Abstract:
A thin-disc piezoelectric actuating ultrasonic motor is disclosed. A stator is commercial available buzz piece consisted of piezoelectric ceramic membrane bonded on a metal plate. It is a concentric disk and posses either electric or mechanical flexural characteristics. Ultrasonic motor driving mechanism is a mechanical vibration by extension and shrinkage of a metal back plate due to the reverse piezoelectric effect, which supplies a single phase AC power. There are two transferring directions in the mechanical vibrating wave. One is a radial component, and another is a transverse component. This, the outer edge of the buzz piece forms various of traveling waves in different directions. These traveling waves may be used to provide a torque so as to drive the rotor to rotate.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a thin-disc piezoelectric actuating ultrasonic motor, wherein an AC voltage is inputted into a piezoelectric buzz piece. The piezoelectric ceramic will generate a pull or push effect due to the reverse piezoelectric effect and a metal back plate is driven to vibrate. The generated mechanical wave transfers along radial or transverse directions. In transferring the wave, each screw can be formed as a reflecting point. By the reflecting points from the peripheral three screws, traveling waves of different directions are formed by the piezoelectric buzz piece at the outer edge. One of the traveling wave is used to provide a torque to drive the rotor to rotate.  
         BACKGROUND OF THE INVENTION  
         [0002]    The current used ultrasonic motor is primarily formed by the piezoelectric (PZT) ceramic of zirconium-titanium-acid-lead material. After a voltage is inputted into a piezoelectric ceramic, the piezoelectric ceramic and the metal back plate will be forced to generate a mechanically extended-contracted phenomenon. Energy is transferred like a wave form. The piezoelectric ceramic can be work within an ultrasonic frequency with the amplitude of several micrometers which is controllable by input voltage. Therefore, it can be used as a driving device or a driving motor of a compact structure or system.  
           [0003]    The aforesaid ultrasonic motor may have alternative extended-contracted function by AC power. By mechanical design, motions in specific directions are generated. The moving distance in each period is only several micrometers. Under the vibration of the ultrasonic frequency, a displacement of several centimeters per second is generated for driving precise devices (such as automatic focusing means of a camera, positioning device for fine machining, etc.). Meanwhile, the ultrasonic motor has the features of small volume, light weighted, lower noise, low speed with a high torque, high retaining force, quick response, not to be affect by electromagnetic interference, etc. Each advantage can be used to different products, such as lower speed, high torque, high retaining force, and lower noise are suitable for silent places (such as hospitals); quick response is suitable for driving a X-Y platform, and not to be affected by electromagnetic wave is suitable for the magnetic floating vehicles and biomedical technology.  
           [0004]    The prior art ultrasonic motors or actuators are made of piezoelectric bulk material or piezoelectric stacking piece, however, the cost is high so that the commercial ultrasonic motor has a high price.  
         SUMMARY OF THE INVENTION  
         [0005]    Accordingly, the primary object of the present invention is to provide a piezoelectric buzz piece inputted into an AC voltage. The piezoelectric ceramic will generate a pull-push effect due to reverse piezoelectric effect and a metal back plate is driven to vibrate. The generated mechanical wave transfers along a radial or transverse path. In transferring the wave, each screw can be formed as a reflecting point. By the reflecting points from the peripheral three screws, traveling waves of different directions can be formed by the piezoelectric buzz piece at the outer edge. One of the traveling wave is used to provide a torque to drive the rotor to rotate.  
           [0006]    Another object of the present invention is to provide a thin-disc piezoelectric actuating ultrasonic motor, wherein only a single phase driving power is used to complete the clockwise or counterclockwise rotation, while in the conventional ultrasonic motor, two phase driving power is used for generating traveling waves and high amplitude input pulse, these defects are improved by the present invention.  
           [0007]    A further object of the present invention is to provide a thin-disc piezoelectric actuating ultrasonic motor, wherein the present invention can be used in semiconductor equipment, medical instruments, hard disk drives and CD drives. Furthermore, the cost of the present invention is low and the present invention has a preferred efficiency.  
           [0008]    To achieve above objects, the present invention provides a thin-disc piezoelectric actuating ultrasonic motor, wherein a main electrode is covered at the uppermost of the piezoelectric buzz piece, and the lowest end of the piezoelectric buzz piece is adhered to a metal back plate. In operation, an AC power is inputted between the main electrode and the metal back plate. The piezoelectric ceramic will extend or shrink (reverse piezoelectric effect). The metal back plate will be operated by the piezoelectric ceramic so as deformation to vibrate the air for emitting a sound. The working frequency is used to among 50 and 20 kHz. In the present invention, a piezoelectric buzz piece is used as a driver operating frequency launched over 30 kHz. The working principle is that a piezoelectric buzz piece is used to vibrate the periphery of the metal back plate for driving the rotor to rotate.  
