The Knowles Positive Open Shed Dobby (dobby shedding)

The Knowles Positive Open Shed Dobby:-

The Knowles dobby , as made by Messrs , Hutchinson and Hollingsworth, is original in construction and positive in action. It forms an open shed , gives a straight lift to the shafts , and governs the shedding , the picking , the shuttle boxes and the taking-up motions; it also cntains a levelling apparatus for placing all the healds in one line before drawing-in broken threads; and the dobby , and all it controls , can be worked backwards manually by turning a wheel.

Movement is derived from one end of the crank shaft by gearing a pinion A fig. 73 with a stud wheel B. The wheel B is compounded with a bevel C to drive a similar wheel D, situated at the base of an upright shafts E. The wheel D, together with the parts G, F, form a clutch for detaching the driving when movement in the dobby is to be reversed. By operating a lever the top piece F will rise to open or sink to close the clutch. Of the three parts F and D are loose upon E , but G' is a hoop which is placed close to D, and fastened to the Shaft E. A hole is drilled through G' and into the upper part of D , to receive a stud from the understand of the moveable piece F. This stud is long enough to pass through the hoop G' and enter D when the clutch is closed , but when the clutch is open the stud is withdrawn from D and the dobby stops . An arrangement by which contact between F and D can only be made when the slay occupies one position is essential, or the shed would open and close at the wrong time. Instead of a manually controlled clutch, a cup, formed in the top of D , may have a cam groove of gradually increasing depth cut to receive a freely fitting pin that passes through G’. When the loom is started this pin travels in the groove until the deepest end is reached, when shaft E begins to rotate. At the same instant the weighted end of a catch swings outward and the catch , by entering a notch in G ', locks the pin in position. So soon as the the loom stops , the catch automatically falls out of the notch and the dobby is free to be turned backwards.

Fig 73. The Knowles Positive Open Shed Dobby.

Two bevel wheels H , I are fitted upon the shaft E and drive similar wheels J, K that are fast upon the lower and upper segment cylinder L, M. The wheel H drives from the top of J , and I from the bottom of K , thus causing one to revolve in opposite direction to the other. The cylinders L, M take the place of griffe bars in ordinary dobbies and luft and dunk the shafts by means of a series of teeth that extend about half-way round each. Their teeth act upon the gears G, the vibrating levers N, and the connecting bars R, Fig. 74 . These three parts fastened together to form one piece . A vibrating lever N is made from two thin plates which are riveted together at different points , and kept apart at others by strips of metal to form a fork, N is centred at O , and rests at O upon a pattern chain which is built up by threading rollers and bushes upon spindles as for an oscillating tappet. Each roller will lift, and each bush will allow a lever N to fall , therefore a vibrating lever equals s needle in other dobbies.

A gear G does duty for hook; it is a toothed wheel 1/8" thick by 5, 1/4" in diameter, from which a tooth is removed at one point , and three or four teeth are removed exactly opposite the first gap. This wheel ia passed between the plates of N, where it is supported by, and turns freely upon a pin. The movement of gear G is limited by a steadying pin in N entering a semi-circular slot in G.

A connecting bar R conveys motion from a gear to a harness jack S . Two metal plates are also used in the construction of R; they are connected in the middle by rivets, but are separated to form forks at each end. A gear G is placed inside one fork and the rivet which unit G , R serves as a crank pin for G will be moved from one dead centre to another, and in so doing will cause E to rock . The opposite end of R notched and hooked upon a nipple in the cranked harness jack S. From , the arm U, rod and strap connections pass over guide pulleys to a top heald shaft, and from the arm V , similar connections pass under guide pulleys to a bottom shaft ; hence , as a jack S oscillates on its center T, each forward movement of the arm U will lift, and each upward movement of V will sink a shaft.

A vibrating lever N , a gear G, a connector R , and a harness jack S , together with bowls , bushes , and connections, are required for each heald shaft , and these parts are so placed that fifteen gears occupy a horizontal space of 8 inches. 

The levelling apparatus consist of a flat bar X , which is furnished with a handle at one end . X is placed at right angles to and immediately below the vibrator levers N, and it has two diagonal slots for the reception of fixed studs. By pulling the bar forward it slides, upon that studs, up two inclined plane and lifts all the levers N, to clear the gears G, from the cylinder L ; then at the next revolution M will engage all gears that have the small gap uppermost , and cause them to make half a revolution. Once the large gaps are at the top , all the heald shafts will be lifted , and they will remain up until the bar X is restored to its normal position. The chain barrel Y is driven by a train of five wheels , and can be stopped moved forward, or backward at pleasure by operating a clutch Z , Fig 73. Thus if Z be half opened , the wheels 1 and 2:are loosened upon L, and the barrel Y becomes stationary. If Z is closed , the wheel 1 drives the wheel 5 Fig. 74, direct, and turns the barrel forward; but ehen Z is fully open the wheel 1 us released from , and 2 us fastened upon , the shaft of L. The stud wheels 4, 3, being compounded , will be driven by 2 , and dunce 1 and 3 both engage with the wheel 5, it follows that 2 will drive 4 and 3 will drive 5 in the opposite direction to that when 1 is driver.

