Patent Publication Number: US-2018048221-A1

Title: Linear actuator and method for manufacturing linear actuator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is the U.S. national stage of application No. PCT/JP2016/059997, filed on Mar. 29, 2016. Priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is claimed from Japanese Applications No. 2015-073348, filed on Mar. 31, 2017; the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     At least an embodiment of the present invention relates to a linear actuator provided with a damper member for suppressing resonance, and a manufacturing method therefor. 
     BACKGROUND 
     As a device for notifying of an incoming call and the like of a mobile phone, by way of a vibration, there is proposed a liner actuator. A linear actuator described in Patent Document 1 is provided with a movable element having a permanent magnet, and a stationary element having a coil. The stationary element supports the movable element so as to be movable, by the intermediary of an elastic member, such as a spring component and the like. In the case of the linear actuator described in the document, an intensity level and a frequency of a vibration vary according to a driving signal supplied to the coil. 
     PATENT DOCUMENT 
     Patent Document 1; Japanese Unexamined Patent Application Publication No. 2006-7161 
     In a linear actuator, sometimes a movable element may resonate, depending on a vibration frequency, at a time when the movable element vibrates. 
     In such a situation, it is conceivable for suppressing resonance to insert a damper member, which is extendable in a moving direction of the movable element, between a movable-element-side facing surface of the movable element and a stationary-element-side facing surface of a stationary element; the movable-element-side facing surface and the stationary-element-side facing surface facing each other in the moving direction of the movable element. Unfortunately, in this case, without controlling a dimension of a distance between the movable-element-side facing surface and the stationary-element-side facing surface where the damper member is inserted, in such a way as to make the dimension of the distance constant, a stroke and a resonance frequency of the movable element vary among manufactured products, due to the damper member inserted between the facing surfaces. 
     SUMMARY 
     With the issue described above being taken into consideration, at least an embodiment of the present invention provides a linear actuator in which a distance between a movable element and a stationary element, where a damper member is inserted, is accurately controlled; and to propose a structure and a manufacturing method of such a linear actuator. 
     In order to solve the issue described above, a linear actuator according to at least an embodiment of the present invention includes: a movable element; a stationary element; and a damper member inserted between a movable-element-side facing surface of the movable element and a stationary-element-side facing surface of the stationary element, the movable-element-side facing surface and the stationary-element-side facing surface facing each other in a moving direction of the movable element; wherein, the stationary element is provided with a first element that supports the movable element by the intermediary of a spring member in such a way as to be movable, and a second element that includes the stationary-element-side facing surface and overlaps with the first element from a side opposite to the movable element in the moving direction; and between the first element and the second element, there is provided a distance adjusting part that has adjusted a distance between the first element and the second element in the moving direction, by way of deforming at least one of the first element and the second element. 
     According to at least an embodiment of the present invention; between the first element and the second element, which make up the stationary element, there is provided the distance adjusting part in order to adjust the distance between the first element, supporting the movable element, and the second element, provided with the stationary-element-side facing surface, in the moving direction. Therefore, by way of adjusting the distance between the first element and the second element with the distance adjusting part, a dimension of the distance between the movable-element-side facing surface and the stationary-element-side facing surface can be set with a specified dimension corresponding to a length of the damper member in the moving direction. Accordingly, it becomes possible to avoid variations in a stroke and a resonance frequency of the movable element, among manufactured products, due to the damper member inserted between the movable-element-side facing surface and the stationary-element-side facing surface. 
     In at least an embodiment of the present invention, the distance adjusting part is a projection part protruding from one of the first element and the second element toward the other; and a tip part of the projection part is crushed. According to this configuration, a distance between the first element and the second element is adjusted by way of crushing the tip part of the projection part that is provided to, at least, one of the first element and the second element, in such a way that the dimension of the distance between the movable-element-side facing surface and the stationary-element-side facing surface can be set with the specified dimension. 
     In at least an embodiment of the present invention, the distance adjusting part is a projection part protruding from the first element toward the second element; and a distance dimension, with which a tip of the projection part in a crushed state and the movable-element-side facing surface are apart from each other in the moving direction, is the same as the length of the damper member in the moving direction. According to this configuration, a stroke of the movable element can easily be secured. 
     In at least an embodiment of the present invention; for accurately crushing the tip part of the projection part formed in the first element, that the first element is made of a resin material; and the tip part of the projection part is melted and crushed by heat. 
     In at least an embodiment of the present invention; for moving the movable element, the linear actuator includes a magnetic drive mechanism for moving the movable element; the magnetic drive mechanism includes a permanent magnet held in the movable element, and a drive coil held in the stationary element; the first element is a coil bobbin that surrounds the permanent magnet from a direction crossing the moving direction; and the drive coil is wound around the coil bobbin. 
     In at least an embodiment of the present invention; for suppressing resonance of the movable element, while allowing the movable element to move, the damper member is a gel damper member. 
     Then, a method for manufacturing the linear actuator, according to at least an embodiment of the present invention, includes; supporting the movable element with the first element by the intermediary of the spring member; making the distance dimension between the tip of the projection part and the movable-element-side facing surface, with a specified dimension that is predetermined, by way of crushing the tip part of the projection part provided to the first element; and overlaying the second element on the first element, from a side opposite to the movable element in the moving direction; and placing the damper member having the specified dimension as a dimension in the moving direction, between the movable-element-side facing surface and the stationary-element-side facing surface. 
     According to at least an embodiment of the present invention; by way of crushing the tip part of the projection part placed between the first element and the second element in the stationary element, the dimension between the movable-element-side facing surface and the stationary-element-side facing surface is made to be the specified dimension corresponding to a dimension of the damper member. Therefore, variations in a stroke and a resonance frequency of the movable element, due to the damper member inserted between the movable-element-side facing surface and the stationary-element-side facing surface, are not observed among manufactured products. Furthermore, the distance between the movable-element-side facing surface and the stationary-element-side facing surface is the same as the length of the damper member, and therefore a stroke of the movable element can easily be secured. 
     According to at least an embodiment of the present invention, the dimension of the distance between the movable-element-side facing surface of the movable element and the stationary-element-side facing surface of the stationary element, where the damper member is inserted, can be made to be the specified dimension. Therefore, it is possible to avoid a variance of the stroke and the resonance frequency of the movable element, due to the damper member inserted between the movable-element-side facing surface and the stationary-element-side facing surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which: 
         FIG. 1  is a perspective view of a linear actuator according to at least an embodiment of the present invention. 
