Bistable solenoid and knitting machine using the same

Abstract: A bistable solenoid has an outer enclosure made of magnetic material, a movable plunger consisting of two end regions (41, 42) of non-magnetic material and a central region of magnetic material and arranged to extend inside and lengthwisely of the outer enclosure, a pair of plunger bearings (63, 64) provided on the outer enclosure for supporting the non-magnetic end regions (41, 42) of the movable plunger during the slide movement, a pair of permanent magnets (11, 12) spaced a predetermined distance apart and arranged around the movable plunger so that their magnetic directions are opposite to each other, and a pair of magnetizing coils (21, 22) sandwiching therebetween the two permanent magnets (11, 12) each of said plunger bearings (63, 64) arranged to have a thickness greater than the predetermined distance, said movable plunger has a low permeability recess formed in a portion of the central region (52) thereof where the magnetic permeability is smaller than the other regions. The central region of the movable plunger is arranged to have a length equal to the sum of the distance between the inner walls of the two plunger bearings (63, 64) and the predetermined distance between the two permanent magnets (11, 12). The permanent magnets and magnetizing coils are spaced a bit distance at inner side from the movable plunger.

Description: The present invention relates to a solenoid arranged for bistable actuation in combination of permanent magnets, and a knitting machine employing the same. A known bistable solenoid is provided with a yoke having two permanent magnets arranged on both sides of a magnetizing coil and a movable ferrous core which has an overall length shorter than the distance between the outer ends of their respective permanent magnets and is movably fitted into the yoke. The disadvantage is that the accurate positioning of the movable ferrous core to a desired point is troublesome. For the purpose of eliminating the disadvantage, a modification has been proposed as shown in Japanese Utility-model Laid-open Publication 63-188910 (1988). As best shown in Fig.6, the modification comprises a solenoid enclosure P11, a couple of magnetizing coils P13 and P14 sandwiching therebetween a permanent magnet P12 which is magnetized in radial polarity orientation, two end plates P15 and P16 arranged on the outer sides of the two magnetizing coils P13 and P14 respectively, and a cylindrical sleeve P17 extending outward across the two end plates P15 and P16. Accordingly, there are developed a pair of left and right magnetic loops between the center permanent magnet P12 and the two end plates P15 and P16 respectively. The cylindrical sleeve P17 accommodates a movable iron core P18 which extends lengthwisely of the sleeve P17 and has two interacting regions P19 and P20 arranged equal in width to their respective end plates P15 and P16. Also, a couple of small-diameter regions P21 and P22 of the movable iron core P18 are formed inside their respective interacting regions P19 and P20. Since the small-diameter regions P21 and P22 of the movable iron core P18 are smaller in the permeability than the other regions, the movable iron core P18 becomes stable when either of its interacting regions P19 or P20 meets the corresponding end plate P15 or P16. Also, the thickness of the end plate P15 or P16 is identical to the width of the interacting region P19 or P20 so that the positioning of the movable iron core P18 can be ensured. A cam drive mechanism of a knitting machine using such a known solenoid is illustrated in Fig.7. The solenoid P2 is fixedly mounted by a retaining member P3 to a base plate P1. A movable plunger P6 of the solenoid P2 is provided for pressing upward one end of a rocking lever P5 pivotably supported by a support P4. The other end of the rocking lever P5 is arranged for actuating a lift-down cam P7 or the like. When the solenoid P2 is deenergized, its moving plunger P6 remains retracted by means of a spring. However, the foregoing solenoid described in Japanese Utility-Model Laid-open Publication 63-188910 still has a drawback that the movable iron core slides directly on the inner surface of the cylindrical sleeve and thus, both will unavoidably be worn away. Particularly, the movable iron core is made of soft iron for enhancement of magnetic characteristics having a low resistance to wear. The magnetic circuit extends up to the end plates where there are slight clearances between the cylindrical sleeve and the interacting regions of the movable iron core. Hence, the magnetic flux tends to leak out and attract unwanted materials, e.g. existing iron dust. Such iron dust may enter the inside the sleeve and accelerate the