Electrical warp stop motion in Northrop & Knowles C-7 loom:-

Electrical warp stop motion in Northrop & Knowles C-7 loom:-

(i) On C-7 loom , the warp stop loom motion operates electrically.

The loom stop instantaneously. The warp stop motion operates through a relay immediately a drop wire falls on the slide bar. When an end breaks, the loom is stopped near the front portion center of the sley. In this position, the broken end is repaired by the weaver.

(ii) On pressing reverse button the limit switch reverse the loom when slay reaches back center position.

(iii) On pressing start button the loom starts weaving . To prevent “start mark" on delicate fabrics , the loom is reversed at its back centre position, before it starts weaving.

Electrical Centre Weft Fork Motion in Crompton & Knowles C-7 Loom:-

On C-7 loom, the centre weft fork motion acts electrically with the elimination of usual shaft and rods. While the centre weft for falls into the well publishes contact with a micro switch located on the motion, it results in the transmission of an impulse to the main control box to initiate stoppage of the loom. Stoppage at the back centre position of the sley is also achieved, through the medium of a secondary switch, when the centre weft fork comes into action in the event of a weft break. This facilitate weft repairing. On pressing the start button the loom again start weaving.

An additional electrical stop motion is provided on the vertical lifting rod to the multiple box motion. With this device, immediately any fault occurs , an impulse is transmitted, and the mechnism is brought into action to stop the loom before the picker moves into the multiple box side.

Mechanical Warp protector motion in Crompton & Knowles C-7 loom:-

The quality woven fabric is more dependent upon smooth running of the shuttle than other factors.

(i) If a shuttle is trapped in the shed for any reason, it causes over stretching and breaking of warp threads in the fabric. Though the mechanical warp protecting motions are very effective in action , yet the destructive effects of the sudden shock , with which a loom is brought to a stop can upset setting and result in the breakages of loom parts. However, by incorporating the protector setting with the basic shuttle checking motion , the effeciency of the latter can be greatly improved.

(ii) It is practically impossible to arrest the movement of the massive sley and all other rotating parts without shock or impact with the aid of a mechanical warp protecter motion. Lightweight metals, such as aluminium, when used for the moving parts, can partially ease the problem by increasing the absorption time to check device, or by separating the translatory and rotary elements at the time of protection. Though these methods offer some degree of relief, but they do not solve the impact problem to any appreciable extent. A complete relief may be obtained by increasing the available time for stopping.

(iii) The loom has to completely stopped at a final position that depends upon the safe clearance of the shed relative to the shuttle. It is ,therefore obvious that any lengthening of the total available stopping time must be obtained by advancing the time of indication. At the back centre position of the sley a greater time interval is obtained, but the stopping effort would be greatly reduced in that the sley is practically stopped at this particular instant. This early shuttle indication presents a serious difficulty, because the shuttle is about midway in its journey at the back centre position. In this position, a mechnical warp protector motion is difficult to employ .

Electrical Warp Protector Motion in Crompton & Knowles C-7 loom:-

(1) Since a mechanical form of indication is difficult to employ at the back centre position of the sley, an electro-magnetic indication for warp protector motion is selected. Two successful magnetic indication method have been developed — (a) One employing electronics and 

(b) the other employing sensitive electrical relays. The former type is used on a large felt looms, and the latter type on common looms.

(2) On the C-7 automatic loom, the magnetic type of detection device is employed. In this device , a permanent magnet is inserted about the center of the sley, and around one of its poles a suitable electrical coil is placed. The magnet is placed so that the pole-faces are just below the sley-wood and the poles are lined up in the direction of the shuttle travel. Thus the flux lines between poles extend in an arc into shed area of the loom . A steel plate inserted in one end of the shuttle just inside the bottom section. While the loom runs , the shuttle with the embedded steel plates passes over the magnet, and the voltage generated in the coil is used to operate a sensitive relay. With these components, contact with the shuttle is established without any need of actual physical contact between the shuttle and the detector.

(3) The timing is achieved by means of a rotary switch, operated by a suitable cam. This rotary switch is so timed that if the detector operates before the switch contacts open, the loom continues to run; but if the detector operates after the switch contacts open, the loom is smoothly stopped. In case of a slow running shuttle, both mechnical and electrical warp protection operate in the same manner, the major difference being the absence of impact and shock when the loom is stopped through the electrical protection system.

