Abstract:
A coil arrangement for radio-frequency identification devices, process and an apparatus for making such a coil arrangement are described herein. The coil arrangement includes first and second terminals having a geometry different from one another and from the active coil winding of the arrangement. The apparatus is in the form of a spindle having three axially adjacent portions defining cross-sectional profiles.

Description:
FIELD OF THE INVENTION 
   The present invention relates to radio-frequency identification devices. More specifically, the present invention is concerned with a coil arrangement therefore and with a process and an apparatus for making such a coil arrangement. 
   BACKGROUND OF THE INVENTION 
   Radio-frequency identification (RFID) technology is well known in the art. RFID systems are usually made of two components, a reader and a tag or card, which will hereinafter be referred to as an RFID device. The RFID device generally comprises an antenna, in the form of an air coil, and a microchip to which the antenna is connected. Since the operation of a RFID system is believed well known in the art, it will therefore not be discussed further herein. 
   The manufacturing of miniaturized RFID devices is generally divided in two sequential steps: the winding of an ultra-fine magnet wire to provide an air-coil and the subsequent electrical connection of the two terminals of the coil to pads of the microchip. 
   One of the difficulties in the mass-production process of RFID devices concerns the handling of the coil terminals and their precise alignment above the microchip pads. Indeed, since the wire used to form the air coil is ultra-fine, usually wire gage AWG 44 to AWG 50, it is difficult to handle and to properly align and maintain during the soldering operation. Accordingly, a complicated dedicated apparatus is often used to connect the antenna to the microchip. This apparatus increases the total cost of production of the RFID device. 
   OBJECTS OF THE INVENTION 
   An object of the present invention is therefore to provide an improved coil arrangement for radio-frequency identification devices and process and apparatus for making same. 
   SUMMARY OF THE INVENTION 
   The present invention provides a coil geometry, a winding method and a winding apparatus that avoid the need to seize and align the coil terminal during the coil to circuit assembly step described hereinabove. The present invention also aims to increase the hardiness of the wire arrangement allowing a very low amount of turns for a coil. Which is particularly useful for coils operating at higher frequencies (13.56 MHz and above) as is sometimes the case in RFID systems. 
   More specifically, in accordance with the present invention, there is provided a coil arrangement for a radio-frequency identification device made of a wire; the coil arrangement comprising:
         a first coil terminal made of one turn of the wire; the first coil terminal having a first coil terminal geometry;   a active coil made of a predetermined number of turns of the wire; the active coil defining a geometry of the coil arrangement;   a second coil terminal made of one turn of the wire; the second coil terminal having a second coil terminal geometry; and   wherein the coil arrangement geometry, the first coil geometry and the second coil geometry are different.       

   According to another aspect of the present invention, there is provided a process for making a coil arrangement for a radio-frequency identification device from a wire; the method comprising:
         making a first coil terminal by winding one turn of the wire; the first coil terminal having a first coil terminal geometry;   making an active coil by winding a predetermined number of turns of the wire; the active coil defining a coil arrangement geometry;   making a second coil terminal by winding one turn of the wire; the second coil terminal having a second coil terminal geometry; and   making a supporting outer layer by winding at least one turn of the wire;   wherein the coil arrangement geometry, the first coil geometry and the second coil geometry are different.       

   According to third aspect of the present invention, there is provided a process for making a coil arrangement for a radio-frequency identification device from a wire; the method comprising:
         providing a mandrel having a rotation axis, a first portion having a predetermined cross-sectional profile, a second portion having a predetermined cross-sectional profile and positioned axially adjacent to the first portion and a third portion having a predetermined cross-sectional profile and positioned axially adjacent to the second portion;   making a first coil terminal by winding one turn of the wire onto the second portion of the mandrel;   making an active coil by winding a predetermined number of turns of the wire onto the first portion of the mandrel; and   making a second coil terminal by winding one turn of the wire onto the third portion of the mandrel.       