wornout of both the movable iron core and the cylindrical sleeve. The clearance between the cylindrical sleeve and the interacting regions of the movable iron core has to be determined to a minimum distance for minimizing the entrance of iron dust and the end plates are not allowed to act as bearing bushes. Also, if the magnetic intensity of the permanent magnet is increased for increasing a force of retention, a greater energy of flux develops across the magnetic circuit. Simultaneously, the magnetic circuit causing not-stable conditions is also increased in the magnetic energy. As the result, the permanent magnet and/or the magnetizing coils have to be increased in the size for producing appropriate rates of retention force and thrust force while the moving distance of the movable iron core has been set to a desired length. The foregoing known knitting machine employs a multiplicity of such solenoids which produce a thrust of 1 kgf for actuating each lift-down cam which can be driven by a thrust as small as 300 gf. The 1-kgf solenoid produces not only a greater thrust but also an unwanted physical impact causing noise and vibration during operation of the knitting machine and the operational durability will be declined. The size of the solenoid has to be increased proportional to the magnitude of a thrust and will never contribute to the compactness of the knitting machine. Furthermore, the foregoing solenoid used for actuating the cam in a knitting machine, as shown in Fig. 7, has to be accompanied with the rocking lever P5 for cam actuation, the retaining member P3, the support P4, etc. Accordingly, the cam drive arrangement will be complicated and hardly decreased in size. Also, the mass of inertia of moving parts becomes great, thus discouraging high-speed operation and requiring large magnetizing power. In addition, the adjustment on the clearance at the stress and action points of the lever P7 has to be carefully carried out, which will be troublesome. Also, disclosed in Japanese Patent Laid-Open Publication 57-29649 (1982) is a cam supporting carriage of a knitting machine which carries a movable cam actuated by an electromagnetic positioning means for outward and inward movement to control the action of knitting needles. The electromagnetic positioning means comprises a permanent magnet exhibiting a small magnetic field and arranged in combination with coils for magnetization and demagnetization and a moving unit of ferromagnetic metal material linked to the cam to be positioned. Also, a magnetization control circuit is provided for allowing the coils to perform a magnetizing and demagnetizing action on the permanent magnet using current pulses. As the result, both the moving unit and the movable cam linked with the moving unit can be actuated by the action of magnetic attraction and repulsion for cam engagement and disengagement. The solenoid of the cam supporting carriage disclosed in Japanese Patent Laid-Open Publication 57-29649 contains a single permanent magnet and is thus provided with a spring which produces a counter-force for bistable movement. For drawing the iron core, a greater force of magnetic attraction is needed than the yielding force of the spring. This results in declination in the efficiency of energy conversion. Also, during returning of the cam to its actuating position, the iron core is abruptly pressed outward by the yielding force of the spring, thus producing a physical shock which may accelerate the wornout of the iron core and its relevant components. DE-C-1253821, upon which the preamble of claim 1 is based, discloses a bistable solenoid having an outer enclosure partly of magnetic material. The solenoid has a movable plunger consisting of two end regions and a central region, and two permanent magnets arranged at a given axial distance apart around the movable plunger so that their magnetic directions are opposite to each other. The two permanent magnets are sandwiched between two magnetising coils. The central region of the plunger is of magnetic material and is coaxial with the outer enclosure which is provided with two end portions of magnetic material. These end portions extend radially inwards and surround the plunger. Each end portion of the outer enclosure has a region adjacent to one of the magnetising coils and has a radial clearance relative to the movable plunger. Each end portion of the outer enclosure also comprises plunger bearings supporting the end regions of the movable plunger, radial clearance being provided between the permanent magnets and the magnetising coils on the one hand and the movable plunger on the other hand. It is an object of the present invention to provide an improved bistable solenoid as well as a knitting machine using that