Abstract:
An electromagnetic actuator comprises a core with a coil wound around a stator magnetically coupled to each end of the cored a movable element that can be displaced relative to the stator, and a supporting means for supporting the movable element. The stator and the movable element each have a projection and a depression parallel to the displacement direction of the movable element and are placed in such a way that the projection and depression of the stator engage with the projection and depression of the movable element.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electromagnetic actuator as an electro-mechanical converter using electromagnetic force, optical scanner and their manufacturing method, and more particularly, to a micro-electromagnetic actuator, which can be manufactured by a micro-machining technology, being easier to control and able to have larger strokes than a conventional electromagnetic actuator, and its manufacturing method.  
         [0003]     2. Related Background Art  
         [0004]     The mainstream of actuators manufactured by conventional micro-machining technologies has been actuators using an electrostatic force or piezoelectric phenomenon. However, actuators using electromagnetic power are also increasingly being developed as it is becoming easier to use magnetic materials by a micro-machining technology in recent years.  
         [0005]      FIG. 7  is an example of an electromagnetic linear actuator for positioning a hard disk head (U.S. Pat. No. 5,724,015). The actuator in  FIG. 7  comprises fixed cores  1004   a  and  1004   b,  coils  1005   a  and  1005   b  wound around the fixed cores fixed on a substrate (not shown in the figure) and a movable element  1003  supported by means of a spring  1007  in such a way that the movable element  1003  is movable relative to the fixed cores  1004   a  and  1004   b.  These structures are manufactured on the substrate using a micro-machining technology.  
         [0006]     When the coil  1005   a  of this actuator is energized, the movable element  1003  is attracted to the fixed core  1004   a  and the movable element  1003  moves leftward in the figure. On the contrary, when the coil  1005   b  is energized, the movable element  1003  moves rightward in the figure. The force F 1  generated by this actuator is given by the following expression: 
 
F 1 =0.5μ 0 N 1   2 i 1   2 w 1 t 1 x 1   −2    (1) 
        where μ 0  is vacuum magnetic permeability; N 1 , the number of coil turns; i 1 , a current that flows through the coils  1005   a  and  1005   b;  w 1 , width of the magnetic pole; t 1 , thickness of the magnetic pole; and x 1 , length of the gap. The displacement of this actuator is calculated from the following relationship, where the spring constant of the spring  1007  is assumed to be k 1 : 
 
F 1 =k 1 x 1    (2) 
       
 
         [0008]     However, as is clear from expression (1), with the actuator above, the generated force F 1  is not determined by the current i 1  alone and is inversely proportional to the square of the gap x 1 . Thus, the actuator above has a problem that it is hard to control.  
         [0009]     Another problem is that when the initial gap is increased, the generated force reduces suddenly, making it impossible to increase strokes.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention has been implemented to solve the above problems of the prior arts and it is an object of the present invention to provide an electromagnetic actuator, optical scanner and their manufacturing method capable of facilitating control over the electromagnetic actuator manufactured by micro-machining technology and increasing strokes.  
         [0011]     The above object will be achieved by an electromagnetic actuator comprising: 
        a core with a coil wound around;     a stator magnetically coupled at both ends of the core;     a movable element that can be displaced relative to the stator; and     a supporting means for supporting the movable element,     wherein the stator and the movable element each have a projection and a depression perpendicular to their respective displacement directions and are placed in such a way that the projection and depression of the stator engage with the projection and depression of the movable element.        
 
         [0017]     The above object will also be achieved by an optical scanner comprising a movable mirror and the electromagnetic actuator mechanically connected with the movable mirror.  
         [0018]     Furthermore, the above object will also be achieved by a method of manufacturing the electromagnetic actuator with a process of manufacturing the stator, the movable element and the supporting means, comprising: 
        a step of forming a sacrificial layer on a substrate;     a step of forming an electrode layer on the substrate and the sacrificial layer;     a step of forming an insulated female mold layer on the electrode layer;     a step of electroplating a magnetic layer in an opening of the insulated female mold layer on the electrode layer; and     a step of removing the insulated female mold layer and the sacrificial layer.        
 
         [0024]     The method of manufacturing the above electromagnetic actuator with a process of manufacturing the core and the coil comprising: 
        a step of forming a coil lower wiring on the substrate;     a step of forming a first insulating layer on the coil lower wiring;     a step of forming an electrode layer on the first insulating layer;     a step of forming an insulated female mold layer on the electrode layer;     a step of electroplating a magnetic layer in the opening of the insulated female mold layer on the electrode layer;     a step of forming a second insulating layer on the magnetic layer; and     a step of forming coil upper wiring on the second insulating layer.        
 
