Abstract:
A needle selector for knitting machines is provided, which includes a finger actuating device, a power supply means for feeding electric power to the finger actuating device, and power supply terminals for supplying power to the power supply means, wherein said finger actuating device fast and steadily operates piezoelectric bodies  7  including piezoelectric elements by bending them while supporting the piezoelectric bodies  7  at the tip, rear end and a prescribed position between the tip and the rear end, and using a power supply means including of bar-shaped electrodes  28  each including at least two conductive parts with an insulating part in-between, resulting in a substantial reduction in size.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a needle selector for use in knitting machines such as circular knitting machines and weft knitting machines, and more particularly to a needle selector for use in knitting machines in which knitting needles are selected by a piezoelectric drive mechanism. 
     2. Description of the Related Art 
     In a knitting machine such as a circular knitting machine or a weft knitting machine, vertical motions of the knitting needle are selected in accordance with a knitting procedure stored in a recording medium, such as a floppy disk or the like, to knit a fabric of the desired texture. Various needle selectors are used for selecting that vertical motions of the knitting needle. 
     Before describing the needle selector according to the present invention, an outline of needle selection in a knitting machine will be explained with reference to a circular knitting machine schematically illustrated in FIGS. 6A through 6C. 
     FIG. 6A shows a schematic perspective view of the basic knitting mechanism of a circular knitting machine. As illustrated in FIG. 6A, in the circular knitting machine, knitting needles  2  are arranged slidably in a plurality of vertical grooves (not shown) around the circumference of a knitting cylinder  1 , rotating in the direction indicated by an arrow A, the grooves being provided along the lengthwise axis of the knitting cylinder  1 . Underneath the knitting needles  2  are usually disposed needle selection jacks  12  to permit contact with the lower parts of the knitting needles  2 . On the other hand, underneath the knitting cylinder  1  is statically arranged a cylindrical cam base  15   a,  and on the upper part of that cam base are disposed a plurality of cams  15  of a prescribed shape at prescribed intervals. 
     The basic principle of knitting is such that each of the knitting needles  2  on the rotating knitting cylinder  1  is thrust upward via the needle selection jack  12 ; a yarn loop is made by feeding yarn  5 , taken up from a yarn bobbin  6  into the hooks of a knitting needle  2  projecting from the upper face of the knitting cylinder  1 , as a result; and one stitch is formed by lowering the knitting needle  2  with a known mechanism (not shown). Therefore, a desired fabric can be knit by opting either to give a vertical motion to each knitting needle  2  or to allow advancing to the next step of knitting without forming a stitch. In order to provide such motions to knitting needles, in a knitting machine, needle selection jacks  12  are usually arranged underneath and in contact with knitting needles  2 , and the vertical motions of the knitting needles are controlled by using a needle selector  3 , operating on the basis of information from a controller  4  with a built-in knit texture memory device, to selectively engage the needle selection jacks  12  with the knitting needles  2 . 
     Next will be described with reference to FIGS. 6B and 6C, illustrating the relationship between the selection jacks and the needle selecting means, an instance in which piezoelectric bodies, which are used according to the present invention, are used as means of knitting needle selection. 
     A piezoelectric body  47  can be either bent in the way shown in FIG. 6B or in the way shown in FIG. 6C, reverse to the bend illustrated in FIG. 6B, depending on how a voltage is applied. At the tip of the piezoelectric body  47  is arranged a finger  9  linked to it. In FIGS. 6B and 6C, the piezoelectric body  47 , the finger  9  and a raising cam  15  are positioned within the frame of a drawing, and the knitting needles  2  and the needle selection jacks  12  move circularly together with the knitting cylinder  1  (not shown) from the top to the bottom of the frame of the drawing (or in the reverse direction). The needle selection jacks  12  can swing pivoting on fulcrums  12   a,  and in the upper part are provided needle selection butts  13  and raising cam butts  14  projecting sideways from the needle selection jacks  12  as illustrated. 
     When the piezoelectric body  47  is curved as shown in FIG. 6B, the needle selection butts  13  of the needle selection jacks  12 , which circularly move, hit the finger  9 , and the resultant thrusting of the needle selection jacks  12  in the clockwise direction, pivoting on the fulcrums  12   a,  prevents the raising cam butts  14  from engaging with the raising cam  15  of the needle selection jacks  12 . Therefore, the needle selection jacks  12  fail to be thrust upward by the raising cam  15 , and at the same time the knitting needles  2  fail to be thrust upward. 
