Patent Publication Number: US-8975849-B2

Title: Motor control apparatus

Description:
This application is a 371 applicatoin of PCT/JP2011/002899 having an international filing date of May 25, 2011, which claim priority of JP2010-122539 May 28, 2010, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a motor control apparatus for controlling a moving operation such as a speed or a position of a motor or a load to be driven by the motor, and more particularly to a motor control apparatus having a function for suppressing machine resonance occurring in driving or the like. 
     BACKGROUND ART 
     Conventionally, a motor control apparatus of this type includes a motor control apparatus described in PTL 1.  FIG. 10  is a block diagram showing a structure of the motor control apparatus described in PTL 1. 
     Conventional motor control apparatus  50  shown in  FIG. 10  is connected to motor  11  and speed detector  13 . Load  12  is linked to motor  11 . Moreover, speed detector  13  detects a rotating speed of motor  11  and outputs speed detection signal Vd indicative of the detected rotating speed. 
     Motor control apparatus  50  has a speed control system for causing speed detection signal Vd to follow command speed signal Vr. Motor control apparatus  50  includes first notch filter  15  as shown in  FIG. 10  in order to suppress an oscillation caused by machine resonance or the like. Furthermore, motor control apparatus  50  includes speed control portion  14 , torque control portion  16 , oscillation extracting filter  17 , second notch filter  18 , and notch control portion  19 . 
     Speed control portion  14  inputs command speed signal Vr and speed detection signal Vd and generates torque command signal τ 1 . First notch filter  15  serves to apply sharp attenuation to a signal having a frequency within a predetermined range around a specific frequency contained in a supplied signal from the same signal. The frequency to be the center is referred to as a notch center frequency, a vicinal frequency range to be attenuated is referred to as a notch width, and a degree of the attenuation to be applied at the notch center frequency is referred to as a notch depth. Moreover, a frequency specified by the notch center frequency and the notch width is referred to as a notch frequency. First notch filter  15  has such a characteristic and attenuates a signal component of the notch frequency with respect to torque command signal τ 1  and supplies, to torque control portion  16 , torque command signal τ 2  subjected to filter processing. Torque control portion  16  controls motor  11  in such a manner that motor  11  outputs a target torque based on torque command signal τ 2  which is input. 
     Moreover, oscillation extracting filter  17  extracts an oscillation caused by machine resonance from speed detection signal Vd and outputs the oscillation as extracting oscillation signal x 1 . Extracting oscillation signal x 1  is input to second notch filter  18 . Second notch filter  18  carries out such filter processing as to attenuate the signal component of the notch frequency over extracting oscillation signal x 1  depending on the control of notch control portion  19 . Second notch filter  18  outputs second notch filter output signal x 2  as the extracting oscillation signal subjected to the filter processing. Notch control portion  19  generates notch frequency set value cn 1  based on extracting oscillation signal x 1  and second notch filter output signal x 2 . Notch control portion  19  controls first notch filter  15  and second notch filter  18  based on notch frequency set value cn 1  in such a manner that the notch frequencies of first notch filter  15  and second notch filter  18  are equivalent to an oscillation frequency of extracting oscillation signal x 1 . 
     In first notch filter  15 , a notch depth in the notch frequency has a fixed value. In second notch filter  18 , moreover, a notch depth in a notch frequency is represented by −∞. 
     In the conventional motor control apparatus having such a structure, the notch frequencies of first notch filter  15  and second notch filter  18  are successively changed in such a manner that an oscillation component generated by an oscillation caused by machine resonance for some reason is decreased if any. 
     Moreover, another example of the conventional motor control apparatus is described in PTL 2.  FIG. 11  is a block diagram showing a structure of the conventional motor control apparatus described in PTL 2. 
     The motor control apparatus shown in  FIG. 11  includes notch filter  15   b , notch frequency deciding portion  41 , adaptive calculating portion  42 , and filter coefficient setting portion  43 . In notch filter  15   b , a notch center frequency is fixed to notch frequency ωn by notch frequency deciding portion  41 . On the other hand, a notch depth and a notch width are variable, and the notch depth and the notch width of notch filter  15   b  are decided based on filter coefficients ξ 1  and ξ 2  output from filter coefficient setting portion  43 . 
     Adaptive calculating portion  42  successively changes adaptive input ξ in accordance with adaptive law based on output τ 2  of notch filter  15   b  and reference signal u, and outputs the changed input. Filter coefficient setting portion  43  outputs filter coefficients ξ 1  and ξ 2  indicative of the notch depth and the notch width in notch filter  15   b  based on adaptive input ξ which is input. 
     In the conventional motor control apparatus shown in  FIG. 11 , the notch depth of notch filter  15   b  is successively changed in such a manner that an oscillation component of an oscillation caused by machine resonance is decreased when the oscillation is caused. 
