Abstract:
An electromagnetic actuator comprising a stationary member, a movable member magnetically coupled with the stationary member with a gap therebetween, and a support member for displaceably supporting the movable member relative to the stationary member. Both the stationary member and the movable member have a core section carrying a coil wound around its periphery. As the coil of the stationary member and that of the movable member are energized with electric current, the movable member is attracted toward or repulsed from the stationary member. The electromagnetic actuator can be used for an optical scanner by providing a mirror or a lens on the movable member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to an electromagnetic actuator, an optical scanner using an electromagnetic actuator and a method of preparing an electromagnetic actuator.  
           [0003]    2. Related Background Art  
           [0004]    Conventional actuators prepared by utilizing the micro-machining technology are mostly based on the use of electrostatic force or piezoelectric phenomena. However, thanks to the availability of the micro-machining technology for utilizing magnetic materials in recent years, actuators using electromagnetic force have been developed.  
           [0005]    [0005]FIG. 1 of the accompanying drawings schematically illustrates a linear actuator that utilizes electromagnetic force for positioning the head of a hard disk as disclosed in U.S. Pat. No. 5,724,015. Referring to FIG. 1, the actuator comprises a pair of cores  1004   a ,  1004   b  rigidly secured to a substrate (not shown) and a pair of coils  1005   a ,  1005   b  wound around the respective cores along with a movable member  1003  so supported by springs  1007  as to be movable relative to the cores  1004   a ,  1004   b . The above structure is formed on the substrate by means of the micro-machining technology.  
           [0006]    As electric power is supplied to the coil  1005   a  of the actuator, the movable member  1003  is pulled toward the core  1004   a  to consequently displace the movable member  1003  to the left in FIG. 1. When, on the other hand, the coil  1005   b  is electrically energized, the movable member  1003  is displaced to the right in FIG. 1. The force F 1  generated in the actuator is expressed by formula (1) below;  
             F   1 =0.5 μ 0   N   1   2   i   1   2   w   1   t   1 ( d   1   −x   1 ) −2   (1)  
           [0007]    where μ 0  is the magnetic permeability of vacuum, N 1  is the number of turns of the coils, i 1  is the electric current made to flow to the coil  1005   a  or  1005   b , w 1  is the width of the magnetic pole, t 1  is the thickness of the magnetic pole and d 1  is the length of the gap. If the spring constant of the springs  1007  is k 1 , the displacement x 1  of the actuator is expressed by using the relationship of formula (2) below;  
             F   1   =k   1   x   1   (2)  
           [0008]    However, since actuators having a configuration as described above by referring to FIG. 1 show a large leakage of magnetic flux, they are accompanied by the problem of a poor energy efficiency. Additionally, since the number of turns of the coils of such an actuator is limited due to the structure where only the stationary members are provided with coils, the actuator is also accompanied by the problem of a weak generated force.  
         SUMMARY OF THE INVENTION  
         [0009]    In view of the above identified technological problems of the prior art, it is therefore the object of the present invention to provide an electromagnetic actuator that can minimize the leakage of magnetic flux and hence the power consumption rate to improve the energy efficiency and remarkably increase the force it can generate, an optical scanner comprising such an electromagnetic actuator and also a method of preparing such an electromagnetic actuator.  
           [0010]    According to the invention, the above object is achieved by providing an electromagnetic actuator comprising:  
           [0011]    a stationary member having a first core section carrying a first coil wound around its periphery;  
           [0012]    a movable member magnetically coupled with the stationary member with a gap therebetween and having a second core section carrying a second coil wound around its periphery;  
           [0013]    a support member for displaceably supporting the movable member relative to the stationary member; and  
           [0014]    an electric current source for displacing the movable member relative to the stationary member by supplying electricity to the first and second coils.  
           [0015]    In another aspect of the invention, there is provided an optical scanner comprising an electromagnetic actuator according to the invention and a mirror arranged on the movable member of the electromagnetic actuator.  
           [0016]    In another aspect of the invention, there is provided an optical scanner comprising an electromagnetic actuator according to the invention and a lens arranged on the movable member of the electromagnetic actuator.  
