JP2009039797A - Grinding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grinding device reducing an impact force and hardly causing the wear of a grinding wheel even if the axial position of a groove deviates when machining a groove formed on the peripheral surface of a workpiece. <P>SOLUTION: The grinding wheel G with a grinding surface S formed on the outer peripheral surface is mounted to a grinding wheel spindle 5 supported to a casing 4 axially and radially in a non-contact manner by control type axial magnetic bearings 6 and control type radial magnetic bearings 7, 8 and rotated by an electric motor 10. The casing 4 is axially positioned and then radially moved to grind a ground part of the workpiece. Before the casing 4 radially moves and the grinding wheel G comes in contact with the workpiece, the stiffness value of the radial magnetic bearings 7, 8 is set at an initialization value lower than a value in the usual grinding time, and after the grinding surface S of the grinding wheel G comes in contact with the workpiece, the stiffness value of the radial magnetic bearings 7, 8 is set at a value higher than the initialization value to grind the workpiece. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grinding wheel that grinds a workpiece with a grinding surface of an outer peripheral surface of a grinding wheel attached to a grindstone shaft, and more particularly, for example, an outer ring of a ball bearing by a grinding wheel having a medium-high grinding surface formed on the outer peripheral surface. The present invention relates to a grinding apparatus suitable for grinding a groove formed on a cylindrical peripheral surface of a workpiece, such as a track groove formed on the inner peripheral surface of the workpiece.

  2. Description of the Related Art An internal grinding machine is known as a grinding device for finish grinding a raceway groove formed on an inner peripheral surface of an inner ring of a ball bearing or an inner peripheral surface of an outer ring.

  In a normal internal grinding machine, a grinding wheel having a grinding surface formed on its outer peripheral surface is attached to a grinding wheel shaft that is rotatably supported by a casing. When grinding a cylindrical surface such as the inner circumferential surface of the inner ring, the grinding surface is cylindrical, and when grinding a groove such as the inner circumferential surface of the outer ring, the grinding surface is medium-high.

In such a conventional internal grinding machine, a contact-type rolling bearing is used as a bearing for rotating and supporting a grinding wheel shaft on which a grinding wheel is mounted on a casing of a spindle device (for example, see Patent Documents 1 and 2). ).
JP 2001-159421 A Japanese Unexamined Patent Publication No. 57-27660

  In the conventional internal grinding machine, as described above, since the rolling bearing is used to support the rotation of the grindstone shaft, there are the following problems.

  When grinding using an internal grinder, rotate the workpiece (workpiece) while holding it with an appropriate gripping device such as a chuck, position the casing in the axial direction of the grinding wheel shaft, and then move the casing in the radial direction. The grindstone is ground by bringing the grindstone into contact with the workpiece.

  In that case, when the casing is moved in the radial direction and the grindstone is brought into contact with the workpiece, an impact force in the radial direction acts on the grindstone.

  In addition, when grinding a groove formed on the cylindrical surface of the workpiece, such as a track groove formed on the inner surface of the outer ring of the ball bearing, in addition to the generation of impact force, the following There's a problem.

  When the outer ring raceway groove is finish-ground using an internal grinding machine, the workpiece (workpiece) with the groove formed on the inner peripheral surface in the previous process is rotated with the gripping device held in the same manner as above. Grind the groove.

  At this time, if there is no error in the axial position of the groove formed on the inner peripheral surface of the workpiece in the previous process, the impact force only acts, but the error occurs and the axial position of the groove is correct. If the position is shifted in the axial direction, in addition to the generation of impact force, a part of the grinding surface of the grindstone is extremely worn (or chipped), so-called grindstone loss occurs, and the grindstone life is shortened.

  For example, as shown in FIG. 6 (a), if the position of the groove (R) of the workpiece (W) is correct, the grinding surface (S) of the grinding wheel (G) will be grooved when the casing is moved in the radial direction. (R) Since the entire surface is contacted almost simultaneously, the ground surface (S) is not locally worn (or chipped). On the other hand, as shown in FIG. 6 (b), if the position of the groove (R) is shifted to the left in the figure in the axial direction, when the casing is moved in the radial direction, the groove (R) is first moved. Only the right edge contacts the grinding wheel grinding surface (S), and only this edge portion is ground. For this reason, only the portion of the grindstone grinding surface (S) that contacts the right edge of the groove (R) is locally worn. Similarly, when the position of the groove (R) is shifted in the axial direction on the right side as shown in FIG. 6 (c), the grinding wheel grinding surface (S) that contacts the left edge of the groove (R) is also the same. Only the part is worn (or chipped) locally.

