Abstract:
Provided is a feed shaft control method, wherein a speed feedback loop having a speed controller is disposed within a position feedback loop having a position controller, forming a cascade coupling, and an acceleration feedback signal which is outputted from a compensator on the basis of an output signal of an acceleration detector is subtracted from a torque instruction. Furthermore, the method implements control wherein a speed is acquired on the basis of the output signal of the acceleration detector, and a signal obtained by multiplying the acquired speed by a gain is added to a speed instruction which is outputted from the position controller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Phase patent application of International Patent Application No. PCT/JP2014/056940, filed Mar. 14, 2014, which is hereby incorporated by reference in the present disclosure in its entirety. 
         [0002]    Field of the Invention 
         [0003]    The present invention relates to a feed axis control method of a machine tool and a numerical control machine tool. 
         [0004]    Background Art 
         [0005]    In conventional techniques, a machine tool which performs machining, such as cutting by relatively moving a tool relative to a workpiece is known. Further, in such a machine tool, a numerical control machine tool which specifies a path of the tool by coordinates of a predetermined axis, and the like, and performs machining by automatically moving the tool relative to the workpiece is known. The numerical control machine tool can perform machining in a desired tool path and at a desired speed by specifying machine coordinates and a movement speed of the tool in a machining program. 
         [0006]    Japanese Laid-open Patent Publication No. 2006-158026 discloses a control device of a machine tool in which a driven element driven by a servo motor is provided with an acceleration detection means. This control device perform correction by obtaining a speed estimation value by integrating an acceleration detection value detected by the acceleration detection means and subtracting a value in which the speed estimation value is multiplied by a coefficient and a value in which the acceleration detection value is multiplied by a coefficient from an electric current command determined by a speed control processing part. Then, the electric current command corrected by the control device is outputted to a servo amplifier. 
       SUMMARY OF THE INVENTION 
       [0007]    In the control device which controls a servo motor which drives each of axes of the machine tool, a position controller generates a speed command based on a position command, and a speed controller generates a torque command based on the speed command. Then, the motor is driven based on the torque command. Further, it is known that a movement device which moves the tool and the workpiece is provided with the position detector and a position feedback loop which subtracts a position signal outputted from the position detector from the position command is arranged. In addition, it is known that the speed detector is disposed at an output axis of the servo motor, and the like and a speed feedback loop which subtracts a speed signal outputted from the speed detector from the speed command is arranged. 
         [0008]    When the workpiece is machined by the machine tool, a disturbance force is applied to the movement device which moves the workpiece and the tool so that a vibration may be generated on the workpiece or the tool. For example, at a machine point at which the tool is in contact with the workpiece, a cutting load and the like are applied to the workpiece and the tool so that a vibration may be generated. To improve a machining accuracy, such a vibration of the workpiece and the tool is preferably restrained. 
         [0009]    In the control device in Japanese Laid-open Patent Publication No. 2006-158026 as described above, an acceleration of the driven element is fed back to the torque command of the motor, thereby restraining the vibration. However, in such a circuit, the acceleration detection means is disposed at the driven element. In other words, the acceleration detection means is disposed at a position away from the output axis of the motor. Consequently, due to the feedback of the acceleration of the driven element, a position deflection is apt to be generated in the position command outputted from the position controller, and a speed deflection is apt to be generated in the speed command outputted from the speed detector. These deflections influence also upon a control of an electric current supplied to the motor, and there is a problem that an effect of restraining the vibration is reduced. 
         [0010]    A first feed axis control method of the present invention is a feed axis control method of a machine tool, including forming a cascade connection in which a speed feedback loop including a speed control part into which a speed command is inputted is provided inside a position feedback loop including a position control part into which a position command is inputted, and controlling a servo motor for driving a feed axis in accordance with a torque command outputted from the speed control part. The feed axis control method includes obtaining an acceleration based on an output signal of a state sensor attached to at least one of a machine structure and an axis feed mechanism, and subtracting an acceleration feedback signal in which the obtained acceleration is multiplied by a predetermined first gain from the torque command outputted from the speed control part. The feed axis control method includes performing at least one of controls consisting of a control in which a speed is obtained based on the output signal of the state sensor and a signal in which the obtained speed is multiplied by a predetermined gain is added to the speed command outputted from the position control part and a control in which a position is obtained based on the output signal of the state sensor and a signal in which the obtained position is multiplied by a predetermined gain is added to the position command inputted into the position control part. 
         [0011]    In the invention as described above, a speed is obtained based on an output signal of the state sensor, and a signal in which the obtained speed is multiplied by a predetermined second gain can be added to the acceleration feedback signal. 
         [0012]    In the invention as described above, a signal in which the speed command outputted from the position control part is multiplied by a predetermined third gain can be subtracted from a signal multiplied by the second gain. 
         [0013]    In the invention as described above, a position is obtained based on an output signal of the state sensor, and a signal in which the obtained position is multiplied by a predetermined fourth gain can be added to the acceleration feedback signal. 
         [0014]    In the invention as described above, a signal in which the position command inputted into the position control part is multiplied by a predetermined fifth gain can be subtracted from a signal multiplied by the fourth gain. 
         [0015]    In the invention as described above, a signal in which the torque command outputted from the speed control part is multiplied by a predetermined sixth gain can be subtracted from the acceleration feedback signal. 
         [0016]    In the invention as described above, the first gain and the second gain can be set so that an additional value of a square of the first gain and a square of the second gain is a predetermined set value. 
         [0017]    A second feed axis control method of the present invention is a feed axis control method of a machine tool, including forming a cascade connection in which a speed feedback loop including a speed control part into which a speed command is inputted is provided inside a position feedback loop including a position control part into which a position command is inputted, and controlling a servo motor for driving a feed axis in accordance with a torque command outputted from the speed control part. The feed axis control method includes obtaining an acceleration based on an output signal of a state sensor attached to at least one of a machine structure and an axis feed mechanism and subtracting an acceleration feedback signal in which the obtained acceleration is multiplied by a predetermined gain from the torque command outputted from the speed control part. The feed axis control method includes performing at least one of controls consisting of a control in which a speed is obtained based on the output signal of the state sensor and a signal in which the obtained speed is multiplied by a predetermined gain is added to the acceleration feedback signal and a control in which a position is obtained based on the output signal of the state sensor and a signal in which the obtained position is multiplied by a predetermined gain is added to the acceleration feedback signal. 
         [0018]    A first numerical control machine tool of the present invention comprises a control device in which a cascade connection in which a speed feedback loop including a speed control part into which a speed command is inputted is provided inside a position feedback loop including a position control part into which a position command is inputted is formed, and which controls a servo motor for driving a feed axis in accordance with a torque command outputted from the speed control part. The control device includes a circuit in which an acceleration is obtained based on an output signal of a state sensor attached to at least one of a machine structure and an axis feed mechanism and signal in which the obtained acceleration is multiplied by a predetermined gain is subtracted from the torque command outputted from the speed control part. The control device includes at least one of circuits consisting of a circuit in which a speed is obtained based on the output signal of the state sensor and a signal in which the obtained speed is multiplied by a predetermined gain is added to the speed command outputted from the position control part and a circuit in which a position is obtained based on the output signal of the state sensor and a signal in which the obtained position is multiplied by a predetermined gain is added to the position command inputted into the position control part. 