     As in PTL 1, however, the notch depth does not take an optimum value in first notch filter  15  having the notch depth fixed. For this reason, there is a problem in that an oscillation is unnecessarily suppressed and a phase delay is thus increased depending on a control target, resulting in an insufficient increase in a control system gain. 
     As in PTL 2, moreover, there is fear that an oscillation caused by machine resonance or the like might not be sufficiently suppressed in the case in which a variation or aging in a characteristic of a machine, a deviation of a fixed notch frequency from a resonance frequency or the like occurs in notch filter  15   b  having the notch frequency fixed. 
     PTL 1: Unexamined Japanese Patent Publication No. 2004-274976 
     PTL 2: Unexamined Japanese Patent Publication No. 2007-293571 
     SUMMARY OF THE INVENTION 
     A motor control apparatus according to the present invention carries out feedback control over a quantity of state of a motor or load. The motor control apparatus includes a first notch filter, an oscillation extracting filter, a second notch filter, a notch control portion, a notch depth control portion, and a control determining portion. The first notch filter is disposed in a feedback control system and a notch center frequency and a notch depth of the first notch filter is changeable. The oscillation extracting filter extracts an oscillation component caused by machine resonance and outputs the oscillation component as an extracting oscillation signal. The second notch filter inputs the extracting oscillation signal and a notch center frequency of the second notch filter is changeable. The notch control portion changes the notch center frequency of the first notch filter and the notch center frequency of the second notch filter to decrease an amplitude of a second notch filter output signal based on the extracting oscillation signal and the second notch filter output signal. The notch depth control portion changes the notch depth of the first notch filter based on the extracting oscillation signal. The control determining portion carries out control to operate either the notch control portion or the notch depth control portion based on the extracting oscillation signal and the second notch filter output signal. 
     By the structure, also in the case in which a characteristic of the apparatus is changed due to aging or an oscillation frequency of machine resonance is varied by an influence of an application of the notch filter or the case in which a control system gain is increased to raise a speed of a command following operation, for example, it is possible to always suppress the machine resonance stably without causing an instability of the control system. 
     According to the motor control apparatus in accordance with the present invention, therefore, it is possible to provide a motor control apparatus which can suppress machine resonance without unnecessarily increasing a phase delay when the machine resonance occurs and controls a moving operation of a motor or a load thereof while always ensuring a stable control state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a structure of a motor control apparatus according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a characteristic chart showing an example of a frequency characteristic and a phase characteristic of a first notch filter in the motor control apparatus. 
         FIG. 3  is a characteristic chart showing an example of a frequency characteristic and a phase characteristic of a second notch filter in the motor control apparatus. 
         FIG. 4  is a flow chart showing a characteristic set processing of the first notch filter in the motor control apparatus. 
         FIG. 5  is a flow chart showing a characteristic set processing of the first notch filter in a structure according to a variant of the motor control apparatus. 
         FIG. 6  is a chart showing a gain characteristic of a transfer function for speed detection signal Vd with respect to command speed signal Vr. 
         FIG. 7  is a chart showing a gain characteristic in the case in which a control system gain is amplified by Kv. 
         FIG. 8  is a flow chart showing a characteristic set processing of a first notch filter in a motor control apparatus according to a second exemplary embodiment of the present invention. 
         FIG. 9  is a flow chart showing a characteristic set processing of a first notch filter in a motor control apparatus according to a third exemplary embodiment of the present invention. 
         FIG. 10  is a block diagram showing a structure of a conventional motor control apparatus. 
         FIG. 11  is a block diagram showing the structure of the conventional motor control apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments according to the present invention will be described below with reference to the drawings. 
     First Exemplary Embodiment 
       FIG. 1  is a block diagram showing a structure of motor control apparatus  10  according to a first exemplary embodiment of the present invention. 
     As shown in  FIG. 1 , motor control apparatus  10  according to the first exemplary embodiment of the present invention is connected to motor  11  and speed detector  13 . Load  12  is linked to motor  11 . Moreover, speed detector  13  measures a rotating speed of a movable member (not shown) provided in motor  11  and outputs speed detection signal Vd to be a state detection signal indicative of a speed quantity depending on the rotating speed. On the other hand, motor control apparatus  10  is notified of command speed signal Vr in order to give a command for the rotating speed of the movable member. Motor control apparatus  10  has a speed control system for carrying out feedback control in such a manner that a rotating operation of the movable member follows a command speed as a control system for carrying out the feedback control. In other words, in the present exemplary embodiment, a speed quantity to be a state quantity is subjected to the feedback control. In the present exemplary embodiment, description will be given by taking an example of a motor control apparatus having a structure including the speed control system. 
