JPH0885083A - Method for deriving and calibrating tool parameter of robot - Google Patents

Abstract

PURPOSE: To provide a method for deriving and calibrating the.tool parameter of a robot, by which the tool parameter of the robot can be more easily derived and calibrated at high precision in a short time. CONSTITUTION: A coordinate system of a flange 4 as an attaching part for a tool 3 is calculated on the basis of respective positioning data at the time of positioning of the tool 3 on the pin tip 5a with at least three attitudes, and at least two straight lines including the tool, position candidacy seen from optional two points on the flange coordinate system to be indicated by using a tool parameter are found, and the tool parameters is derived on the basis of the intersection of mutual straight lines and the flange coordinate system. The calibration value of the tool parameter may be estimated on the basis of the deviation in relation to the mean value of the tool position candidacy seen from the flange coordinate system to be indicated by using the tool parameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tool parameter deriving method and a calibrating method for a robot. For example, when the tool of the robot is exchanged or when the tool collides with a work or the like, the tool parameter is changed. sometimes,
The present invention relates to a method for deriving or calibrating tool parameters that determine the tip position and orientation of a tool.

[0002]

2. Description of the Related Art Conventionally, as a method for deriving or calibrating a tool parameter of a robot, for example, Japanese Patent Laid-Open No. 64-787 has been used.
Japanese Patent Publication No. 74 is disclosed. In this method, the tool tip point is positioned at any one point four times or more, and at this time, the tool tip point is obtained because the flange frame, which is the tool mounting portion, is arranged in a spherical shape. As another method, Japanese Patent Laid-Open Nos. 61-25206 and 61-2
Japanese Patent No. 5207 discloses a method using a calibration jig.

[0003]

The conventional robot tool parameter deriving method and calibrating method described above have the following problems. JP-A-64-7877
In the method disclosed in Japanese Patent No. 4, the operator positions the tool so that the tip of the tool attached to the tip of the robot coincides with the calibration position, but this operation depends on the skill of the operator.
That is, the skill level of the operator affects the positioning accuracy and the leading-edge derivation accuracy of the tool. In addition, this method can only derive the position of the tip of the tool, and it was necessary to use the design value or actually measure the tool direction. In the methods disclosed in Japanese Patent Laid-Open Nos. 61-25206 and 61-25207, the number of measurement points is small, but the accuracy of calibration jig preparation and the setup change for jig installation. Time was a problem. The present invention has been made in view of the above circumstances.
The purpose of is to derive the tool parameters of the robot more simply and in a short time and with high accuracy. The second purpose is to calibrate the robot tool parameters as well.

[0004]

In order to achieve the above first object, a first invention is a method for deriving a tool parameter for determining the position and orientation of a tool attached to the tip of an arm of a robot. The coordinate system of the mounting part of the tool is calculated based on the respective positioning data when positioning is performed on one point in space in at least three different postures, and the coordinate system of the mounting part of the mounting part expressed by using tool parameters is calculated. A tool parameter of a robot, characterized in that at least two straight lines including tool position candidates viewed from arbitrary two are obtained, and the tool parameters are derived based on the intersection of the straight lines and the coordinate system of the mounting portion. It is configured as a derivation method. Furthermore,
At least one of the postures for positioning the tool is a known direction, which is a method for deriving the tool parameter of the robot. In order to achieve the second object, a second invention is a method of calibrating tool parameters for determining the position and orientation of a tool attached to the tip of an arm of a robot, wherein
The coordinate system of the attachment part of the tool is calculated based on each positioning data when the point is positioned in at least three different postures, and the tool position candidate viewed from the coordinate system of the attachment part expressed using the tool parameter is selected. The tool parameter calibration method for a robot is characterized in that the calibration value of the tool parameter is estimated based on the deviation from the average value. Furthermore, in the tool parameter calibration method for a robot, at least one of the postures for positioning the tool is set to a known direction.

