Patent Publication Number: US-2023143311-A1

Title: Coil unit for multi-axis linear motor actuator and manufacturing method therefor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of PCT/JP2021/004283 filed on Feb. 5, 2021, which claims priority under 35 U.S.C. §119 of Japanese Application No. 2020-077350 filed on Apr. 24, 2020, the disclosure of which is incorporated by reference. The international application under PCT article 21(2) was not published in English. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a method of manufacturing a coil unit in a multi-axis linear motor actuator and, more particularly, to a coil unit in a multi-axis linear motor actuator suitable for a multi-axis dispensing device and a method of manufacturing the same. 
     BACKGROUND ART 
     One type of linear motor is referred to as a linear shaft motor. The linear shaft motor has a structure including a coil portion formed by stacking a plurality of cylindrical coils in a center axis direction thereof, and a magnet portion formed by connecting a plurality of permanent magnets in series with the same magnetic poles faced to each other and fixing the plurality of permanent magnets to a support member longer than the plurality of connected permanent magnets to form a shaft, wherein the shaft is inserted through a center hole of the coil portion via a small gap. The plurality of coils are divided into three phases of a U phase, a V phase, and a W phase. AC currents shifted in phase by 120 degrees are made to flow through the coils of the respective phases so that a thrust force for driving the shaft in a center axis direction thereof is obtained by an action of a magnetic field generated by the permanent magnets and the currents flowing through the coils (Patent Document 1). 
      Such a linear shaft motor is applied to various fields such as a handling device for an electronic component, a dispensing device for sucking and discharging a small amount of liquid, and the like. Generally, in any of the handling device, the dispensing device, and the like, the shaft of the linear shaft motor is assumed to be a first shaft and a hollow second shaft is combined with the first shaft in parallel with a center axis direction of the first shaft so as to move up and down integrally with the first shaft, thereby providing a linear motor actuator. A hollow space of the second shaft is configured to be used for handling by air or sucking and discharging the liquid. 
     For example, in the case of the handling device, a jig such as a vacuum suction apparatus is attached to a tip of the second shaft to handle the electronic component in synchronization with up-and-down movement of the first shaft (Patent Document 2). On the other hand, in the case of the dispensing device, a nozzle is attached to the tip of the second shaft to form a dispensing head, and an internal pressure of the nozzle is appropriately increased or decreased in synchronization with the up-and-down movement of the first shaft to thereby suck and discharge the liquid. 
     Prior Art Document 
     Patent Documents 
     
         
         Patent Document 1: JP 2017-139861 A 
         Patent Document 2: JP 2012-090492 A 
       
    
     SUMMARY OF THE INVENTION 
     Problem to Be Solved by the Invention 
     In recent years, there is provided a device called a multi-axis linear motor actuator in which a plurality of the above-mentioned linear motor actuators, each comprising a combination of the first shaft and the second shaft, are arranged in a row and collectively perform the same operation so as to improve work efficiency. For example, the multi-axis linear motor actuator is applied as a multi-axis dispensing device which includes a plurality of the above-mentioned dispensing devices individually manufactured and arranged in a row to perform a dispensing operation in the fields of medicines, cosmetics, biotechnology, etc. According to the multi-axis dispensing device, the plurality of dispensing devices collectively perform the same operation and action. Therefore, the multi-axis dispensing device is effective in achieving significant labor-saving and in preventing dispensing errors as compared with a dispensing operation by a manual operation. 
     For example, when the conventional multi-axis dispensing device is combined with a 96 (8 samples × 12 rows) specimen microplate as a clinical examination device, eight dispensing devices are assembled to be arranged in a row to form an 8-axis simultaneous control, that is, a multi-axis dispensing device. The multi-axis dispensing device is reciprocated by a transport mechanism between a sucking location of a liquid (for example, a reagent) and a discharging location (i.e., the microplate). Therefore, the conventional multi-axis dispensing device is generally manufactured by a combination of the plurality of dispensing devices individually manufactured, and is capable of carrying out only a dispensing operation of discharging the same amount of the reagent to the microplate at the same timing. 
     However, in the conventional multi-axis dispensing device obtained by individually manufacturing each linear motor actuator comprising a combination of the first shaft (linear shaft motor) and the second shaft and then combining a plurality of the linear motor actuators, there is a problem that the number of assembling steps, that is, the number of manufacturing steps is large and the manufacturing cost is difficult to be reduced. 
     On the other hand, for the multi-axis dispensing device, there is an increasing demand that each of the plurality of dispensing devices be independently controllable. According to a multi-axis independent-control dispensing device, it is possible to discharge individual amounts of the reagent to the microplates at individual timings for respective axes even in the same row, and to monitor reaction of specimens. That is, it is possible to set the amount of the reagent to be discharged to the microplate and the timing for each sample, and to execute suction and discharge of the reagent in an automated control mode, thereby obtaining an objective and highly reliable examination result. 
     In view of the problem and the demand described above, it is an object of the present invention to provide a method of manufacturing a coil unit, which is suitable for collectively manufacturing a plurality of coil portions in a multi-axis linear motor actuator. 
     It is a specific object of the present invention to provide a coil unit and a method of manufacturing the same, which are suitable for collectively manufacturing a plurality of coil portions in a multi-axis independent-control dispensing apparatus. 