         [0019]    A second numerical control machine tool of the present invention includes a control device, in which a cascade connection in which a speed feedback loop including a speed control part into which a speed command is inputted is provided inside a position feedback loop including a position control part into which a position command is inputted is formed, and which controls a servo motor for driving a feed axis in accordance with a torque command outputted from the speed control part. The control device includes a circuit in which an acceleration is obtained based on an output signal of a state sensor attached to at least one of a machine structure and an axis feed mechanism and an acceleration feedback signal in which the obtained acceleration is multiplied by a predetermined gain is subtracted from the torque command outputted from the speed control part. The control device includes at least one of circuits consisting of a circuit in which a speed is obtained based on the output signal of the state sensor and a signal in which the obtained speed is multiplied by a predetermined gain is added to the acceleration feedback signal and a circuit in which a position is obtained based on the output signal of the state sensor and a signal in which the obtained position is multiplied by a predetermined gain is added to the acceleration feedback signal. 
         [0020]    Preferably, in the invention as described above, a table to which a workpiece is fixed, a tool support member which supports a tool, and a movement device which moves the table and the tool support member are provided, and the state sensor includes an acceleration detector disposed at the table and an acceleration detector disposed at the tool support member. 
         [0021]    According to the present invention, a feed axis control method of a machine tool and a numerical control machine tool which restrain a vibration at a machine point can be provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic side view of a numerical control machine tool. 
           [0023]      FIG. 2  is a block diagram of the machine tool. 
           [0024]      FIG. 3  is a block diagram of a first control device and a drive mechanism of a machine structure according to a first embodiment. 
           [0025]      FIG. 4  is a block diagram of a control device and the drive mechanism of the machine structure of a reference example according to the first embodiment. 
           [0026]      FIG. 5  is a graph illustrating a speed command and an acceleration detection value when the controls are performed by the control device of the reference example according to the first embodiment. 
           [0027]      FIG. 6  is a graph illustrating the speed command and the acceleration detection value when the controls are performed by the first control device according to the first embodiment. 
           [0028]      FIG. 7  is a block diagram of a second control device and the drive mechanism of the machine structure according to the first embodiment. 
           [0029]      FIG. 8  is a block diagram of the first control device and the drive mechanism of the machine structure according to the second embodiment. 
           [0030]      FIG. 9  is a block diagram of the second control device and the drive mechanism of the machine structure according to the second embodiment. 
           [0031]      FIG. 10  is a block diagram of the first control device and the drive mechanism of the machine structure according to a third embodiment. 
           [0032]      FIG. 11  is a block diagram of the control device and the drive mechanism of the machine structure of the reference example according to the third embodiment. 
           [0033]      FIG. 12  is a block diagram of the first control device and the drive mechanism of the machine structure according to a fourth embodiment. 
           [0034]      FIG. 13  is a block diagram of the second control device and the drive mechanism of the machine structure according to the fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    A feed axis control method of a machine tool and a numerical control machine tool according to a first embodiment will be described with reference to  FIG. 1  to  FIG. 7 . As the machine tool, a horizontal machining center in which a spindle extends in a horizontal direction will be described as an example. 
         [0036]      FIG. 1  is a schematic side view of a numerical control machine tool according to the present embodiment. A machine tool  10  includes a movement device which relatively moves a tool  22  and a workpiece  1 . The movement device moves a driven element in a direction of a plurality of movement axes. The plurality of movement axes include an X-axis, Y-axis, and a Z-axis as linear feed axes which are orthogonal to each other. 
         [0037]    The machine tool  10  includes a bed  12  disposed on a floor surface of a factory and the like. A Z-axis guide rail  28  is fixed to an upper surface of the bed  12 . The Z-axis guide rail  28  extends in a Z-axis direction (left-right direction in  FIG. 1 ). A table base  13  is disposed on an upper surface of the Z-axis guide rail  28 . The table base  13  is guided by the Z-axis guide rail  28  and disposed in a manner movable in the Z-axis direction. A table  14  is fixed to the table base  13 . The workpiece  1  is fixed to the table  14 . 
         [0038]    An X-axis guide rail  36  is fixed on the upper surface of the bed  12 . The X-axis is orthogonal to the Z-axis and further extends in a horizontal direction (a direction vertical to the page). The X-axis guide rail  36  extends along the X-axis. A column  16  is guided by the X-axis guide rail  36  and disposed in a manner movable in an X-axis direction. 
         [0039]    In the column  16 , a Y-axis guide rail  32  is fixed on a front surface opposed to the workpiece  1 . The Y-axis extends in a direction orthogonal to the X-axis and the Z-axis. The Y-axis guide rail  32  extends along the Y-axis. A spindle head  18  is disposed on the Y-axis guide rail  32 . The spindle head  18  is guided by the Y-axis guide rail  32  and formed in a manner movable in a Y-axis direction. The spindle head  18  supports a spindle  20 . 
         [0040]    The movement device includes a Z-axis movement device which relatively moves the tool  22  relative to the workpiece  1  in the Z-axis direction. In the interior of the bed  12 , a ball screw mechanism including a Z-axis feed screw and a nut is disposed. The nut is fixed to a lower surface of the table base  13 . The nut is engaged with the Z-axis feed screw. A Z-axis servo motor  25  is connected to an end portion of the Z-axis feed screw on one hand. The table base  13  moves along the Z-axis guide rail  28  by driving the Z-axis servo motor  25 . As a result, the workpiece  1  moves in the Z-axis direction. 
         [0041]    The movement device includes an X-axis movement device which relatively moves the tool  22  relative to the workpiece  1  in the X-axis direction. Similarly to the Z-axis movement device, the X-axis movement device includes a ball screw mechanism including an X-axis feed screw and a nut. An X-axis servo motor  38  is connected to an end portion of the X-axis feed screw on one hand. The nut which is engaged with the X-axis feed screw is fixed to a lower surface of the column  16 . By driving the X-axis servo motor  38 , the column  16  moves along the X-axis guide rail  36 . As a result, the tool  22  moves in the X-axis direction. 
         [0042]    The movement device includes a Y-axis movement device which relatively moves the tool  22  relative to the workpiece  1  in the Y-axis direction. Similarly to the Z-axis movement device, the Y-axis movement device includes a ball screw mechanism including a Y-axis feed screw and a nut. The nut which is engaged with the Y-axis feed screw is fixed to the spindle head  18 . A Y-axis servo motor  31  is connected to an upper end of the Y-axis feed screw. By driving the Y-axis servo motor  31 , the spindle head  18  moves along the Y-axis guide rail  32 . As a result, the tool  22  moves in the Y-axis direction. 
         [0043]    The tool  22  is mounted through a tool holder  21  on a tip end of the spindle  20 . The spindle  20  functions as a tool support member which supports the tool  22 . In the spindle  20 , a motor for rotating the tool  22  is housed. This motor drives so that the tool  22  rotates about a center axis of the spindle  20  as a rotation axis. 
