JPH0866891A - Robot wrist - Google Patents

Abstract

PURPOSE: To provide a small, lightweight, inexpensive robot wrist which can make effective use of three degrees of passive/active freedom, can make the direction of application of an external force to an end effector coincide with the direction of action of the end effector, and has good controllability. CONSTITUTION: A force sensor 12 at a wrist part 1 is connected to the end of a link 6 at its upper side by a rotary joint 3, and one end of a link 7 is connected to the rear end of the link 6 by a rotary joint 4a and the other end of the link 7 is connected by a rotary joint 4b to the portion of a robot arm 2 slightly off to the rear end from the front end, and one end of a link 8 is connected to the portion of the link 6 slightly off to the rear end from the center, and the other end of the link 8 is connected to the end of a rotary joint 4d by the rotary joint 4d. All of actions can then be achieved by the combination of degrees of freedom of translation in the X, Y and Z directions and degrees of freedom of rotation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a force control robot that requires flexible contact with the environment such as assembly and processing, and more particularly to a mechanism of a robot wrist portion.

[0002]

2. Description of the Related Art In order for a robot to perform a flexible operation while controlling the contact force (external force) with the environment in an end effector that grips an object, a force sensor for detecting an external force and Passive degrees of freedom that allow the effector to react flexibly in the direction of an applied external force (release) and active degrees of freedom for driving the end effector to generate a contact force with the environment are required. This passive / active degree of freedom allows the desired force to be generated for the environment while reacting well to external forces. Of course, a structure having both passive and active degrees of freedom is advantageous for realizing a small, lightweight and inexpensive wrist.

There is also a method in which this passive / active degree of freedom is realized not by providing only the wrist portion but by the degree of freedom of the entire robot arm. However, with this method, it is necessary to move the heavy robot arm from the root to perform the required operation, and it is not possible to expect a high-speed response to an external force. Therefore, securing the necessary degree of freedom only by the operation of the lightweight wrist portion on the robot arm is an essential condition for realizing the force control robot arm.

6 and 7 show a wrist portion of a robot, in which 1 is a wrist portion, 11 is an end effector for gripping an object T, and 12 is a force sensor for detecting an external force F applied to the end effector 11. Shown respectively. Figure 6
As shown in FIG. 7 and FIG.
As shown in FIG. 7, the direction of the external force F in the state of being in contact with the inclined surface is a combination of the Z-axis direction, the X-axis direction, the Y-axis direction, or the three directions in the orthogonal coordinate system set in the drawing. . At this time, the minimum passive required for the list /
The active degrees of freedom are three degrees of freedom of translation in three directions. By combining these three degrees of freedom, the end effect 11 can be flexibly released in the direction of the applied external force F with respect to an arbitrary external force F, and at the same time, the end effector 11 can be driven to generate a contact force with respect to the environment C. You can

Such a robot wrist is conventionally attached to a robot arm as shown, for example, in FIG. 8 or 9 or 10. In the configuration shown in FIG. 8, the wrist unit 1 including the end effector 11 and the force sensor 12 that are integrally configured is connected to the robot arm 2 via the rotary joint 3. The rotary joint 3
It is configured to be rotatable around an X axis that is an axis perpendicular to the paper surface of FIG. 8 and a Y axis that is an axis parallel to the paper surface. Therefore, the wrist unit 1 is rotationally driven around the rotary joint 3 about the X axis and the Y axis.

Further, in the configuration example shown in FIGS. 9 and 10, the wrist portion 1 is connected to the link 4 via a rotary joint 4 rotatable about the X axis, and the link 4 is rotatable about the Z axis. It is connected to the robot arm 2 via a rotary joint 5. Therefore, the link 4 is rotationally driven around the rotary joint 5 around the Z axis, and the end effector 11 and the force sensor 12 of the wrist unit 1 are rotationally driven around the rotary joint 4 around the X axis.

[0007]

However, in the configuration shown in FIG. 8, as shown in FIG. 11, since the wrist portion does not have the degree of freedom of translation in the Z-axis direction, the end effector 11 is not provided.
In order to make the direction of the external force F applied to the robot and the operation direction of the end effector 11 coincident with each other, the robot arm 2 that is heavy and slow is used.
It is necessary to realize a degree of freedom in the Z-axis direction for the entire operation, and high-speed and flexible operation cannot be expected.

Further, in the configurations shown in FIGS. 9 and 10, similarly, since the wrist portion 1 does not have the freedom of translation in the Z-axis direction, the direction of the external force applied to the end effector 11 and the operation direction of the end effector 11 are made to coincide with each other. In order to achieve this, it is necessary to realize the degree of freedom in the Z-axis direction by the operation of the entire robot arm 2. Moreover, since there is no degree of freedom in the direction of the rotation axis of the rotary joint 5, it is impossible to operate in this direction.

Here, it is considered that the force control robot list is constructed by adding a linear movement degree of freedom in the Z-axis direction to the robot list shown in FIG. By doing this,
The direction of the external force applied to the end effector 11 and the operation direction of the end effector 11 can be made to coincide with each other, and a flexible operation can be realized.

