Patent GB-161845-A (GB)
Title: Improvements in artificial limbs
IPC: A61F2/60
Filed: 1920-04-30
Abstract: 161,845. Knudsen, J. P. April 30,1920. Limbs, artificial.-An artificial leg is designed so that it can be made the same length as the natural limb, without danger of the foot knocking against the ground when taking a step, these objects being secured mainly by arranging the lower leg to move outwardly, relatively to the sound leg, when it is moved backwards, and arranging the toe to point outwardly and to be pointed upwards when taking a forward step with the artificial limb. The leg, as illustrated, is designed for a hip amputation and is fitted with a hip-joint H, knee-joint K, and ankle-joint A. The axes of the hip and ankle-joints are parallel, but the knee-joint is arranged in front of the vertical line passing through the centre of the hip-joint and is set askew so as to throw the lower leg outwards as stated above. A leather bandage L, strengthened by metal bands, is strapped round the loins and the hip, and has a sliding metallic tongue-and-groove connection c with the upper leg. Metal side straps on the upper leg, which receive the hip-joint pin H, are fitted with camshaped ends 37 which limit the swing of the hipjoint. The operating-mechanism comprises four main parts as follows: (1) A tilting-lever 10, which is compelled to assume one or other of two extreme positions by a spring 17, and is connected by cords 7, 8 to fixed points on the hip. The cords are crossed. below the lever and connected to oppositely-disposed pawls 1, 2 on the upper leg, so that one pawl is released and the other held up in each position of the lever. The pawls work in conjunction with oppositelytoothed ratchet sectors 3, 4 working freely on the knee-joint axis and having a limited turning- movement between stops. Each sector is connected to the lower leg by a separate spring 14. Each pawl carries a depending arm 12 working frictionally against the face of the corresponding ratchet sector. The arrangement is such that when the pawl 1 is released, the ratchet sector 3 can turn clockwise, but an anti-clockwise movement operates the arm 12 to bring the pawl into engagement to stop the movement. Similarly, the ratchet sector 4 can move anti-clockwise, but is prevented from clockwise movement. (2) The ratchet sector 4 is connected by a cord 42 to a pawl 5 mounted in the foot and normally engaging a doubly-sprung lever 31 pivoted on the ankle joint and movable between stops 22, 25 on the foot and leg respectively. (3) A cord 46, passing in front of the knee-joint to a point 48 on the upper leg, is adapted to move a bell-crank V on the lower leg away from a stop 32 on the heel, against the action of a spring 33. (4) A cord 51, connected to the heel, has a chain-and-pulley connection with a spring 13 secured to the upper leg, and also carries a stop 49 to limit the forward turning movement of the foot. In operation, the taking of a step forward with the sound leg throws the body forward, and by straining the cord 7 releases the pawl 2 ready to engage the ratchet sector 4. At the same time the knee-joint is forced rearwardly until the stops 23 abut. This brings the weight of the bodv on to the front of the foot and bends the toe forcibly upwards by stretching the spring 15 until the stop 32 contacts with the bell-crank V. This movement of the foot also stretches the spring 13. At this stage the outward-pointing of the bent toe causes the bulk of the weight to be transferred to the sound leg. The release of the pressure on the toe allows the stressed spring 13 to commence to bend the knee-joint. Meanwhile the stressed spring 15 tends to bring the toe downwards again, but is prevented by the stop 32 which acts to prevent both forward and backward swinging of the foot. The continued bending of the knee, however, stretches the cord 46 and withdraws the bell-crank V, following which the springs 15 bring the toe down again and the remaining energy stored in the spring 13 assists the movement by raising the heel. At the limit of bending of the knee, the pawl 2 engages the ratchet sector 4 and limits pivotal movement of the bent and lifted lower leg about the kneejoint in the reverse direction under gravity to the amount of play between the ratchet sector and its stop. This limited movement disengages the pawl 5 and allows an elastic band 16 to draw the toe upwards again. The leg can then move forward as a whole about the hip-joint, while the lower leg remains bent and the toe points upwards. This movement stretches the cord 8 and reverses the pawls so that the lower leg is released after passing the upright position and is re-locked in its forward stretched position so that the heel may be placed on the ground and the weight of the body transferred to the leg in preparation for the succeeding step. During the restoring movement of the lower leg, the spring 13 restores the foot by stretching the elastic band: 16, and thus re-engages the lever 31 with the pawl 5. The play in both directions between the ratchet sector 3 and the lower leg allows the latter to turn sufficiently to permit the heel or toe to step upon stones or like obstacles, without disturbing the general balance of the mechanism.