     Means for Solving the Problem 
     According to one aspect of the present invention, there is provided a method of manufacturing a coil unit in a multi-axis linear motor actuator comprising a plurality of linear shaft motors arranged in a row at a predetermined pitch, the linear shaft motors each comprising a magnet portion for the linear shaft motor and a coil portion for the linear shaft motor, the magnet portion including a plurality of permanent magnets which are connected to each other with the same magnetic poles faced to each other and which are fixed to a support member having a length equal to or longer than a total length of the plurality of permanent magnets connected to each other to form a shaft, the coil portion including a plurality of cylindrical coils connected to each other in a center axis direction and combined with the shaft to be relatively movable with respect to an axial direction thereof with the shaft concentrically enclosed in the coil portion via a gap, the method including:
     a step of preparing a coil fixing member having a receiving portion adapted to receive a plurality of the coil portions, same in number as the plurality of linear shaft motors, arranged in a row at the predetermined pitch;   a step of arranging the plurality of coil portions in a row in the coil fixing member and fixing the plurality of coil portions; and   a step of arranging a magnetic shielding plate, longer than the coil portion, along the center axis direction at least at a position corresponding to a space between adjacent ones of the plurality of coil portions arranged in a row.   

     According to another aspect of the present invention, there is provided a coil unit in a multi-axis linear motor actuator comprising a plurality of linear shaft motors arranged in a row at a predetermined pitch, the linear shaft motors each comprising a magnet portion for the linear shaft motor and a coil portion for the linear shaft motor, the magnet portion including a plurality of permanent magnets which are connected to each other with the same magnetic poles faced to each other and which are fixed to a support member having a length equal to or longer than a total length of the plurality of permanent magnets connected to each other to form a shaft, the coil portion including a plurality of cylindrical coils connected to each other in a center axis direction and combined with the shaft to be relatively movable with respect to an axial direction thereof with the shaft concentrically enclosed in the coil portion via a gap, the coil unit including:
     a plurality of the coil portions, same in number as the plurality of linear shaft motors:   a coil fixing member having a receiving portion in which the plurality of coil portions arranged in a row at the predetermined pitch are arranged and fixed; and   a magnetic shielding plate, longer than the coil portion, arranged and fixed along the center axis direction at least at a position corresponding to a space between adjacent ones of the plurality of coil portions arranged in a row.   

     Preferably, the shaft is formed by accommodating the plurality of permanent magnets connected to each other in a cylindrical body made of a non-magnetic material;
     the coil portion includes a coil integration cylinder inserted through the coil portion so as to integrate the plurality of coils, the coil integration cylinder being made of resin and having an inner diameter larger than an outer diameter of the cylindrical body and a length including protruding portions protruding from both ends of the coil portion; and   the receiving portion of the coil fixing member has a bottom wall defining a bottom surface of a receiving space for the plurality of coil portions arranged in a row; a pair of wall members faced to each other so as to define the receiving space with respect to a direction parallel to the center axis direction of the coil portions; and a pair of coil ends which have a plurality of through holes for insertion of the protruding portions protruding from the plurality of coil portions and which are provided between the pair of wall members on both ends of the plurality of coil portions, at least one of the coil ends being removable from the bottom wall.   

     Preferably, the magnetic shielding plate has a length over a movable range of the plurality of permanent magnets, and is fitted to each of a plurality of slits formed in each of the pair of coil ends in a depth direction of the receiving space; and the magnetic shielding plate has a width larger than a depth of the receiving space and, at least at a part corresponding to a partial region of the receiving space, the width is nearly equal to the depth of the receiving space, so that a circuit board is attached to the part corresponding to the partial region of the receiving space. 
     Effect of the Invention 
     According to the present invention, the plurality of coil portions in the multi-axis linear motor actuator can collectively be manufactured. Therefore, the number of assembling steps and the number of manufacturing steps of the multi-axis linear motor actuator can be reduced. As a result, it is possible to provide a coil unit and a method of manufacturing the same, which are effective in reducing the manufacturing cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an 8-axis independent-control dispensing device manufactured by a manufacturing method according to the present invention; 
         FIG.  2    is a perspective view of a plurality of linear shaft motors, a plurality of dispensing heads, and upper and lower connecting members, which are extracted from the 8-axis independent-control dispensing device shown in  FIG.  1   ; 
         FIG.  3    is a perspective view of four combinations of the linear shaft motors and the dispensing heads (4-axis independent-control dispensing device) which are extracted from the 8-axis independent-control dispensing device shown in  FIG.  1    and which are located on the left side in the figure; 
         FIG.  4    is a longitudinal sectional view taken along a line A-A′ in  FIG.  1   ; 
         FIG.  5    is a side view of a combination of the linear shaft motor and the dispensing head, and the upper and lower connecting members, which are extracted from the 8-axis independent-control dispensing device shown in  FIG.  1   ; 
         FIG.  6    is a cross-sectional view of an internal structure of a part of the linear shaft motor shown in  FIG.  5   ; 
         FIG.  7    is a partial cross-sectional side view of the combination of the linear shaft motor, the dispensing head, and peripheral members shown in  FIG.  4   , in a state where a magnetic shielding plate is removed; 
         FIG.  8    is a longitudinal sectional view of a main part of the dispensing head shown in  FIG.  4   ; 
         FIG.  9    is an exploded perspective view of a pair of coil units and a center plate, and connecting plates connecting the coil units and the center plate on lateral sides, in the 8-axis independent-control dispensing device shown in  FIG.  1   ; 
         FIGS.  10 A to  10 D  are perspective views for sequentially describing a manufacturing process of the coil unit in the case where the present invention is applied to the 4-axis independent-control dispensing device; 
         FIG.  11    is a perspective view of a coil portion as a component of the coil unit shown in  FIGS.  10 A to  10 D ; 
         FIG.  12    is a partially-exploded perspective view of the coil unit shown in  FIGS.  10 A to  10 D ; 
         FIG.  13    is a view showing an example of a circuit board attached to the coil unit shown in  FIGS.  10 A to  10 D ; 
         FIG.  14    is a perspective view of the left coil unit in the pair of coil units shown in  FIG.  9    as seen from a different angle; 
         FIG.  15    is a top view showing an arrangement mode of the upper connecting member in the 8-axis independent-control dispensing device shown in  FIG.  1   ; 
         FIG.  16    is a perspective view for describing detecting means for detecting an upper movement position of the upper connecting member in the 8-axis independent-control dispensing device shown in  FIG.  1   ; 
         FIGS.  17 A and  17 B  are views for describing an example of an installation mode of the detecting means shown in  FIG.  16   ; 
         FIG.  18    is a view for describing mounting intervals of a pair of Hall sensors installed for position control in the linear shaft motor; 
         FIG.  19    is a view showing a result of measuring an external magnetic field in a radial direction of the first shaft in the linear shaft motor; and 
         FIG.  20    is a block diagram showing a configuration of a position control system of the linear shaft motor, using the Hall sensor. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Prior to description of a coil unit and a method of manufacturing the same according to a preferred embodiment of the present invention, an 8-axis independent-control dispensing device manufactured by applying the embodiment of the present invention will be described with reference to  FIGS.  1  to  9   . 
