BACKGROUND OF THE INVENTION Automatic knitting machines use banks of large numbers of closely spaced latch needles to interlock threads in a series of connected loops to produce a knitted fabric. The latch needle is a long flat needle having, at one end, a small hook and a latch which swivels to open and close the hook. The hook ends of the latch needles are moved forwards and backwards towards and away from the threads being knitted into the fabric. As a latch needle is moved, its latch alternately opens and closes so that the hook catches a thread close to it, pulls it to create a loop of fabric, and then releases the thread to start the cycle over again and produce another loop of fabric.

Latch needles are arranged parallel to each other, in arrays of many hundreds to thousands of latch needles in modern knitting machines. The latch needles are placed into narrow latch needle slots which are machined into a large rectangular metal plate. The latch needle slots hold the latch needles in position and confine their motion to linear displacements along the lengths of the latch needle slots. The latch needle slots are parallel to each other and equally spaced one from the other. The spacing between the latch needle slots varies depending upon the quality and type of fabric being produced. Spacing of two to three millimeters is typical, but spacing significantly less than two millimeters is also common. The assembly of slots and the plate into which they are machined are hereinafter referred to as a needle bed.

The latch needle slots in a needle bed are deep enough so that all or most of the body of a needle placed into a slot in a needle bed is completely in the slot and below the surface of the needle bed. Generally, only a small square fin which sticks out from one side of the shaft of the latch needle protrudes above the slot and the surface of the needle bed. The fins of all latch needles in a needle bed are accurately aligned in a single straight row perpendicular to the latch needle slots.

The needles are moved sequentially in groups of a few at a time by a shuttle that moves back and forth parallel to and along the length of the needle bed. As the shuttle moves along the needle bed, fins of the latch needles protruding from the needle bed are engaged by a

channel in the shuttle which faces the needle bed. The fin of each latch needle, in turn enters, the channel at one end of the channel, travels along the channel length as the shuttle moves and at the end of the process exits from the other end of the channel. The channel has a bend in it.

When a fin encounters the bend the fin and its latch needle are moved back and forth along the direction of the latch needle slot in which the latch needle is placed.

The conventional method for moving latch needles in a knitting machine as described above has a number of drawbacks.

In the process of knitting a fabric, dust and dirt accumulate in the slots in which the latch needles move. As the dust and dirt accumulate, more force is required to move the latch needles. However, the shuttle is too massive and moves to quickly for it to be practical to have it be sensitive to or respond to the changing force requirements of individual latch needles in a needle bed. At some point a needle jams in its slot and the force applied to the fin of the latch needle by the shuttle breaks the fin or some other part of the jammed latch needle. When this happens damage is often considerably more extensive than the damage to the single needle that was jammed.

It would be advantageous to have a system for moving the latch needles that would be sensitive to and be able to adjust for changes in the force required to move individual latch needles. In particular it would be advantageous to prevent damage to the knitting machine when a latch needle becomes jammed in its slot.

In prior art as described above individual latch needles in a needle bed are moved sequentially as a shuttle moves along the needle bed. Production rates of fabric produced by knitting machines could be increased if different combinations of latch needles could be moved simultaneously.

There are systems in prior art that provide for individual activation of latch needles in a knitting machine using separate actuators for each needle. However, the prior art systems have not been completely satisfactory. The dimensions of the actuators used in the prior art systems to activate the latch needles are large compared to the spacing between latch needles.

Complicated spatial configurations are therefore required to pack large numbers of them in a convenient volume of space near to the latch needles and to couple them effectively to the latch needles.

The response times of the individual actuators used in prior art systems have also been too slow. The advantage in production rate that should result from individually activating latch

needles is at least partly neutralized by the slow response times of the actuators used in prior art' SUMMARY OF THE INVENTION It is an object of one aspect of the present invention to provide a piezoelectric micromotor for operating individual latch needles in a knitting machine. This motor is small, so that large numbers of them can easily be packed very close to each other for moving latch needles in their slots in a needle bed of the knitting machine.

