JPH05241627A - Control method for robot - Google Patents

Abstract

PURPOSE:To fix the direction of a tool at all times by calculating a tool direction vector at time t+DELTAtau from the position vector of a tool head, moving vector, position correcting vector, locus direction vector and tool direction vector at time (t). CONSTITUTION:A position vector P[t] of the tool head at the time (t) and a moving vector U[t] of the tool head after the lapse of unit time DELTAtau from the time (t) are found. A position correcting vector S[t] of the tool head is found from an external element at the time (t), and a locus direction vector D[t] of this tool head is found by the arbitrary number of position vectors for the tool head for fixed time retroacting from the time (t) to the past. A tool direction unit vector T[t+DELTAtau] at the time t+DELTAtau is obtnd. from the respective vectors P[t], U[t], S[t] and D[t] thus obtnd. and the tool direction unit vector at the time (t). Thus, the tool direction can be fixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an industrial robot.

[0002]

2. Description of the Related Art A procedure for calculating the position of the tip of a tool in calculating the trajectory of a robot will be described below.

The position vector of the tool tip at time t is P [t], and the movement vector of the tool tip at unit time Δτ from time t is U [t]. As a result, the position vector P [t of the tool tip at time (t + Δτ) is obtained.
+ Δτ] is

[0004]

[Equation 1]

[0005] The trajectory of the tool tip of the robot is controlled between the plurality of teaching points by the calculation of the formula (1) every unit time. In recent years, along with the expansion of applications of robots, in order to improve work quality, it is necessary for the robot itself to recognize the environment and perform control. As a response to such a request, there is a function of obtaining position information of a work target by an external element such as a sensor and correcting the trajectory of the tool tip in real time.

The procedure for calculating the position of the tool tip in such a robot will be described below. At time t, the position correction vector of the tool tip obtained by the external element is S [t]. The position vector P [t + Δτ] of the tool tip at time (t + Δτ) becomes (Equation 2), and S
The locus is corrected and controlled by [t], and the work quality can be improved.

[0007]

[Equation 2]

[0008]

With the above technique, it is possible to correct the trajectory of the tool tip in real time. But,
Depending on the application of the robot, the direction of the tool may be an important factor for improving work quality. In such an application, it is necessary to control the position of the tool tip and at the same time control the direction of the tool to be constant with respect to the direction of the trajectory.

It is an object of the present invention to provide a robot control method in which the tool direction is always constant.

[0010]

In order to achieve the above object, a robot control method according to the present invention comprises: a tool tip position vector at time t; a tool tip movement vector at a unit time Δτ from time t; A tool tip position correction vector obtained by an external element at time t, a tool tip trajectory direction vector calculated from the position vector of any number of tool tips at a certain time retroactively from time t, and a tool at time t Based on the direction vector, the tool direction vector at time (t + Δτ) is calculated, and control is performed so that the angle formed by the tool direction vector and the trajectory direction vector of the tool tip is constant.

[0011]

By performing the trajectory control of the tool tip by the above procedure, the angle formed by the trajectory direction of the tool tip and the tool direction becomes constant, and as a result, it is possible to improve the work quality.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vector diagram for explaining the control method of the present invention. The symbols in the figure are defined below.

[0013]

[Equation 3]

At time t, a unit vector representing the direction of the trajectory of the tool tip is defined as D [t], and a vector function f for obtaining this is defined. However, m is an arbitrary integer.

[0015]

[Equation 4]

The vector function f is an arbitrary function for obtaining the direction of the movement locus of the tool, and an appropriate function may be selected according to the accuracy of the position correction information of the sensor, the control accuracy of the tool, and the like. For example,

[0017]

[Equation 5]

Alternatively, a regression line or a free curve approximation may be used. Simply

[0019]

[Equation 6]

The reason is not to prevent the tool direction from changing sensitively and frequently due to the accuracy of the position correction information of the sensor.

The position vector of the tool tip at time (t + Δτ) is calculated by the equation (2). Next, at the time (t + Δτ), the tool direction unit vector T [t +
Δτ] is calculated. First, a unit vector D [t + Δτ] representing the direction of the trajectory of the tool tip at time (t + Δτ)
Is

[0022]

[Equation 7]

It is calculated by The unit vector A [t] is defined as follows.

[0024]

[Equation 8]

Using equation (7), in order to make the angle formed by the tool direction and the trajectory of the tool tip at time (t + Δτ) the same as at time t, the torch direction unit vector at time (t + Δτ) T [t + Δt] is as follows.

[0026]

[Equation 9]

Application to an arc welding robot system will be described as an embodiment using the above mathematical expressions. The arc welding robot grips a welding torch as a tool and controls the trajectory of the welding torch to perform welding. At this time, the angle formed by the welding line and the torch is called an advancing angle or a receding angle, which is an important factor affecting welding quality. Therefore, it is desirable to keep this angle constant during welding, and the present invention is applied to improve the welding quality.

FIG. 2 shows the configuration of the arc welding robot system. The controller 3 controls the trajectory and welding of the robot 3 and the arc welder 4. In this system, the arc sensor 1 is used as a welding line scanning sensor. The arc sensor 1 detects the deviation of the welding line from the change of the welding signal, and is the most practical copying sensor in arc welding. From the arc sensor 1, position correction data in the torch direction and in a direction perpendicular to the torch direction and the welding line direction are sent to the controller 2 of the robot, the trajectory of the torch tip is corrected in real time, and the welding line tracing is performed. Done. The control device 2 is loaded with the control procedure of the present invention as a program, and the locus is controlled by the position correction information from the arc sensor 1 so that the angle formed by the locus direction of the torch tip and the torch direction becomes constant. It

[0029]

According to the present invention, it becomes possible to maintain a constant angle between the tool tip trajectory direction and the tool direction in response to a position correction command from an external element such as a sensor, thereby improving work quality. It becomes possible. It can be said that the present invention is indispensable in the future where the demand for robots having a position correcting function utilizing sensors expands, and the industrial contribution is very large.

[Brief description of drawings]

FIG. 1 is a vector diagram for explaining a control method of the present invention.

FIG. 2 is a configuration diagram of an arc welding robot system as an application example of the present invention.

[Explanation of symbols]

 1 arc sensor 2 controller 3 robot 4 arc welder

Claims (2)

[Claims] 1. The time (t + Δ) is calculated by a tool tip position vector at time t, a tool tip movement vector at unit time Δτ from time t, and a tool tip position correction vector obtained by an external element at time t.
(3) A robot control method for calculating a position vector of a tool tip at τ) to perform trajectory control, wherein the three vectors at time t and the positions of any number of tool tips at a certain time retroactively from time t Time (t + Δτ) from the trajectory direction vector of the tool tip calculated by the vector and the tool direction vector at time t
A method for controlling a robot characterized in that the tool direction vector is calculated and the trajectory control is performed so that the angle formed by the trajectory direction vector of the tool tip and the tool direction vector becomes constant. 2. The robot control method according to claim 1, wherein the robot is an arc welding robot, the tool is a welding torch, and the external element is a welding line recognition sensor.