       FIGS.  1  and  2    show the 8-axis independent-control dispensing device (hereinafter may be referred to as an 8-axis dispensing device) to which the present invention is applied.  FIG.  3    shows a half of the 8-axis independent-control dispensing device, that is, a 4-axis independent-control dispensing device (hereinafter may be referred to as a 4-axis dispensing device).  FIG.  4    is a longitudinal sectional view taken along a line A-A′ in  FIG.  1   .  FIG.  5    is a side view of a combination of a linear shaft motor and a dispensing head, and upper and lower connecting members, which are extracted from the 8-axis independent-control dispensing device shown in  FIG.  1   .  FIG.  6    is a cross-sectional view of an internal structure of a part of the linear shaft motor. 
     First, the internal structure of the linear shaft motor will be described. However, since the linear shaft motor of this type is well known, brief description only is given. 
     Referring to  FIG.  6   , the linear shaft motor  10  has a first shaft  11  including a plurality of permanent magnets  12  magnetized in a center axis direction and, in the state of being connected to each other in series with the same magnetic poles faced to each other, accommodated in and fixed to a cylindrical body (support member)  13  made of a non-magnetic material. The cylindrical body  13  has a length equal to or longer than the total length of the plurality of permanent magnets  12 . A part of the cylindrical body  13  that accommodates the plurality of permanent magnets  12  may be referred to as a magnet portion for the linear shaft motor  10 . As will later be described, in the magnet portion, the permanent magnets  12  having the same shape and the same magnetic force are faced to each other so that, in the periphery of the first shaft  11  (magnet portion), N poles and S poles alternately appear at the same pitch in an axial direction. When a surface magnetic flux density thereof is measured, a sinusoidal waveform appears. The linear shaft motor  10  also has, as a coil portion  15 , a plurality of cylindrical coils  14  connected to each other in series so as to concentrically enclose the first shaft  11  via a gap. In the coil portion  15 , the plurality of cylindrical coils  14  are connected to each other in series on an outer periphery of a coil integration cylinder  16  of resin to be integrated. The coil integration cylinder  16  has an inner diameter larger than an outer diameter of the cylindrical body  13 . The first shaft  11  and the coil portion  15  are configured to be movable relative to each other in the center axis direction. Herein, the first shaft  11  is configured to be a movable portion and the coil portion  15  is configured to be a fixed portion. 
     The coil portion  15  is composed of at least three coils  14  of a U phase, a V phase, and a W phase to constitute a three-phase linear motor. AC currents having an electric phase difference of 120 degrees are made to flow through the respective coils  14 . By controlling energization to each coil  14 , a thrust force for driving the first shaft  11  in the center axis direction is obtained by an action of a magnetic field generated from the permanent magnets  12  and the currents flowing through the coils  14 . 
     In this description, the meaning of “connecting the permanent magnets to each other” not only includes direct connection of the permanent magnets  12  as shown in  FIG.  6   , but also includes connection by interposing a soft magnetic material such as soft iron or another permanent magnet magnetized in a radial direction, as a pole piece, between adjacent ones of the permanent magnets  12 , in view of magnetic characteristics and a manufacturing process allowing easy assembling by suppressing a repulsive force. 
      A linear motor drive circuit including a power supply, a linear motor control circuit, and the like are well known and are not essential parts of the present invention. Therefore, illustration and description of those circuits are omitted, and a position control system will briefly be described later. 
     Referring to  FIGS.  4  and  5   , in the linear shaft motor  10 , a lower connecting member  31  and an upper connecting member  32  are fixed to a lower side and an upper side of the first shaft  11 , respectively. Therefore, with up-and-down movement of the first shaft  11  with respect to the coil portion  15  as the fixed portion, the lower connecting member  31  and the upper connecting member  32  integrally move up and down also. 