         FIGS. 2A-2B  include cross-sectional views of the linear actuator shown in  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the linear actuator shown in  FIG. 1 . 
         FIGS. 4A-4B  include perspective views showing a coil bobbin, a driving coil, and a spring. 
         FIGS. 5A-5B  include explanatory drawings of a method for manufacturing the linear actuator shown in  FIG. 1 . 
         FIG. 6  is a perspective view of a linear actuator according to at least an embodiment of the present invention. 
         FIGS. 7A-7B  include cross-sectional views of the linear actuator shown in  FIG. 6 . 
         FIG. 8  is an exploded perspective view of the linear actuator shown in  FIG. 6 . 
         FIGS. 9A-9B  include perspective views showing a coil bobbin, a driving coil, and a spring. 
         FIGS. 10A-10B  include explanatory drawings of a method for manufacturing the linear actuator shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention are explained below, with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a perspective view of a linear actuator according to a first embodiment of the present invention.  FIG. 2  includes cross-sectional views of the linear actuator shown in  FIG. 1 . In  FIG. 2A , the cross section of the linear actuator is seen from an obliquely upward direction; and in  FIG. 2B , the cross section of the linear actuator is seen from a direction perpendicular to a moving direction of a movable element.  FIG. 3  is an exploded perspective view of the linear actuator shown in  FIG. 1 . 
     (General Configuration) 
     As shown in  FIG. 1  through  FIG. 3 , a linear actuator  1  includes a movable element  2 , a stationary element  3 , and a spring (spring member)  4  that connects the movable element  2  and the stationary element  3 . The stationary element  3  supports the movable element  2  in such a way as to be movable, by the intermediary of the spring  4 . Between the movable element  2  and the stationary element  3 , three damper members  5  are placed. The linear actuator  1  further includes a magnetic drive mechanism  7  in order to move the movable element  2 . The magnetic drive mechanism  7  is provided with a permanent magnet  8  held by the movable element  2 , and a drive coil  9  held by the stationary element  3 . In the following explanation, a moving direction of the movable element  2  is dealt with as a direction of an axis line ‘L’. The direction of the axis line ‘L’ is consistent with a central axis line of the permanent magnet  8  mounted on the movable element  2  and a central axis line of the drive coil  9  mounted on the stationary element  3 . For the purpose of convenience, an upside and a downside of the linear actuator  1  are explained as follows, with reference to upward and downward directions in the drawings. That is to say; in the direction of the axis line ‘L’, a side where the stationary element  3  is positioned is a downside, meanwhile a side where the movable element  2  is positioned is an upside. 
     (Movable Element) 
     The movable element  2  is provided with the permanent magnet  8  extending in the direction of the axis line ‘L’ (the moving direction of the movable element  2 ). The permanent magnet  8  is shaped so as to be flattened in such a way as to be short in the direction of the axis line ‘L’, and the permanent magnet  8  is magnetized with a north pole and a south pole in the direction of the axis line ‘L’. The permanent magnet  8  is provided with a top end surface and a bottom end surface that are perpendicular to the direction of the axis line ‘L’. 
     In the meantime, the movable element  2  is provided with a core member  11  that overlaps with the permanent magnet  8  from a downside, and a cap member  12  that covers up the permanent magnet  8  from an upside as well as an outer circumferential side. The permanent magnet  8 , the core member  11  and the cap member  12  are placed coaxially. The core member  11  and the cap member  12  are made of a magnetic material. 
     As show in  FIG. 3 , the core member  11  is a circular plate member having a constant thickness. A planar shape of the core member  11  is the same as a shape of the bottom end surface of the permanent magnet  8 . The core member  11  is fixed to the bottom end surface of the permanent magnet  8  with an adhesive and the like. The core member  11  extends in a direction perpendicular to the axis line ‘L’. 
     The cap member  12  includes an upper cap member  13  and a lower cap member  14 . As shown in  FIG. 2 , the upper cap member  13  includes a circular end plate part  15  having a constant thickness, and an upper cylindrical part  16  protruding downward from an outer circumferential edge of the end plate part  15 . The lower cap member  14  includes a lower cylindrical part  17  that continues downward from a bottom end edge of the upper cylindrical part  16 , and a protrusion plate part  18  protruding toward an inner circumferential side from a bottom end edge of the lower cylindrical part  17 . The protrusion plate part  18  has a constant thickness, and its planar shape is annular. As shown in  FIG. 1 , the bottom end edge of the upper cylindrical part  16  is provided with cutout parts  19  at three circumferential positions. Each of the cutout parts  19  is provided in order to hold a movable-element-side connection part  21  of the spring  4 , by way of sandwiching between the upper cylindrical part  16  and the lower cylindrical part  17 , at a time of connecting the upper cylindrical part  16  and the lower cylindrical part  17  by welding and the like. 
     Moreover, as shown in  FIG. 2  and  FIG. 3 , the cap member  12  is provided with a magnetic plate  23  having a constant thickness, which is put into the upper cap member  13  from a downside. The magnetic plate  23  is provided with a round center hole  24  at a center position, and three through-holes for welding  25 , which are formed at outer circumferential fringe parts around the axis line ‘L’ at equal angular intervals. The magnetic plate  23  is fixed to the end plate part  15  of the upper cap member  13 , by way of welding that is carried out by making use of an open edge part of the three through-holes for welding  25 . Thus, the magnetic plate  23  is laminated on the end plate part  15  in the direction of the axis line ‘L’. 
     The cap member  12  is fixed to the permanent magnet  8 , by way of bonding a bottom end surface of the magnetic plate  23  to the top end surface of the permanent magnet  8  with an adhesive and the like. In the meantime, each of the magnetic plate  23  and the end plate part  15  has a larger diameter than the permanent magnet  8  has. Therefore, under a situation where the cap member  12  is fixed to the permanent magnet  8 , as shown in  FIG. 2 , there is circumferentially formed a gap, having a constant clearance, between an annular outer-circumferential surface of the permanent magnet  8  and both the upper cylindrical part  16  as well as the lower cylindrical part  17 . Meanwhile, at a time when a situation of the cap member  12  being fixed to the permanent magnet  8  is observed from a lateral direction perpendicular to the direction of the axis line ‘L’, the protrusion plate part  18  is placed at a position that partially overlaps with the core member  11 . Moreover, there is circumferentially formed a gap, having a constant clearance, between an annular inner-circumferential surface of the protrusion plate part  18  and an annular outer-circumferential surface of the core member  11 . 