  In addition to the finish grinding of the raceway groove on the inner peripheral surface of the outer ring, there is a similar problem when the groove formed on the cylindrical peripheral surface (inner peripheral surface or outer peripheral surface) of the workpiece is ground.

  The object of the present invention is to solve the above-mentioned problems, reduce the impact force, and even when the groove formed on the peripheral surface of the workpiece is machined, even if there is a deviation in the axial position of the groove, the grinding wheel loses. An object of the present invention is to provide a grinding device that is less likely to cause the occurrence of the problem.

  A grinding apparatus according to a first aspect of the present invention includes a grinding wheel shaft that is supported by a control type axial magnetic bearing and a control type radial magnetic bearing in a noncontact manner in an axial direction and a radial direction with respect to a casing and is rotated by an electric motor. The formed grinding wheel is attached and is a grinding device for grinding a portion to be ground of the workpiece by moving the casing relative to the workpiece, and after positioning the casing in the axial direction, In a grinding device that moves the casing in the radial direction and grinds the part to be ground, before the casing moves in the radial direction and the grindstone contacts the workpiece, the rigidity value of the radial magnetic bearing is determined. The initial set value is lower than the normal grinding value, and after the grinding surface of the grinding wheel comes into contact with the workpiece, the rigidity value of the radial magnetic bearing is higher than the above initial set value. And it is characterized in that it is adapted to perform a grinding with.

  The grinding device is provided with a radial magnetic bearing control means for controlling the radial magnetic bearing based on the radial displacement of the grindstone shaft. The rigidity value of the radial magnetic bearing is changed, for example, by changing the control constant of the radial magnetic bearing control means. The radial control means normally performs PID control. In that case, the stiffness value of the radial magnetic bearing is changed by changing at least one of the control constants of the proportional (P) operating unit, the integral (I) operating unit, and the differential (D) operating unit.

  The contact of the grinding surface of the grindstone with the workpiece is detected, for example, by a change in excitation current supplied to the electromagnet of the radial magnetic bearing.

  When the grinding wheel grinding surface comes into contact with the workpiece, the reaction force backward in the cutting direction with respect to the grinding wheel shaft increases, and the excitation current supplied to the electromagnet on the front side in the cutting direction of the radial magnetic bearing increases. Therefore, it is possible to detect that the grinding wheel grinding surface is in contact with the workpiece by the exciting current of the electromagnet of the radial magnetic bearing.

  Before the casing moves in the radial direction and the grindstone comes into contact with the work piece, the rigidity value of the radial magnetic bearing is set to an initial setting value lower than the value during normal grinding, and the grinding surface of the grindstone is set to the work piece. After the contact, the grinding is performed with the radial magnetic bearing having a rigidity value higher than the initial setting value, so that the grinding wheel is applied to the work piece with the radial magnetic bearing having a low rigidity value. When the grinding wheel comes into contact with the workpiece, the grinding wheel can escape in the radial direction. For this reason, the impact force when a grinding wheel contacts a workpiece is relieved.

  A grinding device according to a second aspect of the present invention is a grinding wheel shaft that is supported in a non-contact axial and radial direction with respect to a casing by a control type axial magnetic bearing and a control type radial magnetic bearing and is rotated by an electric motor. The formed grinding wheel is attached and is a grinding device for grinding a portion to be ground of the workpiece by moving the casing relative to the workpiece, and after positioning the casing in the axial direction, Radial magnetic bearing control means having an integral operation unit for controlling a radial magnetic bearing based on a radial displacement of a grindstone shaft in a grinding apparatus configured to move a casing in a radial direction to grind a portion to be ground When the integral output of the integral operation unit is smaller than a predetermined reference value, the radial magnetic bearing control means has an integral constant of the integral operation unit. Normal to low initial set value than the value at the time of grinding, the integration output is characterized in that when exceeding the reference value, is adapted to increase the integration constant in response to the integrated output.