     As shown in  FIG. 1 , motor control apparatus  10  includes speed control potion  14 , first notch filter  15 , torque control portion  16 , oscillation extracting filter  17 , second notch filter  18 , notch control portion  19 , notch depth control portion  20 , control determining portion  21 , and switching portion  22 . 
     Command speed signal Vr indicative of a command speed and speed detection signal Vd indicative of a detection speed detected by speed detector  13  are input to speed control portion  14 . Speed control portion  14  calculates a deviation quantity of command speed signal Vr from speed detection signal Vd and generates and outputs torque command signal τ 1  for controlling the deviation quantity to be zero. More specifically, speed control portion  14  calculates a difference between command speed signal Vr and speed detection signal Vd, for example, and outputs, as torque command signal τ 1 , a result obtained by carrying out proportional integral over the calculated value. 
     Torque command signal τ 1  is supplied from speed control portion  14  to first notch filter  15 . Furthermore, notch frequency set value cn 1  and notch depth set value cn 2  are supplied from notch control portion  19  and notch depth control portion  20  to first notch filter  15 , respectively. First notch filter  15  serves to apply sharp attenuation to a signal component having a frequency around a specific frequency contained in torque command signal τ 1  from torque command signal τ 1 .  FIG. 2  is a characteristic chart showing an example of a frequency characteristic and a phase characteristic of first notch filter  15  in motor control apparatus  10  according to the first exemplary embodiment of the present invention.  FIG. 2  shows an example of such a frequency characteristic as to attenuate a signal component in a frequency band of a vicinal frequency setting notch width Bn in accordance with notch depth Dn around notch center frequency ωn 1 . In first notch filter  15 , notch center frequency ωn 1  and notch depth Dn are changed based on notch frequency set value cn 1  and notch depth set value cn 2  which are supplied, respectively. Notch depth set value cn 2  has a feature that notch depth Dn is greater (deeper) when notch depth set value cn 2  is smaller and is smaller (shallower) when notch depth set value cn 2  is greater. 
     First notch filter  15  is a secondary recursion type notch filter having transfer function H 1 (s) expressed in the following (Equation 1), for example. 
     
       
         
           
             
               
                 
                   
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     In (Equation 1), ω n1  represents a notch center frequency coefficient corresponding to notch center frequency ωn 1  of first notch filter  15 , ξ 1  represents an attenuation constant, and d 1  represents a notch depth coefficient indicative of notch depth Dn. Notch depth coefficient d 1  is in a range of 0≦d 1 ≦1. In the case of d 1 =1, a gain characteristic in notch center frequency ωn 1  of first notch filter  15  is 0 [dB]. In the case of d 1 =0, a gain characteristic in notch center frequency ωn 1  of first notch filter  15  is −∞ [dB]. In other words, in the case of d 1 =1, an input signal of first notch filter  15  is output as it is from first notch filter  15 . In the case of d 1 =0, moreover, an attenuation quantity of a signal component of notch center frequency ωn 1  is a maximum so that a signal obtained by attenuating a signal component of a frequency in the vicinity of notch center frequency ωn 1  is output from first notch filter  15 . In the present exemplary embodiment, notch center frequency coefficient ω n1  is changed based on notch frequency set value cn 1  so that notch center frequency ωn 1  is varied, and notch depth coefficient d 1  is changed based on notch depth set value cn 2  so that notch depth Dn is varied. Torque command signal τ 2  to be a signal obtained by thus carrying out the filter processing over torque command signal τ 1  is output from first notch filter  15 . 
     Torque command signal τ 2  output from first notch filter  15  is input to torque control portion  16 . Torque control portion  16  controls a rotating operation of motor  11  in such a manner that motor  11  outputs a target torque. 
     Consequently, a speed control system is constituted in motor control apparatus  10 . The speed control system utilizes speed detection signal Vd indicative of a rotating speed of a movable member which is detected by speed detector  13 , thereby carrying out feedback control over a moving operation of the movable member in such a manner that the rotating speed of the movable member depends on command speed signal Vr. Motor control apparatus  10  has a structure in which first notch filter  15  is disposed in the speed control system. 
     In the present exemplary embodiment, moreover, motor control apparatus  10  has a function for automatically suppressing machine resonance occurring in the case in which load  12  is driven or the like. In order to implement the function, motor control apparatus  10  disposes first notch filter  15  described above in the speed control system, and furthermore, includes oscillation extracting filter  17  to be an extracting filter for extracting an oscillation component of machine resonance or the like. Speed detection signal Vd output from speed detector  13  is also supplied to oscillation extracting filter  17 . 
