Poultry leg boning apparatus

Abstract: A poultry leg boning apparatus for removing meat from the upper and lower leg bones of a poultry leg. The apparatus includes a first, cutting machine (A) for cutting open the meat of the poultry leg along one side of the upper and lower leg bones, and a second, tendon cutting machine (B) for removing the lower leg bone from the poultry leg. Also disclosed are methods for cutting open the meat of the poultry leg along one side of the upper and lower leg bones, and removing the meat from the lower leg bone.

Description: The present invention relates to a poultry leg boning apparatus for removing meat from the poultry legs. When the meat is manually removed from the poultry leg, the boning work is carried out with a knife by means of the following steps: (1) cutting the meat of the leg along the upper and lower leg bones; (2) cutting the knee joint so as to separate the upper leg bone from the lower leg bone; (3) pulling up the upper leg bone at the lower end thereof or the knee joint and plucking off the upper leg bone from the leg meat; (4) peeling the meat off the leg along the lower leg bone toward the knee joint so as to make the meat connected only to the knee joint by meat-to-bone connecting tendon tissues; and (5) cutting the meat-to-bone connecting tendon tissues so as to remove the lower leg bone from the leg meat. The above steps of the manual boning require skill and physical stamina so that it has been desirable to automate them. Especially in the step (1), there has been the problem that, if a force biasing the knife against the bones is too large, the knife chips the bones and the chips of the bones are left on the meat, which decreases the economic value of the meat. Or, if the force biasing the knife against the bones is too small, the knife comes to be detached from the bones and a certain amount of meat is left on the bones, which decreases the yield of the meat removed from the leg. In the step (5), there has been the problem that, it is hard to bias the knife against the knee joint stably because the knee joint is round and the meat-to-bone connecting tendon tissues are hard, this results in a hazard to the operator or may decrease the commercial value of the meat because of the rough cut surface. Various types of machines and methods for removing the meat from the poultry leg have been proposed. For example, U.S. Pat. No. 2,897,536 to Bergstrom et al, dated Aug. 4, 1959 discloses a machine wherein the leg is passed through a space between a pair of rotating rollers so that the meat is removed from the leg. U.S. Pat. No. 3,261,054 to Kaplan et al, dated July 19, 1966 discloses a machine wherein the leg is passed through a space between a pair of stripper bars so that the meat is removed from the leg. U.S. Pat. No. 3,965,535 to Kaplan et al, dated June 29, 1976 discloses a machine wherein the leg is passed through a space between a pair of discs rotating with their closely spaced peripheral stripping edges in opposition so that the meat is removed from the leg. U.S. Pat. No. 3,348,261 to Segur dated Oct. 24, 1967 discloses a method wherein the meat of the leg is sliced along at least one side of the leg bone, and thereafter the meat is plowed in opposite directions along the upper leg bone and the lower leg bone toward the knee joint. By means of the above machines and methods, the meat of the leg is forced along the leg bone thereby being removed therefrom. Thus, because of excessive deformation during the boning process, the meat, especially the meat of the upper leg portion, is liable to be damaged more seriously compared with the manually processed meat. Japanese Patent Publication No. 60-23810 dated June 10, 1985 discloses a boning machine having a rotating annular cutter belt. By the machine, the meat between the going run of the cutter belt and the returning run of the cutter belt is left on the leg bone, so that the yield rate of the meat removed from the leg is lower than that by the manual separation. SUMMARY OF THE INVENTION The present invention is a part of a machine for automatically carrying out all of the steps of manual boning work. An object of the present invention is to provide a poultry leg boning apparatus and method according to claims 1, 6 and 11. Preferred embodiments are defined by the dependant claims. Further objects, features and advantages of the present invention will become apparent from the Detailed Description of the Preferred Embodiments when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a perspective view showing a general arrangement of a poultry leg boning apparatus in accordance with the preferred embodiment of the present invention; Figure 2 is a perspective view showing a first, cutting machine for cutting open a poultry leg along the upper leg bone and the lower leg bone, which defines a part of the poultry leg boning apparatus in Figure 1; Figure 3 is an enlarged detail of a clamp assembly for clamping a poultry leg, which defines a part of the cutting machine of Figure 2; Figure 4 is an enlarged detail of cutting blades of the cutter assembly of the cutting machine of Figure 2; Figure 5 is a perspective view showing a biasing roll assembly of the cutting machine of Figure 2; Figures 6A∼ 6D are plan views showing the operation of the cutting machine of Figure 2; Figure 7 is an enlarged detail of another embodiment of the clamp assembly of Figure 3; Figure 8 is a perspective view of another embodiment of the cutting machine; Figure 9 is a perspective view showing a second, tendon cutting machine for removing the lower leg bone of the poultry leg, which defines a part of the poultry leg boning apparatus of Figure 1; Figure 10 is a cross-sectional view showing the construction of a cutter assembly of the second, tendon cutting machine of Figure 9; and Figures 11A ∼ 11C are perspective views showing the operation of the tendon cutting machine of Figure 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 1, a poultry leg boning apparatus in accordance with the preferred embodiment of the present invention comprises a first, cutting machine A for cutting open the poultry leg along the upper leg bone and the lower leg bone, a second, tendon cutting machine B for removing the lower leg bone of the poultry leg, and a working table C disposed between the cutting machine A and the tendon cutting machine B. In the poultry leg boning apparatus, the step (1) in the manual boning process is carried out automatically by the cutting machine A, and the step (5) in the manual boning process is carried out automatically by the tendon cutting machine B. The steps (2)∼(4) in the manual boning process are carried out manually on the working table C. The cutting machine A, the tendon cutting machine B, and the working table C will be described in detail as follows. First, Cutting Machine A The first, cutting machine A will be described with reference to Figures 2 to 8. The cutting machine A described in the following is so constructed as to cut open right poultry legs. In the following descriptions, the directions indicated by arrows I , II , III , IV , V and VI in Figure 2 are referred to as forward direction, rearward direction, leftward direction, rightward direction, upward direction and downward direction, respectively. Moreover, in the following descriptions, the direction parallel to the arrows I , II is referred to as the longitudinal direction, the direction parallel to the arrows III , IV is referred to as the transverse direction, and the direction parallel to the arrows V , VI is referred to as the vertical direction, respectively. In Figure 2, 1a, 1b are sprockets supported by the frame of cutting machine A. Sprockets 1a, 1b are rotatably supported around horizontal axes x₁, X₂, respectively. The horizontal axes x₁, x₂ extend in parallel with one another and in the transverse direction. The frame of the cutting machine A is not illustrated for simplicity. An endless chain 2 engages the sprockets 1a and 1b. A motor 1c drives the sprocket 1b, and thereby drives the upper run 2a of the endless chain 2 forward. As shown in Figure 2, the endless chain 2 has a plurality of clamp assemblies 3 for clamping poultry legs. These assemblies 3 are fixed to the chain 2 at a predetermined distance with each other. The construction