KR101826577B1 - The tool calibration method using robot's wrist axes movements - Google Patents

Abstract

The present invention uses an external sensor and performs tool correction by driving only two wrist axes of a robot without a coordinate conversion relation between the robot base and the sensor base, thereby enabling accurate calibration of the tool without additional devices And a tool correction method using the wrist axis motion.
To this end, the present invention rotates the two wrist axes J5 and J6 of the robot, calculates the tip travel distance by measuring the position of the tip with the sensor S (D2), and calculates the two axes J5 and J6 ) Of the tip relative to the wrist center position or wrist axis center position at which the axes J4, J5, and J6 of the robot meet at one point and calculate the tip travel distance from this result (D1) , And calculates a position of a tip with respect to a flange coordinate system that minimizes the D1-D2, thereby correcting the tool.

Description

[0001] The present invention relates to a tool calibration method using a robot's wrist axis movement,

The present invention relates to a tool correction method using a wrist axis motion of a robot, more specifically, by using only an external sensor, a tool correction is performed by driving only two wrist axes of a robot without a coordinate conversion relation between the robot base and the sensor base And more particularly, to a tool correction method using a wrist axis motion of a robot that can accurately perform tool calibration without a separate additional apparatus.

Industrial robots are widely used as a means of improving productivity and precision work by automation. These industrial robots are made up of joints connecting multiple links and each link, moving within a preset work range, and performing necessary operations such as welding and assembly .

In order to operate the robot, the end of the link equipped with the work device must be moved to the work position.

At this time, the movement of the robot is performed by using an electric device such as a motor mounted on the joint or a hydraulic device. In order to place the end at a position intended by the user during the process of searching for a specific position with the device, The actual angle of rotation of each joint is important as well as the size of the joint.

In the control of the robot, there is an error between the position intended by the user and the position where the actual link is placed. This error is caused by a dynamic error for each link, deflection due to link weight, backlash caused by the mechanical structure, Development, and compliance of joints.

In order to correct the error of the link position, a calibration technique has been developed. The error between the position and orientation of the link of the robot and the mechanical characteristic of the robot is detected, and the error of the kinematic parameter is detected. It is reflected in the control program.

The calibration of the robot depends on the kinematic calibration based on the robot link parameters and the non-kinematic parameters such as joint inertia, link stiffness, assembly tolerance, backlash, coupling error, Can be considered divided into calibrations included.

In the kinematic calibration method, various methods are suggested according to the measurement tool or the constraint condition. However, in the related paper, the necessity of non-kinematic calibration or the influence of the parameter on the entire robot position error is described in the non-kinematic calibration method It is not enough to provide a concrete solution.

In order to carry out the calibration work, it is necessary to measure the position and direction of the tool center point (TCP) in various poses of the robot.

To make these measurements fast and precise, you should have the following conditions.

First, it should be able to measure the maximum amount of information necessary for calibration. Second, the measurement process should be simple and can be standardized. Third, measurement can be always performed even if the field situation changes and the measurement error is minimized. Simple and easy to operate.

In the case of conventional robot calibration, most of the tools have been taught the tool center point (TCP) of a tool attached to the robot to a simple jig and have used the data obtained here to find out only the position of the robot's TCP. We have been performing the calibration of the robot using the method of measuring the position of the tool TCP installed on the robot by using the 3D laser measuring equipment such as the laser tracker.

However, when performing the tool calibration using the conventional laser measurement method, only the position of the tool could be calibrated, and the direction could not be corrected.

Here, the direction of the tool means strictly the working direction of the tool, which means the central axis of the tool or the axis parallel to the tool passing through the TCP.

In other words, in the case of a straight welding gun, the direction from the one end of the welding rod to the other end toward the welding surface means the direction in which the function according to the purpose of the tool is performed. In the case of the painting gun, And means an average direction of each nozzle when equipped.

In order to calibrate the direction of the tool, it is necessary to make precise measurement of more than three points on the tool. Such a measurement requires not only a very complicated and expensive jig but also an excessive measuring time and a poor measurement capability.

Therefore, it was common practice not to calibrate the direction of the tool.

This robot tool calibration fixes the tool center point (TCP) of the robot at a specific point in the space and manually adjusts the posture of the robot to compensate the robot mechanism value (link length, axis angle, etc.) There is a technique of tool compensation.

At this time, the robot operates so that the end of the robot tool maintains the same point, or a fixing jig for the robot is required.

