JPH10159932A - Ball screw drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw drive incorporating therein no spline mechanism, capable of correcting errors in the axial moving distance of its screw shaft caused by the revolution thereof. SOLUTION: A displacement-detecting ball nut 4 is fitted around a screw shaft 2 near the rear end thereof. The displacement-detecting ball nut 4 is placed inside a guide 6 with its rotation being restricted and only its axial movement being permitted. A displacement detector 38 is mounted on the rear end of the screw shaft 2 by means of a bearing 35 so as to only rotate relative to the screw shaft 2, for detecting the axial displacement of the displacement- detecting ball nut 4 relative to the screw shaft 2. Based on the output of the displacement detector 38, a rotating mechanism 5 is controlled to drive a driving ball nut 3 and thus move the screw shaft 2 axially by a distance enough to offset the relative displacement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw driving device for rotating a screw shaft in an axial direction by rotating a driving ball nut, and more particularly to a ball screw driving device having no built-in spline mechanism. The present invention relates to a ball screw driving device having a function of correcting an error in an axial movement amount of a screw shaft.

[0002]

2. Description of the Related Art Conventionally, a ball screw drive has a type in which a spline groove is formed in a screw shaft, and the screw shaft itself has a function of restraining the movement (rotation) in the rotational direction, and there is no such spline groove. There is a type in which the screw shaft itself does not have a function of restricting the movement in the rotation direction.

FIG. 2 shows an outline (part) of a screw shaft having a spline groove of the former type. As shown in FIG. 2, in this type of screw shaft, a spline groove 72 is formed on the screw shaft in addition to the screw groove 71 so that the screw shaft does not rotate with the rotation of the ball nut portion (drive ball nut). The movement of the screw shaft in the rotational direction is restricted by the spline groove 72.

When using a screw shaft of this type,
Since the rotation of the screw shaft is constrained,
It is not necessary to restrict the rotation of the screw shaft, and usually, the screw shaft and the driven object are freely rotatable so that unnecessary torque does not act on the screw shaft with the movement of the driven object. Connected via a joint. On the other hand, when using the latter type of screw shaft, usually by connecting between the screw shaft and the driven object via a joint whose rotation is restricted,
Restricts the rotation of the screw shaft.

FIGS. 3A and 3B show an example of a universal joint capable of tilting about two axes.

FIG. 3A shows a ball joint, which has a spherical seat, is capable of tilting around two axes, and is not restricted in the movement in the rotational direction (that is, the rotational force is not transmitted). On the other hand, FIG.
(B) is called a universal joint, which is capable of tilting about two axes and restricting the movement in the rotational direction (ie,
Torque is transmitted).

FIG. 4 shows an outline of a manipulator based on a parallel mechanism. In this manipulator, a ball screw driving device is used as driving means as described below.

The traveling plate 53 as a movable part
Is suspended from a ceiling 52 of a frame 51 by three ball screw driving devices 55 and a center shaft 54. At the center of the ceiling 52, a universal joint 61 capable of tilting around two axes and restraining movement in the rotational direction is provided. A ball spline bearing (not shown) is provided at a core of the universal joint 61. Built-in. The center shaft 54 passes through the ceiling 52 via the ball spline bearing. Therefore,
The center shaft 54 is in a state where the rotational movement is restrained,
Tilting around two axes and axial movement are possible.

A universal joint 62 capable of tilting around two axes and restraining rotational movement is provided at three places on the peripheral edge of the ceiling 52. A screw shaft 64 is provided at the core of the universal joint 62. Penetrated. The screw shaft 64 has a spline groove, and is of a type in which movement in the rotational direction is restricted. Each of the three ball screw driving devices 55 can tilt these screw shafts 64 around two axes in a state where the rotation is restricted,
Further, it is moved (expanded and contracted) in the axial direction by rotation of a driving ball nut (not shown) attached to the core portion of the universal joint 62.

[0010] Ball joints 63 capable of tilting around two axes and having unrestricted rotational movement are provided at three locations on the peripheral edge of the traveling plate 53. The tip of each screw shaft 64 is attached to the core of the ball joint 63. Section (the ball section).

In the manipulator shown in FIG. 4, the three-dimensional position and attitude of the traveling plate 53 are controlled by rotating and driving the ball nut to independently expand and contract each screw shaft 64.

By the way, in the case of a screw shaft having a spline groove, as shown in FIG. 2, the spline groove 72 is provided between the leads of the screw groove 71, so that the screw lead must be set large. The spline groove 72 cannot be processed (for example, in the case of a ball screw having a screw axis of φ50 mm, the lead of the screw is 50 mm). That is, in the case of a ball screw having a small screw lead, a spline groove cannot be formed on the screw shaft itself. Therefore,
When using a ball screw with a high demand for the stroke accuracy of the screw shaft and a small screw lead, a conventional ball screw having a spline groove and having a function of restraining rotational movement cannot be used.