   According to another aspect of the present invention, there is provided a spindle for making a coil arrangement comprising:
         a flange rotatable about a rotation axis; the flange having a flat face and a mandrel of a predetermined height; the mandrel generally defining a geometry of the coil arrangement via a peripheral coil winding surface; the mandrel having a first slot and a second slot separated by an intermediate wall having a height smaller than the height of the mandrel; the mandrel being also provided with an external wall having a height smaller than the height of the intermediate wall;   a counter-flange rotatable about the rotation axis; the counter-flange having a flat face and a recess configured and sized to receive at least a portion of the mandrel;   one of the flange and the counter-flange being so configured as to be axially movable along the rotation axis to modify the portion of the predetermined height of the mandrel received in the counter-flange, thereby selectively allow a wire forming the coil to enter either the first and second slots.       

   According to another aspect of the present invention, there is provided a spindle for making a coil arrangement comprising:
         a flange rotatable about a rotation axis; the flange having a flat face and a mandrel; the mandrel generally defining a geometry of the coil arrangement via a peripheral coil winding surface; the mandrel having:   a central portion having a predetermined height;   a first semi-circular wall portion separated from the first semi-circular wall portion by a first slot; the first semi-circular wall portion having a height smaller than the predetermined height;   a second semi-circular wall portion opposite the first semi-circular wall portion; the second semi-circular wall portion being separated from the central portion by a second slot and having a height smaller than the predetermined height; the first and second slots being generally parallel;   a counter-flange rotatable about the rotation axis; the counter-flange having a flat face and a recess configured and sized to receive at least a portion of the mandrel;   one of the flange and the counter-flange being so configured as to be axially movable along the rotation axis to modify the portion of the predetermined height of the mandrel received in the counter-flange, thereby selectively allow a wire forming the coil to enter either the first and second slots.       

   According to a final aspect of the present invention, there is provided a spindle for making a coil arrangement, the spindle comprising:
         a flange rotatable about a rotation axis; the flange having a predetermined thickness; the flange having a first cross-sectional profile for a first portion of the predetermined thickness, a second cross-sectional profile for a second portion of the predetermined thickness and a third cross-sectional profile for a third portion of the predetermined thickness;   a counter-flange rotatable about the rotation axis; the counter-flange having a flat face and a recess configured and sized to receive at least a portion of the mandrel;   one of the flange and the counter-flange being so configured as to be movable along the rotation axis to expose either the first, the first and second; and the first, second and third portions of the mandrel.       

   Generally stated, the present invention provides a coil geometry, a winding method and a winding apparatus that avoid the need to seize and align the coil terminal during the coil to circuit assembly step described hereinabove. The present invention also aims to increase the hardiness of the wire arrangement allowing a very low amount of turns for a coil, Which is particularly useful for coils operating at higher frequencies (13.56 MHz and above) as is sometimes the case in RFID systems. 
   Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the appended drawings: 
       FIG. 1  is a side partly sectional view of a spindle according to an embodiment of the present invention; the flange and counter-flange of the spindle being shown in one of their coil winding position; 
       FIG. 2  is a front view of a flange of the winding spindle of  FIG. 1 ; 
       FIG. 3  is a side partly sectional view similar to  FIG. 1  where the flange and counter flange are in a spaced apart position; 
       FIG. 4  is a sectional enlarged view of a portion of  FIG. 3  during the winding of an inner layer of a coil arrangement; 
       FIG. 5  is a front view of the flange during the winding of an inner layer of a coil arrangement; 
       FIG. 6  is a sectional view of the spindle during the winding of a first coil terminal; 
       FIG. 7  is a front view of the flange during the winding of the first coil terminal; 
       FIG. 8  is a sectional view of the spindle during the winding of the main winding layer; 
       FIG. 9  is a front view of the flange during the winding of the main winding layer; 
       FIG. 10  is a sectional view of the spindle during the winding of the second coil terminal; 
       FIG. 11  is a front view of the flange during the winding of the second coil terminal; 
       FIG. 12  is a sectional view of the spindle during the winding of the outer layer of the coil; 
       FIG. 13  is a front view of the flange during the winding of the outer layer of the coil; 
       FIG. 14  is a front view of a coil arrangement according to a first embodiment of the present invention; 
       FIG. 15  is a front view of a coil arrangement according to a second embodiment of the present invention; 
       FIG. 16  is a front view of a flange used to obtain the coil arrangement of  FIG. 15 ; 
       FIG. 17  is a front view of a coil arrangement according to a third embodiment of the present invention; 
       FIG. 18  is a front view of a flange used to obtain the coil arrangement of  FIG. 17 ; 
       FIG. 19  is a front view of a coil arrangement according to a fourth embodiment of the present invention; 
       FIG. 20  is a perspective view of a flange used to obtain the coil arrangement of  FIG. 19 ; 
       FIG. 21  is a front view of a coil arrangement according to a fourth embodiment of the present invention; and 
       FIG. 22  is a front view of a flange used to obtain the coil arrangement of  FIG. 20 . 
