Patent Publication Number: US-2007108869-A1

Title: Driving and control apparatus of piezoelectric ultrasonic motor

Description:
RELATED APPLICATION  
      The present application is based on, and claims priority from, Korean Application Number 2005-106147, filed Nov. 07, 2005, the disclosure of which is hereby incorporated by reference herein in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a driving and control apparatus of a piezoelectric ultrasonic motor, and more particularly, to a driving and control apparatus of a piezoelectric ultrasonic apparatus, which supplies the driving voltage through one of the two electrodes of the piezoelectric ultrasonic motor generating the elliptical vibration, detects the voltage through the other electrode, and making the phase difference between the driving voltage and the detection voltage be zero in a phase locked loop (PLL) scheme, thereby achieving the operation more efficiently.  
      2. Description of the Related Art  
      Generally, a piezoelectric device generates a strain or voltage when an electric field or a stress is applied thereto. A piezoelectric stator using the piezoelectric device is driven at a resonance frequency ranging from several tens of kHz to several hundreds of kHz and can provide a rotor with a strain amplified by a stack or strain expansion structure. Such a piezoelectric stator may use itself as a vibrator, or may be used in combination with a structure with a specific shape.  
      A piezoelectric ultrasonic motor using the piezoelectric device is called a traveling wave, surface wave, or surfing type motor. The piezoelectric ultrasonic motor is driven by a principle of superposing two driving waves with a predetermined phase difference.  
       FIG. 1  is a block diagram illustrating a conventional driving and control apparatus of a piezoelectric ultrasonic motor.  
      Referring to  FIG. 1 , the conventional driving and control apparatus includes a frequency/phase controller  10 , a high-speed inverter  20 , a pulse encoder  40 , a current-voltage phase difference detector  50 , and a microcontroller  60 . The frequency/phase controller  10  receives frequency and phase information to generate square waves with respect to two phases. The high-speed inverter  20  converts the square waves into AC voltages with respect to the two phases and provides the AC voltages to an ultrasonic motor  30 . The pulse encoder  40  accesses and encodes information about the frequency and phase applied to the ultrasonic motor  30 . The current-voltage phase difference detector  50  detects a phase difference between a voltage VA and a current IA applied to the ultrasonic motor  30  and outputs the detected phase difference in a form of an impedance phase angle. The microcontroller  60  receives the impedance phase angle from the current-voltage phase difference detector  50  to output the frequency and phase information for making the ultrasonic motor  30  follow the resonance frequency of the ultrasonic motor  30 .  
      The driving and control apparatus of the piezoelectric ultrasonic motor is disclosed in Korean Laid-Open Patent Publication No. 2002-0055465.  
      However, the conventional driving and control apparatus has to generate two driving waves in order to drive the piezoelectric ultrasonic motor, and also requires a current detector and/or a voltage detector in order to detect the current and the voltage. Thus, the conventional driving and control apparatus has a problem in that its structure is complicated and its manufacturing cost increases.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to a driving and control apparatus of a piezoelectric ultrasonic motor that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
      An object of the present invention is to provide a driving and control apparatus of the piezoelectric ultrasonic motor, which supplies the driving voltage through one of the two electrodes of the piezoelectric ultrasonic motor generating the elliptical vibration, detects the voltage through the other electrode, and making the phase difference between the driving voltage and the detection voltage be zero in a phase locked loop (PLL) scheme, thereby achieving the operation more efficiently.  
      Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
      To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a driving and control apparatus of a piezoelectric ultrasonic motor, which has a first electrode and a second electrode and generates an elliptical vibration according to a driving voltage applied through the first and second electrodes. The driving and control apparatus includes: a controller for controlling a selection of the first channel or the second channel as a driving channel, the first channel and the second channel being connected to the first electrode and the second electrode, respectively; a switch part for selecting one of the first and second channels as the driving channel and the other as a detection channel according to the channel selection control of the controller, and supplying the driving voltage to the piezoelectric ultrasonic motor through the selected driving channel; a phase detector for detecting a voltage outputted from the piezoelectric ultrasonic motor through the detection channel, calculating a phase deviation representing that a phase difference between an oscillation voltage having two times the frequency of the driving voltage and the detection voltage is out of 90°, and outputting a phase difference voltage corresponding to the phase deviation; a voltage controlled oscillator for generating the oscillation voltage and controlling a phase of the oscillation voltage according to the phase difference voltage outputted from the phase detector; and a frequency divider for dividing the oscillation voltage from the voltage controlled oscillator by two to generate the driving voltage, and supplying the divided oscillation voltage to the piezoelectric ultrasonic motor through the driving channel.  
