HEALD RETENTION DEVICE

Abstract: A heald retention device (10) for a magnetically attractable latch or heald hook (30), the latch or hook being deflectable between a latching position and a non-latching position and being resiliently biased toward one of said positions, the retention device including magnet means (40) which are selectively operable for creating an attractive magnetic field of sufficient strength for deflecting the latch or hook against said bias, the magnet means including a permanent magnet (70) having north and south poles, a pair of spaced apart pole pieces (51, 52), one of the pole pieces being magnetically connected with the north pole and the other of the pole pieces being magnetically connected with the south pole, shunt means (80) providing a direct magnetic connection between the pole pieces such that lines of force generated by the permanent magnet flow through the shunt means in preference to flowing externally in between the pole pieces, the shunt means being selectively operable for controlling said flow of lines of force through the shunt means to thereby control change of the strength of an external magnetic field generated in between said pole pieces by said permanent magnet between a maximum and minimum value.

Description: Heald Retention Device The present invention relates to a heald retention device and a pattern control apparatus including a plurality of such devices for a weaving loom. In UK patent 2047755 and European patents 119787 and 188074 there are described heald rod retention devices for controlling the shed position of warp yarns. The retention device may operate on a deflectable latch which is deflected to cause retention of a heald hook by latching engagement therebetween. Alternatively the retention device may operate on a resiliently deflectable heald hook (in the form of a rod or strip) to cause retention of the heald hook by latching engagement between the hook and a static latch. Deflection of the deflectable latch or hook is achieved by an attractive magnetic force created solely by an electromagnet. It is a general aim of the present invention to provide a retention device of the type described in UK patent 2047755, European patent 119787 or 188074 which requires less electrical power for causing deflection of the latch or heald hook. This is highly desirable as reduction in the required electrical power provides a saving on operating cost and reduces problems associated with generation of heat. According to one aspect of the present invention there is provided a heald retention device for a magnetically attractable latch or heald hook, the latch or hook being deflectable between a latching position and a non-latching position and being resiliently biased toward one of said positions, the retention device including magnet means which are selectively operable for creating an attractive magnetic field of sufficient strength for deflecting the latch or hook against said bias, the magnet means including a permanent magnet having north and south poles, a pair of spaced apart pole pieces, one. of the pole pieces being magnetically connected with the north pole and the other of the pole pieces being magnetically connected with the south pole, shunt means providing a direct magnetic connection between the pole pieces such that lines of force generated by the permanent magnet flow through the shunt means in preference to flowing externally inbetween the pole pieces, the shunt means being selectively operable for controlling said flow of lines of force through the shunt means to thereby control change of the strength of an external magnetic field generated in between said pole pieces by said permanent magnet between a maximum and minimum value. The minimum strength value of the magnetic field generated by the permanent magnet is insufficient to retain, against said bias, the latch or hook in its deflected position. The minimum value may be zero. Preferably the shunt means includes an electromagnet having a core and electrical windings surrounding the core, the core being connected to both pole pieces to define said direct magnetic connection. The electromagnet is arranged so that when actuated it generates lines of force within the core which extend in a direction opposite to those created by the permanent magnet. This has a diverting effect on the lines of force passing through the core created by the permanent magnet such that more lines of force created by the permanent magnet are caused to extend externally of the pole pieces. In this condition the maximum strength value of the magnetic field generated by the permanent magnet is produced. The lines of force generated by the electromagnet also extend externally inbetween the pole pieces to supplement the magnetic field generated by the permanent magnet such that said attractive magnetic field of the magnet means for deflecting the latch or hook comprises the combined magnetic fields generated by the permanent and electromagnets. Various aspects of the present invention are hereinafter described with reference to the accompanying