Abstract:
The present invention relates to a ring-type piezoelectric ultrasonic motor that is different from the electro-magnetically driven conventional motors and that has applications in robots and automation equipments. More specifically, the present invention relates to a ring-type piezoelectric ultrasonic motor that is driven by a frictional force between rotor and stator, and stator is produced a mechanical displacement by a piezoelectric ceramics applying an alternate electric field with an ultrasonic frequency (above 16 kHz).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a ring-type piezoelectric ultrasonic motor which is different from the Electro-magnetically driven conventional motors and that has applications in robotics, precise controlling xy stage for semiconductor fabrication and optics, and automation equipments. More specifically, the present invention relates to a ring-type piezoelectric ultrasonic motor that is driven by a frictional force between rotor and stator, and stator is produced a mechanical displacement by a piezoelectric ceramics applying an alternate electric field with an ultrasonic frequency (above 16 kHz).  
           [0002]    The driving methods generally known for piezoelectric ultrasonic motors are operating either through a half-wave batch converter or a quarter-wave batch or several quarter-wave batch converters for the operating shaft with a smaller cross section.  
           [0003]    As an efficient movement of the driving shaft, the energy from the longitudinal oscillation of the half-wave batch converter is converted to a rotational motion of rotor under the condition of S 1 /S 2 ≧5 (S 1 : cross section of the converter, S 2 : total cross section of the shaft) condition (UK Patent GB2023965 B Ultrasonic Oscillating System 1978).  
           [0004]    The basic principle of an ultrasonic drive is using a ring-type stator for bending vibration. On one face of the stator, piezoelectric ceramics that generate a mechanical vibration in order to allow their progression in the form of a wave, are attached and at the other face, protruding teeth that transmit an ellipsoidal phase change to the driving shaft on the pressure between the stator and the rotor are formed.  
           [0005]    Due to an increase in the height of the protruding teeth for a ring-type resonator (stator), the magnitude of bending vibration is magnified and partially the rotational force of the rotor increases.  
         SUMMARY OF THE INVENTION  
         [0006]    One object of the invention is to provide a ring-type piezoelectric ultrasonic motor which increases the rotational force by magnifying the magnitude of the vibration of concentrically protruding teeth attached to a ring type resonator.  
           [0007]    Another object is to provide a ring-type piezoelectric ultrasonic motor which magnifies the magnitude of the vibration of concentrically protruding teeth and the vibration speed of a ring-type resonator (a stator) that is in contact with a rotor, and which can effectively apply a compressive force between a stator and a rotor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 illustrates the essential elements the ring-type piezoelectric ultrasonic motor according to the present invention.  
         [0009]    [0009]FIG. 2 is a detailed diagram of the force affecting the protruding teeth and the rotor in FIG. 1.  
         [0010]    FIG. 3  illustrates a detailed structure of the protruding teeth.  
         [0011]    [0011]FIG. 4 is a detailed diagram of the protruding teeth and the rotor when a resonance occurs.  
         [0012]    [0012]FIG. 5 is a detailed diagram of the protruding teeth of quarter-wave batch converter when no resonance occurs.  
         [0013]    [0013]FIG. 6 is a cross section view of the ring-type piezoelectric ultrasonic motor according to the present invention.  
         [0014]    &lt;Description of the numeric on the main parts of the drawings&gt; 
         [0015]    [0015] 1 : Resonator(Stator)  
         [0016]    [0016] 2 : Piezoelectric Ceramics  
         [0017]    [0017] 3 : Rotor  
         [0018]    [0018] 4 : Frictional Material  
         [0019]    [0019] 5 : Protruding Teeth  
         [0020]    [0020] 6 : Driving Shaft  
         [0021]    [0021] 7 : Plate Spring  
         [0022]    [0022] 8 ,  14 : Gasket  
         [0023]    [0023] 9 : Bearing  
         [0024]    [0024] 10 : Supporting Bed  
         [0025]    [0025] 11 : Cover  
         [0026]    [0026] 12 : Holder  
         [0027]    [0027] 13 : Push Plate  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0028]    The protruding teeth ( 5 ) on one side of the ring-type resonator  1  perform as a resonator for a bending vibration and the number of the protruding teeth ( 5 ) is determined by Equation 1.  
         [0029]    [Equation 1] 
         M≦5Σ mi  
         [0030]    In this case, M is the weight of the ring-type resonator (stator) ( 1 ) and Σ mi is the total weight of the protruding teeth ( 5 ).  
         [0031]    The speed of revolution can be increased by using the vibration frequency relating to the bending vibration of the ring-type resonator ( 1 ).  
         [0032]    The weight of ring-type resonator ( 1 ) and the protruding teeth ( 5 ) are determined by Equation 1. At this time, the damping of the vibration can be prevented by the required pressure P and the work capability of the whole vibration system can be improved by securing a reliable operation of the ultrasonic motor.  
         [0033]    The protruding teeth ( 5 ) plays a role of a quarter-wave batch converter for a bending vibration and the number for the protruding teeth ( 5 ) should be such that the weight of the half-wave batch converter part is no less than 5 times the total weight of the protruding teeth ( 5 ).  