[0005]

According to the first aspect of the invention, when deriving the tool parameters for determining the position and orientation of the tool attached to the tip of the robot arm, the tool is positioned at one point in space in at least three different orientations. The coordinate system of the attachment part of the tool is calculated based on each positioning data at this time. At least two straight lines including tool position candidates viewed from any two of the coordinate systems of the mounting portion expressed using the tool parameter are obtained. The tool parameter is derived based on the intersection of the straight lines and the coordinate system of the mounting portion. In this way, the number of teaching points that change the posture of the robot can be minimized, and the tool parameters of the robot can be derived easily and accurately in a short time without using a dedicated calibration jig. Furthermore, if at least one of the postures for positioning the tool is a known direction, the tool parameter can be derived including the direction component.
According to the second invention, when the tool parameters for determining the position and orientation of the tool attached to the arm tip of the robot are calibrated, the tool is positioned at one point in space in at least three different orientations. The coordinate system of the attachment part of the tool is calculated based on each positioning data of. The calibration value of the tool parameter is estimated on the basis of the deviation from the average value of the tool position candidates viewed from the coordinate system of the mounting portion expressed using the tool parameter. In this way, the number of teaching points that change the posture of the robot can be minimized, and the tool parameters of the robot can be calibrated more easily and accurately in a short time without using a dedicated calibration jig. further,
If at least one of the postures for positioning the tool is a known direction, the tool parameter can be calibrated including the direction component.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. The following embodiments are examples of embodying the present invention and are not intended to limit the technical scope of the present invention. 1 is a flow chart showing a schematic procedure of a method of deriving a tool parameter of a robot according to an embodiment (first embodiment) of the first invention, and FIG. 2 is an embodiment of the second invention ( Second Embodiment) A flow chart showing a schematic procedure of a method for calibrating a tool parameter of a robot according to the second embodiment, and FIG. 3 is a schematic configuration diagram of an apparatus 0 to which the method according to the first and second embodiments can be applied. 4 is an explanatory view showing a state of setting a tool coordinate system, FIG. 5 is an explanatory view showing a principle of deriving tool parameters, and FIG. 6 is an explanatory view showing a principle of tool parameter calibration. As shown in FIG. 1, a method of deriving a tool parameter of a robot according to an embodiment (first embodiment) of the first invention derives a tool parameter that determines the position and orientation of a tool attached to the arm tip of a robot. In doing so, the coordinate system of the flange that is the mounting part of the tool is calculated based on each positioning data when the tool is positioned at one point in space in at least three different postures, and the tool parameters are used. At least two straight lines including tool position candidates viewed from any two of the expressed flange coordinate systems are obtained, and the tool parameters are derived based on the intersection of the straight lines and the flange coordinate system. ing. Further, at least one of the postures for positioning the tool may be set to a known direction. In FIG. 1, the first positioning is performed by aligning the tool direction with a known direction vector g. I am trying. FIG.
Shows a schematic configuration of an apparatus 0 to which the tool parameter derivation method according to the first embodiment can be applied. In the figure, 1 is a robot body, 2 is an arm, 3 is a tool, 4 is a flange, 5 is a pin (5a is its tip), 6 is a controller, 7 is a teaching pendant, and 8 is a personal computer. The personal computer 8 is, for example, a CPU, C
A commercially available product equipped with an RT, a memory, a keyboard, etc. is used.

Hereinafter, by using this device 0, the first actual
The embodiment method is further embodied. Figure 4 shows the tool coordinate system setup.
It shows the fixed situation. In the figure, the flange 4 is located at the center of the flange.
The lunge coordinate system is set. The flange coordinate system is Robo
Is calculated by the controller 6 from the data of each axis of
It Here, the position of one point in space can be easily set.
Thus, the tip 5a of the pin 5 is used. The operator
Without teaching pendant 7, positioning in a certain posture
To do. The position of the pin tip 5a at this time is on the robot coordinates.
At the position p (p_x, P_y, P_z), The coordinate system of the flange
F₁(L _1x, L_1y, L_1z, M_1x, M_1y, M_1z, N_1x, N
_1y, N_1z, O_1x, O_1y, O_1z), On the desired flange
Let the tool position vector be t (t_x, T_y, T_z) And
And the relationship between them can be expressed by the following equation. At this time
The relationship is shown in FIG.