         [0044]    Thus, in the machine tool  10 , the column  16 , the spindle head  18 , and the table base  13  are moved along the movement axes, whereby the tool  22  can be relatively moved relative to the workpiece  1 . Note that the machine tool may include a rotation feed axis which rotates around a predetermined axial line in addition to the linear feed axes. 
         [0045]    The machine tool  10  includes speed detectors for each axis. A speed detector  29  which detects a rotation speed of the Z-axis servo motor  25  is attached to the Z-axis servo motor  25 . The speed detector  29  includes, for example, a rotary encoder, and can detect a speed based on an output of the rotary encoder. Further, a speed detector  33  is attached to the Y-axis servo motor  31 . A speed detector  39  is attached to the X-axis servo motor  38 . The speed detectors  29 ,  33 ,  39  for each axis are disposed, whereby a movement speed in an each axis direction can be detected. 
         [0046]    The machine tool  10  includes position detectors for each axis. A Z-axis position detector includes a slider  13   a  attached to the table base  13  and a Z-axis linear scale  30  attached to the bed  12 . The slider  13   a  moves on the Z-axis linear scale  30 , whereby a position in the Z-axis direction can be detected. Further, a Y-axis position detector includes a slider  18   a  attached to the spindle head  18  and a Y-axis linear scale  34  attached to the column  16 . The slider  18   a  moves on the Y-axis linear scale  34 , whereby a position in the Y-axis direction can be detected. Further, an X-axis position detector includes a slider  16   a  attached to the column  16  and an X-axis linear scale  40  attached to the bed  12 . The slider  16   a  moves on the X-axis linear scale  40 , whereby a position in the X-axis direction can be detected. 
         [0047]    Further, an acceleration detector  45  is disposed at the spindle  20  which supports the tool  22 . The acceleration detector  45  is preferably disposed adjacent to a machine point of the tool  22 . In addition, an acceleration detector  46  is disposed at the table  14 . The acceleration detector  46  is preferably disposed adjacent to a machine point of the workpiece  1 . The acceleration detectors  45 ,  46  can detect an acceleration of each axis. In other words, the acceleration detectors  45 ,  46  can separately detect an acceleration in the X-axis direction, an acceleration in the Y-axis direction, and an acceleration in the Z-axis direction. Note that, when the machine tool includes the rotation feed axis, the acceleration detector is disposed at a position at which a direction of the detector does not change relative to a rotation axis when a movement device of the rotation feed axis operates. 
         [0048]    An output signal of the speed detectors  29 ,  33 ,  39 , the position detectors, and the acceleration detectors  45 ,  46  for each axis is inputted into a control device  50 . 
         [0049]      FIG. 2  shows a block diagram of the machine tool according to the present embodiment. The machine tool  10  includes the control device  50 . The control device  50  is connected to a servo motor  55  of the movement devices. The control device  50  controls the servo motor  55 , whereby the tool  22  can be relatively moved with respect to the workpiece  1 . 
         [0050]    The control device  50  includes a reading interpretation part  52 , an interpolation calculation part  53 , and a servo motor control part  54 . The reading interpretation part  52  reads an input program  51  and transmits a movement command to the interpolation calculation part  53 . The interpolation calculation part  53 , for example, outputs a position command qr at intervals of a predetermined time based on the movement command. The servo motor control part  54  drives the servo motor  55  of each axis based on the position command qr. In the present embodiment, the servo motor  55  of each axis corresponds to the X-axis servo motor  38 , the Y-axis servo motor  31 , or the Z-axis servo motor  25 . 
         [0051]    The servo motor  55  of each axis drives a machine structure  57  through an axis feed mechanism  56 . The machine structure  57  corresponds to a structure which holds the tool  22  or a structure which holds the workpiece  1 . In the present embodiment, the machine structure  57  corresponds to the spindle  20  or the table  14 . In addition, the axis feed mechanism  56  corresponds to a mechanism which drives the machine structure  57 . In the present embodiment, the axis feed mechanism  56  corresponds to the ball screw mechanism connected to the servo motor  55  of each axis. As the axis feed mechanism  56 , in addition to the ball screw mechanism, a reduction gear attached to the servo motor, and the like, can be illustrated. 
         [0052]      FIG. 3  is a block diagram of the servo motor control part of a first control device and a drive mechanism of the machine structure according to the present embodiment. A control circuit as illustrated in  FIG. 3  can be formed for each of the movement axes. For example, the single control circuit as illustrated in  FIG. 3  can be formed in the X-axis movement device in order to drive the X-axis servo motor  38 . In this case, the servo motor  55  corresponds to the X-axis servo motor  38 . A speed detector  58  corresponds to the speed detector  39  attached to the X-axis servo motor  38 . A position detector  59  corresponds to the X-axis position detector including the slider  16   a  and the X-axis linear scale  40 . An acceleration detector  60  corresponds to the acceleration detector  45  attached to the spindle  20  which holds the tool  22 . In the present embodiment, the acceleration detector  45  is used as a state sensor. The state sensor is a sensor which detects a state of a predetermined structure, i.e. an acceleration, a speed, a position, or the like of a predetermined structure irrespective of a feed axis command. 
         [0053]    The position command qr outputted from the interpolation calculation part  53  is inputted into a position controller  71  serving as a position control part. The position controller  71  generates a speed command ωr based on the position command qr. The speed command ωr outputted from the position controller  71  is inputted into a speed controller  72  serving as a speed control part. The speed controller  72  generates a torque command τr based on the speed command ωr. The torque command τr is inputted into an electric current controller  73 . The electric current controller  73  controls an electric current of the servo motor  55  so as to generate a torque corresponding to the torque command τr inputted. 
         [0054]    The drive mechanism which drives the machine structure  57  includes the axis feed mechanism  56 . The axis feed mechanism  56  supports the machine structure  57 . In an example as illustrated in  FIG. 3 , an elastic element  62  is interposed between the axis feed mechanism  56  and the machine structure  57 . The elastic element  62  is a model illustrating that a portion having a low rigidity and serving as a free end vibrates. The elastic element  62  illustrates that a rigidity between the axis feed mechanism  56  and the machine structure  57  is low and the machine structure  57  vibrates relative to the axis feed mechanism  56 . Meanwhile, connection of the servo motor  55  and the axis feed mechanism  56  is made with a high rigidity. 
         [0055]    The elastic element  62  includes an elastic body  62   a  and a damping body  62   b . The elastic body  62   a  is a model which determines a period, an amplitude, and the like of a vibration of the machine structure. The damping body  62   b  is a model which damps a vibration. The drive mechanism includes the elastic element  62  so that the machine structure  57  vibrates. Further, a position, a speed, or an acceleration of the machine structure  57  is retarded relative to an output of the servo motor  55  and a deflection is generated. 