Piezoelectric micromotors comprise ceramic vibrators that can be formed in the shape of a thin flat plate with two relatively large parallel surfaces and a thickness in the range of from one to a few millimeters. The thickness of the vibrators thus have dimensions that are in the range of the dimensions of the spacing between latch needles in a needle bed. It is therefore possible to pack large numbers of thin vibrators close to each other with their large surfaces parallel and their thin edges aligned with individual latch needle slots in the needle bed.

Transmission of motion from a piezoelectric micromotor to a moveable element is easily performed by coupling the moveable element to a thin edge of the vibrator. Each one of the packed vibrators can therefore be easily coupled to the latch needle in the slot opposite its thin edge.

It is an object of another aspect of the present invention to provide a micromotor, for moving latch needles in their slots in a needle bed of a knitting machine, that has a fast response time, a dynamic range of motion of centimeters and that can apply sufficient force to accelerate latch needles to high velocities quickly.

Response times of piezoelectric micromotors can satisfy the response time requirements of modern knitting machines. The dynamic range of motion available from piezoelectric micromotors and the amount of energy that can be transmitted in short periods of time from piezoelectric micromotors to moveable elements are also consistent with the requirements of modern knitting machines.

It is also an object of the present invention to provide a knitting machine for knitting fabric where each latch needle in the knitting machine is moved by its own piezoelectric micromotor.

In a knitting machine in accordance with a preferred embodiment of the present invention a bearing shaft is provided on which a large plurality of annuli are stacked. The annuli rotate freely on the bearing shaft. The bearing shaft is mounted over a latch needle bed

with parallel latch needle slots in which latch needles with fins are placed. The axis of the bearing shaft is perpendicular to the parallel latch needle slots in the latch needle bed and close to the fins of the latch needles. The spacing between the annuli on the shaft is such that each annulus on the shaft is connected by a, preferably rigid, connecting arm to a fin of a latch needle in the latch needle bed. The connecting arm from an annulus to a fin is attached to the fin preferably by a slideable or flexible joint formed by methods known in the art.

Each annulus on the bearing shaft is coupled to one or more piezoelectric micromotors by methods known in the art, as for example, by resiliently pressing the motors against the annulus. Activation of the piezoelectric micromotors coupled to an annulus causes the annulus to rotate. The rotation of the annulus is transmitted to the fin of the latch needle, to which the annulus is connected, by the connecting arm. The joint connecting the connecting arm translates the rotational motion of the connecting arm to a linear motion of the latch needle backwards and forwards in the latch needle slot and parallel to the latch needle slot.

A knitting machine in accordance with an alternative embodiment of the present invention translates the vibration of piezoelectric micromotors directly into linear motion of latch needles placed into latch needle slots in a needle bed of a knitting machine. One or more piezoelectric micromotors in accordance with a preferred embodiment of the present invention are preferably pressed, by resilient forces, directly onto the shaft or onto suitable extensions of the shaft of each latch needle in the latch needle bed. The latch needle slots and/or the surfaces of the needles in contact with the latch needle slots, are preferably provided with bearings or nonstick surfaces so that latch needles do not jam or stick in their latch needle slots under the application of the resilient forces. Coupled in this way, when the micromotor or micromotors that are pressed to a latch needle shaft or extension thereof are activated, the vibration of the micromotor or micromotors cause the latch needle to move backwards and forwards in its latch needle slot.

There is thus provided, in accordance with a preferred embodiment of the invention, a knitting machine comprising: a needle bed with a plurality of latch needles in latch needle slots; and a plurality of piezoelectric micromotors at least equal to the number of latch needles, wherein each micromotor is coupled to one of the latch needles such that activation of the motors coupled to a latch needle causes movement of the latch needle in its latch needle slot.