     When the piezoelectric body  47  is curved as shown in FIG. 6C, the finger  9  at the tip of the piezoelectric body  47  does not hit the needle selection butts  13  of the needle selection jacks  12  which circularly move together with the knitting cylinder  1 , and the needle selection jacks  12  remain in the vertical direction with the result that the raising cam butts  14  at the lower ends of the needle selection jacks  12  are thrust upward along the inclined face of the raising cam  15 , the knitting needles  2  being thrust upward along with the thrust. 
     Selective engagement of the needle selection butts  13  of the needle selection jacks  12  with the finger  9  at the tip of the piezoelectric body  47  enables the knitting needles  2  to move upward freely as desired and thereby enables a knit fabric of any desired texture to be knit. 
     The single most important performance feature for knitting is high productivity, i.e. the possibility to rotate the knitting cylinder faster. In order to turn the knitting cylinder faster, it is necessary to enable the needle selector for controlling upward shifting of the knitting needles to operate faster. For this reason, various fast operating knitting needle selectors have been developed and came into use. 
     For instance, the same applicant as that for patent on the present invention proposed a needle selector configured to enable a plurality of fingers to be swung by an attractive or repulsive force of an electromagnet (see Japanese Patent Laid-Open No. 60-224845), which is both faster and more compact than conventional needle selectors and moreover can save electric power consumption. Further, the same applicant as that for patent on the present invention proposed a piezoelectric needle selector which causes knitting needles to be selected by operating the fingers themselves by the bending of piezoelectric bodies in place of the above-cited electromagnetic needle selector (see Japanese Patent Laid-Open No. 62-28451), which achieved further advances in speed increase, size reduction and energy saving for needle selectors. 
     The same applicant as that for patent on the present invention further invented an improved version of the aforementioned piezoelectric needle selector, and filed on Oct. 5, 1988 the Japanese Patent Application No. 63-249967 for that invention, entitled “Needle Selector for Knitting Machines.” This was registered as the Japanese Patent No. 1969970, and the corresponding U.S. patent application was registered as U.S. Pat. No. 5,027,619. 
     This improved piezoelectric needle selector is illustrated in FIG.  7 A. To describe this improved version on the basis of claim  1  of Japanese Patent No. 1969970 with reference to FIG. 7A, this is a knitting needle selector in which fingers  9  are arranged to be movable relative to piezoelectric bodies  7  each having a piezoelectric element; electric power is applied to the piezoelectric elements to actuate the fingers  9 ; this motion of the fingers  9  causes knitting needles of the knitting machine to be selected (via needle selection jacks); and knitting of a fabric of a prescribed pattern texture is made possible. The rear end of each piezoelectric body  7  is characterized by being movably supported via a spherical body, i.e. a rotary body  20 , by a support  21  or a concave part  22  of a housing; the tip of the piezoelectric body  7  is characterized by being movably linked via a spherical body, i.e. a rotary body  16 , into a U-shaped groove  17  at the rear end of the finger  9 ; a prescribed position between the rear end and the tip of the piezoelectric body  7  is characterized by being pinched by a rotary body  23  rotatably fitted to a support  34  or the housing, and the finger  9  and the piezoelectric body  7  are characterized by being arranged on a straight line. 
     The finger  9 , as illustrated in FIG. 7A, its intermediate part is borne by a support  10   b  through a pin  8 , and this arrangement causes any flexion of the piezoelectric body  9  to move the rear end  9   a  of the finger  9  up and down with the result that the tip  9   b  of the finger  9  projecting through the opening  11  of the support  10   a  is thereby moved up and down and this vertical motion causes the rising motion of the knitting needle  2  to be selected. 
     The bearing of the piezoelectric body  7  movably in a prescribed position enables the piezoelectric body to freely bend, resulting in a significant increase in the acting speed of the finger  9  and moreover, as it was found, an increase in the shifting quantity of the tip of the finger  9 . Furthermore, the use of the piezoelectric body in such a configuration serves to reduce damage to the piezoelectric body and thereby to elongate the useful life of the needle selector. 
     Therefore, this improved piezoelectric needle selector, as its finger actuating device to swing the finger member is innovatively improved, represents a significant enhancement in needle selecting capability, but the electric power supply means to feed power to the finger actuating device in the needle selector is substantially of the same performance standard as any conventional means. Thus, as shown in FIG. 7B illustrating the overall configuration of the aforementioned improved piezoelectric needle selector, in order to supply electric power to the piezoelectric body  7 , electrodes  25  should be provided on the surface of the piezoelectric body  7 , and these electrodes  25  are connected by wires  27  to connectors  26  of a connector supporting board B. Though wire connection is a very simple structure, at least two wires  27  are needed per piezoelectric body  7 , and moreover wire connection of two electrodes requires a space of a certain size, resulting in large hardware dimensions, the risk of accidental wire disconnection and a high cost of wire fitting. Therefore, this configuration lags behind the remarkable performance improvement of the finger actuating device, and has obstructed further size reduction of needle selectors for knitting machines. 
