JPH0372422B2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention involves screwing a ball nut onto a ball screw shaft via a steel ball, and moving the ball screw shaft and the ball nut relative to each other rotationally or axially. The present invention relates to a transfer device using a ball screw for moving a movable table such as a work table connected to a ball nut.

(Prior art) Conventionally, a motor such as a stepping motor is connected to a ball screw shaft that is movable in the rotational direction and fixed in the axial direction and supported by a fixed bed, and a motor such as a stepping motor is connected to the ball screw shaft through a steel ball. A moving table is connected to the combined ball nut, and the ball screw shaft is rotated by driving the motor to move the ball nut in the axial direction of the ball screw shaft, and the moving table connected to the ball nut is moved relative to the fixed bed. Such a transfer device is known.

However, in such conventional transfer devices, the ball screw shaft and the motor are connected via a gear having a pair of gears that mesh with each other, so the rotational driving force of the motor is transferred to the ball due to the backlash between these gears. It is difficult to accurately convey information to the screw shaft,
Furthermore, since the ball screw shaft itself has a relatively large inertia, it is not only impossible to accurately position the movable table connected to the ball nut screwed onto the ball screw shaft, but also the ball screw shaft when changing the rotational direction of the motor. The drawback was poor shaft response. Furthermore, when rotating the ball screw shaft at high speed to increase the feed speed of the moving table, if the rotation speed of the ball screw shaft increases and exceeds a certain value (so-called critical speed), the ball screw shaft will resonate. In order to avoid this, the ball screw shaft must be rotated at a speed lower than the allowable rotational speed determined by the critical speed, which places restrictions on the rapid feeding of the movable table.

(Problems to be Solved by the Invention) As a means of solving such problems in gear transmission mechanisms, conventionally, a hole through which a screw shaft can be inserted is provided in the rotor of a drive motor, and a nut is screwed onto the screw shaft. A ball nut device that connects directly to the rotor without using a gear transmission mechanism is also known (Japanese Patent Laid-Open No. 58
−207563).

However, although this ball nut device can eliminate problems caused by back crushing, since the nut is fixed to the inner circumference of the rotor, the motor becomes larger due to the thickness of the nut, and when installed in a table, the center of gravity of the table becomes There was a problem with the price being high. The point of application of the force that drives the table is the nut-fitting part of the screw shaft, and as the center of gravity of the table becomes higher, the distance between the screw shaft and the center of gravity increases, making the movement of the table unstable.
Particularly when the table is started or stopped, so-called pitting occurs, in which the front and back of the table swings up and down, which deteriorates responsiveness and prevents accurate positioning.

Therefore, the present invention allows the ball nut to rotate with respect to the ball screw shaft, accurately transmits the rotational driving force of a drive source such as a motor to the ball nut, and lowers the center of gravity as much as possible to rotate the ball nut. To provide a transfer device using a ball screw, which can significantly improve the positioning accuracy of a moving table connected to a drive source, and improve the responsiveness of a ball nut and the moving table when changing the rotational direction of a drive source. The purpose is to

Another object of the present invention is to provide a transfer device using a ball screw that allows the feed speed of the moving table to be increased arbitrarily without restrictions.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a movable table supported movably in the axial direction on a fixed bed, a ball screw shaft supported on the fixed bed, The ball nut is screwed onto the ball screw shaft via a steel ball and supported on the movable table so as to be movable in the rotational direction, and a drive source fixed to the movable table to rotationally drive the ball nut. , a hollow rotating shaft is inserted into the drive source, the drive source and a ball nut are spaced apart from each other in the axial direction, and the ball screw shaft is rotatable and axially movable on the hollow rotating shaft of the drive source. One end of the rotating shaft is connected to the ball nut so as to be able to rotate together with the ball nut.

(First Embodiment) Hereinafter, embodiments of the present invention will be described based on the drawings. FIGS. 1 to 8 show a first embodiment of a transfer device using a ball screw according to the present invention. .

First, as shown in FIGS. 1 to 3, a pair of tracks 2, 2 are arranged parallel to each other on the upper surface of the flanges 1a, 1a on both sides of the fixed bed 1. A movable table 4 is provided above the track 2 via four linear sliding bearings 3, 3, 3, 3 so as to be able to slide in the axial direction along the tracks 2, 2.

