JPH11308805A - Linear actuator provided with worm speed reducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of bearings to be used, and to reduce the cost, the size and the weight, by uniting a drive shaft and a worm on the internal diameter side of a radial bearing provided in a housing, for supporting the drive shaft and the worm in a freely rotatable way. SOLUTION: The base end of a worm 6 is united with the tip of a drive shaft 5, inside an internal wheel 16 constituting a ball bearing 11b supporting the tip part of the drive shaft 5. For the sake of this, a cut split 12 is formed over in the diametrical direction in the base end surdace of the worm 6. The tip part of the drive shaft 5 and the base end part of the worm 6 are inserted into the internal wheel 16 constituting the ball bearing 11b, with a protrusion 13 and the cut split 12 engaged tightly. The drive shaft 5 and the worm 6 are rotatably supported in this state at each tip part of base end part of them by the center part of a flange 24 between the housing 1 and a case 17, and are united in a transmittable state of the torque.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The linear actuator with a worm speed reducer according to the present invention is used in a state where it is incorporated in various mechanical devices such as an electric bed, an electric table, an electric chair and a lifter.

[0002]

2. Description of the Related Art For example, a linear actuator with a worm speed reducer is incorporated in an electric bed or the like for nursing care so that the angle of a bed on which a cared person is laid can be freely adjusted using an electric motor as a drive source. The basic configuration of such a linear actuator with a worm speed reducer will be described with reference to FIGS. 1 and 2 showing an example of an embodiment of the present invention.

A rotating shaft 2 is supported inside a housing 1 by a rolling bearing 3 such as a deep groove type ball bearing so as to be rotatable only. An electric motor 4 that can rotate forward and backward is fixed to the side of the housing 1. This electric motor 4
Although the drive shaft 5 does not intersect with the rotary shaft 2, the axial direction of the rotary shaft 2 (the front and back direction in FIG. 1 and the left and right direction in FIG. 2)
Are arranged in a direction perpendicular to (the left-right direction in FIG. 1 and the front-back direction in FIG. 2). A worm 6 is fixed to such a drive shaft 5 coaxially with the drive shaft 5. A worm wheel 7 is provided on the rotating shaft 2.
Are fixed coaxially with the rotating shaft 2. The worm 6 and the worm wheel 7 are meshed with each other to form a worm speed reducer that increases the torque of the drive shaft 5 and transmits the torque to the rotary shaft 2.

[0004] An external thread 8 is provided in the middle part to the first half (right part in FIG. 2) of the rotary shaft 2, and a nut 9 is screwed into the external thread 8. In addition, the male screw part 8
May be a ball screw groove and the nut 9 may be a ball nut, and the ball screw groove and the ball nut may be screwed together through a plurality of balls. In any case, the base end (the left end in FIG. 2) of an output member such as a cylindrical output shaft 10 is fixedly connected to the nut 9. still,
The nut 9 is free to displace only in the axial direction of the output shaft 10 based on the connection between the tip (the right end in FIG. 2) of the output shaft 10 and a driven portion such as a backrest of the electric bed. (Not rotatable).

In the linear actuator with a worm speed reducer constructed as described above, when the drive shaft 5 of the electric motor 4 is rotated, the output shaft 10 expands and contracts, and the backrest of the electric bed is turned upside down. And the driven part can be driven.
In other words, when the rotating shaft 2 is rotated in a predetermined direction by the driving shaft 5 via the worm 6 and the worm wheel 7, the nut 9 moves to the tip side (the right side in FIG. 2) of the rotating shaft 2. Then, the output shaft 10 extends. On the other hand, when the rotating shaft 2 is rotated in the reverse direction by the driving shaft 5, the nut 9 is moved to the base end side of the rotating shaft 2 (FIG. 2).
To the left), and the output shaft 10 contracts.

In the linear actuator with a worm speed reducer constructed and operated as described above, it is necessary to couple the worm 6 to the drive shaft 5 of the electric motor 4 coaxially with the drive shaft 5. Therefore, conventionally, the worm 6 and the drive shaft 5 have been connected and fixed by a structure as shown in FIGS. First, the structure of the first example shown in FIG.
No. 30,879, in which both ends of the worm 6 are placed inside the housing 1 with a pair of ball bearings 11, 11.
And the worm 6
And the distal end of the drive shaft 5 of the electric motor 4 are spline-engaged. In the structure of the second example shown in FIG. 4, the worm 6 is provided integrally with the tip of the drive shaft 5 of the electric motor 4. Further, in the structure of the third example shown in FIG. 5, a notch 12 formed in the base end of the worm 6 in the diametrical direction and the tip end of the drive shaft 5 of the electric motor 4 in the diametrical direction. While fitting with the formed convex part 13,
A cylindrical sleeve 14 is fitted over the worm 6 and the drive shaft 5 so as to extend over the worm 6 and the drive shaft 5. Further, in the structure of the fourth example shown in FIG. 6, a cylindrical worm 6a is externally fitted to the tip of the drive shaft 5 of the electric motor 4, and the locking pin 15 is connected to the worm 6a and the drive shaft 5 To prevent rotation of the worm 6a with respect to the drive shaft 5.