In addition, there is a technique of performing axis correction and tool correction by measuring the tool end position of the robot using an external position measuring device.

However, when the external position measuring device is used, information on the precise positional relationship between the external position measuring device and the robot is required.

FIG. 1 is a block diagram of a conventional tool correction system, and FIG. 2 is a flowchart of a conventional tool correction process.

As shown in Figs. 1 and 2, the conventional tool compensation moves all the axes J1, J2, J3, J4, J5, and J6 of the robot and moves the position of the tip with respect to the sensor base (X1), the position of the tip with respect to the robot base is calculated from the rotation angle of all the axes of the robot (J1, J2, J3, J4, J5, J6) (X2), and the position of the tip with respect to the flange that minimizes X1-X2 is calculated to perform the tool correction.

In this way, the conventional tool compensation moves all axes (J1, J2, J3, J4, J5, and J6) of the robot to positions of the tool tip at various points in the space and measures the position with a position measuring device. The robot tool value (link length, axis angle, etc.), which minimizes the difference between the position of the calculated tool tip and the measured value of the position measurer, is calibrated and the robot tool is calibrated by calculating the tool compensation value.

However, in the conventional method of correcting the tool of a robot, it is necessary to move all the axes of the robot (six axes in the case of a 6-DOF robot, J1, J2, J3, J4, J5 and J6) There is a problem that the accuracy of tool correction is cumulatively accumulated, and a separate additional device such as a jig is required, which leads to an increase in installation cost and complexity and efficiency of the work

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide an apparatus and a method for driving a robot, J6), it is possible to correct the tool without the coordinate transformation relation between the robot base and the sensor base, so as to maximize the performance and work convenience of the product And a tool correction method using the movement of the wrist axis of the robot.

According to an aspect of the present invention, there is provided a method of measuring a tip movement distance (D2) by measuring a position of a tip with a sensor by rotating two wrist axes J5 and J6 of a robot, (J1, J6) from the rotation angle of the wrist (J4, 5, 6) at the point of wrist center position or wrist axis center position, And a tool correction is performed by calculating a position of a tip with respect to a flange coordinate system that minimizes the D1-D2. The present invention provides a tool correction method using a wrist axis motion of a robot.

As described above, since the present invention moves only two axes of the wrist portion of the robot, it is not influenced by the tool correction result due to the error of the axis, and correct tool correction is possible, thereby maximizing the productivity and the work efficiency .

In addition, the present invention can reduce the installation cost by enabling tool correction in a surgical field without using a separate additional device such as a jig using an optical position measuring device used in an operation environment during a surgical operation using a robot, It is possible to maximize the convenience.

FIG. 1 is a block diagram showing a conventional robot tool correction system.
2 is a flowchart illustrating a conventional robot tool calibration;
3 is a block diagram showing a robot tool correction system according to the present invention.
4 is a flow chart illustrating robotic tool calibration according to the present invention.
5 is a calculation flowchart for the Newton-Raphson method used in tool compensation according to the present invention;

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a block diagram showing a robot tool correction system according to the present invention, and FIG. 4 is a flowchart showing a robot tool correction according to the present invention.

3 to 4, the present invention relates to a method of correcting a tool of a jointed-arm robot, wherein a first axis, a second axis, a third axis and a first wrist axis J1, J2, J3 J4 move the second wrist axis and third wrist axis J5 and J6 at an angle predetermined by the user while fixing the reference value and move the tip by measuring the position of the tip with the sensor S, And the first wrist axis to the third wrist axis J4, J5, and J6 of the robot meet at a point from the rotational angle of the second wrist axis and the third wrist axis J5 and J6 of the robot, Calculating a position of a tip with respect to a wrist center position or a center position of the wrist axis and calculating a position of the tip relative to a wrist center position or a wrist axis center position where the first wrist axis (J4, J5, J6) (D1) is calculated from the result of the position calculation of the tip for the tip (D1), and the position of the tip for the flange coordinate system And the calculation tool is the correction of the robot.

In the robot tool calibration process, P _sensor (X _sensor , Y _sensor , Z _sensor ) at the time of input indicates the position of the tip measured by the sensor S, θ5 is the rotation angle of J5, J6, and L is the robot link length from the wrist axis center position to the flange.

In the output, P _tool (X _tool , Y _tool , Z _tool ) shows the position of the tip with respect to the robot flange coordinate system.

