Weft Feeler Mechanism
The function of the feeler mechanism is to sense the weft on the pirn and initiate the pirn changing mechanism to act when the weft has been almost exhausted on the pirn. If the weft is present on the pirn the feeler will allow the loom to continue working.
There are three main types of feelers;
1. Mechanical
2. Electrical and
3. Photo electrical
Mechanical Weft Feeler:
When the sley moves forward the feeler blade A passes through the slots in the front plate of the box and front wall of the shuttle and contacts the pirn. If there is sufficient weft yarn on the pirn, the blade A is pushed straight back into the feeler casing and no direction of a pirn transfer takes place. With the reserve bunch of weft, approximately a length of three picks of yarn is left on the pirn base. The feeler blade contacts the smooth polished surface of base pirn and slide side-ways, contacting the trip lever connecting rod B, which in turn raises the trip lever C through the bell crank lever D.
A tripper heel E attached to the weft fork hammer F, oscillating to and fro along with the weft fork hammer, comes in contact with the raised trip lever C and pushes it back in the direction of the arrow shown in figure. This will cause the change shaft G which runs across the width of the breast beam, to turn and effect a pirn change at the magazine and during the next forward movement of the sley with the shuttle on the magazine side box. The return spring in the feeler casing pulls the feeler blade to its normal position as soon as the contact of the blade with the pirn is over.
Electrical Two Pronged Feeler:
This type of feeler has been designed where the transfer of the fully wound pirn from the weft replenishing unit to the shuttle is initiated electrically. It can be used with advantage on looms weaving delicate weft. The feeler is mounted on a bracket fixed to the rear wall of the starting handle casing. The weft pirn is fitted with a metal sleeve on the barrel. A bunch of reserve of weft, sufficient for four picks across the loom must be wound at the base of the pirn. Under normal running conditions, as the sley moves forward and is almost at the front centre, the weft on the pirn contacts the feeler prongs which are pushed backwards into the feeler casing, against the pressure of return springs. However, when the pirn is empty, except for the reserve weft, the metal sleeve on the pirn barrel is exposed and comes in contact with the feeler prongs.
The feeler prongs are connected to an electrical circuit. The circuit is incomplete until contact is affected across the feeler prongs. As soon as the prongs come in contact with the metal sleeve on the pirn barrel the circuit is completed energizing the solenoid and the electrical magnet box so that the trip lever is lifted in line with the tripper heel which puts the pirn changing mechanism in action. The electrical circuit is broken when the sley moves backwards to break contact between the metal sleeve on the pirn and the feeler prongs.
Area of contact between the feeler and yarn is very small and does not damage the yarn. But it requires special type of pirns with a metal sleeve.
Optical Electronic Weft Feeler:
The weft pirn used for this type of feeler is covered with a reflective strip which has the property of reflecting a beam of light back to its source. The light source and the photocell are housed together in the feeler head and both the searching beam and the reflected ray pass through the same optical system.
Incident light ray is directed on the pirn constantly and as soon as the weft is exhausted the light ray is reflected back to the feeler head. On reaching the photocell, the reflected light is transformed into an electrical impulse and transmitted to the switch box, which contains the whole electrical supply for the feeler and feeds the appropriate selection mechanism in order to initiate the transfer of pirn. Advantage of this feeler is that there is no physical contact between the feeler and the weft yarn. Main disadvantage is that it is very expensive. Now-a-days for filament weaving, this feeler is extensively used.
Shuttle changing mechanism:
The shuttle changing automatic looms are suitable for weaving very delicate wefts like silk, rayon and fine counts of cotton yarns, because there is no hammer action on the weft package. As soon as the weft gets exhausted on the pirn the entire shuttle is replaced by a new shuttle with a fully wound pirn.
There are two main types of shuttle changing looms. They are;
1. One which does not stop for a change or in which changes is affected during the running of the loom.
2. One which stops for a few seconds for a change and restarts automatically.
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