           [0017]    In still another aspect of the invention, there is also provided a method of preparing an electromagnetic actuator comprising a stationary member having a first core section carrying a first coil wound around its periphery, a movable member magnetically coupled with the stationary member with a gap therebetween and having a second core section carrying a second coil wound around its periphery and a support member for displaceably supporting the movable member relative to said stationary member, the method comprising steps of:  
           [0018]    forming the stationary member, the movable member and the support member on a single substrate by means of photolithography and plating; and  
           [0019]    removing the substrate from under the movable member so as to make the movable member to be supported by the substrate by way of the support member.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a schematic view of a known electromagnetic actuator.  
         [0021]    [0021]FIG. 2 is a schematic perspective view of a first embodiment of electromagnetic actuator according to the invention;  
         [0022]    [0022]FIG. 3 is a schematic view of a second embodiment of electromagnetic actuator according to the invention, illustrating the principle underlying the operation thereof;  
         [0023]    [0023]FIG. 4 is a schematic view of a third embodiment of electromagnetic actuator according to the invention, illustrating the principle underlying the operation thereof;  
         [0024]    [0024]FIGS. 5A, 5B,  5 C,  5 D,  5 E,  5 F,  5 G,  5 H,  5 I,  5 J,  5 K and  5 L are schematic cross sectional views of an electromagnetic actuator according to the invention as shown in different preparing steps, illustrating the method of preparing it.  
         [0025]    [0025]FIG. 6 is a schematic perspective view of the electromagnetic actuator used for the reflection type optical scanner in Example 2.  
         [0026]    [0026]FIGS. 7A and 7B are schematic views of the reflection type optical scanner of Example 2, illustrating the principle underlying the operation thereof.  
         [0027]    [0027]FIG. 8 is a schematic perspective view of the electromagnetic actuator used for the transmission type optical scanner in Example 3.  
         [0028]    [0028]FIGS. 9A and 9B are schematic views of the transmission type optical scanner of Example 3, illustrating the principle underlying the operation thereof. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    An electromagnetic actuator according to the invention comprises a movable member and a stationary member having respective coils and cores which are magnetically coupled with each other so that a troidal coil is formed by each of the movable member and the stationary member to reduce the leakage of magnetic flux. Therefore, the electromagnetic actuator can minimize the consumption rate of electric current and maximize the energy efficiency. Additionally, both the movable member and the stationary member are provided with respective coils, the total number of turns of the coils can be increased to consequently raise the force that the actuator can generate.  
         [0030]    The electric circuit of the above arrangement can be simplified by electrically connecting the stationary coil and the movable coil to consequently simplify the process of preparing the actuator. Additionally, the phenomenon that the force generated in the actuator is inversely proportional to the square of the gap separating the stationary member and the movable member can be eliminated when the stationary member and the movable member are provided with projections and depressions and arranged in such a way that they are combined interdigitally and hence the force generated in the actuator can be determined simply as a function of the electric current flowing through the coils. With such an arrangement, it is possible to control an electromagnetic actuator according to the invention provides by far easier than any conventional electromagnetic actuators.  
         [0031]    Still additionally, the stationary member and the movable member of an electromagnetic actuator can be located accurately relative to each other to accurately control the gap separating them by forming both the stationary member and the movable member on a single substrate. It is also possible to simplify the process of preparing an electromagnetic actuator according to the invention by forming the stationary member, the movable electromagnetic and the support member as integral parts thereof. Furthermore, the support member can be made to directly follow the movement of the movable member without friction and play when the support member is formed by using parallel hinged springs. It is also possible to select the rotational direction of the movable coil so that an attraction type electromagnetic actuator or a repulsion type electromagnetic actuator may be prepared freely at will.  
         [0032]    It is possible to prepare an optical scanner comprising an electromagnetic actuator according to the invention by micro-machining to make the deflector show an excellent energy efficiency and a wide angle of deflection.  
         [0033]    Any assembling process can be made unnecessary when the movable member, the stationary member and the support member of an electromagnetic actuator are formed on a substrate by means of photolithography and plating. Then, these components can be aligned highly accurately and the gap separating the movable member and the stationary can be minimized. Additionally, such an electromagnetic actuator is adapted to mass production and cost reduction. If a silicon substrate is used for the substrate, it can be subjected to an anisotropic etching process for accurately forming openings in the substrate.  