(4) In the electrical system the slow shuttle is detected much earlier in its travel. This allows the warp protection stop to be initiated and the reed advance towards the front center position at a considerably slow rate. Because of this slowing down of the advancing sley, the shed clearance is greater even for a slower shuttle. The shuttle has usually enough time to exit completely from the shed before the loom is completely stopped. With the electrical system, the loom is brought to a complete stop sooner in relation to its crank-shaft displacement, than is possible in the mechanical system.

(5) A crankshaft movement of 50° to 60° from the point of the detection is available for stopping the loom. Consequently, early detection and rapid loom stop are achieved. Even a slow running shuttle has therefore , sufficient shed clearance to complete its traverse without getting trapped in the shed.

(6) Again detection of a fast running shuttle can easily be achieved with the electrical system through the medium of the relay and rotary switch. It is possible to determine when the relay operates and when it ceases to operate. This it, can be arranged that a fast running shuttle, which passes over the magnetic detector too early and the interval can be specified will generate a current in the relay which is dissipated before the rotary switch contacts operate , with the result that the loom is brought to a stop.

SHUTTLE CHECKING:-

(1) On the C-7 automatic pirn changi loom the conventional stop rod warp protector motion is substituted by an electro-magnetic system. This electrical system has made possible to the mechnical improvement of the shuttle checking motion in which the swells are positively located at each end. Thus the shuttle protection requirements have been eliminated from the shuttle checking assembly.

(2) This improved shuttle checking assembly performs its function of controlling the shuttle in the box most effectively . While some variation of the functions are sometimes necessary under particular circumstances , it is called upon perform the following duties as shuttle controller:-

( a) To decelarate the shuttle smoothly while entering the box, thereby prevent weft cutting and excessive impact with the picker.

(b) To stop the momentum and hold the shuttle in the box inactive position, thereby preventing the shuttle from rebounding and the shuttle from creeping in an inactive box.

(c) To guide the shuttle smoothly over the sleyrace during picking to ensure smooth acceleration and straight-line flight.

(3) The Shuttle checking by means swell, check strap and box flap in conventional loom does not fulfill all these conditions. On the C-7 loom, the swells are made in one straight section pivoted at each end by means of two parallel links. The movement of these links is restricted and governed by the position of the shuttle . By arranging these links to travel in an arc , the straight face of the swell can be adjusted inwardly or outwardly, depending upon, whether a shuttle is to be picked . By moving the swell assembly inward and holding it in a fixed position, a greater squeeze is placed upon the entering shuttle with a uniform force, which result in the shuttle smoothly decelerating to stop with a minimum impact on the picker.

(4) During picking the assembly is allowed to pivot outward to a position which provides just sufficient against the shuttle to ensure smooth acceleration. Because the face is straight and parallel to the back of the shuttle-box, the shuttle is guided out of the box by the same swell in a smooth manner. The swell assembly designed in this way has proved to be quite effective in maintaining shuttle performance on electrically controlled looms.

Brake Release and Single Pick control:-

The toggle switches incorporated in the electrical control system, serve respectively to operate the brake release for turning the loom over by hand to prevent single pick control. While the turning the loom over by hand and a safety precaution, the loom cannot be started when the brake release toggle is switched off. When the toggle switch is actuated for single pick control and the operator maintains the pressure on the starter button, the loom turns to over single pick, pausing slightly between each pick . This system is useful for studying particular mechanisms of the loom.

Central Electrical Control:

A central control is provided in accessible position on the C-7 loom, to utilise these various elements and electrical devices. The various operating relays are of the plug in type are enclosed to prevent entry of dust. Further, each of the relay is properly polarized with a mating plug, so that an improper relay cannot be placed into a given socket.

The controls are housed in a cabinet. It is made of heavy gauge steel and cast iron. All control wires, running through the loom, are operated at a low voltage to prevent any danger . The controls are equipped with “fail-safe" operation; if any wire leading from the control is broken or loosened, the loom will immediately stop. The control is also provided with safety switches, so that the loom can be made safe against accidental starting. Other features provided on the loom are overload and no-voltage protection.

In conclusion, it may be said that by developing and providing the electrical controls and device , the performance of the loom can be greatly improved. The electrical control take over many of the skills formerly required of the weavers. Finally, the elemination of mechnical protection motions, shipping and braking parts and the partial elimination of parts associated with weft stops and warp stop motion not only simplify design but reduce the work load of the weaving personnel. Thus, the operation, maitainance, performance and efficiency on the Crompton and Knowle’s C-7 automatic pirn changing loom have been greatly proved by the incorporation of electrical components, specifically suited to work they were required to perform.

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