(244) The foregoing description of the winding motion will serve to show the principle of its construction, and its mode of action can now be explained. Suppose first, that the bearings of the pinions C and E are fixed instead of revolving with the wheel L, and that the shaft A is revolved, it is obvious that the revolution of the wheel B would be communicated to C and E. These would rotate on their axes, and would consequently drive the wheel D N at the same speed as B, but in the opposite direction. This may be called one pole of the operation of this motion. The other is reached when the plate wheel L is rotated in the same direction as B at an equal velocity, the wheel D N being then carried round in the same direction, and at the same speed as B. But if the relative velocity of L is reduced, there will be a lessened speed communicated to the wheel D N in the proportion of two revolutions less than that of B for every revolution of L. That is to say, if B was running at 20 revolutions per minute and L in the same time made one revolution, D N would make 18 revolutions. This gives rise to a curious result in working. When the number of revolutions made by L is half of those made by B, the motion of D N entirely ceases, but as the proportion is varied so as to be slower than B, the velocity of D N is reduced as described, but its direction of rotation will be different. That is, if L makes more than half as many revolutions as B, the wheel D N will move in the same direction as B; but if it makes less than half, D N will rotate in the opposite direction to B. This motion is admirably treated in Professor Goodeve’s “Elements of Mechanism,” where its rationale is fully described, and where the student will find ample explanations of the operation of this class of mechanism. It is sufficient for the present purpose, however, to reiterate that the loss of motion in the bobbin wheel D N, is equal to two revolutions of B for each one of L; and that the direction of motion of D N depends on the speed of L. It may be said, in amplification, that when L revolves at less than half the speed of B, the velocity of D N increases as that of L decreases; while if the plate wheel L makes more than one-half the number of turns of B the speed of D N increases with that of L. The middle point thus becomes a sort of zero, a fact which it is desirable to remember. Treated algebraically, the formula may be stated as follows, where b = the velocity of the driving pinion B, l = that of the plate wheel L, and n that of the bobbin D N, if L revolves in the same direction as the shaft, n = b - 2l; but if in the contrary direction, then n = -b - 2l.
(245) The effect of the application of this formula in the latter case is different entirely to the results already described. If the wheel L revolves at the same speed as B, but in the contrary direction, then n = - 3b, if the value of b be substituted for that of l. If L makes half the number of revolutions that B does, then n = -2b. The relations of B and D N can thus be accurately ascertained, and by the aid of this formula the speed of the bobbin wheel can be easily calculated. It is only necessary to know the value of the entire train of gearing from the fixed wheel B to the plate wheel N to be able to apply the formula given above. Thus, if it is found that the ratio of the velocity of L and the fixed wheel B be, say, as 1: 40, and that B makes 250 revolutions per minute, the speed of D N could be arrived at easily. Substituting the arithmetical value of l and b for those signs, the result would be n = 250 - 2(250÷40) = -262·5. As the changing position of the cone strap is the only variable factor in the problem, it is only necessary to know the diameters at various points to ascertain accurately the reduction or acceleration of speed which will occur during the time it is making the necessary traverse. It should be explained, before passing on to deal at greater length with the practice of the subject, that the minus sign merely indicates that the bobbin wheel revolves in a contrary direction to the wheel B and the shaft A.
Fig. 137.J.N.
(246) The application of this mechanism to the purposes of winding depends, therefore, upon the regulation of the speed of L. It has been seen that the motion of the latter is derived from the bottom cone E1. Assuming the plate wheel to run in the same direction as the wheel B, it follows that when the bobbin leads, the wheel L must start at its slowest relative speed, and increase as the bobbin fills. It is for many reasons desirable that the speed of the plate wheel should be as low as possible, which is the course generally adopted. If the flyer leads, the opposite plan is pursued. When, as is the case in the machine made by Mr. John Mason, the plate wheel revolves in the reverse direction to that of the wheel B, it commences at its quickest and finishes at its lowest relative speed, with a bobbin lead. Under these circumstances the full value of the special arrangement, illustrated in Fig. [137], is seen. The highest velocity of the cone is obtained when the bobbins are empty and have in consequence the lightest weight. Where spindles are revolving at 800 to 1,000 revolutions per minute, this is undoubtedly a great consideration, because the strain upon the strap is lessened by reason of the decreased velocity at a time when the strap is on the smallest diameter of the driving cone. It is sometimes the practice to run L and D on the bare jack shaft in the contrary direction, this creating a good deal of friction and necessitating extra driving power. For this reason the introduction of a tubular bush, such as is shown in Fig. [137], is attended with considerable advantage. The friction existing when the wheels run upon the bare shaft, but in the contrary direction, is very great, as will be understood when the speed of the wheels—about 400 revolutions per minute—is remembered. Any rotation of one or more of the wheels in the opposite direction to the shaft is therefore equal to an increase of the friction on the latter by the rate of the movement of the former.
Fig. 138.J.N.
(247) To overcome this defect, therefore, the motion has been re-arranged in one or two cases, so that all the parts revolve in the same direction. Messrs. Curtis, Sons, and Co. employ Curtis and Rhodes’ motion, which is illustrated in section in Fig. [138]. The bobbin wheel A is cast in one piece with, or fixed to, an internal wheel C, which is loose upon the shaft B. The disc D is fastened on the shaft, revolving with it, and carrying a pin or spindle, on each end of which are fastened the pinions E and F. E gears with the internal wheel, and F with a compound pinion G, which in turn engages with the pinion H. The latter is cast on the collar L, which is driven from the lower cone and is loose upon the shaft B, revolving in the same direction. If the collar L is fastened to the shaft, the whole of the wheels become locked together, and the bobbin wheel A and the driving pinion H will revolve together at the same speed and in the same way. This arises from the fact that the disc D is fixed on the shaft, and as it carries the train of wheels the fastening of L keeps the teeth of E and F locked, so causing the rotation of the latter and its attached wheel A. The carrier wheels would be standing under these conditions, while the Holdsworth motion in the same circumstances would have the whole of the wheels in rapid motion. Thus, if in actual work, when the collar L is loose, it is revolved at the same speed as the disc D or at one nearly approaching it, there would be no motion in the carrier wheels, or very little, and the speed of A would equal that of H. As the velocity of the latter is reducing, more motion is given to the wheels, which thus retard the wheel A while allowing it to rotate in the same direction as the shaft. In this way the wear and tear of the parts, and the power required to drive them, are alike materially reduced.
Fig. 139.J.N.