         [0056]    The position detector  59  attached to the axis feed mechanism  56  detects a position of a predetermined axis and feeds back a position signal q to an adder  74 . The adder  74  subtracts the position signal q from the position command qr and performs transmission to the position controller  71 . The position controller  71  multiplies the inputted signal by a gain Cp to calculate the speed command ωr. The gain Cp is a function of a Laplacian s. In the present embodiment, a circuit which corrects the position command qr will be referred to as position feedback loop. 
         [0057]    The speed detector  58  attached to the servo motor  55  detects a speed at a predetermined axis. The speed detector  58  feeds back a speed signal ω to the adder  75 . The adder  75  subtracts the speed signal ω from the speed command ωr and performs transmission to the speed controller  72 . The speed controller  72  multiplies the inputted signal by a gain Cv to calculate the torque command τr. The gain Cv is a function of the Laplacian s. In the present embodiment, a circuit which corrects the speed command ωr will be referred to as speed feedback loop. 
         [0058]    Thus, the speed feedback loop including the speed control part into which the speed command ωr is provided inside the position feedback loop including the position control part into which the position command qr is inputted so as to form a cascade connection. In this control, a position and a speed at present corresponding to the output from the servo motor  55  are detected so that a retard relative to the feed axis command can be corrected. This control is also referred to as servo control. Note that a gain of each compensator included in the control circuit is determined in advance and an optimal value is preferably adopted. 
         [0059]    A control device of a reference example according to the present embodiment will be described.  FIG. 4  is a block diagram of a servo motor control part of the reference example and the drive mechanism of the machine structure according to the present embodiment. Also in the reference example as illustrated in  FIG. 4 , the elastic element  62  is interposed between the axis feed mechanism  56  and the machine structure  57 . From the acceleration detector  60  attached to the machine structure  57 , an acceleration signal is outputted. The acceleration signal is multiplied by a gain K 1  in a compensator  91  and outputted to an adder  141 . 
         [0060]    Meanwhile, the acceleration signal outputted from the acceleration detector  60  is integrated by an integrator  77  to be converted into a speed signal. Then, in an adder  142 , the speed command outputted by the position controller  71  is subtracted from the speed signal outputted from the integrator  77 . In the adder  142 , a speed deflection between a speed of the machine structure  57  and the speed command ωr can be calculated. 
         [0061]    An output signal of the adder  142  is inputted into a compensator  92 . In the compensator  92 , multiplying by a gain K 2  is performed. An output of the compensator  92  is inputted into the adder  141 . 
         [0062]    In the adder  141 , an output signal of the compensator  91  and an output signal of the compensator  92  are added. An output signal of the adder  141  is inputted through a filter  81  into an adder  144 . In the adder  144 , the output signal of the adder  141  is subtracted from the torque command τr outputted from the speed controller  72 . 
         [0063]    A circuit passing through the compensator  91  is a circuit in which an acceleration of the machine structure  57  is fed back. A circuit passing through the compensator  92  is a circuit in which a speed of the machine structure is fed back. The circuits make a vibration of the machine structure  57  to be restrained. In particular, by changing values of the gain K 1  and the gain K 2 , a phase of a speed feedback relative to a phase of an acceleration feedback is adjusted so that a vibration of the machine structure  57  can be restrained. 
         [0064]    However, the elastic element  62  is interposed between the machine structure  57  at which the acceleration detector  60  is disposed and the servo motor  55 . When the torque command τr outputted from the speed controller  72  is corrected by an acceleration feedback signal, there has been a case in which a deflection of the position command qr or the speed command ωr is generated. In particular, when an acceleration of the machine structure  57  changes, a deflection of the position command qr or the speed command ωr becomes large, and the servo control is performed through the position feedback loop and the speed feedback loop, so that there has been a case in which the acceleration feedback signal which restrains a vibration of the machine structure is cancelled by the servo control. 
         [0065]    In the control device according to the present embodiment, an acceleration of the machine structure and the like are detected irrespective of each axis command so as to be reflected upon the each axis command, and a stabilization control for stabilizing a drive of the machine structure is performed. With reference to  FIG. 3 , the control device according to the present embodiment includes a stabilization compensation circuit  121  for machine structure. The stabilization compensation circuit  121  for machine structure restrains a vibration of the machine structure  57 . A signal outputted from the acceleration detector  60  is inputted into the stabilization compensation circuit  121  for machine structure. 
         [0066]    The acceleration signal detected by the acceleration detector  60  is inputted into the compensator  91 . In the compensator  91 , multiplying by a gain K 11  as a first gain is performed. An output signal of the compensator  91  is inputted into the adder  144 , passing through the adder  141  and the filter  81 . This circuit is an acceleration feedback circuit. In other words, the torque command τr outputted from the speed controller  72  is corrected by feeding back an acceleration of the machine structure  57 . 
         [0067]    The acceleration signal detected by the acceleration detector  60  is converted by an integrator  77   a  into a speed signal. The speed signal is inputted into a compensator  101 . In the compensator  101 , multiplying by a gain Ka 3  is performed. An output signal of the compensator  101  is inputted into an adder  151  through the filter  81 . In the adder  151 , the output signal of the compensator  101  is added to the speed command ωr outputted from the position controller  71 . Note that the gain Ka 3  according to the present embodiment is set to be a negative gain. 
         [0068]    Such a control circuit can cancel a speed deflection generated due to a circuit which includes the compensator  91  and in which an acceleration is fed back. The speed command τr in which a speed deflection has been cancelled can be transmitted to the speed controller  72 . In other words, a signal in which a speed deflection has been cancelled can be set as a control target. 
         [0069]    Accordingly, a vibration of the machine structure  57  can be restrained. 
         [0070]    Further, the speed signal outputted from the integrator  77   a  is integrated by an integrator  77   b . A position signal is outputted from the integrator  77   b . The position signal is inputted into a compensator  102 . In the compensator  102 , multiplying by a gain Ka 5  is performed. An output signal of the compensator  102  is inputted into an adder  152  through the filter  81 . In the adder  152 , the output signal of the compensator  102  is added to the position command qr. Note that the gain Ka 5  according to the present embodiment is set to be a negative gain. 
         [0071]    Such a control circuit can cancel a position deflection generated due to a circuit which includes the compensator  91  and in which an acceleration is fed back. The position command qr in which a position deflection has been cancelled can be transmitted to the position controller  71 . In other words, a signal in which a position deflection has been cancelled can be set as a control target. Accordingly, a vibration of the machine structure  57  can be restrained. 
         [0072]    In the present embodiment, both a circuit which includes the compensator  101  and in which a speed deflection is cancelled and a circuit which includes the compensator  102  and in which a positon deflection is cancelled are disposed, but this configuration is not limitative, and disposing one of the circuits can restrain a vibration of the machine structure  57 . 
         [0073]    As the feed axis control method according to the present embodiment, at least one control among the control in which a speed is obtained based on an output signal of the acceleration detector  60  and a signal in which the obtained speed is multiplied by the predetermined gain Ka 3  is added to the speed command outputted from the position controller  71  and the control in which a position is obtained based on the output signal of the acceleration detector  60  and a signal in which the obtained position is multiplied by the predetermined gain Ka 5  is added to the position instruction qr to be inputted into the position controller  71  is performed. By adopting this method, a vibration of the machine structure  57  can be restrained. 
