Abstract:
A driving apparatus is provided for a vibration type motor which obtains a driving force by applying a periodic signal to an electro-mechanical energy conversion element portion of the vibration type motor. When the driven amount of the vibration type motor is small, the vibration type motor is driven by a high voltage in a frequency range with a high lower limit as compared with a case wherein the driven amount is not small, thereby making it possible to realize high-speed focusing and suppress electric power consumption.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical apparatus and vibration type motor driving control method and, more particularly, to an optical apparatus made up of a lens incorporating a vibration type motor for focus adjustment and an apparatus body in which the lens is mounted and which supplies power to the vibration type motor and provides focus detection information, and a vibration type motor driving control method applied to the optical apparatus. 
     The above optical apparatus is, for example, a single-lens reflex camera having a vibration type motor incorporated in an exchangeable lens. 
     2. Related Background Art 
     Of conventional cameras using silver halide films, a single-lens reflex camera, in particular, is capable of exchanging lenses. As such exchangeable lenses, lenses with various focal lengths have been manufactured. 
     As such an exchangeable lens, an automatic focus control lens is available, which can automatically adjust the focus by driving the focus lens using a built-in motor. This motor is driven on the basis of focus detection information generated by the camera body. As this motor, a DC motor has been used. Recently, however, a vibration type motor has been widely used in place of the DC motor. 
     This vibration type motor can maintain high torque up to the range of small numbers of rotations, and hence requires no reduction gear. This motor has many advantages. For example, a reduction in size can be attained, and noise can be suppressed. 
     In the vibration type motor, a driving voltage generated on the basis of a plurality of periodic signals having different phases is applied to a built-in electromechanical energy conversion element to generate travelling waves, thereby rotating a rotating member. The vibration type motor is accelerated by sweeping the frequency (driving frequency) of a periodic signal from a frequency higher than the resonant frequency of the motor to the resonant frequency. 
     Recently, in a super-telephoto lens having a focal length of 300 mm or more, in particular, a strong demand has arisen for an increase in the driving speed of a focus adjustment motor. This is because such a super-telephoto lens is often used to shoot sports activity such as track-and-field events, and focus control that can faithfully follow quick movements of athletes is strongly demanded. 
     For driving the vibration type motor at high speed, there is a method in which the sweeping speed of the driving frequency is simply increased. In this method, however, the characteristics of the vibration type motor cannot follow the sweeping speed of the driving frequency, resulting in awkward movements. 
     In another method, the driving voltage applied to the vibration type motor is raised. FIGS. 1A and 1B are graphs respectively showing the electric power consumption (P) of the vibration type motor and the number of rotations (N) when the driving voltage applied the vibration type motor is doubled, with the ordinate representing a driving frequency f. 
     Referring to FIGS. 1A and 1B, curves Nx and Px respectively represent the number of rotations and electric power consumption at a general driving voltage value, whereas curves Ny and Py respectively represent the number of rotations and electric power consumption at a voltage twice as high as the general driving voltage. 
     As is obvious from FIG. 1B showing the numbers of rotations, when the driving voltage is doubled, the number of rotation almost doubles at the same driving frequency. 
     As is obvious from FIG. 1A, however, when the driving voltage is doubled, the power consumption of the vibration type motor almost doubles as well. 
     In a single-lens reflex camera, since power is supplied from a battery in the camera body to the exchangeable lens (no battery is installed in the exchangeable lens), the power that can be used by the exchangeable lens itself is limited accordingly. 
     As shown in FIGS. 1A and 1B, when the driving voltage to the vibration type motor is raised, and the driving frequency is decreased to f 1  to increase the number of rotations of the vibration type motor to N 3 , the power consumption increases to P 3 . As a result, the voltage of the battery on the camera body side drops. This may cause operation errors in various actuators on the camera body side, resulting in an operation error in the camera. 
     As described above, if the driving voltage to the vibration type motor is simply raised to increase the number of rotations so as to drive the vibration type motor at high speed, a serious problem arises in the camera system. 
