Abstract:
A multi-step microactuator is provided with the multiple supports in a stepper plate to give multi-step displacement to a controlled object. The microactuator has advantages such that multiple motion can be applied to the controlled object and that the object can be controlled in a low driving voltage and that simple motion control is applied by digital controlling and that the degrees of freedom in motion of the object can be chosen by the number of the stepper plate and that only single voltage is needed for driving the micromirror motion. With many advantages, the multi-step microactuator provides a solution to overcome the difficulties in controlling multi-step motion.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The microactuators controlled by electrostatic force can be divided into discrete control or digital control and analogy control. Displacement made by analog control is determined at the equilibrium between electrostatic force and elastic force. Therefore, the microactuator with analogy control has continuous displacement through mechanical deformation. But, it is more complex than the digital or discrete control, and is not compatible with known semiconductor technologies such as MOS, CMOS, etc. In addition, the microactuators with continuous displacement actuated by electrostatic force undergo the classical snap-down phenomenon when the electric force exceeds the elastic force of mechanical structure. The snap-down phenomenon limits the displacement range of the microactuator. The high driving voltage is another disadvantage in use of the microactuator with continuous displacement actuated by electrostatic force. To be compatible with IC components, it is desired that a microactuaor is operated at low voltage which is compatible with the circuit operation. In contrast, discrete control is simple, compatible with known semiconductor technologies such as MOS and CMOS and has a large displacement and low driving voltage. But, it is not easy to get a multi-step displacement with simple structure.  
       SUMMARY OF THE INVENTION  
       [0002]     The present invention provides an advanced microactuator for multi-step position control of an object. The microactuator has many advantages for controlling multi-step position such as that the microactutor uses simple driving method, and that single voltage or discretely separated voltage source is used for multi-step position control.  
         [0003]     In the present invention, multi-step microactuator is provided. The microactuator comprises at least one stepper plate with a plurality of supports, which are introduced for multi-step position control. The stepper plate is inclined by electrostatic force between the electrodes and the stepper plate. When a stepper plate is inclined for a given step toward the selected direction, the pre-programmed position of the support provides a displacement to an object. For example, the support can uphold the micromirror to make a desired motion of the micromirror. Each support on a stepper plate gives a pre-programmed displacement to the micromirror. The displacement amount can be determined by in-plane position of support on stepper plate and different amounts of the rotation angle of the stepper plates for each step. The control system is actuated by the electrostatic force between the stepper plate and the electrodes. Also the electromagnetic and electro-thermal forces can be applied to the system.  
         [0004]     The shape of the stepper plates can be varied to have triangular, square, hexagonal, octagonal, circular or other shapes. The number of the steps in a stepper plate can be determined by the shape of the stepper plate and the electrodes under the stepper plates. If the stepper plate has 8 electrodes, the stepper plates can have up to 8 different steps.  
         [0005]     The control system needs low voltage to control the microactuator by sharing the multiple electrodes. Since defining of a step is only determined by the direction of the inclined stepper plate and the support position, one step in a stepper plate can share neighboring electrodes to have stronger electrostatic force. By using the multiple electrodes together, the driving voltage can be reduced since the effective area for forming the electrostatic force is increased. Electrostatic force can be increased by doubled or tripled the area of the electrode by applying the driving voltage to the on-step electrode accompanying with neighboring electrodes. By applying the voltage to the multiple electrodes together, the stepper plate with supports can give large actuating force. Each step is controlled by the corresponding electrode or electrodes.  
         [0006]     Still another advantage is that the object controlled by N number of microactuators has N degrees of freedom in motion control. The degrees of the freedom can be varied by adding more microactuators to obtain the desired degrees of freedom in the object. When the stepper plate is inclined, a support gives the unique displacement to the controlled object. If the object needs three degrees of freedom motions, three different microactuators are controlled to define the desire motion of the controlled object. The three degrees of freedom motion of the object requires at least three microactuators.  
         [0007]     The multi-step microactuator of the present invention has advantages: (1) multiple displacement control is possible; (2) the microactuator can be controlled in a low driving voltage; (3) simple displacement control is applied by digital controlling; (4) the degrees of freedom in motion of the object can be chosen by the number of the microactuators; (5) only single voltage is needed for driving the microactuator; and (6) the microactuator is controlled in a stepwise way.  
         [0008]     Although the present invention is briefly summarized, the full understanding of the invention can be obtained by the following drawings, detailed description, and appended claims. 