     Oscillation extracting filter  17  has a predetermined frequency band set thereto and extracts an oscillation component contained in the set frequency band from speed detection signal Vd. In other words, an oscillation extracting filter extracts and outputs an oscillation component appearing in speed detection signal Vd which is input, for example, an oscillation component of machine resonance occurring when load  12  is driven by motor  11 . Oscillation extracting filter  17  may be a high pass filter for causing a signal component having a predetermined frequency or more to pass therethrough or a band pass filter for causing a signal component in a predetermined frequency bandwidth to pass therethrough because it is sufficient that the oscillation component can be thus extracted. Oscillation extracting filter  17  outputs extracting oscillation signal x 1  to be a signal passing through the filter of the frequency characteristic, that is, a signal from which an oscillation component appearing in speed detection signal Vd is extracted. 
     Extracting oscillation signal x 1  output from oscillation extracting filter  17  is input to second notch filter  18 , control determining portion  21 , and switching portion  22 . Furthermore, extracting oscillation signal x 1  is input to either notch control portion  19  or notch depth control portion  20  in accordance with switching of switching portion  22 . Moreover, the details will be described below. By these structures, the characteristic of first notch filter  15  is set. 
     First of all, second notch filter  18  outputs a signal which applies sharp attenuation to a signal component having a frequency around a specific frequency contained in extracting oscillation signal x 1 . Furthermore, notch frequency set value cn 1  is supplied from notch control portion  19  to second notch filter  18 . In the present exemplary embodiment, a predetermined value is previously given to a notch width and a notch depth in a notch center frequency is set to be −∞ [dB] as the characteristic of second notch filter  18 . For example, there is set a secondary recursion type notch filter having transfer function H 2 (s) expressed in the following (Equation 2). 
     
       
         
           
             
               
                 
                   
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     Herein, ω n2  represents a notch center frequency coefficient corresponding to notch center frequency ωn 2  of second notch filter  18 , and ξ 2  represents an attenuation constant. A frequency characteristic is the same as that of first notch filter  15 , and there is possessed a characteristic shown in  FIG. 3 . As is apparent from  FIG. 3 , there is possessed a characteristic in which a component having notch center frequency ωn 2  is suppressed. In second notch filter  18 , moreover, a gain characteristic corresponding to notch depth Dn in  FIG. 2  is set to −∞ [dB]. In the present exemplary embodiment, furthermore, notch center frequency coefficient ω n2  is changed based on notch frequency set value cn 1  so that notch center frequency ωn 2  is varied. First notch filter  15  and second notch filter  18  are changed with equal set value cn 1  based on (Equation 1) and (Equation 2). Therefore, notch center frequency ωn 1  and notch center frequency ωn 2  are changed to be an equal frequency. Second notch filter output signal x 2  (hereinafter, appropriately referred to simply as signal x 2 ) to be a signal obtained by carrying out a filter processing over extracting oscillation signal x 1  (hereinafter, appropriately referred to simply as signal x 1 ) is output from second notch filter  18 . Signal x 2  is supplied to notch control portion  19  and control determining portion  21 . 
     When an oscillation frequency of an oscillation component contained in signal x 1  to be an input is greatly different from notch center frequency ωn 2  in second notch filter  18 , an amplitude of signal x 1  is not suppressed. On the other hand, when they are coincident with each other, the amplitude is suppressed. For this reason, the amplitude of signal x 2  is increased gradually when the oscillation frequency of signal x 1  deviates from notch center frequency ωn 2 . In other words, it is apparent that signal x 2  indicates a degree of the deviation of the oscillation frequency of signal x 1  and notch center frequency ωn 2 . 
     Next, notch control portion  19  generates and outputs notch frequency set value cn 1  (hereinafter, appropriately referred to simply as set value cn 1 ) based on signal x 2  and signal x 1  supplied through switching portion  22 . Set value cn 1  is supplied to first notch filter  15  and second notch filter  18 , and notch center frequency ωn 1  and notch center frequency ωn 2  are set depending on set value cn 1 , respectively. Notch control portion  19  uses signal x 1  and signal x 2  to change set value cn 1  in such a manner that the amplitude of supplied signal x 2  is reduced. Based on set value cn 1 , notch center frequency ωn 2  of second notch filter  18  is changed. Notch control portion  19  thus changes set value cn 1  successively to control notch center frequency ωn 2  of second notch filter  18  until the amplitude of signal x 2  is equal to or smaller than a predetermined value or reaches zero. It is possible to implement the control of the notch filter by combining second notch filter  18  with a directional filter or notch filter coefficient correcting means described in PTL 1, for example. Consequently, notch center frequency ωn 2  is controlled to be a frequency of the oscillation component contained in signal x 1 . Therefore, set value cn 1  is caused to correspond to the frequency of the oscillation component. 
