Patent Application
20050160855
1. Field of the Invention
The present invention relates to a linear movement/rotation mechanism that linearly and/or rotationally moves a drive shaft using a ball screw/ball spline mechanism.
2. Related Art
A mechanism that uses a ball screw and a ball spline is known as one example of a mechanism for linearly or rotationally driving a drive shaft. A ball screw/ball spline mechanism constructed so that a ball screw thread and a ball spline groove are formed in an outer circumferential surface of a drive shaft so as to intersect one another and a ball screw nut that engages the ball screw thread and a ball spline nut that engages the ball spline groove are attached to the drive shaft is also known (see Patent Documents 1, 2).
The ball screw/ball spline mechanism 110 is disposed in parallel with the reduction gear 102 and a reduced rotation output shaft 103 of the reduction gear 102 is fixed to a driving-side pulley 104. A driven-side pulley 105 is fixed to one end of the ball spline nut 115 of the ball screw/ball spline mechanism 110, and a timing belt 106 is suspended between the driving-side pulley 104 and the driven-side pulley 105. It should be noted that a separate driven-side pulley 107 is also attached to an end of the ball screw nut 114.
When the motor 101 is driven, the output rotation of the motor is reduced by the reduction gear 102 and transmitted to the ball spline nut 115 of the ball screw/ball spline mechanism 110 via the belt/pulley transmission mechanism 120. When the ball spline nut 115 rotates, the drive shaft 113 integrally rotates with the ball spline nut 115. For example, if the ball screw nut 114 is fixed so as not to rotate, the drive shaft 113 moves in a direction of a center axis 113a thereof while rotating. By controlling the rotational direction and rotation amount of the ball spline nut 115, it is possible to cause the drive shaft 113 to linearly move reciprocally with a predetermined stroke.
Patent Document 1
JP-B 07-9260
Patent Document 2
JP-B 06-84778
A conventional linear movement/rotation mechanism has a configuration in which after the output rotation of the motor is reduced by the reduction gear, the reduced output is transmitted via the belt/pulley transmission mechanism to the ball screw/ball spline mechanism that is disposed in parallel with the motor and the reduction gear. Accordingly, the final stage of a rotational force transmission path for the ball screw/ball spline mechanism is the belt/pulley transmission mechanism. Compared to other transmission mechanisms such as gear trains, positioning accuracy of the belt/pulley transmission mechanism is low, and belt strength is also low. Therefore, in cases such as when a large inertial load is present, the positioning accuracy of the drive shaft falls.
In view of the above problem, it is a main object of the present invention to provide a linear movement/rotation mechanism equipped with a ball screw/ball spline mechanism that can accurately position a drive shaft even when a large inertial load is applied.
To achieve the above and other objects, a linear movement/rotation mechanism according to the present invention includes:
Here, the ball screw nut, the ball spline nut, the hollow planetary reduction gear, and the rotation input member may be disposed in that order along a direction of a center axis of the drive shaft. Alternatively, the ball screw nut, the rotation input member, the hollow planetary reduction gear, and the ball spline nut may be disposed in that order along the direction of the center axis of the drive shaft.
As the hollow planetary reduction gear, it is possible to use a construction including:
In addition to the above construction, a linear movement/rotation mechanism according to the present invention may include a tube-like housing and a common bearing, wherein the ball spline nut and the rear stage internal gear are rotatably supported by the tube-like housing via the common bearing.
In the linear movement/rotation mechanism according to the present invention, the hollow planetary reduction gear is coaxially connected to the ball screw/ball spline mechanism. The final stage of a rotational force transmission path for the ball screw/ball spline mechanism is the planetary reduction gear that has high strength, so that compared to the conventional construction where the final stage is a belt/pulley transmission mechanism with low strength and positioning accuracy, the positioning accuracy of the drive shaft can be increased.
Also, in the case where the ball spline nut of the ball screw/ball spline mechanism and the reduced rotation output element (the rear stage internal gear) of the planetary reduction gear are supported by the tube-like housing via the common bearing, compared to the conventional construction where the ball spline nut and the rear stage internal gear are supported using separate bearings, the construction can be made smaller, more compact and cheaper.