         [0034]    Now, the present invention will be described in greater detail by referring to the accompanying drawings that illustrate preferred embodiments of the invention.  
         [0035]    [0035]FIG. 2 is a schematic perspective view of a first embodiment of electromagnetic actuator according to the invention. Referring to FIG. 2, in the embodiment, the stationary member  102  comprises a stationary core  104   b  and a stationary coil  105   b . A substrate  101  carries thereon the stationary member  102  and a support member  106 , which are rigidly secured to the former. On the other hand, the movable member  103  comprises a movable core  104   a  held at the opposite ends thereof by parallel hinged springs  107  and a movable coil  105   a  wound around the movable core  104   a . The parallel hinged springs  107  are held in position at the support sections  106  thereof. With this arrangement, the movable member  103  is resiliently supported in such a way that it is held in parallel with the substrate  101  and can freely move relative to the latter.  
         [0036]    The stationary member  102  has comb-like teeth arranged at the opposite ends thereof and located in such a way that it is magnetically connected with the movable member  103  having a lateral side that is also toothed in a comb-like manner. The stationary core  104   b  and the movable core  104   a  are respectively provided with a stationary coil  105   b  and a movable coil  105   a  that are wound therearound. Referring to FIG. 2, the stationary coil  105   b , the movable coil  105   a  and electric current source  108  are connected in series so that the operation of the actuator is controlled by the electric current source  108 . As clearly seen from FIG. 2, the stationary core  104   b  and the movable core  104   a  form a closed magnetic path.  
         [0037]    Now, another embodiment of electromagnetic actuator according to the invention will be described by referring to FIG. 3, which is a schematic illustration of the principle underlying the operation of the second embodiment that is a comb-shaped attraction type electromagnetic actuator. As shown in FIG. 3, both the stationary member  502  and the movable member  503  are comb-shaped at the opposite ends thereof. The stationary member  502  comprises a stationary coil  505   b  and a stationary core  504   b , whereas the movable member  503  comprises a movable coil  505   a  and a movable core  504   a . This embodiment is still characterised in that both the stationary member  502  and the movable member  503  are provided with a coil and a core.  
         [0038]    The electric current source  508 , the movable coil  505   a  and the stationary coil  505   b  are electrically connected with each other in series. The movable core  504   a  is resiliently supported by a spring  507  having a spring constant of k. The movable coil  505   a  and the stationary coil  505   b  are made of a low resistance metal such as copper or aluminum and electrically insulated from the movable core  504   a  and the stationary core  504   b . The movable core  504   a  and the stationary core  504   b  are made of a ferromagnetic material such as nickel, iron or Permalloy. As the movable coil  505   a  and the stationary coil  505   b  are fed with an electric current from the electric current source  508 , a magnetic flux is generated in the movable core  504   a  and the stationary core  504   b  to run in the direction of arrows shown in FIG. 3. The magnetic flux circularly runs through the magnetic circuit in the direction as indicated by arrows in FIG. 3 by way of the movable core  504   a , an air gap  510   a  between the oppositely disposed teeth of one corresponding pair of combs, the stationary core  504   b  and another air gap  510   b  between the oppositely disposed teeth of the other corresponding pair of combs to make the movable member  503  and the stationary member  502  attract each other.  
         [0039]    The magnetic resistance R g (x) between the oppositely disposed teeth of the combs is given by formula (3) shown below:  
                 R   g          (   x   )       =     d       μ   0          tn        (     x   +     x   0       )                   (   3   )                               
 
         [0040]    where μ 0  is the magnetic permeability of vacuum, d is the distance of the air gap, t is the thickness of the teeth of the combs, n is the number of unit air gaps, x is the displacement of the movable member and x 0  is the overlapping distance of the teeth of the oppositely disposed combs in the initial state. If the magnetic resistance in areas other than the air gaps is R, the potential energy w of the entire magnetic circuit and the force F generated in the air gaps is expressed by formulas (4) and (5) respectively:  
               W   =         1   2            (     R   +     2          R   g          (   x   )           )       -   1              (   Ni   )     2       =           (   Ni   )     2     2            (     R   +       2      d         μ   0          tn        (     x   +     x   0       )             )       -   1                  
        and           (   4   )               F   =       -          W          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   )                               
 
         [0041]    where N is the sum of the number of turns of the coil  505   a  and that of the coil  505   b  and i is the electric current flowing through the coils  505   a  and  505   b.    