     An object of the present invention is to solve the above-noted problems preventing the overall performance improvement and size reduction of needle selectors for knitting machines, as a result of the lag of improvement of power supply means behind the improvement of the finger actuating device itself in known such selectors according to the prior art, and accordingly to provide a needle selector for knitting machines, which is improved in performance and reduced in dimensions. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a needle selector for knitting machines consisting of a finger actuating device, in which a plurality of piezoelectric bodies are arranged so that the planar surfaces of the piezoelectric bodies overlap one another at prescribed intervals, each of the piezoelectric bodies being movably supported at the tip, in the middle and at the rear end, the piezoelectric bodies are caused to bend by the feeding of electric power and thereby to swing finger members arranged at the tips of the piezoelectric bodies; and a power supply means for feeding electric power to the finger actuating device, characterized in that: the power supply means comprises bar-shaped electrodes each having at least two conductive parts with an insulating part in-between and a slit into which the rear end of one of the piezoelectric bodies can be fitted, and a mechanism for selectively supplying electric power to at least two conductive parts of each of the bar-shaped electrodes, the rear ends of the piezoelectric bodies being inserted into the slits of the bar-shaped electrodes to achieve electrical connection. 
     According to another aspect of the invention, there is provided a needle selector for knitting machines wherein members for supporting the rear ends of the piezoelectric bodies are formed as bar-shaped electrodes, and each of these bar-shaped electrodes has at least two conductive parts and a slit into which the rear end of a piezoelectric body can fit, so that the piezoelectric body can be fed with at least two kinds of electric power by a simple manipulation of merely inserting the rear end of the piezoelectric body into the slit of this bar-shaped electrode, dispensing with the need, as is the case with the conventional needle selector shown in FIG. 7B, to provide electrodes on piezoelectric bodies and to wiring the connection between the electrodes and the power supply terminals of the needle selector, thereby contributing to reducing the dimensions of the needle selector. 
     The cross-sectional shape of the bar-shaped electrodes should be preferably, but need not be round, and it may be square or polygonal as long as the rear end of a piezoelectric body is movable relative to the frame of the needle selector. In that case, the corners of the polygonal cross section should preferably be arc-shaped because this would not only smoothen their turning as piezoelectric body rear end supports for the bar-shaped electrodes but also contribute to enhanced durability. 
     In order to enable the piezoelectric bodies to bend, at least two kinds of electric potentials should be provided as will be described in further detail below with reference to a drawing. Therefore, at least two conductive parts need to be provided via an insulating part in-between in the lengthwise direction of the bar-shaped electrodes. To add, where two conductive parts are used, it is recommended that one of the conductive parts be maintained at a zero electric potential while the other conductive part be fed with a positive potential and a negative potential, alternately. 
     Or where three conductive parts are used, it is recommended to maintain one at a zero electric potential while the other two conductive parts be fed with a positive potential, alternately. Further, the aforementioned at least two conductive parts should preferably be provided continuously over at least the slit part and the area receiving electric power from the power supply mechanism of the bar-shaped electrodes. 
     It is also preferable to coat the aforementioned conductive parts with oxidation-resistant metal, such as gold or palladium. It is further preferable to form this coat by plating necessary parts of the bar-shaped electrode bodies made of plastic material. However, the method of coating is not restricted to plating. For instance, parts required to be conducting may be composed of insert members made of oxidation-resistant metal. 
     Preferably, too, the finger actuating device may comprise a plurality of piezoelectric bodies disposed in parallel; the bar-shaped electrodes may have two conductive parts each; the mechanism for feeding electric power to the conductive parts of the bar-shaped electrodes comprise two power supply plates arranged on the two sides of the plurality of piezoelectric bodies disposed in parallel; and a bar-shaped electrode fitting member having a plurality of concave parts, which keep the two power supply plates at a distance from each other substantially equal to the length of the bar-shaped electrodes and into which the bar-shaped electrodes are inserted; wherein a contact area in contact with both ends of the bar-shaped electrodes for supplying power is provided inside each of the two power supply plates, and power is supplied to the conductive parts via the respective contact areas. 