     SUMMARY OF THE INVENTION 
     According to one aspect of this invention, there is provided a driving apparatus for a vibration type motor which obtains a driving force by applying a periodic signal to an electro-mechanical energy conversion element portion, comprising a setting circuit (e.g., a microcomputer) for setting a driven amount of the vibration type motor, and a power supply circuit for supplying electric power to the driving circuit, wherein when the driven amount set by the setting circuit is smaller than a predetermined amount, the power supply circuit applies to the driving circuit a voltage higher than a voltage to be set when the driven amount is not less than the predetermined value. 
     According to one aspect of this invention, a vibration type motor driving control method is applied to a driving apparatus including a vibration type motor which obtains a driving force by applying a periodic signal to an electro-mechanical energy conversion element portion, a driving circuit for applying a periodic signal to the vibration type motor, and a power supply circuit for supplying electric power to the driving circuit, where the method comprises the setting step of setting a driven amount of the lens, and the power supply voltage selection step of, when the driven amount set in the setting step is smaller than a predetermined value, applying to the driving circuit a voltage higher than a voltage to be set when the driven amount is less than the predetermined value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are graphs respectively showing electric power consumption (P) of the vibration type motor and the number of rotations (N) when the driving voltage applied to the vibration type motor is doubled, with the ordinate representing a driving frequency f; 
     FIG. 2 is a circuit diagram showing the arrangement of a control circuit arranged in a camera body and exchangeable lens according to the first embodiment of the present invention; 
     FIG. 3 is a flow chart showing the operation of the control circuit; and 
     FIG. 4 is a circuit diagram showing the arrangement of a control circuit arranged in an exchangeable lens according to the second embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will be described below with reference to the accompanying drawings. 
     (First Embodiment) 
     FIG. 2 is a circuit diagram showing the arrangement of a control circuit arranged in a camera body and exchangeable lens according to the first embodiment of the present invention. 
     Referring to FIG. 2, this arrangement includes a power supply battery  10  housed in the camera body, a microcomputer  9  on the camera body side, a switch  21  that is turned on when the shutter button (two-stroke button) is pressed to the first-stroke position, and a transistor  8  for power supply which is controlled by the microcomputer  9 . 
     A microcomputer  11  controls the overall circuit on the exchangeable lens side. 
     The camera body has terminals a to f. The terminal a is the positive terminal of the battery  10 ; the terminal b, a power supply terminal; the terminal c, a terminal for transferring data from the microcomputer  9  of the camera body to the microcomputer  11  of the exchangeable lens; the terminal d, a terminal for transferring data from the microcomputer  11  of the exchangeable lens to the microcomputer  9  of the camera body; the terminal e, a terminal for transferring a sync clock for data transfer; and the terminal f, the negative terminal of the battery  10 . 
     Terminals a′ to f′ are those on the exchangeable lens side which correspond to the terminals a to f. When the exchangeable lens is mounted in the camera body, the corresponding terminals are connected to each other. 
     A control circuit  12  controls a DC/DC converter. The control circuit  12  is controlled by I/O data from the microcomputer  11 . 
     The DC/DC converter is a boosting circuit and comprised of a coil  13 , switching FET  14 , feedback resistor  15 , diode  16  for preventing current backflow, rectifying capacitor  17 , and voltage-dividing resistors  18 ,  19 , and  20 . 
     The gate of the FET  14  is controlled by the control circuit  12 . The node between the FET  14  and the feedback resistor  15  is connected to the control circuit  12  to constitute a so-called current feedback type DC/DC converter. The diode  16  serves as a diode for preventing the backflow of a current from the rectifying capacitor  17  to the battery  10 . 