  Before the grinding wheel comes into contact with the workpiece, no external force is applied in the radial direction to the grinding wheel and the wheel shaft. Therefore, the integral output is smaller than the reference value in the integral operation part of the bearing control means, and the integral constant is The initial set value is lower than the value of 1. The radial stiffness value is lower than that during normal grinding. When the grinding wheel comes into contact with the workpiece, an external force in the radial direction acts on the grinding wheel and the grinding wheel shaft. Therefore, the integral output becomes larger than the reference value in the integral operation unit, and the integral constant becomes larger than the initial setting value. The rigidity value of the radial magnetic bearing becomes larger than that before contact. For this reason, as in the case of the first invention, the impact force when the grinding wheel comes into contact with the workpiece is reduced.

  In the first and second inventions, for example, the grinding surface of the grinding wheel is a medium-high grinding surface, and the portion to be ground of the workpiece is a groove formed on the cylindrical peripheral surface of the workpiece.

  The cross-sectional shape of the medium-high grinding surface of the grinding wheel and the cross-sectional shape of the groove of the workpiece are curved as a whole.

  Regarding the cross-sectional shape of the grinding surface of the grinding wheel and the groove of the workpiece, the cross-section is a cross-section (longitudinal section) in a plane passing through the axis of the grinding wheel, that is, the axis of the grinding wheel axis and the axis of the cylindrical surface circumferential surface where the groove is formed. Say. When grinding the groove, the axis of the grindstone axis and the axis of the cylindrical surface of the workpiece on which the groove is formed are parallel to each other.

  As shown in Fig. 6 (a), if the groove (R) is formed at the correct position by pre-processing, and the groove (R) and the grinding wheel (G) are aligned in the axial direction, the casing is removed. When the grindstone (G) is moved close to the workpiece (W) by moving in the radial direction, the grindstone grinding surface (S) contacts the entire groove (R) almost simultaneously. Then, after the grinding wheel grinding surface (S) contacts the entire groove (R), the rigidity value of the radial magnetic bearing is made higher than the initial setting value. When the casing is moved in the radial direction, the grindstone grinding surface (S) contacts the entire groove (G) almost simultaneously, and the rigidity value of the radial magnetic bearing at this time is lower than the value during normal grinding, Since the grinding wheel can escape in the radial direction, the impact is alleviated and the ground surface (S) is not locally worn (or chipped).

  As shown in FIG. 6B, when the position of the groove (R) by the pre-processing is shifted to the left in the drawing in the axial direction, the casing is moved in the radial direction, and the grindstone (G) is moved to the workpiece (W). At first, only the right edge of the groove (R) comes into contact with the grinding wheel surface (S), but the rigidity value of the radial magnetic bearing at this time is lower than the normal grinding value, Since the grindstone can escape in the radial direction, the impact is alleviated and the ground surface (S) is not locally worn (or chipped).

The same applies to the case where the position of the groove by pre-processing is shifted to the right side of the drawing in the axial direction as shown in FIG.

  Two sets of radial magnetic bearings are usually provided. In that case, the change of the stiffness value in the first invention and the change of the integral constant in the second invention may be performed for two sets of radial magnetic bearings, or only for one set of radial magnetic bearings. You may do it. For example, the stiffness value and the integration constant may be changed only when the radial magnetic bearing is closer to the grinding wheel.

  The radial magnetic bearing has two radial control shafts that are orthogonal to each other, and preferably one of the control shafts is aligned with the cutting direction (the moving direction of the casing during grinding). In that case, the change of the stiffness value and the change of the integral constant need only be performed for the control axis that matches the cutting direction.

  According to the grinding devices of the first and second inventions, as described above, the impact force when the grinding wheel comes into contact with the workpiece can be reduced.

  According to the third invention, as described above, the impact force when the grinding wheel comes into contact with the groove portion of the workpiece can be alleviated, and the axial position of the groove is shifted. However, it is difficult for the whetstone to be lost, and the local wear of the whetstone can be prevented.