         [0032]     Details will be given in the embodiments, which will be described later. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]      FIG. 1  is a drawing to explain a linear actuator of Embodiment 1 of the present invention;  
         [0034]      FIG. 2  is a drawing to explain the principle of operation of the present invention;  
         [0035]     FIGS.  3 AM,  3 AC,  3 BM,  3 BC,  3 CM,  3 CC,  3 DM,  3 DC,  3 EM,  3 EC,  3 FM,  3 FC,  3 GM,  3 GC,  3 HM,  3 HC,  31 M,  3 IC,  3 JM and  3 JC are drawings to explain a manufacturing method of Embodiment 1 of the present invention;  
         [0036]      FIG. 4  is a drawing to explain a rotary actuator of Embodiment 2 of the present invention;  
         [0037]      FIG. 5  is a drawing to explain an optical scanner of Embodiment 3 of the present invention;  
         [0038]      FIGS. 6A and 6B  are drawings to explain operation of Embodiment 3 of the present invention; and  
         [0039]      FIG. 7  is a drawing to explain a micro-electromagnetic actuator of prior art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]     Embodiments of the present invention will be explained below.  
         [0041]      FIG. 2  is a drawing to explain the principle of operation of the electromagnetic actuator according to an embodiment of the present invention. When a current is supplied from a power supply  220  to a coil  205 , magnetic flux is generated in the coil  205 . This magnetic flux goes through a magnetic circuit comprised of a core  204 , a fixed magnetic pole  202   a,  air gaps between the comb teeth, a movable magnetic pole  203 , the other air gaps between the comb teeth and a fixed magnetic pole  202   b,  in this order. Reference character K denotes a hinge spring.  
         [0042]     Here, magnetic resistance R g (x) of the air gaps between the comb teeth is given:  
                   R   g     ⁡     (   x   )       =     d       μ   0     ⁢     tn   ⁡     (     x   +     x   0       )             ,           (   3   )             
 
 where μ 0  is vacuum magnetic permeability; d, distance of the air gap; t, thickness of the comb teeth; n, the number of gaps; x, displacement of the movable magnetic pole; and x 0 , initial overlap length. Potential energy W of the entire magnetic circuit and generated force F in the air gaps are expressed:  
             W   =         -     1   2       ⁢     (     R   +     2   ⁢       R   g     ⁡     (   x   )           )     ⁢       (   Ni   )     2       =       -         (   Ni   )     2     2       ⁢     (     R   +       2   ⁢   d         μ   0     ⁢     tn   ⁡     (     x   +     x   0       )             )                 (   4   )                 F   =       -       ⅆ   W       ⅆ   x         =       1   2     ⁢     (       2   ⁢   d         μ   0     ⁢       tn   ⁡     (     x   +     x   0       )       2         )     ⁢       (     R   +       2   ⁢   d         μ   0     ⁢     tn   ⁡     (     x   +     x   0       )             )       -   2       ⁢       (   Ni   )     2           ,           (   5   )             
 
 where R is the magnetic resistance of the area other than the air gaps; N is the number of turns of the coil  205 ; and i is a current that flows into the coil  205 . Here, if the actuator is manufactured with a material with magnetic permeability sufficiently large compared to vacuum magnetic permeability, then R approximates to 0 and the generated force F is given:  
             F   =           μ   0     ⁢   tn       4   ⁢   d       ⁢       (   Ni   )     2               (   6   )             
 
 The equation makes it clear that the generated force F of the actuator of the present invention is determined only by current i but independent of displacement x. In fact, the magnetic permeability cannot become infinite, and therefore the generated force F fluctuates according to displacement x, but the percentage of the fluctuation is extremely small compared to the actuator shown in  FIG. 7 . That is, its control is extremely easy compared to the conventional electromagnetic actuator. In order for such a condition to be established, the magnetic flux that flows through the air gaps between the comb teeth must be sufficiently dominant compared to the magnetic flux that flows from the end of the comb teeth. Namely, h 1  and h 2  in  FIG. 2  must be sufficiently large compared to d. It is preferable that h 1  and h 2  be at least twice as large as d. 
 
         [0043]     At this time, a static displacement of the actuator can be calculated according to the balance between the spring force and the generated force from: 
 
F=kx,   (7) 
 
 where k is a spring constant of the parallel hinge spring. 
 
