Weft stop motion:-

Another Types of weft stop motion (piezoelectric weft stop):-

In the modern looms mainly two types of weft stop motion are used, they are,

1) Piezo electronic weft stop motion.

2) The optical sensor weft stop motion.

(1) Piezo electronic weft stop motion:-

In the case of rapier and projectile loom, mostly used device is provided with piezo electric crystals. These crystals have a double quality, if an electric charge passes through them , they vibrate or vice varsa, if they are made vibrate, they produce a light electric charge.

This second property is used for the weft insertion control. This device , if it detects a correctly insert weft . As this signal is too weak it is first amplified and then controlled against a sample signal ; if the system corresponds , nothing happen.

Image of piezoelectric weft stop motion.

Ref:-textilelearner.net

Otherwise , the absence of charge is interrupted as broken weft and the weaving machine stops. At this point automatic pick finding device enters into action and brings the machine back to the shed where the fault occurred. In this connection must consider that, although the stop signal is given quite quickly, a certain technical time for stopping loom is required. During this time , although the weft presenting device is standing the loom moves forward with some strikes which are compensated recovering tension and space through the reverse running of th evenness rollers.

The optical sensor weft stop motion:-

In the case of fluid jet machine , it is preferable not to hinder the weft fly , therefore optical sensors are used which do not touch the weft . As already mentioned, in the case of the air jet loom (machine), there is a device which permits to restore automatically the broken weft and to start the loom. This mechanism permits to go on weaving if the problem take place inside the shed. However, if defects take place inside in the pre-winding drum or between this and the cone , it is appropriate to have on a board the machine, the device which permits to select automatically the cone being processed. This system enables to by pass the pre-winding drum which has problem and to select a reserve drum which is standing until that movement. The machine does not need long stops and the operator can intervene easily to remedy the problem.

Image of optical weft sensor.

Should the same fault take place again on the new pre-winding drum , this will be excluded in favour of the first drum.

The optical sensor are primarily infrared photocell suited to detect the presence of the thread or the quantity of thread accumulated in prefixed zone. An example of these device is the sensor for weft control on air jet weaving machine, which is described briefly in the following.

The device which is designed to control the correct weft insertion into the shed of an airjet loom has the task of stopping the machine in case of incorrect weft insertion. The sensor is placed on the shaped reed at the desired hight in the zone of weft arrival it reads the presence of the thread , when its front free end arrives in the sensor’s measuring range and crosses it . Two photo-elements are passing as schematically indicated in the figure and constitute an optical barriers , which is disturbed by the weft thread when it is crossed by this thread.

Opto-electronic weft stop motion:-

In case of air jet machine for staple yarn weaving, an photo-electronic weft stop motion in twin arrange ment can be delivered , while the first of the two weft stop motion serves the support one records the weft thread broken in the shed or expelled.

Image of opto electronic weft stop motion.

When the first one gets the weft , which means the weft thread has travelled the predetermined distance, the loom remains running. And in case of the second one gets the weft thread has broken and travelled excess than predetermined distance it knock-off the loom instantly.

Ref:-https://textilelearner.net.