GB2039546A - Looms - Google Patents

Abstract

A gripper shuttle loom in which a gripper shuttle (4) is guided by a number of guide elements (3) during picking has a transducer (10), for generating signals in dependence on shuttle movement, disposed on a guide element (3). Preferably the transducer is a piezoelectroacoustic transducer. The signals may be used for various purposes such as to operate a weft stop motion. <IMAGE>

Description

SPECIFICATION Looms This invention relates to looms of the kind in which a projectile, such as a gripper projectile, is guided by a number of guide elements during picking.

It has already been proposed for such a loom to include an inductive transducer for generating signals in dependence on the projectile movement. The signals generated by the transducer can be used for many purposes, e.g. it is possible to determine whether the arrival of the gripper projectile at the catching motion will correspond with the appropriate angular position of the main shaft of the loom. If the required agreement does not apply, the switching unit can stop the loom. The inductive transducer is disposed at a certain distance ahead of the catching motion and above the projectile path. Even with a ferromagnetic projectile, the inductive transducer must be only a small distance from the projectile to ensure strong inductive coupling with clear signals capable of evaluation but this is difficult to achieve.If a plastics projectile is used, of which only the core is ferromagnetic, this requirement is still more difficult.

According to the present invention, a loom of the kind in which the projectile is guided by a number of guide elements during picking comprises a trans duner for generating signals in dependence on projectile movement, the transducer being disposed on a guide element. With this arrangement, the transducer can be reliably located very close to the projectile path.

Preferably, the transducer is a piezo-electro acoustictransducerwhich is accommodated in a recess in the guide element.

The invention may be carried into practice in various ways but one gripper shuttle loom embodying the invention will now be described by way of example with reference to the accompanying drawing which is a fragmentary cross-section of the sley of the loom and one of the guide teeth mounted thereon.

With the exception of the parts to be described, the loom is of conventional construction so that it will not be referred to in detail.

The drawing shows the sley 1 with a row of guide teeth and a reed 2. The guide teeth which are fixed to the sley by screws 9 are intended to guide a gripper projectile 4, which as it passes from the picking side to the catching side of the machine draws a weft thread 5 with it through a shed 6 formed by the warp yarns 7 and 8. The guide tooth 3 shown in the drawing is provided with a piezo-electroacoustic transducer 10 which is accommodated in a bore-hole 11 in the guide tooth 3. Two leads 12 and 13 from the transducer extend through a transverse bore-hole 14 in the guide tooth 3 to the exterior. If the guide tooth is made of metal, the transducer must be electrically insulated by means of an insulating sheath, e.g. a sleeve shrunk on to the transducer.The piezoelectroacoustic transducer consists of a piezoelectric element in rod or strip form with an electrode on each side, each electrode being provided with a lead. The electrodes may be applied by vapour coating. The leads run to an amplifier which is in turn connected to a switching unit. When the piezo-electric element is mechanically excited by sound pressure, it generates an electrical voltage which is proportional to the amplitude of the sound waves. The sensitivity to acoustic waves is very high so that even a very weak sound level is detected.

The system operates as follows. The gripper projectile 4 travelling through the guide tooth 3 produces sound waves which radiate from it and/or result from contact of the projectile with the guide tooth, and these sound waves produce acoustic surface waves in the piezo-electroacoustic transducer 10, which mechanically excites the latter so that electrical signals are generated. After amplification, these signals reach the switching unit which carries out the required switching operation.

The transducer may be disposed at some point in the guide tooth otherthan that shown in the Figure.

In addition, of course, more than one guide tooth may be provided with a transducer, each transducer generating a signal for a different purpose. More particularly, signals can be generated to control the actuation of devices which take part in the weft thread picking operation, e.g. the weft stop motion, and the weft thread brake.

Also, instead of being accommodated in a borehole in the guide tooth, the transducer may be disposed on the outside thereof. In this case, a different transducer, e.g. a strain gauge, can be used instead of the piezo-electric acoustic transducer.

Although the invention has been described in connection with a loom with a gripper projectile, it can also be applied to other looms, e.g. a loom in which a pirn is carried through the shed by a shuttle.

1. A loom of the kind in which a projectile for picking the weft thread is guided by a number of guide elements during picking, the loom comprising a transducer for generating signals in dependence on projectile movement, the transducer being disposed on a guide element.