improved bistable solenoid. According to the present invention, there is provided a bistable solenoid having an outer enclosure at least partly made of magnetic material, a movable plunger consisting of two end regions and a central region, two permanent magnets arranged a given axial distance apart around the movable plunger so that their magnetic directions are opposite to each other, and two magnetizing coils between which the two permanent magnets are sandwiched, wherein the central region of the plunger is of magnetic material and is arranged to extend coaxially within the outer enclosure and the outer enclosure is provided with two end portions of magnetic material extending radially inwardly to surround the plunger, each end portion of the outer enclosure comprising a region adjacent one of the magnetizing coils and having a radial clearance relative to the movable plunger, the region axially extending at least along a length corresponding to the distance between the two stable positions of the plunger, the length of the central region of the plunger being equal to the sum of the distance between the two stable positions of the plunger and the axial distance between the opposing inner walls of the end portions of the outer enclosure, each end portion of the outer enclosure further comprising plunger bearings for supporting the end regions of the movable plunger, radial clearance being provided between the permanent magnets and magnetizing coils on the one hand and the movable plunger on the other hand, the central region of the movable plunger having a portion in which the magnetic permeability is smaller than in both adjacent portions of the central region, characterised in that the end regions of the movable plunger are of non-magnetic material and in that the central region of the plunger comprises a single central portion in which the magnetic permeability is smaller than in both adjacent portions of the central region, so that the distance between the stable positions of the plunger corresponds to the distance between the centres of the two permanent magnets. According to an embodiment of the present invention a knitting machine employs the foregoing bistable solenoid for cam drive action of a carriage. The solenoid may be fixedly mounted to a base plate of the carriage by a retaining member provided on the outer enclosure thereof and its movable plunger is coupled directly to a cam so that the cam can be actuated by the forward and backward movement of the solenoid. A knitting machine according to the present invention employs the foregoing bistable solenoid for cam drive action of a carriage so that each cam can be actuated by the bistable movement of the solenoid. Also, the solenoid is fixedly mounted to a base plate of the carriage by a retaining member provided on its outer enclosure thus easing its positioning. Furthermore, the movable iron core or plunger of the solenoid is coupled directly to the cam and thus, no link mechanism, e.g. a rocking lever, is needed. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 and 2 are cross sectional plan views of a bistable solenoid showing one embodiment of the present invention; Fig. 3 is a thrust characteristic diagram of the bistable solenoid; Figs. 4 and 5 are cross sectional plan views showing a primary part of a knitting machine according to the present invention; Fig. 6 is a cross sectional view of a prior art bistable solenoid; and Fig. 7 is an exploded perspective view showing a cam drive mechanism of the prior art knitting machine. DESCRIPTION OF THE PREFERRED EMBODIMENT A bistable solenoid of an embodiment of the present invention will be described in more detail referring to the accompanying drawings. Figs. 1 and 2 are cross sectional views of the bistable solenoid of the present invention and Fig. 3 is a thrust force characteristic diagram of the same. The solenoid of Figs. 1 to 3 comprises a couple of permanent magnets 11 and 12 arranged apart so that their magnetic directions are opposite to each other, two magnetizing coils 21 and 22 arranged outside the permanent magnets 11 and 12 respectively, a cylindrical sleeve 3 of magnetic material extending across the permanent magnets 11 and 12 and the magnetizing coils 21 and 22, and a pair of plunger bearings 63 and 64 of magnetic material provided outwardly, as shown in Fig. 1. The cylindrical sleeve 3 accommodates a movable iron core 5 which can slide inside the cylindrical sleeve in no contact relationship while being supported by the two bearings 63 and 64. The movable iron core 5 has a high permeability region 51 and a low permeability region arranged corresponding to the distance between the two permanent magnets 11 and 12. More particularly, a portion of the movable plunger 