[Equation 1] Next, the operator changes the posture of the robot. The flange coordinate system at this time is F ₂ (l _2x , l _2y , l _2z ,
m _2x , m _2y , m _2z , n _2x , n _2y , n _2z , o _2x , o _2y , o
_2z ) and F ₃ (l _3x , l _3y , l _3z , m _3x , m _3y ,
m _3z , n _3x , n _3y , n _3z , o _3x , o _3y , o _3z ), the following two equations hold.

[Equation 2]

Now, consider the i-th and j-th (i, j = 1 to 3; i ≠ j) coordinate systems among these three coordinate systems. The above equations (1) to (3) are all the position vectors p (p _x , _py , p of the pin tip 5a from the robot coordinates.
_{Since z} ) is shown, the following equation holds.

(Equation 3) Generally, coordinate systems having the same origin and different attitudes can be related by a coordinate transformation matrix that rotates θ in a certain vector direction κ as shown in FIG. 5B. Here, the origin is the same, orientation different two coordinate systems, respectively _{(l ix, l iy, l} iz, m ix, m iy, m iz, n ix,
n _iy , n _iz , 0, 0, 0) and (l _jx , l _jy , l _jz ,
m _jx , m _jy , m _jz , n _jx , n _jy , n _jz , 0, 0, 0). When the coordinate transformation matrix expressing the relationship between them is C, the following equation holds.

[Equation 4] From the above equation (5), the transformation matrix C is as follows.

(Equation 5)

As is generally known, the transformation matrix C can be replaced with an equivalent rotation matrix Rot (κ, θ) that represents transformation by an equivalent rotation axis κ and an equivalent rotation angle θ.

(Equation 6) From the above equations (6) and (7), the equivalent rotation angle θ and the equivalent rotation axis κ have the following values.

(Equation 7) This equivalent rotation matrix Rot (κ, θ) does not perform any conversion on the equivalent rotation axis κ which is a direction vector. Therefore,
If α is an arbitrary real number, the following equation holds. Rot (κ, θ) ακ = αCκ = ακ (10)

By multiplying both sides of equation (5) by ακ and transforming using equation (10), the following equation is obtained.

[Equation 8] At this time, v (v _x , v _y , v _z ) means an equivalent rotation axis vector viewed from the robot coordinate system. Now, when the above equation (10) is added to the above equation (4), the following equation is obtained.

[Equation 9]

This is on a straight line on the two flange coordinate systems.
Point t + ακ coincides with each other, and a straight line p + on the robot coordinate system
It means that it is converted into one point on αv. On this straight line
1 point p_ij(P_ijx, P_ijy, P_ijz) (Tool position
Equivalent to), p_ijo_iAnd p _ijo_jOf the two vectors
The outer product is in the direction of the equivalent rotation axis vector v, and two vectors
Set to the point where the angle formed by the tor is θ. Then straight line L
_ijCan be expressed by the following equation.

[Equation 10] The set of flange coordinate systems (i, j) that can be taken here is (1,
There are 3 sets of 2), (1, 3) and (2, 3).
From equation (3), three straight lines can be obtained. Since these three straight lines intersect at one point from the physical sense, the intersection can be calculated by appropriately selecting two straight lines. Since this intersection is the same point p where the tool tip is positioned, 3
The tool position vector t is obtained as follows using one of the two flange coordinate systems F _i (i = 1 to 3).

[Equation 11]

As described above, the tool position vector t can be derived. The above calculation is performed by the CPU of the personal computer 8.
And the result is displayed on the CRT. As described above, the number of teaching points for changing the posture of the robot is minimized, and the tool parameter (t _x ,
_ty , _tz ) could be derived. Next, the principle of deriving the direction of the tool will be described. Tool parameters (t _x , t _y , t _z , ε ₁ , ε ₂ ,
The tool coordinate system in the flange coordinate system is expressed by ε ₃ ) as follows. However, ε ₁ , ε ₂ , and ε ₃ all represent Euler angles.