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

  1 is a plan view showing a part of a magnetic bearing spindle unit which is a main part of the grinding apparatus, FIG. 2 is an enlarged sectional view thereof, FIG. 3 is a sectional view taken along line III-III in FIG. 2, and FIG. It is a block diagram which shows the principal part of a typical structure. 1 and 2 are the upper side, the lower side is the lower side, the upper side is the back side, the lower side is the front side, the left side is the grindstone side, and the right side is the anti-whetstone side. Also, in FIG. 3, the top and bottom are the top and bottom, the right side is the back side, and the left side is the front side.

  Although detailed illustration is omitted, the spindle unit (1) is moved in the direction of the grindstone / anti-whetstone by the grindstone-side / anti-whetstone-side direction drive device (2), and in the back-and-front direction by the back-front direction drive device (3). It is moved separately and positioned at the desired position. The movement and positioning of the spindle unit (1) in the direction of the grinding wheel side, the anti-grinding stone side, and the depth direction are controlled by, for example, a known numerical control device (not shown).

  The spindle unit (1) is a horizontal type in which the horizontal grindstone shaft (5) rotates inside the horizontal casing (4) so that the direction of the grindstone shaft (5) is in the direction of the grindstone or anti-whetstone. Is arranged.

  The axial direction (axial direction) of the grinding wheel axis (5), that is, the control axis (axial control axis) in the direction of the grinding wheel side / anti-grinding stone side is Z axis, two radial directions (radial directions) perpendicular to the Z axis and perpendicular to each other. Of the control axes (radial control axes), the control axis in the depth direction is the X axis, and the control axis in the vertical direction is the Y axis. The positive side of the Z axis is the grindstone side, the positive side of the X axis is the back side, and the positive side of the Y axis is the upper side.

  The spindle unit (1) has a set of control-type axial magnetic bearings (6) that support the grinding wheel shaft (5) in a non-contact manner in the axial direction, and a grinding wheel side / reverse support that supports the grinding wheel shaft (5) in a non-contact manner in the radial direction. Two sets of control-type radial magnetic bearings (7) and (8) on the wheel side, a displacement detector (9) for detecting axial and radial displacement of the wheel shaft (5), and high-speed rotation of the wheel shaft (5) Built-in type electric motor (10), a rotation sensor (11) for detecting the rotation speed of the grindstone shaft (5), and a grinding wheel shaft by restricting the axial and radial movable ranges of the grindstone shaft (5) (5) Magnetic bearings (6) (7) (8) When the wheel shaft (5) is mechanically supported when it is not supported by the bearings (2) ) (13).

  A controller (14) for controlling the magnetic bearings (6) (7) (8) and the electric motor (10) is electrically connected to the spindle unit (1) via a cable. ) And the controller (14) constitute a magnetic bearing device that supports and rotates the grindstone shaft (5) in a non-contact manner with respect to the casing (4).

  The controller (14) is provided with a sensor circuit (15) (16), an electromagnet drive circuit (17), an inverter (18), and a DSP board (19), and the DSP board (19) can have a software program. A DSP (20) as a digital processing means, a ROM (21), a RAM (22) as a nonvolatile memory, AD converters (23) and (24), and DA converters (25) and (26) are provided.

  The displacement detector (9) includes one axial displacement sensor (27) for detecting the axial displacement of the grindstone shaft (5) and the front and rear for detecting the radial displacement of the grindstone shaft (5). Two sets of radial displacement sensor units (28) and (29) are provided.

  The axial magnetic bearing (6) is a pair of axial wheels on the grinding wheel side and anti-whetstone side that are arranged so that the flange (5a) formed integrally with the intermediate part of the grinding wheel shaft (5) is sandwiched from both sides in the Z-axis direction. Electromagnets (30a) and (30b) are provided. Axial magnetic bearings are collectively referred to by reference numeral (30).

  The axial displacement sensor (27) is disposed so as to face the end surface on the side opposite to the grindstone of the grindstone shaft (5) from the rear side in the Z-axis direction, and outputs a distance signal proportional to the distance (gap) from the end surface.

