(248) Messrs. Howard and Bullough use Tweedale’s motion, which is illustrated in Fig. [139]. The shaft A has a boss fastened on it, which is constructed with a second boss G at right angles to, but on one side of it. The latter is bored to receive a short shaft, on each end of which the two wheels F H are fixed. The wheel B is driven from the lower cone, and is compounded with the bevel wheel E, both being free to revolve on the shaft. The bobbin wheel C is cast in one piece with the wheel D, and also runs loosely upon the shaft. It will be noticed that only the wheels F and H are positively rotated on the shaft A, being carried round with the boss. The motion is communicated from E to D as follows: E drives the wheel F, thus rotating the short cross shaft and the pinion H. The latter gears with and drives the wheel D, the pinion F acting merely as a carrier. The action of this mechanism can be readily understood from the preceding explanation, and it need only be pointed out that the regulation comes from the wheel B. There is introduced into this mechanism the element of a double set of driving and driven wheels. Thus G drives the wheel F, and H D, so that there is a difference between this and the Holdsworth motion, in which the intermediate pinions act as carriers only. In order, therefore, to get the speed communicated to the wheel D, it is necessary to multiply the number of teeth in the driving wheels and divide by those of the driven, by which means the proportions of the two are arrived at. By the use of the following formula the speed of D can easily be arrived at. Let m = revolutions of the shaft, n = revolutions of the pinion B, which is variable, a = the constant arrived at as above, and v = the speed of bobbin wheel D, then v = m - a(m + n). Having obtained the speed v it is of course easy to calculate the necessary wheels to give the speed of the bobbins.
(249) The operation of the differential motion is controlled, as has been seen, by the lower cone, the speed of which is carefully regulated by altering the position of the driving strap laterally. It has been pointed out that the cones are correspondingly but conversely curved, the reason for this being that the actual increase which takes place in the diameter of the bobbin is not in the same proportion to the actual diameter at the end as at the beginning of winding. There is a slight decrease occurring as the bobbin fills, and in the early stages of spinning it was the practice to use a rack with uneven teeth cut to a parabola, which was a costly process, and is entirely avoided by the use of cones of that shape. Further, it is found that the bite of the strap is better during a change of position. It will be readily understood that the position of the strap on the two cones determines the speed of the plate wheel L. It is therefore essential to provide means by which the traverse of the strap can be effected, and, as the addition of one layer of roving implies the necessity for a change in the bobbin speed, the movement of the strap is given at the termination of each lift, at the moment of the change of traverse. It follows, therefore, that the mechanism by which the strap is moved, and that by which the reversal of the lift is effected, must be connected. Before proceeding to describe how this is done it may be stated that the strap passes between two guides fastened to the toothed rack or slide P (Fig. [134]), sustained by bearings fixed to the frame of the machine. The operation of traversing the rack is performed by an interesting piece of mechanism which has several functions.
(250) The “building motion,” or “box of tricks” as it is sometimes called, is placed in the position shown in Fig. [133] by the letter Q. In order that its details may be better understood, a front and back elevation and plan of it is given in Figs. [140], [141], and [142], to which special reference will be made. The objects of the building motion are three-fold: 1st, to give the requisite traverse to the cone strap; 2nd, to give the reciprocal traverse to the bobbin; and 3rd, to shorten that traverse or lift at the termination of the winding of each layer. It has been already explained why the two first objects have to be attained, and it will be profitable to explain the reason for the third. Suppose that in commencing winding the tube is 11⁄4 inches diameter, the lift say 10 inches, and the diameter of the roving 1⁄8 inch, there would be wrapped upon that surface during one lift 80 coils or 314 inches of roving. Now, assuming that four layers have been wound, the diameter of the bobbin would be 21⁄4 inches, which, if the lift remained constant, would cause 563 inches to be wound on the surface. But as the rate of delivery by the rollers is definite during the time occupied by the lift, it follows that such a length of roving could not be wound. It, therefore, becomes necessary to reduce the lift after each layer of yarn is wound, so as to compensate for the increased area of the cylindrical surface, and provide that the whole of the length delivered by the rollers is taken up, but no more.