Preferred embodiments of a linear movement/rotation mechanism equipped with a ball screw/ball spline mechanism according to the present invention will now be described with reference to the drawings.
As shown in
The ball spline nut 8 includes an endless track thread in which balls are disposed in a freely rollable state so as to engage the ball spline grooves 10, and is rotatably supported via a left-right pair of support bearings 15, 16 on an inner circumferential surface of a cylindrical housing 17. A large-diameter attachment flange 17a is formed on an outer circumferential surface of the cylindrical housing 17 and is fixed to the tube-like housing 2.
As shown in
Four common planetary shafts 26 that are disposed at intervals of a fixed angle in a circumferential direction (90° in the present embodiment) span a gap between the left and right carrier members 22a, 22b of the carrier 22. On the respective common planetary shafts 26, front stage planetary gears 27 and rear stage planetary gears 28 are supported so as to be freely rotatable and disposed in parallel. In the present embodiment, the front stage planetary gears 27 and the rear stage planetary gears 28 are constructed so that the teeth thereof are formed on an outer circumferential surface of a single gear part.
The front stage planetary gears 27 engage a front stage internal gear 31 disposed so as to surround outside thereof. The front stage internal gear 31 is provided with a large-diameter attachment flange 31a that is fixed to the tube-like housing 2. The rear stage planetary gears 28 also engage a rear stage internal gear 32 disposed so as to surround outside thereof The rear stage internal gear 32 is integrally formed with a disc-like part 32b with a center through hole through which the drive shaft 6 passes. The disc-like part 32b is connected to and fixed in a coaxial state to the ball spline nut 8 via a ring-shaped connecting member 33.
The tube-like housing 2 also includes a tube-like part 41 that covers the ball screw/ball spline mechanism 3, and a tube-like part 42 and an end cap 43 that cover the hollow planetary reduction gear 4. The attachment flange 13a of the cylindrical housing 13 of the ball screw nut 7 is tightened and fixed to an end surface 41a of the tube-like part 41 by a fixing bolt 44. The tube-like part 41 and the tube-like part 42 sandwich the attachment flange 17a of the cylindrical housing 17 of the ball spline nut 8 and are coaxially fastened and fixed together by a fastening bolt 45. An open end of the tube-like part 42 is sealed by the end cap 43, and the tube-like part 42 and the end cap 43 sandwich the attachment flange 31a of the front stage internal gear 31 of the hollow planetary reduction gear 4 and are fastened and fixed together by a fastening bolt 46.
The end cap 43 includes a ring-shaped end plate part 43a and a through-hole inner circumferential surface thereof rotatably supports one end of the hollow rotational shaft 21 via a bearing 47. The other end of the hollow rotational shaft 21 is rotatably supported via a bearing 48 by an inner circumferential surface of the disc-like part 32b of the rear stage internal gear 32. The rear stage internal gear 32 is connected and fixed to the ball spline nut 8, and the ball spline nut 8 is rotatably supported by the cylindrical housing 17 via the support bearings 15, 16. Accordingly, the support bearings 15, 16 function as bearings that are common to the ball spline nut 8 and the rear stage internal gear 32.
On the other hand, the hollow rotational shaft 21 of the hollow planetary reduction gear 4 protrudes outward from the end plate part 43a of the end cap 43 and on an outer circumferential surface of a protruding end 21c a large-diameter attachment flange 49 is attached. The driven pulley 5 is coaxially fastened to and fixed to the attachment flange 49.
In the linear movement/rotation mechanism 1 of the construction described above, when a rotational force is transmitted from a rotational driving source, such as a motor, via a belt/pulley mechanism to the driven pulley 5, an input rotation is reduced by the hollow planetary reduction gear 4 and a reduced speed rotation output is outputted from the rear stage internal gear 32. The rear stage internal gear 32 is connected to and fixed to the ball spline nut 8 of the ball screw/ball spline mechanism 3, so that the reduced rotation output is transmitted to the ball spline nut 8 which rotates at reduced speed.