     An output voltage Vout from the DC/DC converter is sent to a driving circuit  24  (to be described later) and divided by the voltage-dividing resistors  18 ,  19 , and  20  to be fed back from the node (point x) between the voltage-dividing resistors  18  and  19  or the node (point y) between the voltage-dividing resistors  19  and  20  to the control circuit  12 . The control circuit  12  selects the voltage at the point x or the voltage at the point y in accordance with a command from the microcomputer  11 , and controls the output voltage Vout from the DC/DC converter in accordance with the selected voltage. 
     A D/A converter  22  converts digital data output from the output port of the microcomputer  11  and indicating a driving frequency into an analog voltage. A VCO (voltage/frequency converter)  23  is connected to this D/A converter and generates a rectangular wave having a frequency corresponding to the input analog voltage. 
     The driving circuit  24  drives the vibration type motor and uses the output voltage Vout from the DC/DC converter as power. The output terminal of the VCO  23  and the output port of the microcomputer  11  are connected to the driving circuit  24 . A vibration type motor  25  is driven by driving voltages having phases A and B with a phase difference of 90°, transmitted from the driving circuit  24 . 
     The vibration type motor  25  outputs an S-phase signal indicating its own driven state. This S-phase signal is input to the input port of the microcomputer  11  through a phase determining circuit  29 . 
     The exchangeable lens is driven by the vibration type motor  25 . Since the driving mechanism of the vibration type motor  25  is known well, a description thereof will be omitted. 
     A pulse plate  26  rotates with rotation of the vibration type motor  25 . The rotational motion of the pulse plate  26  is detected by a photo interrupter  27 . The detection output from the photo interrupter  27  is input to the input port of the microcomputer  11  on the lens side through a wave forming circuit  28 . 
     The operation of the control circuit having the above arrangement will be described with reference to FIG.  3 . 
     FIG. 3 is a flow chart showing the operation of the control circuit. This operation will be described in the order of step numbers (S). 
     S 01 : When the shutter button of the camera body is pressed to the first-stoke position, the switch  21  is turned on. As a consequence, a focus detection circuit (not shown) on the camera body side starts its operation. In addition, when the switch  21  is turned on, the microcomputer  9  on the camera body side turns on the power supply transistor  8  to start the supply of electric power to the microcomputer  11  and control circuit  12  through the terminals b and b′. 
     S 02 : The defocus information of the photographing lens which is obtained by the focus detecting operation by the focus detection circuit is transferred from the microcomputer  9  of the camera body to the microcomputer  11  on the lens side through the terminals c and c′. The defocus information indicates the degree of defocus. 
     S 03 : The microcomputer  11  calculates the driven amount of the exchangeable lens on the basis of this defocus information, and then determines on the basis of the calculated driven amount whether the necessary driven amount is small. If it is determined that the necessary driven amount is small, the flow advances to step S 04 . Otherwise, the flow advances to step S 07 . Note that a small driven amount is an amount smaller than the predetermined driven amount of the exchangeable lens. 
     S 04 : If it is determined that the necessary driven amount is small, the microcomputer  11  causes the control circuit  12  of the DC/DC converter to select the divided voltage at the point y as a feedback voltage. As a consequence, the driving voltage of the vibration type motor is set to a high voltage. This operation will be described in detail later. 
     S 05 : The microcomputer  11  on the lens side sets digital data indicating the driving frequency of the vibration type motor  25  to a large value first, and sends it to the D/A converter  22 . The microcomputer  11  then gradually decreases the value of the digital data. Since the input analog voltage of the VCO  23  gradually drops from a high value, the frequency (driving frequency) f of the rectangular wave output from the VCO  23  is swept from a high frequency to a lower frequency. The driving circuit  24  of the vibration type motor generates driving voltages having the phases A and B difference of 90° on the basis of this rectangular wave. As shown in FIGS. 1A and 1B, therefore, the number of rotations of the vibration type motor gradually increases with a decrease in driving frequency. Referring to FIG. 3, the vibration type motor is abbreviated as USM. 
