JPH09314487A - Method for controlling manipulator having redundant axis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To move a manipulator while preventing interference by effectively using the redundancy of the manipulator only based on information regarding the surface of an obstacle likely to interfere with the articulated part of the manipulator. SOLUTION: When there is a surface likely to interfere around a manipulator 1 and its direction is recognized, the degree of rotation is calculated for a turning articulated E1 shaft 5 as an elbow and the rotational angle (articulated part binding angle) of a rotary articulated S3 shaft 4 is calculated for rotating the E1 shaft 5. By using the obtained articulated part binding angle of the S3 shaft 4, an evaluation function for deciding redundancy is calculated. For the evaluation function, a S3 shaft function binding angle is used for a value of the S3 shaft 4 and six values other than this are set to 0. Thus, the S3 shaft 4 is particularly bound, and the effect of the obtained S3 shaft articulated part binding angle takes precedence.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a redundant axis 7
The present invention relates to a manipulator control method applied to avoid obstacles and the like of a manipulator having more than one axis.

[0002]

BACKGROUND ART Generally, a manipulator having a six-axis joint is sufficient to move a hand of a manipulator to a certain position in a three-dimensional space in a certain posture. However, recently, manipulators are required to be able to perform complicated tasks while not only moving to a certain fixed position but also skillfully avoiding various obstacles existing in the moving space. For that purpose, 6-axes is not enough, and joints of 7-axes or more are required.

The redundancy increases as the number of joints increases, such that the 7-axis manipulator has one redundant axis and the 8-axis manipulator has two redundant axes. For example, in a 7-axis manipulator, redundancy appears as an elbow trajectory. That is, in the 7-axis manipulator, it is possible to take an infinite number of elbow postures while maintaining the same hand position / posture. You can choose one that avoids obstacles from this infinite number of elbow positions.

FIG. 8 shows a 7-axis manipulator in which one axis is a redundant axis. This manipulator 1 includes an S1 axis 2 which is a rotary joint, an S2 axis 3 which is a rotary joint, an S3 axis 4 which is a rotary joint, an E1 axis 5 which is a rotary joint and corresponds to an elbow, an E2 axis 6 which is a rotary joint, and a rotary axis. It is composed of a W1 shaft 7 which is a joint and a W2 shaft 8 which is a rotary joint. In this manipulator 1, the E1 axis 5 which is an elbow is a redundant axis and can take an infinite number of postures with the hand position and posture fixed.

Conventionally, such a 7-axis manipulator 1
Then, with your posture kept constant, move your hand from point A to point B in Fig. 8.
When moving to a point, avoidance control when there is an obstacle 10 around is performed as shown in FIG. That is, after finely acquiring the information of the obstacle 10 in the movement path space of the manipulator 1 (step (1)), the relation between the surfaces of all the obstacles 10 and the positions of all the axes of the manipulator 1 is calculated. However, it takes a considerable amount of time to reach the optimum elbow posture 7
Obtain the joint angle for the axis (step (2)), and check whether it can be avoided by performing a dry run on the simulation or CAD based on the result (step (3)). The commanding section commands the angle to each joint (step (4)) and controls each joint.

[0006]

However, in the above-described conventional manipulator obstacle avoidance method, the image processing for obtaining the information of the obstacle takes time, and since the simulation etc. must be performed, the manipulator is actually used. It took a considerable amount of time to move, and it was not a versatile method.

[0007]

DISCLOSURE OF THE INVENTION The present invention is to solve the above-mentioned problems, and its configuration is a method of controlling a manipulator having redundant axes, which detects the direction of an obstacle with respect to the manipulator, and detects the direction of the obstacle. To calculate the tilt angle of the redundant axis to avoid interference, to obtain this tilt angle, obtain the rotation angle of the axis that determines the posture of the redundant axis, and control the axis to this rotation angle. It is characterized by.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a manipulator control method according to the present invention will be described. Here, the 7-axis manipulator shown in FIG. 2 is taken as an example of a controlled object.

