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(11) | EP 1 801 273 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Weft stock detector for weft feeders |
| (57) The detector is applied to weft feeders provided with a stationary drum (12) on which
yam loops are wound to form a weft stock (RT). Three feeler arms (22, 24, 26) are
hinged by side of the drum about respective axes (28, 30, 32) and are biased with
their respective contact ends (34a) against the drum for swinging between an active
lifted position and a lowered resting postion in relation to the presence/absence
of loops on the drum. Photoelectric cells (42) arranged to detect the movements of
the feeler arms each comprise an emitting diode (47) generating a stream of photons
through an elongated narrow slot (48) extending radially, and a photodiode (50) in
front of the slot (48). The feeler arm has a shield (52) insertable between the diode
and the photodiod and delimited frontally by a rectilinear edge (54) aligned to the
outer edge of the slot with the feeler arm in its resting position, in order to obscure
the slot.
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[0002] As known, the weft feeders for textile machines comprise a stationary drum on which a motorized swivel arm winds a plurality of yarn loops forming a weft stock. Upon request from the loom, the loops are unwound from the drum, pass through a yarn guide eyelet and then and are fed to the loom.
[0003] With weft feeders of the above type, the weft stock on the drum is controlled by a weft stock detector which generally includes two swinging feeler arms which are arranged at the opposite ends of the drum and are biased against the drum, e.g., by springs and/or by gravity, and a third swinging feeler arm arranged at a middle position, which has the aim of detecting any breaking of the yarn. The feeler arms each can swing between a resting position lowered towards the drum and an active, lifted position, in relation to the presence/absence of loops on the drum in the area engaged by the arm. Photoelectric cells detect the movements of the feeler arms and are connected to send signals to a control unit which, on the basis of the received signals, pilots the rotation of the swivel arm in order to maintain the weft stock substantially constant on the drum, within the limits defined by the positions of the two outermost feeler arms.
[0004] The detectors of the above type have the drawback that they are often inaccurate with thin yarns, because in this case the movement of the arms from the active position to the resting position, and vice versa, is very slight so that the photoelectric-cells are not capable of detecting it. Accordingly, these detection failures affect the reliability of the weft stock detector.
[0005] Therefore, it is a main object of the present invention to improve the above weft stock detector in order to make it more sensitive and reactive in detecting slight movements of the feeler arms even with very thin yarns.
[0006] The above object and other advantages, which will better appear below, are achieved by an improved weft stock detector having the features recited in claim 1, while the dependent claims state other advantageous, though secondary features of the invention.
[0007] The invention will be now described in more detail with reference to a preferred, non-exclusive embodiment, shown by way of non limiting example in the attached drawings, wherein:
Fig. 1 is a view in side elevation of a weft feeder provided with a weft stock detector according to the invention;
Fig. 2 is a front view to a slightly enlarged scale of the weft feeder of Fig. 1 in association with the drum of the feeder;
Fig. 3 is a view in cross section of Fig. 2 along line III-III;
Figs. 4, 5 show a detail of Fig. 3 to a considerably enlarged scale in two different operative configurations;
Fig. 6 is a view in cross section of Fig. 5 along line VI-VI;
Fig. 7 shows a detail of Fig. 5 to an enlarged scale.
[0008] With initial reference to Fig. 1, a weft feeder 10 for textile machines comprises a stationary drum 12 having longitudinal grooves 13 on its surface, on which a swivel arm 14, which is driven by a motor 15 piloted by a control unit CU (only diagrammatically shown in Fig. 3), winds a plurality of yarn loops forming a weft reserve or stock RT. Upon request from the loom, yarn F is unwound from the drum, passes through a yarn-guide eyelet 16 supported at the free end of a stationary arm 17 projecting from the motor housing parallel to the axis of the drum, and then is fed to the loom. Stationary arm 17 also supports a weft stock detector 18 for controlling the weft reserve on the drum.
[0009] Having now particular reference to Figs. 2-7, weft stock detector 18 comprises a housing 20 supporting three feeler arms 22, 24, 26 hinged to respective pins 28, 30, 32 parallel to one another. Two of these feeler arms 22, 26 are arranged near the opposite ends of the drum, while the third feeler arm 24 is arranged at a middle position. With particular reference now to Figs. 2, 4-7, where the outermost feeler arm 26 is shown in detail, the arms each comprise a U-shaped metal rod 34 (Fig. 2) whose free ends are attached to an anchor body 36 integral with a bush 38 that is hinged to a respective one of the pins 32. The curved end 34a of the U is slanting at an angle with respect to the two parallel branches in the running direction of the yarn, and is biased against drum 12 by magnetic action of mutual repulsion between a first permanent magnet 39a incorporated in a projection 40 projecting from bush 38 on the opposite side of the pin, and a second stationary magnet 39b having the same polarity, which is supported in front of first magnet 39a. The feeler arms each can swing between a lowered resting position, when there are no yarn loops wound on the drum in the area engaged by the arm, and a lifted active position, when there are yarn loops. In the resting position (Fig. 5), the curved end or contact end 34a of the feeler arm is received in one of the longitudinal grooves 13 on the drum, while the free end 40a of projection 40 is abutted against an abutment 41 integral with housing 20. In the active position (Fig. 4), the yarn loops wound on drum 12 in the area below the feeler arm cause the arm to lift from its resting position.