     (Stationary Element) 
     Next, the stationary element  3  is explained with reference to  FIG. 2  through  FIG. 4 .  FIG. 4A  is a perspective view showing a situation where a coil bobbin is observed from an upper side; while the coil bobbin around which the drive coil  9  is wound, is provided with the spring  4 ; and meanwhile  FIG. 4B  is a perspective view showing a situation where the coil bobbin is observed from a lower side; while the coil bobbin around which the drive coil  9  is wound, is provided with the spring  4 . As shown in  FIG. 2  and  FIG. 3 , the stationary element  3  is provided with a coil bobbin  31  (a first element) around which the drive coil  9  is wound, and a plate-like base  32  (a second element) that overlaps with the coil bobbin  31  from a side opposite to the movable element  2 . The coil bobbin  31  supports the movable element  2  by the intermediary of the spring  4  in such a way as to be movable in the direction of the axis line ‘L’. 
     (Coil Bobbin) 
     The coil bobbin  31  is made of a resin material. As shown in  FIG. 2 , the coil bobbin  31  is provided with a bottom plate part  35  that faces the core member  11  of the movable element  2  in the direction of the axis line ‘L’, and a cylindrical part  36  that protrudes upward from the bottom plate part  35 . An axis line ‘L’ of the cylindrical part  36  is consistent with an axis line ‘L’ of the permanent magnet  8 . 
     As shown in  FIG. 4A , three holes  37  for inserting the damper members are formed in the bottom plate part  35 . The holes  37  for the damper members are individually provided around the axis line ‘L’ equal angular intervals. A slit  38 , which linearly stretches in a circumferential direction, is formed between two of the holes  37  for inserting the damper members, which are neighboring in a circumferential direction. 
     In a bottom surface of the bottom plate part  35 , at a position corresponding to each slit  38 , there is provided a locating concave part  39  stretching along the slit  38 . The slit  38  is positioned at a bottom of the locating concave part  39 . Furthermore, at an outer circumferential edge part of the bottom plate part  35 , a plurality of projection parts  40  being columnar, projecting downward, are provided at regular intervals. The plurality of projection parts  40  are formed along an outer circumferential edge of the bottom surface of the bottom plate part  35 . Then, a tip part of each of the projection parts  40  is crushed at a time when the linear actuator  1  is assembled. 
     The cylindrical part  36  is provided with three spring retainer projections  43  on its annular top end surface  36   a . The three spring retainer projections  43  are placed around the axis line ‘L’ at equal angular intervals. Each of the spring retainer projections  43  works as a retainer part for retaining a stationary-element-side connection part  45  of the spring  4 , and the cylindrical part  36  supports the stationary-element-side connection part  45  from a lower side. 
     Moreover, as shown in  FIG. 2 , the cylindrical part  36  is provided with; a tubular torso part  46 , wherein the drive coil  9  is wound around an outer circumferential surface of the tubular torso part  46 ; a lower flange part  47  being annular, which is expanded in its diameter at a lower side of the tubular torso part  46 ; and an upper flange part  48  being annular, which is expanded in its diameter at an upper side of the tubular torso part  46 . Then, in a view from the direction of the axis line ‘L’, the upper flange part  48  has a larger diameter than the lower flange part  47  has. Accordingly, in a situation where the drive coil  9  is wound around the tubular torso part  46 ; the lower flange part  47  protrudes a little out of an outer circumferential surface of the drive coil  9  toward an outer side in a radial direction, while the upper flange part  48  protrudes quite a little out of the outer circumferential surface of the drive coil  9  toward the outer side in the radial direction, in comparison with the lower flange part  47 . 
     Between the annular top end surface  36   a  of an outer circumferential surface of the cylindrical part  36  and the upper flange part  48 , there are provided three reinforcing ribs  49  that reinforce the upper flange part  48 . The three reinforcing ribs  49  are provided around the axis line ‘L’ at equal angular intervals. In a view from the direction of the axis line ‘L’, each of the reinforcing ribs  49  has its outer circumferential surface that overlaps with an outer circumferential surface of the upper flange part  48 . Moreover, as shown in  FIG. 3 , each of the reinforcing ribs  49  is provided with; a rectangular leading surface  50  that leads to the annular top end surface  36   a  at an elevation being the same as the annular top end surface  36   a ; and a sloping surface  51  that slopes downward from the leading surface  50  toward one side in a circumferential direction. An end, at the one side in the circumferential direction, of the sloping surface  51  leads to a top surface of the upper flange part  48 . The leading surface  50  of each of the reinforcing ribs  49  is displaced with respect to each of the spring retainer projections  43 , in a circumferential direction, in such a way that there exists the sloping surface  51  at an outer circumferential side of each of the spring retainer projections  43 . 
     (Base) 
     As shown in  FIG. 3 , the base  32  is provided with a disk plate part  55  and a circuit board supporting part  57 , being rectangular, which protrudes outward from the disk plate part  55  in a radial direction. A circuit board  59  is supported by the circuit board supporting part  57 . A terminal of the drive coil  9  is connected to the circuit board  59 . In the meantime, an outer circumferential edge part of a top surface of the disk plate part  55  and the circuit board supporting part  57  may be covered with an adhesive component. In this case, the adhesive component is an adhesive tape or a material to be applied while having an adhesive property. 
     The disk plate part  55  is provided with a locating plate  63 . The locating plate  63  is formed by way of cutting and raising a part of the disk plate part  55 . The coil bobbin  31  is installed on the base  32 , by way of inserting the locating plate  63  into the locating concave part  39  of the bottom surface of the bottom plate part  35 , so as to locate the coil bobbin  31  in a direction perpendicular to the direction of the axis line ‘L’. The coil bobbin  31  is fixed to the base  32  by use of an adhesive filled between the bottom plate part  35  and the base  32 . 
     (Spring) 
     The spring  4  is a flat spring component, whose thickness direction is oriented in the direction of the axis line ‘L’, As shown in  FIG. 3  and  FIG. 4A , the spring  4  is provided with; the movable-element-side connection part  21  connected to the movable element  2  (the cap member  12 ); the stationary-element-side connection part  45 , being annular, connected to the stationary element  3  (the coil bobbin  31 ); and a plurality of arm parts  65  connected to the movable-element-side connection part  21  and the stationary-element-side connection part  45 . The stationary-element-side connection part  45  is placed at an inner circumferential side with respect to the movable-element-side connection part  21  and the arm parts  65 ; and meanwhile the movable-element-side connection part  21  is placed at an outer circumferential side with respect to the arm parts  65 . 
