JP2722345B2 - 2-DOF drive mechanism for industrial robot wrist - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a two-degree-of-freedom drive mechanism capable of performing two types of movements, and more particularly, to a straight-ahead drive mechanism used for a wrist mechanism of an industrial robot. The present invention relates to a two-degree-of-freedom drive mechanism capable of performing a motion and a rotational motion. (Prior Art) Generally, in a machine device such as a machine tool, two types of movements, feed and rotation, are often required. For example, in the case of a horizontal articulated robot, the wrist mechanism at the tip
It is necessary to perform a linear motion in the Z-axis direction and a rotational motion about the Z-axis. FIG. 2 shows a typical example of a two-degree-of-freedom drive mechanism which can perform such a linear motion and a rotational motion, which is conventionally and frequently used. The two-degree-of-freedom drive mechanism includes a fixed frame 31 and a movable frame 33 fitted to the fixed frame 31 via a spline 32. A linear motor 34 is attached to the fixed frame 31, and the movable frame 33 performs a linear motion by rotating a ball screw 35 directly connected to an output shaft of the linear motor 34. . Further, a turning motor 36 is mounted in the movable frame 33, and by operating the turning motor 36, an operating shaft 37 directly connected to the output shaft performs a rotational motion. Therefore, the operating shaft 37 can perform the linear motion and the rotational motion by appropriately operating the linear motor 34 and the turning motor 36. Further, as a modified example of such a two-degree-of-freedom driving mechanism,
A movable frame is rotatably supported by a fixed frame, and the movable frame is rotated by a turning motor mounted on the fixed frame, and the operating shaft is moved straight by a straight motor mounted on the movable frame. Are known. However, in any case, such a two-degree-of-freedom drive mechanism requires a movable frame in addition to the fixed frame, and the movable frame supports either the turning motor or the straight-moving motor. Since it is necessary to perform linear motion or rotational motion, the weight of the movable part is large, high-speed response is not obtained, the overall weight is large, and it is disadvantageous for a wrist mechanism attached to the tip of the manipulator It is difficult to perform high-precision processing, and it is difficult to sufficiently increase reliability. For this reason, as shown in FIG.
A degree of freedom drive mechanism has also been proposed. In this two-degree-of-freedom drive mechanism, the straight-moving motor 41 and the turning motor 42 are both supported by the fixed frame 43. On the fixed frame 43, a ball screw 44 and an operating shaft 46 on which a ball spline 45 is formed are juxtaposed.
The ball screw 44 is rotatably driven by a straight motor 41 via a timing belt 47. The operating shaft 46 is rotated by rotating a nut 48 fitted to the ball spline 45 by a turning motor 42 via a timing belt 49. Further, a nut 52 to which a bearing 51 is integrally attached via a connecting member 50 is screwed to the ball screw 44. The bearing 51 supports the upper end of the operating shaft 46 so as to be rotatable and immovable relative to the axial direction. Accordingly, when the linear motor 41 is operated, the ball screw 44 rotates, the nut 52 moves in the vertical direction, and the operating shaft 46 moves linearly. When the turning motor 42 is operated, the nut 48 rotates, and the operating shaft 46 rotates. According to such a two-degree-of-freedom drive mechanism, the responsiveness is improved because the weight of the movable part can be reduced. However, the number of parts is still large, and the ball screw
Since the 44 and the operating shaft 46 must be arranged side by side, the occupied space becomes large, and it cannot be said that it is necessarily suitable for mounting on the tip of the manipulator. In order to fundamentally solve such a problem, the operating shaft may be made to directly perform a linear motion and a rotary motion. As such, it has been considered to use a differential mechanism as shown in FIG. In the two-degree-of-freedom drive mechanism, a pair of spiral grooves 62 and 63 having the same pitch in opposite directions are formed on the outer peripheral surface of the operating shaft 61.