     Also preferably, the finger actuating device comprises a plurality of piezoelectric bodies disposed in parallel; the bar-shaped electrodes have three conductive parts each; the mechanism for feeding electric power to the conductive parts of the bar-shaped electrodes comprise two power supply plates arranged on the two sides of the plurality of piezoelectric bodies disposed in parallel; and a bar-shaped electrode fitting member having a plurality of concave parts, which keep the two power supply plates at a distance from each other substantially equal to the length of the bar-shaped electrodes and into which the bar-shaped electrodes are inserted; wherein a contact area in contact with both ends of the bar-shaped electrodes for supplying power is provided inside each of the two power supply plates, power is supplied to the conductive parts on the both ends of the bar-shaped electrodes via the respective contact areas, a groove crossing the concave parts is provided along the lengthwise direction of the bar-shaped electrode fitting member in an area matching the conductive parts in the middle of the bar-shaped electrodes, a conductive layer is provided along the groove, and power is supplied via the conductive layer to the conductive parts in the middle. 
     It is further preferable to elastically dispose in the contact area a contact member formed by arranging a plurality of conductive thin wires substantially in parallel. 
     It is also preferable to form the conductive layer by arranging a plurality of conductive thin wires substantially in parallel and disposing them elastically along the groove. 
     As the piezoelectric bodies, unimorphic piezoelectric bodies can be used. In this case, it is advisable to supply electric power from the upper and lower faces of the piezoelectric bodies. 
     As the piezoelectric bodies, bimorphic piezoelectric bodies can also be used. In this case, it is advisable to supply electric power from the upper, lower and side faces of the piezoelectric bodies. 
     When multilayer piezoelectric bodies are used as the piezoelectric bodies, electric power is supplied from the side faces of the piezoelectric bodies. 
     A needle selector for knitting machines according to the present invention can be effectively used for various circular knitting machines and weft knitting machines including hosiery machines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A through 1C illustrate a structure of one preferred embodiment of a needle selector for knitting machines according to the present invention; FIG. 1A is a schematic profile, FIG. 1B, a schematic plan, and FIG. 1C, a schematic perspective view , all depicting the structure of bar-shaped electrodes; 
     FIGS. 2A through 2C are schematic profiles of a piezoelectric body for use in the needle selector for knitting machines according to the invention; FIG. 2A is a schematic profile of a unimorphic piezoelectric body, FIG.  2 B, a schematic profile of a bimorphic double electrode type piezoelectric body, and FIG. 2C, a schematic profile of a bimorphic triple electrode type piezoelectric body; 
     FIGS. 3A through 3E illustrate various modes of forming a bar-shaped electrode for use in the needle selector for knitting machines according to the invention; FIGS. 3A and 3B show an example in which conductive parts are produced by plating; FIG. 3A is an axial cross section passing a slit, and FIG. 3B, a lateral cross section on the line B—B in FIG. 3A; FIGS.  3 C through FIG. 3E illustrate a bar-shaped electrode using an insert member; FIG. 3C is an axial cross section passing the slit, FIG. 3D, a cross section on the line D—D of FIG. 3C, and FIG. 3E, a cross section on the line E—E of FIG. 3C; 
     FIGS. 4A and 4B illustrate the structure of another embodiment of a bar-shaped electrode for use in the needle selector for knitting machines according to the invention; FIG. 4A is a perspective view of the bar-shaped electrode, and FIG. 4B, a cross section on the plane X-Y of FIG. 4A; 
     FIGS. 5A through 5D illustrate one example of power supply means for use in the needle selector for knitting machines according to the invention; FIG. 5A is an exploded perspective view of the power supply means, FIG. 5B, a front view showing the inside of a power supply plate, FIG. 5C, a profile of a bar-shaped electrode fitting member, and FIG. 5D, a front view of the bar-shaped electrode fitting member; 
     FIGS. 6A through 6C illustrate the knitting mechanism of a known circular knitting machine according to the prior art; FIG. 6A is a schematic perspective view of the basic knitting mechanism of a circular knitting machine, FIG. 6B, a schematic profile illustrating the relationship among knitting needles, needle selection jacks and a needle selecting means in a state in which a matching knitting needle is not selected, and FIG. 6C, a schematic profile illustrating the relationship among knitting needles, needle selection jacks and a needle selecting means in a state in which a matching knitting needle is selected; and 
     FIGS. 7A and 7B are schematic profiles illustrating a known knitting machine according to the prior art, which constitutes the basis of a needle selector for knitting machines according to the present invention and uses, as does the present invention, a piezoelectric drive mechanism as the needle selecting means; FIG. 7A is a middle vertical cross section illustrating the configuration of a piezoelectric body corresponding to a finger actuating device hereunder, and FIG. 7B, a schematic profile of a needle selector provided with three units of the piezoelectric body shown in FIG.  7 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be described in detail below with reference to accompanying drawings illustrating preferred embodiments of the needle selector for knitting machines according to the invention. 