As is clear from FIGS. 1 and 2, a bearing case 7 is fixed to an end plate 5 fixed to one end of the bed 1 (the left end in FIGS. 2 and 3), and this bearing case 7 has a track. One end of the ball screw shaft 8 parallel to the bases 2 is rotatably supported via a bearing 9 made of a compound interest angular ball bearing, and the other end is attached to an end plate 10 fixed to the other end of the bed 1. The ball screw shaft 8 is rotatably supported in a bearing case 11 via a bearing 12 made of a double row angular ball bearing, and the free end of the ball screw shaft 8 protruding from the bearing 12 is fixed to the end plate 10 of the bed 1. A rotating shaft 14 of a stepping motor 14 as another drive source attached to the bracket 13
a through a joint 15.

A spiral ball screw (for example, right-handed thread) 8a is carved on the outer peripheral surface of the ball screw shaft 8 over almost the entire length of the ball screw shaft 8, except for the journal portions at both ends. 20 is fitted, and this ball nut 20 is attached to the motor housing 22 which is fixed to the lower surface of the movable table 4 by fasteners 21, 21, etc. such as bolts.
It is supported immovably in the axial direction and movably in the rotational direction via a bearing 25 consisting of a single row angular ball bearing in a ball nut housing 24 attached to the ball nut housing 24, which is attached to the ball nut housing 24 by the ball screw shaft 8. Therefore, the rotation of the ball screw shaft 8 This allows the ball nut 20 to move in the axial direction with respect to the ball screw shaft 8.

The structure of the ball nut 20 will be explained with reference to FIG. 6. The cylindrical ball nut 20 that is fitted onto the outer periphery of the ball screw shaft 8 has an annular groove 28a on the outer periphery of one end for fitting the inner race of the bearing 25.
a cylindrical first nut body 28, a cylindrical second nut body 29, and an annular spacer 30 interposed between the first and second nut bodies 28, 29.
The inner peripheral surfaces of the first and second nut bodies 28 and 29 have spiral thread grooves 28a and 29a having the same lead as the spiral thread groove 8a on the outer periphery of the ball screw shaft 8. are formed in a spiral shape, and a large number of steel balls 31,
31... are arranged, and as the ball screw shaft 8 rotates, the steel balls 31, 31... are connected to the ball screw shaft 8 and the first and second steel balls 31, 31...
Mutually corresponding thread grooves 8 of the nut bodies 28 and 29
a, 28a, 29a to move the ball nut 20, which consists of the first and second nut bodies 28, 29, in the axial direction of the ball screw shaft 8. Further, the first and second nut bodies 28, 29 are urged in the direction of separating from each other by a spacer 30 inserted between them, and the steel balls 31, 31... and the thread grooves 8a, 28a, There is no backlash (axial gap) between 29a, and the response when the ball nut 20 moves in the axial direction due to the rotation of the ball screw shaft 8 is improved.

As shown in an enlarged view in FIG. 4, a stepping motor 35 as a drive source is housed in the motor housing 22, and this motor 35 has a stator 36 fixed to the motor housing 22.
and both end walls 22a, 22 of the motor housing 22.
b is rotatably supported via a double-row angular ball bearing 37 and a single-row radial ball bearing 38, respectively, and has a ball screw shaft 8 inserted into the hollow interior so as to be rotatable and slidable in the axial direction. 39, a rotor 40 fixed to the outer periphery of the rotating shaft 8, and a winding 41 wound around the rotor 40, and an annular mounting flange 39a at one end of the hollow rotating shaft 39. One end of the outer peripheral portion of the ball nut 20 is supported by the flange 39a, and the ball nut 20 and the mounting flange 39a are connected by a key 42 so as to rotate integrally. Ball nuts 20 like this
are provided spaced apart from the motor 35 in the axial direction,
Since it is connected to one end of the rotating shaft 39, the motor 3
5 can be made as small as possible in the radial direction, and the center of gravity of the entire table can be lowered. Therefore, the distance between the rotating shaft 39, on which the driving force for moving the table 4 acts, and the center of gravity of the table 4 is reduced, making it possible to prevent pitting that occurs when starting or stopping.

Note that 43 and 44 are spacers interposed between the radial ball bearing 38 and the double-row angular ball bearing 37, respectively, and the winding 41, and 45 is a stop ring for preventing the outer race of the angular ball bearing 37 from slipping out.