     A dispensing head  40  is attached to the lower connecting member  31  and the upper connecting member  32  in parallel to a center axis of the first shaft  11 . Referring to  FIG.  8    in addition, the dispensing head  40  has a head body  41  comprising a hollow cylindrical body having a length longer than an interval between the lower connecting member  31  and the upper connecting member  32 . The head body  41  has a protruding portion  41 - 1  formed at an upper end portion thereof and slightly protruding from the upper connecting member  32 . On the other hand, a nozzle portion  43  having a chip  42  mounted to its tip is attached to a lower part of the head body  41  protruding from the lower connecting member  31 . The dispensing head  40  moves up and down integrally with the first shaft  11  via the lower connecting member  31  and the upper connecting member  32 . The dispensing head  40  has a structure preventing rotation around its center axis with a part above the nozzle portion  43 , that is, the head body  41 , used as a spline shaft. Specifically, spline grooves (or ridges) extending in the center axis direction are provided on an outer periphery of the head body  41  as the spline shaft. On the other hand, ball splines  44  are provided as a fixed portion near an upper side of the lower connecting member  31 , and ridges (or grooves) extending in the center axis direction are formed on an inner periphery of the ball splines. The head body  41  is attached to the ball splines  44  so that the spline grooves (or ridges) are fitted to the ridges (or grooves). Around the head body  41  between the upper connecting member  32  and the ball spline  44  on an upper side, a compression spring  45  is provided to prevent the dispensing head  40  from falling down and to hold the dispensing head  40  at a predetermined lower limit position when a dispensing operation is off, that is, when the linear shaft motor  10  is powered off. 
     In order to fix an upper end portion of the first shaft  11  to the upper connecting member  32 , in this embodiment, the upper connecting member  32  is provided with a through hole  32   a  for inserting the first shaft  11 , and a slot  32   b  extending from the through hole  32   a  to one end of the upper connecting member  32 , as shown in  FIG.  1   . Furthermore, a hexagonal socket screw  34  can be screwed at the one end of the upper connecting member  32  to extend from one side surface to the other side surface across the slot  32   b . With such a structure, the upper end portion of the first shaft  11  inserted into the through hole  32   a  is fixed in the through hole  32   a  by fastening of the hexagonal socket screw  34 . 
     A fixing structure similar to that described above is also applied at a lower end of the first shaft  11 . Specifically, with reference to  FIGS.  2  and  5    in addition, a lower end portion of the first shaft  11  inserted into a through hole  31   a  formed in the lower connecting member  31  is fixed in the through hole  31   a  by fastening of a hexagonal socket screw  35 . In order to enable the fastening by the hexagonal socket screw  35 , the lower connecting member  31  is provided with a slot  31   b  extending from the through hole  31   a  to one end of the lower connecting member  31 , like in the upper connecting member  32 . 
     By applying a fixing structure (combination of a through hole, a slot, and a hexagonal socket screw) similar to that described above, an upper end of the head body  41  and a middle part of the head body  41  slightly above the nozzle portion  43  are also fixed in a through hole  32   c  of the upper connecting member  32  and a through hole  31   c  of the lower connecting member  31  by fastening of hexagonal socket screws  36  and  37 . 
     A structure for making the coil portion  15  and the ball splines  44  act as the fixed portions will later be described. 
     As will be understood from  FIG.  3   , the 4-axis dispensing device is composed of four combinations of the linear shaft motors  10  and the dispensing heads  40 . The four linear shaft motors  10  and the four dispensing heads  40  are combined so as to be arranged in a row in different planes parallel to each other, respectively. 
     Referring to  FIGS.  4  and  7    in addition, a coil fixing member  50  is used to arrange the four linear shaft motors  10  in a row. On the other hand, a center plate  60  is used to arrange the four dispensing heads  40  in a row. Referring to  FIG.  9    in addition, the center plate  60  is shared by the pair of 4-axis dispensing devices when applied to the 8-axis dispensing device. Therefore, the center plate  60  has eight accommodation spaces  60   a  in which the dispensing heads  40  of one of the pair of 4-axis dispensing devices and the dispensing heads  40  of the other of the pair of 4-axis dispensing devices are alternately arranged and accommodated. Each accommodation space  60   a  accommodates the ball splines  44  and a part of the dispensing head  40  with the compression spring  45  attached thereto. The ball splines  44  are fixed by a plurality of (herein, two) screws  61  screwed through a side wall of the center plate  60  so as not to rotate about the center axis in the accommodation space  60   a .  FIG.  7    shows the screws  61  applied to the ball splines  44  for the dispensing heads  40  of one of the pair of 4-axis dispensing devices. As shown in  FIG.  9   , screws  62  for fixing the ball splines for the dispensing heads  40  of the other of the pair of 4-axis dispensing devices are screwed into an opposite side wall of the center plate  60 . 
     As will later be described and, therefore, is briefly described herein, the 4-axis dispensing device as shown in  FIG.  3    is assembled as follows. However, the 4-axis dispensing device shown in  FIG.  3    is given as a so-called partially-omitted diagram for easy understanding of the description, and is not manufactured in a configuration as illustrated in  FIG.  3   . This is because the dispensing heads  40  are incorporated into the 8-axis dispensing device in a state of being accommodated in the center plate  60  described with reference to  FIGS.  7  and  9   . 
     First, the four coil portions  15  are arranged at predetermined intervals and fixed in the coil fixing member  50  and, thereafter, the first shaft  11  is inserted through each coil portion  15 . Subsequently, the lower connecting member  31  and the upper connecting member  32  are fixed to the lower end portion and the upper end portion of each of the first shafts  11 , respectively. Next, the chips  42  and the nozzles  43  are removed from the four dispensing heads  40  alternately accommodated in the accommodation spaces  60   a  of the center plate  60 . A lower part of the head body  41  is fixed to the lower connecting member  31 , and the upper end of the head body  41  is fixed to the upper connecting member  32 . Thereafter, the nozzle  43  and the chip  42  are mounted to the head body  41 . As described above, the 4-axis dispensing device as a half of the 8-axis dispensing device is assembled on one side wall of the center plate  60  shown in  FIG.  9   . Similarly, another 4-axis dispensing device as a remaining half of the 8-axis dispensing device is assembled on the other side wall of the center plate  60 . As a result, the 8-axis dispensing device as shown in  FIG.  1    is completed. This assembling will later be described also. 
