JPH0570744B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a ball screw device suitable for application to, for example, an operating arm of an industrial robot, particularly a ball capable of rotating and sliding a screw shaft. Relating to screw devices.

[Conventional technology]

As a conventional ball screw device, for example,
There is one described in Publication No. 60-9342.

In this conventional example, a ball screw groove is formed in one half of the ball screw shaft, a spline groove is formed in the other half, a ball bearing nut is engaged with the ball screw groove, and a ball spline is engaged with the spline groove. By driving the ball bearing nut with a motor, the ball screw shaft is moved linearly forward and backward.

[Problem that the invention seeks to solve]

However, in the conventional ball screw device described above, the ball screw groove and the spline groove are formed separately, so the length of the ball screw shaft is longer than its stroke, making the entire device larger. At the same time, since the ball screw shaft only moves in a straight line, when applied to the operating arm of an industrial robot, an actuator with a rotation function is required for the knob attached to the tip of the ball screw shaft. However, there were problems such as the structure of the actuator becoming complicated.

Therefore, the present invention was made by focusing on the problems of the conventional example, and it is possible to reduce the length of the screw shaft with respect to the stroke, thereby downsizing the entire device, and to control the rotation and sliding of the screw shaft. The purpose is to provide a high-precision ball screw device.

[Means for solving problems]

In order to achieve the above object, the present invention provides a helical shaft having a helical ball screw groove and an axially extending ball spline groove, and a first ball that engages with the ball spline groove of the helical shaft. A ball nut that holds a group so as to be endlessly rotatable, a first rotational drive mechanism that rotationally drives the ball nut, and a second ball group that engages with the ball spline groove at a position close to the ball nut. a second rotary drive mechanism that rotatably drives the ball spline nut to rotate the screw shaft; and a supporting housing.

[Effect]

In this invention, the required stroke of the screw shaft is reduced by providing the screw shaft with overlapping ball screw grooves and ball spline grooves, and arranging the ball nut and ball spline nut in close proximity and independently supported by the housing. The overall configuration can be made more compact by shortening the length of the ball spline nut, and the screw shaft can be moved forward and backward by the rotation of the ball nut without being affected by the rotational position of the ball spline nut. Since the screw shaft can be rotated by the rotation of the ball spline nut without being affected by the

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention;
FIG. 2 is a sectional view taken along the - line in FIG. 1, FIGS. 3 and 4 are a longitudinal sectional view and a partially cutaway front view showing an example of a ball spline that can be applied to the present invention, and FIG. 5 a and b are an enlarged longitudinal cross-sectional view and a cross-sectional view, respectively, showing the engagement relationship between the screw shaft and the ball spline.

In FIG. 1, reference numeral 1 denotes a cylindrical housing, both ends of which are closed with end plates 2 and 3. In FIG.
Each of the end plates 2 and 3 includes annular parts 2a and 3a fixed to the ends of the housing 1, and cover plate parts 2b and 3b that cover the center part thereof. and,
A flange 1a formed at the left end is attached to an arm attachment part A of an industrial robot by tightening bolts. Inside the housing 1 are end plates 2 and 3.
Screw seals 2c, 3 provided on the cover plate parts 2b, 3b of
A hollow screw shaft 4 sealed by c is slidably and rotatably inserted through the shaft.

The screw shaft 4 has ball screw grooves 5 of a predetermined pitch on its outer peripheral surface, and six ball spline grooves 6 arranged at equal intervals in the circumferential direction, overlapping and coexisting at the same position, and an electric motor at the tip. A hydraulic or hydraulic type actuator 7 is attached to the actuator 7, and a pair of fingers 8 are attached to the actuator 7. Here, the ball screw groove 5 and the ball spline groove 6
As shown in FIG. 5a, the depth of the ball spline groove 6 is selected to be shallow, about 1/2 of the depth of the ball screw groove 5, and the depth of the ball 11f, which will be described later, in the ball screw groove 5 is selected to be shallow. It is designed not to interfere with rolling. Further, the ball spline groove 6 has a narrow clearance groove 6a carved in its bottom as shown in FIGS. 5a and 5b.