         [0044]     With reference now to the attached drawings, embodiments of the present invention will be explained in detail below.  
       Embodiment 1  
       [0045]      FIG. 1  is a schematic diagram to explain the linear actuator of Embodiment 1 of the present invention. On a substrate  101 , stators  102   a  and  102   b,  and support sections  106  are fixed. A movable element  103  is held at both ends by parallel hinge springs  107  and the parallel hinge springs  107  are held by the support sections  106 . With such a configuration, the movable element  103  is supported onto the substrate  101  elastically with freedom of parallel translation.  
         [0046]     Furthermore, a core  104  is placed so that both ends are magnetically connected to two stators  102   a  and  102   b.  A coil  105  is wound around core  104 . The stators  102   a  and  102   b  and movable element  103  have comb-teeth-like protrusions, which are the features of the present invention and are placed in such a way that these protrusions engage with each other.  
         [0047]     Then, the method of manufacturing the actuator of this embodiment will be explained. This embodiment uses a micro-machining technology to manufacture stators  102   a  and  102   b,  movable element  103 , core  104 , coil  105 , support sections  106  and parallel hinge springs  107 . Furthermore, coil  105  is manufactured in order of coil bottom face wiring  114  as the coil lower wiring, coil side wiring  115  and coil top face wiring  116  as the coil upper wiring. The manufacturing method will be explained in detail using FIGS.  3 AM to  3 JM and FIGS.  3 AC to  3 JC. FIGS.  3 AM to  3 JM and FIGS.  3 AC to  3 JC show respectively cross-sectional views along lines M-M and C-C in  FIG. 1 .  
         [0048]     First, coil bottom face wiring  114  is patterned on substrate  101  and bottom face wiring-core insulting layer  117  is patterned on top of the coil bottom face wiring (FIGS.  3 AM and  3 AC).  
         [0049]     Then, phospho-silica glass (PSG) layer  110  is patterned. The phospho-silica glass layer  110  will become the sacrificial layer and will be removed in a later process and will function to float parallel hinge springs  107  and movable element  103  from the substrate (FIGS.  3 BM and  3 BC).  
         [0050]     Then, chromium is evaporated as a seed electrode layer  111  for electroplating and gold is evaporated on top of it (FIGS.  3 CM and  3 CC).  
         [0051]     Then, a photoresist layer  112  is applied (FIGS.  3 DM and  3 DC). In this embodiment, SU-8 (manufactured by Micro Chem), which is suitable for thick coating, is used to obtain a coating thickness of 300 μm.  
         [0052]     Then, the photoresist layer  112  is exposed and developed and patterning is performed (FIGS.  3 EM and  3 EC). The parts removed in this process will become female molds for stators  102   a  and  102   b,  movable element  103 , core  104 , support sections  106 , parallel hinge springs  107  and coil side wiring  115 .  
         [0053]     Then, a permalloy layer  113  is electroplated while a voltage is applied to the seed electrode layer  111  (FIGS.  3 FM and  3 FC).  
         [0054]     Then, the photoresist layer  112  and seed electrode layer  111  are removed by dry etching (FIGS.  3 GM and  3 GC).  
         [0055]     Then, epoxy resin  119  is applied and the top surface is mechanically polished and flattened (FIGS.  3 HM and  3 HC).  
         [0056]     Then, top face wiring-core insulating layer  118  and coil top face wiring  116  are patterned on the top face of the core  104  (FIGS.  3 IM and  3 IC).  
         [0057]     Finally, the epoxy resin  119  and phospho-silica glass layer  110  are removed (FIGS.  3 JM and  3 JC).  
         [0058]     The electromagnetic actuator configured as shown above of the present invention has less influence of displacement on the generated force under the condition of a constant current, and therefore its control is easier than the conventional electromagnetic actuator.  
         [0059]     Moreover, since the generated force is never reduced inversely proportional to the square of the gap, it is possible to increase strokes.  
       Embodiment 2  
       [0060]      FIG. 4  is a schematic drawing to explain a rotary actuator of Embodiment 2 of the present invention.  FIG. 4  shows a core  204  and a coil  205  separately to make it easier to see.  
         [0061]     Stators  202   a  and  202   b  and support sections  206  are fixed onto a substrate  201 . A rotor  203  is held at four corners by concentric rotary hinge springs  207 . The concentric rotary hinge springs  207  are held by support sections  206 . The concentric rotary hinge springs  207  are placed in such a way that its extensions in the longitudinal direction intersect at the center of the rotor  203 .  
         [0062]     With such a configuration, rotor  203  is supported onto the substrate  201  elastically with freedom of rotation on the substrate  201 .  
         [0063]     Moreover, a core  204  is placed in such a way that its both ends are magnetically connected to the two stators  202   a  and  202   b.    FIG. 4  shows the core  204  disassembled to make it easier to see. This core  204  has a coil  205  wound around. Furthermore, the stators  202   a  and  202   b  and the rotor  203  have concentric comb-teeth like protrusions, which are the features of the present invention and these protrusions are placed in such a way as to engage with each other.  