         [0074]    In addition, the first control device according to the present embodiment corrects the torque command τr based on, in addition to the acceleration feedback signal, a feedback signal of a speed of the machine structure  57  and a feedback signal of a position of the machine structure  57 . A speed signal outputted from the integrator  77   a  is inputted into the compensator  92 . In the compensator  92 , multiplying by a gain Ka 21  as a second gain is performed. An output signal of the compensator  92  is inputted into the adder  141  through the adder  142 . Further, a position signal outputted from the integrator  77   b  is inputted into the compensator  93 . In the compensator  93 , multiplying by a gain Ka 41  as a fourth gain is performed. An output signal of the compensator  93  is inputted through the adders  143 ,  142  into the adder  141 . 
         [0075]    In the adder  141 , the acceleration feedback signal outputted from the compensator  91 , the speed feedback signal outputted from the compensator  92 , and the position feedback signal outputted from the compensator  93  are added. Then, this feedback signal is inputted into the adder  144  through the filter  81 . In the adder  144 , this feedback signal is subtracted from the torque command τr. 
         [0076]    In the control device according to the present embodiment, the speed feedback signal and the position feedback signal are added to the acceleration feedback signal. In circuits of the respective feedback signals, the gain Ka 11  of the compensator  91 , the gain Ka 21  of the compensator  92 , and the gain Ka 41  of the compensator  93  can be independently set. Accordingly, an influence by an acceleration can be adjusted by the gain Ka 11 , an influence by a speed can be adjusted by the gain Ka 21 , and further, an influence by a position can be adjusted by the gain Ka 41 . A value of the gains Ka 11 , Ka 21 , Ka 41  is set to be a appropriate value, whereby a vibration of the machine structure  57  can be effectively restrained. Further, the value of the gains Ka 11 , Ka 21 , Ka 41  is adjusted, whereby, without the elastic element  62 , a control when the machine structure  57  is supported by the axis feed mechanism  56  with a rigid structure can be also performed. 
         [0077]    Further, in the circuit in which an acceleration is fed back, the torque command τr outputted from the speed controller  72  is inputted into a compensator  94 . In the compensator  94 , multiplying by a gain Ka 12  as a sixth gain is performed. The gain Ka 11  and the gain Ka 12  can adopt, for example, the same value. An output signal of the compensator  94  is inputted into the adder  141 . In the adder  141 , the output signal of the compensator  94  is subtracted from the output signal of the compensator  91 . Thus, in the acceleration feedback circuit, the compensator  94  is disposed and a deflection between the acceleration feedback signal and the torque command τr is calculated. 
         [0078]    In the circuit in which a speed is fed back, the speed command ωr outputted from the position controller  71  is inputted into a compensator  95 . In the compensator  95 , multiplying by a gain Ka 22  as a third gain is performed. The gain Ka 21  and the gain Ka 22  can adopt, for example, the same value. In the adder  142 , an output signal of the compensator  95  is subtracted from the output signal of the compensator  92 . Thus, in the speed feedback circuit, the compensator  95  is disposed and a deflection between the speed feedback signal and the speed command ωr is calculated, and the deflection is inputted into the adder  141 . 
         [0079]    In the circuit in which a position is fed back, the position command qr is inputted into a compensator  96 . In the compensator  96 , multiplying by a gain Ka 42  as a fifth gain is performed. The gain Ka 41  and the gain Ka 42  can adopt, for example, the same value. In the adder  143 , an output signal of the compensator  96  is subtracted from the output signal of the compensator  93 . Thus, in the position feedback circuit, a deflection between the position feedback signal and the position command qr is calculated, and the deflection is inputted into the adder  141  through the adder  142 . 
         [0080]    The signal obtained from the acceleration detector  60  includes a component and the like indicating an acceleration serving as an original target value and a vibration component due to a vibration of the machine structure  57 . In each feedback circuit, a command value is subtracted from a value based on a detection value, whereby the component indicating an acceleration and the like serving as an original target value can be subtracted. In other words, only the vibration component can be extracted. Then, the torque command τr is corrected based on a signal in which the vibration component with respect to an acceleration, the vibration component with respect to a speed, and the vibration component with respect to a position are added. In a circuit in which a state of the machine structure is fed back, only the vibration component extracted can be fed back. Consequently, a high vibration-restraining effect can be exhibited. 
         [0081]    In the present embodiment, both the circuit including the compensator  92  in which a speed is fed back and the circuit including the compensator  93  in which a position is fed back are disposed, but this configuration is not limitative, and one of the circuits may be disposed. In addition, in each feedback circuit, circuits including the compensators  94 ,  95 ,  96  in which a deflection is calculated may not be disposed. 
         [0082]    In particular, the stabilization compensation circuit  121  for machine structure can be configured by two compensators which are the compensator  91  and the compensator  94 , the adder  141 , and the filter  81 . Also in this case, in the acceleration feedback circuit, a deflection between the acceleration feedback signal and the torque command τr is calculated in the adder  141 , and the vibration component of the acceleration can be transmitted to the adder  144  so that a vibration of the machine structure  57  can be restrained. 
         [0083]    The filter  81  preferably damps a signal other than a signal in a desired frequency band. For example, the filter  81  is preferably a filter which allows a signal in a band of a resonance frequency of the machine tool  10  to pass. The resonance frequency of the machine tool  10  depends on a structure of the machine tool  10  and the like. As the filter  81 , a desired filter such as a high pass filter, a low pass filter, a notch filter, and a band pass filter can be used. Alternatively, a signal in a desired frequency band is allowed to pass by combining the filters. 
         [0084]    Next, a method for setting the gain K 1  of the compensator  91  and the gain K 2  of the compensator  92  will be described with reference to  FIG. 4 . The gain K 1  corresponds to the first gain and the gain K 2  corresponds to the second gain. The speed signal outputted from the integrator  77  has a phase difference relative to the acceleration signal. The gain K 1  and the gain K 2  are changed, whereby a phase of the speed feedback signal relative to the acceleration feedback signal can be changed. 
         [0085]    When a circuit of the compensator  92  is absent, i.e. when the gain K 2  is zero, the gain K 1  is increased, whereby an effect of the acceleration feedback can be increased. However, when the gain K 1  is increased too largely, an oscillation occurs. Then, the gain K 1  which is large to such an extent that an oscillation does not occur can be selected. In the gain K 1 , an effect of the acceleration feedback can be increased while an oscillation is suppressed. The maximum gain K 1  will be referred to as set value R. The set value R can be determined in advance. Subsequently, the gain K 1  and the gain K 2  are determined so that an output value from the adder  141  does not exceed the set value R. The gain K 1  and the gain K 2  can be set so as to satisfy the following equation. 
         [0000]        K 1 2   +K 2 2   =R   2    (1)
 
         [0086]    Then, using a virtual angle θ, the gain K 1  and the gain K 2  can be expressed by the following equations. 