           [0009]    In the present invention, a thin-disc piezoelectric actuating ultrasonic motor is disclosed. A piezoelectric buzz piece is fixed to a rectangular piece by three asymmetric screws. Then one side of the fixed rectangular piece is fixed to another rectangular piece larger than the former one by a plurality of screws and an elastomer so that an elastic resilient structure is formed between the two rectangular pieces. Then an AC current is inputted into the piezoelectric buzz piece so that the piezoelectric ceramic will extended-contracted motion due to the reverse piezoelectric effect of the ceramic and drive the metal back plate to vibrate. The mechanical waves are transferred along the radial and transverse directions. The outer edge of the piezoelectric buzz piece generates traveling waves along different direction. The traveling waves will provide a torque to drive the rotor to rotate.  
           [0010]    Stator consists of two major element: one is piezoelectric ceramic and another is metal back plate. The principle of the either standing or traveling wave of a stator is that an AC voltage applied to the main electrode of a piezoelectric buzz piece so that the piezoelectric ceramic as the main actuating body of a stator will generate a reverse piezoelectric effect to vibrate the metal back plate. Therefore, wave meaning energy is transferred on the stator. The oscillation of the friction material on the stator causes the shaft of rotor to be rotated along the wave traveling direction. The generation of traveling wave is that a disc with a single frequency vibrates so as to be formed with a multiple reflection as a specific frequency. The traveling difference of these reflecting waves will form wave motion at a specific section.  
           [0011]    The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows one structure of the thin-disc piezoelectric actuating ultrasonic motor in the present invention.  
         [0013]    [0013]FIG. 2 is an exploded perspective view of the thin-disc piezoelectric actuating ultrasonic motor of the present invention.  
         [0014]    [0014]FIG. 3 is an assembled perspective view of the thin-disc piezoelectric actuating ultrasonic motor of the present invention.  
         [0015]    [0015]FIG. 4 is an elevation view of the thin-disc piezoelectric actuating ultrasonic motor in the present invention.  
         [0016]    [0016]FIG. 5 is a schematic view showing the piezoelectric buzz piece input period.  
         [0017]    [0017]FIG. 6 shows the simulation of a piezoelectric buzz piece rotating counterclockwise.  
         [0018]    [0018]FIG. 7 is a simulation of the piezoelectric buzz piece rotating clockwise.  
         [0019]    [0019]FIG. 8 shows a simulation of edge-driving principle.  
         [0020]    [0020]FIG. 9 shows the stator of an edge-driving ultrasonic motor.  
         [0021]    [0021]FIG. 10 shows the rotor of an edge-driving ultrasonic motor.  
         [0022]    [0022]FIG. 11 shows the testing platform for assembly of an edge-driving ultrasonic motor.  
         [0023]    [0023]FIG. 12 is a system block diagram of a driving circuit.  
         [0024]    [0024]FIG. 13 is a circuit diagram of a power converter. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    With reference to FIGS. 2, 3 and  4 , the thin-disc piezoelectric actuating ultrasonic motor of the present invention is illustrated. The thin-disc piezoelectric actuating ultrasonic motor includes a piezoelectric buzz piece  1 , a first fixing plate  2 , a second fixing plate  3 , an elastomer  4 , a plurality of screws  5  and a lead  6 . The piezoelectric buzz piece  1  is fixed to the first fixing plate  2  by the screws  5  at three asymmetric positions passing through the though hole  21 . At one side of the piezoelectric buzz piece  1  fixed to the first fixing plate  2  is fixed to a larger second fixing plate  3  by an elastomer  4  using a plurality of screws  5  passing through the though hole  31  so that between the first fixing plate  2  and second fixing plate  3  has an elastic resilient structure. The main electrode of the piezoelectric buzz piece  1  is connected to a lead  6 . In the present invention, the ultrasonic motor has a piezoelectric buzz piece excited externally. The voltage input portion has only an main electrode  11 . An AC power is inputted between the lead  6  of the main electrode  11  and the second fixing plate  3 . Namely, in using the second fixing plate  3  is held by hand or is fixed to a specific position. The piezoelectric buzz piece  1  is in contact with a rotor  7  so that the rotor  7  is driven to rotate.  