of the clamp assembly 3 will be described with reference to Figure 3. The clamp assembly 3 includes a body 3a, the horizontal cross section of which is hook-shaped. A leg 3a₁ of the body 3a extends in the longitudinal direction, and the other leg 3a₂ of the body 3a extends rightward from the fore end of the leg 3a₁. The leg 3a₁ is fixed to the endless chain 2 by a bracket 3b which extends leftward from the leg 3a₁. A shaft 3c extends in the longitudinal direction through the leg 3a₂. The shaft 3c is carried by the leg 3a₂ so that it rotates around its longitudinal axis and is fixed in the longitudinal direction. A first clamping member 3d is fixed to the rear end of the shaft 3c. The first clamping member 3d comprises a channel bar having an U-shaped groove extending in the longitudinal direction and closed at its fore end. An arm 3e extends at a right angles to the shaft 3c, and is fixed to the fore end of the shaft 3c at one end. The other end of the arm 3e is provided with a guide-roll 3f, which is rotatable around the arm 3e. A stopper 3g is fixed to the upper surface of the fore end of the leg 3a₁. A spring 3h connects the stopper 3g with the arm 3e. The arm 3e is biased toward the stopper 3g around the longitudinal axis of the shaft 3c by the spring 3h, and is abutted against the stopper 3g, so that the arm 3e is held upright when no rightward force works on the guide-roll 3f. When the arm 3e is held upright, the open end of the U-shaped groove of the first clamping member 3d is directed upward. Hereinafter, the condition wherein the arm 3e is abutted against the stopper 3g so as to be held upright, and the open end of the U-shaped groove of the first clamping member 3d is directed upward, is referred to as the initial condition of the clamp assembly 3. A second clamping member 3j is fixed to the right side surface of the leg 3a₁. The second clamping member 3j is bent rightward at a rear end portion 3j₁. A clearance is provided between the rear end portion 3j₁ of the second clamping member 3j and the rear end of the first clamping member 3d. The rear end portion 3j₁ is provided with a U-shaped cutout 3j₂ having an open upper end. The U-shaped cutout 3j₂ is aligned with the U-shaped groove of the first clamping member 3d in the initial condition of the clamp assembly 3. The width L' of the U-shaped cutout 3j₂ of the second clamping member 3j is a little smaller than the width L of the U-shaped groove of the first clamping member 3d. The bracket 3b is provided with a protrusion 3k on its upper surface. As shown in Figure 2, a line cam 4 made of a curved rod is disposed to the right of the upper run 2a of the endless chain 2. The line cam 4 extends in the longitudinal direction. The line cam 4 is disposed to the left of and above the clamp assembly 3 in the vicinity of the rear end of the upper run 2a of the endless chain 2. At the midway point of the upper run 2a, the line cam 4 is bent to the right of the clamp assembly 3 and is also bent downward to a height a little higher than the shaft 3c of the clamp assembly 3. In the vicinity of the fore end of the upper run 2a of the endless chain 2, the line cam 4 is disposed at a height a little higher than the shaft 3c of the clamp assembly 3, to the right of the clamp assembly 3, and extends in the longitudinal direction. The line cam 4 is fixed to the frame ( not shown) of the cutting machine A. As shown in Figure 2, a rectangular table 5 is disposed to the right of the endless chain 2. The rectangular table 5 is disposed a little below the clamp assembly 3 fixed to the upper run 2a of the endless chain 2, and extends horizontally and longitudinally. The rectangular table 5 is also fixed to the frame of the cutting machine A. As shown in Figure 2, a cutter assembly 6 is disposed in the vicinity of the fore end of the upper run 2a of the endless chain 2. The cutter assembly 6 is disposed to the right of the upper run 2a. The cutter assembly 6 has an air cylinder 6a. The air cylinder 6a is fixed to the frame of the cutting machine A by a bracket 6b. The piston 6a₁ of the air cylinder 6a extends downward. The upper end of a rectangular cutter base 6c is connected to the lower end of the piston 6a₁. The cutter base 6c is supported to move only in the vertical direction by guides 6d fixed to the frame of the cutting machine A. A rotation shaft 6e disposed to the rear of the cutter base 6c and extending in the vertical direction is supported rotatably around its vertical axis by two bearings fixed to the cutter base 6c. The two bearings are not illustrated for simplicity. A coil spring 6g fits on the rotation shaft 6e. The coil spring 6g engages, with one end, a hole 6c₂ of an eye plate 6c₁. The eye plate 6c₁ is fixed to the cutter base 6c and extends rearward. The other end of the coil spring 6g is fixed to a plate member 6f which is in turn fixed to the lower end of the rotation shaft 6e. The coil spring 6g applies an initial moment M₀ to the rotation shaft 6e so as to drive the rotation shaft 6e rotationally in the direction indicated by a double arrow, or counterclockwise as viewed downward. An arm 6e₁ is fixed to the upper end of the rotation shaft 6e. The arm 6e₁ abuts against a stopper 6c₃ which is fixed to the cutter base 6c and extends rearward, thereby keeping the rotation shaft 6e from rotating in the direction indicated by the double arrow. The upper end of a connection shaft 6h is fixed to the lower surface of the plate member 6f. The lower end of the connection shaft 6h is fixed to a connection bracket 6j. The connection shaft 6h is located offset leftwardly relative to the rotation shaft 6e. The upper end of a cutter body 6k is fixed to the connection bracket 6j. The cutter body 6k is located offset forwardly relative to the connection shaft 6h. The cutter body 6k comprises a rectangular plate and is provided with a fixed cutting blade 6m at its lower end. As shown in Figure 4, the fixed cutting blade 6m comprises an upper portion 6m₁ made of a rectangular plate, and a lower portion 6m₂. The lower portion 6m₂ has a wedge shaped configuration in horizontal cross section and extends rearward from the lower end of the upper portion 6m₁. The front surface of the upper portion 6m₁ is fixed to the rear surface of the cutter body 6k. The wedge shaped horizontal sectional configuration of the lower portion 6m₂ is formed such that the rear portion is thinner than the fore portion, and the maximum thickness of the fore portion is substantially one half of the width of the upper portion 6m₁. The lower portion 6m₂ is located offset rightward relative to the centerline of the upper portion 6m₁. The lower edge of the lower portion 6m₂ inclines downward from its fore end toward its rear end, so that the rear edge of the lower edge of the lower portion 6m₂ forms a sharp tip 6m₂' . As shown in Figure 2, a motor 6n is mounted on the cutter body 6k. A shaft 6p extends through the cutter body 6k below the motor 6n, and is rotatably supported around its longitudinal axis by the cutter body 6k. The shaft 6p is connected to the output shaft of the motor 6n by a belt 6q. A pin 6r is eccentrically fixed to the rear end of the shaft 6p and extends rearward. A rod 6s is rotatably supported by the rear end portion of the pin 6r around the longitudinal axis of the pin 6r and extends downward. A pin 6t is rotatably supported around its longitudinal axis by the lower end portion of the rod 6s and extends rearward. A rod 6u is rotatably supported by the pin 6t around the longitudinal axis of the pin 6t and extends downward. The rod 6u is supported, movably in the vertical direction, by a guide 6v fixed to the cutter body 6k. A block 6w is fixed to the lower end of the rod 6u. As shown in Figure 4, the upper end of a movable cutting blade 6x, made of a thin rectangular plate, fits within a slit in the block 6w. The slit is formed on the lower surface of the block 6w and extends in the longitudinal direction. The movable cutting blade 6x is fixed to the block 6w by means of a pin 6y. The block 6w is located such that its fore surface abuts against the rear surface of the upper portion 6m₁ of the fixed cutting blade 6m. The movable cutting blade 6x is located so as to abut against the left side surface of the lower portion 6m₂ of the fixed cutting blade 6m. The left side surface defines