     Next, referring to  FIG.  10 A to  14    in addition, a method of manufacturing a coil unit, which is a main part of the present invention, will be described. 
       FIGS.  10 A to  10 D  are perspective views sequentially illustrating a manufacturing process of the coil unit when the present invention is applied to the 4-axis independent-control dispensing device. 
     In  FIGS.  10 A to  10 D , at first, the coil fixing member  50  is prepared ( FIG.  10 A ). The coil fixing member  50  has a receiving portion  51  capable of receiving the four coil portions  15  in a state of being arranged in a row at a predetermined pitch P1. Referring to  FIG.  11    in addition, each of the coil portions  15  is formed by connecting the plurality of coils  14  in series and fixing the coils to the outer periphery of the coil integration cylinder  16  of resin. The coil integration cylinder  16  has an inner diameter slightly larger than an outer diameter of the first shaft  11  and a length including protrusions  16 - 1  protruding from the coils  14  at both ends among the plurality of coils. As described above, the plurality of coils  14  are arranged so that three coils of U phase - V phase - W phase are grouped as a set, and delta or star connection is performed. 
     Next, as shown in  FIG.  10 B , the four coil portions  15  are arranged in a row at the predetermined pitch P1 in the receiving portion  51  of the coil fixing member  50 . 
      Referring to  FIG.  12   , the receiving portion  51  of the coil fixing member  50  is formed by a bottom wall  51   a  defining a bottom surface of a receiving space for the four coil portions  15  arranged in a row, a pair of wall members  51   b  faced to each other so as to define the receiving space with respect to a direction parallel to the center axis direction of the coil portions  15 , and a pair of coil ends  52  provided between the pair of wall members  51   b  at both ends of the four coil portions  15 . Both ends of the coil fixing member  50  are formed as recessed portions for securing a connection space with an electric circuit mounted to a circuit board which will later be described. Each coil end  52  has four through holes  52   a  for insertion of the protruding portions  16 - 1  of the coil integration cylinders  16  that protrude from the both ends of the four coil portions  15 , and is removably fixed to the bottom wall  51   a  by screwing. A protruding length of each protruding portion  16 - 1  is desirably shorter than a plate thickness of the coil end  52 , that is, a length of the through hole  52   a . 
     The coil ends  52  are removable from the bottom wall  51   a  because the total length of the plurality of coils  14  is substantially equal to an interval between the pair of coil ends  52 . Specifically, as shown in  FIG.  12   , the four coil portions  15  are arranged in the receiving portion  51  by inserting the one protruding portions  16 - 1  of the four coil portions  15  into the four through holes  52   a  of one coil end  52  fixed to the bottom wall  51   a  of the coil receiving portion  51 . Thereafter, the other coil end  52  is fixed by screwing to the bottom wall  51   a  in a state where the other protruding portions  16 - 1  of the four coil portions  15  are inserted into the through holes  52   a . 
     The coil end  52  is also provided with five slits (second slits)  52   b  for installing magnetic shielding plates  70  ( FIG.  10 C ), which will later be described, on both sides of the four coil portions  15  disposed in the receiving portion  51  and in parallel to the center axis direction of the coil portions. In other words, the slits  52   b  are formed on both sides of the through holes  52  to extend in a depth direction from an opening side of the receiving space. It should be noted that at least one of the pair of coil ends  52  must be removable from the bottom wall  51   a . 
      Following the step of arranging the coil portions  15  in  FIG.  10 B , referring to  FIG.  10 C , the magnetic shielding plates  70  longer than the coil portions  15  are disposed on both sides of the four coil portions  15  arranged in a row and along the center axis direction of the coil portions. Specifically, the magnetic shielding plates  70 , five in total, are fitted one by one to the slits  52   b  of the pair of coil ends  52 . The magnetic shielding plates  70  serve to prevent adjacent ones of the linear shaft motors from interfering with each other (for example, cogging) by adjacent ones of the coil portions  15  and the permanent magnets  12  in the first shaft  11 . Therefore, each magnetic shielding plate  70  is made of a high magnetic permeability material, for example, an SPCC (cold rolled steel plate), and has a length at least over a movable range of the plurality of permanent magnets  12  in the first shaft  11 . The width of the magnetic shielding plate  70  is larger than the depth of the receiving space of the receiving portion  51 , and the width of at least a part corresponding to a partial region of the receiving space is nearly equal to the depth of the receiving space. This aims to provide a structure that the circuit board  80  can be attached to the part corresponding to the partial region of the receiving space, as will later be described with reference to  FIG.  14   . 
     Subsequently, referring to  FIG.  10 D , a curable resin (adhesive)  75  is poured and cured between the coil portions  15  and the magnetic shielding plates  70  in the receiving portion  51 . Consequently, the coil portions  15  and the magnetic shielding plates  70  are fixed to the receiving portion  51 . 
     It should be noted that the magnetic shielding plates  70  must be provided at least at positions corresponding to spaces between adjacent ones of the coil portions  15 , and the outermost two magnetic shielding plates may be omitted. The coil portions  15  and the magnetic shielding plates  70  may be fixed by a fixing method other than bonding by the curable resin  75 . 