On the other hand, when the latter type having no spline groove is used as the ball screw, as described above, the object to be driven is controlled so that the screw shaft does not rotate with the rotation of the driving ball nut. It is necessary to restrict the movement (rotation) of the screw shaft in the rotation direction via the shaft. That is, the tip of the screw shaft and the driven object are connected via a universal joint, for example, in a state where rotation is restricted. In the case of such a configuration, the three-dimensional movement of the driving object (the traveling plate 53 in the case of the manipulator shown in FIG. 4) causes the screw shaft to rotate, and the screw shaft of the ball screw and the driving ball nut , A relative rotation occurs, and this rotation causes an error in the axial movement amount of the screw shaft.

As described above, when a ball screw having no function of restricting the movement of the screw shaft in the rotational direction is used, if the screw shaft rotates with the movement of the driven object, the shaft of the screw shaft is rotated. An error occurs in the amount of movement in the direction.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a driving apparatus using a ball screw of a type which does not incorporate a spline mechanism. It is an object of the present invention to provide a structure of a ball screw driving device capable of correcting and controlling an error of an amount of movement of a screw shaft in an axial direction caused by rotation of the ball screw.

[0016]

According to the present invention, there is provided a ball screw driving device, comprising: a screw shaft having a thread groove formed along its outer periphery in a longitudinal direction; a driving ball nut fitted to the screw shaft; A ball nut for displacement detection that fits into
A housing for accommodating the driving ball nut in a state where the movement in the axial direction is restricted and only the movement in the rotation direction is possible, and the screw shaft fixed to the housing and rotationally driving the driving ball nut. A rotary drive mechanism for moving the shaft in the axial direction, and fixed to this housing,
A guide for accommodating the displacement detection ball nut in a state in which it can only move in the axial direction while restricting the movement in the rotation direction, and is attached to the screw shaft while restricting at least the axial movement with respect to the screw shaft; A displacement detector that detects a relative displacement of the detection ball nut in the axial direction with respect to the screw shaft, and driving the rotation drive mechanism in accordance with an output of the displacement detector to an amount for correcting the relative displacement. Correction control means for giving a corresponding axial movement amount to the screw shaft.

It is characterized by having the following.

In the ball screw driving device according to the present invention, when the screw shaft rotates along with the movement of the driven object, the axial displacement of the screw shaft caused by the rotation is relative to the screw shaft of the ball nut for displacement detection. Appears as a relative displacement in the axial direction. Therefore, the relative displacement is detected by the position detector, and the rotation drive mechanism is driven based on the detected value, and the driving ball nut is rotated in a direction for correcting the relative displacement. As a result, it is possible to cancel the error of the axial movement amount due to the rotation of the screw shaft.

[0019]

FIG. 1 shows the structure of a main part of a ball screw drive device according to the present invention. In the figure, 1 is a housing,
2 is a screw shaft, 3 is a drive ball nut, 4 is a displacement detection ball nut, 5 is a rotation drive mechanism, 6 is a guide, 8 is a screw groove, 11 is a ball, and 38 is a displacement detector.

In the housing 1, a driving ball nut 3 integrally attached to a timing pulley 17 is provided.
However, it is attached via the bearings 13 and 14 so that only movement in the rotational direction is possible. The screw shaft 2 is fitted to the driving ball nut 3. A screw groove 8 is formed in the screw shaft 2, and a ball 11 incorporated in the driving ball nut 3 is rollably fitted into the screw groove 8, and the driving ball nut 3 is screwed. When rotating with respect to the shaft 2, power is transmitted to the screw shaft 2 via the screw groove 8.

A rotary drive mechanism 5 is provided on the side of the housing 1.
Is arranged. The rotation drive mechanism 5 includes a motor 18, a timing pulley 15, a timing belt 16, and the like. The rotation of the motor 18 is controlled by the timing pulley 15
And the timing pulley 1 via the timing belt 16
7, the drive ball nut 3 is rotated to move the screw shaft 2 in the axial direction.

The thread groove 8 is provided up to the rear end of the screw shaft 2, and the ball nut 4 for displacement detection is fitted into the thread groove 8 at the rear end. This ball nut 4 for detecting displacement
The rotation of the screw shaft 2 is restricted by a key 34 slidably engaged with a key groove 33 of the guide 6 fixed to the housing 1, and moves in the guide 6 in the axial direction as the screw shaft 2 moves in the axial direction. .