Preferably the knitting machine comprises a bearing shaft mounted parallel with the needle bed, wherein the bearing shaft is stacked with a plurality of annuli which are

independently rotatable about the axis of the bearing shaft. Each annulus preferably has at least one of the plurality of piezoelectric micromotors resiliently pressed against it such that activation of the at least one piezoelectric micromotor rotates the annulus. Preferably each latch needle is connected by a, preferably rigid, arm to a single one of the plurality of annuli, such that rotation of an annulus causes linear motion of a latch needle in its latch needle slot.

The arm is preferably connected to the latch needle by a slideable connection.

Alternatively, the arm is preferably connected to the latch needle by a flexible connection.

Alternatively, a shaft of each of the latch needles has preferably at least one of the plurality of piezoelectric micromotors pressed to it so that activation of the at least one micromotor causes linear motion of the latch needle in its latch needle slot.

Preferably, the latch needle slots are provided with bearings. Alternatively or additionally, the latch needle slots are preferably provided with a non stick surface. Preferably, the latch needles are provided with bearings. Alternatively or additionally, the latch needles are preferably provided with non stick surfaces.

There is further provided, in accordance with a preferred embodiment of the invention, a motor system for moving latch needles in a needle bed of a knitting machine comprising: a shaft; a plurality of piezoelectric micromotors; and a plurality of rotatable elements linked to said latch needles rotatably mounted on the shaft, wherein each of the plurality of piezoelectric micromotors resiliently engages an element and rotates the element.

Preferably the rotatable element has a rigid extension adapted for connection to latch needles in a needle bed of a knitting machine. The rigid extension is preferably provided with an end that is adapted for forming a slideable connection to a latch needle. Alternatively, the rigid extension is preferably provided with an end that is adapted for forming a flexible connection to a latch needle.

Alternatively, each of the plurality of rotatable elements is preferably resiliently pressed to a latch needle.

There is further provided, in accordance with a preferred embodiment of the invention, a method for moving latch needles in slots in a needle bed of a knitting machine comprising: rotatably mounting a plurality of annuli on a shaft; connecting each latch needle in the needle bed to a different rotatable annulus; and rotating each annulus. Preferably connecting each needle to a single rotatable annulus comprises connecting the latch needle to an annulus using a rigid arm. Preferably a slideable connection between the arm and the latch needle is provided.

Alternatively, a flexible connection between the arm and the latch needle is preferably provided.

Preferably, rotating each annulus comprises rotating each annulus with at least one motor connected only to that annulus. Preferably, the at least one motor is a piezoelectric micromotor. Preferably, at least one piezoelectric micromotor is resiliently pressed to the edge of each annulus.

Alternatively, the at least one motor is a rotary piezoelectric micromotor. Preferably, a rotor of the rotary piezoelectric motor is resiliently pressed to the outside edge of each annulus.

Alternatively, a rotor of the rotary piezoelectric motor is preferably resiliently pressed to the inside edge of each annulus. Alternatively, a rotor of the rotary piezoelectric motor is preferably resiliently pressed to a plane surface of each annulus.

There is further provided a method for moving latch needles in slots in a needle bed of a knitting machine comprising: pressing at least one piezoelectric micromotor to a shaft of each latch needle; and activating the at least one piezoelectric micromotor. Preferably, the slots in the needle bed are provided with bearings. Alternatively or additionally, the slots in the needle bed are preferably provided with a non stick surface. Alternatively or additionally, the latch needles are preferably provided with bearings. The latch needles are, alternatively or additionally, preferably provided with non stick surfaces.

In a preferred embodiment of the invention the piezoelectric micromotor is a rotary piezoelectric micromotor. Preferably a rotor of a rotary piezoelectric motor is resiliently pressed to the shaft of each latch needle.