       FIG.  13    shows an example of the circuit board  80  to be installed on the opening side of the receiving space in the coil unit manufactured by the manufacturing method of  FIGS.  10 A to  10 D .  FIG.  14    shows an example of the coil unit with the circuit board  80  installed in the receiving portion  51  by screwing. The circuit board  80  has a cutout  81  for exposing a part of the four coil portions  15 , and five slits (first slits)  82  for allowing wide portions, having a large plate width, of the magnetic shielding plates  70  to protrude from the circuit board  80 . The cutout  81  is formed so as to facilitate electrical connection (not shown) between coil connection conductive patterns  84  formed at a peripheral edge of the cutout and the four coil portions  15 . On the other hand, the slits  82  are formed at positions on an upper side of the circuit board  80 . Therefore, even if the magnetic shielding plate  70  is peeled off from the receiving portion  51  during operation due to bonding failure, a lower end portion of the wide portion is caught by a lower end edge of the slit  82  to prevent the magnetic shielding plate  70  from falling down to the microplate. 
     In  FIGS.  13  and  14   , a reference numeral  83  denotes a pair of magnetic sensors for detecting positions of the permanent magnets  12  in the first shaft  11 , for example, analog Hall sensors (hereinafter abbreviated to Hall sensors). The pair of Hall sensors  83  are used for position control of the first shaft  11  in the linear shaft motor  10 . The pair of Hall sensors  83  are installed at positions corresponding to the first shaft  11  and adjacent to the wide portions of the magnetic shielding plates  70  at a predetermined mounting interval in a moving direction of the first shaft  11 . As shown in  FIG.  18   , the mounting interval of the pair of Hall sensors  83  is set to an electrical angle of 90 degrees in the waveform of the surface magnetic flux density of the first shaft  11  (permanent magnets  12 ). This is based on the knowledge, gained by the inventors as a result of measuring an external magnetic field of the linear shaft motor  10  in the radial direction, that the surface magnetic flux density of the first shaft  11  (permanent magnets  12 ) becomes a waveform close to a sine wave away from the surface of the first shaft  11  to some extent as shown in  FIG.  19   . In  FIG.  19   , λ N-N  represents a magnetic pole pitch of the permanent magnets  12 , D represents a diameter of the first shaft  11 , and B 0  represents a peak value of the surface magnetic flux density of the first shaft  11 . 
     In the present embodiment, with reference to measurement data as shown in  FIG.  19   , a position at which the data closer to the sine wave is obtained is determined as an installation location of the Hall sensors  83 . In the present embodiment, for the following reason, the pair of Hall sensors  83  are disposed on a surface of the circuit board  80  (a surface on the side opposite to the receiving portion  51 ) and between large-width parts of the two magnetic shielding plates  70 . That is, by forming the slits  82  in the circuit board  80 , the large-width parts of the magnetic shielding plates  70  are extended into the receiving portion  51  of the coil fixing member  50 . This aims to prevent the influence of the magnetic field from the linear shaft motors  10  adjacent to the pair of Hall sensors  83  installed between the large-width parts of the two magnetic shielding plates  70 . 
     The electric circuit mounted to the circuit board  80  is mainly a circuit connected to the plurality of coils  14  to drive and control the four linear shaft motors  10 . For the circuit, description is omitted. Referring to  FIG.  20   , the position control system of the linear shaft motor  10  will be described. 
       FIG.  20    is a block diagram of the position control system of the linear shaft motor  10 , and the position control system is installed in the linear shaft motor  10  of each axis. However, a microcomputer  88  may be common to the linear shaft motors  10  of all axes. The position control system includes the two Hall sensors  83  installed on the circuit board  80 , an operational amplifier  85  for processing detection signals from the two Hall sensors  83 , an interpolator  86  for digitizing a signal from the operational amplifier  85 , a motor drive circuit  87  for driving and controlling the first shaft  11  of the linear shaft motor  10  based on a digital signal from the interpolator  86 , and the microcomputer  88  for outputting to the motor drive circuit  87  an operation command including a movement amount, a moving speed, a direction signal, and so on, required for driving the linear shaft motor  10 . 
     The position control system has two control modes for a case where, in addition to a positive voltage signal, a negative voltage signal is generated from the detection signals of the two Hall sensors  83  (the case with signal inversion) and a case where only a positive voltage signal is generated from the detection signals of the two Hall sensors  83  (the case without signal inversion).  FIG.  20    shows the case without signal inversion. In the case with signal inversion, the number of output signal lines at the operational amplifier  85  and thereafter is different. 
     In the Case Without Signal Inversion 
     1. The surface magnetic flux density of the first shaft  11  is detected by the Hall sensors  83  and output as analog voltage signals. As described above, the surface magnetic flux density of the first shaft  11  is a sine wave along the axial direction. Therefore, when the two Hall sensors  83  are arranged near the first shaft  11  at a pitch corresponding to ¼ of the magnetic pole pitch (hereinafter referred to as a magnet pitch) of the permanent magnets  12  and the magnetic flux density is detected, two analog voltage signals shifted in phase by an electrical angle of 90 degrees, that is, a sine wave (hereinafter referred to as a Sin wave) voltage signal and a cosine wave (hereinafter referred to as a Cos wave) voltage signal can be generated. 
     2. The analog voltage signals output from the two Hall sensors  83  are input to the operational amplifier  85 . The operational amplifier  85  adjusts output voltages of the two Hall sensors  83  so as to conform to a driver input. 
     3. The interpolator  86  of a driver digitizes the two analog signals input from the operational amplifier  85  and divides the signals by a designated number of bits. The number of division defines resolution (magnet pitch/division number). For example, in the case where the magnet pitch is 24 mm and the division number is  2   14 , the resolution is 1.5 µm. As a result, the two analog voltage signals (Sin wave voltage signal and Cos wave voltage signal) become two rectangular wave signals (position signals) shifted in phase by an electrical angle of 90 degrees. 
     4. The motor drive circuit  87  detects a current position and a moving speed of the first shaft  11  (dispensing head  40 ) by the two rectangular wave signals input from the interpolator  86 , and delivers a position control command defining a stop position to the linear shaft motor  10  (coil unit  15 ). 
