WEFT REPLINISHMENT MOTION (Cop changing):-

Weft replenishment motion (cop changing):-

Under this heading we have discussed about the change of weft in different manner in brief . Now here is the one type of weft change (replenishment) is cop changing mechnism known as Northrop Cop Changing Mechnism.

Northrop Cop Changing Mechanism:-

The parts of the cop changing device ready for cop transfer are represented by the sectional view at fig. 183. The battery magazine, or cop hopper A is freely mounted on stud F. The magazine receives a partial rotation intermittently after each successive change of weft , so as to bring into position another cop to be in readiness the next change of weft . If the magazine is correctly adjusted, the bottom cop must be vertical with the cop in the shuttle, when the loom cranks reach their front center position.

DESCRIPTION AND WORKING:-

(1) The magazine A, shown in the figure, is connected with sockets for 28 cops F; but the space occupied by the transfer hammer B reduces its actual capacity 25 cops. These cops are of special construction. They are disposed in a horizontal position around and between the rims of two discs or plates that are formed with notches for holding the cops , as shown in the diagram. During normal running of the loom the transfer hammer B is up and the battery latch H is down and free from the bunter J of the sley.

(2) The change of weft is effected either by a weft fork motion or by a weft feeler motion , when the weft either breaks or is almost exhausted. When the weft is almost bare and the weft feeler slips sideway, or when the weft is broken , the weft fork holder pushes a straddle lever and through a finger gives a partial rotation to a change motion shaft O. But whether this partial rotation to the change motion shaft is given by the weft fork or by the weft feeler, the object in either case is to cause the notched and free end of the battery latch H to lift upward from its normal position, as is shown in diagram.

Fig. 183 showing Northrop Cop Changing Mechanism.

(3) Now, on the forward movement of the sley K, the shuttle protector S moves across the sley wood to feel the shuttle, if the shuttle has been properly boxed . By the same movement, the battery latch H is lifted , and the bunter J of the sley comes in contact with the V-shaped front of the battery latch and forces the latter backward. The battery latch is loosely mounted on a stud , fixed at the bottom of a short arm of an L-lever which constitute the transfer hammer B , fulcrumed freely on a stud L. Thus it is seen that in the event of the battery latch lifted on the forward movement of the sley, the free end of the transfer hammer, which reaches over the ready positioned cop in the magazine, is suddenly depressed when the sley reaches its full forward position. This causes removing that cop from the magazine A and forcing it into the shuttle M. Now through the bottom of shuttle the previous cop is expelled and passed down a can.

(4) When the transfer hammer B descends , it takes the feed pawl P along with it. As the hammer is drawn up by a powerful coiled spring at E the base of the magazine, the feed pawl turns the latter one tooth forward, and bring the next full bobbin (cop) under the pusher Y of the transfer hammer . The change of cop is effected instantly when the sley is at its full forward center. But when the shuttle protector S moves forward, the finger R and lever Q are lifted and the coiled spring is contacted. A two-pronged curved lever T guides the protector, while the latter is moved forward.

(5) In the next pick the shuttle is threaded by the transverse of the shuttle and the drag on the weft . The remnants of both weft are cut by thread cutters. All these operations occur in proper sequence whilst the loom continues to run at full speed.

Shuttle protector in Northrop Cop Changing Mechnism:-

At the magazine end of the loom, the change motion shaft controls the shuttle protector or shuttle positioner combined with a weft cutter . Before a cop changing can take place , the shuttle protecter is moved across the sleyrace at the entrance of the box by the partial rotation of the change motion shaft to check or to feel the shuttle is fully boxed or not .

The function of the shuttle protector motion are fourfold, namely,

(i) It effects a cop change when the shuttle is fully boxed.

(ii) It pushes the shuttle into the box making the tip of the shuttle as the limit and cop change is affected.

(iii) It cuts the weft of the outgoing cop near the entrance of the shuttle box .

(iv) It prevents a cop change when the shuttle is not properly boxed.

fig.184 shuttle protector.

At figure 184 , the shuttle protector A has fulcrum on the shaft B . The forked bracket C acts as a guide, when the shuttle protector A moves forward by the partial rotation of the change motion shaft D . The shuttle protector is kept in its normal position by the pressure of the lever E. The hooked lever F , fulcrumed at O , has a spring S attached to the change motion shaft D gets partial rotation either by the weft feeler or by the weft fork , the lever E and shuttle protector finger G are lifted.