5 of magnetic material having a high permeability is recessed to have a space filled with air having a low permeability thus constituting the low permeability region 52. In operation, if the low permeability region 52 is displaced off both the permanent magnets 11 and 12, the nearest one (for example, the right magnet 12) of the two permanent magnets 11 and 12 attracts the low permeability region 52 to move rightward for stable positioning. While the lower permeability region 52 of the movable iron core 5 remains engaged with the permanent magnet 12 having the same width, magnetic lines of flux extend from one of the two poles of the axially aligned permanent magnet 12 across a high permeability region 53, located beside the low permeability region 52, and the other high permeability region 51 of the iron core 5 to the other pole of the permanent magnet 11, forming a magnetic circuit. Hence, if the movable iron core 5 is displaced from its stable position, a force of magnetic attraction is activated to return it to the stable position. Accordingly, the magnetically stable condition can be maintained. When the magnetizing coil 21 is energized for producing magnetic flux, a force of attraction is developed between the left end 511 of the high permeability region 51 and the inner side 611 of the yoke 61 causing the movable iron core 5 to move leftward, because the plunger journal 41 is formed of non-magnetic material. After moving leftward, the movable iron core 5 stops at a position where its low permeability region 52 comes opposite to the permanent magnet 11 and remains in a stable state (See Fig. 2). This stable state can be maintained by offsetting a displacement, if caused, with the use of an attracting force of the permanent magnet. When the magnetizing coil 22 is energized, a force of attraction is developed between the inner side of the right yoke 62 and the right end of the high permeability region 53. Hence, the movable iron core 5 is moved rightward and then, remains at a position where its low permeability region 52 comes opposite to the permanent magnet 12 forming a stable state. This stable state can be maintained by offsetting a displacement, if caused, with the use of an attracting force of the permanent magnet. Consequently, each of the two, left and right, stable states can be ensured. The two permanent magnets 11 and 12 have an inner yoke 72 interposed therebetween and two other inner yokes 71 and 73 arranged on their respective outer sides. There are also provided two magnetizing coils 21 and 22 on the outer sides of the inner yokes 71 and 73 respectively. The foregoing assembly is then mounted onto a cylindrical sleeve 3 so that the cylindrical sleeve 3 extends inside and lengthwisely of the assembly. The cylindrical sleeve 3 is then interposed between two yokes 61 and 62 of magnetic material which have bearing portions 63 and 64 respectively. The cylindrical sleeve 3 accommodates a movable ferrous core 5 which has an outer diameter a bit smaller than the diameter of the cylindrical sleeve 3 so that it can slide along the inside of the cylindrical sleeve 3 without touching. The movable ferrous core 5 has a recess in the central portion thereof which is equal in the width to the permanent magnets 11 and 12 and serves as a small-diameter interacting region 52 exhibiting a smaller permeability. Hence, two large-diameter interacting regions 51 and 53 of the movable ferrous core 5 are formed on both sides of the small-diameter interacting region 52. The large-diameter interacting regions 51 and 53 are coupled at outer ends to two plunger journals 41 and 42 of non-magnetic material respectively. The plunger journals 41 and 42 are arranged for sliding movement along their respective bearing portions 63 and 64 of the yokes. In operation, if the small-diameter interacting region 52 is displaced off both the permanent magnets 11 and 12, the nearest one (for example, the right magnet 12) of the two permanent magnets 11 and 12 attracts the small-diameter interacting region 52 for stable positioning. While the small-diameter interacting region 52 of the movable ferrous core 5 remains engaged with the permanent magnet 12 having the same width, magnetic lines of flux extend from one of the two poles of the axially aligned permanent magnet 12 across the large-diameter interacting regions 53 and 51, beside the small-diameter interacting region 52, of the ferrous core 5 to the other pole of the permanent magnet 11, forming a magnetic circuit. Hence, if the movable ferrous core 5 is displaced from its stable position, the magnetic attraction acts as a restoring force to return it to the stable position. Accordingly, the magnetically stable condition can be maintained. When the magnetizing coil 21 is