  The radial magnetic bearing (7) on the grinding wheel side is closer to the grinding wheel side of the axial magnetic bearing (6), and the radial magnetic bearing (8) on the anti-grinding wheel side is farther away from the anti-whetstone side of the axial magnetic bearing (6). Is arranged. The radial magnetic bearing (7) on the grindstone side includes a pair of front radial electromagnets (31a) (31b) and a grindstone shaft (5) arranged so as to sandwich the grindstone shaft (5) from both sides in the X-axis direction. A pair of upper and lower radial electromagnets (31c) (31d) are provided so as to be sandwiched from both sides in the Y-axis direction. These radial electromagnets are collectively referred to by reference numeral (31). Similarly, the radial magnetic bearing (8) on the anti-whetstone side also includes two pairs of radial electromagnets (32a) (32b) (32c) (32d). These radial electromagnets are also collectively referred to by reference numeral (32).

  The radial displacement sensor unit (28) on the grindstone side is disposed immediately on the grindstone side of the radial magnetic bearing (7) on the grindstone side, and on both sides in the X axis direction in the vicinity of the electromagnets (31a) and (31b) in the X axis direction. A pair of front radial displacement sensors (33a) and (33b) arranged so as to sandwich the grindstone shaft (5) from the front, and the grindstone from both sides in the Y-axis direction in the vicinity of the Y-axis direction electromagnets (31c) and (31d) A pair of upper and lower radial displacement sensors (33c) and (33d) are provided so as to sandwich the shaft (5). These radial displacement sensors are collectively referred to by reference numeral (33). The radial displacement sensor unit (29) on the anti-grinding wheel side is arranged immediately on the anti-grinding stone side of the radial magnetic bearing (8) on the anti-grinding stone side. Similarly, two pairs of radial displacement sensors (34a) (34b) ( 34c) (34d). These radial displacement sensors are also collectively referred to by reference numeral (34). Each radial displacement sensor (33) (34) outputs a distance signal proportional to the distance from the outer peripheral surface of the grindstone shaft (5).

  The electric motor (10) is disposed between the axial magnetic bearing (6) and the radial magnetic bearing (8) on the anti-grinding stone side, the stator (10a) on the casing (4) side, and the grinding wheel shaft (5) side. Rotor (10b).

  The electromagnets (30), (31), (32), the displacement sensors (27), (33), (34), and the stator (10a) of the electric motor (10) are fixed to the casing (4).

  The protective bearings (12) and (13) are rolling bearings such as angular ball bearings, the outer ring of each protective bearing (12) and (13) is fixed to the casing (4), and the inner ring is fixed around the grindstone shaft (5). It is arranged with a gap. Both of the two sets of protective bearings (12) and (13) can be supported in the radial direction, and at least one set can also be supported in the axial direction.

  The sensor circuit (15) drives each displacement sensor (27), (33), (34) of the displacement detector (9), and outputs the output signal of each displacement sensor to the DSP (20) via the AD converter (23). Output to.

  The sensor circuit (16) drives the rotation sensor (11), converts the output of the rotation sensor (11) into a rotation speed signal corresponding to the rotation speed of the grindstone shaft (5), and converts this to an AD converter (24) To the DSP (20).

  The DSP (20) is connected to each of the magnetic bearings (6), (7), (8) based on the output signals of the displacement sensors (27), (33), (34) input via the AD converter (23). Obtains the control current value for the electromagnets (30), (31), and (32), and outputs the excitation current signal obtained by adding the control current value to the constant steady-state current value to the electromagnet drive circuit (17) via the DA converter (25) To do. The drive circuit (17) supplies the excitation current to the corresponding electromagnets (30), (31), and (32) of the magnetic bearings (6), (7), and (8) based on the excitation current signal from the DSP (20). Thus, the grindstone shaft (5) is supported in a non-contact manner at a predetermined floating target position. The DSP (20) also outputs a rotation speed command signal for the electric motor (10) to the inverter (18) via the DA converter (26) based on the rotation speed signal from the rotation sensor (11). (18) controls the rotational speed of the electric motor (10) based on this signal. As a result, the grindstone shaft (5) is rotated at high speed by the electric motor (10) while being supported in a non-contact manner at the target position by the magnetic bearings (6), (7) and (8).

  In the above spindle unit, the rigidity value of the pair of electromagnets (31a) (31b) (32a) (32b) in the X-axis direction in each of the radial magnetic bearings (7) and (8) on the grinding wheel side and anti-grinding stone side is set. It can be controlled.