   

   DETAILED DESCRIPTION 
   Turning to  FIGS. 1 and 2  of the appended drawings, a apparatus for forming a coil (herein after referred to as the spindle  10 ) will be described. 
   The spindle  10  includes a flange  12  and a counter-flange  14  shown in sectional view in the appended drawings. 
   The flange  12  includes a shaft  16 , a body  18 , a face  20  and a mandrel  24 . As can be better seen from  FIG. 2 , the center of the mandrel  24  includes a clutch fork male portion  22 . The circular mandrel  24  defines a generally cylindrical coil winding surface  26  having a predetermined height. 
   It is to be noted that the mandrel  24  is associated with a retractable portion  17  of the shaft  16  to thereby allow the disengagement of a finished coil from the mandrel  24 , as will be described hereinbelow. 
   The mandrel  24  includes a first slot  30  defined by a wall  31  and an intermediate wall portion  32 . It is to be noted that the height of the intermediate wall  32  is less than the height of the mandrel  24  (see  FIG. 1 ). The mandrel  24  also includes a second slot  34  defined by the intermediate wall  32  and an external wall portion  36 . The wall portion  36  has a semi-cylindrical outer surface  40  defining a portion of the coil winding surface  26  of the mandrel  24 . It is to be noted that the height of the external wall  36  is less than the height of the intermediate wall  32 . 
   In other words, the mandrel  24  is divided in three portions defining different cross-sectional profiles and hence, the geometry of the coil arrangement as will be described hereinbelow. 
   A first portion of the height of the mandrel, extending from the face  20  of the flange to the top of the external wall  36 , has a generally circular cross-sectional profile. 
   A second portion of the height of the mandrel  24 , extending between the top of the external wall  36  and the top of the intermediate wall  32 , defines a generally inverted D-shaped cross-sectional profile. 
   Finally, a third portion of the height of the mandrel, extending between the top of the intermediate wall  32  and the top of the mandrel  24 , defines a smaller inverted D-shaped cross-sectional profile. 
   As is clearly seen from  FIG. 2 , the slots  30  and  34  are each provided with a respective wire outlet  42  and  44  and with a common wire inlet  46 . 
   Conventionally, the flange includes grooves (not shown) used to hold the end of the wire before it is would. Since this technique is believed well known in the art, it will not be discussed herein. 
   The shaft  16  of the flange  12  is associated with a motor (not shown) that may be precisely controlled to rotate the flange  12  in the direction of arrow  47 . 
   The counter-flange  14  includes a shaft  48 , a body  50  and a clutch fork female portion  52  configured to be engaged by the clutch fork male portion  22  of the flange  12  so as to cooperate therewith. The face  54  of the counter-flange  14  includes a circular recess  56  defining a cylindrical wall  58  having a diameter that is only slightly larger than the diameter of the mandrel  24 . As will be further discussed hereinbelow, the shaft  48  is free-wheeling, i.e. that it may rotate about an axis common to the rotation axis of the shaft  16  of the flange  12 . Furthermore, the shaft  48  is so associated with a displacement mechanism (not shown) that the counter-flange  14  may axially be moved (see double-arrow  60 ) to expose the first portion, the first and second portion or the first, second and third portion of the height of the mandrel. 
     FIG. 3 , which is very similar to  FIG. 1 , shows the counter-flange  14  in an opened position, where the clutch fork portions  22  and  52  are disengaged. 