         [0026]    By the aforesaid structure, a piezoelectric buzz piece  1  is used as a medium for converting the electrical energy to mechanical energy so that the piezoelectric buzz piece  1  is inputted into an AC voltage. The piezoelectric ceramic will generate a pull or push action due to the reverse piezoelectric effect and a metal back plate is driven to vibrate. The generated mechanical waves transfer along radial or transverse paths. In transferring the wave, each screw  5  can be formed as a reflecting point. By the reflecting points from the peripheral three screws  5 , traveling waves of different directions can be formed by the piezoelectric buzz piece  1  at the outer edge. One of the traveling waves is used to provide a torque to drive the rotor  7  to rotate.  
         [0027]    The basic working principle of the traveling wave will be described in the following: At first, an external voltage is applied to the main electrode  11  of the piezoelectric buzz piece  1  so that the stator having a main body of piezoelectric ceramic via reverse piezoelectric effect to induce the vibration of the stator, and then the flexural wave is transferred in the stator. By the stick-sliding effect of the frictional force between the stator and rotor, the rotor  7  moves along the wave traveling path. The generation of the traveling wave is formed by a disk oscillation of a single frequency, and at a specific boundary condition, a multiple reflection is generated, the path difference of the reflecting wave will form the traveling wave.  
         [0028]    In the present invention, a finite element analysis (FEA) is used to analyze the working principle of the ultrasonic motor. When a periodic voltage as illustrated in FIG. 5 is inputted, the motor stator will have a periodic deformation. According to reverse piezoelectric effect, when the inputted voltage is at positive half period or negative half period. Then, the deformation orientation of the piezoelectric buzz piece  1  is respectively different. Therefore, in one period, as illustrated in FIG. 5, in position half period, four points (a), (b), (c) and (d) represents checking points for periodic deformation. When input voltage  20 V p-p = 2 V m , and has a frequency of 66.6 kHz. The periodic variation according to the amplitude of AC power is:  
         [0029]    (a)→(b)→(c)→(d)  
         [0030]    The deformation of the ultrasonic motor is illustrated in FIG. 6. The order of the stator deformation is:  
         [0031]    (a)→(b)→(c)→(d)  
         [0032]    (a) represents that the voltage is inputted initially (V=0+) and the piezoelectric stator is also deformed. (b) represents that the inputted voltage is enlarged gradually (V={fraction (1/2 )} V m ) and the piezoelectric stator deforms and enlarges; (c) An input voltage cause that the piezoelectric stator has a maximum deformation; (d) As the input voltage attains a maximum value, the deformation of the piezoelectric stator is reduced gradually (V=½ V m ). In the negative half period, the piezoelectric stator is shrunk. From the simulation drawing, as the motor stator is at 90 degrees, the R and θ directions will deform, the variation of the deformation will enlarge with the change of the voltage. When the rotor is placed as at a position of the motor&#39;s stator being 90 degrees, the stator will push the rotor to rotate counterclockwise. It is appreciated that at the 120 degrees, the deformation of the motor stator is toward the two screws. At the 150 degrees, the deformation of the motor stator is toward the middle portion of the two screws.  
         [0033]    When input voltage  20 V p-p = 2 V m , and has a frequency of 76 kHz. The periodic variation according to the amplitude of AC power is:  
         [0034]    (a)→(b)→(c)→(d)  
         [0035]    The deformation of the ultrasonic motor is illustrated in FIG. 7. The order of the stator deformation is:  
         [0036]    (a)→(b)→(c)→(d)  
         [0037]    From the simulation drawing, as the deformation of motor stator is at 90 degree region in the R and θ directions, the variation of the deformation will enlarge with the change of the voltage. When the rotor is placed as at a position of the motor stator being 90 degree region as the input frequency is 76 kHz, the stator will push the rotor to rotate clockwise. It is appreciated that, at the 120 and 150 degree region, the deformation of the motor stator is opposite to that as the frequency is 66.6 kHz. Comparing the cases of input frequencies of 66.6 kHz and 76 kHz, from the deformation vector figure of the stator simulation, the driving mechanism in clockwise and counterclockwise rotation is illustrated in FIG. 8.  
         [0038]    When the frequency is 66.6 kHz, the deformation in the driving section is along R and θ directions. The deformation is rearwards as illustrated in FIG. 8( a ). When the frequency is 76 kHz, the deformation is leftwards as illustrated in FIG. 8( b ). When the rotor is tightly against the driving point, as the frequency is 66.6 kHz, the rotor will be driven to rotate clockwise. When frequency is 76 kHz, the rotor will move counterclockwise. Comparing the simulation figures of finite element analysis about 66.6 kHz and 76 kHz, when frequency changes, other than the direction is reversed in the 90 region, the deformations of the 120 and 150 degree region are interchanged. In the edge-driving type ultrasonic motor, a mixed mode of 3-mode and 4-mode is used to get a maximum lateral pushing effect.  