      The driving and control apparatus may further include a low pass filter for removing power noise and AC component contained in the phase difference voltage outputted from the phase detector.  
      The switch part may include: a first switch for connecting an output terminal of the voltage controlled oscillator to the first channel connected to the first electrode of the piezoelectric ultrasonic motor according to the channel selection control of the controller; and a second switch for connecting the output terminal of the voltage controlled oscillator to the second channel connected to the second electrode of the piezoelectric ultrasonic motor.  
      The phase detector may include: a first AND gate for ANDing the driving voltage and the detection voltage; a second AND gate for ANDing an output signal of the first AND gate and the oscillation voltage to detect a phase difference between the driving voltage and the detection voltage; and a phase difference voltage generating unit for calculating the phase deviation, in which the phase difference is out of 90° by the second AND gate, and outputting the phase difference voltage corresponding to the phase deviation.  
      It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
       FIG. 1  is a block diagram illustrating a conventional driving and control apparatus of a piezoelectric ultrasonic motor;  
       FIG. 2  is a block diagram illustrating a driving and control apparatus of a piezoelectric ultrasonic motor according to an embodiment of the present invention;  
       FIGS. 3A and 3B  are block diagrams illustrating switching operations of the driving and control apparatus of  FIG. 2 ;  
       FIGS. 4A  to  4 D are diagrams of the piezoelectric ultrasonic motor of  FIG. 2 ;  
       FIGS. 5A and 5B  are diagrams illustrating an elliptical vibration of the piezoelectric ultrasonic motor of  FIG. 2 ;  
       FIG. 6  is a graph illustrating a vibration mode of the piezoelectric ultrasonic motor of  FIG. 2 ;  
       FIG. 7  is a diagram of a phase detector of  FIG. 2 ;  
       FIGS. 8A and 8B  are timing diagrams illustrating an operation of the phase detector of  FIG. 7 ; and  
      FIGS.  9 ( a ) and  9 ( b ) are graphs illustrating a gain and a phase difference of the piezoelectric ultrasonic motor of  FIG. 2 , respectively. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The same reference numerals are used to refer to the same elements throughout the drawings.  
       FIG. 2  is a block diagram illustrating a driving and control apparatus of a piezoelectric ultrasonic motor according to an embodiment of the present invention.  
      Referring to  FIG. 2 , the driving and control apparatus according to an embodiment of the present invention drives a piezoelectric ultrasonic motor  100  that has a first electrode  110  (shown in  FIG. 4   a ) and a second electrode  120 (shown in  FIG. 4   a ) and generates an elliptical vibration by overlapping a length-direction vibration and a curve-direction vibration according to a driving voltage (Vdrv) applied to the first electrode  110  and the second electrode  120 . The driving and control apparatus includes a controller  200 , a switch part  300 , a phase director  400 , a voltage controlled oscillator (VCO)  600 , and a frequency divider  700 .  
      A first channel CH 1  and a second channel CH 2  are connected to the first electrode  110  and the second electrode  120  of the piezoelectric ultrasonic motor  100 , respectively. The controller  200  controls the switch part  300  to select one of the first and second channels CH 1  and CH 2  as a driving channel.  
      The switch part  300  selects one of the first and second channels CH 1  and CH 2  as the driving channel and the other as a detection channel according to the channel selection control of the controller  200 . The driving voltage (Vdrv) is supplied to the piezoelectric ultrasonic motor  100  through the selected driving channel.  
      The phase detector  400  detects a voltage supplied from the piezoelectric ultrasonic motor  100  through the detection channel. Then, the phase detector  400  calculates a phase deviation (Δφ) representing that a phase difference (dφ) between an oscillation voltage (Vosc) having two times the frequency of the driving voltage and the detection voltage (Vdet) is out of 90°, and outputs a phase difference voltage corresponding to the phase deviation (Δφ).  
      The VCO  600  generates the oscillation voltage (Vosc) and controls the phase of the oscillation voltage (Vosc) according to the phase difference voltage outputted from the phase detector  400 .  
      The frequency divider  700  divides the oscillation voltage (Vosc, F=2a) from the VCO  600  by two to generate the driving voltage (Vdrv, F=a). The driving voltage (Vdrv) is supplied to the piezoelectric ultrasonic motor  100  through the driving channel selected by the switch part  300 .  
      In order to supply a DC voltage in which power noise or AC component is removed, the driving and control apparatus may further include a low pass filter (LPF)  500  for removing the power noise or AC component contained in the phase difference voltage outputted from the phase detector  400 .  