The levelling apparatus consist of a flat bar X , which is furnished with a handle at one end . X is placed at right angles to and immediately below the vibrator levers N, and it has two diagonal slots for the reception of fixed studs. By pulling the bar forward it slides, upon that studs, up two inclined plane and lifts all the levers N, to clear the gears G, from the cylinder L ; then at the next revolution M will engage all gears that have the small gap uppermost , and cause them to make half a revolution. Once the large gaps are at the top , all the heald shafts will be lifted , and they will remain up until the bar X is restored to its normal position. The chain barrel Y is driven by a train of five wheels , and can be stopped moved forward, or backward at pleasure by operating a clutch Z , Fig 73. Thus if Z be half opened , the wheels 1 and 2:are loosened upon L, and the barrel Y becomes stationary. If Z is closed , the wheel 1 drives the wheel 5 Fig. 74, direct, and turns the barrel forward; but ehen Z is fully open the wheel 1 us released from , and 2 us fastened upon , the shaft of L. The stud wheels 4, 3, being compounded , will be driven by 2 , and since 1 and 3 both engage with the wheel 5, it follows that 2 will drive 4 and 3 will drive 5 in the opposite direction to that when 1 is driver.

Instead of the clutch described above, the cylinder M may be loose upon its shaft be lengthened to receive a spur wheels at the front, and a loosely mounted bevel, similar to K, at the back. Both bevels gear with I on the upright shaft E, Fig. 73 . The bevel K is fixed upon the boss of M and drives continually in one direction. Between these bevels a hoop, provided with the a ring groove for a lever to fit in, and a projection at either end to serve as a clutch, may slide in a key way cut in the shaft of M . Each bevel has a recess formed in its boss for the reception of a projection on the loop. When this loop engages the bevel K the chain barrel Y turns in its normal direction. But when the boss engages the loose bevel, the shaft of M rotates in one direction, while the barrel continues to turn normally; the taking-up motion is also reversed with the chain .

Fig.74

The driving gear found between the cylinder M and the chain barrel Y may also differ from the previously described. Thus, a wheel on the shaft of M drives the largest of a pair of compounded wheels , and the smallest drives the barrel wheel 5. But the wheel 5 is now a star wheel with six notches , and between the notches it is furnished with ordinary teeth. The largest compounded wheel carries a stud which engages the notches in 5 in order to accelerate the removal from and replacement of bowls and bushes beneath, the vibrating levers N. The smallest compounded wheel has three teeth is  removed facing the stud in the other wheel , so that when the stud drives the wheel will be inoperative, and when the stud is inoperative the wheel will drive. 

While the gear are turning all the vibrating levers N are locked in position by mounting a knife W on arms that projects from a shaft which is rocked by a cam occurred to the bottom cylinder shaft. Thus cam is shown in fitted lines to behind the wheel 2 ; it thrusts the knife between the lifted and depressed ends of all levers N immediately before the gears begin to move and a weight 6 rests upon the lifted vibrators to assist in steading their movement. Instead of a single weight 6, each vibrator may be steadied independently by the action of a bar and spring. 

A bowl acts through a vibrator lever N to lift a gear G into contact with the teeth of the top cylinder M; then , provided the small gap of G uppermost, G makes half a revolution and will lifts a shaft , but if the large gap is on the top , there is sufficient room for M to pass without touching G. As a consequence, a shaft can remains up for two or more picks in succession. A bush permits a gear to drop into contact with the bottom cylinder L, and if the small gap of G is at the bottom, G will be turned half-way round , but in an opposite direction, and a shaft will sink , if the large gap is below , G will remains stationary.

When a heald shaft in a state of rest, the crank pin used for riveting the gear and connecting lever together is in the same horizontal plane as the centre of the gear; hence movement is from one dead centre to another, and a shaft begins to rise or fall slowly, but increase in velocity to the center, and from that point to the end of its movement a decrease takes place proportionate to the increase. 

When hairy yarn is used it is sometimes necessary to move one portion of the warp slightly in advance of another. This may be accomplished by causing the teeth on the cylinder L, M to diverge slightly from each axis. Or , one shed may close before another opens if one cylinder bevel , J, K, is set a few teeth in advance of the other.

Ref:- The Mechanism of Weaving Book by Shri Thomas W. Fox.