     FIG. 1A is a schematic profile of a preferred embodiment of the needle selector for knitting machines, FIG. 1B, a schematic plan of the same, and FIG. 1C, a schematic perspective view of an embodiment of a bar-shaped electrode for use in the needle selector. 
     In a needle selector  3  illustrated in FIG. 1A, three piezoelectric bodies  7  are arranged in a horizontal direction at substantially equal vertical intervals. The number of piezoelectric bodies  7  in one needle selector  3 , which can be determined as desired according to the type of the knitting machine on which the needle selector  3  is to be mounted, is usually two to eight. At the tip (the left side in FIG. 1A) of each piezoelectric body  7  is fixed a rotational body  16 , and to the rear end (the right side in FIG. 1A) of the same is fitted a bar-shaped electrode  28 . In further detail, the tip of the piezoelectric body  7  is movably engaged into a U-shaped groove  17  at the rear end of a finger  9  via the fixed rotational body  16 , while the rear end of the piezoelectric body  7  is fitted to the bar-shaped electrodes  28  by being fitted into a slit  31  provided into the circumference of the bar-shaped electrodes  28  shown in FIG. 7C in the lengthwise direction. A prescribed position between the tip and the rear end of the piezoelectric body  7  is pinched by a rotational body  23  rotatably fitted to a support  24  or a housing. Further, as shown in FIG. 7A, the finger  9  and the piezoelectric body  7  are arranged on a straight line. 
     The finger  9 , as illustrated in FIG. 1A, is supported in its middle part by a support  10   b  with a pin  18 , so that, when the piezoelectric body  7  is bent, that bending motion causes the rear end (the right side in FIG. 1A) of the finger  9  to move up and down with the result that the tip (the left side in FIG. 1A) of the finger  9  projecting through an opening  11  in the support  10   a  moves vertically and thereby a raising motion of a knitting needle  2  is caused to be selected. 
     As the piezoelectric bodies  7  for use in the needle selector according to the invention, either unimorphic piezoelectric bodies or bimorphic piezoelectric bodies can be used. FIG. 2A is a vertical cross section illustrating an example of unimorphic piezoelectric body. As shown in FIG. 2A, a unimorphic piezoelectric body  7   a  consists of a ceramic piezoelectric element  41  provided with silver layers  42   a  and  42   b  on the top and bottom faces, and underneath the silver layer  42   b  is stuck a thin metallic plate  100 . A conducting circuit extends from the silver layer  42   a  to an electrode  43 A and from the thin metallic plate  100  extends a conducting circuit to the electrode  43 B. 
     Where a unimorphic piezoelectric element shown in FIG. 2A is used, for instance by supplying a potential of 0 V to the electrode  43 A and a positive or negative voltage to the electrode  43 B, either of two states can be achieved in which the piezoelectric element is flexed upward or downward. The states illustrated in FIGS. 6B and 6C can be respectively achieved by these two states of the piezoelectric element. 
     Both FIGS. 2B and 2C are vertical cross sections illustrating on example of a bimorphic piezoelectric body. The bimorphic piezoelectric body consists of a metallic plate  44 , known as a shim, and piezoelectric elements  41 A and  41 B arranged on the two faces of the metallic plate  44 , and silver layers  42   a  and  42   b  are provided over the elements  41 A and  41 B, respectively. The bimorphic piezoelectric body has two versions, i.e. a double electrode type  7   b  shown in FIG. 2B and a triple electrode type  7   c  shown in FIG. 2C, depending on the way of applying a voltage. In the double electrode type  7   b,  conducting circuits extending from the two piezoelectric elements are connected to one electrode  43 A, and the shim  44  is connected to the other electrode  43 B. In this case, the polarizing directions of ceramic are as indicated by arrows  45   a  and  45   b.  In the double electrodes type  7   b,  if the electrode  43 A is kept at a zero potential and a plus potential is provided to the electrode  43 B, i.e. to the shim  44 , the piezoelectric element  41 A will contract and the piezoelectric element  41 B will extend. Conversely, if a minus potential is provided to the electrode  43 B, the piezoelectric element  41 A will extend and the piezoelectric element  41 B will contract. As a result, the piezoelectric body  7   b  will bend significantly, though the piezoelectric elements will tend to become depolarized in this case because a voltage is applied in a direction reverse to the polarizing direction of the ceramic. 