     The movable-element-side connection part  21  is divided into three parts in a circumferential direction. The arm parts  65  individually stretch in the circumferential direction from the three divided parts of the movable-element-side connection part  21 . Each divided part of the movable-element-side connection part  21  is fixed to the movable element  2  by way of pinching between the upper cap member  13  and the lower cap member  14 , while being inserted into each of the cutout parts  19  of the upper cap member  13 . 
     In the stationary-element-side connection part  45 , there are formed retaining holes  66  into which the spring retainer projections  43  of the annular top end surface  36   a  of the coil bobbin  31  are individually fit. The spring  4  is connected to the coil bobbin  31  by way of inserting each of the spring retainer projections  43  into each of the retaining hole  66 . 
     In a situation where the stationary-element-side connection part  45  of the spring  4  is connected to the coil bobbin  31 , and meanwhile the movable-element-side connection part  21  is connected to the cap member  12 ; the permanent magnet  8  of the movable element  2  is positioned at an inner circumferential side of the coil bobbin  31  of the stationary element  3 , as shown in  FIG. 2 . In the meantime, the protrusion plate part  18  of the cap member  12  is located between the lower flange part  47  and the upper flange part  48  of the coil bobbin  31 . Thus, the tubular torso part  46  of the coil bobbin  31  and the drive coil  9  wound around the tubular torso part  46  are placed between an annular inner circumferential surface of the protrusion plate part  18  and an annular outer circumferential surface of the core member  11 . Moreover, an annular outer circumferential surface of the upper flange part  48  of the coil bobbin  31  faces an inner circumferential surface of the lower cylindrical part  17  of the cap member  12  across a narrow space thereof. 
     Under this situation, the upper flange part  48  of the coil bobbin  31  and the lower cylindrical part  17  of the cap member  12  make up a first stopper mechanism to restrict a movable range of the movable element  2  at a time when the movable element  2  moves due to an external force in a direction perpendicular to the axis line ‘L’. In the meantime, the upper flange part  48  of the coil bobbin  31  and the protrusion plate part  18  of the cap member  12  make up a second stopper mechanism to restrict a movable range of the movable element  2  at a time when the movable element  2  moves upward due to an external force. 
     (Damper Members) 
     As shown in  FIG. 3 , each of the damper members  5  is columnar. A length of the damper members  5  in the direction of the axis line ‘L’ is equal to a specified dimension ‘S’ to be described later, as shown in  FIG. 2B . 
     As shown in  FIG. 2A , each of the damper members  5  is placed between the movable element  2  and the stationary element  3 , while being inserted through each of the holes  37  for inserting the damper members, the holes  37  being provided in the bottom plate part  35  of the coil bobbin  31 . Each of the holes  37  for inserting the damper members is a circular opening section having a larger diameter than each of the damper members  5  has. As shown in  FIG. 2B , each of the damper members  5  makes its top end surface contact with a bottom surface  11   a  (a movable-element-side facing surface) of the core member  11  of the movable element  2 , and makes its bottom end surface contact with a top surface  32   a  (a stationary-element-side facing surface) of the base  32  of the stationary element  3 . 
     Incidentally, the damper members  5  of the present embodiment are made of silicone gel having a needle entering level of 90 to 110. The needle entering level shows a value of an entered depth of a ¼-cone needle stressed for five seconds, with a total load of 9.38 grams at 25 degrees Celsius, as specified in JIS-K-2207 or JIS-K-2220; wherein the entered depth being expressed in 1/10 mm. The smaller the value is, the harder the material is. Incidentally, fixing the damper members  5  to the core member  11  as well as fixing the damper members  5  to the base  32  are carried out by use of an adhesive material, a gluing agent, or an adherence property of the silicone gel. 
     (Method for Manufacturing the Linear Actuator) 
       FIG. 5  includes explanatory drawings of a method for manufacturing the linear actuator  1 .  FIG. 5A  is an explanatory drawing with regard to a distance dimension, from the bottom surface  11   a  of the core member  11  to a tip of the projection parts  40  provided at the bottom plate part  35  of the coil bobbin  31 , in the direction of the axis line ‘L’; and meanwhile,  FIG. 5B  is an explanatory drawing with regard to a manufacturing step of crushing tip parts of the projection parts  40 . In  FIG. 5A , a length of the damper members  5  in the direction of the axis line ‘L’ is indicated as reference. 
     At a time of manufacturing the linear actuator  1 , as shown in  FIG. 5A , the movable element  2  is supported by the coil bobbin  31  by the intermediary of the spring  4 . Then, in a situation where the direction of the axis line ‘L’ of the coil bobbin  31  (the moving direction of the movable element  2 ) is oriented to a vertical direction; a distance dimension ‘D’ in the direction of the axis line ‘L’, stretching from the bottom surface  11   a  of the core member  11  to a tip  40   a  of the projection parts  40  provided at the bottom plate part  35  of the coil bobbin  31 , is measured. Then, there are obtained the distance dimension ‘D’, the specified dimension ‘S’ set up in advance, and a difference ‘T’. 
     Then, the coil bobbin  31  is formed in such a way that; a distance dimension from the bottom surface  11   a  of the core member  11  to a bottom surface  35   a  of the bottom plate part  35  of the coil bobbin  31  is shorter than the specified dimension ‘S’ at a time of supporting the movable element  2  by the intermediary of the spring  4 ; and moreover a distance dimension from the bottom surface  11   a  of the core member  11  to the tip  40   a  of the projection parts  40  is longer than the specified dimension ‘S’. 
     Next, the coil bobbin  31  is kept in a stationary situation. Then, as shown with a dotted line in  FIG. 5B ; a jig  70  made of a metallic flat plate, having been heated, is placed at a contact position  70 A for contacting the tip  40   a  of the projection parts  40  from the direction of the axis line ‘L’. After that, as shown with an arrow and a solid line in  FIG. 5B ; the jig  70  is pushed along the direction of the axis line ‘L’, in such a way as to move closer toward the coil bobbin  31  so as to be transferred for the difference ‘T’. Thus, the jig  70  crushes the tip parts of the projection parts  40  for the difference ‘T’, while melting each of the projection parts  40  by heat. As a result of that, the distance dimension ‘D’ from the bottom surface  11   a  of the core member  11  to the tip  40   a  of the projection parts  40  is made to be the specified dimension ‘S’. 
