JP2008087090A - Screw groove cutting method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw groove cutting method and device for improving surface properties of a ball screw groove of a screw shaft. <P>SOLUTION: This cutting device is constituted of a screw shaft supporting means 31 for rotatably supporting the screw shaft 10 spirally formed with a ball screw groove 11, a screw shaft rotating means 33 for rotating the screw shaft supported by the screw shaft supporting means 31, a grinding tool supporting means 32 for rotatably supporting a grinding tool shaft 53 mounted with a grinding tool 21 for cutting a ball rolling surface around an axis passing a substantial center of ball rolling, a relatively moving means for relatively moving the grinding tool supporting means in an axis direction of the screw shaft by being synchronized with the screw shaft rotating means 33, and an oscillation operating means 60 for reciprocatingly rotating the grinding tool shaft 53 supported by the grinding tool supporting means at a prescribed angle. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thread groove cutting method and apparatus for cutting a ball screw groove formed on the outer periphery of a screw shaft.

  In general, in a rack coaxial electric power steering apparatus in which an electric motor is disposed coaxially with a rack shaft, for example, a ball screw shaft is integrally provided on a rack shaft that is moved in the axial direction by rotation of the steering shaft. A ball nut that is screwed onto the shaft via a rolling ball is fixed to the motor shaft of the electric motor, and a ball screw device that converts the rotational motion of the motor shaft into the axial motion of the rack shaft is provided.

The finishing process of the ball screw groove of the ball screw shaft used in this type of electric power steering apparatus is, for example, as described in Japanese Patent Application Laid-Open No. H10-133707, a general grinding wheel having a shape that complements the ball screw groove shape. In synchronization with the rotation of the ball screw shaft, the ball screw shaft and the grinding wheel are moved relative to each other in the axial direction of the ball screw shaft.
Japanese Patent Laid-Open No. 5-138438

  However, as described in Patent Document 1, if the ball screw groove is simply ground using a grinding wheel of the total shape, grinding streaks in the lead direction are generated on the grinding surface of the ball screw groove ground on the grinding wheel. As a result, it is difficult to improve the surface properties of the ball screw groove, and there is a risk that a limit may arise in improving the smooth rolling operation of the rolling ball.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a thread groove cutting method and apparatus capable of improving the surface properties of a ball screw groove of a screw shaft.

  In order to solve the above-mentioned problem, the feature of the invention according to claim 1 is that a screw shaft in which a ball screw groove on which a rolling ball rolls is formed in a spiral shape and a ball rolling surface of the ball screw groove are provided. A thread grinding method for cutting a ball rolling surface of the ball screw groove with the grinding wheel by relatively moving the grinding wheel to be cut in the axial direction of the screw shaft in synchronization with the rotation of the screw shaft, The grinding wheel is oscillated within a predetermined angular range around an axis passing through the approximate center of the rolling ball rolling on the ball rolling surface of the ball screw groove to cut the ball rolling surface of the ball screw groove. This is a thread groove cutting method characterized by the above.

  The invention according to claim 2 is characterized in that a screw shaft support means for rotatably supporting a screw shaft in which a ball screw groove in which a rolling ball rolls on the outer periphery is formed in a spiral shape is rotatably supported by the screw shaft support means. Further, a screw shaft rotating means for rotating the screw shaft and a grindstone shaft attached with a grindstone for cutting the ball rolling surface of the ball screw groove are supported so as to be rotatable about an axis passing through the approximate center of the rolling ball. Grindstone support means, relative movement means for relatively moving the grindstone support means in the axial direction of the screw shaft in synchronization with the screw shaft rotating means, and the grindstone shaft supported by the grindstone support means A thread groove cutting device characterized by comprising an oscillation actuating means that oscillates in an angular range.

  According to a third aspect of the present invention, in the second aspect, the grindstone is composed of at least one grindstone member having a curvature that substantially matches the curvature of the rolling ball, and the grindstone member 2 of the ball screw groove. The thread groove cutting device is characterized in that the ball rolling surfaces of the two locations are simultaneously cut.

