JPH1172154A - Screw driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lightweight, small and compact screw driving device. SOLUTION: A rotor 7 of a motor is installed on an outer periphery of a nut 2 rotatably supported by a case 1, and a stator 8 of the motor is installed on an inner peripheral surface of the case 1. The nut 2 is formed of a synthetic resin, and a male screw 11 formed on an outer periphery of a screw shaft 10 is screwed in and engaged with a female screw 9 formed on its outer periphery, and an outside diameter of the nut 2 is reduced, and weight is reduced. The female screw 9 and the male screw 11 are contacted at two points in a line shape with each other, and frictional resistance of a contact part is reduced, and driving force can be smoothly transmitted with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw driving device for converting a rotary motion of an electric motor into a linear motion by using a screw shaft and a nut engaged with the screw shaft.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No.
A ball screw device described in JP-A-4-65360 is conventionally known.

[0003] As shown in FIG.
Nut 23 by a pair of rolling bearings 22 attached to
Both ends are rotatably supported, and a screw groove formed on the inner periphery of the nut 23 and a ball 25 are incorporated into a screw groove surface formed on the outer periphery of the screw shaft 24 to form the nut 23 and the screw shaft 24. The screw is engaged, and the rotor 26 of the motor is attached to the outer periphery of the nut 23, and the stator 27 of the motor is attached to the inner periphery of the case 21.

[0004]

The above-mentioned ball screw device has a large number of components in which the nut 23 and the screw shaft 24 are screw-engaged via the ball 25. In addition, the diameter of the nut 23 is increased, and the outer diameter of the case 21 is inevitably increased, which causes a problem of increasing the weight of the entire apparatus.

[0005] Further, since the nut 23 is formed by shaving metal, it takes a lot of time to manufacture, and there is a problem that it takes time to attach the rotor 26 of the motor.

It is an object of the present invention to provide a small and compact screw drive with a small number of parts.

[0007]

In order to solve the above problems, according to the present invention, a male screw provided on the outer periphery of a screw shaft is engaged with a female screw on the inner periphery of a nut rotatably supported by a case. In this case, the rotor of the motor is attached to the outer periphery of the nut and the stator of the motor is attached to the case, and the nut is made of synthetic resin.

Here, as the synthetic resin, a resin excellent in heat resistance, abrasion resistance and self-lubricating property is preferable. As such a synthetic resin, a polyimide synthetic resin can be cited.

As described above, since the male screw formed on the outer periphery of the screw shaft is screw-engaged with the female screw formed on the inner periphery of the nut, the ball can be made unnecessary.
The number of parts is reduced, the outer diameter of the nut can be reduced, and a small and compact screw drive device can be provided.

In addition, since the nut is formed of a synthetic resin, molding is possible, and the rotor of the motor can be fixed at the same time as the molding, thereby facilitating the assembly.

Here, by bringing the female screw of the nut and the male screw of the screw shaft into linear contact at two points, the frictional resistance of the contact portion between the female screw and the male screw is reduced, and the driving force is transmitted with a low torque comparable to a ball screw. be able to.

As a method of contacting the female screw and the male screw at two points, one of the female screw and the male screw has a semicircular cross-sectional shape, and the screw groove between the other screw threads is formed by two surfaces inclined in opposite directions. Can be adopted.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, a nut 2 is incorporated in a case 1.

The nut 2 is made of a polyimide-based synthetic resin, and has radial bearing surfaces 3 which are in sliding contact with the inner surface of the case 1 on its outer peripheral end surfaces. A thrust bearing surface 5 is provided outside the annular projections 4 formed on both end surfaces of the outer periphery so as to make sliding contact with the inner end surface of the case 1.

The nut 2 is driven to rotate by a motor 6 incorporated in the case 1. The motor 6 includes a rotor (magnet) 7 and a stator (stator fill) 8. The rotor 7 is mounted on the outer circumference of the nut 2, while the stator 8 is mounted on the inner circumference of the case 1. ing.

A female screw 9 is provided on the inner periphery of the nut 2.
A male screw 1 formed on the outer periphery of a screw shaft 10 on the female screw 9
1 is in screw engagement. The screw shaft 10 is formed of a metal material such as steel or an aluminum alloy. The surface of the male screw 11 is coated with a resin layer 12 made of polytetrafluoroethylene (PTFE) as shown in FIG.