         [0042]    If the movable core  504   a  and the stationary core  504   b  are made of a material showing a magnetic permeability sufficiently higher than the magnetic permeability of vacuum, R is made practically equal to 0 and the generated force F is expressed by formula (6) below.  
             F   =           μ   0        tn       4      d              (   Ni   )     2               (   6   )                               
 
         [0043]    From formula (6) above, it will be seen that the generated force F of this embodiment is proportional to the square of the number of turns of the coils. While the generated force F fluctuates slightly depending on the displacement x because the magnetic permeability cannot be infinitely high, such fluctuations in the generated force are small if compared with conventional magnetic actuators.  
         [0044]    If the spring constant of the parallel hinged springs is k, the static displacement of the actuator is obtained from the balanced relationship of the spring force and the generated force as expressed by formula (7) below.  
           F=kx   (7)  
         [0045]    A comb-shaped repulsion type electromagnetic actuator can be realized by modifying the direction of winding of the movable coil  505   a  or the stationary coil  505   b  of the comb-shaped attraction type electromagnetic actuator.  
         [0046]    Now, still another embodiment of electromagnetic actuator according to the invention will be described by referring to FIG. 4, which is a schematic illustration of the principle underlying the operation of the third embodiment that is a flat surface attraction type electromagnetic actuator. As shown in FIG. 4, both the stationary member  202  and the movable member  203  have flat surfaces at the opposite ends thereof. The stationary member  202  comprises a stationary coil  205   b  and a stationary core  204   b , whereas the movable member  203  comprises a movable coil  205   a  and a movable core  204   a . This embodiment is still characterised in that both the stationary member  202  and the movable member  203  are provided with a coil and a core.  
         [0047]    The electric current source  208 , the movable coil  205   a  and the stationary coil  205   b  are electrically connected with each other in series. The movable core  204   a  is resiliently supported by a spring  207  having a spring constant of k. The movable coil  205   a  and the stationary coil  205   b  are made of a low resistance metal such as copper or aluminum and electrically insulated from the movable core  204   a  and the stationary core  204   b . The movable core  204   a  and the stationary core  204   b  are made of a ferromagnetic material such as nickel, iron or Permalloy.  
         [0048]    As the movable coil  205   a  and the stationary coil  205   b  are fed with an electric current from the electric current source  208 , a magnetic flux is generated in the movable core  204   a  and the stationary core  204   b  to run in the direction of arrows shown in FIG. 4. The magnetic flux circularly runs through the magnetic circuit in the direction as indicated by arrows in FIG. 4 by way of the movable core  204   a , an air gap  210   a  between the oppositely disposed surfaces of one corresponding ends, the stationary core  204   b  and another air gap  210   b  between the oppositely disposed surfaces of the other corresponding ends to make the movable member  203  and the stationary member  202  attract each other.  
         [0049]    The magnetic resistance of one air gap between the oppositely disposed surfaces is given by formula (x+x 0 )/μ 0 tw and since a magnetic path transverses two air gaps, the magnetic resistance Rg(x) of the two air gaps separating the plates is given by formula (8) below:  
                 R   g          (   x   )       =       2        (     x   +     x   0       )           μ   0        tw               (   8   )                               
 
         [0050]    where μ 0  is the magnetic permeability of vacuum, t is the thickness of the end surface sections, w is the width of the end surface sections, x is the displacement of the movable member and x 0  is the length of the air gaps in the initial state. If the magnetic resistance in areas other than the air gaps is R, the potential energy w of the entire magnetic circuit and the force F generated in the air gaps is expressed by formulas (9) and (10) respectively:  
               W   =         1   2            (     R   +       R   g          (   x   )         )       -   1              (   Ni   )     2       =           (   Ni   )     2     2            (     R   +       2        (     x   +     x   0       )           μ   0        tw         )       -   1                  
        and           (   9   )               F   =       -          W          x         =       1       μ   0        tw              (     R   +       2        (     x   +     x   0       )           μ   0        tw         )       -   2              (   Ni   )     2                 (   10   )                               
 
         [0051]    where N is the sum of the number of turns of the coil  205   a  and that of the coil  205   b  and i is the electric current flowing through the coils  205   a  and  205   b.    