[0010] A photoelectric cell 42 is attached to housing 20 above bush 38 for detecting the movements of the feeler arm. Photoelectric cell 42 is shaped as an upside down U, with two opposite longitudinal walls 44, 46 (Fig. 6) which respectively house an emitting diode 47 connected to a power supply AL (which is only diagrammatically shown in Fig. 6) and generating a stream of photons through a narrow rectilinear vertical slot 48 (Figs. 4, 7), and a photodiode 50 arranged in front of slot 48 and connected to control unit CU. A gap is defined between the walls, in which a thin protrusion 52 is insertable which is frontally formed on projection 40 and is delimited by a rectilinear edge 54 extending radially from bush 38 in a position such that it is aligned to the outer vertical edge (i.e., the right edge in the Figures) of slot 48 when the feeler arm is at rest (Fig. 7). Therefore, thin protrusion 52 defines a shield that obscures slot 48 and breaks off the stream of photons when the feeler arm is at rest. Photoelectric cell 42 is connected to send position signals to control unit CU, which is programmed to pilot the rotation of swivel arm 14 on the basis of the received signals, in such a way as to maintain the weft stock RT substantially constant within the limits defined by the positions of the two outermost feeler arms 22, 26. The intermediate feeler arm 24 has the aim of detecting any breaking of the yarn. The programming of control unit CU is not within the scope of the present invention because it belongs to the normal knowledge of the person skilled in the art, and therefore no further description will be given about it. Photoelectric cell 46 is anchored to the upper side of housing 20 by means of a U-shaped anchor member 56 which also defines the above-cited abutment 41 against which the free end 40a of projection 40 abuts when the feeler arm is in its resting position. A magnetic sensor 58 is mounted on housing 20 and is arranged in such a way as to detect the movements of first magnet 39a mounted on the feeler arm. Magnetic sensor 46 is also connected to send position signals to control unit CU and can be adjusted to cooperate with the photoelectric cell, e.g., for giving two subsequent position signals in relation to the position of the feeler arm, or for performing other combined or alternate detections, such as can be easily contrived by the person skilled in the art.
[0011] In the operation, feeler arms 22, 24, 26 are biased against drum 12 by gravity and by mutual repulsion between the magnets 39a, 39b, with a lever-type action about the fulcrum defined by the axes of the pins, and can swing between the lowered resting position and the lifted active position in relation to the absence/presence of loops on the drum. Figs. 4, 5 show the weft stock detector in association with a thin yarn FS, in an active position and in a resting position respectively. As shown in Fig. 4, with the above-described embodiment according to the invention it is sufficient for the feeler arm to make a very slight movement from its resting position, such as the movement determined by a loop of a very thin yarn, to cause protrusion 52 to immediately and completely uncover slot 48. As the person skilled in the art will immediately understand, this circumstance makes the weft stock detector much more sensitive and reactive in detecting very slight movements of the feeler arms, even in case of very thin yarns.
[0012] A preferred embodiment of the invention has been described herein, but of course many changes may be made by the person skilled in the art within the scope of the inventive concept. In particular, the feeler arm could be biased against the drum by biasing means other than the magnets, e.g., by spring, or only by gravity. Furthermore, the presence of sensor magnet 58 should be intended as useful but not indispensable to carry out the invention.
1. A weft store detector for weft feeders provided with a stationary drum (12) on which
yarn loops are wound to form a weft stock (RT), comprising at least two feeler arms
(22, 24, 26) hinged by side of the drum about respective axes (28, 30, 32) and biased
against the drum with their respective contact ends (34a) for swinging between an
active lifted position and a lowered resting postion in relation to the presence/absence
of loops on the drum, and respective photoelectric cells (42) arranged to detect the
movements of the feeler arms, characterized in that said photoelectric cells each comprise an emitting diode (47) connected to generate
a stream of photons through an elongated narrow slot (48) extending in a substantially
radial direction with respect to the pin (32), and a photodiode (50) in front of the
slot (48), and in that said feeler arms are each provided with a shield (52) insertable between the diode
and the photodiod and delimited frontally by a rectilinear edge (54) that is aligned
to the outer edge of the slot (48), with the feeler arm in its resting position, thereby
obscuring the slot (48) and breaking off the stream of photons.
2. The weft stock detector of claim 1, characterized in that said shield (52) is positioned at the opposite side of the axis (32) with respect
to the contact end (34a).
3. The weft stock detector of claim 1 or 2, characterized in that said feeler arm has a projection (40) on the opposite side of the axis (32) with
respect to the contact end (34a), which is shaped fo abutting against a stationary
abutment (41) with the feeler arm in its resting position.
4. The wef stock detector of claim 3, characterized in that said shield (52) consists of a thin protrusion (52) formed frontally on said projection
(40).