     Moreover, notch center frequency ωn 2  is thus changed depending on set value cn 1 , and furthermore, notch center frequency ωn 1  of first notch filter  15  is also changed to be equal to notch center frequency ωn 2 . In other words, when the control is carried out to obtain notch center frequency ωn 2 =ωn by notch control portion  19  and second notch filter  18 , notch center frequency ωn 1  is also set to be notch center frequency ωn 1 =ωn. For this reason, notch center frequency ωn 1  of first notch filter  15  is also controlled to be a frequency of an oscillation component extracted by oscillation extracting filter  17 . 
     Next, notch depth control portion  20  generates and outputs notch depth set value cn 2  (hereinafter, appropriately referred to simply as set value cn 2 ) based on signal x 1  supplied through switching portion  22 . Set value cn 2  is supplied to first notch filter  15  and notch depth Dn is set depending on set value cn 2 . Notch depth control portion  20  monitors whether an oscillation component is contained in supplied signal x 1  or not. If the oscillation component is detected, set value cn 2  is changed to further increase notch depth Dn and is supplied to first notch filter  15 . 
     Subsequently, control determining portion  21  determines whether notch control portion  19  is to be operated or notch depth control portion  20  is to be operated based on signal x 1  and signal x 2  which are supplied. Control determining portion  21  controls switching portion  22  based on the determination. Consequently, signal x 1  is supplied to notch control portion  19  or notch depth control portion  20  in accordance with the determination of control determining portion  21 . More specifically, signal x 1  is first set to be supplied to notch control portion  19 . If control determining portion  21  determines that the oscillation component is detected in signal x 1  and is not detected in signal x 2 , switching portion  22  is switched in such a manner that signal x 1  is supplied to notch depth control portion  20 . If control determining portion  21  determines that the oscillation component is not detected from signal x 1 , switching portion  22  is switched in such a manner that signal x 1  is supplied to notch control portion  19  again. 
     By the structure described above, if it is determined that the oscillation component is contained in extracting oscillation signal x 1 , notch center frequency ωn 1  of first notch filter  15  is set to be the frequency of the oscillation component by notch control portion  19 . After notch center frequency ωn 1  is set, furthermore, notch depth Dn of first notch filter  15  is set to obtain such a notch depth that the oscillation component contained in extracting oscillation signal x 1  can be suppressed by notch depth control portion  20 . In the present exemplary embodiment, by employing the structure, it is possible to prevent an oscillation from unnecessarily being excessively suppressed. Therefore, it is possible to suppress an oscillation caused by machine resonance or the like while ensuring a stable operation of a control system. 
     Next, the operation of motor control apparatus  10  will be described in detail.  FIG. 4  is a flow chart showing a characteristic set processing of first notch filter  15  according to the first exemplary embodiment of the present invention. The processing in  FIG. 4  is repetitively carried out every control cycle. 
     First of all, control determining portion  21  confirms whether an oscillation is generated based on the amplitude of extracting oscillation signal x 1  or not at Step S 101 . If it is determined that the oscillation is generated, that is, the oscillation component is present in signal x 1 , control determining portion  21  further proceeds to Step S 102  in which it is determined whether the oscillation component is present in signal x 2  or not. Whether the oscillation component is present is determined by detecting whether an amplitude of a signal is zero or is not zero or comparing the amplitude of signal x 1  or signal x 2  with a threshold of a predetermined value to determine that the oscillation component is present when the amplitude of the signal exceeds the threshold, for example. 
     If control determining portion  21  determines that signal x 2  has the oscillation component at Step S 102 , the processing proceeds to Step S 103 . In other words, in this case, both signal x 1  and signal x 2  have oscillation components. Therefore, it is determined that oscillation frequency of signal x 1  is not coincident with notch center frequency ωn 2  of second notch filter  18 . Control determining portion  21  operates notch control portion  19  based on the determination to control notch center frequency ωn 1  of first notch filter  15  so as to be the frequency of oscillation component of signal x 1 . In other words, at Step S 103 , control determining portion  21  controls switching portion  22  so as to input signal x 1  to notch control portion  19 . At Step S 104 , then, notch control portion  19  carries out an operation for correcting notch frequency set value cn 1 . The processing from Step S 101  to Step S 104  is repeated every control cycle until it is determined that signal x 2  has no oscillation component at Step S 102 . 
     The processing for repeating Steps S 101  to S 104  is executed in the following manner in more detail. First of all, notch center frequency ωn 2  of second notch filter  18  is decided by set value cn 1  which is always corrected and input until it is determined that signal x 2  has no oscillation component. On the other hand, first notch filter  15  holds set value cn 1  which has not been changed when set value cn 1  is changed, and sets changed set value cn 1  when the change of set value cn 1  is stopped. In other words, in the case in which notch center frequency ωn 1  of first notch filter  15  is also processed to be always corrected, the state of signal x 1  might also be changed correspondingly so that the operation of notch control portion  19  might be unstable. For this reason, by employing a procedure for setting notch center frequency ωn 1  after deciding notch center frequency ωn 2 , it is possible to stably execute the operation of notch control portion  19 . 