the rear edge of the lower portion 6m₂ or a cutting edge 6m₃. The movable cutting blade 6x is located so as to protrude slightly rearward from the cutting edge 6m₃ at its rear edge 6x₁. The lower edge of the movable cutting blade 6x is sharpened to form a sharp cutting edge 6x₃, and is made inclined downward from the fore end to the rear end so that the rear edge of the lower edge of the movable cutting blade 6x forms a sharp tip 6x ' . The movable cutting blade 6x is located such that the cutting edge 6x₃ protrudes slightly downward from the lower edge of the lower portion 6m₂ of the fixed cutting blade 6m when the movable cutting blade 6x is in the lowest position. The movable cutting blade 6x is disposed to the left of and to the rear of the rotation shaft 6e when the initial moment M₀ is applied to the rotation shaft 6e so as to drive the shaft 6e rotationally in the direction indicated by the double arrow. Moreover, the arm 6e₁ abuts against the stopper 6c₃, thereby keeping the rotation shaft 6e from rotating in the direction indicated by the double arrow. In this condition, the movable cutting blade 6x inclines slightly rightward from the fore edge 6x₂ toward the rear edge 6x₁ as viewed downward. Also in this condition, the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m, which defines the cutting edge 6m₃, extends in the longitudinal direction. The cutter assembly 6 is located such that the movable cutting blade 6x is situated in the vicinity of the left end of the cutout 3j₂ of the second clamping member 3j. Hereinafter, what is referred to as the initial rotational condition of the movable cutting blade 6x is the condition in which an initial moment M₀ is applied to the rotation shaft 6e so as to drive the shaft 6e rotationally in the direction indicated by the double arrow. In the initial rotational condition, the arm 6e₁ abuts against the stopper 6c₃ thereby keeping the rotation shaft 6e from rotating in the direction indicated by the double arrow, the movable cutting blade 6x is disposed to the left of and to the rear of the rotation shaft 6e, the movable cutting blade 6x inclines slightly rightward from the fore edge 6x₂ toward the rear edge 6x₁ as viewed downward, and the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m extends in the longitudinal direction. As shown in Figure 2, a biasing roll assembly 7 is disposed to the right of the fixed cutting blade 6m. As shown in Figure 5, the biasing roll assembly 7 has a biasing roll 7b rotatably supported by a shaft 7a which extends in the transverse direction. The shaft 7a is fixed to the lower end portion of an upwardly-extending rectangular plate 7c. The upper end of plate 7c is bent leftward and fixed to the rear end portion of a bracket 7d. The fore end portion of the bracket 7d extends upward and is fixed to the cutter base 6c at its upper end portion. A rod 7e extends in the transverse direction through a hole 7c₁ formed in the mid portion of the plate 7c. The left end of rod 7e is fixed to the bracket 7d. The portion of the rod 7e located to the right of the plate 7c is fitted with a coil spring 7f. A nut 7g engages the right end portion of the rod 7e so as to apply a compressive force to the coil spring 7f. As shown in Figure 2, a limit switch 8a is disposed to the rear of the movable cutting blade 6x of the cutter assembly 6 and just above the upper run 2a of the endless chain 2. A limit switch 8b is disposed to the fore of the movable cutting blade 6x of the cutter assembly 6 and just above the upper run 2a of the endless chain 2. The limit switches 8a, 8b are fixed to the frame of the cutting machine A. The limit switches 8a, 8b detect the existence of the clamp assembly 3 when they abut against the protrusion 3k provided on the upper surface of the bracket 3b of the clamp assembly 3. Based on the detection signal from the limit switch 8a, the piston 6a₁ of the air cylinder 6a advances downward, and the motor 6n starts. Based on the detection signal from the limit switch 8b, the piston 6a₁ of the air cylinder 6a retracts upward, and the motor 6n stops. The operation of the above constructed cutting machine A is described as follows. An electric power supply of the cutting machine A is turned on, the motor 1c starts, and the upper run 2a of the endless chain 2 moves forward as indicated by an arrow in Figure 2. The piston 6a₁ of the air cylinder 6a is in a retracted position so that the cutter body 6k is pulled up. The initial moment M₀ is applied to the rotation shaft 6e so as to drive the rotation shaft 6e in the direction indicated by the double arrow. The arm 6e₁ then abuts against the stopper 6c₃ thereby keeping the rotation shaft 6e from rotating in the direction indicated by the double arrow. The movable cutting blade 6x is disposed to the left of and to the rear of the rotation shaft 6e, the movable cutting blade 6x is inclined slightly rightward from the fore edge 6x₂ toward the rear edge 6x₁ as viewed downward, and the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m extends in the longitudinal direction. That is, the cutting blade 6x is in the initial rotational condition. Then, as shown in Figure 2, a right leg S is set into the clamp assembly 3 by an operator, which assembly 3 is located in the vicinity of the rear end of the upper run 2a of the endless chain 2. The clamp assembly 3 is in the initial condition wherein the open end of the U-shaped groove of the first clamping member 3d is directed upward. The right leg S is set by the following procedure. 1 ○ The inner side surface of the leg S is directed leftward and the outer side surface of the leg S is directed rightward, and the connecting joint between the lower leg bone S₁ and the upper leg bone S₂ or the knee joint S₄ of the leg S protrudes upward. 2 ○ The lower end of the lower leg bone S₁ or the ankle S₃ of the leg S is inserted into the U-shaped groove of the first clamping member 3d, and the portion of the lower leg bone S₁ adjacent to the ankle S₃ is inserted into the U-shaped cutout 3j₂ of the second clamping member 3j. Thus, the ankle S₃ of the leg S is clamped by the first clamping member 3d, and the portion of the lower leg bone S₁ adjacent to the ankle S₃ is clamped by the second clamping member 3j. The leg S set into the clamp assembly 3 then moves forward following the forward movement of the clamp assembly 3 which is driven by the upper run 2a of the endless chain 2. The forward movement of the clamp assembly 3 causes the engagement between the guide-roll 3f and the line cam 4. The guide-roll 3f or the first clamping member 3d is guided by the line cam 4 so as to rotate, against the biasing force of the spring 3h, by 90 ° , clockwise as viewed in the forward direction. Following the rotation of the first clamping member 3d, the right leg S clamped by the first clamping member 3d is also rotated by 90° , so that the inner side surface of the right leg S is directed upward and the outer side surface of the right leg S abuts against the upper surface of the table 5. Thereafter, the upper leg bone S₂, the lower leg bone S₁ and the ankle S₃ are all in the same horizontal plane. As viewed downward, the lower leg bone S₁ inclines slightly rightward from its fore end toward its rear end, the upper leg bone S₂ inclines slightly leftward from its fore end toward its rear end. The open end of the U-shaped groove of the first clamping member 3d is directed rightward, and the open end of the U-shaped cutout 3j₂ of the second clamping member 3j is directed upward. Thus,the ankle S₃ of the leg S can not be released from the first clamping member 3d and the second clamping member 3j in either the vertical direction or the transverse direction. The ankle S₃ of the leg S can not go through the U-shaped cutout 3j₂ of the second clamping member 3j the width L ' whereof is made a little smaller than the width L of the U-shaped groove of the first clamping member 3d, so that the ankle S₃ of the leg S can not be released from the clamping by the first clamping member 3d and the second clamping member 3j further in the longitudinal direction. The width L of the U-shaped groove of the first clamping member 3d is made larger than the width of the ankle S₃ of the leg S and the width L ' of the U-shaped cutout 3j₂ of the second clamping member 3j is made larger than the width