The drive shaft 6 is in ball spline engagement with the ball spline nut 8, so that the drive shaft 6 rotates integrally with the ball spline nut 8 and is free to move in the direction of the center axis 1a. The drive shaft 6 is in ball screw engagement with the ball screw nut 7, so that when the drive shaft 6 rotates in a state where rotation of the ball screw nut 7 is prevented, the drive shaft 6 moves linearly in the direction of the center axis 1a. In a case where the ball screw nut 7 is free to rotate, when the drive shaft 6 rotates, the ball screw nut 7 rotates integrally with the drive shaft 6 and there is no feeding of the drive shaft 6.
Accordingly, if the rotation of the ball screw nut 7 is restricted, the drive shaft 6 moves in the direction of the center axis 1a while rotating. By controlling the rotational direction and amount of rotation of the ball spline nut 8, the drive shaft 6 can be caused to linearly move reciprocally with a predetermined stroke. By allowing the ball screw nut 7 to rotate freely, the drive shaft 6 rotates with no linear movement.
The linear movement/rotation mechanism 1A of the present modification is constructed with the ball screw nut 7, the driven pulley 5 that is the input rotation member, the hollow planetary reduction gear 4, and the ball spline nut 8 aligned in that order along the direction of the center axis 1a.
In this way, in the linear movement/rotation mechanism 1A, the driven pulley 5 and the hollow planetary reduction gear 4 are disposed between the ball screw nut 7 and the ball spline nut 8. A tube-like housing 2A is constituted by tube-like members 51, 52, 53, and 54 that are connected and fixed to one another in that order along the center axis 1a in a coaxial state. At one end of the tube-like housing 2A, the attachment flange 13a of the ball screw nut 7 is fixed to an end surface 51a of the tube-like housing 51 and at the other end of the tube-like housing 2A, the tube-like housings 53 and 54 are fastened and fixed to one another with the attachment flange 17a of the ball spline nut 8 sandwiched in between. In addition, a support flange 52a that protrudes inwards is formed on the tube-like housing 52, with an inner circumferential surface of the support flange 52a rotatably supporting one end of the hollow rotational shaft 21 via the bearing 47.
The hollow rotational shaft 21 of the hollow planetary reduction gear 4 includes an end part 21d that protrudes from the support flange 52a toward the ball screw nut 7 and an attachment flange 49 is attached to an outer circumferential surface part of the end part 21d.The driven pulley 5 is coaxially fixed to the attachment flange 49. An opening 51b through which a belt (not shown) that is suspended on the driven pulley 5 passes is formed in the tube-like housing 51 facing the driven pulley 5. It should be noted that the operation of the linear movement/rotation mechanism 1A is the same as that of the linear movement/rotation mechanism 1 described above.
A hollow planetary reduction gear 4A of the present modification is constructed so that the rear stage internal gear 32 is rotatably supported by a cross roller bearing 60. The cross roller bearing 60 includes an inner ring 61 fixed to the disc-like part 32b of the rear stage internal gear 32, an outer ring 62 functioning as part of the tube-like housing 2, and a roller 63 inserted between the inner ring 61 and the outer ring 62 so as to be freely rollable. The inner ring 61 is connected and fixed to the ball spline nut 8 (not shown) in a coaxial state.
In the hollow planetary reduction gear 4A of this construction, the cross roller bearing 60 is used as a reduction gear output bearing for supporting the rear stage internal gear 32 that is the reduced rotation output element. In the hollow planetary reduction gear 4 described above, the support bearings 15, 16 of the ball spline nut 8 serve as the reduction gear output bearing, which is advantageous in making the construction smaller, more compact, and cheaper. On the other hand, the cross roller bearing 60 is used in the hollow planetary reduction gear 4A of the present modification, so that the hollow planetary reduction gear 4A is suited to applications where a large load is applied.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-17990 | Jan 2004 | JP | national |