  FIG. 5 shows only the part related to the control of the pair of electromagnets (31a) and (31b) in the X-axis direction in the radial magnetic bearing (7) on the grindstone side in the configuration of the controller (14). For (20), only the part related to the control of the pair of electromagnets (31a) and (31b) in the radial magnetic bearing control means is represented by a functional block. Next, the control of the pair of electromagnets (31a) and (31b) by the controller (14) will be described with reference to FIG.

  First, the sensor circuit (15) subtracts the other output signal from one output signal of the pair of radial displacement sensors (33a) (33b) in the X-axis direction in the radial magnetic bearing (7) on the grindstone side. Thus, the displacement of the radial magnetic bearing (7) on the grinding wheel side with respect to the target position (= 0) in the grinding wheel shaft (5) X-axis direction is obtained, and a displacement signal ΔX proportional to this displacement is output. The displacement signal ΔX from the sensor circuit (15) is converted into a digital value (digital displacement signal) ΔX by the AD converter (23) and input to the DSP (19). As will be described later, the DSP (19) DA converts a pair of excitation current signals Ia and Ib as control signals respectively corresponding to the pair of radial electromagnets (31a) and (31b) based on the digital displacement signal ΔX. Output to the device (25). The first excitation current signal Ia is converted into an analog signal by the DA converter (25), then amplified by the first current amplifier of the electromagnet drive circuit (17), and is used as one electromagnet (first magnetizing current Ia). 33a). The second excitation current signal Ib is converted into an analog signal by the DA converter (25), then amplified by the second current amplifier of the electromagnet drive circuit (17), and the other excitation magnet I ( 33b).

  The DSP (19) functionally includes a control current calculator (35) and an excitation current generator (36). The control current calculation unit (35) calculates a control current value Ic for the electromagnets (31a) and (31b) by PID calculation based on the displacement signal ΔX from the AD converter (23). (37), an integration operation unit (38), a differentiation operation unit (39), an integration constant changing unit (40), and an addition unit (41). The proportional operation unit (37) uses a proportional constant and calculates a proportional component Icp of the control current value Ic based on the displacement signal ΔX. The integration operation unit (38) uses the integration constant and calculates the integration component Ici of the control current value Ic based on the displacement signal ΔX. The differential operation unit (39) calculates an integral component Icd of the control current value Ic based on the displacement signal ΔX using a differential constant. The adder (41) obtains a control current value Ic by adding the proportional component Icp, integral component Ici, and differential component Icd, and outputs this to the exciting current generator (36). The excitation current generator (36) adds the control current value Ic to the constant bias current value Io, and outputs the resulting value (Io + Ic) to the DA converter (25) as the first excitation current signal Ia. At the same time, the control current value Ic is subtracted from the bias current value Io, and the resulting value (Io-Ic) is output to the DA converter (25) as the second excitation current signal Ib.

  The integration constant changing unit (40) controls the integration constant in the integration operation unit (38) based on the integration output Ici of the integration operation unit (38). In this example, when the integral output Ici is smaller than a predetermined reference value, the integral constant is set to an initial set value lower than that during normal grinding, and when the integral output Ici exceeds the reference value, the integral output Ici depends on the integral output Ici. The integration constant is increased.

  The configuration of the portion related to the control of the pair of electromagnets (32a) and (32b) in the X-axis direction in the radial magnetic bearing (8) on the anti-grinding stone side is the same as in the case of FIG.

  A pair of electromagnets (31c) (31d) (32c) (32d) in the Y-axis direction in each radial magnetic bearing (7) (8) and a pair of electromagnets (30a) (30b) in the axial magnetic bearing (6) The configuration relating to the control is the same as that shown in FIG. 5 or the same as that shown in FIG. 5 except that the integral constant changing unit (40) is removed.

  The grindstone side portion of the grindstone shaft (5) protrudes from the casing (4) to the grindstone side, and the grindstone (G) is fixed to the tip portion thereof.

  When grinding the groove (R) formed on the inner peripheral surface of the workpiece (W), such as the raceway groove on the inner peripheral surface of the outer ring of the ball bearing, the grinding wheel shaft (5) has a medium-high grinding with a curved cross section on the outer peripheral surface. A grinding wheel (G) on which the surface (S) is formed is attached.