Further, a ball nut 10 is rotatably disposed in the center of the housing 1. This ball nut 10 has a large diameter portion 10a and a small diameter portion 10b.
The large diameter portion 10 is formed in a cylindrical shape in which
A ball bearing 11a is inserted between the outer peripheral surface of the left end of the small diameter portion 10b and the inner peripheral surface of the housing 1, and a ball bearing 11b is inserted between the outer peripheral surface of the right end of the small diameter portion 10b and the inner peripheral surface of the end plate 3. ball nut 10
is independently supported and arranged with respect to the housing 1 so as to be freely rotatable. In addition, 12a and 12b are spacers, 1
3a, 13b are ball bearings 11a, 11b
It is a locking nut that fixes the And large diameter part 1
0a has a ball screw groove 10c formed on its inner peripheral surface, and a ball tube 10e arranged in a notch 10d formed on its outer peripheral surface, which is formed by the ball screw groove 10c and the ball screw groove 5 of the screw shaft 4. A large number of balls 10f (first ball group) are installed in the ball passage and ball tube 10e so as to be able to roll and circulate.

On the other hand, a rotor 15R of a hybrid step motor 15 serving as a first rotational drive mechanism that applies rotational force to the ball nut 10 is fitted onto the outer peripheral surface of the small diameter portion 10b, and is interposed between the rotor 15R and the ball bearing 11b. It is fixed so as not to be slidable in the axial direction by an inserted spacer 16. Note that 17 is a key inserted between the spacer 16 and the small diameter portion 10b.

The stator 15S of the drive motor 15 is fitted into the housing 1 and fixed by the annular portion 3a of the end plate 3 so as not to be slidable in the axial direction. here,
Although not shown in the drawings, the step motor 15 has a stator 15S having, for example, 18 magnetic legs having a plurality of teeth on the inner circumferential surface and wound with excitation windings at equal intervals in the circumferential direction. The rotor 15R is composed of a cylindrical permanent magnet magnetized in the axial direction and a laminated steel plate having a large number of teeth formed on the outer circumferential surface fitted onto the cylindrical permanent magnet.

Furthermore, a ball spline nut 20 is rotatably mounted on the left side of the housing 1.

As shown in FIGS. 2 to 4, this ball spline nut 20 has six ball rolling grooves 21 facing the ball spline groove 6 of the screw shaft 4, and is bored in parallel to the outside thereof. A cylindrical body 23 having six through holes 22, and a semicircular body 23 fixed to both end faces of the cylindrical body 23, spanning the ball rolling groove 21 and the through hole 22 of the cylindrical body 23, and having a narrow relief groove 24 at the bottom. End plates 26a, 26b in which arc-shaped ball passages 25 are formed as recesses, ball rolling grooves 21 of cylindrical body 23, through holes 22, and end plates 26a, 26b.
A large number of balls 27 (second ball group) filled in a ball passage 25 of
a, 26b, which has arcuate bent portions at both ends of the straight portion that engage with the relief grooves 24, and is close to the ball 27 arranged in the ball rolling groove 21 of the cylindrical body 23;
The ball retainer 28 is made of a wire rod and prevents the balls from falling out. The ball spline nut 20 is inserted into the ball spline groove 6 of the screw shaft 4 and the relief groove 6a formed at the bottom thereof, so that the ball spline nut 20 is inserted into the ball spline groove 6 of the screw shaft 4 and the clearance groove 6a formed at the bottom thereof. is installed on.

In addition, at the axial center of the outer peripheral surface of the cylindrical body 23, as shown in FIG.
A locking member 31 fixed to the outer peripheral surface of the
a and 31b so as not to be slidable in the axial direction. Furthermore, ball bearings 3 are attached to the outer ends of the locking members 31a and 31b on the outer peripheral surface of the cylindrical body 23.
The inner rings of 2a and 32b are fitted by shrink fitting,
The outer rings of these ball bearings 32a, 32b are positioned by the spacers 35, 36 and the circular ring portion 2a of the end plate 2, and the ball nut 10 is attached to the housing 1.
It is fitted in a state independent of the .