      In addition, the switch part  300  includes a first switch SW 1  and a second switch SW 2 . According to the channel selection control of the controller  200 , the first switch SW 1  connects the output terminal of the VCO  600  to the first channel CH 1 , which is connected to the first electrode of the piezoelectric ultrasonic motor  100 , and the second switch SW 2  connects the output terminal of the VCO  600  to the second channel CH 2 , which is connected to the second electrode of the piezoelectric ultrasonic motor  100 .  
      An operation of the driving and control apparatus according to the present invention will be described below in detail. First, the controller  200  selects one of the first channel CH 1  and the second channel CH 2 , which are respectively connected to the first electrode  110  and the second electrode  120  of the piezoelectric ultrasonic motor  100 , as the driving channel according to the user&#39;s selection. As illustrated in  FIGS. 3A  or  3 B, the switch part  300  operates to select the first channel CH 1  or the second channel CH 2  according to the channel selection control of the controller  200 . The other channel that is not selected as the driving channel serves as the detection channel.  
       FIGS. 3A and 3B  are block diagrams illustrating the switching operations of the driving and control apparatus of  FIG. 2 . Referring to  FIG. 3A , when the first switch SW 1  is off and the second switch SW 2  is on according to the channel selection control of the controller  200 , the first channel CH 1  is selected as the driving channel and the driving voltage (Vdrv) is supplied through the first channel CH 1  to the first electrode  110  of the piezoelectric ultrasonic motor  100 .  
      Referring to  FIG. 3B , when the first switch SW 1  is on and the second switch SW 2  is off according to the channel selection control of the controller  200 , the second channel CH 2  is selected as the driving channel and the driving voltage (Vdrv) is supplied through the second channel CH 2  to the second electrode  120  of the piezoelectric ultrasonic motor  100 .  
      In this manner, when the driving voltage (Vdrv) is supplied to the piezoelectric ultrasonic motor  100 , the piezoelectric ultrasonic motor  100  generates the elliptical vibration. The piezoelectric ultrasonic motor  100  will be described below in more detail with reference to  FIGS. 4A  to  4 D.  
       FIGS. 4A  to  4 D are diagrams of the piezoelectric ultrasonic motor of  FIG. 2 .  
      Referring to  FIGS. 4A  to  4 D, the piezoelectric ultrasonic motor  100  includes the first electrode  110  and the second electrode  120  and causes the length-direction vibration and the curve-direction vibration according to the driving signal applied through the electrodes  110 ,  111  and  112  and the electrodes  120 ,  121  and  122 , thereby generating the elliptical vibration.  
      For example, as illustrated in  FIG. 4A , the piezoelectric ultrasonic motor  100  includes a first ceramic sheet LY 1 , a middle ceramic sheet LY 2 , and a second ceramic sheet LY 3 . The first ceramic sheet LY 1  has the first upper electrode  111  and the second upper electrode  121  separated from each other on its top surface. The middle ceramic sheet LY 2  is disposed under the first ceramic sheet LY 1  and has a ground electrode  130  on its top surface. The second ceramic sheet LY 3  is disposed under the middle ceramic sheet LY 2  and has the first lower electrode  112  and the second lower electrode  122  on its top surface and a ground electrode  130  on its bottom surface. The electrodes  110 ,  111  and  112  and the electrodes  120 ,  121  and  122  are extended up to the outside of the ceramic sheets LY 1 , LY 2  and LY 3  in a predetermined direction.  
      The ceramic sheets LY 1 , LY 2  and LY 3  are vertically stacked, as illustrated in  FIG. 4B .  
      Polarization directions (arrow directions) of the ceramic sheets LY 1 , LY 2  and LY 3  are alternated in order to simultaneously vibrate the left side of the first ceramic sheet LY 1  and the right side of the second ceramic sheet LY 3 , and the right side of the first ceramic sheet LY 1  and the right side of the second ceramic sheet LY 3 .  
       FIG. 4C  is a perspective view of the piezoelectric ultrasonic motor where external electrodes are formed in the stacked ceramic sheet structure. A first external electrode CCH 1  is formed on a first side of the stacked ceramic sheet structure to connect the first upper electrode  111  to the second lower electrode  112 , and a second external electrode CCH 2  is formed on a second side of the stacked ceramic sheet structure to connect the second upper electrode  121  to the second lower electrode  122 . In addition, a third external electrode CG is formed on a third side of the stacked ceramic sheet structure to connect the ground electrodes  130 , which are formed on the top surface of the middle ceramic sheet LY 2  and the bottom surface of the second ceramic sheet LY 3 .  