The invention will be more clearly understood by reference to the following description of preferred embodiments thereof in conjunction with the figures in which: BRIEF DESCRIPTION OF FIGURES Fig. 1 shows the basic structure of a latch needle; Fig. 2 is a schematic illustration of a conventional system for activating latch needles in a knitting machine; Fig. 3 is a schematic illustration of a system for coupling piezoelectric vibrators to latch needles in a needle bed by rotary transmission, in accordance with a preferred embodiment of the present invention;

Fig. 4 shows a schematic of a system for coupling piezoelectric vibrators to latch needles in a needle bed by linear transmission in accordance with an alternative preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 shows a profile of a latch needle 20. Latch needle 20 is a thin metallic structure with a long shaft 22 having a hook 24 and a tip 30 formed on one of its ends. A latch 26 is rotatable about a pivot 28 and is shown in the figure in the position where it caps tip 30 to close hook 24 and prevents hook 24 from hooking a thread. In an open position latch 26 is rotated clockwise almost to a position where it is parallel to shaft 22. A fin 32 extends out from shaft 22, generally on the same side of shaft 22 as hook 24.

Fig. 2 is a schematic illustration of the arrangement of needle beds in a conventional knitting machine and a shuttle which transmits motion to latch needles in the needle beds.

Two needle beds 36 and 38 are rigidly joined at an angle to each other so that an edge 39 of needle bed 36 is close to and parallel to an edge 40 of needle bed 38. A long narrow space 44 separates edge 39 and edge 40. Needle beds 36 and 38 are identical or very similar and detailed discussion will be confined to needle bed 36 with the understanding that details and structures described for needle bed 36 apply to needle bed 38.

Threads to be woven into fabric (not shown) are held under tension close to and parallel to edges 39 and 40. Fabric (not shown), as it is produced moves downwardly from edges 39 and 40 into space 44. As the fabric moves down it exits the knitting machine.

Needle bed 36 is provided with an array of equally spaced parallel latch needle slots 42 which are perpendicular to edge 39. A latch needle 20 is placed in each latch needle slot 42.

The bodies of latch needles 20 are completely inside latch needle slots 42 and are not visible.

Only fins 32 of latch needles 20 protrude above the surface of needle bed 36 and are visible.

Fins 32 of all latch needles 20 that are at rest in slots 42 are aligned along a straight row which is perpendicular to latch needle slots 42. Each needle 20 is moveable back and forth in its latch needle slot 42.

A shuttle 46, having ends 52 and 54, moves back and forth parallel to edges 39 and 40 along the length of needle bed 36. An interior face 48 of shuttle 46 is parallel to needle bed 36 and has a channel 50 formed in the face. Channel 50 is open on both ends 52 and 54 of shuttle 46. The two open ends of channel 50 are in line with the row of fins 32. A section 56 of

channel 50 is not collinear with the ends of channel 50. Channel 50 is just wide enough and deep enough so that fins 32 can pass into and move through it.

As shuttle 46 moves back and forth with interior face 48 parallel to latch needle bed 36, fins 32 of latch needles 20 enter channel 50 at one end and move along the length of channel 50. When a fin 32 of a latch needle 20 encounters non-collinear section 56 of channel 50 the fin 32 and the latch needle 20 to which fin 32 is attached are displaced parallel to latch needle slot 42 in which the latch needle 20 is found. In Fig. 2, for clarity of presentation, only a few of latch needles 20 that are moving in channel 50 are shown.

Fig. 3 shows a system for coupling each of the latch needles in a needle bed to its own separate piezoelectric micromotor according to a preferred embodiment of the present invention. A long shaft 58 is mounted over a needle bed 60 which is provided with slots 62 into which have been placed latch needles 63. Shaft 58 is mounted with a multiplicity of thin annuli 64, one annulus for each latch needle (for clarity only three are shown). The annuli rotate freely on axis 58. Each annulus is positioned opposite a fin 65 of a particular latch needle 63. A connecting arm 66 connects each annulus 64 to a point 68 on fin 65, to which annulus 64 is opposite. The connection at point 68 is a flexible or slideable connection produced by methods known in the art. One or more piezoelectric micromotors 70, 72, and 74, are resiliently pressed against each annulus 64 by methods known in the art. When piezoelectric micromotors 70, 72, and 74, are activated they cause annulus 64 and connecting arm 66 to rotate, which in turn moves latch needle 63 linearly in its slot 62. The flexible connection at point 68 translates rotational motion of arm 66 to linear motion of latch needle 63. It should be understood that this arrangement allows for a much higher speed of the latch needle than that available from the motor itself.

