The present invention relates to a metering device for use in a fluid jet loom for metering the amount of weft yarn supplied across the warp shed on each weaving cycle of the loom.
It is known from FR-A-2 465 812 to provide a weft metering device having a stationary spool onto which yarn is wound by a yarn supply arm. The spool contains a series of stop fingers located within the spool and which are arranged to move in succession to emerge at a first axial position, move axially along the spool and then retract at a second axial position. The stop fingers are arranged such that when a stop finger retracts at the second position to discharge yarn a succeeding finger has already emerged at the first axial position. A further separate stop is provided which is selectively operable to hold discharged windings to delay discharge of the yarn until a subsequent weaving cycle.
It is known from EP-A-0 024 561 to provide a weft metering device having a stationary spool divided into a storage region and a discharge region. A yarn supply arm is provided which winds yarn onto the storage region and simultaneously transfers windings of yarn from the storage region to the discharge region. Discharge of yarn from the discharge region of the spool is controlled by a pair of stop fingers. The pair of stop fingers are located within the spool and are spaced apart axially along the spool. The stop fingers are arranged to move radially between retracted and projected positions. Discharge of yarn is achieved by moving the fingers furthermost from the storage region to a retracted position.
According to the present invention there is provided a yarn metering device comprising a stationary spool, and having a storage region and a discharge region, a yarn supply arm arranged to wrap yarn onto the storage region of the spool, a yarn guide arm provided for simultaneously transferring yarn from the storage region to the discharge region, a stop means co-operable with the spool for permitting yarn wrapped on the spool to be pulled axially off the spool after a predetermined quantity of yarn has been wrapped onto the spool, the stop means comprising a single finger located outside the spool and being arranged to move both radially and axially relative to the spool, the finger for each discharge of yarn being arranged to move radially inwardly at a first axial position to engage yarn being discharged from the yarn guide arm to thereby simultaneously initiate wrapping of yarn onto the discharge region of the spool by the yarn guide arm and to also define the metered length of yarn discharged from the device, the finger being arranged to then move axially along the spool to a second axial position and at said second axial position moves radially outwardly to release the yarn wrapped on the discharged region and during release of the yarn the finger returns to the first axial position before moving radially inwardly again.
Reference is now made to the accompanying drawings in which:-
Referring initially to Figure 1, the device 10 according to the present invention is a stationary or fixed spool 12 which is of generally cylindrical shape, and a yarn supply arm 14 which extends radially from the axis of the spool and which is rotatably mounted for rotation about said axis. The arm 14 is hollow and is cranked so as to be able to wrap yarn 16 about the spool as will be described in greater detail later. The device also includes a yarn guide arm 17 which is conveniently diametrically opposed to the arm 14 and is rotatable in unison therewith. The guide arm 17 picks up yarn deposited by arm 14 and re-wraps the yarn on the spool at a position further along the spool. The device also includes a yarn stop finger 20 which controls release of yarn from the spool 12 and initiates winding of yarn onto the spool by guide arm 17. As illustrated in Figure 1 the device 10 is arranged to supply yarn to an air jet nozzle 22 which drives the yarn across the warp shed of the loom (not shown). As indicated above, yarn 16 is wrapped onto the spool at two different locations on the spool 12. These locations 24, 25 respectively are separated by a ridge 26 so that the locations are physically separated. At location 24 before operation of the device 10 the yarn is wrapped about the spool 12 by a predetermined minimum number of turns to define a supply coil of yarn 28. The supply coil of yarn 28 has basically two main functions, viz to provide a supply of yarn for yarn guide arm 17 and to prevent slippage of yarn on the spool 12 as the arm 14 draws yarn from the yarn package (not shown). During each weaving cycle of the loom, arms 14 and 17 are continually rotating so that arm 14 winds onto the spool a supply of yarn which is picked up and rewound onto the spool by arm 17. Accordingly since the rate of winding of arm 14 is the same as the rate of unwinding of the guide arm 17 the size of the supply coil 28 remains constant. As guide arm 17 wraps yarn onto the spool 12 the stop finger 20 moves axially along the spool away from arms 14 and 17. At a predetermined time in the weaving cycle after shedding of the warp yarns the finger 20 is moved radially away from the spool to allow the yarn wound thereon by arm 17 to be pulled off by the jet nozzle 22. The finger 20 is simultaneously moved axially back toward the arms 14 and 17 and then moved radially inwardly to enable arm 17 to initiate wrapping of yarn about the spool. The cycle is then repeated.