of the portion of the lower leg bone S₁ adjacent to the ankle S₃, so that the leg S can rotate to some extent around the ankle S₃ in a horizontal plane. When the clamp assembly 3 moves forward further and the rotation of the first clamping member 3d by 90° is completed, the limit switch 8a detects the existence of the clamp assembly 3, the piston 6a₁ of the air cylinder 6a advances downward from the retracted position, and the motor 6n starts. Following the advance of the piston 6a₁, the cutter base 6c or the cutter body 6k moves downward. Following the downward movement of the cutter base 6c, the biasing roll assembly 7 or the biasing roll 7b also moves downward. After the start of the motor 6n, the shaft 6p rotates via the belt 6q, the eccentric pin 6r rotates, and the rod 6u reciprocates in the vertical direction via the rod 6s and the pin 6t, so that the movable cutting blade 6x reciprocates vertically between its lowest and highest positions. When the clamp assembly 3 moves forward further, as shown in Figure 6A, the sharp tip 6m₂ ' of the fixed cutting blade 6m, which has been moving downward, pierces into the meat of the leg S in the vicinity of the lower leg bone S₁ adjacent to the ankle S₃. As described above, the movable cutting blade 6x or the fixed cutting blade 6m is located in the vicinity of the left end of the cutout 3j₂ of the second clamping member 3j and the lower leg bone S₁ inclines slightly rightward from its fore end to its rear end as viewed downward, so that the sharp tip 6m₂' of the fixed cutting blade 6m pierces into the leg S at the left of the lower leg bone S₁. The biasing roll 7b abuts against the leg S at the right of the movable cutting blade 6x and at the right of the lower leg bone S₁ so as to bias the leg S leftward. As a result, the leg S rotates, clockwise as viewed downward, around the ankle S₃. Thus, the lower leg bone S₁ extends in the longitudinal direction and the sharp tip 6m₂ ' of the fixed cutting blade 6m abuts against the left side surface of the lower leg bone S₁. When the sharp tip 6m₂ ' of the fixed cutting blade 6m has pierced into the meat of the leg S to the bone, the piston of 6a₁ of the air cylinder 6a reaches the advanced position, and the sharp tip 6m₂ ' of the fixed cutting blade 6m is retained at that height. The movable cutting blade 6x is in the initial rotational condition so that the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m, the right side surface of which extends in the longitudinal direction, abuts closely against the left side surface of the lower leg bone S₁ which extends in the longitudinal direction. The movable cutting blade 6x, which inclines slightly rightward from the fore edge 6x₂ to the rear edge 6x₁ as viewed downward, abuts against the left side surface of the lower leg bone S₁ extending in the longitudinal direction at its rear edge 6x₁. The movable cutting blade 6x reciprocates in the vertical direction under the guidance of the left side surface of the lower portion 6m₂ of the fixed cutting blade 6m so as to cut open the meat of the leg S. The movable cutting blade 6x is slender and abuts against the left side surface of the lower leg bone S₁ at its rear edge 6x₁, so that the meat of the leg S is cut open at a position adjacent to the left side surface of the lower leg bone S₁. The rear edge 6x₁ of the movable cutting blade 6x protrudes only slightly rearward from the cutting edge 6m₃ of the lower portion 6m₂ of the fixed cutting blade 6m, so that the movable cutting blade 6x neither cuts into nor chips off the lower leg bone S₁. As the clamp assembly 3 moves forward and the leg S moves forward, the meat of the leg S is cut open by the movable cutting blade 6x along the left side surface of the lower leg bone S₁ extending in the longitudinal direction. The opening made by the cutting blade 6x is further enlarged by the wedge shaped lower portion 6m₂ of the fixed cutting blade 6m. When the meat of the leg S is cut open by the lower portion 6m₂, it applies forward resistant force to the rear edge 6m₃ of the lower portion 6m₂. The movable cutting blade 6x and the fixed cutting blade 6m are located offset leftward relative to the rotation shaft 6e, so that a resistant moment, directed opposite to the direction indicated by the double arrow in Figure 2, is generated around the rotation shaft 6e by the forward resistant force applied to the rear edge 6m₃. But, the forward resistant force is small because it is applied by the meat of the leg S, so that the resistant moment generated around the rotation shaft 6e does not exceed the initial moment M₀. Thus, the movable cutting blade 6x is retained in the initial rotational condition. When the clamp assembly 3 moves forward further, as shown in Figure 6B, the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m comes to abut against the portion of the lower leg bone S₁ adjacent to the knee joint S₄. The left side surface of the portion of the lower leg bone S₁ adjacent to the knee joint S₄ is curved and inclines leftward from its fore portion toward its rear portion. The right side surface of the lower portion 6m₂ of the fixed cutting blade 6m, which extends in the longitudinal direction, inclines relative to the left side surface of the lower leg bone S₁. Thus, the left side surface of the lower leg bone S₁ applies forward resistant force to the rear edge 6m₃ of the lower portion 6m₂, which resistant force is larger than that applied by the meat of the leg S. Thus, a resistant moment which is larger than the initial moment M₀ is generated around the rotation shaft 6e by the forward resistant force applied by the left side surface of the lower leg bone S₁, so that the rotation shaft 6e rotates in the direction opposite to the direction indicated by the double arrow in Figure 2 or clockwise as viewed downward against the biasing force of the coil spring 6g. Accordingly, the movable cutting blade 6x and the fixed cutting blade 6m rotate and move to a position to the left of and to the fore of the rotation shaft 6e. The movable cutting blade 6x comes to incline leftward from the fore edge 6x₂ toward the rear edge 6x₁ as viewed downward, and the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m comes to incline leftward from its fore edge toward its rear edge as viewed downward. As a result, the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m abuts again, closely against the left side surface of the lower leg bone S₁ which inclines leftward from its fore portion toward its rear portion. Thus, the operation for cutting open the meat of the leg S along the left side surface of the lower leg bone S₁ continues smoothly. When the lower leg bone S₁ moves forward, the lower portion 6m₂ of the fixed cutting blade 6m applies a rightward force to the lower leg bone S₁, so that the leg S rotates around the ankle S₃ counterclockwise as viewed in Figure 6B, which causes the portion of the lower leg bone S₁ adjacent to the knee joint S₄ to move rightward. This rightward movement allows the portion of the lower leg bone S₁ adjacent to the knee joint S₄, which inclines leftward from the fore portion toward the rear portion to go smoothly through the space between the lower portion 6m₂ of the fixed cutting blade 6m and the biasing roll 7b. When the clamp assembly 3 moves forward further, as shown in Figure 6C, the portion of the lower leg bone S₁ adjacent to the knee joint S₄ passes by the fixed cutting blade 6m. The rear edge 6m₃ of the lower portion 6m₂ of the fixed cutting blade 6m passes by the curved portion of the lower leg bone S₁ adjacent to the the knee joint S₄ and protrudes into the meat in the vicinity of the knee joint S₄, so that the forward resistant force applied to the rear edge 6m₃ decreases, which causes the resistant moment to decrease. Thus, the rotation shaft 6e rotates in the direction indicated by the double arrow in Figure 2, following the biasing force of the spring 6g, which causes the movable cutting blade 6x and the fixed cutting blade 6m to rotate back to their intial rotational position. As a result, the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m abuts closely against the left side surface of the knee joint S₄, which allows the operation for cutting open the meat of the leg S along the left side surface of the knee joint S₄ to be continued smoothly. The