         [0000]      K1=R cos θ  (2)
 
         [0000]      K2=R sin θ  (3)
 
         [0087]    By selecting the angle θ, a phase of the speed feedback signal relative to the acceleration feedback signal can be optionally set. The angle θ can be set so that a vibration of the machine structure  57  is minimum. Alternatively, the gain K 1  and the gain K 2  can be set so that the relationship of equation (1) is satisfied and a vibration of the machine structure  57  is minimum. The gain K 1  and the gain K 2  are thus set so that an oscillation due to a set value of the gains is suppressed while a vibration of the machine structure  57  can be effectively restrained. 
         [0088]    In the control device according to the present embodiment as illustrated in  FIG. 3 , similarly as described above, the gain Ka 11  of the compensator  91  and the gain Ka 21  of the compensator  92  can be set. In other words, the gain Ka 11  and the gain Ka 21  can be set so as to satisfy the following equation. Note that, as described above, the gain Ka 11  corresponds to the first gain and the gain Ka 21  corresponds to the second gain. 
         [0000]        Ka 11 2   +Ka 21 2   =R   2    (4)
 
         [0089]    Then, using the virtual angle θ, the gain Kall and the gain Ka 21  can set as the following equations. 
         [0000]      Ka11=R cos θ  (5)
 
         [0000]      Ka12=R sin θ  (6)
 
         [0090]    Next, with respect to the first control device and the control device of the reference example according to the present embodiment, a result in which a simulation of machining of the machine tool is performed will be described. 
         [0091]      FIG. 5  is a graph of a result of a simulation of a drive by the control device of the reference example as illustrated in  FIG. 4 . A one-dot chain line illustrates a speed command value and a solid line illustrates a detection value of an acceleration of the machine structure. At time t 0 , the speed command value and the acceleration are both zero. Then, it is apparent that after the acceleration is changed, even at an interval in which a command acceleration is constant, the detection value of the acceleration vibrates. For example, at time t 1 , the speed command value is changed to accelerate. From time t 1  to time t 2 , although the command acceleration is constant, the detection value of the acceleration vibrates. In addition, after the acceleration is changed at times t 2 , t 3 , t 4 , t 5 , the detection value of the acceleration vibrates. Further, although the speed command value is configured to be zero at time t 6 , a residual vibration is generated. 
         [0092]      FIG. 6  shows a graph of a result of a simulation of a drive by the first control device according to the present embodiment as illustrated in  FIG. 3 . Note that, in the simulation, the gains of the compensators  93 ,  96 ,  102  are configured to be zero in the circuit of  FIG. 3 . In other words, the simulation is performed without using the circuit in which a position deflection is cancelled and the circuit in which a position is fed back. It is apparent that at an interval from time t 1  to time t 2 , an interval from time t 2  to time t 3 , and the like, a vibration of the detection value of the acceleration is restrained in comparison with the control device of the reference example. It is apparent that the detection value of the acceleration indicates a substantially constant value. Further, it is apparent that a residual vibration after time t 6  is also restrained in comparison with the control device of the reference example. Thus, by adopting the control device according to the present embodiment, a vibration of the machine structure can be restrained. 
         [0093]      FIG. 7  is a block diagram illustrating a second control device and the drive mechanism of the machine structure according to the present embodiment. With reference to  FIG. 3 , in the first control device, the respective feed axis command is inputted into the compensators  94 ,  95 ,  96  in the acceleration feedback circuit, in the speed feedback circuit, or in the position feedback circuit. For example, the speed command ωr is inputted into the compensator  95 . However, the command inputted into the compensators  94 ,  95 ,  96  is a command corrected by the other circuits. For example, the position command qr inputted into the compensator  96  is a command corrected by an output of the compensator  102  in the circuit in which a position deflection is cancelled. 
         [0094]    With reference to  FIG. 7 , in the second control device, a signal based on the position command qr uncorrected is inputted into the compensators  94 ,  95 ,  96 . Into the compensator  96 , the position command qr outputted from the interpolation calculation part  53 , i.e. the position command qr uncorrected is inputted. In other words, a signal before being corrected by the adder  152  is inputted into the compensator  96 . The signal before being corrected by the adder  152  is differentiated by a differentiator  78   a  and inputted into the compensator  95 . Further, an output signal of the differentiator  78   a  is differentiated by a differentiator  78   b  and inputted into the compensator  94 . 
         [0095]    In the second control device according to the present embodiment, since the position command qr outputted from the interpolation calculation part  53  is used, a deflection between the feedback signal of an acceleration, a speed, or a position and the feed axis command can be accurately calculated. In the adder  141 , a deflection between the acceleration feedback signal and the torque command can be accurately calculated. In the adder  142 , a deflection between the speed feedback signal and the speed command can be accurately calculated. In the adder  143 , a deflection between the position feedback signal and the speed command can be accurately calculated. As a result, the vibration component included in the signal obtained from the output signal of the acceleration detector  60  can be accurately extracted. Consequently, an effect of restraining a vibration of the machine structure  57  can be improved. The other configurations, operations, and effects are similar to the first control device. 
         [0096]    The machine tool  10  according to the present embodiment comprises the movement device which moves the table  14  and the movement device which moves the spindle  20  as the tool support member. Then, the acceleration detectors  45 ,  46  serving as the state sensor are disposed at the table  14  and the spindle  20 . The acceleration detectors are respectively disposed at the two machine structures which are moved by the movement devices. Then, the present invention is applied to the servo motor control part which controls the movement device for each movement axis, whereby a vibration of the workpiece  1  fixed to the table  14  can be restrained. In addition, a vibration of the tool  22  supported by the spindle  20  can be restrained. A vibration of the driven element of both the workpiece  1  and the tool  22  can be restrained so that highly accurate machining can be performed. 
         [0097]    The feed axis control method of the machine tool and the numerical control machine tool according to a second embodiment will be described with reference to  FIG. 8  and  FIG. 9 . The machine tool according to the present embodiment differs in a position of the elastic element from the machine tool according to the first embodiment. 
         [0098]      FIG. 8  shows a block diagram of the first control device and the drive mechanism of the machine structure according to the present embodiment. The machine tool according to the present embodiment has a structure having a high rigidity between the machine structure  57  and the axis feed mechanism  56 . On the other hand, the machine tool has a structure having a low rigidity between the axis feed mechanism  56  and the servo motor  55 . In a model of this machine tool, an elastic element  63  is present between the servo motor  55  and the axis feed mechanism  56 . The elastic element  63  includes an elastic body  63   a  and a damping body  63   b . When a disturbance force is applied to the machine structure  57 , the machine structure  57  and the axis feed mechanism  56  integrally vibrate. 
         [0099]    The drive mechanism of such a machine structure  57  is applied, for example, a case in which a constituting member of the ball screw mechanism of the movement device of each axis is elastically deformed. Note that, when the servo motor  55  directly drive the machine structure  57 , this model is not applied. For example, when the drive mechanism is of a direct drive type in which a motor is disposed in the interior of the machine structure  57 , the drive mechanism according to the present embodiment is not applied, but the drive mechanism according to the first embodiment is applied. 