[0007]

In the case of the conventional structure as described above, the following problem arises due to the structure of the joint between the drive shaft 5 of the electric motor 4 and the worms 6, 6a. First, in the case of the first example of the conventional structure shown in FIG. 3, the drive shaft 5 and the worm 6 need to be supported by a total of four rolling bearings, one pair each, and the number of parts increases. In addition to increasing the cost, the drive shaft 5 and the worm 6
The size of the installation portion in the axial direction is increased, and it is difficult to reduce the size and weight. In the case of the second example of the conventional structure shown in FIG. 4, the portion where the worm 6 is formed at the tip of the drive shaft 5 is
The inside of the inner ring 16 of the ball bearing 11 must be inserted. For this reason, the outer diameter of the worm 6 must be smaller than the outer diameter of the drive shaft 5, and it is difficult to secure the strength of the worm 6. In the case of the third example of the conventional structure shown in FIG. 5, the operation of press-fitting the sleeve 14 to the drive shaft 5 and the worm 6 is troublesome, and the assembling workability is poor. If the sleeve 14 is loosely fitted to the drive shaft 5 and the worm 6, it cannot be adopted because the center axes of the drive shaft 5 and the worm 6 cannot be exactly matched. In addition, the provision of the sleeve 14 increases the distance L between the end surface of the case 17 and the worm 6 constituting the electric motor 4 more than necessary, making it difficult to reduce the size and weight of the linear actuator with a worm reducer. . Further, in the case of the fourth example of the conventional structure shown in FIG. 6, the outer diameter of the worm 6a becomes unnecessarily large, and the lead angle of the worm 6a becomes too small. I do. In addition, the strength of the drive shaft 5 is reduced by the holes formed for inserting the locking pins 15. The linear actuator with a worm speed reducer according to the present invention is designed to eliminate any of the above-mentioned disadvantages.

[0008]

SUMMARY OF THE INVENTION A linear actuator with a worm speed reducer according to the present invention has a housing, a rotating shaft supported only rotatably inside the housing, and a forward / reverse rotating fixed to the housing. An electric motor,
A worm coupled to a drive shaft of the electric motor and a worm wheel fixed to the rotation shaft, the worm speed reducer increasing the torque of the drive shaft and transmitting the torque to the rotation shaft; and a part of the rotation shaft. Male thread part provided on the
A nut that is screwed to the male screw portion and that is supported so as to be able to freely displace only the axial direction of the rotary shaft, and to which an output member can be attached. Particularly, in the linear actuator with a worm speed reducer of the present invention, the drive shaft and the worm are separate from each other, and are combined concentrically with each other so as to be capable of transmitting a rotational force. And
The drive shaft and the worm are connected on the inner diameter side of a radial bearing provided in the housing to rotatably support the drive shaft and the worm.

[0009]

According to the linear actuator with worm speed reducer of the present invention constructed as described above, the distal end of the drive shaft and the proximal end of the worm are supported by a single bearing. The reduction enables cost reduction and reduction in size and weight. In addition, since the drive shaft and the worm are separate bodies, and it is not necessary to insert or insert the worm into the bearing except for the base end, the outer diameter of the worm is made smaller than necessary. It can be set arbitrarily without increasing or making it unnecessarily large. Further, the axial dimension of the effective tooth portion of the worm can be secured without making the axial dimension of the installation portion of the drive shaft and the worm unnecessarily large. Thus, it is easy to secure the strength of the worm and the efficiency of the worm reduction gear. Further, since it is not necessary to form a hole for inserting the locking pin in the drive shaft or the worm, it is easy to secure the strength of the drive shaft or the worm.

[0010]

1 and 2 show an embodiment of the present invention. The feature of the present invention lies in the structure of the worm speed reducer for transmitting the rotation of the drive shaft 5 of the electric motor 4 to the rotation shaft 2. Since the basic structure and operation of the linear actuator with a worm reduction gear are as described above, the overlapping description will be omitted or simplified, and the following description will focus on features of the present invention.

Outer rings 18 forming deep groove type ball bearings 11a, 11b are fixedly fitted in the center of both ends of a case 17 forming the electric motor 4, respectively. And
The inner races 16, 1 constituting these respective ball bearings 11 a, 11 b
6, both ends of the drive shaft 5 are internally fitted and fixed. In the illustrated example, the ball bearing 11b for internally fitting and fixing the tip (the left end in FIG. 1) of the drive shaft 5 corresponds to the radial bearing described in the claims. A projection 13 is formed in a portion of the tip end of the drive shaft 5 located inside the inner race 16 constituting the ball bearing 11b in the diametrical direction.