As shown in FIGS. 7 and 8, the movable table 4 has four linear sliding bearings 3, 3, 3, 3.
It is slidably supported on the tracks 2, 2 via. More specifically, loaded ball grooves 50 and unloaded ball grooves 51 extending in the axial direction are alternately formed in the circumferential direction on the inner surface of each bearing 3, and the loaded ball grooves 50 and the unloaded ball grooves 51 adjacent to each other are formed alternately in the circumferential direction. are connected continuously at both ends to form an endless loop,
Further, each track base 2 is also formed with a ball raceway surface 52 corresponding to the loaded ball groove 50 of each bearing 3, and between the loaded ball groove 50 and the ball raceway surface 52 and within the unloaded ball groove 51. A large number of balls 53, 53, . . . are arranged. Each bearing 3
The ball 5 is connected between the track base 2 and each track base 2 by a retainer 54.
3, 53... are held. Therefore, when the bearings 3, 3, 3, 3 move in the axial direction on the tracks 2, 2, the balls 53, 53, . . .
0 and the ball rolling surface 52, enters the no-load ball groove 51, moves there in the axial direction, and returns again between the loaded ball groove 50 and the ball transfer surface 52. In this way, smooth movement of the moving table 4 relative to the tracks 2, 2 can be guaranteed.

(Function) Next, the function of this embodiment will be explained.
First, as the stepping motor 14 connected to the ball screw shaft 8, for example, a stepping motor with 800 divisions, that is, the rotation angle per step is 360/800=0.45 degrees, and a stepping motor 35 directly connected to the ball nut 20. In addition, the ball groove 8a of the ball screw shaft 8 is a right-handed screw, and its lead is 4.
mm.

Now, with the stepping motor 14 stopped, if the stepping motor 35 is rotated one step clockwise, the ball nut 20 will move 360/360 degrees in the same direction.
It is rotated by an angle of 1000 = 0.36° and moved axially to the left by 4 x (0.36/360) = 0.004 mm with respect to the ball screw shaft 8, so that the moving table 4 is moved through the motor housing 22 into the orbit. When the bases 2 and 2 are moved in the same direction (to the left) and the same distance, and when the stepping motor 35 is rotated one step counterclockwise, the ball nut 20 is moved in the axial direction with respect to the ball screw shaft 8.
The moving table 4 is moved to the right by 0.004 mm, and the moving table 4 is also moved the same distance in the same direction (to the right) on the tracks 2, 2.

On the other hand, when the stepping motor 35 rotates clockwise, the stepping motor 14 is
When the ball screw shaft 8 is rotated in the opposite direction (counterclockwise) by the stepping motor 14 through the joint 15, the ball screw shaft 8 is rotated to the left by an angle of 360/800=0.45°. The screwed ball nut 20 extends 4 in the axial direction of the ball screw shaft 8.
Moved to the left by ×(0.45/360)=0.005mm. Therefore, the ball nut 20 is moved by the stepping motor 14 in the axial direction of the ball screw shaft 8.
It is moved leftward by 0.009 mm, which is the sum of 0.005 mm and the moving distance of 0.004 mm by the stepping motor 35, that is, it is rapidly fed.

Furthermore, when the stepping motor 35 rotates clockwise, if the stepping motor 14 is rotated one step in the same direction as the rotation direction of the motor 35 (clockwise), the ball nut 20 is rotated clockwise due to the clockwise rotation of the ball screw shaft 8. moved by a distance of 0.005mm,
Therefore, the ball nut 20 is moved by the stepping motor 14 in the axial direction of the ball screw shaft 8.
It is moved to the right by a difference of 0.001 mm between 0.005 mm and the moving distance of 0.004 mm by the stepping motor 35, that is, it is slightly moved.

In this embodiment, the ball screw shaft 8 is also rotated together with the ball nut 20.
Since the ball nut 20 itself is also rotated, even if the rotational speed of the ball screw shaft 8 is relatively low, if the rotational speed of the ball nut 20 itself is increased, the moving table can be rapidly fed.

(Second Embodiment) Figures 9 to 12 show a second embodiment of a transfer device using a ball screw according to the present invention, and the same members as in the first embodiment are designated by the same reference numerals. Attached. In this embodiment, double nuts 55 and 56 are screwed onto both ends of the ball screw shaft 8.
is fixedly supported on both end plates 5, 10 of the bed 1, and a rotating shaft 39 of a stepping motor 35 serving as a driving source.
are connected to both end walls 22a, 22 of the motor housing 22 via single row angular ball bearings 57, 58, respectively.
The structure is substantially the same as that of the first embodiment, except that it is rotatably supported by the ball screw shaft 8, and the operation is the same as that of the first embodiment when the rotation of the ball screw shaft 8 is stopped. Therefore, detailed explanation will be omitted.

