JP2008023683A - Machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a machine tool improving the machining precision by minimizing accumulation phenomenon (returning the bending deflection of a quill under machining to its original state by a restoring force). <P>SOLUTION: A grinding wheel 2 is supported to a rotary shaft 11 via the quill 12 and an extension shaft part 28 is provided at the tip of the quill 12. Besides magnetic bearings 13, 14 and 15 supporting the rotary shaft 11 in non-contact therewith, an auxiliary radial bearing 30 is provided for radially supporting the extension shaft part 28 in non-contact therewith. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a machine tool such as an internal grinding machine.

  As shown in FIG. 2, the internal grinding machine has a cylindrical grinding wheel (43) attached to the tip of the rotating shaft (41) via a quill (42), and the outer periphery of the grinding wheel (43). The surface is applied to the inner peripheral surface of the workpiece (W) for grinding. That is, the grindstone (43) is applied to the workpiece (W) while being cantilevered by the rotating shaft (41), and as a result, receives a force in a direction orthogonal to the axial direction from the workpiece (W). In the internal grinding machine, the grinding accuracy deteriorates due to its cantilevered support (the quill (42) bends with respect to the rotation center axis during grinding due to the grinding resistance, and the grinding wheel (43) is moved to the workpiece (W) after grinding). When the quill (42) is moved away from it, the bending of the quill (42) returns to its original state by the restoring force, which causes a problem of the work (W) being scraped.

As a grinding machine for coping with quill bending due to grinding resistance, Patent Document 1 discloses cylindricity measuring means for measuring the cylindricity of a workpiece from a difference in grinding force between a forward end and a backward end of a grindstone, and cylindricity measurement results. And a tilting means for tilting a rotating shaft on which a grindstone is mounted with respect to a work has been proposed.
Japanese Patent Laid-Open No. 5-16068

  The thing of the said patent document 1 does not make small the size of a brim itself, and since it is difficult to obtain | require cylindricity practically accurately, the deterioration of the precision accompanying a bristle is fully eliminated. There was a problem that could not.

  An object of the present invention is to provide a machine tool having a reduced size and thus improved machining accuracy.

  A machine tool according to the present invention includes a casing, a rotating shaft disposed in the casing, a spindle device having a plurality of bearings for supporting the rotating shaft, and a tool supported at the tip of the rotating shaft via a quill. The machine tool further includes an extension shaft portion provided in the quill so as to protrude in the axial direction from the tool, and an auxiliary radial bearing that supports the extension shaft portion in a non-contact manner in the radial direction. is there.

  The machine tool includes a spindle device in which a grindstone (or other tool) is attached to the tip of a rotating shaft that is rotationally driven, such as an internal grinding machine. The machine tool may be a grinding device or a cutting device other than the internal grinding machine.

  The spindle device includes, for example, a casing, a rotating shaft arranged horizontally or vertically in the casing, one control type axial magnetic bearing that supports the rotating shaft in a non-contact manner, and two control type radial magnetic bearings in front and rear or upper and lower, and One axial displacement sensor for detecting the axial position of the rotating shaft and two radial displacement sensors for detecting the position of the rotating shaft in the radial direction are provided. Here, each magnetic bearing and each displacement sensor are publicly known, and usually each radial magnetic bearing is composed of an X-axis direction magnetic bearing and a Y-axis direction magnetic bearing, and each radial displacement sensor is X It consists of an axial direction displacement sensor and a Y-axis direction displacement sensor.

  The bearing constituting the bearing device of the spindle device is not limited to the magnetic bearing, and a hydrostatic bearing can be used instead of the magnetic bearing.

  For example, since the grindstone is provided in the quill, it is detachably attached to the quill by screwing a set screw into the screw portion. The quill has, for example, a male screw portion or a tapered portion, and is provided at the tip of the rotating shaft, so that it can be detachably attached to the rotating shaft by being screwed or fitted into the screw portion or the tapered hole portion. It is done.

  The extension shaft portion is formed, for example, by making the entire length of the quill and attaching the tool to the intermediate portion thereof. The extension shaft may be separated from the quill and fixed to the tip of the quill.

