(285) The bevel wheel on the outer end of the taking-in side shaft D gears with a similar one fixed on the upper end of the vertical shaft I, on the lower end of which is loosely placed the friction cone K. With the latter the hollow cone I1 engages, this being able to slide in a vertical direction on a disc keyed to the shaft. It is usually kept out of gear by means of a hinged forked lever, the fork of which fits in the groove shown in I1, and which is sustained at its free end so that it can be readily released to allow the sudden engagement of the friction cone. On the half cone K, at its underside, is cast a small bevel pinion; which engages with a bevel wheel K1 fixed on the shaft L, extending transversely of the headstock at the back. Spirally grooved or “scroll” pulleys L1 are fixed on the shaft L, on which ropes are wound, these being attached to the carriage square as shown in Fig. [168], page 212. An additional scroll is fitted on the shaft L, and is set at such an angle that when the rope is fully drawn off the other scrolls it is wound on the additional one. When the friction cone is in gear the ropes are wound on to the scrolls, and the carriage is drawn in. From the fact that these scrolls are employed, and that their object is to draw in the carriage, the shaft L is called the “scroll” or “taking-in” shaft, and the friction cone is commonly styled the “taking-in friction,” or, more shortly, the “friction.”
(286) The means just described are those which are in use on a large number of mules constructed by Messrs. Platt, and worked satisfactorily until the speed of the rim shaft was largely increased. Up to about 750 revolutions the train of gearing driving the taking-in side shaft could be used, but as the rim is now run at speeds as high as 900 revolutions it is the practice to drive the taking-in side shaft by means of a grooved pulley fastened upon it, and driven by a separate band from the counter shaft. In this way much of the strain is taken from the rim shaft, and the use of gearing obviated for the taking-in and backing-off. When this method is adopted—as is now almost generally done—there are many advantages gained, and it is the most modern practice.
(287) Another method of driving, also largely employed by Messrs. Platt, is a patented system of duplex driving. This is shown in plan in Fig. [157]. Instead of using one belt only, by means of which the power is transmitted, two narrower ones are employed, each of which is 23⁄4 inches wide. The fast pulleys A are also 23⁄4 inches on their face, while the loose pulleys B are 3 inches wide. The strap guide is made, as shown, double, and the distance which it has to traverse is only half that which is usual. The advantages of this arrangement are derived both from the smaller width of the belts, and the shorter distance they need moving. The diminished width causes the belt to be more pliable and less rigid, and in consequence the pressure applied is more readily responded to. The shortened traverse enables the change of the belts to be made more easily and in less time, and, in consequence of the latter fact, the time the edges of the belts are pressed upon by the guider is reduced. This reduction involves considerably less wear of the strap edges, which, alike on this account and because of their easier and less strained motion, are found to have a much longer life. The smooth action of the belts produces another effect. It enables the full speed of the rim shaft to be more readily reached, and so tends to increase the production of the machine. The makers have now constructed a large number of mules with this arrangement, and its use is steadily extending.
(288) The mechanism just described is that on which depends the driving of the whole of the parts, and its mode of action can now be easily explained. Beginning with the commencement of the outward run, when the rim band is traversing in its normal direction, the rollers commencing to deliver yarn, and the spindles revolving, the position of the parts is as follows. The strap is on the fast pulley, and the rim shaft is revolving. The backing-off friction is out of gear, the necessary motion is given to the roller shaft, and as the claw clutch is engaged the front line of rollers is revolved, roving being delivered. At the same time the back shaft is driven, the clutch on it being in gear, and the carriage is drawn out. The scrolls on the back shaft are shaped so as to allow the carriage to move at a constant velocity. While the carriage is running out the rim band is giving the required revolution to the tin roller shaft, and the spindles rotate in consequence at their normal velocity. The carrier pulley on the square shown in Fig. [152] is arranged at such an angle that the rim band passes freely on to and from the pulley on the tin roller shaft. A similarly accurate setting is given to the guide pulleys at the back of the headstock, the wear of the bands being much reduced in consequence. The velocity given to the carriage is slightly in excess of that of the surface speed of the rollers, so that the roving is a little stretched. The excess of the carriage traverse is from 1 to 3 inches, and is known as its “gain.”