Fig. 140.J.N.
(251) Referring now to Figs. [140] and [141] it will be noticed that there are two cradles A and B, centred respectively on the pins A1 and B1. Fixed in the upper cradle A are hooks, one at each side, which are connected, as shown, with double hooks C D, passing through ears on the lower cradle B, having weights attached to their lower ends. The lower cradle B has fixed in it a pin E1, engaging with a slot in the lever E. E is centred on the pin F, and is coupled at its lower end to the rod R, which is connected with the double bevel wheel T T, this connection being shown in Fig. [134]. Two catches G G1, centred at their lower ends to the frame carrying the cradles, are coupled by the helical spring H. It will be noticed that the pawls of the catch levers are differently shaped, so as to engage with the teeth of the rack or ratchet wheel I on the upper and lower side of the centre respectively. The rack wheel is fixed on the same centre as the cradle A, as is also a bevel pinion J, gearing with a similar one J1 fixed on the upright shaft K, Fig. [141]. At a higher point on K a spur pinion P1 is fastened, which gears with the teeth on the rack P, controlling the strap guides. Two levers L L1 are pivoted to the frame as shown, and are coupled at their inner ends by a helical spring M, which is carried round the centre B1. The inner ends of L L1 engage with shoulders or corners N N1, formed in the lower cradle B. Fixed to the bobbin rail is the double slide Q, which has a pin O sliding in it, on which the end of the connecting rod S is centred. This rod passes through bearings placed in the cradle A (see Fig. [140]), and is formed with a toothed rack at its lower side with which a wheel T fixed on the pin A1 gears. These are the whole of the parts of this particular mechanism, but a reference to Fig. [134] will show that the rack P has a weight attached to it by a chain, which is always tending to draw it inwards, and move the strap. In addition to this it causes a torsional strain to be exercised on the shaft K, and consequently on the rack wheel, which causes the latter, when released by the catches, to rotate.
(252) The action of this mechanism is as follows: The slide Q in its reciprocal vertical movement causes by means of the “diminishing rod” or “hanger bar” S, the upper cradle A to oscillate in its centre. When the bobbins are midway in their lift, the centre of the slide Q should be in a line drawn horizontally through the centre of the pin A1, and the rod S should be capable of being moved horizontally without producing any oscillating movement in the cradle A. When this is the case, the two levers L L1 engage respectively with the shoulders N N1. Assuming that the bobbins are descending, the cradle A is turned from left to right when looked at from the back of the frame as in Fig. [141]. In this way the hook D is raised with its pendant weight, while C is simultaneously lowered. As the shoulder on the upper part of the hook C prevents it passing through the hole in the ear on the cradle B, it follows that a pressure is exercised on the latter, which causes it to turn in the same direction as A. The weight attached to D is finally completely taken off the cradle B, and the continuance of the movement causes the point of contact of L and N to become the fulcrum by which the rotary movement of A is arrested for the time. This movement closely resembles the action of an anchor, the cradle B being practically fixed as a ship is by its anchor. In some modifications of the mechanism this resemblance is more pronounced than in the one immediately under notice. Thus the point through which D passes continues to be free, while the whole weight is thrown upon the hook C, which thus exercises a proportionate strain on B. The continued oscillation of A in the direction indicated causes the screw X, fixed in the left hand arm of A, as shown in Fig. [140], to come into contact with the outer end of the lever L. The increasing pressure so applied causes L to turn upon its centre, destroying the contact of its inner end with the shoulder N, and allowing the cradle B to make a sudden movement, which is partially rotary, but is also vertical in character. The movement being reversed, the parts assume the position shown in Fig. [140], shortly after the reversal. The screws fixed in the arms of the cradle A can be readily adjusted and locked so as to make the release of the lower cradle B simultaneous with the termination of the bobbin traverse.
Fig. 141.J.N.