  The auxiliary radial bearing is, for example, a magnetic bearing, but may be a hydrostatic bearing. The radial bearing and the auxiliary radial bearing constituting the bearing device of the spindle device are preferably the same type.

  During machining (for example, grinding), the tool-side radial bearing and the counter-tool-side radial bearing are controlled by the control device, so that the rotary shaft is supported in a non-contact manner at a predetermined position by the tool-side radial bearing and the counter-tool-side radial bearing. Is done. The auxiliary radial bearing is controlled so as to reduce the force acting between the workpiece and the tool. As a result, the restoring force due to the bending of the quill of the grindstone is reduced, and the reduction in machining accuracy associated with the secondary is suppressed.

  When using a magnetic bearing, the magnetic bearing control device has electromagnet control signal output means, electromagnet drive means, etc. for each control axis (X axis and Y axis). An excitation current signal for the pair of electromagnets is output, and the electromagnet driving means supplies an excitation current proportional to the excitation current signal to the pair of electromagnets. The excitation current signal for each electromagnet is a combination of the steady current signal and the control current signal, and the excitation current supplied to each electromagnet is the combination of the steady current and the control current. The steady current (and steady current signal) is a constant value regardless of the position of the rotating shaft in the control axis direction. The control current (and control current signal) varies depending on the position of the rotation axis in the control axis direction. For a pair of electromagnets on each control axis, the absolute values of the control current (and control current signal) are equal to each other, and their signs are opposite to each other.

  When the auxiliary radial bearing is a control-type radial magnetic bearing, a radial displacement sensor is preferably provided in the vicinity thereof, and the spindle device is a magnetic bearing spindle having a radial magnetic bearing, a radial displacement sensor and a control device, and the spindle More preferably, the auxiliary radial bearing is also controlled by the control device of the apparatus.

  According to the machine tool of the present invention, the extension shaft portion provided at the tip of the quill is controlled by the auxiliary radial bearing, so that it can be supported by both ends instead of being cantilevered and acts between the workpiece and the tool. By controlling the auxiliary radial bearing so as to reduce the force, the bristle becomes smaller and the machining accuracy is improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a machine tool according to the invention.

  This machine tool is for internal grinding, and has a magnetic bearing spindle (1) with a grindstone (tool) (2) for grinding the inner surface of the workpiece (W), and a workpiece (W) whose inner surface is the surface to be ground. A workpiece holder (3) that holds and rotates the spindle, a spindle moving means (not shown) that moves the magnetic bearing spindle (1) in the axial direction, and the workpiece holder (3) with respect to the magnetic bearing spindle (1). And a workpiece holder moving means (not shown) for moving the grinding wheel (2) to cut the workpiece (W) relative to each other, and an auxiliary bearing provided on the axial extension line of the magnetic bearing spindle (1) And a device (5).

  The magnetic bearing spindle (1) is a vertical type in which a vertical axis-shaped rotating shaft (11) rotates inside a vertical cylindrical casing (10). In the following description, the control axis (axial control axis) in the vertical axis direction (axial direction) of the rotating shaft (11) is the Z axis, and two horizontal radial directions (radial directions) orthogonal to the Z axis and orthogonal to each other. These control axes (radial control axes) are defined as an X axis and a Y axis.

  The grindstone (2) is supported by the lower end of the rotating shaft (11) via the quill (12). An extension shaft portion (28) is provided at the tip (lower end) of the quill (12). The extension shaft portion (28) is coaxial with the rotating shaft (11) and protrudes downward in the axial direction from the grindstone (2).

  The machine body of the magnetic bearing spindle (1) has a set of control-type axial magnetic bearings (13) that support the rotary shaft (11) in a non-contact manner in the axial direction, and the rotary shaft (11) in a non-contact support in the radial direction. Two sets of upper and lower control type radial magnetic bearings (14), (15), one axial displacement sensor (16) for detecting the axial displacement of the rotating shaft (11), and the radial of the rotating shaft (11) Two sets of upper and lower radial displacement sensors (17) and (18) for detecting the displacement in the direction, built-in type electric motor (19) for rotating the rotating shaft (11) at high speed, and the shaft of the rotating shaft (11) Two sets of upper and lower sets that mechanically support the rotating shaft (11) when the rotating shaft (11) is not supported by the magnetic bearings (13), (14), and (15) by restricting the movable range in the radial and radial directions Protective bearings (20) and (21) for touchdown are provided.