Are formed. The couplings 64 and 65 are engaged with the grooves 62 and 63 via balls, respectively. These couplings 64, 65 are individually driven to rotate by two motors (not shown) via timing belts 66, 67, respectively. According to such a mechanism, when the couplings 64 and 65 are synchronously rotated in the same direction at the same speed, the operating shaft 61 rotates in the same direction as the couplings 64 and 65. Also, coupling 64,
When the 65 are rotated synchronously in the opposite direction and at the same speed, the operating shaft
61 moves straight up and down. Therefore, it is possible to cause the operating shaft 61 to perform arbitrary linear motion and rotational motion only by controlling the rotational direction and the rotational speed of the two motors. In recent years, since motor control technology has advanced considerably, such differential control of the motor can be performed very easily and accurately. (Problems to be Solved by the Invention) However, such a two-degree-of-freedom drive mechanism using a differential mechanism still has the following problems. It is expensive because a special ball screw mechanism is used. Since the pair of grooves 62, 63 intersect, the ball of each coupling 64, 65 may come off from the corresponding groove 62, 63. It is desirable to reduce the pitch of each groove 62, 63 in order to perform a precise linear motion, but in such a case, the load supporting force against rotation decreases. Also,
When the pitch is increased, the load supporting force for straight traveling decreases. Therefore, the range of use is limited to light loads. The present invention has been made in view of such a problem, and an object of the present invention is to provide a wrist mechanism for an industrial robot which can cope with a heavy load and has a simple and compact structure. The goal is to obtain a degree of freedom drive mechanism. (Means for Solving the Problems) In order to achieve this object, in the present invention, a ball screw and a ball spline are provided in series on an operating shaft, and a first and a second nut are provided on the ball screw and the ball spline. Are engaged with each other. The first and second nuts are supported by a frame so as to be rotatable and immovable in the axial direction. And those first
The second nut and the second nut are rotatably driven by a straight-moving motor and a turning motor supported by the frame via first and second transmission mechanisms, respectively. A tool mounting portion for mounting a tool is integrally provided at the tip of the operating shaft. (Operation) With this configuration, when only the first nut is rotated, an axial force acts on the ball screw screwed to the first nut, and the operating shaft moves linearly. At this time, since the operation shaft is engaged with the second nut via the ball spline, the operation shaft does not rotate. When the first nut and the second nut are synchronously rotated in the same direction at the same speed, the rotation of the second nut is transmitted to the operation shaft via the ball spline, and the operation shaft rotates. At this time, the operating shaft is also engaged with the first nut via the ball screw, but since the first nut is rotating at the same speed and in the same direction as the operating shaft, linear motion may occur on the operating shaft. There is no. When the first and second nuts are rotated together while giving a relative rotational speed difference, the operating shaft performs a linear motion and a rotary motion at the same time. As described above, since only the operating shaft performs the rectilinear motion and the rotational motion, the movable portion is lightweight and compact.
In addition, a ball screw and a ball spline, which are commonly used, are formed on the operating shaft, and only nuts are engaged with each other, so that the cost can be extremely low. Since the linear load is supported by the first nut that meshes with the ball screw, and the rotational load is supported by the second nut that meshes with the ball spline, it is possible to sufficiently cope with a large load. (Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional side view showing an embodiment of a two-degree-of-freedom drive mechanism according to the present invention. As is clear from this figure, a cylindrical portion 2 that opens in the vertical direction is provided at the tip of the frame 1. Bearings 3, 3 and 3 are provided at the upper and lower ends of the cylindrical portion 2, respectively.
The first nut 5 and the second nut 6 are rotatably mounted via the fourth and fourth members so as not to move in the axial direction. An operating shaft 7 is fitted into the first and second nuts 5 and 6. A ball screw 8 is formed on an upper half of the outer peripheral surface of the operating shaft 7, and a ball spline 9 is formed on a lower half thereof. That is, the operation shaft 7 is provided with the ball screw 8 and the ball spline 9 in series.
These ball screw 8 and ball spline 9 are nuts
The length is almost equal to the distance between 5,6. And
The first nut 5 is screwed into the ball screw 8, and the second nut 6 is fitted into the ball spline 9.
Accordingly, the second nut 6 is slidable in the axial direction with respect to the ball spline 9, but does not rotate relative to the ball spline 9. In addition, a tool mounting portion 10 for mounting a tool is integrally provided at a lower end portion of the operation shaft 7, and the tool moves integrally with the operation shaft 7. The first and second nuts 5 and 6 have first
The pulley 11 and the second pulley 12 are provided integrally. On the other hand, the frame 1 includes a straight-moving motor 13 and a turning motor 14.
And are attached. The drive pulley 16 provided on the output shaft 15 of the linear motor 13 and the first nut 5
A first timing belt 17 is wound around the pulley 11, and a second timing belt is provided between a drive pulley 19 provided on an output shaft 18 of the turning motor 14 and a second pulley 12 of the second nut 6. The belt 20 is wound around. Belt insertion holes 21 and 22 through which these belts 17 and 20 are inserted are formed in the cylindrical portion 2 of the frame 1. Thus, the first nut 5 is rotationally driven by the straight motor 13 and the second nut 6 is rotationally driven by the turning motor 14. In other words, in this embodiment, the driving pulley 16, the first timing belt 17, and the first pulley 11 constitute a first transmission mechanism 23 that transmits the rotational driving force of the linear motor 13 to the first nut 5. Pulley 19, second timing belt 20, and second pulley 12
As a result, the rotational driving force of the turning motor 14 is