A notch 35a formed in the spacer 35 between the timing belt pulley 29 fixed to the cylindrical body 23 and a pulley 39 attached to the rotating shaft of the pulse motor 38 fixed to the outer peripheral surface of the housing 1 and the housing 1 A timing belt 40 is stretched through the notch 1b formed, and the timing belt pulley 29, pulse motor 38, and pulley 39
The timing belt 40 constitutes a second rotational drive mechanism.

In addition, the actuator 7 and the step motor 15
The pulse motor 38 is connected to a control device (not shown), and its operation is controlled in an open-loop manner by control signals from the control device. For this reason,
A limit switch 41 that detects the most retracted position of the screw shaft 4 as the origin is attached to the left end surface of the end plate 2,
Further, a reflective photoelectric conversion element 43 detects the origin of the rotational position of the ball nut 10 and the rotor 15R of the drive motor 15 by detecting the rotation origin mark 42 formed on the outer peripheral surface of the spacer 16 fitted on the small diameter portion 10b. is attached to the inner peripheral surface of the housing 1, and further includes a reflective photoelectric conversion element 45 that detects the origin of the rotational position of the ball spline nut 20 by detecting a rotational origin mark 44 formed on the outer peripheral surface of the locking member 31a. is attached to the inner peripheral surface of the housing 1. Detection signals from the limit switch 41 and the reflective photoelectric conversion elements 43 and 45 are supplied to the control device, and the control origin is corrected using these signals.

Next, the operation of the above embodiment will be explained. It is now assumed that the screw shaft 4 is located at an intermediate position of the housing 1, as shown in FIG. 1, and that the pulse motor 38 is stopped at a predetermined position. In this state,
In order to maintain the vertical posture of the conveyed object 50 shown by the chain line in FIG. 50, and then the stator 1 of the step motor 15 from the control device.
A predetermined pulse current is supplied to the 5S excitation coil 15C to drive the rotor 15R in forward (or reverse) rotation.

As a result, when the ball nut 10 directly connected to the rotor 15R rotates forward (or reversely) and the screw shaft 4 moves forward (or backward) to a desired position, the drive motor 15 is controlled. When the supply of pulse current from the device is stopped, the forward movement (or backward movement) of the screw shaft 4 is stopped at this position. In this state, the actuator 7 is actuated by the control device to open the fingers 8, so that the object to be transported can be placed at a desired position.

Further, when transporting the transported object 50 to a desired position by rotating its posture by 90 degrees, for example, the control device drives the actuator 7 to grip the transported object, and then the control device generates a pulse. A predetermined number of pulse signals are supplied to the motor 38 to drive it forward (or reverse), thereby driving the ball spline nut 20 via the timing belt 40.
Rotate 90 degrees. As the ball spline nut 20 rotates, the screw shaft 4 also rotates, so that the screw shaft 4 moves forward (or backward) slightly. The amount of movement of the screw shaft 4 at this time can be calculated based on the rotation angle of the screw shaft 4 and the pitch of the ball screw groove 5, and the calculation can be executed by the control device or the movement amount of the screw shaft 4 can be calculated in advance. The relationship between the rotation angle and the amount of movement is determined by the control device by referring to a storage table that stores the relationship, and this is stored in a predetermined storage device. Then, the actual stroke of the screw shaft 4 is calculated by adding or subtracting the movement amount of the screw shaft 4 and the required stroke of the screw shaft 4.
A pulse current is supplied to 5S to rotate the rotor 15R forward (or reverse).

Thereby, similarly to the above, the screw shaft 4 moves forward (or retreats), and the transported object 50 can be transported to a desired position in a sideways state. and,
When the desired position is reached, the actuator 7 is actuated by the control device to open the finger 8 after the conveyed object 50 has been received by a predetermined receiver.

Similarly, by simultaneously operating the drive motor 15 and the pulse motor 38 by the control device,
Ball nut 10 and ball spline nut 2
If both nuts 10 and 2 are rotated in the same direction, only the screw shaft 4 can be rotated, and both nuts 10 and 2 can be rotated.
0 are rotated in opposite directions, the screw shaft 4
can move forward and backward in the axial direction at higher speed.