   The flange  12  of the spindle  10  is so configured as to produce coils such as coil arrangement  100 , as illustrated in  FIG. 14 . The coil arrangement  100  includes a plurality of turn of wire forming the main winding  102  thereof and defining a geometry of the coil arrangement  100 , in this case a circle. The coil  100  also includes one turn of wire forming a first coil terminal  104  and defining a first coil terminal geometry, in this case an inverted D-shape having a straight portion and a curved portion. One turn of wire forms a second coil terminal  106  having a second coil terminal geometry, in this case a smaller inverted D-shape having a straight portion and a curved portion. The first and second coil terminals  102  and  104  defining an angle so that their straight portions converge. As will be discussed hereinbelow, a supporting inner layer of winding and a supporting outer layer of winding are also provided. 
   Turning now to  FIGS. 4 to 13  of the appended drawings, the steps of the formation of a coil arrangement such as  100  from a single wire will be described. 
   The main steps are:
         Formation of the supporting inner wire layer;   Formation of the first coil terminal;   Formation of the active coil;   Formation of the second coil terminal; and   Formation of the supporting outer layer.       

   As will be understood by one skilled in the art, before the winding of the coil arrangement, the end of the wire used must be secured to the spindle  10  according to conventional manner. 
   It is also to be noted that a wire guide (not shown) is used to guide the wire during the winding operation. This wire guide is operated in translation along the rotational axis of the spindle  10  providing a precise placement of the wire during winding. Since guides of this type are believed well known in the art, they will not be further discussed herein. 
     FIGS. 4 and 5  illustrate the first step in the coil arrangement formation process, the winding of the supporting inner wire layer. More specifically, these figures illustrate the state of the spindle  10  after this step is done. It is to be noted that in the following figures the wire forming the coil is often shown in section, for clarity purposes. 
   As can be better seen from  FIG. 4 , the distance separating the faces  20  and  54  of the flange  12  and the counter-flange  14 , respectively, define the width of the coil. It is to be noted that during this step this distance between the faces  20  and  54  is slightly smaller than the height of the external wall  36  of the mandrel  24 . Therefore, only the first portion of the height of the mandrel  24  is exposed. 
   It is to be understood that while the inner wire layer consists of five turns of wire in the appended drawings, this number is arbitrary and depends on the size of the wire used, the width of the desired coil and the desired rigidity of the finished coil arrangement. For example, it would be possible to provide an inner wire layer consisting of only one turn of wire should the faces  20  and  54  be positioned closer than they appear in the appended drawings. Furthermore, in some instances it is possible to forego this step entirely, which would lead to a coil arrangement devoid of supporting inner wire layer. 
   As can be seen from  FIG. 5 , the inner layer of wire follows the winding surface  26  and the external surface  40  of the external wall  36 , thereby defining the coil arrangement geometry. 
     FIGS. 6 and 7  of the appended drawings illustrate the winding of the first terminal  104  (see  FIG. 14 ) of the coil arrangement. More specifically, these figures illustrate the state of the spindle  10  following this step is done. 
   The counter-flange  14  has been moved (see arrow  62 ) so that the distance between the faces  20  and  54  is greater than the height of both the walls  32  and  36  but still smaller than the height of the mandrel  24 . Therefore, the first, second and third portions of the height of the mandrel  24  are exposed. 
   Since the guiding mechanism (not shown) guides the wire so that it is adjacent to the face  54  of the counter-flange  14 , upon rotation of the spindle  10 , the wire will enter the slot  30  via the inlet  46 , abut the wall  31  by passing over the walls  32  and  36  and exit the slot  30  via the outlet  42 . 
     FIG. 7  illustrates the first coil terminal being wounded. As can be clearly seen from this figure, the geometry of the coil terminal is different from the circular geometry of the inner layer since the first coil terminal is wound onto the third portion of the height of the mandrel  24 . 
   Once the first coil terminal is wound, the counter-flange  14  returns to the position illustrated in  FIG. 8  for the next step. 
     FIGS. 8 and 9  illustrate the winding of the active coil of the coil arrangement. More specifically, these figures illustrate the state of the spindle  10  after this step is done. 
   As mentioned hereinabove, the counter-flange  14  has been moved (see arrow  64 ) so that the distance between the faces  20  and  54  is back to being slightly smaller than the height of the wall  36 . Therefore, only the first portion of the height of the mandrel  24  is exposed. 