         [0052]    If the movable core  204   a  and the stationary core  204   b  are made of a material showing a magnetic permeability sufficiently higher than the magnetic permeability of vacuum, R is made practically equal to 0 and the generated force F is expressed by formula (11) below.  
             F   =           μ   0        tw       4          (     x   +     x   0       )     2                (   Ni   )     2               (   11   )                               
 
         [0053]    From formula (11) above, it will be seen that the generated force F of this embodiment is proportional to the square of the number of turns of the coils.  
         [0054]    If the spring constant of the parallel hinged springs is k, the static displacement of the actuator is obtained from the balanced relationship of the spring force and the generated force as expressed by formula (12) below.  
           F=kx   (12)  
         [0055]    A flat surface repulsion type electromagnetic actuator can be realized by modifying the direction of winding of the movable coil  205   a  or the stationary coil  205   b  of the flat surface attraction type electromagnetic actuator.  
         [0056]    The present invention will be described further below by way of examples.  
       EXAMPLE 1  
       [0057]    An electromagnetic actuator having a configuration as shown in FIG. 2 was prepared. Referring to FIG. 2, stationary member  102  comprises a stationary core  104   b  and a stationary coil  105   b . A substrate  101  carries thereon the stationary member  102  and a support member  106 , which are rigidly secured to the former. On the other hand, movable member  103  comprises a movable core  104   a  held at the opposite ends thereof by parallel hinged springs  107  and a movable coil  105   a  wound around the movable core  104   a . The parallel hinged springs  107  are held in position at the support sections  106  thereof. With this arrangement, the movable member  103  is resiliently supported in such a way that it is held in parallel with the substrate  101  and can freely move relative to the latter.  
         [0058]    The stationary member  102  has comb-like teeth arranged at the opposite ends thereof and located in such a way that it is magnetically connected with the movable member  103  having a lateral side that is also toothed in a comb-like manner. The stationary core  104   b  and the movable core  104   a  are provided respectively with a stationary coil  105   b  and a movable coil  105   a  that are wound therearound. The stationary coil  105   b , the movable coil  105   a  and electric current source  108  are connected in series so that the operation of the actuator is controlled by the electric current source  108 .  
         [0059]    Now, the method used for preparing the actuator of this example will be described below. In this example, the stationary member  102 , the movable member  103 , the movable core  104   a , the stationary core  104   b , the movable coil  105   a , the stationary coil  105   b , the support member  106  and the parallel hinged springs  107  are prepared by means of the micro-machining technology. Coil lower surface wiring  114 , coil lateral surface wiring  115  and coil upper surface wiring  116  are prepared in the above mentioned order for both the movable coil  105   a  and the stationary coil  105   b  (see FIG. 5L)  
         [0060]    Now, the method used for preparing the actuator of this example will be described in greater detail by referring to FIGS. 5A through 5L. In each of FIGS. 5A through 5L, the left side and the right side show cross sectional views taken along line A-A′ and B-B′ in FIG. 2 respectively.  
         [0061]    Firstly as shown in FIG. 5A, a copper film was formed as coil lower surface wiring  114  on a substrate  101  by evaporation and subjected to a patterning operation. Subsequently, as shown in FIG. 5B, polyimide was applied to the substrate  101  to form an insulating layer  117  between the coil lower surface wiring  114  and the cores to be formed subsequently and subjected to a patterning operation. Then, as shown in FIG. 5C, chromium was deposited as seed electrode layer  111  for electric plating by evaporation and then gold was deposited thereon also by evaporation.  