lower portion 6m₂ of the fixed cutting blade 6m applies a rightward force to the knee joint S₄, so that the leg S rotates around the ankle S₃ counterclockwise as viewed in Figure 6C, which causes the knee joint S₄ to move rightward. The knee joint S₄ applies a rightward force to the biasing roll 7b, so that the biasing roll 7b moves rightward against the biasing force of the spring 7f, which makes the space between the lower portion 6m₂ of the fixed cutting blade 6m and the biasing roll 7b increase. The aforementioned rightward movement of the knee joint S₄ and the increase of the space between the lower portion 6m₂ of the fixed cutting blade 6m and the biasing roll 7b allows the knee joint S₄ to go smoothly through the space between the lower portion 6m₂ of the fixed cutting blade 6m and the biasing roll 7b. When the clamp assembly 3 moves forward further, as shown in Figure 6D, the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m comes to abut against the upper leg bone S₂. The left side surface of the upper leg bone S₂ inclines leftward from its fore portion toward its rear portion, so that the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m, which now extends in the longitudinal direction, inclines relative to the left side surface of the upper leg bone S₂. Thus, the left side surface of the upper leg bone S₂ applies forward resistant force to the rear edge 6m₃ of the lower portion 6m₂. Thus, a resistant moment which is larger than the initial moment M₀ is generated around the rotation shaft 6e by the forward resistant force applied by the left side surface of the upper leg bone S₂, so that the rotation shaft 6e rotates in the direction opposite to the direction indicated by the double arrow in Figure 2 or clockwise as viewed downward against the biasing force of the coil spring 6g. Accordingly, the movable cutting blade 6x and the fixed cutting blade 6m rotate and move to a position to the left of and to the fore of the rotation shaft 6e. The movable cutting blade 6x comes to incline leftward from the fore edge 6x₂ toward the rear edge 6x₁ as viewed downward, and the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m comes to incline leftward from its fore edge toward its rear edge as viewed downward. As a result, the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m once again abuts closely against the left side surface of the upper leg bone S₂. The upper leg bone S₂ inclines leftward from its fore portion toward its rear portion as viewed downward. Thus, the operation for cutting open the meat of the leg S along the left side surface of the upper leg bone S₂ continues smoothly. When the upper leg bone S₂ moves forward, the lower portion 6m₂ of the fixed cutting blade 6m applies rightward force to the upper leg bone S₂, so that the leg S rotates around the ankle S₃ counterclockwise as viewed in Figure 6D, which causes the upper leg bone S₂ to move rightward. This rightward movement allows the upper leg bone S₂ to go smoothly through the space between the lower portion 6m₂ of the fixed cutting blade 6m and the biasing roll 7b. In the same manner as with the knee joint S₄, the operation for cutting open the meat of the leg S along the left side surface of the coxa S₅ continues smoothly. Thus, the operation for cutting open the meat of the leg S along the lower leg bone S₁ and the upper leg bone S₂ is completed. When the aforementioned operation for cutting open the meat of the leg S is completed, the limit switch 8b detects the clamp assembly 3, the piston 6a₁ of the air cylinder 6a retracts form the advanced position and the motor 6n stops. Following to the retraction of the piston 6a₁, the cutter base 6c or the cutter body 6k moves upward. Thus, the fixed cutting blade 6m and the movable cutting blade 6x move upward so that they leave the leg S. Following the stop of the motor 6n, the movable cutting blade 6x stops reciprocating in the vertical direction. When the clamp assembly 3 moves forward further, the guide-roll 3f passes by the fore end of the line cam 4. The first clamping member 3d is rotated counterclockwise as viewed forward by the biasing force of the spring 3h. Thus, the clamp assembly 3 comes back to the initial condition. Then, the leg S is taken from the clamp assembly 3 by the operator. As described above, the right side surface of the lower portion 6m₂ of the fixed cutting blade 6m always abuts closely against the left side surfaces of the lower leg bone S₁ and the upper leg bone S₂. The movable cutting blade 6x, which is guided by the left side surface of the lower portion 6m₂ of the fixed cutting blade 6m, cuts open the meat of the leg S. The rear edge 6x₁ is always abutted against the left side surfaces of the lower leg bone S₁ and the upper leg bone S₂, so that the meat of the leg S is cut open along the the lower leg bone S₁ and the upper leg bone S₂ without any meat being left on the bones. The rear edge 6x₁ of the movable cutting blade 6x protrudes only slightly rearward from the rear edge 6m₃ of the lower portion 6m₂ of the fixed cutting blade 6m, so that the movable cutting blade 6x neither cuts into nor chips off the bones. The biasing roll assembly 7 may be freed from the cutter base 6c and be moved close to the fixed cutting blade 6m from right and away from the fixed cutting blade 6m to right. The movable cutting blade 6x may be reciprocated by an air cylinder similar to the air cylinder 6a, or by a cam rotated by a flexible shaft driven by a suitable motor. The cutter base 6c may be driven in the vertical direction by a link mechanism engaging a cam driven by the motor 1c. A variation of the clamp assembly as shown in Figure 7 will now be discussed. A clamp assembly 10 shown in Figure 7 has a mechanism for rotating the first clamping member which is different from that of the clamp assembly 3 in Figure 2. The clamp assembly 10 has a bevel gear 10k fixed to the fore end of a shaft 10c. The bevel gear 10k engages a bevel gear 10n fixed to the right end of a shaft 10m. The shaft 10m extends in the transverse direction rotatably through a hole formed in a longitudinal leg 10a₁. The shaft 10m fits in the hole formed in the leg 10a₁ rotatably but tightly. Thus, the shaft 10m rotates only when it is provided with a large torque. A triangular cam plate 10p is fixed to the left end of the shaft 10m. A baffle plate 11 is disposed above the mid portion of the upper run 2a of the endless chain 2. A baffle plate 12 is disposed above the fore end portion of the upper run 2a of the endless chain 2 and above the baffle plate 11. The baffle plates 11, 12 are fixed to the frame of the cutting machine A. As shown in Figure 7, when the clamp assembly 10 is located in the vicinity of the rear end of the upper run 2a of the endless chain 2, the cam plate 10p is in a position indicated by a solid line wherein an apex 10p₁ of the cam plate 10p is directed downward. In this position, the open end of a U-shaped groove of a first clamping member 10d is directed upward. When the clamp assembly 10 moves forward to the mid portion of the the upper run 2a of the endless chain 2, an edge of the cam plate 10p extending upward from the apex 10p₁ abuts against the baffle plate 11 , so that the cam plate 10p rotates by 90 ° in the direction indicated by an arrow. Thus, the cam plate 10p comes to be in a position indicated by a phantom line wherein the apex 10p₁ of the cam plate 10p is directed rearward. Following to the rotation of the cam plate 10p, the first clamping member 10d rotates by 90 ° in the direction indicated by an arrow. Thus, the first clamping member 10d comes to be in a rotated position. As aforementioned, the shaft 10m tightly fits in the hole formed in the leg 10a₁, so that the cam plate 10p is kept in the position indicated by the phantom line in Figure 7 even after it goes through the baffle plate 11. Accordingly, the first clamping member 10d is kept in the rotated position. When the clamp assembly 10 moves forward further to the fore end portion of the upper run 2a of the endless chain 2, an edge of the cam plate 10p extending upward from an apex adjacent to the shaft 10m abuts against the baffle plate 12 , so that the cam plate 10p rotates back to the position indicated by the solid line in Figure 7. Thus, the first clamping member 10d comes back to the position