As shown in FIG. 2, the cross-sectional shape of the female screw 9 in the nut 2 is semicircular, while the screw groove 11a between the male screws 11 in the screw shaft 10 is formed by two surfaces 13 inclined in opposite directions. Formed, female screw 9 and male screw 1
1 is in line contact at two points in the screw advancing direction.

In the screw driving device having the above-described configuration, when the nut 2 is rotated while the case 1 is fixed and the screw shaft 10 is not rotated, the screw shaft 10 moves in the axial direction. Conversely, when the nut 2 is rotated with the screw shaft 10 fixed, the nut 2 and the case 1
Move in the axial direction of.

In the above driving, the female screw 9 of the nut 2 and the male screw 11 of the screw shaft 10 come into line contact at two points,
A polyimide synthetic resin for forming the nut 2 and a PTFE resin layer 12 for covering the surface of the male screw 11 of the screw shaft 10
, The frictional resistance of the sliding contact portion between the female screw 9 and the male screw 11 is extremely small. Therefore, the torque generated when the female screw 9 and the male screw 10 slide is greatly reduced, and a smooth driving force transmission with little torque fluctuation can be performed as in the case of using the ball screw.

FIG. 3 shows another example of the male screw 11 on the screw shaft 10. In this example, the thread groove 11a between the external thread 11, the radius of curvature R _2, R ₂ 2 two arcuate surfaces 14 with largely than the radius of curvature R ₁ of the internal thread 9 of the nut 2, and the center eccentric to one another, 14. As described above, even when the screw groove 11a has a gothic shape, the female screw 9 and the male screw 11 can be brought into linear contact at two points, and the torque loss at the time of driving force transmission can be reduced.

Although the female screw 9 of the nut 2 has a semicircular shape, the male screw 11 of the screw shaft 10 may have a semicircular shape, and the female screw 9 of the nut 2 may be formed by a surface which comes in contact with the two-dotted line.

Here, when the screw shaft 10 is formed of the same kind of polyimide synthetic resin as the nut 2, the linear expansion coefficients of the two become equal, so that even if the temperature environment changes, the female screw 9 of the nut 2 can be formed.
Since the engagement gap between the male screw 11 of the screw shaft 10 and the male screw 11 is kept constant, highly accurate screw driving can be performed. A female screw 9 and a male screw 11 made of synthetic resin are used.
When they come into contact with each other, the frictional resistance at the contact portion is significantly reduced, and seizure is prevented.

The surface of the nut 2 or the female screw 10 formed of a synthetic resin may be coated with a resin layer having a low frictional resistance such as a PTFE resin layer.

[0024]

As described above, according to the present invention, the male screw formed on the outer periphery of the screw shaft is engaged with the female screw formed on the inner periphery of the nut, thereby eliminating the need for a ball screw. Since the number of points is reduced and the outer diameter of the nut can be reduced, a small, compact, and lightweight screw drive device can be provided.

Further, since the nut is made of synthetic resin, molding is possible, and the rotor of the motor can be supported at the same time as the molding, so that the assembly can be facilitated.

Further, by making the female screw of the nut and the male screw of the screw shaft come into line contact at two points, the frictional resistance of the contact portion can be extremely reduced by the line contact and the self-lubricating property of the nut made of synthetic resin. Thus, smooth and highly accurate driving can be performed without using a ball screw.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a screw drive device according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing a screw engagement portion between the nut and the screw shaft according to the first embodiment;

FIG. 3 is a sectional view showing another example of the male screw of the screw shaft of the above.

FIG. 4 is a sectional view showing a conventional ball screw device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 2 Nut 6 Motor 7 Rotor 8 Stator 9 Female screw 10 Screw shaft 11 Male screw 11a Screw groove 13 surface 14 Arc surface

Claims (4)

[Claims] A male screw provided on the outer periphery of a screw shaft is screw-engaged with a female screw on the inner periphery of a nut rotatably supported by a case, and a rotor of the motor is fitted on the outer periphery of the nut.
A screw drive device in which a motor stator is attached to a case and the nut is made of synthetic resin. 2. The screw driving device according to claim 1, wherein the synthetic resin is made of a polyimide synthetic resin. 3. The screw drive device according to claim 1, wherein the female screw of the nut and the male screw of the screw shaft are in linear contact with each other at two points in the direction of travel of the screw. 4. The cross-sectional shape of one of the female screw of the nut and the male screw of the screw shaft is semicircular, and the screw groove between the other screw threads is formed by two surfaces inclined in opposite directions, The screw drive device according to claim 1, wherein each surface is in contact with one thread at two points.