  When the groove (R) formed on the inner peripheral surface of the workpiece (W) as shown in FIG. 1 is ground by the above-described grinding apparatus, the casing (4) is moved in the Z-axis direction, and the grinding wheel grinding surface (S ) Is positioned at a position facing the groove (R), and then the casing (4) is moved in the X-axis positive direction (cutting direction) at a predetermined cutting speed.

  Before the grinding wheel (G) comes into contact with the workpiece (W), the external force in the X-axis direction does not act on the grinding wheel (G) and the grinding wheel shaft (5). Therefore, in the integral operation unit (38) of the controller (14), The integral output Ici is smaller than the reference value, the integral constant is an initial set value lower than the value during normal grinding, and the stiffness value in the X-axis direction is lower than that during normal grinding. When the grindstone (G) contacts the workpiece (W), an external force in the X-axis direction acts on the grindstone (G) and the grindstone shaft (5). Therefore, the integral output Ici is larger than the reference value in the integral operation unit (38). Thus, the integral constant becomes larger than the initial set value, and the stiffness value in the X-axis direction of the radial magnetic bearings (7) and (8) becomes larger than the value before contact. For this reason, the grinding wheel (G) comes into contact with the workpiece (W) with the rigidity value in the X-axis direction of the radial magnetic bearings (7) and (8) being low, and the grinding wheel (G) is in contact with the workpiece (W ), The grinding wheel (G) can escape in the X-axis direction. For this reason, the impact force when the grinding wheel (G) contacts the workpiece (W) is reduced.

  As shown in Fig. 6 (a), if the groove (R) is formed at the correct position by pre-processing, and the groove (R) and the grinding wheel (G) are aligned in the axial direction, the casing is removed. When the grindstone (G) is moved close to the workpiece (W) by moving in the radial direction, the grindstone grinding surface (S) contacts the entire groove (R) almost simultaneously. Then, after the grinding wheel grinding surface (S) contacts the entire groove (R), the rigidity value of the radial magnetic bearing is set to a value higher than the initial set value. When the casing is moved in the radial direction, the grinding wheel grinding surface (S) contacts the entire groove (R) almost simultaneously, and the rigidity value of the radial magnetic bearing at this time is lower than the value during normal grinding, Since the grindstone (G) can escape downward in the X-axis direction, the impact is alleviated and the ground surface (S) is not locally worn (or chipped).

  As shown in FIG. 6B, when the position of the groove (R) by the pre-processing is shifted to the left in the drawing in the axial direction, the casing is moved in the radial direction, and the grindstone (G) is moved to the workpiece (W). At first, only the right edge of the groove (R) contacts the grinding wheel grinding surface (S), but the rigidity value of the radial magnetic bearing at this time is lower than the value during normal grinding, and the grinding wheel Since (G) can escape downward in the X-axis direction, the impact is alleviated and the ground surface (S) is not locally worn (or chipped).

  The same applies to the case where the position of the groove by the pre-processing is shifted to the right side of the drawing in the axial direction as shown in FIG. 6 (c).

  In the above example, when the integral output Ici is smaller than the predetermined reference value, the integral constant is set to an initial set value lower than that during normal grinding, and when the integral output Ici exceeds the reference value, the integral output Ici depends on the integral output Ici. However, before the casing (4) moves in the X-axis direction and the grindstone (G) contacts the workpiece (W), the radial magnetic bearings (7) (8) After setting the stiffness value in the X-axis direction to an initial set value lower than the normal grinding value, after the grinding surface (S) of the grinding wheel (G) contacts the workpiece (W), the radial magnetic bearing (7) Grinding may be performed by setting the rigidity value in the X-axis direction of (8) to a value higher than the initial setting value.

  In that case, the rigidity value in the X-axis direction of the radial magnetic bearings (7) and (8) is, for example, that of the radial magnetic bearing control means for controlling the electromagnets (31a) (31b) (32a) (32b) in the X-axis direction. It is changed by changing at least one control constant of the proportional operation unit, the integration operation unit, and the differentiation operation unit. For example, the stiffness value in the X-axis direction is changed by changing the integration constant of the integration operation unit.

  The fact that the grinding surface (S) of the grindstone (G) is in contact with the workpiece (W) is, for example, an electromagnet (31a) (31b) (32a) (32b) in the X-axis direction of the radial magnetic bearing (7) (8). It is detected by a change in the excitation current supplied to.