[Equation 12] Here, as shown in FIG. 1, the direction coordinate axis w of the tool is made to coincide with the known direction vector g (g _x , g _y , g _z ). At this time, the relationship between the tool coordinate system T, the flange coordinate system F _i, and the direction vector g is as follows.

[Equation 13]

Since the flange coordinate system F _i and the direction vector g are both known, the following equation can be obtained by modifying the above equation (17).

[Equation 14]From this, the Euler angle ε₁, Ε₂Is calculated as follows
It ε₁= Atan2 (r_x, R_y)… (19) ε₂= Atan2 (r_z, ± √ (r_x ²+ R_y ²)) (20) From the above, the above equations (11), (16) and (17)
It is possible to determine the tip of the tool and the direction of the tool.
Wear. This decision calculation is also the CP of the personal computer 8.
It is executed by U and the execution result is displayed on the CRT. Since
When the tool parameters are expressed by Euler angles by the above
(T_x, T_y, T_z , Ε₁, Ε₂, Ε₃) Of 5
Ingredient t_x, T_y, T_z, Ε₁, Ε₂Is required. Remaining
One component, ε₃Is the key for the personal computer 8.
Set value or default by board input
It To find the tool parameters of the robot, do the above.
As in the first embodiment described above, the posture of the robot is changed.
Position the tip of the tool at a predetermined position 5a in the space.
In principle, this can be obtained by changing the posture and performing positioning three times.
However, in reality, changing the posture of the robot,
When positioning is close to the predetermined point 5a, accurate positioning is performed.
There may not be. Assuming these cases, the second departure
In Ming, 3 or more points are positioned, and 3 or more points are positioned.
From the values in the lunge coordinate system, the tool parameter is
It was decided to calibrate the data.

Next, the second invention will be described. As shown in FIG. 2, a method for calibrating tool parameters of a robot according to an embodiment (second embodiment) of the second invention calibrates tool parameters for determining the position and orientation of a tool attached to the tip of an arm of a robot. In doing so, the coordinate system of the flange that is the attachment part of the tool is calculated based on each positioning data when the tool is positioned at one point in space in at least three different postures, and it is expressed using tool parameters. The calibration value of the tool parameter is estimated based on the deviation from the average value of the tool position candidates viewed from the flange coordinate system. Further, at least one of the postures for positioning the tool may be set to a known direction. In FIG. 2, the direction of the first positioning tool is set to match the known direction vector g. . The same apparatus 0 as in the first embodiment can be applied to the tool parameter calibration method according to the second embodiment. Hereinafter, the method of the second embodiment by the device 0 will be further embodied. In the second embodiment, the positioning is performed q times (q ≧ 3), and the tool position vector t is obtained from the respective flange coordinate systems F _{1 to} F _q at that time. FIG. 6 shows the relationship between the flange coordinate systems F _{1 to} F _q and the tool position vector t at this time. In FIG. 6, since the positioning is not performed accurately, the positions of the normals drawn from the respective flange coordinate systems to the equivalent rotation axis κ do not match, and the error ε _ij
Occurs. Here, first, the above equation (4) is modified to obtain the following equation.

(Equation 15)

In this case, the six variables t _x , t _y , t _z ,
Six equations for p _x , p _y , and p _z are derived. However, a solution cannot be uniquely obtained from these equations alone. On the contrary, according to the principle described in the first embodiment, it is apparent that a solution can be uniquely obtained by forming an equation using at least three flange coordinate systems. The following equation is obtained using all flange coordinate systems.

[Equation 16] Now, the tool position vector t has an error Δt (Δt _x , Δ
When t _y , Δt _z ) is included, the following error equation is derived from the above equation (22).

