JP4452981B2 - Ball screw mechanism - Google Patents

Description

  The present invention relates to a ball screw mechanism.

A ball screw mechanism that converts a rotational motion and a linear motion is known. In the ball screw mechanism, smooth relative movement between the screw shaft and the nut is achieved by rolling the ball in a spiral transfer path formed between the screw shaft and the nut. In this case, it is necessary to return the ball that has been rolled to one end of the transfer path to the other end, and a circulation tube for this purpose is provided on the nut (see Patent Document 1).
JP 2003-262261 A

  By the way, in the prior art as described in Patent Document 1, in order to fix the circulation tube to the nut, a flat tube holding member is provided and tightened with a fixing screw. However, if the fixing screw is loosened due to vibration of the nut, etc., the tube restraining member may become loose and the circulation tube may be displaced, which may prevent the ball from being smoothly transferred between the transfer path in the nut and the circulation tube. is there. On the other hand, it is conceivable that the tightening torque of the fixing screw is managed to prevent the fixing screw from loosening.

  The present invention has been made in view of the problems of the related art, and an object of the present invention is to provide a ball screw mechanism that can prevent the circulation tube from coming off without taking time and effort.

The ball screw mechanism of the present invention is
A nut receiving member having a cylindrical inner peripheral surface;
A screw shaft;
Is disposed around the screw shaft, fitted to the inner peripheral surface of the nut receiving member, a substantially cylindrical nut which is part of the outer circumferential plane,
In a ball screw mechanism comprising a ball disposed in a transfer path between the screw shaft and the nut,
In the plane of the nut, a circulation tube for returning the ball from one end of the transfer path to the other end, a tube holding member for fixing the circulation tube, and the tube holding member on the outer peripheral surface of the nut a headed screw to secure the disposed between the head screw and said nut, and a spring washer which is elastically deformed by tightening the head screw is provided,
The spring washer maintains an elastic force based on deformation until the screw with the head comes into contact with an inner peripheral surface of the nut receiving member in a state where the nut is fitted to the nut receiving member. .

In the ball screw mechanism of the present invention, the spring washer has an elastic force based on deformation until the screw with the head comes into contact with the inner peripheral surface of the nut receiving member in a state where the nut is fitted to the nut receiving member. Therefore, even if the screw with the head is loosened due to the influence of vibration or the like and is pulled out to the maximum, if the elastic force of the spring washer still remains in that state, the tube holding member is fixed by such elastic force This makes it possible to appropriately suppress the circulation tube with respect to the nut, and thus it is possible to suppress a rolling failure of the ball.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a linear actuator 50 including a ball screw mechanism according to the present embodiment, and FIG. 2 is a view of the configuration of FIG. 1 taken along line II-II and viewed in the direction of the arrow.

  In FIG. 1, the substantially cylindrical nut housing 1A attached to the frame B is fitted into the inner periphery of the end of the cylindrical motor housing 1B so that the respective axes coincide with each other. The bolts 1C are attached (only one is shown). The nut housing 1A and the motor housing 1B constitute the housing 1. A cylindrical stator 2b is fixed to the inner peripheral surface of the motor housing 1B, and the stator 2b includes a rotor 2c. A rotor 2c is attached to the outer peripheral surface of a hollow rotary shaft 3 rotatably supported by the bearing 4 with respect to the motor housing 1B, and rotates integrally. The electric motor 2 includes a stator 2b, a rotor 2c, and a rotating shaft 3.

  A large-diameter portion 3a is formed at the left end of the rotating shaft 3 constituting the nut receiving member in FIG. 1, and a substantially cylindrical nut 5 is provided on the inner peripheral surface of the key 8 (see FIG. 2). It is fitted and attached so that relative rotation is impossible. The fitting relationship between the large-diameter portion 3a and the nut 5 is an intermediate fit or a slight gap fit. A screw shaft 6 passes through the nut 5. A male screw groove 6b (see FIG. 2) is formed on the outer peripheral surface of the left half portion of the screw shaft 6 in FIG.

  A female screw groove 5b (see FIG. 2) is formed on the inner peripheral surface of the nut 5 so as to face the male screw groove 6b of the screw shaft 6, and a helical space (transfer) formed by these screw grooves 5b and 6b. A large number of balls 7 (see FIG. 2) are arranged on the road so as to freely roll. A circulation tube 5a for returning the ball 7 from one end of the nut 5 to the other end during operation is provided outside the nut 5 in a manner to be described later. The nut 5, the screw shaft 6 and the ball 7 constitute a ball screw mechanism (conversion mechanism).

  A cylindrical portion 5c extending in the axial direction is formed at the left end of the nut 5 in FIG. 1, and is supported by a bearing 9 so as to be rotatable with respect to the nut housing 1A. A washer spring 10 disposed between the motor housing 1B and the bearing 4 presses the bearing 4 leftward in FIG.

  The right half portion of the screw shaft 6 in FIG. 1 is a round shaft, and a pair of engagement surfaces 6a formed by cutting the outer peripheral surface in parallel is formed at the right end. Further, a straight groove 6d is formed on the surface near the right end in FIG. 1 of the screw shaft 6, while a projection 1d protruding radially inward is formed at the end opening of the motor housing 1B. . The protrusion 1d engages with the linear groove 6d, thereby allowing the screw shaft 6 to move in the axial direction with respect to the motor housing 1B, but functions to prevent relative rotation about the axis.

  A bracket 12 is fixed to the left end of the screw shaft 6 in FIG. A pin 11 a attached to the end of the wire 11 is engaged with the notch 12 a of the bracket 12. The wire 11 passes through a guide member 13 fitted in the opening of the frame B and is connected to a driven member (not shown). Note that the wire 11 is always urged to the left in FIG. 1 by a spring incorporated in a driven member (not shown). Accordingly, since a thrust load is always applied to the bearing 9, preload is applied to the bearings 4 and 9 by the washer spring 10 disposed between the bearing 4 and the motor housing 1B.