     In the Case With Signal Inversion 
     1. The surface magnetic flux density of the first shaft  11  is detected by the two Hall sensors  83  and output as analog voltage signals. The surface magnetic flux density of the first shaft  11  is a sine wave along the axial direction. When the two Hall sensors  83  are arranged near the first shaft  11  at a pitch corresponding to ¼ of the magnetic pole pitch (hereinafter referred to as a magnet pitch) of the permanent magnets  12  and the magnetic flux density is detected, two analog voltage signals shifted in phase by an electrical angle of 90 degrees, that is, a Sin wave voltage signal and a Cos wave voltage signal can be generated. 
     2. The two analog voltage signals output from the two Hall sensors  83  are input to the operational amplifier  85 . The operational amplifier  85  generates an inverted signal for each of the two input analog voltage signals (Sin wave voltage signal and Cos wave voltage signal). Thus, in addition to the Sin wave voltage signal and the Cos wave voltage signal output from the Hall sensors  83 , a -Sin wave voltage signal and a -Cos wave voltage signal are generated so that the four analog voltage signals are obtained. The operational amplifier  85  adjusts output voltages of the Hall sensors  83  so as to conform to the driver input. As described above as another control mode, only two signals including the Sin wave voltage signal and the Cos wave voltage signal may be sufficient. However, by generating the -Sin wave voltage signal and the -Cos wave voltage signal, noise robustness is achieved. 
     3. The interpolator  86  of a driver digitizes the four analog voltage signals output from the operational amplifier  85  and divides the signals by a designated number of bits. The resolution represented by the magnet pitch and the number of divisions is as described above. Thus, the four analog voltage signals become four rectangular wave signals (position signals). 
     4. The motor drive circuit  87  detects a current position and a moving speed of the first shaft  10  (dispensing head  40 ) by the four rectangular wave signals (position signals) output from the interpolator  86 , and delivers a position control command defining a stop position to the linear shaft motor  11  (coil unit  15 ). 
     Next referring to  FIG.  9   , a procedure for assembling and manufacturing the 8-axis independent-control dispensing device will be described. The 4-axis independent-control dispensing device described with reference to  FIG.  3    is assembled and manufactured by using the coil unit manufactured by the above-described manufacturing method. Subsequently, in a state where the circuit boards  80  are faced to each other via the center plate  60 , a pair of the 4-axis independent-control dispensing devices are combined to be integrated by connecting plates  90  at longitudinal both ends of the dispensing devices and the center plate  60 . 
     The connecting plates  90  has a laterally-facing H shape with recessed portions formed on both sides and corresponding to the recessed portions formed at the both ends of the coil fixing members  50 . The connecting plates  90  are attached at two positions to each of longitudinal end faces of the pair of coil fixing members  50  and longitudinal end faces of the center plate  60  by hexagonal socket screws  91 . Thus, the pair of 4-axis independent-control dispensing devices and the center plate  60  are integrated. 
     In  FIG.  9   , the linear shaft motors  10 , the dispensing heads  40 , the lower connecting members  31 , and the upper connecting members  32  in the 4-axis independent-control dispensing device described with reference to  FIG.  5    are omitted for convenience. As described above, in a state where the four dispensing heads  40  in the 4-axis independent-control dispensing device shown in  FIG.  3    are accommodated in the accommodating spaces  60   a  of the center plate  60 , the pair of 4-axis independent-control dispensing devices and the center plate  60  are integrated by the two connecting plates  90  at the both ends thereof to form the 8-axis independent-control dispensing device as shown in  FIG.  1   . In particular, when the pitch (interval) of the linear shaft motors  10  is represented by P1, the arrangement of the four linear shaft motors  10  in one of the pair of the 4-axis independent-control dispensing devices and the arrangement of the four linear shaft motors  10  in the other dispensing device are shifted by P2 (= P1/2), as shown in  FIG.  15   . 
     Therefore, the four dispensing heads  40  in one of the pair of 4-axis independent-control dispensing devices and the four dispensing heads  40  in the other dispensing device are integrated in a state of being alternately accommodated in the eight accommodating spaces  60   a  of the center plate  60 . As a result, as the 8-axis independent-control dispensing device, even if the pitch (interval) P2 of the eight dispensing heads  40  is small, the pitch (interval) P1 of the linear shaft motors  10  can be large. Thus, malfunction due to magnetic field interference between adjacent ones of the linear shaft motors  10  can be prevented even if sizes of the permanent magnets  12  and the coils  14  are not reduced. 
     The 8-axis independent-control dispensing device according to the present embodiment is combined with a transport mechanism (not shown) for reciprocating between a sucking position and a discharging position of a liquid. Therefore, the connecting plates  90  may be omitted by fixing the pair of coil fixing members  50  and the center plate  60  to a part of the transport mechanism. 
     Next, with reference to  FIG.  16    and  FIGS.  17 A and  17 B , position detecting means will be described which is necessary for position control for discharging and sucking the liquid by the dispensing heads  40  by detecting an upper movement position (upper limit position) of the upper connecting member  32 .  FIG.  16    is a perspective view for describing a detector  100  for detecting the upper movement position of the upper connecting member  32  in the 8-axis independent-control dispensing device shown in  FIG.  1   .  FIGS.  17 A and  17 B  are views for describing an example of an arrangement mode of the detector  100  shown in  FIG.  16   , wherein  FIG.  17 A  is a side view of the 8-axis independent-control dispensing device and  FIG.  17 B  is a perspective view of the 8-axis independent-control dispensing device. 
