JP2005121114A - Spindle device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the accuracy in rotation of a spindle of a precision lathe and the like. <P>SOLUTION: In a spindle having rotor parts 1a, 1b, a rotation angle by a motor 4 is measured by an encoder 9, the radial external force is detected by displacement sensors 5a, 5b, 7a, 7b detecting the displacement of the spindle at two parts in the circumferential direction, and the external force in the thrust direction is detected by a displacement sensor 11 at a shaft end. Electromagnets 6a-6d, 8a-8d generate the thrust for canceling the external force in the radial direction by every rotation angle on the basis of the outputs of the displacement sensors 5a, 5b, 7a, 7b, and a voice coil motor 10 generates the thrust for canceling the external force in the thrust direction on the basis of the output of the displacement sensor 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a spindle device for rotating a work piece such as a precision lathe or a processing tool such as a cutting tool with high accuracy.

2. Description of the Related Art Conventionally, a spindle that is a main shaft of an ultra-precision machining machine such as a precision lathe is generally configured to be rotatably supported by a hydrostatic air bearing. For example, as shown in FIG. 5, a hydrostatic air bearing having radial hydrostatic bearing pads 102a and 102b and thrust hydrostatic bearing pads 103a and 103b is used as a bearing that rotatably supports the rotor portion 101 of the spindle. Thus, the rotor unit 101 is rotated by the motor 104. A configuration using a hybrid bearing in which a static pressure air bearing is used as a protective bearing in combination with a magnetic bearing is also known.
Japanese Patent Laid-Open No. 04-185910

  However, according to the prior art, a spindle using a hydrostatic air bearing generally has a characteristic that it easily vibrates because the bearing stiffness of the air film and the viscosity of the bearing portion are low. For this reason, when the non-uniform pressure distribution of the air film of the bearing portion or the torque fluctuation due to the motor becomes the excitation force, the shaft shake of the spindle increases. In order to compensate for the drawbacks of such a static pressure air bearing, as described above, a spindle apparatus using a hybrid bearing using both a static pressure air bearing and a magnetic bearing has been proposed.

  However, in the case of a hybrid bearing, the disadvantage of the magnetic bearing can be compensated by the hydrostatic air bearing only in a low frequency band. Magnetic bearings perform feedback control by detecting the bearing clearance displacement so that the bearing clearance with the spindle is kept constant. Generally, when feedback control is used, the stability of the feedback control system is a constraint on the control characteristics. . In the magnetic bearing, the mechanical resonance characteristic of the spindle becomes a factor that makes the feedback control system unstable, and the frequency band in which the effect of the feedback control appears is about 1/2 to 1/3 or less of the resonance frequency. Therefore, the frequency region that can be corrected is limited to a low frequency band.

  That is, a spindle using a hybrid bearing is the same as that using a hydrostatic air bearing for high-frequency vibrations.

  On the other hand, the torque generated by the motor is not an ideal torque that works without fluctuation only in the rotation direction, but it works in the direction of the rotation axis although it is minute. In particular, the motor for driving the spindle is generally a multi-pole multi-layer motor, and phase switching is performed per rotation, and torque fluctuation is likely to occur during this phase switching. That is, the torque generated by the motor also includes a minute high frequency torque fluctuation. A part of the torque generated by the motor is an external force having a high frequency component acting on the spindle bearing.

  Although this external force is a minute force, it becomes a problem when high rotational accuracy is achieved. In conventional hydrostatic air bearings or hybrid bearings that use both hydrostatic air bearings and magnetic bearings, precision machining is required. This has been a cause of deterioration in machining accuracy of machines.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and can effectively reduce the vibration generated in the bearing portion during the rotation of the spindle and greatly improve the rotation accuracy. Is intended to provide.

  In order to achieve the above object, the spindle device of the present invention is a spindle device that rotates a rotor portion that is rotatably supported by a hydrostatic air bearing by a motor, and each of the plurality of portions that are separated in the circumferential direction of the rotor portion in the radial direction. A plurality of radial direction thrust generating means for generating a thrust in the thrust direction, a thrust direction thrust generating means for generating a thrust in the thrust direction on the rotor part, a radial direction external force detecting means for detecting an external force in the radial direction of the rotor part, Based on the thrust direction external force detection means for detecting the external force in the thrust direction of the rotor part, the encoder for measuring the rotation angle of the rotor part, the two external force detection means and the output of the encoder, the radial direction and the encoder The external force in the thrust direction is detected at every predetermined rotation angle, and the external force is canceled out. Characterized in that it has a control means for controlling said plurality of radial thrust generating means and said thrust direction thrust generating means, respectively.