  In addition, since the thrust load is not substantially given to the bearing 4, the bearing 4 can be a radial needle bearing or a bush instead of a ball bearing. Further, instead of the bearing 9, a bush may be provided between the large-diameter portion 3 a of the rotating shaft 3 and the nut housing 1 A, or between the rotating shaft 3 and the round shaft of the screw shaft 6. Further, a bush 24 (indicated by a dotted line in FIG. 2) may be added and supported. However, as in the present embodiment, the bearing 4 is disposed at the end of the rotating shaft 3 and the bearing 9 is disposed at the end of the nut 5, so that the radial dimension can be suppressed and the support span can be suppressed. This increases the support rigidity, which is advantageous from the viewpoint of vibration suppression.

  In FIG. 2, a flat surface 5c is formed on the outer peripheral surface of the nut 5 after the cylinder is scraped off by a parallel surface. Two holes 5d (FIG. 1) communicating with one end and the other end of the transfer path formed by the male screw groove 6b and the female screw groove 5b are formed in the plane 5c, and the substantially U-shaped circulation tube 5a is formed. Both ends are engaged with the holes 5d.

  The circulation tube 5a is restrained by a tube restraining member 5f formed by bending a long and narrow plate, and the vicinity of both ends of the tube restraining member 5f is attached to the nut 5 by two head-attached screws 5e screwed to the flat surface 5c. It is like that. A spring washer 5g, which is an elastic body, is provided between the head 5h of each head screw 5e and the flat surface 5c. The spring washer 5g is deformed by tightening the screw 5e with the head, but the head 5h of the screw 5e with the head is connected to the inner periphery of the large diameter portion 3a in a state where the nut 5 is fitted to the large diameter portion 3a of the rotating shaft 3. The dimensional relationship is such that the elastic force based on the deformation is maintained until the surface abuts.

  Next, the operation of the present embodiment will be described. In FIG. 1, when electric power is supplied from an unillustrated power source to the electric motor 2, the nut 5 connected to the rotary shaft 3 rotates. Further, the rotational displacement of the nut 5 is converted into an axial displacement of the screw shaft 6 (which does not rotate with respect to the housing 1 due to the engagement between the linear groove 6d and the convex portion 1d). At this time, since the ball 7 transfers along the transfer path in the nut 5, such conversion is performed with low friction.

  When the screw shaft 6 moves to the right in FIG. 1 (also referred to as displacement), the wire 11 is pulled through the bracket 12 and the pin 11a and resists the biasing force of the biasing spring provided on the driven member. As a result, the driven member moves. When the power supply to the electric motor 2 is stopped, the urging force of the spring provided on the driven member wins, so the wire 11 moves to the left in FIG.

  FIG. 3 is a cross-sectional view similar to FIG. 2 showing a conventional example. In the conventional example shown in FIG. 3, a spring washer 5g ′ is provided between the head 5h ′ of each head-attached screw 5e ′ and the plane 5c. It is configured such that the elastic deformation of the spring washer 5g 'is lost before' is pulled out and the head 5h 'contacts the inner peripheral surface of the large diameter portion 3a. Accordingly, when the head screw 5e 'is loosened due to vibration or the like, the tube holding member 5f' cannot be fixed, and as a result, the circulation tube 5a may be displaced.

  Here, even if the head-attached screw 5e 'is loosened due to vibration or the like, if the head 5h comes into contact with the inner peripheral surface of the large-diameter portion 3a, further slipping out is prevented. Utilizing this, according to the present embodiment, as shown in FIG. 2, the head 5h of the screw 5e with the head is fitted into the large-diameter portion 3a while the nut 5 is fitted to the large-diameter portion 3a of the rotary shaft 3. Therefore, the spring washer 5g remains elastic even when the head-attached screw 5e is pulled out as much as possible. Therefore, the tube restraining member 5f can be fixed by the elastic force, thereby suppressing the displacement of the circulation tube 5a.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. As an example, an example in which a ball screw mechanism is applied to a linear actuator has been shown, but it goes without saying that the ball screw mechanism of the present invention can be applied to devices other than the linear actuator.

It is sectional drawing of the linear actuator 50 containing the ball screw mechanism concerning this Embodiment. It is the figure which cut | disconnected the structure of FIG. 1 by the II-II line | wire, and looked at the arrow direction. It is sectional drawing similar to FIG. 2 which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Housing 2 Electric motor 3 Rotating shaft 4 Bearing 5 Nut 5a Circulation tube 5f Tube restraining member 5e Screw with head 5g Spring washer 6 Screw shaft 9 Bearing

Claims (1)

A nut receiving member having a cylindrical inner peripheral surface;
A screw shaft;
Is disposed around the screw shaft, fitted to the inner peripheral surface of the nut receiving member, a substantially cylindrical nut which is part of the outer circumferential plane,
In a ball screw mechanism comprising a ball disposed in a transfer path between the screw shaft and the nut,
In the plane of the nut, a circulation tube for returning the ball from one end of the transfer path to the other end, a tube holding member for fixing the circulation tube, and the tube holding member on the outer peripheral surface of the nut a headed screw to secure the disposed between the head screw and said nut, and a spring washer which is elastically deformed by tightening the head screw is provided,
The spring washer maintains an elastic force based on deformation until the screw with the head comes into contact with an inner peripheral surface of the nut receiving member in a state where the nut is fitted to the nut receiving member. Ball screw mechanism.

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