   Once this is done, a predetermined number of turns may be wound onto the previously wound inner layer and first terminal. Of course, the number of turns of wire depends on the desired characteristics of the antenna. For example, up to 1200 turns of wire may be wound to yield the active coil, depending on the requirements of the microchip, the diameter and thickness of the air coil. It is believed to be within the reach of one skilled in the art to determined the number of turns of wire required for a particular application. 
   As can be seen from  FIG. 9 , the active coil follows the winding surface  26  and the external surface  40  of the external wall  36 , thereby following the coil arrangement geometry. 
   Turning now to  FIGS. 10 and 11 , the formation of the second coil terminal  106  (see  FIG. 14 ) will be described. These figures illustrate the state of the spindle  10  after this step is done. 
   As can be seen from  FIG. 10 , the counter-flange  14  has been moved (see arrow  66 ) so that the distance separating the faces  20  and  54  is greater than the height of the external wall  36  but smaller than the height of the intermediate wall  32 . Therefore, only the first and second portions of the height of the mandrel  24  are exposed. 
   Since the guiding mechanism (not shown) guides the wire so that it is adjacent to the face  54  of the counter-flange  14 , upon rotation of the spindle  10 , the wire will enter the slot  34  via the inlet  46 , abut the intermediate wall  32  by passing over the wall  36  and exit the slot  34  via the outlet  42 . 
     FIG. 11  illustrates the second coil terminal being wounded. As can be clearly seen from this figure, the geometry of the coil terminal is different from the circular geometry of the inner layer, the active coil and of the geometry of the first terminal. 
   Once the second coil terminal is wounded, the counter-flange  14  returns to the position illustrated in  FIG. 12  for the next step. 
     FIGS. 12 and 13  illustrate the winding of the supporting outer layer of the coil arrangement. 
   The counter-flange  14  has been moved (see arrow  68 ) so that the distance between the faces  20  and  54  is again slightly smaller than the height of the external wall  36 . Therefore, only the first portion of the height of the mandrel  24  is exposed. 
   It is to be understood that while the supporting outer wire layer consists of five turns of wire in the appended drawings, this number is arbitrary and depends of the size of the wire used and of the width of the finished coil. 
   As can be seen from  FIG. 13 , the outer layer of wire follows the winding surface  26  and the external surface  40  of the external wall  36 , thereby following the coil arrangement geometry. 
   Once the outer layer of wire has been wound, the wire can be cut and the completed coil  100  is ready to be unloaded from the spindle  10 . The counter-flange  14  throws out of gear as illustrated in  FIG. 3 . The retractable portion  17  of the shaft  16  is then moved back (see arrow  70 ), pulling with it the mandrel  24 , forcing the finished coil out of the mandrel  24  since it abuts the face  20  of the flange  14 . 
   It is to be noted that while the description hereinabove states that the flange  12  is connected to a motor (not shown) and that the counter-flange  14  is driven by the engagement of the clutch elements  22  and  52 , it would be within the reach of one skilled in the art to connect the counter-flange  14  to a motor instead and let the flange  12  be driven. 
   Similarly, the counter-flange  14  could be axially fixed and the flange  12  could move axially to selectively expose the first, first and second, or first second and third portions of the height of the mandrel  24 . 
   It is to be noted that while the above description specifies that the first coil terminal goes through slot  30  and the second coil terminal goes through slot  34 , this is not essential to the present invention. Indeed, the first coil terminal could be wound into slot  34  and the second coil terminal could be wound into slot  30 . 
   Similarly, while the appended drawings illustrate that the first and second terminals are would near the face  54  of the counter-flange  14 , it is not necessarily so. 
   Turning now to  FIGS. 15 to 22  of the appended drawings, other possible configurations of coil arrangements made according to embodiments of the present invention will be described. It is to be noted that other configurations and geometries, not shown herein, are possible within the scope of the present invention. 
     FIG. 15  illustrates a coil arrangement  200  also having a circular geometry but where the geometry of the first and second coil terminals  202  and  204  is different. Indeed, while being generally D-shaped, instead of converging as illustrated in  FIG. 14 , the straight portions of the terminals  202  and  204  are parallel and located on the same side of the coil arrangement. 