drawings, in which:- Figure 1 is a front view of an upper portion of a retention device according to the present invention; Figure 2 is a side view of the device shown in Figure i; Figure 3 is a side view similar to Figure 1 showing a further embodiment according to the invention; Figure 4 is a front view of the embodiment shown in Figure 3; Figure 5 is an exaggerated diagrammatic representation of stages of bending of a hook using the embodiment shown in Figures 3 and 4. The retention device 10 is of the same general construction as the retention device 20 described in European patent 188074 and reference should be made thereto for a fuller description of the general construction and mounting of the device in a pattern control apparatus for a loom. The retention device 10 includes an upper body portion 50 having a magnet means 40 for creating an external attractive magnetic field for causing deflection of a pair of resilient magnetically attractable heald hooks 30 (only one of which is shown) . The magnet means 40 includes a pair of pole pieces 51,52 mounted on the body portion 50, a permanent magnet 70 and a shunt means 80 for controlling the external magnetic field inbetween pole pieces 51,52 generated by the permanent magnet 70. Each pole piece includes a planar body portion 54 provided with a pair of opposed longitudinally extending side walls 33. As in the construction disclosed in European patent 188074 the pole pieces 51,52 are seated upon the body portion 50 with side walls 33 extending upon the sides 60 of the body portion 50. Adjacent side walls 33 of pole pieces 51,52 are spaced by a ridge 62 which preferably projects above the outer surface of side walls 33 to define an air gap between a heald hook 30 (only one of which is shown in Figure 1) and the side walls 33 when attracted for co-operation with latch 65. The permanent magnet 70 is located between the body portions 50 of each pole piece with its north pole adjacent one pole piece 51 and its south pole adjacent the other pole piece 52. The permanent magnet 70 contacts the pole pieces 51,52 in such a manner as to create a good magnetic connection therebetween. The magnetic shunt means 80 in the illustrated embodiment is in the form of an electromagnet which is also located between the pole pieces 51,52. The electromagnet includes a core 82 in the form of a rivet which ensures a good magnetic connection between the pole pieces 51,52. The rivet also serves to mechanically hold the pole pieces 51,52 together and thereby maintain a rigid connection therebetween. Accordingly, the core 82 provides a magnetic connection between pole pieces 51,52 and so creates a closed magnetic circuit with lines of force running from the north pole of the permanent magnet through pole piece 51 , core 82 and pole piece 52 to the permanent magnets south pole. The proportion of lines of force generated by the permanent magnet which flow through the core 82 and so are contained within the closed circuit compared to that proportion which flows externally inbetween the pole pieces 51,52 depends upon the choice of material and sizes for the core and pole pieces. These factors are chosen such that in the closed circuit condition most magnetic lines of force are contained within the closed circuit so that the external magnetic attractive field generated by the permanent magnet inbetween the pole pieces 51,52 is of a minimum strength value which is insufficient to maintain a deflected heald hook in its deflected condition. The electromagnet also includes electrical windings 84 surrounding the core 82. The windings 84 and electrical supply thereto are arranged such that on actuation the electromagnet produces a north pole adjacent pole piece 51 and a south pole adjacent pole piece 52. In this way the electromagnet produces lines of force in the core 82 which extend in a direction opposite to the lines of force created by the permanent magnet. Accordingly the electromagnet has a diverting effect on the permanent magnet lines of force in the core 82 and thereby reduces or totally removes the magnetic connection in the closed magnetic circuit of the permanent magnet. Accordingly all or most lines of force generated by the permanent magnet are caused to flow externally inbetween the pole pieces 51,52 to create an external magnetic field of maximum strength which is used for deflecting the heald hook. The lines of force generated by the electromagnet also flow externally inbetween the pole pieces 51,52 to supplement the strength of the magnetic field generated by the permanent magnet. * Accordingly the force of the combined external attractive magnetic field radiated from the pole pieces 51,52 depends upon the strengths of the permanent and electromagnets. It will be appreciated therefore that the electromagnet effectively operates as a switch for changing the strength of the external attractive magnetic field between a maximum value for deflecting the heald hook against its inherent bias and a minimum value for enabling a deflected hook to return under its inherent bias to its non-deflected position. In the illustrated