  It is good to have at least two rotor parts each supported by the hydrostatic air bearing, and the said motor is arrange | positioned between both rotor parts.

  The external force detection means may include a displacement sensor for detecting the displacement of the rotor portion, and may be configured to detect the external force based on the output of the displacement sensor and the bearing rigidity of the hydrostatic air bearing.

  The external force detection means may include an accelerometer that detects the acceleration of the rotor portion.

  The radial direction thrust generating means may include an electromagnet, and the thrust direction thrust generating means may include a voice coil motor.

  By detecting the external force in the radial direction and the thrust direction applied to the rotor part during the rotation of the spindle and the rotation angle at which these external forces act, the thrust in two directions for canceling the external force is generated by a thrust generating means using an electromagnet or the like. And generated at a timing based on the output of the encoder. By canceling the external force for each angular position detected by the encoder, it effectively eliminates disturbances that cause all vibration components from high frequency to low frequency, stabilizes the bearing characteristics of the hydrostatic air bearing, Rotational accuracy can be greatly improved.

  FIG. 1 shows a spindle apparatus according to an embodiment, in which (a) is a schematic sectional view along the axial direction of the spindle, and (b) is a view when viewed from the direction of arrow A in (a). It is a figure which shows arrangement | positioning of a displacement sensor and an electromagnet.

  A spindle that holds and rotates a workpiece (workpiece) or a tool such as a cutting tool of a machine tool has first and second rotor portions 1a and 1b, and radial static pressure air bearing pads 2a and 2b. 2c, supported by a hydrostatic air bearing composed of hydrostatic air bearing pads 3a and 3b in the thrust direction, and rotatably driven by a motor 4 serving as a driving means. On the outer periphery of the rotor portion 1a on the spindle head side, two displacement sensors 5a and 5b for detecting the displacement in the radial direction have an angle shifted by 90 ° in the circumferential direction as shown in FIG. Has been placed. Further, on the spindle head side, four electromagnets 6a to 6d as radial direction thrust generating means for generating thrust in the radial direction have a phase of 90 ° in the circumferential direction of the rotor portion 1a as shown in FIG. It is arranged at a shifted angle. Similarly, two displacement sensors 7a and 7b that detect displacement in the radial direction are also arranged on the outer periphery of the rotor portion 1b on the spindle tail side at an angle that is 90 ° out of phase, and generate thrust in the radial direction. The four electromagnets 8a to 8d, which are the radial direction thrust generating means to be moved, are arranged at an angle shifted by 90 ° in phase.

  Further, on the spindle tail side, an encoder 9 that measures the rotation angle of the spindle, a voice coil motor 10 that is thrust direction thrust generating means for generating thrust in the thrust direction of the spindle, a displacement sensor 11 that detects displacement in the thrust direction, etc. Is arranged.

  In this way, the spindle is divided into two rotor parts 1a and 1b, and the motor 4 is incorporated between them, and the motor 4 is arranged at the moment center of the spindle. The rotor portions 1a and 1b are supported in the radial direction by the hydrostatic air bearing pads 2a to 2c, and supported in the thrust direction by the hydrostatic air bearing pads 3a and 3b. The rotor portions 1a and 1b are integrally rotated by the motor 4. It is done. Vibration in the radial direction is detected by the displacement sensors 5a and 5b on the rotating spindle head side, and vibration in the radial direction on the tail side is detected by the displacement sensors 7a and 7b. Further, the vibration in the thrust direction is detected by the displacement sensor 11, and the angular position of the rotating spindle is detected by the encoder 9.

  The electromagnets 6a to 6d apply thrust in the radial direction on the spindle head side, and the electromagnets 8a to 8d apply thrust in the radial direction on the spindle tail side. The voice coil motor 10 is configured to apply thrust in the thrust direction.

  FIG. 2 is a diagram showing a spindle device control system for controlling the spindle. As described above, the electromagnets 6b and 6d on the spindle head side are arranged at an angle shifted by 90 ° from the electromagnets 6a and 6c as shown in FIG. Similarly, the electromagnets 8b and 8d on the spindle tail side are arranged at an angle shifted by 90 ° from the electromagnets 8a and 8c. Further, the displacement sensor 5b on the spindle head side is arranged at an angle shifted by 90 ° from the displacement sensor 5a as shown in FIG. 1B, and the displacement sensor 7b on the spindle tail side is also phased 90 ° from the displacement sensor 7a. It is arranged at a shifted angle.

