Fig. 166.J.N.
(325) It will be shown, a little later, that the rotation of the spindles during winding is obtained by the pull of the carriage on a chain, which has its other end attached to an oscillating arm, being fastened to a drum on the carriage. To get a clear idea of the action of this part of the mechanism the two diagrams shown in Figs. [166] and [167] are given, a study of which will be profitable. In Fig. [166] the circles B C D represent three positions of the barrel or drum after it has moved in a horizontal plane in the direction of the arrow. To the drum a chain is supposed to be attached, which is held at the point A. It is, of course, understood that the barrel is mounted upon a shaft or axis so that it can freely revolve. If it be now assumed that the barrel is in the left hand of the three positions B, the chain will be wrapped completely round it. As it is moved horizontally in the direction of the arrow it is revolved, as indicated by the curved arrows, and, by the time it has reached its middle position C, has been rotated sufficiently to unwind about half a turn of the chain. A further horizontal motion to the right hand position D will complete the unwinding, and, by this time, the drum will have made one complete revolution. It will be at once seen that the rate at which the drum will be revolved will depend upon two factors—its diameter, and the speed of its horizontal traverse. If the point A at which the chain is held is stationary, and the horizontal movement uniform, then the rotation of the barrel will be constant. But if the barrel be traversed at a variable rate then its rotation will also be variable. In actual practice this uniformity does not exist, for, as was shown in paragraph 315, the taking-in scrolls vary considerably in diameter. Assuming this variation to be 1:3:1, it would follow that the rotation of the barrel would increase and diminish in the same ratio. In practice this is what happens, and the speed of the revolution of the barrel is quicker about the middle of the taking-in than at any other time.
(326) The assumption that the point A is stationary was only made to illustrate the point at issue, and is not founded upon the actual facts of the case. If now it be assumed that not only the barrel but the point at which the chain is held makes a forward movement, a new set of conditions arises. In this case the unwinding of the chain during a given time will be diminished by the amount of the advance of the point A in the same period. Assuming the latter to be made at a regular rate it would be easy to calculate the extent of the unwinding. If the effect of the horizontal movement of the barrel from B to C be to unwind half of one coil of chain—say a length of 7 inches—and that in the same space of time the point A moved 3 inches, the amount unwound would be reduced to 4 inches. But this is not the actual condition of things in practice. The point moves at a variable velocity, its forward motion gradually diminishing, so that the acceleration of the rotary velocity of the barrel is greater at the end of its horizontal traverse than at the beginning. In other words, its terminal velocity is highest.
(327) The point of the attachment of the chain at A is made in an oscillating arm which, during the inward run of the carriage, receives a forward movement at a speed which is controlled by the velocity of the back shaft. As the latter is, in turn, commanded by the scroll shaft during this period—see paragraph [315]—it follows that the variation in the forward movement of the arm is coincident with that of the carriage. Thus the advance of the point A will always be in strict correspondence with the velocity of the carriage traverse.
(328) Referring now to Fig. [167], and, assuming A B to be the arm to which the chain is fastened, and O J and H C to represent the arcs through which the point of attachment of the chain travels at different times, it will be seen that the periods of movement are well marked. In each case the arcs are of the same number of degrees, although the chord of one is shorter than that of the other. Dealing first with the inner arc, which represents the position of the point of attachment when nearer the centre, the whole period of movement is divided into equal parts. These are represented by the letters J K L M N O. Now, if vertical lines are drawn from these, until they terminate in a straight line drawn parallel to a horizontal line through the point B, a clear idea can be formed of the effect of the oscillation of the vertical arm A B. The lines terminate at J1 K1 L1 M1 N1 O1. It can be easily seen that the horizontal movement of the point of attachment of the chain gradually becomes less as the arm is oscillated from its most backward position B C to its most forward one B H, this diminution occurring most after the point L is reached. In the movement from J to K and K to L the horizontal traverse is about equal. It shows a decrease from L to M, a greater one from M to N, and a still greater one from N to O. The same thing happens if the chain be supposed to be attached at the point D. In this case also the decrease in the horizontal forward traverse is variable, but occurs in the same way. The periods here are marked by the letters C to H, and the extent of the forward motion by those C1 to H1. It will be noticed that the amount of the traverse is greater than that previously noted, the total space covered being respectively J1 to O1 and C1 to H1. That is to say, the point at which the chain is fastened moves forward in the same direction as the barrel, but at a different speed. In other words, when the chain is held at K, the total forward movement is comparatively small, and if it were held at a point shown by the small inner circle, it would be still less. On the other hand, its attachment at B implies a greater total forward movement. It therefore happens that the retardation of the chain by the arm is less in the early part of the oscillation of A B—or, to put it differently, the delivery of the winding chain by the arm is greater when it is fixed at D than when it is fixed at K. Therefore the barrel is more slowly rotated during the same period in the former than in the latter case, but as it completes its lateral movement it is rapidly and considerably accelerated.