  The invention according to claim 4 is characterized in that, in claim 2 or claim 3, the oscillation actuating means is configured such that the grinding wheel shaft has an angle region slightly larger than a contact angle at which the rolling ball contacts the ball screw groove. Is a thread groove cutting device configured to reciprocally rotate.

  According to a fifth aspect of the present invention, in any one of the second to fourth aspects, the oscillation operation means includes a motor, an eccentric member that is eccentrically rotated by the motor, and an eccentricity of the eccentric member. It is a thread groove cutting device constituted by a crank mechanism for converting motion into a reciprocating rotational motion of the grinding wheel shaft.

  According to the first aspect of the present invention, the grindstone is reciprocated by a predetermined angle around the axis passing through the approximate center of the rolling ball that rolls on the ball rolling surface of the ball screw groove so as to roll the ball screw groove. Since the moving surface is cut, the grindstone polishes the ball screw groove not only from one direction but also from multiple directions over a predetermined angle, and the surface property of the ball rolling surface of the ball screw groove can be improved. . As a result, streaks remaining in the ball screw groove after cutting with the grindstone are mirror-finished by polishing from multiple directions, and the rolling performance of the rolling ball rolling on the ball rolling surface can be improved.

  According to the invention which concerns on Claim 2, the screw shaft support means which supports a screw shaft rotatably, and the grindstone which supports the grindstone shaft which attached the grindstone rotatably about the axis line which passes along the approximate center of a rolling ball. Oscillating operation of the support means, the relative movement means for relatively moving the grindstone support means in the axial direction of the screw shaft in synchronization with the screw shaft rotation means, and the grindstone shaft supported by the grindstone support means within a predetermined angle range. Since the grindstone oscillation actuating means is provided, a thread groove cutting apparatus capable of performing thread groove cutting that can improve the surface property of the ball rolling surface of the ball screw groove can be easily realized.

  According to the invention of claim 3, the grindstone is composed of at least one grindstone member having a curvature substantially matching the curvature of the rolling ball, and the ball rolling surfaces of the two ball screw grooves are formed by the grindstone member. Since the cutting is performed simultaneously, the ball rolling surface on which the rolling ball rolls can be efficiently finished.

  According to the fourth aspect of the present invention, the oscillation actuating means is configured to reciprocally rotate by an angle region slightly larger than the contact angle at which the rolling ball contacts the ball screw groove. It is possible to efficiently finish and cut the ball rolling surface on which the roller rolls, and to increase the speed of the reciprocating rotational motion.

  According to the fifth aspect of the invention, the oscillation actuating means includes a motor, an eccentric member that is eccentrically rotated by the motor, and a crank mechanism that converts the eccentric motion of the eccentric member into a reciprocating rotational motion of the grindstone shaft. Therefore, the reciprocating rotational movement of the grindstone can be realized with a simple configuration, and the reciprocating rotational movement can be speeded up.

  Embodiments of the present invention will be described below with reference to the drawings. First, a cutting method in super finishing according to the present invention will be described with reference to FIGS.

  In FIG. 1, reference numeral 10 denotes a screw shaft in which a spiral ball screw groove 11 is formed on the outer periphery. The screw shaft 10 is moved in the axial direction (Z-axis direction) of the screw shaft 10 by a screw shaft support means having a configuration described later. It is supported so as to be rotatable around parallel axes, and is rotated by a screw shaft rotating means using a servo motor 13 as a drive source. As shown in FIG. 2, the groove shape of the ball screw groove 11 formed on the screw shaft 10 is a shape in which two arcs C1, C2 having a radius of curvature R1 intersect at an intermediate portion, that is, a Gothic arch shape, A rolling ball 14 interposed between a nut (not shown) is configured to roll on ball rolling surfaces 15 and 16 on two arcs C1 and C2. The ball screw groove 11 of the screw shaft 10 is ground into a Gothic arch shape by a known appropriate grinding method.