Furthermore, since the ball nut 10 and the ball spline nut 20 are supported by the housing 1 independently from each other, high-density operation is possible.

In addition, in the above embodiment, the ball nut 1
Although a case has been described in which a direct drive type step motor is applied as the rotational drive mechanism of the ball nut 10, the ball nut 10 can be rotated from outside the housing 1 via a timing belt similarly to the pulse motor 38. It may also be driven.

Further, the arrangement relationship between the ball nut 10 and the ball spline nut 20 is not limited to the above example, but it is also possible to reverse the left-right relationship, and furthermore, the ball spline nut 20 may be rotationally driven by a direct drive type step motor. good.

Furthermore, the step motor 15 and the pulse motor 38 can be replaced with a DC motor, and in this case, a rotary encoder is attached to the ball nut 10 and the ball spline nut 20,
The output may be input to a control device for closed loop control.

Also, when the pulse motor 38 is stopped and the step motor 15 is driven to move the screw shaft 4 forward or backward,
If the helical shaft 4 swings due to weak holding of the pulse motor 38, an electromagnetic brake is provided between the pulse motor 38 and the pulley 39, and this is controlled by the control device to stop the pulse motor 38 from being driven. It is also possible to apply the brakes at times.

Further, in the above embodiment, the case where the present invention is applied to the operating arm of an industrial robot has been described, but the present invention is not limited to this.
Of course, the present invention can also be applied as an operating mechanism for various other operating members.

〔Effect of the invention〕

As explained above, according to the present invention, there is provided a helical shaft having a helical ball screw groove and an axially extending ball spline groove, and a first ball that engages with the ball screw groove of the helical shaft. A ball nut that holds a group so as to be endlessly rotatable, a first rotational drive mechanism that rotationally drives the ball nut, and a second ball group that engages with the ball spline groove at a position close to the ball nut. a second rotary drive mechanism that rotatably drives the ball spline nut to rotate the screw shaft; Since the structure includes a housing that supports independently, the screw shaft can be moved forward and backward in the axial direction by rotating the ball nut, and the screw shaft can be moved forward and backward in the axial direction by rotating the ball spline nut. By operating both at the same time, the screw shaft can be rotated only or moved forward and backward at high speed in the axial direction.
In addition, the screw shaft has overlapping ball screw grooves and ball spline grooves, and the ball nut and ball spline nut that engage with these grooves are placed close to each other and supported independently of each other, so that the necessary stroke of the screw shaft can be accommodated. The length can be shortened, the entire device can be made simpler and smaller, and high-precision operation can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention;
FIG. 2 is a cross-sectional view taken along the - line in FIG. 1, FIGS. 3 and 4 are a cross-sectional view and partially cutaway front view showing an example of a ball spline that can be applied to the present invention, respectively, and FIG. a and b are an enlarged longitudinal cross-sectional view and a cross-sectional view, respectively, showing the engagement portion between the helical shaft and the ball spline. In the figure, 1 is a housing, 4 is a screw shaft, 5 is a ball screw groove, 6 is a ball spline groove, 7 is an actuator, 8 is a finger, 10 is a ball nut,
15 is a step motor, 20 is a ball spline nut, 29 is a timing belt pulley, 38 is a pulse motor, 40 is a timing belt, and 50 is a conveyed object.

Claims (1)

[Scope of Claims] 1. A helical shaft in which a helical ball screw groove and an axially extending ball spline groove are overlapped, and a first ball group that engages with the hole screw groove of the helical shaft are arranged endlessly. a ball nut rotatably held; a first rotational drive mechanism that rotationally drives the ball nut;
a ball spline nut that rotatably holds a second group of balls that engages with the ball spline groove at a position close to the ball nut;
It is characterized by comprising a second rotational drive mechanism that rotationally drives the ball spline nut to rotate the screw shaft, and a housing that supports the ball nut and the ball spline nut rotatably and independently of each other. ball screw device. 2. The ball screw device according to claim 1, wherein the ball spline groove is selected to have a shallower depth than the ball screw groove. 3. The ball spline nut has a retainer that prevents the balls from falling off.
The ball screw device according to item 1 or 2.