A second transmission mechanism 24 for transmitting the power to the motor is constituted. Next, the operation of the thus configured two-degree-of-freedom drive mechanism will be described. When the operating shaft 7 is caused to perform the linear motion, the linear motor 13 is operated with the turning motor 14 stopped. Then, the rotation driving force of the linear motor 13 is transmitted to the first nut 5 by the first transmission mechanism 23, and the nut 5 rotates in the same direction as the motor 13. At this time, the turning motor
Since the second nut 6 is fixed by the stop of 14, the rotation of the operating shaft 7 fitted to the nut 6 via the ball spline 9 is restricted. Therefore, the first nut 5 rotates relative to the operating shaft 7. Since the nut 5 does not move in the axial direction, an axial force is applied to the ball screw 8 screwed to the nut 5. As a result, the operating shaft 7 moves linearly in the axial direction. Assuming that the pitch of the ball screw 8 is p, the first nut 5 may be rotated at an angular velocity of (60 / 2π) · (v / p) in order to cause the operating shaft 7 to move linearly at the speed v. . When the first nut 5 is rotated in the reverse direction, the operating shaft 7 performs a rectilinear motion in the reverse direction. When the operating shaft 7 is caused to rotate, the linear motor 13 and the turning motor 14 are both operated, and the first
And the second nuts 5, 6 are rotated in the same direction at the same speed. When the second nut 6 is rotated at an angular velocity ω, the operating shaft 7 fitted to the nut 6 via the ball spline 9 also
They rotate in the same direction at the same angular velocity ω. At this time, the ball screw 8 also rotates, but the first nut 5 screwed to the ball screw 8 is also synchronously rotated in the same direction at the same speed. No relative movement occurs. Therefore, the operating shaft 7 does not perform a linear motion, but performs only a rotational motion. When the operating shaft 7 is rotated in the opposite direction, the first and second nuts 5 and 6 may be rotated in the opposite direction at the same speed. In this way, in general, if the first nut 5 is rotated at an angular velocity of ω + (60 / 2π) · (v / p) and the second nut 6 is rotated at an angular velocity of ω, the operating shaft 7 will rotate at a speed v And a rotational motion at an angular velocity ω is performed. Therefore, by controlling the two motors 13 and 14 synchronously, any two
The freedom of movement can be realized. As described above, according to the two-degree-of-freedom drive mechanism, it is possible to cause only the operating shaft 7 to perform linear motion and rotational motion,
Since the weight of the movable portion can be reduced, excellent high-speed response can be achieved. In addition, one operating shaft 7 and nuts 5 and 6 fitted to the operating shaft 7 are provided at the tip of the frame 1.
Since it is only necessary to provide the following, the device can be made compact, which is optimal as a wrist mechanism of the robot. In addition, the operating shaft 7 may be formed with a ball screw 8 and a ball spline 9 which are used in a very ordinary manner.
The first and second nuts 5 and 6 meshing with the first and second nuts 5 and 6 may be ordinary ones, so that they are extremely inexpensive. The linear load is supported by the screwing of the ball screw 8 and the first nut 5, but by reducing the pitch p of the ball screw 8, the supporting force can be sufficiently increased. The rotating load is supported by the fitting of the ball spline 9 and the second nut 6, but since the load supporting characteristic of the ball spline 9 is very good, it can sufficiently cope with heavy load. can do. In the above embodiment, the ball screw 8 and the ball spline 9 are provided above and below the operating shaft 7, but they may be provided in reverse. Further, the operating shaft 7 is not limited to the one that is installed in the vertical direction. Further, the timing belts 17, 20 are used as the transmission mechanisms 23, 24 for transmitting the rotational driving force of the straight-moving motor 13 and the turning motor 14 to the nuts 5, 6, but this is constituted by a gear mechanism or the like. You can also. However, in order for the motors 13 and 14 to be installed on the base side of the frame 1 and to make the whole lighter, it is desirable to use a belt transmission mechanism. (Effects of the Invention) As is apparent from the above description, according to the present invention, a ball screw and a ball spline are formed on an operating shaft, and the first and second nuts are engaged with the ball screw and the ball spline, respectively. Since the rotations of the first and second nuts are controlled synchronously, the linear motion and the rotary motion can be directly performed on the operating shaft, and the weight of the movable portion can be reduced. The number of points is small, and compactness can be achieved. Since the linear motion is performed by the ball screw and the rotational motion is performed by the ball spline, it is possible to handle heavy objects. In addition, since these ball screws and ball splines are ordinary, they can be manufactured at low cost. In this way, the excellent wrist mechanism of the industrial robot 2
A degree of freedom driving mechanism can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional side view showing an embodiment of a two-degree-of-freedom drive mechanism according to the present invention, and FIG. 2 is a longitudinal section showing a typical example of a conventional two-degree-of-freedom drive mechanism. FIG. 3 is a longitudinal sectional side view showing another example of the conventional two-degree-of-freedom drive mechanism, and FIG. 4 is a side view of a main part showing still another example of the conventional two-degree-of-freedom drive mechanism. . 1 Frame 5 First nut 6 Second nut 7 Operating shaft 8 Ball screw 9 Ball spline 13 Linear motor 14 Rotating motor 23 1 transmission mechanism, 24 second transmission mechanism

Claims (1)

(57) [Claims] A ball screw and a ball spline are formed in series on the outer peripheral surface, and an operating shaft provided integrally with a tool mounting portion for mounting a tool at a tip, and a ball screw portion of the operating shaft is screwed into the operating shaft. A first nut, a second nut fitted to the ball spline portion of the operating shaft, and a frame supporting the first and second nuts rotatably and axially immovable; A straight-line motor and a turning motor respectively supported by the frame, a first transmission mechanism and a second transmission mechanism for transmitting the rotational driving force of the straight-line motor and the rotation motor to the first and second nuts, respectively; And controlling the rotation speeds of the linear motor and the turning motor, respectively, so as to cause the tool to perform a linear motion and a rotational motion. 2-DOF drive mechanism for industrial robot wrists.