         [0062]    Thereafter, as shown in FIG. 5D, photoresist was applied to form a photoresist layer  112  that is 300 μm thick. In this example, SU-8 (tradename, available from Micro Chem) was used as photoresist because it is adapted to be applied to a large thickness. Then, as shown in FIG. 5E, the photoresist layer  112  was exposed to light, developed and subjected to a patterning operation. The parts of the photoresist removed in this process provides female moulds for the stationary member  102 , the movable member  103 , the movable core  104   a , the stationary core  104   b , the support member  106 , the parallel hinged springs  107  and the coil lateral surface wiring  115 . Subsequently, as shown in FIG. 5F, Permalloy layers  113 ,  115  were electrically plated by applying a voltage to the seed electrode layer  111 .  
         [0063]    Thereafter, as shown in FIG. 5G, the photoresist layer and the underlying seed electrode layer were removed by dry etching. Then, as shown in FIG. 5H, epoxy resin  119  was applied and the upper surface of the epoxy resin layer was smoothed by polishing it mechanically. Subsequently, as shown in FIG. 5I, polyimide was applied to the upper surface of the epoxy resin layer  119  in parts that eventually make a movable core and a stationary core to form an insulating layer  118  there, which was then subjected to a patterning operation. Thereafter, as shown in FIG. 5J, copper was deposited on the insulating layer  118  between the upper surface wiring  116  and the cores by evaporation and then subjected to a patterning operation. Then, the epoxy resin was removed as shown in FIG. 5K.  
         [0064]    Finally, as shown in FIG. 5L, the substrate  101  was anisotropically etched from the rear surface thereof so that the movable member is supported only by the support member  106 . In FIG. 5L, the components same as those illustrated in FIGS. 2 and 5A through  5 K are denoted respectively by the same reference symbols and will not be described any further.  
         [0065]    Since the electromagnetic actuator of this example that was prepared in a manner as described above showed an excellent energy efficiency because a single troidal coil was formed by the movable member and the stationary member to minimize the leakage of magnetic flux. Additionally, since the movable member and the stationary member comprise respective coils and cores, the number of turns of the coils can be raised to increase the force generated in the actuator.  
       EXAMPLE  2   
       [0066]    [0066]FIG. 6 is a schematic perspective view of the electromagnetic actuator used for a reflection type optical scanner in Example 2. Referring to FIG. 6, stationary member  302  comprises a stationary core  304   b  and a stationary coil  305   b . A substrate  301  carries thereon the stationary member  302  and a support member  306 , which are rigidly secured to the former. On the other hand, movable member  303  comprises a movable core  304   a  held at the opposite ends thereof by parallel hinged springs  307  and a movable coil  305   a  wound around the movable core  304   a . The parallel hinged springs  307  are held in position at the support sections  306  thereof. With this arrangement, the movable member  303  is resiliently supported in such a way that it is held in parallel with the substrate  301  and can freely move relative to the latter.  
         [0067]    Mirror  311  is arranged on the movable member  303 . The stationary member  302  has comb-like teeth arranged at the opposite ends thereof and located in such a way that it is magnetically connected with the movable member  303  having a lateral side that is also toothed in a comb-like manner. The stationary core  304   b  and the movable core  304   a  are provided respectively with a stationary coil  305   b  and a movable coil  305   a  that are wound therearound. The stationary coil  305   b , the movable coil  305   a  and electric current source  308  are connected in series so that the operation of the actuator is controlled by the electric current source  308 . The stationary member  302  and the movable member  303  are provided with teeth projecting like those of combs that are interdigitally arranged. This arrangement could be prepared by way of a process similar to the one described above by referring to Example 1.  
         [0068]    [0068]FIGS. 7A and 7B are schematic views of the reflection type optical scanner of Example 2, illustrating the principle underlying the operation thereof. Referring to FIGS. 7A and 7B, reference symbols  312  and  313  respectively denote a semiconductor laser and a laser beam. The semiconductor laser  312  is arranged in such a way that the laser beam  313  strikes the mirror  311 . The semiconductor laser  312  may be located on the substrate  301  shown in FIG. 6 or at some other position. As the movable coil  305   a  and the stationary coil  305   b  are electrically energized, the movable member  303  and the stationary member  302  attract each other. FIG. 7A shows the state where the movable coil  305   a  and the stationary coil  305   b  in FIG. 6 are not electrically energized, whereas FIG. 7B shows the state where the movable coil  305   a  and the stationary coil  305   b  in FIG. 6 are electrically energized. As seen from FIGS. 7A and 7B, the direction of the laser beam  313  is modified as the movable coil  305   a  and the stationary coil  305   b  are electrically energized. The electromagnetic actuator used in the optical scanner of this example showed an excellent energy efficiency because the leakage of magnetic flux is minimized if compared with conventional electromagnetic actuators. Additionally, since the movable member and the stationary members comprise respective coils and cores, the number of turns of the coils can be raised to increase the force generated in the actuator. Thus, a reflection type optical scanner that shows an excellent energy efficiency and a large deflector angle can be prepared by micro-machining, using an electromagnetic actuator like the one prepared in this example.  