         [0034]    At this instance, A=λ/ 2  in FIG. 3, where λ is the bending vibration frequency of the ring-type resonator ( 1 ).  
         [0035]    The resonant condition of the protruding teeth ( 5 ) can be represented by Equation 2.  
         [0036]    [Equation 2] 
         [0037]    f=[r·c/2π·l2]k2  
         [0038]    In this case, r is the radius of driving shaft, c is the speed of sound, k is the form of the vibration and l is the length of driving shaft. The piezoelectric ultrasonic motor that satisfies the above conditions has the following configuration.  
         [0039]    A thin ring-type piezoelectric ceramic ( 2 ) that generates an elastic traveling wave is attached to the bottom of the stator ( 1 ) and protruding teeth ( 5 ) is formed on the top of the stator ( 1 ). The rotor ( 3 ) on which the thin ring-type frictional material ( 4 ) is attached is put on the protruding teeth ( 5 ) is formed on the top of the stator ( 3 ). Along the same axle of the stator ( 1 ) and the rotor ( 3 ), the shaft ( 6 ) is inserted through the bearing ( 9 ). The bearing ( 9 ) is firmly supported by a cover ( 11 ) and a supporting bed ( 10 ) .  
         [0040]    If the present invention is described in more detail, the motor for a ultrasonic drive has a ring-type resonator ( 1 ) and a thin layer of ring-type piezoelectric ceramics ( 2 ) are attached to bottom of the ring-type resonator ( 1 ).  
         [0041]    According to this invention the above means for attachment is either through a soldering at 80-100° C. or a hard-purpose epoxy at 90-110° C.  
         [0042]    The piezoelectric ceramics ( 2 ) play a role of generating an elastic traveling wave and the rotor ( 3 ) under a compressive contact with the protruding teeth ( 5 ) is covered with a thin layer of frictional material ( 4 ) by the pressure P.  
         [0043]    Protruding teeth ( 5 ) are formed on the upper face of the ring-type resonator ( 1 ). In order to accommodate a free rotation of the bearing ( 9 ), the ring-type resonator ( 1 ) and the rotor ( 3 ) is located on the same shaft. The bearing ( 9 ) is firmly supported by a cover ( 11 ) and a supporting bed ( 10 ) and plays a role of transmitting rotational force to the driving shaft ( 6 ).  
         [0044]    The plate spring ( 7 ) on the upper section of the rotor ( 3 ) is in contact with the gasket ( 8 ) and exerts a force with a fixed magnitude.  
         [0045]    Also, the proper pressure between the rotor ( 3 ) and the ring-type resonator ( 1 ) should be appropriately controlled and a metal gasket ( 14 ) is inserted for this purpose between the pushing plate ( 13 ) that pushes the upper section of the bearing ( 9 ) and the upper case ( 11 ).  
         [0046]    In order to prevent the occurrence of mechanical noises and vibrations between the ring-type resonator ( 1 ) and the rotor ( 3 ), it is preferable to insert a rubber gasket ( 8 ) and the gasket acts as an acoustic insulator.  
         [0047]    The operation of the resonator ( 1 ) with the configuration as described previously is in FIG. 1. The operation of that is to convert the pure mechanical vibration from the piezoelectric ceramic ( 2 ) into an elliptical mechanical vibration by two different phases of the piezoelectric ceramics ( 2 ).  
         [0048]    The protruding teeth ( 5 ) that have the distribution of bending wave act as a bracing strut for the driving of the rotor ( 3 ) and their upper face is in contact with the rotor ( 3 ) in order to rotate. As shown in FIG. 4, during resonance the technical solution for the protruding teeth ( 5 ) is to act as a resonator that generates a bending vibration corresponding to the resonance frequency. During the no resonance, the protruding teeth are bent over a distance above “a” as shown in FIG. 5 in order to move the protruding teeth away from the resonance point.  
         [0049]    When the bent protruding teeth ( 5 ) makes a contact with the rotor ( 3 ), the magnitude of the vibration on the upper section of the protruding teeth ( 5 ) increases and consequently brings about a mechanical change in the rotor ( 3 ) due to mutual reactions of the friction between the upper part of the protruding teeth ( 5 ) and the rotor ( 3 ). Using the distance “a” in FIG. 4 and FIG. 5 can increase the rotating speed.  
         [0050]    According to the condition of the equation of M≦5Σ mi about the half-wave resonator, the needed pressure P and the mass of successive ring-type area of the ring-type resonator ( 1 ) except the protruding teeth ( 5 ), the damping of vibration doesn&#39;t happen and guarantees a reliable operation of ultrasonic motor  
         [0051]    As stated above, the ultrasonic driving according to this invention is capable of increasing the rotational force of the rotor ( 3 ) without altering the variables of the motor, resulting in an overall improvement of the whole vibration system and a reduction in the power consumption.  
         [0052]    The ultrasonic motor proposed according to the present invention has the advantages of being small, light, noise-free, and low on power consumption, low speed and high torque.  
         [0053]    These characteristics can compensate for the shortcomings of the conventional motors as well as having a wide application area such as semiconductor fabrication equipments, precise control driver for optical equipments, robot joint driving motors, motor driven blinders and motor driven curtains, weapon driving system