     If control determining portion  21  determines that signal x 2  has no oscillation component at Step S 102 , moreover, the processing proceeds to Step S 105 . In other words, in this case, the oscillation component is detected in signal x 1  and is not detected in signal x 2 . Therefore, it is determined that the oscillation frequency of signal x 1  is coincident with notch center frequency ωn 2  of second notch filter  18 , and furthermore, is also coincident with notch center frequency ωn 1  of first notch filter  15 . 
     At Step S 105 , control determining portion  21  controls switching portion  22  so as to input signal x 1  to notch depth control portion  20 . At Step S 106 , then, notch depth control portion  20  sets to start the operation for correcting notch depth set value cn 2  from a current value. Moreover, the operation for correcting set value cn 2  is carried out to increase notch depth Dn at Step S 107  by notch depth control portion  20 . The processing from Step S 101  to Step S 107  is repeated every control cycle until it is determined that signal x 1  has no oscillation component at Step S 101 . 
     The processing for repeating Steps S 101  to S 107  is executed in the following manner in more detail. First of all, an initial value of set value cn 2  is set to obtain notch depth coefficient d 1 =1 of first notch filter  15 . Then, a successive changing operation is carried out in such a manner that the notch depth is increased, that is, notch depth coefficient d 1  is reduced. If it is determined that signal x 1  has no oscillation component, the changing operation is stopped. 
     For example, notch depth control portion  20  successively carries out an operation for changing set value cn 2  in such a manner that notch depth coefficient d 1  is decreased by a predetermined quantity if signal x 1  contains the oscillation component. As a result, a gain characteristic in notch center frequency ωn 1  of first notch filter  15  is gradually decreased. Correspondingly, the amplitude of the oscillation component of oscillation frequency ωn 1  contained in signal x 1  is also reduced gradually. In the case in which the amplitude of signal x 1  is zero or is equal to or smaller than a threshold, the successive changing operation for set value cn 2  is stopped. Thus, it is possible to search an optimum value of notch depth coefficient d 1  in first notch filter  15  which can suppress machine resonance occurring in motor driving or the like. When notch depth coefficient d 1  is gradually reduced, furthermore, the changing operation for notch depth set value cn 2  is stopped if set value cn 2  corresponding to notch depth coefficient d 1 =0 is set. In addition, notch depth control portion  20  starts second and subsequent changing operations for notch depth set value cn 2  from a current set value. 
     By the operation described above, the oscillation component is not detected in both signal x 1  and signal x 2 . For this reason, it is determined that signal x 1  has no oscillation component at Step S 101  in  FIG. 4  and the processing proceeds to Step S 108 . Control determining portion  21  controls switching portion  22  so as to input signal x 1  to notch control portion  19  at Step S 108 . By the processing described above, an oscillation in the control system is set to be suppressed by first notch filter  15 . Therefore, the oscillation component is not contained in signal x 1  and notch control portion  19  determines that an oscillation does not occur, and the changing operation for set value cn 1  is not carried out. If a new oscillation component is contained in signal x 1 , for example, a load is changed, moreover, the processing proceeds to Step S 102  from Step S 101  in  FIG. 4  and the processing described above for the new oscillation component is executed. In the case in which signal x 1  is input to notch control portion  19 , zero is input to notch depth control portion  20  and the changing operation for notch depth set value cn 2  is not carried out. If signal x 1  is input to notch depth control portion  20 , moreover, zero is input to notch control portion  19  and the changing operation for notch frequency set value cn 1  is not carried out. 
     Although a first changing operation for set value cn 2  is started from the initial value and second and subsequent changing operations for set value cn 2  are started from the current set value in the present exemplary embodiment, it is also possible to employ a structure in which the current set value and the initial value are switched depending on a change in notch center frequency ωn 2  of second notch filter  18 .  FIG. 5  is a flow chart showing a characteristic set processing of a first notch filter in the structure according to the variant of the present exemplary embodiment. More specifically, signal x 1  is set so as to be input to notch depth control portion  20  at Step S 105  and it is then confirmed whether notch center frequency ωn 2  is changed from a value in a last changing operation or not at Step S 111 . If notch center frequency ωn 2  is changed, a value at a start of the changing operation for set value cn 2  is set to be the initial value at Step S 112 . If notch center frequency ωn 2  is not changed, the value at the start is set to be the current set value at Step S 113 . 
     By the structure, if the notch frequency is changed, the changing operation for set value cn 2  is stopped earlier. Therefore, it is possible to rapidly suppress the machine resonance. 