     After that; while the locating plate  63  of the base  32  is inserted into the locating concave part  39  of the bottom surface of the bottom plate part  35 ; the base  32  overlaps with the coil bobbin  31  from a side opposite to the movable element  2 , and the damper members  5  having the specified dimension ‘S’ as a dimension in the direction of the axis line ‘L’ are placed between the movable element  2  and the stationary element  3 . More specifically to describe, in a situation where the damper members  5  are inserted through the holes  37  for inserting the damper members, in the coil bobbin  31 ; a top end surface of the damper members  5  contacts the core member  11  of the movable element  2 , and meanwhile a bottom end surface of the damper members  5  contacts the base  32  of the stationary element  3 . 
     After that, a space between the bottom plate part  35  of the coil bobbin  31  and the base  32  is filled with an adhesive material, and then the adhesive material is hardened. In this way, a situation shown in  FIG. 2B  is obtained, and the linear actuator  1  is completed. 
     According to the present embodiment; by way of crushing the tip parts of the projection parts  40  of the coil bobbin  31 , the distance dimension ‘D’ from the bottom surface  11   a  of the core member  11  of the movable element  2  to the tip  40   a  of the projection parts  40  of the bottom plate part  35  of the coil bobbin  31  is made to be the specified dimension ‘S’ corresponding to a dimension of the damper members  5 . As a result of that, the distance dimension ‘D’ from the bottom surface  11   a  of the core member  11  of the movable element  2  to the top surface  32   a  of the base  32  is set with the specified dimension ‘S’. Therefore, variations in a stroke and a resonance frequency of the movable element  2 , due to the damper members  5  inserted between the bottom surface  11   a  of the core member  11  and the top surface  32   a  of the base  32  are not observed among manufactured products. 
     In other words, the dimension from the bottom surface  11   a  of the core member  11  to the top surface  32   a  of the base  32  is a value as a result of a calculation, in which a thickness of the end plate part  15  of the cap member  12 , a thickness of the magnetic plate  23 , a thickness of the permanent magnet  8 , and a thickness of the first core member  11  are subtracted from a total dimension of summing a height of the coil bobbin  31 , a thickness of the spring  4 , and a height from the spring  4  to a top surface of the end plate part  15  of the cap member  12 ; and therefore , the value as a result of a calculation includes accumulation of dimensional tolerances of the components described above. Accordingly, it is not easy to obtain an accuracy of the distance dimension ‘D’ from the bottom surface  11   a  of the core member  11  the movable element  2  to the top surface  32   a  of the base  32 , based on dimension accuracies of the components described above. In the meantime, for obtaining the accuracy of the distance dimension ‘D’ from the bottom surface  11   a  of the core member  11  of the movable element  2  to the top surface  32   a  of the base  32 , based on the dimension accuracies of the components described above, the dimension accuracies of the components must be improved so that manufacturing costs of the components increase. 
     On the other hand, according to the present embodiment; the tip parts of the projection parts  40  are crushed for a required dimension (the difference ‘T’) in such a way as to set the distance dimension ‘D’ from the bottom surface  11   a  of the core member  11  of the movable element  2  to the tip  40   a  of the projection parts  40  of the coil bobbin  31  with the specified dimension ‘S’. Therefore, without any relation to the dimensional tolerances of the components, the dimension from the bottom surface  11   a  of the core member  11  of the movable element  2  to the top surface  32   a  of the base  32  can be set with the specified dimension ‘S’ corresponding to the length dimension of the damper members  5 . 
     Furthermore, according to the present embodiment; a distance between the bottom surface  11   a  of the core member  11  and the top surface  32   a  of the base  32  is set with the specified dimension ‘S’ that is the same as the length dimension of the damper members  5 , and therefore a stroke of the movable element  2  can be secured. 
     Moreover, according to the present embodiment; the projection parts  40  of the coil bobbin  31 , which are made of a resin material, are melted and crushed by heat; and therefore it is possible to crush the tip parts of the projection parts  40  accurately for the difference ‘T’. 
     Incidentally, the jig  70  may be provided with a protruding part that can be inserted into the holes  37  for inserting the damper members in the coil bobbin  31 ; the protruding part having its length of the specified dimension ‘S’. In this case; at the time of crushing the projection parts  40  of the coil bobbin  31  by use of the jig  70  that has been heated, the coil bobbin  31  and the movable element  2  are fixed in such a way as not to move in the direction of the axis line ‘L’. Subsequently, the protruding part provided to the jig  70  is inserted into the holes  37  for inserting the damper members, and then the jig  70  is pushed along the direction of the axis line ‘L’, in such a way as to move closer toward the coil bobbin  31 , until a tip part of the protruding part contacts the bottom surface  11   a  of the core member  11 , so as to individually crush the projection parts  40 . In this way, it is also possible to set the distance dimension ‘D’ from the bottom surface  11   a  of the core member  11  to the tip  40   a  of the projection parts  40 , with the specified dimension ‘S’. 
     Second Embodiment 
       FIG. 6  is a perspective view of a linear actuator according to a second embodiment of the present invention.  FIG. 7  includes cross-sectional views of the linear actuator shown in  FIG. 6 . In  FIG. 7A , the cross section of the linear actuator is seen from an obliquely upward direction; and in  FIG. 7B , the cross section of the linear actuator is seen from a direction perpendicular to a moving direction of a movable element.  FIG. 8  is an exploded perspective view of the linear actuator shown in  FIG. 6 . 
     (General Configuration) 
     As shown in  FIG. 6  through  FIG. 8 , a linear actuator  101  includes a movable element  102 , a stationary element  103 , and a spring  104  that connects the movable element  102  and the stationary element  103 . The stationary element  103  supports the movable element  102  in such a way as to be movable, by the intermediary of the spring  104 . Between the movable element  102  and the stationary element  103 , there are placed a first damper member  105  and three second damper members  106  that surround the first damper member  105  from an outer circumferential side. The linear actuator  101  further includes a magnetic drive mechanism  107  in order to move the movable element  102 . The magnetic drive mechanism  107  is provided with a magnet member  108  held by the movable element  102 , and a drive coil  109  held by the stationary element  103 . In the following explanation, a moving direction of the movable element  102  is dealt with as a direction of an axis line ‘L’. The direction of the axis line ‘L’ is consistent with a central axis line of the magnet member  108  mounted on the movable element  102  and a central axis line of the drive coil  109  mounted on the stationary element  103 . For the purpose of convenience, an upside and a downside of the linear actuator  101  are explained as follows, with reference to upward and downward directions in the drawings. That is to say; in the direction of the axis line ‘L’, a side where the stationary element  103  is positioned is a downside, meanwhile a side where the movable element  102  is positioned is an upside. 