     
    
     DESCRIPTION OF THE FIGURES  
       [0009]     These and other features, aspects and advantages of the present invention will become better understood with reference to the accompanying drawings, wherein:  
         [0010]      FIG. 1  shows schematic diagram of a microactuator system giving continuous displacement to the object;  
         [0011]      FIG. 2  shows components of microactuator according to embodiments of the present invention;  
         [0012]      FIGS. 3A-3B  show actuation of the microactuator;  
         [0013]      FIG. 4  shows a stepper plate with quadruple supports and electrodes for generating the multiple motions (4 different motions);  
         [0014]      FIG. 5  shows a stepper plate with multiple supports and electrodes for generating the multiple motions (8 different motions);  
         [0015]      FIG. 6  is a schematic diagram of springless hinge structure.  
         [0016]      FIG. 7  is a schematic diagram showing how two microactuators define the controlled object motions with two degrees of freedom (one rotational and one translational);  
         [0017]      FIG. 8  is a schematic diagram showing how three microactuators define object motions with three degrees of freedom (two rotational and one translational); 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 1  shows schematic diagram of a microactuator system  11  giving continuous displacement to the object  12 . The object  12  is controlled to have a continuous rotation  15  or translation  16 , which is determined by the equilibrium between electrostatic force between the electrode  13  and the object  12  and elastic force of the translational spring  14  and the rotational spring  17 . The object  12  is rotated along the hinge supported by the supporting structure. Since the displacement is determined by the equilibrium of the electrostatic and elastic forces, complex analog control with active feedback is required to have a fine control of the motion.  
         [0019]     On the other hand, the multi-step microactuator has simpler control system. Once the motion is defined and programmed in the microactuator, the control is just applying the on/off voltage for desired channel with respect to the desired motion. No feedback is required and the motion is reproducible regardless of the environment.  
         [0020]     The multi-step microactuator comprises a stepper plate with multiple supports, coupled to the bottom layer, configured to rotate, a bottom layer configured to have multiple electrodes to control the stepper plate. A controlled object is coupled to the stepper plate wherein the microactuator gives the multiple displacements to the controlled object. The displacement is programmed by the positions of the supports or the rotation angles of the stepper plate.  
         [0021]      FIG. 2  shows components of microactuator  26  according to embodiments of the present invention. The microactuator includes stepper plates  22  with multiple supports  23 , coupled to the bottom layer and configured to be rotated to give displacement of the object  21 , and a bottom layer configured to have multiple electrodes  24  to control the stepper plate  22 , and the object  21  coupled to the stepper plate  22 . Also the microactuator can use different types of stops  20 ,  25  to control the displacement of the object. The microactuator  21  has the multiple motions programmed by the positions of the supports  23  or the rotation angles of the stepper plate  22 . The stepper plates are restored due to the restoring forces by the flexible springs  29 . The stop  25  under the stepper plate  22  adjusts the amount of the angle rotated by its position and/or its height. Also the stop  20  at the bottom layer adjusts the amount of the angle rotated by its position and/or its height.  
         [0022]     In  FIG. 3A , the motion defined by the support  33  on the stepper plate  32  is described. The stepper  32  structure is coupled to the bottom layer with electrodes  35 . Each electrode  35  is activated for a given desired motion of the object  31 . The supports  33  on the stepper plate  32  are positioned for defining the position of an object  31 . The height H of the support  33  after the stepper plate is rotated is varied by the distance L from contact point A. The motion of the controlled object  31  is defined by contact position B of the supports  33  after the stepper plate  32  is rotated. More than one support can uphold the object  31 . Two contact points A and C determine the amount of angle of stepper plate, where contact point A is determined by height and position of stop  30 . The stops  30  can be used alone or the combinations of the stops  30 ,  25  can be used. Electrodes  35  pull the stepper plate  32  until the two contact points A, C blocks the rotation of the stepper plate  32 . The motion of the object  31  is defined by the positions of supports on the stepper plate  32 , or the rotation angle limited by the stops under the stepper plates  25 . The stop  30  in the middle of the stepper plate also defines the stepper plate  32 . The support  33  on the stepper plate  32  pushes the object  31  to have the desired motion of the object. The opposite side electrode  35  is applied by the driving voltage. The displacements of the object  31  controlled by the microactuator are obtained by the supports  33  with respect to the inclination direction of the stepper plate.  