     Second Exemplary Embodiment 
     In the first exemplary embodiment, the description has been given by taking the example of the structure in which set value cn 2  is gradually reduced. On the other hand, in a second exemplary embodiment, there is employed a structure further including a processing for gradually increasing set value cn 2 . In other words, motor control apparatus  10  according to the present exemplary embodiment has such a structure as to select either an operation for gradually increasing set value cn 2  or an operation for gradually reducing set value cn 2  as a changing operation for set value cn 2  depending on a variation in a control system gain, for example. 
     First of all, description will be given to a frequency characteristic of a control system containing machine resonance and the like.  FIG. 6  is a chart showing a gain characteristic of a transfer function of speed detection signal Vd with respect to command speed signal Vr. In  FIG. 6 , there is shown an example in which frequency ωn represents a resonance frequency, and machine resonance of resonance frequency ωn occurs when motor control apparatus  10  is used to drive a motor and a load. By setting a gain characteristic in resonance frequency ωn to be equal to or smaller than 0 [dB], the machine resonance is suppressed. In order to suppress the resonance, accordingly, notch depth Dn of first notch filter  15  is required by Dv. In other words, in the processing shown in  FIG. 4 , a successive changing operation for set value cn 2  is carried out until notch depth Dv is obtained from a state of a notch depth of zero to be an initial value of the notch depth by notch depth control portion  20 . When the notch depth reaches set value cn 2  which is equivalent to Dv, the successive changing operation is stopped. In other words, in the case in which motor control apparatus  10  is used for the control system having the gain characteristic illustrated in  FIG. 6 , the notch depth of first notch filter  15  reaches Dv by notch depth control portion  20  so that machine resonance is suppressed. 
     Next, description will be given to the case in which the control system gain is amplified by Kv.  FIG. 7  is a chart showing a gain characteristic in the case in which the control system gain is amplified by Kv. As shown in  FIG. 7 , the gain characteristic is wholly amplified by Kv and a gain in resonance frequency ωn is also increased by Kv as compared with  FIG. 6 . For this reason, machine resonance having resonance frequency on occurs again. In this case, a resonance frequency is not changed for the machine resonance occurring again. For this reason, second notch filter output signal x 2  does not contain an oscillation component. In the processing of  FIG. 4 , therefore, the processing proceeds to Step S 105 , and set value cn 2  is successively changed and notch depth Dn of first notch filter  15  reaches a value which is equivalent to Dv+Kv so that the machine resonance is suppressed again. 
     The above description has been given to the operation to be carried out in the case in which the control system gain is increased. In the case in which the control system gain is reduced, however, notch depth Dn is excessively great with respect to the machine resonance having the resonance frequency con in the processing of  FIG. 4 . 
     In the present exemplary embodiment, there is employed a structure including a processing for gradually increasing set value cn 2  in order to reduce notch depth Dn depending on the change in the control system gain in such a manner that notch depth Dn is prevented from unnecessarily being excessively increased. 
       FIG. 8  is a flow chart showing a characteristic set processing of first notch filter  15  according to the second exemplary embodiment of the present invention. In a comparison with  FIG. 5 , a processing to be executed in the case in which it is determined that signal x 1  has no oscillation component at Step S 101  is different in  FIG. 8 . In  FIG. 8 , it is determined whether the control system gain is changed to be reduced or not at Step S 121 . If the control system gain is changed to be reduced, signal x 1  is input to notch depth control portion  20  at Step S 123  and set value cn 2  is corrected to be gradually increased from a current value in such a manner that notch depth Dn is reduced at Step S 124 . By employing the structure, notch depth Dn is changed to be suitable for the control system gain when the control system gain is changed to reduce the control system gain. According to the structure in accordance with the present exemplary embodiment, thus, optimum notch depth Dn is set depending on the control system gain. It is also possible to employ such a structure as to select, as the changing operation for set value cn 2 , either of the gradual increasing operation and the gradual reducing operation depending on at least one of a change in notch center frequency ωn 1  of first notch filter  15 , a change in notch center frequency ωn 2  of second notch filter  18 , and the change in the control system gain, in addition to the change in the control system gain. 
     Third Exemplary Embodiment 
       FIG. 9  is a flow chart showing a characteristic set processing of first notch filter  15  according to a third exemplary embodiment of the present invention. In the present exemplary embodiment, there is employed a structure in which a change quantity of set value cn 2  is calculated by an arithmetical operation when the control system gain is increased as shown in  FIG. 7 , for example. 
     More specifically, the processing shown in  FIG. 9  has such a structure as to calculate and set the change quantity of set value cn 2  depending on a change quantity of a control system gain in second and subsequent changing operations for set value cn 2 . In other words, set value cn 2  is calculated in such a manner that notch depth Dn is greater than a current value by Kv when the control system gain is to be amplified by Kv. 