     (Movable Element) 
     The movable element  102  is provided with the magnet member  108  being annular. The magnet member  108  is provided with a core member  111  being annular, which is made of magnetic material; and a first magnetic piece  112  and a second magnetic piece  113 , which are annular-shaped and laminated in a vertical direction so as to sandwich the core member  111  therebetween. The magnet member  108  is flat-shaped, having a dimension in the direction of the axis line ‘L’ being short. The magnet member  108  has a top end surface and a bottom end surface that are perpendicular to the direction of the axis line ‘L’ (the moving direction of the movable element  102 ). 
     Moreover, the movable element  102  is provided with a shaft  115  that is fit in a center hole  114  of the magnet member  108 . The shaft  115 , having a constant diameter, stretches in the direction of the axis line ‘L’. Furthermore, the movable element  102  is provided with a cap member  116  that covers the magnet member  108  from an upper side and a lateral side. 
     The cap member  116  includes an upper cap member  117  and a lower cap member  118 . The upper cap member  117  includes a circular end plate part  119  having a constant thickness, and an upper cylindrical part  120  protruding downward from an outer circumferential edge of the end plate part  119 . The lower cap member  118  includes a lower cylindrical part  121  that stretches downward from a bottom end edge of the upper cylindrical part  120 , and a protrusion plate part  122  protruding toward an inner circumferential side from a bottom end edge of the lower cylindrical part  121 . 
     At a middle part of on an upper surface of the end plate part  119 , there is formed a circular concave part  123 . At a middle part of the concave part  123 , there is formed a shaft retaining hole  124 . At an upper end part of an inner circumferential surface of the upper cylindrical part  120 , there is fixed a spacer  126  being annular. In the meantime, while being retained in the shaft retaining hole  124 , an upper end part of the shaft  115  is welded to the end plate part  119   
     Moreover, the movable element  102  is provided with a washer  125  that contacts an opening edge of the center hole  114  of the magnet member  108 , from a lower side. A lower end part of the shaft  115  is inserted into the washer  125 ; and in the situation, the washer  125  is welded to the shaft  115 . Thus, while contacting the end plate part  119  of the cap member  116 , the magnet member  108  is fixed between the cap member  116  and the washer  125 . 
     In the meantime, the end plate part  119  has a larger diameter than the magnet member  108  has. Therefore, in a situation where the cap member  116  is fixed to the magnet member  108 , there is formed a gap having a constant space in a circumferential direction, between an annular outer circumferential surface of the magnet member  108  and the upper cylindrical part  120  as well as the lower cylindrical part  121 . 
     (Stationary Element) 
     Next, the stationary element  103  is explained with reference to  FIG. 7  through  FIG. 9 .  FIG. 9A  is a perspective view showing a situation where a coil bobbin is observed from an upper side; while the coil bobbin around which the drive coil  109  is wound, is provided with the spring  104 ; and meanwhile  FIG. 9B  is a perspective view showing a situation where the coil bobbin is observed from a lower side; while the coil bobbin around which the drive coil  109  is wound, is provided with the spring  104 . As shown in  FIG. 7  and  FIG. 8 , the stationary element  103  is provided with a coil bobbin  131  (a first element) around which the drive coil  109  is wound, and a base  132  (a second element) that overlaps with the coil bobbin  131  from a side opposite to the movable element  102 . The coil bobbin  131  supports the movable element  102  by the intermediary of the spring  104  in such a way as to be movable in the direction of the axis line ‘L’. 
     (Coil Bobbin) 
     The coil bobbin  131  is made of a resin material. As shown in  FIG. 8 , the coil bobbin  131  is provided with a cylindrical part  135  and a protruding part  136  that continuously protrudes downward out of the cylindrical part  135 . 
     (Coil Bobbin) 
     An axis line ‘L’ of the cylindrical part  135  is consistent with an axis line ‘L’ of the magnet member  108 . As shown in  FIG. 7 , the cylindrical part  135  is provided with; a tubular torso part  138 , wherein the drive coil  109  is wound around an outer circumferential surface of the tubular torso part  138 ; a lower flange part  139  being annular, which is expanded in its diameter at a lower side of the tubular torso part  138 ; and an upper flange part  140  being annular, which is expanded in its diameter at an upper side of the tubular torso part  138 . As shown in  FIG. 9B , the lower flange part  139  is provided with three spring retainer projections  141  on its annular bottom end surface. The three spring retainer projections  141  are placed around the axis line ‘L’ at equal angular intervals. Each of the spring retainer projections  141  works as a retainer part for retaining a stationary-element-side connection part  143  of the spring  104 . 
     As shown in  FIG. 8 , the protruding part  136  is provided with; a bottom plate part  145  that faces the magnet member  108  of the movable element  102  in the direction of the axis line ‘L’; and connecting parts  146  stretching in the direction of the axis line ‘L’, which connect the bottom plate part  145  and the tubular torso part  138 . In the meantime, as shown in  FIG. 9B , the bottom plate part  145  is generally a rectangle in its planar shape, and the connecting parts  146  stretch upward from four corners of the bottom plate part  145 . Between two of the connecting parts  146  positioned side by side in a circumferential direction, there is formed a space. At a center of the bottom plate part  145 , there is provided a hole  147  for inserting the damper member. 
     At four corners of a bottom surface of the bottom plate part  145 , there are individually formed projection parts  150  that protrude downward, being shaped to be columnar. A tip part of each of the projection parts  150  is crushed at a time of assembling the linear actuator  101 . 
     Furthermore, on the bottom surface of the bottom plate part  145 , there are provided a pair of ribs  152  that individually stretch along an edge of a long side of the rectangle in the planar shape. Moreover, on the bottom surface of the bottom plate part  145 , there are provided a pair of terminal parts  153 . The pair of terminal parts  153  are formed between two of the projection parts  150  provided at both sides that sandwich a short side of the rectangle in the planar shape of the bottom plate part  145 . Terminals of the drive coil  109  are individually entangled around the terminal parts  153 , and then connected to a circuit board  155 . 