     In this example, apart from the position control of the linear shaft motors  10  by position detection signals from the pair of Hall sensors  83 , the upper movement position of the upper connecting member  32  is detected as the upper limit position to thereby detect the upper movement position of the dispensing heads  40  in the same combination. Therefore, as shown in  FIG.  16   , each of the upper connecting members  32  is provided with a detected protrusion  101  of a hollow shaft shape formed on an upper end face near its center. A photosensor  102  is provided as a limit sensor so that light is blocked when the detected protrusion  101  is moved upward to a predetermined position. As shown in  FIGS.  17 A and  17 B , a sensor installation substrate  111  is fixedly arranged, via a support column  110  fixed to the center plate  60 , at a position higher than the upper movement position of the upper connecting member  32 . Eight photosensors  102  are installed on the sensor installation substrate  111  so as to correspond to the eight detected protrusions  101   of the 8-axis independent-control dispensing device. When the linear shaft motors  10 , the dispensing heads  40 , the lower connecting member  31 , and the upper connecting member  32  are configured to be movable portions in the 8-axis independent-control dispensing device, the sensor installation substrate  111  (photosensor  102 ) is a fixed portion together with the pair of coil fixing members  50  and the center plate  60 . 
     The detector  100  is used not only as means for detecting the upper movement position of the dispensing head  40  associated with a dispensing operation of sucking and discharging the liquid, but also as means for performing origin positioning when the dispensing operation is started. The origin positioning is as follows. 
     At the start of the dispensing operation, the detected protrusion  101  blocks an optical path of the photosensor  102 , and upward movement of each dispensing head  40  is performed until a detection signal is output from the photosensor  102 . By this operation, an offset operation is performed using the detection signal output from the photosensor  102  as a reference. Since an offset position has the same height for the respective axes, this position is used as a reference point for positioning control of the linear shaft motor  10 , which will later be described. 
     In  FIGS.  16  and  17 A and  17 B , a signal transmission cable  103  extends from one end of the photosensor  102 . For convenience, the cable is shown in a cut state, leaving only a part thereof. 
     Effect of the Embodiment 
     (1) As to the above-mentioned 8-axis independent-control dispensing device, the pitch (interval) P1 of the linear shaft motors  10  need not be reduced even with multiple axes such as eight axes, as described above. Therefore, the dispensing device can be constituted without reducing the size of the permanent magnets  12  and the coils  14  correspondingly. This is effective in the following aspects. 
     The multi-axis dispensing device is required to be reduced in pitch (interval) between the dispensing heads. This is because, by reducing the pitch between the dispensing heads, the multi-axis dispensing device as a whole can be compact so as to increase a movable range. However, in the case of the existing multi-axis dispensing device with one-row arrangement of a plurality of dispensing heads, the diameter of the linear shaft motor must be reduced in order to reduce the pitch between the dispensing heads. For this purpose, the diameter of the permanent magnet must be reduced or the diameter of the coil, i.e., the number of turns of the coil must be reduced. This means that a thrust force (driving torque) of each axis becomes small. However, up-and-down movement of the dispensing head requires a predetermined thrust force. This is because, referring to  FIG.  8    for example, removal of the chip  42  attached to the tip of the nozzle  43  is automated by moving the head body  41  upward in a state where a narrow part between the chip  42  and the nozzle  43  is nipped by a jig (not shown) at a position different from sucking and discharging positions of the liquid. In other words, when the thrust force for the up-and-down movement of the dispensing head becomes small, the automated removal of the chip  42  is difficult. 
     In contrast to the above-mentioned situation, according to the 8-axis independent-control dispensing device according to the present embodiment, the pitch between the dispensing heads is reduced and the predetermined thrust force (driving torque) can be obtained during up-and-down movement of the dispensing head without reducing the diameter of the linear shaft motor. Thus, the above-described problem does not occur. 
     (2) In general, the coil portions of the linear shaft motors are accommodated in casings each for each individual coil portion. On the other hand, in the present embodiment, the plurality of coil portions  15  are collectively unitized because of the structure in which the plurality of first shafts  11  are arranged adjacent to each other. Therefore, it is possible to realize reduction in number of components in the coil unit, reduction in number of assembling steps, and space saving. 
     (3) Since the magnetic shielding plates  70  are installed on both sides of each coil portion  15  along the center axis direction and fixation of the coil portions  15  and fixation of the magnetic shielding plates  70  can be performed simultaneously by the curable resin  75 . Therefore, in this respect also, it is possible to realize reduction in number of components in the coil unit, reduction in number of assembling steps, and space saving. 
     While the preferred embodiment has been described in the case where the present invention is applied to the 8-axis independent-control dispensing device, it is needless to say that the present invention is not limited to the above-described embodiment. That is, the present invention is applicable to either an independent-control or a simultaneous-control multi-axis dispensing device with two or more axes, and is also applicable to multiaxis linear motor actuators in general without being limited to the dispensing device. 
     This application claims the benefit of priority based on Japanese Patent Application No. 2020-77350, filed on Apr. 24, 2020, the disclosure of which is incorporated herein in its entirety. 
     DESCRIPTION OF REFERENCE NUMERALS 
       10 : linear shaft motor,  11 : first shaft,  12 : permanent magnet,  13 : cylindrical body,  14 : coil,  16 : coil integration cylinder,  31 : lower connecting member,  32 : upper connecting member,  40 : dispensing head,  41 : head body,  42 : chip,  43 : nozzle,  50 : coil fixing member,  51 : receiving portion,  52 : coil end,  60 : center plate,  70 : magnetic shielding plate,  80 : circuit board,  83 : Hall sensor,  90 : connecting plate,  100 : detector,  102 : photosensor,  111 : sensor installation substrate.