indicated in Figure 7. The cutting machine A for a right leg has been described in the above. In the cutting machine A for a left leg, the clamp assembly 3, the line cam 4, the table 5, the cutter assembly 6 and the biasing roll assembly 7 should be disposed in a mirror image of those shown in Figure 2 in association with a vertical plane which includes the endless chain 2. A second embodiment of the cutting machine A is shown in Figure 8. The same members as in the first embodiment are denoted by the same reference numerals as in the first embodiment. In the following descriptions, the directions indicated by arrows I , II , III , IV , V and VI in Figure 8 are referred to as forward direction, rearward direction, leftward direction, rightward direction, upward direction and downward direction, respectively. Moreover, in the following descriptions, the direction parallel to the arrows I , II is referred to as the longitudinal direction, the direction parallel to the arrows III , IV , is referred to as the transverse direction, and the direction parallel to the arrows V , VI is referred to as the vertical direction. As understood from Figure 8, in the second embodiment, the endless chain 2 is disposed in the transverse direction and the upper run 2a of the endless chain 2 is driven leftward. The body 3a of the clamp assembly 3 is fixed directly to the endless chain 2. The guide roll 3f is mounted on the free end portion of the arm 3e of the clamp assembly 3, which is bent forward. The line cam 4 is disposed to the fore of and above the upper run 2a of the endless chain 2 and extends transversely. The line cam 4 is located sufficiently above the upper run 2a in the vicinity of the right end portion of the upper run 2a. At the midway point of the upper run 2a, the line cam 4 is bent downward to a height a little higher than the upper run 2a. In the vicinity of the left end of the upper run 2a, the line cam 4 is located at a height a little higher than the upper run 2a. The table 5 is disposed to the rear of the endless chain 2, and extends in the transverse direction. The bracket 6b of the cutter assembly 6 is mounted movably in the longitudinal direction on the frame of the cutting machine A. The guides 6d are fixed to the bracket 6b. An air cylinder 6a ' is directed longitudinally and is fixed to the frame of the cutting machine A. The piston 6a₁' of the air cylinder 6a' is connected to the bracket 6b. The operations of the motors 1c, 6n and the air cylinders 6a, 6a ' are controlled not by the limit switches 8a , 8b, but by a sequence controller. Except as described above, the constitution of the second embodiment is the same as the first embodiment. In this embodiment, the operation for cutting open the meat of the leg S is carried out as follows. That is, the leg S is set into the clamp assembly 3 which is located in the vicinity of the right end of the upper run 2a, where the line cam 4 is located sufficiently above the upper run 2a, so that the guide roll 3f does not engage the line cam 4, whereby the clamp assembly 3 is in the initial condition. As the clamp assembly 3 moves leftward, the guide roll 3f engages the line cam 4. Thus, the guide roll 3f and the first clamping member 3d rotate by 90° , clockwise as viewed forward. When the clamp assembly 3 has reached the position just below the cutter assembly 6, the motor 1c is stopped and the leftward movement of the clamp assembly 3 is stopped. Then the piston 6a₁ of the air cylinder 6a is advanced and the cutter assembly 6 is moved downward. After that, the piston 6a₁ ' of the air cylinder 6a' is advanced and the cutter assembly 6 is moved rearward so as to cut open the meat of the the leg S. After the operation for cutting open the meat of the leg S is completed, the pistons 6a₁ and 6a₁ ' retract, so that the cutter assembly 6 is moved upward and forward. Then the motor 1c is restarted and the leftward movement of the clamp assembly 3 is restarted. The guide roll 3f passes by the left end of the line cam 4, so that the first clamping member 3d is rotated counterclockwise as viewed forward by the biasing force of the spring 3h. Thus, the clamp assembly 3 comes back to the initial condition. Then, the leg S is taken from the clamp assembly 3 by the operator. In the second embodiment, a plurality of poultry legs can be processed simultaneously even in a small working space by means of disposing a plurality of cutter assemblies 6 along the endless chain 2. It may be possible that, instead of the provision of the arm 3e, the guide roll 3f, the stopper 3g, the spring 3h and the line cam 4, a cam plate similar to the cam plate 10p in Figure 7 is connected to the fore end portion of the shaft 3c of the clamp assembly 3, and a pair of baffle plates similar to the baffle plates 11, 12 in Figure 7 are disposed transversely above the upper run 2a of the endless chain 2. Working Table C As shown in Figure 1, the working table C has a belt conveyor 20 and a working table 21. The leg S which is cut open by the cutting machine A is taken off the clamp assembly 3 by an operator at the fore end of the upper run 2a of the endless chain 2. Then, the leg S undergoes the sequential steps (2), (3) and (4) in the manual boning work on the working table C. The transportation of the leg S between the steps is achieved by the belt conveyor 20. Second, Tendon Cutting Machine B The tendon cutting machine B will be described with reference to Figures 9 to 11. In the following descriptions, the directions indicated by arrows I , II , III , IV , V and VI in Figure 9 are referred to as forward direction, rearward direction, leftward direction, rightward direction, upward direction and downward direction, respectively. Moreover, in the following descriptions, the direction parallel to the arrows I , II is referred to as the longitudinal direction, the direction parallel to the arrows III , IV , is referred to as the transverse direction, and the direction parallel to the arrows V , VI is referred to as the vertical direction. The tendon cutting machine B has a cutter assembly 31 disposed on the rear end of a rectangular supporting table 30 which extends longitudinally. As shown in Figures 9 and 10, the cutter assembly 31 has an annular cutting blade 31a, the central axis X₃ of which extends in the longitudinal direction. The cutting blade 31a is provided with a cutting edge 31a₁ along its rear surface. The cutting edge 31a₁ is directed rearward. The cutting blade 31a is provided with teeth 31a₂ around its outer side surface. The cutting blade 31a has a sufficient thickness t so that it has a large rigidity. The cutting blade 31a is supported rotatably around the central axis X₃ by a casing 31b which is fixed to the supporting table 30 at its lower end. The portion of the casing 31b which accepts the cutting blade 31a is made dividable into a plurality of pieces so that the the cutting blade 31a can be renewed. An idling gear 31c is disposed below the cutting blade 31a. The idling gear 31c engages both the teeth 31a₂ and a driving gear 31d which is disposed below the idling gear 31c. The gears 31c and 31d are rotatably supported around their own axes by the casing 31b. The axes of gears 31c and 31d extend in the longitudinal direction. The driving gear 31d is connected to a motor 31f by means of a flexible shaft 31e. Thus, the rotation of the motor 31f is transmitted to the cutting blade 31a through the flexible shaft 31e, the driving gear 31d and the idling gear 31c, and causes the cutting blade 31a to rotate around the central axis X₃. A clamp assembly 32 is mounted on the fore end portion of the supporting table 30. As shown in Figure 9, the clamp assembly 32 has a rod 32b which extends in the longitudinal direction through a supporting box 32a fixed to the supporting table 30. The rod 32b is supported by the supporting box 32a slidably in the longitudinal direction. The rod 32b is disposed coaxially with the central axis X₃ of the cutting blade 31a. A pair of clamping arms 32c are disposed parallel to one another and extend in the longitudinal direction. The fore end 32c₁ of clamping arms 32c are connected to the rear end 32b₁ of the rod 32b so as to swing around vertical axes. The clamping arms 32c are provided with curved portions 32c₂ at their rear ends. The curved portions 32c₂ are