embodiment the shunt means 80 is defined by an electromagnet. It is envisaged that other constructions of shunt means may be provided for achieving the control of flow of lines of force along the closed magnetic circuit. For example the shunt means 80 may comprise a switch member of magnetic material which in one position makes a direct magnetic connection between the pole pieces and in another position breaks said direct magnetic connection. In such an example the maximum strength value of the external attractive magnetic field would be created by the permanent magnet alone. It is also envisaged that the magnet means 40 may be incorporated into the type of retention device as described in UK patent 2047755 which effect deflection of a deflectable latch instead of a deflectable heald hook. The heald retention device shown in Figures 1 and 2 above utilises a permanent magnet for deflecting a heald hook into engagement with a latch. When in contact with the latch the deflected hook is held in its deflected condition and is spaced from magnetic poles of the permanent magnet by a ridge 62 which creates an air gap. Due to the presence of the permanent magnet 70, the deflected hook 30 held on the latch is exposed to an external stray magnetic field. Accordingly, the air gap between the deflected hook and poles of the magnet needs to be sufficient to enable the hook to overcome the attractive force of any stray magnetic field so as to reliably return to its non-deflected position after being raised from the latch. If this does not happen it is possible for the hook to remain in its deflected position, i.e. "stick" and re- engage the latch on being lowered with the consequential result of a mis-selection. The problem of sticking is accentuated in use since as wear occurs in the stop creating the air gap, the air gap diminishes and thereby increases the probability of the hook sticking. A further embodiment is illustrated in Figures 3 to 5 which aims to reduce the potential sticking problem. As seen in Figure 1 a resilient hook 30 is illustrated in a non-deflected position and so lies in a normal undeflected, reciprocal path of travel. On energisation of the magnet means 40 (caused by energisation of the electromagnet 80) the upper portion 30a of the hook is deflected toward the adjacent side 60 of the body portion 50 to bring about engagement of the hook 30 with the latch 65. One factor which determines the force required to bend the upper portion 30a of the hook from its normal undeflected reciprocal path of travel is the position of the magnet means 40 relative to the fulcrum point 100 of bending of the hook i.e. the further the magnet means from the fulcrum point of bending the weaker the applied force necessary for causing bending. Desirably therefore this distance is maximised to provide a weak resistance to bending and thereby enable a relatively weak magnetic field to initiate bending. Once the hook portion 30a has been deflected and has engaged the latch 65, the magnet means is de-activated. The hook portion 30a thereafter remains held in its deflected condition by virtue of its engagement with the latch 65. In order to release the hook portion 30a from latch 65, the hook portion 30a is raised to clear the latch 65 and due to its resilience, the hook portion 30a returns to its undeflected state to assume its normal undeflected path of travel and thereby enable the hook to be lowered and subsequently raised without contacting the latch. As indicated above, the force required for initially bending the hook portion 30a is designed to be relatively weak and so the biasing force created for returning the hook portion to its undeflected state is therefore also relatively weak. This weak biasing force for initiating return of the deflected hook to its undeflected state is undesirable as it increases the probability of the hook portion 30a "sticking" to the magnet means 40 should there still be a residual magnetic field on deactivation of the magnet means 40. It is therefore desirable to maximise the biasing force for creating the initial force for returning the hook portion 30a to its undeflected state without sacrificing the relative weak force required for initiating bending of the hook portion 30a from its undeflected state. According to the embodiment shown in Figures 3 to 5, at least two fulcrum points are provided about which the hook portion 30a is bent. A first fulcrum point 100 is provided at a remote distance Db for example 18 mm from the magnet means 40 to provide a relatively weak resistance to initial bending. A second fulcrum point 110 is provided at a near distance _____ from the latch 65 for example 27 mm. In view of the shorter length 30b of hook portion 30a projecting above the fulcrum 110 the force required to bend the hook portion 30b is greater than that required to bend the hook portion 30a about fulcrum 100 and so provides a greater biasing force for initiating movement of the hook portion 30a back to its original undeflected state. The magnetic force generated by the magnet means 40 may be the same as that for the