     (Base) 
     As shown in  FIG. 8 , the base  132  is shaped to be disk-like. On a top surface of the base  132 , there is formed a first concave part  161 , being circular, at a center position. Moreover, three second concave parts  162  are formed at positions that surround the first concave part  161  from an outer circumferential side. The second concave parts  162  are formed around the axis line ‘L’ at equal angular intervals. Meanwhile, the three second concave parts  162  individually have the same distance from the axis line ‘L’ (i.e., a distance from the first concave part  161 ). 
     According to the present embodiment; in a view from the direction of the axis line ‘L’, the three second concave parts  162  are provided at positions that overlap with the three spring retainer projections  141  provided on the lower flange part  139 . A bottom surface  161   a  of the first concave part  161  and a bottom surface  162   a  of the second concave parts  162  are planes perpendicular to the direction of the axis line ‘L’ (the moving direction of the movable element  102 ). The bottom surface  161   a  of the first concave part  161  faces the magnet member  108 , in the direction of the axis line ‘L’. The bottom surface  162   a  of the second concave parts  162  faces the protrusion plate part  122  of the cap member  116  (the lower cap member  118 ), in the direction of the axis line ‘L’. A depth dimension ‘H’ of the first concave part  161  and a depth dimension ‘H’ of the second concave parts  162  are the same. At an outer circumferential edge part of the base  132 , there is provided a cutout part  163  for placing the circuit board  155 . 
     Moreover, in the base  132 , there are provided a pair of slits  164  that stretch in parallel while sandwiching the axis line ‘L’ between them. Each of the slits  164  is placed between the first concave part  161  and the second concave parts  162 . The ribs  152 , provided in the bottom plate part  145  of the coil bobbin  131 , can individually be inserted into each of the slits  164 . The coil bobbin  131  is mounted on the base  132 , while being located in a direction, perpendicular to the direction of the axis line ‘L’, by way of individually inserting the ribs  152  into each of the slits  164  of the base  132 . The coil bobbin  131  is fixed to the base  132 , by use of an adhesive material filled between the bottom plate part  145  and the base  132 . 
     (Spring) 
     The spring  104  is a flat spring component, whose thickness direction is oriented in the direction of the axis line ‘L’, As shown in  FIG. 8  and  FIG. 9 , the spring  4  is provided with; the stationary-element-side connection part  143 , connected to the stationary element  103 ; a movable-element-side connection part  171 , connected to the movable element  102 ; and three arm parts  172  connected to the stationary-element-side connection part  143  and the movable-element-side connection part  171 . The stationary-element-side connection part  143  is placed at an inner circumferential side with respect to the movable-element-side connection part  171  and the arm parts  172 , and meanwhile the movable-element-side connection part  171  is placed at an outer circumferential side with respect to the arm parts  172 . 
     In the stationary-element-side connection part  143 , there are formed retaining holes  173  into which the spring retainer projections  141  of the lower flange part  139  of the coil bobbin  131  are individually fit. The spring  104  is connected to the coil bobbin  131  by way of individually inserting the spring retainer projections  141  into each of the retaining holes  173 . The movable-element-side connection part  171  is pinched between the upper cylindrical part  120  of the upper cap member  117  and the lower cylindrical part  121  of the lower cap member  118 , and welded thereto. Thus, the spring  104  is connected to the cap member  116 . 
     In a situation where the stationary-element-side connection part  143  of the spring  104  is connected to the coil bobbin  131 , and meanwhile the movable-element-side connection part  171  is connected to the cap member  116 ; the magnet member  108  is positioned at an inner circumferential side of the coil bobbin  131 , as shown in  FIG. 7 . Meanwhile, at an outer circumferential side of the core member  111  of the magnet member  108 , there are placed the tubular torso part  138  of the coil bobbin  131  and the drive coil  109  wound around the tubular torso part  138 . In the meantime, the protrusion plate part  122  of the cap member  116  is placed a little bit beneath a bottom surface of the magnet member  108 . Moreover, the upper flange part  140  of the coil bobbin  131  faces the spacer  126 , which is fixed inside the cap member  116 , while having a small gap therebetween. Then, the upper flange part  140  of the coil bobbin  131  and the spacer  126  make up a stopper mechanism to restrict a movable range of the movable element  102  at a time when the movable element  102  moves due to an external force in a direction perpendicular to the axis line ‘L’. 
     (Damper Members) 
     As shown in  FIG. 8 , the first damper member  105  and the second damper members  106  individually have a columnar shape. A diameter of the first damper member  105  is greater than a diameter of the second damper members  106 , and the diameter of the first damper member  105  is consistent with a diameter of the shaft  115 . The first damper member  105  and the second damper members  106  have the same length in the direction of the axis line ‘L’. The length of the damper member  105  and the second damper members  106 , in the direction of the axis line ‘L’, is consistent with a specified dimension ‘S’. 
     As shown in  FIG. 7A , the first damper member  105  is placed between the movable element  102  and the stationary element  3 , while being inserted through the hole  147  for inserting the damper member, the hole  147  being provided in the bottom plate part  145  of the coil bobbin  131 . The hole  147  for inserting the damper member is a circular opening section having a larger diameter than the first damper member  105  has. The first damper member  105  makes its top end surface contact with a bottom surface  115   a  (a movable-element-side facing surface) of the shaft  115  of the movable element  102 , and makes its bottom end surface contact with a bottom surface  161   a  (a stationary-element-side facing surface) of the first concave part  161  provided in the base  132 . 
     The second damper members  106  make their top end surface contact with a bottom surface  122   a  (a movable-element-side facing surface) of the protrusion plate part  122  of the cap member  116 , and makes their bottom end surface contact with a bottom surface  162   a  (a stationary-element-side facing surface) of the second concave parts  162  of the base  132 . 
     Incidentally, the first damper member  105  and the second damper members  106  are made from silicone gel having a needle entering level of 90 to 110. 
     (Method for Manufacturing the Linear Actuator) 
       FIG. 10  includes explanatory drawings of a method for manufacturing the linear actuator  101 .  FIG. 10A  is an explanatory drawing with regard to a distance dimension, from the bottom surface  115   a  of the shaft  115  to a tip of the projection parts  150  provided at the bottom plate part  145  of the coil bobbin  131 , in the direction of the axis line ‘L’; and meanwhile,  FIG. 10B  is an explanatory drawing with regard to a manufacturing step of crushing tip parts of the projection parts  150 . In  FIG. 10A , a length of the damper members  105  in the direction of the axis line ‘L’ is indicated as reference. 