[Equation 17]

The error Δp _i at the same point is defined as the error from the average of the same points derived as follows. This corresponds to the deviation of the tool position candidate from the average value and is proportional to the error ε _ij described above.

[Equation 18]The matrix J consisting of the flange coordinate system on the left side of the above equation (23)
(F₁, F₂,,, F _q)^TPseudo-inverse matrix J of⁺To (2
By multiplying both sides of equation 3), the following equation is obtained.

[Formula 19] From this, the error Δt of the tool position vector t is obtained.
Using this error Δt, the value of the tool position vector t is updated as follows, and the sum of the error Δp _j at the corresponding position is Σ
Repeat until | Δp _j | <ε. However, ε is a predetermined value. t _new = t _old + Δt (26) Further, the direction of the tool can be obtained in the same manner as in the first embodiment by setting the known direction vector g described above to (0, 0, -1), for example. it can. As mentioned above,
According to the second embodiment, the number of teaching points for changing the posture of the robot is reduced as much as possible, and the tool parameters of the robot can be calibrated more simply and accurately in a short time without using a dedicated calibration jig. I was able to.

[0017]

Since the robot tool parameter deriving method and calibration method according to the present invention are configured as described above, the number of teaching points for changing the position and orientation of the robot is minimized, and a dedicated calibration jig is used. Without using tools, the robot tool parameters can be derived and calibrated easily and in a short time with high accuracy.

[Brief description of drawings]

FIG. 1 is a flowchart showing a schematic procedure of a method of deriving a tool parameter of a robot according to an embodiment (first embodiment) of the first invention.

FIG. 2 is a flowchart showing a schematic procedure of a method for calibrating a tool parameter of a robot according to an embodiment (second embodiment) of the second invention.

FIG. 3 is a schematic configuration diagram of an apparatus 0 to which the methods according to the first and second embodiments can be applied.

FIG. 4 is an explanatory diagram showing how the tool coordinate system is set.

FIG. 5 is an explanatory diagram showing the principle of tool parameter derivation.

FIG. 6 is an explanatory diagram showing the principle of tool parameter calibration.

[Explanation of symbols]

 0 ... Robot tool parameter derivation and calibration device 1 ... Robot body 2 ... Arm 3 ... Tool 4 ... Flange (corresponding to mounting part) 5a ... Pin tip (corresponding to one point in space)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Kangaki, Nakahara, Toyohashi City, Aichi Prefecture 2 1 Nakahara, Kobe Steel Co., Ltd. Toyohashi FA / Robot Center (72) Minoru Fujii Inami, Miyachi Town Nakahara No. 1 Address 2 Kobe Steel, Ltd. Toyohashi FA / Robot Center

Claims (4)

[Claims] 1. A method of deriving a tool parameter for determining the position and orientation of a tool attached to the end of a robot arm, wherein each positioning data is obtained when the tool is positioned at one point in space in at least three different postures. Based on the above, the coordinate system of the mounting portion of the tool is calculated, and at least two straight lines including tool position candidates viewed from any two of the coordinate systems of the mounting portion expressed using the tool parameters are obtained, and the straight line is obtained. A method for deriving a tool parameter of a robot, characterized in that the above-mentioned tool parameter is derived based on an intersection of the two and a coordinate system of a mounting portion. 2. The method for deriving a tool parameter of a robot according to claim 1, wherein at least one of the postures for positioning the tool has a known direction. 3. A method for calibrating tool parameters for determining the position and orientation of a tool attached to the tip of a robot arm, wherein each positioning data is obtained when the tool is positioned at one point in space in at least three different postures. The coordinate system of the mounting part of the tool is calculated based on the above, and the calibration value of the tool parameter is estimated based on the deviation from the average value of the tool position candidates viewed from the coordinate system of the mounting part expressed using the tool parameter. A method for calibrating a tool parameter of a robot characterized by the following. 4. The method for calibrating tool parameters of a robot according to claim 3, wherein at least one of the postures for positioning the tool has a known direction.