      Since the driving signal is simultaneously applied through the external electrodes CCH 1 , CCH 2  and CG to the electrodes disposed diagonally, the ceramic sheets disposed diagonally can be vibrated. This vibration is transferred to the outside through a driving tip  140  formed one side of the stacked ceramic sheet structure.  
       FIG. 4D  illustrates a modification of the piezoelectric ultrasonic motors  100  of  FIGS. 4A  to  4 C.  
      In the piezoelectric ultrasonic motor  100 ′ of  FIG. 4D , first ceramic sheets LY 1  and middle ceramic sheets LY 2  are alternately stacked to form an upper vibration region. Here, each of the first ceramic sheets LY 1  has a first upper electrode  111  and a second upper electrode  121  separated from each other on its top surface, and each of the middle ceramic sheets LY 2  is disposed under each of the first ceramic sheets and has a ground electrode  130  on its top surface.  
      In addition, second ceramic sheets LY 3  and middle ceramic sheets LY 2  are alternately stacked under the above-described stacked structure to form a lower vibration region. Here, each of the second ceramic sheets LY 3  has a first lower electrode  112  and a second lower electrode  122  on its top surface, and each of the middle ceramic sheet LY 2  is disposed under each of the second ceramic sheets LY 3  and has a ground voltage  130  on its top surface. Meanwhile, a ground electrode  130  is formed on the bottom surface of the second ceramic sheet disposed at the lowermost position.  
      Polarization directions of the stacked ceramic sheets LY 1 , LY 2  and LY 3  are alternated as illustrated in  FIG. 4B . Also, the first electrode  110 , the external electrodes CCH 1 ,CCH 2  AND CG 1  for connecting the second electrode  120 , and the ground electrodes  130  are formed as illustrated in  FIG. 4C .  
      Through the external electrodes, the portions located at the diagonal positions of the upper vibration region and the lower vibration region can be simultaneously vibrated.  
      In order to generate the vibration in the portions located at the diagonal positions, it is preferable that the number of the ceramic sheets stacked to form the upper vibration region is identical to the number of the ceramic sheets stacked to form the lower vibration region, but the present invention is not limited thereto.  
      Meanwhile, electrode protection sheets (not shown) covering the electrodes may be further stacked in order to protect the electrodes formed on the stacked ceramic sheets of  FIG. 4D .  
      In  FIG. 4 , the piezoelectric ultrasonic motor  100 ′ has the vibration regions located in the diagonal lines among the four vibration regions, that is, the up/down/right/left vibration regions in the vertically stacked ceramic sheets.  
      However, the piezoelectric ultrasonic motor  100 ′ used in the driving and control apparatus according to the present invention simultaneously generates the length-direction vibration of  FIG. 5 ( a ) and the curve-direction vibration of  FIG. 5 ( b ) by the driving signals applied through the first and second electrodes. Therefore, the present invention can be applied to any piezoelectric ultrasonic motors if they generate the elliptical vibration. The piezoelectric ultrasonic motor can have various shapes and structures.  
      The vibrations at the first and second channels when the piezoelectric ultrasonic motor generates the elliptical vibration are illustrated in  FIG. 6 .  
       FIG. 6  is a graph illustrating a vibration mode of the piezoelectric ultrasonic motor of  FIG. 2 .  
      It can be seen from  FIG. 6  that an admittance is highest when a “CH 1 ” graph and a “CH 2 ” graph have a phase difference of 90°. The admittance is an index representing how well the signal flows. That is, it can be seen that the vibration efficiency is high when the piezoelectric ultrasonic motor has the phase difference of 90°.  
      Referring again to  FIG. 2 , the phase detector  400  detects the voltage outputted from the piezoelectric ultrasonic motor  100  through the detection channel, calculates the phase deviation (Δφ) representing that a phase difference (dφ) between an oscillation voltage (Vosc) having two times the frequency of the driving voltage and the detection voltage (Vdet) is out of 90°, and outputs a phase difference voltage corresponding to the phase deviation (Δφ).  
      The VCO  600  generates the oscillation voltage (Vosc) having the preset frequency (F=2a) and controls the phase of the driving voltage (Vdrv) according to the phase difference voltage outputted from the phase detector  400 .  
      The frequency divider  700  divides the oscillation voltage (Vosc) outputted from the VCO  600  by two to generate the driving voltage (Vdrv). The driving voltage (Vdrv) is supplied to the piezoelectric ultrasonic motor  100  through the driving channel selected by the switch part  300 .  