         [0064]     The actuator of this embodiment is manufactured by first manufacturing the stators  202   a  and  202   b,  rotor  203 , support sections  206  and concentric rotary hinge springs  207  on the substrate  201  using a micro-machining technology in the same way as that in Embodiment 1, and then assembling the core  204  that has been manufactured separately with the coil  205  wound around.  
         [0065]     The actuator of this embodiment also operates according to the same principle as that for the actuator described in Embodiment 1. What is different from Embodiment 1 is that the rotor  203  rotates to be displaced because a couple of forces act on the rotor  203 .  
         [0066]     The electromagnetic actuator configured as shown above of the present invention has less influence of displacement on the generated force under the condition of a constant current, and therefore its control is easier than the conventional electromagnetic actuator.  
         [0067]     Moreover, since the generated force is never reduced in inversely proportional to the square of the gap, it is possible to increase strokes.  
       Embodiment 3  
       [0068]      FIG. 5  is a schematic diagram to explain an optical scanner of Embodiment 3 of the present invention.  
         [0069]     Stators  302   a  and  302   b,  support sections  306  and mirror support section  308  are fixed onto a substrate  301 .  
         [0070]     A movable element  303  is held at both ends by parallel hinge springs  307  and the parallel hinge springs  307  are supported by support sections  306 .  
         [0071]     Configured in this way, the movable element  303  is supported onto the substrate  301  elastically with freedom of parallel translation.  
         [0072]     A mirror  311  is connected to the mirror support section with a flat spring  309  and supported with freedom of rotation.  
         [0073]     The mirror  311  is further linked with the movable element  303  with a flat spring  310 . A core  304  is placed in such a way that its both ends are magnetically connected to the two stators  302   a  and  302   b.  This core  304  has a coil  305  wound around. The stators  302   a  and  302   b  and the movable element  303  have comb-teeth like protrusions, which are the features of the present invention, and these protrusions are placed in such a way as to engage with each other. These structures can be manufactured by the same process as that in Embodiment 1.  
         [0074]      FIGS. 6A and 6B  are drawings to explain an operation of this embodiment.  
         [0075]     Reference numeral  312  denotes a semiconductor laser and  313  denotes a laser beam. The semiconductor laser  312  is placed in such a way that the laser beam  313  impinges on the mirror  311 . The semiconductor laser  312  can be placed on the substrate  301  or in a different place.  
         [0076]      FIG. 6A  shows a situation when the coil  305  is not energized and  FIG. 6B  shows a situation when the coil  305  is energized. From these figures, it is clearly seen that the direction of the laser beam  313  changes by energizing the coil  305 .  
         [0077]     The electromagnetic actuator of the present invention has less influence of displacement on the generated force under the condition of a constant current, and therefore is characterized in that its control is easier than the conventional electromagnetic actuator.  
         [0078]     Moreover, since the generated force is never reduced inversely proportional to the square of the gap, it is also characterized by the ability to increase strokes. Therefore, by applying the electromagnetic actuator of the present invention to an optical scanner, it is possible to provide an optical scanner with ease of control and a large angle of deflection that can be manufactured by a micro-machining technology.  
         [0079]     As described above, the electromagnetic actuator of the present invention has less influence of displacement on the generated force of the actuator under the condition of a constant current, it is extremely easy to control the electromagnetic actuator of the present invention compared to the conventional electromagnetic actuator.  
         [0080]     Furthermore, since the generated force of the actuator of the present invention is never reduced inversely proportional to the square of the gap, it is possible to increase strokes.  
         [0081]     Moreover, the present invention adopts a configuration manufacturing the supporting means of the movable element and stators fixed onto the substrate, making it possible to easily manufacture the electromagnetic actuator using a micro-machining technology.  
         [0082]     Furthermore, the present invention adopts a configuration creating the supporting means and fixed and movable magnetic poles from the same material, making it possible to manufacture them all together at a time.  
         [0083]     Moreover, the present invention configures the supporting means with parallel hinge springs, providing directly operated support, free of friction and backlash.  
         [0084]     Furthermore, the present invention can create an optical scanner made of a movable mirror and an electromagnetic actuator mechanically connected to the movable mirror through micro machining, making it possible to implement an optical scanner with ease of control and large angle of deflection.