         [0100]    In the present embodiment, a stabilization control for stabilizing a drive of the axis feed mechanism is performed. The servo motor control part  54  of the control device  50  includes a stabilization compensation circuit  122  for axis feed mechanism. The position signal outputted by the position detector  59  attached to the axis feed mechanism  56  is inputted into the stabilization compensation circuit  122  for axis feed mechanism. In the present embodiment, the position detector  59  functions as the state sensor which detects a state of the axis feed mechanism  56 . 
         [0101]    The position signal of the axis feed mechanism  56  which is detected by the position detector  59  is inputted into a differentiator  78 . An acceleration signal is outputted from the differentiator  78 . Then, the acceleration signal is inputted into the compensator  91  and the integrator  77   a . The other circuits of the stabilization compensation circuit  122  for axis feed mechanism of the first control device according to the present embodiment are similar to the stabilization compensation circuit  121  for machine structure of the first control device according to the first embodiment. The compensators  91 - 96 ,  101 ,  102  are similar to the compensators of the first control device according to the first embodiment (see  FIG. 3 ). The gains Kp 11 , Kp 21 , and the like of the respective compensators are set in accordance with a control circuit according to the present embodiment. 
         [0102]    By a circuit including the compensators  101 ,  102 , a speed deflection and a position deflection of the feed axis command can be cancelled. In addition, a circuit in which an acceleration of the axis feed mechanism  56  is fed back is configured by a circuit including the compensator  91 . A circuit in which a speed of the axis feed mechanism  56  is fed back and a circuit in which a position of the axis feed mechanism  56  is fed back are configured by a circuit including the compensators  92 ,  93 . By the circuit including the compensators  92 ,  93 , a speed feedback signal and a position feedback signal can be added to an acceleration feedback signal outputted from the compensator  91 , and an influence by a speed and an influence by a position can be separately adjusted in addition to an influence by an acceleration. As a result, a vibration of the machine structure  57  can be easily restrained. 
         [0103]      FIG. 9  shows a block diagram of the second control device and the drive mechanism of the machine structure according to the present embodiment. In the second control device according to the present embodiment, similarly to the second control device according to the first embodiment, a signal based on the position command qr uncorrected is inputted into the compensators  94 ,  95 ,  96 . The position command qr outputted from the interpolation calculation part  53  is inputted into the compensator  96 . In addition, the signal before being corrected by the adder  152  is differentiated by the differentiator  78   a  and inputted into the compensator  95 . Further, an output signal of the differentiator  78   a  is differentiated by the differentiator  78   b  and inputted into the compensator  94 . The other configurations of the control circuit are similar to the first control device according to the present embodiment. 
         [0104]    In the second control device according to the present embodiment, a deflection between the feedback signal of an acceleration, a speed, or a position and the feed axis command can be more accurately calculated than the first control device. As a result, a vibration restraining effect is improved. 
         [0105]    In the control device according to the present embodiment, a position detected by the position detector  59  is converted into an acceleration, and then into a speed and a position, but this configuration is not limitative, and as the speed feedback signal, an output signal of the position detector  59  may be differentiated and then multiplied by the gain Kp 21 . In addition, as the position feedback signal, the output signal of the position detector  59  may be multiplied by a gain Kp 41 . 
         [0106]    The other configurations, operations, and effects are similar to the first embodiment, description of which will not be accordingly repeated. 
       THIRD EMBODIMENT 
       [0107]    The feed axis control method of the machine tool and the numerical control machine tool according to a third embodiment will be described with reference to  FIG. 10  and  FIG. 11 . The control device according to the present embodiment performs a stabilization control for stabilizing a drive of the servo motor. 
         [0108]      FIG. 10  shows a block diagram of the control device and the drive mechanism of the machine structure according to the present embodiment. The servo motor  55 , the axis feed mechanism  56 , and the machine structure  57  are connected to each other with a high rigidity. Similarly to the first embodiment, a speed detected by the speed detector  58  is inputted into the adder  75  and the speed feedback loop is configured. In the position feedback loop, a speed signal detected by the speed detector  58  is inputted into the integrator  77 . A position signal outputted from the integrator  77  is inputted into the adder  74 . 
         [0109]      FIG. 11  shows a block diagram of the control device of the reference example and the drive mechanism of the machine structure according to the present embodiment. In the control device of the reference example, the speed signal outputted from the speed detector  58  is inputted into the differentiator  78 . An acceleration signal outputted from the differentiator  78  is inputted into a compensator  103 . In the compensator  103 , multiplying by the gain K 1  is performed. An output signal of the compensator  103  is inputted into the adder  144 . In the adder  144 , the output signal of the compensator  103  is subtracted from the torque command τr. 
         [0110]    The control device of the reference example includes a circuit in which an acceleration of the servo motor  55  is fed back and can restrain a vibration of the torque command τr. However, when a response property of the position controller  71  and the speed controller  72  is increased, a drive of the servo motor  55  may be unstable. For example, when a gain in the position controller  71  or a gain in the speed controller  72  is increased, an oscillation may be generated. In addition, since the optimal gain K 1  in the compensator  103  changes depending on a type of the machine structure  57 , setting the gain K 1  has been difficult. 
         [0111]    With reference to  FIG. 10 , the servo motor control part  54  of the control device  50  according to the present embodiment includes a stabilization compensation circuit  123  for motor. In addition, the speed detector  58  which detects a speed of the servo motor  55  is used as the state sensor. A speed signal outputted from the speed detector  58  is inputted into the differentiator  78 . The differentiator  78  outputs an acceleration signal. The acceleration signal is multiplied by a gain Kv 1  in the compensator  91 . An output signal of the compensator  91  is inputted into the adder  144  through the adder  141  and the filter  81 . In the adder  144 , an output signal of the adder  141  is subtracted from the torque command τr outputted from the speed controller  72 . In other words, a circuit in which an acceleration of the servo motor  55  is fed back is configured. As the filter  81 , a filter such as a low pass filter, which allows a desired frequency band to pass can be used. 
         [0112]    Further, the acceleration signal outputted from the differentiator  78  turns into a speed signal by passing through the integrator  77   a . The speed signal is multiplied by a gain Kv 2  by the compensator  92 . An output signal of the compensator  92  is inputted into the adder  141  through the adder  142 . In other words, a circuit in which a speed of the servo motor  55  is fed back is configured. 
         [0113]    The speed signal outputted from the integrator  77   a  is inputted into the integrator  77   b . A position signal outputted from the integrator  77   b  is multiplied by a gain Kv 3  in the compensator  93 . An output signal of the compensator  93  is inputted into the adder  141  through the adder  142 . In other words, a circuit in which a position of the servo motor  55  is fed back is configured. 
         [0114]    In the adder  142 , the output signal of the compensator  92  and the output signal of the compensator  93  are added. In the adder  141 , an output signal of the adder  142  is added to the output signal of the compensator  91 . In other words, a feedback signal of a speed and a feedback signal of a position are added to a feedback signal of an acceleration of the servo motor. Thus, a state of the servo motor  55  can be fed back and stabilizing a drive of the motor can be performed. As a result, a vibration of the machine structure  57  can be restrained. In addition, a response property of the position controller  71  and the speed controller  72  can be increased. 