     A specific operation will be described with reference to the flow chart of  FIG. 9 . If it is determined that there is no oscillation component at Step S 101 , control determining portion  21  confirms whether or not set value cn 2  has already been set once, that is, a changing operation for notch depth Dn is once stopped and the control system gain is changed at Step S 131 . If the changing operation for notch depth Dn is once stopped and the control system gain is changed, notch depth control portion  20  changes set value cn 2  by a value corresponding to a change quantity of the control system gain from the current value depending on the change quantity of the control system gain at Step S 132 . Then, control determining portion  21  controls switching portion  22  so as to input signal x 1  to notch control portion  19  at Step S 133 . Although signal x 1  is input to notch control portion  19 , extracting oscillation signal x 1  has no oscillation component. Therefore, the changing operation for notch frequency set value cn 1  is not carried out. 
     By the structure, in the case in which the control system gain is changed, there is set notch depth Dn which reflects the change quantity of the control system gain and does not unnecessarily increase a phase delay without an occurrence of an oscillation. 
     As described above, the motor control apparatus according to the present invention includes a first notch filter, an oscillation extracting filter, a second notch filter, a notch control portion, a notch depth control portion, and a control determining portion. The first notch filter is disposed in a feedback control system and can change a notch center frequency and a notch depth. The oscillation extracting filter extracts an oscillation component caused by machine resonance and outputs the oscillation component as an extracting oscillation signal. The second notch filter inputs the extracting oscillation signal and can change the notch center frequency. The notch control portion changes the notch center frequency of the first notch filter and the notch center frequency of the second notch filter to decrease an amplitude of a second notch filter output signal based on the extracting oscillation signal and the second notch filter output signal. The notch depth control portion changes the notch depth of the first notch filter based on the extracting oscillation signal. The control determining portion carries out control to operate either the notch control portion or the notch depth control portion based on the extracting oscillation signal and the second notch filter output signal. 
     Thus, the motor control apparatus according to the present invention can set the notch center frequency which is coincident with the oscillation frequency of the machine resonance and the optimum value of the notch depth coefficient for suppressing the machine resonance, and can always suppress the machine resonance stably. According to the motor control apparatus in accordance with the present invention, therefore, it is possible to always suppress the machine resonance stably. It is possible to provide a motor control apparatus for controlling a moving operation of a motor or a load thereof while always ensuring a stable control state. 
     In each of the exemplary embodiments according to the present invention, the description has been given by taking an example of the speed control system as the control system. In the present invention, however, the same function and effect can be exhibited even if there is employed a system structure using a position control system in place of the speed control system. 
     In each of the exemplary embodiments, moreover, the description has been given by taking an example in which the speed detector detects the speed of the movable portion of the motor. In the present invention, however, it is also possible to employ such a system structure that the speed detector detects the speed of the load. In the present invention, furthermore, it is also possible to employ such a structure that the position of the movable portion or the load of the motor is detected by the position detector and is controlled by the position control system. In the present invention, moreover, it is also possible to employ a control system including a position detector having a structure containing a circuit for differentiating a detection position into a detection speed or a position control system including a speed detector having a structure containing a circuit for integrating a detection speed to detect a position. In other words, the present invention can be applied to a control system for carrying out feedback control in such a manner that the moving operation of the movable portion through the motor follows a moving quantity such as an ordered position or speed. In addition, the moving operation may be a rotating operation of the movable portion through the motor, a rectilinear motion or other motions. 
     In each of the exemplary embodiments, furthermore, if the amplitude of signal x 1  is zero or is equal to or smaller than the threshold, the changing operation for set value cn 2  is stopped. In the present invention, however, there is employed a structure in which the changing operation is stopped depending on a moving average value based on a moving average of the amplitude of signal x 1 . 
     In each of the exemplary embodiments, moreover, set value cn 2  is gradually changed by the notch depth control portion. In the present invention, however, it is also possible to employ a structure in which a change quantity is successively decided based on at least one of a control system gain, a change quantity of the control system gain, and a detection unit of a detection signal. 
     In each of the exemplary embodiments, furthermore, the description has been given to the motor control apparatus for changing the filter coefficient of the notch filter to suppress the machine resonance. However, the present invention is not restricted to the structures described above but the same effect can be obtained depending on the contents described in the exemplary embodiments by any motor control apparatus for detecting an oscillation component and changing a notch frequency or a notch depth of a notch filter disposed in a speed control or position control system based on a result of the detection, thereby suppressing machine resonance. 
     Industrial Applicability 
     A motor control apparatus according to the present invention can suppress an oscillation of machine resonance or the like with high precision and can always control a motor stably. Therefore, the present invention is suitable for an apparatus using a motor such as a component mounting machine or a semiconductor manufacturing apparatus, and particularly, a motor control apparatus for driving such a device as to cause machine resonance.