A displacement detector 3 is provided at the rear end 2a of the screw shaft 2.
8 is rotatably mounted only via a bearing 35, and the displacement detector 38 can rotate relative to the screw shaft 2. Further, the displacement detector 38 is supported by the guide 6 in a state where the rotation with respect to the housing 1 and the driving ball nut 3 is restricted by the key 37 engaging with the key groove 33 of the guide 6, and the axial direction of the screw shaft 2. Moves in the guide 6 with the movement of. The displacement detector 38 faces the rear end face of the ball nut 4 for detecting displacement, and detects a distance 30 to the rear end face.

The housing 1 is used by being attached to, for example, a frame 52 shown in FIG. This universal joint 20
Is a horizontal shaft 21 mounted on the frame 52 (FIG. 4) side, an intermediate body 22 mounted to be tiltable with respect to the horizontal shaft 21, and a tilt between the intermediate body 22 and the housing 1. The vertical axis 23 is freely attached.

As described above, when the rotation of the screw shaft 2 relative to the housing 1 is caused by the movement of the traveling plate 53 shown in FIG. The screw shaft 2 moves in the axial direction because a relative rotation occurs with the ball nut 3. At the same time, relative rotation occurs between the screw shaft 2 and the displacement detection ball nut 4, whereby the displacement detection ball nut 4 moves in the axial direction with respect to the screw shaft 2. This relative movement (displacement) in the axial direction is detected by the displacement detector 38 as a change in the distance from the displacement detector 38 to the rear end face of the ball nut 4 for displacement detection. The output of the displacement detector 38 is input to a correction control unit (not shown), and drives the rotation drive mechanism 5 in accordance with the output of the displacement detector 38 to move in the axial direction due to the rotation of the screw shaft 2. The driving ball nut 3 is rotationally driven in a direction to cancel the amount.
As described above, it is possible to correct an error in the amount of movement in the axial direction due to the rotation of the screw shaft 2.

[0026]

The ball screw driving device according to the present invention comprises:
The amount of movement of the screw shaft in the axial direction caused by the rotation of the screw shaft accompanying the movement of the driven object is detected and corrected by rotating and driving the ball nut for driving. The amount of movement can be controlled accurately. Further, since no spline groove is provided on the screw shaft, it is possible to use a ball screw having a relatively small screw lead.

[Brief description of the drawings]

FIG. 1 is an axial sectional view showing a main part of a ball screw driving device according to the present invention.

FIG. 2 is a diagram showing an outline of a screw shaft of a ball screw having a spline groove.

FIG. 3 is a diagram showing an example of a universal joint, FIG.
(B) is a figure which shows the schematic structure of a universal joint.

4A and 4B are diagrams showing an outline of a manipulator based on a parallel mechanism, FIG. 4A is a partially omitted plan view, and FIG. 4B is a longitudinal sectional view.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Housing, 2 ... Screw shaft, 3 ... Ball nut for drive, 4 ... Ball nut for displacement detection, 5
..Rotation drive mechanism, 6 guide, 8 screw groove,
11 ... ball, 13, 14 ... bearing, 15
... Timing pulley, 16 ... Timing belt, 17 ... Timing pulley, 18 ... Motor,
20: universal joint, 21: horizontal axis,
22 ... intermediate body, 23 ... vertical axis, 33 ... key groove, 34 ... key, 35 ... bearing, 37 ...
・ Key, 38 ・ ・ ・ Displacement detector, 51 ・ ・ ・ Frame,
52: ceiling part of frame, 53: traveling plate, 54: center shaft, 55: ball screw drive, 61: universal joint (universal joint), 62: universal joint (universal) Joint: 63, universal joint (ball joint), 64: screw shaft, 71: screw groove, 72: spline groove.

Claims (1)

[Claims] 1. A screw shaft having a thread groove formed in an outer periphery thereof along a longitudinal direction, a driving ball nut fitted to the screw shaft, a displacement detection ball nut also fitted to the screw shaft, A housing for accommodating the driving ball nut in a state in which the movement in the axial direction is restricted and only the movement in the rotation direction is possible, and the screw shaft is fixed to the housing and the screw shaft is driven by rotating the driving ball nut. A rotation drive mechanism that moves in the axial direction, a guide that is fixed to the housing, and accommodates the ball nut for displacement detection in a state in which movement in the rotation direction is restricted and only movement in the axial direction is possible, and the screw shaft A displacement detector that is attached to at least the axial movement of the ball nut and detects relative displacement of the ball nut for displacement detection in the axial direction with respect to the screw shaft; Correction control means for driving the rotation drive mechanism in accordance with the output of a detector to apply an axial movement amount corresponding to the amount of correcting the relative displacement to the screw shaft. Ball screw drive.