       EXAMPLE 3  
       [0069]    [0069]FIG. 8 is a schematic perspective view of the electromagnetic actuator used for a transmission type optical scanner in Example 3. Referring to FIG. 8, stationary member  402  comprises a stationary core  404   b  and a stationary coil  405   b . A substrate  401  carries thereon the stationary member  402  and a support member  406 , which are rigidly secured to the former. On the other hand, movable member  403  comprises a movable core  404   a  held at the opposite ends thereof by parallel hinged springs  407  and a movable coil  405   a  wound around the movable core  404   a . The parallel hinged springs  407  are held in position at the support sections  406  thereof.  
         [0070]    With this arrangement, the movable member  403  is resiliently supported in such a way that it is held in parallel with the substrate  401  and can freely move relative to the latter.  
         [0071]    Lens  411  is arranged on the movable member  403  to transmit laser beams. The stationary member  402  has comb-like teeth arranged at the opposite ends thereof and located in such a way that it is magnetically connected with the movable member  403  having a lateral side that is also toothed in a comb-like manner. The stationary core  404   b  and the movable core  404   a  are provided respectively with a stationary coil  405   b  and a movable coil  405   a  that are wound therearound. The stationary coil  405   b , the movable coil  405   a  and electric current source  408  are connected in series so that the operation of the actuator is controlled by the electric current source  408 . The stationary member  402  and the movable member  403  are provided with teeth projecting like those of combs that are interdigitally arranged. This arrangement can be prepared by way of a process similar to the one described above by referring to Example 1.  
         [0072]    [0072]FIGS. 9A and 9B are schematic views of the transmission type optical scanner of Example 3, illustrating the principle underlying the operation thereof. Referring to FIGS. 9A and 9B, reference symbols  412  and  413  respectively denote a semiconductor laser and a laser beam. The semiconductor laser  412  is arranged in such a way that the laser beam  413  is transmitted through the lens  411 . The semiconductor laser  412  may be located on the substrate  401  shown in FIG. 8 or at some other position. As the movable coil  405   a  and the stationary coil  405   b  are electrically energized, the movable member  403  and the stationary member  402  are repulsed from each other. FIG. 9A shows the state where the movable coil  405   a  and the stationary coil  405   b  in FIG. 8 are not electrically energized, whereas FIG. 9B shows the state where the movable coil  405   a  and the stationary coil  405   b  in FIG. 8 are electrically energized. As seen from FIGS. 9A and 9B, the direction of the laser beam  413  is modified as the movable coil  405   a  and the stationary coil  405   b  are electrically energized. Thus, a transmission type optical scanner that shows an excellent energy efficiency and a large deflector angle can be prepared by micro-machining, using an electromagnetic actuator like the one prepared in this example.  
         [0073]    As described above in detail, an electromagnetic actuator according to the invention can be operated at a low power consumption rate to improve the energy efficiency if compared with conventional electromagnetic actuators because of a minimized leakage of magnetic flux. Additionally, since both the stationary member and the movable member of an electromagnetic actuator according to the invention are provided with respective coils and cores, the total number of turns of the cores can be increased to raise the force generated in the electromagnetic actuator.  
         [0074]    Furthermore, according to the invention, a reflection type optical scanner showing a large deflection angle and a high energy efficiency and comprising a mirror and an electromagnetic actuator mechanically connected to the mirror can be prepared by micro-machining.  
         [0075]    Similarly, according to the invention, a transmission type optical scanner showing a large deflection angle and a high energy efficiency and comprising a lens and an electromagnetic actuator mechanically connected to the lens can be prepared by micro-machining.