According to this embodiment, the ball screw shaft 8 is fixed to both end plates 5, 10 of the bed 1, eliminating the need for bearings and also eliminating the stepping motor 14 connected to the ball screw shaft 8, resulting in a smaller overall device. In addition to being lightweight, the length of the ball screw shaft 8 can be reduced by pulling both ends of the ball screw shaft 8 using nuts 55, 56, etc. to apply tension to the ball screw shaft 8 and suppress its deflection. By increasing the height, the reciprocating stroke of the ball nut 20 and, by extension, the movable table 4 can be increased.

In the above embodiment, a stepping motor was used as the drive source 35, but other drive sources such as a servo motor may be used.

(Effects of the Invention) In the transfer device of the present invention having the above configuration and operation, the rotational driving force of the drive source is directly connected to the ball nut screwed onto the ball screw shaft and the rotating shaft of the drive source. Can be accurately transmitted to the ball nut. In addition, a hollow rotating shaft is inserted into the drive source, the ball nut and the drive source are spaced apart in the axial direction, and the ball nut is connected to one end of the hollow rotating shaft of the drive source, so that the nut can be inserted into the drive source. The radial size of the drive source can be made smaller than when the drive source is directly fixed to the rotor of the drive source. Therefore, the center of gravity of the entire table can be brought closer to the ball screw shaft on which the driving force acts, and biting during starting and stopping can be minimized.

Further, since no transmission mechanism such as a gear is interposed between the rotating shaft of the drive source and the ball nut, the device can be made smaller and lighter.

Furthermore, if the ball screw shaft is fixed to the base,
Compared to conventional devices that rotate the ball screw shaft, the ball nut is much smaller and lighter than the ball screw shaft, so it has less inertia, and therefore significantly improves the positioning accuracy of the movable table connected to the ball nut. In addition, the responsiveness of the ball nut and the movable table when changing the rotational direction of the drive source can be improved. Further, by increasing the rotation speed of the drive source and rotating the ball nut at high speed, the feed speed of the movable table can be increased arbitrarily without restrictions. Furthermore, since no transmission device such as a gear is interposed between the rotating shaft of the drive source and the ball nut, the device can be made smaller and lighter.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and FIGS. 1 to 8 show the first embodiment of the transfer device according to the present invention. FIG. 2 is a side view of the main parts, FIG. 3 is a sectional view taken along the line of FIG. 1, FIG. 4 is an enlarged vertical side view of the motor equipped with a ball nut, and FIG. 6 is an enlarged vertical sectional side view of the ball nut, FIG. 7 is a partially cutaway side view of the moving table, FIG. 8 is an enlarged front view with a part of the bearing unit cut away, and FIG. Figures 12 to 12 show a second embodiment of the transfer device according to the present invention, in which Figure 9 is a plan view similar to Figure 1, Figure 10 is a side view similar to Figure 2, and Figure 10 is a side view similar to Figure 2.
Figure 11 is an enlarged vertical side view similar to Figure 4;
FIG. 2 is a front view similar to FIG. 5. DESCRIPTION OF SYMBOLS 1...Bed, 4...Moving table, 8...Ball screw shaft, 14...Stepping motor as another drive source, 20...Ball nut, 35...Motor as drive source, 39...Rotating shaft.

Claims (1)

[Scope of Claims] 1. A movable table supported movably in the axial direction on a fixed bed, a ball screw shaft supported by the fixed bed, and screwed to the ball screw shaft via a steel ball. a ball nut supported on the movable table in a state of being movable in the rotational direction; and a drive source fixed to the movable table to rotationally drive the ball nut, a hollow rotating shaft being inserted into the drive source, and , the drive source and the ball nut are arranged apart from each other in the axial direction, the ball screw shaft is rotatably and axially movably inserted through the hollow rotating shaft of the drive source, and one end of the rotating shaft is A transfer device using a ball screw connected to the ball nut so as to be able to rotate integrally with the ball nut. 2. The ball screw according to claim 1, wherein the ball screw shaft is rotatably supported on the fixed bed, and another drive source for rotationally driving the ball screw shaft is connected to the ball screw shaft. Transfer device using 3. A transfer device using a ball screw according to claim 1, wherein the ball screw shaft is fixed to the fixed bed.