While three piezoelectric micromotors are shown in Fig. 3 more or fewer micromotors may be used depending on the speed or torque required for motion of the needle. Also, other types of piezoelectric micromotors of different construction than the ones shown in Fig. 3 and described above may be used to rotate annulus 64 and are advantageous. U.S. patent 4,562,374 and the publication by Hiroshi et al., IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 42, No. 2, March 1995, herein incorporated by reference, describe rotary piezoelectric micromotors comprising a cylindrical, annular or disc shaped rotor which is caused to rotate by coupling to a stator which is a cylindrical, annular or disc shaped vibrator. The rotor and stator are concentric. A vibrating surface of the stator is coupled to an

inside edge surface or an outside edge surface of the rotor to impart a rotary motion to it.

Alternatively, a vibrating surface of the stator may be coupled to a face surface of the rotor to impart rotational motion to the rotor. Annulus 64 can be rotated by the use of stators similar to those described in the above references. Annulus 64 is coupled to the stators in similar fashion to the way that the rotors are coupled to the stators in the described rotary piezoelectric micromotors.

Fig. 4 shows another system for coupling each of the latch needles in a needle bed to its own separate piezoelectric micromotor or micromotors according to an alternative preferred embodiment of the present invention.

A latch needle bed 76 is provided with latch needle slots 78 in which are placed latch needles 80. One or more thin piezoelectric micromotor 82 is resiliently pressed against the shaft 84 of each latch needle 80 (only one is shown for each latch needle for simplicity).

Piezoelectric micromotors 82 on adjacent latch needles 80 are in line with each other so that they form a straight row. Alternatively, piezoelectric micromotors 82 may be staggered with respect to each other so that they are arrayed in two or more parallel rows. Fig. 3 shows an embodiment according to the present invention where piezoelectric micromotors are aligned in two parallel rows. Staggered configurations allow for more space between closely packed vibrators 82 than would be available if vibrators 82 were arrayed in a single row and thus allow for thicker more powerful piezoelectric micromotors to be coupled to latch needles 63.

Vibrations of piezoelectric micromotors 82 are directly translated into linear motion of latch needles 80. Slots 78 are fitted with bearings (not shown) or with a non-stick surface so that the resilient force which presses a vibrator 82 to a shaft 84 of a needle 80 does not result in excessive friction between needle 80 and the bottom or sides of latch needle slot 78 in which needle 80 is placed.

Rotary piezoelectric micromotors similar to those described in U.S. patent 4,562,374 and the publication by Hiroshi et al. cited above may also be used to drive latch needles 80.

The edge surface of a rotor of a rotary piezoelectric micromotor is resiliently pressed against shaft 84 of each latch needle 80. The axes of the rotors are perpendicular to latch needle slots 78 in which latch needles 80 are placed. Frictional forces at the area of contact between the edge surface of a rotor and the surface of shaft 84 of a needle 80 acts to prevent the edge surface of the rotor from slipping on the surface of shaft 84 when the rotor rotates. As the rotor rotates it therefore causes shaft 84 of latch needle 80 to displace linearly in latch needle slot 78

in which latch needle 80 is placed in the direction of motion of the mass points of the edge surface of the rotor which are in contact with the surface of shaft 84.

It is clear from the above discussion that piezoelectric micromotors in accordance with preferred embodiments of the present invention can be conveniently coupled to latch needles in a latch needle bed of a knitting machine so that each latch needle is coupled to its own piezoelectric micromotor.

Variations of the above described preferred embodiments will occur to persons of the art. The above detailed description is provided by way of example and is not meant to limit the scope of the invention which is limited only by the following claims.