The formula for calculating the difference between the moving distance D2 of the tip Tip measured by the sensor S and the moving distance D1 of the tip with respect to the center position of the wrist axis is shown in Equation 1.

(1)

P _{1 , wrist} = R ₁ P _tool , P _{2 , wrist} = R ₂ P _tool ... ... ... ... ... ... ... ... ... (One)

D ₁ ² = (P _{2 , wrist} -P _{1 , wrist} ) ^T (P _{2 , wrist} -P _{1 , wrist} ) ... ... ... ... (2)

D ₂ ² = (P _{2 , sensor} -P _{1 , sensor} ) ^T (P _{2 , sensor} -P _{1 , sensor} ) ... ... ... (3)

f (P _tool ) = f (x _tool , y _tool , z _tool ) = D ₁ ² -D ₂ ² ... ... ... ... ... ... (4)

P _tool : Correction value of the _tool , (x _tool , y _tool , z _tool )

P _{1 , wrist} , P _{2 , wrist} : Position of tip when wrist axis is moved

P ₁ , _sensor , P _{2 , sensor} : Position of the tip measured by the sensor

R ₁ , R ₂ : rotation matrix calculated from the rotation angles (? 5,? 6) of the wrist axis (J5, J6)

D ₁ : The travel distance of the tip calculated from the wrist axis rotation angle

D ₂ : Travel distance of the tip calculated from the point measured by the sensor

f: Difference of squared distance of travel, D ₁ ² -D ₂ ² , function to be minimized

The P _tool minimizing the equation (4) established by (1) - (4) above can be calculated by various mathematical methods, one of which is the Newton-Raphson method.

The equation for the Newton-Raphson method is shown in Equation 2 below.

(2)

The outline of the Newton-Raphson method of the above-

to be.

Also, the flowchart of Equation (2) is as shown in FIG.

As described above, the tool calibration of the robot according to the present invention is different from the existing tool calibration technique in that the coordinate conversion relation between the external measuring instrument and the robot base is not used and the second wrist axis and the third wrist axis J5 , J6), it is possible to achieve accurate tool correction.

Since the conventional tool correction method needs to move all the axes J1, J2, J3, J4, J5, and J6 of the robot, the error of each axis of the robot is accumulated, Since the correction method moves only the second wrist axis and the third wrist axis (J5, J6) of the robot wrist region, it is not influenced by the tool correction result due to the axis error.

In addition, the tool correction method according to the present invention can apply a tool correction in a surgical field without using a separate additional device such as a jig using an optical position measuring device used in an operation environment during operation using a robot, So that it can be conveniently and easily performed.

Therefore, in the tool correction of the robot, the position of the tip with respect to the center of the sensor base and the wrist axis is measured and calculated using only the motion of the second wrist axis and the third wrist axis J5 and J6 of the robot, (D1-D2), and the position of the tip with respect to the flange coordinate system for minimizing the D1-D2 is calculated by the Newton-Raphson method, so that it can be accurately corrected without error.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims and their equivalents. Of course, such modifications are within the scope of the claims.

J1, J2, J3, J4, J5, J6: Axis
S: Sensor

Claims (2)

A method of tool correction of a joint articulated robot in which a tip is disposed on a wrist portion of a robot having a first wrist axis (J4), a second wrist axis (J5), and a third wrist axis (J6)
The second wrist axis and the third wrist axis J5, J6 at an angle predetermined by the user,
The position of the tip is measured by the sensor S to calculate the travel distance of the tip (D2)
The first to third wrist axes J4, J5, and J6 are located at the center of the wrist or the center of the wrist axis where the first to third wrist axes J4, J5, and J6 meet at a point from the rotation angle of the second wrist axis and the third wrist axis Calculate the position,
(D1) a travel distance of the tip from the result of the position calculation of the tip with respect to the wrist center position or the wrist axis center position where the first to third wrist axes J4, J5, and J6 meet at one point,
And calculating a position of the tip with respect to a flange coordinate system that minimizes a movement distance difference (D1-D2) between the D1 and the D2, thereby performing a tool correction of the robot. Way. The method according to claim 1,
A first axis J1, a second axis J2 and a third axis J3 sequentially arranged to be connected to the first to third wrist axes J4, J5 and J6, And the third wrist axes J5 and J6 are rotated and the first to third axes and the first wrist axes J1, J2, J3 and J4 are fixed as reference values. A tool correction method using the wrist axis movement of a tool.

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