     Where a bimorphic double electrode piezoelectric element shown in FIG. 2B is used, for instance by supplying a potential of 0 V to the electrode  43 B and a positive or negative voltage to the electrode  43 A, either of two states can be achieved in which the piezoelectric element is flexed upward or downward. The states illustrated in FIGS. 6B and 6C can be respectively achieved by these two states of the piezoelectric element. 
     In the triple electrode type piezoelectric body  7   c,  as shown in FIG. 2C, the electrode  43 C is connected to the conducting circuit extending from the shim  44 , the electrode  43 A, to the piezoelectric element  41 A, and the electrodes  43 B, to the piezoelectric element  41 B. The electrode  43 C is kept at a zero potential. In this case, when the electrode A is electrified and a voltage is applied to the piezoelectric element  41 A, the electrode B is not electrified and no voltage is applied to the piezoelectric element  41 B. Conversely, when a voltage is applied to the piezoelectric element  41 B, no voltage is applied to the piezoelectric element  41 A. Therefore, this triple electrode type is bent only half as much as the double electrode type, but it is less likely to be depolarized than the double electrode type piezoelectric body  7   b  because, as indicated by arrows  46   a  and  46   b  in FIG. 2C, the voltage is applied in the polarizing direction of ceramic. For this reason, the bimorphic triple electrode type piezoelectric body  7   b  is extensively as used as a multilayer piezoelectric body. 
     Thus, a bimorphic triple electrode type piezoelectric element such as the one shown in FIG. 2C, two states of which one is upward flexion and the other is downward flexion of the piezoelectric element can be achieved by, for instance, supplying a potential of 0 V to the electrode  43 C and alternately applying a positive voltage to the electrodes  43 A and  43 B. The two states illustrated in FIGS. 6B and 6C can be respectively achieved by these two states of the piezoelectric element. 
     FIG. 1C illustrates a bar-shaped conductor of a type preferred for use in the knitting needle selector of this embodiment, and gives a perspective view of the structure of the bar-shaped conductor for use in the triple electrode type piezoelectric body shown in FIG.  2 C. The bar-shaped conductor shown in FIG. 1C is configured to have a round cross section. The reason is that a round cross section enables the support of the rear end of a piezoelectric body to be freely varied when the bar-shaped conductor is held by the support of the needle selector to give a bending motion to the piezoelectric body. However, a round cross section is not necessarily required for the bar-shaped conductor, and the cross section may have any shape as long as it can swing smoothly relative to the support of the needle selector. 
     Since the bar-shaped electrodes  28  of FIG. 1C are a triple electrode type as stated above, three conductive parts  30   a,    30   b  and  30   c  are arranged in the lengthwise direction in the bar-shaped electrode  28  via insulating parts  29   a  and  29   b.  Further, a slit  31  is provided to accommodate the rear end of the piezoelectric body  7  along the lengthwise direction of the bar-shaped electrode  28 . 
     As will be described below with reference to FIGS. 5A through 5D, when the bar-shaped electrode  28  is inserted into the concave part  22  of the power supply means, its conductive part  30   b  comes into contact with a linear conduction band  37 , and the conductive parts  30   a  and  30   b  come into contact with the contact areas  35 L and  35 R of the power supply plate  32 L,  32 R to achieve power supply. 
     As illustrated in FIG. 3A, the body of the bar-shaped electrode  28  is comprised by molding synthetic resin  48 , and its conductive parts are formed by plating the necessary parts of the surface of the synthetic resin body with metal. Preferably, they should be plated with an oxidation-resistant metal, such as gold or palladium. This metallic plating may extend to an end face of the bar-shaped electrode  28  as indicated by  30   c  in FIG.  1 C. Three conductive parts are also provided within the slit  31  via insulating parts (see FIG.  3 B). 
     The metallic coat can as well be provided instead of plating. Instead of plating, for instance, a thin metallic foil may be stuck or, in some cases, insulating parts  50   a  and  50   b  (whose cross-sectional shape is shown in FIG. 3E) and metallic conductive members  49   a,    49   b  and  49   c  (whose cross-sectional shape is shown in FIG. 3D) may be produced as insert members, and combined in a straight line. Combination of these members is so accomplished as to align the slit  31  part straight, using an adhesive for instance. 
     Further, the piezoelectric body  7  is inserted into the slit  31  of the bar-shaped electrodes  28  as illustrated in FIG.  1 . In this state, the conductive parts  30   a,    30   b  and  30   c  have to be electrically connected to the electrodes  43 A,  43 C and  43 B, respectively, of the piezoelectric body shown in FIG.  2 C. Whereas this can be accomplished in various ways, one of them is to coat the surface of the silver layers  42   a  and  42   b  with an insulating layer, and the electrodes to be connected to the silver layers  42   a,    42   b  and shim  44  are formed in only conductive parts  30   a,    30   c  and  30   b,  respectively. Incidentally, the electrodes matching the silver layers  42   a,    42   b  and shim  44  can be taken out of side end faces of the piezoelectric body. 