(289) When the carriage reaches the termination of its outward run, or, as is commonly said, the end of its stretch, it becomes necessary, first to arrest and then to reverse its movement, these operations necessitating a complete change in the positions of the various parts. The chief agent in making these changes is the shaft M, placed parallel to but a little higher than the rim shaft. It is known as the “cam shaft,” and plays an important part in the operation of the machine. It is entirely distinct both by position and function from the rest of the mechanism, and a separate view of it and its connections is given in Fig. [156], which is a detached sectional elevation.
(290) Hinged to one side of the headstock framing is the lever T—known as the “long lever”—at each end of which pins are fastened, which carry the bowls R R1. Fastened to the carriage by bolts are two horn brackets S S1, to which power of adjustment is given. The underside of the brackets is curved, and they are fixed at such a height, that, as the carriage approaches either end of its run, one of them will engage with the bowl or runner carried on a stud fixed in the end of the long lever, as shown very clearly by the dotted lines. At the outer end of the long lever, the bell crank lever Q is pivoted, and is ordinarily drawn towards the end of the long lever by a spiral spring O. In this way, when the latter has assumed a position in consequence of the pressure of the horn brackets S S1, the pressure of Q upon it prevents it from moving until a similar force is again applied. In short, the long lever is locked.
(291) On the cam shaft three cam or eccentric surfaces are placed, marked respectively W Y and Z. These are shown with their connections in detached views. The cam W is compounded with the male half of the friction clutch X, and can slide along with the half clutch upon a feather key fixed in the shaft. The other half of the clutch is loose upon the shaft, and has formed upon its boss a spur pinion which, as shown in Fig. [153], engages with the teeth of the backing-off wheel A1. Thus the continuous rotation of the latter leads to a similar movement of X, and, as a consequence, the latter is always in a state of readiness to rotate the cam shaft. A spiral spring surrounds the cam shaft, being sunk into a recess in the bearing and continually pressing upon a flange formed on the sliding half of the friction clutch, thus tending to force the latter into gear. On the inner side of the flange two cam surfaces are formed, as shown at V, with which the nose of the rocking or escape lever engages. The latter is connected by a short rod to the end of the long lever, the whole attachment being very clearly indicated in the illustration. Suppose the end of the lever to be in the position shown in the left hand view of V, the friction clutch would then be engaged, and the cam shaft would revolve until the outer cam surface on V came into contact with the end of the lever, when the sliding half clutch would be disengaged and arrested, and the motion of the cam shaft would cease. In this position the parts remain until the long lever is again moved, this time having its inner end depressed by reason of the contact of the bracket S1, and bowl R1. The nose of the escape lever is then moved off the outer cam surface into the flat or level portion of the inner cam course. This permits the re-engagement of the friction clutch, and the cam shaft makes the second half turn, causing the inner cam course to engage with the nose of the lever and again disengaging the friction clutch. The raised cam surfaces on V are directly opposite one another, so that the cam shaft can only make a half turn before it is disengaged. The next movement of the long lever, which takes place at the end of the next outward run, is caused by the engagement of S and R, and the escape lever nose is then moved on to the level surface of the outer cam course. This alternate movement of the long lever takes place, as will be readily understood, when the carriage reaches the termination of its inward and outward runs.
(292) If it be assumed that the carriage has reached the end of its outward run, and the cam shaft has made a half revolution, three things take place. The back shaft clutch is disengaged, and the shaft ceases to revolve; the roller clutch is detached, stopping the delivery of roving; and the cam Y is moved into such a position that the strap lever can traverse so as to allow the strap to pass on to the loose pulley.
(293) The back shaft clutch is controlled by the internal cam Z, in which a bowl on a pin fixed in the bell crank lever Z1, Fig. [162], page 201, to which reference will be made for this part of the subject, works. In the groove of the sliding half P of the clutch, the forked end of the lever T fits, this lever being hinged at its lower end and having a horizontal arm, the end or nose of which rests upon the horizontal limb of the rocking lever Z1. Thus, when the latter is rocked so as to make an upward movement, the lever T is raised, and causes a disengagement of the clutch P P1. The back shaft is thus freed, and all motion of the carriage ceases.
(294) The rollers are disengaged by the cam W, which acts upon the cranked lever shown, the vertical arm of which is forked and fits in the groove in the loose half of the roller clutch I. When the cam is in the position shown in Fig. [156], the rollers are engaged, but when the cam shaft makes its half revolution the lever is oscillated and the clutch is detached. As previously noted, the cam course is formed in the loose half of the friction clutch X, which thus serves a double purpose.