(329) The application of this principle is as follows, and it can now be stated that the end of the chain is attached to a nut which slides along the arm, being actuated by the rotation of a screw upon which it fits. Remembering that an acceleration of the terminal velocity and a regulation of the revolution of the spindle is required, the demonstration just given shows that these are obtained by the removal of the nut further from the centre of oscillation. The influence of the pull of the chain upon the barrel when the nut is in the position K is much slighter, and shows less variation than when it is at D. Every inch which the nut travels outwards has an influence upon this factor, and the conditions of winding are thus accurately regulated. When the winding of the cop begins, the nut is in its lowest position, and the rotation of the barrel is then practically equal. As the nut moves away from the centre the barrel gradually rotates more slowly at the beginning of its inward movement. By the time the most outward position is reached—which, in practice, coincides with the formation of the cop bottom—the variation in the velocity has reached its greatest amount. This, it can be easily seen, is what is wanted. Referring again to Fig. [163], one revolution of the spindle when the yarn is being wound on A D would practically take up the same length as would be taken up at the top of the paper tube. But when the faller is guiding the yarn on the conical surface from E to B, one revolution of the spindle would wind on a greater length at E than it would at B. Therefore, the initial velocity requires to be less than the terminal. But when the point E has become the initial position, the conditions of winding remain thereafter constant, except in so far as is affected by the taper of the blade, and there is no further need for an outward movement of the nut.
(330) The theory underlying the method of winding having thus been dealt with, the mechanism employed can be described. This is shown in Fig. [168], which is a diagram of the whole of the apparatus, and in Fig. [169], which is an enlarged view of a portion of it. The winding arm M is centered at its lower end, and has formed on it a toothed quadrant M1. The “quadrant” M oscillates on a short shaft, securely carried by the headstock framing, and receives its forward movement by means of a pinion Z, which engages with its teeth. The extent of the quadrant movement is about a quarter circle. The pinion Z is mounted on the same centre as a grooved pulley, over which a cord from the back shaft H is passed. Thus the rotation of H in either direction produces a similar movement in the pinion Z; and the effect is, that, while the back shaft is drawing the carriage out, the pinion is revolving so as to raise the arm M or cause it to make a backward oscillation. When the back shaft acts as a taking-in shaft, as described in paragraph 315, the pinion Z is revolved so as to move the arm M forward. The velocity at which the forward stroke is made is by this arrangement a variable one, and completely corresponds to that of the carriage traverse. Inside the winding arm a long slot is formed in which a screw P is placed, this being free to revolve. It may be made with a thread of equal pitch throughout, but, as shown, is provided with a thread of varying pitch, which gradually becomes finer towards the outward end of the arm. The reason of this is obvious. The effect of each layer of yarn upon the problem of winding is greater at the beginning of the formation of the cop bottom than when it is more nearly finished. That is, the enlargement of its diameter is relatively greater at the first stage than at any other. For instance, if the diameter is 3⁄8 inch and it be increased 1⁄16 inch, the ratio is 1⁄6th; while if the diameter is 3⁄4 inch, and the same increase takes place, the ratio is 1⁄12th only. The variation required in the speed of winding as each layer is wrapped is therefore less in the latter than in the former case. This is the purpose of the helical screw, which gives a quicker advance to the nut in the earlier stages of winding than when the cop bottom is nearly formed.
Fig. 167.J.N.