  FIG. 3A shows a cutting method in which the ball rolling surfaces 15 and 16 of the ball screw groove 11 ground in advance to a Gothic arch shape are finish-cut. The grindstone 21 that finish-cuts the ball rolling surfaces 15 and 16 is a cutting that simultaneously cuts the ball rolling surfaces 15 and 16 on the two arcs C1 and C2, which are areas slightly wider than the area where the rolling balls 14 contact. It consists of two grindstone members 23, 24 having surfaces 23a, 24a. The grindstone 21 passes through the center of the rolling ball 14 that rolls on the ball rolling surfaces 15 and 16 of the ball screw groove 11, intersects the rotation axis direction (Z-axis direction) of the screw shaft 10, and It is held by a grindstone holding member 25 that can rotate around an axis O1 that is the lead direction. The cutting surfaces 23a and 24a of the two grindstone members 23 and 24 constituting the grindstone 21 have a turning radius slightly larger than the radius of the rolling ball 14 and slightly larger than the curvature of the rolling ball 14. Has curvature.

  As shown in FIG. 4, the grindstone holding member 25 is reciprocally rotated (oscillation operation) within a predetermined angle range θ by an oscillation actuating means having a configuration described later. Further, as shown in FIG. 1, the grindstone holding member 25 is supported so as to be movable in the rotational axis direction (Z-axis direction) of the screw shaft 10 and is driven by the servo motor 13 through the synchronizing means 27. Feed control is performed in the Z-axis direction via the screw mechanism 26. By the synchronizing means 27, the rotation of the screw shaft 10 and the feed of the grindstone holding member 25 are controlled synchronously. That is, according to the lead of the ball screw groove 11 of the screw shaft 10, the grindstone holding member 25 is feed-controlled in synchronization with the rotation of the screw shaft 10, and the two ball rolling surfaces 15, 16 ( 3), the cutting surfaces 23a and 24a of the two grindstone members 23 and 24 are always controlled.

  When finishing the ball rolling surfaces 15 and 16 on the two arcs C1 and C2 of the ball screw groove 11, the screw shaft 10 is controlled to rotate at a relatively low speed by the servo motor 13 in the state shown in FIG. At the same time, in synchronization with the rotation of the screw shaft 10, the grindstone holding member 25 is controlled to be fed in the Z-axis direction at a relatively low speed. At the same time, the grinding wheel holding member 25 presses the respective cutting surfaces 23a, 24a of the grinding wheel members 23, 24 against the respective ball rolling surfaces 15, 16 with a predetermined pressing force, and the oscillation operation means shown in FIG. As described above, the ball is reciprocated at a predetermined angle θ around the axis O1, thereby oscillating and cutting the two ball rolling surfaces 15 and 16 of the ball screw groove 11 simultaneously over a predetermined angular range.

  According to the above-described thread groove cutting method, the surface properties of the ball rolling grooves 15 and 16 on which the rolling ball 14 rolls can be improved, and the rolling performance of the rolling ball 14 can be improved. After the completion of oscillation cutting, the ball rolling grooves 15 and 16 may be cut by holding the grindstone holding member 25 in the state shown in FIG. Therefore, if the screw shaft 10 thus finished and cut is used as a ball screw shaft of an electric power steering device, the rolling ball 14 rolls smoothly in the ball rolling grooves 15 and 16, thereby causing a steering fee. The ring can be improved.

  In this embodiment, the two grindstone members 23 and 24 shown in FIG. 3A are used as the grindstone 21, but one grindstone member 21a may be used as shown in FIG. 3B. .

  Next, a specific configuration of the thread groove cutting device for realizing the above-described thread groove cutting method will be described with reference to FIGS.

  In FIG. 5, reference numeral 30 denotes a thread groove cutting device. The thread groove cutting device 30 mainly includes a screw shaft support means 31 that rotatably supports a screw shaft 10 as a workpiece, and a grindstone support that supports a grindstone 21. A means 32, a screw shaft rotating means 33 for rotating and driving the screw shaft 10, and a ball screw feeding mechanism 34 for controlling the grinding stone support means 32 in the Z-axis direction are constituted.