         [0039]    From above analysis of the vibrating mode through finite element analysis, it is appreciated that the displacement of the ultrasonic motor in the present invention is determined according to the amplitude of the voltage of the sinusoidal wave applied to the stator piezoelectric ceramic and the rotational orientation is determined by the frequency of the sinusoidal voltage. To drive the ultrasonic motor effectively, the driving circuit is illustrated in FIG. 12, in this design, a voltage drop DC to DC  110  buck converter and a single phase half bridge serial resonance inverter (referring to FIG. 13). The duty cycle of the voltage drop DC to DC buck converter is adjusted by way that the output u of the controller of the personal computer is level-adjusted through an D/A conversion and thus a signal u p  is controlled by a PWM circuit. The primary function of this converter is to provide a DC voltage source to the half bridge serial resonance inverter which has a set positive and negative rotating driving frequencies as the driving frequencies and has a fixed voltage amplitude of VCO (1) and VCO (2). By selection of u p  signal, when the u p  is larger than zero (high), f1=(66.6 kHz) is selected, then the ultrasonic motor is rotated clockwise. As the u p  is equal to zero (low), f2=(76 kHz) is selected, the ultrasonic motor rotates counterclockwise.  
         [0040]    The mechanism of the edge-driving type ultrasonic motor is illustrated as FIG. 9. The diameter of the screw  91  is 2 mm. To assure the reflection of the wave of the metal back plate  92 , the screw  91  must be locked tightly. The preload spring  93  is designed conformed to the movable fulcrum  94 . To assure that the stator and rotor may contact anytime, a good insulation must be formed between the fixing aluminum plate  95  and the piezoelectric ceramic  96  so as to avoid the driving power line  97  will short as it is connected to the driving power source.  
         [0041]    As considering the precise in finishing and the balance of the motor rotor, the rotor of the existing small type step motor (used in 5.25″ floppy disk drive) is used as the rotor as illustrated in FIG. 10. The body of the rotor  101  is a permanent magneto and has a saw teeth structure  102  in the surface for increasing the friction between the stator and the rotor and increasing the torque. Two ends of the rotary shaft  104  have bearings  103  for supporting the decoder and carrying rotary disk at the position for measuring the motor rotor  101 . FIG. 11 shows the exploded view of the prototype of the edge-driving type ultrasonic motor and the test platform.  
         [0042]    The difference of the single phase driving power of the thin-disc piezoelectric actuating ultrasonic motor of the present invention with the conventional two phase type driving power is summarized in table 1, totally 10 items are listed.  
                                                                   Differences between a two phase ultrasonic       motor and single phase ultrasonic motor (USM)                    Two phase USM   Single phase USM       item   differences   (Convention)   (Invention)                    1   Input voltage   High frequency sinusoidal   Single phase, high               wave signal with phase   frequency sinusoidal               difference between two   wave signal               phase is 90 degrees       2   Elastic wave   Traveling wave   Standing wave       3   rotation   Determining according to   Determining from           direction of the   the phase shifting of the   the resonant           motors   two phase   frequency along                   rotation in                   clockwise and                   counterclockwise       4   amplitude   Determining according to   Determining               the driving frequency   according to the               assessing the resonant   inputted voltage               frequency   amplitude of the                   stator       5   construction   complex   Simple       6   Arrangement   The electrodes of two   No confinement           of the stator   phases are arranged           polarity   alternatively       7   Driving circuit   Complex   Simple       8   Size (weight,   Bulky   Compact           volume)       9   Band width   Wide   Narrow       10   Boundary   No   Exist           condition of           wave                  
 
         [0043]    The thin-disc piezoelectric actuating ultrasonic motor of the present invention has the following advantages as comparing with the prior art.  
         [0044]    1. In the thin-disc piezoelectric actuating ultrasonic motor of the present invention, a piezoelectric buzz piece is used to make a driver and an AC power is inputted into this piezoelectric buzz piece so that the piezoelectric ceramic generates a push force to drive the metal back plate to vibrate. The generated mechanical wave transfers along the radial and transverse directions. Traveling waves are formed at the outer edges of the piezoelectric buzz piece along different directions so as to provide a torque to drive the rotor to rotate.  
         [0045]    2. In the thin-disc piezoelectric actuating ultrasonic motor of the present invention, only a single phase driving power is used to complete the clockwise and counterclockwise rotation, while in the conventional ultrasonic motor, two phase driving power is used for generating traveling waves and high amplitude input pulse, these defects are improved by the present invention.  
         [0046]    3. The present invention can be used in semiconductor equipment, medical instruments, hard disk drives and optic disk drives. Furthermore, the cost of the present invention is low and the present invention has a preferred efficiency.  
         [0047]    The present invention are thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.