     S 06 : The microcomputer  11  keeps decreasing the digital data while the driving frequency f is higher than a predetermined frequency f 2  (see FIGS.  1 A and  1 B). If the driving frequency f becomes equal to or lower than the predetermined frequency f 2 , the flow advances to step S 10 . 
     S 07 : If the microcomputer  11  determined in step S 03  that the driven amount of the exchangeable lens is not small, the microcomputer  11  causes the control circuit  12  of the DC/DC converter to select the divided voltage at the point x as a feedback voltage. As a consequence, the driving voltage of the vibration type motor is set to a low voltage. This operation will be described in detail later. 
     S 08 : The vibration type motor is accelerated as in step S 05 . 
     S 09 : If the driving frequency f is higher than a predetermined frequency f 1  (f 1 &lt;f 2 ; see FIGS.  1 A and  1 B), the microcomputer  11  keeps decreasing the digital data. If the driving frequency f becomes equal to or lower than the predetermined frequency f 1 , the flow advances to step S 10 . 
     S 10 : The microcomputer  11  on the lens side fixes the digital data, which is to be output to the D/A converter  22 , to the current value, and stops sweeping the driving frequency, thereby holding the rotational speed of the vibration type motor  25  at a constant speed. 
     S 11 : A pulse signal generated in accordance with the rotation of the vibration type motor  25  is input from the wave forming circuit  28  to the input port of the microcomputer  11 . The number of input pulse signals is counted by the microcomputer  11 . The microcomputer  11  holds the rotational speed of the vibration type motor  25  at the constant speed until the count value reaches a first predetermined value. When the count value reaches the first predetermined value , the flow advances to step S 12 . 
     S 12 : Upon determining that the exchangeable lens has moved near to a target driving position, the microcomputer  11  starts decelerating the vibration type motor  25 . That is, the microcomputer  11  gradually increases the driving frequency indicated by digital data sent to the D/A converter  22 . With this operation, the input analog voltage to the VCO  23  rises. As a consequence, the frequency of the rectangular wave output from the VCO  23  is swept to a high frequency, and the frequency of the driving voltage applied to the vibration type motor  25  is also swept to a high frequency. Consequently, as shown in FIGS. 1A and 1B, the number of rotations of the vibration type motor  25  decreases, and the motor is decelerated. 
     S 13 : The microcomputer  11  keeps decelerating the vibration type motor  25  until the number of pulses counted by the microcomputer  11  reaches a second predetermined value (second predetermined value&gt;first predetermined value). When the number of pulses reaches the second predetermined value, the flow advances to step S 14 . 
     S 14 : Upon determining that the exchangeable lens has reached the target driving position, the microcomputer  11  stops driving the vibration type motor  25 . More specifically, the microcomputer  11  abruptly increases the driving frequency indicated by the digital data sent to the D/A converter  22  to abruptly change the frequency of the driving voltage applied to the vibration type motor  25  to a high frequency at which the vibration type motor  25  stops. 
     Assume that the voltage-dividing resistors  18 ,  19 , and  20  respectively have resistances R 18 , R 19 , and R 20 . Letting Vr (not shown) be a reference voltage value in the control circuit  12  of the DC/DC converter, if the divided voltage at the point x is selected as a feedback voltage by the control circuit  12 , the output voltage Vout from the DC/DC converter is given by 
     
       
           Vout =Vr×(R 18 +R 19 +R 20 )/(R 19 +R 20 )  
       
     
     If the divided voltage at the point y is selected as a feedback voltage, the output voltage Vout from the DC/DC converter is given by 
     
       
           Vout =Vr×(R 18 +R 19 +R 20 )/R 20   
       
     
     As described above, when the voltage at the point y is selected as a feedback voltage, the output voltage Vout becomes higher and hence the driving voltage to the vibration type motor  25  becomes higher than when the voltage at the point x is selected. 
     If R 19 =R 20 , the driving voltage obtained by selecting the voltage at the point y is twice that obtained by selecting the voltage at the point x. 