energized for producing magnetic flux, a force of attraction is developed between the inner side of the yoke 61 and the left end of the large-diameter interacting region 51 causing the movable ferrous core 5 to move leftward, because the plunger journal 41 is formed of non-magnetic material. After moving leftward, the movable ferrous core 5 stops at a position where its small-diameter interacting region 52 comes opposite to the permanent magnet 11 and remains in a stable state (See Fig.2). This stable state can be maintained when the magnetizing coil 21 is deenergized. More particularly, the attraction of the permanent magnet 11 acts as a restoring force and allows the removable ferrous core 5 to be returned to its stable position if displaced. Also, when the magnetizing coil 22 is energized, a force of attraction is developed between the inner side of the right yoke 62 and the right end of the large-diameter interacting region 53. Hence, the movable ferrous core 5 is moved rightward and then, remains at a position where its small-diameter interacting region 52 comes opposite to the permanent magnet 12 forming a stable state. This stable state is maintained when the magnetizing coil 22 is deenergized. More particularly, the attraction of the permanent magnet 12 acts as a restoring force and allows the removable ferrous core 5 to be returned to its stable position if displaced. The restoring force acts counter to a thrust produced by the solenoid. The characteristics of the thrust are shown in Fig.3, where 400 gf of a practical thrust and 3 mm of a stroke are produced when the magnetizing voltage is 22 volts. The thrust of such strength is eligible for use in actuating a lift-down cam of a knitting machine. The plunger journals 41 and 42 supporting the movable ferrous core 5 are formed of non-magnetic material allowing no magnetic energy to escape to the outside. Accordingly, no collection of iron powder is caused and the bearing performance will be enhanced. The movable ferrous core 5 can move in no direct contact with the cylindrical sleeve 3, thus avoiding wear of both the materials and increasing the operational life. The movable ferrous core 5 may be provided with a segment material of low permeability arranged in place of the small-diameter interacting region. This provides an advantage that the mechanical strength is increased with no such mechanically disadvantageous small-diameter interacting region arranged. The knitting machine according to the present invention will be further described referring to Figs.4 and 5, which are cross sectional plan views showing a cam actuator section of a carriage in the knitting machine of the present invention. Fig.4 illustrates the engagement of a cam and Fig.5 illustrates the disengagement of the same. As shown in Figs.4 and 5, there are provided a base plate 81 of the carriage, a solenoid 82 fixedly mounted by a retainer 83 to the base plate 81, the cam 84, and a stroke control stopper 85. The solenoid 82 has an interior arrangement identical to that of the foregoing bistable solenoid and will be explained with like components denoted by like numerals. For actuating the lift-down cam in the knitting machine having such a lift-down cam mechanism, short energization of a magnetizing coil 22 produces a force of magnetic attraction between a movable plunger 5 and a yoke 62 causing the movable plunger 5 to move rightward. The movable plunger 5 then stops when a stopper 86 of the cam 84 comes into direct contact with the base plate 81. At the position, while the magnetizing coil 22 is deenergized, the small-diameter interacting region 52 of the movable plunger 5 is located a bit off the position of a right permanent magnet 12. More specifically, a thrust to draw the small-diameter interacting region 52 of the movable plunger 5 rightward is produced by the permanent magnet 12 and thus, the cam 84 remains projecting outward as resisting against a moderate force of exterior pressure caused during operation. As the result, the cam 84 allows a corresponding knitting needle to stay lifted down. When no actuation of the lift-down cam 84 is needed, short energization of another magnetizing coil 21 produces a force of magnetic attraction between the movable plunger 5 and a left-side yoke 61 causing the movable plunger 5 to move leftward. The movable plunger 5 then stops when its left journal 41 comes at left end into direct contact with the stroke control stopper 85. At the position, while the magnetizing coil 21 is deenergized, the small-diameter interacting region 52 of the movable plunger 5 is located a bit off the position of a left permanent magnet 11. More specifically, a thrust to draw the small-diameter interacting region 52 of the movable plunger 5 leftward