     FIG. 4 illustrates an example of bar-shaped electrode  51  whose cross section is square. In this instance, as is the case with the bar-shaped electrodes  28  having a round cross section shown in FIG. 1C, three conductive parts  52   a,    52   b  and  53   c  are provided via insulating parts  53   a  and  53   b,  and a slit  54  is further disposed. If the cross section is square or polygonal, its corners  55  should preferably be arc-shaped. 
     Where double electrode type bar-shaped electrodes are used, conductive parts may be provided on the right and left sides of one insulating part. 
     Further, power supply to cause the piezoelectric body of the finger actuating device to bend may be in either the lengthwise or the widthwise direction of the piezoelectric body. In this embodiment, the bar-shaped electrodes merely happen to be arranged, as a preferable mode of power supply to the piezoelectric body, at the rear end of a piezoelectric body, i.e., on the side opposite the position in which the finger members are arranged. Therefore, by altering the configuration of the power supply means for the finger actuating device, the spherical body  16  in FIG. 1A or the rotational body  23  can as well be adapted to a configuration similar to the bar-shaped electrodes according to the present invention. 
     Next will be described, with reference to FIGS. 5A through 5D, the power supply means for providing electric power to the finger actuating device and power supply terminals for supplying power to the power supply means in the needle selector for knitting machines according to the invention. 
     FIG. 5A is a schematic diagram illustrating in an exploded view of the power supply means and the power supply terminals as they relate to the bar-shaped electrodes in one embodiment of the needle selector for knitting machines according to the invention. As shown in FIG. 5A, the power supply means for use in the needle selector according to the invention consists of two power supply plates  32 L and  32 R arranged on the two sides of a plurality of piezoelectric bodies  7  disposed in parallel (only one of them is shown in FIG.  5 A), and a bar-shaped electrode fitting member  21  for keeping the two power supply plates  32 L and  32 R at a distance from each other substantially equal to the width of the bar-shaped electrodes  28  and having a plurality of concave parts  22  into each of which one or another of the plurality of bar-shaped electrodes  28  is to be inserted. 
     FIG. 5B is a front view illustrating the inside of the power supply plates  32 R; FIG. 5C, a profile of the bar-shaped electrode fitting member  21 ; and FIG. 5D, a front view of the bar-shaped electrode fitting member  21 . 
     Referring to FIG. 5A, which shows an exploded view as mentioned above, by shifting the power supply plate  32 L on the left side of FIG. 5A in the direction of an arrow CL to bring it into contact with the bar-shaped electrode fitting member  21  while shifting the power supply plate  32 R in the direction of an arrow CR on the right side of the same to bring into contact with the bar-shaped electrode fitting member  21 , the power supply means for the needle selector for knitting machines according to the present invention is formed. The two power supply plates  32 L and  32 R so assembled and the bar-shaped electrode fitting member  21  are fixed into a solid unit with bolts, adhesive or any other suitable means. 
     At the right end of eight piezoelectric bodies  7  (only one piezoelectric body  7  is shown in FIG. 5A) are fitted the bar-shaped electrodes  28 , and the piezoelectric bodies  7  provided with the bar-shaped electrodes  28  in this manner can be supplied with electric power via the bar-shaped electrodes  28  by shifting those bar-shaped electrodes  28  in the direction of an arrow D to insert them into the horizontal grooves  22  provided in the surface of the bar-shaped electrode fitting member  21  on the side toward the viewer of the diagram. 
     As described with reference to FIG. 1, the triple electrode type bar-shaped electrodes  28  are provided with three conductive parts  30   a,    30   b  and  30   c  via the two insulating part  29   a  and  29   b.  An instance in which these bar-shaped electrodes  28  are used to maintain the conductive part  30   b  at a potential of zero and a positive potential is alternately provided to the conductive parts  30   a  and  30   c  will be described below. 
