(238) Assuming, then, that the bobbin leads, it is necessary to consider the effect of the gradual increase in the size of the bobbin, caused by the winding on of the yarn. This difficulty is rendered acute by reason of the positive driving of the bobbin. In flyer frames, used for spinning or doubling, the bobbin has a little slip which can be easily adjusted, but which is not obtainable in this case. The slip of the bobbin is caused by the drag of the yarn, a procedure which at this stage is practically impossible. Every traverse of the bobbin rail is, as has been seen, accompanied by an increase of the circumference of the bobbin corresponding to the diameter of the roving. Thus, to take an extreme case, assuming the diameter of the empty tube to be 11⁄2 inch, it would take up at each revolution 4·7 inches of yarn. If the yarn was 1⁄8 inch thick, the diameter of the bobbin would be 13⁄4 inch after one layer, and each revolution would take up 5·5 inches of yarn. This is, of course, assuming that the flyer is absent, and that the bobbin was winding. As the surface velocity of the bobbin and front roller must correspond, and no more sliver is delivered at one time than at another, it follows that the rate of revolution of the bobbin must diminish in exact proportion to the increase of its circumferential speed. It is, therefore, easy to calculate the exact amount of retardation at each traverse by a knowledge of the diameter of the yarn, or the number of layers to be wound on any spool.
(239) It is thus easy to see that with the bobbin leading it should gradually diminish in speed, and it is consequently the practice to run it at a much higher speed at the beginning than at the termination of winding. For instance, an empty spool 1 inch diameter takes up per revolution 3·1416 inches of roving, while one 3 inches diameter would take up 9·42 inches. It thus becomes imperative to reduce the speed of the bobbin wheels, and these being constantly geared with their driving wheels, it is necessary to reduce the velocity of the bobbin shafts. These are driven, as described hereafter, by a train of gearing from the main shaft, and special means are adopted to compass the reduction. The spindles are running at a constant speed, and it follows, in consequence, that the bobbin must run at the same rate, plus the number of revolutions necessary to take up the length of yarn delivered in any given time. If, for instance, the spindles made 100 revolutions while 10 inches of yarn was being delivered, the bobbin must revolve 100 times plus the number necessary to take up the 10 inches of yarn.
(240) When the flyer leads, the application of this principle is not quite so clearly seen at first sight, but a little reflection will make it understood. In this case the winding is effected by the excess of the speed of the flyer over that of the bobbin. This is exactly the reverse of the practice when the bobbin leads, but the essential condition is, as before, the preservation of the relative surface speeds of the bobbin and roller. Suppose that, in starting, the diameter of these two are the same, then the bobbin must lag behind the flyer to the extent of one revolution for each revolution of the roller. But as the bobbin increases in diameter, it requires more yarn to cover its surface, and a less difference in speed is needed, as, if the bobbin continues to lag one revolution, the difference between the speed of delivery and that of winding become so great as to stretch and break the roving. Instead of wrapping it round, for instance, a circumference of three inches it has eventually to be wound on one of six inches, and it is obvious that if the speed of the bobbin remains constant the roving will be drawn and broken. It is, therefore, necessary to gradually increase the speed of the bobbin so that for every inch of yarn delivered, an inch of the circumference will be covered by it. The difference between this and the former case consists in the fact that the roving is wrapped on a concentric surface, revolving in the same direction at a slower speed, while, with the bobbin leading, the surface on which the roving is wound, moving in excess of the speed of the flyer, draws the roving through the flyer eye at a rate equal to that of its delivery. In other words, it is in one case wrapped on by the excess of the flyer speed or the drag of the bobbin, while, in the other, it is drawn on by the excess of speed of the bobbin. The conclusion is thus arrived at that when the flyer leads, the bobbins must start at their slowest speed, and gradually increase; while, when the bobbin leads, it must begin at its highest speed and gradually diminish.