  When the grinding wheel grinding surface (S) comes in contact with the workpiece (W), the reaction force toward the grinding wheel shaft (5) in the cutting direction backward (in the negative direction of the X axis), that is, downward, increases, and the radial magnetic bearing (7) (8) The exciting current supplied to the front side in the cutting direction (positive side in the X-axis direction), that is, the upper electromagnets 31a and 32a is increased. Therefore, the grinding wheel grinding surface (S) is in contact with the workpiece (W) by the exciting current of the electromagnets (31a) (31b) (32a) (32b) in the X-axis direction of the radial magnetic bearing (7) (8). Can be detected.

  In the above example, the stiffness value in the X-axis direction is changed for both of the two sets of radial magnetic bearings (7) and (8) on the grinding wheel side and the anti-grinding stone side. Only for the radial magnetic bearing (7) on the grindstone side close to (G), the stiffness value in the X-axis direction may be changed. The stiffness value in the Y-axis direction may be linked to the X-axis.

  The above grinding apparatus can also grind the grooves formed on the outer peripheral surface of the workpiece. Moreover, the inner peripheral surface, outer peripheral surface, and other surfaces of the workpiece can be ground using a grinding wheel having a cylindrical grinding surface formed on the outer peripheral surface.

  The overall configuration or the configuration of each part of the grinding device and the magnetic bearing device that constitutes the grinding device is not limited to that of the above embodiment, and can be changed as appropriate.

FIG. 1 is a plan view of a main part of a grinding apparatus showing an embodiment of the present invention. FIG. 2 is an enlarged longitudinal sectional view of the grinding apparatus of FIG. 1 viewed from the same direction. FIG. 3 is an enlarged cross-sectional view (transverse cross-sectional view) along the line III-III in FIG. FIG. 4 is a block diagram showing the main part of the electrical configuration of the grinding apparatus of FIG. FIG. 5 is a block diagram showing a part of FIG. 4 in detail. FIG. 6 is an explanatory view showing a state of machining a groove of a workpiece by a grinding wheel.

Explanation of symbols

(4) Casing
(5) Wheel axis
(6) Axial magnetic bearing
(7) (8) Radial magnetic bearing
(10) Electric motor
(19) DSP
(G) Grinding wheel
(S) Grinding surface
(W) Workpiece
(R) Groove

Claims (3)

A grinding wheel with a grinding surface formed on the outer peripheral surface is attached to a grinding wheel shaft that is supported in a non-contact axial and radial direction with respect to the casing by a control type axial magnetic bearing and a control type radial magnetic bearing and is rotated by an electric motor. A grinding device for grinding a portion to be ground of a workpiece by moving the casing relative to the workpiece, and after positioning the casing in the axial direction, the casing is moved in the radial direction, In a grinding device designed to grind the part to be ground,
Before the casing moves in the radial direction and the grindstone contacts the workpiece, the rigidity value of the radial magnetic bearing is set to an initial setting value lower than the value during normal grinding, and the grinding surface of the grindstone is applied to the workpiece. After the contact, the grinding apparatus is characterized in that grinding is performed with a rigidity value of the radial magnetic bearing higher than the initial set value. A grinding wheel with a grinding surface formed on the outer peripheral surface is attached to a grinding wheel shaft that is supported in a non-contact axial and radial direction with respect to the casing by a control type axial magnetic bearing and a control type radial magnetic bearing and is rotated by an electric motor. A grinding device for grinding a portion to be ground of a workpiece by moving the casing relative to the workpiece, and after positioning the casing in the axial direction, the casing is moved in the radial direction, In a grinding device designed to grind the part to be ground,
Radial magnetic bearing control means having an integral operation unit for controlling the radial magnetic bearing based on the radial displacement of the grinding wheel shaft is provided, and the integral output of the integral operation unit is greater than a predetermined reference value. When the value is small, the integral constant of the integral operation unit is set to an initial set value lower than the value during normal grinding, and when the integral output exceeds the reference value, the integral constant is increased according to the integral output. A grinding apparatus characterized by comprising:   The grinding surface according to claim 1 or 2, wherein the grinding surface of the grinding wheel is a medium-high grinding surface, and the portion to be ground of the workpiece is a groove formed on a cylindrical surface of the workpiece. apparatus.

Images