     As is obvious from steps S 03  and S 04 , since the voltage at the point y is selected when the necessary driven amount of the exchangeable lens is small, a high driving voltage is set, and a curve Ny shown in FIG. 1B is used. When the necessary driven amount of the exchangeable lens is small, therefore, the large number of rotations is obtained. In addition, when the necessary driven amount of the exchangeable lens is not small, the obtained number of rotation is small and, therefore, the electric power consumption of the exchangeable lens is reduced. 
     When the necessary driven amount of the exchangeable lens is small, since the vibration type motor  25  is driven for a short period of time without increasing the number of rotations much, the frequency of the driving voltage is kept high. Referring to FIG. 1A, therefore, as the motor is driven while the driving frequency is not decreased below, for example, f 2 , the electric power consumption of the vibration type motor  25  does not increase beyond P 2  even if the driving voltage is doubled. However, since the driving voltage is doubled, the number of rotations reaches N 2 , as shown in FIG.  1 B. This number of rotation is almost equal to that when the driving frequency of a general driving voltage is decreased to f 1 . 
     The electric power consumption of the motor does not exceed P 2  regardless of whether the necessary driven amount of the exchangeable lens is small or not. This eliminates the chance that excessive electric power consumption will cause operation errors in other devices in a camera system as in the prior art. In addition, when the necessary driven amount of the exchangeable lens is small, high-speed driving operation can be performed. 
     In a scene which requires high motion tracking performance as in continuously shooting of some sports activity, the exchangeable lens is often driven in small amounts. The capability of increasing the focusing speed in driving the exchangeable lens in small amounts will provide great effect in terms of motion tracking performance. The feature of raising the driving voltage of the vibration type motor  25  only when the exchangeable lens is driven in small amounts as in the present invention makes it possible to improve the reliability of the camera system without affecting the overall camera system. 
     (Second Embodiment) 
     The second embodiment will be described next. 
     Since the arrangement of the second embodiment is basically the same as that of the first embodiment, only different portions will be described below. 
     FIG. 4 shows the arrangement of a control circuit arranged in an exchangeable lens according to the second embodiment. FIG. 4 mainly shows portions that differ from the control circuit shown in FIG.  2 . The same reference numerals as in FIG. 2 denote the same parts in FIG. 4, and an illustration of the components denoted by reference numerals  22  to  28  and the components of the camera body is omitted. 
     The second embodiment differs from the first embodiment in a portion for switching driving voltage values for the vibration type motor. 
     Two reference voltages Vr 1  and Vr 2  (Vr 1 &gt;Vr 2 ) are input to a control circuit  12  of a DC/DC converter. An output voltage Vout from the DC/DC converter is divided by resistors  30  and  31  to be fed back to the control circuit  12 . Assume that the resistors  30  and  31  respectively have resistances R 30  and R 31 . 
     As in the first embodiment, the control circuit  12  selects the reference voltage Vr 1  or Vr 2  in accordance with the driven amount of the exchangeable lens which is calculated by a microcomputer  11  on the lens side. More specifically, if the necessary driven amount of the exchangeable lens is smaller than a predetermined value, the reference voltage Vr 1  is selected. In this case, the output voltage Vout from the DC/DC converter is given by 
     
       
           Vout =Vr 1 ×(R 30 +R 31 )/R 31   
       
     
     If the necessary driven amount of the exchangeable lens is equal to or larger than the predetermined value, the reference voltage Vr 2  is selected. In this case, the output voltage Vout from the DC/DC converter is given by 
     
       
           Vout =Vr 2 ×(R 30 +R 31 )/R 31   
       
     
     This output voltage Vout is lower than that set when the necessary driven amount of the exchangeable lens is small. 
     Other operations of the control circuit are the same as those in the first embodiment. 
     In this manner, in the second embodiment as well, high-speed focusing operation can be realized, and electric power consumption can be suppressed low. 
     The present invention can be applied to a system made up of a plurality of devices or an apparatus including one device.