2. A loom as claimed in Claim 1 in which the transducer is a piezo-electroacoustic transducer which is accommodated in a recess in the guide element.

3. A loom as claimed in Claim 1 or Claim 2 which is a gripper projectile loom.

4. A loom substantially as described herein with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Looms This invention relates to looms of the kind in which a projectile, such as a gripper projectile, is guided by a number of guide elements during picking. It has already been proposed for such a loom to include an inductive transducer for generating signals in dependence on the projectile movement. The signals generated by the transducer can be used for many purposes, e.g. it is possible to determine whether the arrival of the gripper projectile at the catching motion will correspond with the appropriate angular position of the main shaft of the loom. If the required agreement does not apply, the switching unit can stop the loom. The inductive transducer is disposed at a certain distance ahead of the catching motion and above the projectile path. Even with a ferromagnetic projectile, the inductive transducer must be only a small distance from the projectile to ensure strong inductive coupling with clear signals capable of evaluation but this is difficult to achieve.If a plastics projectile is used, of which only the core is ferromagnetic, this requirement is still more difficult. According to the present invention, a loom of the kind in which the projectile is guided by a number of guide elements during picking comprises a trans duner for generating signals in dependence on projectile movement, the transducer being disposed on a guide element. With this arrangement, the transducer can be reliably located very close to the projectile path. Preferably, the transducer is a piezo-electro acoustictransducerwhich is accommodated in a recess in the guide element. The invention may be carried into practice in various ways but one gripper shuttle loom embodying the invention will now be described by way of example with reference to the accompanying drawing which is a fragmentary cross-section of the sley of the loom and one of the guide teeth mounted thereon. With the exception of the parts to be described, the loom is of conventional construction so that it will not be referred to in detail. The drawing shows the sley 1 with a row of guide teeth and a reed 2. The guide teeth which are fixed to the sley by screws 9 are intended to guide a gripper projectile 4, which as it passes from the picking side to the catching side of the machine draws a weft thread 5 with it through a shed 6 formed by the warp yarns 7 and 8. The guide tooth 3 shown in the drawing is provided with a piezo-electroacoustic transducer 10 which is accommodated in a bore-hole 11 in the guide tooth 3. Two leads 12 and 13 from the transducer extend through a transverse bore-hole 14 in the guide tooth 3 to the exterior. If the guide tooth is made of metal, the transducer must be electrically insulated by means of an insulating sheath, e.g. a sleeve shrunk on to the transducer.The piezoelectroacoustic transducer consists of a piezoelectric element in rod or strip form with an electrode on each side, each electrode being provided with a lead. The electrodes may be applied by vapour coating. The leads run to an amplifier which is in turn connected to a switching unit. When the piezo-electric element is mechanically excited by sound pressure, it generates an electrical voltage which is proportional to the amplitude of the sound waves. The sensitivity to acoustic waves is very high so that even a very weak sound level is detected. The system operates as follows. The gripper projectile 4 travelling through the guide tooth 3 produces sound waves which radiate from it and/or result from contact of the projectile with the guide tooth, and these sound waves produce acoustic surface waves in the piezo-electroacoustic transducer 10, which mechanically excites the latter so that electrical signals are generated. After amplification, these signals reach the switching unit which carries out the required switching operation. The transducer may be disposed at some point in the guide tooth otherthan that shown in the Figure. In addition, of course, more than one guide tooth may be provided with a transducer, each transducer generating a signal for a different purpose. More particularly, signals can be generated to control the actuation of devices which take part in the weft thread picking operation, e.g. the weft stop motion, and the weft thread brake. Also, instead of being accommodated in a borehole in the guide tooth, the transducer may be disposed on the outside thereof. In this case, a different transducer, e.g. a strain gauge, can be used instead of the piezo-electric acoustic transducer. Although the invention has been described in connection with a loom with a gripper projectile, it can also be applied to other looms, e.g. a loom in which a pirn is carried through the shed by a shuttle. CLAIMS

1. A loom of the kind in which a projectile for picking the weft thread is guided by a number of guide elements during picking, the loom comprising a transducer for generating signals in dependence on projectile movement, the transducer being disposed on a guide element.

2. A loom as claimed in Claim 1 in which the transducer is a piezo-electroacoustic transducer which is accommodated in a recess in the guide element.

3. A loom as claimed in Claim 1 or Claim 2 which is a gripper projectile loom.

4. A loom substantially as described herein with reference to the accompanying drawing.