provided with opposed, semicircular cutouts 32c₃ at their rear ends. One of the arms 32c is provided with an air cylinder 32d directed in the transverse direction. The piston 32d₁ of the air cylinder 32d extends through one arm 32c and is pivotally attached to the other arm 32c. When the piston 32d₁ of the air cylinder 32d is in a retracted position, the clamping arms 32c are closed as indicated by the solid line in Figure 9, and the cutouts 32c are close to one another. When the piston 32d₁ advances, the clamping arms 32c swing to an open position indicated by the phantom line in Figure 9, and the cutouts 32c are apart from one another. A bracket 32e is connected to the fore end portion 32b₂ of the rod 32b immovably in the longitudinal direction relative to the rod 32b. The bracket 32e is connected to the piston 32g₁ of an air cylinder 32g which extends parallel to the rod 32b and is fixed to the supporting box 32a by a bracket 32f. When the piston 32g₁ of the air cylinder 32g is in a retracted position, the clamping arms 32c are in the initial position indicated by the solid line in Figure 9, and are close to the cutting blade 31a. When the piston 32g₁ of the air cylinder 32g advances, the rod 32b moves forward and thus the clamping arms 32c move to the working position indicated by the phantom line in Figure 9, and are apart from the cutting blade 31a. A biasing assembly 33 is disposed on the rear end 30a of the supporting table 30 and to the rear of the cutter assembly 31. The biasing assembly 33 has a pair of rods 33a which extend on either side of the axis x₃ and parallel to one another. The rods 33a are inclined upward from their rear ends toward their fore ends. The rods 33a are fixed to a pair of shafts 33c by a pair of brackets 33b. The shafts 33c extend parallel to the axis x₃ and are provided with a pair of gears 33d at their rear ends. The pair of gears 33d engage with one another. One of the brackets 33b is connected to the piston 33e₁ of an transversely disposed air cylinder 33e. The air cylinder 33e is fixed to the rear end 30a of the supporting table 30 by a bracket 33f. When the piston 33e₁ of the air cylinder 33e is in a retracted position, the rods 33a are closed as indicated by the solid line in Figure 9 by the biasing force of a spring 33g which is mounted on the piston 33e₁. When the piston 33e₁ advances, the gears 33d rotate and thus, the pair of rods 33a move to an open position indicated by the phantom line in Figure 9. The supporting table 30 is provided with an inclined shute 34 at its rear end. The table 30 is provided with an opening 35 at its mid portion, below where the cutout 32c₃ of the clamping arm 32c are in the working position. The air cylinders 32d, 32g, 33e, and the motor 31f are controlled by a sequence controller which is not illustrated in Figure 9 for simplicity. The operation of the tendon cutting machine B constructed as above, will be described hereinafter with reference to Figures 11A to 11C. 1 ○ The meat around the lower leg bone S₁ is peeled off manually along the lower leg bone S₁ from the ankle S₃ toward the knee joint S₄, so that the meat S₆ of the leg is connected only to the knee joint S₄ by meat-to-bone connecting tendon tissues. Then, as shown in Figure 11A, the lower leg bone S₁ is passed through the cutting blade 31a from the rear side of the cutting blade 31a toward the fore side of the the cutting blade 31a, with the ankle S₃ being directed forward. The piston 32g₁ of the air cylinder 32g is in the retracted position, so that the clamping arms 32c are in the initial position wherein the clamping arms 32c are close to the cutting blade 31a. The piston 32d₁ of the air cylinder 32d is in the advanced position, so that the clamping arms 32c are in the open position. The piston 33e₁ of the air cylinder 33e is in the advanced position, so that the pair of rods 33a of the biasing assembly 33 are in the open position. The motor 31f does not operate, so that the cutting blade 31a does not rotate. 2 ○ As shown in Figure 11B, the piston 32d₁ retracts so as to close the clamping arms 32c. Thus, the portion of the lower leg bone S₁ adjacent to the ankle S₃ is clamped by the clamping arms 32c at the closely-opposed cutouts 32c₃. The piston 33e₁ of the air cylinder 33e retracts so as to close the rods 33a of the biasing assembly 33. Thus, the lower leg bone S₁ is clamped by the rods 33a. The motor 31f starts so as to rotate the cutting blade 31a. 3 ○ As shown in Figure 11C, the piston 32g₁ of the air cylinder 32g advances so as to move the clamping arms 32c forward to the working position. Thus, the lower leg bone S₁ clamped by the clamping arms 32c moves forward through the cutting blade 31a, and the meat S₆ abuts against the rods 33a of the biasing assembly 33. As meat S₆ moves forward, it moves upward along the upwardly-inclined rods 33a. Thus, the upper portion of the knee joint S₄ is pressed against the cutting edge 31a₁ of the cutting blade 31a, so that the meat-to-bone connecting tendon tissues which connect the meat S₆ to the knee joint S₄ are cut off the knee joint S₄. As a result, the meat S₆ is removed from the lower leg bone S₁. 4 ○ Lastly, the piston 33e₁ of the air cylinder 33e advances so as to open the rods 33a of the clamping assembly 33. Thus, the meat S₆ which is removed from the lower leg bone S₁ falls on to the shute 34 and then falls into a collecting box ( not shown ). When the clamping arm 32c has reached the working position, the motor 31f stops, and then the piston 32d₁ of the air cylinder 32d advances so as to open the clamping arms 32c. Thus, the lower leg bone S₁, which is now free from the meat S₆, falls through the opening 35 into another collecting box ( not shown ). Then, the piston 32g₁ of the air cylinder 32g retracts so as to move the clamping arms 32c rearward back to the intial position. Thus, the tendon cutting machine B returns to the intial condition described in 1 ○. As clearly understood from the above descriptions, according to the second, tendon cutting machine B, the meat-to-bone connecting tendon tissues which connect the meat S₆ to the knee joint S₄ are cut off the knee joint S₄ by the annular cutting blade 31a. The cutting blade 31a is disposed at a predetermined position, has a large rigidity and rotates around the axis x₃, and the knee joint S₄ is biased against the cutting edge 31a₁ of the blade 31a. Thus, different from the existing manual boning process with a knife, the cutting edge 31a₁ can stably abut against the meat-to-bone connecting tendon tissues during the cutting operation. Thus, the boning work is made safe and the cut surface of the meat S₆ is made smooth, which increases the commercial value of the meat S₆. The knee joint S₄ is biased against the cutting edge 31a₁, so that the meat-to-bone connecting tendon tissues are cut in the vicinity of the knee joint S₄. Thus, a high yield of the meat S₆ removed from the lower leg bone S₁ can be achieved. The biasing force is generated by the upward movement of the meat S₆ along the rods 33a, so that the biasing force can be easily controlled by controlling the inclination of the rods 33a, the spring constant of the spring 33g, etc,. The supporting table 30 is provided with a shute 34 and the opening 35, so that the meat S₆ and the lower leg bone S₁ can be collected separately. Thus, the boning process can be carried out efficiently. The clamping arm 32c may further be reciprocally rotated around the longitudinal axis of the rod 32b. Thus, the meat-to-bone connecting tendon tissues can be cut around the knee joint S₄, so that the yield of the meat S₆ removed from the lower leg bone S₁ can be more increased. In this case, as indicated by a phantom line in Figure 9, a rack-pinion mechanism 37 is disposed so as to reciprocally rotate the rod 32b around its longitudinal axis. The rack-pinion mechanism 37 is driven by an air cylinder 36. The cutter assembly 31 and the biasing assembly 33 may be moved in the longitudinal direction instead of the clamping arms 32c. While the present invention has been described with reference to preferred embodiments, one of ordinary skill in the art will recognize that modifications and improvements may be made while remaining within the scope of the present invention. The scope of the invention is determined solely by the appended claims.