     At a time of manufacturing the linear actuator  101 , the movable element  102  is supported by the coil bobbin  31  by the intermediary of the spring  104 . Then, as shown in  FIG. 10A ; in a situation where the direction of the axis line ‘L’ of the coil bobbin  131  (the moving direction of the movable element  102 ) is oriented to a vertical direction, a distance dimension ‘D 1 ’ in the direction of the axis line ‘L’, stretching from the bottom surface  115   a  of the shaft  115  to a tip  150   a  of the projection parts  150  of the bottom plate part  145  of the coil bobbin  131 , is measured. After that, there is calculated a difference ‘T’ between a total dimension (‘D 1 ’+‘H’) and the specified dimension ‘S’ set up in advance; the total dimension (‘D 1 ’+‘H’) being obtained by adding the depth dimension ‘H’ of the first concave part  161  (refer to  FIG. 7B ) to the distance dimension ‘D 1 ’. 
     Then, the coil bobbin  131  is formed in such a way that; a distance dimension from the bottom surface  115   a  of the shaft  115  to a bottom surface  145   a  of the bottom plate part  145  of the coil bobbin  131  is shorter than a dimension as a result of subtracting the depth dimension ‘H’ of the first concave part  161  from the specified dimension ‘S’ at a time of supporting the movable element  102  by the intermediary of the spring  104 ; and moreover a distance from the bottom surface  115   a  of the shaft  115  to the tip  150   a  of the projection parts  150  is longer than the dimension as a result of subtracting the depth dimension ‘H’ of the first concave part  161  from the specified dimension ‘S’. 
     Next, the coil bobbin  131  is kept in a stationary situation. Then, as shown with a dotted line in  FIG. 10B ; a jig  180  provided with an end surface is heated, wherein the end surface being able to contact the tip  150   a  of the projection parts  150  of the coil bobbin  131  and the end surface being perpendicular to the axis line ‘L’, and then the jig  180  is placed at a contact position  180 A where the end surface contacts the tip  150   a  of the projection parts  150 . After that, as shown with an arrow and a solid line in  FIG. 10B ; the jig  180  is pushed along the direction of the axis line ‘L’, in such a way as to move closer toward the coil bobbin  131  so as to be transferred for the difference ‘T’. Thus, the jig  180  crushes the tip parts of the projection parts  150  for the difference ‘T’, while melting each of the projection parts  150  by heat. As a result of that, the distance dimension ‘D 1 ’ from the bottom surface  115   a  of the shaft  115  to the tip  150   a  of the projection parts  150  is made to be the dimension as a result of subtracting the depth dimension ‘H’ of the first concave part  161  from the specified dimension ‘S’. 
     After that; while the ribs  152  of the bottom plate part  145  is inserted into the slits  164  of the base  132 ; the base  132  overlaps with the coil bobbin  131  from a side opposite to the movable element  102 , and the first damper member  105  as well as the second damper members  106 , both having the specified dimension ‘S’ as a dimension in the direction of the axis line ‘L’ are placed between the movable element  102  and the stationary element  103 . 
     More specifically to describe, in a situation where the first damper member  105  is inserted through the hole  147  for inserting the damper member, in the coil bobbin  131 ; a top end surface of the first damper member  105  contacts the shaft  115  of the movable element  102  and gets fixed thereto, and meanwhile a bottom end surface of the first damper member  105  contacts the base  132  (the bottom surface  161   a  of the first concave part  161 ) of the stationary element  103  and gets fixed thereto. In a parallel way, a top end surface of the second damper members  106  contacts the protrusion plate part  122  of the cap member  116  of the movable element  102  and gets fixed thereto, and meanwhile a bottom end surface of the second damper members  106  contacts the base  132  (the bottom surface  162   a  of the second concave parts  162 ) of the stationary element  103  and fixed thereto. 
     After that, a space between the bottom plate part  145  of the coil bobbin  131  and the base  132  is filled with an adhesive material, and then the adhesive material is hardened. In this way, a situation shown in  FIG. 7B  is obtained, and the linear actuator  101  is completed. 
     According to the present embodiment as well, the same operation and effect can be obtained, as being obtained in the first embodiment. 
     Incidentally, the jig  180  may be provided with a protruding part that can be inserted into the hole  147  for inserting the damper member in the coil bobbin  131 . Then, a protruding dimension of the protruding part is made to be the dimension as a result of subtracting the depth dimension ‘H’ of the first concave part  161  from the specified dimension ‘S’. In this case; at the time of crushing the projection parts  150  of the coil bobbin  131  by use of the jig  180  that has been heated, the coil bobbin  131  and the movable element  102  are fixed in such a way as not to move in the direction of the axis line ‘L’. Subsequently, the protruding part provided to the jig  180  is inserted into the hole  147  for inserting the damper member, and then the jig  180  is pushed along the direction of the axis line ‘L’, in such a way as to move closer toward the coil bobbin  131 , until a tip part of the protruding part contacts the bottom surface  115   a  of the shaft  115 , so as to individually crush the projection parts  150 . In this way, it is also possible to set the distance dimension ‘D 1 ’ from the bottom surface  115   a  of the shaft  115  to the tip  150   a  of the projection parts  150 , with the dimension as a result of subtracting the depth dimension ‘H’ of the first concave part  161  from the specified dimension ‘S’. 
     Furthermore, though the first damper member  105  and the second damper members  106  are provided as a damper member in the embodiment described above, only one of the two sorts of damper members may be provided. Moreover, though the second damper members  106  are provided at three locations in the circumferential direction, the second damper members  106  may be provided at four or more locations. Furthermore, a plurality of second damper members  106  may be placed in an annular arrangement. 
     (Modification) 
     Though in the embodiments described above, the projection parts  40  &amp; the projection parts  150  are provided to the bottom surfaces of the bottom plate part  35  &amp; the bottom plate part  145 , which face the base  32  &amp; the base  132 , respectively, in the coil bobbin  31  &amp; the coil bobbin  131 ; the projection parts  40  &amp; the projection parts  150  may be provided to sides of top surfaces, which face the coil bobbin  31  &amp; the coil bobbin  131 , respectively, in the base  32  &amp; the base  132 ; and then in a manufacturing step for the linear actuator  1  &amp; the linear actuator  101 , by way of crushing the projection parts  40  &amp; the projection parts  150 , each distance dimension between the movable element  102  and the base  32  &amp; the base  132  may be made so as to be corresponding to each length of the damper members  5 , the first damper member  105  &amp; the second damper members  106 . 
     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. 
     The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.