     As illustrated in FIGS. 5A and 5C, on the inner surfaces of the power supply plates  32 L and  32 R are provided, in contact with the conductive parts  30   a  and  30   c  on the two sides of the bar-shaped electrodes  28 , contact areas  35 L and  35 R to be supplied with power, from which conducting circuits  33  extend to reach power supply terminals  34 L and  34 R provided at the ends of the power supply plates  32 L and  32 R. Incidentally, these contact areas  35 L and  35 R use contact members each consisting of a plurality of conductive thin wires elastically arranged in parallel to maintain satisfactory electrical contact with the conductive parts  30   a  and  30   c  on both end faces of the bar-shaped electrodes  28 . In this embodiment, for example,  12  wires of 0.2 mm in diameter arranged in parallel are used as contact members. In the embodiment illustrated in FIG. 5A, as it is provided with eight piezoelectric bodies  7 , to each of which electric power is supplied in a different procedure on the basis of information from the controller  4  as described above, one set each of contact areas  35 L and  35 R, conducting circuit and power supply terminals  34 L and  34 R need to be provided for each of the piezoelectric bodies  7 . While the conductive part  30 C of each bar-shaped electrode  28  is provided with power by the set of contact areas, conducting circuit and power supply terminals provided on the power supply plate  32 L, the conductive part  30   a  of each bar-shaped electrodes  28  is provided with power by the set of contact areas, conducting circuit and power supply terminals provided on the power supply plate  32 R. 
     By contrast, as the conductive part  30   b  in the middle of each bar-shaped electrode  28  is maintained at a zero potential, conduction can be accomplished in the same state for the whole piezoelectric body  7 . Then, as a preferred embodiment of the invention in this respect, as illustrated in FIGS. 5A,  5 C and  5 D, a groove  36  is provided in the middle of the bar-shaped electrode fitting member  21  along its lengthwise direction, a linear conduction band  37  is provided at the bottom of that groove  36 , this linear conduction band  37  is extended toward the upper part and bent toward the side of the bar-shaped electrode fitting member  21 , connected to the contact areas  38 L and  38 R of the power supply plates  32 L and  32 R via the contact areas  38 , and connected to the power supply terminals  39  of the power supply plates  32 L and  32 R via conducting circuits similar to the conducting circuit  33 . 
     Incidentally, the linear conduction band  37 , like the contact members arranged in the aforementioned contact areas  35 L and  35 R, consists of a plurality of wires arranged in parallel, and is elastically arranged in the groove  36 . Since eight each of the aforementioned power supply terminals  34  and one each of the power supply terminal  39  are arranged close to each other along both edges of the back of the bar-shaped electrode fitting member  21 , the supply side for supplying power to these terminals (a zero potential is maintained for the terminal  39 ) can be integrated into a single connector (illustrated). To add, the foregoing description concerns a case in which triple electrode type piezoelectric bodies are used, and where two electrode type piezoelectric bodies illustrated in FIGS. 2A and 2B are to be used, no conductive part is provided in the middle of the bar-shaped electrodes  28 , and the groove  36  in the bar-shaped electrode fitting member  21  may be dispensed with. 
     The description of the power supply means with reference to FIG. 5 covers only one example, and essentially, as long as a supply means cleared of wire connection is used, the applicability of the invention is not restricted to the illustrated embodiments. 
     For supplementary information, the external dimensions of the needle selector for knitting machines having a structure disclosed in the Japanese Patent No. 1969970 (referred to below as the prior device), which constitutes the basis of this application for invention, and those of the needle selector according to the present invention (referred to below as the present device) mainly based on improvement of the power supply means are compared in the following table. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Width 
                 Length 
                 Height 
                 Volume 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Prior device (A) 
                 30 mm 
                 125 mm 
                 55 mm 
                 206 mm 3   
               
               
                   
                 Present device (B) 
                 12 mm 
                  90 mm 
                 55 mm 
                  59 mm 3   
               
               
                   
                 Ratio (B/A) 
                 40% 
                  72% 
                 100% 
                 29% 
               
               
                   
                   
               
             
          
         
       
     
     The reduction of the width to as much as 40% means that, for instance 2.5 times as many needle selectors can be accommodated by a circular knitting machine of the same size, resulting in a very significant economic advantage. 
     Industrial Applicability 
     Since the needle selector for knitting machines according to the present invention consists of a finger actuating device, having a configuration substantially similar to the finger actuating device under the Japanese Patent No. 1969970 (U.S. counterpart is U.S. Pat. No. 5,029,619) applied for by the same person as the applicant pertaining to this invention, and a power supply means provided with bar-shaped electrodes having a structure characterizing the present invention, the needle selector for knitting machines hereunder can be substantially smaller than any needle selector according to the prior art, allowing many needle selectors to be arranged along the circumference of the knitting cylinder of a circular knitting machine. This has made it possible to provide a much greater number of yarn inlets for a knitting machine than for any conventional knitting machine, and this feature, coupled with the higher speed of the finger actuating device, serves to further enhance the productivity of knitting machines.