The constant length of yarn stored on the spool in the supply 28 is basically dependent on two variables, viz the number of revolutions made by arm 17 in each cycle and the diameter of the spool. The number of revolutions is controlled by a suitable choice of gearing ratios in drive from the main loom drive shaft and the spool is preferably constructed so that its diameter may be adjusted. Accordingly the amount of yarn stored on the spool may be accurately and easily adjusted.
The finger 20 is timed to move radially inwardly after all the yarn wrapped onto the spool by arm 17 has been pulled off the spool. Thus the yarn is initially stopped by arm 17. However the arm 17 is rotating to unwind yarn from the supply coil 28 and so this yarn is drawn from the arm 17 by the air jet nozzle 22 at a rate determined by the speed of movement of the arm 17 until the arm passes the stop finger 20 when the yarn will then be completely arrested by the stop and continued movement of the arm 17 causes the yarn to be wrapped about the spool. Thus inward movement of the stop finger 20 stops discharge of yarn from the device and simultaneously causes wrapping of yarn onto the spool. By suitably adjusting the rotary position of the arm 17 to the stop finger 20 and/or the timing of moving the finger 20 radially inwards it is possible to adjust the length of yarn metered out at a controlled rate by the arm 17 to a desired value.
By way of example a specific embodiment of the present invention is described below with reference to Figures 2 and 3. In these Figures parts corresponding to similar parts in Figure 1 have been designated by the same reference numerals. In Figure 2, the spool 12 is made up of individual segments 30 (only one of which is shown for the purposes of clarity). The segments 30 include an arcuate outer peripheral surface portion 31 which collectively make up the outer peripheral surface of the spool 12. Each segment has a web 32 depending from the surface portion 31 and the web 32 is secured to an annular boss 34. The web 32 is provided with a radially extending slot (not shown) through which passes a bolt 35 and a guide pin 36 so that each segment may be moved radially inwardly or outwardly so as to alter the effective diameter of the spool 12.
The annular boss 34 houses a bearing 37 which rotatably receives a shaft 40 from which arms 14 and 17 radially project. The annular boss 34 also includes a plurality of magnets 44 spaced about its circumference which co-operate with magnets 45 received in a fixed support 46 of the device 10. Magnets 44 and 45 attract one another so that annular boss 34 and accordingly spool 12 remain stationary despite rotation of shaft 40. The shaft 40 is also mounted in bearings 50 housed in support 46. The shaft 40 has a central bore 40a which communicates with the internal bore 14a of arm 14 to provide a passageway for yarn 16. Air ducts 53 are provided to enable pressurised air to be supplied to bore 40a to enable threading of yarn 16 through bores 40a and 14a. Shaft 40 is provided with a pinion gear 40b which meshes with gear 55 mounted on a drive shaft 56 of the loom.
The stop finger 20 is mounted on a support 60 which is pivotally mounted on a spindle 61. The spindle 61 is mounted in a support 62 which in turn is pivotally mounted on a spindle 63. Spindles 61 and 63 are perpendicular to one another so that the finger 20 may be moved axially along the spool and also moved radially inwardly or outwardly relative to the spool. Such movement of the finger 20 is achieved by a pair of cams 67 which co-operate with a pair of cam followers 68 mounted on support 60. The cam followers 68 are biased into contact with the cams 67 via a spring 67a. The cams 67 are shaped so that at two circumferential locations they have the same profile so as to move the finger radially inwardly or radially outwardly and at other times a different profile so as to cause the support to pivot about spindle 63 and so move the finger 20 axially along the spool whilst it is maintained in either a radially innermost or radially outermost position.
As seen in Figure 2 the ridge 26 has an inclined face 269 facing the terminal end of the spool 12. The purpose of the inclined face 269 is to encourage yarn wrapped about the spool 12 by the arm 17 to move axially along the spool to avoid overlapping of the yarn during winding. The rate of axial movement of finger 20 is arranged to be similar to the axial movement of yarn 16 along the spool. A similar inclined face 12a is provided at location 24 for co-operation with arm 14.