Generally, the linear motion is as follows. Pneumatic cylinder 2. Hydraulic cylinder 3. Ball screw 4. Rack and Pinion 5. It is realized by means such as a linear motor.

However, a pneumatic cylinder is flexible but has poor controllability, and a hydraulic cylinder has good controllability but lacks flexibility. The ball screw has a poor high-speed response due to the large reduction ratio associated with rotation ← → linear motion conversion, and the rack and pinion has a large non-linearity such as friction and backlash and lacks controllability. In addition, the linear motor tends to be heavy because the output / weight ratio cannot be large. In addition, other means than pneumatic cylinders require expensive equipment.

The present invention has been made in view of such circumstances, and an object thereof is to make effective use of passive / active degrees of freedom of three degrees of freedom, and the direction of an external force applied to the end effector and the operation direction of the end effector. The goal is to provide a small, lightweight, inexpensive robot list that can be matched with each other and has good controllability.

[0013]

In order to achieve the above object, a robot wrist of the present invention comprises a wrist portion provided with an end effector for holding an object and a force sensor for detecting an external force applied to the end effector, and one end thereof. A first link rotatably connected to the wrist portion, and both ends rotatably connected to the first link and the arm about a link shaft and an axis substantially orthogonal to the arm shaft, respectively. The second link is rotatable about both ends of the first link and the arm about a link axis and an axis substantially orthogonal to the arm axis so that the both ends are substantially parallel to the second link. And a third link connected thereto.

[0014]

According to the present invention, all operations can be performed by combining the translational degrees of freedom in the X, Y, and Z directions in the orthogonal coordinate system with the rotational degrees of freedom. This allows the robot list to have the minimum degree of freedom required for force control.

[0015]

1 is a block diagram showing an embodiment of a force control robot list according to the present invention, and FIGS.
The same components as those in FIG. 10 are designated by the same reference numerals. That is, 1 is a wrist portion constituted by the end effector 11 and the force sensor 12, 2 is a robot arm, and 3 is a robot arm shown in FIG.
The rotary joints 4a, 4b, 4c and 4d are configured to be rotatable about an X axis which is an axis perpendicular to the paper surface and a Y axis which is an axis parallel to the paper surface, and are configured to be rotatable around the X axis. The revolute joints 6, 7 and 8 respectively indicate links.

In this robot wrist, the upper surface side of the force sensor 12 of the wrist portion 1 is connected to the tip end of a long link 6 by a rotary joint 3, and the link 7 shorter than the link 6 with respect to the rear end of the link 6. One end of the rotary joint 4a
And the other end of the link 7 is connected to the robot arm 2
Of the link 8 is connected to the rear end side of the link 6 by a rotary joint 4b, and one end of a link 8 of the same scale as the link 7 is connected to the rear end side of the center of the link 6 by a rotary joint 4c. The other end side of 8 is connected to the tip of the rotary joint 4d by the rotary joint 4d. As shown in FIG. 1, the link 7 and the link 8 are connected to the robot arm 2 and the link 6 so as to be parallel to each other, and the axis of the robot arm 2 and the link 6 maintain a parallel positional relationship.

The rotary joint 3 is, for example, as shown in FIG.
It is realized by the structure shown in. That is, a rotary shaft 62 parallel to the Y-axis is provided on the mounting portion 61 formed in a substantially U-shape at the tip of the link 6, and the rotary shaft 31 of the rotary joint 3 is provided with respect to the substantially central portion of the rotary shaft 62. Is rotating shaft 6
It is attached so as to be orthogonal to 2.

Next, the operation of the above configuration will be described with reference to FIGS.
Will be described with reference to. First, referring to FIG. 3, Z
The degree of freedom in the axial direction will be described. The link 7 is rotationally driven around the rotary joint 4b, and accordingly, the links 6 and 8 connected by the rotary joints 4a, 4c and 4d.
Are driven as shown in FIG. Strictly speaking, the tip of the link 6 draws an arc as shown by the arrow A in FIG. 3, but it can be considered that the link 7 approximately linearly moves in the Z-axis direction near the neutral position (the area indicated by LN in FIG. 2). ). With this mechanism,
Since all the operations are performed by the rotary joint, the escape (passive operation) against the external force in the Z-axis direction and the generation of the force in the Z-axis direction (active operation) are smoothly performed. However, when the link 6 deviates from the vicinity of the neutral position, it cannot be considered that the tip of the link 6 makes a linear motion in the Z-axis direction (N in FIG. 3).
In the area indicated by LN), the initial target motion cannot be realized. However, a high-speed response corresponds to an operation near the neutral position of the link 6, and while the link 6 deviates from near the neutral position, the entire robot arm moves at a low speed but largely moves.
If the control is performed so as to keep the value near neutral, the initial target motion can be realized.