         [0115]    In addition, in circuits of the respective feedback signals, the gain Kv 1  of the compensator  91 , the gain Kv 2  of the compensator  92 , and the gain Kv 3  of the compensator  93  can be independently set. Accordingly, an influence by an acceleration can be adjusted by the gain Kv 1 , an influence by a speed can be adjusted by the gain Kv 2 , and further, an influence by a position can be adjusted by the gain Kv 3 . A value of the gains Kv 1 , Kv 2 , Kv 3  is set to be an appropriate value, whereby a drive of the servo motor  55  can be effectively stabilized and a vibration of the machine structure  57  can be effectively restrained. 
         [0116]    In the control device according to the present embodiment, a speed detected by the speed detector  58  is converted into an acceleration and then is again converted into a speed, but this configuration is not limitative, and as the speed feedback signal, an output signal of the speed detector  58  may be multiplied by the gain Kv 2 . In addition, as the position feedback signal, the output signal of the speed detector  58  may be integrated and multiplied by the gain Kv 3 . 
         [0117]    The other configurations, operations, and effects are similar to the first embodiment, description of which will not be accordingly repeated. 
       FOURTH EMBODIMENT 
       [0118]    The feed axis control method of the machine tool and the numerical control machine tool according to a fourth embodiment will be described with reference to  FIG. 12  and  FIG. 13 . 
         [0119]    The control device according to the present embodiment has a configuration in which configurations of the control circuits from the first embodiment to the third embodiment are combined. In other words, the control device includes the stabilization compensation circuit  121  for machine structure according to the first embodiment, the stabilization compensation circuit  122  for axis feed mechanism according to the second embodiment, and the stabilization compensation circuit  123  for motor according to the third embodiment. 
         [0120]      FIG. 12  shows a block diagram of the first control device and the drive mechanism of the machine structure according to the present embodiment. The elastic element  63  is interposed between the servo motor  55  and the axis feed mechanism  56 . Between the axis feed mechanism  56  and the machine structure  57 , the elastic element  62  is interposed. In other words, the machine tool according to the present embodiment includes three inertial systems in which the machine structure  57  and the axis feed mechanism  56  are spring-connected and further the axis feed mechanism  56  and the servo motor  55  are spring-connected. 
         [0121]    The first control device according to the present embodiment has a configuration in which the configuration of the first control device according to the first embodiment, the configuration of the first control device according to the second embodiment, and the configuration of the first control device according to the third embodiment are combined. In the position feedback loop, a position signal from the position detector  59  is used. 
         [0122]    The acceleration detector  60  is disposed at the machine structure  57 . An acceleration signal outputted from the acceleration detector  60  is transmitted to the stabilization compensation circuit  121  for machine structure. The position detector  59  is disposed at the axis feed mechanism  56 . A position signal outputted from the position detector  59  is transmitted to the stabilization compensation circuit  122  for axis feed mechanism. Further, to the servo motor  55 , the speed detector  58  is attached. A speed signal outputted from the speed detector  58  is transmitted to the stabilization compensation circuit  123  for motor. 
         [0123]    In the respective stabilization compensation circuits  121 ,  122 ,  123 , a correction signal with respect to an acceleration is generated, and is added in adders  161 ,  162 . An acceleration feedback circuit is configured. An output signal of the adder  162  is subtracted from the torque command τr in the adder  144 . 
         [0124]    In addition, in the stabilization compensation circuit  121  for machine structure and the stabilization compensation circuit  122  for axis feed mechanism, a correction signal with respect to a speed for cancelling a speed deflection generated due to the acceleration feedback circuit is generated and added in an adder  163 . An output signal of the adder  163  is added to the speed command ωr in the adder  151 . Further, in the stabilization compensation circuit  121  for machine structure and the stabilization compensation circuit  122  for axis feed mechanism, a correction signal with respect to a position for cancelling a position deflection generated due to the acceleration feedback circuit is generated and added in an adder  164 . An output signal of the adder  164  is added to the position command qr in the adder  152 . 
         [0125]      FIG. 13  shows a block diagram of the second control device and the drive mechanism of the machine structure according to the present embodiment. The second control device according to the present embodiment has a configuration in which the configuration of the second control device according to the first embodiment, the configuration of the second control device according to the second embodiment, and the configuration of the second control device according to the third embodiment are combined. 
         [0126]    In the second control device, as the feed axis command inputted into the stabilization compensation circuit  121  for machine structure and the stabilization compensation circuit  122  for axis feed mechanism, the position command qr uncorrected is inputted. The position command qr outputted from the interpolation calculation part  53  is inputted into the stabilization compensation circuit  121  for machine structure and the stabilization compensation circuit  122  for axis feed mechanism. The other configurations are similar to the first control device according to the first embodiment. 
         [0127]    Thus, in the machine tool including the three inertial systems, the control circuit according to the first embodiment and the control circuit according to the second embodiment are combined, whereby a vibration of the machine structure  57  can be restrained. Further, the control circuit for stabilizing a drive of the servo motor  55  according to the third embodiment is combined, whereby the stabilization control including stabilizing a drive of the servo motor  55  can be performed. 
         [0128]    The control device according to the present embodiment includes three stabilization compensation circuits which are the stabilization compensation circuit  121  for machine structure, the stabilization compensation circuit  122  for axis feed mechanism, and the stabilization compensation circuit  123  for motor, but this configuration is not limitative, and, out of the three stabilization compensation circuits, two optional stabilization compensation circuits may be included. 
         [0129]    The other configurations, operations, and effects are similar to any of the first to three embodiments, description of which will not be accordingly repeated. 
         [0130]    The embodiments as described above can be suitably combined. In each control as described above, the order of the steps can be changed within a range in which functions and operations are not changed. 
         [0131]    In each drawing as described above, the same or similar components are assigned the same reference signs. Note that the embodiments as described above are illustrative and are not to limit the invention. Moreover, the embodiments include modifications of the embodiments recited in the claims. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  workpiece 
           10  machine tool 
           14  table 
           20  spindle 
           22  tool 
           25  Z-axis servo motor 
           28  Z-axis guide rail 
           29 ,  33 ,  39  speed detector 
           30  Z-axis linear scale 
           31  Y-axis servo motor 
           32  Y-axis guide rail 
           34  Y-axis linear scale 
           36  X-axis guide rail 
           38  X-axis servo motor 
           40  X-axis linear scale 
           45 ,  46  acceleration detector 
           50  control device 
           54  servo motor control part 
           55  servo motor 
           56  axis feed mechanism 
           57  machine structure 
           58  speed detector 
           59  position detector 
           60  acceleration detector 
           71  position controller 
           72  speed controller 
           91 - 96  compensator 
           101 - 102  compensator 
           121  stabilization compensation circuit for machine structure 
           122  stabilization compensation circuit for axis feed mechanism 
           123  stabilization compensation circuit for motor