  The external force estimator 12 that constitutes the radial direction external force detection means and the thrust direction external force detection means together with the displacement sensors 5a, 5b, 7a, 7b, and 11 includes displacement signals from the displacement sensors 5a, 5b, 7a, 7b, and 11 respectively. From the bearing rigidity of the hydrostatic air bearing and the angle signal from the encoder 9, the external force in the radial direction at each of the displacement sensors 5a, 5b, 7a, 7b and the external force in the thrust direction at the displacement sensor 11 and the rotation at which these external forces act. Detect the angle. The thrust controller 13 which is a control means controls the thrust generated by the electromagnets 6a to 6d, the electromagnets 8a to 8d and the boil coil motor 10 so as to cancel these external forces for each angular position where the external force is detected. The motor controller 14 controls the rotation speed of the spindle by the motor 4.

  The spindle control device 15 controls the spindle device using the external force estimator 12, the thrust controller 13, and the motor controller 14. The drive devices 16a to 16d receive a command from the thrust controller 13 as described above, and generate thrust by the electromagnets 6a to 6d on the spindle head side. Similarly, the driving devices 17a to 17d receive a command from the thrust controller 13 and generate thrust by the electromagnets 8a to 8d on the spindle tail side. The driving device 18 drives the boil coil motor 10.

  Torque is generated in the motor 4 by the motor controller 14 to rotate the rotor portions 1a and 1b of the spindle integrally. The vibration of the spindle at this time is mainly determined by the relationship between the external force acting on the rotating shaft and the bearing rigidity of the hydrostatic air bearing.

  Another component of the torque generated by the motor 4 can be considered as a source of external force acting during rotation. That is, a part of the torque generated by the motor 4 acts in the radial direction and the thrust direction of the spindle. Further, since the motor 4 generates torque while performing phase switching during one rotation, torque fluctuation occurs at the time of phase switching. When this torque fluctuation occurs, the external force acting in the radial direction and the thrust direction of the spindle has a high frequency component that is several times the spindle speed. For example, when a motor having a three-phase eight-pole structure is used, phase switching is performed 24 times during one rotation, and a high frequency vibration component of 1200 Hz is obtained when the rotation speed is 3000 rpm.

  The vibration in the radial direction of the spindle due to such an external force having a high frequency is detected as shown in FIG. Detected by the displacement sensors 5a and 5b on the spindle head side, and detected by the displacement sensors 7a and 7b on the spindle tail side. For example, the relationship between the displacement in the Y direction when the vibration is viewed from the displacement sensor 5a and the rotation angle (angular position) of the spindle is as shown in FIG. 3B and is detected as a waveform W1. That is, the external force applied in the Y direction changes for each spindle angle, and the waveform W1 is detected. For example, the external force F1 acting in the Y direction acts at the rotation angle θ1 to cause displacement of P1.

  Therefore, the external force F1 acting on the rotation angle θ1 is obtained, and as shown in FIG. 4B, when the angular position of the spindle based on the output of the encoder 9 is θ1, the thrust G1 is applied by the electromagnets 6a and 6c in the Y direction. By generating and canceling the external force F1, the displacement P1 in the Y direction of the spindle at the angle θ1 can be suppressed to the displacement P2. In this way, by controlling the thrust generated for each angle at which an external force acts, the waveform W1 of the displacement in the Y direction can be suppressed to the waveform W2. Similarly, displacement in the X direction can be suppressed by controlling the thrust for each angle at which an external force acts.

  Thus, the vibration in the radial direction is suppressed as shown in FIG. The thrust in the Y direction on the spindle head side is generated by electromagnets 6a and 6c shown in FIG. 4A, and the thrust in the X direction is generated by electromagnets 6b and 6d. Similarly, thrust in the Y direction on the spindle tail side is generated by the electromagnets 8a and 8c, and thrust in the X direction is generated by the electromagnets 8b and 8d.

  Similarly, the vibration in the thrust direction can be reduced by estimating the external force acting for each angle from the displacement detected by the displacement sensor 11 and generating a thrust force that cancels it out by the voice coil motor 10.

  In the present embodiment, the thrust in the thrust direction is performed by the voice coil motor 10 that can be pushed and pulled, but the same effect can be obtained even if an electromagnet is used in the same manner as in the radial direction.