         [0023]      FIG. 3B  shows the motion obtained by the stops  34  under the stepper plate  32 . In the figure, a stepper plate has the stop  34  under the stepper plate  32 . The amounts of the rotation angles are different as the stop position or the height of the stop or even the existence of the stop under the stepper plate. Also the stop can be existed on the bottom layer and can define the stepper  32  rotation angle thus the motion of the object  31 . While the rotation amount of the stepper is defined, the inside stops  36  plays a role as a motion control point to define a plane for the stepper plate  32 . And the stepper plate  32  or the support  33  on the stepper plate moves the object  31 . The motion of the object is defined by the rotation amounts of the stepper plate  32  which is determined by the height and/or the position of the stops  34 ,  36 .  
         [0024]      FIG. 4  shows a stepper plate  43  with four supports on a stepper plate  43  and electrodes  41  for generating four different motions. If the voltage is applied on one of the electrode  41 , the stepper plate  43  is inclined and snapped down to the direction of the voltage applied electrode  41 . Then the support  42  in opposite side is rotated and raises its tip position by the inclination of the stepper plate  43 . The raised support  42  moves the object (not shown) to the desired position. Since there are four electrodes, the stepper plate  43  is inclined to the corresponding directions of the electrodes  41 . For each inclination direction, the position of the support  42  is determined for generating the desired motion of the object. The position and the height of the support  42  is determined to have the pre-programmed motions and fabricated during making process of the microactuator system. To have larger electrostatic force or lower driving voltage, electric bias can be applied to two or three electrodes at the same time. Since the area of the electrode is doubled or tripled, the electrostatic force becomes larger than that of one electrode case. Different support in a stepper plate gives different motion.  
         [0025]      FIG. 5  shows an  8  steps microactuator. Eight supports and electrodes  51  for generating eight different heights for generating motions. If the voltage is applied on one of the eight electrodes  51 , the stepper plate  52  is inclined and snapped down to the direction of voltage applied electrode  51 . Then the support  52  in opposite side is raised by the inclination of the stepper plate  52 . The raised support  52  moves the object (not shown) to the desired position. Since there are eight electrodes, the stepper plate is inclined to the corresponding directions of the electrodes. For each inclination direction, the position of the support  52  is determined for generating the desired motion of the object. Also to have larger electrostatic force or lower driving voltage, electric bias can be applied to multiple electrodes at the same time. Since the area of the electrode  51  is increased, the electrostatic force becomes larger than that of one electrode case. The system has multiple motions which are constraint by the number of the supports in the stepper plates  53 . Since the stepper plate contacts the bottom layer structure, the stiction can prevent the stepper motion. To reduce the possible stiction problem, the tip  54  on the stepper plate is applied to minimize the contact area.  
         [0026]      FIG. 6  is a schematic diagram of springless hinge structure. The stepper plate  61  is attached to a flexible spring, and the flexible spring is attached to a fixed structure at  FIG. 2  . But the spring can be omitted by using hinge structure as  FIG. 6 . The stepper plate  62  is confined in the hinge structure  63 , while the stepper plate  62  has a motion with inclination.  
         [0027]      FIG. 7  shows how two microactuators  76  define object motions  72 ,  73  with two degrees of freedom. The figure shows one rotational  73  and one translational  72  degrees of freedom case. Two supports  75  from different stepper plates  76  define the motion of the object  74 . In addition to the rotational motion of the object  74 , the translation  72  of the object  74  can be  25  adjusted by the supports  75 . The object  74  motion  72 ,  73  is defined by the two heights of the supports  75  which are determined by the rotation angle of the stepper plate  76  and the distance from the steppercenter to the corresponding support  75 .  
         [0028]     In  FIG. 8 , configuration with three degrees of freedom  85 ,  86  is presented. The motion has two degrees of freedom rotation  85  and one degree of translation  86 . For representing three degrees of freedom motion, at least three supports  84  are needed from different stepper plates  82 . Height and position of each support  84  from three stepper plates  82  defines a specific motion in three dimensional space. These three points by the three supports  84  make a plane for the object  81  representing object motion. Every motion can be specified as a step. In a step, three supports  84  from different stepper plate  82  define a plane of motion. In the same way, three other positions by the three other supports define another plane for the object  81 . As many planes as the numbers of the supports in a stepper plate  82  can be defined by three stepper plates  82 .  
         [0029]     While the invention has been shown and described with reference to different embodiments thereof, it will be appreciated by those skills in the art that variations in form, detail, compositions and operation may be made without departing from the spirit and scope of the invention as defined by the accompanying claims.