  The controller portion of the magnetic bearing spindle (1) includes a sensor circuit (22), an AD converter (23), a DSP (digital signal processor) (24), a DA converter (25), an electromagnet drive circuit (26), and An inverter (27) is provided.

  The axial magnetic bearing (13) includes a pair of axial electromagnets (13a) (13b) arranged so as to sandwich a flange portion (11a) formed integrally with the intermediate portion of the rotating shaft (11) from both sides in the Z-axis direction. ).

  The axial displacement sensor (16) is arranged so as to face the upper end surface of the rotating shaft (11) from the upper side in the Z-axis direction, and outputs a distance signal proportional to the distance (gap) from the upper end surface of the rotating shaft (11). Output.

  Two sets of radial magnetic bearings (14) and (15) are arranged in the vicinity of the upper and lower ends of the rotating shaft (11), and a motor is interposed between the upper radial magnetic bearing (14) and the axial magnetic bearing (13). (19) is arranged. Each radial magnetic bearing (14) (15) includes two pairs of radial electromagnets (14a) (15a) arranged so as to sandwich the rotating shaft (11) from both sides in the X-axis direction and from both sides in the Y-axis direction. ing.

  The upper radial displacement sensor (17) is located near the upper radial magnetic bearing (14), and the lower radial displacement sensor (18) is located near the lower radial magnetic bearing (7). The radial displacement sensors (17) and (18) each output a distance signal proportional to the distance from the outer peripheral surface of the rotating shaft (11).

  The protective bearings (20) and (21) are rolling ball bearings such as angular ball bearings, the outer ring of each protective bearing (20) and (21) is fixed to the casing (10), and the inner ring is fixed around the rotating shaft (11). It is arranged with a gap. The two sets of protective bearings (20) and (21) can both be supported in the radial direction, and at least one set can also be supported in the axial direction. In a state where the magnetic bearings (13), (14), and (15) are not operated due to operation stop or power failure, the rotating shaft (11) is supported by the protective bearings (20) and (21).

  The sensor circuit (22) drives each displacement sensor (16), (17), (18), and based on the output of each displacement sensor (16), (17), (18), the axial direction of the rotating shaft (11). The displacement and the displacement in the X-axis direction and the Y-axis direction in the upper and lower radial displacement sensors (17), (18) are calculated, and the displacement signal as a result of the calculation is converted into the DSP (24 through the AD converter (23). ).

  The DSP (24) controls the electromagnets (13a) (13b) (14a) (15a) of the magnetic bearings (13) (14) (15) based on the displacement signal input from the AD converter (23). The current value is obtained, and an excitation current signal obtained by adding the control current value to the constant steady current value is output to the electromagnet drive circuit (26) via the DA converter (25). Then, the drive circuit (26) is connected to the electromagnets (13a) (13b) (14a) (14) of the magnetic bearings (13) (14) (15) corresponding to the excitation current based on the excitation current signal from the DSP (24). 15a), whereby the rotary shaft (11) is brought into non-contact with a predetermined target position. The DSP (24) also outputs a rotation speed command signal for the motor (19) to the inverter (27), and the inverter (27) controls the rotation speed of the motor (19) based on this signal. As a result, the rotating shaft (11) is rotated at high speed by the motor (19) while being supported in a non-contact manner at the target position by the magnetic bearings (13), (14), and (15).

  The auxiliary bearing device (5) includes a casing (29) that is concentric with the extension shaft portion (28) and fixed to a support (not shown) of the magnetic bearing spindle (1), and an extension shaft portion (28). Are provided with two sets of auxiliary radial magnetic bearings (30) for non-contact support in the radial direction and one set of radial displacement sensors (31) for detecting radial displacement of the extension shaft (28). .