is produced by the permanent magnet 11 and thus, the cam 84 remains withdrawn as resisting against a moderate rate of exterior pulling force caused during operation. As the result, the cam 84 allows its corresponding knitting needle to stay unactuated. The stroke length of the movable plunger 5 can be controlled by the two stoppers 85 and 86. It is a good idea that the cam 84 is arranged detachable from the bearing journal 42 for ease of maintenance. Also, it is understood that this arrangement is not limited to the lift-down cam mechanism. Because the plunger bearings are of non-magnetic material, no magnetic energy escapes to the outside of its enclosure. Hence, unwanted collection of iron powder will be avoided and highly accurate, reliable cam actuating movement will be ensured. The movable plunger or ferrous core is spaced a bit from each permanent magnet so that it can slide regardless of critical wear, thus providing a lifelong durability. The knitting machine according to the present invention employs the foregoing improved solenoids arranged for bistable actuation with the use of a minimum force of desired thrust so that less physical shock is involved during the switching movement of cams. Hence, the operational reliability of the solenoids and their relevant components will be much increased. Also, the solenoid is mounted directly to a carriage of the knitting machine so that it directly actuates a corresponding cam in bistable movement. Accordingly, a known link mechanism, e.g. a rocking lever system, is no more needed and the mass of inertia at the actuating section becomes reduced. This permits high-speed operation, low magnetizing power requirement, and energy saving. Furthermore, no clearance adjustment is needed because each cam is directly actuated unlike the known link mechanism and thus, maintenance and servicing of the components or the machine itself will be facilitated.

Claims: A bistable solenoid having an outer enclosure at least partly made of magnetic material, a movable plunger (5) consisting of two end regions (41, 42) and a central region, two permanent magnets (11, 12) arranged a given axial distance apart around the movable plunger (5) so that their magnetic directions are opposite to each other, and two magnetizing coils (21, 22) between which the two permanent magnets (11, 12) are sandwiched, wherein the central region of the plunger (5) is of magnetic material and is arranged to extend coaxially within the outer enclosure and the outer enclosure is provided with two end portions (61, 62) of magnetic material extending radially inwardly to surround the plunger (5), each end portion of the outer enclosure comprising a region adjacent one of the magnetizing coils (21, 22) and having a radial clearance relative to the movable plunger (5), the region axially extending at least along a length corresponding to the distance between the two stable positions of the plunger (5), the length of the central region of the plunger being equal to the sum of the distance between the two stable positions of the plunger (5) and the axial distance between the opposing inner walls of the end portions (61, 62) of the outer enclosure, each end portion of the outer enclosure further comprising plunger bearings (63, 64) for supporting the end regions (41, 42) of the movable plunger (5), radial clearance being provided between the permanent magnets (11, 12) and magnetizing coils (21, 22) on the one hand and the movable plunger (5) on the other hand, the central region of the movable plunger (5) having a portion (52) in which the magnetic permeability is smaller than in both adjacent portions (51, 53) of the central region, characterised in that the end regions (41, 42) of the movable plunger (5) are of non-magnetic material and in that the central region of the plunger comprises a single central portion (52) in which the magnetic permeability is smaller than in both adjacent portions (51, 53) of the central region, so that the distance between the stable positions of the plunger (5) corresponds to the distance between the centres of the two permanent magnets (11, 12). A knitting machine employing the bistable solenoid according to claim 1 for cam drive action of a carriage, characterized in that the solenoid (82) is fixedly mounted to a base plate (81) of the carriage by a retaining member (83) provided on the outer enclosure thereof and its movable plunger (5) is coupled directly to a cam (84) so that the cam (84) can be actuated by the forward and backward movement of the plunger (5).

Inventors: KOYAMA YOSHITERU, YEYAMA HIROYUKI, KOYAMA, YOSHITERU, YEYAMA, HIROYUKI
Applicants: SHIMA SEIKI MFG, SHIMA SEIKI MFG., LTD.
Application year: 1991
Main classification: H01F7
IPC codes: D04B15, H01F7