  The screw shaft support means 31 is composed of a headstock 37 and a tailstock 38 which are installed on the bed 35 of the thread groove cutting device 30 at a predetermined distance, and one end of the screw shaft 10 is attached to the headstock 37. A main shaft 40 having a main shaft center 39 to be supported is rotatably supported. The rotation of the main shaft 40 is transmitted to the screw shaft 10 via a drive fitting 41 that is attached to the main shaft 40 and engages with one end of the screw shaft 10. The main shaft 40 is rotationally driven via a timing belt transmission means 44 by a servo motor 43 installed on the bed 35. The servo motor 43 and the timing belt transmission means 44 constitute a screw shaft rotating means 33.

  The screw shaft 10 is, for example, a ball screw shaft used in an electric power steering apparatus, and a ball screw groove 11 (see FIGS. 2 to 4) having a Gothic arch shape is spirally formed on the ball screw shaft. Is formed.

  On the other hand, on the tailstock 38, a tailstock shaft 46 to which a tailstock center 45 that supports the other end of the screw shaft 10 is attached is supported so as to advance and retreat in the Z-line direction, and is advanced and retracted by an advancing and retreating cylinder (not shown). It is like that. The screw shaft 10 is supported between the main shaft center 39 and the tailstock center 45 by the advancement and retraction of the tailstock shaft 46, and is rotated via the drive fitting 41 by the rotation of the servo motor 43.

  On the bed 35, a grinding wheel base 48 is guided and supported by a pair of linear guides 49 and 50 so as to be movable in a direction parallel to the axial direction of the screw shaft 10 (Z-axis direction). A ball screw shaft 51 is rotatably supported on the bed 35 in parallel with the moving direction of the grindstone table 48, and a ball nut 52 that is screwed onto the ball screw shaft 51 is attached to the grindstone table 48. The ball screw shaft 51 and the ball nut 52 constitute a ball screw feed mechanism 34.

  One end of the ball screw shaft 51 is connected to the main shaft 40 via a synchronization mechanism 27A composed of a gear train provided in the main shaft base 37, and the main shaft 40 is rotated by the rotation of the servo motor 43, and is synchronized with this rotation. Thus, the ball screw shaft 51 is rotated. As a result, the grinding wheel base 48 is fed and controlled in the Z-axis direction in synchronization with the rotation of the screw shaft 10 according to the lead of the ball screw groove 11 of the screw shaft 10 by the rotation of the servo motor 43. The ball screw feed mechanism 34, the servo motor 43, and the synchronization mechanism 27A constitute relative movement means in the claims.

  A grindstone support means 32 is installed on the grindstone table 48, and a grindstone shaft 53 is supported on the grindstone support means 32 so as to be rotatable around a horizontal axis O <b> 1 intersecting the axis of the screw shaft 10. The horizontal axis O1 is inclined by the lead angle of the ball screw groove 11 with respect to the right angle line that intersects the axis of the screw shaft 10 at right angles, and is parallel to the ball screw groove angle at the upper part of the screw shaft 10, And the axial center height is set to the same height as the virtual center (O1 shown in FIG. 2 and FIG. 3) of the rolling ball 14 which rolls the ball screw groove 11 on the upper part of the screw shaft 10.

  A grindstone head 55 constituting the grindstone holding member 25 is supported at the tip of the grindstone shaft 53 so as to be pivotable about an axis parallel to the axis of the screw shaft 10 via a pivot shaft 56. 6 is turned to a cutting position indicated by a solid line and an escape position indicated by a two-dot chain line. The grindstone 21 is detachably held on the grindstone head 55. As shown in FIG. 3, the grindstone 21 has two plate-shaped grindstone members 23 and 24 for cutting the ball rolling surfaces 15 and 16 on the two arc portions C1 and C2 of the ball screw groove 11 having a Gothic arch shape. It has. Cutting surfaces 23 a and 24 a having a radius slightly larger than the radius of the rolling ball 14 are formed at the tips of the grindstone members 23 and 24, and the cutting surfaces 23 a and 24 a are based on the curvature of the rolling ball 14. Has a slightly larger curvature. Thus, at the cutting position of the grindstone head 55 (state shown by the solid line in FIG. 6), the two ball rolling surfaces 15, 16 of the ball screw groove 11 are simultaneously cut by the two grindstone members 23, 24.