(241) Having thus explained the principle of the machine, it now remains to describe the mechanism by which it is carried into effect, referring for this purpose to Fig. [134]. The driving, or “jack,” shaft A has a fast and loose pulley on its outer end, and has fastened on it two spur wheels. One of these drives, by means of a carrier wheel, a wheel fixed on one of the spindle shafts, and motion is given to the spindles in the way previously described. The speed of the spindles, being independently obtained, can be changed without reference to the other motions. The pinion C is known as the “twist wheel,” and is made as large as convenient. It drives, by the intervention of a carrier wheel, a pinion D fixed on the shaft on which the cone E is also keyed. The shaft carrying D has also fastened on it, within the framing, a pinion which directly gears into a wheel fixed on the roller axis. Thus the twist wheel C drives the cone E and the rollers, so that if it is replaced by a smaller wheel, both of these revolve at a lower speed, or vice versâ. This is important, because as the speed of the rollers and that of the bobbins are both regulated from the twist wheel, the alteration of their velocities is made simultaneously.
Fig. 134.J.N.
(242) This part of the mechanism is easily understood and involves no difficulty, but the driving of the bobbins gives rise to a complex problem which necessitates the employment of some ingenious mechanism. The upper cone E drives, by means of a strap or band, the lower cone E1. The circumferences of each of these cones are accurately turned to corresponding, but converse, parabolic curves, one cone being convex and the other concave. They must be exactly the same in their largest and smallest diameters, and are turned in lathes fitted with “former” plates, by which the slide rest is guided in its correct path. The lower cone is carried in bearings B, formed in two arms connected by a tubular stay, oscillating on a shaft (M, Fig. [134]), on which is the pinion H. This arrangement is shown separately in plan and elevation in Figs. [135] and [136]. A pinion G is fixed on the spindle of the lower cone, and gears with a spur wheel F fastened on the shaft named. Thus, when the cone E1 is raised or lowered, the pinion G rolls round its engaging wheel F, being always fully in gear. This arrangement is utilised to keep the strap tight, the lower cone being coupled by an adjustable connecting rod or chain I to a disc fixed on the cross shaft shown, the former being preferable. By revolving the shaft J, the cone E1 can be raised or lowered, and the tension on the strap can be regulated by means of a right and left-handed nut which couples the two parts of the connecting rod I, Fig. [134]. Motion is given to the pinion H, as will be easily understood, from the cone E1, and from it to the shaft K by the carrier pinion which gears with H1 on K. On K also is fixed a spur pinion L1 driving the plate wheel L, and the worm which engages with the worm-wheel on the upright shaft M. The latter is thus revolved, its precise function being explained hereafter.
Figs. 135 and 136.J.N.
(243) The wheel L forms a part of the ingenious winding, or, as it is sometimes called, “the differential motion,” invented by Mr. Henry Holdsworth. This is one of the class of epicyclic wheel trains, of which many instances are known and which are very interesting. Fig. [137] is a drawing on an enlarged scale of this motion, the reference letters, with the exception of L and N, being used for this figure specially. Upon the shaft A a fixed cast-iron tube is placed, upon which the wheel L and the compound wheel D N revolve. The jack shaft A revolves in the tube, and on the shaft is fastened a bevel wheel B which gears with similar pinions C and E. These are carried in bearings formed in the wheel L at equal distances from its centre, and have perfect freedom of revolution. They also engage with the bevel wheel D, cast in one piece with the spur wheel N, which is known as the “bobbin wheel.” The latter gears with a spur pinion carried in a double swing frame O O1 (Fig. [134]), centred on the jack shaft and attached at its other end to the bobbin rail. In this way, as the latter rises and falls, the swing frame or “swing”—as it is shortly called—oscillates on its centre, and the spur pinion rolls round the bobbin wheel N, being always in full gear. By means of a carrier wheel—also borne by the swing—the motion of the bobbin wheel is communicated to a spur wheel on one of the bobbin shafts, and by equal sized pinions on each shaft to the other. Thus, the bobbins are driven by a train of wheels, which are always in gear, no matter what the vertical position of the bobbin may be. The bobbin wheel and its compound bevel run loose upon the cast-iron tube, as previously stated.