  is approximately 10°. The range of vertical adjustment of the cam cone  60  is 30 millimeters. Consequently, the range of adjustment of the outermost position of the back stop  100  is approximately 5.2 millimeters. In a typical processing situation, this range is adequate to compensate for variations in back thickness between larger and smaller birds typically processed by this machinery. It will be appreciated, however, that the principles of the present invention are certainly not limited to this range of values.  
         [0037]    A processing tool denoted generally by the numeral  114  is mounted on guide rods  24  above each straddle bar  30  for performing a processing operation on the carcass held by the fixture  16 . In the particular embodiment illustrated herein, as noted earlier, the processing tool is a cutter in the form of a knife for making an opening cut into the body cavity of the carcass through the abdominal skin. An alternative embodiment of processing tool  114  may comprise a vent cutter, for example, for cutting the vent from the carcass prior to making the opening cut. It will be appreciated that the principles of the present invention encompass both of such types of processing tools, as well as others specifically not mentioned herein.  
         [0038]    The knife  114  in the illustrated embodiment is mounted on a carrier  116  that is shiftable up and down along guide rods  24 . An actuating head  118  is reciprocable along guide rods  24  above carrier  116  for effecting a cutting stroke of knife  114  after the knife has been inserted into a hole at the vent of the carcass following proper positioning of the carcass by the back stop  100  and other mechanism. The actuating head  118  carries an elongated rack gear  120  that meshes with a pinion gear  122  on the upper end of knife  114  to cause in and out swinging of knife  114  about a pivot  124  when actuating head  118  is moved relative to carrier  116 .  
         [0039]    Movement of carrier  116  and actuating head  118  along guide rods  24 , and movement of the actuating head  118  relative to carrier  116 , are controlled by corresponding cam tracks  126  and  128  in the outer periphery of an annular upper cone  130  supported by central shaft  18 . A following roller  132  on the back side of carrier  116  rides in track  126 , while a following roller  134  rides within cam track  128 .  
         [0040]    Upper cam cone  130  is supported on central shaft  18  in the same way that lower cam cone  60  is supported on shaft  18 . A plurality of radially projecting spokes  136  (FIG. 8) are fixed at their outer ends to the upper cam cone  130  and at their inner ends to a cylindrical hub  138  that surrounds central shaft  18 . Hub  138  has a pair of upper and lower bushings  140  and  142  that adapt hub  138  for vertical sliding movement along shaft  18 . A cross bolt  144  extends transversely through one side of hub  138  and through a vertical slot  146  in the corresponding side of shaft  18  before being threaded into the lower end of an upright link  148  within shaft  18  and disposed alongside link  78 . Link  148  is connected at its upper end to bell crank  86  in the same manner as link  78  such that manipulation of crank  86  causes adjusting up and down movement of link  148  in addition to link  78 . A stabilizer  150  fixed to shaft  18  above hub  138  has a pair of depending forks  152  and  154  that embrace two of the diametrically opposed spokes  136  to hold upper cam cone  130  against rotation relative to shaft  18  during operation.  
         [0041]    As shown in FIG. 9, carrier  116  for knife  114  is configured in such a manner that the pivot  124  is skewed with respect to the line of centers between guide rods  24 . Instead of extending parallel to rods  24 , pivot  124  extends at an oblique angle of approximately 12.5° relative to rods  24 . The rack gear  120  of actuating head  118  is similarly skewed so as to maintain proper meshing relationship with the pinion gear  122  on the upper end of knife  114 .  
         [0042]    As a result of this skewed relationship, the cutting stroke of knife  114  as it swings outwardly after being inserted into the vent hole of the carcass is not perpendicular to the line of centers between rods  24 . Instead, it is at an oblique angle (12.5°) relative to such line of centers. As will be seen, this results in an angled opening cut in the abdominal skin of the carcass.  
         [0043]    In order to assist in the making of the opening cut, each fixture  16  is provided with apparatus for drawing the abdominal skin tight just prior to the cut and for maintaining the skin in a taut condition while the cutting stroke of knife  114  is carried out. Such apparatus comprises a stretcher denoted by the numeral  156  (FIGS.  5 - 7 ) that is located closely adjacent and slightly below one leg of each of the straddle bars  30 . Each stretcher  156  includes an operating shaft  158  located slightly below the adjacent leg of loop  30  and extending in parallel relationship therewith generally radially outwardly from the center of the carousel. At its outer end, shaft  158  is provided with a rigid, transversely extending, plate-like flap  160  that normally projects generally horizontally from shaft  158  laterally into the open space defined by loop  30 . At its opposite, inner end, shaft  158  is journaled by ring segment  28  for oscillation about the longitudinal axis of shaft  158 . During operation, stretcher  156  rotates between a standby position in which flap  160  extends generally horizontally (FIGS. 5 and 6), and an actuated position in which flap  160  projects downwardly after shaft  158  has been rotated almost 90 degrees (FIG. 7).  
         [0044]    In order to operate stretcher  156 , the inboard end of shaft  158  is provided with a cam follower roller  162  mounted on shaft  158  via a crank arm  164 . An oppositely extending crank arm  166  supports a counterweight  168  at its outer end so that shaft  158  is biased toward the standby position of stretcher flap  160 . A stop  170  carried by crank arm  166  abuts the bottom of ring segment  28  when flap  160  is in its standby and operated positions so as to prevent over travel of shaft  158  beyond such extreme positions.  