  The rear end of the grindstone shaft 53 is provided with an oscillation actuating means 60 that reciprocates the grindstone shaft 53 over a predetermined angle range θ, that is, an oscillation operation. As shown in FIGS. 5 and 7, the oscillation actuating means 60 is capable of eccentric rotation provided on an oscillation motor 61 installed on the grindstone table 48 and a rotary shaft 61 a rotated by the oscillation motor 61. The eccentric shaft 62, a crank arm 63 that connects the eccentric shaft 62 and the rear end of the grindstone shaft 53, and a crank mechanism 65 including a bell crank 64 are configured. As a result, the grinding wheel shaft 53 is oscillated at high speed in the predetermined angle range θ through the eccentric shaft 62 and the crank mechanism 65 by the high-speed rotation of the oscillation motor 61.

  Next, the operation of the thread groove cutting device 30 configured as described above will be described. In the pre-process of cutting by the thread groove cutting device 30, a gothic arch-shaped ball screw groove 11 as shown in FIG. 2 is ground or turned by a known method on the outer periphery of the screw shaft 10. The screw shaft 10 in which the Gothic arch-shaped ball screw groove 11 is processed is supported between the main shaft center 39 and the tailstock center 45 of the screw shaft support means 31.

  On the other hand, the grindstone head 55 holding the grindstone 21 composed of the grindstone members 23 and 24 is turned around the turning shaft 56 by the constant pressure cylinder 57 and positioned at the cutting position indicated by the solid line in FIG. In this state, the screw shaft 10 is rotated by the servo motor 43, and the grindstone base 48 in which the grindstone support means 32 is installed in synchronization with this rotation is synchronously controlled according to the lead of the ball screw groove 11. The That is, the rotation of the servo motor 43 causes the screw shaft 10 to be rotated at a predetermined rotational speed via the main shaft 40 and the drive fitting 41, and the ball screw shaft 51 is synchronized with the rotation of the main shaft 40 via the synchronization mechanism 27A. The grindstone support means 32 is fed and controlled in the axial direction (Z-axis direction) of the screw shaft 10. Thereby, as shown in FIG. 3, the ball rolling surfaces 15 and 16 of the spiral ball screw groove 11 can be continuously cut by the cutting surfaces 23 a and 24 a of the two grindstone members 23 and 24.

  At the same time, the oscillation motor 61 is driven, the eccentric shaft 62 is rotated eccentrically, and the eccentric rotation of the eccentric shaft 62 is converted into a reciprocating rotational motion of the grindstone shaft 53 by the crank mechanism 65. As shown in FIG. 4, the members 23 and 24 are oscillated (reciprocatingly rotated) at a high speed in a predetermined angle range θ, and are cut while oscillating the ball rolling surfaces 15 and 16. As a result, the grindstone members 23 and 24 polish the ball screw groove 11 not only from one direction but also from multiple directions over a predetermined angle, so that the surface properties of the ball rolling surfaces 15 and 16 can be greatly improved. it can.

  In the above-described embodiment, the example in which the grinding wheel support means 32 is fed and controlled in the axial direction (Z-axis direction) of the screw shaft 10 in synchronization with the rotation of the screw shaft 10 has been described. It may be fixed in the Z-axis direction and moved in the axial direction while rotating the screw shaft 10 along a spiral.

  In the above-described embodiment, the main shaft 40 that rotates the screw shaft 10 and the grindstone support means 32 that supports the grindstone 21 are synchronized by the mechanical synchronization mechanism 27A. The motor that rotates the wheel and the motor that feeds and controls the grindstone support means 32 can be electrically controlled synchronously.