The manipulator 1 shown in FIG. 2 is the same as that shown in FIG. That is, S1 axis 2 which is a rotary joint, S2 axis 3 which is a rotary joint, S3 axis 4 which is a rotary joint, E1 axis 5 which is a rotary joint and corresponds to an elbow, E2 axis 6 which is a rotary joint, and a rotary joint. It is composed of a W1 shaft 7 and a W2 shaft 8 which is a rotary joint, and an E1 shaft 5 which is an elbow is a redundant shaft, which can take an infinite number of postures with the hand position posture fixed.

The movement control while maintaining the hand posture of the 7-axis manipulator 1 as described above will be described on the assumption that the 7-axis manipulator 1 is linearly moved from the point A to the point B as shown in FIG. As shown in FIG. 5, it is assumed that the obstacle 10 exists around the point B and the joint E1 axis 5 which is the elbow of the manipulator 1 may interfere with the obstacle 10.

The information required when moving linearly from point A to point B is the positional relationship between the obstacle 10 and the manipulator 1. This information means that the manipulator 1 is an obstacle 10
This is essential and minimal information to avoid
Specifically, when the points A and B are connected by a straight line, it does not indicate in which direction the existing obstacle plane exists in the reference coordinate system of the manipulator 1 (XYZ is the coordinate axis in FIG. 5). Only information about As shown in FIGS. 4 and 6, the definition of the surface of the obstacle 10 that may interfere when moving from the point A to the point B is that the shortest distance from the straight line L to the surface of the obstacle 10 is S3. The condition is that it is smaller than the radius r ₁ of the circle of the circular orbit formed by the E1 axis 5 obtained by rotating the shaft 4 (r ₁ > r ₂ ). In FIG. 6, L is a straight line connecting the S2 axis 3 and the tip end position A, r ₁ is the distance from the center of the E1 axis 5 to the straight line L, and r ₂ is the straight line L from the obstacle 10. It is the shortest value of the vertical line.

If the above condition is satisfied, there is a surface that may cause interference. If such a surface is found, a point indicating the tip position of the manipulator 1 (teaching data).
To, the information of the direction of the interference surface and the presence of interference is added. This information is the minimum obstacle information.

To detect the presence of the obstacle 10, for example, a sensor capable of detecting a distant object is attached to the joint of the manipulator, and the presence of the obstacle is detected based on the information of the sensor. A means for recognizing the direction is taken. Since we want to reduce the amount of obstacle information as much as possible, the selection of sensors and the optimization of information are considered accordingly.

Here, the circular orbit formed by the E1 axis 5 will be described. As described above, the 7-axis manipulator has one redundant axis, and allows an infinite number of elbow postures (various combinations of joint angles) while maintaining the hand position posture of the manipulator 1. In the manipulator 1 shown in FIG. 2, the S3 axis 4 is an axis that determines the elbow posture, as described above.

As shown in FIG. 4, while keeping the same hand position posture, the joint angle of the S3 axis 4 is rotated in the plus direction and the minus direction so that the E1 axis 5 becomes the origin in the reference coordinate of the manipulator 1. Manipulator 1
The elbow posture can be changed while drawing a circular orbit whose radius is the length r _{1 of the} perpendicular line centered on the intersection C with the line drawn vertically from the E1 axis 5 on the straight line connecting the hand positions. .

The radius r ₂ of the circular orbit depends on the link length of the manipulator 1, the link configuration, and the hand position of the manipulator 1. Also, the E1 axis 5 is not movable along the entire circumference of the drawn circular locus, and is hardware (structural).
Circular orbit changes to circular orbit depending on the joint limit angle.

In the present embodiment, the direction in which the E1 axis 5 is tilted is obtained from the direction of the surface of the obstacle 10 that may cause interference, and the rotation angle of the S3 axis 4 is obtained in order to realize that direction.
The sum of the calculated rotation angle of the S3 axis 4 and the joint angle of the S3 axis 4 at the point A constrains the joint angle of the S3 axis 4 at the point B.

Next, the elbow control using the above information will be described with reference to FIG.
I will explain. First, get the information needed to avoid obstacles
(Step (1)). That is, as mentioned above,
Shortest distance r from AB to the surface of obstacle 10_TwoBut in Figure 4
E obtained by rotating S3 axis 4 as shown
Radius r of a circular orbit formed by one axis 5 ₁Is less than
Information is taken. If the above conditions are met, interference may occur.
It means that there is a face, and if that face is found,
Point indicating the tip position of manipulator 1 (Teaching data
Information on the direction of the interference surface and interference.