Next, the degrees of freedom in the X-axis direction and the Y-axis direction will be described with reference to FIG. The force sensor 12 and the end effector 11 have the X-axis,
It is driven to rotate around the Y axis. Focusing only on the rotation around the X axis, the tip of the end effector 11 draws an arc as shown by an arrow B in FIG. 4 in a strict sense, but when the end effector 11 is near neutral, the end effector 11 is translated approximately in the Y axis direction. It can be regarded as exercise. In this mechanism, since all the rotary joints 3 perform the operation, escape from external force in the Y-axis direction (passive operation) and generation of force in the X-axis direction (active operation)
Is done smoothly. However, the end effector 11
Is deviated from near neutral, it cannot be considered that the tip of the end effector 11 performs translational movement in the Y-axis direction, and the initial target operation cannot be realized. However, for high-speed response, the end effector 11 operates near the neutral position,
If the robot arm 2 as a whole moves at a low speed but moves largely while the end effector 11 shifts from near neutral, control is performed so that the end effector 11 is maintained near neutral.
The initial target motion can be realized.

The translational motion in the X-axis direction will be described in the same manner as in the Y-axis direction.

Further, by combining the above three degrees of freedom, the direction of the external force F ₁₁ applied to the end effector 11 (end effector 1) as shown in FIG.
1) and the operation direction of the end effector 11, specifically, the operation direction FW ₆ of the end effector 11 by the operation of the link ₆ and the operation direction FW ₃ of the end effector 11 by the operation of the rotary joint 3 can be matched. Therefore, it is possible to realize a flexible operation involving absorption of external force / generation of force.

The rotary joints 4a to 4d shown in FIG.
The rotary joint 3 is usually widely used, matured in both characteristics and control technology, and low cost DC with position detection device.
Since it suffices to incorporate the / AC motor (+ reduction gear-as required), the present invention is very easy to realize.

As described above, according to this embodiment,
The upper surface side of the force sensor 12 of the wrist portion 1 is connected to the distal end portion of the long link 6 by the rotary joint 3, and one end side of the link 7 shorter than the link 6 is connected to the rear end portion of the link 6 by the rotary joint 4a. And the other end of the link 7 is connected to the robot arm 2 from the front end side to the rear end side by a rotary joint 4b. Since one end of 8 is connected by a rotary joint 4c and the other end of the link 8 is connected by a rotary joint 4d to the tip side of the rotary joint 4d, the translational degrees of freedom in the X, Y, and Z directions are rotated. Since all movements can be performed with a combination of degrees of freedom, the robot wrist unit 1 can have the minimum degree of freedom required for force control, and is a high-speed, flexible, lightweight, inexpensive force control robot squirrel. It can be realized.

[0024]

As described above, according to the present invention,
Compared to the robot arm body, the robot wrist is lighter in weight and can operate at high speed. A force sensor that detects an external force, a passive degree of freedom that allows the end effector to flexibly react (release) in the direction of the applied external force, and an end effector. A force that drives an object to generate a contact force with the environment, and these passive / active degrees of freedom respond to external force and generate the desired force for the environment. A control robot can be realized. Moreover, since the structure has both passive and active degrees of freedom, a small, lightweight, inexpensive robot list can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a force control robot list according to the present invention.

FIG. 2 is a diagram showing an example of a mounting structure for a link of a wrist portion by a rotary joint.

FIG. 3 is a diagram for explaining the operation of FIG. 1 and is an explanatory diagram of a degree of freedom in the Z-axis direction.

FIG. 4 is a diagram for explaining the operation of FIG. 1, and is an explanatory diagram of degrees of freedom in an X-axis direction and a Y-axis method.

FIG. 5 is a diagram for explaining the effect of combining degrees of freedom in three directions.

FIG. 6 is a side view showing a configuration example of a robot list.

FIG. 7 is a perspective view showing a configuration example of a robot list.

FIG. 8 is a side view showing an example of a structure for attaching a robot wrist to a robot arm.

FIG. 9 is a side view showing another example of the attachment structure of the robot wrist to the robot arm.

FIG. 10 is a perspective view showing another example of the attachment structure of the robot wrist to the robot arm.

FIG. 11 is a diagram for explaining a conventional problem.

[Explanation of symbols]

 1 ... Wrist part 11 ... End effect 12 ... Force sensor 2 ... Robot arm 3 ... Rotating joint 4a, 4b, 4c, 4d ... Rotating joint 6, 7, 8 ... Link

Claims (1)

[Claims] 1. A robot wrist attached to a tip portion of an arm, the wrist portion including an end effector that grips an object and a force sensor that detects an external force applied to the end effector, and the wrist portion at one end. A rotatably connected first link, and a second link whose both ends are rotatably connected to the first link and the arm about a link shaft and an axis substantially orthogonal to the arm shaft, respectively. And a third link whose both ends are rotatably connected to the first link and the arm about an axis substantially orthogonal to the link axis and the arm axis, respectively, so as to be substantially parallel to the second link. Robot list with links to.