  Furthermore, in the above-described embodiment, the oscillation actuating means 60 includes the eccentric shaft 62 that is eccentrically rotated by the oscillation motor 60, and the eccentric rotation of the eccentric shaft 62, and the oscillation movement (reciprocation) of the grindstone shaft 53. However, the configuration of the oscillation actuating means 60 is not limited to that described in the embodiment, and various configurations can be adopted.

  As described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention described in the claims.

It is a schematic diagram of the thread groove cutting method which shows embodiment of this invention. It is a figure which shows the shape of the ball screw groove of a screw shaft. It is a figure which shows the cutting state of the ball rolling surface of the ball screw groove of a screw shaft. It is a figure which shows the oscillation of a grindstone. 1 is a plan view of a thread groove cutting apparatus showing an embodiment of the present invention. It is a side view of the thread groove cutting apparatus of FIG. It is the figure seen from the arrow 7 direction of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Screw shaft, 11 ... Ball screw groove, 13 ... Servo motor, 14 ... Rolling ball, 15, 16 ... Ball rolling surface, 21 ... Grinding wheel, 23, 24 ... Whetstone member, 23a, 24b ... Cutting surface, 25 ... Wheel holding member, 27 ... Synchronizing means, 27A ... Synchronizing mechanism, 30 ... Thread groove cutting device, 31 ... Screw shaft support means, 32 ... Grindstone support means, 33 ... Screw shaft rotation means, 34 ... Ball screw feed mechanism, 35 ... Bed, 37 ... Spindle head, 38 ... Tailstock Table, 39, 45 ... Center, 40 ... Main shaft, 43 ... Servo motor, 44 ... Belt transmission means, 48 ... Grinding wheel base, 53 ... Grinding wheel shaft, 55 ... Grinding wheel Head, 60 ... oscillation operating means, 61 ... oscillation motor, 62 ... Mandrel, 65 ... crank mechanism, O1 ... rotational center, theta ... angle range.

Claims (5)

A screw shaft in which a ball screw groove on which the rolling ball rolls is formed in a spiral shape and a grindstone that cuts the ball rolling surface of the ball screw groove are synchronized with the rotation of the screw shaft. The thread groove cutting method of cutting the ball rolling surface of the ball screw groove with the grindstone by relative movement in the axial direction of
The grinding wheel is oscillated within a predetermined angular range around an axis passing through the approximate center of the rolling ball rolling on the ball rolling surface of the ball screw groove to cut the ball rolling surface of the ball screw groove. A thread groove cutting method characterized by comprising:   A screw shaft support means for rotatably supporting a screw shaft in which a ball screw groove on which the rolling ball rolls is formed in a spiral shape, and a screw shaft rotation for rotating the screw shaft supported by the screw shaft support means And a grindstone support means for pivotally supporting a grindstone shaft attached with a grindstone for cutting a ball rolling surface of the ball screw groove about an axis passing through a substantially center of the rolling ball, and the grindstone support means Relative to the screw shaft rotating means and relative movement means for relatively moving in the axial direction of the screw shaft, and oscillation operation for oscillating the grindstone shaft supported by the grindstone support means within a predetermined angle range And a thread groove cutting device.   3. The grindstone according to claim 2, wherein the grindstone is composed of at least one grindstone member having a curvature that substantially matches the curvature of the rolling ball, and the two ball rolling surfaces of the ball screw groove are simultaneously cut by the grindstone member. A thread groove cutting device characterized in that:   In Claim 2 or Claim 3, the said oscillation action | operation means is comprised so that the said grindstone axis | shaft may be reciprocatingly rotated only in the angle area | region slightly larger than the contact angle which the said rolling ball contacts the said ball screw groove. A thread groove cutting device.   5. The oscillation operation means according to claim 2, wherein the oscillation actuating means includes a motor, an eccentric member that is eccentrically rotated by the motor, and an eccentric movement of the eccentric member that is reciprocatingly rotated by the grindstone shaft. A thread groove cutting device characterized by comprising a crank mechanism for converting to a crank mechanism.

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