Next, when there is a surface that may interfere with the manipulator 1 and its direction is known, how much the E1 axis 5 should be rotated about the point C is determined (step (2)), S3 axis 4 for rotating E1 axis 5
The rotation angle (joint restraint angle) is calculated (step (3)). The rotation of the S3 axis 4 is based on the E1 axis 5 when the difference between r ₁ and r ₂ reaches a certain threshold value.

An evaluation function for determining redundancy is calculated using the calculated joint restraint angle of S3 axis 4 (step
(Four)). The evaluation function is a 7 × 1 vector that can change the moving direction and moving speed of each joint, and is a value determined by changing a combination of infinite number of joint angles existing in the same hand position / posture.

The evaluation function in this embodiment is S3.
The S3 axis function constraint angle is used as the value for the axis 4, and the other six values are set to zero. By doing so, the S3 axis 4 is particularly restrained, and the obtained S3 axis joint restraint angle gives the highest priority to the effect (step (5)). The angular velocity calculated by each axial angular velocity calculation unit is commanded to each motor to control each axis. Therefore, the E1 shaft 5 can be rotated as required, and a surface that may cause interference can be avoided as shown in FIG.

Each of the above operations is performed by a computer provided in the manipulator.

As a concrete work to which the present invention can be applied, when an article brought into the controlled area of a nuclear power plant is taken out of the controlled area, a contamination measuring device is attached to the tip of the manipulator to remove a complicated article shape. Examples of the work include a follow-up work for inspection while tracing, a painting work for a target with many obstacles at a high speed while avoiding obstacles, and a welding work for performing at a low speed while avoiding obstacles.

[0024]

According to the manipulator movement control method of the present invention, the redundancy of the manipulator can be obtained only by the information on the surface of the obstacle existing in the movement space of the manipulator, which may interfere with the joint of the manipulator. By effectively using it, it is possible to move while avoiding interference. In other words, it is possible to calculate the evaluation function that can avoid interference and the angular velocities of each axis within the current control cycle by using only the information of the hand position and orientation of the movement destination and the direction of the obstacle that may cause interference, and in real time, autonomous It is possible to avoid the interference.

Therefore, in a narrow space where the robot cannot work, or a space where there are many obstacles, it is possible to autonomously avoid complicated interference and collisions and perform complicated work simply by teaching basic points. Yes, it can be used in various environments and is more versatile.

[Brief description of drawings]

FIG. 1 is a flowchart showing the control contents of a manipulator control method according to the present invention.

FIG. 2 is a schematic diagram of a 7-axis manipulator having one redundant axis, which is an example of an application target of the present invention.

FIG. 3 is a schematic view showing movement of the manipulator when the manipulator control method according to the present invention is not applied.

FIG. 4 is a schematic diagram showing a circular orbit of the E1 axis when the manipulator control method according to the present invention is not applied.

FIG. 5 is a schematic diagram showing movement of the manipulator while avoiding an obstacle when the manipulator control method according to the present invention is applied.

FIG. 6 is an explanatory diagram of a fear of interference with an obstacle.

FIG. 7 is a flowchart showing control of a conventional manipulator having redundant axes.

FIG. 8 is an explanatory diagram showing movement of a manipulator that is unable to avoid an obstacle.

[Explanation of symbols]

 1 Manipulator 2 S1 Axis 3 S2 Axis 4 S3 Axis 5 E1 Axis 6 E2 Axis 7 W1 Axis 8 W2 Axis 10 Obstacle

Claims (1)

[Claims] 1. A method of controlling a manipulator having a redundant axis, which detects a direction of an obstacle with respect to the manipulator, calculates an inclination angle of the redundant axis for avoiding interference with the direction, and realizes the inclination angle. Therefore, a method for controlling a manipulator having a redundant axis is characterized in that the rotational angle of the axis that determines the posture of the redundant axis is obtained, and the axis is controlled so that this rotational angle is achieved.