         [0045]    Follower roller  162  of stretcher  156  is disposed for operation by an inclined cam  172  within the interior of the carousel (FIGS.  2 - 4 ). Follower roller  162  bears against the underside of cam  172 , biased to that position by the counterweight  168 . Cam  172  is generally semi-circular when viewed in plan (FIG. 4) and has a shallow general V-shape when viewed in elevation (FIG. 13). Thus, the opposite ends of cam  172  are high and the center is low such that the stretcher is actuated progressively from its standby position to its operated position, is maintained in its operated position for a short period of time, and is then progressively released back to its standby position. Cam  172  is fixed to and supported by the lower stabilizer  96 .  
         [0046]    Operation  
         [0047]    The empty fixtures  16  moving around the machine and approaching guide rail  14  in FIG. 1 correspond to the condition illustrated in FIGS. 15 and 16 in which the knife  114  is fully raised, the lifting and stabilizing mechanism  40  is fully lowered, the back stop  100  is fully retracted, and the stretcher  156  is in its standby position. This condition also corresponds to that designated by the letter A in FIG. 13 which shows one fixture  16  and a flat pattern of the various cam tracks for the machine as the fixture  16  moves around the central axis. It will be appreciated that condition A in FIG. 13 is typical of the fixtures  16  in FIG. 1 approaching the guide rail  14  where they will intersect with the poultry carcasses.  
         [0048]    As the fixtures intercept the moving carcasses, the carcasses are guided into place with their legs straddling the straddle bar  30  and their backs up against the blocks  42  of the lifter mechanisms  40 . By the time a fixture reaches position B in FIG. 1 and FIG. 13, the lifter mechanism  40  will have gripped the carcass on opposite sides of the trunk near the hip joints and will have lifted the carcass up against the tail stop  36  as illustrated, for example, in FIG. 21. This locates the carcass along a longitudinal axis  174  (FIG. 21) extending between the head and tail ends of the carcass.  
         [0049]    Also by the time point B is reached, the back stop  100  will have engaged cam segment  108  and will have been pushed outwardly thereby along an axis  176  (FIG. 21) that is transverse to the carcass, extending generally between the back and breast of the carcass. Thus, by this time, the back stop  100  will have engaged the pelvic bone structure below the tail of the carcass and pushed the carcass outwardly away from the face of block  42  by an amount that is necessary to assure that the vent hole  178  is properly aligned with the tool  114 . Depending upon the size of the birds being processed and the particular run at hand, the back stop  100  may be further extended than that illustrated in FIG. 21 or more retracted than that illustrated in FIG. 21, as determined by the vertically adjusted position of the cam cone  60 .  
         [0050]    At point B the cutter  114  has just started its downstroke toward the vent hole  178 . Both the carrier  116  and the head  118  are moving downwardly at this time and in unison due to the downslope of their respective cam tracks  126  and  128 . This condition is also illustrated in FIG. 17. At the same time, the following roller  162  of stretcher  156  starts under the cam  172 , although cam  172  has no effect on stretcher  156  at this time.  
         [0051]    By the time point C is reached, the operating components are in the positions illustrated in FIGS. 18 and 19. By this time, the knife  114  has reached its lower limit of travel and has entered the vent hole  178  a short distance. Also by this time the stretcher  156  has been actuated so as to engage the abdominal skin  180  (FIG. 21) and pull it over toward one leg of the carcass. This has the effect of stretching the skin tight, in readiness for the cutting stroke of the cutter  114 .  
         [0052]    Between position C and position D, the stretcher  156  remains fully actuated so as to keep the abdominal skin in a taut condition. Cam track  128  for head  118  drops a short distance relative to cam track  126  for carrier  116 . This causes the rack gear  120  to rotate pinion gear  122  in a counterclockwise direction viewing FIG. 10, thus causing knife  114  to flip out in its cutting stroke to the position shown in FIG. 20. During such stroke, the blade  182  on knife  114  slices cleanly through the taut abdominal skin  180  and makes an opening cut into the abdominal cavity. Because the pivot  124  is skewed with respect to the line of centers between the guide rods  24 , knife  114  follows an oblique path of travel  184  as illustrated in FIG. 22, instead of a line of travel that is parallel to or common with the axis of symmetry  186  of the carcass extending between the back  188  and the keel bone  190 . This causes the blade  182  of knife  114  to miss the keel bone and avoid damage thereto.  
         [0053]    It will be noted that at position D the lowermost cam track  58  for lifter mechanism  40  has a spring biased segment  192  (FIGS. 13 and 14). Segment  192  is upwardly biased by a compression spring assembly  194  so that, in the event relief is needed at that instant due to an oversized bird, for example, the cam follower  56  can drop downwardly to provide relief. Similarly, the segment  192  pushes an undersized bird up for proper positioning.  
         [0054]    After point D has been passed, the stretcher  156  is gradually released by cam  172  and returned to its standby position by the counterweight  168 . Head  118  and carrier  116  progressively rise together to withdraw cutter  114  from the carcass, the rate of rise of the head  118  being slightly greater than that of the carrier  116  so that knife  114  is swung back down to its vertical, standby position. Thereafter, lifter mechanism  40  releases its grip on the carcass and retracts downwardly away from straddle bar  30 , which allows the conveyor to pull the carcass away from the fixture and toward the next processing station.  
         [0055]    It will be noted that the most critical time for positioning of the carcass with respect to the transverse axis  176  is just prior to and during insertion of the knife  114  into the vent hole  178 . Once such insertion has been accomplished accurately, the back stop  100  is no longer needed. Therefore, just before position C, cam  108  for back stop  100  terminates all engagement with cam  100 . The back stop  100  is then depressed by the weight of the bird back into its fully recessed position just prior to the time the opening stroke is actually made by knife  114 .  
         [0056]    The preferred forms of the invention described above are to be used as illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention.  
         [0057]    The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.