embodiment described for the embodiment of Figures 1 and 2 since the force required for the initial deflection about fulcrum 100 is unaffected. After initial deflection about fulcrum 100 from its undeflected position UD (Figure 5) , the hook portion 30a approaches the pole faces of the magnet means and thereby progressively moves into a stronger magnetic field. Thus on reaching the second fulcrum 100 indicated by position ID (Figure 5) the hook portion 30a is acted upon by a relatively stronger magnetic field which is able to overcome the additional resistance to bending to cause the hook portion to bend about fulcrum 110 to its fully deflected position FD (Figure 5) . In this position, the hook is spaced from the side walls 33 of the pole pieces 51,52 by ridge 61 to create an air gap. On de-activation of the magnet means, the strongest stray magnetic field will be located immediately adjacent to the side walls 33 of the pole pieces 51,52 and the initial high biasing force provided by fulcrum 110 is able to overcome this stray field. If the air gap diminishes due to wear of ridge 62 the deflected hook progressively becomes closer to the side walls 33 and is exposed to increased strength of the stray magnetic field. The bias generated by fulcrum 110 is therefore preferably chosen to be strong enough to overcome the strength of the stray magnetic field at side walls 33 to thereby enable reliable return of the deflected hook should the air gap reduce in size due to wear of ridge 62. The stray magnetic field will have negligible strength at position ID of the hook portion and so enabling the relatively weak biasing force created about fulcrum 100 is able to return the hook to position UD. It will be appreciated that the fulcrums 100,110 may be formed in different ways. For example, both fulcrums 100,110 may be formed by ridges and/or projections moulded integrally with the body 50. Preferably, as illustrated in Figures 3 and 4, the fulcrum 110 is formed by a projection 120 defined by a flared portion 121 formed integrally with pole pieces 51,52. Preferably the height of fulcrum 110 as defined by flared portion 121 is the same as or less than the height of ridge 61 above side walls 33. In this way the fulcrum 110 does not have an effect until the effective height of ridge 61 has lowered due to wear.

Claims: CLAIMS 1. A heald retention device for a magnetically attractable latch or heald hook, the latch or hook being deflectable between a latching position and a non-latching position and being resiliently biased toward one of said positions, the retention device including magnet means which are selectively operable for creating an attractive magnetic field of sufficient strength for deflecting the latch or hook against said bias, the magnet means including a permanent magnet having north and south poles, a pair of spaced apart pole pieces, one of the pole pieces being magnetically connected with the north pole and the other of the pole pieces being magnetically connected with the south pole, shunt means providing a direct magnetic connection between the pole pieces such that lines of force generated by the permanent magnet flow through the shunt means in preference to flowing externally inbetween the pole pieces, the shunt means being selectively operable for controlling said flow of lines of force through the shunt means to thereby control change of the strength of an external magnetic field generated in between said pole pieces by said permanent magnet between a maximum and minimum value. 2. A device according to claim 1, wherein the shunt means includes an electromagnet having a core and electrical windings surrounding the core, the core being connected to both pole pieces to define said direct magnetic connection, the electromagnet when activated producing times of force within the core to oppose the times of force created by the permanent magnet. 3. A device according to claim 1, wherein the shunt means comprises a switch member of magnetic material which in one position makes a direct magnetic connection between the pole pieces and in another position breaks said direct magnetic connection. 4. A device according to any preceding claim including first and second fulcrums about which the heald hook are bent on deflection caused by the magnet means, the second fulcrum being located closer to the magnet means than the first fulcrum. 5. A device according to claim 4, including a ridge for spacing a deflected hook from the pole pieces, the second fulcrum being located adjacent the ridge and having a height the same as or less than the ridge so as to only become operative after the height of the ridge has reduced due to wear. 6. A device according to claim 5, wherein the second fulcrum is defined by a projection on the pole pieces. 7. A jacquard mechanism for a loom including a plurality of heald retention devices according to any preceding claim.

Inventors: LOGAN JOHN, SANGHA PARMINDER SINGH, LOGAN, JOHN, SANGHA, PARMINDER, SINGH
Applicants: LUCAS IND PLC, LUCAS INDUSTRIES PLC
Application year: 1992
Main classification: D03C3
IPC codes: D03C3