On the other hand, the case 1
Another cylindrical bearing 11c, such as a deep groove type, which can also support a radial load and a thrust load, is installed on a bottomed cylindrical holding portion 19 provided at a portion which is aligned with a portion to which 7 is fixed. The outer ring 18 constituting this another ball bearing 11c is
It is fitted inside the holding portion 19 so as to be freely displaceable in the axial direction (the left-right direction in FIG. 1). The outer peripheral edge of a preload plate 20 made of an elastic material such as a plate spring is abutted against the outer end surface (the left end surface in FIG. 1) of the outer ring 18. Also, the holding section 19
A screw hole 21 is formed in the center of the bottom surface of the adjusting screw 22 screwed into the screw hole 21. The distal end surface (the right end surface in FIG. 1) is connected to the outer surface of the preload plate 20 (the left side in FIG. 1). Surface) It hits the center. Therefore, the outer ring 18 is provided with a rightward elasticity in FIG. The adjusting screw 22
A lock nut 23 is screwed into the outer half (the left half in FIG. 1).

The tip (the left end in FIG. 1) of the worm 6 is fixedly fitted inside the inner ring 16 constituting another ball bearing 11c as described above. On the other hand, the base end (the right end in FIG. 1) of the worm 6 is located inside the inner race 16 that constitutes the ball bearing 11b that supports the tip of the drive shaft 5.
The drive shaft 5 is connected to the tip. For this purpose, a cut 12 is formed in the base end surface of the worm 6 in the diametric direction. The distal end of the drive shaft 5 and the base end of the worm 6 are fitted inside the inner race 16 of the ball bearing 11b in a state where the projection 13 and the cut 12 are fitted without looseness. It is fitting. In this state, the drive shaft 5 and the worm 6 move their respective distal ends or proximal ends,
It is rotatably supported at the center of a flange 24 located between the housing 1 and the case 17 and is coupled to a state where torque can be transmitted.

In the linear actuator with worm speed reducer of the present invention configured as described above, the distal end of the drive shaft 5 and the proximal end of the worm 6 are rotatably supported by a single ball bearing 11b. Therefore, in order to rotatably support the drive shaft 5 and the worm 6 formed separately from each other, only three ball bearings 11a, 11b, and 11c are used. As described above, the first structure of the conventional structure shown in FIG.
By reducing the number of ball bearings used compared to the example,
Cost reduction and reduction in size and weight can be achieved.

Further, the drive shaft 5 and the worm 6 are separately provided, and the worm 6 is removed from the ball bearing 11 except for the base end.
This eliminates the need to insert or insert into the inner ring 16 that constitutes b. Therefore, the outer diameter of the worm 6 can be freely set regardless of the inner diameter of the inner ring 16. In addition, as compared with the case where the sleeve 14 and the locking pin 15 are provided as in the third and fourth examples of the conventional structure shown in FIGS. The axial dimension of the effective tooth portion of the worm 6 can be secured without increasing the dimension more than necessary. Thus, it is easy to secure the strength of the worm 6 and the efficiency of the worm reduction gear. Further, since there is no need to form a hole for inserting the locking pin 15 in the drive shaft 5 or the worm 6,
It is easy to secure the strength of the drive shaft 5 and the worm 6.

In the illustrated example, the worm 6 is attached to the worm 6 via the ball bearing 11c by the preload plate 20 as shown in FIG.
To give a rightward elasticity, thereby applying a preload for causing the worm teeth formed on the worm 6 and the teeth formed on the outer peripheral surface of the worm wheel 7 to elastically contact with each other. Such a configuration prevents rattling at the worm speed reducer. However, when implementing the present invention, it is not always necessary to adopt such a structure for applying a preload. Further, a member to be driven can be directly connected to the nut 9. In this case, the member to be driven corresponds to the output member described in the claims.

[0017]

Since the present invention is constructed and operates as described above, it is possible to inexpensively realize a small and lightweight linear actuator with a worm reducer having excellent durability and transmission efficiency.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing an example of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view similar to FIG. 1, showing a first example of a conventional structure.

FIG. 4 is a partial sectional view showing the second example.

FIG. 5 is a partial sectional view showing the third example.

FIG. 6 is a partial sectional view showing the fourth example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Rotating shaft 3 Rolling bearing 4 Electric motor 5 Drive shaft 6, 6a Worm 7 Worm wheel 8 Male screw part 9 Nut 10 Output shaft 11, 11a, 11b, 11c Ball bearing 12 Split 13 Projection part 14 Sleeve 15 Lock pin 16 Inner ring 17 Case 18 Outer ring 19 Holding part 20 Preload plate 21 Screw hole 22 Adjusting screw 23 Lock nut 24 Flange

Claims (1)

[Claims] 1. A housing, a rotating shaft rotatably supported inside the housing so as to be rotatable only, an electric motor fixed to the housing and capable of normal rotation and reverse rotation, and a worm coupled to a drive shaft of the electric motor. A worm speed reducer, comprising a worm wheel fixed to the rotating shaft, for increasing the torque of the drive shaft and transmitting the torque to the rotating shaft, a male screw part provided on a part of the rotating shaft, and a male screw part A worm that is screwed into the nut and freely supported only in the axial direction of the rotary shaft. A linear actuator with a worm reducer that allows an output member to be freely attached to the nut. The worm and the worm are separate from each other, are combined with each other concentrically, and are capable of transmitting a rotational force. The drive shaft and the worm rotate these drive shafts and the worm. A linear actuator with a worm reducer, characterized in that the linear actuator is connected on the inner diameter side of a radial bearing provided in the housing so as to be supported.