The partial rotation of the change motion shaft causes the shuttle protector A to move forward across the sleyrace when the cranks are advancing towards the front center. Now , if a shuttle is properly boxes , the shuttle protector lifts the battery latch by means of the latch depresser H and the latch finger I. This causes the notched end of the battery latch to come in contact with the bunter in the sley front , when the cranks reach about the front center. Thus a cop change is affected at the full forward position of sley .

ADJUSTMENT:-

(i) There should be a clearance of 1/32 inch or 0.08 cm, between the shuttle protector A and the sley wood , when the protector moves forward and the cranks are on the full front center position.

(ii) If the shuttle failed to enter the box , the shuttle protector is prevented by the shuttle from moving forward and the latch depresser H cannot lift the battery latch, thus no cop change occurs. In this event the transfer mechanism is put out of action until the shuttle again returns to the magazine side and is correctly placed to receive the new cop.

Shuttle protector Cutter:-

A weft cutter consisting of two blades is fitted to the end to the shuttle protector A(fig.184) to cut the weft at the entrance of the shuttle box. The blades are normally open. When the head of the shuttle protector crosses the raceboard , the front of the sley-wood presses the setscrew and closes the blades of the cutter and cuts the weft.

Weft cutters in Northrop Cop Changing Mechnism:-

There are two weft cutters , one with the shuttle protector and another with the right hand temple.

(i) With the shuttle protector cutter the weft is cut near the eye of the shuttle for the ejected bobbin or cop .

(ii) The temple cutter cuts the two strands of weft, one strand of th he ejected bobbin stretching from selvedge to weft cutter and the other strand of the newly inserted bobbin. The temple cutter is simple cutter blade operated by the sley.

The Northrop temple cutter consist of three blades, one in the center and two being at the either side. The central blade is fixed , but the two side cutter or blades are moved by the sley coming in contact with an attached finger on the under side of the temple. When the finger is pressed back, the two operating blades make a downward movement to seize the two strands of weft and then a backward movement of the sley to cut both strands.

Three Miss-Thread Motion in Northrop Cop Changing mechanism:-

(a) Sometimes it so happen that after a cop change the weft fails to properly come out through the eye owing to an obstruction, or badly spun cop, or the weft is broken, or the spare cops get exhausted, or the shuttle does not reach its proper position in the box. In all such cases the change by the weft fork occur continuously, but the loom continues to run without weft.

(b) But if the miss is continuous and the loom continues to run without weft for sometimes , ‘crack’ will be caused in the fabric, unless the take-up pawl is disengaged. So a safety device, known as 'three miss-thread' motion or 'three-try' device, is added to an automatic cop-changing loom to stop it after three such continuous misses.

(c) If the deficiency is removed after the first miss the loom may run alright from the next change . But if the miss is repeated three times , the loom stops.

Fig.185 B & 185 A (Top) of Three Miss-thread' Motion of Northrop Cop Changing Mechnism.

Fig. 185 A is a side section of the three miss-thread mechanism. A is the shifting lever, and B is the setscrew. C is the weft fork motion trip on which the setscrew is fitted . D is the trip feed pawl. E is the trip hold-back pawl. F is the trip spring . G is the pawl-off lever H is the weft fork motion knock.

In case of each miss , the weft fork-holder L pushes the weft fork motion trip C one tooth forward, so that the setscrew B is brought nearer to the shifting lever A. If three continuous misses of cop changing happens, the weft fork motion trip C is brought three teeth forward by the pressure of the weft fork holder. In this event, the setscrew B pushes the shifting lever A to knock off the loom handle to stop the loom as shown in fig. 185 B.

The weft fork motion knock H, attached to the hammer lever I, acts when the loom runs alright after one or two misses and pushes the pawl-off lever G to bring the latter in its original position. The pawl-off lever G is devised to push up the trip feed-pawl D through the trip hold-back pawl E and causes the teeth of both to get out of the trip and to make them come back to the original position: the loom will then continue to run.

Ref:-Weaving Mechanism Book Vol.II by Prof. N. N. Banerjee.