      The driving and control apparatus including the LPF  500  can remove the power noise or AC component contained in the phase difference voltage, thereby providing the clearer phase difference voltage.  
       FIG. 7  is a diagram of the phase detector of  FIG. 2 .  
      Referring to  FIG. 7 , the phase detector  400  includes a first AND gate  410  for ANDing the driving voltage (Vdrv, F=2a) and the detection voltage (Vdet), a second AND gate  420  for ANDing an output signal of the first AND gate  410  and the oscillation voltage (Vosc, F=2a) to detect the phase difference (Δφ) between the driving voltage (Vdrv) and the detection voltage (Vdet), and a phase difference voltage generating unit  430  for calculating the phase deviation (Δφ) in which the phase difference (dφ) is out of 90° by the second AND gate  420  and outputting the phase difference voltage corresponding to the phase deviation (Δφ).  
       FIGS. 8A and 8B  are timing diagrams illustrating an operation of the phase detector of  FIG. 7 . An operation of the phase detector will be described below reference to  FIGS. 7 and 8 .  
      Referring to  FIGS. 7 and 8 A, when the first channel CH 1  is selected as the driving channel, the first AND gate  410  performs the logic AND operation on the driving voltage (Vdrv) and the detection voltage (Vdet). The second AND gate  420  performs the logic AND operation on the output signal A of the first AND gate  410  and the oscillation voltage (Vosc) to detect the phase difference (dφ) between the driving voltage (Vdrv) and the detection voltage (Vdet), and outputs the detected phase difference (dφ) C to the phase difference voltage generating unit  430 . The phase difference voltage generating unit  430  calculates the phase deviation (Δφ) and outputs the phase difference voltage to the LPF  500 .  
      When the phase difference (dφ=dφ1−dφ2) is less than 90°, that is, when the phase deviation (Δφ=dφ−90°) is negative, the phase difference signal (dφ) C outputted from the second AND gate  420  has no pulse, as illustrated in  FIG. 8A . Therefore, the phase difference voltage generating unit  430  recognizes that there is no phase deviation. In this case, the VCO  600  has to decrease the frequency.  
      On the other hand, when the phase difference (dφ=dφ1−dφ2) is greater than 90°, that is, when the phase deviation (Δφ=dφ−90°) is positive, the phase difference signal (dφ) C outputted from the second AND gate  420  has a predetermined pulse, as illustrated in  FIG. 8B . Then, the generation of the phase deviation is notified to the phase difference voltage generating unit  430 . At this point, the phase difference voltage generating unit  430  generates the phase difference voltage according to the predetermined pulse. In this case, the VCO  600  has to increase the frequency.  
      FIGS.  9 ( a ) and  9 ( b ) are graphs illustrating a gain and a phase difference of the piezoelectric ultrasonic motor of  FIG. 2 , respectively.  
      Specifically,  FIG. 9 ( a ) is a graph illustrating the gain of the piezoelectric ultrasonic motor. When the second channel CH 2  is selected as the driving channel, the gain (V 1 /V 2 ) of the piezoelectric ultrasonic motor  100  is given by the “G 1 ” graph. The gain (V 1 /V 2 ) of the piezoelectric ultrasonic motor  100  means the ratio of the output voltage (V 1 ) to the input voltage (V 2 ).  
      When the first channel CH 1  is selected as the driving channel, the gain (V 2 /V 1 ) of the piezoelectric ultrasonic motor  100  is given by the “G 2 ” graph. The gain (V 2 /V 1 ) of the piezoelectric ultrasonic motor  100  means the ratio of the output voltage (V 2 ) to the input voltage (V 1 ).  
       FIG. 9 ( b ) is a graph illustrating the phase difference of the piezoelectric ultrasonic motor. When the second channel CH 2  is selected as the driving channel, the phase difference (φ1−φ2) between the input voltage (V 2 ) and the output voltage (V 1 ) is almost 90°. When the first channel CH 1  is selected as the driving channel, the phase difference (φ2−φ1) between the input voltage (V 1 ) and the output voltage (V 2 ) is almost 90°.  
      As described above, the driving and control apparatus of the piezoelectric ultrasonic motor supplies the driving voltage through one of the two electrodes of the piezoelectric ultrasonic motor generating the elliptical vibration, detects the voltage through the other electrode, and making the phase difference between the driving voltage and the detection voltage be zero in a phase locked loop (PLL) scheme, thereby achieving the operation more efficiently. Since the driving and control apparatus is implemented more simply, its manufacturing cost can be reduced.  
      It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.