  The auxiliary radial magnetic bearing (30) and the radial displacement sensor (31) are the same type as those used in the magnetic bearing spindle (1), and the auxiliary radial magnetic bearing (30) has an extension shaft (28). It has two pairs of radial electromagnets (30a) arranged so as to be sandwiched from both sides in the X-axis direction and both sides in the Y-axis direction, and the radial displacement sensor (31) is located near the auxiliary radial magnetic bearing (30). And a distance signal proportional to the distance from the outer peripheral surface of the extension shaft portion (28) is output.

  The auxiliary bearing device (5) is for supporting both ends of a grindstone that has been conventionally cantilevered, and its control is performed by a DSP (24) that is a control device of the magnetic bearing spindle (1). .

  That is, the radial displacement sensor (31) of the auxiliary bearing device (5) is driven by the sensor circuit (22), and the sensor circuit (22) is based on the output of the displacement sensor (31) based on the extension shaft portion (28 ) In the X-axis direction and the Y-axis direction are calculated, and a displacement signal as a result of the calculation is output to the DSP (24) via the AD converter (23). Then, the DSP (24) obtains a control current value for each electromagnet (30a) of the auxiliary radial magnetic bearing (30) based on the displacement signal input from the AD converter (23), and controls it to a constant steady current value. The excitation current signal with the current value added is output to the electromagnet drive circuit (26) via the DA converter (25). The drive circuit (26) supplies an excitation current based on the excitation current signal from the DSP (24) to each electromagnet (30a) of the auxiliary radial magnetic bearing (30), whereby the extension shaft portion (28) is Non-contact is made at a predetermined target position.

  The auxiliary bearing device (5) is controlled to reduce the force acting between the workpiece (W) and the grindstone (2). As a result, the restoring force due to the bending of the quill (12) is reduced, and A reduction in machining accuracy due to the phenomenon that the bending of the quill (12) is restored by the restoring force to the workpiece (W).

  In the above embodiment, the rotation axis (1) is shown as a vertical axis, but the rotation axis may be a horizontal axis.

  The spindle device is a magnetic bearing spindle. However, the spindle device is not limited to a magnetic bearing. The spindle device uses a hydrostatic bearing instead of the magnetic bearing (14) (15) (16) for rotation. A pair of axial hydrostatic bearings that support the shaft (11) in a non-contact manner, a grinding wheel side radial hydrostatic bearing that supports the rotating shaft (11) in a non-contact manner in the radial direction at a position close to the grinding wheel (2), The shaft (11) may be composed of an anti-grinding wheel side radial hydrostatic bearing that supports the shaft (11) in a radial direction at a position far from the grindstone (2) and a control device that controls each hydrostatic bearing. In this case, the auxiliary radial bearing is also a hydrostatic bearing.

  Alternatively, the spindle device may be of a type that supports the rotating shaft with a rolling bearing such as a ball bearing, and the auxiliary bearing device (5) may be configured as described above and controlled independently.

FIG. 1 is a schematic configuration diagram of a main part showing an embodiment of a machine tool according to the present invention. FIG. 2 is a diagram schematically showing a problem of a conventional machine tool.

Explanation of symbols

(1) Spindle device
(2) Whetstone (tool)
(10) Casing
(11) Rotating shaft
(14) Upper (anti-tool side) radial bearing
(15) Lower (tool side) radial bearing
(24) DSP (control device)

Claims (3)

In a machine tool comprising a casing, a rotating shaft arranged in the casing, a spindle device having a plurality of bearings for supporting the rotating shaft, and a tool supported at the tip of the rotating shaft via a quill,
A machine tool, further comprising: an extension shaft portion provided on the quill so as to protrude from the tool in the axial direction; and an auxiliary radial bearing for supporting the extension shaft portion in a non-contact manner in the radial direction.   2. The machine tool according to claim 1, wherein the auxiliary radial bearing is a control type radial magnetic bearing, and a radial displacement sensor is provided in the vicinity thereof.   3. The machine tool according to claim 2, wherein the spindle device is a magnetic bearing spindle having a radial magnetic bearing, a radial displacement sensor, and a control device, and the auxiliary radial bearing is also controlled by the control device of the spindle device.

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