Claims: A cutting machine for cutting open meat of a poultry leg along one side of the upper leg bone and the lower leg bone, which comprises: first clamping means (3) for clamping the ankle (S₃) of the leg (S) while allowing the leg (S) to rotate around the ankle (S₃); first supporting means (5) for supporting the leg (S); cutting means (6) for cutting open the meat of the leg, which means includes a first cutting blade (6m) having a wedge-shaped cross section and a vertical cutting edge, a second cutting blade (6x) abutting against a first side of the cutting edge of the first cutting blade (6m) and slightly protruding from the cutting edge of the first cutting blade (6m), and first driving means (6n) for vertically reciprocating the second cutting blade (6x) relative to the first cutting blade (6m); first biasing means (7) for biasing the leg (S) against a second side of the cutting edge of the first cutting blade (6m); second driving means (6a) for vertically moving the cutting means (6) into and out of engagement with the meat of the leg (S); third driving means (1c) for horizontally moving the first clamping means (3); and restricting means (6e,6g,6c₃) for restricting rotation of the cutting means (6) around a vertical axis when a force directed to the cutting edge of the first cutting blade (6m) is smaller than a predetermined magnitude, and permitting the rotation of the cutting means (6) around the vertical axis when a force directed to the cutting edge of the first cutting blade (6m) is larger than the predetermined magnitude. A cutting machine of claim 1, wherein said restricting means comprises; a vertical shaft member (6e) fixed to the cutting means (6), which shaft member (6e) is located offset relative to the first and the second cutting blades (6m,6x) in a direction at right angles to the direction of the horizontal movement of the first clamping means (3); spring means (6g) for applying a predetermined initial moment to the cutting means (6), thereby driving the cutting means (6) rotationally around the vertical axis of the shaft member (6e); and stopper means (6c₃) for restricting the rotation of the cutting means (6) by the initial moment when a force directed to the cutting edge of the first cutting blade (6m) is smaller than a predetermined magnitude, thereby making the second side of the cutting edge of the first cutting blade (6m) extend in the direction of the horizontal movement of the first clamping means (3). A cutting machine of claim 1 or 2, wherein said first clamping means (3) comprises: a first clamping member (3d) having a groove extending in the direction of the horizontal movement of the first clamping means (3); a second clamping member (3j) disposed adjacent to the first clamping member (3d) and behind the first clamping member (3d) in the direction of the horizontal movement of the first clamping means (3), which second clamping member (3j) is provided with a cutout (3j₂) facing the groove of the first clamping member (3d), the breadth of the cutout (3j₂) being smaller than that of the groove of the first clamping member (3d); and means (3f,3g,3h,4;10k,10n,10p,11,12) for rotating the first clamping member (3d) relative to the second clamping member (3j) around an axis extending in the direction of the horizontal movement of the first clamping means (3) between a first position wherein the open end of the groove of the first clamping member (3d) is directed in the same direction as the open end of the cutout (3j₂) of the second clamping member (3j) and a second position wherein the open end of the groove of the first clamping member (3d) is directed at right angles to the open end of the cutout (3j₂) of the second clamping member (3j). A cutting machine of claim 3, wherein said means for rotating the first clamping member (3f) relative to the second clamping member (3j) comprises: a guide roll (3f) connected to the first clamping member (3d); a line cam (14) for engaging the guide roll (3f), thereby rotating the guide roll (3f) to a predetermined direction around an axis extending in the direction of the horizontal movement of the first clamping means (3d); a spring (34) for biasing the guide roll (3f) to a direction opposite to said predetermined direction; and a stopper (3g) for engaging the guide roll (3f) when the guide roll (3f) is free from the line cam (4), thereby retaining the guide roll (3f) in a predetermined position in association with the rotation. A cutting machine of claim 3, wherein said means (10k,10n,10p,11,12) for rotating the first clamping member relative to the second clamping member comprises: a first bevel gear (10k) connected to the first clamping member (3d); a second bevel gear (10n) for engaging the first bevel gear (10k); a cam plate (10p) connected to the second bevel gear (10n); and a pair of baffle plates (11,12) for engaging the cam plate (10p), thereby rotating the cam plate (10p). A cutting machine for cutting open meat of a poultry leg along one side of the upper leg bone and the lower leg bone, which comprises: first clamping means (3) for clamping the ankle (S₃) of the leg (S) while allowing the leg (S) to rotate around the ankle (S₃); first supporting means (5) for supporting the leg (S); cutting means (6) for cutting open the meat of the leg (S) which means includes a first cutting blade (6m) having a wedge-shaped cross section and a vertical cutting edge, a second cutting blade (6x) abutting against a first side of the cutting edge of the first cutting blade (6m) and slightly protruding from the cutting edge of the first cutting blade (6m), and first driving means (6n) for vertically reciprocating the second cutting blade (6x) relative to the first cutting blade (6m); first biasing means (7) for biasing the leg (S) against a second side of the cutting edge of the first cutting blade (6m); second driving means (6a) for vertically moving the cutting means (6) into and out of engagement with the meat of the leg (S); third driving means (6a') for horizontally moving the cutting means (6); and restricting means (6e,6g,6c₃) for restricting the rotation of the cutting means (6) around a vertical axis when a force directed to the cutting edge of the first cutting blade (6m) is smaller than a predetermined magnitude, and permitting the rotation of the cutting means (6) around the vertical axis when a force directed to the cutting edge of the first cutting blade (6m) is larger than the predetermined magnitude. A cutting machine of claim 6, wherein said restricting means comprises: a vertical shaft member (6e) fixed to the cutting means (6), which shaft member (6e) is located offset relative to the first and the second cutting blades (6m) in a direction at right angles to the direction of the horizontal movement of the cutting means (6); a spring means (6g) for applying a predetermined initial moment to the cutting means (6), thereby driving the cutting means (6) rotationally around the vertical axis of the shaft member (6e); and stopper means (6c₃) for restricting the rotation of the cutting means (6) by the initial moment when a force directed to the cutting edge of the first cutting blade (6m) is smaller than a predetermined magnitude, thereby making the second side of the cutting edge of the first cutting blade (6m) extend in the direction of the horizontal movement of the cutting means (6). A cutting machine of claim 6 or 7 wherein said first clamping means comprises: a first clamping member (3d) having a groove extending in the direction of the horizontal movement of the cutting means (6); a second clamping member (3j) disposed adjacent to the first clamping member (3d) and in front of the first clamping member (3d) in the direction of the horizontal movement of the cutting means (6), which second clamping member (3j) is provided with a cutout (3j₂) facing the groove of the first clamping member (3d), the breadth of the cutout (3j₂) being smaller than that of the groove of the first clamping member (3d); and means (1c,3f,3g,4;1c,10p,11,12) for rotating the first clamping member (3d) relative to the second clamping member (3j) around an axis extending in the direction of the horizontal movement of the cutting means (6) between a first position wherein the open end of the groove of the first clamping member is directed in the same direction as the open end of the cutout (3j₂) of the second clamping member (3j) and a second position wherein the open end of the groove of the first clamping member (3d) is directed at right angles to the open end of the cutout (3j₂) of the second clamping member (3j). A cutting machine of claim 8, wherein said means (1c,3f,3g,3h,4) for rotating the first clamping member relative to the second clamping member comprises: fourth driving means (1c) for horizontally moving the first clamping means (3) in a direction at right angles to the direction of the horizontal movement of the cutting means (6); a guide roll (3f) connected to the first clamping member (3d); a line cam (4) for engaging the guide roll (3f), thereby rotating the guide roll (3f) to a predetermined direction around an axis extending in the direction of the horizontal movement of the cutting means (6); a spring (3h) for biasing the guide roll (3f) to a direction opposite to said predetermined direction; and a stopper (3g) for engaging the guide roll (3f) when the guide roll (3f) is free from the line cam (4), thereby retaining the guide roll (3f) in a predetermined position in association with the rotation. A cutting machine of claim 8, wherein said means (1c,10p,11,12) for rotating the first clamping member relative to the second clamping member comprises: fourth driving means (1c) for horizontally moving the first clamping means (3) in a direction at right angles to the direction of the horizontal movement of the cutting means (6); a cam plate (10p) connected to the first clamping member (3d); and a pair of baffle plates (11,12) for engaging the cam plate (10p), thereby rotating the cam plate (10p) around an axis extending in the direction of the horizontal movement of the cutting means (6). A method for cutting open meat along the upper and lower leg bones of a poultry leg using the machine of claims 1 or 6, which comprises: clamping an ankle (S₃) of the poultry leg (S) while allowing the leg (S) to rotate around its ankle (S₃); supporting the leg (S); bringing the cutting means (6) comprising the first wedge-shaped cutting blade (6m) and the adjacent second reciprocating cutting blade (6x) in engagement with the meat of the poultry leg (S), wherein the reciprocating blade (6x) protrudes slighly from the cutting edge of the first cutting blade (6m); biasing the leg (S) against the second side of the cutting edge of the first cutting blade (6m); generating a relative movement between the cutting means (6) and clamping means (3) for clamping the leg while reciprocating the second cutting blade; and restricting the rotation of the cutting means (6) around a vertical axis when a force directed to the cutting edge of the first cutting blade (6m) is smaller than a predetermined magnitude, and permitting the rotation of the cutting means (6) around the vertical axis when the force directed to the cutting edge of the first cutting blade (6m) is larger than a predetermined magnitude, whereby the meat is cut open adjacent the upper and lower leg bones without chipping the bones.

Inventors: SEKIGUCHI MITSUAKI, SEKIGUCHI, MITSUAKI
Applicants: FOODCRAFT EQUIP CO INC, GORDEX CORP, FOODCRAFT EQUIPMENT COMPANY, INC., GORDEX CORPORATION
Application year: 1992
Main classification: A22C17
IPC codes: A22C17, A22C21