  In the above control method, it is necessary to measure an external force synchronized with the rotation angle and generate a thrust. Therefore, the external force estimator 12 uses the angle signal of the encoder 9 as a trigger to detect displacement sensors 5a, 5b, 7a, 7b, Each of the 11 data is taken in, and the external force is detected based on the data. The thrust controller 13 outputs a control thrust signal using the angle signal of the encoder 9 as a trigger.

  The spindle control device 15 performs spindle control according to the following sequence.

<Sequence 1>
First, the spindle control device 15 uses the motor controller 14 to rotate the spindle at the operating rotational speed.

<Sequence 2>
When the rotation speed of the spindle is stabilized, the spindle control device 15 uses the external force estimator 12 to arrange each displacement sensor for each predetermined rotation angle from the encoder 9 and the displacement sensors 5a, 5b, 7a, 7b, 11 first. The displacement in the radial thrust direction at a certain angle is detected, and the external force acting in the direction detected by each displacement sensor is estimated from the detected displacement and the rigidity of the known hydrostatic air bearing.

<Sequence 3>
Based on the relationship between the external forces in the two directions estimated in sequence 2 and the angular positions at which they act, the thrust controller 13 thrusts the electromagnets 6a to 6d, 8a to 8d and the voice coil motor 10 to cancel the external forces. Is output.

  Each thrust command is amplified by the driving devices 16a to 16d, 17a to 17d, and 18, and the electromagnets 6a to 6d, the electromagnets 8a to 8d, and the voice coil motor 10 generate thrust on the spindle.

  The thrust generated in the sequence 3 needs to be equal to the external force estimated in the sequence 2, and the stability of the spindle state in the sequence 2 and the sequence 3 is necessary. However, as in the present embodiment, the static pressure air bearing When is used, there is no problem because reproducibility is high.

  The responsiveness of the thrust generated by the sequence 3 is improved by increasing the responsiveness of each electromagnet or voice coil motor drive device, and the effect can be exerted even for an external force having a high frequency.

  In the above embodiment, as an example of estimating the external force, the example in which the external force is estimated based on the displacement detected by the displacement sensor has been described. However, a method for obtaining from the acceleration detected using an accelerometer instead of the displacement sensor. May be adopted.

1 shows a configuration of a spindle device according to an embodiment, in which (a) is a schematic cross-sectional view thereof, and (b) is a diagram showing an arrangement of a displacement sensor and electromagnets as viewed from the direction of arrow A in (a). It is a block diagram explaining a spindle control device. It is a figure explaining the output of the displacement sensor which detects the displacement of the radial direction of a spindle. It is a figure explaining the state which canceled the displacement of the radial direction of the spindle with the electromagnet. It is a figure which shows the spindle apparatus by one prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Rotor part 2a-2c, 3a, 3b Static pressure air bearing pad 4 Motor 5a, 5b, 7a, 7b, 11 Displacement sensor 6a-6d, 8a-8d Electromagnet 9 Encoder 10 Voice coil motor 12 External force estimator 13 Thrust Controller 14 Motor controller 15 Spindle controller

Claims (5)

  In a spindle device that rotates a rotor portion rotatably supported by a hydrostatic air bearing by a motor, a plurality of radial direction thrust generating means that respectively generate a thrust in a radial direction at a plurality of portions spaced in the circumferential direction of the rotor portion; Thrust direction thrust generating means for generating thrust in the rotor portion, radial external force detecting means for detecting the radial external force of the rotor portion, and thrust direction external force for detecting the thrust force of the rotor portion in the thrust direction Based on detection means, an encoder that measures the rotation angle of the rotor section, and the outputs of the two external force detection means and the encoder, the external force in the radial direction and the thrust direction is detected for each predetermined rotation angle, The plurality of radial direction thrust generating means and the slurry so as to cancel the external force The spindle apparatus characterized by comprising control means for controlling the winding direction thrust generating means, respectively.   2. The spindle apparatus according to claim 1, further comprising at least two rotor parts each supported by a hydrostatic air bearing, wherein the motor is disposed between the two rotor parts.   The external force detection means has a displacement sensor for detecting the displacement of the rotor portion, and is configured to detect an external force based on the output of the displacement sensor and the bearing rigidity of the hydrostatic air bearing. The spindle apparatus according to 1 or 2.   3. The spindle apparatus according to claim 1, wherein the external force detecting means includes an accelerometer that detects the acceleration of the rotor portion.   5. The spindle apparatus according to claim 1, wherein the radial direction thrust generating means includes an electromagnet, and the thrust direction thrust generating means includes a voice coil motor.

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