     FIG. 16  illustrates, in a perspective view, a flange  206  provided with a mandrel  208  used to wind the coil arrangement  200 . The mandrel  208  is very similar to the mandrel  24  discussed hereinabove. The slots  210  and  212  are parallel and are separated by two intermediate wall portions  214   a  and  214   b . An external wall  216  completes the circular cross-section of the first portion of the height of the mandrel  208 . 
   As can be clearly be seen from this figure, the intermediate wall is not full length and the main portion of the mandrel  208  includes a generally U-shaped clearance  218 . These features are intended to reduce the surface of contact between the straight portions of the first and second terminals  202  and  204  and thereby to reduce the friction between the straight portions and the mandrel  208  when the finished coil  200  is removed from the flange  206 . In turn, this reduced friction provides terminals that remain straight. 
   One skilled in the art will have no difficulty in transposing these features to the other embodiments of mandrels described herein. 
     FIG. 17  illustrates a coil arrangement  300  also having a circular geometry but where the geometry of the first and second coil terminals  302  and  304  is different. Indeed, instead of being close apart as illustrated in  FIG. 15 , the straight portions of the terminals  302  and  304  are parallel and located on opposite sides of the coil arrangement. The coil arrangement  300  is especially adapted to the ultra small coils for which the terminal spacing is about their diameter. 
     FIG. 18  illustrates a flange  306  provided with a mandrel  308  used to wind the coil arrangement  300  of  FIG. 17 . The mandrel  308  includes two slots  310  and  312  separated by wall portions  314 ,  316  and  318 . The height of the wall portion  318  is smaller than the height of the wall portion  314  which itself is smaller than the height of the wall portion  316 . The winding of the coil arrangement  300  follows generally the same steps as the winding of the coil arrangement  100  describe hereinabove. 
   One skilled in the art will easily understand that the height of the wall portions  314  and  318  could be equal. If this is the case, the terminals would be wound by turning the flange  306  by half a turn. 
     FIG. 19  illustrates a circular geometry coil arrangement  400  provided with coil terminals  402  and  404  extending outside the circular geometry. 
     FIG. 20  illustrates, in a perspective view, a flange  406  provided with a mandrel  408  used to wind the coil  400  of  FIG. 19 . The mandrel  408  is circular and is used to wind the supporting inner and outer layers and the active layer of the coil arrangement  400 . The face  410  of the spindle  406  is generally flat but includes the slots  412  and  414  axially recessed therein. A front wall  418  and an intermediate wall  420  define the slot  412  while the intermediate wall  420  and a rear wall  422  define the slot  414 . 
   The winding steps of the coil arrangement  400  are very similar to the winding steps of the coil arrangement  100  described in detail hereinabove. However, the coiling of the first and second terminals  402  and  404  is done by moving either the flange  406  or the wire guide (not shown) so that the wire is wound in a corresponding slot. 
   To remove the finished coil arrangement from the flange  406 , the mandrel  408  is retracted as discussed with respect to the mandrel  24 , thereby allowing the terminals  402  and  404  to exit their respective slot. 
     FIG. 21  illustrates a fourth variant for a coil arrangement  500 . The geometry of the coil arrangement  500  being generally trapezoid. The geometry of the coil terminals  502  and  504  being generally rectangular and extending outside the geometry of the coil arrangement  500 . 
     FIG. 22  illustrates a flange  506  very similar to the flange  406  discussed hereinbelow. The main difference between these flanges being the cross sectional shape of the mandrel  508  designed to yield the trapezoid shape of the coil arrangement  500 . The other features being identical to the features of the flange  406 . 
   As will easily be understood by one skilled in the art, the coil arrangements made according to the present invention are interesting since they are self-supporting and since the terminals are always indentically positioned from one coil to the next, therefore simplifying the connection of the terminals to the microchip. For example, thermo-compression and ultrasonic welding techniques could be used. 
   It is to be noted that the present invention is very useful for the RFID tags operating at 13.56 MHz and above. In this case, the active coil is formed by no more than 5 or 6 turns. Without the additional wire inner and outer layers, the resulting coil would have been both very difficult to handle and would hardly resist the product lifetime. 
   Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.